Abstract:
A hydrokinetic coupling apparatus for a motor vehicle including a crankcase ( 12 ), designed to link in rotation, about an axis X, an input shaft to an impeller wheel; a turbine wheel ( 18 ) designed to be linked in rotation to an output shaft ( 16 ) via hub ( 14 ) and a flange ( 24 ) transversely oriented extending radially outwards relative to the hub; a lockup clutch ( 28 ) coupling the input and output ( 16 ) shafts comprising a piston ( 30 ) for releasably connecting the turbine wheel ( 18 ) to a substantially transverse wall ( 20 ) of the crankcase ( 12 ) against which the piston ( 30 ) is urged to lock the coupling; and at least a friction stop ( 68 ) interposed axially between the turbine wheel ( 18 ) and the piston ( 30 ). A friction stop ( 68 ) is arranged radially beyond the outer periphery ( 100 ) of the flange ( 24 ).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention concerns a hydrokinetic coupling appliance for a motor vehicle. 
   2. Description of Related Art 
   There is already known, in the prior art, for example according to the document WO 99/45294, a hydrokinetic coupling apparatus, in particular for a motor vehicle, of the type comprising:
         a casing, intended to rotationally connect, about an axis X, a driving shaft and an impeller wheel,   a turbine wheel intended to be rotationally connected to a driven shaft,   a clutch for locking the coupling of the driving and driven shafts comprising a piston for disengageably connecting the turbine wheel to a substantially radial wall of the casing against which the piston is forced for the locking of the coupling, and   a friction stop interposed axially between the turbine wheel and the piston.       

   In general terms, in such a hydrokinetic coupling appliance, the casing provided with a substantially radial wall constitutes the input element and the output element for its part consists of a turbine wheel/hub assembly housed inside the casing. The piston is located between the assembly and the wall and is mounted so as to be able to move axially with respect to the wall, whilst being rotationally connected thereto. 
   In a conventional manner, the turbine wheel is driven by the impeller wheel by virtue of the circulation of a fluid, such as oil, contained in the casing. 
   In the case of a hydrokinetic coupling appliance for a motor vehicle, the driving shaft is the output shaft of the vehicle engine and the driven shaft is connected to gear ratio change means. After the vehicle is started, the locking clutch, also referred to as a “lock-up” clutch, controls the slip between the turbine and impeller wheels by controlling the driving of the driving shaft connected to the casing by the driven shaft connected to the turbine wheel. This drive control of the shafts is effected by clamping an annular friction disc arranged between the piston and the locking wall of the casing. 
   The connecting wall of the hub illustrated in this document comprises a substantially radial plate, made from the same material as the hub, and a damper plate connecting this hub to means of coupling the hub and friction disc with circumferential damping. The turbine is also connected to the plate of the hub. A bracing member, in the form of a flat ring, is interposed axially between the plate of the hub and the piston and forms a friction stop in order to prevent direct contact between this plate and this piston. 
   SUMMARY OF THE INVENTION 
   The aim of the invention is in particular to simplify the manufacture of a lock-up clutch and to minimise its cost whilst reducing in particular the number of parts making up this clutch. 
   To this end the object of the invention is a hydrokinetic coupling apparatus of the type mentioned above, characterised in that the friction stop is disposed radially beyond the external periphery of the plate. 
   By virtue of the invention, the implementation of the friction stop function of the piston is simplified thereby and makes it possible to prevent any direct contact between the piston and, according to the embodiment, any one of the components of the turbine wheel/hub assembly or an element such as the damper plate of a damping device. 
   In addition, the friction stop being disposed radially beyond the external periphery of the plate, the area for transmission of forces from the turbine onto the piston is thus brought closer to the abutment area of the piston. In this way the deformation of the piston and the relative movement between the turbine and the casing are reduced so that the piston suffers less stress. 
