Method and system for transitioning between lean and stoichiometric operation of a lean-burn engine
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United States of America Patent
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Aug 12, 2003
Grant Date -
Dec 19, 2002
app pub date -
Jun 19, 2001
filing date -
Jun 19, 2001
priority date (Note) -
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Abstract
An exhaust treatment system for an internal combustion engine includes a catalytic emission control device. When transitioning the engine between a lean operating condition and a stoichiometric operating condition, as when scheduling a purge of the downstream device to thereby release an amount of a selected exhaust gas constituent, such as NO.sub.x, that has been stored in the downstream device during the lean operating condition, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is sequentially stepped from an air-fuel ratio of at least about 18 to the stoichiometric air-fuel ratio. The purge event is preferably commenced when all but one cylinders has been stepped to stoichiometric operation, with the air-fuel mixture supplied to the last cylinder being stepped immediately to an air-fuel ratio rich of a stoichiometric air-fuel ratio.
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