Abstract:
The invention concerns a clutch mechanism comprising a wear take-up device with a ramp ( 32 ) ring ( 330 ) coupled in rotation into axial mobility with an intermediate part ( 310 ) equipped with a tooting ( 31 ) engaged in an endless screw ( 36 ) integral with a cover. The invention is applicable to a motor vehicle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns friction clutches, notably for motor vehicles, and relates more particularly to the unitary assembly which such a clutch has, described for example in the documents FRY-A-2 242 892 and FRY-A-2 420 690. Such a unitary assembly is referred to as a clutch mechanism. 
     2. Description of the Related Art 
     Conventionally, a friction clutch has a driving flywheel, possibly in two parts in order to form in particular a torsion damming flywheel or a flexible flywheel. The driving flywheel has a reaction plate. 
     The driving flywheel is fixed with respect to rotation to a first shaft, such as a driving shaft, namely the crankshaft of the internal combustion engine in the context of an application to a motor vehicle. 
     The reaction plate has a friction face on the back and is fixed with respect to rotation to a pressure plate able to move axially with respect to the reaction plate. 
     This pressure plate has on the front a friction face opposite that of the reaction plate. 
     The friction linings of a friction disc are interposed between the pressure and reaction plates, or more precisely between the friction faces thereof, forming friction tracks. 
     These linings are fixed to a support, usually elastically deformable axially in order to form a progressive friction disc affording assistance during the declutching operation. This support, possibly duplicated, is rigidly or elastically connected to a hub fixed with respect to rotation to a second shaft, such as a driven shaft, namely the input shaft of a movement transmission, for example a gearbox, in the context of an application to a motor vehicle. As a variant, the support is embedded in a friction lining. In all cases, the friction disc has at its external periphery two friction faces which wear during the service life of the clutch. 
     When the friction lining or linings are clamped between the pressure and reaction plates (clutch engaged), the torque is transmitted from the driving shaft to the driven shaft via the friction disc. When the friction linings are not clamped between the said plates (clutch disengaged), the driven shaft is not driven by the driving shaft. To do this, axially acting engagement means are provided and form an assembly with disengagement means designed to counteract as required the action of the engagement means bearing on a cover for action on the pressure plate, or more precisely for action on support means carried by the pressure plate fixed with respect to rotation to the cover whilst being able to move axially with respect to the latter, for example by means of a connection with axially elastic tongues or by means of a connection of the mortice and tenon type; radial lugs—forming tenons—on the pressure plate being engaged for axial sliding in grooves—forming mortices—in the cover. 
     This cover has at its external periphery fixing means for fixing it to the reaction plate detachably or non-detachably. 
     The engagement means include at least one Belleville washer and the disengagement means of the disengagement levers for action on the disengagement means. Usually these engagement and disengagement means belong to the same axially elastic piece referred to as the diaphragm. This diaphragm, frustoconical in shape in the free state, has a peripheral part in the form of a Belleville washer, extended radially towards the centre by a central part divided into radial fingers by blind slots with broadened bottoms to form broadened orifices at the internal periphery of the Belleville washer constituting the axially acting engagement means, whilst the radial fingers form disengagement levers and therefore the clutch disengagement means. 
     In the documents FRY-A-2 242 892 and FRY-A-2 420 690, the cover constitutes, with the pressure plate, the elastic tongues and the diaphragm, a unitary assembly called a clutch mechanism, which is attached to the reaction plate. Naturally this clutch mechanism can constitute, with the friction disc and reaction plate, a module which is attached in a unitary fashion to the crankshaft of the vehicle engine or to a flange fixed to the crankshaft, the reaction plate then being fixed to the flange, advantageously flexible. 
     SUMMARY OF THE INVENTION 
     This mechanism is advantageously equipped with a compensation device, referred to as a wear take-up device, in order to compensate for the wear on the friction lining or linings and the friction faces of the pressure and reaction plates so that the diaphragm has a substantially constant position when the clutch is engaged, and this throughout the service life of the friction clutch. The diaphragm thus exerts a substantially constant load on the pressure plate in the clutch-engaged position. The travel of the clutch release bearing, acting on the internal end of the fingers of the diaphragm, is, in a known manner, substantially constant during the disengagement operation. 
     This wear take-up device has ramps and counter-ramps acting between the pressure plate and the support means of the diaphragm or between the diaphragm and the cover. 
     A trigger, sensitive to the state of wear on the friction lining or linings, makes it possible to make the ramps turn in the event of wear so that the diaphragm always occupies the same position when the clutch is engaged under the action of the engagement means (linings clamped). 
     The trigger has, in one embodiment, a ratchet wheel and a worm system, forming part of a cartridge as described in the document FR-A-2 753 503. 
     More precisely, an elastic member is provided with a control tongue cooperating with the teeth on the ratchet wheel and a non-return catch. 
     In the event of wear, the control tongue is maneuvered by an actuator, in this case an appendage of the diaphragm, in order to cause the ratchet wheel to turn and compress a take-up spring allowed subsequently to expand. A non-return catch prevents the worm from turning in the opposite direction, notably when the spring expands. The worm comes into engagement with the set of teeth integral with a ring provided with ramps for cooperating with counter-ramps fixed to the pressure plate. 
     Thus, in the event of wear, the thickness of the pressure plate, composed of the pressure plate proper and the ring with ramps, is increased, the said ring carrying support protrusions constituting the support means for the engagement means. 
     The ring therefore comes into engagement directly with the worm. 
     Such an arrangement gives satisfaction, but nevertheless the applicant has wondered whether it is not possible to eliminate the non-return catch in order to simplify the elastic member. 
     According to the invention, an engagement mechanism of the above indicated type is characterised in that the set of teeth belong to an intermediate piece connected with respect to rotation to the ring with ramps by means of connecting with respect to rotation allowing an axial movement of the ring with ramps with respect to the intermediate piece. 
     By virtue of the invention, the non-return catch can be omitted because the set of teeth is solely coupled in rotation to the ring with ramps by the intermediate piece and because the worm can drive the set of teeth in rotation but not vice-versa, the connection being of an irreversible design. Because the set of teeth is not axially connected to the ring with ramps and is therefore not driven by the latter during engagement and disengagement operations, the connection between worm and set of teeth can be reversible. The intermediate piece is axially fixed overall and consists for example of a washer. By virtue of the invention, the presence of a ratchet wheel and control tongue is no longer obligatory. This is because the appendage on the diaphragm can enter a recess in a drum as described in the document FR-A-2 424 442. 
     In one embodiment, the connection is of the cooperation of shapes type with circumferential mounting clearance and the elastic tongues rotatably connecting the pressure plate to the cover are used for gripping a washer, constituting the intermediate piece, between two tongues in the same set of tongues. To do this, the tongues have protuberances for gripping the intermediate washer. In one embodiment, the protuberances are produced at the end fixing the tongues to the cover. The intermediate washer is thus axially fixed and is provided for example with scallops into which there enter lugs on the ring with ramps thus connected with respect to rotation, with axial mobility, to the intermediate washer by cooperation of shapes. 
     Naturally, the structures can be reversed, the washer having radial lugs entering into axial scallops in the ring with ramps. As a variant, the intermediate piece is elastically coupled with respect to rotation to the ring with ramps, for example by means of at least one coil spring replacing the take-up spring abutting the worm. 
     As a variant, the intermediate piece with set of teeth is connected with respect to rotation to the ring with ramps by second axially elastically deformable tongues of the type, referred to as first tongues, acting between the pressure plate and the cover. In this way the friction between the ring with ramps and the intermediate piece is eliminated, the second tongues, in an embodiment with tangential orientation, being coupled at one of their ends to the ring with ramps and at their other end to the intermediate piece carrying the set of teeth. 
     By virtue of the second tongues, the losses of material can be reduced, the intermediate piece and the ring with ramps being able to be made from the same metallic blank by cropping, the intermediate piece surrounding the ring with ramps. 
     It should be noted that the second axially elastic tongues in all cases allow the formation of a sub-assembly consisting of intermediate piece and ring with ramps, which can be manipulated and transported. This facilitates the final assembly. 
     In addition, these second tongues are advantageously mounted with prestressing and exert a return action on the intermediate piece in the direction of at least one stop carried by the cover because of the fact that the ring with ramps is, by means of its support means, in contact with the diaphragm, or more precisely with the external periphery thereof. Thus, because of the prestressing of the second tongues, the sub-assembly consisting of ring with ramps, second tongues and intermediate piece has a thickness in the free state greater than that which it has when it is mounted in the clutch—with clutch engaged between the stop and the diaphragm. The prestressing is advantageously chosen so that the aforementioned sub-assembly is always in contact with the diaphragm and the stop when the clutch is disengaged. The second tongues are arched in order, in a second embodiment, to effect the prestressing. They can have a curved shape. This stop can be formed by means of protuberances belonging to the first tongues. The stop can be divided or continuous. In a variant, the stop is formed by means of rigid pieces serving to grip the first tongues between them and an area of a radial edge which the cover has at its external periphery. Thus the first tongues are protected and they are used to lock the stop or stops with respect to rotation by cooperation of shapes. 
