GB1467064A - Two-circuit compressed air braking systems - Google Patents

Abstract

1467064 Pneumatic boosters ROBERT BOSCH GmbH 13 May 1974 [14 May 1973 13 Aug 1973 14 Aug 1973] 21004/74 Heading F2F A two circuit pneumatic pressure brake booster has two tandem power pistons 20, 24, a working chamber 20<SP>1</SP>, 241 for each piston being controlled by a respective control valve 10, 11 which connects them to atmosphere at an exhaust port 16 or a respective pressure connection 15, 17, the second valve being actuated by the first valve, associated with the booster is a non- return valve 41 in a line from a reservoir to the connection 15, the valve closing in a direction towards the reservoir. Movement of a pedal operated thrust member 8 actuates a piston 31 of the valve 10, via a resilient member 30, communicating a chamber 32 with the pressure connection 15, air passing to the chamber 20<SP>1</SP> via a passage 35, and to a chamber 34 via a passage 33 to operate a piston 19 of the valve 11 which allows air from the pressure connection 17 to flow to the chamber 24<SP>1</SP> via passages in a tubular sleeve 23. The pressure in chamber 24<SP>1</SP> is less than that in 20<SP>1</SP> due to a spring 191 acting on the valve piston 19 to aid the pressure force on the right-hand side in balancing the pressure on the left-hand side thereof. Thus, the power piston 20 provides the power to move the thrust rod 28 to a master cylinder. If pressure fails at the connection 15, a rod 40 operates the valve piston 19 to provide pressure in the chamber 24<SP>1</SP> to operate the piston 24, and if a failure occurs at the connection 17 air still flows to the chamber 20<SP>1</SP> for the actuation of the power piston 20. If a seal 42 on the piston 20 leaks, brake actuation is possible as soon as the valve piston 19 is moved, by means of the power piston 24, air flow past the seal 42 being stopped from passing to a first circuit connected to the connection 15 by meansof the non-return valve 41, as shown, two seals 47, 48, with an intermediate connection 49 to the exhaust port 16 separate the pressure inlet for the valve 11 from the chambers 34 and 32; if the seal 47 leaks during braking compressed air flows from the connection 15 to the exhaust port 16 so that the valve piston 19 is operated mechanically; if the seal 48 leaks, compressed air flows from the connection 17 to atmosphere, the first power piston 20 operating as usual. Alternatively, a single seal may be provided on the left-hand end of the piston 19, a non-return valve being inserted in the circuit associated with the connection 17 to avoid back flow of air from the chambers 32, 34 if the seal leaks.