Grip Margin-Based Control Allocation for Enhanced Vehicle Stability in Four-Wheel Independent Steering Vehicle

This study aims to enhance the control performance of four-wheel independent steering vehicles (4WIS), which are increasingly recognized as a key innovation in electric vehicle technology. 4WIS provides a high degree of freedom and dynamic performance by enabling the independent steering of each wheel. However, as an over-actuated system, it requires the allocation of four steering angles from a single driver input, making control allocation critical. Existing methods often fail to fully consider the friction limits of individual tires, potentially compromising vehicle stability, especially under severe driving conditions. To address this, a grip margin-based control allocation (GMCA) technique is proposed, which distributes control forces according to each tire’s available friction, minimizing yaw rate error and side-slip angle while maintaining stability. GMCA is formulated using computationally efficient algebraic operations, enabling real-time implementation. Validation through Simulink/CarMaker co-simulation confirms that GMCA improves maneuverability and lateral stability over conventional methods, offering practical benefits for precise control of 4WIS vehicles under severe road conditions.