Exhaust purification system of internal combustion engine

An exhaust purification system of an internal combustion engine, the exhaust purification system comprising:

• an engine exhaust passage;
• an exhaust purification catalyst inside of the engine exhaust passage for causing NOX and hydrocarbons that are contained in an exhaust to react,
• wherein the exhaust purification catalyst comprises an upstream side catalyst and a downstream side catalyst, the upstream side catalyst having an oxidation ability, and the downstream side catalyst carrying precious metal catalyst particles on an exhaust flow surface and being formed with basic exhaust flow surface parts around the catalyst particles;
• and
• an electronic control unit, wherein the electronic control unit is configured to control a vibration of a concentration of hydrocarbons flowing into the exhaust purification catalyst within a predetermined range of amplitude and within a predetermined range of period, and is configured to control the vibration period of the hydrocarbon concentration longer than the predetermined range of period, wherein
• when the electronic control unit controls the vibration of the concentration of hydrocarbons flowing into the exhaust purification catalyst within the predetermined range of amplitude and within the predetermined range of period, the exhaust purification catalyst has a property of chemically reducing the NOX that is contained in the exhaust by partially oxidizing the hydrocarbons, activating the NOX to generate active NOX, causing the partially oxidized hydrocarbons and the active NOX to react so as to produce reducing intermediates, and causing the reducing intermediates and the active NOX react, and the exhaust purification catalyst has a property of chemically reducing the NOX that is contained in the exhaust without storing, or storing a fine amount of nitrates in the basic exhaust flow surface parts,
• when the electronic control unit controls the vibration period of the hydrocarbon concentration longer than the predetermined range of period, the exhaust purification catalyst has a property of being increased in a storage amount of NOX that is contained in the exhaust;
• and
• a temperature raising device that raises a temperature of the upstream side catalyst, wherein
• the electronic control unit is configured to set a first judgment temperature based on a temperature at which the upstream side catalyst can partially oxidize the hydrocarbons by a predetermined efficiency or based on a temperature at which the upstream side catalyst can produce reducing intermediates by a predetermined efficiency,
• the electronic control unit configured to set a second judgment temperature based on a temperature at which the downstream side catalyst can react the reducing intermediates and the active NOX by a predetermined efficiency, and
• when the temperature of the upstream side catalyst is less than the first judgment temperature and the temperature of the downstream side catalyst is higher than the second judgment temperature, the electronic control unit is configured to cause the temperature raising device to raise the temperature of the upstream side catalyst.