Exhaust purification device of an engine

• US 5,735,119 A
• Filed: 03/22/1996
• Issued: 04/07/1998
• 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, Katoh, Kenji, Kihara, Tetsuro
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US08/620,623
• Time in Patent Office: 746 Days
• Field of Search: 60/276, 60/285, 60/297, 60/301, 60/311
• 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 2900/0422 measuring the elapsed time
• 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 41/0235 in relation with the state of the exhaust gas treating apparatus control of exhaust gas treating apparatus per se F01N
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An exhaust gas purification device of an engine providing a NO_x absorbent arranged in the exhaust passage. An O₂ sensor is arranged in the engine exhaust passage downstream of the NO_x absorbent. The degree of deterioration of the NO_x absorbent is detected from the output signal of the O₂ sensor. The cycle for making the air-fuel ratio of the air-fuel mixture rich for causing the release of the NO_x from the NO_x absorbent and the rich time at that time are shortened the greater the deterioration of the NO_x absorbent.

Claims

1. An exhaust gas 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;

air-fuel ratio control means for controlling the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent to temporarily change the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from lean to rich at certain time intervals to release NO_x from the NO_x absorbent;

deterioration detecting means for detecting a degree of deterioration of the NO_x absorbent; and

NO_x releasing control means for controlling at least one of a period at which the air-fuel ratio of exhaust gas flowing into the NO_x absorbent is changed from lean to rich and a rich time during which the air-fuel ratio of exhaust gas flowing into the NO_x absorbent is made rich to make one of said period and said rich time shorter as the degree of deterioration of the NO_x absorbent becomes higher.

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 air-fuel ratio control means temporarily changes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from lean to rich when the amount of NO_x absorbed in the NO_x absorbent exceeds a set value larger than the maximum amount of absorption of NO_x of the NO_x absorbent and said deterioration detecting means is provided with air-fuel ratio detecting means disposed in the exhaust passage downstream of the NO_x absorbent for generating an output signal indicating the air-fuel ratio of the exhaust gas flowing out from the NO_x absorbent and NO_x amount calculating means for calculating the entire amount of NO_x stored in the NO_x absorbent based on the output signal of the air-fuel ratio detecting means 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 and said NO_x releasing control means shortens at least one of said cycle and said rich time along with the reduction of the entire amount of NO_x calculated by said NO_x amount calculating means.

4. An exhaust purification device as set forth in claim 3, wherein the entire amount of NO_x calculated by said NO_x amount calculating means indicates the maximum amount of absorption of NO_x of the NO_x absorbent and said set value is made larger by a predetermined rate from said maximum amount of absorption of NO_x.

5. An exhaust purification device as set forth in claim 1, wherein said air-fuel ratio control means is comprised of first air-fuel ratio control means for changing the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent temporarily from lean to rich at said cycle controlled by said NO_x releasing control means so as to cause the release of NO_x from the NO_x absorbent and second air-fuel ratio control means for changing the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent temporarily from lean to rich so as to cause the NO_x to be released from the NO_x absorbent and to detect the degree of deterioration of the NO_x absorbent by said deterioration degree detecting means.

6. An exhaust purification device as set forth in claim 5, wherein said second air-fuel ratio control means temporarily changes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent from lean to rich when the amount of NO_x absorbed in the NO_x absorbent exceeds a set value larger than the maximum amount of absorption of NO_x of the NO_x absorbent and said deterioration detecting means is provided with air-fuel ratio detecting means disposed in the exhaust passage downstream of the NO_x absorbent for generating an output signal indicating the air-fuel ratio of the exhaust gas flowing out from the NO_x absorbent and NO_x amount calculating means for calculating an entire amount of NO_x stored in the NO_x absorbent based on the output signal of the air-fuel ratio detecting means when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is changed from lean to rich by said second air-fuel ratio control means, wherein the entire amount of NO_x calculated by said NO_x amount calculating means indicates the maximum amount of absorption of NO_x of the NO_x absorbent, and said NO_x releasing control means shortens said cycle along with the reduction of the entire amount of NO_x calculated by said NO_x amount calculating means.

7. An exhaust purification device according to claim 6, wherein said NO_x releasing control means shortens the rich time along with the reduction of the entire amount of NO_x calculated by said NO_x amount calculating means.

8. An exhaust purification device as set forth in claim 6, wherein said air-fuel ratio detecting 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.

9. An exhaust purification device as set forth in claim 8, 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.

10. An exhaust purification device as set forth in claim 8, wherein said NO_x amount calculating 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 detecting 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.

11. An exhaust purification device as set forth in claim 10, wherein said NO_x releasing amount determined according to the engine operating state is proportional to the excess fuel amount.

12. An exhaust purification device as set forth in claim 6, wherein said set amount is made larger than said entire amount of NO_x by exactly a predetermined proportion.

13. An exhaust purification device as set forth in claim 12, wherein said proportion is larger than 1.0 and smaller than 1.3.

14. An exhaust purification device as set forth in claim 6, wherein when said entire amount of NO_x becomes smaller than the set amount, said deterioration detecting means decides that the NO_x absorbent is deteriorated.

15. An exhaust purification device according to claim 6, wherein estimating means is provided for estimating an amount of NO_x absorbed in the NO_x absorbent to obtain an estimated amount of the NO_x stored in the NO_x absorbent and correction value calculating means is provided 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 to release the NO_x from the NO_x absorbent indicates said entire amount of NO_x calculated by said NO_x amount calculating means, said second air-fuel ratio control means temporarily changing 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 said set value.

16. An exhaust purification device as set forth in claim 15, 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.

17. An exhaust purification device as set forth in claim 16, 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.

18. An exhaust purification device as set forth in claim 16, wherein said NO_x releasing amount determined according to the engine operating state is proportional to the excess fuel amount.

19. An exhaust purification device as set forth in claim 15, wherein when defining the estimated amount of NO_x estimated by said air-fuel ratio control means as Σ

NOX 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

NOX.

20. An exhaust purification device as set forth in claim 19, 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·

XNO.sub.x /Σ

NKX.

21. An exhaust purification device as set forth in claim 20, 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.

22. An exhaust purification device as set forth in claim 5, wherein when the NO_x is to be released from the NO_x absorbent, the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is made rich for exactly the rich time controlled by said NO_x releasing control means.

23. An exhaust purification device as set forth in claim 5, wherein the frequency of the air-fuel ratio of the exhaust gas being changed from lean to rich by the second air-fuel ratio control means is lower than the frequency of the air-fuel ratio of the exhaust gas being changed from lean to rich by said first air-fuel ratio control means.