JPH0792227B2 - Combustion control device for water heater - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention is provided in a fuel supply path of a burner, in which the valve opening is controlled in response to a valve driving current and the valve opening is fully closed. In some cases, the fuel control valve has a dead zone in which the valve drive current is kept fully closed until the valve drive current increases above a predetermined value, and fuel control that gives a valve drive current to the fuel control valve in response to a valve opening signal. Valve driving means, hot water outlet temperature detecting means for detecting hot water temperature, target temperature setting means for setting a target hot water temperature, and integral operation in response to a deviation between the two temperatures. The valve driving means is provided with a PID control means for giving a valve opening signal for outputting a valve driving current therefrom and performing the integration operation so that the valve driving current is controlled at a predetermined change rate. The present invention relates to a combustion control device for a water heater.

(Summary of the Invention) The present invention reduces the integral value of the PID control means in response to the target temperature being drastically lowered from the detected hot water temperature and the deviation between the two temperatures exceeding a predetermined value. A valve drive current sudden decrease means for rapidly reducing the valve drive current to a value at which the valve opening of the fuel control valve is fully closed, and a decrease value of the integral value of the PID control means by the valve drive current sudden decrease means to a constant value. And a means for rapidly increasing the integration start current for limiting the PID.
The fuel control valve drive means is opened by the valve drive current according to the valve opening signal from the control means so that the target temperature set by the target temperature setting means and the detected temperature detected by the outlet temperature detecting means are balanced. When the deviation of the both temperatures exceeds the predetermined value while driving the fuel control valve at a temperature of 10 degrees, the integral value of the PID control means is reduced by the valve drive current rapid decrease means to reduce the valve drive current. After the valve opening of the fuel control valve is suddenly reduced to a value at which the valve opening of the fuel control valve is fully closed, and then the valve opening of the fuel control valve is fully closed, the integral start current sudden increase means of the integrated value of the PID control means The lowering value is limited to a constant value, and the PID control means starts the integration operation from the integral value limited to this constant value, thereby making it possible to shorten the time until the valve drive current exceeds the dead zone. Detection temperature of hot water temperature and the eye It is obtained so as to improve the responsiveness of the tapping temperature as possible the execution of the combustion control corresponding to the deviation between the temperature.

(Prior Art and Problems Thereof) FIG. 7 shows an example of a conventionally known water heater. In FIG. 7, 1 is a burner, 2 is a fuel supply path connected to the burner 1, and a solenoid valve (source valve) 3, a gas governor 4 and a fuel control valve (proportional valve) 5 are provided in the fuel supply path 2. It is equipped. The fuel control valve 5 generally has a hysteresis (dead zone N) in the characteristic of valve drive current-valve opening as shown in FIG. In the vicinity of burner 1,
A spark plug 6 and a frame rod 7 are arranged. A combustion chamber 8 is provided above the burner 1, and the combustion chamber 8
The exhaust passage 9 communicates with the upper end of the. A fan motor 10 drives a fan 11 provided in the exhaust passage 9. The fan motor 10 controls exhaust gas and supplies combustion air to the burner 1. Reference numeral 12 is a heat exchanger installed in the combustion chamber 8, and an inlet of the heat exchanger 12 is a water supply pipe via an exhaust heat recovery device 13 installed in the combustion chamber 8 and a coil pipe 14 surrounding the combustion chamber 8. The outlet of the heat exchange 12 is connected to a plurality of outlets 17 such as a calan and a shower via a outlet pipe 16. Outlet from the water supply pipe 15
The route to 17 constitutes the water supply route 18. Water supply route 18
A water flow switch 19 as a water flow detecting means is installed in the water supply pipe 15 and a hot water outlet temperature detecting means 20 such as a thermistor is installed in a hot water discharge pipe 16. Reference numeral 21 is an air volume detecting means provided in the exhaust passage 9.

The operation of this combustion control device will be described below.

When the water flow switch 19 is turned on by the water flow to the heat exchanger 12, the solenoid valve 3 is opened and the spark plug 6 is sparked to ignite the fuel gas flowing out from the burner 1, and the fan motor 10 is driven. To be done.

