U.S. patent application number 09/769263 was filed with the patent office on 2002-12-05 for axial fan, centrifugal fan, and electronic equipment employing one of these fans.
Invention is credited to Miyazawa, Atsushi.
Application Number | 20020182053 09/769263 |
Document ID | / |
Family ID | 18547319 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020182053 |
Kind Code |
A1 |
Miyazawa, Atsushi |
December 5, 2002 |
AXIAL FAN, CENTRIFUGAL FAN, AND ELECTRONIC EQUIPMENT EMPLOYING ONE
OF THESE FANS
Abstract
A low-noise axial fan is provided with whining sound minimized.
The axial fan includes a plurality of blades arranged around a
rotation axis at predetermined layout pitches. The blades are
arranged at varied layout pitches. For instance, the layout pitch
between the two adjacent blades may be different from the layout
pitch between the remaining blades. This arrangement controls the
whirring sound of the fan, which would be high in level if the
blades were arranged at an equal layout pitch. A low-noise axial
fan thus results.
Inventors: |
Miyazawa, Atsushi;
(Suwa-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Family ID: |
18547319 |
Appl. No.: |
09/769263 |
Filed: |
January 26, 2001 |
Current U.S.
Class: |
415/77 ;
415/220 |
Current CPC
Class: |
F04D 29/328 20130101;
F04D 29/666 20130101; F04D 29/662 20130101; F04D 29/282
20130101 |
Class at
Publication: |
415/77 ;
415/220 |
International
Class: |
F01D 001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2000 |
JP |
2000-020813 |
Claims
What is claimed is:
1. An axial fan, comprising: a plurality of blades arranged around
a rotation axis at a predetermined layout pitch, the plurality of
the blades being rotated about the rotation axis to take in air in
a direction of a rotation axis and to discharge the air, and some
of the plurality of the blades being different from remaining
blades in shape projected onto a plane perpendicular to the
rotation axis.
2. The axial fan according to claim 1, a number of the plurality of
the blades being a prime number.
3. The axial fan according to claim 1, further comprising an
eccentricity adjusting device that adjusts weight balance around
the rotation axis.
4. An axial fan, comprising: a plurality of blades arranged around
a rotation axis at a predetermined layout pitch, the plurality of
the blades being rotated about the rotation axis to take in air in
a direction of the rotation axis and to discharge the air, and some
of the plurality of the blades being different from remaining
blades in cross-sectional shape taken in a plane in which the
rotation axis lies.
5. The axial fan according to claim 4, a number of the plurality of
the blades being a prime number.
6. The axial fan according to claim 4, further comprising an
eccentricity adjusting device that adjusts weight balance around
the rotation axis.
7. An axial fan, comprising: a plurality of blades arranged around
a rotation axis at a predetermined layout pitch, the plurality of
the blades being rotated on the rotation axis to take in air in a
direction of the rotation axis and to discharge the air, and some
of the plurality of the blades being different from remaining
blades in layout pitch.
8. The axial fan according to claim 7, a pair of blades generally
diametrically symmetrical with respect to the rotation axis among
the plurality of the blades having substantially a same layout
pitch.
9. The axial fan according to claim 7, a number of the plurality of
the blades being a prime number.
10. The axial fan according to claim 7, further comprising an
eccentricity adjusting device that adjusts weight balance around
the rotation axis.
11. Electronic equipment comprising the axial fan according to
claim 1.
12. Electronic equipment comprising the axial fan according to
claim 4.
13. Electronic equipment comprising the axial fan according to
claim 7.
14. A centrifugal fan, comprising: a plurality of blades arranged
around a rotation axis at a predetermined layout pitch, the
plurality of the blades being rotated about the rotation axis to
take in air in a direction of the rotation axis and to discharge
the air in a direction tangential to the rotation of the plurality
of the blades, and at least some of the plurality of the blades
being different from remaining blades in shape projected onto a
plane perpendicular to the rotation axis.
15. A centrifugal fan according to claim 14, a number of the
plurality of the blades being a prime number.
16. A centrifugal fan according to claim 14, further comprising an
eccentricity adjusting device that adjusts weight balance around
the rotation axis.
17. Electronic equipment comprising the centrifugal fan according
to claim 14.
18. A centrifugal fan, comprising: a plurality of blades arranged
around a rotation axis at a predetermined layout pitch, the
plurality of the blades being rotated on the rotation axis to take
in air in a direction of the rotation axis and to discharge the air
in a direction tangential to the rotation of the plurality of the
blades, and some of the plurality of the blades being different
from remaining blades in layout pitch.
19. The centrifugal fan according to claim 18, a pair of blades
generally diametrically symmetrical with respect to the rotation
axis among the plurality of the blades having substantially a same
layout pitch.
20. A centrifugal fan according to claim 18, a number of the
plurality of the blades being a prime number.
21. A centrifugal fan according to claim 18, further comprising an
eccentricity adjusting device that adjusts weight balance around
the rotation axis.
22. Electronic equipment comprising the centrifugal fan according
to claim 18.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to an axial fan which includes
a plurality of blades arranged at a predetermined pitch about a
rotation axis, and which takes in air in the direction of the
rotation axis and discharges the air by rotating the plurality of
the blades about the rotation axis. Further, the present invention
relates to a centrifugal fan which includes a plurality of blades
arranged at a predetermined pitch about a rotation axis, and which
takes in air in the direction of the rotation axis and discharges
air in a direction tangential to the rotation of the plurality of
the blades by rotating the plurality of the blades about the
rotation axis. The axial fan or the centrifugal fan may be used as
an intake fan or an exhaust fan for electronic equipment such as a
computer or a projector.
[0003] 2. Description of Related Art
[0004] Electronic equipment, such as a personal computer or a
projector, conventionally employs an intake fan that cools the
electronic equipment by taking in air from outside the electronic
equipment and by having air impinge on the heat generating
component, or an exhaust fan that outwardly discharges hot air from
within the electronic equipment. As the intake fan or the exhaust
fan, an axial fan and a centrifugal fan are available.
[0005] The axial fan has a plurality of fans arranged at a
predetermined pitch around the rotation axis. By rotating the
plurality of the blades about the rotation axis, air is taken in
and discharged in the direction of the rotation axis.
[0006] The centrifugal fan has a plurality of fans arranged at a
predetermined pitch around the rotation axis. By rotating the
plurality of the blades on the rotation axis, air is taken in the
direction of the rotation axis and discharged in a direction
tangential to the rotation of the plurality of the blades.
