Abstract:
The invention relates to a friction device for a clutch, particularly of a motor vehicle. The inventive friction device comprises first and second axially-spaced coaxial friction lining members which are defined by opposing friction faces. The device also comprises means for linking the two friction lining members which are solidly connected to one another. The first friction lining member is essentially ring shaped. The aforementioned linking means comprise linking tongue elements which are each equipped with a first end for solidly connecting to an inner edge of the first friction lining member and a second end for solidly connecting to the second friction lining member. Moreover, a deviation angle is provided between said first and second connecting ends, which can vary according to the axial spacing of the two friction lining member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a friction device for a clutch, in particular for a motor vehicle. 
     2. Description of the Related Art 
     A motor vehicle clutch is intended to transmit a torque between the engine flywheel of a motor vehicle and the gearbox input shaft. To this end, the clutch comprises a mechanism, rotationally fixed to the engine flywheel, and a friction device rotationally fixed to the gearbox shaft. 
     The mechanism comprises a pressure plate and a reaction plate, intended to cooperate with first and second friction linings of the friction device. These friction linings are carried by at least one support, normally of general form of revolution. 
     The friction device must achieve a compromise between various technical constraints. 
     On the one hand, it is necessary to limit the weight and inertia of the friction device. 
     To this end, it is wished to limit the dimensions of the friction linings, for example the thickness and the radial width of these friction linings. It is also wished to avoid the presence of rivets fixing the linings to their support, opting as far as possible for adhesive bonding of these linings to their support. 
     On the other hand, it is necessary to be able to activate the clutch progressively. 
     To this end, it is wished to incorporate elastic means, in general an elastomer mass, in the friction device, in order to ensure this progressiveness. 
     Shearing effects limit the possibilities of arranging the elastomer mass between a lining and its support. 
     A friction device for a clutch, in particular for a motor vehicle, has therefore been proposed in the prior art, in particular in EP-A-0 419 329, of the type comprising:
         first and second friction lining members, coaxial, separated axially, delimited by opposite friction faces, and   means of connecting the two friction lining members fixed together.       

