Exhaust gas purification apparatus for an internal combustion engine

Abstract

An object of the present invention is to improve preferable promotion of the modification of reducing agent in a precatalyst in the case where the reducing agent is added through a reducing agent addition valve in order to supply the reducing agent to an exhaust gas purification catalyst. According to the present invention, one end of an exhaust passage in which an exhaust gas purification catalyst is provided is connected to an exhaust manifold, and a precatalyst and a reducing agent addition valve are provided in the exhaust manifold. The precatalyst is configured in such a way that the exhaust gas flows through the gap between the outer circumferential surface thereof and the inner wall surface of the exhaust manifold. The precatalyst and the reducing agent addition valve are arranged in such a way that the most part of the reducing agent added through the reducing agent addition valve flows into the precatalyst.

1 . An exhaust gas purification apparatus for an internal combustion engine comprising:
 an exhaust manifold connected to the internal combustion engine;   an exhaust gas purification catalyst provided in an exhaust passage, one end of which is connected to said exhaust manifold;   a precatalyst having an oxidizing ability provided in said exhaust manifold; and   a reducing agent addition valve provided in said exhaust manifold to add a reducing agent to exhaust gas, wherein   said precatalyst is configured in such a way that the exhaust gas flows through a gap between a circumferential surface thereof and an inner wall surface of said exhaust manifold, and   said precatalyst and said reducing agent addition valve are arranged in such a way that said precatalyst is located at a position toward which a spray jet of the reducing agent formed by the addition of the reducing agent through said reducing agent addition valve is directed.   
     
     
         2 . An exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , wherein the internal combustion engine is an internal combustion engine equipped with a turbocharger, and a turbine housing of said turbocharger is provided upstream of said exhaust gas purification catalyst in said exhaust passage. 
     
     
         3 . An exhaust gas purification apparatus for an internal combustion engine according to  claim 2 , wherein said turbocharger is a variable geometry turbocharger having nozzle vanes, and
 when the reducing agent is added through the reducing agent addition valve, the degree of opening of said nozzle vanes is controlled so that the rotational speed of said turbocharger does not change with an increase in the quantity of heat generated in said precatalyst.   
     
     
         4 . An exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , wherein said precatalyst is an NOx storage reduction catalyst. 
     
     
         5 . An exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , further comprising estimation unit for estimating a modification ratio of the reducing agent in the precatalyst,
 wherein the quantity of reducing agent added through the reducing agent addition valve is corrected based on the modification ratio estimated by said estimation unit.