| 摘要 |
PROBLEM TO BE SOLVED: To efficiently eliminate SOx according to its characteristic by controlling a fuel injection means to make the air fuel ratio supplied to an internal combustion engine more rich than the air fuel ratio when NOx is reduced in order to reduce SOx which has strong reaction force so that reduction release from a catalyst is not easy. SOLUTION: During the operation of an engine 1, the absorbed amounts of NOx and SOx absorbed in NOx catalyst 19 and SOx catalyst 18 are respectively estimated by an estimating party 37 in an ECU 30 to first determine whether SOx is saturated or not, and if NO, secondary it is determined whether NOx is saturated or not. If saturation of NOx is determined, making air fuel ratio rich and its execution time for eliminating NOx are decided to make rich. On the other hand, in the case where saturation of SOx is determined, making air fuel ratio rich and its execution time for eliminating SOx are calculated, and in the case where the temperature of a catalyst is below the reference temperature effective for eliminating SOx, it enters NOx elimination process. However, in the case where the temperature of a catalyst is above the reference temperature, the ratio is made rich. |
