JP2001020721A - Diesel particulate filter system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency of trapping small particulate matter without increasing the pressure loss. SOLUTION: This system comprises two filters 10A, 10B made of conductive material disposed within an exhaust passage 11 with a predetermined space d kept therebetween along a flowing direction of exhaust gas from a diesel engine, electrical insulators 12A, 12B that electrically insulate the filters 10A, 10B from the exhaust passage 11, and a high voltage generator 13 that supplies direct current of negative and positive polarities to the adjacent filters 10A, 10B, respectively. Particulate matter with a small particulate diameter that is not trapped by the upstream filter 10A are charged with negative voltage, and the downstream filter 10B traps the particulate matter by static electricity generated between the filter 10A and the downstream filter 10B to which positive voltage is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel particulate filter (hereinafter referred to as "DPF") system for collecting particulate matter contained in exhaust gas of a diesel engine, and more particularly to a system for collecting particulate matter having a small particle diameter. It relates to technology for improving collection efficiency.

[0002]

2. Description of the Related Art Conventionally, a DPF that collects particulate matter contained in the exhaust gas of a diesel engine and improves the exhaust gas properties.
The system is known (Tokyo Metropolitan Institute of Environmental Science Annual Report 199)
8, see p125-p133). As shown in FIG. 7, the DPF system collects particulate matter contained in exhaust gas by a single filter 2 interposed in an exhaust passage 1 of a diesel engine.

[0003]

However, in order to collect particulate matter having a smaller particle diameter and improve the exhaust properties, the mesh of the filter 2 must be made denser. In this case, the filter 2 is likely to be clogged by the particulate matter having a large particle diameter, and a pressure loss occurs. Further, since the filter 2 is likely to be clogged, it is necessary to repeat the regeneration process of burning out the particulate matter attached to the filter 2 with an electric heater or a combustion gas in a short cycle. As the frequency of the regeneration process increases, the battery becomes more exhausted, and the battery becomes larger,
It is necessary to increase the capacity of the alternator, and the fuel efficiency is deteriorated.

Accordingly, the present invention has been made in view of the above-described conventional problems, and has a filter structure in which clogging of the filter is less likely to occur, thereby reducing particulate matter having a smaller particle diameter without increasing pressure loss. It is an object of the present invention to provide a diesel particulate filter system capable of trapping.

[0005]

According to a first aspect of the present invention, a conductive material is provided at a predetermined interval in an exhaust passage along a flow direction of exhaust gas from a diesel engine. A diesel particulate filter comprising: a plurality of filters; an electrical insulating material for electrically insulating the filters from an exhaust passage; and voltage applying means for applying a DC voltage having a different polarity to the adjacent filters. A system is configured.

With this configuration, when the exhaust gas from the diesel engine passes through the diesel particulate filter system, the particulate matter having a large particle diameter contained in the exhaust gas is disposed at the most upstream side of the exhaust passage. Collected by the filter. At this time, the particulate matter having a particle diameter smaller than the mesh of the filter is charged by the voltage applied by the voltage applying means when passing through the filter. Then, when the particulate matter having a small particle diameter passes through the next filter, an electrostatic force is generated between the particulate matter and a filter having a different polarity from the particulate matter, and the particulate matter is collected by the filter. That is, the particulate matter is charged to a certain polarity, an electrostatic force is generated between the filter and the next filter to which a voltage having a different polarity is applied, and the particulate matter having a small particle size is collected.

According to a second aspect of the present invention, the filter includes:
It is characterized in that the mesh is formed so as to be denser from the upstream side to the downstream side of the exhaust passage. According to this configuration, since the mesh of the filter located on the downstream side of the exhaust passage is formed densely, the distance between the charged particulate matter and the filter is shortened, and the electrostatic force acts more strongly between the two. Will be done. in this case,
Since the particulate matter having a large particle diameter is collected by the filter arranged on the most upstream side, the pressure loss increases more than the current level even if the filter located on the downstream side is formed densely. Never.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the attached drawings. FIG. 1 shows a first embodiment of a DPF system according to the present invention.

The DPF system has two filters 10.
A, 10B, filters 10A, 10B and exhaust passage 11
Electrical insulating materials 12A and 12B for electrically insulating between
And a high voltage generator 13 (voltage applying means) for generating a DC high voltage.

[0010] The two filters 10A and 10B are arranged in the exhaust passage 11 along the flow direction of exhaust gas from the diesel engine.
Are arranged at predetermined intervals d. This predetermined interval d
As described later, when a high DC voltage is applied to the two filters 10A and 10B, the filters 10A and 10B
It is intended to electrically insulate between them. Also,
Each of the filters 10A and 10B is made of a conductive material, for example, silicon carbide (SiC), and has a honeycomb-shaped mesh in cross section.

The high voltage generator 13 includes two filters 1
0A and 10B, voltages having different polarities, that is, in this embodiment, the “−” voltage is applied to the upstream filter 10A,
A “+” voltage is applied to the downstream filter 10B. Note that a “+” voltage may be applied to the upstream filter 10A and a “−” voltage may be applied to the downstream filter 10B.

Next, the operation of the DPF system having such a configuration will be described. When exhaust gas from the diesel engine passes through the DPF system, particulate matter having a large particle diameter contained in the exhaust gas is collected by the upstream filter 10A. At this time, the particulate matter having a particle size smaller than the mesh of the upstream filter 10A passes through the upstream filter 10A, but the high voltage generator 13
"-" Applied to the filter by "-"
Is charged. Then, when the particulate matter having a small particle diameter passes through the filter 10B on the downstream side, the filter 10B to which a “+” voltage having a polarity different from that of the particulate matter is applied.
Between the filter 10 and the particulate matter
Collected in B.

In this case, the particulate matter having a small particle size can be removed without making the filter mesh dense, and the clogging of the filter can be maintained at the current level. Therefore, while suppressing an increase in pressure loss due to filter clogging, particulate matter having a smaller particle diameter can be removed, and exhaust properties can be improved. Further, since the clogging of the filter is maintained at the current level, the frequency of the filter regeneration processing does not increase, and the mounting of a large battery or the like becomes unnecessary.

As shown in FIG. 2, the trapping efficiency of the particulate matter according to the present embodiment is significantly improved as the particle diameter becomes smaller, as compared with the prior art. Further, as shown in FIG. 3, the pressure loss becomes substantially constant over the entire range of the collection efficiency, and it is clear that the exhaust property is improved.

FIG. 4 shows a second embodiment of the DPF system according to the present invention. The feature of this embodiment is that the three filters 20 are arranged along the flow direction of the exhaust gas from the diesel engine.
A to 20C are provided. Then, voltages having different polarities, that is, “−”, “+”, and “−” voltages are applied to the filters 20A, 20B, and 20C from the upstream side to the downstream side, respectively, between the adjacent filters. You. With this configuration, when passing through each filter, the particulate matter having a small particle diameter is gradually removed from the particulate matter having a large particle diameter, and the exhaust property can be further improved.

By arranging a large number of filters, the exhaust characteristics can be further improved. However, since the size and cost of the DPF system are increased, the target exhaust characteristics and costs are taken into consideration. , It is desirable to determine the number of filters.

FIG. 5 shows a third embodiment of the DPF system according to the present invention. The feature of this embodiment lies in that, in the first embodiment (see FIG. 1), the mesh of the filter is formed densely from the upstream side to the downstream side of the exhaust passage. That is, the mesh 10A of the upstream filter is formed sparsely (see FIG. 5B), and the mesh of the downstream filter 10B is formed densely (see FIG. 5C). Here, the mesh of the filter 10A on the upstream side has a size suitable for collecting particulate matter having a large particle diameter.

In this manner, as in the first embodiment, the particulate matter having a large particle diameter is removed from the upstream filter 10.
While being collected by A, the particulate matter having a small particle diameter is charged to “−”. When the particulate matter having a small particle diameter passes through the filter 10B on the downstream side, the particulate matter is collected by the filter 10B in which the mesh is densely formed, and a file to which a “+” voltage having a different polarity is applied. An electrostatic force is generated between the filter 10B and the filter 10B, and the particulate matter is collected by the filter 10B. In this case, since the mesh is formed more densely than in the first embodiment, the distance between the particulate matter and the filter 10B is shortened, and the electrostatic force acts more strongly. Therefore, the collection efficiency of the particulate matter having a small particle diameter is improved, and the exhaust property is further improved. In this embodiment, since the particulate matter having a large particle diameter is collected by the upstream filter 10A, even if the mesh of the downstream filter 10B is densely formed, as shown in FIG. Losses do not increase more than they do today.

Further, such a configuration can be applied to the second embodiment (see FIG. 4). That is, the meshes of the filters 20A to 20C may gradually become denser from the upstream side to the downstream side of the exhaust passage 11. In short, the mesh of the filter 20A on the most upstream side may be sparse, the mesh of the filter 20C on the most downstream side may be dense, and the mesh of the filter 20B in the middle may be formed between sparse and dense. In this case, since the particulate matter having a small particle diameter is gradually removed from the particulate matter having a large particle diameter,
The collection efficiency of particulate matter can be further improved while suppressing clogging of the filter.

[0020]

As described above, according to the first aspect of the present invention, it is possible to remove particulate matter having a small particle diameter without making the filter mesh dense, and to prevent the filter from being clogged. Can be maintained at the level. Therefore, the particulate matter having a smaller particle diameter can be removed while suppressing the pressure loss due to clogging of the filter, and the exhaust property can be further improved.

According to the second aspect of the present invention, since the electrostatic force generated between the particulate matter and the filter is increased,
The collection efficiency of particulate matter having a small particle diameter is improved, and the exhaust properties can be further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the particle size of particulate matter and the collection efficiency in the same as above.

FIG. 3 is a diagram showing a relationship between a collection efficiency and a pressure loss in the above.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

5A and 5B show a third embodiment of the present invention, wherein FIG. 5A is an overall configuration diagram, FIG. 5B is a cross-sectional view of an upstream filter, and FIG.
Is the cross-sectional view of the downstream filter

FIG. 6 is a diagram showing a relationship between a collection efficiency and a pressure loss in the above.

FIG. 7 is a configuration diagram of a conventional diesel particulate filter system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10A, 10B Filter 11 Exhaust passage 12A, 12B Electrical insulation material 13 High voltage generator 20A-20C Filter

Claims (2)

[Claims] 1. A plurality of filters made of a conductive material disposed at predetermined intervals in an exhaust passage along a flow direction of exhaust gas from a diesel engine, and electrically connecting the filters and the exhaust passage. A diesel particulate filter system comprising: an electrical insulating material to be insulated; and voltage applying means for applying DC voltages having different polarities to adjacent filters. 2. The diesel particulate filter system according to claim 1, wherein the filter is formed such that its mesh becomes denser from upstream to downstream of the exhaust passage.