EXHAUST GAS CLEANING APPARATUS FOR LEAN BURN INTERNAL COMBUSTION ENGINE

• US 20080314036A1
• Filed: 06/18/2008
• Published: 12/25/2008
• Est. Priority Date: 06/20/2007
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Yokoyama, Masakuni, Kawamura, Jun
• Granted Patent: US 8,091,338 B2
• Time in Patent Office: Days
• US Class Current: 60/303
• CPC Class Codes: F01N 3/021 by means of filters
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• 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 29/0406 Layout of the intake air cooling or coolant circuit
• CPC Class Codes: F02B 3/06 with compression ignition compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02
• CPC Class Codes: F02B 37/00 Engines characterised by provision of pumps driven at least for part of the time by exhaust
• CPC Class Codes: F02D 41/005 according to engine operating conditions
• CPC Class Codes: F02D 41/0235 in relation with the state of the exhaust gas treating apparatus control of exhaust gas treating apparatus per se F01N
• CPC Class Codes: F02D 41/027 to purge or regenerate the exhaust gas treating apparatus
• CPC Class Codes: F02M 26/05 High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
• CPC Class Codes: F02M 26/06 Low pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust downstream of the turbocharger turbine and reintroduced into the intake system upstream of the compressor
• CPC Class Codes: F02M 26/15 in relation to engine exhaust purifying apparatus
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An exhaust gas cleaning apparatus includes a LNT, a fuel adding device, an exhaust gas returning passage, and a controller. The LNT is provided in an exhaust gas passage of an engine. The fuel adding device is located upstream of the LNT to add fuel to exhaust gas flowing through the exhaust pipe. The exhaust gas returning passage branches off from the exhaust gas passage at a position downstream of the fuel adding device. The controller controls the apparatus to selectively operate in one of first and second modes according to the operating condition of the engine. In the first mode, the fuel adding device adds the fuel to the exhaust gas with the exhaust gas returning passage closed; in the second mode, the exhaust gas is partially returned to an intake air passage through the exhaust gas returning passage without the fuel being added by the fuel adding device.

Claims

1. An exhaust gas cleaning apparatus for cleaning exhaust gas from an internal combustion engine, the apparatus comprising:

a Lean NO_x Trap (LNT) provided in an exhaust gas passage of the engine through which the exhaust gas flows, the LNT being configured to absorb NO_x contained in the exhaust gas when the exhaust gas is lean and reduce the absorbed NO_x when the exhaust gas turns to rich;

a fuel adding device located upstream of the LNT to add fuel to the exhaust gas for making the exhaust gas rich;

an exhaust gas returning passage that branches off from the exhaust gas passage at a position downstream of the fuel adding device to return part of the exhaust gas to an intake air passage of the engine; and

a controller that determines an operating condition of the engine and controls the exhaust gas cleaning apparatus to selectively operate in one of first and second operation modes according to the determined operating condition of the engine, in the first operation mode the fuel adding device adding the fuel to the exhaust gas with the exhaust gas returning passage closed, in the second operation mode the part of the exhaust gas being returned to the intake air passage through the exhaust gas returning passage without the fuel being added by the fuel adding device to the exhaust gas.

2. The exhaust gas cleaning apparatus as set forth in claim 1, wherein the controller determines whether the engine operates in a first operation region, in which both the rotational speed and load of the engine is low, or in a second operation region in which either or both of the rotational speed and load of the engine are high, and

the controller controls the exhaust gas cleaning apparatus to operate in the first operation mode when the engine operates in the first operation region and in the second operation mode when the engine operates in the second operation region.

3. The exhaust gas cleaning apparatus as set forth in claim 2, further comprising detecting means for detecting the deterioration degree of a NO_x catalyst of the LNT,

wherein as the deterioration degree of the NO_x catalyst detected by the detecting means increases, the controller reduces the first operation region of the engine while accordingly expanding the second operation region of the engine.

4. The exhaust gas cleaning apparatus as set forth in claim 3, wherein the controller selects a first boundary to separate the first and second operation regions of the engine when the deterioration degree of the NO_x catalyst detected by the detecting means is lower than or equal to a predetermined threshold, and a second boundary to separate the first and second operation regions when the deterioration degree of the NO_x catalyst is higher than the predetermined threshold.

5. The exhaust gas cleaning apparatus as set forth in claim 3, wherein the controller sets an expanding rate of the second operation region of the engine as a function of the deterioration degree of the NO_x catalyst detected by the detecting means, the function being such that the expanding rate of the second operation region set with it increases faster than that set with a liner function.

6. The exhaust gas cleaning apparatus as set forth in claim 1, wherein the internal combustion engine is a diesel engine.