Exhaust gas purification apparatus for an internal combustion engine

Abstract

A decrease in an NOx removal or reduction rate at the time of filter regeneration is suppressed. To this end, provision is made for an NOx selective reduction catalyst, a filter arranged at the upstream side of the NOx selective reduction catalyst, an NH 3 generation catalyst arranged at the upstream side of the NOx selective reduction catalyst to generate NH 3 when the air fuel ratio of an exhaust gas is equal to or less than a stoichiometric air fuel ratio, a regeneration unit to carry out regeneration of the filter, and a generation unit to make the air fuel ratio of the exhaust gas equal to or less than the stoichiometric air fuel ratio, thereby causing NH 3 to be generated in the NH 3 generation catalyst, wherein the regeneration unit inhibits the regeneration of the filter until the generation of NH 3 by the generation unit is completed.

The invention claimed is: 
     
       1. An exhaust gas purification apparatus of an internal combustion engine comprising:
 an NOx selective reduction catalyst that is arranged in an exhaust passage of the internal combustion engine and reduces NOx by using NH3 as a reducing agent; 
 a filter that is arranged in the exhaust passage at the upstream side of said NOx selective reduction catalyst and traps particulate matter contained in the exhaust gas; 
 an NH3 generation catalyst that is arranged in the exhaust passage at the upstream side of said NOx selective reduction catalyst and generates NH3 when the air fuel ratio of the exhaust gas is equal to or less than a stoichiometric air fuel ratio; and 
 an electronic control unit (ECU), wherein 
 the ECU is configured to 
 a regeneration unit that regeneratesregenerate said filter by supplying oxygen to said filter while raising the temperature of said filter; and 
 a generation unit that makesmake the air fuel ratio of the exhaust gas equal to or less than the stoichiometric air fuel ratio, thereby causing NH3 to be generated in said NH3 generation catalyst; 
 wherein said regeneration unit inhibitsinhibit the regeneration of said filter until the generation of NH3 by said generation unit is completedan amount of NH3 required for the regeneration of the filter is adsorbed to the NOx selective reduction catalyst; and 
 said generation unit does not carry out the generation of NH3 during the regeneration of said filter. 
 
     
     
       2. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 1 , wherein the ECU is further configured to
 said generation unit causescause NH3 to be generated until said NOx selective reduction catalyst adsorbs an amount of NH3 required for removing NOx to be discharged from said internal combustion engine when the regeneration of said filter is carried out. 
 
     
     
       3. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 1 , wherein
 in cases where the amount of NH3 having been adsorbed to said NOx selective reduction catalyst becomes equal to or less than a predetermined value when the regeneration of said filter is carried out, said regeneration unit interrupts the ECU is further configured to interrupt the regeneration of said filter. 
 
     
     
       4. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 3 , wherein
 when said regeneration unit has interrupted the regeneration of said filter, said generation unit causesthe ECU is further configured to cause NH3 to be generated, by making the air fuel ratio of the exhaust gas equal to or less than the stoichiometric air fuel ratio when interrupting the regeneration of said filter. 
 
     
     
       5. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 3 , wherein
 even ifbefore the regeneration of said filter is resumed, said generation unit causesthe ECU is further configured to cause NH3 to be generated until said NOx selective reduction catalyst adsorbs an amount of NH3 so that the amount of NH3 adsorbed to said NOx selective reduction catalyst does not become equal to or less than said predetermined value, at the time of carrying out the regeneration of said filterafter the regeneration of the filter is restarted; and 
 even if the regeneration of said filter is resumed, said regeneration unit resumes the ECU is further configured to resume the regeneration of said filter after said NOx selective reduction catalyst has adsorbed an amount of NH3 so that the amount of NH3 adsorbed to said NOx selective reduction catalyst does not become equal to or less than said predetermined value, at the time of carrying out the regeneration of said filter. 
 
