| 摘要 |
PURPOSE:To improve a purifying function of a ternary catalyst, by controlling air-fuel ratio to small fluctuate with a value in a little rich side serving as the center when the target air-fuel ratio is in the vicinity of the theoretical air-fuel ratio, obtained corresponding to the alcohol content in fuel, further with the actual air-fuel ratio within a predetermined width. CONSTITUTION:An electronic control unit 4 controls the valve opening time of an injector 36 on the basis of detection values of an O2 sensor 1, throttle valve opening sensor 31, intake absolute pressure sensor 32, water temperature sensor 33, intake temperature sensor 34 and a crank angle sensor 35 or the like. When a feedback correction coefficient, based on an output of the O2 sensor 1, increases to a predetermined value or more, a value of theoretical air-fuel ratio is calculated by searching for the alcohol content in fuel in accordance with the feedback correction coefficient. When the target air-fuel ratio, which is referred corresponding to an engine speed and intake absolute pressure, is in the vicinity of the calculated theoretical air-fuel ratio further with an error of the actual air-fuel ratio from the theoretical air-fuel ratio within a predetermined width, the air-fuel ratio is controlled small fluctuating with a value, which is in a little rich side from the theoretical air-fuel ratio, serving as the center.
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