JP2010171146A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator that has a long life. <P>SOLUTION: The piezoelectric actuator 1 is formed such that an oxidized gas is enclosed in a closed vessel 11 where piezoelectric elements 2 are contained. With such a structure, the reduction of reaction of an oxidative metal existent in piezoelectric layers 21 and 22 is controlled so as to delay reduction, preventing insulation deterioration from arising over time in the piezoelectric layers 21 and 22, preventing degradation of the piezoelectric actuator's displacement performance caused by the insulation deterioration, and as a result, obtaining a long life of the piezoelectric actuator 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator used in, for example, a fuel injection device.

  Conventionally, a piezoelectric actuator that expands in accordance with an applied voltage is known. The piezoelectric actuator includes a stacked piezoelectric element in which a plurality of piezoelectric layers and internal electrode layers are alternately stacked.

  In order to prevent moisture from the outside from reaching the multilayer piezoelectric element and to prevent creeping discharge from the side surface of the multilayer piezoelectric element, it is accommodated in an airtight container filled with an inert gas, A technique for containing an oxidative degradation inhibitor has been proposed (see, for example, Patent Document 1).

  By the way, in a laminated piezoelectric element that integrally sinters a piezoelectric layer using ceramics and an inner layer electrode using Ag, Ag diffuses into the grain boundaries of ceramics during sintering, and Ag has a high diffusion coefficient. (For example, refer nonpatent literature 1). Therefore, it is known that an oxide of Ag is present in the ceramic piezoelectric layer.

  In general, PZT ceramics contain lead zirconate, which is easily decomposed at high temperatures. Therefore, it is known that lead zirconate decomposes during firing, and PbO forms a liquid phase and exists at grain boundaries. (See Non-Patent Document 2, for example).

JP 2003-180090 A Reaction and diffusion between PLZT ceramics and Ag electrode (Author: Atsushi Nagata) Research on lead-based piezoelectric single crystals for medical ultrasonic probes (Author: Yasuharu Hosono)

  Accordingly, as in the prior art, when an inert gas is sealed in a sealed container or an exterior resin contains an oxidative degradation inhibitor and used for a long time, the metal oxide ( Reduction of (AgO, PbO) is promoted to become a metal, and electrical conductivity is generated in the ceramic of the piezoelectric layer, so that the displacement performance of the actuator may be lowered.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a piezoelectric actuator capable of extending the life.

  A piezoelectric actuator of the present invention that solves the above-mentioned problems is formed by alternately laminating a plurality of piezoelectric layers and an internal electrode layer for supplying an applied voltage, and is expanded by supplying an applied voltage. A piezoelectric actuator having a sealed container that is housed in a state of being shielded from outside air is characterized by having a configuration in which an oxidizing gas is sealed in a sealed container.

  According to the present invention, since the piezoelectric actuator has a configuration in which the oxidizing gas is sealed in the sealed container in which the piezoelectric element is accommodated, the reduction reaction of the metal oxide existing in the piezoelectric layer can be suppressed. . Therefore, it is possible to prevent a decrease in insulation in the piezoelectric layer over time by repeated use for a long time, and it is possible to prevent a decrease in displacement performance of the piezoelectric actuator due to the decrease in insulation. Therefore, the lifetime of the piezoelectric actuator can be dramatically improved.

  As a preferred specific example of the present invention, the oxidizing gas is preferably a dry gas whose moisture is controlled at a preset dew point temperature. By using the dry gas in this way, the humidity of the piezoelectric element can be lowered and the insulation of the piezoelectric layer can be maintained.

  Moreover, it is preferable that the quantity of oxidizing gas is 30 wt%-100 wt% of the gas enclosed in an airtight container. In this case, the amount of the oxidizing gas is most preferably 100 wt%, but even if it is 30 wt%, the reduction reaction of the metal oxide in the piezoelectric layer can be sufficiently suppressed. The oxidizing gas is preferably oxygen or ozone.

  Also, the piezoelectric actuator of the present invention that solves the above-mentioned problems is formed by alternately laminating a plurality of piezoelectric layers and internal electrode layers for supplying an applied voltage, and is expanded by supplying the applied voltage, A piezoelectric actuator having a sealed container that houses an element in a state of being shielded from outside air is characterized by having a configuration in which an oxidizing powder is enclosed in a sealed container.

