Patent ID: 7997067
Filing Date: 2011-08-16
Classification: F01N,F02B,F02D,Y02T

Abstract:
1. An exhaust emission control device for an internal combustion engine, for purifying exhaust gases emitted from the engine into an exhaust system, comprising: a catalyst that is disposed in the exhaust system and has a function of purifying NOx under a reducing atmosphere; a NOx catalyst that is disposed at a location downstream of said catalyst in the exhaust system, for trapping NOx contained in exhaust gases under an oxidizing atmosphere, and reducing the trapped NOx under the reducing atmosphere, thereby purifying the trapped NOx; oxygen concentration-detecting means that is disposed between said catalyst and said NOx catalyst, for detecting a concentration of oxygen in the exhaust gases; NOx emission amount-estimating means for estimating an amount of NOx contained in the exhaust gases emitted from the engine, as a NOx emission amount; purification performance parameter-calculating means for calculating a purification performance parameter indicative of a NOx purification performance of said catalyst; NOx emission amount-correcting means for correcting the estimated NOx emission amount according to the calculated purification performance parameter; trapped NOx amount-calculating means for calculating an amount of NOx trapped by said NOx catalyst as a trapped NOx amount based on the corrected NOx emission amount; trapped NOx amount cumulative value-calculating means for calculating a total amount of NOx trapped by said NOx catalyst as a trapped NOx amount cumulative value, based on the calculated trapped NOx amount; NOx reduction control means for supplying a reducing agent to an upstream side of said catalyst when the calculated trapped NOx amount cumulative value is equal to or greater than a trapped NOx amount reference value, for controlling the exhaust gases flowing into said NOx catalyst by NOx reduction control such that the exhaust gases are under the reducing atmosphere, thereby causing said NOx catalyst to carry out an operation for reducing Nox; reducing agent amount reference value-setting means for setting a reducing agent amount reference value corresponding to the amount of reducing agent required for reduction of the NOx trapped in said NOx catalyst; reducing agent amount-calculating means for calculating an amount of reducing agent supplied to said NOx catalyst during the NOx reduction control, based on the detected oxygen concentration; reducing agent amount cumulative value-calculating means for calculating a total amount of reducing agent actually supplied to said NOx catalyst by the NOx reduction control as a reducing agent amount cumulative value, based on the calculated reducing agent amount; and NOx reduction control-terminating means for terminating the NOx reduction control when the calculated reducing agent amount cumulative value is greater than the set reducing agent amount reference value.