Suspension Kinematics: A Method for Determining Steer Induced Angles and Displacements

Abstract

The lateral force created by a tire necessary for a vehicle to change direction is generated by slip and camber angles. Camber angle may be defined as the angle between a vertical line passing through a wheels’ center and the horizontal projection of this line onto the wheel. If the axis which the tire turns about is not parallel to the vertical axis, a change in camber will be induced as a result of the change in steer angle. This axis is called the steering axis and can be determined by the caster and lean angles relative to the wheel position in a body coordinate frame. The relation between the steer and camber angles may favor or detract from the lateral force being generated by the tire. This paper describes a method for determining the induced camber angle with respect to steer angle. In this method the wheel is defined throughout the steering range as a circle. The lowest point of the circle with respect to the global coordinate frame may then be defined via a method for determining maxima and minima. This point is then used to determine camber angle with respect to steer angle throughout the steering range. The lowest point of the tire may also be used in finding ride height and body roll due to change in steer angle. A sensitivity analysis reflects the suspension behavior for a variety of different suspension parameters. The relative difference between the induced steer angle about the steering axis and the actual steer angle with respect to the body coordinate frame are relevant in developing more accurate vehicle dynamics models.