Exhaust purification system of internal combustion engine

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

• a hydrocarbon feed valve arranged in an engine exhaust passage;
• an exhaust purification catalyst and a particulate filter arranged downstream of the hydrocarbon feed valve in the engine exhaust passage;
• a precious metal catalyst carried on an exhaust gas flow surface of the exhaust purification catalyst;
• a basic exhaust gas flow surface part formed around the precious metal catalyst;
• and
• an electronic control unit configured to control the hydrocarbon feed valve such that a concentration of hydrocarbons flowing into the exhaust purification catalyst vibrates within a predetermined range of amplitude and within a predetermined range of period,
• wherein the exhaust purification catalyst has a property of reducing NOX contained in an exhaust gas, when the electronic control unit controls the hydrocarbon feed valve such that the concentration of hydrocarbons flowing into the exhaust purification catalyst vibrates within the predetermined range of amplitude and within the predetermined range of period, and
• wherein the exhaust purification catalyst has a property of increasing an amount of NOX contained in the exhaust gas when the electronic control unit causes the concentration of hydrocarbons to vibrate for a period longer than the predetermined range of period,
• wherein the electronic control unit is further configured to control the hydrocarbon feed valve to inject the hydrocarbons within the predetermined range of period at the time of engine operation to thereby remove NOX contained in the exhaust gas,
• wherein the exhaust purification system comprises a low pressure exhaust gas recirculation system that makes the exhaust gas in the engine exhaust passage downstream of the exhaust purification catalyst and the particulate filter recirculate to an inside of an intake passage,
• wherein when the electronic control unit controls the hydrocarbon feed valve to inject the hydrocarbons while an exhaust gas recirculation action is performed by the low pressure exhaust gas recirculation system, carbon dioxide produced in the exhaust purification catalyst is recirculated, and after the injection of the hydrocarbons, each time when a time required for recirculation of the carbon dioxide elapses, a temporary drop is repeatedly caused in an air-fuel ratio of an inflowing exhaust gas that flows into the exhaust purification catalyst and the particulate filter,
• wherein the electronic control unit is further configured to allow an injection of the hydrocarbons from the hydrocarbon feed valve that is synchronized with the temporary drop in air-fuel ratio of the inflowing exhaust gas, when the hydrocarbons are injected from the hydrocarbon feed valve within the predetermined range of period for removing NOx contained in the exhaust gas, and
• wherein the electronic control unit is further configured to control the hydrocarbon feed valve to inject the hydrocarbons so as not to overlap with the temporary drop in the air-fuel ratio of the inflowing exhaust gas when the hydrocarbons are periodically injected from the hydrocarbon feed valve for temperature elevation control of at least one of the particulate filter and the exhaust purification catalyst.