Premixing device

Abstract

To provide a premixing device in which a butterfly valve 62 driven by a stepping motor 621 is provided in an air supply passage 6, which comprises detection means 9 composed of a magnet 91, a magnetic switch 92 and a magnetic shielding plate 93 that rotates together with the butterfly valve, and in which the magnetic switch is turned on when the butterfly valve enters a rotation range between an open position and a predetermined position nearby, where even when a malfunction occurs in which the butterfly valve locks within a rotation range where the magnetic switch is turned off just before a closed position, it is possible to detect the malfunction.SOLUTION: A butterfly valve 62 is rotated from a closed position to an open position, to grasp the number of steps of a stepping motor 621 at the time when a magnetic switch 92 switches from off to on. When the number of steps deviates by a predetermined value or more from a reference number of steps required for rotating the butterfly valve 62 from the closed position to a predetermined position, it is determined that there is an abnormality.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a premixing device that mixes fuel gas into air and supplies the mixture to a burner via a fan, in which the downstream end of a gas supply passage is connected to a gas suction section provided in an air supply passage upstream of the fan. [Background technology]

[0002] Conventionally, as a premixing device of this type, Patent Document 1 discloses a butterfly valve provided in a portion of the air supply passage upstream of a gas suction section, a detection means capable of detecting the position of the butterfly valve, and a control means. In this device, the butterfly valve is connected to a rotating shaft driven by a stepping motor controlled by the control means, and is rotatable between at least two positions: an open position parallel to the longitudinal direction of the air supply passage and a closed position perpendicular to the longitudinal direction of the air supply passage. In addition, the detection means is composed of a pair of magnets for open detection and closed detection attached to an output gear in a motor case of the stepping motor, and a pair of magnetic sensing switches for open detection and closed detection arranged in a position facing the output gear in the motor case. When the butterfly valve is rotated to the open position, the open detection magnet is rotated to a position facing the open detection magnetic sensing switch, turning on the open detection magnetic sensing switch, and when the butterfly valve is rotated to the closed position, the close detection magnet is rotated to a position facing the close detection magnetic sensing switch, turning on the close detection magnetic sensing switch.

[0003] In this case, the stepping motor is a dedicated product incorporating a detection means. However, making the stepping motor a dedicated product is not preferable in terms of parts supply and costs. Therefore, in order to use a general stepping motor without a built-in detection means, it is conceivable to configure the detection means by a magnet and a magnetic sensor switch arranged facing each other outside the stepping motor, and a magnetic shielding plate that enters between the magnet and the magnetic sensor switch and prevents the magnetic sensor switch from being turned on by the magnetism of the magnet. Here, the magnetic shielding plate may be connected to a rotating shaft so as to rotate together with the butterfly valve, and may be configured so that when the butterfly valve is rotated to one of the open and closed positions and enters a rotation range between a predetermined position near the one position and the one position, the magnetic shielding plate causes the magnetism of the magnet to act on the magnetic sensor switch to turn on the magnetic sensor switch.

[0004] However, this means that the magnetic sensing switch turns off within a wide rotation range of the butterfly valve, including the other position between the open and closed positions that is different from the one position mentioned above, and therefore even if the butterfly valve locks within the rotation range where the magnetic sensing switch turns off just before the other position, this failure cannot be detected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-187185 A Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, an object of the present invention is to provide a premixing device in which a detection means is constituted by a magnet and a magnetic sensing switch arranged opposite each other on the outside of a stepping motor, and a magnetic shielding plate, which is capable of detecting the above-mentioned failures. [Means for solving the problem]

[0007] 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, the device comprising: a butterfly valve, the downstream end of which is connected to a gas suction section provided in an air supply passage upstream of the fan, and provided in a portion of the air supply passage upstream of the gas suction section; detection means capable of detecting the position of the butterfly valve; and control means, the butterfly valve being connected to a rotating shaft driven by a stepping motor controlled by the control means and being freely rotatable between at least two positions: an open position parallel to the longitudinal direction of the air supply passage and a closed position perpendicular to the longitudinal direction of the air supply passage; the detection means being composed of a magnet and a magnetic sensing switch arranged opposite each other outside the stepping motor, and a magnetic shielding plate that enters between the magnet and the magnetic sensing switch to prevent the magnetic sensing switch from being turned on by the magnetism of the magnet, the magnetic shielding plate being connected together with the butterfly valve The butterfly valve is connected to a rotating shaft so as to rotate, and is rotated to one of an open position and a closed position, and when the butterfly valve enters a rotation range between a predetermined position near the one position and the one position, the magnetism of the magnet acts on the magnetic sensor switch to turn on the magnetic sensor switch, wherein the control means, during non-operation in which the fan is not driven, sequentially executes a first operation of rotating the butterfly valve to the other position between the open position and the closed position which is different from the one position, and a second operation of rotating the butterfly valve to the one position, and is configured to perform control to determine that an abnormality has occurred if the number of steps of the stepping motor from the start of the second operation until the magnetic sensor switch is switched from off to on deviates by a predetermined value or more from a reference number of steps required to rotate the butterfly valve from the other position to the predetermined position.

