Premixing device

Abstract

A premixing device provided with a butterfly valve 62 driven by a stepping motor 621 in an air supply passage 6 includes a detection means 9 composed of a magnet 91, a magnetic switch 92, and a magnetic shielding plate 93 rotating together with the butterfly valve, the premixing device being configured so that when the butterfly valve enters a rotation range between an open position and a predetermined state close thereto, the magnetic switch is turned on. Even if a malfunction occurs in which the butterfly valve is locked within the rotation range where the magnetic switch is turned off just before the butterfly valve reaches a closed position, this malfunction can be detected.　The butterfly valve 62 is rotated from the close position to the open position to ascertain the number of steps of the stepping motor 621 when the magnetic switch 92 is switched from off to on. If the number of steps is deviated by a predetermined value or more from the reference number of steps required for rotating the butterfly valve 62 from the close position to the predetermined position, it is determined that an abnormality is present.

Description

premixing device

[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, 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.

[0002] A known example of this type of premixing device is disclosed in Patent Document 1, which includes a butterfly valve provided in an air supply passage upstream of a gas suction port, 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. The detection means is composed of a pair of magnets for open 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 and closed detection positioned opposite 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 type of valve, the stepping motor is a dedicated part incorporating a detection means. However, using a dedicated stepping motor is undesirable in terms of parts supply and cost. Therefore, to enable the use of a general stepping motor without a built-in detection means, it is conceivable to configure the detection means as a magnet and a magnetic sensing switch arranged facing each other on the outside of the stepping motor, and a magnetic shielding plate that is inserted between the magnet and the magnetic sensing switch to prevent the magnetic field of the magnet from turning on the magnetic sensing switch. Here, the magnetic shielding plate may be connected to a rotating shaft so as to rotate together with the butterfly valve. When the butterfly valve is rotated to one of the open and closed positions and the magnetic shielding plate enters a rotation range between the one position and a predetermined position near the one position, the magnetic field of the magnet acts on the magnetic sensing switch, turning on the magnetic sensing switch.

[0004] However, this means that the magnetic sensing switch will be turned off within a wide rotation range of the butterfly valve, including positions other than the open and closed positions.As a result, even if the butterfly valve were to lock within the rotation range where the magnetic sensing switch would be turned off just before reaching the other position, this failure would not be detected.

[0005] Japanese Patent Application Laid-Open No. 2017-187185

[0006] In view of the above, the present invention aims to provide a premixing device in which the 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, and which is capable of detecting the above-mentioned failures.

[0007] In order to solve the above problems, the present invention provides a premixing device that mixes fuel gas with air and supplies the mixture to a burner via a fan, the device comprising: a gas supply passage whose downstream end is connected to a gas suction section provided in the 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 to 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 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 and prevents the magnetic sensing switch from being turned on by the magnetism of the magnet; the magnetic shielding plate is installed 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 close to the one position and the one position, the magnetism of the magnet acts on the magnetic sensing switch to turn on the magnetic sensing switch, wherein the control means, when not operating and not driving the fan, sequentially executes a first operation to rotate the butterfly valve to the other position of the open position and the closed position that is different from the one position, and a second operation to rotate 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 sensing switch is switched from off to on deviates by more than a predetermined value from the 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, if 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 will be 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 to be an abnormality, and this failure can be detected.

[0009] When using a general stepping motor, it may be necessary to set the rotation angle range of the magnetic shielding plate to be smaller than 90°, which is the rotation angle between the closed and open positions of the butterfly valve, in order to prevent interference of the magnetic shielding plate with the mounting portion of the stepping motor. In this case, the magnetic shielding plate can be connected to the rotation shaft with some play in the rotation direction. This allows the butterfly valve to be rotated between the closed and open positions without any problems, even if the rotation angle range of the magnetic shielding plate is smaller than 90°.

