Stiffness Modeling And Characteristic Research Of Urban Rail Vehicle Air Spring System

With the development of urban rail vehicles in the direction of multi-level,multi-system and high speed,higher requirements are put forward for the running stability and riding comfort of vehicles.Air spring suspension system is an important element of vehicles,which’s mechanical chracteristics directly determine the running safety,stability and ride comfort.The air spring system is a complex system,which reflectes strongly nolinearity due to the effect of material nolinearity,structural parameters nolinearity and constraint nonlinearity.Therefore,the establishment of accurate and reliable stiffness model and damping model to reproduce the mechanical properties of air spring system has become a focus research at home and abroad.In addition,it is of great significance to the study of structure parameters optimization and dynamic performance of railway vehicles.At present,the research on vertical stiffness modeling and damping characteristics of air spring system mainly based on simplified cases,and the parameter variation of the rubber diaphragm can’t expressed definitely.In this doctoral thesis,the work cases were refined into straight track cases,cross-wind cases and curve track cases.Meanwhile,the vertical or lateral stiffness and damping mathematical model were established by means of thermodynamics,fluid –dynamics,Newdon’s laws and so on.The variation equations of rubber diaphragm parameter were solved by using approximate analytical methods,least squares numerical fitting and other methods.In order to verify the feasibility and accuracy of the proposed method,the model results were compared and analyzed with experimental data.The main contents of this doctoral thesis are as follows:First,the relationship between the load variation of the rubber diaphragm and the stiffness and damping characteristics of the urban rail vehicle air spring system under the cases of straight track,cross wind and curve passing case was discussed in detail.The analysis results show that the stiffness characteristics of air spring are not only closely related to its internal pressure,sprung load,geometric parameters,but also affected by the interal pressure gradient,orifice diameter,vibration frequency and amplitude of track irregularity excitation.Furthermore,the advantages and disadvantages of different modeling methods of air spring system were compared and analyzed,which builds a theoretical foundation for the subsequent chapters.Second,under straight track,a vertical stiffness analytical model is proposed to investagete the dynamic characteristics of air spring system,which overcomes the previous simplified modeling method,and takes the complete rubber diaphragm-orifice-auxiliary chamber pneumatic system as the research object.The vertical stiffness model is established based on thermodynamics and fluid-dynamics,an analytical solution of geometric parameters is identified by an approximate analyticalmethod.Meanwhile,experimental tests are performed to verify the accuracy and reliability of the proposed vertical stiffness analutical model.Furthermore,the impact of geometric parameters on the vertical stiffness properties is discussed based on this vertical stiffness analytical model.The conclusions show that an optimal volume ratio,shape coefficient of air spring can be derived by this vertical stiffness analytical model.Third,under the action of track horizontal vibration,air spring will produce coupling effect of lateral deformation and rolling moment.A novel lateral stiffness model was proposed to study the lateral characteristics of air spring system.The nonlinear viscoelastoplasticity of air spring rubber diaphragm was derived by thermodynamics and hydrodynamics,the torisonal stiffness of air spring and horizontal stiffness of emergency spring were calculated by Newton mechanics,and the uncertain parameters are obtained by a numerical fitting method,the impact of the lateral displacement,internal pressure,roll angle and polytropic coefficient on the lateral stiffness was discussed through sensitivity analysis.Furthermore,the proposed lateral model is compared with a full-scale laboratory air spring simulation bench and a quadratic function lateral stiffness model derived based on the finite element method.The comparison results show that the proposed lateral stiffness model agrees with experimental data and more precise than the finite element model.Fourth,a coupling effect of lateral deformation and roll deformation occurs in the vehicle air spring system under cross-wind condition,a lateral stiffness coupling model was established based on thermodynamics,fluid-dynamics and Newton mechanics.The nonlinear super-elastic characteristics,coupling characteristics of the air spring,lateral stiffness characteristics of emergency spring and damping force were considered in this lateral stiffness coupling model.The accuracy of the lateral stiffness model was validated by comparing with experimental data.In addition,the influence of the lateral displacement,roll angle,vibration frequency on the lateral stiffness and damping characteristics was discussed by a sensitivity analysis method,as well as the effect of the lateral stiffness model and damping model on vehicle mechanical performance was analyzed.Which provides theoretical guidance for the parameter design of urban rail vehicles and the improvement of vehicle stability.Finally,under the action of gravity and centrifugal force when a vehicle passing through a curved track,the air spring system undergoes lateral movement and roll deformation.A quasi-static lateral stiffness model was established by considering the lateral stiffness of air spring rubber diaphragm,rolling stiffness of air spring,lateral stiffness of emergency spring,and damping force of air flow orifice.Meanwhile,a full set of vehicle quasi-static experiment was conducted to verify the accuracy of the proposed quasi-static lateral stiffness model.The influence of lateral displacement,super-elevation angle,orifice diameter on the lateral stiffness characteristics was discussed.As well as the effect of lateral stiffness model to the vehicle running stability and ride comfort was analyzed.The results show that the quasi-static lateral stiffness model can well characterize the lateral stiffness and damping performance,and provide a theoretical basis for studying the vehicle curve passability.Figures 74,Tables 30,References 141.