EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine shortening the time required for deterioration determination and performing the further accurate and wasteless deterioration determination. SOLUTION: This exhaust emission control device is provided with an NOx absorbent 21 provided in the exhaust passage of the internal combustion engine mounted on a vehicle, absorbing NOx when the flowing-in exhaust gas is in an oxygen excessive state, and discharging NOx to be reduced and purified when oxygen concentration is lowered, a normal operation control means 27 switching an oxygen excess air-fuel ratio operation, a theoretical air-fuel ratio operation, and a fuel excess air-fuel ratio operation for the operation control of the internal combustion engine according to the operation state of the vehicle, an NOx absorbent deterioration judging means 27 allowing the NOx absorbent to absorb NOx then discharge it and making the deteriration judgment of the NOx absorbent based of the delay time of the change of the air-fuel ratio on the downstream side of the NOx absorbent at the discharge, and an NOx discharge quantity increasing means 27 increasing the NOx quantity flowing into the NOx absorbent in the NOx absorbent deterioration judging means in the normal operation than that in the oxygen excess air-fuel ratio operation.