CENTRIFUGAL FAN

Abstract

There is provided a centrifugal fan including an upper casing which has an air suction opening, a lower casing, and an impeller which is disposed between the upper casing and the lower casing. The impeller includes an upper shroud which is provided on an upper casing side, and a plurality of blades which are arranged along a circumference direction below the upper shroud, and is rotatable around a rotary shaft. A pressure surface of each of the plurality of blades has a convex shape in a rotation direction and is formed with a plurality of protrusions which extend in parallel with the rotary shaft.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal fan, and more particularly, to a centrifugal fan having a casing and an impeller.

2. Description of the Related Art

A centrifugal fan (centrifugal blower) is a fan for blowing air in a radial direction by rotating an impeller including a plurality of blades (also referred to as wings, impeller). One of this kind of fans is a centrifugal multi-blade fan which includes a casing having a suction opening and a discharge opening and accommodating therein an impeller having a plurality of blades around a rotary shaft of a motor. The centrifugal multi-blade fan suctions air from the suction opening, allows the air flow through the blades from the center of the impeller, and discharges the air outward in the radial direction of the impeller by a centrifugal action from the rotation of the impeller. The air discharged from the outside of the outer circumference of the impeller passes through the casing while increasing the pressure of the air, and the high-pressure air is discharged from the discharge opening.

These centrifugal multi-blade fans are widely used for cooling, ventilation, and air-conditioning in home appliances, OA equipment, and industrial equipment, and in blowers for vehicles and the like. The blowing performance and noise of such centrifugal multi-blade fan are largely affected by a blade shape of an impeller and a shape of a casing.

The following patent application publications disclose improvement in blade shapes of fans, for example.

JP-A-H11-247795 discloses an impeller of a centrifugal fan, and the impeller has a plurality of ridges which is formed on a surface of each blade oriented at a rotation direction such that the ridges are substantially parallel with a rotary shaft.

JP-A-H11-294386 discloses an impeller of a centrifugal fan, and the impeller has a plurality of ridges which is formed on a surface of each blade at a rotation direction such that the ridges are substantially parallel with a rotary shaft and the widths and heights of the ridges increase from a side plate toward a main plate.

JP-A-2005-16315 discloses a centrifugal fan which includes a side plate and a main plate provided inside a casing, and a plurality of blades annularly disposed on the main plate. On the back side of each blade in a cross-section of the blade perpendicular to a rotary shaft, a plurality of ridges and grooves are provided from the leading edge of the blade toward the tailing edge of the blade.

JP-A-2001-32794 discloses a centrifugal fan which includes a fan main body having a number of blades arranged along a circumference direction, and a motor for rotating the fan main body, and discharges air from the inner side toward the outer side in the radial direction of the fan by rotation of the fan main body. The blades have ridges (or grooves) formed on a negative pressure surface at a downstream in the rotation direction.

As apparatuses have been reduced in sizes and thicknesses, have increased in assembly densities, and have been reduced in power consumption, it has been strongly required from the market to improve static pressures and efficiency for fan motors for those apparatuses. As for fans, it is also important to reduce noise. Particularly, related-art centrifugal fans tend to cause high discrete frequency noise (narrowband noise) and high wideband noise, so that large noise is caused when the centrifugal fans are installed in apparatuses.

Here, the discrete frequency noise is noise based on a blade passing frequency, and is also called as NZ noise. The discrete frequency noise is noise having a characteristic peak at a specific frequency of a narrow frequency band. This frequency can be expressed by the equation: fnz=n (rotational frequency)×z (number of blades). Since not only the primary component but also the secondary and higher components occur, the discrete frequency noise becomes a big problem even in actual hearing. In other words, when those centrifugal fans are installed in apparatuses, there is a risk that noise might occur as clear sound. Also, since a turbulent flow is a dominant factor of wideband noise, and determines a total noise level, it is also required to reduce the wideband noise.

Further, in addition to implementation of the above requirements, it is also required to improve the productivity of fans.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a centrifugal fan which can suppress noise.

According to an illustrative embodiment of the present invention, there is provided a centrifugal fan comprising: an upper casing which has an air suction opening; a lower casing; and an impeller which is disposed between the upper casing and the lower casing, wherein the impeller includes an upper shroud which is provided on an upper casing side, and a plurality of blades which are arranged along a circumference direction below the upper shroud, and is rotatable around a rotary shaft, and wherein a pressure surface of each of the plurality of blades has a convex shape in a rotation direction and is formed with a plurality of protrusions which extend in parallel with the rotary shaft.

In the above centrifugal fan, the plurality of protrusions may be densely formed in an area in the vicinity of a leading edge of each blade and not formed in an area in the vicinity of a base part of each blade.

In the above centrifugal fan, the plurality of protrusions may protrude from the pressure surface and satisfy at least one of conditions: the number of protrusions for each blade is 3 or more and 15 or less; and the diameter of each of the protrusions is larger than 0 mm and is equal to or less than 1 mm.

In the above centrifugal fan, the plurality of protrusions may have a semicircular shape as seen in a direction parallel to the rotary shaft and satisfy at least one of conditions: the number of protrusions for each blade is 10; a pitch between adjacent protrusions is 1.5 mm; and the diameter of each of the protrusions is 0.5 mm.

