| 摘要 |
An air-fuel ratio control system provided with air-fuel ratio sensors across a three-way catalyst, for performing air-fuel ratio feedback control, wherein, in controlling an air-fuel ratio feedback correction coefficient on the basis of an output value from the air-fuel sensor on the upstream side, a control operation value is corrected on the basis of an output value of the air-fuel ratio sensor on the downstream side. Here, the correction value on the basis of the output from the air-fuel ratio sensor on the downstream side is calculated from a uniform learning correction value uniformly used in the whole of operational regions and an area-by-area learning correction value specific to each of separate operational regions. Further, when the uniform learning correction value is added for correction, a process for subtracting for correction from the area-by-area learning correction value the corrected value is performed only in a region where learning progresses beyond a predetermined value among the respective operational regions in which area-by-area learning correction values are stored. With the above-described arrangement, the promotion of progress of the air-fuel ratio learning control by the air-fuel ratio sensor on the downstream side can be compatible with an improvement in accuracy of learning, and furthermore, the progress of learning can be promoted in the region where the chance of learning is little and learning in separate operational regions is required. |
