JPH0544493Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a particulate filter that removes harmful particles such as soot from engine exhaust gas.

[Prior Art] In recent years, in order to prevent environmental pollution, regulations on automobile exhaust gas have become more stringent.
For diesel engine vehicles, regulations regarding NOx (nitrogen oxides) and particulate matter (particulate matter in black smoke) are being tightened.

The NOx can be reduced by lowering the combustion temperature by, for example, delaying the fuel injection timing, but on the other hand, particulate matter increases. For this reason, a particulate filter is provided in the exhaust passage of the engine to remove particulate matter.

If the particulate filter becomes clogged due to the accumulation of collected particulate matter,
Since the exhaust resistance increases and the engine output decreases, it is necessary to periodically regenerate the particulate filter.

Conventionally, particulate filters of this type have been of the wall flow type as shown in FIG. There are some that use element 2,
A heater 3 is provided at an upstream position of each of the porous elements 1 and 2, respectively. In addition, 4 in Figure 5
6 indicates a shielding material such as ceramic for alternately closing the upstream and downstream open ends of the porous element 1, and 5 in FIG. 6 indicates a shielding material for closing the downstream open end of the porous element 2. A shielding plate made of ceramic or the like is shown.

In any type of particulate filter, the heater 3 is normally not energized, and the exhaust gas flows through the porous element 1 as shown by the arrows in FIGS. 5 and 6. flows from the space opened on the upstream side to the adjacent space opened on the downstream side, and in the porous element 2 flows from the inside to the outside,
Particulate matter in the exhaust gas is collected by the porous elements 1 and 2, and the purified exhaust gas is discharged into the atmosphere.

On the other hand, when regenerating each of the porous elements 1 and 2, the heater 3 is energized to heat the exhaust gas passing through the heater 3 and pass through the porous elements 1 and 2, respectively. Particularly accumulated particulate matter is burned and removed.

[Problems to be Solved by the Invention] However, in the above-described particulate filter, in order to increase the collection efficiency of particulate, it is necessary to increase the thickness of the porous element. When the wall thickness of the porous element was increased, the heat capacity of the porous element became large, and even if the exhaust gas was heated by a heater, the particulate matter accumulated in the porous element could not be easily combusted. .
In addition, when combustion of the particulate occurs, the temperature distribution in the thickness direction of the porous element becomes uneven, and only the inner surface (the surface facing the space where the upstream side is not closed) is locally overheated. At the same time, the temperature of the exhaust gas heated by the heater increases further due to the combustion of the particulate and flows through the filter, and the downstream end of the porous element is overheated compared to the upstream side, resulting in a high temperature. This resulted in melting and damage.

In view of the above circumstances, the present invention aims to provide a particulate filter that ensures the combustion of particulate during regeneration and can even out the temperature distribution of the porous element to prevent melting damage. It is.

[Means for Solving the Problems] The present invention arranges thin porous elements made of conductive ceramic that also serve as heaters in multiple stages, and allows power to be individually supplied to each porous element and to control each power. This feature is characterized in that it is configured to be possible.

[Operation] Normally, exhaust gas sequentially passes through de-energized porous elements arranged in multiple stages, and particulate matter is collected in each of the porous elements.

On the other hand, during filter regeneration, each porous element functions as a heater by supplying power to each porous element, and by controlling the supplied power, combustion of the particulate accumulated in each porous element is ensured. Moreover, the combustion state is averaged out, and the temperature distribution inside the filter is also made uniform, so that localized overheating does not occur.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

As shown in FIG. 1, a wall flow type porous element is divided into three stages in the upstream and downstream directions, and each divided porous element 1a, 1
b and 1c themselves are respectively SiC (silicon carbide)
A heater made of conductive ceramic material such as
Each porous element 1a, 1b, 1c,
Power supply units 6a, 6b, 6c each connected to the main power supply
Connect. Each power supply unit 6a, 6b, 6c includes:
The voltage control device 7 is connected to each power supply section 6a, 6.
b, 6c to each of the porous elements 1a, 1
The power supplied to b and 1c is configured to be adjustable. Note that the porous elements 1a, 1b, 1
c is arranged so that the open ends that are not closed by the shielding materials 4a, 4b, and 4c face each other,
Further, the average pore diameter of each porous element 1a, 1b, 1c is such that the one located on the upstream side is coarsest and the one located on the downstream side becomes finer.

Next, the operation of this embodiment will be explained.

Normally, when collecting particulate matter contained in exhaust gas, each porous element 1a, 1b, 1c, which also serves as a filter and a heater, has a power supply section 6.
Power is not supplied from a, 6b, and 6c, and exhaust gas flows through the multilayer porous element 1a.
Flows into the space partitioned by the upstream opening end where the shielding material 4a is not provided, passes through the porous element 1a, and flows into the space opened on the downstream side, as shown by the arrow in FIG. . At this time, porous element 1 with the coarsest average pore diameter
A part of the particulate contained in the exhaust gas is collected by a. In the same manner, the average pore diameter of the porous element 1 becomes smaller and smaller.
The particulate matter that has passed through the porous element 1a is collected by the parts b and 1b, and the purified exhaust gas is discharged into the atmosphere.

Here, the porous elements 1a, 1b,
Since the porous elements 1c are arranged in a plurality of stages and have different average pore diameters, the particulate collection state by each porous element 1a, 1b, and 1c is averaged. Also, the second
The figure shows the collection efficiency when the wall thickness is changed in porous elements with different average pore diameters (the roughness of the average pore diameter is in the order of A>B>C>D). As is clear from this figure, it is natural that the smaller the average pore diameter and the thicker the wall thickness, the higher the collection efficiency. By arranging them in multiple stages, the overall particulate collection efficiency can be improved even if the wall thickness is thin.

On the other hand, each porous element 1a, 1b,
When the clogging of the porous elements 1c progresses and each porous element 1a, 1b, 1c needs to be regenerated, a control signal is sent from the voltage control device 7 to each power supply section 6a, 6b, 6c. 6a, 6b, 6c
Thus, the power supplied to each porous element 1a, 1b, 1c is adjusted. As a result, each porous element 1a, 1b, 1c itself becomes a heater, and each porous element 1a, 1b, 1c
The particulate matter accumulated in the porous elements 1a, 1 is heated evenly and burned, and
b, removed by exhaust gas passing through 1c,
Clogging of each of the porous elements 1a, 1b, 1c is eliminated.

In this case, each thin-walled porous element 1a, 1 has a particulate matter that is not concentrated in one part.
Since the particulate is stored evenly in each of the porous elements 1 and 1c, combustion of the particulate is carried out easily and reliably, and each porous element 1 serves as a heater.
Since the power supplied to a, 1b, and 1c is adjusted by the voltage control device 7, the combustion state of the particulate is always averaged, and the temperature distribution in the upstream and downstream directions within the filter is also made uniform. Local overheating of porous elements 1a, 1b, 1c,
Melting damage can be prevented.

3 and 4 show other embodiments of the present invention, in which a thin cylindrical porous element 2a is made of a conductive ceramic material with a small diameter, whereas a porous element 2a is made of a conductive ceramic material with a large diameter. The porous element 2b is
The porous elements 2a, 2b are arranged concentrically so that a space 8 is formed between them.
The porous element 2 is connected to the power supply parts 9a and 9b which are connected to the main power supply and to the voltage control device 10, and further located on the center side, that is, on the upstream side.
a has a larger average pore diameter than the porous element 2b located on the outer peripheral side, that is, on the downstream side. Incidentally, reference numeral 11 in FIG. 3 indicates a shielding ring made of ceramic or the like for closing the open end of the space 8 on the upstream side.

Even with such a configuration, the particulate is collected evenly in each of the thin-walled porous elements 2a and 2b, so that the particulate is easily and reliably combusted during regeneration, and the voltage control device 7 controls each porous element that also serves as a heater. element 2
The electric power supplied to the porous elements 2a and 2b is controlled so that the combustion state of the particulate is averaged, and the wall thickness of each of the porous elements 2a and 2b is thin and heat storage is reduced, so that each of the porous elements 2a and 2b is Local overheating and high temperatures will not occur, and melting damage will also be avoided.

In the above two embodiments, the roughness of the average pore diameter of the porous elements arranged in multiple stages is changed, but porous elements with the same average pore diameter are used and the power supplied to each porous element is controlled. By simply doing this, it is possible to ensure the combustion of the particulate during regeneration, and to even out the combustion state and make the temperature distribution uniform, thereby preventing overheating and melting of each of the porous elements.

[Effects of the invention] As described above, according to the invention, the particulate is reliably burned during filter regeneration, the combustion state is averaged, the temperature distribution of the filter is made uniform, and the filter is prevented from melting. It is possible to achieve excellent effects such as preventing damage to the filter and extending the life of the filter.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the present invention;
The figure is a diagram showing the relationship between the wall thickness of the porous element, the average pore diameter, and the collection efficiency, FIG. 3 is an explanatory diagram showing another embodiment of the present invention, and FIG.
The sectional view and FIGS. 5 and 6 are side sectional views showing a conventional example. 1a, 1b, 1c, 2a, and 2b are porous elements, 6a, 6b, 6c, 9a, and 9b are power supply units, and 7 and 10 are voltage control devices.

Claims (1)

[Scope of utility model registration request] A particulate filter characterized in that thin-walled porous elements made of conductive ceramic that also serve as heaters are arranged in multiple stages, and each porous element is configured to be individually supplied with electric power and each electric power can be controlled. .