JP5154580B2 - Multilayer piezoelectric element, injection device including the same, and fuel injection system - Google Patents

Description

  The present invention relates to a laminated piezoelectric element used for, for example, a drive 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 precision positioning device such as an optical device, and a vibration prevention 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 yaw rate sensor. Examples of the circuit element include a piezoelectric gyro, a piezoelectric switch, a piezoelectric transformer, and a piezoelectric breaker.

  Conventionally, multilayer piezoelectric elements are required to be able to ensure a large amount of displacement under a large pressure at the same time as miniaturization proceeds. For this reason, it is required that a higher voltage is applied and that the device can be used under severe conditions in which continuous driving is performed for a long time.

When driving continuously for a long time under a high voltage or high pressure condition, stress is applied to the internal electrode and the piezoelectric body. In particular, a large stress is applied in the vicinity of the boundary between a facing portion sandwiched between two internal electrodes adjacent in the stacking direction and a non-facing portion other than the facing portion in the piezoelectric body. Therefore, it is required to disperse the stress in the vicinity of 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.
JP 2001-267646 A

  However, when the stress relaxation layer described in Patent Document 1 is provided, a crack generated in the stress relaxation layer may extend to the adjacent internal electrode or external electrode through the piezoelectric body. Therefore, an electrical short circuit may occur between internal electrodes adjacent in the stacking direction, and the amount of displacement may be reduced.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a multilayer piezoelectric element in which a decrease in displacement due to long-time driving is improved.

The multilayer piezoelectric element according to the present invention includes a multilayer body having a plurality of piezoelectric bodies and a plurality of internal electrodes, the piezoelectric bodies and the internal electrodes being alternately stacked, and a first side surface of the multilayer body. A first external electrode formed, and a second external electrode formed on a second side surface of the laminate,
The plurality of internal electrodes on the first and second side surfaces are respectively connected to the first external electrodes such that the plurality of internal electrodes are alternately connected to one of the first and second external electrodes. Alternatively, the internal electrodes connected to the second external electrodes and the internal electrodes that are insulated and separated by being formed away from the first side surface or the second side surface are alternately arranged.
The stacked body includes a facing portion where the adjacent internal electrodes face each other in the stacking direction, and a non-facing portion provided along the first and second side surfaces, facing each other of the internal electrodes. A laminated piezoelectric element divided into
At least one of the plurality of internal electrodes has a plurality of internal electrode non-formation sites provided in the internal electrode along a boundary between the facing portion and the non-facing portion.

  According to the multi-layer piezoelectric element of the present invention, at least one of the plurality of internal electrodes includes a plurality of internal electrode non-formation sites surrounded by the internal electrode, and the opposing portion and the non-opposing portion. It has along the boundary.

  Therefore, since the displacement in the vicinity of the boundary with the non-opposing portion among the opposing portions is suppressed, the concentration of stress applied near the boundary between the opposing portion and the non-facing portion can be suppressed. As described above, since the stress is dispersed by making the internal electrode non-formation site a lattice shape or the like surrounded by the internal electrodes, a stress relaxation layer is formed on the piezoelectric body as described in Patent Document 1. Compared with the case where it provides, the possibility that a crack will arise in a piezoelectric material can be reduced.

1 is a perspective view showing a multilayer piezoelectric element according to a first embodiment of the present invention. FIG. 1B is a partial exploded perspective view of the multilayer piezoelectric element of FIG. 1A. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element shown to FIG. 1A and 1B, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element shown to FIG. 1A and 1B, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 2A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element shown to FIG. 1A and 1B, and is sectional drawing which shows the cross section of the internal electrode which does not have an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element which concerns on the modification of 1st Embodiment, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element which concerns on the modification of 1st Embodiment, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 3A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element which concerns on the modification of 1st Embodiment, and is sectional drawing which shows the cross section of the internal electrode which does not have an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 2nd Embodiment which concerns on this invention, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 2nd Embodiment, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 4A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 2nd Embodiment, and is sectional drawing which shows the cross section of the internal electrode which does not have an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element which concerns on the modification of 2nd Embodiment, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element which concerns on the modification of 2nd Embodiment, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 5A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element which concerns on the modification of 2nd Embodiment, and is sectional drawing which shows the cross section of the internal electrode which does not have an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of the 3rd Embodiment concerning this invention, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 3rd Embodiment, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 6A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 3rd Embodiment, and is sectional drawing which shows the cross section of the internal electrode which does not have an internal electrode non-formation site | part. It is a perspective view which shows the lamination type piezoelectric element of the 4th Embodiment concerning this invention. It is a perspective view which shows the lamination type piezoelectric element of the 5th Embodiment concerning this invention. It is AA sectional drawing of FIG. 8A. It is a BB sectional view of Drawing 8A. It is a perspective view which shows the lamination type piezoelectric element of the 6th Embodiment concerning this invention. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element shown in FIG. 9, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element shown in FIG. 9, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 10A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element shown in FIG. 9, and is sectional drawing which shows the cross section of the internal electrode which does not have an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of the 7th Embodiment concerning this invention, and is sectional drawing which shows the cross section of the internal electrode which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 7th Embodiment, and is sectional drawing which shows the cross section of the internal electrode different from FIG. 11A which has an internal electrode non-formation site | part. It is sectional drawing orthogonal to the lamination direction of the lamination type piezoelectric element of 7th Embodiment, and is sectional drawing which shows the cross section of the internal electrode which does not have a 1st site | part and a 2nd site | part. It is a schematic sectional drawing which shows the injection apparatus concerning one Embodiment of this invention. 1 is a schematic block diagram showing a fuel injection system according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 3 ... Piezoelectric body 5, 9 ... Internal electrode 7 ... Laminated body 7a ... Opposing part 7b ... Non-opposing part 7c ... Internal electrode non-formation part 7d: Boundaries 9a, 9c between the facing portion and the non-facing portion, first portions 9b, 9d, second portions 11, external electrodes 11a, having internal electrode non-forming portions. External electrode 11b on the anode side ... External electrode 21 on the cathode side ... Injection device 23 ... Injection hole 25 ... Storage container 27 ... Needle valve 29 ... Fluid passage 31 ... Cylinder 33 ... Piston 35 ... Belleville spring 41 ... Fuel injection system 43 ... Common rail 45 ... Pressure pump 47 ... Injection control unit 49 ... Fuel tank 70 ... Insulation separator

Hereinafter, the multilayer piezoelectric element of the present invention will be described in detail with reference to the drawings.
<First Embodiment>
FIG. 1A is a perspective view showing a multilayer piezoelectric element according to the first embodiment of the present invention. FIG. 1B is an exploded perspective view of a part of the multilayer piezoelectric element according to the embodiment shown in FIG. 1A. 2A, 2B, and 2C are cross-sectional views each including internal electrodes adjacent to each other in the direction perpendicular to the stacking direction in the embodiment shown in FIG.

