Method and apparatus for desulfating a NO.sub.x trap
First Claim
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1. A method of desulfating a NOx trap located in the exhaust passage of an engine having at least a first and a second cylinder comprising the steps of:
- providing a lean fuel mixture to said first cylinder and a rich fuel mixture to said second cylinder;
maintaining separate oaths for the exhaust gases from said first and second cylinders until entry into said trap to produce an exothermic reaction in said trap;
maintaining an average air/fuel ratio to said engine of approximately stoichiometric;
adjusting spark advance for said rich and lean cylinders to minimize event time imbalance, wherein the spark advance adjustments are a function of engine speed, load and air/fuel ratio; and
retarding the spark of said rich cylinder if the lean cylinder event is of longer time duration than the rich cylinder event.
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Abstract
A method and apparatus for desulfating a NOx trap is proposed wherein half of the engine cylinders are operated at a rich air/fuel ratio and half are operated at a lean A/F during the desulfation process. The two exhaust gas streams, the rich stream and the lean stream, are physically or chemically separated until they enter the NOx trap. A catalyzed exothermic chemical reaction is then generated in the trap. The resulting temperature increase is sufficient to remove SOX from the trap. During desulfation spark advance is adjusted to minimize event time imbalance.
155 Citations
16 Claims
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1. A method of desulfating a NOx trap located in the exhaust passage of an engine having at least a first and a second cylinder comprising the steps of:
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providing a lean fuel mixture to said first cylinder and a rich fuel mixture to said second cylinder; maintaining separate oaths for the exhaust gases from said first and second cylinders until entry into said trap to produce an exothermic reaction in said trap; maintaining an average air/fuel ratio to said engine of approximately stoichiometric; adjusting spark advance for said rich and lean cylinders to minimize event time imbalance, wherein the spark advance adjustments are a function of engine speed, load and air/fuel ratio; and retarding the spark of said rich cylinder if the lean cylinder event is of longer time duration than the rich cylinder event. - View Dependent Claims (2)
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3. Apparatus for desulfating a NOx trap located in the exhaust passage of a multi-cylinder engine having exhaust manifold means connected with catalytic converter means located in said exhaust passage upstream of said NOx trap, said apparatus comprising:
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means providing a lean fuel mixture to one half of the cylinders of said engine and providing a rich fuel mixture to the other half of the cylinders of said engine; means for combining the exhaust gases from all lean burn cylinders and all rich burn cylinders no later than upon entry of the exhaust gases into said trap to thereby produce an exothermic reaction in said trap. - View Dependent Claims (4, 5, 6, 7, 8, 9)
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10. A method of desulfating a NOx trap located in the exhaust passage of an engine having at least a first and a second cylinder comprising the steps of:
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providing a lean fuel mixture to said first cylinder and a rich fuel mixture to said second cylinder; combining the exhaust gases from said first and second cylinders to produce an exothermic reaction in said traps; maintaining an average air/fuel ratio to said engine of approximately stoichiometric; adjusting spark advance for said rich and lean cylinders to minimize event time imbalance; and retarding the spark of said rich cylinder if the lean cylinder event is of longer time duration than the rich cylinder event, and advancing the spark of said rich cylinder if the lean cylinder event is of shorter time duration than the rich cylinder event.
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11. An article of manufacture comprising:
a computer storage medium having a computer program encoded therein for causing the computer to control an engine having at least two cylinders, said computer storage medium comprising; code for causing the computer to direct fuel to a first half of the cylinders of said engine to establish a lean air/fuel mixture ratio, and to direct fuel to a second half of the cylinders of said engine to establish a lean air/fuel mixture ratio; code for causing the computer to control spark advance; code for causing the computer to measure cylinder events; code for causing the computer to maintain an average air/fuel ratio to said engine of approximately stoichiometric; and code for causing the computer to adjust spark advance for said rich and lean cylinders to minimize event time imbalance including instructions for accessing vehicle operating condition and instructions for retarding the spark of one half of said cylinders if the cylinder event of the other half of said cylinders is of longer time duration than the cylinder event of said one half of said cylinders, and for advancing the spark of said one half of said cylinders if the cylinder event of the other half of said cylinders is of shorter time duration than the cylinder event of said one half of said cylinders.
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12. A method of desulfating a NOx trap, located in the exhaust passage of a multi-cylinder engine comprising a sequence of the following steps:
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providing a lean fuel mixture to one half of the cylinders of said engine; providing a rich fuel mixture to the other half of the cylinders of said engine; combining the exhaust gases from all lean burn cylinders and all rich burn cylinders no later than upon entry of the exhaust gases into said trap; and producing an exothermic reaction in said trap wherein said NOx trap is located downstream of catalytic converter means that maintain separation of the exhaust gases from said lean burn cylinders and said rich burn cylinders, and wherein said gases are combined prior to entry into said trap. - View Dependent Claims (13, 14, 15)
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16. A method of desulfating a NOx trap located in the exhaust passage of an engine downstream from catalytic converter means, said engine having at least a first and a second cylinder comprising the steps of:
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providing a lean fuel mixture to said first cylinder and a rich fuel mixture to said second cylinder; and maintaining separate paths for the exhaust gases from said first and second cylinders through said converter means until entry into said trap to produce an exothermic reaction in said trap.
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Specification