Abstract:
A hydrokinetic coupling apparatus ( 10 ), in particular for a motor vehicle, comprising a housing ( 12 ) provided with a wall ( 24 ), with globally transverse orientation, a turbine wheel ( 30 ), and a locking engagement ( 16 ), including a piston ( 50 ) linked in rotation with the housing ( 12 ) and a set ( 56 ) of parallel friction discs ( 120, 124, 122 ), which comprises two front ( 120 ) and rear ( 122 ) discs linked in rotation with the turbine wheel ( 30 ) and an intermediate disc ( 124 ) which is linked in rotation with the two elements constituted by the piston ( 50 ) and the transverse wall ( 24 ) of the housing ( 12 ). The piston ( 50 ) and the transverse wall ( 24 ) of the housing ( 12 ) are linked in rotation by straps ( 104 ) substantially elongated tangential to a circumference of the assembly and whereof the opposite ends are attached to these two elements, and the intermediate friction disc ( 124 ) is driven in rotation by means ( 114, 138 ) attaching the ends of the straps ( 104 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a hydrokinetic coupling apparatus, notably for a motor vehicle, of the type described and depicted for example in the document WO-A-93/13339. 
     2. Description of Related Art 
     This document describes and depicts a hydrokinetic coupling apparatus, notably for a motor vehicle, of the type having: 
     a casing provided with a wall, of transverse orientation overall, able to be connected with respect to rotation to a driving shaft; 
     a turbine wheel fixed with respect to rotation to a hub able to be connected with respect to rotation to a driven shaft; 
     a lock-up clutch, acting between the turbine wheel and the transverse wall, which has, arranged axially from front to rear between the turbine wheel and the transverse wall: 
     a damper plate, fixed with respect to rotation to a turbine wheel, in the form of an annulus with a roughly transverse orientation and which has at its external periphery an annular portion, of roughly axial orientation, which circumferentially guides and holds circumferentially acting elastic members, and which has areas, of roughly transverse orientation, of abutment for the circumferential ends of the elastic members; 
     a piston in the form of an annulus, of transverse orientation overall, movable axially and connected with respect to rotation to the casing; 
     and at least one flat annular friction disc, of roughly transverse orientation, which carries, on its front and rear opposite faces, two annular friction linings which are able to clamped axially by the piston between respectively itself and the opposite internal face of the transverse wall of the casing, the friction disc having at its external periphery drive lugs which extend axially towards the rear inside the peripheral annular portion of the damper plate in order each to be received between the circumferential ends of two consecutive circumferentially acting elastic members, and which is able to move axially with respect to the damper plate. 
     In the document FR-A-2.634.849, the lock-up clutch has a set of flat annular parallel friction discs, of roughly transverse orientation, which is able to be clamped axially by the piston between effectively itself and the opposite internal face of the transverse wall of the casing and which includes on the one hand two radially external front and rear discs which are here connected with respect to rotation directly to the turbine wheel and on the other hand a radially internal intermediate disc which is disposed axially between the front and rear discs and which is connected with respect to rotation to the piston, annular friction linings being interposed between the opposite annular faces of the friction discs, the piston and the internal face of the transverse wall. As a result the solution is noisy. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to mitigate this drawback. 
     The invention proposes a hydrokinetic coupling apparatus of the type mentioned above which is the subject of the document FR-A-2.634.849, characterised in that the piston and the wall of the casing are connected with respect to rotation by tongues substantially elongated tangentially to a circumference of the apparatus and whose opposite ends are coupled to these two elements, and in that the intermediate friction disc is driven in rotation by means for coupling the ends of the tongues, to one of the two elements. 
     By virtue of the tongues, the piston is formed and moves easily axially. The solution is not noisy. The friction discs can be made to slip more easily in order, for example, to filter the vibrations at a given vehicle engine speed. 
     Preferably it is the means of coupling the ends of the tongues to the transverse wall which drive the intermediate disc. 
     As a result the piston undergoes less stress than in the prior art and can move rapidly in a quiet manner. 
     The drive washer described in the document FR-A-2 726 620 is for example used. 
     This washer forms part of the coupling means. 
     According to other characteristics of the invention: 
     the tongues are coupled by their first ends to a first one of the two elements which they connect with respect to rotation, by means of a drive washer common to all the tongues and which is coupled to this first element, and the intermediate friction disc is driven in rotation by the common drive washer; 
     the drive washer can be distinct from the tongues or be in a single piece with them; 
     the external radial periphery of the common drive washer has a ferrule of roughly axial orientation having at least one notch through which there extends, radially inwards, a drive lug belonging to the intermediate friction disc; 
     the ferrule of the common drive washer has a series of notches distributed angularly in a regular manner, through each of which there extends, radially inwards, a corresponding drive lug in a series of lugs belonging to the intermediate friction disc; 
     each notch is open axially in the axial end edge of the ferrule of the common drive washer; 
     each drive lug is received with circumferential clearance in a corresponding notch in the ferrule of the common drive washer; 
     each drive lug of the intermediate friction disc lies in the plane of the disc; 
     the ferrule of the common drive washer is an axially oriented cylindrical ferrule; 
     the ferrule of the common drive washer is a frustoconical ferrule; 
     the common drive washer is coupled to the first element by gluing or welding or riveting; 
     the common drive washer is coupled to the transverse wall of the casing; 
     the front and rear friction discs each have at least one drive lug which extends radially outwards in order to be received in a notch in an axially oriented cylindrical annular skirt connected with respect to rotation to the turbine wheel; 
     the front and rear friction discs each have a series of drive lugs distributed angularly in a regular manner in order to be received in corresponding notches in an axially oriented cylindrical annular skirt connected with respect to rotation to the turbine wheel; 
     each notch is axially open; 
     each drive lug extends in the plane of its friction disc; 
     one of the front or rear friction discs has at least one drive lug which extends radially outwards in order to be received in a notch in an axially oriented cylindrical annular skirt connected with respect to rotation to the turbine wheel, and the other one of the rear and front friction discs has at least one drive lug which cooperates with a driving lug of said at least one disc; 
     the drive lug of said other disc extends radially outwards and then axially in the direction of the other disc; 
     the drive lug of said other disc is angled at 90°, and the drive lug of said disc extends in the plane of this disc; 
     the drive lugs of the front and rear friction discs are angled twice so that their free end portions, radially external and of transverse orientation, are substantially coplanar; 
     one of the front or rear friction discs has at least one drive lug angled at 90° which extends radially outwards and then axially in the direction of the other disc opposite a drive lug which extends radially outwards from the periphery of the other one of the rear or front friction discs and whose free end extends radially in a notch formed in an annular cylindrical skirt, of roughly axial orientation, connected with respect to rotation to the turbine wheel. 
