Centrifugal blower

Abstract

This invention provides a centrifugal fan that reduces noise by decreasing the peak noise that appears when the number of blades of the centrifugal fan is multiplied by the rotational speed frequency, and stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan from shifting away from the rotational center (rotor shaft). [Solution] The centrifugal fan 2 has multiple first blades 2c1 formed upright at unequal pitches in the circumferential direction on a main plate 2b that extends radially outward from a hub 2a which is integrally assembled with a rotor yoke 3b. Between the first blades 2c1, second blades 2c2, which are shorter in length than the first blades 2c1, are formed upright at unequal pitches in the circumferential direction, with the spacing between adjacent first blades 2c1 being unequal. A portion of the circumferential region Z1 of the multiple second blades 2c2 is formed so that the length of the radially inner end is shorter than the length of the second blades 2c2 in other regions Z2, so that the center of gravity of the centrifugal fan 2 coincides with the center of rotation.

Description

Technical Field

[0001] The present disclosure relates to a centrifugal blower used, for example, for sheet air conditioning or HVAC (Heating, Ventilation, and Air Conditioning) equipment.

Background Art

[0002] Generally, a centrifugal blower includes a motor having a rotation axis, an impeller that is rotationally driven by the motor to blow out air, and a casing that houses these components. The casing has a scroll portion that houses the impeller (the impeller) and forms a spiral air flow path outside the impeller, and a blower portion provided with a blower outlet that blows air from the scroll to the outside. At the boundary between the scroll portion that circulates around the impeller and the blower portion connected thereto, a partition portion called a tongue portion (see FIG. 2; 4h) is arranged, and the air blown to the blower outlet and the circulating air are partitioned (see Patent Document 1; Japanese Unexamined Patent Application Publication No. 2017-125405).

[0003] Although various shapes of impellers are used, a plurality of blades are erected along the axial direction on a main board that is continuous with a cup-shaped hub serving as the bottom surface. The plurality of blades are connected to each other by an annular connecting member (shroud) at the outer peripheral edge portion. The shroud enhances the blowing efficiency of the air sucked from the radial center portion of the casing to the outside in the radial direction. Each blade erected on the main board has the same shape and is evenly arranged in the circumferential direction of the main board (see Patent Document 2; Japanese Unexamined Patent Application Publication No. 2020-63679).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] In general, centrifugal blowers are required to reduce noise and improve airflow efficiency. However, the impeller configurations described in Patent Documents 1 and 2 above cannot reduce the peak noise that appears in the centrifugal fan, which is caused by pressure fluctuations of the air passing through the so-called tongue, and is calculated as the number of blades × rotational speed frequency.

[0006] Therefore, as shown in Figure 8, it was found that by arranging radially short second blades 53, which are radially short and formed upright between the first blades 52, which are radially short and formed upright at unequal pitches, in addition to the radially long first blades 52 that are radially long and formed upright at unequal pitches, the peak noise that appears in the number of blades × rotational speed frequency of the centrifugal fan 50 can be reduced. However, if the spacing between the first blade 52 and the second blade 53, as shown in Figure 8, is set to an unequal pitch (X1 ≠ X2), the center of gravity of the centrifugal fan 50 shifts from the center of rotation (rotor shaft 54), resulting in an unbalanced rotation of the centrifugal fan 50. To resolve this, an attempt was made to correct the balance by providing a counterweight corresponding to the imbalance on the underside of the main plate 51, but it was found that this generated frequency noise (1st to 3rd order components of rotational speed) separate from the peak sound. [Means for solving the problem]

[0007] This disclosure was made to solve these problems, and its purpose is to provide a centrifugal blower that reduces the peak noise that appears in the number of blades × rotational speed frequency to reduce noise, and stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan from shifting away from the rotation center (rotor shaft).

[0008] The embodiments described below have the following configuration. A centrifugal blower in which a centrifugal fan and a motor that rotates it are housed in a case, and air is drawn in from the radial center of the case and exhausted from an exhaust port provided on the radial outside of the case, wherein the case comprises a first case assembled to cover the centrifugal fan, with an intake opening in the radial center and an annular first air passage formed on the radial outside, and a second case on the outer circumference of the bottom plate that rotatably supports the motor, with an annular second air passage formed radially outside the outer end of the centrifugal fan and combined with the first air passage, and the centrifugal fan The fan is characterized in that a plurality of first blades are formed upright at unequal pitches in the circumferential direction on the main plate which extends radially outward from the hub which is assembled integrally with the rotor yoke, and between the first blades, second blades shorter in length than the first blades are formed upright such that the spacing between adjacent first blades is unequal pitch in the circumferential direction, and the length of the radially inner end of a portion of the plurality of second blades is formed to be shorter than the length of the second blades in other regions, so that the center of gravity of the centrifugal fan coincides with the center of rotation.

[0009] This allows for a centrifugal fan that reduces noise by dispersing the peak noise generated by the number of blades × rotational speed frequency through an unequal spacing between the blades, and also stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan from shifting away from the rotational center (rotor shaft).

[0010] Preferably, the radial length of a portion of the circumferential region of the second blade is formed such that the length on the radially inner end side of the shroud connecting the outer peripheral edges of the first blade and the second blade in an annular manner is shorter than the radial length of the other regions of the second blade. This prevents the centrifugal fan's center of gravity from shifting away from the rotation center (rotor axis), stabilizing the rotational balance. Furthermore, even if a portion of the circumferential region of the second blade is formed such that the length of the radially inner end is shorter than the radial length of the other regions of the second blade, it does not affect the airflow performance. [Effects of the Invention]

[0011] By using the centrifugal blower described above, it is possible to provide a centrifugal blower that reduces the peak noise that appears in the number of blades × rotational speed frequency, thereby reducing noise, and also stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan from shifting away from the center of rotation (rotor shaft). [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a perspective view of a centrifugal blower. [Figure 2] Figure 2 is a plan view of the centrifugal blower shown in Figure 1 with the first case removed. [Figure 3] Figure 3 is an axial cross-sectional view of the centrifugal blower shown in Figure 1. [Figure 4] Figures 4A, 4B, and 4C are plan view, front view, and perspective view of the centrifugal fan. [Figure 5] Figure 5A is a plan view of the centrifugal fan, and Figure 5B is a partial explanatory diagram of the unequal pitch distribution of the first and second blades. [Figure 6] Figure 6A is an FFT analysis graph of noise generated in an unequal-spread impeller, and Figure 6B is an FFT analysis graph of noise generated in an equal-spread impeller. [Figure 7] Figure 7 is a graph comparing the PQ characteristics using an unequal-diameter impeller and an equal-diameter impeller. [Figure 8] Figure 8 is a plan view of a centrifugal fan in which the first and second blades are formed on the main plate at unequal pitches. [Modes for carrying out the invention]

[0013] Hereinafter, an embodiment of the centrifugal blower according to the present invention will be described with reference to the attached drawings. First, the general configuration of the centrifugal blower will be described with reference to Figures 1 to 7. A DC brushless motor is used for the motor M, and in this embodiment, an outer rotor type motor is used. An inner rotor type motor may also be used.

[0014] As shown in Fig. 3, the centrifugal blower 1 has a centrifugal fan 2 (impeller) and a rotor 3 assembled integrally, and a motor M for rotationally driving them is housed in a case body 4. As shown in Fig. 1, the centrifugal blower 1 takes in air from the radially central part of the case body 4 and exhausts the pressurized air from the radial side surface. The case body 4 is formed by combining a first case 4a assembled to cover the centrifugal fan 2 and a second case 4b that rotatably supports the motor M (rotor 3 and stator 5: see Fig. 3).

[0015] In Fig. 1, an intake opening 4c is provided at the central part of the first case 4a, and an annular first air passage 4d is formed on the radially outer side. In Fig. 2, an annular second air passage 4e combined with the first air passage 4d is formed on the radially outer side of the second case 4b. When the first case 4a and the second case 4b are combined, an annular air passage 4f is formed on the radially outer side of the case body 4 (see Fig. 3). As shown in Fig. 2, in the second case 4b, a partition part called a tongue part 4h is provided at the boundary between the second air passage 4e forming the annular air passage 4f and the exhaust port 4g. Although not shown, the same applies to the boundary between the first air passage 4d forming the annular air passage 4f of the first case 4a and the exhaust port 4g. As shown in Fig. 3, a bearing housing 6 and a motor substrate 7 are assembled to the central part of the second case 4b. The lead wire of the stator coil 5b is connected to the motor substrate 7, and a hall sensor or the like for detecting the position of the rotor magnet 3d is mounted. When the motor M is a sensorless type, it is also possible to omit the position detection sensor.

[0016] A stator core 5a is integrally fixed to the outer circumference of a cylindrical metal bearing housing 6, which is held upright in the second case 4b. A rotor shaft 3a is rotatably supported in the shaft hole of the bearing housing 6 via a pair of bearings 6a. A retaining washer 6c is fitted to the end of the rotor shaft 3a to restrict the axial movement of the bearing 6a at the axial lower end. A stator coil 5b is wound around the pole teeth formed on the stator core 5a via an insulator 8, and the tips of the pole teeth are positioned opposite the rotor magnet 3d. One end of the rotor shaft 3a is integrally assembled to the hub 3c of the cup-shaped rotor yoke 3b by press-fitting, shrink-fitting, bonding, or a combination of these. The other end of the rotor shaft 3a is supported by a shaft support portion 6b provided in the second case 4b. A rotor magnet 3d is integrally assembled to the inner circumferential surface of the rotor yoke 3b. Furthermore, the intake opening 4c does not need to have its center precisely coincide with the axis of the rotor shaft 3a of the motor M. It is sufficient that the intake opening 4c is located near the radial center of the case body 4 and within a range in which the centrifugal fan 2 operates without reducing efficiency.

[0017] As shown in Figure 4C, the centrifugal fan 2 has a main plate 2b that extends radially outward from the hub 2a and is formed in a dome shape. The main plate 2b, which is continuous with the hub 2a, extends radially outward and is inclined downstream in the airflow direction, and multiple first blades 2c1 and second blades 2c2 are alternately formed upright on the main plate 2b, curving from the radially inward to the radially outward. As shown in Figures 4A and 4B, an annular shroud 2d is connected to the outer peripheral edges of the first blades 2c1 and the second blades 2c2, and the pressurized air from the rotation of the first blades 2c1 and the second blades 2c2 is rectified and sent out toward the outer annular airflow passage 4f (see Figure 3).

[0018] Furthermore, in Figure 4A, multiple first blades 2c1 are formed upright on the outside of the dome-shaped main plate 2b at unequal pitches in the circumferential direction. Between the multiple first blades 2c1, second blades 2c2, which are shorter in length than the first blades 2c1, are formed upright at unequal pitches in the circumferential direction, with spacing between them and adjacent first blades 2c1.

[0019] As shown in FIG. 5A, a length on the radially inner end side of a partial circumferential region Z1 of a plurality of second blades 2c2 is made shorter than the length of the second blades 2c2 in another region Z2 so that the partial circumferential region Z1 of the plurality of second blades 2c2 coincides with the center of gravity position of the centrifugal fan 2 as the rotation center. Thereby, as shown in FIG. 5B, by making the pitch between the first blade 2c1 and the second blade 2c2 an unequal pitch (FIG. 5B; X1≠X2), the occurrence positions of peak sounds appearing in the number of blades of the centrifugal fan 2×the rotational frequency are dispersed to achieve noise reduction, and it is possible to provide a centrifugal blower 1 that prevents the center of gravity position of the centrifugal fan 2 from shifting from the rotation center (rotor shaft 3a) and stabilizes the rotational balance.

[0020] As shown in FIG. 5A, the radial length of the second blade 2c2 provided in a partial circumferential region Z1 of the centrifugal fan 2 is formed such that the length on the radially inner end side is shorter than the length of the second blade 2c2 provided in another region Z2. Thereby, it is possible to prevent the center of gravity position of the centrifugal fan 2 from shifting from the rotation center (rotor shaft 3a) and stabilize the rotational balance, and even if a partial circumferential region Z1 of the second blade 2c2 is formed such that the length on the radially inner end side is shorter than the length of the second blade 2c2 in another region Z2, it does not affect the blowing performance.

[0021] Also, as shown in FIG. 3, a dome-shaped space portion 4i is formed on the side opposite to the intake opening 4c by the hub 2a of the centrifugal fan 2 and the main board 2b connected thereto. By using this dome-shaped space portion 4i, it is possible to house tall components (such as the electrolytic capacitor 7b) mounted on the motor M and the motor board 7, and the centrifugal fan 2 and the motor M can be assembled compactly. Further, in the dome-shaped space portion 4i, the rotor 3 and the stator 5 of the motor M are housed so as to overlap in the axial direction. Thereby, the axial dimension of the centrifugal blower 1 can be reduced, and even for a centrifugal blower 1 of the same size, it is possible to achieve miniaturization and flattening.

[0022] As shown in Figure 1, the first case 4a and the second case 4b are assembled together by overlapping them with their openings facing each other and locking a locking piece 4j provided on the outer circumference of the side of the first case 4a with a locking portion 4k provided on the outer circumference of the side of the second case 4b. In addition, the first case 4a and the second case 4b have wiring connection ports 4m formed therein for routing wiring connected to the motor board 7 outside the case. The wiring connection ports 4m are formed by fitting a fitting plate 4m1 protruding from the side of the first case 4a into a fitting groove 4m2 protruding from the corresponding side of the second case 4b (see Figures 1 and 2).

[0023] Furthermore, the first blades 2c1 and the second blades 2c2, which are unequally arranged on the main plate 2b, are configured to have their noise levels and spacing changed, and by performing noise measurements and FFT analysis, the optimal arrangement for noise reduction is determined by dispersing the peak noise generation points that appear in the centrifugal fan 2's blade count × rotational speed frequency. However, due to the unequal arrangement of the second blades 2c2 placed between the first blades 2c1, the rotational balance of the centrifugal fan 2 would remain disrupted. For this reason, the length of the radially inner end side of a certain circumferential region Z1 of the second blades 2c2 is formed to be shorter than the length of the radially inner end side of the second blades 2c2 in other regions Z2. If the radial length of the radially outer side of the first blade 2c1 and the second blade 2c2 is shortened to correct the balance, it will have a significant impact on the airflow-static pressure characteristics (PQ characteristics). On the radially inner side of the first blade 2c1, it is close to the radial center of the centrifugal fan 2, so shortening the radial length will have little effect on correcting the rotational balance. Therefore, by shortening the length of the radially inner end of the second blade 2c2, the rotational balance can be corrected without affecting the airflow-static pressure characteristics (PQ characteristics). This prevents the center of gravity of the centrifugal fan 2 from shifting away from the center of rotation (rotor shaft 3a), thereby stabilizing the rotational balance.

[0024] Figure 6A shows an FFT analysis graph of noise generated in centrifugal fan 2 with an unequally spaced impeller, while Figure 6B shows an FFT analysis graph of noise generated in centrifugal fan 2 with an equally spaced impeller. In both cases, noise measurements were performed by varying the rotation frequency with 50 blades in the centrifugal fan 2 (first blade 2c1: 25 blades, second blade 2c2: 25 blades), and FFT (Fast Fourier Transform) analysis (frequency analysis) was performed. In the equally spaced impeller shown in Figure 6B, a peak in noise level (elliptical dashed line) is observed at a frequency of 4685 Hz and a rotation speed of 5622 r / min, but no peak in noise level was observed when using the unequally spaced impeller shown in Figure 6A.

[0025] Here, the airflow-static pressure characteristics (PQ characteristics) of the centrifugal fan 2 with an unequally spaced impeller as shown in Figure 6A and the centrifugal fan 2 with an equally spaced impeller as shown in Figure 6B are shown in the graph in Figure 7. In the graph in Figure 7, the dashed line graph shows the airflow-static pressure characteristics (PQ characteristics) of the centrifugal fan 2 with an unequally spaced impeller, and the solid line graph shows the airflow-static pressure characteristics (PQ characteristics) of the centrifugal fan 2 with an equally spaced impeller. As shown in the dashed line graph, centrifugal fan 2, which has an unequal impeller, shows a slight improvement in airflow-static pressure characteristics (PQ characteristics) in the low to medium flow rate range compared to centrifugal fan 2, which has an equal impeller.

[0026] As explained above, by making the spacing between the first blade 2c1 and the second blade 2c2 an unequal pitch, the points where peak noises appear in the number of blades × rotational speed frequency of the centrifugal fan are dispersed, thereby reducing noise, and a centrifugal blower 1 is provided that prevents the center of gravity of the centrifugal fan 2 from shifting from the center of rotation (rotor shaft 3a), thereby stabilizing the rotational balance.

[0027] In this case, the first blade 2c1 and the second blade 2c2 provided on the main plate 2b of the centrifugal fan 2 were arranged alternately, but the second blade 2c2, which is unequally arranged between the first blades 2c1, may consist of multiple blades. Furthermore, the shorter region on the radially inner end side of the second blade 2c2 may extend not just to one region, but to multiple regions in the circumferential direction of the centrifugal fan 2. Furthermore, although the above embodiment exemplifies an outer rotor type motor used in centrifugal blowers for HVAC (heating, ventilation, and air conditioning), it is not limited to this and may be used as a power source for other equipment. [Explanation of Symbols]

[0028] 1 Centrifugal blower 2 Centrifugal fan 2a Hub 2b Main plate 2c1 First blade 2c2 Second blade 2d Shroud Rotor 3a Rotor shaft 3b Rotor yoke 3c Hub 3d Rotor magnet 4 Case body 4a First case 4b Second case 4c Intake opening 4d First air passage 4e Second air passage 4f Annular air passage 4g Exhaust port 4h Tongue part 4i Dome-shaped space part 4j Locking piece 4k Locking part 4m Wiring connection port 4m1 Fitting plate 4m2 Fitting groove 5 Stator 5a Stator core 5b Stator coil M Motor 6 Bearing housing 6a Bearing 6b Shaft support part 6c Retaining washer 7 Motor board 7a Electrolytic capacitor 8 Insulator

Claims

1. A centrifugal blower is provided in which a centrifugal fan and a motor that rotates it are housed within a case, and air is drawn in from the radial center of the case and exhausted from an exhaust port provided on the radial outer side of the case, The case body is assembled to cover the centrifugal fan, and has an intake opening in the axial center and an annular first air passage formed radially outward, The system comprises a second case having an annular second air passage formed on the outer circumference of a bottom plate that rotatably supports the motor, which is radially outward from the outer circumference end of the centrifugal fan and is combined with the first air passage, The centrifugal fan is characterized in that a plurality of first blades are formed upright at unequal pitches in the circumferential direction on the main plate which is radially outward from the hub which is integrally assembled with the rotor yoke, and between the first blades, second blades shorter in length than the first blades are formed upright such that the spacing between adjacent first blades is unequal pitches in the circumferential direction, and the length of the radially inner end of a portion of the plurality of second blades is formed to be shorter than the length of the second blades in other regions, so that the center of gravity of the centrifugal fan coincides with the center of rotation.

2. The centrifugal blower according to claim 1, wherein the radial length of a portion of the circumferential region of the second blade is formed such that the length on the radially inner end side of the shroud connecting the outer peripheral edges of the first blade and the second blade in an annular manner is shorter than the radial length of the second blade in other regions.

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