JP2014110259A - Lamination piezoelectric element and injector including the same and fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lamination piezoelectric element in which peeling of an external electrode plate and corrosion at an end of the bonding region of the external electrode plate and a lamination is suppressed, and to provide an injector including the same, and a fuel injection system.SOLUTION: A lamination piezoelectric element 1 includes a laminate 4 of a piezoelectric layer 2 and an internal electrode layer 3, and an external electrode plate 5 bonded to the side face of the laminate 4. The external electrode plate 5 has an extension region 52 extending in the lamination direction from one end of the laminate 4. When viewed in a longitudinal section perpendicular to the bonded side face of the external electrode plate 5, a first bend 52a that is convex toward the inside is provided in the extension region 52, and the peak of the first bend 52a is located on the inside of the extension of a bonding region 51 to the laminate 4.

Description

  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 apparatus including the same, and a fuel injection system.

  As a multilayer piezoelectric element, as shown in FIG. 9, a laminate 83 in which a piezoelectric layer 81 and an internal electrode layer 82 are laminated, and a junction joined to the laminate 83 and electrically connected to the internal electrode layer 82. The thing of the structure containing the external electrode plate 84 which has the area | region 841 and the extension area | region 842 extended in the lamination direction from the joining area | region 841 is known. Here, the extension region 842 of the external electrode plate 84 is a portion to which, for example, a lead wire leading to an external circuit is connected. As the shape of the extension region 842, the extension section 842 has a straight section. It is known (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2002-202024

  Here, the laminated piezoelectric element for in-vehicle use may be exposed to a severe vibration environment and cause the following problems. Specifically, the external electrode plate is peeled off due to vibration caused by driving and vibration from the outside, and there is a possibility that current cannot be supplied to the laminated piezoelectric element (internal electrode layer). In addition, when the laminated piezoelectric element is arranged with the end of the extension region facing upward, condensation occurs due to the temperature difference between the heat transmitted from the laminate and the cool air of the outside air. There is a possibility that the displacement amount after long-term driving may be reduced by being transmitted from the end portion of the region and adhering to the end portion of the joining region and corroding the end portion of the joining region. Further, the cold air from the outside air directly hits the end of the joining region, and moisture adheres to the end of the joining region and corrodes, so that the amount of displacement after long-term driving may be reduced.

  The present invention has been devised in view of the above problems, and its purpose is a laminated type in which peeling of the external electrode plate and corrosion at the end of the joint region between the external electrode plate and the laminate are suppressed. A piezoelectric element, an injection device including the piezoelectric element, and a fuel injection system are provided.

  The present invention includes a laminate formed by laminating a piezoelectric layer and an internal electrode layer, and an external electrode plate joined to a side surface of the laminate, and the external electrode plate has one end of the laminate. A first region that has an extension region extending in the stacking direction from the portion, and is convex inward in the extension region when viewed in a vertical cross section perpendicular to the side surface to which the external electrode plate is bonded. The laminated piezoelectric element is characterized in that a bent portion is provided, and the peak of the first bent portion is located on the inner side of the extension of the joining region with the laminated body.

  In addition, the multilayer piezoelectric element of the present invention has the above-described configuration, wherein the extension region has a second convexity toward the outside when viewed in a vertical cross section perpendicular to the side surface to which the external electrode plate is bonded. The bent portion is provided, and at least a pair of the first bent portion and the second bent portion are provided adjacent to each other.

  In the multilayer piezoelectric element of the present invention, in the above configuration, when the adjacent first bent portion and the second bent portion are viewed in the longitudinal section, the peak of the first bent portion is obtained. The midpoint of the line segment that connects the peak of the second bent portion is not located on the extension of the joining region with the laminate.

  In the multilayer piezoelectric element of the present invention, in the above configuration, when the adjacent first bent portion and the second bent portion are viewed in the longitudinal section, the peak of the first bent portion is obtained. The midpoint of the line segment that connects the peak of the second bent portion is located on the inner side of the extension of the joining region with the laminate.

  In the multilayer piezoelectric element of the present invention, the first bent portion and the second bent portion are curved in the above-described configuration.

  In the multilayer piezoelectric element of the present invention, in the above configuration, when the adjacent first bent portion and the second bent portion are viewed in the longitudinal section, the peak of the first bent portion is obtained. The curvature radius is different from the curvature radius at the peak of the second bent portion.

  In the multilayer piezoelectric element of the present invention, in the above configuration, when the adjacent first bent portion and the second bent portion are viewed in the longitudinal section, the peak of the first bent portion is obtained. The curvature radius is smaller than the curvature radius at the peak of the second bent portion.

