System for diagnosing EGR flow rate operation

• US 6,802,302 B1
• Filed: 04/08/2003
• Issued: 10/12/2004
• Est. Priority Date: 04/08/2003
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Li, Xiaoqiu, Stepper, Mark R., Goerges, Stephanie L., Wang, Yue Yun
• Primary Examiner(s): WOLFE JR, WILLIS RAY
• Application Number:
  US10/409,307
• Time in Patent Office: 553 Days
• Field of Search: 123/568.11, 123/568.12, 123/568.16, 123/568.21, 123/568.22, 123/568.23, 123/568.24, 123/568.25, 123/568.26, 123/568.27, 701/108, 731/173, 731/181, 731/182, 606/052
• US Class Current: 123/568.16
• CPC Class Codes: F02B 29/0406 Layout of the intake air cooling or coolant circuit
• CPC Class Codes: F02D 21/08 the other gas being the exhaust gas of engine
• CPC Class Codes: F02D 41/0072 Estimating, calculating or determining the EGR rate, amount or flow sensors in EGR systems F02M26/45
• CPC Class Codes: F02M 26/05 High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
• CPC Class Codes: F02M 26/23 Layout, e.g. schematics
• CPC Class Codes: F02M 26/47 the characteristics being temperatures, pressures or flow rates
• CPC Class Codes: F02M 26/49 Detecting, diagnosing or indicating an abnormal function of the EGR system
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A system is disclosed for diagnosing EGR flow rate operation in an internal combustion engine includes an intake manifold and an exhaust manifold coupled to the engine and an EGR conduit for recirculating exhaust gas from the exhaust manifold to the intake manifold. Means are provided for determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas in a total air charge supplied to the intake manifold. A control computer is configured to continually accumulate at least one EGR fraction error sum as a function of the EGR fraction and a desired EGR fraction, and to diagnose EGR flow rate operation as a function of the accumulated value of the at least one EGR fraction error sum.

Claims

1. System for diagnosing exhaust gas recirculation (EGR) flow rate operation in an internal combustion engine, comprising:

intake and exhaust manifolds each operatively coupled to the engine;

an EGR conduit for recirculating exhaust gas from the exhaust manifold to the intake manifold;

means for determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas in a total air charge supplied to the intake manifold; and

a control computer continually accumulating at least one EGR fraction error sum as a function of the EGR fraction and a desired EGR fraction, and diagnosing EGR flow rate operation as a function of the accumulated value of the at least one EGR fraction error sum.

2. The system of claim 1 wherein the control computer is configured to diagnose the EGR flow rate operation as normal if the accumulated value of the at least one EGR fraction error sum is less than a threshold value upon expiration of a diagnostic period.

3. The system of claim 2 further including a memory having an EGR flow rate diagnostic flag stored therein, the control computer configured to set the EGR flow rate diagnostic flag to PASS upon diagnosing the EGR flow rate operation as normal.

4. The system of claim 1 wherein the control computer is configured to diagnose the EGR flow rate operation as failing if the accumulated value of the at least one EGR fraction error sum meets or exceeds a threshold value during a diagnostic period.

5. The system of claim 4 further including a memory having an EGR flow rate diagnostic flag stored therein, the control computer configured to set the EGR flow rate diagnostic flag to FAIL upon diagnosing the EGR flow rate operation as failing.

6. The system of claim 1 further including a memory having an EGR flow rate diagnostic flag stored therein;

wherein the control computer is configured to set the EGR flow rate diagnostic flag to ABORT if the accumulated value of the at least one EGR fraction error sum meets or exceeds a threshold value upon expiration of a diagnostic period.

7. The system of claim 1 wherein the control computer is configured to continually compute for a diagnostic period an EGR fraction error as a difference between the EGR fraction and the desired EGR fraction, a positive EGR fraction error sum as a maximum of zero and a sum of a previous value of the positive EGR fraction error sum and the EGR fraction error, and a negative EGR fraction error sum as a maximum of zero and a sum of a previous value of the negative EGR fraction error sum and the EGR fraction error.

8. The system of claim 7 wherein the control computer is configured to diagnose the EGR flow rate operation as normal if an accumulated value of the positive EGR fraction error sum remains less than a first threshold value throughout the diagnostic period and an accumulated value of the negative EGR fraction error sum remains less than a second threshold value throughout the diagnostic period, and if the accumulated value of the positive EGR fraction error sum is less than a third threshold value, less than the first threshold value, and the accumulated value of the negative EGR fraction error sum is less than a fourth threshold value, less than the second threshold value, upon expiration of the diagnostic period.

9. The system of claim 8 further including a memory having an EGR flow rate diagnostic flag stored therein, the control computer configured to set the EGR flow rate diagnostic flag to PASS upon diagnosing the EGR flow rate operation as normal.

10. The system of claim 7 wherein the control computer is configured to diagnose the EGR flow rate operation as failing if either of an accumulated value of the positive EGR fraction error sum meets or exceeds a first threshold value during the diagnostic period and an accumulated value of the negative EGR fraction error sum meets or exceeds a second threshold value during the diagnostic period.

11. The system of claim 10 further including a memory having an EGR flow rate diagnostic flag stored therein, the control computer configured to set the EGR flow rate diagnostic flag to FAIL upon diagnosing the EGR flow rate operation as failing.

12. The system of claim 7 further including a memory having an EGR flow rate diagnostic flag stored therein;

wherein the control computer is configured to set the EGR flow rate diagnostic flag to ABORT if an accumulated value of the positive EGR fraction error sum remains below a first threshold value, and an accumulated value of the negative EGR fraction error sum remains below a second threshold value, throughout the diagnostic period, and upon expiration of the diagnostic period either of the accumulated value of the positive EGR fraction error sum meets or exceeds a third threshold value less than the first threshold value, and the accumulated value of the negative EGR fraction error sum meets or exceeds a fourth threshold value less than the second threshold value.

13. The system of claim 1 wherein the control computer is configured to monitor a number of diagnostic enable conditions prior to starting a diagnostic period in which the at least one EGR fraction error sum is continually accumulated, and to start the diagnostic period only if all of the number of diagnostic enable conditions are met.

14. The system of claim 13 wherein the control computer is further configured to monitor the number of diagnostic enable conditions throughout the diagnostic period, and to restart the diagnostic period if any of the number of diagnostic enable conditions is no longer met.

15. The system of claim 14 further including means for determining rotational speed of the engine;

wherein one of the number of diagnostic enable conditions corresponds to the rotational speed of the engine being within a predefined range of engine rotational speeds.

16. The system of claim 14 wherein the control computer is configured to determine an engine load value as a function of an engine fueling command;

wherein one of the number of diagnostic enable conditions corresponds to the engine load value being less than a threshold engine load value.

17. The system of claim 14 further including:

an EGR valve disposed in-line with the EGR conduit, the EGR valve responsive to an EGR valve control command to control a position of the EGR valve relative to a reference position; and

means for determining the position of the EGR valve relative to the reference position;

wherein one of the number of the diagnostic enable conditions corresponds to the position of the EGR valve being greater than a threshold EGR valve position.

18. The system of claim 7 wherein the control computer is configured to continually monitor during the diagnostic period a number of data acquisition conditions, and to compute the EGR fraction error, the positive EGR fraction error sum, and the negative EGR fraction error sum only if all of the number of diagnostic acquisition conditions are met.

19. A method for diagnosing exhaust gas recirculation (EGR) flow rate operation in an internal combustion engine having an intake manifold, an exhaust manifold and an EGR conduit for recirculating exhaust gas from the exhaust manifold to the intake manifold, the method comprising the steps of:

determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas in a total air charge supplied to the intake manifold;

determining a desired EGR fraction;

continually computing an EGR fraction error as a difference between the EGR fraction and the desired EGR fraction and accumulating at least one EGR fraction error sum as a function of the EGR fraction error; and

diagnosing EGR flow rate operation as a function of the accumulated value of the at least one EGR fraction error sum.

20. The method of claim 19 wherein the step of diagnosing EGR flow rate operation includes diagnosing the EGR flow rate operation as normal if the accumulated value of the at least one EGR fraction error sum is less than a threshold value upon expiration of a diagnostic period.

21. The method of claim 20 further including the step of setting an EGR flow rate diagnostic flag stored in memory to PASS upon diagnosing the EGR flow rate operation as normal.

22. The method of claim 19 wherein the step of diagnosing EGR flow rate operation includes diagnosing the EGR flow rate operation as failing if the accumulated value of the at least one EGR fraction error sum meets or exceeds a threshold value during a diagnostic period.

23. The method of claim 22 further including the step of setting an EGR flow rate diagnostic flag stored in memory to FAIL upon diagnosing the EGR flow rate operation as failing.

24. The method of claim 19 wherein the step of diagnosing EGR flow rate operation includes setting an EGR flow rate diagnostic flag stored in memory to ABORT if the accumulated value of the at least one EGR fraction error sum meets or exceeds a threshold value upon expiration of the diagnostic period.

25. The method of claim 19 further including the steps of:

monitoring a number of diagnostic enable conditions;

and executing the continually computing and diagnosing steps only if all of the number of diagnostic enable conditions are met.

26. The method of claim 25 further including the steps of:

monitoring the number of diagnostic enable conditions throughout a diagnostic period in which the EGR fraction error is continually computed; and

restarting the diagnostic period if any of the number of diagnostic enable conditions is no longer met.

27. The method of claim 26 further including the steps of:

determining rotational speed of the engine; and

determining that one of the number of diagnostic enable conditions is met if the rotational speed of the engine is within a predefined range of engine rotational speeds.

