Simulation Research On Dynamics Performance Of Air Spring In Railway Vehicles

Air spring, filled in flexible airtight vessel with compressed air, is a non-metal spring, which acts with air compressibility. In recent years, air spring has been widely used in railway vehicles for the good elastic characteristic. Restricted by conditions and means, when dynamics of the vehicle equipped with air springs is analyzed, the air springs are looked on as linear spring paralleled damper model. However, with different pipe length, orifice diameter and auxiliary tank volume, the dynamic characteristics of air spring will be different, and the linear model can not reflect the influence of the different parameters, also the effect of the leveling valve and differential pressure valve has been ignored. All of these are not conducive to the research and selection of air spring, and may lead larger tolerances in the simulation results of the vehicle system dynamics.Based on the theories of thermodynamics and fluid mechanics, the actual change process of the gas inside the air spring was described with the mathematical and physical equations, then the bellow-fixed orifice-auxiliary tank model, the bellow-pipe-auxiliary model and the leveling valve and differential pressure valve model were established respectively in Matlab/Simulink, the influence of the excitation amplitude, the different air spring parameters and the heat transfer coefficient on the dynamic vertical stiffness and damping of air spring are analyzed. The simulation results showed that:the dynamic vertical stiffness of air spring increase with the excitation amplitude, and under different amplitude, the air spring system damping exist an approximate peak value; when the pipe is long, the inertia of the air mass in the pipe must be taken into account, but the short pipe is equivalent to the fixed throttle. In all cases, the cures of the dynamic vertical stiffness tend to constant level in the low and high frequency respectively. There is a defect of the fixed throttle for that open too large in low frequency and too small in high frequency. The heat transfer coefficient has a great influence on the dynamic characteristic of air spring, for its value choice should establish on the basis of the experimental data.The air spring model and the vehicle system dynamics model of the high speed EMU which was established in SIMPACK are coupled using the co-simulation technique. Then the influence of different type of air spring suspension system and the heat transfer coefficient on the vehicle dynamic performance are investigated. The simulation results showed that:for the selection of leveling system, the two-point configuration and four-point configuration are always match. However, for the two-point configuration, the anti-roll bar with appropriate stiffness must be selected. The air spring system which connected by a fixed orifice, the orifice diameter15mm-20mm is relatively appropriate and the volume of auxiliary tank is generally60L-100L. The air spring parameters and the heat transfer coefficient have significant effects on the vertical running stability of the vehicle system.