JPH10131739A - Emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attempt compatibility between a high collection coefficient and low pressure loss by forming a filter part for collecting particle in exhaust gas by a filter formed in such a way that a flat plate filter material having a three-dimensional frame are folded in a zigzag shape. SOLUTION: In an emission control device in which two trapper 2 are arranged and housed in series in a meal case 1, each trapper 2 is formed by concentricity arranging differential diameter cylindrical filters 3, 4 made of a metal porous body, by forming flow passages 8, 9 which flow from an upstream side and a downstream side inward alternately in a case shaft direction by sealing necessary positions with an end plate 7 and the like, and inserting an electric heater 10 in the flow passage 8. Each filter parts 3, 4 are formed of a filter formed in such a way that a plurality of cylindrical filters having a three-dimensional frame, or a flay plate filter material having a three- dimensional frame are folded in a zigzag condition. Collection areas of the filter part 3, 4 are enlarged toward a trapper arranged on an upstream side, and its axial direction length is enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying device provided in an exhaust system of an engine. More specifically, it is an exhaust gas purifying apparatus that ensures excellent particulate collection performance and pressure loss characteristics, and that further reduces installation restrictions on space for automobiles and the like.

[0002]

2. Description of the Related Art Exhaust gas generated from a diesel engine contains combustible fine particles mainly composed of carbon. These fine particles are made of particulate matter (hereinafter P
M), which causes air pollution.
Various exhaust gas purification techniques have been developed to eliminate this.

For example, a trapper is formed by using a ceramic porous body in a purification device that has already been put into practical use in part, and PM trapped by the trapper is incinerated by a heater or a burner to remove exhaust gas. Some regenerate trappers whose streets have gone bad. Recently, an apparatus for forming a trapper using a porous metal body has also been developed.

[0004] The principle of trapping PM by these devices is filtration by a filter. The apparatus of this type has particularly important performances such as high PM trapping performance and accumulated P
It is required that the pressure loss (hereinafter referred to as pressure loss) in the filter portion caused by M is small.

[0005] Among the two required performances, regarding the trapping performance, there is a method of increasing the trapping efficiency determined by the ratio of the amount of PM flowing into the filter to the amount of PM trapped by making the pores of the filter fine. However, if this method is adopted, PM mainly accumulates on the exhaust gas inflow side surface of the filter, and the pressure loss rises sharply.

In view of this, (1) a structure in which the pores of the filter are made finer and the collection area is enlarged at the same time, and (2) PM collection by the filter is performed three-dimensionally in each part in the thickness direction of the filter. It has been considered that the thickness of the filter is increased to suppress an increase in pressure loss.

[0007] Regarding the structure (2), it has been proposed to increase the collection area by making the filter into a tubular shape or by bending a flat filter material into a folded shape.

(3) As shown in JP-A-56-18016 and JP-A-57-190626, a filter having a coarser filter and a filter having a finer filter are provided on the upstream side of the exhaust passage. There is also a proposal to increase the collection efficiency by arranging them in the axial direction as is. This can also be said to be a type of device utilizing the structure of (2).

[0009]

Among the above-mentioned prior arts, the structure of (1) requires an increase in the trapping area by, for example, forming a fold on the surface of the filter. In addition to the difficulty in manufacturing the filter, the strength of the filter is affected.

In the structure of (2), when the thickness is increased by using a cylindrical filter or a broken filter,
The outer diameter of the trapper increases, and the outer diameter of the device also increases.

An exhaust gas purifying device for a vehicle is usually provided under the floor of the vehicle in place of a muffler, but the height space that can be secured under the floor is limited. In recent years where the floor of vehicles is being reduced, it is particularly difficult to secure a large space, and therefore, a purification device having a large outer diameter is subject to installation restrictions in terms of space.

Further, in the structure (3), filters having different eye sizes are arranged in tandem, and even if the thickness of the filter is increased, only the axial length of the trapper is increased, but the trapper diameter does not increase. In addition, since the collection area of the filter is small, the effect of improving the pressure loss characteristics is small, and frequent regeneration is required, so that the life of the trapper is shortened.

According to the present invention, both characteristics of high collection efficiency and low pressure loss are achieved by using a trapper of a three-dimensional collection principle that does not complicate the shape of a filter. The issue is to make it possible to ease the restrictions on the installation of such facilities.

[0014]

According to the exhaust gas purifying apparatus of the present invention, the filter for collecting fine particles in the exhaust gas comprises:
A trapper formed of a plurality of cylindrical filters having a three-dimensionally inserted skeleton or a filter formed by bending a three-dimensionally inserted skeletal flat plate filter material into a folded state, and having a trapper provided with this filter portion as a case. A plurality of them are arranged in series.

