Premixing device

Abstract

To provide a premixing device in which: a motor drive type butterfly valve 62 is provided in an air supply passage 6 and a motor drive type variable throttle valve 74 is provided in a gas supply passage 7; a controller 8 is provided with a first connector 81 for connecting a first detection switch 7471 which switches from off to on when the opening of the variable throttle valve 74 becomes a predetermined opening and a second connector 82 for connecting a second detection switch 6231 which switches from off to on when the opening of the butterfly valve 62 becomes a predetermined opening; and erroneous connection can be determined even when erroneous connection occurs in the first and second detection switches 7471, 6231 with respect to the first and second connectors 81, 82 respectively.SOLUTION: A controller 8 is configured to perform detection switch determination control for determining whether or not a first detection switch 7471 and a second detection switch 6231 are connected correctly to a first connector 81 and a second connector 82.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a premixing device that mixes fuel gas with air and supplies the mixture to a burner via a fan. [Background technology]

[0002] Conventionally, as this type of premixing device, there is known one that includes an air supply passage upstream of a fan, a gas supply passage whose downstream end is connected to a gas suction section provided in the air supply passage, a zero governor that adjusts the secondary gas pressure to atmospheric pressure and is provided in the gas supply passage, a motor-driven variable throttle valve that is provided in a portion of the gas supply passage downstream of the zero governor, a motor-driven butterfly valve that is provided in a portion of the air supply passage upstream of the gas suction section, and a control means (see, for example, Patent Document 1). Here, the supply amount of fuel gas changes in proportion to the pressure difference between the atmospheric pressure, which is the secondary gas pressure, and the negative pressure acting on the gas suction section. And, since the negative pressure acting on the gas suction section changes according to the fan rotation speed, the supply amount of fuel gas changes in proportion to the fan rotation speed, i.e., the supply amount of air. Also, the ratio of the fuel gas supply amount to the air supply amount changes according to the opening degree of the variable throttle valve. Therefore, by setting the opening of the variable throttle valve to a predetermined standard opening according to the type of gas and controlling the fan speed according to the required combustion amount, an amount of mixture corresponding to the required combustion amount is supplied to the burner with an air excess ratio at a predetermined appropriate value.

[0003] Furthermore, in the above conventional example, the combustion capacity is controlled to be switched between at least two levels, large and small, by changing the opening of the butterfly valve and the variable throttle valve. That is, when the required combustion amount is relatively large, the opening of the butterfly valve is set to a predetermined large capacity opening on the open side, and the opening of the variable throttle valve is set to a large capacity opening as a reference opening, thereby switching the combustion capacity to the large capacity, so that the amount of mixture corresponding to the relatively large required combustion amount and the appropriate air excess ratio is supplied to the burner, and when the required combustion amount is relatively small, the opening of the butterfly valve is set to a predetermined small capacity opening on the closed side, and the opening of the variable throttle valve is set to a predetermined small capacity opening smaller than the reference opening, thereby switching the combustion capacity to the small capacity, so that the amount of mixture corresponding to the relatively small required combustion amount and the appropriate air excess ratio is supplied to the burner.

[0004] Also known in the past is a premixing device provided with a first detection means for confirming the operation of a variable throttle valve having a first detection switch that switches from off to on when the opening of the variable throttle valve reaches a predetermined opening, as disclosed in Patent Document 2, and a premixing device provided with a second detection means for confirming the operation of a butterfly valve having a second detection switch that switches from off to on when the opening of the butterfly valve reaches a predetermined opening, as disclosed in Patent Document 3. When both first and second detection means are provided, the control means is provided with a first connector for connecting the first detection switch and a second connector for connecting the second detection switch.

[0005] Here, in order to reduce costs, it is desirable to use the same type of connector for the first and second connectors. However, in this case, there is a possibility that the second detection switch is mistakenly connected to the first connector and the first detection switch is mistakenly connected to the second connector. Conventionally, even if the first and second detection switches are mistakenly connected to the first and second connectors, it is not possible to determine this. Therefore, the first connector and the second connector are currently different types to prevent mistaken connections. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-25722 [Patent Document 2] JP 2022-150178 A [Patent Document 3] JP 2017-187185 A Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above, an object of the present invention is to provide a premixing device that is capable of detecting erroneous connections of the first and second detection switches to the first and second connectors. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a premixing device that mixes fuel gas into air and supplies the mixture to a burner via a fan, comprising an air supply passage upstream of the fan, a gas supply passage having a downstream end connected to a gas suction portion provided in the air supply passage, a zero governor that adjusts secondary gas pressure to atmospheric pressure and is provided in the gas supply passage, a motor-driven variable throttle valve that is provided in a portion of the gas supply passage downstream of the zero governor, a motor-driven butterfly valve that is provided in a portion of the air supply passage upstream of the gas suction portion, and a valve that switches from off to on when the opening degree of the variable throttle valve reaches a predetermined opening degree. The variable throttle valve has a first detection means for confirming the operation of the variable throttle valve having a first detection switch which switches from off to on when the opening of the butterfly valve reaches a predetermined opening, a second detection means for confirming the operation of the butterfly valve having a second detection switch which switches from off to on when the opening of the butterfly valve reaches a predetermined opening, and a control means having a first connector which connects the first detection switch and a second connector which connects the second detection switch, wherein the control means is configured to perform detection switch discrimination control which determines whether the first detection switch and the second detection switch are correctly connected to the first connector and the second connector.

