Analysis Of Wheel-rail Contact And Dynamic Behavior For Heavy-haul Freight Wagon Under Asymmetric Brake Shoe Forces

The braking mechanism in railway heavy-haul wagons is an important guarantee for vehicle running safety.The problem directly caused by the braking device failure will generally lead to the unequal brake shoe forces on the left and right wheels.Problems found in the operation and maintenance of vehicles,such as unequal wear on left and right wheels,flange wear,and partial wear of brake shoes are partly induced by the effect of asymmetric brake forces.Taking the C80 heavy-haul freight wagon as example,the single vehicle dynamic model is established.And then,a short marshalling train model composed by four one-dimension(1D)simple models and three three-dimension(3D)accurate models is established.The impact of asymmetric brake forces on the wheel-rail contact characteristics and the running safety of heavy-haul wagon are studied based on the proposed dynamic models.Firstly,the asymmetric brake force is regarded as the combination of the unbalanced brake shoe force and braking torque caused by friction,and the difference between the two components is explored using a 3D vehicle model.The results show that the running state of the wheelset and wheel-rail contact state can be affected significantly by the unbalanced brake shoe force.The effect is more obvious when the unbalanced brake shoe force occurs in the leading wheelset.When the vehicle passes through the right-turn curved track,the clockwise movement in wheelset 1 caused by the unbalanced brake shoe force will improve the wheel-rail contact status.Conversely,the counterclockwise yaw torque will deteriorate the wheel-rail contact state.Secondly,based on the measured tread profile of C80 vehicle,the influences of the asymmetric braking force and the worn tread are analyzed.The results show that the wheel-rail contact state will change greatly after the tread is worn.This change has strong non-linear characteristics,and will be more obvious if the unbalanced brake shoe failure occurs.Under the action of the asymmetric brake force,acomparative analysis is carried out on the response characteristics between the single vehicle and the short marshalling train.The results show that the wheel-rail contact characteristics of the short marshalling train are basically the same as that of a single vehicle,but the differences in amplitude can be observed obviously.Due to the constraints of the front and rear vehicles,the intermediate wagon is less affected by the asymmetric brake force,and the wheel-rail contact status of the left and right wheels tends to be consistent with each other.Finally,taking the short marshalling train as an example,the limit value of the asymmetric brake shoe force is analyzed from the aspects of wheel-rail adhesion characteristics and running safety.It is found that,the curve radius will lead to more significant effect on the wheel-rail contact state than the asymmetric brake force.In order to keep the percentage of adhesion area above 60%,it is recommended that the force difference between the left and right wheels should not be bigger than 20 k N.Considering the running safety indicators of the vehicle,it is recommended that the difference of the pressure between the left and right wheels should not be larger than40 k N.