Abstract:
A slave cylinder and a release system, the slave cylinder being configured in particular as a CSC for a hydraulic system of a motor vehicle. While maintaining the axial extension of the working space of the piston axially moveable in the slave cylinder, the force for actuating the clutch is increased in that the pressure chamber is sealed by two sealing elements having different diameters, and in that at least one energy accumulator is disposed in the pressure chamber of the slave cylinder, the energy accumulator generating a preload on the clutch release bearing operative connected to the slave cylinder.

Description:
This is a continuation of prior International Application PCT/DE2008/001559, filed Sep. 18, 2008, which claims priority to German Patent Application DE 10 2007 049 254.7, filed Oct. 15, 2007, the entire disclosures of which are hereby incorporated by reference herein. 
     The invention relates to a slave cylinder that is disposed concentrically on a transmission input shaft, in particular for a hydraulic system of a motor vehicle. 
    
    
     BACKGROUND 
     Hydraulic slave cylinders disposed concentrically on the transmission input shaft, the so-called CSC, are known and are already in operation in diverse embodiments in vehicles. In all embodiments, the objective is to hydraulically pressurize a working piston, executed as an annular piston, which is axially movable within a working chamber with a force for actuating a clutch, for instance, in order to separate the latter. This force is transmitted to a release bearing connected with the piston, whereby its clutch or its rotating diaphragm spring finger on the next disposed ring is in contact with the latter. 
     In these embodiments the pressure chamber is located in direct proximity of the release bearing. These slave cylinders are disposed between the clutch and transmission, thus outside the clutch housing. 
     In case of lack of space between the clutch and transmission, it is moreover known to integrate the actuator for the clutch or at least the release bearing that is in operative connection with the diaphragm spring fingers inside the clutch housing, wherein the corresponding pressure chamber is located outside the clutch. The connection between the release bearing disposed inside the clutch housing, about the transmission input shaft and the axially movable piston inside the pressure chamber, is established via a coupling element, for instance, an push rod. This push rod thereby acts, depending upon the applied clutch, as a tension or compression rod. 
     For the development of the force required for actuating the clutch, on the one hand a correspondingly large hydraulic surface area is required, upon which the size of the pressure chamber depends and on the other hand the seal of the pressure chamber against its surrounding is of great importance. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a slave cylinder of the type mentioned above, for actuating a clutch with which the pressure force for actuating the clutch is increased whilst retaining the axial extension of the working chamber. 
     An embodiment of the present invention provides a slave cylinder that is disposed concentrically on a transmission input shaft, in particular for a hydraulic system of a motor vehicle and consists of housing in which a piston is disposed axially in a displaceable manner within a pressure chamber between two end positions, wherein the pressure chamber is sealed by a sealing element. The piston stands above a push rod with a release bearing in an operative connection, which is prestressed by means of at least an energy accumulator. Since the pressure chamber is sealed with dynamic sealing elements featuring two different diameters and at least one energy accumulator is disposed inside the pressure chamber, despite retaining the axial extension of the work chamber, the compressive force for actuating the clutch is increased. 
     It is thereby advantageous to execute the energy accumulator as a compression spring, wherein the one end of this cylindrical compression spring is supported in a receptacle and the bottom end is supported on the internal contour of the housing. Moreover, it is advantageous for the manufacturing process to form the push rod as a tension- or compression rod. 
     Beside a cylindrical form, the compression spring can also feature a tapered form. 
     An advantageous embodiment of the invention provides for the piston to comprise a piston crown and a piston shaft adjoining the latter, wherein the length of the piston at least consists of the pressure chamber. 
     It is further advantageous that the piston is guide by its piston shaft in a bearing bush provided inside the housing and via the jacket surface of the piston crown inside the housing formed as a sliding surface. 
     For a positive fit accommodation of the sealing element with the larger diameter in the housing, the latter features a bead through which it is connected with a corresponding groove in the housing. 
     To determine the position or stroke length of the piston in an advantageous manner, the slave cylinder is provided with a displacement measuring device. For this purpose, a magnetic or a magnetizable section is integrated in the piston crown or the piston is in connection with a magnetic or magnetizable area. 
     It is particularly advantageous when the displacement measuring device is disposed on the housing of the slave cylinder or in its direct proximity and comprises a non-contact sensor that is in operative connection with the magnetic or magnetizable area. 
     To avoid losses of power transmission in an advantageous manner, the ends of piston and push rod can be connected with one another, wherein the connection is detachable, for instance, by means of a screw connection or non-detachable, for instance, by means of a piston. 
