Method and apparatus for minimizing driver disturbance in a limited by-wire active steering system
View Patent ↗A method is provided for limiting a steering angle overlay applied by a steering actuator in a limited by-wire active front steering (AFS) system. The method includes determining a maximum rate limit for the steering angle overlay in order to minimize an undesired disturbance to the driver in the form of a torque and/or angle feedback while maximizing the rate of steering overlay allowed for a given set of vehicle operating conditions. The maximum rate limit is determined by a function of the input steering rate and braking level. A limited AFS system includes both steering and braking input devices, a steering actuator, and a controller having an algorithm. The controller uses the algorithm to calculate the maximum overlay rate limit and limits the steering actuator to the maximum overlay rate limit.
1. A method for limiting a rate of steering angle overlay that can be applied by a steering actuator in a limited by-wire active front steering (AFS) system for a vehicle, the method comprising:
measuring an input steering angle rate;
measuring an input braking level;
calculating a maximum rate limit for the rate of steering angle overlay as a function of the input steering rate and the input braking level; and
selectively limiting the rate of steering angle overlay to the maximum rate limit based on a predetermined vehicle condition.
2. The method of claim 1 , wherein calculating the maximum rate limit includes accessing a lookup table indexed by at least one of the input steering rate, the input braking level, and a speed of the vehicle.
3. The method of claim 1 , wherein the predetermined vehicle condition is a non-linear stability maneuver.
4. The method of claim 1 , wherein measuring an input steering rate from a steering device includes detecting a rotational velocity of a steering wheel.
5. The method of claim 1 , wherein measuring an input braking level includes one of detecting a fluid pressure of a master cylinder pressure and detecting an electronic braking force signal.
6. The method of claim 1 , further comprising modifying the maximum rate limit when at least one of the input steering rate and the input braking level exceed a corresponding calibrated threshold.
7. A method for controlling a steering actuator in a by-wire steering system of a vehicle, the method comprising:
measuring an input steering rate imparted to a steering wheel of the vehicle;
measuring an input braking level imparted to a master cylinder;
determining a maximum rate limit for a rate of steering angle overlay delivered from the steering actuator based on a function of each of the input steering rate and the input braking level; and
limiting the rate of steering angle overlay to the maximum rate limit.
8. The method of claim 7 , further comprising modifying the maximum rate limit when a predetermined variable exceeds a calibrated threshold.
9. The method of claim 8 , wherein the calibrated threshold is a calibrated braking level, and wherein the predetermined variable is the input braking level.
10. The method of claim 7 , wherein determining the maximum rate limit includes at least one of applying a linear step function to the input braking level and a non-linear function to the input steering rate.
11. A limited by-wire active front steering system for use with a vehicle, the system comprising:
a steering input device having a measurable input steering angle rate;
a braking input device having a measurable input braking level;
a steering actuator configured for overlaying a corrective steering angle to thereby modify the input steering angle; and
a controller configured for calculating a maximum rate limit for the corrective steering angle as a function of the input braking level and the input steering rate, and for limiting a rate of overlay of the corrective steering angle to the maximum rate limit to thereby enhance the stability of the vehicle during a non-linear steering maneuver.
12. The system of claim 11 , wherein the controller is configured for modifying the maximum rate limit when the input braking level exceeds a threshold braking value.
13. The system of claim 11 , wherein the input braking level is one of a master cylinder braking pressure and an electronic braking force.