Title of Invention

"A FRICTION DISC FOR A FRICTION CLUTCH"

Abstract

A friction disc for a friction clutch, comprising two parallel metallic supports, each having an outer peripheral portion, disposed radially towards the outside and being of generally angular form extended radially towards the centre by fastening zones for fastening to a main member of the friction clutch, the fastening zones having at least one hole, each for the passage of a fastening member for fastening to the said main member, two friction liners disposed on either side of the two supports, each friction liner being adhesively bonded, moulded in place, or seamed, on one of the supports, and a progressivity element of elastic material, constituting a spring, being interposed between the two supports, characterized in that each fastening zone consists of a lug which is perforated for the passage of at least one fastening member and in that, radially outside each fastening lug and facing the latter, the supports have slots which are oriented generally circumferentially.

Full Text

A PROGRESSIVELY ENGAGED CLUTCH FRICTION WHEEL FOR A FRICTION CLUTCH, ESPECIALLY FOR MOTOR VEHICLES The present invention relates to a clutch friction wheel for a friction clutch, comprising: two parallel metallic supports, each having an outer peripheral portion disposed radially towards the outside and being of fiat annular form, extended radially towards the centre by fastening zones for fastening the support to a main member of the friction clutch; two friction liners disposed on either s de of the two supports, each friction liner being adhesively bonded, moulded or seamed on one of the supports; and a progressive engagement element of resilient material constituting a spring and interposed between the two supports. A clutch friction wheel, or friction disc, of this kind is described for example in French patent specification No. FR 2 673 984A. This arrangement reduces the inertia of the friction clutch, because to the way in which the friction liners are fastened, which enables the thickness of the liners to be reduced while giving good progressive action during the operation of engaging the clutch, in which the friction liners are progressively more firmly gripped between the pressure plate and reaction plate of the clutch that incorporates within it the clutch friction wheel. In addition, the supports can be of small thickness because each one of them transmits only one half of the power torque. However, because the fastening zones are provided with at least one hole, through which a fastening member is passed for fastening the clutch friction wheel to the main member of the friction clutch, a problem arises due to the fact that the fastening of the clutch friction wheel on one of the main members of the friction clutch applies stresses at this level, which cause local squeezing of the progressive engagement element. As a result, there is a difference in stiffness between the inner and outer peripheries of the progressive engagement element. This difference in stiffness disturbs the friction and wear properties of the friction liners. An object of the present invention is to overcome these drawbacks in a simple and inexpensive way. According to the invention, there is provided a clutch friction wheel for a friction clutch, comprising: two parallel metallic supports, each having an outer peripheral portion disposed radially towards the outside and being of flat annular form, extended radially towards the centre by fastening zones for fastening the support to a main member of the friction clutch; two friction liners disposed on either side of the two supports, each friction liner being adhesively bonded, moulded or seamed on one of the supports; and a progressive engagement element of resilient material constituting a spring and interposed between the two supports, wherein the fastening zones are defined by at least one hole for passage through it of a fastening member for fastening the clutch friction wheel to the said main member, and wherein each support has a plurality of generally circumferential slots, there being one said circumferential slot disposed radially outwardly of, and in register with, the corresponding said fastening zone. The invention separates the functions of fastening and progressive engagement of the clutch. This separation is furthermore obtained in a simple and inexpensive way, with the aid of the circumferential slots, which may be oblong and are formed by simple stamping out where the supports are of metal, or by moulding where the supports are of composite materials, that is to say materials based on synthetic constituents, which may for example be reinforced with fibres such as glass fibres. The progressive engagement element of the clutch friction wheel is accordingly not flanged. The length of the circumferential slots depends on this torque to be transmitted, i.e. the driving torque transmitted from the engine of the vehicle. Accordingly, it therefore also depends on the quality of the material present between the fastening zones and these slots. This length has regard to the homogeneity present in the distribution of the axial pressure, and is therefore a compromise between these various parameters. The circumferential slots preferably extend at right angles to the fastening zones, which are preferably separated from each other. However, in another version the fastening zones may be