To provide an oxygen sensor abnormality-detecting device capable of accurately detecting the abnormality of a downstream oxygen sensor installed downstream of catalyst.
The catalyst is provided in an exhaust passage of an internal combustion engine. The downstream oxygen sensor is installed downstream of the catalyst. As the output of the downstream oxygen sensor (Fig. B) changes from the rich output to the lean output, the exhaust air fuel ratio upstream of the catalyst (Fig. A) is made to change from the lean air fuel ratio to the rich air fuel ratio. As the output of the downstream oxygen sensor changes from the lean output to the rich output, the exhaust air fuel ratio upstream of the catalyst is made to change from the rich air fuel ratio to the lean air fuel ratio (time T1 or T2). While the air fuel ratio control is carried out, the abnormality of the downstream oxygen sensor is determined according to the output of the downstream oxygen sensor (indicated by a solid line or a broken line in Fig. B).
IWASAKI YASUSHI
HATTORI KAZUTAKA
UCHIDA TAKAHIRO
Mamoru Takada
Atsushi Hirayama
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