Low noise consideration of cabin less tractor by using sound source model of internal combustion engine

Abstract

From the viewpoint of hearing protection, many agricultural vehicles exceed the recommended value of acceptable noise level at noise exposure of 8 hours per day, suggesting the need to reduce noise. There is a shielding in the engine room as a measure against airborne sound due to surface vibration of the internal combustion engine. Particularly, in order to efficiently reduce noise, it is necessary to identify a highly contributing route in the sound transmission path from the noise source to the evaluation position represented by the operator's ear position and to shield the part in a part. As a method of identifying this sound transmission path, there is visualization of acoustic intensity indicating sound magnitude and directionality. As a visualization method, in this study, a sound source model that identifies the surface vibration velocity of the internal combustion engine is constructed, and the sound transmission path is predicted by calculating the acoustic intensity with the surface vibration velocity as an input. The sound source model is constructed by an acoustic transfer function calculated by the boundary element method and Inverse-Numerical Acoustic analysis which calculates the surface vibration velocity using the actual sound pressure measured at the field point near the sound source. Furthermore, the effectiveness of this method was confirmed by verifying the shielding method based on the sound transmission path and its effect both on the actual machine and numerical simulation. As a result, both the actual machine and the simulation showed the same value for the noise reduction amount at the operator's ear position. Therefore, the effectiveness of this method was shown.