Patent ID: 8745972

Claim:
An exhaust purification system of an internal combustion engine which arranges in an engine exhaust passage an NO X catalyst device which stores NO X which is contained in exhaust gas when an air-fuel ratio of the inflowing exhaust gas is lean and which releases the stored NO X when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich and which uses SO X release control which raises a temperature of the NO X catalyst device to an SO X releasable temperature when an SO X amount which is stored in the NO X catalyst device exceeds a predetermined allowable amount and which makes the air-fuel ratio of the exhaust gas which flows into the NO X catalyst device a stoichiometric air-fuel ratio or rich so as to make the stored SO X be released, an exhaust purification system of an internal combustion engine characterized in that the NO X catalyst device has a residual SO X storage amount which is dependent on the temperature of the NO X catalyst device when performing SO X release control and finally remains even if performing SO X release control, the system uses the residual SO X storage amount of the current SO X release control as the basis to calculate the SO X release speed at each timing in the current SO X release control, the system uses the SO X release speed which was calculated at each timing of the SO X release control as the basis to calculate a cumulative SO X release amount which is released from the start of SO X release control to the current timing and corrects the calculated SO X release speed at the current timing based on a ratio of a first radius and a second radius where when a releasable SO X amount obtained by subtracting from an SO X storage amount when starting SO X release control said residual SO X storage amount is deemed to correspond to an area of a circle of the first radius, a radius of a circle of an area corresponding to said cumulative SO X release amount is calculated as the second radius.