Patent ID: 8297041

Claim:
An exhaust purification device of an internal combustion engine in which cylinders are divided into a first cylinder group and a second cylinder group, comprising: front stage catalysts having oxidation functions arranged in a first exhaust passage common to the first cylinder group and in a second exhaust passage common to the second cylinder group; and a rear stage catalyst having an oxidation function downstream of the corresponding front stage catalysts, the rear stage catalyst being connected to the first exhaust passage and the second exhaust passage, wherein when the temperature of the rear stage catalyst is to be raised, if a temperature of the rear stage catalyst is lower than a predetermined first temperature, an air-fuel ratio of at least one of the cylinders of the first cylinder group is made rich and an air-fuel ratio of remaining cylinders of the first cylinder group is made lean and an air-fuel ratio of at least one of the cylinders of the second cylinder group is made rich and an air-fuel ratio of remaining cylinders of the second cylinder group is made lean, so as to raise the temperature of the rear stage catalyst by heat of an oxidation reaction at the front stage catalysts; if the temperature of the rear stage catalyst is higher than the predetermined first temperature and lower than a predetermined second temperature, the air-fuel ratio of the at least one of the cylinders of the first cylinder group is made rich and the air-fuel ratio of the remaining cylinders of the first cylinder group is made lean and the air-fuel ratio of the at least one of the cylinders of the second cylinder group is made rich and the air-fuel ratio of the remaining cylinders of the second cylinder group is made lean, an average air-fuel ratio at one of the cylinder groups is made rich and an average air-fuel ratio at the other cylinder group is made lean, so as to raise the temperature of the rear stage catalyst by the heat of the oxidation reaction at the front stage catalysts and of an oxidation reaction at the rear stage catalyst; and if the temperature of the rear stage catalyst is higher than the predetermined second temperature, air-fuel ratios of all of the cylinders of either cylinder group among the first cylinder group and second cylinder group are made rich and the air-fuel ratios of all of the cylinders of the other cylinder group are made lean, so as to raise the rear stage catalyst in temperature by the heat of oxidation reaction at the rear stage catalyst.