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It is necessary to elucidate the noise generating mechanism for reducing engine noise. In a running engine, various impacts in the engine cause excitation sources for structural vibrations and engine noises. Engine noises are classified into the combustion noise, the combustion induced mechanical noise, and the mechanical noise depending on their excitation source. However, it is difficult to measure such noises separately because some impacts generate closely together in time and space. In order to separate the combustion noise from the total engine noise, a transient noise generation model that considers the vibration transmission and the damping effect of the engine structure was proposed. The newly proposed model was verified by conducting the single explosion excitation experiment of a stationary engine. In addition, it was clarified that the time histories of the combustion noise of both gasoline and diesel engines could be estimated at firing condition.

エンジンにおける燃焼衝撃と、それによって発生する騒音との関係を解明するための手法として、静止エンジンの燃焼室を単一爆発加振した。この際、衝撃の主な伝達経路およびエンジン外壁面を、振動的・音響的に遮断し、燃焼衝撃のパワーと、各伝達経路を経て各部から放射される騒音のパワーとの関係を、個別に明らかにした。本供試エンジンでは、燃焼衝撃がピストンを経てシリンダに伝わり、強く騒音を放射していることなどがわかった。

Combustion impact is one of the most predominant sources of engine noise. The transmission-radiation coefficients of combustion noise, which were defined as a conversion power ratio from the combustion impact to the emitted noise, were studied with both a stationary engine excited by a single explosion and an operating engine, respectively. The characteristics of these coefficients obtained in the same engine coincide with each other, so it can be said that the transmission and radiation of combustion noise of an operating engine are analogous with those of a stationary engine, to a certain extent. Then, the vibration response for combustion impact and the noise radiation coefficients were examined for each engine wall to identify their contribution to the total combustion noise.

Combustion impact is one of the most predominant sources of engine noise. The transmission-radiation coefficients of combustion noise, which were defined as a conversion power ratio from the combustion impact to the emitted noise, were studied with both a stationary engine excited by a single explosion and an operating engine. The characteristics of these coefficients obtained in the same engine coincided with each other, so it can be said that the transmission and radiation of combustion noise of an operating engine are analogous with those of a stationary engine, to a certain extent. Then, the vibration response for combustion impact and the noise radiation coefficients were examined for each engine wall to identify their contribution to the total combustion noise.