   According to the characteristic of various embodiments of this apparatus:
         the friction stop is carried by one of the elements of the turbine wheel/hub assembly;   the friction stop is carried by the piston;   the friction stop comprises an active friction part and a passive part comprising means of connection with the element which carries the stop by cooperation of complementary shapes;   the friction stop is in a single piece;   the friction stop is in at least two pieces comprising respectively the active part and the passive part;   the piston comprises at least one element formed in projection which cooperates with complementary assembly means of the friction stop;   the piston comprises at least one hole which receives complementary assembly means of the friction stop;   the hole is blind;   the hole is a through hole and forms a passage orifice for a fixing tool for the means of rotationally connecting the piston and casing;   sealing means intervene between the piston hole and the passive part of the friction stop, and   at least one lubrication groove (R) is formed in the active friction part and/or in the piece against which the said stop bears.       

   The teachings of the present invention can be implemented in any type of hydrokinetic coupling appliance, in particular appliances equipped with a clutch of the dual face type, that is to say comprising two friction surfaces, or in clutches of the multidisc type. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from a reading of the following description, given solely by way of example and made with reference to the drawings, in which: 
       FIG. 1  is a half view in axial section of a hydrokinetic coupling appliance according to a first embodiment of the invention; 
       FIG. 2  is a partial view of an axial section similar to that of  FIG. 1  along a cutting plane offset axially with respect to that in  FIG. 1 ; 
       FIG. 3  is a partial view of a section similar to  FIG. 1  showing a hydrokinetic coupling apparatus according to a second embodiment of the invention; 
       FIG. 4  is a partial view in section of a detail of the third embodiment; 
       FIG. 5  is a partial view in section of a detail of the fourth embodiment; 
       FIG. 6  is a partial view in section of a detail of the fifth embodiment. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the figures the common elements will, for simplicity, be allocated the same reference signs. 
     FIG. 1  depicts a hydrokinetic coupling appliance according to a first embodiment of the invention, designated by the general reference  10 . This appliance  10  is intended to couple two driving and driven shafts, for example in a motor vehicle automatic transmission. In this case, the driving shaft is the output shaft of the vehicle engine and the driven shaft is connected to a gear ratio change means. 
   In a conventional fashion, the hydrokinetic coupling appliance  10  comprises a casing  12 , intended to rotationally connect the driving shaft and an impeller wheel. The driving shaft and the impeller wheel, known per se, are not shown in the figures. 
   The appliance  10  also comprises a hub  14  intended to rotationally connect the driven shaft  16  and a turbine wheel  18 , only part of the profile of which is shown in dot and dash lines in FIG.  1 . 
   Hereinafter the axial and radial orientations are considered with respect to the axis X of the appliance. The casing  12  comprises a substantially radial wall  20  provided with a surface  20 E, external to the casing, carrying conventional means of coupling with the driving shaft. These coupling means comprise in particular a centring member  22  and screwing means  23 . 
   The hub  14  comprises here a substantially radial plate  24  provided with conventional means  26  of connection with the turbine wheel  18 . The hub  14  is coupled to the driven shaft  16  by the cooperation of axial grooves and flutes provided on the latter. 
   The hydrokinetic coupling appliance  10  also comprises a clutch  28  for locking the coupling of the driving and driven shafts. This clutch  28  is activated after starting of the vehicle and hydraulic coupling of the driving and driven shafts. 
   In a conventional manner, the clutch  28  comprises a moving locking piston  30  intended to be forced against the casing  12  for locking the coupling of the shafts or controlling the slip between the turbine and impeller wheels. 
   The clutch is here of the dual face type, in which a friction disc  32  is intended to be clamped between the piston  30  and a surface  20 I of the wall  20 , internal to the casing  12 . The friction disc  32 , interposed axially between the piston  30  and the wall  20 , referred to as the locking wall, comprises friction linings G arranged here and in a manner known per se on its two opposite faces. 
   Naturally other variant embodiments can be envisaged, and thus the friction could be produced directly between the pieces  30 ,  32 ,  20  preferably having been treated with a view to such an application. 