     In a friction device of this type, the friction lining members each comprise a support carrying a friction lining. In this case, the elastomer mass is interposed between the first and second supports. 
     More particularly, each lining support described in EP-A-0 419 329 comprises a peripheral part, annular in shape overall, and a central part connecting with the other lining support. The central parts of the supports are contiguous. The peripheral parts of the supports, separated axially from each other, are connected to the central parts by intermediate parts converging from these peripheral parts towards these central parts. 
     Because of this, when the friction linings are clamped between the pressure and reaction plates, the peripheral parts of the lining supports deform, diverging towards the intermediate parts of the axially relatively rigid supports. Consequently the separation between the peripheral parts of the lining supports does not vary uniformly radially, when the friction linings are clamped between the pressure and reaction plates. 
     As a result the friction linings do not cooperate uniformly radially with the pressure and reaction plates, which impairs the performance of the clutch. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is in particular to propose a friction device provided with friction lining supports moving substantially parallel with respect to each other when they are acted on by the pressure and reaction plates. 
     To this end, the object of the invention is a friction device of the aforementioned type, where the first friction lining member has a general annular shape, the connection means comprising connection tongues each provided with a first end for fixing to an internal contour of the first friction lining member and a second end for fixing to the second friction lining member, the first and second fixing ends having an angular offset between them as a function of the axial separation of the two friction lining members. 
     These connection tongues enable the friction lining members to move with respect to each other substantially by screwing along a rotation center axis of the supports (it will be recalled that screwing along an axis is a simultaneous combination of a rotation on this axis and a translation parallel to this same axis). Thus, when the axial separation of the friction lining members increases, the angular offset between the fixing ends of each tongue decreases, and when the axial separation of the friction lining members decreases, the angular offset between the fixing ends of each tongue increases. 
     By virtue of these connecting tongues, the friction lining members remain substantially parallel to each other when they are acted on by the pressure and reaction plates. 
     A friction device according to the invention can also comprise one of more of the following characteristics:
         the connecting tongues are bent so that their first and second fixing ends are mutually offset axially;   the bent connecting tongues are carried by the friction lining member intended to cooperate with the pressure plate axially;   the first connecting end of each connecting tongue is made in one piece with the first friction lining member;   the first fixing end of each connecting tongue is attached to the first friction lining member;   it is possible to define, on each connecting tongue of the support, a top angular sector coinciding substantially with the second fixing end of this tongue and extending as far as an external contour of the support without any interruption of material, the angular sector forming an angle between 10° and 35°, and where an axis perpendicular to a radius passing through the center of the device is included in the said angular sector;   the connecting tongues are disposed in two opposite circumferential directions, in particular in the form of a V;   the second friction lining member has a generally annular shape and comprises connecting tongues each provided with a first end for fixing to an internal contour of this second friction lining member and a second end for fixing to the second fixing end of a corresponding connecting tongue of the first friction lining member, the first and second fixing ends of the connecting tongues of the second friction lining member having a mutual angular offset;   the friction device comprises elastic means for axial bracing of the first and second friction lining members;   the elastic bracing means comprise an elastomer mass, preferably generally annular in shape, arranged between the first and second friction lining members;   the bracing means comprise elastic bracing tongues each provided with a first end for fixing to one of the friction lining members and a second end free from contact with the other one of the friction lining members, these bracing tongues being bent so that their first and second ends are mutually offset axially;   the elastic bracing tongues are connected to only one of the friction lining members carrying a lining intended to cooperate preferably with an axially movable pressure plate;   the friction device comprises at least two bracing tongues having different axial offsets between their first and second ends;   the friction device comprises at least two bracing tongues having different stiffnesses;   the friction device comprises at least one two bracing tongues, referred to as matched tongues, connected respectively to the first and second friction lining members;   the matched bracing tongues are substantially symmetrical with respect to a plane parallel to the first and second friction lining members;   the matched bracing tongues are substantially symmetrical with respect to a point;   the symmetry point is a point of contact between the matched bracing tongues;   the matched bracing tongues are provided with mutual contact surfaces, the contact surface on one matched tongue being opposite the friction lining member to which it is connected;   the matched bracing tongues are provided with mutual contact surfaces, the contact surface on one matched tongue being opposite the friction lining to which it is not connected;   the connecting tongues and the bracing tongues extend from their first end to their second end respectively in identical circular directions;   the friction device comprises a device for taking up wear on the linings;   the distance between the first and second connecting ends on each connecting tongue is between 5 and 60 mm, preferably between 20 and 40 mm;   at least one of the friction lining members comprises a support carrying a friction lining;   the friction lining is adhesively bonded to the support, the said support is generally made from steel, but it is also possible to produce it from composite material. When the lining is bonded to a support, the latter is generally in the form of a continuous ring, but it can also consist of separate annular segments, even separated from each other;   at least one friction lining member is formed in a single piece, for example injection moulded.       

