WO2022224379A1

WO2022224379A1 - Impeller and centrifugal blower

Info

Publication number: WO2022224379A1
Application number: PCT/JP2021/016185
Authority: WO
Inventors: 一樹蓮池; 一輝岡本; 千景門井; 勇児秋場
Original assignee: 三菱電機株式会社
Priority date: 2021-04-21
Filing date: 2021-04-21
Publication date: 2022-10-27
Also published as: JPWO2022224379A1

Abstract

An impeller (4) which is fixed to a shaft (3a) of a motor (3) and which is rotated about the shaft (3a) comprises: a disc-shaped main plate (4a); a plurality of blades (4b) provided upright and annularly on the outer peripheral portion of the front surface of the main plate (4a); and a cylindrical protruding portion (5) protruding from the back surface of the main plate (4a). The motor (3) is received on the radially inner side of the protruding portion (5). The protruding portion (5) is provided on the radially inner side relative to the outer diameter of the impeller (4) over the entire perimeter.

Description

impeller and centrifugal blower

The present disclosure relates to impellers and centrifugal fans.

A centrifugal fan has a scroll casing that houses an impeller. The scroll casing has an air inlet and an air outlet, and constitutes a flow path for airflow generated by the rotation of the impeller. Noise generated inside the scroll casing due to the rotation of the impeller is emitted outside the scroll casing through the suction port or the blowout port. In particular, the flow velocity inside the centrifugal fan is highest immediately after the air flows out from the impeller. Furthermore, since the distance between the impeller and the wall surface of the scroll casing increases as the direction of rotation advances, the airflow tends to fluctuate.

The airflow flowing out of the impeller is roughly divided into the main flow and the secondary flow. A secondary flow is an air current that flows in a direction perpendicular to the main stream. It is known that this secondary flow causes a secondary loss in the vicinity of the area where the motor exists, which is the rear surface of the impeller, and deteriorates the air blowing performance.

Patent Document 1 discloses that a cylindrical wall is formed on the back surface of the main plate of the impeller, and the outer diameter of the cylindrical wall is the same as the outer diameter of the blades of the impeller. This prevents the secondary flow formed by the rotation of the impeller from flowing into the back surface of the main plate, reduces the secondary loss, and improves the air blowing performance.

JP 2008-169826 A

However, when a centrifugal fan designed based on the centrifugal fan disclosed in Patent Document 1 was subjected to a fluid analysis based on the equation of motion and the equation of continuity, it was found that the leakage flow flowing on the back surface of the main plate was indeed suppressed. However, it was found that interference between the cylindrical wall and the secondary flow generated from the impeller tends to increase the pressure fluctuation on the cylindrical wall. The reason for this is that the outer diameter of the cylindrical wall provided on the back surface of the main plate is the same as the outer diameter of the impeller over the entire circumference, which inevitably induces interference between the cylindrical wall and the secondary flow. it is conceivable that. There is a close relationship between pressure fluctuations and noise, and there is an extremely high possibility that a location with large pressure fluctuations is a source of noise, leading to the problem of worsening noise.

The present disclosure has been made in view of the above, and aims to obtain an impeller and a centrifugal fan that suppress pressure fluctuations caused by interference between the secondary flow and the impeller and reduce noise.

In order to solve the above-described problems and achieve the purpose, the impeller in the present disclosure is an impeller that is fixed to the motor shaft of the motor and rotates around the motor shaft. The impeller includes a disk-shaped main plate, a plurality of blades annularly erected on the outer peripheral portion of the surface of the main plate, and a cylindrical protruding portion protruding from the back surface of the main plate. The motor is accommodated radially inside the protrusion, and the protrusion is installed radially inside from the outer diameter of the impeller over the entire circumference.

The impeller according to the present disclosure has the effect of suppressing pressure fluctuations caused by the interference between the secondary flow and the impeller, thereby reducing noise.

1 is a perspective view of a centrifugal fan according to Embodiment 1 Sectional view of the centrifugal blower according to Embodiment 1 1 is a top view of a centrifugal fan according to Embodiment 1 Cross-sectional view of a centrifugal blower of a comparative example Image diagram showing flow velocity distribution when fluid analysis is performed on the centrifugal fan of the comparative example An image diagram showing the distribution of effective values of pressure fluctuations when fluid analysis was performed on the centrifugal fan of the comparative example. FIG. 2 is an image diagram showing a flow velocity distribution when fluid analysis is performed on the centrifugal fan of Embodiment 1. FIG. FIG. 2 is an image diagram showing the distribution of effective values of pressure fluctuations when fluid analysis is performed on the centrifugal fan of Embodiment 1. FIG. Graph showing the results of an actual machine test of the air volume-specific noise characteristics of the centrifugal fan of the first embodiment and the centrifugal fan of the comparative example. Cross-sectional view of a centrifugal fan according to Embodiment 2 Perspective view of a centrifugal fan according to Embodiment 3

The impeller and centrifugal fan according to the embodiment will be described in detail below based on the drawings.

Embodiment 1.
FIG. 1 is a perspective view of a centrifugal fan 1 according to Embodiment 1. FIG. FIG. 2 is a cross-sectional view of centrifugal fan 1 according to Embodiment 1. As shown in FIG. FIG. 3 is a top view of the centrifugal fan 1 according to Embodiment 1. FIG. FIG. 2 schematically shows a cross section along line II-II in FIG.

As shown in FIGS. 1 to 3, the centrifugal fan 1 according to Embodiment 1 has a motor 3, an impeller 4 rotationally driven by the motor 3, and a scroll casing 11 housing the impeller 4. Centrifugal blower 1 generates airflow by rotating impeller 4 .

The scroll casing 11 has an air inlet 8 and an air outlet 10 . Inside the scroll casing 11 , an airflow is generated from the suction port 8 toward the blowout port 10 . The scroll casing 11 configures a flow path for airflow generated by the rotation of the impeller 4 . By rotating the impeller 4 , air outside the scroll casing 11 is sucked into the scroll casing 11 through the suction port 8 . By rotating the impeller 4 , the air inside the scroll casing 11 is blown out of the scroll casing 11 through the blowout port 10 . As shown in FIG. 1, an air flow Y1 directed from the outside of the scroll casing 11 to the suction port 8 and an air flow Y2 directed to the outside of the scroll casing 11 from the outlet 10 are generated outside the scroll casing 11, as shown in FIG. As shown in FIG. 2, inside the scroll casing 11, a main flow Y3, which is an air flow that flows from the suction port 8 through the impeller 4 and between the impeller 4 and the scroll casing 11, is generated.

The scroll casing 11 has a first wall 11a, a second wall 11b and a third wall 11c. The first wall 11 a and the second wall 11 b face each other in the axial direction of the scroll casing 11 . The third wall 11c connects the first wall 11a and the second wall 11b. The suction port 8 is formed in the first wall 11a. The first wall 11a is formed with a bell mouth 8a whose diameter increases from the suction port 8 toward the outer diameter side. The material of the scroll casing 11 is resin, for example.

The scroll casing 11 has a scroll portion 6, a diffuse portion 7, and a tongue portion 9. The scroll portion 6 is a portion forming a spiral flow path whose width in the radial direction increases toward the downstream side of the air flow. The spiral channel is, for example, an Archimedean spiral. That is, the distance from the rotating shaft 2 of the impeller 4 to the scroll portion 6 increases in the direction of rotation of the impeller 4, as shown in FIG. The diffuse portion 7 is a portion on the downstream side of the scroll portion 6 and constitutes a flow path between the scroll portion 6 and the outlet 10 . The diffuser 7 has the role of efficiently converting the dynamic pressure of the airflow flowing out of the impeller 4 into static pressure and guiding the airflow to the outlet 10 . The tongue portion 9 is a portion that connects the scroll portion 6 and the blowout port 10 so as to enlarge the opening area of the blowout port 10 . The tongue portion 9 guides the air flow swirling inside the scroll casing 11 to the outlet 10 .

The impeller 4 is a multi-blade impeller. The impeller 4 is fixed to the shaft 3 a of the motor 3 . The impeller 4 rotates about the shaft 3a. The impeller 4 includes a disk-shaped main plate 4a, a plurality of blades 4b annularly erected on the outer peripheral side of the front surface of the main plate 4a, and a boss portion 4c fixed to the shaft 3a of the motor 3. Further, the impeller 4 is provided with ribs 4d as blade reinforcing members on the outer diameter edge on the upstream side of the blades 4b. The rear surface of the main plate 4a of the impeller 4 is provided with a projecting portion 5 for straightening the airflow.

