Abstract:
The invention concerns a wear take-up mechanism comprising a housing ( 10 ) borne by the cover ( 52 ) and ramp means ( 54 ) set between the means ( 14 ) supporting the clutch shifting means and a pressure plate ( 51 ). The cassette has two side wings ( 65, 66 ) each provided with a hole ( 61 ), said holes ( 61 ) being axially offset mutually for mounting a rotating endless screw ( 63 ) capable of driving in rotation the ramp means ( 54 ) and extended by a pin ( 67 ). The invention is applicable to motor vehicles.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a friction clutch, notably for a motor vehicle, and relates more particularly to a clutch equipped with a device for compensating for the wear due notably to the wear on at least one friction lining, the said device, referred to hereinafter as a wear take-up device, operating gradually as the wear occurs on the said lining or linings. 
     It relates to the friction clutch mechanisms which such a clutch has. 
     2. Description of the Related Art 
     A conventional friction clutch generally has a reaction plate forming part of an engine flywheel, possibly in two parts in order to form a damping flywheel or a flexible flywheel, fixed with respect to rotation to a first shaft, usually a driving shaft such as the crankshaft of the internal combustion engine, and supporting, through its external periphery, a cover to which at least one pressure plate is attached with axial mobility. 
     The pressure plate is fixed with respect to rotation to the cover and the reaction plate whilst being able to move axially under the action of axially acting engagement means controlled by disengagement means. The disengagement means can consist of helical springs, or two Belleville washers mounted in series, subject to the action of disengagement levers forming the disengaging means. 
     Generally, the engaging and disengaging means form part of the same piece, for example a metallic diaphragm bearing on the cover; the diaphragm can be mounted in series or in parallel with a Belleville washer in order to provide assistance for the disengagement force. 
     A friction disc, carrying friction linings at its external periphery, fixed with respect to rotation to a shaft, usually a driven shaft such as the gearbox input shaft, is interposed between the pressure plate and the reaction plate so as to be gripped between them when the clutch is in the engagement position in order to transmit the torque from the driving shaft to the driven shaft. 
     Conventionally, the friction linings are mounted on an axially elastic support coupled rigidly or elastically to a hub fixed with respect to rotation to the driven shaft. By virtue of this arrangement the friction disc assists the diaphragm during the operation of disengaging the clutch. As a variant, the support is rigid whilst for example being embedded at its external periphery in a single friction lining. 
     Conventionally, the engaging means, the cover and the pressure plate form part of a unitary assembly referred to as a friction clutch mechanism. 
     The engaging means control the axial movement of the pressure plate when they are actuated by a clutch release bearing by means of disengaging means. 
     The clutch release bearing can be controlled mechanically, hydraulically or electrically. The control can be of the manual, automatic or semi-automatic type. 
     During the service life of such a clutch, the friction lining or linings, as well as the counter-materials, pressure plate and reaction plate, wear, which causes a variation in the position of the pressure plate and that of the axially acting engaging means and of the clutch release bearing, resulting in a variation in the clamping force between the friction disc on the one hand and the pressure and reaction plates on the other hand, because of the changes in the working conditions of the engaging means, and the force necessary for disengaging is affected thereby. By providing such a clutch with a wear take-up device, these drawbacks are avoided, the engaging means, and the clutch release bearing, usually in continuous abutment on the disengaging means, occupying the same position when the clutch is in the engagement position so that the axial dimension of the clutch is reduced. 
     In the document FR 96 11297 filed on Sep. 17, 1996 and published under the number 2 753 503, the wear take-up device has, in FIGS. 21 to  26 , a unit comprising, in a unitary fashion, a U-shaped support with a web and two lateral wings each provided with a hole for supporting at least one shaft carrying a worm, a ratchet wheel and a helical spring. The support also carries an elastic member provided, on the one hand, with a control tongue and on the other hand with a non-return catch. 
     The control tongue is able to be maneuvered by an actuator forming part of the engaging means of the clutch and cooperates, as well as the catch, with the teeth on the ratchet wheel. 
     The worm cooperates with the teeth of a set of teeth fixed with respect to rotation to the ramp means placed between the abutment means of the engaging means and the pressure plate. The worm cooperates with the set of teeth and with means of driving in rotation, comprising the helical spring forming a take-up spring, which are made operational by the wear on the friction linings when the clutch is engaged. The worm is mounted tangentially with respect to its associated set of teeth. 
     It is desirable to improve the cooperation of the worm with the set of teeth. 
     The object of the present invention is to meet this requirement simply and economically. 
     According to the invention a clutch mechanism of the type indicated above is characterised in that the holes in the wings are offset axially with respect to each other. 
     SUMMARY OF THE INVENTION 
     Thus it is possible to incline the shaft and therefore the worm. 
     Preferably the shaft is inclined at an angle equal to that of the worm thread. The inclination depends on the angle of the worm. 
     More precisely, the profile of the worm, notably the thread thereof, moves roughly parallel to the flanks of the teeth of the set of teeth. The face of the thread is therefore roughly parallel to the opposite flank of the tooth. 
     By virtue of the invention, the risks of jamming between the worm and the set of teeth fixed with respect to rotation to the ramp means are eliminated. 
     In addition, a good contact area is obtained between the worm and the set of teeth, whose teeth are thus straight. 
     The efficiency of the wear take-up device is high. 
     Certainly, it would have been possible to directly incline the unit but this would have increased the bulk thereof and therefore increased the size of the housing produced in the cover for mounting the unit. 
     By virtue of the invention the size of the unit remains roughly the same. In addition the support is not greatly modified. 
     The solution is therefore simple and economical. 
     In a first embodiment the wings are twisted so as to have inclined areas perpendicular to the shaft. 
     The twisting is simple to effect and is economical. In addition the number of parts is not increased. 
     In another embodiment the wings are not twisted so that the support is not modified. 
     The inclination is effected by means of bearings whose central hole is inclined. The bearings are mounted in the holes in the wings. 
     The holes are advantageously blind at the start and then subsequently closed off partially by crimping tongues in contact with the bearings for automatic mounting and/or formation of a single piece, shaft—worm—ratchet wheel. As a variant, the holes are closed by supplementary pieces fixed to the wings of the support, or by bonding or welding of the bearings to the edges of the blind holes. 
     According to the required inclination of the worm, the teeth of the ratchet wheel cooperating with one end of the control tongue and a non-return catch which the elastic member has are also inclined. 
     By virtue of this arrangement the free end of the control tongue extends parallel to the teeth of the ratchet wheel and the non-return catch is twisted, because of its offset with respect to the control tongue, so that its free end is parallel to the teeth. 
