U.S. patent application number 13/208439 was filed with the patent office on 2012-02-23 for fan.
This patent application is currently assigned to NIDEC SERVO CORPORATION. Invention is credited to Yoshihisa KAGAWA, Osamu SEKIGUCHI.
Application Number | 20120045323 13/208439 |
Document ID | / |
Family ID | 45594221 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120045323 |
Kind Code |
A1 |
KAGAWA; Yoshihisa ; et
al. |
February 23, 2012 |
FAN
Abstract
A centrifugal fan includes an impeller including a main plate
rotating about a center axis and a plurality of vanes fixed to the
main plate in a circumferentially spaced-apart relationship, and a
bell mouth arranged at an air intake side of the impeller to define
an air inlet including a portion whose inner diameter is decreased
toward the impeller. Each of the vanes preferably includes a
protrusion protruding toward the bell mouth and extending into the
air inlet.
Inventors: |
KAGAWA; Yoshihisa; (Gumma,
JP) ; SEKIGUCHI; Osamu; (Gumma, JP) |
Assignee: |
NIDEC SERVO CORPORATION
Kiryu-shi
JP
|
Family ID: |
45594221 |
Appl. No.: |
13/208439 |
Filed: |
August 12, 2011 |
Current U.S.
Class: |
415/206 ;
416/186R; 416/223R |
Current CPC
Class: |
F04D 29/162 20130101;
F25D 2317/0681 20130101 |
Class at
Publication: |
415/206 ;
416/186.R; 416/223.R |
International
Class: |
F01D 1/04 20060101
F01D001/04; F01D 5/14 20060101 F01D005/14; F01D 5/22 20060101
F01D005/22 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2010 |
JP |
2010-182016 |
Aug 30, 2010 |
JP |
2010-192772 |
Claims
1. A centrifugal fan, comprising: an impeller including a main
plate rotating about a center axis and a plurality of vanes fixed
to the main plate in a circumferentially spaced-apart relationship;
and a bell mouth arranged at an air intake side of the impeller to
define an air inlet including a portion whose inner diameter
decreases toward the impeller, each of the vanes including a
protrusion protruding toward the bell mouth and extending into the
air inlet.
2. The fan of claim 1, wherein, when seen in a center axis
direction, each of the vanes is curved in a direction opposed to a
rotating direction of the main plate as each of the vanes extends
from a radial inner end thereof toward a radial outer end
thereof.
3. The fan of claim 1, wherein the impeller is an open impeller
that does not include a shroud that is arranged to be opposed to
the main plate with the vanes interposed therebetween.
4. The fan of claim 1, wherein the protrusion includes a tip end
surface located substantially at the same position in a center axis
direction as a diameter reduction start position where the inner
diameter of the air inlet begins to decrease toward the
impeller.
5. The fan of claim 1, wherein the protrusion includes a tip end
surface including a serration arranged to suppress the generation
of an air vortex on the tip end surface.
6. An axial flow fan, comprising: a hub rotating about a center
axis; a plurality of propeller blades fixed to an outer
circumferential surface of the hub in a circumferentially
spaced-apart relationship to rotate about the center axis together
with the hub to thereby draw air from an air intake side as one
center axis direction side and discharge the air toward an air
discharge side as the other center axis direction side, the
propeller blades including outer peripheral portions interconnected
by a ring member; and a bell mouth provided at the air intake side
with respect to the propeller blades, the bell mouth including a
portion whose inner diameter decreases toward the air discharge
side to guide the air drawn by the propeller blades toward the
propeller blades.
7. The fan of claim 6, wherein the bell mouth has a minimum inner
diameter equal to or smaller than an inner diameter of an air
intake side end of the ring member.
8. The fan of claim 6, wherein the ring member is provided at outer
peripheral ends of the propeller blades.
9. The fan of claim 6, wherein the ring member includes a portion
arranged at the air intake side to have a diameter increasing
toward the air intake side.
10. The fan of claim 6, further comprising: a flow straightening
member provided inside the bell mouth to straighten a flow of the
air drawn by the propeller blades.
11. The fan of claim 6, further comprising: a base member provided
at the air discharge side with respect to the hub to rotatably
support the hub; wherein the base member and the bell mouth are
interconnected by a plurality of connecting members arranged at a
radial outer side of the propeller blades in a circumferentially
spaced-apart relationship with one another, only the connecting
members being provided at the radial outer side of the propeller
blades.
12. The fan of claim 6, wherein the ring member includes an air
intake side end that is substantially flush with air intake side
ends of the propeller blades in a center axis direction and an air
discharge side end spaced apart in the center axis direction from
the air intake side ends of the propeller blades by about 50%
through about 80% of a center axis direction length of the
propeller blades.
13. The fan of claim 6, further comprising: a guide portion
provided at the air discharge side with respect to the propeller
blades to guide the air discharged toward the air discharge side by
the propeller blades so that the air flows radially outwards.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a fan and more specifically
to a fan that is especially suitable for use in a narrow space,
such as a cooling air path of a refrigerator, for example.
[0003] 2. Description of the Related Art
[0004] Household refrigerators are typically configured to send air
that has been cooled in a cooler into storage compartments (a
freezing compartment and a chilling compartment, for example) to
thereby cool the inside of the storage compartments. In this case,
as disclosed in, e.g., U.S. Pat. No. 7,331,193, a fan is arranged
within a duct which extends toward a cooler to circulate air
through storage compartments. In order to make the storage
compartments as large as possible, the duct is designed to have a
narrow space within which the fan needs to be arranged.
[0005] Typically, a centrifugal fan or an axial flow fan is used as
the fan arranged within the duct as mentioned above. The
centrifugal fan includes an impeller, which has a circular main
plate rotating about a center axis and a plurality of vanes fixed
to the main plate in a circumferentially spaced-apart relationship,
and a bell mouth arranged at the air intake side of the impeller to
define an air inlet. The axial flow fan includes a hub rotating
about a center axis, a plurality of propeller blades fixed to an
outer circumferential surface of the hub in a circumferentially
spaced-apart relationship to rotate about the center axis together
with the hub to thereby draw air from one axial side and discharge
the air toward the other axial side, and a housing having an inner
circumferential surface surrounding the outer ends of the propeller
blades.
[0006] In the case of the centrifugal fan, depending on the service
space thereof, there is a need to increase the gap (tip clearance)
between the bell mouth (especially, the portion of the air inlet
closest to the vanes) and the vanes. For example, if a centrifugal
fan having a narrow tip clearance is used in a refrigerator, there
is a possibility that the vanes will become stuck to the bell mouth
due to frost. The reason for increasing the tip clearance is to
avoid this possibility. In case of the axial flow fan, if the gap
(tip clearance) between the outer ends of the propeller blades and
the inner circumferential surface of the housing is small, it is
likely that the propeller blades are stuck to the inner
circumferential surface of the housing by frost and are unable to
feed air into the storage compartments. Thus, there is a need to
increase the amount of tip clearance.
