192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
1999-10-12
2001-08-14
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S090000, C092S16500R, C277S551000, C277S577000
Reexamination Certificate
active
06273231
ABSTRACT:
The present invention relates generally to the hydraulic operation of vehicle friction clutches, and more specifically to a hydraulic piston/cylinder unit for use in a clutch operating system.
Clutch release systems having a slave cylinder as the central release member are known. They comprise a slave cylinder concentrically enclosing a drive shaft and formed as a piston cylinder unit. The cylinder can be detachably fixed on a gearbox housing. The piston can be a ring piston which is displaceable in a circular ring shaped pressure chamber of the cylinder, and the piston can be associated on the pressure chamber side with a seal which is fastened by a seal carrier on the ring piston and is held in positive engagement in the seal carrier.
The invention also relates to a hydraulic piston/cylinder unit, which may be a slave cylinder for a hydraulic release system of a motor vehicle friction clutch (or may be a piston/cylinder unit for some other application). The cylinder pressure housing can have a circular ring shaped pressure chamber with a ring piston displaceably guided in the chamber and an elastic seal fixed with keyed engagement on the ring piston by means of a seal carrier.
The invention further relates to a hydraulic work cylinder which is preferably formed as a component part of a release system for a shit and separate clutch and may be mounted in a vehicle between an internal combustion engine and a manual shift transmission. The release system can comprise a master cylinder unit operated by means of a pedal or an automatic release unit and a pressure transfer mechanism to a further cylinder, which is also to be called a slave cylinder, which concentrically surrounds a drive shaft which connects the internal combustion engine to the transmission. The cylinder forms a pressure chamber which seen in cross-section is circular ring shaped and in which a ring piston is guided axially displaceable between a bore wall of the cylinder and a guide sleeve concentric therewith. On the pressure chamber side the ring piston is associated with a seal.
A release system with the construction explained above is known from DE 196 09 472 A1. The known release system is fitted with a seal carrier which is made without stock removal from steel. This support has on its radially outer projection spaced from the free end a locking nose which in the installation position engages with keyed engagement into a ring groove or local recess of the piston. The locking nose which is shaped semi-circular allows an automatic snap-fit engagement which can become loose by itself e.g. in the event of unfavourable manufacturing tolerances or ill-matched pairings. A seal carrier separated from the ring piston leads to a breakdown or function failure or the slave cylinder. The internal profiled section of the seal carrier which serves to house and fasten the seal has according to the known release system a relatively large axial extension which has a direct detrimental effect on the guide length of the ring piston.
From the French Patent Application FR 2 730 532 on this subject a slave cylinder is known, more particularly for a hydraulic release system of a friction clutch of motor vehicles wherein for the positive locking connection of the seal on the ring piston a retaining plate is provided which is hooked by its ring-shaped part on the outer circumference of the ring piston by means of claws engaging in corresponding recesses and is anchored at the end side in the seal by a radially inwardly directed area. Through this type of fastening a secure hold of the seal on the retaining plate is not guaranteed since the remaining cross-sectional area of the sealing material is now only small and can easily wear away. Furthermore the radial area of the retaining plate engages only from the outside on the seal so that it is easy for the seal to cant.
From DE 34 39 652 A1 a slave cylinder is known for a hydraulic release system of a friction clutch of motor vehicles wherein a stripper element is provided between the ring piston and seal and engages from inside and outside round the seal in dovetailed fashion and thus produces a fixed connection with the seal whereby the stripper element only adjoins the ring piston loose and the problem thereby exists that the contact between the ring piston and stipper element can be lost which leads to function failures of the slave cylinder. Play between the support faces of the seal and the sealing ring support reduces the stiffness and thus degree of efficiency of the operating system associated therewith.
Furthermore from EP 0 168 932 A1 a hydraulic release device is known having a further release shoulder. In order to obtain a surface which favours the wear behaviour of the sealing lips of the ring piston seal the guide faces on the bore wall of the cylinder and on the guide sleeve are subjected to a special mechanical finishing treatment. By way of example the guide faces, i.e. the seal tracks can be enhanced by grinding and/or polishing or honing. These processes extend the manufacturing cycles of the cylinder and are thus disadvantageous from the cost point of view.
For a specific surface treatment of the seal tracks it is generally known to subject these to a sand-blasting treatment in order to improve the wear and/or sliding properties of the seal. By way of example the seal track can be enhanced in an aluminum cylinder by sand-blasting with glass balls. However such a process is very expensive and incurs high costs.
Coating a sealing element can be concluded from DE 40 35 657 A1. To this end in order to influence the sliding ability a foundation body of elastomer can be coated with a material substance. By way of example polyvinyl chloride is used for the coating which is applied onto the foundation body but does not however project into the marginal zone of the foundation body. Such a process is very expensive and demands high production quality. Manufacturing the foundation body and applying the coating must thereby be carried out so that a definite wall thickness of the sealing lips is set in order to obtain for example the elasticity required for the sealing action.
The object of the present invention is therefore to provide a seal carrier which:
ensures an effective permanent fixing on the ring piston;
allows improved support of the seal;
reduces the axial structural length.
The object of the invention is to avoid the faults of the known solutions and to provide a slave cylinder whose sealing assembly ensures precision guidance of the seal in the pressure chamber and furthermore guarantees a permanent fixed connection of the seal relative to the ring piston. Furthermore the seal carrier is to be capable of reliable mass production and able to meet the demands regarding strength whilst taking up minimal axial structural space.
Starting from the technical faults of known solutions it is furthermore the object of the invention to provide a seal for a hydraulic release device.
which is optimised with regard to wear
whose service life is improved
whose friction is reduced and
which cuts down on noise.
Furthermore the release device is to be capable of economic production.
In a hydraulically operable release system of the kind in which a seal is secured on a ring piston by a circular, ring-shaped seal carrier, the object of the invention is achieved by providing the seal with an undercut section that fits snugly into the seal carrier without forming any gaps.
An advantageous embodiment, has a seal carrier with different wall thickness. Starting from the greatest wall thickness in the area of the outer axial projection according to the invention the wall thickness is provided with a reduced thickness in other sections of the seal carrier, more particularly in partial areas of the internal profiled section or opening directed towards the seal. The proposed difference in wall thicknesses takes into account the manufacturing process, i.e. the deep-drawing process which is preferably used allows the seal carrier to be designed with the optimum profile determined for example
Koschmieder Hartmut
Parzefall Walter
Peschke Harald
Winkelmann Ludwig
Darby & Darby
Lorence Richard M.
LuK Lamellen und Kupplungsbau GmbH
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