GB2075631A

GB2075631A - Master cylinders and their manufacture

Info

Publication number: GB2075631A
Application number: GB8013026A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1980-04-21
Filing date: 1980-04-21
Publication date: 1981-11-18
Also published as: ES501490A0; GB2075631B; ES8300548A1; IN152469B

Abstract

In the manufacture of a master cylinder having a body (1) with a bore (2) and first and second pistons (7, 8) slidable in the bore and interconnected by a bolt (16) and sleeve (17), a predetermined spacing between seals (9) carried by the pistons (7, 8) is ensured by assembling the first piston (7), spring (15), bolt (16) sleeve (17) and a member (14) telescoped over the end of the bolt, adjusting the bolt axially relative to the member (14) and then crimping the latter to engage grooves (19) in the bolt to fix the adjusted position. <IMAGE>

Description

SPECIFICATION Master cylinders and their manufacture This invention is concerned with master cylinders for vehicle braking systems, and their manufacture.

Known tandem master cylinders designed for dual circuit braking systems comprise two pistons slidable in a bore in the master cylinder body. One pressure chamber is defined between the end of the bore and the first piston and another pressure chamber is defined between the two pistons. The pistons are spaced apart by means which limit their axial separation and which generally consist of a bolt fixed by screwing into the second piston and a sleeve member adapted to engage the first piston and having an inwardly directed flange for abutting against the underside of the bolt head. The bolt and sleeve telescope together to permit some variation in the distance separating the two pistons.

The pistons carry seals and to avoid excessive lost pedal motion during which there is no pressure generated in the master cylinder, it is important to ensure that the edges of the seals are normally positioned with a predetermined clearance from the ports which connect the pressure chambers to their respective reservoirs. Due to manufacturing tolerances the axial dimensions of the master cylinder components can vary and in order that the seal edges should be separated by the correct axial spacing it is necessary to effect some adjustment before inserting the master cylinder components into the body. To this end it is the normal practice to assemble the components and adjust the screw connection between the bolt and second piston to obtain the desired interseal spacing before staking the bolt to fix it in position.This preliminary adjustment is rather inconvenient insofar as the bolt must be rotated with respect to the piston, and it is rather costly in terms of the time which it takes to complete correctly.

Furthermore, a screw threaded connection is not ideal when the piston is of plastic construction.

The aim of this invention is to reduce the above drawback of the known master cylinder construction and method of manufacture.

According to the present invention there is provided a method of manufacturing a master cylinder comprising a body having a bore, first and second pistons slidable in the bore and interconnected by means including a bolt coupled to the second piston, the second piston having a blind bore with a tubular member received therein and the bolt being fixed to the tubular member, the method comprising the steps of assembling the first piston, interconnecting means and tubular member, adjusting the position of the bolt in the tubular member to obtain a desired interseal spacing, fixing the bolt to the tubular member in the adjusted position by deforming the member radially to engage in a recess in the bolt, and inserting the assembly into the bore of the master cylinder body.

With the method of the invention the preliminary adjustment is easy to perform since only axial displacement between the bolt and tubular member is necessary, and it can be rapidly effected. The tubular member can be thin in the region of its radial deformation so that it can be easily fixed, e.g. by crimping, to the bolt. The bolt is preferably formed with a series of annular grooves into which the tubular sleeve is deformed to provide a secure connection.

The invention also includes a master cylinder manufactured by the method.

A better understanding of the invention will be had from the following detailed description which is given by way of example with reference to the accompanying drawing which shows an axial section through a tandem master cylinder.

The illustrated master cylinder comprises a body 1 with a plain blind bore 2, and outlets 3, 4 for connection to two reservoirs. Two ports 5, 6 communicate each connection 3, 4 with the bore 2. Slidable in the bore 2 are two pistons 7, 8 which each carry front and rear seals 9, 10. The first piston 7 has a bore in which is received an abutment member 11 having a projection 1 2 adapted to engage the end of bore 2 to limit the forward displacement of the piston 7, and a shoulder against which a spring 1 3 acts to urge the piston 7 rearwardly. The second piston 8 has a blind bore in which a metal tubular member 14 is accommodated so that its inner end abuts against the end wall of the piston bore.The member 1 4 can be conveniently formed by deep drawing with some upsetting to provide a shoulder for a spring 1 5 interposed between the pistons to act against. Pistons 7, 8 are interconnected by means comprising a bolt 1 6 having one end fixed in the tubular member 14 in a manner described in more detail below, and its opposite end telescoped inside a sleeve 1 7 which is held in engagement with piston 7 by spring 1 5. A flange on the sleeve 1 7 engages the underside of the bolt head to limit separation of the pistons 7, 8. The master cylinder components are retained in the bore 2 during a transit clip 1 8 fitted to the end of the master cylinder body.

When the master cylinder is manufactured it is important to ensure that the edges of seals 9 have the correct clearance from the ports 5 in the normal brakes off condition of the master cylinder. As the lengths of the components, in particular sleeve 17, bolt 16, member 14 and piston 8 can vary due to manufacturing tolerances, it is necessary to carry out an adjustment during the assembly procedure. Prior to location in the bore of the master cylinder body 1 the components including sleeve 17, bolt 16, tubular member 14, and spring 1 5 are assembled together. It will be noted that the end of bolt 1 6 engaged in member 1 4 has a series of annular groves 19. The position of the bolt 1 6 is adjusted axially relative to the member 14 to obtain the correct spacing between the left hand end of sleeve 17 and the member 14, and the member 1 4 is then deformed radially by crimping to engage in the grooves 1 8 and thereby fix the bolt 1 6 in its adjusted position. A removable collar can be located on member 14 instead of piston 8 suring the adjustment procedure and can remain in position until after crimping is completed. The member 1 4 is then inserted into the blind bore of piston 8, and the sub-assembly is subsequently located in the bore 2 of body 1 with the other components, as illustrated, and the clip 1 8 attached.

Claims

1. A method of manufacturing a master cylinder comprising a body having a bore, and first and second pistons slidable in the -bore and interconnected by means including a bolt coupled to the second piston, the second piston having a blind bore with a tubular member received therein and the bolt being fixed to the tubular member, the method comprising the steps of assembling the first piston, interconnecting means and tubular member an end of the bolt being telescoped into the tubular member, adjusting the position of the bolt end in the tubular member to ensure a predetermined axial spacing between seals carried by the respective pistons when the master cylinder is fully assembled, fixing the bolt to the tubular member in said adjusted position by deforming a portion of said member radially to engage in a recess in the bolt, and inserting the assembly into the bore of the master cylinder body.

2. A method according to claim 1 wherein the recess in the bolt comprises at least one annular groove.

3. A method according to claim 1 or 2, wherein the tubular member is deformed by crimping.

4. A method according to claim 1, 2 or 3 wherein a removable collar is located over the tubular member in place of the second piston during the adjustment and fixing of the bolt, and the collar is replaced by the second piston prior to insertion of the assembly in the bore of the master cylinder body.

5. A method according to any one of claims 1 to 4, wherein the tubular member is formed substantially by deep drawing.

6. A method according to claim 1 and substantially as herein described.

7. A master cylinder manufactured by the method of any one of claims 1- to 6.