     Thus, in spite of the inclination of the shaft, there is a good transmission of forces between the engaging means and the ratchet wheel, and the non-return catch has a large area of contact with the teeth of the ratchet wheel. 
     By virtue of the invention, in spite of the inclination of the shaft, parallel faces are worked with, the thread of the worm being roughly parallel to the flanks of the teeth of the set of teeth, whilst the free ends of the catch and of the control tongue are parallel to the teeth of the ratchet wheel. The holes in the wings are not necessarily the same size. 
     For example, the shaft can have a portion with a reduced diameter passing through a hole of reduced size formed in one of the wings and immobilised axially by means of an elastic washer. 
     A cylindrical extension of the worm passes then through the other larger hole in the other wing. 
     The elastic member has a return carrying the control tongue at its centre. 
     According to one characteristic the return has on each side of the tongue first and second portions with different heights. 
     This return has a non-symmetrical shape, the first portion being opposite the screw and at a height less than that of the second portion located opposite the helical spring. 
     The return is thus mechanically strong. 
     This strength is increased by the fact that the control tongue is provided with an oblong-shaped reinforcing dished part. The dished part is also in the line of transmission of forces between the engaging means of the ratchet wheel, which is favourable to the driving of the ratchet wheel. 
     This wheel has teeth inclined according to the thread of the worm. 
     The control tongue and non-return catch, whose free ends are inclined, operate under very good conditions. 
     Thus, in the event of wear on the linings, it is possible to cock the helical spring adequately and then, subsequently, this spring, during the disengagement operation, can suitably drive the ramp means. 
     Naturally, the support can be in a single piece with the cover and be produced by means of a U-shaped deformation produced at the external periphery of the cover in order to form a housing for the elastic member and the worm mounted on its shaft. 
     As a variant, the support consists of the elastic member. 
     Naturally, the unit may have no take-up spring. This spring can be located between the ramps and counter-ramps of the wear take-up device, as described in the document FR-A-2 606 477. 
     The ramp means can be in a single piece with the set of teeth. As a variant, the set of teeth belong to an intermediate piece connected with respect to rotation to the ramps able to move axially with respect to the intermediate piece overall, axially fixed with respect to the cover. 
     For example, the intermediate piece is gripped between extensions issuing from a set of first tongues rotatably connecting the pressure plate to the cover. 
     As a variant, the intermediate piece is connected to the ramps by second tongues, of the same type as the first tongues, allowing axial movement of the ramps with respect to the intermediate piece. For more information reference should be made to the document FR-98 11991 filed on Sep. 23, 1998. As a result the elastic member may have no non-return catch. 
     The wear take-up device has, by virtue of all these provisions, high efficiency and a long service life. 
     In order to give a better understanding of the object of the invention, a description will now be given, by way of purely illustrative and non-limitative example, an embodiment depicted in the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a clutch equipped with a wear take-up device according to the invention, with local cutaways to show the set of teeth of the ramp means and the tangential tongues; 
     FIG. 2 is a view in section along the line A—A in FIG. 1; 
     FIG. 3 is a view in section along the line B—B in FIG. 1; 
     FIGS. 4,  5 ,  6  are views to a larger scale in the direction respectively of the arrows C, D, E in FIG. 1; 
     FIG. 7 is a view to a larger scale of the inset T in FIG. 2; 
     FIG. 8 is a view in perspective of the wear take-up unit; 
     FIG. 9 is a view in perspective in the direction of the arrow  9  in FIG. 8; 
     FIG. 10 is a view in the direction of the arrow  10  in FIG. 8; 
     FIG. 11 is a view in section along the line  11 — 11  in FIG. 10; 
     FIG. 12 is a view in section along the line  12 — 12  in FIG. 11; 
     FIG. 13 is a view of the support for the unit in the direction of the arrow  10  in FIG. 8; 
     FIG. 14 is a view of the worm—ratchet wheel assembly; 
     FIG. 15 is a view in perspective of the elastic member carried by the support; 
     FIG. 16 is a view in the direction of the arrow  16  in FIG. 15; 
     FIG. 17 is a view in perspective of the ramp means of the wear take-up device; 
     FIGS. 18 and 19 are views similar to FIGS. 10 and 12 for a second embodiment of the unit with inclined shaft; 
     FIGS. 20 and 21 are views similar to FIGS. 10 and 12 for a third embodiment of the unit with inclined axis; 
     FIG. 22 is a partial view showing, in the context of the third embodiment, the hole in a support wing of the unit receiving its bearing before the latter is fixed; 
     FIG. 23 is a view similar to FIG. 2 for a fourth example embodiment; 
     FIG. 24 is a view similar to FIG. 13 for this fourth example embodiment; 
     FIG. 25 is a view in section along the line  25 — 25  in FIG. 24; 
     FIG. 26 is a view of the support in the direction of the arrow  26  in FIG. 23; 
     FIG. 27 is a partial view with local cutaway in the direction of the arrow  26  in FIG. 23; 
     FIGS. 28 to  30  are views similar respectively to FIGS. 9,  10  and  7  for a fifth example embodiment; 
     FIG. 31 is a view in the direction of the arrow  31  in FIG. 28; 
     FIGS. 32 and 33 are views similar to FIGS. 6 and 9 for a sixth example embodiment, part of the ramp means being depicted in FIG. 32; 
     FIG. 34 is a view similar to FIG. 6 for a seventh example embodiment; 
     FIG. 35 is a view of the elastic member alone in FIG. 34; 
     FIG. 36 is a view similar to FIG. 32 for an eighth example embodiment; 
     FIG. 37 is a perspective view of the elastic member of FIG. 36; 
     FIG. 38 is a view similar to FIG. 7, for a ninth example embodiment; 
     FIG. 39 is a view similar to FIG. 38 for a tenth example embodiment. 
    
    
     In the figures, the common elements will be allocated the same reference signs. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The figures depict a clutch equipped with a wear take-up device, of the type described in the French patent application filed on Sep. 17, 1996 under the number 96 11297 (FR-A-2 753 503), to which reference should be made for more details. 
     Referring to the figures, a friction clutch mechanism can be seen, notably for a motor vehicle, with an axial axis of symmetry X—X, which forms a unitary assembly and which comprises a pressure plate  51  intended to cooperate with a friction disc (depicted schematically in FIG. 7 at  100 ), carrying friction linings at its external periphery, which itself cooperates with a reaction plate. The reaction plate, depicted schematically at  101  in FIG. 1, is intended to be fixed with respect to rotation to a driving shaft, such as the crankshaft of the internal combustion engine. The friction disc is fixed with respect to rotation to a driven shaft, such as the gearbox input shaft. 
     The pressure plate  51  is fixed with respect to rotation to the cover  52  by means of tangential tongues  9 , one of which is visible in FIG.  4  and which, axially elastic, constitutes at the same time means of returning the pressure plate  51  towards the cover  52 . 
     The tongues  59  are fixed by riveting at one of their ends to the cover and at their other end to a lug  251  on the pressure plate (reference FIG.  4 ). 
     The tongues  9  allow an axial movement of the pressure plate  51  with respect to the cover  52 . The cover is metallic, being made of pressed sheet metal. This cover  52  has a base, transversely oriented, with a hole in the centre and means  152  for fixing it to a reaction plate, possibly divided in order to form a damping flywheel. 
     Here the cover  52  is roughly in the form of a hollow dish and has at its external periphery a radial flange  152  forming the means of fixing the cover to the reaction plate, the said flange being provided with holes for members such as screws to pass for fixing the cover to the reaction plate. 
     An axially oriented annular skirt connects the base to the flange and is open at the level of the tongues  9  (FIG.  4 ). 
     Here the reaction plate  101  is flat. As a variant this plate has a skirt to which the flange  152  is fixed so that the cover  52  can be less deep. 
     The pressure plate  51 , whilst being fixed with respect to rotation to the cover  52 , can therefore be moved axially with respect to the cover  52  under the action of axially acting engaging means controlled by disengaging means, here a diaphragm  53  mounted articulated on the cover  52  by virtue of small columns  58  carried by the base of the cover  52  with a central hole. 
     The diaphragm  53 , forming an axially acting elastic means, has a frustoconical shape in the free state and has a peripheral part in the form of a Belleville washer extended towards the centre by a central part divided into radial fingers by slots, as can be seen in FIG.  1 . 
     The diaphragm  53  bears, by means of its Belleville washer, on the base of the cover for action on the pressure plate  51  and clamping of the friction linings on the friction disc between the pressure and reaction plates. 
     Here the clutch is of the pushed type, that is to say it is necessary, by means of a clutch release bearing, controlled manually, semi-automatically or automatically and not depicted, to act by pushing on the internal end of the fingers of the diaphragm  53  in order to disengage (declutch) the clutch. To do this (FIG.  2 ), the base of the cover  52  carries on the one hand a primary support consisting for example of a retaining ring, or here a dished part produced in the base of the cover at the internal periphery thereof and, on the other hand, opposite the primary abutment, a secondary abutment in the form of a rolled annulus carried by the small columns  58 , or any other means. The diaphragm  53 , through the internal periphery of its Belleville washer, is mounted so as to tilt or pivot between the said primary and second abutments. Through the external periphery of its Belleville washer, it is in contact with abutment areas  14 , described below. These areas  14 , forming abutment means, are carried by the pressure plate. 
     In order, when the clutch is engaged, to keep the axially acting engaging means  53  in a position independent of the wear on the linings of the friction disc, and to a lesser extend the wear on the pressure  51  and reaction plates whose faces, referred to as friction faces, wear in contact with the disc linings, a wear take-up device  10  is provided. 
     The wear take-up device comprises a unit  10  and ramp means  54  disposed circumferentially; more precisely, these ramp means  54  consist of a ring made of cropped and pressed sheet metal so as to have ramps  56  disposed circumferentially; the said ring also has abutment areas  14  consisting of the rounded top edge of dished parts in the form of arcs of a circle centred on the axis of the clutch and placed radially towards the outside with respect to the ramps  56  (FIGS.  2  and  17 ). 
     The pressure plate  51  has here, made by moulding, on its face turned towards the base of the cover  52 , radially beyond the small columns  58 , studs  57  distributed circumferentially at a distance from each other which corresponds to that which circumferentially separates two successive ramps  56 , the studs  57  being intended to cooperate each with a ramp  56 . 
     The flange  152  has areas offset axially in the direction of the base of the cover in order to carry balancing rivets  1  (FIG. 5) in order to balance the clutch mechanism including in a unitary fashion the cover  52 , the pressure plate  51 , the diaphragm  53  and the wear take-up device. 
     The ramp means  54  are placed axially between the diaphragm  53  and the pressure plate  51  so that the studs  57  receive the ramps  56  and the diaphragm  53  cooperates with the abutment areas  14  which thus constitute the abutment means, here divided in a continuous variant, by means of which the diaphragm  53  acts on the pressure plate  51 . This arrangement is economical and simple, the ramp means  54  being metallic and obtained by pressing. As a variant the studs  57  are replaced by counter-ramps with the same shape as the ramps  54 . 
     At least one of the abutment areas  14  of the ramp means  54  is extended at its external periphery by a flange parallel to the axis of the clutch, ending in a transverse return, that is to say lying in a plane perpendicular to the axis X—X of the clutch, provided at its external periphery with a set of teeth  59 , so that the abutment areas  14  can be continuous and so that the flange is centred by means of a thicker part  157  on the pressure plate  51 . 
     It is in each thicker part  157  that the studs  57  are formed. All the thicker parts  157  can participate in the centring of the ring  54  having a continuous flange. As a variant, all the thicker parts  157  do not participate a centring. Likewise the flange of the ring  54  may not be continuous. This ring  54  therefore has a lesser number of centring areas than there are studs  57 , each centring area being associated with a ramp  56 . 
     Advantageously the studs  57  and therefore the thicker parts  157  are bevelled in order to cooperate in a complementary fashion with the ramps  56 . In all cases the studs  57  form counter-ramps. 
     The number of studs  57  and ramps  56  depends on the application, and the same applies to the complementary centring areas formed respectively at the external periphery of the studs  57  and at the internal periphery of the axial flange or flanges of the ring  54 . 
     Thus twelve ramps  56  and studs  57  can be provided. Twelve thicker parts  157  can form the centring area in association with twelve centring areas belonging to the ring. 
     As a variant, six thicker parts  157  can form the centring area, the ring  54  having six centring areas and viceversa. The pressure plate  51  therefore carries the abutment areas  14  and the ramp means  54  able to move in rotation, whilst the pressure plate is fixed with respect to rotation. This plate  51  thus has a variable thickness. More precisely, the distance between its front face, serving as a friction face for the friction disc  100 , and the abutment areas  14 , varies according to the aforementioned wear. 
     Naturally it is possible to produce the ramps and counter-ramps by means of the nut and screw system. For example, a ring carrying the abutment areas  14  has an internal thread in order to screw onto an external thread on the pressure plate. 
     The wear take-up device also comprises a ratchet wheel  60  with inclined teeth secured to a shaft  67  which also carries a worm  63 ; the thread and pitch of the worm  63  are adapted to the set of teeth  59 ; the worm  63  is caused to cooperate with the set of teeth  59  in a manner which will be described below. The worm  63  extends tangentially with respect to the set of teeth. 