     By way of variant, the stop is formed by means of balancing masses for the clutch mechanism made necessary by the presence of a cartridge including the worm carried by the cover. 
     This cartridge is mounted in a housing which the cover has for this purpose. The cover in reality has more than one housing. The empty housings are used for mounting balancing masses serving as a stop for axially locking, in one direction, the intermediate piece which thus has no need to be gripped since it is immobilised axially in the other direction by the ring with ramps in contact with the diaphragm under the return action exerted in the second tongues for connection in rotation with the ring with ramps. 
     These second tongues can be tongues of the standard type, that is to say of the same type as the first tongues. By virtue of these tongues, the intermediate piece can be centred with respect to a skirt on the cover so that the pressure plate has no need to be machined in order to centre the ring with ramps and so that the ring with ramps is simplified since it is no longer necessary to provide a centring edge on it. 
     The presence of the intermediate piece makes it possible to locate at least one take-up spring between the intermediate piece and the ring with ramps, which simplifies the cartridge carrying the worm. 
     The intermediate piece can be not in the form of a continuous ring, particularly when it is connected by tongues to the ring with ramps. 
     These second tongues can have another shape, for example a concertina shape. The second tongues can also have a circumferential action and thus constitute a take-up spring. To do this, they advantageously have a concertina shape, which makes it possible to eliminate the take-up spring at the level of the cartridge, the tongue being mounted with prestressing between the ring with ramps and the intermediate piece. 
     As a variant the second tongues, instead of being arched, are flat originally and it is the first tongues, whose return force is then increased, which force the intermediate piece in the direction of the ring with ramps. 
     Removable hooks or links, for example in the form of clips, act, in one embodiment, between the intermediate piece and the ring with ramps in order to protect the second tongues before mounting the aforementioned sub-assembly thus created on the cover. As a variant the hooks can be replaced with screws, bolts, etc, which are removed finally in the same way as the hooks. In all cases the intermediate piece is pressed against an axial stop carried by the cover and designed to maintain the intermediate piece in the axial direction going from the cover to the pressure plate. In one embodiment the take-up spring is mounted under prestressing so that the take-up takes place principally during re-engagement and the wear and relative movements between the set of teeth and the screw are reduced. 
    
    
     Other advantages will emerge in the light of the description with regard to the accompanying drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a clutch mechanism according to the invention with local cutaways in order to show the diaphragm, the tangential tongues, the ramp means and the cartridge of the wear take-up device; 
     FIG. 2 is a view to a larger scale of part of the top portion of FIG. 1; 
     FIG. 3 is a view in section along the line A—A of FIG. 1; 
     FIG. 4 is a view in section along the line B—B of FIG. 1; 
     FIGS. 5,  6  are views in the direction of the arrows respectively C and D in FIG. 1; 
     FIG. 7 is a view in section along the line E—E in FIG. 1; 
     FIG. 8 is a view in the direction of the arrow F of the line  1 ; 
     FIG. 9 is a view to a larger scale of the bottom part of FIG. 3 in order to show a set of tongues; 
     FIGS. 10 and 11 are half-views in section similar to those of FIGS. 3 and 4 for a second embodiment of the invention; 
     FIG. 12 is a view similar to FIG. 8 for this second embodiment; 
     FIG. 13 is a partial view in the direction of the arrow F′ in FIG. 10; 
     FIG. 14 is a partial view in the direction of the arrow G in FIG. 13; 
     FIGS. 15 and 16 are views similar to FIGS. 13 and 14 for a third embodiment according to the invention; 
     FIGS. 17 and 18 are views similar to FIGS. 13 and 14 for a fourth embodiment; 
     FIGS. 19 to  21  are views similar to FIGS. 10,  11  and  13  for a fifth example embodiment of the invention; 
     FIG. 22 is a view similar to FIG. 1 with local cutaways for a sixth example embodiment of the invention; 
     FIGS. 23 to  25  are views in section are views in section respectively along the lines A′—A′, B′—B′ and C′—C′ in FIG. 22; 
     FIG. 26 is a front view of the assembly consisting of intermediate piece and adjustment ring with ramps in FIG. 22; 
     FIG. 27 is a view in section along the line  27 — 27  in FIG. 26; 
     FIG. 28 is a view to a larger scale of the cartridge of FIG. 4; 
     FIG. 29 is a view of the assembly consisting of intermediate piece with set of teeth and ring with ramps, and support means for the engagement means, for a seventh example embodiment; 
     FIG. 30 is a view in section along the line  30 — 30  in FIG. 29; 
     FIG. 31 is a view in the direction of the arrow  31  in FIG. 29; 
     FIG. 32 is a view similar to FIG. 24 for this seventh example embodiment; 
     FIGS. 33,  34 ,  36  are views in section along, respectively, the lines  33 — 33 ,  34 — 34  and  36 — 36  in FIG. 35 for an eighth example embodiment; 
     FIG. 35 is a partial view at the level of one of the first tongues for this eighth example embodiment; 
     FIG. 37 is a view in the direction of the arrow  37  in FIG. 35; 
     FIG. 38 is a partial front view with local cutaways for a ninth example embodiment; 
     FIGS. 39 to  41  are views, respectively, along the lines  39 — 39 ,  40 — 40  and the arrow  41  in FIG. 38; 
     FIG. 42 is a partial view similar to FIG. 2 for a tenth example embodiment; 
     FIG. 43 is a view showing the intermediate piece and the second tongue in FIG. 42; 
     FIG. 44 is a partial view similar to FIG. 1 for an eleventh example embodiment; 
     FIGS. 45 and 46 are views respectively along the lines  45 — 45  and  46 ,  47  in FIG. 44; 
     FIG. 47 shows the support of the cartridge in FIG. 46; 
     FIG. 48 is a view similar to FIG. 47 for a twelfth example embodiment; 
     FIG. 49 is a view of the support in FIG. 47; 
     FIG. 50 is a view of the shaft in FIG. 48; 
     FIG. 51 is a perspective view of the assembly consisting of worm and ratchet wheel in FIG.  48 . In the figures the common elements will be allocated the same reference numbers. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     These figures depict a clutch mechanism forming a unitary assembly which is usually attached to a reaction plate belonging to a driving flywheel, possibly divided in order to form a damping flywheel or a flexible flywheel, with the insertion of a friction disc between the reaction plate and the pressure plate which the clutch mechanism has. 
     Where it is a case of an application for a motor vehicle, the driving flywheel is fixed with respect to rotation to the crankshaft of the internal combustion engine, forming a driving shaft, whilst the friction disc has at its external periphery friction linings, fixed for example by riveting or by a connection with no fixing rivets, to a support, possibly duplicated, axially elastically deformable to form a progressive friction disc and coupled rigidly or elastically to a hub fixed with respect to rotation, here to the input shaft of the gearbox, forming a driven shaft. In a variant, the support is embedded at its external periphery in a friction lining. The friction disc has in all cases two friction faces and at least one lining, the support being axially elastic or axially rigid. 
     It is the friction lining or linings which are therefore intended to be clamped disengagably between the pressure and reaction plates in order to transmit torque from the vehicle engine to the input shaft of the gearbox. To do this, axially acting engagement means are provided for clamping the friction linings between a friction face  11  or friction track, which the pressure plate has on the front, and a friction face or friction track on the back of the reaction plate, which can be carried by a flexible disc fixed to the crankshaft. 
     The engagement means form an assembly with the disengagement means provided for intentionally counteracting the action of the engagement means which bear on the one hand on a cover  2  and on the other hand on support means  3 , carried by the pressure plate  1 , or more precisely by the rear face thereof. 
     The disengagement means have disengagement levers, on the internal ends of which there acts a clutch release bearing which is manually controlled, mechanically or hydraulically, or semi-automatic or automatically. The bearing can therefore be maneuvered by an actuator with an electric motor controlled according to programs predetermined by a computer receiving information notably on the rotation speeds of the driving and driven shafts and on the intention of the driver to change gear. The actuator can be connected hydraulically or manually to the clutch release bearing. Thus the clutch release bearing can form part of a hydraulic receiver of the concentric type through which the gearbox input shaft passes and connected to a hydraulic transmitter and maneuvered by the actuator or manually. 
     In the figures, the engagement and disengagement means belong to the same part referred to as the diaphragm  4 . 
     This diaphragm is frustoconical in shape in the free state and has a characteristic curve (the force exerted as a function of its deflection) which is sinusoidal in shape. Thus, starting from the origin, the characteristic curve increases to a maximum and then decreases to a minimum in order to increase once again. In the clutch engaged position, the diaphragm occupies a position in the decreasing part of its characteristic curve, close to its maximum. 
     The same characteristic curve is obtained with a Belleville washer. 
     For the record, it should be noted that the diaphragm  4  has an external peripheral part in the form of a Belleville washer  41  constituting the engagement means. This peripheral part is extended radially towards the centre by a central part divided into radial fingers  42 , by blind slots  43 . 
     The fingers  42  form disengagement levers, whilst the slots  43  open out at their internal periphery into the central opening of the diaphragm  4  and at their external periphery into broadened orifices  44  forming the blind bottoms of the slots  43 . These orifices  44  are here rectangular in shape. 