  Moreover, the multilayer piezoelectric element of the present invention is characterized in that, in the above-described configuration, there are a plurality of pairs of the first bent portion and the second bent portion which are adjacent to each other.

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

  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. And a fuel injection system.

  According to the present invention, the extension region is provided with the first bent portion that protrudes inward, so that the force to swell outward of the external electrode plate (the external electrode plate is peeled off). Force) is reduced. In addition, since the peak of the first bent portion is located on the inner side of the extension of the joining region with the laminate, moisture transmitted from the end portion of the extension region of the external electrode plate is transferred to the laminate. Therefore, corrosion at the end portion of the joining region between the external electrode plate and the laminate is suppressed. Furthermore, since the cold air from the outside air is cut off, the atmosphere around the edge of the bonding area is close to the heat transmitted from the laminate, and the cold air is not directly applied, so corrosion at the edge of the bonding area between the external electrode plate and the laminate Is suppressed. Therefore, it is possible to obtain a multilayered piezoelectric element excellent in long-term durability in which a decrease in displacement is suppressed even when driven for a long time.

  In addition, according to the ejection device of the present invention, since the multilayer piezoelectric element having excellent long-term durability is provided, desired fluid ejection can be stably performed 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 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 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 which shows an example of embodiment of the conventional lamination type piezoelectric element. It is a longitudinal cross-sectional view which shows the other example of embodiment of the conventional lamination type piezoelectric element.

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

  FIG. 1 is a longitudinal sectional view showing an example of an embodiment of a laminated piezoelectric element of the present invention. The laminated piezoelectric element 1 of the example shown in FIG. 1 has a piezoelectric layer 2 and an internal electrode layer 3 laminated. And the external electrode plate 5 joined to the side surface of the laminate 4, and the external electrode plate 5 extends from one end of the laminate 4 in the stacking direction 52. The extension region 52 is provided with a first bent portion 52a that protrudes inward, as viewed in a vertical cross section perpendicular to the side surface to which the external electrode plate 5 is bonded. The peak of the portion 52 a is located on the inner side of the extension of the bonding region 51 with the stacked body 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 made of the piezoelectric layer 2 provided at both ends of the active portion in the stacking direction, for example, 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. Is formed.

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 laminated body 4 is formed by simultaneous firing with the ceramic forming the piezoelectric layer 2 and is alternately laminated with the piezoelectric layer 2 so as 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 drive 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 6 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.

A pair of conductor layers 6 that are electrically connected to the internal electrode layer 3 are provided on the side surfaces of the multilayer body 4. The pair of conductor layers 6 are formed by applying and baking a paste made of, for example, silver and glass, joined to the side surface of the multilayer body 4, and alternately led to the opposite side surfaces of the multilayer body 4. Each is electrically connected to the internal electrode layer 3. The thickness of the conductor layer 6 is, for example, 5 to 500 μm.

  On the surface of the conductor layer 6 provided on the side surface of the multilayer body 4, the external electrode plate 5 is bonded via a conductive bonding material 7.

  The conductive bonding material 7 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 conductive bonding material 7 is formed to a thickness of, for example, 5 to 500 μm.

  In addition, the external electrode plate 5 includes a bonding region 51 with the stacked body 4 and an extending region 52 that extends from one end of the stacked body 4 in the stacking direction. The external electrode plate 5 is made of a metal flat plate such as copper, iron, stainless steel, phosphor bronze, 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. As a shape having a high effect of relieving stress caused by expansion and contraction of the laminate 4, for example, a shape in which a slit is formed in the width direction in the bonding region 51 or a shape in which the bonding region 51 is processed into a mesh shape may be used.

  In the present invention, as shown in FIG. 2, the conductor layer 6 is not provided, and the internal electrode layer 3 is electrically connected to the external electrode plate 5 directly through the conductive bonding material 7. There may be.

  The extension region 52 is provided with a first bent portion 52a that protrudes inward as viewed in a vertical cross section perpendicular to the side surface (side surface of the multilayer body 4) to which the external electrode plate 5 is bonded. The peak of the first bent portion 52 a is located on the inner side of the extension of the joining region 51 with the stacked body 4.

  Here, the fact that the peak of the first bent portion 52a is located on the inner side of the extension of the joining region 51 with the stacked body 4 means that the first bent portion 52a has a shape that protrudes inward. This means that the peak position is inside the virtual extension line extending in the stacking direction from the interface between the external electrode plate 5 and the conductive bonding material 7 in the bonding region 51. For example, as shown in FIG. 3, even if the external electrode plate 5 is bent at the end of the bonding region 51 and the extension region 52 extends outward, the peak position of the first bent portion 52a is A configuration is also included that lies on the inner side of a virtual extension line (indicated by a one-dot chain line in the drawing) extending in the stacking direction from the interface between the external electrode plate 5 and the conductive bonding material 7 in the bonding region 51. Preferably, the peak position of the first bent portion 52a is preferably located on the inner side of the surface of the conductor layer 6, and particularly on the inner side of the side surface of the laminate 4 to which the external electrode plate 5 is bonded. It is good to be located.

  The length of one extending direction of the first bent portion 52a is, for example, 0.1 to 2.0 mm, and the height of the convex protruding inward is, for example, 0.1 to 2.0 mm. It is determined by appropriately adjusting according to the number provided.

  According to this configuration, it is possible to reduce a force that tends to bulge outward of the external electrode plate 5 (a force that tries to peel off the external electrode plate 5).

  In addition, since the peak of the first bent portion 52 a is located on the inner side of the extension of the joining region 51 with the laminate 4, moisture transmitted from the end portion of the extending region 52 of the external electrode plate 5. However, since it falls to the end surface of the laminated body 4 and does not fall to the edge part of the joining area | region 51, the corrosion in the edge part of the joining area | region 51 of the external electrode plate 5 and the laminated body 4 is suppressed.

  Further, the cool air by the outside air is cut off, and the atmosphere around the end portion of the bonding region 51 becomes close to the heat transmitted from the laminated body 4, so that the cold air is not directly applied, so the bonding region 51 between the external electrode plate 5 and the laminated body 4. Corrosion at the end of the is suppressed. Therefore, it is possible to obtain a multilayered piezoelectric element excellent in long-term durability in which a decrease in displacement is suppressed even when driven for a long time.

  In the figure, the configuration in which one first bent portion 52a is provided on the external electrode plate 5 is shown. However, the configuration is not limited to this configuration, and a plurality of first bent portions 52a may be provided. Good.

  Here, when viewed in a vertical cross section perpendicular to the side surface (side surface of the multilayer body 4) to which the external electrode plate 5 is bonded, the extended region 52 is provided with a second bent portion 52b that protrudes outward. It is preferable that at least a pair of the first bent portion 52a and the second bent portion 52b are provided so as to be adjacent to each other. According to this configuration, it is possible to obtain an effect of mitigating against a force to swell outward (force to peel off the external electrode plate 5) and a force to flex inward, and is more durable. A laminated piezoelectric element can be obtained.

  In addition, as a structure provided so that a pair of 1st bending part 52a and the 2nd bending part 52b may adjoin, the 1st bending part 52a is near the laminated body 4 as shown in FIG. An arrangement in which the second bent portion 52b is arranged on the side close to the laminate 4 as shown in FIG.

  The pair of the first bent portion 52a and the second bent portion 52b adjacent to each other is effective in at least one pair, but it is preferable that there are a plurality of pairs. The stress acting in the peeling direction can be dispersed and reduced at a plurality of locations.

  In the above configuration, when the adjacent first bent portion 52a and second bent portion 52b are viewed in a longitudinal section, the peak of the first bent portion 52a and the peak of the second bent portion 52b are connected. It is preferable that the midpoint of the line segment is not located on the extension of the joining region with the laminated body 4, whereby abnormal vibration due to resonance at high frequency is suppressed, and the laminated piezoelectric element having excellent durability Is obtained.

  Further, when the adjacent first bent portion 52a and the second bent portion 52b are viewed in a longitudinal section, the line segment connecting the peak of the first bent portion 52a and the peak of the second bent portion 52b. The point may be located on the inner side of the extension of the joining region 51 with the laminated body 4, and thereby, a force to swell outward (force to peel off the external electrode plate 5). It can be further reduced.

  The first bent portion 52a and the second bent portion 52b may be bent into a bent shape, but preferably have a bent shape as shown in the figure, thereby avoiding stress concentration. it can.

  In particular, when the adjacent first bent portion 52a and second bent portion 52b are viewed in the longitudinal section, the radius of curvature at the peak of the first bent portion 52a and the radius of curvature at the peak of the second bent portion 52b. Are preferably different from each other. As a result, the bending methods of the respective bent portions are different from each other, so that resonance does not occur and vibration can be reduced.

