The vibration acceleration signal mechanisms in normal and defect gears are studied. An improved bending-torsion vibration model is established, in which the effect of time-varying meshing stiffness and damping, torsional stiffness for transmission shaft, elastic bearing support, the driving motor, and external load are taken into consideration. Then, vibration signals are simulated based on the model under diverse sampling frequencies. The influences of input shaft's rotating frequency, the teeth number, and module of gears are investigated by the analysis of the simulation signals. Finally, formulas are proposed to calculate the acceleration signal bandwidth and the critical and recommended sampling frequencies of the gear system. The compatibility of the formulas is discussed when there is a crack in the tooth root. The calculation results agree well with the experiments.
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