| 摘要 |
PROBLEM TO BE SOLVED: To restrain exhaust of HC and CO while efficiently purifying NOx by controlling the air-fuel mixture air-fuel ratio by making a feedback process to reverse the downstream side exhaust air-fuel ratio of an NOx absorbing catalyst to rich just after the target air-fuel ratio of an air-fuel mixture is switched to the theoretical air-fuel ratio or rich from lean. SOLUTION: Air-fuel ratio sensors 10 and 11 are respectively arranged on the upstream-downstream sides of an NOx absorbing catalyst 5 of an exhaust system, and just after the target air-fuel ratio of an air-fuel mixture is switched to the theroretial air-fuel ratio or rich from lean, by an ECU 6, air-fuel ratio feedback control is performed by using the downstream side sensor 11 instead of the upstream side sensor 10. At this time, since reversal to rich of the downstream side sensor 11 delays by removal of NOx and O2 in the catalyst 5, even if the exhaust air-fuel ratio detected by the upstream side sensor 10 reverses to rich, a fuel injection quantity is controlled so as to be gradually increased until the downstream side sensor 11 reverses to rich further, and reversal to rich of the downstream side sensor 11 is quickened.
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