Hydraulic control system with pressure responsive rate control

Claim 1

A hydraulic control system for applying hydraulic fluid flow to a double acting hydraulic actuator having a moveable element comprising a computer means, means for inputting signals to said computer means, said signals defining the desired rate and direction of movement of said moveable element, means for sensing a first hydraulic pressure on a first side of said double acting hydraulic actuator and sending a first signal to said computer means, means for sensing a second hydraulic pressure on a second side of said double acting hydraulic actuator and sending a second signal to said computer means, said second side being opposite said first side, reservoir means, pump means, valve means for controlling flow of said hydraulic fluid to or from each of said first and second sides of said hydraulic actuator and for selectively connecting said flow of said hydraulic fluid between said first or second sides and said pump means or between said first or second sides and said reservoir means, said computer means determining net force applied by said first and second pressures to said actuator based on said first and second pressures and the respective area of said actuator against which said first and second pressures are applied, said computer determining which of said flows between said first or said second sides and said pump means or said reservoir means must be controlled based on said net force applied by said first and second pressures to said double acting hydraulic actuator and said desired direction of movement of said moveable element thereby to select an orifice of said valve means to be controlled, said computer means adjusting said valve means to set said selected orifice to a required orifice area to obtain the required flow rate to obtain said desired rate and direction of movement when said flow is from said pump means to said actuator in accordance with a calculated pump pressure and when said flow is from said actuator in accordance with the one of said first and second pressures from the side of the actuator from which fluid is to flow to obtain the desired movement of said moveable element while compensating for the load on said actuator.