To increase the efficiency of measures targeting combustion noise in complete vehicle development, the authors developed a new sound quality evaluation method by combining two known methods: the time domain combustion noise separation method (T-CNSM) and a psychoacoustic metric, fluctuation intensity.
The T-CNSM was applied to the vehicle interior noise, allowing for precise extraction of the combustion contribution in the time domain. Furthermore, the T-CNSM has enabled a sound quality check of combustion noise using a headphone-playback system. The procedure of this method is as follows. Firstly, simultaneous measurement of vehicle interior noise and in-cylinder pressure of each cylinder is carried out under acceleration. Afterward, the application of digital signal processing using Fourier transform and multiple regression analysis to the measured data extracts the contribution of combustion noise from the vehicle interior noise in the time domain.
Subjective evaluation tests using Scheffe’s paired comparison method were conducted with 14 noise, vibration, and harshness (NVH) development experts via a headphone-playback system. Multiple types of combustion noise in vehicle interiors obtained by the T-CNSM were used for the presentation sound. Based on the results of the subjective evaluation tests, the dissonant combustion noise index (DCNI) was developed as a new objective evaluative index for the sound quality of combustion noise, using fluctuation intensity as a psychoacoustic metric expressing intensity of perceived fluctuation such as rumbling, rattling, and knocking.
The new evaluation method combined the DCNI with the T-CNSM and has made it possible to quantify the high-precision sound quality of the combustion noise in vehicle interior, which is inexpressible with conventional A-weighted sound pressure levels (SPL).
This article provides an overview of this evaluation method’s procedure series and discusses the validity of this method when applied to the comparison of combustion noise sound quality in three mass production Japanese Kei car models.