[0009] According to the present invention, even if an erroneous connection of the first and second detection switches to the first and second connectors occurs, it can be detected by the detection switch discrimination control. Therefore, it is possible to use the same type of connector as the first and second connectors, thereby reducing costs.

[0010] Here, it is possible to perform detection switch discrimination control by rotating the variable throttle valve drive motor and the butterfly valve drive motor in sequence, and determining that the first detection switch is correctly connected to the first connector when the signal input to the first connector during rotation of the variable throttle valve drive motor is switched from an OFF signal to an ON signal or from an ON signal to an OFF signal, and determining that the second detection switch is correctly connected to the second connector when the signal input to the second connector during rotation of the butterfly valve drive motor is switched from an OFF signal to an ON signal or from an ON signal to an OFF signal. However, this requires rotating the variable throttle valve drive motor and the butterfly valve drive motor in sequence, and therefore takes time for detection switch discrimination control.

[0011] Therefore, in the present invention, it is preferable to make the rotation phase difference of the variable throttle valve drive motor between the time when the first detection switch switches from off to on and the time when it switches from on to off different from the rotation phase difference of the butterfly valve drive motor between the time when the second detection switch switches from off to on and the time when it switches from on to off, and the control means performs the detection switch discrimination control based on the rotation phase difference of the drive motor of each valve between the time when the signal from each detection switch input to each of the first and second connectors switches from off signal to on signal and the time when it switches from on signal to off signal. According to this, the variable throttle valve drive motor and the butterfly valve drive motor can be rotated simultaneously to perform the detection switch discrimination control, and the time required for the detection switch discrimination control can be shortened. Furthermore, it is advantageous that not only the operation of switching each of the first and second detection switches from off to on can be confirmed, but also the operation of switching each of the detection switches from on to off can be confirmed. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is an explanatory diagram showing a premixing device according to an embodiment of the present invention. [Diagram 2] Cross-sectional view taken along line II-II in Figure 1. [Diagram 3] FIG. 2 is an exploded perspective view of a main portion of a variable throttle valve provided in the premixing device of the embodiment. [Figure 4] FIG. 4 is a cross-sectional side view taken along line IV-IV in FIG. [Diagram 5] 5(a) is a cross-sectional view taken along line VV in FIG. 4, and FIG. 5(b) is a cross-sectional view corresponding to FIG. 5(a) in the open position of the butterfly valve. [Figure 6] FIG. 2 is an exploded perspective view of a main part of a first detection means provided in the premixing device according to the embodiment of the present invention. [Figure 7] FIG. 4 is a flow chart showing an example of detection switch discrimination control by a control unit in the premixing device of the embodiment. [Figure 8] FIG. 11 is a flow chart showing another example of the detection switch discrimination control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The combustion device shown in Fig. 1 is a heat source machine including a full primary combustion burner 1, a combustion housing 2 that encloses the combustion space of the air-fuel mixture ejected from the combustion surface 1a of the burner 1, and a heat exchanger 3 disposed in the combustion housing 2. An upstream water supply pipe 31 and a downstream hot water outlet pipe 32 are connected to the heat exchanger 3. The combustion gas generated by the combustion of the air-fuel mixture heats the heat exchanger 3 and is then discharged to the outside through an exhaust pipe 4 connected to the end of the combustion housing 2. In addition, a premixing device A according to an embodiment of the present invention mixes fuel gas into air and supplies the mixture to the burner 1 through a fan 5.

[0014] The premixing device A includes an air supply passage 6 on the upstream side of the fan 5, a gas supply passage 7 for supplying fuel gas, and a controller 8 consisting of a microcomputer as a control means. The downstream end of the gas supply passage 7 is connected to a gas suction section 61 provided in the air supply passage 6. A venturi section 63 having a smaller diameter than a section in which a butterfly valve 62 (described later) is arranged is provided in a portion of the air supply passage 6 adjacent to the upstream side of the gas suction section 61. A portion of the air supply passage 6 adjacent to the downstream side of the venturi section 63 is surrounded by a cylindrical section 64 having a larger diameter than the venturi section 63. The downstream end of the venturi section 63 is inserted into the upstream end of the cylindrical section 64 with an annular gap, and this gap constitutes the gas suction section 61. A gas chamber 71 communicating with the gas suction section 61 is provided at the downstream end of the gas supply passage 7 so as to surround the cylindrical section 64. Further, in the gas supply passage 7, a main valve 72, a zero governor 73 that adjusts the secondary gas pressure to atmospheric pressure, and a variable throttle valve 74 are interposed in this order from the upstream side.

