Hydraulic system control method using a differential pressure compensated flow coefficient

An apparatus for operating an electrohydraulic valve that controls flow of fluid to operate a hydraulic actuator, said apparatus comprising:

• a component which produces a desired valve flow coefficient that specifies one of conductivity or resistivity of the electrohydraulic valve;
• a sensor arrangement from which a differential pressure value is produced that indicates a pressure difference across the electrohydraulic valve;
• a signal converter connected to the component and the sensor arrangement, and producing a compensation value in response to the desired valve flow coefficient and the differential pressure value, summing the compensation value with the desired valve flow coefficient to produce a compensated valve flow coefficient, which is compensated for effects that variation of differential pressure has on the flow of fluid, and employing the compensated valve flow coefficient to produce a valve control signal;
• and
• a valve driver which activates the electrohydraulic valve in response to the valve control signal.

A method of operating an electrohydraulic valve that controls flow of fluid to operate a hydraulic actuator, said method comprising:

• characterizing performance of the electrohydraulic valve by producing characterization data that specify how a valve flow coefficient, which specifies one of conductivity or resistivity of the electrohydraulic valve, varies with changes in differential pressure across the electrohydraulic valve;
• specifying desired movement of the hydraulic actuator;
• in response to the desired movement, deriving a desired value for the valve flow coefficient;
• sensing a differential pressure across the electrohydraulic valve;
• producing a compensation value from the desired value for the valve flow coefficient, the differential pressure, and the characterization data;
• summing the compensation value with the desired value for the valve flow coefficient to produce a compensated control signal that is compensated for effects that changes in differential pressure have on flow of fluid through the electrohydraulic valve;
• and
• activating the electrohydraulic valve in response to the compensated control signal.

An apparatus for operating an electrohydraulic valve that controls flow of fluid to operate a hydraulic actuator, said apparatus comprising:

• a device which produces a motion signal designating a desired movement of the hydraulic actuator;
• a component that responds to the motion signal by producing a desired valve flow coefficient that specifies one of a desired conductivity and or a desired resistivity of the electrohydraulic valve;
• a sensor arrangement from which a differential pressure value is produced indicating a fluid pressure difference across the electrohydraulic valve;
• a compensation function which produces a compensation value in response to the desired valve flow coefficient and the differential pressure value;
• a signal processing element which combines the compensation value with the desired valve flow coefficient to produce a compensated valve flow coefficient;
• a transfer function which converts the compensated valve flow coefficient into an electric current setpoint;
• and
• a valve driver which activates the electrohydraulic valve in response to the electric current setpoint.