Exhaust gas purification device for an internal combustion engine

• US 5,974,794 A
• Filed: 04/02/1998
• Issued: 11/02/1999
• Est. Priority Date: 04/03/1997
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Asanuma, Takamitsu, Katoh, Kenji, Gotoh, Masato
• Primary Examiner(s): Lopez, F. Daniel
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/054,172
• Time in Patent Office: 579 Days
• Field of Search: 60/285, 60/286, 60/284, 60/295, 60/303
• US Class Current: 60/286
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/2042 Barium
• 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: 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 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 2610/04 the substance being hydrogen
• CPC Class Codes: F01N 3/0238 for regenerating during engine standstill
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0885 Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/042 for stopping the engine

Abstract

The exhaust gas purification device includes a NO_x absorbent disposed in an exhaust gas passage of an internal combustion engine. The engine is mainly operated at a lean air-fuel ratio. The NO_x absorbent absorbs NO_x in the exhaust gas from the engine when the exhaust gas flowing into the NO_x absorbent is at a lean air-fuel ratio, and releases the NO_x absorbed therein and reduces it when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio. A control circuit is provided for controlling the operating air-fuel ratio of the engine. When the ignition switch of the engine is turned off, the control circuit continues the engine operation for a predetermined period before terminating the engine operation. During this engine operation, the operating air-fuel ratio of the engine is controlled at a rich air-fuel ratio to supply exhaust gas with a rich air-fuel ratio to the NO_x absorbent. Therefore, NO_x absorbed and held therein when the ignition switch is turned off is released and reduced by the rich air-fuel ratio exhaust gas from the engine. Since the NO_x absorbent is maintained at the condition where no NO_x remains in the NO_x absorbent after the engine has stopped, unreduced NO_x is not released from the NO_x absorbent even if the NO_x absorbent is cooled after the engine has stopped.

Claims

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

a NO_x absorbent disposed in an exhaust passage of an internal combustion engine, said NO_x absorbent absorbs NO_x in the exhaust gas of the engine when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is lean, and releases and reduces the absorbed NO_x when the air-fuel ratio of the gas flowing into the NO_x absorbent becomes rich; and

a regenerating means for performing a regenerating operation which causes the NO_x absorbent to release and reduce the absorbed NO_x by supplying rich air-fuel ratio gas to the NO_x absorbent when the engine is stopped.

2. An exhaust gas purification device as set forth in claim 1, wherein said regenerating means starts the regenerating operation after an engine stopping operation is commenced.

3. An exhaust gas purification device as set forth in claim 2, wherein said regenerating means further performs the regenerating operation when a predetermined condition is satisfied during the engine operation.

4. An exhaust gas purification device as set forth in claim 3, further comprising NO_x amount detecting means for detecting the amount of NO_x absorbed in the NO_x absorbent, and wherein said regenerating means performs the regenerating operation when the amount of NO_x in the NO_x absorbent reaches a predetermined value during the engine operation.

5. An exhaust gas purification device as set forth in claim 2, wherein said regenerating means performs the regenerating operation by operating the engine at a rich air-fuel ratio for a predetermined period after the engine stopping operation is commenced.

6. An exhaust gas purification device as set forth in claim 5, further comprising NO_x amount detecting means for detecting the amount of NO_x absorbed in the NO_x absorbent and means for setting the length of the predetermined period in accordance with the amount of NO_x absorbed in the NO_x absorbent when the engine stopping operation is commenced.

7. An exhaust gas purification device as set forth in claim 5, wherein said regenerating means terminates the regenerating operation when substantially all of the NO_x absorbed in the NO_x absorbent is released from the NO_x absorbent and reduced.

8. An exhaust gas purification device as set forth in claim 2, wherein said regenerating means performs the regenerating operation by supplying a reducing agent to the NO_x absorbent for a predetermined period after the engine stopping operation is commenced.

9. An exhaust gas purification device as set forth in claim 8, further comprising NO_x amount detecting means for detecting the amount of NO_x absorbed in the NO_x absorbent and means for setting the length of the predetermined period in accordance with the amount of NO_x absorbed in the NO_x absorbent when the engine stopping operation is commenced.

10. An exhaust gas purification device as set forth in claim 8, wherein said regenerating means terminates the regenerating operation when substantially all of the NO_x absorbed in the NO_x absorbent is released from the NO_x absorbent and reduced.

11. An exhaust gas purification device as set forth in claim 2, wherein said regenerating means terminates the regenerating operation when substantially all of the NO_x absorbed in the NO_x absorbent is released from the NO_x absorbent and reduced.

12. An exhaust gas purification device as set forth in claim 1, wherein said regenerating means further performs the regenerating operation when a predetermined condition is satisfied during the engine operation.

13. An exhaust gas purification device as set forth in claim 12, further comprising NO_x amount detecting means for detecting the amount of NO_x absorbed in the NO_x absorbent, and wherein said regenerating means performs the regenerating operation when the amount of NO_x in the NO_x absorbent reaches a predetermined value during the engine operation.