| 摘要 |
<p>Combustion noise sensors (15a through 15d) are disposed in respective cylinders of an engine (1), and a gate circuit (18) detects combustion noises in the respective cylinders. The combustion noises are subjected to A/D conversion by a high-speed A/D converter (18) and inputted to an ECU (20) as combustion noise signals for the respective cylinders. The ECU (20) performs FFT processings for the inputted combustion noise signals and calculates a combustion noise central value based on sound pressure levels of specific frequency components. The specific frequency components are expressed as (n + (1/2)) x f given that f denotes the inverse of the pilot fuel injection interval (seconds). The specific frequency components cause a more drastic fall of the sound pressure level during the performance of pilot fuel injection with respect to the sound pressure level during the stop of pilot fuel injection in comparison with other frequency components. Therefore, the calculated combustion noise central value is unsusceptible to noises, and hence, accurately reflects the combustion noise deadening effect. <IMAGE></p> |