     It should be noted that the connecting means of the two friction lining members can make it possible either to affix them together directly with contact (this thus means that the securing end is a connecting end), or indirectly with the presence of an intermediate piece between the two friction lining members. 
     According to one embodiment, the intermediate piece is a flange, in particular a guidance washer rotationally fixed to the gearbox shaft. 
     It should be noted that, by virtue of the invention, which makes it possible to optimize the contact of the friction linings with the pressure and reaction plates, it is possible to reduce the radial width of these linings more than in the prior art. 
     Thus another object of the invention is a friction lining for a friction clutch device, in particular for a motor vehicle, annular in shape overall, the ratio between the radial width of the lining and the outside diameter of the lining is less than 0.10, or even less than 0.095. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from a reading of the description that follows, given solely by way of example and made with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded view of a friction device according to a first embodiment of the invention; 
         FIG. 2  is a perspective view of means of connecting two supports of the friction device according to the embodiment of the invention depicted in  FIG. 1 ; 
         FIG. 3  is a partial front view of a first variant of a support of the friction device according to a first embodiment of the invention; 
         FIG. 4  is a front view of a second variant of a support of the friction device according to the first embodiment of the invention; 
         FIG. 5  is a partial front view of a third variant of a support of the friction device according to the first embodiment of the invention; 
         FIG. 6  is an exploded view of a friction device according to a second embodiment of the invention; 
         FIGS. 7 to 12  are schematic views in section respectively of two supports of the friction device depicted in  FIG. 6  and of five variants of these supports. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts a friction device for a clutch, in particular for a motor vehicle. This friction device is designated by the general reference  10 . 
     The friction device  10  comprises first  11  and second  12  friction lining members, substantially annular and coaxial to a center axis C thereof. 
     The first  11  and second  12  friction lining members comprise respectively first  13  and second  14  friction linings, delimited by opposite friction faces, intended respectively to cooperate with a pressure plate and a reaction plate (not shown) fixed to an engine flywheel (not shown) for rotation about the center axis C. 
     The first  11  and second  12  friction lining members also comprise respectively first  16  and second  18  supports, fixed to a gearbox shaft (not shown), to which the first  12  and second  14  friction linings are fixed, for example by adhesive bonding, for rotation about the center axis C. In a variant, at least one friction lining member is formed in a single piece, for example injection moulded. 
     The first  16  and second  18  supports are substantially annular and coaxial to the center axis C thereof, and separated axially from each other. In general, these first and second supports are made from composite material or steel preferably comprising 0.68% or 0.75% carbon (designated respectively XC68 and XC75 according to the French AFNOR standard). 
     It should be noted that, in order to ensure constant efficacy of the friction linings, the friction device  10  preferably comprises a wear take-up device (not shown) for the linings  13 ,  14 . 
     The friction device  10  comprises elastic axial bracing means  19  for the first  16  and second  18  supports, intended to provide the progressiveness of the clutch. According to a first embodiment of the invention, the elastic bracing means  19  comprise an elastomeric member  20  preferably comprising three annular rings, substantially coaxial, arranged between the first  16  and second  18  supports. 
     The friction device  10  also comprises means  21  of connecting the first  16  and second  18  supports together, depicted in more detail in  FIG. 2 . 
     The connecting means  21  comprise first connecting tongues  22 , each provided with a single first end  22 A for fixing to an internal contour of the first support  16 , and second connecting tongues  24 , each provided with a single first end  24 A for fixing to the internal contour of the second support  18 . As depicted in  FIGS. 1 and 2 , the first connection tongues  22  and the second connecting tongues  24  arranged so that each one of the first connection tongues  22  is axially aligned with one of the second connecting tongues  24  in the direction of the center axis C, and each of the first connection tongues  22 ,  24  extends from the first end  22 A,  24 A to the second end  22 B,  24 B thereof in the same circular direction about the center axis C. 
     In the example depicted in  FIG. 1 , the first fixing ends  22 A,  24 A of the tongues  22 ,  24  are made in one piece with the corresponding support  16 ,  18 . 
