JPH0550568B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a burner air control device for a burner used for reburning a diesel particulate filter in a diesel exhaust gas purification 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 adjustment valve 15 and a solenoid valve 16. Note that the reference numeral 19 indicates a fuel regulating valve, and the reference numeral 20 indicates a pressure regulating valve.

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 output to the solenoid valve 16 based on the input signal from the atmospheric pressure sensor 18, and controls 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 the 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.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an improved burner air supply system for a diesel exhaust gas purification device equipped with a diesel particulate filter, which is capable of maintaining a constant weight flow rate of secondary air supplied to a filter regeneration burner with high precision. The purpose is to provide a control device.

The burner air control device according to the present invention includes a relief valve and a flow control valve provided in an air flow path from a positive displacement air pump to a regeneration burner, and a control section that controls the amount of opening and closing of the flow control valve. In this invention, the upstream pressure of the flow control valve is controlled to a constant gauge pressure by the relief valve so that the burner air weight flow rate is constant even if there are variations in the air pump, and the valve opening/closing of the flow control valve is controlled at atmospheric pressure and at the same time. It is controlled in response to changes in atmospheric temperature.

Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

FIG. 6 shows a burner air control device for a diesel particulate filter, which is an embodiment of the present invention. This burner air control device includes the same members as the conventional device shown in FIG. 5, and the same members will be given the same numbers to avoid confusion hereafter, and their repeated explanation will be omitted. The burner 4 that supplies hot air at a predetermined high temperature and with a predetermined excess air ratio to the filter 5 of the exhaust passage 3 receives secondary air from the secondary air pump 11 via the secondary air passage 21 . 2
The secondary air pump 11 causes air to flow into the secondary air passage 21 via the air filter 22, and a flow rate control valve 23 for increasing or decreasing the passage area of this secondary air passage.
It is supplied to the burner 4 via. Secondary air flow path 21
is equipped with a pressure sensor 24 and a temperature sensor 25 immediately before the flow control valve 23, and a pressure sensor 26 behind the flow control valve 23 for detecting the pressure there. These three sensors are connected to transmit their output signals to a controller 27 that controls the flow rate of secondary air. The flow control valve 23 has a valve body 28 integrally connected to a diaphragm 29, and an atmosphere open chamber 30 and a negative pressure chamber 31 equipped with a compression coil spring are opposed to the diaphragm. The valve body 28 is 2
It is attached to the next air flow path 21 so that the flow path area S thereof can be varied. This negative pressure chamber 31 is connected to the vacuum pump 14 via a duty solenoid valve 32. Duty solenoid valve 32 is 10Hz to 20Hz
The valve body is turned on and off at a frequency of Hz, and the pulse width, which is the ON time width of the valve body, is variably controlled by the output signal of the control unit 27, thereby changing the negative pressure value in the negative pressure chamber 31,
The valve body 28 is located at a position where this value and atmospheric pressure are balanced.
is moved to vary the flow path area S. The valve body 28 is displaced from the fully open position to the fully closed position, and the amount of this displacement is fed back to the control unit 27 from the position sensor 33 as an output signal corresponding to the variable electrical resistance value.

A relief valve 34 is attached to the secondary flow path 21 between the flow rate control valve 23 and the secondary pump 11 to release air therefrom to the atmosphere. A diaphragm 36 integral with the valve body 35 of this relief valve faces an atmosphere open chamber 37 and a negative pressure chamber 38. The negative pressure chamber 38 is connected to the vacuum pump 14 via a flow rate regulating throttle 39, and a negative pressure regulating path a between the throttle 39 and the negative pressure chamber 38 is provided with a negative pressure provided upstream of the relief valve 38. One chamber of the regulating valve 40 is connected. The negative pressure regulating valve 40 has an upstream chamber 41 that receives the pressure within the flow path on the inflow side of the flow rate control valve 23 and an atmospheric chamber 42 that is open to the atmosphere, and both chambers are separated by a diaphragm 43. The atmospheric chamber 42 is equipped with a compression coil spring 45, and is attached with a pipe 44 whose opening can be closed by a diaphragm 43 acting as a valve body. The outer end of this pipe is connected to the above-mentioned negative pressure adjustment path a side.

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

When the exhaust pressure upstream of the filter 5 exceeds a set value, the control unit 27 enters the reburning process. First, control section 2
7 issues a signal to turn on the primary and secondary air pumps 9 and 11, the vacuum pump 14, the fuel pump 10, the ignition coil 8, etc. At the same time, based on the output signal of the burner exhaust gas temperature sensor 46, if this is lower than the reference temperature T ₀ , the burner fuel flow rate value q ₀
An output signal is given to the heat amount regulating valve 17 to adjust the amount of heat to a larger q ₁ and vice versa to a smaller q ₂ .
On the other hand, the negative pressure regulating valve 40 detects fluctuations in the pressure inside the flow path on the inflow side of the flow control valve 23, and the inflow of the flow control valve 23 is constantly adjusted to the differential pressure with the atmospheric pressure set in the compression spring 45, that is, the gauge pressure. Relief valve 34 to keep the side
control. That is, when the differential pressure with respect to atmospheric pressure becomes large, the compression spring 45 is compressed, the pipe 44 is closed, all the negative pressure of the vacuum pump 14 is applied to the negative pressure chamber 38, and the valve body 35 moves relatively largely in the valve opening direction P. , the air in the secondary flow path 21 is released into the atmosphere to reduce the differential pressure. In this way, when the differential pressure decreases,
The pipe 44 opens, air flows into the negative pressure adjustment path a from the atmospheric chamber 42 side, and only a relatively weak negative pressure is applied to the negative pressure chamber 38, and the compression spring expands in length and the valve body 35 The valve moves in the valve closing direction C, thereby suppressing the release of air from the secondary flow path 21 and maintaining the differential pressure at a constant gauge pressure set by the spring 45. In this way, the pressure on the inlet side of the flow rate control valve 23 is maintained at a constant gauge pressure only by the pneumatic operation. On the other hand, negative pressure is applied to the negative pressure chamber 31 of the flow rate control valve 23 via the duty solenoid valve 32. In this case, the control unit 27 obtains a position signal for controlling the valve from a previously inputted map based on signals representing the pressure and temperature on the inflow side of the flow control valve and the pressure on the outflow side detected by each sensor. select. Then, the control section 27 changes the duty ratio to the duty solenoid valve 32 and outputs it so that the obtained position signal and the output signal fed back by the position sensor 33 match. As a result, while the secondary air passes through the secondary flow path 21, the weight flow rate is always adjusted to a constant value, and the secondary air is supplied to the burner 4.

