Wheeled vehicle steering system for steering the rear wheels of a vehicle

• US 5,734,570 A
• Filed: 06/26/1996
• Issued: 03/31/1998
• Est. Priority Date: 08/04/1992
• Status: Expired due to Term

• Current Assignee: Lotus Cars Limited (Zhejiang Geely Holding Group Co., Ltd.)
• Original Assignee: Lotus Cars Limited (Zhejiang Geely Holding Group Co., Ltd.)
• Inventors: Arlandis, Thierry Hubert
• Primary Examiner(s): Louis-Jacques, Jacques
• Application Number:
  US08/669,850
• Time in Patent Office: 643 Days
• Field of Search: 364/424.05, 364/424.01, 364/425.01, 364/426.03, 364/565, 364/571.01, 364/424.051, 364/424.052, 364/424.053, 364/424.045 , 364/423.098, 395/905, 180/197, 180/412, 180/446, 180/410, 180/415, 180/407, 180/41, 180/421, 180/422, 280/707, 280/840, 280/772, 280/91.1, 477/108, 477/903, 303/147, 303/146
• US Class Current: 701/42
• CPC Class Codes: B62D 6/00 Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits means for initiating a change in direction B62D1/00; steering valves B62D5/06; combined with means for inclining the vehicle body or wheels on bends B62D9/00
• CPC Class Codes: B62D 7/159 characterised by computing methods or stabilisation processes or systems, e.g. responding to yaw rate, lateral wind, load, road condition

Abstract

The present invention relates to a steering system for the rear wheels (13,14) of a vehicle comprising an actuator (18) for steering the rear wheels (13,14), sensor unit for measuring vehicular parameters (e.g. a vehicle speed sensor (20), an accelerometer (21) and a steer angle sensor (23)) and generating signals indicative thereof, and a control system for controlling the actuator (18) comprising a processor (17) which processes the signals generated by the sensor unit (20,21,23) and controls the rear wheels (13,14) accordingly. The control system of the invention has detection unit to detect when the signals generated by the sensor unit (20,21,23) indicate that the vehicle is sliding and override unit which modifies the operation of the control system when sliding is detected.

Claims

1. A steering system for steering the rear wheels of a vehicle having rear wheels with a controllable variable steering angle comprising:

an actuator for steering the rear wheels;

sensor means for measuring vehicle parameters and generating signals indicative thereof, the sensor means including a sensor which measures displacement of a manually operable steering element of the vehicle, a sensor which measures vehicle speed, a lateral accelerometer, and a yaw rate gyrometer which measures yaw rate of the vehicle; and

a control unit for controlling the actuator to steer the rear wheels comprising a processor which processes the signals generated by the sensor means and controls the steering angle of the controllable variable rear wheels accordingly, the processor determining a desired yaw rate as a function of the measured steering element displacement and the measured vehicle velocity,

wherein the control unit further comprises detection means to detect when the signals generated by sensor means indicate that the vehicle is sliding, override means which modifies the operation of the control system when sliding is detected,

a closed yaw rate error control loop feedback means for controlling the steer angle of the rear wheels having means for generating an error signal from a difference between the measured yaw rate and the determined desired yaw rate, and

means for multiplying the error signal by a variable gain to generate a signal for controlling the controllable variable steering angle of the rear wheels, and

wherein the detection means detects sliding by determining whether the lateral acceleration measured by the lateral accelerometer and the measured steering element displacement are of opposite sense,

the detection means combines the signals indicative of yaw rate, steering angle and lateral acceleration according to a preprogrammed algorithm, to generate a control variable which is compared with a preprogrammed value, the override means only altering the variable gain of the control system when the detection means detects that the control variable exceeds the preprogrammed value, and

the override means alters the variable gain in the yaw rate error control loop when sliding is detected.

2. A steering system as claimed in claim 1 wherein the override means reduces the variable gain of the yaw error control loop when sliding is detected.

3. A steering system as claimed in claim 1 wherein the detection means compares the measured velocity with a preprogrammed velocity threshold, the override means only modifies the operation of the control system when the detection means detects that the measured velocity exceeds the velocity threshold.

4. A steering system as claimed in claim 1 wherein the detection means compares the measured lateral acceleration with a preprogrammed lateral acceleration threshold, the override means only altering the variable gain of the control system when the detection means detects that the measured lateral acceleration exceeds the lateral acceleration threshold.

5. A steering system as claimed in claim 4 wherein the detection means includes a low pass filter by which the measured lateral acceleration signal is filtered and the filtered lateral acceleration signal is compared with the lateral acceleration threshold.

6. A steering system as claimed in claim 1 wherein the override means reduces the variable gain of the control system from a first level to a second lower level when the detection means detects sliding and increases the gain from the second lower level to the first level when the detection means detects that the sliding of the vehicle has stopped, the override means ramping the gain between the first and second levels at preprogrammed rates.

7. A steering system as claimed in claim 6 wherein the rate at which the override means ramps the gain from the first level to the second lower level is faster than the rate at which the override means ramps the gain from the second lower level to the first level.

8. A steering system as claimed in claim 7 wherein the override means compares the measured lateral acceleration with a preprogrammed lateral acceleration threshold and wherein the override means increases the rate at which the variable gain of the control system is ramped from the second lower level to the first level when the measured lateral acceleration is less than the preprogrammed lateral acceleration threshold.

9. A steering system as claimed in claim 1 wherein the override means introduces a phase lead in the closed yaw rate error control loop when the detection means detects sliding.

10. A steering system as claimed in claim 1 wherein the override means introduces a phase lag in the closed yaw rate error control loop when the detection means detects sliding.