Research On Heavy Haul Train Longitudinal Impluse Dynamics

Increase of freight vehicle axle load and wagon numbers in heavy haul train has been an important way to improve the transportation capacity and efficiency, but it will generate larger longitudinal train impulse and results in some dangerous problems, such as damage of vehicle structure, train derailment, and so on. Therefore, it has a great significance for China heavy haul train operation safety to investigate the longitudinal impulses dynamics in theory and test method. In this paper, the key technical problems of longitudinal impulse dynamics in the condition of shunting impact and train operation of China heavy haul train were studied.According to the draft gear dynamics theory, piecewise linear model of friction draft gear was built based on the test data, and then modified by the additional sticking friction force and the additional damping force. The draft gear piecewise linear dynamic modification model was built, then verified by impact simulation, test and displacement excitation which described by trigonometric function. The results indicate as follows:the draft gear piecewise linear dynamic modification model can actually reflect the characteristic of draft gear in shunting impact and vehicle impact test; the parameters of transition velocity, external displacement excitation frequency, and equivalent friction coefficient in additional sticking friction force equation can reflect the nonlinear peak; the additional damping and vehicle structure stiffness make smooth transition between loading curve and unloading curve, and solve the energy dissipation problem.Train air brake characteristic multi-parameter mathematic model was build to study the effect of different parameters on the air inflation characteristic curve of brake cylinder. The air brake system of 150 heavy freight vehicles with 120 type brake valve was simulated to calculate the brake cylinder pressure rising in different brake condition, and the results were compared to the test. The train basic mechanical brake system model was built to analyze the effect of velocity and brake shoe pressure on the friction coefficient. The results indicates as follows:the brake control valve characteristic parameter, brake cylinder inflation characteristic parameter and brake wave propagation characteristic parameter of train air brake characteristic multi-parameter mathematic model have an obvious effect on the train brake characteristics; the combination of different parameters can simulate different brake inflation curves; the simulation agrees well with the test in the emergency and service braking condition; lower brake shoe pressure and velocity lead to larger friction coefficient.On the basis of the vehicle impact equation and draft gear piecewise linear dynamic modification model, the groups of vehicle impact model, vehicle structure stiffness series model and vehicle-coupler-vehicle series model were built to study the effect of different numbers of grouped vehicles, different braking conditions, different coupler gap, loaded and unloaded vehicle state, different vehicle body stiffness and combinations of draft gears of different resistance characteristics on longitudinal impulse characteristics. The results indicate as follows:different numbers of grouped vehicles lead to different coupler force in train interface, and coupler gap has an effect on the maximum coupler force; larger braking force of impacted vehicle results in larger longitudinal impulse; coupler force and velocity are different in the different loaded and unloaded vehicle impact; small vehicle body structure in high velocity impact has obvious effect on coupler force; combinations of draft gears of different resistance characteristics generate different maximum coupler forces and draft gear strokes.Coupler dynamic model and full DOF model of C80 freight vehicle with K6 bogie were built in UM software based on the draft gear dynamic theory, contact element and vehicle system dynamic theory. The 3-dimension vehicle impact dynamics method was used to simulate heavy freight vehicle impact, in order to study the longitudinal impulse and bolster lateral load. The 3D vehicle impact simulation was compared with vehicle impact test. The results shows as follows:the coupler dynamic model with bilateral contact element simulates the coupling process well in the vehicle impact, and low amplitude and high frequency coupler force appears because of the mass of coupler and follower; the coupling relationship of longitudinal and vertical direction, the increase and decrease of vertical load, and the bolster lateral load changing rule are simulated efficiently in the impact model; the velocity should be strictly controlled while loaded vehicle impacts unloaded vehicle in order to prevent the derailment and overriding, and ensure the safety of the structure, such as bolster.On the basis of draft gear dynamic modification model, air brake multi-parameter mathematic method, and longitudinal train dynamic theory, the heavy haul train longitudinal impulse dynamics was calculated in the condition of different brake forces, different gradient lines and different Locotrol delay times, and the simulation results were compared with the running test of 20000t 1+2+1 combination heavy haul train in Daqin railway line. Combined train dynamic model and mixed train dynamic model were built to study the effect of longitudinal impulse on vehicle system dynamics. The results indicates as follows:longitudinal train dynamic model can simulate heavy haul train longitudinal impulse problems well in the condition of emergency brake; the simulation results agrees well with the test in the value and trend except individual parts due to uncertain factors; combined train model and mixed train model can simulate the effect of longitudinal impulse on the vehicle dynamics well, and the impulse reduces of the curve negation performance and running safety; the lateral rail-wheel force and derailment factor in combined model is smaller than that of mixed train model because of the constant coupler deflection angle in combined train model; mixed train model is closer to actual condition because the coupler deflection angle is variable with the train running.