JP2949897B2 - Exhaust filter for internal combustion engine - Google Patents

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 particles such as carbon which are problematic in an internal combustion engine, particularly a diesel engine.

[0002]

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

[0003] A typical example of this exhaust filter is a filtration and collection type represented by a so-called plug-in type filter. The plugged type filter is disclosed in, for example,
As shown in JP-A-124417, a large number of fine channels are formed in a ceramic block along the exhaust flow direction, and the ends of each channel are alternately closed with ceramics. The exhaust gas passes through the ceramic partition between the flow paths, thereby filtering and collecting the exhaust fine particles.

In this type of filtration and collection, while extremely high collection efficiency is obtained, the exhaust particulates are easily collected excessively, and the collection amount of the particulates easily exceeds the burning limit of the filter. That is, if 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 burn rapidly, leading to burnout of the filter. In addition, even Ash components (oxides of oil additives and the like) that cannot be removed by incineration are trapped, which may eventually lead to clogging.

[0005] Therefore, an exhaust filter of an adhesion collection type has been proposed in place of the filtration and collection type. Examples thereof include a filter element made of a ceramic three-dimensional porous body, so-called ceramic foam, as disclosed in JP-A-62-45309, and a catalyst as disclosed in JP-A-51-23615. And a filter element formed by laminating a large number of thin heat-resistant fiberboards carrying the same. In the case of the adhesion trapping type, when exhaust gas flows through a complicated flow path generated in the filter element, exhaust fine particles adhere to and are trapped on the surface of the flow path.

[0006]

SUMMARY OF THE INVENTION The above-mentioned JP-A-62-45
Japanese Patent Publication No. 309 and Japanese Utility Model Laid-Open Publication No. 51-23615 disclose a configuration in which a filter element of an adhesion trapping type 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 the density of the flow path is given equally between the inner peripheral portion and the outer peripheral portion, a considerably large amount of exhaust particulates will be collected also on the outer peripheral portion. Therefore, when the engine is suddenly accelerated, there is a disadvantage that a large amount of exhaust fine particles easily blow off to the outside and are discharged as black smoke.

[0007] If there is a deviation in the close-packed state in each part in the circumferential direction of the cylinder, the exhaust blows through the rough part.
As the collection efficiency decreases, blow-off of the fine particles once collected tends to occur. This is likely to occur when the grids are offset and overlap, particularly when a large number of grid-like metal plates are stacked to form a filter element.

[0008]

SUMMARY OF THE INVENTION Accordingly, an exhaust filter for an internal combustion engine according to the present invention comprises a filter element formed by laminating a plurality of lattice-like filter members in a cylindrical shape. While accommodating in the casing so that the exhaust gas flows from the outer side toward the outer peripheral side, the grid size of each layer is set such that the ratio between the interstitial distance and the winding radius in each layer of the grid filter member is constant. Also, it is characterized in that the lattice intersections are shifted by a fixed ratio in adjacent layers and stacked.

[0009]

In the above construction, the distance between the lattices becomes smaller, that is, the inner circumference becomes smaller, as the inner radius becomes smaller. Conversely, at the outer periphery, the distance between the lattices is large and coarse. Therefore, the collection efficiency becomes extremely large in the inner peripheral portion, and most of the exhaust fine particles are collected in the inner peripheral portion.

Further, since the distance between the lattices is proportional to the winding radius, and the lattice intersections of each layer are regularly arranged, the density of the flow path is uniform at each part in the circumferential direction.

[0011]

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

FIG. 2 is a partially cut-away perspective view showing the overall structure of an exhaust filter according to the present invention. A conical inlet portion 1a is provided at one end of a cylindrical casing 1 and exhaust gas is provided. The inlet pipe 2 is connected. At the other end, a conical outlet portion 1b is provided, and an exhaust outlet pipe 3 having a flange 3a is connected. A first partition wall 4 and a second partition wall 5 are fixed inside the casing 1, and a cylindrical filter element 6 is sandwiched between the two, and the outer peripheral surface of the filter element 6 and the inner circumference of the casing 1 are interposed therebetween. An appropriate space 7 serving as an exhaust passage is secured between the first and second surfaces. The first located on the entrance 1a side
The partition 4 has an annular 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 1b side closes the entire other end face of the filter element 6 including the central portion, and the surroundings are secured so as to secure communication between the space 7 and the outlet 1b. Notched.

Accordingly, the general flow of the exhaust gas flows from the exhaust inlet pipe 2 into the center of the filter element 6 and moves the filter element 6 radially from the inner peripheral side to the outer peripheral side, as indicated by arrows. 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-like metal plate 8 supporting a catalyst. , Are fixed in advance to the second partition walls 4, 5, and a plurality of lattice-like metal plates 8 are laminated in a cylindrical shape around the metal inner cylinder 9. More specifically, lattice-like metal plates 8 formed one by one in a strip shape having a length corresponding to the circumference of each layer are sequentially laminated one by one and fixed by, for example, spot welding or the like.

