WO1989003954A2

WO1989003954A2 - A seal

Info

Publication number: WO1989003954A2
Application number: PCT/GB1988/000926
Authority: WO
Inventors: Keith Vernon Leigh-Monstevens; Leslie Paul Branum; David Lee Wrobleski
Original assignee: Automotive Products Plc
Priority date: 1987-10-29
Filing date: 1988-10-21
Publication date: 1989-05-05
Also published as: WO1989003954A3; GB2229790B; GB2229790A; GB9003287D0; GB8813677D0

Abstract

The seal (50) includes an axially forward portion (50a) defining radially inner and radially outer deflectable lip seals (50c, 50d) and an axially rearward portion (50b) defining radially outer and inner arcuate heel seals (50e, 50f). When positioned in an annular groove (43) in a piston (30) and with the piston slidably received in the bore (27) of a cylinder (28), the annular seal (50) provides fluid pressure sealing at the deflectable lip seals, provides secondary fluid pressure sealing at the arcuate heel seals, provides air sealing at the arcuate heel seals, and functions at the arcuate heel seals to preclude the entry of contaminants into the sealing interfaces. The seal is especially effective when employed in a hydraulic pressure cylinder of the centre feed type since it allows the usage of a single annular seal positioned in a singular annular groove in the piston.

Description

A SEAL

This invention relates to a seal suitable for use in a hydraulie cy1inder.

In a hydraulic cylinder, it is imperative for the effective operation of the cylinder that adequate sealing be provided between a piston in the cylinder and a bore of the cylinder in which the piston is slidable. This sealing is necessary in order to ensure that fluid under pressure in the bore does not leak past the piston in one direction, that air or other fluid does not leak past the piston in the opposite direction, and that contaminants are kept out of the sealing interface to maintain an effective seal between the piston and the bore of the cylinder.

Prior art attempts to provide the pressure fluid, air, and contaminant sealing functions have typically consisted of one or more annular seals either disposed in an external annular groove in the piston or in an internal annular groove in the cylinder. However, the prior art sealing systems have either not provided an effective seal with respect to the air, pressure fluid, or contaminants, or have provided a seal arrangement utilising complex and expensive seals. A prior seal arrangement is described in US-A- 3,563,442 in which two seals are arranged in respective pistons. Each seal has a radially outer lip seal at one end thereof and a radially outer heel seal at an opposite end thereof. However the seal has an inner seal at its forward end only. That is disadvantageous during movement of the piston such that said opposite end of the seal faces the direction of travel where the sealing effect of the inner lip seal will be reduced.

An object of the present invention is to provide a seal in which that disadvantage is reduced.

According to one aspect of the invention there is provided an annular elastomeric seal having a central axis and comprising, in cross-section an axially forward portion defining radially outer and inner deflectable lip seals, an axially rearward portion defining radially outer and inner arcuate heel seals, and an axially rearward annular surface extending from the radially inner arcuate heel seal.

The provision of the inner arcuate heel seal provides improved sealing of the seal, e.g., against the groove in a piston when the seal is located therein. In that way the seal can provide effective sealing in both the forward and rearward directions of piston movement. The inner lip seal and the inner heel seal provide sealing actions which augment the sealing actions of the outer lip seal and the outer heel seal so that four seals provide, in combination, an extremely effective seal with respect to pressure fluid, air and contaminants.

Thus the seal configuration is able to provide in a single annular seal effective pressure fluid, air, and contaminant sealing when the seal is employed in an annular groove in the piston of a hydraulic cylinder. The forward deflectable lip seal can provide pressure fluid sealing, and the rearward arcuate heel seal can provide secondary pressure fluid sealing, air sealing, and can preclude the entry of contaminants into the sealing interfaces.

To improve sealing contact between the inner lip and heel seals and the groove in which the seal is to be located, the seal may include an inner annular groove opening at the radially inner edge of said seal and defining a radially inner annular surface of said inner lip seal and an axially forward annular surface of said heel seal. The seal may include an outer annular groove opening at the radially outer edge of said seal and defining the radially outer annular surface of said outer lip seal and the axially forward annular surface of said outer heel seal.

The.arrangement of inner and outer grooves provides a convenient and inexpensive means of defining the radially inner and radially outer surfaces.

Preferably said seal includes a forward annular groove in said forward portion opening at the front edge of said seal, the groove being substantially symmetrical in cross-section about an axial line passing through the centre of the seal cross-section, the groove defining the radially inner annular surface of said outer lip seal and the radially outer annular surface of said inner lip seal. The substantially symmetrical form of the groove enables the profile of the seal to be less complex than the seal in US-A-3,563,442.

