Patent GB-1456205-A (GB)
Title: Power assisted master cylinder assemblies
IPC: B60T13/14
Filed: 1973-02-20
Abstract: 1456205 Master cylinders; boosters; brake systems; warning devices GIRLING Ltd 12 Nov 1973 [30 Nov 1972 20 Feb 1973] 55397/72 and 8177/73 Headings F2F and F2E A tandem master cylinder 1 with a primary pedal operated piston 4 and a secondary floating piston 5 has its pressure spaces 6, 8 connected to respective balance chambers 30, 31 of a control valve assembly 2 the control valve assembly 2 being responsive to pressure generated in the pressure spaces 6, 8, when the piston 4 is operated, to supply fluid under pressure to a power chamber 10 behind the primary piston 4 to assist its operation. The master cylinder 1 and the control valve assembly 2 may be separate units arranged sideby-side in an integral assembly or they may be connected by external fluid connections. In the embodiment of Fig. 1 the control valve assembly 2 has an inlet port 19 and an exhaust port 22 connected respectively to an accumulator 24 and a reservoir 25 for a pump 26 of a closed centre pressure supply. An outlet 20 is connected to the power chamber 10 and a spring- loaded inlet valve 18 controls the flow of fluid from inlet port 19 to outlet 20 and a spring- loaded exhaust valve 21 controls communication between the outlet 20 and exhaust port 22. The inlet and exhaust valves 18, 21 are actuated by a control piston 23. A self-centering spool 29 located between the piston 23 and a plug 17 defines the chambers 30, 31 and the chambers 30, 31 are connected to respective brake circuits. A groove 34 in the spool 29 locates a ball 35 which is moved outwardly on axial movement of the spool 29 to operate a switch 36 of a warning circuit. When the brake pedal is depressed hydraulic fluid in pressure chambers 6, 8 is delivered by way of chambers 30, 31 to the brake circuits, and pressure in either of chambers 30, 31 moves control piston 23 to close exhaust valve 21, to open inlet valve 18 and to allow pressure fluid from accumulator 24 into power chamber 10 to boost the output from spaces 6, 8. The vehicle driver feels a pedal reaction proportional to the braking effort. Failure in either brake circuit causes the spool 29 to move to operate switch 36. In the embodiment of Fig. 2 (not shown) the control valve assembly (2) is used with an open centre power supply in which the pump (26) continuously pumps fluid through the inlet port (19) to the power chamber (10) and to the reservoir (25) via the exhaust port (22). A normally open exhaust valve (21) is closed to shut off the reservoir return and allow pressure to build up. The master cylinder of Fig. 2 is formed in two parts (3, 4, 6) and the piston (4) is also formed in two parts and has a stationary forward seal (49). The embodiment of Fig. 3 utilizes compressed air as the assisting fluid, the control piston 23 being operable by pressure in either of chambers 30, 31 to move a seating member 58 to close an exhaust valve 21 and open an inlet valve 18 whereby air from a reservoir 66 is admitted to power chamber 10. In chamber 10 the compressed air acts on a diaphragm 54 carried by a sleeve 51. The arrangements disclosed are intended for use in split braking systems in which each braking circuit operates an actuator on each front wheel and one rear wheel, each front wheel brake having two separate actuators.