Iff iotnell IBttt»e«sJtg ptntatg BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF 1891 ^.%AQPA^ i\l\{l.. The date shows when this Telume was taken. To renew this book cojjy the call No. and give to the librarian. HOME USE RULES AU books subject to recall All borrowers must regis- ter in the library to borrow books for home iise. All books must be re- txirned at end of* college year for inspection and repairs. Limited books must be returned within the fojir week limit and not renewed. Students must return all books before leaving tcKvn. Officers should arrange for the return of books wanted during their absence from town. Volumes of periodicals and of pamphlets arcbeld "^ in the library as much as possible. For special pur- poses they are given out for a limited time. Borrowers should not us6 their library' privileges for • the benefit of other persons. Books of special value and gift books, when the giver wishes it, are not allowed to circulate. ' Readers are asked to re- port all cases of books marked or mutilated. Do not deface books by marks and writinc. Cornell University Library TL 145.C59 V.I Text book on motor car engineering 3 1924 022 823 797 WIS Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924022823797 TEXT BOOK ON MOTOR CAR ENGINEERING 2j^ TEXT BOOK ON MOTOR CAR ENGINEERING VOLUME I.-CONSTRUCTIO\ YOLFME II -DESIGN BY A. GEAHAM pLAEK MEMBER OF THE INSTITUTION OF AUTOMOBILE ENGINEERS ; ASSOCIATE MEMBRR OF THE INSTITUTION OF MECHANICAL ENGINEERS ; LECTURER IN MOTOR CAR ENOINEEBTNQ AND IN ENGINF.RRING DESIGN, THE POLYTECHNIC, REGP.NT STREET, W. Volume I.— CONSTEUCTION NEW TOEK D. VAN NOSTEAND COMPANY 23 MURRAY AND 27 WARREN STREETS 1911 I f '7/^ PEEFACE This book is primarily intended for the use of students of Motor Car Engineering ; but it is hoped that many engaged in this branch of Engineering science, including owners of cars, will derive some benefit from a perusal of this volume, which has been mainly written from the notes used by the Author in his lectures to Ordinary and Honours Grade Students at the Polytechnic School of Engineering, Eegent Street, W. An attempt has been made to cover the Syllabus of the City and Guilds of London Institute in this subject, which, as may be seen from pages 404 to 407, is very extensive, but it is believed that nothing vital has been omitted excepting the Materials of Construction and the problem of Balancing, which belong properly speaking to Design, and have therefore been included in Volume II. of this work. The Automobile Engineer should have a good working know- ledge of thermodynamics, mechanics, chemistry, electricity and mathematics, in order that he may intelligently carry out his work. This is often difficult for him to obtain, and although the space available precludes an extensive study of these subjects, the hope is expressed that the information contained in this volume will materially assist him in understanding the principles of Motor Car construction. The Author is indebted, in several instances, to the descriptive matter contained in the booklets issued by the Manufacturers of certain Specialities, for the descriptions which appear in the text. The Author's best thanks are due to the Council of the viii PREFACE Institution of Automobile Engineers and to Dr. Watson, F.R.S., for their kind permission to insert the Tables of the Physical Pro- perties of Petrols given on pages 421 to 425 ; to Messrs. Longmans & Co., and Mr. Archibald Sharp, Wh. Sc, B.Sc, A.M. Inst. C.E., for permission to use the ratios of excess energy given on page 219 ; to Messrs. Macmillan, for allowing him to include the Table of Logarithms on pages 427 to 430, to the various Firms who have loaned him electros of illustrations against which their names appear in the text, and to the Automobile Press. He must also acknowledge his indebtedness to his friend and colleague, Mr. Thos. Wadhams, Wh. Ex., for his assistance in reading through several chapters in this work and in checking over many of the numerical examples distributed in the text. The examination papers set at the examinations held by the City and Guilds of London Institute in Motor Car Engineering have been inserted at the end of the book. The reader will doubtless find it an advantage to omit the Articles marked with an asterisk on first reading. The Author will be grateful for any suggestions or for any corrections that may be made. A. G. C. The Polytechnic School of Engineering, Eegent Street, W., Odoher, 1911. CONTENTS PAGE Preface ... ... . . . vii List of iLLrsTRATiONs ... . . . xv CHAPTER I iNTKODtrCTION 1 CHAPTER II The Generai Principles and Construction of the Petrol Engine . . .... ... 5 The Eour-stroke Engine — The Two-stroke Engine — Crankcase Induction — Separate Cylinder Induction — The Cooper Engine — Desaxe Engines — En-bloc Systems. CHAPTER III Details of Engine Construction 16 Pistons — Methods of securing the Gudgeon Pin — Connecting Rods — Crankshafts — Arrangement of Cranks — Balance — Ely- wheels — Cylinders — Valves and Valve Gears — The Poppet Valve — Arrangements of Valve Gears — Operating Geai' — Valve Tappets — Crossley, Wolseley and Napier Valve Tappets — Valve Setting — Sleeve, Piston and Rotary Valves — The Knight Engine — The Bingham Engine — The Hewitt Engine. CHAPTER IV Petrol . 43 The Suitability of Petrol as a Fuel — ^Physical Properties of Petrol — Source from whence obtained — Distillation — Composition — Volatility of a Fuel — BaiUee's Test Apparatus for Liquid Fuels — Specific Gravity — Boiling Point — Calorific Value — Darling Calorimeter — ^Air required for Combustion. CHAPTER V Fuels other than Petrol 58 Importance of a Good Fuel — Fuel Oil — Paraffin or Kerosene — Alcohol — Conclusion of the United States Board of Agriculture on the use of Alcohol — Benzol — Shale Naphtha — Acetylene — Alkoethine. X CONTENTS CHAPTEE VI PAGE Carburetters and OARBtiRATioN 69 The P unction of a Carburetter — ^Types of Carburetters — ^Floats- Petrol Fuel Systems— Carburation — Mixture Strengths — Influence of Shape of Induction Pipes — Adjustment of Carburetter — The Lanchester Wick Carburetter — The Claudel-Hobson Carburetter — The Soott-Eobinson Carburetter — The Longuemare Carburetter — The Trier and Martin Carburetter — The Brown and Barlow Carburetter — The Polyrhoe Carburetter. CHAPTEE Vn Thermodynamics of the Petrol Engine 93 Fundamental Laws and Definitions — Units of Heat — Specific Heat — Boyle's Law — Charles Law — Isothermal Expansion — Adiabatic Expansion — The Value of n — To Determine the Value ■ of n — Temperature in Adiabatic Expansion and Compression — Combustion. CHAPTEE VIII Horse-power 103 What is Horse-power ? — Indicated Horse-power — Molnnes- Dobbie Indicator — Hopkinson Flashlight Indicator — ^Mean Effec- tive Pressure — Brake Horse -power — Eope Brake — Heenan and Froude Water Dynamometer — Fan Dynamometer — Electrical Brake — Horse-power under E.A.C. Eating — Horse-power at Eoad Wheels. CHAPTEE IX Mechanical, Thermal and Combustion Efpiciencies . . . 120 EfBoiency — Combustion EflB.ciency — ^Thermal Efflcieuoy — Air Standard Efficiency — Eelative Efficiency — Mechanical Efficiency. CHAPTEE X The Principles and Construction op Coil and Accumulator Ignition 126 Early Forms of Ignition — Electric Ignition — Electromotive Force — ^Electrolysis — Dry Cells and Accumulators — ^Leclanche Cell — Dry Cells — Polarisation — ^Accumulators or Storage Cells — Pasted Plates — Capacity of Accumulators — Methods of Ee- oharging Accummulators — To Find the Number of Lamps required, etc. — High and Low-tension Electricity — Low-tension Spark — High-tension Spark — The Trembler Coil — Action of Trembler Coil — The Effect of a Condenser — Coil and Accumulator Wiring — Commutators — E.I.C. Contact-breaker — Simms H.T. Distributor — Sparking Plugs — Double Pole Plugs — Order of Firing — Lodge Igniter. CONTENTS xi OHAPTEE XI PAGE Magneto lajsriTioic 154 Magneto Ignition — Construction of the Magneto — Generation of Current — Low-tension Magneto Ignition — Magnetic Ignition — Bosch Magnetic Igniter — ^Puller High-tension Magneto — Bosch High-tension Magneto — Mea High-tension Magneto — ^Eisemann High-tension Magneto with Automatic Advance — Dual Ignition — Puller Dual System — Bosch Dual System — Simms Dual System (Type A) — Hall Dual System — C. A. V. Dual System — Simms Dual System (Type S) — Bosch Duplex Ignition. CHAPTBE Xn Engine Control Systems 193 Need for Simplicity — Automatic and Mechanical Control — Governors — Extra Air — Ignition — Methods of Control — The Accelerator Pedal — The Main Throttle — A Desirable Control. CHAPTEE XIII Engine Cooling Systems 202 Necessity for a Cooling System — Overheating — Air Cooling — Water Cooling — ^Forced Circulation — Thermo-syphon — Pumps — Honeycomb Gilled Tube and Straight Tube Eadiators — Position of Eadiator — Pans. CHAPTEE XIV Ceank Effokt Diagkams 212 Variation in the Turning Effort on the Shaft — ^Variation in the Angular Speed of Crank — Piston Velocity Diagram — Acceleration — Klein's Construction — Crank Eflort — ^Maximum to Mean Crank Effort — Fluctuation of Energy. CHAPTEE XV Clotches and Beakes 221 Use of Clutch — Eequirements which a good Clutch should Fulfil — Types of Clutches — Cone Clutch — Eeversed Clutch — ^Double- cone Clutch — Crossley Expanding Clutch — Deasy Plate Clutch — Multiple Disc Clutch — Hele-Shaw Clutch — Argyll Clutch- Armstrong- Whitworth Clutch — Lanchester Clutch and Brake — Sheffield Simplex Clutch — Wolseley Clutch — Brakes — Brake Eequirements — Types of Brakes — Armstrong-Whitworth Brakes — Wolseley Foot Brake — Napier Brakes — Sheffield Simplex Brake — ^Front-wheel Brakes — Crossley Front-wheel Brakes — Arrol- Johnston Front- wheel Brakes — Adams' Front- wheel Brakes. xil CONTENTB OHAPTBE XVI PAGE Change-speed Gears 251 Why a Gearbox is Necessary — Position of Gearbox — Suspension of Gearbox — Number of Speeds — Which. Speed should be Direct — Types of Gears — Gate Change — Armstrong-Whitworth, Deasy, Wolseley, and Austin Gearboxes — Napier Gearboxes — ^Epicyclic Gears — Adams Planetary Gearbox — Forms of Teeth — Miscella- neous Gears. OHAPTEE XVII Transmission Gear 271 Methods of Drive — Central Chains — Side Chains — Propeller- shaft and Live Axle — Universal Joints — Differential Gear — Action of the Differential — Bevel-wheel Drive — Worm Drive — Live Axles and Casings — Eatio of Engine Eevolutions to Eevolutions of Eoad Wheels. CHAPTEE XVIII Steering Gears 288 Ackermann Gear — Jeantaud-Ackermann Gear — Other Forms of Steering Gear — Steering Axles and Pivots — Steering Columns — Steering Connections. CHAPTEE XIX Lubricants, Lubrication, Ball and Eoller Bearings . . 301 Importance of Efficient Lubrication — Lubricating Oils — Action of Lubricating Oil — Eequirements ■which a good Lubricating Oil should Fulfil — Flash-point — Gray's Flash-point Apparatus — Cold Test — Burning Test — Fire Test — Eedwood's Viscometer — Gearbox Lubricants — Chassis Lubrication — Engine Lubricating Systems — Splash Lubrication — Trough Lubrication — Forced Lubrication — Armstrong-Whitworth System — Crossley System — Napier System — Wolseley System — Austin System — Oil Pumps — Ball and Eoller Bearings. CHAPTEE XX Chassis Construction 325 Chassis Frame Eequirements — Frame Construction — Methods of Eesisting the Distortion of Framing — Suspension of the Engine and Gearbox — Springs — Shock Absorbers — Torque Eods and Tubes — Eadius Eods — Fixed Axles — Wheels. CONTENTS xiii CHAPTER XXI PAGE General Pkinciples of the Steam Car 347 Essential Parts of the Steam Power Unit — The Generation of Steam — Sensible Heat — Latent Heat — Total Heat of Steam — Dry Saturated Steam — Wet Steam — Superheated Steam — Cycle of Operations in a Steam Engine — Clearance — Ratio of Expansion — Object of Superheating — Use of Condenser — Compound Engines — Feed Heaters. CHAPTER XXII Steam Engines and Condensers . 359 Single-acting and Double-acting Engines — The Cylinder — The Operation of the Plat or D Valve — Lap and Lead — Steam Inside or Outside the Valve — Piston Valves — ^Poppet Valves — Comparison of Different Kinds of Valves — Valve Gears — Stephenson's Link Motion — Joy's Valve Gear — The White Engine — The Stanley Engine — The Turner Engine — Condensers. CHAPTER XXIII Steam Generators and Pipe Diagrams . . . 315 General Considerations — Tubular Boilers — Fire Tube — Water Tube— Flash Boilers— White Boiler— White Burner— White Water System — White Steam System — White Fuel System — White Con- trol — Stanley Fire-tube Boiler — Stanley Water Indicator — Stanley Burner — Stanley Water System — Stanley Steam System — Stanley Fuel System — Stanley Fuel Control — Turner Boiler — Turner Water System — Turner Steam System — Turner Fuel System — ■ Turner Control. CHAPTER XXIV The Electric Car . . . .... 392 Principal Parts of an Electric Oar — Suspension of Motors — Battery — Motors — Series, Shunt and Compound-wound Motors — Shunt-wound Motor used for Charging Battery when descending Hills — Controller — How Variations of Speed are Obtained. Materials used in Motor Car Construction .... 402 Syllabus of City and Guilds of London Institute in Motor Car Engineering . 404 Examination Papers . . . . 408 Physical Properties of Petrols 421 Mathematical Tables and Constants . . ... 426 Index 433 14 MOTOE CAE ENGINEEEING strokes, and rather less than 180 degrees on the exhaust and the compression strokes. The advantage to be gained by this has sometimes been over-estimated, as although the pressure on the piston on the power stroke acts through a greater distance, the gases are subjected to the cooling action of the cylinder walls for a longer period. On the inductioii stroke, however, the piston will be travelling more slowly, so that the explosive charge will be cooler and have a greater volume, the result being that in addition to the increment of compression pressure accruing from a more rapid rate of compression, there will be a larger volume of gas to compress and consequently a higher explosion pressure. It is in these respects, the increase in the compression and explo- sion pressures, combined with the more effective crank effort during the power stroke, that the gain in efficiency and power is to be expected. But this improvement does not stand alone, as there are disadvantages accompanying the introduction of the desaxe cylinder. For the same reason that a greater crank effort is obtained on the power stroke, a greater amount of power will be required to perform the compression and exhaust strokes, and, further, when firing with a retarded spark, the tendency will be to drive the crank backwards, which tendency will be increased as the displacement is increased, thereby preventing low speeds of rotation. Extreme caution should therefore be exercised in determining the amount of offset, as otherwise, instead of a gain there may be a distinct loss. 15. En Bloc System. — This system of casting the cylinders together has, during recent years, come rapidly into favour with manufacturers, on account of the reduced cost of production and because the absence of piping, etc., gives a very clean and compact appearance to the engine. But it is not easy to obtain perfectly sound castings, even of cast iron, when the cylinders are cast in pairs and the inlet and exhaust passages are enclosed ; neither can one be sure that the requisite areas through the ports are maintained. Frequently, too, there is little or no water space between two adjacent cylinders, with the result that unequal expansion takes place in the walls, inducing stresses in the metal that may exceed the normal working stress. Then the castings as received from the foundry may not be free from warp or twist, and the pitch of GENERAL PRINCIPLES AND CONSTRUCTION 15 the cylinders may not correspond with that desired in the finished engine, so that one side of a cylinder may be ^ in. thick and the other side -^^ in., in which event the cylinder will become oval when it is heated up by the explosions. But the great objection to the system arises from the difficulty experienced by the owner in effecting repairs, and from the exten- sive and costly nature of any replacement, should such become necessary ; as the weight of the part, coupled with the skill required to " enter " the pistons in the cylinders without damage, effectually deter the private individual from attempting the removal and replacement of cylinders cast in this manner, while a crack or excessive wear from softer metal in one cylinder may necessitate an entirely new set of cylinders. Questions on Chaptbe II. (1) Describe the sequence of operations which take place in the four-stroke engine and say why it is so largely used. (2) What are the peculiar disadvantages attaching to the two- stroke engine ? Illustrate by what means they have been overcome in modern types. (3) Compare the two and the four-stroke engines from the point of view of their use in automobile work. (4) Why are the cylinders of some engines displaced so that their centre line does not pass through the centre of the crank- shaft ? What are the objections to a large amount of offset ? (5) Discuss the en-bloc system of casting cylinders. (6) Sketch and describe the Cooper engine — pointing out its special features. CHAPTEE III DETAILS OP ENGINE CONSTEUCTION 16. The Piston. — The function of the piston is to transmit the working pressure in the cyHnder to the crosshead, and at the same time to prevent leakage of the gases. While the general form of all pistons is the same, they differ Fig. 7. — Longitudinal Section of 15 h.-p. Standard Engine. somewhat in details, as is to be expected. They may be divided into classes, according to the shape of the head, in the following manner : — The Flat Top. — This is the usual construction and is easy to DETAILS OF ENGINE CONSTBtlCTION 11 manufacture, seeing that it consists of a plain cylindrical casting, with bosses for the attachment of the gudgeon pin, and a flat head, which can be readily turned up. It will be seen Fig. 8. — Armstrong-Whitwortli Engine, Cross-section. from Fig. 7 that the top edge of the piston is rounded, so that should it receive an accidental knock it will not burr the edge over. In some cases (see Figs. 8 and 9) a web is cast across the underside of the piston, and connects it to the gudgeon bosses. This allows a thinner top to be used with safety. M.C.B. C 18 MOTOE CAE ENGINEEEING The Domed Top. — This shape gives a stroDger piston head, as the pressure in the cyUnder induces a compressive stress in the metal. The construction of this form is shown in .Fig. 10. The height, of the engine is, however, slightly increased. .Here again, a web may be placed on the under-side so as to strengthen the top as is seen in Eig. 10. The Coned Top piston is a modification of the domed top, in which, instead of a rounded surface being used, a coned section ^^3 Fig. 9. — lo'9 Armstrong- Whitworth Engine, Longitudinal Section. is employed. The advantage lies in the method of manufacture, because it is easier to turn a straight internal and external cone to a uniform thickness than a curved surface. The Recessed Top Piston is shown in Fig. 18, and is occasion- ally used, as it gives a slight reduction in height and is a good shape for perfect combustion. It is a strong form, but the pressure upon it tends to draw in the sides. Both this and the domed top provide the maximum cooling area to the piston, which is good where large pistons are used. DETAILS OP ENGINE CONSTRUCTION 19 The clearance allowed between the walls of the cylinder and the piston varies slightly in practice, but an average value is one-thousandth per inch of diameter in the body, increasing to about three-thousandths at the upper edge. The extra clearance is necessary at the top because of the greater expansion resulting from the higher temperature to which that part is subjected. c2 20 MOTOR CAR ENGINEERING Rings. — There should he at least three, but preferably four, rings at the top of the piston, and the slots in them should be arranged around the piston, so as to provide a devious path for the gas, should anj' tend to leak past. Some means to prevent turning is also desirable, such as a pin driven into the piston body, the head of which engages with a slot in the ring. A scraper ring is sometimes fitted at the bottom of the piston to prevent an excessive quantity of oil passing into the cylinder. It also serves the useful purpose of distributing the oil well round the piston on the up-stroke. Examples of this are illustrated in Figs. 7 and 18. The thickening of the piston at its lower edge is adopted in some designs in order to stiffen it at this point as well as to provide a little metal that can be removed when the reciprocating parts are being balanced, before fitting in place. Recently, advantage has been taken of the reduction of weight which is permitted by the use of pressed steel pistons instead of those of cast iron. The weight of the reciprocating parts should be as light as possible, in order to reduce the vibration of the engine and to allow of the use of higher speeds of revolution with safety. 17. Methods of Securing the Gudgeon Pin. — The gudgeon pin must be secured against rotary and endwise movement, and several means are adopted to ensure this. A common practice is shown in Pig. 10, where a taper pin is screwed into a boss upon the bosses of the piston, the taper of the pin holding the gudgeon tightly in position. In another form a set screw with a parallel end is used, but this is not so gOQd,'-as"it allows a slight movement should the pin be at all slack in the hole. In addition, the fastening is not self-securing, because it is only held in place by its pressure upon the bottom of the hole. The tapered pin jambs upon its sides and thus assists in holding itself in place. Both forms are fitted with split-pins and nuts. Frequently a ring is fitted around the piston, passing through the ends of the gudgeon pin, these being slightly below the surface of the piston. Such a fitting prevents endwise move- ment, and rotary movement is provided against by the use of a small snug or stop pin driven into one end of the gudgeon pin and recessed into the piston. It is shown in Figs. 8 and 9. Occasionally a complete ring is not fitted, but special end-pieces, DETAILS OP ENGINE CONSTRUCTION 21 which serve the same purpose, are used, which fit into slots cut across the ends of the gudgeon and into the piston walls. A last form which may be noted is of an expanding type. The gudgeon pin is slotted at right angles and the hole through the centre is tapped out. In this screwed end a tapered plug is fitted which jambs the gudgeon pin in the bosses in the piston. 18. Connecting Rods. — The connecting rod transmits the pressure on the piston to the crank pin and is thus subjected to an end load ; but in addition there is a stress induced in it by the motion to and fro, known as the inertia stress, which may amount to as much as that from the pressure on the piston, when running at high speeds of revolution. This latter stress acts in the plane of rotation. The general practice is to use a connecting rod having an H section, as this provides the maximum strength to resist the bending stress, and, at the same time, sufficient area to take the end load, for the minimum of weight. A number of examples are illustrated in this chapter, and attention is specially directed to the methods of attachment to and the lubrication of the gudgeon and the crank pins. The rod is drop-forged, but is more expensive to machine owing to the shape of its section. The tubular form has an annular section and is therefore easy to manufacture ; and, where the lubrication is taken to the gudgeon pin, possesses the advantage that the hole through the rod can serve as an oil duct. Its strength to resist bending stresses is good, although interior to the H section, for which reason its weight must be greater. The solid rod is not often met with, but serves its purpose when slower running engines are adopted and where cheapness is more important than weight. Generally speaking, the connecting rod is made from about four to four-and-a-half times the length of the crank, a shorter rod causing excessive pressures on the cylinder walls, and a longer rod too great a height of engine. The gudgeon pin end is usually provided with a hardened steel bush, as it is unnecessary for this end to be adjustable owing to the small movement and consequent wear upon the pin. The bush should project slightly beyond the end of the connecting rod and be fitted with a stop pin to prevent rotation, as should any movement occur the lubricating holes will be closed up. 22 MOTOR CAR ENGINEERING DETAILS OF ENGINE CONSTRUCTION 23 Sometimes this is prevented by turning a groove either round the outside of the bush or tbe inside of the rod, in the wake of the oil holes, but under any circumstances a stop pin is advisable, for relative movement between the bush and the rod must ultimately cause wear and, consequently, hammering. The big end of the connecting rod is usually fitted with bushes lined with white metal, although it is a common practice to run the white metal into the steel direct. The parts which receive the white metal are first tinned with solder so as to ensure metallic contact, as failure in this direction would soon cause the metal to flake and damage the pin. The thickness of this white metal is generally small — from ^ to j^ in. Bronze bearings are also occasionally employed. 19. Crankshafts. — Crankshafts may be either built up or forged in one piece. At one time it was difficult to obtain a homogeneous metal, and in the process of forging some impurity would frequently be enclosed, or the metal would be imperfectly forged, but as the result of metallurgical research and the improvement in the methods of manufacture, the necessity for built-up shafts does not arise, although in some cases, such as bicycle engines, it is a cheaper method of production. In apply- ing ball bearings it is often the practice to build the crankshaft in several lengths, see Pi>;. 175, the ball-bearing crankshaft on the Sheffield-Simplex cars. An example of a built-up crankshaft is illustrated in Fig. 12, although the manufacturers of this (the Adler) engine have ceased to do so. Fig. 19 also shows another construction. It is very important that the crankshaft should be rigid, as excessive flexibility will cause wear at the bearings, and, by reason of the alternating stress, possible failure. There are two ways in which the rigidity may be obtained — one is by well supporting it in bearings, and the other is by increasing its diameter. The former is a question of design, and the latter one of metal ; and of the two the former is to be preferred, as increase of diameter means extra weight and greater frictional losses at the bearings. Some makers are disposed to dispense with a bearing between the cranks, as by so doing a shorter engine is obtained and less time is required to machine the parts ; but it becomes necessary where the en bloc system of casting the cylinders is employed. On tbe other hand, the provision of such bearings gives a better 24 MOTOR CAE ENGINEERING m g ha -*^ "60 o 1-^ ^ S I— ( ^ 55 DETAILS OF ENGINE CONSTEUCTION 25 support to the crankshaft, and therefore the deflection is less, with the result that wear is less pronounced. The crankshaft may also be made lighter. A crankshaft with bearings between each crank is shown in Fig. 17 — the Knight-Daimler engine. A longer bearing is required at the flywheel end of the shaft, because the weight of the flywheel continuously acting upon that bearing prevents the lubrication from being as efficient as at the other bearings. Hollow crankshafts are frequently employed because, firstly, they are stronger than solid shafts for equal weight ; secondly, the hole through the shaft serves as an oil duct for lubrication purposes ; and thirdly, the probability of fracture from defective material is considerably reduced. The first follows from the fact that the stress in a shaft subject to torsion increases from zero at the centre to a maximum at the circumference, while the stress due to bending is least at or near a plane through the axis of the shaft. Consequently, the increased diameter permissible with the hollow shaft renders it better able to withstand the torsional and bending stresses which it is called upon to bear. The probability of fracture is reduced, because flaws, if there be any, are usually formed in the centre during the process of forging and gradually extend, when in use, through the metal, ultimately causing fracture. In the process of boring the hollow shaft, however, these flaws may be removed, or, at any rate, detected before extensive machining has been done upon the shaft. 20. Arrangements of Cranks. — With the two-crank engine, the cranks may be arranged either on opposite centres or on the same centre. Four-crank engines are always made with 180 degrees between the two outer and the two inner cranks as seen in the illustrations. Six-crank engines may be looked at in the light of two three-throw crankshafts and are arranged so that the cranks at equal distances from the ends are together. For example, supposing the cranks are numbered from 1 to 6, commencing at the front end of the engine, then 1 and 6 are together, 3 and 4 and 2 and 5, and they come on top centre in the order stated for reasons which will be seen later. There are 120 degrees between each pair of cranks. When the piston is approaching or leaving the dead centres, it is either being brought to rest or increasing in velocity, 26 MOTOR CAR ENGINEERING because its velocity at the ends of the strokes is zero (see Pig. 108). To bring about these changes of velocity some force must be exerted ; and hence, near the ends of the strokes, there will be alternately a pull and a thrust upon the crankshaft, which will be transmitted to the chassis, setting up a considerable amount of vibration, unless the reciprocating parts are well-balanced. These forces act in a vertical direction in a vertical engine, but there are, in addition, horizontal transverse forces due to the oscillation of the connecting rod, to and fro, in the plane of rotation, the effect of which will be to tend to displace the engine in the direction in which the force acts. 21. The arrangements of cranks will now be compared on the following bases : — continuity of torque and the balance of the moving parts. It will be obvious that as the number of cylinders or the number of impulses increase, so must also the continuity of effort, as there is not so long a period between the effective strokes (see Fig. 107). The order of superiority will therefore be 6, 4, 2. But there are two arrangements of the two-cylinder engine. When the cranks are at 180 degrees, there will be two explosion strokes in succession and then two non-effective strokes as below : — 1st Cylinder. 2nd Cylinder. Explosion. Compression. Exhaust. Explosion. Induction. Exhaust. Compression. Induction. When the cranks are together there will be an interval of 360 degrees between the explosion strokes in the two cylinders, thus : — 1st Cylinder. 2nd Cylinder. Explosion. Induction. Exhaust. Compression. Induction. Explosion. Compression. Exhaust. The latter arrangement will therefore be the better for con- tinuity of torque. In all that follows the first arrangement will be called two-cylinder (180), and the second arrangement, two- cylinder (360). As regards the balance of the moving parts, the comparison DETAILS OP ENGINE CONSTEUCTION 27 must be between the two two-cylinder arrangements, as both the four and the six-cyUnder engines have only a small unbalanced couple. The six-cylinder engine is, however, slightly superior to the four-cylinder engine. In the two-cylinder (180) arrangement the reciprocating parts move in opposite directions, and there will, therefore, be a tendency to rock the engine in a longitudinal plane. This tendency will be absent in the two-cylinder (360) arrangement, but in its place there will be an increased amount of hammering, because the reciprocating parts of both cylinders will be moving in the same direction at the same time. In practice these effects are, to a large extent, avoided by the use of balance weights, which minimise but do not entirely eliminate them. As regards the transverse forces, it will be clear that in the two-cylinder (180) engine, the inertia forces due to the motion of the connecting rods will act in opposite directions, and conse- quently will oppose one another. On the other hand, in the two-cylinder (360) engine, as both connecting rods travel in the same direction simultaneously, the forces produced will be unbalanced. Both engines are, therefore, at a disadvantage in some respects ; but the two-cylinder (360) engine is generally preferred on account of its greater uniformity of torque. 22. Flywheels. — The function of the flywheel is to equalise the torque on the transmission gear, by storing up and restoring the excess energy given out by the engine when it rises above or falls below that required to propel the car. (See Art. 173.) In all engines there is a fluctuation in the energy given out by the crankshaft, and where, as in automobile work, a fairly uniform torque is essential, the flywheel becomes necessary. A secondary benefit derived from fitting the flywheel is that the full eflfeets of the explosions in the cylinders are not transmitted to the gearing. The flywheel should be bolted to a flange on the crankshaft and not keyed, because of its reversible action. When the flywheel is storing up energy, it is driven by the engine, but when it is restoring its energy it drives the engine ; thus, if fitted on a key, this continual reversing action will cause the key to be worn away. This is one of the most fruitful sources of " knock " in engines so made, and is most difficult to locate 28 MOTOE CAE ENGINEEEING unless one has had previous experience on a similar engine. Examples of attachment are shown in Figs. 7, 9, 11, etc. Pigs. 11 and 106 illustrate a flywheel in which the rim serves as a fan for drawing air through the radiator. (See also Art. 163.) 23. The Cylinders. — The shape of the cylinder will be determined by the space required by and the arrangement of the valves. Theoretically, for the minimum of cooling surface per cubic capacity, the shape of the head should be hemispherical, and it has been so made in some instances, but it is not an easy matter to devise an inexpensive and an efficient valve gear for such a shape without considerably complicating the engine. Thus, with valves in the head and inclined at an angle, the operating gear must be through long rocking levers, while the cost of machining the parts renders the engine costly to produce. The vertically overhead valves are excellent and give a good shape to the combustion chamber, but the gearing often detracts from the otherwise good points. A few years ago the valves were placed on both sides of the engine. The pipe arrangement from an engine so arranged was very satisfactory and a symmetrical engine was obtained, but the ratio of cooling surface to cubic capacity was nearly double that which a truly hemispherical combustion chamber would provide, and, therefore, there was a considerable heat loss to the cooling water. Still, the efficiency of such engines was high, in fact, differed little from those with valves in the head, but comparisons are difficult to make, for to be effective, the conditions must be the same in both cases. As will be clear, this arrange- ment necessitates the use of two camshafts and two sets of timing wheels. At the present time, the valves are generally placed side by side, which, while it necessitates only one camshaft, does not allow the pipe arrangement to be so good, as the pipes have to be bent so as to clear one another. The use of smaller valves is also necessary,- unless the engine is lengthened, as sufficient space is not available for two valves in the pitch of the cylinders. The real reason for the development in this direction is, however, the more compact appearance of the engine — the bonnet is not so full as it formerly was — and where the en bloc system is used, the difficulties with the piping are not so evident. (See also Art. 27.) DETAILS OF ENGINE CONSTKUCTION 29 24. With, regard to the methods of casting cylinders, they are made separately, in pairs, in threes, or e?i hloc. The advantage accruing from separate cylinders is that they are more easily replaced if damaged, and that it avoids the multiplicity of designs ; as the same cylinder can be used for one, two, three, four, or six-cylinder engines. It does, however, increase the length of the engine and is slightly more expensive. The en bloc system has been discussed in Art. 15, so nothing further need be said under this head, except that as manu- facturers now usually cast in twos or threes they avoid the extreme effect of the disadvantages previously pointed out, while the advantages are in some measure obtained. Occasionally one finds examples where separate jackets are provided and the cylinders are machined inside and outside. This is usually done where lightness is important, and has the merit that uniform expansion of the metal is obtained. The jackets may be secured either by riveting or by shrinking on, or they may be spun into place. Sometimes, however, they are provided with a rubber packing ring, which, after a short period of use, becomes vulcanised and lasts for an exceptionally long time. Jackets may also be electrolytically deposited, but this is very expensive and is only carried out in extreme cases. Auxiliary exhaust ports are sometimes fitted to the cylinders of air-cooled engines, so that they are uncovered when the piston is nearly at the bottom of its stroke. These should be provided with a separate exhaust pipe, otherwise they are very dirty. The fact, too, that they weaken the cylinder has to be considered, and, except as regards air-cooled engines, they are a questionable advantage. 25. Valves and Valve Gears. — One of the most important points which a designer has to determine is the type and position of the valves and gearing ; in fact, so important is this question that the success of an engine depends largely upon its valve gear. Until recently the only kind of valve used in petrol engines was that known as the mushroom or poppet valve, but the growing importance of silence and efficiency has resulted in the evolution of piston, rotary and sleeve valves. 26. The Poppet Valve. — This type of valve, being more generally used, will be considered first. It may here be stated 30 MOTOE CAK ENGINEERING that poppet valves will probably continue in use for some time, because of the reluctance of manufacturers and their customers to relinquish a well-tried and excellent design for another, in which radical changes are made ; but the inherent defects possessed by such valves must eventually cause them to be discarded. The principal troubles experienced with poppet valves are those due to mechanical causes, namely : — (1.) Noise due to the hammering of the tappets on the cams and consequent wear. (2.) Eisk of broken valves and springs. (3.) Leakage from warped valves and seats. (4.) Insufficient area in opening and closing, unless excessive lifts or unduly large valves are used. (5.) Power absorbed in operating gear. In modern work the first three defects are almost eatirely eliminated, by the use of special steel in the case of (2) and (3), and by enclosing the tappets or the fitting of supplementaiy springs or buffers in the case of (1), so it is in regard to (4) and (5) that the real defects are found. These valves, in common with the other types mentioned, have a very small movement which takes effect in an infinitesimally short space of time— about one fortieth of a second — but, whereas with the piston and sleeve valves, the reciprocating members are driven through links by the camshaft, the poppet valves are opened by the action of cams and closed by springs, so it will be readily seen that during the period of opening very severe stresses may be set up in the actuating gear. To reduce these inertia losses, the valves and recipro- cating parts are made as light as possible, as the whole of the valve-gear has to be set in motion by the cams and closed by the action of the springs. To do this smoothly and quickly, the cam should have such a contour as will give the parts a uniform acceleration, but such a cam would be expensive to machine, so it is generally made with straight or nearly straight sides, and a small rounded peak. This gives reasonably quiet running, and is easy to manufacture, although it still restricts the valve opening at the position of maximum piston speed. As regards the power required to actuate the valve-gear, this is absorbed in overcoming the friction and the inertia of the reciprocating parts, in opening the valves against the pressure inside the cylinder and in com- pressing the valve springs — the work given out by these springs on closing being quite negligible, as it is highly probable that the cam roller never touches the cam when falling, but drops straight down from the peak to the root, partly because the cam is incorrectly shaped, and partly because of the relative weakness of the spring. Valves at the present day are made in one piece, of steel containing a high percentage of nickel. The valve stem should DETAILS OF ENGINE CONSTKUCTION 31 be joined to the valve head by a well-rounded curve, partly to strengthen the stem at a point where it is subjected to great heat, and partly to direct the gases in and out of the cylinder. This is preferable to increasing the thickness of the head by rounding up the back of the valve. Eegarding the angle which the valve seat should be made, this is usually 45 degrees, although occasionally it is slightly varied ; but it should be remembered that the flatter the seating the greater the likelihood that a piece of carbon or other matter will remain upon it. For this reason, and because the tightness of a valve is not dependent upon the area, but upon the intensity of a pressure between the surfaces, seats should not be wider than, say, -^^ in. Abnormally narrow seatings, on the other hand, soon get hammered into the valve and produce a shoulder which causes leakage. For interchangeability the exhaust and inlet valves should be the same size, and this is generally the case, a lower velocity through the exhaust valve being obtained by increasing the lift of that valve where necessary. 27. Arrangements of Valve Gears. — While the arrangements possible and those which have been made are legion, there are only three which are used in current practice. They are as follows : — (a) Inlet and exhaust valves on one side. (b) Inlet and exhaust valves on opposite sides. (c) Inlet and exhaust valves in the cylinder head. In adopting either of the arrangements, (a) or (b), it is necessarj' to provide side pockets for the valves, but with (c) these are not required ; so that in the two former the cooling surface will be much greater than the latter, and consequently more heat will be carried away in the cooling water. On the other hand, in case (6) these pockets will act as cushions, and reduce the explosive effect on firing the charge, as the fresh gases drawn into the cylinder will not mix so intimately with the spent gases over the exhaust valve. Still, assuming that the compression ratio used is the same in both engines, and also the fuel consumption, it must follow that the mixture in the cylinder of an engine with valves in the head will be weaker, as all the products of combustion from the previous charge will be mixed with the new charge, and the subsequent burning will therefore be less rapid. So it may be said that with regard to silence and combustion, these two engines are practi- cally equal, but that a gain in efficiency is to be expected with overhead valves by reason of the reduction of heat loss to the cooling water. One objection which is often made in respect to the placing the valves in 32 MOTOR CAE ENGINEERING opposite sides of the cylinder is that two camshafts become necessary ; but although this is the case, it is really only an objection ■which affects the cost of manufacture — on the grounds of efficiency it has much to commend it, as the valves may thereby be made as large as desired. With valves on one side, unless the engine is to be unduly lengthened, or excessive lifts are employed, the valve aroas will be much less. The same may also be remarked concerning engines with valves in the head, although, perhaps, not to the same extent, as by slightly recessing the valves into the cylinder walls it is possible to obtain the area necessary in order to prevent the use of high velocities. 28. Operating Gear. — Regarding the position of the actuating gear, undoubtedly the overhead camshaft is much to be preferred, especially where, as in the " Maudslay " engine, the camshaft swings bodily over and permits an immediate examination of the valves. The Maudslay valve gear is shown in Fig. 13. With the standard type of engine the camshaft is enclosed within the crankcase, and access to the valves is obtained by removing caps placed over them ; yet, while this generally gives satisfaction, it will be conceded that any device which contributes towards accessibility must ultimately appeal very strongly to the manufac- turer as well as the private owner. 29. Valve Tappets — The Crossley Valve Tappet. — The valve tappet mechanism fitted to the Crossley engines is shown in Fig. 14. The valve A is kept upon its seat by the spring B. When in operation the cam roller M is lifted by the camshaft and carries with it the valve riser cup H. Inside this cup the_^lunger Pig. 13.— Maudslay Valve Gear, G is free to slide, and between the showing Valve-cage in act bottom of G and the cup H there is of removal. ^ ^^^^^ clearance. As the cup H rises this clearance is first of all taken up, and the further lifting of the cup causes the plunger G to lift and carry with it the valve A. Inside the plunger G is a spring, the object of which is to keep the bottom of the valve-stem in contact with the set screw E and to do away with the noise which would occur if a gap existed DETAILS OF ENGINE CONSTEUCTION 33 between E and the bottom of the valve stem. The adjustment of the set screw E should be such that there is a clearance of about the thickness of a visiting card when the valve is closed and the plunger G is depressed by hand as far as it will go, thus, for the purpose of the adjustment, doing away with the clearance between G and H. The holes K are to allow any oil which may work up to drain back into the crankcase. The Wolseley Valve Tappet. — This tappet is shown in Fig. 15, from which it will be seen that it consists of a plunger having a screw adjusting at the point of engagement with the stem of the valve. The plunger is prevented from rotation by flutes cut upon the sides, which slide in corre- sponding slots in the guide. The valve is quietened by the use of a fibre washer in the end of tbe plunger. The Napier Valve Tappet is shown in Fig. 16. A plunger rod carrying the cam roller works in a guide C attached to the engine casing. At the upper end of this plunger is an adjusting screw A, case-hardened at the top, which may be moved inwards or outwards, as necessary for adjustment. The screw A is secured by a split pin B, which, it will be observed, has a very fine adjustment. The roller is held in position on the cam by a slot cut across the guides. 30. Valve Setting.— The setting of ^ig- 14.— The Crossley Valvn the valves in petrol engines varies considerably in practice, being somewhat affected by the shape and configuration of piping, degree of compression used, the speed of rotation of the engine, and the mechanical perfection or otherwise of the actuating mechanism. In some cases the actual setting is M.G.i:. D 34 MOTOE CAE ENGINEEEING taken by measuring the distance which the piston is from the end or commencement of its stroke — a practice which can- not be too strongly con- demned, owing to the small amount of displacement of the piston for a large angular movement of the crank pin near the dead centres, and because such readings will only apply to engines of one particular stroke. By far the better method is to base the opening and closing of the valve on the position of the crank pin, for if marks are placed upon the flywheel to correspond with the various cranks the setting of the valves can be verified at any time, and, in addition, the same setting will closely apply to all engines having the same speed of revolution. An average setting suit- able for engines running at about 1,200 revolutions per minute is as follows : — Inlet opens 10, degrees after top centre. Inlet closes 20 degrees after bottom centre. Exhaust opens 40 degrees before bottom centre. Exhaust closes 7 degrees after top centre. Dealing first with the inlet ■n , = w 1 1 17 1 m 4. valve, the object of delaying its Fig. 15.— Wolseley Valve Tappet. . ■ ." .(_ ,°,, •' ^^ opening is to ensure that the pressure within the cylinder has fallen to the pressure of the atmosphere. DETAILS OF ENGINE CONSTRUCTION 35 as otherwise there would be a possibility of flame from the previous charge being blown into the inlet pipe and so causing an explosion. Then, as has been already mentioned, on the induction stroke of the engine there is a partial vacuum in the cylinder, so that if when the piston reaches the end of the stroke its motion were suddenly arrested, more gas would continue to enter through the inlet valve. This is, of course, impossible, but, by prolonging the period of opening until the piston has started upon its compression stroke, a greater quantity of gas can be drawn into the cylinder. Eegarding the exhaust valve, it is most important that the products of combustion should be got rid of as soon as possible after they have done their work, so as to reduce the pressure during the exhaust stroke. But, when the piston reaches a position corre- sponding to the crank angle given for the point of opening to exhaust, the crank eiiort is very small compared with the maximum effort, and the gain in power due to the further expansion of the gases to the end of stroke before exhausting, is quite out of pro- portion to the gain from a lower back pressure on the exhaust stroke — so it is found to be more economical to open this valve at the point stated. The closing of the exhaust valve is not so important so long as it is effected before the inlet valve opens— the actual time by which it precedes it being determined by the speed of the engine — the faster the speed of revolution the greater should be the angle, unless excessively strong springs are used. Fig. 16. 31. Sleeve, Piston and Rotary Valve Engines. — Among the claims made for the classes of engines now being considered is that of silence, which will be readily granted by any but the most biassed observers. It is sometimes argued that the gearbox and the engine's explosions cause more noise than the engine, but any device which tends towards silence must receive recognition, and it is for this reason that the tappets are now so universally enclosed in poppet valve engines. Another claim is smoothness of operation, and although this cannot be accepted as fully as the former, because of the impossibility of entirely pre- venting some degree of vibration with an explosive engine, yet, in the sense that there are no cams with their hammering action to set up additional vibrations it must be conceded. D 2 36 MOTOE CAR ENGINEERING Several otlier advantages have been forwarded respecting these engines, some of which refer only to a particular type, and cannot be indiscriminately applied. The principal of these are — an increase in power, efficiency and flexibility, a completely machined inside of cylinder, and consequently a uniform compression. With regard to the increase in power and efficiency, it will be readily understood, in view of the remarks made respecting engines with valves in the cylinder heads, that any engine of similar construction must gain in efficiency, and as less heat is lost to the jacket there must also Fig. 17.— The Knight-Daimler Engine. be a greater amount of power developed for any given size of cylinder. Similarly, the claim for flexibility, or rather control-ability, as Mr. Dugald Clerk very rightly terms it, can hardly be accepted entirely, as it is well known that engines with pockets, having a richer mixture in the body of cylinder, can run on smaller charges, and thus will be more flexible. But the advantage of a machined surface in a cylinder cannot be overestimated when considering compression. In engines which have a part of the surface left as cast it is impossible to secure a uniform combustion space except by fitting different sized valve caps, which after an engine is once dismantled DETAILS OF ENGINE CONSTEUCTION 37 frequently become disarranged. The regularity of running, which is so desirable in an engine, depends largely on the mean pressure on the piston, and should the compression pressure vary, so will also the maximum pressure. This was one of the reasons why a synchronised ignition became imperative in first-class work. There is another feature of these engines to which attention might be drawn, namely, the large valve port opening, whereby the velocity of the gases are considerably reduced. This point is the more important because it enables a larger chai-ge to be taken into the cylinder at high speeds, and makes a freer exhaust possible, both giving an incre- ment of useful power. 32. The Eniglit Engine. — An assembled arrange- ment of the Knight valve gear is shown in Fig. 17, while Fig. 18 shows a sec- tion through the Knight- Rover engine. In the latter figure it will be seen that two sleeves are em- ployed which operate be- tween the piston and the cylinder walls. These sleeves are stiffened at their lower ends by rings A and B to which are attached lugs X and Z by which they are driven through the rods C and D from the valve shaft W. At the upper end of the sleeves are ports — H on the inlet side and F on the exhaust side. In order to render this end gas-tight three narrow rings and one wide ring are fitted into the cylinder head, which is detachable. The wide ring is provided to prevent the edges of the ports striking the edges of the rings. The cooling of this head is effected by the passage of water in at Y and out at E. The valve shaft W is driven from the crankshaft by means of a silent chain (see Fig. 17). The method of operating is as follows : — On the induction Fig. 18.— The Knight-Eover Engine. 38 MOTOE CAR ENGINEEEING > > a 'I m o H DETAILS OF ENGINE CONSTEUCTION 39 stroke of the engine, the inlet ports H are brought into line opposite to the inlet port I in the cylinder body — the inner sleeve moving upwards and the outer sleeve downwards, thus giving a rapid port opening. On the compression stroke the inner sleeve is moved so that it recedes into the cylinder head, and at the point of firing the ports Fig. 20.— The Hewitt Engine. in the inner sleeve are in their uppermost position. This ensures that any chance of leakage will be reduced to a minimum. During the explosion stroke the sleeve descends travelling in the same direction as the piston, and when exhaust occurs the ports P on the exhaust side are in line with the port opening C to the exhaust in the cylinder body. 33. The Bingham Piston Valve Engine. — The construction of this engine is shown in Fig. 19 from which it will be seen that 40 MOTOR CAR ENGINEERING two piston valves are provided which work in annular casings on the two sides of the engine. The valves have a rectangular slot cut in the circumference on the side nearest to the cylinder and are packed by four ^ide piston rings, two being above the slot and two below. The operating shaft is driven by skew gearing from the cranlc- shaft, and connection is made to the valves by the aid of levers Fig. 21. — Section through Hewitt Piston. and links. The method of operation is clearly shown in the illustration. The special point of interest with this gear is the slow rate of movement of the valves — only a quarter of the speed of the engine — which is possible because each valve operates on the up-stroke as well as on the down-stroke when the valves are in the middle of their travel. This slow rate of valvular movement cannot fail to reduce the wear of the parts and minimise vibration, although it is somewhat counterbalanced by the large number of joints between the operating shaft and the valves. The facility with which access may be obtained to any part of the valve gear is worthy of commendation. DETAILS OF ENGINE CONSTRUCTION 41 34. The Hewitt Engine. — In this engine the valves are placed on the same side of the cylinder and are operated from a half-time shaft A, Fig. 21. The inlet valve is IJ inches diameter and the exhaust valve If inches diameter, both having a 3-inch stroke. The charge enters through the inlet passage B (inset Fig. 21), and passes into the cylinder through the port -which is uncovered by the piston valve. The exhaust takes place when the port, seen in the larger section. Fig. 21, is uncovered by the exhaust valve on its down-stroke and passes away through the pipe seen to the right. Fig. 22 shows a section through one of the exhaust valves from which it is seen that exceptional arrangements are made to ensure that the exhaust valve will be kept at a low working temperature, as water- jacketing is provided between the ports. The manner in which the four ground joints are made between the valve casing and the cylinder is shown in Fig. 22. Eie. 22. Questions on Chapter III. (1) Compare the poppet, the sleeve and the piston valve — as applied to petrol car engines — from the standpoints of (a) silence, (6) flexibility, (c) power, (d) life of working parts, and (e) efficiency. (2) Why is an overhead valve gear more desirable than the ordinary type of gear when considered from the point of view of efficiency ? (3) Why is an engine with valves on opposite sides more silent than another with valves in the head ? (4) Sketch a piston with three piston rings, a scraper ring and the gudgeon pin in place and say how the parts are lubricated from the crankcase. (5) What is the function of the flywheel ? How is it generally secured to the crankshaft, and why should this be so ? (6) Make a sketch showing a section through a poppet valve gear, including the valve pocket, valve springs, tappets, and camshaft. 42 MOTOR CAE ENGINEEEING Draw only sufficient of the cylinder and crankoase as is necessary to show the relative position of the parts. (7) What are the respective merits as regards {a) uniformity of torque, and (b) absence of vibration in the two forms of two-cylinder engines. (8) Describe the Knight Engine, and show by the aid of sketches how the sleeves are kept from leaking, and how they are driven. (9) What measures may be taken to silence the poppet valve gear, and give sketches of one method by which this is effected 7 (10) How does the type of valve gear employed influence the shape of the cylinder and what is the best shape ? Give your reasons. (11) Show how the connecting rod is attached to the crank pin and say what materials you would use for the various parts. (12) Give the periods and times of opening and closing the valves of a petrol engine. What influences affect the actual times, and why ? CHAPTER IV PETROL 35. The Suitability of Petrol as a Fuel. — Among the most important questions which had to be decided in applying the internal combustion engine to road vehicles was the source of motive power. Up to that time gas and oil had been in extensive use for stationary purposes, both of -wbiob it would be impossible to adopt, because tbe former requires a large storage capacity and tbe latter cannot be used for starting, gives beavy explosion eflects, and bas an exceptionally evU-smelling exbauat. It is tberefore easy to understand why petroleum spirit was selected as tbe source from wbenoe tbe power sbould be derived. It vaporised freely, was cleanly to bandle, and tbe exbaust was practically inodorous, tbus constituting an abnost ideal fuel. This state of affairs continued to exist for some time, as there was an ample fuel supply of fairly uniform quality ; but with tbe extended use of motor cars for both pleasure and commercial purposes, tbe demand exceeded tbat wbiob tbe Refiners could supply, and tbe price of fuel rose considerably. Tbe shortage was due to the fact tbat petroleum spirit is only one of the many fractions obtained from the crude oil, and not only so, but it forms a very small percentage of the total, and hence, unless there is a sufficient market for the other products of distillation, it will be impossible, on account of the expense, to distil the crude oil for petroleum spirit alone. A Table, illustrating how small a percentage it is, is appended : — . Constituent. Scotch Shale Oil. American Petroleum. Russian Petrolemu. Per Cent. Per Cent. Per Cent. Ether, Gasoline, and j Petroleum Spirit J 5 16 4 Kerosene 35 50 27 Intermediate Oil . 2 — 12 Lubricating Oil . 18 15 32 Paraffin Wax 12 2 1 Eesidue 28 17 24 44 MOTOR CAR ENGINEERING A complete table, showing the products of distillation from American petroleum with their percentages and properties, is given on p. 45. To meet this shortage of spirit, the importers gradually added some of the heavier fractions of the crude oil, with the result that the spirits in use at the present day have a much higher specific gravity and boiling point, and are, consequently, of a much less uniform character. It will be seen later that this lack of homogeneity is the cause of many of the difficulties experienced in carburation. 36. Physical Properties of Petrol. — Petroleum spirit belongs to the paraffin series of hydrocarbons, which have a general com- position of On H2n + 2, and is a mixture of a large number of the series, the exact composition being determined by the limits of distillation and the source from whence it is obtained. The vapour from the spirit is produced at ordinary atmospheric temperatures, and weighs a little more than three times the weight of an equal volume of air. It ignites readily at an open flame, so that extreme care should be exercised in handling the liquid. The fuel has an average specific gravity of about '68 at 15° C, a calorific value of from 18,000 to 21,000 B.T.U., and a boiling point of from 150° to 200° F., while the major constituent is hexane, Ce H14. The explosive range of petroleum spirit at atmospheric pressure is from 2 to 5 per cent, by volume, the maximum explosive effect being produced at about 2*5 per cent. The petrols now supplied to motorists have, however, slightly different physical characteristics, the specific gravity varying from -700 to -760, the calorific value from 17,000 to 20,000 B.T.U., and the boiling point from 150° to 250° F. They no longer belong exclusively to the paraffin or saturated series of hydro- carbons but frequently contain some of the olefines or unsaturated series (On H2n) and some of the benzenes and naphthalenes. (See Table of the Physical Properties of some of the principal constituents of Petrol on p. 47.) 37. Source from Whence Obtained. — Crude petroleum, from whence petrol spirit is distilled, may be obtained either from shale or from petroleum springs or wells. The shale as dug from the pits is a dark, hard slaty-looking substance, and is first broken into small pieces by stone-crushing machinery, in order PETEOL 45 to expose as large a surface as possible to the subsequent action of heat. There have been many methods of extracting the oil from shale, but that now generally employed is known as the "continuous system," in which vertical retorts are used. The shale is continually fed into the top of a retort, in which the temperature rises from about 800° F. in the upper portion to about 2,000° P. at the bottom. Thus, as the shale descends through the retort, it is subjected to a higher temperature, giving off the lighter vapours at the top and the heavier products and ammonia as it passes towards the bottom. The vapours produced by this heat treatment are taken to a stack of vertical pipes, in which the heavier oils are condensed, the remaining gases passing on to scrubbers or coke towers. Here the gases are exposed first to a stream of oil to remove the lighter spirits, and then to a shower of water, to absorb the ammonia, the gases which remain uncondensed being taken back to the retorts, where they are used for heating purposes. The oil used for absorbing the lighter spirits is an intermediate oil, having a specific gravity of about -856, which is made to give up the spirit by subsequent distillation. Crude petroleum is obtained from weUs or springs in many parts of the world, and as pumped from the earth has a thick brownish or greenish appearance, and a very pungent aroma. Its specific gravity varies from •19 to "938, according to the location of the spring. The constituents, with their physical properties, of some of the American oils are given in the accompanying table : — Constituent. Boiling Point. Specific Gravity. Percentage. Petroleum ether 104° to 158° P. •59 to -625 •5 Gasolene 158° to 176° P. •66 to -67 1^5 Petroleum Spirits . 176° to 302° P. •68 to •738 14-0 Kerosene 302° to 572° P. •753 to •864 50 Lubricating Oil 572° P. upwards •844 to -96 15 Paraffin Wax . — — 2 Eesidue . — i — 17 38. Distillation. — The procedure followed in carrying out the distillation of crude petroleum is as follows : — A number of stills of retorts are arranged in series, connected together by pipes led from the bottom of one still to the next in the series. The number of stills is determined by the number of fractions or cuts which it is desired to take. Each still is maintained at the temperature representing the limit up to which the cut should be taken by means of a furnace, although steam- 46 MOTOE CAE ENGINEEEING heating is frequently employed for the lighter fractions. The crude oil is pumped into the first still, where it remains until the mass is thoroughly heated up and the lightest spirits driven off. The residue is then allowed to flow by gravity into the second still and a similar operation performed, and so on until it has been through all the stills in the series, the residue from the last still being a dark, heavy, evil-smelling compound. The vapours driven ofi from each successive still are led to separate condensers, in order to liquefy them and then stored in storage tanks placed beneath the ground. Frequently the distillation is stopped after the kerosene has been extracted, and the oil remaining used as fuel oil for heavy oil engines, liquid fuel for boilers, etc. The calorific value of crude oil is from 20,000 to 21,000 B.T.U., and that of the fuel oil 17,000 to 19,000 B.T.U. It will be seen from the nature of the process that the several cuts are not oils or spirits of uniform density, but a mixture of several other oils or spirits of varying density and boiling point, each cut being capable of further fractionisation. The crude petroleum spirit is then again distilled in special hot- water or steam-heated stills, the process being continued until the desired specific gravity of the condensed vapours is obtained. After this, it is washed with sulphuric acid and with soda, filtered and passed to settling tanks, so that any water which has come over with the vapours may be deposited. The washing with sulphuric acid is carried out for the purpose of removing tarry substances, while caustic soda is subsequently employed to cleanse the spirit from any sulphuric acid which may remain. It is very difficult to entirely eliminate all traces of sulphuric acid, as sulphur is, practically, always found to be present in the petrols upon the market, varying in quantity from 0'05 to 0'07 per cent. 39. Composition. — It is obvious that the degree of utility of an oil or spirit for fuel purposes will be entirely governed by the constituents of that fuel. Mr. G. H. Baillee, in a paper read before the Eoyal Automobile Club in May, 1908, stated that he had found as many as twelve members of the paraffin series in commercial petrols, and that most contained butane, hexane, heptane, nonane, and decane. Decane is the major ingredient of kerosene, so that it may be fairly assumed that one of the constituents added to increase the supply of a usable fuel in petrol engines was that which had previously formed part of the cheaper fuel — kerosene. The following Table gives the physical properties of some of the principal constituents of petrol : — PETEOL 47 Constituent. Chemical Symbol. Boiling Point. Specific Gravity at 15° C. Paraffin Seiies — Centigrade. Butane . d Hio 1° •600 Penfcane (normal) . Cs Hi2 36° •626 Hexane . Ce Hi4 68-5° •674 Heptane C7 H16 98° •688 Octane (normal) Ga His 125° •707 Nonane (normal) C9 H20 150° •722 Decane . Cio H22 160° •738 Naphthalenes — Hexahydrobenzine . Ce H12 69° •760 Hexahydrotoluene . C,Hi2 97° •772 Benzene Series — Benzene . Ce He 80-4° •884 Toluene . C7 Hs 111° •871 Alcohols — Ethyl Alcohol . CaHeO 78-3° •794 Methyl Alcohol CH4O 66-0° •797 40. Volatility of a Fuel. — It will be seen later how much these varying boiling points affect the volatility of a fuel, but for the present it will suffice to show how that volatility may be ascertained. *41. Baillee's Test Apparatus for Liquid Fuels. — In this instru- ment the relative volatility of different fuels is ascertained by measuring the quantity of air required to evaporate a given amount of the fuel, and comparing this with the quantity required to evaporate the same amount of a standard fuel. Heptane has been taken as a standard fuel, since it can be obtained cheaply in a fairly pure form, while its volatility is on a par with that of a good petrol. The apparatus is shown in Kg. 23, from which it will be seen to consist of an inner tube terminating below in a stop-cock, and above in a large bulb with an opening through a funnel to the air. Near the bottom of the tube, a side tube is introduced just above the stop-cock connected to a foot bellows. A water-jacket surrounds both these tubes, and on this jacket is a double scale to indicate the height of the liquid in the inner tube. The petrol to be tested is poured into the inner tube through the funnel and air is blown by the bellows through the side tube, forcing the petrol up into the bulb churning it up violently and rapidly vaporising it. The funnel tube ensures that no petrol is carried away in a state of suspension. 48 MOTOK CAR ENGINEERING Fig. 23.— Baillee's Test Apparatus for Liquid Fuels. PETROL 49 The method of making the test is as follows : — The outer jacket of the apparatus is filled with water which serves to keep the temperature constant during the test. Then a very little fuel is poured into the funnel at the top, and a stroke of the bellows is given to drive this into the bulb and so wet all its surface. This fuel is then run out by opening the stop-cock at the bottom. Then suflficient fuel is poured in to reach above the highest mark on the scale, and, after waiting half a minute, sufficient is run off at the stop-cock to bring the level down to the highest mark. Then two strokes of the bellows are given, which are generally enough to evaporate nearly a twentieth of the fuel ; if not sufficient, further strokes are given until the first twentieth has been evaporated. Then the strokes are continued and are counted until all but the last twentieth has been eva- porated. To obtain the^E.A.C. num- ber of the fuel, the test is repeated, using heptane in- stead of the fuel, and the ratio of the number of strokes of the bellows in the two tests, multiplied by 100, gives the E.A.O. number. Curves of volatility may be obtained by taking read- ings after every five, ten, or twenty strokes. The read- ings are then plotted as in Fig. 24, and from the curves so obtained the number of strokes required to evaporate each successive twentieth separately can be found and plotted as in Fig. 25. These latter curves show the volatility of the different portions of the fuel, and, for any one fuel, are very similar in shape to the boiling point curves. In Fig. 24 the curve for heptane is a straight line up to the nineteenth twentieth, the readings taken being shown by dots, which give an idea of the accuracy attainable by the apparatus. The final bend in the curve is due to impurities in the heptane. This curve becomes in Fig. 25 a horizontal straight hue, as must be the curve of any fuel which is not a mixture. The E.A.C. has decided that the number 100 shall be taken to represent the volatility of heptane, and that the volatility of M.G.E. G 1 MO 1 jao 1 \ > / \ /oo ii f (} / o M M f J " 1 i, '/ 1 1 f / f — / y Yr. 1^ / 1 / .^ / ''/ J 40 / 4 y / / / y^y 7 / / 20 1 1 ^ Yy / ^ / 1 ^ i:^ y cA u^ ^ LA ■^ ■^ 30 *0 so BO /OO y=4Ve C£-A/r Of ri/CL £M/'0f>AT£O. Fig. 24. 50 MOTOR CAR ENGINEERING any fuel shall be expressed by a number equal to 100 times the ratio of the quantities of air required to evaporate the same amounts of the fuel and of heptane as measured in this apparatus. The figures thus obtained are higher the less the volatility of the fuel, so that, properly speaking, they represent the non- volatility of a fuel. In making a test, only the air required to evaporate from the ^ second to the nine- teenth twentieth is taken into account, because the first twentieth consists of very light spirits, which are often lost by evaporation be- fore reaching the engine, while the last twentieth is sometimes a very heavy oil, which it is almost impossible to evaporate, and which, in quantities so small as this, is not detrimental. 