Patent Application
20090181825
The invention relates to a releasing system for controlling a clutch and/or an acceleration coupling in a motor vehicle.
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.
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.
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.
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.
The invention will now be described, by way of example, with reference to the accompanying drawing in which:
The sole FIGURE shows a release system for controlling a friction clutch in a motor vehicle.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 022461.2 | May 2006 | DE | national |
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.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/054016 | 4/25/2007 | WO | 00 | 11/10/2008 |
