EXHAUST EMISSION CONTROL DEVICE AND EXHAUST EMISSION CONTROL METHOD FOR INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To provide an exhaust emission control device and an exhaust emission control method for an internal combustion engine, which improves durability of a catalyst and fuel economy, and accurately judges timing of replacement due to thermal degradation of a catalyst by accurately detecting degradation rate of the catalyst and exactly making air fuel ratio control. SOLUTION: The device is provided with: a first and a second NOXconcentration detection means for detecting NOXconcentrations in an upstream side and a downstream side of an NOXcatalyst; a degradation rate calculation means calculating first storage capacity of the NOXcatalyst at time after predetermined time elapses from start of storage of NOXand operating degradation rate of the NOXcatalyst by comparing the storage capacity with predetermined initial storage capacity before degradation of the NOXcatalyst; and a thermal degradation rate operation means desorbing SOXstored in the NOXcatalyst after operation of degradation rate, calculating second storage capacity of the NOXcatalyst under a condition after desorbing SOX, and operating thermal degradation rate of the NOXcatalyst by comparing the storage capacity with the initial storage capacity. COPYRIGHT: (C)2008,JPO&INPIT