42. Specific Grav- ity. — The specific gravity of any sub- stance is the ratio which the mass of unit volume of that unit volume of a standard 24 \ \ 1 k /li.1. OMO . i ( J / \f' 'A / ^ 5 * i oj^ .^ ' 1 A e^r^ »£■ ^ -^ ^ y / ; *. - ( ___ ^ / 2 V- ^ c ,i.!9 Pig. 26.— Darling Petrol Calorimeter. of the Society of Cliemical Industi-y, June 29th, 1907, from which the following description is extracted : — 54 MOTOR CAR ENGINEERING The complete apparatus consists of a brass lamp, A, of 3 — 4 cc. capacity, having a jet of about -^ in. internal diameter, fitted with an asbestos wick, and a small cap, 0. The lamp rests in a tripod clip, which fits on to the main portion of the apparatus. The bell-jar B (of glass or copper), the neck of which is fitted with a rubber stopper, carrying a glass rod, D, and an electrical conductor, E, for igniting the petrol, forms the combustion chamber, and is held in its place by means of the brass plate, P. The oxygen required for the combustion is conveyed through the glass tube, I, and introduced into the chamber through the copper tube, 0, impinging on to the top of the lamp. For very volatile liquids, such as petrol, the lamp is surrounded by cold water during the combustion, to prevent overheating and consequent boiling and explosion of the contained liquid. This water is introduced through the tube, W, by pouring it down a funnel attached to the rubber connection, N, and then replacing the funnel by a glass rod, E. The hot products of com- bustion pass down the tube, T, and bubble up through the perforated base- plate, H. A copper spiral of '' arch " section fits accurately round the plate, P, and terminates at the top in a circular ring (also of arch section) perforated by small holes. The whole apparatus fits loosely into an outer glass vessel, V. The "water equivalent " of the calorimeter is foimd by weighing the various materials composing the calorimeter, multiplying these weights by the specific heats of those materials, and adding the products together. Example: — ^Weight of Glass X Sp. Ht. (0-18) = Water equivalent = g. Weight of (Copper -|- Brass) x 0-094 = water equivalent =b. Weight of Rubber X O'l = water equivalent = r. Water equivalent of apparatus = g -|- b -|- r. The calorific value of the petrol is calculated as follows: — If M = total weight of water used (in grms.) ; W = water equivalent of apparatus ; E = rise of temperature of the water ; w = weight of petrol biirnt fM + W1 E in grms. : then the calorific value in caloi'ies =-i — and B.T.U. w per lb. = calorific value X I'S. The calorific value of a fuel obtained by this method is the major calorific value, as the steam formed during combustion will be condensed. To find the minor calorific value, the weight of water produced in burning the fuel would have to be found, and the heat given out by it in cooling calculated. * 46. Air Eequired for Combustion. — Explosion is simply a rapid combustion of the elements contained within the cylinder, and combustion is an oxidisation of those elements. Thus, for com- bustion to take place, it is necessary for oxygen to be present in sufficient quantity. In practice, however, it is neither possible nor desirable to use pure oxygen, and so the oxygen present in the atmosphere is utilised to carry out the chemical combustion. PETROL 55 Air contains by weight at 15° C. approximately 23 per cent, of oxygen and 77 per cent, of nitrogen, and by volume 21 per cent, of oxygen and 79 per cent, of nitrogen. But there is always a certain percentage of water vapour and other elements, which, from their small proportions, are always neglected in calculations having the nature of those about to be discussed. From the proportions of nitrogen and oxygen in air, it will be readily found that there is 1 lb. of oxygen in 4'35 lbs. of air, and 1 cubic foot of oxygen in 4'76 cubic feet of air ; the similar values for nitrogen being 1'31 lbs. and 1"27 cubic feet respectively at 15° C. When carbon is burned to carbon dioxide, the equation representing the action is C + O2 - CO2, which shows that by weight 12 x 32 = 44 lbs. of CO3 are produced by burning 12 lbs. of carbon (using their atomic weights), and that 32 lbs. of oxygen are required to burn 12 lbs. of carbon, or 2*67 lbs. of oxygen are required to burn 1 lb. of carbon. Similarly, when hydrogen is burnt to form water, the equation representing the action is : — H2 + = H2O, so that 16 lbs. of oxygen are required to burn 2 lbs. of hydrogen, and 8 lbs. of oxygen are required to burn 1 lb. of hydrogen. If sulphur is present in the fuel in any considerable extent, then the sulphur burns to SO2 and 1 lb. of oxygen is required to burn 1 lb. of sulphur, but for all practical purposes this may be entirely neglected. When desiring to obtain the quantity of air necessary, theoreti- cally,- to burn a given quantity of fuel, it is necessary first to ascertain the constituents of that fuel. Supposing that the fuel is heptane C7H16. Then in 1 lb. of fuel there will be y-^ lb. of carbon and —r^ lb. of hydrogen. 84 Air required to completely burn ^r^ lb. of carbon is, from above : — ^ X 2-67 X 4-85 = 9-756 lbs. 56 MOTOR CAR ENGINEERING 1 ^ Air required to completely burn zr^ lb. of hydrogen : — ^ X 8 X 4-35 = 5-668 lbs. Therefore air required to completely burn 1 lb. of C7H16 = 9-756 + 5-568 = 15-324 lbs. At 15° C. the volume of 1 lb. of air = 18-14 cubic feet. Therefore 1 lb. of heptane requires 15-324 X 18-14 cubic feet of air = 201-36 cubic feet. But specific gravity of heptane = -688 at 15° C. and volume of 1 lb. of heptane = Via o X 'Ooo = -02388 cubic foot. Therefore, ratio of air to liquid petrol by volume _ 201-36 ~ -02333 = 8,630. But from the equation for combustion of heptane, 1 volume of C7 H16 requires 11 volumes of O2 to completely burn it (7 volumes of O2 to burn the carbon, and 4 volumes of O2 to burn the hydrogen), and 11 volumes of O2 are found with 11 X 3-76 volumes of N2 = 41-36 volumes of N2 ; consequently, 1 volume of the vapour of heptane requires (11 + 41-36) volumes of air == 52-86 volumes of air. In practice, however, these figures do not hold good, and it is found to be necessary to adjust the carburetter so that it will admit an excess of air to the cylinder, partly to neutralise the exhaust gases left in the cylinder, as the incoming charge will mix with these inert products of combustion, partly to allow for the presence of water vapour, and partly to compensate for the varying density of the atmosphere. This extra air varies from 20 to 50 per cent., an average value being, say, 30 per cent. Questions on Chapter IV. (1) What do you understand by the boiling point, the calorific value and the volatility of a fuel ? How are these obtained ? ( ) Describe the mode of extraction of petrol from crude oil. PETROL 57 (3) Describe a test for the volatility of a fuel and how is this of use in estimating the value of the fuel for an internal combustion engine. (4) Why is the specific gravity of a fuel of no service in deciding its suitability for internal combustion engines ? (5) What would you say the calorific value of a good petrol to be ? State what physical properties it should possess. (6) How much air is required theoretically to burn 1 lb. of a fuel which has a chemical composition by weight of 83 per cent, of carbon and 17 per cent, of hydrogen ? Why does the actual amount which the engine requires exceed the value you obtain ? (Answer, 15-56 lbs.) (7) What are the relative volumes of air and a petrol of chemical composition 83-5 per cent, of carbon and 16-5 per cent, of hydrogen by weight and whose S. G. = -7 at 15° C. Volume of 1 lb. of air at 15° C. = 13-14 cubic feet ? (Answer, 8,842 to 1.) (8) What objection is there to using a fuel the constituents of which have a large range of boiling points ? (9) What are the sources from whence petrol is obtained ? (10) Two fuels are subjected to a test in Baillee's apparatus and their volatility figures are 105 and 120. Which would you choose for use in an engine, and why ? CHAPTEE V FUELS OTHER THAN PBTKOL 47. Importance of Good Fuel. — In all cases, the fuel ranks high in the minds of owners or prospective owners of cars. The four main conditions which a satisfactory fuel '- must comply with, are : — •. , . (a) It should be moderate in price. ■ {]>) It should not leave deposits in the cylinder. (c) It should be sufficiently volatile to enable the engine to start easily. ■ ■ ~ {d) It should have an exhaust which is free from obnoxious odours. " " - . ^ - It will be seen that petrol fulfils the last three conditions in their entirety, and it is only on the ground of expense that another fuel may displace it. From the nature of the car it is imperative that the fuel should have as small a bulk as possible; consequently it must have a liquid or solid form. The only source of power in solid form is calcium carbide which, when water is added to it, generates acetylene gas. The ase of this gas as a fuel will receive consideration later. In liquid form there are crude petroleum and its distillates, alcohol and benzol. The remaining requirement which a fuel must conform to before its use can be general is that there must be an ample and widespread supply. 48. Fuel Oil. — The use of the heavier products from crude petroleum is, at the present time, confined to stationary and marine work. This is due not so much to the difficulty attendant upon its use, but to the large deposits in the cylinder, to the extreme violence of the explosion, to the foul-smelling exhaust, and to the necessity of maintaining the speed of the engine. The troubles from carbon deposits in the cylinder will always present themselves where oils are used which are mechanical mixtures of FUELS OTHEE THAN PETEOL 59 a large range of hydrocarbons. In all such cases, the lighter and more volatile constituents form a gas first and leave behind a compound which it is more difficult to evaporate, with the result that it is incompletely burnt. For stationary work these defects are not of such importance as in connection with road vehicles ; and in marine work they are minimised by the economy and convenience accruing from their use. Hence the crude oil and the heavier products of distillation are precluded from use on motor vehicles. 49. Parafan or Kerosene. — Kerosene is the distillate from crude petroleum, after taking which the residuum is called " fuel oil," referred to above. Its specific gravity will vary considerably (as will also its calorific value) according to its composition, but will range between "753 and "864 at 15° C, and its calorific value between 21,000 and 24,000 B.T.U. per lb. Its flash point under Abel's close test is between 100° and 125° F., and it boils between 300° and 500° P., giving a vapour density five times that of air. The principal constituent of kerosene is decane (C10H22), and in all calculations relating to this fuel it may be assumed, without any great degree of error, that it is composed entirely from this member of the series. On the score of cost and accessibility of this fuel no objection can be raised, paraffin being obtainable in the most isolated localities at extremely low prices; and, as this forms about 50 per cent, of the crude petroleum, there should be no difficulty in obtaining an ample supply ; further, the fuel does not deteriorate in storage. But some idea of the utility of a fuel can be estimated by observing the range of boiling points possessed by the constituents of that fuel. Petrol has a range of about 100° F., whereas paraffin has about twice this range, namely, about 200° F., so that any trouble in the carburation or combustion of the former, will be greatly magnified with the latter. This range indicates a great lack of homogeneity in the liquid, and, as the engine must be sufficiently hot to vaporise the constitutent having the highest boiling point, it follows that there is a great possibility of decom- posing the lighter fractions and depositing carbon on the internal surfaces. This is one of the troubles — the presence of carbon deposits — with the attendant risk of pre-ignition, excessive wear, sooted plugs, and irregular running of the engine. 60 MOTOR CAR ENGINEERING On account of the incomplete conabustion that takes place, there is always a foul exhaust, which becomes aggravated when a missfire occurs. Pre-ignition too, when it does take place, necessitates stopping the engine to allow it to cool down, owing to the fact that the part causing pre-ignition becomes the centre from which the flame radiates, and, consequently, the hottest part of the engine. Further, an engine cannot be started on paraffin, but requires to run for some time upon a lighter fuel until it is thoroughly warmed up before commencing to burn paraffin. Such engines also lose all flexibility on account of the necessity of maintaining the cylinder temperature, any condition below normal resulting in missfires. Hence it will be seen that paraffin fails to fulfil any of the stated requirements, except that respecting price of fuel, and as such is not suitable for road vehicles. 50. Alcohol.— The question of adopting this fuel for use in stationary internal combustion engines, in the place of petrol and kerosene, has received much attention in France, Germany and the United States of America, on account of the potential advan- tages possessed by it. Its source of supply is practically unlimited, as it can be extracted from any vegetable matter containing starch or sugar ; while its greater safety, due to the non-inflammability of its vapour, makes it specially desirable where unskilled labour is engaged in using it. Mr. Sorel, in 1902, and later on, in 1906, the United States Department of Agriculture carried out a large number of elaborate and exhaustive experiments, using alcohol as a fuel, by the former to stimulate an agricultural industry, and by the latter, with the view of determining the relative values of alcohol and gasoline and to ascertain the difficulties encountered with and the latent possibilities of alcohol. The accounts of these experi- ments formed a most interesting addition to the information then available and must be considered as standard works on the subject. The chemically pure alcohol, called ethyl alcohol (C2H5OH) has a specific gravity of "792 and a boiling point of about 170° F. Its explosive range is from 4 to 13"6 per cent, of vapour, by volume, and its calorific value about 12,600 B.T.U. per 1 lb. Ethyl alcohol is produced by distillation from beetroot, potatoes, cereal grains, sugar cane, etc., but, although analysis will prove FUELS OTHER THAN PETROL 61 that the percentage of starch present in the cereals is far in excess of that in potatoes, the most profitable source of alcohol will be from potatoes or beetroot, because of the larger supply per acre of ground cultivated. Owing to Excise restrictions, the sale of this pure spirit is not permitted until it has been what is termed " denatured " by the addition of some ingredient which will render it undrinkable. The added ingredient should, obviously, possess a calorific power, so that it may assist in generating heat for use in the engine. In Germany the denaturising agent is a special mixture of pyridine bases and benzine, 2J per cent, of which is added to ethyl alcohol, while in France methylene is used in the propor- tion of 1 to 10. In the United States 10 volumes of methyl alcohol and one half of 1 volume of benzine, or 2 volumes of methyl alcohol and one half of 1 volume of pyridine bases are required to be added to 100 volumes of 90 per cent, ethyl alcohol. In England about 10 per cent, of methyl alcohol is employed to denature the pure spirit, the resulting calorific value being approximately 11,320 B.T.U., this value being still further reduced by the presence of from 10 to 20 per cent, of water to 10,380 and 9,800 B.T.U. respectively. The hygroscopic nature of alcohol necessitates the exercise of great care in storing the spirit, although the presence of water in small quantities is not altogether a disadvantage, as then it accelerates combustion. Methyl alcohol or wood naphtha is the product of dry distilla- tion of wood, and has a specific gravity of "812 at 0°C., a calorific value of 9,552 B.T.U. per lb. and boils at 150° F. It has a chemical composition of CH3OH. Taking now the methylated spirit and comparing it with petrol it is seen that the relative calorific values are : — Methylated spirit (-820 S.G.) 10,380 B.T.U. per lb. Petrol (-720 S.G.) . . 19,300 B.T.U. per lb. But the fuels must not be compared on this basis alone. Two engines, one designed for petrol and the other for alcohol gave the following consumptions per B.H.P. hour : — Methylated spirit 1-16 lb. Petrol . . -73 lb. The B.T.U. (total) per H.P. hour were therefore, for alcohol 11,940, and for petrol 14,090, a result which is not favourable to petrol, as their relative thermal efdciencies are as 1"18 to 1. 6'2 MOTOE CAE BNGINEEEING Furthier, the B.T.U. per gallon are 85,116 for methylated spirit, and 138,960 for petrol, that is, as 0-612 to 1. If, then, alcohol is to compete with petrol upon equal terms, and comply with the first condition that a satisfactory fuel should fulfil, the ratio which its price bears to that of petrol must not exceed (1-18 X 0-612) to 1, that is, 0-722 to 1. It will be seen that at the present time this is not complied with, as the price of petrol per gallon is Is. 2d. and that of methy- lated spirit in this country is 2s. 6d. Still, if an extensive use could be found for alcohol as here indicated, there is no doubt that the cost could be, considerably reduced. The increase in thermal ef&ciency noted above is largely due to the increased compression used in this class of engine. Sorel found that engines worked quite satisfactorily with as low as 90 lbs. compression pressure, but observed that the compression could be carried to 180 lbs. quite safely. This high value is permissible because of the non-inflammability and the extreme homogeneity of the spirit which distils over completely at 170° F. while it cannot be ignited below 67° F. * 51. Conclusions of the U. S. Board of Agriculture on the use of Alcohol. — It may here be desirable to indicate the conclusions arrived at by the U. S. Board of Agriculture. They are as follows : — (1.) Any ordinary gasolene engine can be run on alcohol without material change ; the only difficulties are encountered at starting up and in supplying a sufficient quantity of the fuel. (2.) When run on alcohol its operation is more noiseless than when on gasolene. (3.) For air-cooled automobile engines alcohol is especially suitable as a fuel. (4.) The fuel consumption was effected by the time of ignition, by the speed, and by the initial compression of the charge. The consump- tion was better at low speeds than at high speeds. (5.) A petrol engine will give about 10 per cent, more power when burning alcohol, but at the expense of a greater fuel consumption, 20 per cent, more power being obtainable by specially adapting the engine to the fuel. In the main, they are decidedly favourable to the use of alcohol, with the exception of the latter part of (1). This difficulty is inseparably connected with practically all fuels but petrol, and so it appears to be necessary in the case of any substitute to fix an auxiliary tank to supply the engine at start- ing, switching ou to the main supply when the engine has wai-med up. A sufficient quantity of fuel can easily be obtained in engines using a carbu- retter by enlarging the orifice of the jet, and this has already been successfully FUELS OTHEE THAN PETROL (63 done, without any othei' modification ; still, it is desirable to have some mechanical control of the proportioning of fuel to air, wherever a light fuel is used at starting, as otherwise the mixture will be too rich and give trouble in this direction. The control may take the form of a special extra air supply, an adjustable jet, or two distinct carburetters, the first-named being much preferred on account of its simplicity. That alcohol would be an ideal fuel for air-cooled engines is only to be expected, because the non-ignitible properties of the spirit permit an engine to run at a much higher temperature. One of the reasons why a high com- pression is not used in air-cooled petrol engines is the danger of pre-ignition, -and as the thermal efficiency depends upon the amount of compression used, alcohol should, and does, allow a very high efficiency to be obtained. A consideration of the points mentioned under conclusions numbered (2) and (4) brings to light two of the most important features in connection with alcohol engines, both of which are directly traceable to the same cause. The points referred to are the comparative silence and the smaller fuel consump- tion at low speeds. An explosion depends for its violence upon the rapidity of combustion, which in the case of the alcohol engine has been found to be much less than with petrol or gasolene. Thus, although the higher com- pression used would conduce to greater noise and shock on ignition, owing to the low rate of flame propagation, the maximum pressure is not attained, and the force of the explosion thereby reduced. There is a further benefit derived from this slow combustion, as the charge continues to burn through the stroke, raising the effective pressure and giving a more uniform turning effort on the crankshaft. It is presumed that some action of this nature goes on in the cylinders of petrol engines, but not to the same extent as in alcohol engines. The second result of the low flame speed is the reduction of piston speed, which Tjecomes necessary in order that there may be sufficient time for com- bustion to take place before exhaust. This will be seen to directly affect the consumption of fuel, as, unless combustion is complete, a considerable amount of gas will pass from the engine unconsumed ahd be finally burnt in the exhaust pipe. The passage of these flaming gases through the exhaust valve port has also an effect which was for a long time attributed to the use of alcohol, namely, corrosion and pitting. In the process of combustion, aldehyde, acetic acid, etc., are formed, and if the process be not complete, some pi these are left in the cylinder for a sufficient time to set u.pa, -corrosive action. It is, however, not a difficult matter to obtain complete combustion, as the amount of air required is little more than one-third of that required for petrol, and the explosive range of alcohol vapour is rather more than three times that of petrol. The intimate mixture which is so important in carbui-ation is greatly assisted, too, by the presence of oxygen in the fuel itself, and which takes part in the combustion. The average value of the constituents of methylated spirit by weight are : — Carbon . . . . 51 per cent. Hydrogen . . 13 per cent. Oxygen ... 36 per cent. 64 MOTOE CAR ENGINEEEING There will, of course, be some difficulty when running at light loads, which even with the petrol engine is not entirely absent ; but it a well-adjusted carburetter is employed, the trouble under these conditions may be reduced to quite a negligible quantity, while at full or nearly full load the exhaust gases will be quite innocuous. The remaining objection to be urged against the use of alcohol is its high vaporising temperature, which, although conducive to safety, necessitates the heating of the air used in combustion. To obtain equally free evaporation with methylated spirit as with petrol at 60° r. the air should be raised to about 140° F. A reference to the table on p. "78 will make this quite clear, as it will be seen that ethyl alcohol lowers the temperature about four times as much as heptane, and five times as much as decane. The advantages and disadvantages of alcohol as a fuel may be summarised as follows : — Advantages. — Homogeneous spirit and presence of oxygen conduces to better carburation. Low distilling temperature (170° F.). Large range of explosive mixtures (4 to 13*6 per cent.). Less noise in operation. Higher compression, and consequently higher thermal efiicienoy. Greater power per unit of cylinder capacity (10 to 20 per cent.). Pure exhaust, except at very light loads. Greater safety, i'iscicfvania^es.— Present high price. Low calorific value. Slower piston speeds, and therefore a heavier engine. Higher vaporising temperature required. It will be observed that the disadvantages are of a character which would not entirely prohibit its use, but only require favourable conditions to bring it within the range of modern requirements as an admirable source of heat energy. With, the manifold advantages attaching to the use of alcohol, it is, therefore somewhat surprising that greater efforts have not been made in the direction of cheapening the cost of supply, as this is apparently the only obstacle to the adoption of an excellent fuel. Engines could then be designed to meet the special conditions without the necessity for adaptation which now exists. 52. Benzol.— This fuel has proved very attractive to experi- menters during the past few years, because of its low price, and the little alteration necessary to make an engine suitable for using it, while the fact that it is a home product has added somewhat to its attractiveness. Benzol is one of the by-products in the manufacture of coal gas, being a distillate from coal tar, and is largely used FUELS OTHEE THAN PETEOL 65 in the colour industries. But with the ever-ipcreasing quantity required in the production of aniline dyes, a fresh source of supply was found in the establishment of distilleries in con- nection with coke ovens which manufacture the coke for blast furnaces. Here, instead of the by-products being allowed to run to waste, as formerly, they are now absorbed by suitable oils and the benzol distilled therefrom. But the limited quantity available, although widespread, will prevent this fuel from ever having an extensive use, as, like petrol, it forms a very small fraction of the substance from whence it is abstracted. Benzol (Co Hg) is a member of the series of hydrocarbons having a chemical symbol C„ H2n-6> of which toluene and xylene are also members, these latter being frequently found in the commercial petrols. It has a specific gravity of "885 at 60° P., a boiling point of 176° F., and a calorific value of about 18,500 B.T.U. per lb., while its distilling range is from 198° F. to 289° F. Its explosive range is from '2'7 to 6'3 per cent, by volume of vapour. From its chemical composition it will be seen to be very rich in carbon, and so requires a large volume of air for combustion. This is one of the drawbacks with the fuel, as a sufficiently intimate mixture of air and vapour is extremely difficult to obtain in high-speed engines, with the result that sooting frequently occurs. The crude benzol has also a fairly high per- centage of sulphur (about I'o per cent.), which gives to the exhaust gases an exceedingly unpleasant odour, but, by a process of rectifying and washing, this constituent can be reduced to about -5 per cent., and the exhaust rendered less objectionable. The normal price of crude benzol is from Id. to 8rf. per gallon, and that of the refined spirit from 9d. to \Qd. per gallon, so that from the point of view of price no objection can be raised. The trouble at starting, experienced with other fuels, is again apparent, but principally in cold weather, as in warm weather it is not a great deal more difficult to use than are some of the heavier brands of petrol, while the low range of distilling temperatures it possesses, and the homogeneous nature of the spirit, assist carburation to a great extent. In many cases trials have been carried out alternately with petrol, without any alteration to any part whatever, with a fair degree of success, so that if the correct adjustment of the carburetter be made by increasing the size of the orifice, and by the weighting of the float, to maintain the correct height in the jet, decidedly better results maybe anticipated. But the greatest advantage possessed by benzol is the greater mileage per gallon. From a series of trials made by Dr. Eeadman, M.C.E. F 66 MOTOE CAR ENGINEEEING an account of which was presented by him to the Eoyal Scottish Society of Arts, in April, 1910, the following results are recorded : — Fuel. Speoiflo Gravity. Speed in Miles per Hour. Miles per Gallon. Petrol .... •720 26^2 18-3 Benzol 90 % . •880 24-8 20^7 Broxburn Motor Spirit •704 25^2 18^1 Shale Naphtha . •740 26^5 18^8 Benzol 50 %, and Brox- burn Motor Spirit 50 %• •858 26^5 18^7 " 90 per cent." benzol is a spirit of which 90 per cent, comes over when heated in a retort to 250° P. These results might have been somewhat anticipated from the higher calorific value of benzol per gallon— 163,700 against 138,960 per gallon of petrol. In order to obtain the best results in using benzol, the carburetter should be jacketed and expose large surfaces to the atomised spirit. 53. Scotch Shale Naphtha. — This spirit has been mentioned in the preceding remarks, so it will not be out of place to add a few particulars respecting it. Shale naphtha is the name given to a spirit ohtained during the process of distillation of shale oil after the motor spirit has been distilled. It has a specific gravity of about '740 at 15° C. and boils at 180° P., while nearly 60 per cent, distils over at 212° F., thus showing that it possesses very desirable properties as a fuel by reason of its homogeneity. It is found that no difficulty whatever is experienced in starting an engine from cold, neither are any deposits left in the cylinder, although when the speed varies considerably it exhibits a tendency to miss-fire. The consum.p- tion per brake-horse power is slightly less, as is shown in the table above, the trials recorded having been made on the same stretch of road. The exhaust from an engine using this fuel is said to be less pungent than that from a petrol engine. On the whole, therefore, shale naphtha exhibits very promising features, and should prove a useful acquisition to the fuels more commonly in use. 54. Acetylene. — The use of acetylene gas (C2H2) for power purposes lias frequently been proposed, but never with any FUELS OTHEE THAN PETEOL 67 commercial success, because of the extremely violent explosion it generates. Mr. Frederick Grover's experiments showed that for the proportions of air and coal gas which required 025 of a second to reach the maximum pressure after explosion, with the same proportions of acetylene and air the corresponding time was 0"018 of a second. One pound of calcium carbide will generate 5| cubic feet of acetylene gas having a calorific value of about 21,000 B.T.U. per lb., 14J cubic feet of gas weighing 1 lb. Acetylene gas requires 12 J volumes of air for complete combustion. But acetylene gas has been successfully employed in con- junction with alcohol as a source of energy. It was pointed out that alcohol has not only a low calorific value l)ut also a low flame speed, while acetylene has an extremely high flame speed and a high calorific value ; so it will be apparent that should it be possible to mix these two fuels in the requisite proportions a much more desirable fuel will be obtained. Not only so, but the difficulty experienced in starting from cold will also be entirely obviated, as acetylene ignites in air at about 500° F. Such a system has been patented in America, and it is said that the combination gives the same results as when petrol is used. The name of the gas resulting from the process has been called " Alkoethine." The procedure adopted is as follows : — An ordinary carburetter atomises the alcohol, and the mixture of air and alcohol passes to a chamber in which there is a bed of calcium carbide, through which it is drawn by the suction from the engine. Denatured alcohol always contains water, which, as it passes over the carbide, generates acetylene gas. The water, which is under ordi- nary conditions an objectionable constituent, now becomes necessary — in fact, about 13 per cent, more water is usually added — and the heat evolved in the production of acetylene gas is usefully employed in atomising the alcohol. The " alkoethine " then passes to the engine and is compressed, fired and exhausted in the usual manner. If a variation in the rapidity of explosion is desired, the amount of water added to the carbide is increased or decreased, according to whether it is desired to enrich or impoverish it. It is stated that the process gives perfect satisfaction in every way, but it has not yet been placed upon a commercial footing. Questions on Chapter V. (1) What are the reasons why paraffin is unsuitable for use in car engines? F 2 68 MOTOE CAE ENGINEEEING (2) What are the principal requirements which a good fuel should conform with ? How does alcohol answer these requirements ? (3) A number of people imagine that acetylene is a probable source of energy for motor vehicles. Why are they mistaken ? (4) How can acetylene be advantageously utilised for power purposes ? Describe the apparatus necessary. (5) Is there any probability of an extensive use of benzol for motor car engines ? Give the reasons for your answer. (6) What objection is there to the use of fuel oil ? What is fuel oil? (7) State what the various fractions or cuts taken in distilling, say, an American petroleum consist of. Why is the production of petroleum spirit so limited ? (8) What are the advantages and disadvantages attaching to the use of alcohol as a fuel ? Why is a higher compression permissible than with petrol ? (9) Give some figures as to the consumption of engines burning petrol and alcohol, and say why these do not represent the relative value of the two fuels. (10) What substances are employed to denaturise alcohol, and what is their effect upon the burning properties of the mixture? CHAPTER VI CAEBUEETTEKS AND CAEBUEATION 55. The Function of a Carburetter. — Carburation is the most important yet one of the most difficult problems which has to be surmounted by automobile engineers. The function of a carburetter is to impregnate the air with hydrocarbon vapour, usually either that of petrol or of one of its substitutes ; but the conditions under which a petrol engine is employed are such as to render the successful accomplishment of this duty extremely difficult. The general conditions which a good carburetter should fufil are : — (a) It should form a uniform mixture of air and hydro- carbon vapoiir, within a fairly close range of proportions of the two substances. (b) It should carburet the air to any desired extent. (e) It should conform with condition (a) under all the varying conditions of atmospheric or suction pressure, speed, tempera- ture, and power. (d) It should completely vaporise the fuel. The causes from which the difficulty arises in fulfilling these requirements are of two kinds, general and local ; the general applying to all carburetters, and the local to a particular type of carburetter; but before investigating these it will be well first to see what type of carburetters are now used, and then to examine the conditions under which they work. 56. Types of Carburetters. — There are four types of carbu- retters in current practice — the mixing valve, the wick, the measurer, and the jet — distinct varieties of the last mentioned greatly outnumbering those in the other classes. A mixing valve carburetter is one in which the fuel is admitted to the seating of a valve and taken up by the air as it passes through 70 MOTOE CAR ENGINEERING the opening, the most notable of the group being the Cadillac. There are, however, very few of this kind in use, as extreme care is necessary in the design and adjustment and in the arrangement of the inlet piping to ensure the best results. In the wick carburetter the liquid contained in a reservoir is raised through a bundle of wicks by capillary attraction and taken up by the air drawn past or through them, forming a rich mixture, which is afterwards diluted to the desired proportions of air and vapour. It is said, however, that with the spirit now sup- plied by the importers there is a tendency for the wicks to " gum " up and require frequent renewal. The Antoinette carburetter is the best example extant of the measuring car- buretter : that is, one in which the supply of fuel is regulated either automatically or by some mechanical device. In that mentioned it is drawn through a small orifice in the bottom of -vessels placed over the inlet pipes ; but, generally speaking, the design is not good, as it may cause stratification of the gases or an insufficiently intimate mixture, and there is, also, some difficulty in adjusting the quantity of fuel to the ever- varying loads. In the spray carburetter the fuel is led to a jet, around or across which air is drawn by the engine, the aspi- rating effect of the rush of air past the jet causing the spirit to issue from the orifice. The jet is not necessarily formed by a single opening, but may have a number of holes or slots, while in some forms two or three separate jets are employed, graduated in size, in order to obtain better control of the proportions of air and spirit. The types of carburetters enumerated do not by any means exhaust the list, as there are several others, the best known being the surface, the bubbling, the pump, and the film car- buretters ; but from some defect or another, usually either selective evaporation or absence of control, they have gradually sunk into disuse, and it is not, therefore, necessary to consider them here. 57. Floats. — In order that the normal level of petrol in the jet or in the wicks may be kept from rising or falling as the conditions vary in the passage through the carburetter, or as the fuel is consumed, some automatic device must be provided. For this purpose a float is employed, which actuates a needle valve through the medium of a pair of levers, the valve being CAEBUKETTEES AND CAEBUEATION 71 thereby caused to rise and admit fuel when the level commences to fall, and to close again when a sufficient quantity has entered. The actual position at which the level should be maintained will depend upon the type of carburetter, or, rather, upon the type of nozzle ; but whatever the height may be it may be obtained by altering the level at which the float engages with the levers. To raise the level in the nozzle the float must be weighted, in order that it may sink lower in the petrol and so delay the time of closing the supply valve ; while to lower the level the float must be raised, and to do this the height of the collar on the needle valve must be increased, so as to permit the valve to seat earlier. In some cases there is no float fitted, the necessary control on the supply of fuel being obtained by throttling or by some means of a like nature; but where, as in the car engine, the amount of petrol required to be discharged in any given time varies between very wide limits, this lack of definite regulation cannot be recommended. The shape of the float is usually cylindrical, as shown in Fig. 27, although one or two cases are known where conical floats are employed, the object of the latter being to combat the influence of inclination when ascending or descending hills or when on the side of the road. The ideal arrangement of the float would be to have it surrounding the jet,: as is actually the case in one or two examples, the inclination of the car having no effect on the level of petrol within the jet, but this is found to be im- possible in most cases. In the Claudel-Hobson (see Fig. 31) the float chamber is placed extremely close to the jet chamber, as being the next best position. The position of the float chamber in the car should be to the forward side of the jet chamber, towards the centre of the car, so as to ensure a supply of petrol Fig. 27. — Brown and Barlow Float Chamber. 72 MOTOR CAE ENGINEERING when ascending hills, as when descending the mixture may be permitted to weaken without risk of stoppage of the car. In all cases a filter should be fitted before the float chamber, so as to prevent all possibility of foreign substances entering which might prevent the needle valve from closing, or cause \ '5" ^9' ORftlWTAP GAUZE FILTE-R 'SCREWS F.OR CAP lUSTING SCREW FOR PRESSURE SAFETY. VALVE HEBE PRESSURES PIPE TO pRESSURl* PEtROLlf/ TANK :::-;-^ VALVE- . PIPE FROM EXHAUST TO FILTER -INLET VALVE S: '■ „.Tf, WATER DRAINER NA-PIE.R- EXHAUST PflE'SSURt VAUVE"- ./ AMPl Fli TRR fji Fig. 28. — The Napier Exhaust Pressure Filter. stoppage of the jet orifice ; and, if possible, the supply to the jet should have an upward direction, to allow any dirt which may pass the filter to sink to the float chamber and thus free the jet. 58. Petrol Fuel Systems. — To ensure the supply of petrol or other fuel to the carburetter there may be adopted one of two systems — the gravity feed or the pressure feed. In the former CARBURETTERS AND CARBURATION 73 of the two systems mentioned the petrol flows by gravity from a tank placed at a higher level ; in some cases the tank is fitted underneath the front seats, while in others it forms the dash- board. In a pressure-fed system, however, the tank may be placed in any position that the designer desires, but usually it is fitted underneath the car at the rear. The advantage gained by the latter arrangement is that greater, scope is permitted in arranging the chassis design, that a larger tank can be carried, and that a constant head in the supply pipe is obtained. But Fig. 29. — The Wolseley Combined Air and Oil Pump. there are several disadvantages to be taken into consideration. The first is that no matter how carefully the gases from the exhaust are filtered (and it is from these that the pressure is usually maintained) they have always a deteriorating effect upon the fuel ; that free carbon is gradually deposited in the pressure pipes and may eventually choke them ; and that damage often results to the tank itself from stones, etc., thrown up from the road, unless special protection is afforded. The system is, nevertheless, frequently fitted, and gives complete satisfaction in practice when reasonable care is taken to provide against these contingencies. The exhaust pressure filter fitted on the Napier pleasure cars is shown in Fig. 28. Occasionally a special air 74 MOTOR CAE ENGINEEEING pump is provided for supplying pressure to the petrol tank, and • in such cases the objections indicated do not arise. The Wolseley air pump is shown in Fig. 29, and will be seen to be of very simple construction, the spring-loaded plunger being operated by the cam seen in the figure. * 59. Carburation. — As the jet carburetter is so largely used the question of carburation will be considered principally in regard to this type of carburetter. It has already been stated that it is the aspirating effect of the air, due to its velocity around the jet, that induces the fuel to issue therefrom. Now, if the engine ran continuously, at constant speed and with constant load, practically all sources of trouble would be avoided ; but this is not so, as both speed and load vary considerably. When travelling up a steep hill the engine is racing at full speed with full load; but almost immediately afterwards the car may be threading its way through traffic, with throttle nearly closed and the engine just moving round. The aim of carburetter designers is to produce an economical and an explosive mixture at all speeds and powers ; but immediately the throttle is moved from full opening less air will be taken by the engine, and con- sequently its velocity past the jet will decrease if the choke tube is maintained. This means that a reduced quantity of fuel will be drawn from the jet ; but whereas the quantity of air passing is proportional to the velocity of the air the quantity of petrol discharged by the jet is proportional to some function of the square of the velocity ; the proportion of air to petrol will therefore be greatly increased and the mixture weakened. This discrepancy in proportioning will be stUl further aggravated by the presence of inert products of combustion in the cylinder. The volume of these gases are virtually constant for all speeds and positions of throttle, and when a reduced volume of weaker mixture is taken into the cylinder there will be a tendency to prevent the formation of an explosive mixture, especially at high sjieeds and light loads, the explosive range of petrol vapour and air being comparatively small. Thus, a carburetter adjusted to give a perfect mixture at full power would be very defective at low powers, and oon- verselj', one correct at low powers would be unsatisfactoiy at maximum powers. To overcome this difficulty several devices have been adopted. In some carburetters the jet is placed within a cone, which rises as the suction of the engine increases and gives a greater area round the jet, by this means reducing the velocity and aspirating efiect of the air. In others an auto- matic extra air inlet is introduced in the carburetter, between the jet and the throttle, which opens more and more widely as the partial vacuum above the jet increases, admitting air in addition to that which enters in the iTsual manner round the jet. It will be obvious that any such device must be more in the nature of a compromise, in view of what has already been CAEBUEETTEES AND CAEBUEATION 75 stated, a better arrangement being tbat which, is fitted to motor cycles, namely, a hand-controlled extra air inlet. Occasionally, too, one finds an attempt to vary the discharge from the jet in accordance Tvith the throttle opening, and so maintain a more or less constant mixture strength with varying throttle openings. Such devices may be found in the White and Poppe and the Scott- Robinson carburetters. The Scott -Eobin son is dealt with at length on page 85, but in the White and Poppe the rotating drum which forms the throttle carries a cap, which fits over the jet, the orifice in the cap and jet being eccentric to the drum, so that when the throttle is moved it also restricts the jet orifice. Mr. Dugald Clerk, in his paper on " The Principles of Carbui-etting as determined by Exhaust Gas Analysis," read before the Institution of Automobile Engineers, emphasised the necessity of correctly proportioning the mixture by demonstrating that "for the best restilts, purity of exhaust, and maximum thermal efficiency," the carburetter should be adjusted " so that the engine gives its most economical petrol consumption for a given power," but added that for an engine to have an innocuous exhaust depended upon "the nature of the adjustment made by the compensating contrivance working in conjunction with the carburetter." With the ideal carburetter this contrivance would do all that is required, but it will be found that at some speeds the mixture will be too rich, while at others it win be too weak, both conditions resulting in imperfect combustion, the former from insufficiency of oxygen and the latter because of the slowness of the rate of combustion. It will be obvious that these varying mixtures will have different rates of propagation of fiame, making it necessary to alter the time of ignition in accordance with the mixture to be exploded, weak mixtures requiring a greater advance of spark than richer mixtures. Fuiiher, as the charge volume decreases by closing the throttle, the amount of compression will also decrease, and likewise the rate at which combustion progi-esses through the mixture. In this case also the spark lever will be required to have greater advance given to it if combustion is to have reached any degrees of completion before exhaust commences. But there are other local causes which militate against proper carbura- tion, the inertia of the petrol in the jet, for example, which especially affects engines having a small number of cylinders. In a four-cylinder engine the periods of opening of the inlet valves are such as to somewhat equalise the suction round the jet, but in a single-cylinder engine there is a joeriod duiing which there should be no flow of petrol, consequently when the inlet valve opens, some time elapses before petrol issues to carburet the air, and in closing a certain amount of petrol will overflow before its motion is arrested, causing bad carburation. The same effect will also be observed even in multi-cylinder engines, should the speed or the power be suddenly increased or reduced. In order to overcome the harmful effects of the inertia of the petrol within the jet, spirals are sometimes fitted in the passage to the jet, which restrict the flow of petrol. Caps are also provided for a similar purpose. They will, however, only be effective in preventing the d'scharge after suction has 76 MOTOR CAE ENGINEERING ceased, and will not assist, but rather retard, the flow on induction again commencing. Of the other local factors which aflect carburation the following may be cited : the specific gravity of the petrol, its viscosity and its volatility ; all of which will themselves be affected by the temperature of the atmosphere. The first-mentioned affects the carburation in that the level of the petrol in the jet will be raised or lowered according as it has a lower or a higher specific gravity unless the float is correspondingly adjusted, while the viscosity will' determine the rate at which the petrol wUl issue from the orifice. But of the three factors mentioned, the rate at which the spirit is volatilised is perhaps the most important. When starting up an engine it is well known that it is often necessary to cause an excess of petrol to flow from the jet by agitating the float, because the spirit does not evaporate quickly enough to impregnate the air with vapour, and so a larger quantity of petrol is required in order that a sufficient volume of the lighter fractions may be obtained to carburet the air. Especially is this the case in cold weather, when the rate of evaporation is greatly reduced and only the lighter fractions of the spirit come off readily. With the grades of spirit sold at the present day, although they evaporate fairly well when once the engine is started up, this difficulty is very much in evidence, and forms one of the points which militate against the use of some of the substitutes for motor spirit. A test for the volatility of a fuel is given on pages 47 and 48 which may be used for this purpose without actually burning the spirit in an engine, and although its use is restricted to comparative purposes only, yet one is enabled to obtain a fair estimate of the vaporising qualities of a fuel by such means. * 60, The most efficient way to obtain complete combustion in the cylinder is to split up the fuel issuing from the jet, so as to present as great a surface as possible to the air, because only the lighter fractions of the fael are vaporised before entering the cylinder. For this purpose some inventors have fitted serrated cones, fiat pins, round pins, gauzes, and other devices ; but it is doubtful if any advantage is gained by so doing, as from the very nature of the fitting some resistance must be offered, which can only be overcome by the reduction of the temperature of the fuel immediately over the jet. As has already been stated, the constitiients of petrol have different boiling points. They also have different vapour pressures, that is, the pressures exerted by the vapours of the constituents at any given temperature is not constant ; neither can most of these fuels exist as vapour at ordinary temperatures. The amount of piessure exerted, and the temperature of evaporation, will vary according to the degree of saturation of the medium in which they are exposed, so that the strength of the mixture will have a direct effect upon the rate at which each fuel is evaporated. The vapour CARBUEETTEBS AND CARBUEATION 77 pressure or vapour tension of a simple gas may be calculated from the formula : 760 ^ - 1 + Yd. where V is the volume of air in cubic metres necessary for the complete combustion of one kilogram of the constituent at 0" 0. and a pressure of 760 mm. of mercury and x is the density of the vapour at the same temperature and pressure. To ascertain the magnitude of a vapour pressure of a simple gas is therefore not difficult, but this does not hold good when complex fuels are considered, as if the temperature be raised sufficiently to completely vaporise all the constituents, it is probable that some chemical action will have resulted and render the conclusions arrived at quite valueless. Sorel, in " Carbureting and Combustion in Alcohol Engines," described an ingenious method of obtaining the vapour pressure of a mixed fuel, to which the student is referred. The following table and those on pages 47 and 48 are taken from Mr. G. H. Baillee's paper on " Petrol and Petrol Tests," read before the Royal Automobile Club in May, 1908. Minimum Tempbratueb at which Fuel can Exist as Vapour WHEN Mixed with Varying Proportions of Air and Vapour in Degrees Centigrade. Fuel. 20 % Less. Right Amount. 20 % More. 40 % More. Hexane . — 14-2 — 17-7 -20-6 -24-2 Heptane . 7-3 3-6 0-7 2-0 Octane . 22-9 19-0 16-0 13-0 Deeane . 46-1 42-0 39-0 36-5 Benzene . -0-7 -4-3 - 6-9 - 8-3 Ethyl Alcohol. 26-5 23-3 20-7 17-8 But when, a substance alters its state, from liquid to vapour, heat is required to bring about the change. This may be readily observed, in practice, by the coating of ice which forms on the outside of a carburetter, showing that heat has been abstracted from the atmosphere during the process of carburation. The heat thus utilised is termed " the latent heat of evaporation," which may be defined as the quantity of heat required to change the condition of a substance from liquid to gaseous without increase or decrease in temperature. It will be seen that the efiect of this necessity for additional heat may cause a reduction in the temperature of the mixture which will still further retard the formation of an explosive mixture. 78 MOTOR CAR ENGINEERING Drop in Temperature Due to Evaporation with Varying Proportions of Air and Vapour in Degrees Chntigradb. Fuel. 20 % Less. Right Amount. 20 % More. 40 % More. Hexane 23-3 19-0 16-3 14-2 Heptane 22-4 17-9 15-0 12-8 Octane . 21-5 17-2 14-3 12-3 Decane 18-5 14-8 12-4 10-6 Benzene 47-3 32-2 23-5 20-9 Ethyl Alcohol 95-5 76-3 63-7 54-6 Minimum Temperature op Air before Evaporation with Varying Proportions of Air and Vapour in Degrees Centigrade. Fuel. 20 % Less. Right Amount. 20 % More. 40 % More. Hexane 9-1 1-3 -4-3 -10-0 Heptane 29-7 21-5 15-7 10-8 Octane 44-4 36-2 30-3 25-3 Decane 64-6 56-8 51-4 47-1 Benzene 46-6 27-9 16-6 12-6 Ethyl Alcohol 122-0 99-6 84-4 72-4 *61. In order to supply this heat, as well as to raise the temperature of the lic[ui(i fuel and to assist vaporisation, carburetters are now frequently wai'med by passing either the exhaust gases or the circulating water through ' a jacket, and occasionally by heating the air before passing to the car- buretter. But although this is eflective as regards these points, heating has • the disadvantage of reducing the weight of air taken in per stroke, which is- aggravated by the physical fact that as the temperature of the incoming air . rises a given volume of air can take up an increasing quantity of liquid, so that the proportions of air to petrol will be greatly decreased. There is also a limit to which heating may be carried, as if raised too high it may cause the lighter fractions to boil within the jet, forming a gas which would resist or minimise the aspirating effect of the air and so prevent carburation. The function of the heat supply should therefore be confined to simply supplying the latent heat of evaporation, as it is certain that the petrol drawn from the jet passes to the engine in a finely divided state, more or less intimately and uniformly mixed with air, and that complete evaporation or "gasification'' is not reached until after the compression stroke has commenced. CAKBIIRETTEES AND CARBURATION 79 There will, of course, be some heating of the new charge on entrance to the cylinder by the residual gases left from a previous explosion, but it is doubtful if there is sufficient time for vaporisation to take place — certainly not for all the fresh gas which is induced. This brings in another factor — the time element. * 62. All physical changes req[uire time for their consummation, and the change from liquid to gas is a physical change. The velocity of the inlet gas is about 100 feet per second, and therefore if the length of the inlet piping between the carburetter and the inlet valve is 1 foot, there will be xJ^^'^i of a second in which to change the state of the petrol, if it is to be completed before entering the cylinder. This is insufficient, and even if it were sufficient for one constituent it would not be for another. August's Law for the approximate time for the complete saturation of a medium is : t = =7^ natural log fs K ° r — p where K is a constant, P the maximum vapour pressure corresponding to the temperature of the liquid and ^ the existing vapour pressure. The actual value of K is unknown, but the equation is very useful in finding the comparative times of evaporation of the constituents of petrol. 63. Mixture Strengths. — It has been seen on page 56 that the amount of air required theoretically for complete combustion is lo'324 lbs. per 1 lb. of petrol (O7 Hio), but in practice this is incorrect, largely on account of that disturbing factor— the exhaust gases remaining in the cyHnder. Usually the amount of air admitted is from 1 '3 to 1 -Y times that theoretically necessary. Now an explosive mixture is one in which combustion takes place with great rapidity. Explosive mixtures of air and petrol range from about 10 to 1 to 20 to 1, below and beyond these limits the mixture being non- explosive but burning quietly. Thus it will be apparent that there must be a best mixture between the Hmits given which can only be determined by experiment, the best mixture being defined as that which produces the greatest pressure at the beginning of the stroke and the most rapid com- bustion of which it is the cause. When the mixture is weakened or strengthened, the flame does not travel so rapidly, and consequently is not so effective, as a portion of the heat developed is spent in raising the temperature of the residual gases and the excess air in the case of weak mixtures, while the combustion is incomplete, and therefore less heat is generated in strong mixtures. The weakest mixture strength which is explosive depends upon the compression pressure, but a consideration of this is reserved till later. 80 MOTOE CAE ENGINEEEING The whole question of carburation will thus be seen to be a very complex matter, calling for careful consideration and exhaustive experiment before any measure of success can be hoped for. 64. Influence of the Shape of Induction Pipes. — The first requisite which should be fulfilled in arranging the inlet pipes is that all cylinders draw their supply from the same volume of piping and, if possible, from the same shape of piping. Too often one finds cases where this is not observed, with the inevitable result that one or more cylinders are starved, and irregular running takes place. It is most important, if all cylinders are to receive the same charge volume of the same mixture strength, to see that this is carried out. The next condition is that sharp bends should be avoided, as their presence will assuredly cause the liquefaction of the petrol vapour and so destroy any chance of proper carburation. With this object, therefore, the lead of piping should be in as direct a line as possible, and where bends are necessary they should have a large radii, or Y pieces should be inserted. With regard to the length of piping, this will depend somewhat on whether the carburetter is jacketed or not ; if it is warmed, the piping should be as short as possible, while if it is not, a longer length is advantageous, as the mixture can then abstract heat from the atmosphere as it passes through the pipe to supply some of the latent heat of vaporisation. From the point of view of general utility the short pipe is always desirable, as it facilitates engine starting because there is a lesser volume of air in the pipe to draw upon, and consequently the " pull " on the jet is greater ; but, on the other hand, there is less time for atomisation of the spirit, and sudden variations in the speed of the engine have a greater effect upon the discharge from the jet. The joints in the piping should be designed so that they are air-tight, because the leakage of air into the piping is another of the fruitful causes of bad carburation at light loads when the suction pressure above the throttle is very high. 65. Adjustment of Carburetter. — One of the methods adopted until quite recently in adjusting the carburetter was to run the engine on the test bench with the exhaust pipes off and then observe the flame issuing from the exhaust valve. When the tester obtained a short bluish flame, he was fairly satisfied with CAEBUEETTERS AND CARBUEATION 81 his adjustment ; but such a method is very crude and the result by no means conclusive. With the gradual application of more scien- tific methods to the problems of internal-combustion engines, the test by analysis, which had long been carried out for the purpose of determining the efficiency of combustion in boilers, was applied to the exhaust gases from the petrol engines. The results of this analysis proved beyond doubt that the older method was very indeterminate, and now, in many up-to- date establishments, this newer form of testing has taken its place. The exact composition of the exhaust gases will, of course, depend upon the constituents of the petrol used ; but they may always be assumed to be hydrogen and carbon, as any other substance which may happen to be present will generally be of the nature of an impurity, and in such insignifi- cant proportions as to be quite negligible. Making this assumption, the exhaust gases may contain carbon dioxide, carbon monoxide, water, free oxygen, free hydrogen, nitrogen, ethylene and methane, the chemical symbols for which are CO2, CO, II2O, 62, N2, CoHj and CH4. Usually it is only necessary to ascertain the proportions of CO2, CO, and O3, as it is really the quantities of CO and O2 that are the gases which determine the character of the combustion. The presence or absence of CO shows the degree of efficiency reached in combustion — an excess of CO and an absence of O indicating that an insufficient quantity of air has been admitted. The volume of CO should not, with a well-adjusted carburetter, exceed O'o per cent. If the shortened process of analysis is followed, the volumes of II2 and CH4 may be roughly approximated to by calculation, on the lines indicated by Mr. Horatio Ballantyrie, F.I.C., F.C.S., in an appendix to Mr. Dugald Clerk's paper on the " Principles of Carburetting as Determined by Exhaust Gas Analysis." C2H4 is practically never present in the exhaust from petrol engines. The sample of gas to be analysed should be taken from a point in the exhaust pipe as near to the exhaust valve as possible, in order to reduce any possibility of air leakage to a minimum, and so that no burning maj' take place between the exit from the cylinder and the collection in the vessel. The orifice should, preferably, be small, so that a sample from a large number of explosions may be obtained, and that the effect of a, missfire on the constituents of the gas may be minimised. Usually the gases are collected in an aspirator bottle, which is a large glass vessel containing water, and having two glass tubes passing through a rubber stopper. One of tbese tubes extends to the bottom of the vessel, and has its outer end in communication with the atmosphere ; while the other tube ends level with the inside of the stopper, and is connected to a cooler, through which the exhaust passes from the exhaust pipe. It is advisable to reverse the connections for a short time before collecting any gas, and permit the exhaust to bubble through the water, so that it maybe saturated with carbon M.C.E. G 82 MOTOK CAR ENGINEERING dioxide. Leakage of air must be provided against by coating the stopper and the joints in the tubing with paraffin wax. A sample of the exhaust gas may be collected either by syphoning the water from the bottle, or by allowing the pressure of the exhaust to displace it. Mr. Horatio Ballantyne has observed that the percentage of hydrogen (H2) and methane (CH4) in the exhaust from petrol engines bears a definite ratio to the proportion of carbon mon- oxide (CO), namely, 0'36 and 0'12 respectively, and for practical purposes this will suffice. The reader is advised to obtain a copy of Mr. Dugald Clerk's paper on "The Principles of Carburetting," as it represents the most important contribution to the subject under discussion. Carburetters. — It is manifestly impossible in the space available to include a description of all the many types of carburetters in common use on motor cars, but a selection has been made which may be said to fairly represent the various principles involved. 66. The Lanchester Wick Carburetter.— This carburetter is the sole surviving representative of the class known as wick car- buretters, and to the excellence of its design, the ease of control, and its high efficiency, may be attributed the firmness with which it is established upon the Lanchester cars. It depends for its action upon the capillary attraction of cotton wicks for liquids, and the physical fact that hot air will take up a larger quantity of vapour than is chemically necessary for combustion. Thus no selective evaporation will take place, but all the constituents of the fuel will be vaporised ; and further, by the addition of an extra air inlet to the outlet from the car- buretter, the rich mixture may be diluted to any desired extent. The example illustrated is that used with pressure feed to the carburetter, but the same principles are involved in the pump- feed type. Its construction is shown in Fig. 30, from which it will be seen to consist of four superimposed chambers, the lowest of which constitutes the petrol reservoir ; the first and third wiok chambers, and the second the hot air chamber. The portions of the wicks contained in the uppermost chamber are frayed out to allow a free passage to the hot air, whilst the ends in the lower wick chamber are bundled together. The level of petrol witihin the lower wick chamber is maintained by means of a float, in the usual manner, which actuates a needle valve as is necessary in order to regulate the flow of fuel to the wicks. CAEBUKETTEES AND GAEBUBATION 83 The aotion of the carburetter is as follows : — The hot air collected from the vicinity of the exhaust pipe is drawn through the frayed ends of the wicks by the engine, and in its passage becomes richly impregnated with petrol vapour. The saturation of the heated air is facilitated, firstly, by the large surface of petrol exposed to the ah', and secondly, by the supply of the heat necessary to replace that used in vaporising the fuel. The mixture is now so strong as to be incapable of ignition, so as it passes to the engine -fA PETROL. 'PRESSURE INIil -Z^ Pig. 30.— Lanchester Wick Carburetter. it mixes with air at atmospheric temperature introduced through the special extra air valve shown in the figure, and thus forms an explosive mixture. It wUl be observed, that the carburetter is not rigidly attached to the engine, and thus it is free from engine vibrations. The level of petrol in the supply tank is indicated by a special gauge, which consists of an inverted cone, open at its upper end and attached to a graduated stem. Normally the cone is depressed, and sinks in the liquid, but when the amount of petrol in the tank is desired to be known, it is raised and spun between the fingers, in order to eject its contents by centrifugal force, and then allowed to rest upon the surface of the liquid. 67. The Claudel-Hobson Carburetter. — It has been shown in Art. 59 that with a closing throttle the mixture strength is reduced, a 2 84 MOTOE CAE ENGINEEEING but in the Claudel-Hobson carburetter this tendency has been corrected by means which will be subsequently explained. In construction, Fig. 31, it -vvttl be seen to present several novel features, that -which is most readily apparent being the incorporation of the float and the jet chambers in one casting, of very compact form, by means of which any effect that the inclination of the road may have upon the level of petrol within the jet is considerably minimised. The jet is composed of two tubes, the inner constituting the jet proper, and the outer forming a shroud, and having a closed upper end. At both the upper and lower ends of the shroud a number of holes are drilled, two row s being at the bottom and one row at the top of the shroud, and level with the jet. The upper end of the double tube projects into the interior of the drum throttle, which has certain portions of its circumference cut away in order that cer- tain actions may take place when the throttle is moved, as in opening or closing. Before considering the action of the car- buretter, it is well to notice that in the first place the petrol is heated before it leaves the jet, and when it is in a better condition for the Fia. 31. — Olaudel-Hobson Carburetter. reception of the heat, and secondly, that the breaking up of the stream of liquid issuing from the jet is effected at the jet. These two conditions assist greatly in causing the carburetter to be most efficient over a large range of speeds and powers. When in use the petrol passes through a filter in the bottom of the carburetter into the float chamber, and then falls to the warming chamber beneath the jet. It will be observed that this latter chamber is of large size, thereby allowing time for any impurity which may happen to have escaped through the filter (such as water or very finely divided particles of dirt) to settle at the bottom. On reaching the outlet from the jet, it is drawn therefrom, partly by the reduced pressure existing within the passage, and partly by the aspirating eflect of the air which passes through the holes at the bottom of CARBUEETTEKS AND CARBURATION 85 the shroud. This latter eSect is extremely small when the throttle is wide open, but when it is closed, or nearly so, the upper part of the shroud (being within the throttle) is subjected to a high suction pressure, and an added effect from an increased volume of air passing inside the shroud and near to the jet orifice, with the result that a greater quantity of Kquid is drawn from the jet than would otherwise be the case. Thus there is a tendency to increase the richness of the mixture passing to the cylinder, and, con- sequently, the resulting mixture within the cylinder is maintained an explosive gas. In order, primarily, to provide some means whereby the mixtiu-e strength may be varied with a closed or partially closed throttle, a small hole is drilled through the body of the casting. It is shown in Kg. 31, as the smaller and upper of the two screws at the right-hand side of the throttle. As the throttle closes it uncovers the lower end of the orifice, and allows air to pass through the passage without passing over the jet, the actual quantity permitted to so enter being regulated by the small screw seen in the figure. There is also another device embodied in the carburetter, which permits the strengthening or weakening of the mixture over the whole range of throttle opening, namely, the larger and lower screw. By screwing in or out this screw gives a smaller or larger choke-tube, and so causes a greater or smaller velocity to be given to the air passing to the engine. To facilitate starting a shutter is fitted, which may be closed when desired, and produce an excess discharge of petrol from the jet. 68. The Scott-Eobinson Carburetter is another example of the constant mixture type, which in this case is attained by main- taining a constant air velocity past a special jet chamber, and by regulating the effective areas for fuel and air. The jet (Mg. 32) is of large bore, but has its exit restricted by a tapered needle attached to a weighted drum, their relative position being regulated by the screw shown in the figure. The drum is guided at its upper end by a cylinder, and at its lower end by the jet, while from the function which it performs in regulating the openings for air and petrol, it will be obvious that its weight must be a predetermined amount. At the bottom edge of the drum a number of small holes are drilled, axially, communicating with its interior, and it is through these perforations that the petrol drawn out of the jet passes, being taken up by the air flowing by on its passage to the cylinder. When the carburetter is not in action, the drum rests with its lower rim upon the shell, but as the suction from the engine increases the air pressure beneath raises it until there is a certain difference of pressure existing between that in the space below the drum and that in the space beneath the throttle, the exact amount of lift depending upon the weight of the drum and the volume of the charge taken per minute. Now, as the weight of the drum is constant, the balancing difference of pressure must be constant, and therefore the velocity of the air through the annular orifice between the drum and shell will be constant. Thus there will be a definite relation 86 MOTOE CAE ENGINEEEING between the vertical position of the drum and the volume of air taken per minute, or, in other words, the drum will be in equilibrium when air at a definite velocity is passing. So far the control of air only has been considered, but as regards the flow of fuel it will be seen that owing to the constant velocity of the air past the orifices at the base of the drum, the same aspirating effect upon the contents of Fig. 32. — Scott-Eobinson Carburetter. the drum, and, consequently, the same artificial head upon the jet, will be pro- duced at all engine speeds. In order to vary the discharge from the jet in accordance with the volume of air pressing, the effective area of the jet is varied by means of the tapered needle attached to the drum. As the drum rises or falls, permitting a greater or lesser volume of air to pass to the cylinder, it moves the needle out from or in towards the jet — the effective area being thus automatically adjusted so that the amount of petrol ejected is that which is necessary to impregnate the air to the desired extent. The screw attached to the upper part of the needle is for permanent CARBURETTERS AND CARBURATION 87 adjustment. In the event of the mixture being too rich or too weak, by screwing the part down or up the gases may be either weakened or strengthened, and when once correctly adjusted the screw and needle are locked in position by the nut shown. This carburetter is heated by passing either the exhaust or the circulating water round the jacket surrounding the mixing chamber. 