WO2004053350A1

WO2004053350A1 - A hybrid driving device and clutch/damper mechanism therefor and methods relating thereto

Info

Publication number: WO2004053350A1
Application number: PCT/SG2003/000283
Authority: WO
Inventors: Jun Zhu; Shi Jin Tu; Heng Fong Loh
Original assignee: Singapore Technologies Kinetics Ltd
Priority date: 2002-12-10
Filing date: 2003-12-10
Publication date: 2004-06-24
Also published as: AU2003283946A1

Abstract

A parallel hybrid drive has an engine (12) and a transmission (20) with a motor/generator (22) inserted in between, via a power-take-off (22) for either supplying power to or absorbing power from the drive train. A device (16) featuring one way clutch and torsional vibration damping functions is integrated into a compact disc-plate unit with specially aligned sprags (140) and rollers (142) forming the one way mechanism at the outer part and coil springs (122) forming the damper mechanism at the inner part. The outer race (102) of the one-way mechanism is connected directly to the engine flywheel (52) while the centre plate of the damper mechanism is spline-coupled to the input shaft (18) of the transmission. This permits a very compact and robust configuration, which also prevents a high shock load being transmitted to the transmission input shaft (18) and the motor/generator (22) during engine start/stop, while enabling engine disconnection during electric drive and regenerative braking, so that energy usage can be maximised. It also ensures smooth transition from electric drive to engine drive or to motor/engine combined drive, and vice versa.

Description

A HYBRID DRIVING DEVICE AND CLUTCH/DAMPER MECHANISM THEREFOR AND METHODS RELATING THERETO

FIELD OF THE INVENTION

The present invention relates to a hybrid driving device and a clutch/damper mechanism therefor. In particular it relates to a parallel hybrid driving device having an engine disconnection mechanism integrated with a torsional vibration damper into a single unit. This invention has particular use in a heavy military vehicle such as a tank.

BACKGROUND OF THE INVENTION

A parallel hybrid vehicle normally consists of an engine providing torque to a transmission and a motor/generator connected to the drive train of the vehicle to add power or to take it according to the circumstances.

When the motor/generator acts as a motor, torque provided to the drive train is added to that provided by the engine. Thus the motor/generator can function as a boost motor to improve acceleration and mobility. It can also act instead of the engine, functioning as the drive motor when a low driving speed is required to allow engine to stop, subject to the state of charge (SOC) of the battery. This may avoid the engine working in an inefficient manner. Unfortunately, the motor also tends to turn the engine at the same time, thereby wasting a lot of energy. When the motor/generator acts as a generator, it is rotated by a power take off (PTO) from the drive train. Thus it can function as an alternator whenever required, to provide charging to the vehicle battery and the electrical current needed for other vehicle systems. It can also function as a power absorption device, generating electricity (regenerative braking) from excess speed and decelerating the vehicle or reducing its acceleration, for example when descending a slope, whenever the battery management system allows it to do so. This further improves fuel economy and extends the service life of the mechanical brake.

Various approaches and arrangements to incorporate motor/generators in vehicle drives are known. U.S. Pat. No 5,773,904, issued to Schiebold et al, discloses an external rotor electric machine (synchronous motor) with two switchable clutches within the motor stator. The arrangement is intended to improve the torque provided by the motor and to reduce the axial length of the hybrid power train compared with when the rotor is between the two clutches. U.S. Pat. No. 5,789,823, issued to Sherman, discloses an approach to allow a motor/generator to work as the engine start motor and the vehicle drive motor. A one-way drive mechanism, a pair of clutch chambers, a torque converter and the motor/generator are arranged into an integrated unit disposed between the internal combustion (IC) engine and the conventional multi-speed transmission. When battery charging is required, the engine power is transmitted to the motor/generator through the torque converter.

U.S. Pat. No. 5,931,271 , issued to Haka, discloses another approach to permit engine starting and electric drive using a motor/generator, by arranging two one-way devices and a spring torsional vibration damper inside the rotor of the motor/generator. A first one way device is provided by rollers and cam surfaces in an outer race, whilst a second is provided by an array of sprags in an inner race.