     In these figures, the clutch mechanism therefore has, in a unitary fashion, a set of annular parts, namely a pressure plate  1 , a cover  2  and a diaphragm  4 , bearing on the one hand on the cover  2  and on the other hand on the support means  3  for clamping friction linings between the friction faces of the pressure  1  and reaction plates. 
     The pressure plate  1 , made of castable material, here made from cast iron like the reaction plate, is rotatably connected to the cover  2  whilst being able to move axially with respect thereto, here by means of tongues  10 , elastically deformable axially. The tongues  10 , referred to as first tongues, are here tangentially oriented and are fixed, here by riveting, at one of their ends to the cover and at their other end to the pressure plate  1 , or more precisely, each to a lug  12  of the plate  1  projecting radially outwards. As a variant the tongues  10  are radially oriented. 
     In a variant, the lugs  12 , forming tenons, are engaged in axial grooves forming mortices in the cover  2 . 
     The tongues  10  constitute means of returning the pressure plate in the direction of the cover, the diaphragm  4  forcing the pressure plate  1  in the opposite direction to the cover. More precisely, the cover  2  has on the one hand a bottom  21  with a central hole and transversely oriented and on the other hand means  22  of fixing the cover  2  to the reaction plate. The tongues  10  force the pressure plate  1  in the direction of the bottom  21 . 
     In the figures depicted, the cover has roughly the shape of a hollow dish and has a radial end flange  22  directed radially in the opposite direction to the axis of axial symmetry X—X which the clutch mechanism has. This flange  22  is connected, by an axially oriented annular skirt  23 , to the bottom  21 . The skirt  23  is stepped in diameter and open at the level of the tongues  10 , which elastically return the pressure plate in the direction of the bottom of the cover  2 . 
     The flange  22  constitutes the fixing means and is divided into areas  28 ,  27  offset axially for fixing the tongues  10  and for fixing to the reaction plate. The areas  27  for fixing to the reaction plate have holes for the passage of members for fixing to the reaction plate, here screws. In a variant, the reaction plate can be fixed to a flexible disc secured to the crankshaft. The cover  2  can be fixed by its skirt  23  to the flexible disc. For example, the skirt  23  has at its free end lugs fixed by welding or riveting to the flexible disc. The diaphragm  4  bears at the external periphery of its Belleville washer  41  on the support means  3 , whilst the internal periphery of its Belleville washer  4  is mounted so as to tilt between two facing supports, respectively a secondary support  25  carried by the fixing lugs  26  and a primary support  24  carried by the bottom  21 . 
     The fixing lugs  26  originate by cropping and folding from the internal periphery of the bottom  21  of the cover  2 , here made from pressed sheet metal. 
     The lugs  26  are distributed circumferentially in a regular manner and are axially oriented. 
     The lugs  26  pass axially through the broadened orifices  44  in the diaphragm  4  and have, beyond the diaphragm  4 , a free end folded radially outwards, that is to say radially in the opposite direction to the axis of the assembly in order to form a fixing elbow for a spring ring  125 , frustoconical in shape, having at its external periphery a rounded edge  25  constituting the secondary support. The primary support  24  has the form of an annular ring here formed by pressing the bottom  24  of the cover  2 . This ring  24  is here divided. 
     As a variant, this ring  24  is attached to the cover  2 . The internal periphery of the Belleville washer  41  of the diaphragm is interposed axially between these supports  24 ,  25  opposite each other. In the clutch engaged position, the diaphragm  4  is in abutment on the primary support  24  and on the support means  3  of the pressure plate. 
     By acting by pushing on the internal ends of the fingers  42  of the diaphragm  4  by means of a clutch release bearing (not shown), the diaphragm  4  is caused to tilt, which then bears on the secondary support  25 , in order to cancel out the load which it exerts on the pressure plate  1  via the support means  3 ; the tongues  10  return the pressure plate in the direction of the bottom  21  of the cover  2  in order to release the friction linings and disengage the clutch. 
     Naturally, the secondary support can be discontinuous whilst being formed by the free ends of the fixing lugs  26  shaped accordingly in the aforementioned document FR-A-2 242 892. 
     The fixing lugs  26  here alternate circumferentially with support lugs  25 , transversely oriented. 
     These stop lugs are made in a single piece with the bottom  21  of the cover by cropping and extend at the internal periphery of the bottom  21  of the cover  2 , which thus has internally a serrated shape. 
     For more information, reference should be made to the document FR-A-2 242 892 showing the fixing lugs  26  before they are folded and the stop lugs  5 , which are wider circumferentially than the fixing lugs  26 . 
     The stop lugs  5  here cover a slot  43  separating two consecutive fingers  42 . 
     Naturally, all this depends on the size of the cover. The stop lugs  5  therefore form a stop for at least two fingers  42 , forming disengagement levers. These stop lugs  5  here have a trapezoidal shape. The internal diameter of the stop lugs  5  is less than the internal diameter of the fixing lugs  26  after folding. The lugs  5 ,  26  extend radially below the annular-shaped primary support  24 . A scallop  6  separates two consecutive stop lugs  5 . A fixing lug  26  is located at the middle of the of the scallop  6  in order to axially enter a broadened orifice  44  in the diaphragm  4 . 
     The internal periphery of the stop lugs  5  extends radially below broadened orifices  44 . The fixing lugs  26  constitute fixing means for tilting or pivoting mounting of the diaphragm  4  on the cover. In a variant, the fixing lugs can be omitted and the cover can have only stop lugs as described in the document FR-A-2 420 690. In this case, the fixing lugs have holes for mounting an annular piece in the form of a comb, small columns with a profiled head forming a secondary support, etc. All the embodiments, such as also clamps, small columns carrying two support rings etc, described in this document FR-A-2 420 690, to which reference should be made for more information, can be envisaged. The stop lugs  5 , in the form of a tongue, can therefore be fixing lugs. As a variant, the end of the fixing lugs  26  is cut in order to keep only the axial part thereof. The lugs  26  then form centring lugs and the stop lugs  5 , fixing lugs in the aforementioned manner. As a variant, the cover does not have stop lugs, some of which form fixing lugs. 
     As a variant, the fixing lugs  26  can carry a false diaphragm, that is to say a piece whose central part is divided into fingers like that of a diaphragm, whilst the annular peripheral part has no elasticity or has low elasticity. For example, this annular peripheral part, in the form of a washer, is provided with blind radial slots opening out radially at the external periphery of the false diaphragm and of the annular part in the form of a washer. 
     The washer of the false diaphragm is therefore roughly flat in the free state, as well as the false diaphragm. 
     A Belleville washer therefore bears at its external periphery on the cover and at its internal periphery on the peripheral washer of the false diaphragm. Such an example embodiment is described in the document DE-A-4 326 501, to which reference should be made for more information. 
     Naturally, in the light of this document, it can be seen that the false diaphragm can be replaced by a plurality of individual disengagement levers mounted so as to tilt or pivot on the cover by means fixing rings carried by the cover, with the intervention of two Belleville washers mounted in series in order to form engagement means. 
     In all cases, the cover  2  carries disengagement levers  42  mounted so as to pivot or tilt on the cover  2  and the engagement means can include two Belleville washers mounted in series as in the document DE-A-4 326 501 or a diaphragm mounted in series with an assistance washer as described in the document FR-A-9 711 058 of Sep. 5, 1997 published under the number FR-A-2 753 758, which also discloses a wear take-up device with a ratchet wheel, worm and set of teeth, of the type in the embodiment in FIG. 1 of the present invention. 
     Numerous clutches provided with a cover with stop lugs, possibly forming fixing lugs, are currently manufactured. 
     Here this type of cover is used for inserting a shim between the stop lugs and the disengagement levers in order to be able to supply to the car manufacturer or garage operator a new or reconditioned clutch mechanism in a delivery position in which the pressure plate is closer to the bottom  21  of the cover  2  than it is in the storage position when the disengagement levers are in abutment against the stop lugs. 
     More precisely, a support piece  8  carries at its external periphery fastening lugs  7  projecting radially towards the outside. The support piece  8  is in contact with at least a plurality of disengagement levers  42 , whilst the fastening lugs  7  are in contact with the face of the stop lugs  5  turned towards the disengagement levers  42  so that the fastening lugs  7  and the support piece  8  are inserted axially between the disengagement levers  42  and the stop lugs  5  by a mounting of the bayonet type. 
     In the figures, the support piece  8  has an annular shape and has means  9  for coming into engagement with a tool for turning the support piece. 
     These means  9  consist here of holes. The ring  8  forming the support piece extends radially below the stop lugs  5  and radially above the internal periphery of the fingers  42  of the diaphragm, close to the said internal periphery. 
     The ring is here closed whilst being in contact with all the fingers of the diaphragm  4 . The ring  8  has a great height so that it constitutes a centrally open circular plate. 
     Thus the lugs  8  are each introduced initially into a scallop  6  separating two consecutive stop lugs  5 . By pressing centrally on the ring  8 , the fingers of the diaphragm  4  are moved. Then the ring  8  is caused to turn, by means of a tool entering the holes  9 , in order to bring the fastening lugs  7  under the stop lugs  5 , and afterwards the load exerted on the ring  8  is released. The fastening lugs  7  are here circumferentially less broad than the trapezoidal-shaped stop lugs  5 . 
     More precisely, the fastening lugs  7  here have a roughly rectangular shape with rounded edges. The circumferential length of the lug  5 , longer circumferentially than high, is roughly equal to the circumferential length of the internal periphery of the stop lug  5 . The lugs  7  extend radially below the fixing lugs  26 . As a variant, the lugs  7  can have another shape, for example trapezoidal, triangular, semicircular or square. 
     The tool for turning the ring  8  has studs engaged in the holes  9 . 
     Naturally, the ring  8  can be open and thus not come into contact with all the fingers  42  of the diaphragm. It is, in this case, in the form of a circular arch. 
     The number of fastening lugs  7  depends on the application. Here one fastening lug  7  is provided per stop lug. Naturally, the number of fastening lugs  7  can be less than the number of stop lugs  5 . 
     At least two fastening lugs are provided in diametrically opposed positions. 
     Naturally, the holes  9  can be replaced by scallops or lugs formed at the internal periphery of the ring  8 . 
     In all the figures, the central part of the bottom  21  of the cover has the same shape and an arrow can be seen indicating the direction of rotation of the ring  8  during its removal. 
     The ring  8  is here in a single piece with the lugs  7  and is made of pressed sheet metal. 
     This ring can be provided with a coating with a low coefficient of friction at its portion intended to come into contact with the fingers  22  and at the external face of the lugs  7  turned in the direction opposite to the diaphragm. 
     The arrangement facilitates the rotation of the support piece  8 . 
     Naturally, the ring  8  can be made from another material, for example a composite material reinforced with fibres or based on aluminium. It can therefore be made of castable material. After mounting of the clutch mechanism on the reaction plate or a flexible disc fixed thereto the shim is removed by means of the aforementioned tool. 
     By virtue of the shim, the screws for fixing the cover  2  to the reaction plate can be shorter and the tongues are protected before fixing the clutch mechanism to the reaction plate. The support piece  8  with its lugs  7  constitutes a tool for mounting the clutch mechanism on the reaction plate, which is removed after the fixing of the cover to said reaction plate. The converse is possible so that this can constitute a removal tool for taking the friction linings off the pressure plate  1 . Here the shim makes it possible to provide, in the delivery position, the parts of a wear take-up device as well as the tongues  10 . 
     More precisely, in FIGS. 1 to  8 , the ring  8  with its single-piece lugs allows the mounting, without destruction, of a cartridge  30  belonging to a wear take-up device making it possible, in service, to compensate for the wear due principally to the friction lining or linings of the friction disc. The cartridge  30  is mounted on the cover  2  before fixing the pressure plate  1  to the cover. 
     More precisely, the diaphragm  4  is first of all fixed to the cover  2  by means of the fixing lugs  26  in the aforementioned manner, the diaphragm  4  being mounted so as to tilt between the two supports  24 ,  25 . Next the ring  8  with its lugs  7  is mounted in the aforementioned manner between the stop lugs  5  and the internal periphery of the fingers  42  of the diaphragm  4 . The diaphragm then occupies a plane position corresponding to that which it occupies once the clutch mechanism is mounted on the cover  2 . 
     In this position, the clutch is engaged. FIG. 7 depicts schematically at  100  the reaction plate, and at  101  the friction disc, or more precisely the friction linings thereof, makes it possible to reduce the axial bulk of the clutch mechanism, and the wear take-up device holds the diaphragm in this position, which corresponds to the position with clutch engaged new. Afterwards, the cartridge  30  is fixed and a prebalancing operation is carried out. 
     Then the pressure plate  1 , here carrying ramp means  32  and therefore of variable thickness, is brought closer as described below. 
     Next, the pressure plate  1  is mounted on the cover  2 . More precisely, the plate  1  being equipped with tongues  10 , the other ends of the tongues  10  are fixed to the cover  2 . 
     Finally, a balancing operation is finally carried out. 
     Here the cartridge  30  is mounted in a housing  20  formed as a thicker part, here by pressing, in the cover  2 , at its fixing flange  22 . The housing  20 , formed at the external periphery of the cover  2 , affects the flange  22  and the skirt  23  of the raised plate and at the level of the housings  20 . 
     The axial bottom of the housing  20  is formed by a transverse area  123  of the skirt  23  at the bottom  21  of the cover. A window  121  is formed in this area  123  parallel to the bottom  21  whilst being offset axially in the direction of the flange  22  with respect to the bottom  21 . 
     The number of tongues  10  depends on the application. Here three sets of tongues  10  placed one above the other are provided as well as three housings  20 . The housings  20  and the tongues  10  are distributed circumferentially in a regular manner, and in alternation. 
     Only one of the housings  20  is provided with a window  121 , namely the one serving to house the cartridge  30 . Each set of tongues  10  has at least two tongues  10  placed one above the other. Here three tongues  10 , elastically deformable axially, are provided per set of tongues  10 . 
     The cartridge  30 , described below, creates an imbalance. For this reason, before mounting the pressure plate  1 , a prebalancing is carried out by means of prebalancing rivets  201  mounted on the axial bottoms  123 , with no holes, of the housings  20 . Three rivets  201  are provided per housing  20 , not allocated to the housing in the cassette. Another prebalancing rivet  201 ′ is provided diametrically opposite to the cartridge  30 . This rivet  201 ′ serves to fix a set of tongues  10  to the cover  10 , as can be seen in FIG.  5 . The pressure plate  1  is notched locally at the level of the rivet  201 ′. All this is because the pressure plate is notched at the level of the cartridge  30  in order to create a step. 
     Finally, balancing rivets  202  are placed at the required points in order to balance the clutch mechanism. 
     The flange  22  has for this purpose, in advance, balancing holes  47  for mounting the balancing rivet or rivets  202 . To do this, numerous holes  47  must be provided for placing the rivets  202 . 
     The flange  22  also has on the one hand fixing holes  29  for the passage of members—such as screws or rivets—for fixing the flange  22  to the reaction plate, and on the other hand centring holes  48  for the passage of centring studs  148  (FIG. 7) carried by the cover. 
     Openings  129  are produced in the skirt  23 , at the level of the fixing holes  29  for the passage here of the heads of the screws for fixing the cover  2  to the reaction plate. 
     The openings  129  have a non-symmetrical shape. More precisely, they can be seen in dotted lines in FIG. 1, the size of a head of a fixing screw and of a balancing rivet  202 . The fixing  29  and balancing  47  holes are adjacent to each other. One pair of holes  29 ,  47  is provided per opening  129 , thus making it possible to increase the support surface of the flange  22  at this level for the heads of the fixing screws. The opening  129  is therefore elongated circumferentially and is deeper at the level of the hole  29 ; each of the holes  29 ,  47  being located at the circumferential end of an opening  129 . 
     Each balancing rivet  202  is fixed, like the fixing screws, at the level of a broadened area  122  of the flange  22 , formed by means of the opening  129 . 
     The rivet  202  does not project beyond the area  122 , whilst the heads of fixing screws project with respect to the areas  122 . Additional openings  203  are provided in the flange  22  above the housings  20 . 
     The flange  22  thus has three fixing areas  27  for contact with the reaction plate  100 , here slightly hollow in shape as can be seen in FIG.  7 . These areas  27  (FIG. 5) alternate circumferentially with the areas  28 , offset axially with respect to the areas  27  in the direction of the bottom  21  of the cover  2  for fixing, here by riveting, the tongues  10  to the cover. The skirt  23  is therefore open at this level, which allows the passage of fixing lugs  12 , which the pressure plate  1  has, projecting radially at its external periphery. The areas  27  serving for fixing the cover  2  are longer than the fixing areas  28  of the tongues connected continuously to the areas  27 , in order to form a canopy (FIG.  5 ). 
     The areas  27  are affected centrally by housings  20  whilst being less broad at this point. Each end of an area  27  is allocated a broadened zone  122  and an opening  129 . 
     The holes  29 ,  47  are therefore disposed, as well as the zones  122 , on each side of a housing  20  at the ends of a zone  122 . 
     This makes it possible to balance the clutch mechanism well. This is all the more so since, FIG. 3, the pressure plate is notched in order to create a recess for the cartridge  30 . This cartridge  30  has a U-shaped support  34  with a central web extending in contact with the deformation in the skirt  23  forming the top of the housing  20  and two lateral wings, which have holes for the passage of a shaft  35  fixed to a worm  36 , single-piece with a ratchet wheel  37  interposed between the two wings of the support  34 . The screw  36  is adjacent to one of the wings, whilst a helical take-up spring  38  is interposed between the ratchet wheel and the other wing. 
     The shaft  35  is attached to the inside of the screw  36  and the wheel  37 , for example by force fitting. 
     An elastic member  39  is mounted in contact with the internal face of the support web and the screw  36  and between the other wing of the support and the spring  38  (FIG.  8 ). 
     The elastic member  39 , less thick than the support  34  and metallic, has an oblique flange extended by a return carrying a control tongue  390  cooperating with the teeth on the ratchet wheel  37 , and with an actuator  410  formed by an external appendage of the Belleville washer  41  of the diaphragm. The return carrying the control tongue has a non-symmetrical shape since the shaft  35  is inclined. 
     The support  34  has three fixing lugs  34 ′, for fixing it by riveting respectively to the flange  22  and to the zone  123  and therefore to the cover. 
     The worm  36  is disposed tangentially with respect to a set of teeth  31  extending radially outwards in the opposite direction to the axis X—X of axial symmetry of the clutch mechanism and of the clutch. The set of teeth  31  belongs, according to the invention, to an intermediate piece  310 , here in the form of a washer. 
     The intermediate piece is here axially fixed overall. More precisely, each set of first tongues  10  has at least two tongues each provided with a protuberance  10   a  directed roughly radially outwards. These protuberances  10   a  have an end roughly in the shape of an annular sector. The washer  310  is gripped axially between two protuberances  10   a , as can be seen more clearly in FIG. 9, so that it is axially fixed overall since the protuberances  10   a  deform slightly axially because of their low radial height. 
     The protuberances  10   a  are located at the end by which the axially elastic tongues  10  are fixed to the cover. 
     Here the tongues  10  are not identical at the level of their fixing to the cover. The intermediate tongue of each set of first tongues  10  has no protuberance and consists of a conventional tongue. The other two end tongues each have a protuberance  10   a  deformed locally in order to come into abutment on the relevant lateral face of the intermediate washer  310 , thus interposed with predetermined clamping between the two protuberances  10   a , one of which is dished more deeply than the other. The washer  310  is metallic. 
     The washer  310  is connected, directly or indirectly, with respect to rotation according to the invention to a ring  330 , here metallic. In this embodiment the ring  330  is made of pressed sheet metal and has an axially oriented annular flange  33 , which here is connected with respect to rotation by a connection  340 ,  350  with cooperation of shapes with the intermediate washer  310 . This connection  340 ,  350  allows an axial movement of the ring  330  with respect to the washer  310  coming into engagement through its set of teeth  31  with the worm  36 . 
     The connection by cooperation of shapes is of the mortice and tenon type. The washer  310  here has at its internal periphery three mortices in the form of radially oriented notches  340  open radially towards the inside. The set of teeth  31  is formed at the external periphery of the washer  310  by means of a hollow therein (FIG.  2 ). 
     The ring  330  has a flange  33  in the form of a comb with three axially oriented lugs  350  passing through the notches  340 , with circumferential mounting clearance. 
     The intermediate washer  310  therefore meshes here rigidly with the ring  330 . Other types of meshing means can be provided. 
     For example, the washer can have at its internal periphery a set of teeth meshing with a set of teeth provided at the external periphery of the flange  33 . Each set of teeth can consist for example of flutes. 
     The ring  330  has overall in cross-section a U-shape whose external wing consists of the flange  33  with lugs  350  and whose internal wing is intended to be centred by the internal periphery of the studs  13  projecting axially and cast in one piece with the pressure plate. The wings of the ring  330  are axially oriented, the transverse bottom of the ring carrying the support means  3  and ramps. 
     More precisely, the ring is in intimate contact through its internal periphery with the external periphery of a thicker part divided into studs  13 , which the pressure plate has on its back projecting axially. The flange  33  is connected to a divided annular protrusion. This protrusion constitutes the support means  3  for the external periphery of the Belleville washer  41  of the diaphragm. 
     Radially, below the protrusion  3 , ramps  32  are provided for cooperating with the transverse end face, advantageously bevelled, of the studs  13  forming counter-ramps. Thus, in the event of wear, the diaphragm acts through its external actuator  410  on the control tongue  390  in order to cause the ratchet wheel to turn during the re-engagement operation in order to prime the spring  38 , the connection  340 ,  350  preventing a rotation in the reverse direction of the wheel  37  and therefore of the screw  36 , which can drive the set of teeth  31  but not conversely. When the spring  38  is sufficiently primed, the screw  36  can rotate the set of teeth  31  in order to cause the ramps  32  in contact with the studs  13  to turn, so as to increase the thickness of the pressure plate in order to compensate for the wear on the linings and the friction disc so that the diaphragm occupies the same position. 
     For more information, reference e should be made to the application FR-A-2 753 503 of Sep. 17, 1995. Nevertheless, it should be noted that, during engagement and disengagement operations, the ring  330  can move axially, with the pressure plate, with respect to the washer  310  able to move in rotation under the action of the screw  36 . No friction occurs between the screw  36  and the set of teeth  31  during these axial movements of the ring  330  since the washer  310  is overall axially fixed, here with respect to the cover by virtue of the protuberances. Thus this does not interfere with the wear take-up operation. The presence of a non-return catch is no longer necessary. 
     The shim  7 ,  8  therefore prevents damage to the cartridge  30 , or more precisely its elastic member  39  and its control tongue. 
     It should be noted that the fingers  42  have an internal end  45 , offset axially with respect to the zone  46  in which the fingers  42  are rooted in the Belleville washer  41 . This zone  46  is in the plane of the washer  41  and includes the orifices  44 . It is connected by an oblique portion  146  to the internal end  45  offset axially in the e opposite direction to the bottom  21  of the cover. 
     The ring  8  h as at its internal periphery a rim  85  directed axially in the opposite direction to the bottom  21  of the cover  2  for local contact with the internal end  45 . The lugs  7  are in the plane of the ring  8 . 
     Thus the lugs  7  bear against the internal face, directed towards the fingers  42 , of t he stop lugs  5  and the rim  85  is in contact with the external face of the internal end  45  of the diaphragm. 
     The shim  7 ,  8  therefore does not project axially with respect to the bottom  21  of the cover and the pressure plate is set back, so that the clutch mechanism is axially compact. 
     After fixing the cover  2  by screwing to the reaction plate  10 , the internal periphery of the ring  8  is pressed on, as for disengaging, and the ring is turned in the direction of the arrow in FIG. 1 in order to remove the shim  7 ,  8 . 
     The pressure plate  1  therefore carries the hollow ring  330 , ( 32 ,  33 ,  3 )—forming ramp means—and is of variable thickness between its friction face  11  and the support means  3  in order to compensate for the wear on the friction linings. 
     In all cases, the fixing lugs  7  are offset axially with respect to the internal periphery of the support piece  8 , formed by the flange  81  or the rim  85 . 
     Naturally, the ring  8  can be equipped with gripping means for rotating it by means of a tool in order to bring the fixing lugs below the stop lugs. 
     The ring  8  can, like a control button, be provided with a bar projecting in the opposite direction to the diaphragm. The means  9  can therefore consist of projections. In general terms, the circumferential length of a fixing lug  7  is less than the circumferential length between two consecutive stop lugs  5  so that the lugs  7  can be introduced into the scallops  6  so as to effect a bayonet mounting. 
     Openings can be provided between two consecutive fingers  42  forming disengagement levers for the passage of one or more tools affording access to screws for fixing the reaction plate to the crankshaft of the motor vehicle. In this case, the holes  9  in FIGS. 1 to  8  are opposite the said openings for removal of the reaction plate fixed directly or indirectly, for example by means of a plate or mass, to the crankshaft. 
     As mentioned above, the engagement means can have one or more Belleville washers mounted in series, the disengagement means can be distinct from the disengagement means. 
     The first tongues  10  can be radially oriented. 
     In all cases, the first tongues constitute means for rotatably connecting the pressure plate to the cover whilst allowing an axial movement of the pressure plate with respect to the cover. 
     The stop lugs, directed radially inwards, that is to say towards the axis X—X, can also be fixing lugs; the fastening lugs  7  then passing below the fixing means carried by the stop lugs during bayonet mounting. 
     The axial offset of the fastening lugs with respect to the internal periphery of the support piece facilitates bayonet mounting and creates a clearance between the fastening lugs and the disengagement levers. In addition, this prevents a deformation of the spring ring  125 , or in general terms of the secondary support  25 . 
     The disengagement levers  42  are, in all cases, in contact with the engagement means in direct abutment with the support means  3  or in indirect abutment on the support means  3  by means of the disengagement levers. The disengagement means act as required on the engagement means in order to counteract the action thereof. 
     As a variant, the engagement means can consist of a plurality of coil springs bearing on a false diaphragm and on the cover. 
     Naturally, the fastening lugs  7  can be attached fixedly to the support piece, for example by riveting, welding, etc. 
     As a variant, the rotational connection between the intermediate piece and the ring  330  is effected by tangential tongues, referred to as second tongues, coupled at one of their ends to the ring  330  and at their other end to the intermediate piece. 
     The second tongues allow an axial movement of the ring with respect to the intermediate piece, advantageously in the form of a washer. The friction between the ring  330  and the intermediate piece is thus eliminated. 
     Naturally, the intermediate piece can be made axially fixed by protuberances distinct from the tongues  10 . This piece is axially fixed with respect to the cover whilst being arranged inside it. 
     This piece is centred by the pressure plate. 
