JP2017191867A - Piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric actuator, the life of which can be prolonged by passing a lot of heat on the cap side path when displacing a high temperature driven body, thereby suppressing temperature rise of a piezoelectric element.SOLUTION: A piezoelectric actuator 100 displacing upon application of a voltage includes a piezoelectric actuator body 105 having multiple piezoelectric elements 110 coupled in series, and a protrusion 135 provided at one end of the multiple piezoelectric elements 110, and consisting of a shim 125 and a hemisphere 130 supported by the shim 125, a seat 140 for fixing and supporting the other ends of the multiple piezoelectric elements 110, and a metal cap 160 covering the piezoelectric actuator body 105 and sealed by the seat 140, where heat conductivity of the protrusion 135 is lower than that of the cap 160.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piezoelectric actuator that is displaced by application of a voltage.

  2. Description of the Related Art Conventionally, a piezoelectric actuator having a configuration in which a cap is placed on a piezoelectric actuator body in which a plurality of piezoelectric elements in which internal electrodes and piezoelectric layers are alternately stacked is connected is known. Such a piezoelectric actuator is provided with a protrusion made of a shim and a hemisphere for transmitting the displacement of the piezoelectric element, and the protrusion is in contact with the inner wall surface of the tip of the cap. Then, the outer side of the tip of the cap contacts the driven body and transmits the displacement. Such a piezoelectric actuator is used in various environments.

  The piezoelectric element constituting the piezoelectric actuator body can obtain a desired displacement by applying a voltage to the polarized piezoelectric ceramic layer. However, when used in a high temperature environment, the polarization is lost and the characteristics deteriorate. In the piezoelectric actuator described in Patent Document 1, a sleeve for dissipating heat generated in the piezoelectric element is provided for the piezoelectric element that generates heat and rises in temperature. The sleeve is in contact with the lead member in the cap and is held by the case, and is made of ceramic having higher thermal conductivity than piezoelectric ceramic and having insulating properties.

JP 2008-053315 A

  The piezoelectric actuator described in Patent Document 1 is used for an injector, and heat dissipation of self-heating generated in the piezoelectric element during use has been a problem, and it is required to increase heat conduction to the outside. However, unlike such an example, in the piezoelectric actuator used to transmit displacement to a high temperature driven object, in order to suppress the inflow of heat to the piezoelectric element, the heat conduction with the outside is rather reduced. Is required.

  Also, in applications where high-temperature driven objects are displaced, if the temperature rises even if the temperature is not high enough to lose polarization, the insulation resistance deteriorates due to migration, or dielectric breakdown occurs, accompanied by the generation or extension of microcracks. The breakdown voltage is likely to deteriorate or the dielectric breakdown may occur. As a result, insulation deterioration occurs in the piezoelectric element, and the life of the piezoelectric actuator may be shortened.

  The present invention has been made in view of such circumstances, and when a high temperature driven body is displaced, a large amount of heat flows through the path on the cap side, thereby suppressing an increase in temperature of the piezoelectric element and extending its life. An object of the present invention is to provide a piezoelectric actuator that can be used.

  (1) In order to achieve the above object, a piezoelectric actuator of the present invention is a piezoelectric actuator that is displaced by application of voltage, and is provided at a plurality of piezoelectric elements connected in series and at one end of the plurality of piezoelectric elements. A piezoelectric actuator body having a shim and a projection formed of a hemisphere supported by the shim; a seat for fixing and supporting the other ends of the plurality of piezoelectric elements; and covering the piezoelectric actuator body and sealed to the seat. And the protrusion has a thermal conductivity lower than that of the cap.

  As a result, in a use environment where the tip of the piezoelectric actuator is in contact with a high temperature driven body, a large amount of heat can flow through the path on the cap side, and an increase in temperature of the piezoelectric element can be suppressed. As a result, the temperature rise of the piezoelectric element can be suppressed and the life can be extended.

  (2) In the piezoelectric actuator of the present invention, the protrusion is made of steatite, forsterite, cordierite, zirconia or titania, a resin having a thermal conductivity of 10 W / m · K or less, porous ceramics or glass. It is characterized by. Thereby, compared with the heat conductivity of a cap, the heat conductivity of a projection part can be made low and the inflow of the heat | fever to a piezoelectric element can be suppressed.

  (3) Moreover, the piezoelectric actuator of the present invention is characterized in that the cap is made of SUS. Thereby, the heat conductivity of a cap can be made high and a lot of heat can be flowed to the path | route by the side of a cap.

