Exhaust purification device of compression ignition type internal combustion engine

An exhaust purification device for a compression ignition type internal combustion engine having an SOx trap catalyst arranged in an engine exhaust passage and capable of trapping SOx contained in exhaust gas and having an NOx storing catalyst arranged in the exhaust passage downstream of the SOx trap catalyst, the NOx storing catalyst storing NOx contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NOx when the air-fuel ratio of the exhaust gas flowing in becomes the stoichiometric air-fuel ratio or rich, wherein said SOx trap catalyst traps SOx contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst is lean, has the property that the trapped SOx gradually diffuses inside the SOx trap catalyst when the temperature of the SOx trap catalyst rises under a lean air-fuel ratio of the exhaust gas, and has the property of releasing the trapped SOx when the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst becomes rich if the temperature of the SOx trap catalyst is the SOx release temperature or more;

• said device is provided with air-fuel ratio control means continuing to maintain the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst lean, without allowing it to become rich, during engine operation and estimating means for estimating an SOx trap rate showing a ratio of SOx trapped in the SOx trap catalyst in the SOx contained in the exhaust gas;
• and said device makes the temperature of the SOx trap catalyst rise under a lean air-fuel ratio of the exhaust gas when the SOx trap rate falls below a predetermined rate so as to thereby restore the SOx trap rate.