US20130004307A1

US20130004307A1 - Impeller and centrifugal fan having the same

Info

Publication number: US20130004307A1
Application number: US13/490,518
Authority: US
Inventors: Takako Fukuda; Seiya FUJIMOTO; Masaki Ogushi; Yuzuru Suzuki
Original assignee: Minebea Co Ltd
Current assignee: Minebea Co Ltd
Priority date: 2011-06-30
Filing date: 2012-06-07
Publication date: 2013-01-03
Also published as: CN202926712U; DE102012105838A1; JP2013011239A; JP5809859B2

Abstract

An impeller and a centrifugal fan having the same are provided. The impeller includes a lower shroud, an upper shroud, and a plurality of blades which are arranged along a circumference direction between the lower shroud and the upper shroud. The impeller is rotatable around a rotary shaft. An outside diameter of the lower shroud is equal to or smaller than an inside diameter of the upper shroud. 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.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an impeller and a centrifugal fan having the same, and more particularly, to an impeller designed to improve productivity and reduce noise, and a centrifugal fan having the same.
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-2008-267265 discloses a blower which includes a blowing unit having fan blades around a rotor, a casing for accommodating the blowing unit therein, and a motor unit for driving the blowing unit. The blower includes an upper annular disk provided above the fan blades, and a lower annular disk provided below the fan blades. The inside diameter D1 of the upper annular disk is almost the same with the outside diameter D2 of the lower annular disk, and the inside diameter D1 of the upper annular disk is also almost the same with the diameter D3 of an opening formed at the upper portion of the casing. Therefore, it is possible to suppress a vortex from occurring at the upper portion of the blowing unit and the inside of the casing, particularly in the vicinity of the opening, during rotation of the blowing unit, so that noise is reduced.
JP-A-2007-303340 discloses a blower which includes a casing, an impeller which is disposed in the casing, and a motor for rotating the impeller. Inclined parts are provided on the inner peripheral sides of the upper ends of individual blades, and further, an inclined face is provided on a boss part. Therefore, occurrence of a turbulent vortex can be prevented, so that noise is reduced. Further, since no turbulent vortex occurs, air flow resistance can be lowered, so that an air flow characteristic is improved.
JP-A-S51-7509 discloses a technique of providing long blades and short blades to an impeller for a centrifugal blower. An impeller includes a main plate, a side plate, and long blades and short blades which are positioned between the main plate and the side plate. An entrance end of the long blade is in contact with the side plate at a position having an almost same radius with that of an entrance end of the short blade. Further, the entrance end of the long blade is designed to become closer to the main plate as approaching to the center of a rotary shaft.
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 is to provide a high-productivity impeller having a blade shape appropriate for an air flow, and a centrifugal fan having the same.
According to an illustrative embodiment of the present invention, there is provided an impeller comprising: a lower shroud; an upper shroud; and a plurality of blades which are arranged along a circumference direction between the lower shroud and the upper shroud. The impeller is rotatable around a rotary shaft. An outside diameter of the lower shroud is equal to or smaller than an inside diameter of the upper shroud. 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.
In the above impeller, in a range where the upper shroud and the blades exist in a planar view, the upper shroud may be in contact with the blades.
In the above impeller, each of the plurality of blades may have a shape which becomes thinner as separating further from the rotary shaft.
According to another illustrative embodiment of the present invention, there is provided a centrifugal fan comprising: the above impeller; and a lower casing which is provided at a lower portion of the impeller. The lower casing has a protrusion which protrudes toward the impeller in a portion where the upper shroud exists in a planar view. Air suctioned from a suction opening is discharged outward in a radial direction of the impeller by a centrifugal force from the rotation of the impeller.
According to the above configuration, it is possible to provide a high-productivity impeller having a blade shape appropriate for an air flow, and a centrifugal fan having the same.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

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

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;

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 line A-A of FIG. 4;

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

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

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

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

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

DETAILED DESCRIPTION

Hereinafter, an illustrative embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view illustrating a centrifugal fan according to an 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 6 a at the upper portion of the lower casing 6 as shown in FIG. 2 such that the protrusion 6 a 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 6 a 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 6 a 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) 21 a for expending 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 21 a is the same as the outside diameter of the lower shroud 21. The outside diameter of the base plate 21 a 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 21 a, 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 21 a functions as an appendant lower shroud. Since the base plate 21 a 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 21 a 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.
The above-mentioned illustrative embodiment 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. An impeller comprising:

a lower shroud;

an upper shroud; and

a plurality of blades which are arranged along a circumference direction between the lower shroud and the upper shroud,

wherein the impeller is rotatable around a rotary shaft,

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.

2. The impeller according to claim 1,

wherein in a range where the upper shroud and the blades exist in a planar view, the upper shroud is in contact with the blades.

3. The impeller according to claim 1,

wherein each of the plurality of blades has a shape which becomes thinner as separating further from the rotary shaft.

4. A centrifugal fan comprising:

the impeller according to claim 1; and

a lower casing which is provided at a lower portion of the impeller,

wherein the lower casing has a protrusion which protrudes toward the impeller in a portion where the upper shroud exists in a planar view, and

wherein air suctioned from a suction opening is discharged outward in a radial direction of the impeller by a centrifugal force from the rotation of the impeller.