joined together by the material of the support. Preferably, one of these slots is provided for each fastening zone, so as to obtain better homogeneity in the gripping action, and therefore the squeezing action, on the progressive engagement element. Each support is preferably crenellated at its inner periphery so as to define a set of fastening zones, which may for example be in the form of circumferentially elongated lugs. This arrangement further improves the separation between the functions of fastening and progressive engagement of the clutch, due to the fact that the fastening zones are discontinuous. Preferably, each circumferential slot, extending generally at right angles to a corresponding said fastening zone, wholly ot partly covers the latter, i.e. it has a circumferential extent such that the slot lies wholly or partly between the fastening zone and the outer periphery of the support. Preferably also, further slots, open at the outer periphery of the metallic supports are provided in each support. The object of this is to provide radially flexible blades as an integral part of the support, which can deform in sympathy with the friction liners under the influence of heat. This helps to avoid deformation into a conical form. It also enables the supports to be lightened in weight, and thermal stresses to be reduced. It also prevents the occurrence of differential expansion effects due to heating of the clutch friction wheel in service, the friction liners of the friction wheel being adapted to be gripped between the pressure and reaction plates of the clutch. The differential expansion effect is due to the fact that the friction liners have a different coefficient of expansion from the supports. The said further slots may be separate from the circumferential slots, or they may be open at their inner ends into the latter, in a symmetrical or asymmetrical way. In that case, the further slots may be open into one end of the associated circumferential slot. Preferably, a said further slot is joined to an associated circumferential slot through a curved junction portion having as large a radius as possible, so as to reduce stresses at that point. The said further slots are preferably arranged to define asymmetrical blades on the support, in particular so as to transmit a greater torque in one direction than in the other, and to give the blades enhanced flexibility. For this purpose, in some embodiments of the invention, the said further slots are inclined with respect to a radial direction. By suitable choice of the angle of inclination of the further slots with respect to a radial direction, mechanical resistance to the effects of centrifugal force on the blades bounded by the further slots can be optimised, by arranging for the masses pulling on the blades to be made symmetrical, while having asymmetrical blades so as to optimise their strength under torque. The angle of inclination of the further slots may be either positive or negative. The further slots may, in other embodiments, be orientated radially so as to give the best possible resistance to the effects of centrifugal force. It should be noted that a said further slot is not necessarily associated with every circumferential slot. Press-formed portions of the support, for example in the form of beads, may join two circumferential slots together: the effect of this is to produce even better separation of the fastening and progressive engagement functions. Further features and advantages of the invention will appear more clearly from the following description of some preferred embodiments of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of a clutch friction wheel according to the invention, for a motor vehicle friction clutch; Figure 2 is a simplified view in cross section showing part of a friction clutch without its clutch friction wheel, in a first versior; Figure 3 is a view similar to Figure 2 but showing a second version; Figure 4 is a view in axial cross section showing part of a clutch friction wheel mounted on a main part of the friction clutch, in another embodiment; Figure 5 is a view showing the clutch friction wheel of Figure 1 mounted on the main member of the friction clutch; and Figures 6 to 15 show various different forms of slots formed in the supports. The clutch friction wheel, or friction disc, 10 shown in Figure 1 is the input element of the friction clutch working with dry friction, and is coupled elastically or rigidly to an output element, such as an internally splined hub, of the friction clutch for coupling this output element in rotation to a driven shaft. In the context of application to a motor vehicle, the driven shaft consists of the input shaft of a transmission, for example the input shaft of the gearbox. When the clutch is engaged, with the friction wheel 10 gripped between the pressure plate and reaction plate (not shown) of the clutch, the torque is transmitted from a driving shaft, namely the crankshaft of the engine of the vehicle in this application, to the gearbox input shaft via the clutch friction wheel 10. The friction wheel 10 comprises, in the embodiment shown, an assembly of annular and coaxial members with an axial axis of symmetry XX, namely: two friction liners 11 which ;ire disposed on either side of two parallel metallic supports 12, which are themselves disposed on either side of at least one progressive engagement element 13, which is of elastic material