JP2004087731A - Laminated piezoelectric element and jet device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element that is equipped with external electrodes and internal electrodes, which are hardly disconnected from each other, and superior in durability even when it is made to operate continuously in a high electric field under a high pressure for a long time, and to provide a spray device. <P>SOLUTION: The laminated piezoelectric element is equipped with a columnar laminate 1a composed of a piezoelectric materials 1 and the internal electrodes 2 which are alternately laminated and the external electrodes 4 which are provided on the sides of the columnar laminate 1a. A projecting conductive terminals 5 projecting from the side of the columnar laminate 1a is provided to every other end of the internal electrodes 2, the external electrode 4 formed of a plate-like conductive member is joined to the tips of the projecting conductive terminals 5, the external electrode 4 is divided into a plurality of parts in the lamination direction of the columnar laminate 1a, and the divided external electrodes 4a are connected together with a conductive auxiliary member 7. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laminated piezoelectric element and an injection device, for example, a laminated piezoelectric element and an injection device used for a precision positioning device such as a fuel injection device for an automobile, an optical device, and a driving element for preventing vibration. .
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a laminated piezoelectric element, a laminated piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately laminated is known. Multi-layer piezoelectric actuators are classified into two types: a co-firing type and a stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Considering lower voltage and lower manufacturing cost, co-firing The advantage of the multilayer piezoelectric actuator of the type is that it is advantageous for thinning, and is showing its superiority.
[0003]
FIG. 5 shows a conventional laminated piezoelectric actuator. In this actuator, a piezoelectric body 51 and an internal electrode 52 are alternately laminated to form a columnar laminated body 53, and both ends in the laminating direction are inactive. The layer 55 is laminated. One end of the internal electrode 52 is alternately covered with an insulator 61 on the left and right sides, and the band-shaped external electrode 70 is formed so as to be electrically connected to the internal electrode 52 from every other layer on the left and right sides. A lead wire 76 is further fixed on the belt-shaped external electrode 70 by solder 77.
[0004]
By the way, in recent years, in order to secure a large displacement amount under a large pressure with a small piezoelectric actuator, a higher electric field is applied, and the piezoelectric actuator is driven continuously for a long period of time.
[0005]
[Problems to be solved by the invention]
However, in the above-described piezoelectric actuator, when the piezoelectric actuator is continuously driven under a high electric field and a high pressure for a long period of time, peeling occurs between the internal electrode 52 formed between the piezoelectric bodies 51 and the external electrodes 70 for the positive electrode and the negative electrode. As a result, there is a problem that the voltage is not supplied to some of the piezoelectric bodies 51 and the displacement characteristics change during driving.
[0006]
Also, Japanese Patent Application Laid-Open Nos. Hei 7-283451 and Hei 8-51240 disclose that a conductive convex portion is formed by plating at the end of every other internal electrode. Since the bonding strength between the protrusion and the laminate is weak, the conductive protrusion and the end of the internal electrode are peeled off during driving, and a voltage is not supplied to a part of the piezoelectric body, resulting in a problem that the displacement characteristics are reduced. was there.
[0007]
In order to solve such a problem, the present applicant first provides a protruding conductive terminal projecting from the side surface of the columnar laminate at every other end of the internal electrode, and (Japanese Patent Application No. 2002-50252) filed a multilayer piezoelectric element in which an external electrode made of a plate-shaped conductive member is bonded.
[0008]
In such a multi-layer piezoelectric element, when the multi-layer piezoelectric element is driven, the protruding conductive terminals are deformed to absorb the stress generated by the expansion and contraction of the actuator, so that the multi-layer piezoelectric element is operated continuously for a long time under a high electric field and high pressure Even in such a case, the disconnection between the external electrode and the internal electrode can be suppressed, and the durability can be greatly improved. However, if the external electrode is formed of a single plate-shaped conductive member, an excessive amount of the external electrode due to expansion and contraction of the actuator occurs. Because of the occurrence of stress, there is a demand for further improvement of the durability of the external electrode in continuous operation under a high electric field and high pressure for a long period of time.
[0009]
The present invention provides a laminated piezoelectric element and an ejection device that are excellent in durability without disconnection between an external electrode and an internal electrode even when driven continuously for a long time under a high electric field and high pressure. Aim.
[0010]
[Means for Solving the Problems]
A laminated piezoelectric element according to the present invention includes a columnar laminated body in which a piezoelectric body and an internal electrode are alternately laminated, and a pair in which the internal electrodes are alternately connected every other layer provided on a side surface of the columnar laminated body. And a protruding conductive terminal protruding from a side surface of the columnar laminate at every other end of the internal electrode, wherein the protruding conductive terminal is provided. An external electrode made of a plate-shaped conductive member is joined to the tip of the column, and the external electrode is divided into a plurality in the stacking direction of the columnar laminate, and the divided external electrodes are connected by a conductive auxiliary member. It is characterized by having been done.
