Device for detecting deterioration of NO.sub.x absorbent

• US 5,713,199 A
• Filed: 03/27/1996
• Issued: 02/03/1998
• Est. Priority Date: 03/28/1995
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Asanuma, Takamitsu, Iguchi, Satoshi, Tanaka, Toshiaki, Takeshima, Shinichi, Katoh, Kenji, Kihara, Tetsuro
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US08/624,034
• Time in Patent Office: 678 Days
• Field of Search: 60/276, 60/277, 60/285, 60/297, 60/301, 60/311, 73/118.1
• US Class Current: 60/276
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 2200/0808 NOx storage capacity, i.e. maximum amount of NOx that can be stored on NOx trap
• CPC Class Codes: F02D 2200/0814 Oxygen storage amount
• CPC Class Codes: F02D 2200/0816 Oxygen storage capacity
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1441 Plural sensors
• 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 device for detecting deterioration of a NO_x absorbent arranged in the exhaust passage of an engine. An O₂ sensor generating a current proportional to the air-fuel ratio is arranged in the exhaust passage downstream of the NO_x absorbent. When the amount of NO_x absorbed in the NO_x absorbent is almost zero or after the amount of NO_x absorbed in the NO_x absorbent is made almost zero, the air-fuel ratio of the air-fuel mixture is changed from lean to rich, and the amount of oxygen stored in the NO_x absorbent is detected from the output signal of the O₂ sensor at this time. Further, the NO_x absorbing capability is found by using this detected oxygen amount.

Claims

1. A device for detecting deterioration of a NO_x absorbent arranged in an exhaust passage of an engine, said NO_x absorbent absorbing NO_x and storing oxygen therein when an air-fuel ratio of exhaust gas flowing into the NO_x absorbent is lean and releasing absorbed NO_x and stored oxygen therefrom when the air-fuel ratio of exhaust gas flowing into the NO_x absorbent becomes rich, said device comprising:

air-fuel ratio detecting means arranged in the exhaust passage downstream of the NO_x absorbent for producing an output signal indicating an air-fuel ratio of exhaust gas which flows out from the NO_x absorbent;

air-fuel ratio changing means for changing the air-fuel ratio of exhaust gas flowing into the NO_x absorbent from lean to rich when an amount of NO_x absorbed in the NO_x absorbent is almost zero; and

oxygen amount detecting means for detecting an amount of oxygen stored in the NO_x absorbent on the basis of the output signal of said air-fuel ratio detecting means after the air-fuel ratio of exhaust gas flowing into the NO_x absorbent is changed from lean to rich by said air-fuel ratio changing means.

2. A device as set forth in claim 1, wherein the degree of deterioration of the oxidation reduction ability of the NO_x absorbent is judged based on the amount of oxygen detected by said air-fuel ratio detecting means.

3. A device as set forth in claim 1, wherein said air-fuel ratio detecting means generates an output signal showing that the air-fuel ratio is slightly lean in the period after the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is changed from lean to rich by said air-fuel ratio changing means while oxygen is being released from the NO_x absorbent and generates an output signal showing that the air-fuel ratio is rich when the action of releasing oxygen from the NO_x absorbent is completed.

4. A device as set forth in claim 3 wherein said air-fuel ratio detecting means is comprised of an air-fuel ratio detection sensor where the output current increases in proportion to the increase of the air-fuel ratio.

5. A device as set forth in claim 3 wherein said oxygen amount detecting means reduces the amount of storage of oxygen in accordance with the amount of release of oxygen determined by the operating state of the engine during a period from when the air-fuel ratio is changed from lean to rich by said air-fuel ratio changing means to when said air-fuel ratio detecting means generates an output signal showing that the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is rich and thereby calculates the entire amount of the oxygen stored in the NO_x absorbent.

6. A device as set forth in claim 5, wherein said amount of oxygen determined by the engine operating state is proportional to the amount of excess fuel.

7. A device as set forth in claim 1, wherein judgement means is provided for judging if the amount of NO_x absorbed in the NO_x absorbent should be made substantially zero and, when it is judged by said judgement means that the amount of NO_x absorbed in the NO_x absorbent should be made substantially zero, said air-fuel ratio changing means changing the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from rich to lean and then holding it lean temporarily, then changing it from lean to rich and said oxygen amount detecting means detects the amount of oxygen stored in the NO_x absorbent based on the output signal of the air-fuel ratio detecting means after the second switching from lean to rich.

8. A device as set forth in claim 7, wherein said judgement means judges if the amount of NO_x absorbed in the NO_x absorbent is substantially zero and, when the amount of NO_x absorbed in the NO_x absorbent is not substantially zero, judges that the amount of NO_x absorbed in the NO_x absorbent should be made substantially zero.

