WO2013114768A1

WO2013114768A1 - Laminated piezoelectric element, injection device provided with same, and fuel injection system

Info

Publication number: WO2013114768A1
Application number: PCT/JP2012/083480
Authority: WO
Inventors: 山元　堅
Original assignee: 京セラ株式会社
Priority date: 2012-01-30
Filing date: 2012-12-25
Publication date: 2013-08-08
Also published as: JP5744242B2; JPWO2013114768A1

Abstract

[Problem] To provide a laminated piezoelectric element which is suppressed in the occurrence of cracks in a laminate, an injection device which is provided with the laminated piezoelectric element, and a fuel injection system. [Solution] The present invention is characterized by comprising: a laminate (4) wherein a piezoelectric layer (2) and an internal electrode layer (3) are laminated; an external electrode (6) which is electrically connected to the internal electrode layer (3) and fixed to a lateral surface of the laminate (4), with a bonding material (5) being interposed therebetween, such that a part of the external electrode (6) extends beyond one end face of the laminate (4) in the lamination direction; and a fixing member (7) which is formed of a metal and is in contact with the one end face of the laminate (4), while being at a distance from the external electrode (6). The present invention is also characterized in that the external electrode (6) has a bent portion (61) that is bent so as not to come into contact with the one end face of the laminate (4).

Description

Multilayer piezoelectric element, injection device including the same, and fuel injection system

The present invention relates to a laminated piezoelectric element used as, for example, a piezoelectric driving element (piezoelectric actuator), a pressure sensor element, a piezoelectric circuit element, and the like, an injection device including the same, and a fuel injection system.

As a laminated piezoelectric element, a laminated body in which a piezoelectric layer and an internal electrode layer are laminated, and electrically connected to the internal electrode layer and partially extending from one end surface of the laminated body in the laminating direction. In addition, a configuration including an external electrode attached to a side surface of a laminated body via a bonding material is known (see Patent Document 1). Furthermore, as shown in FIG. 9, a configuration is also known in which a metal fixing member 7 is brought into contact with one end face of the laminate 4 so as to be spaced from the external electrode 6. Note that the driving force of the laminated piezoelectric element can be transmitted to the opposite end face by bringing the fixing member 7 into contact therewith.

JP 2005-223014 A

Here, in the configuration in which the metal fixing member 7 is brought into contact with one end surface of the multilayer body 4 of the multilayer piezoelectric element described in Patent Document 1, the external electrode 6 on the end surface of the multilayer body 4 is fixed. Since moisture accumulates between the members 7, the metal fixing member 7 may be corroded by moisture and the fixation of the laminate may be shifted. Further, when the end face of the laminate 4 and the external electrode 6 are repeatedly contacted by long-term driving, the laminate 4 may be cracked.

The present invention has been devised in view of the above-described problems, and an object of the present invention is to provide a multilayer piezoelectric element in which cracks are suppressed in the multilayer body, an injection device including the same, and a fuel injection system. Is to provide.

The present invention provides a laminate in which a piezoelectric layer and an internal electrode layer are laminated, and is electrically connected to the internal electrode layer and partially extends from one end face of the laminate in the lamination direction. A laminate including an external electrode attached to a side surface of the laminate through a bonding material, and a metal fixing member that is in contact with one end face of the laminate so as to be spaced from the external electrode In the piezoelectric element, the external electrode has a bent portion bent so as to avoid contact with one end face of the multilayer body.

Further, the present invention includes a container having an injection hole and the multilayer piezoelectric element described above, and fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. It is the injection device which does.

The present invention also provides a common rail that stores high-pressure fuel, the above-described injection device that injects the high-pressure fuel stored in the common rail, a pressure pump that supplies the high-pressure fuel to the common rail, and a drive signal to the injection device. A fuel injection system comprising: an injection control unit for supplying the fuel.

According to the multilayer piezoelectric element of the present invention, the external electrode and the fixing member on the end surface of the multilayer body have the bent portion bent so as to avoid the external electrode from contacting one end surface of the multilayer body. Since the metal fixing member is less likely to corrode, the stacking of the laminate is not out of alignment and cracks do not occur in the laminate, and the laminate has excellent long-term durability. Type piezoelectric element is obtained.