[0010] 1 is an explanatory diagram showing a premixing device according to an embodiment of the present invention. It is a cross-sectional side view taken along line II-II in FIG. 1. (a) A cross-sectional view taken along line III-III in FIG. 2, and (b) A cross-sectional view corresponding to FIG. 3(a) in a state where the butterfly valve is in an open position. It is a perspective view showing an exploded state of a main part of a detection means provided in a premixing device according to an embodiment of the present invention. It is a flow diagram showing the contents of butterfly valve failure detection control by a control means in a premixing device according to an embodiment.

[0011] The combustion apparatus 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 within the combustion housing 2. The heat exchanger 3 is connected to an upstream water supply pipe 31 and a downstream hot water outlet pipe 32. The combustion gas generated by the combustion of the air-fuel mixture heats the heat exchanger 3 and is then discharged to the outside via 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 with air, and the mixture is supplied to the burner 1 via a fan 5.

[0012] The premixing device A includes an air supply channel 6 upstream of the fan 5, a gas supply channel 7 for supplying fuel gas, and a controller 8 serving as a control means. The downstream end of the gas supply channel 7 is connected to a gas suction section 61 provided in the air supply channel 6. A venturi section 63 having a smaller diameter than the section in which a butterfly valve 62 (described later) is disposed is provided in the portion of the air supply channel 6 adjacent to the upstream side of the gas suction section 61. The portion of the air supply channel 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 therebetween, and this gap forms 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 channel 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 port 61 varies depending on the pressure difference between atmospheric pressure, which is the secondary gas pressure, and the negative pressure acting on the gas suction port 61. Here, the negative pressure acting on the gas suction port 61 varies depending on the rotation speed of the fan 5. Therefore, the amount of fuel gas supplied varies in proportion to the rotation speed of the fan 5, i.e., the amount of air supplied. The ratio of the amount of fuel gas supplied to the amount of air supplied varies depending on the opening of the variable throttle valve 74. By setting the opening of the variable throttle valve 74 to a predetermined reference opening according to the type of gas used, the excess air ratio of the air-fuel mixture becomes a predetermined appropriate value (e.g., 1.3). Then, by controlling the rotation speed of the fan 5 according to the required combustion amount (the amount of combustion required to produce hot water at a set temperature), the amount of air-fuel mixture corresponding to the required combustion amount is supplied to the burner 1 at an appropriate excess air ratio.

[0014] In order to prevent poor exhaust performance due to wind entering the exhaust stack 4, that is, to ensure wind resistance, the lower limit rotation speed of the fan 5 cannot be set too low. If the required combustion rate falls below a predetermined value corresponding to the lower limit rotation speed of the fan 5, it will no longer be possible to supply the amount of air corresponding to the required combustion rate.

[0015] Therefore, in order to switch the airflow resistance of that portion between large and small, a butterfly valve 62 is provided in the portion of the air supply path 6 upstream of the gas suction portion 61. The butterfly valve 62 can be switched between a closed position perpendicular to the longitudinal direction of the air supply path 6, as shown by the solid line in Fig. 1, and an open position parallel to the longitudinal direction of the air supply path 6, as shown by the imaginary line in Fig. 1. When the required combustion amount falls below the predetermined value, the butterfly valve 62 is switched to the closed position, thereby increasing the airflow resistance of the air supply path 6. This makes it possible to supply an amount of air corresponding to a required combustion amount less than 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 acting on the gas suction portion 61, causing the amount of fuel gas supplied to be excessive and 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 and supplying to the burner 1 an amount of mixture corresponding to the appropriate excess air ratio and the relatively small required combustion amount. 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 and supplying to the burner 1 an amount of mixture corresponding to the appropriate excess air ratio and the relatively large required combustion amount.

