Four-wheel steering arrangement for motor vehicles

• US 5,088,573 A
• Filed: 05/09/1991
• Issued: 02/18/1992
• Est. Priority Date: 03/05/1988
• Status: Expired due to Fees

• Current Assignee: Dr. Ing. H.C.F. Porsche Ag
• Original Assignee: Dr. Ing. H.C.F. Porsche Ag
• Inventors: Moll, Patrick
• Primary Examiner(s): HILL, MITCHELL
• Application Number:
  US07/697,626
• Time in Patent Office: 285 Days
• Field of Search: 180/140, 280/91, 280/661, 280/673, 280/675, 280/95.1, 280/696, 280/701
• US Class Current: 180/415
• CPC Class Codes: B62D 7/146 characterised by comprising means for steering by acting on the suspension system, e.g. on the mountings of the suspension arms

Abstract

A four-wheel steering arrangement for motor vehicles is provided with a first steering device for the front wheels operated by a steering wheel and a second steering device for the rear wheels, which are held by wheel suspension links. The rear wheels are controlled by a hydraulic adjusting device and are adjusted at a variable wheel steering angle ratio with respect to the front wheels, as a function of determined driving condition quantities which are fed to an electronic control unit, particularly a vehicle computer. The steering device comprises a hydraulic control cylinder having a restoring device. This restoring device is connected by adjusting elements providing for the adjustment of the rear wheel steering angles so that they can be swivelled around an axis of rotation formed by support joints between the wheel carrier and the wheel suspension link for steering and are slowly returned to a non-steering position upon system failure.

Claims

1. A steering system for a motor vehicle having:

a first steering device for front wheels of the motor vehicle operatively arranged to be actuated by a steering wheel; and

a second steering device for rear wheels of the motor vehicle held by wheel suspension links, comprising (a) an integral semi-trailing arm device for each of the rear wheels linked to a body side of the motor vehicle by bearings to define a swivel axis of the semi-trailing arm device and configured to have two bearing arms rigidly secured with respect to each other and operatively arranged to hold wheel carriers of the rear wheels so that the rear wheels are pivotable about a vertical axis of rotation, (b) support joints arranged in planes one above the other and above and below a wheel axis of the rear wheels and operatively associated with the bearing arms for permitting pivoting of the rear wheels about the vertical axis, (c) a hydraulic control cylinder, (d) a restoring device operatively connected with the hydraulic control cylinder along a common axis, (e) bearing levers integral with the wheel carriers, (f) tie rods operatively connected between, on one hand, a respective one of the hydraulic control cylinder and the restoring device, and, on the other hand, to the bearing levers via a deflecting joint arranged in a swivel axis of the semi-trailing arm device, wherein the tie rods share the common axis of the hydraulic control cylinder and the restoring device, (g) a cross tube secured at the body of the motor vehicle for supporting the semi-trailing arm device via the bearings defining the swivel axis, and (h) an electronic control unit operatively connected with the hydraulic control cylinder for steering of the rear wheels in response to driving conditions fed to the electronic control unit independently of the front wheels.

2. The steering system according to claim 1, wherein the restoring device is a spring restoring device comprising a cylinder tube having end stops, slidable pressure disks supported at the end stops, an adjusting rod guided axially slidably in the cylinder tube, and exterior stop disks secured on the adjusting rod so as to hold the adjusting rod in an adjusted position.

3. The steering system according to claim 2, further comprising a pressure supply unit and a hydraulic pressure circuit having two shut off valves, a feeding pipe and a return pipe, and operatively connected between the pressure supply unit and the hydraulic control cylinder, wherein the spring restoring device is coupled in a throttleable manner to the hydraulic pressure circuit and the two shutoff valves are upstream of the hydraulic control cylinder, one of which shutoff valves is operatively arranged in the feeding pipe of the hydraulic pressure circuit and the other in which shutoff valves is operatively arranged in the return pipe of the hydraulic pressure circuit.

4. The steering system according to claim 3, wherein the shutoff valves are configured to provide an automatic and relatively slow restoration of the rear wheels to a center position.

5. The steering system according to claim 4, wherein a throttle valve is operatively connected between the two shutoff valves and the hydraulic control cylinder and actuatable in response to the electronic control unit, and is configured such that when the electronic control unit does not actuate the throttle valve, a spring force causes the throttle valve automatically to take up a throttling position and the two shutoff valves are moved into a shutoff position to permit the automatic and relatively slow restoration of the rear wheels to the center position.

6. A steering method for a motor vehicle comprising the steps of:

steering front wheels of the motor vehicle in response to actuation of a steering wheel;

steering rear wheels of the motor vehicle independently of the steering of the front wheels in response to determined driving conditions, wherein the steering of the rear wheels includes the steps of (a) supplying the determined driving conditions to an electronic control unit which is operatively connected with a hydraulic pressure circuit which, in turn, is operatively connected with a hydraulic control circuit, (b) varying a steering angle of the rear wheels via a semi-trailing arm device swivelable around an axis operatively associated with the hydraulic control cylinder via a restoring device and integrally configured with connected control arms to hold wheel carriers of the rear wheels so as to be pivotable with a large base about a vertical axis of rotation for varying the steering angle, and, in response to a failure of at least one of the electronic control unit and hydraulic pressure circuit, automatically and relatively slowly restoring the rear wheels to a straight ahead position.