Research On Dynamic Characteristics Of Heavy-haul Locomotive With Asymmetric Brake Shoe Braking Effect

Heavy-haul freight train is an important part of railway transportation.For a long time,brake failure had been reported frequently,which leads to asymmetric brake shoe braking effect of vehicles in emergency braking state in actual operation,resulting in a significant increase of potential operational safety hazards of vehicles.Therefore,the influence characteristics of locomotive dynamics under the action of asymmetric brake shoes need to be solved urgently.In view of this,based on the vehicle system dynamics,this paper studies the dynamic behavior of wheel-rail under the action of asymmetric brake shoe in the fault state of HXD heavy-haul locomotive with 25 t axle load.Firstly,the locomotive vehicle model and short marshalling heavy-haul train model were established by the multi-body dynamics simulation software UM.Non-linear mechanical relationships such as shock absorbers for locomotive suspension systems,free lateral momentum of intermediate wheel pairs,and hysteresis characteristics of buffers in hook-reduction systems were considered in the model.The single-locomotive model was used to calculate the wheel-rail dynamic behavior only under the brake shoe pressure to determine the most serious safety hazards.Then,the actual wear-measured treads at different mileages were imported into the single-locomotive dynamics model,and the results of the dynamic response characteristics of wheel rail under the combined action of wheel wear and asymmetric brake shoe braking were obtained.In addition,the dynamic behavior of wheel-rail under the condition of the maximum potential safety hazard of locomotive in the short marshalling heavy haul train was given.At the same time,the dynamic response law of wheel rail contact creep limit and driving safety threshold was analyzed.It was concluded that the creep limit state and safety threshold changed with the degree of braking force asymmetric under different curve radius conditions.The results show that the wheel-rail dynamic behavior was the most severe when the side-wheel pair was completely in the state of brake failure in the straight running state.Generally speaking,the dynamic response of the wheelset traverse amount,yaw angle,wheel-rail lateral force,and wear power was most obvious under the condition of 1st wheelset braking failure,and the 1st wheelset response at the fault position was the most severe.At the same time,the composite creep force of the wheel-rail contact creep state was difficult to reach the limit friction force and the full slip motion state occurs.The locomotive's safety threshold was the wheel-rail lateral force,wheel unloading rate,derailment coefficient and lateral wheelset force.The wheel unloading rate response shows a high level.The most obvious response was an increase of 12.73% compared to the wheel unloading rate under normal braking conditions.When the curve passes,the brake failure of the inner and outer wheels shows the opposite law with the change of the asymmetric braking force.The dynamic response of wheel-rail decreases gradually with the increase of curve radius.The potential safety hazard of vehicle operation will be increased when the asymmetric brake shoe braking effect occurs when the locomotive passes the curve under the condition of 600 m difficult curve radius and 800 m minimum curve radius.Taken as a whole,the dynamic response of wheel-rail was the most violent when 1st outer wheel breaks down,and the motion level of 1st wheelset was higher.In addition,when the wheel-rail contact creep state changes with the degree of braking imbalance,only 1st inner wheel fault state shows a strong linear rule,while the other 1st outer wheel fault state shows the opposite response changed.When the curve passes,the response amplitude level of driving safety threshold was relatively high.Under the extreme condition of complete failure of 1st outer wheel brake,the derailment coefficient had exceeded the safety limit,which was 0.21 higher than that under the normal braking condition.The effect of unbalanced braking on the locomotive's movement status under wheel-rail wear was relatively weak.The dynamic response of the wheel-rail under different wear treads had little difference,and the wheelset yaw motion was almost the same.In addition,the dynamic response of the locomotive in a short marshalling train in a straight line shows a strong non-linear law.Under the simultaneous action of the longitudinal coupler force and the unbalanced braking force,the dynamic response shows a law of both increase and decrease and shows a strong linear rule when the curve passes.Finally,based on the analysis of the full text,the impact of unbalanced brake shoe braking on wear power was the largest.The maximum abrasion power under the condition of the brake shoe pressure in a straight line and a curve passing state are: 399.89 W and 6.28 k W.Among them,the normal braking wear power of a locomotive was almost negligible compared to the fault state when running in a straight line.Under the wear tread,the wear power response of the next inner wheel was the most obvious at the initial wear of 20 000 km and at the later wear of 90 000 km.The maximum wear power amplitudes in straight and curved operation were 632.54 W and 5.75 k W under complete fault conditions.When the curve passes,the maximum wear power of the wheel corresponds to an increase in wear power of 1.25 k W under balanced braking conditions.The maximum wear power of the locomotive in straight running and curve passing in the short marshalling heavy haul train was 1 482.71 W and 4.25 k W,respectively.It can be seen that the asymmetric braking effect results in a relatively high level of wear power,which increases rail wear and tread wear,increases the potential safety risk of driving,and increases economic investment in maintenance.