Four wheel steering vehicle with valve position retaining means

Abstract

A vehicle has at least two pairs of ground engaging wheels, which vehicle can alternatively be steered with two or four wheels, the vehicle comprising a chassis having first and second pairs of ground engaging wheels which are movable to effect steering of the vehicle, the wheels of each pair being mounted at opposite sides of the chassis and the second pair of wheels being lockable in a position such that simple steering is effected solely by the first pair of wheels, the first pair of wheels being movable to effect steering by a first fluid actuator to which fluid is fed from a steering valve, and the second pair of wheels being movable by a second fluid actuator to which fluid is fed via a steering mode selector valve from the steering valve means, the steering mode selector valve having a first operating condition when fluid from the steering valve is not fed to the second fluid actuator whereby simple steering is effected solely by the first pair of wheels and a second operating condition wherein fluid from the steering valve is fed to the second fluid actuator whereby compound steering is effected by the first and second pairs of wheels the first or second operating condition of the steering mode selector valve being retained until the steering mode selector valve receives a positive control signal to change the operating condition of the steering mode selector valve means so that the steering mode of the vehicle last selected i.e. two or four wheel steering, is remembered by the steering mode selector valve.