Analysis of controllability region and control research for AFS and AIFS systems under extreme operating conditions

Abstract Active Front Steering (AFS) enhances vehicle stability by modifying tire lateral forces through the application of an additional steering angle, thereby generating an additional yaw moment. However, under extreme conditions such as high-speed cornering, AFS may not fully exploit the higher lateral force limits of the outer wheels due to the constraints of the steering mechanism, the non-linear characteristics of tires, and load transfer effects. Active Independent Front Steering (AIFS) can independently control the steering angles of the left and right front wheels, potentially allowing the inner and outer tire forces to reach their respective extremes, thus providing a greater additional yaw moment and a stronger stability control capability. This paper primarily focuses on the stability control capabilities of AFS and AIFS under extreme conditions. A non-linear 2-degree-of-freedom (2-DOF) stability dynamics model is established, considering the constraints of the steering mechanism and the effects of load transfer. A method is proposed to calculate the controllable region of the yaw moment for both AFS and AIFS systems under current states. The impact of different vehicle systems on the controllable regions of the two systems is also analyzed. Subsequently, the yaw control capabilities of AFS and AIFS were validated through simulations in the CarSim-Simulink co-simulation environment. This involved tracking a higher yaw rate to simulate oversteering scenarios and designing a Model Predictive Controller (MPC) to obtain the nominal front wheel steering angle based on the Karush-Kuhn-Tucker (KKT) condition algorithm. Finally, a hardware-in-the-loop (HiL) test platform was established to verify the effectiveness and real-time performance of the proposed control strategy. The results demonstrate that AIFS control can enhance the vehicle’s high-speed cornering limits, offering stronger stability control and path tracking capabilities.