Exhaust gas purification device for an engine

• US 5,433,074 A
• Filed: 07/26/1993
• Issued: 07/18/1995
• Est. Priority Date: 07/30/1992
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Iguchi, Satoshi, Tanaka, Toshiaki, Takeshima, Shinichi, Seto, Satomi
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/097,794
• Time in Patent Office: 722 Days
• Field of Search: 60/274, 60/301, 60/289, 60/299, 60/297, 60/285, 60/286, 422/169, 423/213.7
• US Class Current: 60/301
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2570/16 Oxygen
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0871 Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/18 characterised by methods of operation; Control
• 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 3/22 Control of additional air supply only, e.g. using by-passes or variable air pump drives
• CPC Class Codes: F01N 3/222 using electric valves only
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• 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: Y02T 10/40 Engine management systems

Abstract

An engine comprising an exhaust passage having therein a NO_x absorbent which absorbs the NO_x when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent is lean and releases the absorbed NO_x when the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent becomes the stoichiometric air-fuel ratio or rich. A catalyst having an O₂ storage function is arranged in the exhaust passage downstream of the NO_x absorbent. When NO_x is to be released from the NO_x absorbent, the air-fuel ratio of the exhaust gas is made rich to an extent such that the amount of unburned HC and CO is excessive beyond an amount necessary to reduce the whole NO_x.

Claims

1. An exhaust gas purification device for an engine having an exhaust passage, said device comprising:

an NO_x absorbent arranged in the exhaust passage and absorbing NO_x when an air-fuel ratio of exhaust gas flowing into the NO_x absorbent is lean, said NO_x absorbent releasing absorbed NO_x when said air-fuel ratio of exhaust gas becomes rich;

an air-fuel ratio control means for controlling said air-fuel ratio of exhaust gas to make said air-fuel ratio of exhaust gas lean when NO_x is to be absorbed in said NO_x absorbent, said air-fuel ratio control means changing over said air-fuel ratio of exhaust gas from a lean air-fuel ratio to a rich air-fuel ratio and increasing a richness of exhaust gas flowing into said NO_x absorbent to a predetermined richness in which the exhaust gas flowing into said NO_x absorbent contains therein an excessive amount of unburned components relative to an amount necessary to reduce all of the NO_x when NO_x is to be released from said NO_x absorbent; and

unburned component oxidizing means for oxidizing the unburned components of the exhaust gas discharged from said NO_x absorbent.

2. An exhaust gas purification device according to claim 1, wherein said unburned component oxidizing means comprises a catalyst arranged in the exhaust passage downstream of said NO_x absorbent, and said catalyst has a function of oxidizing the unburned components by oxygen stored in said catalyst.

3. An exhaust gas purification device according to claim 2, wherein said catalyst contains cerium therein.

4. An exhaust gas purification device according to claim 1, wherein said unburned component oxidizing means comprises a secondary air supply device for feeding a secondary air into the exhaust passage downstream of said NO_x absorbent to oxidize the unburned components.

5. An exhaust gas purification device according to claim 4, wherein said secondary air supply device feeds the secondary air into the exhaust passage during the time said air-fuel ratio of exhaust gas is rich.

6. An exhaust gas purification device according to claim 4, wherein an oxidizing catalyst is arranged in the exhaust passage downstream of said NO_x absorbent, and said secondary air is fed into the exhaust passage between said NO_x absorbent and said oxidizing catalyst.

7. An exhaust gas purification device according to claim 1, wherein said predetermined richness is increased as a temperature of said NO_x absorbent becomes high.

8. An exhaust gas purification device according to claim 1, wherein said air-fuel ratio control means gradually reduces the richness of the exhaust gas after increasing it to said predetermined richness and then maintain said air-fuel ratio of exhaust gas at the stoichiometric air-fuel ratio.

9. An exhaust gas purification device according to claim 8, wherein a time during which said air-fuel ratio of exhaust gas is maintained at the stoichiometric air-fuel ratio is made shorter as a temperature of said NO_x absorbent becomes high.

10. An exhaust gas purification device according to claim 1, wherein said air-fuel ratio control means controls said air-fuel ratio of exhaust gas by controlling an air-fuel ratio of air-fuel mixture fed into the engine.

11. An exhaust gas purification device according to claim 1, wherein said NO_x absorbent contains at least one substance selected from alkali metals comprising potassium, sodium, lithium, cesium;

alkali earth metals comprising barium, calcium; and

rare earth metals comprising lanthanum, yttrium and contains platinum.