JPH07232082A - Catalyst converter for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To provide a catalyst converter for purification of exhaust gas wherein the reaction heat of a catalyst carrier on the upstream is efficiently transmitted to a catalyst carrier on the downstream and which can be rapidly started up. CONSTITUTION:A catalyst converter 1 has the first carrier 10 with a relatively low thermal conductivity and the second carrier 20 built in the first carrier 10 and rapidly activated. It is pref. that only the upstream side end face 21 of the second carrier 20 is exposed from the first carrier 10 and it is arranged at the central part where the flow rate of the exhaust gas is large. To activate the second carrier 20 at its early stage, either a low heat capacity region is provided on the upstream side or a metal catalyst is applied. For the first carrier 10 with low thermal conductivity, a ceramic catalyst, etc., can be used. In addition, it is pref. that a cushioning member be placed on the side boundary parts of both the first and the second carrier 10 and 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic converter for purifying exhaust gas of an internal combustion engine, and more particularly to a catalytic converter capable of activating a catalyst early.

[0002]

2. Description of the Related Art Harmful Co and H contained in automobile exhaust
There is a catalytic converter for purifying exhaust gas that converts C, NOx and the like into harmless substances by a chemical reaction. Since the catalytic converter has a considerably large heat capacity, it takes time to raise the temperature to the activation temperature of the catalyst when the vehicle is cold-started, and there is a problem that unpurified exhaust gas is discharged to the atmosphere during that time. .

Therefore, a small-capacity catalyst carrier is arranged upstream of the main catalytic converter, the small-capacity catalyst carrier on the upstream side is activated early, and the heat of reaction accelerates the activation of the main catalytic converter. A method has been proposed (see Japanese Utility Model Publication No. 2-19818).

[0004]

However, the conventional catalytic converter in which a small-capacity catalyst carrier is arranged on the upstream side has the following problems. That is, much of the reaction heat generated in the upstream catalyst carrier is dissipated to the surroundings without contributing to the temperature rise of the main catalytic converter. For example, heat may be taken by a member other than the main catalytic converter (for example, an exhaust pipe line), or heat may be radiated from the outer cylinder of the catalyst carrier to the outside of the exhaust passage.

In order to efficiently heat the main catalytic converter, the reaction heat of the upstream catalyst carrier is transferred only in the exhaust gas flow direction and not in the direction perpendicular to the exhaust gas flow. It is necessary to. In view of such conventional problems, the present invention is an exhaust gas purifying system that can efficiently transfer the reaction heat of an upstream catalyst carrier to a downstream catalyst carrier and can quickly start up a downstream catalyst carrier. It is intended to provide a catalytic converter of.

[0006]

The present invention is a catalytic converter that is disposed in the exhaust path of an internal combustion engine and carries a catalyst for purification of exhaust gas. The first converter has a lower thermal conductivity and the upstream side of the first carrier. The end face is exposed and is installed upstream of the first carrier,
A catalytic converter for purifying exhaust gas, comprising a second carrier that is activated earlier than the first carrier.

What is most noticeable in the present invention is that the second carrier is provided in the upstream side portion of the first carrier, the thermal conductivity of the first carrier is low, and the second carrier is It is to be activated earlier than the first carrier. In order to activate the second carrier earlier than the first carrier, for example, the heat capacity should be reduced so that the temperature of the second carrier rises faster than that of the first carrier in the exhaust gas, and the activation temperature is low. There is a method of using the above method, a combination of the above two methods, and the like.

There is also a method of arranging the second carrier at a position where the flow velocity of exhaust gas is high in order to activate the second carrier early. This is because if the flow velocity (flow rate) of the exhaust gas is large, the amount of heat received will increase, the temperature will rise quickly, and the catalyst will be activated quickly. As a method of activating the second carrier early, there is a method of forming a low heat capacity region on the upstream side of the second carrier. This is because in the low heat capacity region, the heat capacity is small, so it is easy to raise the temperature, and because it is arranged upstream, it can come into contact with high temperature exhaust gas and raise the temperature quickly.

As a method of forming the low heat capacity region, for example, there is a method of providing an opening window on the catalyst supporting surface. This is because the heat capacity of the portion provided with the opening window is reduced by the area corresponding to the opening window, and the temperature can be raised quickly. As a specific example thereof, there is one in which a large number of small opening windows are provided and the catalyst-supporting surface is in a grid pattern (see FIG. 5).

As one of the methods for facilitating the activation of the second carrier, there is a method of using the second carrier as a metal catalyst.
This is because the metal catalyst has a small heat capacity and generally has a low catalyst activation temperature. Some of the metal catalyst carriers have, for example, Fe-Cr-Al as a base material and carry a catalyst such as platinum, palladium, or rhodium via a layer of γ-alumina.