According to a further feature of the invention, the rear edge of the seal comprises a flat annular surface generally normal to the central axis of the seal but rounded at its circumferentially outer and inner edges to respectively form the axially rearward annular surface of the inner and outer heel seals. This rear edge surface allows the seal to fit snugly within the annular groove of the associated piston while further defining the rearward annular surfaces of the outer and inner heel seals.

In an operative condition, the inner deflectable lip seal may have a forward annular edge substantially normal to a central axis of the seal . As the inner edge will be stationary when the seal is located in a groove in the piston, such an arrangement helps to provide optimum sealing under pressure such as will occur, for example, when the piston moves in the forward direction, to place fluid under pressure. On the other hand, the outer deflectable lip seal may have a forward annular edge inclined to the central axis of the seal. In that way good sealing is obtained whilst providing an inclined surface to assist in the smooth running of the seal against the surface of the cylinder bore during movement of the piston.

To ensure firm engagement of the inner lip seal against the groove in the piston, we prefer the radially inner sealing edge of the inner lip seal to lie radially inwardly of the radially innermost point of the inner arcuate heel seal when the seal is in a relaxed condition. Similarly, the radially outer sealing edge of the outer deflectable lip seal may be radially outwardly of the radially outermost point of the outer arcuate heel seal.

To provide a plurality of circumferential sealing edges the inner and/or outer lip seal may be formed with serration means. Where the serration means is provided on the radially outer lip seal the serration means will preferably be provided in part of its radially outer surface. Where the serration means is provided on the radially inner lip seal the serration means may be provided on part of its radially inner surface.

In ϋS-A-3,563,442, the lip seal extends forwards across a radiused corner formed on the step in the groove and projects into an axially wider section of the groove for engagement with a bore wall. The radiused corner is used to maintain an outward force on the lip seal to provide resilient contact with the bore wall. The lip seal has an inclined inner surface which engages the radiused corner and the axial positioning of the corner relative to the inner surface of the lip seal is therefore critical. The stepped groove is not only of complex form but must be dimensioned accurately in both the radial and axial directions to position the radiused corner correctly. The groove is not, therefore, simple to produce. Another object of the present invention is to provide a seal which does not require a complex groove and with a seal in accordance with the invention the groove in the piston can be of constant axial width. In that way the groove can be formed in a more straightforward manner and its dimensions will be less critical particularly as no step with a radiused corner is necessary.

The inner deflectable lip and heel seals preferably seal against a cylindrical surface forming the base of the groove with the axially rearward annular surface of the seal being preferably engageable with an annular shoulder part of the groove.

As the axial width of the groove is not critical the inner deflectable lip seal may be spaced from adjacent annular shoulder part of the groove when the axially rearward annular surface is in engagement with the first said annular shoulder of the groove.

Preferably, said circumferential seal groove is defined between forward and rearward annular faces, the forward annular face extending radially outwardly from a position adjacent the inner deflectable lip seal to a position axially clear of the outer deflectable lip seal. Such an arrangement leaves the

_» radially outer deflectable lip seal to deflect resiliently without interference from the forward annular face.

The forward annular face may extend radially outwardly for a distance less than the radial extent of the rearward annular face.

The piston may include a main body portion and a forward, reduced diameter nose portion forming an annular shoulder at its rearward end with said main body portion, and an annular adapter member fitted at its rearward end over the forward end of said nose portion and having an annular edge spaced from said annular shoulder to define said annular seal groove therebetween of constant axial width. The use of the adaptor member makes formation of the groove particularly easy and such a construction is useful where, as in the present case, the axial width of the groove is not critical unlike that in US-A-2,563,442.

According to another aspect of the invention there is provided a hydraulic cylinder comprising a body defining an axially extending bore open at its rearward end and closed at its forward end and a piston slidably mounted in the bore, the piston having a circumferential groove thereon preferably of constant axial width in which an annular elastomeric seal is located, the seal being of a kind in accordance with said one aspect of the invention and any of the immediately preceding paragraphs related to said one aspect of the invention.

The body preferably includes a wall (which may be a forward wall) with a reservoir port therein for communication with a source of reservoir fluid, and said body further includes valving means operative to open and close said reservoir port in response to reciprocal movement of said piston in said bore. The valving means may include a valve stem extending axially in said bore forwardly of said piston, a valve member carried on the forward end of said valve stem for coaction with said reservoir port, and means coupling the rearward end of said valve stem to the forward end of said piston.

