Global vehicle control using differential braking torques and active suspension forces

Abstract

This article treats the problem of global chassis control of a wheeled-vehicle in a turn. The aim of our research is to design a nonlinear control law that allows the vehicle to follow the desired trajectories in yaw rate and in longitudinal acceleration while stabilizing the behaviours of roll rate, pitch rate and vertical velocity using both braking torques and suspension forces. The research is realized under the collaboration of the Centre de Robotique of the École des Mines de Paris with PSA-Peugeot-Citroën. The global control problem is divided into two subproblems depending on the physical control actuators which are used. First, in the case of horizontal dynamics control, only the braking torques are used. Then, in the second case of vertical dynamics control, only the suspension forces are used. In this case, we show that the system loses its controllability property during the transition phase of the turn, if we consider explicitly the yaw acceleration equation to compute the suspension forces. An alternative solution is proposed, which can regulate the pitch rate, roll rate and vertical velocity, and can act on the yaw rate by adapting a constrained optimal control algorithm. Then the two control subproblems are merged into a global chassis control which achieves our aim. The above mentioned control laws are based on the technique of nonlinear constrained optimization and of singular perturbations theory using natural time scale decomposition in slow/fast subsystems. They have been tested and validated on a complete vehicle model of 14 degrees of freedom developed by PSA-Peugeot-Citroën.