constituting a spring. Each support 12 in this example is of flat form, and accordingly has an outer face 14 adjacent to one friction liner 11, and an inner face 15 adjacent to the progressive engagement element 13. The inner faces 15 face towards each other. Each support 12 is made by a stamping process from thin metal plate. In another version, each support 12 is of a suitable composite material. The supports are of relatively low thickness because they only transmit one half of the driving torque to the output element of the friction clutch. The thickness of these supports therefore depends on the torque to be transmitted. In the present example the friction liners 11 are in the form of endless annular rings. They are fixed on flat outer faces 14 of the supports 12 by rivetless fastening, in particular in order to reduce, in a known way, the inertia of the friction clutch. In addition, there is a wider choice of the nature of the friction material of the friction liners, because this is not determined by mechanical strength requirements arising from the provision of rivets. The friction liners are identical here. In another version, the friction liners 11 may be different from each other, however; for example, they may be of different materials having different coefficients of friction. In the present example, each friction liner 11 is secured by adherence, for example by adhesive bonding, brazing or moulding on an annular portion, in facing relationship with it, of the outer face 14 of the corresponding support 12. In another version, however, each friction liner 11 is secured by clipping to the corresponding support 12, in a manner described in German published patent specification DE 96 26 688A. Each support 12 then has, for example, two sets of lugs which are bent back into two sets of notches, which are formed in a complementary way in each friction liner 11. For example, the two sets of notches may be formed in the inner periphery and the outer periphery of each friction liner 11. In a further version, the liners 11 are divided into annular sectors. The front faces of the friction liners 11 that face away from the supports 12 are arranged to be gripped between the pressure plate and the reaction plate of the clutch. The friction liners 11 therefore become heated in use when the vehicle is travelling, following successive operations of engaging and disengaging the; clutch. As is well known, the same is true for the pressure and reaction plates. The pressure and reaction plates can reach quite high temperatures, and tend to assume a conical shape because of the temperature gradients produced, with one face of the plates being colder than the Other. As a result, a residual conical profile may be produced, especially in the pressure plate. In the same way, the friction liners 11 and the supports 12 may be caused by heating to assume a conical shape. In addition, the friction liners 11 have a coefficient of expansion which is different from that of the support 12, these being then subjected to thermial stresses. In the present example, each support 12 has a set of further slots 16, which will be described later herein. These slots 16 the open at the outer periphery of the support 12, In general terms, the slots 16 prevent the occurrence of deformations due to heating in use, and reduce stresses. The slots 16 enable the weight of the supports 12 to be reduced and their flexibility to be increased. Each support 12 comprises an outer peripheral portion 17 disposed radially towards the outside and having a continuous, flat, annular general form. It is in this peripheral portion 17 that the slots 16 are formed. The corresponding friction liner 11 is secured on the peripheral portion 17, which is extended radially inwards by a set of fastening zones 18 which are spaced apart circumferentially at regular intervals. These fastening zones 18 are elongated circumferentially and this example they consist of lugs. The lugs 18 are generally trapezoidal in shape, and have holes 19 through which one or more fastening members 20 extend. In this example, each lug 18 has two holes 19. The circumferential length of each lug is greater than its radial depth. By virtue of the lugs 18, the supports 12 are crenellated at their inner' periphery. In another version, each lug 18 may have only one hole 19, and its radial depth is then made greater than its circumferential length. In a further version, the fastening zones 18 are joined together and are part of a continuous annular portion, with each zone 18 being defined by the hole or holes 19. In the present example, the fastening zones are in the same plane as the peripheral portion 17 of the support. The progressive engagement element 13 consists in this example of an endless ring of resiliency deformable material, which is interposed between the inner faces 1 5 of the supports 1 2 (facing towards each other) in their flat peripheral zones 17, and in line with the coaxial annular friction liners 11. In this case the resilient material of the progressive engagement element 13 is a material such as an elastomer or rubber. The element 13 contributes to the comfort of the user of the vehicle, and enables progressive transmission of the torque to be obtained during re-engagement of the clutch. It has the advantage that it enables the friction liners 11 to follow intimately the form of the pressure and reaction plates, especially during engagement