Research On Operational Safety Of CRH₃ Series EMU

In order to study the operation adaptability and the safety in service of high-speed Electric Multiple Units(EMUs),the dynamic model of high-speed EMUs coupled with track systems and wheel wear model are set up in this paper.The wheel tread wear and its evolution characteristics of CRH380C,CRH380BL and other CRH3 series high-speed EMUs in service are studied by combining theoretical methods with field tests.The main causes,influence factors and solving measures are studied and verified for handling the problems of lateral acceleration alarm due to hunting bogie frames,low-frequency lateral swaying and shaking of carbodies in operating the EMUs.The main contents and results are given as follows.Firstly,a multi-degree-of-freedom dynamic model of CRH3 series EMUs is established based on the data of the test rig and field test.The natural frequencies and vibration transmission characteristics of the system are investigated based on the linear model.It is found that the most important factors affecting the amplitude-frequency transmission characteristics of wheelsets are the tread taper and longitudinal stiffness.Based on the non-linear model,the factors affecting hunting instability are studied.Two kinds of unstable modes of the vehicle system are summarized as bogie hunting and car body hunting.These two kinds of unstable modes have contradictory requirements on suspension parameters.It needs a comprehensive optimization to improve the operation adaptability and service safety of high-speed EMUs.Secondly,the formation and evolution process of tread wear are simulated based on the established vehicle-track dynamic model and material friction worn model.The influence of system parameters on tread wear is compared and analyzed.It is found that wheel wear tends to be at a certain level in both width and depth with the increase of operating mileage under the conditions of 250 km/h and 300 km/h conditions.The wheel wear tends to develop in the depth direction at the speed of 350 km/h.the most important factor for wheel wear is the anti-hunting damper stiffness and the primary longitudinal stiffness.The amplitude of vertical loads acting on primary springs increases to a certain level in the case of high-speed running with worn wheel on straight lines.The main frequency increases from 15Hz to 20 Hz.The vibration energy of 10-25Hz is dominant in primary spring load characteristics for the case of negotiating turnout at high-speed.In addition,The basic reason for lateral acceleration alarm of frames of CRH3 series EMUis that the worn tread and the undesirable railhead of local track is not well matched.The equivalent taper is too large.The yaw damper with a small dynamic stiffness does not have ability to suppress the bogie hunting which causes the harmonic vibration of the frame and the acceleration to exceed the alarm limit.According to the actual size of wheel-rail clearance,the alarm limit is determined.When the frame hunting frequency of CRH3 series EMUs is more than 6.7Hz,the wheel will not impact the rail.On the premise of ensuring the safety of EMU,the lateral acceleration alarm limit of frame in the frequency range between 7.6 and 9 Hz is increased appropriately,and a new lateral acceleration alarm logic of frame is proposed.Moreover,The basic reason for the low-frequency lateral swaying of CRH3 series EMU is that the equivalent taper of actual wheels matched with rails is low.Furthermore,the yaw dampers are equiped with a large dynamic stiffness.Those result in a strong coupling effect between the car body and the bogie.Consequently,the harmonic vibration occurs.The low frequency lateral swaying of CRH3 series EMUs can be solved by optimizing the parameters of the yaw damper and the primary stiffness.Last but not least,The fundamental reason for the shaking of CRH3 car body is that the unreasonable wheel-rail matching conditions in local regions,which causes the hunting motion of bogie to be transmitted to the carbody.In addition,the hunting frequency of the bogie is closed to the carbody natural frequency,which can enlarge the severe vibration of the car body.The solution is to ensure good matching condition for wheels and rails by grinding rail and repairing tread of the wheel set.At the same time,the local structure of the car body should be improved to avoid coupling between the lowest natural frequency and the bogie hunting frequency.