JPH06182220A - Metal carrier for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a metal carrier excellent in purifying performance at the time of the start of an engine by installing small honeycomb bodies whose length in the axial direction is short placed in series on the most upstream side of the flow of exhaust gas of a metal honeycomb body so that their honeycomb passages may be staggered. CONSTITUTION:Foil consisting of Al-contg. ferrite-based alloy is worked to form it into sheets or corrugated sheets which are put one on top the other and wound in the form of a roll to form a honeycomb body. The honeycomb body is cut crosswise to form four small honeycomb bodies having 5mm length and one large honeycomb body 2 having 90mm length respectively. Next, into a cylindrical outer casing 3 formed with stainless steel, the four small honeycomb bodies 1 and the large honeycomb body 2 are inserted from one edge and from the other edge, respectively and these three bodies are brazed by using a brazing filler metal 4. The small honeycomb bodies 1 are brazed in all circumference thereof. The small honeycomb bodies 1 are installed in a row without leaving gaps between them so that their honeycomb passages may be stagged. Consequently the temperature rise property of a metal carrier is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying metal carrier mounted on an exhaust system of an automobile or the like and used as an exhaust gas purifying catalyst.

[0002]

2. Description of the Related Art For example, as a catalyst for purifying exhaust gas for purifying exhaust gas from an automobile engine, a supporting layer of activated alumina or the like is formed on a honeycomb body made of ceramic or metal, and platinum or rhodium or the like is formed on the supporting layer. The one carrying a catalytic metal is often used. However, the reality is that catalytic metals cannot obtain catalytic activity at temperatures lower than about 300 ° C. Therefore, the temperature of the honeycomb body is low immediately after the engine is started, and the temperature of the exhaust gas causes about 3
There was a problem that harmful substances were discharged without being purified until they were heated to over 00 ° C.

In order to improve such a problem, a metal carrier made of metal, which has a higher thermal conductivity than ceramics and an excellent temperature rising characteristic, is becoming mainstream. Further, for example, Japanese Utility Model Laid-Open No. 63-141632 and Japanese Utility Model Laid-Open No. 2-83320 disclose a tandem type carrier structure in which a metal honeycomb body having a small volume and a small heat capacity is arranged on the upstream side of exhaust gas. By reducing the heat capacity of the upstream honeycomb body in this way, the temperature of the upstream honeycomb body can be quickly raised. Then, the reaction heat in the honeycomb body on the upstream side can warm up the main honeycomb body on the downstream side. In addition, the tandem type also improves the degree of freedom in catalyst design, for example, by loading a large amount of catalytic metal having high low-temperature activity on the upstream carrier.

[0004]

In order to purify HC, CO, etc. in the exhaust gas when starting the engine, it is necessary to warm up the honeycomb body early. In the above-mentioned conventional metal carrier, the upstream side honeycomb body having a small heat capacity is heated early, and the exhaust gas whose temperature is further increased due to the reaction heat also flows into the downstream side honeycomb body, and the downstream side honeycomb body. It is a structure that heats the body. A space is provided between the upstream side honeycomb body and the downstream side honeycomb body, and the high temperature exhaust gas emitted from the upstream side honeycomb body becomes a turbulent flow in the space side and the downstream side honeycomb body is formed. Flow into. This improves the temperature rise characteristics of the downstream honeycomb body.

However, even with this conventional metal carrier, the turbulent flow generation in the space alone is insufficient in the temperature raising characteristics, and the purifying performance at the time of engine starting cannot be said to be satisfactory. The present invention has been made in view of such circumstances, and an object of the present invention is to further improve the temperature rising characteristics of the metal carrier and further improve the purification performance at the time of engine start.

[0006]

An exhaust gas purifying metal carrier of the present invention for solving the above-mentioned problems is a metal case having a large number of honeycomb passages formed of a flat plate and a corrugated plate, and a metal case having both ends opened. In the contained metal carrier, at the position of the most upstream part of the exhaust gas flow of the metal honeycomb body, a plurality of small honeycomb bodies having a short axial length are arranged in series so that their honeycomb passages are displaced from each other. It is characterized by being installed.

The plurality of small honeycomb bodies may form a part of the metal honeycomb body, or may have a tandem structure in which a space is provided between the small honeycomb body group and the remaining large honeycomb body. it can. It is also preferable to have a structure in which space portions are provided between the small honeycomb bodies. If the space portion is provided in this way, the temperature rising characteristic is further improved by the turbulent flow due to the space portion.

The axial length of the small honeycomb body is 5 to 15
The range of mm is desirable. If the axial length of the small honeycomb body is shorter than 5 mm, it becomes difficult to manufacture the honeycomb body.
If it is longer than mm, the exhaust gas flow is rectified in the small honeycomb body, so that a sufficient effect cannot be obtained.

[0009]

The exhaust gas first collides with the inlet end surface of the honeycomb body to be turbulent and enters the honeycomb passage, and moves in the honeycomb passage while colliding with the honeycomb passage wall. As a result, the heat of the exhaust gas is transferred to the honeycomb body and the temperature of the honeycomb body is raised. However, the inventors of the present invention diligently studied the state of the exhaust gas flow in the honeycomb body, and as a result, as shown in FIG.
As shown in FIG.
When entering about mm, Nusseldo number (Nu) decreases,
It has been found that the amount of heat transfer from the exhaust gas to the honeycomb body drops sharply. This indicates that the exhaust gas flow is rectified in the honeycomb passage to become a substantially laminar flow. The laminar exhaust gas has a low probability of colliding with the honeycomb passage wall, and is exhausted from the honeycomb body outlet without heat being transferred, resulting in insufficient improvement of the temperature rise characteristics.

Therefore, in the metal carrier of the present invention, a plurality of small honeycomb bodies having a short axial length are arranged in series at the position of the most upstream part of the exhaust gas flow so that the honeycomb passages are displaced from each other. It has a different configuration. With such a configuration, the exhaust gas from the first small honeycomb body flows into the second small honeycomb body in a state where it is not yet sufficiently rectified or immediately after being rectified and the heat transfer coefficient becomes low. . Since the honeycomb passages of the small honeycomb bodies are offset from each other, the exhaust gas flowing out of the first small honeycomb body collides with the end face on the inlet side of the second honeycomb body, and is turbulent again to generate the second small honeycomb body. It flows into the honeycomb body. Therefore, the exhaust gas flow in the small honeycomb body is surely turbulent,
Since the heat of the exhaust gas is reliably transferred, the temperature rise characteristics of the small honeycomb body group become extremely high.

As a result, in the small honeycomb body group, the catalytic metal reaches the active temperature range at an early stage, and the purification performance at the engine start is improved. And the heat of reaction is added to raise the temperature further,
The heat of the small honeycomb body group is transferred to the honeycomb body on the downstream side via exhaust gas or by heat conduction, and the temperature of the honeycomb body on the downstream side is also raised early.

[0012]

EXAMPLES Hereinafter, examples and comparative examples will be specifically described. (Embodiment 1) FIG. 1 shows a schematic sectional view of a metal carrier according to an embodiment of the present invention. This metal carrier has an axial length of 5
A small honeycomb body group 10 in which four small honeycomb bodies 1 having a size of 10 mm are arranged in series, and a large honeycomb body 2 having a length of 90 mm and arranged coaxially with a space portion 12 having a size of 10 mm between the small honeycomb body groups 10 and. An outer cylinder (case) 3 for accommodating the small honeycomb body group 10 and the large honeycomb body 2.

Hereinafter, the method of manufacturing the metal carrier will be described to replace the detailed description of the structure. Using a foil having a plate thickness of 50 μm made of an Al-containing ferritic alloy, it was processed into a flat plate and a corrugated plate, respectively. Then, the flat plate and the corrugated plate were superposed and wound in a roll shape to form a honeycomb body having a diameter of 86 mm. This honeycomb body is cut into slices, and the length is 5 mm.
4 small honeycomb bodies 1 and 1 large honeycomb body 2 having a length of 90 mm were formed.

Next, a plate thickness 1. made of SUS430 was prepared.
5 mm, outer diameter 89 mm, length 120 mm cylindrical outer cylinder 3
Was prepared, and the four small honeycomb bodies 1 were inserted from one end and the large honeycomb bodies 2 were inserted from the other end. And heat-resistant Ni
Using the system brazing material 4, the small honeycomb body 1 and the large honeycomb body 2 and the outer cylinder 3 were brazed and joined in a high temperature and high vacuum to form the tandem metal carrier of this example. Small honeycomb body 1
Was brazed and joined all around, and the small honeycomb bodies 1 were arranged in a row with no gaps and the honeycomb passages being displaced from each other. Further, the large honeycomb body 2 was cantilevered and brazed only in the range of 30 mm from the end surface facing the small honeycomb body group 10 and the opposite end surface, and heat loss to the outer cylinder 3 due to heat conduction was minimized.

Next, a slurry in which activated alumina, water and a binder are mixed is prepared, the metal carrier is dipped in the slurry, excess slurry is blown off, dried and then fired to form a catalyst supporting layer made of activated alumina. Formed. The formation amount of the catalyst-supporting layer is 100 g per 1 liter of each of the small honeycomb body 1 and the large honeycomb body 2. Then, Pt and Rh were supported on the catalyst supporting layer by a conventional method using a dinitrodiammine platinum aqueous solution and a rhodium chloride aqueous solution. The loading amount of this catalytic metal was 10.0 g of Pt and 0.4 g of Rh per liter of the small honeycomb body 1, and 1.5 g of Pt and Rh of 0.1 g per liter of the large honeycomb body 2. It is 4 g.

The above-mentioned tandem type metal carrier catalyst was attached to the exhaust system of an actual engine having an exhaust volume of 2000 cm ³ . At this time, the small honeycomb body group 10 was positioned on the upstream side of the exhaust gas flow, and the large honeycomb body 2 was positioned on the downstream side. Then, the engine is rotated at an engine speed of 1400.
The exhaust gas was continuously passed through the tandem-type metal carrier catalyst by operating under the constant conditions of rpm, pressure-360 mmHg and A / F = 14.5. Then, the HC concentration before and after the metal-supported catalyst was measured almost continuously for 60 seconds from the start,
The result of obtaining the HC purification rate for each time from these values is shown in FIG. (Comparative Example) As shown in FIG. 4, the structure is the same as that of the example except that an integrated medium honeycomb body 5 having an axial length of 20 mm is used instead of the small honeycomb body group 10.

This metal carrier is arranged so that the middle honeycomb body 5 is on the upstream side of the exhaust system, and is the same as in the embodiment.
The purification rate was measured. Results are shown in FIG. (Evaluation) From FIG. 5, it is understood that the metal carrier of Example 1 has an increased HC purification rate earlier than that of the comparative example, and the metal carrier of Example 1 is effective in purifying exhaust gas at the time of starting. It is clear that (Example 2) In Example 1, the space 12 was provided between the small honeycomb body group 10 and the large honeycomb body 2. However, as shown in FIG. 2, a plurality of small honeycomb bodies 1 and large honeycomb bodies 2 are provided. The space can be eliminated by arranging and closely. (Embodiment 3) If the space portions 13 are provided between the small honeycomb bodies 1 as shown in FIG. 3, the space portions 13 further promote turbulence and further improve the temperature rise characteristics.

[0018]

That is, according to the metal carrier of the present invention,
Since the heat of the exhaust gas can be effectively transferred to the upstream honeycomb body and the early temperature rise can be achieved, the emission of unburned gas such as HC and CO emitted at the time of engine cold start is reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a metal carrier according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a metal carrier according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a metal carrier according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a metal carrier of a comparative example.

FIG. 5 is a graph showing the relationship between the elapsed time after starting and the HC purification rate of the metal carriers of Examples and Comparative Examples.

FIG. 6 is a graph showing the relationship between the length of the honeycomb passage and the heat transfer coefficient to the walls of the honeycomb passage.

[Explanation of Codes] 1: Small honeycomb body 2: Large honeycomb body 3: Outer cylinder (case) 4: Brazing material 5: Medium honeycomb body 12, 1
3: Space section

Front page continued (72) Inventor Seizo Iida 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Norio Yamagishi 1, Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Gozo Kaji 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Hisashi Takei 7800 Chihama, Daito Town, Ogasa County, Shizuoka Prefecture Cataler Industry Co., Ltd. (72) Inventor Katsuyuki Osawa Aichi Prefecture 1 in 41 Chuo-dori, Nagakute-cho, Aichi-gun, Toyota Central Research Institute Co., Ltd. (72) Inventor Naoki Baba 1 in 41-chome, Nagakute-cho, Nagakute-machi, Aichi-gun 1 Toyota Central Research Co., Ltd.

Claims (1)

[Claims] 1. A metal carrier in which a metal honeycomb body formed of a flat plate and a corrugated plate and having a large number of honeycomb passages is housed in a metal case with both ends open, wherein the most upstream part of the exhaust gas flow of the metal honeycomb body is provided. At the position, a plurality of small honeycomb bodies having a short axial length are arranged in series so that the honeycomb passages are displaced from each other in series, and an exhaust gas purifying metal carrier.