Ziqiang Xu

Coupler jackknifing and derailments of locomotives on tangent track

A number of derailments occurred in recent years due to coupler jackknifing, some of them were reported on tangent tracks where conventionally thought to be the safer sections. This article studied coupler jackknifing behaviour and its implications for locomotive safety on tangent tracks from the experience of China heavy haul. Three types of coupler systems were modelled and simulated regarding coupler jackknifing behaviour. Two typical locomotive derailments occurred on tangent tracks were analysed. From the derailment experience, coupler angle self-lock behaviour was introduced and simulated. An approach to determine coupler angles in the jackknifed position was derived and validated with a self-coded program and SIMPACK. Methods to prevent coupler jackknifing were also evaluated with regard to locomotive stability.

Analysis of the rotation angle of a coupler used on heavy haul locomotives

Increases in train length and axle loads have significantly increased in-train forces for heavy haul trains. These forces when combined with the rotation behavior of the coupler can exert an adverse effect on the operational safety of trains. This paper analyzes the rotation behavior of a coupler resulting from the application of a compressive force. A suitable free-rotation angle for the coupler and a stabilization mechanism are also presented. Simulations were performed using a dynamic model of a train consisting of three heavy haul locomotives and two couplers. The obtained results indicate that trains with free-rotation angles of the coupler of 6°have a better dynamic safety and lower levels of wheel tread wear than trains with an initial free-rotation angle of 8°. Variation of the locomotive’s structural parameters, including the secondary stop free clearance, the distance between front and rear stops and the distance between secondary stop and coupler pin, affects the maximum rotation angle of the coupler and, in turn, the operational safety of the train. The matching of the locomotive’s structural parameters and the free-rotation angle of the coupler should be considered when selecting a heavy haul coupler and buffer system so as to avoid safety problems caused by excessive rotation behavior of the coupler.

Stabilizing mechanism and running behavior of couplers on heavy haul trains

Published studies in regard to coupler systems have been mainly focused on the manufacturing process or coupler strength issues. With the ever increasing of tonnage and length of heavy haul trains, lateral in-train forces generated by longitudinal in-train forces and coupler rotations have become a more and more significant safety issue for heavy haul train operations. Derailments caused by excessive lateral in-train forces are frequently reported. This article studies two typical coupler systems used on heavy haul locomotives. Their structures and stabilizing mechanism are analyzed before the corresponding models are developed. Coupler systems models are featured by two distinct stabilizing mechanism models and draft gear models with hysteresis considered. A model set which consists of four locomotives and three coupler systems is developed to study the rotational behavior of different coupler systems and their implications for locomotive dynamics. Simulated results indicate that when the locomotives are equipped with the type B coupler system, locomotives can meet the dynamics standard on tangent tracks; while the dynamics performance on curved tracks is very poor. The maximum longitudinal in-train force for locomotives equipped with the type B coupler system is 2000 kN. Simulations revealed a distinct trend for the type A coupler system. Locomotive dynamics are poorer for the type A case when locomotives are running on tangent tracks, while the dynamics are better for the type A case when locomotives are running on curved tracks. Theoretical studies and simulations carried out in this article suggest that a combination of the two types of stabilizing mechanism can result in a good design which can significantly decrease the relevant derailments.

Research on Bogie Frame Lateral Instability of High-Speed Railway Vehicle

In order to find out the reason for the bogie frame instability alarm in the high-speed railway vehicle, the influence of wheel tread profile of the unstable vehicle was investigated. By means of wheel-rail contact analysis and dynamics simulation, the effect of tread wear on the bogie frame lateral stability was studied. The result indicates that the concave wear of tread is gradually aggravated with the increase of operation mileage; meanwhile the wheel-rail equivalent conicity also increases. For the rail which has not been grinded for a long time, the wear of gauge corner and wide-worn zone is relatively severe; the matching equivalent conicity is 0.31-0.4 between the worn rail and the concave-worn-tread wheel set. The equivalent conicity between the grinded rail and the concave-worn tread is below 0.25; the equivalent conicities are always below 0.1 between the reprofiled wheel set and various rails. The result of the line test indicates that the lateral acceleration of bogie frame corresponding to the worn wheel-rail can reach 8.5m/s2, and the acceleration after the grinding is reduced below 4.5m/s2. By dynamics simulation, it turns out that the unreasonable wheel-rail matching relationship is the major cause of the bogie frame lateral alarm. With the tread-concave wear being aggravated, the equivalent conicity of wheel-rail matching constantly increases, which leads to the bogie frame lateral instability and then the frame instability alarm.

Dynamic simulation to solve protruding issue on axle box rod rubber joint of 2B 0 heavy haul locomotive

This paper aimed at protruding issue on axle box linkage of 2B0 heavy haul locomotive, analyzed why this problem happened. According to SIMPACK dynamic software, built the dynamic model of 2B0 locomotive which considered the actual structure of axle box, calculated all rods force condition on curve passing, then validated its Structural strength by using finite element way. The results showed that: When locomotive curving, maze-shaped rubber joint lateral force and deflection torque are far larger than that of cylindrical tube rubber joint. This means continuing huge stress acting on rubber joint, in the end, protruding happened on the edge of axle box rod rubber joint.