Generally

conventional methods require a large amount of detection data to extract fault features of the sun gear in a planetary gearbox. It makes these conventional methods can hardly be applied in working conditions with fewer rotation cycles in planetary gearboxes. To address this issue

an envelope separation and recombination method is proposed in this paper to extract fault features of the sun gear. In the proposed method

the equi-angle resampling and envelope analysis methods are firstly applied to eliminateinterference caused by speed fluctuations and irrelevant frequency band. Then

the separation and recombination method is utilized on the observed envelope signal to construct the envelope signal of the sun gear. Subsequently

the de-noised envelope signal of the sun gear can be obtained by the envelope synchronous averaging. Finally

fault features of the sun gear are extracted by the envelope spectrum analysis. The effectiveness of the proposed method is verified through the simulation analysis and experimentof the planetary gearbox. Results demonstrate the advantages of the proposed method for the application of the planetary gearbox with fewer rotation cycles.