GB2098287A

GB2098287A - Clutch assembly

Info

Publication number: GB2098287A
Application number: GB8212662A
Authority: GB
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1981-05-09
Filing date: 1982-04-30
Publication date: 1982-11-17
Also published as: DE3118385A1; FR2505426A1; BR8202666A

Abstract

In a clutch assembly comprising a driving disc (5), a clutch housing (3), a pressure plate (2), a clutch disc (12) and a diaphragm spring (1) the latter engages a fulcrum (3b) only on the side thereof which is remote from the pressure plate. The spring characteristics of the diaphragm spring and an opposing pressure plate biasing means (7) are such that the diaphragm spring is held in contact with the fulcrum when the diaphragm spring is deflected into a clutch disengaged position. The biasing means may be coil, disc or leaf springs. <IMAGE>

Description

SPECIFICATION Clutch assembly The present invention is directed to a clutch assembly. The clutch assembly comprises a driving disc having an axis and a driving disc engagement face. A clutch housing is fixed with respect to said driving disc and has a fulcrum carrier portion axially opposite to and spaced from the driving disc engagement face. A pressure plate is located axially between the driving disc and the fulcrum carrier portion. The pressure plate is axially movable with respect to the driving disc and the fulcrum carrier portion. Moreover the pressure plate is connected to the driving disc for common rotation therewith. A pressure plate engagement face is provided on the pressure plate opposite to the driving disc engagement face. A clutch disc unit is provided for transmitting a torque from the driving plate to an output member of the clutch assembly or vice versa.This clutch disc unit comprises a clutch disc having axially opposed clutch disc engagement faces for engagement with the driving disc engagement face and the pressure plate engagement face respectively. A diaphragm spring is located axially between the pressure plate and the fulcrum carrier portion of the clutch housing. This diaphragm spring has a radially outer portion, a radially intermediate portion, and a radially inner portion.

The radially outer portion is to engage the pressure plate. The radially intermediate portion is tiltably mounted on the fulcrum carrier portion by fulcrum means which are substantially circular about the axis of the clutch assembly. The radially inner portion is axially movable along a path of axial movement parallel to the axis of the clutch assembly from a clutch engagement position to a clutch disengagement position nearer to the driving disc. An axially directed resilient force resulting from the diaphragm spring resists to the axial movement of the radially inner portion from the clutch engagement position to the clutch disengagement position. The diaphragm spring is tilted on axial movement of the radially inner portion about the fulcrum means.The radially outer portion is axially movable in response to the axial movement of the radially inner portion along a path of axial movement parallel to said axis from a clutch engagement position in which the pressure plate is urged towards the driving disc to a clutch disengagement position respectively which is more remote from the driving disc.

Pressure plate biasing means are supported by the driving disc or the clutch housing or a member connected thereto and bias the pressure plate towards engagement with the radially outer portion of the diaphragm spring.

A clutch assembly of this type is known from German Offenlegungsschrift 27 58 733. In this known clutch assembly tangential leaf springs are provided which connect the pressure plate to the driving disc and the clutch housing for common rotation therewith. These tangential leaf springs exert an axially directed biasing force onto the pressure plate so as to hold the pressure plate in engagement with the radially outer portion of the diaphragm spring. So the pressure plate continuously follows the axial movement of the radially outer portion of the diaphragm spring. The fulcrum means provided on the fulcrum carrier portion are of such design as to contact the diaphragm spring on both axially directed sides thereof.These fulcrum means are therefore rather complicated in design and comprise not only a circumferential rib of the fulcrum carrier portion engaging the side of the diaphragm spring which is remote from the pressure plate but also a plurality of retaining members connected to the fulcrum carrier portion passing through the diaphragm spring and engaging the diaphragm spring on the side thereof facing the pressure plate.

It is a primary object of this invention to obtain a clutch assembly of the type discussed above which is of less complicated design and which is less expensive in production. A further object of this invention is to obtain a clutch assembly of improved function.

In view of these objects, the fulcrum means according to this invention are of such design as to contact the diaphragm spring only on the side thereof which is remote from the pressure plate.

Moreover the spring characteristics of the diaphragm spring and the pressure plate biasing means are such that the radially intermediate portion of the diaphragm spring is held in contact with the fulcrum means when the radially inner portion of the diaphragm spring is in its clutch disengagement position. So the fulcrum means become far less complicated. It should be considered that with the known type of a clutch assembly considerable care was necessary to locate the diaphragm spring between opposed fulcrum members. This the more as it was necessary to avoid lost motion of the diaphragm spring between the opposed fulcrum means.