28. The method of claim 26 further including the steps of:

determining an engine load value as a function of an engine fueling command; and

determining that one of the number of diagnostic enable conditions is met if the engine load value is less than a threshold engine load value.

29. The system of claim 26 further including the steps of:

determining relative to a reference position a position of an EGR valve disposed in-line with the EGR conduit; and

determining that one of the number of the diagnostic enable conditions is met if the position of the EGR valve is greater than a threshold EGR valve position.

30. The method of claim 19 wherein the step of continually computing an EGR fraction error as a difference between the EGR fraction and the desired EGR fraction and accumulating at least one EGR fraction error sum as a function of the EGR fraction error further includes:

monitoring a number of data acquisition conditions; and

and computing the EGR fraction error and accumulating the at least one EGR fraction sum error only if all of the number of data acquisition conditions are met.

31. A method for diagnosing exhaust gas recirculation (EGR) flow rate operation in an internal combustion engine having an intake manifold, an exhaust manifold and an EGR conduit for recirculating exhaust gas from the exhaust manifold to the intake manifold, the method comprising the steps of:

determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas in a total air charge supplied to the intake manifold;

determining a desired EGR fraction;

continually computing an EGR fraction error as a difference between the EGR fraction and the desired EGR fraction, a positive EGR fraction error sum as a maximum of zero and a sum of a previous value of the positive EGR fraction error sum and the EGR fraction error, and a negative EGR fraction error sum as a maximum of zero and a is sum of a previous value of the negative EGR fraction error sum and the EGR fraction; and

diagnosing EGR flow rate operation as a function of accumulated values of the positive EGR fraction error sum and the negative EGR fraction error sum.

32. The method of claim 31 wherein the step of diagnosing EGR flow rate operation includes diagnosing the EGR flow rate operation as normal if the accumulated value of the positive EGR fraction error sum remains less than a first threshold value, and an accumulated value of the negative EGR fraction error sum remains less than a second threshold value, throughout a diagnostic period, and if the accumulated value of the positive EGR fraction error sum is less than a third threshold value, less than the first threshold value, and the accumulated value of the negative EGR fraction error sum is less than a fourth threshold value, less than the second threshold value, upon expiration of the diagnostic period.

33. The method of claim 32 further including the step of setting an EGR flow rate diagnostic flag stored in memory to PASS upon diagnosing the EGR flow rate operation as normal.

34. The method of claim 31 wherein the step of diagnosing EGR flow rate operation includes diagnosing the EGR flow rate operation as failing if during a diagnostic period either of an accumulated value of the positive EGR fraction error sum meets or exceeds a first threshold value and an accumulated value of the negative EGR fraction error sum meets or exceeds a second threshold value.

35. The method of claim 34 further including the step of setting an EGR flow rate diagnostic flag stored in memory to FAIL upon diagnosing the EGR flow rate operation as failing.

36. The method of claim 34 wherein the step of diagnosing EGR flow rate operation includes setting an EGR flow rate diagnostic flag stored in memory to ABORT if an accumulated value of the positive EGR fraction error sum remains below a first threshold value, and an accumulated value of the negative EGR fraction error sum remains below a second threshold value, during a diagnostic period, and if upon expiration of the diagnostic period either of the accumulated value of the positive EGR fraction error sum meets or exceeds a third threshold value less than the first threshold value and an accumulated value of the negative EGR fraction error sum meets or exceeds a fourth threshold value less than the second threshold value.

37. The method of claim 31 further including the steps of:

monitoring a number of diagnostic enable conditions; and

executing the continually computing and diagnosing steps only if all of the number of diagnostic enable conditions are met.

38. The method of claim 37 further including the steps of:

monitoring the number of diagnostic enable conditions throughout the diagnostic period; and

restarting the diagnostic period if any of the number of diagnostic enable conditions is no longer met.

39. The method of claim 38 further including the steps of:

determining rotational speed of the engine; and

determining that one of the number of diagnostic enable conditions is met if the rotational speed of the engine is within a predefined range of engine rotational speeds.

40. The method of claim 38 further including the steps of:

determining an engine load value as a function of an engine fueling command; and

determining that one of the number of diagnostic enable conditions is met if the engine load value is less than a threshold engine load value.

41. The system of claim 38 further including the steps of:

determining relative to a reference position a position of an EGR valve disposed in-line with the EGR conduit; and

determining that one of the number of the diagnostic enable conditions is met if the position of the EGR valve is greater than a threshold EGR valve position.

42. The method of claim 31 wherein the step of continually computing an EGR fraction error, the positive EGR fraction error sum, and the negative EGR fraction error sum further includes:

monitoring a number of data acquisition conditions; and

and computing the EGR fraction error, the positive EGR fraction error sum, and the negative EGR fraction error sum only if all of the number of data acquisition conditions are met.