Method and system for reducing vehicle tailpipe emissions when operating lean

摘要

A method and system for operating a lean-burn internal combustion engine in cooperation with an exhaust gas purification system having an emission control device, wherein the system includes a controller which calculates current levels of a selected exhaust gas constituent, such as NO_x, during lean engine operating conditions based upon the difference between a determined instantaneous feedgas NO_x concentration and a determined instantaneous device efficiency. The controller discontinues lean engine operation when the tailpipe NO_x, 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 device purge-fill cycle.