JP2020118440A - Gas water heater - Google Patents

Abstract

To provide a gas water heater which can correct the linearity of a signal output in an atmosphere even in a constitution for detecting an oxygen concentration in a combustion pipe by using an A/F sensor under an environment in which the gas water heater is continuously used.SOLUTION: A gas supplied via a gas supply pipe 9 is injected into a combustion pipe 4 which is incorporated in a hot water tank 2 via an injection part 12 together with atmospheric air. A proportional valve control part 11 heats water which is supplied into the hot water tank 2 by controlling a proportional valve 10 arranged at a tip of the gas supply pipe 9, and controlling a combustion state in the combustion pipe 4 on the basis of an oxygen concentration detected by an A/F sensor 14. A blower control part 8 performs purge processing for supplying atmospheric air into the combustion pipe 4 up until a mixture gas in the combustion pipe 4 is reignited from extinguishment after the mixture gas is ignited, and a current measurement part 15 calibrates the linearity of signal output characteristic of the A/F sensor 14 after a finish of the purge processing.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas water heater provided with an A/F sensor that detects oxygen concentration.

Some gas water heaters mainly used in North America or the like use a venturi pipe to supply gas to a combustion chamber. In this case, if the pressure difference before and after the Venturi tube changes due to atmospheric pressure or the like, there is a problem that the combustion efficiency deteriorates and the energy saving performance of the gas water heater deteriorates. Patent Document 1 is an example of a gas water heater using a Venturi tube, although not for a gas supply system.

JP, 2018-66540, A

To solve the above problems, a technique has been devised to optimize combustion efficiency by using a proportional valve in a gas supply system and performing gas injection control using an A/F sensor that detects oxygen concentration. There is. However, as shown in FIG. 10, the accuracy of the A/F sensor deteriorates mainly due to drift of the linearity of the signal output due to deterioration over time. Therefore, it is necessary to correct the linearity of the A/F sensor in the atmosphere.

However, since the hot water heater keeps the hot water by continuously burning, the oxygen concentration in the combustion chamber is in a lowered state. Therefore, it is difficult to correct the linearity of the A/F sensor in the atmosphere.

The present invention has been made in view of the above circumstances, and an object thereof is to output a signal even in a configuration in which an oxygen concentration in a combustion pipe is detected using an A/F sensor in an environment where it is continuously used. It is to provide a gas water heater that can accurately correct the linearity of the.

According to the gas water heater of the first aspect, the gas supplied through the gas supply pipe is injected into the combustion pipe built into the hot water supply tank together with the inhaled atmosphere through the injection unit. The control unit controls the proportional valve arranged at the tip of the gas supply pipe, and controls the combustion state in the combustion pipe based on the oxygen concentration detected by the A/F sensor to control the water supplied to the hot water tank. To heat. Then, the control unit performs a purge process of supplying the atmosphere between extinguishing after igniting the mixed gas in the combustion tube and re-ignition, and the sensor correction unit performs A/F after the purge process is completed. The linearity of the signal output characteristic of the sensor is corrected based on the oxygen concentration detected by the sensor. According to this structure, the sensor correction unit can correct the linearity of the A/F sensor in a state where oxygen is supplied into the combustion pipe by the purging process, and thus the correction can be performed with high accuracy.

According to the gas water heater of the second aspect, the current detector detects the current flowing through the A/F sensor. Then, when the purge process is started, the sensor correction unit starts detection of the oxygen concentration in the combustion pipe based on the current value detected by the current detection unit, and determines that the oxygen concentration has risen above the threshold value. Then, the correction starts. As a result, the sensor correction unit can perform the correction in a state where the oxygen concentration in the combustion pipe is reliably increased.

According to the gas water heater of claim 3, the sensor correction unit causes the control unit to perform the purge process if the oxygen concentration does not reach the threshold value even after a predetermined time has elapsed since the execution of the purge process was started. To extend the execution period of. As a result, the control unit can extend the execution period of the insufficient purge process in response to the instruction from the sensor correction unit.

According to the gas water heater of the fourth aspect, the sensor correction unit instructs the control unit to shorten the execution period of the purge process when the oxygen concentration becomes equal to or higher than the threshold value before the elapse of the fixed time. As a result, the control unit can shorten the execution period of the excessive purge process in response to the instruction from the sensor correction unit.