   The friction linings G can be arranged directly or indirectly on the friction disc  32  or on the piston  30  and/or the surface  20 I. In a variant, at least one of the linings can belong to an additional piece attached by any means, for example by welding. The various embodiments above can of course be combined. 
   In a variant, the external periphery of the disc  32  is embedded in a friction lining. Preferably the linings G are provided with grooves which also, in addition to allowing better cooling, make it possible to work in controlled slip. 
   By varying the pressure on each side of the piston  30 , the latter is moved axially in one direction or the other, so that the said piston is able to move axially with respect to the hub  14 . 
   The friction disc  32  is here connected to the hub  14  by means of a damping device also comprising means  34 ,  38 . The means  34  comprise a damper plate  36  connected to the plate  24  of the hub by means for example of connection means  26 , such as rivets or a weld, common to the turbine wheel  18  and to the damper plate  36 . Circumferentially acting elastic members  38  are interposed, in a manner known per se, between the friction disc  32  and the damper plate  36 , in order to provide the required damping effect. 
   It should be noted that the plate  24  and the damper plate  36  form a substantially radial connecting wall fixed to the hub  14 . 
   The hydrokinetic coupling appliance  10  also comprises at least one sealing means  41 , such as a segment or a joint, intervening between one end of the shaft  16  and the piston  30  and intended to separate two chambers  58 ,  59  which will be described subsequently. Naturally the sealing means  41  can be carried by the shaft  16  or by the piston  30 . 
   It should be noted that the end of the driven shaft  16  is provided with an end bevel in order to facilitate here the mounting of the sealing segment  41  by fitting in. 
   The piston  30  comprises a radially internal substantially axial annular part which internally delimits a cylindrical bearing surface  30 P cooperating by sliding with the sealing segment  41  of the driven shaft  16 . The sealing segment  41 , interposed between the end of the driven shaft  16  and the bearing surface  30 P of the piston is housed for example in an annular groove  54  produced in the driven shaft  16 . 
   It should be noted that the driven shaft  16  is provided with an axial bore  56  opening out at the free end of the shaft  16 . The bore  56  communicates with a chamber  58 , referred to as the control chamber for the lock-up clutch  28 , which is delimited in particular by the radial wall  20  of the casing, the piston  30  and the friction disc  32 . The chamber  58  is supplied with pressurised oil by a conventional hydraulic circuit to which the bore  56  of the driven shaft  16  is connected. 
   The control chamber  58  is isolated from a chamber  59  in which the turbine wheel  18  lies, referred to as the turbine chamber, in particular by the piston  30  and the sealing means  41 . 
   The piston  30  is rotationally connected to the locking wall  20  of the casing by conventional means described for example in the document WO 99/45294. 
   These connection means comprise here tangentially oriented flexible tongues  60  distributed circumferentially. These tongues  60 , interposed between the piston  30  and the locking wall  20  of the casing, allow—by elastic deformation—an axial movement, that is to say the translational guidance of the piston  30 . 
   The number of tongues  60  depends on the application, these preferably being distributed regularly circumferentially in several sets of tongues, each set comprising at least one tongue. The tongues  60  can be transversely oriented, being for example triangular or rectangular in shape, or tangentially oriented. 
   A first end of the tongues  60  is connected to the locking wall  20  here by means of a ring  62  fixed to this wall  20  by rivets  64  made in one piece with the casing  12  (see FIGS.  1  and  2 ). 
   The second end of the tongues  60  is connected to the piston  30  by rivets  66  (see FIG.  2 ). 
   The tongues  60  guide the piston  30  axially between the plate  24  and the locking wall  20 . 
   The mounting of the piston  30  in the casing  12  is known per se. First of all, the tongues  60  are attached to the ring  62  and the piston  30  and then this ring  62  is fixed to the locking wall  20 . In order to perform the latter fixing operation, through holes  30 T provided in the piston  30  substantially in line with the rivets  64  and form passage orifices for the access to the rivets  64  of a fixing and mounting tool and. In order to provide fluidtightness of the control chamber  58 , the orifices  30 T, distributed circumferentially over the piston  30 , are each closed off by means such as plugs  68  after the mounting of the piston  30  in the casing  12 . 