     As a variant, supplementary axially elastic tongues connect the intermediate disc to the drive washer with respect to rotation. 
     As a variant it is the tongues which are extended for driving the intermediate disc. These extensions affect the ends of the tongues. 
     the lock-up clutch has a torsion damper interposed between the turbine wheel and the piston, and the said skirt belongs to an input part of the torsion damper. 
     The front and rear friction discs can be connected with respect to rotation, with axial mobility, to a piece attached to an input part coupled rigidly or elastically to the turbine wheel and therefore fixed to the turbine wheel. 
     For example, a ring can be attached to a first guide washer for a torsion damper having a damper plate fixed to the turbine wheel and coupled elastically to the first guide washer. 
     The ring has an axially oriented annular skirt with teeth for meshing with teeth on at least one of the friction discs, and advantageously with both. 
     As a variant, the ring is attached directly to the damper plate fixed to the turbine wheel. 
     Preferably, two guide washers are provided on each side of the damper plate for symmetrical passage of the torque. The ring, in general terms the attached piece, can have the required thickness for transmitting the torque. It can have the required axial and/or radial size for driving the two friction discs. By virtue of this arrangement, the thickness of the guide washer or of the damper plate to which the attached piece is fixed can be reduced. 
     The front and rear friction discs can come into engagement with each other, to connect them with respect to rotation, radially above drive lugs or, in general terms, a drive connection provided on a piece coupled rigidly or elastically to the turbine wheel. 
     Thus it is possible to reduce the cantilevers and therefore the axial length of the drive lugs, which makes it possible not to excessively weaken the piece from which the said lugs came. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will emerge from a reading of the following detailed description, for an understanding of which reference should be made to the accompanying drawings, in which: 
     FIG. 1 is a half-view in axial section of a first embodiment of a coupling apparatus according to the teachings of the invention; 
     FIG. 2 is a view to a larger scale of a detail of FIG. 1 which illustrates more particularly the set of friction discs; and 
     FIGS. 3 to  5  are views similar to those of FIG. 2 which illustrate respectively second, third and fourth embodiments of the invention. 
     FIGS. 6,  8 ,  9  and  10  are views similar to FIG. 1 for respectively a fifth, sixth, seventh and eighth embodiment of the invention. 
     FIG. 7 is a front view in the direction of the arrow in FIG. 6 showing the drive piece and the discs with the different rotation connections allowing an axial movement. 
     FIGS. 11,  12 ,  16 ,  17 ,  18 ,  22 ,  24 ,  26 ,  28 ,  30 , are views similar to FIG. 1 for yet other example embodiments. 
     FIG. 13 is a partial view showing the disc and studs in FIG.  12 . 
     FIG. 14 is a partial view showing a U-shaped piece. 
     FIG. 15 is a view similar to FIG. 13 for another embodiment. 
     FIG. 19 is a partial view showing the intermediate disc and the tongues of FIG.  18 . 
     FIG. 20 is a view similar to FIG. 19 for another example embodiment. 
     FIG. 21 is a partial view showing a variant projection. 
     FIGS. 23,  25 ,  27 ,  29 ,  31  are partial views showing the intermediate disc and the second tongue of FIGS. 22,  24 ,  26 ,  28 ,  30 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, identical, similar or analogous components will be designated by the same reference numbers. 
     To facilitate the reading of the description and claims, the terms front, rear, upper, lower, vertical, horizontal etc will be used non-limitatively and with reference to the figures. 
     According to a design which is known, for example, from the document WO-A-94/07058, to which reference can be made for more information, a hydrokinetic coupling apparatus  10  able to rotate about an axial symmetry axis X—X, such as the one illustrated in FIGS. 1 and 2, has, arranged in one and the same sealed housing filled with oil and forming a casing  10 , a torque converter  14  and a locking clutch  16 , usually referred to as a lock-up clutch. 
     The casing  12 , here metallic, constitutes a driving element and is able to be connected with respect to rotation to a driving shaft (not shown), namely for example the crankshaft of the internal combustion engine in the case of an application to a motor vehicle, as illustrated in certain figures. 
     The casing  12 , annular in shape overall, consists of two half-shells, front  20  and rear  22 , facing each other and sealingly fixed at their external periphery, usually by a welding operation  21 . 
     The rear shell  22  is able to be connected with respect to rotation to the driving shaft and consists essentially of an annular wall  24  which is of transverse orientation overall, that is to say which extends in a radial plane perpendicular to the axis X—X of the apparatus, and which is extended at its external periphery by an annular cylindrical wall  26  of roughly axial orientation. 
     The front half-shell  20  is shaped so as to define an impeller wheel with vanes  28  in the internal face of this half-shell  20 . 
