JPH04193312A - Exhaust gas filter for internal combustion engine - Google Patents

Abstract

PURPOSE:To nearly uniformly diffuse exhaust gas fine particles with a slow inner blow-off by subjecting filter elements to be dense at both the edge parts and to be gradually coarse toward the central part. CONSTITUTION:A meshed metal plate carrying the catalyst is wound up cylindrically and one or plural filter elements 1 are formed. Also, in a casing 2 inserted into an exhaust gas pipe of an engine, the filter elements 1 are housed in a state that a gas flow paths are remained at the surroundings. In a pair of partition plate 3 provided at the inlet side and the outlet side of the casing 2, respectively each edge part of the filter elements 1 is fixed and supported in a fitting hole. And, the filter elements 1 are such that both edge parts are dense and become gradually coarse toward the central part. Then, with a slow inner blow-off, the exhaust gas fine particles can be diffused nearly uniformly and locally overheating at recycle time and rapid blow-off at quick acceleration are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an exhaust filter for collecting and removing exhaust particulates such as carbon, which are a problem in internal combustion engines, particularly diesel engines.

(Prior art) It has long been thought that exhaust particulates such as carbon, which are a problem in diesel engines, can be collected and removed using an exhaust filter installed in the exhaust system, and various types of exhaust filters are already available. It is proposed.

A typical exhaust filter is of a filtration and collection type, typified by a so-called plugged filter. The above-mentioned sealed filter is, for example, disclosed in Japanese Patent Application Laid-Open No. 56-124417.
As shown in the publication, a large number of fine channels are formed along the exhaust flow direction in a ceramic block, and the ends of each channel are alternately closed with ceramics. , the exhaust gas passes through ceramic partition walls between the flow channels to filter and collect exhaust particulates.

Although this type of filtration collection can achieve extremely high collection efficiency, it tends to collect excessive exhaust particulates, requires frequent forced regeneration using a burner, etc., and requires incineration. Even Ash components that cannot be removed (oxides of oil additives, etc.) may be collected, eventually leading to clogging.

Therefore, instead of this filtration and collection type exhaust filter, an adhesion collection type exhaust filter has been proposed. This is a three-dimensional porous body of ceramics as seen in JP-A No. 62-45309 (L), so-called ceramic foam, and ceramic fibers as seen in JP-A-58-19'3714 as a filter element. When the exhaust gas flows through the plurality of channels created within these filter elements, the exhaust particles forcefully adhere to the walls of the channels and are collected.

(Problems to be Solved by the Invention) Therefore, with such an adhesion collection type, excessive collection is unlikely to occur, and natural regeneration by exhaust heat can be expected without a forced regeneration means such as a burner. However, on the other hand, the collection density tends to be non-uniform in the longitudinal direction, and a large amount of exhaust particulates accumulate at the exhaust inlet side, which may lead to localized high temperatures during regeneration.

In addition, in places where exhaust particulates are locally present, the exhaust particulates do not directly adhere to the surface of the filter material, but are further attached to the collected particulates. However, because the adhesion strength is weak, there is a drawback that when the engine is suddenly accelerated, a large amount of exhaust particulates suddenly blow off to the outside and are emitted as black smoke.

That is, in order to fully utilize the advantages of this adhesion collection type filter, it is desirable to allow slow blow-off inside the filter and to distribute exhaust particulates widely and more uniformly throughout the filter element.

(Means for Solving the Problem) An exhaust filter for an internal combustion engine according to the present invention includes one or more filter elements formed by winding a mesh metal plate carrying a catalyst into a cylindrical shape, and an exhaust pipe of the engine. equipped,
and a casing that accommodates the filter element with a gas flow path left around the casing, and an inlet side and an outlet side Z of the casing, respectively, and each end of the filter element is fixed in the mounting hole. and a pair of supported partition plates, the filter element comprising:
It is characterized by being dense at both ends and gradually becoming coarser towards the center.

(Function) In the above configuration, since exhaust gas flows in from one end of the cylindrical filter element, exhaust particulates are initially collected intensively at the end on the exhaust inlet side. However, these locally accumulated exhaust particles are gradually blown off by the exhaust flow, some of which move downstream of the filter element, and some of which are discharged into the gas flow path around the filter element.

At this time, since the cylindrical filter element is gradually roughened toward the center, there is ventilation resistance for the exhaust gas that tries to flow immediately in the radial direction from one end of the filter element, and ventilation resistance for the exhaust gas that tries to flow in the axial direction from one end of the filter element. are relatively similar, resulting in relatively similar exhaust flow strengths in each direction within the filter element. Therefore, internal blow-off of the exhaust particles occurs in multiple directions, and the exhaust particles are dispersed relatively uniformly within the inlet side portion of the filter element.

In addition, the exhaust gas and exhaust particulates that once flowed into the gas flow path inside the casing try to flow out of the casing by passing through the outlet side of the filter element again, but at that time, they also flow in multiple directions within the filter element. An exhaust flow of relatively similar strength is obtained. Therefore, exhaust particulates are collected relatively uniformly in this portion as well.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 is a sectional view showing the overall structure of an exhaust filter according to the present invention, and FIG. 1 is a partially cutaway sectional view showing only one filter element l in this filter.

In FIG. 2, a casing 2 is installed, for example, in the middle of an exhaust pipe of a diesel engine, and has a cylindrical main body 2.
a, and a substantially conical inlet portion 2b and outlet portion 2c. Furthermore, disk-shaped partition plates 3 are fixed to the front and rear of the main body portion 2a so as to partition the inside of the casing 2.

The pair of partition plates 3 have the same shape, and have a large number of circular mounting holes 4, as shown in FIG.

A plurality of filter elements I are held between the pair of partition plates 3 and housed in the casing 2 together with the partition plates 3. Specifically, each filter element 1 is arranged in parallel with a slight distance from each other, and an appropriate gas flow path is secured between each filter element 1.

As shown in FIG. 1, the filter element l is
It is formed into a cylinder by winding a net-like metal plate carrying a catalyst relatively densely, and is inserted and fixed between both sides of the cylinder. Compared to both ends 1a and la fixed by the mounting holes 4, the central part 1b is set to be loosely tightened, and the diameter of the central part 1b in the tightened state is set to be smaller than that of both ends 1a and l.
It is thicker than a. Therefore, even if the mesh roughness of the mesh metal plate itself is uniform, the cylindrical filter element l
As such, both end portions 1a and la are dense, and the center portion 1b is rough. The mesh metal plate may be a wire mesh made of vertical and horizontal wire rods, or a thin metal plate IA with a large number of slits 5 alternately formed as shown in FIG. A lattice-like structure that is pulled in the same direction is used.

Therefore, as for the internal ventilation resistance of the filter element l, as shown in FIG. 5, the radial ventilation resistance R3 at the central portion 1b is smaller than the radial ventilation resistance R1 at both ends 1a. , the central part 1
Ventilation resistance (R4
+R3) approximates the ventilation resistance R1 at both ends 1a.

Therefore, the exhaust gas flowing into the filter element 1 from one end flows in each direction with relatively similar strength as shown by the arrows in FIG.

Therefore, in the exhaust filter configured as described above, the exhaust gas entering the casing 2 first flows from one end of each filter element 1, and a large amount of exhaust particulates are collected in this part. The accumulated exhaust particles are gradually blown off by the exhaust flow. In other words, some of it diffuses to the downstream side within the filter element 1,
A portion flows out from the filter element into the external gas flow path.

At this time, since the central portion 1b of the filter element 1 is rougher than both end portions 1a, the exhaust particles are easily diffused into the interior and are distributed broadly and approximately evenly throughout.

Further, the exhaust gas that has flowed out into the external gas flow path and the exhaust particles contained therein try to flow out from the gas flow path through the filter element l again toward the outlet portion 2c. Therefore, in this case, the exhaust particulates either adhere in large numbers to the outer periphery of the filter element 1, or are diffused inside by the exhaust flow as shown by the arrows in FIG. In this case as well, since the central portion lb side is rougher than the end portions 1a, the exhaust flow and therefore the exhaust particles do not concentrate on the end portions 1a, and the exhaust particles can be widely distributed.

Therefore, exhaust particulates can be collected almost evenly over the entire filter element 1, and local overheating does not occur during regeneration due to exhaust heat.In addition, the proportion of exhaust particulates directly attached to the surface of the filter material is increased. , the contact efficiency with the catalyst is improved, and sudden blow-off to the outside does not occur even if the exhaust flow rate suddenly increases during acceleration or the like. In particular, since the end portion 1a, which is the final outlet end of the filter element 1, is dense, blow-off to the outside can be more reliably prevented.

In addition, since the collection itself is performed in the form of adhesion collection, excessive collection as in filtration collection is prevented, and clogging due to Ash components is also less likely to occur.

(Effects of the Invention) As is clear from the above explanation, according to the exhaust filter for an internal combustion engine according to the present invention, the filter element of the cylindrical shape and the adhesion collection type is coated with air by slow internal blow-off. It can diffuse exhaust particulates and prevent local overheating during regeneration and rapid blow-off during rapid acceleration. Moreover, the efficiency of contact with the catalyst is improved. Further, excessive collection unlike in filtration does not occur, and regeneration using exhaust heat using catalytic action is fully possible.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway sectional view showing a filter element of an exhaust filter according to the present invention, Fig. 2 is a sectional view of the entire exhaust filter, and Fig. 3 is a perspective view showing the filter element assembled to a partition plate. , FIG. 4 is a plan view showing an example of the material of the net-like metal plate, FIG. 5 is an explanatory diagram of the ventilation resistance of the filter element, and FIG. 6 is an explanatory diagram showing the flow of exhaust air to the filter element. 1... Filter element, 2... Casing, 3
...Partition board. Figure 1 Figure 2 F2---Casing' Figure 3

Claims (1)

[Claims] (1) One or more filter elements formed by winding a net-like metal plate carrying a catalyst into a cylindrical shape, which is interposed in the exhaust pipe of an engine, and leaves a gas flow path around the filter element. A casing that accommodates the condition, and a casing provided on the inlet side and outlet side of this casing, respectively,
and a pair of partition plates in which each end of the filter element is fixedly supported in the mounting hole, and the filter element is dense at both ends and gradually becomes rougher toward the center. An exhaust filter for an internal combustion engine, characterized by: