JP2012182870A - Piezoelectric fan and cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric fan used for cooling an electronic device, which is capable of obtaining higher blowing capacity than ever before at the same applied voltage as conventional ones.SOLUTION: The piezoelectric fan comprises: a plate-like piezoelectric element which expands and contracts according to application of a voltage; a plate-like diaphragm to at least one main surface of which the piezoelectric element is fixed; and a support for fixing one end of the diaphragm. One end of the diaphragm is a fixed end, and the other end is a free end. The piezoelectric element is maintained in a state where tensile stress is applied.

Description

  The present invention relates to a piezoelectric fan used for cooling electronic equipment.

  Fan devices are widely used for cooling electronic devices incorporating heat-generating components such as AV devices and computers. In recent years, there is a demand for a small and highly quiet piezoelectric fan suitable for mounting. Such a piezoelectric fan is disclosed in Patent Document 1, for example. As shown in FIG. 6, this Patent Document 1 discloses a cooling device 100 that uses a piezoelectric fan 110 that discharges warm air between a plurality of radiating fins 121 provided in a heat sink 120.

  As shown in FIG. 6B in particular, the piezoelectric fan 110 includes a piezoelectric element 111 that expands and contracts in response to application of a driving AC voltage having a predetermined frequency, and a diaphragm 112 to which the piezoelectric element 111 is attached. . One end of the diaphragm 112 is fixed to the heat sink 120 by a fixing member 130 to become a fixed end 113, and the other end is a free end 114. The diaphragm 112 is formed by bending at a bent portion 115 at 90 degrees. A region on the free end side from the bent portion 115 is formed by being divided into a rake shape in accordance with the interval between the heat dissipating fins 121.

  The piezoelectric fan 110 is driven by applying a voltage from a driving AC power source to an electrode (not shown) formed on the piezoelectric element 111 and a diaphragm 112 made of a conductor. When the piezoelectric element 111 expands and contracts, the free end 114 of the diaphragm 112 performs bending vibration in a fan shape. Thus, the heat sink 120 is cooled by exchanging the air between the radiation fins 121 provided on the heat sink 120 by the piezoelectric fan.

JP 2010-67909 A

  In such a piezoelectric fan, a higher air blowing capability is desired in order to cope with an electronic device having a large heat generation amount. However, in a conventional piezoelectric fan, since the bending displacement amount of the diaphragm with respect to the applied voltage is small, There was a problem that the amplitude was small and the blowing capacity was not sufficient.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric fan and a cooling device that can obtain a higher blowing capacity than before with an applied voltage comparable to that of the prior art.

  The piezoelectric fan according to the present invention includes a plate-like piezoelectric element that expands and contracts in response to voltage application, a plate-like diaphragm in which the piezoelectric element is fixed to at least one main surface, and one end of the diaphragm is fixed. And one end of the diaphragm is a fixed end, and the other end is a free end, and the piezoelectric element is maintained in a state where a tensile stress is applied.

  In this case, since a tensile stress is applied to the piezoelectric element in addition to the polarization treatment, the polarization directions in the crystal of the piezoelectric element are more easily aligned than in the past. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

  In the present invention, the piezoelectric element is fixed to at least one main surface of the diaphragm by a thermosetting resin, and the diaphragm is made of a material having a smaller linear expansion coefficient than the piezoelectric element. Is desirable. In this case, when the piezoelectric element and the vibration plate are returned to normal temperature after the adhesive is cured, the vibration amount of the vibration plate is so small that the piezoelectric element cannot be sufficiently contracted and tensile stress is applied to the piezoelectric element. Maintained. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