In the above centrifugal fan, the upper casing and the lower casing may configure an open-type casing, the impeller further may include a lower shroud which is provided below the plurality of blades, an outside diameter of the lower shroud may be equal to or smaller than an inside diameter of the upper shroud, and an inside portion of each of the blades may have an inclined portion which connects an inside circle portion of the upper shroud and an inside circle portion of the lower shroud.

According to the above configuration, it is possible to provide a centrifugal fan which can suppress noise.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view illustrating a centrifugal fan according to a first illustrative embodiment of the present invention;

FIG. 2 is a view illustrating the longitudinal section of the middle of the centrifugal fan of FIG. 1;

FIG. 3 is a perspective view illustrating an impeller 3 as seen from a side of the upper shroud 23;

FIG. 4 is a view illustrating a blade shape of the centrifugal fan of FIG. 1 as seen from a side of the upper shroud 23;

FIG. 5 is a cross-sectional view taken along a line A-A of FIG. 4;

FIG. 6 is a cross-sectional view taken along a line B-B of FIG. 4;

FIG. 7 is a cross-sectional view taken along a line C-C of FIG. 4;

FIGS. 8A and 8B are views illustrating the cross-section shape and noise characteristic of a related-art impeller, respectively;

FIGS. 9A and 9B are views illustrating the cross-section shape and noise characteristic of the impeller according to the first illustrative embodiment of the present invention, respectively;

FIG. 10 is a cross-sectional view illustrating an impeller of a centrifugal fan according to a modified illustrative embodiment;

FIG. 11 is a perspective view illustrating a centrifugal fan according to a second illustrative embodiment of the present invention;

FIG. 12 is a view illustrative the longitudinal section of the middle of the centrifugal fan of FIG. 11;

FIG. 13 is a view illustrating an air flow between an upper shroud and an upper casing of the centrifugal fan shown in the section of FIG. 2;

FIG. 14 is a view illustrating an air flow between an upper shroud and an upper casing of the centrifugal fan shown in the section of FIG. 12;

FIG. 15 is a view illustrating the air flow-pressure characteristics of the centrifugal fan shown in the section of FIG. 2 and the centrifugal fan shown in the section of FIG. 12;

FIG. 16 is a view illustrating a cross section structure of a centrifugal fan according to a modified illustrative embodiment;

FIG. 17 is a cross-sectional view illustrating the centrifugal fan according to a modified illustrative embodiment;

FIG. 18 is a cross-sectional view illustrating a half of a centrifugal fan according to a third illustrative embodiment of the present invention;

FIG. 19A is a bottom view of an impeller according to a fourth illustrative embodiment, and FIG. 19B is an enlarged view illustrating a portion ‘B’ of FIG. 19A;

FIG. 20 is a side view illustrating the impeller of FIG. 19;

FIG. 21 is a view illustrating a method of measuring a radius of each protrusion and a pitch (interval) between adjacent protrusions;

FIG. 22 is a view illustrating forming positions of the protrusions in a blade;

FIG. 23 is a view illustrating the static pressure-air flow (P-Q) characteristics of the impeller according to the first illustrative embodiment (comparative example) shown in FIGS. 1 to 7 and the impeller according to the fourth illustrative embodiment (embodiment); and

FIG. 24 is a view illustrating noise characteristic of the impeller according to the fourth illustrative embodiment (embodiment) for comparing with the impeller according to the first illustrative embodiment (comparative example) shown in FIG. 9B.

DETAILED DESCRIPTION

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

First Illustrative Embodiment

FIG. 1 is a perspective view illustrating a centrifugal fan according to a first illustrative embodiment of the present invention, and FIG. 2 is a view illustrating a longitudinal section at a middle part of the centrifugal fan of FIG. 1. FIG. 3 is a perspective view illustrating an impeller 3 as seen from a side of an upper shroud 23, and FIG. 4 is a view illustrating a blade shape of the centrifugal fan of FIG. 1 as seen from the side of the upper shroud 23. FIGS. 5 to 7 are cross-sectional views taken along lines A-A, B-B, and C-C of FIG. 4, respectively.

Referring to FIGS. 1 to 4, in a centrifugal fan 1, a central impeller 3 rotates to blow air. The impeller 3 includes seven blades 2 disposed at regular intervals, and rotates around a rotary shaft 11 by a fan motor 13 provided in the centrifugal fan 1. The direction of the rotation is a clockwise direction in FIG. 4.

The impeller 3 is accommodated in a casing 4. The casing 4 is configured by an upper casing 5 and a lower casing 6 which have plate shape, and in order to place the upper casing 5 and the lower casing 6 evenly spaced apart from each other, four columnar supports 7 are provided at four corners of the casing 4, respectively. At the top of the centrifugal fan 1, an air suction opening 8 is formed. Air discharge openings 9 are provided between the respective columnar supports 7 of the casing 4. In other words, the air discharge openings 9 are provided at four sides of the casing 4 in four directions (open casing type). The casing 4 may have one discharge opening for collecting air discharged from the impeller 3 in one direction (scroll casing type).

