Premixing device

Abstract

To prevent a part of a rotary shaft 71 which is close to an air supply path 3 from becoming easier to stick to a circumferential surface of a shaft support hole 91a as grease runs out owing to a pressure difference between the internal pressure in an air supply path 3 and the internal pressure in a cam chamber 92 in a premixing device that comprises a butterfly valve 7 and a changeover valve 8 which change over the ventilation resistance of the air supply path 3 and a gas supply path 4, and an interlocking mechanism 9 which opens and closes the changeover valve 8 as the butterfly valve 7 is opened and closed, wherein the interlocking mechanism 9 comprises a cam 93 in the cam chamber 92 partitioned off by a partition wall 91 from the air supply path 3 and communicating with a downstream end part of the gas supply path 4. and a cam 93 is fixed to a part of the rotary shaft 71 of the butterfly valve 7 protruding into the cam chamber 92 through the shaft support hole 91a formed in the partition wall 91.SOLUTION: A plurality of recessed grooves 71a which serve as grease reservoirs are formed axially at intervals in an outer peripheral surface of a part of a rotary shaft 71 inserted into a shaft support hole 91a. It is preferred that the plurality of recessed grooves 71a are spirally connected.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] A conventional premixing device of this type is disclosed in Patent Document 1. The downstream end of a gas supply passage for supplying fuel gas via a flow control valve is connected to a gas suction port provided in an air supply passage upstream of a fan. The device includes an air resistance switching means for increasing or decreasing the airflow resistance in the portion of the air supply passage upstream of the gas suction port, and a gas resistance switching means for increasing or decreasing the airflow resistance in the portion of the gas supply passage downstream of the flow control valve. When a proportional valve is used as the flow control valve, the proportional valve is controlled to supply an amount of fuel gas corresponding to the required combustion amount. Furthermore, the fan rotation speed is controlled according to the required combustion amount so that the excess air ratio of the mixture supplied to the burner is constant. Alternatively, the flow control valve may be configured with a zero governor that maintains the secondary gas pressure at atmospheric pressure and an orifice downstream of the zero governor. In this case, the amount of fuel gas supplied varies at a predetermined ratio determined by the orifice depending on the pressure difference between atmospheric pressure (the secondary gas pressure) and the negative pressure acting on the gas suction port. Since the negative pressure acting on the gas suction section changes according to the fan rotation speed, the amount of fuel gas supplied changes at a predetermined rate according to the fan rotation speed, i.e., the amount of air supplied. Therefore, by controlling the fan rotation speed according to the required combustion amount, an amount of air-fuel mixture according to the required combustion amount can be supplied to the burner with a constant excess air ratio.

[0003] To prevent poor exhaust performance due to wind entering the exhaust stack that exhausts combustion gas from the burner, i.e., to ensure wind resistance, the fan's minimum rotation speed cannot be set too low. Furthermore, when the required combustion rate falls below a predetermined value corresponding to the fan's minimum rotation speed, it becomes impossible to supply an amount of air corresponding to the required combustion rate. Therefore, in the system described in Patent Document 1, when the required combustion rate falls below the predetermined value, an air resistance switching device increases the air flow resistance of the air supply passage, so that the fan rotation speed does not fall below the minimum rotation speed and an amount of air-fuel mixture corresponding to the required combustion rate below the predetermined value can be supplied. However, simply increasing the air flow resistance of the air supply passage increases the negative pressure acting on the gas suction section, resulting in an excessive amount of fuel gas being supplied, and the excess air ratio of the air-fuel mixture supplied to the burner falls below the appropriate value. Therefore, when the required combustion amount is relatively small, the air resistance of the air supply passage is increased by the air resistance switching means, and the air resistance of the gas supply passage is increased by the gas resistance switching means, establishing a small capacity state in which the excess air ratio is at an appropriate value and an amount of mixture corresponding to the relatively small required combustion amount is supplied to the burner, and when the required combustion amount is relatively large, the air resistance of the air supply passage is reduced, and the air resistance of the gas supply passage is reduced, establishing a large capacity state in which the excess air ratio is at an appropriate value and an amount of mixture corresponding to the relatively large required combustion amount is supplied to the burner.

