| In order to meet the development requirements of heavy haul freight transportation in China,the requirement of developing 100 t load heavy haul freight car is proposed.During the course of development,the vertical ride index of a certain type of coal hopper car is abnormal in the range of 60km/h~110km/h during the dynamic performance test.In this paper,the vibration characteristics and the stability of the vehicle are studied based on the abnormal of the vertical ride index.Firstly,a brief description of the abnormal phenomenon of the vehicle's ride index is made,and the analysis of the freight car ride index is introduced,and the possible reasons causing the abnormality of the ride index are discussed.Then the vibration characteristics of the system of freight car with wedge friction damper are analyzed,and the vibration response law and the influencing factors are obtained.In order to further analyze the vibration response of vehicle system under random excitation,a multi-body dynamic model is established.Because the wedge friction damper has an important influence on the vehicle dynamics performance,two kinds of modeling methods are adopted for comparative analysis.The results show that the acceleration response,the ride index and the frictional resistance of the two models all have a good consistency,and finally the wedge friction damper is simplified in the form of relative friction coefficient.It is found that the dynamic performance index satisfies the standard in the design parameters,and the vertical ride index does not have obvious over-large phenomenon through the dynamic performance simulation under empty and load conditions.The causes of the differences between the simulation results and the test results may be related to the elasticity of the sub-frame,the eccentric of the wheel,the abnormal vertical stiffness of primary suspensions,and abnormal relative friction coefficient.Rigid-flexible coupling model of vehicle system is constructed by treating the sub-frame as flexible body.By comparing the rigid-flexible coupling model and the Rigid model,it is concluded that carbody?s vertical response considering the flexibility of the sub-frame is slightly larger than that of the rigid model,but the change trend of the two responses is basically the same.The results show that the anomaly of the ride index is not caused by the elasticity of sub-frame.By studying the influence of wheel eccentricity on the ride index of load vehicle,it is concluded that the ride index does not exceed the standard when the wheel eccentricity is within standard range.Only when the eccentricity of the wheel is large,the ride index of the vehicle will be significantly increased.At the same time,when the ?jamming? phenomenon exists in the wedge friction damper,resonance will occur at a speed of 80 km/h resulting in deterioration of the ride index.By studying the influence of vertical stiffness of primary suspension and relative friction coefficient on vehicle?s ride index,the following conclusions are drawn: both empty and load working conditions,ride index increases slightly with vertical stiffness of primary suspension increasing,while ride index increases obviously with the relative friction coefficient increasing.According to the test result of relative friction coefficient,if the relative friction coefficient is too large,the vehicle will appears the phenomenon that ride index is large or even exceed the standard in track test.The study shows that the main reason for the abnormal ride index of 100 t load heavy haul freight car may be that the relative friction coefficient of the damping system is too large and the resonance is caused by the wedge ?jamming? at a certain speed.The vertical abnormal vibration of carbody can be eliminated by optimizing the relative friction coefficient of the wedge friction damper. |
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