A simulator study on the controllability of steering systems with reduced maximum steering wheel angle

Abstract

Active Front Steering shows that with a variable gear ratio, it is possible to reduce the maximum steering wheel angle from zero position to lock to approximately +- 360°. Compared to a conventional power steering system, this is a reduction of about 40%. With technologies like reliable electric power steering or steer-by-wire coming to the market, it is possible to reduce the maximum steering angle even further. To assess the controllability of further reduced maximum steering angles, a driving simulator study with two different steering systems with reduced total steering wheel angle is conducted with 36 experienced normal drivers. The steering systems are modelled within Matlab/Simulink and are integrated into the simulator on a real time target. The steering wheel is controlled by a synchronous AC motor providing up to 24 Nm of steering wheel torque. One system is an adapted conventional steering system without variable gear ratio and a maximum steering wheel angle of +- 180°. The other system employs the advantages of a steer-by-wire system and uses a PID-controller to regulate the vehicles yaw rate proportional to the steering angle. The steering wheel torque is proportional to yaw rate, lateral acceleration and vehicle velocity. The maximum steering angle is set to +- 90°. Both systems are benchmarked with a conventional steering system with a steering wheel travel from zero to lock of +- 600°. For all three systems subjective measurements to evaluate the steering feel and objective measurements, e.g. lane keeping quality to evaluate the controllability, are taken. The study shows that there is a limitation regarding the reduction of the steering wheel stroke between +-180 and +-90°, as the system with a maximum steering angle of +-90° performs worst regarding overall controllability. Furthermore it showed that the system with a limited maximum steering angle of +-180° performed best with respect to subjective steering feel.