| 摘要 |
<p>PURPOSE: An exhaust gas purifying system for an engine is provided to prevent temporary deterioration of the state of the exhaust gas caused by emission of oxygen from the catalyst, while suppressing deterioration of the total fuel efficiency when considered for all operating regions. CONSTITUTION: An exhaust gas purifying system for an engine(1) comprises: a catalyst(32) displaying a three-way purification function when an air/fuel ratio state of at least an exhaust gas corresponds substantially to a theoretical air/fuel ratio; a first air/fuel ratio control means(40a) for controlling an air/fuel ratio in a combustion chamber(6) of the engine by switching to either a state that is leaner than the theoretical air/fuel ratio or a state that is richer than that, depending on the operating state of the engine; and an air/fuel ratio correction means for correcting the air/fuel ratio in the combustion chamber temporarily to a state that is even richer, when the first air/fuel ratio control means switches the air/fuel ratio in the combustion chamber from a lean state to a richer state; wherein, when the air/fuel ratio in the combustion chamber has been switched from a lean state to a richer state, the air/fuel ratio correction means sets the air/fuel ratio in the combustion chamber to a state that is slightly richer than the theoretical air/fuel ratio, so as to match a release of oxygen from the catalyst.</p> |
