| 摘要 |
<P>PROBLEM TO BE SOLVED: To reduce the deterioration in air-fuel ratio control accuracy by the asymmetric deterioration in the rich direction/the lean direction of a useless time, with a relatively simple constitution. Ž<P>SOLUTION: A deterioration degree of the useless time up to changing output of an air-fuel ratio sensor 24 after changing a fuel quantity injected into an engine 11, is respectively detected in the rich direction and the lean direction. A lean side control characteristic change period and a rich side control characteristic change period are discriminated by whether or not a differential value of output of the air-fuel ratio sensor 24 is a plus value. In the lean side control characteristic change period, a control period of air-fuel ratio feedback control is set long as a useless time deterioration degree in the lean direction becomes large, and in the rich side control characteristic change period, the control period of the air-fuel ratio feedback control is set long as the useless time deterioration degree in the rich direction becomes large. The useless time deterioration degree in the respective directions is calculated by the ratio of the useless time in detection (controlling) and its initial value (a design value). Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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