69. The Longuemare Carburetter is shown in Fig. 33, from Pig. 33. — Longuemare Carburetter. which it is seen that the essential features are an adjustable jet and a bye-pass. The petrol is led to the top of the float chamber A, passes through the filter F to the tapered needle valve D, and from thence through H to the jet. The supply to the jet is regulated by a needle valve K, which is kept in contact with the lever L by a spring I. Adjustment of the jet opening is readily effected by the milled headed screw and spindle M. The jet is placed within a choke tube N, and in line with its orifice is a bye-pass P, which makes connection by way of ft with a regulating bye- pass R. The throttle will be seen to be cut away on one edge, and to have a hole drilled throiigh the centre of one side. Under normal running conditions, with full throttle opening, the air enters at X, passes round the jet, through the choke tube to the engine, and the outlet from E is covered by the throttle. When the engine is throttled 88 MOTOK CAR BNGINEEEING down and the throttle is closed, as shown by the dotted lines, air is drawn from the vicinity of the jet by the hollow screw P, and passes through the passage Q to the adjusting screw E. Air also enters by the small hole through the throttle. It is clear, therefore, that any degree of strength of mixture may be obtained by moving P nearer to or further from the jet while the amount of carburetted air passing to the engine can be regulated by the screw E. So far the maximum and minimum positions of throttle opening have been considered, but it is obvious that as soon as the outlet from the bye-pass is disclosed, air will be drawn through Q, and assist in enriching the mixture, so that over all positions of the throttle the effect of the bye-pass will be felt — the degree of enrichment gradually increasing until the throttle completely closes. Thus the jet-adjusting device regulates the strength of mixture passing to the engine over the entire range of opening, and P gives an increasing Fig. 34.— Trier and Martin Carburetter. mixture strength with a closing throttle, while, E controls the amount of the mixture which passes through the bye-pass. Attention is drawn to the filter, which can be readily examined for cleaning by unscrewing the nut head E, and which permits any sediment to collect around the bottom without impairing its efficiency. 70. Trier and Martin Carburetter.^This carburetter, Fig. 34, is of the multiple jet type, having three jets K of graduated size which are brought into action by moving the throttle B. The throttle has two diameters, the larger being the air throttle and the smaller the petrol throttle. In the circumference of the larger diameter CARBURETTERS AND C ARBITRATION 89 shaped holes are cut as shown in Fig. 34, which give a very fine control at low speeds. The main air supply is via. the holes E in the end plate, which is provided with a permanent adjustment, and over the jets K in the choke tube through C to the engine. The ejection of the petrol from the jets is assisted by the air, which enters through small holes drUled through the casting near the base of the jets (not shown). These holes enable a very fine degree of proportioning to be obtained, as it is not necessary for any one jet to be fully exposed in order to come into play ; but as soon as the end of the piston C uncovers the edge of the recess in which the jet is placed, carbura- tion commences at that jet. In order to correctly proportion the amount of air to petrol, an extra air inlet is provided at G, so that as the throttle opening increases and the jets come into opera- tion,extra air is admitted, which passes through the openings in the end of the larger diameter of the throttle of the engine. At high speeds, when the throttle is nearly closed, the extra air inlet Gr is covered by the throttle, but as there will then be a greater suction head within the throttle, this will cause an excessive quantity of petrol to be dischai-ged by the end jet. For the purpose of diluting the mixture, an automatic air inlet D is fitted which consists of a closely coiled helical spring, upon the inner end of which a brass cap is soldered. As soon as the speed rises and the suction in this chamber exceeds a certain amount, this inlet opens and admits air. Thus the jets and the main extra air proportion the mixture over higher powers and the automatic extra air at the lower powers. Heady access is gained to the jets for cleaning by removing a cap, secured to the main casting by a milled screw. 71. The Brown and Barlow Carburetter is shown in Pig. 35. The jet D' will be seen to be separate from the main casting, and is placed within a choke-tube formed by two copper coned sleeves F, which are kept apart by the springG. ■Brown and Barlow Carburetter. 90 MOTOR CAR ENGINEERING Air passes through the inlet E past the jet D' through the throttle Hto the engine. The throttle is of circular form, and is kept upon its seating by a spring, as shown. As soon as the suction from the engine exceeds a certain predetermined amount, the automatic air-valve K comes into operation, and relieves the pressure by permitting extra air to enter the carburetter through the holes N. By accurately adjusting the pressure upon the spring L, which is effected by means of the screw M, it will be seen that various degrees of opening for air can be obtained, and thus the mixture may be diluted to the desired extent. Por very slow running there is a saw- cut (not shown) in the throttle H, so that a small amount of gas can pass even with the throttle closed. A point of merit in the design is the provision for placing the float chamber and main air inlet in any position. It should also be noted that the passage for supply of petrol to the jet is drilled out of the solid, and that a small hole P is drilled in the cast- ing to allow petrol, which overflows from the jet when the car is eased quickly, to escape. 72. The Polyrhiie Carl)ur etter . — This carburetter, which has obtained a high degree of efficiency of a large range of speeds and powers, is illus- trated in Figs. 36 and 37. Its construction is quite unlike that of any other carburetter, in that there are no jets in the ordinary CAEBUEETTERS AND CARBUEATION 91 meaning of the word, but a large number of fine slots which open out into the mixing chamber. The petrol rises from the float chamber (Fig. 37) through the passage shown to a comb. This comb is held between two flat plates, and is seen in Pig. 36 secured by five screws. The outlets from the teeth of the comb are not, however, the full width of the space, but are narrowed so as to present a row of fine holes to the air entering the carburetter. Within the mixing chamber (Pig. 36) there is a piston, which is connected by a hollow tube to another piston working in a larger annular space, closed at the end. A spring is fitted to restore the pistons, as necessary, and a tongue piece is attached to the smaller diameter piston, which moves over the throat (see Pig. 37. — Polyrhoe Carburetter : Cross Section. Pigs. 36 and 37). The throttle valve for regulating the speed of the engine is shown in Fig. 36. Now when the engine is running, the pressure in the mixing chamber, and, therefore, that in the space between the larger piston and the blank end of the carburetter, is below that of the atmosphere ; consequently the unbalanced pressure causes the piston to move to the left, uncovering a length of the throat and exposing a number of the jet openings to the entering air. The remaining jet openings, as no air passes by their orifices, play no part in the carburation. But the quantity of air entering the engine, and the length of the throat, are both dependent upon the difEerence of pressure on the two sides of the throat, although to a different degree ; and as the jets in operation are proportional to the length of the throat disclosed, there wiU therefore be a relation between the quantity of air passing and the quantity of petrol issuing from the jet. It is not difficult, then, to see that it is possible to so adjust the areas that practically the correct proportions of air and petrol are 92 MOTOR CAE ENGINEEEING maintained over all spfieds of the engine. This was indicated in the tests recorded in the Automotor Journal of August 13th, 1910, where the per- centage of 00 never exceeded 0'8 per cent, over a large range of speeds and loads. The regulator slide seen in Kg. 37, is operated by a Bowden wire attach- ment from the dashboard, and compensates for the varying conditions of the atmosphere and the quaKty of the petrol only, by altering the width of the throat. To strengthen the mixture the width is narrowed, and to weaken it the width is increased. The speed of the engine is controlled, as usual, by the throttle shown in Fig. 36. Questions on Chapter VI. (1) Name several types of carburetters and give the principles upon which they are operated. (2) What are the reasons why perfect carburation at all speeds and powers is so difficult to obtain ? (3) What devices are employed to remedy the defects yola mention in Question 2 ? (4) Sketch a pressure-fed fuel system, showing the lead of pressure pipes and where filters are placed. (5) What are the relative advantages of a pressure-fed and a gravity-fed fuel system ? (6) Show the construction of three different types of carburetters and explain in what manner the variations in the amount of air taken to the engine is allowed for. (7) What object is there in heating the air which passes to the engine ? To what extent should heating be permitted ? (8) Sketch and describe some form of carburetter in which there are no moving parts, but where variations in the amount of air passing are automatically allowed for. (9) Explain, with the aid of sketches, .the action of a modern type of carburretter. (10) How would you determine whether the combustion in an engine was complete or not ? (11) In what manner does the float regulate the height of petrol in the jet ? (12) What percentage of carbon monoxide would you expect to find in the exhaust from a petrol engine which was using («) strong mixture, (6) weak mixture, (c) correct mixture ? (13) Why is it that combustion is not complete in very strong or very weak mixtures ? (14) Upon what principles does the Lanchester wick carburetter operate ? CHAPTEE VII THBEMODYNAMICS OF THE PETROL ENGINE *73. Fundamental Laws and Definitions. — Before proceeding with the subject now under review — the thermodynamic principles of the internal-combustion engine — it will be well first to examine the fundamental laws and definitions upon which these principles are based. The Unit of Heat. — The British Thermal Unit is the amount of heat required to raise the temperature of 1 lb. of water through 1° F., when at its maximum density, 39° F. ; but it is sufficiently accurate for engineering purposes to take the rise of 1° at any temperature. The Centigrade heat unit is the amount of heat required to raise the temperature of 1 lb. of water through 1° C. when at its maximum density, 4° C. The French Calorie is the amount of heat required to raise the temperature of 1 kilo, of water through 1° C. when at its maximum density. One B.T.U. = TS C.H.Us. One French Calorie = 3-968 B.T.U. Specific Heat. — The specific heat of a substance — fluid, solid or gaseous, is the ratio which the amount of heat required to raise the temperature of a given mass of that substance through 1°, bears to the amount required to raise an equal mass of water through 1°. It is desirable to note in this connection that Eegnault demonstrated that the specific heat of gases increases as the temperature rises ; and further, that it varies according as the gas is maintained at constant volume or at constant pressure. From Eegnault's experiments, the value for air at constant pressure is '2375 and at constant volume •1691. 94 MOTOE CAE ENGINEERING Boyle's Law. — If the temperature of a gas remains constant, then the pressure varies inversely as the volume — that is PV is constant where P and V are respectively the absolute pressure and volume of a given weight of gas. It should be observed that the curve representing this relation is a hyperbola. Charles' Law. — If the pressure of a given mass of gas remains constant, then the volume will increase by a definite fraction of the volume at 0° C. for each degree rise in temperature. The fraction by which the volume is increased, is for Centigrade units 2-^y and for Fahrenheit units 5^5, and is termed the " coefficient of expansion," the values given being correct within practical lijuits. Thus, if o represents the coefficient of expansion and the volume at 0° C. is Vo then the volume V at ^ degrees will be: V = Vo (1 + a t). Similarly, if a gas be kept at constant volume, the pressure will increase by a definite fraction of its pressure at 0° C. and the equation defining the relation between the pressure of a gas at 0° C, w.ith the same mass of gas at t° C. is : — P = Po (1 + a i) Absolute temperature. — By Charles' Law, when a gas is heated at constant pressure, it expands by ^rs^^ of i^s volume at 0° C. for each degree rise in temperature, so that if a gas could possibly be cooled down sufficiently, and the law held good throughout the whole range of temperature, a point would be reached at which its volume would vanish. This temperature is — 273° C. or — 461° F. and is known as the absolute zero of temperature. Absolute temperatures are, therefore, the Centigrade tempera- tures plus 273 or the Fahrenheit temperatures plus 461. * 74. To combine Boyle's and Charles' Laws.- — In practice these ideal conditions of constant pressure, constant temperature or constant volume do not exist, so it becomes necessary to obtain some expression which will determine the relation between these three variables. Now, if P, Po, be the pressures exerted by a given mass of gas, which has volumes at those pressures of V, Vi, by Boyle's Law : — Po Vi = PV and Vi = ^5- • THERMODYNAMICS OF THE PETROL ENGINE 95 Then, if the temperature of the gas is reduced to 0° and Po remains constant, by Charles' Law : — Vi = Vo (1 + a t) where Vo is the new volume and t is the temperature of the gas when the pressure and volume are P and V respectively. But since a is the coefficient of expansion of the gas = cp^ for Centigrade units At o by substituting this valve of Vi in the original equation PV = PoVo(l + 2|3) - ^(273 + t) But P V = Po Vo = constant for any given mass of gas kept at constant temperature. P V So that ° „° is a constant = E and as (273 + t) is the absolute temperature a gas at a tempera- ture t°G. P V = constant X absolute temperature = R T This may be written in the general form — P V _ PiV] T ~ Ti ■ P V since —pp- = E. This method of using absolute temperatures often facilitates calculations, as it eliminates negative values. * 75. The First Law of Thermodynamics. — " Heat and energy are mutually convertible and Joule's Equivalent (J) is the rate of exchange." That is to say, heat requires for its generation and produces by its disappearance a definite number of units of work per unit of heat, the rate being 774 ft. lbs. of work per B.T.U. This is termed Joule's Equivalent, because it was originated by him, although the value which he placed upon the rate of exchange was 772 ; later experiments have, however, ascertained that the figure quoted previously is more correct. 96 MOTOE CAE ENGINEEEING Second Law of Thermodynamics. — " It is impossible for a self- acting machine unaided by any external agency to convey heat from one body to another at a higher temperature " (Clausius). This defines the limit of heat efficiency — ?= — - where T and Ti are the initial and final absolute temperatures of the substance used in the engine, as this represents the proportion of the total heat abstracted in the engine. * 76. Internal and External Work. — When a gas is heated, the V ^ \ p ^\ ^^s^l J^ i. ^^^;r-— ^^rr^^^ 1 -0 — V, ^ V, - - - -l Fig. 38. units of heat are absorbed in two directions ; firstly, in raising the temperature and expanding the gases, and secondly, in over- coming the external resistance to expansion — the former being known as internal work and the latter as external work. If a gas expanded or compressed without doing external work, and there is no loss from conduction or radiation, its temperature remains constant. The curve showing the relation between pressure and volume under such conditions is an " isothermal line," the operation being an isothermal expansion, and the equation of the curve is PV = a constant, where P is the absolute THERMODYNAMICS OP THE PETEOL ENGINE 97 pressure of a volume V. But when both external and internal work is done at the expense of the heat energy of the gas without gain or loss of heat from or to external sources, the expansion curve is an " adiabatic " having an equation PV = constant, where n is the ratio which the specific heat at constant pressure bears to the specific heat at constant volume. It will be apparent that the heat available during isothermal expansion is in excess of that during adiabatic expansion by the amount of heat required to overcome the external resistances, and thus the curves will be as represented in Fig. 38 where A is the line representing iso- thermal expansion and C represents adiabatic expansion. Both curves, it will be seen, have a common origin, but the adiabatic curve falls below the isothermal curve. The work done during isothermal expansion is represented on the diagram by the area enclosed by the curve and is equal to : — PV loge ^\ Vi But ^ = r = the ratio of expansion of the gases, so that the work done = PV loge r = ET loge r, since PV = RT. See Art. 74. The work done during adiabatic expansion, assuming absolute zero back pressure = ^^-y\ See Fig. 38. n — 1 ° If, however, the absolute temperature of the gas at the com- mencement of the expansion is represented by T and that at the end by Ti, then (PV - PiVi) may be written R (T - Ti) and the expression becomes _ B (T — Ti) n — 1 When heat is supplied to a gas kept under constant pressure, internal and external work is done. The heat absorbed in expanding the gases — the external work = P (V — Vi) = R (T — Ti) since PV = RT. Further, the total number of heat units used = Cj, (T — Ti) from the definition of specific heat, as (T — Ti) represents the change of temperature and Cj, the specific heat at constant pressure. M.C.B. H 98 MOTOR CAR ENGINEERING The heat units utiUsed in raising the temperature and in expanding the gases are therefore : — Internal work = C^ (T - Ti) - R (T - Tx). But if heat is imparted to a mass of gas kept at constant volume, only internal work will he done, which will he equal to the specific heat at constant volume multiplied by the change of temperature, that is C^ (T — Ti). Hence C, (T - Ti) = C, (T - Ti) - R (T - Ti) C« = Cj, — R and Cj, — C„ = R. * 77. The value of n. — The expression for the curve of pressure in an adiabatic expansion is PV" = constant. The work done during such an expansion may be written : — „ , , , R (T - Ti) External work = ij — n — \ Internal work = C„ (T - Ti) .-. Total work = ^ f _~/'^ + C, (T - TO = (T-T0(c.-,-^J But R = (Cj - CJ .-. Total work = (T - Ti) (ji^iLZlA). ^ m — 1 But the expansion has been carried out without any transfer of heat from or to the cylinder walls. .-. heat supplied = (T - Ti) ^" ^^^ J-^^" ^ and since there has been a change of temperature, (T — Ti) is tangible. . n C^ — Cp _ ^ n — \ that is 11 C„ — Cj, = n C« = C„ C,_ 78. Given a perfect gas, the value of n, or rather its mean value derived from the specific heats of the substance when its temperature is changed from T to Ti, could be ascertained with a large degree of accuracy, but in practice this is impossible on account of the influence of the loss of heat by radiation and to the cooling water, the complex constituents of the mixture, etc. n = ^ THEKMODYNAMICS OF THE PETEOL ENGINE 99 upon the working substance. Further, the speed of the engine will also affect the pressure during the expansion, this being greater with high piston speeds (the same charge volume being considered), so it is desirable to always obtain n from an indicator diagram. Appended is a table showing the specific heats of various Specific Heats of Gases. Chemical Symbol. Specific Heat. Gas. Constant Pressure. Constant Volume. Ratio !^ Air . Oxygen . Nitrogen . Hydrogen . Marsh Gas Ethylene . Carbonic Oxide Carbonic Acid . Steam O2 N2 H2 CH4 C2H4 CO C02 H20 -2375 -2175 -2438 3-406 -5929 ■404 -245 -216 -480 -1691 -1551 -1729 2-419 ■4505 -332 •173 -171 •369 1-408 1-403 1-41 1-41 1-317 1-217 1-416 1-263 1-301 * 79. To find the value of n. — To determine the value of n from an actual diagram, the pressure and corresponding volume at any two points upon a curve representing either the expansion or the compression of the gas should be noted. Then if P and Pi, V and Vi be the observed pressures and volumes : — PV" = PiVi" so that log P + ?i log V = log Pi + n log Vi n log V — n log Vi = log Pi — log P and n = '"^ ^i " 'og ^ log V — log Vi' This value n will only be a mean value, because the change in the specific heats of the gas as the temperature rises or falls, as well as the variation in the heat loss to the cooling water from the differences of temperature and cylinder surface exposed to the gases, will cause the rate of increase of pressure to vary throughout the stroke. It is, however, sufficiently accurate for H 2 100 MOTOR CAE ENGINEERING all practical purposes. The value of n will generally lie between 1'15 and 1'3, being slightly greater on the compression curve than on the expansion curve. When selecting the points on the curve at which the pressures and volumes are taken it is advisable to take them some short distance from the ends of the stroke, as on the compression stroke the firing of the mixture causes the pressure to rise before the in-centre is reached ; while on the explosion stroke, the opening of the exhaust valve permits the pressure to fall somewhat before the piston arrives at the out-centre. 80. Temperature in Adiabatic and Expansion. — Prom the formula derived from the combination of Charles' and Boyle's Laws, it was seen that PV = RT, but this relation is only of service for perfect gases under ideal conditions and is subject to considerable error when applied to actual practice. It therefore becomes necessary to obtain an expression which will take into account the same factors as were found to affect the value of n in adiabatic expansion. On p. 97 it is seen that : — and {lj=r- Multiplying both sides by (^j WJ PV RT' where T and Ti are the absolute temperatures when the piston is on its in-centre and out-centre respectively, therefore RTi = ^^(^y' \ Y But :^ is the ratio of the expansion or compression = r. Vi Hence Ti = '^{^^'^'■ Therefore, the temperature on the out-centre is equal to the product of the temperature on the in-centre and the reciprocal of the compression or expansion ratio raised to {n — 1)''^ power. * 81. Combustion. — When the charge has been compressed in the cylinder, the act of firing causes the fuel to burn, giving out heat and raising the temperature of the gases. The heat units liberated are those due to the chemical combination of the air and petrol THEEMODYNAMICS OF THE PETEOL ENGINE 101 vapour, and knowing the weight of petrol admitted per stroke it is easy to find their value if complete combustion takes place. It would not, therefore, be apparently a difficult matter to calculate the rise of pressure due to this liberation of heat, since the con- stituents of the gases are known with a fair degree of accuracy. But in actual practice this is not so, because it is by no means certain that the burning which takes place is completed at or near the end of the stroke ; in fact, it may be fairly assumed, with some substantial grounds for the assumption, that the burning continues throughout the stroke — being often even then uncom- pleted. Further, there must be some heat loss to the walls surrounding the gases, the amount of which it is difficult to estimate, because of the extreme rapidity with which explosion is effected and the high temperatures which are reached in the petrol engine. Then again, if the temperature of a complex gas is raised it undergoes a change in its chemical constitution due to the decomposition of the chemical combinations. These changes necessitate the abstraction of heat from the gases, and prevent the rise of temperature being so great as might otherwise be the case. For example, water vapour produced by the combination of hydrogen and oxygen, commences to split up into the two constituents at about 1,700° F., although these gases re- combine at the lower temperature reached during expansion. This is termed dissociation. There is also the question of the increase in the specific heat of the gases. It has been already observed that as the tempera- ture to which a gas is subjected is increased, so also do the values of the specific heats ; consequently- a greater quantity of heat will be required to raise the temperature through one degree rise of temperature. It will therefore be clear that the determination of the explosion pressure from theoretical considerations cannot be effected, especially when the discrepancy amounts to so much as it actually does. Mr. Dugald Clerk has found that although the theoretical temperature of combustion of hydrogen in air should be over 4,000° C, the actual temperature was only 1,900° C. It is probable that the reason for this loss is a combination of these various factors. Mr. Dugald Clerk believes that the failure to reach the theoretical temperature is due partly to the increase 102 MOTOK CAE ENGINEEEING of the specific heats and partly to the after-burning of the charge ; while Mr. Wimperis suggests that it is probably due to the combined action of cooling and the increase of specific heats. The reader would be well advised to further extend his knowledge by a perusal of Mr. Dugald Clerk's book on " The Gas, Petrol and Oil Engine " and " The Internal Combustion Engine " by Mr. Wimperis. Questions on Chapter VII. (1) What are Boyle's and Charles's laws ? (2) What do you understand by isothermal expansion ? (3) The compression ratio used in an engine is 4-5. If the tem- perature of the gases in the out-centre is 460° F., what will be the temperature of compression? Take n = 1'2. (Answer = 769-6° P.) (4) What should be the compression ratio of an engine in which the compression pressure is 100 lbs. per square inch absolute, if the pressure at the commencement of the compression stroke is 13-|- lb. Q per square inch absolute ? Assume that -^ = 1*28. (Answer = 4-78.) (5) Using the diagram shown in Eig. 44, in which the ordinates are to a scale of 1 in. = 100 lbs. find the value of n for the expansion curve. (Answer ■= 1'05.) (6 What is the specific heat of a gas ? Show that the value of n in an equation of the curve for an adiabatic expansion is the ratio of the specific heat at constant pressure to that at constant volume. (7) Combine Boyle's and Charles's laws. CHAPTEE VIII HOESE-POWER 82. What is Horse-power ? — Considerable confusion frequently exists, especially in the non-technical mind, as to the difference between " work " and " power," which is largely due to the fact that the use of the words is not always restricted to their proper •application. " Work " is done in overcoming a resistance to motion through a certain distance, as when lifting x pounds through y feet or in drawing a ear along a road through a distance D feet against a resistance of F lbs. per ton. The measure of the work done in ft.-lbs. is the product of the force applied in lbs. and the distance through which it moves in feet, and is quite independent of any time factor. " Power " is the amount of work done in unit time or the rate of doing work. The unit of power is the " horse-power," and an engine is said to be developing one horse-power when it performs 33,000 ft.-lbs. of work in 1 minute. When applying this rule in practice, however, it is found from considerations, either of expediency or of convenience, to be necessary to prefix another word, which will limit its meaning and exactly specify how the power is measured. There have therefore, been evolved the terms — " Indicated Horse-power," " Brake Horse-power," " Electrical Horse-power," and " E.A.C. Eating," all of which exactly express how the power is obtained. 83. Indicated Horse-power. — The indicated horse-power gives the actual power developed in the cylinder, and takes account of the compression pressure, strength of mixture, the time taken to obtain maximum explosion pressure, the effect of burning of the charge during expansion, the cooling losses, leakages, etc., in fact, all factors which affect the charge volume of the gases in their passage through the engine. To find the indicated horse-power of an engine it is first 104 MOTOE CAE ENGINEEEING necessary to obtain an indicator diagram from the cylinders. This may be done either by a piston indicator or a flashlight indicator, but generally, it may be stated, the former is unsuitable on account of the effects of the inertia of the recipro- FlG. 39. — Mclnnes Dobbie Indicator. eating parts, looseness or friction at the joints and the piston, the stretching of the actuating cord, effect of long passages between the piston and the cylinder, and the high tempera- tures to which the spring is subjected. In an indicator illus- trated in Fig. 39 these factors which militate against the use of the type have been reduced to a minimum. HORSE-POWEE 105 It will be seen to consist of a cylinder, iu which a piston V attached to a parallel motion G reciprocates. The parallel motion multiplies the piston travel six times, and has at its free end a pencil which moves in a straight line vertically, exactly reproducing the movement of the piston. The piston is of special construction, and is of case-hardened steel. It is turned from the solid, and the central space aflords accommodation for any grit or dirt which may enter the cylinder, removing it from the cylinder walls and preventing tearing and friction. The piston rod S has a collar fixed upon it for the receipt of the spring, the latter being screwed on this collar and also on the upper cap N. The paper drum is earned upon a frame D, and is rotated by the cord running over a pulley as shown, the tension in the cord being produced by the spring A attached to the drum. The connection with the engine cylinder is made by a cock to which the indicator is secured by the nut Y. When connection is made with the engine cyhnder, the pressure acting upon the piston V causes the piston rod to actuate the parallel motion. At the same time, the paper drum receives a rotary movement from some reciprocating portion of the engine, which exactly reproduces on the paper the motion of the engine piston. Thus there are the two motions — the vertical movement of the pencil recording pressures and the rotary move- ment of the drum recording piston displacements — which, combined, produce the indicator diagram such as is shown in Figs. 38 and 42. 84. Hopkinson Flashlight Indicator. — The great advantage attaching to the use of optical indicators is that the sources of error pointed out above are avoided entirely, on account of the extremely small weight and movement of the moving parts. The diagram is traced out by a spot of light reflected from a small mirror that travels so rapidly as to appear as a continuous line. Pig. 40 is a drawing of the instrument partly in section. The block A screwed fin. Whitworth thread is screwed into the ordinary indicator hole of the engine. The frame B fits over the block, sufficient clearance being left to provide for unequal expansion. The frame is held up by a spring mto engagement with the lower face of the nut C (screwed to the top of A), a ball-race being interposed so as to admit of easy rotation of the frame about the axis of A. The spring D is a piece of steel strip resting in grooves at the end of the frame B, and held by the springs B B. The spring is slightly bowed before insertion in the frame, so that when the screws B E are screwed home, the spring is held straight with slight pressure on the four points of support. The piston F slides in a bore in the block A. At the top it is provided with a hook G, the opening of which is slightly larger than the thickness of the spring. The piston is thus free to move laterally, and no binding action is possible between it and the sides of the bore, such as would occur if the piston were rigidly attached to the spring. Three pistons are supplied 106 MOTOR CAR ENGINEERING with the instrument, the areas being in the ratio of 1, 2, and 4. There are two springs which are ground so that their stiffnesses are in the ratio of 1 to 5. A wide range of sensibility is thus obtained. The smaller pistons fit inside liners which are inserted in the bore of the block A. The mirror H is clamped to a steel spindle I, the ends of which are pivoted in small holes in the vertical spring cheeks J J. The motion of the spring D is communicated to the spindle and mirror by means of the piece of vertical spring K. The lower end of this spring is held firmly on the face Fig. 40. — Hopkinson Flashlight Indicator. of the main spring D by means of the jaws L ; the upper end is firmly clamped to the arm M, which projects at right-angles from the mirror spindle. The spring K, while sufficiently rigid to transmit the motion of the main spring to the end of ithe arm M without buckling, is flexible enough to allow for the angular motion of that arm. The mirror is thus turned about the axis of the spindle by an amount which is proportional to' the displace- ment of the main spring D, and therefore to the pressure under the piston. In order to give the other motion to the mirror, the frame B is positively connected by linkage to a reciprocating part of the engine, and is thus HOESE-POWEE 107 caused to rock as a whole about the axis of the block A. The motion thus given to the frame B must be in phase with and proportional to the piston motion. For making the diagram visible a simple and neat form of photographic camera of light weight is made, which is clamped on to the indicator in the mirror shown in Fig. 41. A concave mirror is used in this case, which forms an image of the source of light upon a ground-glass screen. The screen may be replaced by a photographic plate and a record of the diagram thus obtained. Fig. 42 shows a diagram produced by this method. A very small and brilliant spot of light is obtained by the use of an Pig. 41. — Camera. electric lamp filament placed behind and at right angles to a fine slit. Quarter-plate slides are employed. 85. Mean Effective Pressure. — The mean effective pressure is the mean of the pressures acting upon the piston during one cycle of operation in the cylinder. No account is, however, taken of the pressure upon the piston during the suction and exhaust strokes, because of the extreme difficulty of accurately measuring them. To find the mean effective pressure Dr. Watson recommends that the length of the diagram be divided into 20 equal parts and the mean height of each part measured. The mean height is the vertical distance between the lines representing the pressure during the explosion and compression strokes. 108 MOTOR CAE ENGINEERING These mean heights are added together and divided by 20 (thus obtaining the mean height of the diagram) and then multi- pHed by the scale of the spring used in the indicator. The numerical value thus obtained is the mean effective pressure in the cylinder during any one cycle. If n = the number of cylinders, P = the mean effective pressure in lbs. per square inch, L =, the length of stroke in feet, A = sectional area of piston in square inches, N = the number of explosions per minute, then PLA is the work given out on the explosion stroke, minus the work absorbed on the compression stroke in ft.-lbs.. Fig. 42. and as there are N such operations per minute in each cylinder, then PLAN represents the number of ft.-lbs. of work done per minute in each cylinder. n PLAN Therefore — „q „„„ is the indicated horse-power developed by the whole engine. But it is not always convenient to ascertain the indicated horse-power, as special connections must be made to the cylinder, and gearing is necessary in order to reproduce the path of the piston on the indicator diagram, so that this method of measuring the power of an engine is frequently dispensed with entirely, and only the actual power given out by the engine is measured. The lack of information resulting from this method is not so detri- mental to the manufacturer as might be anticipated, as, knowing tlie full performance of an exactly similar type or design of. HOKSE -POWER 109 engine, the actual experimental result which may be anticipated can be very approximately determined, and this for ordinary commercial purposes is all that is required. 86. Actual or Efifective Horse-power. — As is fairly obvious, although a certain horse-power may be developed in the cylinder of an engine, it is not possible to obtain this same amount of power at the coupling, as there must be some losses from the friction of the pistons and other moving parts ; some power must be used in operating the valves, pumps, etc., in drawing the charge into the cylinders and in pushing out the products of combustion. This power, which is that actually given out by the engine, is termed the effective or brake horse-power, and, as will be seen later, is used in conjunction with the indicated horse-power to obtain the mechanical efficiency of the engine. The method adopted for the measurement of the effective horse-power is by means of a dynamometer, which may be of one or two classes — absorption or transmission. The former absorbs the power given out by the engine by means of friction, the heat thus generated being carried away either by radiation and conduction or by some special cooling apparatus, while the latter transmits the power through its mechanism. 87. Kope Brake. — A common form of brake used for small powers is the rope or band brake. This consists simply of a rope wound once or twice round a drum or flywheel secured to an overhead beam, as shown in Fig. 43. A balance S, secured . to an overhead beam, is placed on the upper end of the rope Fig. 43.— Eope Brake. 110 MOTOE CAK ENGINEERING and scalepan W on the other. The scalepan is loaded until the engine runs at the desired speed, and the readings of the balance and the weight in the scalepan are then taken. (W - S) 2 TT EN The brake horse-power where R is the 33,000 distance between the centre of the flywheel and the centre of the rope in feet. This brake is not suitable for large powers because of the heating of the brake drum and because of the variation in the Pis. 44. — Heenan and Froude Water Dynamometer. friction between the rope and the drum. Some more accurate means are therefore desirable, and such is provided by the forms about to be described. 88. Heenan and Froude Water Dynamometer. — This apparatus is one of several types of hydraulic brakes, but it is one upon which a large amount of high-class work has been carried out^ and powers may be very accurately and directly estimated by its aid. The dynamometer, Fig. 44, consists primarily of a turbine or rotator revolving within a casing, which is suitably mounted on friction rollers and connected to a water supply to enable the casing to run full of water when the machine is in use. HORSE-POWEK 111 The rotator, Fig. 45, is fixed to the shaft, which projects on either side of the casing, and to which the engine to be tested is coupled. Engines of either direction of rotation can thus be tested on the one machine. Each disc face of the rotator is formed with a semi-elliptical annular channel, see WATER OUTLET WATER tNLET COUPLINC Fig. 45. — Section through Heenan and Froude Water Dynamometer. Fig. 46, divided into a number of compartments by means of oblique vanes, and the corresponding faces of the casing have similar channels divided in the same way. The channels on the rotator and casing thus form two complete annular channels of elliptical cross-section, each channel being Fig. 46. — Cross-section through Vanes. divided, as stated above, into compartments by means of the oblique vanes. When in action, the water in each annular channel is rotated continuously by the centrifugal force imparted to it by the rotator, and passes from one compartment into the next, and so on. An extremely high speed of rotation of the water is obtained, and the power or energy put into the dynamometer 112 MOTOE CAR ENGINEERING is by this means converted into heat, which passes away in the water leaving the machine. The' motion of the water causes the rotator to re-act on the casing, and tends to tarn it on the friction rollers. This is prevented by means of an extension or arm working between stops, at the end of which are the balance weights and counterbalance, by which the actual power put into the dynamometer is measured. To reduce the power absorbed by the dynamometer when required, thin metallic shields are provided, which are interposed between the faces of the rotator and the casing, thereby cutting ofi a portion of the effective area of the annular channels. In this manner the power may be reduced from the maximum down to about one-thirtieth of that amount. The horse-power given out by the engine is — „„ ^„„ — where W is the effective weight at the end of the dynamometer arm, N is the number of revolutions per minute, and E is the radius at which the weight acts in feet. 89. Fan Dynamometer. — This form of brake is frequently used, when all that is required is to show that a certain horse-power is given out at a particular speed of revolution, as, for example, in the shop testing of ordinary car engines, and the best known, perhaps, is the Walker Fan Dynamometer. The medium through which the power is absorbed, in this case, is the resistance offered by the air to the rotation of two plates attached to revolving arms secured to the engine shaft. By previous calibration tests, the powers which the fan plates will absorb at different speeds and radii are known, and are supplied by the makers in tabular form, there being different sizes of plates for various powers and speeds. Before making a test the table is consulted, and the plate most suitable taken and secured to the arms at the correct radius ; then, knowing the revolutions made by the engine, a reference to the table will give the power developed by the engine. The disadvantage of this system of measuring power is that it is not possible to vary the load at any particular engine speed without stopping the engine, and this is often inconvenient and undesirable to do. With regard to the accuracy of the results obtained, there is no reason why these should be questioned, as the makers take every possible precaution to verify the calibration tables supplied with the apparatus. 90. The Electrical Brake. — A method of power measurement HOESE-POWEE 113 Which has during recent years become much favoured, and which has much to commend it on account of its elasticity, cleanliness, and simplicity, is carried out by means of a shunt-wound dynamo direct-coupled to the engine. Sometimes the dynamo is belt- driven, but this is not desirable. In this arrangement, Fig. 47, the current generated by the dynamo E is led to resistance coils, as shown at A, the load being varied by increasing the number of coils in the circuit. The shunt cur- rent is regulated by the resistance D, by means of which the correct voltage is obtained. As is readily seen, this method renders it pos- sible to vary the revo- lutions and the load quite independently, and thus obtain the flexi- bility which is so neces- sary where exhaustive experiments are con- templated. Before making the tests, the efficiency of the dynamo with vary- ing output is carefully obtained by treating the dynamo as a motor. A current of x amperes at y volts is passed through the dynamo, and the brake horse-power given out while the current is passing is measured. The watts put in are xy, which is equivalent CCl/ to jjp: horse-power, as 746 watts equal 1 horse-power. Then, knowing the power given out by the dynamo to the brake, the efficiency of the dynamo T3TTT> J- -J IV, ^V — 746 X B.H.P. r] = B.H.P. divided by „-7^ = ■^ 746 xy By arranging the result of a sufficient number of tests, a JI.O.B. I Fig. 47. — Electrical Testing Diagram. 114 MOTOE CAK ENGINEEEING diagram may be obtained which will give the value of tj for any particular output. When the dynamo is driven by an engine, if the amount of Current and the voltage is read from the meters B and C, the horse -power given out by the dynamo is -Tfj?,, a^nd as the efficiency of the dynamo is rj, the horse-power given out by the engine and put into the dynamo is 746 X V In figure A, the resistance box containing resistance coils. B, the ammeter to measure the current. C, the voltmeter to measure the voltage. D, the rheostat, by means of which the voltage is regulated. E is the dynamo. F is a fuse. Occasionally, instead of absorbing the current in resistance coils, a '■ bank" of lamps are employed, while in others a water resistance is used. The latter consists of an iron box containing a solution of washing soda, in which an iron plate is suspended. By raising or lowering the plate into the liquid the resistance to the passage of current is increased or decreased. 91. Horse-power under R.A.C. Rating.— The E.A.C. formula was devised for the purpose of comparing the horse-powers of the many different makes of cars taki^ig part in competitiens, and to enable the prospective owner to roughly estimate the relative value of the powers of cars he might happen to be considering. It was based upon the assumption that the piston speed was approximately 1,000 feet per minute and the mean effective pres- sure was about 67'2 per square inch. But with the improvement in materials of construction and methods of manufacture came higher piston speeds, higher compressions and in some cases longer strokes, the result being that the E.A.C. formula no longer held good as a comparison of power. « P L A N Taking the ordinary I.H.P. formula as a basis — „„ ^„„ — ° -^ 33,000 without an actual trial the only known factors are n, L and A, as all the others may vary independently ; and it has even been H0R8E-P0WEE 115 proposed to make n an unknown on account of the extra number of working parts in a multi-cylinder engine resulting in a slight decrease in the mechanical efficiency. With regard to P — the mean effective pressure in the cylinder — it is found by experiment that as the bore increases so does the mean pressure increase, as there is less cooling surface per unit of volume in the larger cylinder ; but owing to the lack of adequate data, the rate of increase is not known. It is also affected by the areas and configuration of the pipes and valves, the shape of the combustion chamber, the compression pressure, the richness of the mixture, the type of the ignition, position of the plugs and many other details of less importance- Then, at the present time it is impossible to state what the absolute limit of piston speed (2LN) is, as although its mean value in pleasure cars is not more than, say, 1,000 feet per minute, yet, over 2,000 feet per minute has been averaged in the case of cars used in racing competitions ; and further it has been proved that an increase in stroke-bore ratio will allow of an increase in the piston speed. This will be obvious when it is remembered that for any given power the longer the stroke the smaller will be the bore and the less will be the load upon the connecting rod, and, as the bending stress in the rod due to its inertia will be but slightly affected, the weight of the reciprocating parts will be reduced and a higher piston speed permissible. In addition to this, by the use of special materials, the reciprocating parts may even still further be lightened. Thus the problem upon which the Eoyal Automobile Club, the Society of Motor Manufacturers and Traders and the Institu- tion of Automobile Engineers is engaged is not v-ery easy of solution, especially as it is particularly desired to avoid the adoption of any formula which will tend in any way to restrict design or to produce freak engines. 92. A number of the formula proposed are appended : — E. A. C. 0-4 D^N Faroux 0-000525 d ^^ N " 1909 "— S.M.M.T. 0-197 D (D - 1) (jr -^ 2^ N " 1911 '•— I.A.E. 0-464 (D -f B) (D — 1-18) N Lanchester 0-46 D^'" S'^ N Eoyce 0-25 (D - J)^ VS N I 2 116 MOTOE CAE ENGINEEEING Callender 0-167 (S + 2 D - 3) N Burls' Valve 6B^ (l - Tq^) N / — S Burls' Inertia 0-5D N (D - 1-18) V ^^ ^ where D = diameter of cj'linder in inches and d in millimetres S = stroke in inches N = number of cylinders S = diameter of valves M = mass of piston and connecting rod. In the " 1909 " S.M.M.T. formula the constant is altered for racing cars to 'SSS. This formula allows for the increase in piston speed with an increase in stroke-bore ratio by taking (=P^ + 2j and a correction is applied for the greater cooling loss in a smaller bore engine by employing D (D — 1) instead of D^. In the " 1911 " I.A.E. formula the mean effective pressure is presumed to be that obtained from 130 (l — i^^ lbs. per square inch and that the maximum piston speed is 600 (c + 1) feet per minute where r is the stroke-bore ratio. Mr. Burls, M.Inst.C.E., has derived two formulae, one based on the effect of the inertia of the reciprocating parts and the other upon the maximum velocity of the gases through the inlet pipe. But for the full consideration of tlie respective merits of these formulae, the reader is referred to the reports of the Committees of the S.M.M.T. on the Eating of Petrol engines and to the Pro- ceedings of the Institution of Automobile Engineers, Vols. III. and V. 93. Horse-power at road wheels. — The resistance offered to the progress of a car is the summation of three variables : — 1. EoUing Eesistance. 2. Eesistance due to gradient which may be positive or negative. 3. Eesistance due to wind which may also be positive or negative. EoUing Resistance is the resistance offered to the motion of the wheel when rolling upon the ground. It has been found in HOKSE-POWEE 117 locomotive work that the value of this resistance varies inversely as the wheel diameter, and that it is independent of the speed. So that, applying this rule to automobiles, if two exactly similar cars were tested, one having tyres of 900 mm. diameter and the other of 1,200 mm. diameter, then the power required to overcome the resistance of the road should be in the ratio of 1,200 to 900 — a strong argument in favour of larger diameter tyres. But in the majority of cases the diameter of the wheels varies so little as to render any discrimination in this respect of no account, especially as the values of the road resistance can only be accepted in the broadest sense. The following figures give the mean road resistance obtained from a number of results expressed in lbs. per ton weight of car : — Wood blocks, dry 27 Macadamised road, hard and dry . . 30 Macadamised road, hard and wet . . 48 Macadamised road, treated with tar. . 24 Asphalte at 60° F 35 Flint and gravel, well rolled and dry . 45 Flint and gravel, well rolled and wet . 60 As has been stated, these values are given only as a general estimate, as any tendency for the road to disintegrate may raise them considerably. The work done per minute is the product of the road resist- ance, the weight of the car in tons and the space passed over by the car per minute. Resistance due to gradient. — This is simply that due to the work done in raising the car from one elevation to another, and is quite independent of the speed at which the car may be travelling. The work done per minute is equal to the weight of the car in lbs., multiplied by the height through which it is raised in feet during one minute. Resistance due to wind. — There are several formulae by means of which this may be approximately obtained — the best known possibly being those due to Mr. Mervyn O'Gorman. The O'Gorman formula is, H.P. = -000004535 V^ A where V is relative velocity of car to air in miles per hour and A is the projected sectional area of the car in square feet. 118 MOTOE CAE ENGINEEEING Summing up, the three components — Eolling, Gradient, and Wind Eesistance — xr-D t 13 ir -D • . WEV X 5,280 H.P. for Eolhng Eesistance = gO X 33,000 = -003636 WEV where E. is the Eoad Eesistance. W X 2,240 X H H.P. for Gradient Eesistance : 33,000 X WH = -0678 ,j, where H is the height of gradient in feet, and T is the time taken to climb the gradient in minutes. H.P. for Wind Eesistance = -000004535 Y^. A. Example. — Find the horse-power required to propel a car at a speed of 15 miles per hour up a hill of 1 in 8. Weight of car 2 tons and projected area 20 square feet. Eoad resistance 40 lbs. per ton. H.P. for Eoad Eesistance = -003636 WEV = -003636 X 2 X 40 X 15 = 4-363 W H H.P. for Gradient Eesistance = -0678 „, _ .OfiTS V 9 V 15 X 5,280 - °^^^ ^ 2 ^ 8X60 = 22-374 H.P. for Wind Eesistance = -000004535 V A = -000004535 X 15^ X 20 = -306 Total H.P. = 4-363 + 22:874 + -806 = 27-043 It will be observed that in hill climbing the gradient resist- ance largely determines the power, and that the wind resistance is for practical purposes quite negligible. But the horse-power required to overcome the wind resistance increases very rapidly with an increase of speed. Questions on Chapter VIII. (1) What are the following ? — One ft.-lb., one horse-power, indicated horse-power, and brake horse-power. HORSE-POWER 119 (2) How may the brake horse-power of an engine be obtained ? Describe a method of carrying out a brake test. (3) If the engine is running at 1,000 revolutions per mimite and a i-in. rope is wound round the brake drum of 16 ins, diameter, what is the brake horse-power given out by the engine if . the spring balance records 20 when a weight of 85 lbs. is placed in the scale- pan ? (Answer = 8-61.) (4) Describe a flashlight indicator. (5) What advantages have flashlight indicators over the ordinary piston indicator? (6) Using the diagram given in Fig. 38, in which 1 in. represents 120 lbs. per square inch, find the indicated horse-power of a 4-cylinder engine running at 1,100 revolutions per minute if the stroke is 5 ins. and the bore i ins. (Answer = 28-2.) (7) Describe by the aid of sketches a water dynamometer. (8) If in carrying out a brake test with an electrical brake the ammeter and the voltmeter recorded 42 amperes and 250 volts re- spectively and the efficiency of the dynamo was 80 per cent., what horse-power was given out by the engine? (Answer = 17'6.) (9) Knd the horse-power required to propel a car weighing 1^ tons along a road having a resistance of 50 lbs. per ton at a speed of 20 miles per hour. If the speed of the car relative to the wind is 30 miles per hour and the sectional area of car is 25 square feet, what is the total power required ? (Answers = 4*0 and 7'06.) (10) What are the principal difficulties experienced in deducing a formula to represent the horse-power of an engine, using the cylinder dimensions only ? CHAPTER IX MECHANICAL, THERMAL AND COMBUSTION EFFICIENCIES * 94. EfiBciency. — The efficiency of a machine is the ratio which the work given out bears to the work put into the machine. In all transformations, whether of reciprocating into rotary motion or of heat into work, some loss always takes place, and many of the improvements which have been made in the modern engine have had as their object the reduction of the magnitude of .these losses. * 95. Combustion Efficiency. — As its name implies, this repre- sents the efficiency of combustion, and indicates the amount of heat that is wasted in the exhaust gases. When the charge is taken into the cylinder of a petrol engine, it consists of hydro- carbon vapour and air. This is fired and the products of combustion are finally expelled from the cylinder. If complete combustion has taken place, the exhaust will contain only inert gases, but generally some proportion of GO will be found to be present and there may possibly be some hydrogen, C H4 or Marsh gas and C2 H4 or Ethylene. This shows that the petrol has not been burnt to the best advantage, as these gases are all consumable and may be made to give out heat. Supposing now, that the composition of the exhaust gases is as follows : — CO2 12 per cent. O3 Nil CO , . . , , 5 „ „ H2 1-5 „ „ CH4 0-5 „ „ N2 ._ . . . , 81 „ „ This may be written : — 12 CO2 -1- 5 CO + 1-5 H2 + 0-5 CH4 + 81 N2 + 14 H2O, since 81 volumesof N2 are found in air with 21-5 volumes of O2 of which only 14-5 have been accounted for in the analysis — the vepi^inder haying combined with hydrogen to form water. MECHANICAL, ETC., EFFICIENCIES 121 The respective weights of the gases will be : — 12(12 + 32) + 5 (12 + 16)+ (1-5 X 2) + 0-5(12 + 4) + (81 X 28) + 14 (2 + 16) = 528 + 140 + 3 + 8 + 2,268 + 252 = 3,199. The proportions of the unburnt gases by weight are therefore : — CO = ^^ X 100 = 4-88 per cent. Ha = 3^ X 100 = 0-094 „ „ CH4 = 3jgy X 100 = 0-25 „ „ If the engine from which the sample of exhaust gas was taken was burning 12 lbs. of air per lb. of petrol of calorific value 18,500 B.T.U. per lb., the weights of the exhaust gases expelled while 1 lb. of the fuel was being consumed were : — CO = ^ X 13 = 0-5694 lbs. 0-094 H2 = ^ X 13 = 0-01222 „ CH4 ^- -^ X 13 = 0-0325 „ and the heat that would have been given out by burning these gases in the cylinder is : — CO = 0-5694 X 4,300 = 2,448-4 B.T.U. H2 = 0-01222 X 51,700 = 631-8 „ CH4 - 0-0325 X 23,515 = 764-2 „ .-. Total number of B.T.U. lost = 3,844-4 The calorific value of the fuel used was 18,500 B.T.U. per lb. ,-. Heat given out in the cylinder = 18,500 — 3,844-4. = 14,655-6 per lb. of fuel. Combustion efficiency ... ... = , ' -,,„ ■' 18,500 = 79-2 per cent. The combustion efficiency of an engine may vary from about 60 to 99 per cent. * 96. Thermal Efficiency. — The thermal efficiency of an engine is its efficiency as a machine for converting heat into work. A certain weight of petrol is burned in the cylinder per minute, 122 MOTOE CAR ENGINEERING and during that time a certain number of ft. lbs. of work are done on the piston, the ratio between these two values is the " thermal efBciency." In more common language, it is the relation between the indicated horse-power and the " petrol horse-power." The petrol horse-power is Weight of petrol burnt per minute X calorific value X 774 33,000 since by multiplying the weight of petrol by the calorific value the number of B.T.U. liberated per minute is obtained, and this is multiplied by 774 to convert units of heat into units of work. For example : — The indicated horse-power of an engine is 50 and it burns 37"2 lbs. of petrol, having a calorific value of 18,000 B.T.U. per lb., per hour. Find the thermal efficiency : — 18,000 X 37-2 B.T.U. liberated per minute = 60 ■r, , , , 18,000 X 37-2 X 774 Fetrol horse-power = - - Thermal efficiency 60 X 33,000 261-7 50 261-7 =; 19-1 per cent. The thermal efficiency at full power generally ranges between 19 and 26 per cent., although as high as 28 per cent, has been obtained in a laboratory. Given any two engines with the same compression ratio and piston speed, the thermal efficiency has been found to be nearly independent of the engine dimensions, as the greater heat loss from the larger proportion of cooling surface to charge volume is counteracted to a large extent by the shorter time that the hot gases are in contact with the cylinder walls. Experiments have also demonstrated that when the supply of petrol is maintained constant and the volume of air is increased, the thermal efficiency will increase slightly, provided that the air initially admitted was just sufficient for complete combustion. This, however, is only true for a very slight decrease in the strength of the mixture. * 97. That it will be impossible to obtain a very high thermal efficiency is quite obvious from the fact that the cooling water abstracts from 30 to 40 per cent, of the heat given out by the MECHANICAL, ETC., EFFICIENCIES 123 petrol on combustion in reducing the working temperature of the cylinder walls to a practical value. Further, if it is required to use all the heat in the gases, they must be expanded down to absolute zero of temperature. The limit of thermal efficiency is represented by the equation T - Ti " = -! — where T and Ti are the absolute temperatures at which the working stuff is admitted and exhausted. This is the Carnot cycle, and assumes that heat is received at the highest tempera- ture and rejected at the lowest temperature, as in the steam- engine. Petrol engines using the Otto cycle, however, are operated on what is known as the " Constant Volume Cycle," in which the heat is received at constant volume and rejected at constant volume. The charge received into the cylinder is com- pressed adiabatically, and heat is added which raises its temperature from T to Ti and increases the pressure. The gas is then expanded down adiabatically, until it has the same volume as before compression, and finally exhausted at constant volume, the temperature falling during exhaust from T2 to T3. The heat added is clearly (Ti — T) C , and the heat rejected is (Ta - Tg) C,, so that _ (Ti - T) C, - (T, - T3) C '' - (Ti - T) C„ -1 _ T2 - T3 ~ Ti - T ■ But as the gases were compressed and expanded to and from the same volumes, %=k=W (See Art. 80) where V^ is the volume after compression and before expansion, and V is the volume before compression and after expansion. V . . . It will be seen that =rT- is the compression ratio r, and therefore by substitution in equation — * 98. This is called the " Ideal Efficiency," and has been adopted as the standard by which to measure the maximum 124 MOTOR CAE ENGINEEEING thermal efficiency of internal-combustion engines ; and as the working substance within the cylinder is composed mainly of air, the value of n to be used in the expression is the ratio of the specific heats of air at constant pressure and constant volume, namely, 1'408. Thus the Air Standard EfBciency of an internal-combustion engine is : — = ^ - © It will be seen that the maximum thermal efficiency of an engine depends upon its compression ratio, an increase in this resulting in the reduction of the part to be subtracted from unity. This explains the higher thermal efficiency of the modern engines, and the reason for the use of higher compression pressures where efficiency is of first importance. Professor Callender's formula for the efficiency of an internal- combustion engine is based on the assumption that the effect of heat loss on the thermal efficiency in similar engines, under similar conditions, should vary as the ratio of surface to volume during and shortly after ignition, or inversely as the diameter D. That if the heat loss varied inversely as the speed in revolutions per minute, the loss of thermal efficiency " would be the same for similar engines at the same piston speed." The formula is Efficiency = 0-75 r, ^1 - ^\ where rj is the air standard efficiency and D is the diameter of the cylinder in inches. * 99. The Relative Efficiency is the ratio between the actual thermal efficiency and the air standard efficiency, and is useful in estimating the real value of the engine as a heat machine, as it shows what loss is sustained beyond that which it is impossible to avoid. The ideal efficiency gives the maximum efficiency obtainable by the engine, while the thermal efficiency is that which is obtained, and the relative efficiency shows the relation which the former bears to the latter. Its value in modern petrol engine work ranges from about 45 to 65 per cent. * 100. Mechanical Efficiency. — The mechanical efficiency is the ratio between the work given out by the engine — the brake horse- MECHANICAL, ETC., EFFICIENCIES 125 power, and the work done upon the piston — the indicated horse- power. It is really the efficiency of the mechanism, and takes account of the losses due to friction of the working parts and the pumping of the charge in and out of the cylinder. The mechanical efficiency may therefore be written : — B.H.P. The mechanical efficiency of the petrol engine has often reached as much as 85 percent., but a good average value is about 80 per cent. Professor Hopkinson's figures for the losses are as follows : — Pumping losses . . . . 3"4 per cent, of I.H.P. Piston and connecting rod friction . 6"! „ „ Other friction . . . . 2'7 ,, „ Total . 12-2 per cent. This gives a mechanical efficiency of (100 — 12"2) = 87'8 per cent. Questions on Chaptee IX. (1) "What is the thermal efficiency of an engine, and what does it express ? (2) If the exhaust gases contain 14 per cent, of COa, 1 per cent, of Oa, 0'5 per cent, of CO, and -15 per cent, of Hj, find the combustion efficiency of the engine, assuming that 15 lbs. of air are burnt per lb. of petrol of calorific value 18,500 B.T.U. per lb. (Answer = 98 per cent.) (3) What is the ideal efficiency of an engine ? An engine has a compression ratio of 5. Find the air standard efficiency. (Answer = 48'1 per cent.) (4) If the actual thermal efficiency of the engine in Example 3 was 24 per cent., what is the relative efficiency 7 (Answer = 49-9.) (5) What weight of petrol per hour of calorific value 18,000 B.T.U. per lb. should an engine of 50 brake horse-power burn at full power, if the mechanical efficiency is 80 per cent, and the thermal efficiency is 20 per cent. ? (Answer = 444 lbs.) (6) What do you understand by the mechanical efficiency of an engine, and why is it so much reduced when running under light loads ? CHAPTEE X THE PRINCIPLES AND CONSTEUCTION OF COIL AND ACCUMULATOR IGNITION It is not too muck to say that the modern petrol engine owes much of its present position to the remarkable efficiency of its ignition apparatus, for without a sure and rapid means of igniting the charge, the high-speed petrol engine would never have been possible. With the high rates of revolution now in common use (up to 2,000 per minute) the firing portion of the stroke is accomplished in approximately one-sixtieth of a second, so that the interval of time for firing the charge must be much less than this, and thus it will be readily apparent why a rapid ignition is so essential for quick-running engines. 101. Early Forms of Ignition. — The earliest source of ignition was that used by Lenoir in 1860 for his gas engine, namely, high-tension electricity, and this was followed by the introduc- tion of the flame, the hot tube, self-ignition and low-tension electricity. These various systems do not in any way represent distinct- cycles in the history of this class of engine, as all, excepting the flame, are in use at the present day, on the type of engine for which they are particularly suited. In its original form in stationary work, high-tension electricity was in a very primitive condition and troubles were so frequent, either from failure of current, or from the breakdown of the insulation of the coils, plugs, etc., that the hot tube soon had an extensive use when successfully introduced, and hence it was quite natural for engineers to adopt this form of ignition on the early automobiles. But that the new conditions under which it was engaged differed considerably from those under which it had given such satisfactory results soon became apparent. Trouble was experienced in keeping the lamp for heating the tube alight on the road ; thefe was danger from the proximity of the naked light to the carburetter and the frequency with which PRINCIPLES AND CONSTEUCTION OP COIL, ETC. 127 pre-ignition occurred. Further, the time of firing could not be varied, neither could the same time of firing be obtained in each cylinder. Hence the hot tube rapidly sunk into disuse when electrical apparatus reached some semblance of efficiency, with the result that electric ignition is alone used on all modern petrol vehicles. 102. Electric Ignition. — With electric ignition the charge is fired by means of a spark which is made to take place within the combustion chamber of the engine. The current from whence the spark is derived may be obtained from three sources — from the dry cell, from the accumulator, or from magneto ; and it may either be at high pressure or low pressure, or as it is generally termed, high tension or low tension. 103. Electromotive Force, or E.M.F., is that which produces or tends to produce a transfer of electricity. When two metals are placed in contact, it may be shown that they are at wtat is termed different potentials. Zinc, tin, iron, copper, silver, gold, lead, and carbon are in order of potential, and if any two of the series are placed in au electrolytic solution with a wire to connect them, a current of electricity will flow from one to the other along the wire. The direction in which the current will flow will be determined by the position of the metals in the list given. For example, supposing tbat the two metals are zinc and copper, copper is at the higher i^otential, and so the current will flow from the copper to the zinc, outside the cell. Further, by Volta's law, if a number of such cells are joined together so as to form a battery, the copper of one to the zinc of the next, then the E.M.F. or potential difference of the first zinc, and the last copper will be equal to the sum of the differences of potential of the separate cells. Thus the E.M.F. of two cells of 1'5 volts (say), joined in series, will be 3'0 volts ; of three such cells, 4"o volts and so on. A Vieu joined in parallel, that is, all the negative plates together and all the positive plates together, the battery then becomes equivalent to one large cell, and while the voltage remains the same, the amperes are douljled or trebled according as there are two or three cells joined up. The terminal having the higher potential is called the positive terminal and the current flows in the direction in which, the "cations" appear to move. 104. Ohm's Law. — If a current is flowing through a conductor and two points on it to be taken, the E.M.F. between these two points bears an invariable ratio to the strength of the current, if the temperature is constant. This ratio is termed the resistance of the conductor. 128 MOTOE CAB ENGINEEBlNG E Hence, the resistance of a conductor = R = ^ where E is E the E.M.F. and C is the strength of current, and C = ^. It is usual to speak of the resistance of a cell as the internal resis- tance, and the resistance of a conductor as the external resistance. Thus, if the plates of a cell are large there will be less internal E resistance. If r is the internal resistance — C = T=i — j — • K + 7- 105. Electrolysis. — "When two plates are immersed in an electrolj'te, and the two terminals are connected, chemical action takes place in the cell, decomposing the liquid and wasting one of the plates. The molecules forming the electrolyte are assumed to split up, and one set travel towards the positive plate and the others to the negative plate. These molecules are termed ions, and in their particular application the former are known as cations and the latter as anions. The positive terminal is also known as the cathode and the negative as the anode. 106. Dry Cells and Accumulators. — Dry cells and accumulators are what are termed " Voltaic cells," and depend for their action upon the chemical substances of which they are formed. A good voltaic cell should — (a) Have a high, constant voltage. (b) Have a small resistance. (c) Not give off fumes. (d) Be perfectly quiescent when circuit is open. (e) Be easy to manage and inexpensive to work. The conventional method of representing a battery is by means of a number of long and short lines, the long lines representing the positive plates and the short ones the negatives. * 107. The Leclanchd Cell. — The commonest form of cell is the Leclanche cell, in which a carbon plate is surrounded by a mixture of manganese dioxide and pulverised carbon, enclosed by a porous pot, which is immersed in a solution of sal- ammoniac in which a zinc rod is placed. The carbon plate is the positive electrode or the cathode. The action of the cell is shown hereunder : — Zn + 2NH4 CI = Zn Gk + 2 NH3 + Ha Ha + 2 MjiOa = Mua O3 + H2O PEINCIPLES AND CONSTRUCTION OF COIL, ETC. 129 The sal-ammoniac at the anode is decomposed, the Gl com- bining the zinc to form zinc chloride, and the NH4 (the cation) travels towards the cathode. The manganese dioxide is used as a depolariser in that it prevents the formation of bubbles of hydrogen gas on the carbon plate which would stop the chemical action. The hydrogen unites with the oxygen in Mn O2 to form water and Mm O3 as shown. 