9. A device as set forth in claim 7, wherein said judgement means judges if the engine operating state is a deceleration state where the supply of fuel should be stopped and, when the engine operating state is a deceleration state where the supply of fuel should be stopped, it is judged that the amount of NO_x absorbed in the NO_x absorbent should be made substantially zero.

10. A device as set forth in claim 9, wherein said air-fuel ratio changing means temporarily holds the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent lean by stopping the supply of fuel.

11. A device as set forth in claim 7, wherein said air-fuel ratio changing means changes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from rich to lean based on an output signal of the air-fuel ratio detecting means after the first change of the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from lean to rich.

12. A device as set forth in claim 1, wherein judgement means is provided for judging if the amount of NO_x absorbed in the NO_x absorbent is substantially zero and, when a lean air-fuel mixture is being burned and said judgement means judges that the NO_x absorbed in the NO_x absorbent is substantially zero, said air-fuel ratio changing means changes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from lean to rich, and said oxygen amount detecting means detects the amount of oxygen stored in the NO_x absorbent based on the output signal of the air-fuel ratio detecting means after this change from lean to rich.

13. A device as set forth in claim 1, wherein judgement means is provided for judging if the amount of NO_x absorbed in the NO_x absorbent is substantially zero and, when an air-fuel mixture of the stoichiometric air-fuel ratio is being burned and said judgement means judges that the NO_x absorbed in the NO_x absorbent is substantially zero, said air-fuel ratio changing means changes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from the stoichiometric air-fuel ratio to lean and then temporarily thereafter maintains it lean, then changes it from lean to rich, and said oxygen amount detecting means detects the amount of oxygen stored in the NO_x absorbent based on the output signal of the air-fuel ratio detecting means after this change from lean to rich.

14. A device as set forth in claim 13, wherein said judgement means judges if the time of continuous operation of the engine at the stoichiometric air-fuel ratio has exceeded a predetermined time and, when said time of continuous operation of the engine at the stoichiometric air-fuel ratio has exceeded the predetermined time, it is judged that the amount of NO_x absorbed in the NO_x absorbent is substantially zero.

15. A device as set forth in claim 1, comprising NO_x amount detecting means for detecting the sum of the amount of oxygen stored in the NO_x absorbent and the amount of NO_x absorbed in the NO_x absorbent based on the output signal of the air-fuel ratio detecting means after the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is changed from lean to rich by the air-fuel ratio changing means and NO_x amount calculating means for calculating the amount of NO_x absorbed in the NO_x absorbent by subtracting the amount of oxygen detected by said oxygen amount detecting means from the sum of the amount of oxygen and the amount of NO_x.

16. A device as set forth in claim 15, wherein the degree of deterioration of the NO_x absorbing ability of the NO_x absorbent is judged based on the amount of NO_x calculated by the NO_x amount calculating means.

17. A device according to claim 15, wherein said air-fuel ratio detecting means generates an output signal indicating that the air-fuel ratio of the exhaust gas flowing into the NO_x, absorbent is slightly lean during a period for which the oxygen and NO_x are released from the NO_x absorbent after the air-fuel ratio of the exhaust gas is changed from lean to rich and generates an output signal indicating that the air-fuel ratio is rich when the oxygen and NO_x releasing action from the NO, absorbent is completed.

18. A device as set forth in claim 17, wherein said air-fuel ratio detecting means comprises an air-fuel ratio detection sensor which increases its output current proportional to the increase of the air-fuel ratio.

19. A device as set forth in claim 17, wherein said oxygen and NO_x amount calculating means decreases the sum of the amount of storage of oxygen and the amount of storage of NO_x in accordance with the sum of the amount of release of oxygen and the amount of release of NO_x determined according to the engine operating state during a period from when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is changed from lean to rich by said air-fuel ratio control means to when said air-fuel ratio detecting means generates the output signal indicating that the air-fuel ratio is rich and thereby calculates the sum of the entire amount of oxygen and the entire amount of NO_x stored in the NO_x absorbent.

20. A device as set forth in claim 19, wherein said sum of the amount of release of oxygen and amount of release of NO_x determined according to the engine operating state is proportional to the excess fuel amount.