[0011]
In the laminated piezoelectric element of the present invention, a protruding conductive terminal protruding from the side surface of the columnar laminate is provided at every other end of the internal electrode, and the protruding conductive terminal and an external electrode comprising a plate-shaped conductive member are provided. When the laminated piezoelectric element is driven in the laminating direction, the protruding conductive terminals are deformed to absorb the stress generated by the expansion and contraction of the actuator. However, disconnection between the external electrode and the internal electrode can be suppressed, and the durability can be greatly improved.
[0012]
Further, in the present invention, since the external electrode is divided into a plurality in the stacking direction of the columnar laminate, the stress acting on the external electrode can be dispersed, and even when driven under a high electric field, the external electrode is There is no problem of cracking or disconnection.
[0013]
Further, a conductive auxiliary member is provided outside the external electrode, and each external electrode is connected by the conductive auxiliary member. Therefore, even when a large current is applied to the actuator and the actuator is driven at a high speed, a large current is applied. Can flow through the conductive auxiliary member, so that the external electrode can be prevented from being locally heated and disconnected, and the durability can be greatly improved.
[0014]
Further, the laminated piezoelectric element of the present invention is characterized in that a concave groove for exposing an internal electrode end is formed between the protruding conductive terminals on the side surfaces of the columnar laminated body. In such a multilayer piezoelectric element, the generated stress can be reduced as compared with a multilayer piezoelectric element having a so-called partial electrode structure, and the thickness of the end of the internal electrode connected to the external electrode via the protruding conductive terminal is reduced to a columnar shape. Since the thickness can be effectively made larger than the thickness of the internal electrode at the center of the laminate, it is possible to prevent the problem of poor contact between the internal electrode and the external electrode.
[0015]
Further, the multilayer piezoelectric element of the present invention is characterized in that a plurality of divided external electrodes are joined to some of the protruding conductive terminals. According to such a configuration, the divided external electrodes are connected in parallel to some of the internal electrodes, and the connection between the divided external electrodes and the protruding conductive terminals is made near the end of the divided external electrodes in the stacking direction. This can be performed reliably, and even when driven under a high electric field, a contact failure between the internal electrode and the external electrode can be prevented.
[0016]
Further, in the laminated piezoelectric element of the present invention, the length of the divided external electrode provided at the end of the columnar laminated body in the laminating direction is the same as that of the divided external electrode provided at the central part of the columnar laminated body in the laminating direction. The length is shorter than the length in the stacking direction. According to such a configuration, the stress generated in the external electrode due to expansion and contraction of the columnar laminate increases as the columnar laminate approaches both ends in the stacking direction. By reducing the length, the stress acting on the divided external electrodes can be dispersed.
[0017]
Further, in the present invention, a plurality of divided external electrodes are linearly arranged on the side surface of the columnar laminate, and a concavo-convex portion is formed at a portion facing the plurality of divided external electrodes, and these concavo-convex portions are meshed with each other. It is characterized by having. According to such a configuration, in the concavo-convex portion of the divided external electrode, the two divided external electrodes are connected in parallel to the internal electrode, and the sum of the widths of the two divided external electrodes in this portion and the single internal The widths of the divided external electrodes connected to the electrodes can be made substantially the same, whereby a reliable external electrode can be formed without increasing the overall width of the external electrodes.
[0018]
In the present invention, the conductive auxiliary member is made of a conductive adhesive in which a conductive mesh member is embedded. According to such a configuration, by using a flexible conductive adhesive as the conductive auxiliary member, it is possible to absorb the stress generated by the expansion and contraction of the actuator, and the conductive auxiliary member is peeled or disconnected. Such a problem can be prevented. Further, since the conductive adhesive is embedded with the conductive mesh member, it is possible to prevent a problem that cracks are generated in the conductive adhesive due to expansion and contraction of the actuator.
[0019]
Further, the injection device of the present invention includes a storage container having an injection hole, the stacked piezoelectric element housed in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. Is provided.
[0020]
In such an injection device, as described above, disconnection between the external electrode and the internal electrode in the multilayer piezoelectric element itself can be suppressed, and the durability can be greatly improved. Therefore, the durability of the injection device can also be improved.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
1A and 1B show an embodiment of a laminated piezoelectric element comprising a laminated piezoelectric actuator according to the present invention, wherein FIG. 1A is a perspective view, and FIG. 1B is a longitudinal section taken along line AA ′ of FIG. FIG. 1C is an enlarged perspective view showing a part of FIG. 1A, and FIG. 2D is an enlarged view near a joint between an internal electrode and an external electrode.