108. Dry Cells. — Dry cells are sometimes used for the purpose of generating current for ignition purposes on account oE their port- ability and cheapness, and because there is no possibility of any acid or other liquid being spilt. But all are liable to deteriorate if kept for any length of time, and they have a much higher internal resistance than the accumulator. They must also be discarded when run down, as it is not practicable to recharge them. For the most part they resemble the Leclanche cell, in having a zinc terminal in contact with the sal-ammoniac and a carbon plate in contact with the manganese dioxide. The sal-ammoniac is not, however, in solution, but in a powder, which, by the addition of water, becomes a paste and keeps sufficiently damp by absorption of water from the air. In the Obach cell the sal-ammoniac is mixed with 85 per cent, of plaster of Paris and 15 per cent, of flour, and the depolariser is about 55 per cent, of manganese dioxide, 44 per cent, of plumbago, and 1 per cent, of gum tragacanth. In the E.C.C. or Burnley cell, zinc chloride in solution is added to the sal-ammoniac, and is also used to moisten the depolarising paste. The E.M.F. of these cells is about 1"5 volts when new, but their resistance depends upon the' surfaces and distances apart of the zinc and carbon — it is usually about 60 ohms. * 109. Polarisation. — The hydrogen which is liberated at the surface of the positive plate of a cell is objectionable, because it forms a non-conducting layer of bubbles, which tend to re-combine with the SO4 or otljer combination present in the cell, producing a counter or back E.M.F. , and tending to drive the current in the opposite direction. When such action does take place, the cell is said to be " polarised," and it is specially in evidence in single fluid cells, the object of the compound cell being to prevent this by inter- cepting it with an oxidising agent. M.C.E. K 130 MOTOR CAR ENGINEERING 110. The Accumulator or Storage Cell. — Tlie earliest storage cell was invented by Sir William Grove, in which the products of electrolysis were stored up and allowed to combine when desired. It had, however, very great bulk on account of the large volume of gases involved, so was of no service for car work. The next cell v/as that known as the Plante cell, which has extensive use at the present day, in a modernised form, for road traction purposes. It consisted of two large curled lead plates which dipped into dilute sulphuric acid. In order to charge the cell a current of electricity was passed through it, which liberated hydrogen at the cathode and oxygen at the anode. This oxygen combined with the lead at the anode and formed peroxide of lead, so charging the cell ; but it was found that such cells did not work for a very prolonged time on account of the thin coaling of peroxide of lead, so an alteration was made in the method of charging. After a first current has been sent through the cell the anode is coated with PtOa; the current is then re- versed to reduce the peroxidised plate to pure lead and to peroxidise the other plate. The current is again reversed, and so on, each reversal of current causing the plate to be left in a more spongy condition, the lead being honeycombed to some depth so as to present a much larger surface to the succeeding oxidisation. This process is termed " forming " the cell, the positive plate being left coated with peroxide of lead and the negative with spongy lead. But the best known storage cell is that in which pasted plates are employed, this being the type most commonly used for ignition purposes. * 111. Pasted Plates. — Instead of using solid lead plates, lead grids are adopted, which are filled at the start with a paste made of, for the positive plate, P63 O4 and sulphuric acid^ and for the negative plate P& and sulphuric acid. These plates (see Fig- 48) are immersed in dilute sulphuric acid in the proportion of about 1 of water to 5 of sulphuric acid, the resulting S.G. being Negative. Positive. Fig. 48. PRINCIPLES AND CONSTRUCTION OP COIL, ETC. 131 about 1'225 when charged. In charging the cell, the litharge on the negative plate is reduced to spongy lead and the positive plate becomes peroxidised. The chemical action which takes place when current is taken from the cell is shown below : — At the cathode :— P6O2 + H2SO4 + H2 = PJSO4 + 2H2O. The SO4 travels towards the anode, or negative plate, and gives PS -|- SO4 = P6 SOd, thus STilphating the pure lead at the negative. It will be observed that the cation, the hydrogen molecules, travel towards the positive plate. In charging after use the following action takes place : — PJ SO4 + 2H = P& + H2 SO4. The sulphate of lead at the negative being changed to spongy lead while at the positive, the sulphate is split up and the lead peroxidised, thus : — PA SO4 + SO4 + 2H2O = P6 0-2 + 2H.2SO1. In charging, the current is sent through the positive terminal to the negative plate. "When fully charged, the positive plate is dark brown in appearance and the spongy negative plate a natural bluish colour, but after use the sulphate of lead changes the colour of the plates, turning the negative to a grey and the positive to a terra- cotta, owing to the addition of the white sulphate particles. This is somewhat of a guide to the experi- enced observer as to the condition of the cell. It is usual to arrange two posi- tives to lie between three nega- tives, or, in other words, to enclose the positives, because a more i^kj. 49._o.a.V. Accumulator. equal action takes place and the positives are not so liable to buckle in discharging (see Fig. 49). It will have been noticed that in charging, two molecules of H2O are exchanged for two molecules of H2SO4, while in dis- charging a reverse action takes place. Thus, in charging the electrolyte becomes more dense, and in discharging less dense — another means of judging the condition of the cell. The cell should never be left discharged or partially discharged, as the sulphate formed is in an extremely finely divided con- K 2 132 MOTOR CAR ENGINEERING ditioia, and if allowed to stand for any length of time will form crystals which are very difficult to decompose again ; and, in addition, they form a hard non-conducting layer on the paste. Sulphate of lead in a cell is, under any conditions, undesirable. The E.M.F. of the accumulator when charging may rise as high as 2"4 volts, or even higher, but soon falls to 2"1 volts, and remains very steady until nearly fully discharged. This high voltage at the end of the charge is due to the presence of strong sulphuric acid, which is formed in the process of charging within the j)ores of the plates. But in course of time this mixes with the dilute acid within the cell and so reduces the voltage to its normal figure. The internal resistance of an accumulator is very small owing to its high conductivity — about ^nn ohm. *112. Capacity of Cells. — It is usual for manufacturers to give the capacity of their cells or accumulators as "so many " ampere- hours, meaning that a current of " so many " amperes can be obtained for 1 hour. For example : a battery is said to be 50 ampere-hours. This means that a current of 10 amperes may be obtained for 5 hours or 25 amperes for 2 hours, and so on. This method is very useful in that it enables one to estimate roughly the length of time an accumulator will last before it requires recharging, as in ignition work current is only taken intermittently. The capacity of accumulators varies with different makes, but it may be roughly taken to be between 0"3 and 0"35 ampere- hours per square inch of positive surface for a 10-hour discharge, observing that the slower the rate of discharge the greater will be the efficiency. For example : a battery giving 50 ampere-hours on a 10-hour discharge will probably only give about 42 ampere- hours on a 3-hour discharge. It should be noted when finding the capacity that the positive plates have two sides. The rate of charging should not exceed, say, 0'05 ampere per square inch of positive surface. Now the action of both accumulators and dry cells depends upon the decomposition of the electrolyte into the cations and anions, the former at the cathode and the latter at the anode. By one of the laws of electrolysis, the weight of an ion liberated per second is proportional to the strength of the current, so that PRINCIPLES AND CONSTRUCTION OF COIL, ETC. 133 if the weight of ion Hberated be known, the strength of the current could be determined. The electro-chemical equivalent of a substance is the weight of that substance Hberated in 1 second by a current of 1 ampere. The cuirent of oneampere is the current -whidi, when passed through a solution of nitrate of silver in water, prepared in aocordanoe with the Board of Trade specification, deposits silver at the rate of 0-001118 gramme per second. The electro-chemical equivalent of silver is therefore O'OOlllS gramme. The electro-chemical equivalent of any other substance may be found by multiplying that of silver by the ratio of the atomic weight of the substance divided by its valency to the atomic weight of silver. For example — the atomic weights of lead and silver are 206'9 and 107 '93 respectively and the valency of lead is 2, so that Electro-chemical equivalent of lead = in'-QS ^ 0-001118 = -001073 gramme per ampere. Hence, in an accumulator, -001073 gramme of lead is transferred in the production of 1 coulomb of electricity per second or 1 ampere. And, further, knowing the weight of spongy lead available for transference, the number of ampere hours may be calculated. Example. — An accumulator having a voltage of 4-2 volts sends a current through a total resistance of 14 ohms. Find the consumption of lead per hour. E From Ohm's Law = ^• 4*2 Number of amperes = -r— = 0-3 Weight of lead used per second = Aanperes X Electro -chemical equivalent = 0-3 X 0-001073 gramme. = -0003219 gramme. Weight of lead consumed per I ^ .0003219 x 60 x 60 = 1-15884 grammes. 113. Methods of Eecharging Accumulators. — Accumulators are recharged in one of the following ways : — (1) From a switch. (2) From a lampholder. (3) From the lighting mains. (4) From a dynamo. (5) From a battery. In all cases the current should be continuous, although by the use of a rectifier or an electric valve, alternating current may be used. The action which takes place during charging has already been 134 MOTOR CAR ENGINEERING described, but there are certain actions which are visible to the eye which should be noted. "When connection is made to the charging source, no apparent action is observed, but as charging proceeds bubbles of gas may be seen coming off from the plates and moving in the liquid. The condition of the cell may be known in some measure by this bubbling or " milking," as towards the end of the charge the electrolyte appears milky, due to the presence of bubbles of gas. When " gassing " freely, the current should be switched off and a voltmeter placed between the terminals. It should read slightly more than 2'4 volts per cell. In charging from a switch, care should be taken that it is in the "off" position. The end of the wire attached to the positive terminal of the battery is connected to the positive terminal of the switch, and the negative terminal wire to the negative of the switch. Charging will then proceed, the amount of current passing through the accumulator depending upon the number of lamps in the circuit, as will be seen in Art. 114. A similar method is adopted when charging from a lampholder, except that it is usual to place a lamp in the lead from the positive terminal. In both cases, it has been stated that the wire from the positive terminal should be attached to + Qc '0 «s?ss Fig. 60.— Chargiug Board, excessive current passing to the battery the positive terminal of the switch. To find out which is the positive terminal, the wires may be placed upon a piece of moistened pole-testing paper, when the part upon which the negative lead rests will become red. Or the two ends of the wire may be dipped into water which is slightly acid. The negative terminal will have bubbles aris- ing from it. It is a good plan to insert a small resistance in the lead to the positive terminal, as in the event of a lamp burning out, it will prevent an PEINCIPLES AND CONSTEUCTION OF COIL, ETC. 135 Fig. 50 shows the arrangement of the charging board when using current from the lighting mains. C and D are the positive and negative terminals, respectively, from the mains, and P and Q are the terminals to which the positive and negative poles of the battery are connected. E is the resistance which regulates the current passing, A is the ammeter and E the voltmeter. S is a switch which should be in the " off " position when the voltage of the accumulator is read. The resistance E may be a series of coils arranged as shown in Fig. 47, or it may be obtained by the use of a number of lamps as shown in the figure. By throwing a greater or lesser number of lamps or coils into the circuit, the current may be increased or decreased as desired. 114. To find the Number of Lamps required in the Resistance to pass a given current. — An ordinary carbon filament lamp when new takes about 3"5 watts per candle power on a 50 to 100 volt circuit and about 3"75 watts per candle power on a 150 to 250 volt circuit. Supposing an accumulator is to be charged with a current of 3 amperes at 200 volts. Watts required = 3 X 200 == 600. Candle power of lamps in the circuit = ^:=^ = 160. Then if 5-32 c.-p. lamps are in the circuit, a current of 3 amperes will pass through the accumulator. If resistance coils are used, the resistance in the circuit will be varied until the ammeter records a current of 3 amperes. Or, generally, the resistance should be such as to cause a drop in voltage in the charging current equal to the difference between the charging and the battery voltage. E - ,: From Ohm's Law C = or E = E E - ,■ C 2 00 - 4-8 b 195-2 3 (55'1 ohms. 136 MOTOR CAR ENGIiNEERING Knowing the number of amperes passing and the capacity of the accumulator, the time required to charge a battery may be determined. In recharging from a dynamo, the dynamo voltage is generally about 10 volts. The arrangement of the board will be somewhat similar to that shown in Fig. 50, except that a variable resistance is usually employed to control the current and allow of a higher rate of charge at the start. Charging by battery is a very simple and economical method. In the Fuller charging battery, six cells are joined in series with the accumulator. If a large current is required the battery may be divided into two parts, the cells in each half being in parallel. To charge the accumulator all that is necessary is to connect the positive terminal of the battery to the positive of the accumulator and the negatives in a similar manner, whereupon charging will proceed. It is advisable to insert a small resistance in the circuit so that the current may be varied. The cells of the Fuller battery each consist of two vessels, one inside the other, the inner vessel being porous. A zinc rod stands in the inner pot and two carbons in the outer jar. Dilute sulphuric acid is poured into the two vessels after a charge of bichromd,te paste has been placed in the outer, and both have been half filled with water. A little mercury is then added to the contents of the inner pot so that the zinc rod stands in the mercury. 115. High and Low -Tension Electricity. — If a continuous conductor be provided between the terminals of an accumulator, the current will flow quietly and freely without producing any visible external effect, and, on interrupting the circuit, the current will cease to flow, because the air between the separated ends of the conductors offers too great a resistance for the passage of electricity from an accumulator. But if the voltage of the current be greatly increased, it will eventually reach a point when the air is no longer capable of withstanding the pressure, and a spark will break across the air gap. The pressure needed to do this will depend upon the condition of the air — the presence of water vapour lowering the voltage required and compression raising it ; bilt in the cylinder of a petrol engine it is certainly not less than 10,000 volts. In a high-tension system, the high pressure necessary is PRINCIPLES AND CONSTEUCTION OF COIL, ETC. 137 obtained by increasing the voltage of the current by the use of an induction coil ; and in the low-tension system by suddenly breaking the circuit within the cylinder. The two principles involved in the production of the spark are, first, the inductive capacity of conductors, and secondly, the inertia of the current. 116. Low-Tension Spark. — It is well known that when the tap at the end of a long water pipe is shut off very quickly, a hammer- blow is immediately heard to take place in the pipe. This effect is produced by the resistance offered by the mass of water to any change in its velocitj', which causes the water remaining in the pipe to endeavour to continue on and momentarily increases the pressure near the outlet. A similar phenomenon is exhibited in arresting the flow of electricity in a conductor when the circuit is suddenly broken. The current which was flowing along the wire previous to separa- tion does not stop immediately, but endeavours to continue its motion, and in so doing increases the pressure at the end of the wire until it is sufficient to jump across the gap and discharge itself by means of a spark. The intensity of the spark will depend upon the quantity of current within the lead before the gap, where the spark takes effect, and it was for this reason that an " intensifier '' was placed in the circuit when the accumulator was used for low-tension ignition. The intensifier consisted simply of a bundle of soft iron wires, surrounded by a coil of the circuit wire, the iron core taking part in increasing the quality of the spark, by virtue of certain magnetic properties which it possesses when encircled by a coil of wire carrying current. An explanation of this will be given later. The accumulator is, however, no longer employed for low- tension ignition, because the large amount of current taken makes it very expensive, so low-tension ignition will be considered in the following chapter on Magnetos. 117. The High-Tension Spark. — The induction coil referred to previously, which is employed in order to obtain a high-tension spark, is shown in the accompanying figure. The type of coil illustrated in Fig. 51 is that known as the "trembler" coil, because the "make" and "break" of th.e battery circuit is effected by the magnetic attraction of the iron core C upon the blade. This form is mostly used for car work as it is more economical 138 MOTOR CAE ENGINEERING of current and produces a succession of sparks at the plug. In its other form, the non-trembler type, a blade is not used, but the circuit is controlled mechanically by the commutator. 118. The Trembler Coil. — The essential parts of a trembler coil are the iron core C, the primary and secondary windings, the To Sparking Plug, 3 v^ itch EiG. ol. — The Induction Ooil. trembler blade B, the bracket A with adjusting screw E and the condenser. The iron core is built up of a number of soft iron rods which are separately varnished in order to prevent the production of eddy currents. The primary winding consists of a number of turns of insulated copper wire wound round the iron core, having one end connected to the contact blade B and the other end to the negative pole of the battery. A switch is placed in the lead returning to the battery. The secondary winding is wound over PEINCIPLES AND CONSTRUCTION OF COIL, ETC. 139 the primary winding and consists of a large number of turns of finer wire, one end of which is taken to the sparking plug and the other end is attached to the primary winding at D. The trembler blade B supports an iron disc which is platinum faced, and in its position of rest makes contact with the adjusting screw E. The condenser is formed by a number of thin sheets of tinfoil, insulated from one another by sheets of paraffined paper, alternate sheets of tinfoil being joined together so as to form the two coatings of a condenser. These coatings are attached to points in the primary circuit which are on opposite sides of the trembler blade as shown. When the blade B is against the adjusting screw E, the current from the battery passes through the bracket A and the blade B to the primary wiring and back through the switch to the negative pole of the battery. As the current passes through the primary coil it magnetises the iron core C, which then attracts the disc B and breaks the circuit, thus stopping the flow of current. The cessation of current causes the iron core to cease from acting as a magnet, so that B then falls back on E remaking the circuit, and the current again passes through the primary wiring. The current through the primary winding is, therefore, continually starting and stopping, and at each " make " and " break " of the circuit a current is induced in the secondary winding of much greater E.M.F., so great, in fact, that a spark leaps across the points of the sparking plugs and fires the charge in the cylinder. * 119. This is the general action, but a more detailed explanation is as follows : — When a wire carries current, lines of magnetic force encircle it and it becomes an electro -magnet, though a weakens. To strengthen the magnetic effect, a soft iron core, which becomes magnetised while the current is passing, is inserted within the primary coil, so that the iron core has a function to perform in addition to that of attracting the blade B. Now it may be experimentally proved that when a magnet is thrust within a coil of wire which has its ends joined, a momentary electric current flows through the coil ; and when it is suddenly withdrawn, a momentary current flows in the opposite direction, the magnitude of the current increasing as the speed of the movement increases. Erom this it may be inferred that the E.M.P. of the current produced in the wire depends upon the rate at which the lines of force surrounding the magnet are cut by the wire — the greater the rate of increase or decrease in the number of lines of force embraced by the circuit, the higher the E.M.E. ; or, as it is sometimes expressed, the greater the number of lines of force threaded through the coil in unit time, the greater the E.M.F. 140 MOTOE CAE ENGINEEEING Thus, tlie starting or cessation of current in the primary winding of a coil is equivalent to moving the magnet within the secondary winding, as when the lines of force extend (and finally collapse on the withdrawal of the current) they pass through the outer coil, generating an induced current in the manner described. But each turn of the secondary winding constitutes a separate coil in which a current is induced, and as each turn is directed the same way round, the E.M.F.'s are also directed the same way round in a long length of a large number of turns. These turns may, in some measure, be compared to a battery of voltaic cells connected in series, the E.M.F. between the end terminals of the battery is the sum of the E.M.F.'s of the separate cells (by Ohm's Law) and the E.M.F. in the secondary winding of the coil is the sum of all the E.M.F.'s in the separate turns of wire. Hence the current induced in the secondary winding will be at an exceedingly high voltage, sufficiently high to break across the gap at the sparking plug and fire the charge within the cylinder. * 120. The Efltect of the Condenser.— However, this high E.M.F. is only rendered possible by the use of a condenser, which plays a most important part in stopping the flow of current through the primary winding of the coil. It has already been observed that when a circuit through which a current is flowing is suddenly broken, the current endeavours to continue on, and in so doing breaks across the gap between the severed connections in the form of a spark. Now this property, which is essential to the production of an efficient spark with low-tension ignition, becomes undesirable with high-tension ignition, because the passage of any current between the contacts of the trembler blade after breaking the circuit, has the effect of retarding the demagnetisation of the core and thus decreasing the induced E.M.F. Further, once a spark does take place, the air between the contacts is electrolysed and a more or less effective circuit re-established. The importance of the stoppage of the flow of current is evidenced by the rate at which the trembler blade operates. Many trembler blades make 10,000 vibrations per minute, that is, there are 10,000 separate and distinct connections made between the battery and the primary winding; consequently, unless the current is interrupted instantaneously, one charge will follow another so quickly as to make the trembler break of non-effect. By attaching a condenser between the two sides of the trembler contacts, the current is diverted into the plates, which absorb the energy of the moving current and bring it slowly to rest. This result is considerably hastened by the PEINCIPLES AND C0N8TKUCTI0N OF COIL, ETC. 141 resistance offered by the portions of current which have ah*eady arrived on the condenser plates to the accumulation of any additional current. But there is still a further benefit derived from the action of the condenser. While the set of tinfoil plates in contact with the battery is being charged with positive electricity, negative electricity is induced in the other set, which when fully charged is sent through the primary winding of the coil and causes another spark to take place at the plug. This continues until the flow of current from the accumulator ceases, so that a succession of sparks, decreasing in effectiveness, will take place at the plug and the combustion be rendered more complete. The action of the condenser may therefore be summarised as follows : — (1) It enables the flow of current through the primary circuit to be interrupted more quickly, thereby increasing the E.M.F. in the secondary. (2) It stops the flow of current from the battery and so economises current. (3) It provides a succession of sparks at the plug, which conduces to a more effective ignition of the charge in the cylinder. From the preceding it will have been observed that there should be a shower of sparks at the plug at " make " and another at " break," but it is extremely doubtful if any spark results from the " make." Lena's Law states that in all cases of electro-magnetic induction the induced currents have such a direction that their action tends to stop the motion that produced them. The effect of this is to cause the primary current to take longer to attain its full strength on completing the circuit than would otherwise be the case and to prolong the existence of the primary current on breaking the circuit. But on account of the assistance derived from the condenser at " break " this counter E.M.F. is somewhat negatived, and the stream of sparks at the plug is entirely due to breaking the circuit. Having surveyed the principles of coil ignition, it is now possible to consider the practical application of these principles. 121. Coil and Accumulator Wiring. — The essential parts of 142 MOTOR CAR ENGINEERING the coil and battery system are illustrated in Fig. 52 and will be seen to consist of : — (1) Battery ; (2) Induction coils ; (3) Wiring with switch ; (4) Commutator or contact breaker ; _ ^ (5) Sparking plugs. When a single coil is used for multicylinder engines, a high- tension distributor is also required. In the upper of the two diagrams shown in Fig. 52, the current is taken from the positive terminal of the battery to the four coils ; and supposing the arm of the low-tension distributor is in contact with the segment marked 1, the current will flow through the primary wiring of coil 1 to the segment, through the distributor arm to the camshaft and the engine framing to the negative pole of the battery. A current will then be induced in the secondary wiring of the coil which will pass across the _ points of the plug to the engine framing. It will be seen that the circuit for the return of the high-tension current is through the return lead of the primary. This is termed the " earth " connection. In the single coil arrangement the battery current is taken through the primary of the coil to a low-tension distributor ring connected to four segments in the insulated ring, so that current only passes when the distributing arm is in contact with a segment. The high-tension current induced in the secondary goes to a high-tension distributor which, when the arm of the L.T. distributor is opposite a segment, also has the corresponding segment in contact with the H.T. distributing arm and thus allows the current to pass to the plug to which the H.T. lead is directed. The return is made as before described. It is very necessary that the segments on the high and low-tension distri- butors should be synchronised. 122. The Commutator or contact breaker or low-tension distri- butor is the device employed to direct the battery current to the coil which has its secondary winding connected to the sparking plug in the particular cylinder which is to be fired. In general there are two forms— the "make and break" and the "wipe" contact, although the former is not used at the present time because of the attention required to the contact studs. These PEINCIPLES AND CONSTRUCTION OF COIL, ETC. 143 studs after a time become pitted and require trueing up, as the production of an efficient spark depends upon the good contact between the platinum-tipped studs. In one type of " make and break " commutator, a spring blade is rigidly attached to a support fitted on, but free to move round, L.T. Distributor Wiring for 4--Cylinder Coil and Accumulator Ignition-^-Coils. 2 Wiring forA- Cylinder Coil and Accumulator Ignition- Single Coil Pig. 52. the half-time shaft, and has at one end a piece of case-hardened steel which engages with a cam keyed on to the end of the cam- shaft. This cam is made with a gradual rise in one side and a radial face on the other, similar to those shown in Fig. 66, so as to give a quick break. Near the middle of the blade two platinum contacts are fixed, one being riveted to the blade and the other to the support, but insulated therefrom, an adjusting screw being 144 MOTOR CAR ENGINEERING provided for the latter contact. The rotation of the cam raises the blade and brings the two studs in contact, permitting current to flow through the junction. But \vhen the rubbing piece on the blade reaches the radial face of the cam the blade spring separates the points, smartly breaking the circuit and producing a spark at the plug. It will be clear that a trembler blade is unnecessary here, as the vibration of the blade causes the studs to come into contact several times very rapidly, giving a spark at each contact. There are several forms of " wipe " commutators. In one form it consists of a ring of insulating material, at intervals around which contact pieces are placed connected to terminals on its exterior. This ring is mounted upon, but insulated from, the half-time shaft, which also carries an arm upon which a lever is pivoted. One end of the lever has a roller which runs upon and is kept in contact with the internal surface of the ring by means of a helical spring fitted at the other end. The spring is secured to a small lever on the half-time shaft. As the camshaft rotates it carries the roller with it, which, when it comes in contact with the strips in the insulated ring completes the battery circuit. In another form an insulator ring is keyed on to the end of the camshaft, but has a metallic segment recessed into its surface which is connected to the half-time shaft. Upon the same shaft a plate is placed, which has free rotary movement relative to the shaft. This plate carries a number of ledges to which insulated brushes are secured. These brushes press upon the surface of the fibre ring, and the primary wiring from the several coils is attached to them. As the insulated ring rotates it brings the segment in contact with the brushes and thus completes the Ijattery circuit. The E.I.C. Contact breaker is shown in Pig. 53, from which it may be seen to be a combination of the " wipe " and " make " and "break" commutator. The rotation of the shaft to which the central cam is keyed causes the inner blade to be pushed outwards, bringing the platinum-tipped studs in contact and allowing the battery current to flow through the circuit while a quick break is effected by the cam. Advance and retard of the time of firing is produced in all commutators by rotating the outer casing a short distance around the shaft. If the casing is moved in the direction of rotation PKINCIPLES AND CONSTEUCTION OF COIL, ETC. l45 the time of firing is delayed, while a similar movement in the opposite direction causes the spark to be advanced, as the contact is made in a relatively earlier position. The commutator is placed upon the half-time shaft, so that the Fig. 53.— E.I.C. Contact Breaker. primary circuit to each cylinder -will be made once in two revolu- tions of the engine, if a four-stroke cycle engine, and it should be noted that in two-cylinder engines with cranks at 180 degrees the angle between the contact pieces must be 90 degrees, while if the cranks are on the same centres, the angle will be 180 degrees. 123. In the Simms H.T. Distributor (Figs. 54 and 55) the lead from the battery positive is attached to L, and th« H.T. lead M.C.B. L 146 MOTOE CAR ENGINEERING from the coil to K. Wires are taken from J, in Pig. 54, to the four cyUnders. These four terminals are connected to the four contacts shown in Fig. 55, while the terminal K is connected to the inner ring. The L.T. terminal L has a brush which presses upon the centre of the contact breaker shown in Pig. 55, and the "make and break " is effected by the roller engaging with the four cams which may be seen in the figure. As the shaft N rotates it carries with it the arm shown in Pig. 55, which has a bridge piece connecting the inner ring with the outer segments. Thus, Fig. 54.-Siimns H.T. Distributor, ^^^en the roller makes contact with the inside cams, it brings the contact points together and completes the primary circuit, while, when a depression is reached by the roller, the circuit is Fig. 55. — Internal Construction of Simms H.T. Distributor. broken. At the same time, the bridge piece completes the secondary circuit by joining up one of the outer segments with the inner ring. PEINCIPLES AND CONSTEUCTION OP COIL, ETC. 147 Fig. 56. — E.I.C. Sparking Plug. 124. Sparking Plugs. — Sparking plugs are constructed in many different ways, but all are on the same principle, namely, that the H.T. lead is connected to a central electrode which is insulated from the body of the plug, the latter being in metallic eon- tact with the cylinder. The current flows through the central electrode, and jumps across the sparking points to the engine framing. The points are usually made of nickel, and the spark gap should be about the thickness of a visiting card — 0'5 mm. The E.I.C. sparking plug is shown in Fig. 56. The insulating medium is of steatite, and is tapered from the inside so that the effect of the explosions is to tend to tighten the joint and prevent leakage. In the Simms spark- ing plug (Fig. 57) the joint is made at the bottom by means of a copper asbestos ring, and the insulating material is a special compound, which is not so liable to crack when subjected to heat. The body is of steel, and so should stand hard wear. The C.A.V. plug, illustrated in Fig. 58, and the substantial form of the electrodes, will be clearly seen, as will also the ready facility with which they may be withdrawn without breaking the joint in the cylinder. In the Bluemel sparking plug (Fig. 59) a special method of jointing has been adopted by the use of a vitreous enamel. This enamel flows between the insulator and the body of the plug, forming a permanent gas- tight joint. 125. Double Pole Plugs. — It has been abundantly proved by experimenters, not- ably by Dr. Watson, that when two sparks occur in a cylinder they effect an increase in L 2 Fig. 5Y. — Simms Plug. 148 MOTOR CAR ENGINEERING power, on account of the better combustion obtained. In some cases two complete sets of wiring have been employed, led to two separate plugs, but such is not desirable because of the increased complication in the wiring. To overcome this difBculty the double pole plug was invented. It consists of two separate electrodes insulated from each other and from the metal body of the plug as 1 Terminal Nut. 2 Lock Nut. 3 Recessed Nut with collar. 4 Spring Washer. 5 Fibre Washer. 6 Porcelain Cover. 7 Asbestos Washer. 8 Upper Hexagon body. 9 Copper and Asbestos Washers. 10 Internal Porcelain. 11 Lower Body or Main Shell. 12 Centafe Nickel Electrode. Pig. 68.— C.A.V. Sparking Plug. shown in Fig. 60. The plug is used in conjunction with an ordinary plug, the two being connected by a wire from the outer electrode of the double pole plug. The current then flows to the double plug, passes in at one terminal, across the points and out at the other terminal to the other plug, causing a spark at both plugs. 126. Order of Firing. — The usual order of firing for a four- cylinder engine, is 1, 3, 4, 2, and for a six-cylinder engine, 1, 4, 2, 6, 3, 5. This will be obvious if the arrangement of cranks is considered, as the order of firing must be such as will give a symmetrical " explosion figure." For example, for PEINCIPLES AND CONSTRUCTION OF COIL, ETC. 149 a four-cylinder engine, let the reader draw eight spaces in two lines and number them from left to right from 1 to 8, com- mencing on the top line. Then draw lines representing the firing from 1 to 7, 7 to 4, 4 to 6, and 6 to 1. For a six- cylinder engine, draw eighteen spaces in three lines and number them in the same way. Then draw lines from 1 to 10, 10 to 8, 8 to 6, 6 to 15, 15 to 17, and 17 to 1. It will be seen that in both cases a symmetrical figure is obtained. 1'27. Lodge Igniter. — One of the most fruitful sources of trouble with the use of high-tension current is the facility with which leaks or short circuits occur. SPECI/VL STEATITE INSULATION ENAMEL rOmiNG GAS TIGHT JDIHT .COPPER-ASBESTOS WASHER STANDARD THREAD .PURE NICKEL PIN Fig. 59.— Bluemel Plug. Pig. 60.~Lodge Double Pole Plug. By the adoption of the Lodge Igniter this trouble is entirely avoided, and it has the additional advantage that the sparks which take place within the cylinder are of greater intensity, with the result that much weaker mixtures and poorer gases can be ignited and more effective combustion can be ob- tained with all mixtures. The principle upon which the igniter is constructed is, that if the rush of current through a conductor be suffi- ciently rapid, no leak or imperfect conductor can exert any influence upon the flow of current. In construction, for multi-cylinder engines, the apparatus consists of a battery, a coil, a high-tension distri- butor, two Leyden jars, a spark gap and an imperfect conductor, the three former differing little in detail from those usually employed for molor-car 150 MOTOR CAR ENGINEERING Pig. 61. work. The expanded arrangement is shown in Fig. 61, in which the two wires from the secondary winding of the coil are led to the inner coatings of two Leyden jar condensers. The outer coating of one of the condensers is connected to the sparking plug and the other to the frame. Between the secondary wires, before they reach the Leyden jar, a spark gap A is placed, and between the wires to the engine an imperfect connection is made by means of a piece of moistened blotting- paper enclosed in a glass tube. The action of the igniter is as follows : — When current is induced in the secondary- winding, the inner lining of the left-hand jar becomes positive and that of the right-hand negative, inducing and binding negative electricity on the outside casing of the left-hand jar and positive on the outside of the right-hand jar, the circuit being completed by the leak. The current continues to accumulate on the lining of the left-hand jar, until a point is reached at which it cannot receive any more, whereupon the current breaks across the spark gap and discharges the inner coatings of the jars at A. At this instant the electricity on the outer coating is released with inconceiv- able rapidity, much more quickly than is possible by any mechanical means, and it rushes through the lead to sparking plug (the leak between the wires being unable to take the current) across the points and charges up the jars in reverse direction. A discharge again occurs only in the opposite direction, and this action continues to take place until the jars are completely dis- charged, so that several sparks result from one original charge from the coil. Thus it is seen that the sparks resulting from a Lodge Igniter will be very intense, differing altogether from the usual sparks obtained from a coil or magneto, just as the character of the flow is difierent. The ordinary current from the coil or magneto flows in one direction only, while that from an igniter flows in either direction alternately. The sparking plug points may be cleaned from the driver's seat by increasing the gap between the points at A, as then a greater current is received by the jars before they dis- charge themselves at A, and, consequently, the spark at the plug is more intense. Sir Oliver Lodge calls the spark which results at A the " A " spark, and that at the sparking plug the "B " spark. A diagram of connections for the Lodge Igniter, type D, is given in Fig. 62, while Fig. 63 shows the construction of an igniter. The reversing switch shown in Fig. 62 is provided to PRINCIPLES AND CONSTRUCTION OP COIL, ETC. 151 reverse the direction of the current. After a time the platinum on one of the contacts of the trembler is transferred to the other by 31 . LJI .TKEMBl.ER RHTREMBLER m ^ — s REVERSING SWITCH 3 H UN/TINCION LtrUlXNSlOH lOCH TENIIM Fig. 62. — Connections for Lodge Igniter— Type D. the sparking which takes place. By reversing the curren this platinum is replaced, and the life of the contacts thereby lengthened. 152 MOTOE CAR ENGINEERING Fig. 63.-^Oonstruction of tlie Lodge Igniter — Type A. Questions on Chaptbe X. (1) What are the relative merits of dry cells and accumulators ? (2) Explain the action of the Leclanche cell. (3) How is it that the electrolyte becomes more dense in re- charging, and why does the voltage fall slightly a short time after charging ? (4) Show a charging board for recharging an accumulator from the lighting mains. If the accumulator has a capacity of 40 ampere hours on discharge, what charging current would you give it and, for how long ? (Answer, 5 amperes for 10 hours.) PEINCIPLES AND CONSTRUCTION OF COIL, ETC. 153 (5) How many 16 c.-p. lamps would you use in charging the accumulator in Question i if the main current is 200 volts ? (Answer 16.) (6) What do you understand by polarisation, E.M.P., electro- chemical equivalent and capacity ? (7) Explain how a current at high pressure is obtained in the secondary winding of a coil from the low-pressure battery current. (8) What is the object of fitting a condenser to a coil ? How does it operate ? (9) Make a diagram of wiring for a two-cylinder engine with cranks on the same centre, using a single coil and showing the com- mutator brushes in the correct positions. (10) Sketch and describe a good form of commutator for a two- cylinder engine with cranks at 180 degrees. (11) Describe the action of the Lodge Igniter. (12) What object is served by fitting a double pole plug in addition to the ordinary plug ? Show how the connections are made. (13) Make a sketch of a good sparking plug and name the materials used. (14) What is the order of firing in a six-cylinder engine? CHAPTER XI MAGNETO IGNITION 128. Magneto Ignition. — At the present time the most popular system of ignition is the high-tension magneto. This is largely due to its freedom from breakdown and because it can be adapted to any engine without the need for extensive alterations. The low-tension magneto was at one time largely used for ignition purposes on motor vehicles ; but on account of the noisy tappet mechanism, the leakage of gas past the working joint in the cylinder walls, and the necessity of constructing the engines to suit the magneto, it declined in public favour as soon as the high- tension magneto attained some semblance of efficiency, and has never seemed to regain the position which it at one time held. The principal source of trouble with any high-tension system is the facility with which a short-circuit occurs. Electricity always takes the path of least resistance, and, consequently, passes through any carbon, oil or damp there may be upon the sparking plug points, in preference to jumping across the electrodes. A similar effect may take place at the collector ring of the magneto, although this is now rarely experienced with modern machines. Further, when the current from the battery is transformed to a higher pressure, the amount of current passing is small, so that any leakage through the insulator is to be guarded against by the use of well-insulated cables. These, in course of time, how- ever, perish or chafe away, with the result that the intensity of the spark within the cylinder diminishes and the ignition of the charge is not so effective or rapid. 129. The Construction of the Magneto. — The essential parts of a magneto are the magnets, the armature, the contact breaker, the distributor, the coil and the base. The field magnets are employed to obtain a magnetic field, in which the armature and coil may rotate, and they consist usually of a number of separate magnets, with cast-iron pole pieces, MAGNETO IGNITION 155 separate magnets being employed in order to obtain more uniform magnetisation, while the pole pieces confine the lines of magnetic force to the space between the magnets. The armature is of H section, secured to two non-magnetic end plates, to which the spindles upon which the armature runs are attached. The body is made of soft iron, as this material readily loses its magnetism and it is usually built up of laminated plates (see Fig. 64) coated with shellac to prevent the generation of eddy currents which spend themselves in heating up the armature. To enable the pole pieces to approach close to the armature, the sides or cheeks are turned to a diameter which will just give sufficient clearance between them and the pole pieces. Fitted on the end of the armature is the contact-breaker, which "makes" or "breaks" the battery circuit when required, and wound round the body of the armature is a coil of insulated wire which forms the low-tension wiring, one end of which is connected to the body and so " earthed" and the other end passed through, but insulated from the armature spindle, either to a collector ring or to a button at the end of spindle, in a low- tension magneto and to the con- tact-breaker in a high-tension magneto. A contact-breaker is not necessary in a low-tension magneto unless used in conjunction with an induction coil. The distributing mechanism rotates on a spindle placed above the armature and completes the firing circuit to each of the sparking plugs or igniters in turn ; although frequently, with low- tension magnetos, the distributor is driven separately by the engine. It is preferable, however, that it should form an integral part of the magneto, as troubles connected with sychron- ism of the firing are thereby avoided. The speed of rotation of the distributor shaft is, for a four-cylinder engine, one half, and for a six-cylinder engine, one-third of the speed of the armature shaft, so that the distributor arm may be in contact with the segments once in two revolutions of the engine, the armature shaft running at the same speed as the engine for a four-cylinder t,S\ SSSSSSS'S^ Fig. 64. 156 MOTOE CAR ENGINEERING engine, and at one-and-a-half times the engine speed for a six- cylinder engine. Finally, the base, made of some non-magnetic material, carries the assembled parts of the magneto and is in metallic contact with the engine, so as to provide a good " earth " connection between the windings of the armature and the engine. In a high-tension magneto there are, in addition, a secondary winding and a condenser, the latter performing the same function as when used in conjunction with an induction coil. The secondary winding may be wound over the primary winding on the arma- ture, as in the Simms and the Bosch ; or it may be incorporated in a separate induction coil placed above the armature, as in the Fuller. A spark gap is provided between the lead from the H.T. collector ring to the distributor and the frame, so that, in the event of the lead to the plug being disconnected or broken, the current may be discharged across the gap to the frame without straining the insulation. The reader should turn to Fig. 90, where the magneto construction is plainly exhibited. * 130. The Generation of Current. — It can be experimentally shown, that when a coil of wire which has its ends joined is rotated at right-angles to the plane of a magnetic field, a momentarily induced current is produced in the coil ; and that the strength of the current is dependent upon the rate of increase or decrease in the number of lines of force passing through the coil. It is upon this effect that the working of the magneto depends. When the armature is rotating in the magnetic field and reaches a horizontal position, the coil being then vertical, the lines of force will pass through the armature core. But when it has turned through 90 degrees, and is in the position shown in Fig. 65, the lines will have left the core and have taken the easier path through the metal cheeks of the armature, while, after a further movement of 90 degrees, they will have returned to the core again. The lines of force do not, however, leave the core at a uniform rate, as the greater number are drawn round with the armature until the cheeks bridge over the space between the magnet poles and the bulk of the lines of force resume the path through the core just before the following edge of the cheek leaves the pole piece. Thus, the number of lines of force passing through the coil is greatest when the armature is in a vertical position, and this is therefore one of " maximum " voltage, and MAGNETO IGNITION 157 there will be two such positions for every revolution of the armature. The horizontal position of the armature is termed the " zero " position ; although this is not strictly correct, owing to the lag which results from the distortion of the lines of magnetic force due to the high speeds of rotation. But it will be noticed that, whereas in the first and third 90 degrees of movement, assuming clockwise rotation, the lines of force pass in at the upper cheek and out at the lower cheek, the direction of the lines of force through the armature is in reality reversed ; as the upper cheek during the first 90 degrees is the lower cheek in the third 90 degrees. Consequently, when the lines of force change their path from the core to the cheeks, they will pass through the coil in a relatively opposite direction and the current produced will therefore be sent through the wiring in a reversed direction. Such a current is said to be "alternating." So far the explanation given applies equally to high and low-tension magnetos, but with regard to the high-tension magnetos, which have the secondary winding over the primary of the armature, a further explanation is necessary. These two windings, form, in effect, an induction coil, the generation and cessation of the current in the primary winding on the armature corre- sponding with the rise and fall of the current round the primary winding of the coil, with this difference, that in the magneto a special mechanical contrivance is fitted to break the primary circuit, called the contact-breaker, while in the coil it is effected by the trembler blade during the period in which the segment of the commutator or low-tension distributor is in contact with the distributing brushes. Thus, any remarks regarding the action of the induction coil on page 139 can be applied equally well to the high-tension magneto, and it will be unnecessary to recapitulate them here. 131. Low-tension Magneto Ignition. — The "make and break" mechanism of low-tension systems of ignition vary somewhat in detail, but they generally follow the arrangement shown in Fig. 66. In this arrangement the cam B, which operates the tappet rod G, is driven by a half-time shaft A. At the lower Fia. 65. 158 MOTOR CAR ENGINEERING end of G is a spring F which holds it against the cam and causes it to drop quickly when the firing position is reached ; while at the upper end there is a slot which engages with the striking lever pivoted at H. At the other end of this pivot pin, and within the cylinder, is an ignition lever. K is a rod which is insulated from the cylinder but connected to the wiring, and is called an igniter pin. As the cam B rotates it raises the tappet rod G and allows the spring J to bring the ignition lever in contact with the rod K, so that current may flow from K to H, and so to " earth." When the roller reaches the radial face of the cam, however, the ^EEh Fig. 66. — Eisemann Lov-Tension Magneto Ignition. spring P asserts itself and causes the rod G to hit the striking lever and separate the points, thus firing the charge. Provision is made for the advance and retard of the time of firing by interposing a lifter C between the rod G and the cam B, which is actuated by the lever D. By moving C in one direction or the other the necessary effect is obtained. N is the position for the retard and V that for the advance of spark. * 132. Magnetic Igniters. — To avoid the use of tappet rods and a working part in the cylinder walls, which are generally asso- ciated with the ordinary low-tension system and so considerably simplifying the actuating mechanism, many attempts have been made to evolve a satisfactory magnetic igniter. The general principle upon which these igniters work is that the " make-and-break " is effected by the magnetic attraction exerted by an electro -magnet formed by passing a current MAGNETO IGNITION 159 Pig. ST.— Bosch Magnetic Igniter. through a coil of wire surrounding a piece of soft iron. In some eases, the cores were spring-actuated, but the heat from the engine cylinder invariably so weakened the spring after a longer or shorter period of use, that it was unable to perform its work. Some were not so ambitious and permitted a working part in the cylinder walls, but endea- voured to substitute a magnetic device for the tappet mechanism, having a plunger to work through a gland into the cylinder. This, again, was unsuc- cessful, on account of the delicacy of adjustment required at the gland, and so it had no extensive use. In the Bosch igniter a much better system of operation is employed. * 133. Bosch Magnetic Igniter. — This is in three parts (see Pig. 67) — the plug body, which is in metallic contact with the cylinder ; the coil body, which is insulated from the plug body ; and an interrupter lever. The interrupter lever rests on a steel knife-edge and is kept in contact with the contact block 21 by the spring 3, which presses against the back of the interrupter just inside the knife edge. The spring, owing to its disposition, has a very slight movement, and is also weU protected from any hot gases, being placed right into the coil body. The coil body has its lower end screwed to the pole piece of the plug, thus forming a complete electro- magnetic system, the armature of which is the upper part of the interrupter lever. The contact pieces 20 and 21 are mounted upon the interrupter lever and the plug body A, the latter reaching into the interior of the combustion chamber. The two contacts are pressed against each other by means of the spring 3, and are separated only at the time of sparking, at which moment a current flows through the coil. Por this purpose one end of the winding is in connection with the current carrying ring 6 and through this also with the insulated terminal 9, whereas the other end is electrically connected by Fig. 68. 160 MOTOE CAE ENGINEEEING means of tlie screw 26 to the body of the coil. The latter, as well as the pole piece and the interrupter, are insulated from the plug body by means of the steatite cone 22 and the mica washers 18. The two contact pieces on this type have a special form, inasmuch as the fixed contact takes the form of V into which the moving contact drops (see Pig. 68). The interrupter lever also has a slight side play. Should, for instance, the left side of the contact (through soot, deposit from oil, etc.) prevent a good connection, the head of the lever when dropping down would slightly slide to the right-hand side of the fixed contact and thus make a perfect conductor. The magneto for generating the current for this igniter is shown in Pig. 69. Between the pole shoes of the double magnet 1 rotates a shuttle arma- ture 2 carrying two current-producing windings, one being a continuation 23 3 4 '6 ^5 Fig. 69. — Magneto for Magnetic Igniter. of the other; these will be described later as the main and auxiliary windings. The beginning of the main winding is connected to the armature core, and the end connection of both windings leads to the contact piece 3 which passes through the hollow portion of the armature spindle, being insulated from the latter. This contact piece 3 carries on the outside the contact breaker disc 6, to which it is electrically connected. The auxiliary winding is connected with the piece 23, into the nose of which screws the fastening screw 4, which fixes the contact-breaker, and at the same time conducts the current to the contact piece 5. The contact pieces 3 and 5 MAGNETO IGNITION 161 as well as the screw 4 are insulated from the armature and also from the contact breaker disc 6. The contact piece 5 carries a platinum screw, which is pressed against the short platinum screw by means of a spring that is fixed to the bell ciank lever. The latter is electrically connected to the contact breaker disc ard thus short-circuits the auxiliary winding so long as the two platinum points are in contact. This circuit is, however, interrupted as soon the bell crank lever is depressed by the steel segments of the timing lever. The connection of the main winding to the distributor is made in the following manner : A brass cap 12 is fitted tightly over the contact breaker, but insulated from same. A carbon brush, mounted on a spring, is fixed into this brass end cap and presses against the electrically con nected fasten- ing screw 4, thus completing the circuit through the cap 13, spring 14 to the centre carbon 16 on the distributor. In the distributor disc 17 carbon brushes are placed round the centre carbon 16. Each of these brushes are in connection with terminals 18 on the outside of the distributor disc, which in turn transmit the current through single-wire cables to the corresponding magnetic plugs. To accomplish this, gear wheels are provided, the larger one carrying a brass segment 19 which distributes the current from the centre contact brush to the various terminals. The electric current is generated in the two windings by revolving the armature in the magnetic field, and attains a maximum voltage twice during each revolution, the two maximums being 180 degrees apart, and thus giving two sparks in one complete revolution of the armature. The auxiliary winding is short-circuited by the contact breaker just previous to the current attaining its maximum. At the moment of sparking, this short circuit is interrupted, and the main current, reinfoiced by the extra current, is con- ducted over the distributor to one of the magnetic plugs. Fig. 70. — Diagram of Connections for Bosch Magnetic Ignition. M.C.E. il 162 MOTOE CAE ENGINEEEING Eig. 70 shows the system of connections for a four-cylinder engine, in which the magnetic plug of No. 1 cylinder is in operation. At the extreme right is shown the contact breaker which short-circuits the auxiliary winding. At the moment of short-circuiting, a sufficient current in the main winding is not produced, but when the ciricuit is broken by the separation of the platinum contacts of the contact breaker, the voltage in the main winding is raised and the current flows through the coil of the _^EC-riO«Al. FlLl^VATlOIM Fig. 71.— Fuller H.T. Magneto. magnetic plug which is then in contact with the segment of the distributor. Owing to the sudden flow of current through the coil of the magnetic plug, the upper portion of the interrupter is vigorously attracted, effecting a quick break of the contacts. This in turn produces a powerful and very hot spark by means of the sudden interruption of the current in the same fashion as the low- tension mechanical break-ajjd-make ignition. 134. The Fuller High-tension Magneto is illustrated in Fig. 71. The armature is wound with a low-tension winding only. One end of his wire is connected to earth or the iron core of the armature (see Fig. 72), and the other end is connected to the insulated stud 1. Upon this stud MAGNETO IGNITION 163 presses a carbon brush. 3 attached to a brass spring 2. This bpring serves to conduct the primary current which is generated in the armature direct to the contact breaker and transformer. The spring is connected in parallel with the insulated part of the contact breaker 4 which carries the platinum screw 0, and is also connected to the primary winding of the trans- former 6. The induction coil is situated within the arch of the magnets 18 above the armature 19, and is held in position by the two end plates. It is placed inside an ebonite tube provided with brass caps. From one end of the tube two brass plungers 14 and 16 project. The plunger 16 makes electrical contact with an insulated brass stud 25 which runs through the Brt»«»S|«.5 ca.^0« a^ta —. T^IACHAM or INTERNAL WlRlttC — . Fig. 72. -Puller H.T. Magneto. contact breaker, and is in electrical connection with the armature winding 26. This plunger is connected to the primary winding of the transformer. The other plunger 14 conveys the current which flows through the primary wiring of the insulation coil back to the earth or frame, and thus completes the primary circtiit through the armature. The high-tension distributor is fixed at the driving end of the magneto. The high-tension spark is taken from the transformer by a spring plunger 12 to the distributor wheel spindle, and thence to the rotating arm and carbon brush 13. Good electrical contact between the spindle and rotating arm is ensured by means of a spring-loaded ball, which runs in a groove on the spindle. The two extreme plugs on top of the distributor are connected to the lower metal segments inside the distributor. The contact breaker arm 7 is actuated by a spring which presses the platinum point 22 of arm against the platinum-tipped screw 5, which M 2 164 MOTOR CAR ENGINEERING is carried by the insulated bracket 4. The cam 9 has two ridges stamped in it, and these quickly separate the platinum points 22. The contact arm is fitled with a fibre roller to minimise friction. Normally, the current generated in the armature passes along this brass arm 2 to the platinum- tipped contact screw 5. It then passes across the platinum points 22 to earth (the frame of the magneto). This completes the circuit of the armature current. Twice during each revolution of the armature, and at the moment when the armature current is at its maximum, the platinum points are separated by means of the raised grooves 8 in the disc cam 9. The current then rushes along the insulated stud 25, across the spring contact 16, through the primary winding 6 of the transformer, and returns to earth through Fm. 73.— Bosch H.T. Magneto. the spring contact 14. This sudden flow of current in the primary of the transformer produces an induced high-tension current in the secondary winding 10, and this is conveyed to the distributor arm by means of the spring contact stud 12. This current is then distributed to the means of four cylinders by the carbon brush 13, and the metal segments in the distributor 17. 135. The Bosch H.T. Magneto (D.TJ.4. Type). — A section through this magneto is shown in Fig. 73. The armature carries two windings — the primary and the secondary — the earthed end of the secondary being attached to the live end of the primary, so that the two wirings form a continuous length of wire. The earthed end of the primary winding is connected to the armature core and the live end is connected to brass plate 1. Through the centre of this disc passes fastening screw 2, which serves^firstly, to hold the contact breaker in place, and, secondly, to conduct the primary current to the platinum screw block 3 MAGNETO IGNITION 165 of tlie contact breaker. Screw 2 and coutaot piece 3 are insulated from the contact breaker disc 4, which is in metallic connection with the armature core. Platinum screw 5 is located in contact piece 3. Pressed against this platinum screw, by means of spring 7, is the bell crank lever 8, with platinum screw 6, which is connected to the armature core, and therefore with the beginning of the primary winding. The primary winding is thus short-circuited as long as the bell crank lever 8 is in contact with platinum screw 5. The circuit is interrupted when the lever is rocked, and the condenser 9 is connected in parallel with the gap formed when the contacts break. The end of the secondary winding leads to the slip ring 10, on which slides a carbon brush 11, held by the carbon holder 12, and thus insulated from the magneto frame. From the brush 11 the secondary current is conducted to terminal 13, from whence it passes to the spring current conducting- rod 14, and to the centre distributor contact 18. From there its path is to the carbon brush 16, the latter rotating with the distributor gear. The metal segments 19 are em- bedded in the distributor disc 17, and as the carbon brush 16 rotates, it makes contact with the respec- tive segments of the distributor. Attached to the metal segments of the distributor are the connection terminals 20 to which are fixed the conducting cables to the sparking plugs. From the end of the secondary winding, the high-tension curreut is distributed to the respective cylinders, according to their firing order. The current produces the spark which causes the explosion ; it then returns through the motor frame and the armature core to the grounded end of the secondary winding. The contact breaker is fitted into the- rear end of the armature shaft, which is bored out and provided with a keyway. The contact breaker is held in position by screw 2 ; by removing same the former can be easily taken out. In replacing same care should be taken that the key fits into the keyway, and that the screw 2 is well tightened. The short-circuiting and interrupting of the primary current is effected twice during each revolution of the armature by means of the contact breaker lever 8 on one hand, and the steel segments 21, which are arranged in the timing lever 116, on the other. As long as the contact breaker lever 8 is pressing against the contact screw 5, the primary current is short-circuited. The rocking of the lever by means of one of the steel segments 21 effects the break of the primaiy circuit, and ignition occurs at this instant. The 166 MOTOE CAE ENGINEEEING distance between the platinum points when the lever is depressed by the steel segments must not exceed 0-4 mm. This distance may be adjusted by means of the screw 5. A safety sparking gap is arranged on the dust cover 22. The variation in the time of ignition is effected by causing the inteiTuption Fig. 1o. — Wiring for Bosch H.T. Magneto. ol the primary circuit to take place earlier or later. Por this purpose the timing lever 116 is arranged to be either advanced or retarded, which pro- duces either an early or a late inter- ruption, and consequently an early or a late ignition. A diagram of wiring for a four- cylinder engine is shown in Fig. 75. 136. The Mea H.T. Magneto. — As stated in Article 130, the current in the primary winding rises and falls in strength as the armature rotates, there being a position at which the current is a maximum. At any other position of the armature the current will be at a reduced pressure, and if the circuit is there broken the spark produced in the cylinder will be less effective than at the maximum position. It is not difficult to see that, if the position of the armature at "break" is far removed from the maximum position, the resultant current pressure in the Pig. 76. MAGNETO IGNITION 167 secondary may be insufficient to give a spark, or, at all events, to produce a rapid ignition of the charge. The claim which is made for this magneto is that the range of effective ignition is greatly increased by the use of a bell-shaped magnet (see Fig. 76). These bell magnets are rotated in order to obtain the advance and the retard of the spark, the contact breaker remaining always in the same position relative to the armature and conse- quently breaking the circuit when the current in the primary winding is at its maximum. 137. The armature 1 rotates within th& bell-shaped magnet 100 in ball races 17 and 18, and is wound with a primary and a secondary winding. 18 104 109^27 Pig. 77.— Mea H.T. Magneto— Types A. and P. The end of- the high-tension wiring of the armature is insulated and con- nected with the slip ring 4 (see Pig. 77). This ring is shown darkened in the illustration, and the centre is covered with a metal ring. The current is taken from this slip ring by a carbon 77, which is fitted in a holder 76 and screwed in the cover 91. Carbon 77 has a spring at one end, and presses on the slip ring. The other carbon 78, which is screwed in the cover, serves the purpose of giving the current from the armature to the casing a better passage. The thick wiring is electrically connected to the thin by the screw 24, this also taking the current to the contact breaker. The con- tact breaker consists of a disc 27, which carries the short platinum 166 MOTOR CAR ENGINEERING screw 33. The other platinum screw 34 is adjustable and fitted to a spring 30 fixed to the insulated contact 28 on disc 27. The contact breaker is actuated by the stud ring 40 (this having two notches), which is screwed on the side of armature. Through the turning of the contact breaker the notches 61 the stud ring 40 press against the roller 31 of the disc 27, and thus lift the spring with the platinum screw. In order that the contact may be easily examined, the case has a piece cut out on top. The cover for same, 101, is fitted on the inside with a spring and carbon 102. This carbon presses against the contact breaker screw 24, Fig. 78.