INTER-CYLINDER AIR-FUEL RATIO IMBALANCE DETERMINING APPARATUS FOR INTERNAL COMBUSTION ENGINE

摘要

An inter-cylinder air-fuel ratio imbalance determining apparatus for an internal combustion engine includes an air-fuel ratio sensor; fuel injection valves; an instructed fuel injection amount control unit; and an imbalance determination unit configured: to acquire a time-differential-value corresponding value that is an amount of change per predetermined time in an output value of the sensor or a detected air-fuel ratio represented by the output value; to acquire a positive gradient corresponding value based on a positive value of the time-differential-value corresponding value; to acquire a negative gradient corresponding value based on a negative value of the time-differential-value corresponding value; to determine an imbalance determination threshold based on a magnitude of a ratio of the negative gradient corresponding value to the positive gradient corresponding value; and to determine whether inter-cylinder air-fuel ratio imbalance has occurred by comparing a magnitude of the negative gradient corresponding value with the imbalance determination threshold.