JPH0443810A - Diesel particulate filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a diesel particulate filter that removes particulate matter (diesel particulates) contained in the exhaust gas of a diesel engine.

(Prior Art) Diesel engines normally perform combustion in an excess air condition, so the concentrations of HC and CO in their exhaust gas are generally low. However, when a diesel engine lacks air, even when there is sufficient air, carbon particles are generated in the exhaust, which is the main cause of the black exhaust characteristic of diesel engines. In recent years, attention has been focused on the relationship between air pollution and particulate matter, including carbon particles, emitted from diesel engines, and air pollution. The equipment of the device is being considered. As a post-processing device 11, there is a particle collector generally called a noticulate trap, which is equipped with a heat-resistant particle collector filter in the middle of the exhaust passage.

Particulate filters for collecting particles include a ceramic wall type with a porous ceramic wall, a wire mesh type with an aluminum-coated wire mesh, and a ceramic foam type with a 7-ohm ceramic.

However, in the case of any particulate fill,
As the amount of trapped particles increases, the air permeability decreases and the flow of exhaust air is obstructed, so it is necessary to periodically remove the trapped particles from the filter to regenerate the filter.

In order to regenerate the diesel particulate filter, there is a method of removing the filter from the exhaust passage of the diesel engine and cleaning it, but the work is complicated, so the methods disclosed in Japanese Utility Model Application Publications No. 1989-1909 and No. 3222-1983 Public notice,
As disclosed in Japanese Unexamined Patent Publication No. 61-25907, etc., a method is often used in which particulates trapped in a filter are burned and removed within the filter.

Methods for determining the timing of filter regeneration through combustion and removal include, for example, a method in which the degree of filter clogging is detected by an increase in engine back pressure, and regeneration is performed when this back pressure exceeds a certain value; There is a method of automatically repeating regeneration every time the engine finishes a predetermined operation, regardless of the actual amount of particulates in the engine.

(Problems to be Solved by the Invention) Specifically, the filter is regenerated by igniting the collected particulates with an electric heater and then blowing secondary air into the filter until the particulates are burned out.

However, in the conventional regenerator, an electric heater of the same standard is used over the entire ignition area of the filter, and the electric heater is energized for the same amount of time. In other words, a uniform amount of heat is supplied regardless of the location, such as the center and the periphery of the filter.

For this reason, the center of the filter is affected by heat from the periphery and is difficult to cool, resulting in a relatively high temperature.
On the other hand, the peripheral area tended to be relatively cold due to heat dissipation to the surrounding area.

Therefore, if the optimum temperature is set at the center of the filter, there will be insufficient heating at the periphery, which may cause the particulates to remain unburned or disappear.On the other hand, if the optimum temperature is set at the periphery, the center may become overheated. This may cause the filter to overheat and melt.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a diesel particulate filter that can uniformly heat an ignition region disposed on one end surface of the filter at an ideal temperature.

(Means for achieving the object) In order to achieve the above object, the diesel particulate filter of the present invention has the following configuration. That is, it is a diesel particulate filter in which the electric heater is divided into at least the central part and the peripheral part of the filter, and the amount of heat supplied by the electric heater in the central part is relatively small, and the amount of heat supplied by the electric heater in the peripheral part is relatively large. . The amount of heat supplied can be changed by changing the capacity of the electric heater, i.e. by making the electric heater's capacity smaller in the center and larger in the periphery, or by changing the energization time, i.e. by shortening the energization time in the center and increasing it in the periphery. This can be achieved by increasing the length at the periphery or by changing both the capacity and the energization time of the electric heater.

(Function) In a diesel particulate filter with such a configuration, the temperature difference between the center and periphery of the filter is reduced,
The entire end surface of the filter is ideally heated at a substantially uniform temperature, and inconveniences such as overheating and melting of the filter in the center, unburned particulates in the periphery, and extinguishing can be prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 and 2 are an end view and a side view on the heater side of a diesel particulate filter 1 according to the present invention. As shown in the figure, this filter l has a cylindrical shape,
The electric heater is divided into two regions R1 and R2. In this embodiment, it is divided into two sections, R1 and R2, but it may be divided into three or more concentric sections. The electric heater in the central circular region R1 has a relatively small capacity,
The electric heater in the peripheral annular region R2 has a relatively large capacity. The location of this filter 1 is specifically shown in the schematic diagram of the diesel particulate filter regeneration system shown in FIG.

First, to explain the outline of the filter regeneration system, the diesel particulate filter 1 is placed in the main passage 3a of the exhaust passage 3 of the diesel engine 2, and has the function of capturing diesel particulates in the exhaust gas and purifying the exhaust gas. . An electric heater 4 is arranged downstream of the filter 1, and the electric heater 4 is connected to an electric heater power source 5 and turned on/off.
It is connected to the off switch 6. An air supply device 7 having an air pump 7a is disposed further downstream of the electric heater 4, and this air supply device 7 supplies secondary air for particulate combustion from the outside into the main passage 3a during filter regeneration. Introduce. Optimal supply capacity Q of air supply device
(ffi/win) varies depending on the size of the filter l, and is calculated by the formula Q=20 to 30V, for example, when the filter volume is V(11).

The exhaust passage 3 is composed of a main passage 3a containing a filter l, and a sub passage 3b that branches from the main passage 3a on the upstream side of the filter l, and the sub passage 3b joins the main passage 3a on the downstream side of the filter 1. ing. Exhaust valves 8a are provided in the main passage 3a and the sub passage 3b, respectively.

8b is provided, and the exhaust valves 8a, gl) are connected to actuators 9a, 9b. Actuators 9a, 9
b is connected to the pressure tank 11 via the control valve 1 (la, 10b) and is connected to the actuator 9a.

9b and thus the exhaust valve are operated by compressed air supplied from the pressure tank 11.

In FIG. 3, 12 is an intake passage of the diesel engine 2, and 13 is an engine control computer. In addition to controlling the operating state of the engine 2, the computer 13
It controls the operation of the on/off switch 6 of the electric heater 4, the operation of the air pump a, and the operation of the control valve 10a110b.

In the figure, 14 indicates the rotation speed of the engine 2 by a computer 13.
15 is an input system for inputting the load of the engine 2 to the computer 13;
Reference numeral 16 indicates an input system for inputting the temperature distribution of the filter 1 to the computer 13.

Further, in the figure, 17 is an output system that transmits a control signal to the on/off switch 6 of the electric heater 4, 18 is an output system that transmits a control signal to the air pump 7a, and 19.20 is an output system that transmits a control signal to the air pump 7a.
are control valves 10a, respectively.

This is an output system that transmits a control signal to 10b.

FIGS. 4 and 5 show an example of filter l used in the present invention. The filter is formed of a porous ceramic material in a generally cylindrical shape, and the interior thereof extends from one end face 23 of the filter 1 to the other end face 24 of the filter 1.
It is partitioned into a honeycomb shape by a plurality of porous walls 22 that extend parallel to the axis of the membrane. One end surface 23 is connected to the downstream side of the exhaust passage, and the other end surface 23 is connected to the downstream side of the exhaust passage.
4 is connected to the upstream side of the exhaust passage.

A plurality of rectangular parallelepiped cells 131 lb defined by four adjacent porous walls 22 are formed inside the filter 1, and each cell la, lb extends from one end surface 23 of the filter 1 to the other end surface 24. extending parallel to the axis of the filter 1 up to . Cell la and cell lb basically have the same shape, both ends thereof are closed with a plug member 25, and the other end is open. One of the cells 1a forms a collection area, the closed end of which is located on one end surface 23 side of the filter l, and the open end thereof located on the other end surface 24 side of the filter l. On the other hand, the other cell lb forms a hollow region, the closed end of which is located on the end surface 24 side of the filter l, and the open end thereof located on the end surface 23 side of the filter l. These cells 1a and lb are arranged adjacent to each other, so that the cells la and lb are alternately located both vertically and horizontally, as shown in FIGS. 3 and 4. It turns out.

An electric heater 4 is provided in each collection area, and each electric heater 4 is connected to a filter l as shown in FIG.
are partially embedded in the plug members 25 on the end face 23 side of the cell 1a, that is, in the plug members 25 of the cell 1a.

As for the type of electric heater, in addition to the above-mentioned plug-in type, electric heaters such as sheathed heaters and ceramic heaters that are disposed close to the filter 1 can also be used.

The reference capacity of the electric heater 4 varies depending on the size of the filter 1. For example, if the filter diameter is D (mm), the reference heater capacity W (watts) is W=0.07 to 0.
．． Calculated using the formula 09D.

In the present invention, the capacity of the electric heater 4 is made different between regions R1 and R2, and in R1 it is set slightly lower than the reference heater capacity, and in R2 it is set slightly higher than the reference heater capacity.

The action will be explained below.

While the engine 2 is operating, the exhaust valve 8a is opened and the exhaust valve 8a is opened.
b is closed. Therefore, diesel engine 2
The exhaust gas flows into the main passage 3a and passes through the filter l through 81!
After particulates are removed by flowing in the directions of arrows c and d in Figure 4, they are discharged into the atmosphere.

As the engine 2 continues to operate, particulates in the exhaust gas are captured by the filter l, and particulates gradually accumulate in the filter l. On the other hand, the engine speed and engine load, which represent the operating state of the engine 2, are sequentially input to the computer 13 via input systems 14 and 15 and are integrated. Since the total amount of particulates trapped in the filter 1 is considered to increase as the engine speed and the integrated value of the engine load increase, when these integrated values reach a predetermined value, the computer 13 indicates that it is time to regenerate the filter 1. judge it as something.

If the computer 13 determines that the filter l should be regenerated, the computer 13 sends a lObJm control signal to the control valve 10a when the diesel engine 2 is stopped, thereby closing the exhaust valve 8a and opening the exhaust valve 8b. At this point, the electric heater 4 is not yet energized, and this state is maintained for approximately 30 seconds to 2 minutes, during which time the filter temperature is stabilized.

Next, the computer 13 turns on the on/off switch 6 of the electric heater 4, and energizes the electric heater 4 to heat the filter 1 and the particulates. however,
At this time, secondary air is not blown yet.

Since the electric heater 4 in the area R1 has a relatively low capacity and the electric heater 4 in the area R2 has a relatively high capacity, the amount of heat supplied to each surface area is small in the area R1 and large in the area R2. However, in the region R2, more heat is dissipated to the surroundings than in the region R1, and the region R1 is affected by the heat from the region R2. Therefore, the heating temperatures in both regions are approximately ideal and equal.

When the temperature of the filter 1 reaches an appropriate temperature of, for example, 750 to 850°C, the particulates are ignited, so the air pump 7a is operated to blow secondary air for particulate combustion into the main passage 3a of the exhaust passage 3. The flow of secondary air at this time is represented by arrows e and f in the fourth section. As a result, the particulates captured by the filter 1 are transferred from the end surface 23 (1'il) to the end surface 24 side through so-called backflow smoldering.
(backflow playback).

After a predetermined period of time has elapsed since the combustion started, there is no longer any danger that it will go out, so in order to reduce power consumption and prevent the filter from overheating, the electric heater 4 is turned off, and from then on, the combustion is continued until the particulates are burned out. It is preferable to continue blowing only the secondary air for a predetermined period of time. This time varies depending on the length of the filter 1. For example, if the axial length of the filter 1 is L (mm), the secondary air blowing time T (minutes) is calculated using the formula T = (103 ~ 0.07L). be done.

The heat generated during combustion of particulates is filtered through filter 1.
Therefore, the air passing through the cell lb, flowing through the porous wall 22, and flowing into the cell la is appropriately preheated without being preheated by the electric heater 4, and the particulates are combusted. promote.

As described above, one embodiment of the present invention has been described, but the present invention reduces the amount of heat supplied by the electric heater to a relatively small amount in the central region of the filter, which is affected by heat from the surroundings and is difficult to cool. Since the amount of heat is relatively increased in the peripheral area where it is easy to cool, in addition to changing the capacity of the electric heater as in the above embodiment, there is also a method of changing the energization time of the electric heater, or a method of changing the power supply time of the electric heater. The object of the present invention can be similarly achieved by a method in which both the capacitance and the energization time are changed.

Further, the number of sections of the electric heater may be three or more, such as a central portion, an intermediate portion, and an outer peripheral portion.

As mentioned above, the above embodiments are shown for illustration only, and the present invention is not limited to the above embodiments.
Various other modifications are possible.

(Effects of the Invention) As explained above, in the diesel particulate filter of the present invention, the electric heater is divided into at least the central part and the peripheral part, and the amount of heat supplied in the central part is relatively small, while the amount of heat supplied in the peripheral part is Since the amount of heat supplied is relatively large, it eliminates the tendency of overheating in the center and underheating in the periphery, which was a problem when supplying a constant amount of heat throughout the ignition area. The temperature can be made constant over the entire area, and therefore inconveniences such as overheating and melting of the filter in the center, unburned particulates, and extinguishing of particulates in the periphery can be prevented.

[Brief explanation of the drawing]

Fig. 1 is an end view on the heater side of a diesel particulate filter according to the present invention, Fig. 2 is a side view of the same filter, and Fig. 3 is an embodiment of a filter regeneration system using the same filter. 4 is a partial sectional view of an embodiment of the diesel particulate filter used in the present invention, and is a sectional view taken along line I-1 or line Il-Il in FIG. FIG. 5 is an end view of the filter of FIG. 4. R1...Central region, R2...Peripheral region 1...
Diesel particulate filter 2...Diesel engine 3...Exhaust passage 4...Electric heater 7...Air supply devices 8a, 8b...Exhaust valve 13...Computer Fig. 1 Fig. 2 Fig. 11, Figure 3 Deputy Attorney Patent Attorney Kyo Yu Asa (4 others) b 8b a 4

Claims (1)

[Claims] A diesel particulate filter is disposed in the middle of an exhaust passage of a diesel engine, and the filter is formed into a honeycomb shape using a porous material, and inside the filter is a particulate filter that communicates with the upstream side of the exhaust passage. A plurality of elongated collection regions and a plurality of elongated hollow regions each communicating with the downstream side of the exhaust passage are formed adjacent to each other alternately, and a downstream end of the collection region has a plurality of elongated collection regions and a plurality of elongated hollow regions each communicating with the downstream side of the exhaust passage. an electric heater for igniting the particulates, and a downstream end of the cavity region is connected to an air supply device for supplying secondary air for particulate combustion into the cavity region;
The electric heater is divided into at least a central part and a peripheral part of the filter, and the electric heater in the central part supplies a relatively small amount of heat, and the electric heater in the peripheral part supplies a relatively large amount of heat. Diesel particulate filter.