412Wheels

Having been developed from the wheels of horse drawn carriages, automotive Fig. 41.3 The Dunlop TD Safety tyre was first applied to the BL Metro car and Michelin applied the same principle to its TDX range. The bead retaining groove holds the tyre on the rim. This was claimed to enable the driver to run with the tyre deflated, at speeds of up to 40 mph (64 km h), for far enough to enable him to choose a safe place to stop and change the wheel. The hatched sections represent the underinflated...

1819 Eccentricrotor pump

Eccentric-rotor-type pumps, such as the Holbourn-Eaton unit in Fig. 18.7, are sometimes used for engine lubrication, though more commonly for powering steering and other auxiliary systems. Invariably, the eccentric star-shaped inner rotor has one fewer lobes than the outer one which it drives. Inner rotors for lubrication systems usually have four lobes, though the larger ones may have five. The inlet and outlet ports are in the walls at the opposite ends of the housing. As the lobes pass over...

1314 Resonant or standing waves

When the air in a pipe is transiently displaced axially, the wave that this displacement generates in it tends to bounce repeatedly from end to end, as indicated in the middle diagrams in Figs 13.20 to 13.22. Each of these diagrams shows the form of the resonant waves in a pipe of a different configuration. Their fundamental frequencies depend on the length of the pipe. Resonance can be initiated by, for example, an external force causing vibration of the pipe, or by some disturbance of the...

441The rigid sixwheeler

This type of vehicle has been intensively developed during the last 20 years and many different arrangements have been evolved both as regards their suspension and transmission systems. The earliest vehicles consisted essentially of a four-wheeled lorry with the addition of a third axle placed behind and as close as possible to the existing rear axle. The third axle was sometimes merely a weight-carrying dead axle and sometimes a live driving axle. This type of vehicle is still widely used, but...

General principles of heat engines

The petrol or oil engine, which is the source of power with which we are immediately concerned, is a form of internal combustion 'heat engine', the function of which is to convert potential heat energy contained in the fuel into mechanical work. It is outside the scope of the present volume to go deeply into the physical laws governing this conversion, for a full study of which a work such as A. C. Walshaw's Thermodynamics for Engineers (Longmans-Green) should be consulted. It will not be out...

65Injection and combustion processes

Extensive research has been and is being carried out to determine the best methods of injection and form of combustion chamber to give smooth and complete combustion of the injected fuel and suppression of the characteristic 'diesel knock' which gives rough and noisy running or the high speed mechanical injection engine. The problem is to inject into the cylinder an extremely small volume of liquid fuel in such a manner and into such an environment that every minute particle of oil shall be...

153 SU pump

Among the early and most successful electrically actuated diaphragm type pumps was the SU unit, which superseded their Petrolift series. The diaphragm comprises several layers of elastomerically impregnated fabric, and its centre is clamped to the armature A. As can be seen from Fig. 15.3, discs having rounded- instead of square-faced peripheries are interposed between the grooved periphery of the armature and the counterbore in the end of the magnet pot M. These not only centre the armature as...

2625An allindirect gearbox

A good example of an all-indirect gearbox is illustrated in Fig. 26.26. This layout is especially suitable for rear-engine rear-wheel-drive or front-engine front-wheel-drive cars in which the engine is installed longitudinally. Clutch shaft A is coupled to the input or driving shaft B by a splined muff C. Five pinions are either integral or fixed to the shaft B and four of these pinions mesh with gears that are carried on the driven or ouput shaft D on needle roller bearings N. The driven shaft...

314 Vehicle design implications of traction control

A prime requirement, especially for road-going vehicles, is that the traction control device should come both into and out of operation rapidly. It must do so, however, entirely unobtrusively, otherwise the traction can become jerky and the steering can be adversely affected. Other problems arising include dissipation of the heat developed by the slipping clutch and the cam devices, wear, juddering and noise generated, and a loss of overall efficiency. Ideally, the slip should be limited to...

321Live back axles

A live axle is one that either rotates or houses shafts that rotate, while a dead axle is one that does neither, but simply carries at its ends the stub axles on which the wheels rotate. Live axles perform two functions (1) To act as a beam which, through the medium of the springs, carries the loads due to the weight of the carriage unit and its contents, and transmits these loads under dynamic conditions through the road wheels - rotating on its ends - to the ground. The dynamic loading is...

39Ring sections

Cross-sectional depth is determined by the radial stiffness required, though it is necessary to ensure that the bearing areas between the ring and the sides Table 3.1 CHEMICAL COMPOSITION, PER CENT Table 3.1 CHEMICAL COMPOSITION, PER CENT of its groove are adequate. Thickness, although it also has an influence on radial stiffness, is primarily determined by the bearing pressures required between the outer face of the ring and the cylinder wall. Simple rectangular-section rings, though often...

Bearings gearing chain and belt drives

When a shaft has to revolve it must be supported in bearings that will allow it to rotate. The simplest bearing is just a cylindrical hole formed in a piece of material and in which the shaft is a free fit. The hole is usually lined with a brass or bronze lining, or bush, which not only reduces the friction in the bearing but also enables an easy replacement to be made when wear occurs. Bushes are usually a tight fit in the hole in which they fit. To reduce the friction to the lowest amount,...

258 Clutch action

Figure 25.7 also serves to show how the clutch enables a car to be started up from rest. When the car is at rest the resistance to be overcome before the car will move is, for the level road A, given by OQ. If the engine were in permanent connection with the driving wheels it would, of course, be at rest and the tractive effort would be zero. The clutch, however, allows the engine to be run at a speed at which a torque giving a greater tractive effort than OQ is developed and enables this...

3617Automatic braking and traction control

Automatic brake systems (ABS) have been covered in detail in Chapter 39 and traction control systems (TRC) and limited slip differentials (LSD) in Chapters 31 and 39. If the wheels lock, the coefficient of friction between the tyres and the road becomes lower than when they are rolling, and the vehicle is liable to become unstable and skid. To prevent the wheels from locking when the brakes are applied, the sensor in a simple ABS system signals to a computer the speed of rotation of the wheels....

44Eight cylinders

Here the proper interval between power strokes is 90 . A 'straight eight' may clearly be formed by placing two fours end to end with their flat crankshafts at right angles, as in the upper diagram of Fig. 4.2. Each set of four cylinders is then in balance for primary forces and couples as explained in Chapter 2, but there remains the secondary effect. This secondary effect acts downwards when the cranks are horizontal and upwards when they are vertical thus, while the downward secondary effect...

1111 SU constantdepression carburettor

The SU carburettor type HS, without its extra emission control features, is illustrated in Fig. 11.23. An air valve G is integral with the piston P and securely attached to the piston rod R, which slides in the close-fitting bore of the suction chamber S. The depression just downstream of the air valve is transmitted through a pair of holes, V, to the suction chamber, above the piston. Because of the very low rate of the return spring, the load to be supported by the vacuum is practically...

267Control mechanism

The sliding of the members M, N and (when required) Q, is effected by means of selector forks, an example of which is shown in Fig. 26.7. The fork fits into a groove formed in the boss of the gear to be moved, so that although the gear is left free to revolve, it must partake of any sideways movement that is given to the fork. There will be a selector fork for each sliding member in the gearbox. The selector forks either slide on rods fixed in the gearbox casing or are fixed to rods which can...

378 Disc brakes

Brakes using flat discs as the friction surfaces have been used in the past but until the last three decades have not been so successful. They are now almost the commonest type for the front wheels of cars and are often used for the rear wheels and on some light vans. The earliest disc brakes wear made on the same lines as a multiple-plate clutch but most present-day designs use a single disc and almost always have sector-shaped friction pads of relatively small area. The great advantages are,...

310 Oil control rings

In the early days of the internal combustion engine, only one compression ring was used. Subsequently, two were found to seal better, and later even three were used. As speeds increased, greater quantities of lubricant had to be supplied and the problem of controlling it had to be faced. In the first instance, this was done simply by using a lower ring having a narrow face-width, to increase its contact pressure. Then stepped, or bevelled or taper-faced rings were employed and, ultimately,...

17General method of conversion of heat to work

All heat engines convert heat into work by the expansion or increase in volume of a working fluid into which heat has been introduced by combustion of a fuel either external to the engine, as in a steam engine, or internally by the burning of a combustible mixture in the engine itself, a process giving rise to the phrase internal combustion (ic) engine. Thus, in all so-called static pressure engines, as distinct from turbines, it is necessary to provide a working vessel, the volume of which is...

389Actuating cylinders for air brakes

Air pressure brakes are usually actuated by diaphragm cylinders in which the diaphragm acts as a piston but has the advantage that no sliding air-tight joints are necessary. To enable a single cylinder to be used for both foot-pedal and hand-lever operation Clayton Dewandre introduced the triple-diaphragm cylinder shown in Fig. 38.15. When the brake pedal is depressed air is admitted to the space A while operation of the handbrake admits air to the space B. The space between A and B is open to...

152 Mechanical diaphragm type pump

The diaphragm type positive displacement pump has the advantage of simplicity and low cost. Moreover, in the presence of water or dirt it is more reliable than an electrical pump. Its principal disadvantages are the pulsating nature of its output and, to provide it economically with a mechanical drive, it generally has to be mounted on the engine. In the latter position it not only has to pump against a large suction head but also may be affected by conducted and radiated heat, especially from...

1414 Air injection and gulp valve

A version of the AC-Delco air injection system made in the UK comprises an engine-driven air pump delivering into an air manifold, and thence through a nozzle or nozzles into either the exhaust ports or, latterly, between the reducing and oxidising catalytic beds. At the junction between the delivery pipe and the manifold, there is a check valve, to prevent back-flow of exhaust gas into the pump and thence to the engine compartment this could happen in the event of failure of the pump or its...

416Tyres

As previously indicated, the primary function of the tyre is to provide a comfortable ride by absorbing the high frequency and low amplitude Fig. 41.13 Left to right respectively inset, central and outset cast alloy wheels Fig. 41.13 Left to right respectively inset, central and outset cast alloy wheels disturbances generated by its rolling along the road. Lower frequency high amplitude deflections are absorbed by the suspension springs. Because acceleration is proportional to the square of...

2414 Driven plate

With the traditional front-engine rear-wheel-drive car, the easiest way to overcome transmission noise problems at the prototype stage is, in most instances, to alter the flexibility of the propeller shift. With front-wheel-drive cars, however, which have short, stiff driveshafts, this option is no longer open. As a result, manufacturers have turned to adjustment of the flexibility of the driven plate of the clutch instead. Originally, the spring centre was incorporated in driven plates solely...

327 Springs serving also as torque and thrust members

This system, Fig. 32.3, known as the Hotchkiss drive, is the most widely used. The springs A are rigidly bolted to the axle casing B. Their front ends are pivoted in brackets on the frame or vehicle structure, and their rear ends connected to the structure by means of either swinging links, or shackles C, or simply sliding in brackets as in Figs 35.7 and 37.18. Obviously torque reaction causes the springs to flex, or wind up, as shown exaggeratedly in Fig. 32.4. Brake torque of course would...

Induction manifold design

For single-cylinder engines one simple pipe is of course all that is needed for transferring the mixture from the carburettor to the inlet port on the cylinder head. To provide for a multi-cylinder engine, however, what is termed an induction manifold is generally needed. It generally comprises a main trunk from which branch pipes are taken, one to each cylinder, and on which is mounted the carburettor or injection equipment. By appropriate design, as explained in Sections 13.5 to 13.25, it is...

1218The electronic ignition control

Control of the ignition system is based on a spark advance characteristic map stored in the memory of the Motronic control unit. The spark advance is continuously changed to correspond to the setting on the map, taking into account throttle position, and engine-coolant and air-intake temperatures. When a spark is required, the electronic controller momentarily opens the circuit to earth, whereupon the collapse of the field around the primary generates the spark voltage in the secondary coil....

1724 The effects of additives on combustion and performance

One of the early entrants, in 1988, into the multi-additive diesel fuels market was Shell's Advanced Diesel. This contains several additives, one of which has raised its cetane number from the 48 required by British Standards, and the minimum of 50 for Shell's base fuel, to typically between 54 and 56. Among the others are a corrosion inhibitor, anti-foam, cold flow and reodorant additives. The benefits claimed include lower noise, 3 better fuel economy, Fig. 17.11, 8.4 less black and white...

1813 Lubrication systems

Early engines had only elementary lubrication systems. Up to the 1920s, some had manual pumps that were actuated intermittently. For others, up to the 1930s, oil was fed by gravity from a tank through a pipe to the crankcase, where it was either piped directly, or passed through ducts in the casting, to the main bearings, the flow generally being manually regulated by a needle valve. Alternatively, it was delivered into the base of the casting, whence it was whipped up by the rotating cranks...

345 Control of the Mechadyne Mitchell system

The friction to be overcome to control the mechanism, by moving the shaft eccentrically, is not great. Consequently, either electric or hydraulic power Modified valve lift with no phase shift - Modified valve lift with phase advance Modified valve lift with no phase shift Modified valve lift with phase advance 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 Fig. 3.34 Characteristics of the Mechadyne-Mitchell system with phase change could be used. Where hydraulic power is...

1420 Oxides of nitrogen NOX

To understand the effects of fuel properties on NOx output certain basic facts must be borne in mind. First, it depends not only on the peak temperature of combustion but also on the rate of rise and fall to and from it. Secondly, the combustion temperatures depend on primarily the quantity and, to a lesser degree, the cetane number of the fuel injected. Increasing the cetane number reduces the delay period, so the fuel starts to burn earlier, so higher temperatures and therefore more NOx are...

155 Air filters and silencers

There are three types of air cleaner dry, centrifugal and wet, or oil bath. For cars, dry filters, with pleated resin impregnated paper or, in a very few instances, felt elements are employed. These elements are mostly of cylindrical shape with deep vertical pleats, so that at least some of the dust stopped by them tends to fall to the base, leaving the surface reasonably clear. Deep pleated paper, as in Fig. 15.6, offers the advantage of a very large surface area, and therefore not only long...

1412 Evaporative emissions

The evaporative emissions are mostly hydrocarbons though, with some special fuels and those that have been modified to increase octane number, alcohols may also be present. In general, the vapour comes from four sources (2) Permeation through the walls of plastics tanks. (3) The carburettor venting system. (4) Through the crankcase breather. Fumes from the fuel tank venting system are absorbed in carbon canisters which are periodically purged, Section 14.17. Permeation through the walls of...

4019Rackandpinion steering mechanism

This is especially suitable for cars with double transverse wishbone or MacPherson strut-type suspension. Its principal advantages, in addition to accommodating relatively easily with the suspension geometry, are the positive feel of such a system, high efficiency, simplicity, the relative ease with which it can be rigidly mounted on the vehicle structure and the consequent precision of the system. Moreover, by increasing the spiral angle of the teeth, a high ratio is obtainable with a pinion...

4111Aspect ratio and tyre markings

The aspect ratio is the inverse of the ratio of the width to the height of the crown of the tyre above the edge of the bead that seats on the rim. Modern tyres are all wider than they are high. Before World War II, Avon, for example, produced their Super Safety range, which were Super Balloon type tyres with an aspect ratio of 95 . By the time that radial tyres were introduced, in the late 1940s, most of the crossply tyres had aspect ratios of 88 (Low Section) or 82 (Super Low Section). These...

4114 Materials

Mixtures of natural and synthetic rubbers are normally used in tyre construction. The synthetics include styrenebutadiene, isoprene, neoprene and butyl. Each of these has different properties which affect the performance of the tyre. In general the requirements are rigidity of the tread and flexibility of the side walls, coupled with durability. The principal reinforcement chemical used is carbon black in very small particle sizes. Since it was first introduced, it has been developed to the...

28Couples due to revolving masses

Referring again to Fig. 2.7, it will be appreciated that the revolving masses at each crank give rise to couples in just the same way as the reciprocating masses, except that here it is an 'all-round' effect instead of acting only in the vertical plane. The revolving couple is unbalanced in Fig. 2.6, while in Fig. 2.7 the two opposite couples are opposed exactly as indicated by the arrows for the reciprocating effects, and the shaft and crankcase assembly must be so stiff as to avoid whip under...

