Exhaust purification device of an internal combustion engine

• US 5,412,945 A
• Filed: 08/26/1993
• Issued: 05/09/1995
• Est. Priority Date: 12/27/1991
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Iguchi, Satoshi, Katoh, Kenji, Nakanishi, Kiyoshi, Muraki, Hideaki, Kihara, Tetsuro, Inoue, Tokuta, Nohira, Hidetaka
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/107,829
• Time in Patent Office: 621 Days
• Field of Search: 60/274, 60/285, 60/286, 60/301, 60/297, 423/213.5, 423/213.7
• US Class Current: 60/285
• CPC Class Codes: B01D 2251/30 Alkali metal compounds
• CPC Class Codes: B01D 2251/40 Alkaline earth metal or magnesium compounds
• CPC Class Codes: B01D 2253/25 Coated, impregnated or composite adsorbents
• CPC Class Codes: B01D 2253/342 Monoliths
• CPC Class Codes: B01D 2257/404 Nitrogen oxides other than dinitrogen oxide
• CPC Class Codes: B01D 2258/01 Engine exhaust gases
• CPC Class Codes: B01D 2259/40009 using sensors or gas analysers
• CPC Class Codes: B01D 2259/4145 arranged in series
• CPC Class Codes: B01D 2259/4566 for use in transportation means
• CPC Class Codes: B01D 53/02 by adsorption, e.g. preparative gas chromatography solid sorbent compositions B01J20/00, preparation of inorganic compounds or elements C01
• CPC Class Codes: B01D 53/0415 Beds in cartridges
• CPC Class Codes: B01D 53/0454 Controlling adsorption controlling temperature swing adsorption B01D53/0462, controlling pressure swing adsorption B01D53/047
• 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 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 2240/18 an adsorber or absorber
• CPC Class Codes: F01N 3/0807 by using absorbents or adsorbents
• 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: F01N 3/18 characterised by methods of operation; Control
• CPC Class Codes: F01N 9/00 : Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• 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: Y02T 10/40 : Engine management systems

Abstract

A NO_x absorbent (18) which absorbs the NO_x when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent (18) is lean and releases the absorbed NO_x when the oxygen concentration of the exhaust gas flowing into the NO_x absorbent (18) is lowered, is arranged in the exhaust passage of the engine. The amount of alkali metals, alkali-earth metals or rare-earth metals contained in the NO_x absorbent (18) positioned on the downstream side, is made lower than the amount of alkali metals, alkali-earth metals or rare-earth metals contained in the NO_x absorbent (18) positioned on the upstream side, to increase a reducing ability of the NO_x absorbent (18) positioned on the downstream side as compared to the reducing ability of the NO_x absorbent (18) positioned on the upstream side.

Claims

1. An exhaust purification device of an internal combustion engine wherein an NO_x absorbent which absorbs NO_x when an air-fuel ratio of an inflowing exhaust gas is lean and releases absorbed NO_x when the oxygen concentration of the inflowing exhaust gas is lowered is arranged in an exhaust passage of the engine, and an amount of alkali metals, alkali-earth metals or rare-earth metals, contained in the NO_x absorbent positioned on the downstream side, is made lower than an amount of alkali metals, alkali-earth metals or rare-earth metals, contained in the NO_x absorbent positioned on the upstream side, to improve the reducing ability of the NO_x absorbent positioned on the downstream side as compared to the reducing ability of the NO_x absorbent positioned on the upstream side, NO_x absorbed in the NO_x absorbent being released from the NO_x absorbent when the oxygen concentration of the exhaust gas flowing into the NO_x absorbent is reduced.

2. An exhaust purification device of an internal combustion engine according to claim 1, wherein said alkali metals comprise potassium, sodium, lithium and cesium.

3. An exhaust purification device of an internal combustion engine according to claim 1, wherein said alkali-earth metal comprises barium, magnesium and calcium.

4. An exhaust purification device of an internal combustion engine according to claim 1, wherein said rare-earth metal comprises lanthanum, cerium, neodymium and yttrium.

5. An exhaust purification device of an internal combustion engine according to claim 1, wherein said NO_x absorbent contains platinum therein.

6. An exhaust purification device of an internal combustion engine according to claim 1, wherein said NO_x absorbent carries said alkali metal, said alkali-earth metal or said rare-earth metal on a carrier, and the amount of the alkali metal, the alkali-earth metal or the rare-earth metal contained in the NO_x absorbent located on an upstream side is more than 0.03 mol per 1 l of the volume of the carrier, the amount of the alkali metal, the alkali-earth metal or the rare-earth metal contained in the NO_x absorbent located on a downstream side being less than 0.01 mol per 1 l of the volume of the carrier.

7. An exhaust purification device of an internal combustion engine according to claim 6, wherein the amount of the alkali metal, the alkali-earth metal or the rare-earth metal, contained in the NO_x absorbent located on the upstream side, is between 0.1 mol and 0.3 mol per 1 l of the volume of the carrier.

8. An exhaust purification device of an internal combustion engine according to claim 6, wherein the carrier of the NO_x absorbent is a single monolithic carrier.

9. An exhaust purification device of an internal combustion engine according to claim 8, wherein the amount of the alkali metal, the alkali-earth metal or the rare-earth metal, contained in a portion of the NO_x absorbent, which is located in the most upstream side, is more than 0.03 mol per 1 l of the volume of the monolithic carrier, and the amount of the alkali metal, the alkali-earth metal or the rare-earth metal, contained in a portion of the NO_x absorbent which is located in the most downstream side, is less than 0.01 mol per 1 l of the volume of the carrier, the amount of the alkali metal, the alkali-earth metal or the rare-earth metal, contained in the NO_x absorbent, being gradually lowered from the portion of the NO_x absorbent located on the most upstream side, toward the portion of the NO_x absorbent located on the most downstream side.

10. An exhaust purification device of an internal combustion engine according to claim 6, wherein the carrier of the NO_x absorbent is formed by a pair of monolithic carriers, comprising a monolithic carrier located on a upstream side and a monolithic carrier located on a downstream side.

11. An exhaust purification device of an internal combustion engine according to claim 6, wherein the carrier of the NO_x absorbent is housed in a single casing.

12. An exhaust purification device of an internal combustion engine according to claim 1, wherein an exhaust gas continuously flows within the NO_x absorbent during the time the engine is operated.

13. An exhaust purification device of an internal combustion engine according to claim 1, wherein the NO_x absorbed in the NO_x absorbent is released from the NO_x absorbent by making the exhaust gas flowing into the NO_x absorbent rich.

14. An exhaust purification device of an internal combustion engine according to claim 1, wherein the NO_x absorbed in the NO_x absorbent is released from the NO_x absorbent by making the exhaust gas flowing into the NO_x absorbent to be substantially the stoichiometric air-fuel ratio.

15. An exhaust purification device of an internal combustion engine according to claim 1, wherein air-fuel ratio control means is provided for controlling the air-fuel ratio of the air-fuel mixture formed in an engine combustion chamber, and the absorption of NO_x into the NO_x absorbent and the releasing of NO_x from the NO_x absorbent are controlled by controlling the air-fuel ratio of the air-fuel mixture formed in the engine combustion chamber by said air-fuel ratio control means.

16. An exhaust purification device of an internal combustion engine according to claim 15, wherein said air-fuel ratio control means makes the air-fuel ratio of the air-fuel mixture formed in the combustion chamber lean when the NO_x should be absorbed into the NO_x absorbent and makes the air-fuel ratio of the air-fuel mixture formed in the combustion chamber the stoichiometric air-fuel ratio or rich when the NO_x should be released from the NO_x absorbent.

17. An exhaust purification device of an internal combustion engine according to claim 16, wherein the internal combustion engine comprises a gasoline engine and said air-fuel ratio control means controls the absorption of NO_x into the NO_x absorbent and the releasing of NO_x from the NO_x absorbent by controlling the fuel amount supplied to the engine.

18. An exhaust purification device of an internal combustion engine according to claim 1, further comprising air-fuel ratio control means which controls the air-fuel ratio of the exhaust gas discharged from the engine combustion chamber and flowing into the NO_x absorbent in the exhaust passage of the engine, and the absorption of NO_x into the NO_x absorbent and the releasing of NO_x from the NO_x absorbent are controlled by controlling the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent by said air-fuel ratio control means.

19. An exhaust purification device of an internal combustion engine according to claim 18, wherein said air-fuel ratio control means makes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent lean when the NO_x should be absorbed into the NO_x absorbent, and makes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent the stoichiometric air-fuel ratio or rich when the NO_x should be released from the NO_x absorbent.

20. An exhaust purification device of an internal combustion engine according to claim 19, wherein said air-fuel ratio control means supplies a reducing agent to the interior of the exhaust passage of the engine when the NO_x should be released from the NO_x absorbent.

21. An exhaust purification device of an internal combustion engine according to claim 20, wherein said reducing agent is made of a hydrocarbon.

22. An exhaust purification device of an internal combustion engine according to claim 21, wherein said hydrocarbon comprises at least one member selected from gasoline, isoctane, hexane, heptane, butane, propane, light oil, and kerosine.

23. An exhaust purification device of an internal combustion engine according to claim 1, further comprising NO_x releasing control means which lowers the oxygen concentration in the exhaust gas flowing into the NO_x absorbent only for a predetermined second set-up period so as to release the NO_x from the NO_x absorbent when the period for which the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is made lean and the NO_x is absorbed into the NO_x absorbent exceeds a predetermined first set-up period.

24. An exhaust purification device of an internal combustion engine according to claim 23, wherein said NO_x releasing control means makes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent the stoichiometric air-fuel ratio or rich when the NO_x should be released from the NO_x absorbent.

25. An exhaust purification device of an internal combustion engine according to claim 23, wherein the said NO_x releasing control means is provided with NO_x amount estimation means for estimating the amount of NO_x absorbed into the NO_x absorbent, and said NO_x releasing control means decides that said first set-up period has lapsed when the amount of NO_x estimated by the NO_x amount estimation means exceeds a predetermined set-up amount.

26. An exhaust purification device of an internal combustion engine according to claim 25, wherein said NO_x amount estimation means decides that the amount of NO_x absorbed in the NO_x absorbent exceeds said set-up amount when a cumulative value of the engine speed exceeds a predetermined set-up value.

27. An exhaust purification device of an internal combustion engine according to claim 25, wherein said NO_x amount estimation means decides that substantially all of the NO_x absorbed in the NO_x absorbent was released when the air-fuel ratio of the air-fuel mixture formed in the engine combustion chamber is maintained at the stoichiometric air-fuel ratio or is rich for a predetermined time or more.

28. An exhaust purification device of an internal combustion engine according to claim 23, wherein said second set-up period is substantially less than 20 seconds.