Method and system for diagnosing deterioration of NOx catalyst

• US 6,167,695 B1
• Filed: 02/12/1999
• Issued: 01/02/2001
• Est. Priority Date: 02/12/1998
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Itou, Yasuyuki, Itou, Hidetoshi, Ishihara, Kouji
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRIEU, THAI BA
• Application Number:
  US09/248,988
• Time in Patent Office: 690 Days
• Field of Search: 602/77, 603/01, 602/76, 602/74, 731/181
• US Class Current: 60/274
• 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 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2550/10 of catalytic converters
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0871 Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A system and method for diagnosing deterioration of a nitrogen oxide (NOx) catalyst for an internal combustion engine. An output signal indicative of concentration of nitrogen oxides (NOx) in exhaust gas passing through the NOx catalyst is generated from a NOx sensor. Rates of change in the detected NOx concentration are calculated a plurality of times over a predetermined period of time after an air/fuel ratio becomes less than a stoichiometric air/fuel ratio. A representative value derived from the calculated rates of change in the detected NOx concentration is compared with a predetermined reference value for determining that the NOx catalyst is deteriorated.

Claims

1. A system for diagnosing deterioration of a nitrogen oxide catalyst coupled to an internal combustion engine, said catalyst being capable of absorbing nitrogen oxides present in exhaust gas emitted from the engine during lean-burn operation and releasing the nitrogen oxides absorbed when an air/fuel ratio is less than a stoichiometric air/fuel ratio, comprising:

a nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst to detect concentration of the nitrogen oxides in the exhaust gas passing through the nitrogen oxide catalyst and generate a signal indicative of the detected concentration of the nitrogen oxides; and

a controller operative, in response to said signal generated from said nitrogen oxide sensor, to calculate a rate of change in the detected concentration of the nitrogen oxides at any point in time during a predetermined period after the air/fuel ratio becomes less than the stoichiometric air/fuel ratio, compare said rate of change in the detected concentration of the nitrogen oxides with a predetermined reference value and determine, in response to the comparison result, that the nitrogen oxide catalyst is deteriorated.

2. A system as claimed in claim 1, wherein said predetermined period of time includes a period of time in which the detected concentration of the nitrogen oxides varies at substantially a constant rate in an increasing direction.

3. A system as claimed in claim 1, wherein said predetermined period starts after a predetermined time has elapsed from a moment the air/fuel ratio becomes less than the stoichiometric air/fuel ratio.

4. A system as claimed in claim 1, wherein said predetermined reference value is determined based on operation condition of the internal combustion engine.

5. A system as claimed in claim 1, wherein said predetermined period of time is determined based on operation condition of the internal combustion engine.

6. The system as claimed in claim 1, wherein said controller calculates the rate of change by using nitrogen oxide concentration signals from only the nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst.

7. A system for diagnosing deterioration of a nitrogen oxide catalyst coupled to an internal combustion engine, said catalyst being capable of absorbing nitrogen oxides present in exhaust gas emitted from the engine during lean-burn operation and releasing the nitrogen oxides absorbed when an air/fuel ratio is less than a stoichiometric air/fuel ratio, comprising:

a nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst to detect concentration of the nitrogen oxides in the exhaust gas passing through the nitrogen oxide catalyst and generate a signal indicative of the detected concentration of the nitrogen oxides; and

a controller operative, in response to said signal generated from said nitrogen oxide sensor, to calculate rates of change in the detected concentration of the nitrogen oxides a plurality of times at any points in time during a predetermined period after the air/fuel ratio becomes less than the stoichiometric air/fuel ratio, compare a representative value derived from the calculated rates of change in the detected concentration of the nitrogen oxides with a predetermined reference value and determine, in response to the comparison result, that the nitrogen oxide catalyst is deteriorated.

8. A system as claimed in claim 7, wherein said predetermined period of time includes a period of time from a moment one of the calculated rates of change in the detected concentration of the nitrogen oxides becomes not less than a predetermined initial value or the detected concentration of the nitrogen oxides becomes not less than a predetermined initial value, to a moment one of the calculated rates of change in the detected concentration of the nitrogen oxides becomes less than a predetermined terminal value or the detected concentration of the nitrogen oxides exceeds a predetermined terminal value.

9. A system as claimed in claim 7, wherein said representative value includes an average of the calculated rates of change in the detected concentration of the nitrogen oxides.

10. A system as claimed in claim 7, wherein said representative value includes the calculated rate of change in the detected concentration of the nitrogen oxides at an inflection point of a characteristic curve thereof.

11. The system as claimed in claim 7, wherein said controller calculates rates of change by using nitrogen oxide concentration signals from only the nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst.

12. A method of diagnosing deterioration of a nitrogen oxide catalyst coupled to an internal combustion engine, said catalyst being capable of absorbing nitrogen oxides present in exhaust gas emitted from the engine during lean-burn operation and releasing the nitrogen oxides absorbed when an air/fuel ratio is less than a stoichiometric air/fuel ratio, comprising:

detecting concentration of the nitrogen oxides in the exhaust gas passing through the nitrogen oxide catalyst;

calculating rates of change in the detected concentration of the nitrogen oxides a plurality of times at any points in time during a predetermined period after the air/fuel ratio becomes less than the stoichiometric air/fuel ratio; and

comparing a representative value derived from the calculated rates of change in the detected concentration of the nitrogen oxides with a predetermined reference value to determine, in response to the comparison result, that the nitrogen oxide catalyst is deteriorated.

13. A method as claimed in claim 12, wherein said predetermined period of time includes a period of time in which the detected concentration of the nitrogen oxides varies at substantially a constant rate in an increasing direction.

14. A method as claimed in claim 12, wherein said predetermined period of time includes a period of time from a moment one of the calculated rates of change in the detected concentration of the nitrogen oxides becomes not less than a predetermined initial value or the detected concentration of the nitrogen oxides becomes not less than a predetermined initial value, to a moment one of the calculated rates of change in the detected concentration of the nitrogen oxides becomes less than a predetermined terminal value or the detected concentration of the nitrogen oxides exceeds a predetermined terminal value.

15. A method as claimed in claim 12, wherein said representative value includes an average of the calculated rates of change in the detected concentration of the nitrogen oxides.

16. A method as claimed in claim 12, wherein said representative value includes the calculated rate of change in the detected concentration of the nitrogen oxides at an inflection point of a characteristic curve thereof.

17. A method as claimed in claim 12, wherein said predetermined period starts after a predetermined time has elapsed from a moment the air/fuel ratio becomes less than the stoichiometric air/fuel ratio.

18. A method as claimed in claim 12, wherein said predetermined reference value is determined based on operation condition of the internal combustion engine.

19. A method as claimed in claim 12, wherein said predetermined period of time is determined based on operation condition of the internal combustion engine.

20. A method as claimed in claim 12, further comprising determining whether or not operation condition of the internal combustion engine is changed.

21. The method according to claim 12, wherein the step of detecting concentration of the nitrogen oxides is only performed downstream of the nitrogen oxide catalyst.