JP2002171003A - Laminated piezoelectric element and injector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a durable laminated piezoelectric element, that prevents external and internal electrodes from being disconnected, even if continuous drive is carried out over a long time, under high electric field and high pressure. SOLUTION: The laminated piezoelectric element has a columnar laminate 1a, formed by alternately laminating a plurality of piezoelectric bodies 1 and the plurality of internal electrodes 2, and the pair of external electrodes 4 where the internal electrodes 2 are connected alternately by every other layer. In this case, the pair of external electrodes 4 is formed by a coil-like elastic member.

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 fuel injection device for an automobile,
The present invention relates to a laminated piezoelectric element used for a precision positioning device such as an optical device and a driving element for preventing vibration, and an ejection device.

[0002]

2. Description of the Related Art Conventionally, as a laminated piezoelectric element, there has been known a laminated piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately laminated. Multi-layer piezoelectric actuators are classified into two types: co-firing type and stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Considering low voltage and lower manufacturing cost, co-firing type Is advantageous in reducing the thickness of the piezoelectric actuator, and is showing its superiority.

FIG. 6 shows a conventional laminated piezoelectric actuator. In this actuator, a piezoelectric body 51 and internal electrodes 52 are alternately laminated to form a columnar laminated body 53, and the outermost layer in the laminating direction is the outermost layer. The inactive layer 55 is provided. The internal electrode 52 has one end covered with an insulator 61 alternately on the left and right sides.
Are formed so as to be electrically connected to the internal electrode 52 at every other left and right layer. A lead wire 76 is further fixed on the band-shaped external electrode 70 by solder 77.

In recent years, in order to secure a large displacement 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]

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, the internal electrodes formed between the piezoelectric bodies and the external electrodes for the positive electrode and the negative electrode are not connected. There is a problem that voltage is not supplied to some of the piezoelectric bodies and the displacement characteristics change during driving.

For example, Japanese Patent Application Laid-Open No. Hei 4-237172 discloses that an end portion of an internal electrode exposed on a side surface of an actuator body is covered with an insulating layer made of glass every other layer, and the internal electrode and piezoelectric members above and below the internal electrode. A laminated piezoelectric actuator has been disclosed in which the insulating layer is firmly joined and the insulating layer is accommodated in a concave portion of the external electrode to ensure insulation between the external electrode and the internal electrode. In the case of continuous driving under a high electric field and high pressure for a long period of time, cracks occur in the insulating layer made of glass, and short-circuits occur between the internal and external electrodes through these cracks. There is a problem that no voltage is supplied to the body and the displacement characteristics change during driving.

That is, since the actuator 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 provided on the end of the internal electrode and the piezoelectric body in the vicinity thereof has a long length. There is a problem that the electrode is destroyed because it cannot withstand the expansion and contraction operation due to the continuous driving for a period, and a short circuit easily occurs between the internal electrode and the external electrode through the broken portion.

[0008] The present invention provides a laminated piezoelectric element and an injection device which 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 a high pressure. The purpose is to do.

[0009]

According to the present invention, there is provided a laminated piezoelectric element comprising: a columnar laminated body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes; and a side wall of the columnar laminated body. A laminated piezoelectric element comprising a pair of external electrodes in which the internal electrodes are alternately connected every other layer, wherein the external electrodes are made of a coiled elastic member.

In the laminated piezoelectric element of the present invention, since the external electrodes are formed by the coil-shaped elastic members, the external electrodes formed by the coil-shaped elastic members can be continuously driven for a long time under a high electric field and a high pressure. Can follow the expansion and contraction of the actuator, thereby preventing the problem of disconnection between the external electrode and the internal electrode, and can greatly improve the durability.

Here, it is desirable that the repetition period of the external electrodes made of the coil-shaped elastic member in the laminating direction is approximately equal to twice the sum of the thickness of the piezoelectric body and the thickness of the internal electrodes. In this case, the contact between the external electrode made of the coil-shaped elastic member and the internal electrode that is the same pole every other layer is reliably formed,
The external electrodes and the internal electrodes can be electrically connected reliably.

Further, in the present invention, it is desirable that the external electrode is composed of a plurality of coil-shaped elastic members. In this case, it is possible to increase the number of contact points between the external electrode and the internal electrode formed of the coil-shaped elastic member, and to apply a large current to the actuator and drive the actuator at a high speed. Can be prevented, and a highly reliable actuator can be provided.

Further, in the present invention, it is preferable that the columnar laminated body has a polygonal columnar shape, and has a flat portion at a portion to which an internal electrode of an external electrode made of a coiled elastic member is connected.
In this case, the connection area between the flat portion of the coiled elastic member and the internal electrode exposed on the side surface of the columnar laminate increases, and even when the actuator is continuously driven at a high speed, the external electrode and the internal electrode are not connected to each other. Can be securely connected.

Further, in the present invention, it is preferable that the external electrode made of a coil-shaped elastic member is provided on the columnar laminated body in a state inclined with respect to the laminating direction. In this case, the cross-sectional area of the external electrodes perpendicular to the laminating direction can be reduced, the volume of the external electrodes can be reduced, and a small laminated piezoelectric element can be obtained.

According to the present invention, there is provided a jetting device comprising: a storage container having an injection hole; the laminated piezoelectric element accommodated in the storage container; and a valve for ejecting a liquid from the injection hole by driving the laminated piezoelectric element. Is provided.

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

[0017]

FIG. 1 shows an embodiment of a laminated piezoelectric element comprising a laminated piezoelectric actuator according to the present invention. FIG. 1 (a) is a perspective view, and FIG. 1 (b) is an AA of FIG. It is a longitudinal cross-sectional view along the line.

As shown in FIG. 1, the laminated piezoelectric actuator has a structure in which a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are alternately laminated on a side surface of a quadrangular columnar laminated body 1a. The ends are covered with an insulator 3 every other layer,
An end of the internal electrode 2 not covered with the insulator 3 is connected to each of the external electrodes 4 made of a coiled elastic member, and a lead wire 6 is connected and fixed to each external electrode 4.

The piezoelectric body 1 is formed of, for example, a lead ceramic zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT), a piezoelectric ceramic material mainly containing barium titanate BaTiO ₃ , or the like. . The piezoelectric ceramics are those piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristic is high is preferable.

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, in order to obtain a larger displacement amount by applying a voltage, a method of increasing the number of layers is adopted for the multilayer piezoelectric actuator. However, when the number of layers is increased, if the thickness of the piezoelectric body 1 is too large, Actuator size and height cannot be reduced,
On the other hand, if the thickness of the piezoelectric body 1 is too small, dielectric breakdown is likely to occur.

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 piezoelectric body 1. It acts to cause the piezoelectric body 1 to be displaced by the inverse piezoelectric effect.

A columnar laminated body 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 includes a calcined powder of a piezoelectric ceramic such as PZT and an organic or acryl-based butyral based powder. A binder made of molecules and a plasticizer such as DBP (dityl phthalate) and DOP (dibutyl phthalate) are mixed to prepare a slurry, and the slurry is formed into a tape by a known doctor blade method or a calender roll method. Thereby, a ceramic green sheet to be the piezoelectric body 1 is produced.

Next, a binder is added to the silver-palladium powder,
A conductive paste is prepared by adding and mixing a plasticizer and the like, 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.

Finally, a green sheet having a conductive paste printed on the upper surface is laminated, and after debinding the laminate at a predetermined temperature, 900 to 120
It is produced by firing at 0 ° C.

Further, after firing, the internal electrodes 2 are exposed on all side surfaces of the columnar laminated body 1a, but at least one side surface of the columnar laminated body 1a is provided on every other end surface of the piezoelectric body 1 including the end of the internal electrode 2. A groove having a depth of 50 to 500 μm and a width of 30 to 200 μm in the lamination direction is formed, and the insulator 3 is formed by filling the groove with glass, epoxy resin, polyimide resin, polyamideimide resin, silicone rubber, or the like. ing.

The insulator 3 alternately insulates the ends of the internal electrodes 2 alternately on the opposing side surfaces of the columnar laminate 1a, and the other uninsulated ends of the internal electrodes 2 are described later. It is connected to a pair of external electrodes 4 made of a coiled elastic member forming a positive electrode and a negative electrode.

The insulator 3 is 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 preferred.

External electrodes 4 each made of a coiled elastic member are fixedly connected to the opposing side surfaces of the columnar laminate 1a. The external electrodes 4 are connected to the laminated internal electrodes 2a and 2b.
Are electrically connected every other layer. The external electrode 4 made of the coiled elastic member has a function of commonly supplying a voltage necessary for displacing the piezoelectric body 1 to the connected internal electrodes 2 by an inverse piezoelectric effect. It is desirable to fill a material having a low elastic modulus, for example, silicone rubber or the like, so as to bury the external electrode in the gap between the external electrodes 4 formed of the coil-shaped elastic member.

As described above, since the external electrode 4 is formed of the coil-shaped elastic member, even when the actuator is continuously driven under a high electric field and high pressure for a long period of time, the external electrode 4 formed of the coil-shaped elastic member can be used. Following the expansion and contraction of the actuator, it is possible to prevent the problem that the external electrode 4 and the internal electrode 2 are disconnected, thereby providing an actuator with excellent durability.

The external electrodes 4 are made of Ag, Ni, Cu, Al,
W, Mo, stainless steel, Fe-Ni-Co alloy and other conductive and elastic metal materials.
Ag, which has good oxidation resistance and good conductivity,
Ni or stainless steel is desirable, and the diameter of the wire forming the external electrode 4 is desirably about 50 to 500 μm from the viewpoint that the wire has low resistance and has high elasticity as a whole.

The external electrode 4 can be connected to the internal electrode 2 while being pressed against the side surface of the columnar laminated body 1a by an external clamping force, or can be connected to the internal electrode 2 by a conductive adhesive, a conductive paste, solder, or the like. The connection with the electrode 2 may be fixed.

Further, a low resistance portion of a thin film may be formed in advance on the exposed side surface of the columnar laminate 1a of the internal electrode 2 connecting the external electrode 4 by vapor deposition, sputtering, plating or the like.

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.

Further, according to the present invention, the repetition period of the external electrode 4 made of a coiled elastic member in the laminating direction is different from that of the piezoelectric body 1.
Is almost equal to twice the sum of the thickness of the internal electrode 2 and the thickness of the internal electrode 2. In other words, the repetition period of the external electrodes 4 is set substantially equal to the distance between the internal electrodes 2 of the same polarity exposed every other layer.

This means that the repetition period of the external electrodes 4 in the laminating direction is about 2 times the sum of the thickness of the piezoelectric body 1 and the thickness of the internal electrodes 2.
By making it equal to twice, it becomes equal to the repetition period of the end of the internal electrode 2 of the same polarity exposed every other side of the columnar laminated body 1a, and the connection between the external electrode 4 and the internal electrode 2 is ensured. can do.

Then, a direct current 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 when 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 a vehicle fuel injection valve that supplies fuel to the engine.

In the multilayer piezoelectric actuator constructed as described above, since the external electrode 4 is formed of a coiled elastic member, the external electrode 4 can sufficiently follow the expansion and contraction of the actuator. And internal electrode 2
And a spark between the external electrode 4 and the internal electrode 2 can be prevented, and a highly reliable actuator can be provided.

