CONCENTRICALLY MOUNTED HYDRAULIC CLUTCH SLAVE CYLINDER

Abstract: A concentric slave cylinder (11) for use in a clutch actuator in which the housing (30) of the slave cylinder is a two-part construction with inner and outer cylindrical members (32, 34) forming an annular chamber (60) therebetween for a sliding piston (74) with one of the cylindrical members (32) comprising an injection moulded polymer member. In one embodiment, both the inner and outer cylindrical members are formed as injection moulded polymer members; in a second embodiment, the outer cylindrical member is formed as an injection moulded polymer member and the inner cylindrical member is formed as a cold formed steel member; and in a third embodiment, the inner cylindrical member is formed as an injection moulded polymer member and the outer member is formed as a cold formed steel member. The use of injection moulded members reduces the cost of the housing assembly and the use of a two-part construction allows the provision of an annular chamber with a small radial dimension (W).

Description: CONCENTRICALLY MOUNTED HYDRAULIC CLUTCH SLAVE CYLINDER This invention relates to so-called "concentric" hydraulic clutch actuator assemblies for motor vehicle clutches It is well known to use an hydraulic actuator system consisting of a master cylinder and a slave cylinder to operate the clutch of a motor vehicle The piston of the master cylinder is mechanically connected to the clutch pedal to move fluid through a conduit into the slave cylinder where a second piston is displaced to operate the clutch When the pedal is released, bias springs in the clutch and/or actuator system force the second piston back to its original position returning fluid from the slave cylinder to the master cylinder So-called concentric slave cylinders are designed in such a way that they may be concentrically mounted relative to the transmission input shaft within a bell-shaped clutch housing placed between the engine and the transmission This is generally illustrated for example in assignee's US Patent Nos 4585106, 4585107, 4585108, 4585109, 4609087, 4264290, 4660694, 4684003, 4687084 and 4708228 The prior art concentric slave cylinders have been either a one-piece construction or a two- piece construction The housing in the concentric slave cylinder consists generally of two concentric inner and outer members having a common base flange in the case of a one-piece construction, or commonly joined base flanges in the case of a two-piece construction In either case the inner wall of the outer cylindrical member is spaced from the outer wall of the inner cylindrical member to define an annular fluid chamber which, when the assembly is completed by addition of an annular piston and an annular piston seal, defines the fluid volume for the concentric slave cylinder The prior art one-piece constructions, while relatively inexpensive, suffer from the disadvantage that the size of the fluid chamber must be relatively large. Specifically, the annular spacing of the walls of the inner and outer cylindrical members must be large enough to permit the entry of a tool to finish the inside surfaces to the degree necessary for proper functioning of the piston and piston seal Typically this has meant that a radial spacing of not less than 6mm has been found necessary. The prior art two-piece constructions, which have had inner and outer cylindrical members of metal, have been relatively expensive to manufacture because of the requirements for close tolerances and costly primary and secondary finishing operations with respect to each piece of the two-part metal construction. The principle objective of the present invention is to provide a concentric slave cylinder for motor vehicle clutches in which the fluid volumes in the master and slave cylinders are significantly reduced and the cost of providing the cylinder is reduced Thus according to the present invention there is provided a concentric slave cylinder assembly comprising a housing including an inner cylindrical member having a first fastening portion extending from one end thereof and a smooth outer cylindrical surface and an outer cylindrical member having a second fastening portion extending from one end thereof and a smooth cylindrical inner surface, said inner and outer cylindrical members being joined by way of said fastening portions in concentric relationship to define an annular fluid chamber between the outer surface of the inner cylindrical member and the inner surface of the outer cylindrical member, an annular piston positioned in the fluid chamber to close off the chamber and axially slideable therein, means defining a fluid port extending from the interior of the fluid chamber to the exterior of the housing, wherein one of said cylinder members is formed as an injection moulded polymer member This arrangement