Enhanced Control for Handling and Stability of 4WD Electric Vehicles With Uncertain Stability Margins

Uncertainties, including parameter variation and unknown external disturbances, are the major concerns in the development of a controller, which may lead to vehicle instability when driven in a critical state under extreme conditions. This article proposes an enhanced control strategy considering uncertain parameter (tire stiffness) and external disturbance (road-tire friction coefficient). Initially, the general polynomial chaos (gPC) is applied to model the randomness of parameters. Subsequently, a stability margin that accounts for stochastic uncertainties, including variations in road conditions and tire characteristics, is established. This foundation enables the precise definition and implementation of a control strategy. A reference generator with a variable desired yaw rate is developed to modify the driving characteristics and facilitate personalized handling-oriented requirements. Furthermore, a second-order sliding mode controller determines the external yaw moment with robustness and simple deployment. Ultimately, the experimental results demonstrate the effectiveness in improving handling and stability, which is robust to road friction uncertainty while reducing the limit load on the motor. Compared to the benchmark method, the maximum sideslip angle is reduced by 8.6%–9.3%, and the response time lag is enhanced by 60%.