Wheel-Rail Vertical Interaction Of 100% Low Floor Trains Passing Through Rail Weld Irregularity

Due to the advantage of moderate transport capacity, green environmental protection, low investment, good comfort and beautiful appearance,100% low floor light vehicle is becoming the important part of urban rail transit. However, with the decrease of axle load, wheel load reduction of light vehicles aggravates, even appears the phenomenon of wheel jumping off the rail which affects vehicle operation safety when passing through the weld joint zone. This paper goes into the analysis of the impact of the rail weld joint on wheel-rail interaction and puts forward the safety threshold of the weld irregularity. It is of great realistic significance to improve the wheel-rail dynamic performance and reduce the rail welding joint maintenance.Following the review of the processing and results of the research done in the field of 100% low floor light vehicle dynamics and rail weld joint, this paper established the 100% low floor vehicle and track vertical dynamics model by combining with the unique structural characteristics of 100% low floor vehicles and basing on the vehicle-track coupled dynamics theory. By this coupled model, the wheel-track interaction of each wheel is studied as 100% low floor vehicles pass through the concave and convex rail weld joints. Results indicate that under the weld irregularity, the wheel-rail interaction changes acutely, even appears the phenomenon of wheel jumping off the rail. And the wheel-rail dynamic response under the weld irregularity is basically similar.Then the influence of parameters of track system on the wheel-rail interaction of 100% low floor vehicles is studied and analyzed under the rail weld irregularity. The analysis shows that when 100% low floor vehicles passing through poor weld joints zone on different rail types, T50 rail is better than T60 rail and 59R2 groove rail in wheel-rail interaction, and T60 rail and 59R2 groove rail are similar in wheel-rail dynamics response. The increase of sleeper pitch can effectively reduce the wheel-rail interaction and improve vehicle operation safety. The wheel-rail interaction is affected both by the stiffness and damping of rail pad. As the stiffness of rail pad grows, the wheel-rail dynamics performance will deteriorate, even appears the phenomenon of wheel-track remaining separate for a period of time.Meanwhile, decrease of the stiffness of rail pad will cause the increase of rail displacements; As the damping of rail pad decreases, the wheel-rail vertical force, rail-sleeper force and wheelset acceleration will decrease. Meanwhile, the rail displacements will increase and the delay of the wheel-rail response became slower. Elastic Bearing Block Track is better than ballast track and Sleeper Buried-Type Track in wheel-rail dynamics response.Finally, with analyzing the impacts of wave length and wave depth in the wheel-rail interaction under the rail weld irregularity, the related safety threshold values are obtained. With the increase of wave depth or the decrease of wave length, the wheel-rail interaction inevitably be enhanced. According to the counting of this paper, results indicate that to the concave weld irregularity, the maximum limit for the short wavelength irregularity is 0.45mm, to the convex weld irregularity, the maximum safety limit is 0.26mm. The weld irregularity with the wave length under 0.35m should be strictly controlled. And it is recommended to polish the wavelength of the short wavelength to 0.5m when polishing rail.