Exhaust gas purification apparatus for internal combustion engine and method of controlling the same

Abstract

A small oxidation catalyst and a fuel supply valve are arranged in an engine exhaust passage. The small oxidation catalyst has a cross-sectional area smaller than a cross-sectional area of the engine exhaust passage, and portion of exhaust gas flowing in the engine exhaust passage flows through the small oxidation catalyst. The fuel supply valve supplies fuel to the small oxidation catalyst. Fuel is intermittently supplied from the fuel supply valve to the small oxidation catalyst to intermittently generate flames downstream of the small oxidation catalyst.

1 . An exhaust gas purification apparatus for an internal combustion engine, comprising:
 a small oxidation catalyst that is arranged in an engine exhaust passage and that has a cross-sectional area smaller than a cross-sectional area of the engine exhaust passage, wherein portion of exhaust gas flowing in the engine exhaust passage flows through the small oxidation catalyst;   a fuel supply valve that is arranged in the engine exhaust passage and that supplies fuel to the small oxidation catalyst;   a determination unit that determines whether flames is generated by supplying fuel from the fuel supply valve; and   a control unit that, when the determination unit determines that the flames is generated by supplying fuel from the fuel supply valve, intermittently supplies fuel from the fuel supply valve to the small oxidation catalyst to intermittently generate flames downstream of the small oxidation catalyst.   
   
   
       2 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , wherein a timing at which fuel is supplied from the fuel supply valve is set so that flame masses sequentially intermittently generated downstream of the small oxidation catalyst do not overlap each other. 
   
   
       3 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 2 , wherein a timing at which fuel is supplied from the fuel supply valve is set so that fuel is intermittently supplied from the small oxidation catalyst. 
   
   
       4 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 2 , wherein a timing at which fuel is supplied from the fuel supply valve is set so that exhaust gas having a rich air-fuel ratio intermittently flows out from the small oxidation catalyst. 
   
   
       5 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , wherein the small oxidation catalyst has a cylindrical shape extending in a direction in which exhaust gas flows. 
   
   
       6 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 5 , wherein fuel is supplied from the fuel supply valve toward an upstream-end face of the small oxidation catalyst. 
   
   
       7 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , wherein an interval of timings, at which supply of fuel from the fuel supply valve is started, is extended as an intake air amount reduces. 
   
   
       8 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , further comprising:
 a secondary air supply device that supplies secondary air into the engine exhaust passage, wherein   when oxygen is insufficient to generate flames, secondary air is supplied into the engine exhaust passage.   
   
   
       9 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , further comprising:
 one of an exhaust gas purification catalyst and a particulate filter arranged in the engine exhaust passage at a portion downstream of the small oxidation catalyst, wherein flames are generated when the temperature of the one of the exhaust gas purification catalyst and the particulate filter needs to be increased.   
   
   
       10 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 1 , further comprising:
 a NOx occlusion catalyst arranged in the engine exhaust passage at a portion downstream of the small oxidation catalyst, wherein the NOx occlusion catalyst occludes NOx contained in exhaust gas when the air-fuel ratio of exhaust gas flowing into the NOx occlusion catalyst is lean, and releases the occluded NOx when the air-fuel ratio of exhaust gas flowing into the NOx occlusion catalyst is rich, and wherein flames of a rich air-fuel ratio are intermittently generated when NOx or SOx needs to be released from the NOx occlusion catalyst.   
   
   
       11 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 10 , wherein, when NOx or SOx needs to be released from the NOx occlusion catalyst, it is determined whether an operating state of an engine is such that flames of a rich air-fuel ratio can be generated, wherein, when NOx or SOx needs to be released from the NOx occlusion catalyst, and when the operating state of the engine is such that flames of a rich air-fuel ratio can be generated, flames are generated, and wherein, when NOx or SOx needs to be released from the NOx occlusion catalyst, and when the operating state of the engine is not such that flames of a rich air-fuel ratio can be generated, the air-fuel ratio of exhaust gas that flows into the NOx occlusion catalyst is made rich without generating flames. 
   
   
       12 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 11 , wherein, when the air-fuel ratio of exhaust gas is higher than the predetermined air-fuel ratio, it is determined that the operating state of the engine is such that flames of a rich air-fuel ratio can be generated. 
   
   
       13 . The exhaust gas purification apparatus for an internal combustion engine according to  claim 12 , wherein, when the engine is operating at a light load or decelerating, it is determined that the operating state of the engine is such that flames of a rich air-fuel ratio can be generated. 
   
   
       14 . A method of controlling an exhaust gas purification apparatus for an internal combustion engine, the exhaust gas purification apparatus including a small oxidation catalyst that is arranged in an engine exhaust passage and that has a cross-sectional area smaller than a cross-sectional area of the engine exhaust passage, wherein portion of exhaust gas flowing in the engine exhaust passage flows through the small oxidation catalyst; and a fuel supply valve that is arranged in the engine exhaust passage and that supplies fuel to the small oxidation catalyst, the method comprising:
 determining whether flames is generated by supplying fuel from the fuel supply valve; and   when it is determined that the flames is generated by supplying fuel from the fuel supply valve, intermittently supplying fuel from the fuel supply valve to the small oxidation catalyst to intermittently generate flames downstream of the small oxidation catalyst.