Study On The Influencing Factors Of Hunting Movement Stability Of A High-speed EMU

Hunting movement is a unique phenomenon of rail vehicle systems,which directly affects the stability of the vehicle system and determines the maximum running speed of trains.To master the characteristics and evolutionary laws of hunting movement is essential to vehicle design and operation safety.Due to the strong non-linear characteristics of the vehicle system,there are still many difficulties in the theoretical study of hunting movement.The existing linear theory cannot fully explain the hunting movement behavior of high-speed vehicles,and the actual engineering problems have not been completely resolved.In particular,the frequency,amplitude,and bifurcation direction of hunting movement have a direct impact on train speed lifting and operation safety,and the factors affecting the stability of hunting movement still need to be explored in all aspects.In this thesis,the tracking test of service performance of a high-speed EMU is carried out,and the behavior of abnormal vehicle body vibration in the local section is analyzed,and the relationship between abnormal vibration and hunting movement is studied.A dynamic model of the vehicle rigid-flexible coupling system is established,and the abnormal vibration is reproduced by simulation,which verified the correctness of the model.The effect of the suspension parameters and the elastic modal of the vehicle body on the hunting movement is analyzed by simulation,and the differences are compared in the characteristics of the hunting movement when the flexible vehicle body model and the rigid vehicle body model are used.The relationship between the wheelset lateral displacement amplitude and the hunting frequency is summarized.Finally,based on the measured wheel and rail profile data,the influence of the equivalent conicity on the critical speed,hunting bifurcation and hunting frequency is discussed.The main research conclusions are as follows:1.When passing through a local section,the hunting instability of vehicle occurs,and the lateral acceleration of the vehicle body is significantly increased.After filtering,it presents a harmonic signal with a single dominant frequency.The abnormal vibration of the vehicle body is caused by abnormal rail wear,and the equivalent conicity matching with the wheel in the later stage of wear is too large.The bogie hunting instability occurs,and the hunting frequency is close to the first-order diamond modal of the vehicle body,resulting in the vehicle body elastic resonance occurs.2.The rigid-flexible coupling dynamics model is established,and the measured wheel/rail profile is imported to restore the abnormal vibration phenomenon.On this basis,it shows that after the vehicle instability occurs,increasing the speed will increase the wheelset lateral displacement amplitude and reduce the hunting frequency.Wheelset lateral displacement amplitude is negatively correlated with hunting frequency.3.For this type of high-speed EMU,the primary stiffness of the axle box has a great impact on the critical speed,while the damping of the secondary lateral damper and yaw damper have a very limited impact on the critical speed.4.If the hunting frequency of the system is close to the diamond modal frequency of the flexible vehicle body model,the wheelset lateral displacement amplitude and the lateral acceleration in the middle of the vehicle body will have a jump in growth,and the hunting frequency will have a jump in decline.The rigid vehicle body model does not have the jump phenomena.5.When the conicity is low and the conicity curve is relatively flat,the vehicle system appears as a subcritical bifurcation;when the conicity is high and the conicity curve has a negative slope,the vehicle system appears as a supercritical bifurcation.The conicity at the lateral displacement of 1 mm has the greatest correlation with the critical speed,so the conicity limit recommendations are given accordingly.