JP2012182164A - Multilayer piezoelectric element and piezoelectric actuator including the same, injector and fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a multilayer piezoelectric element including a ceramic coat layer in which migration due to progress of defects is suppressed; a piezoelectric actuator including the multilayer piezoelectric element; an injector; and a fuel injection system.SOLUTION: A multilayer piezoelectric element 1 includes: a laminate 4 which comprises a plurality of laminated layers of a piezoelectric layer 2 and an inner electrode 3 having a positive electrode and a negative electrode while a part of an end face of the inner electrode 3 reaches a side face; a pair of metallization layers 5 deposited on the side face of the laminate 4 so as to be electrically connected to the inner electrode 3; and a ceramic coat layer 6 deposited on the side face of the laminate 4 so as to cover the end face of the inner electrode 3 of both of the positive electrode and the negative electrode at a portion where at least the pair of metallization layers 5 are not present. The ceramic coat layer 6 has a plurality of voids.

Description

  The present invention relates to a laminated piezoelectric element used in, for example, a fuel injection device of an automobile engine, and a piezoelectric actuator, an injection device, and a fuel injection system including the same.

  As a multilayer piezoelectric element, a piezoelectric body layer and a plurality of internal electrodes having a positive electrode and a negative electrode are stacked, and a multilayer body in which a part of the end surface of the internal electrode reaches the side surface is electrically connected to the internal electrode. A pair of metallized layers deposited on the side surfaces of the laminate, and at least a portion where the pair of metallized layers does not exist, and was deposited on the side surfaces of the laminate so as to cover the end surfaces of both the positive electrode and the negative electrode. What contains the coat layer which consists of inorganic materials is known.

  When this multilayer piezoelectric element is used as a piezoelectric actuator, the multilayer body is used for the purpose of preventing contact damage from the outside to the multilayer body, adhesion due to adhesion of foreign matter, etc., and preventing creeping discharge between both electrodes of the internal electrode. It is known to deposit a coat layer made of an inorganic material on the side surface of the film (see, for example, Patent Document 1).

JP 2007-173842 A

  In recent years, multilayer piezoelectric elements have been required to ensure a large amount of displacement.

  Here, when the coat layer is made of ceramics, there is a possibility that a defect occurs in the crystal grain boundary due to displacement due to the driving of the multilayer piezoelectric element and the defect develops. When the defect progresses, migration occurs in the coat layer deposited on the end faces of both the positive electrode and the negative electrode through the defect in which the metal ions (for example, Ag ions) of the internal electrode have progressed. There is a possibility that the driving ability of the piezoelectric element is lowered.

  The present invention has been made in view of the above circumstances, and provides a laminated piezoelectric element including a ceramic coat layer in which migration due to the progress of defects is suppressed, and a piezoelectric actuator, an injection device, and a fuel injection system including the same. With the goal.

  The multilayer piezoelectric element of the present invention includes a multilayer body in which a plurality of piezoelectric layers and internal electrodes each having a positive electrode and a negative electrode are stacked, and a part of an end surface of the internal electrode reaches the side surface, A pair of metallized layers deposited on the side surfaces of the laminate so as to be connected to each other, and at least a portion where the pair of metallized layers does not exist so as to cover the end surfaces of both the positive electrode and the negative electrode A ceramic coat layer deposited on the side surface of the laminate, and the ceramic coat layer has a plurality of voids.

  The multilayer piezoelectric element of the present invention is characterized in that, in the above-described configuration, the plurality of voids are distributed in a biased manner toward the side surface.

The multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the plurality of voids are located on the side of the piezoelectric layer.

  In the multilayer piezoelectric element of the present invention, the plurality of voids are dispersed so as not to communicate with each other along the thickness direction of the ceramic coat layer.

  The multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the ceramic coat layer is made of a piezoelectric body.

  In addition, the multilayer piezoelectric element of the present invention is a piezoelectric actuator including a case that accommodates the multilayer piezoelectric element therein.

  Further, the present invention includes a container having an injection hole and a multilayer piezoelectric element, and 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, an 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.

  The multilayer piezoelectric element of the present invention has a plurality of voids provided inside the ceramic coat layer, so that the void absorbs stress due to expansion and contraction and vibration of the multilayer body, and the void stops the progress of grain boundary defects. As a result, grain boundary defects in the ceramic coat layer do not progress. As a result, migration is suppressed and stable driving can be performed for a long time.

It is a schematic perspective view which shows an example of embodiment of the lamination type piezoelectric element of this invention. It is the sectional view on the AA line of the lamination type piezoelectric element shown in FIG. It is a principal part expanded sectional view of an example of embodiment of the lamination type piezoelectric element of this invention. It is a principal part expanded sectional view of the other example of embodiment of the lamination type piezoelectric element of this invention. It is a schematic sectional drawing which shows an example of embodiment of the piezoelectric actuator of this invention. It is a schematic sectional drawing which shows an example of embodiment of the injection apparatus of this invention. It is the schematic which shows an example of embodiment of the fuel-injection system of this invention.

  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 schematic perspective view showing an example of an embodiment of a multilayer piezoelectric element of the present invention, and FIG. 2 is a cross-sectional view of the multilayer piezoelectric element shown in FIG.

  A laminated piezoelectric element 1 shown in FIG. 1 and FIG. 2 includes a laminated body 4 in which a plurality of piezoelectric layers 2 and internal electrodes 3 having positive and negative electrodes are laminated, and a part of the end face of the internal electrode 3 reaches the side surface. A pair of metallized layers 5 deposited on the side surfaces of the laminate 4 so as to be electrically connected to the internal electrodes 3, and both positive and negative internal electrodes at sites where at least the pair of metallized layers 5 are not present. 3, and a ceramic coat layer 6 deposited on the side surface of the laminate 4 so as to cover the end face of the laminate 3. The ceramic coat layer 6 has a plurality of voids 7.

