Exhaust gas purification device for an internal combustion engine

• US 5,974,793 A
• Filed: 04/11/1997
• Issued: 11/02/1999
• Est. Priority Date: 04/19/1996
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kabushiki Kaisha
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Kinugasa, Yukio, Itou, Takaaki, Suzuki, Naoto, Takeuchi, Koichi, Tanaka, Hiroshi, Fuwa, Naohide
• Primary Examiner(s): Lopez, F. Daniel
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US08/837,933
• Time in Patent Office: 935 Days
• Field of Search: 60/278, 60/285, 60/286, 60/287, 60/301, 423/237, 423/213.7, 423/213.5
• US Class Current: 60/285
• CPC Class Codes: B01D 53/9454 characterised by a specific device
• 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 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• 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 3/2053 By-passing catalytic reactors, e.g. to prevent overheating
• 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: F02D 41/0082 per groups or banks F02D41/0087 takes precedence
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1475 Regulating the air fuel ratio at a value other than stoichiometry
• CPC Class Codes: F02M 26/15 in relation to engine exhaust purifying apparatus
• CPC Class Codes: F02M 26/38 with two or more EGR valves disposed in parallel
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

In an exhaust gas purification device, a No. 1 cylinder of the engine is operated at a rich air-fuel ratio and other cylinders (No. 2 to No. 4) are operated at a lean air-fuel ratio. The exhaust gases from the No. 1 and No. 2 cylinders are mixed with each other to form a rich air-fuel ratio exhaust gas mixture. Further, since the air-fuel ratio of the No. 2 cylinder is lean, the exhaust gas from the No. 2 cylinder contains a relatively large amount of NO_x. This rich air-fuel ratio exhaust gas mixture which contains a relatively large amount of NO_X is supplied to a three-way catalyst. At the three-way catalyst, part of the NO_X in the exhaust gas mixture is converted to NH₃. The exhaust gas mixture flowing out from the three-way catalyst and the lean exhaust gas from the No. 3 and No. 4 flow into a common exhaust gas passage where they mix with each other to form a lean exhaust gas containing NH₃ from the three-way catalyst and NO_X from the No. 3 and No. 4 cylinders. This lean exhaust gas flows into a denitrating catalyst disposed on the common exhaust gas passage in which NO_X in the exhaust gas is reduced by the NH₃.

Claims

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

conversion means for converting, when the air-fuel ratio of exhaust gas supplied to the conversion means is rich, at least a portion of NO_X contained in the exhaust gas to NH₃ ;

NO_X purification means disposed in an exhaust gas passage of the engine for causing the NO_X in the exhaust gas to react with the NH₃ produced by the conversion means and for causing the NO_X to be reduced to N₂ by the NH₃ ; and

NO_X increasing means for adjusting an air-fuel ratio of the exhaust gas supplied to the conversion means to a rich air-fuel ratio and, at the same time, increasing a concentration of NO_X in the exhaust gas supplied to the conversion means to a value higher than a normal concentration of NO_X in the exhaust gas of the engine, the normal concentration of NO_X being defined as a concentration of NO_X when the engine is operated at an air-fuel ratio the same as that of the exhaust gas adjusted by the NO_X increasing means.

2. A device according to claim 1, wherein the engine includes a plurality of cylinders and wherein at least one of the cylinders of the engine is operated at a rich air-fuel ratio and at least one of the cylinders of the engine is, at the same time, be operated at a lean air-fuel ratio, and wherein the NO_X increasing means comprises mixing means for mixing exhaust gas from the at least one rich air-fuel ratio cylinder and exhaust gas from the at least one lean air-fuel ratio cylinder to form a rich air-fuel ratio exhaust gas mixture to be supplied to the conversion means.

3. A device according to claim 2, wherein the mixing means mixes the exhaust gas from the at least one rich air-fuel ratio cylinder and the exhaust gas from the at least one lean air-fuel ratio cylinder in such a manner that the air-fuel ratio of the exhaust gas mixture becomes a predetermined rich air-fuel ratio at which an amount of NO_X converted to NH₃ by the conversion means is a maximum amount.

4. A device according to claim 3, wherein engine sequentially changes the at least one cylinder to be operated at a rich air-fuel ratio.

5. A device according to claim 2, wherein the NO_X increasing means further comprises NO_X estimating means for estimating an amount of NO_X in the exhaust gas flowing into the NO_X purification means and the mixing means comprises a mixing control means for adjusting an amount of exhaust gas from the at least one lean air-fuel ratio cylinder included in the exhaust gas mixture in accordance with the amount of the NO_X estimated by the NO_X estimating means.

6. A device according to claim 1, wherein the engine is a multi-cylinder lean burn engine in which, under predetermined operating conditions, at least one of the cylinders is operated at a rich air-fuel ratio, and wherein the NO_X increasing means comprises NO_X production promoting means for increasing an amount of NO_X produced in the at least one rich air-fuel ratio cylinders and supplies the NO_X -enriched exhaust gas from the at least one rich air-fuel ratio cylinder to the conversion means.

7. A device according to claim 6, wherein the NO_X production promoting means increases the amount of NO_X produced in the rich air-fuel ratio cylinders by raising a combustion temperature in the at least one rich air-fuel ratio cylinder.

8. A device according to claim 6, wherein the NO_X production promoting means increases the amount of NO_X produced in the at least one rich air-fuel ratio cylinder by advancing an ignition timing of the at least one rich air-fuel ratio cylinder to a timing earlier than an optimum ignition timing.

9. A device according to claim 6, wherein the engine comprises an EGR device for recirculating a part of the exhaust gas of the engine into the cylinders and wherein the NO_X production promoting means increases the amount of NO_X produced in the at least one rich air-fuel ratio cylinders by decreasing an amount of exhaust gas recirculated into the at least one rich air-fuel ratio cylinder.

10. A device according to claim 6, wherein the NO_X production promoting means increases the amount of NO_X produced in the at least one rich air-fuel ratio cylinder by increasing a compression ratio of the at least one rich air-fuel ratio cylinder.

11. A device according to claim 10, wherein the NO_X production promoting means further comprises means for lowering a wall temperature of a combustion chamber of the at least one rich air-fuel ratio cylinder.

12. A device according to claim 6, wherein the NO_X production promoting means increases the amount of NO_X produced in the at least one rich air-fuel ratio cylinder by supplying a material which, when burned, increases an amount of NO_X in the exhaust gas.

13. A device according to claim 12, wherein the material contains at least one substance selected from benzene, toluene, xylene and styrene.

14. A device according to claim 1, wherein the conversion means comprises a three-way catalyst.

15. A device according to claim 1, wherein the NO_X purification means comprises a denitrating catalyst.