It is well known that the most dominant frequency component of the noise and vibration from gear boxes is due to gear tooth-meshing. That behavior could be observed for a gearbox under in this study. In addition, it could be observed that the tooth-meshing component of the sound pressure level from the gearbox took its maximum at a given operational speed.
By investigating the natural frequencies of the gear box, it was found that the natural frequency of the gearshaft-bearing system is closely related to the observed characteristics. Since it is very difficult to obtain the frequency response functions by exciting test under operational conditions, the test was done under non-operational conditions. In order to take into account the stiffness of tooth meshing, transfer matrix method was employed to estimate the natural frequencies under operational conditions.
Based on the transfer matrix model by experimental observations, several improvements were suggested.