| 摘要 |
PROBLEM TO BE SOLVED: To accurately diagnose the abnormality of an air-fuel sensor for linearly increasing/decreasing output to an air-fuel ratio. SOLUTION: An A/F sensor 26 for linearly detecting an air-fuel ratio is arranged in the exhaust tube 12 of an internal combustion engine 1. A CPU 42 in an ECU 41 sets an air-fuel ratio correction factor RAF in accordance with the deviation between a detected air-fuel ratioλby the A/F sensor 26 and a target air-fuel ratio to control air-fuel ratio feedback by using an RAF value, and adopts the ratio, between the integrated valueΣ|Δ'2λSM|of the 2-rank difference value ofλand the integrated valueΣ|Δ'2FAFSM|of the 2-rank difference value of FAF as abnormality diagnonstic parameter to diagnose abnormality by comparedly judging the parameter and a given abnormality judged valueα. That is, the normality of the A/F sensor 26 can be diagnosed whenΣ|Δ'2FAFSM|/Σ|Δ'2λSM|<αis satisfied, and the abnormality of the A/F sensor 26 can be diagnosed when the inequality is not established. |
