JP2004297043A - Stacked piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked piezoelectric element with side electrodes resistant to rupture, having excellent endurance and constructed by stacking unit elements. <P>SOLUTION: The stacked piezoelectric element comprises a unit stack 100 constructed by stacking a plurality of unit elements 2 each composed of alternately stacked piezoelectric layers 21, 22 and internal electrode layers 23, 24; and a pair of side face electrodes 151 and 152 provided on respective side faces 101, 102 of the unit stack 100 for providing electrical connections to every other internal electrode layers 23 and 24. Between the side face electrodes 151, 152 and stack boundaries 200 between respective unit elements 2, there are provided air gaps 10 that are made of grooves opened to the side face electrodes 151, 152. Further, the maximum width of the opening of the air gap 10 along the stack direction is preferably 8 to 20 % of the thickness of the unit element 2 in the stack direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated piezoelectric element constituted by a unit laminated body in which a plurality of unit elements are stacked.

2. Description of the Related Art A laminated piezoelectric element configured from a unit laminated body in which a plurality of unit elements are stacked to reduce stress and improve reliability by reducing a height in a laminating direction has been conventionally known. Each unit element is formed by alternately laminating a piezoelectric layer and an internal electrode layer, and a side surface electrode is provided on a side surface of the unit laminated body to conduct the internal electrode layers every other layer.
In the laminated piezoelectric element, the piezoelectric layer is extended and driven by applying a current to the side electrode to give a potential difference to each piezoelectric layer.

JP-A-10-229227 JP 05-218519 A

However, when a current is applied to the laminated piezoelectric element, if the recessed portion where the internal electrode layer is not formed is partially formed in a region recessed from the outer periphery of the piezoelectric layer, the central portion of the laminated piezoelectric element is 18, the opening between the lamination boundary 200 of the unit element 2 and the side electrode 91 is opened, infinite stress is generated, and the side electrode 91 may be broken as shown in FIG. 18. was there.
That is, as shown in FIG. 16, the distance Y1 between the unit elements 2 is zero before the voltage is applied. When the multilayer piezoelectric element is energized, as shown in FIG. 17, the lamination boundary 200 of the unit lamination is opened from the position facing the side electrode 91, and an opening 92 having a fan-shaped cross section is formed.

Assuming that the distance between the unit elements 2 in the opening 92 is Y2, the strain ε generated in the side electrode 91 in this state is represented by (Y2−Y1) / Y1, and since Y1 is 0, the strain ε is ∞. It is considered that a very large force is applied to the side electrode 91. Accordingly, as shown in FIG. 18, the side electrode 91 is easily broken by the strain ε.
Of course, a countermeasure method for absorbing and relaxing the strain ε by forming the side electrode 91 with various materials having excellent elasticity has been conventionally known, but it has been quite difficult to prevent breakage.

  The present invention has been made in view of such conventional problems, and has as its object to provide a laminated piezoelectric element in which side electrodes are hard to be broken, have excellent durability, and are configured by stacking unit elements.

According to a first aspect of the invention, a plurality of unit elements in which a piezoelectric layer and an internal electrode layer having a notch portion in which an internal electrode layer is not partially formed in a region recessed from the outer periphery of the piezoelectric layer are alternately stacked are stacked. In a multilayer piezoelectric element having a unit laminate and a pair of side electrodes provided on the side surfaces of the unit laminate and conducting the internal electrode layers every other,
A multi-layer piezoelectric element is characterized in that a gap is formed between the side electrode and a lamination boundary between the unit elements, the gap having a groove opening toward the side electrode. .

The operation and effect of the first invention will be described.
As shown in FIG. 5, before applying the voltage, the maximum opening width of the opening in which the gap 10 faces the side electrode 151 along the stacking direction is Y1.
When the piezoelectric layer is energized through the side electrode 151 of the stacked piezoelectric element, the unit element 2 expands in the stacking direction, so that the maximum opening width is widened as shown in FIG. The maximum opening width of the gap 10 at this time is defined as Y2.
The strain ε generated in the side electrode 151 in this state is represented by (Y2−Y1) / Y1, but since Y1 is not 0, the strain ε also has a finite value, and the stress applied to the side electrode 151 is smaller than that in the related art. Is greatly reduced, and side electrode breakage is less likely to occur.