of the clutch, and consequently leads to a reduction in wear. It will be noted that the low thickness of the supports 12 assists this. The ring 13 may include expansion agents and may be for example of a material based on expanded silicone. It may be made of a cellular material having open and/or closed pores, which cause the thickness of the material to be reduced under the effect of compression stresses. When these stresses cease, the pores expand so that the ring 13 reverts to its original thickness. The ring may be formed from materials in the group comprising elastomeric foams, in the manner described in French published patent specification FR 2 673 984A, to Which reference may be made for more detail. In the present example, the progressive engagement ring has an overall radius which is identical to that of the friction liners. In another version, the ring 13 may be replaced by a plurality of projections, in the manner described in United States patent specification No. 5,070,409 and French published patent specification No. FR 2 652 397A, to which, again, reference may be made for more detail. The ring 13 may of course be in the form of a strip which is spiral-wound on the peripheral portions 17 of the supports 12, or adhesive strips which are arranged in concentric circles and fastened on the peripheral portions 17. The ring 13, or the resilient projections mentioned above, of, for example, elastomer or rubber, are secured adhesively, for example by adhesive bonding or In situ vulcanisation, to the inner faces 15 of the supports 12. In the case of the projections mentioned above, some of these projections may of course be fastened to only one of the two supports 12, in the manner described in United States patent specification No. 5,076,409 and French patent specification FR 2 652 397A. In all cases, the progressive engagement element" (such as the ring 13) is interposed between the peripheral portions 17 of the two supports 12, and is secured to at least one of the two supports 12. In another version, the ring 13 is mounted in a floating manner between the two supports 12, without being fixed to the latter. In this example, there are six slots 16 and six fastening zones 18 in each support 12. Each fastening zone 18 has two holes 19 for the passage of the fastening members 20, which in this example are in the form of rivets. These numbers do of course depend on the particular application. In order to maintain the two supports 12 parallel to each other, especially under load, spacers 22 are interposed between the two fastening zones 18, in facing relationship with each other, of the two supports 12. The spacers 22 have a form similar to the fastening zones 18. In the present example, the spacers 22 are accordingly elongated in the circumferential direction, having a circumferential dimension greater than their radial depth. Each of these spacers has two holes 23 in axial alignment with the holes 19 in the fastening zones, so as to enable the fastening rivets to pass through them, In another version, the fastening members 20 may be in the form of pins or screws. The spacers 22 are arranged to be interposed between the mutually facing inner faces of the fastening zones 18, to which they are secured. The supports 12 are therefore able to be flat. In this example, the supports 12 are identical to each other, and the friction disc 10 constitutes a pre-formed unitary sub-assembly without the spacers 22. For the construction of these unitary sub-assemblies, reference should be made for example to French patent specification No. FR 2 673 984A, and more particularly to Figure 3 of the latter, which shows the mould used. The progressive engagement element 13, in the form of a ring, is accordingly fixed on the outer peripheral portion 17 of each support ring 12. This sub-assembly can be fitted on the spacers 22 by means of a bayonet-type fitting in the manner described in French patent specification No. FR 2 737 267A, due to the fact that the fastening zones 18 are arranged alternately with recesses defined naturally between two fastening zones 18. Reference is now made to Figures 2 to 4. As can be seen in these Figures, the spacers 22 may be part of a disc 150 which is fastened flat to one of the guide rings 51 of the friction clutch (as in Figure 2), or to the guide ring 51 of the clutch as shown in Figure 4, or to the damper plate 50 of the clutch as shown in Figure 3. In this case, the spacers are integral with a main part of the friction clutch. In general terms, a conventional friction clutch comprises two guide rings 51 and 52, arranged on either side of a damper plate 50. The damper plate 50 and the guide rings 51 and 52 surround a hub 1 which constitutes the output element of the dry friction clutch. The damper plate 50 is coupled to the guide rings 51 and 52 through interposed circumferentially acting resilient means 2, which typically consist of coil springs and which are mounted in seatings formed in facing relationship in the guide rings 51 and 52 and in the damper plate 50. The seatings 3 may consist of press-formed portions as in Figure 2, or windows as in Figure 3, formed in the guide rings 51 and 52, together with windows (Figures 2 and 3). Alternatively they may consist of outwardly open slots formed in the damper 50. In Figures 2 and 4, the guide rings 51 and 52 are fixed to the clutch friction wheel 10 and freely surround the hub 1, while the damper