Robust wheel torque control for traction/braking force tracking under combined longitudinal and lateral motion

Slip-ratio-based methods are commonly used to control the wheel torque such that the wheel dynamics is stabilized and the desired traction/braking force is attained; however, slip-ratio-based controllers are incompetent for precise longitudinal tire force tracking due to nonparametric tire model uncertainties. Force tracking performance further deteriorates whenever the tire is under combined longitudinal and lateral motion. In this paper, we propose an observer-based tire force control scheme that guarantees to achieve the desired longitudinal tire force accurately and robustly with respect to tire model uncertainties, changes in road conditions, and simultaneous lateral motion. Convergence of the force estimation and tracking errors is rigorously proved by the Lyapunov method. Then, simulations are conducted to verify the robust and accurate performance in longitudinal tire force estimation and tracking under a series of severe driving conditions.