Furthermore, it was necessary to bear the diaphragm spring between the opposed fulcrum means such as to avoid wear during the lifetime of the clutch in order to secure perfect function.

Various designs of such fulcrum means are known e.g. from German Patent 17 75 116, German Auslegeschrift 20 29 334, and German Auslegeschrift 21 32 730.

According to a further aspect of this invention, the spring characteristics of the diaphragm spring and the pressure plate biasing means are such that the diaphragm spring is held in contact with the fulcrum means during a part of the path of axial movement of said radially inner portion adjacent the clutch disengagement position of the radially inner portion. Preferably, the diaphragm spring is held in contact with the fulcrum means along the total path of axial movement of the radially inner portion of the diaphragm spring between the clutch engagement position and the clutch disengagement position thereof.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

In the drawings FIG. 1 shows in diagrammatic way a section along the axis of a clutch assembly of the prior art similar to the type of the clutch assembly as shown in German Patent 27 58 733 in the engaged condition; FIG. 2 shows a section similar to the section of Fig. 1 in the disengaged condition; FIG. 3 shows in a diagrammatic way a section along the axis of a clutch assembly of this invention in the engaged condition; FIG. 4 shows in a corresponding section the clutch assembly of Fig. 3 in the disengaged condition; FIG. 5 shows in more detail a clutch assembly of this invention in a section along the axis with a first type of pressure plate biasing means; FIG. 6 shows a side view according to arrow A of Fig. 5, partly in section; FIG. 7 shows in a section similar to that of Fig. 5 a clutch assembly of this invention with a further type of pressure plate biasing means;; FIG. 8 shows in a side view similar to that of Fig. 6 a clutch assembly of this invention with a third type of pressure plate biasing means; FIG. 9 shows in a view similar to that of Fig. 6 a clutch assembly of this invention with a fourth type of pressure plate biasing means; and FIG. 10 shows a plot indicating the variation of the resilient force P of the clutch spring resisting to axial movement of the radially inner portion of the diaphragm spring and of the biasing force F of the pressure plate biasing means in dependency on the axial position of the radially outer portion of the diaphragm spring.

Figures 1 and 2 each show the upper half of the longitudinal section through a diaphragm spring clutch according to the prior art. In Fig. 1 , the diaphragm spring clutch is represented in the engaged condition. The clutch housing 3 is firmly connected with a driving disc or a flywheel 5 and surrounds the clutch disc 12 with its friction linings 6, the pressure plate 2 and the diaphragm spring 1. The clutch disc 12 is connected for common rotation with a drive-output shaft 13.

The driving disc 5 is likewise connected for common rotation with the crank shaft 14. The diaphragm spring 1 is prestressed so that it has the tendency to become still more conical when the clutch is disassembled. The radially outer portion of the diaphragm spring having the diameter D bears on the pressure plate 2; the radially intermediate portion of the diaphragm spring having the diameter d is supported on a circumferential corrugation 36 of the housing 3. In this way two oppositely directed forces A and B act upon the diaphragm spring 1 ,the two forces being of equal magnitude but opposite directions.

Furthermore, return springs 7 defining pressure plate biasing means are distributed on the circumference of the clutch assembly; these return springs are supported by one end on the driving disc and by the other end on the pressure plate 2 and exert a biasing force F upon the pressure plate 2. Moreover upon the pressure plate 2 there is also exerted the force C which represents the force clamping in the friction linings 6 between the driving disc 5 and the pressure plate 2. The diaphragm spring 1 also has radially inwardly directed spring tongues 4 defining a radially inner portion of the diaphragm spring, upon which spring tongues 4 a release mechanism (R) acts. In the engaged condition according to Fig. 1 no force is applied by the release mechanism to the spring tongues 4.For better understanding let the order of magnitude of the forces occurring here be stated: Let the two forces A and B be assumed as 3,800 N; all the return springs 7 together have a force of 300 N and the pressure application force C amounts to 3,500 N. Thus the two support forces A and B are oppositely directed and of equal magnitude; the pressure application force between pressure plate 2 and driving disc 5 is less by the magnitude of the force F of the return springs 7 than the force between diaphragm spring 1 and pressure plate 2 (3,800 N) so that the pressure application force C results at 3,500 N.

Figure 2 shows in a diagrammatic way a clutch according to Fig. 1 in the disengaged condition.

