CENTRIFUGAL AIR BLOWER

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2024-228254, filed on Dec. 25, 2024, and the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a centrifugal air blower used in a device, such as seat air conditioning or HVAC (Heating, Ventilation, and Air Conditioning) equipment.

BACKGROUND ART

A typical centrifugal air blower is equipped with a motor with a rotational shaft, an impeller that is rotationally driven by the motor to blow out air, and a casing that houses these components. The casing includes a scroll portion, which houses the impeller and forms a spiral airflow path on the outside of the impeller, and a blower portion, which is provided with an air outlet where air is blown from the scroll to the outside. A partition called a “tongue” (see 4h in FIG. 2) is located at a boundary part between the scroll portion, which winds around the periphery of the impeller, and the blower portion, which is connected to the scroll portion and separates air blown to the air outlet from circulating air (see Patent Document 1; Japanese Laid-open Patent Publication No. 2017-125405).

Although impellers of various shapes are used, a plurality of blades are formed to be erected along the axial direction on a main plate that is continuous with a cup-shaped hub that forms the base. Outer edges of the plurality of blades are connected to each other by an annular connecting member (or “shroud”). The shroud improves the blowing efficiency when air that has been drawn in from the radial center of the casing is blown outward in the radial direction. The blades that are erected on the main plate all have the same shape and are evenly spaced in the circumferential direction around the main plate (see Patent Document 2; Japanese Laid-open Patent Publication No. 2020-63679).

SUMMARY OF INVENTION

Technical Problem

For typical centrifugal fans, there is demand for reduced noise and improved blowing efficiency. However, the impeller configurations described in Patent Documents 1 and 2 above are unable to reduce the peak noise that appears at (centrifugal fan blade count×rotational speed frequency) due to pressure fluctuations in the air passing the so-called tongue portion.

It has been discovered that the peak noise that appears at (centrifugal fan 50 blade count×rotational speed frequency) can be reduced by disposing, as depicted in FIG. 8, first blades 52 that are long in the radial direction and are erected at an uneven pitch on the main plate 51 and further disposing

second blades 53, which are formed with a short length in the radial direction and are erected at an uneven pitch between the first blades 52. However, if the spacing between the first blades 52 and the second blades 53 depicted in FIG. 8 is set at an uneven pitch (where X1≠X2), the center of gravity of the centrifugal fan 50 will become displaced from the center of rotation (that is the rotor shaft 54), which makes the rotation of the centrifugal fan 50 unbalanced. To resolve this, attempts have been made to correct the imbalance by providing counterweights corresponding to the imbalance on the underside of the main plate 51, but this was found to generate frequency noise (first to third order components of the rotation speed) separately to the peak noise.

Solution to Problem

The present disclosure was conceived to solve the problems described above, and has an object of providing a centrifugal air blower that reduces noise by reducing the peak noise that appears at (centrifugal fan blade count×rotational speed frequency), and that stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan from becoming displaced from the center of rotation (the rotor shaft).

The embodiment described below has the following configuration. That is, a centrifugal air blower has a centrifugal fan and a motor for rotationally driving the centrifugal fan housed inside a case body, and air is drawn in from a center in a radial direction of the case body and exhausted from an exhaust port provided on an outside in the radial direction of the case body, the case body including: a first case that is assembled to cover the centrifugal fan, is provided with an intake opening at a center in the radial direction, and has a first air passage, which is annular, formed at an outside in the radial direction; and a second case that has a second air passage, which is annular and is combined with the first air passage, formed further outside in the radial direction than an outer circumferential end of the centrifugal fan in an outer periphery of a base plate that rotatably supports the motor, and wherein the centrifugal fan: has a plurality of first blades formed at an uneven pitch in a circumferential direction so as to be erected on a main plate that continuously extends outward in a radial direction from a hub which is integrally assembled with a rotor yoke; and has a plurality of second blades, which are shorter in length than the first blades and are formed upright between the first blades so that a spacing from an adjacent first blade has an uneven pitch in the circumferential direction, wherein a length of inner end parts in the radial direction of a plurality of the second blades is formed shorter than a length of the second blades in another region so that a center of gravity position of the centrifugal fan matches the center of rotation.

With the above configuration, by making the spacings between blades have an uneven pitch, it is possible to provide a centrifugal air blower which has quieter operation by dispersing locations where peak noise, which appears at (centrifugal fan blade count×rotational speed frequency), occurs and which has stabilized rotational balance by preventing a center of gravity position of a centrifugal fan from becoming displaced from the center of rotation (the rotor shaft).