     These vanes  28  face the vanes  29  of a turbine wheel  30  fixed here by riveting, or by welding as a variant, to a plate  32  of the hub produced here in a single piece with a hub  34  fluted internally at  35  for rotational connection to a driven shaft (not shown), namely the input shaft of the gearbox in the case of an application to a motor vehicle. 
     The driven shaft is hollowed out internally to form a channel allowing a control fluid, here oil, to gain access to a blind rear central bore  54  in a guide and thrust ring  38  located axially between the hub  34  and the transverse wall  24  and here forms a centering device. 
     The driven shaft communicates through channels  68  with a chamber  58  as described below. 
     The guide ring  38  is a machined solid piece which consists essentially of a front and radially external portion  40  and a rear and radially internal portion  42 . 
     The function of the rear portion  42 , as will be explained below in more detail, is essentially to provide the positioning and centering and/or fixing of the guide ring  38  with respect to the transverse wall  24 , whilst the front portion  40 , with a larger diameter, is delimited radially towards the outside by a machined cylindrical area  44  for the axial sliding guidance of a piston  50  which has at the centre for this purpose an axially oriented ferrule  48 . 
     The cylindrical guide area  44  has an internal radial groove  52  which receives an annular sealing joint which provides the sealed sliding of the piston  50  on the guide ring  38 . 
     The front portion  40  of the guide ring  38  includes the aforementioned rear central bore  54  in which a free end portion of the driven shaft, which passes through the hub  34 , is able to be rotatably received. 
     According to a design known, for example, from the document FRA-2.634.849, the piston  50  delimits—with the guide ring  38 , the transverse wall  24  and a set  56  of friction discs—a variable-volume chamber  58  fed by the driven shaft through the guide ring  38 . 
     From its rear face  60 , of transverse orientation, the large-diameter front portion of the guide ring  38  has a series of axially oriented studs  62 , which are distributed angularly in a regular manner and which determine, with the internal face  64  of the central part  66  of the transverse wall  24 , as many radially oriented passages which put the internal chamber  58  in communication with one or more channels  68 , which pass through the smaller-diameter rear cylindrical part  42  of the ring  38 , in order to make the chamber  58  communicate with the inside of the ring  38  which is closed axially towards the rear and which opens out axially towards the front inside the hub  34 ,  35 . 
     The hub  34  is coaxial with the other elements of the apparatus, and notably the ring  38 , and is extended radially towards the outside, as from the rear end portion of its socket-shaped body, through the transversely oriented plate  32 . 
     A piece  70  is attached to the plate  32  in order to constitute an axial-abutment piece, on the one hand for the front radial face of the front part of the ring  38  and on the other hand for the front end face of the ferrule  48  for slidably guiding the piston  50 . 
     To this end, the piece consists essentially of a plate in the form of a flat ring which is centred in a countersink  71  in the ring  38 . 
     The rear flat annular face of the plate constitutes a support face for the ferrule  48  and for the front transverse face of the ring  38  which, for its centering, has a complementary countersink. The rear transverse face of the plate  32  has holes which receive axial pins  174  on the attached plate  70 , which therefore provides a centering of the ring  38  with respect to the hub  34 . 
     The plate  70  also forms a strut between the plate  32  and the piston  50 , that is to say, in the disengaged position of the piston  50 , there exists an axial clearance between the opposite front annular face of the internal radial part of the piston  50  and the opposite annular face of the plate. 
     The main central part of the plate  32  is extended radially outwards by an external radial edge  74 , with a greater axial thickness, which has an annular countersink  76  formed in the front transverse face of the plate  32 . 
     The transverse bottom of the countersink  76  constitutes a rearward axial support surface for a transversely oriented flat annular internal radial edge  78 , belonging to a damper plate  80  forming the output element of the lock-up clutch  16 . 
     This internal radial edge  78  is fixed to the thick edge  74  of the plate  32  by a series of rivets  82 , each of which passes through a hole formed in the edge  74  of the plate  32  and a corresponding hole formed in the internal radial edge  78  of the damper plate  80 . Each rivet also passes through a hole formed in a lug  84  belonging to the turbine wheel  30 . 
     The lugs  84  belong to a series of lugs on the turbine wheel  30 , each of which extends radially towards the inside in a transverse plane and is adjacent to the front annular face of the edge  78  of the damper plate  80  so as to be also received inside the countersink  76 . 
     As a variant, the lugs  84  are connected together to form a ring. 
     As from its internal radial edge  78 , the damper plate  80  has, radially towards the outside, an elbow  86  and then a central portion in the form of a flat annulus  88  so as to substantially follow the facing contour of the turbine wheel  30 , and then a portion of roughly frustoconical shape  80 , and an external peripheral annular portion  94 . 
     The annular portion  94  is shaped roughly as an axially oriented recess which is open axially towards the rear in the direction of the transverse wall  24 . 
     In section, the peripheral annular portion  94  has a hollow profile, and receives a series of circumferentially acting coil springs  95 , which act on one and the same circumference. 
     According to a principle known through the document WO-A-94/07058, to which reference should be made for more information, the springs  95  are thus guided circumferentially and are retained axially towards the rear by the input part  98  of a torsion damper  96  of the clutch  16 . 
     The output part of the damper  96  consists of the portion  94 . 
     The springs  95  thus act between the output damper plate  80  and the friction discs belonging to the assembly  56 . To this end, the input part  98  and the guidance portion  94  of the springs  95  have support areas respectively  102 ,  100 , which are circumferential support surfaces consisting of the dished circumferential ends. 
     The areas  102  consist of dished parts and the areas  100  of clefts as described in the aforementioned document WO-A-94/07058. 
