Centrifugal air blower and ventilation device

Abstract

To provide a centrifugal air blower that can reduce noise propagating to the side of a user.SOLUTION: A centrifugal air blower 1 comprises: a motor 2; a cylindrical impeller 3 fixed to a shaft 2a of the motor 2; a scroll casing 10 in which the impeller 3 is housed, and comprising a suction port surface 10a provided with a suction port 5 for sucking air; a bell mouth 7 provided in the suction port 5, and for guiding the air sucked into the suction port 5, to the impeller 3; and an annular shield wall 8 provided in the suction port surface 10a, and surrounding the suction port 5.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a centrifugal fan and a ventilation device equipped with the centrifugal fan. [Background technology]

[0002] Patent Document 1 discloses a centrifugal fan equipped with a bell mouth that covers the end of the intake port in order to straighten the air drawn into the intake port. This centrifugal fan uses the bell mouth to improve its blowing performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3921832 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, the centrifugal blower has a scroll casing that houses an impeller. The scroll casing has an air inlet and an air outlet, forming a flow path for the airflow generated by the rotation of the impeller. Noise generated inside the scroll casing due to the rotation of the impeller or other factors is released to the outside of the scroll casing through the inlet or outlet.

[0005] Centrifugal fans are not only capable of generating airflow efficiently, but also of ensuring static pressure. For this reason, they are widely used in various ventilation equipment, including duct fans. In such ventilation equipment, users are often located on the intake side of the centrifugal fan. For example, if the ventilation equipment is installed on the ceiling of a room with the intake facing downwards, this would be the case if the users living in the room were located below the intake. In such cases, noise generated inside the centrifugal fan is transmitted directly to the users from the intake, making noise control measures on the intake side particularly important.

[0006] However, in the centrifugal blower described in Patent Document 1, noise generated inside the scroll casing is reflected by the curved surface of the bell mouth, causing a large amount of noise to propagate toward the user, resulting in an increase in noise levels.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a centrifugal blower and ventilation equipment that can reduce noise transmitted to the user. [Means for solving the problem]

[0008] The centrifugal blower according to the present disclosure comprises a motor, a cylindrical impeller fixed to the shaft of the motor, a scroll casing that houses the impeller and has an inlet surface with an inlet for drawing in air, a bell mouth that is provided at the inlet and guides the air drawn into the inlet to the impeller, and an annular shielding wall that is provided at the inlet surface and surrounds the inlet. [Effects of the Invention]

[0009] The centrifugal fan and ventilation equipment according to the present disclosure have the effect of reducing noise transmitted to the user. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view showing a centrifugal fan according to a first embodiment. [Figure 2] 1 is a cross-sectional view showing a centrifugal blower according to a first embodiment. [Figure 3] 1 is a cross-sectional view showing a centrifugal blower according to a first embodiment. [Figure 4] 5A and 5B are diagrams illustrating how noise propagates in the centrifugal fan according to the first embodiment. [Figure 5] FIG. 1 is a cross-sectional view showing a centrifugal blower according to a first comparative example. [Figure 6] FIG. 4 is a diagram showing how noise propagates in a centrifugal fan according to a first comparative example. [Figure 7]FIG. 10 is a perspective view showing a centrifugal fan according to a second comparative example. [Figure 8] FIG. 10 is a diagram showing how noise propagates in a centrifugal fan according to a second comparative example. [Figure 9] FIG. 4 is a diagram showing the results of an actual machine test of frequencies and noise levels for the centrifugal fan according to the first embodiment and a centrifugal fan according to a first comparative example. [Figure 10] FIG. 4 is a diagram showing the results of an actual machine test of frequencies and noise levels for the centrifugal fan according to the first embodiment and a centrifugal fan according to a second comparative example. [Figure 11] FIG. 10 is a diagram showing the relationship between the angle between the axis of rotation and a tangent that passes through the upper end of the shielding wall and contacts the curved surface of the bell mouth, and the results of an actual machine test of the noise propagating from the suction port toward the user. [Figure 12] FIG. 2 is a plan view showing a specific structure of the centrifugal fan according to the first embodiment. [Figure 13] FIG. 10 is a plan view showing a centrifugal fan according to a second embodiment. [Figure 14] FIG. 10 is a plan view showing a centrifugal fan according to a third embodiment. [Figure 15] FIG. 10 is a plan view showing a ventilation fan according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In each drawing, identical or corresponding parts are designated by the same reference numerals. Duplicate descriptions of these parts will be appropriately simplified or omitted. Furthermore, the size relationships between the components in each drawing may differ from those in reality.

[0012] Embodiment 1 Fig. 1 is a perspective view showing a centrifugal blower 1 according to embodiment 1. Fig. 2 is a cross-sectional view showing the centrifugal blower 1 according to embodiment 1, which corresponds to the cross section taken along line II-II in Fig. 1. Fig. 3 is a cross-sectional view showing the centrifugal blower 1 according to embodiment 1, which corresponds to the cross section taken along line III-III in Fig. 2.

