Known driven plates for friction clutches comprise a main driven plate assembly including at least one friction lining and a central hub for connection with a shaft, the main assembly being mounted concentrically about and drivingly connected to the hub. Such known driven plates are hereinafter referred to as driven plates of the type described.

Driven plates of the type described are often used in friction clutches for motor vehicles to selectively transfer drive from a flywheel, which may be attached to the crankshaft of an internal combustion engine, to a drive shaft of the vehicle transmission. Such known friction clutches typically comprise a clutch cover assembly attached to the flywheel with the driven plate located between the clutch cover assembly and the flywheel. The clutch cover assembly comprises a pressure plate which is biased axially towards the flywheel when the clutch is engaged to clamp the friction linings of the driven plate between the pressure plate and the flywheel so that drive is transmitted from the flywheel to the driven plate and then via the hub to the transmission drive shaft.

It is known in driven plates of the type described for the main driven plate assembly to be drivingly connected to the hub by means of inter-engaging drive formations which have limited radial and circumferential clearances to allow the main assembly to move radially and circumferentially relative to the hub to a limited extent. Such driven plates may comprise a torsion damper to isolate the drive line from vibrations generated in the engine.

It is also known for such driven plates to have a pre-damper or idle centre between the main driven plate assembly and the central hub to isolate the drive line from low level vibrations which occur when the engine is idling or running at relatively low speed.

Alternatively driven plates of the type described may be of the rigid type in which no torsion damper is provided and the main driven plate assembly is fixed rotationally fast with, or is integral with, the central hub. Such rigid driven plates are often used in conjunction. with twin mass flywheels which comprise a torsion damper to isolate the drive line from vibrations generated by the engine.

Due to manufacturing tolerances et cetera, it is not always possible to ensure that when a vehicle engine and drive line are assembled the axes of the crankshaft and transmission drive shaft are in angular alignment. Where there is some angular misalignment between these axes then there will be a tendency for the friction linings, which are clamped to the flywheel, to rotate about the axis of crankshaft or flywheel whilst the hub is constrained to rotate about the axis of the transmission drive shaft. Because the friction linings and the hub are rotating about separate non-angularly aligned axes, cyclical stresses are set up in the driven plate.

In addition, when the flywheel is attached to an internal combustion engine, the forces acting on the crankshaft of the engine may cause the flywheel to swash or swirl about the axis of the crankshaft. When the clutch is engaged the friction linings will tend to follow the movement of the flywheel and so will swash or swirl about the hub which is constrained to rotate about the axis transmission drive shaft. This again sets up cyclical stresses in the driven plate.

When cyclical stresses are set up in the driven plate, this can lead to fatigue failure in the material of the driven plate. This is a particular problem in driven plates of the rigid type in which the friction linings are mounted on relatively thin spring segments. In such cases most of the relative movement between the friction linings and the central hub are absorbed by the spring segments which are flexible compared to the rest of the driven plate. As a consequence the segments are subjected to cyclical stressing and in extreme cases the material in the segments may fail due to fatigue.

Problems can also arise in driven plates of the type described which have a pre-damper or idle centre. In this type of driven plate the relative movement between the friction linings and the hub may be taken up in the pre-damper. which as a result is no longer able to function correctly.

An object of the invention is to provide an improved driven plate of the type described which overcomes or at least mitigates the problems of the known driven plates.

Thus in accordance with the invention there is provided a driven plate of the type described in which the main driven plate assembly is drivingly connected with the hub by means of inter-engasins drive formations which have limited radial and circumferential clearances to allow the main assembly to move radially and circumferentially relative to the hub to a limited extent the driven plate also having two pairs of opposed surfaces, each pair of opposed surfaces comprising a first surface associated with the hub and a second surface associated with the main driven plate assembly with at least one of the surfaces in each pair being inclined obliquely to the axis of the driven plate. one of the pairs of opposed surfaces acting to inhibit movement of the main driven plate assembly relative to the hub in a first axial direction of the driven plate, the other of the pairs acting to inhibit movement of the main driven plate assembly relative to the hub in the opposite axial direction of the driven plate. the arrangement being such that the main driven plate assembly can tilt relative to the axis of the central hub with the first and second surfaces of each pair sliding relative to one another.

