EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To appropriately release NOX from a NOX absorber. SOLUTION: The NOX absorber 23 which absorbs NOX when air-fuel ratio is lean is positioned inside an engine exhaust passage and an air-fuel ratio sensor 30 and a NOX ammonium sensor 29 are positioned inside the portion of the engine exhaust passage downstream of the NOX absorber 23. After the air-fuel ratio is made rich to release NOX from the NOX absorber 23, the air-fuel ratio is switched from rich to lean when the output voltage of the air-fuel ratio sensor 30 has exceeded a reference level. The reference level is varied according to the concentration of ammonium detected by the NOX ammonium sensor 29.