Exhaust purification system of internal combustion engine

Abstract

An exhaust purification system of an internal combustion engine has a selective reduction type NO X catalyst device which can hold ammonia and a storage reduction type NO X catalyst device which is arranged at an upstream side of the selective reduction type NO X catalyst device, which makes an air-fuel ratio of exhaust gas which flows into the storage reduction type NO X catalyst device change from a lean air-fuel ratio to a rich air-fuel ratio for starting an ammonia generation period, and which makes an air-fuel ratio of exhaust gas which flows into the storage reduction type NO X catalyst device change from a rich air-fuel ratio to a lean air-fuel ratio for ending the ammonia generation period.

1 . An exhaust purification system of an internal combustion engine which is provided with a selective reduction type NO X  catalyst device which can hold ammonia and a storage reduction type NO X  catalyst device which is arranged at an upstream side of said selective reduction type NO X  catalyst device, which makes an air-fuel ratio of exhaust gas which flows into said storage reduction type NO X  catalyst device change from a lean air-fuel ratio to a rich air-fuel ratio for starting an ammonia generation period, and which makes an air-fuel ratio of exhaust gas which flows into said storage reduction type NO X  catalyst device change from a rich air-fuel ratio to a lean air-fuel ratio for ending said ammonia generation period, characterized in that an amount of NO X  which is held at said storage reduction type NO X  catalyst device for starting said ammonia generation period when a temperature of said storage reduction type NO X  catalyst device is less than a set temperature is smaller than that when a temperature of said storage reduction type NO X  catalyst device is said set temperature or more. 
     
     
         2 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein an interval from when ending said ammonia generation period to when next starting said ammonia generation period when the temperature of said storage reduction type NO X  catalyst device is less than said set temperature is made shorter than that when the temperature of said storage reduction type NO X  catalyst device is said set temperature or more such that the amount of NO X  which is held at said storage reduction type NO X  catalyst device for starting said ammonia generation period when the temperature of said storage reduction type NO X  catalyst device is less than said set temperature is smaller than that when the temperature of said storage reduction type NO X  catalyst device is said set temperature or more. 
     
     
         3 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein when the temperature of said storage reduction type NO X  catalyst device is another set temperature which is higher than said set temperature or more, instead of said ammonia generation period, making the air-fuel ratio of the exhaust gas which flows into said selective reduction type NO X  catalyst device change from a lean air-fuel ratio to the stoichiometric air-fuel ratio or another rich air-fuel ratio closer to the stoichiometric air-fuel ratio than said rich air-fuel ratio and making said storage reduction type NO X  catalyst device purify the NO X  which is disassociated from said storage reduction type NO X  catalyst device and the NO X  in the exhaust gas by reduction.