Quasi-zero Stiffness Pneumatic Suspension Dynamic Modeling And Characteristic Analysis For Commercial Vehicle

Commercial vehicles are mainly used for commercial transportation,considering economic factors,overloading and modification are common.The usage environment is harsh and the road is destructive.China’s recently promulgated JT/T325-2018 "Classification and Rating of Operating Bus Types" clearly stipulates that pneumatic suspension must be used for bus suspension,promoting the use of pneumatic suspension on commercial vehicles.Pneumatic springs themselves have strong nonlinear stiffness characteristics,which can effectively reduce the inherent frequency of suspension and improve the smoothness and road-friendliness of commercial vehicles.Meanwhile,with the in-depth research of nonlinear vibration isolation theory,the damping performance of quasi-zero stiffness(QZS)vibration isolators is further improved.Based on this,this paper proposes a new QZS pneumatic suspension structure based on the existing pneumatic suspension system,combined with the nonlinear vibration isolation theory.The structure places pneumatic springs in parallel with double-acting cylinders to achieve QZS.Since the selected elements are all pneumatic elements,the pneumatic process of their internal high-pressure gas affects the output characteristics of the system,the system dynamics modeling and the influence of the system parameters on its stiffness characteristics and vibration damping performance still need to be studied in depth.In this paper,modeling,mechanical characteristics and vehicle vibration performance of the system are studied in a progressive way from the component to the whole vehicle.First,a new QZS pneumatic spring system is characterized.The QZS air spring system is analyzed statically,the expression for the dimensionless stiffness of the system is derived,and the necessary conditions for reaching quasi-zero stiffness at the equilibrium position are calculated.By analyzing the effects of different parameters on the stiffness characteristics of the system,the structural parameters for the system to reach QZS are obtained,and the structure is verified by static tests.Second,this paper introduces the solenoid valve and pipe model to make the QZS pneumatic spring system with two operating states: connected or disconnected.Further,the performance of the two operating states is compared and analyzed.The mathematical model of the connected state is derived by combining the pipe model with the original model of the QZS pneumatic spring system.By analyzing the effect of different pipe parameters on the dynamic stiffness of the system,the appropriate pipe parameters are selected.The differential equation of motion of the QZS pneumatic suspension under harmonic input is analyzed,and the analytical solution of the steadystate response for the system is obtained by using the harmonic balance method to analyze the influence of the system parameters on the vibration isolation performance.The force transmissibility is used as an index to compare the vibration isolation performance of the QZS pneumatic suspension in two operating states with that of the conventional pneumatic suspension.The results show that the QZS pneumatic suspension proposed in this paper has the best vibration isolation performance in the disconnected state.Third,on the 1/4 suspension platform,the droop response of two operating states of the QZS pneumatic suspension system and the conventional pneumatic suspension are analyzed in this paper.The QZS suspension system is simplified to a linear stiffness system and substituted into the 1/4 model for the small range of suspension beating characteristics,and then the curve of the vertical response with frequency is obtained.Simulink is also used to simulate the performance of the 1/4 QZS pneumatic suspension.Both theoretical analysis and simulation results show that the pneumatic suspension system with the introduction of negative stiffness has better smoothness than the conventional suspension system.Finally,the whole vehicle model is established and the evaluation function is designed to determine the operating state switching threshold.Considering the longitudinal and lateral motion of the vehicle,a 7DOF model of the whole vehicle is established.The body acceleration and suspension dynamic deflection are used as the main evaluation indexes to compare the two working states of the QZS pneumatic suspension.Based on above,the evaluation functions are designed and the operating state switching thresholds are determined.Further,the validity of the evaluation function is verified with mixed road inputs.The results show that the QZS pneumatic suspension with state switching effectively reduces the suspension deflection and improves the stability of the vehicle.