U.S. patent application number 12/953555 was filed with the patent office on 2011-03-24 for piezoelectric micro blower.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. Invention is credited to Atsuhiko HIRATA.
Application Number | 20110070110 12/953555 |
Document ID | / |
Family ID | 41376945 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110070110 |
Kind Code |
A1 |
HIRATA; Atsuhiko |
March 24, 2011 |
PIEZOELECTRIC MICRO BLOWER
Abstract
A piezoelectric micro blower includes a blower body that
includes a first wall and a second wall. An opening is provided at
a portion of the first wall that faces an area of the approximate
center of a driver of the piezoelectric micro blower. An opening is
provided at a portion of the second wall. A central space that is
in communication with the openings is provided between the first
and second walls. Inlet passages through which the central space is
in communication with the outside are provided between the first
and second walls. Bottleneck portions are provided at regions at
which the inlet passages are connected to the central space. The
driver vibrates when a voltage is applied to a piezoelectric
element. The first wall vibrates in a corresponding manner as the
driver vibrates.
Inventors: |
HIRATA; Atsuhiko;
(Nagaokakyo-shi, JP) |
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-shi
JP
|
Family ID: |
41376945 |
Appl. No.: |
12/953555 |
Filed: |
November 24, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2009/058968 |
May 14, 2009 |
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12953555 |
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Current U.S.
Class: |
417/413.2 |
Current CPC
Class: |
F04B 43/043
20130101 |
Class at
Publication: |
417/413.2 |
International
Class: |
F04B 17/03 20060101
F04B017/03 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2008 |
JP |
2008-142250 |
Claims
1. A piezoelectric micro blower comprising: a blower body; a driver
including a peripheral portion that is fixed to the blower body and
a piezoelectric element; and a blower chamber provided between the
blower body and the driver; wherein the piezoelectric element is
arranged to receive a voltage to cause the driver to vibrate due to
bending in order to transport a compressible fluid; the blower body
includes a first wall arranged such that the blower chamber is
provided between the driver and the first wall; the first wall
includes a first opening arranged such that an inside of the blower
chamber is in communication with an outside of the blower chamber
through the first opening; a second wall is provided at a side
opposite to the blower chamber with the first wall being provided
between the second wall and the blower chamber, the second wall
being spaced at a distance from the first wall; the second wall
includes a second opening; a central space is provided between the
first wall and the second wall, includes an open area that is
greater than an area of the first opening and the second opening
but less than an area of the blower chamber, and is in
communication with the first opening and the second opening; an
inlet passage is provided and includes an outer end that is in
communication with an outside of the piezoelectric micro blower and
an inner end that is connected to the central space; and a
bottleneck portion including a passage area that is less than that
of the inlet passage is provided in the inlet passage.
2. The piezoelectric micro blower according to claim 1, wherein the
first opening is provided at a portion of the first wall that faces
an area of an approximate center of the driver.
3. The piezoelectric micro blower according to claim 1, wherein the
second opening is provided at a portion of the second wall that
faces the first opening.
4. The piezoelectric micro blower according to claim 1 wherein the
bottleneck portion is provided at a region at which the inlet
passage is connected to the central space.
5. The piezoelectric micro blower according to claim 1, wherein the
passage area of the bottleneck portion gradually decreases in a
direction of a flow from the inlet passage to the central
space.
6. The piezoelectric micro blower according to claim 1, wherein the
open area of the central space is arranged such that the facing
portion of the first wall vibrates as the driver vibrates.
7. The piezoelectric micro blower according to claim 1, wherein the
inlet passage includes a plurality of passages extending in radial
directions from the central space.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a piezoelectric micro
blower that is capable of transporting a compressible fluid, such
as air.
[0003] 2. Description of the Related Art
[0004] A piezoelectric micro pump is used, for example, for a pump
for transporting water for cooling a small-sized electronic device,
such as a notebook computer, and a pump for transporting fuel in a
fuel cell. On the other hand, a piezoelectric micro blower can be
used as a blower that replaces a fan for cooling a CPU or other
heat generating electronic component or as a blower to supply
oxygen that is required for electric power generation in a fuel
cell. A piezoelectric micro pump/piezoelectric micro blower is a
device that includes a diaphragm that is deformed due to flexion
when a voltage is applied to a piezoelectric element. The
piezoelectric micro pump/piezoelectric micro blower has the
advantages of a simple structure, a low-profile body, and low power
consumption.
[0005] When an incompressible fluid, such as a liquid, is
transported, it is common to provide check valves, each of which is
made of a soft material, such as rubber or resin, at an inlet port
and an outlet port. In addition, it is common to drive a
piezoelectric element at a low frequency, such as tens of hertz.
Although the maximum displacement is obtained when a piezoelectric
element is driven approximately at the resonance frequency of a
diaphragm (a first-order resonance frequency or a third-order
resonance frequency), a check valve fails to operate in response
thereto because the resonance frequency has a high frequency in the
kHz range. Therefore, it is preferable to use a piezoelectric micro
blower that does not include any check valve to transport a
compressible fluid.