According to a second aspect of the present invention, there is provided a plurality of unit elements in which a piezoelectric layer and an internal electrode layer having a notch portion in which an internal electrode layer is not partially formed in a region recessed from the outer periphery of the piezoelectric layer are alternately stacked. Stacked unit laminates, dummy unit elements having no piezoelectric characteristics provided at both ends of the unit laminate, and side electrodes provided on the side surfaces of the unit laminate and conducting the internal electrode layers alternately. In the laminated piezoelectric element having
At each of a portion between a first stacked boundary between the unit elements and the side electrode, and a portion between a second stacked boundary between the unit stacked body and the dummy unit element and the side electrode,
A multi-layer piezoelectric element is provided with a void portion formed by a groove opened toward the side electrode.

That is, a first stacking boundary formed between the unit elements, a dummy unit element that does not have piezoelectric characteristics, does not have a potential difference when energized, and does not expand, and a unit stacked body that expands when energizing is interposed. By providing a gap on both the formed second lamination boundary and both sides, the stress generated on the side electrode can be reduced, and the breakage of the side electrode can be further prevented.
The function of preventing the side electrode from breaking at the second lamination boundary is the same as that of the first invention.

  As described above, according to the first and second aspects of the present invention, it is possible to provide a laminated piezoelectric element in which side electrodes are not easily broken, have excellent durability, and are configured by stacking unit elements.

In general, the piezoelectric layer of the unit element according to the first and second inventions is formed of PZT (lead zirconate titanate) or the like, and the internal electrode layer is formed of various noble metal electrodes or the like. It may be formed from other materials.
Each unit element can be joined with an insulating adhesive.However, the unit elements are brought into direct contact with each other and laminated, and the mutual positions of the unit elements are later fixed from the outer periphery of the unit element using a fixture such as an insulating tube. It can be fixed and integrated.

The stacking boundary between the unit elements is a portion formed by the adjacent surfaces of the stacked unit elements. A gap is provided between the lamination boundary and the side electrode, and each lamination boundary and the side electrode do not come into contact with each other owing to the gap.
The same is true for the first stacked boundary and the second stacked boundary according to the second aspect of the present invention. By providing a gap, the first and second stacked boundaries do not come into contact with the side electrodes in principle.
As will be described later, when the unit laminate and the side electrode are joined using a conductive adhesive, the lamination boundary and the side electrode may be indirectly connected via the conductive adhesive.

Next, it is preferable that the maximum opening width of the gap along the stacking direction is 8 to 20% with respect to the thickness of each unit element in the stacking direction.
The maximum opening width of the gap along the stacking direction is a maximum dimension of a portion where the gap and the side electrode face each other, and an example is described in FIG. 2 described later.
By configuring the void portion in the above-described range, the effect according to the first aspect of the present invention can be made more reliable, and breakage of the side electrode can be made more difficult to occur.

  When it is less than 8%, although the breaking rate of the side electrode is reduced, there is a possibility that sufficient durability may not be obtained when used for a long period of time (see Example 2). On the other hand, if it is larger than 20%, the starting point of the chamfered portion reaches the internal electrode layer when, for example, the gap portion is formed of a chamfered portion. To prevent this, the piezoelectric layers at both ends of the unit element in the stacking direction must be thickened.However, however, in order to obtain the same extension characteristics, the size of the stacked piezoelectric element becomes large, and a small element is obtained. There is a problem that it becomes difficult.

Next, it is preferable that the side electrode and the unit laminate are joined by a conductive adhesive (Claim 3) (see FIG. 11).
Thereby, the bonding strength between the side electrode and the unit laminate can be increased.

Next, it is preferable that the conductive adhesive protrudes toward the gap and the portion of the conductive adhesive that protrudes into the gap is discontinuous in the laminating direction. See FIG. 12).
If the conductive adhesive is continuous in the laminating direction, the side electrodes and the unit laminate are connected. In this case, there is a possibility that the effect of reducing the stress obtained by providing the void portion and separating the two may be invalidated, and furthermore, the conductive adhesive may transmit the distortion of the piezoelectric layer to the side electrode and break the side electrode. May occur.

Next, it is preferable that the gap portion is formed of a chamfered portion provided by chamfering one corner of the piezoelectric layer adjacent to each other at the lamination boundary (claim 5).
Since chamfering of the corner can be easily realized, a desired gap can be easily formed.

The maximum width of the chamfer in the stacking direction is preferably 8 to 20% with respect to the average thickness of the unit elements constituting the unit stack in the stacking direction.
By configuring the void portion in the above-described range, the effect according to the first aspect of the present invention can be made more reliable, and breakage of the side electrode can be made more difficult to occur.
When it is less than 8%, although the breaking rate of the side electrode is reduced, there is a possibility that sufficient durability may not be obtained when used for a long period of time (see Example 2).
If it is larger than 20%, for example, when the gap is formed from a chamfered portion, the starting point of the chamfered portion reaches the internal electrode layer. To prevent this, the piezoelectric layers at both ends in the stacking direction of the unit element must be thickened.However, in order to obtain the same extension characteristics, the size of the stacked piezoelectric element becomes large, and a small element is obtained. There is a problem that it becomes difficult.

Next, it is preferable that the gap portion is formed of a chamfered portion provided by chamfering both corners of the piezoelectric layers adjacent to each other at the lamination boundary (claim 7).
Since chamfering of the corner can be easily realized, a desired gap can be easily formed.
Preferably, the maximum width of the chamfered portion in the stacking direction is 4 to 10% with respect to the thickness of each unit element in the stacking direction.
By configuring the void portion in the above-described range, the effect according to the first aspect of the present invention can be further ensured, and breakage of the side electrode can be made more difficult to occur.

When it is less than 4%, although the breaking rate of the side electrode is reduced, sufficient durability may not be obtained when used for a long period of time (see Example 2). If it is larger than 10%, for example, when the gap is formed from a chamfered portion, the starting point of the chamfered portion reaches the internal electrode layer. To prevent this, the piezoelectric layers at both ends in the stacking direction of the unit element must be thickened.However, in order to obtain the same extension characteristics, the size of the stacked piezoelectric element becomes large, and a small element is obtained. There is a problem that it becomes difficult.
The specific shape of the chamfer will be described later in a sixth embodiment, but may be a flat or curved chamfer.

Further, the laminated piezoelectric element can be used as a piezoelectric actuator.
As the piezoelectric actuator, there is, for example, one used for a fuel injection device of an automobile engine. The details of this actuator are described in Example 7 described later.
Since the piezoelectric actuator is used in a severe use environment, the laminated piezoelectric element according to the present invention, in which the gap is less likely to break the side electrode and the durability is improved, can be preferably used.

Further, the maximum opening width of the gap along the laminating direction is preferably 20 μm or more.
As will be described in Example 3 to be described later, the fracture of the side electrode largely depends on the fatigue resistance of the side electrode, and a void having an opening width of 20 μm or more is provided by enhancing the fatigue resistance. Thus, the same effects as those of the first and second inventions can be obtained.
In addition, the maximum opening width is, for example, in order to prevent the base point of chamfering from reaching the inner layer electrode when the gap portion is formed of a chamfered portion, it is necessary to thicken the piezoelectric layers at both ends in the stacking direction of the unit element, However, in order to obtain the same elongation characteristics, the size of the laminated piezoelectric element becomes large, and it is difficult to obtain a small-sized element.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Example 1)
The multilayer piezoelectric element according to the first invention will be described.
As shown in FIGS. 1 to 4, the multilayer piezoelectric element 1 of the present embodiment has a unit multilayer body 100 in which a plurality of unit elements 2 in which piezoelectric layers 21 and 22 and internal electrode layers 23 and 24 are alternately stacked are stacked. And a pair of side electrodes 151, 152 provided on the side surfaces 101, 102 of the unit laminate 100 by making the internal electrode layers 23, 24 alternately conductive.
Between the side electrodes 151 and 152 and the lamination boundary 200 between the unit elements 2, there is provided a gap 10 composed of a groove opened toward the side electrodes 151 and 152.

The details will be described below.
As shown in FIGS. 1 to 4, the multilayer piezoelectric element 1 according to the present embodiment includes a unit multilayer body 100 in which unit elements 2 are stacked. In addition, for the sake of simplicity, the present embodiment has been described in a state in which three unit elements 2 are stacked. For example, a laminated piezoelectric element formed by stacking many unit elements 2 such as 5 to 30 units is known. Thus, the voids described in this example are also effective for such a multilayered device.

  At the lamination boundary 200, the corners of the unit element 2 facing the side electrodes 151 and 152 are chamfered and have a slope shape as shown in FIG. Here, chamfers 251, 252, 261, 262 are formed. Since the chamfers 251, 252, 261, and 262 are located above and below the lamination boundary 200, a groove that opens toward the side electrodes 151 and 152 at the lamination boundary 200 is formed, and the gap 10 is formed.

The cross-sectional shape orthogonal to the laminating direction of the piezoelectric layers 21 and 22 of the unit element 2 according to the present example is substantially square. The chamfered portions 251, 252, 261, 262 forming the void portion 10 of this example are provided along the whole of two opposing sides of a square cross-sectional shape, but at least a surface having the same width as the side surface electrodes 151, 152. The effect of the present example can be obtained by forming the gap 10 from the recess.
In addition, the effects according to the present embodiment can be obtained whether the chamfered portions are opposed to each other as in the present embodiment or not. Further, the effect of the present example can be obtained if the chamfered portion is provided at least on the surface where the side electrodes are joined, but the effect of the present example can be obtained even if it is provided on the entire circumference.

  As shown in FIGS. 1 and 2, the unit element 2 has piezoelectric layers 21 and 22 and internal electrode layers 23 and 24 alternately stacked, and dummy piezoelectric layers 25 and 26 that do not extend when energized are provided at upper and lower ends. is there. Although the dummy piezoelectric layers 25 and 26 are clear from the drawing, since only one of the upper and lower ends is in contact with the internal electrode layers 23 and 24, they are not deformed when energized.

  As shown in FIG. 3, the unit element 2 of the present example has a partial electrode configuration. As shown in FIG. 3, the internal electrode layers 23 and 24 are formed in the remaining regions except for the notches 210 and 220 of the piezoelectric layers 21 and 22. The end surface 230 of the internal electrode layer 23 and the end surface 240 of the internal electrode layer 24 are exposed to the side surfaces 101 and 102 of the unit multilayer body 100, respectively, and are brought into contact with one of the side electrodes 151 and 152 to conduct electricity.

  As shown in FIGS. 2 and 5, the maximum opening width Y1 of the gap 10 in the present example along the laminating direction is 0.3 mm, the thickness of the unit element 2 is 2 mm, which is the maximum with respect to the thickness of the unit element 2. The opening width is 15% and is in the range of 8-20%.

The operation and effect according to this example will be described.
As shown in FIG. 5, the maximum opening width of the gap 10 before applying a voltage is Y1. When the multilayer piezoelectric element 1 is energized through the side electrodes 151 and 152, the opening width is widened as shown in FIG. Assuming that the maximum opening width of the gap 10 at this time is Y2, the strain ε generated in the side electrodes 151 and 152 in this state is represented by (Y2−Y1) / Y1, but since Y1 is not 0, ε is also The value becomes a finite value, and the stress applied to the side electrodes 151 and 152 is greatly reduced as compared with the related art, so that the side electrodes are less likely to break.

  As described above, according to this example, it is possible to provide a laminated piezoelectric element in which side electrodes are hardly broken, have excellent durability, and are configured by stacking unit elements.

  In addition, the voids 10 in this example all have the same shape, but need not have the same shape. In this case, although the maximum opening width differs for each lamination boundary, it is preferable that the condition for the thickness in the lamination direction of each unit element be satisfied for the voids provided at any lamination boundary.

(Example 2)
The determination of the maximum opening width of the void at the lamination boundary will be described.
As to whether or not the side electrode is broken, the amount of distortion of the piezoelectric layer and the fatigue resistance of the side electrode greatly affect.
Incidentally, the maximum amount of strain when a potential difference is applied to the unit laminate is usually about 0.1% of the total thickness of the unit laminate. At this time, the amount of strain on the side surface of the unit laminate where the side electrodes are joined is about 70% of the maximum strain amount of the unit laminate, that is, about 30% of the maximum strain amount of the unit laminate when the unit laminate is elongated. The researchers found that an opening was formed over the unit element stacking boundary on the side of the unit stack connecting the side electrodes.

Further, as shown in FIG. 7, a durability fatigue test was performed on the side surface electrodes used in the multilayer piezoelectric element according to Example 1. That is, the operation of applying a predetermined stress to the side electrode and extending it, stopping the application of the stress, and restoring the original state was repeated, and the number of times until the side electrode was broken was measured. The results are plotted in a diagram according to FIG. 7 in which the vertical axis indicates the strain rate and the horizontal axis indicates the number of repetitions of fracture.
Here, the cross mark with a strain rate of 0.9% and the number of breakage cycles of 1.00E + 05 indicates that the side electrode was stretched 100,000 times by applying a force to the side electrode until the strain rate became 0.9%. It means that it was broken.

  By the way, a laminated piezoelectric element used for a piezoelectric actuator described later is required to be such that a side electrode is not broken after 10 million operations or more. According to FIG. 7, the fracture at the number of operations of 10 million times is when the strain rate exceeds 0.4%.

FIG. 8A shows the maximum opening width Y1 of the gap between the unit elements in the multilayer piezoelectric element shown in the first embodiment. FIG. 8B is a diagram showing the maximum opening width Y1 of the gap shown in FIG. 8A and the approximate distortion rate at the maximum opening width Y1 when the thickness of the unit element is 2 mm. It is.
In the same drawing, the axis at which the opening width is 0 mm is the lamination boundary.

  As is apparent from the figure, in order to reduce the distortion rate to 0.4% or less, both corners of the unit elements adjacent to each other at the lamination boundary are about 0.075 mm, that is, about 0.15 mm at the lamination boundary. This can be achieved by providing a gap. Therefore, the maximum opening width of the gap may be 8% or more with respect to the thickness of each unit element in the stacking direction.

(Example 3)
As described in Example 2, as to whether the side electrode is broken or not, it largely depends on the fatigue resistance of the side electrode. As a matter of course, if the fatigue resistance of the side electrode is improved, the maximum opening width of the void at the lamination boundary can be reduced.
In the second embodiment, the side electrode plate formed in a mesh shape is used, but in the present embodiment, the maximum opening width of the void portion at the lamination boundary when the corrugated side electrode plate having improved fatigue resistance is used. Will be described.
FIG. 9 shows the endurance fatigue test results of the side electrodes used in this example.
It can be seen from FIG. 9 that breaking at the number of operations of 10 million times is a point where the strain rate exceeds 3%.

Here, from the diagram of FIG. 8B, in order to set the distortion rate to 3% or less, a gap of about 0.01 mm is provided in both unit elements adjacent to each other at the stacking boundary, that is, a gap of about 0.02 mm is formed at the stacking boundary. It can be achieved by providing. That is, by providing a gap of 0.02 mm at the lamination boundary, it is possible to provide a laminated piezoelectric element in which side electrode breakage is unlikely to occur and unit elements having excellent durability are stacked.
In this example, the corrugated side electrode was used. However, if the fatigue resistance is improved, the same effect can be obtained regardless of the shape and material.

(Example 4)
As shown in FIG. 10, the laminated piezoelectric element 3 of this example includes a unit laminated body 30 in which a plurality of unit elements 2 in which piezoelectric layers and internal electrode layers are alternately laminated are stacked, and both ends of the unit laminated body 30. Each of the dummy unit elements 33 having no piezoelectric characteristics and the side electrodes 151 and 152 provided on the side surfaces of the unit laminate 30 by conducting every other internal electrode layer.

The unit stacked body 30 according to the present example includes a driving unit 31 at the center in the stacking direction, and buffer units 32 at both ends sandwiching the driving unit 31. Both the drive unit 31 and the buffer unit 32 are composed of unit elements 2 in which piezoelectric layers and internal electrode layers are alternately laminated.
The drive section 31 displaces the piezoelectric layer in the laminating direction by energizing the side electrodes 151 and 152. The piezoelectric layer is also displaced in the laminating direction by energization in the buffer section 32, but the displacement is smaller than in the drive section 31.

  The unit element 2 constituting the drive unit 31 is the same as that of the first embodiment. The basic configuration of the unit elements constituting the buffer section 32 is the same as that of the unit elements 2 for the drive section 31. However, in order to reduce the amount of displacement, the thickness of the piezoelectric layer between the adjacent internal electrode layers is larger than the thickness of the piezoelectric layer of the unit element 2 constituting the drive unit 31.

The dummy unit elements 33 are adjacent to both ends of the buffer section 32.
The dummy unit element 33 does not move even when the side electrodes 151 and 152 are energized. That is, the dummy unit element 31 does not have piezoelectric characteristics.
The buffer section 32 is provided to alleviate the stress on the immovable dummy unit element 33.

In the laminated piezoelectric element 3 according to the present example, the first laminated boundary between the unit elements is defined as a laminated boundary 301 between unit elements formed between the unit elements 2 constituting the driving section 31 and the driving section 31. It is composed of two types of lamination boundaries 302 with the buffer unit 32.
When the buffer section 32 is formed of a plurality of unit elements, the lamination boundary between the unit elements on the buffer section side is also in the category of the first lamination boundary.

  The second stacking boundary indicates a stacking boundary 303 between the unit stack 30 and the dummy unit element 33. Since the buffer section 32 extends between the lamination boundary 303 and the side electrodes 151 and 152 even if the dummy unit element 33 does not move, it is necessary to provide the gap 10 to reduce the stress.

As described above, in the laminated piezoelectric element 3, the voids 10 need to be provided at the lamination boundary formed between the moving parts and the lamination boundary formed between the moving part and the non-moving part. Thereby, the stress generated between each of the lamination boundaries 301 to 303 and the side electrodes 151 and 152 can be reduced, and breakage of the side electrodes 151 and 152 can be prevented.
Other details are the same as those of the first embodiment, and the same operation and effect as those of the first embodiment can be obtained.

(Example 5)
The multilayer piezoelectric element 1 of this embodiment has the same configuration as that of the first embodiment, and the side electrodes are attached to the unit multilayer body with a conductive adhesive.
As shown in FIG. 11, the side electrode 151 and the unit laminate are adhered with conductive adhesives 171 and 172, and the conductive adhesives 171 and 172 do not protrude into the gap 10.

  Alternatively, as shown in FIG. 12, the conductive adhesives 171 and 172 protrude from both sides in the laminating direction into the gap 10, but the protruding state is discontinuous. The protruding portions are denoted by reference numerals 173 and 174.

If the protruding portions of the conductive adhesives 171 and 172 from both sides in the laminating direction are connected, or if the gap 10 is filled with the conductive adhesive 174 as shown in FIG. , 152 are not effective.
For example, as shown in FIG. 13, a crack 175 is generated in the conductive adhesive 174 from the lamination boundary 200 toward the side electrode 152, and the crack 175 causes breakage in the side electrode 151, which is similar to the case where there is no gap. May be subjected to very large stresses.

(Example 6)
In this example, the shape of the chamfer forming the gap will be described.
In FIGS. 14A to 14C, the gap 10 is formed by chamfering the corners of the unit elements 2 located on both sides of the lamination boundary 200 in the same shape and the same size.
In FIG. 14A, a gap is formed by chamfering a corner of the unit element 2 facing the lamination boundary 200 into an arc shape protruding outward.

In FIG. 14B, a gap is formed by chamfering the corner of the unit element 2 facing the lamination boundary 200 in an arc shape so as to go inward.
In FIG. 14C, the corners of the unit element 2 facing the lamination boundary 200 are cut out in a square shape and chamfered to form a gap.
FIG. 14D is a chamfer having the same shape as that of FIG. 14C, but in the unit elements 2 located on both sides of the lamination boundary 200, the chamfer amount with respect to the unit element 2 on the upper side of the drawing is slightly increased. .

14 (e) to 14 (h), the gap 10 is formed by chamfering only the upper corner of the unit element 2 in the drawing.
In FIG. 14 (e), the gap 10 is formed by chamfering the corner of the lower unit element 2 facing the lamination boundary 200 obliquely in a plane.

In FIG. 14F, the gap 10 is formed by chamfering the corner of the lower unit element 2 facing the lamination boundary 200 into an arc shape.
In FIG. 14G, the gap 10 is formed by chamfering the corner of the lower unit element 2 facing the lamination boundary 200 in an arc shape so as to be depressed inward.
In FIG. 14H, the gap 10 is formed by chamfering the corner of the lower unit element 2 facing the lamination boundary 200 into a square shape.
The void 10 having any shape can obtain the same operation and effect as those of the first embodiment.

(Example 7)
This embodiment is an example in which the multilayer piezoelectric element 1 of the first embodiment is used as a piezoelectric actuator of the injector 5.
As shown in FIG. 15, the injector 5 of this example is applied to a common rail injection system of a diesel engine.
As shown in the drawing, the injector 5 includes an upper housing 52 in which the laminated piezoelectric element 1 as a driving unit is housed, and a lower housing 53 fixed to a lower end thereof and having an injection nozzle 54 formed therein. have.

The upper housing 52 has a substantially columnar shape, and the laminated piezoelectric element 1 is inserted and fixed in a vertical hole 521 eccentric to the center axis.
A high-pressure fuel passage 522 is provided in parallel to the side of the vertical hole 521, and an upper end thereof communicates with an external common rail (not shown) through a fuel introduction pipe 523 projecting upward from the upper housing 52. .

A fuel outlet pipe 525 communicating with the drain passage 524 protrudes from an upper portion of the upper housing 52, and fuel flowing out of the fuel outlet pipe 525 is returned to a fuel tank (not shown).
The drain passage 524 passes through a gap 50 between the vertical hole 521 and the drive unit (piezoelectric element) 1, and further extends through the gap 50 downward in the upper and lower housings 52 and 53. It communicates with the valve 551.

  The injection nozzle unit 54 includes a nozzle needle 541 that slides vertically within the piston body 531, and an injection hole 543 that opens and closes the nozzle needle 541 to inject high-pressure fuel supplied from the fuel reservoir 542 into each cylinder of the engine. Have. The fuel reservoir 542 is provided around an intermediate portion of the nozzle needle 541, and a lower end of the high-pressure fuel passage 522 is opened here. The nozzle needle 541 receives fuel pressure in the valve opening direction from the fuel reservoir 542 and receives fuel pressure in the valve closing direction from the back pressure chamber 544 provided on the upper end surface. When descending, the nozzle needle 541 is lifted, the injection hole 543 is opened, and fuel injection is performed.

  The pressure in the back pressure chamber 544 is increased or decreased by a three-way valve 551. The three-way valve 551 is configured to selectively communicate with the back pressure chamber 544 and the high-pressure fuel passage 522 or the drain passage 524. Here, a ball-shaped valve element that opens and closes a port communicating with the high-pressure fuel passage 522 or the drain passage 524 is provided. The valve body is driven by the drive unit 1 via a large-diameter piston 552, a hydraulic chamber 553, and a small-diameter piston 554 disposed below the drive unit 1.

  In this example, the multilayer piezoelectric element 1 is used as a driving source in the injector 5 having the above-described configuration. Since the laminated piezoelectric element 1 has a gap at the lamination boundary as described above, the side electrode is less likely to break, and therefore has excellent long-term durability, and the operation of the nozzle needle 541 can be controlled by the operation of the laminated piezoelectric element 1. Can be controlled accurately.

FIG. 3 is an explanatory diagram of a laminated piezoelectric element according to the first embodiment. FIG. 4 is an explanatory diagram of a maximum opening width along a laminating direction of a unit laminated body and a void portion in the first embodiment. FIG. 3 is an explanatory diagram of a piezoelectric layer forming a unit laminate in the first embodiment. FIG. 4 is a perspective view of a unit laminated body and a chamfer provided in a corner in Example 1. FIG. 3 is an explanatory diagram illustrating a gap portion and a maximum opening width in the first embodiment. FIG. 4 is an explanatory diagram illustrating a maximum opening width when a piezoelectric layer is expanded in the first embodiment. FIG. 9 is a diagram showing a relationship between a strain rate and the number of repeated breaks in Example 2. FIG. 7A is an explanatory diagram illustrating a maximum opening width, and FIG. 7B is a diagram illustrating a relationship between the maximum opening width of a gap and a distortion rate in the second embodiment. FIG. 10 is a diagram showing a relationship between a strain rate and the number of repeated fractures in Example 3. FIG. 13 is an explanatory diagram of a multilayer piezoelectric element having a unit multilayer body and a dummy unit element in a fourth embodiment. FIG. 13 is an explanatory view of a laminated piezoelectric element in which a unit laminated body and a side electrode are joined with a conductive adhesive in Example 5. FIG. 15 is an explanatory view of a laminated piezoelectric element in which a unit laminate and a side electrode are joined with a conductive adhesive in the fifth embodiment, and the conductive adhesive protrudes into voids. FIG. 14 is an explanatory view of a laminated piezoelectric element in which a unit laminate and a side electrode are joined with a conductive adhesive in Example 5, and a gap is filled with the conductive adhesive. FIG. 13 is an explanatory view of a laminated piezoelectric element having voids formed by chamfers of various shapes in Example 6. FIG. 14 is an explanatory diagram of a piezoelectric actuator in a seventh embodiment. FIG. 4 is an explanatory view of a conventional side electrode and the vicinity of a lamination boundary. FIG. 4 is an explanatory diagram showing a state in which the vicinity of a lamination boundary opens as the piezoelectric layer expands. FIG. 4 is an explanatory diagram showing a state in which the vicinity of a lamination boundary is opened with the extension of a piezoelectric layer and a side electrode is broken.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Laminated piezoelectric element 10 Air gap part 100 Unit laminated body 101,102 Side surface 151,152 Side electrode 2 Unit element 200 Stacking boundary 21,22 Piezoelectric layer 23,24 Internal electrode layer

Claims (11)

A unit laminate in which a plurality of unit elements in which piezoelectric layers and internal electrode layers having a notch portion in which an internal electrode layer is not formed partially in a region recessed from the outer periphery of the piezoelectric layer are alternately stacked are stacked; In a laminated piezoelectric element having a pair of side electrodes provided on the side surfaces of the unit laminated body and conducting the internal electrode layers every other,
A multilayer piezoelectric element comprising a gap formed by a groove opened toward the side electrode between the side electrode and a lamination boundary between the unit elements.   2. The multilayer piezoelectric element according to claim 1, wherein the maximum opening width of the gap along the stacking direction is 8% to 20% with respect to the thickness of each unit element in the stacking direction. 3.   3. The multilayer piezoelectric element according to claim 1, wherein the side electrode and the unit multilayer body are joined with a conductive adhesive.   The conductive adhesive according to any one of claims 1 to 3, wherein the conductive adhesive protrudes toward the gap and a portion of the conductive adhesive that protrudes into the gap is discontinuous in a laminating direction. A multilayer piezoelectric element characterized by the above-mentioned.   5. The multilayer piezoelectric body according to claim 1, wherein the gap portion is formed by chamfering one corner of a unit element adjacent to each other at a lamination boundary. element.   The multilayer piezoelectric element according to claim 5, wherein the maximum width of the chamfered portion in the stacking direction is 8 to 20% of the thickness of each unit element in the stacking direction.   The multilayer piezoelectric element according to any one of claims 1 to 4, wherein the gap is formed by chamfering both corners of unit elements adjacent to each other at a lamination boundary. element.   8. The multilayer piezoelectric element according to claim 7, wherein the maximum width of the chamfered portion in the stacking direction is 4 to 10% with respect to the thickness of each unit element in the stacking direction. A unit laminate in which a plurality of unit elements in which piezoelectric layers and internal electrode layers having a notch portion in which an internal electrode layer is not formed partially in a region receded from the outer periphery of the piezoelectric layer are alternately stacked are stacked; A laminated piezoelectric element having a dummy unit element having no piezoelectric characteristics provided at both ends of the unit laminated body and side electrodes provided on the side surfaces of the unit laminated body and conducting the internal electrode layers alternately. At
At each of a portion between a first stacked boundary between the unit elements and the side electrode, and a portion between a second stacked boundary between the unit stacked body and the dummy unit element and the side electrode,
A multi-layer piezoelectric element comprising a void portion formed by a groove opened toward the side electrode.   The multilayer piezoelectric element according to any one of claims 1 to 9, wherein the multilayer piezoelectric element is a piezoelectric actuator.   The multilayer piezoelectric element according to any one of claims 1 to 10, wherein a maximum opening width of the gap along a stacking direction is 20 µm or more.

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