Nonsingular Fast Terminal Sliding Mode-Based Lateral Stability Control for Three-Axis Heavy Vehicles

In order to improve the driving stability of three-axis heavy vehicles (TAHV) under special driving conditions, this paper proposes a novel integrated control scheme combining six-wheel steering (6 WS) and direct yaw moment control (DYC). First, a 9-DOF TAHV dynamics model, which considers the tire nonlinear mechanical properties under combined conditions, is established, and an equivalent stiffness coefficient of the middle and rear axles is introduced to calculate the vertical load of each wheel more accurately. In the 6 WS control strategy, with the goal of zero sideslip angle, the steering ratio coefficients of the middle and rear axles are adjusted in real-time according to the vehicle longitudinal speed based on the Ackerman principle. In the DYC strategy, the tire cornering stiffness of the TAHV reference model is dynamically corrected in real-time based on the Newton interpolation method. In addition, the longitudinal critical speed is determined by using Laplace transform to choose the suitable reference model for different steering modes to calculate the ideal yaw rate value. Then, based on feedforward control and feedback control using nonsingular fast terminal sliding mode (NFTSM) control (SMC) algorithm, the optimal additional yaw moment required for TAHV lateral stabilization is calculated. On this basic, the braking torque of every wheel is obtained by optimal control allocation algorithm. Finally, simulation verification is carried out for four typical driving conditions, and the results show that the integrated control scheme has good control effect on lateral stability of TAHV.