Yoshizumi K., Ohta K., Honda I., Ajiro K.

High-speed diesel engines for motor vehicles and construction machineries are required sound reduction and good sound quality along with high performance and clean exhaust gas emission. Sound level and quality control of internal combustion engine in early design stage enjoins the analytical procedure to estimate excitation forces, vibratory behavior of engine block, sound radiation properties and the time history of engine sound at any point. Theoretical approach has been described in our papers to predict the vibratory response of the crankcase coupled with the rotating crankshaft and the engine sound octave band spectrum. But in order to evaluate the engine sound quality in the design stage, it is need to develop a system to estimate the time history of the engine sound. In this paper, the prediction method of the time history of the engine sound at any point by using the calculated results of vibratory response of the crankcase surface and Boundary Element Method is mentioned. On the other hand, to evaluate the estimated engine sound, it is important that engineers and users listen to the estimated sound by themselves. In this proposed system, they are able to listen to the engine sound calculated by numerical analysis on personal computer. Furthermore, it is possible to modify the engine sound by using Wavelet Transform. Using this system, it becomes to possible to examine the optimum structure shapes and good sound design considering the sound quality at the design stage.