Combined-Slip Trajectory Tracking and Yaw Stability Control for 4WID Autonomous Vehicles Based on Effective Cornering Stiffness

Trajectory tracking is a crucial responsibility for autonomous vehicles as they strive to avoid collisions. During combined-slip emergency situations where steering and driving/braking joint control are required, the nonlinearity and coupling of tire forces become increasingly important, rendering a linear tire model-based controller ineffective and leading to degraded path-tracking performance. Such degradation can ultimately jeopardize vehicle stability. To address the aforementioned issue, we establish a hierarchical coordinated controller for four-wheel independent drive (4WID) autonomous vehicles, specifically tailored to handle combined-slip trajectory tracking and yaw stability control, considering variable tire cornering stiffness. At the upper level, a model predictive lateral motion controller is engineered based on a novel combined-slip UniTire-Ctrl model. The predictive model captures the intricate nonlinear and coupling characteristics of tire forces through an analytical expression of effective cornering stiffness. This enables the controller to account for the impact of longitudinal force on lateral motion control and coordinate the front-wheel steering angle and direct yaw moment in an efficient manner. Additionally, a linear quadratic longitudinal motion controller is developed to follow the desired longitudinal speed. The lower-level torque distribution controller is constructed to prioritize vehicle stability by minimizing tire adhesion utilization. Finally, the effectiveness of the controller under combined-slip conditions is validated through the CarSim and Matlab/Simulink co-simulation platforms, which demonstrates that the developed combined-slip motion controller with UniTire-Ctrl model exhibits superior tracking precision and stability under extreme combined-slip conditions.