Abstract:
The invention relates to a multiple clutch assembly comprising: first ( 5, 9 ) and second ( 7, 11 ) friction elements; first ( 15 ) and second ( 17 ) plates for applying pressure to said respective friction elements; first ( 21 ) and second ( 25 ) diaphragms for actuating said respective plates, each diaphragm being mobile between a disengaged position ( 21   a   , 25   a  or  25   b ) and an engaged position ( 21   b  or  21   c   , 25   c ), said first diaphragm ( 21 ) approaching the second diaphragm ( 25 ) when it passes from the disengaged position thereof to the engaged position thereof; and first ( 23 ) and second ( 27 ) means for actuating said respective diaphragms. Said second actuating means ( 27 ) comprise means for renewing the course of the second diaphragm ( 25 ), in such a way that the second diaphragm ( 25 ) follows a pre-determined course between the disengaged position ( 25   a  or  25   b ) and the engaged position ( 25   c ) thereof, independently of the degree of wear of the second friction element ( 7, 11 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
     This application relates to International Application No. PCT/FR2006/051153 filed Nov. 8, 2006 and French Patent Application No. 0553482 filed Nov. 16, 2005, of which the disclosures are incorporated herein by reference and to which priority is claimed. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiple clutch assembly in particular for a motor vehicle, and to an associated control method. 
     2. Description of Related Art 
     As is known per se, a multiple clutch assembly comprises several clutches, and usually two clutches. 
     Such a clutch assembly has in particular the advantage of allowing gear changes without break in torque. 
     Such a clutch assembly does however have the drawback of having an axial size greater than that of a single clutch. 
     However, this axial size is a critical matter in being able to install the clutch assembly between the engine and the gearbox of certain vehicles. 
     Thus the aim of the present invention is to provide a multiple clutch assembly having a smaller axial size compared with the multiple clutch assemblies currently available on the market. 
     BRIEF SUMMARY OF THE INVENTION 
     This aim of the invention is achieved with a multiple clutch assembly comprising:
         at least first and second friction devices,   at least first and second plates pressing on these respective friction devices,   at least first and second diaphragms for actuating these respective plates, each of these diaphragms being able to move between a disengaged position and an engaged position, the said first diaphragm approaching the said second diaphragm when it passes from its disengaged position to its engaged position, and   at least first and second means of actuating these respective diaphragms,
 
in which at least the said second actuation means comprise means of taking up the travel of the said second diaphragm, so that this second diaphragm covers a predetermined travel between its disengaged and engaged positions, independently of the degree of wear on the said second friction device.
       

     By virtue of the presence of the travel take up means for the means of actuating the second diaphragm, it is possible to obtain a travel of this diaphragm that is independent of the degree of wear on the associated friction device. 
     As will be explained hereinafter, this makes it possible in particular to move the two diaphragms axially closer together without there being a risk of interference between them throughout the life cycle of the clutch. 
     According to other optional characteristics of the clutch assembly according to the invention:
         the said travel take up means comprise a mechanical clearance take up system integrated in the said second actuation means,   the said travel take up means comprise means for memorising the predetermined travel of the said second diaphragm between its disengaged and engaged positions prior to the setting in rotation of the said pressure plates, the second friction device being in a new state, and for readjusting the disengaged position of the said second actuation means so that the said diaphragm covers the same predetermined travel memorised after the setting in rotation of the said pressure plates,   the lever arm of the said second diaphragm is greater than that of the said first diaphragm,   the said first actuation means comprise means of taking up the travel of the said first diaphragm,   the said clutch assembly comprises two normally open clutches.       

     The present invention also relates to a method of controlling a clutch assembly in accordance with the above in which, prior to the setting in rotation of the said pressure plates, the said second actuation means are controlled so as to place the said second diaphragm in the engaged position, and the disengaged position of the said second actuation means is adjusted so that the said diaphragm covers the said travel memorised after the setting in rotation of the said pressure plates. 
     According to other optional characteristics of the control method according to the invention:
         the second friction device being in a new state, there is determined and recorded in the said memorisation means the travel then covered by the said second diaphragm between its disengaged and engaged positions, prior to the setting in rotation of the said pressure plates.       

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Other characteristics and advantages of the present invention will emerge from a reading of the following description and an examination of the accompanying figures, in which: 
         FIG. 1  depicts a view in axial half-section of a clutch assembly according to the invention, and 
         FIG. 2  depicts schematically the travels covered by the diaphragms of the clutch assembly according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to this figure, it can be seen that a normally open double clutch has been chosen as an example. 
     It must however be noted that the present invention is in no way limited to such a clutch and that it is applicable to double clutches and to multiple clutches in general, and to both normally open and normally closed clutches. 
     Referring to  FIG. 1 , it can be seen that the double clutch comprises an internal output shelf  1  mounted coaxial inside an external output shaft  3 . 
     Two friction discs  5 ,  7  are mounted so as to be secured respectively to the two shafts  1 ,  3 , and each comprises at their periphery respective friction linings  9 ,  11 . 
     The discs  5 ,  7  each comprise caution damping means  8   a ,  8   b  known per se, for damping the vibrations transmitted by the crankshaft to the clutch. 
     The linings  9  are disposed between the support plate  13  fixed in axial translation and a pressure plate  15  able to move in axial translation. 
     The linings  9  are associated with the start-up clutch, that is to say the clutch that makes it possible to pass from neutral to the first gear ratio. 
     The linings  11  for their part are disposed between the support plate  13  and another pressure plate  17  able to move in axial translation. 
     The pressure plate  15  is in fact secured to a structure  19  frequently referred to as a “slide”, itself able to move in axial translation under the action of a diaphragm  21 . 
     As is known per se, the diaphragm  21  functions like a lever under the action of actuation means  23  able to move in axial translation, a clutch release bearing  24  being interposed between the diaphragm  21  and the actuation means  23 . 
     Concerning the pressure plate  17 , this is able to move in axial translation under the direct action of another diaphragm  25  itself actuated by other actuation means  27  able to move in axial translation, a clutch release bearing  28  being interposed between the diaphragm  21  and the actuation means  27 . 
     The lever arm of the diaphragm  25  is preferably slightly greater than the lever arm of the diaphragm  21 . 
     In the example shown, the two clutches are said to be “normally open”, that is to say, in the absence of forces exerted by the actuation means  23 ,  27  on the diaphragms  21 ,  25 , the two clutches are in the disengaged position. 
     The positions  21   a  and  25   a  of the diaphragms  21  and  25  correspond to the disengaged positions of these diaphragms for new linings  9 ,  11 . 
     The positions  21   b  and  25   b  of the diaphragms  21  and  25  correspond respectively to the engaged and disengaged positions of these diaphragms for respectively new and worn linings  9 ,  11 . 
     The positions  21   c  and  25   c  of the diaphragms  21  and  25  correspond to the engaged positions of these diaphragms for worn linings  9 ,  11 . 
     The disengaged position  25   b  of the diaphragm  25  for worn linings  11  is different from the disengaged position of this diaphragm for new linings  11  because of the fact that means are provided for taking up the length of travel of the actuation means  27 . 
     These means of taking up the length of travel make it possible to make the parts (“fingers”) of the diaphragm  25  that cooperate with the actuation means  27  always cover the same travel whatever the degree of wear on the linings  11 . 
     In practice, this means that, as the linings  11  wear, the fingers of the diaphragms  25  go further and further in their engaged position, and return less and less in their disengaged positions. 
     The difference between the positions  25   a  and  25   b  illustrates this shift in travel along with the wear on the linings  11 . 
     The means of taking up the length of travel of the actuation means  27  can, according to a first variant, be obtained with a mechanical clearance take up system integrated in the actuation means. Such a system is known per se. 
     According to a second variant, the travel length take up can be obtained by placing the diaphragm  25  in the engaged position before the starting of the engine, for example at the time of turning the ignition key, marking this engaged position, and deducing from this engaged position the disengaged position of this diaphragm, by applying a predetermined length of travel for this diaphragm. 
     This predetermined length of travel is substantially equal to the travel of this diaphragm between its disengaged and engaged positions when the linings  11  are new. 
     In other words, each time the vehicle is powered up, the actuation means  27  “learn” the engaged position of the diaphragm  25 , and deduce its disengaged position from this. 
     It will be noted that the two diaphragms  21  and  25  both bear on a structure  29  frequently called a “clutch cover”, fixed in axial translation and secured to the fixed support plate  13 . 
     The clutch assembly according to the invention can also comprise a flexible plate  30  secured on the one hand to the crankshaft  33  and on the other hand to the assembly comprising the support plate  13  and the structure  19 . 
     The flexible plate  30  comprises at its periphery a toothed starter ring  35 . 
     The operating method and the advantages of the clutch assembly that has just been described result directly from the above description. 
     There is no need here to enlarge in detail on the operating mode of a double clutch, this being known per se. 
     It will simply be stated that, in such a double clutch, the two output shafts  1  and  3  are connected respectively to gearbox input shafts (not shown) supporting gear pinions, respectively odd and even. 
     The actuation means  23 ,  27  are controlled automatically so that, when changing gear, at least one of the two output shafts  1 ,  3  remains under torque, which makes it possible to make gear changes without any sensation of break in torque. 
     As can be seen in  FIGS. 1 and 2 , when the linings  9  and  11  are new, there exists a certain axial clearance J 1  between the fingers of the diaphragm  21  in the engaged position and the fingers of the diaphragm  25  in the disengaged position (positions  21   b  and  25   a  respectively). In other words, there is no interference between the fingers of each diaphragm. 
     On the other hand, it can be seen that, as the linings  9 ,  11  wear, if the disengaged position  25   a  of the diaphragm  25  does not vary there will end up being interference (indicated by the letter Z in  FIG. 2 ) between this disengaged position and the engaged position  21   c  of the diaphragm  21 . 
     Such interference can of course not be contemplated, since its means that, beyond a certain wear on the linings  9 , it would no longer be possible to engage the associated clutch, the diaphragm  21  coming to abut on the diaphragm  25 . 
     However, precisely, providing travel take-up means in the actuation means  27  makes it possible to prevent the second diaphragm  25  returning as far as a disengaged position in which it could interfere with the diaphragm  21 . 
     As can be seen in particular in  FIG. 2 , when both the linings  9  and linings  11  are worn there exists an axial clearance J 2  (typically around 2 mm) between the engaged  21   c  and disengaged  25   b  positions of the respective diaphragms  21  and  25 : no interference between these two diaphragms is therefore possible. 
     Naturally it must be ensured that this absence of interference is guaranteed throughout the wear cycle of the linings  9 ,  11  and not only when they are completely worn. 
     This problem is all the more acute when the diaphragms  9  are associated with the start-up clutch, so that they undergo a greater wear than the linings  11 . 
     Providing a greater lever arm for the diaphragm  25  than for the diaphragm  11  makes it possible to compensate for this differential in rate of wear and to ensure that the travels of the fingers of the two diaphragms  21 ,  25  remain distinct throughout the life cycle of the linings  9 ,  11 . 
     As can be understood in the light of the above, providing length of travel take-up means for the actuation means  27 , and optionally providing a greater lever arm for the diaphragm  25  than for the diaphragm  21 , makes it possible to bring these two diaphragms axially closer together without there being a risk of interference between them throughout the life cycle of the clutch. 
     In this way it is possible to obtain a clutch having a reduced axial size. 
     Naturally the present invention is in no way limited to the example described and depicted, provided solely by way of illustration. 
     Thus it would also be possible to provide means of taking up the length of travel of the actuation means  23 . 
     This it would be possible to extend the precepts of the invention to any type of clutch comprising a plurality of diaphragms liable to interfere with each other when the axial distance separating them is reduced.