Vehicle Integrated Control-An Adaptive Optimal Approach to Distribution of Tire Forces

In this paper, vehicle integrated control based on sliding mode control theory is studied. A new method for adaptive optimal distribution of braking and lateral forces is presented. The effectiveness of proposed integrated chassis control system, especially online balancing of tire forces in an optimal form with and without adaptation mechanism, is demonstrated through digital simulations. A comprehensive nonlinear vehicle dynamics model is utilized for simulation purpose. Control inputs considered are the individual wheel steering and braking for each corner of the vehicle, by means of the steer-by-wire and anti-lock brake system, respectively. Since a unique set of tire forces satisfying control objectives can not be easily determined; an adaptive optimization problem subjected to two equality and four inequality constraints has been solved to achieve the optimal solution. Results indicate the proposed control system most effectively utilizes the friction forces of each tire and it can significantly improve vehicle stability and handling performances. On the other hand, with proper adaptation mechanism, it can minimize the negative effects of direct yaw moment control, such as decreasing the total speed of the vehicle and increasing the stopping distance in emergency situations.