Integrated vehicle lateral stability control with different coordination strategies between active steering and differential braking

This paper investigates several coordination strategies for the integrated use of active steering and differential braking control systems to improve vehicle's lateral stability. Each stand alone control system is developed to achieve a given objective; however, these systems are not designed to work in a cooperative way. By collaborating the work of these individual control systems, the overall performance of the vehicle's dynamics is enhanced by exploiting their advantages according to the driving phase and by minimizing their interaction. First, the stand alone controllers are synthesized using a second order sliding mode law by applying the super twisting algorithm known for its robustness and its reduction of the chattering phenomena. The coordination strategies are based on the stability index which is derived from the phase plane study of the vehicle's side-slip angle and its velocity to judge the vehicle's stability region. The analysis of these coordination strategies is done by simulation on a nonlinear seven degree of freedom four wheels vehicle model.