[0022]
As shown in FIG. 1, the laminated piezoelectric actuator is configured such that an end of the internal electrode 2 is formed on a side surface of a square columnar laminated body 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2. At every other end of the internal electrode 2 covered with the insulator 3 and not covered with the insulator 3, a protruding conductive terminal 5 which is deformable in the direction of expansion and contraction of the laminated piezoelectric element is provided. An external electrode 4 made of a plate-shaped conductive member is joined to the tip of the conductive terminal 5.
[0023]
As shown in FIG. 2, the plate-shaped conductive member is divided into a plurality in the stacking direction of the columnar laminated body 1a, that is, the external electrode 4 includes a plurality of divided external electrodes 4a. As shown in FIG. 1D, the plurality of divided external electrodes 4a are connected by a conductive auxiliary member 7 provided outside thereof, and the conductive auxiliary member 7 is formed of a conductive adhesive 7a. The conductive mesh member 7b is embedded therein. A lead wire 6 is connected and fixed to each conductive auxiliary member 7.
[0024]
The piezoelectric body 1 is formed of, for example, a piezoelectric ceramic material mainly containing lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or barium titanate BaTiO ₃ . The piezoelectric ceramics are those piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristic is high is preferable.
[0025]
The thickness of the piezoelectric body 1, that is, the distance between the internal electrodes 2 is desirably 50 to 250 μm. This is because, in order to obtain a larger displacement amount by applying a voltage, a method of increasing the number of stacked layers is adopted in the stacked piezoelectric actuator. However, when the number of stacked layers is increased, if the thickness of the piezoelectric body 1 is too large, This is because it is impossible to reduce the size and height of the actuator. On the other hand, if the thickness of the piezoelectric body 1 is too thin, dielectric breakdown easily occurs.
[0026]
An internal electrode 2 is disposed between the piezoelectric bodies 1. The internal electrode 2 is formed of a metal material such as silver-palladium, and applies a predetermined voltage to each of the piezoelectric bodies 1. The effect of causing a displacement due to the inverse piezoelectric effect is produced.
[0027]
Further, a concave groove 11 having a depth of 50 to 500 μm and a width of 30 to 200 μm in the laminating direction is formed between the protruding conductive terminals 5 on the side surface of the columnar laminate 1 a. The insulator 3 is formed by filling a resin, a polyimide resin, a polyamideimide resin, a silicone rubber, and the like. The insulator 3 is preferably made of a material having a low elastic modulus that follows the displacement of the columnar laminate 1a, specifically, silicone rubber or the like, in order to strengthen the bonding with the columnar laminate 1a. is there.
[0028]
The protruding conductive terminals 5 and the insulators 3 are alternately formed on the internal electrodes 2 exposed on the side surfaces of the columnar laminate 1a on which the external electrodes 4 are formed.
[0029]
That is, the ends of the internal electrodes 2 are alternately insulated by the insulator 3 filled in the concave grooves 11, and the other ends of the internal electrodes 2 which are not insulated are connected to the protruding conductive terminals 5. It is joined to the external electrode 4 made of a plate-like conductive member through the intermediary.
[0030]
External electrodes 4 each made of a plate-like conductive member are connected and fixed to the internal electrode 2 via a protruding conductive terminal 5 on opposite side surfaces of the columnar laminate 1a. The internal electrodes 2 are electrically connected every other layer. The external electrode 4 functions to commonly supply a voltage necessary for displacing the piezoelectric body 1 to the connected internal electrodes 2 by the inverse piezoelectric effect.
[0031]
As shown in FIG. 1C, the thickness B of the protruding conductive terminals 5 in the same direction as the lamination direction reduces the resistance of the connection between the external electrode 4 and the internal electrode 2 and is generated when the actuator is driven. From the viewpoint of sufficiently absorbing the stress, it is desirable that the thickness be 1 μm or more and 以下 or less of the thickness of the piezoelectric body 1. In particular, the thickness B is desirably 5 to 25 μm.
[0032]
Further, the protrusion height h of the protruding conductive terminal 5 is desirably 1/20 or more of the thickness of the piezoelectric body 1 from the viewpoint that the stress generated by expansion and contraction of the actuator is sufficiently absorbed. In particular, the protrusion height h is desirably 15 to 50 μm.