     The connecting tongues  22  of the first support  16  are each provided with a single second end  22 B for fixing to a single second fixing end  24 B of one of the corresponding connecting tongues  24  of the second support  18 . 
     It should be noted that the first  22 A,  24 A and second  22 B,  24 B fixing ends of each connecting tongues  22 ,  24  have a mutual angular (i.e., circumferential) offset between them with respect to a plane perpendicular to the center axis C (i.e., in a circumferential direction D around the center axis C), as depicted in  FIGS. 1-5 . Generally the distance between the first  22 A (or respectively  24 A) and second  22 B (or respectively  24 B) fixing ends of each connecting tongue  22  (or respectively  24 ) is between 5 and 60 mm, preferably between 20 and 40 mm. 
     Moreover, the connecting tongues  22  of the first support  16  are bent, so that their first  22 A and second  22 B fixing ends are mutually offset axially. 
     Thus, when the first  16  and second  18  supports move axially with respect to each, for example by gripping between the pressure plate and reaction plate, the first  16  and second  18  supports move, parallel with respect to each other, by screwing along their axis. 
     It should therefore be noted that the angular offset between the first  22 A and second  22 B fixing ends of the tongues  22  is variable according to the axial separation of the two supports  16 ,  18 . 
     The invention permitting a substantially parallel movement of the first  16  and second  18  supports with respect to each other, the contact of the friction linings with the pressure and reaction plates is optimized. 
     Thus is it possible to use friction linings  13 ,  14  of reduced dimensions, preferably such that the ratio of their radial width to their outside diameter is less than 0.10 and/or such that their thickness is limited. 
     In a variant, it is also possible to use friction linings  13 ,  14  of dimensions adapted to radially overlap on the first fixing end  22 A,  24 A of the tongues  22 ,  24 . In this way the connection between the tongues  22 ,  24  and their corresponding support  16 ,  18  is reinforced because of the connection by adhesive bonding between the tongues  22 ,  24  and the parts of the friction linings  13 ,  14  overlapping on these tongues  22 ,  24 . 
     The tongues  22 ,  24  being acted on more than the supports  16 ,  18 , it may be advantageous to produce these tongues  22 ,  24  from a steel other than that of the support  16 ,  18  and/or to confer a greater thickness on them, in order to increase their resistance to traction and/or buckling. 
     Thus, according to a first variant of the first embodiment of the invention, depicted in  FIG. 3 , the first fixing end  22 A (or respectively  24 A) of each connecting tongue  22  (or respectively  24 ) is attached, for example by riveting, to the corresponding support  16  (or respectively  18 ). 
     According to a second variant of the first embodiment, the connecting tongues  24  of the second support  18  have the appearance depicted in  FIG. 4 . Each connecting tongue  24  is delimited by two edges, radially external  26 E and internal  261  respectively, diverging with respect to each other from the second end  24 B towards the first end  24 A of the connecting tongue  24 . 
     It should be noted that it is possible to define, on each connecting tongue  24  of the second support  18 , an angular sector A with a vertex coinciding substantially with the second end  24 B of this tongue  24  and extending as far as the internal contour of the second support  18  without any interruption of material, with an angle of between 10° and 35°, where an axis S perpendicular to a radius passing through the center axis C of the friction device  10  is included in the angular sector A. The continuity of material in this angular sector optimizes the resistance of the connecting tongues  24  to the forces undergone by the first  16  and second  18  supports when they transmit a torque between the engine flywheel and the gearbox shaft. 
     The connecting tongues  22  of the first support  16  are similar to the connecting tongues  24  except that they are bent, unlike the connecting tongues  24 . 
     According to a third variant depicted in  FIG. 5 , each connecting tongue  24  is separated from the rest of the second support  18  by a cutting line T emerging in a stress distribution eye  27 . The connecting tongues  22  of the first support  16  are similar to the connecting tongues  24  except that they are bent, unlike the connecting tongues  24 . 
       FIGS. 6 and 7  depict a friction device according to a second embodiment of the invention. In these figures, the elements similar to those in the previous figures are designated by identical references. 
     According to this second embodiment, the bracing means  19  comprise elastic bracing tongues  28 . These bracing tongues  28  are cut from the support  16  and are preferably disposed tangentially to a circle coaxial with the support  16 . In a variant the bracing tongues can be disposed radially. 
     The elastic bracing tongues  28  are shown in more detail in  FIG. 7 . 
