GB2131902A - Master cylinder for an hydraulic pressure - Google Patents

Abstract

A master cylinder for an hydraulic pressure system has a pressure cylinder (1) on which is mounted are servoir (11), the cylinder having an open end closed by a cap (3). The cap is positively coupled to the cylinder (1) by a coupling device (26) arranged so that force resulting from pressure applied to the interior of the cap (3) is transmitted via said device to the cylinder. In Figs 1, 2 the device (26) is a U-shaped flat member passing through apertures in the cap (3) and engaging a groove in the cylinder. In Figs 6, 7 (not shown) an annular coupling member (40) is disposed in an external groove of the cylinder and has inclined tabs or teeth (41) engaging internal recesses in the cap (3). <IMAGE>

Description

SPECIFICATION Master cylinderfor an hydraulic pressure system This invention relates to a master cylinderfor an hydraulic pressure system, primarilyfora vehicle braking system, and more particularly to a master cylinderwhich includes a pressure cylinder having an open end,an initially separate reservoir mounted on the cylinder and communicating with the interior of the cylinder by means of a transverse opening throughthe peripheral cylinder wall, and a closure membermounted on the cylinder and closing said open cylinder end. Examples ofthis general kind of master cylinder are described in our co-pending published Application No. 2082277.

For safety reasons, it is common practice to test the integrity of newly assembled master cylinders by applying high pressure to the interior ofthe cylinder and checking for unacceptable leaks which may be caused, for example, by damaged or incorrectly assembled components such as pistons or seals. In some master cylinders, the closure member is retained in position by or connected to relativelyflimsy structure such as a shell forming part of a booster body and the force transmitted through the closure memberto such structure as a result ofthe application ofthetest pressure can lead to a riskofdamage occuringto the structure.

An object of the present invention is to overcome the aforesaid problem and accordingly provides a master cylinder comprising a pressure cylinder having an open end, an initially separate reservoir communicating with the interior ofthe cylinder by means of a transverse opening through the peripheral cylinder wall, and a closure member mounted on the cylinder and closing said open cylinder end, the closure member being positively coupled to the cylinder body by a coupling device arranged so that force resulting from pressure applied to the interior of the closure member istransmitted via said means to the cylinder.

In one convenientarrangement,the coupling device extendsthrough an opening formed in the closure member and engages a formation in the cylinder wall which provides at least one surface, and preferably two opposed surfaces against which axial force applied to the interior of said closure member may be reacted.

Preferably, said formation provides said surface or surfaces at either side ofthe cylinder and the coupling device has a pair of arms arranged to embrace the cylinder and respectively engage said surface or surfaces at either side thereof.

In an alternative arrangement, the coupling device is in the form of a ring having outwardly extending peripheral teeth which engage recesses formed re spectively in the closure member and cylinder, said recesses providing respectively a pair of opposed surfaces against which axial force applied to the closure member may be reacted through the ring.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure lisa longitudinal cross-section of one form of the master cylinder of the invention; Figure 2 is a split cross-section respectively on the lineA-Aand B-B of Figure 1; Figures 3 and 4 are respectively cross-sections along the lines Y and X of Figure 2; Figure 5 is a detail in plan view of a component ofthe mastercylinderofFigures 1 to4; Figure 6 is a longitudinal cross-section of an alternative form ofthe master cylinder of the invention, and Figure 7 is a cross-section along the line 7-7 of Figure 6.

The drawings illustrate a tandem master cylinder for use in a dual circuit braking system and comprising a pressure cylinder 1 having an axial blind bore 2, the open end of which is closed by a closure member in the form of a sleeve 3. The bore 2 is divided by a piston 4 into pressure chambers 5 and 6, the piston being connected by a device 7 ofvariable length to another piston 8to which is secured an actuating rod 9 extending axially outwardly ofthe cylinder. A spring 10 acts to axially separate the pistons 4 and 8to an extent limited by the telescopic device 7. A reservoir 11 is mounted at the upper side of the cylinder 1 and communicates respectively with the chambers 5 and 6 through ports 12 and 13 formed transversely through the cylinderwall.

Communication between the reservoir and port 13 takes place by way of an axial passage 14formed in the closure member3, the passage 14 leading at one end into a recess 15 registering with the port 13. The passage 14 isformed partly in an axial extension 16 of the closure member, which extension is inserted into a bore portion 17 of a connector 18which is received and sealed within an opening in the base ofthe reservoir 11. A seal 1 6Asurrounds the extension 16 within the connector device 18 and is retained in position by a resilient clip 21, as of spring steel for example. As will be seen from Figure 5, the clip is generally U-shaped in plan and embraces a boss portion 22 ofthe connector 18 with arms 21 A, 21 B thereof resiliently snap-engaged behind the boss portion.The extension 1 6 of the closure member3 extends through the clip 21 for reception within the connector 18 as described.

The bore portion 17 communicates via a passage 18Awith an enlarged opening 19 ofthe connector located within the reservoir, the junction between the passage 18Aand opening 19 being in theform of a conical seat 20 designed to permit the application of a high pressure test probe (indicated in broken lines at P) to the chamber 6 ofthe newly assembled master cylinderforthe purpose oftesting the integrity of the usual piston and seal components thereof. The conical seating permits the test probe a relatively wide angle of approach for connection with the connector 18 in orderto facilitate its use.

Normal operation of the master cylinder described above will be readily apparentto one skilled in the art and will not be further described.

Before the master cylinder is approved for use in a vehicle braking system, the aforesaid pressure testing of the pressure chamber 6 is carried out using the probe P. It will be seen that the test pressure acts on the inner end of the piston8andthe resultantforce on the piston is reacted on a circlip 8A lodged in a groove in the cylinderwall. The test pressure also acts over a relatively large area ofthe closure member 3, defined by the annulus presented by a seal 23 surrounding the actuating rod 9 and it is important that the consider ableforcethus generated on the closure member is not applied to flimsy structure, such as a housing 24 of an associated servo, since this may result in damage to that structure.

The invention provides a means for reacting this force on the cylinder 1 and, in the present embodiment, this is achieved by the use of a coupling device in the form of a generally U-shaped spring steel clip 26 (Figure 2) the arms 27 of which extend through transverse openings 28formed in the end closure 3 and engage in an annular groove 29 formed in the outer peripheral surface ofthe cylinder 1. Inner end portions 27A ofthe arms 27 are ofgreaterwidth than the remainder ofthe arms so that the arms are able to engage in the groove 29 over a substantial part of the arcuate extent of the latter.This effectively keys the closure member3to the cylinder so that any axial force applied to the closure member 3, such as that resulting from the aforementioned high pressure testing, is reacted directly on the cylinder and not, for example, on the booster casing 24. The coupling device 26, in this embodiment, lies within the booster casing 24and is retained in place thereby. It can therefore be fairly readily removed in order to permit the closure member 3to be dismantled to provide access to the interior of the cylinder when required.

The alternative embodiment illustrated in Figure 6 has a cylinder 1 containing pistons 4 and 8, end cap 3, variable length device 7 and actuating rod 9 arranged and operating in a similar mannertothe corresponding components of Figure 1. The reservoir (not shown) is mounted, in this embodiment, on the cylinder 1 by means offlexible resilient plugs 30, each having a body 31 of generally hollow cylindrical form engaged within respective upstanding cylindrical cups 32 secured to the outer cylinder surface. The cups have inwardlyturned flanges 33 attheir outer peripheries which engage within peripheral grooves formed behind radially outwardly extending flanges 34 ofthe plugsto retain the plugs positively in position.

Projecting spigots 35 ofthe reservoir are received within the plugs 36 with some resilient deformation of the latterto ensure a fluid-tight seal and end flanges 36 on the spigots engage behind shoulders 37 within the plugs for positive retention. One of the plugs 30 has a thickened wall portion 38 having transverse bore 39 which receives an axial hollow extension 16 ofthe cap 3 similarto that of the previous embodiment.

In this embodiment, the means for reacting axial force applied to the cap 3, resulting, for example, from pressure testing, is in the form of a locking ring 40 having a numberof peripheral teeth 41 (Figure 7) and housed in a groove 42 in the outer peripheral cylinder wall. The adjacent internal wall ofthe cap 3 has a plurality of internal recesses 43 within which those teeth ofthe locking ring in register with the recesses may engage.

Theteeth4l of the ring 40, when unstressed, project out ofthe peripheral plane of the ring. In orderto assemble the cap 3 on the cylinder 1, the ring 40 is first placed in the cylinder groove 42 and as the cap is passed axially along the bodyto its position of use, the teeth 41 ofthe ring are resiliently compressed against the internal wall ofthe cap. When the cap recesses 43 come into register with the cylinder groove 42, the teeth in registerwith the recesses snap-engage therein to positively lock the cap on the cylinder in a mannerwhich precludes its subsequent removal without damage to the assembly.This action brings oppositelyfacing edges of the ring into facing relationship with oppositely facing edge surfaces of the cap and cylinder, thereby ensuring that axial forces imposed on the cap are reacted directly on the cylinder.

In the arrangement as illustrated, pressure applied to the inner end ofthe piston 8 is transmitted directly to the cap 3 and when high pressure testing is envisaged, it may be desirableto incorporate a circlip similarto 8A in Figure 1, or other device, to react force applied to said piston inner end.

In order to provide an additional bearing surfacefor the piston rod 9, a sleeve 9A is interposed between the outer surface ofthe rod and the inner surface ofthe cylinder, a radial flange 9B ofthe sleeve being disposed between the adjacent end of the cylinder and seal 23 to retain the sleeve in position. Thesleeve 9A provides an elongate bearing surfaceforthe rod 9 which assists in minimising tilting ofthe rod 9 and piston 8, in use. By leaving a smali clearance Y between the cap and cylinder and also between the sleeve flange 9B and the cap, slight leakage of hydraulicfluid is permitted forthe purpose of lubricating the seal 23.

Claims (11)

1. A master cylinderfor an hydraulic pressure system comprising a pressure cylinder having an open end, an initially separate reservoircommunicat- ing with the interior of the cylinder by means of a transverse opening through the peripheral cylinder wall, and a closure member mounted on the cylinder and closing said open cylinder end, the closure member being positively coupled to the cylinder body bya coupling device arranged so that force resulting from pressure applied to the interior of the closure member is transmitted via said means to the cylinder.

2. AmastercylinderaccordingtoClaim 1 wherein the coupling device extends th rough an opening formed in the closure member and engages a formation in the cylinder wall which provides at least one surface against which axial force applied to the interior of said closure member may be reacted.

3. A master cylinder according to Claim 1 or Claim 2wherein said formation providestwoopposed surfacesforthe reaction of said forces.

4. A master cylinder according to any one of the preceding claims wherein said formation provides said surface or surfaces at either side of the cylinder and the coupling device has a pair of arms arranged to embrace the cylinder and respectively engage said surface or surfaces at either side thereof.

5. A master cylinder according to Claim 4wherein said arms extend through transverse openings in the closure member and engage in an annular groove of the cylinder, which groove constitutes said formation of which opposed walls provide said two opposed surfaces.

6. A master cylinder according to Claim wherein the coupling device is of general U-shape with inner end portions ofthe arms of greater width than the remainder, such that the arms are able to engage in the cylinder groove over a substantial part of the arcuate extent of the latter.

7. A master cylinder according to Claim 1 wherein the coupling device is in the form of a locking ring having peripheral teeth and housed in a groove ofthe cylinder, the closure member having internal recesses for reception of at least some of said teeth which, when so received, react axial force applied to the interioroftheclosuremember.

8. A master cylinder according to Claim 7 wherein the teeth, when unstressed, project out ofthe peripheral planeofthe ring, wherebythe teeth are resiliently compressed as the member is passed axially alongthe cylinder and at least some of them snap-engage by resilient deformation into said internal recesses with which they are brought into register thereby positively to lock the closure member on the cylinder.

9. A master cylinder according to any one ofthe preceding claims wherein a bearing sleeve is interposed between the external peripheral surface of an axially extending actuating shaft ofthe cylinder and the internal cylinderwallto provide a bearing surface for said shaft.

10. A master cylinderaccording to Claim 9 where- in said bearing sleeve has a peripheral radial flange which abutstheend ofthecylinder.

11. A master cylinder substantially as hereinbefore described with reference to Figures 1 to 5 or Figures 6 and 7 ofthe accompanying drawings.