Exhaust gas purification device for an engine

• US 5,448,887 A
• Filed: 05/31/1994
• Issued: 09/12/1995
• Est. Priority Date: 05/31/1993
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Takeshima, Shinichi
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/251,821
• Time in Patent Office: 469 Days
• Field of Search: 60/274, 60/278, 60/285, 60/286, 60/289, 60/301
• US Class Current: 60/278
• 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 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 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 3/20 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: F02B 1/04 with fuel-air mixture admission into cylinder
• CPC Class Codes: F02D 41/0052 Feedback control of engine parameters, e.g. for control of air/fuel ratio or intake air amount
• CPC Class Codes: F02D 41/027 to purge or regenerate the exhaust gas treating apparatus
• CPC Class Codes: F02D 41/1474 by detecting the commutation time of the sensor
• CPC Class Codes: F02D 41/1477 characterised by the regulation circuit or part of it,(e.g. comparator, PI regulator, output)
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An exhaust gas purification device of the present invention includes a three-way reducing and oxidizing catalyst disposed on an exhaust passage of an engine, and an NO_x absorbent which absorbs NO_x in the exhaust gas when the air-fuel ratio of the exhaust gas is lean and releases absorbed NO_x when the air-fuel ratio of the exhaust gas is rich; the engine in the present invention is controlled in most of its operating region in such a manner that the operating air-fuel ratio of the engine oscillates between a rich air-fuel ratio and a lean air-fuel ratio about a center value of a stoichiometric air-fuel ratio; when the operating air-fuel ratio of the engine becomes lean, the ability of the three-way catalyst for reducing NO_x in the exhaust gas becomes low, and a part of NO_x in the exhaust gas passes through the three-way catalyst, and, since the air-fuel ratio of the exhaust gas is lean, this NO_x is absorbed in the NO_x absorbent located downstream of the three-way catalyst; when the operating air-fuel ratio of the engine becomes rich, the ability of the three-way catalyst for oxidizing HC and CO in the exhaust gas becomes low, and a part of HC and CO in the exhaust gas passes through the three-day catalyst; since the air-fuel ratio of the exhaust gas is rich, absorbed NO_x is released from the NO_x absorbent and this NO_x is reduced as HC and CO passes through the three-way catalyst; therefore, the pollutants such as HC, CO, NO_x are almost completely removed.

Claims

1. An exhaust gas purification device for an internal combustion engine having an inlet air passage and an exhaust passage, said device comprising:

an air-fuel ratio controlling means for controlling an operating air-fuel ratio of said engine in most of the operating region thereof in such a manner that the air-fuel ratio of the engine oscillates periodically between a rich air-fuel ratio and a lean air-fuel ratio about a stoichiometric air-fuel ratio as the center of the oscillation;

a three-way reducing and oxidizing catalyst disposed in said exhaust passage;

an NO_x absorbent disposed in said exhaust passage of the engine downstream of said three-way catalyst, said NO_x absorbent absorbing an NO_x component in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into said NO_x absorbent is lean, and releasing the absorbed NO_x when the oxygen concentration in the exhaust gas becomes lower.

2. An exhaust gas purification device according to claim 1, wherein said air-fuel ratio control means controls the operating air-fuel ratio of the engine by controlling the amount of the fuel fed to the engine.

3. An exhaust gas purification device according to claim 1, wherein said air-fuel ratio control means controls the operating air-fuel ratio of the engine by controlling the amount of intake air fed to the engine.

4. An exhaust gas purification device according to claim 3, wherein said air-fuel ratio control means comprises an exhaust gas recirculating means for recirculating the exhaust gas of the engine to the inlet air passage of the engine and a recirculation control means for controlling the amount of the exhaust gas recirculating to the intake passage, to thereby control the amount of the intake air fed to said engine.

5. An exhaust gas purification device according to claim 1, wherein said air-fuel ratio control means further comprises a temperature detecting means for detecting the temperature of said NO_x absorbent, and controls the length of the period in the air-fuel ratio oscillation in which the air-fuel ratio of the engine is controlled on rich air-fuel ratio side compared to the stoichiometric air-fuel ratio in accordance with the temperature of the NO_x absorbent.

6. An exhaust gas purification device according to claim 1, which further comprises an exhaust gas air-fuel ratio control means for controlling the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent separately from the operating air-fuel ratio of the engine, and further increases the air-fuel ratio of the exhaust gas flowing into said NO_x absorbent when the air-fuel ratio of said exhaust gas flowing into the NO_x absorbent is lean.

7. An exhaust gas purification device according to claim 6, wherein said exhaust gas air-fuel ratio control means comprises a means for introducing secondary air into the exhaust passage upstream of the NO_x absorbent, and increases the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent by introducing the secondary air into the exhaust passage upstream of the NO_x absorbent.