APPARATUS FOR DETERMINING CYLINDER-TO-CYLINDER AIR-FUEL RATIO IMBALANCE

PROBLEM TO BE SOLVED: To provide a technique for determining whether air-fuel ratios vary among cylinders more simply while maintaining favorable accuracy, and to favorably maintain the accuracy of the determination independently of variation of a volume flow rate of exhaust gas passing through an exhaust passage.SOLUTION: A control apparatus for an internal combustion engine having a plurality of cylinders performs volumetric correction based on atmospheric pressure with respect to an intake air amount to thereby calculate an exhaust flow rate reflecting the magnitude of a volume flow rate of exhaust passing thorough the exhaust passage. Further, the control apparatus performs filtering to extract a 0.5-th order frequency component of rotation speed of the internal combustion engine from a signal indicating a detected air-fuel ratio, integrates the filtered signals for a predetermined period of time to calculate an integration value, corrects the integration value each time the integration value is calculated depending on the exhaust flow rate to calculate a corrected integration value, and after the predetermined time period has elapsed, if the corrected integration value is greater than a predetermined threshold, determines the occurrence of a state where the air-fuel ratios vary among the plurality of cylinders.