Variable caster steering in vehicle dynamics

Abstract

When a car is cornering, its wheels usually lean away from the centre of rotation. This phenomenon decreases lateral force, limits tyre performance and eventually reduces the vehicle lateral grip capacity. This paper proposes a strategy for varying caster in the front suspension, thereby altering the wheel camber to counteract this outward inclination. The homogeneous transformation was utilised to develop the road steering wheel kinematics which includes the wheel camber with respect to the ground during a cornering manoeuvre. A variable caster scheme was proposed based on the kinematic analysis of the camber. A rollable vehicle model, along with a camber-included tyre force model, was constructed. MATLAB/Simulink was used to simulate the dynamic behaviour of the vehicle with and without the variable caster scheme. The results from step steer, ramp steer, and sinusoidal steer inputs simulations show that the outward leaning phenomenon of the steering wheels equipped with the variable caster, is reduced significantly. The corresponding lateral acceleration and yaw rate increase without compromising other handling characteristics. The actively controlled car, therefore, provides better lateral stability compared to the passive car. The tyre kinematic model and the vehicle dynamic model were validated using multibody and experimental data.

Solution of steering angle based on homogeneous transformation

“…Where d = 1/(tan 2 g + tan 2 b) 1/2 . By equation (17), the cosine of the angle between A' D' and X axis is computed as follow:…”

“…Alberding et al 16 detailed explained the position relations between kingpin and wheel and through coordinate transformation, calculated vector of steering wheel center and tire-print center. Vo et al 17 proposed a kind of strategy for varying caster in the front suspension and calculated wheel steering model in the condition of variable and constant camber angle. It is complicated to calculate coordinates of wheel center and tire-print center due to multiple coordinate frames established on wheel in these papers.…”

The Relationship between Car Caster Angle and the Directional Stability of Car

“…The simulation process is that the car runs at different speeds from the static state, and the simulation time is 8 seconds. The driving state includes : (1) the vehicle travels at a uniform speed with a speed of 8m/s, and the center of mass and the ground are constrained by moving deputy; (2) The vehicle travels at a uniform speed, at a speed of 12m/s, and the center of mass and the ground are constrained by moving deputy; (3) The acceleration of the vehicle is 1.6m/s 2 , and the center of mass and the ground are constrained by moving pairs; (4) The vehicle accelerates, with an acceleration of 1.6m/s 2 , and there is no constraint between the center of mass and the ground.…”

“…The front shock absorber of the car is not completely perpendicular to the ground, and most of it is inclined backward, and the angle of the rearward inclination of the shock absorber is called the caster [2]. Caster angle is the angle between the king pin and the suspension system viewed from the side of the car, locomotive, or bicycle body.…”