| 摘要 |
PROBLEM TO BE SOLVED: To change output characteristics of an oxygen sensor and prevent degradation of exhaust emission due to rich control or lean control after fuel cut.SOLUTION: A constant current flows between sensor electrodes in a constant current circuit which is provided outside an oxygen sensor 21 installed on the downstream side of a catalyst 18, to change output characteristics of the oxygen sensor 21. Rich control is executed to control the air-fuel ratio of mixture to a richer side than a normally set target air-fuel ratio after fuel cut of an engine 11. The rich control is finished when the output of the oxygen sensor 21 exceeds a rich determination threshold value. Lean control is executed to control the air-fuel ratio of the mixture to a leaner side than the normally set target air-fuel ratio. During the lean control, the constant current is controlled to further improve the detection responsiveness of the oxygen sensor 21 to lean gas. When the output of the oxygen sensor 21 exceeds a lean determination threshold value, the lean control is finished. |
