JPS6050213A - Burner air controller for diesel exhaust emission control device - Google Patents

Abstract

PURPOSE:To make a rate of weight flow of secondary air so as to keep it constant in an accurate manner, by installing an escape valve and a flow control valve being controlled according to downstream pressure of the flow control valve and atmospheric pressure, in an air flow passage ranging from an air pump to a regenerating burner. CONSTITUTION:An air flow passage 12 makes the air discharged out of an air pump 1 flow in a regenerating burner 4 of a Diesel particulate filter 5. An escape valve 23 makes a part of inflow air into a flow control valve 24 discharged into the atmosphere so as to cause pressure inside the air flow passage at the inflow side of the flow control valve 24 to become constant in terms of gauge pressure. As for the flow control valve 24, since pressure at the downstream side is led into a diaphragm chamber 34 via a pipe 35 and atmospheric pressure is also led into a diaphragm chamber 36, it increases or decreases its opening area according to variation in the downstream pressure, while compensation in time of variation in the atmospheric pressure takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a purification device of a type in which particulates contained in diesel exhaust gas are collected by a filter, and the filter is regenerated by re-burning the collected particulates by a burner. The present invention relates to a burner air control device.

Particulates emitted from diesel engines are usually removed from the exhaust by a ceramic diesel particulate filter for pollution prevention purposes.
At a predetermined time, the filter is re-burned and discharged as a non-polluting substance. This re-burning of particulates requires air that maintains an appropriate combustion temperature and appropriate amount of oxygen, i.e., a predetermined excess air ratio.If the heating temperature is low, the particulates will not be removed, and if heated too much, on the other hand, If the filter itself is damaged by melting, there will be problems with temperature and corrosion.

Incidentally, a burner is often used as a heating source for filters, and in this burner, fuel is atomized using high-pressure, low-flow primary air, and particulates are combusted using low-pressure, high-flow secondary air. Burners are the most improved technology. The primary air supplied to the burner is approximately proportional to the fuel flow rate, and in order to keep the fuel flow constant, a portion of the air flow is normally kept constant. On the other hand, secondary air is required to have a low pressure but a large flow rate, and must be controlled so that only a predetermined amount of air necessary for combustion of the particulate rate is supplied. , 2. Secondary air is normally supplied using a positive displacement air pump, but with this air pump, if only the flow rate is kept constant, the volumetric flowmeter will be constant, but the volume flow meter will be constant depending on changes in atmospheric pressure and temperature. It is susceptible to changes in weight flow rate. For this reason, while taking advantage of the advantage of a positive displacement air pump, which is the ability to secure a large discharge area, the 4. −j#
Changes in volume need to be corrected. For example, as shown in Figure λ・1, the atmospheric pressure decreases as altitude increases, and the differential pressure before and after the air pump, that is, the differential pressure △P between the atmospheric pressure and the air flow path internal pressure, changes accordingly. . The problem is the exhaust path (f
The ill pressure J11 is shown. Fig. 2 shows an example of the volumetric flow rate/discharge pressure characteristics of a positive displacement air pump, and it can be seen that the discharge pressure increases by squeezing the flow rate of aJ: output @1.

Furthermore, Fig. 3 shows an example of the weight flow and t/discharge pressure characteristics when the positive displacement air pump is at a low altitude, indicated by the solid line, and at a high altitude, indicated by the broken line. It has been shown that in order to achieve this, it is necessary to lower the discharge pressure at high altitudes, that is, to lower the discharge pressure by widening the restriction of the air supply path than at low altitudes. Similarly, as shown in Figure 4, even if the discharge pressure is constant, the weight flow rate fluctuates due to variations in the pump itself and changes in the wetness of the air.

Next, an example of a conventional burner air control device using such a positive displacement air pump as a secondary air pump will be described with reference to FIG. The diesel engine 1 is equipped with a turbocharger 2, and a burner 4 is installed downstream of the exhaust path 3.
and a filter 5, and exhaust gas is discharged through a muffler (not shown) on the downstream side thereof. A bypass 7 having a switching valve 6 at its starting end is connected in the middle of the exhaust path 3, and its terminal end is connected to the downstream side of the filter 5. The burner 4 has an ignition device using an ignition coil 8, and uses air from a primary air pump 9 to atomize fuel from a fuel pump 10, and uses air from a secondary air pump 11 to set a predetermined excess air ratio of high-temperature gas. It is configured to maintain a constant value and burns the particulate with excess oxygen.

The flow area of the secondary air supply path 12 is increased or decreased by a flow rate control valve 13, and a vacuum chamber for opening and closing this valve is quickly connected to a vacuum pump 14 via a vacuum adjustment valve 15 and a solenoid valve 16. In addition, code 19 is a fuel adjustment valve, code 2
o represents a pressure regulating valve, and numerals 21 and 22 represent an air cleaner, respectively.

