Abstract:
The invention concerns an apparatus comprising a housing ( 12 ) with a radial wall ( 14 ) coupled with another input shaft, a turbine wheel ( 104 ) coupled with a hub ( 54 ) and an output shaft; and a lockup clutch comprising a piston ( 40 ); an annular friction disc ( 152 ) with global radial orientation, coupled in rotation with the turbine wheel ( 104 )/hub ( 54 ) assembly and bearing on a first surface a first counter-track ( 210 ) co-operating with a first friction track ( 200 ) integral with the piston to define a first annular friction zone (Z 1 ), and which bears on its second surface opposite to the first surface, a second counter-track ( 230 ) co-operating with a second friction track ( 220 ) integral with the radial wall ( 14 ) to define a second annular friction zone (Z 2 ). The invention is characterized in that the first and second friction zones (Z 1,  Z 2 ) are radially offset relative to each other.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Applicant claims priority to International Patent Application Number PCT/FR01/01243, Publication Number WO 01/81792. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fluid coupling apparatus, especially for a motor vehicle, 
     2. Description of the Related Art 
     Although the prior art includes multiple coupling systems, none of these systems are considered directly applicable to the current invention. 
     SUMMARY OF THE INVENTION 
     The said document describes and shows a fluid coupling apparatus, especially for a motor vehicle, of the type comprising: 
     a casing having a generally radially oriented wall adapted to be coupled in rotation to a driving shaft; 
     a turbine wheel coupled in rotation to a hub which is adapted to be coupled in rotation to a driven shaft; 
     a lock-up clutch, operatively interposed between the turbine wheel and the radial wall, and comprising, disposed axially between the turbine wheel and the radial wall, and going from front to rear in this order: 
     a generally radially oriented piston which is movable axially and coupled in rotation to the casing; 
     a generally radially orientated annular friction disc, coupled in rotation to the assembly of the turbine wheel and hub, and carrying on a first face a first counteracting face which is in cooperation with a first friction face fixed to the piston for defining a first annular friction zone, the friction disc carrying on its second face, opposed to the first face, a second counteracting face which is in cooperation with a second friction face fixed to the radial wall for defining a second annular friction zone. 
     The friction disc is accordingly connected releasably to the radial wall of the casing. 
     In the said document, the friction disc is provided at its outer periphery with lugs which extend radially inwards of the piston for meshing with an input member of a torsion damper, which has an output member provided with a radial plate member coupled to the hub. Circumferentially acting resilient means act between the input and output members, which are configured to receive the resilient members, the latter being arranged radially outside the piston and working surfaces. 
     Such a torsion damper installation, above all when it is of large diameter, makes it necessary, in order not to increase radial and axial size, to reduce the external diameter of the friction liners. However, such a reduction in outside diameter of the liners has the consequence that it limits the torque transmitted, and this is a major drawback. 
     The present invention accordingly aims to increase the torque transmission capacity while preserving the same size, and without detriment to the performance of the fluid coupling apparatus. 
     To this end, the invention provides a fluid coupling apparatus, especially for a motor vehicle, of the type defined above, characterised in that the first and second friction zones (Z 1 , Z 2 ) are offset radially from each other. 
     Thanks to the invention, for a given size, the torque capacity is thus increased because the second face and counteracting face are generally offset with respect to the first face and counteracting face, which enables the mean radius, conventionally defined as the arithmetic mean of the inner and outer radii of the friction liners with respect to the axis of symmetry and rotation X-X, to be increased. 
     Due to the invention, torque capacity is increased, as is the pressure force applied, and this is achieved without any increase in the feed pressure, and therefore without any increase in consumption. 
     In addition, the invention lends itself well to standardisation, because the inventory of components remains generally unchanged, which enables the production costs of such an apparatus to be reduced accordingly. In addition, torsion dampers of large diameter, such as preformed curved springs of large circumferential length, may be used in combination with the invention. The size of the resilient members and the volume in which the latter are fitted are not modified by the arrangements according to the invention. 
     As in the prior art, it is possible to make a sub-assembly which can be handled and transported and which consists of the friction disc and the resilient members, which reduces final assembly time. 
     In accordance with further features in different embodiments of the invention: 
     each friction zone (Z 1 , Z 2 ) is delimited radially, firstly by an outer diameter (D 1 ext, D 2 ext), and secondly, by an inner diameter (D 1 int, D 2 int), and the outer diameter (D 1 ext, D 2 ext) of one of the two friction zones (Z 1 , Z 2 ) is greater than the outer diameter (D 2 ext, D 1 ext) of the other one of the two friction zones (Z 2 , Z 1 ), and the inner diameter (D 2 int, D 1 int) of the said other friction zone (Z 2 , Z 1 ) is smaller than the inner diameter (D 1 int, D 2 int) of the said one friction zone (Z 1 , Z 2 ); 
     the outer diameter (D 1 ext, D 2 ext) of the said one friction zone (Z 1 , Z 2 ) is smaller than the inner diameter (D 2 int, D 1 int) of the said other friction zone (Z 2 , Z 1 ); 
     the friction disc is coupled in rotation to the assembly of the turbine wheel and hub through interposed damping means comprising two coupling members, one of which is coupled in rotation to the friction disc while the other is coupled in rotation to the assembly of the turbine wheel ( 104 ) and hub, the said coupling members being in cooperation with each other through interposed circumferentially acting resilient members; 
     a first coupling member is fixed with respect to the assembly of the turbine wheel and hub, and the second coupling member is fixed to the friction disc; 
     the second coupling member is attached, for example by welding, on the friction disc; 
     the second coupling member is attached on the opposite side to the second counteracting face; 
     the second coupling member is disposed generally in facing relationship with the second counteracting face; 
     the second coupling member is integral with the friction disc; 
     a first coupling member is fixed to the friction disc, and the second coupling member is fixed to the assembly of the turbine wheel and hub; 
     the first coupling member is attached on the friction disc; 
     the first coupling member is integral with the friction disc; 
     the first coupling member comprises a member for guiding the circumferentially acting resilient members and has zones for engagement with the said resilient members; 
     the member for guiding the resilient members comprises a substantially annular portion configured with an axial groove in which the circumferentially acting resilient members are lodged; 
     the axial groove is open towards the radial wall; 
     the axial groove is open away from the radial wall; 
     the second coupling member includes elements for abutment of the circumferentially acting resilient members; 
     the abutment elements are each received between the circumferential ends of two consecutive circumferentially acting resilient members; 
     the abutment elements of the second coupling member penetrate into the axial groove of the annular portion whereby each of them is received between the two circumferential ends of two consecutive circumferentially acting resilient members; 
     the abutment elements project from a crown which may be divided into annular sectors; 
     the abutment elements are generally at right angles to the friction disc; 
