Working depth control system for vehicle with ground working implement.

摘要

A tractor (10) includes a hitch (26) for pulling a ground-working implement. A hydraulic cylinder (34) is extensible and retractable to lower and raise the implement. A control system (50) senses operating parameters, including wheel slip, engine speed, draft force and implement or rockshaft position. Error signals are derived from the sensed wheel slip, engine speed and draft force and correspond set point signals. The error signals are combined into a composite or combined error signal. The larger of (a) the combined error signal and (b) a separately determined position error signal, is selected and converted to a pulsewidth modulated valve control signal which is applied to a control valve (42) which then actuates the cylinder to move the implement to reduce the magnitude of the selected error signal. Certain set point signals are derived from the corresponding parameter signals themselves.