Device and method for controlling oxygen storage amount in three-way catalyst

Abstract

An exhaust passage (14) of an internal combustion engine (1) is provided with a three-way catalyst (15), and the air-fuel ratio is feedback controlled so as to maintain the oxygen storage amount in the three-way catalyst (15) at a target oxygen storage amount. An estimated oxygen storage amount (b1) is obtained from an intake air amount and an exhaust air-fuel ratio detected by an air-fuel ratio sensor (19), and a target air-fuel ratio is set in accordance with the difference between the target oxygen storage amount (b2) and the estimated oxygen storage amount (b1). The target oxygen storage amount (b2) is set with the characteristic of becoming lower as the intake air amount becomes higher, on the basis of the intake air amount corresponding to the flow rate of gas flowing into the three-way catalyst (15). The foregoing cancels out an increase in the NOx slip ratio when the gas flow rate is high.

Dependencies are inferred from the claim text.