Abnormal vibration characteristics and modal coupling mechanism of low-floor tram gearbox

Abnormal vibration of gear transmission systems is one of the key factors affecting the operational reliability of tram vehicles. However, the vibration characteristics and excitation mechanisms of gearbox systems under actual operating conditions are not yet fully understood. In this study, field vibration tests were conducted on a tram gearbox system to investigate the characteristics of abnormal vibration. The vibration signals were analyzed using spectral analysis and operational modal analysis methods, and the relationship between gear meshing excitation and structural vibration was examined through theoretical analysis and simulation. The results show that the abnormal vibration is closely related to gear meshing excitation, and significant vibration amplification occurs when the meshing excitation frequency approaches the natural frequencies of the drivetrain structure. The identified modal characteristics reveal that structural resonance plays an important role in the vibration response of the gearbox system. The findings provide useful insights for the diagnosis of abnormal vibration in tram drivetrain systems and offer a reference for vibration control and maintenance of railway gear transmission equipment.