JPH0379611B2 - - 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.

FIG. 8 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. In addition, 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. In this example, propane gas is used as the fuel.

As you can see from the time chart in Figure 8,
Shifting the air-fuel ratio to the lean side slows the combustion rate and lifts the flame for a short period of time (in this example, 15
sec) Misfire occurs. Conversely, shifting the air-fuel ratio toward the richer side increases the combustion rate and takes a longer time (in this example
200 seconds).

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 as the time when the actual combustion state exists on the lean side. Because of the heat, the actual combustion state remained on the lean side for a long time, increasing the possibility of misfire.

Therefore, when the actual air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio, it is conceivable to lengthen the time the air-fuel ratio remains rich and conversely shorten the time it remains lean. As a specific means for this, it is conceivable to increase the speed at which the air-fuel ratio shifts to rich, and conversely to slow down the speed at which the air-fuel ratio shifts to rich.

Therefore, the present applicant provides a control device with a rich control means for increasing the transition speed when the air-fuel ratio is transitioned to rich, and also provides a lean control means for slowing down the transition speed when transitioning the air-fuel ratio to lean. suggest something.

[Problems to be Solved by the Invention] The combustion used in the time chart shown in FIG. 8 is so-called A gas, such as propane gas, which has a slow combustion rate. However, with so-called C gases, such as city gas and natural gas, which burn at a high rate, flashback occurs in a relatively short period of time (90 seconds in this example), as shown by the solid line in FIG.

Therefore, it is necessary to change the speed at which the lean control means shifts to lean depending on the combustion state of the fuel used.

In other words, a dedicated control device is required depending on the combustion state of the fuel, such as the combustion speed of the fuel used.
As a result, there is a problem in that fuels with different combustion states, such as different gas types, cannot be used.

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

[Means for Solving the Problems] In order to achieve the above object, a control device for a 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 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 in a controlled manner.
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 fuel or decreases the amount of air blown when the air-fuel ratio shifts to the rich side, and also includes a rich control means 6 that increases the amount of fuel or decreases the amount of air blown when the air-fuel ratio shifts to the lean side. The lean control means 7 includes a lean control means 7 for increasing the air-fuel ratio, and the lean control means 7 performs the following steps when shifting the air-fuel ratio to the lean side.
The technical means is that a lean transition speed variable means 8 is provided to change the speed at which the fuel decreases or the speed at which the air flow increases.

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

When the speed at which the air-fuel ratio is shifted to the lean side is slowed down by the lean shift speed variable means, when the air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio, the actual air-fuel ratio becomes lower than the target air-fuel ratio. The time it takes to shift to the rich side becomes longer.

Conversely, if the speed at which the air-fuel ratio is shifted to the lean side is increased by the lean shift speed variable means, when the air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio, the actual air-fuel ratio will be lower than the target. The time during which the air-fuel ratio shifts to the rich side becomes shorter.

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

By changing the speed at which the air-fuel ratio shifts to the lean side using the lean transition speed variable means, when the air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio, the actual air-fuel ratio changes to the target air-fuel ratio. The time during which the fuel ratio shifts to the rich side can be changed.

As a result, when using fuels with different combustion states, the rich side existence time can be set according to the fuel by means of the lean transition speed variable means. As a result, when using fuels with different combustion states, misfires due to flame lift can be prevented without replacing the control device.

[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.

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.

A combustion passage 10 and a ceramic surface combustion type burner 12 are arranged inside. Upstream of this burner 12 is a blower 13 that forcibly supplies combustion air necessary for combusting the gas supplied from the gas supply pipe 20 in the combustion section 11 on the upper surface of the burner 12 to the combustion section 11. It is installed from. 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 that opens on the inner circumference 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. An orifice 26 is provided on the other side.
The main solenoid valve 22, the main solenoid valve 23, and the switching solenoid valve 25 are connected to the gas supply pipe 2 by energization control.
The proportional valve 24 has an opening ratio that changes depending on the amount of electricity supplied, and adjusts the amount of gas supplied to the nozzle 21.

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 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 temperature of the flame of the burner 12;
The thermocouple 47, the electric water flow control device 33, and the throttle valve 3, which are air-fuel ratio detection means of the present invention, detect the air-fuel ratio by detecting the temperature of the flame of No. 2.
potentiometers 48 and 49 that are linked to the valve body No. 4 and detect the opening degree of the valve body, a rotation speed sensor 50 that detects the rotation speed of the blower 13, the temperature of water upstream of the heat exchanger 31 and the bypass water channel 32. An incoming water temperature sensor 51 detects the temperature of hot water that has passed through the heat exchanger 31, a temperature sensor 52 that detects the temperature of hot water that has passed through the heat exchanger 31 and the bypass waterway 32, and an outlet temperature sensor 53 that detects the temperature of the mixed hot water that has passed through the heat exchanger 31 and the bypass waterway 32. A water amount detection sensor 54 is provided to detect the amount of water flowing into the 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 advance type of this embodiment determines the rotational speed of the blower 13 so that the amount of air blown can be obtained according to the combustion amount determined by the control device 40, and from the rotational speed of the blower 13, the amount of gas that 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 that the amount of air is supplied to the burner 12 according to the determined combustion amount. And blower 1
The comparison valve 24 and the switching solenoid valve 25 are energized and controlled so that a gas amount corresponding to the rotational speed of the burner 12 and the flame temperature of the burner 12 is obtained. In addition, the amount of combustion is
The temperature of the hot water that has passed through the heat exchanger 31 is determined so as to be maintained above a temperature (for example, 60° C.) at which water generated by combustion (drain water) does not adhere to the heat exchanger 31.

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 opening degree of the throttle valve 34 is fixed when the amount of water entering is small or when the temperature of hot water coming out is lowered, and the opening degree of the throttle valve 34 is fixed so that the opening degree is calculated according to the amount of water entering and the temperature of hot water coming out. Energization is controlled.

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 in 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 electromotive 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. When the air-fuel ratio shifts to a richer side than the target air-fuel ratio, the combustion speed becomes faster and the flame temperature becomes higher.On the other hand, when the air-fuel ratio shifts to a leaner side, the combustion speed becomes slower and the flame temperature becomes lower. Therefore, by correcting and controlling the gas amount so that an electromotive force corresponding to the combustion amount is obtained, the air-fuel ratio can be maintained at an appropriate value.

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 electromotive 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 electromotive 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 rich control means 55 described above, and the rate of decrease is changeable by the lean transition speed variable means 57 so that it can be changed according to the type of gas. There is.

The lean transition speed variable means 57 includes a variable volume 58 whose resistance value is manually varied by an assembler or an installer who installs the gas water heater. And lean transition speed variable means 5
7, the rate at which the gas is reduced by the lean control means 56 is set to 1/5 to 1/20 of the rate at which the rich control means 55 increases the amount of gas supplied, depending on the resistance value set by the variable volume 58. It slows down the speed to .

In this embodiment, propane gas is used as fuel. The time chart in FIG. 8 shows the relationship between the output of the thermocouple 47 and the state of the flame when the air-fuel ratio of propane gas is changed. As shown by the solid line in this figure, when the air-fuel ratio is shifted to the rich side, it takes a long time, about 200 seconds, for flashback to occur.

Therefore, in this embodiment, in order to prolong the time that the actual air-fuel ratio remains on the rich side when it repeatedly overshoots and converges to the target air-fuel ratio, the rate at which the gas is reduced by the lean control means 56 is adjusted to be rich. The gas supply rate of the control means 55 is slowed down to 1/16 of the rate of increase. In other words, the variable volume 5
8 to set the fuel reduction rate by the lean transition speed variable means 57 for propane gas. Specifically, the rate of gas decrease is approximately
Limit to 30kcal/s.

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 an electromotive force corresponding to a temperature lower than the actual flame temperature.
Therefore, the microcomputer 41 erroneously determines that the combustion state is moving toward a leaner side than the target air-fuel ratio, and activates the rich control means 55. Due to the function of this rich control means 55,
Rapidly increase gas supply. By rapidly increasing the amount of gas supplied, the air-fuel ratio quickly shifts to the rich side, the combustion speed increases in a short period of time, and the actual amount of combustion 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. The lean control means 56 slowly reduces the amount of gas supplied. 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, and 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 temperature higher than the actual flame temperature.
Therefore, the microcomputer 41 erroneously determines that the combustion state has shifted to the richer side than the target air-fuel ratio, and activates the lean control means 56. Due to the function of this lean control means 56,
Slowly reduce the gas supply. As the supply amount of this gas gradually 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 56.

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 combustion amount 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.

In addition, on the contrary, although it exists on the rich side for a long time,
Since there is a long margin of time (approximately 200 seconds from Figure 8) for flashback to occur due to the presence on the rich side, flashback will not occur even if the time on the rich side is long.

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 case where the combustion amount changes is shown as an example, but when the gas supply amount or the combustion air amount changes, the actual The 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. Furthermore, even if the rotational speed of the blower is constant, the amount of combustion air supplied during combustion changes due to the change in air amount that occurs when the ceramic burner 12 changes from a low temperature state at the initial stage of ignition to a high temperature (normal temperature). Alternatively, an air resistance object may be placed at the opening for introducing combustion air into the combustion passage 10.

Next, a case where the gas used is changed from propane gas to natural gas or city gas will be described. As shown in Figure 9, gases such as natural gas and city gas have a fast combustion speed, and the time it takes for the air-fuel ratio to shift to the rich side and flashback to occur is about 200 seconds, compared to propane gas, which takes about 200 seconds. It is short at about 90 seconds.

Therefore, when changing the gas type, the variable volume 58 is operated to set the fuel reduction rate by the lean transition speed variable means 57 for so-called C gas such as natural gas or city gas. In other words, the rate at which the gas is reduced by the lean control means 56 is reduced to 1/8 of the rate at which the rich control means 55 increases the gas supply amount. in particular,
This limits the gas reduction rate to approximately 60 kcal/s.

According to this embodiment, the lean transition speed variable means 5
7, by changing the speed at which the air-fuel ratio shifts to the lean side, when the actual air-fuel ratio repeatedly overshoots and converges to the target air-fuel ratio, the actual air-fuel ratio becomes lower than the target air-fuel ratio. You can change the time it takes to move to the rich side.

Thereby, when changing the gas being used to a gas having a different combustion state, the rich side existence time can be set according to the type of gas to be changed using the lean transition speed variable means.

As a result, when changing to a gas with a different combustion state, misfires due to flame lift can be prevented without changing the control device 40.

(Modified example) Although we have shown an example in which the speed of transition to the lean side is changed by the resistance value of the variable volume, it is also possible to input data according to the type of gas into the microcomputer and provide a means to select that data. good.

Similarly to the lean transition speed variable means, a rich transition speed variable means for changing the speed of transition to the rich side may be provided.

Although we have shown an example in which a thermocouple is used as the air-fuel ratio detection means, any device that can detect the temperature of the flame may be used.
Other temperature detection means may also be used.

Although an example has been shown in which the control device is implemented by programming a microcomputer, the control device may also be configured by a discrete circuit configured by combining operational amplifiers, transistors, and the like.

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 in advance (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.

The speed of transition to the lean side and the speed of transition to the rich side were controlled only by increasing or decreasing the amount of fuel supplied, but it is also possible to control the rate of transition to the lean side and the speed of transition to the rich side by increasing or decreasing the amount of combustion air supplied in combination, or by changing the amount of combustion air supplied. The speed of transition to the lean side and the speed of transition to the rich side may be controlled only by increase/decrease.

We used a water heater equipped with a bypass waterway as an example;
The present invention may be applied not only to water heaters that do not have a bypass waterway, but also to other forced combustion combustion devices such as combustion heating devices.

Although an example using gas as fuel has been shown, the present invention may be applied to a combustion device using other fuels such as kerosene or heavy oil.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 is a block diagram showing the configuration of the present invention.
The figure is a schematic block diagram of a bypass mixing type gas water heater, Figure 3 is a schematic block diagram of the control device, and Figure 4 is a schematic block diagram of the control device.
The figure 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 is a graph showing the change in the air-fuel ratio when increasing the combustion amount. Figure 7 is a time chart to explain the change in air-fuel ratio when the combustion amount is varied. Figure 8 is a time chart to explain the change in air-fuel ratio when propane gas is used as fuel, and misfire and backfire. Figure 9 is a time chart showing the relationship between the air-fuel ratio and misfire and flashback when natural gas or city gas is used as the fuel. Figure 10 is a time chart showing the relationship between the air-fuel ratio and misfire and flashback when natural gas or city gas is used as fuel. This is a time chart showing the actual change in the air-fuel ratio when the air-fuel ratio changes. 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, 8...Lean transition speed variable means.

Claims (1)

[Scope of Claims] 1. A combustion section that supplies 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 fuel 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 fuel or decreases the amount of air blown when the air-fuel ratio shifts to the rich side, and also includes a rich control means that increases the amount of fuel or decreases the amount of air blown when the air-fuel ratio shifts to the lean side. The present invention is characterized by comprising a lean control means for increasing the air-fuel ratio to the lean side, and the lean control means comprising a lean transition speed variable means for changing the speed at which the fuel decreases or the speed at which the air flow increases when the air-fuel ratio shifts to the lean side. Control device for forced combustion type combustion equipment.