Abstract:
The clutch mechanism for friction clutch comprises a reaction plate, a friction disk ( 7 ), a pressure plate ( 1 ), a cover ( 2 ), clutching means ( 3 ), operating axially and controlled by declutching means, operating between the cover ( 2 ) and the pressure plate ( 1 ) through support means ( 14 ), the pressure plate ( 1 ) being integral in rotation with the cover ( 2 ) while being capable of moving axially relative to it. Said clutch also comprises a wear take-up device comprising ramp means ( 11 ), with ramps ( 15 ) axially set between the support means ( 14 ) and the pressure plate ( 1 ), said ramps ( 15 ) being adapted to co-operate with counter-ramp means ( 4 ) while stop means ( 20 ) borne by the cover ( 2 ) are provided and adapted to limit the travel of the clutching means ( 3 ), in a position for storing the mechanism in the proximity of their operative position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a clutch mechanism for a friction clutch, in particular for a motor vehicle, and relates more particularly to a clutch mechanism equipped with a device for compensating for wear due notably to wear on the friction linings, the said device, hereinafter referred to as the wear take-up device, operating as the said linings wear. 
     2. Description of Related Art 
     The conventional friction clutch generally has a reaction plate, possibly in two parts in order to form a damping flywheel, fixed with respect to rotation to a first shaft, usually a driving shaft such as the crankshaft of the internal combustion engine, and supporting through its external periphery a cover to which at least one thrust plate is attached. 
     The thrust plate is fixed with respect to rotation to the cover and reaction plate whilst being able to move axially under the action of axially acting engagement means and controlled by disengagement means, generally having a metallic diaphragm bearing on the cover, whilst a friction disc, carrying friction linings at its external periphery, fixed with respect to rotation to a shaft, usually a driven shaft such as the input shaft of the gearbox, is interposed between the thrust plate and reaction plate so as to be clamped between them when the clutch is in the engagement position. The diaphragm controls the axial movement of the thrust plate when it is actuated by a clutch release bearing. 
     During the life of such a clutch, the friction linings, as well as the counter-materials, thrust plate and reaction plate, wear, which causes a variation in the position of the thrust plate and the positions of the axially acting elastic means and of the clutch release bearing, giving rise to a variation in the clamping force between the friction disc on the one hand and the thrust and reaction plates on the other hand, because of the changes in the working conditions of the diaphragm, and the force needed to declutch is affected thereby. By providing such a clutch with a wear take-up device, these drawbacks are avoided, the diaphragm, and the clutch release bearing, usually in constant abutment on the diaphragm, occupying the same position when the clutch is in the engagement position. 
     There has been proposed, notably in the French patent application FR-A-2 753 503 filed on Sep. 17, 1996 under the number 96 11297, a clutch mechanism for a friction clutch, in particular for a motor vehicle, of the type having a reaction plate intended to be fixed with respect to rotation to a driving shaft, a friction disc, carrying friction linings at its external periphery, intended to be fixed with respect to rotation to a driven shaft, the said mechanism comprising a thrust plate, a cover intended to be fixed to the reaction plate, engagement means, acting axially and controlled by disengagement means, acting between on the one hand the cover and on the other hand the thrust plate by means of abutment means, the thrust plate being fixed with respect to rotation to the cover whilst being able to move axially with respect to it and being subjected to the action of elastic return means returning the thrust plate axially towards the cover, the said mechanism also including a wear take-up device comprising ramp means having circumferentially disposed ramps, the said means being placed axially between the abutment means and the thrust plate, the said ramps being adapted to cooperate with counter-ramp means. 
     Naturally, the clutch being equipped with a wear take-up device, it is necessary, after it has fulfilled its function, to put it in its so-called zero position corresponding to linings in the new state, after changing the friction disc whose linings have been worn: means have already been provided for this operation to be easy to implement, as is for example described in the French patent application filed on May 30, 1997 under the number 97 06655. 
     It is advantageous for this operation also to be carried out on the clutch mechanism alone, consisting of the cover, engagement means, the wear take-up device and the thrust plate, constituted a subassembly, before mounting on the reaction plate or flywheel. 
