METHOD AND SYSTEM FOR REDUCING LEAN-BURN VEHICLE EMISSIONS USING A DOWNSTREAM REDUCTANT SENSOR

摘要

A method and system for controlling the operation of a lean-burn engine whose exhaust gas is directed through an emission control device and a downstream reductant-concentration sensor, wherein a stored value for the device's instantaneous capacity to store a selected exhaust gas constituent, such as NOx, is periodically adaptively updated when the sensor's output signal falls outside a predetermined range during a device purge event. A device purge event is scheduled when an accumulated measure of instantaneous feedgas NOx concentration during lean engine operation exceeds the stored NOx-storage capacity value. The purge event is discontinued when the sensor's output signal exceeds the upper limit of the predetermined range, or when a determined value representing a cumulative amount of excess fuel supplied to the engine during the purge event exceeds a threshold value calculated based upon previous values for stored NOx and stored oxygen.