JP2010159659A - Multi-blade blower - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that a conventional multi-blade blower requires another component having a large loss coefficient such as rubber ring so as to suppress resonance of an impeller with respect to excitation from an electric motor which results in complication of a structure to increase the cost and that vibrations from the electric motor is transmitted to the impeller to excite a resonance phenomena which results in the production of noise when deterioration of rubber through long term use lowers an effect of insulating vibrations. <P>SOLUTION: An outer peripheral ring 11 is arranged keeping a certain distance from an intake side opening end 12 so as to make a natural vibration mode frequency of an impeller 5 different with respect to frequency of excitation force of an electric motor as shown in Fig.2, which leads to the suppression of the excitation of a resonance phenomena. As a result, the production of noise can be stably prevented for the long term while simplifying the structure and reducing the cost. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a multi-blade blower used for a ceiling-embedded ventilation fan used for indoor ventilation.

  Conventionally, as shown in FIG. 12, this type of multiblade blower includes a fan casing 102 having a bell mouth 101, an impeller 103 that is rotatably installed in the fan casing 102, and an electric motor that drives the impeller 103. 104. The impeller 103 has a plurality of blades 106 on the outer peripheral side of the main plate 105, and an outer peripheral ring 107 having a larger outer diameter than the outer periphery of the blade 106 is provided at the suction side end portion 108 of the impeller 103. (For example, refer to Patent Document 1).

  In this configuration, when the frequency of the electromagnetic vibration generated from the electric motor matches the frequency of the natural vibration mode of the impeller, the resonance phenomenon is excited, the vibration of the impeller is amplified, and noise is generated. Since the excitation force of electromagnetic vibration acts in the circumferential direction of the rotating shaft, the main plate and the suction side opening end are in the circumferential direction due to the bending deformation of the blade with the main plate and outer ring as the support point. When the behavior is twisted in the opposite phase, the response to vibration is easy, and the blades act as a diaphragm of the speaker, which tends to cause excessive noise. In addition, since the frequency of the natural vibration mode depends on the distance between the main plate and the outer ring, that is, the blade length, it is most effective to change the blade length to suppress the resonance phenomenon. is there. However, the length of the blades is determined by the air blowing performance as a multiblade fan and cannot be easily changed.

  In view of this, a structure in which vibration from an electric motor is insulated to suppress excitation of a resonance phenomenon and prevent generation of noise is widely known. (For example, refer to Patent Document 2).

  The multiblade fan will be described below with reference to FIG.

The inner diameter of the blade boss 110 of the impeller 109 is made larger than the outer diameter of the rotating shaft 111 of the electric motor, the recess 113 into which the rubber ring 112 is inserted is provided at both ends of the blade boss 110, and the blade boss 110 is inserted into the rotating shaft 111. The impeller 109 is pressed by the washer 114 and the screw 115 and is lifted from the rotating shaft 111 by applying the washer 114 and stopping with the screw 115. Since electromagnetic vibration from the rotating shaft 111 is insulated by the ring 112 and is not transmitted to the impeller 109, it does not resonate with the natural frequency of the impeller 109, and noise can be prevented.
JP 2001-173596 A (FIG. 2) Japanese Utility Model Publication No. 5-1899 (Fig. 2)

  In such a conventional multiblade fan, another part made of a material having a large loss factor such as a rubber ring is required to insulate vibration, so that the structure is complicated and the cost is increased. In addition, when the rubber deteriorates due to long-term use and the effect of insulating the vibration is reduced, the vibration from the motor is transmitted to the impeller, the resonance phenomenon is excited, and noise is generated.

  The present invention solves such a conventional problem, and provides a multiblade fan that is simple in structure, can suppress excitation of a resonance phenomenon at low cost, and can stably prevent generation of noise for a long period of time. With the goal.

  In order to achieve the above object, the multiblade fan of the present invention has a plurality of blades along the circumferential direction on the outer peripheral side of the disk-shaped main plate, and an outer ring is provided along the outer peripheral surface of these blades. In the multiblade fan in which the rotation shaft of the motor is connected to the rotation center of the resin impeller, the outer diameter of the outer ring is larger than the diameter of the outer peripheral surface of the blade, and the circumferential direction generated by the motor is increased. The outer ring is arranged so that the frequency of the vibration force and the frequency of the natural vibration mode in which the main plate and the suction side opening end are twisted in the opposite phases in the circumferential direction due to the bending deformation of the blade existing in the impeller Thus, excitation of the resonance phenomenon of the impeller can be suppressed.

  According to the present invention, since the excitation of the resonance phenomenon can be suppressed by arranging the outer ring so that the frequency of the natural vibration mode of the impeller is different from the frequency of the excitation force of the electric motor, the structure is simple and the cost is low. Therefore, it is possible to provide a multiblade fan that can stably generate noise for a long period of time.

  The multiblade fan according to claim 1 of the present invention has a plurality of blades along the circumferential direction on the outer circumferential side of the disk-shaped main plate, and is made of a resin provided with an outer ring along the outer circumferential surface of these blades. In the multiblade fan in which the rotating shaft of the electric motor is connected to the rotation center of the impeller, the outer diameter of the outer peripheral ring is larger than the diameter of the outer peripheral surface of the blade, and the circumferential excitation force generated from the electric motor is The outer ring is arranged so that the frequency and the frequency of the natural vibration mode in which the main plate and the suction side opening end are twisted in the opposite phase in the circumferential direction due to bending deformation of the blade existing in the impeller, It has the effect of suppressing the excitation of the resonance phenomenon of the impeller.

  The multi-blade fan according to claim 2 of the present invention is the multi-blade fan according to claim 1, wherein the blades are disposed only on one side of the main plate, and the outer ring is disposed at a constant distance from the suction side opening end. Since the bending rigidity of the blades can be changed by changing the distance between the fulcrums by the main plate and the outer ring, the frequency of the natural vibration mode can be changed.

  The multiblade fan according to claim 3 of the present invention is the multiblade fan according to claim 2, wherein the distance between the outer peripheral ring and the suction side opening end is 25 to 50% of the total blade length, It has the effect | action that a frequency can be changed effectively.

  The multi-blade fan according to claim 4 of the present invention is the multi-blade fan according to claim 1, wherein the blades having different lengths in the rotation axis direction are arranged on both sides of the main plate, and the outer ring is attached only to the blade having a long length. It is characterized by a certain distance from the suction side opening end. In addition to dividing the blades on both sides of the main plate, the connection position is changed to shorten the apparent blade length. By doing so, the frequency of the natural vibration mode can be effectively changed.

  The multiblade fan according to claim 5 of the present invention is characterized in that in the multiblade fan according to claim 4, a plurality of holes through which air passes are arranged in the main plate, and air is passed through the plurality of holes. Since it can pass, it has the effect | action that it can be used also for the structure which a suction inlet has only in one side.

  The multiblade fan according to claim 6 of the present invention is the multiblade fan according to claim 4 or 5, wherein the ratio of the lengths of the blades arranged on both sides of the main plate is in the range of 8: 2 to 6: 4. The distance between the outer peripheral ring in the rotation axis direction and the suction side opening end is set to 25 to 50% of the length of the long blade, and the frequency of the natural vibration mode can be effectively changed. .

  The multi-blade fan according to claim 7 of the present invention is the multi-blade fan according to claim 2 or 6, wherein the thickness of the outer peripheral ring in the rotation axis direction is 3% or more of the entire blade length. By increasing the rigidity of the connecting portion, the frequency of the natural vibration mode can be effectively changed.

  The multiblade fan according to claim 8 of the present invention is the multiblade fan according to any one of claims 2 to 7, characterized in that the inner diameter of the outer peripheral ring is larger than the outer diameter of the main plate, and the rotating shaft By having a structure in which there are no overlapping portions in the direction, it is possible to mold with a general upper and lower two-side mold, and the manufacturing cost can be reduced.

  The multiblade fan according to claim 9 of the present invention is characterized in that in the multiblade fan according to claim 8, the diameter of the outer peripheral surface of the blade is larger than the inner diameter of the outer ring, By increasing the joint surface, the stress generated during operation can be reduced.

  The multi-blade fan according to claim 10 of the present invention is the multi-blade fan according to any one of claims 2 to 9, wherein a circumferential cross-sectional shape of the outer peripheral ring is a U-shape, and the main plate side in the rotation axis direction is The feature is that there is a dent on the surface. By reducing the weight while maintaining the rigidity of the outer ring, the mass added to the blades can be reduced and the load on the motor applied during startup and operation is reduced. Has the effect of being able to.

  In the multiblade fan according to claim 11 of the present invention, in the multiblade fan according to any one of claims 2 to 10, the section coefficient in the cross section in the direction of the rotation axis of the blade is the largest on the main plate side, and the closer to the suction side opening end side. This is characterized in that the frequency is reduced, and the frequency of the natural vibration mode can be increased by moving the center of gravity of the blade toward the main plate.

  The multi-blade fan according to claim 12 of the present invention is the multi-blade fan according to any one of claims 2 to 11, wherein the circumferential shape of the outer peripheral ring is a parallelogram, and the main plate side toward the outer peripheral side. It is characterized by the fact that it is inclined, and has the effect that the generation of turbulent noise can be reduced by reducing the generation of vortices by blowing while maintaining the rigidity of the outer ring.

  The multi-blade fan according to claim 13 of the present invention is the multi-blade fan according to any one of claims 2 to 12, wherein a corner of the inner peripheral surface of the outer peripheral ring on the main plate side is formed by a curved surface. It has the effect | action that generation | occurrence | production of turbulent flow noise can be reduced by reducing the eddy generation by ventilation.

  The multiblade fan according to claim 14 of the present invention is characterized in that in the multiblade fan according to any one of claims 2 to 13, the inner peripheral side of the suction side opening end of the blade is formed by a curved surface. There is an effect that generation of turbulent noise can be reduced by reducing vortex generation due to interference between the suction flow and the blade end face.

  The multi-blade fan according to claim 15 of the present invention is characterized in that in the multi-blade fan according to any one of claims 2 to 14, the joint in the rotational axis direction of the blade and the outer ring is a curved surface, By reducing the stress concentration factor at the corresponding location, the stress generated during operation can be reduced.

  The multi-blade fan according to claim 16 of the present invention is characterized in that in the multi-blade fan according to any one of claims 2 to 15, the joint portion between the blade and the main plate is formed with a curved surface. By reducing the stress concentration factor, the stress generated during operation can be reduced.

  The multi-blade fan according to claim 17 of the present invention is characterized in that, in the multi-blade fan according to any of claims 2 to 16, the outer peripheral side of the suction side opening end of the blade is formed with a curved surface. Since the impact absorbability of the corresponding part can be increased, it has the effect of preventing the blade from being damaged due to an unexpected drop when the impeller is disassembled for maintenance or cleaning.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a side sectional view of Embodiment 1 of the present invention, and FIG. 2 is a side sectional view of an impeller.

  As shown in FIG. 1, the multiblade blower 1 is connected to a fan casing 4 having an inlet 2 and an outlet 3, an impeller 5 disposed inside the fan casing 4, an impeller 5, and a rotating shaft 6. The motor 7 is fixed to the fan casing 4. The motor 7 is driven to rotate the impeller 5, suck air from the suction port 2, and blow air from the blower port 3.

  The electric motor 7 uses, for example, a DC brushless motor. Due to its structure, it is known that an excitation force is generated in the circumferential direction of the rotating shaft 6 during operation, and the excitation frequency changes in proportion to the rotational speed. ing. For example, when the excitation frequency is Fm (Hz), the rotation speed is Rm (1 / min), and the coefficient is α, it can be expressed as Fm = α × Rm / 60 (Hz). In the case of a DC brushless motor with a coefficient α of 18, when the rotational speed Rm is 740 (1 / min), the excitation frequency Fm is 220 (Hz).

  The impeller 5 is an integrally injection-molded product made of resin, and the material thereof is, for example, polypropylene (PP). However, other thermoreversible resins such as acrylonitrile, butadiene, styrene (ABS) may be used. Because it is made of resin, it has a high vibration damping rate and it is difficult to generate excessive vibration and noise radiation even if the excitation force is transmitted. However, when the resonance phenomenon is excited, it produces a large response to the excitation force and causes excessive vibration. May occur.

  As shown in FIG. 2, the impeller 5 has a plurality of blades 9 along the circumferential direction on the outer peripheral side of the disk-shaped main plate 8, and an outer ring 11 is provided along the outer peripheral surface 10 of these blades 9. ing. The outer ring 11 is arranged with a distance from the suction side opening end 12 of the impeller 5 to the main plate 8 side, and the blade length is L1, and the distance between the outer ring 11 and the suction side opening end 12 is L2. For example, L1 = 90 mm, L2 = 30 mm, and L2 / L1 × 100 = 33%. If the thickness of the outer peripheral ring 11 in the rotation axis direction is T1, T1 = 3 mm, and T1 / L1 × 100 = 3.3% with respect to the blade length L1. In this way, when the outer peripheral ring 11 is arranged at a position that maintains a certain distance from the suction side opening end, the bending rigidity of the blade 9 can be changed by changing the distance between the fulcrum by the main plate 8 and the outer peripheral ring 11. 5 can change the frequency of the natural vibration mode in which the main plate 8 and the suction side opening end 12 existing in 5 are twisted in the opposite phase in the circumferential direction.

