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

Abstract

An exhaust gas control apparatus for an internal combustion engine includes a NOx adsorbent that is provided in an exhaust passage of an internal combustion engine, and that adsorbs nitrogen monoxide; an active oxygen supply device that supplies active oxygen to an area upstream of the NOx adsorbent; and a control portion that performs a first control that does not cause the active oxygen supply device to supply the active oxygen while exhaust gas flows to the NOx adsorbent at a time of cold start of the internal combustion engine, whereby the nitrogen monoxide is adsorbed by the NOx adsorbent, wherein the control portion performs a second control that causes the active oxygen supply device to supply the active oxygen after the first control is finished, whereby the nitrogen monoxide adsorbed by the NOx adsorbent is converted to a nitrate or a nitrate ion on the NOx adsorbent.

1 . An exhaust gas control apparatus for an internal combustion engine, comprising:
 a NOx adsorbent that is provided in an exhaust passage of an internal combustion engine, and that adsorbs nitrogen monoxide;   an active oxygen supply device that supplies active oxygen to an area upstream of the NOx adsorbent; and   a control portion that performs a first control that does not cause the active oxygen supply device to supply the active oxygen while exhaust gas flows to the NOx adsorbent at a time of cold start of the internal combustion engine, whereby the nitrogen monoxide is adsorbed by the NOx adsorbent, wherein the control portion performs a second control that causes the active oxygen supply device to supply the active oxygen after the first control is finished, whereby the nitrogen monoxide adsorbed by the NOx adsorbent is converted to a nitrate or a nitrate ion on the NOx adsorbent.   
     
     
         2 . The exhaust gas control apparatus according to  claim 1 , wherein
 the first control is finished when an elapsed time after the start of the engine reaches a predetermined time.   
     
     
         3 . The exhaust gas control apparatus according to  claim 1 , wherein
 the first control is finished when a temperature of the NOx adsorbent reaches a predetermined temperature.   
     
     
         4 . The exhaust gas control apparatus according to  claim 3 , wherein
 the predetermined temperature is equal to or lower than 100° C.   
     
     
         5 . The exhaust gas control apparatus according to  claim 1 , wherein
 the control portion calculates an amount of the nitrogen monoxide adsorbed by the NOx adsorbent while performing the first control, and performs the second control when the calculated amount of the nitrogen monoxide is equal to or larger than a predetermined amount.   
     
     
         6 . The exhaust gas control apparatus according to  claim 1 , wherein
 the control portion starts the second control before a temperature of the NOx adsorbent reaches a desorption temperature at which the nitrogen monoxide adsorbed by the NOx adsorbent is desorbed from the NOx adsorbent.   
     
     
         7 . The exhaust gas control apparatus according to  claim 1 , wherein
 the control portion calculates an amount of the nitrogen monoxide adsorbed by the NOx adsorbent while performing the first control; and   the control portion controls an amount of the supplied active oxygen during the second control, based on the calculated amount of the nitrogen monoxide.   
     
     
         8 . The exhaust gas control apparatus according to  claim 1 , wherein
 when the NOx adsorbent adsorbs NOx, a main component of the NOx is the nitrogen monoxide.   
     
     
         9 . The exhaust gas control apparatus according to  claim 1 , wherein
 when NOx is desorbed from the NOx adsorbent, a main component of the NOx is nitrogen dioxide.   
     
     
         10 . The exhaust gas control apparatus according to  claim 1 , further comprising
 a NOx reduction catalyst that reduces NOx desorbed from the NOx adsorbent.   
     
     
         11 . The exhaust gas control apparatus according to  claim 10 , further comprising
 a temperature-increasing portion that performs a temperature-increasing control to increase a temperature of the NOx reduction catalyst after the second control is started.   
     
     
         12 . The exhaust gas control apparatus according to  claim 10 , wherein
 the NOx reduction catalyst is disposed downstream of the NOx adsorbent.   
     
     
         13 . The exhaust gas control apparatus according to  claim 10 , wherein
 the NOx reduction catalyst is provided integrally with the NOx adsorbent.   
     
     
         14 . The exhaust gas control apparatus according to  claim 13 , wherein
 the NOx reduction catalyst and the NOx adsorbent are provided in a manner such that the NOx reduction catalyst is mixed with the NOx adsorbent.   
     
     
         15 . The exhaust gas control apparatus according to  claim 13 , wherein
 a NOx reduction catalyst layer, which is a layer of the NOx reduction catalyst, and a NOx adsorbent layer, which is a layer of the NOx adsorbent, are stacked.   
     
     
         16 . The exhaust gas control apparatus according to  claim 15 , wherein
 the NOx adsorbent layer is provided on an upper surface of the NOx reduction catalyst layer.   
     
     
         17 . The exhaust gas control apparatus according to  claim 16 , further comprising
 an HC adsorbent layer is provided on an upper surface of the NOx adsorbent layer, and the HC adsorbent layer has HC adsorption ability higher than that of the NOx adsorbent layer.   
     
     
         18 . The exhaust gas control apparatus according to  claim 1 , wherein
 the NOx adsorbent is made of zeolite.   
     
     
         19 . The exhaust gas control apparatus according to  claim 18 , wherein
 the control portion starts the second control before a temperature of the zeolite reaches 70° C.   
     
     
         20 . A method of controlling an exhaust gas control apparatus for an internal combustion engine, which includes a NOx adsorbent that is provided in an exhaust passage of an internal combustion engine, and that adsorbs nitrogen monoxide; and an active oxygen supply device that supplies active oxygen to an area upstream of the NOx adsorbent, the method comprising:
 performing a first control that does not cause the active oxygen supply device to supply the active oxygen while exhaust gas flows to the NOx adsorbent at a time of cold start of the internal combustion engine, whereby the nitrogen monoxide is adsorbed by the NOx adsorbent; and   performing a second control that causes the active oxygen supply device to supply the active oxygen after the first control is finished, whereby the nitrogen monoxide adsorbed by the NOx adsorbent is converted to a nitrate or a nitrate ion on the NOx adsorbent.