SAE International Performance Analysis of Active Independent Front Steering (AIFS) for Commercial Vehicles with Greater Lateral Load Shift Propensity 2013-01-2355

An Active Independent Front Steering (AIFS) offers attractive potential for realizing improved directional control performance compared to the conventional Active Front Steering (AFS) system, particularly under more severe steering maneuvers. The AIFS control strategy adjusts the wheel steer angles in an independent manner so as to utilize the maximum available adhesion at each wheel/road contact and thereby compensate for cornering loss caused by the lateral load transfer. In this study, the performance potentials of AIFS are explored for vehicles experiencing greater lateral load transfers during steering maneuvers such as partly-filled tank trucks. A nonlinear yaw plane model of a two-axle truck with limited roll degree-of-freedom is developed to study the performance potentials of AIFS under different cargo fill conditions. The lateral movement of the cargo within a partly-filled cylindrical tank is described by the resulting lateral load shift, lateral force and the roll moment using the quasi-static fluid motion. The AIFS control strategy based on a simple PI controller is subsequently integrated and simulations are performed under different loading conditions for a steady- turning maneuver. Simulation results in general show that while both the AFS and AIFS can achieve the target response to a steering command, the AFS control causes the inner wheel to saturate under lateral accelerations well below the rollover threshold limit. The AIFS strategy, on the other hand, realizes the target response at far greater speeds, while the steered wheels do not encounter cornering force saturation until the vehicle approaches rollover condition. The results further show superior tire work-load performance of the vehicle with AIFS, irrespective of the load.