Exhaust gas purifying apparatus for internal combustion engines

An exhaust gas purifying apparatus for internal combustion engines, in which a NOx adsorbing/reducing catalyst device for adsorbing NOx and decreasing an oxygen concentration to feed a reducing agent to release and reduce NOx when exhaust gases are lean in air-fuel ratio is provided in an exhaust pipe of an internal combustion engine, the apparatus comprising:

• a first NOx adsorbing catalyst;
• a second NOx adsorbing catalyst provided in parallel to the first NOx adsorbing catalyst and having a small adsorbing capacity as compared with that of the first NOx adsorbing catalyst;
• exhaust gas flow passage switchover means for switching an exhaust gas flow between the first NOx adsorbing catalyst and the second NOx adsorbing catalyst;
• first NOx releasing and reducing means for causing a gas containing a reducing agent to flow toward the first NOx adsorbing catalyst to decrease an oxygen concentration and releasing and reducing NOx while exhaust gases flow toward the second NOx adsorbing catalyst;
• second NOx releasing and reducing means for causing a gas containing a reducing agent to flow toward the second NOx adsorbing catalyst to decrease an oxygen concentration and releasing and reducing NOx while exhaust gases flow toward the first NOx adsorbing catalyst;
• and
• NOx releasing/reducing control means, by which switchover of the exhaust gas flow passage caused by the exhaust gas flow passage switchover means, and NOx releasing/reducing operations caused by the first and second NOx releasing and reducing means are performed at predetermined time intervals.

An exhaust gas purifying apparatus for internal combustion engines, in which a NOx adsorbing/reducing catalyst device for adsorbing NOx and decreasing an oxygen concentration to feed a reducing agent to release and reduce NOx when exhaust gases are lean in air-fuel ratio is provided in an exhaust pipe of an internal combustion engine, the apparatus comprising:

• a first NOx adsorbing catalyst;
• a second NOx adsorbing catalyst provided in parallel to the first NOx adsorbing catalyst and having a small adsorbing capacity as compared with that of the first NOx adsorbing catalyst;
• exhaust gas flow passage switchover means for switching an exhaust gas flow between the first NOx adsorbing catalyst and the second NOx adsorbing catalyst;
• first NOx releasing and reducing means for causing a gas containing a reducing agent to flow toward the first NOx adsorbing catalyst to decrease an oxygen concentration and releasing and reducing NOx while exhaust gases flow toward the second NOx adsorbing catalyst;
• second NOx releasing and reducing means for causing a gas containing a reducing agent to flow toward the second NOx adsorbing catalyst to decrease an oxygen concentration and releasing and reducing NOx while exhaust gases flow toward the first NOx adsorbing catalyst;
• NOx accumulation checking means for checking a NOx accumulation in the first NOx adsorbing catalyst;
• and
• exhaust gas flow passage switchover/control means for permitting exhaust gases to flow toward the first NOx adsorbing catalyst when the engine is normally operated, and permitting exhaust gases to flow toward the second NOx adsorbing catalyst when a NOx accumulation in the first NOx adsorbing catalyst exceeds a predetermined value.