Ackerman angle correction in a steering system for a low speed turn
A method of calculating feed-forward lateral acceleration of a moving vehicle is provided. The method includes the use of a corrected steering angle of the vehicle. The steering angle is corrected by using the Ackerman steer angle of the vehicle. Depending upon the speed at which the vehicle is traveling the steering angle may be corrected using the full Ackerman steer angle, a fraction of the Ackerman steer angle or not at all.
1. A method of calculating a feed-forward lateral acceleration of a moving vehicle comprising the steps of:
measuring a speed of the moving vehicle;
measuring a steering angle of the moving vehicle;
calculating an Ackerman steer angle of the moving vehicle;
calculating a corrected steering angle of the moving vehicle using the Ackerman steer angle of the moving vehicle; and
calculating the feed-forward lateral acceleration of the moving vehicle using the measured speed of the moving vehicle and the corrected steering angle.
2. The method of claim 1 , wherein the corrected steering angle is calculated by subtracting the Ackerman steer angle from the measured steering angle.
3. The method of claim 1 , wherein the step of calculating the Ackerman steer angle includes measuring or calculating a yaw rate of the vehicle.
4. The method of claim 1 , wherein the step of calculating the Ackerman steer angle includes measuring the speed of an outside vehicle wheel in a turn and measuring the speed of an inside vehicle wheel in the turn.
5. The method of claim 1 , further including a step of calculating drive torque for each wheel of the vehicle on the basis of the calculated feed-forward lateral acceleration of the vehicle.
6. The method of claim 1 , wherein the Ackerman steer angle is scaled as the speed of the moving vehicle increases.
7. The method of claim 1 , wherein the vehicle speed is used to look up a lateral acceleration predictor using a predetermined table specific to the vehicle.
8. The method of claim 2 wherein the corrected steering angle is multiplied by an estimated lateral acceleration of the vehicle.
9. A system of calculating feed-forward lateral acceleration of a moving vehicle comprising:
means for measuring a speed of a moving vehicle;
means for measuring a steering angle of the moving vehicle;
means for calculating an Ackerman steer angle of the moving vehicle; and
means for calculating the feed-forward lateral acceleration of the moving vehicle using the measured speed of the moving vehicle and a steering angle corrected by using the Ackerman steer angle.