     According to an arrangement which is known from the document FR-A-2.726.620 and French patent applications FR 97 07758 and FR-97 08386, the piston  50  is connected with respect to rotation to the transverse wall  24  by a series of elastic tongues  104  arranged substantially along a circumference and which act tangentially between protrusions  106  on the piston  50  to which longitudinal ends (visible in FIGS. 7,  9  and  10 ) of the tongues  104  are connected by riveting, the tongues  104  being connected at their other ends by rivets  110  to brackets or lugs  112  on a drive washer  114  which is common to all the tongues and which is connected, for example by bonding, riveting or welding, to a facing portion  116  of the internal face  64  of the transverse wall  24  of the casing  12 . 
     The lugs  112  are offset axially towards the piston  59  with respect to the main part of the washer adjacent to the portion  116 . 
     Each of the tongues  104 , elastically deformable axially, consists here of an axial stack of two identical tongues made from cropped sheet metal. The tongues  104  are four in number are driven angular in a regular manner about the axis X—X of the hydrokinetic coupling device. 
     As can be seen in the figures, each tongue  104  is adjacent to the opposite transverse face of the corresponding protrusion  106  which, in the clamped or engaged position of the piston  50 , is substantially coplanar with the plane in which there extend the transverse faces of the lugs or brackets  112  against which the ends  108  of the tongues  104  are axially clamped by riveting. These lugs  112  are hollowed out opposite the rivets for fixing the tongues  104  to the piston  50 . 
     Thus, in the clamped position of the clutch  16 , the tongues  104  all extend substantially in the same plane as the median transverse plane of the set  56  of friction discs externally delimiting the chamber  58 . 
     A description will now be given in detail of the set  56  of friction discs, and their means of driving in rotation, of the first embodiment referring more particularly to FIG.  2 . 
     The set  56  includes three adjacent friction discs, amongst which can be seen a front disc  120  and a rear disc  112 , between which there is axially disposed an intermediate friction disc  124 . 
     Each of the three friction discs, which belong to the set  56 , is roughly in the form of a flat annular disc, of roughly transverse orientation, which is a piece of cropped sheet metal, where applicable folded. 
     In order to constitute a set  56  of friction discs, certain lateral faces of the discs are provided with a friction lining. 
     In the example illustrated in FIGS. 1 and 2, given by way of non-limitative example, each of the opposite lateral faces of the front  120  and rear  122  friction discs is provided with a friction lining  126  which is for example bonded to the corresponding metal face, the free face of each friction lining being able to be smooth or grooved according to a design known from the document PCT/EP 92/02480 to allow a controlled progressive sliding. 
     In this example embodiment, the opposite lateral faces of the intermediate friction disc  124  therefore have no friction linings, just like the opposite annular face  128  of the external periphery of the piston  50  and the opposite annular portion  130  of the internal face  64  of the transverse wall  24  of the casing  12 . 
     As a variant the intermediate friction disc  124  and the faces  128 ,  130  are provided with friction linings  126 , whilst the discs  120 ,  122  have no friction linings. All combinations are possible. 
     According to one characteristic of the invention, the intermediate disc  124  is connected with respect to rotation to the subassembly consisting of the two elements—piston  50  and transverse wall  24 —which are connected with respect to rotation by tangential tongues  104 . 
     To this end, and in accordance with the teachings of the invention, the intermediate friction disc  124  is more particularly connected with respect to rotation to the means of coupling the ends of the tongues  104  to one of the two elements  50  and  24 . The coupling means include here the washer  114  driving the tongues  104 . 
     More precisely, the intermediate disc  124  in the form of a flat annulus has at its internal radial periphery  132  a series of drive lugs  124  which are angularly distributed in a regular manner and each of which extends radially inwards in the transverse plane of the body of the intermediate friction disc  124 . 
     Each of the radial drive lugs  134 , for the purpose of driving the intermediate friction disc  124  in rotation, is received, with circumferential clearance, in a notch  136  formed in an axially oriented annular cylindrical ferrule  138  which belongs to the common washer  114  for driving the tongues  104  in rotation, described previously. 
     To this end, the ferrule  138  has a series of cutouts which extend axially from the front axial end edge  140  of the ferrule  138  so as to constitute notches  136  which open out axially in the free end edge  140  of the ferrule  136  and each of which is delimited circumferentially by two consecutive axially oriented lugs  139 . 
     The axial length of the notches  136  is such that the driving lugs  134  for the intermediate friction disc  124  can move axially in the notches  136  and therefore with respect to the piston  50  and transverse wall  24 . 
     The front  120  and rear  122  friction discs, the main annular parts of which, which carry friction linings  126 , are situated radially at the same dimension as the annular central part of the intermediate friction disc  124  which is received clamped between the friction linings  126  carried by the discs  120  and  122 . The front  120  and rear  122  friction discs are driven in rotation by the damper  96  of the lock-up clutch  16 , or more precisely by the input part  98 . 
     To this end, the input part  98  has on the inside an axially oriented skirt  142  which is produced in one piece by pressing and which has an annular cylindrical shape arranged radially towards the inside with respect to the springs  95 , and whose parts  156  dished radially towards the inside  144  delimit between them notches  146  which are open axially in both directions and radially towards the inside. Flutes are thus formed, and this in a continuous manner. 
     The notches  146  are distributed angularly in a regular fashion and each of them is designed to receive, with circumferential clearance, a radial lug  148  for driving the front friction disc  120  in rotation. The drive lugs  148  also serve for centering this front friction disc  120  since their external radial end edge  152  cooperates with the concave cylindrical portion  154  of the dished parts  156  of the skirt  152 . 