[0006] A flow generation device is disclosed in Japanese Examined
Patent Application Publication No. S64-2793. The flow generation
device disclosed therein includes a substrate that includes a
pressurizing chamber that is filled with a fluid, a nozzle plate
that includes nozzles that are directed to the pressurizing
chamber, an opening, and an electric vibrator that is attached to
the nozzle plate such that the nozzles are located approximately at
the center of the opening. The nozzle plate and the electric
vibrator are attached to the substrate. An alternating current that
has a frequency that is close to the resonance frequency of the
electric vibrator is supplied to the electric vibrator. When such a
structure is used, a check valve can be omitted. In addition, it is
possible to increase the flow rate by driving the vibrator at a
high frequency. In a structure illustrated in FIG. 5 of Japanese
Examined Patent Application Publication No. S64-2793, an air
chamber into which air flows is provided in front of the nozzle
plate. A fluid that is ejected through the nozzles sucks ambient
air into the air chamber. The fluid is discharged through an exit
port together with the ambient air. However, since the open area of
the air chamber is relatively large, the pressure energy of the
fluid that is ejected through the nozzles is dissipated into the
periphery of the air chamber. For this reason, the structure
disclosed in Japanese Examined Patent Application Publication No.
S64-2793 has a disadvantage in that it is difficult to increase the
flow rate through the exit port.
[0007] A micro blower that includes an ejection unit that sucks air
from the outside and ejects the air, a cover that includes an exit
port to discharge the air ejected from the ejection unit, and a
base unit that is connected to the ejection unit is disclosed in a
Japanese Unexamined Patent Application Publication No. 2005-113918.
The micro blower includes an ejection plate that includes a suction
hole and an ejection hole. A vibration plate that is provided with
a magnetic sheet is attached to the back of the ejection plate. A
pressurizing chamber is provided between the ejection plate and the
vibration plate. A coil is used to vibrate the magnetic sheet.
Ejection airflow is generated from a cavity as a result of the
vibration of the magnetic sheet. The airflow sucks ambient air into
a cover cavity that is located in front of the ejection plate. The
fluid ejected is discharged through the exit port together with the
ambient air. Since the open area of the cover cavity is greater
than that of the pressurizing chamber, the pressure energy of the
fluid that is ejected through the ejection hole is dissipated into
the cover cavity. For this reason, the structure disclosed therein
has the same disadvantage as that of the structure disclosed in the
Japanese Examined Patent Application Publication No. S64-2793, that
is, it is difficult to increase the flow rate through the exit
port.
SUMMARY OF THE INVENTION
[0008] To overcome the problems described above, preferred
embodiments of the present invention provide a piezoelectric micro
blower which is capable of transporting a compressible fluid
efficiently without using a check valve and achieving an increased
flow rate.
[0009] A preferred embodiment of the present invention provides a
piezoelectric micro blower including a blower body, a driver
including a peripheral portion that is fixed to the blower body and
a piezoelectric element, and a blower chamber provided between the
blower body and the driver, wherein a voltage is applied to the
piezoelectric element to cause the driver to vibrate due to flexion
to transport a compressible fluid. The piezoelectric micro blower
preferably includes a first wall of the blower body, the blower
chamber being provided between the driver and the first wall, a
first opening that extends through the first wall, the inside of
the blower chamber being in communication with the outside of the
blower chamber through the first opening, a second wall that is
provided at a side opposite the blower chamber with the first wall
being provided between the second wall and the blower chamber, the
second wall being spaced at a distance from the first wall, a
second opening that extends through the second wall, a central
space that is provided between the first wall and the second wall,
has an open area that is greater than the first opening and the
second opening but less than the blower chamber, and is in
communication with the first opening and the second opening, and an
inlet passage that includes an outer end that is in communication
with the outside of the piezoelectric micro blower and an inner end
that is connected to the central space, wherein a bottleneck
portion that has a passage area that is less than that of the inlet
passage is provided in the inlet passage.
[0010] When a voltage is applied to the piezoelectric element to
cause the driver to vibrate due to flexion, a fluid flows at high
speed from the first opening to the second opening as the driver
becomes displaced. With this arrangement, it is possible to suck a
fluid from the inlet passage into the central space. That is, it is
possible to suck a fluid from the inlet passage into the central
space not only when the driver is displaced into a convex shape
that is oriented downward but also when the driver is displaced
into a convex shape that is oriented upward. The fluid sucked from
the inlet passage and the fluid pressed out of the blower chamber
flow into each other. The confluent fluids are discharged together
through the second opening. Therefore, it is possible to obtain a
discharging flow, the quantity of which is greater than the
displacement volume of the driver. The inlet passage is connected
to the central space between the first opening and the second
opening. Since the inlet passage is not directly connected to the
blower chamber, the inlet passage is less susceptible to a pressure
change in the blower chamber. Even though a check valve is not
provided, a fluid that flows at high speed from the first opening
to the second opening does not flow backward into the inlet
passage. Thus, it is possible to effectively increase the flow
rate. The open area of the central space is preferably greater than
the first opening and the second opening but less than the blower
chamber. The fluid entering from the inlet passage temporarily
accumulates in the central space. Entrained by the flow of a fluid
that is blown out through the first opening, the fluid that has
accumulated in the central space is discharged through the second
opening together with the fluid blown out through the first
opening.
