JPH0532655B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention detects an air-fuel ratio based on the temperature of a flame formed in a combustion section, and maintains the detected air-fuel ratio within an appropriate range. The present invention relates to a control device for a forced combustion combustion device that controls at least one of the amount of fuel supplied and the amount of combustion air.

[Prior art] In addition to supplying fuel to the combustion section, combustion air necessary for complete combustion of the fuel supplied to the combustion section is forcibly supplied to the combustion section, and the fuel is combusted in the combustion section. There is a forced combustion type combustion device that performs this.

In this forced combustion type combustion device, the fuel supplied to the combustion section must be completely combusted by the combustion air forcibly supplied to the combustion section. Therefore, at least one of the fuel supply amount and the combustion air amount is controlled by the control device so that the air-fuel ratio is maintained within an appropriate range with excess air (lean).

Note that this control device requires an air-fuel ratio detection means to detect the air-fuel ratio. As this air-fuel ratio detection means, there is one that detects the air-fuel ratio from the temperature of the flame formed in the combustion section. As shown in Figure 5, this is because the air-fuel ratio is approximately 0.9 and the flame combustion speed is fast.
This takes advantage of the fact that the combustion rate slows down as the air-fuel ratio moves away from 0.9. This is because when the temperature of the flame is detected (assuming that combustion is on the lean side of the stoichiometric air-fuel ratio), as the temperature rises, the air-fuel ratio decreases (shifts to the rich side).
Conversely, as the temperature decreases, the air-fuel ratio increases (shifts to the lean side).In other words, by comparing the flame temperature and combustion amount,
It is capable of detecting the air-fuel ratio.

For example, a thermocouple is used as a means for detecting the flame temperature. This thermocouple takes time to heat up or cool down when the air/fuel ratio changes and the flame temperature changes. Similarly, when the amount of combustion changes, it takes time for the thermocouple to heat up or cool down.
Therefore, a time error occurs between the actual change in the combustion state and the change in the combustion state detected by the thermocouple.

Therefore, if the air-fuel ratio changes or the combustion amount changes, the actual combustion state and the combustion state detected by the thermocouple will differ. Then, the control device controls at least one of the fuel supply amount or the combustion air supply amount based on a value different from the actual combustion state detected by the thermocouple, and keeps the air-fuel ratio within an appropriate range. try to keep it. As a result, as shown in FIG. 10, the air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio.

The speed at which the conventional air-fuel ratio shifts to the rich side and the speed at which the air-fuel ratio shifts to the lean side are:
It was at a similar speed. In other words, in order to control the air-fuel ratio, the control device maintains the same speed at which the fuel increases or decreases or the speed at which the air flow increases or decreases. As a result, under the control of the conventional control device, the time period during which the combustion state exists on the rich side from the target air-fuel ratio due to overshoot and the time period during which the combustion state exists on the lean side are basically the same length.

[Problems to be Solved by the Invention] FIG. 11 shows a time chart showing the relationship between the output of the thermocouple and the state of the flame when the air-fuel ratio is changed. Note that the solid line in the figure shows the air-fuel ratio shifted from an appropriate value to the rich side, and the solid line shows the air-fuel ratio shifted from the appropriate value to the lean side.

As can be seen from the time chart in Figure 11, when the air-fuel ratio is shifted to the lean side, the combustion speed slows down, the flame lifts, and misfire occurs in a short time (15 seconds in this example). Conversely, when the air-fuel ratio is shifted to the rich side, the combustion speed increases,
There is a long margin of time (200 seconds in this example) for a flashback (for example, the formation of a flame on the back side of a ceramic burner) to occur.

In other words, the actual combustion state may be on the rich side from the target air-fuel ratio for a long time, but the longer the time on the lean side, the higher the possibility of lift and misfire.

For this reason, in conventional control devices, as mentioned above, the time when the actual combustion state exists on the rich side from the target air-fuel ratio due to overshoot is basically the same length as the time when the actual combustion state exists on the lean side. Therefore, the actual combustion state remains on the lean side for a long time, increasing the possibility of misfire.

