JPH0561448B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for treating exhaust gas from a diesel engine.

Prior art In order to prevent particulates, mainly carbon, contained in the exhaust gas of a diesel engine from being released into the atmosphere, a particulate capture filter and an electric heater are installed in the exhaust passage of the diesel engine, and the electric heater generates heat. There is known an exhaust treatment device that burns and removes particulates captured and deposited on a filter. In such an exhaust treatment device, if a certain amount of particulates are not captured and deposited in the heater and filter, even if the heater is made to generate heat, the particulates deposited on the heater will ignite, but the particulates in the filter will not be able to ignite and burn. Even if the heater generates heat at times like this, it would just eat up electricity and be wasteful. On the other hand, if the heater is made to generate heat when excessive particulates are deposited on the filter, the combustion heat of the particulates in the filter will become too high and there is a risk that the filter will melt. Conventionally, therefore, the time when the optimum amount of fine particles will be deposited on the heater and filter is estimated in advance, and the heater is made to generate heat at predetermined fixed time intervals based on this assumption.

However, in reality, particulates tend to accumulate on the filter when the engine is operating at high load, and it is difficult for particulates to accumulate on the filter when the engine is operating at low load, so the amount of particulates that accumulate on the filter changes depending on the operating state of the engine. Therefore, if the heater is simply made to generate heat at fixed time intervals as in the past, the amount of particulates deposited on the filter when the heater heats up will be insufficient or excessive, and if the amount of particulates is insufficient, Problems arise in that the electric power used to generate heat from the heater is wasted, and if the amount of fine particles is excessive, the filter is melted and damaged.

Purpose of the Invention The present invention provides an exhaust gas treatment method that suppresses wasteful consumption of electric power for heat generation by a heater, prevents the filter from melting, and allows fine particles accumulated on the filter to be ignited and burned in a good manner. There is a particular thing.

Structure of the Invention The structure of the present invention is to provide a particulate capture filter and an electric heater in the exhaust passage of a diesel engine, and to make the heater generate heat every time a predetermined period of time elapses to burn and remove particulates trapped and deposited in the filter. In the exhaust treatment method, the electric heaters are divided into at least two groups, and the heaters in the first group are made to generate heat every time a predetermined first period of time elapses, and the heaters in the second group are The purpose is to generate heat every time a predetermined second fixed period different from the first fixed period elapses.

Embodiment Referring to FIG. 1, 1 is the diesel engine body, 2 is an exhaust turbocharger, and 3 is an exhaust pipe connected to the exhaust outlet of the exhaust turbocharger 2. Exhaust gas is usually passed through the exhaust pipe as shown by arrow A. Flows within 3. A particulate capture filter 4 made of, for example, cordierite and having a three-dimensional mesh structure is inserted into the exhaust pipe 3, and a heating device 5 is disposed in front of the filter 4. On the other hand, a bypass passage 6 is formed in the exhaust pipe 3 to bypass the filter 4 and the heating device 5, and a bypass valve 7 is inserted into the bypass passage 6. The bypass valve 7 is connected to a negative pressure actuator 9 via a rod 8, and the opening and closing of the bypass valve 7 is controlled by the negative pressure actuator 9. Negative pressure actuator 9 is diaphragm 1
The negative pressure chamber 11 has a negative pressure chamber 11 isolated from the atmosphere by a solenoid switching valve 1 that can communicate with the atmosphere.
2 to a negative pressure tank 13. The negative pressure chamber 11 is normally open to the atmosphere via the electromagnetic switching valve 12, and the bypass valve 7 is closed as shown in FIG. Therefore, the exhaust gas is normally discharged into the atmosphere through the filter 4 as indicated by arrow A. At this time, the particulates contained in the exhaust gas adhere and accumulate inside the filter 4 having a mesh structure, thus suppressing release of the particulates into the atmosphere. When the vehicle travels a predetermined distance or when the engine rotates a predetermined number of revolutions, the negative pressure chamber 11 is connected to the negative pressure tank 13 and the bypass valve 7 is activated.
is opened, and as a result, most of the exhaust gas is discharged to the atmosphere via the bypass passage 6. When the bypass valve 7 opens, the heating device 5 generates heat, thereby igniting and burning the particulates deposited on the end face of the filter 4 on the side of the heating device 5. The ignition flame then moves through the filter 4 in the direction of arrow A, and all the particulates deposited within the filter 4 are burned. Then, the heat generating action of the heating device 5 is stopped, and the bypass valve 7 is closed again. In this way, the emission of particulates into the atmosphere is suppressed.

FIG. 2 shows a front view of the heating device 5 and a circuit diagram of the electronic control unit 20. Referring to FIG. 2, the heater 5 includes six sector-shaped electric heaters 15a, 15b, 15c, arranged at equal angular intervals.
These heaters 15a, 15b, 15c, 15d, 15e,
15f respectively No.1, No.2, No.3, No.4, No.5, No.
It is called 6 heater. The inner end of each heater is grounded and
The outer end of each heater has a corresponding terminal 16a, 16
b, 16c, 16d, 16e, and 16f, respectively. Heaters No. 1 to No. 6 are placed in three adjacent heaters.
It is divided into three heaters: No. 1 heater, No. 2 heater, No. 3 heater, and three adjacent heaters: No. 4 heater, No. 5 heater, and No. 6 heater. 2 heaters, no.
3 heaters make up the first heater group, No. 4 heater,
The No. 5 heater and the No. 6 heater form a second heater group, respectively. As will be described later, the No. 1 heater, No. 2 heater, and No. 3 heater belonging to the first heater group are made to generate heat every time a predetermined first period of time elapses, and the No. 4
The heaters, No. 5 heater, and No. 6 heater are made to generate heat every time a predetermined second fixed period different from the above-mentioned first fixed period elapses.

On the other hand, the electronic control unit 20 is composed of a digital computer, and includes a ROM (read only memory) 22 and a ROM (read only memory) 22 connected to each other by a bidirectional bus 21.
It includes a RAM (random access memory) 23, a CPU (microprocessor) 24, an input port 25, and an output port 26. Furthermore, the electronic control unit 20 communicates with the CPU 24 via a bidirectional bus 27.
It is equipped with a backup plum 28 connected to.
A rotation speed sensor 30 is connected to the input port 25 . On the other hand, the output port 26 is connected to the drive circuits 32 and 3.
Corresponding heater terminals 16a, 16b, 16c, 16d, 16 via 2, 33, 34, 35, 36
e, 16f, and further connected to the electromagnetic switching valve 12 via a drive circuit 37.

Next, a heating control method for the heater will be explained with reference to the flowchart shown in FIG. Referring to FIG. 3, first, in step 40, it is determined whether or not it is currently playback time. This regeneration timing is determined by the first heater group and the second heater group as shown in Figure 4.
There are differences in heater groups. That is, the heat generation time interval of the first heater group is X as shown in (), and the heat generation time interval of the second heater group is Y and X as shown in ().
is longer than Y. Note that the periods X and Y are determined based on the distance traveled by the vehicle or the cumulative rotational speed of the engine. In the embodiment shown in FIG. 2, these periods X and Y are determined based on the cumulative rotational speed of the engine. That is, the engine rotation speed is accumulated and stored in the backup plum 28 based on the output signal of the engine rotation speed sensor 30, and the engine rotates by a certain rotation speed X or Y from this accumulated rotation speed. It is determined that it is the playback time each time.

If it is determined in step 40 that it is time for regeneration, the process proceeds to step S41 where it is determined whether the engine is in an operating state that requires regeneration, for example, the current engine speed is
It is determined whether or not it is 2500r.pm or less. If the current engine speed is less than 2500 rpm, the process proceeds to step 42, where it is determined whether the heater to be generated is the first heater group or the second heater group. When the heater to generate heat is the first heater group, the process advances to step 43, and the fifth heater group
The heater is energized by the energization method shown in the figure.
In FIG. 5, No. 1 to No. 6 indicate the heater numbers, and E indicates the electromagnetic switching valve 12. As shown in FIG. 5, when the heater that should generate heat is the first heater group, first the electromagnetic switching valve 12
is energized and the negative pressure chamber 11 is connected to the negative pressure tank 13, thereby opening the bypass valve 7, and then sequentially from the No. 1 heater to the No. 3 heater.
For example, the power is turned on for 30 seconds at a time. As a result, No.
The fine particles on the end face of the filter 4 facing the No. 1 heater to the No. 3 heater are sequentially burned. When the energization of the No. 3 heater is completed, the electromagnetic switching valve 12 is deenergized and the bypass valve 7 is closed.

On the other hand, when it is determined in step 42 of FIG. 3 that the heaters that should generate heat belong to the second heater group, the process proceeds to step 44, and at this time also, the heaters are energized using the energization method shown in FIG. That is,
At this time, the electromagnetic switching valve 12 is first energized to open the bypass valve 7, and then the No. 4
The heaters are sequentially energized, for example, for 30 seconds each, and then, when the energization of the No. 6 heaters is completed, the electromagnetic switching valve 12 is deenergized and the bypass valve 7 is closed.

In this way, in the present invention, the long interval X shown in FIG.
This causes the first heater group to generate heat,
The second heater group is made to generate heat even with the short interval Y shown in FIG. The heat generation interval X of the first heater group is determined based on the assumption that the engine is continuously operated at a low load.
is getting longer. On the other hand, the heat generation interval Y of the second heater group is determined based on the assumption that the engine is continuously operated under high load.
is getting shorter. Therefore, no matter what kind of operation is performed, particles will always be ignited by either the first heater group or the second heater group.

The first heater group 1 as shown in FIG.
5a, 15b, 15c are arranged in the upper half semicircular area, and the second heater group 15d, 15
e and 15f are arranged in the lower half semicircular area. Therefore, for example, when the first heater group generates heat, the particles on the end face of the filter 4 are ignited.
The ignition flame then travels inside the filter 4 in the axial direction of the filter 4 while expanding laterally. Therefore, at this time, the area where the particulates are burned and removed is most of the area, as shown by P in FIG. 6, and a small part of the particulates, shown by Q in FIG. 6, remain without being burned. The unburned particulates are combusted when the second heater group is heated.

Even if high-load operation is continued in this way and a large amount of particles accumulate on the filter 4 in a short period of time, transient particles will accumulate on the filter 4 because the heat generation time interval of the second heater group is short. Most of the particulates are burnt off before being removed. The unburned particulates are then combusted by the first heater group, but since the amount of particulates to be combusted at this time is small, the heat of combustion of the particulates is also small, and the filter 4 will not be damaged by melting.

On the other hand, when low-load operation continues and it takes time for sufficient particulates to accumulate in the heater and filter 4, the particulates in the filter 4 are ignited by the first heater group with a long interval X. . At this time, even if the second heater group is made to generate heat, ignition may not occur because sufficient particulates are not deposited inside the heater and filter 4. However, since only the second heater group, which is a part of the heaters, is made to generate heat, the power required for generating heat is not wasted so much.

In the embodiments described so far, the case has been described in which the heaters are divided into two groups, but the heaters can also be divided into three or more groups and the heat generation intervals of each heater group can be made different from each other. Moreover, each heater configuring each heater group can be composed of every other heater.

Effects of the Invention No matter what operating conditions the engine is operated under, most of the particulates are burned and removed before excessive particulates accumulate on the filter, thus preventing the filter from being eroded due to combustion of excessively deposited particulates. I can do it. Furthermore, even if some of the heaters are made to generate heat, the particulates may not be combusted, but since only some of the heaters are made to generate heat, unnecessary power consumption can be reduced.

[Brief explanation of the drawing]

Figure 1 is an overall view of the internal combustion engine, Figure 2 is a diagram showing the electronic control unit and heating device, Figure 3 is a flowchart of heater energization control, Figure 4 is a time chart of heater energization control, and Figure 5 is a diagram showing the heater energization control. A time chart of heater energization control for each heater group, FIG. 6 is a side sectional view of a filter schematically shown. 3...Exhaust pipe, 4...Filter, 5...Heating device, 7...Bypass valve, 15a, 15b, 15
c, 15d, 15e, 15f...heater, 20...
...Electronic control unit.

Claims (1)

[Claims] 1. An exhaust treatment method in which a particulate capture filter and an electric heater are provided in the exhaust passage of a diesel engine, and the heat is generated every time a predetermined period of time elapses to burn and remove particulates trapped and deposited in the filter. The electric heaters are divided into at least two groups, the heaters in the first group are made to generate heat every time a predetermined first period of time elapses, and the heaters in the second group are made to generate heat every time a predetermined first period elapses, and the heaters in the second group are made to generate heat every time a predetermined first period elapses. A diesel engine exhaust treatment method in which heat is generated every time a second predetermined period of time different from the above elapses.