[0007] Such an axial fan or centrifugal fan is arranged over a
microprocessor unit forming a computer, or in the vicinity of a
liquid-crystal display panel as an electro-optical device forming a
projector or a lamp as a light source system in the projector. By
having cooling air impinge on these heat generating components or
discharging hot air out, efficient cooling is attained.
SUMMARY OF THE INVENTION
[0008] The axial fan installed in the electronic equipment
conventionally employs five to eleven blades having the same shape
and arranged about a rotation axis at a predetermined equal
pitch.
[0009] The axial and centrifugal fans, provided with the blades
having the same shape and arranged at the predetermined equal
pitch, suffer from wind noise caused by the flow of air and a
whirring sound unique to the fan. For instance, when an axial fan
having nine blades arranged around a rotation axis at an equal
pitch is rotated at a rotational speed of 4000 rpm, a whirring
sound of 4000/60.times.9 (Hz) is generated. Since nine is not a
prime number, a whirring sound of 4000/60.times.3 (Hz), attributed
to a divisor of 3 for 9, is also generated.
[0010] The whirring sound becomes noise when the electronic
equipment is in use, and a user may be uncomfortable with such
noise. There is a need for a fan having low whirring sound
level.
[0011] It is an object of the present invention to provide an axial
fan and a centrifugal fan, featuring at least low-noise
characteristics with low whirring sound level, and electronic
equipment employing these fans.
[0012] An axial fan according to various exemplary embodiments of
the present invention introduces the layout diversity of the
blades, thereby lowering the level of whirring sound. The whirring
sound would be high if a plurality of equally spaced blades were
rotated. Specifically, the following methods are implemented.
[0013] An axial fan of an exemplary embodiment of the present
invention includes a plurality of blades arranged around a rotation
axis at a predetermined layout pitch. The plurality of the blades
are rotated about the rotation axis to take in air in the direction
of the rotation axis and to discharge the air. Some of the
plurality of the blades-are different from the remaining blades in
shape thereof projected onto a plane perpendicular to the rotation
axis.
[0014] Here, the clause "some of the plurality of the blades are
different from the remaining blades in the shape thereof projected
onto a plane perpendicular to the rotation axis" means that the
width dimension of some blades is different form the width
dimension of the remaining blades if viewed in the direction of the
rotation axis. The shape of some blades is made different from the
shape of the remaining blades by expanding an opening angle of the
blades with respect to the rotation axis or by reducing a bending
angle of the blade.
[0015] Since some of the plurality of the blades are different from
the remaining blades in the shape thereof projected onto a plane
perpendicular to the rotation axis in this exemplary embodiment,
the layout diversity around the rotation axis is introduced. The
whirring sound may be lower in level, compared with that which is
caused by the blades having the same shape and arranged at an equal
pitch. A low-noise axial fan may thus result.
[0016] An axial fan according to another exemplary embodiment of
the present invention includes a plurality of blades arranged
around a rotation axis at a predetermined layout pitch. The
plurality of the blades are rotated about the rotation axis to take
in air in the direction of the rotation axis and to discharge the
air. Some of the plurality of the blades are different from the
remaining blades in the cross-sectional shape taken in a plane in
which the rotation axis lies.
[0017] The clause "some of the plurality of the blades are
different from the remaining blades in the cross-sectional shape
taken in a plane in which the rotation axis lies" means that the
cross-sectional shape of some blades is made different from that of
the remaining blades by setting some blades to be greater or
smaller than the remaining blades in the angle of each blade made
between a plane perpendicular to the rotation axis and a
cross-sectional shape of the blade.
[0018] Since some of the plurality of the blades are different from
the remaining blades in the cross-sectional shape, the layout
diversity around the rotation axis is introduced in the same manner
as in the previous embodiment. The whirring sound may thus be lower
in level, compared with that which is caused by the blades having
the same shape and arranged at an equal pitch. A low-noise axial
fan may thus result.
[0019] An axial fan according to another exemplary embodiment of
the present invention includes a plurality of blades arranged
around a rotation axis at a predetermined layout pitch. The
plurality of the blades are rotated about the rotation axis to take
in air in the direction of the rotation axis and to discharge the
air. Some of the plurality of the blades are different from the
remaining blades in the layout pitch thereof.
[0020] The clause "some of the plurality of the blades are
different from the remaining blades in the layout pitch thereof"
means that, for instance, some of the nine blades are arranged
around the rotation axis at a pitch of 30.degree. or 50.degree.,
while the remaining blades are arranged on the rotation axis at a
pitch of 40.degree. degrees.
[0021] Since some of the plurality of the blades are different from
the remaining blades in the layout pitch in this exemplary
embodiment, the whirring sound may thus be lower in level, compared
with that which is caused by the blades having the same shape and
arranged at an equal pitch. A low-noise axial fan may thus
result.
[0022] In this exemplary embodiment, from among the plurality of
the blades, a pair of blades arranged to be generally diametrically
symmetrical with respect to the rotation axis preferably have
substantially the same layout pitch.
[0023] Specifically, if a first blade is changed in the layout
pitch thereof in a nine-blade axial fan, a fifth blade, which is
diametrically oppositely arranged across the rotation axis, is also
equally changed in the layout pitch thereof.
[0024] Without greatly impairing the weight balance around the
rotation axis of the axial fan, this arrangement may prevent
clattering noise from being generated by the eccentricity of the
axial fan during the rotation of a drive motor, thereby relieving a
large load on the drive motor.
[0025] In the above-described exemplary embodiments, the number of
the plurality of the blades is preferably a prime number.
[0026] Specifically, if the number of blades of an axial fan is 8
or 9 which is divisible by divisors 2 and 3 or 4, the whirring
sound attributed to the divisors 2 and 3 or 4 is generated in
addition to the whirring sound of the number of the blades. With
the number of the blades of the fan set to a prime number, the
whirring sound attributed to the divisors may be prevented. The
low-noise characteristic of the axial fan may be even more
enhanced.
[0027] In the above-described exemplary embodiments, the axial fan
preferably includes an eccentricity adjusting device for adjusting
weight balance around the rotation axis.
[0028] The eccentricity adjusting device can be formed by
symmetrically arranging weights diametrically opposite with respect
to the rotation axis where blades varied in planar shape,
cross-sectional shape, or layout pitch are mounted. Specifically,
the axial fan, formed of a plastic mold, includes a plurality of
blades and a blade support member rotatably supported about the
rotation axis. A projection or a notch is formed on the blade
support member at the symmetrical positions diametrically opposite
with respect to the rotation axis where the blades having different
planar shapes are mounted. The weight balance is thus assured to
compensate for the varied blades.
[0029] The, axial fan thus has the eccentricity adjusting device.
Even if some blades are varied in planar shape, cross-sectional
shape, or layout pitch, the cccentricity adjusting device may
assure the weight balance of the plurality of the blades and the
blade support member around the rotation axis, thereby preventing a
load from acting on the drive motor.
[0030] The above-referenced inventions are implemented not only in
the axial fan but also in the centrifugal fan. The same operation
and advantages will be enjoyed even if the above-referenced
inventions are implemented in the centrifugal fan. The centrifugal
fan refers to the one which includes a plurality of blades,
arranged around a rotation axis at a predetermined layout pitch,
wherein air is taken in the direction of the rotation axis and
discharged in a direction tangential to the rotation of the
plurality of the blades, by rotating the plurality of the blades
around the rotation axis. For instance, a Sirocco fan is a
centrifugal ran.
[0031] Since the centrifugal fan discharges air in the direction
tangential to the rotation, discharged air pressure is large for a
low rotational speed, compared with the axial fan. With the above
inventions implemented, the whirring sound level may be lowered,
and the low-noise characteristic of the centrifugal fan may be
enhanced.
[0032] With one of the axial fan and the centrifugal fan discussed
above incorporated in a personal computer or a projector, sound
noise involved in the rotation of the fan during use is lowered in
level, and low-noise electronic equipment thus results.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is an external perspective view of a projector of an
exemplary embodiment of the present invention, viewed from
above;
[0034] FIG. 2 is an external perspective view of the projector of
FIG. 1, viewed from below;
[0035] FIG. 3 is a perspective view showing the internal
construction of the projector of FIG. 1;
[0036] FIG. 4 is a perspective view showing an optical system of
the projector of FIG. 1;
[0037] FIG. 5 is a perspective view showing the construction of the
optical system of FIG. 4;
[0038] FIG. 6 is another perspective view showing the construction
of the optical system of FIG. 4;
[0039] FIG. 7 is an elevational sectional view of the projector,
taken along line VII-VII' in FIG. 1;
[0040] FIG. 8 is an elevational sectional view of the projector,
taken along line VIII-VIII' in FIG. 7;
[0041] FIG. 9 is a diagrammatic view showing the function of the
optical system of FIG. 4;
[0042] FIG. 10 is a plan view showing the construction of an axial
fan such as an exhaust fan or air intake fan in the above exemplary
embodiment;
[0043] FIG. 11 is a plan view showing the construction of an axial
fan of another exemplary embodiment of the present invention;
[0044] FIG. 12 is a plan view showing the construction of an axial
fan of another exemplary embodiment of the present invention;
[0045] FIG. 13 is a sectional view showing blades of an axial fan
of the exemplary embodiment in a plane in which a rotation axis
lies; and
[0046] FIG. 14 shows the cross section and side of a centrifugal
fan as a modification of each of the above exemplary
embodiments.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0047] One exemplary embodiment of the present invention is now
discussed, referring to the drawings.
[0048] (1) General Construction of the Fan Device
[0049] FIG. 1 and FIG. 2 are diagrammatic perspective views of a
projector 1 of a first exemplary embodiment, FIG. 1 is the
perspective view looking toward the projector 1 from above, and
FIG. 2 is the perspective view looking toward the projector 1 from
below.
[0050] The projector 1 separates a light beam emitted from a light
source device as a light source into the three primary color lights
of red (R), green (G), and blue (B), modulates the respective color
light beams through liquid-crystal display panels as an
electro-optical device in response to video information,
synthesizes the modulated color light beams through a
cross-dichroic prism (a color synthesizing system) into a color
image, and enlarges and projects the image onto a projection screen
through a projection lens 6. The components are housed in an outer
casing 2, and the projection lens 6 is projected out of the outer
casing 2 by a zoom mechanism as necessary.
[0051] (2) Construction of the Outer Casing
[0052] The outer casing 2 basically includes an upper case 3 for
covering the top of the projector 1, a lower case 4 for forming the
bottom portion of the projector 1, and a front case 5 for covering
the front of the projector 1. The upper case 3 and the lower case 4
are fabricated of magnesium die-casting, and the front case 5 is
fabricated of resin.
[0053] An air intake port 240, associated with a resin filter
exchange cover 241, is arranged on the top left surface (on the
right-hand side, viewed from the front) of the upper case 3. The
filter exchange cover 241 has slits 241A for taking in air from
outside as cooling air into the projector 1. The filter exchange
cover 241 is loaded with an air filter 242 (see FIG. 8) on the
inner side thereof. By detaching and attaching the filter exchange
cover 241 from and to the upper case 3, the air filter 242 inside
is replaced.
[0054] A number of communication holes 251 for a loudspeaker 250
(see FIG. 7) are drilled in front of the filter exchange cover 241
on the forward section of the top surface of the upper case 3.
Arranged beside the holes 251 is an operation panel 60 for
adjusting image quality of the projector 1. As shown in FIG. 7 and
FIG. 8, the filter exchange cover 241, the communication holes 251,
and the operation panel 60 are arranged in an extended portion 3A
where the upper case 3 is partly upwardly extended. The internal
space of the extended portion 3A partly serves as the spacing for
accommodating the air filter 242, the loudspeaker 250, and a
circuit board 61 for the operation panel 60.
[0055] As shown in FIG. 2, a lamp exchange lid 27, which is opened
to replace a light source lamp unit 8 mounted inside (see FIG. 3
and FIG. 4), is arranged on the bottom surface of the lower case 4.
Feet 31R and 31L are attached to the front comers on the bottom
surface of the lower case 4, and a foot 31C is attached to the
front center on the bottom surface of the lower case 4. The feet
31R and 31L are adjusted for projection or recession in the
longitudinal direction thereof by turning the dial portion thereof
or by operating levers 32R and 32L. The height and inclination of a
projected image are thus adjusted.