The length in the radial direction of the second blades in the partial region in the circumferential direction is preferably set so that a length of end parts further inward in the radial direction than a shroud, which connects outer edge parts of the first blades and the second blades in a ring shape, is formed shorter than a length in the radial direction of the second blades in another region. By doing so, rotational balance is stabilized by preventing the center of gravity position of a centrifugal fan from becoming displaced from the center of rotation (the rotor shaft), and air blowing performance is unaffected even if the second blades are formed in a partial region in the circumferential direction so that the length of the inner end parts in the radial direction is shorter than the length in the radial direction of the second blades in another region.

Advantageous Effects of Invention

By using the centrifugal air blower described above, it is possible to provide a centrifugal air blower that has quieter operation by reducing the peak noise that appears at (centrifugal fan blade count×rotational speed frequency), and has a stabilized rotational balance by preventing a center of gravity position of a centrifugal fan from becoming displaced from the center of rotation (the rotor shaft).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a centrifugal air blower.

FIG. 2 is a plan view of a state where the first case has been removed from the centrifugal air blower appearing in FIG. 1.

FIG. 3 is an axial cross-sectional view of the centrifugal air blower appearing in FIG. 1.

FIGS. 4A, 4B, and 4C are a plan view, a front view, and a perspective view of a centrifugal fan.

FIG. 5A is a plan view of the centrifugal fan, and FIG. 5B is a partial explanatory view of the uneven pitch of first blades and second blades.

FIG. 6A is an FFT analysis graph of noise generated in a unevenly spaced impeller, and FIG. 6B is an FFT analysis graph of noise generated in an evenly spaced impeller.

FIG. 7 is a graph comparing the PQ characteristics of a unevenly spaced impeller and an evenly spaced impeller.

FIG. 8 is a plan view of a centrifugal fan with first and second blades formed at an uneven pitch on a main plate.

DESCRIPTION OF EMBODIMENTS

One embodiment of a centrifugal air blower according to the present invention is described below with reference to the accompanying drawings. First, the overall configuration of the centrifugal air blower will be described with reference to FIGS. 1 to 7. A DC brushless motor is used as a motor M. In the present embodiment, an outer rotor motor is used. Note that the motor may be an inner rotor motor.

As depicted in FIG. 3, the centrifugal air blower 1 includes a centrifugal fan 2 (impeller) and a rotor 3 that are integrally assembled, and the motor M that drives such components is housed inside a case body 4. As depicted in FIG. 1, the centrifugal air blower 1 draws air from the center in the radial direction of the case body 4 and exhausts pressurized air from a side surface in the radial direction. The case body 4 is formed by combining a first case 4a, which is assembled with and covers the centrifugal fan 2, and a second case 4b, which rotatably supports the motor M (that is, the rotor 3 and a stator 5, see FIG. 3).

In FIG. 1, an intake opening 4c is provided in the center of the first case 4a, and an annular first air passage 4d is formed on the outside in the radial direction. In FIG. 2, an annular second air passage 4e, which combines with the first air passage 4d, is formed on the outside in the radial direction of the second case 4b. The first case 4a and the second case 4b are assembled to form an annular air passage 4f on the outside in the radial direction of the case body 4 (see FIG. 3). As depicted in FIG. 2, a partition called a “tongue portion 4h” is provided on the second case 4b at the boundary between the second air passage 4e, which forms the annular air passage 4f, and the exhaust port 4g. Although not illustrated, the same applies to the boundary in the first case 4a between the first air passage 4d, which forms the annular air passage 4f, and the exhaust port 4g. As depicted in FIG. 3, a bearing housing 6 and a motor board 7 are assembled in the center of the second case 4b. The output wires of the stator coil 5b are connected to the motor board 7, and a Hall sensor or the like detects the position of a rotor magnet 3d is also mounted. If the motor M is a sensorless type, this position detection sensor can be omitted.