U.S. Pat. No. 6,258,001 , issued to Wakuta et al, discloses a detailed design comprising a motor/generator with its rotor connected to the engine crankshaft via a flexible-plate damping device at one end and to a torque converter via a torus arm at the other end. A multi-disc clutch incorporating a spring damper mechanism resides in the torus drum, which is radially aligned inside the rotor of the motor/generator. The clutch/damper bridges and cushions or releases the drive torque from the engine/motor to the input shaft of the transmission. During pure electric drive the motor/generator has to crank the engine. These known systems are all complex. All increase the axial and/or radial sizes of the drive systems compared with systems without an additional motor /generator, for instance because they all integrate the rotor and/or stator directly into the drive unit (mostly to drive the output shaft directly). This may be acceptable where a new car can be designed and built around the new unit and hundreds of thousands of such will be sold. However, it is of little use where the cost of redesigning components such as the transmission or the engine compartment is not justified by the potential numbers of sales or not acceptable due to other constraints or if the system is wanted for retrofitting. This can be particularly true of large or heavy vehicles, for instance military vehicles, which might only be built in their hundreds.

Accordingly, an aim of the present invention is to provide a different hybrid driving device, or at least parts therefor, or a different approach to such a device. Preferably it would at least partially alleviate some of the problems with the prior art.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a clutch and damper unit for use in a drive mechanism, said unit having an axis of rotation with a radial plane extending therefrom and comprising: clutch means; and shock damper means; wherein the clutch and shock damping means are in the same radial plane.

According to a second aspect of the present invention, there is provided a hybrid driving apparatus, comprising: a transmission input shaft; power input and take-off means for mounting on said transmission input shaft to transfer power between a motor/generator and said shaft; and clutch means for mounting on said transmission input shaft and for coupling to an engine output.

The clutch means may be part of a clutch and damper unit as above. According to a third aspect of the present invention, there is provided a method of installing a hybrid drive into a vehicle, including the step of coupling a clutch/damper unit as above to an engine output and to a transmission input.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described by way of non-limitative example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic view of an arrangement of a hybrid driving device; Figure 2 is a partial, non-straight, sectional view of a hybrid driving device;

Figure 3 is an exploded perspective view of a one-way clutch/damper device;

Figure 4 is a first cross-sectional view, through a portion of the device of Figure 2; Figure 5 is a second cross-sectional view, through another portion of the device of Figure 2;

Figure 6 is a cross-sectional view showing the mounting of a sprag; and

Figure 7 is a cross-sectional view showing the mounting of a roller.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Figure 1 is a schematic view of a hybrid drive device 10 according to an embodiment of the invention. An engine 12, such as an internal combustion engine, drives a crankshaft 14. A clutch/damper unit 16 attached to the crankshaft is driven by it and drives a transmission input shaft 18. This, in turn, drives a transmission 20. To one side a motor/generator 22 is connected to the transmission input shaft 18 by way of a power take off mechanism 24 (which can also act to drive the transmission input shaft). An inverter/controller 26 runs between the motor/generator 22 and a battery 28. With this arrangement, the motor/generator 22, acting as a motor and driven by the battery 28, can provide additional drive torque or the sole drive torque to the drive shaft 18. Alternatively, acting as a generator, the motor/generator 22, can take power from the transmission input shaft 18 to recharge the battery 28.

Figure 2 is a cross-section through a portion of an embodiment of a parallel hybrid drive train according to one aspect of the invention. It is not a straight cross-section but is angled about the central drive shaft as shown in Figures 4 and 5. Moreover, the clutch/damper mechanism in the middle is not shown hatched, although it is a sectional view, to improve the ease of understanding. The left side of Figure 2 is the engine side and the right side is the transmission side.

An engine flywheel 52 is attached to a crankshaft 14 to rotate therewith. This, in turn, is linked to a transmission input shaft 18, through a clutch/damper unit 16. A motor/generator 22, positioned parallel to the engine crankshaft 14 and transmission input shaft 18, is linked to a power take-off gear train 24 (in this instance of three gears 62, 64, 66), which is also coupled to the transmission input shaft 18.