   In operation, when the hydraulic coupling is established between the impeller and the turbine  18 , the driving shaft, connected to the impeller wheel by the casing  12 , is connected to the driven shaft  16 , connected to the turbine  18  by the hub  14 , by movement of the piston  30  against the internal surface  20 I of the locking wall so as to clamp the friction disc  32  between this wall  20  and this piston  30 . The locking (also referred to as clamping) of the clutch  28  and the unlocking (also referred to as unclamping) of this clutch  28  are performed in a manner known per se by varying the pressure between the control chamber  58  and the turbine chamber  59 . 
   In the first embodiment depicted in  FIG. 1 , a friction stop  68  is interposed axially between the turbine wheel  18  and the piston  30 , so that any direct contact between the piston  30  and a facing element, here the damper plate  36 , is prevented. 
   According to the invention, the friction stop  68  is disposed radially beyond the external periphery  100  of the plate  24 . 
   The plate should not be interpreted limitingly to the embodiments depicted in which the said plate  24  is made in one piece with the hub  14 , thus in a variant the plate  24 , which designates here a substantially radial wall, consists of the turbine wheel or an element rotationally connected thereto or to the hub, the damper plate of the damper could for example constitute this element. 
   In this way the area for transmission of forces from the turbine to the piston is brought closer to the abutment area of the piston, that is to say the area in which the friction linings G are disposed and, in this way, the deformation of the piston  30  and the relative movement between the turbine  18  and the casing  12  are reduced, so that the piston is subjected to lower stresses than in the case where the friction stop is disposed for example radially at the internal periphery of the plate  24 . 
   The friction stop  68  comprises an active friction part  68 A and a passive part  68 P comprising means  68 J of connection with the element which carries the stop, here the piston  30 . The stop is here in a single piece. 
   The connection of the stop  68  and the piston  30  is here achieved by cooperation of complementary shapes but it could of course be achieved by any other means, for example by welding or adhesive bonding. 
   In this first embodiment according to the invention, at least some of the plugs forming means of closing off the orifices  30 T also advantageously constitute friction stops  68  interposed between the turbine wheel/hub assembly and the piston  30 . 
   Assembly within the meaning of the present invention should be taken to mean one of the turbine wheel or hub elements or any element rotationally connected to the latter. 
   In the example illustrated in  FIG. 1 , the friction stop  68 , that is to say here one of the plugs, is preferably manufactured from a material chosen from amongst thermoplastic or thermosetting synthetic materials, mixtures of synthetic materials, these materials being reinforced or not by fibres such as glass fibres, aramids (in particular sold under the name Kevlar) or carbon fibres or glass balls. 
   It is therefore possible, according to the application, to choose the coefficient of friction of the stop  68  of the piston appropriately according to the material used. The plug  68  forming stops preferably each comprise a support head  68 T constituting the active part  68 A of the friction stop, here against the damper plate  36 . The head  68 T is extended by a skirt  68 J which is fitted in the passage orifice  30 T and which constitutes the passive part  68 P of the stop. The skirt  68 J constitutes the means of connecting the stop  68  to the piston  30  by cooperation of shapes. 
   Naturally the skirt  68 J can be discontinuous, the assembly means can then be produced in the form of axial lugs, preferably at least two diametrically opposed with respect to the through hole  30 T. 
   The connection by cooperation of shapes of the skirt  68 J, or of the lugs, can for example consist of a snapping in or elastic fitting in. 
   Preferably at least one lubrication groove R is provided in the active part  68 A of the friction stop  68 , here in its support head  68 T in contact with the damper plate  36 , in order to facilitate the sliding between the pieces by establishing a passage of the fluid or at least the formation of a film. Naturally the groove or grooves could be produced conversely on the piece against which the friction stop  68  comes into abutment, that is to say here the damper plate  36 , but also in other possible embodiments one of the turbine wheel/hub assembly elements  18 ,  36 ,  24 . 
