Abstract: A vehicle is operable in either one of two modes to control the turning of steerable vehicle wheels. During operation of the vehicle in a manual steering mode, the steerable vehicle wheels are turned in response to rotation of a steering wheel. During operation of the vehicle in an automatic steering mode, the steerable vehicle wheels are turned to maintain a predetermined relationship between the vehicle and a reference during movement of the vehicle relative to the reference. Upon initiation of operation of the vehicle in either of the two steering modes, a valve assembly is operated from an initial condition to either one of two actuated conditions to effect turning movement of the steerable vehicle wheels toward either the left or the right. During the manual steering mode, the valve assembly is operated in response to rotation of the vehicle steering wheel.

Abstract: A system for controlling a steering motor for turning a steerable vehicle wheel. The system includes a shaft which is angularly rotatable about its longitudinal axis. The system includes a plurality of sensors. Each of the plurality of sensors provides a signal. The signal of each of the plurality of sensors is indicative of the rotational position of the shaft for different portions of a revolution of the shaft. At least one signal is indicative of the rotational position of the shaft for each rotational position of the shaft. The signal of each of the plurality of sensors being non-indicative of the rotational position of the shaft for different and non-overlapping portions of the revolution of the shaft. A control means receives the signals indicative of the rotational position of the shaft. The control means operates the steering motor alternately in response to first and second signals provided by the sensors.

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.