Exhaust gas purification device for an engine

• US 5,746,052 A
• Filed: 09/08/1995
• Issued: 05/05/1998
• Est. Priority Date: 09/13/1994
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Itou, Takaaki, Takaoka, Toshifumi, Igarashi, Kouhei, Kinugasa, Yukio, Yaegashi, Takehisa
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/525,892
• Time in Patent Office: 970 Days
• Field of Search: 60/274, 60/276, 60/289, 60/288, 422/170, 422/171, 423/213.7
• US Class Current: 60/274
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9454 characterised by a specific device
• CPC Class Codes: B01D 53/9477 with catalysts positioned on separate bricks, e.g. exhaust systems
• 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 2240/25 an ammonia generator
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• 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 3/206 Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents F01N3/2066 takes precedence
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

In the present invention, the exhaust gas from the engine is divided into a first and a second branch exhaust passages after it passes through a three-way reducing and oxidizing catalyst, and the two branch exhaust passages merge into an exhaust gas outlet passage. In the first branch exhaust passage, an oxidizing catalyst is disposed, and in the exhaust gas outlet passage, a denitrating and oxidizing catalyst is disposed. NO_x in the exhaust gas from the engine is all converted to N₂ and NH₃ by the three-way reducing and oxidizing catalyst and a part of the NH₃ generated by the three-way catalyst flows into the first branch exhaust passage and is converted to NO_x again by the oxidizing catalyst. The amount of NO_x produced by the oxidizing catalyst and the amount of NO_x flowing through the second branch exhaust passage is determined by the flow distribution ratio of the first and the second branch exhaust passages. In this invention, the flow ratio is determined in such a manner that the amount of the NO_x produced by the oxidizing catalyst and the amount of the NH₃ passing through the second branch exhaust passage are stoichiometric to produce N₂ and H₂ O. Therefore, when these exhaust gases flow into the denitrating and oxidizing catalyst after they mix with each other in the exhaust gas outlet passage, all the NO_x and the NH₃ are converted to N₂ and H₂ O by the denitrating and oxidizing catalyst without producing any surplus NO_x or NH₃.

Claims

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

a ratio determining means disposed in an exhaust gas passage of an internal combustion engine for converting substantially all of NO_x in the exhaust gas into N₂, NH₃ and NO_x, wherein an amount of NH₃ and an amount of NO_x generated by the conversion are adjusted so that the amount of NH₃ and the amount of NO_x are stoichiometrical, and wherein the NO_x generated by the conversion is essentially NO₂ and a molar ratio of the amount of NO₂ generated to the amount of NH₃ generated is 3;

4; and

purification means disposed in the exhaust gas passage downstream of the ratio determining means for causing the NH₃ generated to react with NO_x generated to produce N₂ and H₂ O components.

22. A device according to claim 1, wherein said engine is operated at an air-fuel ratio lower than the stoichiometric air-fuel ratio.

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

a ratio determining means disposed in an exhaust gas passage of an internal combustion engine for converting substantially all of NO_x in the exhaust gas into N₂, NH₃ and NO_x, wherein an amount of NH₃ and an amount of NO_x generated by the conversion are adjusted so that the amount of NH₃ and the amount of NO_x are stoichiometrical, wherein the NO_x generated is essentially composed of NO₂, and wherein a molar ratio of the amount of NO₂ generated to the amount of NH₃ generated is 1;

1; and

purification means disposed in the exhaust gas passage downstream of the ratio determining means for causing the NH₃ generated to react with NO_x generated to produce N₂ and H₂ O components.

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

a ratio determining means disposed in an exhaust gas passage of an internal combustion engine for converting substantially all of NO_x in the exhaust gas into N₂, NH₃ and NO_x, wherein an amount of NH₃ and an amount of NO_x generated by the conversion are adjusted so that the amount of NH₃ and the amount of NO_x are stoichiometrical, wherein the NO_x generated is composed of a mixture of NO₂ and NO, and wherein a ratio of total moles of NO₂ and NO generated to an amount of moles of NH₃ generated is larger than 3/4 and smaller than 1; and

purification means disposed in the exhaust gas passage downstream of the ratio determining means for causing the NH₃ generated to react with NO_x generated to produce N₂ and H₂ O components.

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

a ratio determining means disposed in an exhaust gas passage of an internal combustion engine for converting substantially all of NO_x in the exhaust gas into N₂, NH₃ and NO_x, wherein an amount of NH₃ and an amount of NO_x generated by the conversion are adjusted so that the amount of NH₃ and the amount of NO_x are stoichiometrical, wherein said ratio determining means comprises;

NH₃ generating means for converting substantially all of the NO_x in the exhaust gas into N₂ and NH₃ ; and

NO_x generating means for converting a portion of the NH₃ generated by the NH₃ generating means into NO_x, wherein the amount of NO_x generated by the NO_x generating means and an amount of NH₃ remaining in the exhaust gas are adjusted so that the amount of NO_x and the remaining amount NH₃ are stoichiometrical; and

purification means disposed in the exhaust gas passage downstream of the ratio determining means for causing the NH₃ generated to react with NO_x generated to produce N₂ and H₂ O components.

5. A device according to claim 4, wherein said NO_x generating means converts 3/7 of the amount of the NH₃ component generated by the NH₃ generating means into an NO₂ component.

6. A device according to claim 4, wherein said NO_x generating means converts 1/2 of the amount of the NH₃ component generated by the NH₃ generating means into an NO component.