     The shaft  67  of the ratchet wheel  60  is carried rotatably by a support  62 , more clearly visible in FIGS. 8 and 13, made from cropped and bent sheet metal, in the shape of a U having a web  64  and two wings  65 ,  66  intended to support the shaft  67 . To this end, each of the wings carries a circular hole  61  (FIG. 12) adapted to receive it; the web  64  carries laterally a square lug  68  directed radially towards the outside and intended to be fixed to an area  154  on the external flange  152  of the cover  52  by two rivets  155 , the said area being offset axially towards the base of the cover  52 . The cover  52  has an opening  156  (FIG. 7) for the web to pass and is simplified. 
     According to one characteristic, the axially oriented web  64  bears on the edge  158  of the opening  156  affecting the base of the cover  52 . The web  64  can be fixed to the edge  158  belonging to the base of the cover  2 , for example by bonding, welding or crimping. 
     In the case of fixing by crimping, the web  64  is shouldered and passes through a notch produced in the flange  158 . After passing through the flange, the lateral ends of the web are crushed hot in order to effect the crimping. 
     More precisely, the web  64  of the support  62  has, on the side opposite to the one where the lug  68  is situated, an axial extension  170  intended to be fixed to the base of the cover  52 . This extension is provided with returns  71  extending perpendicular to the web  64  and intended to constitute control stops whose role will become clear hereinafter; the ends of the said returns  71  are at a sufficient distance from each other to allow, without in terfering with it, movement of the actuator  55  during operations of engaging and disengaging. 
     The actuator  55  consists of a protuberance (or appendage) which the diaphragm  53  has radially projecting at its external periphery. 
     In practice the returns  71  extend radially above the actuator  55  and are inclined (FIGS. 7,  8 ,  9  and  13 ). These returns  71  issue, by cropping and bending, from the axial extension  170  of the web  64 , whose flat area has been hatched in FIG.  13 . The returns  71  are thus disposed on each side of an axial lug  171  and are separated therefrom by scallops with a semi-circular base  172 . 
     This lug  171  extends in axial projection with respect to the returns and bears at its free end against the edge  158 . This lug  171  is fixed at its free end to the edge  158  in the aforementioned manner, for example by welding, as can be seen in FIG.  7 . The edge  158  forms an abutment surface for the lug  171 . 
     The support  62  is thus simple in shape and is stable. 
     It is much simpler than the on e described in the aforementioned document FR 96 11297 since the returns  71  do not issue from the wings of the support. In addition the lug  171  makes it possible to decrease the number of fixing rivets and is a fixing and stabilisation lug. 
     By virtue of the invention the number of lugs for fixing to the cover is reduced. 
     Because of the opening  156  affecting the cover  52  at the level of the area of connection of the skirt of the cover to the base of the cover, it is easy to weld, bond or crimp the lug  171  to the edge  158  of the opening. 
     The support  62  is adapted to receive an elastic member  72 . 
     Here the elastic member  72 , more clearly visible in FIG. 15, is in the shape of a staple and comprises an elongate flat body  73  carrying at each of its ends an arm  74  provided with a hole  75  adapted to receive the shaft  67 ; the two arms  74  are parallel, as described below, and extend on the same side and roughly perpendicular with respect to the body  73 . 
     On one of its longitudinal ends, the body  73  is extended in a slanting extension  84  on the same side as the one where the arms  74  are placed; scallops  82  and  83  provided in the body  73  limit the extension  84  with respect to the ends of the body  73  carrying the arms  74 ; in addition, these scallops  82  and  83  give the extension  84  a certain elasticity. 
     The free end of the extension  84  is provided with a return  85  which is extended in a control tongue  76  extending in the direction of the body  73  whilst being roughly parallel thereto. 
     A cut-out  77  is provided in the extension  84 ; by means of this cut-out  77  and scallops  79  and  80  in the body  73 , a non-return catch  78  in the form of a blade is produced. The free end of the catch  78  extend s roughly perpendicular to the body  73 . 
     Here, as can be seen more clearly in FIG. 11, the control tongue  76  and catch  78  are slightly inclined respectively with respect to the plane of the body  73  and the plane perpendicular to the plane of the body  73 . 
     The catch  78  is offset with respect to the tongue  76 , the free ends of the catch  78  and of the tongue  76  being offset circumferentially. 
     A helical compression spring  86  is placed between the ratchet wheel  60  and the free end of the arm  74 , whilst being wound around the shaft  67 ; the worm  63  and ratchet wheel  60  are cut from the same piece. 
     The ratchet wheel  60  is located between the worm  63  and spring  86 . 
     The helical spring  86  constitutes the elastic take-up means; the ratchet wheel  60  is in line with the non-return catch  78  which, by cooperation with the inclined teeth of the ratchet wheel  60 , prevents the ratchet wheel  60 , and the worm  63 , from turning in the anticlockwise direction, as seen in FIG.  1 . 
     The support  62  carrying the ratchet wheel  60 , the worm  63  and the helical spring  86  being fixed to the cover  52 , the diaphragm  53  moves with respect to it during the disengagement and re-engagement operations; the diaphragm  53  carries, at its periphery, a radial appendage (or radial protuberance), referred to as the actuator  55 , extending radially outside the Belleville washer part of the diaphragm  53  in order to cooperate with the extension  84  of the elastic member  72 , or more precisely with a rounded area  184  connecting the main part of the extension to the return  85  (FIG.  7 ); it will be understood that, by virtue of this arrangement, when the diaphragm  53  tilts during operations of disengagement and re-engagement, the actuator  53  moves the extension  84  from right to left, as seen in FIG. 1, and the control tongue  76 , by cooperation with the teeth of the ratchet wheel  60 , is caused to make the ratchet wheel  60  turn in the clockwise direction and therefore to make the screw  63  turn whilst compressing the spring  86 ; when the actuator  55 , in return, is moved from left to right, the elasticity of the extension  84  of the elastic member  72  and the inclination of the teeth mean that the tongue  76  moves towards the right, climbing up the teeth which are held fixed with respect to rotation by the non-return catch  78 . 
     The functioning of the clearance take-up device which has just been described is known and will be not be detailed; if necessary reference can be made to the French patent application 96 11 297 already cited, part of whose corresponding description should be considered to form part of the present application, knowing that, during the disengagement operation, the return travel or cocking travel of the control tongue  76  is limited by the extension  84 , or more precisely the rounded area  186 , coming into abutment against the returns  71  of the support  62 , thicker than the member  72 . 
     The role of the returns  71  ( 271  in the other figures) is to preserve the elastic member  72 . 
     Here, the worm  63  and ratchet wheel  60  are in a single piece and are force-fitted on the shaft  67  carried by the support  62 . The shaft  67  is fluted for its force-fitting in the piece  60 ,  63  and passes through the holes  61  in the wings  65  and  66  of the support  62 . In this way an assembly—shaft  67 , wheel  60  worm  63 , spring  86 —carried by the wings  66 ,  65  is formed. Here the shaft  67  is therefore fixed to the single-piece assembly consisting of worm  63  and ratchet wheel  60 , which is immobilised axially by the two arms  74  and the two wings  65 ,  66  respectively of the elastic member  72  and support  62 . To do this the arms  74  have a free end in the form of a washer  174  (FIG. 15) with a hole at  75 . 
     One of the washers  174  is interposed axially between the internal face of the wing  65  and the free end of the worm  63 , extending here over less than two turns, here {fraction (1/25)} of a turn, whilst the other washer  174  is interposed between the internal face of the wing  66  and the free end of the helical spring  86 . 
     In this way there is formed, in a unitary fashion, a manipulatable and transportable unit  10  having parts, here all metallic, namely the support  62 , the elastic member  72 , the helical spring  86 , the ratchet wheel  60 , the worm  63  and the shaft  67 , the elastic member  72  (FIGS. 8 and 11) having, at its end opposite to the extension  83 , a radially oriented lug  168  abutting the lug  68  of the support  62 . The body  73  abuts the web  64 . The lug  168  has, like the lug  68 , two holes for the passage of fixing rivets  155 . 
     It will be noted that the external periphery of the pressure plate is cut away locally for housing the unit  10  (FIG. 7) and reducing the axial bulk. 
     Naturally, a housing  110  is formed as a thicker part, here by deformation on a press, at the level of the area  154  of the flange  152  on the cover  52  for mounting the unit  10  (FIGS.  1  and  7 ). 
     The housing  110  is delimited by the area  154  fixed to a centrally oriented web (not referenced), whose end opposite to the area  154  is provided with the opening  156 . 
     Here three housings  110  are provided, as can be seen in FIG.  1 . Only one housing is used for mounting the unit  10 . 
     Two inclined lateral portions  111  connect the web to holed areas of the flange  152  for passage of the members fixing the cover to the reaction plate. 
     The housing  110  protects the unit  10  and is open at the level of the area  154 . 
     Cut-outs (not referenced) are produced in the portions  111  extending on each side of the central web of the housing  110 . The ends of the shaft  67  project beyond the wings  65 ,  66 . The shaft  67  has a slot  167  at its end projecting beyond the flange  65 . In this way there are created means of re-setting the wear take-up device to zero. 
     For this re-setting to zero, a tool is provided, not visible. 
     This tool can be in the form of a screwdriver, whose blade enters the slot  167 . As a variant the tool consists of a rod whose end carries a manoeuvring knob, for example knurled, and whose other end is flat for entering the slot  167 . 
     The cut-outs produced in the portions  111  of the cover  52  define a passage in alignment with the shaft  67  for passage of the tool. 
     The operation of re-setting the wear take-up device to zero easily results from the above description. 
     For more information reference should be made to the document FR 97 06655 of May 30, 1997 showing a form of tool. 
     When the tool is in place, the fixing with respect to rotation of the worm  63  with respect to the tool makes it possible, by turning the tool, to turn the worm  63  with respect to the cover  52  and therefore the set of teeth  59  with respect to the pressure plate  51 , and the ramps  56  with respect to the studs  57 . 
     The circumferential length of the set of teeth  59  corresponds to the quantity of wear which it has been decided to take up, having regard obviously to the few teeth with which the worm  63  meshes in the initial state. 
     When the chosen quantity of wear corresponding to the circumferential length of the set of teeth  59  has been taken up, the worm  63  no longer cooperates with the set of teeth  59 . 
     When the friction disc is changed, in order to reset the wear take-up device to zero, it suffices, with any tool, to cause the ramp means  54  to turn about their shaft so that the ramps  56  climb up the studs  57  until the first tooth on the set of teeth  59  encounters the first thread of the worm  63 ; by rotating the worm  63  by means of the zeroing tool, a few of the first teeth of the set of teeth  59  are brought into engagement with the threads on the worm  63 . 
     The angle through which it is necessary to turn the ramp means  54  in the first phase of the zeroing depends on the number of wear take-up devices; usually there is only one wear take-up device so that the angle is large. In order to minimise this angle whatever the number of devices, it is possible to provide a set of teeth  59  composed of several teeth elements such as the elements  59 A,  59 B,  59 C shown in FIG.  17 : advantageously, as mentioned above, there are as many teeth elements as ramps  56 , each element corresponding to the chosen wear on a friction disc; the ramps  56  are opposite the teeth elements  59 A,  59 B,  59 C. 
     Naturally the elastic member  72 , here metallic, has a lower thickness than that of the support  62  so as to make flexible the catch  78  and the control tongue  76 , which has at its centre a protrusion  176 , here oblong in shape. By virtue of this protrusion  176  all the mechanical stresses are taken to the centre of the tongue  76  so that the tongue  76  is less fragile. This arrangement increases the service life of the tongue  76 , the protrusion  76  being a pressed part. 
     As can be seen more clearly in FIG. 14, the teeth on the ratchet wheel  60  are inclined with respect to the axis Z—Z of axial symmetry of the assembly consisting of ratchet wheel  60  and worm  63 . The teeth on the wheel  60  are in line with the catch  78 , forming a non-return catch, and the control tongue  76 . 
     According to one characteristic of the invention the shaft  67  and therefore the single-piece assembly consisting of worm  63  and wheel  60  is inclined. 
     In all the figures this inclination is produced by an axial offsetting of the centres of the holes  61  in the wings  66 ,  65  perpendicular to the web  64 . 
     More precisely (FIGS. 1 to  17 ) the centre of the hole  61  in the wing  65  adjacent to the worm  63  is closer axially to the base of the cover  52  than is the centre of the hole  61  in the wing  66  adjacent to the spring  86 . The inclination of the shaft  67  and therefore of the worm  63  is a function of the inclination of the thread and the pitch of the worm  63 . 
     Here the system consisting of worm  63  and set of teeth  59  is irreversible, the worm  63  can drive the set of teeth  59  but not vice-versa. 
     Here the angle of inclination of the shaft  67  is roughly an angle equal to that of the thread of the worm. 