Further, according to the ejection device of the present invention, it is possible to suppress the occurrence of cracks on the end face of the multilayer piezoelectric element, and therefore it is possible to stably eject a desired fluid over a long period of time.

Further, according to the fuel injection system of the present invention, desired injection of high-pressure fuel can be stably performed over a long period of time.

It is a longitudinal cross-sectional view which shows an example of embodiment of the lamination type piezoelectric element of this invention. It is a longitudinal cross-sectional view which shows the other example of embodiment of the lamination type piezoelectric element of this invention. It is a longitudinal cross-sectional view which shows the other example of embodiment of the lamination type piezoelectric element of this invention. It is a perspective view which shows the principal part of the other example of embodiment of the lamination type piezoelectric element of this invention. It is a perspective view which shows the principal part of the other example of embodiment of the lamination type piezoelectric element of this invention. It is a longitudinal cross-sectional view which shows the other example of embodiment of the lamination type piezoelectric element of this invention. It is a rough sectional view showing an example of an embodiment of an injection device of the present invention. It is a schematic block diagram which shows an example of embodiment of the fuel-injection system of this invention. It is a longitudinal cross-sectional view of a conventional multilayer piezoelectric element.

Hereinafter, an example of an embodiment of the multilayer piezoelectric element of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of an embodiment of a multilayer piezoelectric element of the present invention. A laminated piezoelectric element 1 shown in FIG. 1 includes a laminated body 4 in which a piezoelectric layer 2 and an internal electrode layer 3 are laminated, and is electrically connected to the internal electrode layer 3 and part of one of the laminated bodies 4. The external electrode 6 attached to the side surface of the multilayer body 4 via the bonding material 5 so as to extend from the end surface in the laminating direction, and one end surface of the multilayer body 4 so as to be spaced from the external electrode 6 The external electrode 6 includes a bent portion 61 that is bent so as to avoid contact with one end face of the laminate 4.

A multilayer body 4 constituting the multilayer piezoelectric element 1 is formed by laminating piezoelectric layers 2 and internal electrode layers 3. For example, an active portion in which a plurality of piezoelectric layers 2 and internal electrode layers 3 are alternately stacked. And an inactive portion composed of the piezoelectric layer 2 provided at both ends of the active portion in the stacking direction, and is formed in a rectangular parallelepiped shape having a length of 0.5 to 10 mm, a width of 0.5 to 10 mm, and a height of 5 to 100 mm, for example. .

The piezoelectric layer 2 constituting the multilayer body 4 is formed of ceramics having piezoelectric characteristics. As such ceramics, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), Lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. The thickness of the piezoelectric layer 2 is, for example, 3 to 250 μm.

The internal electrode layer 3 constituting the multilayer body 4 is formed by simultaneous firing with the ceramics forming the piezoelectric layer 2, and is alternately stacked with the piezoelectric layer 2 to sandwich the piezoelectric layer 2 from above and below. By arranging the positive electrode and the negative electrode in the order of lamination, a driving voltage is applied to the piezoelectric layer 2 sandwiched between them. As this forming material, for example, a conductor mainly composed of a silver-palladium alloy having low reactivity with piezoelectric ceramics, or a conductor containing copper, platinum, or the like can be used. In the example shown in FIG. 1, the positive electrode and the negative electrode (or the ground electrode) are led out alternately to a pair of opposing side surfaces of the multilayer body 4 to electrically connect with the pair of conductor layers 8 provided on the side surfaces of the multilayer body 4. It is connected to the. The internal electrode layer 3 has a thickness of 0.1 to 5 μm, for example.

The pair of conductor layers 8 provided on the side surfaces of the multilayer body 4 and electrically connected to the internal electrode layer 3 are formed by applying and baking a paste made of, for example, silver and glass. It is joined to the side surface and electrically connected to the internal electrode layers 3 that are alternately led to the opposite side surface of the laminate 4. The thickness of the conductor layer 8 is, for example, 5 to 500 μm.

An external electrode 6 is provided on the conductor layer 8 via a bonding material 5.

The bonding material 5 used here is preferably made of a conductive adhesive made of an epoxy resin or a polyimide resin containing a metal powder having good conductivity such as Ag powder or Cu powder. The bonding material 5 is formed to a thickness of 5 to 500 μm, for example.

In addition, the external electrode 6 is electrically connected to the internal electrode layer 3 and partly extends from one end face of the multilayer body 4 in the laminating direction so that the external electrode 6 is connected to the side surface of the multilayer body 4 via the bonding material 5. It is attached. The external electrode 6 is made of a flat metal plate such as copper, iron, stainless steel, phosphor bronze, etc., and is formed to have a width of 0.5 to 10 mm and a thickness of 0.01 to 1.0 mm, for example. Examples of the external electrode 6 include a shape having a slit in the width direction and a metal plate processed into a mesh as a shape having a high effect of relieving stress generated by expansion and contraction of the laminate 4.

In the present invention, as shown in FIG. 2, the pair of conductor layers 8 is not provided, and the internal electrode layer 3 is electrically connected to the external electrode 6 via the bonding material 5 directly. There may be.

A metal fixing member 7 is in contact with one end face of the laminate 4 so as to be spaced from the external electrode 6. The fixing member 7 is used to transmit the driving force of the multilayer piezoelectric element 1 to the opposite end face of the multilayer body 4 by abutting the fixing member 7, and is 2 to 5 mm square and 2 to 10 mm in height, for example. . The material of the fixing member 7 includes a metal having sufficient rigidity, such as SUS.

The external electrode 6 has a bent portion 61 that is bent so as to avoid contact with one end face of the multilayer body 4.

When the external electrode 6 extends from the end surface of the multilayer body 4, the bent portion 61 has the external electrode 6 and the fixing member on the end surface of the multilayer body 4 so as to avoid contact with one end surface of the multilayer body 4. The shape is such that moisture does not accumulate between the two, in other words, the shape allows moisture to escape.

For example, the external electrode 6 is bent so as to be further 0.2 to 2.0 mm away from the corner of the end face of the laminate 4 so as to avoid contact with one end face of the laminate 4. Further, the distance of 0.2 to 2.0 mm means that the surface of the external electrode 6 is 0.2 to 2.0 mm away from the surface bonded to the laminate 4.

Thereby, since the metal fixing member 7 in contact with the end face of the laminate 4 is not corroded by moisture, it is possible to prevent the laminate 4 from being fixed and cracked in the laminate 4. Further, it is possible to prevent a short circuit between the metal fixing member 7 and the external electrode 6 through the accumulated moisture.

Here, the bent portion 61 is preferably bent so as to swell in a direction perpendicular to the side surface to which the external electrode 6 is attached.

The bent shape so as to avoid contact with one end face of the laminate 4 may be bent in a direction parallel to the side surface of the laminate 4 to which the external electrode 6 is attached, but the external electrode 6 is attached. By bending so as to swell in a direction perpendicular to the side surface of the laminated body 4, vibration due to driving can be absorbed and the external electrode 6 can be prevented from peeling off. Therefore, a multilayer piezoelectric element having excellent long-term durability can be obtained. In addition, since the heat generated by driving is easily escaped from the bent portion 61 because it is bent outward, the heat generation at the joint portion with the joint material 5 is suppressed, and the external electrode 6 is hardly peeled off and the durability is improved.

Specifically, as shown in FIG. 1, the bent portion 61 has one side of the laminate 4 that is bent so as to swell in a direction perpendicular to the side surface of the laminate 4 to which the external electrode 6 is attached. The form containing the site | part bent in the direction away from the side surface of the said laminated body 4 at the laminated body 4 side rather than an end surface is mentioned.

In the shape shown in FIG. 1, for example, it is bent 0.1 to 2.0 mm inside from the end face of the laminate 4 and away from the side surface of the laminate 4, and further 0.2 to 2.0 mm away from the side surface of the laminate 4. There is a structure that bends toward the stacking direction at a position and bends in a direction approaching a virtual extension surface extending from the side surface of the stacked body 4 outside the end surface of the stacked body 4 by 0.5 to 3.0 mm. In the present invention, the bending portion 61 means a configuration including these three bent portions (bent portions).

Further, as shown in FIG. 3, it is desirable that the bending portion 61 has a curved shape when viewed in a longitudinal section. In this case, it is bent 0.1 to 2.0 mm inside from the end face of the laminate 4, and the maximum bulge portion is further 0.2 to 2.0 mm away from the side face of the laminate 4, and is 0.5 to 3.0 from the end face of the laminate 4. A structure that bends on the outside of mm. Since the bent portion 61 is curved, it is possible to reduce stress concentration applied to the bent portion 61 of the external electrode 6 by driving. And there is no destruction of the external electrode 6 by long-term drive, and durability improves.

Furthermore, when there are a pair of external electrodes 6, the bent portion 61 in each external electrode 6 of the pair of external electrodes 6 is curved, so that the bent portion 61 repeats according to the expansion and contraction of the laminate 4. Since it bends, the volume of the space inside the bent portion 61 changes, airflow is generated, and it is possible to prevent moisture from accumulating between the external electrode 6 and the fixing member 7 on the end surface of the laminate 4 due to the airflow. Corrosion of the fixing member 7 can be prevented.

Also, as shown in FIG. 4, it is preferable that a hole 62 is provided in the bent portion 61. Specifically, the hole 62 penetrating in a direction crossing a plane parallel to the side surface to which the external electrode 6 is attached is formed. It is preferable to be provided. According to this configuration, even if heat due to self-heating of the laminated body 4 due to driving is accumulated and becomes water vapor in the bent portion 61, the external electrode 6 and the fixing member 7 are prevented from getting water vapor from the holes 62. Water vapor can be released. The size of the hole 62 is preferably 30% to 80% with respect to the area of the bent portion 61. If it is 30% or more, it is easy to release water vapor, and if it is 80% or less, the bending portion 61 also has sufficient strength. As long as the area ratio is satisfied, there may be a large number or a small number.

Further, as shown in FIG. 5, it is desirable that the hole 62 is located on the side of the laminate. It is because the part which accumulate | stores a water | moisture content is near by being provided in the side of the laminated body 4, and water vapor | steam tends to come out.

Further, as shown in FIG. 6, it is desirable that the bonding material 5 is provided so as to extend to the region of the bent portion 61 and to be in contact with a part of the bent portion 61. For example, the bonding material 5 extends 5% or more of the distance between the base of the bent portion 61 and the end face of the laminate 4. According to this configuration, the bonding strength of the external electrode 6 can be increased. Further, when a large current flows, the current can flow at a stroke to the base of the bent portion 61, and a spark can be prevented from occurring with the internal electrode layer 3.

Further, as shown in the figure, the laminate 4 includes an active portion in which piezoelectric layers 2 and internal electrode layers 3 are alternately laminated, and an inactive portion in which piezoelectric layers are laminated at both ends of the active portion. It is desirable that the bent portion 61 is located on one end face side of the active portion. In other words, it is desirable to extend from the position facing the inactive portion to the position extending in the stacking direction beyond the one end face. According to this configuration, the active part is not short-circuited by the accumulated water.

Next, a method for manufacturing the multilayer piezoelectric element 1 of the present embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 2 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

Next, a conductive paste to be the internal electrode layer 3 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is applied on the ceramic green sheet in the pattern of the internal electrode layer 3 using a screen printing method. Further, a plurality of ceramic green sheets printed with this conductive paste are laminated, subjected to a binder removal treatment at a predetermined temperature, fired at a temperature of 900 to 1200 ° C., and then subjected to a predetermined grinding using a surface grinder or the like. A laminated body 4 including the piezoelectric layers 2 and the internal electrode layers 3 that are alternately laminated is manufactured by performing a grinding process so as to have a shape.

The laminate 4 is not limited to the one produced by the above manufacturing method, and any laminate 4 can be produced as long as the laminate 4 formed by laminating a plurality of piezoelectric layers 2 and internal electrode layers 3 can be produced. It may be produced by a manufacturing method.

Thereafter, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer, and a solvent to a mixture of conductive particles mainly composed of silver and glass is used to form a side surface of the laminate 4 in the pattern of the conductor layer 8. Then, after printing by screen printing or the like and drying, baking is performed at a temperature of 650 to 750 ° C. to form the conductor layer 8.

Next, the external electrode 6 is connected to the surface of the conductor layer 8 through the bonding material 5 and fixed.

The bonding material 5 is controlled to a predetermined thickness and width by screen printing or dispensing method using an adhesive or solder made of epoxy resin or polyimide resin containing metal powder with good conductivity such as Ag powder or Cu powder. Can be formed.

The external electrode 6 is made of a flat metal plate such as copper, iron, stainless steel, phosphor bronze, etc., and has a width of 0.5 to 10 mm and a thickness of 0.01 to 1.0 mm, for example. Examples of the external electrode 6 include a shape having a high effect of relieving stress caused by expansion and contraction of the laminate 4, for example, a shape having slits in the width direction, a metal plate processed into a mesh shape, and the like. Here, the bending portion 61 is provided at the tip of the external electrode 6, and for example, when the external electrode 6 is formed by a punching die, the bending portion 61 can be simultaneously formed by the bending die. The hole 62 may be punched to a predetermined size before punching.

Thereafter, a DC electric field of 0.1 to 3 kV / mm is applied to the external electrodes 6 respectively connected to the pair of conductor layers 8 to polarize the piezoelectric layer 2 constituting the multilayer body 4, whereby the multilayer piezoelectric element 1 is completed. To do. In this multilayer piezoelectric element 1, the conductor layer 8 is connected to an external power source via the external electrode 6 and a voltage is applied to the piezoelectric layer 2, thereby greatly increasing each piezoelectric layer 2 by the inverse piezoelectric effect. Can be displaced. This makes it possible to function as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

Next, an example of an embodiment of the injection device of the present invention will be described. FIG. 7 is a schematic cross-sectional view showing an example of an embodiment of the injection device of the present invention.

As shown in FIG. 7, in the injection device 19 according to the present embodiment, the multilayer piezoelectric element 1 according to the present embodiment is stored in a storage container (container) 23 having an injection hole 21 at one end. .

In the storage container 23, a needle valve 25 capable of opening and closing the injection hole 21 is disposed. A fluid passage 27 is disposed in the injection hole 21 so that it can communicate with the movement of the needle valve 25. The fluid passage 27 is connected to an external fluid supply source, and fluid is always supplied to the fluid passage 27 at a high pressure. Therefore, when the needle valve 25 opens the injection hole 21, the fluid supplied to the fluid passage 27 is discharged from the injection hole 21 to an external or adjacent container, for example, a fuel chamber (not shown) of the internal combustion engine. It is configured.

Further, the upper end portion of the needle valve 25 has a large diameter, and is a piston 31 slidable with a cylinder 29 formed in the storage container 23. In the storage container 23, the multilayer piezoelectric element 1 of the above-described example is stored in contact with the piston 31.

In such an injection device 19, when the laminated piezoelectric element 1 is extended by applying a voltage, the piston 31 is pressed, the needle valve 25 closes the fluid passage 27 leading to the injection hole 21, and the supply of fluid is stopped. The When the voltage application is stopped, the laminated piezoelectric element 1 contracts, the disc spring 33 pushes back the piston 31, the fluid passage 27 is opened, and the injection hole 21 communicates with the fluid passage 27. Fluid injection is performed.

Note that the fluid passage 27 may be opened by applying a voltage to the multilayer piezoelectric element 1 and the fluid passage 27 may be closed by stopping the application of the voltage.

The injection device 19 according to the present embodiment includes a container 23 having injection holes and the multilayer piezoelectric element 1 according to the present embodiment, and the fluid filled in the container 23 is driven by the multilayer piezoelectric element 1. Thus, it may be configured to discharge from the injection hole 21. In other words, the multilayer piezoelectric element 1 does not necessarily have to be inside the container 23, as long as the multilayer piezoelectric element 1 is configured to apply pressure for controlling the ejection of fluid to the inside of the container 23 by driving the multilayer piezoelectric element 1. Good. In the injection device 19 of the present embodiment, the fluid includes various liquids and gases such as a conductive paste in addition to fuel and ink. By using the ejection device 19 of the present embodiment, the fluid flow rate and ejection timing can be stably controlled over a long period of time.

If the injection device 19 of the present embodiment that employs the multilayer piezoelectric element 1 of the present embodiment is used for an internal combustion engine, the fuel is supplied to the combustion chamber of the internal combustion engine such as an engine over a longer period than the conventional injection device. It is possible to inject with high accuracy.

Next, an example of an embodiment of the fuel injection system of the present invention will be described. FIG. 8 is a schematic view showing an example of an embodiment of the fuel injection system of the present invention.