The radially outer portion 68 of the clutch/damper unit 16 is bolted to the flywheel 52 and these always rotate together. Both the radially inner portion 70 of the clutch/damper unit 16 and the inner gear wheel 66 of the power take-off gear train 24 are spline-coupled to the transmission input shaft 18 and thus always rotate together, thereby always rotating accordingly with the motor/generator 22 too.

A stationary flywheel housing 72 houses the flywheel 52. A stationary transmission housing 74 is bolted to the flywheel housing 72. The end of transmission housing 74 includes an input flange 76, which with the flywheel housing 72 seals the flywheel 52 and clutch/damper unit 16 off from the power take-off gear train 24 and rest of the transmission. The take-off gear train 24 passes through a hole 78 in one side of the transmission housing 74. The middle gear wheel 64 is rotatably mounted within the hole 78. The motor/generator 22 is mounted outside the transmission housing 74. In use, when the engine crankshaft 14 is going faster than or no slower than the transmission input shaft 18, for example during normal driving, the inner and outer portions 68, 70 of the clutch/damper unit 16 are engaged together and rotate together. When the engine crankshaft 14 is slower than the transmission input shaft 18, for example during deceleration or motor only driving, the inner and outer portions 68, 70 of the clutch/damper unit 16 are disengaged from each other and do not rotate together.

In this embodiment, the motor/generator 22 is a conventional electric power device which is controlled by a inverter controller (not shown) capable of both supplying output power (when in motor mode) from a battery source (not shown) and generating power (when in generator mode) to recharge the battery and meanwhile providing electric power for onboard electrical systems.

The power take-off gear train 24 connects the motor/generator 22 to the transmission input shaft 18, hence allowing the motor/generator 22 to be installed parallel to the centreline of the engine crankshaft 14 and transmission input shaft 18, either on the transmission side (as shown in Figure 2) or on the engine side (not shown), without increasing the axial length or general radial size, as might otherwise be required. The power take-off gear train 24 has a gear ratio greater than 1 , thereby favouring adoption of a compact high speed motor/generator 22 (e.g. an AC induction machine) matching to the engine speed range (once gear ratio is taken into account). Additionally, the torque provided by the motor/generator 22 is multiplied by the gear ratio to allow it to provide suitable driving force to move the vehicle off or allow it to negotiate a slope during the electric drive mode, and to enhance the benefits of the motor drive when combined with the drive from the engine.

The clutch/damper unit 16 is shown in more detail in Figures 3 to 7. In brief, clutch/damper unit 16 is a one-way clutch mechanism and a torsional damping mechanism integrated into one coaxial disc-shaped unit.

The component parts of clutch/damper unit 16 are shown separately in the exploded view of Figure 3. The main components are outer race 102, inner race 104, first clutch member holder 106, second clutch member holder 108, damper plate 110 and cover plate 112. When assembled into the clutch/damper unit 16, these components are all mounted concentrically. These components are all generally annular and all fit together into a unit with an outside diameter defined by the outer surface of outer race 102 and an inside diameter defined by the inner, splined surface of damper plate 110. The thickness of each of the outer race 102, inner race 104, two clutch member holders 106, 108 combined and damper plate 110 is substantially the same, although with some variations, and being substantially the thickness of the whole unit.

Radially outer portion 68 of the clutch/damper unit 16, mentioned above, consists of outer race 102. Radially inner portion 70 of the clutch/damper unit 16, mentioned above, consists of inner race 104, damper plate 110 and cover plate 112.

Figures 4 and 5 show the arrangement of these components in a unit in cross-sectional elevations. In the case of Figure 4, this is through the line A-A of Figure 2 and in the case of Figure 5, this is through the line B-B of Figure 2. The line C-C in both Figures 4 and 5 is the line corresponding to the section shown in Figure 2.