     By virtue of this arrangement the teeth in the set of teeth  59  are straight, which facilitates driving by meshing and prevents any jamming, the contact surface area between the thread of the worm  63  and the teeth of the set of teeth being at a maximum. The shaft  67  is therefore inclined with respect to a plane perpendicular to the axis of axial symmetry X—X of the clutch and of the clutch mechanism, the screw  63  extending tangentially with respect to the set of teeth  59 . 
     By virtue of these provisions the system consisting of set of teeth  59  and worm  63  has good efficiency, the thread of the worm extending roughly parallel to the flanks of the teeth of the set of teeth. 
     The teeth on the ratchet wheel  60  are inclined as a function of the inclination of the shaft  67  corresponding to the angle which the lines V—V and Y—Y make between them in FIG.  13 . 
     More precisely, a straight (parallel) contact is sought between on the one hand the teeth of the ratchet wheel  60  and on the other hand the non-return catch  78  and the control tongue  76 . As a result, according to one characteristic of the invention, the free end of the catch  78  is inclined by an angle which is a function of the inclination of the shaft  67 , itself dependent on the thread on the worm  63 . This inclination can be seen for example in FIGS. 8,  15 ,  16 . 
     This inclination depends on the circumferential offset between the free ends of the catch  78  and tongue  76  (FIGS.  7  and  11 ). 
     The areas of contact between the teeth on the wheel  60  on the free ends of catch  78  and of the tongue are at a maximum and linear. 
     The catch  78  and tongue  76  bear on the entire surface of the relevant tooth of the ratchet wheel. 
     More precisely, by virtue of the inclination of the teeth on the ratchet wheel, the free end of the control tongue  76  is parallel to the facing tooth on the ratchet wheel  60 , and therefore the teeth on the said wheel. 
     On the other hand, because of the offset of the catch  78  with respect to the tongue  76 , the free end of the catch  78  is then not parallel to the opposite teeth on the wheel  68  if precautions are not taken. 
     Thus, as can be seen more clearly in FIGS. 15 and 16, the catch is twisted in order to take account of this offset. This twisting results in inclining the free end of the catch  78  with respect to the straight free end of the control tongue  76 . 
     The catch  78  is therefore twisted in order to cooperate in a straight manner, that is to say in a manner parallel with the teeth on the ratchet wheel  60 . 
     By virtue of these provisions the area of contact between the actuator  55  and the elastic member  72  is at a maximum, in the clutch engaged position the diaphragm being roughly in a plane perpendicular to the axis X—X of the clutch mechanism and the clutch. 
     The elastic member  72  is in linear contact through its rounded area  184  with the entire surface of the actuator  55  of the diaphragm, in all positions of the diaphragm. 
     When the clutch is re-engaged, good transmission of forces is obtained, by virtue notably of the dished part  176  forming a protrusion, with maximum contacts between on the one hand the actuator  55  and the elastic member  72  and on the other hand between the teeth on the wheel  60  and the control tongue  76 . The wear take-up device therefore has further improved efficiency with even more minimised risks of jamming. 
     According to one characteristic the return  85  on the elastic member  72  has a non-symmetrical shape which takes account of the inclination of the shaft  67  of the pieces  63 ,  60 ,  86  located between the two wings  66 ,  65 . 
     The return  85  carries the tongue  76  centrally in projection and has two portions on each side of the tongue. 
     The first portion, located opposite the worm  63 , is less high than the second portion located opposite the take-up spring  86 . 
     Thus the return  85  has a maximum mechanical strength in connection with the dished part  176  affording good transmission of forces since it is perpendicular to the rounded area  184 . Naturally the free end of the tongue  76  and of the catch  78  is less wide than the teeth on the worm  60 . 
     Here the wings  65  and  66  are twisted, as well as the arms  74 , in order to incline the shaft  67  according to the thread on the tangential worm  63 . 
     More precisely, the free ends of the wings  65  and  66  of the arms are inclined relative to a radial line symmetrically disposed there between situated in a plane perpendicular to a rotational axis of the clutch. The lateral wings  65  and  66  being perpendicular to the shaft  67  with symmetry line Y—Y inclined with respect to a second line V situated in a plane perpendicular to the axis X—X and to the web  64  (FIG.  13 ). The inclination of the lateral wings  65  and  67  thereby establishes inclination of the worm ( 63 ) and shaft ( 67 ) relative to the second line V situated in the plane and perpendicular to said radial line. 
     Thus the wings  65 ,  66  have a main part perpendicular to the web  64  and, at the level of the holes  61 , inclined areas  165 ,  166  parallel to each other and perpendicular to the line Y—Y and to the shaft  67 . The areas  165 ,  166  are inclined towards the inside of the web  65  and have the holes  61 . 
     By virtue of this arrangement, the bulk is not overmuch increased. 
     Likewise the end washers  174  of the arms  74  of the member  72  are inclined and parallel to each other and to the areas  165 ,  166 . 
     Thus the unit  10 , notably the support  62  thereof, has a smaller bulk than if the entire unit had been inclined, whilst being simpler in shape. 
     Naturally (FIGS. 18,  19 ), the shaft may not be secured to the worm  63  and wheel  60  assembly. 
     In this case, without modifying the wings  65 ,  66 , it suffices to reduce the size of the holes in the inclined areas  165 ,  166  of the wings  65 ,  66 . 
     Thus the shaft  67  has an end with a reduced diameter  267  passing through the washer  174  and a hole  161  in the inclined area  166  of the wing  66 . The shaft enters the bore of the single-piece part  63 ,  60 . 
     The worm  63  has a cylindrical extension  163 , with a diameter greater than that of the shaft passing through the washer  174 , and a hole  261  in the inclined area  165  of the wing  65 . The hole  261  has a diameter greater than that of the hole  161  and the extension  163  has a slot  367  in order to be able to turn the worm  63  by means of a tool and to reset to zero as in FIGS. 1 to  17 . 
     The shaft  67  is immobilised axially by virtue of the shoulder formed by its change in diameter and in contact with the face of the washer  174  turned towards the spring  86  and by virtue of an elastic washer  2  having arms in contact with the end  267 , the said washer  2  being in contact with the external face of the area  166  of the wing  66 . 
     The holes  161 ,  261  are offset axially with respect to each other. The piece  60 - 63  turns on the shaft also immobilised with respect to rotation by the washer  2 . 
     In general terms the assembly consisting of the pieces  63 ,  60 ,  86 ,  87  is carried by the wings  66 ,  65  with holes in and the shaft  67  passes through at least the hole  61 ,  161  in one of the wings  66 ,  65 . 
     In a variant (FIGS. 20,  21 ) the wings  65 ,  66  are not twisted, as well as the arms  74 . The holes  361  formed in the wings  65 ,  66  are offset axially and have the same size for mounting a shouldered bearing  3  with a central hole. 