retains the advantage of the two-piece construction with respect to a small fluid chamber while eliminating finishing operations with respect to the polymer housing member and thereby reducing the overall cost of the slave cylinder In one embodiment of the invention, both the inner and outer cylindrical members are formed as an injection moulded polymer member In a second embodiment, the inner cylindrical member is formed as a cold formed metallic member and the outer cylindrical member is formed as an injection moulded polymer member In a third embodiment, the outer member is formed as a cold formed metallic member and the inner cylindrical member is formed as an injection moulded polymer member The inner and outer cylindrical members may have integral base flanges which are positioned in confronting relation in the assembled housing and which are suitably secured together to provide the cylinder housing assembly The use of the two-piece construction allows the annular gap or spacing between the two cylindrical portions to be minimised For example, a gap of the order of about 3 or 4 mm may be provided utilising the two-piece construction as compared to a minimum 6mm gap when utilising a one-piece construction Further, the use of at least one injection moulded polymer member significantly reduces the overall cost of the housing assembly since the injection moulded polymer member, as compared to a cast metallic member, eliminates the need for the secondary finishing operations required in the cast metallic member to provide the surface finish required for proper functioning of the piston and seal in the annular chamber The invention also provides a method of forming a concentric slave cylinder of the type including an outer cylindrical member having a flange and a separate inner cylindrical member having a flange, the inner cylindrical member being fitted concentrically within the outer cylinder member to define an annular chamber for sliding receipt of a piston and the flanges being disposed in juxtaposed relation, the method comprising: forming one of said members as an injection moulded polymer member; positioning the moulded polymer member and the other member in closely spaced concentric relation to form a narrow annular piston chamber; and securing the juxtaposed flanges together Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which like reference numerals refer to like parts and wherein' Figure 1 is a schematic view of an hydraulic clutch actuator system employing a concentric slave cylinder according to the invention, Figure 2 is a cross-sectional view taken on line 2-2 of Figure 1, Figure 3 is an end view of the concentric slave cylinder housing, Figure 4 is an exploded view of the concentric slave cylinder housing, Figure 5 is a cross-sectional view of the assembled concentric slave cylinder housing taken on line 5-5 of Figure 3; Figure 6 is a fragmentary view taken within the circle 6 in Figure 5 showing an alternate housing fastening arrangement, Figure 7 is a fragmentary view of a further alternate housing fastening arrangement, Figure 8 is a fragmentary view of a still further alternate housing fastening arrangement, Figures 9 and 10 are cross-sectional views of a further alternate housing construction; and Figures 11 and 12 are end views of the housing construction of Figures 9 and 10 Referring to Figures 1 and 2 an hydraulic clutch actuator system 10 is illustrated The actuator system 10 includes a concentric slave cylinder 1 1 positioned within a clutch bell casing 14 The bell casing 14 is positioned between and attaches to the forward end of a transmission casing 12 and a rearward end of a motor vehicle engine, not shown. The concentric slave cylinder 1 1 surrounds a transmission input shaft 16 which extends axially from the motor vehicle engine, not shown, through the slave cylinder 1 1 and into the transmission casing 12 Actuator system 10 further includes a master cylinder 20 connected to the slave cylinder 1 1 by a conduit 22 placing the master cylinder 20 in fluid flow communication with the slave cylinder 1 1 Master cylinder 20 is connected to a clutch pedal 24 in the passenger compartment of the motor vehicle by a piston rod 26. Referring to Figures 2, 3, 4 and 5, slave cylinder 1 1 includes a housing 30 having an outer cylindrical member 32 and an inner cylindrical member 34 Inner cylindrical member 34 defines an axial bore 40 and includes an integral base flange 36 extending radially outwardly from one end of the inner member 34 Bore 40 is slightly larger than the diameter of input shaft 16 Inner member 34 has a relatively smooth outer cylindrical surface 42, a portion of which defines an inner piston surface The rearward face of base flange 36 of inner member 34 mounts to the forward surface 13 of transmission casing 12 within bell casing 14 Outer cylindrical member 32 defines an axial bore 57 and includes an integral base flange 50extending radially outwardly from an end of outer member 32. Bore 57 is greater in diameter than the outer surface 42 of inner member 34 Outer member 32 further defines a fluid port 52 (Figure 5) having a channel 54 in fluid communication with bore 57 Base flange 50 further includes a plurality of mounting apertures 55 Axial bore 57 defines a smooth inner cylindrical surface 58. Outer cylindrical surface 42 and inner cylindrical surface 58 and the forward surface of base flange 36 define an annular fluid chamber 60. The radial dimension or width W (see Figure 5) of the annular fluid chamber 60 between the outer cylindrical surface 42 and inner cylindrical surface 58 is no more than about 4 mm and is preferably about 3 mm. Annular fluid chamber 60 significantly reduces the overall size or diameter of the outer member 32 and thus the concentric slave cylinder 11 as a whole The reduction in size or volume of annular piston chamber 60 provides additional benefits of requiring less hydraulic fluid to fill chamber 60 and thereby allows a reduction in size of master cylinder 20 which further reduces the space requirements and weight of the entire clutch hydraulic actuator system 10 Inner cylindrical member 34 is fabricated from a steel sheet which is cold formed in a stamping and/or deep drawing operation to form internal base flange 36 and inner cylinder member 34 without a substantial reduction in wall section or strength The steel material provides the advantages of thin wall sections on the order of about 1 to 1 5 mm thick, with 1 mm being preferred, over that of prior materials used such as cast iron and aluminium as well as injection moulded polymers which typically were 3 mm or greater in thickness Although approximately 1 mm thick wall sections are preferred, it is contemplated that thicker or thinner steel may be used to achieve the strength, size and weight characteristics for a particular application as described herein. The steel material further reduces the size or outside diameter of inner member 34 thereby allowing a reduction in size of the outer cylindrical member 32 end of the housing 30 as a whole The reduced wall section thickness also reduces the axial length of the housing 30 through reduced thickness in the base flange 36 The steel material further reduces weight due to the thin wall section. Although steel is preferred material, it is contemplated that other lightweight, high strength ferrous and non-ferrous allow materials may be used to achieve the desired size and weight reducing characteristics previously described Outer cylinder member 32 is formed in an injection moulding operation from a polymeric material, for example, an injection moulded glass reinforced Nylon Other suitable polymer materials, for example, include polyamide-imide, polyetheretherketone, and polyphenylene sulphide Preferably, the nominal thickness of the outer member 32 is approximately 3 mm although it is contemplated that thicker or thinner areas may be used to achieve the size, strength and weight characteristics described herein The preferred polymeric material has advantages of forming relatively thin wall sections and complex geometries, reducing size, weight, and secondary finishing operations while maintaining strength over other conventional materials such as aluminium or cast iron Referring to Figures 2 and 5, outer cylindrical member 32 is preferably assembled to inner cylindrical member 34 by inserting inner member 34 through bore 57 of outer member 32 such that base flange 50 rests upon base flange 36 of inner member 34 compressing an annular O- ring seal 64 positioned in an annular groove 62 in annular base 50 Upon assembly and joinmg through the base flanges, inner member 34, outer member 32, bore 40, and bore 57 are in concentπc relationship to one another Inner member 34 may be permanently or removably attached to outer member 32 by many known conventional methods Preferably, as shown in Figure 2, base flange 36 of inner member 34 includes two or more apertures allowing conventional fasteners such as bolts or screws 66 to pass through and engage threaded bores 44 m the base flange 50 to further compress O-πng seal 64 and place outer member 32 in tight surface and sealing engagement with inner member 34 In the alternate fastening arrangement shown m Figure 6, base flange 50 of outer member 32 includes two or more raised prongs or projections 48 extending rearwardly to coincide with aligned apertures 45 in base flange 36 Projection 48 may be cold-headed or deformed, as shown in dash lines 48', to secure outer member 32 to inner member 34 In the further alternative fastening arrangement shown n Figure 7, base flange 36 includes deformable tabs 46 extending forwardly and passing through apertures 47 in base flange 50 Tabs 46 are deformed, as shown in dash lines 46', to secure outer member 32 to inner member 34 As will be understood, there are many other methods available to secure the inner and outer members such as mechanical staking or the use of adhesives or other welding and bonding techniques suitable for the member mateπals uses Inner 34 and outer 32 members are attached to the transmission casing 12 by common fasteners through mounting apertures 55 confining inner member 34 therebetween Refemng again to Figure 2, concentπc slave cylinder 1 1 further includes an annular piston 74 in fluid chamber 60 and an annular piston seal 76 m sliding sealing engagement in the fluid chamber 60 with outer surface 58 and inner surface 42 Piston seal 76 and O-πng seal 64 provide a fluid-tight seal preventing hydraulic fluid from leaving piston chamber 60 to the exteπor of slave cylinder 11 other than through fluid port 54 Concentπc slave cylinder 11 further includes a release beaπng 78 attached to piston 74 and a preload compressions coil spπng 100 which biases piston 74 to the extreme forward extent of fluid chamber 60 as shown in Figure 2 Upon installation m the vehicle, clutch spπng fingers 18 counteract and compress spπng 100 forcing piston 74 and seal rearward (I e to the πght as viewed in Figure 2) into the fluid chamber 60 Upon disengaging the clutch through pressure on pedal 24, fluid pressure forces piston 74 forward (1 e to the left as viewed in Figure 2) to the extreme end of fluid chamber 60 further compressing diaphragm spring fingers 18 which separate the clutch pressure plate from the friction plate to disengage the transfer of energy from the motor vehicle engine, not shown, through the transmission input shaft 16 to the transmission 12 as shown in Figure 1 In the alternate housing construction seen in Figure 8, both outer member 50 and inner member 34' are formed in an injection moulding operation from a polymer material, for example, glass reinforced Nylon Other suitable polymer mateπals, for example, include polyamide-imide, polyetheretherketone, and polyphenylene sulphide The use of a polymeric mateπal for the inner cylmdπcal member is advantageous in its ability to form complex geometries and relatively thin wall sections while reducing weight and secondary manufactuπng operations over other conventional mateπals such as cast iron an aluminium In the alternate concentπc slave cylinder housing construction seen in Figures 9-12, the inner cylindrical member 82 is formed as an injection moulded polymer member and the outer cylindπcal member 84 is formed as a cold formed steel member Inner cylindπcal member 82 includes a cylindπcal portion 82a, a flange portion 82b, a hub portion 82c at the intersection of cylindrical portion 82a and flange portion 82b, and an inlet portion 82d Inlet portion 82d defines an inlet port 82e which communicates with an annular chamber 82f formed in hub portion 82c Outer steel member 84 includes a cylindπcal portion 84a, a conical portion 84b, and a plurality of prongs or tabs 84c (Figure 10) provided at circumferentially spaced locations around the free annular edge of conical portion 84b In the assembled relation of inner member 82 and outer member 84, the cylindπcal portion 84a of the outer member is fitted over hub portion 82c of the inner member to define an annular chamber 86 between the cylindπcal portions of the inner and outer members, conical portion 84b flares outwardly for engagement with a confronting face of the base portion 82b of the inner member, and tab portions 84c extend through circumferentially spaced apertures 82g in the flange portion 82b Tabs 84c are bent over as seen in dash lines 84c' in Figure 10 to fixedlv secure the outer member to the inner member and an O-πng 88 is positioned in an annular groove in the hub portion 82c of the inner member to provide a seal between the inner and outer members In each of the disclosed embodiments, it will be that the use of a two-part construction allows minimisation of the size of the annular chamber between the inner and outer members with consequent reductions m component and system size, and the use of an injection moulded polymer member as one or both of the components of the two-part housing reduces secondary finishing operations and thereby reduces the overall cost of the slave cylinder While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover vaπous modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law

Claims: CLAIMS 1 A concentric slave cylinder assembly comprising a housing including an inner cylindrical member having a first fastening portion extending from one end thereof and a smooth outer cylindrical surface and an outer cylindrical member having a second fastening portion extending from one end thereof and a smooth cylindrical inner surface, said inner and outer cylindrical members being joined by way of said fastening portions in concentric relationship to define an annular fluid chamber between the outer surface of the inner cylindrical member and the inner surface of the outer cylindrical member, an annular piston positioned in the fluid chamber to close off the chamber and axially slideable therein, means defining a fluid port extending from the interior of the fluid chamber to the exterior of the housing, wherein one of said cylinder members is formed as an injection moulded polymer member 2 A slave cylinder assembly according to claim 1 wherein the other of said cylinder members is formed as a cold formed metallic member 3 A slave cylinder assembly according to claim 1 wherein the other of said cylinder members is formed as an injection moulded polymer member 4 A slave cylinder assembly according to claim 3 wherein the moulded polymer member is a moulded reinforced member 5 A slave cylinder assembly according to claim 2 wherein the other of said cylinder members is formed as a steel member 6 A slave cylinder assembly according to any one of claims 1 to 5 wherein said one of the cylinder members is the outer member 7 A slave cylinder assembly according to any one of claims 1 to 5 wherein said one of the cylinder members is the inner member 8. A slave cylinder assembly according to any one of claims 1 to 7 wherein the fastening portions of the cylinder members comprise generally radially outwardly extending integral flanges on each member which are secured together in a generally parallel relationship. 9. A slave cylinder according to claim 8 wherein the integral flanges are joined by two or more deformable projections on the flange of one of the members extending through two or more apertures in the flange of the other member 10 A slave cylinder assembly according to any one of claims 1 to 7 wherein one end of the outer cylinder member has a conical fastening portion which extends over a hub portion of the inner member, deformable fastening projections on said end of the outer cylinder member extending through corresponding apertures in a generally radially outwardly extending flange-like fastening portion of the inner cylinder member 1 1 A slave cylinder assembly according to any one of claims 8 to 10 wherein sealing means is compressed between the fastening portions 12 A slave cylinder assembly according to any one of claims 1 to 1 1 wherein the radial dimension of the annular fluid chamber is not more than 4mm. 13 A slave cylinder assembly comprising a housing including an inner cylindrical member having a first fastening portion extending from one end thereof and a smooth outer cylindrical surface and an outer cylindrical member having a second fastening portion extending from one end thereof and a smooth cylindrical inner surface, said inner and outer cylindrical members being joined by way of said fastening portions in concentric relationship to define an annular fluid chamber between the outer surface of the inner cylindrical member and the inner surface of the outer cylindrical member, an annular piston positioned in the fluid chamber to close off the chamber and axially slideable therein, means defining a fluid port extending from the interior of the fluid chamber to the exterior of the housing, wherein the radial dimension of the annular fluid chamber is not more than 4mm. A method of forming a concentric slave cylinder of the type including an outer cylindrical member having a flange and a separate inner cylindrical member having a flange, the inner cylindrical member being fitted concentrically within the outer cylinder member to define an annular chamber for sliding receipt of a piston and the flanges being disposed in juxtaposed relation, the method comprising forming one of said members as an injection moulded polymer member; positioning the moulded polymer member and the other member in closely spaced concentric relation to form a narrow annular piston chamber, and securing the juxtaposed flanges together A method according to claim 14 wherein the other member is formed as a cold formed metallic member A method according to claim 14 wherein the other member is formed as an injection moulded polymer member A method according to claim 15 wherein the other member is formed as a steel member A method according to any one of claims 14 to 17 wherein the flanges are joined by inserting two or more deformable projections on the flange of one of the members through corresponding apertures in the flange of the other member and deforming the projections to secure the flanges together

Inventors: CORRIA LARRY RAY JUNIOR, DANGEL TIM M, LEIGH-MONSTEVENS KEITH VERNON, STEVENS BRYAN M, CORRIA, LARRY, RAY, JUNIOR, DANGEL, TIM, M., LEIGH-MONSTEVENS, KEITH, VERNON, STEVENS, BRYAN, M.
Applicants: AUTOMOTIVE PROD USA, AUTOMOTIVE PRODUCTS (USA) INC.
Application year: 2001
Main classification: F16D25
IPC codes: F16D25