Patent ID: 7299625

Claim:
An exhaust purifying apparatus for sulfur release control in an internal combustion engine that performs lean combustion, the engine having an exhaust purifying catalyst that is caused to release sulfur accumulated from exhaust gas produced, the exhaust purifying apparatus comprising: detecting means for detecting the air-fuel ratio of exhaust gas of the internal combustion engine; determining means for repeatedly determining at a predetermined timing during a feedback control, whether the air-fuel ratio detected by the detecting means has reached a stoichiometric air-fuel ratio at which sulfur is released from the exhaust purifying catalyst; and abnormality diagnosing means for counting the number of times the determining means has determined that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and when the number of times becomes greater than or equal to a permissible value, for determining that there is an abnormality in the sulfur release control; wherein, when executing sulfur release control, the feedback control is executed to equalize the air-fuel ratio with either of the stoichiometric air-fuel ratio or a target air-fuel ratio richer than the stoichiometric air-fuel ratio by selectively increasing and decreasing a correction value for richening the air-fuel ratio of exhaust gas of the internal combustion engine in accordance with said air-fuel ratio.