Patent ID: 7618605

Claim:
An exhaust emission control device for an internal combustion engine, including: an upstream catalyst that is disposed in an exhaust passage of the engine, and has an oxidation function as well as purifies exhaust gases, a NOx catalyst that is disposed in the exhaust passage at a location downstream of said upstream catalyst, for trapping NOx contained in an oxidizing atmosphere of exhaust gases, and reducing the trapped NOx by being supplied with a reducing atmosphere of exhaust gases containing reducing agent to thereby purify the trapped NOx, and reduction control means for carrying out reduction control in which the reducing agent is supplied to an upstream side of said upstream catalyst to thereby control the exhaust gases flowing into said NOx catalyst to the reducing atmosphere so as to cause said NOx catalyst to carry out a NOx reducing operation, wherein said reduction control means comprises: reducing agent consumption amount-calculating means for calculating an amount of the reducing agent in the exhaust gases consumed by said upstream catalyst during execution of the reduction control, as a reducing agent consumption amount; cumulative reducing agent amount-calculating means for calculating a total amount of the reducing agent supplied to said NOx catalyst during the execution of the reduction control, as a cumulative reducing agent amount, according to the calculated reducing agent consumption amount; and reduction control-terminating means for terminating the reduction control when the calculated cumulative reducing agent amount exceeds a predetermined value during the execution of the reduction control.