192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
1999-10-21
2001-06-12
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S090000, C092S107000, C092S169100, C277S437000, C277S439000
Reexamination Certificate
active
06244409
ABSTRACT:
The present invention relates to an hydraulically operated release system for a motor vehicle clutch.
A slave cylinder, which can also be called a central release unit, is mounted inside a clutch housing and concentrically surrounds a drive shaft which connects an internal combustion engine to a gearshift transmission. The central release unit comprises a housing in which a ring piston is axially displaceable. The ring piston axially defines a pressure chamber and is guided and sealed between an outer sleeve and an inner guide sleeve. The housing which is made of plastics is provided with an integral radially aligned pressure pipe which is guided through an opening in the clutch housing and through which the central release unit can be biased with a pressurised fluid. A hydraulic pipe attachable to the pressure pipe leads to a master cylinder which is connected indirectly or directly to a pedal device mounted in the passenger cell of the vehicle. The hydraulic release system is activated by manually operating the clutch pedal.
Furthermore the sealing track or guide track in the outer sleeve and guide sleeve of the housing can be formed so that these reduce sealing friction and at the same time lead to a reduction in noise when operating the release device.
Various solutions have been proposed to design the sealing track on the outer sleeve and guide sleeve of a slave cylinder housing made from plastics.
DE 43 31 728 A1 discloses a central release unit whose housing is made from a fibre glass reinforced material on a resin base. The entire surface of the housing is nickel-plated in order to improve in particular the sliding properties of the sealing element on the walls defining the pressure chamber. A high bearing proportion of the sealing lips which can be achieved through a smooth flat surface produces a lower sealing leakage. Against this advantage however is increased sealing friction. The high bearing proportion causes at the same time a so-called stick-slip effects i.e. a squeaking noise of the sealing lips of the sealing element. Applying the nickel coating requires a separate work process which impairs, i.e. extends, the production run, and at the same time considerably increases the manufacturing costs.
DE 42 29 370 A1 describes a further slave cylinder made from plastics. This central release unit is provided with relatively large wall thickness which increases the structural space required. The housing is provided with an integral short pressure pipe for connecting the hydraulic pipe. The drawback with this known solution is a pipe connection located in the clutch housing and which in the event of a possible break in the tightness needs a great deal of expense to remove the leak. Furthermore the seal is guided on an untreated guide or sealing track of the outer sleeve or guide sleeve of the housing. This sealing guide results in increased wear on the sealing lips and leads to premature breakdown of the slave cylinder.
Based on the technical faults of known solutions the object of the invention is to improve the rigidity of the component parts for the housing of the slave cylinder made from plastics and to provide measures to reduce the noise and wear of the seal.
This is achieved according to the invention through a plastics housing which is made as an injection moulded part. The injection moulding tool used for production ensures that when manufacturing the housing a structured sealing track or guide track is produced for the sealing lips of the sealing element which is formed as a grooved sealing ring. The sealing track according to the invention thus has a surface structure which is neither too flat and smooth nor has an unacceptably high roughness. Rather this surface condition represents an optimum compromise between a sealing leak and a bearing portion of the sealing lips and thus allows minimum wear on the sealing lips and reduced noise development of the groove ring seal.
According to the invention the sealing tracks of the housing have micro cavities in a texture, with a desired irregularly defined surface structure. The texture thereby forms sealing tracks having lubricating pockets in which the hydraulic fluid, i.e. the brake fluid, can be deposited and thus improve the sliding process of the seal. At the same time the surface structure according to the invention avoids the detrimental stick-slip effect and thus reduces the sealing lip wear of the groove ring seal.
The surface structure according to the invention consequently makes it possible to produce a housing provided with optimised sealing tracks for the sealing element without any further work process. The measures according to the invention lead to a clear increase in the service life and stability of the groove ring seal and thus of the entire slave cylinder.
Further developments of the invention are the subject of claims
2
to
23
.
According to an advantageous further development of the invention it is proposed to form the micro cavities of the sealing tracks in the form of rounded surface topology which on an enlarged scale matches the outer contour of a golf ball. A rounded topology formed in this way on the one hand has an advantageous effect on the wear of the sealing lips and on the other improves the bearing proportion of the sealing element and reduces or eliminates the development of noise through the sealing lips.
As a further measure for improving the sliding properties of the sealing track provided with the micro cavities it is proposed to provide the tracks with deposits serving as sliding improvement means. PTFE can preferably be used as sliding improvement means which can be embedded by way of example in the form of threads disc like or coil like in the sealing track.
To improve the sliding guide the invention further includes a ring piston having sliding improvement means incorporated in the sleeve face and/or bore wall. On the one hand the wear of the sealing track on the outside sleeve is reduced and on the other the friction between the ring piston and the outer sleeve and thus the required displacement force when operating the central release unit. MoS
2
is used for example as the sliding improvement means.
A further design of the invention provides a two-part housing. An outer sleeve or guide sleeve which is prefabricated separately is connected non-detachably to the housing to make up the central release unit. It is thereby advantageous to fix the outer sleeve or guide sleeve non-detachably on the housing by ultrasound welding or adhesive The two-part design allows an advantageous shortened axial structural space for the central release unit. Furthermore the two-part construction of the housing extends the piston stroke as a result of an axially off-set arrangement of the pressurised medium supply in the pressure chamber.
Furthermore the inventive idea comprises an outwardly moulded taper of the outer sleeve from the pressure housing of at least 0.5°. The outwardly moulded taper is thereby formed so that the largest diameter of the outer sleeve is provided on the release bearing side and the internal width of the sealing track on the outer sleeve tapers continuously over the entire length of the outer sleeve. Since as the wear on the follower disc of the friction clutch increases so the neutral position of the piston is moved in the direction of the gearbox and the piston seal is also subjected to a certain wear, the outwardly moulded taper according to the invention ensures that the wear on the piston seal is compensated The reduction in diameter produced by the moulded-out taper thus compensates sealing lip wear of the piston seal and thereby causes a practically constant contact pressure of the outer sealing lip of the piston seal. Consequently an improved service life of the seal is achieved as a result of the practically constant contact pressure force over the useful life of the friction clutch which effectively eliminates the risk of leaks.
As an alternative the invention includes a guide sleeve having an outwardly moulded taper whose sealing track runs in reverse
Liebezeit Bernd
Meyer Gerhard
Prosch Gerhard
Winkelmann Ludwig
Darby & Darby
Lorence Richard M.
LuK Lamellen und Kupplungsbau GmbH
LandOfFree
Slave cylinder for a centered clutch release system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Slave cylinder for a centered clutch release system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Slave cylinder for a centered clutch release system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2479054