Derivation of air spring model parameters for train simulation

In railway vehicles, air springs are used for isolating vibrations and improving comfort for the passengers. For the prediction of the vibrations in the car body, a valid model of the air spring is needed. A new model for simulation of the air springs behavior has recently been developed at the Royal Institute of Technology, Sweden. The model is three-dimensional and consists of two parts, describing vertical and horizontal behavior. The thirteen input parameters of the model have, until now, been determined experimentally. Since experiments are time demanding and equipment expensive the question arose, in-house Bombardier, if there is a way to derive the parameters without experiments, using knowledge of the air springs physical behavior. The ambition of this report is to answer that question.

The report begins with a literature study of air springs. Topics like history, behavior, thermodynamics and physical relations are covered. A few existing air spring models are investigated to give an understanding of air spring modeling. As for the rest, this report focuses on describing the new air spring model and determining the input parameters of it.

Five of the model parameters are determined by means of thermodynamic and fluid dynamic constitutions. All of these belong to the vertical model. The parameters are calculated and simulated for a certain air spring. The simulation is made in a MATLAB code, developed in-house Bombardier. The result of the simulations is a plot of the total vertical stiffness versus frequency. This plot shows a sufficiently good agreement to the stiffness measurements for the specific air spring.

The remaining eight parameters, which depend on rubber properties, are not dealt with in this report. These parameters need, even henceforth, to be determined with experiments and experimental analysis.

Author: Presthus, Malin

Source: LuleƄ University of Technology

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