  According to the present invention, since the piezoelectric actuator has a configuration in which the oxidizing powder is enclosed in a sealed container in which the piezoelectric element is accommodated, the oxidizing powder is present before the metal oxide present in the piezoelectric layer. Can be reduced to a stable metal oxide, and the reduction of the metal oxide in the piezoelectric layer can be delayed.

Therefore, it is possible to prevent a decrease in insulation in the piezoelectric layer over time by repeated use for a long time, and it is possible to prevent a decrease in displacement performance of the piezoelectric actuator due to the decrease in insulation. Therefore, the lifetime of the piezoelectric actuator can be dramatically improved. The oxidizing powder is preferably a metal peroxide powder having any of PbO ₂ , Pb ₃ O ₄ , and AgO.

  According to the present invention, the reducing reaction of the metal oxide existing inside the piezoelectric layer can be suppressed and the reduction can be delayed by the oxidizing gas sealed in the sealed container. Therefore, it is possible to prevent deterioration of insulation in the piezoelectric layer over time due to repeated use for a long time, prevent deterioration of displacement performance of the piezoelectric actuator due to insulation deterioration, and dramatically increase the life of the piezoelectric actuator. Can be improved.

Sectional drawing of the piezoelectric actuator concerning this Embodiment. The top view of the ceramic layer and internal electrode layer of a piezoelectric actuator. FIG. 3 is a plan view of a piezoelectric layer and an internal electrode layer stacked adjacent to the piezoelectric layer of FIG. 2. The perspective expansion view of a piezoelectric element. The graph which shows transition of the insulation resistance in the endurance test of a conventional product and an invention product.

[First Embodiment]
Next, a first embodiment of the present invention will be described in detail below with reference to the drawings.
1 is a sectional view of a piezoelectric actuator according to the present embodiment, FIG. 2 is a plan view of a piezoelectric layer and an internal electrode layer of the piezoelectric actuator, and FIG. 3 is a piezoelectric layer laminated adjacent to the piezoelectric layer of FIG. FIG. 4 is a perspective development view of the piezoelectric element.

  As shown in FIG. 1, the piezoelectric actuator 1 includes a piezoelectric element 2 and a sealed container 11 that accommodates the piezoelectric element 2. As shown in FIGS. 1 to 4, the piezoelectric element 2 is a laminate in which a plurality of piezoelectric layers 21 and 22 that expand in response to an applied voltage and internal electrode layers 210 and 220 for supplying an applied voltage are alternately stacked. It has a structure. The side surface (reference numeral 201, reference numeral 202, etc.) of the laminated structure is entirely covered with the exterior resin 25, and is further accommodated in the sealed container 11 to be blocked from the outside air.

  As shown in FIGS. 2 to 4, the piezoelectric element 2 can alternately form the internal electrode layers 210 and 220 between the piezoelectric layers 21 and 22 made of ceramics and apply the piezoelectric layers 21 and 22 alternately positively and negatively. It is configured as follows. As shown on the left side of FIG. 2, the internal electrode layer 210 adjacent to the piezoelectric layer 21 has an electrode non-formed portion 211 on one end side, and the internal electrode layer 220 adjacent to the piezoelectric layer 22 is positioned on the right side of FIG. As shown, an electrode non-formed part 221 is provided on the other end side. The internal electrode layer 210 is disposed so as to be exposed on one side surface 201 of the piezoelectric element 2, and the internal electrode layer 220 is disposed so as to be exposed on the other side surface 202.

  As shown in FIG. 1, side electrodes 23 and 24 made of a noble metal such as silver are provided on the side surfaces 201 and 202 of the piezoelectric element 2 so that the exposed ends of the internal electrode layers 210 and 220 are electrically connected to each other. Each is formed. On the side electrodes 23 and 24, external electrodes 231 and 241 are joined by conductive adhesives 230 and 240 made of epoxy resin. These external electrodes 231 and 241 are connected to a drive power supply (not shown).