  According to the present invention, the support is made of a material having a larger linear expansion coefficient than the diaphragm, the support has an elongated shape, and the support has a longitudinal direction shorter than the diaphragm. It is desirable that one end of one main surface of the diaphragm is fixed with a thermosetting resin so as to reach both ends in the direction, and the diaphragm is maintained in a state where a tensile stress is applied. In this case, when the temperature returns to room temperature after the support and the diaphragm are bonded and cured, the amount of contraction of the diaphragm is small, and the support warps convexly toward the diaphragm. Since the diaphragm is sufficiently thin relative to the support, a state in which a tensile stress is applied from substantially the center of the support to the diaphragm and the piezoelectric element is maintained. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

  In the present invention, the support has an elongated shape, and the piezoelectric element is fixed to one main surface of the support so that the longitudinal direction reaches both ends of the diaphragm in the short direction. It is fixed to the other main surface of the diaphragm, and the fixed surface of the support body with respect to the diaphragm is formed in an arc shape so that a central portion in the longitudinal direction of the support body protrudes toward the diaphragm side. It is desirable. In this case, when the diaphragm to which the piezoelectric element is fixed is joined to the support, the diaphragm warps convexly toward the one main surface, so that a state in which tensile stress is applied to the piezoelectric element is maintained. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

  The cooling device of the present invention includes the piezoelectric fan as described above and a housing, and the support of the piezoelectric fan is fixed at two points by pressing both ends of the piezoelectric fan with screws. The fixing surface is formed flat, and the support of the piezoelectric fan is in contact with the fixing surface so that the center portion in the longitudinal direction is fixed so as to protrude toward the diaphragm side of the piezoelectric fan. The main surface of the support body of the piezoelectric fan is formed to be inclined with respect to the fixed surface.

  In this case, since the support is bent and fixed so as to protrude toward the diaphragm, a state in which tensile stress is applied from the substantially center of the support to the diaphragm and the piezoelectric element is maintained. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

  According to the present invention, since tensile stress is applied to the piezoelectric element in addition to the polarization treatment, the polarization directions in the crystal of the piezoelectric element are more easily aligned than in the past. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

1 is a perspective view of a piezoelectric fan according to Embodiment 1 of the present invention. 1 is a side view of a piezoelectric fan according to Embodiment 1. FIG. It is a figure which shows the value of the curvature amount of the piezoelectric fan which concerns on Embodiment 1. FIG. The piezoelectric fan which concerns on Embodiment 2 of this invention is shown, The same figure (A) is a perspective view, The same figure (B) is a front view. It is a front view of the cooling device concerning Embodiment 3 of the present invention. The conventional cooling device is shown, (A) is a perspective view, and (B) is a perspective view of a conventional piezoelectric fan.

  Below, the piezoelectric fan and cooling device which concern on embodiment of this invention are demonstrated.

(Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the piezoelectric fan 10 of Embodiment 1 includes a piezoelectric element 11 that expands and contracts in response to application of a drive AC voltage having a predetermined frequency, a diaphragm 12, and a support 13. The piezoelectric element 11 is fixed to both main surfaces of the diaphragm 12. One end of the main surface of the diaphragm 12 is supported by the support body 13. One end of the diaphragm 12 is a fixed end 14 and the other end is a free end 15. The fixed end 14 refers to a fixed end serving as a vibration node.

The diaphragm 12 is formed in a thin plate shape having a width of 46 mm, a length of 50 mm, and a thickness of 50 μm. The vibration plate 12 is provided with a bending portion 16 at the center in the length direction, and is bent at about 90 degrees on the side where the support body 13 is provided at the bending portion 16 and is formed in an L shape. The length from the fixed end 14 to the bent portion 16 is 25 mm, and the length from the free end 15 to the bent portion 16 is 25 mm. The width of the diaphragm 12 changes with the bent portion 16 as a boundary, the width of the diaphragm 12 on the free end 15 side with respect to the bent portion 16 is 46 mm, and the width of the diaphragm 12 on the fixed end 14 side with respect to the bent portion 16. Is processed to 35 mm. On the free end 15 side of the bending portion 16 of the diaphragm 12, the diaphragm 12 is divided into seven divided plates 12a and formed in a rake shape, and the divided plates 12a are formed at equal intervals. Each divided plate 12a has a width of 4.5 mm. The diaphragm 12 is made of, for example, 42Ni. The linear expansion coefficient of 42Ni is 4.4 × 10 ⁻⁶ / ° C.

The piezoelectric element 11 has a plate shape of width 33.4 mm × length 15.8 mm × thickness 55 μm, and electrodes (not shown) are formed on both main surfaces. The piezoelectric element 11 is made of, for example, lead zirconate titanate ceramic. The linear expansion coefficient of the piezoelectric element is 8.3 × 10 ⁻⁶ / ° C. The piezoelectric element 11 is fixed to the fixed end 14 side of the bending portion 16 of the diaphragm 12.

  The support 13 has a rectangular parallelepiped shape with a width of 48 mm, a length of 5 mm, and a thickness of 3 mm, and is made of, for example, a glass epoxy resin. The support body 13 is supported by a housing (not shown) by being screwed at two locations on both ends.

  As shown in FIG. 2, the piezoelectric fan 10 is driven by applying a voltage from a drive AC power supply 17 to one electrode (not shown) formed on the piezoelectric element 11 and a diaphragm 12 made of a conductor. . When the piezoelectric element 11 expands and contracts in the length direction of the piezoelectric element 11, the bending portion 16 vibrates in the thickness direction of the piezoelectric element 11 because one end of the diaphragm 12 is fixed. As a result, the free end 15 performs bending vibration in a fan shape in the length direction of the piezoelectric element 11 and is driven as a piezoelectric fan.

  In the present embodiment, the piezoelectric element is maintained in a state where a tensile stress is applied. Since the piezoelectric element is formed in this way, tensile stress is applied to the piezoelectric element in addition to the polarization treatment, so that the polarization directions in the crystal of the piezoelectric element are more easily aligned than in the past. Since the displacement amount of the piezoelectric element becomes larger than this, the blowing capacity of the piezoelectric fan increases. The experimental results that serve as the basis are described below.

(Experimental Example 1 and Comparative Example 1)
An experiment was conducted using the piezoelectric fan 10 shown in FIG. 1 as Experimental Example 1 and a piezoelectric fan partially different from Experimental Example 1 as Comparative Example 1.

The difference between Experimental Example 1 and Comparative Example 1 is the linear expansion coefficient of the diaphragm. As Experimental Example 1, 42Ni was used for the diaphragm, and as Comparative Example 1, SUS was used for the diaphragm. The linear expansion coefficient of 42Ni is smaller than the linear expansion coefficient of the piezoelectric element, and is 4.4 × 10 ⁻⁶ / ° C. The linear expansion coefficient of SUS is larger than the linear expansion coefficient of the piezoelectric element, and is 17.3 × 10 ⁻⁶ / ° C. Detailed conditions are shown in Table 1.

  In this experiment, using these two piezoelectric fans, the amplitude of the diaphragm when driven by the fundamental wave was measured, and the blowing capacity was compared. In addition, the amplitude in this specification is both amplitudes. The air blowing capacity is determined by frequency × amplitude.

  A laser displacement meter was used to measure the amplitude, and the amplitude in the length direction of the piezoelectric element at the free end of the diaphragm was measured. The voltage applied to each piezoelectric fan was 20 Vpp.

  The experimental results are shown in Table 1. When comparing the blowing capacity between Experimental Example 1 and Comparative Example 1, the blowing capacity of Experimental Example 1 was 596.3 Hz · mm, and the blowing capacity of Comparative Example 1 was 512.9 Hz · mm.

  From this, it can be said that it is more desirable that the diaphragm is made of a material having a smaller linear expansion coefficient than that of the piezoelectric element, since the amplitude of the piezoelectric fan increases, so that the air blowing capability increases.

  This is because when the piezoelectric element and the vibration plate return to room temperature after the adhesive is cured, the vibration amount of the vibration plate is so small that the piezoelectric element cannot be sufficiently contracted, and a state in which tensile stress is applied to the piezoelectric element is maintained. It is to be done. For this reason, the displacement amount of the piezoelectric element increases, and the amplitude of the piezoelectric fan increases.

(Experiment 1 and Experiment 2)
Experiment 1 was conducted using the piezoelectric fan 10 shown in FIG. 1, and Experiment 2 was conducted using a piezoelectric fan partially different from the experiment example 1. The difference between Experimental Example 1 and Experimental Example 2 is the linear expansion coefficient of the support 13. As Experimental Example 1, a thermosetting resin having a lower linear expansion coefficient than that of the diaphragm was used, and as Experimental Example 2, a thermosetting resin having a higher linear expansion coefficient than that of the diaphragm was used. Detailed conditions are shown in Table 1.

  In this experiment, using these two piezoelectric fans, the amplitude of the diaphragm when driven by the fundamental wave was measured, and the blowing capacity was compared. In this experiment, the voltage applied to each piezoelectric fan was 20 Vpp.

  The experimental results are shown in Table 1. When comparing the blowing capacity between Experimental Example 1 and Experimental Example 2, the blowing capacity of Experimental Example 1 was 596.3 Hz · mm, and the blowing capacity of Experimental Example 2 was 701.3 Hz · mm.

  FIG. 3 shows the amount of displacement depending on the position of the diaphragm under the conditions in Table 1. The distance from one end of the diaphragm refers to one fixing point X in the width direction of the diaphragm 12 and the support 13 shown in FIG. 1 as a starting point and the other fixing point X ′ as an end point. Indicates a linear distance. The amount of warpage indicates a distance from a reference point when a straight line between one point X and the other point X ′ on the main surface of the diaphragm 12 is used as a reference.

  Comparing Experimental Example 1 and Experimental Example 2, in Experimental Example 1, when the position of the diaphragm is 19 mm from the initial value, the minimum value is −11.6 μm, and the displacement amount increases toward the center of the diaphragm. There was a tendency to protrude downward. On the other hand, in Experimental Example 2, when the position of the diaphragm was 24 mm from the initial value, the maximum value was 36.1 μm, the displacement amount was larger toward the center of the diaphragm, and the graph tended to be convex upward. .

  From this, the support body is made of a material having a larger linear expansion coefficient than the diaphragm, the support body has a rectangular parallelepiped shape, and the support body reaches the both ends in the width direction of the diaphragm, If one end of one of the main surfaces of the diaphragm is fixed with a thermosetting resin, and the diaphragm is maintained in a state where a tensile stress is applied, the amplitude of the piezoelectric fan increases, so the blowing capacity increases. Is more desirable.

  This is because when the support body and the diaphragm return to room temperature after adhesion and curing, the support body warps convexly toward the diaphragm side because the contraction amount of the diaphragm is small. This is because the diaphragm is sufficiently thin with respect to the support, and a state in which a tensile stress is applied from the approximate center in the thickness direction of the support to the diaphragm and the piezoelectric element is maintained. For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is further increased.

  In the above embodiment, the diaphragm is made of 42Ni, but is not limited to this. For example, any material having a linear expansion coefficient smaller than that of the piezoelectric element may be used.

  In the above embodiment, the piezoelectric element is fixed to both main surfaces, but is not limited thereto. The piezoelectric element may be fixed to at least one main surface.

(Embodiment 2)
4A and 4B show a piezoelectric fan according to Embodiment 2 of the present invention, where FIG. 4A is a perspective view and FIG. 4B is a front view. In the present specification, the front view is schematically shown for easy understanding.

  As shown in FIG. 4A, the piezoelectric fan 20 of the present embodiment includes a piezoelectric element 21, a diaphragm 22 to which the piezoelectric element 21 is attached, and a support 23 that fixes one end of the diaphragm 22. Prepare. The vibration plate 22 is provided with a bending portion 26 at the center in the length direction, and is bent at about 90 degrees on the side where the support 23 is provided at the bending portion 26 to be bent into an L shape. The region on the free end 25 side of the diaphragm 22 is divided into a plurality of divided plates 22a.

  A different place from Embodiment 1 in this embodiment is the shape of the support body 23. Specifically, the fixed surface of the support 23 to the diaphragm 22 is formed in an arc shape so that a central portion in the length direction of the support 23 is convex toward the diaphragm 22 side.

  With this configuration, when the diaphragm is joined to the support, the diaphragm warps convexly toward the one main surface, so that a tensile stress is applied to the piezoelectric element and the displacement of the piezoelectric element increases. . For this reason, since the amplitude of the piezoelectric fan is increased, the air blowing capability is increased, which is more desirable.

  In the said embodiment, although the support body is integrally molded and formed in circular arc shape, it does not restrict to this. For example, you may form in circular arc shape by using another body.

(Embodiment 3)
FIG. 5 is a front view of the cooling device 50 according to the third embodiment. In the present specification, the front view is schematically shown for easy understanding.

  The cooling device 50 according to this embodiment includes a piezoelectric fan 30 and a heat sink 40. The piezoelectric fan 30 includes a piezoelectric element, a diaphragm 32 to which the piezoelectric element is attached, and a support 33 that fixes one end of the diaphragm 32. One end of the diaphragm 32 is a fixed end, and the other end is a free end. A region on the free end side of the diaphragm 32 is formed by being divided into a plurality of divided plates 32a.

  In the present embodiment, the support body 33 of the piezoelectric fan 30 is fixed at two points by pressing both ends against the heat sink 40 by screwing, and the fixing surface 41 of the heat sink 40 with the support body 33 is a flat main surface without unevenness. Formed on the surface.

  The support 33 is formed such that the main surface 34 that contacts the fixed surface 41 is inclined toward the center in the length direction with respect to the fixed surface 41. Since the support body 33 is formed in this way, when the support body 33 is pressed and fixed to the heat sink 40, the support body 33 is fixed to warp so that the central portion in the length direction is convex toward the diaphragm 32 side. A state in which a tensile stress is applied from substantially the center in the thickness direction to the diaphragm and the piezoelectric element is maintained. For this reason, the displacement amount of the piezoelectric element is increased and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased, which is more desirable.

(Experimental Example 3 and Comparative Example 2)
An experiment was conducted using the cooling device 50 shown in FIG. 5 as Experimental Example 3, and an experiment was conducted using a cooling device that was partially different from Experimental Example 3 as Comparative Example 2. The difference between Experimental Example 3 and Comparative Example 2 is the shape of the main surface 34 of the support. As Experimental Example 3, the main surface of the support in contact with the fixed surface is fixed to the fixed surface so that the central portion in the length direction of the support is warped and fixed so as to protrude toward the diaphragm side of the piezoelectric fan. As a comparative example 2, a cooling device in which the main surface of the support that is in contact with the fixed surface is formed parallel to the fixed surface is used. Using. Detailed conditions are shown in Table 2.

  In this experiment, using these two cooling devices, the amplitude of the diaphragm when the piezoelectric fan in the cooling device was driven with a fundamental wave was measured to compare the blowing capacity. In this experiment, the voltage applied to each piezoelectric fan was 20 Vpp.

  The experimental results are shown in Table 2. When comparing the blowing capacity between Experimental Example 3 and Comparative Example 2, the blowing capacity of Experimental Example 3 was 602.5 Hz · mm, and the blowing capacity of Comparative Example 2 was 553.0 Hz · mm.

  From this result, the support surface is inclined toward the center in the length direction with respect to the fixed surface so that the support surface protrudes toward the diaphragm when both ends of the support member are pressed. If it is formed, the air blowing capacity of the piezoelectric fan increases, which is more desirable.

