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Shock and Vibration
Volume 8, Issue 6, Pages 339-348

Sliced Wigner Fourth Order Moment Spectra Smoothed by γ-Method and Its Application to Detection of Valve System Faults in an Engine

Sang-Kwon Lee

Department of Mechanical Engineering, Inha University, Yong-Hyun Dong 253, Inchon, 402-751, South Korea

Received 25 August 2000; Revised 25 August 2000

Copyright © 2001 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The research proposes a method for detecting valve system faults in an engine. The methodology is based on the detection of impulsive sound embedded in the high level of background noise by using the sliced Wigner fourth order moment spectra (SWFOMS) which is inherently more robust in the presence of random (Gaussian) noise. However, in previous work, the SWFOMS for multiple signals had problems with its application which were due to the existence of non-oscillating cross-terms not smoothed by conventional methods. In this paper, the γ-method is developed to smooth non-oscillation cross-terms. Finally, the techniques developed are applied to the diagnosis of valve system faults in an engine.