     An elastic pot-shaped protection cap, by which the cylindrical section is provided with grooves distributed over the internal circumference so that segments remain between these slits, for increasing the elasticity when lowering it on the housing in an axial direction, serves for closing the pressure-chamber-side housing of the slave cylinder and hence of the pressure chamber as well as for protecting it against dirt. The segments are formed hook-shaped inwards for the formation of snapping segments that interlock with a groove provided in the housing. 
     Moreover, an embodiment of the invention provides a release system in which a master cylinder is connected via a pressure line with a slave cylinder according to the invention, which actuates the release bearing, wherein the actuation of at least a release bearing occurs through at least a transmission input shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in detail on the basis of an exemplary embodiment and associated drawings. 
       The following are shown: 
         FIG. 1  shows a double clutch with actuation devices for each partial clutch. 
         FIG. 2  shows a section of a slave cylinder according to the invention, without a release bearing. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1  a part of a drive train of a motor vehicle with the corresponding actuation apparatus  1 ,  32  is depicted in half-section, wherein the twin clutch is formed of two partial couplings, thus a first partial clutch  20  and a second partial clutch  30 . Every partial clutch  20 ,  30  is concentrically disposed about an associated transmission input shaft  28 ,  29  and is in operative connection with one of the respective partial clutches  20 ,  30  based on the assigned release bearing  16 ,  17 . Every release bearing  16 ,  17  is hydraulically pressurized by a corresponding actuating device  1 ,  32  with an actuating force. Just like the actuating device  32 , the actuating device  1  is formed by a slave cylinder that is likewise disposed concentrically on the corresponding transmission input shaft  28 ,  29 .  FIG. 1  shows that, owing to the reasons of adaptation to a reduced assembly space, it is common at least that the release bearing  16  assigned to the first partial clutch  20  is integrated inside the clutch housing and the slave cylinder  1  according to the invention and connected with the latter is transferred to an assembly space outside the interstice of the twin clutch or respectively of clutch bell housing  60  and transmission  50 . 
     In  FIG. 2  the part of the slave cylinder  1  disposed outside the clutch housing is depicted as a single piece. In further description of the Figures, the same reference symbol is used for the same components. 
     The twin clutch depicted in  FIG. 1  is disposed between a drive unit in particular of an internal combustion engine from which a crankshaft  40  extends, and the transmission  50 . The partial clutch  30 , in that case, depicts a closed clutch; the partial clutch  20  depicts an open clutch. Both partial clutches  20 ,  30  are respectively disposed on one side of a central flywheel that simultaneously acts as an intermediate pressure plate  33 , so that the pressure plate  34 ,  35  is located opposite both partial clutches  20 ,  30 . 
     Furthermore, from this  FIG. 1 , it is evident that an external damper  31  is disposed between the drive unit and the twin clutch. The crankshaft  40  of the internal combustion engine is connected permanently via screw connections with an input part  36  of the damper  31 . The input part  36  of the damper  31  has essentially the shape of a circular disk extending in radial direction, which forms a vibration damper cage radially outside. Radially outside is a starter ring gear  23  attached to the input part  36 . In the vibration damper cage at least an energy accumulator device, in particular a spring device is at least accommodated partially. In this spring device an output part  37  interlocks in the damper  31 . 
     With the help of screw connections  21 ,  22  both clutch covers  38 ,  39  of the clutches  20 ,  30  are fixed on the common intermediate pressure plate  33 . On the drive side, friction linings of a first clutch disk  26  can be clamped between a pressure plate  34  in operative connection with the clutch  20  and the intermediate pressure plate  33 . This first clutch disk  26  is connected non-rotatably with the first transmission input shaft  28  via a hub part that is executed as a hollow shaft. The first transmission input shaft  28  is disposed rotatably in the second, transmission input shaft  29  likewise formed as a hollow shaft. A hub part of a second clutch disk  27  is connected non-rotatably with the drive-side end of the second transmission input shaft  29 . On the second clutch disk  27  of the clutch  30 , friction linings are fixed radially outside, said friction linings can be clamped between the intermediate pressure plate  33  and the pressure plate  35  in operative connection with the clutch  30 . The first transmission input shaft  28 , in the application of this kind of partial clutches, encloses a tie bar  5 , so that this is supported and guided in the center of both transmission input shafts  28 ,  29 . 
