JPH0745930B2 - Air-fuel ratio controller for gas combustion equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is a gas in which a ratio of a gas supply amount supplied to a gas burner and a combustion air supply amount (hereinafter simply referred to as an air-fuel ratio) is kept substantially constant. The present invention relates to an air-fuel ratio control device for combustion equipment.

[Prior art]

In order to make the gas combustion equipment compact, the air-fuel ratio is set to an appropriate ratio, or in the completely premixed gas combustion equipment in which all of the air required for combustion is mixed with the gas as primary air In order to obtain stable combustion without lift and backfire, it is necessary to keep the air-fuel ratio at a nearly constant and appropriate value. As a technique satisfying such a need, for example, there is a gas combustion control device disclosed in Japanese Patent Laid-Open No. 60-8018. In this technique, a gas amount adjusting means is controlled by a combustion amount adjusting signal, and the same combustion is performed. The air amount adjusting means is controlled by a signal obtained by correcting the air amount signal calculated by the amount adjusting signal. The need to keep the air-fuel ratio at an almost constant and proper value in order to obtain stable combustion is not limited to the fully premixed type combustion equipment described above, but the electric fan is used to send combustion air into the combustion chamber. Therefore, it is also present in a forced draft combustion device in which a part of it is mixed with gas as primary air and the rest is used as secondary air.

[Problems to be solved by the invention]

The gas combustion equipment is supplied with gases of different gas species depending on the installation area, and the unit calorific value, gas pressure, combustion characteristics, etc. differ depending on the gas species. Therefore, even with the same gas combustion equipment, the characteristics between the applied current to the solenoid valve that controls the gas supply amount and the voltage that is applied to the electric fan that controls the combustion air supply amount are shown in FIG. , C, it is necessary to make it different depending on the gas type, or else it is not possible to obtain stable combustion by giving an appropriate air-fuel ratio according to the gas type, or the maximum combustion capacity of the equipment. Therefore, there arises a problem that the durability is lowered and the combustion efficiency becomes lower than the minimum combustion ability, and the combustion becomes unstable. For this reason, it is necessary to make a characteristic map or an arithmetic expression that gives characteristics between the current applied to the solenoid valve and the voltage applied to the electric fan different for each gas type. Since the specifications vary depending on the region where the product is used, there are problems that the total number of stocks increases, the cost increases, and the labor of inventory management and delivery control increases. According to the present invention, the characteristics between the opening degree of the solenoid valve and the rotation speed of the electric fan for obtaining an appropriate air-fuel ratio quantitatively vary greatly depending on the gas species, but are qualitatively similar. Focusing on, the above problem is solved.

[Means for solving problems]

For this reason, the air-fuel ratio control device for gas combustion equipment according to the present invention, as illustrated in FIG. 1, has a gas burner 10 for heating the feed water passing through the heat exchanger 20 and a continuous opening according to the applied current. Solenoid valve 11 for controlling the gas supply amount to the gas burner 10 by changing to, and an electric fan for controlling the combustion air supply amount to the gas burner 10 by continuously changing the rotation speed according to the applied voltage. In an air-fuel ratio control device for gas combustion equipment comprising 12, a hot water temperature setting device 40 for setting the hot water temperature,
Hot water temperature sensor 43 for detecting hot water temperature from the heat exchanger 20.
An opening range setting means 1 for setting the maximum and minimum openings of the solenoid valve 11 to predetermined values in advance, and a rotation speed range setting for setting the maximum and minimum rotation speeds of the electric fan 12 to predetermined values in advance. And means 2 and a ratio of the applied current to the solenoid valve 11 based on the maximum and minimum applied currents corresponding to the maximum and minimum openings, and a maximum and minimum applied voltage corresponding to the maximum and minimum rotation speeds. The storage means 3 for storing a preset characteristic between the ratio of the voltage applied to the electric fan 12 and the set temperature set by the hot water temperature setting device 40 and the hot water temperature sensor 43 are detected. The solenoid valve 11 is configured to reduce the difference between the tapping temperature and the set temperature within the range of the maximum and minimum applied currents by comparing the tapping temperature.
Calculating means 4 for calculating an applied current for changing the opening degree of
And a solenoid valve drive device 45 for applying the applied current calculated by the first calculating means to the solenoid valve 11, and the maximum and minimum currents of the applied current calculated by the first calculating means 4 as a reference. Second calculation means 5 for calculating the ratio, and third calculation for calculating the ratio of the voltage applied to the electric fan 12 from the characteristic stored in the storage means 3 based on the ratio calculated by the second calculation means. Means 6, fourth calculating means 7 for calculating the applied voltage to the electric fan 12 based on the ratio calculated by the third calculating means and the maximum and minimum applied voltages, and the fourth calculating means. Motor drive device 46 for applying an applied voltage to the electric fan 12
It is characterized by having.

