Optimal yaw-rate control for electric vehicles with active front-rear steering and four-wheel driving-braking force distribution

Direct yaw-moment control (DYC) is an effective method for achieving stable vehicle motion. In the DYC systems of vehicles with in-wheel motors and active front and rear steering systems, some control inputs are generally redundant. This means that input variables cannot be decided uniquely to control each longitudinal, lateral, and yawing motion. The equalization of workloads of each wheel based on longitudinal and lateral force distributions enhances the cornering performance of vehicles. Therefore, we propose a method for obtaining longitudinal-and lateral-force distributions based on least-squares solutions of the equations of longitudinal, lateral, and yawing motions. Furthermore, we propose a lateral-force control method using tire lateral force sensors, active front and rear steering systems, and a DYC method for enhancing the yaw-rate control performance. In this study, through simulations and experiments, we show that the equalization of the workload on each wheel and quick yaw-rate response are achieved by adopting the proposed methods.