2610 Steering column gear shift control

Gear change levers situated just below the steering wheel are now rarely used, except for some light commercial vehicles, such as forward control vans, in which there is a need for the floor to be free from obstruction so that the driver can move freely from one side of the cab to the other. A typical example of a steering column-mounted control is shown in Figs 26.9 and 26.10. The gearbox concerned is a four-speed and reverse type and there are three striking forks A, B and C, of which A is...

910Compressionignition twostroke engine

Since in the compression-ignition engine no fuel enters the cylinder until all ports and valves are closed, and cannot therefore be lost through the exhaust ports, one of the greatest objections to the two-stroke cycle is eliminated, and it is with this type of engine that the cycle tends to make greatest progress. There is another important merit of the high-compression ci engine in its application to the two-stroke form. The high expansion ratio results in lower exhaust temperature and...

H

H H H H H H H h C C C C C C C H Fig. 17.3 Examples of the long chain heavier alkanes are iso-octane (top) and -octane (below) Fig. 17.4 Molecules of methyl cyclo-pentane and ethyl cyclo-pentane. This is a simplified diagram, in which only the carbon molecules are shown. Such simplifications are often used and are justified because we can take it that, at least in hydrocarbon fuels, each carbon atom has four arms to which either carbon or hydrogen atoms must be attached atom is associated with...

85 Relative merits of spark ignition and ci engines

In spite of the inherent disadvantages of greater weight and bulk per horsepower and rougher running, the ci engine has fully consolidated its position. Greater economy, greater security from risk of fire, and with modern bearing materials and methods of manufacture a degree of general reliability at least as good, if not better, than that of the petrol engine, are definitely attained. The injection equipment, provided proper care is taken with filtration of the fuel, is proving itself more...

2618 Multi and doublecone synchronisers

Smiths Industries Ltd had developed a multi-cone synchromesh mechanism by 1963, but never put it into quantity production. Meanwhile, synchromesh gearboxes have been increasingly demanded for heavy commercial vehicles and ZF have introduced their D-type synchroniser and have applied it to, for example, their Ecolite gearboxes. The Smiths version is illustrated in Fig. 26.19, in which the parts have been annotated with the same letters as the corresponding parts in Fig. 26.18. The important...

2010 Hybrid power

For many years experiments have been carried out with diesel- or petrol-electric hybrid power units. All suffer the disadvantage that two power units are required an internal combustion engine and an electric motor. The implications therefore are of complexity, high initial cost, two power units that could malfunction, and large bulk. In the past, controlling two power units for economical operation was difficult. However, the introduction of electronic engine management systems virtually...

1814 Pressure lubrication

In the meantime, from 1905, a Lanchester car was introduced having a pump for delivering oil to the main bearings, and pressure lubrication systems were soon widely applied. Examples of modern pressure lubrication systems are illustrated in Chapters 3 and 4. The principles are similar to that illustrated in Fig. 18.5. In the early days, pipes were widely employed to take oil to the main bearings and up to the valve gear. However, because they add to installation costs and are vulnerable to...

151 Rollercell positive displacement type pump

Bosch produce a roller-cell type, high pressure fuel pump, driven by a permanent magnet d.c. motor. The output of such a pump does not pulsate as much as most of those of the other positive displacement types. Its pumping element is in the armature housing and the fuel flows right through, from one end to the other, to cool and lubricate all the rotating parts, Fig. 15.1. A permanentmagnet d.c. electric motor drives a radially slotted disc rotating in a housing, the inner cylindrical wall of...

1821 Oil circulation and pressure indicators

The only indication that the oil is circulating properly is the reading of a pressure gauge or illumination of a warning lamp if it is not. This is far from satisfactory, but so far nothing better has been found. Oil pressure is of course dependent on viscosity but, in general, any deviation from normal should be regarded with suspicion. Oil pressure used to be indicated invariably by means of a bourdon tube-actuated pointer in an instrument on the dash fascia. This called for the oil to be...

418 Tread design

The tread itself is of a special rubber mix formulated to provide good wear resistance, firm grip on the road surface and high strength to cope with the various loads applied to it in the contact patch area. Indeed, different types of rubber may be employed for the treads, side walls, beads and fillers. Tread materials and patterns are determined by the type of duty required. Racing cars, for example, have what are termed dry and wet alternatives which may be interchanged during a single race...

4110Noise

Noise is generated by the impacts of the individual elements of the tread on the road surface, and it can be reduced in several ways. First, the tread elements are pitched at irregular intervals, to avoid resonance of components in the vehicle structure at the frequencies of their contacts with the road surface. Second, tread materials of high hysteresis are employed, to provide internal damping. This, of course, has to be a compromise, since high hysteresis is associated with the generation of...

254Total resistance

The total resistance to the motion of a vehicle is the sum of the above three resistances and is thus composed of two parts that are independent of the speed of the vehicle - the rolling resistance and the gradient resistance - and of one part that is dependent on the speed - the air resistance. A curve of total resistance against speed is therefore obtained by shifting the curve of Fig. 25.1 up vertically by the amount of the rolling and gradient resistances as is shown in Fig. 25.3. Thus when...

1732Ignition delay

The first point of note is that liquid diesel fuel will not burn it has to be evaporated first. Obviously therefore some delay occurs from the outset, but this is not what is meant by the term 'ignition delay', which occurs even though the temperature of the air in the combustion chamber is above the auto-ignition temperature of the vaporised fuel-air mixture. Ignition delay is the interval between the evaporation and mixing of the fuel in the air at or above auto-ignition temperature and the...

74 Lucas DPS pump

The DPS pump, Fig. 7.7, was introduced to provide both torque and boost control for four- and six-cylinder engines. It operates on principles virtually identical to those of the DPA, but it has some additional features. For instance it can have either two or four opposed plungers, in one or two diametrical bores respectively, in the rotor. The axes of the plungers are all in a common plane. The four plunger version is for large engines of the in-line and 90 and 60 V layouts. Alternatives of...

1613Exhaust manifold layouts for turbocharging

Efficiency of pulse turbocharging can be considerably enhanced by appropriate matching of the exhaust manifold layout to the engine. Consider a single cylinder as the exhaust valve cracks open, the pressure in the cylinder may be of the order of 90 to 120 bar, while that in the manifold will be little, if any, higher than atmospheric. After a short pause for the inertia of the gas to be overcome, the pressure in the manifold will rise steeply to a peak at around BDC, Fig. 16.4. During this...

1626 Other methods of supercharging

A method that, prior to the Second World War, was fairly widely used for two-stroke engines was to have double the number of cylinders needed for generating the power required. The additional cylinders were used for compressing the air for scavenging and pressure charging those adjacent to them. Well-known examples were the Trojan engines, Section 9.5. This method, however, considerably adds to the bulk, weight and cost of the engine. 1000 1200 1400 1600 1800 2000 R.p.m. 1000 1200 1400 1600...

386 Poweroperated brakes

These may employ either oil or air as the working medium and in what follows the term fluid may often be used since it covers both media and the systems using them have much in common. A fluid system that has been widely used is the Lockheed design shown in Fig. 38.6. The pump supplies fluid to the cut-out valve and in normal operation when the pump is running and the accumulators are charged up this fluid flows from A to B and thence from C to D through the driver's foot valve and so back to...

84 Cummins 10litre diesel

This is a power unit designed for eight-wheel rigid vehicles and lightweight tractors. because it is only 280 mm high it can be installed vertically in cabs that are too low to accept the earlier Cummins in-line engines. Additionally, its compactness and light weight, 850 kg, render it particularly suitable for rear engine installation in buses or coaches for which, because they are not so heavy as the trucks, it is normally derated from its 186 kW to either 164 or 134 kW. Derating, of course,...

1217Bosch Motronic system

Given that a microcomputer is used for regulating fuel injection, it can be even more cost-effective to employ it for other control functions too. Primarily the Bosch Mono-Jetronic system integrates injection and ignition controls, but it can also be adapted for controlling other parameters such as exhaust gas recirculation and evaporative emission canister purging, which are explained in Sections 14.16 and 14.17. Comprehensive information on the electronic components of the Motronic and other...

2418 Clutch brakes or stops

When a clutch is disengaged while the engine is running the inertia of the driven member will tend to keep it revolving. This inertia is proportional to the weight of the member and to the square of the 'radius of gyration' which is the equivalent radius at which the weight may be considered to act. Since this tendency to continue revolving rendered gear changing difficult, small brakes have been arranged to act on the driven member when the clutch was fully withdrawn. The stop member or brake...

222 Gear ratio of toothed gearing

When two shafts are connected by toothed gearing of any of the types described, the ratio between the speeds of those shafts will always be constant. This constant ratio is called the gear ratio. In all the types of gearing considered when one wheel drives another the gear ratio between them will be the inverse ratio of the numbers of teeth in the wheels. Thus if a wheel A drives a wheel B then and the bigger wheel goes slower than the smaller one. This will be clear when it is realised that in...

342Some simple VVT mechanisms

Variable phase control (VPT) can be effected in a number of ways. One is to advance and retard the camshaft by means of a sliding muff coupling on a divided shaft, with spiral splines on the driven and straight splines on the drive interfaces, or vice versa. This, however, suffers the disadvantage of high frictional resistance to control operation. Another method is to install, in the belt or chain drive to the camshaft, a movable idler pulley in combination with a tensioner having a longer...

219Flexible mountings

An engine which is perfectly balanced for forces and couples in the sense described above will have no tendency to move, or to transmit vibration to the frame or foundation to which it is attached, as a result of the sources of disturbance so far enumerated. Small imperfections of actual balance may be troublesome in extreme circumstances, but the presence of the unbalanced secondary inertia forces in four-cylinder engines not provided with harmonic balancers may involve considerable vibration...

214Compactness of engine

Arrangements Nos 1 and 4 provide the most compact engine transversely to the crankshaft, while No. 6 forms the shortest engine with the simplest shaft, but has large unbalanced couples. No. 3 is a compact and favourable arrangement with perfect balance except for secondary couples, which are not a serious objection. With suitable form of crank webs, arrangements Nos 2 and 5 can be made more compact in the axial direction than can Nos 1 and 4. Nos 4 and 5 would be the most expensive crankshafts...

35Slipper and articulated pistons

For applications in which running temperatures are relatively constant and therefore large cold clearances are acceptable, slipper type pistons can be used. These have no skirt, the function of which is performed by two thrust pads separated from the crown and supported directly by the gudgeon pin bosses, Fig. 3.6(a). With this arrangement, the shape of the piston in plan view can be virtually a true circle, which improves the oil film distribution and bearing characteristics. Such a piston is...

