| 摘要 |
PROBLEM TO BE SOLVED: To suppress NOX emissions, when an engine operating condition is shifted to a heavy-load state, when feedback control based on an output of an air/fuel sensor at downstream side of catalysts is continuing under a light- load state and a constant involved in air/fuel ratio feedback control based on an output of an air/fuel ratio sensor at upstream side of the catalysts is indicating a large value in a direction toward a lean side of an air/fuel ratio. SOLUTION: In a case where sub air/fuel ratio feedback control is continuing for more than a specific time and a rich skip quantity, or there is a possibility that a constant involved in air/fuel ratio feedback control stays at an excessively small value. To avoid such a state, an air/fuel ratio is made to be directed toward a rich side by lifting the value of the RSR, when an engine operating condition is switched over to a heavy-load state, or an intake air quantity GA is increased.
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