Patent Application
20090282972
The application claims priority under 35 U.S.C. ยง119(e) of German Patent Application No. DE 102008024163.6, filed on May 19, 2008, which is hereby incorporated by reference in its entirety.
Composite pistons for a motor vehicle transmission are known from DE 199 15 022 B4 and DE 202 09 125 U1. The pressure portion occurring at the annular gap is transmitted to the piston via the annular seals as an axial force. This axial force needs to be supported by the piston in a suitable manner, where the mechanical load capacity of an elastomer seal might be exceeded at common pressures unless the constructional configuration is very accurate. An eccentric displacement can already occur when mounting such a piston, as the reset force of the sealing lips in particular in the pre-loaded state is not always sufficient for a complete centering of the piston.
In rotating applications the reset force of the sealing lips is not sufficient for compensating the occurring centrifugal forces so that the piston abuts on the sliding surface. The eccentricity causes the sealing gap on one side to possibly increase to the twice, resulting in a severe reduction of the mechanical load capacity of the sealing lip. The sealing lip may possibly break off in the event of overload so that the functioning of the piston is no longer guaranteed. Therefore, a perfect centering of the piston is a precondition for its functioning also at high engine speeds as they often occur for example in vehicle transmissions.
However, also in non-rotating applications it may possibly not be permissible that the weight of the piston is transmitted via the sealing lips if for example a non-permissible eccentricity would occur due to a heavy weight of the piston.
U.S. Pat. No. 2,386,668 discloses a piston of a pressure differential operated, double acting motor.
US 2008 0289489 A1 discloses a composite piston unit comprising a shift rod and two control pistons securely connected with respectively one end of the shift rod.
DE 37 10 403 A1 discloses a piston unit designed to be pressurized from both sides by a pneumatic medium, and comprises a clamping flange and a sealing element attached to the clamping flange.
Embodiments of the invention provide a functionally reliable composite piston, in which an overload of the sealing lip as a result of an exceedingly large eccentricity of the piston is avoided.
Embodiments of the invention incorporate a support body; and at least one annular seal, wherein each of the at least one annular seal comprises: a sealing lip interacting in a sealing manner with a component forming a cylindrical sliding surface, wherein the composite piston can be displaced translationally relative to the component forming the cylindrical sliding surface; and an annular bead displaced axially relative to the sealing lip and arranged to have a distance d1 from the sliding surface in a non-loaded state, where d1 is greater than or equal to zero. Under radial load the annular bead comes in contact with the sliding surface and the sealing lip is mechanically relieved as a result of introducing forces into the sliding surface via the annular bead. Embodiments of the invention realizes a functional separation by completely uncoupling the sealing element from the guiding element: the annular bead serves for absorbing the radial forces generated by the piston and for introducing the same into the sliding surface so that the flexibility of the sealing lip is not affected adversely and the sealing function is therefore optimally guaranteed. Because of the annular bead according to the invention an optimal centering of the piston is therefore already realized during the assembly.
In pistons inserted into rotating components the annular bead helps to reduce an eccentricity due to the imbalance of the piston.
Preferably the annular bead is radially supported on the support body over its total axial length such that the annular bead can essentially completely absorb and transmit the radial forces exerted by the piston. Through this feature the annular bead is distinguishable from an additional sealing lip or protecting lip.
Advantageously, at least one axial gap, and preferably a plurality of axial gaps, in particular evenly distributed over its circumference, is provided in the annular bead. These allow oil to reach the seal also from the low pressure side in order to prevent the bead from obstructing the lubrication of the sealing lip. The gap further reduces the risk of the piston being clamped, since additional volume is provided to which the elastomer can pass for example upon excessive expansion.
The annular bead preferably is dimensioned in such a way that under pressure load a radial deformation occurs. Thereby, the annular bead comes in contact with the sliding surface earlier and the possible eccentricity of the piston is further reduced.
In the following, the invention is described in more detail on the basis of preferred embodiments with reference to the attached figures, wherein:
Embodiments of the invention relate to a composite piston for a motor vehicle transmission comprising a support body and at least one annular seal connected thereto with an elastomer sealing lip. Such pneumatically or hydraulically actuated composite pistons are for example used in automatic vehicle transmissions, in particular for shifting multi-disc clutches or brake bands, as well as in hydraulically or pneumatically actuated servo mechanisms of motor vehicles.
The composite piston 10 shown in
The uniform elastomer layer 15 is vulcanized to the support body 14 on the outer surface of the U-profile. The elastomer layer 15 forms an outer dynamic annular sealing lip 16 at the outside of an outer bracket 30 of the U-form support body 14 for dynamically sealing the annular gap between the cylinder 11 and the outer diameter of the composite piston 10. The elastomer layer 15 furthermore forms an inner dynamic annular sealing lip 17 at the inside of an inner bracket 31 of the U-form support body 14 for dynamically sealing the annular gap between the shaft 12 and the inner diameter of the composite piston 10. As a result of this sealing, loading the composite piston 10 with a hydraulic or pneumatic pressure on the pressure side 18 causes a translational displacement of the composite piston 10 towards the low pressure side 19. The piston 10 is preferably unidirectional, i.e. designed to be pressurized by a pressure medium on one side 18, only, and may therefore be distinguished from bidirectional pistons designed to be pressurized by a pressure medium on both sides.
The elastomer layer 14 forms an annular bead 20 on the low pressure side of the sealing lip 16 at a distance l1. The annular bead 20 comprises a cylindrical contact surface 26 for interacting with the sliding surface 21 having a small distance d1 from the cylindrical inner surface 21 of the component 11. As can be seen from
The distance l1 preferably is in the range of 1 mm to 10 mm, more preferably in the range of 1 mm to 4 mm and for example is 2.5 mm. The distance d1 preferably is less than 0.4 mm, more preferably less than 0.3 mm, for example approximately 0.2 mm. The axial length L1 of the annular bead 20 preferably is in the range of 1 mm to 10 mm, more preferably in the range of 1 mm to 3 mm. The radial height h1 of the annular bead 20 above the elastomer layer preferably is in the range of 0.1 mm to 1 mm, more preferably in the range of 0.1 mm to 0.4 mm and for example is approximately 0.2 mm. The depth t1 of the depression 21 formed between the sealing lip 16 and the annular bead 20 preferably is at least 0.1 mm.
The elastomer layer forms a similar annular bead 22 on the low pressure side of the sealing lip 17 at a distance l2, which annular bead has a small distance d2 from the cylindrical outer surface or rather sliding surface 23 of the component 11. The statements relating to the outer annular bead 20, in particular to the dimensions d1, D1, l1, L1, h1 and t1, also apply to the inner annular bead 22 and the corresponding dimensions d2, D2, l2, L2, h2 and t2.
Axial gaps 24 and 25 respectively are provided in the annular beads 20, 22, which gaps preferably are evenly distributed over the circumference of the composite piston 10, as can be seen from
The unit of composite piston 10 and cylindrical housing 11 and shaft 12 respectively can have an overall rotary configuration. In this kind of application the annular beads 20, 22 help to reduce an eccentricity effected due to the imbalance of the piston 10. In another application the unit of composite piston 10 and cylindrical housing 11 and shaft 12 respectively can have a non-rotary configuration.
In the preferred embodiment shown in
The annular beads 20, 22 can be located on the high pressure side of the sealing lip 16 and 17, respectively.
All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 024 163.6 | May 2008 | DE | national |
