Methods of controlling four-wheel steered vehicles

1. A method for controlling a vehicle, the vehicle comprising a pair of steerable front wheels and a pair of steerable rear wheels, the method comprising:

detecting a front wheel steering angle of at least one of the steerable front wheels;

detecting a rear wheel steering angle of at least one of the steerable rear wheels;

determining an overall Ackerman angle;

determining an effective rear wheel steering angle value from the rear wheel steering angle and a scaling factor;

determining a double Ackerman geometry steering angle value based upon the overall Ackerman angle and an Ackerman scaling factor;

determining a feed-forward lateral acceleration value based upon the front wheel steering angle, the effective rear wheel steering angle value, and the double Ackerman geometry steering angle value, the feed-forward lateral acceleration value facilitating feed-forward control of the steerable front wheels and the steerable rear wheels; and

controlling operation of the steerable front wheels and the steerable rear wheels in response to the feed-forward lateral acceleration value.

2. The method of claim 1 further comprising:

detecting a vehicular speed; and

decreasing the Ackerman scaling factor from a first magnitude to a second magnitude when the vehicular speed increases from a first speed value to a second speed value.

3. The method of claim 1 further comprising:

detecting a vehicular speed; and

controlling operation of the steerable front wheels and the steerable rear wheels in response to the feed-forward lateral acceleration value when the vehicular speed is below a threshold value.

4. The method of claim 3 wherein the threshold value is about 15 KPH.

5. The method of claim 1 wherein determining an overall Ackerman angle comprises determining the overall Ackerman angle based upon the front wheel steering angle and the rear wheel steering angle.

6. The method of claim 1 wherein determining an overall Ackerman angle comprises:

detecting a speed of each of the rear wheels; and

determining the overall Ackerman angle based upon the difference in speed between the rear wheels.

7. A method for operating a vehicle, the vehicle comprising a pair of steerable front wheels and a pair of steerable rear wheels, the method comprising:

detecting a front wheel steering angle of at least one of the steerable front wheels; and

detecting a rear wheel steering angle of at least one of the steerable rear wheels;

detecting a vehicular yaw rate;

detecting a vehicular speed;

determining a yaw-based scaling factor based upon the vehicular yaw rate;

determining a speed-based scaling factor based upon the vehicular speed;

determining an effective rear wheel steering angle value from the rear wheel steering angle, the yaw-based scaling factor, and the speed-based scaling factor;

determining an overall Ackerman angle;

determining a double Ackerman geometry steering angle value based upon the overall Ackerman angle and an Ackerman scaling factor;

if the vehicular speed is above a threshold speed, determining a feed-forward lateral acceleration value based upon the front wheel steering angle and the effective rear wheel steering angle;

if the vehicular speed is equal to or below the threshold speed, determining a feed-forward lateral acceleration value based upon the front wheel steering angle, the effective rear wheel steering angle, and the double Ackerman geometry steering angle value; and

controlling operation of the steerable front wheels and the steerable rear wheels in response to the feed-forward lateral acceleration value, wherein the feed-forward lateral acceleration value facilitates feed-forward control of the steerable front wheels and the steerable rear wheels.

8. The method of claim 7 further comprising decreasing the speed-based scaling factor from a first magnitude to a second magnitude when the vehicular speed increases from a first vehicular speed value to a second vehicular speed value.

9. The method of claim 8 further comprising decreasing the yaw-based scaling factor when the vehicular yaw rate increases.

10. The method of claim 9 further comprising decreasing the Ackerman scaling factor from a first magnitude to a second magnitude when the vehicular speed increases from a first speed value to a second speed value.

11. The method of claim 10 wherein the threshold value is about 15 KPH.