plate 50 is arranged to be locked up to the hub 1 for rotation with the latter, possibly after a circumferential clearance, determined by loose coupling means interposed between the damper plate 50 and the hub 1, has been taken up. In Figure 3, the structures are reversed and the guide rings 51 and 52 are fixed to the hub 1, while the damper plate 50 freely surrounds the hub 1 and Is fixed to the friction disc 10. In Figure 4, spacers in the form of spacer bars 40 join the guide rings 51 and 52 together, and extend, with a circumferential clearance, through the damper plate 50. In a known way, this enables the relative angular displacement between the damper plate 50 and the guide rings 51 and 52 to be limited. In this case, the spacer bars 40 are also used for securing the clutch friction wheel 10. However, in another version (as described in French patent specification No. FR 2 411 991 A), the spacers consist of an axially oriented annular radial flange 140 (see Figure 2) formed at the outer periphery of the guide ring 51. This flange 140 has mortices in which tenons of the other guide ring 52 are arranged to be engaged. Assembly is obtained by seaming in the region of the edges of the mortices, leading to plastic flow of the material so as to upset the latter over the tenons. In another version, welding operations can be performed. All the variations in the above mentioned French patent specification may be employed. The disc 150, which may for example be in the of a crown crenellated at its outer periphery, is applied flat to the guide ring, and is then fixed to it. Because of its particular form, spacers are thus defined at the outer periphery of the element 1 50. The damper plate 50 of Figure 3 and the guide ring 51 of Figure 4 are of crenellated form at their outer periphery, the spacers being formed integrally with these components. In another version, the spacers are in the form of individual lugs complementary to the fastening lugs, and are applied on the guide ring 51 of Figure 2 or on the damper plate 50 of Figure 3. In all cases, the spacers have a form complementary to that of the fastening lugs 18, and the friction disc 10 is fixed by means of zones 18 to a main member of the friction clutch. Assembly is achieved quite simply, by (for example) ntroducing the fastening lugs 18 into the recesses defined by the spacers or vice versa, after which rotation is carried out so as to bring the holes 19 in the lugs 18 into alignment with the holes 23 in the spacers. The supports 12 are then fastened on the spacers using the fastening members 20. In the embodiment shown in Figure 1, individual spacers 22 are inserted in advance between the fastening lugs 18, after which the assembly consisting of the friction disc 10 and the individual spacers 22 is fastened on the guide ring 51 of Figure 2 by means of the rivets 20, so as to form an assembly consisting of the guiding 51 and the friction disc 10, as can be seen in Figure 5. This assembly can be handled and transported readily, and is of reduced inertia because of the individual spacers 22. When fastening is carried out in this way, stresses are set up in the region of the fastening zones 18 in all cases. These stresses act at the inner periphery of the progressive engagement element 13, thus squeezing the element 13 and increasing the stiffness of the latter. This results in a reduction in the performance of the progressive engagement element and friction liners 11, especially as regards wear. In order to overcome these disadvantages, each support 12 is formed with generally circumferentially orientated slots 30 radially outside the fastening zones 18, and therefore radially outside the holes 19, as can be seen in Figure 1. These slots 30 are oblong in form and are formed in the outer peripheral portions 17 of the supports 12, being radially in register with the corresponding fastening zones 18, In the embodiment shown in Figure 1, one of these slots 30 is provided for each fastening zone 18, which gives good separation between the functions of fastening and progressive engagement. In another version, some of the fastening zones 18 may be without the slots 30. The length of each circumferential slot 30 depends on the application, and in practice it will be a compromise between the mechanical strength required for transmitting the driving torque and the degree of homogeneity required in the axial pressure distribution. It will be appreciated that the set of fastening zones 18, here spaced apart in circumferentially regular intervals, plays a part in the separation of the two functions of fastening aid progressive engagement which are obtained by virtue of the circumferential slots 30. It is therefore of advantage for the supports 12 to be crenellated at their inner periphery. In Figure 4, one circumferential slot 30 is associated with each spacer. This slot can be seen in Figure 13, and it has a circumferential length L which is greater than the circumferential length L-, of the fastening zone 18, measured across its junction zone with the outer peripheral portion 17 of the support 12. In another version, the length L is less than the length L1. The relationship between these dimensions again depends on the application. The length L of the slot 30 is preferably greater than, or equal to, the circumferential length that separates the endmost holes 19 in the zones 18. Where only a single hole 19 is provided to each fastening