The impeller 4 has a shape such that the projecting portion 5 branches off from the middle of the main plate 4a. The projecting portion 5 preferably has a shape rotationally symmetrical or axially symmetrical with respect to the rotating shaft 2 of the centrifugal fan 1 from the viewpoints of preventing leakage flow generated on the back surface of the main plate 4a and reducing noise. In FIG. 2, the protrusion 5 presents a cylindrical wall shape that is axially symmetrical. A part of the motor 3 is accommodated in the space surrounded by the cylindrical wall of the projecting portion 5 . The reason for this is to minimize the distance between the motor 3 and the back surface of the impeller 4 in order to reduce the size of the centrifugal fan 1 as a whole.

Further, as shown in FIG. 3, the main plate 4a of the impeller 4 is provided with a plurality of ventilation holes 4e. The reason for providing the ventilation holes 4e is to suppress the temperature rise of the motor 3. FIG. In short, it is provided to promote the air-cooling effect of the motor 3 . Incidentally, the ventilation holes 4e can be eliminated if necessary, and there is no need to provide six as shown in FIG. The number of ventilation holes 4e is not limited.

The positional relationship and shape of the impeller 4 and the scroll casing 11, the presence or absence of the ventilation holes 4e, and the shape of the ventilation holes 4e are not limited to those shown in FIGS. In short, the positional relationship and shape of various parts may be appropriately determined at the time of design.

Here, in FIG. 3, a dashed-dotted line connecting the outer diameter side ends of the plurality of ventilation holes 4e is denoted as 4f, and a dashed line circle connecting the outer diameter side ends of the plurality of blades 4b of the impeller 4 is denoted by 4f. 4g, and a dashed-dotted line connecting the inner diameter side ends of the plurality of blades 4b of the impeller 4 is shown as 4h. 2 and 3, the inner diameter of the impeller 4 is defined as D1, the outer diameter of the impeller 4 as D2, the outer diameter of the motor 3 as Dc, and the outer diameter of the protrusion 5 as Da. The inner diameter D1 of the impeller 4 is defined as the diameter of the circle that corresponds to the dashed-dotted circle 4h and connects the inner diameter side ends of the plurality of blades 4b of the impeller 4 . The outer diameter D2 of the impeller 4 is defined as the diameter of a circle that corresponds to the dashed line circle 4g and connects the outer diameter side ends of the plurality of blades 4b of the impeller 4 . Also, as shown in FIGS. 2 and 3, Db is the diameter of a circle 4f of a dashed-dotted line connecting the outer peripheral side ends of a plurality of ventilation holes 4e with the rotating shaft 2 as the central axis, that is, the outer diameter of the ventilation holes 4e. Define.

In Embodiment 1, the outer diameter Da of the projecting portion 5 that defines the mounting position of the projecting portion 5 satisfies D2>Da>Dc. The reason for this is that, as will be described later with reference to FIGS. 4 to 7, the distance between the projecting portion 5 and the scroll casing 11 is increased to increase the effect of suppressing mutual interference.

Further, in Embodiment 1, the outer diameter Da of the projecting portion 5 is made smaller than the inner diameter D1 of the impeller 4 . The reason for this, which will also be described in detail in FIG. is. Moreover, it is desirable that the outer diameter Da of the projecting portion 5 is larger than the outer diameter Db of the ventilation hole 4e. Therefore, by installing the protruding portion 5 so as to satisfy the condition of D1>Da>Db, it is possible to suppress the secondary flow from colliding with the protruding portion 5 and suppress the generation of noise due to the secondary flow.

Also, from the viewpoint of reducing the cost of the material used for the projecting portion 5, it is preferable that the peripheral length of the projecting portion 5 is small. Therefore, it is better to provide the projecting portion 5 so as to satisfy the condition D1≧Da>Db.

Also, as shown in FIG. 2, the gap Hb between the projecting portion 5 and the scroll casing 11 in the direction along the rotating shaft 2 is preferably as close to 0 as possible from the viewpoint of preventing leakage of the secondary flow. However, if it is close to 0, the impellers 4 may collide with each other during rotation. Therefore, it is necessary to balance leakage prevention and collision avoidance, and in practice it is appropriate to provide a gap of about 3 to 7 mm.

In addition, in the main plate 4a of the impeller 4, the area from the outer peripheral portion of the main plate 4a to the portion where the projecting portion 5 is provided is a flat surface. The reason for this is to suppress abrupt turning of the airflow flowing out of the impeller 4 and to allow the main flow Y3 to reach the outlet 10 with as little loss as possible. This effect will be described in detail in FIG.

