Abstract: An apparatus is disclosed for controlling at least two driven wheels of a vehicle. The apparatus includes two hydraulic motors, each motor drivably connected to an associated drive wheel. A load sense piston pump provides a source of pressurized fluid for operating the hydraulic motors. Associated with each hydraulic motor is an electrically controllable load sense flow control valve assembly, an electrically controllable directional control valve, and a set of counterbalance valves. A microcomputer controls operation of the electrically controllable load sense flow control valve assemblies and the electrically controllable directional control valves in response to electrical signals indicative of rotary position of a steering wheel, position of an operator controlled speed and direction input device, and the speed of the vehicle engine. Steering ratio can be selected by the operator. Vehicle speed is controlled so as to prevent pump cavitation and engine stalling.

Abstract: A control apparatus for a power steering system comprises an electrically actuated flow control valve that varies the power assist available, a speed sensor for generating a signal indicative of vehicle speed, and a selector switch for selecting one of a plurality of power assist control options. The apparatus further includes a microprocessor that controls the electrically actuated flow control valve in response to the signal from the speed sensor and the setting of the selector switch. The apparatus also provides manually selectable power assist that is set by the operator and remains constant independent of variations in vehicle speed. A display provides a visual indication to the operator of the power assist available.