[0011] When the driver vibrates up and down due to bending as
described above, a fluid is sucked from the inlet passage into the
central space by utilizing the pressure energy of a fluid pressed
out of the blower chamber. The fluid sucked from the inlet passage
and the fluid pressed out of the blower chamber flow into each
other to be discharged through the second opening. If the inlet
passage was directly connected to the central space, the pressure
energy of the fluid in the central space would be dissipated into
the inlet passage. To avoid such pressure energy dissipation, in a
preferred embodiment of the present invention, a bottleneck portion
having a passage area that is less than that of the inlet passage
is preferably provided in the inlet passage. Since the bottleneck
portion is provided in the inlet passage, the pressure energy that
is present inside the central space is much less likely to be
dissipated into the inlet passage. Accordingly, it is possible to
efficiently direct the pressure energy toward the second opening,
thereby achieving an increase in the flow rate of a fluid
discharged through the second opening.
[0012] Preferably, the first opening is provided at a portion of
the first wall that faces an area of the approximate center of the
driver. With this preferred structure, since the first opening is
arranged such that it faces an area of approximate the center of
the driver, which is the area at which the displacement of the
driver is the greatest, it is possible to obtain the maximum flow
rate. In addition, preferably, the second opening provided at a
portion of the second wall that faces the first opening. With this
preferred structure, it is possible for a fluid ejected at high
speed from the first opening to pass through the central space and
be discharged through the second opening with reduced
resistance.
[0013] Preferably, the bottleneck portion is provided at a region
in which the inlet passage and the central space are connected. The
bottleneck portion may be provided anywhere in the inlet passage.
However, it is preferable to provide the bottleneck portion at a
position close to the central space because the pressure energy
that is present inside the central space is less likely to be
dissipated into the inlet passage. Thus, it is possible to
efficiently direct the pressure energy toward the second
opening.
[0014] Preferably, the passage area of the bottleneck portion
should gradually decrease in a direction of flow from the inlet
passage to the central space. Since the average pressure in the
central space is less than that in the inlet passage, a pressure
gradient exists therebetween. Although pressure loss occurs in a
flow channel because of friction between a fluid and wall surfaces,
if no bottleneck portion is provided therein, vena contracta would
be produced in the vicinity of the entrances to the central space
because the pressure of the central space is less than the pressure
decrease caused by the pressure loss. A vortex would develop in the
vicinity of the vena contracta, which would result in loss. For
this reason, the flow rate would decrease. To reduce such a flow
loss, the bottleneck portion is preferably provided in the inlet
passage. The passage area of the bottleneck portion preferably
gradually decreases in a direction of a flow from the inlet passage
to the central space. Thus, it is possible to suppress a vortex of
a fluid that flows from the inlet passage into the central space
from developing, which would thereby further reduce the average
pressure in the central space. Therefore, the quantity of a fluid
sucked into the central space is increased, which makes it possible
to further increase the flow rate of a fluid discharged through the
second opening.
[0015] Preferably, the inlet passage should include a plurality of
passages extending in radial directions from the central space. In
addition, preferably, the outer ends of the plural passages of the
inlet passage should be respectively in communication with inlet
ports. With this preferred structure, it is possible to ensure that
the inlet passage has a sufficiently large passage area, which
advantageously reduces the flow channel resistance. Therefore, it
is possible to further increase the flow rate.
[0016] Preferably, the open area of the central space should be
arranged such that the portion of the first wall that faces the
central space vibrates when the driver vibrates. The vibration of
the first wall acts to increase the quantity of a fluid that is
caused to flow by the driver. Since the quantity thereof increases
because of the displacement of the first wall, it is possible to
achieve a further increase in the flow rate. It is more preferable
that the portion of the first wall that faces the central space
should vibrate in a sympathetic manner as the driver vibrates. That
is, it is possible to cause the first wall to vibrate in a
sympathetic manner in response to or by following the displacement
of the driver by making the natural vibration frequency of the
portion of the first wall that faces the central space close to the
vibration frequency of the driver. When the first wall vibrates in
a sympathetic manner, it is not always necessary that the first
wall and the driver must vibrate in the same resonance mode. For
example, both the first wall and the driver may vibrate in the
first-order mode or a higher-order mode (e.g., third-order mode).
Alternatively, one of the first wall and the driver only may
vibrate in the first-order mode, while the other may vibrate in a
higher-order mode.
[0017] The driver according to a preferred embodiment of the
present invention may preferably be, for example, a unimorph-type
driver that includes a piezoelectric element that expands and
contracts in a planar direction and that is attached to one surface
of a diaphragm, e.g., a resin plate or a metal plate, for example,
a bimorph-type driver that includes piezoelectric elements that
expand and contract in opposite directions and that are attached
respectively to both surfaces of a diaphragm, or a bimorph-type
driver that includes a multilayer piezoelectric element that is
deformed due to flexion by itself and that is attached to one
surface of a diaphragm. Alternatively, for example, the entire body
of the driver may preferably be defined as a multilayer
piezoelectric element. The shape of the piezoelectric element may
be a disc, a rectangle, or a ring, for example. An intermediate
plate may preferably be sandwiched between the piezoelectric
element and the diaphragm. The structure may be modified in various
ways as long as the driver vibrates in the direction of thickness
due to flexion when an alternating voltage, which is either a
sinusoidal-wave voltage or a rectangular-wave voltage, is applied
to the piezoelectric element.
