| 摘要 |
<P>PROBLEM TO BE SOLVED: To start air-fuel ratio feedback control by activating an exhaust gas sensor as early as possible after starting of an engine while preventing the element crack of the exhaust gas sensor. Ž<P>SOLUTION: This air-fuel ratio control device includes the exhaust gas sensor (oxygen sensor) having a heater for heating a sensor element in an exhaust passage. When performing air-fuel ratio feedback control based on output of the oxygen sensor, at S11, a cooling water temperature Tw at the start of the engine is read, and at S12, based on the cooling water temperature Tw, a basic heater energization prohibiting period Ls is calculated. At S13, a temperature difference ΔT between the cooling water temperature at an operation stop of the engine and the cooling water temperature at the start of the engine is calculated. At S14, based on the temperature difference ΔT, a period correction coefficient H is calculated. At S15, the basic heater energization prohibiting period Ls is multiplied by the period correction coefficient H, and a final heater energization prohibiting period L is calculated. Energization to the heater is started after the passage of the heater energization prohibiting period L from start of the engine and air-fuel ratio feedback control is performed. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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