Exhaust emission purification apparatus for an internal combustion engine

摘要

An exhaust emission gas purification apparatus for an internal combustion engine is disclosed, in which a proper purification rate can be maintained even at a transient time by suppressing an excessive temperature increase of a lean NOx catalyst. In order to improve the purification efficiency of a lean NOx catalyst 307, diesel fuel constituting a hydrocarbon material capable of reducing the NOx is supplied by way of a diesel fuel injection hole 311. A basic amount of diesel fuel to be supplied is determined on the basis of a space velocity SV providing a quantity of state representing the operating conditions of the catalyst calculated from the intake air amount detected by an air flowmeter 302 and the catalyst temperature detected by an outlet exhaust gas temperature sensor 322. The basis amount of diesel fuel to be supplied is corrected based on the difference between the catalyst temperature and the inlet exhaust gas temperature detected by the inlet exhaust gas temperature sensor 321. The purification rate of the catalyst can thus be prevented from being deteriorated at a transient time.