| 摘要 |
PROBLEM TO BE SOLVED: To provide an air-fuel ratio control system of an internal combustion engine whose purifying capability of a catalyst can be improved in the internal combustion engine equipped with both an air-fuel sensor at its upstream side of the catalyst and an oxygen sensor at its downstream side thereof. SOLUTION: There is provided an air-fuel control method by which an output target value of the oxygen sensor 77 is set so as to become slightly richer than an oxygen value determined by a theoretical air-fuel ratio for an exhaust system equipped with both the air-fuel sensor 76 at the upstream side of the catalyst 42 and the oxygen sensor 77 at the downstream side thereof. In the air-fuel control method, when a state that an output value of the oxygen sensor 77 has been converged to the output target value is continued for a prescribed time, the output target value of the oxygen sensor 77 is forcibly changed to a lean side, and then poisoning by S is eliminated and an HC component is exhausted by oxidization. COPYRIGHT: (C)2009,JPO&INPIT
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