  FIG. 3 shows a result calculated using eigenvalue analysis by the finite element method as an example in which the frequency of the natural vibration mode can be changed.

  (A) has an outer peripheral ring provided at the suction side opening end, the natural vibration mode frequency is 220 Hz, (b) is according to the first embodiment of the present invention, and the natural vibration mode frequency is 315 Hz. As shown in FIG. 3, both (a) and (b) show the behavior in which the main plate 8 and the suction-side open end 12 are twisted to the opposite phase in the circumferential direction, and the natural vibration mode is obtained by changing the position of the outer peripheral ring 11. It can be seen that the frequency of is increased by about 40% from 220 Hz in (a) to 315 Hz in (b).

  FIG. 4 is a graph showing changes in the frequency of the natural vibration mode when the distance between the outer ring 11 and the suction side opening end 12 is changed. When L2 / L1 increases, the frequency increases, and there is an effect of increasing the frequency from the original 220 Hz to 300 Hz to 320 Hz at 25% to 50%. However, when L2 / L1 exceeds 50%, a phenomenon in which the outer ring 11 and the suction side opening end 12 act as a cantilever occurs, and the natural vibration mode tends to decrease. In order to effectively increase the frequency, the distance between the outer peripheral ring 11 and the suction side opening end 12 is preferably 25 to 50%.

  FIG. 5 is a graph of changes in frequency when the thickness T1 of the outer ring 11 is changed. As shown in FIG. 5, it can be seen that when T1 / L1 is 3% or more, it is increased to 300 Hz or more with respect to 200 Hz with a thickness T1 = 0 mm, and a great effect is obtained. The greater the thickness, the greater the effect, but if this thickness is simply increased, the air volume is reduced by increasing the area that blocks the flow path on the blade outlet side. Considering the influence on the air blowing performance, it is desirable to keep it at 5% or less.

  In the above configuration, if the excitation frequency of the motor 7 is 220 Hz, when the outer peripheral ring 11 is provided at the suction side opening end 12, the frequency of the natural vibration mode of the impeller 5 coincides at 220 Hz, and the resonance phenomenon is excited. Since the frequency of the natural vibration mode can be changed to 300 Hz or more by changing the position of the ring 11, the excitation of the resonance phenomenon is suppressed and the generation of noise can be prevented. Further, since no separate parts such as rubber that insulates vibration are used, the effect of suppressing the resonance phenomenon stably for a long time without deterioration can be obtained. In addition, since the excitation frequency of the electric motor 7 changes with rotation speed, it is necessary to change the frequency of the natural vibration mode of the impeller 5 in consideration of the use rotation speed range as the multiblade fan 1.

  Recently, due to the development of computer performance and software, an environment where eigenvalue analysis by the finite element method can be easily performed has been established, so even if it is a resin integral molded product, eigenvalue analysis can be performed before mold design. It is possible to determine an appropriate position of the outer ring.

  In addition, the impeller 5 is a resin-integrated molded product and does not need to be manufactured by separate parts or complicated divided molds. As shown in FIG. 2, the inner diameter D2 of the outer ring is larger than the outer diameter D1 of the main plate so that there is no overlapping portion in the direction of the rotation axis 6, for example, D1 = 236 mm and D2 = 240 mm. It is possible to mold with a simple upper and lower two-side mold, and it is possible to reduce the cost.

(Embodiment 2)
FIG. 6 is a side sectional view of an impeller according to Embodiment 2 in which blades having different lengths are arranged on both sides of the main plate, and FIG. 7 is a partial side sectional view of an outer peripheral ring. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 6, blades 9 are arranged on both sides of the main plate 8 of the impeller 5, and when the lengths are L1 and L3, L1 = 70 mm, L3 = 20 mm, and the length ratio is 3: 1. The outer peripheral ring 11 is provided at a position of L2 = 20 mm from the suction side opening end 12 of the longer blade 9, and L2 / L1 = 30%. By dividing the blade 9 in the middle, the distance between the fulcrums by the main plate 8 and the outer peripheral ring 11 can be made shorter than that in the first embodiment without changing the overall length of the blade 9, so that the frequency of the natural vibration mode of the impeller 5 can be reduced. It can be changed greatly. As a result, even if the excitation frequency of the electric motor 7 changes greatly depending on the rotation speed, an effect that resonance can be suppressed in a wide frequency range is obtained.

