Exhaust purification device of internal combustion engine

• US 5,473,887 A
• Filed: 06/14/1993
• Issued: 12/12/1995
• Est. Priority Date: 10/03/1991
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Iguchi, Satoshi, Hirota, Shinya, Tanaka, Toshiaki, Takeshima, Shinichi, Araki, Yasushi, Nakanishi, Kiyoshi, Kobashi, Kiyoshi
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/066,100
• Time in Patent Office: 911 Days
• Field of Search: 60/274, 60/276, 60/297, 60/301, 60/285
• US Class Current: 60/276
• CPC Class Codes: B01D 53/9422 for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/0093 the purifying devices are of the same type
• CPC Class Codes: F01N 2240/18 an adsorber or absorber
• CPC Class Codes: F01N 2390/02 using electric components only
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• 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 3/101 Three-way catalysts
• 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 10/12 Improving ICE efficiencies

Abstract

An NO_x absorbent (18) is disposed in an exhaust passage of an internal combustion engine and the exhaust gas is constantly made to circulate through the NO_x absorbent (18) during the operation of the engine. The NO_x absorbent (18) 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 air-fuel ratio of the exhaust gas flowing into the NO_x absorbent (18) becomes the stoichiometric air-fuel ratio or rich. In the majority of the engine operation region, the lean air-fuel mixture is burned in the combustion chamber (3), and the NO_x generated at this time is absorbed into the NO_x absorbent (18). The air-fuel ratio of the exhaust gas flowing into the NO_x absorbent (18) is periodically made the stoichiometric air-fuel ratio or rich, and the NO_x absorbed in the NO_x absorbent (18) is released, and simultaneously reduced.

Claims

1. An exhaust purification device of an internal combustion engine including an exhaust passage and means for controlling an air-fuel ratio of exhaust gas from the engine, comprising an NO_x absorbent disposed within the exhaust passage, wherein the NO_x absorbent absorbs NO_x included in the exhaust flowing into the NO_x absorbent when the air-fuel ratio control means makes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent lean and releases an absorbed NO_x when an oxygen concentration in the exhaust gas flowing into the NO_x absorbent is lowered, and wherein, at all times while the engine is running, the exhaust gas continuously flows into the NO_x absorbent so that the NO_x absorbed in the NO_x absorbent while the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is lean is released from the NO_x absorbent when the oxygen concentration of the exhaust gas flowing into the NO_x absorbent is lowered.

2. An exhaust purification device of an internal combustion engine according to claim 1, wherein the air-fuel ratio control means operates to release NO_x absorbed in the NO_x absorbent by making the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent rich.

3. An exhaust purification device of an internal combustion engine according to claim 1, wherein the air-fuel ratio control means operates to release NO_x absorbed in the NO_x absorbent by making the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent substantially the stoichiometric air-fuel ratio.

4. An exhaust purification device of an internal combustion engine according to claim 1, wherein the air-fuel ratio control means maintains the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent lean for a first predetermined time and decreases the oxygen concentration in the exhaust gas flowing into the NO_x absorbent for a second predetermined time so as to release the NO_x from the NO_x absorbent, wherein the first predetermined time is at least 50 times as long as the second predetermined time.

5. An exhaust purification device of an internal combustion engine according to claim 1, wherein NO_x is absorbed into the NO_x absorbent when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is more than 18.0.

6. An exhaust purification device of an internal combustion engine according to claim 1, wherein the NO_x absorbent contains at least one substance selected from alkali metals comprising potassium, sodium, lithium, or cesium, alkali earth metals comprising barium or calcium, rare earth metals comprising lanthanum and yttrium and contains platinum.

7. An exhaust purification device of an internal combustion engine according to claim 1, wherein the NO_x absorbent comprises a composite oxide of barium and copper.

8. An exhaust purification device of an internal combustion engine according to claim 1, wherein the air-fuel ratio control means controls the air-fuel ratio of an air-fuel mixture formed in an engine combustion chamber so that the absorption of NO_x into the NO_x absorbent and the release 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.

9. An exhaust purification device of an internal combustion engine according to claim 8, 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 is not lean when the NO_x should be released from the NO_x absorbent.

10. An exhaust purification device of an internal combustion engine according to claim 9, 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.

11. An exhaust purification device of an internal combustion engine according to claim 10, wherein said air-fuel ratio control means maintains the air-fuel ratio of the air-fuel mixture formed in the combustion chamber at almost a constant lean air-fuel ratio of more than 18.0 when the NO_x should be absorbed into the NO_x absorbent.

12. An exhaust purification device of an internal combustion engine according to claim 10, further comprising memory means which stores in advance the amount of fuel determined in accordance with the operation state of the engine, said air-fuel ratio control means determines the amount of fuel supplied to the engine based on the fuel amount stored in said memory means.

