Research On Control Algorithm Of Vehicle Active Suspension Based On Differential Geometry Decoupling Theory

The vehicle suspension system influences not only harshness, but also handling stability of the vehicle. In the aspect of harshness, four wheels undergo the excitation from road; the vibration of the vehicle body is the resultant which all the wheels cause. In the aspect of handling stability, due to the influence of the front wheel angle, the roll motion of the vehicle body gets aggravated in steering condition. When the vehicle is in an emergence steering condition, since the longitude and the lateral load transferring, the vertical force of four suspensions alter, so the holding ability of the tires changes correspondingly and that influences the handling stability of the vehicle. The control objectives of the vehicle in different conditions are different. The vehicle suspension control system is a MIMO nonlinear system. The control of vehicle active suspension is essentially the control allocation of a MIMO system, namely the well-known Morgan problem in mathematics. The differential geometry control theory is a powerful tool to solve the control problem of the nonlinear systems and can realize the reasonable allocation of the active suspension force.Considering the different working conditions of vehicles, the decoupling control algorithms on the active suspension have been researched by using differential geometry theory in this project.(1) In straight line driving condition, the control objective of the active suspension is to improve the harshness of the vehicle. The EDDC (excluding damper decoupling control) algorithm is proposed. The vertical motion, pitch motion and roll motion of the vehicle body are independent of each other by decoupling, and the suspension system is separated into multi independent linear subsystems. Through the pole assigned of the linear subsystem, the vertical motion, pitch motion and roll motion of the vehicle body attenuate greatly. The simulation of the time domain, the frequency domain, and the real time simulation based on dSPACE hardware verify the effectiveness of the decoupling control algorithm.(2) In steering condition, the control objective of the active suspension is the roll control of the vehicle body. Through the symbol computing, the items associated with the front wheel corner are expressed explicitly in the roll equation of the vehicle body and makes the influence on the roll motion which caused by the front wheel corner clear. By using the EDDC decoupling algorithm, the posture of the vehicle body is decoupled and makes the motion on each direction independent of each other, and the interference item to the roll motion caused by the front wheel corner is restrained by decoupling. The simulation results of the step and sine input signal verify the effectiveness of the decoupling algorithm.(3) In emergency steering condition, the lateral stability is the key objective of the active suspension control. The lateral stability control mathematic model of the whole vehicle which including the Burckhardt nonlinear tire model is established, and the model is expressed in affine nonlinear form. The above lays the foundation for differential geometry decoupling control.(4) The union algorithm of the vehicle lateral stability control based on the PI braking and the active suspension decoupling is proposed. Using PI braking strategy the yaw motion of the vehicle in emergency steering condition is improved. Set the actors of the active suspensions as input, using the decoupling algorithm to adjust the vertical load, improve the holding ability of the tires thus its lateral force is adjusted correspondingly, as a result, the aim to decrease the side slip angle of the vehicle is achieved. Simulations are carried out both on the dry and the wet surface road, the step and the sine signal are the input respectively, the results verify the effectiveness of the union control algorithm.