Exhaust purification apparatus of internal combustion engine

An exhaust purification apparatus of an internal combustion engine, comprising:

• an internal combustion engine comprising a plurality of cylinders, an exhaust passage connected to the cylinders and a common catalyst in the exhaust passage;
• in which cylinders are divided into a pair of cylinder groups, exhaust gas exhausted from each cylinder group is exhausted to a common catalyst, and, when said catalyst should be held in a raised temperature state, an average air-fuel ratio of one cylinder group is made rich and an average air-fuel ratio of other cylinder group is made lean so that an air-fuel ratio of the exhaust gas flowing into said catalyst becomes the substantially stoichiometric air-fuel ratio, wherein at least two different target air-fuel ratios are preset for each operating state of the engine for the air-fuel ratio of each cylinder of said one cylinder group when the average air-fuel ratio is to be made rich, at least two different target air-fuel ratios are preset for each operating state of the engine for the air-fuel ratio of each cylinder of said other cylinder group when the average air-fuel ratio is to be made lean, and the air-fuel ratio of each cylinder of said one cylinder group is made a target air-fuel ratio selected from the corresponding at least two said target air-fuel ratios corresponding to the operating state of the engine and differing among at least part of the cylinders and the air-fuel ratio of each cylinder of said other cylinder group is made a target air-fuel ratio selected from the corresponding at least two said target air-fuel ratios corresponding to the operating state of the engine and differing among at least part of the cylinders so that the temperature of said catalyst is made to become a predetermined target temperature.