Exhaust purification device of internal combustion engine

• US 5,450,722 A
• Filed: 02/14/1994
• Issued: 09/19/1995
• Est. Priority Date: 06/12/1992
• 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, Tanaka, Toshiaki, Takeshima, Shinichi, Katoh, Kenji, Kihara, Tetsuro
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/196,144
• Time in Patent Office: 582 Days
• Field of Search: 60/274, 60/285, 60/284, 60/286, 60/301
• US Class Current: 60/285
• CPC Class Codes: B01D 53/0454 Controlling adsorption controlling temperature swing adsorption B01D53/0462, controlling pressure swing adsorption B01D53/047
• CPC Class Codes: B01D 53/9445 Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
• 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 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2240/18 an adsorber or absorber
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/12 Hydrocarbons
• 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 3/20 specially adapted for catalytic conversion F01N3/22 takes precedence; Methods of operation or control of catalytic converters
• 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: F01N 9/005 using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
• CPC Class Codes: F02B 1/04 with fuel-air mixture admission into cylinder
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 2200/0811 NOx storage efficiency
• CPC Class Codes: F02D 41/027 to purge or regenerate the exhaust gas treating apparatus
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1446 : the characteristics being exhaust temperatures
• CPC Class Codes: F02D 41/146 : the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/1462 : with determination means using an estimation
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

A NO_x absorbent (17) is disposed in an exhaust passage of an internal combustion engine. This NO_x absorbent (17) absorbs the NO_x when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent (17) is lean and releases the absorbed NO_x when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent (17) becomes rich. When making the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent (17) rich to release the NO_x from the NO_x absorbent (17), the degree of richness is made larger and the time the ratio is made rich is made shorter the higher the temperature of the NO_x absorbent (17).

Claims

1. An exhaust purification device of an internal combustion engine comprising:

an engine exhaust passage;

an NO_x absorbent disposed within the engine exhaust passage, wherein the NO_x absorbent absorbs NO_x included in exhaust gas from the engine when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is lean and wherein the NO_x absorbent releases the absorbed NO_x when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent becomes rich;

temperature detecting means for detecting a temperature representing the temperature of the NO_x absorbent; and

NO_x release controlling means for making the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent a predetermined rich air-fuel ratio for a predetermined period of time when the NO_x is to be released from the NO_x absorbent and wherein the NO_x release controlling means determines one of the predetermined rich air-fuel ratio and the predetermined period of time based on the temperature of the NO_x absorbent, so that, when the NO_x release controlling means determines the predetermined rich air-fuel ratio based on the temperature of the NO_x absorbent, the predetermined rich air-fuel ratio is made richer as the temperature of the NO_x absorbent increases and, when the NO_x release controlling means determines the predetermined period of time based on the temperature of the NO_x absorbent, the predetermined period of time is shortened as the temperature of the NO_x increases.

2. An exhaust purification device of an internal combustion engine according to claim 1, wherein said NO_x release controlling means determines both the predetermined rich air-fuel ratio and the predetermined period of time based on the temperature of the NO_x absorbent and so that the predetermined rich air-fuel ratio is made richer and the predetermined time is shortened as the temperature of the NO_x absorbent increases.

3. An exhaust purification device of an internal combustion engine according to claim 2, further comprising means for determining an amount of NO_x released from the NO_x absorbent, wherein said NO_x release controlling means changes the predetermined rich air-fuel ratio so that a pattern of change of the predetermined rich air-fuel ratio resembles a pattern of change of the amount of NO_x released from the NO_x absorbent when NO_x is released from the NO_x absorbent.

4. An exhaust purification device of an internal combustion engine according to claim 3, wherein, when NO_x is to be released from the NO_x absorbent, said NO_x release controlling means increases the richness of the predetermined rich air-fuel ratio to a first value by a predetermined rate of rise and then reduces the richness of the predetermined rich air-fuel ratio by a predetermined rate of reduction and wherein the NO_x release controlling means increases the rate of rise, the first value, and the rate of reduction as the temperature of the NO_x absorbent increases.

5. An exhaust purification device of an internal combustion engine according to claim 1, wherein the temperature representing the NO_x absorbent is the temperature of the exhaust gas flowing into the NO_x absorbent.

