Cornering Force Maximization With Variable Slip Ratio Control for Independent-All-Wheel-Drive Electric Vehicle

The improvement of the maneuverability using fast and precise control of the electric motor is a crucial subject. A driving force controller (DFC) is considered to be a simple yet excellent method to secure the traction of the tire by directly limiting the slip ratio of the wheel. A conventional variable slip ratio limiter (VSRL) used for the DFC changed the limit value according the sideslip angle of the wheel, effectively maximizing either longitudinal or lateral forces of the tire. However, this did not necessarily maximize the cornering force, which is perpendicular to the vehicle body speed vector. This study presents a new variable slip ratio control method to maximize the cornering forces when the wheels have a large sideslip angle, with the aim of increasing maximum available lateral acceleration. An improved VSRL is proposed so that even when the sideslip angle of the tire is large, the tire force direction faces perpendicular to the vehicle body speed vector and the cornering force can be maximized. Simulations and experimental results using a real EV confirm that cornering maneuverability can be improved, increasing the yaw rate and lateral acceleration during cornering with a large sideslip angle of the tire on slippery roads.