An Optimal Approach to Nonlinear Control of Vehicle Braking System during Severe Braking and Turning

Severe braking during turning is one of the vehicle critical maneuvers. In this case, achieving the minimum stopping distance while maintaining the vehicle steerability is important. The conventional anti-lock braking system attains the minimum stopping distance by generating the maximum braking forcesbut, cannot control the vehicle steerability directly. In this paper, in order to direct control of vehicle longitudinal and lateral dynamics, an optimal nonlinear algorithm based on the prediction of system responses is presented to distribute the wheels braking forces properly. In this algorithm, the maximum braking forces of one side wheels are reduced to the extent that the required stabilizing yaw moment is produced. In this way, a compromise between the stopping distance and vehicle steerability can be easily made by the regulation of weighting ratio, as a free parameter of the yaw moment control law. In the special case, when the external yaw moment takes to be zero(expensive control), this algorithm is changed to the conventional anti-lock braking system. With any increase of the external yaw moment, the stopping distance is increased but the vehicle steerability is improved. The simulation results performed by an 8-DOF vehicle model show a suitable and robust performance of the proposed control system.