Exhaust purification system for internal combustion engine

Abstract

In a treatment for regenerating the purification capability of an exhaust emission control system, a technique for improving exhaust emission more positively is provided by supplying a reducing agent to the exhaust emission control system and allowing part of exhaust to bypass the exhaust emission control system. When an addition synchronous bypass control is carried out in which an reducing agent is added when an NSR is subject to NOx reduction treatment and the volume of exhaust passing through a bypass pipe out of exhaust passing an exhaust pipe is increased to thereby decrease the volume of exhaust passing through the NSR, a judgment is made (S 106 ) as to which is larger a reduction in volume of Nox exhausted (S 105 ) due to an increase in conversion efficiency of the NSR as the result of the addition synchronous bypass control carried out or an increase in volume of Nox exhausted (S 103 ) due to an increase in exhaust passing through the bypass pipe. When a reduction in volume of NOx exhausted due to an increase in conversion efficiency of the NSR is judged to be larger than an increase in volume of Nox exhausted due to an increase in exhaust passing through the bypass pipe, the addition synchronous bypass control is executed ( 107 ).

1 .- 6 . (canceled) 
   
   
       7 . An exhaust purification system for an internal combustion engine comprising:
 an exhaust purification device provided in an exhaust passage of said internal combustion engine, for purifying exhaust gas passing through said exhaust passage;   a bypass passage branching from said exhaust passage on an upstream side of said exhaust purification device and merging into said exhaust passage on a downstream side of said exhaust purification device, for causing said exhaust gas passing through said exhaust passage to bypass said exhaust purification device;   reducer supply device for supplying a reducer to said exhaust gas passing through said exhaust passage on the upstream side of said exhaust purification device; and   regeneration device for performing a regeneration treatment for regenerating purification performance of said exhaust purification device, when an amount of a purification substance accumulated in said exhaust purification device becomes equal to or larger than a predetermined value, said regeneration treatment being a treatment for regenerating the purification performance of said exhaust purification device by supplying said reducer from said reducer supply device to said exhaust gas to introduce said reducer into said exhaust purification device,   regeneration exhaust flow rate control device for executing regeneration exhaust flow rate control when said regeneration device performs said regeneration treatment, said regeneration exhaust flow rate control being a control operation in which, of said exhaust gas passing through said exhaust passage, an amount of exhaust gas passing through said bypass passage is increased and an amount of exhaust gas passing through said exhaust purification device is reduced; and   purification substance amount determination device for determining the magnitude relation between the following two values which are obtained when said regeneration exhaust flow rate control is executed during execution of said regeneration treatment: the decrease in the amount of said purification substance discharged from said exhaust purification device due to the increase in the rate of purification by said exhaust purification device; and the increase in the amount of said purification substance discharged from said bypass passage due to the increase in said exhaust gas passing through said bypass passage, wherein   said regeneration exhaust flow rate control is executed when said purification substance amount determination device determines that the decrease in the amount of said purification substance discharged from said exhaust purification device due to the increase in the rate of purification by said exhaust purification device is larger than the increase in the amount of said purification substance discharged from said bypass passage due to the increase in said exhaust gas passing through said bypass passage.   
   
   
       8 . The exhaust purification system for an internal combustion engine according to  claim 7 , wherein said purification substance amount determining device determines the magnitude relation between the following two values which are obtained in a period from start of supplying said reducer in said regeneration treatment to start of supplying said reducer in a next regeneration treatment: the decrease in the amount of said purification substance discharged from said exhaust purification device due to the increase in the rate of purification by said exhaust purification device; and the increase in the amount of said purification substance discharged from said bypass passage due to the increase in said exhaust gas passing through said bypass passage. 
   
   
       9 . An exhaust purification system for an internal combustion engine comprising:
 a storage-reduction type NOx catalyst provided in an exhaust passage of said internal combustion engine, for purifying exhaust gas passing through said exhaust passage;   a bypass passage branching from said exhaust passage on an upstream side of said storage-reduction type NOx catalyst and merging into said exhaust passage on a downstream side of said storage-reduction type NOx catalyst, for causing said exhaust gas passing through said exhaust passage to bypass said storage-reduction type NOx catalyst;   reducer supply device for supplying a reducer to said exhaust gas passing through said exhaust passage on the upstream side of said storage-reduction type NOx catalyst; and   regeneration device for performing a regeneration treatment for regenerating purification performance of said storage-reduction type NOx catalyst, when an amount of NOx accumulated in said storage-reduction type NOx catalyst becomes equal to or larger than a predetermined value, said regeneration treatment being a treatment for regenerating the purification performance of said storage-reduction type NOx catalyst by supplying said reducer from said reducer supply device to said exhaust gas to introduce said reducer into said storage-reduction type NOx catalyst; and   regeneration exhaust flow rate control device for executing regeneration exhaust flow rate control when said regeneration device performs said regeneration treatment, said regeneration exhaust flow rate control being a control operation in which, of said exhaust gas passing through said exhaust passage, an amount of exhaust gas passing through said bypass passage is increased and an amount of exhaust gas passing through said storage-reduction type NOx catalyst is reduced, and   an oxidation catalyst that has an oxidation ability and is provided in said exhaust passage on a downstream side of a merging portion of said exhaust passage and said bypass passage, wherein   whether said regeneration exhaust flow rate control is executed or not is determined based on the following three values which are obtained when said regeneration exhaust flow rate control is executed during execution of said regeneration treatment: a decrease in an amount of NOx discharged from said storage-reduction type NOx catalyst due to an increase in the rate of purification by said storage-reduction type NOx catalyst; an increase in an amount of NOx discharged from said bypass passage due to an increase in said exhaust gas passing through said bypass passage; and an increase in an amount of NOx through oxidation of NH3 discharged from said storage-reduction type NOx catalyst by said oxidation catalyst.   
   
   
       10 . The exhaust purification system for an internal combustion engine according to  claim 9 , further comprising
 said exhaust purification system further comprises NOx amount determining device for determining the magnitude relation between the following two values which are obtained when said regeneration exhaust flow rate control is executed during execution of said regeneration treatment: the decrease in the amount of NOx discharged from said storage-reduction type NOx catalyst due to the increase in the rate of purification by said storage-reduction type NOx catalyst; and a sum of the increase in the amount of NOx discharged from said bypass passage due to the increase in said exhaust gas passing through said bypass passage and the increase in the amount of NOx through oxidation of NH3 discharged from said storage-reduction type NOx catalyst by said oxidation catalyst, wherein   said regeneration exhaust flow rate control is executed when said NOx amount determining device determines that the decrease in the amount of NOx discharged from said storage-reduction type NOx catalyst due to the increase in the rate of purification by said storage-reduction type NOx catalyst is larger than the sum of the increase in the amount of NOx discharged from said bypass passage due to the increase in said exhaust gas passing through said bypass passage and the increase in the amount of NOx through oxidation of NH3 discharged from said storage-reduction type NOx catalyst by said oxidation catalyst.   
   
   
       11 . The exhaust purification system for an internal combustion engine according to  claim 10 , wherein said NOx amount determination device determines the magnitude relation between the following two values which are obtained in a period from start of supplying said reducer in said regeneration treatment to start of supplying said reducer in a next regeneration treatment: the decrease in the amount of NOx discharged from said storage-reduction type NOx catalyst due to the increase in the rate of purification by said storage-reduction type NOx catalyst; and the sum of the increase in the amount of NOx discharged from said bypass passage due to the increase in said exhaust gas passing through said bypass passage and the increase in the amount of NOx through oxidation of NH3 discharged from said storage-reduction type NOx catalyst by said oxidation catalyst.