[0013] The centrifugal fan 1 according to the first embodiment includes a motor 2, a cylindrical impeller 3 fixed to a shaft 2a of the motor 2, and a scroll casing 10 in which the impeller 3 is housed. The impeller 3 is a multi-blade impeller. The impeller 3 rotates around the shaft 2a of the motor 2 and generates a centrifugal airflow. The impeller 3 includes a disk-shaped main plate 3a, a plurality of blades 3b arranged in an annular shape on the outer periphery of the front surface of the main plate 3a, and a boss portion 3c fixed to the shaft 2a of the motor 2. In the centrifugal fan 1 according to the first embodiment, the impeller 3 includes 43 blades 3b. The impeller 3 also includes ribs 3d, which are blade reinforcing members, on the outer periphery of the upstream side of the blades 3b. The positional relationship and shape of the impeller 3 and scroll casing 10 are not limited to those shown in Figures 1 to 3. The positional relationship and shape of each part may be determined appropriately at the time of design.

[0014] The scroll casing 10 houses the impeller 3 and rectifies the air blown out from the impeller 3. The scroll casing 10 has a pair of side walls 10a, 10b and a peripheral wall 10c. The pair of side walls 10a, 10b cover the impeller 3 in the axial direction. The pair of side walls 10a, 10b are spaced apart from each other in the axial direction. The impeller 3 is disposed between the pair of side walls 10a, 10b. One of the side walls 10a has an intake port 5 formed therein for drawing air into the scroll casing 10. The other side wall 10b has a motor 2 attached thereto. The peripheral wall 10c covers the impeller 3 in the radial direction. The peripheral wall 10c has an outlet port 6 formed therein for blowing air out of the scroll casing 10. The scroll casing 10 is made of a material such as resin. One side wall 10a is also referred to as the "suction port surface." The axial direction is a direction parallel to the rotation axis 4 of the impeller 3. The radial direction is a direction perpendicular to the rotation axis 4 of the impeller 3.

[0015] The scroll casing 10 includes a scroll section 11 and a diffuser section 12 . The scroll section 11 rotatably houses the impeller 3 and forms a flow path that guides the airflow generated by the impeller 3 to the outlet 6. The scroll section 11 is a part that forms a spiral flow path whose width in the radial direction of the impeller 3 increases toward the downstream side of the airflow. The spiral flow path is, for example, an Archimedes spiral. That is, in the scroll section 11, the distance from the rotation axis 4 of the impeller 3 to the peripheral wall 10c increases in the rotation direction of the impeller 3, as shown in FIG. 3.

[0016] The diffuser section 12 is provided downstream of the scroll section 11 and constitutes a flow path between the scroll section 11 and the outlet 6. The diffuser section 12 efficiently converts the dynamic pressure of the airflow flowing out of the impeller 3 into static pressure, and guides the airflow to the outlet 6. The scroll section 11 has a tongue section 13 that is located between the diffuse section 12 and the winding start portion S of the peripheral wall 10c and forms a curved surface. The tongue section 13 guides the airflow generated by the impeller 3 to the diffuse section 12 and branches a portion of the airflow to be recirculated inside the scroll section 11.

[0017] The suction port 5 formed in the side wall 10a of the scroll casing 10 has a circular shape. The impeller 3 is disposed so that the center of the suction port 5 substantially coincides with the center of the rotary shaft 4. The shape of the suction port 5 is not limited to a circular shape, and may be other shapes, such as an elliptical shape. A bell mouth 7 is provided at the suction port 5. The bell mouth 7 is formed so that the opening diameter gradually decreases from the outside to the inside of the scroll casing 10. For this reason, the surface of the bell mouth 7 is curved. The bell mouth 7 straightens the air taken in at the suction port 5 and guides it to the impeller 3.

[0018] The air guided into the impeller 3 is blown out in the centrifugal direction by the rotation of the impeller 3 and moves along the peripheral wall 10c of the scroll section 11 toward the diffuser section 12. The air that reaches the diffuser section 12 is blown out of the scroll casing 10 through the outlet 6. In this way, a flow path for the airflow generated by the rotation of the impeller 3 is formed inside the scroll casing 10.

[0019] An annular shielding wall 8 is provided on the side wall 10a of the scroll casing 10, surrounding the suction port 5. The inner diameter of the shielding wall 8 may be the same as or larger than the opening diameter of the suction port 5. The outer diameter of the shielding wall 8 is smaller than the line segment that has its ends at the outer peripheral end of the side wall 10a and passes through the rotation shaft 4. The shielding wall 8 has a perfect circular shape in a plan view. In other words, the shielding wall 8 has a shape that is rotationally symmetrical with respect to the rotation shaft 4 of the impeller 3. The material of the shielding wall 8 is, for example, sheet metal or resin. The appropriate thickness of the shielding wall 8 is approximately 1 to 3 mm, and it may be the same thickness as the scroll casing 10.

