Four wheel steering control utilizing front/rear tire longitudinal slip difference
First Claim
1. A method of improving vehicle handling for use with a vehicle having manually operable front steerable wheels and electronically controlled rear steerable wheels, the front and rear steerable wheels each including a tire, said method comprising the steps of:
- calculating a desired rear steer angle based on vehicle speed and front wheel angle during operation in a linear region of the tires;
determining if the vehicle is operating in a nonlinear region of the front tires;
calculating a handling term if the vehicle is operating in the nonlinear region of the front tires;
determining if the magnitude of average rear tire longitudinal slip is greater than the magnitude of average front tire longitudinal slip;
adjusting the handling term to compensate for reduced rear cornering force if the magnitude of the average rear tire longitudinal slip is greater than the magnitude of the average front tire longitudinal slip;
modifying the desired rear steer angle based on the handling term to obtain a modified desired rear steer angle; and
steering the rear steerable wheels toward the modified desired steer angle.
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Accused Products
Abstract
A four wheel steering strategy determines when the rear tire longitudinal slip becomes greater than the front tire longitudinal slip, either due to braking or acceleration, such that the rear tire slip angles must be increased to maintain vehicle balance with respect to the level of understeer/oversteer. The out-of-phase rear steering angle is reduced or the in-phase rear steering angle is increased to increase the rear tire slip angles and thereby correct vehicle balance. Three embodiments are disclosed which use estimated tire longitudinal slips, wheel speeds, and engine throttle information, respectively. The required inputs for the various embodiments can be obtained from independent sensors or preferably are available from other vehicle systems such as an anti-lock braking system, a traction control system or an engine management system. Advantageously, the present invention operates without requiring expensive sensors such as yaw sensors which are currently not feasible for mass market use.
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Citations
7 Claims
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1. A method of improving vehicle handling for use with a vehicle having manually operable front steerable wheels and electronically controlled rear steerable wheels, the front and rear steerable wheels each including a tire, said method comprising the steps of:
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calculating a desired rear steer angle based on vehicle speed and front wheel angle during operation in a linear region of the tires; determining if the vehicle is operating in a nonlinear region of the front tires; calculating a handling term if the vehicle is operating in the nonlinear region of the front tires; determining if the magnitude of average rear tire longitudinal slip is greater than the magnitude of average front tire longitudinal slip; adjusting the handling term to compensate for reduced rear cornering force if the magnitude of the average rear tire longitudinal slip is greater than the magnitude of the average front tire longitudinal slip; modifying the desired rear steer angle based on the handling term to obtain a modified desired rear steer angle; and steering the rear steerable wheels toward the modified desired steer angle. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification