Exhaust gas purification device for an internal combustion engine

• US 6,109,024 A
• Filed: 05/08/1998
• Issued: 08/29/2000
• Est. Priority Date: 05/12/1997
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Takeuchi, Koichi, Itou, Takaaki, Kinugasa, Yukio
• Primary Examiner(s): Ryznic, John E.
• Application Number:
  US09/075,358
• Time in Patent Office: 844 Days
• Field of Search: 60/285, 60/286, 60/301, 60/303
• US Class Current: 60/285
• 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 2900/0418 using integration or an accumulated value within an elapsed period
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/101 Three-way catalysts
• CPC Class Codes: F02B 2075/125 Direct injection in the combustion chamber for spark ignition engines, i.e. not in pre-combustion chamber
• CPC Class Codes: F02D 2041/389 for injecting directly into the cylinder
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/405 with post injections
• 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 three-way catalyst, an NO_x absorbing-reducing catalyst and an NH₃ adsorbing-denitrating catalyst are disposed in an exhaust gas passage of the internal combustion engine. The engine is provided with direct cylinder injection valves which inject fuel directly into the respective cylinders. A control circuit controls the amount of fuel injected from the injection valve so that the air-fuel ratio of the combustion in the cylinders becomes a lean air-fuel ratio during the normal operation of the engine. Therefore, a lean air-fuel ratio exhaust gas is discharged from the cylinders during the normal operation and NO_x, in the exhaust gas is absorbed by the NO_x absorbing-reducing catalyst. When the amount of NO_x absorbed in the NO_x absorbing-reducing catalyst increases to a predetermined level, the control circuit performs an additional fuel injection during the expansion stroke or exhaust stroke of cylinders in order to adjust the air-fuel ratio of the exhaust gas leaving the cylinders to a rich air-fuel ratio. The rich air-fuel ratio exhaust gas leaving the cylinders flows into the three-way catalyst and NO_x in the exhaust gas is converted into NH₃ at the three-way catalyst. When the rich air-fuel ratio exhaust gas flows through the NO_x absorbing-reducing catalyst, NO_x is released from the NO_x absorbing-reducing catalyst and is reduced to N₂ by NH₃ in the exhaust gas.

Claims

1. An exhaust gas purification device for an internal combustion engine capable of operating on lean air-fuel combustion, the engine being provided with a direct cylinder injection valve for injecting fuel directly into a cylinder thereof and an exhaust gas passage extending through which exhaust gas travels away from the cylinder, said device comprising:

exhaust gas air-fuel ratio adjusting means for adjusting an air-fuel ratio of exhaust gas produced by lean air-fuel ratio combustion in the cylinder from a lean air-fuel ratio to a rich air-fuel ratio by injecting additional fuel into the cylinder from the direct cylinder injection valve during one of an expansion stroke and an exhaust stroke of the cylinder;

NH₃ conversion means disposed in the exhaust gas passage downstream of the cylinder wherein, when additional fuel is injected to the cylinder by the exhaust gas air-fuel ratio adjusting means, the exhaust gas air-fuel ratio adjusting means provides rich air-fuel ratio exhaust gas to the NH₃ conversion means, the NH₃ conversion means producing NH₃ by converting at least a portion of NO_x contained in the exhaust gas to NH₃ ; and

purification means disposed in the exhaust gas passage downstream of the NH₃ conversion means for purifying both NO_x and NH₃ included in the exhaust gas by reacting the NO_x with the NH₃.

2. An exhaust gas purification device as set forth in claim 1, wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means by changing a length of a period of time during which the air-fuel ratio of the exhaust gas is adiusted to a rich air-fuel ratio.

3. An exhaust gas purification device as set forth in claim 1, wherein the engine includes a plurality of cylinders and wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means by changing a length of a number of cylinders to which additional fuel is directly injected during the one of the expansion and exhaust strokes.

4. An exhaust gas purification device as set forth in claim 1, wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means by changing the air-fuel ratio to which the air-fuel ratio of the exhaust gas after is adjusted.

5. An exhaust gas purification device as set forth in claim 1, wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means in accordance with an operating condition of the engine.

6. An exhaust gas purification device as set forth in claim 1, wherein the purification means comprises an NH₃ adsorbing-denitrating catalyst which adsorbs NH₃ in the exhaust gas and reduces NO_x in the exhaust gas using one of the adsorbed NH₃ and the NH₃ in the exhaust gas.

7. An exhaust gas purification device as set forth in claim 1, wherein the purification means comprises an NO_x absorbing-reducing catalyst which absorbs NO_x in the exhaust gas when the exhaust gas is at a lean air-fuel ratio and releases and reduces absorbed NO_x when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio.

8. An exhaust gas purification device as set forth in claim 1, wherein the purification means comprises both of an NH₃ adsorbing-denitrating catalyst which adsorbs NH₃ in the exhaust gas and reduces NO_x in the exhaust gas using one of the adsorbed NH₃ and the NH₃ in the exhaust gas and an NO_x absorbing-reducing catalyst which absorbs NO_x in the exhaust gas when the exhaust gas is at a lean air-fuel ratio and releases and reduces absorbed NO_x when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio.

9. An exhaust gas purification device as set forth in claim 8, wherein the NO_x absorbing-reducing catalyst is disposed in the exhaust gas passage upstream of the NH₃ adsorbing-denitrating catalyst.

10. An exhaust gas purification device as set forth in claim 8, wherein the NO_x absorbing-reducing catalyst is disposed in the exhaust gas passage downstream of the NH₃ adsorbing-denitrating catalyst.

11. An exhaust gas purification device as set forth in claim 2, wherein the purification means comprises an NH₃ adsorbing-denitrating catalyst which adsorbs NH₃ in the exhaust gas and reduces NO_x in the exhaust gas using one of the adsorbed NH₃ and the NH₃ in the exhaust gas and wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means in accordance with an amount of NO_x emitted from the engine.

12. An exhaust gas purification device as set forth in claim 5, wherein the purification means comprises an NH₃ adsorbing-denitrating catalyst which adsorbs NH₃ in the exhaust gas and reduces NO_x in the exhaust gas using one of the adsorbed NH₃ and the NH₃ in the exhaust gas and wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means in accordance with an amount of NO_x emitted from the engine.

13. An exhaust gas purification device as set forth in claim 2, wherein the purification means comprises an NO_x absorbing-reducing catalyst which absorbs NO_x in the exhaust gas when the exhaust gas is at a lean air-fuel ratio and releases and reduces absorbed NO_x when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio and wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means in accordance with an amount of NO_x emitted from the engine.

14. An exhaust gas purification device as set forth in claim 5, wherein the purification means comprises an NO_x absorbing-reducing catalyst which absorbs NO_x in the exhaust gas when the exhaust gas is at a lean air-fuel ratio and releases and reduces absorbed NO_x when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio and wherein the exhaust gas air-fuel ratio adjusting means controls an amount of NH₃ produced by the NH₃ conversion means in accordance with an amount of NO_x emitted from the engine.

15. An exhaust gas purification device as set forth in claim 1, wherein the purification means comprises an NH₃ adsorbing-denitrating catalyst which adsorbs NH₃ in the exhaust gas and reduces NO_x in the exhaust gas using one of the adsorbed NH₃ and the NH₃ in the exhaust gas and wherein the exhaust gas air-fuel ratio adjusting means adjusts the exhaust gas air-fuel ratio to a rich air-fuel ratio when an amount of NH₃ adsorbed in the NH₃ adsorbing-denitrating catalyst becomes smaller than a predetermined value.

16. An exhaust gas purification device as set forth in claim 1, wherein the purification means comprises an NO_x absorbing-reducing catalyst which absorbs NO_x in the exhaust gas when the exhaust gas is at a lean air-fuel ratio and releases and reduces absorbed NO_x when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio and wherein the exhaust gas air-fuel ratio adjusting means adjusts the exhaust gas air-fuel ratio to a rich air-fuel ratio when an amount of NO_x absorbed in the NO_x absorbing-reducing catalyst becomes larger than a predetermined value.

17. An exhaust gas purification device as set forth in claim 1, wherein the NH₃ conversion means comprises a three-way reducing and oxidizing catalyst.

18. An exhaust gas purification device as set forth in claim 1, wherein the NH₃ conversion means comprises an NO_x absorbing-reducing catalyst which absorbs NO_x in the exhaust gas when the exhaust gas is at a lean air-fuel ratio and releases and reduces absorbed NO_x when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio.