JPH051524A - Exhaust filter for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a sudden blow-off at the time of a quick acceleration of an engine, and reduce a pressure loss at the time of a low load for an exhaust filter of an attachment collection type. CONSTITUTION:A filter element 2 is composed of a number of filter element members 4. The filter element members 4 are rolled to be flat having a hollow and carrying catalyst, and they are disposed with their side surfaces tightly applied to each other. An end part 4b of the filter element member 4 is formed like an arc, and a wedge-like recessed part 6 is formed at a boundary part. Exhaust flows in toward the end part having the recessed part 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust filter for collecting and removing exhaust particulates such as carbon, which is a problem in internal combustion engines, especially diesel engines.

[0002]

2. Description of the Related Art It has been conventionally considered to collect and remove exhaust particulates such as carbon, which is a problem in diesel engines, by an exhaust filter interposed in an exhaust system, and various types of exhaust filters have already been proposed. Has been done.

A typical one of the exhaust filters is a filtration and collection type, which is represented by a so-called plugged filter. The above-mentioned plugged filter is disclosed, for example, in Japanese Patent Laid-Open No. 56-
As disclosed in Japanese Patent No. 124417, many fine flow passages are formed in a ceramic block along the exhaust flow direction, and the ends of the flow passages are alternately closed with ceramics. Then, the exhaust gas passes through the ceramic partition walls between the flow paths to filter and collect the exhaust fine particles.

[0004] With this filtration and collection type, although very high collection efficiency is obtained, exhaust particulates are easily collected excessively, and the particulate collection amount easily exceeds the burnout limit of the filter. In other words, when the timing of forced regeneration using a burner or the like or regeneration by exhaust heat is slightly delayed, a large amount of exhaust fine particles may rapidly burn, resulting in burnout of the filter. In addition, even Ash components that cannot be removed by incineration (such as oxides of oil additives) are collected, and eventually there is a possibility that clogging will occur.

Therefore, an exhaust filter of adhering trapping type has been proposed in place of the filter trapping type. As one example thereof, a three-dimensional porous body of ceramics, that is, a so-called ceramics foam as disclosed in Japanese Patent Laid-Open No. 58-72610, is used as a filter element, and a catalyst as disclosed in Japanese Utility Model Laid-Open No. 51-23615 is used. It is known that a plurality of thin heat-resistant fiberboards carrying the are laminated to form a filter element. In this adhering and collecting type, when exhaust gas flows through a complicated flow path generated in the filter element, exhaust gas particulates are adhered and collected on the wall surface of the flow path. for that reason,
Excessive collection is less likely to occur and clogging due to the Ash component is less likely to occur.

[0006]

Blow-off of exhaust particulate matter becomes the most serious problem in the above-mentioned exhaust filter of the adhering and collecting type. In other words, when a large amount of exhaust particulates are collected, the exhaust particulates do not directly adhere to the surface of the filter material such as ceramics, but the exhaust particulates further adhere to the collected exhaust particulates, and the adhesion strength is Since it decreases, a large amount of exhaust particulate is suddenly blown off to the outside when the engine is suddenly accelerated, and it is discharged as black smoke. In particular, if the thickness of the filter element in the exhaust flow direction is reduced in order to reduce the pressure loss in the exhaust filter, the amount of exhaust particulates that can be retained decreases, and blow-off to the outside is more likely to occur.

[0007]

Therefore, an exhaust gas filter for an internal combustion engine according to the present invention uses a plurality of adhering and collecting type filter element members, and a part of the filter element members are arranged in close contact to form a filter element. At the same time, it is characterized in that a substantially wedge-shaped recess facing the exhaust gas flow is formed at the boundary of each filter element member.

[0008]

In the above structure, since the exhaust gas easily flows along the boundary portion of the filter element member having the concave portion, the pressure loss becomes relatively small. In an operating state in which the exhaust flow velocity is low, the exhaust flow rate ratio from the concave portion to the boundary portion is relatively large, so that a large amount of exhaust particulate is collected in the concave portion. Most of the exhaust particulates deposited in the recesses do not come into direct contact with the surface of the filter element member and have a low adhesion strength, but when the engine is rapidly accelerated,
The proportion of the exhaust flow that tries to pass through the inside of the filter element member from the recess increases, and the exhaust particulates having a small adhesion strength diffuse into the inside of the filter element member from the recess. That is, the collection efficiency naturally increases, and the slow internal blow-off progresses inside the filter element.
Rapid blow-off to the outside is suppressed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a cross-sectional view showing the overall structure of the exhaust filter according to the present invention, in which a substantially rectangular filter element 2 is housed in a casing 1.

