Abstract
This paper describes the method which abnormal condition of engine is diagnosed by radiated sound from it. Tappet clearance of the exhaust valve on 4 cycle diesel engine is selected as an abnormal part. A series of experiments carried out by changing tappet clearance whose range was from 0. 1 to 1. 45 mm, and the spectral analysis of the radiated aound was made by FFT analyzer. Using the analyzed data, multivariate analysis was made to infer the degree of the clearance. Thus, ten categories (clearance) were obtained from the data, and a category which a given sample belonged to was determined by Mahalanobis' generalized distance. As the result, the ratio of cases judged correct to sample cases was 96. 9 percent when mic distance (distance from the mic to the tappet) was 3 cm. In order to minimize the analysis time, the discriminant analysis was carried out by using appointed variables, and its effect was discussed. As a conclusion, tappet clearance value by its radiated sound proved to be successfully estimated by the proposed method.
