An independently controllable active steering system for maximizing the handling performance limits of road vehicles

This study explores the effectiveness of an active independent front steering system capable of applying a corrective steering at each wheel selectively and in an independent manner. In doing this, it is possible to generate the required adhesion force for active steering control while ensuring that none of the tyres approaches saturation. A non-linear yaw-plane model of a two-axle truck with a limited number of roll degrees of freedom is used to evaluate the effectiveness of the active independent front steering under a range of steering manoeuvres. A simple proportional-integral controller is synthesized to track the reference response based on the neutral steering system as well as to limit the steering correction considering the saturation limit of the tyres, which is defined from the normalized cornering stiffness properties of the tyres. The directional responses obtained for the vehicle model integrating the active independent front steering controller are compared with those of the conventional active front steering system for each of the selected manoeuvres. The results show that, while both the control strategies can effectively track the target yaw rate of the vehicle, the proposed active independent front steering control can yield enhanced performance limits without any of the tyres approaching the saturation limit, irrespective of the road condition and the steering manoeuvre. Furthermore, the active independent front steering design permits some adhesion reserve for each wheel for generating additional traction and braking forces during a severe steering manoeuvre.