[0008] According to the present invention, even if the butterfly valve locks before the other position within the rotation range where the magnetic sensing switch turns off, this failure can be detected. That is, when the butterfly valve locks before the other position, the number of steps of the stepping motor from the start of the second operation until the magnetic sensing switch switches from off to on is less than the above-mentioned reference number of steps by the number of steps from the other position to the locked position. Therefore, according to the present invention, if the butterfly valve locks before the other position, it is determined that an abnormality has occurred, and this failure can be detected.

[0009] However, when using a general stepping motor, in order to prevent the magnetic shielding plate from interfering with the mounting portion of the stepping motor, it may be required that the rotation angle range of the magnetic shielding plate be smaller than 90°, which is the rotation angle between the closed position and the open position of the butterfly valve. In this case, the magnetic shielding plate can be connected to the rotation shaft with some play in the rotation direction. In this way, even if the rotation angle range of the magnetic shielding plate is smaller than 90°, the butterfly valve can be rotated between the closed position and the open position without any problems. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is an explanatory diagram showing a premixing device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional side view taken along line II-II in FIG. [Diagram 3] 3(a) is a cross-sectional view taken along line III-III in FIG. 2, and FIG. 3(b) is a cross-sectional view corresponding to FIG. 3(a) in the open position of the butterfly valve. [Figure 4] FIG. 2 is an exploded perspective view of a main part of a detection means provided in the premixing device according to the embodiment of the present invention. [Diagram 5] FIG. 4 is a flow chart showing the contents of butterfly valve failure detection control by a control unit in the premixing device of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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.

[0012] 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 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.

[0013] 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.

[0014] 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.

[0015] Therefore, in order to switch the ventilation resistance of the air supply passage 6 upstream of the gas suction section 61 between large and small levels, a butterfly valve 62 is provided that can be switched between a closed position perpendicular to the longitudinal direction of the air supply passage 6 as shown by the solid line in Fig. 1 and an open position parallel to the longitudinal direction of the air supply passage 6 as shown by the imaginary line in Fig. 1. 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 ventilation resistance of the air supply passage 6. This makes it possible to supply an amount of air corresponding to a required combustion amount below a predetermined value without lowering the rotation speed of the fan 5 below the lower limit rotation speed.

[0016] However, simply increasing the air flow resistance of the air supply passage 6 by closing the butterfly valve 62 increases the negative pressure in the air supply passage 6, 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 butterfly valve 62 is closed 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 relatively small required combustion amount and the appropriate excess air ratio is supplied to the burner 1, and when the required combustion amount is relatively large, the butterfly valve 62 is opened 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 relatively large required combustion amount and the appropriate excess air ratio is supplied to the burner 1.

[0017] 2 to 4, the butterfly valve 62 is connected to a rotating shaft 622 driven by a stepping motor 621 controlled by the controller 8, and rotated between a closed position and an open position. The rotating shaft 622 is composed of a first shaft 6221 directly connected to the stepping motor 621 and a second shaft 6222 with the first shaft 6221 fitted to its tail end. 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 surrounding the portion 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 peripheral surface of the cylindrical portion 601. When the rotating shaft 622 rotates in the closing direction (counterclockwise in FIG. 3, clockwise in FIG. 4) 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. 3(a) to prevent the butterfly valve 62 from being in the closed position, and when the rotating shaft 622 rotates in the opening direction (clockwise in FIG. 3, counterclockwise in FIG. 4) 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. 3(b) to prevent the butterfly valve 62 from being in the open position.

[0018] The butterfly valve 62 has four ventilation openings 62a at 90° intervals in the circumferential direction through which air flows from the upstream side of the butterfly valve 62 to the downstream side 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 right side in FIG. 4), 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 left side in FIG. 4). 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.

