Exhaust gas purification device for an internal combustion engine

• US 5,970,707 A
• Filed: 09/09/1998
• Issued: 10/26/1999
• 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): Look, Edward K.
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/150,266
• Time in Patent Office: 412 Days
• Field of Search: 60/277, 60/285, 60/286, 60/276, 123/691, 123/703
• US Class Current: 60/277
• 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 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 2250/12 absorption or adsorption, and catalytic conversion
• 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 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• 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 for an internal combustion engine, a three-way catalyst and a NO_X occluding and reducing catalyst (a NORC) are disposed in the exhaust gas passage of an engine in this order from the upstream side. A first air-fuel ratio sensor is disposed in the exhaust gas passage between the three-way catalyst and the NORC, and a second air-fuel ratio sensor is disposed in the exhaust gas passage downstream of the NORC. An engine electronic control unit (ECU) changes the operating air-fuel ratio of the engine from a lean air-fuel ratio to a rich air-fuel ratio and a rich air-fuel ratio to a lean air-fuel ratio in order to evaluate the abilities of the three-way catalyst and the NORC. The ECU evaluates the catalytic abilities based on the output of the first air-fuel ratio sensor when the engine air-fuel ratio is changed. Further, the ECU evaluates the catalytic ability and the NO_X absorbing capacity of the NORC based on the outputs of the first and the second air-fuel ratio sensor when the engine operating air-fuel ratio is changed. The evaluation of the abilities of both the three-way catalyst and the NORC in one successive changing operation of the engine operating air-fuel ratio is based on only the outputs of the first and the second air-fuel ratio sensor.

Claims

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

a three-way catalyst disposed in the exhaust gas passage of an internal combustion engine;

a NO_X occluding and reducing catalyst disposed in the exhaust gas passage downstream of the three-way catalyst and absorbing NO_X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the NO_X occluding and reducing catalyst is at a lean air-fuel ratio and releasing and reducing the absorbed NO_X when the air-fuel ratio of the exhaust gas flowing into the NO_X occluding and reducing catalyst is at a stoichiometric or a rich air-fuel ratio;

a first air-fuel ratio sensor disposed in the exhaust gas passage at the position between the three-way catalyst and the NO_X occluding and reducing catalyst;

a second air-fuel ratio sensor disposed in the exhaust gas passage downstream of the NO_X occluding and reducing catalyst;

air-fuel ratio control means for switching the air-fuel ratio of the exhaust gas flowing into the three-way catalyst either from a rich air-fuel ratio to a lean air-fuel ratio or from a lean air-fuel ratio to a rich air-fuel ratio; and

evaluating means for evaluating the abilities of both of the three-way catalyst and the NO_X occluding and reducing catalyst when the air-fuel ratio control means switches the air-fuel ratio of the exhaust gas either from a rich air-fuel ratio to a lean air-fuel ratio or from a lean air-fuel ratio to a rich air-fuel ratio, wherein the evaluating means evaluates the ability of the three-way catalyst based on the output signal of the first air-fuel ratio sensor and evaluates the ability of the NO_X occluding and reducing catalyst based on the output signals of both the first and the second air-fuel ratio sensors.

2. An exhaust gas purification device as set forth in claim 1, wherein the evaluating means evaluates the ability of the three-way catalyst based on the length of the period in which the fist air-fuel ratio sensor outputs a signal corresponding to a stoichiometric air-fuel ratio when the air-fuel ratio control means switches the air-fuel ratio of the exhaust gas either from a rich air-fuel ratio to a lean air-fuel ratio or from a lean air-fuel ratio to a rich air-fuel ratio.

3. An exhaust gas purification device as set forth in claim 1, wherein the evaluating means evaluates the ability of the three-way catalyst based on the output signals of the first air-fuel ratio sensor when the air-fuel ratio control means switches the air-fuel ratio of the exhaust gas both from a rich air-fuel ratio to a lean air-fuel ratio and from a lean air-fuel ratio to a rich air-fuel ratio.

4. An exhaust gas purification device as set forth in claim 1, further comprising correcting means for correcting at least one of the abilities of the three-way catalyst and the NO_X occluding and reducing catalyst evaluated by the evaluating means based on the condition of the exhaust gas flowing into the three-way catalyst.

5. An exhaust gas purification device as set forth in claim 2, further comprising correcting means for correcting at least one of the abilities of the three-way catalyst and the NO_X occluding and reducing catalyst evaluated by the evaluating means based on the condition of the exhaust gas flowing into the three-way catalyst.

6. An exhaust gas purification device as set forth in claim 3, further comprising correcting means for correcting at least one of the abilities of the three-way catalyst and the NO_X occluding and reducing catalyst evaluated by the evaluating means based on the condition of the exhaust gas flowing into the three-way catalyst.