Patent ID: 9506416
Filing Date: 2016-11-29
CPC Classification: F02D

Claim Text:
1. An inter-cylinder air-fuel ratio variation abnormality detection apparatus for a multicylinder internal combustion engine, the apparatus being configured to calculate a first parameter correlated with a degree of a variation in output from an air-fuel ratio sensor installed in an exhaust passage common to a plurality of cylinders and comparing the calculated first parameter with a predetermined determination value to detect variation abnormality in air-fuel ratio among cylinders, the apparatus being configured to carry out: (A) a step of calculating the first parameter; (B) a step of determining a possible range of a second parameter different from the first parameter, the second parameter representing a degree of a variation in air-fuel ratio among the cylinders based on the calculated first parameter, the second parameter being a value representing a rate at which a cylinder subjected to air-fuel ratio shift deviates from the cylinders free from the air-fuel ratio shift; (C) a step of calculating the first parameter with an air-fuel ratio of a predetermined cylinder forcibly changed; (D) a step of calculating a difference between the unchanged first parameter and the forcibly changed first parameter; (E) a step of determining a first characteristic representing a relation between the second parameter and the difference based on the possible range of the second parameter and the difference; and (F) a step of correcting one of the determination value and the first parameter calculated in the step (A) based on inclination of the determined first characteristic, wherein, in the step (B), second characteristics which are preset for the tolerance upper limit product and the tolerance lower limit product of the air-fuel ratio sensor and which represent relations between the first parameter and the second parameter are utilized to determine the possible range of the second parameter.