クランクケースの振動・音響特性予測法

概要

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The key to designing quieter engines lies in understanding the response of the main engine structure to the forces imposed during the engine cycle. Detailed analysis of the noise and vibration characteristics of the engine crank case yields important information on the significance of structural features for engine noise reduction. This paper presents the theoretical methods to determine the vibratory and acoustic characteristics of the crank case. A finite element model of the crank case, that employs the plate and beam elements, is adopted to determine the dynamic characteristics such as natural frequency, mode shape and modal mass. Using the dynamic characteristics obtained by FEM, frequency response functions from excitation point to the surface of noise radiation of the engine block are calculated by use of the modal analysis technique with measured modal damping. And a theoretical procedure using Boundary Element Method is developed to obtain the noise radiation property of the crank case. These methods above mentioned are applied to the crank case of an actual diesel engine. The calculated results of vibratory characteristics, space averaged square mobilities over the surface of noise radiation, acoustic intensities and acoustic radiation efficiencies are agreed well with the measured data. These techniques would enable us to investigate a low noise structural design of the engine block.