Research On Instability Mechanism And Security Measures Of Heavy Haul Couplers With Friction Arc Surfaces During Braking

Due to the insufficient coupler stability capacity,the lateral instability behavior of couplers with friction arc surface during braking influences the normal heavy haul railway transportation and the running safety.It is one of the urgent needs to explore the instability behavior of couplers with friction arc surfaces during braking and to propose safety technical measures.Therefore,with the help of the TTRI research team,the instability mechanism and security measures of heavy haul couplers with friction arc surface during braking are studied based on simulation and experiment.The author of this thesis mainly conducted most of the research work.This thesis systematically analyzes the stability measures of couplers with friction arc surface,focuses on the stability mechanism of the friction arc surfaces,and calculates the critical angle of the serving couplers.For the used coupler,its critical angle is generally no more than 2.22~°.There is the positive feedback mechanism between the heavy haul locomotive and the coupler.The correlation relationship between the car body yaw angle and the coupler angle is analyzed,and the calculation formula is given.The dynamic behaviors and characteristics of the coupler instability behavior are studied based on the fie ld braking test.The test results show that the coupler and the car body can keep stable under 350kN.Coupler angle has the similar tendency to the car body yaw angle,however,their yaw directions are opposite.Once the coupler instability behavior occurs during braking,there is a remarkable low-frequency vibration 1.2Hz on the car body and the bogie frame.Thus,the locomotive has the risk of the lateral instability,and reduces the running quality.The locomotive-coupler coupled model is developed,considering the coupler service conditions,installation errors and interaction with heavy haul locomotives.The model includes heavy haul locomotives models,coupler systems with friction arc surfaces and a dummy freight model.The accuracy of the model is verified by the test data.The model can simulate the coupler instability behavior and interaction with locomotives during braking.Based on the model,the influence key parameters of couplers and locomotives on coupler stability capacity can be studied.The coupler static measurements results indicate that the precision of manufacturing and installation is low,and flat pin hole and pear-shaped hole have a great errors,which weaken the coupler stability capacity.The manufacturing precision of the coupler should be improved.Based on the model,the influence of the friction coefficient on the coupler stability capacity is analyzed.Simulation results indicate that the friction coefficient should be not less than 0.35 for the 10000t heavy haul train.The theoretical analysis shows that increasing the difference of radii of the coupler end can improve coupler compressed instability capacity.There are two problems of the serving coupler,too large coupler angle and wheelset lateral force instantaneous excessive caused by the flat pin.In order to solve two problems,an optimized coupler is proposed,and its stability capacity and the running safety of locomotives are analyzed based on simulation model.The maximum coupler angle of the optimized coupler recommends no more than 4°.According to the test results,increasing the friction coefficient can improve the coupler stability capacity during braking,however,the coupler stability performace gets rapidly worse.Thus,the overhauling suggestions of couplers are proposed.Optimized couplers have excellent stability performance,can effectively limit coupler lateral behavior during braking,and have less influence on dynamic performance of the test locomotive.According to the car body measurement results,there is widespread mismatch between the front and the rear coupler box of the car body.The lateral errors of the coupler boxes focus on 8~16mm,considering the installation errors of couplers.It is one of important reasons that lead to eccentric wear of the coupler end.Thus,the accuracy of manufacturing of the locomotive should be improved,and the lateral deviation of the coupler box should be strictly controlled.The simulation model and field braking tests are used to analyze the influences of the coupler boxes lateral errors,secondary suspension systems and secondary lateral stopper on coupler stability performance during braking,to evaluate the effect on limiting coupler instability behavior,and to analyze the dynamic performance characteristic of locomotives.Simulation results show that the lateral errors of the coupler boxes should be no more than 4mm.Increasing secondary lateral stiffness has an influence on the coupler stability capacity.The parameters of the secondary lateral stoppers have an important effect on the coupler stability capacity during braking.Such as,decreasing the free clearance,increasing lateral stiffness and longitud inal distance can control the coupler angle and the car body yaw angle during braking.According to the test results,when the secondary lateral stiffness is increased to 600kN/m,coupler angle and car body yaw angle are decreased by 23%,11%,respectively.However,car body vibration becomes too great to decrease the locomotive running stability.For the secondary lateral stoppers,decreasing free clearance and increasing stiffness have the similar effects.Coupler angle and car body yaw angle are decreased by 40%,20%,respective ly.Both of them mainly influence locomotive lateral dynamic performance during braking.Finally,in order to solve coupler instability problem of the Bao-Xi railway when10000t class trains are electric braking on the long down-gradients,this thesis analyzes the reason of the coupler instability that occurs on Bao-Xi railway,evaluates the effects of the different safety measures,and propose the feasible safety measure to improve coupler stability capacity.The safety measure is decreasing the free clearance to 10 mm and increasing lateral stiffness to 7.87 MN/m for the secondary lateral stoppers.Based on the dynamic model,the optimized locomotive dynamic behavior and running safety are studied.Simulation results shows that the optimized scheme can effectively decrease the coupler angle and the car body yaw angle during braking.Besides,the optimized locomotive can pass through the R300m curve track.Two fie ld braking tests were conducted to evaluate the real effect of the safety measure,and obtain the coupler force,coupler angle,car body yaw angel,and acceleration of the car body.According to the test results,the maximum coupler angle is only 5.37~°,which is 43.7%of the origina l locomotive test results.The car body does not occur the lateral instability behavior during braking.Besides,the optimized locomotive running quality belongs to the good level,and the running safety indexes are far less than the safety value.Therefore,the safety measure can effective ly improve coupler compressed capacity and limit car body lateral instability behavior during braking.