Electrically operated hydraulic power lift system

摘要

A control system for a tractor hydraulical power lift system having an electrohydraulic actuator (22) coupled to a main hydraulic valve (21), comprising a feedback electronic control circuit including a circuit for mathematically combining a plurality of transducer generated signals into a command signal. The command signal comprises the output signal of a first differential summing device (32) receiving a first input signal for a control handle transducer (24) from which is substracted a second input signal produced as the output of a signal mixer that combines input signals from a rockshaft transducer (25), a draft selector transducer (26) and a draft load transducer (27). The command signal and a signal from a transducer (28) coupled to the electrohydraulic actuator are fed into a differential summing device (49) that has as its output an error signal representing the actual and desired positions of an implement to be positioned by the power lift system. The control circuit includes a sample-and-hold unit (51) adapted to receive the error signal. Clock logic transmits the error signal at predetermined times as determined by a sampling frequency clock (52) from the sample-and-hold unit (51) to the electrohydraulic actuator.