   In a variant the grooves R are produced on the two pieces, that is to say on the plug  68  and on the piece against which it bears  18 ,  36 ,  24 . 
   Such grooves make it possible to renew the oil (fluid) film between the support head  68 T of the plug  68  and the damper plate  36  so that wear resulting from the friction is reduced and the risk of sticking between the parts avoided. 
   Moreover, sealing means  70 , such as a joint, intervene between the passive part  68 P comprising the means of assembling the plug forming a stop and the contour of the passage orifice  30 T. 
   The design of the grooves is favourable to an increase in the service life of the friction stop  68 , and the reliability of the whole. 
   The locking, also referred to as clamping, of the clutch  28 , which consists of moving the piston  30  against the wall  20  whilst clamping the friction disc  32 , and the unlocking (also referred to as unclamping) of this clutch  28  are achieved in a fashion known per se by varying the pressure between the control chamber  58  and the turbine chamber  59 . 
   A second embodiment of the hydrokinetic coupling appliance according to the invention will now be described with reference to FIG.  3 . In this figure, the elements similar to those depicted in  FIGS. 1 and 2  are designated by identical references. 
   In this embodiment, the friction stop  68  is carried by the piston  30 , is arranged radially beyond the external periphery  100  of the plate  24 , and is produced in a single piece. 
   In this case, the friction stop  68  also consists of the obturation means, here metallic plugs preferably produced from pressed sheet metal, and which are for example force-fitted in the corresponding passage orifices  30 T. Each plug  68  has the general form of a bowl and comprises a re-entrant rolled edge  68 R here constituting the active part  68 A of the friction stop  68 , the edge  68 R being in abutment against the damper plate  36 . 
   Naturally the metallic plugs, in particular the active part  68 A, can be given treatment with a view to improving the properties, for example their coefficients of friction. 
   The passive part  68 P comprising the means of assembly with the piston  30  by cooperation of complementary shapes consists here of the edges of the plug  68  which cooperate with those of the orifice  30 T. 
   In this embodiment, when the metallic plug  68  is force-fitted in the orifice  30 T in the piston  30 , the seal is provided without its being necessary to add additional means such as a joint  70 . 
   Naturally other shapes and plugs can be envisaged, in which it would be possible to produce at least one lubrication groove R in the active part  68 A and/or in the piece against which it bears. 
   In the embodiments depicted in  FIGS. 4  to  6 , the friction stop  68  is carried by the piston  30 , radially beyond the external periphery  100  of the plate  24  and is produced in two pieces comprising respectively an active part  68 A and a passive part  68 P. 
   The friction stops  68  also constitute obturation means or plugs for the passage orifices  30 T produced in the piston  30 , the passive part  68 P of which comprises means of assembly with the said piston by cooperation of complementary shapes. 
   In these embodiments the passive part  68 P consists of a first metallic piece  168 , for example made from sheet metal, having substantially a bowl shape, this piece being force-fitted in the holes or passage orifices  30 T. No sealing means is then necessary between the hole  30 T in the piston and the passive part  68 P. 
   In these embodiments the active part  68 A of the friction stop consists of a second piece  268 , preferably made from synthetic material, which is attached to the first piece  168 . Advantageously the piece  268  forming the active part  68 A has a support head  68 T. 
   At least one lubrication groove (R) can be provided in the active part  68 A of the stop  68 , here more particularly in the head  68 T, and/or in the piece against which the said stop bears. 
   In a third embodiment illustrated in  FIG. 4 , the second piece  268  forming the active part  68 A of the stop consists of a plug force-fitted in the first piece  168 . 
   In a variant, the second piece  268  has an axial clearance with respect to the first piece  168  without however being able to completely emerge from the bowl  168 . 
   In a fourth embodiment illustrated in  FIG. 3 , the first piece  168  in the form of a bowl has, on the side of where it is open, at least two lugs  168 P whilst the second piece  268  consists of a plug fitted in the said opening and which comprises a head  68 T in which a groove  110  is formed. The connection between the first and second pieces forming the friction stop  68  is made by crimping, the lugs  100  being folded over into the groove  110 . 
   In a fifth embodiment illustrated in  FIG. 6 , the second piece  268  forming the active part  68 A comprises at its external periphery a skirt or lugs  268 P for its clipping or elastic fitting on the first piece  168 . 
   The invention is not limited to the embodiments described above. In particular, the plug  68  forming a friction stop can cooperate with any wall fixed to the turbine wheel  18 , namely in particular a connecting wall fixed to the hub  14 , as described above, or a wall delimiting the turbine wheel  18  itself. 
   Many variants can be envisaged. Thus, in a variant, only some of the plugs forming the obturation means  68  thus constitute friction stop means  68  for the piston  30 . In the case of a design with a plurality of plugs evenly distributed over the piston  30 , only one plug out of two combines for example the two functions of closure and friction stop. 
   The obturation means  68  and friction stop means can consist of one and the same part such as a plug, according to the embodiments detailed above, but they can also, without departing from the scope of the present invention, be distinct. 
   In a variant, a piece forming the friction stop is attached to one or more of the obturation means  68 . By way of example, such a plug, preferably metallic, carries a piece fulfilling the function of friction stop, which is for example produced from synthetic material or any other material. In the case of a friction stop made from synthetic material, many variant embodiments for attaching this element to a plug of the metallic type can be envisaged. The plug then comprises a part such as a head to which the friction stop would be attached. 
   Amongst the possibilities for attaching the friction stop, it is possible to cite non-limitingly clipping, moulding on, snapping on, fitting in, buttoning, screwing, riveting or bayonet mounting. 
   For each mode, it is possible to adapt the plug  68 , thus, for example in order to mould the stop onto the plug, it is possible to provide on the latter a flat head extended by a rim for better mechanical strength, that is to say substantially the shape of a rivet head. 
   Likewise it is possible to produce, for example by moulding from synthetic material, stops comprising lugs in order to attach them to the obturation means by clipping or snapping on, and thus to form an assembly consisting of friction stop and obturation plug  68 . The holding can also be provided by an additional piece such as clips. 
   For a mounting of the bayonet type, it is possible to produce a thicker part on the obturation means which, in a first step, enters a complementary part of the element forming a front stop, and secondly effecting a rotation in order to implement the said bayonet mounting. 
   Whatever the embodiment adopted, if the friction stop is of the synthetic material type, it is possible to produce as many stops as there are plugs which form shoes, these shoes having different geometries according to the required application, for example circular, rectangular or oblong. 
   It can be envisaged producing sectors forming friction stops  68  between two successive plugs, fixed to at least one head of one of the plugs. Likewise, in a variant, the friction stop  68  consists of one and the same piece having substantially the shape of a ring or annulus. 
   It should be noted that, in some of the embodiments, several functions are advantageously combined by the same component, in particular here the combining of the functions of seal and friction stop by at least one plug  68 . It is thus possible to reduce the number of elements constituting the lock-up clutch and to reduce the manufacturing cost of the hydrokinetic coupling appliance. 
   Thus it is no longer necessary to modify or adapt elements such as the hub  14 , in particular the plate  24 , or the piston  30  in order to arrange the friction stop means. This is particularly advantageous for parts such as the hub  14  or a guidance ring in so far as these parts are treated parts, in particular the hub in order to be able to slide along the driven shaft. 
   In a variant, the hole receiving the complementary assembly means of the friction stop  68  is a blind hole. 
   The invention is in no way limited to the embodiments described above in which the friction stop  68  is carried by the piston. This is because, in a variant, the friction stop is carried by the turbine wheel or a damper plate such as the damper plate of the damping device.