JP2990761B2 - Exhaust gas purification device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus that collects soot contained in exhaust gas of a diesel engine or the like with a filter and incinerates the collected soot.

[Prior Art] Diesel engine exhaust gas contains carbon fine particles (soot) mainly generated by combustion.
Is contained at a high concentration, which causes pollution. For this reason, the exhaust system of a vehicle equipped with a diesel engine is provided with an exhaust gas purifying device that collects soot in the exhaust gas with a filter.

In recent years, in order to prevent the filter from being clogged, compressed air (backwash air) is applied to the filter in a direction opposite to the flow of the exhaust gas, soot is separated and dropped from the filter, and collected in a heater chamber. A technique has been developed in which incineration is carried out (for example, JP-A-2-45609 "Particulate trap device").

[Problems to be Solved by the Invention] Soot adhering to the above-mentioned filter is not only separated and dropped from the filter at the time of backwashing in which backwash air is applied to the filter, but not only at this time but also during normal operation of the engine. Peeling / falling from a small amount Therefore, in the conventional exhaust gas purifying apparatus, the electric heater is always operated to burn this soot. However, this has a problem that the electric heater consumes a large amount of power, and the battery and the generator of the vehicle have a large burden.

By the way, according to the study of the present inventor, soot collected in the heater chamber ignites and burns at approximately 600 ° C. or higher, but once it ignites, it spreads and self-ignites. It turned out that there was no need to keep working. That is, if the electric heater is operated after soot has accumulated to some extent in the heater chamber and the self-ignition combustion of the soot is used, it is not necessary to continue operating the electric heater.

An object of the present invention, which has been made in view of the above circumstances, is to provide an exhaust gas purifying apparatus that reduces power consumption of a heater.

Means for Solving the Problems In order to achieve the above object, the present invention provides a filter provided in an exhaust system for adhering soot in exhaust gas, and the filter has a direction opposite to the flow of the exhaust gas. Backwash means for supplying air to the filter to separate and drop soot from the filter, a heater chamber for collecting and incinerating the dropped soot, and detecting at least one of the temperature and the amount of collected soot in the heater chamber. Control means for turning on the heater in the heater chamber only when at least one of the condition that the temperature is equal to or lower than the predetermined temperature and the condition that the soot collection amount is equal to or higher than the predetermined amount is provided.

[Operation] The heater is turned on by the control means only when the soot temperature in the heater chamber is equal to or lower than a predetermined temperature (for example, the self-ignition combustion temperature) or when the soot collection amount in the heater chamber becomes equal to or higher than the predetermined amount. It is turned off when the soot temperature is higher than a predetermined temperature (self-ignition combustion temperature) or when the soot collection amount is less than the predetermined amount. As a result, the power consumption of the heater is reduced.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an outline of an exhaust gas purifying apparatus 1 for removing soot from exhaust gas of a diesel engine. As shown in the figure, the soot removal chamber 3 is formed by expanding the diameter of the exhaust pipe from the engine 2 to the muffler. The soot removal chamber 3 is vertically partitioned by a filter 4 into an exhaust introduction chamber 5 and a heater chamber 6.

The filter 4 is made of, for example, a porous gas-permeable material such as a ceramic porous material, and has a plurality of cylindrical exhaust gas passages 7 formed vertically. More specifically, the filter 4 includes an upper plate 8 that partitions the side of the exhaust introduction chamber 5, a lower plate 9 that partitions the side of the heater chamber 6, and a space between the upper plate 8 and the lower plate 9. And a plurality of exhaust gas passages 7 formed of a porous ventilation material so as to communicate with the exhaust gas passage 6.

As shown in FIG. 1, the side of the filter 4 having such an exhaust gas passage 7 communicates with the muffler-side exhaust pipe 10. The muffler-side exhaust pipe 10 is separated from the exhaust introduction chamber 5 and the heater chamber 6 by the filter 4. A seal member 11 is provided at each of the contact portions between the muffler-side exhaust pipe 10, the exhaust introduction chamber 5, the heater chamber 6, and the filter 4, to prevent exhaust leakage.

According to this configuration, as shown in FIG.
Exhaust gas 12 flows from the exhaust introduction chamber 5 into the heater chamber 6 through the exhaust gas passage 7 of the filter 4, and fills the inside of the heater chamber 6 and the exhaust gas passage 7. Thereafter, the exhaust gas 12 is permeated and discharged from the side of the exhaust gas passage 7 into the muffler-side exhaust pipe 10, and at this time, the soot 13
Will adhere to the inner surface of the exhaust gas passage 7.

