Vehicle steering system

Details

Inventors: Wright, Peter G.; Williams, David A.;
Assignee: Group Lotus PLC (Norwich, GB2)
Primary Examiner: Pekar; John A.
Assistant Examiner:
Attorney, Agent or Firm: Young & Thompson

A road vehicle has steerable front and rear wheels, the rear wheels being steered by an electro-hydraulic system responsive to the manual control input to the front wheels. The hydraulic actuator of the system is biased to the straight-ahead steering position by springs, so that the rear wheels are centered in the event of electric or hydraulic failure, and an hydraulically restrained latch element is spring biased to then latch the actuator piston in its centered position.

DETAILED DESCRIPTION The invention provides a steering system for a vehicle, the system being adapted to assume a straight ahead wheel orientation in the event of system failure.
The system can thus include biassing means permanently opposing changes of the condition of the steering system from a straight ahead condition.
In the event of any failure in the control or operation of the system, the biassing means urge the system to its central position.
A vehicle with front and rear wheel steering which incorporates the system for the rear wheels could then still be steered, by means of the front wheels only, by way of the conventional direct or power assisted control normally provided.
The invention thus also provides a rear wheel steering system for a vehicle with front and rear wheel steering, the system comprising means responsive to failure of control or operation to lock the system in the central steering position thereof.
The steering orientation of the rear wheels is then unaffected by for example road conditions, so that steering by way of the front wheels can be affected wholly as for a conventional vehicle.
The invention can conveniently be embodied as a rear wheel steering system having a double acting hydraulic output device which operates against a centering spring or springs and of which the two interiors of the devices on opposite sides of the piston are arranged to be put in communication with each other, as through a normally closed by-pass valve, in the event of a system failure.
The by-pass valve is preferably held open hydraulically, the hydraulic pressure being applied through a solenoid valve held open during normal system operation.
The system is then quickly centred on either a hydraulic or an electric failure.
The hydraulic output device can also incorporate a latch element biased to engage the piston either directly or by means of a series of balls so as to lock the piston in a position corresponding to straight-ahead rear wheel orientation, the latch element being held from such engagement during normal operation of the system, as by hydraulic pressure

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