[0017] 2 to 4, the butterfly valve 62 is connected to a rotary shaft 622 driven by a stepping motor 621 controlled by the controller 8, and is rotated between a closed position and an open position. The rotary shaft 622 is connected to a first shaft 622 directly connected to the stepping motor 621. １ and the first axis 622 １ The second shaft 622 is fitted to the tail end. ２ The second shaft 622 is ２ is connected to the butterfly valve 62 along a predetermined diameter line of the butterfly valve 62. ２ The tail end of the ２This flange portion 622 ２ a is housed in a cylindrical portion 601 integrally molded on the outer surface of a case 60 that surrounds the portion of the air supply passage 6 where the butterfly valve 62 is disposed. A stopper protrusion 602 is protruded from one location in the circumferential direction on the inner peripheral surface of the cylindrical portion 601. When the rotary shaft 622 rotates in the closing direction (counterclockwise in FIG. 3, clockwise in FIG. 4) and the butterfly valve 62 assumes a closed position, the flange portion 622 ２ One end 622 of a ２ As shown in FIG. 3A, when the stopper protrusion 602 abuts against the stopper protrusion 602, the butterfly valve 62 is stopped in the closed position. When the rotary 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 flange portion 622 ２ The other end 622 of a ２ As shown in FIG. 3B, the stopper protrusion 602 abuts against the stopper protrusion 602, so that the butterfly valve 62 is stopped in the open position.

[0018] The butterfly valve 62 has four vent openings 62a spaced 90° apart around the periphery, through which air flows from the upstream side to the downstream side of the butterfly valve 62 when the butterfly valve 62 is in the closed position. When the butterfly valve 62 is in the open position, some of the air strongly impacts the downstream portion of the vent openings 62a (the right portion in FIG. 4 ), potentially causing dust to adhere and accumulate in this portion. Therefore, each side of the butterfly valve 62 is provided with a protrusion 62b that protrudes in the thickness direction of the butterfly valve 62, positioned around the vent openings 62a in the upstream portion of the butterfly valve 62 when the butterfly valve 62 is in the open position (the left portion in FIG. 4 ). This allows the protrusion 62b to function as a windbreak when the butterfly valve 62 is in the open position, preventing air from strongly impacting the downstream portion of the vent openings 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 sensing switch 92 arranged facing each other outside the stepping motor 621, and a magnetic shielding plate 93 inserted between the magnet 91 and the magnetic sensing switch 92 to prevent the magnetic field of the magnet 91 from turning on the magnetic sensing switch 92. The magnetic sensing switch 92 is, for example, a reed switch, but it may also be configured using a Hall element or an MR element. A first magnet holder 603 and a second switch holder 604 are integrally molded on the upper portion of the cylindrical portion 601 of the case 60 and aligned in the axial direction of the rotation shaft 622. The magnet 91 is held by the first holder 603, and the magnetic sensing switch 92 is held by the second holder 604 so as to face, with a gap between them, a sidewall portion 603a of the first holder 603 facing the second holder 604. A side wall 603 a of the first holding part 603 is provided with a transmission opening 603 b through which the magnetic field of the magnet 91 passes.

[0020] The magnetic shielding plate 93 is located between the side wall 603 a of the first holding part 603 and the magnetic sensing switch 92 and includes an arc-shaped main body 931 that can close the transmission opening 603 b, and a first shaft 622 １ 3B, the magnetic shielding plate 93 has a shaft connecting portion 932 offset from the main body 931 in the axial direction of the pivot shaft 622 and having an engagement hole 932a through which the magnet 91 passes, and a neck portion 933 connecting the main body 931 and the shaft connecting portion 932. The magnetic shielding plate 93 is connected to the pivot shaft 622 at the shaft connecting portion 932 so as to rotate together with the butterfly valve 62. When the butterfly valve 62 is rotated to the open position and enters a rotation range between the open position and a predetermined position close to the open position (for example, a position rotated 70° from the open position to the closed side), 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 FIG.

[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. On the other hand, within a wide rotation range of the butterfly valve 62 that includes the closed position, the permeation 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 locks 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 switching of the magnetic sensing switch 92 alone.