  (4) Further, the piezoelectric actuator of the present invention is characterized in that the protrusion is made of liquid crystal polymer (LCP) or polyphenylene sulfide (PPS). Thereby, the thermal conductivity can be further reduced while maintaining the strength of the protrusion.

  According to the present invention, when a high temperature driven body is displaced, a large amount of heat flows through the path on the cap side, thereby suppressing the temperature increase of the piezoelectric element and extending the life.

It is sectional drawing which shows the piezoelectric actuator which concerns on this invention. (A), (b) is the perspective view and sectional drawing which respectively show the pseudo model for simulation. (A), (b) It is the whole figure and enlarged view which show the temperature distribution simulation result calculated on the conditions of the tip 130 degreeC-seat 60 degreeC by making each protrusion into aluminum. (A), (b) It is the whole figure and enlarged view which show the temperature distribution simulation result calculated on the conditions of 130 degreeC-60 degreeC of a front-end | tip with a projection part as zirconia, respectively. (A), (b) It is the whole figure and enlarged view which show the temperature distribution simulation result calculated on the conditions of the tip 130 degreeC-seat 100 degreeC, respectively, with the protrusion part as aluminum. (A), (b) It is the whole figure and enlarged view which show the temperature distribution simulation result computed on the conditions of a seat 130 degreeC-tip 100 degreeC by making each protrusion part into zirconia.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Configuration of piezoelectric actuator)
FIG. 1 is a cross-sectional view showing the piezoelectric actuator 100. The piezoelectric actuator 100 includes a piezoelectric actuator body 105, a seat 140, and a cap 160, and is displaced when a voltage is applied.

  The piezoelectric actuator main body 105 includes a plurality of piezoelectric elements 110, lead members 120, and protrusions 135. The plurality of piezoelectric elements 110 are connected to each other in series (stretching direction due to voltage application) by bonding the piezoelectric elements 110 to each other at the end faces. The piezoelectric actuator body 105 has a projecting portion 135 made up of a shim 125 and a hemisphere 130 at one end, and the other end is bonded to the seat 140 as a bottom, so that a voltage is applied to the multiple piezoelectric elements 110. It expands and contracts with.

  In the piezoelectric element 110, piezoelectric layers and internal electrodes are alternately stacked. An external electrode 115 connected to the internal electrode is provided on the side surface of the piezoelectric element 110. The piezoelectric layer is made of a piezoelectric material such as PZT or barium titanate. The internal electrode is made of Ag-Pd or the like.

  The lead member 120 is made of metal and formed in a plate shape, and is bonded to the external electrodes 115 formed on both side surfaces of the piezoelectric element 110. The pair of lead members 120 are connected to the pair of terminals 150 at the seat 140.

  The protrusion 135 is provided at the end of the piezoelectric actuator body 105 on the displacement side, is accommodated in contact with the closed end of the cap 160, and transmits the displacement of the piezoelectric actuator body 105 to the tip of the cap 160. The protrusion 135 is preferably formed of a material having sufficient strength to transmit displacement and low thermal conductivity.

  The protrusion 135 is preferably steatite, forsterite, cordierite, zirconia or titania. Alternatively, it is preferably made of a resin, porous ceramics or glass having a thermal conductivity of 10 W / m · K or less. As a result, the thermal conductivity of the protrusion 135 can be made lower than the thermal conductivity of the cap 160, and the inflow of heat into the piezoelectric element 110 can be suppressed.

  The protrusion 135 may be formed of a liquid crystal polymer (LCP) or polyphenylene sulfide (PPS). These are all materials in the field called super engineering plastics, are excellent in heat resistance and strength, and have a thermal conductivity of 0.2 to 0.5 W / m · K. As a result, the thermal conductivity can be further reduced while maintaining the strength of the protrusion 135. Further, when the shim 125 is formed of a resin, it may be formed with a hollow structure.

  The shim 125 is formed as a plate having a shape that matches the shape of the end surface of the piezoelectric actuator main body 105, and is bonded to the end of the piezoelectric actuator main body 105 on the displacement side. The shim 125 fixes and supports the hemisphere 130 on the shim 125 and transmits the displacement of the piezoelectric element 110.

  The seat 140 is formed in a substantially disc shape, and fixes and supports the other end of the piezoelectric actuator main body 105. A voltage is applied to the external electrode 115 through the lead member 120 and the piezoelectric actuator body 105 expands and contracts with the seat 140 as a reference. As a result, the hemisphere 130 is displaced by the expansion and contraction of the piezoelectric actuator body 105.

