GB2197400A - Pressure cylinder - Google Patents

Abstract

A pressure cylinder (1) of plastics material, for use primarily as a master cylinder, has an integral mounting flange (9) carried by a surrounding cylindrical sleeve (10) which is connected to the cylinder by a web (11). The location of the web is chosen so that, although it is traversed by the piston (3) during actuation of the latter, it lies outside the working stroke of the single seal (4) carried by the piston at its trailing end. Alternative embodiments are described in which the piston carries one seal (Fig. 1, not shown) or a pair of seals (4A, 4B) operating in the respective chambers (A, B) of a dual cylinder, the web location being then chosen so that it is not traversed by either seal during working travel of the piston. <IMAGE>

Description

SPECIFICATION Pressure cylinder This invention relates to a pressure cylinder such as a master cylinder, primarily for use in a vehicle brake or clutch hydraulic system, and particularly to such a cylinder moulded from plastics material and having an integral mounting flange.

Because the mounting flange of such a cylinder is usually of significantly greater thickness than the cylinder wall, differential contractions occur upon cooling after moulding, resulting in cylinder bore distortion in the region of the flange. Such distortion can create problems in maintaining an adequate seal between the cylinder internal wall and an internal co-operating piston assembly and can also result in the snagging of the piston and/or its associated seals and possible consequent jamming of the piston assembly within the cylinder.

One attempt to solve this problem consists in mounting the flange by way of an outer cylindrical formation generally co-axial with and surrounding the cylinder proper, said formation being connected to the cylinder at a position beyond the inward iimit of piston travel. This arrangement removes any bore distortion resulting from the flange moulding to a location at which it does not significantly adversely effect the travel or sealing of the piston assembly.However, unless the cylindrical formation carrying the flange is made relatively short, there is a risk of untoward flexing of the formation and consequent movement of the cylinder taking place during operation of the master cylinder, in use; alternatively, by making the formation as short as possible an undesirably long portion of the cylinder extends rearwardly of the flange and can be difficult to accommodate.

An object of the present invention is to provide an improved master cylinder of plastics material having an integrally moulded mounting flange, which is not subject to the aforesaid drawbacks.

According to a first aspect of the invention, there is provided a pressure cylinder of plastics material comprising a piston slidable therein, the piston having a single seal disposed towards its trailing end relative to its direction of working travel, the cylinder having an integrally moulded mounting flange and the arrangement being such that the location of the connection between the flange and cylinder is traversed by the piston, but not by the seal, during the working travel of the piston.

Conveniently, the piston carries a pair of longitudinally spaced seals and the flange is disposed between the seals such that said connection location is not traversed by either seal during the working travel of the piston.

Preferably, the flange is mounted by way of a cylindrical external formation surrounding the cylinder and being connected to the latter at a location spaced from the flange in the direction of working travel of the piston.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is part of a longitudinal cross-section of a pressure cylinder of one form of the master cylinder of the invention; Figure 2 is a longitudinal cross-section of an alternative embodiment of the invention, and Figure 3 is a view similar to Figure 2 of another alternative embodiment of the invention.

Referring to Figure 1 of the drawings, the master cylinder partially illustrated therein includes a pressure cylinder 1, moulded from plastics material, having an internal bore 2 within which slides a piston 3 carrying a single seal 4 towards its rear end when considered in relation to the direction (indicated by arrow A) of working travel of the piston. The piston is connected by a rod and spring assembly 5 to a centre valve 6 which controls the flow of hydraulic fluid from a reservoir (not shown) via a port 7 into the bore 2 of the pressure cylinder, the operation of these components being entirely conventional. When the piston 3 is actuated by a force input rod 3A to perform a working stroke along the bore 2, fluid under pressure is expelled via an outlet port 8 which would be connected, in use, to a vehicle brake.

The master cylinder of the invention is mounted in its position of use on a vehicle by way of a radial flange 9 which is carried by an external generally cylindrical sleeve 10 connected to the cylinder 1 by a connecting web 11, the flange 9, cylindrical portion 10 and web 11 being moulded integrally with the pressure cylinder 1. This arrangement ensures that distortion arising in the cylinder as a result of the significant disparity in thickness between the material of the flange 9 and the cylinder wall is reduced to a minimum, although it is still possible for minor distortions to occur in the region of the web 11.In the present embodiment, the location of the web 11 is chosen such that, although the main body of the piston 3, which essentially performs a supporting rather than a sealing role, is able to traverse the junction between the web 11 and cylinder in order to reach the forward limit of its travel, indicated by the line B, the working travel of the seal 4 occurs in its entirety along a length of the cylinder lying rearwardly of the web 11. It will therefore be seen that the seal 4 never crosses the area of the bore lying opposite to the web 11, so that any bore distortion in the region of the web 11 will not disturb the sealing integrity of the seal 4 which slides in a truly cylindrical part of the bore.This arrangement enables the flange 9 to be disposed nearer to the rear ward extremity of the pressure cylinder than in some conventional arrangements, thereby minimising possible problems resulting from flexing of the cylindrical portion 10 during operation of the cylinder.

