HYDRAULIC ACTUATORS

Abstract: An hydraulic actuator comprises a piston (13) slidable within a bore (14) to define a working chamber (12) on one side of the piston (13) which is pressurised via a chamber inlet (19) to axially displace the piston (13) along the bore (14), the inlet (19) is connected with an external hydraulic connection (19) on a housing (11) of the actuator via passage means (20) provided between a tubular sleeve (15) which provides the bore (14) and the actuator housing (11) which surrounds the sleeve (15).

Description: HYDRAULIC ACTUATORS This invention relates to hydraulic actuators and in particular, though not exclusively, to actuators in the form of hydraulic slave cylinders for operation by a master cylinder associated with a clutch operating pedal to operate an associated vehicle clutch. Such actuators have traditionally had sufficient stroke to accommodate the release travel, the wear travel and the installation tolerances of the associated clutch assembly. There is an increasing requirement to make such actuators more compact and to provide flexibility as to the position of the inlet connection on the actuator. It is an object of the present invention to provide an improved actuator suitable for operating a clutch which meets the above requirements. Thus according to the present invention there is provided an hydraulic actuator comprising a piston slidable within a bore to define a working chamber on one side of the piston which is pressurised via a chamber inlet to axially displace the piston along the bore, the actuator being characterised in that the chamber inlet is connected with an external hydraulic connection on a housing of the actuator via passage means provided between a tubular sleeve which provides the bore and the actuator housing which surrounds the sleeve. The above connection enables the external hydraulic connection to be positioned at a location anywhere along the axial length of the actuator housing and for the passage means to axially extend between this external connection and the chamber inlet between the sleeve and surrounding housing. In a preferred construction the sleeve and surrounding housing are both made from plastics material. In such a construction the . sleeve may be ultrasonically welded to the housing to avoid the necessity for any separate hydraulic sealing between the sleeve and housing. In alternative arrangements the sleeve may be metallic and the housing may be of plastics material with the sleeve and housing mechanically secured together by, for example, forming one end of the sleeve over a flange on the housing. The passage means may be formed by stepping the internal diameter of the housing and/or the external diameter of the sleeve between the external connection and chamber inlet. Alternatively one or more axially extending grooves could be provided in the internal diameter of the housing and/or the external diameter of the sleeve between the external connection and the chamber inlet. The end of the sleeve at which the passage means enter the working chamber is preferably provided with one or more circumferentially spaced notches through which hydraulic fluid enters or leaves the working chamber. The invention is particularly applicable to a concentric slave type of actuator for the operation of a vehicle clutch in which an annular piston is axially displaceable between concentric inner and outer cylinder walls one of which is defined by the sleeve and the other by the housing. In the preferred arrangement it is the outer cylinder wall which is defined by the sleeve. A hydraulic actuator in accordance with the present invention will now be described, by way example only, with reference to the accompanying drawings in which; Figure 1 is a longitudinal section through a clutch operating slave cylinder in accordance with the present invention showing the fully extended condition of the actuator, and Figure 2 is a longitudinal section through the actuator of Figure 1 showing the fully retracted condition. Referring to Figures 1 and 2 an actuator in the form of a concentric slave cylinder 10 comprises a plastics housing 1 1 within which a working chamber 12 is defined by a slidable plastics piston 13. Piston 13 slides between an outer cylinder wall defined by the inner surface 14 of a plastics sleeve 15 and an inner cylindrical surface 16 which is formed integrally with housing 11. Working chamber 12 is sealed by a rubber seal 17 which is carried on the end of piston 13. Sleeve 15 is ultrasonically welded into housing 11 by a continuous annular weld 18 thus obviating the need to provide any further seal between housing 11 and sleeve 15. Fluid enters and leaves working chamber 12 via an external connection 19 which is moulded into housing 11. Fluid flows between the working chamber 12 and the inner end 19a of connection 19 via an annular passage means 20 provided by a reduced external diameter portion 15a of sleeve 15. The inner end of sleeve 15 is notched at a number of locations 21 to ensure unrestricted communication between the passage 20 and chamber 12. Housing 11 is provided with a flange portion 22 via which the actuator is secured to a bulkhead or other support in the engine compartment of the vehicle. In the arrangement shown the flange portion 22 is clipped to the bulkhead by a metal plate 23 which is bolted or otherwise secured to the bulkhead and which has quick attach tabs 24 which snap over flange 22 to secure the cylinder to the bulkhead. Piston 13 operates on a clutch release bearing 25 which in turn bears against the radially inner ends of diaphragm spring levers 26 in the known manner. A spring 27 acts between housing 11 and release bearing 25 to ensure a pre-load on the clutch release fingers 26. Figure 1 shows the actuator in its fully extended condition which is the condition occupied when the actuator is actuated to release the associated clutch. As the driven plate of the associated clutch wears the position occupied by piston 13 in the clutch fully disengaged position will gradually move to the left as viewed in Figure 1 until the clutch becomes fully worn and must be replaced. Figure 2 shows the actuator in the fully retracted condition when the clutch is fully worn and begins to slip. As will be appreciated between the fully extended condition showed in Figure 1 and the fully retracted position showed in Figure 2 the clutch seals 17 do not have to pass over any inlet into the working chamber on each movement of the piston and thus seal wear is greatly reduced. Also because the inlet passage 20 is provided between sleeve 15 and housing 11 it is possible to position the external connected 19 anywhere along the axial length Y of the housing. This is a particularly useful feature in modern crowded engine compartments where it may be necessary to position the connection 19 in a whole series of different locations to meet the space available in a variety of different engine bay arrangements. Although in the construction described above both the housing 11, the sleeve 15 and the piston 13 are formed from plastics material (so that the sleeve 15 can be ultrasonically welded to the housing 11 thereby obviating the need for sealing between the sleeve and housing) it will be appreciated that sleeve 15 could be formed from metal and mechanically secured or bonded to housing 11. Also piston 13 could be made from metal if so desired. Passage 20 between housing 11 and sleeve 15 could be provided by forming shoulder portions both on sleeve 15 and/or on the inside diameter of the bore of housing 11 which receives sleeve 15. Alternatively, instead of producing the passage way 20 by shouldering the cooperating bores, axially extending grooves could be provided either in the internal diameter of the bore of housing 11 and/or in the external diameters of sleeve 15 which extend between the inner end of the sleeve and the inner end 19a of external connection 19.

