In order to diagnose the abnormal sound fault of the diesel without disassemble, dual microphones are used to collect noise signal of the engine in this paper, and the sound pressure signal is decomposed with wavelet decomposition technique. By comparing different wavelet decomposition techniques, it determines the sound feature parameter for fault diagnosis, and establishes a BP neural network for pattern recognition. The test result shows that diagnosing engine fault with dual microphones is accuracy, and it can be applied to diagnose the abnormal sound fault of engine.

The vibration signals from engines contain information about the engine conditions. Engine power is an important parameter that indicates the state of an engine. In this manuscript, a method for measuring the engine power, using the vibration signals from the engine, is developed. In our proposed method, the power of the engine is measured based on the principle of no-load measurement. The discrete values of rotation speed are computed from the vibration signal, using wavelet transforms, the Hilbert envelope, and three autocorrelations. By comparing various curve-fitting and interpolation methods, an optimal method for curve fitting the discrete acceleration data is chosen, and the corresponding times of the starting speed and terminal speed are calculated using the analytical formulas of the fitted curve. Finally, the maximum engine power is obtained from the calibration tests. Experimental results show that the overall performance is good and that the maximum power measurement accuracy is 98.4 % after accurate calibration. This meets the requirements of the power measurement accuracy under the condition of no load.

In order to compute the exact position of default in vehicle's transmission shaft, the cyclostationary of vibration signal in vehicle's transmission shaft is analyzed, and the method about extracting imbalance vibration signal characteristic of transmission shaft by using SOCS(second order cyclostationary) is proposed, then through comparing the SOCS-peaks in different imbalance conditions, the imbalance direction of transmission shaft was found out. Experimental result shows that using the method of SOCS, the demodulation of signal can be effective, the special frequency in vibration signal of transmission shaft can be extracted, and the characteristic is obvious in base-frequency, and half of base-frequency of signal in vehicle's transmission shaft.