     The bearing  3 , advantageously made of mouldable material or sintered material, with a low coefficient of friction, such as plastics material, has a change in diameter in order to form a shoulder for axially immobilising the relevant arm  74  between the said shoulder and the internal face of the relevant wing  65 ,  66 . 
     The central hole in the bearing  3  is inclined according to the application. The shaft passes through the bearings  3 . 
     Thus, by virtue of the inclined central holes in the bearings  3 , the shaft  67  is inclined by the required value for maximum contact between the tangential worm  63  and the teeth in the set of teeth  64 . As in all the figures, the thread on the worm  63  has a path (movement) parallel to that of the teeth of the set of teeth  59 , the dorsal faces of the bearings are inclined so as to be parallel respectively to the end face of the worm  63  and to the end of the spring  86 . 
     The shaft  67  has slots  167  for resetting to zero, the shaft  67  being force-fitted as in FIGS. 1 to  17  in the piece  60 ,  63 . 
     Naturally, the shaft  67  can be of a single piece with the wheel  60  and worm  63 . In this case (FIG. 22) it is necessary to open the passage holes produced in the wings  65 ,  66 . 
     Thus the hole  461  can initially be a blind hole (FIG. 22) with a semicircular base. This hole  461  has a U-shape and is delimited by two tongues  462  which are then folded over in order to trap the bearing  3 . 
     The bearing  3  is therefore fixed by crimping by virtue of the tongues  462 , on its associated wing. This type of design applies also where the shaft is not inclined. This assists automatic mounting of all the pieces  3 ,  60 ,  63 ,  67 ,  86  on the wings. This mounting is simple and rapid. 
     Naturally, FIGS. 23 to  27 , in a variant, the wings  66 ,  65  can carry the returns  71  and come into contact with the edge  158  of the opening  156  then higher radially, the diaphragm  53  being mounted for articulation on a dished part of the cover and on the heads of the small columns profiled accordingly. The returns  71  are directed towards each other and are inclined with respect to the wings  66 ,  65 . 
     The solution is compact. 
     It is possible to weld the wings to the edge  158  forming a surface for the wings  66 ,  65 . 
     In general terms the number of lugs for fixing to the cover is reduced still further. 
     Naturally the structures can be reversed, the shaft  67  or screw  63  has projections in order to be driven by a tool having slots for receiving the projections. 
     The means  152  of fixing the cover  52  to the reaction plate can consist of the skirt of the cover  52  fixed directly to the reaction plate, for example by crimping. 
     In general terms it is possible to form a module including the reaction plate, the friction disc whose friction linings are interposed axially between the reaction plate and the pressure plate of the friction clutch mechanism, whose cover is then fixed by its fixing means  152  detachably or non-detachably to the reaction plate. 
     It is for this reason that, in FIG. 1, holes can be seen in the fingers of the diaphragm. These holes allow the passage of at least one screwing tool in order to cooperate with the heads of the screws for fixing the reaction plate (possibly in two parts) to the crankshaft of the motor vehicle engine. 
     The reaction plate can then belong to a double damping flywheel having a first mass fixed to the crankshaft and carrying a bearing, such as a ball bearing, carrying the reaction plate with a hole or holes for passage of the screwing tool or tools as described in the document FR-A-2 716 511 with radial springs coupling the first mass to the reaction plate. 
     Naturally the axially acting engagement means can have another form and include two Belleville washers mounted in series with disengagement means in the form of levers as described in the document FR 96 11058 filed on Sep. 5, 1997. The screw  63  and wheel  60  can be two parts fixed to each other with respect to rotation. 
     The axis  76  is engaged inside a central hole in the worm  63  or in a single piece with the worm  63 . In general terms the shaft  67  extends the worm  63 . The abutment areas  14  can be connected to each other. 
     In all cases abutment means  14  are provided which, as a variant, can be distinct from the ramps  56  whilst being connected thereto as described in the document FR-A-2 684 151. 
     The presence of the arms  74  of the elastic member  72  is not essential, as the elastic member can be fixed for example by welding points to the web  64 . 
     Thus, in FIGS. 28 to  30 , the elastic member  72  bears directly on the bearings  3  or more precisely on the largest part  30  of the bearing  3 , whose dorsal face is inclined, as can be seen in FIG.  29 . 
     The member  72  bears elastically on the top of the parts  30 . 
     The part  30  is therefore of variable width, as in FIGS. 20 and 21, in which the largest part is not referenced. 
     The assembly consisting of worm  63 , ratchet wheel  60  and shaft  67  is in a single piece and is mounted with the spring  86  and the two bearings between the non-twisted wings  65 ,  66 . 
     The two parts  30  of the bearings are in contact with the internal faces respectively of the wings  66 ,  65 . 
     The parts  31  of reduced diameter of the bearing  3 , made of mouldable plastics material or sintered material, are slipped into the blind holes  461  of the type in FIG. 22, and then the tongues  462  are folded over in order to axially lock the bearings  3  by crimping. 
     It should be noted that the free end  471  of the fixing and stabilising lug is offset radially towards the shaft with respect to the web  64 . 
     Thus the opening  356  is higher than that of FIG. 7, which makes it possible to produce it easily by press, the material of the opening being easily discharged. 
     The same applies to FIG.  23 . 
     The axial end  471  therefore bears on the edge of the surface  158  of the opening  356  and is fixed thereto. 
     Naturally, FIGS. 32 and 33, rear fixing lugs  371  can issue from the wings  65 ,  66  as in the document FR 96 11297. The lugs  371  extend perpendicularly to the wings  66 ,  65  outside the support  62 . The front fixing lug  268  is less wide than the front fixing lug in the previous figures and has only one hole. 
     The cover  52  is fixed by means of three fixing lugs  271 ,  268  and three rivets. 
     The returns  271  are identical to those of FIGS. 23 to  27 , these returns, formed by bending of the wings  66 ,  65 , are inclined. 
     The wings  66 ,  65  are twisted over a greater length, the wing  65  being twisted outwards. 
     In all cases the returns  71 ,  271  are control stops preserving the elastic member  72 . 
     In all cases the contact faces (the free ends) of the twisted catch  78  and of the tongue  76  work in parallel with the teeth on the wheel  60 . 
     The same applies to the worm  63  and set of teeth  59 . 
     The pressure plate also advantageously has a recess on its dorsal face in order to prevent any interference with the unit. 
     By virtue of the invention, in the case of wear, precise functioning in at least three phases is obtained. 
     In a first phase, when the clutch is re-engaged, the tongue causes the wheel  60  to turn and the catch jumps a tooth. During the disengagement operation following this first phase, nothing happens. A second re-engagement phase starts, during which the tongue  76  causes the wheel  60  to turn, which then moves axially since the set of teeth  59  cannot turn because of the load exerted by the diaphragm. 
     The spring  86  is compressed. During the following disengagement operation a third phase starts in which the spring can expand and cause the set of teeth to turn if there is not too much friction to overcome. Otherwise it is necessary to recommence the operation. 
     In the preceding figures the support  62  is distinct from the cover  52 . 
     As a variant, the support can be in a single piece with the cover  52 . To do this, use can be made directly of the housing  110  since the latter has a cross section roughly in a U-shape with an axially orientated central web, forming the top wall of the housing  110 , and two lateral wings  111 . 
     It therefore suffices to produce three axially offset holes in the wings in order, according to the invention, to incline the worm and shaft. 
     Naturally, the take-up spring  86  may not belong to the unit  10 . This spring can act between the ramps and counter-ramps of the wear take-up device. Thus, in FIGS. 34 and 35, the support is produced by means of the housing  110   a  of the cover  52  formed as a thicker part in the cover  52  like the housing  110  in the previous figures. The housing  110   a  therefore has, in cross section, roughly a U-shape with an axially oriented web  112  forming the top wall of the housing  110   a  affecting the skirt of the cover  52  and two lateral wings  111  in each of which a blind hole  561  is formed for mounting a bearing  3  identical to that of FIGS. 28 to  31 , so that the bearing  3  is easily fixed by crimping, bonding or welding to the wings  111 . 
     There is formed a unit  10  comprising the elastic member  72  between the wings  74 , between which there are interposed the bearings  3  and an assembly consisting of ratchet wheel  60  and worm interposed between the two bearings. The unit is slipped by means of its bearings  3  into the blind holes  561  and then immobilised by locking its bearings  3  on the wings  111 . The unit  10  has a shaft  67  passing, as in the previous figures, through the bearings  3 , the wings  74  and member  72  finally being trapped between the wings  111  of the housing and the bearings  3  with an inclined central bore. The housing  110   a  is less wide because of the absence of the take-up spring in the unit. As a result the catch  78  and control tongue  76  extend on one side of the return  184  in order to be able to cooperate with the ratchet wheel  60  through which a first shaft passes centrally, a first end of which is engaged in a blind hole  363  in the worm  63  and the second end of which passes through the wing  74 , the bearing  3  and the relevant hole  561 . This first shaft is force-fitted in the hole  363  and the wheel  60  in order to secure it to the worm  63  and to the ratchet wheel  60 . 
     In a variant, the shaft is fixed by bonding or any other means to the worm  63  and to the wheel  60 . The worm  63  is extended, here in a single piece, by a second shaft passing through the other wing  74 , the other bearing  3  and the other hole  561  so that the shaft  67  is in two parts, which makes it possible to form the aforementioned unit  10 . The control stops are produced by means of a scallop  212  in the web  112 , preferably T-shaped in order to form two end shoulders constituting the control stops. The shaft  67  has slots at its ends for resetting to zero as mentioned above. 
     The elastic member  72 , having roughly a U-shape with a central web  73  and two wings  74 , can constitute by itself the support for the unit thus simplified as shown in FIGS. 36 and 37. 
     This unit will therefore have a reduced number of components, is lighter and therefore easier to balance. In these figures, the same reference signs are used for the elements common to the other figures. The elastic member  72  is a piece of sheet metal cropped and bent as in the other figures. The web  73  is extended towards the rear and then obliquely radially towards the inside by an oblique extension  84  delimited by scallops  82 ,  83  so that the extension is elastic and is cut centrally by a cut-out  77 , which divides the extension into two arms. The free end of the extension forms a return  85  in the form of a tangentially oriented bar extended by the control tongue  76 . 
     The catch  78  is produced by means of the cut-out  77  and scallops  79 ,  80  formed in the web  73 . As a result, the catch  76  and tongue  78  are inclined with respect to the plane of the web  73  and the catch  70  is offset with respect to the tongue  78 . The ratchet wheel  60  has a lateral face  200  adjacent to the worm  63  and a lateral face  202  on which there acts the helical take-up spring in contact with the twisted wing  74  at the level of the passage hole  75  for the shaft. The other wing  74  is also twisted at the level of the other hole  75  for passage of the other end of the shaft  67 . 
     The holes  75  are offset axially for inclination of the shaft  67  immobilised axially at one of its ends by cooperation of a larger-diameter portion with the relevant wing  111  of the housing  110  and at the other end by a circlip. The shaft passes through the single-piece assembly consisting of worm  63  and wheel  60  and is fixed to this assembly, by force-fitting or bonding etc. 
     Two rear lateral fixing lugs  371  extend transversely towards the outside from the rear vertical edge of the wings  74 . Each lug has a hole  372  for passage of the rivet  373  for fixing to the central web  112  of the housing  110 . One fixing lug  168  extends at right angles from the front edge  30  of the web  73  and is intended to be fixed by a rivet  155 , passing through a hole  36  in the lug  166 , to an area of the flange  152  on the cover. The wings  74  extend beyond the rear edges by means of a horizontal arm  42  itself extended by a return  71  directed transversely towards the inside and constituting a control stop for the tongue, the ends  69  of the return  71  being directed towards each other. 
     In a variant (FIG.  39 ), the elastic take-up means consist of an elastic blade  183  produced in one piece with the member  72 . The blade  186  has an anchoring part  204  which connects it to the rear edge of a wing  74 . This blade  186  extends in an inclined fashion towards the inside of the unit and has a curved free end  208  with two spaced-apart branches for passage of the shaft of the assembly  60 ,  63 . The end  208  cooperates with the relevant lateral face of the ratchet wheel. 
     Naturally, FIG. 38, the support can be fixed horizontally to the web  112  of the housing  110 , the top face  169  of the web  164  being in contact with the bottom face  203  of the web  112 . The rivets  155  serve for fixing lugs  268 ,  368  of the pieces  62 ,  72  to the web  112 . 
     The window  156  is delimited by top  221  and bottom  222  edges, whilst the appendage  55  acts on a rounded part of the return  84 . The flange  210  for centring the wing  54  on the thicker part bears the reference  210 . 
     It will be noted in FIG. 2 that the base of the cover is extended radially inwards in order to form, at its internal periphery, a stop  301  offset axially with respect to the primary abutment of the cover, and this in the opposite direction to the pressure plate in order to enable the diaphragm to abut before mounting of the engagement mechanism on the reaction plate of the engine flywheel in order to protect the unit  10  to prevent the latter from being damaged.