Exhaust gas purification device for an engine

• US 5,740,669 A
• Filed: 11/16/1995
• Issued: 04/21/1998
• Est. Priority Date: 11/25/1994
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Itou, Takaaki, Takaoka, Toshifumi, Igarashi, Kouhei, Kinugasa, Yukio
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US08/559,107
• Time in Patent Office: 887 Days
• Field of Search: 60/274, 60/286, 60/301, 60/285, 60/298
• US Class Current: 60/285
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2240/18 an adsorber or absorber
• CPC Class Codes: F01N 2390/02 using electric components only
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• 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 3/30 Arrangements for supply of additional air control, e.g. using by-passes or variable air pump drives, F01N3/22
• 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 2200/0802 Temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: Y02C 20/10 of nitrous oxide (N2O)
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

In the present invention, a NO_x absorbent is used for removing the NO_x in the exhaust gas. The NO_x absorbent absorbs NO_x in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and releases the absorbed NO_x and reduces it to nitrogen when the air-fuel ratio of the exhaust gas is rich or stoichiometric. To prevent the NO_x absorbent from being saturated with the absorbed NO_x, the NO_x absorbent must be regenerated periodically by causing the NO_x in the absorbent to be released and reduced. However, it is found that when the regenerating process by supplying a rich air-fuel ratio exhaust gas to the NO_x absorbent is carried out at high NO_x absorbent temperature, a part of NO_x flows out from the NO_x absorbent at the beginning of the regenerating process without being reduced. In the present invention, this outflow of NO_x is suppressed by, for example, carrying out the regenerating process only when the temperature of the NO_x absorbent is lowered to a predetermined temperature. This predetermined temperature is set low enough to ensure that the amount of the outflow of NO_x is minimized.

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, wherein the NO_x absorbent absorbs NO_x in exhaust gas from the engine 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 oxygen concentration in the exhaust gas becomes lower;

temperature detecting means for detecting a temperature of the NO_x absorbent;

regenerating means for causing the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent to become one of a rich air-fuel ratio and a stoichiometric air-fuel ratio to cause the NO_x accumulated in the NO_x absorbent to be released from the NO_x absorbent and to be reduced to nitrogen; and

regeneration control means for activating the regenerating means to cause the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent to become one of a rich air-fuel ratio and a stoichiometric air-fuel ratio only when the temperature of the NO_x absorbent is lower than a predetermined temperature and an amount of NO_x accumulated in the NO_x absorbent is at least a predetermined amount.

2. An exhaust gas purification device according to claim 1, wherein said regeneration control means prohibits the regenerating means from causing the air-fuel ratio of the exhaust gas to-become rich or stoichiometric when the temperature of the NO_x absorbent is higher than or equal to said predetermined temperature.

3. An exhaust gas purification device according to claim 1, wherein said regeneration control means comprises a temperature control means for keeping the temperature of the NO_x absorbent at lower than said predetermined temperature at least when the regenerating means causes the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent to become rich or stoichiometric.

4. 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, wherein the NO_x absorbent absorbs NO_x in exhaust gas from the engine 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 oxygen concentration in the exhaust gas becomes lower;

regenerating means for causing the air-fuel ratio of the exhaust gas flowing into the NO_x absorbent to become one of a rich air-fuel ratio and a stoichiometric air-fuel ratio to cause the NO_x accumulated in the NO_x absorbent to be released from the NO_x absorbent and to be reduced to nitrogen;

activating means for activating the regenerating means when the amount of NO_x accumulated in the NO_x absorbent reaches a predetermined value;

temperature detecting means for detecting a temperature of the NO_x absorbent; and

regeneration timing control means for controlling the activating means in such a manner that the timing of the activation of the regenerating means is delayed as the temperature of the NO_x absorbent increases.

5. An exhaust gas purification device according to claim 4, wherein said activating means comprises NO_x amount detecting means for detecting the amount of the NO_x accumulated in the NO_x absorbent and activates the regenerating means when the amount of the NO_x accumulated in the NO_x absorbent becomes larger than a predetermined set value, and wherein said regeneration timing control means increases said set value as the temperature of the NO_x absorbent becomes high.