Exhaust gas purifying device

Abstract

A NOx occluding reduction catalyst that occludes NOx is efficiently regenerated by carrying our post-injection of a necessary and sufficient quantity of fuel without diluting engine oil on the inner wall surface of a cylinder. A NOx absorbing agent and an active metal are carried on the NOx occluding reduction catalyst ( 16 ) provided in an exhaust gas passage ( 14 ) of an engine ( 11 ), and the fuel is supplied to the NOx occluding reduction catalyst ( 16 ) by adding the fuel to the exhaust gas in the exhaust gas passage ( 14 ) with a fuel adding means ( 17 ). The fuel adding means ( 17 ) is an accumulator fuel injector that carries out post-injection, following main injection into a cylinder ( 22 ) of the engine ( 11 ), at timing such that the fuel does not ignite in the cylinder ( 22 ). The post-injection with the accumulator fuel injector ( 17 ) is carried out in divided 3 to 20 times at the later period of the expansion stroke of the engine ( 11 ).

1 . An exhaust gas purifying device comprising a NOx occluding reduction catalyst ( 16 ) that is provided in an exhaust gas passage ( 14 ) of an engine ( 11 ) and carries a NOx absorbing agent and an active metal; and a fuel adding means ( 17 ) that adds a fuel ( 15 ) to the exhaust gas in the exhaust gas passage ( 14 ) and thereby supplies the fuel ( 15 ) to the NOx occluding reduction catalyst ( 16 ), wherein
 the fuel adding means ( 17 ) is an accumulator fuel injector that carries out post-injection, following main injection into a cylinder ( 22 ) of the engine ( 11 ), at timing such that the fuel ( 15 ) does not ignite in the cylinder ( 22 ), and   the post-injection is carried out at the later period of the expansion stroke of the engine ( 11 ) in divided 3 to 20 times.   
   
   
       2 . The exhaust gas purifying device according to  claim 1 , wherein when the top dead center position of a piston ( 26 ), which is the start time of the expansion stroke of the engine ( 11 ), is a crank angle of 0 degree, among the post-injections carried out in divided 3 to 20 times at the later period of the expansion stroke, the first post-injection is started in the range of 90 to 120 degrees of the crank angle. 
   
   
       3 . The exhaust gas purifying device according to  claim 1 , wherein the NOx occlusion quantity of the NOx occluding reduction catalyst ( 16 ) is integrated from a prediction map based on an engine load and an engine rotational speed. 
   
   
       4 . The exhaust gas purifying device according to  claim 1 , wherein the injection quantities of post-injections carried out in divided 3 to 20 times are equal to each other or decrease gradually after the first post-injection.