JP2001003738A - Catalyst device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To be excellent in durability and to purify exhaust gas with high efficiency by effectively utilizing the heat of exhaust gas. SOLUTION: A metal honeycomb body 3, having a catalyst layer, and a ceramic honeycomb body 4 are situated, in order, from the upper stream side of the internal part of an outer cylinder 2 connected to an exhaust pipe 5. An outer cylinder part 3a with which the metal honeycomb body 3 is joined is inserted in the exhaust pipe 5 and a space (c) is formed at an outer periphery and the end part of the exhaust pipe 5 is coupled to an outer cylinder part 4a in a position where the ceramic honeycomb body 4 is mounted. A space (c) formed in the outer periphery of the outer cylinder part 3a of the metal honeycomb body 3 forms an air heat insulation layer to improve heating by exhaust gas of the metal honeycomb body 3 and the efficiency of purification of exhaust gas. Further, expansion by heating is approximately uniformized over the whole of the metal honeycomb body 3 and durability is provided by preventing the occurrence of distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Engines mounted on automobiles are designed to purify exhaust gases and discharge them to the outside of the vehicle due to exhaust gas regulations. The present invention relates to a catalyst device for purifying exhaust gas.

[0002]

Catalytic device for purifying the exhaust gas of an automobile is connected to the downstream side of the exhaust pipe, oxidation HC, CO, and NO _X ·
Some use a three-way catalyst that purifies by a reduction reaction. There has been proposed a structure in which a catalyst device has a honeycomb structure having a passage cross section to increase a contact area of a passage wall and a catalyst supporting layer such as alumina is provided on the passage wall.

In general, a predetermined temperature (for example, 350.degree. C.) is required for the above-mentioned catalyst to start working. However, when the engine is started, the temperature is raised to such an extent that the above-mentioned catalyst works efficiently. However, the initial rise of the exhaust gas purification performance is delayed. In the exhaust gas passage, the catalyst on the most upstream side is exposed to the highest temperature. Therefore, the better the temperature raising characteristics of this portion, the better the catalytic action. Therefore, it is conceivable to use a metal honeycomb carrier for the catalyst device. However, since the metal honeycomb body is not sufficiently warm and easy to cool, it takes a long time to raise the temperature again when restarting after stopping the engine. For this reason, by using a short metal honeycomb body, the temperature of the metal honeycomb body can be quickly raised at the time of initial heating at the time of starting the engine, etc., and the catalyst can be activated early to improve efficiency, and even after the temperature is raised. A reduction in purification ability can be prevented.

A catalyst device 1 shown in FIG. 5 has a short metal honeycomb body 3 joined to an end of a long outer cylinder 2 by brazing or the like, and a ceramic honeycomb body 4 is disposed immediately inside the outer cylinder. Thus, the metal honeycomb body 3 side is the upstream side of the exhaust gas. Further, an outer cylindrical portion 3a to which the metal honeycomb body 3 is joined and an end of the exhaust pipe 5 are joined. A buffer member 6 for reducing vibration and impact is interposed between the ceramic honeycomb body 4 and the outer cylinder 2, and a downstream end face of the ceramic honeycomb body 4 is a plate-shaped stopper joined to the outer cylinder 2. 7 supported.

[0005] As described above, since the heat capacity is reduced by shortening the metal honeycomb body 3 on the uppermost stream side, the temperature rise characteristics are good, and the initial purification of exhaust gas can be performed efficiently. Also,
When the heat capacity is reduced by using the ceramic honeycomb body 4, the exhaust gas pressure increases when the cross-sectional area is reduced, and the mounting is troublesome when the cross section is shortened. However, by using the metal honeycomb body 3, the mounting is facilitated. I have. Therefore, the purification efficiency is improved by providing the ceramic honeycomb body 4 at the subsequent stage.

[0006]

However, the above-mentioned metal honeycomb body 3 has a small specific heat, and as shown in FIG. 5, is heated by the temperature of the outer peripheral portion near the outer cylinder 2 in contact with the outside air and the exhaust gas. There is a temperature difference with the temperature at the center,
Since the thermal expansion amounts of the central portion and the outer peripheral portion are different, the outer peripheral portion cannot cope with the expansion of the central portion, and the structure of the metal honeycomb body 3 may be shifted or damaged. In addition, at the time of low load or restart, the heat of the exhaust gas leaks from the outer cylindrical portion 3a of the metal honeycomb body 3 to the outside, so that the temperature of the ceramic honeycomb body 4 is delayed and the purification efficiency is reduced. Furthermore, since the diameter of the metal honeycomb body 3 is larger than the diameter of the ceramic honeycomb body 4 inside the outer cylinder 2 and the connection between the two ends is in close contact, the exhaust gas that has passed through the metal honeycomb body 3 is discharged from the ceramic honeycomb body 4. And the exhaust gas pressure increases, thereby decreasing the flow of the exhaust gas.

