| As an important part of the vehicle, vehicle suspentions have very significant influence for the smooth-going as well as stability of the car. Due to stiffness inflexibility of passive suspension, passive suspension cannot have satisfied people’s car performance requirements. The electronic control air suspention (ECAS) can adjust the stiffness and body height of suspensions, make drive more safety and feel more comfortable in different condition. In our country, electric control air suspension technology is still not mature, and electronic control air suspension technology must be used widely, for its promising prospect.therefore, the research on electronic control air suspension including air spring, control unit and software making is very necessary.In this thesis, the author established air spring modelof single gas chamber and air spring modelwith additional gas chamber in order to analysis the factors that influence spring stiffness using Small deviation linearization method. Through the analysis of the characteristics of air spring stiffness and affecting factors of air spring stiffness, a conclusion is aganed that adjusting the size of throttling mouth between main and auxiliary air chamber can adjust the stiffness of the air spring to the right degree and improve the car smooth by using stepping motor. A quarter of vibration model of the active air suspension is established for simulation analysis of active air suspension using Matlab/Simulink software.From the simulation analysis, the results show that active suspension for improving auto smooth play a large role.The design of the control unit is the core content in the paper. In terms of hardware design, the paper select the MC9S12DP256as processor and use ProtelDXP to design circuit including the power supply circuit, clocking circuit and phase lock loop circuit, signal acquisition circuit, output control circuit. According to reliable and practical principles, C languageis used for writing program with structured and modular method in the system software design. The paper use Codewarrior software to compile and download the program.When the car need stiffness adjustment, the control unit body gain vertical acceleration signal as the target numerical value and get acceleration sensor data,then acceleration data is processed with joining the fuzzy control for adjust stepping motor Angle with the steering. When the car needs height adjustment, micro controller compare received data and the current target date with PID algorithm, and output time for adjusting the air suspension stiffness. Finally, freescale MC9SDP256is Chose as the controller chip for matching test circuit, building the experimental environment, watching the experiment phenomenon.In the simulated tests, through the observation of the phenomena and variable changing, it show that the electronic control unit can not only detect input signals, but also can accurate control output, and the experimental effect is good. |
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