ESTIMATION OF VALVE CLEARANCE OF ENGINE BY WAVELET ANALYSIS

摘要

In this paper, we proposed a new technique to estimate valve clearance in order to assure the quality and performance of the automobile engine. To estimate valve clearance, a microphone was used to measure engine noise. At first, we measured the acceleration of the valve in both the axial and the bending direction with several valve clearances. We found that (a) the vibration start-time delays and the amplitude of the vibration decreases as the valve clearance decreases, and (b) this strong vibration content induced by the valve close-operation causes a specific valve operation sound. According to the experimental facts, we developed the following estimation technique: (1)Filtering by analog high-pass filter: The exhaust noise was reduced to a very low level. (2)De-noising signals: The de-noising technique based on the wavelet analysis was carried out. This process involved two aspects: breaking up a signal to obtain the wavelet coefficients and modifying the small wavelet coefficients to zero. In this process, signals dissimilar to the mother wavelet were removed. (3) De-noising coefficients: The de-noising technique based on the wavelet analysis was applied to the wavelet coefficients obtained in the above process. Any signal induced by chance was removed in this step. (4) Reassembling coefficients: The de-noised signal was reassembled from obtained coefficients in step 3. (5) Averaging de-noised signals: De-noised signals were averaged to improve the reliability. Next, we carried out experiments to evaluate the above technique. Applying above technique, we achieved the following results: 1. The delay of the peak time in the valve close sound is proportional to the valve clearance and the 2. We can use the proposed technique to estimate valve clearance within an accuracy of 0.1 mm.