Exhaust purification system of internal combustion engine

Abstract

An exhaust purification system of an internal combustion engine is provided with a hydrocarbon feed valve which is arranged in an engine exhaust passage and an exhaust purification catalyst which reacts the NO X which is contained in exhaust gas and reformed hydrocarbons. It is formed to perform first operational control which feeds hydrocarbons from the hydrocarbon feed valve by within a predetermined range of amplitude and within a predetermined range of period and second operational control wherein the amount of feed of hydrocarbons from the hydrocarbon feed value in a predetermined time becomes greater than in the first operational control. In the second operational control, hydrocarbons are fed from the hydrocarbon feed valve by an injection pressure which is smaller than the injection pressure of hydrocarbons in the first operational control.

1 . An exhaust purification system of an internal combustion engine which arranges a hydrocarbon feed valve for feeding hydrocarbons inside of an engine exhaust passage and arranges an exhaust purification catalyst for reacting NO X  which is contained in exhaust gas and reformed hydrocarbons in the engine exhaust passage downstream of the hydrocarbon feed valve, a precious metal catalyst being carried on an exhaust flow surface of the exhaust purification catalyst and basic exhaust flow surface parts being formed around the precious metal catalyst, wherein
 the exhaust purification catalyst has a property of reducing the NO X  which is contained in exhaust gas if making a concentration of hydrocarbons which flow into the exhaust purification catalyst vibrate by a predetermined range of amplitude and a predetermined range of period and has a property of a stored amount of NO X  which is contained in the exhaust gas increasing if making a vibration period of the concentration of hydrocarbons longer the predetermined range,   the system is formed to perform first operational control where the amplitude of change of the concentration of hydrocarbons which flow into the exhaust purification catalyst at the time of engine operation is made to become within the predetermined range of amplitude by controlling the amount of feed of hydrocarbons from the hydrocarbon feed valve and the concentration of hydrocarbons which flow into the exhaust purification catalyst is made to vibrate by within the predetermined range of period by controlling a feed interval of the hydrocarbons from the hydrocarbon feed valve and second operational control where the amount of feed of hydrocarbons from the hydrocarbon feed value in a predetermined time becomes greater than the amount of feed of hydrocarbons of the first operational control,   the system is further provided with an injection pattern changing device which can change an injection pattern of hydrocarbons of the hydrocarbon feed valve,   the injection pattern changing device is formed so as to enable change of an injection pressure of the hydrocarbon feed valve,   the first operational control includes control so as to raise the injection pressure of the hydrocarbon feed valve the more an engine speed increases, and   in the first operational control, the injection pressure, which is set based on an operating state of the internal combustion engine, is used to feed hydrocarbons from the hydrocarbon feed valve, while in the second operational control, an injection pressure smaller than the injection pressure of hydrocarbons at the first operational control is used to feed hydrocarbons from the hydrocarbon feed valve.   
     
     
         2 . The exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein
 the injection pattern changing device is formed so that an injection time of injecting hydrocarbons from the hydrocarbon feed valve and the feed interval of the hydrocarbons can be changed and,   in the second operational control, the injection time of injecting hydrocarbons from the hydrocarbon feed valve is made longer than the injection time of first operational control and the feed interval of the hydrocarbons is made shorter than the feed interval of the hydrocarbons of the first operational control.   
     
     
         3 . The exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein
 the operating state of the internal combustion engine is used as the basis to set in advance a reference value of an air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst, and,   during a period of the second operational control, the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst is detected and, when a detected air-fuel ratio of the exhaust gas is smaller than the reference value of the air-fuel ratio of the exhaust gas, correction is performed to lower the injection pressure of the hydrocarbon feed valve.   
     
     
         4 . The exhaust purification system of an internal combustion engine as set forth in  claim 3 , wherein
 when the detected air-fuel ratio of the exhaust gas is smaller than the reference value of the air-fuel ratio of the exhaust gas, correction is performed to extend an injection time of the hydrocarbon feed valve and correction is performed to shorten the feed interval of the hydrocarbons.   
     
     
         5 . The exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein
 the operating state of the internal combustion engine is used as the basis to set in advance a reference value of a temperature of the exhaust gas which flows into the exhaust purification catalyst, and,   during a period of the second operational control, the temperature of the exhaust gas which flows into the exhaust purification catalyst is detected and when a detected temperature of the exhaust gas is smaller than the reference value of the temperature of the exhaust gas, correction is performed to lower the injection pressure of the hydrocarbon feed valve.   
     
     
         6 . The exhaust purification system of an internal combustion engine as set forth in  claim 5 , wherein
 when the detected temperature of the exhaust gas is smaller than the reference value of the temperature of the exhaust gas, correction is performed to extend an injection time of the hydrocarbon feed valve and correction is performed to shorten the feed interval of the hydrocarbons.   
     
     
         7 . The exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein
 the operating state of the internal combustion engine is used as the basis to set in advance a reference value of an amount of air which is fed from outside air to a combustion chamber,   during a period of second operational control, the amount of air which is fed from the outside air to a combustion chamber is detected and, when a detected air amount is smaller than the reference value of the amount of air, correction is performed to lower the injection pressure of the hydrocarbon feed valve.   
     
     
         8 . The exhaust purification system of an internal combustion engine as set forth in  claim 7 , wherein
 when the detected air amount is smaller than the reference value of the air amount, correction is performed to extend an injection time of the hydrocarbon feed valve and correction is performed to shorten the feed interval of the hydrocarbons.   
     
     
         9 . The exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein
 the second operational control includes control which increases an oxidation reaction of hydrocarbons at the exhaust purification catalyst over the first operational control so as to raise a temperature of the exhaust purification catalyst.