GB576122A - Improvements in or relating to fluid pressure mechanism - Google Patents

Abstract

576,122. Brakes. BENDIX-WESTINGHOUSE AUTOMOTIVE AIR BRAKE CO. Jan. 20, 1942, No. 845. Convention date, March 26, 1941. [Class 103 (i)] A pressure reducing valve adapted to be disposed in the supply pipe of an actuator or actuators, for example the brake actuators of the front wheels of a vehicle or of a tractor vehicle comprises valves operated by a differential piston whereby the actuator pressure is less than but proportional to the varying supply pressure. The valve may also be set to give actuator pressure equal to the supply pressure and in one form it may give an actuator pressure equal to the supply pressure up to a predetermined value and a reduced but proportional pressure above that value. It may also act as a quick-release valve. In Fig. 1, front and rear brake actuators 10, 11 respectively are supplied from a compressed air reservoir 12 through a drivers self-lapping valve 20, the actuators 11 being directly supplied and the actuators 10 through a reducing and release valve device 22 comprising a differential piston 28 operating supply and release valves 43, 44. The annular chamber 32 is normally connected to atmosphere by a manually operated valve 38. Normally, the valve 44 is unseated as shown so that the actuators 10 are connected to atmosphere through the passage 26. In applying the brakes, pressure fluid at a pressure dependent upon the degree of depression of the pedal 21 of the valve 20 is supplied to the actuators 11 and through pipes 14, 15 to the upper chamber of the valve 22 thereby depressing the piston 28 to seat valve 44 and open valve 43 so that the fluid is supplied to the actuators 10 until the pressure therein and in chamber 31 acting on the lower larger piston area is sufficient with that of the springs 45, 46 to move the piston upwards against the supply pressure acting on the upper piston area thus seating the valve 43 without reopening the valve 44. A graduated application of the brakes and by reducing the pressure in the pipes 14, 18 a graduated release may be obtained. If it is desired to obtain equal pressures in the actuators 10, 11 the chamber 32 is connected by the valve 38 to the pipe 14 so that the piston areas, subject to the pressure in the actuators 10 and in pipe 14, are equal. Vibration of the valve parts during operation is prevented by a frictional damping device comprising a split ring 47 and in order that this device may not increase the slight inequality of the pressure set up in the actuators 10 relatively to that in the pipe 14 due to the return springs 45, 46 when the chamber 32 is connected to that pipe by the valve 38, a by-pass 49 with a non-return valve 50 is provided between the pipe 14 and the chamber 31 and actuators 10. A choke 52 ensures build-up of pressure in chamber 30 to effect closing of the exhaust valve 44 when a brake application is effected. In the modified valve shown in Fig. 2, a spring 74 acts on the piston 58 and with the annular chamber 57 connected to atmosphere by the valve 38 the piston 58 remains in the position shown with the supply and exhaust valves 71, 72 respectively unseated and seated during the initial stage of application so that the pressure set up in the actuators 10, connected by the pipe 16, is equal to that in the pipe 14 and actuators 11 until this pressure acting on the upper and lower areas of the piston overcomes the spring 74. At higher pressures the valve operates in a similar manner to that of the valve shown in Fig. 1 to set up a pressure in the actuators 10 which as regards the excess above that due to the spring 74 is less than but proportional to that in the actuators 11. If the chamber 57 is connected by the valve 38 to the pipe 14, the piston and valves 71, 72 remain in the position shown during an application so that the pressure in the actuators 10 equalises with that in the pipe 14 and actuators 11 but during release if the pressure reduction in pipe 14 is sufficiently rapid, the piston moves up closing valve 71 and opening valve 72 through which the actuators 10 exhaust until the pressure therein falls to a value which exceeds that in the pipe 14 by an amount corresponding to the pressure'of the spring 74, when the parts assume the lapped position. If equality of the pressure is desired, a by-pass 76 with a non-return valve 78 may be provided between the chambers 55, 56. The valves may also be provided in the connections of the tractor brake actuators of a tractor and trailer vehicle brake system.