GB883129A - Hydraulic transmission - Google Patents

Abstract

883,129. Hydraulic transmission of power. NEW YORK AIR BRAKE CO. Sept. 16. 1960 [Oct. 15, 1959], No. 31926/60. Class 69 (2). An hydraulic transmission comprises a reversible, variable displacement pump 1 having a pair of ports 2, 3 connected by conduits 7, 8 to the ports 5, 6 of a motor 4, a reservoir 12 connected to a replenishment pump 11, in turn, connected by check valves 17, 19 to the conduits 7, 8, and a shuttle valve 22 operable in response to the pressure differential between the conduits 7, 8 to connect whichever of the conduits is at the higher pressure to the inlet port 43 of a high-pressure relief valve 42 and simultaneously to connect the conduit at the lower pressure with both the exhaust port 48, 49 of the high-pressure relief valve and the inlet port of a low-pressure relief valve 21 having an exhaust port connected to the reservoir. The conduits 7, 8 leading from the pump 1, which may be of the rotating barrel, reciprocating piston type, to the motor 4 are connected by conduits 25, 26 to ports 23, 24, 27, 28 in the valve 22 which has a shuttle piston 32 urged to a central position by springs 35, 36. Other ports 44, 45 in the valve are connected to the inlet port 43 of the highpressure relief valve 42 which contains a metering orifice 53 in a pilot piston 54 and a spring-loaded member 52 controlling an exhaust port 49 connected to a port 29 in the valve leading to the low-pressure relief valve 21 joined by conduits 37, 38 and a passage in the motor 4 to a cooler 39, filter 41 and the reservoir 12. The reservoir is connected by conduits 13, 14 and a passage in the pump 1 to the replenishment pump 11; the passages in the pump and motor assist in the cooling thereof. The direction of fluid flow from the pump 1 may be controlled by a reversing valve, by reversing the direction of rotation of the driving shaft of the pump, or by movement of a control linkage 9 connected to the cam-plate of the pump. Assuming the pump discharge is supplied to the conduit 7, the pressure at port 27 of the valve 22 moves the shuttle piston 32 to the right so that conduit 7, which is at the higher pressure, is connected by conduit 25 and ports 27, 44 to the inlet port 43 of the high-pressure relief valve 42, and the low-pressure conduit 8 is connected by conduit 26 and the ports 24, 29 to the low-pressure relief valve 21 and to the exhaust ports 48, 49 of the high-pressure relief valve. The liquid supplied by the replenishment pump 11 is in excess of that lost by leakage, and the excess liquid ensures that a continuous flow passes through the low-pressure relief valve to the cooler and reservoir. Excess pressure in the high-pressure conduit 7 causes a pressure differential across the orifice 53 which displaces a pilot piston 54 and valve head 52 to pass excess liquid through the ports 48, 49 to the port 29 of the valve 22 which is connected to the low-pressure relief valve and by port 24 and conduit 26, to the low-pressure conduit 8. The connections of the conduits 7, 8 to the valve 22 are reversed when the discharge from the pump 1 is reversed.