Abstract: A closed-loop height control for the header of a combine harvester permits adjustment of height setpoint and deadband from the operator's platform without stopping the combine. A variable capacitance is rotated in accordance with minimum clearance between header and ground to generate a continuous electrical header height signal which is compared to a setpoint signal indicative of desired header height to derive a height error signal whose value is at a null level when actual header height is equal to desired height indicated by the setpoint signal and which deviates in both magnitude and direction from the null level as a function of the variation between actual header height and setpoint height. Raise and lower command signals are derived in response to a predetermined deviation of the height error signal in opposite directions respectively from the null level by first and second Schmitt trigger circuits having switching levels which respectively are greater than and less than the null value.

Abstract: A hydraulic system is provided in which a single variable displacement pump supplies the hydraulic fluid requirements of both an open center hydraulic circuit and a closed center hydraulic circuit. The hydraulic output from the variable displacement pump is delivered to a pressure compensated flow divider which at all times delivers a priority minimum and constant flow to the open center hydraulic circuit despite variations in pump output pressures. Unless there is a demand for hydraulic flow by a device or devices in the closed center hydraulic circuit, there is no hydraulic flow delivery from the flow divider to the closed center hydraulic circuit, and the variable displacement pump operates at relatively low power input required to supply the demands of the open center hydraulic circuit.