  This is because the support is bent and fixed so as to protrude toward the diaphragm side, so that a state in which tensile stress is applied from substantially the center of the support to the diaphragm and the piezoelectric element is maintained. . For this reason, the displacement amount of the piezoelectric element is increased, and the amplitude of the piezoelectric fan is increased, so that the air blowing capability is increased.

  Note that the piezoelectric fan and the cooling device according to the present invention are not necessarily subjected to tensile stress finally. When a compressive stress is unavoidably applied for reasons such as manufacturing, a state in which a compressive stress is relaxed by a structure by applying a tensile stress is also included.

  In addition, the piezoelectric fan and cooling device which concern on this invention are not limited to the said embodiment, It can change variously within the range of the summary.

  In the said embodiment, although the piezoelectric element is comprised from the lead zirconate titanate ceramics, it is not restricted to this. For example, it may be composed of a lead-free piezoelectric ceramic material such as potassium sodium niobate and alkali niobate ceramics.

  In the embodiment, the bent portion provided in the central portion of the diaphragm is bent into an L shape, but the present invention is not limited to this. For example, it may be bent into a U shape or a V shape, or may be a diaphragm that is not bent or bent.

  In the said embodiment, although the division plate is provided in the free end side rather than the bending part of the diaphragm, it is not restricted to this. For example, the free end may not be divided.

  In the above-described embodiment, the piezoelectric element is fixed to sandwich the diaphragm from both sides to configure the bimorph type vibrator. However, the unimorph type vibrator in which the piezoelectric element is bonded to only one main surface of the diaphragm is configured. May be.

DESCRIPTION OF SYMBOLS 10, 20, 30 ... Piezoelectric fan 11, 21 ... Piezoelectric element 12, 22, 32 ... Diaphragm 12a, 22a, 32a ... Dividing plate 13, 23, 33 ... Support body 14, 24 ... Fixed end 15, 25 ... Free end DESCRIPTION OF SYMBOLS 16, 26 ... Bending part 17 ... Drive alternating current power supply 34 ... Main surface of support body 40 ... Heat sink 41 ... Fixed surface 50 ... Cooling device

Claims (5)

A plate-like piezoelectric element that expands and contracts in response to voltage application;
A plate-like diaphragm in which the piezoelectric element is fixed to at least one main surface;
A support for fixing one end of the diaphragm,
One end of the diaphragm is a fixed end, the other end is a free end,
The piezoelectric fan, wherein the piezoelectric element is maintained in a state where a tensile stress is applied.   The piezoelectric element is fixed to at least one main surface of the diaphragm by a thermosetting resin, and the diaphragm is made of a material having a smaller linear expansion coefficient than the piezoelectric element. Item 2. The piezoelectric fan according to Item 1. The support is made of a material having a larger linear expansion coefficient than the diaphragm,
The support has an elongated shape,
One end of one main surface of the diaphragm is fixed with a thermosetting resin so that the longitudinal direction of the support reaches both ends of the diaphragm in the short direction, and the diaphragm gives a tensile stress. The piezoelectric fan according to claim 1, wherein the piezoelectric fan is maintained in a state where the piezoelectric fan is maintained. The support has an elongated shape,
The support body is fixed to the other main surface of the diaphragm where the piezoelectric element is fixed to one main surface so that the longitudinal direction reaches both ends in the short direction of the diaphragm,
The fixing surface of the support to the diaphragm is formed in an arc shape so that a central portion in the longitudinal direction of the support is convex toward the diaphragm. The piezoelectric fan described. A piezoelectric fan according to any one of claims 1 to 4, and a housing,
The support body of the piezoelectric fan is fixed at two points by pressing both ends against the casing, and the fixing surface of the casing is flat.
The main surface of the piezoelectric fan support that is in contact with the fixed surface so that the longitudinally central portion of the piezoelectric fan support is fixed so as to protrude toward the diaphragm side of the piezoelectric fan. Is formed with an inclination with respect to the fixed surface.

Images