13. An exhaust purification device of an internal combustion engine according to claim 10, further comprising memory means which stores in advance the basic fuel amount determined in accordance with the operation state of the engine and an air-fuel ratio sensor which is provided in the exhaust passage of the engine and detects the air-fuel ratio of the exhaust gas flowing in the exhaust passage, said air-fuel ratio control means corrects the basic fuel amount so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio by a feedback correction coefficient varied in accordance with the output signal of said air-fuel ratio sensor.

14. An exhaust purification device of an internal combustion engine according to claim 13, wherein said air-fuel ratio control means corrects the basic fuel amount so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio by the feedback correction coefficient when the NO_x should be absorbed into the NO_x absorbent and, at the same time, corrects said feedback correction coefficient by a learning coefficient so that said feedback correction coefficient fluctuates around a reference value, and said air-fuel ratio control means fixes the feedback correction value to said reference value when the NO_x should be released from the NO_x absorbent and, at the same time, determines the amount of fuel to be supplied to the engine based on the learning coefficient and the basic fuel amount.

15. An exhaust purification device of an internal combustion engine according to claim 9, wherein the internal combustion engine comprises a diesel engine equipped with a fuel injector which injects the fuel into the combustion chamber and a throttle valve disposed in the intake passage of the 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 amount of injection from the fuel injector and the opening degree of throttle valve.

16. An exhaust purification device of an internal combustion engine according to claim 15, wherein said air-fuel ratio control means increases the injection amount and decreases the throttle valve opening degree 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 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.

18. An exhaust purification device of an internal combustion engine according to claim 17, 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, while 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.

19. An exhaust purification device of an internal combustion engine according to claim 18, 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.

20. An exhaust purification device of an internal combustion engine according to claim 19, wherein said reducing agent is made of a hydrocarbon.

21. An exhaust purification device of an internal combustion engine according to claim 20, wherein said hydrocarbon comprises at least one member selected from gasoline, isoctane, hexane, heptane, butane, propane, light oil, and kerosine.

22. An exhaust purification device of an internal combustion engine according to claim 1, wherein the air-fuel ratio control means lowers the oxygen concentration in the exhaust gas flowing into the NO_x absorbent during a first predetermined set-up period of time so as to release the NO_x from the absorbent when a period of time during which the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent has previously been made lean and, during which NO_x has been absorbed into the NO_x absorbent, exceeds a predetermined second set-up period of time.

23. An exhaust purification device of an internal combustion engine according to claim 22, 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.

24. An exhaust purification device of an internal combustion engine according to claim 22, wherein the 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 second set-up period has elapsed when the amount of NO_x estimated by the NO_x amount estimation means exceeds a preliminarily determined set-up amount.

25. An exhaust purification device of an internal combustion engine according to claim 24, 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 an engine speed exceeds a preliminarily determined set-up value.

26. An exhaust purification device of an internal combustion engine according to claim 24, wherein said NO_x amount estimation means decides that substantially all of the NO_x absorbed in the NO_x absorbent has released when the air-fuel ratio of the air-fuel mixture formed in the engine combustion chamber is not lean for a predetermined time or more.

27. An exhaust purification device of an internal combustion engine according to claim 22, wherein said second set-up period is substantially less than 20 seconds.

28. An exhaust purification device of an internal combustion engine according to claim 22, wherein said NO_x releasing control means is provided with a temperature sensor for detecting a temperature of the exhaust gas flowing into the NO_x absorbent, and said NO_x releasing control means is provided with prohibition means which prohibits the lowering of the oxygen concentration in the exhaust gas flowing into the NO_x absorbent even if the period for which the NO_x is absorbed into the NO_x absorbent exceeds said first set-up period when the temperature of the exhaust gas flowing into the NO_x absorbent becomes lower than a limit temperature at which the NO_x can be absorbed by the NO_x absorbent.

29. An exhaust purification device of an internal combustion engine according to claim 28, wherein said NO_x releasing control means immediately lowers the oxygen concentration in the exhaust gas flowing into the NO_x absorbent when the temperature of the exhaust gas flowing into the NO_x absorbent becomes higher than said limit temperature after the oxygen concentration in the exhaust gas flowing into the NO_x absorbent is lowered by said prohibition means.

30. An exhaust purification device of an internal combustion engine according to claim 1, wherein a catalyst which can reduce at least the NO_x is disposed in the exhaust passage of the engine downstream of the NO_x absorbent.

31. An exhaust purification device of an internal combustion engine according to claim 30, wherein said catalyst comprises a three-way catalyst.

32. An exhaust purification device of an internal combustion engine-according to claim 1, wherein a catalyst which can purify the unburnt HC and CO is disposed in the exhaust passage of the engine upstream of the NO_x absorbent.

33. An exhaust purification device of an internal combustion engine according to claim 32, wherein said catalyst comprises a three-way catalyst.