AIR-FUEL RATIO CONTROL UNIT FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To emit NOx from an NOx absorber in a short period of time while maintaining an air-fuel ratio near the stoichiometry. SOLUTION: An absorber 18 is positioned in an exhaust passage of an engine by which NOx is absorbed when an air-fuel ratio of an in-flow exhaust gas is lean and the absorbed NOx is emitted when the air-fuel ratio of the in-flow exhaust gas is stoichiometric or rich. Feed-back control is performed so that an average value of the air-fuel ratio is slightly richer when the stoichiometric air-fuel ratio should be changed to rich.