Research Of Engine Fault Diagnosis Based On Vibration Signal Of Cylinder Head

Engine has a high probability of fault, high maintenance costs and spends a long time to maintain as the automobile’s power source. In all the faults, engine valve clearance abnormality fault is the most common engine mechanical fault in the use, if the engine is in the case of no disintegration, the technological state of the engine can be judged accurately through vibration signal monitoring diagnosis methods and it will be of great significance.At present, many vibration monitoring diagnosis methods extract fault features in the time domain or frequency domain to execute fault identification by measuring vibration signals of valve bolt and cylinder head. Wavelet packet analysis is a signal processing method based on multi-resolution analysis and it is able to distinguish the frequency to any details. The method is not only to the low-frequency signal for further decomposition, but also has the same resolution to the high-frequency signal, and therefore it has been widely used in fault diagnosis.In this paper, DA462 engine is the research object, and successfully build a set of simple and practical vibration signal test system. In the experiment, artificially adjust valve clearance to different states to simulate engine valve clearance abnormality, and with BSWA VS302 USB portable dual-channel vibration analyzer to measure groups of the cylinder head vibration signals in different engine valve clearances and different speeds. The measured signals are compared in the time domain and find out the relationship among the engine vibration, valve clearance and engine speed. The excitation response signal of engine cylinder head surface vibration signal can use wavelet packet analysis for wavelet packet decomposition, the frequency bands of the excitation response signals can be determined by calculating the various RMS of the reconstruction of frequency bands, meanwhile the application of power spectral analysis can also distinguish the frequency band of the characteristics signal.The experimental results are consistent with a number of theories mentioned in the related literature, which proves that the method used in the paper is effective and feasible. Using this method above, the working engine valve clearance abnormality fault can be judged accurately and it also provides a new way of thinking and method for engine mechanical fault diagnosis.