Exhaust purification system for internal combustion engine

Patent metadata

Field	Value
Publication number	US-9297288-B2
Application number	US-201114232694-A
Country	US
Kind code	B2
Filing date	Dec 16, 2011
Priority date	Jul 15, 2011
Publication date	Mar 29, 2016
Grant date	Mar 29, 2016

Abstract

Provided is an exhaust purification system for an internal combustion engine. The exhaust purification system comprising: a NO X purifying catalyst arranged in an exhaust passage of the internal combustion engine, wherein the NO X purifying catalyst comprises a base metal supported on a catalyst support; an oxygen sensor arranged at the downstream side of the NO X purifying catalyst in the exhaust passage; and an air-fuel, ratio control means for controlling the air-fuel ratio of exhaust gas flowing into the NO X purifying catalyst; wherein when the NO X purifying catalyst suffers from predetermined oxygen poisoning, the air-fuel ratio control means controls the air-fuel ratio of the exhaust gas, which flows into the NO X purifying catalyst, to a first air-fuel ratio wherein the first air-fuel ratio is richer than a theoretical air-fuel ratio, and then the air-fuel ratio control means switches the air-fuel ratio of the exhaust gas, which flows into the NO X purifying catalyst, to a second air-fuel ratio on the basis of an output value from the oxygen sensor wherein the second air-fuel ratio is leaner than the first air-fuel ratio.

First claim

The invention claimed is:

1. An exhaust purification system for an internal combustion engine comprising:
a NO X purifying catalyst arranged in an exhaust passage of said internal combustion engine, wherein said NO X purifying catalyst comprises a base metal supported on a catalyst support;
an oxygen sensor arranged at a downstream side of said NO X purifying catalyst in the exhaust passage; and
an air-fuel ratio controller configured to control an air-fuel ratio of exhaust gas flowing into said NO X purifying catalyst;
wherein when said NO X purifying catalyst suffers from a predetermined oxygen poisoning, said air-fuel ratio controller controls the air-fuel ratio of the exhaust gas, which flows into said NO X purifying catalyst, to a first air-fuel ratio wherein said first air-fuel ratio is richer than a theoretical air-fuel ratio, and then said air-fuel ratio controller switches the air-fuel ratio of the exhaust gas, which flows into said NO X purifying catalyst, to a second air-fuel ratio based on a differential value of an output value from said oxygen sensor wherein said second air-fuel ratio is leaner than said first air-fuel ratio.

2. The exhaust purification system for an internal combustion engine as claimed in claim 1 , wherein said first air-fuel ratio is switched to said second air-fuel ratio when or after a differential value of an output value from said oxygen sensor becomes maximum.

3. The exhaust purification system for an internal combustion engine as claimed in claim 1 , wherein said base metal is at least one metal selected from the group consisting of Cu, Mn, Ni, Fe, Co, Mo, W, Zn, V, and Mg.

4. The exhaust purification system for an internal combustion engine as claimed in claim 3 , wherein said base metal is Cu or Ni.

5. The exhaust purification system for an internal combustion engine as claimed in claim 1 , wherein said second air-fuel ratio is richer than a theoretical air-fuel ratio.

6. The exhaust purification system for an internal combustion engine as claimed in claim 5 , wherein said first air-fuel ratio is 14.0 or less and said second air-fuel ratio is 14.4 to less than 14.6.

7. The exhaust purification system for an internal combustion engine as claimed in claim 1 , wherein after said first air-fuel ratio is switched to said second air-fuel ratio, a switching control is performed to alternately switch between said second air-fuel ratio and a third air-fuel ratio wherein said third air-fuel ratio is richer than said second air-fuel ratio.

8. The exhaust purification system for an internal combustion engine as claimed in claim 7 , wherein said second air-fuel ratio is 14.6 to 15.0 and said third air-fuel ratio is 14.4 or less.

9. The exhaust purification system for an internal combustion engine as claimed in claim 8 , wherein said second air-fuel ratio is 14.8 to 15.0.

10. The exhaust purification system for an internal combustion engine as claimed in claim 7 , wherein said second air-fuel ratio and said third air-fuel ratio are alternately switched at same time intervals.

11. The exhaust purification system for an internal combustion engine as claimed in claim 10 , wherein a switching time of said second air-fuel ratio and said third air-fuel ratio is 0.1 seconds to 1 second.

12. The exhaust purification system for an internal combustion engine as claimed in claim 11 , wherein the switching time of said second air-fuel ratio and said third air-fuel ratio is 0.1 seconds to 0.5 seconds.

13. The exhaust purification system for an internal combustion engine as claimed in claim 10 , wherein when an amount of fluctuation of an output value from said oxygen sensor exceeds a first value, a switching time of said second air-fuel ratio and said third air-fuel ratio is made shorter.

14. The exhaust purification system for an internal combustion engine as claimed in claim 13 , wherein the switching time of said second air-fuel ratio and said third air-fuel ratio is made shorter so that the amount of fluctuation of the output value from said oxygen sensor is controlled to a second value or less, wherein said second value is smaller than said first value.

15. The exhaust purification system for an internal combustion engine as claimed in claim 14 , wherein said oxygen sensor is a zirconia oxygen sensor, said first value is 0.05V, and said second value is 0.02V.

16. The exhaust purification system for an internal combustion engine as claimed in claim 10 , wherein a switching time of said second air-fuel ratio and said third air-fuel ratio is set so that an amount of oxygen derived from oxidizing gas in exhaust gas flowing into said NO X purifying catalyst is equal to or lower than an allowable oxygen amount of said NO X purifying catalyst.

17. The exhaust purification system for an internal combustion engine as claimed in claim 10 , wherein said second air-fuel ratio and said third air-fuel ratio are set so that when a switching time of said second air-fuel ratio and said third air-fuel ratio reaches a predetermined value, an average A/F value of said second air-fuel ratio and said third air-fuel ratio becomes smaller.

18. The exhaust purification system for an internal combustion engine as claimed in claim 17 , wherein an average A/F value of said second air-fuel ratio and said third air-fuel ratio is calculated based on an intake air amount of the internal combustion engine, and the values of said second air-fuel ratio and said third air-fuel ratio are set based on said average A/F value.

19. The exhaust purification system for an internal combustion engine as claimed in claim 18 , wherein said base metal is Cu and said average A/F value is calculated by the following formula:
Average A/F value=−0.00132 Ga 2 +14.6, wherein Ga is an intake air amount (g/s) of the internal combustion engine.

20. The exhaust purification system for an internal combustion engine as claimed in claim 18 , wherein said base metal is Ni, said NO X purifying catalyst further comprises Au, and said average A/F value is calculated by the following formula:
Average A/F value=−0.00065 Ga 2 +14.55, wherein Ga is an intake air amount (g/s) of the internal combustion engine.

21. The exhaust purification system for an internal combustion engine as claimed in claim 17 , wherein when said average A/F value reaches a predetermined value, said switching control is stopped to control an air-fuel ratio of the exhaust gas, which flows into said NO X purifying catalyst, to an air-fuel ratio leaner than a theoretical air-fuel ratio.

22. The exhaust purification system for an internal combustion engine as claimed in claim 1 , further comprising an oxidation catalyst arranged at an upstream side of said NO X purifying catalyst in the exhaust passage, wherein said oxidation catalyst comprises at least one element selected from the group consisting of Fe, Co, Ag, Zn, and Mn supported on a catalyst support.

23. The exhaust purification system for an internal combustion engine as claimed in claim 1 , further comprising:
an additional oxidation catalyst for purifying HC and CO by oxidation, wherein said additional oxidation catalyst is arranged at a downstream side of said NO X purifying catalyst in the exhaust passage; and
an air introducer configured to introduce air in the exhaust gas upstream of said additional oxidation catalyst, wherein said air introducer is arranged at a downstream side of said NO X purifying catalyst in the exhaust passage.

Assignees

• Osaki Mayuko
• Akashi Kazutoshi
• Watanabe Masao
• Takagi Shigeharu
• Nobukawa Takeshi
• Toyota Motor Co Ltd

Inventors

• Osaki Mayuko
• Akashi Kazutoshi
• Watanabe Masao
• Takagi Shigeharu
• Nobukawa Takeshi

Classifications

• F02D41/0295

  Control according to the amount of oxygen that is stored on the exhaust gas treating apparatus · CPC title

• F01N3/30

  Arrangements for supply of additional air (control, e.g. using by-passes or variable air pump drives, F01N3/22) · CPC title

• F01N2570/14

  Nitrogen oxides · CPC title

• F02D41/126

  transitional corrections at the end of the cut-off period · CPC title

• F02D41/1439

  characterised by the position of the sensor · CPC title