Exhaust purifying apparatus and exhaust purifying method for internal combustion engine

摘要

During sulfur release control in an internal combustion engine, a rich period and a lean period are alternately repeated. The air-fuel ratio of exhaust gas is controlled toward a target air-fuel ratio (14.3) by adding fuel from a fuel adding valve in the rich period. An ECU determines whether the actual air-fuel ratio of exhaust gas detected by an air-fuel ratio sensor has reached a stoichiometric air-fuel ratio each time the rich period ends at which addition of fuel from the fuel adding valve is stopped. A counter counts the number of times the ECU has determined that the actual air-fuel ratio of exhaust gas has not reached the stoichiometric air-fuel ratio. When the value of the counter becomes greater than or equal to a permissible value, the ECU determines that there is an abnormality in the sulfur release control.