| 摘要 |
PROBLEM TO BE SOLVED: To prevent an engine air-fuel ratio control system from erroneously learning a value for evaporation and thus improve accuracy in air-fuel ratio control when an air-fuel ratio feedback control is provided independently for each of a plurality of cylinder groups and evaporative gas is supplied to a common air intake passageway in common to each cylinder group. SOLUTION: The present invention relates to an air-fuel ratio feedback control system that uses O2 sensors 13L, 13R installed, respectively, in a left bank 1L and a right bank 1R, to provide an independent air-fuel ratio control for each bank. In this system, a learned value for evaporation is individually determined for each of the right and left banks based on an air-fuel ratio feedback correction value when a purge valve 35, which supplies evaporative gas from a canister 30 to an air intake passageway 3 shared by the two banks, is open. If evaporative gas of a high concentration is detected in either of the two banks, determination of the learned value for evaporation is inhibited for both banks. Determination of the learned value for evaporation is resumed after the lapse of a predetermined period of time after evaporative gas of a high concentration has no longer been detected in either of the two banks.
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