     In all cases, a strong gripping of the driving piece is prevented so that the latter can turn. It should be noted that the pressure plate centres the intermediate piece. 
     The scallops in the intermediate piece can be closed. 
     The set of teeth  31  can be formed directly at the external periphery of the intermediate piece, in the figures the set of teeth being formed in the bottom of a trapezoidal-shaped scallop produced at the external periphery of the intermediate piece. 
     In all the figures, the cover  2  and therefore the clutch mechanism is fixed by means of its fixing flange  22  or its skirt  23  to a driving flywheel fixed to the crankshaft of the vehicle engine, the said flywheel having a reaction plate and possibly being divided to form a torsion-damping flywheel—also referred to as a double-damping flywheel—or a flexible flywheel. 
     By virtue of the invention, the take-up spring  38  may not belong to the cartridge  30  and the intermediate piece can be elastically connected in rotation with the ring with ramps. This is because the take-up spring can be made to act between the intermediate piece  310  and the ring  330  with ramps  32  constituting an adjustment ring so that the engagement means  4  always occupy the same position when the clutch is engaged or clutched. 
     Thus, in the embodiment of FIGS. 10 to  14 , a take-up spring can be seen at  380 , of the coil spring type, bearing at one of the circumferential ends on a lateral edge  441  of a scallop in the form of a notch  440 , forming a mortice, provided at the internal periphery of the intermediate piece  310  in the form of a flat washer as in FIGS. 1 to  10 . The other end of the take-up spring  380  bears on the lateral edge  451  of an axially oriented lug  450  issuing in a single piece from the ring  330  with ramps  32 , constituting an adjustment ring with ramps  32  and support means  3  as in FIGS. 1 to  9 . The spring  380  acts on the other lateral edge of the lug  450  in abutment on the other lateral edge of the notch  440 . 
     The edges  451 ,  441  have an apex in the form of a triangle. The edge  451  extends opposite the edge  441  so that the take-up spring  380  is firmly held, the apexes of the edges  451 ,  441  entering the spring  380  in order to hold it firmly. The apexes of the edges  441 ,  451  extend in perpendicular planes. The other lateral edges of respectively the lug  450  and notch  440  are straight so that the straight lateral edge of the lug  450  comes into contact with the straight lateral edge of the notch  440  under the action of the spring  380 . 
     Naturally, according to one characteristic, the circumferential width of the axially oriented lug  450 , forming a tenon, is less than the circumferential width of the radially oriented notch  440  inside which are mounted on the spring  380  and the lug  450 . 
     The height of the lug  450  is less than the height of the notch  440 , as in the embodiment in FIGS. 1 to  9 . 
     Naturally, the number of lugs  450 , springs  380  and notches  440  depends on the application. By virtue of this arrangement the cartridge  30 , mounted in the housing  20 , is simplified since the ratchet wheel is adjacent to one of the wings of the support  34  having a high stop (not referenced) for limiting the movement of the control tongue  390  cooperating with the teeth on the ratchet wheel  37 . The circumferential bulk of the cartridge  30  is therefore reduced so that the housing  20  is of smaller size. The clutch mechanism is therefore easier to balance, the spring or springs  380 , lug or lugs  450  and notch or notches  440  being distributed in a regular manner. 
     The control tongue  390  is also simplified since the non-return catch is eliminated. It should be noted that in FIG. 12 the shaft  35 , the worm  36  and the ratchet wheel  37  are single-piece. As described in the document FR 98/01453 filed on Feb. 5, 1998 and published under the number FR-A-2 774 441, it can be seen that the cartridge  30  is inclined by means of bearings (not referenced) each having an inclined central hole, the wings on the support  34  being straight. This support is fixed solely by two rivets to the cover. The mounting of the assembly  35 ,  36 ,  37  with its bearings is effected by opening the passage holes produced in the wings of the support  34  and by closing the said holes partially, after mounting of the aforementioned assembly, by crimping in contact with the bearings, as can be seen in FIG. 31 of the aforementioned document FR 98/01453, to which reference should be made for more information. 
     In operation—clutch mechanism mounted on the driving flywheel—the friction lining or linings wear so that the diaphragm acts on the elastic member  39  in order to cause the ratchet wheel, the worm and the intermediate piece  310  to turn in order to prime the take-up spring or springs  380  which, during one or more operations of engagement or disengagement (declutching) of the clutch cause the ring  380  to turn by acting on the lugs  450 . Naturally this occurs when the spring or springs  380  are sufficiently primed to overcome the phenomenon of friction and when the load exerted by the diaphragm on the ring has decreased sufficiently. 
     Friction occurs between the straight edges of the lug  450  and of the notch  440 . 
     In order to reduce this friction, it is proposed, in FIGS. 15 and 16, to mount two take-up springs  380  and  381  by means of the notch  440 . The springs  380 ,  381  are mounted on each side of an axially oriented lug  550 , forming a tenon and replacing the lug  450  in FIGS. 10 to  14 . 
     The lug  550  is therefore in a single piece with the adjustment ring  330  with ramps. In this case, the two lateral edges  451  of the lugs  550  and the two lateral edges  441  of the notch  440  have a pointed shape in order to hold the coil springs  380 ,  381  internally. 
     The springs  380 ,  381  are therefore mounted in opposition under prestressing, one of the springs  380 ,  381  expanding, whilst the other is compressed without the appearance of any clearance. 
     By virtue of this arrangement, the movement of the ring  330  with respect to the intermediate piece  310  is facilitated, without noise and without direct contact of the lug  550  with the lateral edges of the scallop  440 . In addition, the torsion vibrations are damped and the friction is reduced. 
     In a variant, FIGS. 17 and 18, the springs can be inclined in opposition,  380   381 . In this case, the notch  440  is identical to that in FIG.  16 . The lug  650  issuing from the adjustment ring is modified. The lateral edges  551  of this lug have a pointed shape in order to internally hold the springs  380 ,  381  mounted under prestressing. 
     Here the edges  551  are inclined so that the lug  650  has a trapezoidal shape with lateral edges  551  with a projecting point for holding the springs  380 ,  381 . 
     By virtue of the inclination, an axial component is obtained forcing the one hand the intermediate piece in the direction of the pressure plate  1  and the protuberances  10   a  and on the other hand the ring  330  in the direction of the diaphragm. 
     This can be taken advantage of in order to omit the protuberances  10   a  on the tongues  10  closest to the diaphragm  4 . 
     The intermediate piece no longer has any need to be gripped, its axial holding is effected by virtue of the springs  380 ,  381  axially forcing the intermediate piece in the opposite direction to the bottom of the cover  2  and the ring  330  in contact with the diaphragm  4 . 
     Under these conditions, the protuberances  10   a  in the previous figures can be replaced with stop pieces  10   b  (FIGS. 19 to  21 ) which are rigid and distinct from the first tongues  10  thus simplified. 
     The stop pieces  10   b  are fixed to the cover by the same rivets for fixing the first tongues  10  to the cover  2 . The pieces  10   b  are in the form of an annular sector at their internal periphery. As will have been understood, the thickness of the sub-assembly consisting of ring  330 , springs  380 ,  381  and intermediate piece  310  decreases when the sub-assembly is mounted between the stops  10   b  and the diaphragm so that the ring is always in contact with the diaphragm. 
     In FIGS. 15 to  21 , the ring  330  is rotatably connected to the intermediate piece  310 , in the form of a ring or washer, by an elastic connection, by means of springs  380 ,  381  allowing an axial movement of the ring with respect to the intermediate piece. 
     As a variant, this connection can be effected by means of second axially elastic tongues allowing an axial movement of the ring  330  and permitting the formation of an assembly which can be handled and transported. 
     In a first embodiment, the second tongues  200  have a shape identical to the first tongues  10 . It is therefore possible to use tongues of the standard type of a clutch mechanism of smaller size. 
     These tongues are therefore tangentially oriented overall and are fixed by means of fixing members at one of their ends to the adjustment ring  330  with ramps  32  and to the intermediate piece. 
     According to one characteristic the intermediate piece  310  and the ring  330  with ramps come from the same metal blank. 
     Thus, starting from a pressed metal sheet, the latter can form the ring  330  with ramps  32 , and then the intermediate piece  310  is cut out, which thus surrounds the ring  330  without loss of material. This embodiment is therefore simple and economical. 
     It also makes it possible to centre the intermediate piece  310  with respect to the cover. 
     Thus in FIGS. 22 to  28  it can be seen that the intermediate piece  310  is a form of ring or washer provided at its external periphery with an axially oriented annular flange  311  interrupted by the set of teeth  31 . This flange  311 , possibly divided into lugs, is in intimate contact at its external periphery with the internal periphery of the skirt  23  of the cover  2  so that the intermediate piece  310  is centred at its external periphery with respect to the cover  2 . 
     The tongues  200  are here fixed by riveting to brackets  312  on the intermediate piece  310  and to the ring  330 , so that the pressure plate which is simplified because it no longer needs to be machined in order to form a centring surface for the ring  330 . This is because, by virtue of the second tongues  200 , axially elastic and tangentially oriented, the ring is centred with respect to the intermediate piece  310  surrounding the ring  330 . Naturally in a variant the second tongues  200  can be curved in shape, that is to say in the form of an arc of a circle. 
     Brackets  312  are formed at the internal periphery of the intermediate piece  310  in the form of a ring. A clearance can be seen around the brackets  312 , resulting from the final cropping of the intermediate piece. The ring  330  therefore has cutouts  313  at its external periphery in order to form the clearance around the brackets  312  and thus prevent interference, in particular with the rivets fixing the tongues. 
     By virtue of the divided support means  3 , the heads of the fixing rivets  314 , located between two annular sectors in the form of protrusions on the support means  3 , do not extend in axial projection with respect to the ring  330  and therefore do not come into contact with the diaphragm. 
     In FIG. 22 a rigid stop piece  10   b  can be seen, identical to that in FIG. 20, except that in FIG. 22 the piece  10   b  forming a stop is not in contact with the cover but with the head of the rivet fixing the set of tongues  10  to the edge  22  of the cover. 
     In the two figures, the piece  10   b  has a peripheral part in the form of an inclined lug, connected by a fold to a central part in the form of a shoe, that is to say in the form of an annular sector for contact with the annular part of the intermediate piece  310 . The peripheral part is thus offset axially with respect to the central part by means of the fold parallel to the set of first tongues by virtue of the inclination of the lug. The central part of the piece  10   b  extends without the set of tongues  10  and by virtue of the fold, the piece  10   b  is locked with respect to rotation by the tongues  10  (FIG.  28 ). 
     The second tongues  200  are fixed to the intermediate piece roughly radially below the fixing of the first tongues  10  to the pressure plate  1 . 
     The number of first and second tongues  10  depends on the application. Here the second tongues  200  are located radially below the first tongues and alternate circumferentially with the central part of the pieces  10   b . Between two housings  20 , there is therefore a set of first tongues  10  and radially below the central part of the stop  10   b  and a set of second tongues  200 . 
     In order to have a tangent contact between the worm  36  and the set of teeth  31  the axis of the screw is inclined as described in the aforementioned document FR 98/01453. 
     In this document, a problem is also posed since the screw is not tangent with respect to the set of teeth  31 , which is desirable from the efficiency point of view. 
     To do this, the support  34  of the cartridge  30  carries a protrusion  341  able to cooperate with the contour of the housing  20 . 
     The protrusion  341  is formed, in line with the screw  36 , in the central web of the support  34  with a U-shaped cross-section. 
     The protrusion  341  cooperates with the internal periphery of the axially oriented apex of the housing  20  with a U-shaped cross-section overall. Naturally, the structures can be reversed, the protrusion being formed on the apex, constituting the central web of the housing  20 . 
     As a result, compared with the embodiment in FIG. 1, the two fixing lugs  34 ″,  34 ′, disposed on each side of the central fixing lug  34 ″, as can be seen in FIG. 28, have non-aligned centres. More precisely, use is made of the holes, for the passage of rivets fixing the fixing lugs, for fixing a normal cover in FIG.  1  and by virtue of the protrusion  341  the cartridge  30  is inclined to make the screw tangent to the set of teeth. As a variant new holes are created for a tangent contact of the screw with the set of teeth. 
     The support  34  is fixed here by riveting of the lugs  34 ,  34 ′,  34 ″ to the cover. Naturally, the intermediate piece  310  may not surround the ring  330  (FIGS. 29 to  32 ) and extend radially below the external periphery of the ring  330 . 
     The second tongues  200  act, as in FIGS. 22 to  28 , between the ring  330  and the piece  310  in order to rotatably connect the ring  330  to the piece  310  with the possibility of axial movement. 
     The tongues  200  are fixed at one of their ends, here by rivets  315 , to the piece  310 , and at their other end, here by rivets  314 , to the ring  330 . 
     More precisely, the second tongues  200  have a curved shape, in the form of an arc of a circle, whilst being axially elastic, and are fixed by means of rivets  314  to a lug  331  on the ring  330 . 
     The lugs  331  extend between two sectors of the support means  3  whilst projecting radially outwards with respect to them. 
     Axially, the lugs  331  are offset axially towards the piece  310  and the plate  1  with respect to the support means  3 , as in FIGS. 22 to  28 , so that the heads of the rivets  314  do not interfere with the diaphragm. 
     The piece  310  is dished locally at the level of the rivets  315  (FIG. 31) so that the said rivets  315  do not extend in axial projection with respect to the face of the piece  310  turned towards the plate  1 . 
     The piece  310  is therefore dished locally axially in the direction of the ring  330  for the fixing of the rivets  315 . 
     In all cases, the piece  310  has a step at the level of the set of teeth  31  as well as an axially oriented annular flange extending at one of its external and internal peripheries. In FIGS. 22 to  28 , the said flange  311  extends at the external periphery of the piece  310  for centring thereof with respect to the skirt  23  of the cover. 
     In FIGS. 29 to  32 , the flange  321  extends at the internal periphery of the piece  310 . The flange  311 ,  321  stiffens the intermediate piece. 
     In FIGS. 29 to  32 , the ring  330  has, as in FIGS. 1 to  9 , an annular flange  333  at its internal periphery. This flange  333  is axially oriented and cooperates through its external periphery with the internal periphery of the thicker part of the pressure plate carrying the studs  13  forming counter-ramps. 
     In FIGS. 22 to  28 , the ring  330  has no such flange since it is centred by means of the flange  311  on the intermediate piece. In FIGS. 22 to  32 , the intermediate piece  310  is offset axially with respect to the ring  330 , in the direction of the pressure plate  1 . 
     Naturally, the stops  10   b  can be joined together in order to form a ring and the take-up spring can be integrated into the second tongues. 
     In the light of FIGS. 31 and 32, it can be seen that the intermediate piece  310  in the form of a ring is stiffened circumferentially by the ribs  316  each extending between two consecutive fixing rivets  315 . It should be noted that the rivets  314  are located between two consecutive protrusions on the support means  3  and that the tops of the ramps  32  are located radially below protrusions, in the middle thereof, in order to stiffen the ring subjected to the action of the diaphragm. 
     It may be desirable to reduce the axial bulk of the clutch mechanism. It may also be desirable to simplify the intermediate piece  310  and the ring  330  with ramps. It may finally be desirable to reduce the axial bulk of the pressure plate  1 . 
     To do this, in FIGS. 33 to  37 , the diaphragm  4  is shaped so that its internal periphery is offset axially in the direction of the pressure plate with respect to its external periphery. 
     Thus the fingers  42  of the diaphragm have an external periphery  42   a  in the plane of the Belleville washer  41  of the diaphragm and an internal periphery  42   b  offset axially in the direction of the pressure plate  1  with respect to the external periphery  42   b . A sinuous connecting portion  43   b  connects the peripheries  42   a ,  42   b  together. By virtue of this arrangement, the axial dimension between the engine and gearbox is reduced since the internal periphery  42   b  of the fingers enters the pressure plate  1  during the maneuvering of the clutch in order to disengage it. 
     The adjustment ring  330  is simplified since it has no flange at its external and internal periphery. The ring  330  has at its centre a pointed shape divided in order to form support means, in the form of an annular protrusion, for the diaphragm. 
     The ring  330  is connected by second tongues  200  to the intermediate piece  310  with a flat shape and therefore a simplified shape. 
     The axial retaining stop of the piece  310  consists of radial extensions  10   c  of the ends of the first tongues  10  to the areas  28  of the cover. The lateral edges of these areas  28  are connected together by a bridge  20 ′ extending above the tongues  10  so that the cover is stiffened. 
     By virtue of the extensions  10   c , the stop pieces  10   b  in FIGS. 22 to  32  are eliminated, which makes it possible to reduce the axial bulk of the clutch mechanism, as well as the number of parts. 
     In order to reduce the axial bulk still further, the pressure plate  1  is notched at  210 , at the level of its rear face, so that the extensions  10   c  enter the notches  210  without interference. In FIGS. 38 to  41  the cartridge  30  is inclined so that the worm is tangent to the set of teeth  31  as in the embodiment in FIGS. 22 to  28 . Thus the fixing lugs  34 ″,  34 ′ disposed on each side of the central lug  34 ″ have non-aligned centres. The intermediate piece  310  and the ring with ramps  300  have a configuration of the type in FIG. 29 with stiffening flanges  321 ,  333 . In this embodiment in FIGS. 38 to  41  second tongues are used. These second tongues  300  have a supplementary function. More precisely, at least one set of second tongues  300  is circumferentially elastic. This set, here of two tongues placed one on top of the other (FIG.  41 ), replaces the take-up spring so that the cartridge  30  is simplified since it has no such spring. 
     The cartridge  30  is therefore less bulky, as more clearly visible in FIG. 38, so that it is more economical particularly because its support requires less material. 
     Here all the sets of tongues  300  are circumferentially elastic and naturally axially elastic. To do this the second tongues  300  have at least one fold, here in the form of a corrugation. Here the tongues  300  are folded like a concertina, the number of folds depending on the application and the required circumferential elasticity. 
     In this embodiment the tongues  300  have corrugations of different magnitudes (FIG.  38 ). 