In a driven plate in accordance with the invention the main driven plate assembly is able to tilt relative to the hub in a controlled manner to allow the friction linings to rotate about an axis which is not angularly aligned wilh the axis of rotation of the hub, and/or to allow the friction linings to follow the swashing movement of a flywheel, without setting up stresses in the driven plaie. This reduces the risk of fatigue failure and permits proper operation of the torsion damper or pre-damper where provided. By providing two pairs of opposed surfaces in accordance with the invention the relative tilting between the main driven plate assembly, and the hub can be controlled in a manner which does not generate a frictional force between the surfaces so ensuring that main driven plate assembly and hub can tilt freely relative to one another.

Other aspects of the invention will be clear from the subject matter of the various dependent claims.

In order to more clearly describe the invention several embodiments will now be described. by way of example only, with reference to the drawings in which: Figure 1 is a cross sectional view of a driven plate in accordance with the invention ; Figure 2 is an enlarged view of a detail of Figure 1 ; Figure 3 is a view similar to Figure 2 showing a modification to the driven plate of Figure 1 ; Figure 4 is a cross sectional view of a second embodiment of a driven plate in accordance with the invention; Figure 5 is an enlarged view of a detail of Figure 4 ; Figure 6 is a view similar to that of Figure 5 showing a modification to the driven plate of Figure 4 : Figure 7 is a cross sectional view of a third embodiment of a driven plate in accordance with the invention : and Figure 8 is a view similar to that of Figure 7 showing a modified version of the driven plate of Figure 7 Figures 1 and 2 show a driven plate 10 for use in a friction clutch for a motor vehicle. The drive plate 10 comprises a main driven plate assembly 11 mounted on a central hub 12.

The hub 12 has internal splines 13 for connection with a gearbox input shaft and an annular array of circumferentially spaced teeth 14 extending radially outwards from the outer surface of the hub.

The main driven plate assembly 11 is mounted co-axially about the hub 12 and comprises an annular flange 20 having an array of circumferentially spaced teeth 21 which extend radially inwardly from an inner periphery of the annular flange 20 for engagement with the teeth 14 on the outer surface of the hub 12. Limited circumferential and radial clearances are provided between the teeth 14 on the hub 12 and the teeth 21 on the flange 20 so that the flange 20 is able to move radially and circumferentially relative to the hub 12 to a limited extent. A first side plate 17 is arranged on the on the right hand side (as viewed in Figure I) of the annular flange 20 whilst a second side plate 18 is arranged on the left hand side (as viewed in Figure 1) of the annular flange 20. The first and second side plates 17.

18 are rigidly connected by means of a number of rivets 19 which pass through corresponding openings 20a in the annular flange 20. The second side plate 18 carries a pair of friction linings 15 which are mounted to the side plate via spring segments 16.

In a manner known in the art, the side plates 17, 18 are capable of limited rotational movement relative to the annular flange 20 and a set of main torsion damping springs 22 are housed in aligned apertures 23 and 24 in the annular flange 20 and the side plates 17,18 respectively, to control the rotational movement therebetween. In the embodiment shown there are six circumferentially equi-spaced main torsion damper springs 22. However the number of springs 22 used is not essential and more or less than six can be used as required. The springs 22 may each comprise two separate springs, one arranged concentrically inside the other.

