JP2000257512A - EGR cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent PM(particulate matter) and soot from sticking and depositing on an exhaust gas flow path of an EGR cooler by covering a metallic thin film having oxidation activity on an inner surface of the exhaust gas flow path of the EGR cooler disposed in an EGR(exhaust gas return flow) passage. SOLUTION: An exhaust gas flow path 84 is constituted by covering a metallic thin film 89 having oxidation activity such as Pt, Pd on an inner surface of an external pipe 88 made of a metallic material such as SUS having a good corrosion resistance by means of coating. The metallic thin film 89 is sufficient in the case having a film thickness of 5 nm or more while taking corrosion resistance and the like in consideration. The exhaust gas flow path 84 is formed in such a way that a plate material such as SUS on which the metallic thin film 89 is coated is worked in a pipe shape. PM and soot in exhaust gas which return-flows are brought into contact with the metallic thin film 89 having oxidation activity formed in an inner surface of the flow path 84, and oxidizing process is carried out, and thereby, it is possible to prevent them from depositing on the flow path 84 and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR cooler provided in an exhaust gas recirculation passage (EGR passage) for recirculating a part of exhaust gas in an engine, particularly in a diesel engine to an intake passage.

[0002]

2. Description of the Related Art In a diesel engine, a part of exhaust gas is recirculated to an intake passage through an EGR passage to reduce NOx, and is recirculated by disposing an EGR cooler in the EGR passage. It has been proposed to lower the temperature of exhaust gas to further reduce NOx (for example, see Japanese Patent Application Laid-Open No. 6-66208).

[0003] In such an EGR cooler, in order to increase the contact area with the exhaust gas and increase the cooling efficiency, there are those in which the exhaust gas flow path is narrowed or fins are provided inside the exhaust gas flow path.

[0004] However, particulate particles (PM) and soot in the exhaust gas adhere to the exhaust gas flow path, and gradually accumulate, causing a decrease in cooling efficiency and an increase in pressure loss. There is a problem that corrosive components such as SOF contained in the engine adversely affect the engine (for example, JP-A-5-187329, JP-A-9-3).
No. 10996).

Conventionally, in order to solve such a problem, there is an EGR cooler having an oxidation catalyst on the inner surface of an exhaust gas passage of an EGR cooler or an oxidation catalyst device provided upstream of the EGR cooler (see the above-mentioned feature). Kaihei 6-
No. 66208).

[0006]

SUMMARY OF THE INVENTION As described above, the conventional E
In the GR device, it is advantageous to provide an oxidation catalyst directly in the exhaust gas flow passage itself of the EGR cooler in consideration of the problem of mounting space and the like, but it is preferable to use alumina or the like which is used when a conventional honeycomb catalyst is supported. There is a method of adapting the method of coating the wash coat of the above, and incorporating the active ingredient therein, but this method has a disadvantage that the cooling efficiency is reduced because the wash coat component such as alumina generally has low thermal conductivity. May occur.

[0007] The present invention solves the above-mentioned conventional drawbacks, and reduces PM and soot by adhering or accumulating PM and soot in an exhaust gas passage of an EGR cooler, thereby increasing pressure loss. It is intended to prevent the adverse effects of corrosive components such as SOF contained in the PM, as well as to prevent adverse effects.

[0008]

In order to solve the above-mentioned problems, according to the present invention, exhaust gas is recirculated to an intake passage side.
The exhaust gas passage of the EGR cooler provided in the GR passage is coated with a thin film of a metal having an oxidizing activity. Specifically, it is preferable to use Pt, Pd, or the like as the metal having the oxidation activity.

[0009]

[Operation] According to the above configuration, a wash coat layer having poor heat conductivity is not required, so that the cooling efficiency is not impaired.

Further, it is possible to prevent PM and soot from adhering and accumulating in the exhaust gas passage of the EGR cooler.
A decrease in cooling efficiency and an increase in pressure loss due to adhesion and deposition of soot can be prevented. Further, corrosive components such as SOF components contained in the PM are also oxidized by contacting the metal thin film having an oxidizing activity, thereby preventing the corrosive components from adversely affecting the engine.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to the accompanying drawings. In FIG. 1, 1 is a diesel engine, 2 is an intake path, 3 is an air cleaner provided at an inlet thereof, 4 is an exhaust path, and a catalytic converter 5 is provided in the middle thereof.

6, one end is branched from the middle of the exhaust path 4,
The other end is connected in the middle of the intake passage 2 and is an exhaust gas recirculation passage for recirculating a part of the exhaust gas G to the intake passage 2 side, that is, an EGR passage. In the middle of the EGR passage 6, the EGR valve 7 and the EGR
Coolers 8 are provided respectively.

As shown in FIG. 2, the EGR cooler 8 has an inlet 82 and an outlet 83 for the exhaust gas G to be recirculated on the left and right sides of a main body 81, respectively. Exhaust gas passages 84 composed of a plurality of pipes are arranged in a predetermined arrangement at the center of the main body 81, and the cooling water of the engine 1 as a cooling medium is provided around the outer periphery of the exhaust gas passages 84. A W circulation path 85 is formed. The main body 81 has an inlet 8 for introducing cooling water W from the engine 1 to a circulation path 85.
6 and an outlet 87 for returning the cooling water W from the circulation path 85 to the engine 1 are provided.

As shown in FIG.
An inner surface of an outer tube 88 made of a metal material having high corrosion resistance such as US is coated with a thin film 89 of a metal having an oxidizing activity such as Pt or Pd by coating.

It is sufficient that the metal thin film 89 has a thickness of about 5 nm or more in consideration of corrosion resistance and the like. In addition, as a method of forming the exhaust gas flow path 84, a metal thin film 89 is used in advance.
It is preferable to process a plate material such as SUS coated with SUS into a pipe shape.

In the EGR cooler 8 of the present invention configured as described above, PM and soot in the recirculated exhaust gas G come into contact with the oxidizing metal thin film 89 formed on the inner surface of the flow passage 84. Since the oxidation treatment is performed, they can be prevented from accumulating in the flow path 84 and the like, and the heat conduction does not decrease, so that the cooling efficiency does not decrease. Therefore, an increase in pressure loss can be prevented.

Further, the corrosion component of the SOF contained in the PM is also oxidized by the catalytic action of the metal thin film 89,
Since no corrosive components are sucked into the engine, the adverse effects thereof can be prevented. Further, since a wash coat layer made of alumina or the like having poor heat conductivity, which is applied to a conventional engine, is not formed, the cooling effect is not impaired.

[0018]

As described above, in the present invention, since the inner surface of the exhaust gas passage of the EGR cooler is coated with a metal thin film having an oxidizing activity, a wash coat layer having poor heat conductivity is not required, and cooling is not required. Efficiency is improved.

Further, it is possible to prevent PM soot from adhering to and accumulating in the exhaust gas passage of the EGR cooler, and it is possible to prevent a decrease in cooling efficiency and an increase in pressure loss due to the adhering and accumulating of PM soot. Further, corrosive components such as SOF components contained in PM are also oxidized by the metal thin film having an oxidizing activity, so that adverse effects on the engine due to the corrosive components are prevented.

[Brief description of the drawings]

FIG. 1 is an overall system diagram of an engine showing an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing an EGR cooler according to the embodiment of the present invention.

FIG. 3 is an enlarged view of a main part of a part of the EGR cooler according to the embodiment of the present invention, showing an exhaust gas flow of the exhaust gas.

[Explanation of symbols]

 Reference Signs List 1 engine 6 EGR passage 8 EGR cooler 81 main body 84 exhaust gas passage 85 cooling water circulation passage 88 outer tube 89 metal thin film

Claims (2)

[Claims] An EGR system for recirculating exhaust gas to an intake passage.
An EGR cooler characterized in that an inner surface of an exhaust gas passage of an EGR cooler disposed in a passage is coated with a thin film of a metal having an oxidizing activity. 2. The EGR according to claim 1, wherein the metal having an oxidizing activity is Pt, Pd, or the like.
cooler.