Dynamic Unbalance Analysis And Monitoring Method Of Cardan Shaft In High-speed Train

To reduce the dynamic forces between wheel and rail,the motors in one type of high-speed train of China are suspended under the car body.Thus,the longitudinal distance between the motor and the gearbox is relatively long,cardan shafts with length of 1.8 meters are equipped in transmission system of the train to transmit driving torque.As the train mainly serves in northwest and northeast area of China where the weather is harsh,the cardan shaft faces some challenges in its operation.During the service of the cardan shafts,it was found that the gearboxes and motors were seriously damaged due to the dynamic unbalances of the cardan shafts.Hence,China Railway Rolling Stock Co.LTD(CRRC)in collaboration with Southwest Jiaotong University launched the project of state monitoring of the cardan shaft of high-speed train.Aiming at the monitoring threshold values and the monitoring method of dynamic unbalance of cardan shaft,this thesis applies analytical dynamics,wheel?rail contact theory and finite element analysis method to establish the dynamics models of the unbalanced cardan shaft,and the train?track coupling dynamics models containing dynamic unbalanced cardan shafts.According to the present allowable unbalance standard of cardan shaft and locations of measuring points in transmission system,the threshold values of acceleration for train speeds of 160?250 km/h are calculated.Applying the dual-tree complex wavelet packet transform(DTCWPT)algorithm and envelop demodulation algorithm,the methods recognizing alarm excitation source are proposed based on characters of excitations due to cardan shaft dynamic unbalance.The main research contents of this thesis are as follow.(1)Based on theoretical mechanics and analytical dynamics,the kinematical equation of dynamic unbalanced cardan shaft is derived,and dynamics model of cardan shaft driving system is established.The correlation between unbalance values and the excited unbalance forces is deduced according to the principle of dynamic balance test of cardan shaft.The limit deviation sizes corresponding to allowable unbalance values are calculated.(2)An analytical algorithm is proposed for calculating the generated unbalance force when the input shaft and the output shaft are under non-precession state,and a numerical algorithm for calculating the generated unbalance force when the input shaft and the output shaft are under precession state is proposed.(3)By applying analytical dynamics,coordinate matrix transformation and wheelrail contact theory,the train-trcak coupling dynamics model including dynamic unbalanced cardan shaft is established.The position variation of mass centers of universal joints and connecting shaft are considered in the model,the dynamic stiffness of meshing gears is introduced into the vehicle dynamics model through potenticalenergy function.(4)The dynamics model of the dynamic unbalanced cardan shaft is validated through the experimental bench test data.The train-trcak coupling dynamics model of the high speed train is validated by the line test data under train speed of 160 km/h,180km/h and 200 km/h,the results indicate that the accuracy of the two models are over 80 percent.(5)The influences of cardan shaft dynamic unbalance on dynamic performances of the train are investigated,including vehicle operation safety,stability,comfort,and wheel?rail forces.The influence on fatigue life of the motor connecting bolts subjected to the generated unbalance forces when the cardan shaft is under allowable unbalance state is analyzed by applying finite element analysis,and the fatigue life of bolts under different unbalance amount are calculated,the results indicate that the fatigue life of the bolts are about 6.5 years under the allowable unbalance amount.(6)According to the relation between rotating speed of the cardan shaft and speed of the train,the monitoring threshold values and the threshold curves for train speeds of 160?250 km/h are calculated.According to the signal characteristics of the acceleration response due to the cardan shaft dynamic unbalance and the wheel polygon,the algorithms recognizing alarm excitation sources are proposed based on the DTCWPT algorithm and envelop demodulation algorithm,outlier indexes are applied to reflect features of the signals to improve the alarm accuracy.