As shown in FIGS. 2 to 7, the impeller 3 has an annular lower shroud 21, an annular upper shroud 23, and a plurality of blades 2 which are arranged along a circumference direction between the lower shroud 21 and the upper shroud 23, and is rotatable around the rotary shaft 11.

As shown in FIG. 4, the annular lower shroud 21 has an inside circle 21A and an outside circle 21B in a planar view. The inside circle 21A and the outside circle 21B are circles in a planar view. The annular upper shroud 23 has an inside circle 23A and an outside circle 23B in a planar view. The inside circle 23A and the outside circle 23B are circles in a planar view. The outside circle 21B of the lower shroud 21 overlaps the inside circle 23A of the upper shroud 23. In other words, the outside circle 21B of the lower shroud 21 is the same as the inside circle 23A of the upper shroud 23. However, the outside circle 21B of the lower shroud 21 may be slightly smaller than the inside circle 23A of the upper shroud 23.

In FIG. 4, the shape of each blade 2 seen from the internal space of the inside circle 23A of the upper shroud 23 is shown by a solid line. Further, the shape of each blade 2 hidden between the inside circle 23A and outside circle 23B of the upper shroud 23 by the upper shroud 23 is shown by a dotted line.

As shown in FIG. 4, each blade 2 has a shape tapering from the inside (rotary shaft) to the outside in a planar view. In other words, each blade 2 has a shape becoming thinner as separating further from the rotary shaft 11. Each blade 2 has an inlet angle of 45° and an outlet angle 22°. The diameter of the outside circle 23B is 120 mm, and the diameter of the inside circle 21A is 70 mm. The blades 2 are backward inclined blades.

As shown in FIGS. 3 to 7, the upper portion of each blade 2 is fixed to the lower surface of the upper shroud 23, and the lower portion of each blade 2 is fixed to the upper surface of the lower shroud 21. Here, since the outside circle 21B of the lower shroud 21 is designed to be the same as the inside circle 23A of the upper surface (or the outside circle 21B of the lower shroud 21 is smaller than the inside circle 23A of the upper surface), it is possible to integrally form the impeller 3 only by using upper and lower molds.

As shown in FIGS. 4 to 7, the inside circle side (the side close to the rotary shaft) of the upper portion of each blade 2 is connected to the inside-circle-side end portion of the upper shroud 23. From this position to the outside-diameter-side end portion of the upper portion of each blade 2, the upper portion of each blade 2 is connected to the lower surface of the upper shroud 23. In other words, as shown in FIG. 4, in a range where the upper shroud 23 and the blades 2 exist (a place surrounded by a dotted line) in a planar view, the upper shroud 23 is in contact with the blades 2.

Further, the lower portion of each blade 2 is connected to the lower shroud 21.

As shown in FIG. 5, the inside circle side of the upper portion of each blade 2 is connected to the inside-circle-side end portion of the upper shroud 23. The upper portion of each blade 2 has a tapered portion (inclined portion) from that position toward the inside circle side. In other words, the inside circle portion of each blade 2 has an inclined portion which connects the inside circle portion (inside-circle end portion) of the upper shroud 23 and the inside circle portion of the lower shroud 21.

The tapered portion of each blade 2 forms an inclined surface having an angle γ of 42° with respect to a vertical direction. In FIG. 4, a portion of each blade 2 shown by a solid line is a tapered portion, and a portion of each blade 2 shown by a dotted line shows a portion in which the upper portion of the corresponding blade 2 is connected with the upper shroud 23. Further, the portion of each blade 2 shown by the solid line shows a portion in which the lower portion of the corresponding blade 2 is connected with the lower shroud 21. The portion of each blade 2 shown by the dotted line shows a portion in which the lower portion of the corresponding blade 2 is not connected with the lower shroud 21 (a portion below which the lower shroud 21 does not exist).

The angle γ, which is 42° in FIG. 5, is called a taper angle, and the angle γ is not limited to 42°.

In the impeller 3, in a portion in which the upper shroud 23 exists in a planar view, the lower shroud 21 does not exist. Therefore, it is preferable to provide a protrusion 6a at the upper portion of the lower casing 6 as shown in FIG. 2 such that the protrusion 6a protrude upward and takes place of the lower shroud 21 at the portion of the impeller 3 in which the lower shroud 21 does not exist. The protrusion 6a is formed at the portion where the upper shroud 23 exists (the portion where the lower shroud 21 does not exist) in a planar view such that a distance between the lower portion of each blade 2 and the lower casing 6 becomes shorter. The protrusion 6a protrudes to a height at which the lower shroud 21 exists. In this way, it is possible to allow the lower casing 6 to have a structure for acting as the lower shroud.

In the above-mentioned impeller 3, the inside circle portion of each blade 2 has a tapered shape. The base portion of the tapered portion is integrated with the lower shroud 21. The upper portion of each blade 2 is entirely integrated with the upper shroud 23 except for the tapered portion. Further, as shown in FIG. 5, the inside diameter Dl of the upper shroud 23 is the almost the same as the outside diameter D2 of the lower shroud 21 (D1≈D2) or may be larger than the outside diameter D2 of the lower shroud 21 (D1>D2). This shape makes it possible to integrally form the impeller 3 only by upper and lower molds and provide the high-productivity impeller 3 and the high-productivity centrifugal fan 1.

