| Due to the complex road condition, body posture will change when the vehicle running on it. Even on a flat road, wheel hop will also be caused by road bumps or pits, which transmits road shock and vibration to the vehicle. And thus vehicle performance and passengers’ ride feeling will be affected. As the continuous improvement of requirements of vehicle performance, enhancing the active control capability of vehicle to adapt to different conditions is needed. And subsystems involved in operating under different conditions vary. Meanwhile, control objectives of body posture are not the same. It’s necessary to take advantages of integrated control in subsystems of vehicle chassis to ensure body posture controlled within an appropriate range and improvement of driving performance. In this paper, considering coupling relationship of suspension, steering and braking systems in the lateral, longitudinal and vertical directions, the optimization of body posture at the condition of emergency braking when traveling straight, high-speed cornering and turning braking is researched with three active chassis control technology including four-wheel steering, active suspension and anti-lock braking system.Firstly, a brief description of research status about vehicle chassis integrated control and body posture control. Based on the theory of vehicle system dynamics, considering road roughness actuators and the nonlinear characteristics of tire model, the mathematical models of chassis subsystem of the half vehicle and the whole vehicle are established. And the tire vertical load variation model under different conditions is given.Then, based on modern control theory, the active controllers of suspension, steering and braking systems are designed. Results of simulation modeling in the use of MATLAB/Simulink illustrate that the designed active controllers have advantages in terms of body posture and performance improvement.Finally, the control strategies of straight line braking, cornering, turning braking are appropriately designed for simulation analysis. In the straight line braking, a coordinated control strategy involved with brake system and suspension of the half vehicle is proposed. Simulation results on two kinds of pavement show that the proposed coordinated control can restrain pitch motion and improve braking efficiency. The research on turning condition is conducted from two aspects which are body roll angle control and anti-rollover control. A fuzzy adaptive PID controller is designed, and the combination of four-wheel steering and active suspension treat body roll posture and lateral stability. Roll stability during steering at high speed of the vehicle is studied by using differential braking control method for anti-roll control. In turning braking, suspension, steering and braking system are integrated. Put forward a integrated control strategy. The simulation result shows that the proposed integrated control under four combinations is effective in optimizing body posture and improving handling stability, riding comfort and driving safety. |
