Automotive drift control beyond the stability limits with a nonlinear vehicle dynamic model

In order to improve the steering performance of vehicles on low adhesion roads, this paper proposed a drift control method by coordinating the steering angle and the rear wheel slip ratio. Because lateral force of rear wheels is saturated with high longitudinal slip ratio under the drift condition, a vehicle dynamic model considering the coupling of the rear wheels’ longitudinal and lateral force is established. In view of the fact that the lateral tire force is affected by the nonlinearity of sideslip angle and slip ratio, the vehicle dynamic model is complex and makes it difficult for controller design. Due to this, a description method of the nonlinear relationship is presented for simple which introduces a virtual control quantity representing the influence of slip ratio on lateral tire forces based on the function of tire force with sideslip angle and slip ratio. Then, a sliding mode control method is proposed to ensure the stability of the closed-loop system and an off-line two-dimensional map is constructed to convert the virtual control quantity into the actual control quantity. The simulation results in the high-precision vehicle dynamics simulation software show that even if the initial state is far from the equilibrium point of drift, the drift controller also can ensure the stability of the closed-loop system and achieve a good drift performance.