Rear steering control with longitudinal shift in ackerman center
First Claim
1. A method of determining a steering angle for a rear wheel in a vehicle steering system comprising the steps:
- measuring vehicle speed;
deriving a desired lateral acceleration;
measuring an actual lateral acceleration;
if the derived desired lateral acceleration and the measured actual lateral acceleration are in the same direction, (a) determining a dynamic yaw center on a vehicle longitudinal axis in response to the measured vehicle speed, (b) determining a cornering radius, (c) determining a rear wheel steering angle corresponding to a wheel direction perpendicular to a straight line connecting the center of the rear wheel to an instantaneous Ackerman center defined at a distance of the cornering radius from the dynamic yaw center in a direction perpendicular to the vehicle longitudinal axis.
2 Assignments
0 Petitions
Accused Products
Abstract
A rear wheel steering control determines, when desired and actual lateral accelerations of a vehicle have the same direction, an instantaneous dynamic yaw center on a vehicle longitudinal axis in response to the measured vehicle speed. It further determines a cornering radius and an instantaneous Ackerman center as a point at the outer end of the cornering radius extended outward perpendicular to the vehicle longitudinal axis from the instantaneous Ackerman center. The control then directs a rear wheel of the vehicle to be perpendicular to a line connecting the instantaneous Ackerman center to the center of the wheel. The dynamic yaw center, and thus the instantaneous Ackerman center, is preferably shifted rearward with increasing vehicle speed to shift vehicle steering in a direction from oversteer at very low speeds for greater ease of steering in parking maneuvers to understeer for vehicle stability in high speed driving conditions. The method and apparatus preferably include a reverse lock routine to control the rear wheels when the desired and actual lateral accelerations of the vehicle have opposing directions, to control the vehicle in a four wheel drift; and the reverse lock routine may further adjust suspension damping.
12 Citations
7 Claims
-
1. A method of determining a steering angle for a rear wheel in a vehicle steering system comprising the steps:
-
measuring vehicle speed;
deriving a desired lateral acceleration;
measuring an actual lateral acceleration;
if the derived desired lateral acceleration and the measured actual lateral acceleration are in the same direction, (a) determining a dynamic yaw center on a vehicle longitudinal axis in response to the measured vehicle speed, (b) determining a cornering radius, (c) determining a rear wheel steering angle corresponding to a wheel direction perpendicular to a straight line connecting the center of the rear wheel to an instantaneous Ackerman center defined at a distance of the cornering radius from the dynamic yaw center in a direction perpendicular to the vehicle longitudinal axis. - View Dependent Claims (2, 3)
-
-
4. A rear wheel steering control for a vehicle comprising:
-
a vehicle speed sensor;
means for deriving a desired lateral acceleration;
a lateral acceleration sensor; and
means for, when the derived desired lateral acceleration and the measured actual lateral acceleration are in the same direction, (a) determining a dynamic yaw center on a vehicle longitudinal axis in response to the measured vehicle speed, (b) determining a cornering radius, (c) determining a rear wheel steering angle corresponding to a wheel direction perpendicular to a straight line connecting the center of the rear wheel to an instantaneous Ackerman center defined at a distance of the cornering radius from the dynamic yaw center in a direction perpendicular to the vehicle central longitudinal axis. - View Dependent Claims (5, 6, 7)
-
Specification