Abstract: An electro-hydraulic proportional actuator in which the actuator piston position is hydraulically controlled by fluid flow through solenoid valves operable by an electronic control system. An operator control provides an input voltage representing a desired piston position and a transducer generates a voltage representing the actual piston position. The difference between the input and output voltages generates a difference or error signal that is fed into a feedback system including a sample-and-hold circuit. A clock logic system is provided for transmitting the signal from the feedback system to the solenoid valves at predetermined intervals to activate either valve to move the actuator piston in either direction or to activate both valves to hold the piston at a desired position.

Abstract: In combination, a tractor having at its rear end an implement hitch and a lift system and an implement coupled at one end to the hitch and having at its other end a height adjusting system for controlling the working depth of the implement. The lift includes a first hydraulic cylinder and the height adjusting system includes a second or remote hydraulic cylinder. The tractor has a pump providing a source of fluid under pressure. An auxiliary services valve is in communication with the fluid source and a phasing valve, the two valves being selectively in communication with one another.The auxiliary services valve is operable to independently actuate the first hydraulic cylinder to raise the hitch or to coact with the phasing valve to serially couple the second hydraulic cylinder to the first hydraulic cylinder to provide synchronous actuation of both cylinders to raise both ends of the implement to a fully raised position.

Abstract: An application of the basic system of patent application Ser. No. 149,065 for operating a remote hydraulic valve. An electro-hydraulic actuator is mechanically linked to the control member of the remote valve. An input control signal is generated by multiplying a signal from a control handle position transducer by a scale factor constant produced by a full control setting with a gain control circuit. The gain control circuit also operates to set the constant to unity in case the signal from the handle position transducer exceeds a predetermined level corresponding to a maximum control handle setting.The control handle itself has four positions: Float, Lower, Neutral and Raise. The handle is biased so that if the handle is released from any position other than Neutral, the handle will go to the Neutral position provided a detent is off. The detent is put in the "off" position by an electrical solenoid which is actuated whenever the supply pressure to the remote valve exceeds a set value.

Abstract: 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.