Research On Control Strategy Of Charging And Deflating Characteristics Of Electronically Controlled Active Air Suspension

The working conditions are complex and changeable in the process of vehicle driving,such as road conditions,speed and other changes in the driving state of the car directly affect the ride comfort of the passengers.The air suspension has been widely used due to its advantages of light weight,low noise and great ride comfort.The height,stiffness and damping of the traditional passive suspension cannot be automatically adjusted when the driving conditions of the vehicle such as the vehicle speed,turning and road conditions are changed,resulting in the passing performance,smoothing performance and steering stability of the vehicle in complex and harsh driving environments cannot meet people’s needs.In order to solve the above problems,after the unremitting efforts of researchers,the research idea of automotive electronic control active air suspension(ECAS)began to gradually enter people’s field of vision.When the car is driving in complex and variable working conditions,automotive electronic control active air suspension can automatically adjust the height,stiffness and suspension damping of the air spring according to the driving demand to reduce the phenomenon of "acceleration back","brake nod" and "turning to the side" that occur during the driving process.Due to the complexity of the electronically controlled air suspension structure and the relatively high cost,only high-end cars are used in the market.At present,domestic universities and enterprises have cooperated vigorously to deeply research and develop the control strategy of electronically controlled air suspension,and have made great progress.This paper studies the vehicle ride comfort by using fuzzy PID controller and BP-PID controller when simulating the change of free film type air spring height drove under a certain road.Firstly,the working principle,main components and functions of the electronically controlled air suspension are elaborated.According to the quadratic function fitting curve of the spring height and stiffness during the air spring charging and discharging process,the spring stiffness is theoretically determined according to the height.The relationship between the changes,the damping characteristics of the damper is analyzed,and a quarter-vehicle dynamics model that reflects the vertical motion of the vehicle body and a time-domain model of the road surface irregularity that can simulate the driving of the vehicle are established.According to the PID control and fuzzy control theories,a closed-loop fuzzy PID controller capable of real-time online adjustment of PID parameters(、 、)is designed.Aiming at the variation of the stiffness caused by the spring height adjustment and the damping characteristics of the damper during the air suspension charging and discharging process,a fuzzy PID controller simulation model of 1/4 vehicle dynamics model is established in Matlab/Simulink which used the charging and deflation time as the control variable,comparative analysis of vehicle smoothing performance before and after fuzzy PID controller control.Then based on the 1/4 vehicle kinematics model and the air suspension variation characteristics,a BP-PID controller capable of adjusting the PID parameters(、 、)in real time is constructed,and the BP-PID controller and the fuzzy PID controller are paired with the established dynamic simulation results which was verified the superiority of the control effect of the BP-PID controller.Under the input excitation of a certain Gaussian white noise road,the simulation results of two controllers established in simulink show that the influence of the height adjustment of the air spring during the charging and discharging process on the ride comfort of the electronically controlled active air suspension is: the fuzzy PID control greatly reduces the maximum amplitude of the vertical acceleration of the vehicle body,and controls the amplitude variation of the vertical acceleration of the vehicle body to a small range.At the same time,the fuzzy PID has a certain degree of reduction on the suspension dynamic deflection and the tire travel.It shows that the suppression effect of fuzzy PID controller on vehicle ride comfort is very significant and relatively stable.According to the simulation results of BP-PID controller and fuzzy PID controller,when the vertical acceleration of the vehicle body is greater than 0.8m/,the BP-PID controller has better suppression effect and reduces the damage caused to the human body when the car vibrates.