FIG. 4 is a cross-sectional view of a centrifugal blower of a comparative example. In the comparative example shown in FIG. 4, similarly to Patent Document 1, a projecting portion 20 is provided at the same position as the outer diameter D2 of the impeller 4 on the back surface of the main plate 4a. The projecting portion 20 has a cylindrical wall as in the first embodiment. In FIG. 4, the structure and shape of the constituent elements other than the projecting portion 20 are the same as those of the first embodiment. Therefore, in the comparative example, the outer diameter Da of the projecting portion 20 is equal to the outer diameter D2 of the impeller 4 .

FIG. 5 is an image diagram showing the flow velocity distribution when fluid analysis was performed on the centrifugal fan of the comparative example. FIG. 5 shows the flow velocity distribution in the AA cross section of FIG. 3 in the comparative example shown in FIG. The motor 3, the impeller 4, and the scroll casing 11 are indicated by white lines for convenience. In the flow velocity distribution in FIG. 5 , the higher the flow velocity (25 m/s), the blacker the figure, and the lower the flow velocity (15 m/s), the whiter the figure.

　In FIG. 5, the black area is the area of the main flow Y3 flowing out from the impeller 4. A secondary flow Y4 is formed that flows in a direction perpendicular to the main flow Y3. As in the comparative example, if the outer diameter Da of the protrusion 20 is the same as the outer diameter D2 of the impeller 4, the distance to the secondary flow Y4 will inevitably become short, and the protrusion 20 and the secondary flow Y4 will inevitably become closer. becomes more susceptible to interference.

FIG. 6 is an image diagram showing the distribution of effective values of pressure fluctuations when fluid analysis was performed on the centrifugal fan of the comparative example. In FIG. 6, the distribution of effective values of pressure fluctuations is shown so that the larger the pressure fluctuation (35 Pa), the blacker, and the smaller the pressure fluctuation (20 Pa), the whiter.

According to FIG. 6, it can be seen that the pressure fluctuation on the surface of the projecting portion 20 provided on the impeller 4 is about 30 to 40 Pq or more. The cause of the pressure fluctuation is considered to be that the secondary flow Y4 interfered with the protrusion 20, the airflow around the protrusion 20 was disturbed, and the pressure fluctuation occurred.

FIG. 7 is an image diagram showing the flow velocity distribution when fluid analysis is performed on the centrifugal fan 1 of Embodiment 1. FIG. FIG. 8 is an image diagram showing the distribution of effective values of pressure fluctuations when fluid analysis is performed on the centrifugal fan 1 of Embodiment 1. FIG. In Embodiment 1, the outer diameter Da of the projecting portion 5 is not the same as the outer diameter D2 of the impeller 4, and the entire circumference of the cylindrical wall is provided on the inner diameter side of the outer diameter D2 of the impeller 4. Also in FIG. 7, the motor 3, the impeller 4, and the scroll casing 11 are indicated by white lines for the sake of convenience. In the flow velocity distribution of FIG. 7, as in FIG. 5, the higher the flow velocity (25 m/s), the blacker the figure, and the lower the flow velocity (15 m/s), the whiter the figure. As in FIG. 6, the distribution of effective values of pressure fluctuations shown in FIG. 8 is shown so that the larger the pressure fluctuation (35 Pa), the blacker, and the smaller the pressure fluctuation (20 Pa), the whiter.

According to FIG. 7, it can be seen that the secondary flow Y4 is generated in the same way as in the case of the comparative example. However, in Embodiment 1, since the projecting portion 5 is provided on the inner diameter side of the impeller 4, the distance between the secondary flow Y4 and the projecting portion 5 can be increased, and the secondary flow Y4 projects by that amount. It can be seen that the interference of the portion 5 is suppressed. Incidentally, as a result of investigating to what extent the secondary flow Y4 is conspicuous, it was found that it is most conspicuous between the inner diameter D1 and the outer diameter D2 of the impeller 4 . Therefore, by installing the projecting portion 5 inside the inner diameter D1 of the impeller 4, it is possible to suppress the collision of the secondary flow Y4 with the projecting portion 5 and suppress the generation of noise due to the secondary flow Y4. .

Furthermore, since the main plate 4a of the impeller 4 has a horizontal surface from the outer peripheral portion of the main plate 4a where the plurality of blades 4b are arranged to the portion where the protrusion 5 is provided, the main flow Y3 is directed to the main plate 4a of the impeller 4. It can be seen that the water flows almost horizontally. Since the main flow Y3 flows out substantially horizontally with respect to the main plate 4a, it can reach the outlet 10 with little loss without causing a sudden change in direction of the airflow. Furthermore, there is an effect of effectively separating the secondary flow Y4 and the main flow Y3, and interference between the main flow Y3 and the secondary flow Y4 can be effectively suppressed.

