System and method of controlling a vehicle having yaw stability control

• US 6,640,173 B1
• Filed: 02/11/2003
• Issued: 10/28/2003
• Est. Priority Date: 02/11/2003
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Inventors: Zheng, Bing
• Primary Examiner(s): Camby, Richard M.
• Application Number:
  US10/364,618
• Time in Patent Office: 259 Days
• Field of Search: 701/41, 701/36, 701/37, 701/38, 701/1, 340/465, 180/410, 180/400-409
• US Class Current: 701/41
• CPC Class Codes: B60T 2230/02 Side slip angle, attitude angle, floating angle, drift angle
• CPC Class Codes: B60T 2260/02 Active Steering, Steer-by-Wire
• CPC Class Codes: B60T 8/1755 Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve road vehicle drive control systems for control of driving stability otherwise than by controlling a particular sub-unit B60W30/02
• 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

The present invention involves a method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance. The method includes generating a steering angle signal of the steer-by-wire system. The steering angle signal is indicative of a steering angle. The method further includes generating an extra road wheel angle signal using a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy configured to attenuate after a predetermined time lapse from a time zero. The extra road wheel angle signal is indicative of an extra road wheel angle to compensate for the yaw motion disturbance defining the time zero. The method further includes generating a road wheel angle signal indicative of a road wheel angle and applying torque to the road wheels to move the road wheels consistent with the road wheel angle based on the road wheel angle signal.

Claims

1. A method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, the method comprising:

sensing a steering wheel angle, speed, and yaw rate of the vehicle;

generating a steering angle signal of the steer-by-wire system, the steering angle signal being indicative of a steering angle based on steering wheel angle and steering ratio;

generating an extra road wheel angle signal implementing a gain schedule proportional-integral control strategy and an instant proportional-integral control strategy, the extral road wheel angle signal being indicative of an extra road wheel angle to compensate for the yaw motion disturbance defining a time zero;

generating a road wheel angle signal indicative of a road wheel angle, the road wheel angle being based on the extra road wheel angle and the steering wheel angle before a predetermined time lapse, the road wheel angle being based on the steering wheel angle after the predetermined time lapse relative to a time zero; and

applying torque to the road wheels to move the road wheels based on the road wheel angle.

2. The method of claim 1 wherein the Gain scheduled proportional-integrated control strategy includes:

$K_p=\frac{P_1}{P_2+k_p<br><br>V_{\mathrm{spd}}},\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>K_i=\frac{I_1}{I_2+k_i<br><br>V_{\mathrm{spd}}},$

where K_p is indicative of proportional gain;

K_i is indicative of integral gain;

V_spd is indicative of Vehicle speed;

P₁, P₂, k_p are constants for gain-scheduled proportional control; and

I₁, I₂, k_i are constants for gain-scheduled integral control.

3. The method of claim 2 wherein the instant Proportional and Integral control strategy includes:

$K_{\mathrm{ip}}<br><br>\left(z\right)=k_{\mathrm{ip}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{a_{\mathrm{p0}}<br><br>z^2+a_{\mathrm{p1}}<br><br>z^1+a_{\mathrm{p2}}}{z^2+b_{\mathrm{p1}}<br><br>z^1+b_{\mathrm{p0}}},\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$$K_{\mathrm{ii}}<br><br>\left(z\right)=k_{\mathrm{ii}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{a_{\mathrm{i0}}<br><br>z^2+a_{\mathrm{i1}}<br><br>z^1+a_{\mathrm{i2}}}{z^2+b_{\mathrm{i1}}<br><br>z^1+b_{\mathrm{i0}}},$

where z^k is indicative of time shift operator which shifts the time by k units;

k_ip is indicative of gain for P attenuator;

k_ii is indicative of gain for I attenuator;

a_pk, b_pk are indicative of constants for P attenuator; and

a_ik, b_ik are indicative of constants for I attenuator.