The phase of the fan motor 10 is controlled based on the deviation between the target temperature signal from the target temperature setting means (not shown) and the detected temperature signal from the hot water temperature detecting means 20, and the PID control means (based on the deviation) The opening degree of the fuel control valve 5 is adjusted by PID control (not shown), whereby the air-fuel ratio is automatically maintained within a predetermined range.

However, the conventional example having such a configuration has the following problems.

(A) In the forced combustion type water heater configured as described above, the time constant of the heat exchanger 12 itself is short and its response is high. Therefore, the characteristic of the valve drive current based on the I operation in the PID control is made steep as shown in FIG.
When the operating time is shortened, the fuel supply amount increases rapidly, and the outlet heated water temperature rises rapidly as shown in FIG. Since this overshoot is attempted to be suppressed by PID control, hunting occurs in the tapping temperature.
And, the hunting causes a significant discomfort to the user of the hot water.

(B) In order to prevent overshoot and hunting, it is necessary to lengthen the I operation time. That is, it is necessary to make the characteristic of the valve drive current based on the I operation gentle as shown in FIG. By doing this,
As shown in FIG. 3B, the hot water temperature changes smoothly, and the discomfort given to the user is reduced.

(C) However, if the rate of change of the valve drive current based on the I operation is set small, for example, when the target temperature is drastically reduced, the response speed of the tapping temperature is low,
The problem still remains that it makes the user of the hot water uncomfortable. That is, as described above, the fuel control valve 5 having the hysteresis of the valve drive current-valve opening characteristic has, as its control characteristic, a valve drive current rapid decrease means (Fig. Based on the operation of (not shown), the valve drive current is once flowed so that the valve is fully closed. In the case of the characteristics shown in FIG. 8, the valve drive current is suddenly reduced to 20 mA. Then, the valve drive current is increased by the I operation to the current value corresponding to the target temperature under the above-mentioned small set change rate.

By the way, in this case, from 20 mA to 130 mA, the fuel control valve 5 remains in the fully closed state due to the hysteresis characteristic. That is, this area is a dead zone N.

(D) The problem caused by performing the I operation in the dead zone N will be described in detail with reference to FIG.

When the target temperature is suddenly decreased at the time t ₀ as shown in FIG.
The valve drive current sharply decreases to 20mA as shown in. As a result, the fuel control valve 5 is fully closed, the fuel supply amount to the burner 1 becomes zero as shown in FIG. (C), and the hot water outlet temperature once drops sharply as shown in FIG. (D). Then the time
At t ₁ , the valve drive current increases from 20 mA by the I operation at the small rate of change described above.
The fuel control valve 5 maintains the fully closed state up to 0 mA. Therefore, the fuel supply amount remains zero, and the hot water discharge temperature also remains low. After the time t ₂ when the valve drive current reaches 130 mA, the valve opening becomes proportional to the valve drive current, the fuel control valve 5 is opened, the fuel supply amount increases, and the outlet heated water temperature reaches the target temperature. Rise towards. Then, at time t ₃ , the temperature stabilizes at the target temperature. As described above, the fuel control valve 5 having the dead zone N (20 to 130 mA) due to the hystericim characteristic allows the valve drive current to flow once so as to be fully closed when the valve opening degree is greatly reduced. Therefore, if the rate of change in the valve drive current is reduced to prevent overshoot, the time T ₁ from the target temperature setting time t ₀ to the target temperature arrival time t ₃ will be considerably long. Is inevitable.

(E) From the above, when the target temperature is drastically decreased, the user of hot water still feels uncomfortable because the response speed of the hot water temperature is slow. Moreover, especially when using the shower, the degree of discomfort is large,
Since the body is left with the hot water without running it, the hot water and fuel are wasted.

(Object of the invention) The present invention has been made in view of such circumstances, and improves the response of the hot water discharge temperature when the target temperature is rapidly lowered from the hot water discharge temperature. It is intended to prevent the user from feeling uncomfortable.

