Patent GB-797035-A (GB)
Title: Combination master cylinder and power valve
IPC: B60T13/16
Filed: 1956-07-30
Abstract: 797,035. Fluid-pressure brakes. BENDIX AVIATION CORPORATION. July 30, 1956 [Aug. 15, 1955], No. 23494/56. Class 103 (1). In a combination power valve and master cylinder unit that functions as a power valve as long as power fluid is available at a useful pressure and automatically functions as a pump when the pressure of the power fluid is less than that it is desired to deliver, the pedal reaction rises at a greatly increased rate during power operation when the delivered pressure exceeds a predetermined value to limit the maximum value of the delivered pressure. In the embodiment illustrated, the unit comprises a master cylinder 11 containing a master piston 12 adapted to be moved into cylinder 11 by an actuating lever 13 fulcrumed to body 10 at 14; a reaction piston 20 being provided between the master cylinder chamber 11 and a reaction chamber 16 having a working port 17 and line 18 leading to the wheel brake cylinders. Fluid pressure is supplied by pump 27 to the pressure port 26 past check valve 28 into pressure chamber 32 and when this pressure exceeds the highest desired pressure required for full power operation in the working port 17, stop 65 is extended against the force of spring 68 by the pressure in chamber 67 to limit movement of the master piston 12 by the adjusting lever 13 and poppet valve 57 is opened to permit free communication of the fluid between the master cylinder 11 and the return port 29 and move lever 13 in an anti-clockwise direction to advance master piston 12 which is opposed only by springs 23 and 15. A slight initial movement of the master piston 12 compresses piston-ring 23 to a point where its force exceeds that of spring 22 such that the reaction piston 20 is advanced to close passage 41 against poppet valve 40 to disconnect the return port 29 from the reaction chamber 16 and then move valve 36 off its seat to admit pressure fluid from the chamber 32 into reaction chamber and thence in working port 17 and line 18 to the wheel brake cylinders. The increase in pressure in the reaction chamber 16 as the pressure rises in the port 17 produces a reaction force opposing pedal movement which is proportional to the pressure being delivered through port 17. Output pressure may rise to 400 lbs. per square inch during movement of the master cylinder piston to engagement with the very stiff spring 24 and thereafter rise to 900 lbs. per square inch (maximum) with a very slight additional movement - prior to engagement of arm 13a with stop 65. Should the power pressure be too low to be of any appreciable value, poppet valve 57 is closed by a spring 63 so that escape of fluid from master cylinder 11 to return port 29 is prevented; the master cylinder performing its natural function such that advance of the piston 12 into the master cylinder displaces fluid therefrom through a passage 75, past check valve 76 directly to working port 17 and the reaction piston 20 also moves with the piston 12 to close poppet valve 40 on to its seat and prevent escape of fluid from the reaction chamber 16 to the return port 29. The power poppet valve 36 is also opened but fluid cannot escape through the power port 26 because of the check valve 28 in the power supply line. Repeated strokes of the master cylinder may be necessary to provide sufficient pressure to the wheel brake cylinders; fresh fluid from the reservoir 30 being drawn into the master cylinder via return port 29 past check valve 46. A modification is described and illustrated in the Specification wherein the stop 65 is replaced by a relief valve for limiting the pressure that can be produced in the working port.