Preferably, said piston includes a main body portion and a reduced diameter nose portion at its forward end forming an annular shoulder with said main body portion, and an annular adapter member, e.g., as aforesaid, fitted at its rear end over the front end of said nose portion with its rearward annular edge spaced forwardly from said annular shoulder to define said annular seal groove therebetween. The adaptor may define said valve stem coupling means at its forward end. This arrangement allows the adapter to function both as a means partly defining the annular groove of the piston and as a means of coupling the forward end of the valve stem. Preferably the adaptor member is arranged to pull the valve member out of seating engagement with the reservoir port as the piston assembly moves to its fully retracted position but to allow relative movement between the piston and valve stem in response to forward stroking movement of the piston.

The piston may be formed with a forwardly facing axial blind bore which receives the valve stem during forward movement of the piston. This arrangement allows the piston assembly to be employed in conjunction with a centre feed cylinder assembly and, specifically, allows the valve stem of the centre feed piston assembly to move reciprocally in the forward blind axial bore provided in the piston. The blind bore may extend through said nose portion and possibly into the piston main body.

Preferably the piston is devoid of any further annular seal grooves. This arrangement, in which only a single annular seal groove is employed in the piston, allows the remainder of the body of the piston to be designed to maximise piston strength and to maximise the manner in which the associated pushrod is mounted in the rear end of the piston.

The hydraulic cylinder may be a master or slave cylinder which may be used in a clutch or brake system of a vehicle.

Embodiments in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:-

Fig.1 is a schematic view of a hydraulic apparatus including a master cylinder and a slave cylinder constructed in accordance with the invention,

Fig.2 is a fragmentary cross-sectional view of the master cylinder of the hydraulic apparatus of Fig.1,

Fig.3 is a fragmentary perspective view of a valve stem retainer embodied in the master cylinder of Fig.2,

Fig.4 is a cross-sectional view of the valve stem retainer embodied in the master cylinder of Fig.2, Fig.5 is a detailed view of the valving structure at the forward end of the valve stem in the master cylinder of Fig.2,

Fig.6 is a perspective view of the piston assembly employed in the master cylinder of Fig.2,

Fig.7 is a fragmentary view of an annular elastomeric seal in accordance with the invention employed in the master cylinder of Fig.1 as well as in the slave cylinder of Fig.1,

Fig.8 is a fragmentary detail view taken within the circle 8 in Fig.2,

Fig.9 is a cross-sectional view of part of the seal of Fig.7 drawn to a larger scale,

Fig.10 is a fragmentary cross-sectional view of a modified form of in accordance with the invention seal and

Fig.11 is a cross-sectional view of the slave cylinder of Fig.1. The hydraulic apparatus shown schematically in Fig.1 includes a reservoir 10, a centre feed master cylinder assembly 12, a slave cylinder assembly 14, a high pressure conduit 16 interconnecting the outlet of master cylinder 12 and the inlet of slave cylinder 14 and a low pressure supply conduit 18 interconnecting the outlet of reservoir 10 and the inlet of master cylinder 12. The hydraulic apparatus of Fig.1 may be utilized for example in a motor vehicle wherein actuation of a clutch pedal 20 by the vehicle operator strokes the piston rod 22 of the master cylinder 12 to force pressurized fluid outwardly from cylinder 12 through conduit 16 to slave cylinder 14 where the pressurized fluid acts to move output member 24 outwardly to actuate a clutch release lever 26. An hydraulic apparatus of the general type shown in Fig.1 is disclosed, for example, in U.S. A-4,599,860 of Automotive Products, pic, Warwickshire, England.

Master cylinder assembly 12 includes a cylinder 28, a piston 30, a annular insert 32, an adapter member 34, a valving assembly 36, and a valve guide member 38.

Cylinder 28 may be formed of plastic or other suitable rigid material and includes a main body portion 28a, an axially extending bore 27 defining a pressure chamber 28b, an open rear end 28c, a front end wall 28d, a reservoir port 28e defined centrally in front end wall 28d, an inlet fitting 28f communicating with reservoir port 28e and receiving the lower end of supply conduit 18, a discharge fitting 28g communicating with the upper end of working pressure conduit 16 and defining a discharge port 28h, and a flange portion 28i for use in securing the cylinder to a suitable vehicular bulkhead 40. Slave cylinder 14 is similarly secured to a vehicle bulkhead 42 by the use of slave cylinder flange portion 14a.