Further, since it is unnecessary to increase or decrease the diameter of the air suction opening, it is possible to suppress a static pressure and an air flow from being reduced.

Furthermore, in the centrifugal fan 1 according to this illustrative embodiment, it is possible to improve an air flow by the tapered shape of each blade 2. Moreover, it is possible to cover the suction opening portion with the shrouds. Therefore, it is possible to reduce noise. This feature will be described below.

FIGS. 8A and 8B are views illustrating a cross-sectional shape and noise characteristic of a related-art impeller, respectively.

As shown in the cross-sectional view of FIG. 8A, a related-art impeller 3′ includes a lower shroud 21′, an upper shroud 23′, and a plurality of blades 2′ disposed between the lower shroud 21′ and the upper shroud 23′. The outside circle of the lower shroud 21′ is the same as the outside circle of the upper shroud 23′. Therefore, it is not possible to integrally form the impeller 3′ only by upper and lower molds.

FIG. 8B shows a noise characteristic during driving of the impeller 3′ of FIG. 8A by taking frequencies on a horizontal axis and noise values (dB(A)) on a vertical axis.

Noise is 58.0 dB(A) in total, and both of discrete frequency noise and wideband noise (turbulence noise) shows high values as shown in FIG. 8B.

FIGS. 9A and 9B are views illustrating a cross-sectional shape and noise characteristic of the impeller according to the illustrative embodiment of the present invention, respectively.

As shown in the cross-sectional view of FIG. 9A, the impeller 3 according to the present illustrative embodiment includes the lower shroud 21, the upper shroud 23, and the plurality of blades 2 disposed between the lower shroud 21 and the upper shroud 23. The outside circle of the lower shroud 21 is almost the same as the inside circle of the upper shroud 23. Therefore, it is possible to integrally form the impeller only by upper and lower molds.

FIG. 9B shows a noise characteristic during driving of the impeller of FIG. 9A by taking frequencies on a horizontal axis and noise values (dB(A)) on a vertical axis.

Noise is 57.3 dB(A) in total. Further, as shown in a solid line circle of FIG. 9B, discrete frequency noise (the primary and secondary noise of the blades) is lower than that in FIG. 8B. Furthermore, as shown in a dotted line circuit of FIG. 9B, wideband noise (turbulence noise) is also lower than that in FIG. 8B.

FIG. 10 is a cross-sectional view illustrating an impeller of a centrifugal fan according to a modified illustrative embodiment.

An impeller 3 according to the modified illustrative embodiment is different from the impeller shown in FIGS. 1 to 7 in that a base plate (plate) 21a for extending the outside circle of the lower shroud 21 outward is attached at the lower portion of the impeller 3. The diameter (inside diameter) of a hollow portion of the base plate 21a is the same as the outside diameter of the lower shroud 21. The outside diameter of the base plate 21a is the same as the outside diameter of the upper shroud 23. Therefore, it is possible to make the outside circle of the upper shroud 23 coincide with the outside circle of the base plate 21a, and to secure the same P-Q characteristic as that of the configuration of the impeller 3 as shown in FIGS. 8A. In other words, the base plate 21a functions as an appendant lower shroud. Since the base plate 21a is attached, it is also possible to reduce noise while maintaining the P-Q characteristic.

Even in this modified illustrative embodiment, the portion of the impeller 3 except for the base plate 21a can be integrally formed only by upper and lower molds, such that the productivity of the impeller is improved.

[Other(s)]

The fan according to the illustrative embodiment is adaptable to all centrifugal fans such as a turbo type, a multi-blade type, and a radial type. The fan can be mainly installed in products requiring suction and cooling (such as home appliances, PCs, OA equipment, and in-vehicle equipment) and the like.

Effect(s) of Illustrative Embodiment

As described above, the impeller according to the illustrative embodiment, the upper shroud does not overlap the lower shroud at all in a planar view. Therefore, it is possible to manufacturing the impeller by integral molding using upper and lower molds, and thus the productivity of the impeller is high.

The upper portion of the inside circle portion of each blade contacts the top of the upper shroud. The inside circle portion of each blade lowers from that position to a lower portion with an inclination (the taper angle γ), so that the lower portion of the inside circle portion of the corresponding blade comes into contact with the lower shroud. Therefore, the diameter of the suction opening does not increase, and thus the highest static pressure is not reduced.

Further, according to the illustrative embodiment, it is possible to make an efficient blade shape in view of an air flow such that a flow increases, the static pressure increases, and noise is reduced.

Second Illustrative Embodiment

FIG. 11 is a perspective view illustrating a centrifugal fan according to a second illustrative embodiment of the present invention, and FIG. 12 is a view illustrating the longitudinal section of the middle of the centrifugal fan of FIG. 11.

The centrifugal fan of FIG. 11 is different from the centrifugal fan of FIG. 1 in a structure of an upper casing 5A. That is, the upper casing 5A has an upper surface formed with a plurality of recesses 54, and ribs 52 between the adjacent recesses 54.