According to FIG. 8, it can be seen that the magnitude of the pressure fluctuation of the projecting portion 5 is greatly reduced to 15 to 30 Pa in the first embodiment. The reason for this is considered to be that the interference between the secondary flow Y4 and the projecting portion 5 is effectively suppressed, as described with reference to FIG.

　There is a close relationship between noise and pressure fluctuations, and locations with large pressure fluctuations are sources of noise. Therefore, it goes without saying that reducing the pressure fluctuation on the surface of the projecting portion 5 leads to a reduction in noise. In short, as shown in FIG. 8, installing the projecting portion 5 on the inner diameter side of the impeller 4 is effective for achieving low noise.

FIG. 9 is a diagram showing the results of an actual machine test of the air volume-specific noise characteristics of the centrifugal fan 1 of Embodiment 1 and the centrifugal fan of the comparative example. The horizontal axis indicates air volume, and the vertical axis indicates specific noise. Black circles are plots for the centrifugal fan of the comparative example, and white circles are plots for the centrifugal fan 1 of the first embodiment.

According to FIG. 9, the noise value in the minimum specific noise, which is the operating air volume band of the centrifugal fan, is 12.8 dB in the comparative example and 12.2 dB in the first embodiment, which is a noise reduction of 0.6 dB. can be confirmed. The reason why such a noise reduction could be confirmed is that by offsetting the protrusion 5 to the inner diameter side of the impeller 4, interference between the protrusion 5 and the secondary flow Y4 can be suppressed, and the surface of the protrusion 5 It is considered that this is because the pressure fluctuation of

As described above, according to Embodiment 1, since the entire circumference of the projecting portion 5 is offset radially inward from the plurality of blades 4b of the impeller 4, the projecting portion 5 and the secondary flow Y4 can be suppressed, pressure fluctuations on the surface of the projecting portion 5 can be effectively reduced, and noise reduction can be achieved.

Embodiment 2.
FIG. 10 is a cross-sectional view of a centrifugal fan according to Embodiment 2. FIG. In the second embodiment, the projecting portion 5 of the first embodiment is replaced with a projecting portion 30 . The configuration of the second embodiment other than the protruding portion 30 is the same as that of the first embodiment, and redundant description will be omitted. The projecting portion 30 is not branched from the main plate 4a, but is bent from the main plate 4a to have a V-shaped cross section. The impeller 4 of Embodiment 2 is designed in consideration of resin molding. Since it is not branched from the main plate 4a like the projecting portion 5 of the first embodiment, it is preferable from the viewpoint of mass production of resin-molded blades. Further, as in the first embodiment, when the outer diameter of the impeller 4 is defined as D2, the inner diameter of the impeller 4 as D1, the outer diameter of the motor 3 as Dc, and the outer diameter of the ventilation hole 4e as Db, the projecting portion 30 The mounting position of is within a range that satisfies D2>Da>Dc and D1≧Da>Db.

As described above, according to the second embodiment, since the projecting portion 30 has a V-shaped cross section, in addition to the effects of the first embodiment, it is possible to mass-produce the impeller 4 by resin molding.

Embodiment 3.
11 is a perspective view of a centrifugal fan according to Embodiment 3. FIG. In the third embodiment, the projecting portion 5 of the first embodiment is replaced with a projecting portion 40 . The configuration of Embodiment 3 other than the protrusion 40 is the same as that of Embodiment 1, and redundant description will be omitted.

The projecting portion 40 has a rotationally symmetrical shape, for example, an elliptical shape. The elliptical protrusion 40 has a center aligned with the rotating shaft 2 of the motor 3, a major axis of the ellipse equal to or smaller than the outer diameter D2 of the impeller 4, and a minor axis of the ellipse equal to or larger than the outer diameter Db of the ventilation hole 4e. do. The major axis of the ellipse and the minor axis of the ellipse are measured by the outer diameter of the projecting portion 40, for example. Thus, the elliptical protruding portion 40 is installed on the entire circumference of the protruding portion 40 in the range from the outer diameter D2 of the impeller 4 to the outer diameter Db of the ventilation hole 4e.

