Abstract:
A release system ( 1 ) for a clutch and/or an accelerating coupling ( 2 ) in a motor vehicle, which automatically compensates for wear on the clutch and/or accelerating coupling ( 2 ). The release system ( 1 ) includes of a piston-cylinder unit ( 24 ), which is arranged concentrically with a transmission input shaft ( 12 ) and features a cylinder ( 13 ) and two pistons ( 14, 17 ) that delimit two pressure chambers ( 16, 19 ). The piston-cylinder unit is controlled both pneumatically and hydraulically.

Description:
[0001]    This application is a national stage completion of PCT/EP2007/054016 filed Apr. 25, 2007, which claims priority from German Application Serial No. 10 2006 022 461.2 filed May 13, 2006. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a releasing system for controlling a clutch and/or an acceleration coupling in a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    A clutch and/or an acceleration coupling, which may be configured as a friction clutch, is an element of a motor vehicle drive train that is subjected to great strain. Even though the quality and lifetime of clutch linings have improved considerably, they are subject to operational wear even when used sparingly. A reduction in the thickness of the clutch lining influences the position of a clutch spring, for example a membrane or disk spring, such that a releasing force or a contact force and thus also the necessary pedal force, increase. In the state of the art, friction clutches and releasing systems are described that automatically compensate for clutch lining wear. 
         [0004]    DE 44 07 665 B4 discloses a hydraulically actuatable releasing system for a motor vehicle friction coupling. The releasing system consists of a piston-cylinder unit arranged concentrically to an incoming gear shaft, whose cylinder is affixed to the transmission housing. A piston is arranged inside the cylinder, whose lateral surface is at least partially encompassed by a guiding element. A preloading spring arranged on the releasing system serves to hold the release bearing of the releasing system in contact with the contact spring of the friction clutch. Through a retaining mechanisms for the guiding element, the guiding element functions as a stationary component during the inward and outward movement of the piston. The guiding element is initially forced to perform an axial movement when, with wear on the friction linings of the friction clutch, the piston is pushed deeper into the cylinder chamber by the contact spring of the friction clutch. The effect of the retaining mechanism is thereby canceled and the guiding element is displaced by an axial distance until the change in position of the contact spring of the friction clutch is compensated for. As soon as a new balance of forces has been established, the guiding element comes to a stop. On the basis of this new position of the guiding element, the piston performs its inward movement with the usual piston stroke, where its stroke path is displaced in an axial direction compared to the stroke path of a clutch that is as good as new. 
         [0005]    The object of the present invention is to disclose a releasing system for controlling a clutch and/or an acceleration coupling in a motor vehicle, by way of which clutch wear can be securely and simply compensated for and which can be manufactured with little complexity of manufacturing technique. 
       SUMMARY OF THE INVENTION 
       [0006]    A releasing system for a clutch and/or an accelerating coupling in a motor vehicle consists of a piston-cylinder unit, arranged concentrically to a transmission input shaft. The clutch and/or accelerating coupling is configured as a friction clutch, which can show wear over its lifetime. The piston-cylinder unit features a cylinder and two pistons, such that two pressure chambers in the cylinder are bounded. The cylinder can be arranged on a transmission housing. The first piston of the piston-cylinder unit serves as a working piston, where the second piston of the piston-cylinder unit represents a final position of the releasing system. The friction clutch is operated by the inward and outward movement of the working piston. The two pressure chambers of the piston-cylinder unit can be separately controlled with a pressure medium. The first pressure chamber of the piston-cylinder unit, which is bounded by the two pistons of the piston-cylinder unit, is preferably pneumatically controlled, while the second pressure chamber of the piston-cylinder unit is hydraulically controlled. The second pressure chamber, which is filled with a hydraulic pressure medium, is closed by a check valve in a pressure medium line and by a control valve in a back flow line, as soon as the releasing system fills the first pressure chamber with the corresponding operating pressure. During the rest phase of the clutch, a certain pressure will be maintained in the second pressure chamber of the piston-cylinder unit by way of an overflow valve in the hydraulic back flow line; the pressure corresponding to the resting force of a preloading spring. In this way, it is assured that a release bearing of the releasing system always abuts the contact spring of the clutch, which means that a preloading spring can be dispensed with. If wear occurs between a contact disk and the friction linings of the friction clutch, a force is exerted on the release bearing and thus an axial force on the piston-cylinder unit. The two pistons of the piston-cylinder unit will be displaced by this force in the direction of the transmission-side end of the cylinder, until the change in position of the contact spring of the friction clutch that is caused by wear, is compensated for. As soon as a new balance of forces has been established, the two pistons come to a standstill. Through the compensation for wear and tear, the final position of the second piston of the piston-cylinder unit is also displaced in the direction of the transmission-side end of the cylinder, such that there is an axial displacement of the piston stroke when there is a clutch release. Based on this new position of the two pistons, the working piston performs its inward and outward movement with the usual piston stroke, because the first pressure chamber of the piston-cylinder unit is always supplied with a constant pressure by way of the pressure generating device. With continuing operation of the release system, the pistons, due to increasing wear on the friction clutch, will be increasingly displaced in the direction of the transmission-side end of the cylinder. With maximum clutch wear, the second piston of the piston-cylinder unit reaches a final position on the transmission-side of the cylinder. In this position as well, the working piston performs the usual piston stroke. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The invention will now be described, by way of example, with reference to the accompanying drawing in which: 
           [0008]    The sole FIGURE shows a release system for controlling a friction clutch in a motor vehicle. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    A release system  1  for a friction clutch  2  in a motor vehicle shown in the FIGURE consists of a piston-cylinder unit  24  that is arranged concentrically to a transmission input shaft  12 . The friction clutch  2  consists of a flywheel  3 , a clutch housing  8 , a clutch disk  4  that features two friction linings  5 ,  6  and a contact spring  10  that is connected, via spacer bolts  9 , to a contact disk  7 . The contact spring  10  can be configured as a membrane or plate spring and is in connection with a release bearing  11  of the release system  1 . For a more exact description of the friction clutch  2 , see the patent application publications DE 32 41 248 A1 and DE 197 03 333 B4. The piston-cylinder unit  24  features a cylinder  13  and a first piston  14  and a second piston  17 , which delimit a first pressure chamber  16  and a second pressure chamber  19  of the piston-cylinder unit  24 . The first piston  14  of piston-cylinder unit  24  serves as a working piston, where the second piston  17  of the cylinder-piston unit  24  represents a final position of the release system  1 . In addition, the release system  1  features a hydraulic circuit, consisting of a pressure generating device  23 , a pressure regulating means  21 , a check valve  20 , an overflow valve  27 , a control valve  31 , a pressure medium line  22 , as well as a back flow line  26  and a container that serves as a pressure-medium sink  25 . The devices already present in a transmission for supplying lubricants to the transmission can preferably be used as the pressure generating device  23  and the pressure medium sink  25 . The pressure medium line  22  and the back flow line  26  are connected to the second pressure chamber  19  of the piston-cylinder unit  24 , while the first pressure chamber  16  of the piston-cylinder unit  24  is connected to a further pressure medium line  29 . The pressure medium line  29  is connected to a pneumatic pressure generating device  28 , for example a pneumatic pump. The control valve  31  in the hydraulic circuit is connected to an additional pressure medium line  30 , which is connected to the pneumatic pressure generating means  28 . The first pressure chamber  16  of the piston-cylinder unit  24  can therefore be pneumatically controlled, while the second pressure chamber  19  of the piston-cylinder unit  24  is hydraulically controlled. Between the cylinder  13  and the first piston  14  of the piston-cylinder unit  24 , at least one sealing means  15  can be arranged. At least one sealing means  18  can also be arranged between the cylinder  13  and the second piston  17  of the piston-cylinder unit  24 . In order to operate the clutch, the first pressure chamber  16  of the piston-cylinder unit  24  is filled via the pneumatic pressure generating device  28  with a corresponding operating pressure. The second pressure chamber  19  of the piston-cylinder unit  24 , which is filled with a hydraulic pressure medium, is closed during clutch operation by the check valve  20 , which is arranged in the pressure medium line  22 , and by a control valve  31  arranged in the back flow line  26 . The control valve  31  in the hydraulic back flow line  26  is controlled by way of the pneumatic operating pressure that controls the clutch release, such that the back flow line  26 , between the second pressure chamber  19  of the piston-cylinder unit  24  and the pressure medium sink  25 , is interrupted. During the rest phase of the friction clutch  2 , a specific pressure is maintained in the second pressure chamber  19  of the piston-cylinder unit  24  by way of an overflow valve  27  in the hydraulic back flow line  26 . The pressure produces a rest force which corresponds to a rest force of a preloading spring. This ensures that the release bearing  11  abuts on the contact springs  10  of the clutch  2 , which means that a preloading spring can be dispensed with. If wear occurs between the contact disk  7  and the friction linings  5 ,  6 , the contact disk moves in the direction of the flywheel  3  and the position of the contact spring  10  changes. This produces a force on the release bearing  11 , such that an axial force acts on the piston-cylinder unit  24 . By way of this axial force, the pistons  14 ,  17  will be displaced to the right in the drawing plane, until the change in position of the contact spring  10  of the friction clutch  2 , that is due to wear and tear, is compensated for. As soon as a new balance of forces has been established, the pistons  14 ,  17  come to a standstill. The final position of the release system  1 , which is realized by the second piston  17  of the piston-cylinder unit  24 , is also displaced to the right in the drawing plane, where there is an axial displacement of the piston stroke with a clutch release. Based on this new position of the pistons  14 ,  17 , the first piston  14  of the piston-cylinder unit  24  performs its inward and outward movement with the usual piston stroke, because the first pressure chamber  16  of the piston-cylinder unit  24  can be supplied with a constant pressure via the pressure generating device  28 . With continuing operation of the release system  1 , the pistons  14 ,  17 , due to increasing wear on the friction clutch  2 , will be increasingly displaced more to the right in the drawing plane. With maximum clutch wear, the second piston  17  of the piston-cylinder unit  24  reaches a final position at the transmission-side end of the cylinder  13 . In this position as well, the first piston  14  of the piston-cylinder unit  24  performs the usual piston stroke. 
         [0010]    By way of the release system  1 , the operating volume of the clutch release path remains constant during the entire lifetime. Since the piston-cylinder unit  24  has two pistons  14 ,  17 , wear and tear on the friction clutch  2  can be automatically compensated for and clutch operation with a constant piston stroke can be carried out. In that way, the friction clutch  2  or the release system  1  demonstrates the same response during each operation, such that an equal short response time can be realized and maintained. 
       REFERENCE NUMERALS 
       [0000]    
       
           1  release system 
           2  friction clutch 
           3  flywheel mass 
           4  clutch disk 
           5  friction lining 
           6  friction lining 
           7  contact disk 
           8  clutch housing 
           9  spacer bolts 
           10  contact spring, membrane or plate spring 
           11  release bearing 
           12  transmission input shaft 
           13  cylinder 
           14  first piston or the piston-cylinder unit, working piston 
           15  sealing means 
           16  first pressure chamber of the piston-cylinder unit 
           17  second piston of the piston-cylinder unit 
           18  sealing means 
           19  second pressure chamber of the piston-cylinder unit 
           20  check valve 
           21  pressure regulating means, throttle 
           22  pressure medium line 
           23  pressure generating device 
           24  piston-cylinder unit 
           25  pressure medium sink 
           26  back flow line 
           27  overflow valve 
           28  pressure generating device 
           29  pressure medium line 
           30  pressure medium line 
           31  control valve