Research On Control Strategy Of Air Suspension System For Vehicle

Electronically controlled air suspension system is one of the most advanced automotive suspension systems at present.Through controlling the height of air springs and the damping of shock absorbers,it can excellently coordinate the ride comfort,handling performance and trafficability of cars,electronically controlled air suspension system has brought a brand-new and feasible way of improving the performance of vehicles.Based on the summary of domestic and foreign achievements of researches on electronically controlled air suspension of passenger cars,this dissertation has made an in-depth study into the intelligent control method of electronically controlled highly adjustable air springs and variable damping shock absorbers,aiming at the optimal coordination of vehicles.The control method is verified by simulation experiments.The main research work is summarized as follows:(1)Study the characteristics of electronically controlled air springs and variable damping shock absorbers theoretically and experimentally.As for the diaphragm type air spring,with the effective area and the effective volume properties of the air spring,the mathematical model of the air spring is built.The dynamics model of quarter vehicle with 2 degrees of freedom is established by Newton’s law of motion in order to describe its vertical vibrational characteristics.On the basis of this,the full vehicle model with 9 degrees of freedom is built considering both vibration and handling characteristics.At the same time,based on the established air spring model,the simplified model of air suspension vehicle is established and simulated.(2)Due to the weakness of traditional weighting coefficient choice,Linear Quadratic Gaussian algorithm integrated with Simulated Annealing Particle Swarm is put forward in this dissertation.Considering the advantages and disadvantages of both algorithms,annealing operation from Simulated Annealing Algorithm are introduced into Particle Swarm Algorithm to optimize weighting coefficients.Optimal weighting coefficients are found by this algorithm and then applied to the design of the controller.The validation of the algorithm is proved by the simulation results from a simplified 2-degree-of-freedom vehicle model.(3)Not only can the electronically controlled suspension damp the vibration caused by uneven road surface,but it can effectively modify the attitude of vehicles during severe maneuvers.Aiming at various maneuvers on uneven road surface,a coordinated control method of ride and handling performances combining Simulated Annealing Particle Swarm Optimization Algorithm and Fuzzy control is proposed.The control system is divided into three parts:overall performance control module,roll angle control module and coordination control module.On the one hand,the overall performance control module sustainably improves the ride comfort.On the other hand,Fuzzy control performance by reducing the roll angle and then the roll movement.The distribution module of suspension forces takes the outputs of the other two controllers above as input variables.It determines the overall force of suspensions.With the help of air suspension vehicle model,the comparative research is conducted in J-turn driving scenario and single sine driving scenario on a random-rough road.The results of simulations illustrates that the control algorithm can effectively coordinate the ride and handling performances.(4)According to the working principle of ECAS system,the height control method based on module structure is put forward for ECAS system,which included the target height decision and the target height tracking.According to the running state of bus,the target height decision control is divided into three modules:vehicle starting control,vehicle dynamic driving control and vehicle kneeling control,and then the modular design is done for the three modules.According to the suspension frequency design and height of air spring the working heights of the air spring are designed.To solve the problems of "over-charging","over-discharging" and oscillation during the process of height adjustment,PID/PWM controller is designed to realize the tracking control of the target heights.Through the static and dynamic height switching control simulation,the control strategy is verified by simulation.