The relative rotational movement between the side plates 17,18 and the annular flange 20 is also controlled by a friction damper 25. The friction damper comprises first and second friction washers 26,27 (see figure 2) arranged between the second side plate 18 and the annular flange 20 and a third friction washer 28 located between the annular flange 20 and the first side plate 17. A spring washer 29 acts between the third friction washer 28 and the first side plate 17 to clamp the friction washers. the annular flange and the second side plate together so that rotational movement of the side plates 17. 18 relative to the annular flange 20 results in the generation of a friction damping force in a manner known in the art.

The driven plate also has a torsion pre-damper 30 to control the circumferential and radial movement permitted between the annular flange 20 and the hub due to the circumferential and radial clearances between the teeth 14 and 1 The pre-damper 30 comprises four circumferentially equi-spaced springs 31 which are arranged in enlarged spaces between consecutive teeth 14 and 21 on the hub 12 and annular flange 20 respectively. The springs 31 are aligned generally tangential to a pitch circle drawn concentric with the axis of the driven plate and serve to oppose the circumferential and radial movement of the annular flange 20 relative to the hub 12 in a manner well known in the art.

In accordance with the invention, the driven plate has two pairs of opposed surfaces 32, 33 and 4. 35 respectively. Each pair comprises a first surface 32, 34 associated with the hub 12 and a second surface 33, 35 associated with the main driven plate assembly 11. In the embodiment shown, the first surfaces 32, 34 are each provided on a respective annular bearing ring 36, 37 which are located about the outer periphery of the central hub whilst the second surfaces 33, 35 are each provided on a splayed out portion of the radially inner peripheries of the side plates 17 and 18 respectively. One of the pairs of opposed surfaces 32, 33 is provided on the right hand (as viewed in Figure 2) axial side of the driven plate whilst the other pair of opposed surfaces 34, 3 5 is provided on the opposite (left hand, as viewed) axial side of the driven plate. Each of the pairs of opposed surfaces 32,33 and 34, 35 are arranged generally at an oblique angle to the axis of the hub 12 and the arrangement is such that one of the pairs of opposed surfaces 32,33 inhibits axial movement of the driven plate main assembly 11 to the right (as viewed in Figure 2) relative to the hub 12 whilst the other of the pairs of opposed surfaces 34, 35 inhibits axial movement of the main driven plate assembly to the left (as viewed) relative to the hub 12.

The profile or shape of the surfaces 39, 33 and 34, 35 is such that the main driven plate assembly 11 can tilt relative to the axis of the hub 12 as indicated by the arrows W (see Figure 1), with the first and second surfaces in each pair sliding relative to each other. In the embodiment shown, the first surfaces 32, 34 are both part-spherical with the surface 32 having a centre X located on the axis of the hub 12 whilst the surface 34 has a centre Y also located on the axis of the hub 12. The profiles of the second surfaces 33. 35 are such as to generally conform with the profiles of their respective first surfaces 32, 33.

A small working clearance may be provided between each pair of opposed surfaces 32, 33 and 34, 35 so that the main driven plate assembly 11 is able to freely tilt about the axis of the hub 12. The total working clearances between the surfaces 32. 33 and 34. 35 may be in the order of 0. 05 to 0.5 mm. It should be noted that the opposed surfaces in each pair are not biased in to contact with each other so that frictional resistance is kept to a minimum.

In particular it should be noted that the friction damper 25 is loaded between the two side plates 17 and 18 and does not produce any loading between the opposed surfaces 32. 33 and 34, 3 5.

The bearing rings 36 and 37 can be made from any suitable material but preferably they are made from a plastics material having a relatively low coefficient of friction so that the opposed surfaces 32, 33 and 34, 35 slide freely over each other to further ensure that the main driven plate assembly 11 can tilt easily relative to the hub 12. The bearing rings 36, 37 may each have projections 40 which engage with the teeth 14 on the hub 12 to ensure that the rings rotate with the hub 12.