An object of the present invention is to provide a catalyst device which is excellent in durability and can purify exhaust gas efficiently by effectively utilizing the heat of the exhaust gas.

[0008]

Means for Solving the Problems In order to achieve the above object, the present invention is directed to a metal honeycomb body having a catalyst layer at an upstream end inside an outer cylinder, A catalyst device in which a ceramic honeycomb body having a catalyst layer is positioned downstream, and a heat insulating holding member is interposed between the ceramic honeycomb body and the outer cylinder to hold the ceramic honeycomb body, wherein an upstream exhaust pipe A space is provided between the outer periphery of the outer cylinder and the inner wall of the exhaust pipe by inserting an outer cylinder fitted with the metal honeycomb body of the catalyst device into the inside of the catalyst device, and the downstream end of the exhaust pipe is It is characterized in that it is connected to the outer cylinder.

According to a second aspect of the present invention, in the first aspect of the invention, the outer cylindrical portion for joining the metal honeycomb body is reduced in diameter to form a reduced outer cylindrical portion, and the reduced outer cylindrical portion and the ceramic honeycomb body are combined. A step is provided between the outer cylindrical portion to be mounted, the step covers the upstream end of the heat insulating holding member, and the cross section of the metal honeycomb body is substantially the same as the passage cross section of the ceramic honeycomb body. It is characterized by.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, a short metal honeycomb body 3 is joined to the inside of the outer cylinder 2 at the upstream end of the cylindrical catalyst device 1, and thereafter, an interval a (for example, a gap of about 40 mm or narrower) is opened. A ceramic honeycomb body 4 is provided. The ceramic honeycomb body 4 is the outer cylinder 2
Are supported with a heat insulating holding member 8 interposed therebetween. Note that a thermal expansion mat, a heat-resistant sponge, or the like is used for the heat insulating holding member 8, and a connecting pipe 9 is provided at the downstream end of the outer cylinder 2.
Are connected inside, and the end of the connecting pipe 9 prevents the heat insulating holding member 8 from shifting.

As shown in FIG. 2, in the catalyst device 1, after joining the metal honeycomb body 3 to the end of the outer cylinder 2 by brazing or the like, the heat insulating holding member 8 and the ceramic honeycomb body 4 are press-fitted. The heat-insulating holding member 8 is wound around the ceramic honeycomb body 4 in the circumferential direction, and the front and rear ends thereof are aligned with a gap b therebetween, so that the gap b is closed at the time of press-fitting.

The exhaust pipe 5 on the upstream side is enlarged so as to be connected to the catalyst device 1, is made larger than the outer cylinder 2 of the catalyst device 1, and the outer cylinder portion 3a at the mounting position of the metal honeycomb body 3 is an exhaust pipe. 5, an air heat insulating layer (space) c is provided between the outer periphery of the outer cylinder portion 3a and the inner wall of the exhaust pipe 5. The end of the exhaust pipe 5 is joined to the outer cylindrical portion 4a to which the ceramic honeycomb body 4 located downstream of the exhaust pipe 5 is attached.

The above-described catalyst device 1 includes a metal honeycomb body 3
Since the air heat insulating layer c is provided between the outer cylinder 3a equipped with the outer cylinder and the exhaust pipe 5, the outer cylinder 3a is not cooled by the external temperature, and heat is radiated from the outer cylinder 3a to the outside. Nothing to do. Also, the efficiency of the catalyst can be enhanced by effectively utilizing the heat of the exhaust gas by the heat insulating holding member 8 for the ceramic honeycomb body 4. That is, when the heat of the exhaust gas at the time of startup heats the short metal honeycomb body 3, the short metal honeycomb body 3 rapidly rises in temperature from its low heat capacity, while radiating heat from the outer cylinder portion on which the metal honeycomb body 3 is mounted. Therefore, the catalytic action is activated to purify the exhaust gas at an early stage, and during that time, the long ceramic honeycomb body 4 disposed immediately downstream is heated by the exhaust gas passing therethrough. After that, the exhaust gas is efficiently purified by the catalyst of the metal honeycomb body 3 and the ceramic honeycomb body 4.

Even when the engine is under a low load, the exhaust pipe 5
Since the air heat insulating layer c is provided between the outer cylindrical portion 3a on which the metal honeycomb body 3 is mounted, the outer cylindrical portion 3a on which the metal honeycomb body 3 is mounted is not directly exposed to the outside air. Therefore, since the heat of the exhaust gas does not escape to the outside, the metal honeycomb body 3 and the ceramic honeycomb body 4 can be efficiently heated, and the catalytic action is enhanced and the exhaust gas purifying action is improved. Further, even after the engine is stopped, the temperature of the ceramic honeycomb body 4 does not suddenly cool down. Therefore, if the engine is stopped for a short time, the catalyst function is recovered immediately after restarting, and the exhaust gas can be purified.

Further, since the outer cylindrical portion 3a on which the metal honeycomb body 3 is mounted protrudes into the atmosphere of the exhaust gas in the exhaust pipe 5, the temperature difference of the entire metal honeycomb body 3 is eliminated, and distortion due to thermal expansion is prevented. Prevent and improve durability. In addition, since there is an air heat insulating layer c between the exhaust pipe 5 and the outer cylindrical portion 3a on which the metal honeycomb body 3 is mounted (a gap a is provided in the front-rear direction of the flow path), the metal honeycomb body 3 Can freely expand and contract, so that the metal honeycomb carrier can be prevented from being displaced or damaged. That is, as shown in FIG. 4, the temperature distribution of the cross section of the metal honeycomb body 3 (solid line A) is more uniform than the temperature distribution of the cross section of the conventional metal honeycomb body 3 (dotted line B).
Such a sudden change in temperature (dashed-dotted line C) is eliminated, the occurrence of distortion is suppressed, and the durability is improved.

Further, since the gap a is provided between the metal honeycomb body 3 and the ceramic honeycomb body 4, the flow of the exhaust gas passing through the metal honeycomb body 3 is once integrated, and the exhaust gas pressure is made uniform. The flow of the exhaust gas passing through the ceramic honeycomb body 4 becomes smooth.

Next, another embodiment will be described with reference to FIG. The difference from the above embodiment is that the outer cylindrical portion 3a on which the metal honeycomb body 3 is mounted is reduced in diameter so that the passage cross section of the metal honeycomb body 3 becomes substantially the same as the passage cross section of the ceramic honeycomb body 4. Thus, a step 2a is formed at the boundary between the reduced outer tube 3a and the outer tube 4a of the ceramic honeycomb body 4, so that the step 2a covers the upstream end of the heat insulating holding member 8 so that the exhaust gas does not directly hit. That is what we did.

As a result, the exhaust gas is hindered by the step 2a and does not approach the heat-insulating holding member 8. In particular, when the heat-insulating holding member 8 is a heat-expandable mat, the life of the heat-insulating holding member 8 is extended, and Since the exhaust gas passage diameter is not narrowed at the connecting portion between the metal honeycomb body 3 and the ceramic honeycomb body 4, the exhaust gas flows smoothly, thereby improving the purification of the exhaust gas. Further, the rigidity of the outer cylinder 2 is improved by the step portion 2a.

[0019]

The present invention is as described above. According to the first aspect of the present invention, since the space is provided between the outer periphery of the metal honeycomb body and the exhaust pipe, the outer cylindrical portion of the metal honeycomb body has Since it is not directly exposed to the outside air and the heat of the exhaust gas does not escape to the outside, the action of purifying the exhaust gas is improved. In addition, since the temperature of the metal honeycomb body near the outer cylinder can be prevented from lowering and the metal honeycomb body can expand and contract freely,
The damage of the metal honeycomb body due to the temperature difference between the metal honeycomb body and the outside can be prevented. According to the second aspect of the present invention, by forming a step portion on the outer cylinder and reducing the diameter of the outer cylinder portion where the metal honeycomb body is located, the cross sections of the metal honeycomb body and the ceramic honeycomb body become substantially the same, and exhaust gas is reduced. It flows smoothly and improves the purifying action. Further, since the exhaust gas after passing through the metal honeycomb body does not directly hit the heat insulating holding member, the durability of the heat insulating holding member is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a catalyst device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing assembling of a catalyst used in the catalyst device of FIG. 1;

FIG. 3 is a sectional view of a catalyst device according to another embodiment of the present invention.

FIG. 4 is a graph showing a temperature distribution of a metal honeycomb body of the catalyst device according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional catalyst device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalyst apparatus 2 Outer cylinder 2a Step part 3 Metal honeycomb body 3a Outer cylinder part 4 Ceramic honeycomb body 4a Outer cylinder part 5 Exhaust pipe 8 Insulation holding member c Air insulation layer (space)

Claims (2)

[Claims] 1. A metal honeycomb body having a catalyst layer is joined to an upstream end inside an outer cylinder, a ceramic honeycomb body having a catalyst layer is positioned downstream of the metal honeycomb body, and the ceramic honeycomb body and the outer cylinder are connected to each other. A catalyst device that holds the ceramic honeycomb body with a heat insulating holding member interposed therebetween, wherein an outer cylindrical portion on which the metal honeycomb body of the catalyst device is mounted is inserted into an exhaust pipe on an upstream side. A catalyst device, wherein a space is provided between an outer periphery of an outer cylinder and an inner wall of the exhaust pipe, and a downstream end of the exhaust pipe is connected to the outer cylinder. 2. A step of forming a reduced-diameter outer cylindrical portion by reducing the diameter of an outer cylindrical portion to which a metal honeycomb body is joined, and a step between the reduced-diameter outer cylindrical portion and the outer cylindrical portion to which a ceramic honeycomb body is mounted. 2. The catalyst device according to claim 1, wherein the step covers the upstream end of the heat insulating holding member, and the cross section of the metal honeycomb body has substantially the same shape as the cross section of the ceramic honeycomb body. .