As shown in FIG. 8, the fuel injection system 35 of the present embodiment includes a common rail 37 that stores high-pressure fuel as a high-pressure fluid, and a plurality of injections of the present embodiment that inject high-pressure fluid stored in the common rail 37. A device 19, a pressure pump 39 that supplies a high-pressure fluid to the common rail 37, and an injection control unit 41 that supplies a drive signal to the injection device 19 are provided.

The injection control unit 41 controls the amount and timing of high-pressure fluid injection based on external information or an external signal. For example, if the injection control unit 41 is used for fuel injection of the engine, the amount and timing of fuel injection can be controlled while sensing the situation in the combustion chamber of the engine with a sensor or the like. The pressure pump 39 serves to supply fluid fuel from the fuel tank 43 to the common rail 37 at a high pressure. For example, in the case of the fuel injection system 35 of the engine, the fluid fuel is fed into the common rail 37 at a high pressure of, for example, 1000 to 2000 atmospheres (about 101 MPa to about 203 MPa), preferably 1500 to 1700 atmospheres (about 152 MPa to about 172 MPa). In the common rail 37, the high-pressure fuel sent from the pressure pump 39 is stored and sent to the injection device 19 as appropriate. The injection device 19 injects a certain fluid from the injection hole 21 to the outside or an adjacent container as described above. For example, when the target for injecting and supplying fuel is an engine, high-pressure fuel is injected in a mist form from the injection hole 21 into the combustion chamber of the engine.

In addition, this invention is not limited to the example of said embodiment, A various change may be performed within the range which does not deviate from the summary of this invention. For example, the cross-sectional shape in the direction orthogonal to the stacking direction of the stacked body 4 is not limited to the quadrangle shape as an example of the above embodiment, but a polygonal shape such as a hexagonal shape or an octagonal shape, a circular shape, or a straight line and an arc. You may be the shape which combined.

The multilayer piezoelectric element 1 according to the present embodiment is used for, for example, a piezoelectric drive element (piezoelectric actuator), a pressure sensor element, a piezoelectric circuit element, and the like. Examples of the driving element include a fuel injection device for an automobile engine, a liquid injection device such as an inkjet, a precision positioning device such as an optical device, and a vibration prevention device. Examples of the sensor element include a combustion pressure sensor, a knock sensor, an acceleration sensor, a load sensor, an ultrasonic sensor, a pressure sensor, and a yaw rate sensor. Examples of the circuit element include a piezoelectric gyro, a piezoelectric switch, a piezoelectric transformer, and a piezoelectric breaker.

Examples of the present invention will be described.

A piezoelectric actuator provided with the multilayer piezoelectric element of the present invention was produced as follows. First, a ceramic slurry was prepared by mixing calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) having an average particle size of 0.4 μm, a binder and a plasticizer. Using this ceramic slurry, a ceramic green sheet serving as a piezoelectric layer having a thickness of 50 μm was prepared by a doctor blade method.

Next, a binder was added to the silver-palladium alloy to produce a conductive paste to be an internal electrode layer.

Next, a conductive paste serving as an internal electrode layer was printed on one side of the ceramic green sheet by a screen printing method, and 200 ceramic green sheets printed with the conductive paste were laminated. Also, a total of 15 ceramic green sheets not printed with the conductive paste serving as the internal electrode layer were laminated above and below the 200 ceramic green sheets printed with the conductive paste serving as the internal electrode layer. . Then, it was fired at 980 to 1100 ° C. and ground to a predetermined shape using a surface grinder to obtain a laminate having an end face of 5 mm square.

Next, a conductive paste in which silver and glass were mixed with a binder was printed by screen printing on the conductor layer forming portion on the side surface of the laminate, and baked at 700 ° C. to form a conductor layer.

Next, a bonding material in the form of a mixed paste of Ag powder and polyimide resin was applied to the surface of the conductor layer with a dispenser, and external electrodes were connected and fixed parallel to the surface of the laminate.

Then, a 4 mm square fixing member made of SUS was fixed with a very small amount of adhesive so as to come to the center of the end face of the element.

Here, as the sample 1, a laminated piezoelectric element was manufactured using an external electrode having a cross section shown in FIG. Specifically, the bent portion is bent 1 mm inside from the end surface of the laminated body, bent at a distance of 1 mm from the side surface, and bent 1 mm outside from the end surface of the laminated body.

Further, as Sample 2, a laminated piezoelectric element was manufactured using an external electrode having a cross section shown in FIG. Specifically, the bent portion is bent 1 mm inside from the end face of the laminate, is bent in a semicircular shape so as to be further 1 mm away from the side face, and is bent 1 mm outside from the end face of the laminate. .

Further, as Sample 3, a multilayer piezoelectric element using an external electrode having a bent portion shown in FIG. 4 in which one hole was provided in the bent portion of Sample 2 was produced. The diameter of the hole was 0.5 mm, and was provided at a position outside the end face of the laminate.

As a comparative example, a laminated piezoelectric element (sample 4) using an external electrode having the cross section shown in FIG. 9 was also produced.

These multi-layer piezoelectric elements were subjected to polarization treatment by applying a 3 kV / mm DC electric field to the external electrodes for 15 minutes via lead members welded to the external electrodes. When a DC voltage of 160 V was applied to these stacked piezoelectric elements, a displacement of 30 μm was obtained in the stacking direction of the stacked body. Further, an endurance test was performed in which an alternating voltage of 0 V to +160 V was applied at a frequency of 150 Hz in a humidity of 30 ° C. and 90%.

As a result, the laminated piezoelectric element of Sample 4 was corroded in the fixed member by continuous driving of 1 × 10 ⁴ times, cracks occurred on the end face of the laminated body, and the driving was stopped.

On the other hand, the laminated piezoelectric elements of Sample 1, Sample 2, and Sample 3 were all driven without cracks even after continuous driving 1 × 10 ⁷ times.

From the above results, it can be seen that according to the present invention, a multilayer piezoelectric element having excellent long-term durability can be realized.

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 2 ... Piezoelectric layer 3 ... Internal electrode layer 4 ... Laminated body 5 ... Bonding material 6 ... External electrode 61 ... Bending part 62 ... Hole 7 ... Fixing member 8 ... Conductor layer 19 ... Injection device 21 ... Injection hole 23 ... Storage container (container)
25 ... Needle valve 27 ... Fluid passage 29 ... Cylinder 31 ... Piston 33 ... Belleville spring 35 ... Fuel injection system 37 ... Common rail 39 ... Pressure pump 41 ... Injection control unit 43 ・・・ Fuel tank

Claims

A laminate in which a piezoelectric layer and an internal electrode layer are laminated, and the laminate that is electrically connected to the internal electrode layer and partially extends from one end face of the laminate in the lamination direction. A laminated piezoelectric element comprising: an external electrode attached to a side surface of the laminated body via a bonding material; and a metal fixing member in contact with one end face of the laminated body so as to be spaced from the external electrode. There,
The multilayer piezoelectric element, wherein the external electrode has a bent portion bent so as to avoid contact with one end face of the multilayer body.
The multilayer piezoelectric element according to claim 1, wherein the bent portion is bent so as to swell in a direction perpendicular to a side surface of the multilayer body to which the external electrode is attached.
3. The multilayer piezoelectric element according to claim 2, wherein the bent portion includes a portion bent in a direction away from the side surface of the multilayer body on the multilayer body side with respect to one end face of the multilayer body.
4. The multilayer piezoelectric element according to claim 2, wherein the bent portion has a curved shape when viewed in a longitudinal section.
The multilayer piezoelectric element according to claim 1, wherein a hole is provided in the bent portion.
The multilayer piezoelectric element according to claim 5, wherein the hole is located on a side of the multilayer body.
The multilayer piezoelectric element according to any one of claims 1 to 6, wherein the bonding material extends to a region of the bent portion and is in contact with a part of the bent portion.
The laminate includes an active portion in which piezoelectric layers and internal electrode layers are alternately stacked, and an inactive portion in which piezoelectric layers are stacked at both ends of the active portion, and the bending portion is The multilayer piezoelectric element according to claim 1, wherein the multilayer piezoelectric element is located closer to the one end surface than the active portion.
A container having an injection hole and the laminated piezoelectric element according to any one of claims 1 to 8, wherein fluid stored in the container is discharged from the injection hole by driving the laminated piezoelectric element. An injection device.
A common rail for storing high-pressure fuel, an injection device according to claim 9 for injecting the high-pressure fuel stored in the common rail, a pressure pump for supplying the high-pressure fuel to the common rail, and a drive signal for the injection device A fuel injection system comprising an injection control unit.