— Mea H.T. Magneto— Types A. and F. End View. is insulated, and is connected with screw 103, Ihis latter being necessary when it is required to fit a cut-out switch. A condenser 12 is fitted parallel to the contact breaker and in the right-hand side of the armature cap. The variation of the timing is effected by the movement of the bell-shaped magnet in the casing 104 by the contact-breaker case, which is kept in its place on the outside cover by the screw 105. On the bearing cover 61, above the front ball race, is fitted the distributor plate 70, which has 4 metal segments, these being connected with the holes in which the terminals 108 are inserted. The distributor plate is so made that at the bottom end it fits MAGNETO IGNITION 169 firmly on a ledge, whilst at the top end it is fixed with an adjust ■ able screw 107, which presses it on the bearing cover. On the > 60 W d s GO C5 M inside of this distributor revolves the distributor finger 66 with carbon 68. The current is led to this carbon 68 by carbon 76 by a detachable bridge 84, and is then distributed to the various 170 MOTOE CAR ENGINBEEING EiG. 80. — Contact Breaker. segments. The distributor finger is rotated by the gear wheels 7 and 72. The top gear wheel 72 has marked on one side of it numbers or lines which correspond to the cylinder, and these numbers can be seen through the window 62. The figures or lines shown at the window give the posi- tion of the distributor finger and which cylinder is just about to receive the spark. The spark gap is constructed by a small wheel on the distri- butor axle, and above it in the case is fitted the pin 110 across to Avhich the spark would jump. 138. Eisemann H.T. Magneto, with automatic advance. — The construction of this magneto is shown in Figs. 79 — 81. There is a primary and secondary wiring wound upon the armature core, one end of the former being attached to the armature body while the other end is taken to the centre of the contact breaker d, being insulated from the armature by the bush e. The live end of the secondary winding is also insulated from the armature and is connected to the live ring jj, which is locked in position by the ring washers n and o. A carbon pencil m is pressed against this " live " ring and carries the H.T. current along the rod /t and tube j to the distributor finger c, upon which a carbon brush b is mounted. The H.T. current to the plugs is taken by the plunger g. A spark gap k is provided between the H.T. lead j and the frame to discharge the current induced in the secondary in the event of a lead being disconnected from the plug. Normally the current flows through the primary winding to d, across the contact studs on the contact breaker (Fig. 80) to the frame. But when the rubber strikes either of the two screw leads shown in the figure, the contact studs are separated, breaking the circuit. MAGNETO IGNITION 171 So far, it will be seen that the magneto differs little except in the details of construction from the ordinary type of magneto ; but there are two points of interest in this machine — the pole- pieces and the automatic advance. The pole-pieces are not made parallel through their length, but are tapered as shown in Fig. 81. By this construction it will be observed that in all positions the armature will be partially overhung by the pole-pieces at diagonally opposite corners— the direct result of which is that the armature will act as a "keeper," even when vertical, and thus assist the magnets in the retention of their magnetism. But the electrical effect is, however, of greater importance, for the lines of force which leave the core when the armature reaches its vertical position are immediately re-established there, though in an opposite direction — thus permitting a current of greater maximum strength to be induced than would otherwise be the case. 139. Automatic Advance and Retard, — The disadvantages attaching to the use of fixed ignition are referred to in Art. 153. With the object of simplifying the method of control, and at the same time gaining the benefit to be derived by the variation in the position of the timing lever, the Eisemann automatic advance and retard was devised, as shown in Fig. 79. Instead of driving the armature shaft from the engine direct, a rapid thread is turned on the spindle driven by the engine, which moves in a 172 MOTOR CAR ENGINEERING corresponding nut sliding in a two-faced guide attached to the armature. Two balls are pivoted at one end on the end of the armature, and at the other are connected through links to the nut mentioned previously. As the armature rotates, the balls fly outwards gradually, the greater the speed the greater their displacement, and in so doing draw the nut towards the armature. As the nut moves along the thread, it gives the armature a forward movement, thereby advancing the spark. It will be seen that the effect of this action serves another desirable object, namely, it enables the contact breaker to be fixed relative to the armature, so as to always break the primary circuit when the current is at its maximum voltage. 140. Dual Ignition. — The intensity of the spark produced at the plug is proportional to the speed of rotation of the armature ; consequently, at low speeds of rotation, the spark obtained in the cylinder may be insufficient to fire the charge effectively ; and as it is necessary to retard the spark when starting up, in order to prevent a. back-fire, the spark is still further reduced in intensity just at the time when a hot spark is desired. The result of this is that if the magneto is timed for easy starting, the highest speeds are not possible, while if high speeds are aimed at, the amount of retard is insufficient to prevent some little risk and difficulty in starting up the engine. The first method employed to obviate this was to use two separate sets of plugs, one being connected to a magneto and the other to a coil. But from the fact that one set of plugs were not in use under normal running conditions, these often became sooted up and when next required would not fire ihe charge. There was also an increased complication in the wiring which, to say the least, was undesirable. For these reasons dual ignition came into existence and is now largely fitted on up-to-date cars, while on small cars a "duplex" system is sometimes employed. It will be seen later that the dual system provides not only for easy starting and switch-starting but also a stand-by system of ignition for use in the eveni of the failure of the magneto. In the dual system it is generally the custom to use two contact breakers, because of the "lag" of the coil and accumulator system. With the magneto, the current is already MAGNETO IGNITION 173 flowing through the primary wiring when the break occurs, but with the coil and accumulator the current is only started in the primary at the position of " make " ; con- sequently, an additional advance is required to be given to the contact breaker when on coil and accumulator. The manner in which this is effected will be seen as the systems are described. 141. The Puller Dual System.— This is shown in the Fig. 82, and will be seen to differ from the ordinary magneto system in Ei«iti. FiG. 82. — Diagram of Wiring for Dual System. Fuller H.T. Magneto. the addition of a stationary distributor, a dashboard switch and an accumulator. The magneto coil is used for transforming the battery current to a higher voltage. When the magneto is used for firing the charge, the current flows through the centre of the armature spindle to the brass piece at the right, along the upper of the three wires shown in Fig. 96 to the switch. The two smallest contacts in the switch are bridged over and connected to the largest segmental contact. The current, therefore, passes from across the two small contacts and out through the lowest horizontal wire to the left- hand finger of the stationary distributor, and from thence to the contact breaker to earth. When the points of the contact breaker are separsited, he current at the switch passes over the bridge to th'< larger segment. 174 MOTOE CAE ENGINEEEING along the middle of the horizontal wires to the middle finger, and then through the primary to " earth." When running on the accumulator, the switch has the largest segment connected to the bottom left-hand contact. The current from the accumu- lator positive then passes across the bridge to the largest segment, through the middle horizontal wire and the middle finger, through the coil to "earth" — then through the contact breaker and the left-hand finger of distributor and the lower of the three wires to the switch and from thence to the negative pole of the battery. Should there be gas in the cylinders of the engine, it may be fired by quickly rotating a handle on the front of the switch on the dashboard, when the switch is in the " on " position for the accumulator. 142. Bosch Dual System. — In this system a coil is used on the dashboard and may be either horizontal or vertical. The ver- tical type is shown in Fig 83. The coil body, consisting of a start- ing device with trembler, condenser, coil and switch, is constructed as seen in the figure. The movable gun -metal cover 2, with a wing-shaped switch handle 1 , is attached to the coil body 3, which is made of insulating material by means of a recess and a collar. The starting press button 4 projects through the centre of this cover, which is connected to the coil body by a catch bolt, so that both can be rotated together by means of the wing-shaped switch handle, and be brought into one of the positions marked "O" (" ofl " position) " A " (battery ignition) or " M " (magneto ignition). The base of the coil case is formed by the connection plate 6, and the contacts of the rotating switch plate 7 press against it. The connecting up of the various circuits takes place, therefore, between these two plates whenever the switch handle 1 is moved to one of the indicating marks. The cable connections are protected by an insulating cover, fastened on the horizontal coil by a milled-edged nut, which is also used to carry the cable connecting the coU with the frame ; this protecting cover is slotted so that the other five cables can be passed through (see Pig. 86). On the vertical coil, however, the frame connection is inside the cover, the latter being screwed on the connection plate. Bosch Dual Coil. MAGNETO IGNITION 175 The coil body consists of the cylindrical iron core 10, which carries the winding. This winding is made up in two parts, the primary and the secondary, the former consisting of a few turns of heavy wire, and the latter of many turns of fine wire. The beginning and the end of both windings are each connected to a metal segment on the switch plate 7 and soldered. The end of the primary winding is, however, first taken to the starting arrangement and is then led to the metal segment. The primary circuit is arranged outside the coil, so that the beginning of the primary winding is led to the battery, and the end through the battery contact breaker on the magneto to the frame. The secondary circuit outside the coil leads from the end of the secondary winding through the distributor Pig. 84. — Bosch Dual Magneto. and the sparking plugs to the frame, and from there back to the beginning of the secondary winding. The starting device is fitted on the plate 11, this plate being screwed on to the iron core 10, and carrying in addition the condenser 12. The starting arrangement consists mainly of the press button 4, the contact spring 13, trembler 14, and the auxiliary contact breaker 15 and 16. By depressing the button 4 fully, the platinum points are brought into contact and the trembler begins to operate. If the contacts on the contact breaker are separated, then the sparks caused by the trembler will start the motor, provided, of course, that the cylinders contain a suitable charge of gas. Should the battery contact breaker be closed, the engine can still be started from the driver's seat, since the act of depressing the press button 4 opens the circuit which would be closed in the ordinary way by the auxiliary contact breaker 15 and 16, and consequently a spark is produced. The separation of the contacts is obtained . by depressing the button. 176 MOTOE CAR ENGINEERING 183 which causes the fiat spring 15 of the contact breaker to separate from the upper contact of the bridge 16. _ As the flat spring 15, however, touches the lower contact of the bridge 16, the circuit is again closed and consequently ouly one spark is obtained, and not a series of sparks, when the button is ])ressed and released again. If it is impossible to start the engine with these single sparks, then the depressing and releasing can be repeated several times. It is, of course, always to be understood that the cylinders are filled with a s litable gas mixture for starting. If this is not the case, then the engine can only be started in the usual way by means of the starting handle. This method of starting, however, is greatly facilitated witli the later pattei'n of the Bosch coil, since the staiting press button 4 can be put per- manently into the depressed position, so that the trembler is continually operated by merely turning the button to an angle of 90 degrees. With the button in this position, the circuit is closed by the auxiliary contact breaker, and consequently a trembler ignition can be obtained only during the periods when the contents on the accumulator con- tact breaker on the magneto are opened, which is the case when the armature is being rotated. For this reason it is impossible to get a back-fire. The magneto for use with this coil differs somewhat from the ordinary "D.U.4." type (see Figs. 84 and 85). Pig. 85. — Bosch Dual Magneto. In place of the connecting bridge and of the carbon holder on the front end plate, a new carbon holder 127b is used, having a terminal nut and at spring 128, the latter forming a connection to the safety sparking gap. The special triangular clamp 129 is provided with a carbon holder 130b and with a brass connecting piece 131 for short circuiting the magneto. The new ebonite cover 132a has a tapered hole through which passes the carbon holder 130b. The new rotating distributor piece 133b shows on the front a metal plate, which is in connection with the distributor carbon 15 and the carbon holder 130b. The new end plate cover 13'la is designed to carry the additional timing lever 136d, in the interior of which the battery contact breaker is arranged. MAGNETO IGNITION 177 The latter consists of a bell crank lever 136c, which is held in such a position that the short platinum screw 138 presses against the long platinum screw 139a. The platinum screw 139d is fitted to the battery terminal 140d, which is insulated from the timing lever 135d, and is provided with a milled nut for fixing a cable. The battery contact breaker is operated by the revolving steel cam, which is placed behind the new magneto contact breaker 141, so that the battery contact breaker, and the magneto contact breaker, open simultaneously. The action, of the magneto contact breaker is the same with the dual ignition system as on a normal machine. The fibre deflection rollers 19 are, however, fitted in a roller bearer 142d, Fig. 86.— Bosch Dual Wiring. which is detachable from the timing lever. The new magneto breaker 141 is fixed on the rear end of the armature by means contact breaker screw 143. contact of the The wiring diagram for this system is shown in Fig. 100. Under ordinary conditions of running 3 and 4 on the coil are bridged over, and the H.T. current generated in the secondary winding of the armature flows in at 3 on the coil, out at 4 to the H.T. distributor at 4 and from thence to the plugs. When using the accumulator, the current from the battery positive goes to " earth," and from " earth " through the magneto to the coil contact breaker — out at 1 on magneto to 1 on the coil, through the primary winding of the coil, out at 5, to the M.C.E. N 178 MOTOE CAE ENGINEEEING negative terminal of the battery. The induced current in the secondary winding of the coil is then taken from 4 to the 4 on the H.T. distributor. The L.T. lead of the magneto 2 is short-circuited when using the accumulator. 143. Simms Dual System (Type A). — This system is illus- trated in Pigs. 87 to 89. The coil consists of a'laminated iron core 1 (see Fig. 87), on which are wouad the primary and secondaiy windings, and to which is fixed the casing 2, containing the condenser 3. On casing 2 is fixed the trembler starting arrangement, a vulcanite plate 4 carrying the connections 5, a connection plate 6 fixed to core 1, an insulating tube 1, a cover 8 to protect connections 5, and a cover 9. To cover 9 is fixed a handle for partially rotating the switch. In casing 2 is a screw, which engages with the Fig. 81. — Simms Dual Coil — Type A. cover 9 ; thus when the latter is partially rotated, the whole internal system o f the coil moves with it, and can be brought into any of the positions M (magneto position), O ("off" position, when both systems are in- operative), or A (accumulator position). The contacts 12, fixed in the plate 4, press against connection plato 6, thus when the handle 10 is brought into position opposite the letters M, 0, A, the various circuits are connected for the position indicated. The iron core 1 carries two windings, the primary and the secondary. One end of the primary winding is connected to the connection plate 6, then to the battery through the connections 5 on vulcanite plate 4. The other end goes to the contact breaker (battery) and then to the frame. The secondary circuit leads from one end of the secondary winding through the distributor to the sparking plugs, then to the frame, and then to the other end of the secondary winding. The trembler arrangement is fixed to casing 2. The trembler blade 13 is pivoted on piece 14, and is held in position by spring 15. Trembler spring 16 is connected to the condenser connection 17, and to which is fixed a platinum point 18. In starting, the switch is turned to the A position >- MAGNETO IGNITION 179 the plunger 19 is depressed until the platinum point 20 makes connection with platinum point 18. Thus the primary circuit is completed through casing 2, iron core 1, connection plate 6, and stud 21 to frame. The trembler 13 vibrates, owing to the attraction of the iron core 1 and pull of spring 16. A high-tension current is induced in the secondary winding, a series of sparks taking place at the plug of the cylinder favourable for firing. The trembler action ceases when plunger 19 is released. The Simms Dual Magneto (Type A) is shown in Eig. 88, and diSers from their ordinary type in that on the contact end plate is fitted an additional timing lever 23 carrying a bell crank lever, which moves about a pivot, and into it is screwed a platinum-pointed screw which makes contact with a platinum-pointed screw. Behind the magneto contact breaker 28, and Fig. 88. — Simms Dual Magneto — Type A. fixed to it by screws is a cam which, in revolving, produces the ' ' make- and-break " of the battery contact breaker. Hxfed to, and insulated from,ithe timing lever 23 is a bracket, into which the battery connection is screwed. A locking clamp is provided with a carbon brush-holder, through which the high-tension cui-rent is conducted to the distributor by means of a stud and brush. On the collecting brush-holder is a terminal for high-tension connection to coil. The diagram of connections for dual ignition is shown in Fig. 89. 144. Hall Dual System. — The construction of the magneto used in conjunction with this system is shown in Fig. 90. In this case the armature has a double winding — the primary and secondary — connected as shown, one end of the primary N 2 180 MOTOE CAR ENGINEERING MAGNETO IGNITION 181 182 MOTOR CAR ENGINEERING to the armature body and from thence through the earth brush to frame, and the other end to the magneto contact breaker. The condenser connections are clearly seen in the figure. A carbon brush presses against a disc at the end of the armature, and makes contact with the brass spring attached to the insulated rod -extending to the left from the condenser. The other side of the condenser is in metallic contact with the frame. The secondary winding has one end attached to the primary and the other to a central pin in the end of the armature spindle — a lead being provided to the collector ring on which a carbon brush presses. A flexible H.T. wire conveys the current from the end of this brush to the centre of the H.T. distributor shown to the right, from which it is distributed to the several cylinders when the magneto is used as an ordinary magneto, but in the Dual system it is first taken to the coil and then back to this terminal (see Pig. 91). The distributor runs at one-half the speed of the armature, and has on its under-side a contact breaker for use with the accumulator. It is driven off the armature shaft by the worm seen in the figure. The advance and retard is effected by the rod underneath the magneto. It operates the magneto contact breaker in the usual manner, but the requisite and greater movement of the coil contact breaker is produced by lifting a sleeve on the vertical shaft which carries the distributor driving gear. As the worm wheel is raised or lowered, it moves round along the teeth of the worm, and so causes an advance or retard to be given to the contact breaker and the distributor. The coil is placed upon the dashboard, and consists of a trembler coil, condenser, and switch with suitable terminals.. The diagram of wiring is shown in Fig. 91. "When using the magneto for firing the charge, the high tension current is taken to E on the coil, and passes out at C to the centre of the H.T. distributor. When running on the accumulator, the current is taken to A, passes through the coil to D and from thence to the battery contact breaker and earth. The induced current in the secondary is then led to the centre of the H.T. distributor as before. B is then " earthed." For switch-starting, the switch is tapped over smartly by the foot, which " earths " D and permits a current to pass through MAGNETO IGNITION 183 To FRAME I HTDlSTRietrri I HoBi-ror4TAL TYPE tauAL COlL SHOWirJq ARRANCifMENT OF cotgNEcrioNs- Fig, 91. — ^Hall Dual Wiring Diagrain . 184 MOTOR CAR ENGINEERING the primary of the coil and cause a spark at the plug should one of the pistons be in a suitable position. 145. C. A. V. Dual System.— Fig. 92 shows the construction of the C. A. V. Dual magneto. This also has a primary and secondary wiring on the armature, and the connections to the collector ring and earth are much the same as previously detailed. The live end of the primary winding is taken to the insulated portion of the contact breaker 171, against which a carbon brush 618 625 131 Fig. 92.— 0. A. V. Dual Magneto. 393 presses. This brush is connected through the steel spring and pillar 618, which keeps the vulcanite cover in position on the end of the contact breaker to the terminal marked M P on the coil (Fig. 93). For accumulator ignition this terminal is " earthed." The vulcanite cover 687 to the contact breaker has four segments on its inner face, the two opposite of which are in connection with the terminal 187. A carbon brush (not shown), carried upon the contact breaker base, rubs upon these segments and completes the circuit for the battery. When the magneto is in operation, the H,T. current from the MAGNETO IGNITION 185 186 MOTOR CAE ENGINEEEING collector ring is carried from 640 to the terminal M on coil (Fig. 93), passes from thence to D and to the middle terminal on the top of the H.T. distributor, where it is led to the centre carbon brush and directed by the distributing arm 675 and carbon brushes 392 to the sparking plugs. When running on the accumulator, the primary winding of the armature is earthed by a lead taken from 131 to the M P on the coil. The battery current enters the coil at A, passes through the coil out at C C T to the terminal on the vulcanite cap which is in com- munication with the brass segments on the inner face. Here the circuit is broken, and the induced current in the secondary winding of the coil leaves at D on the coil for the distributor as before. The return of the primary current to the negative pole of the battery is through the frame. Advance and retard is effected by the rotation of the contact breaker easing, a stud being fitted so that any movement given to the contact breaker is communicated to the block ti79 carrying the four distributor terminal segments. 146. Simms Dual System (Type S). — The object of this system of ignition is to enable easy starting to be effected at the minimum of expense and alteration. The priiicipal modification necessary in the standard machine lies in the contact breaker. From Figs. 94 and 95 it will be seen that fitted to the timing lever is a fibre communicator cover A, into the inner face of which fopr brass segments are fixed. To two opposite ones B, Bi are fixed terminals C. On the contact breaker are two brushes, one D in contact with the contact breaker base, the other E in contact with the contact piece, and insulated from " earth." In the centre of the commutator cover A is a brush- holder F, in which is a brush G, which malies contact with the hexagon -headed screw H. The brush holder F projects through the cover A and forms the connection through spring J for "earthing" the magneto. Fitted within the timing lever is a cam ring in which are two recesses at 180 degrees. The fibre heel of the contact breaker rubs on the inside of the cam ring, the rounded faces formed by the recesses forming the make and break. The platinum points are brought together just prior to breaking. The brushes D and E make contact with the segments B, Bi only when the platinum points of the contact breaker are open and leave the segments before the points close. MAGNETO IGNITION 187 EH 03 3 P a 188 MOTOR CAR ENGINEERING The switch is shown in Pigs. 96 and 97 and consists of a casing K, in which partially rotates a cover L to M-hich is Fig. 95. — Simms Contact Breaker Cover. attached a handle M. Partial rotation to the left or right is limited by screw N and ends of slot 0. Fixed to the inside of cover L and insulated from it is a brass bar P, which carries a Pig. 96.— Simms Dual Switch. platinum-pointed screw which forms part of the trembler spring. To adjust platinum-pointed screw remove cap Q. Moving the cover to the left switches the accumulator system on ; to the right it switches the magneto on ; the mid position makes both systems MAGNETO IGNITION 189 ElG. 97.— Simms Dual SwitcK. inoperative, and in that position it is located by a ball and spring. Fixed to the brass bar P are laminated forked contacts E and S, the former being insulated from the bar. T is a fibre ring into which five contacts are fixed, and are arranged to come beneath the con- tacts E and S. V is the soft iron core, around which is wound a coil. On the core is fixed a brass plate I, which carries the trembler system. W is a condenser, being held in position in casing X by a spring. This spring forms the connection from the condenser to the coil, and is brought out on fibre ring T. On the fibre ring are four terminals for receiving the various external wires, two of which are from the magneto, one from a 6-volt battery, and the remaining terminal is coupled to earth. Figs. 98 A, B and c show the connections in the "accumulator," "off" and "magneto" positions, the magneto connections being omitted. In the " accumu- lator " position the current flows from the accumulator to contact Z, through switch contact E to con- tact Zi, through coil and trembler, switch contact S to contact Y, segment B in commutator A, through primary winding of magneto to segment B i, and then to battery. Thus the coil within the switch acts as a trembler for the primary winding of the armature. Hence the necessary high- tension current is produced in the secondary winding, and is Fig.- 98a. 190 MOTOE CAE ENGINEEEING Fig. 98b. distributed to the plugs in the usual way. It will be observed that the battery ignition is timed a little later than the magneto, this being necessarily so, as otherwise the contact breaker on the magneto would tend to short-circuit the self-starter just at the time when it was being brought into operation. The result, however, is that imme- diately after the engine has got under way by virtue of the battery and cpil, the magneto takes up its ordinary function and does the work of igni- tion, even though other later sparks may still be caused to jump across the plugs under the imme- diately following influence of the battery system. In the "off" position the battery is cut out of action, since the switch contact E malies no connection between the contacts Z and Zi, and the switch contact S makes contact between the contact Y and the contact Y2, thus " earth- ing" the magneto in the usual way. In the "mag- neto " position, the accumu- lator is switched off as in the "off" position, the switch contact S being off the con- tacts Yi and Y2. 147. Bosch Duplex Igni- tion. — This is another system for facilitating the operation of starting up. The coil (see Fig. 99) con- sists of a cylindrical coil case 1 provided with a flange. Inside this coil case is the switch plate 2, securely fitted to the iron core 3, the two ends of the winding of which are connected to the switch plate. The iron core carries the cover 4 with switch handle 5, by means of which the armature, as well as the switch plate 2, can be rotated inside the coil case. On the end of the coil case the connection plate 6 is arranged, and the Fig. 98c. MAGNETO IGNITION 191 terminals 7 of this connection plate are connected to the contact springs 8. These establish the various connections when the switch is being operated by means of the handle 5. The movement of the switch is limited by the guide screw 9, which passes through the coil body and so comes in front of the coil itself, which on this account has three recesses which hold the coil in the various desired posi- tions. For this purpose also the contact springs 8 are so arranged that they press heavily against the pj^, gg coil and push it against the guide screw. In order to prevent any ill-usage of the coil or the starting of the car by an unauthorised person a locking arrange- Pig. 100.— Bosoh Duplex System of Wiring. ment is provided on the coil, so that it can be locked by means of the special removable key 10. For starting, the switch handle 5 is put in a vertical position, so that the winding of the coil is in connection with the primary Following Page is Damaged Best Image Available 190 MOTOR CAB .ENGINBEEING ^ ^^ binding of the .agneto, the ^ ^^ %U of the current from a 4-vo t ""^'^^^iJ^^^Z^ therefore, f , in Fig. 100. (j„3„„,„«0HM.™»XI. A (1) N».. »a St* the use ol the a„e,.l P«ts .1 • l' 7.) tsteh s„». How is lulTmoe and retard effeetod in tne ? E.pl™ the ootionof the Bosch m.gnefo .gn« "';rM-'sSsrw£;ttf™r»d-h.e..»ee-. %rit;is'^r^w..nsi.^^^^^^^^^^ (10) What is the essential ditterence dbiwb ^IS wTs tTeCt o^ automatically advancing ajr. (11) 7'i**f J''°° J . achieved in the Eisemann system ^' nrEi laU - a dual system of igniti. g SSbe the Euller system of dual igmtion, * ^tBtXfdual system in which the magneto .. J winding upon the armature, and show the comiectioos Mt ^Is) VT'Cater amount of advance necessary .fc . and accumulator than with a magneto ? (16) How is this increased advance obtamed m mt<, ^^fm What is duplex iguition, and why is it fitted ? (18) Draw a diagram of wiring for a two-cyhnder engu with duplex ignition. ,.-.,■ i ■ ^v, x (19) Explain the Bosch duplex ignition, showmg the dit (20) 'Point out the relative merits of dual and duplex igniti Following Page is Damaged Best Image Available CHAPTER XII ENGINE CONTROL SYSTEMS •3 somewhat strange, seeing to what an extent stan- ■' -las been carried out in the modern car, that a more iem of control has not been adopted. At the '^me one frequently sees examples where the design of Trol mechanism does not appear to have received that Q which its importance merits. In order to clear various the engine or the chassis, it has been necessary to mtro- multitude of levers, joints and cranked rods, which, no how securely they may be fastened in the first mstance, to become loose after they have been in use for a time ; ^ multiplying effect of wear at a large number of pins ./es itself felt. It is sometimes the practice to use wires ismitting motion to the various levers, the replacement Ih is effected by the aid of springs. This method cannot wnmended, as the seizure of the mechanism which it )r the breakage of a spring, may not be discovered until xdent has become imminent. Simplicity should be the of all engine control, whether automatic or mechanical, ' all possibility of trouble from some mechanical defect ^ hereby reduced to a minimum. Automatic and Mechanical Control.-There are two forms ol of the car— automatic and mechanical— the former jually applied to the engine alone, while the latter is both the engine and the transmission gear. ■tomatic control is generally obtained by the use of a il governor, although, occasionally, governors operated essure in the circulating water system or the exhaust ^'rnve been employed. A system in which the time of , automatically controlled by a governor, but not for the i^'i controlling the engine, is described m Art. 139. 194 MOTOE CAE ENGINEEEING With the centrifugal governor it may operate in three different ways : — (a) By throttling the exhaust. (6) By altering the lift of valves. (c) By actuating an auxiliary throttle in the inlet pipe. Methods (a) and (b) have now been discarded, and are not likely to be revived, so it is unnecessary to discuss them here. But with regard to (c), this form of control is sometimes success- fully applied to the engine, and will, therefore, receive some attention. * 150. The Centrifugal Governor may be constructed in many ways, but a common type has two bell-crank levers pivoted about a fixed point on the framing, the free ends of the lever being loaded with balls, while the other ends engage with a grooved sleeve, sliding upon a central driving shaft. The sleeve is kept in position along the length of the spindle by means of a spring. By suitably proportioning the arms of the bell cranks and the weight of the balls, the speed of rotation can be made to be the same for all positions of the balls, that is, for all positions of the throttle. The governor is then said to be " isochronous." When the engine is running at the speed for which the governor is set, the pressure exerted by the spring just equalises the centrifugal force transmitted from the balls. But as soon as any increase of speed takes place, the increment Of centrifugal force causes the sleeve to be moved, until the total load on the spring balances the centrifugal force, thereby clositig the throttle. Further increase of speed causes the throttle to be closed still more, until a speed is reached which the engine cannot exceed, as sufficient gas is prevented from entering the cylinder. It will be seen that much of the efficiency of the governor depends upon the accuracy of its adjustment ; and seeing that it must be capable of acting over a large range of powers, it is obvious that this is not a very easy matter. Even with some of the very best governors used in generator work, difficulty is experienced in setting them, so that they will not allow any given speed to be exceeded when running light, and, at the same time, allow the highest loads to be carried at the highest speeds. It is this trouble with the adjustment that has sometimes caused owners to disconnect the governor altogether. But there is no doubt that when in good working order it prevents those ENGINE CONTROL SYSTEMS 195 excessive speeds which are so destructive to the hfe of the engine. The governor should be free from a tendency to " hunt." Hunt- ing is due to the friction of the parts composing the mechanism. Supposing now that the load on the engine is reduced, the immediate effect is an increase in speed ; but before the governor can act, the centrifugal force has to overcome the friction at the joints, etc., and by the time this is effected, the engine speed may have risen considerably above the limit. On the governor operat- ing it cuts down the revolutions, but in doing so it closes the throttle too much for the correct speed, with the result that there is an alternate rise and fall of the revolutions. Governors are all subject to this tendency, to a greater or lesser extent, and, once started, is difficult to stop except by steadying the engine with the throttle, but the liability to this defect can be reduced considerably by efficient design and the elimination of friction as far as possible. * 151. Mechanical Control. — The driver may control the action of the following parts of the ear if fitted : — (1) The clutch. (2) The brakes. (3) The main throttle. (4) The auxiliary throttle. (5) The ignition. (6) The extra air inlet. Obviously the clutch and the brakes must be placed under mechanical control. They are operated as follows : The clutch by the left foot and the front wheel or the propeller shaft brakes by the right, while the rear brakes are hand-operated by a side lever. This is the general practice and is not departed from in a single instance, so far as is known. A drawing of the pedal gear is given in Pig. 101. * 152. With regard to the provisions of an extra air control, it is much to be regretted that this is not oftener fitted. It is true that the multiplicity of levers frequently causes bad driv- ing, and in the hands of the average driver is undesirable, yet it must be conceded that there are many who would be quite capable of using such a device effectively. Too much reliance is placed upon the accuracy of carburetter adjustment and of the automatic air fitting there frequently provided. If the extra air o 2 196 MOTOR CAR ENGINEERING on the carburetter is correctly adjusted, a difficulty is often experienced in starting the engine ; so in order to obtain easy starting, one is prone to tighten up the spring to enrich the mixture. With an extra air valve under mechanical control, this ENGINE CONTEOL SYSTEMS 197 would be entirely avoided, and a driver would gradually get to feel when his engine is working most efficiently, and thus obtain a better petrol consumption. * 153. Although the importance of simplicity has been empha- sised at the beginning of this chapter, there is a limit to which it may be efficiently carried. With the view of simplifying the control, the lever for advancing and retarding the ignition has in some cases been dispensed with. As has already been pointed out, different mixture strengths require different times of firing, so unless a uniform strength of mixture is always maintained in the cylinder, at some times the engine will be running on a retarded spark and at others on an advanced spark. This will be very wasteful to fuel. Some results of tests made on a standard engine fitted with fixed ignition were recorded in the Autocar for May 21st, 1910, and on the diagram given it was shown, that for the same powei' at 650 revolutions of 23 b.h.p. under both fixed and variable ignition, the power obtainable under the two systems was 29 b.h.p. and 33 b.h.p. respectively at 1,050 revolutions, and 13 b.h.p. and 15"7 b.h.p. respectively at 400 revolutions per minute, a. reduction of over 12 per cent, at the higher speed and over 17 per cent at the lower. In addition, with some positions of the spark- ing lever, it was found to be impossible to run the engine slowly without knocking. The disadvantages of the system may therefore be summed up as follows : loss of power at high and low speeds, inability to run at low speeds and a noisier engine. No doubt there are cases where engines have good petrol consumptions with fixed ignition, but these would be improved upon if timing levers were provided and used. * 154. Methods of Control. — The methods of controlling the speed of the engine may be briefly summarised in the following manner : — Main Throttle Ignition, Extra Air. From steering column with accelerator pedal. From steering column with accelerator pedal. Accelerator pedal. Inteiconnected From steering column Fixed Fixed From dashboai'd. Automatic Carburetter. 198 MOTOE CAE ENGiNEEElNG The simplest method of control is that indicated at 3, to fix the ignition — use an automatic carburetter and fit an accelerator pedal for opening the throttle. On a car so fitted, the driver has only to depress or raise the accelerator pedal in order to regulate the speed of the car. The merit of such a system is, that once the gear is adjusted to give the best average conditions of running over the entire range of speeds and fixed in that position, the car may be placed in the hands of the novice, and the maker will know that a moderate efficiency will be obtained. It is also assured thait he must remove his foot from the accelerator pedal and so slow the engine down before he declutches or before he applies the brakes, according as the pedal is between the clutch and brake pedals or to the extreme right of them. But where a large amount of continuous driving is indulged in, such a system is extremely tiring, because it is necessary to keep the foot in a more or less fixed position, unless the car is driven with a full throttle, when the foot merely rests upon the pedal. The operation of the throttle by a pedal is, however, good in principle, as harmonious working is more likely to be obtained between the feet than between a hand and a foot. This is of importance when changing gear, and has the additional advantage, that while the left hand retains control of the steering, the right hand is free to operate the change speed gear lever. The accelerator pedal is, therefore, to be found on practically all cars, sometimes alone, but more often in conjunction with a separate throttle lever. The pedal may operate an auxiliary throttle in the inlet pipe, but is generally connected with the main throttle, as by such an arrangement the jnain throttle lever can be placed so as to allow the engine to just run when declutched and the control effected by the pedal. At the same time, the driver is free to use either the pedal or the hand lever. The main throttle, as well as the ignition lever, should be placed on the steering wheel in order to be readily accessible, and it seems somewhat of an advantage for them to rotate with the wheel rather than to move over a fixed quadrant, as is frequently the case ; for then the levers may be grasped between the two fingers, and there is not the liability to knock one of them over when it is necessary to suddenly alter the direction of the car. ENGINE CONTEOL SYSTEMS 199 It is desirable that the connections with the operating levers should move forward for acceleration, as that is the more natural movement. Occasionally the throttle and the ignition are controlled by a single lever on the steering wheel, a link being interposed between the lever on the throttle and the distributor or the contact breaker so that the throttle and the ignition are inter-connected. But the timing is not dependent upon the position of the throttle alone, for the speed of the engine has as much, if not more, influence upon the correct time for firing the charge. It will therefore be clear that the best results will not be obtainable with this form Fig. 102.— Sheffield-Simplex Pedal Control. of control, although it is hardly necessary to add they will be an improvement upon those from an engine having fixed ignition. * 155. An interesting system of foot control is illustrated in Fig. 102 in which the throttle is operated by the pedal there shown. This pedal is mounted on ball-bearings, and connected on its underside to levers and connecting rods, so that a sideways movement actuates the throttle. This system is fitted to the Sheffield- Simplex car, and, as is apparent, is extremely simple, while it dispenses with the necessity of keeping the foot in a cramped position for any length of time. In Fig. 103 an arrangement seen on the 15 h.p. Standard ear is shown by means of which pure air can be admitted to the 200 MOTOR CAR ENGINEERING cylinder. An adjustable screw is provided which limits the movement of the throttle lever on the steering wheel when closing. By depressing the pedal lever, the block against which the screw presses can be displaced, and a further movement of the throttle made possible, thus allowing pure air to enter through the inlet seen in the figure. * 156. On the whole, the most desirable system seems to be that in which the throttle in the inlet pipe is actuated by a lever on the steering wheel acting in conjunction with an accelerator pedal, with an extra air inlet lever on the dashboard, while the THROTTLE Fig. 103.— 15 li.-p. Standard Throttle Gear. ignition is controlled by a lever on the steering wheel. By this means a position can be obtained for the extra air lever, which gives the best mean results, and then the driver who wishes for the minimum of trouble has only the levers on the steering column to attend to. The objection which is taken to the full control is mainly due to the lack of knowledge on the part of the driver, but as his acquaintance with the car becomes more close, he will gradually find himself using the extra air lever and thus obtain better performances. A switch should always be fitted upon either the dashboard or the steering column, in order to permit the ignition to be switched on and off at will. ENGINE CONTROL SYSTEMS 201 Questions on Chapter XII. (1) Make a diagram showing the levers for the full control of a car. (2) What objections are there to fixed ignition, and why should the ignition be advanced or retarded according to the speed and power of the engine ? (3) How does the governor operate in controlling the speed of an engine, and why is it not more often fitted ? (4) Sketch a governor together with the controlling levers. (6) Why is the accelerator pedal so universally employed ? Sketch the system of levers between the pedal and the throttle. (6) Sketch and describe the inter-connected system of control. (7) Why should the extra air valve be under mechanical control ? (8) Make a diagram showing the connections between the brake lever and the rear brakes. Note. — The reader is referred to the Autocar for Wth February, 1909, in tuhich various systems of engine control are clearly shown. CHAPTEE XIII ENGIKB COOLIKG SYSTEMS 157. The water jacket or other cooling device upon the cylinders of an internal-combustion engine is necessary in order that it may be possible to retain some lubricant between the piston and the cylinder walls, and thus prevent excessive loss of power through the friction between the surfaces. The question of lubrication is therefore connected with that of cooling, and an air-cooled engine must be supplied with an oil having a greater viscosity than is necessary for a water-cooled engine, because the higher temperature of the cylinder walls causes a greater reduc- tion in viscosity. This necessity for cooling is one of the disadvantages of the petrol engine, between 30 and 40 per cent, of the heat of the petrol being carried away by the cooling medium, and even then no less than 7 per cent, of the power developed in the cylinder is absorbed in overcoming the friction of the pistons, that is, about 30 per cent, of the heat contained in the petrol. These figures are for the full power of the engine, but the heat lost to the water with a reduction of power, and the work lost in friction, are but slightly reduced, and consequently at light loads the mechanical efficiency of the engine is very low. This is one of the reasons why the steam engine can compete on such level terms as regards fuel consumption with the petrol engine. 158. Overheating. — The importance of efficient cooling can be j udged by the behaviour of the engine when overheating occurs, as when driving in traffic or when ascending a long hill. Under these circumstances, there is insufficient air passing through the radiator (or around the cylinders in an air-cooled engine) to abstract the heat from the water, with the result that the hot water is returned to the cylinders, but slightly reduced in temperature, where it receives more heat, until at length boiling ENGINE COOLING SYSTEMS 203 takes place. If a thermo- syphon system of cooling is fitted, the trouble may be aggravated by the formation of a steam-lock in the piping, for then the circulation ceases. It must not be imagined that the metal forming the cylinders is kept at the temperature of the cooling agent, for the outside of the cylinder is only slightly above that temperature, which gradually rises as the inner surface is approached, where it reaches a maximum still far below the temperature actually existing in the cylinders. Thus overheating causes, firstly, a great waste of power in piston friction, and secondly, may permit the inside temperature to rise sufficiently as to cause pre-ignition, with its harmful effects. The temperature at which the cooling water should be depends not only upon the class of lubricant employed, but also upon the size of the cylinder. Strictly speaking, no best temperature can be specified ; but from experiments which have been made with a varying temperature of cooling water, it seems to lie for all engines between 150° and 200° F., generally about 170° F. 159. Air Cooling. — This system of cooling has been used very extensively in America on motor cars and generally on motor cycles, but its sphere of usefulness must be limited to the latter class of vehicle, unless high continuous speeds are possible. For car use in England the air-cooled engine as usually con- structed is not suitable, but it may be made so by fitting a casing round the cylinders and inducing air to pass in close contact with the walls by means of guide blades. But when this is done, the question arises as to whether the power required to drive the fan, plus the additional complication and expense in fitting the cooling casing, is not at least equal to that met with in the water system, and unquestionably the latter is more efficient as a cooling system. Air cooling has been successfully employed on motor cycles, because of the exposed position of the engine, and because it is free from complications. Attempts have been made to use cooling water, but the increased weight and space required, combined with faulty construction in some cases, has led many- people to prefer the air-cooled engine with its simplicity, even though it has a tendency to overheat. It has also been adopted on some forms of aero-engines, notably the rotary type, where the conditions of use are quite different from those met with in car work. But none would even suggest that such cooling is to 204 MOTOE CAR ENGINEERING be preferred, as the great power required to revolve the cyhnders in a rotary engine and the frequency of break-downs cause it to be considered as the "refuge of the destitute," and as time goes on, even if it has not now arrived, the disadvantage in weight of the water-cooled engine will not be regarded as of any importance compared with its greater efficiency and reliability. The object of casting ribs or fins upon the cylinders of air- cooled engines is to present a greater cooling surface to the air. Metal is a good conductor of heat, and so the heat from the cylinders travels rapidly along the fins and is taken up by the air passing over them. The fins should be so placed as to allow the air to flow freely over the surface, as unless the direction of motion of the air is along the ribs, the fullest benefit will not be obtained. As dull black surfaces are the best radiators of heat for the highest efficiency, the outside surface should be dull black, but occasionally this is sacrificed for appearance. 160. Water Cooling. — This system is almost universally adopted both here and on the Continent. It consists of a jacket which embraces the cylinder and contains water, the circulating pipes and a means for cooling the water. Frequently a pump is also fitted to ensure the rapid circulation of the water. There are therefore two systems of water cooling — thermo- syphon and forced circulation. Between the two there is not much to choose, except that one can rely upon the water circulation and absence of a steam or air lock when the latter is fitted. It is more important, however, that the pipes used in a thermo-syphon system shall be of large bore, so that the velocity of flow through them may be small, and all bends should be avoided. It is sometimes averred that the forced system breaks down in the event of pump failure, but if a centrifugal pump is used this is not so, as there is a clear space for the flow of water and thus thermo-syphon cooling is automatically instituted. The thickness of the water space is relatively unimportant, being determined rather by considerations of casting the cylin- ders, but the positions of the inlet and outlet pipes require care in placing. The flow of water should be such that the cooler water enters the jacket at the coolest part and rises to the hottest part. The outlet should therefore be over or near the exhaust valve, and the inlet in such a position that the flow of water carries it over the hottest portions of the cylinder. There ENGINE COOLING SYSTEMS 205 should preferably be a large body of water around the exhaust valve. The depth to which the jacket should extend down the cylinder is a matter of opinion, but it would seem to be always desirable to cool down to the level of the top of the piston when on the bottom centre. Equal cooling is necessary in order that there may be no distortion due to the heat from combustion, as, unless this is effected, there may be some places where the flow is very small and overheating thereby caused. This is one of the demerits of casting cylinders en hloc, especially when no water space is allowed between two adjacent cylinders, as the uniform thickness of metal cannot be guaranteed. The flow of water in a thermo-syphon system is obtained because water when heated is lighter, bulk for bulk, than when at a lower temperature, consequently it rises and cooler water flows in to take its place. But if the temperature is sufficient to cause steam to be generated, and there is a bend downwards in the outlet pipe, such steam prevents the circulation of water, and thus more steam is produced, which makes matters still worse. The water should therefore rise continuously through a pipe from the top of the cylinder to the upper portion of the radiator where it is cooled and sinks to the bottom, being cooled still further as it passes downwards. The accompanying figure shows the diagram of circulation on the 20-28 h.p. Wolseley car. All branches taken off a pipe should be taken in the direction of motion of the water, and where the water divides up into two or more pipes, a Y piece should be fitted in order that the flow may be continuous. A drain cock should be fitted at the lowest point of the system, so that the water may be drained off when standing during cold weather. 161. Pumps. — The types of pumps used in a forced circulation system are three in number — centrifugal, gear and shutter — although the plunger pump has been employed on some large engines. The shutter pump is not now very often used, on account of excessive wear and its liability to derangement. The centrifugal pump shown in Fig. 105 is used on the Wolseley car. It consists of a disc, having fins directing radially and inclined in the direction of motion, which fits 206 MOTOR CAR ENGINEERING within a casing. The water supply is to the centre of the disc, which, as it rotates, throws the water out at its circumference, as seen from the figure. In the diagram, in addition to the main supply, there is also one from the carburetter which is heated by the cooling water. The disc is driven from the engine by a shaft which runs in very long bearings, being kept in a central position in the casing by collars upon the shaft. The length of these shaft bearings is important, as wear would permit the ENGINE COOLING SYSTEMS 207 208 MOTOE CAE ENGINEEEING vanes to engage with the sides of the casing and cause jambing. The shaft is made water-tight by the metallic packing shown, while provision for lubrication is made by fitting a grease cup. The gear pump is formed by two wheels which gear together in a casing, one wheel driving the other (see Fig. 29). As the wheels rotate, they carry round water between the teeth and the easing, which, when the teeth mesh together on the outlet side, is forced out through the pipe. A shallow groove is cut on the sides of the wheels and along each tooth, which fill with water and prevent leakage past the teeth. It is an excellent form of pump and lends itself to simplicity of driving. 162. Radiators. — One method of cooling the water after it has ■ received heat from the cylinders, and that which is almost universally employed, is by means of a radiator. This is formed by two casings between which tubes are placed ; sometimes the water is passed through the tubes, as in the gilled tube and straight tube types, and sometimes outside the tubes, as in the honeycomb type. The radiator is filled from the top, and a strainer should be placed over this inlet in order to prevent impurities from gaining entrance into the system. The gilled tube is the oldest form of radiator, and has given good service in the past, but is gradually giving way to the honeycomb form with its lighter construction and greater efficiency. It is formed by either a single length or a number of lengths of copper tubes, along which rings are soldered so as to provide a larger cooling surface. When a single length of tube is employed, it is folded upon itself, so as to be of compact form and also to allow the gradual descent of water from one end to the other. This radiator carries a large quantity of water, as the tubes must be of sufficient bore to allow the free passage of water, but it has only one joint to each tube, which is a great advantage. The honeycomb type has risen rapidly into favour on account of its clean appearance, lighter construction and its high efficiency. It provides the maximum surface for the minimum of weight, both of metal and of water. It is built up of a large number of short lengths of tubes having their expanded ends so shaped that when placed in position they butt up against each other, leaving a space around the tubes and between the ends through which the water passes. The tubes are tinned and soldered ENGINE COOLING SYSTEMS 20S together at the ends and to an upper and lower chamber, thus forming one complete vesseL The air passes through the tubes, and as there is only a small quantity of water in contact with a large external surface, the cooling effect is very great. There is, however, a maximum length which these tubes can be made for any given bore, on account of the friction of the air through the tubes. In modern radiators with the usual diameter tubes this length seems to be about 5 ins. after which any increase in length is not accompanied by any increase in cooling, because the quantity of air passing is reduced. Tbe presence of the many soldered joints is, however, a dis-' advantage which has to be recognised, as, although they are easily plugged in the event of leakage, such stopping must reduce the efficiency of the radiator, apart fi'om the unsightly appearance which it causes. The straight tube type is one which is occasionally seen, and has its low cost to recommend it. It is very heavy compared with either the honeycomb or the gilled tube types, and is not so efficient^ while it takes up a greater amount of space for the same effective cooling area. The outlet and inlet pipes from and to the engine are not directly connected to the radiator, but a short length of rubber tubing is interposed, secured against leakage by clips which are fastened over the. tubing. This is necessary in order that the radiator and its attachments may not be subjected- to the vibra- tion of the engine and also to allow for expansion when the engine and the radiator warm up. 163. Position of Radiator. — Of late there has been a tendency towards the dashboard radiator, and this has much to cause it td be more extensively employed. So far as appearance is concerned , much must be allowed for convention, but there is a distinctive note when the radiator is fitted to the rear of the engine. On the score of efficiency there is little advantage in placing it either to the front or at the rear, except that it cannot be considered good practice to allow dust-laden air to pass all over the engine and possibly draw some into the cylinder. With the dashboard radiator this is avoided, while in addition the engine is more accessible when the bonnet is raised. Several examples are illus- trated in Figs. 11, 187 and 192. M.C.E. P 210 MOTOE CAE ENGINEEEING When the dashboard radiator is employed, the air passes in at the upper half of the tubes, is directed downwards and leaves underneath the footboard. The flywheel is then either fitted with blades on its rim or else its arms form the blades, so as to act as a fan and draw air through the radiator (see Figs. 11, 106 Pig. 106.— 15'9 Armstrong-Whitwortli Engine, Flywheel End. and 1 92) . Under these circumstances the engine casing must be made air-tight. 164. Fans. — In order that the radiator may be cooled when standing still with the engine running or travelling at low speed, as in traffic, and also to assist in cooling when on the road, a fan is fitted behind the radiator. This is driven by a belt from the engine or the gear shaft, usually the latter. Care should be taken that provision is made for tightening the belt, as after a short time the belt stretches and, unless the tension is maintained. ENGINE COOLING SYSTEMS 211 will slip and be of no service. About the simplest way in which this can be effected is by mounting the fan spindle upon an eccentric bush, which, on being rotated, displaces the centre of the spindle and thus tightens the belt. Ball-bearings, although eminently desirable, are not absolutely necessary. The fan may be made out of sheet steel in one piece, but often the blades are separately riveted to a central disc. The construction of these fans may be seen on reference to Figs. 7, 12, 19, 186, etc. Questions on Chapter XIII. (1) Why is it necessary to fit a cooling device to the cylinders of internal-combustion engines ? (2) Make a sketch showing the construction of a centrifugal pump, giving the direction of rotation of the wheel and the flow of water. (3) Sketch a thermo-syphon system of cooling. (4) Compare honeycomb, gilled tube and straight tube radiators. (5) How is overheating caused in petrol engines ? (6) What is the use of a fan, and how is it constructed? (7) Discuss the relative advantages of placing the radiator in front and at the dashboard. f 2 CHAPTER XIV CEANK EFFORT DIAGEAMS * 165. In all engines, excepting the turbine, there is a variation in the torque transmitted by the crankshaft, the magnitude o£ the variation depending principally upon the number of impulses per revolution, the range of effective pressure upon the piston and the speed of revolution of the engine. In addition, the manner in which the pressure upon the piston is converted into a turning effort on the shaft. is not conducive to a uniform torque. The factor which affects this variation to the largest extent is the number of impulses given by the engine, and, consequently, the twisting moment on the crankshaft of a petrol engine, working as it does on a cycle in which only one stroke in two revolutions is a power stroke, will be far from constant. Some means are therefore desirable in order to reduce this lack of uniformity of torque, as the resistances offered to the passage of the car are virtually constant, and any effort above that necessary to over- come these resistances is utilised in increasing the rotational speed of the flywheel and the transmission gear, which in turn increases the speed of the car. This, however, canuot be rapidly effected, owing to the inertia of the moving vehicle, and therefore excessive stresses are induced in the mechanism and damage done to the tyres. The flywheel which is fitted to all car engines has as its func- tion the removal of these damaging shocks upon the transmis- sion gear ; but in order to be fully effective at all speeds with single-cylinder engines, it would require to be of large size and weight, which is in itself some detriment. Uniformity of torque has therefore been obtained in modern engines by increasing the number as cylinders, as, by suitably arranging the cranks, the twisting moment due to one cylinder can be made to overlap that from another, the maximum value from one crank being attained when that from another crank is at its minimum. The effect of this piay be seen on reference to Art. 172 where the CRANK EFFORT DIAGRAMS 213 ratios of the excess energy over the average energy of a number of engines have been tabulated. * 166. Before the crank effort diagram for an engine can be drawn, it is first necessary to take an indicator diagram from the cylinder of the engine under consideration, and the curve of crank effort which is finally obtained is correct only for the Fig. 107.— Crank Bfiort Diagrams. particular speed of revolution at ivhich the engine was running when the diagram was taken. Frequently, however, it is suffi- ciently accurate for practical purposes to construct a theoretical indicator diagram. Using the diagram given in Fig. 38, it is first set out for the four strokes represented thereon as shown in diagram A Fig. 107 by the full line. This diagram then represents graphically 214 MOTOE CAR ENGINEERING the pressure acting on the piston at any instant in the cycle, and it should be noted that the pressures within the cylinder on the second, third, and fourth strokes retard the engine, and so for the purposes of crank effort are negative. But the load due to the pressures here recorded is not the effective load at the gudgeon pin, as some force is required to overcome the inertia of the piston and the parts which reciprocate with it, so the diagram must be corrected for inertia. The velocity of the piston is changing from instant to instant, starting from zero velocity at the ends of the stroke, and reaching a maximum value near the position where the crank makes a Fig. 108. — Piston Velocity Diagram. right-angle with the connecting rod. This variation in velocity is shown graphically in Fig 108 and is obtained as follows : — * 167. Piston Velocity Diagram. — Draw the crank in the position for which the velocity is required, and produce the connecting rod until it cuts the line ON in M. Then to the same scale that 00 represents the velocity of the crank, OM represents the velocity of the piston. These values have been plotted to the right of the figure on a stroke base. Proof. — The velocity of the piston V is along PO which has a resolved part along the connecting rod of V cos . The velocity of C is at right-angles to 00 — tangential to the crank circle — which is the resultant of the velocity of T cos oc along the rod and T sin « at right-angles to it, So that V cos = T cos oc But cos = sin OMP and cos x = sin MCO V : T : : sin MCO : sin OMP That is as OM : 00. CEANK EFFOKT DIAGRAMS 215 * 168. Acceleration. — The force necessary to produce this change of velocity and accelerate the reciprocating parts must be supplied by the engine during the time that the velocity is increasing, but in the latter half of the stroke this inertia will assist in producing the rotation of the crankshaft. At any instant the magnitude of the force is the product of the mass of the reciprocating parts and the acceleration or generally — P = Mass X Acceleration. This acceleration pressure is positive, and must be subtracted from the pressure on the piston during the first half of the stroke, and negative, and so must be added to the pressure during the latter half of the stroke. Its value at the in-centre is uy^r (l H — j and at the out-centre co^r ( 1 j , where co is the angular velocity in radians, r is the radius of the crank in feet and n is the ratio of the length of connecting rod to crank. It should be noted that the mass of a body is its weight divided by the acceleration due to the force of gravity, W i.e. M = — .9 W so that F = — X acceleration. 9 The parts which are considered as reciprocating are the piston, gudgeon pin and a portion of the connecting rod. The weight of the portion of the connecting rod is found by supporting the connecting rod horizontally on spring balances and taking the weight recorded by the balance at the gudgeon pin end. * 169. Klein's Construction. — The values for the acceleration of the piston at any point of the stroke may be found by Klein's Construction (see Fig. 109). In the figure, the position of the piston at which its acceleration is desired to be known is drawn and the connecting rod is pro- duced to cut the vertical diameter at T. On PC describe a circle having its centre on the middle point of the connecting rod, and with C as centre and radius CT draw another circle cutting the circle NCM in N and M. Join NM. Then to the same scale as CO represents the centripetal accelera- tion of the crank pin, OQ represents the acceleration of the piston. 216 MOTOE CAR ENGINEERING CD the acceleration of P along the rod, and QD the acceleration of P about C. The acceleration of the crank pin is ojV so that the acceleration of the piston is »^r X QO oc- The acceleration of P being known, the force required to produce this acceleration is M mV x ^. It is usual to assume that the angular velocity of the crank is Fig. 109. — Klein's Construction for Piston Acceleration. constant, and calculations are much simplified by making this assumption. These values are then calculated and expressed as the pressure per square inch of piston, the resultant pressures being plotted on the diagram A. They are shown in diagram A in Fig. 107 by the dotted lines, and seeing that on the second and fourth strokes of the cycle the pressure within the cylinder is negative, the acceleration pressures are reversed in the spaces representing these on the diagram. The effective pressures per square inch of piston which exert a thrust in the connecting rod are section lined from left to right, while those which retard the engine are section lined from right to left. These have been plotted on a gtyoke base in diagram B, fig, I07, CEANK EFPOET DIAGEAMS 217 But as the reciprocating masses, the angular velocity, the crank radius and the area of the piston are constant, a large amount of numerical labour can be avoided by taking them out of the expression for the acceleration pressure and substituting their value. The acceleration pressure per square inch of piston is McoZr QO -I. , ,. McoV 1.- 1 • u i, — T— X ^. jbivaluatmg — ^— and multiplying by the actual length of QO on the drawing, a constant is obtained which it is only necessary to multiply by the lengths of OC for the varying crank position in order to obtain the acceleration pressure. * 170. Crank Effort. — Having obtained the pressures which are transmitted to the crankshaft, it is necessary to find the turning effort on the shaft. The force acting at P may be resolved in the two directions — one along the rod and the other at right-angles P to the direction of motion. The force along the rod is S = : " eos<^ where P is the resultant force on the piston and (j) is the angle between the connecting rod and the centre line of cylinder. Its tangential component is T = B sin MCO _ P sin MCO ~ cos ^ OM OC' Therefore, if the pressure on the piston is multiplied by the intercept on the vertical diameter of the crank circle and divided by OC, the result will be the equivalent crank effort, for T X OC is the twisting moment on the shaft. It will be noted that the diagram of twisting moment is also the diagram of piston velocity to a suitable scale, when the pressure upon the piston throughout the stroke is con- stant. These values of twisting moment are then plotted on a crank- angle base and represent the crank effort of a single-cylinder engine. (See Fig. 107, Diagram C.) From this diagram- the crank effort for an engine having any number of cylinders of the same dimensions can be obtained by drawing the curves 218 MOTOE CAR ENGINEERING of effort upon the same crank-angle base, but commencing the curve for any one cylinder at the correct position in the cycle. The diagram for a four-cylinder engine is illustrated in dia- gram D, summarised for four separate single-cylinder diagrams as shown. These diagrams C and D are very instructive, as showing what effect the inertia of the reciprocating parts have upon the actual turning effort upon the crank, especially at high speeds. It will also be clear that there will be some speed of revolution at which the engine will run with the minimum of vibration. * 171. Maximum to Mean Crank Effort. — Then, seeing that the curve represents the twisting moment on the shaft at any position of the crank in the cycle, it is clear that the mean height of the diagram will represent the mean crank effort. This is best obtained by finding the area enclosed by the curve and dividing it by the length ; then upon setting up the length of this ordinate on the diagram and drawing a horizontal line through its upper end, the mean crank effort during the cycle will be shown. This has been represented in diagrams C and D by the line MK. The ratio of maximum to mean crank effort will obviously be the ratio of the height of the maximum ordinate to the height of the mean ordinate, that is, as BN is to ES. The mean crank effort is equal to -^ — ^^rr^ lbs. feet where R is the radius of the ^ 2 77 RN crank in feet and N is the number of revolutions per minute, so that RS equals the value of this expression. * 172. The Diagram as a Measure of Energy. — In obtaining the diagram, the ordinates were made to represent crank efforts and the abscissae angles through which the crank turned, therefore the area enclosed by the curve represents the work done per cycle which is also represented by the rectangle MKTL. Similarly the shaded areas ABC, etc., represent the excess of energy supplied by the engine which is expended in increasing the speed of the car. Therefore, according as the point on the curve is located aljove, on, or below the line MK, so the effort is more than, equal to, or less than that required to propel the car at the required speed. Mr. Archibald Sharp, in his "Balancing of Engines," gives the following values for the ratios of excess energy to CKANK EFFOET DIAGEAMS 219 the average energy of one revolution for four-stroke cj engines : — Eatio of Excess Energy. Number of Cylinders. Average Energy of One RevoliiHon. 1 1-6 to 1-8 2 0-8 toll 3 0-25 to 0-40 4 0-15 to 0-25 5 0-07 to 0-12 6 0-05 to 0-08 8 0-02 to 0-04 * 173. Fluctuation of Energy. — It has been stated that the shaded areas above and below the line MK represent the excess of, and deficiency of, energy over the mean resistance. If the largest of these areas is denoted by AE, and that of the rect- angle MXYL, that is, the energy required to propel the car during one stroke or half a revolution is E, then ^p- = Fluctuation of energy and AE is the energy which must be stored up and restored by the flywheel during the one stroke. To enable the flywheel to do this, its angular speed must be either increased or decreased, and the change of kinetic energy will be such as will be produced by the change of speed of rotation. If the weight of the rim of the flywheel is W, its radius of gyration is r feet, and its angular velocity is i radians per 0)^), and if m is the mean angular speed of m) is second is — I mi 9 ^ rotation and wi the permissible highest speed, then (mi the permissible increase of speed, and 9 The fluctuation in speed permitted varies greatly, according to the will of the designer, but, whatever value is chosen, it represents the difference between the highest and the lowest 220 MOTOR CAR ENGINEERING speed of the engine and consequently ((»i — oj) is only one-half of this. Note. — The flywheel is mainly of service at slow speeds, as may he readily seen if calculations are made for the weights of flywheels required for any given speed fluctuation at varying speeds and corresponding powers. Questions on Chapter XIV. (1) What does the crank effort diagram show ? (2) Draw a piston velocity diagram for an engine running at 1,000 revolutions per minute which has a stroke of 5 ins. and a connecting rod 10 ins. long. (3) What is the maximum value of the acceleration pressure, in lbs. per in., in the engine given in Question 2, if the diameter of the cylinder is 4 ins. and the weight of the reciprocating parts is 7 lbs ? (Answer, 49-4 lbs.) (4) State what procedure you would follow in making a crank effort diagram. (5) If the permissible fluctuation in speed is 10 per cent., what weight of flywheel is it necessary to provide for a 4-cylinder engine, giving out 10 b.h.p. at 550 revolutions per minute ? Assume a radius AE of gyration of 8 ins., and that -^ of one revolution = 0'25. (Answer, 84f lbs.) CHAPTER XV CLUTCHES AND BRAKES The clutch is the mechanism by means of which the transmis- sion gear is connected to, or disconnected from, the engine. 174. Use of Clutch. — Owing to the fact that the petrol engine is not self-starting, and that the working fluid has first to be drawn into the engine by some external agency, it is impossible to have a rigid connection between the engine and the transmis- sion gear. The necessity for gradually increasing the speed of the car from rest, so that its occupants may not be subjected to a back-breaking jar, nor the gear wheels, propeller shaft and tyres to destructive shocks, provide additional grounds for the adoption of an elastic medium between the engine and the road wheels. The considerations given in the preceding paragraph may be said to be the primary or obvious reasons for the existence of such a fitting ; but there is another, and quite as important reason, namely, the act of gear-changing. Without such a device the whole of the regulation necessary to equalise the peripheral speeds of the two wheels in the gearbox which are to be brough into mesh would have to be done at the engine, with the result that the operation would be as uncertain as it would be lengthy. There is also the question to be considered of the damage and noise that might ensue at every attempt at putting gear into mesh at high speeds, or when starting from rest, or when revers- ing ; so it is clear that the provision of such a piece of mechanism is very desirable with the engine now fitted to automobiles. 175. Eequirements wMch a good Clutch should fulfil. — One of the most desirable features which a clutch should possess is simplicity. This is not the simplicity which comes from the avoidance of many parts, but rather from the absence of the need for many adjustments which it is too often necessary to make. 222 MOTOR CAR ENGINEERING The multiple disc clutch contains many separate parts, but an unskilled man can dismantle and re-assemble one without any trouble. It is easily understood. The clutch should also be self-aligning and self-contained. That is to say, if wear takes place in any part of the mechanism on either side of the clutch, the services through which the drive is taken should be true with one another; and further, that if springs are used to bring the surfaces in contact, the pressure exerted by the spring should be against some rotating part and not upon a fixed portion of the chassis. Occasionally one finds that the latter method is employed, with the result that during the whole time the car is in motion, the clutch spring, or a washer against which it presses, is rubbing against a fixed part and wearing it away. A ball-bearing improves matters, but does not eliminate the defect. It is obvious that the clutch should be quite free when out of gear and that small movement of the clutch member should suffice to take out the clutch, as, unless the parts are completely separated, some motion may result at an inopportune moment ; whilst small movement is desirable in order that both the pressure exerted by the foot on the clutch pedal, and also the magnitude of its move- ment may be small. It is also desirable that the clutch should permit of a certain amount of slipping before complete engagement is effected in order that the car may be gradually accelerated and shock upon the tyres and transmission gear prevented. There is another requirement which ranks high' in importance, namely, a clutch should have small rotating inontpjitum. This is necessary when changing gear, as if the clutch slia'ft takes a long time to come to rest, it prolongs the time required to bring about the change. In order to arrest the motion of the clutch, makers frequently fit a clutch brake, which is a leather -faced pad against which the rotating part rubs when disengaged. Easiness of repair is also desirable, from an owner's point of view, for reasons which are readily seen. 176. Types of Clutclies. — There are six different types of clutches : the cone, the reversed cone, the double cone, the expanding, the plate, and the disc, all of which are in use at the present day in modern work. The simplest form is the cone clutch, and it is also the cheapest to manufacture ; an example is shown in Fig. 20 fitted to the CLUTCHES AND BRAKES 223 Hewitt engine. It is usually incorporated in the flywheel, which forms the outer shell on which the male portion of the clutch engages. The internal surface of the flywheel and the external surface of the sliding clutch member are turned to a taper (about 15 degrees for leather and cast-iron surfaces), so that when the two parts are brought together by the action of the spring, a wedge action is set up, pressing the surfaces together and enabling the drive to be taken by the friction between the leather and the cast iron. Unfortunately, however, there is a maximum diameter up to which a flywheel can be made and consequently there is a limit to the power that a clutch of this type can transmit unless excessive pressures are used between the driving surfaces. If fitted for high powers, high pressures are necessary, with the result that sooner or later trouble is experienced owing to the abrasion and disintegration of the leather, and if slipping is permitted to take place for any length of time, the leather becomes charred and requires renewal. The clutch in the illustration referred to above is self-aligning and self-contained, as the pressure of the spring is taken by an extension of the crankshaft. Disengagement is effected by means of levers, which terminate in a forked arm, partially encircling the grooved collar secured to the male portion of the clutch. The drive is transmitted from the clutch by two fingers which connect up to a shaft from the gearbox and thus allow of some inaccuracy in the axes of the clutch and the gearbox shaft without inter- fering with the good contact of the driving surfaces. The reversed cone clutch is illustrated in Fig. 110, and differs from that already described only in the direction in which the cone is formed, so that for disengagement the sliding portion of the clutch is pushed forward instead of being drawn backward. This enables the nut on the extension of the crankshaft, which was previously necessary to support the spring, to be dispensed with, without impairing the efficiency of the arrangement. The spring will be seen to press against a ball-bearing, which thus prevents any drag upon the spring when the clutch is disengaged. The method by which the power is transmitted to the gearbox is clearly shown in the figure. The double-eone clutch is a combination of these two clutches, the front cone being of the ordinary type, while the rear cone is reversed. It is an excellent type, and has the advantage that by 224 MOTOE CAR ENGINEERING reducing the length of the cone a slightly increased diameter is permissible. The improvements which have been made in these clutches in recent times have been in the direction of simplifying the work entailed in renewing the leather. This has been done by sub- stituting tee-headed bolts for rivets, so that it is only necessary Fig. 110.— Reversed Cone Clutch. to remove the bolts and replace the leather instead of the elaborate process which was previously required. Leather clutches have a tendency to become fierce unless atten- tion is frequently paid to them, and it is a good plan to give them a dressing of coUan oil occasionally. Expanding Clutclies. — The construction of the Crossley clutch is shown in Fig. Ill, and this is of the metal type, both of the engaging surfaces having a separate covering of metal riveted to the respective parts, thereby facilitating renewal. The expanding portions are in the form of two shoes C, secured at one end to a CLUTCHES AND BRAKES 225 framework which is attached to the clutch-shaft, and at the other to two levers. The engagement is effected by the spring shown in the figure at the back of the clutch-shaft, and the ends of which hook on the free ends of the levers. To disengage the clutch the cone which slides upon the shaft D is pushed forward, causing the free ends of the levers to diverge and the other ends attached to the shoes to come together and bring the shoes away from the interior of the flywheel. It is essential in this type of clutch that the parts have small weight, otherwise the eerrtrifugal force to be overcome by the driver will be excessive and the operation of declutching prove laborious. In the example illus- trated, by good, design and light construction this is avoided, and its long - continued use upon the Crossley cars is sufficient evidence' that no trouble is experienced in practice from this source. 177. Deasy Plate Clutch. — The Deasy clutch is shown in Fig. 112. Its separate details are a phosphor-bronze driving plate, presser pads, a ring B, and an outer cover which encloses the parts, and forms, with the flywheel, an oil-tight casing. The ring B is threaded on its outer circumference and screws into the flywheel as shown, the necessary adjustment for wear being .made by screwing it further into the flywheel casting. It is locked in position by the rib seen on the bottom of the inside of the outer casing. The toggle levers which transmit and multiply the force exerted by the central spring are pivoted on the pressers, one end of each lever engaging with the ring B, while the other end rests in a groove in the sleeve which is actuated by the clutch pedal. M.C.E. Q i'lG. 111.- -Orossley Expanding Clutch. 2^6 MOTOE CAB ENGINEEEING When the clutch is put into engagement, the pressure of the spring upon the sleeve on the clutch shaft, causes the inner end of the levers to move forward. These, pivoting about their outer Fig. 112.— Deasy Plate Clutcli. ends which rest in the grooved ring B, force forward the pressers, which grip the plate between them and the face of the flywheel and so take up the drive from the engine. CLUTCHES AND BEAKES 227 178. The Multiple Disc Clutch. — This is the type par excellence, as it embodies in its construction all the desirable features of the ideal clutch. Its great advantages lie, however, in the large Fig. 113.— Tlie Hele-Shaw Multiple Disc Clutch. amount of slipping which it is possible to allow without fear of injury, to the facility with which starting is effected, and to the high powers which it is able to transmit. Q 2 228 MOTOR CAR ENGINEERING The principles involved will be clearly seen as the details of several examples are examined. 179. " Th.e Hele-Shaw" Clutch. — The construction of this clutch is shown in Pig. 113, from which it may be seen to consist of a number of V-grooved twin plates, an outer case A, which is attached to the flywheel, a steel inner portion B, which is secured to the clutch-shaft 0, and the central controlling spring P. The outer plates, which are made of phosphor-bronze, are driven by tkd Outer casing and transmit the power through the mild steel inner t)lat6s to the olutch^shaft. Around the inner side of casing A there are teeth, Or feathers, which engage with notches in the outer plates, while the core B has feathers in its outer circumference which engage with the inner steel plates. The plates are normally kept in contact by the pressure of the spring F against the presser E, the other end of which is held by the spring adjusting cap Gr, screwed into the boss at end of the case. The spring adjuster is locked in position by the wire spring H, which can be raised out of engagement while the spring pressure is being adjusted. While the full spring pressure is keeping the outer and inner plates pressed together, the full power of the engine will be transmitted. To disengage the clutch, the presser is moved backwards by the actuator K, which is connected to the clutch through the pins or trun- nions shown. When the pressure has been taken off the plates, there is a tendency for them to stick together, owing to the necessity of breaking the film of oil between the plates. To prevent this the outer plates are fitted with small flat springs, which are in compression when the clutch is engaged. These are shown in Fig. 114, which exhibits an assembled pack of plates. When the clutch is slowly allowed to engage, the film of oil between the plates transmits a small amount of power through its resistance to shear, this resistance gradually increasing as the thickness of the film is lessened by the pressure of the clutch spring, until at last the surfaces come into con- tact and the full drive is taken up. The resistance offered by the oil enables a gradual start to be made. But in disc clutches a certain amount of friction is always present between the surface of the plates and the oil, and if the Fig. 114. — Hele-Shaw Disc Clutch, showing discs assembled. CLUTCHES AND BRAKES 229 gear are out of mesh, as when gear-changing, this may be suffi- cient to cause the continued rotation of the clutch-shaft. To allow for this the actuating gear terminates in an internal cone, and there is a male cone, P, turned upon the clutch-shaft. "When the clutch pedal is depressed, it first disengages the clutch, and then brings the actuator K against the clutch-shaft cone P, thereby preventing its rotation. This clutch-brake is adjustable, in order to allow for the wear of the plates. The Hele-Shaw clutch has one salient feature which distin- guishes it from all other clutches, namely, the V-groove, This acts as a wedge and reduces the force which is necessary to transmit the drive. The makers state that the pedal pressure is reduced to one-third of that which would otherwise be required. It will be seen from Fig. 115 that the flat surfaces do not come into contact, but that the power is transmitted through the sides of the V-grooves, and further, that these grooves also act as stiffeners, Pia. 115. — Hele-Shaw Disc Clutch, showing construction of discs. preventing the buckling which might take place when overheated. The oil, too, which is enclosed within the grooves and between any pair of plates, enables the drive to be taken up silently and without shock when the clutch is let in rapidly. 180. The Argyll 14-16 h.-p. Clutch.— This clutch (see Eig. 116) is carried in the flywheel B, and consists of two sets of flat steel plates. The inner set of plates N is held in frictional contact with the outer set of plates P by means of coiled springs C acting through a presser plate G. The inner set of plates are mounted on a disc H, which revolves with the main shaft K and the outer set in the flywheel on three studs Q screwed into the flywheel. When the clutch pedal is depressed, the presser plate is drawn back, removing the pressure of the springs holding the plates in contact. When the clutch is fully released, a disc S on the casing carrying the actuating ball race L on the clutch-shaft, is brought into contact with a disc E on the main shaft of gearbox, causing immediate stoppage, which renders gear changing simple and noiseless. The clutch runs in oil retained inside the flywheel by an oil-tight cover M fixed to the rear end. To overcome any tendency for the lubrication to hold the plates together, small helical springs are tjireaded on 230 MOTOE CAE ENGINEBEING the studs Q between the outer plates to ensure the immediate freeing of the clutch when the pedal is depressed. 181. 16-9 Armstrong-Whitworth Clutch.— Fig. 117 shows the construction of this clutch. The ckitch casing is a steel casting fitted with four keys, which transmit the drive from the engine through the outer set of plates to the inner set of plates secured Fig. 116.— Argyll Plate Clutch. on a boss attached to the cone end of the clutch- shaft. There are twenty-six driving and twenty-six driven plates alternately assembled in the casing. The spring barrel slides upon the clutch-shaft and contains the spring which keeps the plates in contact when in action. The load upon the spring is adjusted by means of the lock-nuts at the rear end of the clutch-shaft, while the forward end of this shaft has a small universal joint to permit of slight displacement of the axes of the crank and clutch-shaft. CLUTCHES AND BRAKES 231 When the clutch pedal is depressed, the spring barrel is drawn to the rear by the trunnions at the rear end, releasing the plates. The locking device to the nut-securing boss which carries the inner set of plates to the clutch-shaft is shown in inset. 182. The Lanchester Clutch. — As with many other details of the Lanchester car, the clutch and brake illustrated in Fig. 118 are distinctive and differ from the usual practice in that they are 232 MOTOE CAR ENGINEERING placed after the gearbox, and are incorporated in one oil-tight casing. They have also a separate oil pump for supplying oil to the working parts. The arrangement of plates is similar to that already described, •CLUTCH / CLyTCH ACTUATINO ^ IIUKt ACTUATINa THRUST / LEVER ^^^^ LEVER EXTEBN RINGS BRAKE INTERN RINGS f J DHVING fOT ' COUNTER THRUST BEARIKC Fig. 118.— Lanohester Clutch and Brake. and they are operated through the end of the clutch casing by plunger rods, these rods being actuated by the clutch spring out- FlG. 119.— Sheffield Simplex Clutch. side the casing. The inner set of plates slides over six keys and the outer set over four. The reaction of the clutch thrust is taken through to the counter thrust bearing near the driving pot. The brake is similar in construction to the clutch, but i? CLUTCHES AND BRAKES 233 operated by the lever shown, which presses upon a ring at the rear of the rings. 188. The SheflBeld Simplex Clutch is shown in Fig. 119, and is similar in general design to, though differing in detail from, the Armstrong- Whitworth clutch. The method of operation is, however, distinctive, as the depression of the clutch pedal first declutches the gear through the medium of a cam and a further movement applies the brakes. This is shown in the figure, the 234 MOTOR CAR ENGINEERING cam being in engagement on the end of the lever which pivots about a centre forward of the clutch pedal axis. 184. Wolseley Clutch.— In this clutch (Pig- 120) the casing which carries the outer set of plates is bolted to the flywheel casting, and that for the inner set to a universal joint, the whole being mounted upon an extension of the crankshaft. It will be seen that the direction of action of the spring is towards the rear. The thrust necessary to actuate the clutch is taken through the universal joint, which is fitted in order to allow for the dis- placement of the axes of gear and crankshafts due to the wear of the bearings for the latter. The rear end of the universal jointed shaft works in a sliding universal joint, which accommodates itself to variations in the relative position of clutch and gearbox from any distortion of the chassis framing. The clutch is operated by a lever pressing upon a ball-bearing flanged ring, as shown. 185. Brakes. — The primary reason for fitting braking mechanism to a car is to enable the driver to bring it rapidly to rest if desired, and to lock the car in position when standing still. If a car was permitted to travel down hill with the brakes removed, it would soon attain such a s.peed as to be beyond the control of the driver, so it is highly essential for the braking gear to be efficient and in good order, as the safety of both the passengers and the public depends upon its satisfactory condition. The reader should see in what manner the brakes reduce the speed of a vehicle. A body travelling at a velocity of v feet per second has energy stored up in it which is called "kinetic energy," and equals -= — , where W is the weight of the car in lbs. and g is the acceleration due to gravity (32'2 feet per second per second). If the velocity of that body is changed to one of v^ feet per second, then the kinetic energy stored in the oar is altered to , and in eifecting the variation in velocity energy has either been added or abstracted equal to the difference in the value of kinetic energy. This is represented by the equation : — W Kinetic energy given out by the vehicle = -h~ (i"^ — ''i^). When the car is brought to rest vi = 0, and so the value of the right-hand W v'^ side of the equation becomes — = — . This energy has to be absorbed by some medium, so is effected by applying the brakes and converting it into heat at the brake drums. The brake shoes are pressed against the drums by a total CLUTCHES AND BEAKES 235 force F, and if the coefficient of friction between tlie surfaces is n, the retarding force at the drums is F ii., and if the rim of the brake drum passes through a distance D during the time that the change of speed is effected, the work required to be done to overcome this friction is P m D ft.-lbs. This must equal the kinetic energy given out by the car, and therefore ; W ^1-Ufl _ ,:■?) = F f, D. Thus it is seen that the energy stored up in a moving vehicle is absorbed by the friction at the brake drums, which dissipate the heat there generated by radiation to the atmosphere and by conduction to the metaUic parts in contact. It is obvious that the materials of which the brakes are composed should be able to withstand the rise of temperature caused by this heat, and there- fore it is preferred that they be made of metal and have large area. Leather is not desirable, because it soon becomes charred and requires frequent attention. In the Mercedes' chassis a special water tank is provided for supplying the brake drums with cooling water, which is used at the discretion of the driver. There is, however, a limit to which a car can be braked, which is dependent upon the friction between the tyres and the road. The energy stored up in the car impels it forward, and is resisted by the force acting at the po'int of contact of the road wheels with the ground due to the action of the brakes in attempting to prevent rotation. The limit to the magnitude of this force is the product of the weight of the car supported by the wheels on which the brakes are acting and the coefficient of friction (/^i) between the tyres and the road, and if the car travels through a distance S feet during the reduction in speed, the work, do no by friction at the road wheel is Wi ij-i S. This must also equal the kinetic energy given out during the change of velocity. W Therefore Wi mi S = ^ {v^ — v-^), where Wi is the weight on the braking wheels. The value of the coefficient of friction is a maximum when the wheels are rolling upon the ground and no slipping is taking place, as from experiment it has been determined that the friction of rest is greater than the friction of motion, or, in other words, that the coefficient of friction when rolling is greater than when sliding. Thus the brakes are most effective when the retarding force exerted by them is just below that which would 236 MOTOR CAR ENGINEERING cause slipping. It may be noted that there is probably not a single car upon the road on which it is not possible to lock the wheels by putting the brakes hard on. Brakes require very careful design, every part receiving the fullest attention, as a weak spot, either in the brake itself or the actuating mechanism, may prove fatal. There are generally two brakes upon a car — the foot-brake, for general service, and the hand-brake, for use when stopped. But when long declines are being negotiated, it is well to alternate the hand and foot-brakes in order to rest the foot and to give the brakes an opportunity for cooling. It need hardly be stated that adjustment for wear must be provided. 186. Brake EecLuirements. — It is necessary for brakes to be effective when descending a hill, but it is as important to see that the brakes are capable of holding a car in making an ascent, as it is frequently desired to stop the car when only some portion of the hill has been traversed. Brakes should not be of the type that happily has long since been dispensed with, in which the action of the brake drum in the forward direc- tion, caused the band to tighten up and produce locked wheels ; while in reverse the brake was of little service because the tendency was to unwind the band and reduce the braking effect. Brakes should also be constructed so that the minimum of adjustment is required even after long periods of use. Nothing could be more objectionable than the frequent attention which is sometimes necessary to brake gear, as when the shoes do not have a very great amount of movement between their " on " and '■off" positions. The necessity for the use of materials which are neither subject to damage from long use, nor liable to seizure from the same cause has already been mentioned. 187. Types of Brakes. — Brakes may be divided into two classes— the internal and the external, the former being generally used for the axles and the latter for the propeller shaft. The internal brake has some advantage in that it may be practically entirely enclosed and thus be made so as to exclude all dust and grit. The tendency at the present day is towards the calliper or locomotive type of brakes with metal surfaces (see Fig. r24). They may also be classified according as they are applied to the front or the rear wheels. The advantage attaching to the CLUTCHES AND BRAKES 237 use of front-wheel brakes, beyond those which will be detailed later, is the increased braking effect obtained. It was stated in Art. 185 that there was a limit imposed to braking by the weight upon the wheel. If the brakes are placed upon all four wheels, it is clear that the total retarding force must be greater than if they are on the rear wheels only. But there is another aspect of the question, namely, that in connection with the distribution of load upon the axles. When a car is ascending a hill, the load on the rear axle is greater than that on the front axle, as the weight always acts vertically through the centre of gravity of the car ; while when descending the loading is reversed, and' consequently the brakes are more effective in the front than on the rear axles. The same remarks apply also to driving upon the level, as when braking the load is increased on the front axles due to the action of the brakes. The propeller shaft or foot-brake is also mechanically bad, as it cannot be considered good practice to transmit the braking force right through the transmission gear, even though an equal retarding action is produced at road wheels. It was the difiSiculty of applying and actuating front-wheel brakes that delayed their adoption"; but during recent years much has been done in this direction, with the result that satisfactory designs are in everyday use giving efficient service. When brakes are applied to the road wheels, there is a separate brake drum to each wheel, and as it is necessary that the force exerted by the driver should be equally divided between the two brakes, a balance gear is fitted as shown in Fig. 123. The rod from the brake lever is attached from the middle of a link, the ends of which are held by levers. These levers are separately secured to two tubes, and at each side of the chassis a lever is fitted, one to the inner tube and one to the outer — to which the brake actuating rods are attached. In the illustration (which is for the 15"9 Armstrong-Whitworth Chassis) it will be observed that the ends of the compensating link are spherical, so that freedom of movement is ensured in all directions. 188. 15"9 Armstrong-WMtwortli Brakes. — The foot-brake fitted to this chassis is shown in Eig. 121, from which it may be seen to be of the band type. Two steel stampings, faced with cast- iron liners, are pivoted about pins which are screwed into the lower portion of the gearbox. At the upper ends of these 238 MOTOE CAR ENGINEERING bands rollers are fitted which engage with right and left-hand cams on the cross-brake shaft (see plan), and a disengaging spring is placed between them. When the brake shaft is rotated by the lever at the off-side end the bra;ke bands may be made ■^ m F4 60 a o a to engage or to free the brake drum according to the direc- tion in Avhich the lever moves. The adjustment is effected by moving the cams round upon the shaft and locking them with lock-nuts provided. The hand-brakes which are of the expanding form are CLUTCHES AND BRAKES 239 240 MOTOE CAR ENGINEEEING t Cy ±j^ ^^z^ sih. ss^ I CLUTCHES AND BEAKE8 241 illustrated in Fig. 122, and act within drums attached to the back-wheel hubs. Inside these drums the expanding shoes ai^ fitted, which are pivoted on brackets secured to the axle casing. The shoes are expanded by means of cams between the two lower ends, being held against the cams and free from the drums by the springs shown. The brake cam is lubricated by grease-cups. The attachment to the compensating gear, Fig. 124. — ^Wolseley Propeller-sliaffc Brake. as well as the method of adjustment, is clearly seen from the figure. 189. The Wolseley Poot-Brake is illustrated in Fig. 124, and is of the calliper or so-called locomotive type, the actuating gear and connections with the brake pedal being shown in Fig. 125. It is pivoted about a pin secured to a bracket placed on top of the gearbox, so that the two shoes are able to swing freely in a vertical plane. The adjustment of the brake is effected by the long nut seen in the lower portion of the figure, which is self- locking from the nature of its contact with the brake lever. M.C.E. B 242 MOTOR CAR ENGINEERING The position of the pedal is adjusted by means of the nut on the actuating rod (Fig. 125). This may be carried out on the road. The left-hand shoe is kept clear of brake drum by the spring shown, which withdraws the shoe until it touches the adjustable stop near the left-hand corner, and the separation of the other Fig. 125.— Wolseley Pedal Gear. shoe is effected by the spring placed between the lower ends of the shoes and around the adjusting screws. 190. Napier Brakes. — The foot-brake for the 30, 40,- and 60 h.p. Napier cars is of the same type as that on the Armstrong-Whitworth, but the attachments for actuating, as well as the adjusting mechanism, are somewhat different. The lever for engaging the brake is connected directly to the brake shoes (see Eig. 126), while the adjustment is made by means of the nut seen in the illustration. Engagement and disengagement is caused by the movement of the brake lever without the use of springs. The side brakes used on the chain-driven six-cylinder car are as shown in Fig. 127, and these are of the expanding type. By CLUTCHES AND BRAKES 243 rotating the lever pivoted on the radius rod, it is caused to engage with a bent lever, to the extreme end of which the brake shoes are connected, thus applying the brakes. The bent lever is kept in contact with the roller on the actuating lever by a spring attached to the brake shoes. The brakes, as may be seen from the diagram, are within the chain wheel. 191. Sheflaeld Simplex Rear Brakes (Fig. 123). — These expanding brakes are very interesting in that both the head and Pig. 126.— Foot-Brakes for 30, 40 and 60 h.-p. Napier Cars. foot brakes are enclosed in one casing — the inner brake being pivoted in the front and the outer brake at the rear of the axle. The inner brake is operated by the pedal and the outer brake by the hand-lever. 192. Front-wheel Brakes. — The principal advantages attaching to the use of this class of brakes have already been mentioned, namely, the increased braking effect obtained and the removal of braking stresses from the transmission gear. But there is another and almost as important benefit that may be derived from their adoption, as the tendency of the brakes to cause side- slipping is practically eliminated. E 2 244 MOTOK CAE ENGINEERING When a car is travelling along a road and the brakes are applied so that the rear wheels are locked, the car will continue to move in the same direction so long as the steering wheels are pointing straight ahead ; the coefficient of friction is the same at both wheels, and the centre of gravity of the car is near the middle line, but immediately these are departed from, a turning CLUTCHES AND BRAKES 245 couple is produced which tends to cause the rear of the car to move sideways. Now in practice, the conditions necessary for straight Une motion are seldom present, and therefore, if the surface is in any way greasy, a side-slip takes place. If, how- ever, the front wheels are locked, the wheels lose their power of directing the, car, and as the friction of slipping is less than the friction of rolling, there is less resistance to the motion of the locked wheels, which therefore continue on in a straight line. Side-slip may be produced in a small degree when the surface over which the front wheels are travelling has a much higher 1 1 1 R I^HBii^ wKKr^\^^m^n^^ ■ -^^^^BBI ^ ^^»*t^ ^" ^fe ^^K^ a: " fm ^^■/*-;' AH ^ K d H tm K '^K wH MH^Hb 1 Wa ^ Y wm K^ ^^^^HI^^^^Hr vr^aH ^ " jp ■ ^^^^^L\. i ■ Mis^mM Eia. 128. — Sheffield Simplex Eear Brakes. coef&cient of friction than that on which the rear wheels are moving and the front wheels are in any way retarded, but this condition may be said to be so severe as to be out of the bounds of possibility in actual service. Similarly, if a corner is being negotiated, the centrifugal force will cause the rear to diverge if rear brakes are fitted, while with front-wheel brakes the car will continue on in a straight line, as the friction of rolling is greater than the friction of sliding. But this may be corrected by the release of the brakes, and applying them again immediately the wheels commence rolling and resume their directive capacity. In applying front-wheel brakes it is, however, very desirable that centre-pivot steering should be employed, aS' otherwise 246 MOTOR CAR ENGINEERING excessive forces will react upon the steering gear, while there is a tendency towards side motion if unequal braking is obtained. Further, the front axle and its attachments require to be stronger in order to withstand the braking stresses. 193. The Crossley Front-wheel Brakes. — These brakes embody centre-pivot steering, and as practically all the operating gear is mounted oh the wheel, the disturbing effect of the rise and fall CLUTCHES AND BRAKES 247 of the axle due to inequalities in the road is avoided. The con- struction of the brake may be seen from Fig. 129, and the method of operation is as follows : The rod A running along the axle is operated by the foot pedal, and carries at one end the trigger B, which, on depressing the foot pedal lifts the pin C passing through the centre of the axle swivel. The top end of this- pin thus causes the rocking lever D to operate, rotating the circular cam E from right to left. The rotation of the cam lifts the four brake shoes G, pressing them against the inside of the brake drum H. As the brake shoes are pivoted about points K, on the brake pedal being released, the cam is returned to the off position by means of the springs shown on the drawing, and the rollers P lift the tail of the shoes, and thus posi- tively release the brake. The detach- able wire wheel M is removable by means of the special spanner provided for the purpose, and the wheels are driven by the driving studs L, which are securely attached to the inner hub R. The whole of the brake mecha- nism is most accessible, as the inner hubs can be very quickly removed simply by removing the cover plate T and unscrewing the nut S. The stub axle P, complete with the inner hub E, can then be removed, leaving the brake mechanism in position. The front-wheel brakes which were formerly fitted to Crossley cars are shown in Fig. 130. They consisted of two expanding shoes placed within the wheel hub and were operated by a lever which pressed down a rod passing through the steering pivot. The movement given to this rod acted upon two toggle levers and brought the shoes into contact with the drum. 194. Arrol-Johnston Front-wheel Brakes. — These are illustrated in Fig. 131, and present a very simple solution of the front- wheel braking problem. It will be observed that the axis of steering pivot is sloped so that it intersects the point of contact of the tyre with the ground. The brake is formed by a band which is interposed between the brake drum and a spider frame, and has a short rack cut on WB M LvVt:-^ ^^ ih^%f lH Fig. 130. 248 MOTOR CAR ENGINEERING CLUTCHES AND BEAKES 249 its free ends. The racks engage with two toothed sectors which are also geared together. To one sector a lever is secured, carrying an adjusting screw which rests on the boss of the operating lever. The operating lever fits over a cam upon the top of the steering pivots, so that when this lever is moved by the brake pedal, the lever to which the sector is attached is raised and the sector itself rotated, bringing the brake into action. Springs are provided to take the band out of i rs «f ^ m /A^^^ ;: HH^WMHp'J^ -|^ jy.g^aMFFT. : ^4-' Fig. 132. — Adams' Front-wheel Brakes. action and prevent rattling at the teeth, while the adjustment of the brake is determined by the position of the adjusting screw. 195. Adams' Front- wheel Brakes are of the expanding type, and may be seen on reference to Fig. 132. The brake shoes are brought into engagement with the drums by a wedge-shaped piece connected to a rod passing through steering pivot. This rod is operated by a lever of trigger form, and is kept in contact with it by a spring at the upper end. The release of the brake is effected by the springs shown in the figure. Adjustment for wear is provided by a screw fitted to the end of the trigger lever, and connection is made with the brake pedal by a Bowden wire attached to a compensating gear near the pedal. 250 MOTOE CAE ENGINBEEING Questions on Chaptee XV. (1) Name the requirements which a good clutch should fulfil. (2) Compare the various types of clutch used in automobile work on the basis of : — (ft) Cheapness of manufacture. (6) Base of engagement. (c) Long life. (d) Power transmitted. (3) Sketch and describe a good type of clutch, preferably either a plate or a multiple disc clutch. (4) In what distance can a car, travelling at 20 miles per hour, be brought to rest if the weight of the car is 1-J- tons and the coef&cient of friction between the tyres and the road is 0'4. You may assume that three-fifths of the weight of the car is on the braking wheels. (Answer. 55"6 feet.) (5) Name several types of brakes and point out their merits or demerits. (6) Sketch and describe a good type of foot-brake. (7) Why is braking through the transmission gear to be deprecated ? (8) "What arguments may be used in favour of front-wheel braking ? (9) Name one type of front- wheel brake and discuss its principal points. (10) Why is a compensating gear necessary for the rear-wheel brakes ? Sketch an arrangement which may be fitted. CHAPTEE XVI CHANGE-SPEED GBAES 196. The necessity for a change-speed gear arises from the fact that the speed of maximum torque of the petrol engine is practically at full power, and that as the speed of revolution is decreased, the torque from the engine decreases also. It is not, however, desirable to always drive the car at high speed, and, further, the nature and resistance of the road surface varies greatly, so much so, that it is often requisite for the full power of the engine to be developed at a comparatively low speed of the car; so obviously some means are necessary whereby the car's speed may be reduced without effecting a great reduction in the power of the engine. Lastly, the petrol engine cannot be reversed, yet it is occasionally desired to propel the car back- wards, so some mechanism must be employed to render this possible. To do this silently, efficiently and conveniently has been the aim of many inventors, but there are only two forms of gear which have attained any extended practical use, namely, the sliding gear and the epicyclic gear, and these both use toothed gearing. Friction gearing, hydraulic gears and other means of transmitting power have received attention, but do not seem to have had sufficient merit to more than compensate for the existence of some vital defect in their construction. It is, therefore, the sliding and epicyclic gears that will receive the greatest attention in this chapter. 197. Position of Gearbox. — The general practice in automobile work is to place the gearbox immediately after the clutch, but in modern work examples may be found where it is incorporated in the differential casing. It is claimed for this method of construc- tion that, firstly, a reduction of noise and vibration is effected because the gearbox is completely separated from the chassis frame ; secondly, that a longer propeller shaft is made possible, and therefore less wear takes place at the universal joints and 252 MOTOR CAR ENGINEERING strains on the mechanism ; thirdly, that an increased efficiency is obtained by reason of its compact and rigid construction, and,, lastly, that the transmission gear is simplified and the cost of manufacture reduced. These points indicate that the back-axle gearbox is not without merit, as all are fairly well substantiated on closer examination. Examples of the rear-axle gearbox are shown in Figs. 133 and 134. Against these advantages, however, there is the disadvantage that the unsprung weight is increased. The direct result of this is that the road shocks will be much more severe upon the tyres and the transmission gear, and, consequently, a heavier construc- tion is desirable. It remains to be seen whether the gain in the Fig. 133. — Sheffield Simplex Three-speed Geaihox. directions indicated above more than compensate for the extra expense involved by the, additional wear upon the tyres. 198. Number of Speeds. — There has been a considerable amount of discussion as to whether three or four speeds are necessary, but the question really resolves itself into whether three or four speeds are used. It is obviously of little use for manufacturers to provide a ear with three speeds if the driver only uses the direct and, perhaps, a low speed for starting on hills, yet this is what happens daily, especially in the high-powered cars. The ideal gearbox would be capable of giving an infinite range of speeds, because in order to obtain a high efficiency and low petrol consumption, engines must be run at nearly their full speed, and the larger number of gear ratios the nearer would the engine approach that which is correct for the particular running conditions. The improvements which have been made in engines have CHANGE-SPEED GEAES 253 254 MOTOR CAR ENGINEERING been largely with the object of eliminating vibration at high speed, with the result that they are as quiet under load at 1,000 revolutions per minute as at 500. If, therefore, it is possible to run an engine at the higher rate and thereby increase the mileage per gallon, the change-speed gearbox must be used to the fullest extent. These remarks apply principally to those conditions which exist when the engine is required to develop its full power, for the engine should never be loaded as to cause its speed to decrease. The gearbox is provided so that the engine speed may be maintained and the car speed reduced. Circum- stances do not always, however, permit of the full power of the engine to be generated as traffic, and other restrictions govern the speed at which it is safe to drive a car, and then the regulation of the engine speed must be effected by -the control levers, but where the nature of the road necessitates high powers, it is better to change down than allow the engine to labour, as is frequently the case. One of the factors which should govern the number of gears to be provided is the relation which the power bears to the weight of the car — the smaller this ratio the greater the number of gears, because it will be necessary to change speed oftener. With high- powered cars it is seldom requisite to change down, as under few circumstances, if any, is it possible to run the engine "all out" in this country, consequently such cars do not require a large number of gears. But with smaller and medium-powered cars, especially those with heavy bodies, it is of first importance that sufficient and appropriate choice is given to the driver. The locality in which the car will generally be used is also a matter which merits some attention, as in many cases cars are either under-geared or over-geared. But from the conditions of manufacture it is not possible to provide a large number of gears (although some firms offer alternative gear ratios), except by greatly increasing the cost of the car, so a compromise has been effected by adopting either three or four speeds. Bearing in mind what has already been said, it will be clear that the latter is the more desirable, but in cars with a high power-weight ratio the former suffices for any work which is likely to be met with in England, and in most cases for Continental travel also. The increase of the number of gears is not, however, without CHANGE-SPEED GEAES 255 some drawbacks — the additional gear necessitates a greater length of box and therefore an increase in its weight and in the diameter of the shafts, while the actuating gear must also be more complicated. Still, the saving effected by having a greater range of gears, if suitably chosen, would in many cases counter- balance any extra expense from these causes. An interesting case where provision has been made for the different ratios of gearing required in town service and when touring is shown in Fig. 134. This gearbox is supplementary in its character, as a three-speed gearbox is provided in the usual position on the chassis, the object of the gearing illustrated being to allow of a direct drive on two ratios of gear. A is the propeller shaft carrying the sliding clutch B, which is actuated by a hand lever. C is a bevel pinion, with eleven teeth, solid with shaft to which the clutch D is secured. E is a bevel pinion with fourteen teeth, solid with the extension sleeve and clutch F, the shaft carrying pinion C being free to revolve in the sleeve carrying E, the pinions engaging respectively with the two rings of teeth on crown wheels H. When clutch B on the propeller shaft is in engagement with clutch D and pinion C, the lower gear ratio is in use, whereas if B is in engagement with F, the higher gear ratio is in service. The shaft carrying C does not revolve rapidly in the sleeve carrying E, as they both rotate together, but at speeds varying as the number of teeth in the two pinions. 199. Which Speed should be Direct? — The answer to this question is — that speed upon which most work is done. One of the reasons why drivers will not change down to an indirect gear, although they are fully aware that they should do so, is that it is not so quiet. No matter how carefully a gearbox is designed and manufactured, there must be some loss of power where gearing is interposed between two shafts, and therefore not only is the direct drive more silent but it is more efficient. At the present time the direct is usually on top, but in some cases where four speeds are provided the third speed is direct. In the latter case the ratio of the gears must be carefully chosen, as otherwise, instead of the speed being increased it may be actually decreased on changing to the indirect, because the power required at the road wheels to enable the car to travel at the higher speed is greater than the engine is capable of 256 MGTOE CAK ENGINEERING transmitting through the gearing, and consequently the engine "flags." If the throttle of an engine is nearly fully open on the direct drive, it is of little use changing to the indirect higher gear. It is usual to arrange the gear ratios in geometrical progression, as this gives a fairly suitable range of speeds, provided that the upper and lower limits of speed are well- chosen for the power and weight of the car. 200. Types of Gears. — The two principal types of gears have already been mentioned — the sliding and the epicyclic gears. The sliding gears may be divided into two sections — the CHANGE-SPEED GEARS 257 M.C.K, 258 MOTOR CAR ENGINEERING straight-through or " shaft-to-shaft " gear and the " return- shaft" gear. With the straight-through gearbox there is no direct drive, but the power is transmitted from the clutch-shaft through one set of wheels to the propeller-shaft, which lies parallel to it. This is not without merit, as the loss due to the gearing is only from one pair of wheels, and not two pairs as in the indirect of the return-shaft gearbox, so that although a loss is always experienced, its magnitude is only one-half that which it would otherwise be. The gearbox is therefore very suitable for small-powered cars where changes of gear are inevitable and frequent. In the return-shaft gearbox, of which several illustrations are given, the clutch-shaft and the propeller- shaft are in line, the forward end of the latter running in an extension of the former, or vice versa, while a separate shaft, known as the lay-shaft or secondary shaft, is placed parallel to it, and carries a sleeve upon which one set of gear wheels are mounted. This lay-shaft is usually continuously driven by gearing from the clutch-shaft at the front end of the box, but in one example the gear is arranged at the rear end, so that when the car is standing the lay-shaft is stationary. There are, however, other devices employed to avoid the continuously rotating lay-shaft. Dog-clutches for transmitting the direct dirive are provided at the junction of the clutch and propeller-shaft, and are brought into engagement by sliding one part relative to the other. In some cases internal- toothed wheels come into engagement for the direct drive, as in the Deasy and Napier clutches. The gear wheels which enable changes of speed to be effected are assembled upon a sleeve, which slides on the part of the propeller-shaft within the gear- box. For the indirect speeds the drive is taken from the clutch- shaft to the wheel on the propeller-shaft, which has been brought into mesh with it, and from thence to the road wheels. Trouble was at one time experienced in efficiently lubricating the ends of the clutch and propeller-shafts, which worked one within the other, but this has been overcome by the adoption of improved methods of construction and by the use of ball-bearings at that part (see Figs. 136, 138, 140, etc.). Formerly the sliding wheels upon the propeller-shaft extension transmitted the drive either through a sqi;ared shaft or through a single key, but both methods were difficult to manufacture so CHANGE-SPEED GEARS 259 that free sliding of the sleeve was permitted without rattling taking place, especially when wear occurred, and they have since given place to either octagonal or castellated shafts, which do Fig. 137. — Armstrong- WhiWortli Change-speed Gear Levers. not wear as rapidly, nor are the effects produced as marked. Examples of the latter are shown in Figs. 135, 139, and 141, where it may be seen that sometimes four and sometimes six s 2 260 MOTOR CAR ENGINEERING castellations are provided. These take the form of raised keys upon the surface of the shaft, and may be made either solid with or be recessed into the shaft. Of the two, the former is to be preferred, as a more substantial job is produced. Another method has been used, namely, the toothed shaft, which is some- what similar to the castellated shaft but has finer castellations, so that the surface appears to be a long-toothed wheel. In all these forms, however, careful design is necessary in order to prevent continual use in a more or less limited length of the shaft from causing a distortion of the projections, with subsequent jambing when changing to another gear. 201. Gate Change. — The gate change which is so universally fitted to modern cars is, perhaps, one of the most marked improvements made in the history of automobilism. Prior to its introduction the ordinary locomotive type of lever, with its continual motion in one direction, was used for changing gears, with the result that to change from one gear to another would doubtless mean the meshing of gears in between. This was not, however, its only disadvantage, for if care was not exercised there was a probability of overshooting the gears, and the lever was also often in an inaccessible position, because of the large movement of the levers necessary to effect the changes. The sliding wheels on the lay-shaft were assembled upon one sleeve, and to change speed necessitated the movement of all the wheels. By the adoption of the gate change the sleeve carrying the gear wheels on the lay-shaft was divided, each half being actuated by separate rods, so arranged that either could be moved independently of the other, thereby reducing the range of movement in the gearbox. This permitted of a reduction in the length and weight of the gearbox, and as shunter shafts were possible, the deflection was less, so that better action of the teeth was also obtained together with a longer life. Further, the change-speed lever, owing to its limited motion, was always in an accessible position, and any gear could be at once put into mesh- These advantages caused its extended use as soon as this became possible, so that now it has become almost general. It is sometimes pointed out that, whereas in the older gear only one motion was necessary to change speed, in this form three are required ; but this is a matter of very little importance as the opuration is never required to be readily effected. CHANGE-SPEED GEARS 261 The gate change takes its name from the form of the bracket in which the change-speed lever moves. This is a curved jjlate having two slots in it for a three-speed gearbox and three slots for a four-speed gearbox, the bar between the slots beihg cut away at the middle, so as to permit the lever to move from one slot to the next. When the lever is at the far end of any one slot, a gear is in mesh, and when in the middle all wheels are out of gear, the lever being in the " neutral " position. Thus for three speeds the ends of the first slot will be the top and second gears, and the ends of the second slot the first and reverse gears. Deasy Gearbox — Plan. To change from the top gear to the first, the lever will be brought to the neutral position, moved inwards towards the car and then forward to the end of the second slot. An excellent example of this type of gear is shown in Figs. 135 and 136 for the four-speed and reverse gearbox on the Armstrong- Whitworth 15"9 chassis, while others are given in Figs. 138, 140 and 141 for the Deasy, Wolseley, and Austin cars. In Fig. 137 the change-speed lever is shown attached to a shaft, to the other end of which a striking lever is secured within the gearbox. The lower end of the striking lever engages with a slot in a rod, Fig. 135 (there are three shown), to which the shifting forks (Fig. 136) are attached. When the gears are in neutral, the slots in the striking rods are in line, and by moving 262 MOTOR CAE ENGINEERING the change-speed lever across the car the striking lever may be brought into engagement with any one of the three rods, and then any gear can be operated direct. This is called the selector i32 I mechanism. The position of the reverse pinion with its striking gear is clearly shown in Figs. 135 and 139. To prevent any possibility of two gears being in engagement at the same time, as might happen if one striking rod was in operation and another moved from its neutral position through the vibration of the car, a locking device is provided (see the two CHANGE-SPEED GEAK8 268 upper sections in Fig. 135). This consists of a pendulum in the form of a sector of a circle having a notch cut in its circum- ference through which the striking lever is allowed to pass, the remainder of the circumference fitting in jaws on the striking rods which are not in engagement with the striking lever. Thus the rod which it is desired to operate is free to move, while the others are prevented from sliding in either direction. The pendulum swings with the striking lever. Another form of locking gear, though of somewhat diiTerent design, is illustrated Fig. 140.— 20-28 Wolseley Gearbox. in Fig. 139, as the locking pendulum is replaced by a part which slides upon a rod secured as shown. Provision is also made to prevent the gears from moving when in engagement or in neutral. This is done by fitting spring- loaded balls, which rest in recesses in the ends of the striking rods, so that some force must be applied to the rod in order to move it, and is clearly shown in Figs. 135 and 140. Balls are provided for the three positions of each rod. Various forms of striking gear are clearly illustrated in the various figures, and require little explanation. Occasionally a catch is provided, which must be raised before 264 MOTOR CAR ENGINEERING CHANGE-SPEED GEAES 265 the reverse can be put into mesh, so that it may not be inadvertently engaged. 202. Napier 45 and 65 h.-p. Gearboxes : — These are illustrated in Fig. 142. It will be seen that the indirect gears slide upon the secondary shaft and that only the direct drive is in the Fig. 142. — 45 and 65 h.-p. Gearbox. clutch-shaft. There is another feature of interest in this box, in that the small gear wheel C, which is shown driving the lay- shaft, is also used for the top direct speed. To do this it is taken out of mesh with the wheel on the lay-shaft and engaged with internal teeth in the larger of the wheels D, and therefore in this position leaves the lay-shaft stationary. The action of coming out of top speed again puts the lay-shaft in gear. 266 MOTOE CAR ENGINEERING 203. Epicyclic Gears. — The superiority of this type of gear over the ordinary sliding gear must be at once recognised, as the gear change is so simple that even the most inexpert cannot make a mistake — it is practically foolproof. But this is not the only point which recommends it, as the constant meshing of the gears, together with the short shafts which are fitted, enable the iteeth to engage correctly and thus contribute to the longevity and silence of the mechanism. But it is presumed that it has not been greatly used, except on two or three makes of car, because epicyclic gears are largely proprietary, and also because owners like to fully understand the operation of the component parts of their car. The latter difficulty is often a very real one, but if the problem is attacked correctly, little trouble should be experienced in see- ing exactly how the gear ratios are produced. The question of cost and the difficulty of designing for any number of gear ratios must enter into the question of its adoption by any particular manufacturer. Fig. 143. Fig- 143 shows diagrammatically the construction of an epicyclic gear, in which B is the sun wheel driven by the engine, A are two planet wheels supported upon a frame connected to the propeller-shaft, and is the brake drum which is held stationary when the gear is in action, and which has teeth cut on its inner surface. It will be clear that if the is free to rotate, the centres of the wheels A will remain stationary, and the rotation of B will simply rotate thb wheels A on their centres, which will in turn rotate anti-clockwise, because the resistance to O's motion is less than the eflort required to move the car. Therefore, when is released by the brake drum, no effort will be transmitted to the road wheels. But when is held by the brake drum, a clockwise motion of B will cause an anti-clockwise movement of A, and A will roll on the teeth in in a clockwise direction. This is the general explanation of the action, and must be clearly seen before proceeding further. Now it is a matter of indifference whether the motion is derived from the propeller-shaft or from the sun wheel, so far as the ratio of the gear and CHANGE-SPEED GEARS 267 the action is concerned ; all that is is required is to find the relation between the revolutions of the propeller-shaft and those of the engine. It simplifies the explanation, or rather it enables one to see the actions more clearly, if the propeller- shaft is rotated and causes the rotation of the engine, although this is the reverse of what exists in practice. Let the propeller-shaft make one revolution, that is, let the centre of A make one revolution in the clockwise direction shown. If it is assumed that the teeth in C are out of engagement with A, and that the two teeth in contact in B and A are soldered together, then B will receive one revolution due to the mass rotation of the centre of A and in a clockwise direction. But when the teeth of C are in engagement with A, B will still receive this one revolution plus an additional angular movement due to A rolling on C. If A has 20 teeth, B 40 teeth, and C 80 teeth. Then in one revolution of the mass centre of A, 80 A will rotate ^77='^ times on C in an anti-clockwise direction, which will 20 produce ttt X 4 = 2 40 revolutions of B in a clockwise direction. Thus, with the numbers of teeth stated, when the propeller-shaft makes one revolution, B makes one revolution due to the mass rotation of A and two revolutions due to the rolling of A upon C, that is a total of three revolutions. Conversely, for three revolutions of the engine the propeller-shaft makes one revolution, and the gear is a three to one reduction gear. And generally if A has p teeth, B j teeth, and C r teeth, the reduction of gear will be 1 -f ( -X - ] to 1 = M + -') to 1. 204. Adams' Planetary Gear. — The construction of this gear is illustrated in Fig. 144, in which X is the engine shaft and K Fig. 144. — Adams' Planetary Gear. the continuation of the propeller-shaft. The pinion H is keyed to the engine shaft and gears -with the wheels E on the shafts T "268 MOTOR CAR ENGINEERING and V, which are secured to the casing as shown. The pinions D and S gear respectively with G and P — G being attached to the propeller-shaft and F to the brake frame upon which the brake band A operates. The pinion R on shaft V engages with J on the brake frame upon which the brake band C presses. For the first speed, A is tightened on brake drum. Then H drives D and ES E' -drives S, S drives F, and D drives G. But as F is prevented from rotating by the brake drum, the casing carrying the shafts T and V rotates. The revolutions made by the shaft K will therefore be the revolutions due to those trans- mitted by D to G minus the revolutions made by the casing. For the second speed, B is tightened on the casing, and the revolutions of K will be due simply to the revolutions of the gearing H, E, D and G. For the third speed, the casing and th-s drum upon which C presses are held by coil brake L on the drum Y, which is operated by the lever Q from the cone N and the lever M, so that direct drive is obtained. For the reverse, the drum upon which C presses is held and an epicyclic drive is obtained through H, E^, R, 8 and F. 205. Forms of Teeth. — There are two forms of teeth used in transmission gear — the cycloidal and the involute, but by far the greater number are made of the involute shape, as this form of tooth permits of the displacement of the wheel centres without disturbing the accuracy of contact. All teeth must be con- structed so that one tooth will roll upon another without sliding, for as soon as sliding takes place there is a great loss due to friction. When wheels are in permanent engagement, the teeth are sometimes cut at an angle instead of parallel to the axis of the shaft. The object of so doing is to render the gears less noisy, as any shock which may come upon the teeth is minimised by reason of the angle at which it strikes the tooth. There is, however, considerable end pressure due to the resolved part of the force which acts on the teeth along the axis of the shaft. To minimise this, double helical teeth are employed so, that the end pressures may balance each other. This form is somewhat expensive to manufacture if made from one piece of metal, and it is frequently the practice to cut two wheels with the teeth angled in oppbfeite directions and then bolt them together. CHANGE-SPEED GEAKS 269 Note. — The attention of the reader is particularly drawn to the methods by means of which the gearboxes are made oil- tight, the construction of the bearings, the manner in which the wheels are assembled upon the shafts, and the facilities provided for the inspection of the- wheels and fastenings and for the repair of any part. 206. Miscellaneous Gears. — These may be summarised as friction gears, hydraulic gears and the Humphris gear. So far as the hydraulic gears are concerned, by reason of the direct action of the drive, hopes are felt that more of this will be heard of in the near future, but up to now little has been done with the few that have reached the practical stage, as it is believed that the efficiency of the drive is low. In the Humphris gear, a direct drive is given to the road wheels at all speeds. The driver consists of a number of spherical projections instead of the usual teeth, and these gear into spherical recesses in a plate. By moving the driver nearer to or further from, the rear axle, any desired gear ratio can be obtained. Friction gears have attracted a large number of inventors, but they have not been extensively used, because it is a difficult matter to take up the side thrust which it is necessary to have in order to transmit the power, as the drive is taken up by the pressure between two surfaces. The magnitude of this pressure must, in any case, be large, and consequently the gear is only suitable for small powers. The efficiency of transmission will likewise be affected by the weather, as a damp atmosphere will cause the friction between the surfaces to be reduced. Questions on Chaptbe XVI. (1) Why is it necessary to fit a gearbox tea petrol car ? (2) Discuss the question : "Are three or four speeds desirable " ? from the point of view of (a) cost, (/;) weight, (c) convenience. (3) What is the difference between the " straight -through " gear- box and the " return -shaft " gearbox, and in what respects is the former superior to the latter ? (4) Sketch a four-speed gearbox with direct drive on third speed. (5) What advantages has the gate change over the old quadrant type? 270 MOTOR CAR ENGINEERING (6) Sketch the looking gear in a gate change. What is this gear provided for ? (7) Explain the action of an epicyclic gear. (8) Sketch the Adams' planetary gearbox. (9) What is the advantage gained by using involute teeth wheels ? (10) Show by sketches two methods whereby the gearbox is made oil-tight. CHAPTEE XVII TEANSMISSION GBAE 207. Strictly speaking, the transmission gear includes the whole of the gear between the engine and the road wheels, but on account of the importance of the clutch and the gearbox, these parts have received special treatment elsewhere. This chapter will therefore deal with the connections between the gearbox and the rear axle. 208. Methods of Drive. — The drive to the road wheels may be taken in one of the following ways, and in the order stated : — (1) By central chains, differential and live axle. (2) By differential, cross-shaft and side chains. (3) By propeller-shaft, differential and live axle. The last drive may be sub-divided according as the differential, gear is driven through : — (a) Bevel gearing. (b) Worm gearing. 209. Central Chains. — This type of gear is not now used except on a few of the older cars, and even on these is only applied to those of low power. The wheel on the rear axle which receives the drive from the engine is secured to the exterior of the differential casing, and this in turn is supported on the axle. This arrange- ment, it will be seen, does not lend itself to a rigid construction, and from the nature of the stresses to which it is subjected cannot be considered good practice. That this is the case will be readily obvious, seeing that in addition to the torsional stress from the engine and the vertical bending stress due to the weight of the chassis, there is also a horizontal bending stress, due to the pull of the chain, applied at the centre of the axle, where it is least able to resist it. This latter stress may, and often does, exceed that due to the weight of the chassis, as, for example, when the engine is exerting its full power at low speed. 272 MOTOK CAR ENGINEERING There is also the further disadvantage attaching to the use of a central chain in that it is difficult to effectively exclude dust and dirt, while the removal of the chain cannot be very readily effected owing to its position. 210. Side Chains. — When side chains are employed, the differential is either incorporated in or attached to the gear- box from which cross-shafts, fitted with universal couplings are taken to the side of the car. Sprocket wheels are secured to these cross-shafts, and drive through chains to similar sprocket wheels bolted to the rear wheels. This construction permits of the use of dead axles, and for this reason has been much favoured, especially for heavy vehicles, where the live axle was somewhat at a discount. There is, however, still a difficulty in properly protecting the parts from dust, so much so that frequently no attempt is made to enclose the chains, with the result that wear soon takes place and a noisy drive is at once established. Casings, where pro- vided, are usually so flimsy that after being dismantled a few times they rattle; or else they are so heavy that they are objectionable from this cause. Under any circumstances, wear is undesirable, but never more so than in such an important part of the mechanism as the transmission gear, when, the lives of the occupants of the vehicle may be imperilled should the chain break. Frequent attention is therefore necessary to ensure freedom from trouble in this direction. The noise which usually accompanies a chain drive may also be traced to another source, namely, the bad action of the chain and the wheel over which it runs. No matter how well a chain may be made, sooner or later the links permanently elongate and cause the pitch of the links to be greater than the pitch of the teeth ; so that instead of rolling on the teeth, they slip and possibly cause the drive to be taken on one or two teeth only. This defect is overcome in the Renold chain by the construction of the links, which rise upon the teeth and adjust themselves on the wheel. There is a further point in connection with chain drives which must receive some attention — the fluctuation of the angular velocity of the road wheels, due to the rise and fall of the back axle. On meeting an obstruction in the road, the rear axle rises, and in doing so unwinds a portion of the chain on the driving wheel and winds up an equal length of chain on the rear wheel, TRANSMISSION GEAR 273 while in descending the converse takes place. If these wheels are of unequal diameter, it will mean that on the up movement of the axle the road wheels will be accelerated, and as some force is required to produce this acceleration, the chains will be sub- jected to a sudden extra load, which is clearly objectionable, as it must cause wear on the tyres, and may snap the chain. In the old Lanehester chain drive this was obviated by interposing a fixed wheel of equal diameter to that on the road wheel. It may be noted that the chain drive lends itself admirably to Fig. 145. — Sheffield Simplex 45 h.-p. Diflferential Gear. rapid changes of gear ratios, which may be desirable if the car is about to be used in a mountainous district. In this case, all that need be done is to remove the driving sprockets from the cross- shafts and substitute others having a lesser number of teeth. This can be much more easily effected than any alteration to the bevels in the differential casing. 