Flow sensing based variable pump control in a hydraulic system with open centre control valves

摘要

A hydraulic system 30 has a variable displacement pump 60 that sends fluid from a tank 61 into a supply conduit 66 from which separate open-centre control valves 51 - 58 convey the fluid to each one of a plurality of hydraulic functions 31 - 38. The control valves 51 58 have open-centre orifices connected in series between a bypass node 90 and the tank 61, thereby forming a bypass passage 83. The pressure at the bypass node 90 controls displacement of the pump 60. A valve arrangement 87, 88, 89 is connected between an outlet 66 of the pump 60 and the bypass node 90 and is responsive to an amount of fluid flow through the supply conduit to the plurality of hydraulic functions 31 38. As the amount of fluid flow increases, the valve arrangement causes fluid flow to the bypass node to decrease. Thus the pressure at the bypass node varies as a function of the operation of the control valves.