[Action]

Depending on the type of gas to be used in advance, the opening range setting means 1 is adjusted so that the amount of gas does not exceed the maximum combustion capacity of the equipment and does not fall below the minimum combustion capacity. And the rotation speed range setting means 2 is adjusted so that the maximum and minimum rotation speeds of the electric fan 12 are adjusted so that the air-fuel ratio at the maximum and minimum opening is an appropriate value according to the gas type. When the gas combustion equipment is set, the first calculation means 1 compares the hot water temperature detected by the hot water temperature sensor 43 with the preset temperature preset by the hot water temperature setting device 40 and sends it to the solenoid valve 11. The solenoid valve drive device 45 applies the applied current of this value to the solenoid valve 11, and if there is a difference between the two tapping temperatures, the opening of the solenoid valve 11 is changed to change the gas to the gas burner 10. By changing the supply amount, the hot water temperature from the heat exchanger 20 can be set by the hot water temperature setting device. Close to the value set by 40. The applied current is calculated so as to be within the range of the maximum and minimum applied currents corresponding to the maximum and minimum openings of the solenoid valve 11.

The second calculation means 5 calculates the ratio of the applied current calculated by the first calculation means 4 with the maximum and minimum applied current as a reference, and the third calculation means 6 stores it in the storage means 3 based on this ratio. The ratio of the voltage applied to the electric fan 12 is calculated from the obtained characteristics. The fourth calculation means 7 calculates the voltage applied to the electric fan 12 based on the ratio calculated by the third calculation means 6 and the maximum and minimum applied voltages corresponding to the maximum and minimum rotation speeds of the electric fan 12, and the motor The drive device 46 applies the applied voltage of this value to the electric fan 12. As a result, the rotation speed of the electric fan 12 becomes a value according to the opening degree of the solenoid valve 11, and the combustion air in an amount corresponding to the gas supply amount is supplied to the gas burner 10.
Is supplied to.

Opening of solenoid valve 11 and electric fan to obtain appropriate air-fuel ratio
The characteristics between the rotational speed of 12 and the rotational speed of 12 greatly vary quantitatively depending on the gas type, but are qualitatively similar, so the ratio of the current applied to the solenoid valve stored in the storage means 3 and the electric fan. The characteristics between the ratios of the applied voltages are substantially the same for different gas species.

〔The invention's effect〕

As described above, according to the present invention, by adjusting the opening range setting means and the rotation speed range setting means in advance according to the gas type to be used, the gas combustion equipment of the same specifications can be adapted to various different gas types. To obtain an appropriate gas supply amount and air-fuel ratio, and to prevent deterioration of durability and combustion instability due to gas supply of an amount above or below the combustion capacity of the equipment or an inappropriate air-fuel ratio. You can Also, the adjustment by the gas type is performed at the maximum and minimum opening of the solenoid valve and the corresponding maximum and minimum rotation speed positions of the electric fan, but the opening and the solenoid of the solenoid valve to obtain an appropriate air-fuel ratio are adjusted. Since the characteristics between the rotation speeds of the fans are qualitatively the same even if the gas type is different, the air-fuel ratio is maintained at a predetermined value corresponding to the gas type even at values other than the maximum and minimum values.

〔Example〕

First, an embodiment of the completely premixed gas combustor shown in FIGS. 2 to 4 will be described.

As shown in FIG. 2, a water supply pipe 21 is connected to one end of the heat exchanger 20, and a hot water supply pipe 22 having a hot water supply plug 23 at the tip is connected to the other end. Water pipe with hot water tap 23 open
The feed water supplied from 21 is heated by the gas burner 10 when passing through the heat exchanger 20, reaches a predetermined hot water temperature, and is tapped from the hot water tap 23. Mixing chamber connected to gas burner 10
A gas supply pipe 13 provided with a solenoid valve 11 whose opening changes according to an applied current and an air supply pipe 14 from an electric fan 12 whose rotation speed changes according to an applied voltage are connected to 15. . The opening degree of the solenoid valve 11 and the rotation speed of the electric fan 12 are controlled in conjunction with each other by an electronic control unit 30 described later, and the gas supply pipe
All of the air required for combustion of gas from 13 is supplied as primary air from an air supply pipe 14, mixed in a mixing chamber 15 and supplied to the gas burner 10.

The electronic control unit 30 is a microprocessor (hereinafter simply referred to as CPU
31), read-only memory (hereinafter simply referred to as ROM) 32, and writable memory (hereinafter simply referred to as RAM) 33
Is a main component, and the solenoid valve 11 and the electric fan 12 are connected to the CPU 31 via a solenoid valve driving device 45 and a motor driving device 46, respectively. In the present embodiment, the solenoid valve 11 is a proportional solenoid valve that changes the gas pressure on the downstream side in proportion to the applied current, and the motor of the electric fan 12 changes its rotation speed in proportion to the applied voltage. It is a brushless DC motor.

A hot water temperature sensor 43 such as a thermistor for detecting the hot water discharge temperature is provided in the hot water discharge pipe 22 immediately after the heat exchanger 20, and the electric fan 12 is rotated to generate a number of pulses proportional to the rotation speed thereof. A speed sensor 44 is provided, and both sensors 43, 44 are connected to the CPU 31 via an interface (not shown). The CPU 31 also has a target value of hot water temperature (set temperature)
A hot water temperature setting device 40 for setting, an opening degree input device 41 for the opening degree range setting means 1, and a rotation speed input device 42 for the rotation speed range setting means 2 are connected via an interface (not shown). ing. In this embodiment, the hot water temperature setting device
40 is mainly a variable resistor that can be adjusted by a knob provided outside, and each input device 41, 42 is a semi-fixed type with two maximum and minimum values set according to the gas type. Mainly variable resistors. Each variable resistor of the opening input device 41 limits the maximum applied current and the minimum applied current to the solenoid valve 11 by the adjustment so that the gas supply amount to the gas combustion equipment does not exceed the maximum combustion capacity, Further, the maximum and minimum opening of the solenoid valve 11 are limited so as not to fall below the minimum combustion capacity. Further, each variable resistor of the rotation speed input device 42 sets the maximum applied voltage and the minimum applied voltage to the electric motor 12 corresponding to the maximum and minimum opening of the solenoid valve 11 by the adjustment, and the air-fuel ratio at that time. Is to set the maximum and minimum rotation speeds of the electric fan 12 so that is a predetermined appropriate value depending on the gas type. The adjustment of each variable resistor of both the input devices 41 and 42 is performed according to the gas type of the shipping area at the time of shipping from a factory or a store, and then sealed so that the adjustment cannot be performed thereafter.

In ROM32, the maximum applied current (AImax, BImax, CImax, etc. in FIG. 6) of the applied current to solenoid valve 11 is set to 100%, and the minimum applied current (AImin, BImin, CImin, etc. in FIG. 6) 0%
The ratio Ri and the maximum applied voltage (AVmax, BVmax, CVmax, etc. in FIG. 6) of the voltage applied to the electric fan 12 is set to 100%, and the minimum applied voltage (AVmin, BVmin, CVmin in FIG. 6).
The characteristics between the ratios Rv where 0) is 0% are stored as a characteristic map. FIG. 3 is a graphic representation of such a characteristic map. In the present embodiment in which the proportional solenoid valve and the brushless DC motor as described above are used as the motors for the solenoid valve 11 and the electric fan 12, the air-fuel ratio is changed. To keep it constant, theoretically the ratio of applied voltage Rv is the ratio of applied current.
The characteristic P may be set to increase in proportion to the square root of Ri.

The reason is as follows. The amount of gas supplied to the mixing chamber 15 is proportional to the square root of the pressure difference before and after a gas nozzle (not shown) having a small opening area provided in the tip of the gas supply pipe 13 and located in the mixing chamber 15. On the other hand, the cross-sectional area of the gas supply pipe 13 from the solenoid valve 11 to the mixing chamber 15 is considerably large and the distance is short compared to the opening area of the gas nozzle described above, and therefore the loss of gas pressure in the gas supply pipe 13 is neglected. Therefore, the pressure difference before and after the gas nozzle at the tip of the gas supply pipe 13 becomes the same as the pressure difference between the secondary pressure of the solenoid valve 11 and the pressure in the mixing chamber 15.
Since the pressure in the mixing chamber 15 is almost equal to the atmospheric pressure (0 atm in gauge pressure), the gas supply amount to the gas burner 10 is proportional to the square root of the secondary pressure of the solenoid valve 11. And this secondary side pressure is proportional to the current applied to the solenoid valve 11, while the combustion air amount is proportional to the rotation speed of the electric fan 12, so in order to keep the air-fuel ratio constant, The ratio Rv of the applied voltage may be a characteristic P that increases in proportion to the square root of the ratio Ri of the current applied to the solenoid valve 11. In the present embodiment, since the ratios Ri and Rv are both values digitized to 255 bits, the characteristic map is not continuous as shown by P but along P as shown by p. It will be stepped. The ROM 32 also stores a control program for executing the control operation shown in the flowchart of FIG.

Next, the control operation of the present invention will be described mainly with reference to the flowchart shown in FIG.

When the power for operating the gas combustion equipment is turned on, the electronic control unit 30 first sets each variable to 0 or a predetermined initial value, and then water is supplied to the water supply pipe 21 by a control flow not shown. Judge whether or not. If the hot water tap 23 is opened and water is supplied to the water supply pipe 21, the electronic control unit 30 activates a timing flow (not shown) to generate an interrupt signal every 0.3 seconds, and the flow chart of FIG. 4 each time. The execution of the control operation by is started.

First, CPU 31 reads in step 101 the set temperature T1 set by the hot water temperature setting device 40 as a digitized signal, and in step 102 similarly reads the hot water temperature T2 detected by the hot water temperature sensor 43. Then step
Similarly, the rotational speed N2 of the electric fan 12 detected by the rotational speed sensor 44 in 103 is read, and the subsequent step 10
In step 4, from the applied voltage V output to the electric fan 12 in step 117 of the previous control operation, the set rotational speed N1 of the electric fan 12 is set on the basis of the applied voltage of the electric fan 12 and the rotation speed characteristics stored in the ROM 32. After calculating, the rotational speed error ratio β of the electric fan 12 is calculated in step 105 by the following equation β = (N1−2N) / N2.
Next, in step 106, the CPU 31 sets the absolute value of the rotation speed error ratio β to a predetermined error ratio limit value K (= 0.1.
~ 0.2), and if | β |> K, the next step 1
If | β |> K is entered in step 07, the electromagnetic valve 11 is fully closed and the electric fan 12 is stopped to stop the combustion of the gas burner 10 in step 119, and then all the controls including the above-described timing flow are performed. Stop the flow. This rotational speed error ratio β is used in step 117 described later to correct the voltage applied to the electric fan 12 and bring the rotational speed of the electric fan 12 closer to the set rotational speed according to the opening degree of the solenoid valve 11. However, | β |> K means that some abnormality has occurred in the electric fan 12 or a portion related thereto, and steps 106 and 119 perform an emergency stop in such a case. It is for.

In step 107, the CPU 31 calculates the increase rate ΔI of the current I applied to the solenoid valve 11 by the following equation ΔI = α (T1-T2) α: proportional constant determined by the operating condition,
In the following step 108, the following equation I = I + ΔI (Imax-Imin) Imax, Imin: The applied current I is calculated by the maximum and minimum applied currents corresponding to the maximum and minimum opening of the solenoid valve 11 set by the opening input device 41. To do. In the following steps 109 to 112, the applied current I has the maximum value Imax and the minimum value Imin.
After the limit is set within the range, the CPU 31 outputs the applied current I to the solenoid valve 11 via the solenoid valve driving device 45 in step 113.

