AIR-FUEL RATIO CONTROL DEVICE FOR ENGINE

摘要

PROBLEM TO BE SOLVED: To correct an error of a detected air-fuel ratio by a air-fuel ratio sensor in which an output is linearly changed with respect to an air-fuel ratio. SOLUTION: A stoichiometric oxygen sensor is arranged at a catalyst downstream side. When the stoichiometric oxygen sensor generates a rich or lean output though the air-fuel ratio sensor detects an approximately stoichimetric air-fuel ratio, a correction valueαfor correcting the detected air-fuel ratio is changed by a step change amountΔαevery predetermined periodΔt in order to correct the detected air-fuel ratio by the air-fuel ratio sensor. When the output of the stoichiometric oxygen sensor is within a range of the stoichimetric air-fuel ratio by control based on an air-fuel ratio corrected by the correction valueα, the updating of the correction valueαis stopped. The periodΔt and/or the step change amountΔαare changed based on a catalyst temperature.