Velocity based method of controlling an electrohydraulic proportional control valve

A method for controlling a hydraulic actuator that has a first port and a second port wherein the hydraulic actuator is part of a circuit branch that includes a first electrohydraulic proportional valve coupling the first port to a supply line containing pressurized fluid and a second electrohydraulic proportional valve coupling the second port to a return line connected to a tank, said method comprising:

• requesting a desired velocity for the hydraulic actuator;
• sensing a parameter which varies with changes of a force acting on the hydraulic actuator;
• employing the desired velocity and the parameter to derive a first value for a first valve flow coefficient which characterizes fluid flow through the first electrohydraulic proportional valve, and to derive a second value for a second valve flow coefficient which characterizes fluid flow through the second electrohydraulic proportional valve;
• in response to the first value for the first valve flow coefficient, producing a first valve activation signal representing an amount that the first electrohydraulic proportional valve is to open;
• in response to the second value for the second valve flow coefficient, producing a second valve activation signal representing an amount that the second electrohydraulic proportional valve is to open;
• activating the first electrohydraulic proportional valve based on the first valve activation signal;
• and
• activating the second electrohydraulic proportional valve based on the second valve activation signal.

A method for controlling fluid flow in a circuit branch which has a hydraulic actuator with a first port to which a first electrohydraulic proportional valve is connected and a second port to which a second electrohydraulic proportional valve is connected, said method comprising:

• requesting a desired velocity for the hydraulic actuator;
• producing an indication of how much force is acting on the hydraulic actuator;
• employing the desired velocity and the indication to derive a first value for a first valve flow coefficient which characterizes fluid flow through the first electrohydraulic proportional valve, and a second value for a second valve flow coefficient which characterizes fluid flow through the second electrohydraulic proportional valve;
• in response to the first value for the first valve flow coefficient, producing a first valve activation signal representing an amount that the first electrohydraulic proportional valve is to open;
• in response to the second value for the second valve flow coefficient, producing a second valve activation signal representing an amount that the second electrohydraulic proportional valve is to open;
• activating the first electrohydraulic proportional valve based on the first value for the first valve activation signal;
• and
• activating the second electrohydraulic proportional valve based on the second value for the second valve activation signal.

In a hydraulic system having a circuit branch in which a first electrohydraulic proportional valve couples a first port of a hydraulic actuator to a supply line containing pressurized fluid, and a second electrohydraulic proportional valve couples a second port of the hydraulic actuator to the supply line, a third electrohydraulic proportional valve couples the first port to a return line connected to a tank, and a fourth electrohydraulic proportional valve couples the second port to the return line, a method for controlling the hydraulic actuator comprising:

• designating a direction in which the hydraulic actuator is to move;
• designating a commanded speed at which the hydraulic actuator is to move;
• selecting a pair of the first, second, third and fourth electrohydraulic proportional valves to be operated to produce movement of the hydraulic actuator in the direction that is designated;
• sensing pressure in the supply line to produce a supply pressure measurement;
• sensing pressure in the return line to produce a return pressure measurement;
• sensing pressure at the first port to produce a first port pressure measurement;
• sensing pressure at the second port to produce a second port pressure measurement;
• deriving an equivalent flow coefficient, Keq, characterizing fluid flow in the hydraulic circuit branch, wherein the equivalent flow coefficient is based on the commanded speed and selected ones of the supply pressure measurement, the return pressure measurement, the first port pressure measurement and the second port pressure measurement;
• deriving valve flow coefficients for the pair of the first, second, third, and fourth electrohydraulic proportional valves based on the equivalent flow coefficient;
• and
• activating the pair of the first, second, third and fourth electrohydraulic proportional valves in response to the valve flow coefficients to move the hydraulic actuator in the direction that is designated.