The clutch disc 12 with the friction linings 6 is in this case arranged completely freely between the pressure plate 2 and driving disc 5. The release mechanism (R) acts with the force P upon the radially inner ends of the spring tongues 4 of the diaphragm spring 1. Let this release force P be assumed as 1,250 N. During the build-up of this release force P the internal moment of the diaphragm spring 1 is diminished, at the same time the abutment force between the diaphragm spring 1 and the housing 3 in the diameter zone d is reduced and from equilibrium of moments onwards the diaphragm spring 1 changes its bearing point and now is supported on the opposite side on a wire ring 26 supported by retaining rivets 27. Now the supporting force B is effective in the opposite direction compared with Fig. 1, and in the present example has a value of 950 N. The supporting force A has remained in its direction, but now it possesses only the same value as the force F of the return springs 7, namely the value 300 N. Now an equilibrium of forces prevails in the disengaged condition too, in that the two forces A and B acting from one side upon the diaphragm spring 1 together amount in magnitude to the release force P, but are oppositely directed. Thus with this embodiment of diaphragm springs according to the prior art it is necessary to support the diaphragm spring 1 from both sides in the region of its circular fulcrum on the housing 3 at the diameter d.This double supporting not only requires a considerable number of individual parts, the arrangement of these individual parts in the clutch housing and in the diaphragm spring, and the expensive fitting, but also problems arise due to the fact that the diaphragm spring wears away in the region of this supporting, due to its tilting movement, so that lost motion occurs due to wear and is lost to the release travel.

In Figs. 3 and 4 the formation of the diaphragm spring clutch according to the invention is reproduced in an illustration of principle. The same conditions as in the prior art according to Figs. 1 and 2 are here assumed, that is to say the clutch has substantially the same dimensions and it has to supply the same pressure application force too for the friction linings of the clutch disc. As is immediately apparent, the diaphragm spring 1 bears only against the clutch housing 3; no further support elements of any kind are provided at the position of the diameter don the other side of the diaphragm spring. In the engaged condition the diaphragm spring 1 again bears on the pressure plate 2 at the diameter D and on the housing 3 at the diameter d.The forces A and B then acting upon the diaphragm spring 1 are likewise oppositely directed, of equal magnitudes, and made greater than in the prior art, at about 5,000 N. The total force F of the return springs 7 is also made significantly higher, namely in the present case 1,500 N. Since the force F of the return springs 7 is deducted from the pressure application force C, the latter results as 3,500 N, from the difference between the force A and the force F. This force is of the same size as according to the prior art. In the disengaged condition again the release force P of the magnitude of 1,250 N, supplied by the release device (not shown) acts upon the inner ends of the spring tongues 4.Due to this release force P the diaphragm spring 1 is tilted about the diameter don the housing 3, so that the clutch disc 1 2 with the friction linings 6 is liberated, since the internal moment of the diaphragm spring 1 has been diminished and the pressure plate 2 is held by the force F of the return springs 7 in constant abutment on the diaphragm spring 1. The force A here exerted by the pressure plate 2 upon the diaphragm spring 1 corresponds to the force F of the return springs 7, at the level of 1,500 N. As difference between the force A and the release force P an abutment force B at the level of 250 N results, with which the diaphragm spring 1 in the disengaged condition abuts constantly on the housing 3. Thus all support means on the left-hand side of the diaphragm spring can be omitted without replacement.In all operational conditions it is ensured that the diaphragm spring always bears, due to the forces acting upon it, upon the housing 3. In this connection it should be mentioned that according to Fig. 2 (prior art) the lever arm a is decisive for the overcoming of the internal moment of the diaphragm spring 1 by the release force P, while in the embodiment according to the invention, as shown in Fig. 4, the lever arm b is decisive which due to its correspondingly larger dimensions renders possible releasing of the diaphragm spring clutch by the same release force P even with the reinforced diaphragm spring present here, this release force P overcoming the internal moment of the diaphragm spring 1. The release travel relationships remain the same both in Figs. 1 and 2 and in Fig. 3 and 4, since the diaphragm spring 1 is tilted about the diameter din both cases.The free supporting of the diaphragm spring 1 on the housing 3 at the diameter d according to Figs. 3 and 4 is here guaranteed by the fact that during the release operation, in all operational conditions, the force A acting from the pressure plate 2 upon the diaphragm spring 1, according to the greater force F of the return springs 7, is greater than the release force P. Thus in contrast to the prior art it is possible by increasing the force F of the return springs 7 from about 300 N to 1 ,500 N and by increasing the initial stress forces of the diaphragm spring 1 by about 30% from 3,800 N to 5,000 N, to guarantee a unilateral abutment of the diaphragm spring 1 on the clutch housing 3 even during the release action, and thus to omit the support rivets 27 of the prior art without replacement.