211. Propeller-shaft and Live Axle. — This system is by far the most popular, owing to the greater efficiency and the longer life of the gear and the quieter action, as all wearing parts are M.C.E. T 274 MOTOE CAR ENGINEERING enclosed in an oil-tight casing. Several examples of this con- struction are distributed in various parts of the book. The drive to the rear axle is here taken through a shaft, known as the propeller or cardan shaft, to a differential gear. At the two ends of the propeller-shaft universal or Hooka's joints are TRANSMISSION GEAR 275 fitted, to ajlow for the rise and fall of the rear axle ; but they are also necessary because the axis of the gear and the differential shaft are not in line. To enable a uniform angular velocity to be transmitted, two universal joints should be fitted, and the intermediate shaft should make equal angles with the two shafts to which it is attached. This usually means that the two end shafts must be parallel. The angle between the shafts should preferably not exceed 5 degrees ; but the joints will work satis- factorily up to about 15 degrees. Occasionally only one joint is fitted, and the differential shaft is inclined so that it is in line with the propeller-shaft, but this should not be done, although it does reduce the angle between the gear and the propeller-shafts and therefore the wear due to rotation. The angle is often reduced by inclining the engine and the gear in between it and the rear axle ; and this is much to be preferred, provided that the engine lubrication is not affected. 212. Universal Joints. — It will be seen that in all cases the axes of the pins of the universal joints always pass through the same point. This is an important feature, and constitutes another requisite for a uniform angular motion ; it also assists in giving a good rigid connection. The actual construction varies considerably in practice, but the principle upon which they operate is that the joint allows of motion in two planes at right- angles to one another. This is clear on reference to Figs. 112, 119, 120, 136, etc. The joint may be made by hinging two forks, fitted on the ends of the shafts at right-angles to one another about a central block, as in Fig. 135. But as a connection is also necessary, which will compensate for the shortening up of the propeller-shaft when the rear axle rises, a common form allows the trunnions on one shaft to work within a muff secured to the other shaft, the inner surface of which is grooved so as to permit sliding to take place. The trunnions are provided with gun- metal bushes, and the slots in the muffs are steel-faced. Instead of having trunnions, balls may be substituted, as shown in Fig. 112. Provision for the movement of the axle is sometimes made by either cutting a hexagon or by forming solid keys on the end of the propeller-shaft, as in the 15-9 Armstrong-Whitworth car. On account of the exceedingly severe work which these universal joints are called upon to perform during every revo- lution of the propeller-shaft, it is important to well lubricate X 2 276 MOTOE CAE ENGINEEEING the parts and to totally enclose them so as to exclude all dirt. It is a good practice to fill the coverings with grease, as frequent attention is thereby rendered unnecessary. 213. The Differential Gear. — The differential is fitted so that both rear wheels may revolve freely when turning. As will be seen in Art. 219, when a car deviates from a straight course, the TRANSMISSION GEAR 277 wheels should rotate about one point, and to do this the length of the path traversed by the inner wheel must be less than that over which the outer wheel travels. The drive from the engine is taken to a pinion which engages with a crown wheel secured to a frame carrying a number of bevel wheels. Where a worm drive is used, the worm engages with a wheel attached to a frame. On the two ends of the axle- shafts are secured two bevel wheels, which are in mesh with the four bevel wheels carried in the frame. 214. The Action of the DiflPerential. — When the car is travelling straight ahead, the four bevel wheels do not rotate on their axes but about the centre of the axle, carrying round the bevels on the live axle. No relative motion is produced between the bevel wheels on the frame. But as soon as the car commences to turn, one road wheel lags behind the other. If the road wheel on the side to which the car is turning is stopped by the turning of the car, the bevel wheel on the axle on that side is also stopped, so that the motion trans- mitted to the other road wheel is caused by the rotation of the bevel wheels on the frame about the centre of the axle and the rotation of the same wheels upon their own axis. Supposing that the bevel wheels on the axles have 60 teeth and those on the frame have 20 teeth. Then, if the frame makes one revolution, the bevel wheels on it will make one revolution about the axis of the axle, and consequently the outer road wheel will make one revolution due to this. The bevel wheels on the frame fin will also make ^pr revolutions on their axes and therefore will urge the bevel wheel on the outer axle forward n?; X ^ revolu- tions, that is one revolution. Thus the outer road wheel will make two revolutions while the frame carrying the bevel wheels makes one revolution, if the inner road wheel is stationary. It is clear, therefore, that by whatever amount the inner road wheel is retarded, the outer road wheel will be accelerated. Occasionally the wheels which produce the differential action are spur wheels (see Fig. 148). The merit of this construction is that it is easier to manufacture well-fitting and correctly-actioned spur wheels than bevel wheels, but there is not a great deal to be 278 MOTOR CAR ENGINEERING TEANSMISSTON GEAR 279 said to the advantage of either, as the wheels are so seldom in action and then only for a very short period of time. 215. Bevel-gear Drive. — Until recently the rear axle was almost universally driven by bevel wheels, and this method is still used on the greater number of cars. A small pinion (Fig. 149) gears with a larger bevel or crown wheel on the differential frame, and this transmits the power through the differential wheels to the live axle. To the outer ends of the axle shafts the hubs of the road wheels are secured either by keys or by suitably shaped ends as in Figs. 147, 148, 155, etc. From the figures mentioned it will be seen that all the bevel- wheels are carried in ball-bearings ; while the thrust, when the wheels are transmitting power, is taken in every case on ball thrust bearings. This is very desirable, because, from the position of the gear and the enclosed nature of the construction, frequent attention to the lubrication is not desirable. By occasionally supplying a small quantity of oil to the casing, sufiBeient lubricant is splashed about by the crown wheel to well lubricate every part. The exceptionally rigid design of the supports to the small bevel on the Austin car is shown in Fig. 149, where this wheel is pro- vided with a ball-bearing on the inside as well as the outside. Attention is also directed to Fig. 147, the 15"9 Armstrong-Whit- worth rear axle, where the axle shaft is free to move slightly endwise in the differential wheels (see also Fig. 146). The easy access to the gear within the differential casing should also be noted, as by taking off the rear cover plate all the wheels are exposed, and may be lifted out bodily by withdrawing the live axle shafts and removing the keeps from the ball-bearings. The ratio of the gearing in the differential casing should not be greater than 4 to 1, as otherwise it is impossible to prevent noise ; and, because of the small diameter of the bevel pinion, the wear caused by its rapid revolution soon becomes apparent. 216. ■Worm Drive to Differential Gear. — Under any circum- stances it is not easy to machine a truly shaped tooth on bevel wheels, although machines, such as the Bilgram bevel-gear planer, have been designed which enable a very close approximation to be obtained. But as the differential wheels are subjected to such hard wear, it is necessary for them to be hardened, and in the process of hardening they become slightly distorted ; consequently 280 MOTOR CAR ENGINEERIN TEANSMISSION GEAR 281 there is generally a small amount of clearance between the teeth. In some cases these bevels are ground in, so that a better Fig: 150.— 12-16 Wolseley Differential Gear. action may be produced, but although the slight hammering is much reduced, it is not entirely eliminated. With the worm drive, however, which has been favoured by many designers, a very silent action is obtained, as the worm Fig. 151.— 12-16 Wolseley Worm-driven Axle. slides over the teeth in the wheel when transmitting the load. But given a perfectly cut bevel wheel and a truly shaped worm, the efficiency of the former would be greater than that of the latter, as the friction of the bevel is rolling friction while the 282 MOTOR CAE ENGINEERING friction of the worm is sliding friction. However, in actual practice it is really questionable whether one is more efficient than the other when well fitted — much depends upon the way in which the worm is made and how it is lubricated. There are two forms of worms, the straight worm and the hour- glass worm (see Figs. 151, 152, 155, etc.), but although the former is much more easily cut, the latter is much to be preferred for the following reasons. The friction between two surfaces is dependent upon, the maintenance of a film of oil ; as soon as the intensity of pressure is sufficient to squeeze out the lubricant the two Pig. 152. — ^Lanchester Worm Drive. surfaces come into contact and abrasion results. With the straight worm, where the pitch line is parallel to its axis, it is doubtful whether more than one wheel tooth is in contact with the worm at any time, but as the hour-glass worm embraces a portion of the circumference of the wheel, and the pitch line of the worm coincides with the pitch circle of the wheel, an increased number of teeth are in contact, and, assuming the worms are similarly loaded, the pressure on each tooth is much reduced ; the oil has, therefore, a better chance of remaining between the teeth, and the worms are better lubricated. There is a further advan- tage to be derived from the hour-glass worm, as seeing that a greater number of wheel teeth lake the load, the stress in any one TEANSMISSION GEAE 283 tooth is much reduced, and if the same dimensions are used in both forms of worm, the latter will be much stronger. From the fact that when declutched the gearing is driven by the road wheels, it is essential that worms should be capable of being driven as well as drive, and thus they are reversible — the threads on the worm being placed, usually, at an angle of 45 degrees. This necessitates the use of multiple threaded worms. It should be observed that it is not possible to adjust the worms for wear. Ball-bearings are provided to take the thrust of the worm in both directions, as shown in Figs. 150, 151, and 152. The worm may be placed above the wheel (see Fig. 148), or beneath it, as in Figs. 150, 152 and 155. When placed above the wheel, the road clearance can be shghtly reduced, and a straighter drive from the engine obtained, but as regards lubri- cation there is not really any special merit in either position. At one time, when both the worms and the wheels were badly formed, it was essential that the worms should run in an oil bath, but nowadays, so long as the wheel teeth dip in a well of oil, sufiBcient adheres to the teeth to well lubricate the parts. ^'^- '^l-~iit^^^^t''^^''^ On the other hand, the worm is subjected to very hard usage, and if it is bathed in oil it is more likely to keep cool than if the heat generated by friction has to be conducted away along the shaft. . The worm is usually made of hard steel and the wheel of phosphor bronze. 217. Live Axles. — One of the objections which have been raised to the use of the live axle for heavy vehicles has been its apparent weakness-; but such is more imaginary than real, as by the adop- tion of a suitable design it can be made as strong as a fixed axle. The impression had some foundation in fact, because all metals take some permanent set after being in use for a short time, with the result that if the axles were initially straight, they would sooner or later slightly deflect and cause the wheels to come nearer together at the top giving an appearance of weakness. For this reason the arched axle came into being, as is illustrated in Fig. 154. Further, cast iron is far weaker in tension than in compression, and the weight of the chassis naturally causes the 284 MOTOK CAE ENGINEERING upper portion of the axle casing to be in compression and the lower portion in tension. In order to support the casing and make the axle equally strong c ) "^ on both sides, a tie rod is often fitted beneath the casing and attached to the two ends. Adjusting screws are provided, so that when deflection occurs these rods may he shortened and the axles straightened again. This also gives flexibility to the axle. In construction, the axle casing may be cast in the halves TRANSMISSION GEAE 285 286 MOTOR OAR ENGINEERING divided down the centre, as in Fig. 155, it may be of conical form and bolted to the differential casing, or it may be of tubular form enclosing the axle, as in Fig. 148. It will be seen that the first named gives very free access to the full length of the axle, and is for that reason excellent. Pressed steel axle casings have now come into general use, and are giving good res^jlts. Reference should also be made to the Maudslay forged steel axle, which from its exceptionally strong construction deserves great praise. The reader's attention is directed to the methods employed to prevent oil from creeping along inside the casing, the lubri- cating arrangements to the bearings and the manner in which the springs and braking mechanism are secured to the axle casing. 218. Ratio of Engine Revolutions to Revolutions of the Road Wheels.— In finding the reduction produced in the revolution of the engine by the interposition of gearing, it should be remembered that the ratio which the revolutions made by a driving wheel bear to those of the drhen is inversely as the number of teeth. This is best shown in an example. Supposing that the engine makes 1,200 revolutions per minute and that the indirect drive is in operation. Number of teeth in wheel on clutch-shaft is 40, and this gears into a 60-toothed wheel on lay-shaft. An 80-toothed wheel on lay -shaft gears with a 50-tootbed wheel on propeller-shaft. The pinion in differential has 20 teeth, and the crown wheel 64 teeth. 1,200 X 40 The number of revolutions made by the lay-shaft = 60 and this will give ' X ^ revolutions of the propeller- shaft. The revolutions of the rear axle therefore will be 1,200 X 40 X 80 X 20 _ 60 X 50 X 64 ~ ^""• If the diameter of the road wheels is 30 iiis., the car will then travel at 400 X 30 X ir ins. per minute = 35J miles per hour (nearly). It will be seen that by multiplying the number of revolutions of the engine by the number of teeth in the driving wheels and dividing by the number of teeth in the driven wheels, the number of revolutions made by the final wheel are obtained. TRANSMISSION GEAR 287 Questions on Chapter XVII. (1) What drawbacks are there to the use of the central chain drive ? (2) Compare the propeller-shaft drive with the side-chain drive. (3) Sketch the transmission gear between the gearbox and the rear wheels in a chain-driven car. (4) Describe the action of the differential. (5) Compare the worm drive with the bevel drive to the differential casing. (6) Make a sketch of a good form of universal joint in which provision is made for end movement due to the rise and fall of the rear axle. (7) Why is the hour-glass or globoid worm to be preferred to the ordinary or straight worm ? (8) What objections have been raised to the use of live axles on cars ? Show by the aid of sketches how the axle is strengthened. (9) Make. a sketch showing the construction of the rear axle and casing. (10) Mention two ways in which the rear axle casing is manufac- tured, and poipt out any merit that they may have. (11) Sketch a method of attachment of the springs to the axle casing. (12) How are the bevel wheels in the differential casing and the road wheels attached to the axle ? CHAPTER XVIII STBEEING GBAES 219. That the form of central pivot employed on horse carriages would be altogether unsuitable for use on automobiles is readily apparent ; for the shocks received by the wheels when travelling at high speeds would be transmitted through to the steering wheel and make driving impossible. But another reason, which is not so obvious, is that when turning, skidding would ensue, with disastrous effects upon the tyres. The early patent of 1818 by Lenkensperger and later by Eudolph Ackermann of London of a side-pivoted fore-carriage really anticipated the time when such a device would be imperative. The essence of this invention was that the wheels were carried upon short axles pivoted at the ends of the front axle and were coupled together by a tie rod, so that a displacement of one wheel was accompanied by a corresponding displacement of the other. The levers attached to the two pivots were, however, parallel, and consequently the same angular movement was given to both wheels. The invention did not, therefore, give correct steering, as the wheels had not a common centre of rotation when displaced. This was modified by Jeantaud, who produced the gear now known as the " Jeantaud- Ackermann " steering gear, which is shown in Fig. 156. In this gear the steering arms are made to converge towards the back axle, so that on the steering wheel being displaced in turning the car, one wheel will receive a greater angular move- ment than the other, as the angular displacement of the steering arms produced by the same longitudinal motion in the rod will be different for the two wheels. If, therefore, the angle between the steering arms is made a certain value, the centre line of the stub axles, if produced, will meet on a line drawn through the rear axles, and all four wheels of the car will turn about this STEERING GEARS 289 common centre without any lateral skidding. The loci of the points of intersection of the stub axles over the full range of lock should lie upon the centre line of the back axle produced, and this is the condition which a gear should fulfil in order to be geometrically correct. It is frequently stated that if the centre / I'. Pig. 156. — Jeantaud-Ackermann Steering Gear. lines of the steering arms intersect on the rear axle, perfect rolling of the wheels is obtained. But this is not so, as the point of intersection may- be in front, at the rear, or on the back axle, depending upon the ratio of the length of wheel base to the pitch of steering pivots, and even then only a compromise is effected. The error involved may rise to as much as three degrees in the displacement of one wheel at the position of maximum lock, but can be reduced so that the maximum error over the whole range M.C.B. u 290 MOTOR CAR ENGINEERING will not exceed one degree (see J. L. Napier on " The Geometry of Steering Gears " — Automobile Engineer for July, 1910). It usually commences by one wheel having too great a displace- ment, which gradually increases as the angular movement increases, so that the object of the designer is to reduce the value of the maximum error. This may easily be effected by a trial and error method, in which the wheels are set so as to have the same instantaneous centre of rotation and the length of the tie rod fixed correctly for this position. The loci of the points of intersection of the lines through the stub axles is then drawn, and the length of the tie rod adjusted as may be necessary, in order that the wheel which has too great a displacement in the early part of its movement will afterwards have too little displacement. There will, therefore, be three correct positions of steering — when the wheels are directed straight ahead and at one position on each side ; at any other position one of the wheels will skid laterally, but the magnitude will be so small as to be quite negligible. The question as to whether the tie rod should be at the front or at the back of the front axle does not really affect the problem to any great extent from a purely geometrical standpoint, but it may be considered from its mechanical features. When forward arms are employed, the shocks which may be experienced at the road wheels cause a tensile stress to be induced in the rod, and thus its length does not affect its strength ; but a rod in such a position and low down on the car is more liable to damage than when placed at the back of the axle. There is also some difficulty in obtaining sufficiently long levers for the steering arms unless rather longer stub axles are employed than is desirable. When placed at the rear, however, in addition to being guarded from damage in the event of a collision, it permits the wheels to be placed as near the steering pivots as is required and thus enables the stresses in the stub axle to be reduced, but it is subjected to a compressive stress from road shocks. Both forms are employed, and the choice of position must be made when a full knowledge of the conditions of use are known. On account of the exposed position of the steering levers and arms, it is desirable that all joints should be enclosed and provided with some form of permanent lubrication. 220. Other Forms of Steering Gear. — In the form of gear just STEERING GEARS 291 described, by increasing the ratio of the length of wheel base to the pitch of the steering pivots, the error involved is reduced. Lepape, Roger and Jenatsy took advantage of this fact when designing the steering gears which bear their names. In the Jenatsy double trapezium gear the reduction of the pitch of the steering pivots is effected by dividing the tie rod into two parts and connecting one end of each to the steering arms, while the other ends are attached to a bell crank lever pivoted on the front axle. The whole of the gear is on the forward side of the axle, and from its construction reduces the virtual distance apart of the steering pivots by one half. The Bollee gear presents a somewhat similar arrangement only on the rear side of the axle, and the centre lines of the steering arms and one arm of the bell crank lever converge upon a point about a quarter of the width of the rear axle from the wheel. In the Lavenir concave pentagon gear, the tie rod is jointed at the middle and attached to a lever situated on the fore side of the axle. None of these gears profess to be geometrically correct but to give very accurate results, so that for all practical purposes they may be considered so. Absolute accuracy in any mechanism is obviously desirable, but to produce such a mechanism requires a large number of links in order to constrain the movements of the steering arms, and because of the inaccuracies which would be introduced as soon as slight wear takes place, would be of doubtful advantage. The Bourlet sliding gear is one of the most promising of the gears which produce correct steering. In this the steering arms are formed by two slotted levers in which blocks slide, the blocks being connected to a tie rod which moves endwise in two guides attached to the front axle. But it will be seen that it is subject to the mechanical defect of having its accuracy of motion affected immediately wear of the block takes place, and on account of its exposed position and the rattle which would be caused by this wear it is not considered suitable for general use. Great care should be taken that the wheels are exactly parallel when running, and in order that this may be so, the distance apart of the centre lines of the wheels in front should be slightly less than at the back when the car is stationary, as when the u 2 292 MOTOR CAR ENGINEERING give" slightly and cause the car is in motion the gear will wheels to run parallel. 221. Steering Pivots and Axles. — In order that the effort required to steer a car may be as small as possible, and that the ■3 5 .S H oo M^ .^ ~ 00 a ;5 CHASSIS CONSTEUCTION 331 of these members is to stiffen the longitudinal girders, which, on account of the thin metal from which they are manufactured (about ^\. in.), might fail through budding under a vertical or a PCS r>i_&TE side load. When in use these parts are subjected to alternating loads, and, unless the connection is made over a fair surface, may weaken the joint and perhaps tear the plate. 332 MOTOR CAR ENGINEERING 246. Suspension of the Engine and Gearbox. — Frequently the engine and gearbox are attached directly to the side members, a universal joint being provided between the clutch and the gearbox to allow relative motion to take place. As has been already stated, however, the crankcase arms must not be subject to any stress due to the movement of the frame, otherwise, being of past metal, they are liable to snap off. In Fig. 185 the gearbox and engine will be seen to be supported by an under- frameformed by twochannel girders which pass between the transverse member at the front of the car and the tubular strut already referred to, a universal joint being interposed, as stated above. Another construction which is often seen is the unit system of suspension, and this is, on the whole, excellent, provided that suffi- cient care is taken in the design that free access may be had to the crankcase, clutch, gearbox, etc. In this system, a portion of the crankcase and a support for the gearbox are either cast in one piece or else bolted rigidly together, the front end being pivoted at the front CHASSIS CONSTRUCTION 333 of the chassis, and the rear end secured to a girder between these frames, thus securing a three-point suspension and reHeving the casing from the twists and strains to which the frame is sub- jected. The importance of this advantage cannot be too highly estimated, while, in addition, a better align- ment of the clutch and gear-shafts is permitted, thereby benefiting both the owner and the manu- facturer, and substantially improving the construction of the chassis. The Crossley unit system is shown in Fig. 186, the Arrol-Johnston in Fig. 187, and the Adler in Fig. 12. 247. Springs.— The func- tion to be performed by the springs is to absorb the shocks due to irregularities of the road surface, and thus prevent the occupants of the car from being sub- jected to a succession of jolts. If a car is observed as it travels along a road, it will be seen that the axles are continually rapidly rising and falling, and were it not for the fact that springs are fitted, even moderate speeds would not be pos- sible, because the car would soon be shaken to pieces. The class and strength of spring to be applied to any car will 334 MOTOR CAR ENGINEERING depend upon the conditions of use ani upon the weight of tha spring-supported load. If itjs_intended that the car should be Pig. 186.— Crossley Unit. employed on fairly smooth roads at low speeds, the spring may be made to have a much greater deflection, though a vehicle which will probably run on very rough ground or at high speeds. Fig. 187.— Arrol- Johnston Unit. racing cars, for example, would have short stiff springs, because any tendency to tilt the car at corners would probably be fatal. Similarly, the weight will influence the choice of springs, in that, if the springs are too weak, travelling will be extremely uncom- CHASSIS CONSTRUCTION 335 fortable, because excessive rolling will be produced and perhaps cause bumping ; while if too strong, they will not reduce road shock sufficiently. Long springs are, however, desirable for rough roads, in order that the deflection may be great. A large number of leaves to the springs also assist in giving an easy motion, because the friction between the leaves deadens shock by retarding the motion of the spring. There are four principal types of springs : — (1) The full elliptic, seen in Fig. 189, fitted to the rear axle. (2) The three-quarter elliptic. (3) The semi-elliptic, shown in Fig. 189, on the front axle. (4) The C spring. Another type of spring is shown in Fig. 192 fitted to the Deasy chassis. This, it will be seen, is suspended from the axle ' 'TjzTS^mmKS'^ "" ' ^"Tf ■ ^^^2M^V ^^BSlP ^ S^ l^'M^IMII^^^RH^' Mf^^^M^Kiifm^ *~ -^^^^i'^^ci ^\'gjlmf^ Jr-'^^^^.^^r^X^ Fig. 188. — Sheffield Simplex Car Eear Spring. at the rear and attached to the side members in two places. The suspension is said to be excellent. The semi-elliptic spring is very largely fitted on both front and rear axles, as there is practically no tendency to oscillatory motion, and when the drive is taken through springs it is almost universally employed, the forward end of the spring being pivoted on the frame and the shackled end at the rear. Occasionally the three-quarter elliptic is used, but mainly on the front axle, where the upper quarter is sometimes embodied in the ends of the side frame members, forming dumb irons. At the rear it is usual for the upper quarter of the spring, which is secured to the frame, to be suspended by a shackle beneath the lower half. In order to obtain an easier motion when semi-elliptic springs are used, a cross spring is attached to the two side springs and the body suspended at the centre. Examples of this are seen in 336 MOTOE CAK ENGINEERING Fig. 188, fitted to the Sheffield Simplex car, and also in Pig. 183 on the Napier chassis. It is sometimes stated that the three-point suspension of the body permits of rolling taking place, but this is rather a matter of design, and cannot be seriously considered as an objection to it as a system. In the Napier chassis a bracket is taken off the framing for attachment to the centre of the spring, but in the Sheffield Simplex the chassis is extended so as to come right out over the transverse spring. The C spring is seldom fitted, except on a few foreign cars, but it gives a very easy suspension, albeit it permits excessive lateral movement of the body and is not suitable for high speeds. Where the full ellip- tic springs are em- ployed, means must be adopted to prevent the lateral displacement of the chassis. On the Arrol- Johnston chassis this is arranged for by connecting the axle to the frame by a parallel motion, so that it CHASSIS CONSTEUCTION 337 is free to move vertically. The bracket for effecting this is seen in Fig. 189, near the forward end of the lower half of the spring. The almost invariable practice as regards the attachment of front springs to the framing is to pivot them on the dumb irons and to shackle them at the rear. This is so because the effect of the forward movement of the car with the rear driving axle is to cause the forward axle to pull upon the front attachment, and this is better for the spring than for a thrust to be exerted through the spring to the rear attachment. It is most important that the shackles are fitted with some form of lubrication, so as to avoid excessive wear and noise, and this applies equally well to the leaves of the spring, which by their grinding action soon squeeze out or wear away the lubricating composition with which they are painted by the carriage builders. 248. Shock Absorbers. — There is a considerable diversity of opinion as to the advisability of fitting shock absorbers to a car. If the general character of the road traversed is level but rough, the pneumatic tyres will absorb the vibrations due to these irregularities, and if occasionally there are ruts or sudden depressions, the action of the springs will prevent the full effects of the fall and rise of the axle from being transmitted to the body. But the action which takes place when the road has a smooth undulating surface is somewhat different. In travelling over such a surface the springs are alternately compressed and extended according as the car is ascending or descending an incline, because the inertia of the car body prevents an immediate change in its direction of motion, and some force is required to be exerted by the springs to produce the necessary upward or downward acceleration. These move- ments of the springs react upon the body, giving it an upward motion on the ascent, while on the descent the reduction of the spring deflection allows the force of gravity to cause the body to receive a downward motion, which will thus be continually vibrating in a vertical direction. If, therefore, the natural period of oscillation of the car coincides with the time at which the car is receiving the vertical accelerations from road shock, the motion of the body may ultimately become altogether so excessive that, apart from the discomfort to the occupant of the car, injury may be caused to the springs. It is clear that no M.C.E. Z 338 MOTOE CAE ENGINEEEING spring can effect any diminution of this action, so shock absorbers have been fitted in order to damp these vibrations of the chassis frame by retarding the action of the springs. But the beneficial effects of shock absorbers in the circum- stances stated are accompanied by others which are not so desirable. When a road wheel meets an obstacle upon the ground, the tyre receives a blow which causes the wheel to rise, the magnitude of the acceleration being found from S = i af, where a is the acceleration, 8 is the height of the obstacle, and t is the time taken, assuming that the accelera- FiG. 190. — EoUs-Eoyce Shock Absorber. tion is uniform. If the car is travelling at 20 miles per hour and the height of the obstacle is 1 in., and the point of contact with the tyre is, say, 6 ins. from the centre of the wheel, the magnitude of the acceleration will be 472 feet per second^, or 14"7 times the acceleration due to gravity alone. The wheel will therefore not ' fall down immediately it passes the obstacle, but at a distance beyond it, which will be increased because the springs will have to absorb the energy in the rising wheel before returning it to the ground aided by gravitation. During the time that the wheel remains in the air the engine will accelerate its speed by the action of the differential, as less resistance will be offered; consequently when the tyre again CHASSIS CONSTRUCTION 339 meets the ground it will be travelling faster than the car, and therefore will be subjected to severe stresses. By the appHca- tion of the shock absorber it will be seen that the period during which the wheel is in the air will be prolonged and the harmful effects greatly accentuated. Shock absorbers are of two forms, both of which are similar in their action. In the hydraulic type various fluids are employed which by their viscosity prevent the rapid motion of the springs ; while in the frictional shock ab- sorber the friction between the surfaces in contact produces the same result. Supplementary springs which are occasionally used are for the purpose of giving an easy motion without excessive deflection. In the Eolls-Royce frictional shock absorber, Figs. 190 and 191, a base A secured to the frame is keyed to a washer B. Between these parts a steel lever C is free to move, but is separated from them by two leather washers D and E, which prevent the lever C seizing and also tend to keep the effort constant. The pieces A and B are drawn together by means of a spring P and bolt G, so that the circular portion of the lever C is subjected to compression, which is adjusted by the nut H. The spring thus allows of wear taking place without the continual neces- sity for adjustment. The -^connection with the axle is by means of the adjustable ball- jointed rod J, which allows all a o

Ml II h 1 1(11 11 111 ( II if fl r II 1 II II lltl *' I'll III II 1 1 II II lUI 1 II II II 1^ ( { * 1 '') Ml II 1 uii II 1 III II II 1 1 II nil ( (" ! 1 ) Itll 1 Mill 1 1 II lltl IIMI 1 ' 1 HI 1. m 1 llfl ,/ ^ "Itl Mil 1 IM III 1 s II ' hi 1 II 1 iti 1 1 III II \ \ ■ \ .• } 1 1 ( ': ' ) Fig. 202.— Oifoulation in White Boiler. tangentially and thus given a swirling motion, which produces a very intimate mixture of air and petrol. The pilot lamp is situated to one side, so as to be readily accessible, and is enclosed in a casing L. At the bottom of this casing is a shallow ring trough into which a little petrol is admitted for heating the pilot vaporiser when starting up. On the side of the casing is a small door, through which a match for igniting the petrol is dropped. The main vaporiser H is situated across the pilot burner, so that when the burner is started it heats up the main vaporiser. The pilot lamp also serves the purpose of lighting the main burner when the petrol vapour is admitted to the vaporiser. The vaporiser is a steel forging, having a number of holes drilled through it, along which the peti'ol passes on its way to the burner. 289. The White Water System. — On the White steam ear the water is pumped from the tank by the pumps P (see Fig. 203) into a common main, from which a lead is taken off to the water 380 MOTOR CAR ENGINEERING regulator W. The main lead divides into two paths, one of which goes to the flowmotor D and the other to the thermostat H (A in Fig. 201). The water sent through the thermostat is returned to the flowmotor, and joining with the water which is passing through the flowmotor is led to the feed heater A, and from thence to the boiler. The thermostat is a copper rod, one end of which is fixed and the other presses against the bell crank lever (see Pig. 201). When the temperature oi the steam reaches the limit for which the instrument is set, it raises the valve within the casting at B and permits the passage of water from the main lead to the flowmotor. The flowmotor is in two parts — D is a cylindrical casting having three branches, one from the pumps, one from the thermostat, and one for the delivery to the boiler. Within the casting is a spring-loaded loose-fitting plunger attached to a rod, which actuates the fuel valve in E. The delivery orifice is below this piston, so the water which enters from the main has to pass through the space between the piston and the wall of the chamber. As the flowmotor piston moves inwards or outwards, it opens or closes tlie fuel valve, and thus proportions the supply of fuel to the burner in accord- ance with the quantity of water passing. The water regulator has a steam connection at one end which allows the pressure of steam generated in the boiler to act upon a spring-loaded piston. When the pressui-e reaches a predetermined amount (about noO lbs. per square inch), the piston is moved sufficiently to actuate a lever and open u. valve, which permits the water to be returned direct to the tank without entering any of the automatic devices. 290. The White Steam System. — The steam generated leaves the boiler at F, enters the thermostat casing at G (Fig. 201), and passes out at E to the engine. After doing work in the H.P. cylinder, it enters the L.P. cylinder, then passes to the feed heater A, where it raises the temperature of the feed water, and is finally taken to the condenser at Q. A pump C (Fig. 203) draws the condensed water from the bottom of the condenser at R and returns it to the water tank. 291. The White Fuel System.— An air pump B (Fig. 203) maintains the air pressure in the fuel tank through the connec- tion at N. The fuel leaves the tank at M and is forced to the fuel valve E (controlled by the flowmotor), and from thence by the main vaporiser to the main burner at G. A pipe is taken off this lead to supply the pilot burner F through the pilot vaporiser K. The connections at the burners are clearly shown in Fig. 201. The supply from the flowmotor comes through the pipe Q, where STEAM GENEEATOES AND PIPE DIAGEAMS 381 it branches at E to the main vaporiser H and the nozzle W, and at S to the j)ilot fuel filter K, the pilot stop valve N, and the pilot burner at L. 292. The "White Control.— This control is effected on both the supply of fuel to the burners and of water to the boiler. The water regulator is operated, as has been already stated, by the pressure of steam, which, when it reaches about 550 lbs. per square inch, causes the water to be returned to the supply tank. But the diminution of the supply of water to the boiler would result in an increase in the temperature of the steam, so the thermostat OS--- r > I I < m ' I I y- ^ ^_y >_l - Fig. 203. — Diagram of Piping for White Steam Car. is fitted, and the manner in which it operates will now be described. The flowmotor is for the purpose of proportioning the fuel dis- charge to the burners to the water delivered to the boiler. Now the water may reach the boiler in two ways — either through the flowmotor or through the thermostat and the flowmotor. When it passes through the flowmotor it depresses the piston and causes an increase of heat at the burners ; but when it goes through the thermostat and the flowmotor, the water passing decreases the supply of fuel, because it enters and leaves on the under side of the piston and decreases the quantity of water which enters from the flowmotor alone. Thus, when the heat liberated at the burner is excessive, the thermostat raises the water valve and 382 MOTOR CAR ENGINEERING allows water to be admitted to the boiler direct, thereby reducing the supply of fuel. The combined effect of these automatic devices is that the quality and pressure of the steam remain virtually constant under all running conditions, because the supply of water and fuel is only such as the conditions which exist at the time render necessary. 293. The Stanley Fire-tube Boiler. — This boiler is built up in two parts, the vertical shell' and bottom plate forming one piece and the top plate the other. The latter plate is secured to the shell by welding, and in order to strengthen and support the joint an electrically welded steel ring is shrunk on the outside after the plate is in position. A similar ring is shrunk on the bottom, and it will be seen that by this construction riveted joints are entirely dispensed with. After this is done, piano wire under tension is bound round the shell between the rings, to a depth of about ^ in., the object of so doing being to reduce the stress in the shell when work- ing, and thereby produce a part that will withstand a greater pressure without bursting. The manner in which this is effected is due to the fact that as the wire is wound it induces a compressive stress in the shell and a tensile stress in itself. When steam is raised in the boiler, the internal pressure has first to relieve the shell of this initial compressive stress before any load comes upon the material of the shell, and consequently the working stress in the plate is much lower than it otherwise would be. Naturally the stress in the wire is increased, but the load on the wire when being wound is adjusted so as to bring the total load within practical limits. The system is by no means peculiar to the Stanley generator, being used in connection with steam piping in marine engineeiing work of the highest class. The tubes are placed vertically and are secured to the two end plates by being expanded into reamered tapered holes, thus constituting, in some measure, a number of stays supporting the tube plates. The boiler normally works under a pressure of 500 lbs. per square inch, but is tested to considerably above this. The 10 h.-p. boiler has 473 tubes, and the 20 h.-p. boiler 736 tubes of J-in. diameter, the heating surfaces being 66 square feet and 104 square feet respectively. Two safety devices are fitted to the boiler, the first being a safety valve which is set normally to blow off at a pressure of 650 lbs. per square inch and the other is a fusible plug, shown in Fig. 207. This plug is so applied that if the water-level in the boiler falls to within 3 ins. of the bottom, a lead plug is exposed to the heat of the fire and melts, releasing the steam and calling the driver's attention to the low water. No trouble is experienced in remedying the defect, as the burner is at once turned out, the STEAM GENEEATOES AND PIPE DIAGEAMS 383 plug tube which projects through the side of the firebox is removed and a new one inserted, after which water is pumped into the boiler, fires relighted and a restart made. 294. Water Indicator. — The Stanley boiler has a device, also, for indicat- ing the water-level in the boiler ; it is shown in Fig. 206 at G-, and also in Fig. 204. It is not desirable to have a gauge glass subject to the high Fig. 204. — Stanley Automatics. pressure of steam used in these boilers, so at G there is a gun-metal vessel divided into two portions, one part, the boiler-chamber, being in connection with the boiler at S and the other part, the feed-chamber, being a passage through which the feed water circulates on its way to the boiler from T to U. In the the first-mentioned compartment a tube completely filled with water is inserted having a. sealed end, the free end H being connected up to an open glass tube on the dash-board, so that there is about 2 ins. or 3 ins. of water in the gauge glass. From the method of attachment it is clear that if there is water in the boiler above S there will be water in the boiler 384 MOTOR CAR ENGINEERING chamber, otherwise it will contain steam. If the water-level in the boiler falls below S,then steam will fill the chamber, raising the temperature and causing some of the water in the sealed tube to be converted into steam, thus forcing the level of the water in the dash-board indicator higher up the tube. On pumping more water into the boiler, the steam in the boiler chamber and the tube will be condensed, and the water level fall to its normal position. It the car is allowed to stand for a time, the same effect will be evident, because there will be no water circulating through the feed chamber and consequently the temperature of the water in that compartment will be raised, but on restarting the pumps, the indicator will assume its ordinary working level. 295. The Stanley Burner. — This is shown in Fig. 205, and its position beneath the boiler in Fig. 206. The makers recommend FlGr. 205. — Stanley Burner. that either petrol or benzine be used, although the burner can consume paraffin successfully. As may be seen, the burner plate consists of a thin casting in the form of raised hollow corrugations which cross the circular plate in parallel lines. The tops of these corrugations are slotted across at light-angles with fine slots from which the gas issues and burns with the blue flame typical of perfect combustion. Towards the left-hand side the pilot light i^^placed, as in Fig. 205, and the who?e casting is fixed in a sheet-iron box which is attached below boiler by studs and nuts. Across the box over the burner plate lie the vaporising tubes, through which the fuel passes on its way to the nozzles which direct the gas through air-mixing tubes under the plate. These vaporisers are brazed together, and so placed that they pass directly over the pilot flame, the latter serving tlie double purpose of keeping the vaporisers hot and lighting the main fire. The pilot light will burn for many hours without attention, and keep sufficient steam on the boiler to start the car any moment. When first STEAM GENEEATORS AND PIPE DIAGRAMS 385 starting the fire, the pilot vaporiser is heated by applying a small hand-torch for a couple of minutes on the nozzle, and the pilot flame lit through a jmall circular door in the side of the firebox. 296. Stanley Water System. — The supply to the boiler is fed by the pumps A A^ in Fig. 206, operated direct from the engine _J ii LjJ z 1^ h^ 't-^ cross-head, which are of the tandem type and deliver more water than is required for ordinary requirements, so a by-pass valve is fitted at F, actuated from the steering column and leading back M.C.E. c c 386 MOTOR CAB ENGINEERING into the tank. This valve when open allows the flow from both pumps to pass back to the tank, and an auxiliary by -pass valve E is now fitted to one pump only, so that, if desired, by closing the first valve F and opening the auxiliary one E, the delivery of one pump may be kept regularly directed to the boiler, and that from the other may be by-passed until the full service of both may be required. A hand-pump D is supplied for filling the boiler in the first instance. The circuit under normal conditions is from the water tank at W by the pumps A A^ to the water indicator G, through the feed chamber and into the boiler at the top. 297. Stanley Steam System. — The steam generated in the boiler leaves at R, Fig. 206, passes through the throttle K to the superheater tubes J, where it divides into two pipes which run down through the boiler and around over the burner, rising back through the boiler again and on to the engine, after which it goes to exhaust in the atmosphere. 298. Stanley Fuel System. — In the Stanley system only about two pints of fuel are under pressure, and this is contained in the pressure tanks shown in Fig. 206. The faelis drawn from the fuel tank by the pump B and sent into the fuel main near P, which is a pressure retaining valve for use when the car is standing. From thence it passes to the valve M, where a small quantity is taken for the pilot light, the main portion passing to the vaporising coil L. Here its temperature is raised and it is sent through the main burner valve M B which regulates the supply to the main burners. The delivery is then split up into two parts at the steam automatic and both leads are taken through the main fire vaporisers over the burner and finally discharged into the induction tube of the main burner. A hand-pump is fitted at C for use when starting up. The fuel during this time is under a pressure of about 120 lbs. per square inch which is obtained by the use of the pressure tanks, Fig. 207. STEAM GENERATORS AND PIPE DIAGRAMS 387 as in the right-hand one there is air under this pressure. The fuel pump always delivers an excess over the maximum demands of the burner, so whatever pressure there may be at the start due to the air pumped in by a hand-pump will be maintained. The gasoline automatic valve is fitted so as to operate when the pressure in the fuel system reaches 120 lbs. per square inch, but it may be adjusted to suit any pressure. Its construction is shown in Eig. 204, from which it will be seen to simply consist of a spring loaded valve attached to a diaphragm. When the valve lifts, it allows the fuel to pass and return to the main fuel tank at Z. 299. Automatic Control. — The necessity of some form of automatic control has already been emphasised. The control in this case is only on the fuel, and consists of a copper diaphragm (see Fig. 204) upon which is mounted a strong spiral spring carrying a needle valve, which shuts o£f the whole supply of fuel from the main burner when forced on to its seat, although the main burner valve is left open. The spring is set to withstand a pressure of 500 lbs., but can be adjusted as desired. The boiler steam pressure is led to the under side of the diaphragm, and when it reaches 500 lbs., the spring is compressed, and the valve stem forced up on its seat. The main fire is thus extinguished, and remains so till the steam pressure falls again below 500 lbs., when the spring immediately reasserts itself and opens the valve again, so renewing the flow of fuel to the burner, where it is relit by the pilot. By this contrivance steam is generated only when required, and in proportion to the demands of the engine. 300. Turner Boiler. — The Turner boiler is of the true flash type. It is built up of eight complete generator sections of solid drawn steel, bent into the form of a double gridiron, thus giving sixteen layers of tubing. The bottom eight layers have a bore of ^ in. and an external diameter of | in., while the c c 2 Fig. 208. 388 MOTOR CAR ENGINEERING upper eight layers are jg in. bore and f in. external diameter, the whole having a total length of 200 feet. The method of eonne'cting up these layers together is shown in Fig. 208. 301. The Turner Burner. — This burner uses paraffin as its standard fuel, and its construction may be seen by referring to the accompanying Fig. 209. It consists of an induction tube P (Fig. 209), a mixing chamber and eight burner tubes — one burner tube being slightly longer than the others for supporting the unit. The paraffin is vaporised in a coiled tube placed near the burner (Fig. 210). The burner Fig. 209. tubes are perforated on the upper side by about 1,200 pin holes, this fine division of the fuel contributing largely to the efficiency of the combustion. This burner is very silent in its action, and when standing the heat of the burner can be regulated by the valve Q (Fig. 211). The paraffin is supplied to the burner under air pressure, the air being forced into the paraffin tank by a hand pump connected to the nozzle E (Fig. 211) at starting. When the engine is running, the air pressure is maintained by the pump V, the actual pressure being regulated by the valve X. F is a relief valve adjusted to a given pressure in the tank, any surplus escaping by the pipe shown in the figure. W is a valve for retaining pres- sure in the tank when at rest. When starting up, before paraffin is permitted to pass through the vaporising coil, one end of coil near R is Fig. 210. heated by a blow lamp, and when it is sufficiently heated the paraffin is turned on, so that it issues in the form of vapour. This passes into the induction tube and from thence to the burner tubes to be consumed. STEAM GENEEATOES AND PIPE DIAGEAMS 389 302. Turner Water System. — The feed water for the generator is drawn from the water tank through the valve C (Fig. 211) and Water Steam Fuel /lir Fig. 211. — Diagram of Piping for Turner Car. enters the pump box at U, from which it is pumped either by the hand-pump A or the punip worked from engine at B, through G to the bottom of the boiler at N. No gauge glass or similar 390 MOTOR CAR ENGINEERING fitting is necessary, as the generator never contains more than a pint of water. 303. Turner Steam System. — From the diagram of end con- nections (Fig. 208) it will be seen that steam is taken from the second layer of tubing. The water is fed into the lowest gridiron and is converted into steam, which rises through the tubing and leaves the boiler as shown. It then passes through the steam pipe (Fig. 211), through the main throttle T to the engine, leaving by the exhaust pipe for the condenser, from which it is sent to the feed water tank. On its way between the exhaust and the condenser it passes through a feed water heater. 304. Turner Fuel System. — The paraffin is under air pressure in the fuel tanks, from whence it is taken to the vaporising coils, where it is completely gasified and then led through the regula- ting valve Q to the induction tube P (Fig. 211). 305. Turner Control. — The control on this car is by means of the valve D on the steering column and the pedal-operated throttle T. To regulate the speed of the car the valve D is opened to a greater or lesser extent, and thus more or less water allowed to return to the feed tank by way of H on pump box. Too much water will cause an excessive speed of the ear, while if no water is injected to the boiler the engines will stop. When it is desired to stop the car, the pedal is depressed and the throttle valve T closes, a further movement of the pedal causing the application of the brakes to the drum Y on the engine-shaft. When the car is to be left standing, the valve R oh fuel supply is closed, thus putting out the fires, and the steam remaining in the generator is discharged through the condenser by opening the valve J. For short stops, the needle valve Q in the induction tube P is adjusted, so that only a very small light is kept going. There is neither automatic control nor pilot light on this car, but the regulation of the amount of heat required is by means of the valve X, which adjusts the air pressure in the fuel tank, and consequently the discharge at the burners. Questions on Chapter XXIII. (1) What do you understand by a flash boiler ? (2) Sketch and describe the White pipe systems, detailing the functions of the automatic devices, STEAM GENERATOKS AND PIPE DIAGRAMS 391 (3) Describe some form of automatic control fitted upon a steam car. (4) What is the object of wire-winding the Stanley Boiler ? (5) Name the various types of boilers found in automobile work, and mention the advantages or disadvantages of each. (6) Sketch a burner for a steam generator, and say what alteration would be necessary to enable it to burn paraffin. (7) What is the object of fitting a pilot lamp? Describe some burner in which such a device is not used. (8) Explain with the aid of sketches the Stanley water indicator. (9) Compare the two systems of control (a) in which every part is automatic and (6) in which the failure of, say, the water supply causes the stoppage of the car. CHAPTER XXIV THE ELBCTBIC CAE 306. Obviously, from the nature of the service upon which the automobile is engaged, the supply of energy must be self-contained, no matter what class of vehicle is referred to. For this reason, therefore, the electric car must carry its charge of electricity in some convenient form, and to this the accumulator lends itself, but is subject to a great disadvantage in regard to its weight. The future of the electric car is bound up in the evolution of a light, efficient and cheap battery, and it is on this problem that the keenest intellects have been and still are engaged. Whether they will be successful in their endeavours or not it is difficult to determine, but it cannot be denied that should even only a modicum of success attend their efforts it would cause a much more extended use in town work. 307. Principal Parts of an Electric Car. — The three principal parts of the electric car, in so far as it differs from the petrol- driven vehicle, are the battery, the motors and the controller. The current from the battery is taken to the controller and from thence to the motors, where the electrical energy is converted into mechanical power. The battery is generally supported upon an underframe, which is slung from the side members of the chassis frame. Such an arrangement allows of free access to the cells and distributes the weight of the battery fairly equally over the wheels, but at the same time gives a clear upper surface upon which the body may be placed. The controller itself is fitted near the driver's seat, either beneath the floor of the car or within a casing at the foot of the steering column — in either position it may be operated by a lever placed on the column or at the side. 808. Suspension of Motors. — The method of suspension and THE ELECTEIC CAR 393 arrangement of the motor depends upon the number of motors employed and whether the car is front or rear driven. When a single motor is fitted, a differential gear becomes necessary, the drive to the differential casing being taken through either spur- gearing, chain-gearing, or worm-gearing. If spur-gearing is used, some provision must be made to allow of the rise and fall of the axle due to inequalities of the road surface. This is generally arranged for by attaching the motor frame to the rear axle by means of lugs, so that it is free to rotate to a slight extent about the axle, a limit being imposed by securing the forward side of the motor to a laminated spring fixed to a bracket on the chassis frame. The motor pinion is thus always at the same distance from the centre of the rear axle and the correct meshing of the gears is ensured, while any shock at stopping or starting is taken up by the spring. When the drive is through either a worm or a chain, the motor is suspended by lugs from the framing of the car. If two motors are employed, the motors may be either incorporated in the hub of the wheel or a spur-gearing may be interposed and the spring attachments already referred to fitted. Of the two the latter is preferred, as the former necessitates the employment of large hubs and a motor running at a much slower speed, which causes the weight of the parts to be rather heavy; while, in addition, the motor is subjected directly to any shocks which may come upon the road wheels. On the other hand, the total weight need not be much greater, if any, than when spur-gearing is used, and the efficiency of the transmission is increased because the use of gearing is obviated. In the front-driven vehicle, two motors are employed which may be connected to the driving wheels through the spring attachments already described, but another form is sometimes used, and is seen on the Krieger Chassis. In this, the steering pivot is within the hub, and a spur wheel is bolted direct to the hub of the wheel which is in gear with a small pinion carried on a framing surrounding the hub on its inner side. The framing is concentric with the wheel hub and forms a dust-proof oil bath. The pinion is driven by a motor rigidly attached to the axle hub. The pinion is usually made of fibre or raw hide, so as to render the reduction gear quiet, but wear takes place very rapidly unless all dust is excluded. 394 MOTOR CAR ENGINEERING 309. The Battery. — The battery used on electric automobiles differs little from the ignition cells, which have been already examined in Chapter X, except that on account of the more severe nature of the work upon which they are employed, a stronger construction is necessary. At times, too, it is desirable that the battery should be capable of giving an increased output for a limited period, so, generally speaking, it is designed so that an overload of approaching 100 per cent, can be made without any risk of straining the plates. Both Plante and pasted plates are used. The capacity of the cells in ampere hours varies greatly for the type of cell considered, ranging from about five ampere hours to eight ampere hours per lb. for a five- hour discharge. Care is, however, neces- sary in making any comparison, as the capacity is somewhat increased by a slower rate of discharge. The time required for charging is from three to five hours. The life of the cells also varies greatly, but may be taken as being from 4,000 to 5,000 miles before repasting is necessary and 2,000 miles after repasting. The battery usually consists of from forty to fifty cells, which thus give from 80 to 100 volts when grouped in series. 310. Motors. — The simplest form of motor is that with a shuttle-wound armature and a two-part commutator. Its essential parts which constitute the motor are — the field magnets, the armature, the commutator and the brushes (see Fig. 212). The field magnets are magnetised by the current which passes through the field coils and which always flows in the same direction, giving the magnets the same polarity continuously. Around the armature are wound a large number of turns of wire, the ends of which are connected to the two insulated portions of the commutator. Brushes press upon the commutator and carry the current from the source of supply to the armature coils. The action of rotation is produced as follows : — The current flows in at one terminal, dividing up and Terminal Term in a I Fig. 212. THE ELECTKIC CAR 395 traversing both the armature and the field coil circuits. By suitably connecting up the armature coil to the commutator the current passing through the armature coil will cause one side of the shuttle to be a N pole and the other side a S pole. Similarly the left-hand side of the field magnet will be a N pole and the right-hand a S pole. The upper end of the armature will, therefore, be repelled by the N pole of the magnets and attracted by the S pole, and the bottom end of the armature will be similarly affected only in a reversed sense, so that the armature will be caused to rotate in a clockwise direction. On a movement of 180 degrees being effected, the polarity of the magnets will remain unchanged, but that of the shuttle will have been reversed, because the current will now be passing through the armature coil in a reversed direction. The same rotative effect will therefore be produced, because the upper end of the armature will always be a N pole, and as the polarity of the shuttle is automatically changed by the commutator, the armature will continue to rotate in a clockwise direction. It will be seen that it is necessary for the direction of the flow of current through the armature coil to be reversed at the correct position, as if it is changed too soon or too late, the armature will be arrested. This is the function of the commutator, and the current should be reversed when the shuttle is in a horizontal position, that is just when the poles of the armature are passing the poles of the magnets. But if the armature is in a horizontal position, it is clear that the repulsion or attraction of the magnet poles will simply exert a thrust on the bearings and will not tend to cause rotation. Under these circumstances no rotary movement would result, and the armature is then said to be on " dead point." By the addition of other magnet poles, or by the adoption of a different construction in the armature in which a large number of coils are employed, these dead points are avoided and continuous rotation ensured. In this construction, the magnets consist of cores of soft iron which are secured to what is termed the magnet casting. Around these cores are the field coils, while in order that the pole pieces may approach close to the armature, suitably shaped pole shoes are fitted. The armature is built up of laminated plates of soft iron, having grooves cut in their circumference along the axis 396 MOTOR OAR ENGINEERING of the shaft in which coils of well insulated copper wire are wound, the ends of each coil being connected to two insulated com- mutator segments, so placed that the brush attached to the positive terminal presses upon one segment and the other brush upon the other segment. The segments are made of hard drawn copper and are well insulated by strips of mica from each other. The ends of the coils are soldered to lugs which are provided on the segments. It is important that the commutator should be perfectly true with the armature spindle, as otherwise serious damage may result. The brushes may be made of compressed copper gauze or of carbon and are attached to the wires from the battery by means Series tvound Motor. Terminals Shant wound motor ElG. 213. Terminals Compound wound Motor of a terminal fastened to the body of the brush. When carbon brushes are used, the ends are usually copper plated in order to ensure better contact with the holders in which they are placed. The brushes are arranged in suitable carriers which permit of their rotation about the commutator. 311. Series, Shunt and Compound-wound Motors. — There are three principal types of motors — the series, the shunt and the compound-wound. In the series-wound motor the field coils are in series with the armature coil, so that the same current passes through both the field and the armature. See Fig. 218. The magnetising current will therefore depend upon the current passing through the armature. THE ELECTRIC CAR 397 The shunt-wound motor is also shown in Pig. 213, where it may be seen that the current from the source of supply is divided, one part passing through the armature and the other through the field. By this means the strength of the magnetic field will be constant, but may be varied by placing an external resistance in the shunt circuit. The compound-wound motor is a combination of the two previously mentioned in that the magnetising current is due to the current through the armature plus that through the shunt. By cutting either out of the circuit, the strength of the magnetic field may be varied at will. It will be seen that this motor is really a shunt-wound motor with a series winding added to it. To enable the reader to comprehend the characteristics of the various types of motors, attention is drawn to Art. 130, where it is seen that when a coil of wire which has its ends joined rotates in a magnetic field, a current of electricity is generated within the wire. Now the ends of the armature coils of the motor are successively joined by the brushes which press upon the commutator segments, so when the armature rotates between the poles of the magnets, a pressure is generated in them. The direction in which this pressure acts is opposite to that of the current which flows through them from the battery, and, there- fore, the pressure generated is termed the "counter E.M.F." The magnitude of the counter E.M.F. varies as the speed of revolution. 312. In the series-wound motor the current which passes through the armature passes also through the field coils, and they therefore depend upon the armature current for their excitation. The torque from the armature depends upon the strength of the magnetic field (which, as has just been shown, depends upon the current in the armature) and upon the current passing through the armature coils, and will thus vary approximately as the square of the current through the armature. For light loads the torque required to overcome the resistance of the car is low, and since ■pi C = , where E is the E.M.F. from the battery and e is the R counter E.M.F., and R is always small (about '05 ohms), (E — e) must be small, in order that the current may be low. The E.M.F. from the battery is, however, constant, so that the speed of 398 MOTOE CAR ENGINEERING revolution must be high to generate a high counter E.M.F. and reduce (E — e) to a low value. Similarly, for heavy loads the counter E.M.F. must be small, so that (E — e) can be large, and therefore the armature must rotate at low speeds. When the car meets an increased resistance, a greater torque is required to be exerted by the motor, which, when the load comes upon it, slackens in speed and thus reduces the counter E.M.F. in the armature coils. This reduction of the counter E.M.F. will cause the value of (E — e) to increase, and consequently the current passing through the armature will like- wise be increased and the magnetic field strengthened. But as the magnetic field becomes stronger, the counter E.M.F. tends to rise and prevent any great increment in the armature current. Hence, the motor will give practically constant power with a varying speed. On the other hand, the magnetising current through the field coils of a shunt-wound motor is constant and independent of the armature current, so the magnetic field will be of constant strength. When the load on the motor increases, a reduction of speed immediately takes place, but a very small reduction in speed is sufficient to cause a relatively large increase in (E — e), and there- fore a large increase in the armature current. But seeing that a constant current passes through the field coils, e will depend upon the speed of the motor, which has been but little reduced. Con- sequently the shunt-wound motor will run at nearly constant speed with a varying load. The object of winding the magnets of compound-wound motors with a few turns of wire in series with the armature coils is to increase the strength of the magnetic field in which the armature rotates, when the speed tends to decrease due to increased load and the motor is taking a greater current through the armature. By adjusting the number of turns of series winding on the magnets it is possible to obtain a constant speed of revolution with a varying load. 313. The Shunt-wound Motor used for Charging the Battery when Descending Hills. — One of the advantages accruing from the use of shunt-wound motors on electric vehicles is that when descend- ing long hills a considerable portion of the energy which would otherwise be wasted in heating the brake drums, can be usefully employed in charging up the accumulators. This is permissible. THE ELECTRIC CAR 399 because when the motor becomes a dynamo driven by the road wheels, the polarity of the magnets is unaffected, as the current through the field coils is sent in the same direction in both cases. With a series motor, the reversal of current through the armature reverses the current through the field coils also. This may be clearly seen if the reader will place arrows on the wiring, to show the direction in which the current flows. The compound-wound motor can be used for charging the accumulators by cutting out the coils in series with the armature winding, as it is then virtually shunt-wound only. A powerful braking effect may be obtained from the motor by short-circuiting the terminals, the electrical energy being converted into heat in the armature. This method of braking, however, cannot be recommended, as there is a great risk of the destruction of the armature insulation from overheating. 314. Controller. — By means of the controller the whole of the operations necessary for controlling the speed of the car and the connections between the battery and the motor are affected. It consists of a circular cylinder of some insulating material upon which strips of copper are secured, the number, shape and position of the strips being such that the various terminals on the battery and the motor are automatically connected up in the desired combination when the cylinder is rotated and placed in a suitable position. Against this cylinder springs or fingers press which are connected up to the terminals before-mentioned. The rotation of the cylinder is produced by means of a lever which is generally placed upon the steering column but is sometimes fitted at the side of the driver. 