Exhaust gas purification system for internal combustion engine

Abstract

There is provided an exhaust gas purification system for an internal combustion engine in which exhaust gas that is in a state in which an even concentration distribution of reducing agent is achieved is caused to flow into an exhaust gas purification apparatus. The system includes a small-diameter catalyst 7 that is provided in an exhaust pipe 3 upstream of an NOx catalyst 4 and adapted in such a way that not the entire amount but a portion of the exhaust gas flowing in the exhaust pipe 3 passes through it, a fuel addition valve 5 that is provided upstream of the small-diameter catalyst 7 and adds fuel to the exhaust gas flowing into the small-diameter catalyst 7 , and an isolation pipe 8 that separates the cross section of the exhaust pipe 3 into a catalyst side passage 8 a through which catalyst outflowing exhaust gas is caused to pass and a detour side passage 3 c through which catalyst detouring exhaust gas is caused to pass, over a region from the downstream end of the small-diameter catalyst 7 to a predetermined position between the small-diameter catalyst 7 and the NOx catalyst 4.

1 . An exhaust gas purification system for an internal combustion engine comprising:
 an exhaust gas purification apparatus provided in an exhaust passage of an internal combustion engine;   a pre-stage catalyst that is provided in the exhaust passage upstream of said exhaust gas purification apparatus and adapted in such a way that not the entire amount but a portion of exhaust gas flowing in the exhaust passage passes through it;   a reducing agent addition unit provided upstream of said pre-stage catalyst for adding reducing agent to exhaust gas flowing into the pre-stage catalyst; and   a separation member that separates a cross section of the exhaust passage into a catalyst side passage through which catalyst outflowing exhaust gas flowing out of said pre-stage catalyst is caused to pass and a detour side passage through which catalyst detouring exhaust gas that has detoured around the pre-stage catalyst is caused to pass, over a region from the downstream end of said pre-stage catalyst to a predetermined position between the pre-stage catalyst and said exhaust gas purification apparatus,   wherein an expanding portion in which the cross sectional area of the exhaust passage becomes larger as compared to the portion of the exhaust passage in which the separation member is disposed is connected to the upstream end of said exhaust gas purification apparatus, and   the axis of the expanding portion is inclined relative to the axis of said pre-stage catalyst.   
     
     
         2 . (canceled) 
     
     
         3 . An exhaust gas purification system for an internal combustion engine according to  claim 1 , further comprising:
 a turbocharger having a turbine disposed in the exhaust passage upstream of said reducing agent addition unit and a compressor disposed in an intake passage of the internal combustion engine; and   a cylindrical member disposed on a front end face of said pre-stage catalyst to guide a portion of exhaust gas flowing out of said turbine to the front end face of the pre-stage catalyst,   wherein the side wall of said cylindrical member is provided with an opening, and   said reducing agent addition unit adds liquid reducing agent to exhaust gas introduced in said cylindrical member in such a way that a spray of the reducing agent is ejected toward the center of the cylindrical member through said opening of the cylindrical member.   
     
     
         4 . (canceled) 
     
     
         5 . An exhaust gas purification system for an internal combustion engine according to  claim 3 , wherein said cylindrical member is arranged to be offset from the axis of the exhaust passage toward an inner surface of the exhaust passage. 
     
     
         6 . An exhaust gas purification system for an internal combustion engine according to  claim 5 , wherein a portion of said cylindrical member is in contact with the inner surface of the exhaust passage. 
     
     
         7 . An exhaust gas purification system for an internal combustion engine according to  claim 1 , wherein the cross sectional area of the channel of said catalyst side passage is constant over a region from the upstream end to the downstream end of said separation member. 
     
     
         8 . An exhaust gas purification system for an internal combustion engine according to  claim 1 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         9 . An exhaust gas purification system for an internal combustion engine according to  claim 3 , wherein the cross sectional area of the channel of said catalyst side passage is constant over a region from the upstream end to the downstream end of said separation member. 
     
     
         10 . An exhaust gas purification system for an internal combustion engine according to  claim 5 , wherein the cross sectional area of the channel of said catalyst side passage is constant over a region from the upstream end to the downstream end of said separation member. 
     
     
         11 . An exhaust gas purification system for an internal combustion engine according to  claim 6 , wherein the cross sectional area of the channel of said catalyst side passage is constant over a region from the upstream end to the downstream end of said separation member. 
     
     
         12 . An exhaust gas purification system for an internal combustion engine according to  claim 3 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         13 . An exhaust gas purification system for an internal combustion engine according to  claim 5 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         14 . An exhaust gas purification system for an internal combustion engine according to  claim 6 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         13 . An exhaust gas purification system for an internal combustion engine according to  claim 7 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         14 . An exhaust gas purification system for an internal combustion engine according to  claim 9 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         15 . An exhaust gas purification system for an internal combustion engine according to  claim 10 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion. 
     
     
         16 . An exhaust gas purification system for an internal combustion engine according to  claim 11 , wherein said expanding portion is provided in a region from a location between the downstream end of said separation member and the upstream end of said exhaust gas purification apparatus to the upstream end of said exhaust gas purification apparatus, and the cross sectional area of the channel of the exhaust passage is constant in a region from the downstream end of said separation member to the upstream end of said expanding portion.