JPS60125715A - Method of treating exhaust gas of diesel engine - Google Patents

Abstract

PURPOSE:To suppress wasteful consumption of power and to prevent the filter from being molten and lost by causing heaters of a first group to generate heat every time a predetermined first constant period elapses and also causing heaters of a second group to generate heat every time a predetermined second constant period elapses. CONSTITUTION:The minute particle arresting filter 4 and the electric heater 5 are provided within the exhaust gas passage 3 of the Diesel engine, and the heater 5 is caused to generate heat every time a predetermined constant period elapses so as to burn and remove minute particles arrested and piled up within the filter 4. Upon this occasion, the electric heater 5 is divided into at least two groups. The heater 5 of the first group is caused to generate heat every time the first predetermined constant period elapses and the heater 5 of the second group is caused to generate heat every time the second predetermined period which is different from the above described first constant period elapses.

Description

[Detailed description of the invention] Industrial applications 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 provided 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 trapped and deposited on a filter. In such an exhaust treatment device, if more particles are not captured and deposited to the extent that they can be used in the heater and filter, the heater generates heat, but the particles accumulated in the heater will ignite, but the particles in the filter cannot be ignited and burned. Even if the heater generates heat in such a case, it will only consume electricity and it is wasteful. On the other hand, if the heater is made to generate heat when excessive particulates are deposited on the filter, the heat of combustion of the particulates in the filter becomes too high and there is a risk that the filter will melt. Therefore, in the past, the time when the optimum amount of particles would be deposited on the heater and filter was estimated in advance, and the heater was 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 particles deposited on the filter when the heater generates heat will be insufficient or excessive, and if the amount of particles is insufficient, the heater will not generate heat. In addition to wasting electric power, if the amount of particulates is too large, the filter may be eroded.

OBJECTS OF THE INVENTION The present invention provides an exhaust treatment method that suppresses unnecessary 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 heat the heater 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 a diesel engine main 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 normally discharged as shown by arrow A. It flows through the exhaust pipe 3-. A particulate capture filter 4 having a three-dimensional mesh structure made of, for example, cordierite is inserted into the exhaust pipe 3, and a heating device 5 is further 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.

The negative pressure actuator 9 has a negative pressure chamber 11 isolated from the atmosphere by a diaphragm 10, and the negative pressure chamber 11 is connected to a negative pressure tank 13 via an electromagnetic switching valve 12 that can communicate with the atmosphere. 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 to the atmosphere through a 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 the particulates from being released into the atmosphere. When the vehicle travels a predetermined distance or the engine rotates at a predetermined number of revolutions, the negative pressure chamber 11
is connected to the negative pressure tank 13, the bypass valve 7 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 of the five heating devices. The ignition flame then travels through the filter 4 in the direction of arrow A, and all particulates deposited within the filter 4 are combusted. 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, and 15d arranged at equal angular intervals.

15e and 15f, and these heaters 15a.

15b, 15c, 15d, 15e, 15f are respectively NO, 1, N112° teeth 3. Pottery 4. They are called NO, 5, positive 6 heaters. The inner end of each heater is grounded, and the outer end of each heater is connected to a corresponding terminal 16a, 16b, 16c, 16d.
, 16e, and 16f, respectively. The heaters on floors 1 to 6 are the three adjacent heaters No. 1, No. 2 heat, and the heaters on floor No. 3 and the three heaters No. 4 adjacent to each other.
No, 5 heak.

Divided into 11k16 heaters, positive 1 heater, No.
2 heaters, tooth 3 heaters are the first heater group, No.
, the 4th heater, the 5th floor heater, and the 6th floor heater form a second heater group, respectively. As described later, No. 1 heater, N12 heater, N11 belonging to the first heater group
The three heaters are made to generate heat every time a predetermined first period of time elapses, and the three heaters belong to the second heater group.
, No. 4 heater, 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 2o is composed of a digital computer, and R
OM (read only memory) 22, RAM (random access memory) 23, CPU (microprocessor) 24, input port 25 and output port 26. Furthermore, electronic control unit 20 is equipped with bidirectional bus 2.
A hack-up RAM 28 is connected to the CPU 24 via 7. The input boat 25 has a rotation speed sensor 3o
is connected.