[0007] However, if the amount of tip clearance is increased in the
centrifugal fan, a large space will exist between the inner end of
the air inlet and the impeller. This space serves as a negative
pressure space in which the flow of air becomes unstable. Due to
the increase in the volume of this space, a problem is caused in
which noises become greater during the operation of the centrifugal
fan (during the rotation of the impeller). If the amount of tip
clearance is increased in the axial flow fan, air tends to flow
backwards from a discharge side to an intake side in the tip
clearance between the outer ends of the propeller blades and the
inner circumferential surface of the housing. This poses a problem
of impairing the characteristic relationship between a
discharge-side static pressure (P) and a flow rate (Q) in the axial
flow fan and increasing the noises.
SUMMARY OF THE INVENTION
[0008] Preferred embodiments of the present invention preferably
provide a configuration capable of suppressing impairment of the
noise performance of a centrifugal fan installed in a narrow space
even when the amount of tip clearance between a bell mouth and
vanes is increased.
[0009] Preferred embodiments of the present invention also
preferably provide a configuration capable of minimizing an
impairment of the PQ characteristic (as mentioned above, P
corresponds to static pressure and Q corresponds to a flow rate)
and the noise performance of an axial flow fan installed in a
narrow space.
[0010] In accordance with one preferred embodiment of the present
invention, a centrifugal fan includes an impeller including a main
plate rotating about a center axis and a plurality of vanes fixed
to the main plate in a circumferentially spaced-apart relationship;
and a bell mouth arranged at an air intake side of the impeller to
define an air inlet including a portion whose inner diameter is
decreased toward the impeller, each of the vanes including a
protrusion protruding toward the bell mouth and extending into the
air inlet.
[0011] With the centrifugal fan of this configuration, the
protrusion of each of the vanes extends into the air inlet of the
bell mouth. The drawing in of the air in the inner portion of the
air inlet is accelerated by the protrusion. This works to stabilize
the airflow in the inner portion of the air inlet even when the
amount of tip clearance is set to be larger, consequently reducing
the volume of a negative pressure space in which the airflow
becomes unstable. Accordingly, it is possible to suppress an
increase in noises generated during the operation of the
centrifugal fan.
[0012] In accordance with another preferred embodiment of the
present invention, an axial flow fan includes a hub rotating about
a center axis; a plurality of propeller blades fixed to an outer
circumferential surface of the hub in a circumferentially
spaced-apart relationship to rotate about the center axis together
with the hub to thereby draw air from an air intake side as one
center axis direction side and discharge the air toward an air
discharge side as the other center axis direction side, the
propeller blades including outer peripheral portions interconnected
by a ring member; and a bell mouth provided at the air intake side
with respect to the propeller blades, the bell mouth including a
portion whose inner diameter is decreased toward the air discharge
side to guide the air drawn by the propeller blades toward the
propeller blades.
[0013] With the axial flow fan of this configuration, even if a
wall exists near the air intake side of the axial flow fan, the air
drawn through the inside of the bell mouth is guided by the bell
mouth toward the propeller blades so that the air can smoothly flow
in a center axis (fan axis) direction. This works to reduce any
separation of airflow caused by the increase in an attack angle of
the propeller blades. In cooperation with the bell mouth, the ring
member serves to guide the flow of the air drawn by the propeller
blades so that the air passing through the ring member can flow in
the center axis direction.
[0014] In a case where the outer peripheral ends of the propeller
blades are surrounded by a cylindrical housing, the members
arranged around the bell mouth to support the bell mouth serves to
cover the air intake side end of the clearance space between the
outer peripheral ends of the propeller blades and the inner
circumferential surface of the housing. Therefore, even if the
amount of tip clearance is made greater, it is possible to prevent
the air from flowing backwards from the air discharge side toward
the air intake side through the clearance space.
[0015] In accordance with the preferred embodiments of the present
invention, it is also possible for the ring member to prevent the
air flowing through the inside of the ring member from leaking
radially outwards. Accordingly, even if the axial flow fan is
arranged in a narrow space where the propeller blades risk being
held stationary by frost and where walls are present near the air
intake side and the air discharge side of the axial flow fan, it is
possible to suppress impairment of the PQ characteristic and to
also suppress any increase in noises.
[0016] The above and other elements, features, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a sectional view showing a centrifugal fan
according to a first preferred embodiment of the present invention,
which is arranged in a fan arrangement space of a refrigerator.
[0018] FIG. 2 is a front view of the centrifugal fan shown in FIG.
1, which is seen from an air intake side.
[0019] FIG. 3 is a perspective view of the centrifugal fan shown in
FIG. 1, which is obliquely seen from the air intake side.
[0020] FIG. 4 is a front view of an impeller of the centrifugal fan
shown in FIG. 1, which is seen from the air intake side.
[0021] FIG. 5 is a perspective view of the impeller of the
centrifugal fan shown in FIG. 1, which is obliquely seen from the
air intake side.
[0022] FIG. 6 is a perspective view showing a modified example of
the impeller of the centrifugal fan shown in FIG. 1.
[0023] FIG. 7 is a graph representing the PQ characteristics and
the noise characteristics of the centrifugal fan according to the
first preferred embodiment and the centrifugal fan according to a
comparative example.
[0024] FIG. 8 is a section view showing an axial flow fan according
to a second preferred embodiment of the present invention, which is
arranged in a fan arrangement space of a refrigerator.
[0025] FIG. 9 is a front view of an impeller (a hub and propeller
blades) of the axial flow fan shown in FIG. 8, which is seen from
an intake side.
[0026] FIG. 10 is a perspective view of a bell mouth defining
member of the axial flow fan shown in FIG. 8, which is obliquely
seen from an intake side.
[0027] FIG. 11 is a front view showing a modified example of the
axial flow fan shown in FIG. 8, in which support legs are replaced
by static vanes.
[0028] FIG. 12 is a section view showing a modified example of the
ring member of the axial flow fan shown in FIG. 8.
[0029] FIG. 13 is a perspective view showing a modified example of
the flow straightening members of the axial flow fan shown in FIG.
12.
[0030] FIG. 14 is a section view showing an axial flow fan
according to a further preferred embodiment of the present
invention, which is arranged in a fan arrangement space of a
refrigerator.
[0031] FIG. 15 is a graph representing the PQ characteristics and
the noise characteristics of the axial flow fan shown in FIG. 8 and
the axial flow fans according to comparative examples.
[0032] FIG. 16 is a graph representing the PQ characteristics and
the noise characteristics of the axial flow fan shown in FIG. 8 and
the axial flow fan according to another comparative example.
[0033] FIG. 17 is a graph representing the PQ characteristics and
the noise characteristics of the axial flow fan shown in FIG. 8 and
the axial flow fans according to further comparative examples.
[0034] FIG. 18 is a graph representing the PQ characteristics and
the noise characteristics of the axial flow fan shown in FIG. 8 and
the axial flow fans according to still further comparative
examples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Preferred Embodiment
[0035] FIG. 1 shows a centrifugal fan 1 according to a first
preferred embodiment of the present invention. In this preferred
embodiment, the centrifugal fan 1 is arranged to send a cooling air
toward a freezing compartment 51 of a refrigerator and is arranged
in a fan arrangement space 52 defined inwards of the freezing
compartment 51. At the inner side of the fan arrangement space 52,
there is defined a cooler arrangement space 53 in which a cooler
(not shown) and the like are arranged. The fan arrangement space 52
and the cooler arrangement space 53 are divided by a first
partition wall 54 extending in the vertical direction. The freezing
compartment 51 and the fan arrangement space 52 are divided by a
second partition wall 55 extending parallel or substantially
parallel to the first partition wall 54 in the vertical
direction.
[0036] In the fan arrangement space 52, an attachment member 57 for
attachment of the centrifugal fan 1 is provided to extend in the
vertical direction. A first path 58 through which the cooling air
passes is defined between the attachment member 57 and the first
partition wall 54. A second path 59 through which the cooling air
passes is defined between the attachment member 57 and the second
partition wall 55. The first path 58 and the second path 59 extend
in the vertical direction perpendicular or substantially
perpendicular to the center axis J of a main plate 3 to be set
forth later.
[0037] The cooling air cooled in the cooler is fed from the cooler
arrangement space 53 to the first path 58 of the fan arrangement
space 52. The cooling air flows along the first path in the
vertical direction and reaches a position where the centrifugal fan
1 exists. Then, the cooling air is sent to the second path 59 of
the fan arrangement space 52 by the centrifugal fan 1. After
flowing through the second path 59 in the vertical direction, the
cooling air is blown into the freezing compartment through an air
outlet (not shown) defined in the second partition wall 55.
Hereinafter, the cooling air will be just referred to as "air".
[0038] As shown in FIGS. 1 through 5, the centrifugal fan 1 of the
present preferred embodiment preferably includes a main plate 3
rotating about the center axis J extending in the horizontal
direction or substantially in the horizontal direction and an
impeller 2 having a plurality of vanes 4 (preferably eleven vanes
in the present preferred embodiment) fixed to the main plate 3 in a
circumferentially spaced-apart relationship. The impeller 2
preferably is an open impeller that does not have a shroud opposed
to the main plate 3 across the vanes 4. Hereinafter, the center
axis J of the main plate 3 (or the center axis of the impeller 2)
will be just referred to as "center axis J". The direction in which
the center axis J extends (the left-right direction in FIG. 1) will
be referred to as "center axis direction". The direction
perpendicular or substantially perpendicular to the center axis
direction will be referred to as "radial direction".
[0039] The vanes 4 rotate about the center axis J together with the
main plate 3. The vanes 4 draw the air from the air intake side
(the left side in FIG. 1, i.e., the side of the first path 58),
which is one side of the impeller 2 in the center axis direction
(the opposite side from the main plate 3), and discharge the air
radially outwards (into the second path 59) at the radial outer end
of the impeller 2 (see the airflow indicated by arrows in FIG.
1).
[0040] As shown in FIGS. 4 and 5, the vanes 4 are interconnected by
a ring member 5 at the air intake side and at the radial outer ends
thereof. The main plate 3, the vanes 4 and the ring member 5 are
preferably made of, e.g., a resin, and are provided as a single
monolithic piece.
[0041] The central portion of the main plate 3 protrudes toward the
air intake side. As a consequence, a space in which a motor 11
arranged to rotate the main plate 3 can be arranged is defined at
the opposite side of the main plate 3 from the air intake side (at
the right side in FIG. 1). The motor 11 preferably includes a rotor
12 rotating about the center axis J and a stator 13 arranged inside
the rotor 12. The rotor 12 preferably includes a cylindrical rotor
holder 15 closed only at the air intake side of the axially
opposite sides thereof, field magnets 16 fixed to the inner surface
of a sidewall portion of the rotor holder 15, and a shaft 17 fixed
to the central area of the air intake side end portion of the rotor
holder 15 to rotate together with the rotor holder 15.
[0042] The shaft 17 extends from the air intake side end portion of
the rotor holder 15 toward the opposite side to the air intake side
and is rotatably supported, preferably by a couple of bearings 20.
The air intake side end portion of the rotor holder 15 is fixed to
the portion of the main plate 3 protruding toward the air intake
side. Accordingly, the main plate 3 rotates about the center axis J
together with the rotor holder 15 (the rotor 12).
[0043] A substantially disc-shaped flat base member 21 is arranged
at the opposite side of the rotor holder 15 from the air intake
side. A cylindrical bearing support portion 22 extends toward the
air intake side from the center portion of the air intake side
surface of the base member 21. The bearings 20 are fixed to the
inner surface of the bearing support portion 22 at two points
spaced apart in the center axis direction. The base member 21 is
held by a below-described bell mouth support member 32 through
connecting members 35, which are also described later.
[0044] The stator 13 preferably includes a substantially
cylindrical stator core 25 installed on the outer circumferential
surface of the bearing support portion 22 and defined by steel
plates laminated one above another along the center axis direction
and coils 26 wound around the stator core 25. A board support
portion 27 arranged to support a circuit board 28 is installed on
the opposite surface of the stator 13 from the air intake side.
When a drive current is supplied to the coils 26 via the circuit
board 28, rotation torque is generated between the field magnets 16
and the stator core 25 whereby the impeller (the main plate 3 and
the vanes 4) will be caused to rotate about the center axis J. The
rotating direction of the impeller 2 is indicated by an arrow R in
FIGS. 4 and 5 (This also holds true in FIG. 6 showing a modified
example).
[0045] In the present preferred embodiment, the centrifugal fan 1
is preferably a turbo fan, which means that the vanes 4 of the
impeller 2 have a shape of turbo fan vanes. More specifically, when
seen in the center axis direction, each of the vanes 4 is curved
against the rotating direction R of the impeller 2 (the main plate
3) as it extends from a radial inner end thereof toward a radial
outer end thereof.
[0046] At the air intake side of the impeller 2, there is arranged
a bell mouth 31 including a portion whose inner diameter is
decreased toward the impeller 2. The bell mouth 31 preferably
includes a bell mouth support member 32 that supports the bell
mouth 31 in the outer periphery thereof as a single monolithic
piece. The bell mouth 31 includes an air inlet 31a whose center
coincides with the center axis J. In the present preferred
embodiment, the air inlet 31a is arranged such that the inner
diameter thereof becomes smaller toward the impeller 2 over the
entire center axis direction portion. Alternatively, a portion of
the air inlet 31a in the center axis direction (especially, the end
portion of the air inlet 31a near the impeller 2) may have an inner
diameter kept constant or increased toward the impeller 2, and the
remaining portion of the air inlet 31a may have an inner diameter
decreased toward the impeller 2.
[0047] The base member 21 and the bell mouth support member 32 are
interconnected by a plurality of connecting members 35 (preferably
four connecting members in the present preferred embodiment, for
example) arranged at the opposite side of the impeller 2 from the
air intake side and at the radial outer side of the impeller 2 in a
circumferentially spaced-apart relationship with one another. Thus,
the base member 21 is supported on the bell mouth support member 32
through the connecting members 35. In the outer edge portion of the
bell mouth support member 32, there is provided a flange portion
32a through which the centrifugal fan 1 is attached to the
attachment member 57. When the centrifugal fan 1 is in this
attachment state, the bell mouth support member 32 (the bell mouth
31) is positioned in the first path 58 while the air-discharging
radial outer end of the impeller 2 is situated in the second path
59. In the air intake side radial inner end portions of the vanes 4
(in the portions of the vanes 4 opposed to the air inlet 31a),
protrusions 4a protruding toward the bell mouth 31 and extending
into the air inlet 31a are provided.
[0048] In this regard, the size of the gap (tip clearance) between
the bell mouth 31 and the vanes 4 including the protrusions 4a is
set at such a dimension that the vanes 4 will not become stuck to
the bell mouth 31 due to frost. In a hypothetical case in which the
protrusions 4a are absent with the tip clearance set at this
dimension, noises are increased during the operation of the
centrifugal fan 1 (during the rotation of the impeller 2). In the
present preferred embodiment, the protrusions 4a preferably are
defined in the vanes 4. Therefore, even if the tip clearance is set
at the dimension noted above, it is possible to suppress the
increase in noises during the operation of the centrifugal fan 1.
In other words, the drawing of the air in the inner portion of the
air inlet 31a is accelerated by providing the protrusions 4a. This
helps stabilize the airflow in the inner portion of the air inlet
31a even when the tip clearance is set at the dimension noted
above, consequently reducing the volume of a negative pressure
space in which the airflow becomes unstable. Accordingly, it is
possible to suppress the increase in noises during the operation of
the centrifugal fan 1.
[0049] It is preferred that the tip end surfaces of the protrusions
4a of the vanes 4 be located substantially in the same positions in
the center axis direction as the diameter reduction start position
where the inner diameter of the air inlet 31a begins to decrease
toward the impeller 2 (the air intake side end of the air inlet 31a
in the present preferred embodiment). This makes it possible to
reduce the volume of a negative pressure space in which the airflow
becomes unstable. Alternatively, the deviation amount in the center
axis direction between the positions of the tip end surfaces of the
protrusions 4a and the diameter reduction start position may be
greater than zero and equal to or smaller than a specified value.
The specified value may preferably be, e.g., about 10% of the
center axis direction length of the air inlet 31a. More preferably,
the tip end surfaces of the protrusions 4a are arranged beyond the
diameter reduction start position, and the deviation amount in the
center axis direction between the positions of the tip end surfaces
of the protrusions 4a and the diameter reduction start position is
greater than zero and equal to or smaller than the specified value
(see FIG. 1). In other words, it is particularly preferable that
the protrusions 4a protrude beyond the air inlet 31a into the air
intake side external space (the first path 58) by the specified
value or less.
[0050] As shown in FIG. 6, serrations 4b arranged to suppress the
generation of a vortex of the air on the tip end surfaces of the
protrusions 4a of the vanes 4 may be provided on the tip end
surfaces of the protrusions 4a. The serrations 4b are preferably a
series of notches continuously defined on the tip end surfaces of
the protrusions 4a along the longitudinal direction of the vanes 4.
Since the flow of the air drawn by the impeller 2 is straightened
by the serrations 4b, the airflow in the inner portion of the air
inlet 31a becomes stable. This enhances the noise performance of
the centrifugal fan 1.
[0051] While the first preferred embodiment of the present
invention has been described above, the shape of the vanes 4 of the
impeller 2 is not limited to the shape of the turbo fan vanes and
could instead be provided in any desirable shape. For example, as
an alternative example, the vanes 4 may extend straight in the
radial direction (all the vanes 4 may be arranged in a radial
shape). Additionally, the impeller 2 is not limited to the open
impeller but may be a closed impeller including a casing provided
with a shroud. In the preferred embodiment described above, the
centrifugal fan 1 is used to blow the cooling air into the freezing
compartment 51 of a refrigerator. However, the present invention is
not limited thereto. As an alternative example, the centrifugal fan
1 could instead be used as a blower arranged to cool electronic
devices. If the centrifugal fan 1 is used in an application where
there is a need to increase the tip clearance as in the preferred
embodiment described above, it is possible to produce a great
silencing effect.
[0052] In the preferred embodiment described above, the first
partition wall 54 preferably is present near the air intake side of
the centrifugal fan 1 (this will be referred to as "with wall" in
the following examples and comparative examples). However, the
present invention is also applicable to a case where the first
partition wall 54 (and even the second partition wall 55) does not
exist (This will be referred to as "without wall" in the following
examples and comparative examples). In this case, even if the tip
clearance is made greater, it is possible to suppress the increase
in noises during the operation of the centrifugal fan 1.
[0053] A centrifugal fan like the one described above in respect of
the foregoing preferred embodiment was prepared to evaluate the
change of the static pressure against the flow rate (air flow
rate), i.e., the PQ characteristic, at the air discharge side and
the change of the noise level against the flow rate (air flow
rate), i.e., the noise characteristic, at the air discharge side.
In the centrifugal fan thus prepared, the vanes 4 are provided with
the protrusions 4a. The tip end surfaces of the protrusions 4a is
arranged beyond the diameter reduction start position. The
deviation amount in the center axis direction between the positions
of the tip end surfaces of the protrusions 4a and the diameter
reduction start position is equal to or smaller than the specified
value. The tip clearance is set at the same dimension as in the
foregoing preferred embodiment. The PQ characteristic and the noise
characteristic were evaluated with respect to a case (an test
example with wall) where the centrifugal fan is arranged in a space
between two walls like the first partition wall 54 and the second
partition wall 55 of the foregoing preferred embodiment and a case
(an test example without wall) where the centrifugal fan is
arranged in a space having no wall.
[0054] For the purpose of comparison, a centrifugal fan in which
the protrusions 4a are not provided in the vanes 4 (other
configurations of which remain the same as those of the test
example mentioned just above) was prepared. The PQ characteristic
and the noise characteristic were evaluated with respect to a case
(a comparative example with wall) where the centrifugal fan is
arranged in a space between two walls and a case (a comparative
example without wall) where the centrifugal fan is arranged in a
space having no wall.
[0055] The results of evaluation are shown in FIG. 7. Comparison of
the test example (with wall) and the comparative example (with
wall) reveals that, over the entire flow rate sections, the noise
level in the test example (with wall) is lower than that in the
comparative example (with wall). It can be seen that little
difference in the PQ characteristic exists between the test example
(with wall) and the comparative example (with wall), which means
that the centrifugal fans of the test example (with wall) and the
comparative example (with wall) exhibit desired PQ performance.
Comparison of the test example (without wall) and the comparative
example (without wall) reveals that, over most of the flow rate
sections, the noise level in the test example (without wall) is
lower than that in the comparative example (without wall). The
centrifugal fans of the test example (without wall) and the
comparative example (without wall) exhibit desired PQ performance.
Accordingly, it can be appreciated that, even if the tip clearance
is made greater, the noises generated during the operation of the
centrifugal fan can be reduced by providing the protrusions 4a in
the vanes 4.
Second Preferred Embodiment
[0056] Next, an axial flow fan 101 according to a second preferred
embodiment of the present invention will be described with
reference to FIGS. 8 through 11. In the present preferred
embodiment, the axial flow fan 101 is preferably arranged to send a
cooling air toward a freezing compartment 151 of a refrigerator and
is arranged in a narrow fan arrangement space 152 defined inwards
of the freezing compartment 151. At the inner side of the fan
arrangement space 152, there is defined a cooler arrangement space
153 in which a cooler (not shown) and the like are arranged. The
fan arrangement space 152 and the cooler arrangement space 153 are
divided by a first partition wall 154 extending substantially in
the vertical direction. The freezing compartment 151 and the fan
arrangement space 152 are divided by a second partition wall 155
extending parallel or substantially parallel to the first partition
wall 154 in the vertical direction.
[0057] In the fan arrangement space 152, an attachment member 157
arranged to attach the axial flow fan 101 is provided to extend in
the vertical direction or substantially in the vertical direction.
A first path 158 through which the cooling air passes is defined
between the attachment member 157 and the first partition wall 154.
A second path 159 through which the cooling air passes is defined
between the attachment member 157 and the second partition wall
155. The first path 158 and the second path 159 extend in the
vertical direction perpendicular or substantially perpendicular to
the fan axis (the center axis J to be set forth later).
[0058] The cooling air cooled in the cooler is fed from the cooler
arrangement space 153 to the first path 158 of the fan arrangement
space 152. The cooling air flows along the first path 158 in the
vertical direction and reaches a position where the axial flow fan
101 exists. Then, the cooling air is sent to the second path 159 of
the fan arrangement space 152 by the axial flow fan 101. After
flowing through the second path 159 in the vertical direction, the
cooling air is blown into the freezing compartment 151 through an
air outlet (not shown) defined in the second partition wall 155.
Hereinafter, the cooling air will be just referred to as "air".
[0059] In the present preferred embodiment, the axial flow fan 101
preferably includes a cylindrical hub 102 rotating about the center
axis J extending in the horizontal direction or substantially in
the horizontal direction and a plurality of propeller blades 103
(preferably seven propeller blades in the present preferred
embodiment as shown in FIG. 7) fixed to the outer circumferential
surface of the hub 102 at a regular interval in the circumferential
direction. The propeller blades 103 are preferably defined by a
single monolithic piece with the hub 102. The hub 102 and the
propeller blades 103 are collectively referred to as "impeller".
Hereinafter, the center axis J of the hub 102 will be just referred
to as "center axis J". The direction in which the center axis J
extends (the left-right direction in FIG. 8) will be referred to as
"center axis direction". The direction perpendicular to the center
axis direction will be referred to as "radial direction".
[0060] The propeller blades 103 rotate about the center axis J
together with the hub 102. The propeller blades 103 draw the air
from the air intake side (the left side in FIG. 8, i.e., the side
of the first path 158), which is one side in the center axis
direction, and discharge the air toward the air discharge side (the
right side in FIG. 8, i.e., the side of the second path 159), which
is the other side in the center axis direction. The hub 102
preferably has a cup shape opened only at the air discharge side of
the center axis direction opposite sides thereof. A shaft 105 is
fixed to the central area of the air intake side end portion of the
hub 102 to rotate together with the hub 102. The shaft 105 extends
from the air intake side end portion of the hub 102 toward the air
discharge side along the center axis J.
[0061] A base member 110 is arranged at the air discharge side of
the hub 102. The base member 110 is provided into a flat disc shape
having substantially the same outer diameter as that of the hub
102. A cylindrical bearing support portion 111 extending toward the
air intake side is preferably defined by provided as a single
monolithic piece with the central portion of the air intake side
surface of the base member 110. A sleeve beating 112 is preferably
fixed to the inner surface of the bearing support portion 111. The
shaft 105 is inserted into, and rotatably supported by, the sleeve
bearing 112. This enables the base member 110 to rotatably support
the hub 102. The base member 110 is held by a below-mentioned
housing 130 through support legs 131 to be set forth below.
[0062] A motor 115 arranged to rotate the hub 102 is mounted
between the inner circumferential surface of the hub 102 and the
outer circumferential surface of the bearing support portion 111.
The motor 115 preferably includes a rotor 116 installed on the
inner circumferential surface of the hub 102 and a stator 120
installed on the outer circumferential surface of the bearing
support portion 111. The rotor 116 preferably includes a magnet
holder 117 fixed to the inner circumferential surface of the hub
102 and rotor magnets 118 held by the magnet holder 117. The stator
120 preferably includes a substantially cylindrical stator core 121
defined by steel plates laminated one above another along the
center axis direction and coils 122 wound around the stator core
121. If a drive current is supplied to the coils 122, rotation
torque is generated between the rotor magnets 118 and the stator
core 121 whereby the hub 102 and the propeller blades 103 (the
impeller) can rotate about the center axis J. The rotating
direction of the hub 102 and the propeller blades 103 is indicated
by an arrow R in FIGS. 9 through 11 and 13.
[0063] As shown in FIG. 9, the propeller blades 103 are provided by
forward-swept blades in the present preferred embodiment. In other
words, when the propeller blades 103 are seen in the center axis
direction, the intersection point P1 between the leading edge 103a,
i.e., the front end in the rotating direction R, of each of the
propeller blades 103 and the outer circumferential edge 103b of
each of the propeller blades 103 is positioned ahead of the
intersection point P2 between the leading edge 103a and the outer
circumferential surface of the hub 102 in the rotating direction
R.
[0064] The outer peripheral portions of the propeller blades 103
are interconnected by a cylindrical ring member 125. In the present
preferred embodiment, the ring member 125 is attached to the outer
peripheral ends of the propeller blades 103 in a coaxial
relationship with the hub 102 (The center of the ring member 125
lies on the center axis J). The ring member 125 is preferably
defined by a single monolithic piece with the propeller blades 103.
In cooperation with a below-mentioned bell mouth 135, the ring
member 125 serves to guide the flow of the air drawn by the
propeller blades 103 so that the air passing through the ring
member 125 can flow in the center axis direction. Moreover, the
ring member 125 serves to prevent the air flowing inside thereof
from leaking radially outwards from the outer peripheral ends of
the propeller blades 103.
[0065] The air intake side end of the ring member 125 is
substantially flush with the air intake side ends of the propeller
blades 103. On the other hand, the air discharge side end of the
ring member 125 is spaced apart in the center axis direction from
the air intake side ends of the propeller blades 103 by about 50%
through about 80% of the center axis direction length of the
propeller blades 103. In other words, the ring member 125 is
installed near the air intake side ends of the propeller blades 103
in the center axis direction.
[0066] The center axis direction section of the ring member 125 is
not limited to the section near the air intake side ends of the
propeller blades 103. Alternatively, the ring member 125 may be
arranged in the section near the air discharge side ends of the
propeller blades 103, in the axially middle portions of the
propeller blades 103 or in the axially entire portions of the
propeller blades 103. However, if the axial flow fan 101 is
arranged in the narrow fan arrangement space 152 as in the present
preferred embodiment, it is preferred that the ring member 125 be
installed near the air intake side ends of the propeller blades 103
in the center axis direction. More specifically, the flow of the
air discharged by the propeller blades 103 is finally struck
against the second partition wall 55 positioned near the air
discharge side of the axial flow fan 101 and is sharply curved
radially outwards. If the ring member 125 is not provided in the
air discharge side end portions of the propeller blades 103, the
air is discharged toward the air discharge side in a direction
inclined to the outwardly radial direction. Accordingly, the flow
of the air discharged by the propeller blades 103 is gently curved
radially outwards under the guidance of a guide portion 141 to be
set forth later.
[0067] It is not always necessary to provide the ring member 125 at
the outer peripheral ends of the propeller blades 103.
Alternatively, the ring member 125 may be installed in the outer
peripheral portion (e.g., in the position spaced apart from the
roots of the propeller blades 103, i.e., the outer circumferential
surface of the hub 102, by about 70% or more and less than 100% of
the length of the propeller blades 103). It is however preferred
that the ring member 125 be provided at the outer peripheral ends
of the propeller blades 103 as in the present preferred embodiment.
This ensures that all the air drawn to the propeller blades 103 can
flow toward the air discharge side without leaking radially
outwards from the outer peripheral ends of the propeller blades
103.
[0068] The axial flow fan 101 preferably further includes a
substantially cylindrical housing 130 installed in a coaxial
relationship with the hub 102 to surround the outer peripheral ends
of the propeller blades 103. The size of the gap (tip clearance)
between the outer circumferential surface of the ring member 125
and the inner circumferential surface of the housing 130 is
preferably set at such a dimension that the propeller blades 103
will not become stuck to the inner circumferential surface of the
housing 130 due to frost.
[0069] A plurality of support legs 131 extending straight in the
radial direction is arranged in the air discharge side opening of
the housing 130 at a regular interval along the circumferential
direction (The number of the support legs 131 may be equal to or
may differ from the number of the propeller blades 103 although
eight support legs are preferably included in the illustrated
example). The radial outer ends of the support legs 131 are fixed
to the air discharge side end portion of the inner circumferential
surface of the housing 130. The radial inner ends of the support
legs 131 are secured to the outer circumferential surface of the
base member 110.
[0070] FIG. 11 shows a modified example of the housing 130 in which
the support legs 131 are replaced by static vanes 131'. However,
the shape of the housing 130 remains the same in the modified
example and the present preferred embodiment. Referring now to FIG.
11, the contour of the housing 130 has a substantially rectangular
shape when seen in the center axis direction. Near the four corner
portions of the housing 130, there are provided fixing portions
130a to which a below-mentioned bell mouth defining member 136 is
fixed. The fixing portions 130a have thread holes 130b to which
screws, for example, are fitted to fix the bell mouth defining
member 136 in place.
[0071] A bell mouth 135, by which the air drawn by the propeller
blades 103 is guided toward the propeller blades 103, is provided
at the air intake side of the propeller blades 103 (more
specifically, at the axially outer side of the housing 130 and near
the air intake side opening of the housing 130). The bell mouth 135
includes a portion whose inner diameter becomes smaller toward the
air discharge side. The bell mouth 135 is defined in the portion of
the bell mouth defining member 136 other than the outer peripheral
portion. The bell mouth defining member 136 is fixed to the housing
130 so that the bell mouth 135 can be coaxial with the hub 102.
[0072] As shown in FIG. 10, the bell mouth defining member 136 has
a substantially rectangular shape when seen in the center axis
direction. Near the four corner areas of the air discharge side
surface of the bell mouth defining member 136, bosses 136a are
arranged in a corresponding relationship with the four fixing
portions 130a of the housing 130 to protrude toward the air
discharge side (see FIG. 8). The tip end surfaces of the bosses
136a make contact with the fixing portions 130a. Through-holes 136b
through which the screws can pass are defined in the center
portions of the bosses 136a. The bell mouth defining member 136 is
fixedly secured to the housing 130 by inserting the screws through
the through-holes 136b and fitting the screws to the thread holes
130b. In this manner, the outer peripheral portion of the bell
mouth defining member 136 serves to support the bell mouth 135.
[0073] The bell mouth defining member 136 has a sidewall portion
136c extending toward the air discharge side from the entire
peripheral edge portion of the air discharge side surface thereof.
The air intake side end portion of the housing 130 is fitted to the
inside of the sidewall portion 136c. The sidewall portion 136c is
fitted and secured to the opening of the attachment member 157. The
housing 130 is fixed to the attachment member 157 through the bell
mouth defining member 136. Alternatively, the housing 130 may be
directly fixed to the attachment member 157.
[0074] In the manner described above, the axial flow fan 101 is
attached and fixed to the attachment member 157. In the attached
state, the bell mouth defining member 136 (the bell mouth 135) is
positioned in the first path 158 and is opposed to the first
partition wall 154. On the other hand, the air discharge side
opening of the housing 130 is positioned in the second path 159 and
is opposed to the second partition wall 155.
