Patent ID: 6694726
Filing Date: 2004-02-24
Classification: F01N,F02D,Y02T

Abstract:
An air-fuel ratio control device for an internal combustion engine, the engine comprising a first exhaust passage connected to a first cylinder and provided with a first exhaust gas purification device which has an oxygen storage function, a second exhaust passage connected to a second cylinder and provided with a second exhaust gas purification device which has an oxygen storage function, and a collective exhaust passage which collects exhaust gas from the first exhaust passage and the second exhaust passage; the control device comprising:a first fuel supply device which supplies fuel to the first cylinder to generate an air-fuel mixture to be burned in the first cylinder; a second fuel supply device which supplies fuel to the second cylinder to generate an air-fuel mixture to be burned in the second cylinder; a first oxygen sensor which reacts to an oxygen concentration in exhaust gas in the first exhaust passage upstream of the first exhaust gas purification device; a second oxygen sensor which reacts to an oxygen concentration in exhaust gas in the second exhaust passage upstream of the second exhaust gas purification device; a third oxygen sensor which reacts to an oxygen concentration in exhaust gas in the collective exhaust passage; and a programmable controller programmed to: calculate a first feedback correction coefficient for controlling an air-fuel ratio of the air-fuel mixture in the first cylinder to a target air-fuel ratio based on a reaction of the first oxygen sensor; feedback control a fuel supply amount of the first fuel supply device using the first feedback correction coefficient; calculate a second feedback correction coefficient for controlling an air-fuel ratio of the air-fuel mixture in the second cylinder to the target air-fuel ratio based on a reaction of the second oxygen sensor; feedback control a fuel supply amount of the second fuel supply device using the second air-fuel ratio feedback correction coefficient; determine whether or not a predetermined condition for performing deterioration diagnosis of the exhaust purification devices is satisfied; and perform the deterioration diagnosis of the exhaust purification devices, when the predetermined condition is satisfied, based on a reaction of the third oxygen sensor while feedback controlling the fuel supply amount of the first fuel supply device and the fuel supply amount of the second fuel supply device using the first feedback correction coefficient; wherein the controller is further programmed to calculate a first learning correction coefficient of the first feedback correction coefficient, perform open loop control of the fuel supply amount of the first fuel supply device using the first learning correction coefficient, calculate a second learning correction coefficient of the second feedback correction coefficient, perform open loop control of the fuel supply amount of the second fuel supply device using the second learning correction coefficient, determine whether or not both the first learning correction coefficient and the second learning correction coefficient have converged, and when one of the first learning correction coefficient or the second learning correction coefficient have not converged, determine that the predetermined condition is not satisfied.