HITCH ANGLE ESTIMATION

1 . A system for estimating hitch angle between a trailer having a transmitter disposed thereon coupled to a vehicle having a trailer mount and a receiver disposed on the vehicle a first distance from the trailer mount, comprising:

a controller to calculate a second distance between the transmitter and the receiver as a function of path loss propagation and estimating a hitch angle using the first distance, the second distance and a trailer length.

2 . The system as claimed in claim 1 wherein the trailer length is stored in controller memory.

3 . The system as claimed in claim 1 further comprising a hitch angle sensor for sensing a hitch angle and wherein the controller compares the estimated hitch angle with the sensed hitch angle to verify an accuracy of the sensed hitch angle.

4 . A method executed by a controller on a vehicle for calculating an angle between a vehicle and a trailer coupled thereto, comprising:

monitoring power returns of a signal transmitted from a transmitter at one end of the trailer to a receiver on the vehicle located a first distance from a trailer mount;

estimating a second distance between the transmitter and the receiver, the second distance being a function of a path loss propagation of the transmitted signal;

calculating an angle between the vehicle and the trailer using the second distance, the first distance and a trailer length; and

outputting the calculated angle to a vehicle system.

5 . The method as claimed in claim 4 wherein the trailer length is stored in controller memory.

6 . The method as claimed in claim 4 wherein the trailer length is calculated and the method further comprises the steps of:

estimating, over time, the distance between the transmitter and the receiver at predetermined time intervals;

storing a predetermined number of second distances;

identifying which of the stored distances is largest; and

deducting the first distance from the largest stored distance to define the trailer length.

7 . The method as claimed in claim 4 wherein the trailer length is calculated and the method further comprises the steps of:

monitoring, over time, an output signal of a yaw rate sensor;

defining a zero hitch angle when the yaw rate sensor output is zero for a predetermined amount of time:

for a signal transmitted from the transmitter to the receiver during the defined zero hitch angle, estimating a zero-hitch-angle-distance between the transmitter and the receiver that is a function of path loss propagation of the transmitted signal; and

deducting the first distance from the zero-hitch-angle distance to define the trailer length.

8 . The method as claimed in claim 4 wherein the vehicle further comprises a hitch angle sensor and the method further comprises the steps of:

receiving a hitch angle sensed by the hitch angle sensor; and

comparing the calculated angle with the sensed hitch angle to verify an accuracy of the sensed hitch angle.

9 . A hitch angle estimation system for a vehicle having a trailer mount and a receiver disposed thereon a first distance from the trailer mount, the vehicle being coupled to a trailer having a transmitter, comprising:

a controller that monitors power returns of a signal transmitted between the transmitter and the receiver as a function of path loss propagation of the transmitted signal and estimates a distance between the transmitter and the receiver, the controller calculates a hitch angle using the first distance, the estimated distance and a trailer length.

10 . The system as claimed in claim 9 wherein the trailer length is stored in controller memory.

11 . The system as claimed in claim 9 wherein the trailer length is calculated by the controller, the controller stores a predetermined number of estimated distances, the controller identifies a largest of the stored distances, and the controller defines the trailer length by deducting the first distance from the largest distance.

12 . The system as claimed in claim 9 wherein the trailer length is calculated by the controller, the controller monitors, over time, signal information from a yaw rate sensor or the vehicle that is representative of a vehicle yaw rate, the controller defines a zero hitch angle when the sensed yaw rate is zero fir a predetermined amount of time, the controller estimates a zero-hitch-angle-distance between the transmitter and the receiver for the defined zero hitch angle, the zero-hitch-angle-distance being a function of a path loss propagation of the transmitted signal, and the controller sets the trailer length equal to the zero-hitch angle distance less the first distance.

13 . The system as claimed in claim 9 further comprising a hitch angle sensor for providing a sensed hitch angle to a vehicle system and wherein the controller compares the estimated angle with the sensed hitch angle to verify an accuracy of the sensed hitch angle.