Air-fuel ratio control apparatus for engine

An air-fuel ratio control apparatus that controls an air-fuel ratio of air-fuel mixture combusted in an engine to a target air-fuel ratio by correcting a fuel supply amount in accordance with an air-fuel ratio feedback correction value and an air-fuel ratio learning value, the apparatus comprising:

• an air-fuel ratio feedback control section, which updates the air-fuel ratio feedback correction value such that the difference between the air-fuel ratio and the target air-fuel ratio is reduced;
• and
• an air-fuel ratio learning control section, wherein
• the air-fuel ratio learning control section performs, in each of a plurality of learning regions divided in accordance with an operating condition of the engine, learning of the air-fuel ratio learning value, in which the air-fuel ratio learning value is updated to reduce the air-fuel ratio feedback correction value and the updated air-fuel ratio learning value is stored, and
• if the air-fuel ratio feedback correction value converges to a value less than or equal to a specified value in each learning region, the air-fuel ratio learning control section determines that learning of the air-fuel ratio learning value in the learning region has been completed,
• wherein, if it has not yet been determined that learning of the air-fuel ratio learning value has been completed in any of the learning regions, the air-fuel ratio learning control section collectively updates the air-fuel ratio learning values of all the learning regions at the time of updating the air-fuel ratio learning value through the learning in any of the learning regions.