Patent ID: 6370870
Filing Date: 2002-04-16
Classification: B01D,F01N,F02D,Y02T

Abstract:
A device for purifying exhaust gas containing nitrogen oxides in an exhaust passage of a combustion device, comprising:a nitrogen oxide absorbing material which absorbs nitrogen oxide when a reduction component concentration of the exhaust gas is lower than a predetermined concentration, and discharges nitrogen oxide when the reduction component concentration of the exhaust gas is higher than the predetermined concentration, a catalyst which promotes reduction of discharged nitrogen oxide by a reduction component in the exhaust gas, means for decreasing the reduction component concentration of the exhaust gas, means for increasing the reduction component concentration of the exhaust gas, and a microprocessor programmed to: determine whether the nitrogen oxide should be discharged from the nitrogen oxide absorbing material or the catalyst, control the decreasing means for a first predetermined time period when it is determined that the nitrogen oxide should be discharged from the nitrogen oxide absorbing material or the catalyst, so that the reduction component concentration of the exhaust gas is less than a first predetermined concentration of 100 ppm, control the increasing means so that the reduction component concentration of the exhaust gas is higher than a second predetermined concentration for a second predetermined time period after the first predetermined time period has elapsed, and maintain the amount of oxygen in the exhaust gas at a level of 4.5% or greater.