[0004] In addition, in the device described in Patent Document 1, the air resistance switching means is provided in a portion of the air supply passage upstream of the gas suction port and is composed of a butterfly valve that rotates about a rotation axis between 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 gas resistance switching means is composed of a switching valve that is freely opened and closed and is provided in the gas supply passage. An interlocking mechanism is provided that opens and closes the switching valve in conjunction with the rotation of the butterfly valve between the open and closed positions. The interlocking mechanism includes a cam in a cam chamber that is separated by a partition wall from the portion of the air supply passage where the butterfly valve is provided and that communicates with the downstream end of the gas supply passage. The butterfly valve's rotating shaft protrudes into the cam chamber through a shaft support hole formed in the partition wall, and a cam is fixed to the portion of the rotating shaft protruding into the cam chamber. The interlocking mechanism is configured so that the cam rotates via the rotating shaft as the butterfly valve rotates between the open and closed positions, opening and closing the switching valve.

[0005] Although not disclosed in Patent Document 1, a common approach to preventing the rotating shaft from adhering to the circumferential surface of the shaft support hole is to form a wide groove in the axial direction of the rotating shaft on the outer peripheral surface of the portion of the rotating shaft that is inserted into the shaft support hole. However, due to negative pressure acting on the gas suction section, the internal pressure of the cam chamber, which communicates with the downstream end of the gas supply passage, becomes lower than the internal pressure of the portion of the air supply passage separated from the cam chamber by the partition wall. Therefore, the grease in the groove is biased toward the cam chamber due to the pressure difference between the internal pressure of the air supply passage and the internal pressure of the cam chamber. As a result, the portion of the rotating shaft closer to the air supply passage is more likely to adhere to the circumferential surface of the shaft support hole due to grease depletion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-187177 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 can prevent the rotary shaft from adhering to the peripheral surface of the shaft support hole. [Means for solving the problem]

[0008] 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 that supplies fuel gas via a flow rate control valve, the downstream end of which is connected to a gas suction section that is provided in the air supply passage upstream of the fan; air resistance switching means that switches between large and small air flow resistance in a portion of the air supply passage upstream of the gas suction section; and gas resistance switching means that switches between large and small air flow resistance in a portion of the gas supply passage downstream of the flow rate control valve, the air resistance switching means being provided in the portion of the air supply passage upstream of the gas suction section and comprising a butterfly valve that is rotated about a rotation axis between an open position that is parallel to the longitudinal direction of the air supply passage and a closed position that is perpendicular to the longitudinal direction of the air supply passage; and the gas resistance switching means having a valve in the gas supply passage that is connected to ... The interlocking mechanism is configured so that the switching valve is opened and closed by rotation of the butterfly valve between the open and closed positions, and is provided with a linkage mechanism that opens and closes the switching valve in conjunction with the rotation of the butterfly valve between the open and closed positions, the linkage mechanism having a cam in a cam chamber that is separated by a partition wall from the part of the air supply passage in which the butterfly valve is provided and that communicates with the downstream end of the gas supply passage, the rotating shaft of the butterfly valve protruding into the cam chamber through a shaft support hole formed in the partition wall, and the cam is fixed to the part of the rotating shaft that protrudes into the cam chamber, and the interlocking mechanism is configured so that the switching valve is opened and closed by rotation of the cam via the rotating shaft as the butterfly valve rotates between the open and closed positions, and is characterized in that a plurality of grooves that serve as grease reservoirs are formed at intervals in the axial direction of the rotating shaft on the outer surface of the part of the rotating shaft that is inserted into the shaft support hole.

[0009] According to the present invention, the grease is dispersed and held in the axial direction by the multiple grooves. Even if the grease in each groove is concentrated toward the cam chamber, grease is supplied from the groove adjacent to the air supply passage to the sliding contact between the portion of the rotating shaft and the circumferential surface of the shaft support hole between the groove and the adjacent groove on the air supply passage side. This prevents the rotating shaft from adhering to the circumferential surface of the shaft support hole.

