| 摘要 |
PROBLEM TO BE SOLVED: To control temperature of upstream/downstream catalysts appropriately, leading to excellent exhaust emission purification. SOLUTION: A three-way catalyst 14 is disposed upstream side of an exhaust pipe 12 of an engine 1, and an NOx catalyst 15 is disposed downstream thereof. When it is judged that the NOx catalyst 15 is in non-activated state or deteriorated NOx catalyst 15 is regenerated, a CPU 31 of an ECU 30 executes a dither control for injection. During the dither control, an exhaust air-fuel ratio is switched over between lean and rich in a period when a lean component and a rich component in exhaust emission in the upstream three-way catalyst 14 is reacted, and in a subsequent period when non-reacted exhaust gas passes through the upstream three-way catalyst 14. In this case, temperature rise in the upstream three-way catalyst 14 is suppressed, while non-reacted component in the exhaust gas in the downstream NOx catalyst 15 is reacted, facilitating heat generation and thus increasing the temperature. |
