| 摘要 |
PROBLEM TO BE SOLVED: To accurately find a true stoichiometric air-fuel ratio. SOLUTION: When an output of a subsidiary O<SB>2</SB>sensor at a downstream side of a catalyst is inverted to a lean output, a target air-fuel ratio at an upstream side of the catalyst is made to rich target value, and when the output is inverted to a rich output, the target air-fuel ratio is made to the rich target value. A value in which an oxygen desorption estimate value calculated based on a difference between the rich target value and a stoichiometric air-fuel ratio is integrated during a period in which the target air-fuel ratio is made to the rich target value is defined as Cmax<SB>R</SB>. A value in which the oxygen desorption estimate value calculated based on the difference between a lean target value and the stoichiometric air-fuel ratio is integrated during a period in which the target air-fuel ratio is made to the lean target value is defined to be Cmax<SB>L</SB>. The stoichiometric air-fuel ratio satisfying Cmax<SB>R</SB>=Cmax<SB>L</SB>is calculated as the true stoichiometric air-fuel ratio ST in this air-fuel ratio control device. COPYRIGHT: (C)2005,JPO&NCIPI
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