  The main plate 8 has a plurality of holes 13 that are rotationally symmetrical. Since air passes through this hole 13, it can be used in a configuration in which the suction port 2 is only on one side, and the blades 9 on both sides work effectively, so that the effect of maintaining the blowing performance is obtained.

  As shown in FIG. 7, the cross-sectional shape of the outer peripheral ring 11 in the circumferential direction is a U-shape, and there is a recess 14 on the surface on the main plate side. Without changing the connection distance between the outer ring 11 and the blades 9, the inner wheel can be reduced while maintaining the cross-sectional rigidity to reduce the weight of the impeller 5, so that the load on the motor 7 applied during start-up and operation can be reduced. .

(Embodiment 3)
FIG. 8 is a side sectional view of an impeller according to Embodiment 3 of the present invention, and FIG. 9 is an enlarged perspective view of a joint between the blade and the main plate. The same parts as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 8, in order to make the section modulus of the blade 9 largest on the main plate 8 side and smaller as the suction side opening end 12 is reached, the blade chord length is the largest on the main plate 8 side with a constant plate thickness. It is distributed so as to become larger and smaller as it becomes the suction side opening end 12. If the chord length on the main plate 8 side is B1 and the chord length on the suction side opening end 12 is B2, for example, B1 = 25 mm and B2 = 20 mm. Since the section modulus becomes the largest on the main plate 8 side, the center of gravity of the blade 9 moves to the main plate 8 side, so that the frequency of the natural vibration mode can be increased.

  Further, the diameter D3 of the outer peripheral surface 10 of the blade 9 is larger than the inner diameter D2 of the outer ring 11, and for example, D3 = 244 and D2 = 240, thereby connecting the blade and the outer ring in a three-dimensional combination. ing. By increasing the joint surface between the outer ring 11 and the blade 9, the stress generated at this point during operation can be reduced.

  As shown in FIG. 9, the joint 15 between the blade 9 and the main plate 8 is formed as a curved surface, and the stress generated during operation can be further reduced by reducing the stress concentration coefficient at this portion.

(Embodiment 4)
FIG. 10 is a partial sectional side view of the outer peripheral ring of the impeller according to Embodiment 4 of the present invention, and FIG. 11 is an enlarged top view of the impeller. The same parts as those in the first to third embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 10, the circumferential cross-sectional shape of the outer peripheral ring 11 is a parallelogram, and is inclined toward the main plate 8 toward the outer peripheral direction. Even if the cross-sectional shape is a parallelogram, the rigidity can be maintained because the section modulus is equal to that of the original rectangle. Moreover, the corner | angular part 16 by the side of the main board 8 of the internal peripheral surface of the outer peripheral ring 11 is formed in the curved surface. If the outer peripheral ring 11 is arranged at a distance from the suction-side opening end 12, the vortex is likely to be generated by being exposed to a flow field with a high wind speed coming out of the impeller 5, but it is shaped along the direction of the flow, and at the same time most counteracted. Vortex generation can be reduced by making the corners 16 where vortices are likely to be curved into curved surfaces. Furthermore, since the inner peripheral side 17 of the suction side opening end 12 is formed with a curved surface, vortex generation due to interference between the suction flow and the blade end surface can be reduced. Thus, by the structure which reduces eddy generation | occurrence | production, the effect that generation | occurrence | production of the turbulent flow noise at the time of driving | operation can be suppressed low is acquired.

  Moreover, since the shock absorption can be improved by forming the outer peripheral side 18 of the suction side opening end 12 of the blade 9 with a curved surface, the blade caused by an unexpected drop when the impeller 5 is disassembled for maintenance or cleaning. 9 can be prevented from being damaged.

  Further, as shown in FIG. 11, the joint portion 19 in the direction of the rotation axis 6 between the blade 9 and the outer ring 11 is formed to be connected by a curved surface. By reducing the stress concentration factor of this portion, the stress generated during operation can be reduced.

  The multiblade fan of the present invention is useful as an application used for a ceiling-embedded ventilation fan used for indoor ventilation. Moreover, it can also be suitable for the use as a blower such as an indoor unit of an air conditioner or an air cleaner.