7. A device according to claim 4, wherein said NO_x generating means converts between 3/7 and 1/2 of the amount of the NH₃ component generated by the NH₃ generating means into NO₂ and NO components.

8. A device according to claim 4, wherein said NO_x generating means comprises:

a first branch exhaust passage and a second branch exhaust passage which divide the exhaust gas flow containing the NH₃ generated by the NH₃ generating means into a first portion and a second portion, respectively;

a converting means disposed on said first branch exhaust passage for converting substantially all of the NH₃ in the first portion of the exhaust gas into NO_x ; and

an exhaust gas outlet passage merging the first and second branch exhaust passages, where the first and second portions of the exhaust gas mix with each other;

wherein an amount of the first portion of the exhaust gas and an amount of the second portion of the exhaust gas are adjusted so that the amount of the NO_x generated by the converting means and the amount of NH₃ in the second portion of the exhaust gas are stoichiometrical.

9. A device according to claim 8, wherein the converting means converts substantially all of the NH₃ in the first portion of the exhaust gas into an NO₂ component, and wherein the ratio of the amount of the first portion of the exhaust gas to the amount of the second portion of the exhaust gas is 3:

4.

10. A device according to claim 8, wherein the converting means converts substantially all of the NH₃ in the first portion of the exhaust gas into an NO component, and wherein the ratio of the amount of the first portion of the exhaust gas to the amount of the second portion of the exhaust gas is 1:

1.

11. A device according to claim 8, wherein the converting means converts substantially all of the NH₃ in the first portion of the exhaust gas into NO₂ and NO components, and wherein the ratio of the amount of the first portion of the exhaust gas to the amount of the second portion of the exhaust gas is larger than 3:

4 and smaller than 1;

1.

12. A device according to claim 8, wherein said NO_x generating means further comprises a flow resistance means disposed on the second branch exhaust passage for generating a flow resistance substantially the same as the flow resistance generated by said converting means in the first branch exhaust passage.

13. A device according to claim 11, wherein said NO_x generating means further comprises a flow resistance means disposed in the second branch exhaust passage for generating a flow resistance substantially the same as the flow resistance generated by said converting means in the first branch exhaust passage.

14. A device according to claim 4, wherein said NH₃ generating means comprises a three-way reducing and oxidizing catalyst disposed in the exhaust gas passage, said NO_x generating means comprises an oxidizing catalyst disposed in the exhaust gas passage downstream of said three-way reducing and oxidizing catalyst, and said purification means comprises a denitrating and oxidizing catalyst disposed in the exhaust gas passage downstream of said oxidizing catalyst.

15. A device according to claim 7, wherein said NH₃ generating means comprises a three-way reducing and oxidizing catalyst disposed in the exhaust gas passage, said NO_x generating means comprises an oxidizing catalyst disposed in the exhaust gas passage downstream of said three-way reducing and oxidizing catalyst, and said purification means comprises a denitrating and oxidizing catalyst disposed in the exhaust gas passage downstream of said oxidizing catalyst.

16. A device according to claim 15, wherein said NO_x generating means further comprises a variable means for adjusting the amount of the NH₃ converted by said NO_x generating means in the range between 3/7 and 1/2 of the amount of the NH₃ generated by said NH₃ generating means in accordance with the temperature of said oxidizing catalyst.

17. A device according to claim 8, wherein said NH₃ generating means comprises a three-way reducing and oxidizing catalyst disposed in the exhaust gas passage, said converting means comprises an oxidizing catalyst disposed in the first branch exhaust passage, and said purification means comprises a denitrating and oxidizing catalyst disposed in the exhaust gas outlet passage.

18. A device according to claim 12, wherein said NH₃ generating means comprises a three-way reducing and oxidizing catalyst disposed in the exhaust gas passage, said converting means comprises an oxidizing catalyst disposed in the first branch exhaust passage, and said purification means comprises a denitrating and oxidizing catalyst disposed in the exhaust gas outlet passage.

19. A device according to claim 13, wherein said NH₃ generating means comprises a three-way reducing and oxidizing catalyst disposed in the exhaust gas passage, said converting means comprises an oxidizing catalyst disposed in the first branch exhaust passage, and said purification means comprises a denitrating and oxidizing catalyst disposed in the exhaust gas outlet passage.

20. A device according to claim 18, wherein said NO_x generating means comprises a variable means for adjusting the ratio of the amount of the first portion of the exhaust gas to the amount of the second portion of the exhaust gas to maintain the ratio in the range between 3/4 and 1, in accordance with the temperature of the oxidizing catalyst.

21. A device according to claim 19, wherein said NO_x generating means comprises a variable means for adjusting the ratio of the amount of the first portion of the exhaust gas to the amount of the second portion of the exhaust gas to maintain the ratio in the range between 3/4 and 1, in accordance with the temperature of the oxidizing catalyst.

23. A device according to claim 4, wherein said engine is operated at an air-fuel ratio lower than the stoichiometric air-fuel ratio.

24. A device according to claim 8, wherein said engine is operated at an air-fuel ratio lower than the stoichiometric air-fuel ratio.

25. A device according to claim 14, wherein said engine is operated at an air-fuel ratio lower than the stoichiometric air-fuel ratio.

26. A device according to claim 15, wherein said engine is operated at an air-fuel ratio lower than the stoichiometric air-fuel ratio.

27. A device according to claim 17, wherein said engine is operated at an air-fuel ratio lower than the stoichiometric air-fuel ratio.