Method and system for reducing NOx tailpipe emissions of a lean-burn internal combustion engine

摘要

A method and apparatus for operating a lean-burn internal combustion engine in cooperation with an exhaust gas purification system having a three-way catalyst and a NOx trap located downstream of the three-way catalyst includes a controller which calculates current levels of tailpipe NOx during lean engine operating conditions based upon the difference between a determined instantaneous feedgas NOx concentration and a determined instantaneous trap efficiency. The controller discontinues lean engine operation when the tailpipe NOx, expressed in terms of either grams-per-mile or grams-per-hour, exceeds a predetermined threshold level, either instantaneously or as averaged over the course of a trap purge-fill cycle.