     Such an operation is difficult when the engagement means, expanding, when the mechanism is in this storage position, in some way axially jam the ramp means against the thrust plate, itself held, with respect to the cover, by the return means or other axial stops. 
     The clutch mechanism being equipped with a wear take-up device, the engagement means almost always occupy, as explained above, the same working position with respect to the cover. This is taken advantage of by the present invention in order to limit the travel of the engagement means with respect to the cover. 
     SUMMARY OF THE INVENTION 
     According to the invention, a clutch mechanism, for a friction clutch of the above type, is characterised by the fact that stop means are provided, carried by the cover and adapted to limit the travel of the engagement means, in the storage position of the mechanism, close to their working position. Thus, because of the presence of the wear take-up device, it is certain that the engagement and/or disengagement means of the mechanism mounted on the reaction plate will not come into contact with the said stop means nor with any element constituting the wear take-up device other than the abutment means. 
     This arrangement is particularly advantageous where the clutch is of the pulled type, the engagement means having a diaphragm. 
     In the case of a clutch of the pulled type, in which the diaphragm bears on the cover at points situated radially outwards with respect to the abutment means, in the position of storage of the mechanism the diaphragm has a tendency to move away from the cover; up until now, in order to limit this moving-away travel, it has been proposed, in a clutch mechanism not equipped with a wear take-up device, to provide the thrust plate with stop means placed at its external periphery, adapted to cooperate with the external face of a radial rim on the cover in the storage position of the clutch mechanism: such an arrangement has the drawback that the moving-away travel must be designed to be sufficiently great to enable the thrust plate to move away from the cover in operation as the linings of the friction disc wear; this moving-away travel, still too long in storage, does not facilitate the operation of mounting the mechanism on the reaction plate: in order to avoid having to use long screws for this fixing, storage shims are placed in line with the stop means, which requires fitting and removal operations. 
     It has also been proposed to limit the moving-away travel of the diaphragm by causing it to cooperate, in storage, with stop means carried by the cover: this is the case notably with certain variants described in the document FR-A-2 135 637; here also the same drawbacks as above are found, the storage shims also being difficult to fit. 
     The present invention avoids the above drawbacks. 
     Thus, preferably, the engagement means consist of a diaphragm which bears on the cover at points situated radially outwards with respect to the abutment means, the clutch being of the pulled type. 
     Advantageously, the stop means consist of lugs issuing from the base of the cover and comprising an axial part which passes through holes in the diaphragm and whose free end is folded in a plane roughly perpendicular to the axis of the clutch in order to constitute a radial rim. 
     According to a variant, the stop means consist of small columns having a body which passes through holes in the diaphragm, a tail crimped onto the base of the cover and a head on which a stop line is defined which faces the base of the cover and with which the diaphragm is adapted to cooperate in the storage position. 
     According to another variant, the stop means consist of a ring placed between the thrust plate and the diaphragm and fixed to the base of a cover by rivets passing through holes in the diaphragm. 
     Preferably, the diaphragm cooperates, in the storage position of the mechanism, directly with the stop means. 
     Advantageously, the diaphragm cooperates, in the storage position of the mechanism, with the stop means by means of an elastic assistance washer. 
     According to another variant, the stop means consist of an elastic assistance washer placed axially between the thrust plate and the diaphragm and fixed to the base of the cover by rivets passing through holes in the diaphragm. 
     When there is an elastic assistance washer, advantageously the elastic assistance washer has, at its internal periphery, extensions delimited by radial slots and intended to cooperate with the fingers of the diaphragm. 
     Preferably, the elastic characteristics of the assistance washer are chosen so that, when the clutch is engaged, the clutch friction member being new, the action exerted by the assistance washer is very small, or even nil. 
     Advantageously, the elastic characteristics of the assistance washer are chosen so that, during the declutching operation, the action exerted by the assistance washer increases and then decreases to a given value, which can be very low or even nil, the clutch being disengaged. 
