Spiral bevel gears are essential units in the accessories system of the aero-engine. The rotor transmits torque to the accessories system through the spiral bevel gears, which also change the direction of rotation. With the wide application of elastic support and the reduction in the number of bearing frames, the fulcrum stiffness and the rotor shaft stiffness is on the same order of magnitude of the gear meshing stiffness. For these multi-axis gear transmission systems, the effects of time-varying relative displacement between the gear meshing points and its additional constraint on the dynamic characteristics of the rotor ought be considered. In this paper, a coupled mechanical model of the bevel gear-coupled two-shaft rotor system is established. Besides, the coupled vibration mode of the gear-rotor system is studied. Finally, the influence of nonlinearify relative displacement and its additional constraint on the vibration characteristics of the rotor system are analyzed. The results show that the driven gear will produce elastic additional constraint on the rotor under the specific vibration mode. When the gear meshing stiffness is on the same magnitude as the support stiffness of the rotor, and the relative vibration displacement between the driving and driven gears is large enough, it is necessary to consider the influence of additional constraints on the rotor dynamics. The analysis in this paper provide a reference for dynamic optimization designs, fault monitoring and diagnosis of gear-rotor systems. Key words: coupled vibration, gear-rotor system, additional constraint, nonlinearify relative displacement.
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