GB2135003A - Master cylinder for vehicle braking system - Google Patents

Abstract

A master cylinder of the quick-fill type has a pressure cylinder (1), a reservoir (11) mounted thereon and a quick-fill chamber (13). The reservoir forms a compartment housing a valve assembly (21) controlling communication between the quick-fill chamber (13) and reservoir (11). <IMAGE>

Description

SPECIFICATION Master cylinder for vehicle braking system This invention relates to a master cylinder of the "quick-fill"tepe, primarilyfor use in a vehicle braking system. Such a master cylinder is one which, when actuated, initiatlyexpells a large quantity offluid into the braking system to cause rapid take-up of brake clearances and thereby minimise the amount of brake pedal travel requiredforthis purpose. Examples of quick-fill master cylinders are described in our published co-pending Patent Application No. 2074675.

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 relativelythin uniform wall thickness, with a separate reservoir, usually of plastics material, mounted on the cylinder and communicating with the interior of the latterthrough transverse portsformed in the cylinder wall. The provision of a quick-fill I facility in a master cylinderofthis kind gives rise to considerable problems because a largechamberhasto be provided forthe low pressure quick-fill fluid, and, valve means is also required to control communication between this chamber and the reservoir.Because of the nature ofthe pressure cylinder there is insufficient material availabletoenable previous proposalsforincorporat ingthevalvemeans in the structure ofthecylinderto be practicable.

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

According to the invention, a master cylinder of the quick-fill type comprises a pressure cylinder, a separate reservoir mounted on and communicating with the pressure cylinder, a quick-fill chamber, pistons slidable respectivelyinthe pressurecylinderand quick-fill chamber, and valve means arranged and operable to control communication between the quick-fill chamber and the reservoir,thevalve means being contained in a compartmentformed at least partially by the reservoir body.

In one convenient arrangement,thecomponents of the valve means are retained permanently within said compartmentsothatthe reservoir and valve means together form a complete sub-assembly.

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 a closure member of the cylinder.

The invention wilt now be described, by way of example, with reference to the single accompanying drawing which is a longitudinal cross-section of part ofoneform of the master cylinder of the invention.

The drawing illustrates part of a tandem master cylinderfor use in a dual circuit braking system and comprising a pressure cylinder 1, shown as a thin wallecttube 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 ofthe 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 rearwardly extending sleeve 6 through which extends an actuating rod 7 connected, in conventional manner, to an actuating member8 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 atthe upper side of the cylinder 1 and communicates respectively with the internal chambers of the cylinder th rough ports 2A and 3Aformed transversely through the cylinder wall.

The closure member 3 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 of the 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 1 A of the pressure cylinder 1 by means ofthe booster body shell 10 which is itself clamped againstthe flange by a spring 18 forming 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.

A compartment 21Aformed by the reservoir body houses the valve means 21, the reservoir having, for this purpose, an additional wall portion 1 which extends downwardly into engagement with the pressure cylinder 1 and is apertured to receive the axially extending portion 20 of the closure element sleeve 12.

The valve means includes a valve mechanism which comprises a resilient annular seal 29 snugly fitted within a n an annularspaceformed between a central spigot30 of a valve support member 30A and the inner wall of the valve chamber, a generallytubularvalve member 31 having an outwardly projecting flange 32 which rests upon the valve member 29, and a spring 33 acting between the flange 32 and an internal shoulder 32A of the reservoirto urge the valve member 31 into sealing engagement with the valve member 29.The upper end ofthe valve member 31, as seen inthedrawing, hasa port31Atherethrough around which informed 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.

The support member 30A has a central boss 41 having an undercut edge 42 and the valve member 29 is provided on its undersurface with a recess 42A of appropriate shape to receive the boss 41,the valve member being snap-engaged over the boss so as to be retained thereon by the undercut edge 42 and thereby form asub-assemblywith support member 30A. The support member provides an extension 43 of the axially extending passage 20A of the closure member 12, communicating with the valve chamber 24 via a perpendicular branch 23.

The provision ofthe compartment defined by the reservoir enables the valve means to be assembled into the compartment from below the reservoir, the base member being finally placed in the position illustrated and permanently secured to the reservoir by a weld 44. The valve means and reservoirthen form togethera complete sub-assembly which may conve niently be stored until required for use. It may readily be connected to the quick-fill chamber 13 by means of the sleeve extension 20 which enters a corresponding openinginthewall 11A.

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 14 from the large volume quick-fill chamber 13. The strength of the spring 33 is chosen so that the pressure generated initially by the piston 14 is not large enough to liftthe valve member 29 against the action of the spring 33.

Since, however, the pressure causes the ball 34 to close the port 31A in the valve member 31 fluid from the quick-fill chamber is urged pastthe seal 5 ofthe piston 4 into the pressure chamber 2 and thence to the braking system so as rapidly to take up brake clearances in known manner. When pressure has built up in the chamber 2to an extent preventing further flow of fluid into this chamber from the quick-fill chamber30, the valve member 31 is lifted out of sealing engagement with the resilientvalve member 29, thereby permitting fluid from the quick-fill chamber 13 to be expelled along the axial passage 20A past the valve member 31 and through a port 27 into 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 pistons 4 and 15 return towards their rest positions after braking, the ball 34 moves downwardly awayfrom the port in the valve member31 to the extent limited by the tags 35 and fluid is thereby permitted to be drawn from the reservoir into the quick-fill chamber.

It will be seen thatthe invention provides a convenient means of providing a control valve means in afabricated mastercylinderwhich has little substantial structure suitable for incorporating such components.

Claims (9)

1. A master cylinder of the quick-fill type comprising a pressure cylinder, a separate reservoir mounted on and communicating with the pressure cylinder, a quick-fill chamber, pistons slidable respectively in the pressure cylinder and quick-fill chamber, and valve means arranged and operable to control communica tion betweenthequick4illchamberandthereservoir, the valve means being contained in a compartment formed at least partially by the reservoir body.

2. A master cylinder according to Claim 1 wherein the components of the valve means are retained permanentlywithin said compartment so thatthe reservoir and valve meanstogetherform a complete sub-assembly.

3. A maste' cylinder according to Claim 1 or Claim 2 wherein the valve means communicates with the quick-fill chamber via a passageway which extends axially ofthe cylinder.

4. A master cylinder according to Claim 2 wherein the components of the valve means are retained permanently within the compartment by a closure device which acts as a support within the compart mentor a valve member forming part ofthe valve means.

5. A master cylindèraccording to Claim 4 wherein said closure device and valve member are provided respectively with interengageableformations such as to enable said members and said deviceto be connected together.

6. A master cylinder according to Claim 4 or Claim Swherein said closure deviceforms a ,Irassageway providing communication between the quick-fill chamber and the reservoir.

7. A master cylinder according to Claim 3wherein said passageway is defined, at least partially, by a closure member of the cylinder;

8. A master cylinder according to Claim 6 or Claim 7 wherein said cylinder closure member is provided with an axial extension defining said passageway, said extension passing through an opening in a wall of said compartmentto establish communication between said extension passageway and said closure device passageway.

9. Amastercylindersubstantiallyas hereinbefore described with reference to the accompanying drawing.