  As shown in FIGS. 1A to 2C, the multilayer piezoelectric element 1 (hereinafter also simply referred to as element 1) of the present embodiment has a plurality of piezoelectric bodies 3 and a plurality of internal electrodes 5, and the piezoelectric body 3. And a laminated body 7 in which the internal electrodes 5 are alternately laminated.

  The multilayer piezoelectric element 1 includes two external electrodes 11. For example, one (cathode side) external electrode 11 is formed on the first side surface, which is one side surface of the multilayer body 7, and the other (anode side) external electrode. The electrode 11 is formed on the second side surface facing the first side surface (FIG. 1A). In the laminated body 7, the internal electrodes 5 and 9 serving as the negative electrode are formed so as to reach the first side surface, are connected to the external electrode 11 on the first side surface, are formed apart from the second side surface, and are external on the anode side. It is electrically separated from the electrode 11. On the other hand, the internal electrodes 5 and 9 serving as positive electrodes are formed so as to reach the second side surface, are connected to the external electrode 11 on the second side surface, are formed away from the first side surface, and are external to the cathode side. It is electrically separated from the electrode 11. In the laminate 7, the internal electrodes 5, 9 serving as the negative electrode and the internal electrodes 5, 9 serving as the positive electrode are alternately arranged, and each piezoelectric body 3 is sandwiched between the internal electrodes 5, 9 of the negative electrode and the positive electrode. A structure is realized. In the present specification, the portions where the electrodes are not formed on the piezoelectric body 3 formed by forming the internal electrodes 5 and 9 away from the end portions (first side surface or second side surface) are insulated and separated. This is referred to as part 70.

  In the multilayer piezoelectric element 1 configured as described above, the active region where the piezoelectric body 3 is sandwiched between the positive and negative internal electrodes 5 and 9 and voltage is applied to the sandwiched portion is the first side surface and the second side region. An inactive region that is formed away from the side surface by the width of the insulating separation portion 70 and that has the same polarity of the internal electrodes facing each other with the insulating separation portion 70 interposed therebetween is an inactive region where no voltage is applied to the piezoelectric body 3. It is formed along the side. In this manner, the stacked body 7 is divided into an active region and a non-active region other than the pair of positive and negative internal electrodes 5 adjacent to each other in the stacking direction. In the present specification, an active region in which the piezoelectric body 3 is sandwiched between the positive and negative internal electrodes 5 and 9 facing each other is referred to as a facing portion 7a, and the inactive where the positive and negative internal electrodes 5 and 9 are not facing each other. The region is referred to as a non-facing portion 7b.

Here, in particular, in the present invention, at least one internal electrode 9 among the plurality of internal electrodes 5 has a plurality of openings (referred to as internal electrode non-formation sites 7 c) each surrounded by the internal electrode 9. It has along the boundary 7d of the opposing part 7a and the non-opposing part 7b, It is characterized by the above-mentioned.
In the following description, the internal electrode 9 has a plurality of internal electrode non-formed portions 7c (hereinafter also referred to as non-formed portions 7c) and is positioned so as to straddle the boundary 7d between the facing portion 7a and the non-facing portion 7b. The portion will be referred to as the first portion 9a and will be described as the other second portion 9b.
Here, the 1st site | part 9a is an area | region which has several non-formation site | parts 7c, Comprising: The boundary with the 2nd site | part 9b is defined as follows.
When a voltage is applied to the external electrode 11, the electric field transmitted to the internal electrode 9 is once disturbed by the internal electrode non-formation site 7c, but the electric field intensity distribution is once disturbed. A phenomenon occurs in which the intensity is aligned in a single line. The boundary between the first part 9a and the second part 9b is defined as the position of the line where the electric field strengths are aligned. Specifically, by providing the internal electrode non-formation site 7c along the boundary between the facing portion 7a and the non-facing portion 7b, the insulating separation portion 70 is generally separated from the boundary 7d between the facing portion 7a and the non-facing portion 7b. It is a position away from the external electrode 11 by a distance of.

  In the cross section perpendicular to the stacking direction and including the internal electrode 5, the ratio of the internal electrode 5 in the first part 9a is smaller than the ratio of the internal electrode 5 in the second part 9b. It is preferable. In this case, the multilayer piezoelectric element 1 continuously undergoes dimensional changes when driven, but the piezoelectric element 3 is driven in close contact with the internal electrode 5 so that the element 1 is large as a whole. Drive deformation. Therefore, a relatively large stress is applied to the end portion of the element 1. However, since the non-formation part 7c of the first part 9a is in the above-described form, the amount of displacement at the end portion close to the end face of the element 1 can be reduced. As a result, the stress applied to the end portion of the element 1 can be reduced, and the durability of the element 1 can be improved.

  Thus, in this embodiment, at least one of the plurality of internal electrodes 5 and 9 has a plurality of internal electrode non-formation sites 7c each surrounded by the internal electrode 9 as opposed to the opposing portion 7a. Since it has along the boundary 7d with the opposing part 7b, the driving force in the boundary 7d vicinity with the non-opposing part 7b can be made small among the opposing parts 7a. That is, the driving force is small as compared with the central portion of the facing portion 7a along the boundary 7d between the facing portion 7a and the non-facing portion 7b, in the facing portion 7a or across the facing portion 7a and the non-facing portion 7b. A portion is formed, and the driving force can be reduced stepwise toward the non-opposing portion 7b. As a result, stress concentration at the boundary 7d can be suppressed, and high durability can be realized.

Further, as shown in FIG. 2, the first portion 9 a is located between the portion of the internal electrode 9 that is located in the facing portion 7 a and contributes to driving the element 1 and the portion that is connected to the external electrode 11. ing. As described above, it is preferable that the ratio of the internal electrode 5 in the first part 9a is smaller than the ratio of the internal electrode 5 in the second part 9b. Therefore, in the portion where the plurality of internal electrode non-formation sites 7c are formed, the current path when the current flows becomes narrow, so the current density when the overcurrent flows is higher than the other portions, Damage is likely to occur. That is, when the first portion 9a is located at a location where current is passed from the external electrode 11 to the portion of the internal electrode 9 that contributes to driving of the device 1, a very strong voltage is applied to the device 1. A part of the first portion 9a is broken. Thereby, it is suppressed that an excessive voltage is applied to the portion of the internal electrode 9 that contributes to driving of the element 1. As a result, it is possible to suppress the piezoelectric body 3 from being displaced excessively and causing cracks.
In the present invention, in consideration of protection of the piezoelectric body 3 when an excessive voltage is applied, for example, when a voltage higher than a certain level is applied, the electrode portion between adjacent internal electrode non-formation sites 7c is damaged. As described above, the interval between the internal electrode non-formation sites 7c can also be set.

  Further, even when the portion of the internal electrode 9 located between the non-formed portions 7c is broken and no voltage is applied to the portion of the internal electrode 9 that contributes to driving of the element 1, this breakage occurs. The internal electrode 9 is sandwiched between the internal electrodes 5 connected to the external electrodes of the same polarity. Therefore, the displacement amount of the two piezoelectric bodies 3 adjacent to the internal electrode 9 in the stacking direction is suppressed. As a result, it is possible to suppress the generation of stress that causes cracks in these piezoelectric bodies 3.

  In particular, as shown in FIG. 2, the first portion 9a is located between the portion contributing to driving of the element 1 and the portion connected to the external electrode 11, and only in the first portion 9a. By disposing the non-formed part 7c, stress is easily applied to the first part 9a. Therefore, since it is known in advance that the first portion 9a of the internal electrode 9 is likely to break, it is easy to predict the driving state of the element 1 over a long period of time. As a result, the reliability with respect to the displacement amount of the element 1 can be improved.

Further, in the present invention, as shown in FIGS. 1B and 2A to 2B, the plurality of internal electrode non-formed portions 7c are aligned in a direction parallel to the boundary 7d between the facing portion 9b and the non-facing portion 9a. It is more preferable that the plurality of aligned internal electrode non-formed sites 7c are arranged at equal intervals. In this specification, the plurality of internal electrode non-formation sites 7c are arranged at equal intervals in one direction, and the first site 9a has a lattice shape with the internal electrode non-formation sites 7c as lattices. That's it.
As described above, when the first portion 9a has a lattice shape with the internal electrode non-forming portion 7c as a lattice, variation in stress applied in the vicinity of the boundary 7d can be reduced. Therefore, the durability in the vicinity of the boundary 7d between the facing portion 7a and the non-facing portion 7b can be enhanced. As shown in FIGS. 1 and 2, in the present embodiment, the lattice shape of the lattice shape may be arranged in a row or in a plurality of rows.

<Modification of First Embodiment>
3A to 3C are cross-sectional views orthogonal to the stacking direction of the multilayer piezoelectric element 1 according to the modification of the first embodiment, and illustrate cross sections including the internal electrodes 5 and 9. When the internal electrode 9 shown in FIG. 3B is used as a reference, FIG. 3A shows the internal electrode 9 shown in FIG. 3B and the internal electrode 9 adjacent to one end face side of the laminate 7. FIG. 3C shows the internal electrode 9 shown in FIG. 3B and the internal electrode 5 adjacent to the other end face side of the stacked body 7.
Here, in this specification, the end surface of the laminated body 7 refers to the outer surface orthogonal to the lamination direction of the internal electrodes 5 and 9 and the piezoelectric body 3, and refers to the upper surface and the lower surface in FIG. 1A.

The laminated piezoelectric element 1 of this modification is different from the element 1 of the first embodiment in which the internal electrode non-forming part 7c is circular, except that the internal electrode non-forming part 7c is rectangular. The configuration is the same as the element 1 of the first embodiment.
As described above, the lattice shape in the present invention includes a circular shape as shown in FIG. 3, and the lattice shape as shown in FIG. 2 is not limited to a square shape. In addition, since the stress applied to the vicinity of the boundary between the facing portion 7a and the non-facing portion 7b of the multilayer body 7 only needs to be relieved, the lattice in the first portion 9a of the internal electrode 9 is substantially square. It is also effective that the corners have a curved shape.

  In the present invention, as shown in the first embodiment and its modification, the internal electrode non-forming portion 7c is a boundary between the facing portion 7a and the non-facing portion 7b when the internal electrode 9 is viewed in plan view. 7d is preferred. That is, it is preferable that the internal electrode non-formation site 7c is formed across the facing portion 7a and the non-facing portion 7b. In this case, it is possible to reduce the driving force at the boundary 7d between the facing portion 7a and the non-facing portion 7b where the stress is most likely to concentrate among the facing portions 7a, so that the durability of the element 1 can be further increased. it can.

  Further, in the first embodiment and the modification thereof, the configuration in which the plurality of internal electrodes 9 have the first portion 9a is shown. However, in the present invention, at least one internal polarization 9 is the first What is necessary is just to have the site | part 9a. However, as shown in the first embodiment and its modifications, it is preferable that two or more internal electrodes 9 have a first portion 9a. This is because the stress can be dispersed in a wider range by the plurality of internal electrodes 9 having the first portion 9a. Thereby, the durability of the element 1 can be further increased.

