Method and algorithm for performing an NH3 sensor rationality diagnostic

• US 9,429,062 B2
• Filed: 09/08/2014
• Issued: 08/30/2016
• Est. Priority Date: 03/07/2012
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Osburn, Andrew W., Liu, Feng, Geveci, Mert
• Primary Examiner(s): Tran, Binh Q
• Application Number:
  US14/479,643
• Publication Number:
  US 20140373511A1
• Time in Patent Office: 722 Days
• Field of Search: 602/74, 602/76, 602/77, 602/86, 602/95, 602/97, 603/01, 603/03
• US Class Current: 1/1
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2560/021 for measuring or detecting ammonia NH3
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• CPC Class Codes: F01N 2900/0416 using the state of a sensor, e.g. of an exhaust gas sensor
• CPC Class Codes: F01N 3/103 Oxidation catalysts for HC and CO only
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An example method includes interpreting an NH₃ composition value at a position upstream of a selective reduction catalyst (SCR) element fluidly disposed in the exhaust conduit of an engine, interpreting a NO_x composition value at a position downstream of the SCR element, and determining an NH₃ sensor rationality threshold in response to the upstream NH₃ composition value. The method further includes determining an NH₃ sensor health value as indicating a sensor failure in response to the downstream NO_x composition value exceeding the NH₃ sensor rationality threshold.

Claims

1. A system, comprising:

an internal combustion engine producing an exhaust stream as a byproduct of operation;

an exhaust conduit fluidly coupled to the engine, and structured to receive the exhaust stream;

a selective reduction catalyst (SCR) element fluidly disposed in the exhaust conduit, the SCR catalyst having an upstream side and a downstream side;

an NH₃ sensor operationally coupled to the exhaust conduit and structured to provide an upstream side NH₃ composition value;

a NO_x sensor operationally coupled to the exhaust conduit at a position downstream of the SCR element and structured to provide a downstream side NO_x composition value; and

a controller, comprising;

a composition module structured to interpret the upstream NH₃ composition value and the downstream NO_x composition value;

an NH₃ sensor threshold module structured to determine an NH₃ sensor rationality threshold in response to the upstream NH₃ composition value; and

an NH₃ sensor diagnostic module structured to determine an NH₃ sensor health value for the NH₃ sensor in response to a comparison of the downstream NO_x composition value and the NH₃ sensor rationality threshold.

2. The system of claim 1, wherein the NH₃ sensor diagnostic module is further structured to determine the NH₃ sensor health value as indicating a sensor failure in response to the downstream NO_x composition value exceeding the NH₃ sensor rationality threshold.

3. The system of claim 2, wherein the NH₃ sensor diagnostic module is further structured to determine the NH₃ sensor health value as indicating an in-range failure in response to the upstream NH₃ composition value being an in-range value.

4. The system of claim 1, further comprising a second SCR element disposed in the exhaust conduit at a position upstream of the NH₃ sensor.

5. The system of claim 1, further comprising an ammonia oxidation catalyst (AMOX) disposed in the exhaust conduit at a position downstream of the NH₃ sensor and upstream of the NO_x sensor.

6. The system of claim 5, further comprising a second SCR element disposed in the exhaust conduit at a position upstream of the NH₃ sensor.

7. The system of claim 6, wherein the NH₃ sensor diagnostic module is Wither structured to determine the NH₃ sensor health value as failed in response to the euuation

8. The system of claim 7, wherein the NH₃ sensor diagnostic. module is further structured to determine the NH₃ sensor health value as failed in-range in response to the NH₃ sensor health value being failed, and the value x being within operational limits of the NH₃ sensor.

9. The system of claim 6, wherein the NH₃ sensor diagnostic module is further structured to determine the NH3 sensor health value as failed in response to the equation

10. The system of claim 9, wherein the NH₃ sensor diagnostic module is further structured to determine the NH₃ sensor health value as failed in-range in response to the NH₃ sensor health value being failed, and the value x being within operational limits of the NH₃ sensor.

11. The system of claim 1, wherein the NH₃ sensor rationality threshold comprises the downstream NO_x composition value.

12. The system of claim 1, wherein the NH₃ sensor rationality threshold comprises a multiple of the downstream NO_x composition value, wherein the multiple comprises a value between 0.9 and 8.0.

13. The system of claim 1, wherein the NH₃ sensor diagnostic module is further structured to determine the NH₃ sensor health value as failed in response to the equation

14. The system of claim 13, wherein the NH₃ sensor diagnostic module is further structured to determine the NH₃ sensor health value as failed in-range in response to the NH₃ sensor health value being failed, and the value x being within operational limits of the NH₃ sensor.