zone, the corresponding circumferential slot 30 extends on either side of that hole. In this example, at right angles to (and therefore radially in register with) each fastening zone 18, there is therefore one generally circumferentially orientated slot 30 which wholly or partly covers the fastening zone 18. The slots 30 are preferably located radially inwardly of the friction liners 11 and the progressive engagement element 13, the outer peripheral portion 17 of the support 12 having a radial depth which is greater than that of the friction liners 11 and the progressive engagement element 13. This enables very good separation to be obtained between the fastening and progressive engagement functions, and is also favorable as regards ventilation of the clutch friction wheel 10. In Figure 4 the peripheral portions 17 of the supports 12 are endless outside the slots 30. In other versions, as shown in Figures 1 and 5 to 12, Figure 14 and Figure 15, the slots referred to herein as "further slots" in the supports 12 are slots 16, 116, 216 which are open at the outer periphery of the supports 12. These slots 13, 116, 216 are open in the circumferential slots 30 at their inner ends. The slots 16, 116, 216 inhibit the conical deformations described earlier herein. They also increase the flexibility of the supports 12 and reduce the weight of the latter. In general terms, the conical deformations are limited by these slots in combination with the circumferential slots 30, which enable air to flow radially inwardly of the friction liners 11 and progressive engagement element 13. In general, thermal stresses and heating effects are avoided due to the slots 16, 116, 216 in combination with the circumferential slots 30. The above mentioned further slots may be inclined by an angle 6 with respect to a radial direction (see for example the slots 16 in Figures 1, 6, 14 and 15). Alternatively they may be inclined in the other direction by an angle 0, as with the slots 116 in Figure 7; or indeed they may be orientated radially as are the slots 216 in Figures 8 to 12. In this way, the supports 12 can be optimised by varying the angles 0 and 9' in Figures 1, 6, 7, 14 and 15 according to the particular application. This angle may be either positive or negative. In Figures 6, 7, 8, 11, 14 and 1 5 the further slots 16, 116, 216 are open at one end of a slot 30. By contrast, in Figures 9 and 12 the slots 216 are open symmetrically in the middle of a circumferential slot 30. In Figure 10, the slot 216 terminates non-symmetrically in a slot 30, at an intermediate point along the latter. In Figures 11 and 15, the end of the slot 30 remote from the slot 16, i.e=. its blind end, is enlarged. It will of course be understood that a further slot 16, 116 or 216 is not necessarily associated with each one of the slots 30. For example, a circumferential slot 30 which is not associated with such a further slot may be flanked by two other slots 30 having such further slots. In another version, the further slots may be arranged so that they do not terminate in a circumferential slot 30. It will be noted that in Figure 12, the circumferential length L4 of the slot 30 is generally equal to the circumferential length L3 of a fastening zone 18, and that the circumferential length L2 separating two slots 30 is shorter than the lengths L4 and L3. The length L2 is a function of the torque to be transmitted. It will also be noted that the slots in Figures 1, 6, 14 and 15 are favourable to the transmission of the torque in a preferred direction corresponding to the direct sense of torque transmission, i.e. the sense in which the torque is transmitted from the crankshaft to the gearbox input shaft. According to the direction of rotation of the engine, thanks to the inclination of the so-called further slots joined to one end of a circumferential slot 30 (preferably through a rounded portion), a larger torque can be transmitted in one direction. This effect can be obtained by suitable choice of the angle 9 which enables the material to be increased. With reference to Figure 15, it is important that the inclined slot 16 should be joined through a rounded portion, having a radius R17, to the slot 30 so as to reduce local stresses. The groater the radius R17, the more these stresses are reduced. Similarly, the radially oriented side edges 118 of the fastening zones 18 in Figure 15 are joined to the inner periphery of the peripheral portion 17 of the support 12 through rounded portions of radius R15, in order to reduce stresses. Similar rounded edge portions, for reducing local stresses, can be seen in the other Figures. The inclination of the slot 16 is preferably such as to balance out centrifugal forces. Thus, in Figure 15, an inclined first slot 16 defines, with the radii R1 and R2 passing through the ends of a slot 30, two zones of area S1 and S2, with their centres of gravity at g1 and g2 respectively. If R1 and R2 are the radii of the centres of gravity g1 and g2 respectively (0 being the centre of the support 12), having the relationship S1.R1 = S2.R2, the applied forces due to centrifugal force are balanced out. It is of course necessary to take into consideration the zones S1 and S2 in any on>3 blade of the support 12 defined by two slots 16. In this way the masses that pull on the blades are made symmetrical. The invention enables the clutch friction wheel 10 to work under favorable conditions in a simple and