Exhaust gas purification device for an internal combustion engine

• US 5,974,791 A
• Filed: 02/24/1998
• Issued: 11/02/1999
• Est. Priority Date: 03/04/1997
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Hirota, Shinya, Tanaka, Toshiaki
• Primary Examiner(s): Denion, Thomas E.
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/028,916
• Time in Patent Office: 616 Days
• Field of Search: 60/286, 60/276, 60/289, 60/297, 60/300, 60/301, 60/303, 60/307, 60/311, 60/288, 423/235, 423/244.01, 423/244.06, 423/244.09, 423/244.1
• US Class Current: 60/276
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/1025 Rhodium
• CPC Class Codes: B01D 53/8696 Controlling the catalytic process
• CPC Class Codes: B01D 53/945 characterised by a specific catalyst
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 3/0253 adding fuel to exhaust gases
• CPC Class Codes: F01N 3/027 using electric or magnetic heating means
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0878 Bypassing absorbents or adsorbents
• CPC Class Codes: F01N 3/0885 Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
• 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: F02D 2200/0818 SOx storage amount, e.g. for SOx trap or NOx trap
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/029 the exhaust gas treating apparatus being a particulate filter
• CPC Class Codes: F02D 41/405 with post injections
• CPC Class Codes: Y02A 50/20 : Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• 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, an exhaust gas passage of a diesel engine diverges into two branch pipes and a particulate filter (DPF) is disposed in each of the branch pipes. The DPF uses a metallic substrate and NO_x absorbent is attached to the wall of the paths in the DPF. Therefore, the DPF act as both a normal particulate filter and a NO_x absorbent. During the operation of the engine, SO_x, as well as NO_x, in the exhaust gas is absorbed in the NO_x absorbent in the DPF. An electronic control unit (ECU) monitors the amount of SO_x absorbed in the DPF during the operation and, when the amount of SO_x absorbed in one DPF increases, switches the exhaust gas flow to the other DPF. The ECU further performs the SO_x recovery operation to release the absorbed SO_x from the DPF. After completing the SO_x recovery operation, the ECU performs the regenerating operation of the DPF in which the particulate matter trapped in the DPF is burned. Since SO_x in DPF is already released by the previous SO_x recovery operation when the regenerating operation of the DPF is performed, the growth of sulfate particle in the DPF does not occur even if the DPF is exposed to a high temperature lean air-fuel ratio atmosphere of the regenerating operation.

Claims

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

a NO_x absorbent disposed in an exhaust gas passage of an internal combustion engine, wherein said NO_x absorbent absorbs NO_x in the exhaust gas of the engine when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases the absorbed NO_x when the oxygen concentration in the exhaust gas is lowered, and wherein said NO_x absorbent absorbs SO_x in the exhaust gas when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases the absorbed SO_x when the oxygen concentration in the exhaust gas is lowered and when the temperature of the NO_x absorbent is higher than a SO_x releasing temperature;

SO_x releasing means for raising the temperature of the NO_x absorbent to a temperature higher than the SO_x releasing temperature and for lowering the oxygen concentration of the exhaust gas flowing into the NO_x absorbent to, thereby, release the absorbed SO_x from the NO_x absorbent; and

SO_x control means for controlling the amount of SO_x absorbed in the NO_x absorbent by controlling the SO_x releasing means in such a manner that, when it is expected that the temperature of the NO_x absorbent increases to a first predetermined temperature when the air-fuel ratio of the exhaust gas is lean, substantially all of the absorbed SO_x is released from the NO_x absorbent by the SO_x releasing means before the temperature of the NO_x absorbent reaches said first predetermined temp.

2. An exhaust gas purification device as set forth in claim 1, wherein said NO_x absorbent holds the absorbed SO_x therein in the form of a particle of sulfate, and wherein said first predetermined temperature is a temperature at which the sulfate particles in the NO_x absorbent starts to grow in a lean air-fuel ratio exhaust gas.

3. An exhaust gas purification device as set forth in claim 1, wherein said SO_x control means further comprises an exhaust gas temperature detecting means for detecting the temperature of the exhaust gas flowing into the NO_x absorbent and activates the SO_x releasing means when the temperature of the exhaust gas increases to a second predetermined temperature which is lower than the first predetermined temperature.

4. An exhaust gas purification device as set forth in claim 1, further comprising:

purifying means disposed in the exhaust gas passage upstream of the NO_x absorbent for removing a specific component contained in the exhaust gas; and

burning means for burning the specific component trapped by or attached to the purifying means by raising the temperature of the purifying means and by supplying a lean air-fuel ratio exhaust gas to the purifying means,

wherein said SO_x controlling means activates the SO_x releasing means before activating the burning means.

5. An exhaust gas purification device as set forth in claim 4, wherein said specific component is a soluble organic fraction, and said purifying means is an oxidizing catalyst or three-way catalyst which oxidizes the soluble organic fraction in the exhaust gas.

6. An exhaust gas purification device as set forth in claim 4, wherein said specific component is particulate matter in the exhaust gas, and said purifying means is a particulate filter which traps the particulate matter in the exhaust gas.