15. An electronic controller with instructions on a non-transitory computer readable medium operable to execute a method, comprising:

interpreting an NH₃ composition value from an output of an NH₃ sensor at a position upstream of a selective reduction catalyst (SCR) element fluidly disposed in the exhaust conduit of an engine;

interpreting a NO_x composition value at a position downstream of the SCR element;

determining an NH₃ sensor rationality threshold in response to the upstream NH₃ composition value; and

determining an NH₃ sensor health value for the NH₃ sensor as indicating a sensor failure in response to the downstream NO_x composition value exceeding the NH₃ sensor rationality threshold.

16. The method of claim 15, further comprising determining the NH₃ sensor health value in response to determining that the SCR catalyst element temperature is within a NOx conversion efficiency range.

17. The method of claim 15, further comprising determining the NH₃ sensor health value in response to determining that an ammonia oxidation catalyst (AMOX) positioned downstream of the SCR element is within an NH₃ conversion efficiency range.

18. The method of claim 15, further comprising determining the NH₃ sensor health value in response to determining that the SCR catalyst element temperature is greater than a storage capacity threshold temperature.

19. The method of claim 15, further comprising estimating a stored NH₃ variation value, and wherein the determining an NH₃ sensor health value further comprises compensating for the stored NH₃ variation value.

20. The method of claim 15, further comprising determining a NO_x conversion efficiency value of the SCR catalyst element, and wherein determining the NH₃ sensor rationality threshold is further in response to the NO_x conversion efficiency value.

21. The method of claim 15, further comprising determining a NO_x conversion efficiency value of the SCR catalyst element, determining an NH₃ conversion efficiency value of an ammonia oxidation catalyst (AMOX) positioned downstream of the SCR element, and wherein determining the NH₃ sensor rationality threshold is further in response to the NO_x conversion efficiency value and the NH₃ conversion efficiency value.

22. A system for diagnosing a sensor in an exhaust conduit fluidly coupled to an internal combustion engine operable to produce an exhaust stream as a byproduct of operation, the system comprising:

a selective reduction catalyst (SCR) element fluidly disposed in the exhaust conduit, the SCR catalyst having an upstream side and a downstream side;

an NH₃ sensor operationally coupled to the exhaust conduit and structured to provide an upstream side NH₃ composition value;

a NO_x sensor operationally coupled to the exhaust conduit at a position downstream of the SCR element and structured to provide a downstream site NO_x composition value; and

an electronic controller to determine an NH₃ sensor health value for the NH₃ sensor in response to the upstream NH₃ composition value and the downstream NO_x composition value.

23. The system of claim 22, wherein the electronic controller is further configured to determine an NH₃ sensor rationality threshold in response to the upstream NH₃ composition value.

24. The system of claim 23, wherein the electronic controller is further configured to indicate a sensor failure in response to the downstream NO_x composition value exceeding the NH₃ sensor rationality threshold.

25. The system of claim 24, wherein the electronic controller is further configured to determine the NH₃ sensor health value indicates an in-range failure.

26. The system of claim 24, wherein the NH₃ sensor rationality threshold comprises at least one value selected from the values consisting of:

the downstream NO_x composition value, a multiple of the downstream NO_x composition value, wherein the multiple comprises a value between 0.9 and 8.0.

27. The system of claim 24, wherein the multiple comprises a value selected from the values consisting of:

0.4, 0.5, 0.8, 0.9, 1.0, 2.0, 2.5, 3.0, and 8.0.

28. The system of claim 22, further comprising an ammonia oxidation catalyst disposed in the exhaust conduit at a position downstream of the NH₃ sensor and upstream of the NO_x sensor.

29. The system of claim 28, wherein the electronic controller is further configured to determine whether NH₃ sensor check conditions are present, and prevent determining the NH₃ sensor health value in response to the NH₃ sensor check conditions not being present.

30. The system of claim 29, wherein the NH₃ sensor check conditions comprise at least one condition selected from the conditions consisting of:

an SCR catalyst element storage capacity being lower than a threshold value, the SCR catalyst element being saturated with adsorbed NH₃, a temperature of the SCR catalyst element exceeding a threshold, and an exhaust flow value exceeding a threshold.

31. The system of claim 29, wherein the controller is further configure to perform a sensor failure verification operation.

32. The system of claim 31, wherein the sensor failure verification operation comprises at least one operation selected from the operations consisting of averaging a plurality of sensor test results, incrementing a fault counter in response to a sensor test indicating a failed sensor, decrementing a fault counter in response to a sensor test indicating a passed sensor, integrating the upstream NH₃ composition value and the downstream NO_x composition value over a predetermined period of time and comparing the integrated values to the NH₃ sensor rationality threshold, and modeling NH₃ storage on the SCR catalyst and accounting for the storage in the sensor failure verification operation.