Preview lateral control for automated driving

• US 9,731,755 B1
• Filed: 02/16/2016
• Issued: 08/15/2017
• Est. Priority Date: 02/16/2016
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Moshchuk, Nikolai K., Chen, Shih-Ken, Litkouhi, Bakhtiar B.
• Primary Examiner(s): Ortiz, Angela
• Assistant Examiner(s): Dunn, Alex C
• Application Number:
  US15/044,851
• Publication Number:
  US 20170233001A1
• Time in Patent Office: 546 Days
• CPC Class Codes: B62D 1/28 non-mechanical , e.g. following a line or other known markers
• CPC Class Codes: B62D 15/025 Active steering aids, e.g. helping the driver by actively influencing the steering system after environment evaluation B62D1/28 takes precedence
• 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 for providing vehicle lateral steering control. The method includes providing a mathematical model of vehicle dynamics that includes a state variable, a steering control variable and a future road disturbance factor that defines the upcoming road curvature, banks and slopes of the roadway. The method determines an optimal steering control signal that includes a feedback portion and a feed-forward portion, where the feed-forward portion includes the road disturbance factor. The method determines a state variable and a control variable for the current roadway curvature, bank and slope for stationary motion of the vehicle for constant speed, yaw rate and lateral velocity. The method then introduces a new state variable and control variable for dynamic vehicle motion for variable speed, yaw rate and lateral velocity that is a difference between the state and control variables for predicted future times and the steady state variables.

Claims

1. A method for providing lateral steering control for an autonomously driven or semi-autonomously driven vehicle traveling along a roadway, said method comprising:

providing a mathematical model of vehicle dynamics that includes a state variable, a steering control variable and a future roadway disturbance factor that defines curvature, bank and/or slope of the roadway, wherein providing a mathematical model includes providing a four-degree of freedom mathematical model or a six-degree of freedom mathematical model where the model uses a one-track bicycle model for the four-degree of freedom mathematical model and uses a combination of a one-track bicycle model and a one-degree of freedom steering model for the six-degree of freedom mathematical model;

determining a steering control goal using the steering control variable that reduces a difference between a current vehicle path and a desired vehicle path;

determining an optimal steering control signal using the mathematical model that provides the steering control goal and that includes a feedback portion and a feed-forward portion, where the feed-forward portion includes the road disturbance factor; and

providing the control signal to a steering controller.

2. The method according to claim 1 wherein providing a mathematical model includes using the one-track bicycle model to provide model dimensions of lateral offset Δ

y of a vehicle center of gravity from the desired vehicle path, a vehicle heading angle error Δ

ψ

, vehicle lateral velocity Δ

y and vehicle yaw rate r, and the one-degree of freedom steering column model to provide steering wheel angle φ and

steering wheel angle rotation rate {dot over (φ

)}.

3. The method according to claim 2 wherein a derivative of the state variable is defined as:

{dot over (X)}=AX+BU+h

where X is the state variable, U is the steering control variable, h is the road disturbance factor, and A and B are matrices.

4. The method according to claim 3 wherein providing a mathematical model includes defining the state variable X by lane position dynamics and the bicycle model for an angle interface steering control as:

X=[Δ

y,Δ

Ψ

,V_y,r]^T

where the state variable X is a road wheel angle, and defining the state variable X by the lane position dynamics, the bicycle model and the steering model for a torque interface steering control as;

X=[Δ

y,Δ

Ψ

,V_y,r,{dot over (φ

)},φ

]^T

where the state variable X a combined torque command and a road wheel angle.

5. The method according to claim 4 wherein the road disturbance factor h is defined as:

6. The method according to claim 1 wherein determining a steering control goal includes defining a relationship between a steering command and a cost function.