815. How Variations of Speed are Obtained. — One of the commonest methods of varying the speed of the motor is by varying the voltage at the motor terminals, as the speed of revolution depends upon the voltage in the circuit. If the voltage at the brushes is reduced, the speed at which the motor will run will also be reduced in nearly the same proportion. The way in which this is carried out will be seen, as several systems are described. Supposing now that a single series motor is employed, to obtain the various speeds the following procedure may be followed : — For first speed the battery may be coupled up so that it is divided into four parts in parallel. The pressure at 400 MOTOR OAR ENGINEERING the terminals, if ten cells are grouped in each set in series, is then 20 volts, and the first speed is obtained. For the second speed the cells are divided into two parts of, say, twenty cells, and the voltage then rises to 40. By coupling up all cells in series, a pressure of 80 volts is at the terminals, and the third speed is obtained. A further variation in the speeds may be made by introducing a resistance in the circuit, for by so doing the voltage is reduced as the current passes through the resistance. When two series-wound motors are employed, the first and second speeds may be obtained by adopting a similar grouping of the cells for the second and third speeds in the single motor arrangement, but with the motors in series, as then the drop of voltage of 40 and 80 volts is divided between the two motors. For the top speed the cells may be grouped in series and connected to the motors arranged in parallel, as the full pressure of, say 80 volts, will be on both motor terminals. For varying the speed of shunt-wound motors a similar method of grouping may also be employed, but seeing that the field coils are now a separate circuit, and that the speed of a motor is nearly inversely proportional to the strength of the magnetic field in which the armature rotates, it is possible to effect a reduction of speed by this means. To do this a resistance E is inserted in the field circuit, for by Ohm's Law C = ^p, if, therefore, the resistance R is doubled, the current C passing through the shunt will be halved. The voltage may also be reduced by connecting the terminals of the shunt or field coils to one, two or four groups of cells in series which will produce a corresponding variation in the strength of the field. For a compound-wound motor the speed may also be varied by cutting out the field coils in series with the armature, the motor being thereby converted into a shunt-wound motor, and may be then used for charging the batteries when on a long decline. Obviously, the arrangements indicated may be supplemented by others, but sufficient have been noted to enable the reader to see how the variations of speed are effected in electric vehicles. The reverse speed is obtained by reversing the current through the armature without affecting the direction of the current THE ELECTEIC CAR 401 through the field coils, so that the polarity of the magnets remains unaltered. Questions on Chaptbe XXIV. (1) Explain the difference between the shunt and the series-wound motor. (2) Give a sketch showing one method of transmittmg the power from the motor to the road wheels. (3) Make a diagram of wiring for a car having four speeds and reverse with 40 cells and two shunt-wound motors. (4) Enumerate the various parts of a motor, and say what each part is for. (5) What is the controller, and in what way does it effect its purpose ? (6) Explain why the armature rotates when a current is sent through the armature windings of a series-wound motor. (7) What is the "Counter E.M.F.," and how does it affect the running of the car ? M.C.B. D D 402 MOTOE CAE ENGINEEEING MATEEIALS USED FOE THE PEINCIPAL PAETS OP THE MODEEN CAE. Name of Part. Conditions which determine the Icind of Material. Material used. Cylinders Valves . Camshafts Pistons . Gudgeon pins Connecting rods Crankshafts . Flywheel Gear shafts . Gear wheels . Gearboxes Intricate casting — good wearing surface — low tensile and bending High burning tempera- tures — warping— shock. Torsional and bending stresses — hard and severe wear — shock needing fibrous struc- ture. Rigidity — good wearing qualities — lightness and strength in compression. Hard surface Compressive and bending stresses — lightness — reversible stress. Bending and torsional stresses — shock — hard surface at journals for wear — reversible stress. Weight — rigidity — low cost. Bending and torsional stresses — freedom from distortion — hardsurface. High intensity of pressure teeth — hard surface — bending stresses — alter- nating load. Rigidity — ease of manu- facture. Oast iron or cast steel. Cast steel is not generally used when steel pistons are employed, because these two metals do not work well together. High percentage nickel or nickel-chrome steel. Forged steel, case-hardened. Cast iron or pressed steel. When the latter is used, cast-iron rings are often fitted so as to bear upon the bottom of the groove and stand " proud " of the surface. High-tension steel, either case-hardened or oil- hardened according to the grade of steel. Nickel chrome or forged steel with a high elastic limit and good elonga- tion. Hard forged steel — ^Nickel chrome or vanadium steels. Oast iron. Forged steel or nickel chrome steel. Nickel chrome steel, oil- tempered. Casting of either aluminium or cast ii'on. MATERIALS USED IN MOTOR CAR CONSTRUCTION 403 Materials, ■etc.— continued. Name of Part. Clutch member Orankcase Axles . Swivel axles . Ball-bearings Springs . Frames . Axle casing . Conditions which determine the kind of Material. Eigidity — ■ lightness or small rotating momen- tum. Intricate casting — ^rigidity. and torsional -wear at bear- Bending stresses ings. Severe bending stresses — shock. Hard surface, yet not brittle. EesiKence — bending and torsional stresses. Shock — bending — vibra- tion — must be capable of easily taking any shape. Bending stresses — facility of manufacture. Material used. Forged steel or cast alum- .Cast iron or aluminium. When the latter is used, case must be -well ribbed. Bottom half is sometimes of sheet metal. Forged steel of good quality or a nickel chrome steel. High-tension steel with high elastic limit and good elongation. Special steel, case-hardened or oU-tempered — the lat- ter for preference. Fre- quently a nickel chrome steel is employed. Specially tempered steel — generally blister steel. A low carbon steel. Occasionally, higher grades of steel are used — nickel chrome. Malleable cast iron, steel, or steel tubing. D D ^ CITY AND GUILDS OF LONDON INSTITUTE REVISED SYLLABUS IN MOTOR CAE ENGINEERING. The course of instruction in this subject should occupy at least three years. Examinations will he held at the end of each yearns cowrse. Students are advised to take a cou/rse of instruction in some or all of the subjects included in the first stage of " Practical Mathematics" "Heat Engines," " Machine Gonstruction and Drawing," and" Magnetism and Electricity," of the Board of Education, or their equivalents, before commencing this subject. Slide rules and tables of logarithms may be used at the Examination. In problems involving calculations, more importance will be attached to method than to arithmetical accuracy. SYLLABUS ;— Geadb I. Petrol. — Source, distillation, density, and calorific value. Handling and storage. Carburation. — -The properties of petrol, explosive mixtures, cooling effect of evaporation. Carburetters. — General principle of the action of a float-fed spray carburetter and description of the forms in common use. Variable mixture supplied by simple " jet-in-tube " carburetter, and the prin- ciples of the devices in common use attempting to correct this defect. Location of faults in fuel system. Indicated and Brake Horse-power, compression ratios, heat of compression, difference between adiabatic and isothermal compression. Graphic representation of work, indicator diagrams. Difficulty of measuring indicated horse-power accurately. Brake horse-power and method of measuring same. Mechanical efficiency. Thermal efficiency. Heat losses. Ihiel consumption. Calculations involved in connection with the above. SYLLABUS IN MOTOK CAR ENGINEERING 405 Engines. — General construction of two- and four-stroke-cycle engines, various forms of engines, valves and operating mechanisms in common use. Valve timing ; lubrication, cooling, practical treat- ment generally and locating faults. Such elementary information regarding balancing and torque as will enable the student to under- stand the advantages of various forms of engines and the principles governing their design. Gearing. — Angular ratio of trains of gear wheels other than epicyclic gears. Relative torque in shafts, properties of differential gears. Efficiencies of different forms of gearing. Tractive force. Eoad and wind resistance and gradients. Braking effect. Problems involving simple calculations with the above. Chassis Parts. — General description of the construction of various tjrpes in common use of the following : — Clutches, change speed gears, universal joints, transmission to road driving wheels, brakes, steering gears, circulating pumps, fans, radiators, bearings, lubricators, springs, shackles, torque rods, radius rods, silencers, etc. Means for operating clutches, speed gears and brakes. Locating faults in and practical treatment of the above. Materials of Construction. — Composition, properties, methods of working and treatment of the materials in common use. Electeic Ignition.— Electricity. — Such elementary information regarding electricity and magnetism as will enable the student to form an intelligent idea of the operation of batteries, coils, and magnetos, as used for ignition. Batteries. — Brief description of primary batteries. Secondary batteries, general construction, charging and treatment generally. Ohm's law. Coils and Magnetos.— High and low tension sparks, effect of pressure on the length of spark. Electro-magnetic induction. Con- struction and theory of working of ignition coils, high and low tension magnetos, operating mechanism, timing ignition. High and low tension distributors. Sparking JPlugs. — Construction, weaknesses and general treatment. Wiring. — Various systems in common use. High and low tension distribution. (Note : Students should be encouraged to use coloured inks or pencils when drawing diagrams of coils, magnetos, and ignition systems ; say, red for low-tension conductors, blue or green for high, and black for other constructional parts.) Locating faults in ignition systems. 406 MOTOR CAR ENGINEERING Geadb II. Candidates for this grade must have previously passed the examination in Grade I. Candidates ivill be expected to possess a more advanced knovjledge of the subjects mentioned in the syllabus for Grade I., and in addition a knowledge of the- following subjects : — Petrol. — Methods for testing. Other fuels in commercial use on internal combustion motor road vehicles. Carburation. — Effect of air-petrol ratio on composition of exhaust gases, on rates of combustion, on mean effective pressure and on efficiency. Carburetters. — Pressure-fed systems. Effect of valve stem leakage, condensation in induction pipe and throttled petrol supply. Causes of flooding. Brief description of carburetters, other than the float- fed spray kind. Indicated and Brake Horse-power. — Thermo-dynamie principles of the internal combustion motor. High-speed engine indicators, analysis of diagrams, torque or crank effort curves from the indicator diagram. Horse-power formulae based on engine dimensions. Engines. — Calculation of stresses in engine parts, problems on balancing and the effect of inertia on the torque diagram. Effect of obliquity of the connecting-rod, forced vibration in shafts, design of poppet-valves and cams. Gearing. — Bpicyclio gears. Geometrical properties and con- struction of various forms of tooth gearing. Side slip. Efficiency. — The problem of the efficiency of the machine as a whole and in detail, studied quantitatively. Chassis Parts, — Calculation of stresses in members of transmission. Means for adjustment for wear. Governors, shock absorbers, detach- able wheels and rims. Lubricants. — Properties, flash point, composition, impurities. Ignition. — Synchronised ignition, two-point ignition, and effect of nature of spark on ignition. EiNAL Examination. Candidates for the Final Examination must hold a certificate in Grade II. The examination in this grade will consist of two parts — a ivritten examination, and a drawing examination to test the candidate's knowledge of proportion and his quickness and accuracy in, designing. SYLLABUS IN MOTOR CAR ENGINEERING 407 1. Written Examination. — In addition to a more advanced know- ledge of the matter comprised in the syllabuses for Grades I. and II., candidates will be expected to possess a knowledge of steam road vehicles, and of the general problems of motor car engineering. The questions will not necessarily be limited to the subjects specified in the foregoing syllabuses. 2. Drawing Examination. — Candidates may be asked to design any of the mechanical details in a petrol or steam car; a choice of subjects will be given. Plain paper or paper ruled in i-in. squares will be provided by the Institute; all necessary instruments must be provided by the candidates or the school. Neat, carefuUy proportioned hand sketches are all that is required, and these should contain sufficient detail to enable a draughtsman to prepare working drawings from them. The dimensions of parts should be judged by eye and should not be inserted. Marks wiU be awarded for correct proportions. CITY AND GUILDS OF LONDON INSTITUTE EXAMINATION PAPEES IN MOTOE CAE ENGINEEEING. 1908. Oedinaey Geadb. All candidates must attempt Question 1, and not more than six others. 1. Draw the outline of the battery, coils, distributor or " commu- tator " and cylinders of a four-cylinder engine, and show the wiring — preferably with coloured pencils or inks — for ignition for the ordinary form of high-tension battery ignition with four coils. (40 marks.) 2. If the engine in Question No. 1 is found to be missfiring on one cylinder, how would you systematically set about to find which cylinder is not firing, and then to locate the fault ? (Note. — Your method of locating the fault should be sufficient to detect any defect which is likely to occur, and you should not merely state how you would prove it to be due to one particular cause.) (50.) 3. Sketch diagrammatically two common types of two- cylinder engines, and mention the disadvantages of each with regard to balance, continuity of torque, and adaptability to motor cars. (40.) 4. Eepresent the motion of the crank pin by a circle, and indicate the direction of revolution with an arrow ; mark on this circle the dead centres and the positions where the inlet and exhaust valve should open and close in an Otto cycle or ordinary petrol engine ; or, if you are not accustomed to this method of setting the valves, state whe n they should open and close in an engine of 5-inch stroke. (40.) 5. Sketch the essential parts of an automatic carburetter — without the float chamber — write the names on the different parts, and explain when the automatic device comes into operation, and why it is necessary. (40.) 6. Draw a three-speed and reverse gearbox, with the gears in " neutral," giving a direct drive on top, suitable for a live-axle car. EXAMINATION PAPERS 409 Put a figure on each wheel to indicate that it is for the reverse, 1st, 2nd, or top gear. (40.) 7. Show how the cooling of a single-cylinder engine, situated under a bonnet in front of a small car, is effected. Sketch the cylinder jacket, radiator, and pump in their respective positions, and indicate the direction of circulation by arrows. Make a separate sketch of the pump in section. (40.) 8. In an ordinary ignition coil, suppose the low-tension or primary winding to be quite separate from the high-tension or secondary winding, how is it that by passing a current through the former you are able to get a current from the latter ? (40.) 9. Sketch the system of steam and water pipes used on a steam car which condenses its steam and re-uses the water, state where the various pumps and valves are situated, and indicate the complete circuit of steam and water with arrows. (50.) 1908. HoNOUES Gbadb [Candidates for Hoiiours must have previously passed in the Ordinary Grade.) All candidates must attempt Question 1, and not mm-e than six others. 1. Name some high-tension magneto ignition system with which you are familiar. Show diagrammatically its internal construction and external connections to plugs, etc. Wires carrying current should be drawn with coloured pencils or inks. (40 marks.) 2. If an engine, fitted with the ignition system you have described in Question No. 1 is found to be missfiring on one cylinder, how would you systematically set about to find which cyUnder is not firing, and then locate the fault ? (Note. — Your method of locating the fault should be sufficient to detect any defect which is likely to occur, and you should not merely state how you would prove it to be due to one particular cause.) (50.) 3. Sketch and describe the action of some two-stroke cycle engine with which you are familiar. (40.) 4. Engines sometimes make a noise called " coughing," which is caused by an explosion in the inlet or induction pipe ; explain care- fully the cause of " coughing," and how the mixture in the inlet pipe is able to get fired when the inlet valves are mechanically operated and do not leak. (40.) 410 MOTOE CAE ENGINEEEING 5. An ordinary " live-axle " car, fitted with 30-in. road wheels and a foTir-to-one reduction in the bevel drive, with direct drive on top gear, has an engine which gives 15 brake horse-power. Neglecting friction in transmission, calculate the tractive force which is available for propelling the vehicle along the road when on the top gear. (40.) 6. Describe a good system for lubricating the bearings, pistons, and gudgeon pins for a four-cylinder engine ; sketch the lubricator and crankcase, giving just sufficient detail to indicate clearly how the lubrication of the parts is effected. (40.) 7. Discuss the relative advantages and disadvantages of low-tension magneto ignition as compared with high-tension magneto. (40.) 8. Sketch the burner, the storage tank, and fuel system of a steam car ; name the parts, and state whether the fuel is paraffin or petrol. (50.) 9. Describe briefly why the armature of an electric motor tends to rotate when a current is supplied to the motor in the ordinary way. (40.) 1908. HoNOUES Geade. {Drawing Examination.) One sheet of drawing paper is supplied to each candidate. Candidates may use ordinary drawing instruments, but sketches only, not scale drawings, are required. The dimensions of parts drawn should be judged by eye, and need not he inserted. Marks will be awarded for correct proportion. 1. Sketch in section an epicyclic gear giving two forward speeds and a reverse, suitable for a small car. (100 marks.) 2. Draw two views of a universal joint suitable for the front end of a " cardan " or propeller-shaft of a live-axle car. (100.) 3. Sketch a multiple disc clutch complete, about half full size, giving separate views of the two kinds of discs used. Enough detail should be given to enable a draughtsman to prepare a working drawing from your sketch. (100.) 4. Draw a sparking plug in section, about twice full size, and name the insulating materials used. (80.) EXAMINATION PAPERS 411 1909. Oedinaby Grade. 1. Describe briefly the construction of any small car with which you may be familiar ; taking each organ in turn, giving its situation and the type to which it belongs, also noting any special or good features. (50 marks.) 2. Supposing the ignition gear in the car described in question 1 to be in perfect working order, but that you cannot get the engine to start, how would you systematically set about to locate the fault before attempting to put it right or to alter any adjustments ? (40.) 3. Sketch in section, a good design of clutch and flywheel, showing the clutch pedal. State briefly what are its good features. (40.) 4. What horse-power is required to move a motor delivery van, weighing 3| tons at 12 miles per hour along a level road, the necessary tractive force to overcome road resistance being 45 lbs. per ton ? (40.) 5. State precisely what materials are generally used for con- structing the following car parts : — Engine cylinders, crankshaft, balls in the ball-bearings, core or centre part of magneto, armature, ordinary sparking plugs points. What is the white metal made of which is commonly used for lining big end bearings ? (40.) 6. Answer either of the following : — (a) Suppose you have a 3-ampere hour 4-volt accumulator to be recharged, show in a diagram the necessary connections and apparatus for recharging, using any source of current supply you like. State what current you would give, for how long you would charge, and how you would regulate the current ; or, (b) Draw just a line diagram showing the wiring for a non- trembler coil ignition system, for a motor cycle with a 4-volt battery. If the coil takes 3 amperes, what is its resistance in ohms ? 7. Show the construction of a trembler ignition coil by a sketch, taking care to make the connections quite clear, preferably with coloured pencils or inks, stating which terminal has to be connected to the sparking plug and which to the battery, &c. (50.) 8. Eepresent, diagrammatically, a low-tension magneto, and show the connections to a four-cylinder engine. Show the make and break mechanism for one of the cyhnders, and state the relative speed of the armature to the crankshaft. (40.) ' 9. Sketch a liquid fuel burner, and show the tank and necessary 412 MOTOR CAR ENGINEERING pipe connections, etc., for a steam car. State the fuel used and how it is forced to the burner. (40.) 10. What are the chief necessary electrical parts in an electric carriage ? Why are electric cars not more commonly used for country work ? (40.) 1909. HONOUES Geadb. 1. Draw up a short catalogue specification of a complete chassis ; take the engine, gearbox, and other organs in turn, briefly indicating the good points and selling features which you think you could include at the price. The prices of the parts should not be given, but the specification should conclude with the words : " Price. Chassis only £250." (50 marks.) 2. Suppose that the engine of the car you have described in ques- tion 1 stops pulling when you are out driving and the car soon comes to rest, how would you systematically set about to ascertain the cause of the trouble ? (40.) 3. Answer either of the following : — ■ (a) Sketch the apparatus you would use to determine the flash-point of a lubricating oil. State how you would use it and what you would expect the flash-points of two oils to be, one suitable for water-cooled engines and the other for air-cooled engines. or, (6) Sketch the apparatus you would use to determine the calorific value of a liquid fuel. If -008 lb. of fuel raises 12 lbs. of water from 55° F. to 67° ¥., calculate the calorific value of this fuel. (40.) 4. Give the name of, or describe, a steel suitable for constructing some part of a motor chassis, mention the part for which this steel is suitable, and describe the treatment to which you would subject it in order to render it serviceable. (40.) 5. An engine being tested with a rope brake round a 2-feet. flywheel gives a torque of 92 lbs. feet, e.g., 100 lbs. one end of rope and 8 lbs. the other. If this engine were to be put on a car weighing 1 ton altogether, what is the steepest gradient it could climb on the slow speed, neglecting all friction ? A 23-tooth pinion on clutch-shaft in gearbox meshes with a 57-tooth wheel on cardan shaft extension, and the bevel in the back axle has 19 teeth meshing with a crown wheel of 60 teeth ; tyres 810 by 90. (50.) EXAMINATION PAPEES 413 6. What is the difference between isothermal and adiabatio com- pression ? How would you try to obtain each of these ? If it were possible in an internal-combustion engine to obtain adiabatic or isothermal compression and expansion when required, indicate on an imaginary indicator diagram the parts of the curve which you would arrange to have adiabatic and isothermal respectively. (40.) 7. Calculate one of the following : — (a) The tensile strain in the rim of a cast-iron flywheel, 2 ft. diameter, at 2,500 revolutions per minute. One cubic inch of cast iron weighing 0'28 lb. (6) The maximum tension in a connecting rod due to the inertia of piston and gudgeon pin weighing 8 lbs. in an engine 5-in. bore 6-in. stroke, at 1,500 revolutions, neglecting the obliquity of the connecting rod. (40.) 8. Show, diagrammatically, the wiring for ignition for a two-cylinder engine, cranks at 180 degrees, fitted with two tumbler coils and battery. (40.) 9. Sketch the engine of a steam car with which you are familar and name the make. (40.) 10. In an electric car, how is the necessary increase in torque obtained for hill climbing. (40.) 1909. HoNouBS Grade. {Drawing Examination.) One sheet of special drawing paper is supplied to each candidate. Candidates may use ordinary draiving instruments, but sketches only, ■not scale drawings are required. The dimensions of parts drawn should be judged by the eye, and need not be inserted. Marks will be awarded for correct proportion. Only three questions to be attempted. 1. Draw nearly half full size a sectional view of the flywheel with a leather cone clutch, preferably a type in which the spring gives no end thrust on the crankshaft or gearbox shaft when driving. Show the necessary mechanism for removing the clutch for re-hning, and describe briefly how this is carried out. (60 marks.) 2. Draw twice full size part of the pitch circle and two involute teeth of an ordinary gear wheel having 30 teeth, 6 diametrical pitch, 6-in. diameter pitch circle. Show how the curve is set out and insert the dimensions of one tooth. (40.) 414 MOTOR CAR ENGINEERING 3. Sketch about quarter full size a well-designed back spring (not of the transverse type). Draw two full-sized views of one of the shackles in position, showing every detail of importance to its efficient use. (50.) 4. Draw full size a piston for a double-acting engine used on a steam oar, and show clearly a satisfactory form of piston ring for same. (40.) 1910. Oedinaby Grade. Instructions. All candidates must attempt Questions 1 and 2, and not more than five others. 1. If you had an ordinary chassis, fitted with a four-cylinder vertical engine under a bonnet and a bevel-driven live axle, to tune up for the road, how would you determine the following points ? : — (a) Whether all the mechanically operated poppet valves are seating ; (&) Whether the sparking plugs or valve caps leak ; (c) Whether the porcelains of any of the sparking plugs are cracked ; (d) Whether the cooling water is circulating ; (e) Whether the clutch is slipping ; (/) Whether the engine is getting sufficient lubrication ; (g) Whether some evident loss of pulling power is due to the engine, or is due to friction in some other portion of the chassis. Do not give remedies for above defects. (42 marks.) 2. Explain, with sketches, how the spark advance and retard are obtained in a four-cylinder vertical engine (a) with an ignition system consisting of accumulator and four trembler coils ; (6) with some well-known high-tension magneto. Explain how, with each of the above systems of ignition, you would ascertain exactly when in the cycle of operations the spark takes place in each cylinder for any one position of the advance spark lever. Neglect the period of vibration of the tremblers, etc. (42) 3. State briefly aU the advantages and disadvantages of two similar vertical engines of equal power, the one being a four- and the other a six-cylinder. Give the concise reasons for each statement. (42) 4. Describe, with sketches, any method with which you may be familiar for measuring the brake horse-power of a petrol engine. Assume certain figures as if you had obtained them experimentally, EXAMINATION PAPEE8 415 and show your calculations for obtaining the horse-power therefrom. (48.) 5. Sketch one of the well-known and extensively used carburetters without the float chamber. Name the make, describe its action and any good features it may possess. (42.) 6. The gearbox of the chassis described in question 1 gives a straight through or " direct drive " on the top gear, but has two pairs of spur wheels transmitting the drive on the first speed. Sketch the arrangement roughly, and determine the ratio of engine revolutions to road- wheel revolutions on the first speed when a spur wheel A on the clutch-shaft drives a wheel B on the lay-shaft, and C on the latter drives D on the foot-brake shaft. D transmits the power through the propeller-shaft to the bevel pinion E, which drives the large bevel E on the back axle. The wheels A, B, 0, D, E and P have 24, 36, 18, 42, 14 and 55 teeth respectively. (42.) 7. If when recharging an ignition accumulator you cause the current to pass through an ammeter to the positive terminal, and through a second ammeter after it leaves the negative, will both these meters show the same current ? If so, how does the accumulator become charged? In a four- volt accumulator the positive of one cell is connected or bridged to the negative of the other cell. If this bridge is brought to zero potential by being connected to the gas pipe or " earthed," state what the voltage of the other two terminals will be, regarding " earth " as zero. (42.) 8. Sketch a good make of sparking plug, name the materials of which it is constructed, and state how it may become ineffective in working. (42.) 9. Sketch in detail any automatic device used on a steam car either for regulating the boiler water or the supply of fuel. (42.) 1910. HoNOUES Grade. 1. If you had an ordinary chassis fitted with four-cylinder vertical engine under a bonnet and bevel driven live axle to tune up for roadj how would you determine the following points ? : — (a) Whether all mechanically operated valves were seating. (&) Whether sparking plugs or valve caps leak. (c) Whether porcelains of sparking plugs are cracked. (d) Whether cooling water is circulating. (e) Whether clutch is slipping. 416 MOTOK CAR ENGINEEEING (/) Whether engine is getting sufficient lubrication. (g) Whether some evident loss of pulling power is due to engine or due to friction in some other portion of the chassis. (42.) 2. Consider each of defects in question (1) except (&), (/), and the engine in (g) in turn and give likely causes for these defects after the chassis is once in order. (42.) 3. Two samples of petrol have same density and calorific value. How would you proceed, without actually using them in an engine, to ascertain which is likely to be more serviceable for motor work. (42.) 4. Describe with sketches the trough and sump system of engine lubrication, with a pump for feeding troughs. (42.) 5. In an ordinary four-cylinder vertical engine the forces belonging to the fundamental or first period of vibration are balanced. Explain chief inertia forces which are not balanced and sketch diagrammati- cally a design of engine which is practically free from this defect, giving sufficient explanation to indicate just how defect has been eliminated. (42.) 6. Bpicyclic gear consists of sun wheel A with 24 teeth meshing with planet wheel B with 16 teeth and in which B meshes with a large internal toothed wheel C. Calculate number of teeth in C. Assume C is stationary. Calculate how many revolutions the planet case or arm will make while A is revolving once. (42.) 7. Suppose each cell of an ordinary 4-volt accumulator contains two positions and three negative plates each 6 ins. x 4 ins. What charging current would you give it and for how long ? Make a diagram of wiring for this accumulator to two side lamps and a tail lamp each containing a 4-volt Osram lamp consuming 1 ampere and giving 4 c.-p. and all controlled by one switch on dash-board How long ought this battery to keep lamps alight ? (42.) 8. Sketch H.T. Magneto and name the make. Show internal con- nections and external connections to a six-cyUnder vertical engine to fire in correct order. Number the cylinders and distributor and name the other parts. (48.) 9. Discuss relative advantages and disadvantages of slide valves, piston valves, and poppet valves in steam engines for road vehicles. 10. Describe the construction of commutator of an electric motor. Why is the iron core built up with laminated plates. Illustrate with sketches what would take place if a solid core was used. (42.) EXAMINATION PAPERS 417 1910. Honours Grade. Drawing Examination. 1. Draw two views of a centrifugal water circulating pump. (50 marks.) 2. Design and draw exhaust cam to give valve lift of f in., the distance of highest portion of cam to be 1 in. from the centre of cam- shaft. Valve to commence lifting when crank pin is 40 degrees from outward dead centre and to close 5 degrees after crank pin has passed inner dead centre. (50.) 3. Sketch lines of some well-known car with four-seated body with glass screen and cape cart hood up, but without lamps. Name the make. Drawing to be about 8 ins. long. (35.) 4. Draw an external foot-brake, preferably of locomotive type suitable for an ordinary live-axle car where foot-brake is situated just behind gearbox. (50.) 1911. Obdinaey Grade. Instructions. All candidates must attempt Questions 1 and 2 and not more than five others. 1. Show a complete wiring diagram for an ordinary four-cylinder vertical engine fitted with duplicate ignition (battery andH.T. magneto). If possible, use different coloured pencils or inks for wires carrying high and low-tension currents. (48 marks.) 2. A single-cylinder car with the engine under the body has about 7 feet of H.T. lead from the plug to the coil on the dash. If the insulation of this wire gradually perishes, what are the first symptoms you expect ? Describe how, when these symptoms are observed, you would proceed to locate the fault exactly, and prove it to be due to a leak in the H.T. wire and nothing else. What other defects would give similar symptoms. (42.) 3. Given a new 4-volt ignition accumulator or lead secondary battery (without any printed instructions) to fill with acid and charge for use, state what acid you would use, how you would dilute it, and to what density. If you find there are two negative plates and one positive plate each measuring 5 ins. by 4 ins. in each cell, what charging current would you give, and for how long ? (42.) M.C.B. B E 418 MOTOR CAR ENGINEERING 4. Sketch carefully a section of a well- designed cheap piston, showing rings, gudgeon, small end of connecting rod and bush. Indicate with arrows the materials of which the parts are constructed. 5. A ear fitted with live axle and two universal joints in the pro- peller drive has a torque rod 4 feet long to prevent the axle case from rotating ; the car weighs 1 ton, and is climbing a hill of 1 in 7. Calculate the force (due to gradient only, neglecting road resistance, etc.) which the former end of the torque rod exerts on its support. Tyres 810 and 90 (25-4 mm. = 1 in.) (42.) 6. Draw a modern locomotive type foot-brake suitable for the car described in Question 5. Show method of adjustment and means for preventing rubbing and rattling. (42.) 7. Eepresent the motion of the crank pin by a circle about 3 ins. diameter, and indicate the direction of rotation with an arrow. Mark on this circle, for an ordinary four-stroke cycle engine, the dead centres and the positions of the crank pin when the inlet and exhaust valves should open and close, and when the magneto spark should occur for fully advanced and retarded ignition. Give the angle in. degrees of each point from the nearest dead centre. (42.) 8. Carefully draw two curves indicating the relation between pres- sure and volume when the engine piston is on its compression stroke. One curve should show the rise in pressure when the engine is pulled over compression very slowly by hand (isothermal compression) ; the second curve should represent the result of sudden compression (adiabatic). Insert a few figures of pressures and volume if possible. (42.) 9. Sketch two kinds of boilers in use on steam motor road vehicles. Give the working pressures and blow-off pressures and approximate diameters and lengths of boiler tubes in each case. Name a manufacturer of each type. (42.) 1911. Honours Geadb. All candidates must attempt Questions 1 and 2 and not more than five others. 1. Show diagrammatically all the electrical connections for a duplicate ignition (battery and H.T. magneto), for a four-cylinder horizontal engine. A plan of the engine should be roughly represented to show the crankshaft and cylinders, Nos. 1 and 3 should be on one side of the crankshaft, and Nos. 2 and 4 on the other. If possible. EXAMINATION PAPEK8. 419 use different coloured pencils or inks for wires carrying high and low- tension currents. (42 marks.) 2. A single- cylinder car with the engine under the body has about 7 feet of H.T. lead from the plug to the coil on the dash. If the insulation of this wire gradually perishes, what are the first symptoms you expect ? Describe how, when these symptoms are observed, you would proceed to locate the fault exactly, and prove it to be due to a leak in the H.T. wire and nothing else. What other defects would give similar symptoms ? (42.) 3. What is the chief fault of a simple " jet-in-tube" carburetter used for motor car work ? Sketch diagrammatically three carburetters (without float chambers) in common use, with different devices for overcoming or correcting this fault. One of these examples should have no moving parts sensitive to the suction of the engine. (42.) 4. Calculate the brake horse-power actually developed by the engine of a small racing car under the following conditions. The car is climbing a gradient of 1 in 22 on its second speed (the third being direct drive) at 40 miles per hour, against a headwind of 20 miles per hour and a road resistance of 40 lbs. per ton. Weight of car, 25 cwt. Wind resistance on whole car at 20 miles per hour on a calm day, 15 lbs. (48.) 5. Draw a- typical full-load indicator diagram about 3 in. long for a single-cylinder engine, 4-in. bore, 6-in. stroke, running at 1,000 revolutions. Assume whatever figures are necessary, as if you had obtained them by measurement, and calculate the indicated horse- power. Explain, with assistance of sketches, how you would obtain a torque diagram or crank effort curve therefrom. (42.) 6. Calculate one of the following : — ■ (a) A |-in. diameter sample test piece cut from a IJ-in. diameter round cardan shaft is found to break with a torque or twisting moment of 1,000 lb. ins. Using the formula : — Breaking torque T = -^o- f where / = the breaking shearing stress of the material in lbs. per square inch, what torque would cause the cardan shaft to fracture ? or, (b) It is found by experiment that the sudden application of the brakes will bring a certain car (on which the brakes are not very good) to rest in 15 feet when travelling at 10 miles per hour. Show, by a numerical example, how you would proceed to reduce the probable stopping distance at some higher speed. (42.) 7. With the aid of clear sketches show the working of some system B E 2 420 MOTOE CAR ENGINEEEING of mechanical lubrication suitable for a four-cylinder vertical engine in which an oil-pump is used. (42.) 8. Show by a sketch how the reversing of some steam car with which you are familiar is effected. Name the make. 9. Describe briefly the battery you would use in an electric brougham or similar electric carriage, giving the total weight of battery, its output, the number of cells, and the size and number of plates in each cell. (42.) 1911. HoNouEs Grade. (Drawing Examination.) One sheet of special drawing paper is supplied to each candidate. Candidates may use ordinary drawing instruments, but sketches only, not scale drawings are required. The dimensions of parts drawn should be judged by the eye, and need not be inserted. Marks will be aivarded for correct proportion. Only three questions to be attempted. 1. Draw the box, shafts, gears, operating mechanism. and bearings in position for an ordinary gate change three-speed box, giving a direct drive on the top. Shafts, 4-in. centres ; scale, about half full size. (50 marks.) 2. Plot a curve showing the position of the piston for any angular position of the crank pin, using the following scales : — Stroke of piston 3 ins., represented as ordinates, and positions of crank pin, 6 ins. = 360 degrees, as abscissEe (horizontally), (a) For an infinitely long connecting rod, (6) for a 6-in. connecting rod. Plot both curves on the same diagram (b) as a dotted line. A 6-in rod has been chosen to demonstrate the effect of a short connecting rod on the motion of the piston. (50.) 3. Draw a sectional view of a steering gear and box at the base of the column, showing methods of adjustment for wear. (50.) 4. Show, about half full size, a section taken right through one cylinder and base chamber of a four-cylinder vertical engine, 3-in. bore and 5-in. stroke, with opposite valves. (36.) PHYSICAL PEOPERTIES OF PETROL 421 THE FOLLOWING TABLES ARE TAKEN FROM THE PAPER, " THE THERMAL AND COMBUSTION EFFICIENCY OF A FOUR CYLINDER PETROL MOTOR," BY W. WATSON, D.Sc, F.R.S.^ Densities and Coefficients op Expansion. (Densities in grms. per cc, i.e., in terms of -water at 4° 0.) Petrol. Density at 6°C. Density at 15»(;. Density at 26° C. Mean Coefficient of Expansion (a) at 15° C. Bowley's Special Carless Express . Eoss .... Pratt (a) . Pratt (b) . Carburine . Sbell (ordinary) Dynol Simcar Benzol ■760 (BaiUee) . ■760 Shell . Coaline ■693 ■714 ■714 •724 •728 •729 •730 •731 •735 ■770 •775 •775 ■855 •684 ■704 •707 •714 ■719 •720 •720 •721 ■725 •762 ■767 •767 •846 ■675 •695 •700 •705 •710 ■712 ■712 ■713 •714 •753 •759 •759 ■836 •00131 •00131 ■00100 ■00133 ■00125 ■00121 ■00121 ■00121 ■00145 •00111 •00105 ■00105 ■00109 Pentane . Hexane Heptane . ■640 •689 •743 •630 ■680 ■736 ■620 ■671 •728 ■00155 •00133 •00100 The relation between change of density and temperature is very approxi- mately linear over the range 5° to 25°, i.e., if Dj = density at t° C. Dis = density at 15° C. dt = di, {1 -a(<-15)}. 1 Proceedings I.A.E., Volume III. 422 MOTOR CAR ENGINEERING Vapour Densities. Petrol V.ipour Density (Gmi. per CO, at 0° C. and 760 mm.). Relative Vapour Densitj'. H = 2 Air = 1 Bowley's Special . Carless . Express . Eoss Pi-att (a) Pratt (b) Carburine Shell (ordinary) Dynol Simoar Benzol ■760 (BailUe) . •760 Shell Coaline . ■00395 •00402 ■00434 ■00430 •00409 ■00414 •00424 •00423 •00443 ■00419 •00425 •00436 •00428 87^8 89-3 96^4 95^7 91^0 92-0 94^4 94^1 98-5 93-3 94-6 96^7 95^1 305 3'11 3-35 3^33 316 3^20 3-28 3^27 3^43 3-24 3^29 3-26 3-31 Pentane Hexane Heptane .... •00325 •00386 •00446 72^2 85^7 99^2 2-51 2^99 3^46 The vapour density at 0° C. and 760 mm., given in this Table, is obtained by calculation on the assumption that the vapour behaves as a perfect gas, and could be cooled down to this extent without condensation. PHYSICAL PEOPERTIES OF PETROL 423 Calorific Values (Lower). Density at IS-'C. Calories per grm. Calorific Value (Lower). Petrol. Calories per 0.0. at 16° C. B.T.U. per lb. B.T.U. per gall, at 16= C. Bowley's Special •684 10,660 7,290 19,190 131,500 Carless •704 10,420 7,340 18,760 132,300 Express •707 10,020 7,080 18,040 127,600 Boss . •714 10,370 7,400 18,670 133,600 Pratt (a) . •719 10,340 7,430 18,610 134,100 Pratt (b) . •720 10,330 7,440 18,590 134,200 Carburine . •720 10,380 7,470 18,680 135,000 Shell (Ordinaiy). •721 10,400 7,500 18,720 135,300 Dynol •725 10,290 7,460 18,520 134,600 Simcar Benzol . •762 9,490 7,230 17,080 130,400 •760 (BaUlie) •767 10,300 7,900 18,540 142,500 •760 Shell . •767 10,140 7,780 18,350 140,300 Ooaline •846 9,270 7,840 16,690 141,500 Pentane •630 10,230 6,450 18,410 116,300 Hexane •680 10,430 7,090 18,770 127,900; Heptane •736 10,400 7,650 18,720 138,100 424 MOTOE CAE ENGiNEEEiNG Viscosity. Petrol. Density at 15° C. Viscosity u.g.s. Units, )yne sec. cm .2 ■ 6°0. 16° C. 25° C. Bowley's Special . •684 ■00380 ■00352 •00332 Oarless •704 ■00406 ■00380 •00359 Express .... •707 •00445 ■00420 ■00398 Boss •714 •00431 ■00404 ■00385 Pratt •719 •00445 ■00420 ■00398 Carburine .... •720 •00450 ■00421 ■00400 Shell (Ordinary) . •721 •00454 ■00421 ■00400 Dynol ■725 •00486 ■00454 ■00430 Simcar Benzol ■762 •00520 ■00482 ■00454 •760 (BailKe) •767 •00518 ■00485 ■00475 ■760 Shell .... •767 •00634 ■00498 ■00472 Ooaline .... •846 ■00609 ■00572 ■00539 Hexane .... •680 ■00376 ■00342 •00319 (a) The weight of a liquid of density A, -which flo-ws in t seconds through a fine tube of radius r cm. and length I cm. [l being gi-eat compared to r), when driven by a head H cm. of the liquid, is given by W: grm.. where »j is the viscosity of the liquid as above, and g is the acceleration of •i , cm. gravity = 9Sl — ^ (b) The weight of a liquid of density A, which flows in t seconds through a fine tube of radius r cm. and length I cm. {I being great compared to r), when forced by a pressure P dynes per square cm., is given by ^ ^ TT P A'-' it 8 Iri PHYSICAL PROPEETIES Of PETROL 425 Capillarity. Density at 150 c_ Sui- face Tension '^y'""'- Petrol. cm. 6=0. 15° C. 26° C. Bowley's Special . •684 19^5 18-8 18-2 Oaxless . . . . •704 19^8 19^4 19^0 Express .... ■707 20-4 20^0 19^6 Boss . . . . . •744 21-0 20^4 20^0 Pratt . . . . •719 20-8 20-2 19-6 Oarburine . . . . •720 21 •O 20^4 19^8 Shell (ordinary) •721 21-3 20^5 20^0 Dynol •725 2V1 21^0 20^3 Simcar Benzol •762 22-9 22^4 21^9 •760 (BailHe) . . . . •767 23^5 22-7 22-0 •760 Shell . •767 23-6 22-8 220 Coaline . ... •846 26^9 26^1 2o^3 Hexane. •680 20-1 19^5 18^9 The variation of surface tension with temperature is yery approximately linear over the above range of temperature. 426 MOTOR CAR ENGINEERING USEFUL CONSTANTS. 1 Inch = 25-40 millimetres. 1 mm. = -03937 inch. 1 Gallon = -1604 cubic foot = 10 lb. of water at 62° P. 1 Knot = 6080 feet per hour = 1 Nautical mile per hour. Weight of 1 lb. in London = 445,000 dynes. One pound avoirdupois = 7000 grains = 453'6 grammes. 1 Cubic foot of water weighs 623 lb. 1 Cubic foot of air at 0° C. and 1 atmosphere, weighs -0807 lb. 1 Cubic foot of Hydrogen at 0° C. and 1 atmosphere, weighs -00559 lb. 1 Foot-pound = 1-3562 x 107 ergs. 1 Horse-power-hour = 33000 x GO foot-pounds. 1 Electrical unit = 1000 watt-hours = 1-34 horse-power-hours. T 1 > -ri • 1 J. . •, T. u' TT • f 774 ft.-lb. = 1 Eah. unit. J oules Equivalent to suit Eeenault sH, IS -,.„„,,,, ,„ , ^ ° i 1393 ft.-lb. = 1 Cent. „ 1 Horse-power = 33000 foot-pounds per minute = 746 watts. Volts X amperes = watts. 1 Atmosphere = 14-7 lb. per square inch = 2116 lb. per square foot = 760 mm. of mercury = 10'' dynes per sq. cm. nearly. A column of water 2-3 feet high corresponds to a pressure of 1 lb. per sq. inch. Absolute temp. * = (9° C. + 273° or 6° F. -f 461°. Eegnault's H = 606-5 + -305 6° C. = 1082 + -305 6° F. p mI-0646 = 479. log lop = 6-1007 - ? _ ^ where log i^B = 3-1812, log ipC. = 5-0882. p is in pounds per sq. inch, t is absolute temperature Centigrade. «( is the volume in cubic feet per pound of steam. TT = 3-1416. One radian = 57-30 degrees. To convert common into Napierian logarithms, multiply by 2-3026. The base of the Napierian logarithms is e = 2-7183. The value of g at London = 32-182 feet per sec. per sec. Logarithms. 427 1 2 3 ■h 6 7 8 9 1 2 a ^ 5 6 7 8 9 10 0000 0043 0086 0128 0170 0212 0253 0294 0334 0374 4 4 9 13 17 8 12 16 21 20 26 30 34 88 24 28 32 37 11 0414 0463 0492 0631 0669 0607 0645 0682 0719 0755 4 4 8 12 16 7 11 15 19 19 23 27 31 35 22 26 30 83 12 0792 0828 0864 0899 0934 0969 1004 1038 1072 1106 3 8 7 11 14 7 10 14 18 17 21 25 28 32 20 24 27 31 13 1139 1173 1206 1289 1271 1303 1335 1367 1399 1430 3 3 7 10 13 7 10 12 16 16 20 23 26 30 19 22 25 29 H 1461 1492 1523 1563 1684 1614 1644 1673 1703 1732 8 3 6 6 9 12 9 12 16 15 18 21 24 28 17 20 23 26 18 irei 1790 1818 1847 1876 1903 1981 1969 1987 2014 3 8 6 5 9 11 8 11 14 14 17 20 23 26 1619 22 25 16 2041 2068 2096 2122 2148 2175 2201 2227 2253 2279 3 3 5 6 8 11 8 10 14 18 16 19 22 24 15 IS 21 23 n 2304 2830 2355 2380 2405 2430 2466 2480 2504 2529 3 2 6 6 8 10 7 10 18 12 15 18 20 28 16 17 19 22 18 2653 2677 2601 2625 2648 2672 2696 2718 2742 2706 2 2 6 5 7 9 7 9 12 11 14 16 19 21 14161S21 19 2788 2810 2833 2866 2878 2900 2923 2945 2967 2989 2 2 4 4 7 9 6 8 11 11 13 18 18 20 13 15 17 19 20 3010 3082 3054 3076 3096 3118 8139 3160 8866 3660 3747 8927 3181 8201 2 4 6 8 11 l:l 15 17 19 21 22 23 24 3222 3424 8S17 8802 8243 3444 3636 3820 3263 3464 3655 8838 8284 3483 3074 8866 3304 8602 3092 3874 3324 3522 3711 8S92 3346 3541 3729 8809 3385 35T9 3766 3945 3404 3598 8784 3962 2 2 2 2 4 4 4 4 6 8 6 8 6 7 5 7 10 10 9 9 12 14 16 18 12 14 15 17 11 13 15 17 11 12 14 16 25 3979 8997 4014 4031 4048 4065 4082 4099 4266 4425 4679 4728 4116 4133 2 3 6 7 9 10 12 14 15 26 27 28 29 4160 4314 4472 4624 4166 4330 44S7 4639 4183 4346 4502 4654 4200 4862 4518 4660 4216 4878 4633 4683 4232 4893 4548 4698 4249 4409 4664 4713 4281 4440 4594 4742 4298 4456 4609 4757 2 2 2 3 3 3 3 6 7 6 6 5 6 4 6 8 8 8 7 1011 13 16 Oil 13 14 9 11 12 14 9 10 12 13 30 4771 4786 4800 4814 4829 4848 4857 4871 4886 4900 3 4 6 7 9 10 11 13 31 32 33 24 4914 6051 6186 6315 4928 6065 6198 63-'8 4942 5(i79 52)1 5340 4966 5002 5224 6363 4969 5105 5287 63t6 49S3 5119 5260 6378 4997 5182 6263 5391 6011 5146 5276 5403 5024 5169 5289 6416 5038 5172 5302 6428 3 3 3 3 4 6 4 5 4 5 4 6 7 7 6 6 8 10 11 12 8 9 11 12 8 10 12 8 9 10 11 35 6441 6463 5465 6478 5490 6602 5514 5627 6639 5561 2 4 6 6 7 9 10 11 36 37 38 39 5663 6682 6798 6911 6575 6694 5809 6922 6687 6706 6821 6933 5699 5717 5832 6944 6611 5729 6848 6965 6623 6740 5866 5966 .'686 6762 6866 6977 5647 5763 6877 6988 6668 6775 6888 6999 6670 57S6 6899 6010 2 2 2 2 4 5 3 5 8 6 8 4 6 8 6 6 7 8 1011 7 8 9 10 7 8 9 10 7 8 910 40 6021 6081 6042 6058 6064 0075 6085 6096 0107 6117 2 3 4 6 6 8 9 10 41 42 43 44 6128 0282 6335 6486 6138 6243 6H46 6444 6149 6263 6865 6454 6160 6263 6365 6464 6170 6274 6376 6474 6180 6284 6386 6484 6191 6294 6895 6493 6201 6804 6406 6503 6212 6314 6415 6613 6222 6325 6425 6622 2 2 2 2 3 4 3 4 3 4 3 4 5 6 5 5 7 8 9 6 7 8 9 6 7 8 9 6 7 8 9 45 6632 6542 6661 6561 6671 6680 6690 6699 0699 6618 2 3 4 6 6 7 8 9 46 47 48 49 6628 6721 6812 c.nm 6637 6730 6821 6911 6646 6739 6830 6920 6656 6749 6839 692S 6665 6768 6848 6937 6675 6767 6867 6946 0684 6776 6866 6955 6693 6785 6875 6!'64 6702 6794 6884 6972 6712 6803 6893 6981 2 2 2 2 3 4 3 4 3 4 3 4 5 5 4 4 6 7 7 8 6 6 7 8 5 6 7 8 6 6 7 8 SO 0998 7007 7016 7024 7033 7042 7060 7059 7067 1 2 3 3 4 6 6 7 8 The copyright of that portion of the above table which gives the logarithms of numbers from 1000 to 2000 is the property of Messrs. Macmillan and Company, Limited, who, however, have authorised the use of the form in any reprint published for educational purposes. 428 MOTOR CAE bngi:neering Logarithms. 1 2 3 1 B 6 7 8 9 12 3 4 5 6 7 8 9 81 92 53 Si 7076 7160 7243 7321 7084 7168 7251 7332 7093 7177 7259 7340 7101 7186 7267 7348 7110 7193 7276 7356 7118 7202 7284 7364 7126 7210 7292 7372 7135 7218 7300 7380 7143 722« 7303 7388 7152 7235 7316 7396 12 3 3 12 2 8 12 2 3 12 2 3 4 4 4 4 6 6 7 8 5 6 7 7 6 6 6 7 5 6 6 7 58 7404 7412 7419 7427 7436 7443 7461 7459 7460 7474 12 2 3 4 6 5 6 7 56 57 98 59 74S2 7669 7634 7709 7490 7666 7642 7716 7497 7674 7649 7723 7506 7582 7667 7731 7613 7689 7664 7738 7520 7597 7672 7746 7628 7604 7679 7752 7536 7612 7686 7760 7643 7619 7694 7767 7551 7627 7701 7774 12 2 3 12 2 3 112 3 112 3 4 4 4 4 6 6 6 7 5 5 6 7 4 5 6 7 4 5 6 7 60 7782 7789 7796 7803 7810 7818 7826 7832 7839 7846 112 3 4 4 6 6 6 61 62 63 64 7863 7924 7993 8062 7860 7931 8000 8069 7868 7938 8007 8075 7876 7945 8014 8082 7882 7952 8021 8089 7889 7959 8028 8096 7896 7966 8035 8102 7903 7973 8041 8109 7910 7980 8048 8116 7917 7987 8065 8122 112 3 112 3 112 3 112 3 4 3 3 3 4 5 6 6 4 5 6 6 4 5 6 6 4 6 6 6 65 8129 8136 8142 8149 8166 8162 8169 8176 8182 8189 112 3 3 4 6 6 6 66 67 68 69 8195 8261 8326 S383 8202 8267 8331 8396 8209 8274 8338 8401 8216 8280 8344 8407 8222 8287 8361 8414 8228 8293 8367 8420 8235 8299 8363 8426 8241 8306 8370 8432 8248 8312 8376 8439 8254 8319 8382 8445 112 3 112 8 112 3 112 2 3 3 3 S 4 6 5 4 6 6 6 4 4 5 6 4 4 5 6 70 8451 8467 8463 8470 8476 8482 8488 8494 8600 8606 112 2 3 4 4 6 6 71 72 73 74 8613 8673 8633 8692 8519 8579 8639 8698 8525 8685 8646 8704 8531 8591 8061 8710 8537 8597 8657 8716 8543 8603 8653 8722 8649 8609 8669 8727 8555 8616 8675 8733 8661 8621 8681 8739 8567 8627 8686 8745 112 2 112 2 112 2 112 2 3 3 3 3 4 4 5 5 4 4 6 6 4 4 6 6 4 4 6 5 75 8761 8766 8762 8768 8774 8779 8785 8791 8797 8802 112 2 3 3 4 6 5 76 77 78 79 8t08 8866 8921 8976 8814 8871 8927 8982 8820 8876 8982 8987 8825 8382 8938 8993 8831 8887 8943 8998 8837 8893 8949 9004 8842 8899 8054 9009 8848 8904 8960 9016 8854 8910 8965 9020 8869 8915 8971 9026 112 2 112 2 112 2 112 2 3 3 3 3 3 4 5 5 3 4 4 5 3 4 4 6 3 4 4 5 80 9031 9036 9042 9047 9053 9068 9063 9069 9074 9079 112 2 3 3 4 4 6 81 82 83 8i 9086 9138 9191 9243 9090 9143 9196 9248 9096 9149 9201 9263 9101 9164 9206 9268 9106 9169 9212 9263 0112 9166 9217 9269 9117 9170 9222 9274 9122 9175 9227 9279 9128 9180 9232 9284 9133 9186 9238 9289 112 2 112 2 112 2 112 2 3 3 3 3 3 4 4 5 3 4 4 6 3 4 4 6 3 4 4 5 85 9294 9299 9S04 9309 9316 9320 9326 9330 9335 9340 112 2 3 3 4 4 6 86 87 88 80 9345 9396 9446 9494 9360 9400 9450 9499 9366 9406 9465 9504 9360 9410 9460 9609 9365 9415 9466 9613 9870 9420 9469 9618 9876 9426 9474 9623 9380 9430 9479 9528 9386 9435 9484 9633 9390 9440 9489 9638 112 2 112 112 112 3 2 2 2 3 4 4 6 3 3 4 4 3 3 4 4 3 3 4 4 90 9542 9547 9562 9567 9562 9566 9671 9576 9681 9686 112 2 3 3 4 4 91 92 93 9i 9690 9638 9686 9731 9595 9643 9689 9736 9600 9647 9694 9741 9605 9652 9699 9745 9609 9667 9708 9760 9614 9661 9708 9764 9619 9666 9713 9759 9624 9671 9717 9763 9628 9676 9722 9768 9633 9680 9727 9773 112 112 112 112 2 2 2 2 3 3 4 4 3 3 4 4 3 3 4 4 3 3 4 4 95 9777 9782 9786 9791 9795 9300 9805 9809 9814 9818 112 2 3 3 4 4 96 97 98 99 9823 9S68 9912 9966 9827 9872 9917 9961 9832 9877 9921 9965 9836 9881 9926 9969 9841 9886 9930 9974 9845 9890 9934 9978 9860 9894 9939 9983 9854 9899 9948 9987 9869 9903 9948 9991 9863 9908 9952 9996 112 112 112 112 2 2 2 2 3 3 4 4 3 3 4 4 3 3 4 4 3 3 3 4 MATHEMATICAL TABLES 429 Antilogaeithms. 1 2 3 i 8 6 7 8 9 12 3 4 3 6 7 8 9 ■00 1000 1002 1006 1007 1009 1012 1014 1016 1019 1021 11 1 12 2 2 ■01 •02 03 '0< 1023 1047 1072 1096 1026 1050 1074 1099 1028 1062 1076 1102 1030 1064 1079 1104 1033 1057 1081 1107 1035 1059 1084 1109 1038 1062 1086 1112 1040 1064 1089 1114 1042 1067 1091 1117 1045 1069 1094 1119 11 11 11 111 1 1 1 1 12 2 2 12 2 2 12 2 3 2 2 2 2 •OS 1122 1126 1127 1130 1132 1185 1138 1140 1143 1146 111 1 2 2 2 2 ■00 ■07 ■08 ■09 114S 1175 1202 1230 1151 1178 1205 1233 1163 1180 1208 1236 1166 1183 1211 1239 1159 IISO 1218 1242 1161 1189 1216 1245 1164 1191 1219 1247 1167 1194 1222 1260 1169 1197 1226 1253 1172 1199 1227 1256 111 111 111 111 1 1 1 2 2 2 2 2 2 2 2 2 2 2 3 2 2 2 3 •10 1259 1262 1266 1268 1271 1274 1276 1279 1282 1285 111 1 2 2 2 3 ■11 ■12 ■13 ■14 1288 1318 1849 1380 1291 1321 1352 1384 1294 1324 1355 1387 1297 1327 1358 1890 1300 1330 1861 1393 1303 1334 1366 1396 1806 1337 1368 1400 1309 1340 1371 1403 1312 1343 1374 1406 1315 1346 1377 1409 Dili 111 111 111 2 2 2 2 2 2 2 3 2 2 2 3 2 2 3 3 2 2 3 3 ■15 1418 1416 1419 1422 1426 1429 1432 1435 1439 1442 111 2 2 2 3 3 ■16 ■17 ■18 ■19 1416 1479 1614 1549 1449 1483 1617 1552 1452 1486 1621 1666 1465 1489 1624 1660 1459 1493 1628 1563 1462 1496 1631 1667 1466 1600 1535 1570 1469 1508 1538 1574 1472 1507 1642 1678 1476 1510 1546 1581 111 111 111 111 2 2 2 2 2 2 3 3 2 2 3 3 2 2 3 3 2 3 3 3 ■20 1685 1689 1692 1596 1600 1608 1607 1611 1614 1618 111 2 2 3 3 3 ■21 ■22 ■23 ■24 1622 1660 1698 1788 1626 1663 1702 1742 1629 1667 1706 1746 1683 1671 1710 1750 1637 1675 1714 1754 1641 1679 1718 1768 1644 1683 1722 1762 1648 1687 1726 1766 1652 1690 1730 1770 1656 1694 1734 1774 112 112 112 112 2 2 2 2 2 3 3 3 2 3 3 3 2 8 3 4 2 3 3 4 ■28 1778 1782 1786 1791 1795 1799 1803 1807 1811 1816 112 2 2 3 3 4 •26 ■27 ■28 ■29 1820 1862 1903 1960 1824 1866 1910 1964 1828 1871 1914 1950 1832 1876 1919 1963 1837 1879 1923 1968 1841 1884 1928 1972 1845 1888 1982 1977 1849 1892 1936 1982 1864 1897 1941 1986 1868 1901 1946 1991 112 112 112 112 2 2 2 2 3 3 3 4 3 3 3 4 3 3 4 4 3 3 4 4 ■30 1996 2000 2004 2009 2014 2018 2023 2028 2032 2037 112 2 3 3 4 4 •31 •32 ■33 ■34 2042 2089 2138 2188 2046 2094 2143 2193 2061 2099 2148 2198 2056 2104 2168 2203 2061 2109 2168 2208 2066 2118 2163 2213 2070 2118 2168 2218 2075 2123 2173 2223 2080 2128 2178 2228 2084 2133 2183 2234 112 112 112 112 2 2 2 2 3 3 3 4 4 3 3 4 4 3 3 4 4 3 4 4 5 ■33 2239 2244 2249 2254 2269 2266 2270 2276 2280 2286 112 2 3 3 4 4 5 '36 ■37 ■38 ■39 2291 2344 2399 2456 2296 ■2350 2404 2460 2301 2355 2410 2466 2307 2360 2415 2472 2312 2366 2421 2477 2817 2371 2427 2483 2323 2377 2482 2489 2828 2382 2438 2496 2333 2388 2443 2600 2339 2393 2449 2606 112 2 112 2 112 2 112 2 3 3 3 3 3 4 4 6 3 4 4 6 3 4 4 6 3 4 5 5 ■M 2612 2618 2523 2629 2536 2541 2547 2663 2569 2664 112 2 3 4 4 6 5 ■il ■42 ■43 ■44 2570 2630 269i 2764 2570 2636 2098 2761 2582 2642 2704 2767 2588 2649 2710 2773 2591 2665 2716 2780 2600 2661 2723 2786 2606 2667 2729 2793 2612 2673 2735 2799 2618 2679 2742 2805 2624 2685 2748 2812 112 2 112 2 112 3 112 3 3 3 3 3 4 4 5 6 4 4 5 6 4 4 5 6 4 4 6 6 '45 281S 2825 2831 2838 2844 2861 2868 2864 28V1 2877 112 3 3 4 5 5 6 ■46 ■47 ■48 ■49 2SS4 2951 3020 8090 2891 2958 8027 3097 2897 2905 3084 3106 2904 2972 3041 3112 2911 2979 8048 3119 2917 2986 3065 3126 2924 2u92 3062 3133 2931 2999 3069 3141 2938 3006 3076 3148 2944 3013 3083 8155 112 3 112 3 112 8 112 3 3 3 4 4 4 5 6 6 4 5 6 6 4 6 6 6 4 5 6 6 430 MOTOR CAR ENGINEERING Antilogarithms. 1 2 3 4 5 6 7 8 9 12 3 4 5 6 7 8 9 •so 3162 3170 8177 3184 3192 3199 3206 3214 3221 3228 112 3 4 4 5 6 7 ■81 •52 •53 •5J 32S6 3311 3388 3467 3243 3319 3396 3476 8251 3327 3404 3483 8268 3334 8412 3491 3266 3342 3420 3499 3*73 3350 3428 3508 3281 3357 3436 3516 3289 3365 3443 3624 3296 3373 3451 3532 ii304 3381 3459 3640 12 2 3 12 2 8 12 2 3 12 2 3 4 4 4 4 5 5 6 7 5 5 6 7 5 6 6 7 5 6 6 7 •55 3648 3666 3565 3673 3681 8689 3597 3608 3614 3622 12 2 3 4 5 6 7 7 •56 S7 •68 •59 8631 3715 3802 3890 3639 3724 3811 3899 3643 3733 3819 3908 3656 3741 3828 3917 8664 3750 8837 3926 3673 3768 8816 3986 3681 3767 3856 3946 3690 3776 3864 3954 3698 3784 3873 3963 3707 3793 3882 3972 12 3 3 12 3 3 12 3 4 12 3 4 4 4 4 5 5 6 7 8 5 6 7 8 5 6 7 8 6 6 7 8 •60 8981 3990 3999 4009 4018 4027 4036 4046 4056 4064 12 3 4 5 6 6 7 8 •81 ■82 •63 •6i 4074 4169 4266 4365 4083 4178 4276 4376 4093 4188 4285 4385 4102 4198 4296 4395 4111 4207 4305 4406 4121 4217 4316 4416 4130 4227 4325 4426 4140 4230 4336 4436 4160 4246 4346 4446 4169 4!!66 4366 4467 12 3 4 12 3 4 12 3 4 12 3 4 5 6 6 6 6 7 8 9 6 7 8 9 6 7 8 9 6 7 8 9 •65 4467 4477 4487 4498 4608 4519 4529 4539 4550 4560 12 3 4 5 6 7 8 9 •66 •8T •68 •69 4571 4677 4786 4898 4581 4688 4797 4909 4692 4699 4808 4920 4603 4710 4819 4982 4613 4721 4831 4943 4624 4732 4842 4955 4684 4742 4863 4966 4645 4763 4S64 4977 4666 4764 4876 4989 4867 4776 48S7 5000 12 3 4 12 3 4 12 3 4 12 3 5 6 5 6 6 6 7 9 10 7 8 9 10 7 8 a 10 7 8 9 10 •70 6012 6023 5036 6047 6058 6070 5082 6093 5105 6117 12 4 6 6 7 8 9 11 •71 •72 •73 •7J 5129 6'24S 5370 6495 5140 6260 6383 5608 6152 6272 6396 5621 6164 6284 5408 6634 6176 6297 6420 6546 6183 5309 5433 6669 6200 6321 5446 5672 5212 6333 6458 5586 6224 5346 5470 6598 6230 5358 6483 5610 12 4 5 12 4 6 13 4 5 13 4 6 6 6 6 6 7 8 10 11 7 9 10 11 8 9 10 n 8 9 10 12 •75 5623 5636 5649 5662 5676 6089 5702 6716 5728 6741 13 4 5 7 8 9 10 12 •76 •77 •78 •79 5754 58S8 6026 6166 5768 6902 6039 6180 5781 5916 6053 0194 5794 6929 0067 6209 5808 6943 6081 6223 6821 6967 6095 6237 6834 5970 6109 6252 6848 5984 6124 6266 5861 59U8 6138 62S1 6875 6012 6152 6295 18 4 6 13 4 6 18 4 6 18 4 6 7 7 7 7 8 9 11 12 8 10 11 12 8 10 11 13 9 10 11 13 ■80 6310 6324 6339 6353 6368 6383 6397 6412 6427 6442 13 4 6 7 9 10 12 13 ■81 ■82 •83 •84 6467 6607 6761 6918 6471 6622 6776 6934 6486 6637 6792 6950 6501 6668 6S08 6966 6616 6668 6823 69S2 6631 6683 6839 6998 6646 6699 0855 7015 6561 6714 6871 7031 6577 6730 6887 7047 6692 6746 6902 7068 2 3 5 6 2 8 5 6 2 3 5 6 2 3 6 6 8 8 8 8 9 11 12 14 9 11 12 14 9 11 13 14 10 11 13 15 ■83 7079 7096 7112 7129 7145 7161 7178 7194 7211 7228 2 3 5 7 8 10 12 13 15 -86 ■87 ■88 •89 7244 7413 7686 7762 7261 7430 7603 7780 7278 7447 7621 7798 7296 7464 7638 7816 7311 7482 7666 7S34 7828 7343 7499 7616 7674- 7691 7852 7870 7362 7534 7709 7889 7379 7661 7727 7907 7896 766S 7745 7923 2 3 5 7 2 3 6 7 2 4 5 7 2 4 6 7 8 9 9 9 10 12 13 15 10 12 14 16 11 12 14 16 11 13 14 16 ■90 7943 7962 7980 7998 8017 8035 8064 8072 8091 8110 2 4 6 7 9 11 IS 16 17 ■91 ■92 ■93 ■94 8128 8318 8611 8710 8147 8337 8531 8730 8166 8356 8661 8760 8186 8375 8570 8770 8204 8395 8590 8790 8222 8241 8414 8433 8610 8630 8SlO 8831 8260 8453 8650 8851 8279 8472 8670 8872 8299 8492 8690 8392 2 4 6 8 2 4 6 8 2 4 6 8 2 4 6 8 9 10 10 10 11 13 15 17 12 14 16 IT 12 14 16 18 12 14 16 18 ■95 8913 8933 8954 8974 8996 9016 9086 9057 9078 9099 2 4 6 8 10 12 15 17 19 ■96 ■97 ■98 ■99 9120 9333 9650 9772 9141 9364 9672 9796 9162 9376 9594 9817 9183 9397 9616 9840 9204 9419 9638 9863 9226 9247 9441 9402 9661 9888 9886 1 9908 9268 9484 9705 9931 9290 9506 9727 9954 9311 9528 9730 9977 2 4 6 8 2 4 7 9 2 4 7 9 2 5 7 9 11 11 11 11 13 16 17 19 13 15 17 20 13 16 18 20 14 16 18 20 MATHEMATICAL TABLES 431 Angle. Chord. Sine. Tangent. Co-tangent. Oo.iine. De- grees. Radians, 0° 00 1 1^414 V570S 1-5533 1-6359 1-5184 1-5010 90° 1 2 3 4 •0175 •0349 •0524 •0693 •017 •035 •052 •070 •0175 •0349 •0523 •0J9S •0175 •0349 •0624 •0609 67^2900 28 •6363 111 0811 14^3007 -9998 •9994 •9986 •9976 1-402 1-389 1-377 1-364 89 88 87 86 6 •0S73 •087 •0872 •0875 1 1^4301 •9902 1-361 1-4835 85 6 7 8 9 ■1047 ■1-222 •1396 •1571 •106 •122 •140 ■157 •10« •1219 •1392 •1564 •1051 •12-28 ■1405 •1684 9 6144 S^1443 7^1164 0^S138 •9946 •9926 ■9903 •9877 1-338 1-325 1-312 1-209 1-4681 1-4486 1-4312 1-4137 84 83 82 81 10 •1745 •174 •1736 ■1763 6 6713 •9848 1-286 1^3963 80 11 12 13 14 •1920 •2094 •2269 •2443 •192 ■209 •226 •244 •1908 •2079 •2250 •2419 •1944 •2126 •2309 •2493 5^1446 4^7046 4-3315 4^0108 •9816 •9781 •9744 •9703 1-272 1-269 1-245 1^231 1-3788 1-3614 1-3439 1-3265 79 78 77 76 15 •261S •261 •2588 •2679 3 •7321 •9659 1^218 1-3090 76 16 ir IS 19 •2793 •2967 ■3142 •3316 •278 •296 •313 •330 •2756 •2924 •3090 ■3256 •2867 •3057 •3249 •3443 3^4874 32709 3^0777 2^9042 •9613 •9663 •9511 •9466 1^204 1^190 1^176 - 1^161 1-2915 1-2741 1-2666 1-2392 74 73 72 71 20 •3491 •347 ■3420 •3640 2 7475 •9397 1-147 1-2217 70 21 22 23 24 •3665 •3840 •4014 •4189 •364 •382 •899 •416 •3684 •3746 •3907 •4067 •38i9 •40-10 •4215 •4462 2 ■6061 2-4751 2-3559 2-2460 •9336 •9272 •9205 •9135 1^133 1^118 1^104 1^089 1-2043 1-1808 1-1694 1-1519 69 68 67 66 25 •4863 •433 •4226 ■4663 2-1445 -9063 1^075 1-1345 65 26 27 2S 29 •4538 •4712 •4887 •6061 •450 •467 •484 •601 •4384 •4540 •4695 •4848 •4877 ■6095 •6317 •5543 2-0503 1-9626 1-8807 1-8040 •8988 •8910 •8829 •8746 1^060 1^045 1^030 1^015 1-1170 1-0996 1-0821 1-0647 64 63 62 61 30 •5236 •618 •6000 •5774 1-7321 •8660 l^OOO 1-0172 60 31 32 33 34 •5411 •5685 •5760 •6934 •634 •561 •668 •685 •6160 •6299 •6446 •6692 •6009 •6249 •6494 •6745 1-6643 1-6003 1-6399 1-4826 •8672 •8480 •8387 •8290 •985 •970 •954 •939 1-0297 1-0123 -9948 -9774 59 68 67 66 35 •6109 •601 •5736 •7002 1-4281 •8192 •923 -9699 55 36 37 38 39 ■6283 •6458 •6632 •6S07 •618 ■686 •661 •868 •6878 •6018 ■6157 •6293 •7266 •7636 ■7813 ■8098 1-3764 1-3-270 1-2799 1-2349 •8090 •7986 •7880 •vvvi •908 •892 •877 •861 -9425 -9250 -9076 •8901 64 53 52 51 40 •6981 •6S4 •642S •8391 1-1918 •7660 •846 ■8727 60 41 42 43 44 •7166 •7330 •7505 •7679 •700 •717 •733 •749 •6561 •6691 •6820 •6947 •8693 •9004 •9326 •9657 1-1604 1-1106 1-07-24 1-0335 •7647 •7431 •7314 •7193 •829 •813 •797 •781 •8562 •8378 •8203 •8029 49 48 47 46 45° •7864 •765 •7071 l^OOOO 10000 •7071 ■766 •7854 45° Cosine. Oo-tangent. Tangent. Sine. Cliord. Radians. De- grees. Angle. INDEX The numbers refer to pages. Absolute temperature, 94 Acceleration of reciprocating parts, 215 Accumulators, 130 — 136 „ capacity, 132, 394 charging of, 131—133 ,, chemical action, 131 ,, construction, 130 Acetylene, 66 Adiabatic expansion, 96 — 98 ,, ,, teniperature in, 100 Adjustment of carburetter, 80 Air, constituents of, 55 ,, cooling, 203, 204 ,, proportions of, 50, 66 ,, required for combustion, 64, 56 ,, standard of efficiency, 124 Alcohol, 60 Alkoethine, 67 Arrangement of valves, 31, 32 Automatic advance and retard, lYl Axle casings, 283—286 „ front, 342, 343 „ Uve, 273—275, 283—286 Bailleb's test apparatus, 47 — 50 Balance, 26, 27 Ball bearings, 321—323 Battery ignition, 141, 142 Benzol, 64—66 Bevel gearing, 279 Bingham engine, 39, 40 Boilers, flash, 376 Stanley, 382 tubular, 375, 376 Turner, 387 White, 377 M.O.E. Boiling point, 51, 348 Boyle's law, 94, 95 Brake horse-power, 109 — 114 Brakes, 234—249 clutch, 229 ,, electrical, 112 — 114 external, 241, 242 front wheel, 243—249 ,, internal, 239 ,, rope, 109 Brown & Barlow carburetter, 89 Burning test, 307 SPRINGS, 336 Calorific value, 52 Calorimeter, Darling's, 53 Carburation, 74—80 Carburetter, function of, 69 types of, 69 Brown & Barlow, 89 Claudel-Hobson, 83 Lanchester, 82 Longuemare, 87 Polyrhoe, 90 Scott-Eobinson, 85 Trier & Martin, 88 Centrifugal pumps, 205 Chain drives, 271—273 Change speed gears, 251 Characteristics of series, shunt and compound wound motors, 396 — 398 Charles' law, 94, 95 Chassis requirements, 325, 326 Circulating pumps, 205 — 207 Claudel-Hobson carburetter, 83 Clutches, cone, 222 , disc, 227—234 ,, double cone, 223 F F 434 INDEX Clutches, expanding, 224 ,, plate, 225 ,, reversed cone, 223 Ooil-trembler, 138—140 Gold test, 306 Combustion, 100—102 „ air required for, 54 „ chamber, 31, 32, 35 Commutators, 142 — 145 Composition of exhaust, 81, 82 Compound engines, 357 Compression, 98—100, 352, 353 Condensers, 140, 141, 356, 373 Connecting rods, 21, 23 Control systems, 197 Controllers, 399 Cooling, Chap. XIII. air, 203 ,, water, 204 Cooper engine, 12 Coupling for flywheel, 27 Crank efiort. Chap. XIV. Crankshafts, 23, 25 Cranks, arrangement of, 26, 27 „ sequence of, 25 Cross springs, 335, 336 Current, generation of, 156, 157 Cylinders, 28, 29 Dead axles, 342, 343 Desaxe engines,- 13 Differential gear, 276, 277 Direct drive in gearbox, 255 Disc clutches, 227—234 Dissociation. 101 Distributors, 145, 146 Dry cells, 128, 129 Dual systems, 172—186 Duplex ignition, 186 — 192 Dynamometers, 110 — 113 EFFEfiTiVB pressure, 107, 108 Efficiency, air standard, 124 ,, combustion, 120 „ ideal 123, 124 ,, mechanical, 124 ,, relative, 124 Efficiency, thermal, 121 Effort, crank, 218 „ tractive, 116, 117 Electric car. Chap. XXIV. ,, ignition. Chaps. X., XL „ motor, 394—398 Electrolysis, 128 Electromotive force, 127 En-bloc systems, 14 Engine control systems. Chap. XII. Equivalent twisting moment, 217 Exhaust, composition of, 81, 82 Expanding brakes, 241, 2J2 Expansion, 96—100, 355, 361 Explosion, 100—102 Eans, 210, 211 Eeed-heaters, 357, 358 Fixed ignition, 197 Elash boilers, 376 Flash-point apparatus, 305 Flexibility, 14, 36, 74 Float feed, 71 Floats, 70 Fluctuation of energy, 219 Flywheel, 27, 212, 219 Forced lubricalion, 312 — 315 Four-stroke cycle, 5 Framing, 326—333 Front axle, 342, 343 Fuel systems, 72, 73 Q-AS, exhaust, 81, 82 Gate change, 260—265 Gearbox, necessity for, 251 Gearing, number of speeds, 251 — 255 Gears, Chapter XVI. ,, epicyclic, 266—268 ,, types of, 256—260 Generation of current, 156, 157 Governors, 194, 195 Gudgeon pin — how secured, 20 Heat of combustion, 100—102 ,, specific, 93, 99 „ units of, 93 Hewitt engine, 41 INDEX 435 High-tension current, 136, 13Y ,, magnetos, 162 — 192 Hoptinson flash-light indicator, 105—107 Horse-power, Chapter VIII. ,, brake, 109 ,, indicated, 103 ,, road -wheels, 117, 118 E.A.O. rating, 114—116 Hyperbolic expansion, 96, 97 Ideai efficiency, 123, 124 Ignition, Chapters X., XI. ,, coil and accumulator, 141 — 146 dual, 172—186 duplex, 186—192 high-tension, 137, 162—192 low-tension, 157, 158 magnetic, 158 — 162 Indicated horse-power, 103 Indicators, diagrams from, 98 — 103 ,, Dobbie Mclnnes, 104, 105 Hopkinson, 105— 107 „ types of, 104 Induction coil, 138-140 „ pipes, shape of, 80 ,, stroke, 5 Inertia of reciprocating parts, 214 — 216 Internal brakes, 239 Isothermal expansion, 96, 97 Jackets, 29 Jet carburetters, 63, 83 — 92 Joule's equivalent, 95 Joy's valve gear, 366—368 Kerosene, 59 Kinetic energy, 219, 234, 235 Klein's construction, 215, 216 Knight engine, 37—39 Lanchestee carburetter, 82 Lenz's law, 141 Live axle, 273—275 Lodge igniter, 149 — 152 Longuemare carburetter, 87 Low-tension current, 136, 137 Lubricants, Chapter XIX. „ for gearbox, 309, 310 Lubricating oils, 301 ,, ,, action of, 302 ,, „ requirements for, 303—305 Lubrication for chassis, 310 systems, 310—320 Magnetic field, 139, 140, 156, 157 ,, igniters, 158 ,, Bosch, 159—162 Magneto construction, 154 — 156 „ ignition, Chapter XL Magnetos, Bosch, 164—166, 174—177 C.A.V., 184—186 ,, Eisemann, 170—172 Fuller, 162—161, 173, 174 Hall, 179-183 high-tension, 162—192 ,, low-tension, 157 — 159 „ Mea, 166—168 Simms, 178, 179 ,, speed of, 155 Mass, 215 Materials used in car construction, 402, 403 Mean effective pressuie, 107, 108 Mechanical efficiency, 124 Methylated spirit, 61 Mixture of air and petiol, 79 Multiple disc clutches, 227—234 Naphtha, Scotch shale, 66 Needle valve, 71 Non-trembler coils, 144 Ohm's law, 127 Oil pumps, '.VZO Order of firing, 1-J9 Otto cycle, 5 — 7 Overheating, 202, 203 Pakappin, 59 Petrol, Chapter IV. ,, composition of, 46 436 INDEX Petrol, pliysical properties, 44, 421, 425 ,, source and distillation, 45 Piston velocity, 214 Pistons, 16—20 Plugs, sparking, 147, 148 Polarisation, 129 Polyrhoe carburetter, 90 Position of carburetter, 71, 72 „ „ valves, 28, 31, 32 Pressed steel framing, 326, 327 ,, ,, pistons, 20 Primary winding, 138, 139, 156, 157 Propeller shaft, 273—277 Pumps, oil, 320, 321 water, 205—208 Eadiatoes, 208, 209 position of, 209, 210 Eadiusrods, 341, 342 Eating, E.A.O., 114—116 Eatio, compression; 30, 100, 123, 124 ,, gear; 252 — 255 ,, of expansion, 354 Eequirements fulfilled by good brake, 236 ,, ,, bygoodclutcb, 221, 222 „ „ by good fuel, 58 „ by good oil, 303—305 Eesistance of a conductor, 127 ,, gradient, 117 road, 116, 117 wind, 117 EoUer bearings, 323 E.A.O. rating, 114—116 Saturated steam, 349 Saturation of a medium, 79 Scott-Eobinson carburetter, 85 Secondary winding, 138, 139, 156, 157 Sensible beat, 348 Shock absorbers, 337 — 340 Sparking plugs, 147, 148 Specific gravity, 50 „ heafr, 93 Splash lubrication, 310, 311 Springs, 333—337 Stanley boiler and burner, 382 — 384 ,, engine, 370 ,, pipe diagram, 386 — 387 Steam engine cycle, 351, 353 Steering axles and pivots, 292 — 294 ,, columns, 294—298 ,, connections, 298 — 300 Stephenson's link motion, 365, 366 Superheated steam, 350, 351 ,, ,, object of using, 354—356 Suspension of engine and gearbox, 332, 333 ,, ,, motors, 393 Tappets, 32—35 Teeth of wheels, 268 Temperature in adiabatic expan- sion, 100 Thermal efiaoiency, 121—124 Thermosyphon cooling, 201 Thrust bearings, 323 Timing of valves, 33 — 35 Torque rods and tubes, 340, 341 Total heat of steam, 349 Transmission gear, Chapter XVII. Trembler coil, 138—140 Trier & Martin carburetter, 88 Trough lubrication, 312 Tubular boilers, 375, 376 Turner boiler and burner, 387, 388 engine, 370—373 ,, pipe diagram, 389, 390 Two-stroke cycle, 7 Types of clutches, 222, 223 Units of heat, 93 Universal joints, 275, 276 Valve arrangements, 31, 32 ,, gears for steam engine, 365 ,, setting, 33 Valveless engine, 8 D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STREETS New York SHORT=TITLE CATALOG OF OF SCIENTIFIC AND ENGINEERING BOOKS This list includes the technical publications of the following English publishers: SCOTT, GREENWOOD & CO. CROSBY LOCKWOOD & SON CONSTABLE & COMPANY, Ltd. TECHNICAL PUBLISHING CO. ELECTRICIAN PRINTING & PUBLISHING CO. for whom D. Van Nostrand Company are American agents. February, 1911 Short-Title Catalog OF THE Publications and Importations OF D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STREETS, N. Y. Prices marhed with an asterisJe '(*) are NET. All bindings are in cloth, unless otherwise noted. 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The material in Foster is logically arranged and is indexed in a full table of contents and a voluminous index that alone covers sixty pages, and to this is added a set of patent thumb index tabs that make reference to any section of the book practically instantaneous. The index is most thorough and reliable. It points right to the spot where the information sought is. If you ever need information on electricit)', you ought to have a copy of the new Sixth Edition, completely revised and eniargea, with four-fifths of tne old matter replaced fay new, UD-to-date material, and containing ali the ex- cellent features named above, with 1,636 pages, 1,128 illustrations and 718 tables. The price is $3.00. CIVIL ENGINEERS' POCKETBOOK By ALBERT I. FRYE, M. Am. Soc. C. E. A COMPREHENSIVE Ireatment of Civil Engineering, in seventy sections, comprising about 1 ,400 pages ; with 500 tables and 1 ,000 illustrations. Also a complete glossary of engineering terms. Each main subject receives economic consideration and analysis, and is reinforced with excerpts from, and references to, the most important cost and other data in our leading technical publications — including hundreds of illustrations of up-to-date engineering structures and details. "How to design engineering structures economically" has received careful study in the preparation of this work. The fundamental prin-. ciples laid down can be followed readily by every young engineer, and carried to practical completion in the finished structure. Most of the tables are new and have been prepared regardless of time and expense. Many of them have been arranged in a novel manner which will appeal especially to engineers ; and all have been carefully checked and rechecked to eliminate the possibility of errors. Graphical methods have been illustrated freely throughout the work, in connection with analytical solutions. 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