Piston cylinder arrangement, in particular a slave cylinder for a hydraulic clutch actuating device

The invention relates to a piston-cylinder arrangement, in particular a slave cylinder for a hydraulic clutch actuating device, comprising a cylinder housing which is made of a plastic, in which an annular pressure chamber is formed in which a piston is mounted so as to be axially movable for actuation of a clutch release bearing, wherein the inner wall of the pressure chamber forms a guide sleeve. In the case of a piston-cylinder arrangement which stands up to the pressures and temperatures that occur in operation of the clutch actuating device, a stop is situated on the guide sleeve facing the clutch release bearing, the stop being in the form of a threaded connection.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national stage application pursuant to 35 U.S.C. § 371 of International Application No. PCT/DE2013/200123, filed Aug. 14, 2013, which application claims priority from German Patent Application Nos. DE 10 2012 215 182.6, filed Aug. 27, 2012, and DE 10 2012 223 735.6, filed Dec. 19, 2012, which applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The invention relates to a piston-cylinder arrangement, in particular a slave cylinder for a hydraulic clutch actuating device, comprising a cylinder housing which is made of a plastic, in which an annular pressure chamber is formed in which a piston is mounted so as to be axially movable for actuation of a clutch release bearing, wherein the inner wall of the pressure chamber forms a guide sleeve.

BACKGROUND

Central clutch releases for hydraulic clutch actuation are known, in particular for dual-clutch transmissions, in which the cylinder housing is made of a plastic. A cylinder wall of the cylinder housing delimits an annular pressure chamber radially toward the outside, in which a ring piston which is operationally connected to the clutch is movably accommodated. In this case, the cylinder housing is formed of two cylinder walls arranged concentrically to each other, where the inner cylinder wall forms the boundary of the pressure chamber and is referred to as a guide sleeve.

In operating states of the slave cylinder, in particular at the boundary zone of the forces and beyond, it may be that the clutch release bearing loses the partner for power transmission, preferably the diaphragm spring of the clutch. At the same time it must be ensured that the release unit is not able to travel beyond the specified maximum extension, which is guaranteed by a stop anchored on the cylinder housing. If this cannot be guaranteed, the slave cylinder will destroy itself and cause consequential damage. In addition to the strong forces occurring in the slave cylinder during operation of the clutch actuating system, thermal stress occurs.

It is known to use a sheet metal ring as a transport stop for a slave cylinder of the clutch actuating device. The shaft of this sheet metal ring is flanged in an undercut in the cylinder housing. A sheet metal ring of this sort functions only as a transport restraint, and is designed for the stresses that develop during transport from the manufacturer of the clutch actuating device to the recipient, and prevents breakup of the slave cylinder during transport.

Thus there exists a long felt need for a simply and economically producible piston-cylinder arrangement which has a stop for the piston that stands up both to the pressures which occur in operation of the clutch actuating device and to the thermal stresses.

SUMMARY

The object is fulfilled according to the invention by a stop being positioned on the guide sleeve, the stop being in the form of a threaded connection. The stop having a radially outward facing surface that faces the clutch release bearing, and a radially inward facing surface that faces the guide sleeve. In this way, a stop is provided which prevents the piston from being able to travel beyond the maximum permissible extension under operating conditions, which reliably prevents destruction of the system.

According to the aspects illustrated herein, there is provided a piston-cylinder arrangement, in particular a slave cylinder for a hydraulic clutch actuating device, comprising a cylinder housing comprising an inside wall, wherein the cylinder housing is made of a plastic, a guide sleeve formed by the inside wall of the cylinder housing, a stop arranged on the guide sleeve, the stop facing a clutch release bearing, wherein the stop is a threaded connection and, an annular pressure chamber formed by the cylinder housing, wherein the piston is arranged in the annular pressure chamber and is axially movable in order to actuate the clutch release bearing.

In a preferred embodiment, the threaded connection consists of a threading formed on the guide sleeve, onto which a stop nut is screwed. Such a stop is simple to realize when assembling the slave cylinder, the stop nut being provided as the actual stop for the piston. In the event of misuse, the piston will now come into contact with the stop nut when the maximum extension is exceeded, which prevents the escape of hydraulic fluid, since over traveling the exterior wall of the cylinder housing by the piston is reliably prevented with the help of the stop, so that the pressure chamber is always sealed.

In one design, a thread-locking adhesive is applied between the stop nut and the threading. Through the use of this thread-locking adhesive, the stop nut is simultaneously used as a transport restraint and prevents breakup of the slave cylinder during transport from the manufacturer of the clutch actuating device to the recipient.

Alternatively, the stop nut is secured by hot caulking or laser welding or by a positive lock with an elastic element on the guide sleeve. This fastening method also prevents the stop out from turning, which reliably prevents the stop nut from loosening due to vibrations occurring in the motor vehicle.

In one variant, the threading is formed on a side of the guide sleeve facing the piston. In this case, the threading serves as a male thread for the stop nut.

In one design, the piston has a free cut on a side facing the guide sleeve, which is engaged by the stop nut at the maximum extension of the piston. This design results in a space-saving version of the slave cylinder, which is reliably prevented from maximum extension.

In another variant, the threading is formed on a side of the guide sleeve facing away from the piston. The threading is thus formed as a female thread, into which the stop out is screwed. In a space-saving variant of this type, the overhang of the stop nut, which encircles the guide sleeve, is used simultaneously as a stop for the piston at maximum extension.

In a refinement, flanks of the threading rise flatly in the direction of force. Through this design measure, the axial force introduced by the piston is well introduced into the threaded connection, which prevents stripping of the threads and increases the holding strength of the threaded connection.

In a preferred embodiment, the stop nut and the threading are produced using a plastic, or the stop nut consists of a metal. Production of the stop nut and of the guide sleeve carrying the threading is conceivable in various material pairings. In particular, if the guide sleeve is made of a plastic, it can be produced in a single piece with the cylinder housing during construction of the latter. This reduces production steps and lowers the cost.

DETAILED DESCRIPTION

FIG. 1depicts a first embodiment of slave cylinder1, which is employed in a dual-clutch transmission. In this case, slave cylinder1consists of cylinder housing2made of plastic, which comprises annular pressure chamber3in which piston4is supported so that it is axially movable. Through a connector, not shown in further detail, of cylinder housing2, the hydraulic fluid reaches pressure chamber3and results in actuation of piston4and thus actuation of clutch release bearing6.

Preloading spring7, which is pre-stressed against clutch release bearing6, presses against cylinder housing2in the area of attachment5of the slave cylinder. To form pressure chamber3, cylinder housing2has an outer wall8and an inner wall designated as guide sleeve9. Formed on guide sleeve9is outer threading10onto which stop nut11is screwed. At maximum extension of piston4, stop nut11engages free cut12of piston4, whereby piston4is prevented from further axial movement. Free cut12is a radial cutout or notch on the radially inward facing surface of piston4. Free cut12comprises a radially inward facing surface and an axial surface facing a first axial direction. The axial surface of free cut12engages and/or abuts against stop nut11which prevents further axial movement of piston4. Free cut12may preferably be reinforced by changes in material, or may be realized by dividing the components in two, which causes the introduction of force at stop nut11to be realized through higher-strength components.

Between stop nut11and outside threading10a thread-locking adhesive13is situated, which prevents stop nut11from loosening from outside threading10during transport of the clutch actuating device from the manufacturer to the recipient. Stop nut11serves simultaneously as a transport restraint.

FIG. 2depicts a second embodiment of slave cylinder1, which differs from the first embodiment only in the configuration of the stop nut and the threading. The threading is now formed on guide sleeve9as female thread14, into which stop nut15is screwed. Stop nut15has an overhang16which encircles the end of guide sleeve9and serves as a stop for the maximum extension of piston4. Here too, bonding female threading14with stop nut15is advantageous, in order to achieve securing against rotation fir stop nut15.

As an alternative to introducing the thread-locking adhesive, hot caulking of female thread14is possible using two additional studs, not depicted in further detail, which point in the direction of clutch release bearing6. Besides the described options, securing of stop nut15against rotation is also guaranteed by laser welding, by means of which stop nut15is reliably connected to guide sleeve9and can no longer rotate. These alternative means of securing rotation also apply to stop nut11and male threading10depicted in connection withFIG. 1. In addition, other frictional, positive or material securing options are also conceivable.

Flanks17of the threads, both of male thread10and of female thread14, are formed so that an optimal introduction of force into the component occurs when the thread is subjected to an axial load.

Stop nuts11,15and guide sleeve9which carries threading10,14may be made in various material pairings. Thus plastic-plastic pairings are just as realizable as steel or aluminum designs for stop nuts11,15in combination with a plastic design for guide sleeve9which carries threading10,14.

LIST OF REFERENCE NUMBERS