Exhaust purification system of internal combustion engine

An exhaust purification system of an internal combustion engine comprising:

• a hydrocarbon feed valve for feeding hydrocarbons arranged inside of an engine exhaust passage,
• an exhaust purification catalyst for reacting NOx and reformed hydrocarbons contained in exhaust gas arranged downstream of the hydrocarbon feed valve inside of the engine exhaust passage,
• a precious metal catalyst carried on an exhaust gas flow surface of the exhaust purification catalyst and a basic exhaust gas flow surface part is formed around the precious metal catalyst,
• wherein the NOx which is contained in exhaust gas is reduced in the exhaust purification catalyst if a predetermined amount of hydrocarbons is injected by a predetermined feed period from the hydrocarbon feed valve and NOx which is contained in exhaust gas is stored in the exhaust purification catalyst if the feed period of the hydrocarbons is lengthened more than the predetermined feed period, and
• an electronic control unit configured to detect a degree of clogging of a nozzle opening of the hydrocarbon feed valve, inject the predetermined amount of hydrocarbons from the hydrocarbon feed valve by the predetermined feed period at the time of engine operation, and, at this time, estimate an NOx purification rate from the clogging degree of the nozzle opening of the hydrogen feed valve which is detected by the electronic control unit,
• wherein a temperature elevation control which makes a temperature of a catalyst or particulate filter which is arranged inside of the engine exhaust passage rise to a target temperature by increasing an injection time of hydrocarbons from said hydrocarbon feed valve is performed by the electronic control unit, wherein said electronic control unit detects the clogging degree from an increased amount of injection time of the hydrocarbons when said temperature elevation control is being performed.