Aiming at the fault signal separation and fault characteristics extraction of gears under variable rotational speed, an adaptive time-frequency filtering method based on the chirplet path pursuit (CPP) and S transform was proposed. In the method, the gear mesh frequency was estimated from an original gear vibration signal by using the CPP, meanwhile, the timefrequency distribution of the original gear vibration signal was obtained by using the S transform. An adaptive time-frequency filter was designed according to the gear mesh frequency, and the time-frequency filtering was carried out on the time-frequency distribution of the original signal, which was followed by the inverse S transform so as to get the filtered signal containing gear fault informations. Then, the gear fault diagnosis was carried out according to the modulation sideband in the order spectrum, which was obtained by using order tracking to the filtered signal. The local faults of the gear were analysed both by simulations and examples. The results show that the adaptive timefrequency filter can adaptively change its centre frequency and bandwidth according to the frequency variation characteristics of the gear. It has a good adaptability for signal analysis, moreover,the filtered signal is without phase distortion. Therefore, the adaptive time-frequency filtering method is very suitable for analyzing non-stationary gear signals under variable rotational speed.
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