Vehicle with control system for raising and lowering implement

摘要

A tractor includes a hitch for pulling a ground-engaging implement. A hydraulic cylinder is extendable and retractable to lower and raise the implement. A control system senses operating parameters, including wheel slip, engine speed, draft force and implement or rackshaft position. Error signals derived from the sensed wheel slip, engine speed and draft force are combined into a composite or combined error signal. The larger of the combined error signal, or a separately determined position error signal, is selected and converted to a pulsewidth modulated valve control signal which is applied to a control valve which then actuates the cylinder to move the implement to reduce the magnitude of the selected error signal.