GB1333540A - Variable displacement pumps - Google Patents

Abstract

1333540 Reciprocating pumps CATERPILLAR TRACTOR CO 14 June 1972 [28 June 1971] 27894/72 Heading F1A [Also in Division G3] The swash-plate inclination of a variable-displacement, axial-piston pump is controlled by cartridge assemblies 46, 70 detachably mounted in the pump housing and interchangeable to reverse the direction of flow of the pump, assembly 46 including a spring 40 for biasing the swash-plate 32 into its maximum displacement position shown, and assembly 70 including a piston responsive to a pilot pressure to bias the swash-plate into its minimum displacement position. For reversing the flow direction, housing end 16 is removed and the cartridge assemblies and stops 52, 84 interchanged. In operation, e.g. for operating a plurality of implements in a backless hydraulic circuit, the driving engine is started with the swash-plate at maximum inclination. If all the implement valves are closed, a pilot pressure is applied to a valve (54), Fig. 1 (not shown), which connects the pump output pressure via pipe 60 to chamber 68 of piston 80 to reduce the swash-plate inclination to a minimum. When an implement control valve is opened, the pilot-operated valve (54) connects both pipe 60 and pipe 62 to output pressure, which acts via pipe 62, groove 86 and passages in assembly 46 on a piston 48 in chamber 116, Fig.3, to move the swash-plate into maximum inclination. When a predetermined output pressure is reached, piston 122 is moved upwardly against spring 124 to supply a predetermined proportion of the output pressure to a servovalve spool 102, Fig.3, in assembly 46, which moves upwardly against a spring 158 to connect chamber 116 to tank (the pump housing interior) via passage 172. The swash-plate inclination is then reduced by piston 80, thereby moving servovalve sleeve 44 to provide a follow-up action. When a further predetermined pressure is reached, valve 106 opens and directs output pressure to move the servovalve spool and sleeve upwardly for rapid movement of the swash-plate into minimum inclination. In Fig. 5 (not shown), an underspeed valve provides an external pressure source for actuating the servovalve assembly. In Fig.6 (not shown), the servovalve assembly is connected by a rod to a spring-loaded piston connected to groove 128 receiving the controlled proportion of output pressure. Alternatively, the groove connection and rod connection may be replaced by a connection from an external pressure source to the servovalve connection (204).