| The performance of the vehicle suspension system is directly related to the driving quality of the vehicle and the comfort of the driver and passengers.The analysis and control of its vibration characteristics is an important way to improve the performance of the system.Determining the response frequency domain distribution characteristics of the suspension system and the control frequency band is a key issue to improve the control efficiency and accuracy of the suspension system.Previous studies on vehicle suspension systems have mainly focused on the vibration characteristics of the suspension system when the vehicle is traveling at a constant speed,that is,the stationary random vibration process.However,the actual vehicle is mostly driving at a non-uniform speed,and the suspension system’s vibration is a non-stationary random process.At this time,the objects and methods of analyzing are significantly different from the stationary random vibration process.Generally,traditional time-frequency analysis methods are used in the researches,such as Short-Time Fourier Transform,to analyze the vibration characteristics of the vehicle’s non-stationary random excitation or response signals in the time-frequency domain.However,it is difficult for these analysis methods to obtain high-quality signal resolution in both the time domain and the frequency domain.Therefore,the traditional time-frequency analysis methods cannot accurately quantify the non-stationary random vibration characteristics of the vehicle suspension system.According to these non-stationary random vibration characteristics,experts can redesign the control algorithm of the active suspension system,so that the active suspension system can control the vibration frequency band more accurately,and improve the car ride comfort.Therefore,it is necessary to use some new methods to quantitatively analyze the time-frequency domain vibration characteristics of the non-stationary random vibration of the suspension system,and optimize the control frequency band of the active suspension according to the obtained,so that the suspension system can obtain excellent damping performance.The main research contents of this paper are as follows:(1)Wiener model method and filtered white noise method are used to construct road surface non-stationary excitation in the time domain,then excitation can be inputted into quarter-vehicle model,half-vehicle model and 7 degree vehicle model to obtain non-stationary response time-domain signals.Then,the excitation and response time-domain signals under different methods and different models can be compared.Finally,a conclusion is reached,that is,when the vehicle is traveling at a non-uniform speed,the excitation and response time-domain vibration amplitude of the suspension system will increase with the increase of the vehicle speed.(2)Aiming at the problem that traditional time-frequency analysis methods cannot improve the time-frequency resolution at the same time,this paper innovatively combines the filtering white noise method,the covariance equivalent method,and the pseudo excitation method to derive the non-stationary pseudo excitation of the four wheels of the vehicle suspension system.Substituting the non-stationary pseudo excitation into the quarter-vehicle model,the half-vehicle model,and 7 degree vehicle model respectively,and can be found that the obtained non-stationary response,which is evolution power spectrum,has extremely high resolution in the time and frequency domain.This result proves that the non-stationary pseudo excitation method enabled in this paper can analyze the non-stationary random vibration characteristics of the suspension system more efficiently.(3)In order to study the resonance characteristics of the suspension system under non-uniform speed driving conditions,the concept of‘dynamic frequency domain’is proposed in this paper,and Short-Time Fourier Transform and non-stationary pseudo excitation method is used to prove the changing characteristics of the dynamic frequency domain.It is concluded that when the vehicle is accelerating,the resonance area of the suspension system will expand to the low frequency area,and the greater the driving acceleration,the faster the expansion speed.Finally,a real car test of the vertical vibration of the four columns is designed in this paper to effectively verify the conclusion.(4)The dynamic frequency domain analysis results are used in the design of the active suspension control algorithm.By selecting the control frequency band of the active suspension limited frequency band H_∞control algorithm,the vibration reduction effect of passive suspension,traditional control frequency band H_∞control and dynamic frequency domain H_∞control are compared and analyzed.Finally,it is concluded that when the vehicle is traveling at a non-uniform speed,if the active suspension control frequency domain is selected according to the dynamic frequency domain characteristics,then the driving comfort of the vehicle can be more effectively improved. |
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