The plurality of recesses 54 are formed to surround the rotary shaft 11. The ribs 52 are formed radially around the rotary shaft 11. The number of the recesses 54 is 16 as shown in FIG. 16. The number of ribs 52 is also 16. The number of recesses 54 or ribs 52 is not limited thereto.

As shown in FIG. 12, the upper surface of the upper shroud 23 (the surface facing the upper casing 5A) has a portion (first portion) which becomes closer to the lower casing 6 as separating further from the rotary shaft 11. In this portion, the upper surface of the upper shroud 23 has a curved surface.

Each recess 54 is shallow at a portion close to the rotary shaft 11 and is deep at a portion away from the rotary shaft 11, such that the bottom surface of the recess 54 connecting the two portions becomes a curved surface. The thickness of a portion between the bottom surface of each recess 54 and the lower surface of the upper casing 5A (the surface facing the upper shroud 23) on a side of the upper casing 5A opposite to the bottom surface of the recess 54 is kept constant. In this portion where the thickness is kept constant, the lower surface portion (second portion) of the upper casing 5A has a curved surface which has almost same shape as (or is the same as) that of the bottom surface of the recess 54. In other words, the curved surface of the first portion is almost same as (or is same as) the curved surface of the second portion.

According to this configuration, the centrifugal fan according to the illustrative embodiment has the following features.

(1) The lower surface of a case (the upper casing 5A) having the air suction opening 8 has a shape having a curvature which is close to (or the same as) that of the upper surface of the upper shroud 23. Therefore, air coming from a discharge opening side of the impeller 3 can be suppressed from flowing back toward the suction opening 8 in a space between the upper casing 5A and the upper shroud 23. Therefore, deterioration of the characteristic of the fan can be prevented.

(2) If the lower surface of the upper casing 5A is formed simply in the shape described in (1), the upper casing 5A becomes thick. However, since the recesses 54 are provided, it is possible to prevent the upper casing 5A from becoming thick (it is possible to reduce the use of a material). Instead of the recesses 54, one recess having a doughnut shape with the center at the rotary shaft 11 may be formed. In this case, if the ribs 52 are provided at predetermined angular intervals, it is possible to give a constant rigidity to the upper casing 5A.

(3) As the impeller 3, any one of the impellers of FIGS. 1 to 10 may be used (even a related-art impeller may be used). Further, the shape of the blades 2 is arbitrary.

FIG. 13 is a view illustrating an air flow between an upper shroud and an upper casing of the centrifugal fan shown in the section of FIG. 2, and FIG. 14 is a view illustrating an air flow between an upper shroud and an upper casing of the centrifugal fan shown in the section of FIG. 12.

As shown in FIG. 13, in a case where the surface of the upper casing 5 facing the impeller 3 is flat, a small room is formed between the impeller 3 and the upper casing 5, and a portion of air discharged from the impeller 3 flows back in the small room toward the air suction opening 8. Further, a portion of the back-flow air swirls inside the small room.

In contrast, as shown in FIG. 14, if the recesses 54 are provided to the upper casing 5A such that the surface of the upper casing 5A facing the impeller 3 has a shape with the same curvature as that of the upper shroud of the impeller 3, it is possible to suppress (improve) a back flow of air.

FIG. 15 is a view illustrating the air flow-pressure characteristics of the centrifugal fan shown in the section of FIG. 2 and the centrifugal fan shown in the section of FIG. 12.

In FIG. 15, the characteristic of the centrifugal fan shown in the section of FIG. 12 is shown by a mark of ‘PRESENT EMBODIMENT (BACK-FLOW PREVENTION CASE)’, and the characteristic of the centrifugal fan shown in the section of FIG. 2 is shown by a mark of ‘RELATED ART (FLAT CASE)’. That is, the structure of the upper casing 5 having the flat lower portion shown in FIG. 2 is called as a flat case, and the structure of the upper casing 5A shown in FIG. 12 is called as a back-flow prevention case.

As shown in FIG. 15, if the structure for preventing a back flow of air is used, it is possible to improve the characteristic of the fan.

FIG. 16 is a view illustrating a cross section structure of a centrifugal fan according to a modified illustrative embodiment, and FIG. 17 is a cross-sectional view illustrating the centrifugal fan according to the modified illustrative embodiment.

The centrifugal fan according this modified illustrative embodiment is configured by forming flanges 56A and 56B for attachment of the centrifugal fan, integrally with the upper casing 5A of the fan shown in FIGS. 11 and 12. The flanges 56A and 56B are formed with screw holes. Therefore, it is possible to easily attach the fan to another component by inserting screws into the screw holes. One or more flanges may be provided, and it is possible to facilitate attachment of the fan.

Third Illustrative Embodiment

FIG. 18 is a cross-sectional view illustrating a half of a centrifugal fan according to a third illustrative embodiment of the present invention. This centrifugal fan uses an impeller shown in FIGS. 3 to 7.

Referring to FIG. 18, the centrifugal fan according to the third illustrative embodiment includes an impeller 103 having a plurality of blades 104, and a casing which houses the impeller 103. The impeller 103 is rotationally driven by a motor 102.