Piston 30 may also be formed of a suitable plastic material such, for example, as glass reinforced nylon or a lubricated plastic including an internal lubricant such as molybdenum disulfide or a low friction polymer such as polytetrafluoroethylene. Piston 30 includes a reduced diameter nose portion 30a at its front end and a main body portion 30b. Main body portion 30b includes a central spool portion 30c, a front flange or land portion 30d, an enlarged diameter rear portion 30e, and a rear flange or land portion 30f. Nose portion 30a forms an annular shoulder 30g with land portion 30d. A blind bore or socket 30h is provided in the rear face of the piston and includes a main body cylindrical portion 30i extending forwardly from the rear face of the piston and a generally hemispherical front end portion 30j . Socket 30h is centred on the centre line of piston 30 and on the centre line of cylinder 28.

Annular insert 32 is located in a socket 30h in the piston. The annular insert 32 is formed as a metal stamping and includes a cylindrical main body portion 32a, a generally hemispherical front end portion 32b, and an annular flange portion 32c at the rear end of the insert member. A plurality of prongs or tabs 32d are struck inwardly from main body portion 32a at circumferentially spaced locations thereabouts. Prong portions 32d extend inwardly and forwardly toward hemispherical front end portion 32b. Insert 32 is preferably formed of a ferrous material but may also be formed of other metallic materials.

Adapter member 34 is generally annular and is preferably formed of a suitable plastic material, preferably identical to the material utilized for the piston 30. Adapter member 34 includes an annular main body portion 34a defining a bore 34b, a rear flange portion 34c, a hub portion 34d defining a central bore 34e which in turn forms an annular shoulder 34f with bore 34b, and a plurality of resilient finger portions 34g extending forwardly in cantilever fashion from hub portion 34d in circumferentially spaced relation about central bore 34e.

Bore 34b and shoulder 34f together define a socket 34h sized to telescopically receive nose portion 30a of piston 30 e.g., in a frictional push-fit manner or to enable the nose portion and adapter member 34 to be interconnected by ultrasonic welding. Bore 34b has an axial length substantially less than the axial length of piston nose portion 30a so that, with the rear end of adaptor member 34 fitting over the front end of nose portion 30a and the front end of the nose portion abutted against shoulder 34f, the rear annular edge face 34i of retainer 34 coacts with piston nose portion 30a and piston annular shoulder 30g to define an annular, radially outwardly opening seal groove 43 of constant axial width.

Each finger portion 34g includes a head portion 34j at the free forward end of the finger portion. Each head portion 34j extends radially inwardly from the main body portion of the associated finger portion to define a radially inwardly extending shoulder surface 34k. Each head portion further defines a camming surface 34m.

Valve assembly 36 includes a valving member 36a, a valve stem 36b, and a valve stem head portion 36c. Valving member 36a includes axially spaced flange portions 36d and 36e at the forward end of valve stem 36b and a cup-shaped resilient sealing member 48 fitted around flange portion 36d, filling the space between flange portions 36d and 36e, and extending forwardly from flange portion 36d to present an annular sealing surface 36f for coaction with cylinder end wall 28d around reservoir port 28e. Valve stem head portion 36c is generally conical in configuration and defines a conical camming surface 36g at the rear face of the head portion and an annular shoulder 36h at the front face of the head portion.

Valve guide member 38 may be formed of a suitable plastics material and includes a main body generally cylindrical portion 38a defining a central bore 38b at its rear face slidably receiving the forward end of the valve stem 36b and an annular flange portion 38c at the front face of the guide member. A plurality of circumferentially spaced openings (not shown) are provided in main body portion 38a. To assemble the centre feed master cylinder, annular insert 32 is positioned in socket 30h, an annular elastomeric seal 50 is positioned on nose portion 30a of the piston against the annular shoulder 30g, adapter member 34 is fitted over the nose portion 30a of the piston to position the rear annular face 34i of the retainer member against a seal 50 and to complete seal groove 43, the adaptor member 34 is secured to the piston by push fitting ultrasonic welding or the like, valve assembly 36 is assembled to valve guide 38 with a valve guide return spring 52 positioned between valving member flange 36e and the front end of valve guide member main body portion 38a, a main return spring 54 is positioned over valve guide member 38 with its front end bearing against valve guide flange portion 38c, and the sub-assembly comprising valve assembly 36, valve guide member 38, and return spring 54 is moved axially relative to the piston sub-assembly to pass valve stem head portion 36c between fingers 34g and seat the free end of spring 54 against adapter member flange portion 34c. As head portion 36c of valve stem 36b engages the front ends of fingers 34g, the cam surface 36g on head portion 36c coacts with the cam surfaces 34m on the head portions 34j of the finger portions 34g to move the free ends of the finger portions cammingly and resiliently outwardly to allow valve stem head portion 36c to pass therethrough, whereafter the shoulder surfaces 34k defined by finger portions 34g snap into place behind the annular shoulder 36h defined by head portion 36c to define the snappingly engaged coacting position of the valve stem and the adapter member. The entire assembly is now fitted axially into cylinder 28 to position valve guide 38 against end wall 28d of the cylinder. In the fully inserted position of the assembly, return spring 54 biases adapter member 34 and piston 30 rearwardly to press flange portion 32c of annular insert 32 against a split ring 56 positioned in the open rear end 28c of the cylinder. In this assembled condition, valving member 36a is maintained by finger portions 34g in a position in which it is axially withdrawn from reservoir port 28e so as to allow fluid communication from the reservoir through port 28e, past annular seal 36f, and through openings 38d to thereby allow the reservoir to fill the pressure chamber 28b. Note that return spring 54 is significantly stronger than valve guide spring 52 so that spring 52 is maintained in a compressed condition in the retracted position of the piston.30.

It will be understood that a head portion (not shown) of piston rod 22 of master cylinder 28 is snappingly received in insert 32 with prongs 32d engaging an annular shoulder defined on the head portion of the piston rod to preclude inadvertent withdrawal of the piston rod from the retainer. Further details of the construction of annular insert 32 and the manner in which it coacts with the head of the piston rod are disclosed in PCT/GB88/00317.

When piston 30 is moved forwardly in cylinder 28 (i.e. to the left as viewed in Fig.2) upon depression of clutch pedal 20 to actuate piston rod 22, valve assembly 36 initially moves forwardly with piston 30 and adapter member 34 under the urging of valve guide spring 52 to seal annular sealing surface 36f around reservoir discharge port 28e and preclude communication between the reservoir and pressure chamber 28b, whereafter continued forward movement of piston 30 under the impetus of piston rod 22 to discharge pressure fluid through conduit 16 to slave cylinder 14 is accommodated by the axial movement of head portion 36c and valve stem 36b within blind axial bore 30k formed in the forward end of piston 30 and extending through nose portion 30a and into piston spool portion 30c. When clutch pedal 20 is thereafter released, the piston and valve stem retainer are moved through their return stroke under the urging of return spring 54. As the piston and retainer approach their fully retracted position as defined by engagement of flange portion 32c of insert 32 with slit ring 54, shoulder surfaces 34k on finger portions 34e engage annular shoulder 36h on valve stem head portion 36c and move the valve assembly 36 rearwardly against the resistance of spring 52 to move annular valving surface 36f away from end wall 28d to establish fluid communication between the reservoir and the cylinder pressure chamber to ensure total filling of the pressure chamber behind the retreating piston.

In addition to facilitating the assembly and disassembly of the valve assembly, adapter member 34 further coacts with the piston 30 to define an annular seal groove 43 which is totally free of the flash lines that would be present in groove 43 if the piston was formed of one piece and the groove was formed in a moulding operation. That arrangement, by eliminating the mould flash lines, contributes to the effectiveness and the life of the seal.

Annular elastomeric seal 50, viewed in cross-section as best seen in Figs.8 and 9, includes an axially forward portion 50a and an axially rearward portion 50b. Axially forward seal portion 50a defines a outer circumferentially extending deflectable lip seal 50c and a inner circumferentially extending deflectable lip seal 50d.

Seal rear portion 50b defines a radially outer circumferentially extending arcuate heel seal 50e, and a radially inner circumferentially arcuate heel seal 50f.

An annular groove 50g is provided in forward portion 50a opening at the front edge of the seal and defining a radially inner annular surface 50h of outer lip seal 50c and the radially outer annular surface 50i of inner lip seal 50d. The groove 50g is V-shaped and is substantialy symmetrical about a line 150 passing axially through the approximate centre of the seal cross-section.

Seal 50 further includes an outer annular groove 50j opening at the radially outer edge of the seal and respectively defining the radially outer annular surface 50k of outer lip seal 50c and the axially forward annular surface 501 of outer heel seal 50e.

Seal 50 further includes an inner annular groove 50m opening at the radially inner edge of the seal and respectively defining the radially inner annular surface 50n of the inner lip seal 50d and the axially forward annular surface 50p of the inner heel seal 50f.

The rear portion 50b of the seal has a flat annular surface 50r generally normal to the seal central axis but rounded at its circumferentially outer and inner edges to respectively form an axially rearward annular surface 50s of the outer heel seal 50e and an axially rearward annular surface 50t of axially inner heel seal 50f.