265Fourth or top gear

The gear N occupies the position shown in Fig. 26.1, while the gear M is slid over to the left as shown in Fig. 26.3 (d). The dog teeth on M then engage in the spaces between the dog teeth on B, thus connecting B and M and giving a direct drive between the engine and the mainshaft. The gear ratio is then 1 1. The layshaft now revolves idly. On all the above gears the direction of rotation of the layshaft is the opposite to that of the engine shaft, while the direction of rotation of the...

The twostroke engine

Both the specific power output and the potential for smoothness of torque at any given speed are restricted with the four-stroke engine, because it has only one power stroke every two revolutions. This has led to a quest for a cycle giving one power stroke per revolution. The answer was to exhaust the cylinder as the piston approached and passed the bottom, or outer, dead centre, and to use the depression caused by the inertia of the high speed flow of the outgoing gases to assist the induction...

253Rolling resistance

All the remaining forces resisting motion at a constant speed come under the heading of rolling resistance. In some circumstances, they include not only the resistance of the tyres but also the effects of the friction in the transmission system. In general, however, the latter differ according to which gear is engaged so, for calculation purposes, they are normally deducted from the torque available from the engine in that gear. Rolling resistance is attributable to both the dissipation of...

199Fan drives

With increasing emphasis on fuel economy, the traditional pulley-driven directly-coupled pressed steel fan is tending to give way to more efficient systems. Moulded plastics - nylon or polypropylene - fans are lighter, easier to balance, look better and, above all, can be made more efficient aerodynamically. Incidental benefits are reduced noise and vibration, and less risk of serious injury if the rotating fan blades strike fingers carelessly contacting them. Basically, there are two...

3812 The loadconscious valve

This valve, Fig. 38.20, has a shouldered piston similar to that of Fig. 38.18 E Force applied by external spring E Force applied by external spring Fig. 38.20 The simple load-conscious brake pressure apportioning valve E Force applied by external spring E Force applied by external spring Fig. 38.21 The revised load-conscious brake pressure apportioning valve but loaded by an additional spring acting externally on the piston. Since the deflection of the internal spring is no more than that...

1624Advantages of blowing

An advantage of both the vane- and roots-type machines is rapid response under transient conditions. An inherent disadvantage of the latter is that, in contrast to machines that compress the air internally, the power absorbed increases continuously as the pressure in the induction manifold pressure rises. However, by incorporating a butterfly valve, electronically controlled on the basis of load and speed inputs, to return back to the inlet a proportion of the air delivered, parasitic losses...

4112 Tyre design considerations

The design requirements of tyres are as follows 1. Adequate capacity to support both the static and dynamic loads. 2. Ability to withstand centrifugal loading. 3. Structural stability, to resist degeneration. 4. Reasonable protection against abuse such as striking kerbs. This implies side walls of adequate strength. Some tyres have a rib around each side wall to take some of the wear and shock loading involved. 5. Cooling, to avoid overheating. This implies good thermal conductivity, low...

622Injector assemblies

Some typical injector assemblies are illustrated in Figs 6.13, 6.17, 6.18 and 6.19. In each, provision is made for collecting and returning to the supply pipe any leakage of fuel between the differential valve and its guide. This leakage is reduced to a minimum by the extreme precision and lapped finish of the stem and guide assembly, tolerances of the order of 0.0025 mm being common. Valves and bodies must be kept in pairs, never being interchanged. In Fig. 6.13, the nozzle N is of the pintle...

2112 Leyland gas turbine

In March 1967, the Rover team engaged in gas turbine work was regrouped to form Leyland Gas Turbines Ltd. They have developed a new, larger unit developing 260-300 kW intended for commercial vehicles. This engine is the type 2S 350 R and in design it is basically similar to the 2S 150 R, mentioned in Section 21.9. A minimum fuel consumption of 0.2373 kg kWh at 20 C is quoted. At 26.7 C, the mass flow of air is 1.7 kg s. The compressor idling speed is 19 000 rev min, and the output speed range...

134 Materials

Until relatively recently, manifolds have been of either cast iron or aluminium, but now various types of plastics are used as alternatives. Cast iron is the cheapest, but heavy. Aluminium is light, offers good thermal conductivity, and therefore rapid warm-up, and can be cast accurately. However, it has some disadvantages. For example, because of its high thermal conductivity, the rate of heat transfer through it to the injectors can adversely affect hot starting. Production of cast aluminium...

51 Burt singlesleeve valve

The Burt-McCullum single-sleeve valve is given both rotational and axial movement, because with a single sleeve having only axial reciprocation, it is impossible to obtain the necessary port opening for about one-quarter of the cycle and closure for the remaining three-quarters, if both inlet and exhaust are to be operated by the same sleeve. It will be found that a second opening occurs when the ports should be shut. The sleeve may be given its combined axial and rotational motion in a variety...

612 Precombustion chamber

Illustrated in Fig. 6.4 is a pre-chamber developed in the 1920s by Benz and Co. and used by several other manufacturers. The action gives an approximation to the characteristics of air blast injection and limits the maximum pressure. The pre-chamber represents about 40 of the total clearance volume, and the fuel is injected into this air and partly burned, the spread of ignition being helped by the turbulence arising from the passage of the air through the communicating pepper-castor holes...

334Seat inserts in cylinder heads

In aluminium heads seat inserts are essential, though they are also employed in some cast iron heads, especially for diesel and other heavy-duty or highlyrated engines. High-quality inserts are produced by compressing a metal powder in a ring shape mould to produce what is called a green moulding, which is then transferred into a sintering furnace. Some others, however, are Stellite faced ferrous metal cobalt, and nickel-based alloys or least costly, a high-quality cast iron such as in the case...

635Types of governor

For automotive applications, two categories of governor are in general use two-speed and the all-speed governors. The latter exercises control over the whole speed range, while the former does so over only at maximum and idling speeds, the driver exercising direct control at all other speeds. There are also combinations of both types, in which additional governor springs have to be installed. Two-speed governors are suitable for agricultural tractors, fire-fighting vehicles, road sweepers and...

1618 Bypassing the gas flow

The most widely used method of varying the output of the turbocharger to suit the engine characteristics is wastegating, Fig. 16.14. A compressor large enough to deliver the air needed at slow engine speeds is fitted, and its output at higher speeds reduced by opening what is, in effect, a pressure relief valve by passing some of the exhaust gas around the turbine into the downpipe. Thus the over-boosting of the engine at the higher speeds, as a result of fitting the larger compressor, is...

2711 The auxiliary trains in the Wilson gearbox

As previously indicated, to drive the annulus at different speeds auxiliary epicyclic gear trains are used. Those for second gear are shown in Fig. 27.8(c). The sun gear S2, in common with S1 adjacent to it, is driven by the engine, the planet carrier C2 is coupled to the annulus A1 and, to obtain second gear, a brake is applied to the annulus A2. So long as this brake is holding A2 stationary, the coupled carrier C2 and annulus A1 rotate in the same direction as the engine but at a lower...

73 DPA pump governor

In general, the basic principles of the all-speed governing system are identical to those of governors for in-line pumps. A spring is interposed between the governor control arm and the linkage to the accelerator pedal. This spring is compressed increasingly with speed, thus opposing the force exerted by the governor weights, to a degree such that the engine speed remains constant regardless of load. Hydraulic governing, Fig. 7.5, used to be an option. However, owing to lack of demand, it is no...

323 Singlereduction live axles

An elementary single-reduction live axle - with a differential - is illustrated diagrammatically in Fig. 32.1. It has a hollow casing A, which carries on its ends the road wheels B. The weight of the body and load is supported by the casing A through the springs which are attached to the body and to the axle in a manner which will be described later. The casing in turn is supported at its ends by the road wheels. It therefore acts as a beam and is subjected to a bending action as is shown in...

117Indicated and brake power

The power obtained in Section 1.15 from the indicator diagram (that is, using the mep) is known as the indicated power output or indicated horsepower (ipo or ihp), and is the power developed inside the engine cylinder by the combustion of the charge. The useful power developed at the engine shaft or clutch is less than this by the amount of power expended in overcoming the frictional resistance of the engine itself. This useful power is known as the brake power output or brake horsepower (bpo...

2424 Prevention of leakage

It has been tacitly assumed that the fluid cannot escape between the faces of the rotors and it might be thought that those faces would have to be in rubbing contact in order to prevent such leakage. In actual fact, however, there is a gap of about 1.5 mm between the faces and escape of the fluid is prevented by making one rotor with a cover which embraces the other rotor as will be seen in Fig. 24.20. The relative position of the rotors has been changed in Fig. 24.20 to correspond with the...

406Cornering power

The cornering power of tyres has been found to depend on many factors such as the construction of the tyre itself, the value of the vertical force between the tyre and the road (referred to in what follows as the load on the tyre), the inflation pressure, the size of the tyre and the extent of any tilting of the wheel. Thus the cornering power of a tyre falls off as the load on the tyre departs from the normal load for the tyre, but the extent of this falling off is small provided the variation...

422Construction of Veight

A cross-section of the early Ford side-valve engine is given in Fig. 4.29, which shows the salient special features. The two banks of cylinders and the crankcase are formed in a single monobloc casting, the sump which forms the lower half of the crankcase being a light steel pressing. Detachable heads with side valves operated from a single camshaft are conventional features, while the somewhat inaccessible position of the tappets and valve springs is mitigated by the special construction...

119 Limiting factors

Let us see to what extent these factors may be varied to give increased power. It has been shown that the value of p depends chiefly on the compression ratio and the volumetric efficiency, and has a definite limit which cannot be exceeded without supercharging. The diameter of the cylinder D can be increased at will, but, as is shown in Section 1.24, as D increases so does the weight per horsepower, which is a serious disadvantage in engines for traction purposes. There remain the piston speed...

128 Suspendedplatetype flow sensor

For the Bosch K-Jetronic system the suspended-plate-type flow meter, Fig. 12.11, was developed. Essentially, it comprises a circular plate on one end of an arm swinging about a pivot at its opposite end. The plate is suspended in a horizontal plane in a circular throat of complex tapered form. This plate-and-lever assembly is balanced by a small weight, sited beyond the pivot, at the end of the lever remote from the plate. Consequently, when the engine is switched off, the plate settles down in...

129 Swinginggatetype air flow sensor

This type of air sensor, Fig. 12.12, is especially convenient for use in conjunction with electronic control, which is why it forms part of the Bosch L-Jetronic and Motronic systems. It has two other advantages first, the rotational inertia of the gate is less than the linear inertia of the suspended-plate-type sensor, so its response to changes in throttle opening is slightly faster and, secondly, there is still a momentary lag between the opening of the gate and the inflow of air into the...

