| 主权项 |
1. An exhaust purification system of an internal combustion engine in which an exhaust purification catalyst is arranged in an engine exhaust passage and a hydrocarbon feed valve is arranged in the engine exhaust passage upstream of the exhaust purification catalyst, a precious metal catalyst is 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, the exhaust purification catalyst has a property of reducing NOX which is contained in exhaust gas if making a concentration of hydrocarbons which flow into the exhaust purification catalyst vibrate by within a predetermined range of amplitude and by within a predetermined range of period and has a property of being increased in storage amount of NOX which is contained in the exhaust gas if making the vibration period of the hydrocarbon concentration longer than the predetermined range, a first NOX removal method which injects hydrocarbons from the hydrocarbon feed valve by a predetermined injection period to thereby remove the NOX which is contained in the exhaust gas and a second NOX removal method which makes an air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst rich to make the exhaust purification catalyst release a stored NOX when the NOX which is stored in the exhaust purification catalyst exceeds a first allowable value are selectively used, and in the second NOX removal method, the period by which the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst is made rich is longer than said predetermined injection period, wherein, temperature regions which the exhaust purification catalyst can take at the time of engine operation are divided into three regions of a low temperature region, an intermediate temperature region, and a high temperature region, in the high temperature region, an NOX removal action by the first NOX removal method is performed, in the low temperature region, an NOX removal action by the second NOX removal method is performed, and in the intermediate temperature region, hydrocarbons are injected from the hydrocarbon feed valve by said predetermined injection period and, when the NOX which is stored in the exhaust purification catalyst exceeds a predetermined second allowable value of a value smaller than the first allowable value, the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst is made rich. |