(Composition and Effect of the Invention) A combustion control device for a water heater according to the present invention for achieving the above object is installed in a fuel supply path of a burner, and the valve opening is controlled in response to a valve drive current. Further, when the valve opening is in the fully closed state, the fuel control valve has a dead zone in which the valve closing current is maintained until the valve drive current increases above a predetermined value, and the fuel control in response to the valve opening signal. Fuel control valve driving means for applying a valve driving current to the valve, tapping temperature detecting means for detecting tapping temperature, target temperature setting means for setting a target temperature of tapping temperature, and integral operation in response to a deviation between the two temperatures. The integrated value is given to the fuel control valve drive means as a valve opening signal for outputting a valve drive current from the fuel control valve drive means, and the integral operation is controlled at a predetermined change rate of the valve drive current. Of a water heater with PID control means In the combustion control device, the target temperature is drastically lowered from the detected hot water temperature and the integrated value of the PID control means is lowered in response to the deviation of both temperatures exceeding a predetermined value to drive the valve. A valve drive current rapid decrease means for rapidly reducing the current to a value at which the valve opening of the fuel control valve is fully closed, and an integral for limiting the decrease value of the integrated value of the PID control means by the valve drive current rapid decrease means to a constant value. Start current sudden rise means, the fuel control valve drive means by the valve opening current from the valve opening signal from the PID control means, the target temperature set by the target temperature setting means and the hot water temperature detection means When the fuel control valve is being driven at an opening degree that is in equilibrium with the detected temperature detected, when the deviation between the two temperatures exceeds the predetermined value, the valve drive current sudden decrease means
After reducing the integral value of the PID control means to rapidly reduce the valve drive current to a value at which the valve opening of the fuel control valve is fully closed, the valve opening of the fuel control valve is once fully closed. In the integration start current sudden rise means, the decrease value of the integral value of the PID control means is limited to a constant value, and the PID control means starts the integral operation from the integral value limited to this constant value.
It is characterized in that the time until the valve drive current exceeds the dead zone can be shortened, and the combustion control corresponding to the deviation between the detected temperature of the outlet heated water temperature and the target temperature can be executed.

In the above configuration, when the target temperature drops sharply below the hot water discharge temperature and the deviation between the two temperatures exceeds the predetermined value, the integral value of the PID control means is reduced by the valve drive current rapid reduction means to drive the fuel control valve. The valve drive current value from the means is sharply reduced,
The fuel control valve is once fully closed. In this case, the integration value of the PID control means is in a state where the decrease value is limited to a constant value by the integration start current sudden increase means. And PI
Since the D control means starts the integration from the integral value limited to the constant value, as a result, the integration operation can be performed so that the target temperature rapidly converges the deviation from the tapping temperature within a predetermined value. Even if the target temperature is suddenly lowered below the tapping temperature, the PID control means is set to an integral operation that prevents overshooting of the tapping temperature or hunting It will be possible to control so as to eliminate.

Therefore, according to the present invention, the fuel control valve driving means changes the predetermined rate of change with respect to the fuel control valve so that the hot water temperature changes smoothly without overshooting or hunting and does not cause discomfort to the user. If the integration operation is set so that the PID control means can output a valve opening signal to the fuel control valve drive means so as to output the drive current, the integration of the PID control means with respect to the change of the tap water temperature will be performed. The response of the operation is based on the combustion control device of the water heater set to be slow, and for example, when the target temperature suddenly drops below the hot water temperature, the valve drive by reducing the integral value of the PID control means. Even if the fuel control valve is fully closed with the electric current,
Since the integral value is limited to a fixed value, the limited integral value can be added to the integral value in the next integral operation to start the integral operation, and the tapping temperature is exceeded regardless of the dead zone of the fuel control valve. The target temperature is quickly reached without shooting and the discomfort to the user of the hot water is eliminated.

In addition, when the target temperature is drastically lowered, if the response of the hot water reaching the target temperature is slow, the user of hot water is also not using the hot water from the shower etc. during that time. Where hot water or fuel is wasted,
Since the response is quick, there is an additional effect that the waste can be eliminated.

(Description of Embodiments) Hereinafter, the present invention will be described in detail based on embodiments illustrated in the drawings.

1 is a block circuit diagram of a combustion control device for a water heater according to an embodiment of the present invention, and FIG. 2 is a block circuit diagram of a portion of FIG.

This combustion control device is applied to the water heater shown in FIG. 7, but it goes without saying that it can also be applied to other water heaters having similar configurations.

In FIG. 1, 20 is a hot water outlet temperature detecting means, 22 is a target temperature setting means for hot water outlet temperature, and 23 is a hot water outlet temperature detecting means 20.
It is a deviation detecting section for producing a deviation signal c between the detected temperature signal a from the target temperature signal b and the target temperature signal b from the target temperature setting means 22. Reference numeral 24 is motor rotation speed control means for calculating the conduction phase of the drive current of the fan motor 10 based on the deviation signal c and outputting a trigger signal d for phase control to the fan motor driving means 25, and 26 is for the deviation signal c. The PID control means calculates the opening degree of the fuel control valve 5 by PID calculation based on the PID calculation and outputs the valve opening degree signal e to the fuel control valve driving means 27. 28,29,30
Are P (proportional) operation control means, I (integral) operation control means, and D (differential) operation control means in the PID control means 26, respectively. Reference numeral 31 denotes a valve drive current sharply decreasing means (also referred to as a braking means) for rapidly reducing the drive current for the fuel control valve 5 to a current value at which the fuel control valve 5 is fully closed when the value of the deviation signal c is a predetermined value or more. The control signal f for this purpose is output to the fuel control valve drive means 27. Further, 32 is, when the deviation signal c is a predetermined value or more,
The control signal g from the valve drive current sudden decrease means 31 is input, and in response thereto, the integral start current sudden increase means for rapidly increasing the integral start current of the I operation control means 29 in the PID control means 26. The control signal h is output to the I operation control means 29. As the integration start current sudden increase means 32, for example, a limiter for limiting the integration value of the PID control means 26 to a constant value is used (described later).

Specific circuits of the target temperature setting means 22 and the outlet heated water temperature detecting means 20 will be described with reference to FIG. In FIG. 2, 33 is a bridge circuit composed of a resistor R ₁ , a thermistor TH, a variable resistor VR, and resistors R ₂ and R _3. The thermistor TH in the bridge circuit 33 is the hot water outlet temperature detecting means in FIG. Corresponding to 20,
The variable resistance VR corresponds to the target temperature setting means 22 in FIG. In the PID control means 26, the output of the P operation control means 28 is input to the D operation control means 30 and the output of the D operation control means 30 is input to the I operation control means 29. This is for smoothly performing the valve opening control of the valve 5. As shown in FIG. 3, the characteristic of the valve drive current based on the I operation of the I operation control means 29 in the PID control means 26 is gradual so as to prevent the hot water temperature overshoot or hunting. . As shown in FIG. 4, the valve drive current sudden decrease means 31 does not output the control signals f and g when the level of the deviation signal c is lower than the reference value E ₀ ,
When the reference value E ₀ is exceeded, the signals f and g are output.

Next, the operation of this embodiment will be described with reference to FIG.

Before time t _4, it is assumed that the temperature detected by the outlet heated water temperature detection means 20 and the target temperature set by the target temperature setting means 22 are in agreement and are in an equilibrium state.

At time t ₄ , variable resistance VR (target temperature setting means 22)
It is assumed that the target temperature is rapidly lowered by the operation of as shown in FIG. Then, a change occurs in the equilibrium state of the bridge circuit 32, the deviation signal c is input to the D operation control means 30,
At the same time, the deviation signal c is input to the valve drive current rapid decrease means 31. Since the target temperature is suddenly reduced, the level of the deviation signal c exceeds the reference value E ₀ , the control signal f is sent from the valve drive current rapid decrease means 31 to the fuel control valve drive means 27, and the integration start current rapid increase means 32 is sent. On the other hand, the control signal g is output.

The fuel control valve drive means 27 rapidly reduces the valve drive current to 20 mA by the control signal f as shown in FIG. As a result, the fuel control valve 5 is fully closed.

The integration start current sudden increase means 32 outputs a control signal h to the I operation control means 29 based on the control signal g at time t ₄ . As a result, the time that has elapsed very short time from the time t ₄
At t ₅ , the valve drive current suddenly rises from 20 mA to 130 mA. That is, the same operation is performed as if there is substantially no dead zone N. The I motion by the I motion control means 29 is 13
Starting from 0mA. In other words, in order to prevent the overshoot of the tap water temperature, the valve drive current is set to 130 mA
After the time t ₅ when the fuel supply amount reaches, the valve opening becomes proportional to the valve drive current, and as the fuel control valve 5 opens, the fuel supply amount immediately increases as shown in FIG. As shown in Figure (D), the outlet heated water temperature immediately rises toward the target temperature.
Then, at time t ₆ , the temperature stabilizes at the target temperature. That is, the time T ₂ required for the fuel control valve 5 to open to the degree of opening corresponding to the target temperature is significantly shortened as compared with the time T ₁ in the conventional example.

On the other hand, between times t ₄ and t ₆ , the motor rotation speed control means 24 calculates the rotation speed of the fan motor 10 based on the deviation signal c, and controls the phase of the fan motor drive means 25. As a result, the rotation speed of the fan motor 10 increases and stabilizes at time t ₆ . Therefore, the opening degree of the fuel control valve 5, that is, the burner 1
The amount of fuel supplied to the burner 1 becomes proportional to the number of revolutions of the fan motor 10, that is, the amount of air supplied to the burner 1, and the air-fuel ratio is maintained within a predetermined range.

In FIG. 6, the valve drive current sudden decrease means 31, the integration start current sudden increase means 32 and the I operation control means 29 are concretely shown in a circuit. The I operation control means 29 is composed of a resistor R ₄ and a capacitor C. The charge charged in the capacitor C is accumulated as an integrated value corresponding to the deviation by the I operation control means 29, and the I operation control means 29 also causes an overshoot or the like in the valve opening signal to the fuel control valve drive means 27. It is set so that it changes with the integral operation corresponding to the deviation so that it does not occur. A resistor R5 is provided in the discharge path of the charged electric charge of the capacitor C,
A switching transistor Q and a Zener diode ZD are inserted. Then, the valve drive current sudden decrease means 31
Includes a switching transistor Q in this discharge path, and the integration start current rapid rising means 32 is similarly composed of a resistor R ₅ in this discharge path, between the collector and emitter of the switching transistor Q, and a Zener diode ZD. The valve drive current sudden decrease means 31 generates the control signal i based on the deviation signal c, and inputs the generated control signal i to the base of the transistor Q. Here, in FIG. 6, the control signal i is shown in the form of a trigger signal, but this is sharply lowered in the direction in which the target temperature is lower than the hot water temperature, and the deviation between the two temperatures exceeds a predetermined value. , And is shown in the form of a trigger signal merely to explicitly indicate that the switching transistor Q is conducting in that form of the trigger signal.

Referring to FIG. 5, when the target temperature sharply decreases at time t ₄ and the target temperature falls below the hot water discharge temperature by a predetermined value or more, the valve drive current rapid decrease means 31 responds to the deviation between the two temperatures by the same value. Times of Day
A control signal i that suddenly falls at t ₄ is generated, and the generated control signal i is applied to the base of the switching transistor Q to make the transistor Q conductive and form a charge discharge path of the capacitor C. Since the capacitor C is discharged through this discharge path, the integral value of the I operation control means 27 is rapidly reduced, whereby the valve drive current is rapidly reduced to 20 mA as shown in FIG. 5 (B), and the fuel control valve 5 Is fully closed. Here, the valve drive current becomes 20 mA because the fuel control valve has the hysteresis characteristic shown in FIG.