When the filter 5 of the engine 1 has excessive particulate matter attached to it, the controller 17 starts re-combustion, for example, by detecting that the exhaust passage pressure on the upstream side of the filter 5 has exceeded a set value. In this case, if the atmospheric pressure is low at a high altitude, the controller 17 outputs an output to the solenoid valve 16 based on an input signal from the atmospheric pressure sensor 18, and controls the flow area of the secondary air to be increased by a certain amount from the reference value. As a result, a decrease in weight flow rate due to a decrease in air density can be prevented by increasing the volumetric flow rate. However, in this method, where changes in atmospheric pressure are simply controlled by a diaphragm-type flow control valve that receives constant negative pressure, the secondary air pump 11
In addition to the variations in the secondary air flow 5-! [It has the disadvantage of being poor quality. Also, while the filter 5 is being regenerated, the exhaust gas from the engine 1 is flowing into the burner 4.
In order not to adversely affect the combustion conditions in the
is activated to pass the exhaust gas through the bypass 7. However, when the engine is operated under high load, the exhaust gas pressure increases and this acts as back pressure on the filter 5 and burner 4, which reduces the amount of secondary air. The flow rate will change.

Of course, if another muffler is attached to the bypass 7 to make the system independent, this problem will not occur, but an additional muffler will be required.

Therefore, an object of the present invention is to provide an improved burner air control device that can accurately maintain a constant weight flow rate of secondary air supplied to a filter regeneration burner in a diesel exhaust gas purification device equipped with a diesel particulate filter. Our goal is to provide the following.

The burner air control device according to the present invention is equipped with a relief valve and a flow rate control valve in the air flow path for guiding the air discharged from the positive displacement air pump to the regeneration burner of the diesel particulate filter. Also burner air mold technology.

The relief valve controls the upstream pressure of the flow control valve to a constant gauge pressure so that the flow rate remains constant, and the opening area of the flow control valve is increased or decreased according to the downstream pressure of the flow control valve, that is, the downstream pressure When the pressure rises above atmospheric pressure, the valve opening area is increased and a large amount of air is supplied to keep the weight flow meter constant.

In this invention, since the upstream pressure of the flow control valve is maintained at a constant gauge pressure VC, variations in the flow meter of the air pump can be absorbed, and the lift amount of the flow control valve is controlled according to the downstream pressure of the flow control valve. Therefore, flow rate fluctuations due to burner back pressure can be corrected. In this invention, it is not possible to correct the weight flow rate when atmospheric pressure fluctuates, but since there is a certain correlation between back pressure and atmospheric pressure,
Correction by back pressure can be replaced by correction by atmospheric pressure. Rather, the invention is well suited for application in systems where burner backpressure varies widely.

Hereinafter, one embodiment of the present invention will be described with reference to Fig. 6. The basic configuration of the burner combustion system is the same as the conventional example shown in FIG. 5, but the control system for supplying secondary air to the burner 4 is different from the conventional example. Air flow path 12 from air cleaner 22 to burner 4 via secondary air pump 11
A relief valve 23 and a flow control valve 24 are provided from the upstream side to l1liW. The lower chamber 26 separated by the diaphragm 25 of the relief valve 23 is connected to the conduit 27
The relief valve 23 is connected to the air passage 12 upstream of the relief valve 23 by a two-stream pressure intake means such as ``,'' and the chamber 28 is open to the atmosphere. A compression coil spring 31 is provided in the upper chamber 28 for constantly pressing the valve body 29 connected to the diaphragm 25 in a direction to close the valve opening 30. The strength of the spring 31 is set to a certain gauge pressure, for example 4
The pressure is determined to be such that a discharge pressure of 0 mmHg is maintained, and a part of the air in the air flow path 12 flows through the relief path 3.
It is released into the atmosphere through 2. On the other hand, the relief valve 23 with
The downstream flow rate control valve 24 has an upper chamber 34 partitioned by a diaphragm 33 that communicates with the downstream air passage 12 through a downstream pressure intake means such as a conduit 35, and a lower chamber 34 that is separated by a diaphragm 33. 36 leads to the atmosphere. Upper room 34
A compression coil spring 39 is provided for constantly pressing the valve body 37 connected to the diaphragm 33 in a direction to open the valve opening 38.

Next, the operation of this air control device will be explained.