[0033]
Further, the thickness t of the divided external electrode 4a follows the expansion and contraction of the actuator and does not cause disconnection between the divided external electrode 4a and the protruding conductive terminal 5, or between the protruding conductive terminal 5 and the internal electrode 2. From this point, it is desirable that the thickness be 50 μm or less.
[0034]
In the present invention, since the external electrode 4 is connected to the internal electrode 2 via the protruding conductive terminal 5, even when the actuator is continuously driven for a long time under a high electric field and high pressure, the protruding conductive terminal is used. 5 absorbs the stress generated by expansion and contraction of the actuator, can suppress disconnection between the external electrode 4 and the internal electrode 2, and can provide an actuator with excellent durability.
[0035]
Further, as shown in FIG. 2, the external electrode 4 is divided into a plurality in the laminating direction of the columnar laminate 1a, and each is connected by a conductive auxiliary member 7 provided outside thereof. In FIG. 2, the conductive auxiliary member 7 is omitted.
[0036]
In the present invention, since the external electrodes 4 are divided in the stacking direction, the stress generated by the expansion and contraction of the actuator can be dispersed, and the reliability of the external electrodes 4 can be improved. That is, if the external electrode 4 is formed of a single plate-shaped conductive member, there is a danger that the external electrode 4 may generate excessive stress due to expansion and contraction of the actuator and break. Is composed of a plurality of divided external electrodes 4a arranged in the stacking direction of the columnar laminate 1a, so that stress generated in the external electrodes 4 due to expansion and contraction can be dispersed, and the reliability of the external electrodes 4 can be improved.
[0037]
Further, as shown in FIG. 1, the lead wire 6 is connected and fixed to the conductive auxiliary member 7 by soldering. The lead wire 6 serves to connect the conductive auxiliary member 7 and the external electrode 4 to an external voltage supply unit.
[0038]
Outside the divided external electrodes 4a, each divided external electrode 4a is electrically connected, and a conductive auxiliary member capable of preferentially flowing a large current to be supplied when driving the actuator at high speed. 7, even when a large current is applied to the actuator and the actuator is driven at a high speed, a large current can flow to the conductive auxiliary member 7, so that the divided external electrodes 4 a generate local heat and are disconnected. Can be prevented, and the durability can be greatly improved.
[0039]
The internal electrode 2 is made of a metal and an alloy mainly composed of silver, such as silver, a silver-palladium alloy, and a silver-platinum alloy. It is also desirable that the main component of the protruding conductive terminal 5 and the divided external electrode 4a be silver. This is because the main components of the internal electrode 2, the protruding conductive terminal 5 and the divided external electrode 4 a are made of the same silver, so that the space between the protruding conductive terminal 5 and the internal electrode 2 and the protruding conductive terminal 5 This is because silver is mutually diffused between the and the divided external electrodes 4a, and thereby, the bonding strength between them can be strengthened. In addition, silver having a low Young's modulus or an alloy containing silver as a main component is preferable for the protruding conductive terminal 5 and the split external electrode 4a from the viewpoint of sufficiently absorbing the stress generated by expansion and contraction of the actuator.
[0040]
As shown in FIGS. 2 (b-1), (b-2), (c-1) and (c-2), the divided external electrodes 4a divided in the laminating direction of the columnar laminate 1a are partially parallel to the internal electrodes. 2 is desirably connected. That is, the joint portions of the divided external electrodes 4a overlap when viewed from the side of the columnar laminate 1a, and a plurality of the divided external electrodes 4a are joined to some of the protruding conductive terminals 5. It is desirable.
[0041]
As a result, the divided external electrode 4a is reliably connected to the protruding conductive terminal 5 near the end of the divided external electrode 4a in the stacking direction, and the internal electrode 2 and the external electrode are electrically connected even when driven under a high electric field. Contact failure of the electrode 4 can be prevented. The number of the internal electrodes 2 connected to the plurality of divided external electrodes 4a may be any number as long as it is at least one layer.
[0042]
2 (a-1) shows a state in which the divided external electrodes 4a are linearly arranged with one insulator 3 interposed therebetween, FIG. 2 (a-2) shows a state in which the divided external electrodes 4a are separated on the side of the piezoelectric body 1, (B-1) shows a state in which two divided external electrodes 4a are connected in parallel to one layer of internal electrodes 2 and (b-2) shows a state in which two divided external electrodes 4a are connected in parallel to two layers of internal electrodes 2. In the connected state, (c-1) shows that the two divided external electrodes 4a have L-shaped tips, which are engaged with each other, and the two divided external electrodes 4a are connected in parallel to the single-layered internal electrode 2. In the state (c-2), the leading ends of the two divided external electrodes 4a are L-shaped, they are engaged with each other, and the two divided external electrodes 4a are connected in parallel to the two layers of the internal electrodes 2. It shows the state where it is.
[0043]
In the divided external electrodes 4a shown in FIGS. 2 (c-1) and 2 (c-2), the tip portions are L-shaped uneven portions 4a1 and 4a2, but the uneven portions may be saw-toothed, and at least one projecting portion may be provided. What is necessary is just to have.
[0044]
Further, the closer the split external electrode 4a is to both ends in the stacking direction of the columnar laminate 1a, the shorter the length of the split external electrode 4a is, that is, the length of the split external electrode 4a provided at the end of the columnar laminate 1a in the stacking direction is increased. Is preferably shorter than the length in the stacking direction of the divided external electrodes 4a provided at the center of the columnar stacked body 1a in the stacking direction.
[0045]
This is because the stress generated by expansion and contraction of the columnar laminate 1a is greater at the divided external electrodes 4a closer to both ends in the stacking direction. Can be dispersed.
[0046]
Further, as shown in FIGS. 2 (c-1) and 2 (c-2), a plurality of divided external electrodes 4a are linearly arranged on the side surface of the columnar laminated body 1a, and the opposing divided external electrodes 4a are opposed to each other. It is desirable that uneven portions 4a1 and 4a2 are formed at the portions where the irregularities are formed, and these uneven portions 4a1 and 4a2 are meshed with each other. Thereby, the sum of the width (length in the direction orthogonal to the laminating direction) of the portion where the two divided external electrodes 4a are connected to the internal electrode 2 in parallel and the portion where the single divided external electrode 4a is connected to the internal electrode 2 Can be made substantially the same, and a reliable external electrode 4 can be formed without increasing the width occupied by the external electrode 4 at the connection portion of the two divided external electrodes 4a. Further, since the divided external electrodes 4a are linearly arranged, the formation of the conductive auxiliary member 7 is also easy.
[0047]
Further, as shown in FIG. 1D, the conductive auxiliary member 7 provided outside the plurality of divided external electrodes 4a and connecting each divided external electrode 4a has a conductive mesh member 7b embedded therein. Desirably, the conductive adhesive 7a is used. This is because, when the conductive auxiliary member 7 is made of a flexible conductive adhesive 7a, the stress generated by the expansion and contraction of the actuator can be absorbed, and the conductive auxiliary member 7 is separated or disconnected. Can be prevented from occurring. In addition, since the conductive mesh member 7b is embedded in the conductive adhesive 7a, it is possible to prevent a problem that a crack occurs in the conductive adhesive 7a due to expansion and contraction of the actuator.
[0048]
In this case, the conductive adhesive 7a is desirably one in which silver powder is dispersed in polyimide in consideration of heat resistance and resistance value. The conductive mesh member 7b is a mesh or mesh plate made of a conductive metal such as silver, nickel, copper, gold, or aluminum, or an alloy thereof, and the conductive adhesive 7a has cracks. It has the role of preventing it from occurring.
[0049]
Next, a method for manufacturing the multilayer piezoelectric element of the present invention will be described. First, the columnar laminate 1a is manufactured. The columnar laminated body 1a formed by alternately laminating the plurality of piezoelectric bodies 1 and the plurality of internal electrodes 2 includes a calcined powder of a piezoelectric ceramic such as PZT and a binder formed of an organic polymer such as an acrylic or butyral system. And a plasticizer such as DBP (dityl phthalate) and DOP (dibutyl phthalate) to form a slurry, and the slurry is mixed with the piezoelectric body 1 by a tape forming method such as a well-known doctor blade method or calender roll method. To produce a ceramic green sheet.
[0050]
Next, a conductive paste is prepared by adding and mixing a binder, a plasticizer, and the like to the silver-palladium powder, and this is printed on the upper surface of each green sheet to a thickness of 1 to 40 μm by screen printing or the like.
[0051]
Then, a green sheet on which a conductive paste is printed is laminated on the upper surface, a binder is removed from the laminated body at a predetermined temperature, and the laminate is fired at 900 to 1200 ° C.
[0052]
Thereafter, as shown in FIG. 3A, the concave grooves 11 are formed on the side surfaces of the columnar laminated body 1a by using a dicing apparatus or the like.
[0053]
Next, as shown in FIG. 3B, 50 to 80% by volume of silver powder having a particle size of 0.1 to 10 μm is provided on the side surface of the columnar laminate 1a between the concave grooves 11, and the balance is 0.1%. A silver glass conductive paste 21 prepared by adding a binder to a mixture of 20 to 50% by volume of glass powder having a softening point of 600 to 950 ° C. and containing silicon as a main component and coated with silicon is applied and dried.
[0054]
Further, as shown in FIG. 3C, the silver glass conductive paste 21 is heat-treated at 700 to 950 ° C. while applying a load so as to press the divided external electrodes 4 a made of a plate-shaped conductive member. As a result, the glass in the silver glass conductive paste 21 is melted, and the silver component present in the melted glass is collected at the end of the internal electrode 2, and as shown in FIG. The protruding conductive terminal 5 protruding from the side surface is formed, and the divided external electrode 4 a can be joined to the tip of the protruding conductive terminal 5.
[0055]
Further, at the time of heat treatment, the silver component in the silver glass conductive paste 21 diffuses to the end 2a of the internal electrode 2, and the thickness of the end 2a of the internal electrode 2 becomes smaller than the internal electrode 2 () at the center of the columnar laminate 1a. It is thicker than the thickness of the central portion 2b) of the internal electrode 2. Thereby, the bonding strength of the protruding conductive terminal 5 at the end 2a of the internal electrode 2 can be improved.
[0056]
That is, by dispersing the glass component in the paste, the glass softens during the above-described heat treatment, and in this state, silver which is difficult to diffuse into the piezoelectric body 1 diffuses and gathers at the end 2 a of the internal electrode 2. Therefore, the protruding conductive terminal 5 as shown in FIG. 3D can be formed. Then, the silver component in the internal electrode 2, the silver glass conductive paste 21 and the divided external electrode 4 a are diffused with each other, and between the internal electrode 2 and the protruded conductive terminal 5 and between the protruded conductive terminal 5 and the divided external electrode 5. Strong bonding is made between the electrodes 4a. In the vicinity of the base of the protruding conductive terminal 5, the glass in the silver glass conductive paste 21 gathers to form a raised portion 5 a, which holds the protruding conductive terminal 5.
[0057]
The protruding conductive terminal 5 is formed on a part of the side surface of the columnar laminate 1a, is formed in a rail shape, and has a length substantially equal to the width of the divided external electrode 4a. Note that the length of the protruding conductive terminal 5 may be shorter than the width of the divided external electrode 4a.
[0058]
The reason why the silver powder in the silver glass conductive paste 21 is 50 to 80% by volume and the remaining glass powder is 20 to 50% by volume is that the silver component constituting the protruding conductive terminal 5 is within this range. And the protruding height h of the formed protruding conductive terminal 5 can be increased, and the glass component that is the remaining solid content in the silver glass conductive paste 21 becomes an appropriate amount. The glass component that melts at the time of baking 21 is also an appropriate amount, the silver component easily gathers at the end of the internal electrode 2, and the protrusion height h of the protruding conductive terminal 5 can be increased.
[0059]
The load applied during the formation of the protruding conductive terminals 5 and the heat treatment for bonding the protruding conductive terminals 5 and the divided external electrodes 4a is preferably 2 to 500 kPa in pressure. By setting the thickness within this range, diffusion bonding can be sufficiently performed between the protruding conductive terminal 5 and the plate-shaped conductive member 4a, and the strength of the bonding portion can be increased, and the pressure becomes appropriate. The deformation of the conductive terminal 5 can be prevented.
[0060]
In addition, a silver glass conductive paste 21 is applied to portions of the divided external electrodes 4a corresponding to the spaces between the concave grooves 11 of the columnar laminate 1a, and dried, and a load is applied so as to press the divided external electrodes 4a against the columnar laminate 1a. The heat treatment may be performed in a state in which is added. Further, a silver glass conductive paste 21 is applied to the entire surface of the divided external electrode 4a and dried, and the divided external electrode 4a is pressed against the surface on which the internal electrode 2 of the columnar laminate 1a is exposed, with the conductive paste applied surface side, Even when the heat treatment is performed, the protruding conductive terminals 5 are formed, and the divided external electrodes 4a can be connected to the tips. In this case, the steps can be further reduced.
[0061]
Thereafter, as shown in FIG. 3 (e), a non-spherical silver powder such as a needle or flake is used as a conductive material outside the divided external electrode 4a in an amount of 15 to 80% by volume, and the remainder has a matrix as an elastic modulus. After applying a conductive adhesive paste obtained by mixing a solvent having a resin of 20 GPa or less and an elongation of 10% or more with a volume of 20 to 85% by volume and embedding a conductive mesh member 7b in the conductive adhesive 7a, The conductive adhesive 7 a is cured by heating at 150 to 300 ° C. to form the conductive auxiliary member 7.
[0062]
Thereafter, as shown in FIG. 3F, the insulator 3 is filled in the concave groove 11 and the lead wire 6 is connected thereto, thereby completing the multilayer piezoelectric element of the present invention.
[0063]
Then, a DC voltage of 0.1 to 3 kV / mm is applied to the pair of external electrodes 4 via the lead wires 6 to polarize the columnar laminate 1a, thereby completing a laminated piezoelectric actuator as a product. If the lead wire 6 is connected to an external voltage supply unit and a voltage is applied to the internal electrode 2 via the lead wire 6 and the external electrode 4, each piezoelectric body 1 is greatly displaced by the inverse piezoelectric effect, thereby, for example, It functions as an automotive fuel injection valve that injects fuel into the engine.
[0064]
In the above example, the example in which the external electrodes 4 are formed on the opposing side surfaces of the columnar laminate 1a has been described. However, in the present invention, for example, a pair of external electrodes 4 may be formed on the adjacent side surface.
[0065]
FIG. 4 shows an injection device of the present invention. In the drawing, reference numeral 31 denotes a storage container. An injection hole 33 is provided at one end of the storage container 31, and a needle valve 35 that can open and close the injection hole 33 is stored in the storage container 31.
[0066]
A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate therewith. The fuel passage 37 is connected to an external fuel supply source, and the fuel is constantly supplied to the fuel passage 37 at a constant high pressure. Therefore, when the needle valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is ejected at a constant high pressure into a fuel chamber (not shown) of the internal combustion engine.
[0067]
The upper end of the needle valve 35 has a large diameter, and serves as a piston 41 that can slide with a cylinder 39 formed in the storage container 31. The above-mentioned piezoelectric actuator 43 is stored in the storage container 31.
[0068]
In such an injection device, when the piezoelectric actuator 43 expands by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. Further, when the application of the voltage is stopped, the piezoelectric actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 to perform the fuel injection.
[0069]
【Example】
First, a columnar laminate was prepared. The piezoelectric body was formed of PZT having a thickness of 150 μm, the internal electrode was formed of a silver-palladium alloy having a thickness of 3 μm, and the number of layers of the piezoelectric body and the internal electrode was 300. The total length of the columnar laminate was set to 50 mm including the inactive portion.
[0070]
Next, a concave groove having a depth of 150 μm and a width of 75 μm was formed on the side surface of the columnar laminate including the ends of the internal electrodes that were exposed on the external electrode formation surface of the columnar laminate. Then, on the side surfaces of the columnar laminate between the concave grooves, 60 volume% of silver powder having an average particle size of 5 μm, and 40 volume% of glass powder having an average particle size of 5 μm and a softening point mainly composed of silicon of 750 ° C. A silver glass conductive paste prepared by adding a binder to the resulting mixture was applied and dried.
[0071]
Further, a heat treatment is performed on the silver glass conductive paste at 900 ° C. while a plurality of 25 μm-thick plate-shaped conductive members made of silver are pressed at 30 kPa to form protruding conductive terminals protruding from the columnar laminate. At the same time, a plate-shaped conductive member (divided external electrode) was joined to the tip of the protruding conductive terminal. The plate-shaped conductive member has a wedge shape as shown in FIG. 2 (c-2), and its length is 5 mm, 10 mm, 18 mm, 10 mm, and 5 mm from the end of the columnar laminate. The portion connected in parallel was for two internal electrodes as shown in FIG. 2 (c-2).
[0072]
Thereafter, 50 vol% of flake-shaped silver powder having an average particle size of 5 μm as a conductive material and 50 vol% of a polyimide resin having an elastic modulus of 10 GPa and an elongation of 30% as a matrix are provided outside the plate-shaped conductive member. % And a solvent are mixed, a 50 μm-thick mesh member made of nickel is embedded in the conductive adhesive paste, and the conductive adhesive is cured by heating at 220 ° C. An auxiliary member was formed.
[0073]
After that, the concave groove is filled with silicone rubber as an insulator, a lead wire is connected to the conductive auxiliary member, and a 3 kV / mm DC electric field is applied to the external electrodes of the positive electrode and the negative electrode via the lead wires for 15 minutes to be polarized. The processing was performed to produce a laminated piezoelectric actuator as shown in FIG.
[0074]
Note that silver and palladium were dispersed in the protruding conductive terminals. At this time, the height of the protruding conductive terminal was 20 μm on average, and the void ratio of the conductive adhesive was 10%. The base of the protruding conductive terminal was covered with glass to form a raised portion.
[0075]
As a result of applying a DC voltage of 150 V to the obtained laminated piezoelectric actuator, a displacement of 40 μm was obtained in the laminating direction. Furthermore, an AC voltage of 0 to +150 V was applied to this actuator at room temperature at a frequency of 120 Hz, and a drive test was performed. As a result, when the actuator was driven up to 1 × 10 ⁹ cycles, a displacement of 40 μm was obtained. I couldn't see it.
[0076]
On the other hand, as a comparative example, one end of the internal electrode is alternately covered with an insulator made of glass on the left and right, the above-mentioned silver glass conductive paste is applied thereon, and heat treatment is performed at 700 ° C. to produce actuator shown in FIG. 5 which is electrically connected to the internal electrode right respectively every other layer, was subjected to the same test as above, the spark occurs in the external electrode at 1 × 10 ⁵ cycles driving test.
[0077]
【The invention's effect】
According to the multilayer piezoelectric element of the present invention, the protruding conductive terminals protruding from the side surfaces of the columnar laminate are provided at every other end of the internal electrode, and the columnar lamination is provided at the tip of the protruding conductive terminals. Split external electrodes made of a plate-like conductive member divided into a plurality in the stacking direction of the body are joined, and the split external electrodes are connected by a conductive auxiliary member. Oscillates and can sufficiently absorb the stress generated in the external electrodes. Further, since the external electrodes are divided in the laminating direction, the stress generated by expansion and contraction of the multilayer piezoelectric element can be dispersed, whereby the external electrodes can be dispersed. It is possible to prevent a problem such as a contact failure between the internal electrode and the internal electrode or a disconnection of the external electrode, and to provide a laminated piezoelectric element having high reliability.
[Brief description of the drawings]
1A and 1B show a laminated piezoelectric element of the present invention, wherein FIG. 1A is a perspective view, FIG. 1B is a longitudinal sectional view taken along line AA ′ of FIG. 1A, and FIG. FIG. 3D is a perspective view showing an enlarged part of FIG. 4D, and FIG. 4D is a sectional view showing an enlarged part of FIG.
FIG. 2 is a side view showing an arrangement of divided external electrodes on a side surface of a columnar laminate.
FIG. 3 is a process diagram for explaining a method of manufacturing a multilayer piezoelectric element of the present invention.
FIG. 4 is an explanatory view showing an injection device of the present invention.
FIG. 5 is a longitudinal sectional view of a conventional laminated piezoelectric actuator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 1a ... Columnar laminated body 2 ... Internal electrode 2a ... End part 2b of an internal electrode ... Central part of an internal electrode 4 ... External electrode 4a ... Divided external electrode 4a1, 4a2... Uneven portion 5... Protruding conductive terminal 7... Conductive auxiliary member 7a... Conductive adhesive 7b... Conductive mesh member 11... ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator

Claims (7)

A columnar laminate formed by alternately laminating piezoelectric bodies and internal electrodes; and a pair of external electrodes provided on side surfaces of the columnar laminate, wherein the internal electrodes are alternately connected every other layer. A laminated piezoelectric element, wherein a protruding conductive terminal protruding from the side surface of the columnar laminate is provided at every other end of the internal electrode, and a tip end of the protruding conductive terminal is provided from a plate-shaped conductive member. Wherein the external electrodes are divided into a plurality of parts in the laminating direction of the columnar laminate, and the divided external electrodes are connected by a conductive auxiliary member. Type piezoelectric element. 2. The multilayer piezoelectric element according to claim 1, wherein a concave groove exposing an end of the internal electrode is formed between the protruding conductive terminals on the side surfaces of the columnar laminate. The multilayer piezoelectric element according to claim 1, wherein a plurality of divided external electrodes are joined to some of the protruding conductive terminals. The length in the stacking direction of the divided external electrodes provided at the end in the stacking direction of the columnar stacked body is shorter than the length in the stacking direction of the divided external electrodes provided at the center in the stacking direction of the columnar stacked body. The multilayer piezoelectric element according to any one of claims 1 to 3, wherein A plurality of divided external electrodes are arranged in a straight line on the side surface of the columnar laminate, and a concavo-convex portion is formed at a portion facing the plurality of divided external electrodes, and these concavo-convex portions are engaged. The multilayer piezoelectric element according to claim 1. The multilayer piezoelectric element according to any one of claims 1 to 5, wherein the conductive auxiliary member is made of a conductive adhesive in which a conductive mesh member is embedded. A storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 6, which is stored in the storage container, and ejecting liquid from the injection hole by driving the multilayer piezoelectric element. An injection device comprising a valve.

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