A forward annular edge 50u of deflectable inner lip seal 50d is generally normal to the central axis of the seal and a forward annular edge 50d of outer deflectable lip seal 50c is inclined with respect to the central seal axis and is disposed generally normal to the midline 50z of the lip seal 50c. In the relaxed seal posture as seen in Fig.9, the radially outer annular sealing edge 50w of deflectable lip seal 50c is disposed radially outwardly of the radial outermost point of heel seal 50e by a distance X and the radially inner annular sealing edge 50x of deflectable lip seal 50d is similarly disposed a distance X from the radial innermost point of arcuate heel seal 50f. The positioning of seal 50 within annular groove 43 is seen in Fig.8 with the piston assembly seen disposed slidably in the bore 28b of cylinder 28. The axial width of the seal as measured between rear surface 50r and front surface 50u is slightly less than the axial width of seal groove 42 so that the seal fits snugly in the seal grove with seal edge 50u juxtaposed to the annular shoulder 34i of adapter member 34 and seal annular rear surface 5Or juxtaposed to the annular shoulder 30f defined by piston land portion 30d. This arrangement means that the axial width W of the groove 43 is particularly critical. The radial height of the seal is slightly greater than the radial height of shoulder 30g so that, in the assembled condition of Fig.8, arcuate heel seals 50e and 50f are slightly compressed respectively against the adjacent surface of piston nose portion 30a and cylinder bore 28b and the deflectable lip seals 50c and 50d are deflected relative to the arcuate heel seals by a distance slightly greater than the distance X so that the deflectable lip seals are constantly urged radially outwardly and inwardly respectively so as to urge annular sealing edge 50w against cylinder bore 28b and urge annular sealing edge 50x against the adjacent annular surface of piston nose portion 30a. The flange portion 34 of adapter member 34 is axially clear of the radially outer lip seal 50c.

As described and as disposed in the manner seen in Fig.8 seal 50 serves to provide all of the necessary sealing functions for the associated cylinder assembly. Specifically, seal 50 provides a fluid pressure seal, an air seal, and a contaminant seal. The fluid pressure seal is provided by seal edges 50 and 50x of deflectable lip seals 50c and 50d, and the arcuate heel seals 50e and 50f provide secondary fluid pressure sealing, preclude the entry of air into the sealing interface and into the pressure chamber of the cylinder, and preclude the entry of contaminants into the sealing interface.

Since seal 50 provides all of the required sealing functions, piston 30 may be constructed without further annular grooves to receive further annular seals. As a result, the front end 30f of the piston is not violated or weakened by a piston groove so that the forward end of the piston may be designed, with regard to an annular groove, in a manner to optimize the mounting and receipt of the associated pushrod 22. A modified form of the invention seal 50 is seen in Fig.10. The seal of Fig.10 is identical to the seal previously described with the exception that a plurality of annular serrations or ridges 50y are provided on radially outer annular face 50k of outer lip seal 50c. The serrations function to provide a plurality of annular sealing edges interfacing with the bore 28b of the cylinder so as to augment the sealing action of annular sealing edge 50w. The use of the serrations has also been found to reduce judder of the piston when utilising a cylinder formed in plastics material.

A seal in accordance with the invention is seen in Fig.11 in use as the sealing member of the slave cylinder 14. In the slave cylinder 14, the seal 50 is received in an annular groove 58a provided at the rearward end of slave piston 58. Piston 58 is slidably received in the bore 14b of the slave cylinder and includes a socket 58b at its forward end for receipt of pushrod 24. As with its usage in the master cylinder 12, seal 50 functions in the slave cylinder 14 to provide inner and outer deflectable lip seals and inner and outer arcuate heel seals with the deflectable lip seals functioning to provide the pressure fluid seal and the arcuate heel seals functioning to provide a secondary pressure fluid seal, provide an air seal, and preclude the entry of contaminants into the sealing interfaces.

The invention will be seen to provide a novel and advantageous annular elastomeric seal, to provide a piston utilizing the invention elastomeric seal, and to provide a hydraulic cylinder utilizing the invention elastomeric seal. The invention elastomeric seal in accordance with the invention provides an inexpensive and effective means of providing pressure fluid sealing, air sealing, and contaminant exclusion in a single seal member.

Whereas preferred embodiments of the invention have been illustrated and described in detail, it will be apparent that various changes may be made in the disclosed embodiments without departing from the scope or spirit of the invention as defined in the appended claims.

Claims

1. An annular elastomeric seal having a central axis and comprising, in cross-section an axially forward portion defining circumferentially outer and inner deflectable lip seals, an axially rearward portion defining circumferentially outer and inner arcuate heel seals, and an axially rearward annular surface extending from the radially outer arcuate heel seal to the radially inner arcuate heel seal.

2. A seal according to Claim 1 , wherein said seal includes an inner annular groove opening at the radially inner edge of said seal and defining a radially inner annular surface of said inner lip seal and an axially forward annular surface of said inner hee1 se 1.

3. A seal according to Claim 1 or 2 wherein said seal includes a forward annular groove in said forward portion opening at the front edge of said seal, the groove being substantially symmetrical in cross-section about an axial line passing through the centre of the seal cross-section, the groove defining the radially inner annular surface of said outer lip seal and the radially outer annular surface of said inner lip seal.

4. A seal according to Claim 1, 2 or 3 wherein said seal includes an outer annular groove opening at the radially outer edge of said seal and defining the radially outer annular surface of said outer lip seal and the axially forward annular surface of said outer heel seal.

5. A seal according to any preceding claim wherein in an operative condition, the inner deflectable lip seal has a forward annular edge substantially normal to a central axis of the seal.

6. A seal according to any preceding claim wherein in an operative condition, the outer deflectable lip seal has a forward annular edge inclined with respect to a central axis of the seal.

7. A seal according to any preceding claim wherein in a relaxed condition a radially inner sealing edge of the inner deflectable lip seal lies radially inwardly of the radially innermost point of the inner arcuate heel seal.

8. A seal according to any preceding claim wherein in a relaxed condition a radially outer

_* sealing edge of the outer deflectable lip seal lies radially outwardly of the radially outermost point of the outer arcuate heel seal .

9. A seal according to any preceding claim wherein one of the inner and outer deflectable lip seals is formed with serration means to provide a plurality of sealing edges.

10. A seal according to Claim 9 wherein the radially outer deflectable lip seal is formed with the serration means on part of its radially outer surface.

11. A lip seal according to Claim 9 or 10 wherein the radially inner deflectable lip seal is formed with the serration means on part of its radially inner surface.

12. A seal according to any preceding claim in a circumferential seal groove on a piston concentric to the central longitudinal axis of said piston assembly, the groove being of a constant axial width.

13. A seal according to Claim 12 wherein the inner deflectable lip and heel seals sealing engage a circumferential surface of the groove.

14. A seal according to Claim 12 or 13 wherein the axially rearward annular surface of the seal is engageable with an annular shoulder part of the groove.

15. A seal according to Claim 14 wherein the inner deflectable lip seal is axially spaced from an adjacent annular shoulder part of the groove when the axially rearward annular surface is in engagement with the first said annular shoulder of the groove.

16. A seal according to any of Claims 12 to 15 wherein said piston is devoid of any further annular seal grooves.

17. A seal according to any of Claims 12 to 16 wherein said circumferential seal groove is defined between forward and rearward annular faces, the forward annular face extending radially outwardly from a position adjacent the inner deflectable lip seal to a position axially clear of the outer deflectable lip seal.

18. A seal according to Claim 17 wherein the forward annular face extends radially outwardly for a distance less than the radial extent of the rearward annular face.

19. A seal according to any of Claims 12 to 18 wherein said piston assembly includes a piston main body portion and a forward, reduced diameter nose portion forming an annular shoulder at its rearward end with said main body portion, and an annular adapter member fitted at its rearward end over the forward end of said nose portion and having an annular edge spaced from said annular shoulder to define said annular seal groove therebetween of constant axial width.

20. A seal according to Claim 19 wherein said adapter member includes coupling means at its forward end for attachment to a valve stem.

21. A hydraulic cylinder comprising a body defining an axially extending bore open at its rearward end and closed at its forward end and a piston slidably mounted in the bore, the piston having a circumferential groove thereon of constant axial width in which an annular elastomeric seal is located, the seal comprising in cross-section an axially forward portion defining circumferentially outer and inner deflectable lip seals, an axially rearward portion defining circumferentially outer and inner arcuate heel seals, and an axially rearward annular surface extending from the radially outer arcuate heel seal to the radially inner arcuate heel seal.

22. A hydraulic cylinder according to Claim 21 wherein said seal includes an inner annular groove opening at the radially inner edge of said seal and defining a radially inner annular surface of said inner lip seal and an axially forward annular surface of said inner heel seal .

