This invention relates to cylinder assemblies and more particularly to a master cylinder of the center feed type.

A master cylinder of the center feed type typically includes a cylinder defining an axially extending pressure chamber and including a reservoir port proximate the front end of the cylinder for communication with a fluid reservoir; a piston ' slidably positioned in the cylinder and adapted for coaction with a piston rod extending into the rear end of the cylinder; a valve assembly in the pressure chamber including a valving member proximate the reservoir port and a valve stem secured to the valving member and extending axially rearwardly in the pressure chamber; and a retainer on the front end of the piston connected to an enlarged head portion on the free end of the valve stem.

In operation, when the piston is moved forwardly in the cylinder by actuation of the piston rod, the pressure fluid forwardly of the piston moves the valving member into seating engagement with the reservoir port ^an ^ the valve stem moves axially into a central axial bore in the fornt end of the piston to allow the piston to continue to move toward the front end of the cylinder to discharge pressure fluid from the cylinder through a suitable discharge port. As the piston thereafter moves rearwardly in the cylinder upon retraction of the piston rod, the valve stem slides axially in the central bore in the piston until the piston approaches the end of its return stroke at which time the retainer on the piston engages the head portion of the valve stem and pulls the valving member out of seating engagement with the reservoir port to establish fluid communication between the reservoir and the cylinder pressure chamber to ensure total filing of the pressure

chamber behind the retreating piston. An example of a center feed master cylinder of this type is shown in U.S. Patent No.4,407.125.

Whereas center feed master cylinders of this type provide a relatively compact and efficient overall package, assembly and disassembly of the cylinder is difficult and time consuming, in part because of the complex procedure required to assemble and disassemble the retainer to and from the head portion of the valve assembly. Master cylinders are also shown in GB No.859,911 and 2,076,095and EP-A-0 169 560 but, again, the connecting of the valve stem to the piston is not straightforward.. . _.

An object of the present invention is to provide improved valve stem retention which, when utilized in a center feed master cylinder assembly, greatly simplifies the assembly of the master cylinder.

According to one aspect of the present invention there is provided a cylinder comprising a cylinder defining pressure chamber, a piston slidable within the pressure chamber and valve means for controlling communication between the pressure chamber and reservoir, the valve means including a valve stem and the piston including retaining means which snap-fits on to the valve stem to secure the valve stem to the piston.

The snap-fitting on to the valve stem of the retaining means makes the cylinder easy to assemble when compared to earlier proposals.

Preferably the valve stem includes a head portion and the retaining means snap-fits behind the head portion.

The securing means is preferably a member mounted on the piston.

The retaining means may comprise one or more resilient fingers extending axially of the piston for snapping engagement with the valve section. The fingers may be arranged in a circumferentially spaced manner.

Preferably the fingers co-act in their relaxed condition to define §n opening of smaller size than the transverse dimension of the head portion and are yieldable radially outwardly in response to axial movement of the valve stem therebetween when connecting the piston and valve stem together. This feature makes the assembly of the stem and piston particulary straightforward.

One or more of the fingers may include a shoulder for retaining the head portion after the head portion of the stem has been moved through said opening and the fingers have snapped radially inwardly.

Preferably, the head portion has a tapered surface thereon which acts as a camming surface to urge the fingers radially outwardly when connecting the valve stem to the piston.

The retaining means may include an axial bore through which the valve stem can pass.

The piston may be formed with an axial bore through which the valve stem can pass.

Preferably, the axial bore in the retainer member and/or piston is dimensioned to allow the head portion to pass therethrough.

The fingers may be arranged circumferentially around the axial bore.

Preferably, the head portion includes a radial surface which co-operates with a radial surface on said fingers to secure the valve stem to the piston.

Preferably, the retaining means permits relative axial movement between the piston and valve stem in one direction but inhibits separation thereof as a result of relative axial movement in the opposite direction. This arrangement allows the valve stem head portion to move into snapping engagement with free ends of the resilient fingers o-f the retainer member and thereafter, upon actuation of the piston of the master cylinder assembly, move into the bore in the piston to allow the piston to complete a power stroke.

In order to prevent unwanted yielding of the fingers and inadvertant withdrawal of the valve stem from between the fingers, a member such as a sleeve or 0-ring may at least partly encircle the fingers. In such a case at least one of the fingers may include means for retaining the member on the fingers . The means may comprise an outwardly extending surface on one or more of the fingers.

The member may be movable axially into a position to permit outward yielding of the fingers to enable the stem and retaining means to be disassembled.

The retaining member may comprise an auxiliary piston member which co-acts with the piston to define a circumferential location for a fluid seal. The location may be in the form of a groove. This arrangement provides a seal groove that is devoid of mold flash lines so as to maximise the life and

effectiveness of the seal.

Preferably, a return spring is provided for the piston, which return spring acts against part of said retaining means, such as an outwardly extending flange. The flange may co-act with the piston to define said location for the fluid seal.

