METHOD AND SYSTEM FOR REDUCING LEAN-BURN VEHICLE EMISSIONS USING A DOWNSTREAM REDUCTANT SENSOR
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United States of America Patent
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-
Dec 3, 2002
Grant Date -
Dec 19, 2002
app pub date -
Jun 19, 2001
filing date -
Jun 19, 2001
priority date (Note) -
Granted
status (Latency Note)
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Abstract
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 NO.sub.x, 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 NO.sub.x concentration during lean engine operation exceeds the stored NO.sub.x-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 NO.sub.x and stored oxygen.
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