JP2003218416A - Laminated piezoelectric device and injection equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric device which hardly suffers from disconnection between an external electrode and an internal electrode and is superior in durability even if it is operated in a high electrical field under a high pressure for a long term and an injection equipment. <P>SOLUTION: Piezoelectric bodies 1 and internal electrodes 2 are alternately laminated into a columnar laminate 1a provided with two external electrode forming surfaces 1b on its side faces, and external electrodes 4 to which the internal electrodes 2 are alternately, electrically connected are formed on the external electrode forming surfaces 1b of the columnar laminate 1a. A laminate piezoelectric device is composed of the columnar laminate 1a and the external electrodes 4, and the waviness of the external electrode forming surfaces 1b of the columnar laminate 1a is 20 μm or below in amplitude. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element and an injection device, for example, a laminated piezoelectric element used for a precision positioning device such as a fuel injection device for an automobile or an optical device, a drive element for preventing vibration, and the like. And an injection device.

[0002]

2. Description of the Related Art Hitherto, as a laminated piezoelectric element, a laminated piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately laminated has been known. Multilayer piezoelectric actuators are classified into two types: simultaneous firing type and stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated.
From the viewpoint of manufacturing cost reduction, the co-firing type laminated piezoelectric actuator is advantageous for thinning, and is therefore showing its superiority.

FIG. 7 shows a conventional laminated piezoelectric actuator. In this actuator, piezoelectric bodies 51 and internal electrodes 52 are alternately laminated to form a columnar laminated body 53, and both end faces in the laminating direction are formed. The inactive body 55 is laminated. The inner electrode 52 is formed such that one end of the inner electrode 52 is alternately covered with the insulator 61, and the strip-shaped outer electrodes 70 are electrically connected to the inner electrode 52 on every other layer. A lead wire 76 is further fixed on the strip-shaped external electrode 70 by solder 77.

By the way, in recent years, in order to secure a large amount of displacement under a large pressure with a small piezoelectric actuator, a higher electric field is applied and continuous driving is performed for a long period of time.

[0005]

However, in the above-described piezoelectric actuator, when continuously driven under a high electric field and a high pressure for a long period of time, the internal electrodes 52 formed between the piezoelectric bodies 51 and the positive and negative electrodes are formed. There is a problem that peeling occurs with the strip-shaped external electrode 70, voltage is not supplied to a part of the piezoelectric body 51, and the displacement characteristic changes during driving.

[0006] For example, in Japanese Patent Laid-Open No. 4-237172, the end portions of the internal electrodes exposed on the side surfaces of the columnar laminated body are covered with an insulating layer made of glass every other layer.
A laminated type in which the internal electrode and the piezoelectric bodies above and below the electrode are firmly bonded, and an insulating layer that insulates the end of the internal electrode is housed in the recess of the external electrode to ensure insulation between the external electrode and the internal electrode. Although a piezoelectric actuator is disclosed, in such a piezoelectric actuator, when the piezoelectric actuator is continuously driven under a high electric field and a high pressure for a long period of time, a crack is generated in an insulating layer made of glass, and the internal electrode and the outside are broken through the crack. There is a problem that a short circuit occurs between the electrodes and a voltage is not supplied to a part of the piezoelectric body, and the displacement characteristic changes during driving.

That is, since the columnar laminated body expands and contracts in the laminating direction of the piezoelectric body and the internal electrode, the insulating layer made of glass having a high Young's modulus is provided on the end portion of the internal electrode and the side surface of the piezoelectric body in the vicinity thereof. However, there is a problem in that it cannot withstand the expansion and contraction operation due to continuous driving for a long period of time and is destroyed, and a short circuit is likely to occur between the internal electrode and the external electrode via this destroyed portion.