[0022] Therefore, when the fan 5 is not being driven and the controller 8 is not operating, for example, after the burner 1 has been extinguished and after-purging has been performed, the controller 8 performs the control shown in Figure 5 to detect the above-mentioned failure of the butterfly valve 62. In this control, first, in STEP 1, a first operation is performed to rotate the butterfly valve 62 to a closed position. After the first operation is completed, in STEP 2, it is determined whether the magnetic sensing switch 92 is off. If it is off, the controller 8 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, it is determined in STEP 4 whether the magnetic sensing switch 92 is on. If it is on, the controller 8 stores in STEP 5 the number of steps NS1 of the stepping motor 621 from the start of the second operation until the magnetic sensing switch 92 switches from off to on. Next, in STEP 6, it is determined whether or not 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] After the second operation is completed, in STEP 7, it is determined whether the magnetic sensing switch 92 is ON. 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 predetermined position (the position at which the magnetic sensing switch 92 switches from OFF to ON) and the stored number of steps NS1 is less than a predetermined value (e.g., 50 steps). 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 start of the second operation until the magnetic sensing switch 92 switches from OFF to ON is the number of steps required to rotate the butterfly valve 62 from the locked position to the predetermined position, which is smaller than the reference number of steps NS0. Therefore, if a malfunction occurs in which the butterfly valve 62 locks some distance before the closed position, the determination in STEP 8 is "NO" and the process proceeds to STEP 11, where it is determined to be an abnormality. Therefore, this malfunction can be detected.

[0024] If the determination in STEP 8 is "YES," a third operation is executed in STEP 9, in which the butterfly valve 62 is rotated 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, a "NO" determination is made in STEP 2 or STEP 10, and the process proceeds to STEP 11, where it is determined that an abnormality has occurred. Therefore, even if an open fault has occurred, this fault can be detected. Furthermore, 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, a "NO" determination is made in STEP 7, and the process proceeds to STEP 11, where it is determined that an abnormality has occurred. Therefore, even if a close fault has occurred, this fault can be detected.

[0026] The case 60 is provided with bosses 605 located on both sides of the lower portion of the cylindrical portion 601, for fastening the stepping motor 621. An axial step 601a is formed on the left side of the end of the cylindrical portion 601 facing the stepping motor 621 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 terminal 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 terminal position of the magnetic shielding plate 93 toward the opening side. The rotation angle range of the magnetic shielding plate 93, which is the angle between the rotation terminal position toward the closing side and the rotation terminal position toward the opening side, is approximately 85°, which is smaller than the 90° rotation angle of the butterfly valve 62 between the closed and open positions. Therefore, in this embodiment, the engagement hole 932 a of the shaft connecting portion 932 of the magnetic shielding plate 93 is inserted into the first shaft 622 of the rotating shaft 622 １ The cross section of the magnetic shielding plate 93 is formed slightly larger than that of the rotary shaft 622, so that the magnetic shielding plate 93 is connected to the rotary shaft 622 with some play in the rotation direction. In this way, even if the rotation angle range of the magnetic shielding plate 93 is less than 90°, the butterfly valve 62 can be rotated between the closed position and the open position without any hindrance.

[0027] Although the embodiments of the present invention have 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 magnetism from the magnet 91 to the magnetic sensing switch 92 to turn on the magnetic sensing switch 92 when the butterfly valve 62 enters a rotation range between a predetermined position near the open position and the open position. However, it is also possible to configure the magnetic sensing 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. Furthermore, 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.

[0028] A...premixing device, 1...burner, 5...fan, 6...air supply path, 61...gas suction part, 62...butterfly valve, 621...stepping motor, 622...rotating shaft, 7...gas supply path, 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 gas supply passage whose downstream end is connected to a gas suction section provided in the air supply passage upstream of the fan; a butterfly valve provided in 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 rotating shaft driven by a stepping motor controlled by the control means, and can rotate to 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. A premixing device according to claim 1, characterized in that said magnetic shielding plate is connected to said rotating shaft with some play in the rotational direction.

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