Exhaust purification system of internal combustion engine

摘要

In an internal combustion engine, inside of an engine exhaust passage, a hydrocarbon feed valve (16), an exhaust purification catalyst (13), a particulate filter (14), and an NO2 reduction catalyst (15) are arranged. At the time of engine operation, the amplitude of change of the concentration of hydrocarbons which flow into the exhaust purification catalyst (13) is made to become within a predetermined range of amplitude by control of the injection amount of hydrocarbons from the hydrocarbon feed valve (16). When the NO2 which is produced at the particulate filter (14) should be reduced to NO, the injection amount of hydrocarbons is increased whereby the pass through amount of hydrocarbons which pass straight through the exhaust purification catalyst (13) is increased.

主权项

1. An exhaust purification system of an internal combustion engine comprising:
an engine exhaust passage; a hydrocarbon feed valve for feeding hydrocarbons arranged inside of the engine exhaust passage; an exhaust purification catalyst for reacting NOx contained in exhaust gas and reformed hydrocarbons arranged inside of 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; an NO2 reduction catalyst that is able to reduce NO2 that is contained in exhaust gas to NO when hydrocarbons are fed to the NO2 reduction catalyst arranged inside of the engine exhaust passage downstream of the exhaust purification catalyst; 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, a reducing intermediate containing nitrogen and hydrocarbons is produced on the precious metal catalyst and held on the basic exhaust gas flow surface part, the NOx contained in the exhaust gas catalyst is chemically reduced by a reducing action of the reducing intermediate held on the basic exhaust gas flow surface part in the exhaust purification catalyst, and the exhaust purification catalyst has a property of chemically reducing the NOx is contained in the exhaust gas without storing, or storing a fine amount of nitrates in the basic exhaust gas flow surface part,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 storage amount of NOx that is contained in exhaust gas,the electronic control unit is configured to control, when needed, an injection amount of hydrocarbons from the hydrocarbon feed valve so that an amplitude of a change of concentration of hydrocarbons flowing into the exhaust purification catalyst becomes within the predetermined range of amplitude, and is configured to control, when needed, an injection period of hydrocarbons from the hydrocarbon feed valve so that the concentration of hydrocarbons flowing into the exhaust purification catalyst vibrates within the predetermined range of period, andthe electronic control unit is further configured to determine when the NO2 that is contained in the exhaust gas should be reduced to NO, and when the electronic control unit determines that the NO2 that is contained in the exhaust gas should be reduced to NO, the electronic control unit is configured to control an amplitude of a change of the concentration of hydrocarbons flowing into the exhaust purification catalyst to cause an increase in a pass through amount of hydrocarbons that pass through the exhaust purification catalyst without being oxidized.