Method and system for preventing instability in a vehicle-trailer combination

1. A method of preventing instability in a vehicle-trailer combination, the method comprising:

monitoring relative movement between the vehicle and the trailer using optical sensing means, wherein the optical sensing means comprises a camera;

determining a trailer yaw condition in dependence on a signal output from the optical sensing means;

comparing the determined trailer yaw condition to a predetermined threshold yaw condition;

when the determined trailer yaw condition is equal to or greater than the predetermined threshold yaw condition, outputting an alert signal indicative of the onset of instability in the vehicle-trailer combination directly to a driver of the vehicle in order to allow the driver to take corrective measures;

capturing a reference image of the trailer using the camera;

monitoring the trailer during towing using the camera; and

determining the trailer yaw condition based on at least one difference between a monitored image of the trailer and the reference image.

2. A method according to claim 1 , wherein the step of determining a trailer yaw condition comprises determining one or both of a trailer yaw angle and a trailer yaw frequency.

3. A method according to claim 1 , comprising determining the trailer yaw condition in dependence on a signal output from at least one further sensing means.

4. A method according to claim 3 , wherein determining the trailer yaw condition comprises performing a Fourier Transform analysis of the respective signals output from said optical sensing means and said at least one further sensing means.

5. A method according to claim 3 , comprising determining the trailer yaw condition in dependence on a weighting factor associated with each of the optical sensing means and said at least one further sensing means, the weighting factor being indicative of the expected accuracy with which the trailer yaw condition can be determined using the optical sensing means and the at least one further sensing means, respectively, a higher weighting factor being associated with a greater expected accuracy.

6. A method according to claim 3 , wherein said at least one further sensing means is at least one of a contactless sensor, an ultrasonic sensor, a radar sensor, an encoder arrangement, or a rotary encoder disposed at a trailer hitch point.

7. A method according to claim 1 , wherein determining the trailer yaw condition comprises registering the relative dimensions of at least a portion of the trailer, as viewed by the camera in a neutral condition, and comparing those registered relative dimensions to relative dimensions viewed by the camera during towing of the trailer in order to determine the yaw condition.

8. A computer program stored in a memory, such that when a processor of a vehicle is programmed by the computer program, the processor is adapted to perform the method of claim 1 .

9. A system for preventing instability in a vehicle-trailer combination, the system comprising;

optical sensing means disposed on the vehicle for sensing relative movement between the vehicle and the trailer;

a controller having a processor and a memory;

wherein the memory contains a computer program used by the processor to control the system to perform the method of claim 1 .

10. A vehicle having the system of claim 9 .

11. A method of preventing instability in a vehicle-trailer combination, the method comprising;

sensing relative movement between the vehicle and the trailer using first and second sensors;

outputting a signal from each of the first and second sensors;

determining first and second trailer yaw conditions in dependence on respective signals from the first and second sensors;

applying a weighting factor to each of the first and second trailer yaw conditions in dependence on the expected accuracy of the respective first and second sensors, a higher weighting factor being associated with a greater expected accuracy; and

determining a composite trailer yaw condition in dependence on the weighted first and second trailer yaw conditions;

comparing the determined composite trailer yaw condition to a predetermined threshold yaw condition; and

when the determined composite trailer yaw condition is equal to or greater than the predetermined threshold yaw condition, outputting an alert signal indicative of the onset of instability in the vehicle-trailer combination.

12. A method according to claim 11 , comprising outputting the alert signal directly to the driver of a vehicle in order to allow the driver to take corrective measures.

13. A method according to claim 11 , comprising outputting the alert signal to an electronic stability system of the vehicle in order to allow the electronic stability system to take corrective measures.

14. A method according to claim 11 , wherein the step of determining the first and second trailer yaw conditions comprises determining one or both of a trailer yaw angle and a trailer yaw frequency.

15. A method according to claim 11 , wherein determining the first and second trailer yaw conditions comprises performing a Fourier Transform analysis of the respective signals output from the first and second sensors.

16. A method according to claim 11 , wherein the first and second sensors are one of an optical sensor, a camera, an ultrasonic sensor, a radar sensor and an encoder arrangement.

17. A computer program stored in a memory, such that when a processor of a vehicle is programmed by the computer program, the processor is adapted to perform the method of claim 11 .

18. A system for preventing instability in a vehicle-trailer combination, the system comprising;

first and second sensors disposed on the vehicle for sensing relative movement between the vehicle and the trailer;

a controller having a processor and a memory;

wherein the memory contains a computer program used by the processor to control the system to perform the method of claim 11 .

19. A vehicle comprising the system of claim 18 .