A three-dimensional coupled dynamics model of the air spring of a high-speed electric multiple unit train

Although air springs are widely applied on high-speed electric multiple unit (EMU) trains, there is no accepted method to model the dynamics of these air springs. In this paper, a three-dimensional (3D)-coupled dynamics model of an air spring used on a high-speed EMU train was created through the derivation of thermodynamics equations and using a curve-fitting method. Experimental and simulated stiffness tests were performed to verify the accuracy of the 3D-coupled model, which was then implemented in the MBS vehicle dynamics model. The influence of the nonlinear behaviour of the air spring on the vehicle's dynamic performance was analyzed by a dual-simulation approach using the 3D-coupled model of the air spring and the dynamics model of the vehicle. From the results, it can be concluded that the air spring can improve the vehicle's vertical ride comfort, due to its ability to adjust the vertical stiffness and damping based on the level of vibration. However, the vehicle's ability to negotiate curves is reduced due to an increase in the air spring's lateral and longitudinal stiffness, a result of the lateral displacement of the car body. Furthermore, the operation of the leveling valve in the 3D-coupled model can slightly reduce the vehicle's overturning coefficient, which is a phenomenon that the normal air spring models cannot simulate. Finally, the 3D-coupled model was applied to simulate a leakage process, which is a complex series of chain reactions, in the air spring system. The calculation results indicate that, even though the ride comfort is severely degraded by the leakage, the vehicle's running safety can still be guaranteed.