Exhaust gas purification device

Abstract

An exhaust gas purification device includes a NO x adsorption catalyst ( 36 ) and HC supply means ( 48 ) for adding HC to the exhaust gas flowing to the NO x adsorption catalyst ( 36 ). The HC supply means ( 48 ) is controlled first to supply an amount of HC required to keep the temperature of the NO x adsorption catalyst ( 36 ) at a second temperature which is derived by subtracting a temperature rise caused by rich spike from a first temperature predetermined as a temperature necessary for S purge, thereby increasing the temperature of the NO x adsorption catalyst ( 36 ), and then to additionally perform the rich spike for the S purge while continuing the HC supply.

1 . An exhaust gas purification device comprising:
 a NO x  adsorption catalyst arranged in an exhaust passage of an engine, for adsorbing, in an oxidizing atmosphere, NO x  contained in an exhaust gas and for releasing and reducing, in a reducing atmosphere, the adsorbed NO x ;   HC supply means for adding HC to the exhaust gas flowing to the NO x  adsorption catalyst; and   control means for causing the HC supply means to supply HC to raise temperature of the NO x  adsorption catalyst and also causing the HC supply means to supply HC by rich spike to create the reducing atmosphere and thus carry out S purge of the NO x  adsorption catalyst,   wherein the control means controls the HC supply means by first causing the HC supply means to supply an amount of HC required to raise the temperature of the NO x  adsorption catalyst to a second temperature which is derived by subtracting a temperature rise caused by the rich spike from a first temperature predetermined as a temperature necessary for the S purge, to raise the temperature of the NO x  adsorption catalyst, and then additionally performing the rich spike while continuing the HC supply.   
   
   
       2 . The exhaust gas purification device according to  claim 1 , wherein the control means controls the HC supply means such that the S purge by means of the rich spike is started after the temperature of the NO x  adsorption catalyst is kept at the second temperature over a predetermined time. 
   
   
       3 . The exhaust gas purification device according to  claim 1 , wherein, if the temperature of the NO x  adsorption catalyst becomes higher than the second temperature while the temperature of the NO x  adsorption catalyst is being raised to the second temperature by the HC supply from the HC supply means, the control means decreases the amount of the HC supply. 
   
   
       4 . The exhaust gas purification device according to  claim 1 , wherein, if the temperature of the NO x  adsorption catalyst becomes higher than the first temperature while HC is being supplied by the rich spike to create the reducing atmosphere around the NO x  adsorption catalyst, the control means decreases the amount of the HC supply.