Dynamic load analysis of gearbox suspenders for metro vehicles based on field tests and numerical simulation

The gearbox suspender is a critical suspension component that ensures the operational stability of the traction transmission system in metro vehicles. However, after 1.3 million km of service operation, cracks were detected at the same position on the gearbox bracket of multiple bogie frames for a certain type of metro vehicle, which indicates potential structural safety hazards related to the gearbox suspender. Currently, simplified equations are commonly adopted in bogie design and verification to evaluate the static load of gearbox suspenders, while dynamic loads are not fully considered. In this study, the dynamic load calculation equation for the suspender was further improved based on test results. Field tests were carried out on the target metro vehicle to acquire vibration acceleration, suspender load, and stress data at critical positions. A dynamic model of the metro train consisting of one motor car and one trailer car was established to investigate the key factors affecting the dynamic load of the suspender. The results show that under wheel-rail impact loads, the rotational inertia of the motor rotor affects the meshing impact response of the gear pair, thereby changing the suspender load. In addition, track irregularity, vehicle running speed, and node stiffness of the suspender all alter the vibration characteristics of the gearbox system, leading to significant variations in the suspender force. The improved dynamic load equation can accurately calculate the load of the gearbox suspender and effectively predict its structural fatigue life.