JPS614813A - Fine particle trap for combustion exhaust gas - Google Patents

Abstract

PURPOSE:To decrese a shearing force, exerted on a filter element by the back pressure of exhaust gas, by means of a case formed in a tapered shape and to prevent the occurrence of damage, by a method wherein a filter element made of ceramic used on a fine particle trap is formed in a tapered shape. CONSTITUTION:A filter element 1a made of ceramic used in a fine particle trap is formed in a tapered shape, a portion having a large cross section is located, being pointed to the incoming side A of exhaust gas, and a portion having a small cross section is situated, being pointed to the outgoing side B thereof. The element is contained in a conical trapezoidal case 2 having a tapered shape conforming to the tapered shape of the element. In this case, a number of gas passages 7a and 7b are located to the interior of a filter element 1a and formed by a ceramic wall 8, and the opposite ends of the adjoining gas passages 7a and 7b are alternately blocked up with a blocking piece 9. This enables the back pressure of exhaust gas, produced by accumulated fine particles and exerted on the filter element 1a, to be converted into a radial compression force by means of stress produced by the case 2, and permits reduction of a shearing force exerted on the filter element 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a particulate trap for combustion exhaust gas, and more particularly to a particulate trap in which a ceramic filter element having a honeycomb structure is enclosed in a case.

Conventional Structure and Problems Exhaust gas from a diesel engine contains a large amount of fine particles whose main component is carbon. Recently, it has become clear that these fine particles have an effect on living organisms, and devices have been developed to collect the fine particles before they are released into the atmosphere.

One such device is a particulate trap that uses a ceramic filter element. Ceramic filter elements are used because they provide heat resistance when the collected particulates are incinerated. Moreover, the ceramic filter element has a large number of gas flow paths arranged in a honeycomb shape (in the case of Mizuhiki 111H?J3, the pore cross section is not limited to a hexagonal shape). This gas flow path is alternately blocked by obturators at both ends of the adjacent flow paths, so that the exhaust gas that has entered the flow path does not pass through the flow path from the inlet side to the outlet side. It enters the adjacent channel across the ceramic wall forming the wall and flows to the outlet side. In other words, the ceramic wall that constitutes the flow path serves as a filtration surface. Conventional Hiramic filter elements have a cylindrical or elliptical external shape, and are in contact with the storage case with their outer surfaces parallel to the flow of exhaust gas. However, the ceramic filter element having this shape has a problem in that the ceramic walls constituting the flow path are subjected to a large shearing force in the flow direction of the exhaust gas due to the back pressure received from the engine and are damaged.

In addition, immediately after the fine particles are sintered, the center becomes hot, and due to thermal expansion, a large tensile force is generated at the outer periphery, resulting in damage.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a particulate trap having a Hiramic filter element of a novel configuration that can withstand high shear forces experienced by the internal walls and high tensile forces experienced by the outer periphery.

1) A ceramic filter element having a tapered portion whose outer diameter decreases from the gas inlet u4u/J1 toward the outlet side is used, and the filter element is inserted along the tapered portion. For example, by making the outer shape into a truncated cone shape, a truncated square pyramid shape, or a drum shape, the engine can be supported by a case that supports it. ,: Because the force in the flow direction of the exhaust gas due to back pressure is inwardly compressed, this compressive force reduces the shearing force that the ceramic wall receives, and also reduces the tensile force on the outer periphery that occurs when the internal temperature is high. Durability is improved by offsetting the force.

The present invention will be described in detail below based on embodiments shown in the accompanying drawings.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a perspective view of a ceramic filter element 1a used in a particulate trap for a diesel engine, which is an embodiment of the present invention, and has the shape of a circular Glt stand on its side. As shown in the vertical cross-sectional view of the particulate trap in FIG. 2, this filter element 1a is placed inside the truncated conical case 2 with the larger cross-sectional diameter facing the exhaust gas inflow side Δ and the smaller cross-sectional diameter facing the exhaust gas outflow side B. Store it in. A non-mechanical material mat 3 having vibration absorbing and heat insulating properties is interposed between the filter element 1a and the case 2, and the inflow side B end is fixed with a stopper 4. In the case 2, an engine side connecting pipe 5 is attached at the inlet side Δ, and a muffler side connecting pipe 6 is attached at the outlet side. Inside the filter element 1a, a large number of gas channels 7a, 7b are formed in the axial direction of the circle 111 in a honeycomb shape with the ceramic wall 8. gas flow path 7a,
7b is closed at one end by an obturator 9, and adjacent gas flow paths 7a, 7 are formed at the end of the filter element.
b is occluded by intersection n. As a result, the gas flow path 7
1, where the wall 8 forming parts a and 7b serves as a filter;
The filter element material has pores of 4'° of 60 to 90.
%, a material with very low ventilation resistance is used.

According to this particulate 1-lap, the exhaust gas containing /υ particles flowing from the engine side connecting pipe 5 enters the gas passage 7a which is open to the inflow side A, and enters the wall 8 which becomes the filter body. , enters the gas flow path 7b opened on the outflow side B, and flows out to the muffler side connecting pipe 6.On the other hand, the fine particles contained in the exhaust gas are transferred to the gas flow path 7a on the wall 8, which serves as a filter. The deposited particulates act as a resistance to the flow of the JJI gas and exert a large back pressure on the filter element 1a.

This may be 20 KPa or more, although it depends on the operating condition of the engine. This back pressure causes the filter element 1 to
The force in the flow direction of the exhaust gas that a receives is the force exerted on filter element 1
The outer circumferential surface of the circular nail trapezoid shape of a comes into contact with the inner surface of the case 2,
The stress due to case 2 changes to a compressive force in the radial direction. Therefore, the inner wall 8 of the filter element 1a is not subjected to large shear forces in the exhaust gas flow direction. Further, the back pressure applied to the filter element 1a increases the loss load of the engine, so when a large amount of fine particles have accumulated, the engine is operated under high load, and the exhaust gas temperature is raised to about 600° C. to incinerate the carbon. At this time, the center of the filter element 1a is heated to 800° C. or higher due to the heat of combustion of the particulates. .

However, the peripheral portion of the filter element 1a is maintained at a relatively low temperature by radiating heat to the outside air through the case 2. The difference in thermal expansion between the center and the outer periphery due to this temperature difference generates a large tensile force in the periphery. However, as described above, compressive stress is applied to the peripheral portion of the filter element 1a due to the back pressure, and this is offset, so that the peripheral portion is not damaged.

Next, other embodiments will be described. In the following embodiments, only the shape of the filter element will be described, but as in the above embodiments, a case that follows the tapered portion thereof is used.

Fig. 3 shows a filter element 1b in the shape of a truncated cone (similar to the truncated cone filter element 1a, the one with the larger cross-sectional area perpendicular to the axis of the truncated pyramid is located on the exhaust gas inflow side), and has fine particles -f. The filter element 1b is housed in a trap case, and compressive force is applied to the entire filter element 1b by the back pressure of the exhaust gas. The internal structure has a large number of gas channels arranged in the axial direction in a honeycomb shape, just like the frustoconical filter element 1a.

FIG. 4 shows a filter element 1G called an ellipsoid or a drum shape, which is thick near the center of the column axis and thin at both ends. When this filter element 1c is housed in a case of a particulate l-ship and placed in a flow of exhaust gas, the rear half of the filter element 1c, which gradually becomes thinner with respect to the flow, is compressed by back pressure.

FIG. 5 shows a @-shaped filter element 1d, which is thin near the center of the column axis and thick at both ends.

When this filter element 1d is housed in a case of a particulate trap and placed in a flow of exhaust gas, the front half, which is gradually tapered with respect to the flow, is compressed by back pressure. The internal structure of the ellipsoidal filter element 1C and the hourglass-shaped filter element 1d has a large number of gas passages arranged in the axial direction in a honeycomb shape, just like the truncated conical filter element 1a.

Integral honeycomb-shaped filter elements 1 a, 1 b, 1 c, 1 d having different cross-sectional areas perpendicular to the column axis of these examples
can be manufactured using any of the following methods: (1) press molding using a mold, (2) firing the portion where the cross-sectional area is to be reduced at a high temperature, and (3) adjusting the shape using the cutting method 1.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, in the present invention, the ceramic filter element of the particulate trap has a tapered shape, so that the back pressure of the exhaust gas is converted into an inward compression saw by the case surface supporting the tapered part. This reduces the shear forces experienced by the filter element due to back pressure and offsets the tensile forces on the outer periphery due to heat during particulate incineration, resulting in an undamaged particulate trap.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a truncated conical filter element included in a particulate trap for diesel engines according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a particulate trap for diesel engines according to the same embodiment. FIGS. 3 to 5 are perspective views C of other embodiments of the filter element related to the light 111J. 1a, 1b', 1c, 1d...filter element 2.
・・Case 3・Nut 4・Stopper 5・
...Engine side connecting pipe 6...Muffler side connecting pipe 7
a, 7 b... Gas flow path 8... Wall 9... Obturator Patent applicant Matsushita Electric Industrial Co., Ltd. Representative patent attorney Satoru Yoshimura 7=, -1, 1 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (5)

[Claims] (1) In a particulate trap in which a ceramic filter element with a honeycomb structure is housed in a case to remove particulates in combustion exhaust gas, the outer diameter decreases from the exhaust gas inlet side to the outlet side. A particulate trap for combustion exhaust gas, characterized in that the ceramic filter element having a shaped part is enclosed in the case having a tapered part opposite to the outer periphery of the tapered part. (2) The particulate trap for combustion exhaust gas according to claim (1), wherein the outer shape of the filter element is a truncated cone shape. (3) The particulate trap for combustion exhaust gas according to claim (1), wherein the outer shape of the filter element is a truncated quadrangular pyramid shape. (4) The outer shape of the filter element is a drum shape with a diameter expanded at the center in the flow direction of exhaust gas.
The particulate trap for combustion exhaust gas described in item 1). (5) Claim No. 1, wherein the outer shape of the filter element is a drum shape with a diameter reduced at the center in the flow direction of exhaust gas.
) A particulate trap for combustion exhaust gas as described in section 2.