JPH0261313A - Structure for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To prevent movement and the damage of a ceramic honeycomb by a method wherein, in a device in which a ceramic honeycomb is contained in a heat resistant container through a cushioning material, an uneven surface is formed on a surface where the cushioning material makes contact with the ceramic honeycomb. CONSTITUTION:A structure utilized for a catalyst converter for purifying exhaust gas from an internal combustion engine is formed such that a ceramic honeycomb 1 is contained in a heat resistant container 6 through a cushioning material 5. The ceramic honeycomb 1 is provided at its interior with cells 2a and 2b each forming a flow passage and formed by a cell wall 3. In this case, the cushioning material 5 is formed with a sheet having a number of holes 7 so that uneven surface processing is applied on a surface where the cushioning material makes contact with the ceramic honeycomb 1. The cushioning material 5 prevents backward movement of the honeycomb 1 by means of a back pressure and the occurrence of a crack to the ceramic honeycomb 1 due to a temperature difference between the inside and the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an exhaust gas purifying structure used in a catalytic converter or filter for purifying exhaust gas from an internal combustion engine.

BACKGROUND OF THE INVENTION In recent years, in order to purify exhaust gas from internal combustion engines, it has become possible to install catalytic converters and filters using honeycomb-shaped ceramics in the middle of exhaust pipes. This ceramic honeycomb is made of ceramic into a honeycomb shape by extrusion molding or corrugate rolling. Catalytic converters are mainly used in gasoline engines to oxidize hydrocarbons and carbon monoxide in exhaust gas, and are made by supporting a precious metal catalyst such as platinum on a ceramic honeycomb with relatively fine cell density. Filters are mainly used in diesel engines to remove particulates (soot) from exhaust gas, and are made of ceramic honeycomb cells made of a material with high porosity and relatively coarse cell density.One end of the cell and the other end of the adjacent cell. The cell is closed with a plug, and the exhaust gas that has entered the cell cannot escape unless it passes through the cell wall. In either case, the ceramic honeycomb is used by covering its outer periphery with an inorganic fiber mat or corrugated metal mesh that serves as a cushioning material, and storing it in a metal container that has exhaust gas connection ports at the front and rear.

Problem to be Solved by the Invention When such a ceramic honeycomb application is placed in the exhaust gas flow of an internal combustion engine, back pressure is applied due to its ventilation resistance, and the ceramic honeycomb tends to be pushed rearward. Therefore, the cushioning material has the function of not only simply protecting the ceramic honeycomb from external mechanical vibrations, but also firmly gripping and holding the ceramic honeycomb. However, in order to grip the ceramic honeycomb with a force that resists back pressure, a hard and dense cushioning material must be used. On the other hand, when high-temperature exhaust gas flows through the ceramic honeycomb, or when particulates accumulate inside and burn, heat is radiated to the outside air through this cushioning material, causing a large temperature between the center and the outer periphery of the ceramic honeycomb. It makes a difference. Therefore, the outer periphery is subjected to large tensile stress due to internal thermal engraving. The ceramic cannot withstand this stress, and a ring-shaped crack called a ring-off occurs on the outer periphery.

The present invention securely holds a ceramic honeycomb in a container, prevents ring-shaped cracks from occurring even when the center is heated to a high temperature, maintains the original shape of the structure, and effectively exhausts the honeycomb. The object of the present invention is to provide an exhaust gas purification structure that can perform a gas purification function.

Means to solve the problem: A thick sheet made of inorganic fibers and an organic binder as the main ingredients, with many small holes and many thin grooves on the surface, is made, and this sheet is buffered around the outer periphery of a ceramic honeycomb that has an exhaust gas purification function. The ceramic honeycomb is then radially pressurized from above the sheet and housed in a container connected to the engine exhaust pipe.

Effect: According to the above configuration, the large number of holes and grooves formed on the surface of the cushioning material increase the frictional force between it and the outer peripheral surface of the ceramic honeycomb, and the back pressure from the engine causes the ceramic honeycomb to move downstream. Prevent it from being pushed out. Additionally, the cushioning material has a large number of holes and grooves, so its overall density is low. Therefore, the thermal conductivity toward the outer circumference is relatively low, and even if the ceramic honeycomb is heated by high-temperature engine exhaust gas or high-temperature combustion gas, heat radiation to the outside air that has passed through the container is blocked, so the temperature generated inside is reduced. The difference is small. As a result, the thermal stress generated on the outer periphery of the ceramic honeycomb is also reduced, and there is no deformation that would cause internal cracks.

EXAMPLE 1 An example of the exhaust gas purifying structure of the present invention will be described below with reference to the accompanying drawings.

Figure 1 shows an exhaust gas purification structure applied as a filter to remove particulates contained in the exhaust gas of a diesel engine, and shows a vertical cross-sectional view when it is connected to the exhaust pipe of an engine (not shown). It is something. In the figure, 1 is a cylindrical ceramic honeycomb. Ceramic honeycomb 1 has cells 2 (2a, 2b) that form rectangular flow paths inside.
It is a structure consisting of cell walls 3 that constitute a. Plugs 4 are connected alternately to one end of the cell 2a and the other end of the adjacent cell 2b.
It is sealed by. After wrapping a cushioning material 5 around the outer periphery of the ceramic honeycomb 1, it is stored in a container 6 made of heat-resistant stainless steel. The cushioning material 5 is a mixture of thermally expandable vermiculite, inorganic fibers, and an organic binder, which is wet-molded into a sheet having a large number of holes 7 on the surface. Therefore, with this configuration, the whole is heated to about 400° C. to engrave the vermiculite contained in the buffer material 5, and the ceramic honeycomb 1 is compressed in the radial direction. Both ends of the container 6 are tapered into a cone shape, and one end is an engine connection port 8 and the other end is a muffler connection port 9. Stoppers 10a and 10 are provided inside the container 6 to fix the cushioning material 5 before and after the ceramic honeycomb 1.
b is welded.

Next, the operation of the configuration of this embodiment will be explained. First, the normal operation of the diesel engine will be explained.

Exhaust gas containing particulates flows into the engine connection port 8 connected to the exhaust pipe of the diesel engine due to engine operation. From there, the exhaust gas enters the cell 2a that is open to the engine connection port 8, and there, it passes through the cell wall 3 to the cell 2b that opens to the muffler connection port 9.
to go into. At this time, particulates contained in the exhaust gas cannot pass through the cell wall 3, and remain and accumulate within the cell 2a that is open to the engine connection port 9 side. On the other hand, the exhaust gas, which has been made clean by removing particulates, enters the muffler connection port 9 and is discharged to the atmosphere through the exhaust muffler.

While the work of depositing particulates continues, the ventilation resistance of the ceramic honeycomb 1 gradually increases due to clogging of the particulates, and the increased back pressure pushes the ceramic honeycomb 1 backward. However, the outer periphery of the ceramic honeycomb 1 and the buffer material 5
The ceramic honeycomb 1 continues to be held against the large perforated surface by a large frictional force against that force. Then, a sufficient amount of particulates accumulates in the ceramic honeycomb 1, and if any more particulates accumulate, it will enter a generation stage where it will adversely affect the engine. For regeneration, the diesel engine's intake port is first throttled and the engine is overloaded. If this state is maintained for 5 minutes, the exhaust gas temperature will rise to 600°C or higher. The temperature inside the ceramic honeycomb 1 also rises to about 600° C., and the particulates deposited inside begin to burn. The internal temperature of the ceramic honeycomb 1 reaches from 800°C to 1000°C due to the heat of combustion. Further, the outer periphery of the ceramic honeycomb 1 radiates heat from the container 6 to the outside through the buffer material 5, but the amount of heat is relatively low (reduced) by the air insulation of the many holes in the buffer material 5. The temperature difference between and the outer periphery is 200℃
The mechanical displacement that occurs on the outer periphery due to thermal engraving at the center is kept to a minimum.

As a result, the ceramic honeycomb 1 will not be pushed downstream of the container 6 and will not be destroyed. In addition, cracks do not occur on the outer periphery of the ceramic honeycomb 1, and it will not be destroyed even under usage conditions such as being placed in the exhaust gas of an internal combustion engine and repeatedly subjected to rapid heating.

The cushioning material 5 has many thin grooves 11 on its surface as shown in FIG.
The same effect as described above can be achieved by the shape of the ceramic honeycomb 1 being inclined with respect to the axis of the ceramic honeycomb 1.

Effects of the Invention According to the present invention, by providing a large number of holes and thin grooves on the surface of the cushioning material interposed between the ceramic honeycomb and the container housing it, back pressure caused by exhaust gas can be sufficiently eliminated. Can exhibit grip strength. In addition, air insulation generated in the cross section of the cushioning material reduces the amount of heat radiated to the outside air, reduces the temperature difference between the inside and the outer periphery of the ceramic honeycomb, and reduces the axial tension that the outer periphery receives due to internal thermal expansion. Displacement due to force can be minimized and cracks generated on the outer periphery can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of an exhaust gas purification structure according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a state in the middle of assembly of an exhaust gas purification structure according to another embodiment of the present invention. It is. 1...Ceramic honeycomb, 4...Plug, 5
...Buffer material, 6...Container, 7...Hole, 11
····groove.

Claims (4)

[Claims] (1) Ceramic honeycomb with a large number of cells inside,
In an exhaust gas purification structure comprising a buffer material wrapped around the outer periphery of the ceramic honeycomb, and a metal container enclosing the buffer material and having an exhaust gas inlet facing the front and rear sides of the ceramic honeycomb, at least the ceramic of the buffer material An exhaust gas purifying structure characterized by having a textured surface that contacts the honeycomb. (2) The exhaust gas purifying structure according to claim 1, the main component of which is a mixed composition of inorganic fibers, vermiculite, and an organic binder. (3) The structure for exhaust gas purification according to claim 1, characterized in that a large number of holes are formed in the plane of the buffer material. (4) The structure for exhaust gas purification according to claim 1, characterized in that a large number of grooves are provided within the plane of the buffer material.