Husco International, Inc.

Robert Jonathan Valenta

Mark J Jervis

Lynn A Russell

Paul Edward Pomeroy

Sean M Haggerty

A hydraulic system has a variable displacement pump that sends fluid from a tank into a supply conduit from which separate open-center control valves convey the fluid to each one of a plurality of hydraulic actuators. The control valves have open-center orifices connected in series between a bypass node and the tank, thereby forming a bypass passage. Pressure at the bypass node controls displacement of the pump. A valve arrangement is connected between an outlet of the pump and the bypass node and is responsive to an amount of fluid flow through the supply conduit to the plurality of hydraulic functions, wherein 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.

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

A member that is driven by a hydraulic actuator tends oscillate when fluid flow to the hydraulic actuator is terminated. A pressure relief device reduces that oscillation by connecting first and second first relief valves to the hydraulic actuator. The first relief valve provides a relatively large first relief passage as long as pressure in the hydraulic actuator remains above a threshold. A second relief valve opens a second relief passage at substantially the same threshold pressure and thereafter remains open as long as the pressure remains above another lower threshold. A timer causes the second relief valve to close a given interval of time, if the pressure does not drop below the other lower threshold.

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Altrincham, United Kingdom

Robert Jonathan Valenta