Research On Integrated Control Of Vehicle Suspension And 4WS

Vehicle is a complicated system composed of several assemblies. The research on control method, which aims at single object of specific subsystem, has been developed at certain extent. But how to make the subsystems work harmoniously and reduce the interference, for the purpose of improving the multi-objective performance of vehicle, has been put into a high level estate. This paper describes the effect on vehicle performance by suspension and steering system both of which are the main component of chassis. Combined with Linear-Quadratic (LQ) optimal control theory, the active suspension and four-wheel steering (4WS) system integration is tried and analyzed. The paper first discussed the feasibility and inevitable tendency on the integration of suspension and steering system. The 2-DOF and 7-DOF model for suspension system and the 2-DOF model for steering system are constructed. The uniform mathematical model with 14 DOF is constructed on the foundation of analyzing the steering influencing factor and the intercoupling of vertical and lateral movement. It includes 6-DOF on vertical, pitching, rolling, yaw, lateral and longitudinal movement, 4-DOF on the four unsprung part, and 4-DOF on four tire turning angle. The virtual prototype is adopted to get the parameters of vehicle. And the simulation is used to validate the uniform model. By means of uncoupling the uniform model, combining the LQ optimal control technology, the plan on integrated control of active suspension and 4WS is presented on the purpose of improving the handling and ride comfort of vehicle. The virtual prototype is used to simulate the real vehicle, which has non-linear and parameter uncertainty. The co-simulation of ADAMS&Matlab/Simulink is used to test the vehicle fixed with integrated controller. The results are presented and discussed. The researches indicate that the characteristics of suspension not only have an impact on ride comfort directly, they take effect on the steering motion indirectly by the roll-steer action. The steering system impacts the performance of steering and body rolling motion which acts on ride comfort partially. The active-roll control, which is the part of active suspension, can reduce the body-rolling angle caused by steering or lateral force, and it has the possibility to control the roll-steer angle. By controlling the dynamic load of tire, active suspension can reduce the change of the tire characteristics, which has the main influence in steering, and it can reinforce the limited contribution of 4WS in ride comfort. The 4WS control the steering action effectively by regulating the yaw rate of vehicle, which reinforces the limited contribution of active suspension in steering control. It makes the yaw angle close to zero, get better tracking performance, and improve the steering security. The integrated vehicle chassis control technology considers the vehicle as an undivided system. Active suspension combined with 4WS act as complement for each other. The theory analysis and simulation test indicate that the integrated control of suspension and 4WS can make positive influence on handling and ride comfort of vehicle.