Investigation of excitation force on noise and vibration caused by combustion in a gasoline engine

This study focused on the piston system and targeted vehicle interior noise caused by combustion, which is mainly due to vibration transmission in the high-speed, high-load region. Vehicle interior noise is defined as having both a combustion excitation force, which causes the piston to move due to combustion, and a structural excitation force, which causes the engine block to vibrate due to piston movement. The purpose of this study was to index these forces to develop noise and vibration suppression technologies and adapt them to design concepts. Conventionally, the relationship between combustion and noise and vibration is discussed in terms of ensemble averages. However, due to the nonstationary properties of noise and vibration, this paper analyzed both excitation force characteristics for vibration on a cycle-by-cycle basis. Engine vibration is affected by heat release characteristics, even with the same engine structure specifications. As heat release characteristics, combustion speed: the maximum second derivative of heat release value and combustion phase: CA50 were identified as indicators of the excitation force of combustion. Engine vibration is also affected by piston specifications, even when heat release characteristics are the same. The maximum piston tilt angle, maximum piston tilt speed, and maximum piston translation speed were identified as indicators of the structural excitation force. Based on these indicators, various means have been devised to suppress noise and vibration caused by combustion.