The casing 1 is inserted, for example, in the middle of an exhaust pipe of a diesel engine, and is composed of a main body portion 1a having a rectangular tubular shape, a pyramidal inlet portion 1b and an outlet portion 1c. In addition, this casing 1 is
The filter element 2 is divided and formed, and after the filter element 2 is housed together with the cushioning material 3, they are integrated by welding or the like.

FIG. 1 shows the filter element 2 described above. The filter element 2 has a structure in which a large number of filter element members 4 are integrated by a frame 5 having a substantially rectangular tubular shape. Each filter element member 4 is formed by winding a strip-shaped mesh metal plate a plurality of times,
It is a flat hollow tube, and as shown in the cross-sectional shape of FIG. 3, both side portions 4a are parallel surfaces, and both front and rear end portions 4b are circular arc surfaces. A plurality of the filter element members 4 are arranged in a state where their parallel side surfaces are in close contact with each other, and the plurality of sets are arranged in two stages in the front and rear. Specifically, the arcuate ends 4b of each filter element member 4 are arranged so as to be exposed at the front and rear opening surfaces of the frame 5, so that exhaust gas flows along the longitudinal direction of the cross-sectional shape shown in FIG. It has become.
Each filter element member 4 is in a state of carrying an appropriate catalyst.

By arranging the plurality of filter element members 4 as described above, a large number of substantially wedge-shaped recesses 6 are formed in the front end surface of the filter element 2. That is, since the end portion 4b of each filter element member 4 has an arc shape, the concave portion 6 having a wedge-shaped cross section is formed in a groove shape along the boundary portion of each filter element member 4. In addition, similar recesses 6 are formed at the boundary portions of the filter element members 4 of the latter set. The upper and lower ends of the hollow portion 7 of each filter element member 4 are closed by a frame 5.

In the above structure, when exhaust gas passes through the filter element 2 as shown by the arrow in FIG. 1, exhaust particulates such as carbon are collected. The mesh of the mesh metal plate forming the filter element member 4 is sufficiently larger than the particle size of the exhaust particles, and the exhaust particles are not collected by filtration but in the form of adhesion and collection on the surface of the mesh metal plate. To be captured.

Here, in an operating state in which the flow velocity of exhaust gas is relatively low, a relatively large amount of exhaust gas tends to flow along the boundary portion of the filter element member 4, so that a large amount of exhaust gas particles are deposited in the concave portion 6. Since the exhaust gas easily flows along the boundary portion, the pressure loss becomes relatively small. If the engine suddenly accelerates from this state, a part of the exhaust flow flows into the hollow portion 7 across the mesh-like metal plate, so that exhaust particulates such as carbon accumulated in the recess 6 especially the adhesion strength therein. Those having a low air flow rate are separated and ride on the exhaust flow and diffuse into the hollow portion 7. Then, on the inner surface side of the hollow portion 7, it is also adhered and collected on the mesh metal plate. That is, when the amount of accumulated fine particles in the concave portion 6 becomes large, the flow path along the boundary between the concave portions and each filter element member 4 becomes partially clogged, and the exhaust flow diffuses into each filter element member 4. I will go. Therefore, the exhaust particulates do not suddenly blow off to the outside through the boundary portion, gradually diffuse to each portion of the filter element member 4, and the collection efficiency thereof increases. In addition, in the case of this adhering and collecting, since the surface adhering on the outer surface which is in direct contact with the exhaust is important, by forming the filter element member 4 in the hollow portion as described above, the substantial collecting surface area is large. Therefore, the adhered and collected can be efficiently collected.

Further, similarly, the exhaust particulates gradually diffuse from the filter element member 4 located at the front stage to the filter element member 4 at the rear stage, and abrupt blow-off to the outside is prevented.

In short, in the exhaust filter having the above structure,
In the low-speed low-load region where the amount of exhaust particulates generated is small, the exhaust flow relatively smoothly flows through the boundary portion of each filter element member 4, and the pressure loss can be kept low, and at the same time,
Exhaust gas diffuses into the filter element member 4 in a high-speed and high-load region where a large amount of exhaust particles are generated
The collection efficiency naturally increases, and abrupt blow-off of exhaust particulates to the outside can be reliably prevented.

Next, FIGS. 4 and 5 show different embodiments of the present invention.

FIG. 4 is a cross-sectional view showing the overall structure of the exhaust filter of this embodiment, which is a cylindrical casing 1
An exhaust inlet pipe 12 is integrally formed at one end of the pipe 1. A cover 13 is welded so as to cover the opening at the other end of the casing 11, and the exhaust outlet pipe 1 is provided at the center of the cover 13.
4 are formed.

A filter element 15 assembled in a substantially cylindrical shape as a whole is housed in the casing 11. The end surface of the filter element 15 on the exhaust outlet pipe 14 side is closed by a disc-shaped spring seat 16, and the spring seat 16 is closed.
A coil spring 17 disposed in a compressed state between the cover 13 and the cover 13 presses the end surface of the casing 11 on the exhaust inlet pipe 12 side. The casing 11
An annular cushioning material 18 is interposed between the wall surface and the end surface of the filter element 15. In addition, a sufficient gap serving as an exhaust passage is provided between the outer periphery of the filter element 15 and the inner periphery of the casing 11.

Therefore, as a general flow of the exhaust gas, as shown by an arrow, the exhaust gas flows from the exhaust inlet pipe 12 into the central portion of the filter element 15, and the filter element 15 flows.
In the radial direction, and flows out from the outer peripheral gap to the exhaust outlet pipe 14.

FIG. 5 is a perspective view showing the above-mentioned filter element 15. A plurality of cylindrical filter element members are formed so as to surround the outer circumference of the inner cylinder 19 made of a mesh having a relatively high rigidity. Twenty are arranged in parallel. The filter element member 20 is formed by winding a mesh-shaped metal plate supporting a catalyst in a roll shape, and is sequentially arranged on the surface of the metal inner cylinder 19 and fixed by, for example, spot welding. The filter element members 20 adjacent to each other have a part of their outer peripheral surfaces in close contact with each other. As a result, a substantially wedge-shaped recess 21 facing the exhaust flow is formed at the boundary of each filter element member 20.

Therefore, also in this embodiment, the exhaust gas smoothly flows through the boundary portion of each filter element member 20 in the low speed and low load region where the generation amount of exhaust particulates is small, so that the pressure loss can be suppressed to a low level. Then, in the high-speed and high-load region where the amount of exhaust particulates generated is large and the exhaust flow velocity is also large, the exhaust gas diffuses and flows into the inside of each filter element member 20, so that high trapping efficiency is obtained and the recess 21 is formed. Exhaust particulates with weak adhesion strength that have accumulated in the filter element member 20 gradually diffuse into the inside of the filter element member 20 to prevent its sudden blow-off.

Next, FIGS. 6 and 7 show an embodiment in which a three-dimensional porous ceramic body, so-called ceramic foam, is used as the filter element member 20 constituting the filter element 15.

In the embodiment of FIG. 6, the plurality of filter element members 20 arranged on the outer circumference of the metal inner cylinder 19 are solid cylindrical, and in the embodiment of FIG. 7, they are hollow cylindrical. .. In each case, the catalyst metal is supported on the ceramic foam.

Even when the ceramic foam is used as described above, the reduction of pressure loss and the prevention of blow-off can be achieved at the same time by the same action as that of the above-mentioned embodiment.

[0027]

As is apparent from the above description, according to the exhaust gas filter of the internal combustion engine according to the present invention, each filter element member is used in the operating region where the exhaust flow velocity is low, that is, in the low speed and low load region where the amount of exhaust particulates is generally small. Exhaust gas flows relatively smoothly through the boundary portion of, so that the pressure loss is reduced. On the other hand, in the operating region where the exhaust gas flow velocity is high, that is, in the high-speed and high-load region where the amount of exhaust particulates is generally large, the exhaust gas diffuses and flows into each filter element member, so that the trapping efficiency naturally increases and moreover Exhaust particles with low adhesion strength that have accumulated spread widely inside the filter element member, so that rapid blow-off to the outside is prevented.

[Brief description of drawings]

FIG. 1 is a perspective view showing a filter element of an exhaust filter according to the present invention.

FIG. 2 is a sectional view showing the entire exhaust filter.

FIG. 3 is a sectional view of a main part of a filter element.

FIG. 4 is a cross-sectional view showing another embodiment of the exhaust filter according to the present invention.

FIG. 5 is a perspective view showing a filter element according to this embodiment.

FIG. 6 is a perspective view showing another embodiment of the filter element.

FIG. 7 is a perspective view showing still another embodiment of the filter element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Casing 2 ... Filter element 4 ... Filter element member 6 ... Recessed portion 15 ... Filter element 20 ... Filter element member 21 ... Recessed portion

Claims (1)

Claim: What is claimed is: 1. A plurality of adhering and collecting type filter element members are used, a part of which is arranged in close contact with each other to form a filter element, and at the boundary of each filter element member, An exhaust filter for an internal combustion engine, wherein a substantially wedge-shaped recess facing the exhaust flow is formed.