Patent ID: 8640532

Claim:
An apparatus for detecting an abnormal air-fuel ratio variation between cylinders, comprising: an air-fuel ratio sensor provided in an exhaust passage of a multi-cylinder internal combustion engine; an acquisition device configured to acquire an output of the air-fuel ratio sensor at each given sampling interval; a parameter calculation device configured to calculate a parameter correlated with a degree of fluctuation of the sensor output from a plurality of the sensor outputs acquired by the acquisition device; a determination device configured to compare the parameter calculated by the parameter calculation device with a given determination value and determine whether the abnormal air-fuel ratio variation between cylinders is present or absent; an estimation device configured to estimate a cylinder air amount as an amount of air having flown into a cylinder at each sampling interval; a storage device configured to store time-series data on the cylinder air amount at each sampling interval estimated by the estimation device; a corresponding determination value calculation device configured to determine, every time the acquisition device acquires the sensor output, a value of the cylinder air amount at a point of time earlier, by a transport delay time, than a point of time of the acquisition based on the time-series data and calculate a corresponding determination value corresponding to the value of the determined cylinder air amount; and a determination value determination device configured to determine a determination value based on a plurality of the corresponding determination values calculated by the corresponding determination value calculation device.