7. The method according to claim 6 wherein the cost function is a quadratic function.

8. The method according to claim 7 wherein the quadratic function is defined by the equation:

9. A method for providing lateral steering control for an autonomously driven or semi-autonomously driven vehicle traveling along a roadway, said method comprising:

providing a mathematical model of vehicle dynamics that includes a state variable, a steering control variable and a future roadway disturbance factor that defines curvature, bank and/or slope of the roadway;

determining a steering control goal using the steering control variable that reduces a difference between a current vehicle path and a desired vehicle path;

determining an optimal steering control signal using the mathematical model that provides the steering control goal and that includes a feedback portion and a feed-forward portion, where the feed-forward portion includes the road disturbance factor, wherein determining a steering control signal includes using the mathematical model to define a state variable and a control variable for a vehicle steady state or stationary motion condition, where the stationary motion has a constant speed, yaw rate and lateral velocity, for a current curvature, bank and slope of the roadway; and

providing the control signal to a steering controller.

10. The method according to claim 9 wherein determining a steering control signal includes transforming the state variable and the control variable for the vehicle steady state condition by subtracting the state variable and the control variable for the steady state condition from the state variable and the control variable at future sample times to obtain a new state variable and a new control variable for each sample time that provides a deviation of the dynamic motion of the vehicle from the stationary motion.

11. The method according to claim 10 wherein determining a steering control signal includes using model predictive control.

12. The method according to claim 10 wherein determining a steering control signal includes using the equation:

13. The method according to claim 9 wherein determining a steering control goal includes defining a relationship between a steering command and a cost function.

14. The method according to claim 13 wherein the cost function is a quadratic function.

15. A method for providing lateral steering control for an autonomously driven or semi-autonomously driven vehicle traveling along a roadway, said method comprising:

providing a four-degree of freedom or a six-degree of freedom mathematical model of vehicle dynamics that includes a state variable, a steering control variable and a future roadway disturbance factor that defines curvature, bank and/or slope of the roadway;

determining a steering control goal using the steering control variable that reduces a difference between a current vehicle path and a desired vehicle path;

determining an optimal steering control signal using the mathematical model that provides the steering control goal and that includes a feedback portion and a feed-forward portion, where the feed-forward portion includes the road disturbance factor, wherein determining the steering control signal includes defining a state variable and a control variable for a vehicle steady state or stationary motion condition for a current curvature, bank and slope of the roadway, where the stationary motion has a constant speed, yaw rate and lateral velocity, and transforming the state variable and the control variable for the vehicle steady state condition by subtracting the state variable and the control variable for the steady state condition from the state variable and the control variable at future sample times to obtain a new state variable and a new control variable for each sample time that provides a deviation of the dynamic motion of the vehicle from the stationary motion; and

providing the control signal to a steering controller.

16. The method according to claim 15 wherein determining a steering control signal includes using the equation:

17. The method according to claim 15 wherein providing a mathematical model includes providing a mathematical model that uses a one-track bicycle model for the four-degree of freedom mathematical model and uses a combination of a one-track bicycle model and a one-degree of freedom steering model for the six-degree of freedom mathematical model.

18. The method according to claim 17 wherein providing a mathematical model includes using the one-track bicycle model to provide model dimensions of lateral offset Δ

y of a vehicle center of gravity from the desired vehicle path, a vehicle heading angle error Δ

ψ

, vehicle lateral velocity Δ

y and vehicle yaw rate r, and the one-degree of freedom steering column model to provide steering wheel angle φ and

steering wheel angle rotation rate {dot over (φ

)}.

19. The method according to claim 18 wherein a derivative of the state variable is defined as:

{dot over (X)}=AX+BU+h

where X is the state variable, U is the steering control variable, h is the road disturbance factor, and A and B are matrices.

20. The method according to claim 19 wherein providing a mathematical model includes defining the state variable X by lane position dynamics and the bicycle model for an angle interface steering control as:

X=[Δ

y,Δ

Ψ

,V_y,r]^T

where the state variable X is a road wheel angle, and defining the state variable X by the lane position dynamics, the bicycle model and the steering model for a torque interface steering control as;

X=[Δ

y,Δ

Ψ

,V_y,r,φ

;

φ

]^T

where the state variable X is a combined torque command and a road wheel angle.

21. The method according to claim 20 wherein the road disturbance factor h is defined as: