Abstract:
The friction clutch comprises a reaction plate designed to be blocked on a driving shaft, a friction disk, bearing at its external periphery friction linings, a pressure plate, a cover ( 52 ) fixed on the reaction plate, an axially operating clutching device ( 53 ) controlled by a disengaging device and which operate between the cover ( 52 ) and the pressure plate through a support device, the pressure plate being integral in rotation with the cover ( 52 ) and being subjected to the action of an elastic return device ( 9 ) axially returning the pressure plate towards the cover ( 52 ). The clutch also comprises a wear take-up device comprising a toothed gear ( 59 ) with which a worm screw ( 63 ) co-operates and a device ( 90 ) for resetting in the position corresponding to linings in new condition, the device ( 90 ) being placed at the worm screw ( 63 ) tip to drive the latter in rotation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a friction clutch, in particular for motor vehicles, and more particularly a clutch provided with a device for compensating wear due in particular to wear of the friction linings, said device, referred to hereinafter as a wear compensator device, operating as and when said linings wear. 
     2. Description of Related Art 
     A conventional friction clutch generally includes a reaction plate, possibly in two parts to form a damper flywheel, constrained to rotate with a first shaft, usually a driving shaft such as the crankshaft of the internal combustion engine, its outside periphery supporting a cover to which at least one pressure plate is attached. 
     The pressure plate is constrained to rotate with the cover and the reaction plate but can be moved axially by axially acting clutch engaging means operated by clutch release means; the clutch engaging means can be coil springs or two Belleville washers disposed in series and acted on by clutch release levers forming the clutch release means; the clutch engaging and clutch release means are generally part of the same component, for example a metal diaphragm bearing on the cover; the diaphragm can be disposed in series as described in document FR-A-2 753 758 or in parallel with a Belleville washer to assist the clutch release force. 
     A friction disc carrying friction linings at its outside periphery and constrained to rotate with a shaft, usually a driven shaft such as the input shaft of the gearbox, is disposed between the pressure plate and the reaction plate so that it is clamped between them when the clutch is in the engaged position. The clutch engaging means move the pressure plate axially when they are actuated by a clutch release thrust bearing through the intermediary of the clutch release means. 
     During the service life of a clutch of the above kind the friction linings and the materials on which they bear on the pressure plate and the reaction plate wear away, which varies the position of the pressure plate and the positions of the axial action clutch engaging means and the clutch release thrust bearing, which in turn varies the clamping force between the friction disc and the pressure and reaction plates because of modifications to the working conditions of the clutch release means, and this affects the force needed to release the clutch. Providing a clutch of the above kind with a wear compensator device avoids the above drawbacks because the clutch engaging means and the clutch release thrust bearing, usually bearing at all times on the clutch release means, occupy the same position when the clutch is in the engaged position. 
     If a clutch is provided with a wear compensator device it is beneficial, after it has exercised its function, to return it to a position corresponding to new friction linings, for example after changing the friction disc because its linings have been worn down; this also facilitates placing the clutch in a storage configuration. 
     SUMMARY OF THE INVENTION 
     The present invention consists in a clutch including a wear compensator device in which the above manoeuvre is possible and simple to carry out, naturally without demounting the assembly constituting the clutch mechanism. 
     In accordance with the invention, a friction clutch, in particular for motor vehicles, of the kind including a reaction plate adapted to be constrained to rotate with a driving shaft, a friction disc carrying friction linings at its outside periphery and adapted to be constrained to rotate with a driven shaft, a pressure plate, a cover fixed to the reaction plate, axially acting clutch engaging means operated by clutch release means and operative between the cover and the pressure plate through the intermediary of bearing means, the pressure plate being constrained to rotate with the cover, able to move axially relative to the cover and acted on by return spring means biasing the pressure plate axially towards the cover, said clutch also including a wear compensator device, is characterised in that the wear compensator device comprises means for resetting it to a position corresponding to new friction linings. 
