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

A hydraulic system in which fluid is drawn from a tank by a pump having a displacement that varies in response to pressure applied to a control port, wherein fluid flow produced at an outlet of the pump is controlled to operate a plurality of hydraulic functions, each hydraulic function has a hydraulic actuator and an open-center type control valve that controls flow of fluid from the outlet to the hydraulic actuator, said hydraulic system further comprising:

• a flow restriction through which fluid flows from the outlet of the pump into a supply conduit to which the plurality of hydraulic functions connect;
• a bypass node coupled to the control port for controlling displacement of the pump, wherein the open-center type control valves in the hydraulic functions have a variable open-center orifice connected in series forming a bypass passage between the bypass node and the tank;
• and
• a variable pressure compensated orifice providing fluid communication between the supply conduit and the bypass node, and limiting fluid flow through the bypass passage.

A method for controlling displacement of a pump in a hydraulic system that has a plurality of hydraulic functions, each hydraulic function includes a hydraulic actuator and an open-center type control valve that controls flow of fluid from a supply conduit to the hydraulic actuator, wherein the open-center type control valves in the hydraulic functions have variable open-center orifices connected in series to form a bypass passage between a bypass node and a tank, said method comprising:

• sending fluid from an outlet of the pump through a supply orifice to the supply conduit thereby producing a pressure drop across the supply orifice;
• in response to the pressure drop, varying a bypass orifice through which fluid flows from the outlet of the pump to the bypass node, wherein the bypass orifice decreases in size as fluid flow through the supply conduit increases;
• and
• applying pressure at the bypass node to a control the displacement of the pump.