The damper mechanism of damper plate 110 works in a known manner and relies upon the presence of cover plate 112 and inner race 104. The damper plate 110 is of a uniform thickness with a central hole. It has an outer wall portion 120, with six very stiff compression springs 122 spaced equiradially about the outside, with a recess 124 in the outer form of the wall portion 120 between each spring 122. A centre plate 126 is bolted to one side of the damper plate 110 and has an axial extension 128, of a smaller diameter, inserted within the central hole of the damper plate 110. The centre plate 126 (including the axial extension 128) also has a hole through its middle, which is splined to match the transmission input shaft 18. Alternative couplings are also possible, for example a keyed transmission input shaft 18 and a keyway through the centre plate 126, or vice versa. Alternatively the centre plate 126 can be provided as an extension of the damper plate 110. The springs 122 are of a greater diameter than the thickness of the wall portion 120. Inner race 104 has both a circumferential wall 130 and a side wall 132, which extends outwards from approximately half way along the radius of the inner race 104. There are six inner race spring recesses 134 in this side wall 132, spaced and sized to correspond to the springs 122 of the damper plate 110. The damper plate 110 is mounted within the inner race 104, with the wall portion 120 in contact with the side wall 132. One of the sides of each spring extends through a separate one of the inner race spring recesses 134. The cover plate 112 likewise has correspondingly six cover plate spring holes 114. The cover plate 112 also fits within the inner race 104 and lies against the wall portion 120 (on the other side of the wall portion 120 from the side wall 132), with the other of the sides of each spring extending through a separate one of the cover plate spring holes 114. The cover plate 112 is bolted to the inner race side wall 132, with the bolts extending through the recesses 124 in the damper plate wall portion 120 and a gap between the bolts and the wall portion 120. The cover plate 112 has a centre hole of sufficient diameter to fit over the centre plate 126.

These compression springs 122 control relative rotation between the damper plate 110 and the inner race 104 and cover plate 112. Any major shocks, for example from bumps, sudden acceleration or the like, will tend to cause a sudden speed change in one of the engine crankshaft 14 and transmission input shaft 18. These will translate into a difference in speed between the damper plate 110 on the one hand and the inner race 104 and cover plate 112 on the other. The sides of the spring recesses 134 and holes 114 will press against the sides of the springs 122 in one direction or the other, which will compress, thereby allowing a smoother change of speed without a shock. The two clutch member holders 106, 108 fit together to form an annular layer, with an inner surface having a diameter that is just larger than the outer diameter of the inner race 104 and an outer diameter that is just smaller than the inner diameter of the outer race 102. The two clutch member holders 106, 108 also have relatively thin outer side walls, with flanges having an outer diameter that is larger than the inner diameter of the outer race 102 and an inner diameter that is smaller than the outer diameter of the inner race 104. The outer side surfaces of the outer and inner races 102, 104 are recessed accordingly to receive those flanges. The two clutch member holders 106, 108 thereby sandwich the outer and inner races 102, 104 between these flanges. By bolting the two clutch member holders 106, 108 together, the whole clutch/damper unit 16 is held together.

The clutch layer made up of the two clutch member holders 106, 108 contains clutch member in the form of a plurality of pairs of friction sprags 140 and a plurality of rollers 142 spaced equiradially between the inner surface of the outer race 102 and the outer surface of the inner race 104. The sprags 140 and rollers 142 are axially limited and circumferentially aligned by recesses within the two clutch member holders 106, 108.