The capacitor C is discharged until the voltage across the capacitor C becomes equal to the Zener voltage of the Zener diode ZD. Here, the Zener diode ZD limits the integrated value to a constant value even if the capacitor C of the I operation control means 29 of the PID control means 26 is discharged. Next, when the fuel control valve 5 is fully closed, the hot water outlet temperature decreases, and the deviation between the two temperatures does not exceed a predetermined value.
The control signal i for turning it on is not given to the base of T at time t ₅ . Then, at that time t ₅ , the transistor Q is turned off, but at this time, the charge corresponding to the Zener voltage of the Zener diode ZD remains in the capacitor C, that is, the integrated value of the I operation control means 27 is Since the limit value is limited to a constant value, the integral value limited to the constant value is added to the integral value of the next integral operation.
It rapidly increases from 20mA to 130mA. The meaning of the sudden increase from 20 mA to 130 mA at once is that the integrated value at the start of integration of the I operation control means 29 due to the residual charge of the capacitor C is a value corresponding to the hysteresis width of 20 mA to 130 mA, When the switching transistor Q is turned off, the discharge path of the capacitor C is lost, and the I operation control means 29 starts the integration operation corresponding to the deviation between the two tapping temperatures at time t ₅ , The valve opening signal from the PID control means 26 is supplied to the fuel control valve driving means 27 to 13
It is a signal that gives a valve drive current of 0 mA to the fuel control valve 5.
Therefore, after the fuel control valve 5 is fully closed at the time t ₄ , after the time t ₅ after the dead zone has passed in a very short time, that is, without being substantially affected by the hysteresis characteristic of the fuel control valve 5, The valve opening is controlled so that the outlet temperature approaches the target temperature by the integration operation so that the target temperature does not overshoot or hunt.

[Brief description of drawings]

1 to 6 relate to a combustion control device for a water heater according to an embodiment of the present invention, FIG. 1 is a block circuit diagram of the combustion control device for a water heater, and FIG. 2 is a block circuit of a part of FIG. Figure,
FIG. 3 is a characteristic diagram of PID control, FIG. 4 is a waveform diagram of the deviation signal, FIG. 5 is a time chart for explaining the operation, and FIG. 6 is a circuit diagram of a main part of the present invention. Further, FIGS. 7 to 11 relate to a conventional example, FIG. 7 is a schematic sectional view showing an example of a water heater, FIG. 8 is a hysteresis characteristic diagram of valve drive current-valve opening degree, FIG. 9 and FIG. FIG. 10 is a characteristic diagram for explaining the basic operation, and FIG. 11 is a time chart for explaining the operation. In the figure, reference numeral 1 is a burner, 2 is a fuel supply path, 5 is a fuel control valve, 20 is hot water outlet temperature detecting means, 22 is target temperature setting means,
26 is PID control means, 29 is I operation control means, 31 is valve drive current sudden decrease means, and 32 is integration start current sudden increase means.

Claims (1)

[Claims] 1. A burner, which is interposed in a fuel supply path, controls a valve opening in response to a valve driving current, and when the valve opening is in a fully closed state, the valve driving current exceeds a predetermined value. A fuel control valve having a dead zone in which the valve is fully closed until it increases, fuel control valve drive means for applying a valve drive current to the fuel control valve in response to a valve opening signal, and hot water discharge for detecting hot water temperature. A temperature detecting means, a target temperature setting means for setting a target temperature of the outlet heated water temperature, an integral operation in response to a deviation between the two temperatures, and the integrated value is output to the fuel control valve driving means as a valve driving current. In the combustion control device of the water heater, which is provided as a valve opening signal for causing the integration operation to perform the integral operation so that the valve drive current is controlled at a predetermined change rate, the target The temperature is higher than the detected hot water temperature. A value at which the valve opening of the fuel control valve is fully closed by reducing the integral value of the PID control means in response to the temperature being drastically reduced and the deviation between both temperatures exceeding a predetermined value. And a valve drive current sudden decrease means for suddenly decreasing, and an integral start current sudden increase means for limiting the decrease value of the integral value of the PID control means by the valve drive current sudden decrease means to a constant value, and from the PID control means Fuel control is performed at an opening such that the target temperature set by the target temperature setting means by the fuel control valve driving means and the detected temperature detected by the tapping temperature detecting means are balanced by the valve driving current based on the valve opening signal. When driving the valve, when the deviation between the two temperatures exceeds the predetermined value, the integral value of the PID control means is reduced by the valve drive current sudden reduction means to reduce the valve drive current to the fuel control valve. Value at which the valve opening of is fully closed After the fuel control valve is opened to a fully closed position, the integral start current sudden increase means limits the decrease value of the integrated value of the PID control means to a constant value, and the PID control means By starting the integral operation from the integral value limited to this constant value, it is possible to shorten the time until the valve drive current exceeds the dead zone,
A combustion control device for a water heater, which is capable of performing combustion control corresponding to a deviation between the detected temperature of the hot water discharge temperature and the target temperature.