Patent ID: 6519933
Filing Date: 2003-02-18
Classification: F01L,F01N,F02D,Y02T

Abstract:
An apparatus, comprising:an internal combustion engine of a lean-burn type capable of burning an oxygen-rich air-fuel mixture, the internal combustion engine including an intake valve and an exhaust valve for each of a plurality of cylinders thereof; an NOx catalyst disposed in an exhaust passage of the internal combustion engine so as to remove nitrogen oxides contained in an exhaust gas emitted from the engine, the NOx catalyst comprising an occlusion-reduction type NOx catalyst that occludes nitrogen oxides contained in the exhaust gas when the exhaust gas to which the NOx catalyst is exposed has a lean air/fuel ratio, and releases and reduces the occluded nitrogen oxides when the exhaust gas to which the NOx catalyst is exposed has a stoichiometric or rich air/fuel ratio; a variable valve control system capable of changing at least one of the opening and closing timing and a lift of at least one of the intake valve and the exhaust valve for said each cylinder of the engine; and a controller configured to control the variable valve control system to thereby control the exhaust gas to which the NOx catalyst is exposed, such that the controlled exhaust gas is suitable for removing a selected gaseous component from the NOx catalyst when the selected gaseous component should be removed, and the controlled exhaust gas contains a reducing agent for reducing the nitrogen oxides occluded in the occlusion-reduction type NOx catalyst, when the occluded nitrogen oxides should be reduced, wherein the controller controls the variable valve control system so that the exhaust gas containing the reducing agent is emitted from only one cylinder selected from the plurality of cylinders of the engine.