Research On Control Strategy Of Air Suspension Applied On A SUV

As the elastic element of electronically controlled air suspension,air spring not only has a good stiffness and frequency characteristics,but also can be charged and discharged by controlling the solenoid valve on-off,vehicles with electronically controlled air suspension can achieve body height adjusting and other functions,which contribute much to vehicle ride comfort,handling stability and driving safety.There is "overcharge and over discharge" in the height adjusting process due to the body inertia and shock absorber damping.And the structure of the air suspension and uneven vehicle load distribution will lead to body instability,increasing pitch angle,how to ensure the accuracy of the car height adjustment and stable body posture is the key to the quality of height adjustment.The control strategy is studied for a SUV with electronically controlled air suspension.The main research contents are as followed.(1)Research on air spring characteristics.The stiffness and damping characteristic equation of air spring were established,and the adjustable stiffness and basically the same vibration frequency as the load change of the air spring were analyzed.Based on AMESim,the air spring model was established and the stiffness curve of air spring was obtained.The air spring test rig was set up and the experimental results were compared with the simulation results to verify the correctness of the air spring simulation model.(2)Construction of dynamic model and simulation platform.The gas mass flow equation and the pressure gradient equation of the charging and discharging process were established,and the mathematical model of the single wheel height adjustment and the vehicle height adjustment were established.The correctness of AMESim model was verified by simulation between AMESim model and vertical dynamic model.The construction of the Carsim-AMESim-Simulink joint simulation platform was completed,which was the basis of the vehicle height adjustment controlling algorithm and the sliding mode observer design.(3)Design of height adjustment controller.A fuzzy controller for the single-wheel height adjustment model was designed.Sliding mode controller for the single-wheel was designed based on non-linearization feedback.PWM pulse width modulation was used to convert continuous output into the duty cycle of solenoid valve switch state,to achieve direct control on high-speed switching valve.Based on the nonlinear feedback estimation error of output,the sliding mode pressure observer was designed to observe the gas pressure value inside the air spring.The vehicle height adjustment model was established based on the single-wheel model.The sliding mode controller considers the pitch angle and roll angle of the vehicle body to avoid the overshoot and vehicle body instability.(4)Analysis of height adjustment mode and simulation on simulation platform.Based on the Carsim-AMESim-Simulink joint simulation platform,the effectiveness of the control strategy was verified by open-loop control,fuzzy control and sliding mode control.Different height adjustment modes were designed,and the simulation are carried out on simulation platform to verify the function and stability of the controller.