In this apparatus, trappers having different collection areas of the filter section are arranged such that the trapper having a larger collection area is located on the upstream side of the exhaust path, or the difference in the axial length of the filter section is reduced. It is desirable to arrange the attached trappers so that the trapper having a longer filter portion is located on the upstream side of the exhaust path.

It is also effective to increase the thickness of the filter and decrease the size of the filter hole as the trappers arranged in series are located downstream of the exhaust path.
It is more preferable to use this structure in combination with the above-mentioned desirable structure.

[0017]

[Effect] Collection efficiency η when collecting PM three-dimensionally
Is defined as n (a dimensionless number) a ratio t / t ₀ of the thickness t of the filter constituting the trapper and the unit thickness t ₀ of the filter, and η _{0 as} a collection efficiency per unit thickness of the filter. ,
It is expressed by the following equation.

Η = 1− (1−η ₀ ) ⁿ In the device of the present invention, a plurality of trappers are arranged in series, and as a whole, it is equivalent to a filter having a multilayer structure. Therefore, the substantial thickness of the filter increases, and the collection efficiency η improves. Furthermore, since there are a plurality of filter surfaces most effective for PM collection and the collection on the surface is repeated a plurality of times, the collection efficiency is further improved.

Further, each trapper is formed using a cylindrical or serpentine filter, and since each filter is independent, a trapping area is large and a large amount of P
An increase in pressure loss when M is collected can be suppressed to a small value.

Further, if the number of trappers is reduced to one, and the trapping performance and pressure drop characteristics are improved by increasing the thickness of the cylindrical filter or the broken filter of the trapper, the outer diameter of the trapper increases, and the manufacture of the filter also increases. Although it becomes difficult (thicker ones are difficult to manufacture), the device of the present invention does not require the filters of each layer to be thicker in order to secure the required thickness with a filter having a multi-layer structure. Diameter) can be kept small, and there is no difficulty in manufacturing the filter.

Although the length of the device is increased by arranging a plurality of trappers in series, the space under the floor of the vehicle has a sufficient margin in the length direction. Even if it increases, installation regulations will be relaxed.

Next, if the trapping area of the trapper on the upstream side is increased, the increase in pressure loss can be suppressed, and the size of the apparatus can be further reduced. The reason is described below.

Since the PM concentration in the exhaust gas decreases by passing through the trapper, the amount of PM flowing in decreases as the trapper is located downstream, so that the amount of PM trapped decreases. on the other hand,
Pressure loss generally increases as the amount of trapped PM increases. Therefore, the trapper on the downstream side, which requires a small amount of trapping, can secure the same pressure loss characteristics as the trapper on the upstream side by reducing the trapping area, and the apparatus is further downsized by reducing the trapping area. .

Here, the collection area can be reduced by (a) shortening the length of the filter, (b) reducing the number of cylinders in the case of a multi-cylinder filter, and (c) flat plate in the case of a broken filter. It can be performed by each method of reducing the number of times the filter material is bent. When the method (a) is employed, the length of the apparatus is reduced, and when the methods (b) and (c) are employed, the diameter of the apparatus is reduced. As mentioned earlier, the device length has little effect on the device installation regulations, but the device is still smaller in terms of ease of handling and reduction of wasted installation space. In this regard, it can be said that shortening the length is also effective.

The trapping performance is improved by increasing the thickness of the trapper filter. Regardless of the upstream side or the downstream side, the trapping performance can be improved by increasing the filter thickness of each trapper, but from the viewpoint of pressure loss characteristics, it is desirable to increase the filter thickness of the downstream trapper. The pressure loss is collected P
Since it increases quadratically with respect to the amount of M, the average pressure loss of the apparatus can be suppressed to be smaller by collecting a plurality of filters on average than by collecting a large amount of PM by one filter. is there. The downstream trapper has a smaller total PM amount flowing in than the upstream trapper, and therefore, if the filter thickness of the downstream trapper is increased and the collection efficiency of the downstream trapper is made higher than the collection efficiency of the upstream trapper. In addition, the amount of PM trapped by the plurality of filters can be averaged.

Although the trapping efficiency of the downstream trapper can be increased by reducing the size of the holes in the filter, in the present invention, a filter is used which is collected by a three-dimensional trapping mechanism. It is more advantageous to increase the filter thickness to increase the collection efficiency than to make the structure smaller.

FIG. 1 compares the change in the collection efficiency and the change in pressure loss when the thickness and the filling rate (the smaller the pore size, the higher the filling rate) of the filter. As can be seen, the collection efficiency can be improved by either increasing the filter thickness or increasing the filter filling rate (reducing the pore size). However, increasing the filling rate increases the pressure loss. When the filter thickness is increased, the pressure loss does not increase, and the trapping performance can be improved without deteriorating the pressure loss characteristics.

In the apparatus of the present invention, a plurality of trappers are housed in one case. The serial arrangement of a plurality of trappers can also be realized by a structure in which devices in which one trapper is housed in one case are connected in series, but this is not advisable in terms of pressure loss characteristics and thermal efficiency during trapper regeneration. That is, the pressure drop in the PM collection, particularly in the initial stage, is much larger in the case than in the trapper. The pressure loss due to this case is as follows.
After that, it is caused by repeating expansion and contraction to a small-diameter pipe again. Therefore, if the cases (that is, devices) are arranged in multiple stages, the pressure loss increases in proportion to the number of stages.

Further, when the cases are arranged in multiple stages, the heat efficiency when the collected PM is heated by the electric heater and burned is also reduced. The outer periphery of the case can be wrapped with a heat insulating material to prevent heat from escaping, but the ends of the case cannot be wrapped with the heat insulating material, which serves as a heat radiating surface to allow the internal heat to escape. As the number of cases increases, the heat radiation surface increases and the amount of heat escaping to the outside increases, and an extra heater output is required for stable PM combustion. The device of the present invention having one case does not have such a problem.

[0030]

2 to 8 show a simplified embodiment of an exhaust gas purifying apparatus according to the present invention. The apparatus shown in FIG. 2 has two trappers 2 housed in a metal case 1 arranged in series.

The trapper 2 has concentrically arranged cylindrical filters 3 and 4 made of a porous metal body and covers necessary portions with an end plate 7 or the like, and alternately has an internal portion in the case axial direction from the upstream side and the downstream side. Channels 8 and 9 are formed to enter, and an electric heater 10 is inserted into the channel 8. Electric heater 10
May be arranged in the flow path 9, but in the case of being incorporated in either of the flow paths 8 and 9, a planar heater widely facing the surface of the filter is preferable.

In this apparatus, when the left side in the figure is an inlet, the exhaust gas flowing into the case 1 therefrom flows as shown by the arrows, and passes through the two trappers 2 to be purified.

The exhaust gas may be introduced into the case 1 from the right side in the figure, and at this time, the flow of the gas is opposite to that in the figure.

The apparatus shown in FIG. 3 is configured such that the length of the filter section of the downstream trapper 2 (right side in the figure) is shorter than the length of the filter section of the upstream trapper to average the pressure loss of each trapper. The number of trappers 2 accommodated in the case 1 is three, and the length of the filter portion is shorter in the trapper on the downstream side (right side in the figure), so that the pressure loss of each trapper is averaged.

In the apparatus shown in FIG. 5, the trapper 12 is formed by using one cylindrical filter 3 made of a porous metal body, and the filter thickness of the downstream (right side in the figure) trapper 12 is adjusted by the upstream trapper 12. , And two of the trappers 12 are housed in series in the metal case 1, so that the effect of reducing the outer diameter of the apparatus is particularly high. In addition, the trapping efficiency of the downstream trappers is high, and the pressure loss of each trapper is averaged.

In the apparatus shown in FIG. 6, three trappers 12 are accommodated in series in the metal case 1, and the length of the filter portion of the downstream trapper is made shorter than the length of the filter portion of the most upstream trapper at the left end in the figure. This filter differs from the apparatus in FIG. 5 in that the filter thickness is increased in the downstream trapper.

The apparatus shown in FIG. 7 includes a trapper 22 formed by concentrically combining different diameter cylindrical filters 3, 4, and 5 made of a porous metal body, and a trapper having the same configuration as the trapper of the apparatus shown in FIG. 2 are inserted in series in the metal case 1 so that the trapper 22 is located on the upstream side of the exhaust path. Since the trapping area of the upstream trapper is large, the pressure loss of each trapper can also be averaged. . The filter used in the above device may be a rectangular tube.

In the apparatus shown in FIG. 8, the trapper 32 is formed using a filter 6 formed by folding a flat filter material made of a porous metal body and closing both sides and the outer periphery thereof with side plates (not shown) and end plates 7. And the trapper 32 is
The pieces are stored in series. Here, the length of the filter portion of the downstream trapper (right side in the figure) is made shorter than the length of the filter portion of the upstream trapper to average the pressure loss of each trapper. However, this device also has the filter of the upstream trapper and the filter of the downstream trapper. The pressure loss of each trapper can be averaged by making a difference in the thickness, the collecting area, or the pore size of the filter.

Although the apparatus shown in FIG. 2 has no direction, FIG.
8 is used by disposing the left side of the case 1 on the upstream side of the exhaust path.

Further, the illustrated apparatus uses Ni-Cr- as a filter material for each trapper, which is excellent in heat resistance and corrosion resistance.
Al alloy, Ni-Cr alloy, etc. are used, but the same performance is obtained even when the filter used is made of an aggregate of ceramic fibers composed of Al ₂ O ₃ and its composite component. Can be.

Hereinafter, more detailed examples will be described.

[0042]

EXAMPLE An exhaust gas purifying apparatus of A to G having the specifications shown in Tables 1 and 2 was prototyped.

[0043]

[Table 1]

[0044]

[Table 2]

FIG. 9 shows a purifying apparatus having a conventional structure in which one trapper same as the apparatus shown in FIG. 2 (sample A in Table 1) is housed in a case 1 (this is referred to as Comparative Example H). FIG.
Is a device in which the filter thickness of the device of FIG. 9 is doubled (this is referred to as Comparative Example I).

FIG. 11 shows a comparison result obtained by selecting A in Table 1 as a representative from the prototypes and examining the trapping performance of Comparative Examples H and I. Thus, the invention product A has improved collection efficiency as compared with the comparative example H. It should be noted that the comparative example I of FIG. 10 has almost the same trapping performance as the inventive product A of Table 1, but the inventive product A is slightly better. On the other hand, in terms of dimensions, Comparative Example I has an outer diameter of the outermost layer filter of 136 mm.
And the outer diameter of the device becomes larger.

FIG. 12 shows the result of comparing the pressure loss characteristics of the invention product A and the comparative example H. The invention product A is superior to the comparative example H in the pressure loss characteristics.

[0048]

As described above, the exhaust gas purifying apparatus of the present invention has excellent trapping performance and pressure loss characteristics. Further, the outer diameter of the device can be reduced without sacrificing such performance, and the device can be installed under the floor of a vehicle where a large space in the height direction cannot be secured. Therefore, it is particularly effective when used as an exhaust gas purifying device for a vehicle equipped with a diesel engine, which has a severe space restriction and has a problem of PM emission.

[Brief description of the drawings]

FIG. 1 is a diagram comparing pressure loss and trapping efficiency when the thickness and filling rate of a trapper filter are changed.

FIG. 2 is a simplified cross-sectional view showing an embodiment of an exhaust gas purifying apparatus of the present invention.

FIG. 3 is a cross-sectional view schematically showing another embodiment.

FIG. 4 is a simplified cross-sectional view showing another embodiment.

FIG. 5 is a cross-sectional view schematically showing another embodiment.

FIG. 6 is a simplified cross-sectional view showing another embodiment.

FIG. 7 is a cross-sectional view showing another embodiment in a simplified manner.

FIG. 8 is a simplified cross-sectional view showing another embodiment.

FIG. 9 is a simplified cross-sectional view showing a conventional example.

FIG. 10 is a sectional view of an apparatus in which the filter thickness is doubled as compared with that of FIG.

FIG. 11 is a diagram comparing the trapping performance of the devices of FIGS. 2, 9 and 10;

FIG. 12 is a diagram comparing the pressure drop characteristics of the devices of FIGS. 2 and 9;

[Description of Signs] 1 Case 2, 12, 22, 32 Trapper 3, 4, 5 Cylindrical filter 6 Filter with broken shape 7 End plate 8, 9 Flow path 10 Electric heater

Claims (5)

[Claims] 1. An exhaust gas purifying device installed in the middle of an exhaust system of an engine, wherein a filter section for trapping fine particles in the exhaust gas has a plurality of cylindrical three-dimensionally skeletons. A filter or a filter formed by bending a flat filter material having a three-dimensionally inserted skeleton into a zigzag state, and a plurality of trappers having this filter portion are arranged in series in a case and installed. Exhaust gas purifying device. 2. The exhaust gas purifying apparatus according to claim 1, wherein the trapping area on the upstream side of the exhaust path has a larger collecting area of the filter section. 3. The exhaust gas purifying apparatus according to claim 1, wherein the trapper located on the upstream side of the exhaust path has a longer axial length of the filter portion. 4. The exhaust gas purifying apparatus according to claim 1, wherein the thickness of the filter is increased in the trapper on the downstream side of the exhaust passage. 5. The exhaust gas purifying device according to claim 1, wherein the trapper located on the downstream side of the exhaust path has a smaller hole in the filter section.