According to a second aspect of the invention there is provided a cylinder comprising an axially extending pressure chamber; a piston slidably positioned in said pressure chamber, defining a rearwardly opening socket at its rear face, and including a blind central bore opening at its front face; an annular insert member positioned in said socket; and a retainer member secured to the front end of said piston member and defining a plurality of forwardly extending fingers circumferentially arranged about said central bore for retaining a stem of a valve in the cylinder.

The cylinder may include a reservoir port proximate the front end thereof; and a valve assembly including a valving member proximate said reservoir port, said valve stem being secured to said valving member and extending axially rearwardly within said pressure chamber; said valve stem including a head portion at its rearward end; each of said fingers including a head portion at its forward end for snapping coaction with said valve stem head portion.

According to a third aspect of the invention there is provided a cylinder defining an axially extending pressure chamber; a piston slidably positioned in said pressure chamber; a piston rod secured to the rear end of said piston; an auxiliary piston member secured to the front end of said piston and coacting with said piston to define an annular radially

outwardly oening groove at the interface of said piston and said auxiliary piston member; and an annular seal positioned in said groove and sealingly engaging the inner walls of said cylinder.

Preferably, said cylinder includes a reservoir port proximate the front end of the cylinder for communication with a fluid reservoir; said assembly further includes a valve assembly in said pressure chamber including a valving member proximate said reservoir port and a valve, stem secured to said valving member and extending axially rearwardly into said chamber and having a head portion at its rearward end; and said auxiliary piston member includes means on the front end thereof operative in response to axial movement between said piston and said stem to snappingly secure said valve stem head portion to said auxiliary pi-ston member.

In the latter case, said securing means may comprise a plurality of circumferentially spaced resilient fingers extending axially forwardly from the front end of said auxiliary piston member for snapping engagement with said valve stem head portion.

Preferably said auxiliary piston member includes a central bore sized to pass said valve stem head portion; said fingers are circumferentially arranged about said central bore; and said piston includes a blind bore opening in the front face thereof sized to pass said valve stem head portion, and axially align with said central bore in said auxiliary piston member.

Said valve stem may include an annular shoulder defined at the front face of said head portion; and each of said fingers may include a head portion at its front end defining a radially inwardly extending

shoulder surface for coaction in the snappingly engaged positions of said auxiliary piston member and said valve stem with said annular shoulder on said valve stem.

Said piston may include a main body portion and a reduced diameter nose ^' "portion at its front end forming an annular shoulder with said main body portion; said auxiliary piston member defining a socket at its rear end sized to receive telescopically said piston nose portion with the rear face of the auxiliary piston member spaced forwardly from said shoulder to define said seal groove.

Preferably said auxiliary piston member includes a radially outwardly extending flange portion; and said assembly further includes a return spring extending . between the front end of said cylinder and said flange portion. In such a case said flange portion may be at the rear end of said auxiliary piston member in surrounding relation to said socket to form the front annular wall of said seal groove.

In any of the foregoing aspects of the invention, the piston and retaining means may be formed of plastics material joined together by, e.g., ultrasonic welding.

In any of the foregoing aspects of the invention the piston may include a bore having an insert therein through which axial load is applied to the piston to move the piston axially off the pressure chamber. This functions to provide a convenient means for locating a piston rod in one end of the piston in a manner to distribute the loading on the piston over a wise area of the piston to thereby minimize the stress loading on the piston.

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

Fig.l is a schematic view of an hydraulic apparatus including a master cylinder and a slave cylinder,

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

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

Figs.4 and 5 are cross-sectional views of the valve stem retainer embodied in the master cylinder of Fig.2, and

Fig.6 is a detail view of the structure within the circle 6 of Fig.2.

The hydraulic apparatus shown schematically in Fig.l includes a reservoir 10, a,master cylinder assembly 12, 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.l may be utilized for example in a motor vehicle wherein actuation of a clutch pedal 20 by the vehicle operator actuates 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 extend output member 24 outwardly to actuate a clutch relief lever 26. An hydraulic apparatus of the type shown in Figure 1 is disclosed, for example, in U.S. Patent No. 4,599,860.

Master cylinder assembly 12 includes a cylinder 28, a piston 30, a annular insert 32, a valve stem retainer 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 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 communica ing 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 polytetraf luoroethylene. Piston 30 includes a reduced diameter nose portion 30a at its front end, a ^" main body portion 30b, a trailing or rear portion 30c, a flange 30d at the front end of main body portion 30b forming an annular shoulder 30e with reduced diameter central bore portion 31 , and a rear flange portion 30f.

A socket 30g is provided in the rear face of the piston and includes a main body cylindrical portion 30h extending forwardly rom the rear face of the piston and a generally hemispherical front end portion 30i. Socket 30g is centered on the centerline of piston 30 and on the centerline of cylinder 28. Annular insert 32 is formed as a metal stamping and includes a cylindrical main body portion 32a, a generally hemisphe ical 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 inwarcl f om m in bo --- portion 32a at

circumferential ly spaced locations thereabout. Prong portions 32d extending 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.

Valve retainer 34 is generally annular and is preferably formed of a suitable plastic material, preferably identical to the material utilized for the piston 30. Retainer 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 circumferential ly 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. Bore 34b has an axial length substantial ly less than the axial length of piston nose portion 30a so that, with retainer 34 fitted over nose portion 30a and the front e d of the nose portion abutted against shoulder 34f, the rear annular face 34i of retainer 34 coacts with piston nose portion 30a and piston flange portion 30d to define an annular, radially

outwardly opening seal groove 43.

Each finger portion 34g includes a head portion 34j at the free forward end of the finger portion of generally triangular configuration. Each head portion 34 j extends radially inwardly from the main body portion of the associated finger portion to define a radially inwardly extending shoulder surface 34k and extends radially outwardly from the main body portion of the associated finger portion to define a radially outwardly extending shoulder surface 3 i. Each head portion further defines a camming surface 34m.

An annular member 44 is _. .provide ^' dto encircle the finger portions 34g rearwardly of radially outwardly extending shoulder surfaces 341 and delimit radially outward expansion of the finger portions. The annular member may comprise an annular sleeve 44 as seen in Figure 4 or may comprise a resilient 0-ring 46 as seen in Figure 5.

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 and a cup shaped resilient sealing member 48 fitted around valve stem 36b between flange

portions 36d and 36e and presenting an annular sealing surface 36f for coaction with cylinder end wall 28d

aroun _d 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 plastic material and includes a main body generally conical portion 38a defining a central bore

38b at i _t s rear face and an annular flange portion 38c at the front face of the guide member. A plurality of circumferential ly spaced openings 38d are provided in main body portion 38a.

To assemble the master cylinder, annular insert 32 is positioned in socket 30g ^; an annular seal 50 is positioned on nose portion 30a of the piston against the forward annular face of piston

« flange portion 30d; retainer member 34 is fitted over the nose portion 30a of the piston to position the rear annular face 34i of the retainer member against seal 50 and complete seal groove 43; the retainer member is secured to the piston by 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 a shoulder 38- on the valve guide member main _b o _d y 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 subassembly comprising valve assembly 36, valve guide member 38, and return spring 54 is moved axially relative to. the piston subassembly to pass valve stem head portion 36c between fingers 34g and seat the free end of spring 54 against valve stem retainer 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 34c 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 valve stem retainer. The entire assembly is now fit axially into cylinder 28 to position valve guide 38 against end wall 28d of the cylinder. In the ful-ly inserted, position of the assembly, return spring 54 biases valve stem retainer 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 the head portion 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 inadvertant withdrawal of the piston ro.d 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 applicant's co-pending United States Patent application, Serial No. 056 058 filed on 1st J r.e 1987 and PCT/GB88/00317 filed simultaneously herewith.

When piston 30 is moved forwardly in cylinder

28 upon depression of clutch pedal 20 to actuate piston rod 22, valve assembly 36 initially moves forwardly with piston 30 and valve stem retainer 34 under the urging of

valve guide spring 52 to seat 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 axial bore 31. When clutch pedal 20 is thereafter released, the piston and valye 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 split ring 56, 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.

It will be seen that valve retainer 34 acts effectively to allow the rapid assembly of the valve assembly to the piston while further acting to

efficiently move the valve assembly away from i s seated

position relative to the reser'voir port as the piston approaches the end of its return stroke. It will be appreciated that the valve assembly may also be readily disassembled from the piston by the use of a suitable tool (not shown) which is moved axially along valve stem

36b and into camming enagement with head portions 34j of finger portions 34g to allow the finger portions to flex resiliently outwardly and allow the ready withdrawal of valve stem 36 to disconnect the valve assembly from the piston assembly. It will be understood that O-ring 46 delimits the radial outward expansion of finger portions 34g to discourage inadvertant separation of the valve assembly from the piston assembly and yet allows controlled radial expansion of the finger portion to facilitate assembly and disassembly of the valve assembly relative to the ^' piston assembly,

When the sleeve 44 of Figure 3 is employed with the valve stem retainer, the sleeve is slid to the right as viewed in Figure 3 to allow assembly or disassembly of the valve assembly to the piston assembly and is slid to the left following insertion of the valve stem to preclude inadvertent separation of the valve stem from the retainer.

In addition to facilitating the assembly and disassembly of the valve assembly, retainer 34 further

- 1.

acts as an auxiliary piston member which 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 molding operation. The invention arrangement, by eliminating the mold flash lines, contributes to the effectiveness and the life of the seal.

The term "snappingly secure" wherever used herein includes a mechanical connection between two components achieved by causing a drive member on one of the components to cam open a gap or aperture between resiliently related members on the other of the components when the two components are urged together, until at a given degree of proximity the drive member passes sufficiently through the aperture to allow the resiliently related members to rapidly close relative to one another and thereafter resist disassociation of the two components. Whereas a preferred embodiment of the invention has been illustrated and described in detail it will be apparent that various changes may be made in the disclosed embodiment without departing from the scope or spirit of the invention.

SUBSTITUTE SHEET