     the abutment elements are integral with a member fixed to the assembly of the turbine wheel and hub or to the friction disc; 
     the apparatus includes elements for entrapment of the resilient members, formed integrally with the member, the abutment elements being formed integrally with the member and interposed between the entrapment elements for the resilient members; 
     the friction disc is coupled in rotation to the assembly of the turbine wheel and hub through interposed rigid means; 
     the first and second counteracting faces are each part of at least one friction liner attached directly or indirectly, either on the friction disc or on the piston and the radial wall, or on at least one of the faces of the friction disc and on the piston or the radial wall of the casing; 
     the abutment elements are formed by bending so as to project from the outer periphery of the friction disc; 
     the abutment elements are each joined through a bend to a portion which is generally parallel to the plane of the friction disc, which is itself joined through a 180° bend to the outer periphery of the friction disc; 
     the crown is joined through a bend to an annular portion parallel to the plane of the disc, which is itself joined through an annular 180° bend to the outer periphery of the friction disc; 
     the abutment elements are joined to the outer periphery of the friction disc carrying the first counteracting face, and the second counteracting face is part of at least one supplementary member fixed on at least one of the abutment elements or on the friction disc; 
     the supplementary member has a transversely oriented annular ring, which may be divided into annular sectors and which is fixed to the second counteracting face, and the annular ring lies radially outside the first counteracting friction face; 
     the transverse annular ring is joined to its outer periphery through a second bend which may be of divided form, and the second bend lies radially outside the first bend; 
     the said first and second bends are portions of conical form, and the second bend is in contact with the first bend; 
     the second bend is joined to at least one tongue associated with one of the abutment elements, to which it is fixed; 
     the supplementary member has a thickness smaller than that of the friction disc, whereby the transversely oriented annular ring is elastically deformable; 
     each tongue of the supplementary member is interposed between, and fastened to, an abutment element and a reinforcing finger parallel to the abutment member, and the said finger has, at its outer end turned towards the transverse wall, a stop element for limiting the displacement of the transverse annular ring of the supplementary member; 
     the supplementary member has a thickness generally equal to that of the friction disc, so that the transverse annular member is rigid; 
     the transverse annular ring is offset axially towards the radial wall with respect to the friction disc; 
     the transverse annular ring is situated in the plane of the friction disc; 
     the abutment elements are formed by pressing and bending to project from the friction disc; 
     the abutment elements are joined to the friction disc through a bend, and the second counteracting face is fixed to a first shim which covers at least a major part of openings defined by the friction disc radially outwards of the abutment elements whereby to define the latter, and the shim extends transversely, radially inwards of the bend, to provide sealing between the radial wall and the friction disc when the latter is gripped between the first and second faces; 
     the second counteracting face is formed on a friction liner fixed on the said first shim; 
     the first shim is flat, and is fixed in contact with the friction disc; 
     the first shim is fixed at its outer and inner peripheries with respect to the friction disc, and has at least one boss, which may be of divided form, for fastening the friction liner, constituting the second counteracting face; 
     the first counteracting face is formed on a friction liner fixed directly on the friction disc; 
     the first counteracting face is fixed with respect to a second shim fixed on the friction disc; 
     fastening members secure the first and second shims together to the friction disc, each shim having for this purpose a fastening zone for receiving the said fastening members; 
     the fastening members are interposed between the inner periphery of the first shim and the outer periphery of the second shim, so that the first and second counteracting faces extend transversely on either side of the fastening members; 
     the first shim is extended transversely so that it lies radially inside the first counteracting face, and fastening members are interposed between the inner peripheries of the shims, radially inside the first counteracting face; 
     the first counteracting face is formed on a friction liner fixed on the second shim; 
     each shim has a support zone for its associated friction liner, and the support zones are offset axially away from the friction disc with respect to the fastening zones in contact with the friction disc; 
     the tongue of the supplementary member has a form identical to that of the abutment member associated with it; 
     the tongues of the supplementary member are of different size to the abutment elements; 
     at least one of the elements consisting of the abutment element and the tongue of the supplementary member include two opposed pads which extend circumferentially, and each of which constitutes a centring pad which is received in a complementary housing formed at the outer end of an adjacent resilient member; 
     the reinforcing finger has a form identical to that of the associated abutment element; 
     the reinforcing fingers are of different size from the abutment elements; 
     at least one of the elements consisting of the reinforcing finger and the tongue of the supplementary member include two opposed pads which extend circumferentially, and each of which constitutes a centring pad which is received in a complementary housing formed at the circumferential end of an adjacent resilient member; 
     the first coupling member is welded on the friction disc; 
     the friction disc is configured in two parts, namely an outer part and an inner part respectively, the outer part of the said friction disc constituting the annular portion of the guide member, and the inner part of the said friction disc defining a collar which extends the annular portion radially; 
     the first and second counteracting faces are attached on a base which delimits the axial groove, and on the collar which extends the annular portion radially; 
     the annular portion of the guide member is coupled in rotation to the assembly of the turbine wheel and hub by meshing of teeth with complementary notches formed on the annular portion and the assembly of the turbine wheel and hub, the said teeth extending substantially at right angles to the complementary notches; 
     the annular portion of the guide member extends into an annular rebate formed in the radial wall of the casing; 
     the friction disc is formed with an inner axial stiffening flange; 
     the friction disc is coupled in rotation to the assembly of the turbine wheel and hub by meshing of teeth with complementary notches formed on the friction disc and the assembly of the turbine wheel and hub the teeth being for example substantially at right angles to the complementary notches; 
     the teeth and complementary notches are carried by a peripheral axial flange of the friction disc, and by a peripheral radial portion of a component of the assembly of the turbine wheel and hub; 
     the teeth and complementary notches are carried by a peripheral axial flange of a component of the assembly of the turbine wheel and hub, and by a peripheral radial portion of the friction disc; 
     the axial peripheral flange of the said member of the assembly of the turbine and hub extends partly into a clearance space formed in the radial wall of the casing; 
     the apparatus includes at least one member for coupling the radial wall in rotation to the driving shaft, offset axially with respect to the friction liner in contact with the radial wall of the casing; 
     the internal junction radius of the radial wall with the axially oriented annular portion of the casing is relatively large, so as to limit stresses in the casing. 
