GB2135004A - Master cylinder for vehicle braking system - Google Patents

Abstract

A master cylinder of the quick-fill type has an open-ended pressure cylinder (1) extended by a cylindrical member (3) and a reservoir (11) mounted on the cylinder. The member (3) partially defines a quick-fill chamber (13) in which slides a piston (14) connected to a piston (4) of the pressure cylinder. Valve assembly (21) controls communication between the quick-fill chamber and the reservoir. <IMAGE>

Description

SPECIFICATION Master cylinder for vehicle braking system This invention relates to a master cylinder ofthe "qu ick-fill" type, primarily for use in a vehicle braking system. Such a master cylinder is one which, when actuated, initially expells a large quantity of fluid into the braking system to cause rapid take-up of brake clearances andthereby minimisethe amount of brake pedal travel required forthis purpose. Examples of quick-fill master cylinders are described in our published co-pending Patent Application No. 2074675.

Master cylinders have been proposed having a pressure cylinderwith an open end which is closed by a closure member mounted on the cylinder over said open end. Examples of such a master cylinder are described in our published co-pending PatentApplication No. 2082277.

There is an increasing trend in modern vehicle braking systems to use fabricated master cylinders in which the pressure cylinder is a simple steel tube of relatively thin uniform wall thickness, with a separate reservoir, usually of plastics material, mounted on the cylinder and communicating with the interior of the latterthrough transverse ports formed in the cylinder wall. The provision of a quick-fill facility in a master cylinder of this kind gives rise to considerable problems because a large chamber has to be provided for the low pressure quick-fill fluid, as well as valve means to control the operation of the quick-fill chamber, and there is insufficient material available in the components of the master cylinderto enable such items to be incorporated in the structure of the master cylinder.

It is, therefore, an object ofthe present invention to provide means for incorporating a quick-fill facility primarily, but not exclusively, in a fabricated master cylinder.

According to one aspect ofthe present invention, a mastercylinderofthe quick-fill type comprises a pressure cylinder having an open end, a reservoir communicating with the pressure cylinder, a closure member arranged to close said cylinder open end, the closure member at least partially defining a quick-fill chamber, pistons slidable respectively in the pressure cylinder and quick-fill chamber, and valve means arranged and operable to control communication between the quick-fill chamber and the reservoir.

In one convenient arrangement, the quick-fill chamber piston forms an end wall ofthe closure member.

This piston may conveniently be carried by, and is preferablyfastfor axial movement with, a rearwardly extending support member connected to the pressure chamber piston. Such support member is preferably hollow and surrounds at least part of an actuating rod forthe pressure chamber piston.

The valve means is preferably contained within a recessformed at least partially bythe reservoir, the valve means being contained eitherwithin a separate housing member lodged in the recess, orwithin a compartment defined by the recess itself. The valve means may conveniently communicate with the quick fill chambervia a passageway which extends axially of the cylinder and is preferably defined, at least partially, by the closure member.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure lisa longitudinal cross-section of part of one form ofthe master cylinder of the invention; Figure 2 is a longitudinal cross-section of part of an alternative embodiment ofthe master cylinder ofthe invention, and Figure 3 isaviewsimilarto Figure 2 of part of a further embodiment ofthe master cylinder of the invention.

Figure 1 ofthe drawings illustrates part of a tandem master cylinderfor use in a dual circuit braking system and comprising a pressure cylinder 1, shown as a thin-walledtube of uniform wall thickness having an axial blind bore 2, the open end of which is closed by a closure member indicated generally at 3. The internal components of the pressure cylinder are conventional and have not be shown in detail. However, the rearmost one 4 of a pair of pistons within the bore 2 is illustrated, the piston 4 being provided with a seal 5 and having a rearwardlyextendingsleeve6through which extends an actuating rod 7 connected, in conventional manner, to an actuating member 8 of a booster, of which a power piston hub is indicated at 9 and a body shell portion at 10.A reservoir 11 is mounted at the upper side of the cylinder 1 and communicates respectively with the internal cham bers ofthe cylinderthrough ports 2A and 3A formed transversely through the cylinder wall.

The closure member3 includes a sleeve 12 of relatively large diameter compared with the pressure cylinder 1 and partially defining a quick-fill chamber 13 having a relatively large volume. The open end of the sleeve 12 is closed by a cup like piston 14slidable within the sleeve 12, the base 15 of the piston 14 being apertured to receive the rear end portion ofthe sleeve 6therethrough. The base 15 is held captive between a radial shoulder 16 of the sleeve 6 and a circlip 17 lodged in a groove in the sleeve 6. Thus, it will be seen thatthe pistons 4 and 14 move together as a unit in response to actuating force transmitted via the rod 7.

The closure member3 is retained in position against a fixing flange 1A of the pressure cylinder 1 by means ofthe booster body shell 10 which is itself clamped againsttheflange by a spring 18forming part of the booster mechanism and traps a shoulder 19 of the sleeve 12 between itself and the flange 1A. The sleeve 12 has an axial tubular extension 20 of which a bore 20A provides communication between the quick-fill chamber 13 and control valve means 21 for controlling operation of the quick-fill chamber.The extension 20 sealingly engages within a housing 22 of the valve means and the passage 20A is continued buy a corresponding passage 22Awithin the housing 22, a branch 23 leading to a valve chamber 24. The housing 22 is lodged within a recess 25 defined between the body ofthe reservoir 11 and the pressure cylinder 1, the housing being sealed to the reservoir by a sealing ring 26 engaging the reservoir around a port 27 ofthe reservoir and engaging a retaining ring 28forthe valve components which permits communication between the port 27 and valve chamber 24.

The valve means includes avalve mechanism which comprises a resilient annular seal 29 snugly fitted within an annularspaceformed between a central spigot 30 ofthe housing 22 and the inner wall ofthe valve chamber, a generallytubularvalve member 31 having an outwardly projecting flange 32 which rests upon the valve 29, and a spring 33 acting between the retaining ring 28 and the flange 32 to urge the valve member 31 into sealing engagement with the valve member 29.The upper end ofthevalve member 31, as seen in the drawing, has a port 31A therethrough around which is formed a valve seatfor co-operation with a ball 34 which acts as a one-way valve, the ball being held captive within the valve member 31 by means of inwardly projecting tags 35 on the latter.

During actuation ofthe master cylinder, the pistons 4 and 14 move forward in unison from the positions illustrated and fluid is expelled by the piston 14from the large volume quick-fill chamber 13. The strength of the spring 33 is chosen so that the pressure generated initially by the piston 14is not large enough to liftthe valve member 29 against the action ofthe spring 33.

Since, however, the pressure causes the ball 34to close the port 31A in the valve member3l,fluidfrom the quick-fill chamber is urged pastthe seal 5 ofthe piston 4 into the pressure chamber2 and thence to the braking system so as rapidly to take up brake clearances in known manner.When pressure has built up in the chamber2 to an extend preventing further flow of fluid into this chamber from the quick-fill chamber 30, the valve member 31 is lifted out of sealing engagement with the resilient valve member 29, thereby permitting fluid from the quick-fill cham bey 1 3to be expelled along the axial passage 20A past thevalve member31 and through the port 27into the reservoir.The resilient valve member 29 is provided at its upper surface with a groove 29A, preferably of spiral configuration, to facilitate flow offluid between the valve members 29 and 31.When the pistons4 and 15 return towards their rest positions after braking,the ball 34 moves downwardly away from the port in the valve member 31 to the extent limited by the tags 35 and fluid is thereby permitted to be drawn from the reservoir into the quick-fill chamber.

Figure 2 illustrates an alternative arrangement of valve mechanism 21, in which the arrangement and operation of the valve components is generally similar to that described in relation to Figure 1, but differs in thatthe resilientvalve member 29 forms a subassembly with a base member40 upon which it is snap-engaged over a central boss 41 having undercut side edges 42. The base member 40 provides an extension 43 ofthe axially extending passage 20A of the closure member 12. In this embodiment, the valve components are placed in the valve chamber 24, through the upper end of the housing 22 before assembly of retaining ring 28 which, in this case forms a screwthreaded connection with the housing.

Figure 3 shows a further alternative arrangement of the valve means 21. In this embodiment, the arrange ment and operation ofthe valve components are identical with those of Figure 2, butthe separate housing 22 is dispensed with and the valve mechan ism is housed, instead, within a compartment formed integrally as part of the reservoir body. For this purpose, an additional wall portion 11A is provided, extending downwardly into engagementwiththe pressure cylinder 1 and being apertured to receive the axially extending portion 20 ofthe closure element sleeve 12. This embodiment also makes use of a separate base member 40, upon which resilient valve member 29 is retained in the manner described in Figure 2.However, in this embodiment, the valve components are assembled into the compartment from below the reservoir and the base member 40, having been placed in the position illustrated, is then permanently secured to the reservoir by a weld 44 so that the valve means 21 andthe rese oir now, together form a compl'ete sub-assen.bly.

Itwill be seen that the invention provides a simple and convenient means of incorporating a quick-fill chamber and its associated piston and valve components into a master cylinderwhich is particularly convenientforusewith fabricated mastercylinders, although it may, of course, be used with other master cylinders embodying an end closure means.

Claims (13)

1. A master cylinder of the quick-fill type comprises a pressure cylinder having an open end, a reservoir communicating with the pressure cylinder, a closure member arranged to close said cylinder open end, the closure member at least partially defining a quick-fill chamber, pistonsslidable respectivelyinthe pressure cylinder and quick-fill chamber, and valve means arranged and operable to control communication between the quick-fill chamber and the reservoir.

2. A master cylinder according to Claim 1 wherein the quick-fiil chamber piston forms an end wall ofthe closure member.

3. A master cylinder according to Claim 1 or Claim 2 wherein the quick-fill cylinder piston is connected for axial movementwith the pressure chamber piston.

4. A master cylinder according to any one ofthe preceding claims wherein the quick-fill chamber piston is carried buy a rearwardlyoxtending support member connected to the pressure chamber piston.

5. A master cylinder according to Claim 4 wherein the quick4ill cylinder piston isfastfor axial movement with said support member.

6. A master cylinder according to Claim 5 wherein the quick-fill piston is located between a radiai flange of said support member and a retaining clip carried by the latter.

7. A master cylinder according to any one of Claims 4to 6 wherein thesupport member is hollow and surrounds at least part of an actuating rod for the pressure chamber piston.

8. A master cylinder according to any one of the preceding claims wherein the valve means is contained within a recessformed at least partially bythe reservoir.

9. A master cylinder according to Claim 8 wherein the valve means is contained within a separate housing member lodged within the recess.

10. A master cylinder according to Claim wherein the valve means is disposed within a compartment defined by the recess itself.

11. A master cylinder according to any one of Claims 8 to 10 wherein the valve meanscommuni- cateswiththequick-fill chambervia a passageway which extends axially of the cylinder.

12. Amastercylinderaccording to Claim 11 wherein said passageway is defined, at least partially, bythe closure member.

13. A mastercylinderofthe quick-fill type, substantially as hereinbefore described with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.