Valve control system for hitch motor

A system for the control of a fluid flow control valve which controls the supply of fluid to an actuator to control the movement of a component in response to a selected parameter, the system comprising:

• means for setting a desired value of the selected parameter,
• means for sensing the actual value of the selected parameter,
• first comparator means for comparing the desired and actual values of the selected parameter to provide a parameter error signal,
• control means for supplying a control signal to the valve dependent on the error signal to move the component so as to tend to reduce the error signal to zero,
• means for providing a signal indicating that the component has begun to move in response to the imposition of a given valve control signal, and
• a start-up control function which on detection of a parameter error signal applies a start-up signal to the valve to initiate movement of the component and, if no movement results, increases the start-up signal until movement of the component is detected whereupon the increase in the start-up signal is stopped and the magnitude of the signal applied to the valve is dependent on the error signal so as to tend to reduce the error signal to zero.