Patent ID: 7204081

Claim:
An exhaust gas purifying apparatus for an internal combustion engine comprising: a NOx selective reduction catalyst disposed in an exhaust passage of said internal combustion engine for purifying NOx in exhaust gases flowing through said exhaust passage under the existence of a reducing agent; a NOx detector disposed in said exhaust passage at a location downstream of said NOx selective reduction catalyst for detecting a NOx concentration in exhaust gases; a reducing agent supply unit for supplying the reducing agent to said NOx selective reduction catalyst; exhaust gas volume detecting means for detecting an exhaust gas volume of said internal combustion engine; basic supply amount determining means for determining a basic supply amount of the reducing agent to said NOx selective reduction catalyst in accordance with the detected exhaust gas volume; estimated value calculating means for calculating an estimated value of a detected value detected by said NOx detector on the basis of a model indicative of a relationship between the estimated value and a correction coefficient for correcting the basic supply amount of the reducing agent; and supply amount determining means for determining an amount of the reducing agent supplied to said NOx selective reduction catalyst by said reducing agent supply unit by determining the correction coefficient on the basis of said model such that the estimated value reaches an extreme value.