     In the first embodiment illustrated in FIGS. 1 and 2, the rotation of the rear friction disc  122 , simultaneously with the front friction disc  120  and by the input part  98 , is ensured, radially below the skirt  142 , indirectly by means of the front friction disc  120 . The skirt  142  is directed axially towards the damper plate  80  in the opposite direction to the wall  24 . 
     To this end, the external radial periphery  158  of the rear friction disc  122  has a series of drive lugs  160  which are angularly distributed in a regular manner and each of which is angled at 90° so as to extend first of all radially towards the outside and then axially, from the rear to the front in the direction of the front friction disc  120 . 
     Thus each of the angled drive lugs  160  terminates in an axially oriented free end portion  162  which is received circumferentially between two consecutive lugs  148  for driving the front friction disc  120  in rotation. 
     A description will now be given of the second embodiment illustrated in FIG. 3, which is merely a variant of the first embodiment described previously. 
     In fact it is here the rear friction disc  122  which by means of its lugs  160  is driven in rotation directly by the input part  98  of the torsion damper  96  with springs  95  and which indirectly drives in rotation the front friction disc  120 , the means of driving in rotation the intermediate disc  124  by the washer  114  common to the tongues  104  being identical to those described previously. 
     The angled lugs  160  for driving the rear friction disc  122  in rotation cooperate directly, through the axial end portions  162 , with notches  146  in the input element  98 . 
     Each notch  146  is here delimited by lugs  164  angularly distributed in a regular manner, and each of which extends radially towards the inside from the skirt  142 , these drive lugs  164  being produced by cropping and bending the material making up the skirt  142 . 
     The lugs  148  for driving the front friction disc  120  in rotation here have an external radial length which is shorter, if they are compared with the previous embodiment, and are received circumferentially in notches, each of which is delimited by two consecutive angled lugs  160 , that is to say more precisely between two consecutive axial end portions  162 . 
     A description will now be given of the third embodiment illustrated in FIG.  4 . 
     In this embodiment, it is found first of all that the ferrule  138  belonging to the washer  114  common to the tongues  104  here has a roughly frustoconical shape whilst having, as in the case of the cylindrical annular ferrules  138  illustrated in FIGS. 2 and 3, notches  136  for driving in rotation the intermediate friction disc  124  with its drive lugs  134 . The contact surfaces between the edges of the notches  136  and the lugs  134  are thus increased in order to reduce wear. 
     The front  120  and rear  122  friction discs are here identical, with a particularly simple design, and are driven in rotation simultaneously and directly by the skirt  142  of the input element  98  of the elastic damper. 
     To this end, as in the case of the first two embodiments, the drive lugs  148  of the front friction disc  120  extend radially toward the outside in the transverse plane of the disc  120  and, in the same way, the drive lugs  160  of the rear friction disc  122  also extend radially outwards in the transverse plane of the rear friction disc  122 . 
     The skirt  142  has a series of notches  146  which are angularly distributed in a regular manner and each of which is delimited circumferentially by two consecutive lugs  164  on the skirt  142  which are here axially oriented and which delimit between them notches  146  open axially towards the rear. 
     In the fourth embodiment illustrated in FIG. 5, if it is compared with the third and previous embodiment, the rear friction disc  122  is driven directly in rotation by the skirt  142  whilst the front friction disc  120  is driven indirectly in rotation by the rear friction disc  122 . 
     To this end, the drive lugs  160  for the rear friction disc  122  are angled twice at 90°, that is to say in an S, so that their radially external free end portion extends in a median transverse plane substantially coplanar with the plane in which the intermediate friction disc  124  lies. 
     In the same way, but symmetrically with respect to this median plane, the drive lugs  148  of the front friction disc  120  are angled twice so as to have an S-shaped profile. The radially external free end portions of the drive lugs  148  also lie in the same plane as the drive lugs  160  and are nested and interposed between the drive lugs  160  of the rear friction disc  122 . 
     By way of variant, not shown, it is the drive lugs  126  for the front friction disc  120  which can be the longest, radially towards the outside, in order to directly ensure the driving of the disc  120  in rotation by the ferrule  142 , the drive lugs  160  for the rear friction disc  122  then being shorter. 
     It will be noted that, in FIGS. 4 and 5, the skirt  142  is directed towards the wall  24 , that is to say in the opposite direction to the damper plate  80 . 
     Naturally, in a variant, the tongues  104  are extended radially towards the outside, by means of lugs, and the intermediate disc  124  has a ferrule with notches of the same type as the ferrule  138  of the drive washer  114 . 
     The extensions of the tongues  104  then enter the notches in the ferrule of the intermediate disc  124  in order to drive the nut in rotation. The extension is produced at the end fixing the tongues  104  to the washer  114 . 
     As a variant, second tongues located radially above the tongues  104 , connect the intermediate friction disc  124  to the drive washer  114  with respect to rotation. These second tongues are carried by the washer  114 , or more precisely by the external periphery of the washer  114 . 
     The second tongues are axially elastic to allow an axial movement of the intermediate disc. 
     They extend for example tangentially. 
     To do this the drive lugs  134  of the disc  124  and lugs of the washer  114  similar to the lugs  112  and offset radially with respect to these are used. 
     Naturally, as can be seen for example in FIG. 7 of the document FR-A-2 726 620, the tongues  104  are in a single piece with the drive washer and therefore carry, as in FIGS. 1 to  5 , the tongues  104 . 
     In this case the wall  24  is dished locally axially in the direction of the damper plate  80  in order to be in the same plane as the lugs  112  in FIG.  1 . 
     This single drive piece can be provided at its external periphery with second tangential tongues fixed directly to the flat-shaped intermediate disc  124 , or more precisely to drive lugs for the latter. The single piece therefore carries the second axially elastic tongues. 
