Exhaust gas purification device for an internal combustion engine

• US 6,138,453 A
• Filed: 09/10/1998
• Issued: 10/31/2000
• Est. Priority Date: 09/19/1997
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Sawada, Hiroshi, Kako, Junichi
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/151,230
• Time in Patent Office: 782 Days
• Field of Search: 60/285, 60/277, 60/276, 60/286, 60/295, 60/297, 60/301, 123/443, 123/691
• US Class Current: 60/277
• CPC Class Codes: B01D 53/9409 Nitrogen oxides
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• 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 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2200/0816 Oxygen storage capacity
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

In an exhaust gas purification device for an internal combustion engine, a NO_X occluding and reducing catalyst is disposed in the exhaust gas passage of an engine. The NO_X occluding and reducing catalyst absorbs NO_X in the exhaust gas when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases and reduces NO_X when the air-fuel ratio of the exhaust gas is at a rich air-fuel ratio. The air-fuel ratio of the exhaust gas flowing out from the catalyst is detected by an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst. When the air-fuel ratio of the exhaust gas flowing into the catalyst is changed from a rich air-fuel ratio to a lean air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the catalyst stays at a stoichiometric air-fuel ratio before it changes to a lean air-fuel ratio. The length of the period in which the air-fuel ratio of the exhaust gas flowing out from the catalyst stays at a stoichiometric air-fuel ratio corresponds to the magnitude of the ability of the NO_X occluding and reducing catalyst as a reducing catalyst. Thus, by measuring the length of the stoichiometric air-fuel ratio period of the exhaust gas flowing out from the NO_X occluding and reducing catalyst, the ability of the NO_X occluding and reducing catalyst as a reducing catalyst can be precisely evaluated.

Claims

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

a NO_X occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NO_X in exhaust gas when an inflowinq air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NO_X when the inflowinq air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio;

an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst;

air-fuel ratio control means for switching the inflowing air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio; and

evaluating means for evaluating an ability of the catalyst based on length of time during which the outflowing air-fuel ratio is maintained at a stoichiometric air-fuel ratio after the inflowing air fuel ratio is switched by the air-fuel ratio control means.

2. An exhaust gas purification device as set forth in claim 1, further comprising correcting means for correcting the ability evaluated by the evaluating means based on a condition of the exhaust gas flowing into the catalyst.

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

a NO_X occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NO_X in exhaust gas when an inflowing air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NO_X when the inflowing air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio;

an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst;

air-fuel ratio control means for changing the inflowing air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio and, after maintaining the inflowing air-fuel ratio rich for a predetermined period, changing the inflowing air-fuel ratio to a lean air-fuel ratio; and

evaluating means for evaluating an ability of the catalyst based on changes in the outflowing air-fuel ratio when the inflowing air fuel ratio is changed from a rich air-fuel ratio to a lean air-fuel ratio.

4. An exhaust gas purification device as set forth in claim 3, further comprising correcting means for correcting the ability evaluated by the evaluating means based on a condition of the exhaust gas flowing into the catalyst.

5. An exhaust gas purification device for an engine, comprising:

a NO_X occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NO_X in exhaust gas when an inflowing air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NO_X when the inflowing air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio;

an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst;

air-fuel ratio control means for changing the inflowing air-fuel ratio from a rich air-fuel ratio to a predetermined lean air-fuel ratio; and

evaluating means for evaluating an ability of the catalyst based on an amount of deviation of the outflowing air-fuel ratio from the predetermined lean air-fuel ratio after the air-fuel ratio of the inflowing air fuel ratio is changed to the predetermined lean air-fuel ratio by the air-fuel ratio control means.

6. An exhaust gas purification device as set forth in claim 5, further comprising correcting means for correcting the ability evaluated by the evaluating means based on a condition of the exhaust gas flowing into the catalyst.