Disturbance Observer Based Active Independent Front Steering Control for Improving Vehicle Yaw Stability and Tire Utilization

In the currently used steering systems, the front tires are steered dependently during turning maneuvers. During these maneuvers, the weight transfer causes the inner tire to have less vertical force compared to the outer tire. Therefore, it generates less lateral tire force and can be saturated easily in some extreme conditions. On the other hand, the outer tire can provide more lateral force due to the higher vertical force, but its potential may not be utilized because the steering of the inner and outer tires is dependent. Thus, an independent steering capability can provide potential benefits by eliminating the saturation of the inner tire and getting more lateral force from the outer tire. Therefore, an active independent front steering system is proposed by combining a yaw-rate PI controller with disturbance observers on tire forces to improve the yaw stability at the acceptable limits. The coefficients of the PI controller are calculated analytically. The cut-off frequency in the disturbance observer is determined by the robust stability analysis considering the variance in the vehicle dynamic parameters. Finally, by taking into account the tire utilization coefficient (TUC), the performance of the proposed system is compared to conventional active steering systems in CarSim simulation environment.