The sprags 140 are generally parallelepiped. They are substantially the same length as the distance between the sides of the two clutch member holders 106, 108, but are taller than the distance between the adjacent, friction surfaces of the outer and inner races 102, 104. Therefore they are angled relative to those two surfaces, with the recesses within the two clutch member holders 106, 108 preventing them from falling over. Further, two spring strings 144, 146, pass around the clutch layer, one passing through a hole passing through one end of each sprag 140 and the other passing through a hole passing through the other end of each sprag 140. The holes are generally square relative to the sprags (making them angled relative to the friction surfaces of the races), so that the spring tension tends to pull the sprags 140 in the direction of being upright, thereby biasing them so that they are normally in good contact with the adjacent surfaces of the outer and inner races 102, 104. The direction in which the sprags 140 are angled determines the direction in which the clutch works. The recesses within the clutch member holders 106, 108, which hold the sprags 140, are trapeziums in cross-section, as shown, which allows the sprags 140 to be angled in either direction, according to the setup and clutch direction required during construction. The rollers 142 are cylindrical, being substantially the same diameter as the gap between the adjacent surfaces of the outer and inner races 102, 104. They are coaxial with the central axis of the clutch/damper unit 16 and are held within generally cylindrical recesses but which lack side walls facing the adjacent surfaces of the outer and inner races 102, 104. The rollers ensure that the outer and inner races 102, 104 remain concentric. The rollers are shorter than the distance between the sides of the two clutch member holders 106, 108, as the two spring strings 144, 146 do not pass through them, but have to pass around their ends. The situation of the sprags 140 within the clutch member holders 106, 108 is shown in more detail in Figure 6 whilst that of the rollers 142 is shown in more detail in Figure 7.

The outer and inner races 102, 104, sprags 140, rollers 142, tension springs 144, 146 and clutch member holders 106, 108 when coupled together form a one-way clutch mechanism. The majority of the clutch/damper unit 16 will normally be made of steel.

However, the clutch member holders 106, 108 are made of aluminium in this particular embodiment.

The operation of the one-way clutch mechanism will now be described, particularly with reference to Figure 4. Figure 4 shows a clutch/damper unit 16 and flywheel 52 where, under normal drive, when the flywheel 52 rotates as the prime mover, it rotates anticlockwise. When the rotation of the flywheel 52 tends to be anti-clockwise relative to the transmission input shaft 18 (for example during normal driving other than free-wheeling or if the transmission input shaft 18 tends to rotate faster in the clockwise direction), the two races 102, 104, tend to move relative to each other (the outer race 102 anti-clockwise relative to the inner race 104). The tops and bottom surfaces of the sprags 140, being in contact with the inner surface of the outer race 102 and the outer surface of the inner race 104, respectively (due to the bias of the string springs 144, 146), also therefore tend to rotate anti-clockwise. In doing this, they lock those two surfaces and thereby the two races 102, 104 together, thereby engaging the engine power to the transmission input shaft 18 via the damping mechanism. This will also drive the motor/generator 22 in the same direction as the engine (if it is not already acting as a motor and turning in that direction anyway). It can then work as a generator to provide electricity for vehicle usage and/or to charge the battery. Upon vehicle braking, the engine throttle is released thereby reducing the engine speed. Due to the kinetic inertia of the vehicle, the transmission shaft will tend to rotate faster than the engine, causing inner race 104 to tend to rotate faster than outer race 102 in the anti-clockwise direction. This action releases the sprags 140, causing them to lose firm contact with the surfaces of the outer and inner races 102, 104 and tip further in the direction in which they are angled. The two races 102, 104 are therefore free to rotate relative to each other, using the rollers 142, and hence the power path is disconnected from the transmission shaft 18 to the engine 12. The outer race 102 still rotates with the engine at idling speed while the inner race 104 rotates faster with the transmission input shaft 18. This continues to rotate the motor/generator 22 and can be used to generate electricity to recharge the battery. This has a braking effect (regenerative braking) on the transmission input shaft 18 avoiding engine braking while using vehicle kinetic energy more efficiently. This will stop only when the vehicle speed has reduced substantially so that the speed of the transmission input shaft 18 tends to be lower than the engine idling speed, at which point the clutch members will recouple the outer and inner races 104, 102. Under emergency braking, this feature also helps to prevent engine stop.

When full throttle acceleration is demanded, both the engine and the motor/generator 22 are activated to provide maximum power to the transmission input shaft 18. As the engine is now on full throttle effort and has more effect than the motor/generator 22, the speed of the transmission input shaft 18 is mainly determined by the engine speed. This is the same as the position mentioned above and shown in Figure 4 (that is the outer race 102 rotates anticlockwise relative to the inner race 104). Hence the sprags 140 will be in the connecting position to continue to transmit engine power to the transmission input shaft 18. When low speed electric drive is required, the vehicle driving effort is provided by motor/generator 22 alone. In this case the inner race 104 rotates in the anti-clockwise direction whilst the outer race 102 is stationary as the engine is shut off. In terms of the positions of the sprags and the clutching/declutching effect, this is similar to during braking.

In the described embodiment, a parallel hybrid drive has an engine and a transmission with a motor/generator inserted in between, via a power-take-off for either supplying power to or absorbing power from the drive train. A device featuring one way clutch and torsional vibration damping functions is integrated into a compact disc-plate unit with specially aligned sprags and rollers forming the one way mechanism at the outer part and coil springs forming the damper mechanism at the inner part. The outer race of the one-way mechanism is connected directly to the engine flywheel while the centre plate of the damper mechanism is spline coupled to the input shaft of the transmission. This permits a very compact and robust configuration, which also prevents a high shock load being transmitted to the transmission input shaft and the motor/generator during engine start stop, while enabling engine disconnection during electric drive and regenerative braking, so that energy usage can be maximised. It also ensures smooth transition from electric drive to engine drive or to motor/engine combined drive, and vice versa.

The present invention as described and embodied is particularly useful in heavy vehicles, for instance heavy military vehicles, such as tanks or APCs. For military vehicles especially, the use of electric driving is important, as it allows running that, compared with normal running, stealthy (as the use of the motor alone does not turn the engine). Apart from reducing noise, this reduces the chances of being spotted by thermal imagery and destroyed by the enemy.

In addition, the present invention provides a compact solution, allowing ease of access to the power train for the motor/generator, and ease of introducing a clutch mechanism, while avoiding high integration efforts. Thus off- the-shelf standard motors can be used and, the existing engine and transmission designs can be retained or with minimum level of interface modifications. This is especially meaningful for the design or retrofit of military vehicles (for example where a new transmission can cost tens of thousands of dollars).

Thus the present invention includes the modification of an existing design to add a power take-off to a transmission input shaft and a one way clutch mechanism to an engine output. Where a shock damper may be useful, one can be added, for instance in a clutch/damper unit. Where a shock damper exists in the design, it can be replaced with a clutch/damper unit. This does not just apply to the designs, but also to retrofitting existing models. For example for an APC, a clutch/damper unit weighing less than 20kg and able to transmit 1500Nm torque can be installed, with the clutch/damper unit replacing a damper unit attached to a flywheel, with the overall axial length of the drive train increased by just 0.03m or so.

For example, for a Bradley ™ Infantry Fighting Vehicle (IFV), the present invention could be installed with little or no modification to its flywheel or transmission shaft. It would only need modification to the existing PTO gearbox to allow for replacing the alternator with a motor/generator and to replace its current damper with the clutch/damper of the present invention.

The above main embodiment has a particular form for the clutch/damper unit. Not all aspects of the invention require the presence of the damper mechanism, a clutch alone may suffice. The clutch portion has been described in terms of sprags to provide torque transmission and rollers to act as bearings. Such rollers may not be necessary in all scenarios. Additionally, the sprags can be replaced with other clutch members to achieve a one way clutch.

If a damper is used, it does not have to have the coil springs and other features as described, it could have other forms, instead. If there are springs, it does not have to have six. Other numbers can be present. Further, the stiffness of the springs or their equivalent can depend on the intended use.

The above described arrangement is particularly useful for a high torque situation. However, for a high shock, low torque situation, the damper mechanism can be radially outside the clutch mechanism. The power input and take-off gear train is described with three gears. More or fewer are possible or other mechanisms can be used for the same function. The gear on the transmission input shaft is described as spline- coupled, but where such exists, it can be coupled in other ways, whether to the transmission input shaft or elsewhere.

The above described embodiment includes an engine flywheel to which the clutch/damper unit is attached. However, the unit itself can act as a suitable flywheel, for instance by increasing the outer diameter and/or width of the outer race. Other modifications are also possible in the general construction of this unit, including having additional or differently placed bolt holes to allow other attachments.

The above embodiments assume a vehicle with wheels or tracks. The invention can however be used in non-locomotion or non-vehicle applications.

Although the invention has been explained in relation to preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as described and claimed.

Claims

1. A clutch and damper unit for use in a drive mechanism, said unit having an axis of rotation with a radial plane extending therefrom and comprising: clutch means; and shock damper means; wherein the clutch and shock damping means are in the same radial plane.

2. A clutch and damper unit according to claim 1 , wherein the shock damper means is radially inside of the clutch means.

3. A clutch and damper unit according to claim 1 or 2, wherein the clutch and shock damper means are coaxial.

4. A clutch and damper unit according to any one of the preceding claims, wherein the clutch means is a one-way clutch means.

5. A clutch and damper unit according to any one of the preceding claims, further comprising first and second coupling means for coupling said unit to an engine output and a transmission input respectively, said first and second coupling means having said clutch means between them.

6. A clutch and damper unit according to claim 5, wherein said first coupling means comprises means for mounting said unit onto an engine flywheel.

7. A clutch and damper unit according to claim 5 or 6, wherein said second coupling means comprises means for mounting said unit directly onto a transmission input shaft.

8. A clutch and damper unit according to claim 7, wherein said second coupling means comprises a splined hole coaxial with said axis of rotation.

9. A clutch and damper unit according to any one of claims 5 to 8, wherein the clutch means comprises coaxial outer and inner races with clutch members therebetween and said first coupling means are provided on said outer race.

10. A clutch and damper unit according to claim 9, wherein said clutch members comprise a plurality of sprags arranged equiradially from said axis of rotation and further comprising a plurality of rollers arranged equiradially with and amongst said sprags.

11. A clutch and damper unit according to any one of claims 5 to 10, wherein the shock damper means is operable to damp shocks being transmitted between said first and second coupling means.

12. Hybrid driving apparatus, comprising: a transmission input shaft; power input and take-off means for mounting on said transmission input shaft to transfer power between a motor/generator and said shaft; and clutch means for mounting on said transmission input shaft and for coupling to an engine output.

13. Apparatus according to claim 12, wherein said clutch means is arranged to be coupled to an engine flywheel.

14. Apparatus according to claim 12 or 13, further comprising a transmission shaft housing and said power input and take-out means is arranged to transfer power between a motor/generator outside said transmission shaft housing and said shaft inside said transmission shaft housing.

15. Apparatus according to claim 14, wherein said power input and take-out means is mounted on said transmission shaft housing.

16. Apparatus according to any one of claims 12 to 14, further comprising shock damper means and said clutch and shock damper means are arranged in a clutch/damper unit.

17. Apparatus according to claim 16, wherein said clutch/damper unit is as claimed in any one of claims 1 to 11.

18. A vehicle having an engine cavity designed for use with a non-hybrid driving device, having hybrid driving apparatus as defined in any one of claims 12 to 17 fitted therein without any change to the dimensions of the engine cavity.

19. A vehicle retrofitted with hybrid driving apparatus as defined in any one of claims 12 to 17.

20. A vehicle according to claim 19, wherein the engine cavity dimensions are not affected by the retrofitting of said hybrid driving apparatus.

21. A vehicle according to claim 19 or 20, having had a non-hybrid drive prior to being retrofitted.

22. A vehicle according to any one of claims 18 to 21 , being a tracked vehicle.

23. A method of installing a hybrid drive into a vehicle, including the step of coupling a clutch/damper unit as claimed in any one of claims 1 to 11 to an engine output and to a transmission input.

24. A method according to claim 23, wherein the clutch/damper unit is mounted on an engine flywheel and to a transmission input shaft.

25. A method according to claim 23 or 24, being a method of retrofitting said hybrid drive, further comprising the step of decoupling a damper from the engine output and replacing it with said clutch/damper unit.

26. A method according to any one of claims 23 to 25, further comprising the step of coupling a power input and take-out means to said transmission input to transfer power between a motor/generator and said transmission input.

27. A method according to claim 26, wherein the step of coupling a power input and take-out means to said transmission input comprises mounting the power input and take-out means on a transmission input shaft within a shaft housing, to transfer power between the shaft and a motor/generator without said housing.