Patent ID: 6761024
Filing Date: 2004-07-13
Classification: F01N,F02D,Y02T

Abstract:
An air-fuel ratio control system for an internal combustion engine including an exhaust passage and a catalyst disposed in the exhaust passage, comprising:intake volume obtaining means for obtaining a value corresponding to an intake volume of the internal combustion engine; upstream-side air-fuel ratio detecting means for detecting an air-fuel ratio upstream of the catalyst; downstream-side air-fuel ratio detecting means for detecting an air-fuel ratio downstream of the catalyst; target air-fuel ratio setting means which sets a target air-fuel ratio to a predetermined rich air-fuel ratio that is rich of a stoichiometric air-fuel ratio when it is determined that the air-fuel ratio downstream of the catalyst has changed from a rich air-fuel ratio to a lean air-fuel ratio, and which sets the target air-fuel ratio to a predetermined lean air-fuel ratio that is lean of the stoichiometric air-fuel ratio when it is determined that the air-fuel ratio downstream of the catalyst has changed from a lean air-fuel ratio to a rich air-fuel ratio; fuel supply amount calculating means which calculates, as a feed-forward fuel supply amount, a fuel amount required for an air-fuel ratio of an air-fuel mixture, to be supplied to the internal combustion engine, to become rich of the stoichiometric air-fuel ratio on the basis of at least the detected intake volume when the target air-fuel ratio is set to the predetermined rich air-fuel ratio; which calculates, as the feed-forward fuel supply amount, a fuel amount required for the air-fuel ratio of the air-fuel mixture, to be supplied to the internal combustion engine, to become lean of the stoichiometric air-fuel ratio on the basis of at least the detected intake volume when the target air-fuel ratio is set to the predetermined lean air-fuel ratio; which calculates a feedback correction amount based on the air-fuel ratio detected by the upstream-side air-fuel ratio detecting means and the target air-fuel ratio such that the air-fuel ratio detected by the upstream-side air-fuel ratio detecting means matches the target air-fuel ratio; and which determines the feed-forward fuel supply amount corrected by the feedback correction amount as a final fuel supply amount; and fuel supplying means for supplying the internal combustion engine with the same amount of fuel as the final fuel supply amount.