Method of determining a steering angle in a motor vehicle

1. A method of operating a motor vehicle, comprising:

an electronic control unit setting a relative steering angle equal to an arbitrary initial value that is not related to an actual position of a steered wheel while a steering shaft is in an initial angular position immediately following an ignition on event;

after the electronic control unit has set the relative steering angle equal to an arbitrary initial value, the electronic control unit receiving information from a rotation sensor, the rotation sensor being configured to determine an amount of motor angle rotation of a motor that is configured to facilitate turning the motor vehicle;

when the steering motor has rotated, the electronic control unit determining an amount of steering angle rotation of the steering shaft of the motor vehicle according to the amount of motor angle rotation;

the electronic control unit adding the amount of steering angle rotation to the relative steering angle to determine a new relative steering angle;

the electronic control unit continuing to update the value of the relative steering angle value according to information received from the rotation sensor; and

wherein the initial value is independent of the initial angular position of the steering shaft.

2. The method according to claim 1 , wherein the rotation sensor is a resolver.

3. The method according to claim 2 , wherein the resolver is disposed adjacent to the motor.

4. The method according to claim 1 , wherein the relative steering angle is reset to the initial arbitrary value by the electronic control unit following each ignition on event.

5. The method according to claim 1 , wherein the method includes a step of calculating an adjusted steering angle that is approximately equal to an actual steering angle of the steering shaft.

6. The method according to claim 5 , wherein the adjusted steering angle is equal to the relative steering angle plus a steering angle offset and wherein the value of the steering angle offset depends on the value of the initial angular position of the steering shaft.

7. The method according to claim 5 , wherein the adjusted steering angle is used to control a vehicle stability assist system.

8. The method according to claim 1 , wherein the arbitrary initial value is zero.

9. The method according to claim 1 , wherein the motion of the steering motor is related to the motion of the steering shaft by a fixed gear ratio, and wherein the electronic control unit multiplies the number of degrees the steering motor has rotated by the fixed gear ratio to obtain the amount of rotation of the steering shaft.

10. The method of claim 1 , wherein the electronic control unit comprises at least one of a power steering electronic control unit and a vehicle stability assist system electronic control unit.

11. A motor vehicle comprising:

An electronic control unit configured to set a relative steering angle equal to an arbitrary initial value that is not dependent upon any zero angular position value while a steering shaft is in an initial angular position immediately following an ignition on event;

a rotation sensor configured to determine an amount of motor angle rotation of a motor that is configured to facilitate turning the motor vehicle;

the electronic control unit configured to determine an amount of steering angle rotation of the steering shaft of the motor vehicle according to the amount of motor angle rotation, when the steering motor has rotated;

the electronic control unit configured to add the amount of steering angle rotation to the relative steering angle to determine a new relative steering angle;

the electronic control unit configured to continually update the value of the relative steering angle value according to information received from the rotation sensor; and

wherein the initial value is independent of an absolute steering shaft angle of a steering motor.

12. The motor vehicle of claim 11 , wherein the electronic control unit is configured to calculate an adjusted steering angle that is approximately equal to an actual steering angle of the steering shaft.

13. The motor vehicle of claim 12 , wherein the adjusted steering angle is equal to the relative steering angle plus a steering angle offset and wherein the value of the steering angle offset depends on the value of the initial angular position of the steering shaft.

14. The motor vehicle of claim 11 , wherein the electronic control unit is configured to reset the relative steering angle to the initial arbitrary value by the electronic control unit following each ignition on event.