As shown in FIG. 4, a plurality of slits 10 are formed in a base material 8A made of a thin metal plate.
Are formed alternately, and this is formed by an arrow A orthogonal to the slit 10.
It is stretched in the -A direction to form a rhombic lattice shape as shown in detail in FIG. 5, and is coated with ceramics individually or in a cylindrically assembled state to support a catalyst. . And when laminating the grid-like metal plate 8 of each layer, as shown in FIG.
The grid intersections 11 of the grid-like metal plates 8 adjacent to each other
Do not match, for example, at a fixed rate, for example, the interstitial distance S
Are shifted in the circumferential direction by 1/2 of each other.

Further, the lattice-shaped metal plate 8 located on the inner peripheral side of the cylindrical filter element 6 and the lattice-shaped metal plate 8 located on the outer peripheral side are different in the rhombic shape of the lattice, and are located on the outer peripheral side. The grid-like metal plate 8 has a larger open grid. In other words, the layer number of each of the stacked layers is n,
Assuming that the winding radius of the layer n is Rn and the interstitial distance is Sn, the lattice of each layer n has a constant value (Sn / Rn) between the interstitial distance Sn of each layer and the winding radius Rn. The distance Sn is set larger on the outer peripheral side. Note that the slits 1 were formed so that the lattice shape of each layer was completely similar.
The length of 0 may also be changed.

Therefore, in the above configuration, as shown in FIG. 1, even when the layer numbers n are even or when the layer numbers n are odd, the grid intersections 11 are arranged at the same angular position on the circumference. For example, as illustrated in FIG. 1, intersections 11 of even layers are arranged on lines L1 and L2 along the radial direction, and L1 and L2
The intersections 11 of the odd-numbered layers are arranged in the middle position of the line 2. This positional relationship is maintained over the entire circumference of the cylindrical filter element 6.

Therefore, a uniform flow path is formed in each part in the circumferential direction, and local exhaust blow-through and variation in collection efficiency are prevented. Since the grids do not unnecessarily overlap, a substantial adhesion collection area is secured, and each part of the grid can be effectively used for the adhesion collection. Similarly, the contact efficiency with the catalyst is improved, and the regeneration ability and the exhaust gas purifying action by the catalytic action are improved.

Further, since the lattice shape of the inner peripheral portion becomes denser than that of the outer peripheral portion, the collection efficiency at the inner peripheral portion becomes extremely high.
Most of the exhaust fine particles are collected in the inner peripheral portion. Therefore, even if the exhaust gas flow velocity suddenly increases during engine acceleration or the like, blow-off of the exhaust fine particles to the outside hardly occurs. When the exhaust gas flows through the filter element 6 in the radial direction, the flow actually becomes complicated and turbulent as shown by the arrow in FIG. 6, so that the exhaust fine particles separated from the inner peripheral portion are captured again at the outer peripheral portion. Therefore, blow-out to the outside is more reliably prevented. In addition, since the outer peripheral portion has a rough lattice shape, pressure loss can be suppressed as compared with the collection efficiency.

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

In the above configuration, the lattice intersections 11 of the adjacent layers are stacked while being shifted in the circumferential direction by 1/2 of the interstitial distance S. For example, the layers are stacked by being shifted by 1/3 or 1/4. It is also possible.

[0022]

As is apparent from the above description, in the exhaust filter for an internal combustion engine according to the present invention, it is possible to uniformly obtain the coarse / dense state of the flow path in each part in the circumferential direction of the cylindrical filter element. In addition to preventing the reduction of the collection efficiency and the blow-by of exhaust gas, unnecessary collection of grids can be avoided, and efficient collection can be performed. Further, since a large amount of exhaust particulates is collected in the inner peripheral portion and the ventilation resistance in the outer peripheral portion is reduced, blow-off during acceleration of the engine is prevented, and pressure loss can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a main part 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 the 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-like metal plate.

FIG. 5 is an enlarged view of a main part in a state where two lattice-shaped metal plates are stacked.

FIG. 6 is an explanatory diagram showing a flow of exhaust gas in the filter element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Housing 2 ... Exhaust inlet pipe 3 ... Exhaust outlet pipe 6 ... Filter element 8 ... Lattice metal plate 11 ... Lattice intersection S ... Lattice distance

Claims (1)

(57) [Claims] A filter element is formed by laminating a plurality of lattice-shaped filter members in a cylindrical shape, and the filter element is housed in a casing such that exhaust gas flows from an inner peripheral side toward an outer peripheral side. In addition, the lattice size of each layer is set so that the ratio between the interstitial distance and the winding radius in each layer of the lattice filter member is constant, and the lattice intersections are shifted by a fixed ratio in adjacent layers. An exhaust filter for an internal combustion engine, comprising: