Deterioration diagnosis of exhaust gas purification catalyst for internal combustion engine

摘要

In an internal combustion engine (1,100), a first exhaust passage (10A) having an oxygen storing catalyst (11A) is connected to cylinders of a first group (1A), and a second exhaust passage (10B) having an oxygen storing catalyst (11B) is connected to cylinders of a second group (1B). These exhaust passages are joined as a collective exhaust passage (10C). Normally, the air-fuel ratio of the first group (1A) is feedback controlled based on the oxygen concentration of the first exhaust passage (10A), and the air-fuel ratio of the second group (1B) is feedback controlled based on the oxygen concentration of the second exhaust passage (10B). When deterioration of the catalysts is diagnosed, the phases of the air-fuel ratio are made to coincide with each other between the groups by performing feedback correction of the air-fuel ratio of all groups based on the oxygen concentration of the first exhaust passage (10A).