Using Vibration Signal To Diagnose Abnormal State Of Engine Valves Clearance

Abnormal fault of Internal Combustion Engine valves clearance have the very big percent in various type of Internal Combustion Engine faults, so it has important meaning to make diagnosis of this kind fault. This paper take the DA 462 type engine as research object, putting forward diagnosis method based on vibration analysis according to abnormal state of valves clearance.In this paper, author take analysis such as the Internal Combustion Engine structure and the operation characteristic as the foundation, making sure that the combustion excitation ,the piston slap excitation, the inertia force encourage, the valve falling impact and throttle impact when valve opens act as main excitation source, and analyze the propagation path of engine vibration. Combining this subject study, choose response of the combustion excitation and exhaust valve excitation as fault characteristic signal. Through studying the method of analyzing vibration signal in details, adopt the method of signal analysis combining the time domain analysis together with the frequency domain analysis. Basing on the analysis of modern vibrate measuring and testing techniques, built a set of practical vibration signal measuring and testing system successfully. Through the experiment, verify that this system can get fault characteristic signal accurately. Adopt the method of"shuang pai bu jin"to adjust the valve clearance data which are 0.15 mm,0.25 mm,0.35 mm and 0.45 mm. Among those data, normal clearance is 0.15mm, using the other data to simulate abnormal state of valve clearance. Using the measuring and testing system that was built for my subject, we can get the vibration signal in condition of different rotation speed and valve clearance, making conclusion that different rotation speed and valve clearance influence on the degree of the characteristic signal. The frequency band of the fault characteristic signal through the theories analysis is taken certainly, in next step observing range of frequency band's variation when we adjust clearance data, then we can judge the size of the valve clearance in the light of time domain and frequency domain's wave figure of fault characteristic signal .