Next, the CPU 31 calculates the ratio Ri of the applied current I by the following equation Ri (I-Imin) / (Imax-Imin) in step 114, and then,
At 115, the ratio Rv of the voltage applied to the electric fan 12 corresponding to this ratio Ri is calculated from the characteristic map of FIG. 3 stored in the ROM 32. In the following step 116, the CPU 31 uses the following equation: V = Rv (Vmax-Vmin) + Vmin Vmax, Vmin: The maximum and minimum applied voltage corresponding to the maximum and minimum rotation speed of the electric fan 12 set by the rotation speed input device 42. Calculate the applied voltage V to 12 and step
In 117, the applied voltage V is corrected by the following equation V = V (1 + β), and then in step 118, the applied voltage V is output to the electric fan 12 via the motor drive device 46, and the flow chart of FIG. Stop the control operation by. In step 117, even if the characteristics of the voltage applied to the electric fan 12 during the rotation speed vary from product to product or change over time, the rotation speed of the electric fan 12 is controlled by the solenoid valve.
This is to prevent an error from occurring in the air-fuel ratio by making a correction to a predetermined value according to the opening degree of 11.

The control operation according to the flowchart of FIG. 4 is as described above.
This is repeated every 0.3 seconds, whereby the electronic control unit 30 increases the opening degree of the solenoid valve 11 within the range of the maximum opening degree or less when T2 <T1, and when T2> T1. The opening degree of is reduced within a range not less than the minimum opening degree, and the hot water outlet temperature T2 from the heat exchanger 20 is brought close to the set temperature T1 set by the hot water temperature setting device 40 so that the temperatures T1 and T2 coincide with each other.
The solenoid valve 11 is used to adjust the air-fuel ratio depending on the gas type at the time of shipment.
Of the maximum and minimum opening of, and the corresponding maximum and minimum rotational speed of the electric fan 12 is performed,
Opening of solenoid valve 11 and electric fan to obtain appropriate air-fuel ratio
As shown in FIG. 6, the characteristics with respect to the rotation speed of 12 are qualitatively the same even if the gas species are different. Therefore, by using one characteristic map shown in FIG. Even if the value is other than the above value, the air-fuel ratio can be maintained at a predetermined value according to the gas type.

In the above embodiment, the characteristic map between the ratio Ri of the applied current and the ratio Rv of the applied voltage is theoretically the third as described above.
Although it is a square root curve P as shown in the figure, both ratios Ri, Rv
Since all are values digitized to 255 bits, they are actually stepwise as shown by p. In the case of such a characteristic map, the ratio Rv of the applied current is small (the opening degree of the solenoid valve 11 is small). Therefore, in the range where the gradient of the curve P is large, the ratio Rv of the applied voltage is a unit exceeding 1 bit. Since it changes, the error with respect to the theoretical value of the ratio Rv of the applied voltage to be output becomes 2 bits or more, which increases the error from the theoretical value of the supplied primary air amount. In this state, the absolute value of the primary air amount is also small, the relative error further increases, and the error of the air-fuel ratio increases, so that combustion is likely to be unstable or incomplete.
As shown graphically in FIG. 5, the problem is that the horizontal axis of the characteristic map stored in the ROM 32 is the digitized value of the square of the applied current ratio Ri, and the vertical axis is the applied voltage ratio Rv. It is possible to solve by setting it as a converted value.
By doing so, the characteristic map between the square of the ratio Ri and the ratio Rv theoretically becomes as shown by the straight line Q in FIG. 5, and if it is digitized, it becomes a stepwise form along the straight line Q. It becomes q. According to the characteristic map shown in FIG. 5, the ratio of the applied current Rv changes by 1 bit in most cases in the entire range of the square of the ratio Ri of the applied current. The error with respect to the theoretical value of is almost never more than 1 bit. As a result, the error in the amount of primary air supplied is reduced, so the error in the air-fuel ratio is also reduced, and combustion becomes stable. In this case, the fourth
In the flowchart of the figure, step 115 is different from the above description, and after the ratio Ri of the applied current calculated in step 114 is squared, the fifth step is performed based on the square of this ratio Ri.
The ratio Rv of the applied voltage is calculated from the characteristic map shown in the figure.

