| 摘要 |
PROBLEM TO BE SOLVED: To accurately monitor a lean operation condition based on sensed information of an O2 sensor by sophisticatedly designing output treatment of the O2 sensor. SOLUTION: An air-fuel ratio is determined whether it is rich or lean compared to a theoretical ratio by an O2 sensor 1 arranged on an exhaust passage of an engine from density of oxygen in exhaust gas. An oxygen density signals output from the O2 sensor 1 is smooth treated by an smoothening treatment means 2. The averaged oxygen density signal is compared to a preset threshold value. When the oxygen density signal is less than the threshold value alone, lean operation of an engine is indicated.
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