inexpensive way, the circumferential slots 30 and the further slots 16, 116, 216 being obtained by stamping out or moulding of the flat supports 12. Figure 14 shows another version in which each circumferential slot 30 is separated from another slot 30 by a press-formed bead 200 which improves control of the progressive engagement action. The beads 200 therefore join adjacent slots 30 together. It will of course be understood that the present invention is not limited to the embodiments described above. In particular, the supports 12 may have the same form as those shown in Figure 2 of French patent specification No. FR 2 673 984A. More precisely, at least one of the supports 12 may include a tola or pleat, through which it joins the other support so as to be applied and fixed to that other support. Each of the two supports may include a fold whereby they are joined together so that they can be fastened together by means of the above mentioned fastening members 20 or 40. It is then not essential to provide spacers such as the spacers 22. The progressive engagement ring 13 in Figure 1 may have a radial dimension which is different from that of the frictior liner 11. For example, the ring 13 may overlap the inner periphery of the friction liners 11. The ring 13 may have a radial dimension which is smaller than that of the friction liners 11, so as to be thus slightly withdrawn with respect to the inner periphery of the friction liners 11, that is to say the internal diameter of the friction liners 11 may be slightly smaller than the internal diameter of the ring 13. This economises material, and enables the stiffness of the ring 13 to be reduced. The circumferential slots 30 may straddle the ring 1 3 or the projections entioned earlier herein which constitute the progressive engagement element. The individual spacers of Figure 1 may be joined together at their inner periphery so as to constitute a one-piece crenellated annular ring. In that case, this ring is inserted between the two supports 12, before the progressive engagement element is fixed or at least one of the supports. With this arrangement, the spacer may be endless. The progressive engagement ring 13 may have slots identical to, and orientated in line with, the so-called further slots in the supports. WE CLAIM: 1. A clutch friction wheel for a friction clutch, comprising: two parallel metallic supports, each having an outer peripheral portion disposed radially towards the outside and being of flat annular form, extended radially towards the centre by fastening zones for fastening the support to a main member of the friction clutch: two friction liners disposed on either side of the two supports, each friction liner being adhesively bonded, moulded or seamed on one of the supports; and a progressive engagement element of resilient material constituting a spring and interposed between the two supports, wherein the fastening zones are defined by at least one hole for passage through it of a fastening member for fastening the clutch friction wheel to the said main member, and wherein each support has a plurality of generally circumferential slots, there being one said circumferential slot disposed radially outwardly of, and in register with, the corresponding said fastening zone. 2. A clutch friction wheel according to Claim 1, wherein each circumferential slot wholly or partly covers a corresponding said fastening zone and extends generally at right angles to the latter. 3. A clutch friction wheel according to Claim Z, Wherein the circumferential slots are joined together by press-formed elements. 4. A clutch friction wheel according to Claim 2, wherein each said support has a plurality of further slots open at the outer periphery of the support. 5. A clutch friction wheel according to Claim 4, wherein the said further slots are distinct from the circumferential slots. 6. A clutch friction wheel according to Claim 4, wherein the further slots are open into the circumferential slots. 7. A clutch friction wheel according to Claim 6, wherein one said further slot is associated with each said circumferential slot. 8. A clutch friction wheel according to Claim 7, wherein a said further slot is joined by a radius to the end of a circumferential slot, the further slot being inclined with respect to a radial direction. 9. A clutch friction wheel according to Claim 2 wherein each said support is crenellated at its inner periphery so as to define a set of said fastening zones. 10. A clutch friction wheel according to Claim 9, wherein there is associated with each said fastening zone a spacer of complementary form, the said supports being flat and each said spacer being interposed between two mutually facing said fastening zones. 11. A clutch friction wheel according to Claim 2, wherein the progressive engagement element is fastened to at least one of the two said supports. 12. A clutch friction wheel for a friction clutch substantially as herein described with reference to the accompanying drawings.

Documents:

1468-del1998-abstract.pdf

1468-del1998-claims.pdf

1468-del1998-correspondence-others.pdf

1468-del1998-correspondence-po.pdf

1468-del1998-description (complete).pdf

1468-del1998-drawings.pdf

1468-del1998-form-1.pdf

1468-del1998-form-13.pdf

1468-del1998-form-19.pdf

1468-del1998-form-2.pdf

1468-del1998-form-3.pdf

1468-del1998-form-4.pdf

1468-del1998-form-6.pdf

1468-del1998-gpa.pdf

1468-del1998-petition-137.pdf