The present invention was made in view of the above circumstances, and
The purpose is to provide a control device for a forced combustion type combustion device that can shorten the time during which the actual combustion state exists on the lean side from the target air-fuel ratio, and can prevent misfires due to flame lift.

[Means for Solving the Problems] In order to achieve the above object, the control device for the forced combustion type combustion apparatus of the present invention includes a combustion section that burns fuel, as shown in the schematic block diagram of FIG. 1
and a fuel supply means 2 for supplying fuel to the combustion section 1.
and a blower 3 that forcibly supplies combustion air necessary for burning the fuel supplied to the combustion section 1 by the fuel supply means 2 to the combustion section 1.
and air-fuel ratio detection means 4 for detecting the air-fuel ratio based on the temperature of the flame formed in the combustion section 1, and the amount of fuel supplied by the fuel supply means 2 according to the air-fuel ratio detected by the air-fuel ratio detection means 4. , or the blower 3
In the forced combustion type combustion apparatus, the forced combustion type combustion apparatus includes a control device 5 that corrects and controls at least one of the air flow rates and maintains the air-fuel ratio within an appropriate range.
is equipped with a rich control means 6 that increases the rate of increase in fuel or decreases the rate of air flow when shifting the air-fuel ratio to the rich side, and controls the rate of increase in fuel when shifting the air-fuel ratio to the lean side. The technical means is to include lean control means 7 that slows down the rate of decrease or slows down the rate of increase in air flow.

[Operation] The operation of the control device for the forced combustion type combustion device configured as described above will be explained.

(b) The amount of fuel supplied to the combustion section increases, the amount of combustion air supplied decreases and the actual air-fuel ratio shifts to the rich side, or the amount of combustion increases and the flame Air-fuel ratio control when the temperature rises will be explained.

As the actual temperature of the flame increases, the temperature of the flame detected by the air-fuel ratio detection means also increases. However, the temperature of the flame detected by the air-fuel ratio detection means is
Since there is a time delay with respect to the actual change in flame temperature, a temperature lower than the actual temperature is detected.

When the air-fuel ratio detection means detects a temperature lower than the actual temperature, the control device attempts to maintain the air-fuel ratio within an appropriate range based on the temperature lower than the actual flame temperature. In other words, the rich control means operates to shift the air-fuel ratio to the rich side and return the air-fuel ratio to an appropriate value.

The rich control means shifts the air-fuel ratio to the rich side in a short time by increasing the rate of increase in fuel or increasing the rate of decrease in air flow. As a result, the air-fuel ratio is lower than the target air-fuel ratio.
The time it takes to shift to the rich side is longer than before.

(b) Conversely, if the amount of fuel supplied to the combustion section decreases, the amount of combustion air increases and the actual air-fuel ratio shifts to the lean side, or the amount of combustion decreases. , air-fuel ratio control when the flame temperature drops will be explained.

As the actual flame temperature decreases, the flame temperature detected by the air-fuel ratio detection means also decreases. However, the temperature of the flame detected by the air-fuel ratio detection means is
Since there is a time delay with respect to the actual change in flame temperature, a temperature higher than the actual temperature is detected.

When the air-fuel ratio detection means detects a temperature higher than the actual flame temperature, the control device attempts to maintain the air-fuel ratio within an appropriate range based on the temperature higher than the actual flame temperature. In other words, the lean control means operates to shift the air-fuel ratio to the lean side and return the air-fuel ratio to an appropriate value.

The lean control means slow down the rate of fuel loss;
Alternatively, the air-fuel ratio is slowly shifted to the lean side by slowing down the rate of increase in the amount of air blown.
As a result, the time during which the air-fuel ratio is leaner than the target air-fuel ratio can be suppressed to be shorter than in the past.

[Effects of the Invention] Since the present invention is configured as described above, it produces the effects described below.

When the air-fuel ratio is shifted to the rich side by the air-fuel ratio detection means, the time to shift to the rich side becomes longer, and conversely, when the air-fuel ratio is shifted to the lean side, the time to shift to the lean side is shortened. .

Therefore, it is possible to shorten the time that the air-fuel ratio exists on the lean side from the target air-fuel ratio, and prevent misfires due to flame lift. In addition, conversely, the time required to exist on the rich side is longer than before, but there is a long margin of time for problems (for example, misfires and backfires) to occur due to being on the rich side. Even if the existing time is a little longer than before, no problem will occur.

[Embodiment] Next, a control device for a forced combustion type combustion apparatus of the present invention will be described based on an embodiment shown in the drawings.

(First Embodiment) FIG. 2 shows a schematic diagram of a bypass mixing type gas water heater to which the present invention is applied.

This gas water heater is broadly divided into a combustion passage 10 having a combustion section 11 for burning gas, a gas supply pipe 20, a water pipe 30, and a control device 40.

The combustion passage 10 has a ceramic surface combustion type burner 12 disposed therein. This burner 12
Upstream of the gas supply pipe 20, the combustion air necessary for combusting the gas supplied from the gas supply pipe 20 in the combustion part 11 on the upper surface of the burner 12 is forced into the combustion part 11.
A blower 13 is attached to supply air to the air. Further, downstream of the combustion passage 10, an exhaust port (not shown) is provided for discharging the combustion gas generated in the combustion section 11.

The gas supply pipe 20 is a fuel supply means of the present invention, and supplies fuel gas to a nozzle 21 opening on the inner periphery of the centrifugal fan 14 of the blower 13. Note that the gas flowing out from the nozzle 21 is transferred to the blower 13.
The combustion air is mixed with the combustion air by the air flow generated by the combustion air, and is supplied to the combustion section 11. Gas supply piping 20
A main solenoid valve 22, a main solenoid valve 23, and a proportional valve 24 are provided in this order from the upstream side. The downstream side of the proportional valve 24 is branched into two parts, one of which has a switching solenoid valve 2.
5, the other is provided with an orifice 26. The main solenoid valve 22, the main solenoid valve 23, and the switching solenoid valve 25 open and close the gas supply pipe 20 through energization control, and the proportional valve 24 has an opening ratio that changes depending on the amount of energization, and This is to adjust the amount of gas supplied to the

One end of the water pipe 30 is connected to a water supply source,
The other side is connected to the hot water supply port, and heat exchanger 31 exchanges heat generated by combustion of gas with water flowing inside to heat the water passing through the inside.
and a bypass waterway 32 that bypasses this heat exchanger 31.

The water pipe 30 upstream of the branch path between the heat exchanger 31 and the bypass waterway 32 is equipped with a governor valve that keeps the amount of water flowing into the heat exchanger 31 and the bypass waterway 32 constant even if the water pressure flowing into the heat exchanger 31 and the bypass waterway 32 changes. An electric water flow control device 33 is provided which combines the function of a water flow control valve and the function of a water flow control valve that adjusts the water flow. Further, the bypass waterway 32 is provided with a throttle valve 34 that can adjust the amount of water passing through the bypass waterway 32 and open and close the bypass waterway 32 .

Note that the throttle ratio of the electric water flow control device 33 is set to be the same as or smaller than the throttle valve 34 in order to regulate the total amount of water flowing into the heat exchanger 31 and the bypass waterway 32. Further, the electric water flow control device 33 and the throttle valve 34 use a geared motor to drive a valve body that can open and close the waterway as means for adjusting the water flow.

As shown in FIG. 3, the control device 40 is composed of a microcomputer 41, a relay circuit 42, and a drive circuit 43, and according to the outputs of a controller 44 and various sensors operated by the user, Sparker 4 ignites burner 12
5, original solenoid valve 22, main solenoid valve 23, proportional valve 24,
The switching solenoid valve 25, the electric water flow control device 33, and the throttle valve 34 are energized and controlled.

Various sensors of the control device 40 include a flame rod 46 that detects the flame of the burner 12, and a flame rod 46 that detects the air-fuel ratio by detecting the temperature of the flame of the burner 12.
Thermocouple 4 which is the air-fuel ratio detection means of the present invention
7. Potentiometers 48 and 49 that are linked to the electric water flow control device 33 and the valve body of the throttle valve 34 to detect the opening degree of the valve body, a rotation speed sensor 50 that detects the rotation speed of the blower 13, and a heat exchanger 31 an incoming water temperature sensor 51 that detects the temperature of water upstream of the bypass waterway 32; a temperature sensor 52 that detects the temperature of the hot water that has passed through the heat exchanger 31; It includes an outlet hot water temperature sensor 53 that detects the temperature, a water amount detection sensor 54 that detects the amount of water flowing into the heat exchanger 31 and the bypass waterway 32.

Next, combustion control by the computer 41 will be briefly explained.

The combustion control in this embodiment is a fan-driven type.
The fan preceding type of this embodiment determines the rotational speed of the blower 13 so that the airflow amount is obtained according to the combustion amount determined by the control device 40, and from the rotational speed of the blower 13, the gas is The opening degree of the proportional valve 24 and the opening/closing of the switching solenoid valve 25 are determined so that the combustion section 11 obtains the following. The amount of gas supplied to the combustion section 11 is corrected based on the temperature of the flame detected by the thermocouple 47 to keep the air-fuel ratio constant. Note that the rotational speed of the blower 13 may be corrected based on the temperature of the flame detected by the thermocouple 47 so that the amount of gas supplied does not change.

Specifically, when the user operates a collar connected to the hot water supply inlet and a water flow is generated in the water pipe 30, the water amount detection sensor 54 detects the water flow and combustion is started. The amount of combustion after combustion starts is determined by controller 4.
In order to obtain the set temperature set by step 4, the temperature is determined from the amount of water obtained by various sensors, the temperature of incoming water, the temperature of hot water passing through the heat exchanger 31, the temperature of mixing hot water (temperature of hot water coming out), etc. . The voltage of the blower 13 is controlled so as to supply the burner 12 with an air volume corresponding to a determined combustion amount. Then, the proportional valve 24 and the switching solenoid valve 25 are controlled to be energized so that a gas amount corresponding to the rotational speed of the blower 13 and the temperature of the flame of the burner 12 is obtained. The amount of combustion is determined so that the temperature of the hot water passing through the heat exchanger 31 is maintained at a temperature (e.g., 60°C) or higher at which water generated by combustion (drain water) does not adhere to the heat exchanger 31. be done.

Next, the water amount control by the computer 41 will be briefly explained.

The throttle valve 34 is fixed at an appropriate opening calculated from the incoming water temperature, the set temperature, the temperature of the hot water that has passed through the heat exchanger 31, and the outlet temperature. Note that this fixation is set so that the flow rate flowing through the bypass waterway 32 is twice the amount of water flowing through the heat exchanger 31. That is, the ratio of flow resistance between the bypass waterway 32 and the heat exchanger 31 is set to about 2:1 by the throttle valve 34.
Further, the fixed opening degree of the throttle valve 34 is released when the amount of water entering is small or when the temperature of hot water exiting is to be lowered.
The throttle valve 34 is energized and controlled so as to have an opening degree calculated according to the amount of water entering and the temperature of hot water exiting.

Further, the electric water flow rate control device 33 is controlled to be energized so as not to exceed the maximum flow rate required to obtain the hot water temperature.

Next, the rich control means 55 and lean control means 56 programmed into the computer 41 will be explained.

As mentioned above, the air-fuel ratio in the combustion section 11 is
The gas supply amount is changed and controlled according to the output of the thermocouple 47.

The starting force of the thermocouple 47 corresponds to the combustion amount, as shown in FIG. Further, as shown in FIG. 5, when the air-fuel ratio changes, the combustion rate changes. Then, when the combustion speed shifts to the rich side compared to the target air-fuel ratio, the combustion speed becomes faster and the flame temperature becomes higher. Conversely, when the combustion speed shifts to the lean side, the combustion speed becomes slower and the flame temperature becomes lower. Therefore, the air-fuel ratio can be maintained at an appropriate value by correcting and controlling the gas amount so that a starting force corresponding to the combustion amount is obtained.

The microcomputer 41 of the control device 40 of this embodiment controls the combustion state to be lower than the target air-fuel ratio when the temperature of the flame detected by the thermocouple 47, that is, the starting force is lower than the electromotive force corresponding to the combustion amount. The rich control means 55 is activated. This richness control means 5
5 shifts the air-fuel ratio to the rich side, and in this embodiment, the proportional valve 24 and the switching solenoid valve 25
control and increase the amount of gas supplied. The rate of increase is faster than the rate of decrease by the lean control means 56 described below, and the rate of increase is limited to, for example, 500 kcal/s.

Conversely, the microcomputer 41 determines that when the temperature of the flame detected by the thermocouple 47, that is, the starting force is higher than the electromotive force corresponding to the combustion amount, the combustion state shifts to the richer side than the target air-fuel ratio. The lean control means 56 is activated.
The lean control means 56 shifts the air-fuel ratio to the lean side, and in this embodiment controls the proportional valve 24 and the switching solenoid valve 25 to reduce the amount of gas supplied. The rate of decrease is slower than the rate of increase by the above-mentioned rich control means 55, and the rate of decrease is limited to, for example, 30 kcal/s.

Note that the temperature of the thermocouple 47 does not suddenly change even if it is heated or cooled due to a change in the temperature of the flame. As a result, the air-fuel ratio fluctuates,
When the combustion amount changes and the actual flame temperature changes, the flame temperature detected by the thermocouple 47 will be
A time error occurs between the temperature and the actual flame temperature.

Next, the operation of air-fuel ratio correction will be briefly explained.

(α) Immediately after the amount of combustion increases, such as immediately after the amount of water detected by the water amount detection sensor 54 increases, or immediately after the set temperature of the controller 44 is set to a high temperature side, the times a to b in FIG. As such, the temperature detected by the thermocouple 47 does not follow the actual flame temperature and lags behind.

In other words, due to the delay in the detection speed of the thermocouple 47, the thermocouple 47 outputs a starting force corresponding to a temperature lower than the actual flame temperature. Therefore, the microcomputer 41 determines that the combustion state has shifted to the leaner side than the target air-fuel ratio, and operates the rich control means 55. The rich control means 55 rapidly increases the amount of gas supplied. By rapidly increasing the amount of gas supplied, the air-fuel ratio quickly shifts to the rich side, the combustion speed increases over time, and the actual combustion amount also increases in a short period of time. As a result, the actual flame temperature increases rapidly.

As the temperature of the actual flame increases, the electromotive force of the thermocouple 47 exceeds the electromotive force set according to the rotational speed of the blower 13 (time b).

Since the actual air-fuel ratio was in a rich state between times a and b, the thermocouple 47
It overshoots and outputs an electromotive force higher than the electromotive force set according to the rotational speed of the blower 13 (times b to c). Therefore, the microcomputer 41 determines that the combustion state has shifted to the richer side than the target air-fuel ratio, and operates the lean control means 56. By the function of this lean control means 56, the amount of gas supplied is gradually reduced. As the amount of gas supplied decreases, the air-fuel ratio gradually shifts to the lean side, the combustion speed gradually slows down, and the actual combustion amount also gradually decreases. As a result, the actual flame temperature decreases over a long period of time.

As the actual temperature of the flame decreases, the electromotive force of the thermocouple 47 falls below the electromotive force set according to the rotational speed of the blower 13 (time c).

In the latter half of times b to c, the actual air-fuel ratio was considered to be lean, so the thermocouple 47
overshoots again and outputs an electromotive force lower than the electromotive force set according to the rotational speed of the blower 13 (times c to d). Therefore, the microcomputer 41 determines that the combustion state has shifted to the leaner side than the target air-fuel ratio, and operates the rich control means 55.

The rich control means 55 and the lean control means 5
6 work alternately, the actual air-fuel ratio repeatedly overshoots the target air-fuel ratio, and the actual air-fuel ratio converges to the target air-fuel ratio.

(β) Contrary to the above example, immediately after the amount of water detected by the water amount detection sensor 54 decreases, or immediately after the set temperature of the controller 44 is set to a low temperature side, immediately after the combustion amount decreases, the seventh Figure time e
As shown in ~f, the temperature detected by the thermocouple 47 does not follow the actual flame temperature and lags behind.

In other words, due to the delay in the detection speed of the thermocouple 47, the thermocouple 47 outputs an electromotive force corresponding to a higher temperature than the actual flame temperature. Therefore, the microcomputer 41 determines that the combustion state has shifted to the richer side than the target air-fuel ratio, and operates the lean control means 56. The lean control means 56 gradually reduces the amount of gas supplied. As the amount of gas supplied increases and decreases, the air-fuel ratio gradually shifts to the lean side from the target air-fuel ratio, and the combustion speed gradually slows down.
The actual combustion amount also decreases slowly. As a result, the actual temperature of the flame also slowly decreases.

As the actual temperature of the flame decreases, the electromotive force of the thermocouple 47 becomes lower than the electromotive force set according to the rotational speed of the blower 13 (time f).

Since the actual air-fuel ratio was in a lean state during times e to f, the thermocouple 47
It overshoots to the lean side and outputs an electromotive force lower than the electromotive force set according to the rotational speed of the blower 13 (times f to g). For this reason,
The microcomputer 41 determines that the combustion state is moving toward a leaner side than the target air-fuel ratio, and operates the rich control means 55. Due to the function of the rich control means 55, the amount of gas supplied is quickly increased. By increasing the amount of gas supplied, the air-fuel ratio quickly shifts to the rich side, and the combustion rate increases in a short period of time.
The actual amount burned also increases quickly. As a result, the actual flame temperature also rises quickly.

As the temperature of the actual flame increases, the electromotive force of the thermocouple 47 exceeds the electromotive force set according to the rotation speed of the blower 13 (time g). In other words, in the second half of time f to g, the actual air-fuel ratio was in a rich state, so the thermocouple 47 overshot again.
A higher electromotive force is output than the electromotive force set according to the rotational speed of the blower 13 (times gh to h).
Therefore, the microcomputer 41 determines that the combustion state has shifted to the richer side than the target air-fuel ratio, and operates the lean control means 55.

That is, the lean control means 56 and the rich control means 55 work alternately, and the actual air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio.

As shown above, when the amount of sintering changes,
The actual air-fuel ratio repeatedly overshoots the target air-fuel ratio and converges to the target air-fuel ratio. When this overshoot is repeated, the actual air-fuel ratio takes a longer time to shift to the rich side than the target air-fuel ratio, and conversely, the time it takes to shift to the lean side becomes shorter.

In other words, the time during which the actual air-fuel ratio exists on the lean side from the target air-fuel ratio can be shortened. Therefore, misfires due to flame lift can be prevented.

On the other hand, the time it remains on the rich side is longer than before, but since there is a long margin of time for backfire to occur due to its presence on the rich side, the time it remains on the rich side is longer than before. No backfire occurs even after aging.

Note that although the air-fuel ratio changes due to overshoot, the range of the change is within a proper air-fuel ratio range, and no problem occurs in combustion.

In addition, in the above embodiment, the example was shown when the combustion amount changed, but when the gas supply amount or the combustion air amount changes,
Through the same operation as above, the actual air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio. When overshooting is repeated, the actual air-fuel ratio takes a longer time to shift to the richer side than the target air-fuel ratio, and conversely, the time it takes to shift to the leaner side becomes shorter. Therefore, the time that the air-fuel ratio remains on the lean side from the target air-fuel ratio can be shortened, and misfires due to flame lift can be prevented.

Note that possible causes of the change in the amount of gas supplied during combustion include changes in the amount of gas used by other gas appliances connected to the same gas supply pipe and fluctuations in the gas supply pressure. In addition, even if the rotational speed of the blower is constant, the amount of combustion air supplied during combustion changes.
Possible causes include a change in the amount of air blown that occurs during the transition to combustion, and a case where an air resistance object is placed at the opening that takes in combustion air into the combustion passage 10.

(Second example) FIG. 8 shows a schematic configuration diagram of the second embodiment.

In this embodiment, when the air-fuel ratio is shifted to the lean side by the lean control means 56, the air-fuel ratio is shifted to the lean side quickly at first, and then shifted to the lean side at a slow speed.

Further, in the forced combustion type combustion apparatus of this embodiment, as in the above embodiment, the blower is driven at a rotational speed according to the combustion amount determined by the control device 40, and the rotational speed of the blower 13 and the thermocouple 47 are controlled. The opening of the proportional valve 24 is determined by the temperature of the flame detected by the fan.

As in the embodiment described above, the lean control means 56 determines that the air-fuel ratio is rich and starts subtracting the amount of current supplied to the proportional valve 24 when the temperature detected by the thermocouple 47 exceeds the target temperature. The lean control means 56 of this embodiment includes a lean transition speed switching means 57 to change the transition speed to the lean side. This lean moving speed switching means 57
includes a counting means 58, a rapid transition means 59,
It consists of a low speed transition means 60. Note that the counting means 58, the rapid shifting means 59, and the slow shifting means 6
The lean movement speed switching means 57 including 0 is programmed into the microcomputer 41 of the control device 40.

When the detected temperature of the thermocouple 47 exceeds the target temperature and the subtraction of the energization amount of the proportional valve 24 is started, the counting means 58 counts the total amount of the subtracted energization amount.

The rapid transition means 59 operates until the total amount of subtraction counted by the counting means 58 reaches a predetermined value.
This is to increase the speed at which the amount of current supplied to the proportional valve 24 is subtracted. The gradient of this subtraction speed is set to be gentler, for example, by 2/3, than the gradient of the addition speed of the proportional valve energization amount by the rich control means 55. In other words, the speed at which the air-fuel ratio shifts to the lean side is set to be slightly slower than the speed at which the air-fuel ratio shifts to the rich side.

The low-speed shifting means 60 slows down the speed at which the proportional valve energization amount is reduced when the total amount of subtraction counted by the counting means 58 reaches a predetermined value. To give a specific example, the speed at which the proportional valve energization amount is subtracted by the rapid transition means 59 is reduced to about 1/10. As a result, when the total amount of subtraction counted by the counting means 58 reaches a predetermined value, the speed at which the air-fuel ratio shifts to the lean side becomes very slow.

Next, the above operation will be briefly explained using the time chart shown in FIG.

Immediately after the combustion amount increases due to the action of the control device 40, the temperature detected by the thermocouple 47 does not follow the actual flame temperature and lags behind, as shown at times a1 to b1 in FIG.

As a result, the thermocouple 47 outputs an electromotive force corresponding to a temperature lower than the actual flame temperature due to the delay in the detection speed of the thermocouple 47. Therefore, the microcomputer 41 determines that the combustion state has shifted to the leaner side than the target air-fuel ratio, and operates the rich control means 55. This rich control means 55 rapidly increases the amount of gas supplied. By rapidly increasing the amount of gas supplied, the air-fuel ratio quickly shifts to the rich side, causing the actual flame temperature to rise rapidly.

As the temperature of the actual flame increases, the electromotive force of the thermocouple 47 exceeds the electromotive force set according to the rotational speed of the blower 13 (time b1).

Since the actual air-fuel ratio was in a rich state between times a1 and b1, the thermocouple 47
It overshoots and outputs an electromotive force higher than the electromotive force set according to the rotational speed of the blower 13 (times b1 to d1).

When the electromotive force of the thermocouple 47 exceeds the set electromotive force (time b1), the counting means 58 starts counting the total amount of the proportional valve energization amount subtracted, and the rapid transition means 59 is activated. Since the rapid transition means 59 reduces the opening degree of the proportional valve 24 at a high speed, the actual air-fuel ratio rapidly shifts to the lean side. As a result, the actual air-fuel ratio quickly approaches the target air-fuel ratio.

Then, when the total amount of subtraction counted by the counting means 58 reaches a predetermined value (time c1), the slow shifting means 60 operates instead of the rapid shifting means 59. Since this low-speed transition means 60 reduces the opening degree of the proportional valve 24 at a slow speed, the actual air-fuel ratio slowly shifts to the lean side, and the actual flame moves at a slow speed. Head to the lift.

As the actual temperature of the flame decreases, the electromotive force of the thermocouple 47 falls below the set electromotive force at time d1. During the second half of time c1 to d1, the actual air-fuel ratio was considered to be lean, so the thermocouple 4
The output of 7 overshoots to the lean side.
The rich control means 55 is then actuated to open the proportional valve 24 at a relatively high speed. Then, the actual air-fuel ratio shifts to the rich side, and the actual flame becomes smaller as it approaches backfire.

Thereafter, the rich control means 55 and the lean control means 56 work alternately, causing the actual air-fuel ratio to repeatedly overshoot the target air-fuel ratio, until the actual air-fuel ratio converges to the target air-fuel ratio. When overshooting to the rich side for the second time, since the overshoot time is short, the rich control means 55 operates before switching from the rapid shift means 59 to the low speed shift means 60.

Note that this embodiment can suppress misfires due to lift and shorten the time during which the engine overshoots toward the rich side. In other words, the difference between the actual air-fuel ratio and the target air-fuel ratio can be reduced, and the actual combustion state can be brought closer to the ideal combustion state than in the first embodiment.

In this embodiment, the speed at which the shift to the lean side shifts is changed by counting the total amount of subtraction, but the speed may be switched using a timer.

(Modification) Although an example is shown in which a thermocouple is used as the air-fuel ratio detection means, other temperature detection means may be used as long as the temperature of the flame can be detected.

Although we have shown an example in which the rich control means and lean control means are programmed into a microcomputer, the rich control means and lean control means can be configured using discrete circuits that combine operational amplifiers, etc., without using a microcomputer. You may do so.

Although the combustion control method is a fan-driven type, other combustion control methods such as a type that controls the amount of fuel supplied first (for example, a proportional valve-driven type) or an independent type that controls the amount of air flow and the amount of fuel supplied independently may be used. The present invention may be applied to the system.

Although we have shown an example in which the speed of transition to the rich side and the speed of transition to the lean side are controlled solely by increasing or decreasing the amount of fuel supplied, it is also possible to The speed of transition to the rich side and the speed of transition to the lean side may be controlled only by increasing or decreasing the supply amount of.

Further, although a water heater with a bypass waterway is shown as an example, the present invention may be applied to a water heater without a bypass waterway, as well as other forced combustion type combustion devices such as a combustion type heating device.

Further, although an example using gas as fuel has been shown, the present invention may also be applied to a combustion device using liquid fuel such as kerosene or heavy oil.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. 2 to 7 show a first embodiment of the present invention, in which FIG. 2 is a schematic block diagram of a bypass mixing type gas water heater, FIG. 3 is a schematic block diagram of a control device, and FIG. 4 is a schematic block diagram of a control device. is a graph showing the relationship between the combustion amount and the target output of the thermocouple, Fig. 5 is a graph showing the air-fuel ratio and combustion speed, and Fig. 6 explains the change in the air-fuel ratio when increasing the combustion amount. FIG. 7 is a time chart for explaining changes in the air-fuel ratio when the combustion amount is reduced. Fig. 8 and Fig. 9 show a second embodiment of the present invention, Fig. 8 is a schematic diagram of a forced combustion type combustion device, and Fig. 9 shows a change in the air-fuel ratio when the combustion amount is increased. This is a time chart for explanation. FIG. 10 is a time chart showing changes in the air-fuel ratio when the air-fuel ratio is corrected by a conventional control device;
FIG. 11 is a time chart showing the relationship between air-fuel ratio, misfire, and flashback. In the figure, 1... combustion section, 2... fuel supply means, 3
...Blower, 4...Air-fuel ratio detection means, 5...Control device, 6...Rich control means, 7...Lean control means.

Claims (1)

[Scope of Claims] 1. A combustion section that burns fuel, a fuel supply means for supplying fuel to the combustion section, and a fuel supply means necessary for combusting the fuel supplied to the combustion section by the fuel supply means. A blower that forcibly supplies combustion air to the combustion section, and an air-fuel ratio detection means for detecting an air-fuel ratio based on the temperature of a flame formed in the combustion section, the air-fuel ratio being detected by the air-fuel ratio detection means. and a control device that corrects and controls at least one of the amount of fuel supplied by the fuel supply means or the amount of air blown by the blower in accordance with the control, and maintains the air-fuel ratio within an appropriate range. The device includes a rich control means that increases the rate of increase in fuel or decreases the rate of air flow when the air-fuel ratio shifts to the rich side, and increases the rate of increase in fuel when the air-fuel ratio shifts to the lean side. 1. A control device for a forced combustion type combustion device, characterized by comprising lean control means for slowing down the rate of decrease or slowing down the rate of increase in the amount of air blown.