Patent ID: 7121086

Claim:
An exhaust gas purification device for a vehicle engine comprising: a nitrogen oxide trapping catalyst which traps nitrogen oxides in exhaust gas, the engine comprising a mechanism which removes sulphur oxides which have poisoned the nitrogen oxide trapping catalyst from the nitrogen oxide trapping catalyst; a sensor which detects a running condition of the vehicle; and a programmable controller programmed to: calculate a sulphur oxide poisoning amount of the nitrogen oxide trapping catalyst from the running condition of the vehicle; start operation of the mechanism when the sulphur oxide poisoning amount reaches a predetermined amount; set a decrease amount per unit time of the sulphur oxide poisoning amount during operation of the mechanism as a parameter based on the sulphur oxide poisoning amount; calculate the sulphur oxide poisoning amount during operation of the mechanism based on an integral value of the decrease amount per unit time; after operation of the mechanism has started, stop operation of the mechanism when the sulphur oxide poisoning amount has decreased to a predetermined desulphating completion equivalent value; wherein the controller is further programmed to set the decrease amount per unit time of the sulphur oxide poisoning amount during operation of the mechanism by the following equation (A): RSMILE=SOXMILE −1 ·RSMILE 1 +RSMILE 2 where RSMILE=the decrease amount per unit time, SOXMILE −1 =the sulphur oxide poisoning amount SOXMILE one unit time ago, RSMILE 1 =a coefficient which becomes smaller as an elapsed time from start-up of the mechanism increases, and RSMILE 2 =a coefficient which becomes larger as the SOXMILE −1 becomes larger.