It should be understood that the invention is not limited to the arrangement disclosed in the embodiment shown in Figures 1 and 2 in which the first surfaces 32, 34 are part spherical and the second surfaces 33,35 conform generally to the profile of their respective first surfaces. The invention embraces any arrangement in which the two pairs of opposed surfaces 32, 33 and 34,35 permit relative tilting or pivotal movement between the main driven plate assembly 11 and the central hub 12. For example the first surfaces 32, 34 could be spherical or part-spherical with a common centre, they could be conical or part- conical, tapered, contoured, or may have a radius which is not spherical, they could be convex or concave.

Furthermore, it will be understood that the opposed surfaces 32, 33 and 34, 35 in each pair need not fully conform in profile with each other in order for the invention to be applied.

Indeed it is sufficient for the surfaces 39 33 or, 4 35 in each pair to make only line contact with each other.

It can be seen that in an arrangement according to the invention the two pairs of opposed surfaces 32,33 and 4, 35 work in combination to guide the main driven plate assembly I I pivotally about the hub 12. This enables the friction linings 15 to rotate about an axis which is not in angular alignment with the axis of rotation of the hub 12 without setting up cyclical stresses in the driven plate 10 and without affecting the operation of either the main torsion damper or the pre-damper 30. In a typical arrangement, the main driven plate assembly 11 miaht be expected to pivot by. for example, 0. 25 to lmm in either direction from the vertical measured at the outer diameter of the side plates 17,18 and the central flange 20.

It should also be noted that the radial clearance between the teeth 21 on the flange 20 and the teeth 14 on the hub 12 enables the main driven plate assembly 11 to move radially relative to the hub 12 to a limited extent. Such movement might occur for example when the axis of an associated crankshaft (or flywheel) and the axis of an associated transmission drive shaft are radially offset due to misalignment. This relative radial movement will be resisted by the springs 31 of the pre-damper which will tend to centre the hub 12 relative to the main driven plate assembly 11 in a manner known in the art. Thus when the invention is applied to a driven plate having a pre-damper of the type described, the driven plate can compensate for both angular and radial misalignment.

Figure 3 shows a modified form of the driven plate of Figures 1 and 2. The driven plate in Figure 3 is substantially the same as that shown in Figures 1 and 2 except that the first surfaces 32, 34 are formed directly on the hub 12, whilst the second surfaces 33, 35 are formed on bearing rings 38 and 39 which are located on the radially inner edges of the first and second side plates 17,18 respectively. In this arrangement the side plates 17,18 can be flat at their radially inner peripheries making them simpler to produce and so reducing manufacturing costs. The bearing rings 38, 39 can be made from any suitable material but again are preferably made from a plastics material having a low co-efficient of friction.

The bearing rings have a number of slots 41 for engagement by drive lugs 42 on the side plates 17, 18 to ensure that the rings are rotationally fast with the side plates.

A further embodiment of a driven plate 110 in accordance with the invention is shown in Figures 4 and 5. The driven plate 110 is substantially the same as the driven plate 10 of Figures I and 2 and features which perform the same function are given the same reference numeral but increased by 100.

In driven plate 110, both pairs of opposed surfaces 132, 133 and 134 135 are arranged on the same axial side of the driven plate. One pair of opposed surfaces 132, 133 comprises a first surface 132 on a first bearing ring 136 located on the outer periphery of the hub 112 adjacent to the right hand (as viewed in Figure 5) axial side of the teeth 114. The second surface 133 of this pair is formed on the axially inner surface of a splayed out portion of the radially inner periphery of the first side plate 117. The other pair of opposed surfaces 134, 13 5 comprises a first surface 134 provided on a second bearing ring 137 adjacent to the first bearing ring 136 whilst the second surface 135 of this pair is formed on the axially outer side of the splayed out portion of the first side plate 117. The second bearing ring 137 is also located on the outer peripheral surface of the hub 112 and has a first portion 137a which abuts the first bearing ring 136. A circlip 138 locates both bearing rings 136, 137 axially on the hub. The second bearing ring has a second portion 137b which extends radially. outwardly from the first portion 137a at an oblique angle to the axis of the driven plate and generally parallel to the surface 132 on the first bearing ring 136. The surface 134 is provided on the axially inner surface of the second portion 137b facing towards and spaced from the surface 132. The splayed out portion of the first side plate 117, which carries the second surfaces 133, 135 on either axial side thereof, fits between the surfaces 132, 134 with a small working clearance. It should be noted that one of the pairs of surfaces 132,133 inhibits movement of the main driven plate assembly 111 to the left (as viewed in Figure 5) relative to the hub whilst the other pair of opposed surfaces 134, 135 inhibits movement to the right.

The profile of the surface 132 is part-spherical having a centre Z located on the axis of the driven plate whilst the profile of the surface 134 is also part-spherical but is concave whereas the surface 132 is convex. The second surfaces 133, 135 have profiles which conform generally with the profiles of their respective first surfaces 132, 1, 4 As with the previous embodiment the opposed surfaces in either pair may have any suitable profile which permits the driven plate main assembly 111 to tilt relative to the hub 112.

The first and second bearing rings can be formed of any suitable material but are preferably formed from a plastics material having a low co-efficient of friction. The first bearing ring 136 may have projections 140 which locate in the side of the teeth 114 of the hub to ensure that ring 136 rotates with the hub 112.

Because both pairs of opposed surfaces are provided on the right hand side (as viewed in Figure 5) of the teeth 114 of the hub 112, the friction washer 126 can be extended radially inwardly to provide an increased area of contact with the second side plate 118 A modified version of the friction driven plate 110 is shown in Figure 6. This driven plate is identical to the driven plate shown in Figure 5 except that the first portion 137a of the second bearing ring 137 has a reduced axial dimension. This is compensated for by providing an axial extension 136a to the first bearing ring 136. This results in the second bearing ring 137 having a more even cross-section which is easier to manufacture.

A further embodiment of a driven plate 210 in accordance with the invention is shown in Figure 7. The driven plate 210 is similar to the driven plate 10 and features which perform the same function are given the same reference numeral but increased by 200.

Driven plate 210 has two pairs of opposed surfaces 232, 233 and 234,235 respectively. In a manner similar to that of the embodiment shown in Figure 3, the first surfaces 232, 234 of each pair are formed directly on the hub 212. However, in this embodiment the second surfaces 233,235 are not mounted on the side plates 217, 218 but are provided on side of the annular flange 220 and are held rotationally fast with each other and the annular flange 220 by means of a number of axially extending arm portions 245 on plate 244 which extend the through corresponding openings in the annular flange 20 and 243. The arm portions 245 may be arranged so as to clip on to the intermediate plate 243 so holding the intermediate plates 243,244 and the annular flange 20 together to form a sub-assembly for manufacturing purposes. The plates 243, 244 have windows or recess 246 which align with damping springs 231 arranged between consecutive teeth 214 on the hub 212. The windows or recess 246 engage with the ends of the springs so that relative rotational movement between the intermediate plates 243, 244 and the hub 212 results in the springs being compressed between the recesses 246 and the teeth 214 of the hub in a manner well known in the art.

Driven plate 210 has two friction dampers 225, 247 which provide hysteresis damping for the main torsion damper and the pre-damper respectively The first friction damper 225 comprises a friction washer 248 having a radially extending portion 248a which is in contact with the axially outer face of the intermediate plate 243, and a number of axially extending lugs 248b which engage in corresponding openings 217a in the side plate 217 A spring washer 229 acts between the friction washer 248 and the side plate 217 clamping the radially extending portion 248a against the intermediate plate 243 and also clamping intermediate plate 244 against the second side plate 218. Relative rotational movement between the side plates 217, 218 and the annular flange 220 will result relative rotational movement between the friction washer 248 and the intermediate plate 243 and between the intermediate plate 244 and the second side plate 218 generating a friction damping force for the main torsion damper in a manner well known in the art.