On the other hand, one example of the first carrier having a low thermal conductivity is a ceramic catalyst. For the ceramic catalyst carrier,
For example, there is one in which cordierite is used as a base material and a catalyst such as platinum, palladium or rhodium is supported through a γ-alumina layer.

Although the second carrier is installed in the upstream side portion of the first carrier, only the end face of the second carrier on the upstream side is made the first carrier.
Suitably, it is exposed from the carrier and the other surface is embedded in the first carrier. This is because the upstream end face needs to be exposed to allow the exhaust gas to flow in, but the side face (the outer peripheral surface parallel to the exhaust gas flow) has less heat loss when it is buried in the first carrier (details will be described later). (See [Effect]].

However, the term "incorporation into the first carrier" does not mean only a mode in which all the other surfaces except the end surface on the upstream side of the second carrier are buried in the first carrier as described above. For example, a part of the side surface parallel to the flow of the second carrier is
It may be exposed from the first carrier, and the more the buried portion of the second carrier in the first carrier is, the more effective it is.

A buffer member is preferably arranged at the boundary between the first carrier and the second carrier, which is parallel to the flow direction of the exhaust gas. By providing the cushioning member, it is possible to absorb the vibration and the difference in the coefficient of thermal expansion between the first and second carriers.

[0015]

In the catalytic converter according to the present invention, the second carrier activated early is located upstream. Therefore, the reaction heat of the second carrier activated early is transferred to the first carrier from the end face on the downstream side along with the flow of exhaust gas. In addition, since the second carrier is installed in the first carrier, the heat lost from the side surface of the second carrier by heat conduction is
Most will be transferred to the first carrier. And the first
Since the thermal conductivity of the carrier is low, the amount of heat lost from the side surface of the second carrier to the first carrier is extremely small.

That is, most of the reaction heat of the second carrier is carried on the exhaust gas and transferred to the downstream first carrier, and the amount of heat lost from the side surface in the direction perpendicular to the flow of the exhaust gas is extremely small. Therefore, the reaction heat of the second carrier is efficiently transferred to the first carrier,
The temperature of the carrier can be rapidly raised to start up.

As described above, according to the present invention, the reaction heat of the upstream catalyst carrier (second carrier) can be efficiently transferred to the downstream catalyst carrier and the downstream catalyst carrier can be quickly started up. It is possible to provide a catalytic converter for exhaust gas purification.

[0018]

【Example】

Example 1 A catalytic converter according to an example of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. This example is a catalytic converter 1 which is arranged in the exhaust passage 31 of an engine of an automobile as shown in FIG. 1 and carries a catalyst for exhaust gas purification. The catalytic converter 1 includes a first carrier 10 having a low thermal conductivity,
The upstream end face 21 is exposed, the upstream side of the first carrier 10 is installed, and the second carrier 20 is activated earlier than the first carrier 10.

As shown in FIGS. 1 and 3, the second carrier 20 is installed in the first carrier 10 so that only the upstream end surface 21 is exposed and the other surface is embedded in the first carrier 10. . The second carrier 20 is installed in the center of the first carrier 10 where the flow velocity of the exhaust gas 80 is high.

The first carrier 10 is a ceramic catalyst and the second carrier 20 is a metal catalyst. And
A buffer member 15 (FIG. 2) is arranged at a boundary portion between the first carrier 10 and the second carrier 20, which is parallel to the flow direction of the exhaust gas 80.

A supplementary explanation will be given below for each of these. As shown in FIG. 1, the catalytic converter 1 accommodates the first carrier 10 and the second carrier 20 in an outer cylinder 30 and is connected to an exhaust passage 31. The first carrier 10 is a ceramic catalyst made of cordierite and has an upstream end surface 11
A recess 12 for accommodating the second carrier 20 is formed in the central part of the. The first carrier 10 is formed by extruding cordierite, drying it, and then cutting it to form a recess 12.

As shown in FIG. 4, the second carrier 20 is a honeycomb-shaped catalyst carrier in which corrugated plates 22 and corrugated flat plates 23, which are not uneven, are alternately laminated and wound. The adjacent flat plate 23 and corrugated plate 22 are joined by brazing, resistance welding, laser welding, discharge welding or the like.

On the upstream side of the second carrier 20, there is formed a small diameter portion 24 in which the number of windings of both plates 22 and 23 is smaller than that on the downstream side. The flat plate 23 and the corrugated plate 22 are Fe-based alloys, in which Cr is 18 to 24 wt% and Al is 4.5%.
~ 5.5wt%, rare earth metal (REM) 0.01 ~
It is a ferritic heat-resistant steel containing 0.2 wt% and has a thickness of several tens of μm.

The second carrier 20 is fixed by inserting it into the recess 12 of the first carrier 10 as shown in FIG. 2 and then mounting a stopper 16 between the recess 12 and the small diameter portion 24. The stopper 16 is fixed to the inner wall of the recess 12 with an inorganic adhesive 17.

