Adaptive steering control using vehicle slip angle and steering rate

• US 5,684,700 A
• Filed: 12/05/1995
• Issued: 11/04/1997
• Est. Priority Date: 12/05/1995
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Crocker, Jonathan Andrew
• Primary Examiner(s): Chin, Gary
• Application Number:
  US08/567,615
• Time in Patent Office: 700 Days
• Field of Search: 364/424.051, 364/424.052, 364/424.054, 364/424.058, 364/426.01, 364/426.037, 364/426.015, 364/426.016, 180/410-415, 180/421, 180/422, 180/443, 180/446
• US Class Current: 701/41
• 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 6/04 responsive only to forces disturbing the intended course of the vehicle, e.g. forces acting transversely to the direction of vehicle travel

Abstract

A method and apparatus are provided for improving vehicle steering in unfamiliar safety critical situations by controlling power steering assist in response to the slip angle of the vehicle and the steering rate of the vehicle. When a vehicle is in a slide or a slide is imminent, the steering wheel should be turned in the direction of the slide to stabilize the vehicle and take the vehicle out of the slide or possibility of a slide. Accordingly, a positive supplemental steering assist is provided for the steering system if the driver is turning the steering wheel in the direction to correct the slide. If, on the other hand, the driver is turning the steering wheel in the direction which will increase the slide, a negative supplemental assist is provided for the steering system. That is, a feedback is provided to the driver in the form of increased steering assist if the steering wheel is being turned in the proper direction and a decreased steering assist if the steering wheel is being turned in the improper direction. In this way, the driver of a motor vehicle is advised of the proper steering action to take in the event of an actual or imminent vehicle slide by the resistance the driver feels in turning the steering wheel.

Claims

1. A method for controlling power steering assist in a motor vehicle including a power steering system, said method comprising the steps of:

determining a slip angle of the vehicle;

determining a steering rate of the vehicle;

combining said slip angle with said steering rate; and

controlling steering assist provided by the power steering system of the vehicle based on the combination of said slip angle and said steering rate.

2. A method for controlling power steering assist as claimed in claim 1 wherein the step of determining a slip angle of a motor vehicle comprises the step of calculating said slip angle.

3. A method for controlling power steering assist as claimed in claim 2 wherein the step of calculating said slip angle comprises the steps of:

measuring lateral acceleration of the vehicle;

measuring forward velocity of the vehicle;

dividing said lateral acceleration by said forward velocity to define a reference yaw rate for the vehicle;

determining an actual yaw rate of the vehicle;

comparing said reference yaw rate to said actual yaw rate to define a yaw rate error;

integrating the yaw rate error to define a raw slip angle; and

filtering the raw slip angle through a high pass filter to define said slip angle.

4. A method for controlling power steering assist as claimed in claim 3 wherein the step of comparing said reference yaw rate to said actual yaw rate comprises the step of determining the difference between said reference yaw rate and said actual yaw rate.

5. A method for controlling power steering assist as claimed in claim 1 wherein the step of determining a slip angle of the vehicle comprises the step of measuring the vehicle slip angle.

6. A method for controlling power steering assist as claimed in claim 1 wherein the step of controlling steering assist comprises the steps of:

determining a supplemental assist value from the combination of said slip angle and said steering rate; and

algebraically combining said supplemental assist value and a base assist value.

7. A method for controlling power steering assist as claimed in claim 1 wherein said step of combining said slip angle and said steering rate comprises the steps of:

assigning a value to said slip angle proportional to the size of the slip angle;

assigning a value to said steering rate proportional to the rate at which a steering direction is changed; and

multiplying said slip angle value by said steering rate value to obtain a supplemental assist value.

8. A method for controlling power steering assist as claimed in claim 7 wherein a negative slip angle value corresponds to a vehicle slip in a first direction, a positive slip angle value corresponds to a vehicle slip in a second direction opposite to said first direction, a negative steering rate value corresponds to turning a steering wheel in said first direction, and a positive steering rate value corresponds to turning said steering wheel in said second direction.