FIG. 7 shows a flowchart for flow rate control in such a control section 27.
First, it is determined whether or not the secondary air pump 11 is on, and if it is not, the control ends, and the process returns to the original routine to proceed to other routine processing. When it is on, the pressure sensors 24 and 26 detect the pressure before and after the flow control valve ACV, and the temperature sensor 25 detects the pressure before and after the flow control valve ACV.
The pre-temperature of the OCV is detected and the opening area of the ACV is calculated from the reading from the position sensor 33.
Next, based on these data, calculate the weight flow rate of the secondary air.
Qg is calculated. This Qg is the differential pressure before and after the ACV,
It is determined from the air density before the ACV (calculated from the pressure and temperature before the ACV) and the ACV opening area.
The duty solenoid valve 32 is controlled so that if the calculated Qg is smaller than the target value, the valve opening area is increased, and if it is larger than the target value, the valve opening area is decreased. The pressure sensor 24 may be provided immediately after the air cleaner 22 to detect atmospheric pressure. This is because there is a correlation between atmospheric pressure and gauge pressure within the flow path. Of course, in this case, from the detected atmospheric pressure
The ACV front pressure will be calculated.

The burner air control device shown in FIG. 6 detects the inflow side pressure of the flow rate control valve 23 with a negative pressure regulating valve 40,
According to this detected value, the negative pressure value of the negative pressure adjustment path a is corrected and the relief valve 34 is operated. Instead, as shown in FIG.
It may be operated at an upstream pressure of . In this case, the diaphragm 55 separates an atmospheric chamber 53 equipped with a compression spring 52 that presses the valve body 51 in the valve-closing direction C and an upstream chamber 54 that receives upstream pressure of the flow rate control valve 23 . In this case, the upstream pressure is kept constant at the gauge pressure by the strength of the spring 52, and when the pressure in the secondary flow path 21 exceeds the set gauge pressure, the compression spring 52 is compressed and the valve body 51 is moved in the valve opening direction. P and vice versa, the compression spring 52 can expand and the valve body 5
1 moves in the valve closing direction C. As a result, the gauge pressure on the inflow side of the flow control valve 23 is always kept constant,
The effects of variations in the secondary pump itself are removed.
On the other hand, the flow rate control valve 23 maintains an appropriate flow path area S based on the output signals of the pressure sensors 24, 26 and the temperature sensor 25, as described in FIG. Therefore, the weight flow rate of the air that is more suitable for the burner 4 than the secondary flow path 21 can always be maintained constant.

As described above, according to the burner air control device of the present invention, the upstream pressure of the flow control valve is kept constant at the gauge pressure, so a constant weight flow rate of secondary air is supplied to the burner without being affected by variations in the flow rate of the air pump itself. Moreover, even if the downstream pressure of the flow control valve fluctuates, the load on the air pump remains almost constant, improving the durability of the pump, and the pump's discharge pressure remains constant even if the atmospheric pressure fluctuates. Since it is a constant gauge pressure, an inexpensive pump with a small capacity can be used. In addition, since the valve opening/closing amount of the flow control valve is controlled according to the pressure signal and/or temperature signal in the flow path, fluctuations in the weight flow rate of the secondary air due to fluctuations in atmospheric pressure, burner back pressure, and/or atmospheric temperature can be effectively accommodated. Can be corrected.

[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 is a graph showing 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 is a graph showing the conventional FIG. 6 is a control circuit diagram showing an example of a burner air control device.
A control circuit diagram showing an example of a burner air control device according to the present invention, FIG. 7 is a flow chart for burner air control in one embodiment of the present invention, and FIG. 8 is a control circuit diagram in another embodiment of the present invention. It is. 1...Engine, 3...Exhaust path, 4...Burner, 5...Filter, 6...Switching valve, 7...Bypass, 11...Secondary air pump, 14...Vacuum pump, 21...Air flow 22... Air cleaner, 23... Flow rate control valve, 24, 26... Pressure sensor, 25... Temperature sensor, 32... Duty solenoid valve, 34, 50... Relief valve, 40...
...Vacuum adjustment valve.

Claims (1)

[Claims] 1. An air flow path through which air discharged from a positive displacement air pump flows into a regeneration burner of a diesel particulate filter, a flow control valve for varying the flow path area of the air flow path, and a flow control valve for controlling the flow rate control valve. In order to maintain the pressure in the air flow path on the inflow side at a constant gauge pressure, there is a relief valve that releases part of the air flowing into the flow control valve into the atmosphere, and a pressure signal in the flow path to the flow control valve. A burner air control device comprising: and/or a control section that controls the amount of valve opening/closing according to a temperature signal.