Compressed air 14 (hereinafter referred to as "backwash air 14") is supplied into the muffler-side exhaust pipe 10 in a direction opposite to the flow of the exhaust gas 12, so that the soot 13 adhering to the inner surface of the exhaust gas passage 7 is separated and dropped. A backwashing means 15 is provided. This backwashing means 15
An air nozzle 16 provided in the muffler side exhaust pipe 10 toward the side of the filter 4, an air tank 17 for supplying backwash air 14 to the air nozzle 16, and an air tank 17 between the tank 17 and the nozzle 16. It comprises an on-off valve 18 provided in the air pipe and an on-off valve 19 provided in the muffler-side exhaust pipe 10 on the downstream side of the flow of the exhaust gas 12 from the air nozzle 16. A compressor (not shown) is connected to the air tank 17, and the inside of the air tank 17 is maintained at a predetermined pressure.

The backwashing means 15 is automatically operated by the CPU 20 when the cumulative rotation speed of the engine 2 or the cumulative fuel injection amount of the injection pump exceeds a predetermined value.

That is, when the cumulative number of revolutions of the engine 2 or the cumulative fuel injection amount of the injection pump exceeds a predetermined value, the CP 4 is used to prevent clogging of the filter 4 caused by long-term use.
As shown by the dashed line in FIG. 1, U20 gives a valve closing command to the on-off valve 19, closes the on-off valve 19, and closes the muffler side exhaust pipe 10. Thereafter, the CPU 20 gives an opening / closing command to the opening / closing valve 18, controls the opening / closing of the opening / closing valve 18, and supplies the backwash air 14 intermittently (pulsewise) from the air nozzle 16 toward the side of the filter 4.

Then, the backwash air 14 acts on the filter 4 in a direction opposite to the flow of the exhaust gas 12, soot 13 attached to the inner surface of the exhaust gas passage 7 of the filter 4 is separated, and the lower heater chamber 6 is removed. Will fall inside.

As shown in FIG. 1, an electric heater 21 for burning the fallen soot 13 is accommodated in the heater chamber 6. When the soot 13 is burned, a combustion residue (hereinafter referred to as “ash”) is generated. In order to remove this ashes from the heater chamber 6, the inside of the heater chamber 6 and the inside of the muffler side exhaust pipe 10 are communicated by a bypass passage 22. I have. That is, the assembly inside the heater chamber 6 is sent to the muffler side exhaust pipe 11 through the bypass passage 22 together with the combustion gas. The bypass passage 22 is provided with an orifice 23 for reducing the passage area.

In the heater chamber 6, a soot temperature sensor 24 for measuring the temperature of the soot 13 collected in the heater chamber 6 is provided.
A soot collection amount sensor 25 for measuring the collection amount of thirteen is provided.

The soot temperature sensor 24 uses a general thermocouple. The soot temperature sensor 24 is connected to the CPU 20 online. Then, when the soot temperature is 600 ° C. or less, the CPU 20 turns on the switch 26 of the electric heater 21, and when the soot temperature exceeds 600 ° C., the soot self-ignites and burns, so the switch 26 of the electric heater 21 is turned off. It has become.

On the other hand, as shown in FIG. 2, the soot collection amount sensor 25 includes a chamber wall 27 of the grounded heater chamber 6 and an electrode housed in the heater chamber 6 so as not to contact the heater chamber wall 27.
28, and a resin 29 coated on the electrode 28. According to this configuration, soot 13 is provided in heater chamber 6.
When the soot 13 accumulates, the soot 13 is substantially made of carbon and has conductivity, so that the heater chamber wall 27 and the electrode 28 are short-circuited via the soot 13 and the resin 29.

At this time, the capacitance between the heater chamber wall 27 and the electrode 28 is
Heater chamber wall 27 and electrodes short-circuited by soot 13 (conductor)
28 and the capacitance of the resin 29. That is, the capacitance between the heater chamber wall 27 and the electrode 28 is, as shown in FIG.
It will increase as the soot 13 is stacked. Therefore, if the capacitance is measured, the amount of soot 13 collected in the heater chamber 6 can be determined.

The soot collection amount sensor 25 is also connected to the CPU 20 online, similarly to the soot temperature sensor 24. When the capacitance of the soot collection amount sensor 25 exceeds the predetermined value x, the CPU 20 determines that the collection amount of the soot 13 in the heater chamber 6 has exceeded X, and the electric heater in the heater chamber 6 21 switches 16
Is turned on.

Soot temperature sensor 24, soot collection amount sensor 25 and CP
U20 serves as control means for controlling ON / OFF of the heater 21 based on the temperature of the soot 13 in the heater chamber 6 and the amount of soot 13 collected.

 The operation of the present embodiment having the above configuration will be described.

During operation of the engine 2, when the CPU 20 detects that the cumulative number of revolutions of the engine 2 or the cumulative fuel injection amount of the injection pump has exceeded a predetermined value, the CPU 20 sets the muffler side exhaust pipe 1 shown in FIG.
A valve closing command is given to the on-off valve 19 in 0, the on-off valve 19 is closed, and the muffler side exhaust pipe 10 is closed. Thereafter, the CPU 20 gives an open / close command to the open / close valve 18 on the air pipe, controls the open / close valve 18 to open / close, and intermittently (pulses) the backwash air 14 from the air nozzle 16 toward the side of the filter 4. Supply. Then, the backwash air 14 acts on the filter 4 in a direction opposite to the flow of the exhaust gas 12, and separates the soot 13 attached to the inner surface of the exhaust gas passage 7 of the filter 4. The stripped soot 13 falls into the lower heater chamber 6 and is collected there.

The soot 13 collected in the heater chamber 6 measures the soot temperature T and the soot collection amount M by the soot temperature sensor 24 and the soot collection amount sensor 25 in the heater chamber 6, as shown in FIG. Is done. This measurement may be performed at all times, or may be performed intermittently at appropriate time intervals.

When the condition of T <600 ° C. and M> X is satisfied, the CPU 20 turns on the heater 21. If this condition is not satisfied, the CPU 20 turns off the heater.

That is, the heater 21 operates only when the temperature T of the soot 13 is 600 ° C. or less in a state where the amount M of the soot 13 is somewhat larger (X or more in FIG. 2). Conversely, if the temperature T of the soot 13 is equal to or higher than 600 ° C., the heater 21 is turned off because the soot 13 self-ignites and burns.

As described above, since the heater 21 is appropriately turned ON and OFF in accordance with the temperature T of the soot 13 collected in the heater chamber 6 and the soot collection amount M, the power consumption of the heater 21 is reduced. Become. Therefore, the burden on the battery and generator of the vehicle is reduced.

FIG. 5 shows a modified example of the soot collection amount sensor 25. As shown in the figure, the soot trapping amount sensor 25 is composed of a light emitting diode 30 and a phototransistor 31 provided on the heater chamber walls 6a and 6b opposite to the heater chamber 6, respectively. The light emitting diode 30 and the phototransistor 31 form a circuit shown in FIG.
When the soot 13 accumulates, the optical path from the light emitting diode 30 to the phototransistor 31 is blocked by the soot 13, so that the output voltage is reduced as shown in FIG. Has become.

In addition, only one of the temperature sensor 24 and the soot collection amount sensor 25 is provided, and as shown in FIG. 8, the soot temperature T or the soot collection amount M is measured, and either T or M is measured. If the condition of T <600 ° C., M> X is satisfied, the heater 21 may be turned on, otherwise, the heater 21 may be turned off.

[Effects of the Invention] As described above, according to the exhaust gas purification device of the present invention, the heater is turned on only when the soot temperature is equal to or higher than the predetermined temperature or the soot collection amount is equal to or higher than the predetermined amount. Since the heater is turned off, an excellent effect that the power consumption of the heater can be greatly reduced can be exhibited.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an exhaust gas purifying apparatus showing one embodiment of the present invention, FIG. 2 is a side sectional view showing a soot collecting amount sensor in FIG. 1, and FIG. FIG. 4 is a flowchart showing the control means, FIG. 5 is a side sectional view showing a modified example of the soot collection amount sensor, FIG.
FIG. 7 is a circuit diagram of the soot trapping amount sensor, FIG. 7 is an output voltage characteristic diagram of the soot trapping amount sensor, and FIG. 8 is another flowchart of the control means. In the figure, 1 is an exhaust gas purifying device, 4 is a filter, 6 is a heater chamber, 12 is exhaust gas, 13 is soot, 14 is backwash air as compressed air, 21 is a heater, and 20, 24, and 25 are control means. is there.

Claims (1)

(57) [Claims] 1. A filter provided in an exhaust system for adhering soot in exhaust gas, and a reverse air for supplying soot to the filter in a direction opposite to the flow of the exhaust gas to separate and drop soot of the filter. Washing means, a heater chamber for collecting and incinerating soot that has fallen, and detecting at least one of the temperature and the amount of soot in the heater chamber. The condition that the soot temperature is equal to or lower than a predetermined temperature and the amount of soot collection are determined. A control unit for turning on the heater in the heater chamber only when at least one of the conditions equal to or more than a fixed amount is satisfied.