WO2008072768A1

WO2008072768A1 - Laminated piezoelectric element, jetting device provided with the laminated piezoelectric element and fuel jetting system

Info

Publication number: WO2008072768A1
Application number: PCT/JP2007/074243
Authority: WO
Inventors: Ichitaro Okamura; Takeshi Okamura
Original assignee: Kyocera Corporation
Priority date: 2006-12-15
Filing date: 2007-12-17
Publication date: 2008-06-19
Also published as: JPWO2008072768A1; JP5084745B2

Abstract

A laminated structure is provided with a plurality of opposing sections where a pair of internal electrodes adjacent to each other in a laminating direction oppose the laminating direction, and a non-opposing section other than the opposing sections. In at least one of the opposing sections, the internal electrodes adjacent to each other in the laminating direction oppose each other through a low rigidity layer and a piezoelectric layer. The opposing sections have a first portion in contact with at least a part of the boundary between the opposing section and the non-opposing section, and a second portion other than the first portion. In the laminated piezoelectric element, such laminated structure suppresses deterioration of a displacement amount.

Description

Specification

Multilayer piezoelectric element, injection device including the same, and fuel injection system

Technical field

The present invention relates to a laminated piezoelectric element used for, for example, a driving element (piezoelectric actuator), a sensor element, and a circuit element. Examples of the driving element include a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precise positioning device such as an optical device, and a vibration preventing device. Examples of the sensor element include a combustion pressure sensor, a knock sensor, an acceleration sensor, a load sensor, an ultrasonic sensor, a pressure sensor, and a short rate sensor. Examples of the circuit element include a piezoelectric gyro, a piezoelectric switch, a piezoelectric transformer, and a piezoelectric breaker.

Background art

Conventionally, multilayer piezoelectric elements have been required to ensure a large amount of displacement under a high pressure at the same time as miniaturization proceeds. For this reason, it is required that a higher electric field is applied, and that it can be used under harsh conditions in which the driving force is continuously driven for a long time.

[0003] When continuously driven for a long time under the condition of a high electric field or high pressure, stress is applied to the internal electrode and the piezoelectric layer. In particular, a large stress is applied in the vicinity of the boundary between the opposing portion sandwiched between two internal electrodes adjacent in the stacking direction of the piezoelectric layer and the non-opposing portion other than the opposing portion. Therefore, it is required to disperse the stress applied near the boundary. Therefore, as disclosed in Patent Document 1, an element having a structure in which a stress relaxation layer is provided in a non-opposing portion has been proposed.

Patent Document 1: Japanese Patent Laid-Open No. 2001-267646

Disclosure of the invention

Problems to be solved by the invention

However, when the stress relaxation layer described in Patent Document 1 is provided, the crack force S generated in the stress relaxation layer, the force that extends through the piezoelectric layer to the adjacent internal electrode or external electrode There is S. Therefore, an electrical short circuit may occur between internal electrodes adjacent to each other in the stacking direction, and the amount of displacement may be reduced. [0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a multilayer piezoelectric element in which the amount of displacement is reduced by long-time driving.

Means for solving the problem

[0006] The multilayer piezoelectric element of the present invention includes a multilayer structure and positive and negative external electrodes formed on the side surfaces of the multilayer structure. The laminated structure includes a laminated portion and a low rigidity layer. In the laminated portion, a plurality of piezoelectric layers and a plurality of internal electrodes are alternately laminated. An internal electrode is connected to the external electrode on the anode side and the cathode side. In addition, the laminated structure has a plurality of opposing portions in which a pair of internal electrodes adjacent in the laminating direction oppose each other in the laminating direction, and non-opposing portions other than the opposing portions. In at least one of the plurality of facing portions, the internal electrodes adjacent in the stacking direction face each other through the low-rigidity layer and the piezoelectric layer. The opposing part has a first part that touches at least part of the boundary between the opposing part and the non-opposing part, and a second part other than the first part! / .

Brief Description of Drawings

[0007] FIG. 1 is a perspective view showing a multilayer piezoelectric element that exerts force on a first embodiment of the present invention.

2A is a cross-sectional view of the embodiment shown in FIG. 1 including a low-rigidity layer in a direction perpendicular to the stacking direction.

2B is an exploded perspective view of the embodiment shown in FIG.

3 is an enlarged cross-sectional view in a direction parallel to the stacking direction of the embodiment shown in FIG.

FIG. 4 is a cross-sectional view in a direction parallel to the laminating direction, showing a laminated piezoelectric element that exerts force on the second embodiment of the present invention.

FIG. 5 is a cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing a multilayer piezoelectric element that exerts a force according to a third embodiment of the present invention.

FIG. 6A is a cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing a multilayered piezoelectric element according to a fourth embodiment of the present invention.

6B is an exploded perspective view of the embodiment shown in FIG. 6A.

FIG. 7A is a cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing a multilayered piezoelectric element that exerts a force according to a fifth embodiment of the present invention.

7B is an exploded perspective view of the embodiment shown in FIG. 7A. FIG. 8A] A cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing the multilayer piezoelectric element according to the sixth embodiment of the present invention.

8B] is an exploded perspective view of the embodiment shown in FIG. 8A.

FIG. 9] A sectional view in a direction parallel to the laminating direction, showing a multilayered piezoelectric element according to the seventh embodiment of the present invention.

FIG. 10A] is a cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing a multilayered piezoelectric element that exerts a force according to an eighth embodiment of the present invention.

10B] is an exploded perspective view of the embodiment shown in FIG. 10A.

FIG. 11A] A cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing the multilayer piezoelectric element according to the ninth embodiment of the present invention.

11B] is an exploded perspective view of the embodiment shown in FIG. 11A.

FIG. 12A is a cross-sectional view including a low-rigidity layer in a direction perpendicular to the stacking direction, showing a stacked piezoelectric element according to a tenth embodiment of the present invention.

12B] is an exploded perspective view of the embodiment shown in FIG. 12A.

13] A sectional view in a direction parallel to the laminating direction, showing the multilayer piezoelectric element according to the eleventh embodiment of the present invention.

14A] A cross-sectional view in a direction parallel to the stacking direction, showing the multilayer piezoelectric element according to the twelfth embodiment of the present invention.

14B] is an exploded perspective view of the embodiment shown in FIG. 14A.

15] A sectional view in a direction parallel to the laminating direction, showing a multilayered piezoelectric element according to a thirteenth embodiment of the present invention.

FIG. 16 is a cross-sectional view showing an injection device according to an embodiment of the present invention.

FIG. 17 is a schematic view showing a fuel injection system according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIGS.! To 3, a laminated piezoelectric element 1 (hereinafter also referred to as element 1) according to a first embodiment of the present invention includes a laminated structure 7 and an external electrode 9. In the laminated structure 7, a plurality of piezoelectric layers 3 and a plurality of internal electrodes 5 are alternately laminated. The external electrode 9 is located on the side surface of the multilayer structure 7. Further, the plurality of internal electrodes 5 are anode-side and cathode-side external electrodes 9. Connected to one of the two.

In addition, the laminated structure 7 includes a low-rigidity layer 15 that is less rigid than the piezoelectric layer 3 and the internal electrode 5. The low rigidity layer 15 is located between the two piezoelectric layers 3. The presence of at least one low-rigidity layer 15 can relieve stress concentrated on the boundary between the facing portion 11 and the non-facing portion 13. This is because cracks are likely to occur in the low-rigidity layer 15 as compared with the piezoelectric layer 3 and the internal electrode 5. Therefore, it is possible to suppress the occurrence of cracks in the piezoelectric layer 3 and the internal electrode 5. As a result, durability can be improved when element 1 is driven for a long time under high voltage and high voltage.

[0010] At least one of the plurality of facing portions 11 has a first portion 17 and a second portion 19 other than the first portion 17. Here, the first portion 17 refers to the internal electrode 5 adjacent in the stacking direction facing through the low-rigidity layer 15 and the piezoelectric layer 3 and at least one of the boundaries between the facing portion 11 and the non-facing portion 13. The part which touches the part is shown. In FIG. 3, in the facing portion 11, a portion where the internal electrodes 5 adjacent in the stacking direction face each other via the low-rigidity layer 15 and the piezoelectric layer 3 is a first portion 17. Further, the second portion 19 is a portion where the internal electrodes 5 adjacent to each other in the stacking direction face each other only through the piezoelectric layer 3.

By having the first portion 17 as described above, the stress at the boundary between the facing portion 11 and the non-facing portion 13 can be relieved. Further, since the first portion 17 is provided, the stress on the piezoelectric layer 3 that undergoes piezoelectric displacement can be relaxed. Therefore, it is possible to suppress the occurrence of cracks in the piezoelectric layer 3 located in the facing portion 11.

[0012] In addition, in the cross section of the laminated structure 7 in the direction perpendicular to the laminating direction, the entire opposing portion 11 formed by the second portion 19 is the first portion as in the case where the entire cross section is the low-rigidity layer 15. In the case of the part 17, the displacement amount of the element 1 becomes small. This is because the piezoelectric layer 3 that drives the element 1 by piezoelectric displacement is replaced with the low-rigidity layer 15. However, by having the second portion 19 as described above, the piezoelectric displacement by the piezoelectric layer 3 can be ensured. Can suppress the amount of displacement

[0013] The second portion 19 may include the internal electrode 5 that is not connected to the external electrode or the piezoelectric layer 3 having a gap. However, as shown in FIG. 3, the second portion 19 is It is preferable that adjacent internal electrodes 5 are opposed to each other only through the piezoelectric layer 3. As a result, when stress is applied to the element 1, the force S for deforming the crystal structure in accordance with the direction of the stress can be increased, so that the effect of absorbing the stress in the second portion 19 is enhanced. As a result, an element with a small decrease in displacement can be obtained even when driven for a long time.

In the present embodiment, the low-rigidity layer 15 refers to a layer having a low rigidity and a weaker coupling force in the layer and / or a coupling force with an adjacent layer than the piezoelectric layer 3 and the internal electrode 5. . Specifically, the low-rigidity layer 15 is made of a material having rigidity lower than that of the piezoelectric layer 3 and the internal electrode 5 and contains more voids 21 than the piezoelectric layer 3 and the internal electrode 5. Therefore, the layer with reduced rigidity can be mentioned.

[0015] The rigidity of the low-rigidity layer 15, the piezoelectric layer 3, and the internal electrode 5 can be easily compared by, for example, applying a load to the element 1 from a direction perpendicular to the stacking direction. Specifically, it can be judged by applying a load to element 1 from a direction perpendicular to the stacking direction by JIS 3-point bending test (JIS R 1601). This is because it is only necessary to confirm at which part the element 1 breaks when the above test is performed. The broken part is the part with the lowest rigidity in the element 1.

[0016] Since the element 1 of the present embodiment includes the low-rigidity layer 15, when the JIS three-point bending test is performed, the low-rigidity layer 15 or the low-rigidity layer 15 and the piezoelectric layer 3 and the internal electrode 5 Breakage easily occurs at the interface with the piezoelectric layer 3. Therefore, the presence or absence of the low-rigidity layer 15 is determined depending on whether the fractured portion is the piezoelectric layer 3 or the internal electrode 5 or the interface between the low-rigidity layer 15 or the low-rigidity layer 15 and the piezoelectric layer 3. Can be confirmed.

[0017] When the above-mentioned bending test cannot be used because the test piece is small, it may be confirmed by the following method. That is, in accordance with the above JIS three-point bending test, the element 1 is processed into a rectangular prism and a test piece is produced. And place this specimen on 2 fulcrums arranged at a certain distance. In addition, load is applied to one central point between the fulcrums. From the above, the presence or absence of the low-rigidity layer 15 can be confirmed.

[0018] Next, a second embodiment of the present invention will be described.

As shown in FIG. 4, the low-rigidity layer 15 preferably has a gap 21 and a metal portion 23 that is separated from each other via the gap 21. Metal components are easily deformed, so stress is relieved This is because the effect is great. In addition, since the material is different from the piezoelectric particles constituting the adjacent piezoelectric layer 3, the cracks generated in the metal part 23 are easily retained inside the metal part 23 or the surface of the metal part 23. As a result, it is possible to prevent cracks from extending in the piezoelectric layer 3. Further, since the plurality of metal portions 23 are separated from each other via the gaps 21, the respective metal portions 23 are more easily displaced.

[0020] Further, even when the low-rigidity layer 15 is exposed to the side surface of the laminated structure 7 and contacts the external electrode 9, the plurality of metal portions 23 are separated from each other via the gap 21. As a result, an electrical short circuit through the metal part 23 can be suppressed.

[0021] The ratio (void ratio) of the voids 21 in the piezoelectric layer 3, the internal electrode 5, and the low-rigidity layer 15 can be measured, for example, as follows. First, the laminated structure 7 is polished using a known polishing means so that a cross section perpendicular to the stacking direction is exposed. For example, polishing is performed with diamond paste using a table polishing machine KEMET-V-300 manufactured by Kemet Japan Co., Ltd. as a polishing apparatus. The cross section exposed by the polishing process is subjected to image processing using a scanning electron microscope (SEM), an optical microscope, or a metal microscope to obtain a cross section image. In this cross-sectional image, the ratio (%) occupied by the area of the void 21 is measured. In this way, the force S is used to measure the ratio of the voids 21 of the piezoelectric layer 3, the internal electrode 5, and the low rigidity layer 15.

Specifically, with respect to the images of the internal electrode 5 and the low-rigidity layer 15 taken with an optical microscope, the void 21 is painted black and the portions other than the void 21 are painted white. Then, the void ratio can be calculated by calculating the ratio of the black portion, that is, (area of the black portion) / (area of the black portion + area of the white portion) and expressing it as a percentage. If the cross-sectional image is color, it can be converted to grayscale and divided into a black part and a white part. At this time, if it is necessary to set a threshold value for the two-tone gradation in the black part and the white part, the image processing software visually determines the presence or absence of the gap 21 and determines the boundary threshold! /, Set the value and binarize it.

[0023] The material of the low-rigidity layer 15 is not particularly limited, and examples thereof include a single metal such as Cu or Ni, or an alloy such as silver platinum or silver palladium. In particular, it has migration resistance and oxidation resistance, has a low Young's modulus, and is inexpensive. From the point of view, it is preferable to use silver-palladium as a main component. In addition to the metal components as described above, it is possible to use a material made of ceramics and containing more voids 21 than the piezoelectric layer 3 as the low-rigidity layer 15.

[0024] In addition, when the low-rigidity layer 15 has a plurality of metal portions 23 that are separated from each other via the gap 21, the porosity of the low-rigidity layer 15 is 20% to 99.9%. preferable. By setting it to 20% or more, a sufficient space is secured by the air gap 21, so that each metal part 23 has a force that can be displaced greatly. Further, by setting the ratio to 99.9% or less, the adhesiveness of the low-rigidity layer 15 having a high porosity can be improved, so that it is easy to maintain the shape of the element.

[0025] The low-rigidity layer 15 preferably has a thickness of 0 .; This is because the crack is more likely to develop in the low-rigidity layer 15 during driving due to being 0.1 μm or more. In addition, when it is 40 m or less, it is possible to maintain the strength required for normal handling while providing a layer with a high porosity, so that it is excellent in mass productivity!

Next, a third embodiment of the present invention will be described.

As shown in FIG. 5, it is preferable that the central portion 25 of the facing portion 11 is joined by the internal electrode common piezoelectric layer adjacent in the stacking direction. In other words, the central part 25 is preferably the second part. In the present embodiment, the central portion 25 means the following portions.

That is, in the cross section perpendicular to the laminating direction of the element 1 and including the low-rigidity layer 15, a portion having a similar shape in which the opposing portion 11 is reduced to a force of the center of the opposing portion 11, that is, halved. Central part 2 5 Further, in the facing portion 11, a region other than the central portion 25 is defined as a peripheral edge portion 27. In the present embodiment, the center of the facing portion 11 means an intersection of diagonal lines when the facing portion 11 is rectangular, and means the center of a circle when the facing portion 11 is circular.

Yes

[0029] The central portion 25 is a portion where the piezoelectric layer is most easily stretched. Since the low-rigidity layer 15 is not provided in this portion, and only the piezoelectric layer is provided, it is possible to secure a large displacement amount as an element. Therefore, a desired amount of displacement can be ensured while the stress is relaxed by the low rigidity layer 15 that increases the number of stacked layers and makes the element unnecessarily large. Results and And it can be set as the structure excellent in productivity which does not need to increase the number of lamination | stacking.

Further, as shown in FIG. 5, it is preferable that the low-rigidity layer 15 is disposed on the peripheral edge 27. In other words, the first portion 17 is preferably located at the peripheral edge 27. The peripheral portion 27 is a portion where stress is likely to concentrate in the facing portion 11, but by providing the low-rigidity layer 15 in this portion, the stress can be effectively relieved. As a result, the stress can be effectively relieved at the boundary between the opposed portion 11 and the non-opposed portion 13 where the stress tends to concentrate without greatly reducing the displacement amount of the element 1.

Further, as shown in FIG. 5, the low-rigidity layer 15 may be disposed across the boundary between the facing portion 11 and the non-facing portion 13 rather than being disposed only in the facing portion 11. I like it. Since the expansion and contraction of the facing portion 11 is suppressed by the non-facing portion 13, stress tends to concentrate on the boundary between the facing portion 11 and the non-facing portion 13. By disposing the low-rigidity layer 15 as described above, the stress can be relaxed not only from the facing portion 11 side but also from the non-facing portion 13 side, so that the stress can be effectively relaxed. At the same time, since the suppression of the displacement of the facing portion 11 by the non-facing portion 13 can be reduced, the force S for increasing the amount of displacement of the element can be achieved. As a result, it is possible to obtain a highly reliable multi-layer piezoelectric element having excellent durability while ensuring a large amount of displacement.

At this time, it is preferable that the low-rigidity layer 15 extends over the non-facing portion 13 by 5 m or more. That is, it is preferable that the force S is 5 inches or more in the direction perpendicular to the boundary line between the non-facing portion 13 and the facing portion 11. This can enhance the effect of relieving the stress.

In addition, as shown in FIG. 5, it is preferable that the low-rigidity layer 15 is disposed in a strip shape along the boundary between the facing portion 11 and the non-facing portion 13. This is because even if the crack extends in the low rigidity layer 15 due to stress concentration during driving, the crack extends in the longitudinal direction of the band due to the low rigidity layer 15 being arranged in a band shape. . For this reason, it becomes easy to keep the crack inside the low-rigidity layer 15. This can reduce the possibility of cracks extending to the piezoelectric layer 3 located in the second region and the piezoelectric layer 3 adjacent to the low-rigidity layer 15 in the stacking direction.

Further, as shown in FIG. 5, the belt-like low-rigidity layer 15 is disposed along the boundary. As a result, a force S that suppresses stress concentration over a wide range at the boundary between the facing portion 11 and the non-facing portion 13 can be achieved. Here, the belt-like low-rigidity layer 15 refers to the low-rigidity layer 15 formed with a substantially constant width, excluding irregularities that are unavoidable in the manufacturing process. The width of the belt-like low-rigid layer 15 is preferably 5 Hm or more! /. Low stiffness layer Having a width of 15 force m or more makes it easier to keep cracks inside the low stiffness layer 15.

[0035] Next, a fourth embodiment of the present invention will be described.

[0036] As shown in FIGS. 6A and 6B, in the cross section perpendicular to the stacking direction, a plurality of low-rigidity layers 15 that are separated from each other exist along the boundary between the facing portion 11 and the non-facing portion 13. preferable. When the low-rigidity layer 15 exists along the boundary between the opposed portion 11 and the non-opposed portion 13, a stress relaxation function can be locally provided to the boundary where stress is likely to concentrate.

[0037] Further, since the plurality of low-rigidity layers 15 are separated from each other, the two piezoelectric layers 3 located on both sides in the stacking direction of the low-rigidity layers 15 are located between the low-rigidity layers 15. Joined by piezoelectric material. In this way, the piezoelectric body disposed between the plurality of low-rigidity layers 15 serves as a bridge between the respective piezoelectric body layers 3 on both sides in the stacking direction. Therefore, the bonding strength at this interface is increased, and the force S that reduces the possibility of bending or deformation that occurs during handling can be achieved.

[0038] Further, when there are a plurality of low-rigidity layers 15 that are separated from each other in this manner! /, Each low-rigidity layer 15 is disposed so as to straddle the boundary. Sometimes, a greater stress relaxation effect is obtained at the boundary between the facing portion 11 and the non-facing portion 13. Further, as shown in FIG. 6, when a plurality of low-rigidity layers 15 that are spaced apart from each other are provided, each low-rigidity layer 15 preferably has a size of 25 m ² or more. By setting the size as described above, even when a crack occurs in the low-rigidity layer 15, the extension of the crack to the piezoelectric layer 3 can be suppressed.

[0039] Generally, each internal electrode is not formed on the entire main surface of the piezoelectric layer, and has a so-called partial electrode structure. A plurality of internal electrodes of this partial electrode structure are arranged so as to be exposed on opposite side surfaces of the laminated structure every other layer.

[0040] As shown in FIGS. 2A and 2B, the internal electrode 5 is provided with the external electrode 9 having a different polarity. When only the side surface is not exposed, the boundary between the facing portion 11 and the non-facing portion 13 is shown by two lines, as shown by the one-dot chain line in FIG. In such a case, since the two low-rigidity layers 15 are respectively disposed on the boundary, the force S can be used to efficiently relieve the stress.

Next, a fifth embodiment of the present invention will be described.

Further, as shown in FIGS. 7A and 7B, when the internal electrode 5 is exposed only on the side surface of the laminated structure 7 connected to the external electrode 9, and is not exposed on the other side surface. Is represented by a closed line between the opposed portion 11 and the non-opposed portion 13 as shown by a one-dot chain line in FIG. 7A! /. In such a case, since the low-rigidity layer 15 is disposed along the boundary, it is possible to suppress the decrease in the displacement more reliably.

[0043] Next, a sixth embodiment of the present invention will be described.

As shown in FIGS. 8A and 8B, a configuration in which the low-rigidity layer 15 is disposed in the piezoelectric layer 3 along the boundary between the facing portion 11 and the non-facing portion 13 is also effective. In this case, the desired low-rigidity layer 15 can be formed by disposing the four belt-like low-rigidity layers 15. Since the belt-like low-rigidity layer 15 is easy to dispose, it can be disposed precisely at the desired position. Therefore, although it is a simple process, the force S suppresses the change of the displacement while relaxing the stress at the boundary.

[0045] The low-rigidity layer 15 is preferably arranged so as to be rotationally symmetric with respect to the central axis in the stacking direction of the stacked structure. This is because the bias of the stress distribution is reduced. For this reason, it is possible to suppress the concentration of stress on a part and to stabilize the direction and amount of displacement of the element. Here, the rotational symmetry may be, for example, 180 ° rotational symmetry as shown in FIG. 2, or 90 ° rotational symmetry as shown in FIGS.

[0046] By disposing the low-rigidity layer 15 in this manner, the expansion / contraction direction of the drive of the element becomes closer to the parallel to the stacking direction, so that the stress relaxation effect is enhanced. As a result, it is possible to improve durability in the case of continuous driving for a long time.

[0047] Next, a seventh embodiment of the present invention will be described.

[0048] As shown in FIG. 9, the low-rigidity layer 15 is at the boundary between the opposed portion 11 and the non-opposed portion 13, and The effect of stress relaxation by the low-rigidity layer 15 can also be obtained by being disposed at a location close to either the facing anode side or cathode-side external electrode 9.

In addition, when it is desired to suppress the deflection in the displacement direction of the element, it is preferable that the low-rigidity layer 15 is embedded in the piezoelectric layer 3. This is because, since the low-rigidity layer 15 is embedded in the piezoelectric layer 3, changes in the shape of the element can be suppressed. This is because the side surface portion of the multilayer structure 7 is held by the piezoelectric layer 3 having a high density, so that deformation of the low-rigidity layer 15 during driving can be suppressed from appearing on the side surface of the multilayer structure 7. By suppressing the deformation of the element shape in this way, deflection in the displacement direction is suppressed. As a result, it is possible to provide the element 1 with a small decrease in displacement during driving. In this case, it is preferable that the low-rigidity layer 15 is embedded in the interior of the laminated structure 7 by 10 m or more from the side surface.

On the other hand, when a large displacement amount is required for the element, the low-rigidity layer 15 is preferably exposed on the side surface of the laminated structure 7. When the low-rigidity layer 15 is exposed on the side surface of the multilayer structure 7, the entire side surface portion of the multilayer structure 7 is not held by the piezoelectric layer 3! / It is because it can enlarge.

Next, the eighth, ninth, and tenth embodiments of the present invention will be described.

As shown in FIGS. 10 to 12, by providing the low-rigidity layer 15, a multilayer piezoelectric element having a larger displacement can be obtained. Specifically, the low-rigidity layer 15 is disposed on the boundary between the facing portion 11 and the non-facing portion 13 so as to be exposed on the entire opposing side surface of the laminated structure 7.

[0053] In these forms, since the restraint by the piezoelectric layer 3 on the side surface of the multilayer structure 7 is reduced, an element having a larger displacement can be obtained. In addition, it is possible to suppress an increase in deflection in the displacement direction of the element due to exposure on the opposite side surfaces.

In particular, as shown in FIGS. 11A and 12A, the low-rigidity layer 15 is arranged so as to be exposed to the entire side surface of the laminated structure 7 in a cross section that is perpendicular to the stacking direction and includes the low-rigidity layer 15. By being provided, an element having a larger displacement can be obtained.

In addition, as shown in FIG. 12A, the boundary between the low-rigidity layer 15 and the piezoelectric layer 3 is curved in a cross section that is perpendicular to the stacking direction and includes the low-rigidity layer 15. Click on the piezoelectric layer 3. The possibility that a rack is generated can be reduced.

[0056] Also, as shown in FIG. 2A, two low-rigidity layers 15 may be exposed to the side surfaces V /! I like it! The piezoelectric layer 3 is constrained by the external electrode 9 on the side surface on which the external electrode 9 is arranged! /, And the external electrode 9 is arranged on the side surface! /, Na! / Because there is no, the side displacement is large. For this reason, a relatively large stress is applied to the side surface on which the external electrode 9 is not disposed. Here, since the low-rigidity layer 15 is exposed, the effect of relaxing the stress is enhanced. In addition, since the low-rigidity layer 15 is not exposed on the side surface where the external electrode 9 is disposed, the possibility of an electrical short circuit between the pair of external electrodes 9 via the low-rigidity layer 15 is greatly increased. Can be reduced.

Next, an eleventh embodiment of the present invention will be described.

As shown in FIG. 13, it is preferable that the two internal electrodes 5 adjacent to the first part in the stacking direction are connected to the external electrode 9 on the same polarity side. When these two internal electrodes 5 are connected to the external electrode 9 on the same polarity side, the portion sandwiched between these internal electrodes 5 hardly undergoes piezoelectric displacement. For this reason, stress is particularly likely to concentrate on the portion sandwiched between these internal electrodes 5. In addition, since the low-rigidity layer 15 is disposed in this portion where stress is particularly likely to concentrate, the effect of relaxing the stress can be improved. Even if the stress concentrates and cracks occur in the low-rigidity layer 15, the internal electrodes 5 adjacent to each other through the low-rigidity layer 15 have the same polarity, so that an electrical short circuit can be suppressed.

[0059] When the two internal electrodes 5 adjacent to the first part in the stacking direction are connected to the external electrodes 9 having the same polarity, the stress can be effectively relieved, Piezoelectric displacement increases and the amount of displacement decreases. On the other hand, when the two internal electrodes 5 adjacent to the first part in the stacking direction are connected to the external electrodes 9 having different polarities, an increase in the portion that hardly undergoes piezoelectric displacement can be suppressed. The force S can be increased to increase the amount of displacement. Therefore, it is also preferable that the two internal electrodes 5 adjacent to the first part in the stacking direction are connected to the external electrodes 9 having different polarities from each other!

[0060] This is because a large stress force S is likely to be applied to the boundary between the facing portion and the non-facing portion, but since this stress can be concentrated on the low-rigidity layer 15, the stress can be effectively controlled. It is. Furthermore, only the low-rigidity layer 15 is selectively deformed, and the surrounding piezoelectric layer Since deformation can be suppressed, a change in element dimensions during driving can be suppressed. As a result, highly accurate driving is possible.

Next, a twelfth embodiment of the present invention will be described.

[0062] As shown in FIG. 14A and FIG. 14B, between at least one of the internal electrodes 5 and two internal electrodes 5 adjacent to both sides in the stacking direction via the piezoelectric layer 3 with respect to the internal electrode 5 It is desirable that the low-rigidity layer 15 is disposed respectively. By disposing the low-rigidity layer 15 so as to be adjacent to each other on both sides of the internal electrode 5, the stress generated at the boundary between the non-opposing part and the opposing part can be more evenly distributed in the element. It is.

[0063] Further, it is preferable that there are a plurality of low-rigid layers 15 and these are regularly arranged in the stacking direction. By arranging them regularly, it is possible to disperse the restraining force of the entire laminated structure 7, so that the change rate of displacement is small when driving for a long time and the durability during driving can be improved. is there.

[0064] At this time, it is preferable that the low-rigidity layers 15 disposed so as to be adjacent to each other on both sides of the internal electrode 5 are plane-symmetric with respect to the plane including the internal electrode 5 and perpendicular to the stacking direction. . By disposing in this way, the stress S in the element can be absorbed more uniformly by the entire low-rigidity layer 15 by the force S.

Next, a thirteenth embodiment of the present invention is described.

As shown in FIG. 15, it is preferable that the low-rigidity layers 15 are arranged in the element 1 at equal intervals in the stacking direction. Thereby, since the stress generated in the element 1 can be alleviated evenly, durability during driving can be improved.

Specifically, the low-rigidity layer 15 is preferably provided for every 40 or less piezoelectric layers 3. The stress relaxation effect is reduced by increasing the arrangement interval. However, the effect of relieving stress can be enhanced by disposing the low-rigidity layer 15 for each piezoelectric layer 3 having 40 layers or less.

[0068] Further, it is preferable that low active layers 29 are formed on both end faces of the laminated structure 7 in the laminating direction. Compared with the piezoelectric layer 3, the low-rigidity layer 15 has a small displacement due to piezoelectric displacement and a small deformation. Therefore, since the low active layer 29 is formed, the distortion of the multilayer structure 7 that occurs when a voltage is applied can be suppressed. The low active layer 29 has a titanate buffer. A piezoelectric ceramic material mainly composed of lithium BaTiO can be used.

Three

Furthermore, the low active layer 29 is preferably formed by using the same material as that of the piezoelectric layer 3, specifically, by laminating a plurality of piezoelectric layers 3. By using the same material as the piezoelectric layer 3, it is possible to suppress the distortion that occurs when the laminated structure 7 and the low active layer 29 are fired or when a voltage is applied, thereby forming a denser element 1. .

[0070] Further, at this time, the internal electrode is formed in the green sheet of the piezoelectric layer 3 forming the low active layer 29.

5 is preferably added. Alternatively, when the green sheet of the piezoelectric layer 3 that forms the low active layer 29 is laminated, a slurry made of the metal powder and the inorganic compound, the binder, and the plasticizer constituting the internal electrode 5 such as silver palladium is green sheet. It is preferable to print on top. By forming the low active layer 29 in this manner, the shrinkage behavior and shrinkage rate during sintering of the low active layer 29 and the laminated structure 7 can be made closer, so that a more dense element 1 can be formed. Can do.

[0071] Furthermore, when the low active layer 29 is provided, the element 1 has a plurality of low rigidity layers 15, and from the center in the stacking direction of the stacked structure 7 toward both end surfaces. It is preferable that the interval between the low rigidity layers 15 is gradually shortened. As a result, the stress generated at the boundary with the low active layer 29 at both ends in the stacking direction can be reduced. That is, the multilayer structure 7 having a structure in which the number of piezoelectric layers 3 positioned between the adjacent low-rigidity layers 15 is reduced from the central portion of the multilayer structure 7 in the stacking direction toward both end faces.

[0072] As shown above, the low-rigidity layer 15 is provided between at least one of the internal electrodes 5 and the two internal electrodes 5 adjacent to the internal electrode 5 via the piezoelectric layer 3. In the case where they are respectively arranged, it is preferable that the pair of low-rigid layers 15 are regularly arranged in the stacking direction. By disposing the low-rigidity layer 15 in this way, it is possible to distribute the stress in the element 1 and reduce the bias S. As a result, it is possible to reduce the decrease in displacement even during long-term driving at a low temperature.

[0073] The material of the piezoelectric layer 3 may be any ceramic having piezoelectricity. Preferably, ceramics having a high piezoelectric strain constant d is used. Specifically, for example, Chita

33

Lead zirconate lead Pb (Zr, Ti) ○ or barium titanate BaTiO

3 3

It is possible to use electroceramic material. [0074] The thickness of the piezoelectric layer 3 is preferably 0.05 mm or more. By setting the thickness of the piezoelectric layer 3 to 0.05 mm or more, the electrical insulation between the adjacent internal electrodes 5 can be maintained even when a high voltage is applied to the element 1. Thereby, a larger displacement amount can be obtained. The thickness of the piezoelectric layer 3 is preferably 0.25 mm or less. By making the thickness of the piezoelectric layer 3 0.25 mm or less, the element 1 can be downsized.

[0075] The thickness of the piezoelectric layer 3 existing between the low-rigidity layer 15 and the adjacent internal electrode 5 is such that the low-rigidity layer 15

10% to 500% of the thickness of the piezoelectric layer 3 in which 15 does not exist is preferable. By setting it to 10% or more, high durability of the piezoelectric layer 3 can be secured. Further, by setting it to 500% or less, the stress can be reliably concentrated by the low rigidity layer 15. Thereby, the effect of stress relaxation can be obtained more reliably.

[0076] The material of the internal electrode 5 only needs to have conductivity. For example, it is possible to use a single metal such as Cu or Ni, or an alloy such as silver-platinum or silver-palladium. In particular, silver-palladium is preferred as the main component because it has migration resistance and oxidation resistance, has a low Young's modulus, and is inexpensive.

[0077] On the side surface of the laminated structure 7, external electrodes 9 on the anode side and the cathode side are formed. The internal electrode 5 is electrically connected to these external electrodes 9. The external electrodes 9 on the anode side and the cathode side may be formed on adjacent side surfaces because the internal electrodes 5 need only be electrically connected every other layer.

[0078] As the material of the external electrode 9, a material having good conductivity can be used. For example, a metal such as Cu or Ni or an alloy thereof can be used. Low electrical resistance is easy to handle, and therefore silver or a silver-based alloy is preferably used.

[0079] Next, a method of manufacturing a laminated piezoelectric element that can be applied to an embodiment of the present invention will be described. First, calcined powder of piezoelectric ceramics of perovskite type oxide made of Pb ZrO 2 -PbTiO etc.,

3 3

A slurry is prepared by mixing a binder made of an organic polymer such as acrylic or butyral and a plasticizer such as DBP (dibutyl phthalate) or DOP (diethyl phthalate). From this slurry, a ceramic green sheet to be the piezoelectric layer 3 is produced by using a known tape forming method such as a doctor blade method or a calender roll method. Next, a conductive paste is prepared by adding and mixing a binder and a plasticizer to the metal powder constituting the internal electrode 5 such as silver palladium. This conductive paste is printed on the upper surface of the green sheet to a thickness of 1 to 40 m by screen printing or the like. By changing the ratio of the binder and plasticizer to the metal powder, changing the frequency of the screen mesh, and changing the thickness of the resist that forms the screen pattern, the thickness of the internal electrode 5 and the internal electrode 5 The amount of the void 21 can be changed.

[0081] The low-rigidity layer 15 is prepared by mixing a metal powder such as silver palladium with a binder and a plasticizer, and preparing a conductive paste. This conductive paste is printed on the upper surface of the green sheet to a thickness of 1 to 40 111 by screen printing or the like. The porosity is adjusted by changing the ratio of the binder and plasticizer to the metal powder, the aperture ratio and pattern of the screen, and the resist thickness.

[0082] When the internal electrode 5 is mainly composed of silver / palladium, a conductive paste having a higher silver-palladium silver ratio than the conductive paste used as the internal electrode 5 is used as the low-rigidity layer 15. Thus, the low-rigidity layer 15 can be formed without going through a complicated process.

[0083] This is because when the conductive paste having a high silver ratio is disposed at the position where the low-rigidity layer 15 is formed and the laminated structure 7 is formed by simultaneous firing, the conductive paste having a high silver ratio is converted into silver. This is because it spreads. As silver diffuses, voids 21 are formed, and a plurality of metal portions 23 spaced apart from each other are formed. As a result, the conductive paste having a high silver ratio becomes a low-rigidity layer 15 having lower rigidity than the piezoelectric layer 3 and the internal electrode 5.

[0084] Then, a plurality of green sheets on which conductive paste is printed are laminated to produce a laminate. A weight was placed on this laminate, and the binder was removed at a predetermined temperature. Furthermore, the laminated structure 7 is produced by removing the weight and firing at 900 to 1200 ° C.

Next, a binder is added to the glass powder to produce a silver glass conductive paste, which is formed into a sheet. By drying and scattering the solvent, the sheet whose raw density is controlled to 6 to 9 g / cm ³ is transferred to the formation surface of the external electrode 9 of the columnar laminated structure 7. Baking is performed at a temperature not higher than the melting point (965 ° C) of silver higher than the softening point of the glass and not higher than 4/5 of the firing temperature (° C) of the laminated structure 7. Porous that forms a three-dimensional network structure due to the scattering of binder components in the sheet produced using silver glass conductive paste An external electrode 9 made of a conductor can be formed.

[0086] The external electrode 9 is preferably composed of a plurality of layers. Further, at this time, the paste constituting the external electrode 9 may be baked after being laminated on a multilayer sheet, or may be baked after being laminated one by one. Baking is better for mass production.

[0087] When the external electrode 9 is composed of a plurality of layers, the amount of the glass component in each layer is preferably different. And when changing a glass component for every layer, what changed the quantity of the glass component for every sheet should just be used. In particular, when it is desired to form a very thin glass rich layer on the surface in contact with the piezoelectric layer 3, first, a glass rich paste is printed on the laminated structure 7 by a method such as screen printing. Then, a multilayer sheet may be laminated on the glass rich paste. At this time, a sheet of 5 m or less may be used instead of printing.

[0088] The baking temperature of the silver glass conductive paste is preferably 500 to 800 ° C. This is because the neck portion is effectively formed, the silver in the silver glass conductive paste and the internal electrode 5 are diffusion-bonded, and the void 21 in the external electrode 9 is effectively left.

Here, the neck portion refers to a constricted portion that is formed at the time when the contact points between the silver and glass powder particles are joined in the initial stage of sintering. After the silver glass conductive paste is heated and the binder is volatilized, sintering proceeds from the portion where the remaining silver and glass powder particles are in contact. In the initial stage of sintering, a neck portion that is a constricted portion at the time when the contact points of the particles are joined is formed. By maintaining the formation of the neck after sintering, a porous conductor having a three-dimensional network structure can be obtained without growing huge particles.

The above temperature is also preferable from the viewpoint of partially bonding the external electrode 9 and the side surface of the columnar laminated structure 7. The softening point of the glass component in the silver glass conductive paste is preferably 500 to 800 ° C.

[0091] When the baking temperature is 800 ° C or lower, excessive sintering of the silver powder of the silver glass conductive paste is suppressed. As a result, the porous conductor having a three-dimensional network structure is efficiently formed, so that the external electrode 9 is prevented from becoming too dense. For this reason, the Young's modulus of the external electrode 9 does not become too high, so that the effect of absorbing the stress during driving can be increased. As a result, disconnection of the external electrode 9 can be suppressed. Also preferred It is better to bake at a temperature within 1.2 times the softening point of the glass.

On the other hand, when the baking temperature is 500 ° C. or higher, sufficient diffusion bonding is performed between the end of the low rigidity layer 15 and the external electrode 9. Thereby, since the neck portion is suitably formed, it is possible to suppress the occurrence of spark between the low-rigidity layer 15 and the external electrode 9 during driving.

Next, the laminated structure 7 on which the external electrode 9 is formed is immersed in the silicone rubber solution, and the silicone rubber solution is vacuum degassed. Thereafter, the laminated structure 7 is pulled up from the silicone rubber solution, and the side surface of the laminated structure 7 is coated with silicone rubber. Thereafter, the silicone rubber coated on the side surface of the laminated structure 7 is cured.

[0094] Then, the lead wire 31 is connected to the external electrode 9, and the laminated structure 7 is subjected to polarization treatment. As the polarization treatment, a DC voltage of 0.;! To 3 kV / mm may be applied to the pair of external electrodes 9 via the lead wires 31.

In this way, a piezoelectric actuator including the multilayer piezoelectric element 1 of the present embodiment is obtained. By connecting the lead wire 31 to an external voltage supply unit and applying a voltage to the low-rigidity layer 15 via the lead wire 31 and the external electrode 9, each piezoelectric layer 3 is greatly displaced by the inverse piezoelectric effect. Thus, for example, it can be used as a fuel injection valve for an automobile for supplying fuel to an engine.

[0096] Further, a conductive auxiliary member made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded on the outer surface of the external electrode 9 may be formed. This is because even when a large current is supplied to the actuator and driven at a high speed, the force S can be applied to the conductive auxiliary member, and the current flowing through the external electrode 9 can be reduced. As a result, the possibility of the external electrode 9 causing local heat generation and disconnection can be reduced, so that the durability S of the element 1 can be greatly improved by the force S.

[0097] Next, a description will be given of an injection device according to an embodiment of the present invention. As shown in FIG. 16, in the injection device 33 of this embodiment, the multilayer piezoelectric element 1 typified by the above embodiment is stored in a storage container 37 having an injection hole 35 at one end. A needle valve 39 that can open and close the injection hole 35 is disposed in the storage container 37. A fuel passage 41 is arranged in the injection hole 35 so as to communicate with the movement of the needle valve 39. This fuel passage 41 is connected to an external fuel supply source, and the fuel passage 41 is always connected to a constant high pressure. The fuel is being supplied. Therefore, when the needle valve 39 opens the injection hole 35, the fuel supplied to the fuel passage 41 is jetted into a fuel chamber (not shown) of the internal combustion engine at a constant high pressure.

Further, the upper end portion of the needle valve 39 has a large inner diameter, and a cylinder 43 formed in the storage container 37 and a slidable piston 45 are disposed. In the storage container 37, the element 1 described above is stored.

In such an injection device 33, when the element 1 is extended by applying a voltage, the piston 45 is pressed, the needle valve 39 closes the injection hole 35, and the supply of fuel is stopped. In addition, when the voltage application is stopped, the element 1 contracts, the disc spring 47 pushes the piston 45 back, and the injection hole 35 communicates with the fuel passage 41 so that fuel is injected.

Yes

[0100] In addition, the injection device 33 of the present embodiment includes a container having the injection holes 35 and the laminated piezoelectric element 1, and the liquid filled in the container is discharged from the injection holes 35 by driving the element 1. You may be comprised so that it may. That is, the element 1 does not necessarily have to be inside the container, and the element 1 may be configured so that pressure is applied to the inside of the container by driving the element 1. In the present embodiment, the liquid includes various liquid fluids such as a conductive paste in addition to fuel and ink.

Next, a fuel injection system according to an embodiment of the present invention will be described.

As shown in FIG. 17, the fuel injection system 49 of the present embodiment includes a common rail 51 that stores high-pressure fuel, a plurality of the above-described injection devices 33 that inject the fuel stored in the common rail 51, and a common rail. A pressure pump 53 for supplying high-pressure fuel to 51 and an injection control unit 55 for supplying a drive signal to the injection device 33 are provided.

[0103] The injection control unit 55 controls the amount and timing of fuel injection while sensing the state of the combustion chamber of the engine with a sensor or the like. The pressure pump 53 plays a role of feeding the fuel from the fuel tank 57 to the common rail 51 at about 1000 to 2000 atmospheres, preferably 1500 to about 1700 atmospheres. In the common rail 51, the fuel sent from the pressure pump 53 is stored and sent to the injector 33 as appropriate. As described above, the injector 33 injects a small amount of fuel from the injection hole 35 into the combustion chamber in the form of a mist. It should be noted that the present invention is not limited to the above-described embodiment, and does not depart from the gist of the present invention, and various modifications may be made within the scope.

Example

[0105] A piezoelectric actuator provided with the multilayer piezoelectric element 1 of the above embodiment was manufactured as follows. First, lead zirconate titanate (? 2 0 -PbTiO) with an average particle size of 0.4 111

A slurry was prepared by mixing the calcined powder of piezoelectric ceramic mainly composed of 3 3, binder and plasticizer. Using this slurry, a ceramic green sheet serving as the piezoelectric layer 3 having a thickness of 150 m was produced by the doctor blade method.

[0106] On one surface of the ceramic green sheet, and the silver one palladium alloy (silver 95% by weight Palladium © arm 5 weight ^_0/0) as an internal electrode 5 by adding a binder to the conductive paste is screen printing. As a paste comprising a porosity of high low-rigidity layer 15, a silver-palladium alloy - a (silver 95 mass ^_0/0 palladium 5 weight ^_0/0) of the conductive paste, the binder addition rates than paste for forming the internal electrode 5 The one with increased is used. The paste that becomes the low-rigidity layer 15 was printed on one side of the ceramic green sheet by changing the screen printing pattern. 300 layers of ceramic green sheets printed with the paste to be the internal electrode 5 and ceramic green sheets printed with the paste to be the low rigidity layer 15 were laminated and fired. Firing was carried out at 800 ° C for 90 minutes, and then fired at 1000 ° C for 200 minutes.

Further, in the present example, the pattern shown in FIG. 5 was used as the pattern of the low rigidity layer 15. Furthermore, the low-rigidity layer 15 is divided into a case where it is arranged in the piezoelectric layer 3 adjacent to one side in the stacking direction of the internal electrodes 5, and a case where the low-rigidity layer 15 is arranged on both sides as shown in FIG. It was.

In addition, as described above, the low-rigidity layer 15 disposed on one side (the embodiment shown in FIG. 9) or both sides (the embodiment shown in FIG. 10) of the internal electrode 5 is set as one set, and the following lamination is performed. Structure 7 was produced. In Sample Nos. 2 and 6, one set of low-rigidity layers 15 was disposed on the 150th layer of the piezoelectric layer 3. In sample numbers 4 and 8, two sets of low-rigidity layers 15 were arranged in total on the 1st and 300th layers. Sample Nos. 3 and 7 consisted of a total of 5 low-oka IJ Tosei 15 layers on the 50, 100, 150, 200, and 250 layers. Sample Nos. 5 and 9 consisted of a total of 7 low-oka IJ Tosei 15 layers in layers 1, 50, 100, 150, 200, 250, and 300. [0109] Next, an amorphous glass powder having a softening point of 40 ° C, mainly composed of flaky silver powder having an average particle size of 2 [I m, and the balance being a key particle having an average particle size of 2 μm. And mixed. Furthermore, 8 parts by mass of a binder was added to this mixture with respect to 100 parts by mass of the total mass of silver powder and glass powder. The above mixture and binder were sufficiently mixed to produce a silver glass conductive paste. The silver glass conductive paste thus produced was formed on a release film by screen printing. After drying, a sheet of silver glass conductive paste was obtained by peeling off from the release film.

[0110] Then, the sheet of silver glass paste was transferred to the surface of the laminated structure 7 where the external electrodes 9 were formed. Further, the external electrode 9 was formed by baking at 700 ° C. for 30 minutes. After that, the lead wire 31 was connected to the external electrode 9, and a 3 kV / mm DC electric field was applied to the positive and negative external electrodes 9 through the lead wire 31 for 15 minutes for polarization treatment. Thus, a piezoelectric actuator unit was manufactured.

When a DC voltage of 170 V was applied to the obtained element 1, displacement was obtained in the stacking direction in all piezoelectric actuators. Moreover, the piezoelectric Akuchiyueta was applied at a frequency of 150Hz AC voltage of 0 to + 170 V at room temperature, was you continuous driving test to 1 X 10 ⁹ times. The results are shown in Table 1.

[table 1]

[0112] From Table 1, Sample No. 1, which is a comparative example, is not provided with the low-rigidity layer 15 that relieves stress at the interface between the non-facing portion 13 and the facing portion 11. Therefore, it broke in 3 X 10 ⁷ cycles without waiting for the prescribed 1 X 10 ⁹ cycles continuous drive test. On the other hand, sample numbers 2 to 9, which are examples of the present invention, satisfied a predetermined continuous driving test of 1 × 10 ⁹ cycles. Furthermore, it has been found that the element 1 has the required amount of displacement without showing any extreme deterioration from the initial amount of displacement. In this way, a laminated piezoelectric element having excellent durability could be produced.

[0113] In particular, Sample Nos. 7 and 9 ensured an effective displacement amount from the beginning, and the element performance remained almost unchanged after continuous drive, indicating that they were extremely durable. all right. In this way, it was possible to produce a laminated piezoelectric element with a very stable displacement.

Claims

The scope of the claims

[1] A laminated structure in which a plurality of piezoelectric layers and a plurality of internal electrodes are alternately laminated, and an anode side and a negative electrode formed on a side surface of the laminated structure and connected to the plurality of internal electrodes An external electrode on the pole side,

The multilayer structure includes a plurality of opposing portions in which a pair of the internal electrodes adjacent to each other in the stacking direction are opposed to each other in the stacking direction, and includes a lower rigidity layer than the piezoelectric layer and the internal electrode. It consists of a non-opposing part other than the opposing part,

At least one of the plurality of facing portions is

A first portion where internal electrodes adjacent to each other in the stacking direction are opposed to each other via the low-rigidity layer and the piezoelectric layer, and are in contact with at least a part of a boundary between the facing portion and the non-facing portion; A laminated piezoelectric element having a second part other than the above part.

[2] The multilayer piezoelectric element according to [1], wherein the low-rigidity layer includes a void and a metal portion that is spaced apart from the void.

[3] The multilayer piezoelectric element according to [1], wherein internal electrodes adjacent to each other in the stacking direction are joined by the piezoelectric layer at a central portion of the facing portion.

[4] The multilayer piezoelectric element according to [1], wherein the low-rigidity layer is disposed at a peripheral edge of the facing portion.

5. The multilayer piezoelectric element according to claim 1, wherein the low-rigidity layer is disposed across a boundary between the facing portion and the non-facing portion!

6. The multilayer piezoelectric element according to claim 1, wherein the low-rigidity layer is disposed in a band shape along a boundary between the facing portion and the non-facing portion!

7. The multilayer piezoelectric element according to claim 1, wherein the plurality of low-rigidity layers spaced apart from each other are scattered along a boundary between the facing portion and the non-facing portion! / .

8. The multilayer piezoelectric element according to claim 1, wherein the low-rigidity layer is disposed so as to be rotationally symmetric with respect to a central axis in the stacking direction of the multilayer structure.

9. The multilayer piezoelectric element according to claim 1, wherein the low-rigidity layer is embedded in the piezoelectric layer.

[10] The low-rigidity layer is exposed on a side surface of the laminated structure.

2. The laminated piezoelectric element according to 1.

11. The multilayer piezoelectric element according to claim 1, wherein the two internal electrodes adjacent to the first part in the stacking direction are respectively connected to external electrodes having the same polarity! / .

12. The stacked piezoelectric element according to claim 1, wherein the two internal electrodes adjacent to the first part in the stacking direction are respectively connected to external electrodes having different polarities! .

[13] The low-rigidity layer is disposed between at least one of the internal electrodes and two internal electrodes adjacent to both sides of the internal electrode in the stacking direction via the piezoelectric layer. The multilayer piezoelectric element according to claim 1, wherein! /.

14. The multilayer piezoelectric element according to claim 1, wherein a plurality of the low-rigid layers are present and are regularly arranged in the lamination direction.

15. An injection apparatus comprising the multilayer piezoelectric element according to claim 1 and an ejection hole, wherein the ejection hole force liquid is ejected by driving the multilayer piezoelectric element.

[16] A common rail that stores high-pressure fuel,

The injection device according to claim 14, which injects fuel stored in the common rail, a pressure pump that supplies high-pressure fuel to the common rail,

An injection control unit for providing a drive signal to the injection device;

A fuel injection system.