Study Of Automotive Engine Fault Diagnosis Based On Model Simulation And Vibration Analysis

The structure of automotive engine becomes increasingly complicated and therequirement for installation precision increasing too. How to diagnose the fault’s type andlocation under the non-overhaul condition has been the key and difficult points of researchnowadays. We need to measure the change of relative parameters, know the fault informationand exact fault features while studying the engine fault, however it’s difficult to collect theabove information.And,if the engine’s faults are made artificially, it will result in severedamage of engine and high testing cost, which limit the further survey.Aimming at the existed weakness of engine fault diagnosis techniques, the faults’mechanism, feature extraction and diagnosis methods of the whole engine is studied for thefirst time by modeling and simulation. The results will become more accurate and reliable byjoint modeling under the finite element and multi-body dynamics. By analyzing the vibrationresponse on the surface of engine body considering the inner factor of exciting force, thereasons and characteristics of abnormal engine body vibration caused by the fault is obtained.By the trend analysis of vibration signals of the body surface under the normal and faultconditions, the fault feature is extracted, and which provided a new way for the engine faultdiagnosis. By the multi-body dynamics and the finite element technique, high qualitybenchmarking engine simulation model is builded. Faults including the engine misfire，largevalve clearance, cam bearing looseness, piston knocking and main bearing wears can besimulated by the related parameters setting. The fault features are extracted and verifiedaccordingly.A fault feature extraction method is proposed by the application of wavelet packetdecomposition and demodulation method to extract the faults of the excessive valve clearanceand looseness of camshaft. The faults of the excessive valve clearance and looseness ofcamshaft are analyzed using the engine simulation model established. It is found that with theincreasement of valve clearance, the valve seating force and the bearing force increasing too.And because of the increasing impact forces, three significant impacts in a working cycleappear in the time domain vibration signal of cylinder head, which arouses the notablevibration energy in the high frequency. By wavelet packet decomposition, the signal of the high frequency band is decomposed. For the faults of excessive valve clearance and camshaftlooseness, the demodulation spectrum appears obvious1.5order component and the0.5ordercomponent, respectively. It is found that this kind of fault has significant high frequencymodulation phenomenon in theory, which provides strong reference to failure featureextraction and fault diagnosis. The reason why the energy of high frequency over2500Hzincreased when piston knock is analyzed theoretically. A method of fault diagnosis based onratio’s change trend with rotate speed between the total energy of wavelet packetdecomposition under fault condition and normal condition is presented. The reason why thevibration energy of medium-low frequency between200and1000Hz increased is analyzed intheory, which is caused by the fluctuations of main bearing reaction force caused by excessiveclearance of main bearing. The method can provide theoretical basis for this kind of faultdiagnosis research.