6. An exhaust purification device of an internal combustion engine according to claim 5, further comprising a memory in which the temperature of the exhaust gas flowing into the NO_x absorbent is stored as a function of the engine load and the engine rotational speed and wherein the temperature of the NO_x absorbent is also stored in the memory.

7. An exhaust purification device of an internal combustion engine according to claim 1, wherein said NO_x release controlling means makes the air-fuel ratio of the air-fuel mixture fed into the combustion chamber rich when releasing NO_x from the NO_x absorbent.

8. An exhaust purification device of an internal combustion engine according to claim 1, wherein NO_x estimating means is provided for estimating the amount of NO_x absorbed in said NO_x absorbent and wherein the NO_x release controlling means makes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent rich to release the NO_x from the NO_x absorbent when the amount of NO_x estimated to be absorbed in the NO_x absorbent by the NO_x estimating means exceeds a predetermined allowance.

9. An exhaust purification device of an internal combustion engine according to claim 8, further comprising means for determining-an amount of NO_x discharged from the combustion chamber to the engine exhaust passage, wherein said NO_x estimating means estimates the amount of NO_x absorbed in the NO_x absorbent on the basis of the amount of NO_x discharged from the combustion chamber to the engine exhaust passage.

10. An exhaust purification device of an internal combustion engine according to claim 9, further comprising means for determining an engine load and an engine rotational speed, wherein said NO_x estimating means is comprised of an NO_x calculating means for calculating the amount of NO_x discharged per unit time from the engine to the engine exhaust passage in accordance with the engine load and the engine rotational speed and a cumulative adding means for cumulatively adding the amounts of NO_x calculated by the NO_x calculating means.

11. An exhaust purification device of an internal combustion engine according to claim 10, wherein said NO_x calculating means is provided with a memory in which is previously stored the amount of NO_x discharged per unit time from the engine to the engine exhaust passage as a function of the engine load and the engine rotational speed and wherein the cumulative adding means cumulatively adds the amounts of NO_x stored in the memory and determined from the engine load and the engine rotational speed.

12. An exhaust purification device of an internal combustion engine according to claim 10, further comprising a throttle valve disposed in the engine intake passage for controlling the engine load and means for determining the magnitude of a vacuum inside the engine intake passage downstream of the throttle valve, wherein the means for determining the engine load determines the engine load based on the magnitude of the vacuum inside the engine intake passage downstream of the throttle valve.

13. An exhaust purification device of an internal combustion engine according to claim 8, wherein said allowance is the maximum NO_x absorption capacity of the NO_x absorbent.

14. An exhaust purification device of an internal combustion engine according to claim 13, wherein said allowance is a function of the temperature representing the temperature of the NO_x absorbent.

15. An exhaust purification device of an internal combustion engine according to claim 8, wherein said NO_x estimating means makes the amount of NO_x estimated to be absorbed in the NO_x absorbent zero when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is made rich due to the amount of NO_x estimated by the NO_x estimating means exceeding the allowance.

16. An exhaust purification device of an internal combustion engine according to claim 8, wherein air-fuel ratio control means is provided for making the air-fuel ratio of the air-fuel mixture fed to the combustion chamber rich in accordance with the operating state of the engine regardless of whether the amount of NO_x estimated by the NO_x estimating means exceeds the allowance.

17. An exhaust purification device of an internal combustion engine according to claim 16, wherein said air-fuel ratio control means makes the air-fuel ratio of the air-fuel mixture fed into the combustion chamber rich when the engine load is higher than a predetermined load.

18. An exhaust purification device of an internal combustion engine according to claim 17, wherein said NO_x estimating means makes the amount of NO_x estimated as being absorbed in the NO_x absorbent zero when the air-fuel ratio of the air-fuel mixture is made rich for more than a predetermined time.

19. An exhaust purification device of an internal combustion engine according to claim 1, wherein the NO_x absorbent includes at least one substance selected from alkali metals such as potassium, sodium, lithium, and cesium, alkali earths such as barium and calcium, and rare earths such as lanthanum and yttrium and platinum.

20. An exhaust purification device of an internal combustion engine according to claim 1, wherein the NO_x absorbent is comprised of a compound oxide of barium and copper.

21. An exhaust purification device of an internal combustion engine according to claim 1, wherein a three-way catalyst is disposed in the engine exhaust passage downstream of the NO_x absorbent.