[0018] It is preferable to drive the driver including the
piezoelectric element in a first-order resonance mode because the
greatest amount of displacement is obtained in the first-order
resonance mode. However, since the first-order resonance frequency
is within an audible range, a problem of excessive noise might
arise. In contrast, if a third-order resonance mode is used, it is
possible to obtain an amount of displacement that is greater than
that obtained when a resonance mode is not used at all, although
the amount of displacement is less than that obtained in the
first-order resonance mode. In addition, it is possible to drive
the driver at a frequency that is not within the audible range.
Therefore, noise will not be generated. The term "first-order
resonance mode" means a mode in which the center portion of the
driver and the peripheral portion thereof are displaced in the same
direction. The term "third-order resonance mode" means a mode in
which the center portion of the driver and the peripheral portion
thereof are displaced in opposite directions.
[0019] As described above, a piezoelectric micro blower according
to various preferred embodiments of the present invention produce
the following advantageous effects. A driver is caused to vibrate
due to bending so as to suck a fluid from a central space into a
blower chamber through a first opening. The fluid is pressed out of
the blower chamber at high speed to be discharged through a second
opening. In the course of flowing, the fluid pressed out thereof
entrains a fluid that is present inside the central space to be
discharged together. Therefore, it is possible to obtain a
discharging flow, the quantity of which is greater than the
displacement volume of the driver, without providing a check valve.
Thus, it is possible to provide a blower that is capable of blowing
a large quantity of a fluid. In addition, since a bottleneck
portion is provided in an inlet passage, the bottleneck portion
reduces the likelihood that the energy of a pressure fluctuation in
the central space will be dissipated into the inlet passage.
Therefore, it is possible to efficiently direct the pressure energy
toward the second opening. Consequently, it is possible to achieve
a further increase in the flow rate.
[0020] 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
[0021] FIG. 1 is a perspective view that illustrates an overall
configuration of a piezoelectric micro blower according to a first
preferred embodiment of the present invention.
[0022] FIG. 2 is an exploded perspective view of the piezoelectric
micro blower illustrated in FIG. 1.
[0023] FIG. 3 is a sectional view taken along the line III-III of
FIG. 1.
[0024] FIG. 4 is a sectional view taken along the line IV-IV of
FIG. 3.
[0025] FIGS. 5A to 5E are diagrams that illustrate the operation of
the piezoelectric micro blower illustrated in FIG. 3.
[0026] FIG. 6 is a sectional view of a piezoelectric micro blower
according to another example of a preferred embodiment of the
present invention.
[0027] FIGS. 7A and 7B are diagrams that illustrate flow rate
characteristics relative to an applied voltage and flow rate
characteristics relative to power consumption that were obtained
from samples in which the material and thickness of separators are
different from each other.
[0028] FIG. 8 is a sectional view of a micro blower having
bottleneck portions according to another example of a preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] With reference to the accompanying drawings, preferred
embodiments of the present invention will now be explained.
First Preferred Embodiment
[0030] A piezoelectric micro blower according to a first preferred
embodiment of the present invention is shown in FIGS. 1 to 4. A
piezoelectric micro blower A according to the first preferred
embodiment of the present invention is an air blower that is
preferably used to cool electronic equipment, for example. The
piezoelectric micro blower A includes a top plate (second wall) 10,
a flow channel formation plate 20, a separator (first wall) 30, a
blower frame member 40, a driver 50, and a bottom plate 60, which
are attached to define a layered structure in this order as viewed
from the top. The peripheral portion of the driver 50 is fixed by
bonding between the blower frame member 40 and the bottom plate 60.
The members described above, except the driver 50, that is, members
10, 20, 30, 40, and 60, are components that define a blower body 1.
Each of the members 10, 20, 30, 40, and 60 is preferably made of a
flat rigid flat material, such as a metal plate or a hard resin
plate, for example.
[0031] The top plate 10 is preferably a quadrangular flat plate,
for example. A discharging port (second opening) 11 is provided as
a through hole at the approximate center of the top plate 10.
[0032] The flow channel formation plate 20 is preferably also a
flat plate that has substantially the same outer shape as that of
the top plate 10. As illustrated in FIG. 4, a center hole (central
space) 21 that preferably has a diameter greater than that of the
discharging port 11 is provided at the approximate center of the
flow channel formation plate 20. A plurality of inlet passages (in
the illustrated example, preferably four inlet passages) 22
extending in radial directions toward four corners are provided in
the flow channel formation plate 20. The outer ends of the inlet
passages 22 are respectively in communication with inlet ports 8,
which will be explained later. In the first preferred embodiment of
the present invention, the inlet passages 22 are preferably in
communication with the center hole 21 from four different
directions. Because of such a structure, a fluid can be sucked into
the center hole 21 without substantial fluid resistance when the
driver 50 performs a pumping operation. Therefore, it is possible
to increase the flow rate. Each of the inlet passages 22 preferably
includes a bottleneck portion 23. The bottleneck portion 23 is
defined by the tapered portion of the inlet passage 22 at which the
width thereof is reduced toward the center hole 21. In the first
preferred embodiment of the present invention, the bottleneck
portions 23 are preferably provided at regions at which the inlet
passages 22 are connected to the center hole 21. However, the
regions at which the bottleneck portions 23 are provided are not
limited thereto. The bottleneck portions 23 may be provided
anywhere in the inlet passages 22.
[0033] The separator 30 is preferably also a flat plate that has
substantially the same outer shape as that of the top plate 10. A
communication hole (first opening) 31 is provided at the
approximate center of the separator 30, specifically, at a location
corresponding to the position of the discharging port 11. The
communication hole 31 preferably has a diameter that is
substantially the same as that of the discharging port 11, for
example. The diameter of the communication hole 31 may preferably
be exactly the same as that of the discharging port 11. The
diameter of the communication hole 31 may preferably be different
from that of the discharging port 11. However, it is required that
the diameter is less than that of the center hole 21. Inlet holes
32 are provided near four corners of the separator 30,
specifically, at locations corresponding to the outer ends of the
inlet passages 22, respectively. In an assembled state in which the
top plate 10 and the separator 30 are attached to the flow channel
formation plate 20, the center of the discharging port 11, the
center of the center hole 21, and the center of the communication
hole 31 are preferably aligned on the same or substantially the
same axis. The center of the aligned openings 11, 21, and 31
corresponds to the center of the driver 50, which will be explained
later. As will be explained later, preferably, the separator 30 is
made of a thin metal plate so that a portion of the separator 30
that is located at an area corresponding to the center hole 21 can
be vibrated in a sympathetic manner.
[0034] The blower frame member 40 is also preferably a flat plate
that has substantially the same outer shape as that of the top
plate 10. A circular cavity 41 having a large diameter is
preferably provided at the approximate center of the blower frame
member 40. Inlet holes 42 are preferably provided near four corners
of the blower frame member 40, specifically, at locations
corresponding to the positions of the inlet holes 32, respectively.
Since the blower frame member 40 is fixed by bonding between the
separator 30 and the driver 50, the cavity 41 of the blower frame
member 40 defines a blower chamber. The blower chamber 41 is not
limited to an enclosed space. The blower chamber 41 may be a
partially open space.
[0035] The bottom plate 60 is also preferably a flat plate that has
substantially the same outer shape as that of the top plate 10. A
cavity 61 is preferably provided at the approximate center of the
bottom plate 60. The two-dimensional shape of the cavity 61 is
substantially the same as that of the blower chamber 41. The bottom
plate 60 preferably has a thickness that is greater than the sum of
the thickness of a piezoelectric element 52 and the amount of
displacement of a diaphragm 51. With this structure, when the
piezoelectric micro blower A is mounted on, for example, a
substrate, the piezoelectric element 52 is prevented from
contacting the substrate. The wall of the cavity 61 surrounds the
piezoelectric element 52 of the driver 50, which will be explained
later. Inlet holes 62 are preferably provided near four corners of
the bottom plate 60, specifically, at locations corresponding to
the positions of the inlet holes 32 and 42, respectively.
[0036] The driver 50 preferably includes the diaphragm 51 and the
piezoelectric element 52. The piezoelectric element 52 preferably
has a circular shape, for example, and is attached to the lower
surface of the diaphragm 51 at the central area thereof. Besides
various metal materials, such as stainless or brass, resin can be
used as the material of the diaphragm 51, for example. For example,
a resin plate that is made of glass epoxy resin may preferably be
used as the diaphragm 51. The piezoelectric element 52 preferably
has a disc shaped having a diameter less than that of the cavity 41
of the blower frame member 40. In the first preferred embodiment of
the present invention, a single-plate piezoelectric ceramic
including electrodes on both surfaces is preferably used as the
piezoelectric element 52, for example. The piezoelectric element is
attached to the back of the diaphragm 51 (i.e., one surface of the
diaphragm 51 that is opposite to the other surface facing the
blower chamber 41). That is, the driver 50 is preferably configured
as a unimorph driver, for example. When an alternating voltage
(either a sinusoidal wave or a rectangular wave) is applied to the
piezoelectric element 52, the piezoelectric element 52 expands and
contracts in a planar direction. As a result, the displacement of
the entire body of the driver 50 in the direction of its thickness
occurs due to bending. The alternating voltage applied to the
piezoelectric element 52 causes the driver 50 to become displaced
either in a first-order resonance mode or in a third-order
resonance mode due to bending. Since such a voltage is applied
thereto, it is possible to significantly increase the displacement
volume of the driver 50 as compared to a case in which a voltage
having any frequency other than the above-described frequency is
applied thereto. Consequently, it is possible to significantly
increase the flow rate.
[0037] Inlet holes 51a are preferably provided near four corners of
the diaphragm 51, specifically, at locations corresponding to the
locations of the inlet holes 32, 42, and 62, respectively. The
inlet holes 32, 42, 51a, and 62 are aligned such that they define
each of the inlet ports 8. One end of the inlet port 8 is defined
as a downward open end. The other end of the inlet port 8 is in
communication with the inlet passage 22.
[0038] As illustrated in FIG. 3, the inlet ports 8 of the
piezoelectric micro blower A are open at the bottom of the blower
body 1. In addition, the discharging port 11 is open at the top of
the blower body 1. A compressible fluid can be sucked into the
inlet ports 8 through the open ends thereof, which are preferably
provided at the reverse side of the piezoelectric micro blower A,
and then can be discharged from the discharging port 11, which is
preferably provided at the front side of the piezoelectric micro
blower A. Such a structure is suitable for use as a blower to
supply air to a fuel cell or a blower to cool a CPU using air. It
is not always necessary that the open ends of the inlet ports 8 be
oriented downward, and instead, the open ends may be open at the
sides.
[0039] Although the driver 50 illustrated in FIG. 3 preferably
includes the diaphragm 51 and the piezoelectric element 52, the
structure of the driver 50 is not limited to the illustrated
example. For example, as illustrated in FIG. 6, the driver 50 may
preferably further include an intermediate plate that is sandwiched
between the diaphragm 51 and the piezoelectric element 52. A plate
that is preferably made of metal, such as SUS, for example, can be
used as the intermediate plate 53. Since the intermediate plate 53
is sandwiched between the diaphragm 51 and the piezoelectric
element 52, a neutral plane at the time of the displacement of the
driver 50 due to bending is located inside the intermediate plate
53, which results in greater displacement efficiency. Therefore, it
is possible to provide a piezoelectric micro blower that can
produce a high flow rate with a low voltage.
[0040] FIGS. 5A to 5E are diagrams that schematically illustrate an
example of the operation of the piezoelectric micro blower A. To
facilitate understanding, displacement is shown in an exaggerated
manner. An initial state (when no voltage is applied thereto) is
shown in FIG. 5A. FIGS. 5B to 5E illustrate the displacement of the
driver 50 and the separator 30 at intervals of 1/4 of a cycle of a
voltage (e.g., sinusoidal wave) applied to the piezoelectric
element 52. As a result of the application of an alternating
voltage to the piezoelectric element 52, operations shown in FIGS.
5B to 5E are repeated in a cycle. As illustrated therein, the
vibration of the driver 50 causes the sympathetic vibration of the
separator 30. The vibration of the separator 30 occurs with a delay
of a predetermined phase (in this example, approximately
90.degree.) with respect to the vibration of the driver 50. Because
of the sympathetic vibration of the separator 30, a large pressure
wave is generated from the first opening 31 in an upward direction.
Air is forced out of the central space 21 through the second
opening 11 to the outside due to the pressure wave. Therefore, it
is possible to increase the flow rate as compared to a case in
which the separator 30 is not vibrated in a sympathetic manner.
Since the air is forced out of the central space 21, new air is
sucked from the inlet passages 22 into the central space 21,
thereby generating a continuous airflow exiting from the second
opening 11.
[0041] In FIGS. 5A to 5E, an example of the displacement of the
driver 50 in a first-order resonance mode is illustrated. The same
principle holds true for displacement in a third-order resonance
mode. In the illustrated example, it is assumed that the amount of
displacement of the separator 30 is greater than that of the driver
50. However, depending on the dimensions of the central space 21,
the Young's modulus of the separator 30, the thickness of the
separator 30, and other factors and parameters, there is a
possibility that the amount of displacement of the separator 30 is
less than that of the driver 50. The phase delay of the separator
30 with respect to the driver 50 is not limited to approximately
90.degree.. The above-described structure may be modified as long
as the vibration of the separator 30 occurs with a certain delay
with respect to the vibration of the driver 50, and, for this
reason, an actual change in the distance between the driver 50 and
the separator 30 is greater than a change that would occur if the
separator 30 did not vibrate at all.
[0042] A flow-rate measurement was performed for a piezoelectric
micro blower A having the following specifications.
[0043] Driver: A unimorph element that includes a diaphragm, a
single-plate piezoelectric ceramic element, and an intermediate
plate that is sandwiched between the diaphragm and the
piezoelectric ceramic element was used as the driver. The diaphragm
was made of a 42Ni plate having a thickness of about 0.08 mm. The
intermediate plate was an SUS430 plate having a thickness of about
0.15 mm and a diameter of about 11 mm. The piezoelectric ceramic
element had a thickness of about 0.2 mm and a diameter of about 11
mm.
[0044] Blower chamber: about 0.15 mm in height, about 16 mm in
diameter
[0045] Blower body: about 20 mm in length, about 20 mm in width,
about 2.4 mm in height
[0046] Separator: SUS430 having a thickness of about 0.05 mm
[0047] First opening: about 0.6 mm in diameter
[0048] Second opening: about 0.8 mm in diameter
[0049] Central space: about 6 mm in diameter, about 0.5 mm in
height
[0050] Inlet passages: about 2.5 mm in width, about 0.5 mm in
height, four passages
[0051] Bottleneck portions: about 1 mm in width
[0052] A voltage having a sinusoidal waveform of 24 kHz and 20 Vp-p
was applied to the piezoelectric micro blower A having the
above-described specifications. As a result of the measurement, the
flow rate was about 0.9 L/min under a condition of about 100 Pa.