[0056] A light receiving section 70 for receiving a light signal
from an unshown remote controller is arranged on the right-hand
side of the front case 5. An air-exhaust port 160 for discharging
air from within the projector 1 is formed in the generally central
portion of the front case 5.
[0057] Arranged on the back side of the outer casing 2 near the air
intake port 240 are an AC inlet 50 for connection with an external
power source and a terminal bank 51 having a variety of
input/output terminals.
[0058] (3) Internal Construction of the Projector
[0059] FIG. 3-FIG. 8 show the internal construction of the
projector 1. FIG. 3 is a diagrammatic perspective view showing the
internal construction of the projector 1, FIG. 4 is a perspective
view showing an optical system of the projector 1, FIG. 5 and FIG.
6 are perspective views showing the internal construction of the
optical system of the projector 1, and FIG. 7 and FIG. 8 are
elevational sectional views of the projector 1.
[0060] As shown, the outer casing 2 houses the light source lamp
unit 8, a power source unit 9 as a power source, an optical unit
10, a driver board 11 (see FIG. 8), a main board 12, and an AV
board 13. As shown in FIG. 9, in this exemplary embodiment, the
light source lamp unit 8, the optical unit 10, and the
already-discussed projection lens 6 form an optical system having a
letter-U-shaped configuration in a plan view, and a control system
is composed of the boards 11, 12, and 13.
[0061] The power source unit 9 is composed of a first power source
block 9A arranged beside the projection lens 6 of the optical
system, a second power source block 9B arranged in a central
opening 14 in the letter-U-shaped configuration optical system,
namely, between the projection lens 6 and the light source lamp
unit 8, and a third power source block 9C arranged beside the light
source lamp unit 8 of the optical system.
[0062] The first power source block 9A includes the AC inlet 50,
and distributes power supplied through the AC inlet 50 from the
external power source, to the second power source block 9B and the
third power source block 9C.
[0063] The second power source block 9B transforms the voltage
supplied from the first power source block 9A, and then feeds the
transformed voltages to the main board 12 that constitutes the
control system. Attached to the air-exhaust port 160 of the second
power source block 9B is an auxiliary air-exhaust fan 15 driven by
power supplied from the second power source block 9B.
[0064] The third power source block 9C transforms the voltage
supplied by the first power source block 9A, and feeds the
transformed voltage to a light source device 183 (sce FIG. 9) as a
light source in the light source lamp unit 8. Specifically, since
the third power source block 9C needs to supply power to the light
source device 183, which consumes power most, the third power
source block 9C, coextending within the projector 1 from the front
to the back thereof, is larger than the first and second power
source blocks 9A and 9B.
[0065] The first through third power source blocks 9A, 9B, and 9C
are secured to the lower case 4 with screws, prior to the
installation of the projection lens 6 and the optical unit 10.
Alternatively, the first power source block 9A may supply power to
the second power source block 9B only, and the third power source
block 9C may be supplied with power by the second power source
block 9B.
[0066] The light source lamp unit 8 constitutes a light source
section of the projector 1. As shown in FIG. 7 and FIG. 9, the
light source lamp unit 8 includes the light source device 183,
composed of a light-source lamp 181 and a concave mirror 182, and a
lamp housing 184 holding the light source device 183.
[0067] As shown in FIG. 4, in the lamp housing 184, the light
source lamp unit 8 as the light source device is covered with a
container 9021 that is integrally formed with an upper light guide
901, constituting a light guide 900 to be discussed later. As
already discussed, the light source lamp unit 8 is dismounted by
opening the lamp exchange lid 27. A main air-exhaust fan 16, larger
than the auxiliary air-exhaust fan 15, is installed in a position
corresponding to the air-exhaust port 160 in front of the container
9021. The main air-exhaust fan 16 is also driven by the second
power source block 9B.
[0068] The optical unit 10 forms an optical image corresponding to
video information, by optically processing the light beam emitted
by the light source lamp unit 8, and includes the light guide 900.
The light guide 900 is composed of the box-like upper light guide
901, fabricated of resin, and a lid-like lower light guide 902,
fabricated of magnesium. The light guide 900 houses an illumination
optical system 923, a color separating optical system 924, an
electro-optical device 925 as a modulator system, and a
cross-dichroic prism 910 as a color synthesizing optical system. A
vertically aligned head plate 903, to which the projection lens 6
is affixed, is attached to the lower light guide 902. The optical
elements of the optical unit 10, other than the electro-optical
device 925 and the cross-dichroic prism 910, are clamped and held
between the upper and lower light guides 901 and 902. The upper
light guide 901 and the lower light guide 902 are joined together,
and are secured to the lower case 4.
[0069] The cross-dichroic prism 910 is arranged behind the head
plate 903, and is secured to the lower light guide 902.
Liquid-crystal display panels 925R, 925G, and 925B, forming the
electro-optical device 925, are arranged to face three sides of the
cross-dichroic prism 910, and are bonded to the respectively sides
of the cross-dichroic prism 910 with a fixing member interposed
therebetween. As for the positional relationship of the
liquid-crystal display panels 925R, 925G, and 925B, the
liquid-crystal display panel 925B and the liquid-crystal display
panel 925R are opposed to each other with the cross-dichroic prism
910 interposed therebetween, and the liquid-crystal display panel
925G and the projection lens 6 are opposed to each other with the
cross-dichroic prism 910 interposed therebetween. The
liquid-crystal display panels 925R, 925G, and 925B are cooled by
cooling air supplied by an air-intake fan 17 which is mounted over
the cross-dichroic prism 910 in a position facing the air intake
port 240. The driving the air-intake fan 17 is supplied with power
by the main board 12 via the driver board 11.
[0070] The driver board 11 controls the liquid-crystal display
panels 925R, 925G, and 925B of the above-referenced electro-optical
device 925, and is mounted above the optical unit 10.
[0071] The main board 12 includes a control circuit for generally
controlling the entire projector 1, and is arranged behind the
optical unit 10. The main board 12 and the driver board 11 are
arranged to be mutually perpendicular to each other, and are
mutually electrically connected to each other with connectors.
[0072] The AV board 13 is a circuit board having the terminal bank
51 thereon. The AV board 13 is erected between the optical unit 10
and the main board 12, and is electrically connected to the main
board 12.
[0073] In the above internal construction, cooling air taken in by
the air-intake fan 17 cools the electro-optical device 925, and is
then guided while cooling the boards 11, 12, and 13 as the
air-exhaust fans 15 and 16 rotate, and travels toward the light
source lamp unit 8. Along with new cooling air taken in through an
intake port 4A (see FIG. 2) arranged in the bottom surface of the
lower case 4, the cooling air mainly flows into the light source
lamp unit 8, thereby cooling the light source device 183. A portion
of the cooling air flows beside the second power source block 9B,
thereby cooling it. Another portion of the cooling air flows beside
the third power source block 9C, thereby cooling it. The cooling
air is then frontwardly discharged out of the projector 1 through
the air-exhaust port 160 by the air-exhaust fans 15 and 16.
[0074] (4) Construction of the Optical System
[0075] Referring to FIG. 5 and FIG. 9, the optical unit 10 of the
optical system is now discussed in detail.
[0076] The optical unit 10 is composed of the illumination optical
system 923, the color separating optical system 924, and a relay
optical system 927 respectively housed in the upper light guide
901, and the electro-optical device 925, and the cross-dichroic
prism 910 as the color synthesizing optical system respectively
secured to the lower light guide 902, and the projection lens 6
secured to the head plate 903 of the lower light guide 902.
[0077] The illumination optical system 923 is an integrator
illumination optical system for substantially uniformly
illuminating the image forming regions of the three liquid-crystal
display panels 925R, 925G, and 925B of the electro-optical device
925. The illumination optical system 923 includes the light source
device 183, a first lens array 921, a second lens array 922, a
reflective mirror 931, and a superimposing lens 932. The lens
arrays 921 and 922, the superimposing lens 932, and the reflective
mirror 931 are supported by vertical portions of the upper light
guide 901 and are secured by clips 7 as fastening members. Even if
the upper light guide 901 is placed upside down from the state
shown in FIG. 5, these components remain fastened.
[0078] The light source device 183, forming the illumination
optical system 923, includes the light-source lamp 181 serving as
an illumination light source for emitting a light beam, and the
concave mirror 182 that collimates the light beam emitted from the
light-source lamp 181 into a substantially parallel light beam. The
light-source lamp 181 is typically a halogen lamp, a metal halide
lamp, or a high-pressure mercury lamp. The concave mirror 182
preferably has a parabolic surface or an ellipsoidal surface.
[0079] The first lens array 921 has a matrix of M rows by N columns
of small lenses 9211, each having a rectangular shape. The small
lenses 9211 split the collimated light beam from the light source
into a plurality of collimated partial beams (i.e., M.times.N
partial beams), and focuses these partial beams in the vicinity of
the second lens array 922. The outline of each small lens 9211 is
substantially analogous in shape to the image forming region of
each of the liquid-crystal display panels 925R, 925G, and 925B. For
instance, if the aspect ratio (the ratio of the horizontal width to
the vertical height) of the liquid-crystal display panel is 4:3,
the aspect ratio of the small lens is also set to be 4:3.
[0080] The second lens array 922 has a matrix of M rows by N
columns of small lenses 9221, correspondingly to the micro lenses
9211 of the first lens array 921. The second lens array 922 has the
function of aligning the central axis of each partial beam
(principal beam) so that the central axis is incident on the
incident surface of the superimposing lens 932 at a right angle
thereto. The superimposing lens 932 has the function of
superimposing the plurality of the partial beams on each of the
three liquid-crystal display panels 925R, 925G, and 925B. With
reference to FIG. 5, the reflective mirror 931 extends along the
right angle made between the first lens array 921 and the second
lens array 922.
[0081] The reflective mirror 931 guides the partial beams from the
first lens array 921 to the second lens array 922, and may be
dispensed with, depending on the construction of the illumination
optical system in use. For instance, if the first lens array 921 is
arranged in parallel with the second lens array 922, the reflective
mirror 931 is not needed.
[0082] The color separating optical system 924 includes two
dichroic mirrors 941 and 942 as optical components of the present
invention, and a reflective mirror 943, and has the function of
separating light from the superimposing lens 932 of the
illumination optical system 923 into the three color light beams of
red, green, and blue. In a way similar to the one described above,
the mirrors 941, 942, and 943 are supported by vertically aligned
portions of the upper light guide 901 and secured by the clips 7 to
the upper light guide 901.
[0083] The relay optical system 927 includes an entrance lens 954,
a relay lens 973, and reflective mirrors 971 and 972. The
reflective mirrors 971 and 972 are also secured to the upper light
guide 901 by clips 7.
[0084] The three liquid-crystal display panels 925R, 925G, and 925B
of the electro-optical device 925 are of a type employing
polysilicon TFTs as switching devices. The three liquid-crystal
display panels 925R, 925G, and 925B are arranged within the
internal spacing 904 (see FIG. 5) surrounded by the upper light
guide 901 so that these panels, facing the three sides of the
cross-dichroic prism 910, are bonded to the respective sides of the
cross-dichroic prism 910 with the fixing member interposed
therebetween. Arranged on the light entrance sides of the
liquid-crystal display panels 925R, 925G, and 925B are respectively
entrance polarizers 960R, 960G, and 960B. Arranged on the light
exit sides of the liquid-crystal display panels 925R, 925G, and
925B are respectively exit polarizers 961R, 961G, and 961B.
[0085] The cross-dichroic prism 910 has the function of forming a
color image by synthesizing the three color light beams, and is
secured to the top surface of the lower light guide 902 by screws.
The cross-dichroic prism 910 is constructed by gluing four
right-angle prisms with a dielectric multilayered film reflecting
the red light and a dielectric multilayered film reflecting the
blue light interposed in a cross configuration in the interfaces
between the right-angle prisms. These dielectric multilayered films
synthesize the three color light beams.
[0086] The projection lens 6 is the heaviest optical component in
the projector 1, and is secured to the head plate 903 of the lower
light guide 902 with a flange 62 (FIG. 6) of the support end
thereof fixed to the head plate 903, using screws.
[0087] The above optical unit 10 is assembled in the following
procedure.
[0088] The box-like upper light guide 901 is placed with the
opening thereof facing upward. The optical components (such as
reflective mirrors and lenses), forming the illumination optical
system 923, the color separating optical system 924, and the relay
optical system 927 are arranged, and secured to the upper light
guide 901 with the clips 7.
