Master cylinder for vehicle braking systems

A master cylinder for an hydraulic pressure system has a pressure cylinder (1) on which is mounted a reservoir (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 resulting from pressure applied to the interior of the cap (3) is transmitted via said device to the cylinder.

This invention relates to a master cylinder for an hydraulic pressure 
system, primarily for a vehicle braking system, and more particularly to a 
master cylinder which 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 through 
the peripheral cylinder wall, and a closure member mounted on the cylinder 
and closing said open cylinder end. Examples of this 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 of 
the 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 conected to relatively flimsy structure such as a shell 
forming part of a booster body and the force transmitted through the 
closure member to such structure as a result of the application of the 
test pressure can lead to a risk of damage occurring to 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 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 by a 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. 
In one convenient arrangement, the coupling device extends through 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 of 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 of 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 
respectively 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 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 of variable length to 
another piston 8 to which is secured an actuating rod 9 extending axially 
outwardly of the cylinder. A spring 10 acts to axially separate the 
pistons 4 and 8 to 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 cylinder wall. 
Communication between the reservoir and port 13 takes place by way of an 
axial passage 14 formed in the closure member 3, the passage 14 leading at 
one end into a recess 15 registering with the port 13. The passage 14 is 
formed partly in an axial extension 16 of the closure member, which 
extension is inserted into a bore portion 17 of a connector 18 which is 
received and sealed within an opening in the base of the reservoir 11. A 
seal 16A surrounds 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 FIG. 5, the clip is generally U-shaped in 
plan and embraces a boss portion 22 of the connector 28 with arms 21A, 21B 
thereof resiliently snap-engaged behind the boss portion. The extension 16 
of the closure member 3 extends through the clip 21 for reception within 
the connector 18 as described. 
The bore portion 17 communicates via a passsage 18A with an enlarged 
opening 19 of the connector located within the reservoir, the junction 
between the passage 18A and opening 19 being in the form 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 of the newly assembled 
master cylinder for the purpose of testing 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 order to facilitate its use. 
Normal operation of the master cylinder described above will be readily 
apparent to 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 piston 8 and the resultant force on the piston is reacted 
on a circlip 8A lodged in a groove in the cylinder wall. The test pressure 
also acts over a relatively large area of the closure member 3, defined by 
the annulus presented by a seal 23 surrounding the actuating rod 9 and it 
is important that the considerable force thus 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 (FIG. 2) 
the arms 27 of which extend through transverse openings 28 formed in the 
end closure 3 and engage in an annular groove 29 formed in the outer 
peripheral surface of the cylinder 1. Inner end portions 27A of the arms 
27 are of greater width than the remainder of the 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 member 3 to 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 
24 and is retained in place thereby. It can therefore be fairly readily 
removed in order to permit the closure member 3 to be dismantled to 
provide access to the interior of the cylinder when required. 
The alternative embodiment illustrated in FIG. 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 manner to the 
corresponding components of FIG. 1. The reservoir (not shown) is mounted, 
in this embodiment, on the cylinder 1 by means of flexible 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 inwardly turned flanges 33 at their outer 
peripheries which engage within peripheral grooves formed behined radially 
outwardly extending flanges 34 of the plugs to retain the plugs positively 
in position. Projecting spigots 35 of the reservoir are received within 
the plugs 36 with some resilient deformation of the latter to 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 a transverse bore 39 which receives an 
axial hollow extension 16 of the cap 3 similar to 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 number of peripheral teeth 41 (FIG. 7) and housed 
in a groove 42 in the outer peripheral cylinder wall. The adjacent 
internal wall of the cap 3 has a plurality of internal recesses 43 within 
which those teeth f the locking ring in register with the recesses may 
engage. 
The teeth 41 of the ring 40, when unstressed, project out of the peripheral 
plane of the ring. In order to 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 body to its position of use, the teeth 41 of the ring 
are resiliently compressed against the internal wall of the cap. When the 
cap recesses 43 come into register with the cylinder groove 42, the teeth 
in register with the recesses snap-engage therein to positively lock the 
cap on the cylinder in a manner which precludes its subsequent removal 
without damage to the assembly. This action brings oppositely facing 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 of the 
piston 8 is transmitted directly to the cap 3 and when high pressure 
testing is envisaged, it may be desirable to incorporate a circlip similar 
to 8A in FIG. 1, or other device, to react force applied to said piston 
inner end. 
In order to provide an additional bearing surface for the piston rod 9, a 
sleeve 9A is interposed between the outer surface of the rod and the inner 
surface of the cylinder, a radial flange 9B of the sleeve being disposed 
between the adjacent end of the cylinder and seal 23 to retain the sleeve 
in position. The sleeve 9A provides an elongate bearing surface for the 
rod 9 which assists in minimising tilting of the rod 9 and piston 8, in 
use. By leaving a small clearance Y between the cap and cylinder and also 
between the sleeve flange 9B and the cap, slight leakage of hydraulic 
fluid is permitted for the purpose of lubricating the seal 23.