Further, in the present invention, as shown in FIG.
The external electrode 4 may be formed of two coiled elastic members for both the positive electrode and the negative electrode. In this case, the number of contacts between the external electrode 4 made of a coiled elastic member and the internal electrode 2 can be increased, and even when the actuator is driven at a high speed, a contact failure or disconnection between the external electrode 4 and the internal electrode 2 is caused. Such a problem can be prevented.

In the present invention, as shown in FIG. 3, it is desirable to have a flat portion 4a at a portion where the internal electrode of the external electrode 4 made of a coiled elastic member is connected. That is,
The external electrode 4 may be formed of a coiled elastic member having a substantially quadrangular or elliptical cross section perpendicular to the laminating direction, and may be connected to the internal electrode 2 exposed at the long side of the columnar laminated body 1a.
In this case, the connection area between the external electrode 4 and the internal electrode 2 can be increased, and the external electrode 4 and the internal electrode 2 can be reliably connected even when the actuator is driven at a high speed.

Further, in the present invention, as shown in FIG.
The external electrode 4 made of a coiled elastic member may be connected to the columnar laminate 1a in a state where the external electrode 4 is inclined with respect to the lamination direction. That is, in the external electrode 4 of FIG. 1B, the winding direction of the coiled elastic member is substantially perpendicular to the laminating direction, but the external electrode of FIG. 4 is different from the external electrode 4 of FIG. Columnar laminate 1a
Side to incline the winding direction. In this case, the cross-sectional area of the external electrodes 4 perpendicular to the laminating direction can be reduced, the volume of the external electrodes 4 can be reduced, and the size of the laminated piezoelectric actuator can be reduced. The external electrode 4 of FIG. 4 may be further pressed toward the columnar laminate 1a to form a coiled elastic member to be wound along the columnar laminate 1a. In this case, the size of the laminated piezoelectric actuator can be further reduced.

The multilayer piezoelectric element of the present invention is not limited to these, and various changes can be made without departing from the scope of the present invention.

FIG. 5 shows the injection device of the present invention.
In FIG. 5, 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 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 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 jetted 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 storage container 31. The above-mentioned piezoelectric actuator 43 is stored in the storage container 31.

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. When the application of the voltage is stopped, the piezoelectric actuator 43 contracts and the disc spring 45
Pushes the piston 41 back, and the injection hole 33
And the fuel is injected.

[0046]

EXAMPLE 1 First, external electrodes were formed using a coil-shaped elastic member made of stainless steel having a wire diameter of 100 μm, a repetition cycle of 300 μm, and a center diameter of 2 mm. A piezoelectric actuator was manufactured.
The cross section of the columnar laminate perpendicular to the lamination direction is a square with a side length of 7 mm.

The piezoelectric body is formed of PZT having a thickness of 147 μm, the internal electrode is formed of a silver-palladium alloy having a thickness of 3 μm, and the number of layers of each of the piezoelectric body and the internal electrode is three.
00. Further, on the external electrode forming surface on the opposite side surface of the columnar laminated body, grooves were alternately formed on the exposed ends of the internal electrodes every other layer, and the grooves were filled with silicone rubber as an insulator.

By inserting the columnar laminated body including the external electrode into the tube made of fluororesin, the external electrode formed of the coiled external electrode is brought into contact with the internal electrode by the holding force of the tube. The columnar laminate was pressed and fixed to opposing side surfaces.

Thereafter, a polarizing treatment was performed by applying a DC electric field of 3 kV / mm to the external electrodes of the positive electrode and the negative electrode via the lead wires for 15 minutes to obtain a laminated piezoelectric actuator.

In the obtained laminated piezoelectric actuator, 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, an AC voltage of 0 to +150 V was applied to this actuator at room temperature at a frequency of 60 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. In Table 1, the sample No. Described in 1.

(Example 2) Next, the structure of the external electrode is shown in Table 1.
A multilayer piezoelectric actuator having the same configuration as that of Example 1 except that the piezoelectric actuator was changed as shown in FIG. Sample N
o. Reference numeral 2 denotes an external electrode formed by using two coiled elastic members similar to those in Example 1 except that the center diameter is 1 mm, as shown in FIG. Sample No. Reference numeral 3 shows an external electrode as shown in FIG. 3 formed by using the same coil-shaped elastic member as in Example 1 except that the cross-sectional shape perpendicular to the laminating direction is substantially square. Further, the sample No. of the comparative example. Reference numeral 4 shows an external electrode formed as shown in FIG. 6 using a paste in which silver powder is dispersed in glass.

An AC voltage of 200 V was applied at room temperature to the obtained piezoelectric actuator at a frequency of 60 Hz.
A driving test was performed. The displacement amount obtained in the initial stage was 50 μm in all the samples (Nos. 1 to 4). Table 1 shows the obtained results.

[0053]

[Table 1]

Sample No. In the case of No. 4, since the external electrode was formed of a silver-dispersed glass paste having a high Young's modulus, the external electrode could not follow the expansion and contraction of the actuator and was pulled between the external electrode and the actuator in 1 × 10 ⁴ cycles. Stress was generated, cracks were generated at the connection between the external electrode and the internal electrode, and sparks were generated.

On the other hand, Sample No. 1 in which an external electrode was formed using the coiled elastic member of the present invention. In the case of 1 to 3, the external electrodes can sufficiently follow the expansion and contraction of the actuator, and 1 × 1
Even in the case of continuous driving for ⁰⁹ cycles, the displacement amount hardly decreased.

Further, using two coil-shaped elastic members,
Sample No. in which the external electrodes were formed 2 and perpendicular to stacking direction
Sample No. having a substantially square cross-sectional shape. At 3
Is high due to the large contact area between the external and internal electrodes.
1 × 10 at high speed with low applied voltage ^TenDrived continuously for cycles
Contact failure between the external and internal electrodes
It can be seen that high reliability is provided without any problem.

[0057]

According to the laminated piezoelectric element of the present invention, since the external electrodes are formed by the coiled elastic members, the external electrodes can sufficiently follow the expansion and contraction of the laminated piezoelectric element.
Problems such as poor contact between the external electrode and the internal electrode and sparking of the external electrode can be prevented, and a highly reliable laminated piezoelectric element can be provided.

[Brief description of the drawings]

FIGS. 1A and 1B show a laminated piezoelectric actuator of the present invention, in which FIG. 1A is a perspective view, and FIG. 1B is a longitudinal sectional view taken along line AA of FIG.

FIG. 2 is a perspective view of another laminated piezoelectric actuator of the present invention formed using external electrodes formed of two coil-shaped elastic members.

FIG. 3 is a cross-sectional view of yet another laminated piezoelectric actuator of the present invention formed using external electrodes having flat portions.

FIG. 4 is a longitudinal sectional view of still another laminated piezoelectric actuator of the present invention in which an external electrode is inclined.

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

FIG. 6 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 4 ... External electrode 4a ... Flat part 31 ... Storage container 33 ... Injection hole 35 ... Valve 43. ..Piezoelectric actuators

Claims (5)

[Claims] 1. A columnar laminated body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and provided on a side surface of the columnar laminated body, wherein the internal electrodes are alternately connected every other layer. And a pair of external electrodes, wherein the external electrodes are made of a coiled elastic member. 2. The multilayer piezoelectric element according to claim 1, wherein the external electrode comprises a plurality of coil-shaped elastic members. 3. The laminated piezoelectric element according to claim 1, wherein the columnar laminate has a polygonal columnar shape, and has a flat portion at a portion where an internal electrode of an external electrode made of a coiled elastic member is connected. element. 4. The lamination according to claim 1, wherein the external electrode made of a coil-shaped elastic member is provided on the columnar laminate in a state inclined with respect to the lamination direction. Type piezoelectric element. 5. A storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 4 stored in the storage container, and the injection hole by driving the multilayer piezoelectric element. And a valve for ejecting a liquid from the device.