     In this way the number of parts is reduced because of the elimination of the take-up spring in the cartridge  30 . In addition the risks of jamming are reduced because several sets of second tongues  300  are provided so that the ring  330  can turn during a wear take-up operation in a sure fashion. To reduce still further the number of parts, the stop pieces are joined together in order to form a stop ring  10   d  with lugs for fixing to the areas  28 . This ring  10   d  serves as a support for the intermediate piece  310  and replaces the sectors  10   b . As can be seen in FIG. 38 the support for the cartridge  30  has two high stops for limiting the movement of the elastic member  39 , extending below the central web of the U-shaped support  34 . The high stops are produced by 90° folds extending in the bottom part of the lateral wings of the supports, these stops being adjacent to the bottom of the cover. 
     The elastic member  39  extends below the central web of the support whilst being in contact with the bottom face of the said web. 
     In the previous figures the intermediate part has an annular shape but naturally the intermediate piece  310  can be reduced to a toothed sector  31  connected by a second elastic tongue to the ring with ramps. Such an assembly consisting of second tongue  400  and toothed sector  310  is visible in FIGS. 42 and 43. 
     This arrangement improves the meshing of the worm  30  and set of teeth  31  at a high speed of rotation since the sector  310  is elastically connected to the cover by the curved-shaped tongue  400  (in the form of an annular sector). 
     This arrangement can block the wear take-up at very high rotation speeds in order in particular to eliminate excessive take-up related to vibration at very high speeds of rotation. In these figures the intermediate piece is elastically suspended by means of the second tongue. 
     In the previous figures a single housing  20  was used for mounting the cartridge  30 . 
     In FIGS. 44 to  47  the other two housings are used for mounting pieces  10   f  forming an axial stop for the intermediate piece  310 . The piece  10   f  centres the intermediate piece  310 , which for this purpose is in intimate contact through its external periphery with the internal periphery of an axially oriented portion which each piece  10   f  has in the form of a hook for axially retaining the intermediate piece. 
     The pieces  10   f  therefore have a radially oriented stop portion radially directed towards the inside for contact with the face of the intermediate piece  310  directed in the opposite direction to the bottom of the cover. 
     The stop pieces  10   f  are therefore in the form of an angle bracket. Here each piece  10   f  has a fixing lug connected to the free end of the axial portion of the piece  10   f . The fixing lug extends radially overall towards the outside and is fixed to the bottom  123  of the housing  20  by at least one rivet, which is here a rivet, which is here a balancing rivet  201 ′. The housings  20  are here all identical so that the bottoms  123  are provided with a window. The pieces  10   f  also form balancing masses. The lateral wings of the support  34  each have a lug  10   e  directed radially towards the inside in order to serve as an axial stop for the intermediate piece in association with the pieces  10   f . The support  34  therefore has an additional function, and this in a simple and economical fashion. In this embodiment the housings are used for mounting the axial stops  10   f ,  10   e  for holding the intermediate piece  310 . One of the high stops has been referenced at  10   g , the support in FIG. 42 being identical to that in FIGS. 44 to  47 . 
     In all cases the intermediate piece is in rubbing contact with at least one axial stop  10   a ,  10   b ,  10   d ,  10   f ,  10   e  axially retaining the intermediate piece in one direction, namely in the direction going from the bottom of the cover  2  to the pressure plate  1 , the intermediate piece  310  being in contact with the face of the said stop turned towards the bottom of the cover. 
     In the other axial direction the other intermediate piece is either retained by an extension  10   a  (FIG.  9 ), or by the diaphragm via the ring  3  and the second tongues. 
     In all the figures the elastic member is located radially below the central web of the U-shaped support  34 . 
     As a variant the elastic member  39  is located radially above the support  34  whilst being in contact with the top face of the central web  134  of the support  34 , which makes it possible to extend the control tongue  390  of the elastic member  39 . A radial clearance exists between the housing  20  and the member  39  fixed by riveting to the central web  134  of the support  34 . 
     More precisely the radial clearance exists between the deformation of the skirt of the cover forming the top of the housing (see FIG. 3) of the cartridge  30 , and the rivet  234  for fixing the member  39  is made by extrusion of the web  134  so that it extends in projection with respect to the member  39  over a small height e (FIG.  48 ), which is advantageous for reducing the bulk. 
     In this FIG. 48 it can be seen that the distance h is well controlled when the clutch is engaged. The elastic member is therefore fixed at two points, namely at the level of the central lug  34 ′ and fixing of the support  34  and at the level of the rivet  234 . 
     The shaft  35  is provided, in the embodiment in FIGS. 48 to  51 , with a cylindrical head  135 , a barrel  235  with a diameter D less than that of the head  135  and an end tail  335  with a diameter less than that of the barrel  235 . The assembly consisting of worm  36  and ratchet wheel  37  is mounted so as to slide along the barrel  235  extending axially between the two wings  334  of the support  34 . The take-up spring  38  is mounted around the barrel  235  and bears on the head  135  passing for this purpose through a hole  336  in the relevant wing  334 . The shaft  35  is locked axially on the other wing  334  by virtue of its tail  335  bearing through its shoulder, formed by means of the change in diameter of the connection of the tail  335  with the barrel  235 , on the internal face of the flange  334  and through the end of the tail  335 , which is crushed after the tail  335  passes through an opening  335  produced in the said flange. Naturally the diameter of the opening  337  is less than that of the opening  336 . 
     The take-up spring  38  is calibrated, that is to say prestressed accordingly in order to keep the screw  337  in abutment on the adjacent wing  334 . Thus, in this embodiment, the assembly consisting of wheel  37  and screw  36  is slipped onto the barrel  235  and the spring  38  no longer bears on the adjacent wing  334  so that the said wing has no need to be treated. In addition the elastic member  39  is simplified and has a greater length. For more information on the prestressing of the take-up spring  38 , reference should be made to the document FR 98 16456 filed on Dec. 29, 1998. This prestressing makes it possible to have a relative movement between the screw  36  and the set of teeth  31  only during a wear take-up operation, which makes it possible to reduce wear. When the control tongue  39  has skipped a tooth on the ratchet wheel  37 , the assembly consisting of ratchet wheel  37  and worm  36  is caused to turn only during the operation of reclutching or re-engaging the clutch. During this phase the spring  38  remains under prestressing, this being such that the spring  38  is not compressed overall. During an operation of disengaging the clutch the screw  36  cannot turn because of the spring  38 . 
     Naturally all combinations are possible. 
     It should be noted that the pressure plate has a recess flat at the level of the cartridge  30 , as can be seen for example in FIG. 42, and that the set of teeth  31  is located in the bottom of a recess or scallop in the intermediate piece  310  so that the set of teeth extends radially below the external periphery of the intermediate piece. All this is designed so that the worm  36  comes into engagement in a sure manner with the set of teeth  31  whilst reducing the transverse bulk. 
     In FIG. 30 it is possible to protect the second tongues  200  when the sub-assembly consisting of intermediate piece  310 , tongues  200  and ring with ramps  330  is not yet mounted within the clutch. To do this it suffices to mount removable clips  1000  on the ring  330  and the intermediate piece  310 . 
     It should be noted that the balancing pieces  10   f  in FIG. 44 are fixed by three rivets  201 ′ to the bottom  123  of the housing  20 . The pieces  10   b , in a variant, are connected together at their internal periphery in order to form a ring extended at its external periphery by lugs for fixing to the cover. In this case the end of the tongues, intended to be fixed to the cover, are interposed between the lugs on the ring  10   b  and the cover, here areas thereof. All combinations are possible, and thus in FIG. 9 at least one of the protuberances  10   a  can be replaced by a rigid piece  10   b  of the type in FIG.  22 . 
     In the embodiment in FIGS. 48 to  51 , a protrusion of the same type as the protrusion  341  in FIG. 38 can be provided. In FIG.  38  and in these FIGS. 48 to  51  it is possible to provide, on the other side of the lug  34 ″, a second protrusion on the central web of the support. This second protrusion, depicted at  341 ′ in FIG. 52, can be less high than the protrusion  341 . Thus, under the effect of centrifugal force, this second protrusion is allowed to come into contact with the internal periphery of the top of the housing  20 . The protrusions  341 ,  341 ′ are advantageously obtained by pressing. The cartridge in FIGS. 48 to  52  is therefore particularly economical. 
     As a variant, instead of having lugs  34 ′ and  34 ″ which are different as in FIG. 40, it suffices to incline the bottom  123  of the housing so that the worm is tangent to the set of teeth  31  forming a rack, whilst having a cartridge  30  with lugs as in FIG.  8 . 
     The high stop or control stop for the tongue  390  can come from the cover  2 , as described in the document FR 98 165 47 filed on Dec. 29, 1998. 
     By virtue of the second tongues, a sub-assembly mounted under prestressing between the diaphragm and the stop or stops is formed with the intermediate piece and the ring with ramps. 
     By virtue of the prestressing of the tongues the thickness of this sub-assembly decreases when it is mounted between the diaphragm and the stop or stops. The ring is always in abutment on the diaphragm.