Patent GB-1191377-A (GB)
Title: A Master Cylinder Assembly for a Vehicle Brake System and which Embodies a Bleeding Seal Member.
IPC: B60T11/20
Filed: 1968-10-18
Abstract: 1,191,377. Master cylinders for hydraulic braking systems. MIDLAND-ROSS CORP. 18 Oct., 1968 [11 Dec., 1967], No. 49583/68. Heading F2F. A master cylinder assembly for a vehicle brake system includes (a) a main housing having a cylindrical bore open at one end of the housing, (b) a piston reciprocable in the bore and having a recess in one end opening in the direction of the same end of the housing, there being an annular seal between the side wall of the piston and the inner wall of the bore, (c) a push rod extending into the recess for operating the piston, and (d) a flexible resilient seal member mounted in sealing relationship to the same end of the housing the seal member having an annular radially-inwardly-directed lip portion surrounding the push rod adjacent to the recess and deflectable into sealing relationship with the same end of the piston in response to a pressure differential on axially opposite faces of the lip portion, whereby when the master cylinder assembly is subjected to a vacuum for bleeding purposes, the seal member will provide a seal between piston and bore if the other seal (between the walls of piston and bore) should permit leakage of air into the assembly. As shown in Fig. 1, a tandem master cylinder 10 includes a first sump chamber 16 and a second sump chamber 18, covered by seal member 20, cap 22 and retainer 24. A cylinder barrel 26 having a bore 28 accommodates a first piston 32 with cavity 34 receiving push rod 36, a second floating piston 38 and a compression spring 44. A high pressure work chamber 40 located beyond piston 38 and containing a compression spring 46 communicates with the second sump chamber 18 via compensating port 56, while a low pressure chamber 60 around piston 38 likewise communicates via replenishing port 58. A high pressure work chamber 42 between the pistons and a low pressure chamber 66 around piston 32 communicate with the first sump chamber 16 in a similar manner. High pressure chamber 42 has an outlet 74 leading to the rear brake system, and high pressure chamber 40 has an outlet and conduit 76 leading to the front brake system. A conventional resilient lip seal 73 is seated near the outer end of the first piston 32. A flexible resilient seal member 78 is provided for the purpose set forth in the first paragraph above. It comprises a base portion 80 seated in an annular groove 82 extending around barrel 26, an axially-extending sleeve portion 84, and a radially-directed lip portion 86 converging inwardly toward cavity 34 but terminating short of push rod 36 so that during normal movements of the push rod the lip portion will not be moved. During the normal bleeding operation a vacuum connection is made to the compensating. port 70, and the replenishing port 72 is closed. During this phase a face seal 64 mounted on the inner end of piston 32 collapses, resulting in air being evacuated from the low pressure chamber 66. If the resilient lip seal 73 should also collapse, air would be drawn from the environment past it into chamber 66, thus jeopardizing the bleeding operation, but with the further flexible resilient seal member 78 now provided, the pressure differential created by collapse of seal 73 serves to force the flexible lip portion 86 of member 78 against the recess in piston 32, as shown in Fig. 1. Preferably the lip portion, near its inner end, is inclined towards the recess to facilitate this movement. In Fig. 2 the flexible resilient seal member, now numbered 178, is integral with a collapsible boot 188.