The driver was energized in the third-order mode. Alternatively,
the driver may be energized in the first-order mode. Another
experiment was performed for comparison with the use of a
piezoelectric micro blower having the same specifications as
described above except that it does not include any bottleneck
portion. As a result of the measurement, the flow rate was about
0.77 L/min under the condition of about 100 Pa. From the
above-described results, it was discovered that the bottleneck
portions contribute to an increase in the flow rate.
[0053] It can be inferred that for the following reasons, the
quantity of flow is relatively large in the above-described
structure in which the inlet passages include the bottleneck
portions.
[0054] When the driver 50 vibrates, a pressure wave having high
energy is generated from the first opening 31. Because of the
pressure wave, air is forced out of the central space 21 through
the second opening 11. As the driver 50 vibrates, a portion of the
separator 30 that defines the bottom wall of the central space 21
also vibrates (refer to FIG. 5). The vibration of the separator 30
generates a large pressure fluctuation in the central space 21. The
pressure energy acts to be dissipated not only through the second
opening 11 but also into the inlet passages 22. If the sectional
area of the inlet passage 22 is configured to be large so as to
reduce air resistance, pressure energy loss is large. In contrast,
since the inlet passages 22 include the bottleneck portions 23, the
pressure energy that is present inside the central space 21 is less
likely to be dissipated into the inlet passages 22. Accordingly, it
is possible to efficiently direct the pressure energy that is
present inside the central space 21 toward the second opening 11,
thereby achieving an increase in the flow rate.
[0055] Since there is a high-speed flow inside the central space
21, its average pressure is less than pressure in the inlet
passages 22. For this reason, a pressure gradient is produced in a
flow channel. The pressure gradient generates a flow from the inlet
passages 22 toward the central space 21. Although pressure loss
occurs in the inlet passages 22 because of friction between air and
wall surfaces, if no bottleneck portion was provided in the flow
channel, vena contracta would be produced in the vicinity of
entrances to the central space 21 because the pressure of the
central space 21 is less than the pressure decreased due to the
pressure loss. Therefore, loss due to a vortex being developed
would occur in the vicinity of the vena contracta. Consequently,
the flow rate of the blower would decrease. In contrast, since the
bottleneck portions 23 are preferably provided in the vicinity of
entrances to the central space 21, the conformity of the shape of
the flow channel to the shape of the flow increases. With the
increased conformity, it is possible to prevent a vortex from
developing and thus to reduce flow loss. Consequently, the flow
rate of the blower is increased.
[0056] The separator 30 is preferably attached to the flow channel
formation plate 20. The central area of the separator 30 that
corresponds to the central space 21 is configured as a regional
portion that can vibrate. As illustrated in FIGS. 5A to 5E, the
vibration of the central area of the separator 30 has a strong
affect on the flow rate. In view of these considerations, the size
of the central space 21 (open area) is designed to have an
appropriate diameter that makes it easier for the central area of
the separator 30 to vibrate. However, it is impossible to restrain
the separator 30 at regions at which the inlet passages 22 are
connected to the central space 21. In the flow channel formation
plate 20 including the bottleneck portions 23, since the front end
of each of the bottleneck portions 23 has a tapered shape, the area
at which the sidewalls of the central space 21 exist is relatively
large. That is, as compared to a case in which no bottleneck
portions are provided, it is possible to increase the area in which
the separator 30 is supported. The shape of the area in which the
separator 30 is supported is preferably substantially circular.
With the bottleneck portions 23, the flow channel formation plate
20 can support the central area of separator 30 more securely,
which contributes to an increase in the flow rate.
[0057] Table 1 shows the flow rate obtained when the drive
frequency of the driver 50 and the diameter of the central space 21
are changed. The unit of the flow rate is L/min. A diaphragm (42Ni
plate) having a thickness of about 0.08 mm was used for a drive
frequency of about 24.4 kHz. A diaphragm (42Ni plate) having a
thickness of about 0.1 mm was used for a drive frequency of about
25.5 kHz.
TABLE-US-00001 TABLE 1 Diameter of Central space .PHI. 5 mm .PHI. 6
mm Frequency 24.4 kHz 0.7 L/min. 0.8 L/min. 25.5 kHz 0.78 L/min.
0.71 L/min.
[0058] As shown in Table 1, the flow rate increases as the
frequency increases when the diameter of the central space 21 is
about 5 mm, whereas the flow rate increases as the frequency
decreases when the diameter of the central space 21 is about 6 mm.
As described above, it can be understood that the vibration of the
central area of the separator 30 that corresponds to the central
space 21 has a strong affect on the flow rate. The following reason
can be inferred. The natural vibration frequency of the driver 50
differs depending on the material of the diaphragm 51 and the
thickness thereof. It is possible to make the natural vibration
frequency of the central area of the separator 30 that corresponds
to the central space 21 close to the natural vibration frequency of
the driver 50 by adjusting the diameter of the central space 21,
thereby producing the sympathetic vibration of the separator 30,
which increases the flow rate.
