Time-delay analysis between car body vertical acceleration and longitudinal track irregularity for EMUs

Purpose This paper aims to explore the time-delay mechanism between longitudinal track irregularity excitation and car body vertical acceleration of high-speed electric multiple units (EMUs). It addresses the existing research gap that previous studies mainly focus on vibration amplitude characteristics while ignoring the temporal transmission law of vehicle-track vibration. Design/methodology/approach This study combines theoretical modeling and measured data analysis. A mass-spring-damper vehicle dynamic model is established to clarify the delay generation mechanism during vibration transmission. Based on field inspection data, filtering and sliding window correlation analysis are adopted to compare vibration responses in bridge and subgrade sections. The Complete Ensemble Empirical Mode Decomposition with Adaptive Noise method is employed to extract the periodic irregularity component of 32 m simply supported beams, and the time delay is quantified through signal peak matching. Findings The suspension deformation of primary and secondary systems during vibration transmission is the essential cause of the time delay, which presents as a phase difference in the linear vehicle-track system. Owing to the periodicity of 32 m beam bridges, the track irregularity shows a higher correlation with car body acceleration (max correlation coefficient = 0.75) than subgrade sections. For typical high-speed EMUs, the stable time delay ranges from 0.4 s to 0.6 s, and the delay difference between the left and right tracks is extremely small (0–0.037 5 s). Originality/value This study systematically clarifies the physical mechanism of vibration transmission time delay in the vehicle-track system and develops a hybrid analysis method combining theoretical derivation and advanced signal processing. The quantified delay characteristics provide effective support for suspension parameter optimization, vibration model improvement and precise track maintenance of high-speed railways.