According to Figs. 5 and 6, the return springs 8 have the form of approximately tangentially proceeding leaf springs which on the one hand are secured to the noses 1 6 of the pressure plate 2 and on the other hand bear resiliently on the driving disc 5. These return springs 8 now supply the whole force F in accordance with Figs. 3 and 4. The common rotation of the pressure plate 2 with the clutch housing 3 is guaranteed in the present case in that the radially outwardly protruding noses 1 6 of the pressure plate 2 penetrate corresponding apertures 1 8 of the clutch housing 3, and are guided in these apertures 18.

The example of embodiment according to Fig. 7 shows a similar embodiment to the two preceding ones, but in this case return springs 9 are provided which are made as helical compression springs.

They again bear on the one hand on the driving disc 5 and on the other on noses 1 6 of the pressure plate 2 which penetrate the clutch housing 3 in apertures 1 8. These apertures 1 8 in this case can at the same time guarantee the common rotation of the pressure plate 2 with the clutch housing 3. Naturally it is readily possible to guarantee the common rotation of the pressure plate with the clutch housing by other elements, for example by conventional radial or tangential leaf springs as well-known in the art.

Figure 8 shows a diaphragm spring clutch from radially outside corresponding to arrow A of Fig. 5.

This view partially shows the clutch housing 3 and the pressure plate 2. Both are connected for common rotation by means of several tangential leaf springs 11 distributed on the circumference.

The tangential leaf springs 11 are in this case arranged in a deflection 1 5 of the clutch housing 3 and riveted on the one hand to the clutch housing 3 and on the other hand to noses 1 7 of the pressure plate 2, which noses extend radially into the deflection 1 5. The rivets 20 for connecting the tangential leaf springs 11 with the noses 1 7 are prolonged, the prolongations pointing away from the driving disc (not shown). The prolongations penetrate the deflection 15 of the housing 3 by apertures 22, and are provided with a head 19, so that return springs 10 in the form of plate springs can be accommodated between this head 19 and the flange defined by the deflection 1 5. Now these return springs 10 supply the force F according to Figs. 3 and 4.This force F can in part also be supplied by the tangential leaf springs 11 Such an arrangement is attractive due to its simple assembly and the possibility of varying the desired spring force by using various return springs 10 or by varying their number.

Figure 9 shows an arrangement similar to that already described in Fig. 8. The common rotation of the pressure plate 2 and the clutch housing 2 is obtained by tangential leaf springs 11 connecting the clutch housing 3 and noses 1 7 of the pressure plate 2. Hollow rivets 21 are fixed to the noses 17.

These hollow rivets 21 have prolongations extending towards the driving disc. These hollow rivets 21 here penetrate through appropriate apertures 24 in flanges 25 of the housing 3, so that plate springs defining the return springs 10 and being arranged between the tangential leaf springs 11 and the flanges 25 can generate the force F according to Figs. 3 and 4. Here again the force F can be supplied by the return springs 10 alone or partially by the return spring 10 and partially by the tangential leaf springs 11.

Naturally it is possible in principle, without additional springs, to form the tangential leaf springs so that they supply the relatively high force F quite alone. In this case however multilayer tangential leaf springs would have to be used.

Figure 10 shows, in an illustration of principle, the variation of the forces F and P in dependence upon the axial movement of the pressure plate.

The curve showing the variation of the release force P corresponds to the curve of usual diaphragm springs or plate springs. x represents the distance of the pressure plate 2 from the driving disc 5. x1 represents the magnitude of this distance when the clutch is engaged (Fig. 3) and the linings 6 have their full width in new condition.

x2 represents the magnitude of this distance when the width of the linings 6 has reached the minimum permissible value in engaged condition of the clutch: x3 represents the magnitude of this distance when the clutch is disengaged (Fig. 4). It can be seen from Fig. 10 that with linings of decreasing width the releasing or clutch disengaging force P increases, what is regarded as a favourable aspect. It is further to be noted that the force F of the return springs 7 is always greater than the release force P, the difference being substantially constant between x2 and x3, so that the diaphragm spring is reliably held in contact with the clutch housing without excessive wear.

In Fig. 3, 5a designates a driving disc engagement face, 2a designates a pressure plate engagement face, 6a designates a first clutch disc engagement face and 6b designates a second clutch disc engagement face. 3a designates a fulcrum carrier portion of the clutch housing 3, and 3b designates a circular corrugation acting as fulcrum means. The return spring 7 in Fig. 3 defines pressure plate biasing means. The clutch release or clutch disengagement force P in Fig. 4 corresponds to the resilient force resisting to the axial movement of the tongues 4 against movement from the position in Fig. 3 to the position in Fig. 4.

It is to be noted that modifications are possible without deviating from the principle of this invention.

It is further to be noted that the reference numerals used in the following claims are not to be understood as limiting but only as a help for a better understanding of the claims.

Claims

1. In a clutch assembly comprising a) a driving disc (5) having an axis and a driving disc engagement face (5a); b) a clutch housing (3) fixed with respect to said driving disc (5) and having a fulcrum carrier portion (3a) axially apposite to and spaced from said driving disc engagement face (5a); c) a pressure plate (2) axially between said driving disc (5) and said fulcrum carrier portion (3a), said pressure plate (2) being axially movable with respect to said driving disc (5) and being connected to said driving disc (5) for common rotation therewith, said pressure plate (2) having a pressure plate engagement face (2a) opposite to said driving disc engagement face (5a);; d) a clutch disc unit comprising a clutch disc (12) having axially opposed clutch disc engagement faces (6a, 6b) for engagement with said driving disc engagement face (5a) and said pressure plate engagement face (2a) respectively; e) a diaphragm spring (1) axially between said pressure plate (2) and said fulcrum carrier portion (3a), said diaphragm spring (1) having a radially outer portion (D) for engagement with said pressure plate (2), a radially intermediate portion (d) tiltably mounted on said fulcrum carrier portion (3a) by fulcrum means (3b) which are substantially circular about said axis, and a radially inner portion (4) which is axially movable along a path of axial movement parallel to said axis from a clutch engagement position (Fig. 3) to a clutch disengagement position (Fig. 4) nearer to said driving disc (5) against an axially directed resilient force (P), said diaphragm spring (1) being tilted on such axial movement of said radially inner portion (4) about said fulcrum means (3b), said radially outer portion (D) being axially movable in response to said axial movement of said radially inner portion (4) along a path of axial movement (x) parallel to said axis from a clutch engagement position (x1 - Fig. 3) in which said pressure plate (2) is urged towards said driving disc (5) to a clutch disengagement position (x3 - Fig. 4) respectively which is more remote from said driving disc (5);; f) pressure plate biasing means (7) supported by one of said driving disc (5) and said clutch housing (3) and biasing said pressure plate (2) towards engagement with said radially outer portion (D) of said diaphragm spring (1), the improvement comprising said fulcrum means (3b) contacting said diaphragm spring (1) only on the side thereof which is remote from said pressure plate (2), and the spring characteristics of said diaphragm spring (1) and said biasing means (7) being such that said radially intermediate portion (d) of said diaphragm spring (1) is held in contact with said fulcrum means (3b) when said radially inner portion (4) is in said clutch disengagement position (Fig. 4).

2. A clutch assembly as set forth in claim 1, said diaphragm spring (1) being held in contact with said fulcrum means (3b) during a part of said path of axial movement of said radially inner portion (4) of said diaphragm spring (1) which part is adjacent said clutch disengagement position (Fig. 4) of said radially inner portion (4).

3. A clutch assembly as set forth in claim 1, said radially inner portion (4) of said diaphragm spring (1) being held in contact with said fulcrum means (3b) along the total path of axial movement of said radially inner portion (4) of said diaphragm spring (1) between said clutch engagement position (Fig. 3) and said clutch disengagement position (Fig. 4).

4. A clutch assembly as set forth in claim 1, the biasing force (F) of said pressure plate biasing means (7) being greater than said axially directed resilient force (P) when said radially inner portion (4) of said diaphragm spring (1) is in said clutch disengagement position (Fig. 4).

5. A clutch assembly as set forth in claim 1 ,the biasing force (F) of said pressure plate biasing means (7) being greater than said axially directed resilient force (P) when said radially inner portion (4) is in any axial position within a part of said path of axial movement of said radially inner portion (4) which part is adjacent said clutch disengagement position (Fig. 4) of said radially inner portion (4).

6. A clutch assembly as set forth in claim 1, the biasing force (F) of said pressure plate biasing means (7) being greater than said axially directed resilient force (P) when said radially inner portion (4) is in any axial position along the total path of movement of said radially inner portion (4) between said clutch disengagement position (Fig. 4) and said clutch engagement position (Fig. 3).

7. A clutch assembly as set forth in claim 1, said axially directed resilient force (P) being variable along the path of movement of said radially outer portion (D) of said diaphragm spring (1) between said clutch engagement position (Fig. 3) and said clutch disengagement position (Fig. 4) of said radially outer portion (D), said biasing force (F) of said pressure plate biasing means (7) being variable along said path of movement of said radially outer portion (D) of said diaphragm spring (1) between said clutch engagement position (Fig.3)3) andsaid clutch disengagement position (Fig. 4) of said radially outer portion (D), said biasing force (F) being always greater than said axially directed resilient force (P).

8. A clutch assembly as set forth in claim 7, the axial distance of said clutch disc engagement faces (6a, 6b) being variable over the useful lifetime of said clutch disc between a maximum value when said clutch disc is new and a minimum permissible value when said clutch disc has been used, said axial distance determining said clutch engagement positions (x1, x2 respectively) of said radially outer portion (D) and said radially inner portion (4) of said diaphragm spring (1), the spring characteristics of said diaphragm spring (1) and said pressure plate biasing means (7) being such that the difference between the biasing force (F) of said pressure plate biasing means (7) on the one hand and said resilient force (P) on the other hand is substantially constant along the paths of movement of said radially inner portion (4) and said radially outer portion (D) between the respective engagement positions (Fig. 3) corresponding to said minimum value of distance of said clutch disc engagement faces (6a, 6b) and the respective disengagement positions (Fig. 4).

9. A clutch assembly as set forth in claim 1, said pressure plate (2) being connected to one of said driving disc (5) and said clutch housing (3) by leaf spring means (11) permitting axial movement of said pressure plate (2) with respect to said driving disc (5), said pressure plate biasing means being at least in part defined by said leaf spring means(11).

10. A clutch assembly as set forth in claim 1, said pressure plate biasing means (7) being separate from connecting means connecting said pressure plate (2) and said driving disc (5) for common rotation.

11. A clutch assembly as set forth in claim 1, said pressure plate (2) being provided with radially outwardly projecting lugs (16), said lugs (16) extending through recesses (18) of said clutch housing (3), said pressure plate biasing means (8) being supported by said lugs (16) on the one hand and one of said clutch housing (3) and said driving disc (5) on the other hand.

12. A clutch assembly as set forth in claim 11, said pressure plate (2) being connected to said driving disc (5) for common rotation by said lugs (16) engaging edges of said recesses (18).

13. A clutch assembly as set forth in claim 11, said biasing means (8) comprising substantially axially directed helical compression springs (9).

14. A clutch assembly as set forth in claim 11, said pressure plate biasing means comprising substantially arc-shaped leaf springs (8).

1 5. A clutch assembly as set forth in claim 14, said arc-shaped leaf springs (8) being connected by their apices to said lugs (1 6) and contacting said driving disc (5) by their end portions.

16. A clutch assembly as set forth in claim 11, said clutch housing (3) being provided with flange portions (1 5) substantially perpendicular to said axis, said pressure plate biasing means (10) being supported by said lugs (17) on the one hand and said flange portions (15) on the other hand.

17. A clutch assembly as set forth in claim 16, said pressure plate biasing means comprising substantially axially extending bolt members (20) fixed to a respective lug (17) and passing through a passage (22) of a respective flange portion (15) and compressive biasing means (10) surrounding the respective bolt member (20).

18. A clutch assembly as set forth in claim 17, said lug (17) being nearer to said driving disc (5) than said flange portion (15), a spring support head (19) being provided on said bolt (20) at the end remote from said lug (17), said compressive biasing means (10) being located axially between said spring support head (19) and said flange portion (15).

19. A clutch assembly as set forth in claim 17, said lug (17) being more remote from said driving disc (5) than said flange portion (25), said compressive biasing means (10) being positioned axially between said flange portion (25) and said lug (17).

20. A clutch assembly as set forth in claim 17, said bolts (21) being hollow rivets.

21. A clutch assembly as set forth in claim 20, said hollow rivets comprising a radially outwardly expanded portion, one end of said compressive biasing means (10) being supported by said expanded portion.

22. A clutch assembly as set forth in claim 17, said compressive biasing means (10) comprising at least one pair of plate springs.

23. A clutch assembly as set forth in claim 1, said diaphragm spring (1) and said pressure plate biasing means (7) being prestressed in the respective clutch engagement positions of said radially inner portion and said radially outer portion respectively.

24. A clutch assembly substantially as described with reference to the accompanying drawings.