  Further, at least one of the internal electrodes 5, 9 connected to the anode-side external electrode 11a and the internal electrodes 5, 9 connected to the cathode-side external electrode 11b has a first portion 9a. More preferably. Thereby, since the bias of the stress distribution can be reduced, the driving direction of the element 1 can be stabilized.

  Moreover, it is more preferable that a pair of internal electrodes 5 and 9 adjacent to each other in the stacking direction has a first portion 9a. This is because the amount of displacement of the piezoelectric body 3 sandwiched between the internal electrodes 5 and 9 can be further reduced, and the effect of absorbing stress in the piezoelectric body 3 can be further enhanced.

  Furthermore, it is preferable that all the internal electrodes 5 and 9 have the 1st site | part 9a. As a result, the stress can be dispersed in a wider range, and the bias of the stress distribution can be further reduced.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. 4A to 4C are cross-sectional views orthogonal to the stacking direction in the multilayer piezoelectric element 1 according to the second embodiment of the present invention, and illustrate a cross section including the internal electrode 5. When the internal electrode 9 shown in FIG. 4B is used as a reference, FIG. 4A shows the internal electrode 9 shown in FIG. 4B and the internal electrode 9 adjacent to one end face side of the laminate 7. FIG. 4C shows the internal electrode 9 shown in FIG. 4B and the internal electrode 5 adjacent to the other end face side of the multilayer body 7.

  In the multilayer piezoelectric element of the second embodiment, as shown in FIGS. 4A to 4C, the non-formed portion 7 c in the first portion 9 a of the internal electrode 9 is a boundary between the facing portion 7 a and the non-facing portion 7 b. The point which is arranged in a plurality of rows in parallel with 7d is different from the first embodiment. By arranging the non-formation site 7c in the first site 9a in this way, stress can be dispersed in a wider range of the piezoelectric body 3, and therefore stress in the vicinity of the boundary 7d between the facing portion 7a and the non-facing portion 7b. The distribution bias can be further reduced.

  In particular, when the non-forming portion 7c in the first portion 9a is arranged in a plurality of rows in parallel with the boundary 7d between the facing portion 7a and the non-facing portion 7b, one of the plurality of rows is the facing portion 7a. It is preferably located on the boundary 7d between the non-opposing portion 7b.

  As shown in FIGS. 4A to 4C, when the internal electrode 5 is not exposed except the surface connected to the external electrode 11, that is, three side surfaces other than the side surface to which the external electrode 11 is connected in the laminate 7. When the outer peripheries of the internal electrodes 5 along the line are positioned inside the three side surfaces, it is particularly effective that the non-formed sites 7c are arranged in a plurality of rows as in the second embodiment. . This is because when the internal electrode 5 has the above-described structure, the boundary 7d between the facing portion 7a and the non-facing portion 7b is not exposed on the side surface of the stacked body 7, and stress tends to concentrate on the boundary 7d portion. . Since the first portion 9a is located between the portion of the internal electrode 9 that is located at the facing portion 7a and contributes to driving the element 1 and the portion that is connected to the external electrode 11, stress is generated at the non-forming portion 7c. Can be relaxed. Thereby, it can suppress that stress concentrates on the peripheral part of the internal electrode 5. FIG.

  5A to 5A are cross-sectional views orthogonal to the stacking direction of the multilayer piezoelectric element 1 according to the modification of the second embodiment illustrated in FIG. 4, and illustrate cross sections including the internal electrodes 5 and 9. Yes. When the internal electrode 9 shown in FIG. 5B is used as a reference, FIG. 5A shows the internal electrode 9 shown in FIG. 5B and the internal electrode 9 adjacent to one end face side of the laminate 7. FIG. 5C shows the internal electrode 9 shown in FIG. 5B and the internal electrode 5 adjacent to the other end face side of the multilayer body 7.

  Furthermore, as shown in FIGS. 5A to 5C, the non-forming part 7c constituting the row located on the boundary 7d between the facing part 7a and the non-facing part 7b may be larger than the other non-forming part 7c. Even more preferred. This is because the driving force at the boundary 7d between the opposing portion 7a and the non-opposing portion 7b where stress is most likely to concentrate can be reduced, and the durability of the element 1 can be further increased.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. 6A to 6B are cross-sectional views orthogonal to the stacking direction in the multilayer piezoelectric element 1 according to the third embodiment of the present invention, and illustrate a cross section including the internal electrode 5. When the internal electrode 9 shown in FIG. 6B is used as a reference, FIG. 6A shows the internal electrode 9 shown in FIG. 6B and the internal electrode 9 adjacent to one end side in the stacking direction. 6C shows the internal electrode 5 shown in FIG. 6B and the internal electrode 5 adjacent to the other end side in the stacking direction.

  As shown in FIG. 6, the anode-side and cathode-side external electrodes 11a, 11b are respectively located on opposite side surfaces of the multilayer body 7, and a boundary 7d between the facing portion 7a and the non-facing portion 7b is separated from each other. In the case where it is present at two locations (two locations facing each other in FIG. 6), it is preferable that at least one internal electrode 9 of the plurality of internal electrodes 5 has a first portion 9a on each boundary 7d. That is, the internal electrode 9 having the internal electrode non-forming portion 7c along the boundary 7d between the facing portion 7a and the one non-facing portion 7b further extends along the boundary 7d between the facing portion 7a and the other non-facing portion 7b. It is preferable to have a plurality of internal electrode non-formation sites 7c. This is because the bias of the stress distribution on the plane orthogonal to the stacking direction can be reduced.

  Further, when the boundary 7d between the facing portion 7a and the non-facing portion 7b exists at a plurality of locations separated from each other, among the plurality of internal electrodes 5, the internal electrodes 9 adjacent to each other in the stacking direction It is preferable that the 1st site | part 9a is located on each boundary 7d of the electrode 9. FIG. Thereby, in the pair of adjacent internal electrodes 9, the first portions 9 a are positioned to face each other, so that the drive shaft of the element 1 is less shaken and the durability is improved.

<Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described. FIG. 7 is a perspective view showing a multilayer piezoelectric element according to the fourth embodiment of the present invention.

  In the fourth embodiment, as shown in FIG. 7, the plurality of internal electrodes 9 having the first portion 9a of the internal electrodes 5 are periodically arranged according to a certain rule in the stacking direction, This is a more preferable embodiment according to the present invention. Thereby, since the stress applied to the entire element 1 can be dispersed in the stacking direction, the element 1 having high durability can be provided.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described. FIG. 8A is a perspective view showing a multilayer piezoelectric element according to the fifth embodiment of the present invention. FIG. 8B is a cross-sectional view taken along line AA in the fifth embodiment shown in FIG. 8A and including the internal electrode 9. FIG. 8C is a cross-sectional view taken along the line BB in the fifth embodiment shown in FIG. 8A and including the internal electrode 9.

  As shown in FIG. 8, a pair of internal electrodes 9 adjacent in the stacking direction each have a first portion 9 a, and the internal electrode 9 occupies the first portion 9 a of the internal electrode 9 close to the end face of the stacked body 7. The ratio is preferably smaller than the ratio occupied by the internal electrode 9 in the first portion 9 a of the internal electrode 9 that is far from the end face of the multilayer body 7. That is, of the pair of internal electrodes 9 having the internal electrode non-formation site 7 c, the ratio of the internal electrode 9 near the end surface of the multilayer body 7 to the internal electrode non-formation site 7 c is located far from the end surface of the multilayer body 7. It is preferable that the ratio of the internal electrode 9 occupied by the internal electrode non-formation site 7c is larger.

  Unlike ordinary multilayer electronic components such as capacitors, the multilayer piezoelectric element 1 continuously undergoes dimensional changes when driven. When all the piezoelectric bodies 3 are driven in close contact via the internal electrodes 5, the element 1 is largely driven and deformed integrally. Therefore, a relatively large stress is applied to the end portion of the element 1.

  However, since the non-formation part 7c of the first part 9a is in the above-described form, the amount of displacement at the end part close to the end face of the element 1 can be reduced, so that the stress applied to the end part of the element 1 is reduced. Can be reduced. As a result, the durability of the element 1 can be improved.

Furthermore, it is more preferable that the non-formation site 7c gradually increases toward the end face side of the laminate 7, and it is even more preferable that the degree of increase is regular.
As already shown, since the multilayer piezoelectric element 1 is largely driven and deformed as a unit, the stress applied gradually increases as the end face of the element 1 is closer. However, the stress generated at the boundary 7d between the facing portion 7a and the non-facing portion 7b becomes closer to the end surface of the element 1 because the non-forming portion 7c gradually increases toward the end surface side or gradually according to a certain rule. This is because the effect of relaxing the stress can be gradually increased, so that the bias of the stress distribution in the stacking direction of the element 1 can be further reduced.

  Moreover, it is preferable that the internal electrode 9 located in the end surface side of the lamination direction among the several internal electrodes 5 has the 1st site | part 9a. Although a relatively large stress is likely to be applied to the end portion close to the end surface of the element 1, the internal electrode 9 located on the most end surface side in the stacking direction has the first portion 9a, so that the stress can be efficiently applied. This is because it can be relaxed. As a result, the durability of the element 1 can be further increased.

<Sixth Embodiment>
Next, a sixth embodiment of the present invention will be described. FIG. 9 is a perspective view showing a multilayer piezoelectric element according to the sixth embodiment of the present invention. 10A to 10C are cross-sectional views orthogonal to the stacking direction in the embodiment shown in FIG. 9, and show cross sections including the internal electrodes 5. When the internal electrode 9 shown in FIG. 10B is used as a reference, FIG. 10A shows the internal electrode 9 shown in FIG. 10B and the internal electrode 9 adjacent to one end face side of the laminate 7. FIG. 10C shows the internal electrode 9 shown in FIG. 10B and the internal electrode 5 adjacent to the other end face side of the multilayer body 7.

  As shown in FIGS. 9 and 10, the multilayer piezoelectric element 1 of the sixth embodiment includes a plurality of piezoelectric bodies 3 and a plurality of internal electrodes 5, and the piezoelectric bodies 3 and the internal electrodes 5 are alternately stacked. The laminated body 7 is provided. As in the first embodiment, the stacked body 7 is divided into a pair of positive and negative internal electrodes 5 adjacent to each other in the stacking direction, a facing portion 7a facing in the stacking direction and the other non-facing portion 7b. At least one internal electrode 9 among the plurality of internal electrodes 5 has a lattice shape, and includes a first portion 9c and a second portion 9d having a finer lattice than the first portion 9c. That is, in the internal electrode 9 having the internal electrode non-forming part 7c, the second internal electrode non-forming part 7e having a smaller area than the internal electrode non-forming part 7c is further away from the boundary 7d than the internal electrode non-forming part 7c. Have And the 1st site | part 9c is located on the boundary 7d of the opposing part 7a and the non-opposing part 7b. In addition, external electrodes 11 a and 11 b are located on the side surface of the multilayer body 7. The plurality of internal electrodes 5 are connected to one of the anode-side and cathode-side external electrodes 11a and 11b, respectively.

  As described above, in the multilayer piezoelectric element 1 according to the sixth embodiment, since the lattice of the first portion 9c is larger than the lattice of the second portion 9d, a voltage is applied to the first portion 9c. Thus, the driving force applied to the piezoelectric body 3 is smaller than the driving force applied to the piezoelectric body 3 by applying a voltage to the second portion 9d. And since the 1st site | part 9c is located on the boundary 7d of the opposing part 7a and the non-opposing part 7b, the driving force in the vicinity of the boundary 7d with the non-opposing part 7b is relatively made among the opposing parts 7a. Since it becomes small, it can suppress that the stress concerning this boundary 7d vicinity concentrates. As a result, the multilayer piezoelectric element 1 having high durability can be provided.

  As shown in the first to fifth embodiments, even if the second portion 9b does not have the non-forming portions 7c and 7e, on the boundary or the boundary between the facing portion 7a and the non-facing portion 7b By having the first part 9a in which a plurality of internal electrode non-formation parts 7c are arranged along the surface, the stress applied near the boundary 7d between the facing part 7a and the non-facing part 7b can be reduced. . On the other hand, when the first part 9c and the second part 9d have the first part 9c and the second part 9d as in the sixth embodiment, the internal electrode 9 having the first part 9c and the second part 9d The displacement amount of the entire adjacent piezoelectric body 3 can be reduced. As a result, the stress can be relaxed in the entire piezoelectric body 3, so that the stress applied to the end portion on the end face side of the element 1 can be reduced.

<Seventh Embodiment>
Next, a seventh embodiment of the present invention will be described. 11A to 11C are cross-sectional views in the direction orthogonal to the stacking direction in the stacked piezoelectric element according to the seventh embodiment of the present invention, and show cross sections each including the internal electrode 5 adjacent in the stacking direction. Yes. Here, the cross section shown in FIG. 11A is located closer to the end side of the element than the cross section shown in FIG. 11C.

  As shown in FIG. 11, the multilayer piezoelectric element 1 of the seventh embodiment is that the lattice in the second portion 9 d of the internal electrode 9 becomes gradually rough toward the end face side in the sixth embodiment. This is a more preferable form in this respect. That is, the area of the second internal electrode non-forming portion 7e formed on the internal electrode 9 near the end face of the multilayer body 7 is larger. As already shown, since the multilayer piezoelectric element 1 is largely driven and deformed as a unit, a greater stress is applied to the end of the element 1 closer to the end. However, since the non-formation site 7c is gradually roughened toward the end portion, the effect of dispersing the stress generated at the boundary between the facing portion 7a and the non-facing portion 7b increases as the end portion of the element 1 is closer. . Thereby, the bias of the stress distribution in the stacking direction of the element 1 can be further reduced.

  Next, a method for manufacturing the multilayer piezoelectric element 1 according to the present embodiment will be described.

First, a ceramic green sheet to be the piezoelectric body 3 is produced. Specifically, a calcined powder of piezoelectric ceramic, a binder composed of an acrylic or butyral organic polymer, and a plasticizer are mixed to prepare a slurry. And a ceramic green sheet is produced by using this slurry for tape forming methods, such as a known doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of PbZrO ₃ —PbTiO ₃ or the like can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode 5 is produced. Specifically, a conductive paste can be prepared by adding and mixing a binder, a plasticizer, and the like with a metal powder such as silver-palladium. This conductive paste is disposed on the ceramic green sheet using a screen printing method. Further, a plurality of ceramic green sheets on which the conductive paste is screen-printed are stacked. Then, as will be described later, the laminate 7 including the piezoelectric body 3 and the internal electrode 5 can be formed by firing.

  Further, the internal electrode 9 having the lattice-shaped first portion can be formed, for example, by changing the pattern shape of the screen. The lattice roughness can also be changed by changing the pattern shape of the screen.

  The laminated body 7 is not limited to the one produced by the above manufacturing method, and any method can be used as long as a laminated body 7 in which a plurality of piezoelectric bodies 3 and a plurality of internal electrodes 5 are alternately laminated can be produced. It may be formed by any manufacturing method.

  Thereafter, the external electrodes 11 are formed so as to be electrically connected to the internal electrodes 5 and 9 of the piezoelectric body 3 whose ends are exposed on the outer surface of the multilayer piezoelectric element 1. The external electrode 11 can be obtained by adding a binder to glass powder to produce a silver glass conductive paste, printing it, and then drying and bonding or baking.

  Next, the laminate 7 on which the external electrode 11 is formed is immersed in a resin solution containing an exterior resin made of silicone rubber. Then, the silicone resin solution is vacuum degassed to bring the silicone resin into close contact with the concavo-convex portions on the outer peripheral side surface of the laminate 7, and then the laminate 7 is pulled up from the silicone resin solution. Thereby, a silicone resin (not shown) is coated on the side surface of the laminate 7. Then, the lead wire is connected to the external electrode 11 as a current-carrying portion with a conductive adhesive (not shown) or the like.

  The laminated piezoelectric element 1 according to the embodiment is completed by applying a DC electric field of 0.1 to 3 kV / mm to the pair of external electrodes 11 via the lead wires to polarize the laminated body 7. By connecting the lead wire to an external voltage supply unit (not shown) and applying a voltage to the piezoelectric body 3 via the lead wire and the external electrode 11, each piezoelectric body 3 can be largely displaced by the inverse piezoelectric effect. it can. This makes it possible to function as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  Next, a fluid ejecting apparatus according to an embodiment of the present invention will be described. FIG. 12 is a schematic cross-sectional view showing an injection device according to an embodiment of the present invention.

  As shown in FIG. 12, the injection device 21 of the present embodiment has the stacked piezoelectric element 1 typified by the above embodiment stored in a storage container 25 having an injection hole 23 at one end.

  A needle valve 27 capable of opening and closing the injection hole 23 is disposed in the storage container 25. A fluid passage 29 is arranged in the injection hole 23 so as to be able to communicate with the movement of the needle valve 27. The fluid passage 29 is connected to an external fluid supply source, and fluid is constantly supplied to the fluid passage 29 at a high pressure. Therefore, when the needle valve 27 opens the injection hole 23, the fluid supplied to the fluid passage 29 is ejected to the outside or an adjacent container, for example, a fuel chamber (not shown) of the internal combustion engine. .

  The upper end portion of the needle valve 27 has a large inner diameter, and a piston 31 slidable with a cylinder 31 formed in the storage container 25 is disposed. In the storage container 25, the multilayer piezoelectric element 1 described above is stored.

  In such an injection device 21, when a voltage is applied to the piezoelectric actuator to extend, the piston 33 is pressed, the needle valve 27 closes the injection hole 23, and the supply of fluid is stopped. When the application of voltage is stopped, the piezoelectric actuator contracts, the disc spring 35 pushes back the piston 33, and the injection hole 23 communicates with the fluid passage 29 to inject fluid.

  The fluid passage 29 may be opened by applying a voltage to the multilayer piezoelectric element 1 and the fluid passage 29 may be closed by stopping the application of the voltage.

  Further, the ejection device 21 of the present invention includes a container having the ejection holes 23 and the multilayer piezoelectric element 1 described above, and discharges the fluid filled in the container from the ejection holes 23 by driving the multilayer piezoelectric element 1. You may be comprised so that it may make. That is, the multilayer piezoelectric element 1 does not necessarily have to be inside the container, and may be configured so that pressure is applied to the inside of the container by driving the multilayer piezoelectric element 1. In the present invention, the fluid includes various liquid fluids (such as conductive paste) and gas in addition to fuel and ink. By using the ejection device 21, the flow rate of the fluid and the ejection timing can be controlled.

  When the injection device 21 employing the multilayer piezoelectric element 1 of the present invention is used in an internal combustion engine, fuel can be injected into the fuel chamber of the internal combustion engine such as an engine with a longer period of time with higher accuracy than the conventional injection device 21. .

  Next, a fluid ejection system according to an embodiment of the present invention will be described. FIG. 13 is a schematic block diagram showing a fuel injection system according to an embodiment of the present invention.

  As shown in FIG. 13, the fluid ejection system 41 of the present embodiment includes a common rail 43 that stores high-pressure fluid, a plurality of the above-described injection devices 21 that inject the fluid stored in the common rail 43, and a high pressure applied to the common rail 43. A pressure pump 45 that supplies fluid and an injection control unit 47 that supplies a drive signal to the injection device 21 are provided.

  The ejection control unit 47 controls the amount and timing of fluid ejection based on external information or an external signal. For example, when an injection control unit is used for fuel injection of the engine, the amount and timing of fuel injection can be controlled while sensing the condition in the combustion chamber of the engine with a sensor or the like. The pressure pump 45 plays a role of feeding fluid fuel from the fluid tank 49 to the common rail 43 at a high pressure. For example, in the case of an engine fuel injection system, the fluid is fed into the common rail 43 at about 1000 to 2000 atmospheres (about 101 MPa to about 203 MPa), preferably about 1500 to 1700 atmospheres (about 152 MPa to about 172 MPa).

  In the common rail 43, the fuel sent from the pressure pump 45 is stored and sent to the injection device 21 as appropriate. As described above, the injection device 21 injects a certain fluid from the injection hole 23 to the outside or an adjacent container. For example, in the case of an engine, fuel is injected into the combustion chamber in the form of a mist.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. In addition, the present invention relates to a multilayer piezoelectric element, an injection device, and a fuel injection system, but is not limited to the above-described embodiment, and can be implemented as long as the element utilizes piezoelectric characteristics.

  A multilayer piezoelectric element was produced as follows.

  First, a slurry is prepared by mixing a raw material powder mainly composed of lead zirconate titanate (PZT) powder having an average particle diameter of 0.4 μm, a binder and a plasticizer, and a ceramic green sheet having a thickness of 150 μm is formed by a doctor blade method. Produced.

  Next, a conductive paste was prepared by adding a binder to a raw material powder containing a silver-palladium alloy powder having a metal composition of 95% by mass of Ag and 5% by mass of Pd.

  Then, the conductive paste was printed on one surface of the ceramic green sheet so as to have a thickness of 30 μm by screen printing. And each green sheet on which the conductive paste was printed was laminated to produce a laminate. Note that the number of internal electrodes was 300 so that the number of internal electrodes was 300, and only 20 ceramic green sheets on which no conductive paste was printed were stacked at both ends in the stacking direction of the stack.

  In Sample No. 1, each internal electrode was not provided with a lattice-shaped first portion, and the conductive paste was printed so that the cross-sectional areas of the internal electrodes were all the same. In Sample Nos. 2 to 6, the conductive paste was printed so that the internal electrodes located at 1, 2, 299, and 300th in the stacking direction had the first part of the lattice shape as shown in Table 1. .

  In sample number 2, as shown in FIG. 2, the first part of the lattice shape having a square lattice is located on the boundary between the facing part and the non-facing part. In sample number 3, as shown in FIG. 3, the lattice-shaped first portion having a circular lattice is positioned on the boundary between the facing portion and the non-facing portion. In Sample No. 4, as shown in FIG. 5, the first part having a shape in which the lattice is arranged in a plurality of rows parallel to the boundary between the facing part and the non-facing part is the facing part. Located on the boundary with the non-opposing part.

  In Sample No. 5, as shown in FIG. 6, the boundary between the facing portion and the non-facing portion exists at a plurality of locations separated from each other, and the first portion is located on each boundary of the internal electrodes. . In Sample No. 6, as shown in FIG. 10, the internal electrode has a lattice shape and has a first portion and a second portion having a finer lattice than the first portion. And the 1st site | part is located on the boundary of an opposing part and a non-opposing part.

  Next, the raw laminate of each sample number was subjected to binder removal treatment at a predetermined temperature, and then fired at 800 to 1200 ° C. to obtain a laminate.

  And after processing the laminated body of each sample number to a desired dimension, the external electrode was formed, respectively. First, a conductive paste for an external electrode was prepared by adding and mixing a binder, a plasticizer, glass powder and the like to a metal powder containing silver as a main component. This conductive paste was printed by screen printing or the like on the side surface of the laminate on which the external electrodes were to be formed. Furthermore, the external electrode was formed by baking at 600-800 degreeC.

  Driving evaluation was performed using the sample thus prepared. As drive evaluation, high-speed response evaluation and durability evaluation were performed. First, a lead wire is connected to the external electrode 11, a 3 kV / mm DC electric field is applied to the positive electrode and the negative external electrode via the lead wire for 15 minutes to perform polarization treatment, and a piezoelectric actuator using a laminated piezoelectric element Was made. A DC voltage of 170 V was applied to the obtained piezoelectric actuator, and the amount of displacement in the initial state was measured.

As a high-speed response evaluation, an AC voltage of 0 V to +170 V was applied to each piezoelectric actuator at a room temperature with a frequency gradually increased from 150 Hz. For durability evaluation, an AC voltage of 0 V to +170 V was applied to each piezoelectric actuator at a frequency of 150 Hz at room temperature, and a test was continuously performed up to 1 × 10 ⁹ times.

  As shown in Table 1, as a result of the responsiveness evaluation, the piezoelectric actuator of sample number 1 emitted a beat sound when the frequency exceeded 1 kHz. This is because the multilayered piezoelectric element of sample number 1 does not have the first portion of each internal electrode, and the cross-sectional area of each internal electrode is constant, so that the piezoelectric body located near the end of the element This is because the deformation of is large. This is probably because the high-speed response was hindered by the large deformation of the piezoelectric body located near the end of the element, and as a result, the frequency of the applied AC voltage could not be followed.

  In order to confirm the drive frequency, the pulse waveform of sample number 1 was confirmed using an oscilloscope “DL1640L” manufactured by Yokogawa Electric Corporation. As a result, harmonic noise was found at a location corresponding to an integer multiple of the drive frequency. confirmed.

  As shown in Table 1, as a result of the durability evaluation, in Sample No. 1, the displacement after the evaluation test was 5 μm, which was nearly 90% lower than that before the evaluation test. Further, in the piezoelectric actuator of sample number 1, peeling was observed on a part of the element.

  On the other hand, in the piezoelectric actuators of sample numbers 2 to 6, no peeling was confirmed. Moreover, the drop of the displacement amount after the evaluation test was 2 μm or less, and the drop of the displacement amount was suppressed to 5% or less compared to before the evaluation test. In particular, in the piezoelectric actuators of sample numbers 5 and 6, it was found that the displacement amount was not lowered and had very high durability.

  Further, after the durability evaluation, the multilayer piezoelectric element was cut, and the first internal electrode closest to the end in the stacking direction was observed using a microscope. In any of the sample numbers 2 to 6, a part of the portion located between the internal electrode non-formation sites 7c on the cut surface was broken. As described above, it is confirmed that, when a part of the internal electrode breaks, stress is absorbed, cracking of the piezoelectric body is suppressed, and peeling of the internal electrode from the piezoelectric body is suppressed. It was done.

  In Sample Nos. 5 and 6, the amount of displacement in the initial state was relatively small. This is because the internal electrode has many lattice-shaped portions that reduce the amount of displacement and improve the durability.

Claims (15)

A laminated body having a plurality of piezoelectric bodies and a plurality of internal electrodes, wherein the piezoelectric bodies and the internal electrodes are alternately laminated; and a first external electrode formed on a first side surface of the laminated body; And a second external electrode formed on the second side surface of the laminate,
The plurality of internal electrodes on the first and second side surfaces are respectively connected to the first external electrodes such that the plurality of internal electrodes are alternately connected to one of the first and second external electrodes. Alternatively, the internal electrodes connected to the second external electrodes and the internal electrodes that are insulated and separated by being formed away from the first side surface or the second side surface are alternately arranged.
The stacked body includes a facing portion where the adjacent internal electrodes face each other in the stacking direction, and a non-facing portion provided along the first and second side surfaces, facing each other of the internal electrodes. A laminated piezoelectric element divided into
At least one of the plurality of internal electrodes has a plurality of internal electrode non-formation sites provided in the internal electrode along a boundary between the facing portion and the non-facing portion. Type piezoelectric element.   2. The multilayer piezoelectric element according to claim 1, wherein the plurality of internal electrode non-formation sites are aligned in a direction parallel to the boundary between the facing portion and the non-facing portion.   The multilayer piezoelectric element according to claim 1, wherein the internal electrode non-formation site is formed across the facing portion and the non-facing portion.   4. The multilayer piezoelectric element according to claim 2, wherein the plurality of internal electrode non-formation sites are arranged in a plurality of rows parallel to the boundary between the facing portion and the non-facing portion. .   The plurality of internal electrode non-formation sites are aligned on the boundary between the facing portion and the non-facing portion and on one or more lines parallel to the boundary, and the internal electrode non-formation sites arranged on the boundary 2. The multilayer piezoelectric element according to claim 1, wherein an area of the multilayer piezoelectric element is larger than an area of the internal electrode non-formation portion arranged on another line.   The internal electrode having the internal electrode non-forming portion along the boundary between the facing portion and one non-facing portion further includes the plurality of the internal electrodes along the boundary between the facing portion and the other non-facing portion. 6. The multilayer piezoelectric element according to claim 1, further comprising an internal electrode non-formation site.   3. The multilayer piezoelectric element according to claim 1, wherein two or more of the plurality of internal electrodes include a portion where the internal electrode is not formed. 4.   The multilayer piezoelectric element according to claim 7, wherein two or more internal electrodes including the internal electrode non-formation site are periodically arranged in a stacking direction.   The stacked piezoelectric element according to claim 7 or 8, wherein each of the pair of internal electrodes adjacent to each other in the stacking direction has the internal electrode non-forming portion.   Of the pair of internal electrodes each having the internal electrode non-formation site, the ratio of the internal electrode non-formation site of the internal electrode near the end surface of the multilayer body is located far from the end surface of the multilayer body The multilayer piezoelectric element according to claim 9, wherein the ratio is larger than a ratio of the internal electrode to the portion where the internal electrode is not formed.   The internal electrode located in the most end surface side of the laminated body among the plurality of internal electrodes has the internal electrode non-formation site. The laminated piezoelectric element described.   The internal electrode having the internal electrode non-formation site further includes a second internal electrode non-formation site having a smaller area than the internal electrode non-formation site at a position away from the boundary from the internal electrode non-formation site. The multilayer piezoelectric element according to any one of claims 1 to 11.   13. The multilayer piezoelectric element according to claim 12, wherein the area of the second internal electrode non-formation part formed on the internal electrode near the end surface of the multilayer body is larger.   An ejection apparatus comprising: the multilayer piezoelectric element according to any one of claims 1 to 13; and an ejection hole, wherein liquid is ejected from the ejection hole by driving the multilayer piezoelectric element.   15. A fuel injection system comprising: a common rail including high-pressure fuel; an injection device according to claim 14 that injects fuel stored in the common rail; and an injection control system that provides a drive signal to the injection device. .

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