In Embodiment 3, the impeller 4 may have no ventilation holes 4e. In that case, the projecting portion 40 is installed in a region radially inward from the outer diameter of the impeller 4 over the entire circumference, and at least part of the entire circumference of the projecting portion 40 is outside the impeller 4. It is installed with an offset radially inward from the diameter. In the case of FIG. 11 , the longer diameter portion of the projecting portion 40 is installed on the outer diameter portion of the impeller 4 , and the portions other than the longer diameter portion are offset radially inward from the outer diameter of the impeller 4 .

As for the shape of the projecting portion 40, it is desirable that the difference between the major axis and the minor axis is large. For example, it is desirable that the difference between the major diameter and the minor diameter is at least half the difference between the outer diameter D2 of the impeller 4 and the outer diameter Db of the ventilation holes 4e. That is, it is desirable that (Dx−Dn)>(D2−Db)/2, where Dx is the major axis and Dn is the minor axis.

The projecting portion 40 of Embodiment 3 has an elliptical shape instead of a perfect circular shape. In the case of an elliptical shape, the distance from the central axis to the wall surface of the protrusion 40 differs depending on the location, so that the sound wave existing inside the protrusion 40 and the sound wave having the same frequency and propagating in the opposite direction are less likely to overlap each other. Therefore, standing waves are less likely to occur, and resonance can be effectively suppressed.

As described above, according to Embodiment 3, since the projecting portion 40 is formed in an elliptical shape, standing waves are less likely to occur, resonance can be effectively suppressed, and noise can be further reduced. The protruding portion 40 is installed in a region radially inward from the outer diameter of the impeller 4 over the entire circumference, and at least part of the entire circumference of the protruding portion 40 is the outer diameter of the impeller 4. Any shape other than an ellipse may be used as long as it satisfies the condition of being offset further inward in the radial direction.

The configuration shown in the above embodiment shows an example of the content of the present disclosure, and can be combined with another known technology. It is also possible to omit or change the part.

1 Centrifugal blower, 2 Rotating shaft, 3 Motor, 3a Shaft, 4 Impeller, 4a Main plate, 4b Blade, 4c Boss, 4d Rib, 4e Ventilation hole, 4f, 4g, 4h Circle, 5, 20, 30, 40 Projection Part, 6 Scroll Part, 7 Diffuse Part, 8 Suction Port, 8a Bell Mouth, 9 Tongue Portion, 10 Blowout Port, 11 Scroll Casing, 11a First Wall, 11b Second Wall, 11c Third Wall, Y1 Air Flow, Y2: air flow, Y3: main flow, Y4: secondary flow.

Claims

An impeller fixed to a motor shaft of a motor and rotating around the motor shaft,
a disk-shaped main plate;
a plurality of blades annularly erected on the outer peripheral portion of the surface of the main plate;
a cylindrical protruding portion protruding from the back surface of the main plate;
with
The motor is housed inside the protrusion in the radial direction,
An impeller according to claim 1, wherein the projecting portion is arranged radially inward from an outer diameter of the impeller over the entire circumference.
The impeller according to claim 1, wherein the main plate has a plurality of ventilation holes arranged in a circumferential direction.
The impeller according to claim 1, wherein the protrusion has a shape that is rotationally symmetrical with respect to the rotation axis of the motor shaft.
The impeller according to claim 3, wherein the protruding portion is cylindrical.
5. The blade according to claim 4, wherein D2>Da>Dc is satisfied, where Da is the outer diameter of the protrusion, D2 is the outer diameter of the impeller, and Dc is the outer diameter of the motor. car.
The main plate has a plurality of ventilation holes arranged in a circumferential direction,
The protruding portion has a cylindrical shape,
2. The blade according to claim 1, wherein D1≧Da>Db, where Da is the outer diameter of the protrusion, D1 is the inner diameter of the impeller, and Db is the outer diameter of the ventilation hole. car.
3. The impeller according to claim 1 or 2, wherein at least a portion of the entire circumference of the protruding portion is offset radially inward from the outer diameter of the impeller.
The impeller according to claim 7, wherein the projection has an elliptical shape centered on the rotation axis of the motor shaft.
The impeller according to any one of claims 1 to 8, wherein a portion of the main plate from the outer peripheral portion to the projecting portion is a flat surface.
an impeller according to any one of claims 1 to 9;
the motor;
a scroll casing housing the impeller, having an air inlet and an air outlet, and forming a flow path for an air flow generated by rotation of the impeller;
A centrifugal blower comprising: