The Motor Vehicle 2010 Part 12 potx

795Epicyclic and pre-selector gearboxes R Q A D P C (a) Fig. 27.4 than the rotating sun wheel, the situation is similar, but P becomes the fulcrum so, although the planet carrier still rotates anti-clockwise, the sun wheel S 1 rotates in the opposite direction. Although there are many other forms of planetary gearing, the two described here are those most commonly used in automotive applications. The broad principles already explained apply to them all. Heavy duty epicyclic gearing is to be found mostly in pre-selector and automatic gearboxes and back axle differentials. In the latter, bevel type planetary gears are usually used for turning the drive through 90°; they have also the advantage of compactness. Examples of bevel gear types are illustrated in Chapters 31, 33, and 34, the clearest being Fig. 34.7. As is explained in those chapters, the terminology for differentials is different: the planets are housed in a carrier called the differential cage bolted to the crown wheel. The latter, in effect, is substituted for the annulus. There are two sun wheels, termed differential gears, one on the inner end of each halfshaft. These mesh with the planet, or differential, pinions. 27.3 Epicyclic gear ratios For ease of recognition of the various gears in all that follows, the annulus gear is called A, the planet carrier C, the sun gear S, and the planet gear P, and it is assumed that the gears have respectively A, S and P teeth. If either end of the planet carrier arm is integral with a tubular shaft and coaxial with the gear shaft at that end, the arm can be used as either the input or output. First, take the case of the planet being fixed and the carrier arm, serving as the input, turned through one revolution, clockwise about the axis of S, Fig. 27.4(a). If the wheel S were not in mesh with P and were fixed to the planet arm, it too would have been orbited through 360 °. However, since it is in mesh with P, it will also have rotated P/S times about its own axis, so its total rotation will be 1 + P/S revolutions. Therefore, the planet wheel has 20 and the sun wheel 40 teeth, the planet wheel will have turned 1 1 / 2 revolutions β α R P D A Q C β α R Q A P D C (b) (c) 796 The Motor Vehicle for 1 revolution of the carrier arm, so the gear ratio of this arrangement is 1.5:1. Now consider the situation if the sun wheel S is fixed, with the carrier, still the input, rotating around it, Fig. 27.4(b). In this case, the planet wheel P will have turned 1 + S/P, giving a gear ratio of 1 + 40/20 = 3 : 1. Finally, if the carrier arm is fixed and P is rotated, the ratio is P/S, giving a gear ratio of 0.5 : 1, but if S is rotated, the ratio is A/P giving a ratio of 2 : 1. Note that, in both instances, the driven and driving gears rotate in opposite directions. With such an epicyclic arrangement, therefore, it is possible to obtain four different ratios, simply by applying a brake or clutch to stop one of the elements in the gear train. This, however, is not of much significance for automotive transmissions because the space it takes up is similar to that obtained with a two shaft gearbox, some of the ratios are unsuitable and, in any case, it becomes more complex if a reverse gear is to be provided. 27.4 Simple planetary epicyclic gearing For automotive applications, a coaxial layout comprising an annulus gear with planet gear, or gears, and a sun gear is widely used. From Fig. 27.5(a), it can be seen that, if the annulus A is locked, and the input is clockwise through the sun gear S, the latter will rotate the planet gear anti-clockwise, so it will roll around the stationary annulus and therefore drive the planet carrier clockwise. The speed of the planet gear carrier will be: S/(S + A) (1) so, if the sun gear has 40 and the annulus 80 teeth the gear ratio will be 40/(40 + 80) = 1/3. In other words, this arrangement will give a reduction of 3.0 : 1. However, if the drive is from A to S instead of S to A, the result will be an overdrive ratio of 0.33 : 1. Note that the planet gear, rotating in the direction opposite to that of the sun gear, is simply an idler and therefore has no influence on the gear ratio. If, on the other hand, the planet carrier C is locked, and the input is still the sun gear, Fig. 27.5(b), the output will, of course, be the annulus which is driven, through the idling planet gear, anti-clockwise. The gear ratio is: S/A (2) Brake onBrake on Brake off Brake off Brake on A A A A SS S S Drive Locked Drive Locked (c) (d)(b)(a) Fig. 27.5 C C C C P P P P Drive Drive 797Epicyclic and pre-selector gearboxes so S will drive P anti-clockwise and this, in turn, will drive the annulus anti- clockwise at a speed of S/A times that of S, giving a ratio of 40/80 = 1/2 : 1. In other words, for one revolution of the sun gear, the annulus will rotate half a revolution (a reduction ratio of 2 : 1). With the sun gear locked, and the input from the planet carrier, Fig. 27.5(c), the annulus gear A is driven faster in the same direction. The gear ratio is: (S + A)/A (3) the planet and annulus gears rotate in the same direction and the ratio is 120/80 = 1.5 : 1, so the annulus is rotated one and a half turns for every turn of the planet carrier. If the annulus gear A is locked and the planet carrier C is the input, Fig. 27.5 (d), the annulus is driven in the same direction. Again the gear ratio is: (S + A)/A (4) and the ratio is 1.5 : 1. 27.5 Simple planet epicyclic gearing in general From the foregoing, it can be concluded that, with an epicyclic gear train comprising an annulus, sun gear and planet carrier, any one of these can be fixed and the drive inputted through one of the other two, then the third will be driven at a different speed. The characteristics of such a gear train are as follows: 1. The output can be driven at a reduced speed relative to the input and in the same direction. 2. The output can be driven at a higher speed in the same direction. 3. The output can be driven at an alternative higher speed in the same direction. 4. The output can be driven at a lower speed than the input but in the opposite direction, to provide a reverse gear. 5. If any two of the gears locked together, the third cannot rotate relative to the others so the whole system turns as one solid mass, giving direct drive at a 1 : 1 ratio. 6. All ratios are dependent upon only the numbers of teeth on the sun and annulus gears, and are independent of the number of teeth on the planet gears. 7. With this arrangement, it is therefore possible to have direct drive, three forward gears, and one reverse gear. 27.6 Compound planet epicyclic gearing An alternative to Fig. 27.3, in which two integral idler gears are used, is to have two independent but intermeshing planetary idler gears, one meshing with the sun and the other with the annulus, Fig. 27.6(a), in which case the gear ratio between these two comes into play. Consequently, if the annulus is fixed, the sun gear is the input and the planet carrier the output, the gear ratio is: P 1 /P 2 × S/(S + A) (5) 798 The Motor Vehicle so, if A had 80 teeth, P 1 10, P 2 20 and S 40, the overall ratio would be that of the two planet gears times that in equation (1), which is 10/20 × 40/(40 + 80) = 0.5 × 0.33 = 0.166 : 1. Note that equation (5) is equation (1) multiplied by the planet gear ratio. It follows that to find the ratios in the other cases, all that is necessary is to multiply the ratios obtained in equations (2), (3) and (4) by the planet gear ratio. However, because there are two intermeshing planet gears, the output will rotate in the opposite direction to that previously obtained. Indeed, all epicyclic gear trains fall into two categories: given that the planet carrier is locked, the first is when the input and output gears rotate in the same direction and the second when they rotate in opposite directions. In Fig. 24.6(b), the principle is the same, but one of the two gears is an integral pair, so we have three planet gears on two wheels, or a compound planet gear. This arrangement offers the possibility of axially offsetting the sun gear from the annulus so that a wider choice of planet ratios is obtainable than would be possible if two separate planets had to be accommodated between the periphery of the sun gear and the tooth ring in the annulus. With this three wheel arrangement and, as before, the annulus fixed and the sun wheel the input, the overall gear ratio is: P 1 /P 2 × S/(S + A) (6) In this instance the planet gear P 3 behaves similarly to that in a simple sun– planet–annulus train except that its speed of rotation is influenced by the meshing pair of planet gears with which it is associated. Consequently, the comments that followed equation (5), and those in the subsequent paragraph, also apply here. 27.7 Numbers of teeth Assembly of an epicyclic gear train is practicable only if the numbers of teeth on the gears has been appropriately chosen. For simple planet epicyclic gearing, the sum of the numbers of teeth on the sun and annulus gears divided by the number of planet pinions N PP must be an integer. For compound planet epicyclic gearing, and when the direction of rotation of the input and output are the same, (P 2 × A) – (S × P 3 ) divided by N PP × H CF must be an integer, where H CF is the highest common factor between P 2 and S. If the relative direction of rotation is not the same, (P 2 × A) + (S × P 3 ) divided by N PP × H CF must be an integer. During assembly of the gear train, a vernier effect may be experienced, R A P 2 S A P 2 P 3 S R P 3 P 2 R P 1 S (a) (b) P 1 Fig. 27.6 Double planet pinnions P 1 799Epicyclic and pre-selector gearboxes allowing the planet pinions to be inserted incorrectly within the backlash. This can be avoided if the numbers of teeth on the sunwheel and annulus are each divisible by the number of planet pinions, and datum teeth on the planets are marked. 27.8 Another way of applying epicyclic gearing An alternative to stopping one of the elements of an epicyclic gear train completely is to reduce its speed of rotation, by connecting it to a resistance of some sort. An example already mentioned is the differential gear for splitting the torque equally between two halfshafts driving either the front or rear road wheels. A particularly interesting application of this principle was made in 1964 by F. Perkins Ltd (now Varity Perkins). An auxiliary drive from an engine was geared up and taken through a differential train, to drive a supercharger. The engine drove the planet carrier and the output was taken through the annulus see I.Mech.E Auto. Div. paper presented by Dawson and Hayward on 14 April 1964. In automotive practice, the brakes or clutches, either pneumatically or hydraulically actuated, are applied gradually to the appropriate gears. The object is to vary the relative speeds progressively during the ratio changes and thus to provide smooth gear shifts. In this way, the need for a separate pedal-actuated clutch is obviated. In modern transmissions, because they require much less attention in service, clutches have largely superseded brakes even though the latter are less costly. 27.9 Epicyclic gearboxes For car gearboxes, forward gear ratios of from 1 : 1 to about 5 : 1 and one reverse are needed. Moreover, as explained in Section 25.10, the forward ratios must be arranged in a geometrical progression. Epicyclic gearboxes used to be commonly installed in Daimler, Lanchester and Armstrong Siddeley cars, mostly to provide preselection of gears and to eliminate the clutch, although the pedal control was retained for changing gear instead of operating the clutch. However, they have now been superseded by automatic transmissions with two pedal control. In heavy commercial vehicles in which optimum fuel economy is an overriding requirement, the inefficiency of a torque converter is unacceptable so epicyclic gearboxes are still widely used. For this type of application, extra gear trains are needed for providing large numbers of gear ratios needed for coping with the heavy loads carried. As previously stated, given that top speed is direct drive, seven different drives are obtainable from a simple train comprising a sun, annulus and carrier. However, this calls for complex construction and, moreover, some of the ratios are unsuitable. Consequently, even for cars, an alternative method is better. This entails interconnecting several epicyclic trains in series, so that suitable ratios can be selected. Generally, the first train is the primary one, the others modifying its ratio before transmitting the drive back through the primary planet carrier to the road wheels. An overall ratio of 1 : 1 is obtainable by locking the whole set of gear trains together. With such arrangements, the number of ratios obtainable rises rapidly with the number of trains although, as previously indicated, some are unsuitable for automotive gearbox applications. 800 The Motor Vehicle The trains can be all of the same type or of different types. Several arrangements with spur gears are illustrated in Fig. 27.7, in which the brakes are labelled B and the clutches C: in practice multi-plate clutches are employed. The input is on the left and the output on the right. In diagram (a) two simple trains are in tandem while at (b) two trains with double-sun gears are similarly arranged. By making some individual members function as part of two trains, the arrangement can be simplified, but fewer ratios are obtainable. An example is shown at (c), where the sun gears are integral and a single planet carrier serves both trains. With this arrangement, only one clutch is needed, but only three ratios are obtainable, as compared with four in (a). At (d) two of the suns S 1 and S 2 are integral and there is a third sun S with a carrier common to all three sets of planet gears. The sun S and its meshing planet gear serves both trains. Because S 2 is larger than the driven sun S, reverse is obtained when brake B 2 is applied and, since S 1 is smaller than S, a forward drive ratio is obtained when brake B 1 is applied. A third method of designing an epicyclic gearbox is to compound several simple epicyclic gear trains. This was the basis of the Wilson transmission, originally known as the Wilson-Pilcher gearbox, developed at the beginning of the 20th century. Later Vauxhall Motors worked with Major Wilson to develop it further but dropped it in 1927, when General Motors took the company over. Subsequent development was done by the Daimler company for their cars. 27.10 Basic principle of the Wilson gearbox A Wilson type gearbox is illustrated in Fig. 27.8(a), and the functioning of its various secondary trains is shown in (b) to (f). The primary epicyclic gear train is common to all the ratios. Its sun S1, Fig. 27.8(b), is driven by shaft D, which is coupled directly to the engine crankshaft, while its planet carrier C 1 is coupled directly to the transmission line to the road wheels. In other Fig. 27.7 Epicyclic gearbox arrangements C 1 B 1 B 1 C 2 B 2 B 2 (a) (c) (d) (b) B 2 B 1 C 1 B 2 C 2 B 1 C S S 1 S 2 C 801Epicyclic and pre-selector gearboxes words, these two elements are respectively the input and output regardless of ratio selected. The required gear ratios are obtained by driving the annulus at different speeds in relation to engine speed. How this is done is as follows. If engine speed were constant, at 1000 rev/min, and the annulus braked (zero rev/min), the speed of the carrier would be 1000 × S 1 /(A 1 + S 1 ) where, in general, A, S and C throughout what follows are the numbers of teeth on the annulus and sun wheel respectively, as in Section 27.9. If A 1 = 100 and S 1 = 25, the speed of C 1 = 200 rev/min and the reduction ratio is 5 : 1. On the other hand if, with engine speed still at 1000 rev/min, the annulus is driven at 100 rev/min in the same direction as the engine by other elements in the compounded series of epicyclic gears, the speed of rotation of the sun gear relative to the annulus would be only 900 rev/min. So the speed of the planet carrier would be 900 × 25 = 22 500 divided by 125 = 180 rev/min but, as the carrier would rotate faster because the annulus was rotating, the 100 rev/min of the latter (in these circumstances not multiplied by the sun-to- planet ratio) must be added, giving 280 rev/min for the speed of the planet carrier. Therefore, when the annulus is stationary, the equation in the previous paragraphs is in fact 0 + (1000 × S 1 /A 1 + S 1 ) and, when the annulus is rotating at 100 rev/min, it becomes 100 + (1000 × S 1 /A 1 + S 1 ). In more general terms, the equation is (R E – C A ) × (S 1 /A 1 + S 1 ) + R A , where R A and R E are respectively the speeds of rotation of the annulus and engine crankshaft. It follows that, if R E had been 200 rev/min, the output speed of the planet carrier would have been 380 rev/min. Fig. 27.8 Wilson gear ratios (a) (d) F A 3 C 2 A 1 C 1 S 3 S 1 A 1 F G E (b) S 2 C 3 (f) (c) A 1 C 1 S 1 C 1 A 4 C 4 S 1 S 4 S 1 C 1 A 1 A 2 C 2 S 2 D A 2 (e) 802 The Motor Vehicle If the annulus is driven in the opposite direction, its speed relative to the crankshaft becomes negative. So given an annulus rotating at a negative speed of 400 rev/min we have (1000 + 400) × (25/100 + 25) – 400 = – 120 rev/min, or in other words a reverse gear ratio of 0.12 : 1. 27.11 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 S 2 , in common with S 1 adjacent to it, is driven by the engine, the planet carrier C 2 is coupled to the annulus A 1 and, to obtain second gear, a brake is applied to the annulus A 2 . So long as this brake is holding A 2 stationary, the coupled carrier C 2 and annulus A 1 rotate in the same direction as the engine but at a lower speed. Consequently, C 1 rotates at a higher speed than it did in first gear when, as described in the second paragraph of Section 24.10, A 1 was the stationary element. The actual speed will, of course, depend on the numbers of teeth on the gears involved. To obtain third gear, Fig. 27.8(d), annulus A 1 and therefore also the planet carrier C 2 must be made to rotate faster than in second gear. This entails causing A 2 to rotate in the same direction as the engine, by applying the brake to drum F to stop S 3 . The other two elements in the second gear train, C 3 and A 3 , are coupled respectively to A 2 and C 2 . With S 3 fixed and A 3 rotating in the same direction as the engine, C 3 , S 2 and A 2 will also be rotating in that direction, the last two because C 3 is coupled to A 2 . Consequently, the speed of rotation of C 2 must be greater than when A 2 was fixed: therefore annulus A 2 must be rotating faster than in second gear. Again, the actual speeds depend on the numbers of teeth on the gears. Direct drive, Fig. 27.8(e), is obtained by sliding the male cone G along the splines on the shaft D, and locking it in the female cone in the drum F which is fixed to S 3 . This locks the whole epicyclic gear assembly together, so that it rotates en bloc. Obtaining reverse gear, Fig. 27.8(f), entails bringing the fourth epicyclic train into operation by applying the brake to A 4 . Sun S 4 is fixed to A 1 , and carrier C 4 is fixed to the driven shaft D. Sun S 1 is driven forwards by the engine, and the planet pinion, acting as an idler, drives the annulus A 1 , and with it the sun S 4 , backwards. Since A 4 is braked, S 4 drives the planet carrier C 4 backwards too. Moreover, since both C 1 and C 4 are fixed to the output shaft to the road wheels, both have to rotate at the same speed in the same direction. This speed is in fact determined by the numbers of teeth on A 1 and S 1 relative to those on S 4 and A 4 , the last mentioned pair determining the speed of rotation of the annulus A. This is not easy to visualise, so let us take an example in which S 1 has 25, A 1 100, S 4 40 and A 4 80 teeth. To represent the conditions in reverse gear, apply the brake to A 4 , and then rotate C 4 , and with it the integral carrier C 1 , backwards one revolution. Now consider the sequence of events as this rotary motion is transmitted through each of the intermeshing gear pairs in turn. With A 4 fixed, the planet carrier C 4 will rotate S 4 , and with it the annulus A 1 , backwards 80/40 = 2 revolutions. This, in turn would have rotated S 1 backwards 100/25 = 4 revolutions which, at first sight, appears to make an overall ratio of 8 : 1. However, the driven shaft has rotated minus 1 turn and the driving shaft plus 8 turns, so the overall ratio is in fact 7 : 1. 803Epicyclic and pre-selector gearboxes 27.12 The clutches and brakes in the Wilson gearbox To simplify in Fig. 27.8(e) a cone clutch was shown, but this, of course, would be too harsh for the purpose. In practice, a pneumatically or hydraulically actuated multi-plate clutch such as that illustrated in Fig. 27.9 is employed. The clutch illustrated is air actuated. A control valve lets fluid under pressure enter cylinder A beneath the piston, to actuate the lever B. This moves the ring C to the right, about its pivot D. Mounted on gimbal pivots F (one on each side) within ring C is the housing E for the ball thrust bearing. Consequently, the axial displacement of the centre of C causes the ball thrust bearing to compress the clutch plates between the presser plate G and the clutch hub H, to which are splined the driving plates of the clutch. The drum K, to which the driven plates are splined, is in turn splined to the hub of the sun gear S 1 . When the fluid pressure is released by the control valve, the clutch is released by a set of coil springs, equally spaced around the hub (only one can be seen in the illustration). A typical brake, Fig. 27.10, for acting upon the periphery of the annulus in this type of gearbox has an outer and an inner band, A and B respectively, having friction linings L. The outer band is anchored by the hooked link D, and the inner one by the lug F projecting through a slot in the outer band. The reactions to the brake torque, at these two diametrically opposite anchorage points, are equal and opposite and therefore do not add to the load on the bearings on which the annulus rotates. A tie rod G pulls the outer band on to the inner band, and thus the inner band on to the drum, which is the periphery of the annulus. Note that the pull of the tie rod on the lower end of the brake band is reacted by an equal and opposite pull applied by the hook on its upper end, and the direction of rotation relative to the fixed anchorage point is such that the brake band is automatically wrapped around the drum. Stop C actuates an automatic adjustment device for compensating for wear. The actuation mechanism is shown in more detail in Fig. 27.11 and the automatic adjustment mechanism in Fig. 27.12. Fluid pressure, in this case E F L A C D G L B Fig. 27.9 Fig. 27.10 E C D K S 3 D E H G A B J C F 804 The Motor Vehicle air, on the piston A lifts the piston rod Q in Fig. 27.11. This, in turn, rotates the lever B about its pivot O. Roller C, on the other end of the lever, moves along the cam-shaped lower surface of the lever K, termed the bus bar. As it does so, it lifts the tie rod, G in Fig. 27.10, to apply the brake. The shape of the cam is such that the initial movement of the lever is rapid, to take up the clearance between the drum and brake bands. Subsequently, the slope of the cam is less steep so that the tie lifts more slowly, and the ratio of force on the piston to the leverage on the tie is therefore greater. This effect is enhanced by the fact that, as the roller approaches the end of bus bar K, the lever B on which it is mounted comes up to its top dead centre position, relative to the axis P of the pivot. 27.13 Automatic compensation for wear In the upper diagram of Fig. 27.12, the adjustment device is in the ‘brake off’ position and in the lower one it is in the ‘brake on position’ with zero wear on the lining. Surrounding the round nut screwed on the top of the tie rod G is a coil spring B. One end of this spring is fixed to a pin projecting upwards from plate A. It is then coiled several times round the nut and secured to a second pin, which is fixed to the knife-edge pivot plate J and projects upwards through a slot in plate A. Plate A is free to rotate relative to the nut H. Each time the bus bar K, Fig. 27.11, is pulled upwards to apply the brake, the upper end of the tie rod, and with it the plate-and-spring assembly, moves over to the left until the lug on plate A just makes contact with the adjacent stop C, which is C in Fig. 27.10. For all gears except top, where it is fixed to the gearbox casing, this stop is mounted on the brake band. When wear has occurred, the stop goes further than just contacting the lug: it strikes it and, deflecting it, rotates the plate A anti-clockwise. This uncoils the spring around the nut H, which therefore is then free to rotate, except that the friction between it and its conical seating in the pivot plate prevents it from doing so. When the brake is released, however, the coils tighten around the nut. Then, as the tie rod is lowered and the whole assembly retracts to the right in the illustration, the plate rotates back to its original ‘brake off’ position, and the lug on the other side of the plate comes up against the stop D fixed to the casing. At this point, the coil spring grips the P K C B O A C A B J G H A D Fig. 27.11 Fig. 27.12 Q [...]... while the plate B is connected to the impeller of the torque converter The rotor of the latter is connected through the freewheel D to the shaft C and thus to the output shaft The intermediate plate E of the clutch can be pressed either to the left or to the right When pressed to the right it grips the plate B and thus drives the impeller of the torque converter and the drive passes through the torque... critical level, the control unit switches on the cooling fan Should the temperature still continue to rise, the control changes the shift pattern over to another for obtaining minimum power loss in the converter In the event of either partial or complete failure of the automatic control unit, the defective circuit is either partly or completely switched off, depending on the circumstances In the event of... in the left-hand end of the box and is driven off the sleeve of the impeller so that it is working whenever the engine is running while the other is seen at the right-hand side and is driven off the output shaft of the box so that it will be running when the car is in motion The principle underlying the action of the control system is Casing B1 E B2 P1 A H R D I F R G C1 C2 S2 S1 P2 Fig 28.16 818 The. .. are engaged The indications in the automatic modes are: ‘CITY D’, ‘ICE D’ and ‘SPORT D’ In manual mode, only the number of the gear selected is displayed The engine can be started only with the gear lever in either P or N To start the vehicle moving, it is necessary to depress the brake pedal and then, if the lever is in the P position, lift the release device beneath its knob to change into the drive... is engaged and the brake B2 is applied, the drive then goes from S1 to P1 and thence to the annulus A, the planet carrier being fixed The teeth seen on the outside of the annulus in Fig 28.17 are engaged by a detent when the control lever is put into the parking position and this holds the car stationary Two oil pumps provide the oil pressures required to engage the clutches and apply the brakes One... coupled by the shaft G to the sun S2 of the second epicyclic train If the annulus of the train 2 is fixed then the sun S2 will drive the planet carrier R2, which is the output member of the box, with a reduction of 2.55 : 1 The four forward gear ratios are therefore obtained as shown in Table 28.1 Because some slip will occur in the coupling B the sun S2 will be driven at a lower speed than that of the planet... in the cover N of the coupling which will permit the oil to be discharged by the action of centrifugal force The operation of this ‘dumping’ valve is by means of oil pressure which is admitted to the space W and thence through passages in the cover N to the valve When the clutch Y is engaged the engine torque is divided at train 1; part of the torque is transmitted direct from the arm R1 through the. .. impulses being given to the driven member, one when the direction of the fluid is changed in the blades B and a second when the direction of the fluid is changed in the blades C When the torque acting on the driven member BCD is greater than the engine torque applied to the driving member A, there will be a reaction torque acting on the blades E and F; this will be transmitted by the pawls and ratchet... embodied in the system For example, to discourage the driver from parking the vehicle in N, the ignition key can be withdrawn only with the gear lever in the P position In an emergency, however, the driver can remove the key after depressing a release button adjacent to the ignition lock Moreover, to avoid the possibility of inappropriate movements of the vehicle when setting off on a steep slope, the lever... blades, the tangential component of the velocity of any particle, for example, Vt in view (a), being abstracted, more or less completely, so that the velocity of the particle on leaving the blades B is more or less radial as indicated by the arrow Vb The particle being considered has therefore lost momentum in the tangential direction and this momentum has been gained by the blades B, that is, by the rotor . meshing with the sun and the other with the annulus, Fig. 27.6(a), in which case the gear ratio between these two comes into play. Consequently, if the annulus is fixed, the sun gear is the input and the. and therefore has no influence on the gear ratio. If, on the other hand, the planet carrier C is locked, and the input is still the sun gear, Fig. 27.5(b), the output will, of course, be the. and therefore do not add to the load on the bearings on which the annulus rotates. A tie rod G pulls the outer band on to the inner band, and thus the inner band on to the drum, which is the