A buffer member 15 is provided in the remaining space between the second carrier 20 and the recess 12. The stopper 16 is a ceramic made of the same material as the first carrier 10. The cushioning member 15 is made of ceramic fiber.

Next, the function and effect of the catalytic converter 1 of this example will be described. The exhaust 80 flowing through the exhaust passage 31 has a higher flow velocity and a higher temperature in the central portion. Therefore, the exhaust gas 80 flowing into the second carrier 20 has a large amount and a higher temperature than the outer peripheral portion.

The second carrier 20 is a metal catalyst having the above composition and has a small heat capacity and a rapid temperature rise. Further, the activation temperature of the catalyst itself is lower than that of the ceramic catalyst of the first carrier 10. Therefore, the second carrier 20 is activated in a short time and the temperature rises.

On the other hand, the exhaust gas 80 on the outer peripheral side having a relatively low flow velocity and low temperature passes through the first carrier 10 near the outer peripheral portion. As a result, a temperature difference occurs in the outer peripheral direction (direction perpendicular to the flow of exhaust gas) between the second carrier 20 and the first carrier 10, and heat flow in the outer peripheral direction occurs.

However, since the first carrier 10 is a ceramic catalyst having a very small thermal conductivity, the heat flow (heat dissipation) in the outer peripheral direction is extremely small. Since the second carrier 20 has the first carrier 10 in between and is not directly connected to the outer cylinder 30, there is no heat flow to the outer cylinder 30. Therefore, the heat of reaction generated in the second carrier 20 is efficiently used for raising the temperature of the first carrier 10 without being taken away by others.

Further, since the buffer member 15 made of ceramic fiber is interposed between the first carrier 10 and the second carrier 20, the relative difference due to the difference in the coefficient of thermal expansion between the two carriers 10, 20 is caused. It is possible to absorb the movement and also the transmission of the vibration between the both 10 and 20. As described above, according to this example, the exhaust heat that can efficiently transfer the reaction heat of the upstream second carrier 20 to the downstream first carrier 10 and quickly start up the downstream first carrier 10 Purification catalytic converter 1
Can be provided.

Example 2 This example is the same as Example 1 except that FIG.
As shown in, on the upstream side of the meridian portion 24 of the second carrier 20,
It is another embodiment in which a low heat capacity region 25 having a plurality of opening windows 26 is formed. That is, upstream of the minor part 24,
A large number of small opening windows 26 are provided so that the catalyst supporting surface has a lattice pattern.

As a result, the heat capacity of this area is much smaller than the other areas, and the low heat capacity area 25 is formed. As a result, the rate of temperature rise and activation of the low heat capacity region 25 is further increased, and the early activation of the second carrier 20 is further accelerated. Others are the same as those in the first embodiment.

[Brief description of drawings]

FIG. 1 is a plan view (cross-sectional view) of a catalytic converter according to a first embodiment.

FIG. 2 is an enlarged view of the vicinity of the second carrier in FIG.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a perspective view of a second carrier according to the first embodiment.

FIG. 5 is a perspective view of a second carrier according to the second embodiment.

[Explanation of symbols]

 1. ． ． Catalytic converter, 10. ． ． First carrier, 20. ． ． Second carrier, 21. ． ． End face,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/40 ZAB A F01N 3/20 ZAB H // B01J 35/04 ZAB 301 N 321 A

Claims (8)

[Claims] 1. An internal combustion engine is arranged in the middle of an exhaust path,
A catalytic converter carrying a catalyst for purifying exhaust gas, the first carrier having a lower thermal conductivity, the upstream end face being exposed, and being installed upstream of the first carrier. A catalytic converter for exhaust gas purification, comprising a second carrier that is activated earlier than the above. 2. The catalytic converter for exhaust gas purification according to claim 1, wherein the second carrier is incorporated in the first carrier so as to expose only the end face on the upstream side. 3. The catalytic converter for exhaust gas purification according to claim 1 or 2, wherein the second carrier is installed in a position where the flow velocity of exhaust gas is relatively high in the first carrier. . 4. The exhaust gas purifying device according to claim 1, wherein the second carrier has a low heat capacity region formed at least on the upstream side of the exhaust passage. Catalytic converter. 5. The catalytic converter for exhaust gas purification according to claim 4, wherein the catalyst supporting surface in the low heat capacity region is provided with a plurality of opening windows for reducing heat capacity. 6. The catalytic converter for exhaust gas purification according to any one of claims 1 to 4 or 5, wherein the first carrier is a ceramic catalyst. 7. The catalytic converter according to any one of claims 1 to 5 or 6, wherein the second carrier is a metal catalyst. 8. The cushioning member according to claim 1, wherein a boundary portion between the first bearing surface and the second bearing surface, which is parallel to a flow direction of exhaust gas, is provided. A catalytic converter for purifying exhaust gas, which is characterized in that