The chamber 26VC below the relief valve 23 is connected to the relief valve 23.
Since the upper chamber 28 is open to the atmosphere, when the upstream pressure of the relief valve 23 becomes higher than the set gauge pressure, the upstream pressure chamber 26 pushes up the diaphragm 25, so that the valve body 29 rises, part of the air on the upstream side is released into the atmosphere, and the upstream pressure decreases. Conversely, when the upstream pressure becomes lower than the set gauge pressure, the atmospheric pressure *28 pushes down the diaphragm 25, so the valve body 29 descends to suppress the release of air, and the upstream pressure increases. In this way, the upstream pressure of the flow control valve 24 is kept constant at the gauge pressure. When the upstream pressure is kept constant at the gauge pressure in this way, even if there is variation in the performance of the air pump 11, it is possible to absorb this and keep the weight flow rate control of the secondary air supplied to the burner 4 constant. On the other hand, the flow rate side (the downstream pressure of the control valve 24 is atmospheric)
- When the pressure is higher than the upper chamber 34, the diaphragm 33
Since the valve body 37 opens the valve opening 38 by pushing down, the weight flow rate of the secondary air increases. As mentioned above, when there is only one muffler, when the engine is under high load while the burner is operating, the exhaust gas passing through the bypass 7 becomes back pressure and pushes up the downstream pressure of the flow control valve 24, so this situation will not occur. It often occurs.

In another embodiment of the present invention shown in FIG. 7, the operation of the relief valve 23 is more precisely controlled by a vacuum regulating valve 40 provided in connection therewith. Negative pressure from a vacuum pump is applied to the chamber 28 above the relief valve 23 via a restriction 41, and atmospheric pressure is applied to the chamber 26 below. A left chamber 43 partitioned by a diaphragm 42 of one of the vacuum regulating valves 40 is applied with upstream pressure of the flow control valve 24 through a conduit 44, and a right chamber 45 is applied with atmospheric pressure. The end of a conduit 47 leading to the chamber 28 above the relief valve 23 faces the surface of the diaphragm 42 facing the right chamber 45 and having the compression coil spring 46 .

When the upstream pressure of the flow control valve 24 increases, the vacuum circumference is adjusted.
0--Diaphragm 42 of valve 40 is depressed to block the end of conduit 47. As a result, the full angular pressure from the vacuum pump is applied to the chamber 28 above the relief valve 23, so the diaphragm 2
5 is sucked and the valve body 29 is lifted, releasing a part of the air in the flow path into the atmosphere, and lowering the pressure upstream of the flow control valve 24. When the upstream pressure decreases in this way, the diaphragm 42 of the vacuum regulating valve 40 is pushed back by the pressing force of the spring 46 provided in the right chamber 45, and the gfA section of the conduit 47 is opened, so that the pressure in the right chamber 450 is reduced. through conduit 47 into chamber 28 above relief valve 23, and diaphragm 25 is connected to spring 3 for setting the gauge pressure.
Since it is pushed down by the pressing force of J, the valve body 29 throttles the valve opening 3 () to keep the upstream pressure of the flow control valve 24 constant at the gauge pressure.

As described above, according to the burner air control device of the present invention, since the upstream pressure of the flow device σ41 valve is kept constant at the gauge pressure,
Even if the air pump flow rate varies, a constant air weight flow rate required for stable combustion in the burner can be obtained, and since the flow rate control valve is controlled by its downstream pressure, it is stable even when the back pressure fluctuates due to engine load fluctuations. can follow well.

Furthermore, even if such back pressure fluctuates, the upstream pressure is kept constant at the gauge pressure, so the load on the air pump remains constant, improving the durability of the pump.

Further, even if the atmospheric pressure fluctuates, the discharge pressure of the pump is maintained at 19 gauge pressure, so a small-capacity, inexpensive pump can be used.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between altitude changes and atmospheric pressure, Figure 2 is a graph showing the discharge pressure/volume flow characteristics of positive displacement pumps at different drive voltages, and Figure 3 is a graph showing the relationship between altitude changes and atmospheric pressure. Figure 4 shows a graph showing the discharge pressure/weight flow rate characteristics to explain the variation in the flow rate of the air pump itself. Figure 5 shows an example of a conventional burner air control device. Control circuit diagram shown, spear 6
Figures 2 and 7 are control circuit diagrams showing examples of the burner air control device according to the present invention. ]... Engine, 3... Exhaust 1t, 4... Burner,
5...Filter, 6...Switching valve, 7...Bypass, 11...Secondary air pump, 12...Air flow path,
22... Air cleaner, 23... Relief valve, 24...
...Flow control valve, 40...Vacuum adjustment valve 13-

Claims (1)

[Claims] A burner air control device for a diesel exhaust gas purification device, which is equipped with a relief valve and an elementary control valve from upstream to 7+@ in an air flow path that guides air discharged from a positive displacement air pump to a regeneration burner of a diesel particulate filter. , the relief valve includes means for taking in the upstream pressure of the flow control valve and releasing a portion of the pressure so as to maintain it at a constant gauge pressure; A burner air control device comprising means for taking in downstream pressure on one side and means for taking in atmospheric pressure in opposition to the downstream pressure so as to increase the valve opening area.