Profile shift is a powerful tool for increasing the gear tooth thickness and enhancing bending fatigue strength. However, it is one-sided to only improve the bending fatigue life of positive profile-shifted spur gear by strengthening the gear tooth body. Furthermore, the current research has not revealed the effect of profile shift on the dynamic load of the gear system with tooth root crack. Therefore, this paper establishes a novel analytical model. Based on the revised tooth shape, the model considers bending, shear, axial compressive, contact Hertzian, and fillet foundation potential energies. The results show that the negative profile shift is more sensitive to the root mean square value (RMS) of time-varying meshing stiffness (TVMS) than the positive. The negative profile-shifted gear provides high TVMS due to the high contact ratio under the health state. In comparison, it loses more TVMS with the crack propagation. Moreover, the positive profile-shifted gear has a lower effective meshing force and vibration intensity value in crack propagation than the negative. Overall, the positive profile shift can increase gear tooth life because it thickens the gear tooth and simultaneously decreases the dynamic load.
Abstract. In order to obtain a rail steel with high strength, high toughness and good resistance against contact fatigue failure, vanadium and niobium were added into the bainite steel, and roles of V and Ni were discussed. With the addition of V and Ni, the bainite steel is obtained grain refining, high strength and toughness. The mechanical properties are as follows: Rm is 1467 MPa, Rp 0.2 is 850 MPa, A is 17%, Z is 46%, hardness is 44 HRC, and α k is 60 J/cm 2 .
Gear tooth spalling is one of the inevitable fault modes in the long-term service of the traction transmission system of railway vehicles, which can worsen the dynamic load of the rotating mechanical system and reduce the operating quality. Therefore, it is necessary to study its fault mechanism to guide fault diagnosis scientifically. This paper established a planar railway vehicle model with a traction transmission system and an analytical time-varying meshing stiffness (TVMS) model of the spalling spur gear. Then, it analyzed the dynamic characteristics under traction conditions. The research found that the spalling length and depth affect the amplitude of the TVMS at the defect, while the width affects the range of the TVMS loss. The crest factor is the best evaluation indicator in ideal low-noise environments due to its sensitivity and linearity, but it is not good in strong-noise environments. Similarly, a time–frequency analysis tool cannot significantly detect the sideband characteristics that are excited by spalling. After high-pass filtering, the root mean square and variance exhibit excellent classification and vehicle speed independence in strong-noise environments. This research achievement can provide adequate theoretical support for feature selection and making strategies for fault diagnosis of railway vehicle gear systems.
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