Trailer length estimation method using trailer yaw rate signal

1. A backup assist system for a vehicle reversing a trailer, comprising:

a trailer sensor outputting a trailer yaw rate;

a vehicle sensor system outputting a vehicle yaw rate and a vehicle speed; and

a controller:

estimating a hitch angle between the vehicle and the trailer using an integration of a difference between the trailer yaw rate and the vehicle yaw rate over time;

estimating a length of the trailer using the estimated hitch angle, the vehicle yaw rate, the vehicle speed, and the trailer yaw rate in a kinematic relationship; and

using the trailer length in the kinematic relationship to control the vehicle.

2. The system of claim 1 , wherein the estimated hitch angle is a reference estimated hitch angle.

3. The system of claim 2 , wherein the reference estimated hitch angle is further determined by adding an initial reference hitch angle to the integration of the difference between the trailer yaw rate and the vehicle yaw rate over the predetermined period of time, the initial reference hitch angle corresponding to a start point of the predetermined period of time.

4. The system of claim 3 , wherein the initial reference estimated hitch angle is determined using an equation derived from the kinematic model that is independent of a trailer length measurement.

5. The system of claim 2 , wherein the system performs the integration of the difference between the trailer yaw rate and the vehicle yaw rate over the predetermined period of time before estimating the length of the trailer.

6. The system of claim 2 , wherein the controller:

sequentially derives a plurality of estimated trailer lengths based on corresponding ones of a plurality of reference estimated hitch angles; and

derives a final weighted trailer length estimate by one of averaging and filtering the plurality of instantaneous estimated trailer lengths.

7. The system of claim 1 , wherein the system determines the estimated length of the trailer using the reference estimated hitch angle in view of the kinematic relationship.

8. The system of claim 7 , wherein the controller simultaneously and instantaneously determines the estimated hitch angle and the estimated length of the trailer.

9. The system of claim 8 , wherein the controller instantaneously determines the estimated hitch angle using the estimated length of the trailer.

10. The system of claim 8 , wherein the controller:

compares the estimated hitch angle with the reference estimated hitch angle to determine an error signal; and

adjusts the trailer length estimate using the error signal.

11. The system of claim 1 , further including a curvature input device outputting a first curvature signal, wherein:

the controller further implements a trailer backup mode including reversing the trailer based on the first curvature signal, the estimated length of the trailer, and the estimated hitch angle in view of the kinematic relationship.

12. A backup assist system for a vehicle reversing a trailer, comprising:

a first sensor coupled with the trailer for determining a trailer yaw rate;

a second sensor coupled with the vehicle for determining a vehicle yaw rate; and

a controller:

estimating a hitch angle between the vehicle and the trailer using an integration of a difference between the trailer yaw rate and the vehicle yaw rate over time;

determining an estimated length of the trailer using the estimated hitch angle, the vehicle yaw rate, the vehicle speed, and the trailer yaw rate as inputs to a kinematic relationship between the trailer and the vehicle; and

controlling a steering system of the vehicle using the estimated length of the trailer as a further input to the kinematic relationship.

13. The system of claim 12 , wherein the estimated hitch angle is a reference estimated hitch angle.

14. The system of claim 13 , wherein the controller:

sequentially derives a plurality of estimated trailer lengths based on corresponding ones of a plurality of reference estimated hitch angles; and

derives a final weighted trailer length estimate by one of averaging and filtering the plurality of instantaneous estimated trailer lengths.

15. The system of claim 12 , wherein the controller simultaneously and instantaneously determines the estimated hitch angle and the estimated length of the trailer.

16. The system of claim 15 , wherein the controller:

compares the estimated hitch angle with a reference estimated hitch angle to determine an error signal; and

adjusts the trailer length estimate using the error signal.

17. A method for reversing a trailer towed by a vehicle, comprising:

receiving a trailer yaw rate signal;

receiving a vehicle yaw rate signal;

receiving a vehicle speed signal;

estimating a hitch angle between the vehicle and the trailer using an integration of a difference between the trailer yaw rate signal and the vehicle yaw rate signal over time;

determining an estimated length of the trailer using the estimated hitch angle, the vehicle yaw rate signal, the vehicle speed signal, and the trailer yaw rate signal as inputs to a kinematic relationship between the trailer and the vehicle; and

controlling a vehicle steering system using the estimated length of the trailer as a further input to the kinematic relationship.

18. The method of claim 17 , wherein the estimated hitch angle is a reference estimated hitch angle.

19. The method of claim 18 , further comprising:

sequentially determining a plurality of estimated trailer lengths based on corresponding ones of a plurality of reference estimated hitch angles; and

deriving a final weighted trailer length estimate by one of averaging and filtering the plurality of instantaneous estimated trailer lengths.

20. The method of claim 19 , wherein the estimated hitch angle and the estimated length of the trailer are simultaneously and instantaneously determined, the method further comprising:

comparing the estimated hitch angle with a reference estimated hitch angle to determine an error signal; and

adjusting the trailer length estimate using the error signal.