| With the continuous expansion of China’s urban rail network,public rail transport modes such as metro trains have become the primary choice for people to travel.However,with the increase in the mileage of metro trains,the number of traction and braking operations,as well as the operating load of metro trains in the morning and evening peak hours,the wheel-rail contact status of metro trains changes during operation,resulting in wheel flat scars and other defects on the wheel treads.The long-term operation of metro trains under the influence of wheel flat scars and random track unevenness is likely to cause severe vertical vibration impacts on the wheel-rail system during operation.Considering that the large driven gears of metro trains are installed on the wheel pairs of metro trains,when the wheel pairs are subjected to severe shocks,the smooth meshing of the gearing system is bound to be affected,making the transmission gears more prone to fatigue failure.In this paper,the wheel flat scar damage and track random unevenness is imposed into the metro vehicle-track coupling dynamics model,the metro vehicle transmission gear dynamic characteristics and fatigue life research,the main research content such as the following three aspects:(1)Based on the mathematical geometry of wheel scars and the impact of wheel scars on the track at different driving speeds,a wheel scar damage model applicable to the wheel treads of metro vehicles is established,followed by the construction of a coupled dynamics model of metro vehicles-rail considering the gearing system based on the coupled vehicle-rail dynamics theory and the introduction of the dynamics solution integration method used in this paper.The reliability of the coupled vehicle-rail dynamics model is verified by comparing the results of the non-linear critical speed analysis of the metro vehicle with the literature data.(2)The dynamic forces on the wheels and rails,the dynamic characteristics of the bearings and the dynamic characteristics of the transmission gears in the gear train of a metro vehicle under the damage of a flat wheel scar are specifically analyzed,and then the smoothness index of the vehicle dynamics evaluation index and the derailment coefficient and wheel weight reduction rate of the vehicle operational safety index are further selected according to the gear train dynamics results to determine the dynamic characteristics of the metro vehicle under the damage of a flat wheel scar,in order to pave the way for the next chapter to study the dynamic meshing force and service life of the transmission gear system under the influence of a flat wheel scar.(3)According to the dynamic transmission error results of the transmission gear pair in the calculation of the metro vehicle-track coupling dynamic model,the reliability of the gear transmission system dynamic model is verified,and then the simulation solution and analysis are carried out separately four operating conditions,namely,no external excitation,random unevenness of the track only,wheel flat scars only and wheel flat scars and random unevenness of the track together.Then,the dynamic meshing force of the transmission gear under the four working conditions is calculated and converted into the relationship diagram of the contact fatigue stress-time history of the transmission gear,and the rainflow counting method is used for cycle statistics to determine the number of stress cycles of the dynamic meshing force of the transmission gear.Finally,according to Palmgren-Miner’s law predicts the fatigue life of transmission gears under the influence of wheel flat scars,and provides certain theoretical guidance for the prediction of dynamic fatigue life of transmission gears in metro trains. |