A stator core 5a is integrally fixed to the outer circumference of the bearing housing 6 that is in the form of a metal tube and is held upright on the second case 4b, and a rotor shaft 3a is rotatably supported via a pair of bearings 6a in a shaft bore of the bearing housing 6. A retaining washer 6c is fitted onto one axial end of the rotor shaft 3a, and restricts movement in the axial direction of the bearing 6a at the lower end in the axial direction. A stator coil 5b is wound via an insulator 8 around pole teeth formed on the stator core 5a, and the tips of the pole teeth are positioned facing the rotor magnet 3d. One end of the rotor shaft 3a is integrally attached to the hub 3c of a rotor yoke 3b, which is cup-shaped, by press-fitting, shrink-fitting, adhesive bonding, or a combination of such methods. The other end of the rotor shaft 3a is supported by a shaft support 6b provided on the second case 4b. The rotor magnet 3d is integrally assembled on an inner circumferential surface of the rotor yoke 3b. Note that the center of the intake opening 4c does not need to be precisely aligned with the axis of the rotor shaft 3a of the motor M, and it is sufficient for the intake opening 4c to be located near the center in the radial direction of the case body 4 within a range where the centrifugal fan 2 operates without a drop in efficiency.

As depicted in FIG. 4C, the centrifugal fan 2 has a dome-shaped main plate 2b formed so as to extend radially outward from the hub 2a. The main plate 2b, which is continuous with the hub 2a, extends radially outward and is inclined toward a downstream side in the direction of airflow. A plurality of first blades 2c1 and second blades 2c2, which are curved from the inside toward the outside in the radial direction, are alternately formed so as to be erected on the main plate 2b. As depicted in FIGS. 4A and 4B, an annular shroud 2d is connected to the outer peripheral edges of the first blades 2c1 and the second blades 2c2. Air pressurized by the rotation of the first blades 2c1 and the second blades 2c2 is rectified and sent toward the annular airflow passage 4f in the outer periphery (see FIG. 3).

In addition, as depicted in FIG. 4A, a plurality of first blades 2c1 are formed so as to be erected at an uneven pitch in the circumferential direction at the outside of the dome-shaped main plate 2b. Second blades 2c2, which are shorter in length than the first blades 2c1, are formed upright between the first blades 2c1 so that a spacing from an adjacent first blade 2c1 has an uneven pitch in the circumferential direction.

As depicted in FIG. 5A, in a partial region Z1 in the circumferential direction, the plurality of second blades 2c2 are formed so that the length of inner end parts in the radial direction is shorter than the length of the second blades 2c2 in the other region Z2, which results in the center of gravity position of the centrifugal fan 2 matching the rotational center. By doing so, by making the spacing between the first blades 2c1 and a second blade 2c2 have an uneven pitch as depicted in FIG. 5B (see FIG. 5B, where X1≠X2), the location where the peak noise appearing at (blade count of centrifugal fan 2×rotational speed frequency) occurs becomes dispersed, resulting in quieter operation. Also, by preventing the center of gravity of the centrifugal fan 2 from becoming displaced from the center of rotation (the rotor shaft 3a), it is possible to provide a centrifugal air blower 1 whose rotational balance is stabilized.

As depicted in FIG. 5A, the length in the radial direction of the second blades 2c2 provided in a partial region Z1 in the circumferential direction of the centrifugal fan 2 is formed shorter than the length of the inner end parts in the radial direction of the second blades 2c2 provided in the other region Z2. Doing so prevents the position of the center of gravity of the centrifugal fan 2 from becoming displaced from the center of rotation (the rotor shaft 3a), which stabilizes the rotational balance. In addition, even if the length of the inner end parts in the radial direction of the second blades 2c2 in the partial region Z1 in the circumferential direction is formed shorter than the length of the second blades 2c2 in the other region Z2, this will not affect the blowing performance.

Also, as depicted in FIG. 3, the hub 2a of the centrifugal fan 2 and the main plate 2b that is continuous with the hub 2a form a dome-shaped space 4i on the opposite side to the intake opening 4c. This dome-shaped space 4i can be used to accommodate tall components (such as an electrolytic capacitor 7a) mounted on the motor M and the motor board 7, which enables the centrifugal fan 2 and the motor M to be compactly assembled. The rotor 3 and the stator 5 of the motor M are housed inside the dome-shaped space 4i and coincide in the axial direction. By doing so, the axial dimension of the centrifugal air blower 1 is reduced, which makes it possible to achieve a smaller, flatter structure, even for a centrifugal air blower 1 of the same size.

As depicted in FIG. 1, the first case 4a and the second case 4b are integrally assembled by placing the cases 4a and 4b over each other with their openings facing each other and placing locking pieces 4j provided on the outer periphery of the sides of the first case 4a in engagement with locking pieces 4k provided on the outer periphery of the side of the second case 4b. A wiring connection port 4m through which wires connected to the motor board 7 can be routed outside the case is also formed on the first case 4a and the second case 4b. The wiring connection port 4m is formed by fitting a mating plate 4m1 that protrudes from the side of the first case 4a into a mating channel 4m2 that protrudes from the facing side of the second case 4b (see FIGS. 1 and 2).

Note that for the first blades 2c1 and the second blades 2c2 that are in an uneven arrangement on the main plate 2b, by measuring noise and performing FFT analysis while varying the number of blades and the blade spacing, the optimal arrangement for reducing noise by dispersing the locations of peak noise that occurs at (blade count of centrifugal fan 2×rotational speed frequency) is determined. However, due to the uneven arrangement of the first blades 2c1 and the second blades 2c2 provided between the first blades 2c1, in this state, the rotational balance of the centrifugal fan 2 will remain unbalanced. For this reason, in the partial region Z1 in the circumferential direction, the length of the inner end parts in the radial direction of the second blades 2c2 is formed shorter than the length of the inner end parts in the radial direction of the second blades 2c2 in the other region Z2. If the length in the radial direction of the outer end parts in the radial direction of the first blades 2c1 and the second blades 2c2 were shortened to correct the balance, this would significantly impact the airflow-static pressure characteristics (the “P-Q characteristics”). Meanwhile, even if the inner end parts in the radial direction of the first blades 2c1, which are close to the center in the radial direction of the centrifugal fan 2, were shortened, this would have little effect in correcting the rotational balance. For this reason, shortening the length of the inner end parts in the radial direction of the second blades 2c2 makes it possible to correct the rotational balance without affecting the airflow-static pressure characteristics (the “P-Q characteristics”). By doing so, the center of gravity position of the centrifugal fan 2 is prevented from becoming displaced from the center of rotation (the rotor shaft 3a), which stabilizes the rotational balance.

FIG. 6A is an FFT analysis graph of noise generated by the centrifugal fan 2, which has an uneven impeller pitch, and FIG. 6B is an FFT analysis graph of noise generated by the centrifugal fan 2, which has an even impeller pitch, for comparison purposes. In both cases, measurement of noise was performed on a centrifugal fan 2 with 50 blades (that is, 25 first blades 2c1 and 25 second blades 2c2) at various rotational frequencies, and FFT (Fast Fourier Transform) analysis (frequency analysis) was performed. For the evenly spaced impeller depicted in FIG. 6B, a noise peak (the area indicated by the dotted oval) was observed at a frequency of 4685 Hz and a rotational speed of 5622 r/min. However, no noise peak was observed with the unevenly spaced impeller depicted in FIG. 6A.

FIG. 7 depicts the airflow-static pressure characteristics (P-Q characteristics) for the centrifugal fan 2 with the unevenly spaced impeller depicted in FIG. 6A and the centrifugal fan 2 with the evenly spaced impeller depicted in FIG. 6B. In the graph in FIG. 7, the dashed line indicates the airflow-static pressure characteristics (P-Q characteristics) of the centrifugal fan 2 with an unevenly spaced impeller, and the solid line indicates the airflow-static pressure characteristics (P-Q characteristics) of the centrifugal fan 2 with an evenly spaced impeller. As indicated by the dashed line, the centrifugal fan 2 with the unevenly spaced impeller has slightly improved airflow-static pressure characteristics (P-Q characteristics) in the low to medium flow rate range compared to the centrifugal fan 2 with the evenly spaced impeller.

As described above, by setting the intervals between the first blades 2c1 and the second blades 2c2 at an uneven pitch, it is possible to provide a centrifugal air blower 1 that achieves quieter operation by dispersing the number of locations where peak noise, which appears at (centrifugal fan blade count×rotational speed frequency) occurs, and stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan 2 from shifting from the center of rotation (the rotor shaft 3a).

Note that although the first blades 2c1 and the second blades 2c2 provided on the main plate 2b of the centrifugal fan 2 are alternately disposed, a plurality of second blades 2c2 may be disposed in an uneven arrangement between the first blades 2c1. The region where the length of the inner end parts in the radial direction of the second blades 2c2 is shorter is not limited to one region and a plurality of such regions may be provided in the circumferential direction of the centrifugal fan 2. Also, although an outer rotor type motor used in a centrifugal air blower for HVAC (heating, ventilation and air conditioning) has been described as an example in the present embodiment, the present disclosure is not limited to this and the motor may also be used as a driving source for other equipment.