Further, in Japanese Patent Laid-Open No. 7-283453, a conductive convex portion is provided at an end portion of every other internal electrode exposed on the side surface of the laminated body, and a side surface of the laminated body on which the conductive convex portion is formed. Is covered with an insulating film, and a mesh made of a conductive metal wire serving as an external electrode is pressed from the upper surface of the insulating film toward the laminate, whereby the metal wire of the mesh breaks through the insulating film and There is disclosed a laminated piezoelectric element that is in contact with the conductive convex portion and is electrically connected to every other internal electrode, but in such a laminated piezoelectric element,
By abutting the mesh that is the external electrode, it is electrically joined to the conductive protrusions that are provided at the ends of the internal electrodes, and it is difficult to press the mesh that becomes the external electrode evenly on all conductive protrusions. Therefore, when continuously driven in a high electric field,
The contact between the conductive protrusion and the external electrode causes a contact failure,
There was a problem of sparking.

Further, the present inventor first provided the protruding conductive terminals projecting from the side surface of the columnar laminate at every other end of the internal electrode, and the protruding conductive terminals and the plate conductive terminals were provided. A multilayer piezoelectric element in which an external electrode made of a member is joined has been proposed (Japanese Patent Application No. 2001-052410). In such a laminated piezoelectric element, the protruding conductive terminals can relieve the stress generated by the expansion and contraction of the columnar laminated body, and thus the durability can be significantly improved. However, there is a possibility that a contact failure may occur due to a spark at the contact between the protruding conductive terminal and the internal electrode or the external electrode made of a plate-shaped conductive member.

The present invention provides a laminated piezoelectric element and an ejection device which are excellent in durability without disconnection between external electrodes and internal electrodes even when continuously driven under a high electric field and a high pressure for a long period of time. The purpose is to do.

[0011]

A laminated piezoelectric element of the present invention comprises a columnar laminated body which is formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and has two external electrode forming surfaces on its side surfaces. A multilayer piezoelectric element provided on each of the external electrode forming surfaces of the columnar laminated body, the external electrodes being electrically connected alternately every other layer,
The waviness of the external electrode forming surface of the columnar laminate is 20 μm or less.

In such a laminated piezoelectric element, since the undulation of the external electrode forming surface of the columnar laminated body is 20 μm or less, for example, all the internal electrodes of every other layer are evenly distributed through the protruding conductive terminals. In addition, it is possible to surely bond to the plate-shaped conductive member, and it is possible to prevent sparks between the protruding conductive terminal and the internal electrode or the plate-shaped conductive member due to defective bonding.

That is, for example, a laminated piezoelectric element in which a protruding conductive terminal protruding from the external electrode forming surface of the columnar laminated body is provided at the end of the internal electrode, and the protruding conductive terminal is connected to a plate-shaped conductive member. Is formed by applying a paste containing metal and glass on the external electrode forming surface of the columnar laminate, arranging a plate-shaped conductive member on this surface, and heating the plate-shaped conductive member while pressing it toward the columnar laminate. However, since the undulation of the external electrode forming surface is a flat surface of 20 μm or less, it is possible to uniformly and surely join the protruding conductive terminal to the internal electrode end portion and the plate conductive member. It is possible to prevent sparks between the protruding conductive terminal, the end of the internal electrode, and the external electrode (plate-shaped conductive member).

Here, the external electrode forming surface is a side surface of the columnar laminated body in which the external electrode is connected to the internal electrode, and a side surface of the columnar laminated body corresponding to a width in which the external electrode is joined to the columnar laminated body. An active part that is a part and contributes to expansion and contraction.

Further, in the present invention, external electrode forming surfaces are formed on the opposite side surfaces of the columnar laminated body, and the parallelism between the opposed external electrode forming surfaces is preferably within 20 μm. As a result, even on the two opposing external electrode forming surfaces, the bonding of all internal electrodes and external electrodes can be made uniform and reliable, so that the protruding conductive terminals are separated from the internal electrodes or external electrodes during driving. It is possible to prevent the occurrence of such a problem as described above, and it is possible to provide a laminated piezoelectric element having excellent durability.

