| 摘要 |
<p>PROBLEM TO BE SOLVED: To effectively make the harmful components such as NOx in leans burn exhaust gas harmless by first chemically adsorbing NOx on an adsorption catalyst after creating a state in which more oxidizer than reducer is present, and then creating a state wherein an equal or greater amount of reducer than oxidizer is present, and reducing the adsorbed NOx to N2 . SOLUTION: While an engine is in operation, output signals from various sensors are input to an ECU 25 where an operational air-fuel ratio is determined through the evaluation of the state of internal combustion operation and the state of a NOx adsorption catalyst 18, so as to maintain a fuel concentration in the mixture at a predetermined value by controlling an injector 5. At this time, if the engine is in lean burn operation, the presence or lack of NOx adsorption ability of the NOx adsorption catalyst is determined. If the NOx catalyst has NOx adsorption capability, a state wherein the amount of oxidizer is greater than that of the reducer is created so as to chemically adsorb NOx on the adsorption catalyst 18. On the other hand, if the NOx catalyst lacks NOx adsorption capability, the air-fuel ratio is shifted to the rich side for a predetermined duration to create a state where there is equal or greater amount of reducer than oxidizer so as to make the NOx absorbed by the adsorption catalyst 18 react with the reducer to reduce NOx to N2 .</p> |