The figure which shows the structure of the gas water heater of this embodiment. Flowchart showing combustion control executed mainly by the integrated control unit The figure which shows the state in which the temperature of water changes with the process of FIG. Flowchart centering on purge processing performed when calibrating the A/F sensor A diagram showing a state in which the oxygen concentration in the combustion pipe changes as the purge process is performed. Diagram showing an example of determining the initial value of the execution time of the purging process The figure which shows the image which calibration is performed in the state where the oxygen concentration of the intake pipe side of the A/F sensor and the combustion pipe side are equal. Flowchart showing details of purge time extension processing Flowchart showing details of purge time reduction processing The figure explaining the calibration performed about the linearity of an A/F sensor.

Hereinafter, one embodiment will be described with reference to FIGS. 1 to 9. FIG. 1 shows the configuration of a gas water heater 1 of this embodiment. Water is supplied to the inside of the hot water supply tank 2 from a water supply (not shown) through the water supply pipe 3. The hot water supply tank 2 has a built-in combustion pipe 4, and when gas is burned inside the combustion pipe 4, water is heated to become hot water. The hot water is supplied to the outside via the discharge pipe 5. The discharge pipe 5 is provided with a temperature sensor 16 for detecting the temperature of the hot water.

An intake pipe 6 is connected to the hot water supply tank 2, and a blower 7 is arranged inside the intake pipe 6. The blower 7 is drive-controlled by a blower control unit 8 provided outside the intake pipe 6, and sucks the atmosphere from the outside. A gas supply pipe 9 is connected to a midway portion of the intake pipe 6 via a proportional valve 10. The proportional valve 10 is driven and controlled by a proportional valve control unit 11 outside the gas supply pipe 9. As a result, the gas supply amount into the intake pipe 6 is adjusted.

The mixed gas of the gas inside the intake pipe 6 and the atmosphere is supplied to the combustion pipe 4 via the injection unit 12. The mixed gas in the combustion tube 4 is ignited and burned by an igniter (not shown). The combustion pipe 4 is connected to the intake pipe 6 at the upper portion of the hot water supply tank 2 in the figure, and has a main portion 4a extending below the hot water supply tank 2, a folded portion 4b extending upward from below the hot water supply tank 2, and a main portion from there. 4a, and a spiral portion 4c which surrounds the circumference of 4a in a spiral shape and extends downward. An exhaust pipe 13 is connected to the spiral portion 4c, and the gas after combustion is exhausted to the outside of the hot water supply tank 2.

An A/F sensor 14 is arranged inside the combustion pipe 4 on the right side of the injection unit 12 in the figure. The A/F sensor 14 is connected to a current measuring unit 15 outside the hot water supply tank 2. As shown in FIG. 5, the current measuring unit 15 measures the oxygen concentration inside the combustion tube 4 by measuring the current value flowing through the A/F sensor 14 while the A/F sensor 14 is driven. The current measuring unit 15 corresponding to the control unit also performs a process of correcting the linearity of the signal output characteristic of the A/F sensor 14. The current measuring unit 15 corresponds to a current detecting unit.

The overall control unit 17 communicates with the blower control unit 8, the proportional valve control unit 11, and the current measuring unit 18, and controls each control unit and the like in an integrated manner. Further, the temperature detected by the temperature sensor 16 is input to the overall control unit 17. The current measuring unit 15 and the integrated control unit 17 correspond to a sensor correction unit. Note that, hereinafter, the “purge process” refers to a process of supplying oxygen and atmosphere into the combustion chamber in order to prevent extinction due to incomplete combustion immediately after igniting gas, which is performed in a general gas water heater.

Next, the operation of this embodiment will be described with reference to FIGS. 2 to 9. FIG. 2 is a flowchart showing combustion control executed mainly by the integrated control unit 17. When the igniter ignites the gas (S40), the overall control unit 17 measures the temperature of the water with the temperature sensor 16 (S41). Then, it is judged whether or not the measured temperature is lower than the set temperature (S42), and if it is lower than the set temperature (YES), the combustion state of the gas is continued (S43), and if it is higher than the set temperature (NO) extinguishing the fire. Is performed (S44).

Then, it is determined whether or not the condition for executing the purge process is satisfied (S45), and if the condition is satisfied (YES), the purge process is executed (S46), and if the condition is not satisfied (NO). ) Return to step S41. Here, the “condition for executing the purging process” is statically or dynamically set according to the specifications of each product, the operating status of the product, the operating environment, and the like. The condition of "execute every time the fire is extinguished" may be used. After executing step S44, when it is determined to be “YES” in step S42, ignition of gas is performed by the igniter in step S43. As a result of the control as described above, the extinction and ignition of the igniter are repeated, and the temperature of the water in the hot water supply tank 2 fluctuates up and down with the set temperature in between, as shown in FIG.

