Patent GB-736373-A (GB)
Title: Improvements in or relating to hydraulic power system
IPC: F16H61/44
Filed: 1953-05-14
Abstract: 736,373. Rotary pumps and engines. BORGWARNER CORPORATION. May 14, 1953 [May 24, 1952], No. 13511/53. Class 110 (2). [Also in Group XXIX] A hydraulic power supply system comprises at least one pump which is provided with means for applying its output pressure to its axially movable seal bushings and is drivingly coupled to an auxiliary pump, spring means urging control valve means toward an open position to relieve the pressure acting on said bushings and conduit means for applying the output pressure of said auxiliary pump to a portion of said control valve means and in opposition to said spring means so as to urge said valve means toward the closed position, thereby allowing a build-up of pressure on said bushings. The system, Fig. 1, comprises two different capacity gear pumps P<SP>1</SP>, p<SP>2</SP> for driving at least one motor M coupled to the drive wheels of a vehicle. The capacity of the pumps P<SP>1</SP>, P<SP>2</SP> are controlled by a pilot pump P<SP>3</SP>  which is drivingly associated with the pumps p<SP>1</SP>, p<SP>2</SP> and controls means A which in turn controls the supply of pressure fluid to the bushings of the pumps P<SP>1</SP>, P<SP>2</SP>. The control means A comprises a spring-loaded valve 75 and a differential biasing mechanism 78. The spool 76 of the valve 75 is normally urged to the left to cause a shift to a lower speed ratio by lowering the capacity of the pump unit P and the mechanism 78 urges the spool 76 towards the right in accordance with the speed of rotation of the pump P<SP>3</SP> in order to cause a shift to a higher speed ratio by increasing the capacity of the pump unit P. The arrangement is such that as the speed of the pump P<SP>3</SP>  increases it first loads the bushings of the pump p<SP>1</SP> then loads the bushings of the pump P<SP>2</SP>  only and finally loads both sets of bushings, thereby providing a differential speed ratio between the motor M and the pump unit P. The output of the pump P3 is fed back to the sump when the bushings of the pumps P<SP>1</SP>, P<SP>2</SP>  are loaded, the bushings of at least one of the pumps being unloaded by a torque sensitive device T which overrides the means A when the motor M encounters an unusual load &c. With the control means A in the position shown, the bushings are connected by passages 90, 91, 94 and 95 to the sump and the pumps P<SP>1</SP>, P2 are unloaded. The mechanism 78 comprises a flexible diaphragm 99 responsive to the pressure across the pump P<SP>3</SP> through conduits 107, 108 as shown. The conduits 107, 108 are interconnected through a restriction orifice 110 and are connected to the inlet pipe 71 of the pump P<SP>3</SP> by way of conduits 114 and 109 respectively, the conduit 114 incorporating a pressure relief valve 115. The outlet of the pumps P1, P2 is fed to the motor M through passages 60, 61, check valves 64, 65, to manifold 62 and a fourway selector valve 122. The valve 122 comprises a housing 124 which communicates with the sump through ports 140, 141 and has a central port 134 communicating with the manifold 62 ; the spool 126 of the valve 122 having an interconnecting bore 142 as shown. A pressure relief valve R is disposed between the manifold 62 and the conduit 71. The device T comprises a plunger 157 which is responsive to the pressure within the manifold 62 and is adapted to compress the spring 77 of the valve 75. A choke valve 164 is arranged in the circuit as shown for preventing free wheeling of the motor M. In a modification, Fig. 6, the pump unit P<SP>1</SP> comprises two different capacity gear pumps 181, 182 arranged in parallel. Low torque starting means S are provided to unload the bushings of the pump 18 until a predetermined speed has been reached. Pressure unloading means U are provided for overriding the means S when a predetermined pressure has been reached in the outlet manifold 210. Check valves 214, 224 are disposed in the outlet conduits of the pumps 181, 182 respectively, and a maximum pressure relief valve R<SP>1</SP> is disposed in the outlet manifold 210. A restriction orifice 276 is disposed between the outlet port 212 of the pump 182 and the check valve 224; the outlet port 212 being connected by a conduit 277 to the member S. The arrangement is such that on starting the pump unit P<SP>1</SP> the pressure in the port 212 is at a low value so that the valve 259 of the member S is in the position shown whereby the bushings of the pump 181 are unloaded through passages 242, 272, 274 and 244. As the speed of the pump 182 increases the valve 259 is depressed, thereby allowing the pump 181 to load its bushings. The pump units may be directly driven by or geared to an internal combustion engine or an electric motor. Specification 572,967 is referred to.