| 摘要 |
PURPOSE:To eliminate an expensive oxygen sensor and reduce the cost, by calculating an oxygen concentration according to an output signal from a fuel injection quantity deciding section, an output signal from a correction control section for feedback controlling an air-fuel ratio, and an output signal from an air-fuel ratio sensor. CONSTITUTION:An oxygen enriching device (not shown) for supplying an oxygen enriched air is provided in a suction passage 4, and an air flow sensor 16 is provided downstream of the oxygen enriching device in the suction passage 4. An air-fuel ratio sensor 18 for detecting an air-fuel ratio in an exhaust system is provided in an exhaust passage 12. A suction quantity of the oxygen enriched air is measured by a fuel injection quantity deciding section 22 according to an output from the air flow sensor 16, and a fuel injection quantity is decided according to a measured value. An air-fuel ratio is feedback controlled to be corrected to a target air-fuel ratio by a correction control section 24 according to an output signal from the air-fuel ratio sensor 18. Then, an oxygen concentration is calculated by an oxygen concentration calculating section 26 according to the output signals from the fuel injection quantity deciding section 22, the correction control section 24 and the air-fuel ratio sensor 18.
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