| The main function of suspension system is to isolate the chassis from the ground to improve the ride comfort of the vehicle. To improve the performance, large amounts of effort were focused on stiffness and damping, research results showed that adjusting stiffness and damping under different working conditions can improve the vehicle’s ride comfort effectively.Air Suspension with adjustable volumes of auxiliary chamber can adjust stiffness by changing the volumes of auxiliary chamber, while the stiffness of traditional air suspension could not be adjusted because there is no auxiliary chamber, thereby enhancing vehicle’s ride comfort. The research object of this thesis is the new type semi-active air suspension and the purpose of this paper is to develop a controller based on the fuzzy control theory research and dynamic iteration tracking algorithm to control stiffness and damping of suspension to improve vehicle dynamic performance.Firstly, the mathematical model of this system was established based on the theory of engineering thermodynamics and fluid dynamics. The force of the spring instead of the fixed stiffness is used to build the 1/4 vehicle model and whole vehicle simulation model. In order to validate the model of air suspension system with auxiliary chamber, we have designed and built 1/4 vehicle test bench of air suspension with auxiliary chamber.Secondly, the optimal design of the suspension stiffness(auxiliary chamber volume)and damping. The main evaluation indicators of suspension system performance includes body acceleration, dynamic suspension travel and tire load. These three indicators in the design of the suspension system are irreconcilable in a certain degree. To solve this problem,setting sprung mass acceleration, dynamic suspension travel and dynamic tire load RMS value as the objective function, setting suspension stiffness(auxiliary chamber volume) and damping as the design variables, multi-objective optimization model of air suspension system with auxiliary chamber is established. Linear weighted sum method is used to transfer multi-objective optimization problem into a single objective optimization problem,Analytic Hierarchy Process method is used to determine the weighting coefficients of each sub-objective function. The preparation of the MATLAB genetic algorithm optimizationprogram is to optimize suspension stiffness(auxiliary chamber volume) and the shock absorber damping coefficient.Finally, based on fuzzy control theory and dynamic iteration tracking algorithm, the Fuzzy Logic Toolbox is used in MATLAB/Simulink software to design the Fuzzy Inference System of semi-active air suspension on whole vehicle and then implanted the Fuzzy Inference System in the Fuzzy Logic Controller. Simultaneously, dynamic iteration tracking algorithm is used to control damping. The simulation results show that, the semi-active air suspension that controller provided better ride comfort than the passive air suspension under different loads and road levels. The fuzzy controller received the expected control purpose,and the design of the controller is successful. |
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