Mechanism and countermeasures of coupler separation of middle locomotive for long heavy-haul trains

A three-dimensional dynamics model of the middle locomotive-wagon system for a 20 000-ton heavy-haul train was established based on the multi-body dynamics theory. The effects of the key factors such as the initial height difference between the connected coupler and the friction coefficient of the coupler head on the coupler separation were analyzed. The formation mechanism of the middle locomotive-wagon connected coupler separation under air brake release and traction conditions was analyzed, and the corresponding countermeasures were proposed. Research results indicate that the connected couplers can remain stable under the compressive force. However, during the changing process of the coupler and draft gear system from the compressive state to the pulling state, the electric braking/traction force of the locomotive will cause a certain vertical relative movement between the couplers. After the coupler force changes to the pulling state, the self-locking force between the couplers is insufficient owing to the large initial coupler height difference and the small friction coefficient of the coupler head, causing a rapid increase in the vertical relative displacement between the couplers. If the limit of the vertical rotation angle of the locomotive coupler is too large, the vertical relative displacement between the couplers will increase dramatically with the increase in the pulling force (no less than 300 mm), thereby eventually leading to the coupler separation. When the friction coefficient of the coupler head and the limit of the vertical relative displacement of the locomotive coupler are 0.08 and 8°, respectively, the minimum initial height difference of the connected couplers and the applied ratio of the braking force inducing coupler separation under the air braking release condition are 40 mm and 40%, respectively, whereas the minimum initial height difference of the connected couplers and the applied ratio of the traction force induced to coupler separation under the traction condition are 30 mm and 50%, respectively. Meanwhile, when the initial height difference of the connected couplers is 50 mm and the applied ratio of the electric braking force is 70%, the minimum friction coefficient of the coupler head and the limit of the vertical rotation angle of the locomotive coupler resulting in coupler separation under the air braking release condition are 0.09 and 6°, respectively. Furthermore, when the initial height difference of the connected couplers is 50 mm and the applied ratio of the electric traction force is 100%, the minimum friction coefficient of the coupler head and the limit of the vertical rotation angle of the locomotive coupler resulting in coupler separation under the traction condition are 0.10 and 7°, respectively. Hence, to prevent coupler separation accidents, it is necessary to strictly limit the initial height difference between the connected couplers, appropriately reduce the electric braking force/traction of the locomotive, increase the friction coefficient of the coupler head, and limit the vertical free angle of the locomotive coupler. 9 figs, 30 refs.