It is an effective and also practical method to diagnosing the faults of diesel engine in way of measuring vibration signal. But because diesel is a complex reciprocating machine, the vibration signal of diesel body is very complex, and it is difficult to processing this kind of signals. Especially when vibration signal is measured on vehicle, the body vibration of diesel is always interfered by the vibration of other vehicle parts. So the signal-to-noise ratio is reduced when monitoring the diesel on vehicle. Using traditional filtering method to processing the vibration signal would sometimes lose useful information because of not knowing the frequency characteristic. This paper has measured the body vibration signal of diesel engine in order to diagnose misfire fault on armored vehicle. In this paper, the vibration signal was processed with method of wavelet analysis. In way of wavelet packet decompose and reconstruction, the vibration signal was decomposed successfully into the vehicle vibration and engine vibration, so the noise of vehicle vibration could be suppressed and the signal-to-noise ratio was improved. The signal with characteristic frequency was reconstructed, so the vibration mechanism could be analyzed in particular. The result shows that in way of analyzing the high-frequency component of body vibration through wavelet analysis, the misfire fault can be diagnosed and the misfiring cylinder can be recognized.
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