[0020] It is preferable that the wall surface 8a of the shielding wall 8 is parallel to a line extending from the center of the motor 2 to the user. By providing the shielding wall 8 in this manner, part of the noise generated near the center of the motor 2 or the impeller 3 is diffracted at the upper end 8b of the shielding wall 8 and propagates in a direction different from the direction of the user. As a result, it is possible to reduce noise generated near the center of the motor 2 or the impeller 3 and propagated to the user beyond the air inlet 5. This effect will be described later.

[0021] Next, the operation of the centrifugal blower 1 according to the first embodiment will be described. When the motor 2 is driven to rotate the impeller 3, air outside the scroll casing 10 is drawn into the suction port 5 as airflow Y1. The air that has passed through the suction port 5 is rectified by the bell mouth 7 and reaches the impeller 3. The air that has reached the impeller 3 is blown out from the impeller 3 in the centrifugal direction and flows along the peripheral wall 10c. The air flowing along the peripheral wall 10c heads toward the outlet 6 as airflow Y2 and is blown out of the scroll casing 10 from the outlet 6. In this way, the rotation of the impeller 3 generates an airflow Y1 that flows from the outside toward the air inlet 5 and an airflow Y2 that flows from the air outlet 6 toward the outside.

[0022] Generally, in a motor, the iron core of the stator inside the motor vibrates due to its electromagnetic force, generating electromagnetic noise through the frame. In addition, the motor generates mechanical noise due to vibration of the bearings inside the motor, and the vibration and noise propagate through the shaft to the rotating body to which it is connected. The centrifugal fan 1 according to the first embodiment also exhibits the same phenomenon as described above. When the centrifugal fan 1 is operating, not only does the motor 2 generate electromagnetic noise, but the vibration and noise of the motor 2 propagate through the shaft 2a to the impeller 3, causing the impeller 3 to generate vibration and noise as well.

[0023] In addition to the vibrations and noise transmitted from the motor 2, the impeller 3 also generates noise called discrete frequencies. Discrete frequency noise is generated by periodic changes in the suction flow of the impeller 3 or periodic changes in the flow around the blades 3b. Periodic changes in the flow around the blades 3b are generated when the impeller 3 sucks in a highly turbulent airflow. For example, discrete frequency noise generated around the blades 3b of the impeller 3 of the centrifugal blower 1 is likely to occur in areas where the distance between the impeller 3 and the scroll casing 10 is short, due to interference between the secondary flow and the impeller 3. For this reason, if the flow from the bellmouth 7 side toward the main plate 3a side of the impeller 3 becomes stronger, pressure fluctuations on the back side of the main plate 3a of the impeller 3 increase, which could lead to an increase in discrete frequency noise of the centrifugal blower 1.

[0024] In addition to the fact that the location where the electromagnetic noise generated by the motor 2 and the location where the discrete frequency noise generated by the impeller 3 are generated are relatively close to each other, the motor 2 and the impeller 3 rotate at the same rotation speed via the shaft 2a, and the vibration noises are also in a relatively similar frequency band. From the above phenomenon, it is believed that the main source of noise generated by the centrifugal fan 1 is near the center of the motor 2 and impeller 3 inside the scroll casing 10. In the following description, the center of the motor 2 is taken as an example of a noise source X1.

[0025] The noise X2 emitted from the noise source X1 propagates to two main destinations: one is beyond the air outlet 6, which is in the same direction as the airflow Y2, and the other is beyond the air inlet 5, which is in the opposite direction to the airflow Y1. When analyzing the destination of the former, it is found that in many cases there is a duct beyond the air outlet 6, and in addition to this, phenomena such as attenuation over distance also occur, so there are relatively few cases in which noise X2 becomes a problem.

[0026] On the other hand, when analyzing the destination of the latter noise, there are many cases where a user is generally located beyond the air inlet 5 of the centrifugal fan 1. For example, if the centrifugal fan 1 is installed on the ceiling of a room with the air inlet 5 facing downwards, this would be the case where the user living in the room is located below the air inlet 5. Furthermore, in this case, the air inlet 5 and the user are not that far apart, so noise reduction through distance attenuation is unlikely. As a result, there are relatively many cases where noise X3 beyond the air inlet 5 becomes a problem. Note that noise X3 represents the sum of the user-direction components of noise X2 that is generated at noise source X1 and propagates radially, passing through the air inlet 5 and heading toward the user.

[0027] In light of the above, it is important to reduce noise X3, which is generated from centrifugal fan 1 and propagates in the direction of the user. One possible measure to reduce the magnitude of noise X3 is to reduce the rotation speed of motor 2 or impeller 3. However, reducing the rotation speed of motor 2 or impeller 3 not only reduces the noise of centrifugal fan 1, but also reduces characteristics such as air volume and static pressure, which is an issue.

[0028] Another possible measure to reduce the magnitude of noise X3 is to distance the motor 2 from the suction port 5 by, for example, extending the shaft 2a of the motor 2, thereby moving the user at the end of the suction port 5 away from the noise source X1. However, extending the shaft 2a of the motor 2 poses a problem in that it increases the size of the centrifugal fan 1. Another possible measure to reduce the intensity of noise X3 is to displace the center of air inlet 5 from the center of rotary shaft 4, thereby making it difficult for noise X2 emitted from noise source X1 to propagate to the user at the end of air inlet 5. However, displacing the center of air inlet 5 from the center of rotary shaft 4 poses a problem in that the air blowing characteristics deteriorate.

[0029] The centrifugal fan 1 according to the first embodiment reduces the magnitude of the noise X3 propagating toward the user without using any of the countermeasures described above. Specifically, the centrifugal fan 1 provides a shielding wall 8 surrounding the air inlet 5, thereby effectively reducing the noise X3.

[0030] Here, the mechanism by which the shielding wall 8 reduces the noise X3 will be described with reference to FIG. Fig. 4 is a diagram showing noise propagation in the centrifugal fan 1 according to the first embodiment. As shown in Fig. 4, part of the noise X2 generated by noise source X1 at the center of the motor 2 reaches the wall surface 8a and the upper end 8b of the shielding wall 8. At this time, a diffraction phenomenon occurs, which is a characteristic of sound. Diffraction is a phenomenon in which, when there is an object of finite length on the sound propagation path, the sound propagates by wrapping around the back of the object. Therefore, the noise X2 that reaches the upper end 8b of the shielding wall 8 travels in a direction away from the user located beyond the air inlet 5 after being diffracted. By using this mechanism, the centrifugal fan 1 according to the first embodiment can effectively reduce the noise X3 propagating toward the user.

[0031] Next, a comparative example of the centrifugal fan 1 according to the first embodiment will be described. (First Comparative Example) Fig. 5 is a cross-sectional view showing centrifugal fan 20 according to a first comparative example. Fig. 6 is a diagram showing noise propagation in centrifugal fan 20 according to the first comparative example. As shown in Figs. 5 and 6, centrifugal fan 20 does not include shielding wall 8, unlike centrifugal fan 1 according to embodiment 1. For this reason, noise X2 generated at noise source X1 at the center of motor 2 propagates radially and travels directly toward the user from air inlet 5 as noise X4 without being diffracted at upper end 8b of shielding wall 8. As a result, part of noise X2 travels directly toward the user without being diffracted at upper end 8b of shielding wall 8, and therefore noise X4 on the user side becomes relatively large.

[0032] (Second Comparative Example) Fig. 7 is a perspective view showing a centrifugal fan 30 according to a second comparative example. Fig. 8 is a diagram showing noise propagation in the centrifugal fan 30 according to the second comparative example. As shown in Figs. 7 and 8, the centrifugal fan 30 does not include a shielding wall 8, unlike the centrifugal fan 1 according to the first embodiment. Furthermore, the centrifugal fan 30 has a bell mouth 7a that extends toward the motor 2, as compared to the centrifugal fan 1 according to the first embodiment. For this reason, part of the noise X2 directed toward the air inlet 5 is reflected by the inner surface of the bell mouth 7a, which extends toward the motor 2, and propagates toward the user. As a result, even if the airflow Y2 toward the air inlet 5 can be rectified by extending the bell mouth 7a, the noise X5 directed toward the user is worse than that of the centrifugal fan 1 according to the first embodiment.

[0033] As described above, neither the centrifugal fan 20 according to the first comparative example nor the centrifugal fan 30 according to the second comparative example has the shielding wall 8. Therefore, the centrifugal fans 20 and 30 do not have the effect of reducing noise to the user, as does the centrifugal fan 1 according to the first embodiment.

[0034] Fig. 9 is a diagram showing the results of an actual machine test on the frequency and noise level for the centrifugal fan 1 according to the first embodiment and the centrifugal fan 20 according to the first comparative example. Fig. 10 is a diagram showing the results of an actual machine test on the frequency and noise level for the centrifugal fan 1 according to the first embodiment and the centrifugal fan 30 according to the second comparative example. The measurement position of the noise value was on the extension of the rotary shaft 4, at a position 1 m away from the side wall 10a of the scroll casing 10 in the direction of the user. The graph showing the results of the actual test has noise levels on the vertical axis and frequency on the horizontal axis. Note that this graph is a semi-logarithmic graph, with only the frequency on the horizontal axis being expressed in logarithm.

[0035] As shown in Fig. 9, it can be seen that noise X3 generated by centrifugal fan 1 according to embodiment 1 is reduced in a frequency band of approximately 1000 Hz or less compared to noise X4 generated by centrifugal fan 20 according to the first comparative example. Similarly, as shown in Fig. 10, it can be seen that noise X3 generated by centrifugal fan 1 according to embodiment 1 is reduced in a frequency band of approximately 1000 Hz or less compared to noise X5 generated by centrifugal fan 30 according to the second comparative example. This is because, as described above, noise in a relatively low frequency band, which is mainly caused by vibration of motor 2, is effectively reduced.