[0015] The amount of fuel gas supplied through the gas suction section 61 changes according to the pressure difference between the atmospheric pressure, which is the secondary gas pressure, and the negative pressure acting on the gas suction section 61. Here, the negative pressure acting on the gas suction section 61 changes according to the rotation speed of the fan 5. Therefore, the amount of fuel gas supplied changes in proportion to the rotation speed of the fan 5, that is, the amount of air supplied. In addition, the ratio of the amount of fuel gas supplied to the amount of air supplied changes according to the opening degree of the variable throttle valve 74. By setting the opening degree of the variable throttle valve 74 to a predetermined reference opening degree according to the type of gas used, the excess air ratio of the mixture becomes a predetermined appropriate value (for example, 1.3). Then, by controlling the rotation speed of the fan 5 according to the required combustion amount (the amount of combustion necessary to discharge hot water at a set hot water temperature), the mixture is supplied to the burner 1 in an amount according to the required combustion amount with an appropriate excess air ratio.

[0016] In order to prevent exhaust failure caused by wind entering the exhaust pipe 4, that is, to ensure wind resistance, the lower limit rotation speed of the fan 5 cannot be set too low. When the required combustion amount falls below a predetermined value corresponding to the lower limit rotation speed of the fan 5, it becomes impossible to supply the amount of air corresponding to the required combustion amount.

[0017] Therefore, in order to switch the airflow resistance of the portion of the air supply passage 6 upstream of the gas suction portion 61 between large and small, a butterfly valve 62 that can be switched between a closed position shown by a solid line in Fig. 1 and an open position shown by a virtual line is disposed. When the required combustion amount falls below the above-mentioned predetermined value, the butterfly valve 62 is switched to the closed position to increase the airflow resistance of the air supply passage 6, so that an amount of air corresponding to the required combustion amount below the predetermined value can be supplied without causing the rotation speed of the fan 5 to fall below the lower limit rotation speed.

[0018] However, simply increasing the air flow resistance of the air supply passage 6 by closing the butterfly valve 62 increases the negative pressure acting on the gas suction section 61, causing the amount of fuel gas supplied to be excessive, and causing the excess air ratio of the mixture supplied to the burner 1 to fall below the appropriate value. Therefore, when the required combustion amount is relatively small, the opening of the butterfly valve 62 is set to a predetermined small capacity opening, which is the opening when the butterfly valve 62 is in the closed position, and the opening of the variable throttle valve 74 is set to a predetermined small capacity opening smaller than the reference opening, thereby switching the combustion capacity to small capacity, so that the amount of the mixture corresponding to the appropriate excess air ratio and the relatively small required combustion amount is supplied to the burner 1, and when the required combustion amount is relatively large, the opening of the butterfly valve 62 is set to a predetermined large capacity opening, which is the opening when the butterfly valve 62 is in the open position, and the opening of the variable throttle valve 74 is set to the large capacity opening, which is the reference opening, thereby switching the combustion capacity to large capacity, so that the amount of the mixture corresponding to the appropriate excess air ratio and the relatively large required combustion amount is supplied to the burner 1.

[0019] However, even if the same type of gas is used as the fuel gas, the calorific value of the fuel gas (Wobbe index) may vary over time. In this case, if the ratio of the fuel gas supply to the air supply is constant, the fluctuation in the calorific value of the fuel gas will cause the excess air ratio of the mixture to fluctuate, resulting in poor combustion.

[0020] Therefore, an excess air ratio detection means 9 is provided to detect the excess air ratio of the mixture. In this embodiment, the excess air ratio detection means 9 is configured with a flame rod provided facing the combustion surface 1a of the burner 1. The excess air ratio of the mixture is detected from the flame current flowing through the flame rod. Since the flame approaches or moves away from the combustion surface 1a depending on the excess air ratio of the mixture, the back surface temperature of the combustion surface 1a changes depending on the excess air ratio of the mixture. Therefore, the excess air ratio detection means 9 can also be configured with a temperature sensor that detects the back surface temperature of the combustion surface 1a.

[0021] The controller 8 performs feedback control to adjust the opening of the variable throttle valve 74 so that the excess air ratio of the mixture detected by the excess air ratio detection means 9 becomes constant, i.e., so that it is kept at a predetermined appropriate value. Specifically, when the excess air ratio of the mixture decreases due to an increase in the heat value of the fuel gas, the opening of the variable throttle valve 74 is decreased to decrease the ratio of the supply amount of fuel gas to the supply amount of air so that the excess air ratio becomes an appropriate value, and when the excess air ratio of the mixture increases due to a decrease in the heat value of the fuel gas, the opening of the variable throttle valve 74 is increased to increase the ratio of the supply amount of fuel gas to the supply amount of air so that the excess air ratio becomes an appropriate value. In this way, even if the heat value of the fuel gas fluctuates, the excess air ratio of the mixture can be kept at an appropriate value, and poor combustion can be prevented.

