| With the increase of the vehicle axle load and wagon numbers in heavy haul train and the increase of the running speed of rapid speed wagon,the longitudinal impulse of the train will increase significantly and results in some dangerous problems,such as the rupture of draft gear structure,train derailment,and so on.As the core component of railway vehicle’s interconnection,the draft gear plays the role of transferring,absorbing,and easing longitudinal impact energy between vehicles during starting,braking,and shunting impact.The performance of draft gear affects the traction weight,running speed,and efficiency of shunting operation.Therefore,this thesis takes the frictional draft gear and the elastic polymer draft gear commonly used in railway freight cars as the research objects,constructs two kinds of draft gear segmented dynamic model,and then carries out the optimization research on the characteristics of two kinds of draft gear through the combination of simulation and experiment,to provide theoretical guidance for the design of new type buffer.The main contents and achievements of this thesis are as follows:(1)According to the working process of loading,unloading,and transition of the dry frictional draft gear,a multi-segment linear dynamic model of the friction draft gear reflecting the working characteristics of the draft gear is established.In the model,the transition process is treated by deflection compensation and additional sticking impedance force.Based on the vehicle impact test data of MT-2 draft gear,the model is analyzed and verified by using a shunting impact simulation system.The simulation results show as follows: the multi-segment linear dynamic model of draft gear well reflects the characteristics of the mounting preload,loading,peak,and unloading.In the model,the method of deflection compensation and additional sticking impedance can effectively solve the problem of the lock unloading in the transition process,and simulates the energy consumption phenomenon caused by the reciprocating vibration during vehicle impact.(2)According to the structural principle of the elastic polymer draft gear and the speed-dependent characteristics of the elastic polymer,a three-stage dynamic model of elastic polymer draft gear based on the speed-dependent characteristics was built by combining its working mechanism with the loading,unloading,and transition process of a draft gear.Based on the drop-hammer test data of JN30 the elastic polymer draft gear,the parameters of the dynamic model are determined by using the improved particle swarm optimization algorithm,and the accuracy of the optimized draft gear model is verified by the drop-hammer simulation system.The comparison between the simulation and test results shows that the optimized draft gear model can better reflect their actual working characteristics.(3)Based on the research background of railway shunting impact in China,taking the frictional draft gear as the research object,the response characteristics of draft gear in shunting impact is analyzed by using a simulation system.The influence of the coupler slack and draft gear stiffness on marshaling mode of shunting impact is studied and the influence of vehicle total weight,impact speed,body stiffness,and the impedance characteristics of draft gear on the required capacity of draft gear is studied.The simulation results show as follows:with smaller the coupler slack or the greater the stiffness of draft gear,the more energy consumption of the draft gear,the greater the coupler force.When the work of the draft gear and the coupler force reaches the maximum,the number of impact and impacted vehicles is relatively large.Under the simulation conditions of this thesis,when the coupler slack between vehicles is small or the stiffness of draft gear is large,the work of the draft gear and the coupler force reaches the maximum when both the impacting vehicles and impacted vehicles consist of three vehicles respectively,and then it is not related to the number of vehicles as the vehicles increase.With the increase of the coupler slack or the decrease of the stiffness of draft gear,the work of the draft gear and coupler force will reach the maximum value when both the impacting vehicles and impacted vehicles consist of two vehicles respectively.When there are a large number of impact vehicles and impacted vehicles,the total weight of the vehicle,impact speed,and the impedance characteristic of draft gear are the main factors affecting the required capacity of draft gear.The required capacity of draft gear is directly proportional to the total weight of the vehicle and the square of the impact speed respectively.To ensure that the draft gear has a larger capacity,the impedance characteristic curve of friction draft gear should adopt the combination of the flexible and rigid characteristic curve.(4)Taking the 10000 t heavy haul train as the research object,the integrated model of air brake and longitudinal dynamics of the train was used to study the influences of different segment impedance characteristic of the frictional draft gear(such as the mounting preload,the interim segment range and slowly changing segment)on the longitudinal impulse of the heavy haul train.The simulation results indicate as follows: proper increasing mounting preload of draft gear and reducing the change rate of the interim segment range can decrease the train’s longitudinal impulse.when proper deducing the impedance value of draft gear in a slowly changing segment,the train’s maximum couple force and acceleration will reduce and improve the energy absorption of draft gear,which ease the train’s longitudinal impulse.However,excessive reduction of the impedance force in this section will easily increase the deflection of the draft gear and lead to the phenomenon of the draft gear being crushed.(5)Combining the required capacity of frictional draft gear with the adjustment of impedance characteristic,under the premise of ensuring a certainly required capacity of the friction draft gear,the method of gradually selecting points according to the compression of the draft gear from small to large is adopted,the improved particle swarm optimization algorithm is used to optimize the impedance value of each selected point.In the process of optimization,the impedance values of each point are gradually determined from small deflection to large deflection,which further improves the performance evaluation method of the frictional draft gear.Compared with the test results of MT-2 draft gear,the impedance characteristics of the optimized draft gear are better than that of MT-2 draft gear under the same conditions.(6)Taking the elastic polymer draft gear as the research object,the influence of key parameters of the model such as the mounting preload,comprehensive equivalent stiffness and flow index of the elastic polymer draft gear on the longitudinal impulse of a marshaling form of 20 rapid speed wagons under emergency braking conditions is analyzed,optimizes the structural parameters of the elastic polymer draft gear and the characteristics of the draft gear before and after the optimization were compared and analyzed in a marshaling form of20 and 40 rapid speed wagons.The simulation results show that since the dynamic characteristics of the elastic polymer draft gear are related to its working speed,the longitudinal dynamic performance of the optimized draft gear under large braking reduction conditions is better than that of the draft gear before optimization under the same conditions.Under small braking reduction conditions,the characteristics of the draft gear before and after optimization are the same. |