  The entire side surface including the side surfaces 201 and 202 of the piezoelectric element 2 is covered with the exterior resin 25 by a dipping method or the like, and a part of the side electrodes 23 and 24 and the external electrodes 231 and 241 are embedded in the exterior resin 25. Yes.

  The sealed container 11 includes a cylindrical metal case 12, an upper plate 14 that closes the upper end opening of the metal case 12, and a lower plate 13 that closes the lower end opening of the metal case 12. Is welded and hermetically joined to the metal case 12.

  As shown in FIG. 1, the metal case 12 has a bellows-like bellows structure that can be expanded and contracted in the case axis direction, so that the expansion and contraction of the piezoelectric element 2 is not hindered. Further, the upper plate 14 is provided with insertion holes 140 for the external electrodes 231 and 241, and the gap between the insertion hole 140 and the external electrodes 231 and 241 is sealed with a sealing material 151 made of silicone resin or the like. It has been stopped.

  In the sealed container 11, a dried oxidizing gas, for example, an oxygen gas whose moisture is controlled to −40 ° C. is enclosed. As the oxidizing gas, oxygen, ozone or the like is preferable. The amount of the oxidizing gas is preferably 30 wt% to 100 wt% of the gas sealed in the sealed container 11, and in particular, 100 wt%, that is, most of the internal atmosphere in the sealed container 11 is the oxidizing gas. preferable.

  In order to assemble the piezoelectric element 2 to the hermetic container 11 to obtain the piezoelectric actuator 1, first, the lower plate 13 is fixed to the metal case 12 by welding, and the piezoelectric element 2 is accommodated in the metal case 12. Then, the upper plate 14 is temporarily fixed at a predetermined position of the metal case 12 while the external electrodes 231 and 241 are inserted through the insertion holes 140 of the upper plate 14.

  Then, the upper plate 14 and the metal case 12 are welded and fixed, and an oxidizing gas is filled into the sealed container 11 from the gap between the insertion hole 140 and the external electrodes 231 and 242, and then the insertion hole 140 and the external electrode The gap between 231 and 241 is filled with a sealing material 151 and sealed. Thereby, the piezoelectric actuator 1 in which the piezoelectric element 2 is accommodated in the sealed container 11 and the oxidizing gas is sealed is obtained.

  According to the piezoelectric actuator 1 having the above configuration, since the oxidizing gas is sealed in the sealed container 11 in which the piezoelectric element 2 is accommodated, the reduction reaction of the metal oxide existing in the ceramics of the piezoelectric layers 21 and 22 is performed. Can be suppressed. Therefore, it is possible to prevent a decrease in insulation in the piezoelectric layers 21 and 22 over time by repeated use for a long time, and it is possible to prevent a decrease in displacement performance due to a decrease in insulation. Therefore, the life of the piezoelectric actuator 1 can be dramatically improved. In addition, by using a dry gas whose moisture is controlled at a preset dew point temperature as the oxidizing gas, the humidity of the piezoelectric element 2 is lowered, and the insulating properties of the piezoelectric layers 21 and 22 are appropriately maintained. Can do.

[Second Embodiment]
Next, a second embodiment will be described below. What is characteristic in the present embodiment is that an oxidizable powder made of a metal peroxide is enclosed in a sealed container 11 in which the piezoelectric element 2 is accommodated. The oxidizing powder is filled in the gap portion 19 between the sealed container 11 and the piezoelectric element 2.

Metal peroxides such as PbO ₂ and AgO are likely to be reduced at room temperature, and are likely to become stable PbO and Ag ₂ O by reduction. By utilizing this reduction action, the metal peroxide sealed in the sealed container 11 is reduced before the metal oxides of the piezoelectric layers 21 and 22 and changed into stable metal oxides, Reduction of the metal oxide present in the 22 ceramics can be delayed.

Therefore, by repeatedly using for a long time, it is possible to prevent a decrease in insulation in the ceramics of the piezoelectric layers 21 and 22 with time, and it is possible to prevent a decrease in displacement performance due to a decrease in insulation. Therefore, the lifetime of the piezoelectric actuator 1 can be improved. As the examples of the oxide _{powders, PbO 2, Pb 3 O 4} , AgO and the like are preferable.

[Example]
FIG. 5 is a graph showing the transition of the insulation resistance during the durability test of the conventional product and the invention.
The invention product 1 realizes the piezoelectric actuator 1 according to the first embodiment, and in the sealed container 11 in which the piezoelectric element 2 is accommodated, as an enclosed gas, dry (dew point temperature −40 ° C.) Air 10 wt. % + Oxidizing gas 90 wt% is used.

The invention product 2 realizes the piezoelectric actuator 1 according to the second embodiment, in which an oxidizing powder of PbO ₂ which is a metal peroxide is enclosed in a sealed container 11 in which the piezoelectric element 2 is accommodated. Yes.

  Then, for each of the products 1 and 2, the temperature is maintained at 150 ° C., a voltage of 150 V is applied from the external electrodes 231 and 241, the cycle frequency is 150 Hz, and driving is performed until the insulation resistance becomes zero. A test was conducted.

  As a result, the invention product 1 maintains the insulation resistance in the vicinity of 4.0E + 03 [MΩ] until the number of driving times exceeds 2.0E + 09 [cyc], and after the number of driving times exceeds 2.0E + 09 [cyc] The insulation resistance began to decrease at a time, and the insulation resistance became 0 when the number of driving times was 3.2E + 09 [cyc].

  Inventive product 2 maintains the insulation resistance in the vicinity of 4.0E + 03 [MΩ] until the number of driving times exceeds 1.6E + 09 [cyc], and gradually after the number of driving times exceeds 1.6E + 09 [cyc]. The insulation resistance started to decrease, and the insulation resistance became almost zero when the number of driving times was 2.8E + 09 [cyc].

  As a comparative example, a conventional piezoelectric actuator having the same configuration as in Example 1 but filled with an inert gas in the sealed container 11 was prepared, and the same durability test was performed. As a result, the insulation resistance of the conventional product suddenly decreased when the number of driving times exceeded 5.0E + 08 [cyc], and the insulation resistance became zero when the number of driving times was 1.0E + 09 [cyc]. Therefore, the inventive products 1 and 2 can obtain a life that is about three times as long as that of the conventional product, and the life can be remarkably improved as compared with the conventional product.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the piezoelectric actuator 1, the case where the sealed container 11 is cylindrical and the shape of the piezoelectric element 2 is rectangular has been described as an example. However, the shape is not limited to such a shape, and other shapes may be used. Good. Moreover, in Example 1, although oxygen and ozone were preferable as an example of oxidizing gas, it should just be oxidizing gas. Similarly, in Example 2, PbO ₂ , Pb ₃ O ₄ , AgO, and the like are preferable as examples of the metal peroxide, but any metal peroxide that is stabilized by reduction may be used.

DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 2 Piezoelectric element 11 Sealed container 21, 22 Piezoelectric layer 210, 220 Internal electrode layer

Claims (6)

A piezoelectric element that is formed by alternately laminating a plurality of piezoelectric layers and an internal electrode layer for supplying an applied voltage, and expands when supplied with an applied voltage, and a sealed container that accommodates the piezoelectric element in a state of being shielded from outside air A piezoelectric actuator having:
A piezoelectric actuator having a configuration in which an oxidizing gas is sealed in the sealed container.   The piezoelectric actuator according to claim 1, wherein the oxidizing gas is a dry gas whose moisture is controlled to a preset dew point temperature.   3. The piezoelectric actuator according to claim 1, wherein the amount of the oxidizing gas is set to 30 wt% to 100 wt% of the gas sealed in the sealed container.   4. The piezoelectric actuator according to claim 1, wherein the oxidizing gas is oxygen or ozone. A piezoelectric element that is formed by alternately laminating a plurality of piezoelectric layers and an internal electrode layer for supplying an applied voltage, and expands when supplied with an applied voltage, and a sealed container that accommodates the piezoelectric element in a state of being shielded from outside air A piezoelectric actuator having:
A piezoelectric actuator having a structure in which an oxidizing powder is sealed in the sealed container. 6. The piezoelectric actuator according to claim 5, wherein the oxidizing powder is a metal peroxide powder containing any one of PbO ₂ , Pb ₃ O ₄ , and AgO.

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