  The cap 160 has a diaphragm 165 that covers the piezoelectric actuator main body 105 and is sealed by the seat 140, and the hemisphere 130 comes into contact with the dome-shaped portion. A side wall portion of the cap 160 is formed in a straight pipe cylinder from the center to the bottom of the cap 160. A dome-shaped diaphragm 165 is formed at the tip of the cap. The cap 160 is preferably made of a material having excellent spring properties such as SUS, particularly SUS316, SUS316L. In addition, the cap 160 is preferably made of SUS, so that the heat conductivity of the cap 160 can be increased and a large amount of heat can flow through the path on the cap 160 side. Thus, it is also effective to use a material having a high thermal conductivity for the side wall of the cap 160.

  In the piezoelectric actuator 100, the thermal conductivity of the protrusion 135 is lower than the thermal conductivity of the cap 160. Accordingly, in a use environment where the tip on the hemisphere 130 side is high and the seat 140 side is low, heat can flow through the path on the cap 160 side, and the temperature rise of the piezoelectric element 110 can be suppressed. As a result, the temperature rise can be suppressed and the life can be extended when the high temperature driven body is displaced. The thermal conductivity of the protrusion 135 is preferably 10 W / m · K or less.

  Moreover, it is preferable that the thickness of the side wall of the cap 160 is 0.1 to 0.4 mm. As a result, a sufficient amount of heat can flow through the side wall of the cap 160. Then, the amount of heat flowing to the piezoelectric actuator main body 105 can be adjusted with respect to the amount of heat flowing to the cap 160 by changing the material of the protrusion 135.

  Note that the inflow of heat to the piezoelectric element 110 can also be suppressed by making the plane cross section (cross section perpendicular to the displacement direction) of the hemisphere 130 smaller than the conventional size. Further, the same effect can be obtained by designing the hemisphere 130 to have a longer length along the displacement direction or to increase the thickness of the shim 125.

(Method for manufacturing piezoelectric actuator)
A method for manufacturing the piezoelectric actuator 100 configured as described above will be described. First, the piezoelectric element 110 in which piezoelectric layers and internal electrodes are alternately stacked is manufactured. Specifically, an electrode paste such as Ag or Ag-Pd is printed on a green sheet of piezoelectric ceramic such as PZT, laminated, pressure-bonded, and fired. Next, the external electrode 115 connected to the internal electrode is formed on the side surface of the piezoelectric element 110 along the stacking direction. The external electrode 115 can be formed by printing and baking an electrode paste on the side surface of the piezoelectric element 110.

  An end face in the stacking direction of the obtained plurality of piezoelectric elements 110 is coated and bonded with an adhesive such as epoxy and connected in series. In this way, multiple linking is performed and the adhesive is cured. Then, the shim 125 and the hemisphere 130 are bonded to one end of the multiple piezoelectric elements. The shim 125 and the hemisphere 130 are prepared in advance with a material having a lower thermal conductivity than the material of the cap 160.

  Finally, the plate-like lead member 120 made of metal is fixed to the external electrode 115, so that the piezoelectric actuator main body 105 can be manufactured in a multiple connection. The piezoelectric actuator main body 105 is placed on the seat 140, and the cap 160 is put on and sealed. In this way, the piezoelectric actuator 100 can be manufactured.

(simulation)
A simulation model having the same structure as that of the piezoelectric actuator 100 was constructed, and the simulation was executed by the finite element method. Since the mesh shown in FIG. 1 is complicated and difficult to calculate, the simulation is performed using a model having a simple shape. 2A and 2B are a perspective view and a sectional view, respectively, showing a simulation pseudo model.

  As shown in FIGS. 2A and 2B, in the pseudo model, the diaphragm at the tip of the cap is formed in a flat plate shape. In addition, the hemisphere was formed as a cylinder having a bottom surface perpendicular to the stacking direction, and the piezoelectric element was formed as a unitary piezoelectric body with a length corresponding to six elements to constitute a piezoelectric actuator body.

  The cylinder representing the hemisphere was designed with a diameter of 2.5 mm and a height of 2.5 mm. The shim was formed in a plate shape of 6 mm × 6 mm × 0.625 mm, and the element part was formed in 6 mm × 6 mm × 60 mm. The seat was formed in a disk shape of 6 mm × 6 mm × 0.625 mm. The cap was formed with a diameter of 11.4 mm and a height of 63.65 mm. The thickness of the disc representing the diaphragm at the tip of the cap was 0.5 mm, and the thickness of the cap side wall was 0.25 mm. The seat was formed with a diameter of 11.4 mm and a thickness of 3.0 mm.

