Influence of leakage during cyclic pneumatic braking on the dynamic behavior of heavy-haul trains

The pneumatic braking system (PBS) is a critical component in the cyclic braking process of heavy-haul trains (HHTs) in China. However, when a leakage fault occurs in the PBS, the dynamic behavior of the HHT becomes exceedingly complex. To investigate the impact of leakage on the dynamic behavior of HHTs, a PBS model based on fluid dynamics principles is first developed. The leakage in the brake pipe and the characteristics of the brake wave are considered in the PBS model, and the boundary conditions of the brake pipe under leakage are derived. Subsequently, a HHT longitudinal-vertical coupled dynamic model integrating the PBS is established. The dynamic interactions between the longitudinal and vertical motions in the vehicle system are comprehensively involved. Then, a joint simulation of the PBS and HHT dynamics system is conducted in this study to reveal the dynamics performance of HHTs more realistically. The PBS model is validated using a PBS test facility. Finally, the effects of different leakage rates on the longitudinal train impulse, wheel-rail interaction, and vehicle vibration of HHTs during cyclic braking are analyzed sequentially. The results indicate that leakage worsens the longitudinal impulse during the release process, resulting in a heightened coupler tensile force. The longitudinal wheel-rail interaction is significantly affected by the leakage, particularly in rear-train vehicles. Additionally, the leakage amplifies vehicle vibrations during cyclic braking, with the greatest effects observed in middle-train vehicles. These results offer important insights for optimizing the design of PBS and ensuring the safe operation of HHT.