Exhaust emission control system of an internal combustion engine

Abstract

An exhaust emission control system of an internal combustion engine desorbs SO x by reversing a flow of an exhaust gas through an NO x storage-reduction catalyst, of which a structure is simplified as follows. A first exhaust pipe connected to an engine is connected to a first port of an emission switching valve having four ports. A second exhaust pipe 10 , through which the exhaust gas is discharged into the atmospheric air, is connected to a second port, a third exhaust pipe connected to an inlet of a catalytic converter is connected to a third port. A fourth exhaust pipe connected to an outlet of the catalytic converter 30 is connected to a fourth port. When the emission switching valve is set in a forward flow position, the first exhaust pipe is connected to the third exhaust pipe, and the second exhaust pipe is connected to the fourth exhaust pipe, whereby the exhaust gas flows toward the outlet from the inlet within the catalytic converter. When the emission switching valve is set in a backward flow position, the first exhaust pipe is connected to the fourth exhaust pipe, and the second exhaust pipe is connected to the third exhaust pipe, whereby the exhaust gas flows toward the inlet from the outlet within the catalytic converter.

1. An exhaust emission control system of an internal combustion engine, comprising:
 exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    wherein said flow direction switching means can be switched over to a first position for permitting the exhaust gas to flow in a direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port.    
     
     
       2. An exhaust emission control system of an internal combustion engine according to  claim 1 , wherein said exhaust gas purifying means is an NO x  storage-reduction catalyst for absorbing NO x  when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO x  absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases. 
     
     
       3. An exhaust emission control system of an internal combustion engine according to  claim 2 ,  An exhaust emission control system of an internal combustion engine, comprising:
   exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    
   flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    
   a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    
   a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    
   a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    
   a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    
   wherein said flow direction switching means is switched over to a first position for permitting the exhaust gas to flow in a first direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port,    
   wherein said exhaust gas purifying means is an NO   x    storage - reduction catalyst for absorbing NO   x    when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO   x    absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases,   
 wherein when in a SO x  desorbing process of desorbing SO x  absorbed to said NO x  storage-reduction catalyst from said NO x  storage-reduction catalyst, said flow direction switching means is switched over to the first position and the second position, thereby making a flow direction of the exhaust gas flowing through said NO x  storage-reduction catalyst opposite to the direction when absorbing NO x .  
 
     
     
       4. An exhaust emission control system of an internal combustion engine according to  claim 3 , wherein said exhaust gas purifying means composed of said NO x  storage-reduction catalyst is such that, a NO x    storage - reduction catalyst disposed on inlet side in the flow direction of the exhaust gas when absorbing NO   x  exhibits higher SO x  absorbing power than that of an NO x  storage-reduction catalyst disposed on an outlet side in the flow direction of the exhaust gas when absorbing NO x . 
     
     
       5. An exhaust emission control system of an internal combustion engine according to  claim 3 , further comprising heating means for heating a portion close to an inlet of said NO x  storage-reduction catalyst in the flow direction of the exhaust gas when said NO x  storage-reduction catalyst absorbs NO x . 
     
     
       6. An exhaust emission control system of an internal combustion engine according to  claim 3 , wherein the switch-over of said flow direction switching means when in the SO x  desorbing process is executed when an exhaust gas temperature or a catalytic temperature of said NO x  storage-reduction catalyst rises. 
     
     
       7. An exhaust emission control system of an internal combustion engine according to  claim 3 , wherein lengths of said third exhaust passageway and of said fourth exhaust passageway are set so that a distance from said internal combustion engine to said NO x  storage-reduction catalyst is shorter when in the SO x    desorbing process than  when absorbing NO x  than when in the SO x  desorbing process  by switching over said flow direction switching means to the first position or the second position. 
     
     
       8. An exhaust emission control system of an internal combustion engine according to  claim 2 , wherein a sweeper is provided at said second exhaust passageway. 
     
