Patent ID: 7572637

Claim:
A method for controlling an exhaust emission control device with selective reduction catalyst incorporated in an exhaust pipe, a reducing agent being added upstream of the catalyst by reducing agent addition means so as to reduce and purify NO x , which comprises the steps of detecting an exhaust temperature upstream of the catalyst, using a first-order lag response model corresponding to the detected temperature to estimate a temperature of each of cells into which the catalyst is minutely divided, summing up cell volumes for each of temperature zones on the basis of the estimated temperatures for the cells, dividing the cell volume summation for each of the temperature zones by a whole volume of the catalyst to determine temperature distribution volume ratio for said temperature zone, multiplying the determined temperature distribution volume ratio for each of the temperature zones by a reference injection amount of the reducing agent determined for said temperature zone in consideration of a current engine operation status on the assumption that catalyst temperatures are all within said temperature zone, and summing up the calculated values for the temperature zones into a directive injection amount of the reducing agent to the reducing agent addition means, wherein, upon estimation of catalyst temperature for each of cells, temperature correction is effected in consideration of endotherm in cooling action through addition of the reducing agent and exotherm due to NO x purification reaction.