Exhaust purification device of an engine

• US 5,715,679 A
• Filed: 03/22/1996
• Issued: 02/10/1998
• Est. Priority Date: 03/24/1995
• 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:
  US08/620,768
• Time in Patent Office: 690 Days
• Field of Search: 60/276, 60/285, 60/297, 60/301, 60/311
• US Class Current: 60/276
• CPC Class Codes: B01D 53/9481 Catalyst preceded by an adsorption device without catalytic function for temporary storage of contaminants, e.g. during cold start
• 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 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: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1402 Adaptive control
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An exhaust purification device of an engine providing a NO_x absorbent arranged in the exhaust passage. An O₂ sensor generating a current proportional to the air-fuel ratio is arranged in the engine exhaust passage downstream of the NO_x absorbent. The amount of NO_x actually absorbed in the NO_x absorbent at the time of release of the NO_x is calculated on the basis of the output signal of this O₂ sensor. On the basis of this calculated amount of NO_x, correction is made so that the estimated amount of NO_x represents the actual amount of absorption of NO_x. When this corrected estimated amount of NO_x reaches a set value, the action of releasing the NO_x from the NO_x absorbent is carried out.

Claims

1. An exhaust purification device of an engine having an exhaust passage, comprising:

an NO_x absorbent arranged in the exhaust passage, said NO_x absorbent absorbing NO_x therein when an air-fuel ratio of exhaust gas flowing into the NO_x absorbent is lean and releasing absorbed NO_x therefrom when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent becomes rich;

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

NO_x amount calculating means for calculating an entire amount of NO_x stored in the NO_x absorbent on the basis of the output signal of said air-fuel ratio detecting means when the air-fuel ratio of exhaust gas flowing into the NO_x absorbent is changed from lean to rich so as to release NO_x from the NO_x absorbent;

correction value calculating means for calculating a correction value for said estimated amount of NO_x, which correction value is a value by which 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 so as to release NO_x from the NO_x absorbent indicates said entire amount of NO_x calculated by said NO_x amount calculating means; and

control means for controlling the air-fuel ratio of exhaust gas flowing into the NO_x absorbent to change the air-fuel ratio of exhaust gas flowing into the NO_x absorbent from lean to rich to release NO_x from the NO_x absorbent when said estimated amount of NO_x corrected by said correction value exceeds a predetermined amount.

2. An exhaust purification device as set forth in claim 1, wherein the NO_x absorbent contains at least one component selected from alkali metals consisting of potassium, sodium, lithium, and cesium, alkali earth metals consisting of barium and calcium, and rare earth metals consisting of lanthanum and yttrium and platinum.

3. An exhaust purification device as set forth in claim 1, wherein said estimation means increases an NO_x storage amount in accordance with the amount of absorption of NO_x determined according to the engine operating state when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is lean, and then decreases the NO_x storage amount in accordance with the NO_x releasing amount determined according to the engine operating state when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is rich, thereby to find said NO_x estimated amount.

4. An exhaust purification device as set forth in claim 3, 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.

5. An exhaust purification device as set forth in claim 3, wherein said NO_x releasing amount determined according to the engine operating state is proportional to the excess fuel amount.

6. An exhaust purification device as set forth in claim 1, wherein said air-fuel ratio detection means generates an output signal indicating that the air-fuel ratio is slightly lean during a period for which the NO_x is released from the NO_x absorbent after the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is changed from lean to rich and generates an output signal indicating that the air-fuel ratio is rich when the NO_x releasing action from the NO_x absorbent is completed.

7. An exhaust purification device as set forth in claim 6, wherein said air-fuel ratio detection means comprises an air-fuel ratio detection sensor which increases its output current proportional to the increase of the air-fuel ratio.

8. An exhaust purification device as set forth in claim 6, wherein said NO_x amount calculation means decreases the NO_x storage amount in accordance with the NO_x releasing amount 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 to when said air-fuel ratio detection means generates the output signal indicating that the air-fuel ratio is rich, and thereby said entire amount of NO_x stored in the NO_x absorbent is calculated.

9. An exhaust purification device as set forth in claim 8, wherein said NO_x releasing amount determined according to the engine operating state is proportional to the excess fuel amount.

10. An exhaust purification device as set forth in claim 1, wherein when defining the estimated amount of NO_x estimated by said estimation means as Σ

NOX and defining the correction value calculated by said correction value calculation 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

NOX.

11. An exhaust purification device as set forth in claim 10, wherein when defining said entire amount of NO_x calculated by said NO_x amount calculation means as XNO_x, said correction value KX is updated on the basis of the following equation:

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

XNO.sub.x /Σ

NKX.

12. An exhaust purification device as set forth in claim 11, wherein when the difference between the estimated amount of NO_x Σ

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

13. An exhaust purification device as set forth in claim 1, wherein the predetermined amount in said control means is smaller than the maximum amount of absorption of NO_x of the NO_x absorbent.

14. An exhaust purification device as set forth in claim 1, wherein the predetermined amount in said control means is larger than the maximum amount of absorption of NO_x of the NO_x absorbent, and deterioration decision means deciding the degree of deterioration of the NO_x absorbent on the basis of said entire amount of NO_x calculated by said NO_x amount calculation means is provided.

15. An exhaust purification device as set forth in claim 14, wherein said predetermined amount is made larger than said entire amount of NO_x by exactly a predetermined proportion.

16. An exhaust purification device as set forth in claim 15, wherein said proportion is larger than 1.0 and smaller than 1.3.

17. An exhaust purification device as set forth in claim 14, wherein when said entire amount of NO_x becomes smaller than the predetermined amount, said deterioration decision means decides that the NO_x absorbent is deteriorated.

18. An exhaust purification device as set forth in claim 1, wherein said NO_x amount calculation means comprises first NO_x amount calculation means for calculating said entire amount of NO_x for only releasing NO_x from the NO_x absorbent and second NO_x amount calculation means for calculating said entire amount of NO_x for releasing NO_x from the NO_x absorbent and detecting the degree of deterioration of the NO_x absorbent, when the entire amount of NO_x is calculated by the first NO_x amount calculation means, the predetermined amount in said control means is made smaller than the maximum amount of absorption of NO_x of the NO_x absorbent, and when the entire amount of NO_x is calculated by the second NO_x amount calculation means, the predetermined amount in said control means is made larger than the maximum amount of absorption of NO_x of the NO_x absorbent.

19. An exhaust purification device as set forth in claim 18, wherein the frequency of that the entire amount of NO_x is calculated by the second NO_x amount calculation means is lower than the frequency of that the entire amount of NO_x is calculated by the first amount of NO_x calculation means.

20. An exhaust purification device as set forth in claim 18, wherein the entire amount of NO_x calculated by said second NO_x amount calculation means represents the maximum amount of absorption of NO_x VNO_x of the NO_x absorbent, when the entire amount of NO_x is calculated by the first NO_x amount calculation means, the predetermined amount is made smaller than the maximum amount of absorption of NO_x VNO_x by exactly the predetermined proportion, and when the entire amount of NO_x is calculated by the second NO_x amount calculation means, the predetermined amount is made larger than the maximum amount of absorption of NO_x VNO_x by exactly the predetermined proportion.

21. An exhaust purification device as set forth in claim 20, wherein deterioration decision means is provided for deciding the degree of deterioration of the NO_x absorbent on the basis of said maximum amount of absorption of NO_x VNO_x.