Methods of controlling four-wheel steered vehicles

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.

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.