     Said wear compensator device advantageously includes ramp means comprising circumferentially distributed inclined ramps, said ramp means being disposed axially between the bearing means and the pressure plate and adapted to co-operate with counter-ramp means, said wear compensator device also including teeth with which a tangentially disposed lead screw co-operates, one of the two ramp members and the counter-ramp means being attached to said teeth, means for rotating the lead screw being rendered operative by wear of the friction linings when the clutch is engaged. 
     The axially acting clutch engaging means preferably comprise a diaphragm. 
     The ramp means advantageously comprise a ring comprising the ramps and the bearing means. 
     The counter-ramp means preferably consist in studs adapted to co-operate with the ramps of the ramp means. 
     The lead screw is advantageously mobile along its axis and is acted on by compensator spring means. 
     The means for rotating the lead screw preferably comprise a ratchet wheel constrained to rotate with the lead screw. 
     The lead screw and the means for rotating the lead screw are advantageously carried by a support attached to the cover. 
     The lead screw and the means for rotating the lead screw preferably rotate on a shaft carried by the support, the means for resetting the wear compensator device comprising rotational coupling means at the end of the lead screw for rotating the lead screw. 
     The rotational coupling means are advantageously adapted to receive a complementary shape end of a tool. 
     The rotational coupling means preferably comprise at least one axial notch adapted to receive a finger at the end of the tool; alternatively the rotational coupling means comprise a slot flanked by transverse rims. 
     The cover advantageously has a passage for the tool aligned with the shaft. 
     The teeth preferably comprise a plurality of circumferentially spaced teeth elements. 
     Each teeth element is advantageously globally radially aligned with a ramp. 
     The number of teeth elements is preferably the same as the number of ramps. 
     The present invention also consists in a tool for resetting a wear compensator device fitted to a clutch, said tool having features adapted to co-operate with the wear compensator device of the above clutch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To explain the subject matter of the invention in more detail one embodiment of the invention will now be described by way of purely illustrative and non-limiting example with reference to the accompanying drawings, in which: 
     FIG. 1 is a partial view in section taken along the line I—I in FIG. 5 of a clutch fitted with a wear compensator device in accordance with the invention; 
     FIG. 2 is a perspective view showing the wear compensator device without its support; 
     FIG. 3 is a perspective view of the support; 
     FIG. 4 is a perspective view of the spring device; 
     FIG. 5 is a partial plan view of the clutch from FIG. 1; 
     FIG. 6 is a lateral view in the direction of the arrow VI in FIG. 5; 
     FIG. 7 is a perspective view of the resetting tool; 
     FIG. 8 is a perspective view showing a variant of the ramp means; 
     FIG. 9 is a partial view analogous to FIG. 5 showing a variant. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 through 6 show a clutch fitted with a wear compensator device of the kind described in French Patent Application FR-A-2 753 503 filed Sep. 17, 1996 to which reference should be had for more details. 
     The figures show a friction clutch mechanism, in particular for a motor vehicle, that comprises a pressure plate  51  designed to co-operate with a friction disc shown diagrammatically at  200  in FIG.  1  and carrying friction linings  201  at its outside periphery, itself co-operating with a reaction plate. The reaction plate, not shown, is adapted to be constrained to rotate with a driving shaft such as the crankshaft of the internal combustion engine. The friction disc is constrained to rotate with a driven shaft such as the input shaft of the gearbox. A friction disc is disclosed in documents GB-A-2 310 898, GB-A-2 294 301, FR-A-2 739 159 and FR-A-2 605 692. 
     The pressure plate  51  is constrained to rotate with the cover  52  by tangential tongues  9  one of which can be seen in FIG.  5  and which are elastic to constitute also means for biasing the pressure plate  51  towards the cover  52 . 
     The cover  52  is pressed from sheet metal. The cover  52  has a back and means for fixing it to a reaction plate, which is possibly subdivided to form a damper flywheel. For more information see document GB-A-2 294 301 showing the reaction plate and a damper flywheel (FIGS.  35  and  36 ). Here the cover  52  is broadly dish-shaped and has at its outside periphery a radial rim forming means for fixing the cover to the reaction plate, said rim having holes in it for fixing members such as screws for fastening the cover to the reaction plate. 
     Although the pressure plate  51  is constrained to rotate with the cover  52  it is movable axially relative to the cover  52  by axially acting clutch engaging means operated by clutch release means, here a diaphragm  53  articulated to the cover  52  by columns  58  carried by the back of the cover  52 , which has a central hole in it. 
     Here the clutch is of the push type, which means that a clutch release thrust bearing, not shown, must push on the inside end of the fingers of the diaphragm  53  to disengage the clutch. To this end the back of the cover  52  carries a primary support consisting of a ring, for example, or as here a pressed portion of the inside periphery of the back of the cover and, facing the primary support, a secondary support in the form of a rolled ring carried by the columns  58 , or any other means. The inside periphery of the Belleville washer of the diaphragm  53  is mounted so that it can tilt between said primary and secondary supports. The outside periphery of its Belleville washer is in contact with bearing areas  14  described hereinafter. 
     A wear compensator device is provided to maintain the axially acting clutch engaging means  53  in a position independent of the wear of the friction disc linings and to a lesser degree independent of the wear of the pressure plate  51  and the reaction plate, the friction faces of which wear because they are in contact with the disc linings when the clutch is engaged. 
     The wear compensator device  10  comprises ramp means  54  disposed circumferentially; to be more precise, the ramp means  54  comprise a sheet metal ring cut out and bent to shape to feature ramps  56  disposed circumferentially; said ring also has bearing areas  14  consisting of the rounded top edge of circular arc-shape pressed portions centred on the axis of the clutch and radially outside the ramps  56 . 
     The pressure plate  51  has integral circumferentially spaced studs  57  on its face that faces towards the back of the cover  52 , radially beyond the columns  58 ; the distance between the studs corresponds to the circumferential distance between two successive ramps  56 , the studs  57  each being adapted to co-operate with a ramp  56 . 
     The ramp means  54  are disposed axially between the diaphragm  53  and the pressure plate  51  so that the studs  57  receive the ramps  56  and the diaphragm  53  co-operates with the bearing areas  14  which thus constitute the bearing means through which the diaphragm  53  acts on the pressure plate  51 . This arrangement is simple and economic, the ramp means  54  being of metal and obtained by pressing. 
     One of the bearing areas  14  of the ramp means  11  is extended at its outside periphery by a rim parallel to the axis of the clutch and terminating in a transverse lip, i.e. a lip in a plane perpendicular to the axis of the clutch, having teeth  59  at its periphery so that the bearing areas  14  can be continuous and the rim is centred by an increased thickness of the pressure plate  51 . 
     The wear compensator device further includes a ratchet wheel  60  with inclined teeth attached to a shaft  67  which also carries a lead screw  63 ; the thread and the pitch of the lead screw  63  match the teeth  59 ; the conditions of co-operation between the lead screw  63  and the teeth  59  are described hereinafter. 
     The shaft  67  of the ratchet wheel  60  is rotatably carried by a support  62 , seen more clearly in FIG. 3, cut from sheet metal and bent into a U-shape having a core  64  and two wings  65 ,  66  for supporting the shaft  67 ; to this end, each of the wings features a circular hole  61  adapted to receive the shaft; the core  64  carries a right-angled lateral lug  68  directed outwards and designed to be fixed to an area of the outside rim of the cover  52  by a rivet, this area being offset axially towards the back of the cover  52 . The simplified cover  52  includes an opening through which the core  64  passes. 
     On the side opposite the lug  68 , the wings  65  and  66  of the support  62  have an axial extension the end of which is bent outwards to constitute a fixing lug  69  parallel to the lug  68  and designed to be fixed to the back of the cover  52  by a rivet  70 ; the edge of said extension directed towards the core  64  is provided with rims  71  extending towards each other globally parallel to the core  64  and designed to constitute abutments whose function will become apparent hereinafter; the facing ends of said rims  71  are at a sufficient distance apart to enable unimpeded movement of the actuator  55  during clutch engagement and release. 
     The support  62  is adapted to receive a spring member  72 . 
     Here the spring member  72 , seen better in FIG. 4, is stirrup-shaped and has an elongated flat body  73  with an arm  74  at each end in which there is a hole  75  adapted to receive the shaft  67 ; the two arms  74  are parallel, on the same side of the body  73  and globally perpendicular to the body. 
     On one longitudinal edge the body  73  is extended by an oblique extension  84  on the same side as the arms  74 , notches  82  and  83  in the body  73  delimiting the extension  84  relative to the ends of the body  73  carrying the arms  74 ; the notches  82  and  83  also impart some elasticity to the extension  84 . 
     The free end of the extension  84  has a rim  85  extended by an operating tongue  76  extending towards the body  73 , to which it is parallel. 
     A cut-out  77  is formed in the extension  84 ; this cut-out  77  and notches  79 ,  80  and  81  in the body  73  provide a ratchet  78  made up of two blades  78   a  and  78   b  ; their free ends are perpendicular to the body  73  are slightly different lengths; the difference in their lengths is such that when the blades  78   a  and  78   b  bear elastically on the ratchet wheel  60  they are offset parallel to the arms  74  by an amount less than the length of a tooth on the ratchet wheel  60 . 
     A compression coil spring  86  is disposed between the ratchet wheel  60  and the free end of the arm  66 , around the shaft  67 ; the lead screw  63  and the ratchet wheel  60  are in one piece. 
     The coil spring  86  constitutes the compensator spring means; the ratchet wheel  60  is in line with the ratchet  78  which by co-operating with the inclined teeth on the ratchet wheel  60  prevents the ratchet wheel  60  and the lead screw  63  turning in the anti-clockwise direction, as seen in FIG.  1 . 
     The support  62  carrying the ratchet wheel  60 , the lead screw  63  and the coil spring  86  being attached to the cover  52 , the diaphragm  53  moves relative to it during clutch release and clutch engagement; the diaphragm  53  carries a radial appendix at its periphery and this actuator  55  (FIG. 2) extends radially outside the Belleville washer part of the diaphragm  53  to cooperate with the extension  84  of the spring member  72 . Because of this arrangement, when the diaphragm  53  tilts during clutch release and clutch engagement the actuator  55  moves the extension  84  from right to left, as seen in FIG. 1, and the operating tongue  76 , co-operating with the teeth on the ratchet wheel  60 , turns the ratchet wheel  60  clockwise; when the actuator  55  returns, moving from left to right, the elasticity of the extension  84  of the spring member  72  and the inclination of the teeth are such that the actuator  55  is moved towards the right, rising up the teeth, which are prevented from rotating by the ratchet  78 . 
     The operation of the play compensator device just described is known in itself and will not be described in detail; if necessary reference may be had to French Patent Application FR-A-2 753 503 already mentioned, the corresponding part of the description of which must be considered to be an integral part of the present application. When the friction linings wear, the diaphragm tilts and its actuator operates on the spring member  72  and the operating tongue to turn the ratchet wheel and compress the spring  86  when the clutch is engaged. When the clutch is released the spring  86  expands and operates on the screw  63  which, via the teeth  59 , turns the ring  54  to compensate wear due at least to wear of the friction linings. 
     Here the lead screw  63  and the ratchet wheel  60 , which are in one piece, are threaded onto the shaft  67  carried by the support  62 ; the shaft  67  passes through the wings  65  and  66  of the support  62  and is positioned axially relative to the support on one side by a circlip  88  which co-operates with the outside face of the wing  66  and immobilises it from right to left, as shown in FIGS. 5 and 6, and on the other side by the end of the shaft  67  abutting against the re-entrant part  96  of the skirt of the cover  52 , which immobilises it in the other direction. 
     On the side opposite the ratchet wheel  60  the lead screw  63  is extended by a sleeve  89  around the shaft  67  and passing through the corresponding arm  74  of the spring member  72  and the ring  65  of the support  62 ; a shouldered bush  91  forming a bearing is advantageously disposed radially between the sleeve  89  and said arm  74  and said wing  65 . 
     The sleeve  89  projects axially outwards of the wing  65  of the support  62  and the shoulder bush  91 ; here the projecting part of the sleeve  89  has two axial cut-outs or notches  90  in diametrally opposed positions constituting means for preventing rotation of the lead screw  63  and forming part of the means for resetting the wear compensator device. 
     A resetting tool  100  is provided. 
     The tool  100 , seen better in FIG. 7, comprises a rod  94  one end of which carries an operating knob  95 , here a knurled knob, and the other end of which is hollow and cut to a shape comprising two diametrally opposed fingers  93  complementary to the axial notches  90  in the sleeve  89  of the lead screw  63 . 
     The inside diameter of the recess in the tool matches the outside diameter of the shaft  67  that it is to receive, the end of the shaft  67  advantageously extending axially beyond the sleeve  89 : this facilitates centring of the tool  100  relative to the sleeve  89  to facilitate bringing the fingers  93  of the tool  100  into coincidence with the axial notches  90  of the sleeve  89 . 
     Cut-outs in the cover  52  define a passage  92  for the tool  100  aligned with the shaft  67 . 
     The operation to reset the wear compensator device is evident from the foregoing description. 
     When the tool is in place, the fact that the lead screw  63  is prevented from rotating relative to the tool  100 , the fingers  93  of which co-operate with the axial notches  90 , means that turning the tool  100  turns the lead screw  63  relative to the cover  52  and so the teeth  59  can be turned relative to the pressure plate  51  and the ramps  56  can be turned relative to the studs  57 . 
     The circumferential length of the teeth  59  corresponds to the amount of wear to be compensated, allowing obviously for the few teeth with which the lead screw  63  meshes in the initial configuration. 
     Of course, a plurality of equiangularly spaced wear compensator devices can be provided, for example three devices at 120 degrees to each other. 
     When the chosen amount of wear corresponding to the circumferential length of the teeth  59  has been compensated, the lead screw  63  no longer co-operates with the teeth  59 . 
     To reset the wear compensator device when the friction disc is replaced it is sufficient to use a tool of any kind to turn the ramp means  54  about their axis so that the ramps  56  rise up the studs  57  until the first tooth  59  meets the first thread of the lead screw  63 ; by rotating the lead screw  63  using the resetting tool  100  the first few teeth  59  are then engaged with the threads of the lead screw  63 . 
     The angle through which the ramp means  54  must be turned in the first phase of resetting depends on the number of wear compensator devices; usually there is only one wear compensator device and the angle is therefore large. To minimise the angle regardless of the number of devices it is possible to provide teeth  59  made up of a plurality of teeth elements like the elements  59 A,  59 B,  59 C shown in FIG. 8; the number of teeth elements is advantageously the same as the number of ramps  56 , each element corresponding to the chosen wear of a friction disc; the ramps  56  face the teeth elements  59 A,  59 B,  59 C. 
     FIG. 9, which is analogous to FIG. 5, shows a variant of the resetting means; in FIG. 9 identical parts or parts having the same function compared to FIG. 5 carry the same reference numbers. 
     Here the lead screw  63  is extended at the end opposite the ratchet wheel  60  by a sleeve  189  around the shaft  67  and having at its end a diametral stop  190  flanked by transverse rims  190 A,  190 B. 
     By virtue of this arrangement the resetting tool no longer needs to be a special tool, and an ordinary screwdriver can be used. 
     By virtue of the rims  190 A,  190 B the shaft  67  is axially immobilised in the direction from right to left as shown in the figure and no circlip like the circlip  88  from FIG. 5 is needed. 
     Here the sleeve  189  passes directly through the arm  74  of the spring member  72  and the wing  65  of the support  62 : of course, as previously, a shouldered bush like the bush  91  from FIG. 5 forming a bearing could be disposed between the sleeve  189  and said arm  74  and said wing  65 . 
     Alternatively, the sleeve  189  passes through the parts  74 ,  72  and  65  and has a polygonal external profile, the tool then having at the end opposite the knob  95  a blind hole with a polygonal profile complementary to that of the sleeve. The structures can therefore be interchanged, the tool having a recess co-operating with the complementary end of the sleeve.