| 摘要 |
<p>PROBLEM TO BE SOLVED: To attain favorable operation feeling and fuel consumption and to reduce NOx exhaust amount while lean combustion operation is performed by determining whether the adsorption amount of nitrogen oxide reaches the saturation quantity or not in an exhaust emission controlling catalyst device, and lowering the combustion temperature of an internal combustion engine according to the determination result. SOLUTION: During the operation of an engine, according to the determination result of an operation mode setting mechanism 31, it is determined whether the operation mode can be switched from the lean combustion operation to the theoretical air-fuel ratio operation or not by an air-fuel ratio switching means 30. In the case where the determination is NO and NOx reducing operation is not performed, NOx exhaust amount is estimated according to the NOx adsorption amount discharged from an exhaust emission controlling catalyst device by an adsorption amount estimating means 33 of an adsorption saturation determining means 32. Subsequently, it is discriminated whether the estimated value of NOx exhaust amount is larger than a designated threshold or not by a comparator 34, and in the case of NO, EGR amount is increased more than that during normal lean combustion operation time by a combustion temperature lowering means 36 to lower the combustion temperature and reduce NOx exhaust amount.</p> |