The impeller 103 includes the plurality of blades 104 arranged along a circumferential direction at regular intervals and an annular shroud 105 which supports one end sides of the blades 104. On the other-end sides of the blades 104, a main plate is not provided. An upper surface of the annular shroud 105 is formed as a predetermined curved surface, and a cylindrical portion 109 is formed at the center of the shroud 105. The inner side of the cylindrical portion 109 configures an air suction opening.

The impeller 103 has a cup-shaped boss section 106 at the center there of. The blades 104 have a curved shape with a predetermined curvature and all are formed in the same shape. The blades 104 are backward inclined blades, have a blade shape inclined backward with respect to a rotation direction, and configure a turbofan. The blades 104, the annular shroud 105, and the boss section 106 are formed of a synthetic resin by integral molding. To the inner side of the cup-shaped boss section 106, a rotor of the motor 102 is jointed. As the rotation of the motor 102, the impeller 103 rotates.

The casing has a quadrangular shape. The casing has an upper plate 111 made of a synthetic resin and having a circular opening at the center. In the vicinities of four corner portions of the upper plate 111, substantially cylindrical supporting columns are provided, respectively. At the periphery of the opening of the upper plate 111, a folding portion 112 is formed to protrude downward. On the inner side of the folding portion 112 (the rotary shaft side of the impeller 103), the cylindrical portion 109 of the shroud 105 is disposed with a predetermined interval.

A motor base 114 is disposed to face the upper plate 111. Between the upper plate 111 and the motor base 114, the four supporting columns are interposed. The upper plate 111 and the supporting columns are jointed by joint members 128 (such as bolts, screws, rivets, and the like). The supporting columns and the motor base 114 are jointed by joint members 128 (such as bolts, screws, rivets, and the like). The supporting columns and the upper plate 111 may be formed by integral molding, and the supporting columns and the motor base 114 may be jointed by the joint members 128.

Portions surrounded by adjacent supporting columns of the plurality of supporting columns, the upper plate 111, and the motor base 114 become openings. The openings become air discharge opening.

As described above, all of the four sides of the casing of the centrifugal fan according to the present illustrative embodiment have the openings. In other words, the sides of the casing are configured by only the supporting columns (the openings are formed at portions except for the supporting columns).

The outside diameter of the impeller 103 to be housed in the casing is set to be smaller than the dimension of one side of the casing. In a case where the outside diameter of the impeller 103 is larger than the dimension of one side of the casing, since the rotating impeller 103 protrudes from the outer edge of the casing, there are fears such as contact with other members and damage due to contact, which is not preferable. For this reason, it is preferable to set the outside diameter of the impeller 103 such that the impeller 103 does not protrude from the outer edge of the casing.

The motor 102 is an outer rotor type brushless motor. The rotor is configured by a cup-shaped rotor yoke 125, a ring-shaped magnet 127, and a shaft 107. The magnet 127 is fixed to the inner circumferential surface of the rotor yoke 125. The shaft 107 is fixed to a boss 126 formed at the center portion of the rotor yoke 125.

The shaft 107 is supported to be rotatable by one pair of bearings 119 installed in a bearing holder 118. On the outer circumferential surface of the bearing holder 118, laminated stator cores 120 are mounted. On the stator cores 120, an insulator 122 with a coil 121 wound thereon is mounted. The bearing holder 118 is mounted on the motor base 114. The stator cores 120 mounted on the bearing holder 118 is disposed to face the magnet 127 in the radial direction (the horizontal direction of FIG. 18) with a predetermined gap. The motor base 114 is formed by pressing a metal plate (for example, an iron plate). The motor base 114 has a quadrangular shape, similarly to the casing, and has a recess 115 formed at the center. The peripheral edge is bent in an axial direction (the vertical direction of FIG. 18) to form a side plate 116. Since the side plate 116 is formed, it is possible to improve the rigidity of the motor base 114. At the center of the recess 115 of the motor base 114, an opening is formed. The bearing holder 118 is mounted in the opening of the recess 115, and the motor 102 is housed in the recess 115.

The blades 104 of the impeller 103 jointed to the rotor yoke 125 are disposed to face a flat surface portion 117 of the motor base 114 in the axial direction (the vertical direction of FIG. 18) with a gap having a predetermined length G. In other words, the impeller 103 has the plurality of blades 104 such that at least a part of a lower portion of each blade 104 is exposed to the flat surface portion 117 of the motor base 114. The lower portion of each blade 104 may be entirely exposed to the flat surface portion 117 of the motor base 114. A lower surface of the insulator 122 has a PCB board 123 attached thereto. The PCB board 123 has an electronic component 124 mounted thereon for controlling the motor 102.

If the impeller 103 rotates by driving of the motor 102, air is suctioned from the air suction opening, passes through the blades 104 of the impeller 103, and is discharged toward the outer side in the radial direction of the impeller 103 by a hydrodynamic force based on a centrifugal action according to the rotation of the impeller 103.

The motor base 114 has the function of a main plate (lower shroud) which is provided at the bottom of an impeller in the related-art structure, and also has the function of a lower plate of the casing (lower casing). Therefore, it may be important to setting the length G of the gap formed between the impeller 103 and the flat surface portion 117 of the motor base 114. In a case where the gap length G is excessively large, air suctioned from the inlet flows even in the gap while passing through the blades 104. As a result, the pressure of the air discharged from the blades 104 is reduced, and thus an air flow characteristic is reduced. Meanwhile, in a case where the gap length G is excessively small, if a variation occurs in the accuracy of the dimensions of each component, it is feared that the blades 104 of the impeller 103 will come into contact with the flat surface portion 117 of the motor base 114. In order to prevent this contact, it is necessary to manage the accuracy of the dimensions of each component, and thus the cost of the centrifugal fan increases.