     Each elastic bracing tongue  24  is provided with a first end  26 A for connection to the first support  16  and a second free end  28 B. The bracing tongues  28  are bent so that their first  28 A and second  28 B ends are offset axially from each other. Thus the second end  28 B of each bracing tongue  28  is able to come into contact with the second support  18 , in particular when the first  16  and second  18  supports move towards each other, so as to ensure progressiveness of the clutch. 
     Preferably the connecting tongues  22  and the bracing tongues  28  each extend from their first end  22 A,  28 A towards their second end  22 A,  28 A in identical respective circular directions. Thus, when the first  16  and second  18  supports move axially with respect to each other, by screwing, the free ends  28 B of the bracing tongues  28  that deform remain substantially fixed with respect to the second support  18 . 
     Preferably also, the support  16  provided with the elastic bracing tongues  28  is the support carrying the lining  12  intended to cooperate with the pressure plate. 
     According to a variant depicted in  FIG. 8 , the support  16  comprises at least two bracing tongues  28  having different axial offsets between their first  28 A and second  28 B ends. These tongues  28  can also have different stiffnesses. In this way it is possible to optimize the progressiveness of the clutch. 
     Some bracing tongues  28  can also be connected to the opposite support  18 , for example by adhesive bonding, welding or snapping on. These bracing tongues  28 , connected to the two supports  16 ,  18 , make it possible, in addition to their progressiveness function, to limit the separation of these supports  16 ,  18 . 
       FIGS. 9 to 12  depict four other variants of the second embodiment of the invention in which the first  16  and second  18  supports are each provided with at least one bracing tongue  28 ,  30 . These tongues  28 ,  30 , referred to as matched, are respectively connected to the first  16  and second  18  supports. 
     According to the variant depicted in  FIG. 9 , the free ends of the matched bracing tongues  28 ,  30  extend from their first end  28 A,  30 A towards their second free end  28 B,  30 B respectively in opposite circular directions. 
     According to the variant depicted in  FIG. 10 , the free ends of the matched tongues  28 ,  30  are provided with mutual contact surfaces  28 C,  30 C, such that the contact surface of a matched tongue  28 ,  30  is opposite the support  18 ,  16  to which it is not connected. The matched bracing tongues  28 ,  30  are substantially symmetrical with respect to a plane parallel to the first  16  and second  18  supports. 
     According to the variant depicted in  FIG. 11 , the free ends of the matched tongues  28 ,  30  are also provided with mutual contact surfaces  28 C,  30 C such that the contact surface of a matched tongue  28 ,  30  is opposite the support  18 ,  16  to which it is not connected. However, according to this variant, the bracing tongues  28  and  30  are substantially symmetrical with respect to a point of contact between the matched bracing tongues. 
     According to the variant depicted in  FIG. 12 , the free ends of the matched bracing tongues  28 ,  30  are provided with mutual contact surfaces  28 C,  30 C such that the contact surface of a matched tongue  28 ,  30  is opposite the support  16 ,  18  to which it is connected. Thus the matched tongues  28 ,  30  cooperate with each other so as to limit the separation of the supports  16  and  18 . 
     Four examples of embodiments according to the invention have been manufactured and have made it possible to obtain very good resistance to centrifugation. 
     The linings are adhesively bonded to a metal support of approximately 0.3 mm made from XC 68 steel. In this way the presence of fixing rivets is avoided. The dimensions of the linings are set out in the following table: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                 Radial width of 
               
               
                 Outside diameter 
                 Inside diameter 
                 Radial width of 
                 the lining/outside 
               
               
                 (mm) 
                 (mm) 
                 lining (mm) 
                 diameter 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 180 
                 145 
                 17.5 
                 0.097 
               
               
                 180 
                 148 
                 16 
                 0.089 
               
               
                 215 
                 175 
                 20 
                 0.093 
               
               
                 215 
                 190 
                 22.5 
                 0.096 
               
               
                   
               
             
          
         
       
     
     It is also found that the friction devices thus produced have a low overall inertia. 
     It should be noted that the invention is not limited to the embodiments previously described. 
     This is because it is for example possible to combine various characteristics of the different embodiments and/or of the different variants without departing from the scope of the invention.