[0022] Next, the structure of the variable throttle valve 74 will be described. With reference to Fig. 2 and Fig. 3, the variable throttle valve 74 is of a motor-driven type and includes a valve body 742 that moves axially toward and away from a valve seat 7411 in a valve housing 741, a drive motor 743 consisting of a stepping motor controlled by a controller 8, and a motion conversion mechanism that moves the valve body 742 in the axial direction by the rotation of the drive motor 743. A primary gas chamber 7412 having a gas inlet 7412a and a secondary gas chamber 7413 having a gas outlet 7413a communicating with the gas chamber 71 are provided in the valve housing 741. A member 744 on which a valve seat 7411 that separates the primary gas chamber 7412 and the secondary gas chamber 7413 is formed is attached to the secondary gas chamber 7413.

[0023] The motion conversion mechanism includes a cam pin 7421 fixed to the valve body 742, a guide tube 745 having an axially extending long hole 7451 formed therein with which the cam pin 7421 slidably engages, and a cylindrical cam body 746 having a spiral cam portion 7461 with which the cam pin 7421 engages through the long hole 7451. A shaft portion having a non-circular cross section of a connector 7432 connected to an output shaft 7431 of a drive motor 743 is fitted into an end of the guide tube 745, so that the guide tube 745 rotates with the rotation of the drive motor 743.

[0024] The valve body 742 has a needle portion 742a that can be inserted into a valve hole 7411a formed in the valve seat 7411, and also has a tube portion 7422 that is inserted into the guide tube 745. A cam pin 7421 is provided at the end of the tube portion 7422 so as to protrude radially outward. The base end of the cam pin 7421 is slidably engaged with an elongated hole 7451 formed in the guide tube 745. Therefore, the valve body 742 is connected to the guide tube 745 so as to be movable in the axial direction and to rotate together with the guide tube 745.

[0025] The cam body 746 is prevented from rotating relative to the valve housing 741. Specifically, a rib 7462 protruding from the outer peripheral surface of the cam body 746 engages with a groove 7414 formed on the inner peripheral surface of the valve housing 741, thereby preventing the cam body 746 from rotating relative to the valve housing 741. In addition, in order to reduce the number of parts, the cam body 746 is formed integrally with the member 744 on which the valve seat 7411 is formed. The cam portion 7461 provided on the cam body 746 is composed of a spiral inclined side against which the cam pin 7421 can abut. In addition, a spring member 7423 is provided to bias the cam pin 7421 toward the cam portion 7461. Then, by forward and reverse rotation of the drive motor 743, the cam pin 7421 rotates and is guided by the cam portion 7461 to move in one axial direction and the other, and the valve body 742 moves in a closing direction approaching the valve seat 7411 and in an opening direction moving away from the valve seat 7411.

[0026] Furthermore, the valve body 742 is movable between a stroke end position in the closing direction where the valve body 742 abuts against the valve seat 7411 and a stroke end position in the opening direction where a protrusion 7452 protruding from the tail end of the guide tube 745 abuts against a stopper portion (not shown) provided inside the valve housing 741, preventing further rotation of the guide tube 745 (rotation in the direction that would move the valve body 742 in the opening direction).

[0027] The variable throttle valve 74 is also provided with a first detection means 747 for confirming the operation of the variable throttle valve 74, which has a first detection switch 7471 that switches from OFF to ON when the opening of the variable throttle valve 74 reaches a predetermined opening. More specifically, the first detection means 747 is composed of the first detection switch 7471, which is a reed switch provided at a position facing the needle portion 742a on the outer surface of the secondary gas chamber 7413, and a magnet 7472 built into the needle portion 742a. ​​The first detection switch 7471 switches from OFF to ON by receiving a magnetic force from the magnet 7472 when the valve body 742 of the variable throttle valve 74 moves in the closing direction and the opening of the variable throttle valve 74 reaches a predetermined opening close to the fully closed opening. The rotation direction of the drive motor 743 when the first detection switch 7471 switches from off to on is the forward direction, with the counterclockwise rotation direction of the drive motor 743 seen from the connector 7432 side being taken as the forward direction.

[0028] 4 to 6, the butterfly valve 62 is connected to a rotating shaft 622 driven by a driving motor 621 consisting of a stepping motor controlled by the controller 8, and is a motor-driven type that is rotated between a closed position and an open position. The rotating shaft 622 is composed of a first shaft 6221 directly connected to the driving motor 621 and a second shaft 6222 whose tail end is fitted with the first shaft 6221. The second shaft 6222 is connected to the butterfly valve 62 along a predetermined diameter line of the butterfly valve 62. A fan-shaped flange portion 6222a is provided at the tail end of the second shaft 6222. This flange portion 6222a is housed in a cylindrical portion 601 integrally molded on the outer surface of the case 60 that surrounds the part of the air supply passage 6 in which the butterfly valve 62 is disposed. A stopper protrusion 602 is provided at one circumferential position on the inner circumferential surface of the cylindrical portion 601. When the rotating shaft 622 rotates in the closing direction (clockwise in FIG. 5, counterclockwise in FIG. 6) and the butterfly valve 62 is in the closed position, one end 6222b of the flange portion 6222a abuts against the stopper protrusion 602 as shown in FIG. 5(a) to prevent the butterfly valve 62 from being in the closed position, and when the rotating shaft 622 rotates in the opening direction (counterclockwise in FIG. 5, clockwise in FIG. 6) and the butterfly valve 62 is in the open position, the other end 6222c of the flange portion 6222a abuts against the stopper protrusion 602 as shown in FIG. 5(b) to prevent the butterfly valve 62 from being in the open position.

