| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine that can suppress the deterioration of exhaust gas emissions during responsiveness diagnosis operation, with respect to the internal combustion engine performing the responsiveness diagnosis operation of an air-fuel ratio sensor disposed at an upstream side of a catalyst. <P>SOLUTION: A start catalyst 44, an under-floor catalyst 45, an A/F sensor 46 at the upstream side of the start catalyst 44, and an O<SB>2</SB>sensor 47 at the downstream side of the start catalyst 44 are provided in an exhaust system. If O<SB>2</SB>atmospheres in the respective catalysts 44, 45 are not in favorable states for exhaust gas purification, when the execution condition of A/F active control for diagnosing the responsiveness of the A/F sensor 46 is established, the A/F active control is prohibited so that the deterioration of exhaust gas emissions is prevented. Furthermore, if the inside of the catalyst is lean, a target air-fuel ratio is shifted to a rich side. If the inside of the catalyst is rich, the target air-fuel ratio is shifted to a lean side so that the A/F active control is started earlier. <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
