JPH0438891B2 - - 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 composed of 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. An exhaust gas treatment method is known in which a heater is made to generate heat for a certain period of time every time a certain period of time elapses to burn and remove particulates trapped and deposited in a filter. However, since this electric heater is supplied with power from the battery, when the battery voltage decreases, the temperature at which the heater generates heat also decreases, so even if the heater is allowed to generate heat for a predetermined period of time, it will not burn off the particles that have accumulated on the filter. The problem is that it is difficult to do so. On the other hand, if the set voltage of the heater is lowered in consideration of a decrease in battery voltage, the problem arises that the heater is overheated when the battery voltage is normal, resulting in damage to the heater.

OBJECTS OF THE INVENTION An object of the present invention is to provide an exhaust gas treatment method that can reliably burn off particulates deposited on a filter without damaging the heater even if the battery voltage fluctuates.

Structure of the Invention The structure of the present invention is to provide a particulate capture filter and a plurality of electric heaters in the exhaust passage of a diesel engine, and to sequentially heat the heaters every time a predetermined period of time elapses to trap particles in the filter. In the exhaust treatment method for burning off the particles, the battery voltage is detected, and as the battery voltage becomes lower, the time for energizing the heater is lengthened.

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 fire then advances within 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, 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 suppression 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.

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 battery 29 and a rotation speed sensor 30 are connected to the input port 25 . On the other hand, the output port 26 is connected to the corresponding heater terminals 16a, 16b, 16 via drive rotations 31, 32, 33, 34, 35, 36.
c, 16d, 16e, and 16f, and further connected to the electromagnetic switching valve 12 via a drive circuit 37.

Next, a method for controlling overheating of 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 the reproduction conditions are met. 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 this engine rotation speed reaches a predetermined rotation speed (for example, 100,000 rotations). When the current engine speed exceeds 2500 r.p.m or less, for example, it is determined that the regeneration condition has been met, and the process proceeds to step 41. step 41
Then, it is determined whether or not the output voltage of the battery 29 is within the range of 16 to 15 V. If it is within this range, the process proceeds to step 42 and the heater is energized using the energization method shown in FIG. In addition, No. 1 in Figure 4
~No. 6 indicates the heater number, and E indicates the electromagnetic switching valve 12. In the energization method shown in FIG. 4, 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
is opened, and then the No. 1 heater to the No. 6 heater are sequentially energized for a period of time t, for example, 30 seconds each. The current application time t at this time is indicated by _t1 in FIG. In addition, in FIG. 5, the horizontal axis t indicates the time during which electricity is applied to the heater, and the vertical axis T indicates the surface temperature of the heater. Further, on the vertical axis T in FIG. 5, P indicates the ignition temperature at which fine particles are ignited, and Q indicates the limit temperature at which the heater melts. The curve in FIG. 5 shows the rise in the heater surface temperature when the battery voltage is 16 to 15 V, and the heater is energized for a time _t1 until the heater surface temperature T reaches the ignition temperature P. In this manner, when each heater is sequentially energized during time _t1 , the particulates on the end face of the filter 4 facing each heater are sequentially burned. When the energization to the No. 6 heater is completed, the electromagnetic switching valve 12 is deenergized and the bypass valve 7 is closed.

Returning to FIG. 3 again, if it is determined in step 41 that the battery voltage is not within the range of 16 to 15V, the process proceeds to step 43, and the battery voltage is determined to be within the range of 15 to 14V.
It is determined whether or not it is within the range of . When the battery voltage is in the range of 15 to 14 V, the process proceeds to step 44, where the No. 1 heater to the No. 6 heater are sequentially energized for t ₂ hours, which is longer than t ₁ hour. As the battery voltage decreases, the rise of the heater surface temperature T is slow as shown in the curve, but by energizing the heater for ₂ hours, the heater surface temperature T reaches the ignition temperature P, and thus deposits are deposited on the filter 4. It is possible to burn off the fine particles.

On the other hand, when the battery voltage is lower and in the range of 14 to 11V, the process proceeds from step 45 to step 46, and at this time, the No. 1 heater to the No. 6 heater are energized for a period of time _t3 , which is longer than the time _t2 . At this time, the heater surface temperature T
The rise of the temperature becomes worse, but by energizing the heater _{for t3} hours, the heater surface temperature T reaches the ignition temperature P, and thus the particulates deposited on the filter 4 can be burned.

Effects of the Invention By lengthening the energization time to the heater as the battery voltage decreases, it is possible to reliably ignite and burn the particulates deposited on the filter even if the battery voltage decreases. Further, by increasing the energization time of the heater when the battery voltage decreases in this way, there is no need to increase the set voltage of the heater, so there is no risk of the heater being damaged.

[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 the heater energization control. FIG. 3 is a diagram showing the relationship between heater energization time and heater surface temperature. 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. A particulate capture filter and a plurality of electric heaters are installed in the exhaust passage of a diesel engine, and the heaters are sequentially made to generate heat every time a predetermined period of time elapses to burn and remove particulates trapped and deposited in the filter. In the exhaust gas treatment method for a diesel engine, the battery voltage is detected, and as the battery voltage decreases, the time for energizing the heater is lengthened.