[0029] The butterfly valve 62 has four ventilation openings 62a at 90° intervals in the circumferential direction through which air flows from the upstream side to the downstream side of the butterfly valve 62 in the closed position. When the butterfly valve 62 is in the open position, part of the air strongly collides with the portion of the circumferential surface of the ventilation opening 62a that is the downstream side in the open position of the butterfly valve 62 (the left side portion in FIG. 6), and dust may adhere to and accumulate in this portion. Therefore, a protrusion 62b that protrudes in the thickness direction of the butterfly valve 62 is provided on each side of the butterfly valve 62, positioned in the portion of the periphery of the ventilation opening 62a that is the upstream side in the open position of the butterfly valve 62 (the right side portion in FIG. 6). According to this, when the butterfly valve 62 is in the open position, the protrusion 62b functions as a windbreak wall, and it is possible to prevent air from strongly colliding with the downstream peripheral surface portion of the ventilation opening 62a and causing dust to adhere and accumulate there.

[0030] The butterfly valve 62 is provided with a second detection means 623 for confirming the operation of the butterfly valve 62, the second detection means 623 having a second detection switch 6231 that switches from OFF to ON when the opening degree of the butterfly valve 62 reaches a predetermined opening degree. More specifically, the second detection means 623 is composed of the second detection switch 6231 made of a reed switch, a magnet 6232 arranged to face the second detection switch 6231, and a magnetic shielding plate 6233 that is inserted between the second detection switch 6231 and the magnet 6232 to prevent the first detection switch 6231 from being turned on by the magnetism of the magnet 6232. Here, a first holding portion 603 and a second holding portion 604 are integrally formed on the upper portion of the cylindrical portion 601 of the case 60, aligned in the axial direction of the rotation shaft 622. The magnet 6232 is held by the first holding part 603, and the second detection switch 6231 is held by the second holding part 604 so as to face, with a gap, a side wall part 603a of the first holding part 603 facing the second holding part 604. A transmission hole 603b through which the magnetism of the magnet 6232 passes is opened in the side wall part 603a of the first holding part 603.

[0031] The magnetic shielding plate 6233 has an arc-shaped main body 62331 that is located between the side wall 603a of the first holding part 603 and the second detection switch 6231 and is capable of closing the transmission port 603b, a shaft connecting part 62332 that has an engagement hole 62332a through which the first shaft 6221 passes and is offset in the axial direction of the rotating shaft 622 from the main body 62331, and a neck part 62333 that connects the main body 62331 and the shaft connecting part 62332. The magnetic shielding plate 6233 is connected to the rotating shaft 622 at the shaft connecting part 62332 so as to rotate together with the butterfly valve 62. Then, when the butterfly valve 62 is rotated to the open position and the opening degree of the butterfly valve 62 becomes a predetermined opening degree close to the large capacity opening degree which is the opening degree in the open position, the main body 62331 of the magnetic shielding plate 6233 rotates to a position where the transparent opening 603b is almost fully opened as shown in Fig. 5(b), and the magnetism of the magnet 6232 acts on the second detection switch 6231 through the transparent opening 603b, and the second detection switch 6231 is switched from OFF to ON. Note that the rotation direction of the drive motor 621 viewed from the rotating shaft 622 side is defined as the counterclockwise direction, which is the forward rotation direction, and the rotation direction of the drive motor 621 when the second detection switch 6231 is switched from OFF to ON is the reverse direction opposite to the forward rotation direction.

[0032] Referring to FIG. 1, the controller 8 is provided with a first connector 81 for connecting the first detection switch 7471 and a second connector 82 for connecting the second detection switch 6231. In order to reduce costs, the same type of connector is used for each of the first and second connectors 81 and 82. Therefore, there is a possibility that the second detection switch 6231 is mistakenly connected to the first connector 81 and the first detection switch 7471 is mistakenly connected to the second connector 82. Therefore, the controller 8 performs detection switch discrimination control to determine whether the first detection switch 7471 and the second detection switch 6231 are correctly connected to the first connector 81 and the second connector 82 during an inspection operation before shipping. Hereinafter, the detection switch discrimination control will be described in detail with reference to FIG. 7.