     This single piece is fixed for example by riveting by means of extruded rivets issuing from the wall  24 , as described in the aforementioned application FR-A-2 726 620. 
     As a variant each tongue  104  is attached by individual pieces to the wall  24  and has for example lugs or notches for meshing with notches or lugs provided at the internal periphery of the disc  124 . 
     Naturally the structures can be reversed, for example the single drive piece can be fixed to the piston. The fixing to the transverse wall  24  is achieved by means of rivets. For this the piston has, opposite the rivets fixing the tongues to the transverse wall, passage holes allowing the riveting operation. These holes are then closed off at the end by an obturator, such as a plug mounted in the passage hole. It is possible to operate in the same way to fix the tongues to the piston after having previously fixed the tongues to the wall  24 . 
     The passage holes finally closed off by the obturators being produced in the wall. 
     The obturators can be fixed by bonding, screwing, welding, crimping, snapping on etc to the wall or piston. 
     In all cases the coupling means, for example the drive washer, the individual pieces, the single drive piece or even the tongues themselves are used for driving the intermediate friction disc in rotation either by meshing, or by means of supplementary tongues or extensions. 
     The presence of a damper  96  is not obligatory. The damper plate  80  can be fixed for example directly to the turbine wheel  30 , for example by welding. In a variant it is fixed to the hub. 
     This damper plate, in one embodiment, has a skirt similar to the skirt  124  of the input element  98  in order to drive in rotation at least one of the discs  120 ,  122  as in FIGS. 1 to  5 . The input element is omitted. 
     Naturally, the torsion damper  96  can have another shape and the discs  120 ,  122 ,  124  can be embedded in a friction lining. Thus, for example, in FIG. 4, the discs  120  and  124  can be embedded in a friction lining  126 . The friction lining associated with the disc  120  has a first face allowed to rub against the face or surface  128  of the piston  50 , and a second face allowed to rub against the intermediate disc  124 . 
     Likewise the friction lining associated with the disc  122  has a first face allowed to rub against the portion or surface  130  of the wall  24  and a second face allowed to rub against the intermediate disc  124 . 
     All combinations are possible. The surfaces  128 ,  130  can belong to pieces attached to the piston and/or the wall  24 . These pieces can be provided with grooves in order to cool the friction linings. 
     FIG. 6, similar to FIG. 4, illustrates one of these variants in which the front  120  and rear  122  friction discs, flat in shape, each have teeth meshing with teeth belonging to an axially oriented annular skirt- 242  belonging to a ring  222 . The discs  120 ,  122  are identical. 
     This ring  222  is fixed to a flange  450  belonging to a first guide washer  170 , coupled, by means of elastic members  95 , to the damper plate  80  fixed to the plate  32  of the hub  34  by the rivets  82  also making it possible to fix the internal annulus  84  of the turbine wheel  30 . 
     The hub  34  enters here into the rear central bore  54  of the ring  38 . The bore  54  forms a blind hole and the ring  38 , a centering device, for centering the apparatus on the driving shaft. 
     The hub  34  carries internally a lip joint  320  for cooperating with the end of the driven shaft. A ring  330 , forming a bearing, and a sealing ring  340  act between the external periphery of the hub  34  and the internal periphery of the ring  38 , forming a centering device. 
     A needle bearing  350  acts between the rear face of the plate  32  of the hub and the front face of the ring  38 . The bearing  350  is radially oriented. The ring  222  can be in a single piece with the flange  450  whilst being obtained by rolling and folding in reverse directions as from the flange  450  in order to double the latter in thickness. Likewise needle bearings  550  are provided at the level of the reactor  14 . The joint cooperating with the  48  of the piston  50  can be seen at  152 . 
     Here, the ring  222  is fixedly attached to the flange  450  whilst being in intimate contact with at least part of the external periphery of the flange  450  which is annular in shape and axially oriented. The flange  450  surrounds the damper plate  80  and extends at the external periphery of the washer  170 . 
     The first guide washer  170  is fixed to a second guide washer  180  adjacent to the turbine wheel  30 . More precisely, the guide washers  170 ,  180  are disposed on each side of the damper plate  80  and are fixed together at their internal periphery, in the form of a plate, by small columns  190  each passing, with circumferential clearance, through an opening (not referenced) produced in the damper plate. The torsion damper  96  is therefore located for the major part between the turbine wheel  30  and the piston  50 . 
     The ring  222  extends radially above the piston  50 . The elastic members  95 , here concentric helical springs, are housed in scallops provided at the external periphery of the damper plate  80 . 
     These scallops are delimited by radial lugs on which the circumferential ends of the springs  95  bear. The guide washers  170 ,  180  are shaped at their external periphery so as to match the shape of the springs  95 . For more information, reference should be made to the document FR-B-2 749 634 showing this type of damper and notably to FIG. 5, the connection of the flange  450  to the second guide washer  180 , using crimped lugs each passing through a rectangular opening produced in the second guide washer. Each guide washer  170 ,  180  therefore has a rounded part respectively  500 ,  510  matching the shape of the springs  95 . These parts are interrupted locally by dished parts so that the springs  95  are compressed between the dished parts and the lugs on the damper plate  80  when there is a relative movement between the damper plate  80  and the wall  24 . 
     The ring  222  has a connection area  540  partially matching the rounded shape  500  of the first guide washer. The area  540  connects the ring  222  proper to the skirt  242  in the form of an annular comb because of the presence of an alternation of notches  246 , open axially towards the wall  24 , and driving lugs  264 , distributed in a regular fashion. Two lugs  264  are depicted in dotted lines in FIG.  7 . 
     The lugs  264  and the notches constitute the teeth on the ring. These teeth  264 ,  246  are offset radially towards the inside with respect to the ring  222  attached here by welding to the flange  450 . In FIG. 6, the bead resulting from this welding can be seen in black. Another bead exists between the rounded part and the skirt  242 . As a variant, the fixing is effected by riveting, bonding etc. 
     The ring  222  is thicker than the guide washers  170 ,  180 , which have great strength since the skirt  242  is not formed in the first guide washer  170 . 
     This increase in thickness in the skirt makes it possible to reduce wear and to have the required number of lugs  264  so that heat treatment and other hardening processes can be avoided. In addition the axial length of the skirt  242 , which is stronger, is better controlled. 
     Thus the discs  120 ,  122 , here identical, each have a radially oriented set of teeth made from an alternation of lugs respectively  148 ,  160  and radially open notches. The lugs  148 ,  160  enter the notches  246  in the axially oriented set of teeth in the skirt  242  and vice-versa, the lugs  264  entering the notches in the discs  120 ,  122 . 
     The discs  120 ,  122 , forming drive discs, are therefore connected with respect to rotation, with axial mobility, as in the other figures, with the input part, here formed by the ring  222  with skirt  242 , of the torsion damper  96 . The area  130  is formed by pressing the part  24 . The area  130  extends in axial projection in the direction of the piston  50  with respect to the rest of the wall  24 . 
     The torsion damper  96  can have several stages as described in the document FR-A-2 749 634. 
     Here the intermediate disc  124 , flat in shape, meshes with the common washer  114  driving the tongues as in the embodiment in FIG.  1 . The disc  124  therefore has at its internal periphery a radially oriented set of teeth with an alternation of lugs  134  and notches  134 ′ (FIG.  7 ). 
     The washer  114  has at its external periphery a ferrule  138  with axially oriented teeth formed by an alternation of lugs  136  and notches  136 ′ (FIG.  7 ). 
     The lugs  134  of the disc  124  enter with mounting clearance in the notches  136 ′ in the annular axially oriented ferrule  138  and vice-versa. 
     The skirt can be produced in the first guide washer  170  as described in the document FR-A-2 749 634. In this case, the skirt (FIG. 8) is produced by means of lugs  364  cut in the rounded piece  50 . For example, provision can be made, as in the document FR-A-2 749 634, for three lugs  364  between two dished parts supporting the springs. 
     With the ring  222  of FIG. 6, the lugs have the required axial length, notably because of the increase in thickness of the ring. With lugs  364  cut in the first guide washer  170 , this is not always possible, notably for reasons of strength of the guide washer  170 . 
     Thus, according to one characteristic, the front  120  and rear  122  discs come into engagement with each other radially above the lugs  364  cut out locally, and here regularly annularly in the first guide washer  170 . These lugs come into engagement with the front disc  170 . Thus the lugs  364  can have a reduced length, connections by cooperation with shapes of the lug and notch type act respectively between the discs  120 ,  122  and between the lugs  364  and the disc  122 . 
     Thus, in FIG. 8, the front disc  120  is flat and has at its external periphery radially oriented teeth  442  consisting of a regular angular alternation of lugs and notches open radially towards the outside. The teeth  442  extend radially above the lugs  364  obtained by cropping and folding from the rounded part  500  of the first guide washer  170 . The rear disc  122  has at its external periphery axially oriented teeth  542  directed towards the front disc. 
     The teeth  542  consist of a regular angular alternation of lugs and notches open axially towards the turbine wheel. The lugs in the set of teeth  442  pass through the notches in the set of teeth  542  and vice-versa. 
     In FIG. 8, the different sets of teeth  542 ,  442  can be seen, as well as the teeth acting between the ferrule  138  and the intermediate disc  124 , as described in the other figures. The number of lugs and notches depends on the application. 
     In FIG. 9, the discs  120 ,  122  each have at their external periphery a set of teeth  642 ,  742  inclined in the direction of the other with an alternation of drive lugs and notches entering the notches and lugs of the other set of teeth, and this radially above the lugs  365  coming into engagement with the disc  120 , as in FIGS. 7 and 8. The lugs  364  also have a reduced length. 
     Naturally, in FIG. 10, the lugs  364  can be longer and drive the two discs like the ring  222  in FIG.  6 . 
     Naturally, all the connections with cooperation of shapes between the discs  120  and  122  described in relation to the embodiment in FIGS. 1 to  5  are applicable to the embodiments in FIGS. 6 to  10 . Thus, in FIG. 9, teeth can be provided with drive lugs angled twice as in FIG. 5, the lugs  364  meshing with the disc  120  radially below the connection between the discs  120 ,  121 . 
     In FIGS. 1 to  5 , it is possible to attach the supplementary pieces, advantageously thicker, to the input part  98  of the torsion damper  96  in order to effect the connection with the disc or discs  120 ,  122 . 
     Naturally, the part  98  can be fixed to the turbine wheel. 
     In general terms, the attached piece, such as the ring, is fixed to an element, such as the washer  170 , connected with respect to rotation to the turbine wheel. 
     The connections can be made by means of flutes. Any connection by cooperation of shapes can be envisaged. Naturally, the ring  222  can mesh with a first disc, the second disc coming into engagement with the first disc. A first one of the friction discs  120 ,  122  meshes with the second one of the friction discs over a circumference with a diameter less than that of the skirt  142  (FIGS. 2 and 5) or over a circumference with the same diameter as the set of teeth issuing from the skirt (FIG.  3 ). In FIGS. 8 and 9, a first disc  122  meshes with a second disc  120 , over a circumference with a diameter greater than the skirt formed by the lugs  364 . In FIGS. 4,  6  and  10 , the skirt  142  directly drives the two discs  120 ,  122 . As a variant, the two front  120  and rear  122  discs are connected with respect to rotation to the other one of the rear  122  and front  120  discs by axially elastic tongues. 