     Further features and advantages of the invention will appear on a reading of the following detailed description, for an understanding of which reference should be made to the attached drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a half view in an axial cross section of a fluid coupling apparatus in a first embodiment according to the features of the invention, in which the abutment elements are attached on the friction disc; 
     FIG. 2 is a scrap view in axial cross section, showing a modified version of the first embodiment in which the disc is provided with an axial stiffening flange; 
     FIG. 3 is a scrap view in axial cross section of a second embodiment of the invention, in which the abutment elements are integral with the friction disc and are caused to project from it by bending; 
     FIGS. 4 and 5 are views in axial cross section showing, respectively, part of a third and a fourth embodiment of the invention, in which the abutment elements are joined to the outer periphery of the friction disc, and in which the second counteracting face is part of at least one supplementary member fixed on at least one of the abutment elements; 
     FIGS. 6 to  9  are views in axial cross section which show part of a fifth, a sixth, a seventh and an eighth embodiment of the invention, in which the abutment elements are caused to project by press-forming and bending from the friction disc; 
     FIGS. 10 to  16  are views similar to those in FIGS. 3 to  9 , and show further embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, those components which are similar or analogous to each other will be designated by the same reference signs. 
     In order to facilitate reading of the description and claims, the terms front, rear, upper, lower, vertical, horizontal and so on will be used in a non-limiting way and by reference to the Figures of the drawings. 
     The drawings show a fluid coupling apparatus  10 , especially for a motor vehicle transmission, of the type comprising a sealed casing  12  filled with oil, and consisting of two shells which are connected sealingly together at their outer periphery. One of the shells, shown in the drawings, includes a wall, called a radial wall  14 , which extends generally transversely in a plane at right angles to the general axis X—X of rotation and axial symmetry of the coupling apparatus  10 . 
     The radial wall  14  is made integrally by press-forming in one piece, from sheet metal of constant thickness, and it is extended beyond its outer radial edge by an axially oriented annular portion  16  in the form of a cylindrical skirt, the free terminal edge of which is so designed, in a manner known per se, to enable the said shell  12  to be joined with the other shell of the casing (not shown in the drawings), which is so configured as to constitute the impulse wheel. 
     In its central portion the radial wall  14  includes a central sleeve portion  20 . The radial wall  14  is coupled in rotation to a driving shaft (not shown in the drawing), which in this case is the crankshaft of the vehicle, by means, in this example, of a flexible radial plate (not shown) which is secured on threaded fastening members  300  fixed to the wall  14 . 
     The sleeve portion  20  extends axially towards the rear from a central portion  22  of the radial wall  14 , which is offset axially forward with respect to the radial mid plane in which the wall  14  lies. 
     The annular rear free terminal edge  24  of the sleeve portion  20  is welded to the rear portion  26  of smallest diameter of a stepped thrust sleeve  28 , which is extended axially towards the rear outside the casing  12 , by means of a cylindrical rear end portion  30  constituting a centring element. In this way the sleeve  28  is fixed to the wall  14 . 
     The front portion  32 , of largest diameter, of the thrust ring  28  extends axially within the casing  12  and radially partly in facing relationship with the inner front face  34  of the central portion  22  of the wall  14 . 
     The front portion  32  of the thrust ring  28  defines an external annular cylindrical surface  35 , oriented axially, which constitutes an outer axial sliding peripheral surface, sealed in this case, of an internal radial sleeve portion  38  of a generally radially oriented piston  40 . 
     The surface  35  has a radial groove  42  which is arranged to receive a sealing ring  11 . 
     Going from its radially oriented rear face  44 , the large diameter portion  32  of the thrust ring  28  includes a set of axially oriented teeth  36 , which are spaced apart angularly, preferably at regular intervals, and which determine, together with the face  34  of the central portion  22  of the radial wall  14 , a corresponding number of radially oriented passages which put an internal control chamber  48 , delimited axially by the wall  14  and piston  40 , into communication with one or more ducts  50  that extend through the cylindrical front portion  26  of smaller diameter of the thrust ring  28 , so as to enable the control chamber  28  to communicate with the interior of the thrust ring  28 , which is closed axially at the front by the cylindrical portion  30  and which is open axially towards the rear within the body  52 , the latter being in the form of a hollow cylindrical sleeve portion of a hub  54  which is splined internally at  56  for coupling it in rotation with a driven shaft (not shown in the drawings). 
     The thrust ring  28  therefore has a blind central bore for supplying fluid to the chamber  48  via the duct  50 , the teeth  36  and the driven shaft, which is formed in the known way with a feed duct for the chamber  48 . 
     The hub  54  is coaxial with the other elements of the apparatus  10 , and in particular with the thrust ring  28 , and it is extended, radially outwards from the rear end portion  58  of its sleeve portion  52 , by a radially oriented plate portion  60 . 
     A member  62  is attached on the plate portion  60  or, in another version, on the thrust ring  28 , so as to constitute an axial abutment member, firstly for the radial front face  64  of the front portion  32  of the thrust ring  28 , and secondly for the annular front end face  66  of the sleeve portion  38  for guiding the piston  40  in sliding movement. 
     The member  62  accordingly avoids any metal to metal contacts and has a low coefficient of friction. 
     For this purpose, the member  62  consists essentially of a plate in the form of a flat annular ring which constitutes an abutment plate. 
     The flat rear annular face  74  of the plate  62  constitutes an abutment face for the sleeve portion  38  and for the radial front face  64  of the sleeve  28 , which has a shoulder for centring it on the inner cylindrical edge of the plate  62 . 
     The attached member  62  therefore also provides centring for the sleeve  28  with respect to the hub  54 . 
     The member  62  also acts as a spacer between the plate portion  60  and the piston  40 , that is to say that, when the piston  40  is in a released position, there is an axial clearance between the front annular face  80  in facing relationship with the inner radial portion  82  of the piston  40 , and the facing annular face  84  of the plate portion  60 . 
     The central main part of the plate portion  60  is extended radially outwards by an external radial flange  86  which includes an annular rebate  88  formed in the radial front face  90  of the plate portion  60 . The plate portion  60  is therefore thinner at the level of the flange  86 . 
     The radial base of the rebate  88  constitutes an axial rearward abutment surface for a radially oriented, flat annular inner radial edge  92  of a radial plate member  94 . 
     This inner radial edge  94  is fixed to the flange  86  of the plate portion  60  by means of a set of rivets  95 , each of which extends through a hole  96  formed in the flange  86  of the plate portion  60 , and a corresponding hole  98  formed in the inner radial flange  92  of the plate member  94 . Each rivet  95  also extends through a hole  100  formed in an internal annular ring  102  of a turbine wheel  104 . 
     The ring  102  extends radially inwards in a radial plane and is adjacent to the front annular face  106  of the flange  92  of the plate member  94 , so that it is also received within the rebate  88 . 
     The plate member  94  includes, reading radially outwards from its inner radial edge  92 , a cranked portion  108  and then a central portion  118  in the form of a flat annular ring, such as substantially to fit the facing contour of the turbine wheel  104 , followed by a generally frusto-conical portion and an outer peripheral annular portion  114  which is generally in the form of a half torus. This portion  114  lies mostly radially outwards of the piston  40 , and it is fitted at the outer periphery of the bladed turbine wheel  104 . 
     The annular portion  114 , which is concave in form, is generally configured with an axially oriented groove which is open axially towards the rear in the direction of the radial wall  14  and which is very close to the piston  40 , extending to the outer periphery of the apparatus  10  and turbine wheel  104 . 
     As can be seen in FIG. 1, in which the annular portion  114  is shown in axial cross section, the said portion includes an annular outer portion  116 , orientated axially, which extends axially towards the rear from a concave front portion or base  118 , which in this example is of generally semicircular cross section and which lies in a radial plane, being joined to the outer peripheral edge of the frusto-conical portion through a generally axially oriented internal annular portion. 
     More precisely, the front portion  118  is flat in the region of the zone in which it is joined to the inner portion  120 , so as to come very close to the turbine wheel  114 , tangentially in this example, and so as to occupy all of the space available at the outer periphery of the turbine wheel  104 . 
     In cross section, the annular peripheral portion  114  has a C-shaped profile, and it receives circumferentially acting resilient members which in this example are in the form of a set of coil springs  122  which work circumferentially on a common pitch circle, their outer diameter being slightly smaller than the vertical height of the annular peripheral portion  114  between its portions  116 ,  120 . 
     In accordance with a known principle, the springs  122  are thus guided circumferentially. 
     It will be noted that the outer portion  116  is longer in the axial direction than the inner portion  120 , which is slightly inclined towards the axis of symmetry X—X, for introduction of the springs  122  into the annular peripheral portion  114 . The said inner portion  120  provides good clearance for the springs  122 . The outer portion  116  includes at its axial end press-formed stop elements  13  for retaining the springs  122 . 
     The springs  122  work between the plate member  94  and a friction disc  152 . For this purpose, the annular portion  114  includes abutment zones which are circumferential abutment surfaces consisting of the circumferential ends of mutually facing press-formed elements  124  and  126 , which are formed on the radially inner and outer sides respectively in the outer annular portion  116  and inner annular portion  120 . 
     The disc  152  is a component in the general form of a flat annular ring. 
     It consists of a body or central portion  154  in the form of a flat annular ring, the annular flat faces of which, which are opposed to each other at the front and rear, carry a first counteracting face  210  and a second counteracting face  230 , the said faces  220 ,  230  each being part of, respectively, an annular friction liner  245 ,  245 ′ attached on the friction disc  152 . The friction liners  245 ,  245 ′ are secured for example by adhesive bonding, each on the appropriate face of the central portion  154 . 
     The second counteracting face  230 ,  245 ′ of the friction disc  152  is arranged to cooperate releasably with a second annular friction face  220  which is fixed to the radial wall  14 , being in this example formed in the inner face of the radial wall  14  in facing relationship with the second counteracting face  230 ,  245 ′. 
     More precisely, the second friction face  220  is machined in the inner face of a portion of the radial wall  14  which is made, in an axial annular press-formed element, in such a way as to lie in a vertical plane which is offset axially forward, that is to say towards the left with respect to FIG. 1, in relation to the median vertical plane in which the radial wall  14  lies. 
     The friction liner  245  constituting the first counteracting face  210  is arranged to cooperate releasably with an annular first friction face  200  oriented axially towards the rear, which is fixed to the piston  40  and which in this example is formed on the corresponding face of the outer peripheral radial portion  178  of the piston  40 . 
     Thus, in accordance with the invention, the first face  200  and first counteracting face  210 , and the second face  220  and second counteracting face  230 , which define, respectively, the first and second friction zones Z 1 , Z 2 , are characterised by the fact that the said friction zones Z 1 , Z 2  are offset radially with respect to each other. 
     In addition, each friction zone Z 1 , Z 2  is delimited radially, firstly by an outer diameter (D 1 ext, D 2 ext), and secondly, by an inner diameter (D 1 int, D 2 int), the outer diameter (D 1 ext, D 2 ext) of one of the two friction zones (Z 1 , Z 2 ) being larger than the outer diameter (D 2 ext, D 1 ext) of the other one of the two friction zones (Z 2 , Z 1 ), and the inner diameter (D 2 int, D 1 int) of the said other friction zone (Z 2 , Z 1 ) being smaller than the inner diameter (D 1 int, D 2 int) of the said one friction zone (Z 1 , Z 2 ). 
     The invention is thus derived from the feature of the current state of the art which consists in causing the first and second friction zones Z 1 , Z 2  to coincide radially so that, according to this feature of the current state of the art, the outer diameters of the first and second friction faces were generally both limited, to the detriment of the torque transmitted, as soon as any size constraints were imposed on one of the friction faces, and not necessarily on both friction faces. 
     Thanks to the invention, the torque capacity is increased, by increasing the mean radius of that one of the friction zones that is subjected to the most severe dimensional constraints. The torque capacity is thus increased, as is the applied thrust force, and this is achieved without any increase in either supply pressure or consumption. 