     The twin clutch consisting of both partial clutches  20 ,  30  is actuated via the slave cylinder  1 ,  32  disposed concentrically about the transmission input shaft  28 ,  29  with corresponding release bearings  16 ,  17  respectively. These release bearings  16 ,  17  again interact with the actuating levers  24 ,  25 . The actuating levers  24 ,  25  involve a diaphragm spring  24  on the one hand and on the other hand a lever spring  25 . By means of the latter, both pressure plates  34 ,  35  can be displaced limitedly in axial direction relatively to the intermediate pressure plate  33 . The release bearings  16 ,  17  are pressurized hydraulically. The tie bar  5  in this case serves for actuating the release bearing  16 , which is disposed at this end inside the clutch housing. Axial actuation of the tie bar  5  occurs via the slave cylinder  1  disposed outside the clutch housing. The assembly space between the twin clutch and the transmission  50  is reduced in this way. The end of the tie bar  5  projecting inside the clutch housing is provided with a thread so that the release bearing  16  can be fixed on the latter by means of a nut  15 . The release bearing  16  is in operative connection with the diaphragm spring  24  by means of an appropriately formed attachment in radial direction of the external bearing race. In contrast to this, in this example, the internal bearing ring of the release bearing  17  is formed such that the latter can undergo an operative connection with the lever spring  25 . The actuation of the release bearing  17  occurs by an axial movement of the piston supported inside the housing of the slave cylinder  32  that can be pressurized hydraulically with a compressive force. The release bearing  17  of this slave cylinder  32  is used, space-optimized, flush with the fixed bearing disposed in the clutch cover  39  on the driven side. 
       FIG. 2  shows in section the slave cylinder  1  according to the invention. In the housing of this slave cylinder  1 , a piston  6  is disposed in an axially movable manner The latter consists of a piston crown  6   b  with a diameter adapted to the internal diameter of the cylinder housing, to which a long-drawn piston shaft  6   a  adjoins with a significantly smaller diameter. The piston  6  is guided inside the housing  4  over the jacket surface of the piston crown  6   b , so that this acts as sliding surface  12   c . A pressure chamber  18  is formed between the face surface of the piston crown  6   b  and the cylinder chamber enclosed by a protective cap  13 . With the help of a sealing element  2  integrated inside the piston crown  6   b , this pressure chamber  18  is sealed in radial direction and thus the sliding surface  12   c  during the motion of the piston  6  is sealed against the surrounding. Radial lip seal is used preferably for this dynamic sealing element  2 . Besides axial fixation of this sealing element  2 , a ring-shaped magnet  12   a  disposed on the step of the piston crown  6   b  serves for determining the position or stroke length of the piston  6 . Axially, this magnet  12   a  is positioned by means of a cup-shaped receptacle  11  formed as ring, which is additionally fixed radially with the help of at least a pin  44  formed as lock against rotation, preferably near its internal diameter. 
     Towards the clutch side, the housing  4  is closed by means of a protective cap  13  that protects the latter from the access effect of dirt. 
     In this figure, in which the piston  6 , additionally guided on its shaft  6   a  by means of a bearing bush  41  inserted directly in the passage of the piston  6  through the housing  4 , assumes one of its two end positions, it is apparent that its path on this side is limited by a limit stop. This limit is implemented by means of the appropriately formed internal contour of the housing  4 . The bearing bush  41  is fixed axially by means of a limit stop disk  45  anchored inside the housing  4 . The distance limit in the other direction occurs by means of a limit stop disk  46  inserted in the tie bar  5 , which is limited with its face surface in this position of the piston  6  on which the limit stop disk  45  is limited in the housing  4 . 
     The protective cap  13  already mentioned above preferably consists of elastic material and is pot-shaped in form, wherein a cylindrical part  14   a  of the protective cap  13  is provided with grooves  13   b  extending up to their crown, so that segments distributed over the circumference occur inside the cylindrical part. These segments are provided with elevations directed inwards in the end section. These elevations acts on the housing when the protective cap  13  comes in contact on the housing  4  as snapping segments  13   a , since they are first widened radially so that when they hit the crown the snapping segments  13   a  can snap back into one of the circular grooves  4   a  provided in the housing  4 . 
     In this shown position of the piston  6 , the pressure chamber  18  is very well visible. Besides the moving dynamic sealing element  2 , this is also sealed by a dynamic sealing element  7   c  through the housing  4  fitted in the latter upright in the tie bar  5  passage section. This sealing element  7   c  preferably, is formed likewise as radial lip seal is provided with a bead  7   c   1  on the circumference, through which it is axially fixed in a groove  4   a  formed in the housing  4 . 
     The hydraulic sealing of the slave cylinders  1  and thus of the pressure chamber  18  occurs therefore over the length of the piston  6  and further over the sealing element  2 , and additionally via the sealing element  7   c  used in the housing  4 , which serves for sealing of the piston shaft  6   a . Therefore the pressure chamber  18  is enclosed by the piston  6 , the sealing elements  2  and  7   c  and the housing  4 , wherein the length of the piston  6  at least corresponds to the axial extension of the pressure chamber  18 . 