An alternative form of the master cylinder of the invention is illustrated in Figure 2 and comprises a body 1' to which is connected a mounting flange 9' by way of a cylindrical sleeve 10' connected to the body by a web 11'. A piston 3' is slidably reciprocable in the cylinder and carries a pair of seals 4A, 4B at respective end portions thereof. The seal 4A divides the cylinder into high and low pressure chambers A, B and hydraulic fluid in the high pressure chamber A is expelled, upon actuation of the piston by a force input rod 3A, through an outlet port C which would be connected, in use, to a vehicle brake, in conventional manner.

Fluid is fed to the chambers A, B from an external source, such as a reservoir, via a connecting port 15, which communicates with the chamber A through a recuperation hole 16 and with chamber B through a fluid supply hole 17, which holes are disposed at either side of the seal 4A when the piston is in its retracted position, as shown. The port 15 is carried by the sleeve 10' and is connected to the cylinder wall by a relatively thin web 15A, the moulding of which causes no significant bore distortion. The port 15 communicates with the hole 17 by way of the annular space 10" defined by the sleeve 10' and outer cylinder wall, the open end of the space being closed by a rubber seal 18 disposed between the flange 9' and said outer cylinder wall. Operation of the master cylinder is conventional and will be understood by a person familiar with the art.

The web 11' is located just behind the retracted position of the seal 4A and the working stroke of the piston (in the direction of arrow A) is such that the seal 4B does not reach the web 11' during actuation of the piston. The two seals 4A, 4B never traverse the web 11' and always work in portions of the body not subjected to significant deformation by the formation of the web 11' Two kinds of retention devices for the rod 3A are illustrated respectively above and below the longitudinal centre line 'Y' of the cylinder. The upper device 20 is a simple cup engaged over the open end of the body 1 and having prongs 21 engaging notches in the body. The device retains an arcuate bearing part 22 engaged by an eniarged head 23 of the rod 3A. The lower device 24 is similar in shape and function to the upper one but has a portion 25 extending along the body to engage and retain the seal 18.

In the master cylinder illustrated in Figure 3, the flange 9' is again mounted on the body 1' by way of a surrounding cylindrical sleeve 10' connected to the body 1' by a web 11' at a location just behind the forward piston seal 4A. As in the Figure 2 embodiment, the piston working stroke is such that neither the seal 4A nor the rearmost piston seal 4B traverses the location of the web 11' during operation of the cylinder.

Working fluid is supplied to the cylinder, in this embodiment, from a reservoir 26 moulded integrally from plastics material with the body 1' and connected to the latter partly by cylindrical sleeve 10', to which it is attached, and partly by an additional web 27 connected to the body at a location remote from the web 11' of the sleeve 10'. Ports 28, 29 place the reservoir in communication respectively with the chambers A and B of the body. The port 29 is formed through the web 11' which may be thickened locally if necessary, as shown, to accommodate it. The other port 28 is formed partly through the wall of the body 1' and partly through a small web 30 formed between the base 26A of the reservoir 26 and the outer surface of the body 1. The operation of the master cylinder is identical to that of Figure 2.

It will be understood that the nature of the flange connection may be varied as desired consistent with allowing the single seal or rearmost seal to work in an undistorted part of the cylinder bore. For example, when the master cylinder is of the centre valve type in which the valve parts are at the closed end of the cylinder, the cylindrical sleeve 10, 10' may be dispensed with and the flange 9, 9' connected directly to the wall of the cylinder body at a location not traversed by the piston seal or seals. The various other details of the master cylinder of the invention may be varied in accordance with conventional master cylinder practice.

Claims (7)

1. A pressure cylinder of plastics material comprising a piston slidable therein the piston having a single seal disposed towards its trailing end relative to its direction of working travel, the cylinder having an integrally moulded mounting flange and the arrangement being such that the location of the connection between the flange and cylinder is traversed by the piston, but not by the seal, during the working travel of the piston.

2. A pressure cylinder according to Claim 1 wherein the piston carries a pair of longitudinally spaced seals and the flange is disposed between the seals such that said connection location is not traversed by either seal during the working travel of the piston.

3. A pressure cylinder according to Claim 1 or Claim 2 wherein the flange is mounted by way of a cylindrical external formation surrounding the cylinder and being connected to the latter at a location spaced from the flange in the direction of working travel of the piston.

4. A pressure cylinder according to Claim 3 wherein said cylindrical fprmation carries a connecting port serving for the connection to the cylinder of a fluid conduit.

5. A pressure cylinder according to Claim 4 wherein the connecting port communicates with a port in the wall of the cylinder via a space defined between said cylindrical formation and the outer wall of the cylinder.

6. A pressure cylinder according to Claim 4 wherein a fluid reservoir is carried on the cylinder partly by way of said cylindrical formation.

7. A pressure cylinder of plastics material, substantially as hereinbefore described, with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.