     In the embodiments of the invention shown in FIGS. 1 to  12 , the outer and inner diameters of the first friction face ( 200 ) are smaller than the outer and inner diameters respectively of the second friction face ( 220 ). 
     On the other hand, in the embodiments of the invention shown in FIGS. 13 to  15 , the outer and inner diameters of the first friction face ( 200 ) are greater than the outer and inner diameters, respectively, of the second friction face ( 220 ). 
     Thus, in this case it is the first friction zone (Z 1 ) which is offset axial outboards with respect to the second friction zone (Z 2 ). 
     Preferably, in a fluid coupling apparatus  10  according to the invention, its size, and in particular its radial and axial dimensions, is at least identical to that in the prior art. 
     In addition, the invention lends itself well to standarisation since the assembly of the components remains unchanged, which enables the production cost of such an appartus to be reduced accordingly. Large diameter torsion dampers, in particular those that include pre-formed curved springs of high circumferential length, may be used in combination with the invention. 
     In another version, the disc  152  does have liners  245 ,  245 ′, and is in direct frictional contact on the faces  200 ,  220 . It is then possible to obtain direct friction between the first and second faces  200 ,  220  and the first and second counteracting faces  210 ,  230 , or to attach, for providing the friction, friction liners  245 ,  245 ′ which may be made fixed with respect to the friction disc  152  by any means, such as riveting or adhesive bonding. Similarly, the structure could be reversed, and it could be envisaged that the friction liners  245 ,  245 ′ be attached on the faces so that friction takes place between the counteracting faces  210 ,  230  and not the faces  200 ,  220 . 
     In general terms, the friction disc  152  is arranged to be gripped axially and releasably by the piston  40  between, respectively, a first friction face  200  fixed to the piston and a second friction face  220  fixed to the radial wall  14  of the casing  12 , the friction disc  152  carrying for this purpose a first counteracting face  210  for contact with the first face  200  fixed to the piston and a second friction face  220  fixed to the radial wall  14  of the casing  12 , the friction disc  152  carrying for this purpose a first counteracting face  210  for contact with the first face  200  and a second counteracting face  230  for contact with the second face  220 . 
     As can be seen in the drawings, the outer radial peripheral portion  178  of the piston  40  is offset axially towards the rear with respect to the general radial plane in which the piston  40  lies. 
     The piston  40  is coupled in rotation to the radial wall  14  by means of a set of elastic tongues  180  which are arranged substantially on one circumference, and which work tangentially between the cover plate  12  and the piston  40 , while permitting relative axial displacement of these two elements in the manner described in the document FR-A-2 772 103 of the Dec. 8, 1997. 
     As can be seen in particular in FIG. 1, the friction disc  152  includes engagement or driving lugs  128  which extend axially forwards in the direction of the annular portion  114 , substantially at mid-height between the annular portions  116  and  120 . 
     In a first embodiment of the invention shown in FIG. 1, the lugs  128  are attached on the friction disc  152  on the opposite side from the second counteracting face  230 . The lugs may be attached in any way on the disc  152 , but here they are preferably attached by welding or adhesive bonding. This welding may be of the electrical type such as resistance welding, or be of the laser type, or again it may be friction welding. In another version the joint between the lugs  128  and the friction disc  152  may be obtained using rivets, extruded or otherwise, or by a seaming system. 
     As a result, the driving lugs  128  may be of a material different from that of the friction disc  152 , according to the method of fastening that is envisaged. Thus, the driving lugs  128  are, in one embodiment, made of metal and are adhesively bonded on a friction disc  152  of plastics material. This friction disc  152  may then have a thickened portion on which the first counteracting face  210  and second counteracting face  230  are formed, so that the friction disc  152  is adapted to be gripped directly between the piston  40  and the transverse wall  14 . 
     The driving lugs  128  may be attached individually on the disc  52  or they may project from a crown, which may be divided into annular sectors, and they are also generally situated in facing relationship with the second counteracting face  230 . 
     The driving lugs  128  may be spaced apart circumferentially at regular intervals, with each of them being attached on the friction disc  152  at right angles to the latter, or again through a right angle connecting bend. 
     Each driving lug  128  includes, in the vicinity of its axial front end, two fingers or pads opposed to each other. For more detail, reference should be made to the document FR-A-2 775 747, or W 0 99/45294, and particularly to FIG. 2 of the latter document. Thus, each pad is a pad for centring and maintaining a spring  122  which extends circumferentially from a lateral edge and which penetrates into the open end of the adjacent spring. In this example the pads are of trapezoidal form. The circumferential spacing of the driving lugs  128  and the length of each spring  122  are such that each spring is mounted between two pads or fingers  134  in facing relationship, between which it is maintained so as to constitute an integral structure with the friction disc  152  before the latter is fitted, with its springs  122  having been fitted beforehand, into the apparatus  10 . With respect to the friction disc  152 , the springs are held axially towards the rear by retaining lugs which extend radially outwards from the peripheral edge of the friction disc  152 , being slightly bent axially forward to come into contact with the upper portion of the springs  122  radially outwards of the lugs  128 , and in this example radially inwards of the press-formed elements  124 . There are for example two retaining lugs between two consecutive driving lugs  128 , and the retaining lugs are spaced apart circumferentially at regular intervals. 
     The circumferential length of each spring  122 , in position when mounted between two pads  134 , is slightly smaller than the distance which separates the two mutually facing and consecutive abutment surfaces  124 ,  126 , so that the sub-assembly that consists of the friction disc  152  which carries the springs  122  can be introduced axially from the back into the annular portion  114  in the form of a groove. After fitting, there remains a possibility of relative axial displacement of the disc  152  with respect to the plate member  94  and portion  114 . 
     It will be recalled that the turbine wheel  114  is driven by an impulse wheel (not shown), by virtue of the flow of fluid contained in the casing between the blades of the said wheels, and that after the vehicle has been started, and in order to prevent sliding effects between the turbine and impulse wheels, the lock-up clutch couples the driven shaft coupled to the turbine wheel fixedly with the driving shaft which is coupled to the radial wall  14  of the casing. 
     The lock-up clutch thus works between the turbine wheel and the radial wall. It slides, through its piston  40 , on the thrust sleeve  28  fixed to the radial wall  14 . Control of the gripping or clamping and of release of the clutch is obtained, in accordance with a known method, by varying the pressure in the chamber  48 , which is delimited axially by the piston  40  and the radial wall  14  and radially on the inside by the thrust ring  28  and radially on the outside by the friction disc  152 . 
     The wall  14  constitutes the input element proper of the fluid coupling apparatus  10 , because it is coupled to the driving shaft, while the turbine wheel  104 , through the hub  54  which is fixed to the latter, constitutes the output element of the said apparatus  10 . 
     The present invention is of course not limited to the embodiment described. In particular, the piston  40  may be coupled in rotation to the radial wall  14  by means of an annular ring fixed to the piston and having annular grooves defining mortices, in which radial lugs defining tenons are engaged, these lugs being part of a plate fixed to the wall  14  and constituting a friction face for the rear friction liner. In another version, this plate has axial lugs, each of which is engaged in two press-formed elements formed in the piston. 
     The friction liners  245 ,  245 ′ may be fixed, for example by adhesive bonding, to the portion  178  of the piston  40  and to the radial wall  14  which constitutes the second face  220 , respectively. In all cases, the disc  152  is a friction disc adapted to be gripped releasably between the wall  14 , which may be given a coating, and the piston  40 , which may be given a coating. The friction liners  245 ,  245 ′ may of course be formed with grooves as is described in the document WO-A-93 13339 mentioned above. These grooves enable controlled sliding of the liners  245 ,  245 ′ to be achieved. 
     The friction disc  152  may be interposed between the two friction liners  245 ,  245 ′, which may be formed in one piece with the friction disc  152 . 
     Cup members may protect the lugs  128  and may have a central cylindrical projection, in this case in the form of hollow pins, penetrating into the interior of a spring  122  so as to serve as an abutment for the end face of a coil spring surrounded by the spring  122 . 
     Thus the springs  122  are mounted concentrically and the cup member bears against the side edge of the lug  128 , being maintained by the central pad  134  penetrating into the projecting element, which is oriented circumferentially, of the cup member, so as to retain the latter in position. 
     The cup member is thus in the form of a hat, and serves to centre the spring  122  and as an abutment for the inner spring. 
     It will be noted that the concentric mounting of the springs is made possible by the fact that a large amount of space is released at the outer periphery of the fluid coupling apparatus  10  radially outside the outer periphery of the piston  40 . 
     When the lock-up clutch is engaged, the engine torque is transmitted from the wall  14  to the turbine wheel via a torsion damper which comprises, firstly, two torque transmission members, namely the friction disc  152  and the radial plate member  94 , and secondly, resilient members working between these two components and guided by the annular peripheral portion  114  which is integral with the plate member  94 . 
     The inner portion  120  of the portion  114  may come very close to the piston  40 , the outer periphery of which is chamfered so that it does not interfere with the junction zone of the portion  120  with the frusto-conical portion  126  of the plate member. 
     In this example, the resilient members  122 , carried by the friction disc  152 , are radially outside the outer periphery of the piston  40 . 
     The springs  122  project slightly axially towards the rear with respect to the upper portion  116 . 
     The lugs  128  engage the springs symmetrically, that is to say diametrally. 
     The lugs  128  may of course be inclined axially, as may the upper portion  116 . 
     The presence of a radial plate member  94  is not essential, and the annular portion  114  may be fixed directly on the turbine wheel  104 . All combinations are possible. The lugs, by virtue of their inclination, facilitate fitting of the springs  122 . The front portion  118  of the concave portion  114  in this example has an outer portion  116 , oriented axially, which extends towards the rear from the front portion  118 , of concave annular form, which extends in an arc of a circle over more than 180° and which is connected to an inner portion inclined towards the axis X—X and joined to the plate member  94 . 
     Similarly, the abutment zones formed in the outer portion  116  may be press-formed and consist of bands of material. 
     In general terms, all of the arrangements described in the document WO99/45294 may be envisaged. Thus, as in FIG. 7 of that document, the fingers or pads may serve for mounting of thrust cups interposed between the circumferential ends of the springs  122 , which also permits a supplementary spring to be fitted concentrically inside the spring  122 . The annular portion  114  may be fixed directly to the turbine wheel  104 , for example by welding or upsetting as can be seen in FIGS. 11 to  13  of that document. Similarly, the presence of the springs is not indispensable, as can be seen in FIG. 5 of that document. 
     In the first embodiment of the invention, the lugs  128 , fixed on the disc, may have a different thickness from that of the disc  152 , which is preferably flat. In particular, they may be thicker than the disc  152  and thereby offer a larger zone for engagement of the springs which reduces their wear. The lugs  128  may be hardened, in particular locally, using heat treatment. 
     In another version and as indicated in FIG. 2, and in a way similar to the first embodiment of the invention, the friction disc  152  is provided with an internal axial stiffening flange  500 . 
     According to a second embodiment of the invention as shown in FIG. 3, the driving lugs  128  are integral with the friction disc  152 , the said lugs  128  being in particular formed by bending so as to project from the outer periphery of the friction disc  152 . 
     Thus, as can be seen in FIG. 3, each of the lugs is joined through a bend  240  to a portion generally parallel to the plane of the disc, the said portion being itself joined through a bend  241  at 180° to the outer periphery of the disc  152 . The lugs  128  may easily be formed in a bending operation on the friction disc  152 , the lugs  128  being generally at right angles to the disc  152 . 
     In a further version, the driving lugs  128  project from a crown which is joined through a bend  240  to an annular portion parallel to the plane of the disc, the said portion being itself joined through a bend  241  at 180° to the outer periphery of the disc  152 . 
     In this second embodiment of the invention, the first and second counteracting faces  210 ,  230  each form part of a friction liner  245  which is attached on the friction disc  152  or on the piston  40  and the wall  14  of the casing  12 . 
     It will be appreciated that the bending operation in this second embodiment is very robust and enables a high degree of perpendicularity to be obtained between the driving lugs  128  and the disc  152 . 
     In a third and fourth embodiment according to the invention, as shown in FIGS. 4 and 5, the driving lugs  128  are joined to the outer periphery of the friction disc  152  carrying the first counteracting face  210 , by a portion which may for example be an elbow portion or a rounded portion, or a frusto-conical portion, comprising a flat portion on which the corresponding portion of the supplementary member  242  may be engaged. 
     This portion may of course also take some different geometrical form, for example the portion could consist of a right angled bend. 
     In these embodiments, the second counteracting face  230  is formed on at least one supplementary member  242  fixed on at least one of the driving lugs  128  or on the friction disc  152 . 
     Thus, the supplementary member  242  has a transversely oriented ring  243  which may be divided into annular sectors, and which is fixed to the second counteracting face  210 , and the ring  243  lies radially outside the first counteracting friction face. 
     The transverse ring  243  is joined at its inner periphery to a second bend  244 , which may be of divided form, and the second bend  244  lies radially outside the first bend  246 . 
     In the case where the first and second bends  244 ,  246  are in the form of conical portions, the second bend  244  is preferably in contact with the first bend  246  as can be seen in FIGS. 4 and 5. 
     The second bend  244  is joined to at least one tongue associated with one of the driving lugs  128 , being fixed to the latter. 
     In FIG. 5, illustrating the fourth embodiment, the supplementary member  242  has a thickness smaller than that of the friction disc  152 , so that the transversely oriented ring  243  is elastically deformable. 
     Each tongue of the supplementary member  242  is interposed fixedly between a driving lug  128  and a reinforcing finger  248  parallel to the driving lug  128 , and the said finger  248  has, at its axial end directed towards the transverse wall, an abutment element  249  for limiting the displacement of the transverse ring of the supplementary member. 
     In another version, as shown in FIG. 4 in a third embodiment, the supplementary member  242  has a thickness which is generally equal to that of the friction disc  152 , so that the transverse ring  243  is rigid and there is no need for a reinforcing finger  248 . 
     The transverse ring  243  is offset axially towards the transverse wall  14  with respect to the friction disc  152 , especially where the second bend  244  is, with advantage, in contact with the first bend  246 , which reduces the overall axial size. 
     In a further version, the transverse ring  243  is situated in the plane of the friction disc  152 , when for example the portion consists of a right angled bend. 
     In these embodiments it is possible to retain the friction disc of the prior art, and wear is reduced in the region of the springs by means of the supplementary member  242  or the reinforcing finger  248 . 
     Fastening of the supplementary member  242  or reinforcing finger  248  on the driving lugs  128  may be obtained by welding as shown in FIGS. 4 and 5. In another version, this fastening is obtained by riveting or adhesive bonding. In a further version, the welded joint is formed by resistance or laser welding. 
     In a fifth, a sixth, a seventh and an eighth embodiment according to the invention, which are shown in FIGS. 6 to  9 , the driving lugs  128  are made by press-forming and bending so as to project from the friction disc  152 . 
     The driving lugs  128  are joined through a bend  246  to the friction disc  152 , and the second counteracting face  230  is fixed with respect to a first shim  251  which covers at least the greater part of the cut-out  253  formed in the friction disc  152  radially outside the driving lugs  128  to define the latter, and the shim  251  extends transversely, radially inwards of the bend  246 , so as to provide a seal between the transverse wall  14  and the friction disc  152  when the latter is gripped between the first and second surfaces  200 ,  220 . 
     The second counteracting face  230  is formed on a friction liner  245 ′ fixed on the said first shim  251 , which in this case is of metal and is by definition thinner than the friction disc  152 . 
     In FIG. 6 the first shim  251  is flat and is fixed in contact with the friction disc  152 . 
     In FIGS. 7 to  9 , the first shim  251  is fixed at its outer and inner peripheries with respect to the friction disc  152 , and it has at least one boss  254 , which may be of divided form, for fastening the friction liner  245  constituting the second counteracting face  230 . 
     In FIG. 7, the first counteracting face  210  is formed on a friction liner  256  fixed directly on the friction disc  152 . 
     In FIGS. 8 and 9, the first counteracting face  210  is fixed to a second shim  252  fixed on the friction disc  152 . 
     In these Figures, fastening members  260  secure the first and second shims  251 ,  252  together to the friction disc  152 , each shim having for this purpose a fastening zone  261  for receiving the said fastening members  260 . The shims  251 ,  252  are of metal and are of the same thickness, which is smaller than that of the disc  252 . In another version, the shims may have different thicknesses according to the torque that each of them is to transmit. 
     These shims  251 ,  252  are elastic. In another version, fastening of the shims to the disc  152  is obtained by riveting or adhesive bonding. In a further version the connection is made by welding and is of the resistance or laser type. 
     In FIG. 8, the fastening members  260  are interposed between the inner periphery of the first shim  251  and the outer periphery of the second shim  252 , so that the first and second counteracting faces  210 ,  230  extend transversely on either side of the fastening members  260 . 
     In FIG. 9, the first shim  251  is extended transversely so that it extends radially inwards of the first counteracting face  210 , and the fastening members  260  are interposed between the inner peripheries of the shims  251 ,  252 , radially inwards of the first counteracting face  210 . 
     In FIGS. 7 to  9 , the first counteracting face  210  is formed on a friction liner  245  fixed on the second shim  252 . 
     Each shim  251 ,  252  has a support zone for its associated friction liner  245 ,  245 ′, and the support zones are offset axially away from the friction disc  152  with respect to the fastening zones  260  in contact with the friction disc  152 . In another version, the first counteracting face  210  is defined directly by the face of the second shim  252  that faces towards the piston  40 , and of course the second counteracting face  230  may be defined directly by the transverse face of the first shim  251  facing towards the transverse wall  14 . 
     In FIG. 7, the first counteracting face  210  may be defined directly by the face of the friction disc  152  that faces towards the piston  40 . In FIGS. 7 to  9 , the bend  246  is a 90° bend, so that the driving lugs  128  are at right angles to the friction disc  152 . In another version, the bend  246  may be slightly greater than 90°. 
     The driving lugs  128  are thus generally at right angles to the friction disc  152 . 
     In another version, the bend  246  may have a form similar to that in FIGS. 4 and 5. 
     As mentioned above, the driving lugs  128  are coupled in rotation rigidly to the assembly consisting of the turbine wheel  104  and hub  54 . 
     In this example, the driving lugs  128  are coupled elastically to the assembly consisting of the turbine wheel  104  and hub  54  in the same way as in FIGS. 2 to  5 , by means of circumferentially acting resilient members  122  which act between the said assembly  104 - 54  and the driving lugs  128 , and the said driving lugs  128  are each received between the circumferential ends of two consecutive circumferentially acting resilient members  122 . 
     The lock-up clutch has a peripheral annular portion  114  which is configured with an axial groove open towards the radial wall  14  and coupled in rotation to the assembly of the turbine wheel  104  and hub  54 , being fitted at the outer periphery of the turbine wheel  104 . The annular portion  114  guides circumferentially, and retains in the forward direction, circumferentially acting resilient members  122 . The annular portion  114  has abutment zones  124 ,  126 . The driving lugs  128  penetrate into the axial groove of the peripheral annular portion  114 , so that each of them is received between the two circumferential ends of two consecutive circumferentially acting resilient members  122 . 
     The tongue of the supplementary member  242  in FIGS. 4 and 5 has a form identical with that of the driving lug  128  which is associated with it. 
     In a further version, the tongues of the supplementary member  242  are of different size to that of the driving lugs  128 . 
     The present invention is of course not limited to the embodiments described, and accordingly in one embodiment not shown, the tongues of the supplementary member have a different circumferential dimension from that of the driving lugs  128 , so that at least one of the elements consisting of the driving lugs  128  on the one hand, and the tongue of the supplementary member  242  on the other, includes two opposed pads  134  which extend circumferentially, and each of these pads constitutes a centring pad which is received in a complementary housing formed at the circumferential end  138  of an adjacent resilient member  122 . 
     In FIG. 5, the reinforcing finger  248  has a form identical to that of the driving lug  128  associated with it. 
     Grooves may be formed in the faces  200 ,  220  and in the counteracting faces  210 ,  230  in a manner known per se. 
     FIG. 10 shows a fluid coupling apparatus in a ninth embodiment of the invention. 
     In this case, by contrast with the first embodiment of the invention, the annular portion  114  for guiding the springs  122  is fixed to the friction disc  152 , being for example secured on the latter by welding. The groove defined by the annular portion  114  is open away from the radial wall  14 . 
     In addition, the abutment lugs  128  are fixed to the plate member  94 , being for example formed integrally with the plate member  94 , or any other support member fixed to the assembly consisting of the turbine wheel  104  and hub  54 . 
     Lugs  262 , for preventing escape of the springs  122 , may optionally be formed integrally with the plate member  94  or any other support member fixed to the assembly consisting of the turbine wheel  104  and hub  54 , as in the tenth embodiment of the invention shown in FIG.  11 . These entrapment lugs  262 , which are divergent towards the radial wall  14 , are interposed between the abutment lugs  128 . 
     It will be noted in FIG. 11 that the inner annular portion  120  of the annular portion  114  is formed with tongues  264  for engagement of the springs  122  and stamped out in the said portion  120 . 
     FIG. 12 shows a fluid coupling apparatus  10  in an eleventh embodiment of the invention. 
     In this case, the friction disc  152  is reinforced in two portions, an outer and an inner portion respectively. The outer portion of this friction disc  152  constitutes the annular portion  114  for guiding purposes, and the inner portion of the friction disc  152  defines a collar  266  which radially extends the annular portion  114 . 
     The friction liners  245 ,  245 ′ are attached on the base  118  of the annular portion  114  and on the collar  266  which radially extends the annular portion  114 . 
     FIG. 13 shows a fluid coupling apparatus  10  in a twelfth embodiment of the invention. 
     In this case, the annular guide portion  114  is coupled in rotation to the assembly consisting of the turbine wheel  104  and hub  54  by meshing of teeth  268  with complementary notches  270  formed in the annular portion  114 , and the assembly of the turbine wheel  104  and hub  54 . The teeth are substantially at right angles to the complementary notches. 
     In this example, the teeth  268  and complementary notches  270  are formed, firstly, in the axially oriented outer annular portion  116  of the annular portion  114 , and secondly in a radial peripheral portion  272  of the plate member  94 . 
     The annular portion  114  extends into an annular space  274  defined in the radial wall of the casing. 
     Preferably, the entrapment lugs  262  for the springs  122  are formed integrally with the friction disc  152  or any other support member fixed to the disc  152 . These entrapment lugs  262  are interposed between the abutment lugs  128 , which are themselves formed integrally with the friction disc  152 . 
     It will be noted that in this twelfth embodiment of the invention, the torsion damper is located axially between the radial wall  14  of the casing and the friction disc  152 , and that in the eleven foregoing embodiments, the torsion damper is located axially between the friction disc  152  and the assembly of the turbine wheel  104  and hub  54 . 
     FIGS. 15 and 16 show further embodiments of the fluid coupling apparatus  10  according to the invention, in which the friction disc  152  is coupled in rotation to the assembly of the turbine wheel  104  and hub  54  through interposed rigid means. 
     Thus, in the examples shown in FIGS. 15 and 16, the friction disc  152  is coupled in rotation to the assembly of the turbine wheel  10  and hub  54  by meshing engagement of teeth  276  and complementary notches  278  formed on the friction disc  152  and on the assembly of the turbine wheel  104  and hub  54 , and more particularly the plate member  94 . The teeth extend substantially at right angles to the complementary notches. 
     In the thirteenth embodiment shown in FIG. 14, the teeth  286  and complementary notches  278  are carried by a peripheral axial flange  280  of the plate member  94  (or any other member of the assembly consisting of the turbine wheel  104  and hub  54 ), and by a radial peripheral portion  282  of the friction disc  152 , the latter being preferably flat. 
     The axial peripheral flange  280  extends partially into a clearance space  284  formed in the radial wall  14  of the casing, for example by pressing. 
     In the fourteenth and fifteenth embodiments shown in FIGS. 15 and 16, the teeth  276  and complementary notches  278  are carried by an axial peripheral flange  286  of the friction disc  152  and by a radial peripheral portion  288  of the plate member  94  (or any other member of the assembly of the turbine wheel  104  and hub  54 ). 
     The outer and inner diameters of the first friction face  200  being greater than the outer and inner diameters respectively of the second friction face  220 , the internal junction radius of the radial wall  14  with the axially oriented annular portion  16  of the casing may be relatively large in order to limit stresses in the casing (see FIG.  15 ). 
     For the same reasons that the friction faces  200 ,  220  are offset, the connecting member  300  or the like, welded on the radial wall  14 , is preferably offset radially with respect to the friction liner  245 ′ in contact with the radial wall  14  of the casing, so as to avoid frictional contact of the said friction liner  245 ′ with the weld zone of the connecting member  300  (see FIG.  16 ).