[0089] The cross-dichroic prism 910, with the liquid-crystal
display panels 925R, 925G, and 925B affixed thereto, is mounted on
the top surface of the lid-like lower light guide 902, and the
projection lens 6 is secured to the head plate 903. The upper light
guide 901 having the optical components mounted thereon is inverted
in position, and is mounted onto the lower light guide 902 to cover
it, and is fixed.
[0090] The light guide 900 thus assembled is fastened to the lower
case 4 with screws.
[0091] Alternatively, the lower light guide 902, with the
liquid-crystal display panels 925R, 925G, and 925B, the
cross-dichroic prism 910, and the projection lens 6 installed
thereon, may be beforehand fixed to the lower case 4, the upper
light guide 901 having the optical components mounted thereon may
be inverted in position, and mounted to the lower light guide 902
to cover it, and the upper light guide 901 may be then secured to
the lower case 4 with screws.
[0092] Alternatively, the lower light guide 902 only may be
beforehand secured to the lower case 4, the liquid-crystal display
panels 925R, 925G, and 925B, the cross-dichroic prism 910, and the
projection lens 6 may be then installed thereon, and the upper
light guide 901 having the optical components mounted thereon may
be inverted in position, and mounted to the lower light guide 902
to cover it, and the upper light guide 901 may be then secured to
the lower case 4 with screws.
[0093] In this exemplary embodiment, the securing of the
cross-dichroic prism 910 and the projection lens 6 to the lower
light guide 902 and the securing of the upper light guide 901 and
the lower light guide 902 to the lower case 4 are performed using
screws. Alternatively, the securing may be performed using an
adhesive, or fit, or any other fixing technique.
[0094] (5) Functions of the Optical System
[0095] In the optical unit 10 shown in FIG. 9, the substantially
collimated beam from the light source device 183 is split into the
plurality of the partial beams through the first and second lens
arrays 921 and 922 forming the integrator optical system (the
illumination optical system 923). The partial beams from the small
lenses 9211 of the first lens array 921 are superimposed by the
superimposing lens 932 onto the image forming region of each of the
liquid-crystal display panels 925R, 925G, and 925B. As a result,
the liquid-crystal display panels 925R, 925G, and 925B are
illuminated by illumination light having uniform distribution
within the screen thereof.
[0096] The first dichroic mirror 941 of the color separating
optical system 924 reflects the red color component of the light
beam emitted from the illumination optical system 923 while
transmitting the blue color component and the green color component
of the light beam therethrough. The red color light reflected from
the first dichroic mirror 941 is then reflected from the reflective
mirror 943, and is transmitted through a field lens 951, and
reaches the red-color liquid-crystal display panel 925R. The field
lens 951 collimates each partial beam from the second lens array
922 to be parallel with the central axis (principal beam) of the
partial beam. Field lens 952 and 953 respectively arranged on the
remaining liquid-crystal display panels 925G and 925B work in a
similar manner.
[0097] The green light, out of the green light and the blue light,
transmitted through the first dichroic mirror 941, is reflected
from the second dichroic mirror 942, is then transmitted through
the field lens 952, and reaches the green-color liquid-crystal
display panel 925G. The blue light is transmitted through the
second dichroic mirror 942, the relay optical system 927, the field
lens 953, and reaches the blue-color liquid-crystal display panel
925B. Since the optical path of the blue color light is longer than
those of the other color light rays, the relay optical system 927
is used for the blue color optical path. The relay optical system
927 thus avoids a drop in the utilization of light arising from
light diffusion or the like. Specifically, the relay optical system
927 transmits the partial beams incident on the entrance lens 954
directly to the field lens 953 with no loss involved.
[0098] The red, green, and blue color light beams are respectively
polarized through the entrance polarizers 960R, 960G, and 960B
prior to the entrance to the liquid-crystal display panels 925R,
925G, and 925B. The respective polarized light beams are modulated
by the liquid-crystal display panels 925R, 925G, and 925B in
accordance with video information, and then the modulated light
beams respectively travel to the exit polarizers 961R, 961G, and
961B. The exit polarizers 961R, 961G, and 961B permit respective
polarized light of the modulated light beams to transmit
therethrough, and to reach the cross-dichroic prism 910. The
polarized light beams output are synthesized through the
cross-dichroic prism 910 as a synthesized light beam, and is then
directed to the projection lens 6. The synthesized light beam is
projected onto a projection screen as a color image by the
projection lens 6.
[0099] (6) Construction of the Exhaust Fan and the Intake Fan
[0100] Each of the main air-exhaust fan 16 and the air-intake fan
17, arranged in the projector 1 thus constructed, employs an axial
fan 40 as shown in FIG. 10. The axial fan 40 includes a plurality
of blades 411-421 arranged around a rotation axis C, a blade
support member 43 rotatably supported about the rotation axis C for
supporting the plurality of the blades 411-421 at the base portions
thereof, and a casing 45 housing the plurality of the blades
411-421. Though not shown, a drive motor for driving the plurality
of the blades 411-421 of the axial fan 40 is installed behind the
blade support member 43. The blade support member 43 is rigidly
attached to the rotary shaft of the drive motor. When the drive
motor rotates, the blade support member 43 also rotates, and the
plurality of the blades 411-421 rotate about the rotation axis C,
thereby causing air to flow.
[0101] The axial fan 40 includes the eleven blades 411-421. All
blades 411-421 are not arranged at an equal pitch about the
rotation axis C, and some of the blades 411-421 are arranged at a
pitch different from that of the remaining blades. The eleven
blades 411-421 are thus arranged at varied pitches.
[0102] As for the actual layout pitches in this embodiment, as
shown in FIG. 10, .alpha.1 (degrees) represents a pitch angle
between the blade 411 and the blade 412, .beta.1 (degrees)
represents an angle spacing between the blade 411 and the blade
412, and .gamma.1 (degrees) represents a blade angle width of the
blade 411 with respect to the blade support member 43. With respect
to the blade 411 as a reference, layout pitch angles
.alpha.1-.alpha.11, angle spacings .beta.1-.beta.11, and angle
widths .gamma.1-.gamma.11 are set up around the rotation axis C. By
setting these parameters to desired values, the varied pitch is
attained in the axial fan 40. For instance, by setting the angle
widths .gamma.1-.gamma.11 of the blades 411-421 to a constant value
of .gamma.=15.7.degree., the layout pitch angles
.alpha.1-.alpha.11, and the angle spacings .beta.1-.beta.11 may be
set as listed in Table 1.
1TABLE 1 PITCH ANGLE ANGLE SPACING BLADE ANGLE BLADE NO. .alpha.
.beta. WIDTH .gamma. 411 .alpha.1 = 17.7.degree. .beta.1 =
2.degree. .gamma.1 = 15.7.degree. 412 .alpha.2 = 26.7.degree.
.beta.2 = 11.degree. .gamma.2 = 15.7.degree. 413 .alpha.3 =
34.7.degree. .beta.3 = 19.degree. .gamma.3 = 15.7.degree. 414
.alpha.4 = 42.7.degree. .beta.4 = 27.degree. .gamma.4 =
15.7.degree. 415 .alpha.5 = 32.7.degree. .beta.5 = 17.degree.
.gamma.5 = 15.7.degree. 416 .alpha.6 = 22.7.degree. .beta.6 =
7.degree. .gamma.6 = 15.7.degree. 417 .alpha.7 = 30.7.degree.
.beta.7 = 15.degree. .gamma.7 = 15.7.degree. 418 .alpha.8 =
38.7.degree. .beta.8 = 23.degree. .gamma.8 = 15.7.degree. 419
.alpha.9 = 47.7.degree. .beta.9 = 32.degree. .gamma.9 =
15.7.degree. 420 .alpha.10 = 37.7.degree. .beta.10 = 22.degree.
.gamma.10 = 15.7.degree. 421 .alpha.11 = 27.7.degree. .beta.11 =
12.degree. .gamma.11 = 15.7.degree.
[0103] In the layout pitch angles .alpha.1-.alpha.11 of the blades
of the axial fan 40 listed in table 1, the layout pitch angle al
between the blade 411 and the blade 412 is set to be subtantially
equal to the layout pitch angle .alpha.6 between the blade 416 and
the blade 417, which are diametrically opposed to and symmetrically
arranged with the blade 412 with respect to the rotation axis C.
The layout pitch angle .alpha.1 between the blade 411 and the blade
412 is set to be close to the layout pitch angle .alpha.2between
the adjacent blades 412 and 413, and the layout pitch angle
.alpha.11 between the adjacent blade 421 and the blade 411.
[0104] The designing of the axial fan 40 with the blades 411-421
having varied pitch angles is based on the angle spacing .beta.
between the adjacent blades.
[0105] 1) First, the minimum angle the angle spacing .beta. can
take is set. When the axial fan 40 is manufactured through
injection molding, the angle spacing .beta. needs to be 2.degree.
or larger, because the blades are not separated from each other
with an angle spacing .beta. smaller than 2.degree.. The minimum
angle spacing .beta. is thus set to be 2.degree..
[0106] 2) If the eleven blades are equally spaced around the
rotation axis C, the layout pitch of the blades are 360.degree./11
blades, i.e., 32.7.degree.. If an average angle spacing is
17.degree., the maximum angle is 15.degree.. The maximum angle
spacing is thus set to be 32.degree..
[0107] 3) If .beta.1 is set to the minimum angle spacing of
2.degree. under the condition of
2.degree..ltoreq..beta..ltoreq.32.degree., .beta.2 is set by
increasing .beta.1 by 9.degree.. The angle spacings .beta.3, . . .
, are gradually stepwise increased. When .beta.max reaches about
32.degree., .beta. is then determined by decreasing .beta.max by
10.degree..
[0108] 4) When .beta.1-.beta.11 are set, a fixed angle width
.gamma.=15.70 is added to each of .beta.1-.beta.11, thereby
determining .alpha.1-.alpha.11.
[0109] (7) Advantages of the First Embodiment
[0110] The above first embodiment provides the following
advantages.
[0111] 1) Since the blades 411-421 are arranged around the rotation
axis C at varied pitches, the whirring sound, which is high in
level with the plurality of equally pitched blades, may be lowered.
A low-nose axial fan 40 may thus result.
[0112] 2) Since the axial fan 40 is employed for the main
air-exhaust fan 16 and the air-intake fan 17 in the projector 1,
noise arising from the rotation of the main air-exhaust fan 16 and
the air-intake fan 17 may be reduced during the operation of the
projector 1. A low-noise projector may thus result.
[0113] 3) Referring to Table 1, the layout pitch angle .alpha.1
between the blade 411 and the blade 412 is set to be substantially
equal to the layout pitch angle .alpha.6 between the blade 416 and
the blade 417, which are diametrically opposed to and symmetrically
arranged with the blade 411 and the blade 412 with respect to the
rotation axis C, and thus the weight balance of the plurality of
the blades 411-421 and the blade support member 43 is assured
around the rotation axis C. This arrangement controls the
generation of the clattering noise during rotation, and the
eccentricity of the axial fan 40, thereby relieving a large load on
the drive motor.
[0114] 4) Since the number of the blades 411-421 of the axial fan
40 is set to be 11, no whirring sound attributed to any divisor
takes place, unlike in the case where the whirring sound attributed
to divisors 2, 3, and 4 takes place when 8 blades or 9 blades are
used. The low-noise characteristic of the axial fan 40 is even more
enhanced.
[0115] (8) Construction and Advantages of a Second Exemplary
Embodiment
[0116] A second exemplary embodiment of the present invention is
now discussed. In the following discussion, like components are
designated with like reference numerals, and the discussion
thereabout is omitted.
[0117] In the first exemplary embodiment, the axial fan 40 has a
fixed blade angle width of 15.7.degree. as the angle width
.gamma.1-.gamma.11, and the plurality of the blades 411-421 having
the same configuration are arranged at the varied pitches. The
whirring sound involved in the rotation of the plurality of the
blades 411-421 of the axial fan 40 is thus controlled.
[0118] In contrast, as shown in FIG. 11, in an axial fan 340 of the
second embodiment, the angle width of some of the 11 blades
341-351, for instance, the angle width .gamma.2 of the blade 342 is
set to be larger than the angle width .gamma.1 of the blade 341 so
that the planar shape of the blade 342 in a plane perpendicular to
the rotation axis is thus varied. In this exemplary embodiment, the
layout pitches of the blades 341-351 are set to be different as in
the first exemplary embodiment. Alternatively, the plurality of the
blades may be arranged about the rotation axis at an equal pitch,
the angle spacing between adjacent blades .beta.1, for instance,
may be adjusted, and the angle width .gamma.1 may be modified.
[0119] The constant angle width .gamma. of the blades 341-351 of
the axial fan 340 is now determined. The maximum value of the
constant angle width with respect to the blade support member 43 is
set. In accordance with the maximum value of the constant angle
width, the constant angle width .gamma. is gradually reduced,
thereby adjusting the layout pitch. The fixed angle width .gamma.
of the blades 341-351 is set to be smaller than
(360.degree.-2.times.11)/11 blades=30.7.degree./blade. The layout
diversity of the blades 341-351 around the rotation axis C is thus
introduced. The minimum value of the fixed angle width of the blade
is determined to assure sufficient strength thereof
[0120] If the blades 341-351 thus designed are rotated with the
drive motor rotating within the blade support member 43, a poor
weight balance around the rotation axis C can generate the
clattering noise. Referring to FIG. 11, the weight balance of the
blade support member 43 and the blades 341-351 around the rotation
axis C may be assured, by forming a projection 431 on the blade
support member 43 where the blades 341-351 are coarsely arranged,
and by forming a notch 433 inwardly aligned to the rotation axis C,
on the blade support member 43 where the blades 341-351 are closely
arranged. The projection 431 and the notch 433 serve as the
eccentricity adjusting device. The eccentricity adjusting device
assure that the blades 341-351 and the blade support member 43
reliably rotate about the rotation axis C with a well weight
balance maintained. The blade support member 43 and the blades
341-351 may be manufactured into a one-piece plastic construction
through injection molding. In this case, the blade support member
43 is loaded with a weight or is notched to confirm the
configuration that results in a good weight balance, and an
injection mold tool is modified to reflect the configuration. As a
result, the projection 431 and the notch 433 are formed
concurrently with the forming process of the blade support member
43.
[0121] Besides the advantages of the first exemplary embodiment,
the second exemplary embodiment provides the following
advantages.
[0122] 5) Since the planar shape of the blade 342, out of the
blades 341-351, projected onto a plane perpendicular to the
rotation axis C is different from that of the blade 341, the
generation of the whirring sound is controlled in the same way as
in the first exemplary embodiment. A low-noise axial fan 340 may
thus result.
[0123] 6) Beside the varied pitch design, the axial fan has the
varied angle width of the blade. This arrangement provides a
substantially increased design freedom. An axial fan with the
whirring sound controlled and flexible in configuration and
specifications is thus manufactured.
[0124] 7) To assure the weight balance, not only the layout pitch
angles .alpha.1-.alpha.11 around the rotation axis C is adjusted,
but also the eccentricity adjusting device, such as the projection
431 and the notch 433, is employed. The weight balance of the blade
support member 43 and the blades 341-345 around the rotation axis C
may be even more easily adjusted. The design of the axial fan 340
is simplified. This is also true of the first exemplary
embodiment.
[0125] (9) Construction and Advantages of an Exemplary
Embodiment
[0126] A third exemplary embodiment of the present invention is now
discussed.
[0127] In the second exemplary embodiment, the planar shape of the
blade 342 is different from that of the blade 341 in a plane
perpendicular to the rotation axis C of the blades 341-351 so that
the layout diversity is assured to reduce the blade whirring sound
level.
[0128] In contrast, as shown in FIG. 12, an axial fan 440 of the
third exemplary embodiment includes blades 441-451 having the same
shape in a plane perpendicular to the rotation axis C, namely,
having the same fixed angle width .gamma., and arranged around the
rotation axis C at an equal layout pitch angle .alpha..
[0129] In this exemplary embodiment, however, some of the blades
are different from the remaining blades in cross-sectional shape
taken in a plane in which the rotation axis C lies, so that the
layout diversity of the blades 441-451 is assured. For instance, if
the cross-sectional shapes of the blades 441 and 442 are compared,
the two blades 441 and 442 are identical in width dimension W, but
the bending angle .theta.2 of the blade 442 is smaller than the
bending angle .theta.1 of the blade 441 as shown in FIG. 13. By
arranging the blades 441-451 having bending angles .theta.1 and
.theta.2 around the rotation axis C, the layout diversity of the
plurality of the blades 441-451 is assured. The weight balance
around the rotation axis C is assured by arranging the blades
441-451 in balance. Alternatively, the weight balance may be
assured by forming a projection and a notch in the blade support
member 43.
[0130] Since the blades 441-451 are different in cross-sectional
shape thereof in the third exemplary embodiment, the layout
diversity of the blades 441-451 around the rotation axis C may be
assured, thereby reducing the whirring sound. A low-noise axial fan
440 may thus result.
[0131] (10) Modifications of the Exemplary Embodiments
[0132] The present invention is not limited to the above exemplary
embodiments, and includes the following modifications.
[0133] The present invention may be implemented in the axial fans
40, 340, and 440 in the above exemplary embodiments, but if the
present invention is implemented in a centrifugal fan 540 shown in
FIGS. 14(A)-(B), the same advantages as those of the above
exemplary embodiments will be enjoyed. The centrifugal fan 540
includes a blade support member 43, blades 541-551, and a casing
55. The casing 55 includes an opening 55A serving as an exhaust
port, and an opening (not shown) arranged on one side in a plane
perpendicular to the rotation axis C thereof serving as an air
intake port. When the blades 541-551 rotate, air is taken in the
rotation axis C from the air intake opening, and air taken is
routed in a direction tangential to the rotation of the fan by the
blades 541-551, and is then discharged through the opening 55A.
Since such a centrifugal fan 540 assures a large quantity of air
discharged through the opening 55A, a heat generating electronic
component may be efficiently cooled at a small rotational speed
when the component is locally cooled. If the above-referenced
exemplary embodiments of the present invention are implemented in
the centrifugal fan 540, the whirring sound involved may be lowered
in level. A low-noise centrifugal fan 540 may thus result.
[0134] In the above exemplary embodiments, the axial fan 40, 340,
or 440 is employed in the projector 1. The present invention is not
limited to the projector 1. The axial fan or the centrifugal fan of
the present invention may be incorporated in electronic equipment,
if the electronic equipment, such as an overhead projector or a
personal computer, is equipped with a heat generating component.
The same advantages as those of the above exemplary embodiments may
be enjoyed.
[0135] The axial fan and the centrifugal fan of the above-reference
present invention may lower fan whirring sound in level, becoming
low-noise axial fan and centrifugal fan. With these fans
incorporated, low-noise electronic equipment may result.
* * * * *