Research On Longitudinal Impulse Of Heavy-Axle-Load Freight Train Effected By Profile Parameters

With the increasement of the axle load of heavy haul and railway marshalling, the relationship between the vertical section setting and longitudinal dynamic performance is becoming closer and closer. In practical engineering, the longitudinal section design parameters restricts the economic characteristics of line engineering, so reasonable setting of longitudinal profile parameters is crucial. Based on the heavy-axle-load train longitudinal dynamics model, the relationship between profile parameters and dynamic performance in different line conditions and different traction mode was studied and the research results are as follows:(1) The research on longitudinal impulse of heavy train effected by profile parameters in single and double traction mode was carried out.The results showed that the most disadvantaged line profile of the emergency brake is recessed section and which of the release is convex section conversely; The slope of the ramp,vertical curve radius and the length of level stretch between opposite sign gradient has no effect on the longitudinal impulse basically; The coupler force changes by the difference in gradients linearly, when the train is tracted by single locomotive and the gradient is 30‰, the maximum coupler force of emergency braking and release is 1736.54kN and 1848.62kN respectively, when the train is tracted by double locomotives and the brake delay time is 2s, the maximum coupler force of emergency braking and release is 1715.70kN and 1813.50kN respectively, they did not exceed the longitudinal dynamics of train safety evaluation index requirements, so in practical engineering, the algebraic difference between adjacent gradients of heavy-axle-load train can be selected to two times of the limited slope.(2) The brake delay time has a great impact on the longitudinal impulse.In emergency braking, the coupler force on the condition that the delay time is 2s is 26.3% bigger than that of the delay time is 1s;The longitudinal performance of light-heavy mixed vehicles is worse compared with pure heavy vehicles, the coupler force of heavy-light and light-heavy modes is 12% and 52.7% bigger than that of pure heavy vehicles respectively.(3) The safety issues when the train is braking on the long steep slope was analyzed. The results showed that heavy-haul train in 80km/h velocity on the ramp decelerates to 40km/h and releases to initial velocity by 100kPa high brake pressure, the whole process takes about 400s and walking distance is 3500m.When the ramp length is longer, due to the excessive numbers of cycle braking, the train braking force will decrease and the braking heat load will increase which results the initial velocity of next round cycle-braking increased and the effective braking distance shortened; reducing the train braking or release initial speed of every time and adding the slight gradient can effectively reduce the times of cycle braking in each ramp.