Patent ID: 8245568

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; an abnormality determination portion that determines presence/absence of abnormality of the air/fuel ratio sensor by using the data acquired; and a distribution width determination portion that finds a distribution width of the data acquired by performing acquisition of the data via the data acquisition portion a plurality of times, in an increase/decrease direction of the data, wherein: the abnormality determination portion determines that the air/fuel ratio sensor has abnormality if the distribution width is determined as being less than an abnormality criterion value based on comparison between the distribution width and the abnormality criterion value; and the abnormality determination portion determines that the air/fuel ratio sensor does not have abnormality if the distribution width is determined as being greater than or equal to the abnormality criterion value based on comparison between the distribution width and the abnormality criterion value.