Side sectional view of Embodiment 1 of the present invention Side sectional view of the impeller of Embodiment 1 of the present invention (A) The figure which shows the analysis result which provided the outer periphery ring in the suction side opening end, and (b) The figure which shows the analysis result which calculated Embodiment 1 of this invention Graph showing the frequency change of natural vibration mode when the distance between the outer ring and suction side opening end is changed Graph of change in frequency of natural vibration mode when the thickness of the outer ring is changed Side sectional view of Embodiment 2 of the present invention Partial sectional side view of the outer peripheral ring of Embodiment 2 of the present invention Side sectional view of the impeller of Embodiment 3 of the present invention The perspective enlarged view of the junction part of the wing | blade and main plate of Embodiment 3 of this invention Partial sectional side view of the outer periphery ring of Embodiment 4 of the present invention The upper surface enlarged view of the impeller of Embodiment 4 of this invention Cross-sectional view showing a conventional multiblade fan Partial sectional view showing a blade boss portion of a conventional multiblade fan

DESCRIPTION OF SYMBOLS 1 Multiblade blower 2 Suction port 3 Outlet 4 Fan casing 5 Impeller 6 Rotating shaft 7 Electric motor 8 Main plate 9 Blade 10 Outer peripheral surface 11 Outer peripheral ring 12 Suction side opening end 13 Hole 14 Depression 15 Joint portion 16 Corner portion 17 Inner peripheral side 18 Outer peripheral side 19 Joint

Claims (17)

The rotating shaft of the motor is connected to the center of rotation of a resin impeller having a plurality of blades extending in the circumferential direction on the outer peripheral side of the disk-shaped main plate and provided with an outer ring along the outer peripheral surface of these blades. In the multiblade fan, the outer diameter of the outer peripheral ring is larger than the diameter of the outer peripheral surface of the blade, the frequency of the circumferential excitation force generated from the electric motor, and the bending of the blade existing in the impeller A multiblade fan in which the outer ring is arranged so that the frequency of a natural vibration mode in which the main plate and the suction side opening end are twisted in the opposite phase in the circumferential direction due to deformation. The multiblade fan according to claim 1, wherein the blades are arranged only on one side of the main plate, and the outer ring is arranged at a constant distance from the suction side opening end. The multiblade fan according to claim 2, wherein a distance between the outer peripheral ring and the suction side opening end is set to 25 to 50% of a blade length. The blades having different lengths in the direction of the rotation axis are arranged on both sides of the main plate, and the outer ring is arranged at a certain distance from the suction side opening end only on the blades having a long length. Multi-blade blower. The multiblade fan according to claim 4, wherein a plurality of holes through which air passes are arranged in the main plate. The ratio of the length of the blades arranged on both sides of the main plate is in the range of 8: 2 to 6: 4, and the distance between the outer peripheral ring in the rotation axis direction and the suction side opening end is 25 to 25 of the long blade length. The multiblade fan according to any one of claims 4 and 5, which is 50%. The multiblade fan according to any one of claims 2 to 6, wherein the thickness of the outer peripheral ring in the direction of the rotation axis is 3% or more of the blade length. The multiblade fan according to any one of claims 2 to 7, wherein an inner diameter of the outer peripheral ring is larger than an outer diameter of the main plate. The multiblade fan according to claim 8, wherein the diameter of the outer peripheral surface of the blade provided with the outer peripheral ring is larger than the inner diameter of the outer peripheral ring. The multiblade blower according to any one of claims 2 to 9, wherein a cross-sectional shape of the outer peripheral ring in a circumferential direction is a U-shape, and a recess is formed on a surface on a main plate side in a rotation axis direction. The multiblade blower according to any one of claims 2 to 10, wherein a section coefficient in a cross section in a rotation axis direction of the blade is the largest on the main plate side and becomes smaller toward the suction side opening end side. The multi-blade fan according to any one of claims 2 to 11, wherein a cross-sectional shape in a circumferential direction of the outer peripheral ring is a parallelogram, and is inclined toward the main plate toward the outer peripheral side. The multiblade fan according to any one of claims 2 to 12, wherein a corner of the inner peripheral surface of the outer peripheral ring on the main plate side is formed as a curved surface. The multiblade fan according to any one of claims 2 to 13, wherein the inner peripheral side of the suction side opening end of the blade is formed as a curved surface. The multiblade fan according to any one of claims 2 to 14, wherein a joint portion in a rotation axis direction between the blade and the outer ring is a curved surface. The multiblade fan according to any one of claims 2 to 15, wherein a joint portion between the blade and the main plate is formed by a curved surface. The multiblade fan according to any one of claims 2 to 16, wherein an outer peripheral side of a suction side opening end of the blade is formed by a curved surface.

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