| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device in which an exhaust gas temperature is effectively raised without using a dedicated electric heater even if the exhaust gas temperature is low during operation. <P>SOLUTION: This exhaust emission control device having an NOx absorber 42 is installed in an exhaust passage 22. The exhaust emission control device comprises a three-way conversion catalyst 41 installed on the upstream side of the NOx absorber 42, an exhaust gas temperature detection means 38 detecting the temperature of exhaust gas flowing into the NOx absorber 42, and an air-fuel ratio control means 3 controlling the air-fuel ratio of the air-fuel mixture for each of cylinders 7a to 7d. When predetermined requirements for raising the exhaust gas temperature are met, the air-fuel ratio control means 3 makes lean the average air-fuel ratio of the air-fuel mixture for each of the cylinders 7a to 7d and performs first air-fuel ratio control for raising the exhaust gas temperature by alternately repeating lean and rich. In this case, when the exhaust gas temperature is rather low, the degree of lean for the cylinder in which lean air-fuel ratio combustion is performed is raised more than that when the exhaust gas temperature is rather high. <P>COPYRIGHT: (C)2007,JPO&INPIT |