[0059] FIGS. 7A and 7B show the results of an experiment conducted
on a piezoelectric micro blower B having a structure in which the
driver 50 includes the diaphragm 51, the piezoelectric element 52,
and the intermediate plate 53 that is sandwiched between the
diaphragm 51 and the piezoelectric element 52. As shown in Table 2,
the experiment was performed to compare the flow rate obtained when
the material of the separator 30 and the thickness thereof are
changed. A plate that is made of phosphor bronze with a thickness
of about 0.05 mm was used as a separator in a first sample. A plate
that is made of SUS304 with a thickness of about 0.1 mm was used as
a separator in a second sample. Except for the above component, the
specifications of the piezoelectric micro blower B are the same or
substantially the same as those of the piezoelectric micro blower
A. The specifications of the first sample are the same or
substantially the same as those of the second sample except for the
separator. The drive frequency of about 24.4 kHz was used for both
the first sample and the second sample.
TABLE-US-00002 TABLE 2 First Sample Second Sample Material of
Separator phosphor SUS304 bronze Thickness of Separator (mm) 0.05
0.1 Diameter of First Opening 0.6 0.6 (mm) Material of Top Plate
nickel silver nickel silver Diameter of Second Opening 0.8 0.8 (mm)
Material of Blower Chamber nickel silver nickel silver Height of
Blower Chamber (mm) 0.15 0.15 Diameter of Blower Chamber 16 16 (mm)
Material of Diaphragm 42 Ni 42 ni Thickness of Diaphragm (mm) 0.08
0.08 Thickness of Intermediate 0.15 0.15 Plate (mm) Diameter of
Intermediate 11 11 Plate (mm) Thickness of Piezoelectric 0.20 0.20
Element (mm) Diameter of Piezoelectric 11 11 Element (mm) Diameter
of Central space 6 6 (mm) Height of Central space (mm) 0.5 0.5
[0060] Typically, a plate that is made of SUS304 and has a certain
thickness is one and a half times as rigid as a plate that is made
of phosphor bronze and has the same thickness. Since the separator
of the second sample is twice as thick as the separator of the
first sample, the rigidity of the separator of the second sample is
far greater than the rigidity of the separator of the first sample.
In other words, a portion of the separator of the first sample that
faces the central space vibrates, whereas a portion of the
separator of the second sample that faces the central space does
not significantly vibrate. The purpose of the experiment is to
measure the influence of the vibration of a portion of the
separator that faces the central space on the flow rate.
[0061] As illustrated in FIG. 7A, for example, the flow rate of the
second sample obtained when a voltage of about 20 Vp-p was applied
thereto was approximately about 0.42 L/min. The flow rate of the
first sample obtained when the same voltage of about 20 Vp-p was
applied thereto was approximately about 0.78 L/min. Therefore, the
flow rate of the first sample is roughly twice that of the second
sample. That is, the vibration of the portion of the separator
significantly contributes to an increase in the flow rate. FIG. 7B
shows the results of a comparison of the flow rate based on power
consumption. Although power consumption changes due to a change in
impedance, the first sample is advantageous when compared based on
the same power consumption.
Second Preferred Embodiment
[0062] FIG. 8 illustrates the shape of bottleneck portions
according to a second preferred embodiment of the present
invention. Since the structure of the flow channel formation plate
20 according to the second preferred embodiment of the present
invention is substantially the same as that of the first preferred
embodiment of the invention (refer to FIG. 4) except for the shape
of bottleneck portions, the same reference numerals are used for
the components described earlier. The components described earlier
are not explained below. In the second preferred embodiment of the
present invention, bottleneck portions 24 that are not tapered are
provided at regions at which the inlet passages 22 are connected to
the central space 21. The bottleneck portions 24 prevent the energy
of a pressure fluctuation in the central space 21 from being
dissipated into the inlet passages 22. Thus, it is possible to
achieve an increase in the flow rate.
[0063] In the foregoing preferred embodiments of the present
invention, a portion of a separator (first wall) that corresponds
to a central space preferably vibrates in a sympathetic manner as a
driver vibrates. However, it is not always necessary for the
separator to vibrate in a sympathetic manner. Any alternative
structure in which the vibration of a driver excites a separator,
and, in addition, the separator vibrates in response to or by
following the vibration of the driver makes it possible to achieve
an increase in the flow rate. The shape of an inlet passage is not
limited to a linear passage extending in a radial direction as
shown in FIG. 4. That is, the shape of the inlet passage may be
arbitrarily selected. The number of inlet passages may also be
arbitrarily selected depending on the required flow rate and the
required level of noise.
[0064] In the foregoing preferred embodiments of the present
invention, a plurality of plate members are preferably attached in
layers to define a blower body. However, the structure of the
blower body is not limited thereto. For example, the top plate and
the flow channel formation plate 20 may be integrally molded as a
single component that is made of resin or metal. The same applies
to, for example, the separator 30 and the blower frame member 40,
or the flow channel formation plate 20 and the separator 30.
[0065] 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 the scope and spirit of the present invention. The scope
of the present invention, therefore, is to be determined solely by
the following claims.
* * * * *