In such a period in which the temperature fluctuates up and down, the purge process may be started between the extinguishing and the next ignition, and the purge process may be completed by the next ignition. Further, in the above temperature fluctuation period, the temperature sensor 16 measures the temperature of the hot water at intervals of, for example, 5 to 10 seconds to extinguish/ignite. Therefore, the purge process may be executed if the fire is extinguished after the elapse of a certain period corresponding to the above interval.

FIG. 4 is a flowchart showing the purging process in step S46. The current measuring unit 15 clears the counter for measuring the execution time of the purge process to zero (S2). At this time, the proportional valve control unit 11 fully closes the proportional valve 10 to stop the gas supply, and the blower control unit 8 drives the blower 7. As a result, only the atmosphere is supplied into the combustion pipe 4 and the purge process is started. Then, it waits for a certain period of time such as several seconds to several tens seconds (S3).

When a certain time has elapsed, the counter is incremented (S4), and it is determined whether the value of the counter exceeds "10" (S5). If the counter value is "10" or less (NO), the current value flowing in the A/F sensor 14 is detected to measure the oxygen concentration in the combustion pipe 4 (S6). Then, it is determined whether or not the absolute value of the difference between the oxygen concentration measured last time and the oxygen concentration measured this time is less than a threshold value of 0.3% (S7). If the difference in oxygen concentration is 0.3% or more (NO), the oxygen concentration measured this time is substituted for the previous oxygen concentration (S8), and the process proceeds to step S3.

If the counter value exceeds “10” while executing the loop of steps S3 to S8 (S5; YES), the difference in oxygen concentration in the combustion pipe 4 is 0 even if the purging process is executed for a predetermined time. It shows that it does not exceed 3%. Therefore, the current measuring unit 15 cooperates with the blower control unit 8 to perform the purge process time extension process to be performed next time (S9). The details will be described later.

Further, when the difference in oxygen concentration decreases to less than 0.3% while executing the loop of steps S3 to S8 (S7; YES), the oxygen in the combustion pipe 4 is terminated before the purging process for the predetermined time is completed. It shows that the difference in concentration was less than 0.3%. Therefore, the current measuring unit 15 performs a process of shortening the time of the purge process to be performed next time (S10). The details will be described later. Then, if the calibration execution condition is satisfied (S11; YES), the calibration of the A/F sensor 14 is executed (S12). The conditions for performing the calibration also differ depending on the specifications of each product, but for example, the condition is that the user first uses the gas water heater 1 after several days and ignites.

FIG. 5 shows a state in which the oxygen concentration in the combustion tube 4 changes with the execution of the purging process. The horizontal axis represents the number of oxygen concentration samples, and the vertical axis represents the oxygen concentration percentage. The sampling interval is, for example, about 0.3 seconds. The sampling of the oxygen concentration is always performed in parallel with the purging process shown in FIG.

Further, FIG. 6 shows an example of determining the initial value of the execution time of the purging process, referring to the change rate of the concentration difference for the sample of the measured oxygen concentration, and performing the purging process for how long. It is determined depending on whether the difference in oxygen concentration is sufficiently small. FIG. 7 shows an image in which the calibration is executed in a state where the oxygen concentrations on the intake pipe 6 side and the combustion pipe 4 side of the A/F sensor 14 are equal.

FIG. 8 is a flowchart showing details of the purge time extension process in step S9. Let d1, d2, d3,..., dN be the oxygen concentration samples that have been sampled by the time the execution of step S9 is started, and the differences dS1, dS2,. dS1=d2-d1, dS2=d3-d2,..., dS(N-1)=dN-d(N-1)
It is defined as. In addition, dRate
dS1/dS2, dS2/dS3,..., dS(N-2)/dS(N-1)
It is defined as the average value of these.

In the next purge extension process, the counters C and n are set to zero (S20), and the difference predicted value is set to rDiff.
rDiff=dn-d(n-1)
Is calculated (S21). Next, it is determined whether or not the predicted value rDiff is less than 0.3 (S22), and if it is 0 or 3 (NO), the predicted value rDiff is set to rDiff=rDiff*dRate.
And the counters C and n are respectively incremented (S23). Then, the process returns to step S21.

When the predicted value rDiff becomes less than 0.3 while executing the loop of steps S21 to S23 (S22; YES), the purge processing time is extended by the amount of the value of the counter C at that time multiplied by the sampling interval. The blower control unit 8 is notified of the instruction (S24).

FIG. 9 is a flowchart showing details of the purge time shortening process in step S10. First, it is determined whether the value of the counter at the time of shifting to step S10 is less than "10" (S31). If it is less than "10" (YES), the time obtained by multiplying the difference between the value "10" and the counter value by the sampling interval is transmitted to the blower controller 8 (S32). Based on this, the blower control unit 8 shortens the execution time of the next purge process. Then, the calibration of the A/F sensor 14 is executed (S33). On the other hand, if the value of the counter is "10" or more in step S31 (NO), the execution time cannot be shortened (S34), and the process directly proceeds to step S33.

As described above, according to the gas water heater 1 of the present embodiment, the gas supplied through the gas supply pipe 9 and the inhaled air together with the combustion pipe 4 built in the hot water supply tank 2 through the injection unit 12 are connected. Is injected into. The proportional valve control unit 11 controls the proportional valve 10 arranged at the tip of the gas supply pipe 9 and controls the combustion state in the combustion pipe 4 based on the oxygen concentration detected by the A/F sensor 14. The water supplied to the hot water supply tank 2 is heated.

Then, the blower control unit 8 performs a purge process of supplying the atmosphere into the combustion pipe 4 between extinguishing after igniting the mixed gas in the combustion pipe 4 and re-ignition, and the current measuring unit 15 After the purging process is completed, the linearity of the signal output characteristic of the A/F sensor 14 is calibrated. According to this structure, the current measuring unit 15 can correct the linearity of the A/F sensor 14 in a state where oxygen is supplied to the combustion pipe by the purging process, and thus can perform highly accurate correction. .. In addition, the calibration can be efficiently performed along with the execution of the purging process.

Further, the current measuring unit 15 detects the current flowing through the A/F sensor 14, and when the purging process is started, it starts detecting the oxygen concentration in the combustion pipe 4 based on the detected current value, and the oxygen concentration If it is determined that the value has risen above the threshold value, the calibration is started. As a result, the calibration can be performed in a state where the oxygen concentration in the combustion tube 4 is surely increased.

In addition, the current measuring unit 15 instructs the blower control unit 8 to extend the execution period of the purge process if the oxygen concentration does not reach the threshold value even after a lapse of a certain time after the execution of the purge process is started. To do. Thereby, the blower control unit 8 can extend the execution period of the insufficient purging process in response to the instruction from the current measuring unit 15.

Further, the current measuring unit 15 instructs the blower control unit 8 to shorten the execution period of the purging process when the oxygen concentration becomes equal to or higher than the threshold value before the elapse of the certain period of time. As a result, the blower control unit 8 can shorten the execution period of the excessive purging process in response to the instruction from the current measuring unit 15.

The present invention is not limited to the embodiments described above or illustrated in the drawings, and the following modifications or expansions are possible.
The threshold value of the oxygen concentration is not limited to 0.3% and may be appropriately changed according to the individual design.
The purging time extension process and the purging time reduction process may be performed as necessary.

In the drawings, 1 is a gas water heater, 2 is a hot water tank, 4 is a combustion pipe, 6 is an intake pipe, 8 is a blower control unit, 12 is an injection unit, 14 is an A/F sensor, and 15 is a current measurement unit.

Claims (4)

Hot water supply tank,
A combustion tube that is placed in this hot water supply tank and burns gas,
An intake pipe for inhaling the atmosphere,
A proportional valve for supplying the gas supplied through the gas supply pipe to the inside of the intake pipe;
An injection unit that is disposed at the tip of the intake pipe and injects a mixed gas of gas and atmosphere into the combustion pipe,
An A/F sensor for detecting the oxygen concentration in the combustion pipe,
A controller that controls the proportional valve and controls the combustion state in the combustion pipe based on the oxygen concentration detected by the A/F sensor to heat the water supplied to the hot water tank.
A sensor correction unit that corrects the linearity of the A/F sensor,
The control unit performs a purging process of supplying the atmosphere into the combustion pipe from extinguishing after igniting the mixed gas in the combustion pipe to re-ignition.
The gas water heater which corrects the linearity of the signal output of the sensor based on the oxygen concentration detected by the A/F sensor after the purging process is completed. A current detector for detecting a current flowing through the A/F sensor,
When the control unit starts execution of the purge process, the sensor correction unit starts detection of the oxygen concentration in the combustion pipe based on the current value detected by the current detection unit, and the oxygen concentration rises above a threshold value. The gas water heater according to claim 1, wherein the correction is started when it is determined that the correction is performed. If the oxygen concentration does not reach the threshold value even after a lapse of a fixed time after the execution of the purge process is started, the sensor correction unit may extend the execution period of the purge process to the control unit. The gas water heater according to claim 2, which instructs. The gas water heater according to claim 3, wherein the sensor correction unit instructs the control unit to shorten the execution period of the purging process when the oxygen concentration becomes equal to or higher than the threshold value before the predetermined time has elapsed.

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