     In order to attain a possibly great actuating force for the release bearing  16  in  FIG. 1  with the piston  6  with a default hydraulic pressure, the hydraulic surface of the pressure chamber  18  required for it should be as large as possible. This hydraulic surface results from the difference between the sealing surfaces of the two seals  2  and  7   c . For this reason, in this slave cylinder  1  according to the invention, two sealing elements of different diameters are used for sealing the pressure chamber  18  instead of a single sealing element, whereby the sealing element  2  features a larger diameter and the sealing element  7   c  a smaller diameter. The sealing of the slave cylinders  1  against the transmission  50 , or transmission cavity, in which the transmission fluid is under atmospheric pressure, in this exemplary embodiment is implemented by means of a seal  19  executed as O-ring, which is used in the contact surface of the housing  4  towards the transmission  50 . 
     As apparent from  FIG. 2 , an energy accumulator  3   b  is disposed concentrically on the piston shaft  6   a  inside the pressure chamber  18 . This energy accumulator  3   b , in this example, formed as a tapered compression spring is supported with one end on the cup-shaped receptacle  11 , with which it is at the same time connected. Therefore, the energy accumulator  3   b  is secured against rotation by means of this receptacle  11 , whereby the drag torque arising from the release bearing  16  can be supported. It is supported on the internal contour of the housing  4  with its other end. This energy accumulator  3   b , fitted directly inside the pressure chamber  18 , as well known, serves the transmission of prestressing force to be applied to the release bearing  16 . Through this constructive measure, the required assembly space is shortened significantly. 
     To determine the respective piston position within the piston stroke, on the one hand, the magnet  12   a  is integrated in or linked to the piston  6  and, on the other hand, a displacement measuring device  9  is formed as a non-contact sensor. This is disposed outside the housing  4 . A permanent magnet is used advantageously as magnet  12   a . However, also local magnetization of the piston material or a disc with a magnetic or magnetizable section is considerable instead of the magnet  12   a.    
     The magnitude of the piston stroke is determined by its two limit stops. For the movement of the piston  6 , i.e. during the piston stroke, the air trapped inside will be compressed between the protective cap  13  and the chamber up to the piston crown  6   b , which, by acting as buffer, shortens the default piston stroke and hence influences the release process inconveniently. For this reason, the snapping segments  13   a  of the protective cap  13  simultaneously assume a valve function owing to its radial spreading possibility. 
     As already mentioned, the release bearing  16  depicted in  FIG. 1  is connected with the piston  6  via the tie bar  5 . This connection is implemented, as depicted in  FIG. 2 , for instance, by means of a screw connection through which the ends of the piston  6  and tie bar  5  are connected with one another. To boost the tightening torque during the screwing process, a cutout is embossed in the form of an hexagon  43   a  in the center of the face surface of the piston crown  6   b , on to which a blind hole  43   b  adjoins, in order to be capable of receiving a corresponding tool. Lower connections, both detachable as well as non-detachable are likewise considerable. In this manner, also a detachable connection, for instance a bayonet connection or a simple bolt-hole connection can be chosen, and radially fixes this connection axially and radially by means of a pin penetrating the latter. A non-detachable connection, for instance, could be established by adhesion or by corresponding material selections by means of frictional welding. The choice of the connection is based on the dimensions to be adapted in accordance with the assembly space conditions of the two components, as well as their materials and the forces to be expected at the connection point. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  slave cylinder/actuating device 
           2  sealing element 
           3   b  energy accumulator 
           4  housing 
           4   a  groove 
           4   b  groove 
           5  tie bar 
           6  piston 
           6   a  piston rod 
           6   b  piston crown 
           7   c  sealing element 
           7   c   1  bead 
           9  displacement measuring device/sensor 
           11  annular receptacle 
           12   a  magnet/magnetized section 
           12   c  sliding surface 
           13  protective cap 
           13   a  snapping segment 
           13   b  groove 
           15  nut 
           16  actuating bearing/release bearing for first partial clutch 
           17  actuating bearing/release bearing for second partial clutch 
           18  pressure chamber 
           19  seal 
           20  first partial clutch (drawn clutch) 
           21  screw connection 
           22  screw connection 
           23  starter ring gear 
           24  diaphragm spring/actuating lever 
           25  diaphragm spring/actuating lever 
           26  first clutch disk 
           27  second clutch disk 
           28  first transmission input shaft 
           29  second transmission input shaft 
           30  second partial clutch (pressed clutch) 
           31  damping device 
           32  slave cylinder/actuating device 
           33  central flywheel/intermediate pressure plate 
           34  pressure plate 
           35  pressure plate 
           36  input part 
           37  output part 
           38  clutch cover 
           39  clutch cover 
           40  crankshaft 
           41  bearing bush 
           42  thread 
           43   a  hexagon screw 
           43   b  blind hole 
           44  non-rotational lock/pin 
           45  limit stop disk 
           46  limit stop disk 
           47  screw connection 
           50  transmission 
           60  clutch housing