     
     
       6. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 1 , wherein
 said regeneration unitthe ECU is further configured to  
 startsstart the regeneration of said filter when an amount of particulate matter trapped in said filter becomes equal to or greater than a threshold value, and 
 setsset said threshold value in such a manner that the NOx to be discharged from said internal combustion engine in a period of time from when the regeneration of said filter is started until it is completed becomes able to be removed by the amount of NH3 having been adsorbed to said NOx selective reduction catalyst. 
 
     
     
       7. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 1 , wherein
 the larger the an extent of the a deterioration of said NOx selective reduction catalyst, the shorter said regeneration unit makes the ECU is further configured to make the interval in which the regeneration of said filter is carried out. 
 
     
     
       8. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 1 , wherein
 said generation unit adjusts the air fuel ratio of the exhaust gas flowing into said NH3 generation catalyst to such a value that falls within a predetermined range including an air fuel ratio at which the amount of generation of NH3 becomes the largest.   
     
     
       9. The exhaust gas purification apparatus for an internal combustion engine as set forth in  claim 1 , wherein
 at the time of carrying out the regeneration of said filter, said regeneration unit interrupts the ECU is further configured to interrupt the regeneration of said filter, in cases where the temperature of said NOx selective reduction catalyst becomes higher than a temperature able to adsorb NH3; and 
 when said regeneration unit has interrupted the regeneration of said filter, said generation unit causesthe ECU is further configured to cause NH3 to be generated, by making the air fuel ratio of the exhaust gas equal to or less than the stoichiometric air fuel ratio when interrupting the regeneration of said filter. 
 
     
     
       10. An exhaust gas purification apparatus of an internal combustion engine comprising:
 an NOx selective reduction catalyst arranged in an exhaust passage of the internal combustion engine and which reduces NOx by using NH3 as a reducing agent:   a filter arranged in the exhaust passage at an upstream side of the NOx selective reduction catalyst and which traps particulate matter contained in the exhaust gas:   an NH3 generation catalyst arranged in the exhaust passage at the upstream side of the NOx selective reduction catalyst and which generates NH3 when the air fuel ratio of the exhaust gas is equal to or less than a stoichiometric air fuel ratio: and   a controller configured to:   perform a first control in which the air fuel ratio of the exhaust gas introduced into said NH3 generation catalyst is equal to or less than the stoichiometric air fuel ratio: and   after the first control, perform a second control in which oxygen is supplied to the filter while raising the temperature of the filter to regenerate the filter,   wherein the second control is performed when NH3 generated by the first control remains on the NOx selective reduction catalyst; and   the second control is performed while NH3 on the NOx selective reduction catalyst exceeds the amount of NH3 on the NOx selective reduction catalyst prior to performing the first control.   
     
     
       11. The exhaust gas purification apparatus of an internal combustion engine as set forth in claim 10, wherein during the first control, the temperature of the filter is raised from 500 degrees C. to 600 degrees C. 
     
     
       12. The exhaust gas purification apparatus of an internal combustion engine as set forth in claim 10, wherein the first control is performed until the NOx selective reduction catalyst adsorbs an amount of NH3 equal to or greater than a regeneration amount of NH3 consumed during regeneration of the filter. 
     
     
       13. The exhaust gas purification apparatus of an internal combustion engine as set forth in claim 10, wherein the controller is further configured to interrupt the second control when an amount of NH3 adsorbed on the NOx selective reduction catalyst is less than a predetermined value. 
     
     
       14. The exhaust gas purification apparatus of an internal combustion engine as set forth in claim 10, wherein the controller is further configured to interrupt the second control when a temperature of the NOx selective reduction catalyst exceeds a threshold value. 
     
     
       15. The exhaust gas purification apparatus of an internal combustion engine as set forth in claim 10, wherein the controller is further configured to:
 set a period of time for performing the first control: and   perform the first control until the period of time has expired.   
     
     
       16. The exhaust gas purification apparatus for an internal combustion engine as set forth in claim 15, wherein
 the period of time is reduced upon a determination that the NOx selective reduction catalyst has deteriorated.