Hunting motion of high-speed emu during cross-line operation: Mechanism and countermeasures

During the operation of the Chinese 250 km/h-level EMU, hunting occurs when the EMU crosses from Line B to Line A. Numerous tests and simulations have been conducted to investigate the mechanism of this phenomenon. Comparisons of the measured rail profiles of the two lines indicate that the left rail in Line A is higher than that in Line B at the inner rail shoulder. In addition, the top position of the right rail in Line A is approximately 2–3 mm closer to the inside than that of the right rail in Line B, with the right rail in Line A being higher than that in Line B at the inner rail shoulder. These differences cause a significant increase in the wheel–rail equivalent conicity when the EMU crosses from Line B to Line A and further cause the hunting phenomenon. Moreover, simulations and experiments are conducted to investigate the countermeasures for EMU cross-line hunting. Field test results show that both increasing the damping of the yaw damper and wheel reprofiling can improve the stability during EMU cross-line operation; however, the effect of increasing the damping of the yaw damper is limited under particularly poor wheel–rail relationship. Simulation results reveal that rail grinding of Line A referring to the Chinese 60N rail profile can also improve the stability of the EMU during cross-line operation.