JPH0544432A - Exhaust filter for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] In an adhering trap type exhaust filter in which a grid-shaped metal plate 8 is wound in a cylindrical shape and exhaust gas is allowed to flow from the inner circumference to the outer circumference, overlapping of the grids in multiple layers is avoided. , The density is made uniform in each part in the circumferential direction. [Structure] The grid-shaped metal plate 8 forming the cylindrical filter element 6 has a single continuous band shape and has a grid of a fixed shape. When the plate thickness of the grid-shaped metal plate 8 is t and the inter-grid distance along the circumferential direction is x, 2πt / x
Is a non-integer value.

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, so-called ceramics foam, as disclosed in Japanese Patent Laid-Open No. 62-45309, is used as a filter element, and a catalyst as disclosed in Japanese Utility Model Laid-Open No. 51-23615. 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 the exhaust gas flows through a complicated flow path generated in the filter element, the exhaust fine particles are adhered and collected on the surface of the flow path.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention JP-A-62-45
Japanese Patent Laid-Open No. 309 and Japanese Utility Model Laid-Open No. 51-23615 disclose a structure in which an adhering and collecting type filter element is formed in a cylindrical shape and exhaust gas is allowed to flow from the inner peripheral side to the outer peripheral side. However, in such a cylindrical filter element, if there is a deviation of the coarse and dense state at each portion in the circumferential direction, the exhaust gas will blow through the rough portion, so that the collection efficiency is lowered, and the fine particles once collected. Blow-off is likely to occur. In particular, when a large number of grid-like metal plates are laminated to form a filter element, if a large number of layers of the grid overlap at the same position in a certain portion in the circumferential direction, the grid becomes partially rough and the efficiency of the filter is significantly reduced. ..

[0007]

Therefore, according to the present invention, a filter element is constructed by sequentially laminating one continuous grid-like metal plate having a grid of a constant shape in a cylindrical shape. In an exhaust gas filter of an internal combustion engine housed in a casing so that exhaust gas flows in a radial direction, when the plate thickness of the grid-shaped metal plate is t and the inter-grid distance along the circumferential direction is x, The feature is that each dimension is set such that 2πt / x is a value that is not an integer.

[0008]

In the above construction, the filter element is constructed by winding one continuous grid-like metal plate in a cylindrical shape. However, the number of grids included in one turn of the n-th layer is the winding radius. if a and r _n, 2.pi.r indicated by _n / x, overlaps to (n + 1) number of grids included in one round th layer likewise 2π
It is represented by r _{n + 1} / x. Since the difference (r _{n + 1} −r _n ) between the two winding radii is equal to the plate thickness t, the difference in the number of lattices of both layers is represented by 2πt / x. When the difference in the number of grids is an integer, the grids are always completely overlapped at a specific position in the circumferential direction. On the other hand, if 2πt / x is a value other than an integer, the overlapping of the lattices of each layer occurs randomly at each portion in the circumferential direction, and the specific portion does not become rough.

[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 partially cutaway perspective view showing the overall structure of the exhaust filter according to the present invention, in which a conical inlet portion 1a is provided at one end of a cylindrical casing 1 and the exhaust gas is exhausted. The inlet pipe 2 is connected. Further, a conical outlet portion 1b is provided at the other end, and an exhaust outlet pipe 3 having a flange 3a is connected thereto. The first partition wall 4 and the second partition wall 5 are fixed inside the casing 1, and the cylindrical filter element 6 is sandwiched between the both, and the outer peripheral surface of the filter element 6 and the inner periphery of the casing 1 are An appropriate space 7 serving as an exhaust passage is secured between the surface and the surface. First located on the side of the entrance 1a
The partition wall 4 has a circular ring shape with an open center, and closes the end face of the cylindrical filter element 6 and one end of the space 7. The second partition wall 5 located on the outlet portion 1b side closes the entire other end face of the filter element 6 including the central portion, and the periphery is so arranged as to ensure communication between the space 7 and the outlet portion 1b. It is cut out.

Therefore, as a general flow of the exhaust gas, as shown by the arrow, it flows from the exhaust inlet pipe 2 into the central portion of the filter element 6, and the filter element 6 is radially moved from the inner peripheral side to the outer peripheral side. After flowing, it flows out to the exhaust outlet pipe 3 through the space 7.

As shown in FIG. 3, the filter element 6 is mainly composed of a thin grid-shaped metal plate 8 carrying a catalyst, and the mesh-shaped metal inner cylinder 9 of relatively high rigidity is the first. , Which are fixed to the second partition walls 4 and 5 in advance, and in which the lattice-shaped metal plates 8 are laminated in a plurality of layers in a cylindrical shape centering on the metal inner cylinder 9. Specifically, the grid-shaped metal plate 8 is in the form of one continuous strip, which is sequentially and continuously wound and then fixed by, for example, spot welding.

As shown in FIG. 4, the grid-shaped metal plate 8 has a large number of slits 10 in a base material 8A made of a thin metal plate.
Are alternately formed, and the arrow A perpendicular to the slit 10 is formed.
It is stretched in the −A direction to form a rhombic lattice shape as shown in detail in FIG. 5, and in a cylindrically assembled state, a ceramic coating is applied and a catalyst is supported. The grid shape of the grid-shaped metal plate 8 is constant over the entire length, that is, each layer has a grid of the same size.

Here, the plate thickness of the grid-shaped metal plate 8 is t, the distance between the grids in the circumferential direction is x (see FIG. 5), the layer number of each layer counted from the lower layer, that is, the center side is n, and the layer n thereof. The dimension of each part is set so that 2πt / x is a value that is not an integer, where r _n is the winding radius.

As an example, the thickness t of the grid-shaped metal plate 8 is about 0.2 mm, and the grid distance x is 2 to 3 m.
It is set to about m, and this is wound 50 times or more.

FIG. 1 is an explanatory view schematically showing the degree of circumferential overlap of the grid intersections 11 (see FIG. 5) of the cylindrical filter element 6 constructed as described above, and is clearly shown in FIG. As described above, the number of lattices included in one turn of the n-th layer is represented by 2πr _n / x, and the number of lattices included in one turn of the (n + 1) -th layer which overlaps with this is also 2πr _{n + 1} / indicated by x. Although the second layer and the third layer are illustrated in FIG. 1, the difference in the number of lattices of the two layers overlapping each other is (2πr _{n + 1} −2πr _n ) / x, and Since the radius difference (r _{n + 1} −r _n ) is equal to the plate thickness t, the above difference in the number of lattices is shown as 2πt / x.

Therefore, if 2πt / x is an integer, then the lattice intersection point 11 between the (n-1) th layer and the nth layer is 11
In the place where is coincident with each other, the lattice intersection 11 is sure to coincide with the next (n + 1) th layer. Since this relationship is established for all the layers, the lattice intersections 11 eventually match at a specific location over the entire layers from the inner peripheral portion to the outer peripheral portion of the filter element 6. As an example, FIG. 6 shows the case of 2πt / x = 2, but as shown in the figure, the lattice intersection points 11 are the same at two points (C and D) 180 ° apart. It will be in the state of doing. In other words, the fine flow passages in the grid are linearly continuous, allowing the passage of exhaust gas.
It should be noted that FIG. 6 shows only the overlap of one lattice representative of the C portion and the D portion. However, in this vicinity, the deviation of each layer at the lattice intersection 11 is extremely small, and the lattice is substantially completely covered. It will be in a state of overlapping over layers. Therefore, the two parts, C and D, become locally rough, and the exhaust gas blows through as it is.

On the other hand, as in the above embodiment, if 2πt / x indicating the difference in the number of lattices is not an integer,
Even if there is a location where the lattice intersection 11 coincides with the (n-1) th layer and the nth layer, it overlaps (n).
In the (+1) th layer, the grid intersections 11 are always displaced as shown in FIG. That is, the lattice intersections 11 are randomly overlapped at each portion in the circumferential direction, and a locally rough portion does not occur. If 2πt / x is a value approximate to an integer, the amount of deviation of the grid intersection 11 that occurs in the (n + 1) th layer is small, so that value, especially the part after the decimal point is 0.25 to 0. It is preferably in the range of about 75, more preferably around 0.5.

As described above, in the above-described structure, uniform flow passages are formed in each portion in the circumferential direction, and local blow-through of exhaust gas and variation in trapping efficiency are prevented. Further, since the overlapping of the lattices is minimized, a substantial adhering and collecting area is secured, and each part of the lattice can be effectively used for the adhering and collecting. Similarly, the contact efficiency with the catalyst is improved, and the regeneration ability and exhaust gas purification action by the catalytic action are improved.

Further, in the above construction, since the collection itself is carried out in the form of adhesion collection, excessive collection such as filtration collection is prevented, and clogging due to the Ash component hardly occurs.
And since the entire filter element 6 is made of metal,
The heat capacity is very small, and the temperature rise characteristics after engine start are excellent.

[0021]

As is apparent from the above description, in the exhaust gas filter for an internal combustion engine according to the present invention, the overlapping of the lattices in multiple layers is avoided, and the coarse and dense flow passages are formed at each portion in the circumferential direction of the cylindrical filter element. The state can be obtained almost uniformly. Therefore, it is possible to prevent a local decrease in collection efficiency and blowout of exhaust gas, and it is possible to perform efficient collection while effectively utilizing each part of the lattice.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a grid intersection point position of a filter element of an exhaust filter according to the present invention.

FIG. 2 is a partially cutaway perspective view showing an embodiment of an exhaust filter according to the present invention.

FIG. 3 is a perspective view showing a filter element of this embodiment.

FIG. 4 is an explanatory view showing a method for forming a grid-shaped metal plate.

FIG. 5 is an enlarged view of an essential part showing a state where two grid-shaped metal plates are stacked.

FIG. 6 is an explanatory diagram showing the positions of lattice intersections when 2πt / x = 2.

[Explanation of symbols]

 1 ... Housing 2 ... Exhaust inlet pipe 3 ... Exhaust outlet pipe 6 ... Filter element 8 ... Lattice metal plate 11 ... Lattice intersection

Claims (1)

[Claims] 1. A filter element is constructed by sequentially laminating one continuous grid-shaped metal plate having a grid of a fixed shape in a cylindrical shape, and exhaust gas flows through the filter element in the radial direction. In an exhaust gas filter for an internal combustion engine housed in a casing, when the plate thickness of the grid-shaped metal plate is t and the inter-grid distance along the circumferential direction is x,
An exhaust filter for an internal combustion engine, wherein each dimension is set so that 2πt / x is a value that is not an integer.