On the other hand, the output port 26 is connected to the drive circuits 32, 32, 33, 3
4° 35, 36 to the corresponding heater terminal 16a
, 16b.

16c, 16d, 16e, and 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 described with reference to flowchart 1- shown in FIG. Referring to FIG. 3, first, in step 4o, it is determined whether or not it is the current playback time. This regeneration timing is different between the first heater group and the second heater group, as shown in FIG. That is, the heat generation time interval of the first heater group is (
As shown in I), the heat generation time interval of the second heater group is Y as shown in (+1), and
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 amplifier 28 based on the output signal of the engine rotation speed sensor 30, and from this accumulated rotation speed, the engine rotates at a constant rotation speed X or Y. Each time, it is determined that it is time to play.

If it is determined in step 40 that it is time for regeneration, the process proceeds to step 41, where it is determined whether the engine is in an operating state that requires regeneration, for example, whether the current engine speed is 2500 r, p, m or less. be done. The current engine speed is 25
If it is less than 0 Or, p, m, the process proceeds to step 42 and determines whether the heater that should generate heat is the first heater group or the second heater group.
It is determined whether it is a heater group. If the heater to generate heat is the first heater group, step 4
3, the heater is energized using the energization method shown in FIG. In addition, in FIG. 5, No. 1 to 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, the electromagnetic switching valve 12 is first energized and the negative pressure chamber 11 is connected to the negative pressure tank 13, so that the bypass valve 7 The valve is opened, and then the heaters No. 1 to I1lo and No. 3 are energized in sequence, for example, for 30 seconds each. As a result, the particulates on the end face of the filter 4 facing the heaters 111o and 1 to heaters 3 are sequentially burned. When the energization of the l1io, 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 as well, the heaters are energized using the energization method shown in FIG. That is, at this time as well, first the electromagnetic switching valve 12 is energized and the bypass valve 7 is opened, and then! The 1kL4 heater to the N[L6 heater are sequentially energized for, for example, 30 seconds each, and then, when the energization to the tooth 6 heater is completed, the electromagnetic switching valve 12 is deenergized and the bypass valve 7 is closed.

As described above, in the present invention, the first heater group is made to generate heat with the long interval X shown in FIG. 4, and the second heater group is made to generate heat with the short interval Y shown in FIG. The heat generation interval X of the first heater group is determined assuming that the engine is continuously operated at low load.
Therefore, since it takes time for the fine particles to accumulate at this time, the heating interval X becomes long. 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. It's 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.

As shown in FIG. 2, a first heater group 15a,
The heater groups 15b and 15c are arranged in a semicircular region in the upper half, and the second heater groups 15d, 15e and 15f are arranged in a semicircular region in the lower half. Therefore, for example, when the first heater group generates heat, particles on the end face of the filter 4 are ignited, and then the ignition flame travels inside the filter 4 in the axial direction of the filter 4 while spreading laterally. Therefore, at this time, the area in which 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 in the area shown by Q in FIG. 6 remain without being burned. The unburned particulates are combusted when the second heater group generates heat.

Even if high-load operation continues in this way and a large amount of particles accumulate on the filter 4 in a short period of time, the second
Since the heat generation time interval of the heater group is short, most of the particulates are burned off before the transient particulates are deposited on the filter 4.

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 eroded.

On the other hand, when low load operation continues and it takes time for sufficient particulates to accumulate on the heater and filter 4, the particulates in the filter 4 are ignited by the first heater group having a long interval X.

In this case, 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 example described so far, the heaters are divided into two groups, but it is also possible to divide the heaters into three or more groups and make the heat generation intervals of each heater group 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 particulates are burned off before excessive particulates accumulate on the filter, thereby 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, the amount of wasted power can be reduced.

[Brief explanation of drawings]

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 each FIG. 6 is a time chart of the heater energization control of the heater group, and is a side sectional view of the filter schematically shown. 3... Exhaust pipe, 4... Filter, 5... Heating device, 7... Bypass valve, 15a, 15b, 15c, 15d, 15e, 15f -
...Heater, 20...Electronic control unit. Patent applicant: Toyota Motor Corporation Patent agent: Akira Aoki, patent attorney: Kazuyuki Nishidate, patent attorney: Kyosuke Donakayama, patent attorney: Akira Yamaguchi, patent attorney: Masaya Nishiyama

Claims (1)

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