JP2002289934A - Laminated piezoelectric element and jetting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a durable laminated piezoelectric element, together with a jetting device where no disconnection occurs between an external electrode and an internal electrode, even at extended continuous driving in a high electric field and under high pressure. SOLUTION: The laminated piezoelectric element comprises a columnar laminate 1a in which a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are laminated alternately, and a pair of external electrodes 4, in which are provided on the side surface of the columnar laminate 1a, the internal electrodes 2 are connected alternately at every other layer. The external electrode 4 comprises a corrugated conductive member 4a, while a protruding part 13 which protrudes on the columnar laminated body 1a side of the corrugated conductive member 4a is connected to the end part of the internal electrode 2.

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, an optical device, and a driving element for preventing vibration. 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. 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. 3 shows a cross section of 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.
Is formed, and an inactive layer 55 is formed as the outermost layer in the laminating direction. One end of the internal electrode 52 is alternately covered with an insulator 54 on the left and right sides, and a band-shaped external electrode 56 is formed so as to be electrically connected to the internal electrode 52 from every other layer on the left and right sides. On the belt-like external electrode 56,
Further, a lead wire 57 is fixed by solder 58.

[0004] 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 to drive the piezoelectric actuator 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. However, there is a problem in that a contact failure occurs between the electrodes, voltage is not supplied to some piezoelectric bodies, and displacement characteristics change during driving.

For example, Japanese Patent Application Laid-Open No. 4-237172 discloses that an end portion of an internal electrode exposed on a side surface of a columnar laminated 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. Are laminated, and the insulating layer is accommodated in a concave portion of the external electrode, and a laminated piezoelectric actuator in which insulation between the external electrode and the internal electrode is ensured has been disclosed. In the actuator,
When continuously driven for a long period of time under a high electric field and high pressure, cracks occur in the insulating layer made of glass, and short-circuits occur between the internal electrode and the external electrode through these cracks. However, there is a problem that the voltage is no longer supplied to the device and the displacement characteristic changes during driving.

That is, since the columnar laminate 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 is formed by: There has been a problem that the device is destroyed because it cannot withstand the expansion and contraction operation due to continuous driving for a long period of time, and a short circuit easily occurs between the internal electrode and the external electrode via the broken portion.

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 provided with a columnar laminated body in which a plurality of piezoelectric bodies and a plurality of internal electrodes are alternately laminated, and provided on a side surface of the columnar laminated body. A laminated piezoelectric element comprising a pair of external electrodes in which the internal electrodes are alternately connected to every other layer, wherein the external electrodes are formed of a corrugated conductive member, and the corrugated conductive member is provided on the columnar laminate side. A protruding protruding portion is connected to an end of the internal electrode.

In the multilayer piezoelectric element of the present invention, the external electrode is formed of a corrugated conductive member, and the protruding portion of the corrugated conductive member protruding toward the columnar laminate is connected to the end of the internal electrode. The corrugated conductive member connecting the electrodes is deflected, and the external electrode made of the corrugated conductive member follows the expansion and contraction of the columnar laminate even when driven continuously for a long time under a high electric field and high pressure. Therefore, no unreasonable load acts on the connection between the internal electrode and the external electrode, the disconnection between the external electrode and the internal electrode can be prevented, and the durability can be greatly improved.

In the present invention, it is preferable that the corrugated conductive member has a plate shape or a linear shape. By using a plate-shaped corrugated conductive member, a plurality of connecting portions between the internal electrode and the corrugated conductive member can be provided. By providing a plurality of such plate-shaped corrugated conductive members, the number of connection portions can be further increased, the number of contacts with the internal electrodes can be increased, and the external electrodes can be firmly connected to the internal electrodes. it can. Thus, even when a large current is applied to the external electrode and the device is driven at a high speed, a contact failure between the external electrode and the internal electrode can be prevented, and a highly reliable laminated piezoelectric element can be provided. .

[0012] Also, by forming the external electrode from a plurality of linear corrugated conductive members, the external electrode and the internal electrode can be firmly connected.

Further, in the present invention, it is preferable that a terminal portion connected to the internal electrode is formed on an outer surface of the columnar laminate, and a projecting portion of the corrugated conductive member is joined to the terminal portion.

In this case, the connection area between the corrugated conductive member and the internal electrode exposed on the side surface of the columnar laminate is increased, and the bonding strength is increased. In addition, the external electrodes and the internal electrodes can be reliably connected for a long time.

Further, according to the present invention, the corrugated conductive member is made of A
It is desirable to be made of at least one of u, Ag, Cu, Al, Ni and Fe.

By using the above-mentioned metal as the corrugated conductive member, the specific resistance of the corrugated conductive member can be reduced, heat generation due to a large current flowing through the corrugated conductive member can be suppressed, and the inner electrode and the outer electrode can be reduced. Can be prevented from being fused by abnormal heat generation, and a highly reliable laminated piezoelectric element can be provided.

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.

[0018]

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, a laminated piezoelectric actuator according to the present invention has a rectangular columnar laminated body 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 on the side surface. The other end of the electrode 2 is insulated by the insulator 3 every other layer, and the end of the internal electrode 2 not covered with the insulator 3 is connected to the external electrode 4 composed of a plate-shaped corrugated conductive member 4a. A lead wire 6 is connected and fixed to the electrode 4.

The piezoelectric body 1 is made of, for example, a piezoelectric ceramic material mainly composed of 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.

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 to the laminated piezoelectric actuator, a method of increasing the number of laminated layers is adopted. However, when the number of laminated layers is increased, the thickness of the piezoelectric body 1 is too thick. And the actuator cannot be reduced in size and height.
On the other hand, if the thickness of the piezoelectric body 1 is too thin, dielectric breakdown is likely to occur.

An internal electrode 2 is arranged between the piezoelectric bodies 1. The internal electrode 2 is formed of a metal material such as silver-platinum, and a predetermined voltage is applied to each piezoelectric body 1. The piezoelectric element 1 has a function of causing the piezoelectric body 1 to be displaced by an 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 is composed of a calcined powder of piezoelectric ceramic such as PZT and an organic high-molecular substance such as acrylic or butyral. A slurry containing a binder composed of molecules as a main component is prepared, and a ceramic green sheet to be the piezoelectric body 1 is prepared from the slurry by a tape forming method such as a well-known doctor blade method or calender roll method.

Next, a binder, a plasticizer and the like are added to and mixed with the silver-platinum powder to form a conductive paste, and this is paste-printed on the upper surface of each green sheet by screen printing or the like.
Print to a thickness of ３０30 μm.

Finally, a plurality of green sheets on which the conductive paste is printed are laminated, and a plurality of green sheets on which no conductive paste is printed (being an inactive body) are laminated on the upper and lower surfaces of the laminate. After the binder is removed from the laminate at a predetermined temperature, 900 to 1200 ° C.
By firing, the columnar laminate 1a is manufactured.

Further, after firing, the end portions of the internal electrode 2 are exposed on all side surfaces of the columnar laminate 1a, but the end surfaces of the piezoelectric body 1 including the end portions of the internal electrode 2 are exposed on the two opposing side surfaces. A groove having a depth of 50 to 500 μm and a width of 30 to 100 μm in the stacking direction is formed every other layer, and glass, epoxy resin, polyimide resin, polyamideimide resin,
The insulator 3 is formed by filling with silicone rubber or the like.

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. Corrugated conductive member 4a forming a positive electrode and a negative electrode
Are connected to a pair of external electrodes 4. The external electrode 4 may be formed by a plurality of corrugated conductive members 4a. In this case, the connection reliability of the external electrode 4 to the internal electrode 2 can be further improved.

The insulator 3 is made of a material having a low elastic modulus that follows the shrinkage 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 made of corrugated conductive members 4a are connected and fixed to the opposing side surfaces of the columnar laminate 1a. That is, terminal portions 11 connected to the internal electrodes 2 are alternately formed on the opposing outer surfaces of the columnar laminate 1a, and the terminal portions 11 are provided with the projecting portions 1 of the corrugated conductive member 4a.
3 are joined by, for example, spot welding. The terminal portion 11 has a width that does not make contact with the adjacent internal electrode 2, and the terminal portion 11 is connected to the corrugated conductive member 4 a in terms of ensuring the connection between the external electrode 4 and the internal electrode 2. It is desirably formed of a joinable material and has a thickness of 10 to 100 μm.

The terminal portion 11 can be formed on the exposed side surface of the columnar laminate 1a of the internal electrode 2 by low-resistance deposition, sputtering, plating, or the like.

The corrugated conductive member 4a is an elastic body because of its shape, and 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 the gap between the columnar laminate 1a and the corrugated conductive member 4a with an insulating material having a low elastic modulus, such as silicone rubber, so as to bury the external electrode 4 from the viewpoint of preventing creeping discharge. .

The external electrode 4 made of the corrugated conductive member 4a
From the viewpoint of reducing the specific resistance, Au, Ag, Cu,
Desirably, it is made of at least one of Al, Ni and Fe. Of these, Au, Ag, Al, and Ni are desirable from the viewpoint of good oxidation resistance and good conductivity.
Further, the thickness is preferably 20 to 100 μm, which is easily deformed so as to follow expansion and contraction of the laminated piezoelectric element.

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.

In the present invention, the height h of the corrugated conductive member 4a protruding from the columnar laminate 1a, that is,
a and the gap between the internal electrode 2 portion insulated from the corrugated conductive member 4a is preferably at least 0.5 times the sum of the thickness of the piezoelectric body 1 and the thickness of the internal electrode 2.

This corresponds to the height h of the projection of the corrugated conductive member 4a.
Is set to be at least 0.5 times the sum of the thickness of the piezoelectric body 1 and the thickness of the internal electrode 2, the tensile stress generated at the joint between the internal electrode 2 and the external electrode 4 can be reduced as much as possible. And the internal electrode 2 can be reliably connected.

Further, by reducing the cross-sectional area of the external electrode 4 perpendicular to the laminating direction and reducing the volume of the external electrode 4,
From the viewpoint that the laminated piezoelectric actuator can be miniaturized, it is desirable that the protruding height h of the external electrode is not more than 10 times the sum of the thickness of the piezoelectric body 1 and the thickness of the internal electrode 2.

Then, a direct current voltage of 0.1 to 3 kV / mm is applied to the pair of external electrodes 4 through the lead wires 6 to polarize the columnar laminated body 1a, thereby obtaining a laminated piezoelectric actuator as a product. When 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 automobile fuel injection valve that injects fuel to the engine.

In the multilayer piezoelectric actuator configured as described above, since the external electrode 4 is formed by the corrugated conductive member 4a, the external electrode 4 is bent between the internal electrodes 2 and the external electrode 4 is bent. Since the electrode 4 can sufficiently follow the expansion and contraction of the actuator and there is almost no stress generated at the connection between the external electrode 4 and the internal electrode 2, the connection strength between the external electrode 4 and the internal electrode 2 can be improved, The problem that sparks occur between the electrode 4 and the internal electrode 2 can be prevented, and a highly reliable actuator can be provided.

The end of the internal electrode 2 which is not connected to the external electrode 4 has a large driving voltage by forming a groove on the outer surface of the columnar laminate 1a and filling the groove with the insulator 3 for insulation. Can be prevented from creeping discharge phenomenon.

In the above example, the external electrode 4 is
Although the example using one plate-shaped corrugated conductive member 4a has been described, the present invention is not limited to the above example,
For example, the external electrodes may be formed using a plurality of corrugated conductive members. In this case, the connection reliability between the internal electrode and the external electrode can be further improved.

Even when a linear corrugated conductive member is used as the corrugated conductive member 4a, substantially the same effect as in the above example can be obtained. In this case, from the viewpoint of improving the connection reliability between the internal electrode and the external electrode, it is preferable to use a plurality of corrugated conductive members, and the wire diameter of the wire is low,
In addition, from the viewpoint of being rich in elasticity as a whole, 25 to 5
Desirably, it is 00 μm.

Incidentally, the corrugated conductive member of this wire may have a circular or polygonal cross section, but is desirably a polygonal shape in that the contact area with the terminal portion can be increased.

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

FIG. 2 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 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 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.

[0048]

EXAMPLE First, a square columnar laminate having a cross section of 5 mm on each side was prepared. The piezoelectric body of this columnar laminate is PZ
It was formed of T, and its thickness was 100 μm. The internal electrode was 3 μm in thickness and was formed of a silver-platinum alloy.
The number of layers of each of the piezoelectric body and the internal electrode was 350. 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.

A terminal portion is formed on the opposite side surface of the columnar laminate by plating so as to cover a portion where the end of the internal electrode is exposed, and the terminal portion has a thickness t of 50 μm and a width B of 500 μm. The protruding portion of a thin plate-shaped corrugated conductive member made of aluminum, whose length is slightly shorter than the columnar laminate, is abutted, and in this state, an external electrode is formed by spot welding to form a laminated piezoelectric as shown in FIG. An actuator was manufactured. Note that the protrusion height h of the protrusion of the corrugated conductive member is 300.
μm, which is about three times the sum of the thicknesses of the piezoelectric body and the internal electrode.

Thereafter, silicone rubber was filled between the columnar laminate and the protruding portion, and the external electrodes were covered with silicone rubber.

Thereafter, 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 a polarization treatment, thereby obtaining 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. Further, an AC voltage of 0 to +150 V was applied to this actuator at room temperature at a frequency of 200 Hz, and a drive test was performed. As a result, when the actuator was driven up to 2 × 10 ⁹ cycles, the change amount of the displacement amount was 2.3%. No abnormality of the external electrode was observed.

On the other hand, as a comparative example, using the above-described columnar laminate, one end of the internal electrode was alternately covered with an insulator made of glass on the left and right, and a silver-dispersed glass paste was applied from above on the insulator. A laminated piezoelectric actuator having external electrodes formed thereon as shown in FIG. 3 was produced.

15 was added to the obtained laminated piezoelectric actuator.
As a result of applying a DC voltage of 0 V, a displacement amount of 40 μm was obtained in the stacking direction.
A drive test was performed by applying an AC voltage of +150 V at a frequency of 200 Hz. As a result, at 1 × 10 ⁶ cycles, the external electrode could not follow the expansion and contraction of the columnar laminate, and the tensile stress was applied between the external electrode and the columnar laminate. , Cracks occurred at the connection between the external electrode and the internal electrode, and sparks occurred.

[0055]

According to the multilayer piezoelectric element of the present invention, the external electrode is formed of a corrugated conductive member, and the protruding portion of the corrugated conductive member protruding toward the columnar laminate is connected to the end of the internal electrode. Therefore, the corrugated conductive member connecting the internal electrodes is deflected, so that the external electrode composed of the corrugated conductive member has a columnar laminate even when driven continuously for a long time under a high electric field and high pressure. It can follow the expansion and contraction, and no excessive load acts on the connection between the internal electrode and the external electrode.
Disconnection between the external electrode and the internal electrode can be prevented, and the durability can be greatly improved.

[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 an explanatory view showing an injection device of the present invention.

FIG. 3 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 ... Corrugated conductive member 11 ... Terminal part 13 ... Projection part 43 ... Piezoelectric actuator

Claims (5)

[Claims] 1. A columnar laminated body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and a pair provided on a side surface of the columnar laminated body, wherein the internal electrodes are alternately connected every other layer. A multilayer piezoelectric element comprising:
The multilayer piezoelectric element according to claim 1, wherein the external electrode is formed of a corrugated conductive member, and a protruding portion of the corrugated conductive member protruding toward the columnar laminate is connected to an end of the internal electrode. 2. The laminated piezoelectric element according to claim 1, wherein the corrugated conductive member has a plate shape or a linear shape. 3. The columnar laminate has a terminal portion formed on an outer surface thereof and connected to an internal electrode, and a protruding portion of a corrugated conductive member is joined to the terminal portion.
The laminated piezoelectric element according to any one of the preceding claims. 4. The wave-shaped conductive member is made of Au, Ag, Cu, Al,
4. The multi-layer piezoelectric element according to claim 1, comprising at least one of Ni and Fe. 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.