All-wheel steering for motor vehicles

• US 5,168,948 A
• Filed: 04/12/1991
• Issued: 12/08/1992
• Est. Priority Date: 09/07/1988
• Status: Expired due to Fees

• Current Assignee: Daimler Chrysler Company LLC (Stellantis NV)
• Original Assignee: Mercedes-Benz AG (Mercedes-Benz Group AG)
• Inventors: Worner, Gunter, Rohringer, Arno
• Primary Examiner(s): HILL, MITCHELL
• Application Number:
  US07/684,158
• Time in Patent Office: 606 Days
• Field of Search: 180/140, 280/91
• US Class Current: 180/414
• CPC Class Codes: B62D 7/148 provided with safety devices
• CPC Class Codes: B62D 7/1518 comprising a mechanical interconnecting system between the steering control means of the different axles

Abstract

A rear wheel steering is operated by a mechanical gear, which is connected on an input side to a front wheel steering. The gear has a controllable transmission ratio, a control element controlling the transmission being adjusted against spring force by a self locking free positioning motor. In the event of failure of a control unit operating the positioning motor as a function of the travelling speed, a maximum transmission ratio for deflection in the same direction of the front wheels and rear wheels is set by spring force.

Claims

1. An all wheel steering system for a motor vehicle having front and rear wheels, manually operated front steering means, and rear wheel steering means, the system comprising:

transmission means for positively coupling said front wheel steering means to said rear wheel steering means, said transmission means having a transmission ratio which is infinitely variable over a range of values between a maximum positive ratio and a maximum negative ratio;

non-self-locking control means for adjusting said variable transmission ratio in response to speed of said vehicle, said transmission ratio being adjusted to said maximum positive ratio when said speed exceeds a first predetermined speed, and to said maximum negative ratio when said speed is less than a second predetermined speed which is less than said first predetermined speed;

means for detecting a malfunction of said non-self-locking control means, and for adjusting said transmission ratio to said maximum positive ratio in response thereto.

2. An all wheel steering system for a motor vehicle having front and rear wheels, manually operated front wheel steering means, and rear wheel steering means, the system comprising:

transmission means for positively coupling the front wheel steering means to the rear wheel steering means, said transmission means having a transmission ratio which is infinitely variable over a range of values between a maximum positive ratio and a maximum negative ratio;

said transmission means including non-self-locking piston means for adjusting said transmission ratio in response to position of said piston means, said piston means having a first end position wherein said transmission ratio is adjusted to said maximum positive ratio, a second end position wherein said transmission ratio is adjusted to said maximum negative ratio, and intermediate positions wherein said transmission-ratio is adjusted to a ratio that is between said maximum positive ratio and said maximum negative ratio;

spring means for biasing said piston means toward said first end position;

control means, responsive to speed of said motor vehicle, for moving said piston means to said first end position when said speed exceeds a first predetermined value, to said second end position when said speed is less than a second predetermined value which is less than said first predetermined value, and to intermediate positions when said speed is between said first and second predetermined values;

said control means having an inoperative state in which said piston means is freely displaceable by said spring means; and

error detecting means for placing said control means in said inoperative state when a malfunction of the control means is detected, thereby enabling the spring means to move said piston means into said first end position.

3. An all wheel steering system according to claim 2, further comprising force limiting means for limiting an input force applied to the transmission means.

4. An all wheel steering system according to claim 2, further comprising force limiting means for limiting force transmitted between the front wheel steering means and the transmission means, the force limiting means including a pretensioned spring unit.

5. An all wheel steering system according to claim 2, further comprising means for resiliently actuating the rear wheel steering means into a straight ahead position.

6. An all wheel steering system according to claim 2, further comprising servomotor means for controlling the rear wheel steering means coupled to an output side of the transmission means.

7. An all wheel steering system according to claim 2, wherein said piston means comprises at least one of a hydraulic piston-cylinder unit for controlling the transmission ratio of the gear means.

8. An all wheel steering system according to claim 2, further comprising interlocking means for holding said piston means in said first end position thereof, said interlocking means being released from said first position by a force of the piston means counteracting said spring means.