[0036] 11 is a diagram showing the relationship between the angle α formed between the rotation axis 4 and a tangent line that passes through the upper end 8b of the shielding wall 8 and touches the curved surface of the bell mouth 7, and the results of an actual machine test of the noise X3 that propagates from the air inlet 5 toward the user. The noise reduction effect in FIG. 11 indicates how much the noise X3 generated by the centrifugal fan 1 according to Embodiment 1 is reduced compared to the noise X4 generated by the centrifugal fan 20 according to Comparative Example 1. For example, if the noise X4 generated by the centrifugal fan 20 according to Comparative Example 1 has a noise value of 50 dB and the noise X3 generated by the centrifugal fan 1 according to Embodiment 1 has a noise value of 49.5 dB, the noise reduction effect of the centrifugal fan 1 is 0.5 dB. The angle α can be changed by changing the height or diameter of the shielding wall 8 .

[0037] 11, the noise value of noise X3 generated by centrifugal fan 1 according to embodiment 1 is plotted as a circle. For comparison, the noise value of noise X4 generated by centrifugal fan 20 according to the first comparative example is plotted as a triangle, and the noise value of noise X5 generated by centrifugal fan 30 according to the second comparative example is plotted as a square. Note that in the measurement environment in which the actual machine test was conducted, there was a measurement variation of about 0.2 dB. The results of this actual test show that the noise reduction effect is maximized when the angle α between the tangent line that passes through the upper end 8b of the shielding wall 8 and touches the surface of the bell mouth 7 and the rotation axis 4 is approximately 30 degrees.

[0038] 4, a tangent line that passes through the upper end 8b of the shielding wall 8 and touches the surface of the bell mouth 7 passes through the center of the motor 2. That is, in the centrifugal fan 1, the shielding wall 8 is provided so that the upper end 8b of the shielding wall 8 is located on an extension line of the tangent line that touches the surface of the bell mouth 7 and the center of the motor 2, which is the center of the noise of the motor vibration. As a result, the centrifugal fan 1 can diffract the noise X2 generated at the center of the motor 2 at the upper end 8b of the shielding wall 8.

[0039] In Figure 4, noise X2 traveling near the tangent line to the surface of the bellmouth 7 is scattered by the surface of the bellmouth 7 and spreads in multiple directions before traveling. Here, because the centrifugal blower 1 is provided with a shielding wall 8, noise X2 that reaches wall surface 8a of the shielding wall 8 is shielded by wall surface 8a of the shielding wall 8. On the other hand, if the centrifugal blower 1 were not provided with a shielding wall 8, the axial component of noise X2 that spreads in multiple directions on the surface of the bellmouth 7 would reach the user side, increasing noise X3. That is, in the centrifugal blower 1, part of the noise X2 is blocked by the wall surface 8a of the shielding wall 8, and part of the noise X2 is diffracted at the upper end 8b of the shielding wall 8, thereby reducing the component of the noise X2 in the axial direction of the rotating shaft 4. As a result, the centrifugal blower 1 can suppress the noise X3 that reaches the user side.

[0040] 11, when the angle α is in the range of 20 degrees to 60 degrees, the noise value of the noise X3 generated by the centrifugal fan 1 according to embodiment 1 is reduced by 0.3 dB or more compared to the noise X4 generated by the centrifugal fan 20 according to comparative example 1. Thus, it can be seen that the noise reduction effect is high when the angle α is in the range of 20 degrees to 60 degrees.

[0041] As described above, the shielding wall 8 has a shape that is rotationally symmetrical with respect to the rotation shaft 4 of the impeller 3. Therefore, at any position on the upper end 8b of the shielding wall 8, a tangent that passes through the upper end 8b and touches the surface of the bell mouth 7 passes through the center of the motor 2. As a result, noise X2 generated at the center of the motor 2 is diffracted over the entire upper end 8b of the shielding wall 8. In this way, the centrifugal blower 1 can reduce the component of noise X2 in the axial direction of the rotation shaft 4 by diffracting noise X2 over the entire upper end 8b of the shielding wall 8. Therefore, the centrifugal blower 1 can effectively suppress noise X3 that reaches the user.

[0042] Next, a specific structure of the centrifugal fan 1 according to the first embodiment, taking into consideration industrial mass productivity, will be described with reference to FIG. Fig. 12 is a plan view showing a specific structure of the centrifugal blower 1 according to the first embodiment. As shown in Fig. 12, four fixing members 22 are provided at 90-degree intervals on the annular shielding wall 8. As described above, the scroll casing 10 can be made of, for example, a resin. In this case, however, it is difficult to mass-produce the scroll casing 10 and the shielding wall 8 by integral molding, and even if this could be achieved, there is a problem that the cost would be high. Therefore, the scroll casing 10 and the shielding wall 8 are molded separately, and the shielding wall 8 is fixed onto the side wall 10 a of the scroll casing 10 using a fixing member 22 .

[0043] The number of fixing members 22 is not limited to four, and may be one or more. However, providing a plurality of fixing members 22 allows for more reliable fixing of both the scroll casing 10 and the shielding wall 8. When providing a plurality of fixing members 22, it is appropriate to limit the number to about two to four, taking into account the balance between the fixing effect and mass production costs. When a plurality of fixing members 22 are provided, it is preferable that the angle β formed by a line 23 passing through the center position of a first fixing member 22a of these fixing members 22, which is provided at a position closest to the tongue portion 13, and the rotation axis 4, and a reference axis 24 that is parallel to the airflow Y2 blown out from the air outlet 6 and passes through the rotation axis 4, be between 0 and 70 degrees. The reason for this is as follows.

[0044] When the centrifugal blower 1 according to the first embodiment is operating, the airflow Y1 flows into the scroll casing 10 through the air inlet 5 and, due to the rotation of the impeller 3, flows out of the scroll casing 10 as the airflow Y2 through the air outlet 6. At this time, not all of the airflow Y1 becomes the airflow Y2, but part of the airflow Y1 becomes a recirculation flow within the scroll casing 10. This phenomenon is particularly noticeable near the tongue portion 13 where the air passage is narrow.

[0045] For this reason, in a typical centrifugal blower such as the centrifugal blower 20 according to the first comparative example, the fluctuations in the air flow near the tongue portion 13 are relatively large. Therefore, when viewed inside the scroll casing 10, the flow near the tongue portion 13 is unstable, and vibrations caused by the air flow are likely to be excited, so care must be taken when attaching components to the scroll portion 11. The airflow tendency is the same in the centrifugal fan 1 according to the first embodiment as in the above situation, so similar care must be taken when attaching components and the like.

[0046] For these reasons, it is effective to provide the first fixing member 22a near the tongue 13, i.e., in the branch region A where the tongue 13 branches off a portion of the airflow. This is because attaching the first fixing member 22a to the side wall 10a of the branch region A improves the rigidity of the shielding wall 8 against the aforementioned "vibration caused by the airflow." Specifically, the angle β formed by a line 23 passing through the center of the first fixing member 22a and the rotating shaft 4 and a reference axis 24 that is parallel to the blowing direction of the airflow Y2 blown out from the outlet 6 and passes through the center of the rotating shaft 4 should be between 0 and 70 degrees. Fixing the first fixing member 22a at such an angle increases the rigidity of the shielding wall 8 and improves the durability of the centrifugal blower 1. The angle β may be adjusted as appropriate depending on the direction of the airflow Y2 and the degree of radial expansion of the rotating shaft 4 in the scroll section 11. Furthermore, when multiple fixing members 22 are provided, it is preferable to first provide the first fixing member 22a near the tongue portion 13, and then provide the second fixing member 22b, the third fixing member 22c, ..., the nth fixing member 22n at angles obtained by dividing 360 degrees into n equal parts.

[0047] Embodiment 2 13 is a plan view showing a centrifugal fan 40 according to embodiment 2. Centrifugal fan 40 according to embodiment 2 differs from centrifugal fan 1 according to embodiment 1 in that centrifugal fan 40 according to embodiment 2 is provided with a shielding wall 41 instead of shielding wall 8. Other configurations of centrifugal fan 40 are the same as or similar to those of centrifugal fan 1, and therefore, redundant explanations will be omitted.

[0048] The shielding wall 8 of the centrifugal blower 1 according to embodiment 1 has a shape in which the distance from the rotation shaft 4 of the impeller 3 to the shielding wall 8 is equal in any direction in a plane perpendicular to the rotation shaft 4 of the impeller 3, but the shape may be such that the distance from the rotation shaft 4 of the impeller 3 to the shielding wall 8 varies depending on the direction. 13, the shielding wall 41 of the centrifugal fan 40 according to the second embodiment has an elliptical shape. The elliptical shape is an example of a shape in which the distance from the rotation shaft 4 of the impeller 3 to the shielding wall 41 varies depending on the direction. With this shape, the distance from the noise source X1 to the upper end 41a of the shielding wall 41 changes depending on the circumferential position at the upper end 41a. As this change occurs, the wavelength corresponding to this distance also changes, so that a noise reduction effect can be achieved over a wide frequency band for noise X2 that has peaks at multiple frequencies.

[0049] Embodiment 3 14 is a plan view showing a centrifugal fan 50 according to embodiment 3. The centrifugal fan 50 according to embodiment 3 differs from the centrifugal fan 1 according to embodiment 1 in that it includes a shielding wall 51 instead of the shielding wall 8. Other configurations of the centrifugal fan 50 are the same as or similar to those of the centrifugal fan 1, and therefore, redundant explanations will be omitted.

[0050] The shielding wall 8 of the centrifugal blower 1 according to embodiment 1 has a shape in which the height of the shielding wall 8 is the same at any position in the circumferential direction, but the height of the shielding wall 8 may also be a shape in which the height of the shielding wall 8 varies along the circumferential direction. 14, the upper end 51a of the shielding wall 51 has a wave shape. The wave shape is an example of a shape in which the height of the shielding wall 51 changes along the circumferential direction.

[0051] As mentioned above, the impeller 3 also generates noise known as discrete frequency noise. Discrete frequency noise is generated by periodic changes in the suction flow of the impeller 3, or by periodic changes in the flow around the blades 3b caused by the impeller 3 sucking in a highly turbulent airflow. Due to this phenomenon, discrete frequency noise is characterized by having peaks at integer multiples of a frequency expressed as the product of the number of blades 3b and the rotation speed of the impeller 3.

[0052] In contrast, some of the vibrations caused by the motor 2 often become noticeable at 4 to 6 times the rotation speed of the motor 2. Therefore, by separating the peak of this part of the vibration noise caused by the motor 2 from the peak of the discrete frequency noise, it is possible to reduce the noise generated by the centrifugal fan 1. Specifically, by setting the number of blades 3b to a prime number, the peak of the discrete frequency noise is separated from the peak of some of the vibration noise caused by the motor 2, thereby achieving noise reduction. As such, it is generally necessary to pay attention to the noise generated by the motor rotation speed and the associated factors.

[0053] Given the above-mentioned background for centrifugal fans in general, it is preferable to design the shape of the intake port 5 upstream of the impeller 3 and the shielding wall 41 in a manner that can isolate noise peaks. Specifically, when the number of blades 3b is 43, the number of wave crests or wave troughs on the upper end 51a of the shielding wall 51 may be set to 41, 47, etc.

[0054] As described above, the upper end 51a of the shielding wall 51 has a wave shape. With this shape, the distance from the noise generation source X1 to the upper end 51a of the shielding wall 51 changes depending on the circumferential position at the upper end 51a. As this change occurs, the wavelength corresponding to this distance also changes, so that a noise reduction effect can be obtained over a wide frequency band for noise X2 that has peaks at multiple frequencies.

[0055] Here, the apparent height of the shielding wall 51 is defined as the midpoint between the height of the shielding wall 51 at its highest position and the height of the shielding wall 51 at its lowest position. For this reason, in the centrifugal blower 50 according to the third embodiment, the angle α formed between the rotation axis 4 and a tangent line that passes through the upper end 51 a of the shielding wall 51 and is in contact with the curved surface of the bell mouth 7 may be calculated with reference to the apparent height of the shielding wall 51. As mentioned above, when the angle α is in the range of 20 degrees to 60 degrees, a particularly low noise effect is obtained, so it is advisable to appropriately adjust both the position where the height of the shielding wall 51 is highest and the position where the height of the shielding wall 51 is lowest so that they are both within the above-mentioned range of angle α.

[0056] Embodiment 4 FIG. 15 is a plan view showing a ventilation fan 60 according to embodiment 4. Note that parts that are the same as or equivalent to those of the centrifugal blower 1 according to embodiment 1 are given the same reference numerals, and descriptions of these parts will be omitted. Furthermore, ventilation fan 60 is an example of a ventilation device equipped with centrifugal blowers 1, 30, 40. The ventilation device equipped with centrifugal blowers 1, 30, 40 is not limited to ventilation fan 60, and may be other devices such as a blower or an air conditioner.

[0057] As shown in FIG. 15, ventilation fan 60 according to the fourth embodiment is a ventilation fan for use in a duct. Ventilation fan 60 is installed above the ceiling through an opening formed in the ceiling, and is connected to a duct leading to the outdoors to ventilate the air inside the room. Ventilation fan 60 includes ventilation fan main body 61, duct connection port 62, and centrifugal blower 1 according to the first embodiment housed in ventilation fan main body 61. Ventilation fan main body 61 is also referred to as a "housing." A shielding wall 8 is provided on the side wall 10a of the scroll casing 10 of the centrifugal blower 1. As described above, part of the noise X2 generated near the center of the motor 2 or the impeller 3 is diffracted at the upper end 8b of the shielding wall 8 and propagates in a direction different from the direction of the user. As a result, the noise X3 generated near the center of the motor 2 or the impeller 3 and propagated to the user beyond the suction port 5 can be reduced.

[0058] As described above, the ventilation fan 60 according to the fourth embodiment has the effect of reducing the noise X3 propagated to the user side. Ventilation fan 60 according to embodiment 4 may include centrifugal fan 40 according to embodiment 2 or centrifugal fan 50 according to embodiment 3, instead of centrifugal fan 1 according to embodiment 1. In these cases, too, shielding wall 41 or shielding wall 51 diffracts a portion of noise X2 and propagates it in a direction different from the direction in which the user is located, thereby reducing noise X3 propagated to the user beyond air inlet 5.

[0059] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies. Furthermore, the embodiments may be combined with each other, and some of the configurations may be omitted or modified without departing from the spirit of the invention.

[0060] Various aspects of the present disclosure are summarized below as appendices.

[0061] (Appendix 1) A motor; a cylindrical impeller fixed to the shaft of the motor; a scroll casing that houses the impeller and has an inlet surface provided with an inlet for sucking air; a bell mouth provided at the suction port and guiding the air drawn into the suction port to the impeller; a ring-shaped shielding wall provided on the suction port surface and surrounding the suction port. (Appendix 2) The scroll casing comprises: An outlet for blowing out air; a scroll portion that rotatably accommodates the impeller and forms a spiral flow path that guides an airflow generated by rotation of the impeller to the air outlet; a diffuser section that configures a flow path between the scroll section and the outlet; 2. The centrifugal blower according to claim 1, further comprising: a tongue portion provided in the scroll portion, which guides the air flow to the diffuser portion and branches a portion of the air flow to recirculate within the scroll portion. (Appendix 3) The shielding wall includes a fixing member fixed to the suction port surface, 3. The centrifugal blower according to claim 2, wherein the fixing position of the fixing member is a branching region where part of the airflow is branched by the tongue portion. (Appendix 4) 4. The centrifugal blower according to claim 3, wherein an angle formed by a straight line passing through a center position of the fixing member and the rotation axis of the impeller and a reference axis that is parallel to the blowing direction of the airflow blown out of the air outlet and passes through the rotation axis of the impeller is between 0 and 70 degrees. (Appendix 5) 5. The centrifugal blower according to claim 1, wherein the outer diameter of the shielding wall is smaller than a line segment passing through the rotation axis of the impeller and having the outer peripheral end of the suction port surface as both ends. (Appendix 6) 6. The centrifugal blower according to any one of claims 1 to 5, wherein the inner diameter of the shielding wall is larger than the opening diameter of the suction port. (Appendix 7) 7. The centrifugal blower according to any one of claims 1 to 6, wherein the shielding wall has a shape that is rotationally symmetrical with respect to the rotation axis of the impeller. (Appendix 8) Supplementary note 1. The centrifugal blower according to any one of Supplementary note 1 to Supplementary note 7, wherein an angle formed between a tangent line that passes through an upper end of the shielding wall and contacts a surface of the bell mouth and the rotation axis of the impeller is between 20 degrees and 60 degrees. (Appendix 9) 9. The centrifugal blower according to any one of claims 1 to 8, wherein a distance from the rotation axis of the impeller to the shielding wall varies depending on the direction in a plane perpendicular to the rotation axis of the impeller. (Appendix 10) 10. The centrifugal blower according to any one of claims 1 to 9, wherein the height of the shielding wall varies along the circumferential direction. (Appendix 11) A centrifugal blower according to any one of Supplementary Note 1 to Supplementary Note 10; A ventilation device comprising: a housing in which the centrifugal blower is housed. [Explanation of symbols]

[0062] 1, 20, 30, 40, 50 centrifugal blower, 2 motor, 2a shaft, 3 impeller, 4 rotating shaft, 5 suction port, 6 outlet, 7 bell mouth, 8, 41, 51 shielding wall, 10 scroll casing, 10a side wall (suction port surface), 11 scroll section, 12 diffuser section, 13 tongue section, 22 fixing member, 60 ventilation fan, 61 ventilation fan body (housing), 62 duct connection port, A branch area, X1 noise source, X2, X3, X4, X5 noise, Y1, Y2 air flow.

Claims

1. A motor; a cylindrical impeller fixed to the shaft of the motor; a scroll casing that houses the impeller and has an inlet surface provided with an inlet for sucking air; a bell mouth provided at the suction port and guiding the air drawn into the suction port to the impeller; a ring-shaped shielding wall provided on the suction port surface and surrounding the suction port.

2. The scroll casing comprises: An outlet for blowing out air; a scroll portion that rotatably accommodates the impeller and forms a spiral flow path that guides an airflow generated by rotation of the impeller to the air outlet; a diffuser section that configures a flow path between the scroll section and the outlet; 2. The centrifugal blower according to claim 1, further comprising a tongue provided in said scroll section for directing said airflow to said diffuser section and branching a portion of said airflow to recirculate within said scroll section.

3. The shielding wall includes a fixing member fixed to the suction port surface, 3. The centrifugal blower according to claim 2, wherein the fixing position of the fixing member is a branching region where a part of the airflow is branched by the tongue portion.

4. 4. The centrifugal blower according to claim 3, wherein an angle between a line passing through a center position of the fixing member and the rotation axis of the impeller and a reference axis that is parallel to the blowing direction of the airflow blown out from the air outlet and passes through the rotation axis of the impeller is between 0 and 70 degrees.

5. 5. The centrifugal blower according to claim 1, wherein an outer diameter of the shielding wall is smaller than a line segment that passes through the rotation axis of the impeller and has both ends at the outer peripheral end of the suction port surface.

6. The centrifugal blower according to any one of claims 1 to 4, wherein an inner diameter of the shielding wall is larger than an opening diameter of the suction port.

7. The centrifugal blower according to any one of claims 1 to 4, wherein the shielding wall has a shape that is rotationally symmetrical with respect to the rotation axis of the impeller.

8. 5. The centrifugal blower according to claim 1, wherein an angle formed between a tangent line that passes through an upper end of the shielding wall and contacts a surface of the bell mouth and the rotation axis of the impeller is between 20 degrees and 60 degrees.

9. 5. The centrifugal blower according to claim 1, wherein a distance from the rotation axis of the impeller to the shielding wall varies depending on a direction in a plane perpendicular to the rotation axis of the impeller.

10. The centrifugal blower according to any one of claims 1 to 4, wherein the height of the shielding wall varies along the circumferential direction.

11. The centrifugal blower according to any one of claims 1 to 4; A ventilation device comprising: a housing in which the centrifugal blower is housed.

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