In the above-described embodiment and its modification, the ROM 32 is stored in advance as a characteristic map between the ratio Ri of the applied current and the ratio Rv of the applied voltage, which is composed of a set of a large number of values calculated in advance or experimentally. An arithmetic expression may be stored instead of such a characteristic map, and the applied voltage ratio Rv may be calculated by this arithmetic expression every time the applied current ratio Ri or its square is calculated.

Further, in the above-described embodiment and its modified example, the complete premixing type gas combustion apparatus for mixing all of the combustion air sent by the electric fan into the gas as the primary air has been described, but the present invention is not limited to this. Instead, it can be implemented in a forced ventilation type combustion device in which a part of the combustion air sent into the combustion chamber by an electric fan is mixed with the gas as primary air and the rest is used as secondary air, and the same effect can be obtained. .

[Brief description of drawings]

FIG. 1 is a diagram showing an example of the configuration of an air-fuel ratio control device for a gas combustion device according to the present invention, FIGS. 2 to 4 show an example of the present invention, FIG. 2 is an overall configuration diagram, and FIG. FIG. 4 is a diagram showing a characteristic map showing the relationship between the ratio of the current applied to the solenoid valve and the ratio of the voltage applied to the electric fan, FIG. 4 is a flow chart showing a control program, and FIG. FIG. 3 is a diagram corresponding to FIG. 3, and FIG. 6 is a diagram showing characteristics between the current applied to the solenoid valve and the voltage applied to the electric fan for each gas type. Explanation of reference numerals 1 ... opening range setting means, 2 ... rotational speed range setting means, 3 ... storage means, 4 ... first computing means, 5 ... second
Computing means, 6 ... third computing means, 7 ... fourth computing means,
10 …… Burner, 11 …… Solenoid valve, 12 …… Electric fan, 20…
… Heat exchanger, 40 …… Hot water temperature setting device, 43 …… Hot water temperature sensor,
45: Solenoid valve drive device, 46: Motor drive device.

Claims (2)

[Claims] 1. A gas burner for heating feed water passing through a heat exchanger, an electromagnetic valve for controlling a gas supply amount to the gas burner by continuously changing an opening according to an applied current, and an applied voltage. In the air-fuel ratio control device for gas combustion equipment, which comprises an electric fan for controlling the amount of combustion air supplied to the gas burner by continuously changing the rotation speed, a hot water temperature setting device for setting the hot water temperature, A hot water temperature sensor for detecting the hot water temperature from the heat exchanger, opening range setting means for setting the maximum and minimum openings of the solenoid valve to a predetermined value in advance, and maximum and minimum rotational speeds of the electric fan in advance. Corresponding to the rotation speed range setting means for setting a predetermined value, the ratio of the current applied to the solenoid valve based on the maximum and minimum applied currents corresponding to the maximum and minimum openings, and the maximum and minimum rotation speeds. Maximum and minimum markings A storage unit that stores a preset characteristic between the ratio of the voltage applied to the electric fan based on a voltage, a set temperature set by the hot water temperature setting device, and a hot water temperature detected by the hot water temperature sensor. First computing means for comparing the tapping temperature and computing the applied current for changing the opening of the solenoid valve so that the difference between the tapping temperature and the set temperature is reduced within the range of the maximum and minimum applied currents; A solenoid valve driving device that applies the applied current calculated by the first calculating means to the solenoid valve, and a second that calculates a ratio of the applied current calculated by the first calculating means based on the maximum and minimum currents. Calculating means, third calculating means for calculating the ratio of the voltage applied to the electric fan from the characteristics stored in the storing means based on the ratio calculated by the second calculating means, and the third calculating means A fourth calculating means for calculating a voltage applied to the electric fan based on the maximum and minimum applied voltage and the computed ratio by stages, the fourth
An air-fuel ratio control device for gas combustion equipment, comprising a motor drive device for applying the applied voltage calculated by a calculation means to the electric fan. 2. The characteristic stored by the storage means is a characteristic map made up of a digitized value of the square of the ratio of the applied current and a digitized value of the ratio of the applied voltage corresponding thereto. Claim 1 characterized by
An air-fuel ratio control device for a gas combustion device according to item.