That is, for example, a laminated piezoelectric element in which a protruding conductive terminal protruding from the external electrode forming surface of the columnar laminated body is provided at the end of the internal electrode, and the protruding conductive terminal is connected to a plate-shaped conductive member. Is formed by applying a paste containing metal and glass on the external electrode forming surface of the columnar laminate, arranging a plate-shaped conductive member on this surface, and heating the plate-shaped conductive member while pressing it toward the columnar laminate. However, since the parallelism between the opposing external electrode forming surfaces is within 20 μm, the pressing force applied to the columnar laminated body via the plate-shaped conductive member can be made substantially constant, and the protruding conductive terminals can be formed. The end portions of the internal electrodes and the plate-shaped conductive member can be joined more reliably, and the durability can be improved.

Further, in the present invention, the external electrode is constituted by including a plate-shaped conductive member, and a protruding conductive terminal projecting from the external electrode forming surface of the columnar laminate is provided at the end of the internal electrode. It is desirable that the protruding conductive terminals are connected to the plate conductive member. That is, by connecting the internal electrode and the plate-shaped conductive member through the protruding conductive terminal protruding from the side surface of the columnar laminated body, the protruding conductive terminal is deformed even when the columnar laminated body expands and contracts in the stacking direction. Since it absorbs the stress generated by the expansion and contraction of the columnar laminate, it is possible to suppress the disconnection between the external electrode and the internal electrode even during continuous operation under high electric field and high pressure for a long time. Can be improved.

Further, in the ejection device of the present invention, the container having the ejection hole, the above-mentioned laminated piezoelectric element accommodated in the container, and the liquid being ejected from the ejection hole by driving the laminated piezoelectric element. And a valve that allows it.

In such an injection device, as described above, disconnection between the external electrode and the internal electrode can be suppressed in the laminated piezoelectric element itself, and the durability can be greatly improved, so that the durability of the injection device is also improved. it can.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a laminated piezoelectric element comprising a laminated piezoelectric actuator according to the present invention. (A) is a perspective view, (b) is AA 'in (a). It is a longitudinal cross-sectional view along the line. FIG. 2 is a perspective view for explaining the external electrode forming surface in which the external electrodes 4 made of the plate-shaped conductive member 4a and the lead wires 6 are omitted in FIG. 1 (a).

As shown in FIG. 1, the laminated piezoelectric actuator has a rectangular columnar laminated body 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2, that is, opposite side surfaces, that is, FIG. The external electrode 4 including the plate-shaped conductive member 4a is provided on the external electrode forming surface 1b indicated by. Inactive bodies F are provided on both end surfaces of the columnar laminated body 1a, and the external electrodes 4 are extended and joined to these inactive bodies F as well.

The end portion of the internal electrode 2 is covered with an insulator 3 every other layer, and the end portion of the internal electrode 2 which is not covered with the insulator 3 is a protruding conductive material which is deformable in the expansion / contraction direction of the columnar laminated body 1a. A conductive wire 5 is connected to the external electrode 4 made of a plate-shaped conductive member 4a, and a lead wire 6 is connected to each plate-shaped conductive member 4a.

The insulation by the insulator 3 at the end of the internal electrode 2 is
A depth of 50 to 500 μm and a width in the stacking direction of 30 to 2 every other layer on the side surface of the columnar stack 1a having the external electrode forming surface 1b.
A groove of 00 μm is formed, and glass, epoxy resin, polyimide resin, polyamide-imide resin, silicone rubber or the like is filled in the groove. The groove is a columnar laminate 1a
It may be formed only on the external electrode forming surface 1b. The protruding conductive terminals 5 and the insulator 3 are the internal electrodes 2 exposed on the external electrode forming surface 1b of the columnar laminated body 1a on which the external electrodes 4 are formed.
Are alternately formed at the ends of the.

That is, the end portions of the internal electrodes 2 are alternately insulated by the insulator 3 filled in the groove, and the other non-insulated end portions of the internal electrodes 2 are protruded conductive terminals 5. It will be joined to the external electrode 4 made of the plate-shaped conductive member 4a via.