9. A method for controlling power steering assist as claimed in claim 8 wherein the step of combining said slip angle and said steering rate further comprises the step of assigning a zero value to said slip angle value if said slip angle value does not exceed a predetermined threshold value.

10. A method for controlling power steering assist as claimed in claim 9 wherein the step of controlling steering assist comprises the steps of:

increasing the amount of steering assist when the supplemental assist value is positive;

decreasing the amount of steering assist when said supplemental assist value is negative; and

maintaining a base amount of steering assist when the supplemental assist value is zero.

11. A method for controlling power steering assist as claimed in claim 10 wherein the amount of increased steering assist is proportional to the positive supplemental assist value and wherein the amount of decreased steering assist is proportional to the negative supplemental assist value.

12. Apparatus for controlling power steering assist in a motor vehicle including a power steering system, said apparatus comprising:

a slip angle sensor for generating a vehicle slip angle signal;

a steering rate sensor for generating a steering rate signal for a steering wheel of said vehicle;

a multiplier, connected to said slip angle sensor and said steering rate sensor, for generating a supplemental assist signal in response to said slip angle signal and said steering rate signal;

a base power steering assist unit generating a base assist signal; and

an adder, connected to said multiplier and said base power steering assist unit, for combining said supplemental assist signal and said base assist signal to generate a control signal for the power steering system of said vehicle.

13. Apparatus for controlling power steering assist as claimed in claim 12 wherein said slip angle sensor comprises a threshold detector.

14. Apparatus for controlling power steering assist as claimed in claim 12 wherein said slip angle sensor comprises a vehicle slip angle measuring device.

15. Apparatus for controlling power steering assist as claimed in claim 12 wherein said slip angle sensor comprises:

an accelerometer for measuring lateral acceleration of said vehicle;

a speed sensor for measuring forward velocity of said vehicle;

a yaw rate sensor for measuring yaw rate of said vehicle;

a divider connected to said accelerometer and said speed sensor for dividing said lateral acceleration by said forward velocity to generate a reference yaw rate;

an adder connected to said divider and said yaw rate sensor for generating an error yaw rate;

an integrator connected to said adder for integrating said error yaw rate to generate a raw slip angle signal; and

a high pass filter connected to said integrator for filtering said raw slip angle signal to generate said slip angle signal.

16. Apparatus for controlling power steering assist as claimed in claim 15 wherein said high pass filter passes frequencies above about 0.1 to 0.5 hertz.

17. A method for controlling power steering assist in a motor vehicle including a power steering system, said method comprising the steps of:

determining a signed slip angle for the motor vehicle;

comparing the signed slip angle to positive and negative thresholds to generate a positive or a negative slip angle signal corresponding in magnitude to the extent the slip angle exceeds said thresholds;

measuring a steering rate for a steering wheel of the motor vehicle;

generating a signed steering rate signal representative of the directional steering rate of the steering wheel of the motor vehicle; and

multiplying said signed slip angle signal by said signed steering rate signal to generate a steering control signal for controlling steering system power assist.

18. A method for controlling power steering assist as claimed in claim 17 wherein the step of determining a signed slip angle comprises the steps of:

measuring a signed lateral acceleration of the vehicle;

measuring forward velocity of the vehicle;

dividing said signed lateral acceleration by said forward velocity to define a reference yaw rate of the vehicle;

determining an actual yaw rate of the vehicle;

comparing said reference yaw rate to said actual yaw rate to define a yaw rate error;

integrating the yaw rate error to define a raw slip angle; and

filtering the raw slip angle through a high pass filter to define said slip angle.

19. A method for controlling power steering assist as claimed in claim 17 wherein the step of determining a signed slip angle comprises the step of measuring the signed slip angle.

20. A method for controlling power steering assist as claimed in claim 17 wherein said steering control signal is algebraically combined with a base steering control signal.