Further, when the adjacent first bent portion 52a and second bent portion 52b are viewed in a longitudinal section, the radius of curvature at the peak of the first bent portion 52a is larger than the radius of curvature at the peak of the second bent portion 52b. In addition to the effect of reducing resonance and reducing vibration, the force to swell outward (force to peel off the external electrode plate 5) is preferable.
The effect of reducing can also be obtained.

  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. Furthermore, after laminating a plurality of ceramic green sheets printed with this conductive paste and performing a binder removal treatment at a predetermined temperature, firing at a temperature of 900 to 1200 ° C., 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, if necessary, 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 laminated in the pattern of the conductor layer 6. After the surface of 4 is printed by a screen printing method or the like and dried, a baking process is performed at a temperature of 650 to 750 ° C. to form the conductor layer 6.

  Next, the external electrode plate 5 is connected and fixed to the surface of the conductor layer 6 through the conductive bonding material 7.

  The conductive bonding material 7 uses an adhesive made of an epoxy resin or a polyimide resin containing a highly conductive metal powder such as Ag powder or Cu powder, solder, etc., and has a predetermined thickness and width by screen printing or dispensing method. It can be formed in a controlled manner.

  The external electrode plate 5 is made of a metal flat plate such as copper, iron, stainless steel, phosphor bronze, 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. Here, the first bent portion 52a and the second bent portion 52b are provided at the distal end portion of the external electrode plate 5, and the first bent portion 52a and the second bent portion 52b are formed by, for example, a punching die. Thus, the external electrode plate 5 can be punched and simultaneously formed using a bending mold having the shape of the first bent portion 52a and the second bent portion 52b.

  After that, by applying a DC electric field of 0.1 to 3 kV / mm to the external electrode plates 5 respectively connected to the pair of conductor layers 6 to polarize the piezoelectric layer 2 constituting the multilayer body 4, the multilayer piezoelectric element 1 is completed. The multilayer piezoelectric element 1 connects each conductor layer 6 to an external power source via an external electrode plate 5 and applies a voltage to the piezoelectric layer 2, thereby causing each piezoelectric layer 2 to have a reverse piezoelectric effect. It can be displaced greatly. This makes it possible to function as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  Next, the example of embodiment of the injection device of the present invention is explained. FIG. 6 is a schematic cross-sectional view showing an example of an embodiment of the injection device of the present invention.

  As shown in FIG. 6, 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. .

  A needle valve 25 that can open and close the injection hole 21 is provided in the storage container 23. A fluid passage 27 is disposed in the injection hole 21 so as to be able to communicate with the movement of the needle valve 25. The fluid passage 27 is connected to an external fluid supply source, and fluid is constantly supplied to the fluid passage 27 at a high pressure. Accordingly, 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 multilayer 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.

  In addition, the ejection device 19 according to the present embodiment includes a container 23 having ejection holes and the multilayer piezoelectric element 1 according to the present embodiment, and the fluid filled in the container 23 is driven to drive the multilayer piezoelectric element 1. May be configured to discharge from the injection hole 21. That is, the multilayer piezoelectric element 1 does not necessarily need to be inside the container 23, and may be 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 ejection 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 according to the present embodiment, the flow rate and ejection timing of the fluid 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, the example of embodiment of the fuel-injection system of this invention is demonstrated. FIG. 7 is a schematic view showing an example of an embodiment of the fuel injection system of the present invention.

  As shown in FIG. 7, 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 condition 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. As described above, the ejection device 19 ejects a certain fluid from the ejection holes 21 to the outside or an adjacent container. For example, when the target for injecting and supplying fuel is an engine, high-pressure fuel is injected from the injection hole 21 into the combustion chamber of the engine in a mist form.

  Note that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present 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 laminated piezoelectric element 1 of 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 a calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) having an average particle diameter 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. Further, a total of 15 ceramic green sheets not printed with the conductive paste serving as the internal electrode layer were laminated on the top and bottom of the 200 ceramic green sheets printed with the conductive paste serving as the internal electrode layer. . And it fired at 980-1100 degreeC, it ground to the predetermined shape using the surface grinder, and obtained the laminated body whose end surface is 5 mm square.

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

  Next, a conductive 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 the external electrode plate was connected and fixed parallel to the surface of the laminate.

  Here, as an example of the present invention, a multilayer piezoelectric element of Sample 1 was manufactured using an external electrode plate having a longitudinal section of 100 μm and a width of 1.2 mm shown in FIG. Specifically, the distance L1 shown in the figure was 5 mm.

  As a comparative example, a multilayer piezoelectric element of Sample 2 was manufactured using an external electrode plate having a vertical cross section shown in FIG. 8 and having a thickness of 100 μm and a width of 1.2 mm. Specifically, the distance L2 shown in the figure was 5 mm.

  As a comparative example, a laminated piezoelectric element of Sample 3 was also manufactured using an external electrode plate having a longitudinal section shown in FIG. 9 and having a thickness of 100 μm and a width of 1.2 mm. This has a shape extending from the end face of the laminated body in the laminating direction and extending straight in this direction, and the distance L3 shown in the figure is also 5 mm.

  These laminated piezoelectric elements were subjected to a polarization treatment by applying a DC electric field of 3 kV / mm to the external electrodes for 15 minutes via a lead member welded to the external electrode plate. 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.

  After that, for each sample, under a test environment at a temperature of 25 ° C. and a humidity of 60%, 50 cycles of a cooling cycle that was driven for 1 hour with a sine waveform with a frequency of 150 Hz and stopped for 1 hour was performed.

  As a result, the decrease rate of the displacement amount of Sample 1 after continuous operation was 1%. Sample 2 had a displacement reduction rate of 5%. Sample 3 has a displacement reduction rate of 10%.

  Moreover, since the moisture by the dew condensation which generate | occur | produces during a drive stop does not apply to the edge part of a joining area | region, the sample 1 suppressed the corrosion of the edge part of a joining area | region by a water | moisture content, and suppressed the fall rate of the displacement amount low. On the other hand, in Sample 2 and Sample 3, moisture due to condensation that occurs while the drive is stopped is transmitted to the end of the joining region, which corrodes, decreases in conductivity, and increases the rate of displacement reduction. . In particular, since the sample 3 was straight and moisture was easily transferred, corrosion progressed and the rate of decrease was the largest.

  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 ... External electrode plate 51 ... Bonding region 52 ... Extension region 52a .... First bent part 52b ... Second bent part 6 ... Conductive layer 7 ... Conductive bonding material 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 (10)

Including a laminate in which a piezoelectric layer and an internal electrode layer are laminated, and an external electrode plate joined to a side surface of the laminate,
The external electrode plate has an extension region extending in the stacking direction from one end of the laminate, and the extension is seen in a vertical cross section perpendicular to the side surface to which the external electrode plate is joined. The protruding region is provided with a first bent portion that protrudes inward, and the peak of the first bent portion is located on the inner side of the extension of the bonding region with the laminate. A laminated piezoelectric element.   When viewed in a vertical cross section perpendicular to the side surface to which the external electrode plate is bonded, the extension region is provided with a second bent portion that protrudes outward, and the first bent portion and the first bent portion are provided. 2. The multilayer piezoelectric element according to claim 1, wherein at least one pair is provided so that the two bent portions are adjacent to each other.   The midpoint of the line segment connecting the peak of the first bent portion and the peak of the second bent portion when the adjacent first bent portion and the second bent portion are viewed in the longitudinal section. The laminated piezoelectric element according to claim 1, wherein the laminated piezoelectric element is not positioned on an extension of a bonding region with the laminated body.   The midpoint of the line segment connecting the peak of the first bent portion and the peak of the second bent portion when the adjacent first bent portion and the second bent portion are viewed in the longitudinal section. The laminated piezoelectric element according to claim 1, wherein the laminated piezoelectric element is located on an inner side than an extension of a bonding region with the laminated body.   The multilayer piezoelectric element according to claim 1, wherein the first bent portion and the second bent portion are curved.   When the adjacent first bent portion and second bent portion are viewed in the longitudinal section, the radius of curvature at the peak of the first bent portion and the radius of curvature at the peak of the second bent portion are: The multilayer piezoelectric element according to claim 1, wherein the stacked piezoelectric elements are different from each other.   When the adjacent first bent portion and the second bent portion are viewed in the longitudinal section, the radius of curvature at the peak of the first bent portion is larger than the radius of curvature at the peak of the second bent portion. The multilayer piezoelectric element according to claim 5, which is small.   The multilayer piezoelectric element according to any one of claims 1 to 7, wherein there are a plurality of pairs of the first bent portion and the second bent portion that are adjacent to each other.   A container having an injection hole and the multilayer piezoelectric element according to any one of claims 1 to 8, wherein the fluid stored in the container is driven by the multilayer piezoelectric element to form the injection hole. An ejection device characterized by being discharged from the nozzle.   A common rail for storing high-pressure fuel, the 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.

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