     
       9. An exhaust emission control system of an internal combustion engine according to  claim 8 ,  An exhaust emission control system of an internal combustion engine, comprising:
   exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    
   flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    
   a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    
   a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    
   a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    
   a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    
   wherein said flow direction switching means is switched over to a first position for permitting the exhaust gas to flow in a first direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port,    
   wherein said exhaust gas purifying means is an NO   x    storage - reduction catalyst for absorbing NO   x    when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO   x    absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases,    
   wherein a sweeper is provided at said second exhaust passageway, and   
 wherein said sweeper is a selective reduction type NO x  catalyst for reducing or dissolving NO x  under an existence of hydro carbon in an over-oxygen atmosphere.  
 
     
     
       10. An exhaust emission control system of an internal combustion engine according to  claim 8 ,  An exhaust emission control system of an internal combustion engine, comprising:
   exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    
   flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    
   a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    
   a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    
   a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    
   a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    
   wherein said flow direction switching means is switched over to a first position for permitting the exhaust gas to flow in a first direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port,    
   wherein said exhaust gas purifying means is an NO   x    storage - reduction catalyst for absorbing NO   x    when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO   x    absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases,    
   wherein a sweeper is provided at said second exhaust passageway,   
 wherein another catalyst is provided in said first exhaust passageway, and  
 said flow direction switching means is switched over to the third position for connecting the first port to the second port for an initial predetermined time during the SO x  desorbing process and, after the predetermined time has elapsed, switched over to make the flow direction of the exhaust gas flowing though said NO x  storage-reduction catalyst opposite to the direction when absorbing NO x .  
 
     
     
       11. An exhaust emission control system of an internal combustion engine according to  claim 8 ,  An exhaust emission control system of an internal combustion engine, comprising:
   exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    
   flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    
   a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    
   a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    
   a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    
   a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    
   wherein said flow direction switching means is switched over to a first position for permitting the exhaust gas to flow in a first direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port,    
   wherein said exhaust gas purifying means is an NO   x    storage - reduction catalyst for absorbing NO   x    when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO   x    absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases, and    
   wherein a sweeper is provided at said second exhaust passageway,   
 wherein said NO x  storage-reduction catalyst and said sweeper are integrated into one unit so that the exhaust gas can not  cannot flow therebetween and the heat can be  is transmitted therebetween.  
 
     
     
       12. An exhaust emission control system of an internal combustion engine according to  claim 2 ,  An exhaust emission control system of an internal combustion engine, comprising:
   exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    
   flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    
   a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    
   a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    
   a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    
   a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    
   wherein said flow direction switching means is switched over to a first position for permitting the exhaust gas to flow in a first direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port,    
   wherein said exhaust gas purifying means is an NO   x    storage - reduction catalyst for absorbing NO   x    when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO   x    absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases,   
 wherein said first exhaust passageway is provided with a SO x  absorbing agent for absorbing SO x  when the air/fuel ratio of the inflow exhaust gas is lean, and desorbs SO x  absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases, and  
 said flow direction switching means can be  is switched over to the third position in which to connect the first port to the second port, and is selectively switched over to the third position when said internal combustion engine comes to a continuous stoichiometric ratio operation.  
 
     
     
       13. An exhaust emission control system of an internal combustion engine according to  claim 12 , wherein said SO x  absorbing agent and said NO x  storage-reduction catalyst are concentrically disposed. 
     
     
       14. An exhaust emission control system of an internal combustion engine according to  claim 2 ,  An exhaust emission control system of an internal combustion engine, comprising:
   exhaust gas purifying means provided in an exhaust passageway of said internal combustion engine;    
   flow direction switching means including four ports and provided at an exhaust passageway disposed more upstream than said exhaust gas purifying means;    
   a first exhaust passageway connected to said internal combustion engine and further to a first port of said flow direction switching means;    
   a second exhaust passageway communicating with the atmospheric air and further to a second port of said flow direction switching means;    
   a third exhaust passageway connected to one side of said exhaust gas purifying means and further to a third port of said flow direction switching means; and    
   a fourth exhaust passageway connected to the other side of said exhaust gas purifying means and further to a fourth port of said flow direction switching means,    
   wherein said flow direction switching means is switched over to a first position for permitting the exhaust gas to flow in a first direction through said exhaust gas purifying means by connecting the first port to the third port and connecting the second port to the fourth port, to a second position for permitting the exhaust gas to flow in a direction opposite to the first direction through said exhaust gas purifying means by connecting the first port to the fourth port and connecting the second port to the third port, and to a third position in which the first port is connectable to the second port,    
   wherein said exhaust gas purifying means is an NO   x    storage - reduction catalyst for absorbing NO   x    when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO   x    absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases,   
 wherein said first exhaust passageway is provided with a three-way catalyst exhibiting SO x  absorbing power, and  
 said flow direction switching means can be  is switched over to the third position in which the first port is connectable to the second port, and is selectively switched over to the third position when said internal combustion engine comes to a continuous stoichiometric ratio operation.  
 