The piezoelectric body 1 is made of, for example, lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material containing barium titanate BaTiO ₃ as a main component. . It is desirable that this piezoelectric ceramic has a high piezoelectric strain constant d ₃₃ showing its piezoelectric characteristics.

The thickness of the piezoelectric body 1, that is, the internal electrode 2
The distance between them is preferably 50 to 250 μm. This is because the laminated piezoelectric actuator has a method of increasing the number of laminated layers in order to apply a voltage to obtain a larger displacement amount, but when the number of laminated layers is increased, the piezoelectric body 1 is too thick. The actuator cannot be made smaller and the height cannot be reduced,
On the other hand, if the piezoelectric body 1 is too thin, dielectric breakdown is likely to occur.

Internal electrodes 2 are arranged between the piezoelectric bodies 1. The internal electrodes 2 are made of a metal material such as silver-palladium, and a predetermined voltage is applied to each piezoelectric body 1. This serves to cause the piezoelectric body 1 to be displaced by the inverse piezoelectric effect.

In the present invention, the waviness of the external electrode forming surface 1b of the columnar laminated body 1a is 20 μm or less, that is, the unevenness difference between the facing external electrode forming surfaces 1b of the columnar laminated body 1a is 20 μm or less. It is characterized by being a surface. The waviness of the external electrode forming surface 1b is particularly 10 μm
The following is preferable. From the point of view of ease of manufacturing,
It is desirable that the waviness of the entire side surface of the columnar laminated body 1a having the external electrode forming surface is 20 μm or less.

Here, the waviness of the external electrode forming surface 1b is 2
As shown in FIG. 3, when the columnar laminated body 1a of the columnar laminated body 1a is cut in the laminating direction (stretching direction) by a plane perpendicular to the external electrode formed surface 1b, as shown in FIG. When the contour appearing at the cut is the sectional curve X of the external electrode forming surface 1b, the straight line that minimizes the sum of squares of the deviations up to the sectional curve X is the average line Y of the sectional curve X, and the average line Y It means that the distance L between the two straight lines when the sectional curve X is sandwiched by the two parallel lines is 20 μm or less.

That is, the waviness of the external electrode forming surface 1b is 20
The flat surface having a size of μm or less means that all the bonding parts are bonded when the protruding conductive terminals 5 and the external electrodes 4 composed of the plate-shaped conductive members 4a are bonded in the method for manufacturing a laminated piezoelectric element of the present invention described later. Since a uniform load can be applied to all of the internal electrodes 2 of every other layer through the protruding conductive terminals 5, the external electrodes 4 made of the plate-shaped conductive member 4a can be bonded uniformly and reliably, resulting in poor bonding. Protruding conductive terminal 5 by
This is because sparks between the internal electrodes 2 or the external electrodes 4 can be prevented. It is desirable that the external electrode 4 is formed up to the inactive portion F, but since it is not necessary to connect the external electrode 4 and the protruding conductive terminal 5, the inactive body F needs to have a waviness of 20 μm or less. Absent.

Further, in the present invention, it is desirable that the parallelism between the two external electrode forming surfaces 1b on the opposite side surfaces of the columnar laminated body 1a is within 20 μm, and particularly within 10 μm. Here, the parallelism between the two external electrode forming surfaces 1b is 2
The term “within 0 μm” means the distance between the other ends when the cross-section curves X and X ′ of the external electrode forming surface 1b are moved in parallel so that the end portions on the same side of the columnar stacked body 1a overlap each other. Indicates that the distance is 20 μm or less.

As a result, the protruding conductive terminals 5 are connected to the internal electrodes 2 even on the two opposing external electrode forming surfaces 1b.
Since it is possible to more reliably connect to the external electrode 4 composed of the plate-shaped conductive member 4a and to make it uniform and strong, there arises a problem that the protruding conductive terminal 5 is separated from the internal electrode 2 or the external electrode 4 during driving. Therefore, it is possible to provide a laminated piezoelectric actuator having excellent durability.

The thickness t of the plate-shaped conductive member 4a follows the expansion and contraction of the actuator and is between the external electrode 4 and the protruding conductive terminal 5, or between the protruding conductive terminal 5 and the internal electrode 2.
It is desirable that the thickness is 50 μm or less, which has elasticity to some extent, from the viewpoint that no wire breakage occurs between them.

Further, the protruding conductive terminals 5 are preferably made of silver having a low Young's modulus or an alloy containing silver as a main component in order to sufficiently absorb the stress generated by the expansion and contraction of the actuator.

The plate-shaped conductive member 4a is made of silver, nickel, copper,
It is composed of a metal having conductivity such as gold and aluminum and alloys thereof, and has strong joint strength with the protruding conductive terminal 5 made of silver or an alloy containing silver as a main component, and has a low Young's modulus. From the viewpoint, silver or an alloy containing silver as a main component is preferable.

The insulator 3 is made of a material having a low elastic modulus that follows the displacement of the columnar laminated body 1a, specifically, silicone rubber or the like, in order to strengthen the bonding with the columnar laminated body 1a. Is preferred.

External electrodes 4 each made of a plate-shaped conductive member 4a are connected and fixed to two facing external electrode forming surfaces 1b of the columnar laminated body 1a through protruding conductive terminals 5, respectively. The laminated internal electrodes 2 are electrically connected to the alternate layer 4 every other layer. The external electrode 4 composed of the plate-shaped conductive member 4a has a function of commonly supplying a voltage necessary for displacing the piezoelectric body 1 to each connected internal electrode 2 by the inverse piezoelectric effect.

Further, a lead wire 6 is connected and fixed to the external electrode 4 by soldering. The lead wire 6 serves to connect the external electrode 4 to an external voltage supply section. A coating resin (not shown) is provided between the side surface of the columnar laminated body 1a, the upper surface of the plate-shaped conductive member 4a, and the space between the plate-shaped conductive member 4a and the side surface of the columnar laminated body 1a.

A method of manufacturing the laminated piezoelectric element having the above structure will be described. First, the columnar laminated body 1a is manufactured. A columnar laminated body 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 is a calcined powder of piezoelectric ceramics such as PZT and a binder made of an organic polymer such as an acrylic or butyral type. , DBP (diotyl phthalate), DOP (dibutyl phthalate) and other plasticizers are mixed to prepare a slurry, and the slurry is formed into a piezoelectric body 1 by a well-known tape molding method such as a doctor blade method or a calendar roll method. The following ceramic green sheet is prepared.

Next, a binder is added to the silver-palladium powder,
A plasticizer or the like is added and mixed to prepare a conductive paste, which is printed on the upper surface of each green sheet to a thickness of 1 to 40 μm by screen printing or the like.

Then, a plurality of green sheets having a conductive paste printed on the upper surface thereof are laminated, and a plurality of green sheets having no conductive paste printed thereon are laminated on the upper and lower surfaces of the laminated body, which are then heated at a predetermined temperature. After debinding, firing is performed at 900 to 1200 ° C. to produce a fired body having an inactive body formed on the upper and lower surfaces of the columnar laminate.

After that, the fired body is surface-ground to a predetermined size and then subjected to lapping or the like so that the undulations of the external electrode forming surfaces 1b for the positive and negative electrodes are flat surfaces within 20 μm, and are opposed to each other. The parallelism between the external electrode forming surfaces 1b can be processed to 20 μm or less.

Then, a silver glass paste prepared by adding a binder to a mixture consisting of 50 to 80% by volume of silver powder and the balance of glass powder is applied to the opposing external electrode forming surfaces 1b of the columnar laminate 1a, and 700 By baking at ˜940 ° C., the silver in the silver glass paste gathers at the ends of the internal electrodes 2, and the protruding conductive terminals 5 in the shape of a brush or mushroom can be formed.

Thereafter, a groove is formed every other layer on the external electrode forming surface 1b of the columnar laminated body 1a on which the protruding conductive terminals 5 are formed by a dicing device or the like.

Then, as shown in FIG. 4, the plate-shaped conductive member 4a is placed on the protruding conductive terminal 5, and the plate-shaped conductive member 4a is pressed toward the columnar laminated body 1a side to remove silver from the silver. The plate-shaped conductive member 4a is heat-treated at 700 to 950 ° C. while being pressed against the protruding conductive terminal 5, so that the main component, silver, is present between the protruding conductive terminal 5 and the plate conductive member 4a. The protrusion-shaped conductive terminals 5 and the plate-shaped conductive member 4a are bonded by diffusing and so-called silver diffusion bonding.

After that, the insulator 3 is filled in the groove and the lead wire 6 is connected to complete the laminated piezoelectric element of the present invention.

After the grooves are formed on the side surface of the columnar laminated body 1a every other layer, the columnar laminated body 1a in which no groove is formed is formed.
Alternatively, the protruding conductive terminals 5 may be formed by applying a silver glass paste on the external electrode forming surface 1b and baking it.

Next, another method for manufacturing the laminated piezoelectric element of the present invention will be described. After forming the columnar laminated body 1a in the same manner as described above, grooves are formed on the side surface of the columnar laminated body 1a in every other layer.

After that, the same silver glass paste as that described above is applied to the external electrode forming surface 1b of the columnar laminated body 1a in which the groove is not formed, and the plate-shaped conductive member 4a is placed on the paste and externally formed. With the silver glass paste interposed between the electrode forming surface 1b and the plate-shaped conductive member 4a, the plate-shaped conductive member 4
a is pressed against the side of the columnar laminated body 1a, and the plate-shaped conductive member 4a, the silver glass paste, and the columnar laminated body 1a are brought into pressure contact with each other.
By heat treatment at 00 to 950 ° C., the silver component in the silver glass paste gathers at the end of the internal electrode 2 to form the protruding conductive terminal 5 protruding from the external electrode forming surface 1b of the columnar stack 1a. And the protruding conductive terminal 5
Can be connected to the plate-shaped conductive member 4a.

Thereafter, the groove 3 is filled with the insulator 3 and the lead wire 6 is connected to complete the laminated piezoelectric element of the present invention.

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 laminated body 1a, whereby a laminated piezoelectric actuator as a product is obtained. When completed, 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 largely displaced by the inverse piezoelectric effect, With this, for example, it functions as a fuel injection valve for an automobile that injects fuel to the engine.

In the laminated piezoelectric element having the above-described structure, the two external electrode forming surfaces 1b on the opposite side surfaces of the columnar laminated body 1a have flat undulations of 20 μm or less, and the two external electrodes are formed. The parallelism between the forming surfaces 1b is 20
Since it is within μm, the inner electrode 2 and the protruding conductive terminal 5, and the protruding conductive terminal 5 and the outer electrode 4 can be bonded uniformly and firmly over all layers, and the plate-shaped conductive Since the external electrode 4 composed of the member 4a is connected to the internal electrode 2 via the protruding conductive terminal 5, the protruding conductive terminal 5 absorbs the stress generated by the expansion and contraction of the actuator, and the external electrode 4 and the inside The breakage of the electrode 2 can be suppressed, and the durability can be improved even when the actuator is continuously driven for a long period under a high electric field and a high pressure.

The laminated piezoelectric element of the present invention is not limited to these, and various modifications can be made without departing from the scope of the present invention. For example, the plate-shaped conductive member 4
The external electrode 4 may be formed by providing a conductive auxiliary member outside a. In this case, by providing a conductive auxiliary member on the outer surface of the plate-shaped conductive member 4a, a large current can be supplied to the actuator, and even when the actuator is driven at a high speed, a large current can be passed through the conductive auxiliary member. Since the current flowing through the external electrode 4 can be reduced, it is possible to prevent the external electrode 4 from causing local heat generation and disconnection, and the durability can be significantly improved.

Since the conductive auxiliary member follows the expansion and contraction of the actuator and prevents the conductive auxiliary member from breaking during driving, a flexible conductive adhesive or conductive coil,
Alternatively, it is made of a conductive corrugated sheet or a conductive fiber aggregate (wool-like). In particular, the resistance and Young's modulus are low,
A conductive corrugated plate made of silver is preferable because it is highly stretchable and the cross-sectional area of the actuator can be reduced.

FIG. 5 shows the injection device of the present invention.
In the figure, reference numeral 31 indicates 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.

A fuel passage 37 is provided so as to be able to communicate with the injection hole 33. The fuel passage 37 is connected to an external fuel supply source so that fuel is always 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.

The upper end of the needle valve 35 has a large diameter and serves as a piston 41 slidable with a cylinder 39 formed in the container 31. The piezoelectric actuator 43 described above is stored in the storage container 31.

In such an injection device, when the piezoelectric actuator 43 is expanded by being applied with a voltage, the piston 41 is expanded.
Is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. Further, when the voltage application is stopped, the piezoelectric actuator 43 contracts, and the disc spring 45
Pushes back the piston 41, and the injection hole 33 moves into the fuel passage 37.
Fuel injection is performed in communication with the.

[0059]

Example 1 First, an element body having an inactive body on the upper and lower surfaces of a columnar laminate was prepared. The piezoelectric body is made of PZT having a thickness of 150 μm, the internal electrodes are made of silver-palladium alloy having a thickness of 3 μm, and the number of laminated layers of the piezoelectric body and the internal electrodes is 300.
Layered. In such an element main body, a conductive paste containing a silver-palladium alloy is applied on a green sheet containing PZT, a plurality of layers are laminated, and the conductive paste is applied to the upper and lower surfaces of this laminated body. It was produced by stacking a plurality of green sheets that were not stacked and firing them.

To shape the element body having the columnar laminated body, after grinding the entire side surface of the element body with a surface grinder, the two side surfaces facing each other of the element body having the external electrode forming surface are ground. Lapping was performed to finish each external electrode forming surface into a flat surface with a waviness of 5 μm and the parallelism between the opposing external electrode forming surfaces to 5 μm.

Next, a silver glass paste was prepared by adding a binder to a mixture of 60% by volume of silver powder having an average particle diameter of 5 μm and the balance of 40% by volume of glass powder having an average particle diameter of 5 μm and a softening point of 750 ° C. Then, the silver glass paste is applied to the external electrode forming surface of the element body and baked at 800 ° C.,
A protruding conductive terminal was formed on the end of the internal electrode exposed on the side surface of the columnar laminate.

Thereafter, grooves are formed every other end layer of the internal electrode including the protruding conductive terminals, and then a thickness of silver 25 is formed.
Place a plate-shaped conductive member of μm on the protruding conductive terminal, and
The columnar laminate was pressed at 0 kPa and joined at 900 ° C.

Then, the groove was filled with silicone rubber as an insulator, and the lead wire was connected to the external electrode.

After that, a direct current electric field of 3 kV / mm was applied to the external electrodes of the positive electrode and the negative electrode through the lead wires for 15 minutes to perform polarization treatment, and a laminated piezoelectric actuator as shown in FIG. 1 was produced.

The laminated piezoelectric actuator thus obtained has 15
As a result of applying a DC voltage of 0 V, a displacement amount of 40 μm was obtained in the stacking direction. Furthermore, as a result of conducting a drive test by applying an AC voltage of 0 to +150 V to the actuator at a frequency of 60 Hz at room temperature, a displacement amount of 40 μm was obtained when the actuator was driven up to 5 × 10 ⁸ cycles. I couldn't see it. Example 2 Next, control of grinding and lapping by a surface grinder,
A multilayer piezoelectric actuator similar to that of Example 1 was manufactured except that the size of the waviness of each external electrode formation surface was changed.

A driving test was conducted on the obtained laminated piezoelectric actuator at the initial stage after manufacturing the defective rate due to the defective contact between the external electrode and the internal electrode and by applying an AC voltage of 0 to +150 V at a frequency of 60 Hz. Those driven at up to 5 × 10 ⁸ cycles were examined. Regarding the defect due to the contact failure, cross-section observation was performed, and the case where the connection between the external electrode and the internal electrode was broken even at one place was determined as the bonding failure.

The obtained results are shown in FIG. From FIG. 6, in the sample subjected to the drive test, the defect rate increased when the undulation of the external electrode formation surface was larger than 20 μm, whereas the defect rate was extremely small when the undulation was 20 μm or less. In the case of 10 μm or less, the defective rate due to the defective contact between the external electrode and the internal electrode was 0.

Further, the waviness of the external electrode forming surface is 50 μm.
When it was larger, the defect rate in the initial stage was also larger.

Therefore, by setting the waviness of the external electrode forming surface to 20 μm or less as specified in the present invention, the external electrode and the internal electrode can be bonded uniformly and surely, and the contact between the external electrode and the internal electrode can be achieved. It can be seen that defects can be significantly reduced.

[0070]

According to the laminated piezoelectric element of the present invention, since the undulation of the external electrode formation surface of the columnar laminated body is 20 μm or less, for example, every other internal electrode is provided through the protruding conductive terminals. Can be uniformly and surely bonded to the plate-shaped conductive member, sparks between the protruding conductive terminal and the internal electrode or the external electrode (plate-shaped conductive member) can be prevented, and defective bonding can be prevented.

[Brief description of drawings]

FIG. 1 is a view showing a laminated piezoelectric element of the present invention, (a)
Is a perspective view and (b) is a vertical cross-sectional view taken along the line AA ′ of (a).

FIG. 2 is a perspective view illustrating an external electrode formation surface.

FIG. 3 is an explanatory diagram for explaining undulations on a surface on which external electrodes are formed.

FIG. 4 is a process drawing showing a state in which a plate-shaped conductive member is joined to the tip of a protruding conductive terminal.

FIG. 5 is an explanatory view showing an injection device of the present invention.

FIG. 6 is a graph showing the relationship between the amount of waviness and the percent defective.

FIG. 7 is a vertical sectional view showing a conventional laminated piezoelectric actuator.

[Explanation of symbols]

1 ... Piezoelectric body 1a: Columnar laminated body 1b ... External electrode forming surface 2 ... internal electrodes 4 ... External electrode 4a: plate-shaped conductive member 5: protruding conductive terminal 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator

Claims (4)

[Claims] 1. A columnar laminate having a plurality of piezoelectric bodies and a plurality of internal electrodes alternately laminated and having two external electrode forming surfaces on its side surfaces, and a columnar laminate provided on the external electrode forming surface of the columnar laminated body, respectively. A multilayer piezoelectric element in which the internal electrodes are provided with external electrodes electrically connected alternately to every other layer, wherein waviness of an external electrode forming surface of the columnar laminate is 20.
A laminated piezoelectric element having a thickness of not more than μm. 2. The laminate according to claim 1, wherein external electrode forming surfaces are formed on opposite side surfaces of the columnar laminate, and the parallelism between the opposing external electrode forming surfaces is within 20 μm. Type piezoelectric element. 3. The external electrode comprises a plate-shaped conductive member, and a protruding conductive terminal protruding from the external electrode forming surface of the columnar laminated body is provided at an end of the internal electrode. 3. A laminated piezoelectric element according to claim 1, wherein a conductive terminal is connected to the plate-shaped conductive member. 4. An accommodating container having an ejection hole, the laminated piezoelectric element according to claim 1 housed in the accommodating container, and the ejection hole driven by driving the laminated piezoelectric element. An injection device comprising a valve for ejecting liquid from the injection device.