Patent ID: 6698185
Filing Date: 2004-03-02
Classification: B01D,F01N,F02D,F02M,Y02T

Abstract:
An exhaust gas purification apparatus for an internal combustion engine, comprising:a NOx trap catalyst disposed in an exhaust passage of the internal combustion engine, the NOx trap catalyst being capable of trapping thereon NOx in exhaust gas when an air-fuel ratio of the exhaust gas is lean and reductively purifying the trapped NOx when the air-fuel ratio of the exhaust gas is rich; and a control unit configured to: decide on a purification timing at which NOx trapped on the NOx trap catalyst is purified; determine a space velocity of the exhaust gas; at the purification timing, select either one of a first air-fuel ratio control mode for controlling the air-fuel ratio of the exhaust gas to a rich air-fuel ratio with no need to decrease a concentration of oxygen in the exhaust gas and a second air-fuel ratio control mode for not only controlling the air-fuel ratio of the exhaust gas to a rich air-fuel ratio but also making the concentration of oxygen in the exhaust gas lower than that of the first air-fuel ratio control mode, according to the determined space velocity; and control the air-fuel ratio of the exhaust gas in the selected air-fuel ratio control mode, thereby purifying NOx trapped on the NOx trap catalyst.