     
     
       15. An exhaust emission control system of an internal combustion engine according to  claim 1 , wherein lengths of said third exhaust passageway and of said fourth exhaust passageway are set so that a distance from said internal combustion engine to said exhaust gas purifying means becomes different by switching over said flow direction switching means to the first position or the second position. 
     
     
       16. An exhaust emission control system of an internal combustion engine according to  claim 13 , wherein the switch-over of said flow direction switching means is executed based on an exhaust gas temperature or a temperature of said exhaust gas purifying means. 
     
     
       17. An exhaust emission control system of an internal combustion engine according to  claim 16 , wherein said exhaust gas purifying means is an NO x  storage-reduction catalyst for absorbing NO x  when an air/fuel ratio of the inflow exhaust gas is lean, and desorbing NO x  absorbed thereto when a concentration of oxygen in the inflow exhaust gas decreases. 
     
     
       18. An exhaust emission control system of an internal combustion engine according to  claim 17 , wherein said flow direction switching means is switched over by selecting a flow path having a shorter distance from said internal combustion engine to said NO x  storage-reduction catalyst when in the SO x  desorbing process of desorbing SO x  desorbed to said NO x  storage-reduction catalyst from said NO x  storage-reduction catalyst. 
     
     
       19. An exhaust emission control system of an internal combustion engine according to  claim 17 , wherein said flow direction switching means is switched over by selecting a flow path having a longer distance from said internal combustion engine to said NO x  storage-reduction catalyst when said NO x  storage-reduction catalyst absorbs NO x  and when the exhaust gas temperature or the catalytic temperature of said NO x  storage-reduction catalyst is over a predetermined temperature, and selecting a flow path having a shorter distance from said internal combustion engine to said NO x  storage-reduction catalyst when said NO x  storage-reduction catalyst absorbs NO x  and when the exhaust gas temperature or the catalytic temperature is lower than the predetermined temperature. 
     
     
       20. An exhaust emission control system of an internal combustion engine according to  claim 17 , wherein a cooling device for cooling the exhaust gas is provided at either said third exhaust passageway or said fourth exhaust passageway, which increases the distance from said internal combustion engine to said NO x  storage-reduction catalyst. 
     
     
       21. An exhaust emission control system of an internal combustion engine according to  claim 17 , wherein a sweeper is provided at said second exhaust passageway, and said flow direction switching means can be  is switched over to a third position in which the first port can be connected to the second port,
 when the exhaust gas temperature or the catalytic temperature of said NO x  storage-reduction catalyst is higher than a NO x  absorbable temperature range of said NO x  storage-reduction catalyst, said flow direction switching means is selectively switched over to the third position.  
 
     
     
       22. An exhaust emission control system of an internal combustion engine according to  claim 1 , wherein said exhaust gas purifying means is a catalyst,
 any one of said third exhaust passageway and of said fourth exhaust passageway is provided with an HC adsorbing agent for adsorbing hydro carbon, and    said flow direction switching means is switched over to select a flow path on which said catalyst is positioned more upstream than said HC adsorbing agent when the temperature of the exhaust gas or of said HC adsorbing agent is in a temperature region where said HC adsorbing agent adsorbs the hydro carbon, and to select a flow path on which said HC adsorbing agent is positioned more upstream than said catalyst when the temperature of the exhaust gas or of said HC adsorbing agent is in a temperature region where said HC adsorbing agent desorbs the hydro carbon.