Ammonia sensor control, with NOx feedback, of an SCR aftertreatment system

Patent metadata

Field	Value
Publication number	US-9476338-B2
Application number	US-201113097947-A
Country	US
Kind code	B2
Filing date	Apr 29, 2011
Priority date	May 3, 2010
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

An exemplary method includes determining an NH 3 reference target in an exhaust conduit between a first SCR catalyst and a second SCR catalyst. The method includes determining a present amount of NH 3 in the exhaust conduit between the first SCR catalyst and the second SCR catalyst, and determining an NH 3 error term in response to the NH 3 reference target and the present amount of NH 3 . The method further includes determining an amount of NO x downstream of the second SCR catalyst, and adjusting one of the NH 3 reference target and a reductant doser command in response to the amount of NO x downstream of the second SCR catalyst. The method further includes providing a reductant doser command in response to the NH 3 error term.

First claim

What is claimed is:

1. A method, comprising:
determining an ammonia (NH 3 ) reference target comprising a target amount of NH 3 in an exhaust conduit, wherein the exhaust conduit includes a first selective catalytic reduction (SCR) catalyst and a second SCR catalyst, and the NH 3 reference target is the target amount of NH 3 that occurs at a mid-bed position between the first SCR catalyst and the second SCR catalyst in response to injection of a targeted amount of reductant upstream of the first SCR catalyst;
determining a present amount of NH 3 in the exhaust conduit between the first SCR catalyst and the second SCR catalyst with an ammonia sensor that defines a separation point between the first SCR catalyst and the second SCR catalyst at the mid-bed position;
determining an NH 3 error term in response to the NH 3 reference target and the present amount of NH 3 ;
determining a reductant closer command in response to the NH 3 error term;
determining an amount of NO x downstream of the second SCR catalyst, and further comprising determining a rate of change of the present amount of NH 3 and adjusting one of the NH 3 reference target and the reductant closer command in response to the rate of change; and
injecting, with a reductant injector, an amount of reductant in response to the adjusted one of the NH 3 reference target and the reductant doser command.

2. The method of claim 1 , further comprising determining a rate of change of the amount of NO x downstream of the second SCR catalyst, and further adjusting the one of the NH 3 reference target and the reductant closer command in response to the rate of change of the amount of NO x downstream of the second SCR catalyst.

3. The method of claim 1 , further determining an amount of NH 3 downstream of the second SCR catalyst, and further adjusting the one of the NH 3 reference target and the reductant closer command in response to the amount of NH 3 downstream of the second SCR catalyst.

4. The method of claim 3 , further comprising determining an adjusted downstream NO x amount by subtracting the amount of NH 3 downstream of the second SCR catalyst from the amount of NO x downstream of the second SCR catalyst, and further adjusting the one of the NH 3 reference target and the reductant doser command in response to the adjusted downstream NO x amount.

5. The method of claim 4 , further comprising determining an excess downstream NO x amount in response to the adjusted downstream NO x amount and a NO x reference target, and further adjusting the one of the NH 3 reference target and the reductant doser command in response to the excess downstream NO x amount.

6. A method, comprising:
determining an ammonia (NH 3 ) reference target comprising a target amount of NH 3 in an exhaust conduit, wherein the exhaust conduit includes a first selective catalytic reduction (SCR) catalyst and a second SCR catalyst, and the NH 3 reference target is the target amount of NH 3 that occurs at a mid-bed position between the first SCR catalyst and the second SCR catalyst in response to injection of a targeted amount of reductant upstream of the first SCR catalyst;
determining a present amount of NH 3 in the exhaust conduit between the first SCR catalyst and the second SCR catalyst with an ammonia sensor that defines a separation point between the first SCR catalyst and the second SCR catalyst at the mid-bed position;
determining an NH 3 error term in response to the NH 3 reference target and the present amount of NH 3 ;
determining a reductant doser command in response to the NH 3 error term;
determining an amount of NO x downstream of the second SCR catalyst;
determining a rate of change of the present amount of NH 3 and the amount of NO x downstream of the second SCR catalyst;
determining a product of the rate of change of the present amount of NH 3 and the rate of change of the amount of NO x downstream of the second SCR catalyst, and further adjusting one of the NH 3 reference target and the reductant doser command in response to the product; and
injecting, with a reductant injector, an amount of reductant in response to the adjusted one of the NH 3 reference target and the reductant doser command.

7. The method of claim 6 , further comprising determining a rate-based adjustment amount as a function of the product, and further adjusting the one of the NH 3 reference target and the reductant doser command in response to the rate-based adjustment amount.

8. The method of claim 7 , further comprising limiting the rate-based adjustment amount to a proportion of an amount of NO x upstream of the first SCR catalyst.

9. The method of claim 8 , wherein the proportion comprises an amount less than one-half of the amount of NO, upstream of the first SCR catalyst.

10. A method, comprising:
interpreting an NH 3 reference target comprising a target amount of NH 3 present at a mid-bed position, wherein two selective catalytic reduction (SCR) catalysts define the mid-bed position, wherein the NH 3 reference target is the target amount of NH 3 that occurs at the mid-bed position between the SCR catalysts in response to injection of a targeted amount of reductant upstream of the SCR catalysts;
interpreting, with an ammonia sensor that defines a separation point between the SCR catalysts at the mid-bed position, an amount of NOx downstream of the SCR catalysts and a present amount of NH 3 in the exhaust conduit between the SCR catalysts in response to an output from the ammonia sensor;
interpreting a rate of change of the amount of NO x downstream of the SCR catalysts;
interpreting a rate of change of an amount of NH 3 between the SCR catalysts;
determining a product of the rate of change of the amount of NO x downstream of the SCR catalysts and the rate of change of the amount of NH 3 between the SCR catalysts;
adjusting the NH 3 reference target in response to the amount of NO x downstream of the SCR catalysts, the present amount of NH 3 , and the NH 3 reference target, wherein the adjusting further comprises adjusting the NH 3 reference target in response to the product; and
injecting, with a reductant injector, an amount of urea upstream of the SCR catalysts in response to the adjusted NH3 reference target.

11. The method of claim 10 , wherein the adjusting comprises reducing the NH 3 reference target in response to the product being negative, and increasing the NH 3 reference target in response to the product being positive.

12. The method of claim 11 , wherein the increasing has a higher gain than the decreasing.

13. The method of claim 12 , further comprising limiting the adjusting to a proportion of an amount of NO x upstream of the SCR catalysts.

14. The method of claim 10 , further comprising interpreting an amount of NH 3 downstream of the SCR catalysts, determining an adjusted amount of NO x downstream of the SCR catalysts in response to the amount of NH 3 downstream of the SCR catalysts, and wherein the adjusting is further in response to the adjusted amount of NO x downstream of the SCR catalysts.

15. The method of claim 14 , further comprising interpreting a NO x reference target comprising a target amount of NO present at a position downstream of the SCR catalysts, determining an excess downstream NO x amount in response to the adjusted amount of NO downstream of the SCR catalysts and the target amount of NO x , and wherein the adjusting is further in response to the excess downstream NO x amount.

16. The method of claim 15 , further comprising filtering the excess downstream NO x amount w

Assignees

• Geveci Mert
• Osburn Andrew W
• Cummins Inc

Inventors

• Geveci Mert
• Osburn Andrew W

Classifications

• F01N3/208 Primary

  Control of selective catalytic reduction [SCR], e.g. by adjusting the dosing of reducing agent · CPC title

• F01N2900/0402

  using adaptive learning · CPC title

• F01N2610/02

  the substance being ammonia or urea · CPC title

• F01N2610/146

  Control thereof, e.g. control of injectors or injection valves · CPC title

• F01N2560/021

  for measuring or detecting ammonia NH3 · CPC title