[0033] In the detection switch discrimination control, first, in STEP 1, the drive motor 743 of the variable throttle valve 74 is rotated in the reverse direction so that the valve body 742 reaches the stroke end in the opening direction, and the drive motor 743 is returned to its original position, and the drive motor 621 of the butterfly valve 62 is rotated in the forward direction so that the butterfly valve 62 is in a closed position, and the drive motor 621 is returned to its original position. Next, in STEP 2, the drive motor 743 of the variable throttle valve 74 is rotated in the forward direction so that the opening of the variable throttle valve 74 decreases from the original position. Then, in STEP 3, it is determined whether the signal input to the first connector 81 has switched from an OFF signal to an ON signal. If the signal input to the first connector 81 remains an OFF signal, in STEP 4, it is determined whether the signal input to the second connector 82 has switched from an OFF signal to an ON signal, and if it has not switched, the process returns to STEP 3 and is repeated.

[0034] If the signal input to the first connector 81 has switched from an OFF signal to an ON signal, the process proceeds to STEP 5, in which the drive motor 621 of the butterfly valve 62 is rotated in the reverse direction from the origin so that the opening of the butterfly valve 62 increases. Then, in STEP 6, it is determined whether the signal input to the second connector 82 has switched from an OFF signal to an ON signal. If the signal input to the second connector 82 has switched from an OFF signal to an ON signal, the process proceeds to STEP 7, in which it is determined that the first detection switch 7471 and the second detection switch 6231 are correctly connected to the first connector 81 and the second connector 82, i.e., that they are normally connected, and a message to that effect is displayed.

[0035] If the second detection switch 6231 is erroneously connected to the first connector 81 and the first detection switch 7471 is erroneously connected to the second connector 82, while the drive motor 743 of the variable throttle valve 74 is rotating in the forward direction, the signal input to the second connector 82 switches from an OFF signal to an ON signal, and the result of the determination in STEP 4 is "YES." In this case, the process proceeds to STEP 8, where it is determined to be erroneous connection and a message to that effect is displayed.

[0036] It is also possible to omit STEP 5 and STEP 6, and proceed directly to STEP 7 to determine that the connection is normal if STEP 3 is determined to be "YES". However, there are cases where the signal input to the second connector 82 does not switch to an ON signal even if the second detection switch 6231 is turned on due to a poor connection of the second detection switch 6231 with the second connector 82, or where the second detection switch 6231 remains off due to forgetting to install the magnet 6232, etc. Therefore, STEP 5 and STEP 6 are provided, and proceed to STEP 7 to determine that the connection is normal if STEP 6 is determined to be "YES".

[0037] Incidentally, once the first detection switch 7471 is turned on as the opening degree of the variable throttle valve 74 decreases to a predetermined opening degree close to the fully closed opening degree, it does not turn off until the opening degree of the variable throttle valve 74 increases to an opening degree somewhat larger than the predetermined opening degree. The rotation phase difference of the drive motor 743 of the variable throttle valve 74 between the point when the first detection switch 7471 switches from off to on and the point when it switches from on to off is about 170 steps in terms of the number of steps. On the other hand, the rotation phase difference of the drive motor 621 of the butterfly valve 62 between the point when the second detection switch 6231 switches from off to on and the point when it switches from on to off is about 120 steps in terms of the number of steps. Therefore, it is also possible to perform detection switch discrimination control based on the rotation phase difference of the drive motors 743, 621 of the valves 74, 62 between the time when the signal from each detection switch 7471, 6231 input to each of the first and second connectors 81, 82 switches from an OFF signal to an ON signal and the time when the signal switches from an ON signal to an OFF signal. Such detection switch discrimination control will be described in detail below with reference to FIG. 8.

[0038] First, in STEP 101, similarly to STEP 1 described above, the drive motor 743 of the variable throttle valve 74 is rotated in the reverse direction so that the valve element 742 reaches the stroke end in the opening direction, thereby returning the drive motor 743 to its original position, and the drive motor 621 of the butterfly valve 62 is rotated in the forward direction so that the butterfly valve 62 is in a closed position, thereby returning the drive motor 621 to its original position. Next, in STEP 102, the drive motor 743 of the variable throttle valve 74 is rotated in the forward direction from the original position, and in STEP 102', the drive motor 621 of the butterfly valve 62 is rotated in the reverse direction from the original position. Next, in STEPs 103 and 103', it is determined whether the first and second flags F1 and F2, whose initial values ​​are set to "0", are "0" or not, and if they are "0", it is determined in STEP 104 whether the signal input to the first connector 81 has switched from an OFF signal to an ON signal, and in STEP 104' it is determined whether the signal input to the second connector 82 has switched from an OFF signal to an ON signal. Then, when the signal input to the first connector 81 has switched from an OFF signal to an ON signal, in STEP 105, the number of steps N1on from the origin of the drive motor 743 of the variable throttle valve 74 at the time of switching is stored, and when the signal input to the second connector 82 has switched from an OFF signal to an ON signal, in STEP 105', the number of steps N2on from the origin of the drive motor 621 of the butterfly valve 62 at the time of switching is stored.

[0039] Next, in STEPs 106 and 106', the first and second flags F1 and F2 are set to "1", and then in STEP 107, it is determined whether or not the signal input to the second connector 82 is an ON signal, and in STEP 107', it is determined whether or not the signal input to the first connector 81 is an ON signal. If the determination in STEP 104 or STEP 107 is "NO", the process returns to STEP 102 to continue the rotation of the drive motor 743 of the variable throttle valve 74 in the forward direction, and similarly, if the determination in STEP 104' or STEP 107' is "NO", the process returns to STEP 102' to continue the rotation of the drive motor 621 of the butterfly valve 62 in the reverse direction. Here, STEP 107 is a process for rotating the drive motor 743 of the variable throttle valve 74 in the forward direction until the first detection switch 7471 is turned on when the first detection switch 7471 is erroneously connected to the second connector 82, and similarly, STEP 107' is a process for rotating the drive motor 621 of the butterfly valve 62 in the reverse direction until the second detection switch 6231 is turned on when the second detection switch 6231 is erroneously connected to the first connector 81. Note that if "NO" is determined in STEPs 107 and 107' and the process proceeds to STEPs 103 and 103' via STEPs 102 and 102', the first and second flags F1 and F2 have already been set to "1", so that "NO" is determined in STEPs 103 and 103' and the process proceeds directly from STEPs 103 and 103' to STEPs 107 and 107'.

[0040] If the determination in STEP 107, 107' is "YES", the drive motor 743 of the variable throttle valve 74 is rotated in the reverse direction in STEP 108, and the drive motor 621 of the butterfly valve 62 is rotated in the forward direction in STEP 108'. Next, in STEP 109, 109', it is determined whether the third and fourth flags F3, F4, whose initial values ​​are set to "0", are "0" or not, and if they are "0", it is determined in STEP 110 whether the signal input to the first connector 81 has switched from an ON signal to an OFF signal, and in STEP 110' it is determined whether the signal input to the second connector 82 has switched from an ON signal to an OFF signal. Then, when the signal input to the first connector 81 switches from an on signal to an off signal, in STEP 111, the number of steps N1off from the origin of the drive motor 743 of the variable throttle valve 74 at the time of the switch is stored, and when the signal input to the second connector 82 switches from an off signal to an on signal, in STEP 111', the number of steps N2off from the origin of the drive motor 621 of the butterfly valve 62 at the time of the switch is stored.

[0041] Next, in STEP 112, 112', the third and fourth flags F3, F4 are set to "1", and then in STEP 113, it is determined whether or not the signal input to the second connector 82 is an OFF signal, and in STEP 113', it is determined whether or not the signal input to the first connector 81 is an OFF signal. If the determination in STEP 110 or STEP 113 is "NO", the process returns to STEP 108 to continue the rotation of the drive motor 743 of the variable throttle valve 74 in the reverse direction, and similarly, if the determination in STEP 110' or STEP 113' is "NO", the process returns to STEP 108' to continue the rotation of the drive motor 621 of the butterfly valve 62 in the forward direction. Here, STEP 113 is a process for rotating the drive motor 743 of the variable throttle valve 74 in the reverse direction until the first detection switch 7471 is turned off when the first detection switch 7471 is erroneously connected to the second connector 82, and similarly, STEP 113' is a process for rotating the drive motor 621 of the butterfly valve 62 in the forward direction until the second detection switch 6231 is turned off when the second detection switch 6231 is erroneously connected to the first connector 81. Note that if "NO" is determined in STEPs 113 and 113' and the process proceeds to STEPs 109 and 109' via STEPs 108 and 108', the third and fourth flags F3 and F4 have already been set to "1", so that "NO" is determined in STEPs 109 and 109' and the process proceeds directly from STEPs 109 and 109' to STEPs 113 and 113'.

[0042] If the result of STEPs 113 and 113' is "YES", the process proceeds to STEP 114, where it is determined whether the difference between N1on and N1off (=N1on-N1off), which represents the rotational phase difference of the drive motor 743 of the variable throttle valve 74 between the point at which the signal input to the first connector 81 switches from an off signal to an on signal and the point at which it switches from an on signal to an off signal, is greater than 140 steps, and whether the difference between N2on and N2off (=N2on-N2off), which represents the rotational phase difference of the drive motor 621 of the butterfly valve 62 between the point at which the signal input to the second connector 82 switches from an off signal to an on signal and the point at which it switches from an on signal to an off signal, is less than 140 steps. If the first detection switch 7471 is correctly connected to the first connector 81, N1on-N1off is about 170 steps, which is larger than 140 steps, and if the second detection switch 6231 is correctly connected to the second connector 82, N2on-N2off is about 120 steps, which is smaller than 140 steps. Therefore, the determination in STEP 114 is "YES" and the process proceeds to STEP 115, where the connection is determined to be normal and a message is displayed to that effect. On the other hand, if the second detection switch 6231 is incorrectly connected to the first connector 81 and the first detection switch 7471 is incorrectly connected to the second connector 82, N1on-N1off is about 120 steps and N2on-N2off is about 170 steps, and the determination in STEP 114 is "NO". In this case, the process proceeds to STEP 116, where the connection is determined to be incorrect and a message is displayed to that effect.

[0043] Here, in the detection switch discrimination control shown in FIG. 7, it is necessary to rotate the drive motor 743 of the variable throttle valve 74 and the drive motor 621 of the butterfly valve 62 in sequence. Therefore, the detection switch discrimination control takes time. In contrast, in the detection switch discrimination control shown in FIG. 8, the drive motor 743 of the variable throttle valve 74 and the drive motor 621 of the butterfly valve 62 can be rotated simultaneously to perform the detection switch discrimination control. Therefore, there is an advantage that the time required for the detection switch discrimination control can be shortened. Furthermore, in the detection switch discrimination control shown in FIG. 8, not only the operation check of the switching from off to on of each of the first and second detection switches 7471, 6231 can be performed, but also the operation check of the switching from on to off of each of the detection switches 7471, 6231 can be performed, which is advantageous.

[0044] Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited thereto. For example, in the detection switch discrimination control, the drive motor 743 of the variable throttle valve 74 is rotated in the forward direction so that the valve body 742 reaches the stroke end in the closing direction to return to the origin, and the drive motor 621 of the butterfly valve 62 is rotated in the forward direction so that the butterfly valve 62 is in the closed position to return to the origin, and if the signal input to the first connector 81 in this state is an ON signal and the signal input to the second connector 82 is an OFF signal, it is determined that the connection is normal, and if not, it is determined that the connection is incorrect, or the drive motor 743 of the variable throttle valve 74 is rotated in the reverse direction so that the valve body 742 reaches the stroke end in the opening direction to return to the origin, and the drive motor 621 of the butterfly valve 62 is rotated in the reverse direction so that the butterfly valve 62 is in the open position to return to the origin, and if the signal input to the first connector 81 in this state is an OFF signal and the signal input to the second connector 82 is an ON signal, it is determined that the connection is normal, and if not, it is determined that the connection is incorrect. However, in this case, even if there is a fault in the first and second detection switches 7471, 6231 remaining off due to poor connection of the first and second connectors 81, 82, or forgetting to install the magnets 7472, 6232, the detection switches 7471, 6231 will be determined to be connected normally. For this reason, it is desirable to perform detection switch discrimination control as shown in Figs. 7 and 8 described above.

[0045] In addition, in the above embodiment, the first and second detection switches 7471, 6231 are configured as reed switches, but it is also possible to configure each detection switch 7471, 6231 as a magnetic detection switch using a Hall element or an MR element, and further, it is also possible to configure each detection switch 7471, 6231 as a microswitch that works in conjunction with a dog that displaces in conjunction with each drive motor 743, 621. [Explanation of symbols]

[0046] A...premixing device, 5...fan, 6...air supply passage, 61...gas suction section, 62...butterfly valve, 621...butterfly valve drive motor, 623...second detection means, 6231...second detection switch, 7...gas supply passage, 73...zero governor, 74...variable throttle valve, 743...variable throttle valve drive motor, 747...first detection means, 7471...first detection switch, 8...controller (control means), 81...first connector, 82...second connector.

Claims

1. A premixing device that mixes fuel gas into air and supplies the mixture to a burner via a fan, an air supply passage upstream of a fan, a gas supply passage having a downstream end connected to a gas suction section provided in the air supply passage, a zero governor arranged in the gas supply passage for regulating secondary gas pressure to atmospheric pressure, a motor-driven variable throttle valve arranged in a portion of the gas supply passage downstream of the zero governor, a motor-driven butterfly valve arranged in a portion of the air supply passage upstream of the gas suction section, first detection means for confirming operation of the variable throttle valve having a first detection switch which switches from off to on when the opening of the variable throttle valve reaches a predetermined opening, second detection means for confirming operation of the butterfly valve having a second detection switch which switches from off to on when the opening of the butterfly valve reaches the predetermined opening, and control means having a first connector for connecting the first detection switch and a second connector for connecting the second detection switch, The premixing device is characterized in that the control means is configured to perform detection switch discrimination control to determine whether the first detection switch and the second detection switch are correctly connected to the first connector and the second connector.

2. 2. The premixing device according to claim 1, wherein a rotational phase difference of a drive motor of the variable throttle valve between a point in time when the first detection switch switches from off to on and a point in time when the first detection switch switches from on to off is made different from a rotational phase difference of a drive motor of the butterfly valve between a point in time when the second detection switch switches from off to on and a point in time when the second detection switch switches from on to off, and the control means performs the detection switch discrimination control based on a rotational phase difference of the drive motor of each valve between a point in time when the signal from each detection switch input to each of the first and second connectors switches from an off signal to an on signal and a point in time when the signal switches from an on signal to an off signal.

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