JPH0550569B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for regenerating the filter by re-burning the collected particulate by a burner in a purification device of the type in which particulate matter contained in diesel exhaust gas is collected by a filter. This invention relates to a burner air control device.

To prevent pollution, particulate matter discharged from a diesel engine is usually removed from the exhaust by a ceramic diesel particulate filter, which is then re-burned at a designated time to regenerate the filter itself, and is discharged as a non-polluting substance. Ru. This re-burning of the particulate hydrate requires air that maintains an appropriate combustion temperature and an appropriate amount of oxygen, that is, a predetermined excess air ratio.If the heating temperature is low, the particulate ylate will not be removed, and if it is heated too much, the filter itself will burn out. However, there is a disadvantage in that it causes melting loss.

Incidentally, burners are often used as heating sources for filters, and among these, the most popular is the atomizing burner, which atomizes the fuel with high-pressure, small-flow primary air and burns particulate with low-pressure, large-flow secondary air. This is an 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 rate constant, the primary air amount 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 weight flow rate value necessary for combustion of the particulate is supplied. This secondary air is normally supplied using a positive displacement air pump, and although this air pump has a constant volume flow rate by keeping only the rotation speed constant, the weight flow rate changes depending on changes in atmospheric pressure and atmospheric temperature. susceptible to change. For this reason, it is necessary to take advantage of the advantage of positive displacement air pumps, which is ensuring a large discharge amount, while also correcting changes in weight flow rate. For example, as shown in FIG. 1, the atmospheric pressure decreases as the altitude increases, and the differential pressure across the air pump, that is, the differential pressure ΔP between the atmospheric pressure and the internal pressure of the air flow path changes accordingly. Note that b indicates pressure loss on the exhaust path side. FIG. 2 shows an example of the volume flow rate/discharge pressure characteristics of a positive displacement air pump, and it can be seen that the discharge pressure increases by reducing the flow rate on the discharge side. Furthermore, Fig. 3 shows an example of the weight flow rate/discharge pressure characteristics when the positive displacement air pump is located at a low altitude, indicated by a solid line, and when it is located at a high altitude, indicated by a broken line.When obtaining the same weight flow rate, It has been shown that 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 FIG. 4, even if the discharge pressure is constant, the weight flow rate fluctuates due to variations in the pump itself, changes in atmospheric temperature, etc.

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 includes a turbocharger 2, and a burner 4 and a filter 5 on the downstream side of an exhaust path 3,
Exhaust gas is released through a muffler (not shown) on the downstream side. 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;
The air from the secondary air pump 9 atomizes the fuel from the fuel pump 10, the air from the secondary air pump 11 maintains the excess air ratio of high temperature gas at a predetermined value, and the excess oxygen burns the particulate. 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 connected to a vacuum pump 14 via a vacuum control valve 15 and a solenoid valve 16. Note that reference numeral 19 indicates a fuel regulating valve, reference numeral 20 indicates a pressure regulating valve, and reference numerals 21 and 22 indicate an air cleaner.

If the filter 5 of the engine 1 is excessively coated with particulate matter, the controller 1
7 starts re-combustion, for example, by detecting that the exhaust passage pressure on the upstream side of the filter 5 exceeds a set value. In this case, if the atmospheric pressure is low at a high altitude, the controller 17 outputs an input signal from the atmospheric pressure sensor 18 to the solenoid valve 16 to control the flow area of the secondary air to increase by a certain amount from the reference value. This makes it possible to prevent a decrease in the weight flow rate due to a decrease in air density by increasing the volumetric flow rate. However, this method in which changes in atmospheric pressure are simply controlled by a diaphragm type flow control valve 13 that receives a constant negative pressure has the disadvantage that the accuracy of the flow rate of the secondary air is poor due to variations in the secondary air pump 11 itself. Also, while the filter 5 is being regenerated, the engine 1
In order to prevent the exhaust gas from having an adverse effect on the combustion conditions in the burner 4, the switching valve 6 is operated to pass the exhaust gas to the bypass 7, but when the engine is operated under high load, the exhaust gas pressure increases. This acts as a back pressure on the filter 5 and burner 4, which changes the flow rate of the secondary air. 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 diesel exhaust gas purification device equipped with a diesel particulate filter that can maintain a constant weight flow rate of secondary air supplied to a filter regeneration burner with high precision. An object of the present invention is to provide a burner air control device.

The burner air control device according to the present invention is equipped with a relief valve and a flow rate control valve in an air flow path that guides air discharged from a positive displacement air pump to a regeneration burner of a diesel particulate filter.
In order to keep the burner air weight flow rate constant even if there are variations in the air pump, the upstream pressure of the flow control valve is controlled to an absolutely constant pressure by the relief valve, and the valve opening area of the flow control valve is controlled according to the downstream pressure of the flow control valve. In other words, when the downstream pressure decreases, the valve opening area is decreased, and when the downstream pressure increases, the valve opening area is controlled to increase or decrease.

In this invention, since the upstream pressure of the flow control valve is maintained at an absolutely constant pressure, variations in the flow rate 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, so the burner Fluctuations in flow rate due to back pressure and changes in atmospheric pressure can be corrected.

An embodiment of the present invention will be described below with reference to FIG. The basic configuration of the burner combustion system is the same as the conventional example shown in FIG.
The control system for supplying secondary air is different from the conventional one. Secondary air pump 1 from air cleaner 22
A relief valve 23 and a flow control valve 24 are provided in the air flow path 12 leading to the burner 4 through the burner 4 in this order from the upstream side. Diaphragm 2 of relief valve 23
The lower chamber 26 partitioned by 5 is a conduit 27
The relief valve 23 is connected to the air passage 12 on the upstream side by an upstream pressure intake means such as
is connected to a constant pressure holding means, such as a constant pressure valve CPV or an aneroid bellows, which generates an absolutely constant pressure. 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 balanced with the operating pressure of this relief valve 23, and a portion of the air in the air flow path 12 is released to the atmosphere through the relief path 32. On the other hand, the flow rate control valve 24 on the downstream side of the relief valve 23 has a lower chamber 34 partitioned by the diaphragm 33 which is connected to the air flow path 12 on the downstream side by a downstream pressure intake means such as a conduit 35. The upper chamber 36 is connected to the constant pressure valve CPV.
or aneroid bellows. In the upper chamber 36, there is a diaphragm 33.
A compression coil spring 39 for constantly pressing the valve body 37 connected to the valve opening 38 in a direction that closes the valve opening 38.
is provided.

Next, the operation of this air control device will be explained. The pressure upstream of the relief valve 23 is applied to the chamber 26 below the relief valve 23, and the pressure upstream of the relief valve 23 is applied to the chamber 28 above.
Since an absolutely constant pressure is applied from the CPV, if the operating pressure of the relief valve 23 is, for example, 800 mmHg,
If the upstream pressure becomes higher than this, the upstream pressure chamber 26
pushes up the diaphragm 25, so the valve body 29
rises, some of the air on the upstream side is released into the atmosphere, and the upstream pressure decreases. Conversely, the upstream pressure is 800mmHg
When the pressure becomes lower than the constant pressure chamber 28, the diaphragm 25
, 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 maintained at an absolutely constant pressure. When the upstream pressure is maintained at an absolutely constant pressure in this way, even if there is a variation in the performance of the air pump 11, this can be absorbed and the weight flow rate control of the secondary air supplied to the burner 4 can be kept constant. However, if the upstream pressure of the flow control valve 24 is kept constant at 800 mmHg, the discharge pressure of the air pump 11 will be 40 mmHg at low altitude conditions where the atmospheric pressure is 760 mmHg, and the discharge pressure of the pump 11 will be 200 mmHg at high altitude conditions where the atmospheric pressure is 600 mmHg. If necessary, a large flow of secondary air will be supplied in the case of high altitude conditions. In the present invention, such flow rate fluctuations due to atmospheric pressure fluctuations are self-corrected by applying a constant pressure to the chamber 36 above the flow rate control valve 24 and applying its downstream pressure to the chamber 34 below. That is, when the downstream pressure of the flow control valve 24 becomes lower than its operating pressure due to high altitude conditions, the upper chamber 36 pushes down the diaphragm 33 and the valve body 37 narrows the valve opening 38,
Next, the weight flow rate of air is reduced. On the other hand, when the downstream pressure becomes higher than the operating pressure due to low altitude conditions, the lower chamber 34 pushes down the diaphragm 33 and the valve body 37 widens the valve opening 38, so that the weight flow rate of the secondary air increases. If there is only one muffler, when the engine is under high load during burner operation, the exhaust gas passing through the bypass 7 becomes back pressure and pushes up the downstream pressure of the flow control valve 24, so the valve body 37 rises at this time as well. The amount of secondary air is increased.

In an alternative embodiment of the invention shown in FIG. 7, the operation of the relief valve 23 is more precisely controlled by an associated vacuum regulating valve 40. 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. Upstream pressure of the flow rate control valve 24 is applied through a conduit 44 to the left chamber 43 partitioned by the diaphragm 42 of one vacuum regulating valve 40, and to the right chamber 45, a constant pressure valve CPV or an aneroid bellows is applied. A constant pressure is applied from a low pressure holding means. 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 .

As the pressure upstream of the flow control valve 24 increases, the diaphragm 42 of the vacuum regulating valve 40 is pushed down and closes the end of the conduit 47. As a result, the entire negative pressure from the vacuum pump is applied to the chamber 28 above the relief valve 23, so that the diaphragm 25 is suctioned and the valve body 29 is lifted, releasing some of the air in the flow path to the atmosphere. The upstream pressure of the flow control valve 24 is reduced. When the upstream pressure decreases in this way, the vacuum regulating valve 4
The diaphragm 42 of 0 is pushed back by the pressing force of the spring 46 provided in the right chamber 45, and the conduit
Since the end of is opened, a portion of the absolute pressure in the right chamber 45 escapes through the conduit 47 and enters the chamber 28 above the relief valve 23 by the action of the restriction 41 and presses the diaphragm 25 down, so that the valve body 29 throttles the valve opening 30 to maintain the upstream pressure of the flow control valve 24 at an absolutely constant pressure.

As described above, according to the burner air control device of the present invention, the upstream pressure of the flow control valve is maintained at an absolutely constant pressure, so even if the air pump flow rate varies, the constant air weight necessary for stable combustion in the burner is maintained. Since the flow rate is obtained and the flow rate control valve is controlled by the downstream pressure and an absolutely constant pressure, it is possible to follow fluctuations in atmospheric pressure and back pressure. However, since the upstream pressure is maintained at an absolutely constant pressure, the load on the air pump remains constant, improving the durability of the pump.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between altitude change and atmospheric pressure, Figure 2 is a graph showing discharge pressure/volume flow characteristics at different drive voltages of a positive displacement pump, and Figure 3 is a graph showing the relationship between altitude change and atmospheric pressure.
The figure shows the discharge pressure/weight flow rate characteristics at high and low altitudes, Figure 4 is a graph showing the discharge pressure/weight flow rate characteristics to explain the variation in the flow rate of the air pump itself, and Figure 5 shows the conventional FIG. 6 and FIG. 7 are control circuit diagrams showing an example of a burner air control device according to the present invention. DESCRIPTION OF SYMBOLS 1...Engine, 3...Exhaust path, 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 rate control valve, 40...Vacuum adjustment valve.

Claims (1)

[Claims] 1. A burner air control device for a diesel exhaust gas purification device, which is equipped with a relief valve and a flow rate control valve in order from upstream to an air flow path in which air discharged from a positive displacement air pump is sent to a regeneration burner of a diesel particulate filter, The relief valve is
The flow control 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 an absolutely constant pressure, and the flow control valve A burner air control device comprising means for taking in downstream pressure on one side so as to reduce the opening area, and means for taking in a constant pressure on the other side.