Claims: CLAIMS 1) An hydraulic actuator comprising a piston slidable within a bore to define a working chamber on one side of the piston which is pressurised via a chamber inlet to axially displace the piston along the bore, the actuator being characterised in that the chamber inlet is connected with an external hydraulic connection on a housing of the actuator via passage means provided between a tubular sleeve which provides the bore and the actuator housing which surrounds the sleeve. 2) An actuator according to claim 1 in which the passage means is formed by stepping the internal diameter of the housing and/or the external diameter of the sleeve between the external connection and chamber inlet. 3) An actuator according to claim 1 in which the passage means is formed by one or more axially extending grooves provided in the internal diameter of the housing and/or the external diameter of the sleeve between the external connection and the chamber inlet. 4) An actuator according to any one of claims 1 to 3 in which the end of the sleeve at which the passage means enters the working chamber is provided with one or more circumferentially spaced notches through which hydraulic fluid enters or leaves the working chamber. 5) An actuator according to any one of claims 1 to 4 of the concentric type in which an annular piston is axially displaceable between concentric inner and outer cylinder walls one of which is defined by the sleeve and other by the housing. 6) An actuator according to claim 5 in which it is the outer cylinder wall which is defined by the sleeve. 7) An actuator according to any one of claims 1 to 6 in which the sleeve and surrounding housing are both made from plastic material. 8) An actuator according to claim 7 in which the sleeve is ultrasonically welded to the housing. 9) An actuator according to any one of claims 1 to 6 in which the sleeve is metallic and the housing is made from plastics material. 10) An actuator according to any one of claims 1 to 9 in which the housing is adopted to be secured to a bulkhead or other support via a quick-attach fastening. 11) An hydraulic actuator constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Inventors: COME OLIVIER, COME, OLIVIER
Applicants: AUTOMOTIVE PROD FRANCE, COME OLIVIER, AUTOMOTIVE PRODUCTS FRANCE S.A., COME, OLIVIER
Application year: 1997
Main classification: F16D25
IPC codes: F16D25