Patent ID: 8833056

Claim:
An exhaust purification system of an internal combustion engine, the exhaust purification system comprising: a hydrocarbon feed valve for feeding hydrocarbons arranged inside an engine exhaust passage; an exhaust purification catalyst for causing a reaction between the hydrocarbons injected from the hydrocarbon feed valve and NOx contained in exhaust gas arranged in the engine exhaust passage downstream of the hydrocarbon feed valve; 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, wherein the electronic control unit is configured to control the injection of the hydrocarbons from the hydrocarbon feed valve at predetermined intervals by a first hydrocarbon feed method and a second hydrocarbon feed method, so that an air-fuel ratio of the exhaust gas falls to a predetermined air-fuel ratio, and is configured to control the feed intervals of the hydrocarbons longer than the predetermined feed intervals, wherein when the electronic control unit is configured to control the injection of hydrocarbons from the hydrocarbon feed valve at the predetermined intervals, the exhaust purification catalyst has a property of chemically reducing the NOx that is contained in the exhaust gas, in the first hydrocarbon feed method, the electronic control unit is configured to control the injection of hydrocarbons from the hydrocarbon feed valve at the predetermined feed intervals so that the air-fuel ratio of the exhaust gas falls to the predetermined air-fuel ratio, thereby chemically reducing the NOx contained in the exhaust gas, in the second hydrocarbon feed method, the electronic control unit is configured to control the feed amount of the hydrocarbons from the hydrocarbon feed valve at the predetermined feed intervals in a feed amount that is lower than that of the first hydrocarbon feed method, and the electronic control unit is configured to simultaneously control the feeding of a fuel required for lowering the air-fuel ratio of the exhaust gas to the required air-fuel ratio into a combustion chamber during a second half of an expansion stroke or an exhaust stroke, thereby chemically reducing the NOx contained in the exhaust gas, and the electronic control unit is configured to selectively perform the first or the second hydrocarbon feed method in accordance with an operating state of the engine, and when the electronic control unit controls the injections of the hydrocarbons from the hydrocarbon feed valve longer than the predetermined intervals, the exhaust purification catalyst has a property of being increased in a storage amount of NOx that is contained in the exhaust gas.