As described above, the gap length G is an important factor having an effect on the air flow characteristic of the centrifugal fan. Specifically, the gap length G is set in view of the air-flow characteristic and cost of the centrifugal fan. In a related-art centrifugal fan having a scroll casing, the noise was 61 dB(A). In contrast, in the centrifugal fan according to the present illustrative embodiment, when the length G of the gap between the impeller 103 and the flat surface portion 117 of the motor base 114 was set to 0.5 mm, the noise was 58 dB(A). That is, according to the present illustrative embodiment, it is possible to suppress the noise.

Fourth Illustrative Embodiment

FIG. 19A is a bottom view of an impeller according to a fourth illustrative embodiment of the present invention, and FIG. 20 is a side view illustrating the impeller of FIG. 19A. FIG. 19B is an enlarged view illustrating a portion ‘B’ of FIG. 19A.

The impeller according to the present illustrative embodiment has the same configuration as that of the impeller shown in FIGS. 1 to 14 and 16 to 18 except that protrusions are provided on pressure surfaces of blades. Specifically, a pressure surface of each blade 2 has a convex shape in the rotation direction, and is formed with a plurality of protrusions (ridges) 2a which extend in parallel with the rotary shaft. This impeller can be disposed between an upper casing (correspond to the upper plate 111 in FIG. 18) disclosed with respect to FIGS. 1, 2, 11, 12, and 16 to 18, and a lower casing (correspond to the motor base 114 in FIG. 18), whereby a centrifugal fan can be configured.

The plurality of protrusions 2a are densely formed in an area in the vicinity of the leading edge (on the outer side) of each blade 2, and are not formed in an area in the vicinity of the base (on the inner side) of each blade 2. In FIGS. 19A to 20, ten protrusions 2a are formed at each blade 2, and the intervals (pitches) between the protrusions are the same. Further, as shown in FIGS. 19A and 19B, the protrusions 2a protrude from the pressure surface of each blade, and have a semicircular shape in a plan view. As shown in FIG. 20, each protrusion 2a is a stripe-shaped protrusion extending from the upper edge portion to the lower edge portion of a corresponding blade 2.

FIG. 21 is a view illustrating a method of measuring a radius of each protrusion 2a and a pitch (interval) between two adjacent protrusions.

The protruding height H of a protrusion from a pressure surface is referred to as a radius of the protrusion in a plan view, and an interval between adjacent protrusions is referred to as a pitch P. The height H is also ½ of the diameter (hereinafter, referred to as a diameter of the protrusion) of a circle obtained by extrapolating from the semicircular shape of the protrusion in the plan view. If the height H, the pitch P, and the number of protrusions change, the static pressure-air flow (P-Q) characteristic and noise of the fan would change as follows. Therefore, it is possible to obtain the optimal fan characteristic by adjusting the height H, the pitch P, and the number of protrusions, which will be described below.

Experiments were conducted while changing the number of protrusions for each blade so as to obtain various static pressure-air flow (P-Q) characteristics, air flows, and noises.

According to the following manner, it was found that an impeller is an optimum embodiment, in which the number of protrusions for each blade is 10, the pitch P is 1.5 mm, and the protrusion diameter is 0.5 mm (the height H is 0.25 mm) in a plan view.

Compared to the impeller of the optimal embodiment (embodiment) having 10 protrusions (ridges) for each blade, a comparative example A1 having 3 protrusions (ridges) for each blade, a comparative example A2 having 15 protrusions (ridges) for each blade, a comparative example A3 having 20 protrusions (ridges) for each blade, and a comparative example A4 having 25 protrusions (ridges) for each blade were prepared, and graphs representing the static pressure-air flow (P-Q) characteristics and noises of the embodiment and the comparative examples were obtained.

Although the number of protrusions changed, the static pressure-flow (P-Q) characteristics were within a range of error. The noise was the lowest when the number of protrusions for each blade was 10. Also, it was seen that the noise is reduced when the number of protrusions for each blade is 3 or more and 15 or less. As compared to a case where the number of protrusions (the number of ridges) for each blade is 0, the noise is significantly reduced in a case of forming protrusions.

Experiments were performed while changing the pitch between adjacent protrusions so as to obtain various static pressure-air flow (P-Q) characteristics, flows, and noises.

Compared to the impeller of the optimal embodiment (embodiment) having a pitch P of 1.5 mm, a comparative example A5 having a pitch P of 1 mm, a comparative example A6 having a pitch P of 2 mm, and a comparative example A7 having a pitch P of 2.5 mm were prepared, and graphs representing the static pressure-air flow (P-Q) characteristics and noises of the embodiment and the comparative examples were obtained.

Although the pitch P changed, the static pressure-air flow (P-Q) characteristics were within the range of error. The noise was the lowest when the pitch P is 1.5 mm.

