Patent GB-1456206-A (GB)
Title: Power assisted master cylinder assemblies
IPC: B60T13/14
Filed: 1972-11-30
Abstract: 1456206 Master cylinders; boosters; brake systems; valves; warning devices GIRLING Ltd 12 Nov 1973 [30 Nov 1972 1 Dec 1972] 52286/73 and 55567/72 Divided out of 1456205 Headings F2F and F2E A power-assisted master cylinder assembly comprises a pedal-operated piston 11 movable in a cylinder bore, a pressure space 30 ahead of the piston 11 having an outlet for connection to a first brake circuit, and a power chamber 16 behind the piston 11 and having an inlet 16a for connection to the outlet of a control valve assembly which control valve assembly includes a valve-actuating piston 22 controlled by movement of the piston 11 to control the supply of pressure from a pressure source (e.g. accumulator 37) to the power chamber 16; the power chamber 16 is defined radially between a sleeve 7 and the cylinder bore and axially between a seal 14 and a radial flange 6 and the sleeve 7. The sleeve 7 is slidably received in a bore 11<SP>1</SP> in the piston 11 and a pedal-operated actuating rod 8 extends through the sleeve 7 to engage piston 11. The sleeve 7 shields the rod 8 from fluid pressure in the power chamber 16. As shown, the piston 22 is arranged in tandem with piston 11 with a lost motion connection between piston 11 and piston 22. Piston 22 is formed with a circumferential groove 32 registering with a port 34 connected to the reservoir 35 for a pump 36 which charges the accumulator 37. A radial passage 38 is piston 22 connects groove 32 with an axial passage 39 which opens into a valve recess 40. An exhaust valve member 42 is co-operable with the passage 39 to control flow therethrough and an inlet valve member 48 co-operable with a seating member 46 controls flow of pressure fluid between an inlet port 53 connected to the accumulator 37 and a pressure space 51. The pressure space 51 has an outlet 54 connected to a second brake circuit and also to the power chamber 16 via a passage through the cylinder housing 1.  In operation when the brake pedal is depressed movement of piston 11 is transmitted to the piston 22 by hydraulic pressure and by a return spring 23, and movement of the piston 22 causes closure of the exhaust valve 39, 42 to disconnect pressure space 51 from the reservoir 35 and thereafter via a Belleville washer 52 opens the inlet valve 48, 46 to connect pressure space 51 to accumulator 37. The second brake circuit and the pressure chamber 16 are pressurized and with power assistance the piston 11 closes off a reservoir port 20 and delivers fluid from the pressure space 30 to the first brake circuit. The driver of the vehicle continuously feels a pedal reaction proportional to the braking effort. If the first circuit fails piston 22 can be moved by pin 24. If the power circuit fails then the pressure space 30 is pressurized without power assistance.  Figs. 2, 3 (not shown) correspond respectively with Figs. 1, 2, of the complete Specification 1,456,205. In these embodiments the second piston (22) is contained in a control valve assembly (61) formed as a separate unit from a tandem master cylinder (60) containing the pedaloperated piston (11). The master cylinder assemblies of the described embodiments 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.