| 摘要 |
An exhaust purification system of an internal combustion engine comprises an exhaust purification catalyst (20), a downstream side air-fuel ratio sensor (41) and a control device (31). The control device performs a feedback control of the air-fuel ratio of the exhaust gas upstream of the catalyst to a target air-fuel ratio and switches the target air-fuel ratio to a lean air-fuel ratio when an output air-fuel ratio of the downstream side air-fuel ratio sensor becomes equal to or less than a rich judged air-fuel ratio and switches the target air- fuel ratio to a rich air-fuel ratio when an output air-fuel ratio of the downstream side air-fuel ratio sensor becomes equal to or more than a lean judged air-fuel ratio. The control device calculates a first and a second cumulative values (Fn, Rn), relating to an amount of oxygen becoming in excess or deficient in the catalyst. The control device judges that the downstream side air-fuel ratio sensor (41) is normal when the average value (Ave) of the first cumulative value (Fn) or of the second cumulative value (Rn) is larger than a predetermined limit value (Lim), which is smaller than the maximum storable oxygen amount when the exhaust purification catalyst (20) is new. |
