Source identification and reduction of engine noise

Engine acoustic behavior is inherently complicated because it depends on many design and manufacturing factors. Therefore, identifying engine noise sources is a challenging task. For an engine model, a further challenge is to define engine acoustic refinement targets for the noise level for the car models equipped with the engine of interest. Based on the automaker’s feedback of the vehicle acoustic assessments, a significant engine-induced interior noise occurred at 400 to 410 Hz. This paper addresses the critical engine noise problem—from source identification to countermeasure validation—to resolve the noise at 400 to 410 Hz. To identify the dominant engine noise sources, conventional sound pressure measurements and advanced microphone array technique were performed in a hemi-anechoic chamber. Spectrum and order analyses were used to identify the air cleaner and the oil pan as the major sources at frequencies from 400 to 410 Hz. Furthermore, a microphone array system visually confirmed secondary noise sources as the alternator and oil pump. A resonator for the air cleaner and enhanced structural ribs for the oil pan were used to successfully reduce the engine noise. In turn, the related vehicle interior booming noise was also abated.