(Comparative Example 1)
First, assuming that the hemisphere was made of bearing steel and the shim was made of aluminum among the protrusions, the respective thermal conductivity was set for the elements of the protrusions. The temperature distribution in this case was calculated on the assumption that the end face of the tip of the piezoelectric actuator was designated as 130 ° C. and the end face on the seat side was designated as 60 ° C. Calculations were made without taking into account the exchange of radiant heat to or from others, and no heat transfer due to residence. In addition, the numerical value of 1/3 of alumina was used for the thermal conductivity of PZT. The cap was assumed to be composed of SUS316.

  FIGS. 3A and 3B are an overall view and an enlarged view showing a temperature distribution simulation result calculated under the condition of a tip 130 ° C. and a seat 60 ° C., respectively, with the protruding portion being aluminum. The regions a to j shown in the figure correspond to the temperature gauges a to j shown on the right side and show the temperature distribution (the same applies hereinafter). As shown in FIGS. 3A and 3B, the upper part of the sixth element, which is the sixth element from the seat side, reaches 120 ° C. or more, and it has been found that the characteristics of the piezoelectric element can be impaired.

Example 1
Based on the same conditions as in Comparative Example 1, and assuming that the protrusions are made of zirconia, the thermal conductivity of zirconia was set in the protrusions. Zirconia has a thermal conductivity of about 1/10 that of alumina. FIGS. 4A and 4B are an overall view and an enlarged view showing a temperature distribution simulation result calculated under the condition of the tip 130 ° C. and the seat 60 ° C. with the protrusions being zirconia, respectively.

  As shown in FIGS. 4 (a) and 4 (b), when simulation was performed with the protrusions made of zirconia, the temperature near the protective layer boundary on the tip side of the sixth element, which is the sixth element from the seat side, is 100. It became below 20 degreeC compared with the case of the comparative example 1, and it turned out. The protective layer is a layer at the end in the stacking direction that is not sandwiched between internal electrodes.

(Comparative Example 2)
Next, based on the same conditions as in Comparative Example 1, the temperature on the seat side was set to 100 ° C., and the temperature distribution in the piezoelectric actuator was calculated. FIGS. 5A and 5B are an overall view and an enlarged view showing a temperature distribution simulation result calculated under the condition of a tip 130 ° C. and a seat 100 ° C., respectively, with the protruding portion being aluminum. As shown in FIGS. 5A and 5B, the upper portion of the sixth element was found to be 127 ° C. or higher.

(Example 2)
The temperature distribution of the piezoelectric actuator was calculated based on the same conditions as in Comparative Example 2, assuming that the protrusion was made of zirconia under the condition of 100 ° C. on the seat side. FIGS. 6A and 6B are an overall view and an enlarged view showing a temperature distribution simulation result calculated under the conditions of a seat 130 ° C. and a tip 100 ° C. with the protrusions being zirconia, respectively.

  As shown in FIGS. 6A and 6B, the temperature at the top of the sixth element is 118 ° C. or lower, and the temperature near the protective layer boundary on the tip side of the sixth element is 10 ° C. as compared with the case of Comparative Example 2. I found that it was down. It was also found that the difference between Comparative Example 2 and Example 2 was smaller than the difference between Comparative Example 1 and Example 1.

  As a result of the above simulation, it is confirmed that heat flows to the seat side through the cap and the temperature rise of the piezoelectric element can be suppressed by making the shims and hemispheres constituting the protrusions as materials having a thermal conductivity as low as zirconia. I was able to prove.

100 Piezoelectric Actuator 105 Piezoelectric Actuator Body 110 Piezoelectric Element 115 External Electrode 120 Lead Member 125 Shim 130 Hemisphere 135 Protrusion 140 Seat 150 Terminal 160 Cap 165 Diaphragm

Claims (4)

A piezoelectric actuator that is displaced by application of a voltage,
A plurality of piezoelectric elements connected in series, a piezoelectric actuator body provided at one end of the plurality of piezoelectric elements, and having a protrusion made of a shim and a hemisphere supported by the shim;
A seat for fixing and supporting the other ends of the plurality of piezoelectric elements;
A metal cap that covers the piezoelectric actuator body and is sealed to the seat;
The piezoelectric actuator according to claim 1, wherein the thermal conductivity of the protrusion is lower than the thermal conductivity of the cap.   2. The piezoelectric actuator according to claim 1, wherein the protrusion is made of steatite, forsterite, cordierite, zirconia, titania, resin having a thermal conductivity of 10 W / m · K or less, porous ceramics, or glass.   The piezoelectric actuator according to claim 1, wherein the cap is made of SUS.   4. The piezoelectric actuator according to claim 1, wherein the protrusion is made of liquid crystal polymer (LCP) or polyphenylene sulfide (PPS). 5.

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