The second friction damper 247 comprises a radially extending friction washer 249 which contacts the axially inner surface of the first side plate 217. The friction washer 249 has a number of radially inwardly directed drive formations 249a which engage with splines 250 formed on the outer periphery of the hub 212 so that the friction washer 249 is rotationally fast with the hub. A spring washer 251 acts between the intermediate plate 243 and the friction washer 249 to bias the friction washer into contact with the side plate 217. Relative rotational movement between the hub and side plate 217 results in relative movement between the friction washer 249 and the side plate 217 generating a friction damping force operative over the complete range of movement of both the pre-damper and the main torsion damper. The spring force of the spring washer 251 is small in comparison with the spring force of the spring washer 229 so that the damping force generated by the damper 247 is small compared to the'friction damping force generated by the damper 225. It should also be noted that the spring force of the spring washer 251 is not sufficient to cause an axial loading to be generated between the opposed surfaces 232, 233. Since neither of the friction dampers 225, 247 results in axial loading of the two pairs of opposed surface 232, 233 and 234, 235 the friction forces between the opposed surfaces are kept to a minimum. The intermediate plates 243, 244 can be made of any suitable material but preferably are made from a plastics material.

In an alternative arrangement (not shown), the first surfaces 232, 234 could be provided on separate bearing rings mounted about the periphery of the hub 212. Such bearing rings may be rotationally fixed to the hub by having drive formations for engagement with splines formed on the periphery of the hub.

Figure 8 shows driven plate 310 which is a modified version of the driven plate 210 and features of plate 310 which perform the same function of those of plate 210 are given the same reference numeral but increased bv 100. In this embodiment the first surface 332 is formed on a bearing ring 336 which is mounted about the outer periphery of the hub 312.

The bearing ring 336 has a number of radially inwardly directed drive formations 336a which engage with splines 350 formed on the outer periphery of the hub 312 so that the bearing ring 336 rotates with the hub 312. The second surface 333, which opposes the first surface 332. is provided on a modified friction washer 349 of the friction damper 347. The modified friction washer 349 is generally L-shaped having a radially extending portion 349a biased into contact with the axially inner face of the first side plate 317 by spring washer 351 and an axially extending portion 349b which lies adjacent the radially inner end of the side plate 317. The surface 333 is formed at the junction of the radially 349a and axially 349b extending portions of the friction washer 349 facing the surface 332 on the bearing ring 336. A number of drive lugs 333a project from the surface 333 for engagement with corresponding grooves 332a in the surface 332. This ensures that the friction washer 349 rotates with the bearing ring 336 which in turn is constrained to rotate with the hub 312 as described above. The arrangement is such that relative rotational movement between the hub 312 and the side plate 317 results in relative movement between the radially extending portion 349a of the friction washer 349 and the side plate 317 to generate a friction damping force. It will be noted that the spring washer 351 acts between the intermediate plate 343 and the radially extending portion 349a of the friction washer 349 and so does not produce an axial loading between the surfaces 332, 333.

Driven plate 310 has the advantage that by arranging the second surface 333 on the modified friction washer 249, it is possible for the pairs of opposed surfaces to be spaced further apart axially. This provides a greater degree of control over the tilting movement of the main driven plate assembly relative to the hub.

It should be understood that the invention is not limited to application in driven plates, according to the preferred embodiments but can be applied to any driven plate of the type described. In particular whilst the preferred embodiments relate to driven plates having torsional dampers. the invention can equally be applied to so called rigid driven plates in which no torsional damper is provided or to driven plates of the type described which have only an idle damper for isolating the drive line from low level vibrations Furthermore, whilst the invention is particularly useful and has been described in relation to friction clutches for use in motor vehicles, it is not limited to such applications and can be applied to driven plates of the type described for use in clutches for any application in which the ability to compensate for angular misalignment between the axes of an input member to the clutch and an output member is useful.