4. The method of claim 1 wherein the estimated side slip includes a saturator for control output including:

$\mathrm{control}=\{\begin{array}{cc}\left(K_{\mathrm{ip}}<br><br>\left(z\right)<br><br>K_p+K_{\mathrm{ii}}<br><br>\left(z\right)<br><br>K_i\right)*{\mathrm{Yaw}}_{\mathrm{error}}& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{abs}<br><br>\left(\mathrm{contol}\right)<<br><br>{\mathrm{control}}_{\mathrm{thd}}\\ {\mathrm{control}}_{\mathrm{thd}}& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{control}><br><br>=\text{\hspace{1em}<br><br>}<br><br>{\mathrm{control}}_{\mathrm{thd}}\\ -{\mathrm{control}}_{\mathrm{thd}}& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{control}<<br><br>=-{\mathrm{control}}_{\mathrm{thd}}\end{array}$

where Yaw_error is indicative of a difference between the measured yaw rate and the desired yaw rate; and

Control_thd is indicative of a control threshold, the control threshold being determined by;

${\mathrm{control}}_{\mathrm{thd}}={\mathrm{control}}_{\max }*\min <br><br>\left\{\frac{1}{{\mathrm{control}}_{\mathrm{Vpd}}+k_{\mathrm{vpd}}<br><br>V_{\mathrm{spd}}},\text{\hspace{1em}<br><br>}<br><br>\frac{1}{{\mathrm{control}}_{\mathrm{lat}}+k_{\mathrm{lat}}<br><br>\mathrm{Lat}},\text{\hspace{1em}<br><br>}<br><br>\frac{1}{{\mathrm{control}}_{\mathrm{ss}}+k_{\mathrm{ss}}<br><br>\mathrm{sideslip}}\right\}$

where Control_max is indicative of maximal control output;

Lat is indicative of lateral acceleration;

Sideslip is indicative of sideslip angle;

Control_vpd, k_vpd is indicative of constants of saturator with respect to vehicle speed;

Control_lat, k_lat is indicative of constants of saturator with respect to vehicle'"'"'s lateral acceleration; and

Control_ss, k_ss is indicative of constants of saturator with respect to vehicle'"'"'s sideslip angle.

5. The method of claim 1 further comprising comparing the yaw error with the error thresholds.

6. The method of claim 1 wherein the steer-by-wire system includes a sampling period of about 1 microsecond.

7. The method of claim 1 wherein the predetermined time lapse is about 0.5 second.

8. The method of claim 1 further comprising generating the road wheel command reference signal indicative of a road wheel command reference, the road wheel command reference being based on a predetermined steering ratio and the steering wheel angle.

9. The method of claim 1 further comprising:

calculating the extra road wheel angle, if the yaw error is determined to be greater than an error threshold; and

calculating a road wheel angle based on the extra road wheel angle.

10. The method of claim 4 further comprising:

calculating the estimated side slip angle based on the road wheel angle, speed and the yaw rate of the vehicle.

11. The method of claim 1 further comprising:

sensing lateral acceleration of the vehicle;

generating a desired yaw rate signal indicative of a desired yaw rate, the desired yaw rate being based on the steering wheel angle and the vehicle speed;

generating a yaw error signal indicative of a yaw error, the yaw error being based on the desired yaw rate and the measured yaw rate;

determining the desired yaw rate based on the steering wheel angle and the vehicle speed; and

determining the yaw error based on the desired yaw rate and the measured yaw rate.

12. The method of claim 11 further comprising determining whether an estimated side slip is greater than a side slip threshold.

13. The method of claim 12 further comprising:

generating an estimated side slip signal indicative of the estimated side slip of the vehicle based on the road wheel angle, speed, and the yaw rate of the vehicle; and

generating a steering wheel angle signal indicative of the steering wheel angle, a lateral acceleration signal indicative of lateral acceleration, a vehicle speed signal indicative of vehicle speed, a yaw rate signal indicative of yaw rate, and an estimated side slip signal indicative of the estimated side slip.

14. The method of claim 1 wherein the compensating steering angle has a maximum angle based on the speed of the vehicle.

15. The method of claim 14 wherein the maximum steering angle is about +/−

3°

if the vehicle speed is determined to be less than 20 miles per hour and the maximum steering angle is about +/−

1°

, if the vehicle speed is determined to be greater than 60 miles per hour.

16. The method of claim 1 wherein generating the desired yaw rate signal includes:

receiving the steering wheel angle and the vehicle speed; and

prefiltering the steering wheel angle and vehicle speed.

17. The method of claim 16 wherein the step of filtering includes:

$r_{\mathrm{des}}=\frac{\mathrm{VhSpd}*\mathrm{Steeringratio}*\mathrm{SWA}}{L+K*{\mathrm{VhSpd}<br><br>\text{\hspace{1em}<br><br>}}^2}$

r_des is indicative of desired yaw rate;

L is indicative of wheelbase of the vehicle;

K is indicative of understeer coefficient;

Vh Spd is indicative of vehicle speed; and

SWA is indicative of steering wheel angle.

18. The method of claim 1 wherein generating the compensating steering angle signal and generating the extra road wheel angle signal are performed, if a yaw error is determined to be greater than an error threshold.

19. The method of claim 18 wherein the error threshold is 1 degree per second.

20. The method of claim 1 wherein the error threshold is about 0.1 to 2.0 degrees per second.

25. The method of claim 1 further comprising comparing the yaw error with the error thresholds.

26. The method of claim 1 wherein the error threshold is 1 degree per second.

27. The method of claim 1 wherein the predetermined time lapse is about 0.5 second.

28. The method of claim 1 further comprising generating the road wheel command reference signal indicative of a road wheel command reference, the road wheel command reference being based on a predetermined steering ratio and the steering wheel angle.

29. The method of claim 1 further comprising:

calculating the extra road wheel angle, if the yaw error is determined to be greater than an error threshold; and

calculating a road wheel angle based on the extra road wheel angle.

30. The method of claim 4 further comprising:

calculating the estimated side slip angle based on the road wheel angle speed and the yaw rate of the vehicle.

34. The method of claim 1 wherein the compensating steering angle has a maximum angle based on the speed of the vehicle.

35. The method of claim 14 wherein the maximum compensating steering angle is about +/−

3°

if the vehicle speed is determined to be less than 20 miles per hour and the maximum compensating steering angle is about +/−

1°

if the vehicle speed is determined to be greater than 60 miles per hour.

36. The method of claim 1 wherein generating the desired yaw rate signal includes:

receiving the steering wheel angle and the vehicle speed; and

prefiltering the steering wheel angle and vehicle speed.

37. The method of claim 16 wherein the step of filtering includes:

$r_{\mathrm{des}}=\frac{\mathrm{VhSpd}*\mathrm{Steeringratio}*\mathrm{SWA}}{L+K*{\mathrm{VhSpd}<br><br>\text{\hspace{1em}<br><br>}}^2}$

r_des is indicative of desired yaw rate;

L is indicative of wheelbase of the vehicle;

K is indicative of understeer coefficient;

VhSpd is indicative of vehicle speed; and

SWA is indicative of steering wheel angle.

21. A method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, the method comprising:

sensing a steering wheel angle, lateral acceleration, speed, and a yaw rate of the vehicle;

generating a desired yaw rate signal indicative of a desired yaw rate, the desired yaw rate being based on the steering wheel angle and the vehicle speed;

generating a yaw error signal indicative of a yaw error, the yaw error being based on the desired yaw rate and the measured yaw rate;

generating a compensating, steering angle signal of the steer-by-wire system implementing a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy the compensating steering angle signal being indicative of a compensating steering angle, if the yaw error is determined to be greater than an error threshold;

generating an extra road wheel angle signal indicative of an extra road wheel angle to compensate for the yaw motion disturbance defining a time zero, if the yaw error is determined to be greater than an error threshold;

generating a road wheel angle signal indicative of a road wheel angle, the road wheel angle being based on the extra road wheel angle and a steering wheel angle before a predetermined time lapse, the road wheel angle being based on the steering wheel angle after the predetermined time lapse relative to the time zero; and

applying torque to the road wheels to move the road wheels consistent with the road wheel angle.

22. The method of claim 21 wherein the Gain scheduled proportional-integrated control strategy includes:

$K_p=\frac{P_1}{P_2+k_p<br><br>V_{\mathrm{spd}}},\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$$K_i=\frac{I_1}{I_2+k_i<br><br>V_{\mathrm{spd}}},$

where K_p is indicative of proportional gain;

K_i is indicative of integral gain;

V_spd is indicative of Vehicle speed;

P₁, P₂, k_p are constants for gain-scheduled proportional control; and

I₁, I₂, k_i are constants for gain-scheduled integral control.

23. The method of claim 22 wherein the instant Proportional-integral control strategy includes:

$K_{\mathrm{ip}}<br><br>\left(z\right)=k_{\mathrm{ip}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{a_{\mathrm{p0}}<br><br>z^2+a_{\mathrm{p1}}<br><br>z^1+a_{\mathrm{p2}}}{z^2+b_{\mathrm{p1}}<br><br>z^1+b_{\mathrm{p0}}},\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$$K_{\mathrm{ii}}<br><br>\left(z\right)=k_{\mathrm{ii}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{a_{\mathrm{i0}}<br><br>z^2+a_{\mathrm{i1}}<br><br>z^1+a_{\mathrm{i2}}}{z^2+b_{\mathrm{i1}}<br><br>z^1<br><br>b_{\mathrm{i0}}},$

where z^k is indicative of time shift operator which shifts the time by k units;

k_ip is indicative of gain for P attenuator;

k_ii is indicative of gain for I attenuator;

a_pk, b_pk are indicative of constants for P attenuator; and

a_ik, b_ik are indicative of constants for I attenuator.

24. The method of claim 23 wherein the estimated side slip includes a saturator for control output including:

$\mathrm{control}=\{\begin{array}{cc}\left(K_{\mathrm{ip}}<br><br>\left(z\right)<br><br>K_p+K_{\mathrm{ii}}<br><br>\left(z\right)<br><br>K_i\right)*{\mathrm{Yaw}}_{\mathrm{Error}}& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{abs}<br><br>\left(\mathrm{control}\right)<<br><br>{\mathrm{control}}_{\mathrm{thd}}\\ {\mathrm{control}}_{\mathrm{thd}}& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{control}><br><br>={\mathrm{control}}_{\mathrm{thd}}\\ -{\mathrm{control}}_{\mathrm{thd}}& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{control}<<br><br>=-{\mathrm{control}}_{\mathrm{thd}}\end{array}$

where Yaw_error is indicative of a difference between the measured yaw rate and the desired yaw rate; and

Control_thd is indicative of a control threshold, the control threshold being determined by;

${\mathrm{control}}_{\mathrm{thd}}={\mathrm{control}}_{\max }*\min <br><br>\left\{\frac{1}{{\mathrm{control}}_{\mathrm{Vpd}}+k_{\mathrm{vpd}}<br><br>V_{\mathrm{spd}}},\text{\hspace{1em}<br><br>}<br><br>\frac{1}{{\mathrm{control}}_{\mathrm{lat}}+k_{\mathrm{lat}}<br><br>\mathrm{Lat}},\text{\hspace{1em}<br><br>}<br><br>\frac{1}{{\mathrm{control}}_{\mathrm{ss}}+k_{\mathrm{ss}}<br><br>\mathrm{sideslip}}\right\}$

where Control_max is indicative of maximal control output;

Lat is indicative of lateral acceleration;

Sideslip is indicative of sideslip angle;

Control_vpd, k_vpd is indicative of constants of saturator with respect to vehicle speed;

Control_lat, k_lat is indicative of constants of saturator with respect to vehicle'"'"'s lateral acceleration; and

Control_ss, k_ss is indicative of constants of saturator with respect to vehicle'"'"'s sideslip angle.

31. The method of claim 21 further comprising:

determining the desired yaw rate based on the steering wheel angle and the vehicle speed; and

determining the yaw error based on the desired yaw rate and the measured yaw rate.

32. The method of claim 31 further comprising determining whether an estimated side slip is greater than a side slip threshold.

33. The method of claim 32 further comprising:

generating an estimated side slip signal indicative of the estimated side slip of the vehicle based on the road wheel angle, speed, and the yaw rate of the vehicle; and

generating a steering wheel angle signal indicative of the steering wheel angle, a lateral acceleration signal indicative of lateral acceleration, a vehicle speed signal indicative of vehicle speed, a yaw rate signal indicative of yaw rate, and an estimated side slip signal indicative of the estimated side slip.

38. A system for controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, the system comprising:

a driver interface system for sensing a steering wheel angle of the vehicle;

an electronic control unit configured to generate a road wheel angle signal to compensate for the yaw motion disturbance, the road wheel angle being based on an extra road wheel angle and a steering wheel angle before a predetermined time lapse, the road wheel angle being based on the steering wheel angle after the predetermined time lapse relative to the time zero; and

a road wheel actuating system for sensing lateral acceleration, speed, and measured yaw rate of the vehicle and for applying torque to the road wheels to move the road wheels consistent with the road wheel angle based on the road wheel angle signal and the predetermined steering ratio.

39. The system of claim 38 wherein the electronic control unit is configured to generate a desired yaw rate signal based on the steering wheel angle and the vehicle speed and generate a yaw error signal based on the desired yaw rate and the measured yaw rate.

40. The system of claim 39 wherein the electronic control unit is configured to generate a compensating steering angle signal of the system implementing a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy.

41. The system of claim 40 wherein the electronic control unit is configured to generate the compensating steering angle signal, if the yaw error is determined to be greater than an error threshold.