23. A hydraulic cylinder according to Claim 21 or 22 wherein said seal includes a forward annular groove in said forward portion opening at the front edge of said seal, the groove being substantially symmetrical in cross-section about an axial line passing substantially through the centre of the seal cross-section, the groove defining the radially inner annular surface of said outer lip seal and the radially outer annular surface of said inner lip seal.

24. A hydraulic cylinder according to any of Claims 21 , 22 or 23 wherein said seal includes an outer annular groove opening at the radially outer edge of said seal and defining the radially outer annular surface of said outer lip seal and the axially forward annular surface of said outer heel seal.

25. A hydraulic cylinder according to any of Claims 21 to 24 wherein in an operative condition, the inner deflectable lip seal has a forward annular edge substantially normal to a central axis of the seal.

26. A hydraulic cylinder according to any of Claims 21 to 25 wherein in an operative condition, the outer deflectable lip seal has a forward annular edge inclined with respect to a central axis of the seal.

27. A hydraulic cylinder according to Claim 26 wherein in a relaxed condition a radially inner sealing edge of the inner deflectable lip seal lies radially inwardly of the radially innermost point of the inner arcuate heel seal.

28. A hydraulic cylinder according to any of Claims 21 to 27 wherein in a relaxed condition a radially outer sealing edge of the outer deflectable lip seal lies radially outwardly of the radially outermost point of the outer arcuate heel seal.

29. A hydraulic cylinder according to any of Claims 21 to 28 wherein one of the inner and outer deflectable lip seals is formed with serration means to provide a plurality of sealing edges.

30. A hydraulic cylinder according to Claim 29 wherein the radially outer deflectable lip seal is formed with the serration means on part of its radially outer surface.

31. A hydraulic cylinder according to Claim 29 or 30 wherein the radially inner deflectable lip seal is formed with the serration means on part of its radially inner surface.

32. A hydraulic cylinder according to any of Claims 21 to 31 wherein the inner deflectable lip and heel seals sealing engage a circumferential surface of the groove.

33. A hydraulic cylinder according to Claim 32 wherein the axially rearward annular surface of the seal is engageable with an annular shoulder part of the groove.

34. A hydraulic cylinder according to Claim 33 wherein the inner deflectable lip seal is axially spaced from an adjacent annular shoulder part of the groove when the axially rearward annular surface is in engagement with the first said annular shoulder of the groove.

35. A hydraulic cylinder according to any of Claims 21 to 34 wherein said piston is devoid of any further annular seal grooves.

36. A hydraulic cylinder according to any of Claims 21 to 35 wherein said circumferential seal groove is defined between forward and rearward annular faces, the forward annular face extending radially outwardly from a position adjacent the inner deflectable lip seal to a position axially clear of the outer deflectable lip seal.

37. A hydraulic cylinder according to Claim 36 wherein the forward annular face extends radially outwardly for a distance less than the radial extent of the rearward annular face.

38. A hydraulic cylinder according to any of Claims 21 to 37 wherein the body includes a wall with a reservoir port therein for communication with a source of reservoir fluid, and said body further includes valving means operative to open and close said reservoir port in response to reciprocal movement of said piston in said bore.

39. A hydraulic cylinder according to Claim 38 wherein said valving means includes a valve stem extending axially in said bore forwardly of said piston, a valve member carried on the forward end of said valve stem for coaction with said reservoir port, and means coupling the rearward end of said valve stem to the forward end of said piston assembly.

40. A hydraulic cylinder according to Claim 39 wherein said piston includes a main body portion and a reduced diameter nose portion at its forward end forming an annular shoulder with said main body portion, and an annular adapter member fitted at its rear end over the front end of said nose portion with its rearward annular edge spaced forwardly from said annular shoulder to define said annular seal groove therebetween.

41. A hydraulic cylinder according to Claim 40, wherein said adapter member defines said valve stem coupling means at its forward end.

42. A hydraulic cylinder according to Claim 39, 40 or 41 , wherein the piston is formed with a forwardly facing axial blind bore which receives the valve stem during forward movement of the piston.

43. A hydraulic cylinder according to Claim 42 and where the piston includes said reduced diameter nose portion, wherein the axial blind bore extends through said nose portion.

44. A hydraulic cylinder according to Claim 43, and where the piston includes said main body portion, wherein the axial blind bore extends into the piston main body portion.

45. A hydraulic cylinder according to any of Claims 21 to 44 wherein the hydraulic cylinder is a hydrau1ic master cy1inder.

46. A hydraulic cylinder according to any of Claims 21 to 37 wherein the hydraulic cylinder is a hydraulic master cylinder.