Patent ID: 8056323

Claim:
A method of controlling an exhaust gas purification system provided with an exhaust gas purification device in an exhaust passage of an internal combustion engine, comprising: supplying a reductant into the exhaust gas flowing into the exhaust gas purification device while adjusting a supply amount and a supply period of the reductant; detecting a temperature of the exhaust gas; detecting an oxygen concentration, a CO concentration, and an HC concentration in the exhaust gas flowing into the exhaust gas purification device; controlling the reductant being supplied, when the detected temperature is a prescribed judgment temperature or more; using two or more of the detected oxygen concentration, the CO concentration, and the HC concentration as a control parameter when controlling the supply amount of the reductant; and setting the prescribed judgment temperature from the detected oxygen concentration, the CO concentration, and the HC concentration, based on a relationship of the oxygen concentration, the CO concentration, and the HC concentration and the prescribed judgment temperature when supplying the reductant.