Dual steering system for off-highway vehicles

Abstract

A dual vehicular steering system with a primary system for normal operation and a secondary system for emergency operation triggered by pressure sensitive switching and valving means. Both systems have in common a pair of single rod hydraulic steering cylinders with each cylinder being connected to a steerable wheel of the vehicle, a vehicular engine and hydraulic fluid stored in a tank. Cylinder shuttle valves connected to each steering cylinder function as gate devices to separate the primary steering system from the secondary system. The primary system includes a main pump driven by the engine, a high pressure filter, a priority flow divider to divert fluid in excess of an acceptable flow level, a control valve, an integrated valve package to proportionately regulate fluid flow between the cylinders, and means to direct fluid from the tank to the pump, through the filter, through the priority flow divider, through the control valve, through the integrated valve package and to the steering cylinders. The secondary system includes a secondary pump, an electric motor driven by the battery to drive the secondary pump, and means to conduct fluid from the secondary pump, through the switching and valving means and to the steering cylinders. The secondary system also includes an accumulator, pressure sensitive switching and valving means to conduct fluid from the secondary pump to the accumulator, and means to conduct fluid from the accumulator to the steering cylinders. Steering in the secondary system is accomplished by applying equal pressure to both ends of each steering cylinder thereby locking the cylinders in a single mode and by selectively draining fluid from selected ends of the steering cylinders. Operator controlled secondary steering switch and valve means operate the selective drain means.