341 Both steps at the centre of the axle

This type of double-reduction final drive is shown in Figs 34.1 to 34.5. Referring to Fig. 34.1, the bevel pinion A is driven by the propeller shaft and gears with a small crown wheel B. The latter is fixed to a layshaft C, to which is also fixed a spur pinion D. The layshaft is carried in ball or roller bearings at its ends in the axle casing, suitable thrust bearings being provided to take the thrust of the bevel gears. The spur pinion D meshes with a large spur wheel E which is bolted to the...

29Balanced throws

The stresses and whip to the revolving masses may be reduced by adding counterweights to the individual throws, as shown in the crankshaft illustrated in Fig. 3.15, thus eliminating the couples. In the modern highly-rated engines, serious crankshaft whip has been eliminated only by the addition of these balance masses. They may be incorporated in the forging or be separately attached. Clearly their employment makes the crankshaft construction more expensive and in straight six-and...

172 The principal refining processes

The principal refining processes for the production of fuels are thermal, catalytic and hydrocracking, and catalytic reforming. There are many others, such as alkylation, isomerisation and polymerisation, for producing high-octane fuels, and the finishing processes such as caustic washing for removal of certain chemical contaminants, the Merox sweetening and extraction processes for the removal of others, and hydro-desulphurisation. However, we do not have space here for going into details. For...

1210 Massflow sensors

Clearly, it is better to measure the mass flow directly than to measure volume flow and density separately and compute the mass flow from these two parameters. Mass air flow meters operate on the basis that the temperature loss from a heated element is a function of the velocity and density of the fluid flowing past it. The ECU calculates mass flow from the diameter of the passage, the velocity of flow and its density, the last two factors being indicated by a voltage in the electric circuit....

413 Rims

A wide variety of rims is in use, so many in fact that they cannot all be included here. Readers needing to know more are therefore advised to consult Fig. 41.6 Wheel disc configurations left, inset nave centre, central nave right, outset nave Fig. 41.6 Wheel disc configurations left, inset nave centre, central nave right, outset nave Fig. 41.7 A two-piece wheel for a relatively light vehicle Fig. 41.7 A two-piece wheel for a relatively light vehicle BS Au 50 Part 2. Where tyres are to be...

423 Damping

As mentioned previously, the dampers, or shock absorbers as they are sometimes called, are required to cause a rapid die-away of any vibrations forced either randomly or periodically at the natural frequency of the suspension system and thus introducing a state of resonance. To do this, they apply a force in a direction opposite to that of the instantaneous motion of the suspension. Early cars had friction dampers, which were generally packs of friction material interleaved between blades, or...

3710 Brake linkages

Hydraulic actuation is now almost universal for the service brakes of vehicles but linkages consisting of levers, rods and wires are generally required for the operation of the parking brakes for cars, and these may conveniently be considered first. A simple linkage for applying the two rear brakes of a vehicle is shown in Fig. 37.27 it is called an uncompensated linkage because Fig. 37.26 Girling self-energising disc brake Fig. 37.26 Girling self-energising disc brake there is nothing to...

312 Cylinder bore wear and corrosion

The life of an engine between re-bores of the cylinders is determined by both abrasion and corrosion wear, the chief factors in the former being the nature of the prevailing atmospheric conditions and the efficiency of the air and oil filtration, while the latter is due to corrosive products of combustion formed during the warming-up period, and is most apparent in engines whose duty involves frequent starting from cold. Piston, piston rings and cylinder bore have to be considered together, and...

417 Tyre construction

Details of the construction of a Dunlop crossply tyre are shown in Fig. 41.14 and radial ply tyres in Fig. 41.15. In each type, the beads comprise parallel hoops of steel wire bound with fabric to form a tightly wrapped bundle in the form of a ring. The ends of the plies are wrapped around them. In crossply tyres, there are generally several plies, or layers, of fabric reinforcement in the form of cords of rayon, nylon or polyester. The cords are rubberised and set at an angle of approximately...

1627 The pressurewave supercharger

The pressure-wave, or Comprex, supercharger has been developed by Brown Boverie. Basically it takes energy, in form of pressure pulses, directly from the exhaust gas, in contrast to the turbocharger, which does so mechanically. Consequently, the losses are small and pressure ratios of up to 3 1 are said to be attainable. The principle is illustrated in Fig. 16.29. Energy interchange between the exhaust and inlet gases occurs in a set of straight tubular cells of approximately trapezoidal...

1324 Application to Vengines

An objection to the Helmholtz resonator is that it tends to be bulky and therefore difficult to accommodate beside the cylinder head. On the other hand, it can be fitted conveniently between the banks of cylinders in an engine of Vlayout, especially a V-8 unit. The alternative of fitting long induction pipes to improve volumetric efficiency at low speeds is, by comparison, relatively unattractive. Application to six-cylinder and V-8 engines has been discussed by Watson, in IMechE Paper C40 82....

2813 Hydramatic Stratoflight gearbox controls

The steering column control lever has six positions, parking (P), neutral (N), normal driving (A Dr), fast accelerating, driving (Dr A), low range (Lo) and reverse (Rev). Parking differs from neutral in that a positive lock engages the teeth U, Fig. 28.20, to lock the output shaft of the gearbox when (P) is selected. At the rear end of the gearbox there is a governor which is driven by the output shaft and whose speed is thus proportional to the road speed of the vehicle. The governor is...