21. A device as set forth in claim 1, wherein said device comprises

estimating means for estimating an amount of NO_x absorbed in the NO_x absorbent to obtain an estimated amount of NO_x stored in the NO_x absorbent;

air-fuel ratio control means for changing the air-fuel ratio of exhaust gas flowing into the NO_x absorbent from lean to rich separately from the operation of changing the air-fuel ratio by said air-fuel ratio changing means;

oxygen amount-NO_x amount detecting means for detecting the sum of an amount of oxygen stored in the NO_x absorbent and an amount of NO_x absorbed in the NO_x absorbent on the basis of the output signal of said air-fuel ratio detecting means after the air-fuel ratio of exhaust gas flowing into the NO_x absorbent is changed over from lean to rich by said air-fuel ratio control means;

NO_x amount calculating means for calculating an entire amount of NO_x absorbed in the NO_x absorbent by subtracting the amount of oxygen detected by said oxygen amount detecting means from the sum of the amount of oxygen and the amount of NO_x ; and

correction value calculating means for calculating a correction value for said estimated amount of NO_x, which correction value is a value whereby said estimated amount of NO_x corrected by said correction value when the air-fuel ratio of exhaust gas flowing into the NO_x absorbent is changed from lean to rich by said air-fuel ratio control means indicates said entire amount of NO_x calculated by said NO_x amount calculating means, said air-fuel ratio control means changing over the air-fuel ratio of exhaust gas flowing into the NO_x absorbent from lean to rich when said estimated amount of NO_x corrected by said correction value exceeds a predetermined set value.

22. A device as set forth in claim 21, wherein said estimating means finds the estimated amount of the NO_x by increasing the amount of storage of NO_x in accordance with the amount of absorption of NO_x determined by the engine operating state when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is lean and decreasing the amount of storage of NO_x in accordance with the amount of release of NO_x determined by the engine operating state when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is rich.

23. A device as set forth in claim 22, wherein said amount of absorption of NO_x determined according to the engine operating state is a function of the engine speed and the engine load.

24. A device as set forth in claim 22, wherein said NO_x releasing amount determined according to the engine operating state is proportional to the excess fuel amount.

25. A device according to claim 21, wherein said air-fuel ratio detecting means generates an output signal indicating that the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is slightly lean during a period for which the oxygen and NO_x are released from the NO_x absorbent after the air-fuel ratio of the exhaust gas is changed from lean to rich and generates an output signal indicating that the air-fuel ratio is rich when the oxygen and NO_x releasing action from the NO_x absorbent is completed.

26. A device as set forth in claim 25, wherein said air-fuel ratio detecting means comprises an air-fuel ratio detection sensor which increases its output current proportional to the increase of the air-fuel ratio.

27. A device as set forth in claim 25, wherein said oxygen and NO_x amount calculating means decreases the sum of the amount of storage of oxygen and the amount of storage of NO_x in accordance with the sum of the amount of release of oxygen and the amount of release of NO_x determined according to the engine operating state during a period from when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is changed from lean to rich by said air-fuel ratio control means to when said air-fuel ratio detecting means generates the output signal indicating that the air-fuel ratio is rich and thereby calculates the sum of the entire amount of oxygen and the entire amount of NO_x stored in the NO_x absorbent.

28. A device as set forth in claim 27, wherein said sum of the amount of release of oxygen and amount of release of NO_x determined according to the engine operating state is proportional to the excess fuel amount.

29. A device as set forth in claim 21, wherein when defining the estimated amount of NO_x estimated by said air-fuel ratio control means as Σ

NO_x and defining the correction value calculated by said correction value calculating means as KX, the estimated amount of NO_x Σ

NKX corrected by said correction value is represented by the following equation;

space="preserve" listing-type="equation">Σ

NKX=KX·

Σ

NO.sub.x.

30. A device as set forth in claim 29, wherein when defining said entire amount of NO_x calculated by said NO_x amount calculating means as XNO_x, said correction value KX is updated on the basis of the following equation:

space="preserve" listing-type="equation">KX=KX·

Σ

XNO.sub.x /Σ

NKX.

31. A device as set forth in claim 30, wherein when the difference between the estimated amount Σ

NKX of NO_x corrected by said correction value and said entire amount XNO_x of NO_x is larger than a predetermined value, said correction value KX is updated.

32. A device as set forth in claim 21, wherein the predetermined set value in the air-fuel ratio control means is larger than the maximum amount of absorption of NO_x of the NO_x absorbent and the degree of deterioration of the NO_x absorbing ability of the NO_x absorbent is judged based on the entire amount of NO_x calculated by the NO_x amount calculating means.

33. A device as set forth in claim 32, wherein said predetermined set value is made larger than said entire amount of NO_x by exactly a predetermined proportion.

34. A device as set forth in claim 33, wherein said proportion is larger than 1.0 and smaller than 1.3.

35. A device as set forth in claim 21, wherein the frequency of the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent being changed from lean to rich by the air-fuel ratio changing means is lower than the frequency of the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent being changed from lean to rich by said air-fuel ratio changing means.