No exhaust emission control method and arrangement

• US 5,992,142 A
• Filed: 03/16/1999
• Issued: 11/30/1999
• Est. Priority Date: 09/28/1996
• Status: Expired due to Term

• Current Assignee: Volkswagen AG
• Original Assignee: Volkswagen AG
• Inventors: Pott, Ekkehard
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/270,020
• Time in Patent Office: 259 Days
• Field of Search: 60/274, 60/278, 60/299, 60/301, 60/285, 422/171, 422/177, 422/180, 422/170, 423/213.2, 423/213.5, 423/213.7
• US Class Current: 60/274
• CPC Class Codes: B01D 2255/908 O2-storage component incorporated in the catalyst
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: B01J 35/19 Catalysts containing parts with different compositions
• 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 11/002 the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2330/06 Ceramic, e.g. monoliths
• CPC Class Codes: F01N 2340/02 characterised by the distance of the apparatus to the engine, or the distance between two exhaust treating apparatuses
• CPC Class Codes: F01N 2430/00 Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2510/06 for exhaust purification, e.g. catalytic reaction
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/16 Oxygen
• 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 3/0864 Oxygen
• 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: F01N 3/2803 : characterised by structure, by material or by manufacturing of catalyst support
• CPC Class Codes: F01N 3/2828 : Ceramic multi-channel monoliths, e.g. honeycombs
• CPC Class Codes: F02B 1/04 : with fuel-air mixture admission into cylinder
• CPC Class Codes: F02D 41/0275 : the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02M 26/15 : in relation to engine exhaust purifying apparatus
• CPC Class Codes: F02M 26/46 : for determining the characteristics of gases, e.g. composition
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

NO_X conversion of exhaust gases from lean mixture engines such as Diesel engines is improved by providing a catalytic converter having three zones, the first zone containing an NO_X storage material on a γ-aluminum oxide layer, the second zone having a layer with a noble metal, and the third zone containing an oxygen storage layer.

Claims

1. An emission control method for a self-igniting internal combustion engine comprising:

supplying exhaust gases from a self-igniting internal combustion engine to an NO_X accumulator that is suitable for storing NO_X from the supplied exhaust gas under a first set of operating conditions, and from which, under a second set of operating conditions, the stored NO_X is released for reduction of the NO_X with little or no noble metal in the NO_X accumulator; and

thereafter bringing the exhaust gases into contact with a higher content of a noble metal in the NO_X accumulator or in a downstream catalytic converter.

2. A method in accordance with claim 1 wherein the exhaust gases are brought into contact with an NO_X accumulator region having little or no capacity for oxygen storage, and the exhaust gases are thereafter brought into contact with an accumulator region having a higher capacity for oxygen storage either in the NO_X accumulator or in a downstream region.

4. A method in accordance with claim 1 or claim 3 wherein the exhaust gases are conducted through at least three different treatment zones, including a first zone that is in the NO_X accumulator and has little or no noble metal, a second zone that is in the NO_X accumulator and has more noble metal than the first zone, and a third zone that is in the oxygen accumulator and has a noble metal coating.

5. A method in accordance with claim 4 wherein the exhaust gas flows through a zone preceding the third zone which has little or no NO_X storage capacity and which contains more noble metal than the first zone and has a lower oxygen storage capacity than the third zone.

6. A method in accordance with claim 4 wherein at least two of the treatment zones are in one carrier body.

7. A method in accordance with claim 1 or claim 3 wherein the second set of operating conditions are established when there is at least one condition selected from the group consisting of:

low loading;

coasting; and

idling, of the internal combustion engine.

8. A method in accordance with claim 1 or claim 3 wherein the average length of time of the duration of the first set of operating conditions is a multiple of the average length of time of the duration of the second set of operating conditions.

9. A method in accordance with claim 1 or claim 3 wherein the second set of operating conditions is dependent upon the NO_X accumulator loading.

10. A method in accordance with claim 1 or claim 3 wherein the second set of operating conditions are established only when the NO_X loading of the NO_X accumulator exceeds a predetermined level.

11. A method in accordance with claim 1 or claim 3 wherein a partial stream of the exhaust gases is supplied through an exhaust gas recirculation system to an air intake of the internal combustion engine and including the step of establishing an exhaust gas partial stream/intake air ratio under the first set of operating conditions, and increasing the exhaust gas partial stream/intake air ratio under the second set of operating conditions.

12. A method in accordance with claim 11 wherein the increase in the exhaust gas partial stream/intake air ratio occurs only in a lower partial load operating region of the internal combustion engine.

13. A method in accordance with claim 1 or claim 3 including the step of reducing the intake of air to the internal combustion engine under the second set of operating conditions.

14. A method in accordance with claim 1 or claim 3 wherein the internal combustion engine includes a direct fuel injection system.

15. A method in accordance with claim 1 or claim 3 wherein the internal combustion engine is a Diesel engine.

16. A method in accordance with claim 1 or claim 3 wherein the exhaust gases before being supplied to an NO_X accumulator region having little or no noble metal under the first set of operating conditions are passed through a converter in which an NO₂ /NO ratio present in the exhaust gases is increased and/or in which, at a temperature ≧

230°

C., at least 50% of the NO contained in the exhaust gas supplied is converted into NO₂.

17. A method in accordance with claim 1 or claim 3 wherein the reduction of the stored NO_X takes place at a λ

≦

1.05.

18. A method in accordance with claim 1 or claim 3 wherein the NO_X accumulator contains an aluminum oxide.

19. A method in accordance with claim 18 wherein the aluminum oxide is γ

aluminum oxide.

20. A method in accordance with claim 1 or claim 3 wherein the NO_X accumulator contains an element from the group consisting of alkali metals, alkaline earth metals, rare earths, lanthanum, titanium, copper and manganese.

21. A method in accordance with claim 1 or claim 3 wherein the NO_X accumulator absorbs NO_X and SO_X from the exhaust gases when there is an oxygen excess in the exhaust gases.

22. A method in accordance with claim 1 or claim 3 wherein the NO_X accumulator releases at least one of NO_X and SO_X in one of:

a reducing atmosphere; and

an atmosphere with low oxygen concentration.

23. A method in accordance with claim 1 or claim 3 wherein an oxygen concentration determining device provides a signal representing the oxygen concentration as an input to a control unit which establishes the first or second set of operating conditions.

24. A method in accordance with claim 23 wherein the control unit receives signals representing both the oxygen concentration and the exhaust gas temperature as input signals.

25. A method in accordance with claim 1 or claim 3 wherein the NO_X accumulator releases at least one of NO_X and SO_X at high temperatures.

26. A method in accordance with claim 25 wherein a temperature determining device provides a signal representing the temperature of the exhaust gases or of the NO_X accumulator.

27. A method in accordance with claim 26 wherein the control unit receives signals representing both the oxygen concentration and the exhaust gas temperature as input signals.

3. An emission control method for an internal combustion engine comprising:

supplying exhaust gases from an internal combustion engine to an NO_X accumulator that is suitable for storing NO_X from the supplied exhaust gas under a first set of operating conditions, and from which, under a second set of operating conditions, the stored NO_X is released for reduction of the NO_X ;

bringing the exhaust gases into contact with an NO_X accumulator region having little or no capacity for oxygen storage; and

thereafter bringing the exhaust gases into contact with an accumulator region having a higher capacity for oxygen storage either in the NO_X accumulator or downstream.

28. An internal combustion engine comprising an engine having an exhaust system and an NO_X accumulator in the exhaust system which is suitable for storing NO_X from exhaust gases under a first set of operating conditions, and from which the stored NO_X can be released under a second set of operating conditions for reduction of the NO_X wherein the NO_X accumulator includes at least a first region having little or no noble metal and including a second region in the exhaust system downstream from the first region having a higher content of a noble metal than the first region.

29. An internal combustion engine in accordance with claim 28 wherein the NO_X accumulator has little or no oxygen storage capacity in a third region and wherein the exhaust system includes an oxygen accumulator in a fourth region downstream of a third region which works in cooperation with an oxidation catalyst.

33. An internal combustion engine in accordance with one of claims 28, 30 or 31 wherein a plurality of the exhaust gas treatment regions are arranged on one carrier.

34. An internal combustion engine in accordance with one of claims 28, 30 or 31 including a throttle in an air intake for the internal combustion engine and upstream of the outlet from an exhaust gas recirculation system by which the quantity of air flowing to the air intake of the internal combustion engine can be changed.

35. An internal combustion engine in accordance with one of claims 28, 30 or 31 including a converter which has an overall volume in the range from 10% to 25% of the displacement of the engine and which contains at least 60 g/ft³ of platinum and is located between the NO_X accumulator and an exhaust gas outlet from the internal combustion engine.

36. An internal combustion engine in accordance with one of claims 28, 30 or 31 including a direct fuel injection unit in the engine.

37. An internal combustion engine in accordance with one of the claims 28, 30 or 31 wherein the engine is a Diesel engine.

30. An internal combustion engine comprising an engine having an exhaust system, an NO_X accumulator in the exhaust system which is suitable for storing NO_X from exhaust gases under a first set of operating conditions, and from which the stored NO_X can be released under a second set of operation conditions for reduction of the NO_X, wherein the NO_X accumulator contains a first region with little or no oxygen storage capacity and, including a second region downstream from the first region containing an oxygen accumulator which works in cooperation with an oxidation catalyst.

31. An internal combustion engine comprising an engine having an exhaust system, at least three exhaust gas treatment regions in the exhaust system including an NO_X accumulator, a first region in the NO_X accumulator containing little or no noble metal, a second region in the NO_X accumulator downstream from the first region containing more noble metal than the first region, and a third region in the exhaust system downstream from the second region containing an oxygen accumulator with a noble metal coating.

32. An internal combustion engine in accordance with claim 31 including a fourth region downstream from the first region and upstream from the third region which has little or no NO_X storage capacity and little or no oxygen storage capacity and which has a higher noble metal content than the first region.