Experiments were performed while changing the diameters of protrusions so as to obtain various static pressure-air flow (P-Q) characteristics, flows, and noises.

Compared to the impeller of the optimal embodiment (embodiment) having protrusion diameters R of 0.5 mm, a comparative example A8 having protrusion diameters R of 1 mm, and a comparative example A9 having protrusion diameters R of 1.5 mm were prepared, and graphs representing the static pressure-air flow (P-Q) characteristics and noises of the embodiment and the comparative examples were obtained.

In a high static pressure area, the static pressure-air flow (P-Q) characteristic was the best when the diameters were 0.5 mm. Further, the noise was the lowest when the diameters were 0.5 mm. Also, it was seen that, in a case where the diameter of each of a plurality of protrusions is larger than 0 mm and is equal to or less than 1 mm, there is an effect of reducing a certain degree of noise.

FIG. 22 is a view illustrating a protrusion forming position of each blade.

As shown in FIG. 22, when the impeller having 10 protrusions for each blade is formed such that the pitch P is 1.5 mm and the diameter of each protrusion is 0.5 mm (the height H of each protrusion is 0.25 mm), if the length of each pressure surface from the outer circumferential surface 21B of the lower shroud (which is equal to the inner circumferential surface 23A of the upper shroud) to the leading edge portion of a blade 2 is L1, the length of the pressure surface from the outer circumferential surface 21B of the lower shroud to the position of the innermost protrusion 2a in the radial direction is L2, and the length of the pressure surface from the position of the outermost protrusion 2a in the radial direction to the leading edge portion of the blade 2, L1 is 56 mm, L2 is 40 mm, and L3 is 2.6 mm. In other words, the plurality of protrusions 2a are densely formed in an area in the vicinity of the leading edge of each blade 2, and is not formed in an area in the vicinity of the base of each blade 2. Also, it is known by an experiment that it is preferable to set the ratio of L2 to L1 to 50% or more and to set the ratio of L3 to L1 to about 0% to 10%.

FIG. 23 is a view illustrating the static pressure-air flow (P-Q) characteristics of the impeller (comparative example) according to the first illustrative embodiment shown in FIGS. 1 to 7 and the impeller (embodiment) according to the fourth illustrative embodiment. Also, FIG. 24 is a view illustrating the noise characteristic of the impeller according to the fourth illustrative embodiment (embodiment) for comparing with the impeller according to the first illustrative embodiment (comparative example) shown in FIGS. 9A and 9B.

As shown in FIG. 23, the static pressure-air flow (P-Q) characteristic rarely changed due to provision of the protrusions. As described above, the noise in FIG. 9 was 57.3 dB(A) overall, but the noise in FIG. 24 was 54.3 dB(A) overall. From this, it was seen that the noise is improved by 3.0 dB(A) by providing the protrusions.

[Others]

The impeller according to the fourth illustrative embodiment is not limited to the turbo type, but can be used for all centrifugal fans such as a multi-blade type and a radial type. The impeller can be preferably used for products requiring suction and cooling (such as home appliances, PCs, OA equipment, and in-vehicle equipment).

The shape of each protrusion in the plan view is not limited to a semicircular shape, but may be a triangular shape, a rectangular shape, a polygonal shape, a wedge type, and so on. At each blade, two or more protrusions may be provided. Also, in a case where three or more protrusions are provided to each blade, the protrusions may be provided at regular pitches (such that the distances between every two adjacent protrusions are the same) or at irregular pitches (such that the distances between every two adjacent protrusions are different).

The protrusions may be provided at the leading edge portion, center portion, or tailing end portion of each blade, or may be an entire surface of each blade. A plurality of assemblies of protrusions 2a as shown in FIG. 22 may be formed at each blade.

It is preferable to integrally form the protrusions by a mold for resin molding such that the protrusions are parallel with the direction of the rotary shaft.

The above-mentioned illustrative embodiments should be considered as illustrative in all aspects, but not restricting. The scope of the present invention is defined by the appended claims rather than the foregoing description, and is intended to include all modifications in the equivalent meaning and range to the scope of the claims.

Claims

1. A centrifugal fan comprising:

an upper casing which has an air suction opening;

a lower casing; and

an impeller which is disposed between the upper casing and the lower casing,

wherein the impeller includes an upper shroud which is provided on an upper casing side, and a plurality of blades which are arranged along a circumference direction below the upper shroud, and is rotatable around a rotary shaft, and

wherein a pressure surface of each of the plurality of blades has a convex shape in a rotation direction and is formed with a plurality of protrusions which extend in parallel with the rotary shaft.

2. The centrifugal fan according to claim 1,

wherein the plurality of protrusions are densely formed in an area in the vicinity of a leading edge of each blade and not formed in an area in the vicinity of a base part of each blade.

3. The centrifugal fan according to claim 1,

wherein the upper casing and the lower casing configure an open-type casing,

wherein the impeller further includes a lower shroud which is provided below the plurality of blades,

wherein an outside diameter of the lower shroud is equal to or smaller than an inside diameter of the upper shroud, and

wherein an inside portion of each of the blades has an inclined portion which connects an inside circle portion of the upper shroud and an inside circle portion of the lower shroud.