[0075] Despite the existence of the first partition wall 154 near
the air intake side of the axial flow fan 101, the air drawn
through the inside of the bell mouth 135 (the inside of the portion
having an inner diameter decreased toward the air discharge side)
is guided by the bell mouth 135 toward the propeller blades 103 so
that the air can smoothly flow in the center axis direction. This
helps reduce separation of airflow caused by the increase in an
attack angle of the propeller blades 103. The outer peripheral
portion of the bell mouth defining member 136 (including the
sidewall portion 136c) serves to cover the air intake side end of
the clearance space between the outer circumferential surface of
the ring member 125 and the inner circumferential surface of the
housing 130. Therefore, even if the tip clearance is made greater,
the air is prevented from flowing backwards from the air discharge
side toward the air intake side through the clearance space.
[0076] In the present preferred embodiment, the minimum inner
diameter of the bell mouth 135 (the inner diameter of the air
discharge side end of the bell mouth 135) is preferably set to be
equal to or smaller than the inner diameter of the air intake side
end of the ring member 125. This makes it possible to introduce all
the air drawn through the inside of the bell mouth 135 into the
ring member 125. In order to smoothly draw the air into the ring
member 125 as much as possible, it is preferred that the minimum
inner diameter of the bell mouth 135 be equal to the inner diameter
of the air intake side end of the ring member 125 or smaller than
or approximate to the inner diameter of the air intake side end of
the ring member 125.
[0077] As shown in FIG. 10, a plurality of flow straightening
members 137 extending in the radial direction to straighten the
flow of the air drawn by the propeller blades 103 is arranged
inside the bell mouth 135 at a regular interval along the
circumferential direction (The number of the flow straightening
members 137 may be equal to or may differ from the number of the
propeller blades 103 although nine flow straightening members are
preferably employed in the illustrated example). The radial outer
ends of the flow straightening members 137 are fixed to the inner
circumferential surface of the bell mouth 135. The radial inner
ends of the flow straightening members 137 are secured to the outer
circumferential surface of a flat disc-shaped central portion 138
having an outer diameter substantially equal to that of the hub
102. The flow straightening members 137 and the central portion 138
are preferably defined by a single monolithic piece together with
the bell mouth 135 (the bell mouth defining member 136). When seen
in the center axis direction, each of the flow straightening
members 137 is curved against the rotating direction R as it
extends from a radial inner end thereof toward a radial outer end
thereof. The flow straightening members 137 act to reduce
turbulence of the airflow drawn through the inside of the bell
mouth 135.
[0078] The guide portion 141, by which the air discharged toward
the air discharge side by the propeller blades 103 is guided to
flow radially outwards, is arranged at the air discharge side of
the propeller blades 103 (between the air discharge side surface of
the base member 110 and the second partition wall 155). The guide
portion 141 is defined by the conical surface of a conical guide
member 142 fixed to the air discharge side surface of the base
member 110. The guide portion 141 obliquely extends radially
outwards toward the air discharge side. The guide portion 141 is
arranged to smoothly guide the air discharged by the propeller
blades 103 to flow radially outwards.
[0079] A flow path defining member 143 cooperating with the guide
portion 141 to define a flow path of the air discharged by the
propeller blades 103 is arranged along the full perimeter of the
air discharge side end portion of the outer circumferential surface
of the housing 130. The flow path is defined so that the
cross-sectional area thereof can be gradually increased in the flow
direction of the air. In other words, the guide portion 141 and the
flow path defining member 143 serves as a diffuser, thereby
increasing the static pressure at the air discharge side.
[0080] As mentioned earlier, the first partition wall 154 and the
second partition wall 155 are respectively installed near the air
intake side and the air discharge side of the axial flow fan 101.
At the air intake side, therefore, the air flows into the axial
flow fan 101 from the radial direction. In the present preferred
embodiment, however, the air drawn through the inside of the bell
mouth 135 is guided by the bell mouth 135 to smoothly flow in the
center axis direction. This makes it possible to reduce any
separation of airflow caused by the increase in an attack angle of
the propeller blades 103. In cooperation with the bell mouth 135,
the ring member 125 serves to guide the drawn airflow. Thus, the
air passing through the ring member 125 flows in the center axis
direction.
[0081] Despite the fact that the tip clearance is increased to
prevent the propeller blades 103 from becoming fixed to the inner
circumferential surface of the housing 130 due to frost, it is
possible to prevent the air from flowing backwards from the air
discharge side toward the air intake side through the clearance
space between the outer circumferential surface of the ring member
125 and the inner circumferential surface of the housing 130. This
is because the outer peripheral portion of the bell mouth defining
member 136 serves to cover the air intake side end of the clearance
space.
[0082] It is also possible for the ring member 125 to prevent the
air flowing through the inside of the ring member 125 from leaking
radially outwards from the outer peripheral ends of the propeller
blades 103. Since the ring member 125 does not exist in the air
discharge side end portions of the propeller blades 103, the air is
leaked radially outwards from the outer peripheral ends of the
propeller blades 103. Due to the presence of the guide portion 141,
however, the airflow discharged by the propeller blades 103 is
smoothly curved radially outwards.
[0083] Accordingly, even if the axial flow fan 101 is arranged in
the narrow fan arrangement space 152 and even when the tip
clearance is made greater, it is possible to suppress an impairment
of the PQ characteristic of the axial flow fan 101 and to suppress
the increase in noises.
[0084] The present invention is not limited to the preferred
embodiments described above but may be modified without departing
from the scope of the invention defined in the claims. For
instance, as shown in FIG. 11, a plurality of static vanes 131' may
be provided at a regular interval along the circumferential
direction, instead of the support legs 131 extending in the radial
direction. In this case, it becomes possible to increase the static
pressure at the air discharge side. When seen in the center axis
direction, each of the static vanes 131' is curved against the
rotating direction R as it extends from a radial inner end thereof
toward a radial outer end thereof.
[0085] While the ring member 125 preferably extends straight in the
center axis direction in the preferred embodiment described just
above, the diameter of the air intake side portion of the ring
member 125 may be increased toward the air intake side. This makes
it easy to introduce the air drawn through the bell mouth 135 into
the ring member 125. In cooperation with the outer peripheral
portion of the bell mouth defining member 136, the increased
diameter portion of the ring member 125 serves to cover the air
intake side end of the clearance space between the outer
circumferential surface of the ring member 125 and the inner
circumferential surface of the housing 130. Accordingly, it is
possible to effectively prevent the air from flowing backwards
through the clearance space.
[0086] While the flow straightening members 137 are provided
preferably inside the bell mouth 135 in the preferred embodiment
described just above, the flow straightening members 137 are not
essential and may be omitted if so desired. In case of providing
the flow straightening members 137, the shape of the flow
straightening members 137 is not limited to the shape illustrated
and described in the preferred embodiments. For example, as shown
in FIG. 13, it would also be possible to provide four flow
straightening members 137 in a cross shape (in which case the
central portion 138 included in the foregoing preferred embodiment
does not exist).
[0087] The housing 130 may be omitted. In this case, as shown in
FIG. 14 by way of example, the base member 110 and the bell mouth
defining member 136 are interconnected by a plurality of connecting
members 147 arranged at the air discharge side and the radial outer
side of the propeller blades 103 in a circumferentially
spaced-apart relationship with one another. Only the connecting
members 147 exist at the radial outer side of the propeller blades
103. The base member 110 is held by the attachment member 157
through the bell mouth defining member 136 and the connecting
members 147. The portions 147a of the connecting members 147
positioned at the air discharge side of the propeller blades 103
may be allowed to serve as static vanes (like the static vanes 131'
shown in FIG. 11). If the housing 130 is omitted in this manner,
only the connecting members 147 exist at the radial outer side of
the propeller blades 103. There exists no flow path through which
the air can flow backwards. Even if the housing 130 is omitted in
this manner, the ring member 125 causes the air to flow toward the
air discharge side without leaking radially outwards from the outer
peripheral ends of the propeller blades 103.
[0088] An axial flow fan like the one described above in respect of
the foregoing preferred embodiment (not including the guide portion
141, the flow path defining member 143 and the flow straightening
members 137) was prepared to evaluate the change of the static
pressure against the flow rate (air flow rate), i.e., the PQ
characteristic, at the air discharge side and the change of the
noise level against the flow rate (air flow rate), i.e., the noise
characteristic, at the air discharge side. The results of
evaluation are shown in FIG. 15. The fan (A) shown in FIG. 15 is an
axial flow fan like the one described above in respect of the
foregoing preferred embodiment. The fan (A) is arranged in a narrow
space (like the fan arrangement space 152) between walls existing
at the air intake side and the air discharge side thereof.
[0089] For the purpose of comparison, axial flow fans (B) and (C)
that do not include the ring member 125 and the bell mouth 135 (the
bell mouth defining member 136) were prepared to evaluate the PQ
characteristic and the noise characteristic thereof. The results of
evaluation are all shown in FIG. 15. The tip clearance of the fan
(B) is smaller than that of the fan (A) mentioned above. Other
configurations of the fan (B) remain the same as those of the fan
(A). The fan (B) is arranged in a broad space with no wall existing
at the air intake side and the air discharge side thereof. The tip
clearance of the fan (C) is substantially equal to that of the fan
(A) mentioned above. Other configurations of the fan (C) remain the
same as those of the fan (A). Just like the fan (A), the fan (C) is
arranged in a narrow space between walls existing at the air intake
side and the air discharge side thereof.
[0090] As can be seen in FIG. 15, if the fan (C) including an
increased tip clearance but not provided with the ring member 125
and the bell mouth 135 is arranged in a narrow space, the PQ
characteristic thereof is bitterly impaired as compared with the
fan (B) including a reduced tip clearance and arranged in a broad
space. The noise level of the fan (C) becomes greater than that of
the fan (B) if the flow rate exceeds a certain value. In the fan
(A) provided with the ring member 125 and the bell mouth 135, the
maximum flow rate thereof is smaller than that of the fan (C).
However, it can be seen that, as compared with the fan (C), the
static pressure of the fan (A) is increased and the noise level of
the fan (A) is decreased in the flow rate sections other than
maximum flow rate section. In particular, the static pressure and
the noise level of the fan (A) are equal to those of the fan (B) in
the low flow rate section excluding the zero flow rate point.
Accordingly, it can be appreciated that the characteristics of a
fan are greatly enhanced by the ring member 125 and the bell mouth
135.
[0091] For evaluation of the effects provided by the ring member
125, the fan (A) was compared with a fan (D) differing from the fan
(A) only in that the fan (D) is not provided with the ring member
125. The fans (A) and (D) are all arranged in narrow spaces like
the fan arrangement space 152 mentioned above. The results of
evaluation of the PQ characteristics and the noise characteristics
of the fans (A) and (D) are shown in FIG. 16. It can be seen in
FIG. 16 that, as compared with the fan (D), the static pressure of
the fan (A) is increased and the noise level of the fan (A) is
decreased in most flow rate sections other than some sections.
[0092] For evaluation of the effects provided by the bell mouth
135, the fan (A) was compared with fans (E) through (G), all of
which are not provided with the bell mouth 135. The fan (E) differs
from the fan (A) only in that the fan (E) is not provided with the
bell mouth 135 (the bell mouth defining member 136). The fan (F)
differs from the fan (A) in that the fan (F) is not provided with
the bell mouth 135. Moreover, the fan (F) differs from the fan (A)
in the position of the ring member 125 in the longitudinal
direction of the propeller blades 103. In the fan (F), the ring
member 125 is installed in the position spaced apart from the roots
of the propeller blades 103 by about 80% of the length of the
propeller blades 103. The fan (G) differs from the fan (A) in that
the fan (G) is not provided with both the bell mouth 135 and the
ring member 125. All the fans (E) through (G) are arranged in
narrow spaces like the fan arrangement space 152 mentioned
above.
[0093] The results of evaluation of the PQ characteristics and the
noise characteristics of the fan (A) and the fans (E) through (G)
are shown in FIG. 17. It can be seen in FIG. 17 that, in the fan
(A), the maximum flow rate thereof is smaller than those of the
fans (E) through (G). However, as compared with the fans (E)
through (G), the static pressure of the fan (A) is increased and
the noise level of the fan (A) is decreased in the flow rate
sections other than maximum flow rate section. In particular, the
static pressure of the fan (A) is sharply increased in the low flow
rate section excluding the zero flow rate point.
[0094] For evaluation of the effects provided by the flow
straightening members 137, the fan (A) was compared with a fan (H)
in which the flow straightening members 137 shown in FIG. 13 are
provided inside the bell mouth 135 of the fan (A) and a fan (I) in
which the flow straightening members 137 shown in FIG. 10 are
provided inside the bell mouth 135 of the fan (A). The results of
evaluation of the PQ characteristics and the noise characteristics
of the fans (A), (H) and (I) are shown in FIG. 18. It can be seen
in FIG. 18 that, in the PQ characteristic, the static pressure at
the zero flow rate point (cut-off point) is increased if the flow
straightening members 137 are provided inside the bell mouth 135.
This is because the turbulence of the airflow drawn through the
inside of the bell mouth 135 is mitigated by the flow straightening
members 137.
[0095] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing from the scope and spirit of the present invention. The
scope of the present invention, therefore, is to be determined
solely by the following claims.
* * * * *