     Another object of the invention is a subassembly consisting of a cover and diaphragm, in which the diaphragm is in abutment on the cover through its external periphery, a subassembly in which the cover and diaphragm have the characteristics of the cover and diaphragm of the aforementioned mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to give a better understanding of the object of the invention, a description will now be given, by way of purely illustrative and non-limitative examples, of embodiments depicted in the accompanying drawings, in which: 
     FIG. 1 is a partial view in section of a clutch mechanism according to the invention, equipped with a wear take up device in its position which corresponds to the engaged state of the clutch, with new linings; 
     FIG. 2 is a view in section of the clutch mechanism according to FIG. 1 in its storage position; 
     FIG. 3 is a view similar to FIG.  1  and corresponds to a variant; 
     FIG. 4 is a view in section along IV—IV in FIG. 3 showing the stop means alone; 
     FIG. 5 is a view showing the mechanism of FIG. 3 equipped with an assistance washer; 
     FIG. 6 is a partial view in the direction of the arrow VI in FIG. 5; 
     FIG. 7 is a view in section of the clutch mechanism according to FIGS. 5 and 6 in its storage position; 
     FIG. 8 is a view similar to FIG.  1  and corresponds to another variant; 
     FIG. 9 is a view showing the mechanism of FIG. 8 equipped with an assistance washer; 
     FIG. 10 is a view similar to FIG.  1  and corresponds to yet another variant, the mechanism being equipped with an assistance washer; 
     FIG. 11 is a partial view in the direction to the arrow XI in FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 to  4 , a friction clutch mechanism can be seen, notably for a motor vehicle, which comprises a thrust plate  1  intended to cooperate with a friction disc  7  carrying at its external periphery friction linings  8 , and which itself cooperates with a reaction plate. The reaction plate, depicted schematically at  100  in FIG. 1, is intended to be fixed with respect to rotation to a driving shaft, such as the crankshaft of the internal combustion engine. The friction disc  7  is fixed with respect to rotation to a driven shaft such as the input shaft of the gearbox. 
     The thrust plate  1  is fixed with respect to rotation to a cover  2 , here hollow in shape, by means of tangential tongues  9  which, being elastic, constitute at the same time means of returning the thrust plate  1  towards the cover  2 , here metallic and made from pressed metal. 
     This cover  2  has a base  12  and means for fixing it to the reaction plate, possibly divided in order to form a damping flywheel; this cover  2  is roughly in the form of a hollow dish and has, at its external periphery, a radial rim forming means of fixing the cover  2  to the reaction plate, the said rim being provided with holes for members such as screws to pass for fixing the cover to the reaction plate. 
     The thrust plate  1 , whilst being fixed with respect to rotation to the cover  2 , is therefore able to move axially with respect to the cover  2  under the action of the engagement means, axially acting and controlled by disengagement means, here a diaphragm  3  bearing on the cover  2 , through the external periphery of its part  16  in the form of a Belleville washer, on a rod  6  placed at the internal periphery of the base  12  of the cover  2 , the clutch being of the pulled type; the disengagement operation is effected by acting on the end of the fingers  18 , of the diaphragm  3 , in the direction of the arrow F in FIG.  1 ; the Belleville washer  16  of the diaphragm  3  is in contact with a support  14  described below. 
     In order, when the clutch is engaged, to maintain the axially acting elastic means  3  in a position independent of the wear on the linings  8  of the friction disc  7 , and to a lesser extent the wear on the thrust plate  1  and reaction plate, whose so-called friction faces wear in contact with the linings  8  on the disc  7 , a wear take-up device  10  is provided. 
     The wear take-up device  10  comprises ramp means  11  disposed circumferentially; more precisely, these ramp means  11  consist of a ring having ramps  15  disposed circumferentially; the said ring also has abutment areas  14  consisting of a rounded top edge centred on the axis of the clutch placed axially towards the outside with respect to the ramps  15 . 
     The thrust plate has, here cast in one piece, on its face turned towards the base  12  of the cover  2 , studs  4  distributed circumferentially at a distance from each other which corresponds to that which circumferentially separates two successive ramps  15 , the studs  4  being intended to cooperate each with a ramp  15 . 
     The ramp means  11  are placed axially between the diaphragm  3  and the thrust plate  1  so that the studs  4  receive the ramps  15  and the diaphragm  3  cooperates with the abutment areas  14 , which thus constitute the abutment means by means of which the diaphragm  3  acts on the thrust plate  1 . 
     The ramp means  11  have, at their external periphery, a cylindrical wall  17  parallel to the axis of the clutch cooperating with a cylindrical hollow  5  with the same axis, which the thrust plate  1  has on its face opposite the base of the cover  2  so that the ramp means  11  are centred with respect to the thrust plate  1 . 
     The wear take-up device  10  can be of any type; it will simply be indicated here that it can also comprise a ratchet wheel carried by a spindle which also carries a worm, the said spindle being carried by a support being adapted to receive an elastic member in the general shape of a C, one end of which, in the shape of a T, carries at its end a control tongue adapted to cooperate with the teeth on the ratchet wheel. 
     The thread and pitch of the worm are adapted to teeth carried by a piece of bent metal sheet in the general shape of a flattened Z and fixed by its ends to protrusions on the thrust plate  1 . For more information, reference should for example be made to the aforementioned document FR-A-2 753 503, the content of which is considered to be annexed to the present invention. 
     According to the invention, the clutch mechanism has stop means  20  for, in storage, limiting the travel of the diaphragm  3  with respect to the cover  2  close to its working position; moreover, these stop means  20  prevent any interference between the diaphragm  3  and here the ratchet wheel of the wear take up device  10  located radially below the ramp means  11 . 
     Here, these stop means  20  consist of folded cut lugs issuing from the base  12  of the cover  2 . 
     As is known, the diaphragm  3  comprises a peripheral part  16  in the form of a Belleville washer, which cooperates with the stops  6  and  14  and which is extended towards the inside by fingers  18  separated by radial slots which open out in holes  19  regularly distributed at the internal periphery of the peripheral parts  16  of the diaphragm  3 . The holes  19  are wider than the radial slots and form the bases thereof. 
     The lugs  20  constituting the stop means are regularly distributed peripherally and can be three, four or more in number. The lugs comprise an axial part  21  which passes through holes  19  in the diaphragm  3 , whose free end is bent in a plane roughly perpendicular to the axis of the clutch in order to constitute a radial return  22  here directed towards the axis of the clutch; it is with the face of the rim  22  which is turned towards the base  12  of the cover  2  that the diaphragm  3  cooperates in the storage position of the mechanism, as shown in FIG. 2; by limiting the travel of the diaphragm  3  in storage, that of the thrust plate  1  is limited; advantageously, the thrust plate  1  has, opposite the base  12  of the cover  2 , radial undercuts  31  in which the radial returns  22  of the lugs  20  can extend. 
     It will also be appreciated that, by virtue of the invention, there has been produced, in the context of a mechanism of the pulled type, a subassembly comprising the cover  2  and diaphragm  3 , which facilitates manipulation as well as the operations of manufacturing the mechanism. 
     In addition, by virtue of the stop means  20 , the diaphragm  3  is centred with respect to the cover, which avoids having to provided special centring means for the diaphragm  3 , such as for example axial pins located in the thrust plate  1 , as has been done up until now. 
     According to the variant in FIG. 3, the stop means  20  consist of small columns having a cylindrical body  23  passing through holes  19  in the diaphragm  3 , a cylindrical tail  24 , with a smaller diameter than that of the body  23 , crimped to the base  12  of the cover  2 , and a head  25 , semicylindrical in shape and with a diameter greater than that of the body  23 ; on this head  25 , on the side which faces the base  12  of the cover  2  there is defined a semicircular stop line  26  for the diaphragm  3 , slightly curved in shape. 
     FIGS. 5 and 6 show the clutch mechanism of FIGS. 3 and 4 incorporating an elastic assistance washer  40  acting in parallel with the diaphragm  3 , in order to assist the declutching operation. 
     The elastic assistance washer  40  bears, on the one hand, on an element which is fixed with respect to the cover  2  and, on the other hand, on the fingers  18  of the diaphragm  3  so that it is adapted to act in the direction of disengagement of the clutch. More precisely, the assistance washer  40  is disposed axially between the diaphragm  3  and the thrust plate  1 , being placed radially in line with the fingers  18  of the diaphragm  3 , roughly radially inside the area delimited by the holes  19  in the diaphragm  3 ; here the assistance washer  40  comprises an external Belleville washer part  41  extended radially towards the axis along extensions  42  separated by radial slots; these extensions  42  extend roughly towards the free end of the fingers  18  of the diaphragm  3 . 
     Here, the external periphery of the Belleville washer part  41  of the assistance washer  40  is in abutment on the stop line  26  which faces the base  12  of the cover  2  and which is presented by the head  25  of the small columns  20 . 
     The assistance washer  40  has elastic characteristics such that, when the clutch is engaged and the linings  8  on the friction disc  7  are new, it generates no axial force on the fingers  18  of the diaphragm  3 ; the clamping force for the linings gripped between the reaction plate and the thrust plate  1  is that which is given by the peripheral part  16  of the diaphragm  3 ; when the fingers  18  of the diaphragm  30  are acted on in the direction of the arrow F, for disengaging the clutch, the assistance washer  40  acts on the fingers  18  of the diaphragm  3 , in the direction of the arrow F, bearing on the cover  2  by means of the small columns  20 , thus relieving the force necessary for declutching. 
     By virtue of the presence of the wear take-up device  10 , the positions of the diaphragm  3  and assistance washer  40 , on engagement and disengagement, are fixed, independent of the wear on the linings: assistance for declutching supplied by the assistance washer  40  is therefore independent of this wear, as is the clamping force. 
     Here, in the storage position of the mechanism, shown in FIG. 7, it is by means of the assistance washer  40  that the stop means  20  limit the travel of the diaphragm  3 . As can be seen, by virtue of the invention, an assistance washer  40  has been associated with a diaphragm and with a wear take-up device without it being necessary to modify the cover  2 ; moreover, the latter has been placed in a free space between the thrust plate  1  and diaphragm  3  and its presence has not affected the axial bulk of the clutch mechanism. 
     According to the variant in FIG. 8, the stop means  20  comprise a circular annulus  50 , centred on the axis of the clutch mechanism and provided with a circular stop line  56  also centred on the said axis; extending in a transverse plane between the thrust plate  1  and diaphragm  3 , the annulus  50  is fixed to the base  12  of the cover  2  by doubly shouldered rivets  60 , one shoulder being provided at each end of their body which passes through holes  19  in the diaphragm  3 . Each of these ends is crimped, one to the base  12  of the cover  2 , the other to the annulus  50 . 
     FIG. 9 shows a variant of the mechanism of FIG. 8 equipped with an assistance washer  40 , similar to that described with regard to FIGS. 5 to  7 . 
     According to the variant in FIGS. 10 and 11, the stop means  20  comprise an assistance washer  70 ; this assistance washer  70  has a peripheral part  71  extended internally by radial extensions  72  which cooperate with the fingers  18  of the diaphragm  3 ; advantageously, there are as many extensions  72  as diaphragm fingers  18 , this being valid also for the assistance washer  40  in FIGS. 5 to  7  and  9 ; at its external periphery, the assistance washer  70  has attachment areas  73  for fixing it to the base  12  of the cover  3  by rivets  60  similar to those in FIGS. 8 and 9. Thus, according to this variant, it is the assistance washer  70  itself which in storage limits the travel of the diaphragm. 
     Naturally, these structures can be reversed; for example, the return  22  in FIG. 1 can be directed radially towards the outside; the rod  6  can be formed directly by press forming of the cover. 
     The cover is not necessarily hollow in shape. For example, the reaction plate can have, at its external periphery, an axially oriented annular skirt to which the cover is fixed. 
     Likewise, a mechanism has been described in which the engagement and disengagement means are produced in a single piece, the diaphragm  3 . The engagement means and the disengagement means can be formed independently: for example, the engagement means can consist of a Belleville washer or helical springs, and the disengagement means of levers or a false diaphragm, that is to say a diaphragm whose peripheral part in the form of a Belleville washer has no elasticity, because for example of the presence in this part of slots opening up to the outside.