Threshold current control system for hydraulic valves

Abstract

A system or method for controlling the position of an implement coupled to a work vehicle. The implement is moveable by a hydraulic positioning assembly including an actuator and a valve assembly which control the flow of fluid to the actuator in response to control signals. The valve assembly includes raise and lower valves, each valve requiring a control signal equal to a threshold value before the valve opens and fluid begins to flow. The system includes a sensor to detect the position of the implement and a control circuit. In response to a change in a position command, the control circuit applies a control signal to the appropriate raise or lower valve based upon the respective threshold value. The control signal may include a component for moving the implement at a desired rate of movement. After undesirable implement movement is detected, the control circuit modifies the threshold value. The modification may occur when the control circuit detects that the implement is moving at an excessive rate due to the effects of valve hysteresis and implement weight. The control circuit may detect the undesirable movement by determining that the position error value is more negative than a predetermined value. The modified threshold value then replaces the threshold value for subsequent implement movement. The new threshold value prevents the undesirable movement in subsequent implement movement.