Patent ID: 8245569

Claim:
An abnormality detection apparatus for an air/fuel ratio sensor that outputs a signal that corresponds to air/fuel ratio of an internal combustion engine based on oxygen concentration in exhaust gas of the internal combustion engine, comprising: an air/fuel ratio control portion that performs an active air/fuel ratio control of periodically fluctuating the air/fuel ratio of the internal combustion engine between a rich state and a lean state; a data acquisition portion that acquires, as data for detecting abnormality, a parameter that corresponds to responsiveness during change of output of the air/fuel ratio sensor between a rich peak and a lean peak during the active air/fuel ratio control performed by the air/fuel ratio control portion; and an abnormality determination portion that when the number of acquisitions performed by the data acquisition portion becomes equal to or greater than a first set number, if the average value of the data acquired is not in a pending region wherein a difference made by the presence/absence of abnormality of the air/fuel ratio sensor is less likely to appear in the parameter, the abnormality determination portion determines the presence/absence of abnormality of the air/fuel ratio sensor based on comparison between the average value and an abnormality criterion value, and when the number of acquisitions performed by the data acquisition portion becomes equal to or greater than the first set number, if the average value of the data acquired is in the pending region, the acquisition of the data is performed by the data acquisition portion until the number of acquisitions of the data performed when intake air amount of the internal combustion engine is larger than a predetermined value reaches a second set number, and the abnormality determination portion determines the presence/absence of abnormality of the air/fuel ratio sensor based on comparison between the average value of the data acquired by the second set number of acquisitions and the abnormality criterion value.