[0010] In the present invention, it is also desirable that the grooves are connected in a spiral shape. In this way, grease that has concentrated toward the cam chamber in each groove is pushed back in the opposite direction by rotating the rotating shaft in one direction, thereby expanding the area of ​​grease adhesion to the circumferential surface of the shaft support hole. As a result, it is possible to more effectively prevent the rotating shaft from adhering to the circumferential surface of the shaft support hole. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cutaway side view illustrating a premixing device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional plan view taken along line II-II in FIG. [Figure 3] Cross-sectional view taken along line III-III in Figure 1. [Figure 4] FIG. 2 is a perspective view of a butterfly valve and a rotating shaft provided in the premixing device of the embodiment. [Figure 5] 4A and 4B are enlarged cutaway side views of a main part showing the movement of grease accompanying the rotation of a rotary shaft of a butterfly valve provided in the premixing device of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Referring to Fig. 1, reference numeral 1 denotes a burner such as a full primary combustion burner having a combustion surface 1a from which an air-fuel mixture is ejected and burned. A fan 2 is connected to the burner 1. A premixing device A according to an embodiment of the present invention mixes fuel gas into air, and the mixture is supplied to the burner 1 via the fan 2.

[0013] The premixing device A includes an air supply passage 3 upstream of the fan 2 and a gas supply passage 4 for supplying fuel gas. As shown in Fig. 3, a main valve 5 and a flow control valve 6 composed of a zero governor 6a and an orifice 6b downstream of the zero governor 6a are provided in the upstream portion of the gas supply passage 4. Furthermore, the downstream end of the gas supply passage 4 is connected to a gas suction section 31 provided in the air supply passage 3.

[0014] The premixing device A also includes an air resistance switching means for switching between high and low airflow resistance in the portion of the air supply passage 3 upstream of the gas suction section 31, and a gas resistance switching means for switching between high and low airflow resistance in the portion of the gas supply passage 4 downstream of the flow rate control valve 6. When the required combustion amount falls below a predetermined value, the air resistance switching means increases the airflow resistance of the air supply passage 3 and the gas resistance switching means increases the airflow resistance of the gas supply passage 4, thereby establishing a low-capacity state so that an amount of air-fuel mixture corresponding to the required combustion amount below the predetermined value can be supplied. When the required combustion amount exceeds the predetermined value, the air resistance switching means decreases the airflow resistance of the air supply passage 3 and the gas resistance switching means decreases the airflow resistance of the gas supply passage 4, thereby restoring the state to a high-capacity state.

[0015] An inner cylinder 33 is provided in a portion of the air supply passage 3 upstream of the gas suction section 31, with a gap between it and the peripheral wall surface 32 of the air supply passage 3. The gap between the peripheral wall surface 32 of the air supply passage 3 and the outer circumferential surface of the inner cylinder 33 forms a sub-passage 3b parallel to the main passage 3a inside the inner cylinder 33. A plurality of arc-shaped through holes 33b are formed in the flange portion 33a at the downstream end (upper end in FIGS. 1 and 2) of the inner cylinder 33, which serve as outlets of the sub-passages 3b.

[0016] Also provided within the inner cylinder 33 is a butterfly valve 7 that rotates about a rotary shaft 71 between an open position, shown by phantom lines in FIG. 2 , parallel to the longitudinal direction of the air supply passage 3, and a closed position, shown by solid lines in FIG. 2 , perpendicular to the longitudinal direction of the air supply passage 3. This butterfly valve 7 constitutes an air resistance switching means. An actuator 72, such as a stepping motor, is connected to the rotary shaft 71 of the butterfly valve 7. When switching to a low-capacity state, the actuator 72 rotates the butterfly valve 7 clockwise in FIG. 2 to the closed position. When switching to a high-capacity state, the actuator 72 rotates the butterfly valve 7 counterclockwise in FIG. 2 to the open position. When the butterfly valve 7 is switched to the closed position, the main passage 3a is nearly closed, and air flow is substantially restricted to the sub-passage 3b, increasing the airflow resistance of the air supply passage 3.

[0017] A venturi section 34 having a smaller diameter than the section of the air supply path 3 in which the inner tube 33 is disposed is provided in a section of the air supply path 3 adjacent to the upstream side of the gas suction section 31. The section of the air supply path 3 adjacent to the downstream side of the venturi section 34 is surrounded by a tube section 35 having a larger diameter than the venturi section 34. The downstream end of the venturi section 34 is inserted into the upstream end of the tube section 35 with an annular gap therebetween, and this gap forms the gas suction section 31.

[0018] At the downstream end of the gas supply path 4, a gas chamber 41 is provided that surrounds the cylindrical portion 35 and communicates with the gas suction portion 31. A passage portion 42 that is constantly in communication with the gas chamber 41 and a valve chamber 81 that is parallel to the passage portion 42 are provided in the portion of the gas supply path 4 adjacent to the upstream side of the gas chamber 41. A selector valve 8 is provided in the valve chamber 81 and opens and closes a valve hole 83 that is formed in a valve seat 82 at the lower end of the valve chamber 81 and communicates with the passage portion 42, and this selector valve 8 constitutes a gas resistance switching means. When the selector valve 8 is seated on the valve seat 82 and placed in a closed state that blocks the valve hole 83, the flow of gas through the valve chamber 81 is blocked, and the airflow resistance of the gas supply path 4 increases.

[0019] The switching valve 8 is opened and closed via an interlocking mechanism 9 in accordance with the rotation of the butterfly valve 7 between the open position and the closed position. As shown in Figures 1 and 3, the interlocking mechanism 9 includes a cam 93 in a cam chamber 92 that is separated by a partition wall 91 from the portion of the air supply passage 3 in which the butterfly valve 7 is provided and that communicates via a passage portion 42 with a gas chamber 41 that is the downstream end of the gas supply passage 4. The rotating shaft 71 of the butterfly valve 7 protrudes into the cam chamber 92 through a shaft support hole 91a formed in the partition wall 91. The cam 93 is fixed to the portion of the rotating shaft 71 that protrudes into the cam chamber 92. The interlocking mechanism 9 further includes a rod 94 that extends upward and is connected to the switching valve 8, the lower end of which abuts against the cam 93. When the butterfly valve 7 is rotated to the open position, the rod 94 is pushed up by the rotation of the cam 93 via the rotary shaft 71, and the switching valve 8 moves up against the biasing force of the valve spring 84, i.e., is opened. When the butterfly valve 7 is rotated to the closed position, the rotation of the cam 93 via the rotary shaft 71 releases the pushing-up of the rod 94, and the switching valve 8 moves down by the biasing force of the valve spring 84, i.e., is closed.

[0020] Meanwhile, the internal pressure of the cam chamber 92, which communicates with the downstream end of the gas supply passage 4, becomes lower than the internal pressure of the portion of the air supply passage 3 that is separated from the cam chamber 92 by the partition wall 91, due to the negative pressure acting on the gas suction portion 31. Therefore, if a single axially wide groove serving as a grease reservoir is formed on the outer peripheral surface of the portion of the rotating shaft 71 inserted into the shaft support hole 91a, the grease in the groove will be biased toward the cam chamber 92 due to the pressure difference between the internal pressure of the air supply passage 3 and the internal pressure of the cam chamber 92, as described above. As a result, the portion of the rotating shaft 71 closer to the air supply passage 3 will be prone to sticking to the peripheral surface of the shaft support hole 91a due to grease depletion.

[0021] Therefore, in this embodiment, a plurality of grooves 71a serving as grease reservoirs are formed at intervals in the axial direction of the rotating shaft 71 on the outer peripheral surface of the portion of the rotating shaft 71 that is inserted into the shaft support hole 91a. Furthermore, these plurality of grooves 71a are connected in a spiral shape, as shown in Fig. 4. In this embodiment, the spiral connecting the plurality of grooves 71a is inclined toward the air supply passage 3 in a clockwise direction in Fig. 2 with respect to a direction perpendicular to the generatrix of the rotating shaft 71.

[0022] As a result, the grease is held in a dispersed manner in the axial direction of the rotating shaft 71 by the multiple recessed grooves 71a. Even if the pressure difference between the internal pressure of the air supply passage 3 and the internal pressure of the cam chamber 92 causes the grease G in each recessed groove 71a to be concentrated toward the cam chamber 92, as shown in Fig. 5(a), the grease G is supplied from the recessed groove 71a adjacent to the air supply passage 3 side to the sliding contact portion between the portion of the rotating shaft 71 and the peripheral surface of the shaft support hole 91a between each recessed groove 71a and the recessed groove 71a adjacent to that groove 71a on the air supply passage 3 side. Therefore, it is possible to prevent the rotating shaft 71 from sticking to the peripheral surface of the shaft support hole 91a. Furthermore, by rotating the rotary shaft 71 in a direction in which the spiral connecting the multiple recessed grooves 71a progresses toward the air supply passage 3 as viewed from the side, i.e., counterclockwise in Fig. 2, and switching the butterfly valve 7 and the switching valve 8 from closed to open, the grease G that has concentrated toward the cam chamber 92 in each recessed groove 71a is pushed back a distance L in the direction opposite the cam chamber 92, as shown in Fig. 5(b), and the area where the grease G adheres to the circumferential surface of the shaft support hole 91a is expanded. As a result, the rotary shaft 71 can be more effectively prevented from sticking to the circumferential surface of the shaft support hole 91a.

[0023] 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 rotation direction of the rotary shaft 71 is opposite when the butterfly valve 7 and the switching valve 8 are switched from open to closed and when they are switched from closed to open. However, the rotary shaft 71 may be rotated counterclockwise in FIG. 2 so that the grease is pushed back in the opposite direction from the cam chamber 92 when the butterfly valve 7 and the switching valve 8 are switched from open to closed and when they are switched from closed to open. Also, in the above embodiment, the spiral connecting the multiple grooves 71a is inclined clockwise in FIG. 2 toward the air supply passage 3, and the rotation direction of the rotary shaft 71 is counterclockwise in FIG. 2 when the butterfly valve 7 and the switching valve 8 are switched from closed to open and clockwise in FIG. 2 when they are switched from open to closed. However, the rotation direction may be clockwise in FIG. 2 when they are switched from closed to open and counterclockwise in FIG. 2 when they are switched from open to closed. Furthermore, the spiral connecting the multiple grooves 71a can be tilted counterclockwise in Figure 2 toward the air supply path 3, so that the rotation direction of the rotating shaft 71 is reversed when the butterfly valve 7 and the switching valve 8 are switched from closed to open and when they are switched from open to closed, as described above. Alternatively, the rotation direction of the rotating shaft 71 can be set to the clockwise direction in Figure 2 when switching from closed to open and when they are switched from open to closed. It is also possible to form the multiple grooves 71a so that they are not connected to each other. Furthermore, in the above embodiment, the flow rate control valve 6 provided in the gas supply path 4 is composed of the zero governor 6a and the orifice 6b downstream of it, but the flow rate control valve may also be composed of a proportional valve. [Explanation of symbols]

[0024] A...premixing device, 1...burner, 2...fan, 3...air supply passage, 31...gas suction section, 4...gas supply passage, 6...flow rate control valve, 7...butterfly valve, 71...rotating shaft, 71a...groove, 8...switching valve, 9...interlocking mechanism, 91...partition wall, 91a...shaft support hole, 92...cam chamber, 93...cam.

Claims

1. A premixing device that mixes fuel gas with air and supplies the mixture to a burner via a fan, a downstream end of a gas supply passage, through which a flow rate control valve is disposed, for supplying fuel gas, is connected to a gas suction section provided in an air supply passage on the upstream side of the fan, and the system is provided with air resistance switching means for switching between large and small ventilation resistance in a portion of the air supply passage upstream of the gas suction section, and gas resistance switching means for switching between large and small ventilation resistance in a portion of the gas supply passage downstream of the flow rate control valve; the air resistance switching means is provided in a portion of the air supply passage upstream of the gas suction portion, and is composed of a butterfly valve that is rotated about a rotation axis between 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 gas resistance switching means is composed of a switching valve that is provided in the gas supply passage so as to be able to open and close freely, and is provided with an interlocking mechanism that opens and closes the switching valve in conjunction with the rotation of the butterfly valve to the open position and the closed position; The interlocking mechanism has a cam in a cam chamber that is separated by a partition wall from the part of the air supply passage in which the butterfly valve is provided and that communicates with the downstream end of the gas supply passage, the rotating shaft of the butterfly valve protruding into the cam chamber through a shaft support hole formed in the partition wall, and the cam is fixed to the part of the rotating shaft that protrudes into the cam chamber, and the interlocking mechanism is configured so that the switching valve is opened and closed by the rotation of the cam via the rotating shaft as the butterfly valve rotates between the open position and the closed position, A premixing device characterized in that a plurality of grooves for grease reservoirs are formed at intervals in the axial direction of the rotating shaft on the outer peripheral surface of the portion of the rotating shaft that is inserted into the shaft support hole.

2. 2. The premixing device according to claim 1, wherein the plurality of grooves are connected in a spiral shape.

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