     It should be noted that, in FIGS. 8 and 9, the rear disc  122  is fixed with respect to rotation to the front disc  120  in the top part of the springs  95 . 
     In a variant (FIG. 11) the piston  50  has a set of teeth  842  with a circumferential alternation of teeth and notches. The teeth in the set of teeth  842  enter with mounting clearance into the notches  134 ′ in the disc  124 . This arrangement makes it possible to omit the ferrule  138  of the drive piece and to simplify the latter. 
     The connection with respect to rotation by cooperation of shapes between the disc  124  and the piston  50  is effected above the drive piece. 
     The same applies in FIGS. 12 and 13. In this, studs  942 , of axial orientation, are fixed by welding to the piston  50  radially above the drive washer  114 . 
     In a variant the studs  942  are replaced (FIGS. 14 and 15) by U-shaped pieces  1042  attached by welding to the piston  50 . The lugs  134  on the disc  124  enter the pieces  1042  for meshing of the disc  124  with the piston  50 . 
     In a variant (FIG. 16) the studs  942  are fixed by riveting to the piston  50 . 
     Thus in FIGS. 11 to  16  the piston  50  carries means for rotatably connecting the intermediate disc  124  with the piston, and this radially above the drive piece  114 . 
     Naturally the studs can issue from a ring welded to the piston. 
     Naturally the means for rotatably connecting the disc  124  can be carried by the transverse wall. Thus the disc  124  is connected with respect to rotation either to the piston, or to the wall  24 , and this between the area  130  and the drive washer  124 . It will be appreciated that the connection with the wall  24  limits wear. Thus, in FIG. 17, the wall  24  carries a ring  1242  attached by welding to the wall  24  below the area  130 . The ring  1242  carries studs  1342  passing through the notches  134 ′ in the disc  124 . 
     The disc  124  can be extended at its internal periphery in order to mesh with the rivets  110  for fixing the tongues  104 . Thus, in FIGS. 18 and 19, the disc  124  has at its internal periphery scalloped lugs  1442 , the rivets  110  each entering the scallop  1542  in a lug  1442  for rotational connection of the disc  124  with the rivets  110  and therefore with the drive washer  114 . The scallop  1542  is open towards the inside. 
     In a variant the piece  114  carries supplementary rivets  111 , FIG.  20 . Thus pairs of rivets  110 ,  111  are formed. The disc  124  has at its internal periphery projections  1642  with rounded lateral edges. Each projection  1642  enters between two rivets  110 ,  111  in a pair for rotational connection of the disc  124  with the rivets  110 ,  111  and the drive washer  114 . In a variant (FIG. 21) the projection  1642  is trapezoidal in shape. 
     Naturally the intermediate disc  124  can have at its internal periphery a plurality of tongues  1742  distributed circumferentially in a regular manner (FIGS.  22  and  23 ). The tongues  1742  are axially elastically deformable and are here inclined whilst extending at the internal periphery of the disc  124 . Rivets  112  fix the free ends of the tongues  1742 , constituting the aforementioned second tongues, to the drive washer. 
     In the previous figures the disc  124  was rotatably connected to one of the elements piston  50 —transverse wall  24 —drive washer  114  by cooperation of shapes. In FIGS. 22 and 23 as in the other figures this connection is effected by second axially elastic tongues acting between the disc  124  and one of the aforementioned elements  50 ,  24 ,  114 . This connection reduces friction and therefore wear. It reduces the risks of jamming and allows rapid movement of the disc  124 . 
     In FIGS. 18 to  23  the rotational connection of the disc  124  is effected at a distance from the transverse wall  24 . 
     In FIGS. 24 and 25 this connection acts between the disc  124  and the wall  24 . This connection is effected by means of second elastically deformable tongues advantageously distributed in a regular manner. 
     In these figures the number of second tongues is equal to that of the tongues  104  referred to as the first tongues. 
     The second tongues  1842  are fixed by riveting at  113  at one of their ends to brackets  125  which the disc  124  has at its internal periphery. At their other end the tongues  1842  are fixed by rivets  115  to the wall  24 . 
     The first tongues  104  are fixed between the rivets  113 ,  115  to the second tongues  1842  by rivets  114 . The second tongues  1842  are inclined between the rivets  113  and  114  and have a curved shape between the rivets  114  and  115 . 
     In FIGS. 26 and 27 the first tongues  104  are in a single piece with the second tongues  1942  and form the internal branch thereof. These second tongues  1942  have roughly the shape of an inverted C with a top leg of curved shape extends at a short distance with respect to the internal periphery of the disc  124 . The internal leg  104  is rectilinear. The two legs issue from an area  116  offset axially in order to be fixed by means of rivets  115  to the wall  24 . 
     In FIGS. 28 and 29 the second tongues have the same shape as that of the tongues  1842 , and the first tongues are fixed to the brackets  125  whilst extending on the other side of the plane P with respect to the second tongues  1842 , whilst in FIGS. 24 to  27  the second tongues and the first tongues extend on the same side of the plane P. 
     In these FIGS. 24 to  29  the washer  114  has been omitted. 
     In FIGS. 30 and 31 the drive washer  114  is present. The second tongues  2042  have a shape identical to that of the tongues  1942 , the only difference lying in the embedding area  216 , which is in the same plane. 
     This area  216  is gripped between the brackets  112  of the washer  114  and the piston  50 . It is the fixing members in two parts  126  which fix these second tongues. Such members are also visible in FIGS. 6 to  29  and are in two parts, as described in the document FR-A-2726620, to which reference should be made for more information.