FLUID-OPERATED PISTON

Abstract: A fluid-operated friction torque-transmitting device, such as a clutch or brake, has a piston (38). The piston has a body member (40) that is made of a rigid material, such as metal or plastics material, and is encased in an elastomeric cover (42). The elastomeric cover is a moulded structure, and is bonded to the rigid body member of the piston. The elastomeric cover has integrally formed therewith, during moulding, a pair of annular lip seals (44,46), a valve structure (54) and a spring portion (48). A reaction plate or reaction ring (50) is moulded or bonded to the spring portion of the elastomeric cover.

Description: This invention relates to fluid-operated friction torque-transmitting devices having a piston, as specified in the preamble of claim l. It is known for piston assemblies usable in fluid-operated friction torque-transmitting devices to include an elastomeric cover (cover portion). However, such assemblies do not include integral lip seals, or reaction plate and spring members. The present invention is concerned with providing an improved fluid-operated friction torque-transmitting device which has a piston with a rigid body and an elastomeric cover (covering) moulded thereto, and in which the elastomeric cover includes integrally therewith a pair of annular lip seals, a valve member and a spring. To this end a friction torque-transmitting device in accordance with the present invention is characterised by the features specified in the characterising portion of claim l. It is thereby within the scope of the present invention for an improved fluid-operated friction torque-transmitting device to have a piston with a rigid body and an elastomeric cover moulded thereto, with the elastomeric cover including integrally therewith a pair of annular lip seals, a valve member and an annular spring, the piston further including a reaction ring integrally moulded to the spring. A friction torque-transmitting device in accordance with the present invention may include an integrally moulded valve arrangement that can provide an air bleed in a brake or an air bleed and a centrifugal control in a clutch. In the drawing: Figure l is a fragmentary elevational sectional view, with parts in elevation, of a preferred embodiment of a friction torque-transmitting device in accordance with the present invention, including a piston; Figure 2 is an enlarged fragmentary sectional view of a portion of the piston shown in Figure l; and Figure 3 is a fragmentary view on the line 3--3 of Figure 2, in the direction of the arrows. With reference now to the drawing, in which like characters represent like or corresponding parts throughout the several views, there is shown in Figure l a section of a transmission including a housing l0 having a splined portion l2 formed therein. The housing l0 is closed at the left-hand end by an end cover which forms a pump housing l4 and has formed therein an annular cavity l6 forming a cylinder. The cavity l6 has in communication therewith a hydraulic passage l8. The cover l4 has secured thereto a support sleeve 20 on which is rotatably mounted a clutch housing 22. The clutch housing 22 has operatively connected thereto a one-way device 24 that includes an inner race 26 and an outer race 28. The outer race 28 has a splined periphery 30. The splined portion l2 has meshing therewith a brake backing plate (back-up plate) 32 and a plurality of friction plates 34. The splined periphery 30 of the outer race 28 has meshing therewith a plurality of friction plates 36 which are spaced alternately with respect to the friction plates 34. The annular cavity l6 has slidably disposed therein a piston assembly 38 that is responsive to fluid pressure admitted to the cavity l6 by way of the passage l8 to effect selective and controllable interengagement and disengagement of the friction plates 34 and 36, such that a torque-transmitting connection is thereby established between the outer race 28 and the transmission housing l0. As is best seen in Figures l and 2, the piston assembly 38 includes an annular piston body 40 that is formed from a rigid material such as metal or hard plastics material. The body 40 is covered by an elastomeric cover portion 42 that is preferably bonded to the piston body 40. The cover portion 42 has integrally moulded therewith a pair of annular lip seals 44 and 46 that are adapted to slidably engage and fluidly seal with the outer and inner annular walls of the cavity l6. The co-operation of these annular lip seals with the cavity l6 prevents fluid leakage from the cavity l6 in the direction towards the friction plates 34 and 36. The elastomeric cover portion 42 also has an annular spring portion 48 moulded integrally therewith and extending annularly about the main portion of the elastomeric cover portion. The spring portion 48 has integrally bonded thereto a reaction ring 50 that is adapted to abut an annular shoulder 52 formed in the transmission housing l0. When the pressure in the cavity l6 is reduced, the spring portion 48 is effective to move the piston assembly 38 leftwardly in the cavity l6 such that disengagement of the friction plates 34 and 36 will occur. A valve 54 is moulded integrally with the elastomeric cover 42. As is seen in Figures 2 and 3, the valve 54 includes a hexagonal or oval-shaped wall 56 surrounding three fluid passages 58 which are effective to communicate fluid between the cavity l6 and the area of the friction plates 34, which is a low-pressure (exhaust) area. The hexagonal wall 56 is designed to collapse inwardly at a predetermined pressure such that the passages 58 will thereby be closed off from the cavity l6, so sealing the cavity l6 from fluid exhaust. Thus, when a sufficiently high apply pressure is admitted to the cavity l6, the valve 54 will close and the piston 38 will be moved rightwardly against the biasing force of the annular spring 48 to enforce interengagement of the friction plates 34 and 36, thereby engaging the torque-transmitting mechanism comprising the piston assembly 38, the friction plates 34 and 36 and the brake backing plate 32. In the above description, the friction torque-transmitting device is a brake. However, the friction torque-transmitting device can alternatively be used as a clutch if the stationary housing l0 which includes the cavity l6 is simply replaced by a rotary housing. The valve 54 is effective to prevent the build-up of centrifugal pressure within the cavity l6 when the device is used as a clutch. The valve is equally effective to provide quick exhaust of the torque-transmitting device (either a clutch or a brake) whenever the engaging fluid pressure is reduced to a level below the pressure required to maintain the valve 54 closed. As is seen in Figure l, the clutch housing 22 slidably supports a piston 60. This is a conventional clutch piston arrangement wherein the clutch piston acts by way of a diaphragm spring member 64 to provide controlled engagement and disengagement of the friction plates incorporated in the clutch assembly. From the description of the piston assembly 38, it will be evident that the construction of the piston 60 can be changed whilst nevertheless retaining the unique advantages of the piston assembly 38. Thus, the reaction ring 50 of the piston 60 can be made to react against a lock ring 62 disposed in the clutch housing 22 such that the diaphragm spring 64 is eliminated and the piston 60 is brought to bear directly on a pressure plate 66. Also, a ball dump centrifugal valve 68 shown in the piston 60 would be eliminated by the use of an integral valve. The above-described piston assembly is thus effective to reduce the number of parts needed in the construction of friction torque-transmitting devices, so providing for reduced inventory costs and assembly costs, by reason of the unique integration of the annular lip seals, valve assembly, return spring and apply ring into a single assembly. This form of construction reduces the number of parts which must be handled either during assembly of the piston or during assembly of the friction torque-transmitting device. Thus useful cost reductions are available by the use of a fluid-operated torque-transmitting device in accordance with the present invention in current mass-produced transmissions.

Claims: 1. A fluid-operated friction torque-transmitting device in which a piston (38) is slidably disposed in a cylinder (l6) and is adapted to be selectively pressurised therein for controlling the engagement of a plurality of friction plates (34), characterised in that the piston (38) comprises a rigid piston body (40) having a generally U-shaped cross-section, an elastomeric cover portion (42) bonded on to the piston body (40) and incorporating therein a pair of lip seal portions (44,46) effective to engage the cylinder (l6) and co-operate therewith to form a fluid-tight joint, valve means (54) formed in the cover portion (42) for permitting air bleed from the cylinder (l6), a reaction ring (50) bonded to the elastomeric cover portion (42), and a spring portion (48) integral with the elastomeric cover portion (42) and operatively disposed between the piston body (40) and the reaction ring (50). 2. A fluid-operated friction torque-transmitting device according to claim l, characterised in that the valve means (54) also prevents engagement due to centrifugal force, the reaction ring (50) constitutes an apply ring, and the spring portion (48) is bonded integrally with the elastomeric cover portion (42).

Inventors: LEDERMAN, FREDERICK EDWARD
Applicants: GENERAL MOTORS CORPORATION
Application year: 1986
Main classification: F16D25
IPC codes: F16D25, F16D65, F16D55