Patent ID: 6347514
Filing Date: 2002-02-19
Classification: F02D

Abstract:
An air-fuel ratio control system for an engine, the air-fuel ratio control system comprising:a first cylinder group; a second cylinder group; a first catalytic converter disposed in a first exhaust passage from the first cylinder group; a second catalytic converter disposed in a second exhaust passage from the second cylinder group; a first air-fuel ratio sensor sensing an air-fuel ratio of an exhaust gas mixture flowing into the first catalytic converter; a second air-fuel ratio sensor sensing an air-fuel ratio of an exhaust gas mixture flowing into the second catalytic converter; and a controller calculating a first air-fuel ratio feedback correction coefficient in accordance with an output of the first air-fuel ratio sensor, feedback-controlling an air-fuel ratio of the first cylinder group by using the first air-fuel ratio feedback correction coefficient, determining whether a predetermined phase synchronization request is present for synchronizing air-fuel ratio variation of the first and second cylinder groups, measuring a rich time and a lean time in the air-fuel ratio variation of the second cylinder group in accordance with an output of the second air-fuel ratio sensor to determine a second cylinder group's ratio between the rich time and the lean time, calculating a correction quantity to bring the second cylinder group's ratio closer to a target ratio when the synchronization request is present, determining a modified coefficient by modifying the first air-fuel ratio feedback correction coefficient with the correction quantity, and feedback-controlling the air-fuel ratio of the second cylinder group by using the modified coefficient as a second air-fuel ratio feedback correction coefficient when the phase synchronization request is present.