[0019] The premixing device A further includes a detection means 9 capable of detecting the position of the butterfly valve 62. The detection means 9 includes a magnet 91 and a magnetic sensor switch 92 arranged facing each other outside the stepping motor 621, and a magnetic shielding plate 93 that is inserted between the magnet 91 and the magnetic sensor switch 92 to prevent the magnetic sensor switch 92 from being turned on by the magnetism of the magnet 91. The magnetic sensor switch 92 is, for example, a reed switch, but the magnetic sensor switch 92 can also be configured using a Hall element or an MR element. In addition, a first holder 603 for the magnet and a second holder 604 for the switch are integrally molded in the upper part of the cylindrical part 601 of the case 60, aligned in the axial direction of the rotation shaft 622. The magnet 91 is held by the first holder 603, and the magnetic sensor switch 92 is held by the second holder 604 so as to face the side wall part 603a of the first holder 603 facing the second holder 604 with a gap therebetween. A side wall portion 603a of the first holding portion 603 is provided with a transmission hole 603b through which the magnetic field of the magnet 91 passes.

[0020] The magnetic shielding plate 93 has an arc-shaped main body 931 that is located between the side wall 603a of the first holding part 603 and the magnetic sensing switch 92 and is capable of closing the transmission port 603b, a shaft connecting part 932 that has an engagement hole 932a through which the first shaft 6221 passes and is offset in the axial direction of the rotating shaft 622 from the main body 931, and a neck part 933 that connects the main body 931 and the shaft connecting part 932. The magnetic shielding plate 93 is connected to the rotating shaft 622 at the shaft connecting part 932 so as to rotate together with the butterfly valve 62. Then, when the butterfly valve 62 is rotated to the open position and enters a rotation range between a predetermined position close to the open position (for example, a position rotated 70° from the open position to the closed side) and the open position, the main body 931 of the magnetic shielding plate 93 rotates to a position where the transparent opening 603b is almost fully opened as shown in Figure 3(b), and the magnetism of the magnet 91 acts on the magnetic sensing switch 92 through the transparent opening 603b, turning on the magnetic sensing switch 92.

[0021] Therefore, when the magnetic sensing switch 92 is turned on, it may be determined that the butterfly valve 62 has rotated to the open position. Meanwhile, within a wide rotation range of the butterfly valve 62 including the closed position, the transmission port 603b is blocked by the magnetic shielding plate 93, and the magnetic sensing switch 92 is turned off. Therefore, even if a malfunction occurs in which the butterfly valve 62 is locked in the half-open position, for example, within the rotation range where the magnetic sensing switch 92 is turned off just before the closed position, this malfunction cannot be detected by the on / off of the magnetic sensing switch 92 alone.

[0022] Therefore, the controller 8 performs the control shown in FIG. 5 to detect the above-mentioned failure of the butterfly valve 62 during non-operation when the fan 5 is not driven, for example, after the burner 1 is turned off and after-purging is performed. In this control, first, in STEP 1, a first operation is performed to rotate the butterfly valve 62 to a closed position. Then, after the first operation is completed, in STEP 2, it is determined whether the magnetic sensor switch 92 is off or not, and if it is off, the process proceeds to STEP 3 to start a second operation to rotate the butterfly valve 62 to an open position. When the second operation is started, in STEP 4, it is determined whether the magnetic sensor switch 92 is on or not, and if it is on, in STEP 5, the number of steps NS1 of the stepping motor 621 from the beginning of the second operation until the magnetic sensor switch 92 is switched from off to on is stored. Next, in STEP 6, it is determined whether the butterfly valve 62 has reached the open position based on the number of steps of the stepping motor 621, and when it is determined that the butterfly valve 62 has reached the open position, the second operation is completed.

[0023] When the second operation is completed, in STEP 7, it is determined whether the magnetic sensor switch 92 is on or not. If it is on, the process proceeds to STEP 8, where it is determined whether the difference between the reference number of steps NS0 required to rotate the butterfly valve 62 from the closed position to the above-mentioned predetermined position (the position at which the magnetic sensor switch 92 is switched from off to on) and the stored number of steps NS1 is less than a predetermined value (for example, 50 steps). Here, if the butterfly valve 62 locks before the closed position during the first operation, the number of steps of the stepping motor 621 from the beginning of the second operation until the magnetic sensor switch 92 is switched from off to on becomes the number of steps required to rotate from the locked position to the above-mentioned predetermined position, which is smaller than the reference number of steps NS0. Therefore, if a malfunction occurs in which the butterfly valve 62 locks at a certain position before the closed position, the result in STEP 8 is "NO" and the process proceeds to STEP 11, where it is determined to be abnormal. Therefore, this malfunction can be detected.

[0024] If the answer is "YES" in STEP 8, the third operation is executed in STEP 9 to rotate the butterfly valve 62 to the closed position. After the third operation is completed, it is determined in STEP 10 whether the magnetic sensing switch 92 is off. If it is off, it is determined that there is no malfunction and the series of malfunction detection controls is terminated.

[0025] Here, if the butterfly valve 62 cannot rotate to the closing side due to an open fault, the magnetic sensing switch 92 remains on even after the first and third operations are completed. Therefore, the determination is "NO" in STEP 2 and STEP 10, and the process proceeds to STEP 11, where it is determined that there is an abnormality. Therefore, even if an open fault occurs, this fault can be detected. Also, if the butterfly valve 62 cannot rotate to the opening side due to a close fault, the magnetic sensing switch 92 remains off even after the second operation is completed. Therefore, the determination is "NO" in STEP 7, and the process proceeds to STEP 11, where it is determined that there is an abnormality. Therefore, even if a close fault occurs, this fault can be detected.

[0026] The case 60 is provided with bosses 605 located on both sides of the lower part of the cylindrical part 601 and fastening the stepping motor 621. An axial step 601a is formed on the left side of the end of the cylindrical part 601 on the stepping motor 621 side in FIG. 3. The position shown in FIG. 3(a) where the neck 933 of the magnetic shielding plate 93 abuts against the step 601a is the rotation end position of the magnetic shielding plate 93 toward the closing side, and the position shown in FIG. 3(b) where the right edge of the main body 931 of the magnetic shielding plate 93 abuts against the right boss 605 is the rotation end position of the magnetic shielding plate 93 toward the opening side. Here, the rotation angle range of the magnetic shielding plate 93, which is the angle between the rotation end position on the closing side and the rotation end position on the opening side, is approximately 85°, which is smaller than the rotation angle of the butterfly valve 62 between the closing position and the opening position, which is 90°. Therefore, in this embodiment, the engagement hole 932a of the shaft connecting portion 932 of the magnetic shielding plate 93 is formed slightly larger than the cross section of the first shaft 6221 of the rotating shaft 622 so that the magnetic shielding plate 93 is connected to the rotating shaft 622 with some play in the rotation direction. With this, even if the rotation angle range of the magnetic shielding plate 93 is smaller than 90°, the butterfly valve 62 can be rotated between the closed position and the open position without any trouble.

[0027] 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 above embodiment, the magnetic shielding plate 93 is configured to apply the magnetism of the magnet 91 to the magnetic sensor switch 92 to turn on the magnetic sensor switch 92 when the butterfly valve 62 enters a rotation range between a predetermined position near the open position and the open position, but it is also possible to configure the magnetic sensor switch 92 to turn on when the butterfly valve 62 enters a rotation range between a predetermined position near the closed position and the closed position. In addition, in the above embodiment, the butterfly valve 62 is configured to be rotatable between two positions, the open position and the closed position, but it may be configured to be rotatable between three or more positions including positions between the open position and the closed position. [Explanation of symbols]

[0028] A...premixing device, 1...burner, 5...fan, 6...air supply passage, 61...gas suction section, 62...butterfly valve, 621...stepping motor, 622...rotating shaft, 7...gas supply passage, 8...controller (control means), 9...detection means, 91...magnet, 92...magnetic sensing switch, 93...magnetic shielding plate.

Claims

1. A premixing device that mixes fuel gas into air and supplies the mixture to a burner via a fan, the device comprising: a downstream end of a gas supply passage connected to a gas suction section provided in an air supply passage upstream of the fan; a butterfly valve provided in a portion of the air supply passage upstream of the gas suction section; detection means capable of detecting the position of the butterfly valve; and control means; the butterfly valve is connected to a rotary shaft driven by a stepping motor controlled by the control means, and is rotatable between at least two positions: an open position parallel to the longitudinal direction of the air supply passage and a closed position perpendicular to the longitudinal direction of the air supply passage; the detection means comprises a magnet and a magnetic sensor switch disposed facing each other outside the stepping motor, and a magnetic shielding plate that enters between the magnet and the magnetic sensor switch to prevent the magnetic sensor switch from being turned on by the magnetism of the magnet, the magnetic shielding plate being connected to a rotating shaft so as to rotate together with the butterfly valve, and configured such that when the butterfly valve is rotated to take one of an open position and a closed position and the magnetic shielding plate comes within a rotation range between a predetermined position near the one position and the one position, the magnetic field of the magnet acts on the magnetic sensor switch to turn on the magnetic sensor switch, the control means, during non-operating time when the fan is not being driven, sequentially executes a first operation of rotating the butterfly valve to one of an open position and a closed position which is different from the one of the open position and a closed position, and a second operation of rotating the butterfly valve to the one of the positions, and determines that an abnormality has occurred if the number of steps of the stepping motor from the start of the second operation to the time when the magnetic sensing switch is switched from off to on deviates by a predetermined value or more from a reference number of steps required to rotate the butterfly valve from the other position to the predetermined position.

2. 2. The premixing device according to claim 1, wherein the magnetic shielding plate is connected to the rotary shaft with some play in the rotary direction.

Images