The multilayer body 4 constituting the multilayer piezoelectric element 1 includes, for example, an active portion in which a plurality of piezoelectric layers 2 and internal electrodes 3 are alternately stacked, and piezoelectric layers 2 provided at both ends of the active portion in the stacking direction. It has an inactive portion, 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 1 to 100 mm, for example.

The piezoelectric layer 2 constituting the multilayer body 4 is formed of ceramics having piezoelectric characteristics, and as such ceramics, for example, perovskite type oxidation made of lead zirconate titanate (PZT: PbZrO ₃ -PbTiO ₃ ). For example, lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO ₃ ) can be used. The thickness of the piezoelectric layer 3 is, for example, 3 to 250 μm.

  The internal electrode 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 containing silver, silver-palladium alloy, silver-platinum, copper, or the like can be used. In the example shown in FIG. 1, part of the end faces of the positive electrode and negative electrode (or ground electrode) internal electrodes 3 reach a pair of opposing side surfaces of the stacked body 4 and are alternately led out to be provided on the side surfaces of the stacked body 4. The pair of metallized layers 5 are electrically connected. In addition, another part of the end faces of both the positive electrode and the negative electrode 3 reaches the side surface of the laminate 4 at a portion where the pair of metallized layers 5 do not exist. The thickness of the internal electrode 3 is, for example, 0.1 to 5 μm.

  In the laminate 4, for example, a conductor layer (porous layer) having a plurality of pores may be disposed instead of a part of the plurality of internal electrodes 3. Since this porous layer is lower in strength than the internal electrode 3 and easily cracks due to stress, the porous layer is destroyed by cracks or the like prior to the internal electrode 3 due to the stress generated in the laminate 4 when driven. As a result, the layer 4 functions as a layer that relieves stress.

The pair of metallized layers 5 provided on the side surfaces of the laminate 4 and electrically connected to the internal electrodes 3 are formed by applying and baking a paste made of silver and glass, for example. Are connected to the internal electrodes 3 that are alternately led to the opposite side surfaces of the laminate 4. The thickness of the metallized layer 5 is, for example, 5 to 500 μm. In FIG. 1, the width of the metallized layer 5 is narrower than the width of the surface on which the metallized layer 5 is formed, but these widths may be the same, for example, the shape of the laminate 4 When a hexagonal column or an octagonal column is used, it is preferable to form them with the same width.

A ceramic coat layer 6 is attached to the side surface of the laminate 4 so as to cover the end surfaces of both the positive electrode and the negative electrode 3 at a portion where at least the pair of metallized layers 5 do not exist. The ceramic coat layer 6 is formed to have a thickness of, for example, 5 to 30 μm in consideration of the effect as a protective layer and followability. Further, examples of the material for forming the ceramic coat layer 6 include oxides such as alumina, PLT ((Pb La) TiO ₃ ), and piezoelectric materials, and the same kind as the piezoelectric material constituting the piezoelectric layer 2 in particular. It is preferable to use a piezoelectric material such as PbZrO ₃ —PbTiO ₃ (PZT: lead zirconate titanate). By forming the ceramic coat layer 6 with a piezoelectric body (preferably a piezoelectric body of the same type as the piezoelectric body forming the piezoelectric layer 2), a leakage electric field from the internal electrode 3 (an electric field generated in a region not sandwiched between the electrodes) As a result, the ceramic coat layer 6 exhibits a piezoelectric effect, can be deformed following the expansion and contraction of the laminate 4, and the grain boundary defects of the ceramic coat layer 6 can be further suppressed.

The fact that the ceramic coat layer 6 is deposited on the side surface of the laminate 4 so as to cover the end surfaces of both the positive electrode and the negative electrode 3 at a portion where at least the pair of metallized layers 5 does not exist.
In addition to the part where the end faces of both the positive and negative internal electrodes 3 reach the side surface of the laminate 4, it may be applied to the part where the end face of one of the positive and negative internal electrodes 3 reaches, Furthermore, it means that the metallized layer 5 may be applied up to the site. Specifically, in FIG. 1, the ceramic coat layer 6 is provided on the side surface where the end surfaces of both the positive electrode and the negative electrode 3 reach, but the metallized layer 5 is the side surface provided with the metallized layer 5. The ceramic coat layer 6 may be provided also on the portion where the end face of the internal electrode 3 on one side of the positive electrode or the negative electrode which is not covered with the metal coat layer 6 may be provided. Good.

  The ceramic coat layer 6 has a plurality of voids 7 as shown in FIG. The plurality of voids 7 have a diameter of, for example, 0.05 to 2 μm, and this value is included in an arbitrary line segment by observing the cross section of the ceramic coating layer 6 with an electron microscope such as a scanning electron microscope (SEM) or a metal microscope. The number of voids and the length of the line segment included in the void can be measured, and the total distance of the length of the line segment included in the void can be determined by dividing the total distance by the number of voids. Moreover, the area ratio which the some void 7 occupies in the arbitrary cross sections in the ceramic coat layer 6 is 5 to 60%, for example, and this value also observes a cross section with electron microscopes and metal microscopes, such as a scanning electron microscope (SEM). Can be determined by

  By having the plurality of voids 7 in the ceramic coat layer 6, the plurality of voids 7 absorb the stress due to expansion and contraction and vibration of the laminate 4. Further, the void releases the stress that the defect at the crystal grain boundary is about to develop, so that the void prevents the defect at the crystal grain boundary from developing and the defect does not progress. As a result, migration due to metal (Ag) ions is suppressed, and the multilayer piezoelectric element 1 can be driven stably for a long period of time.

  Here, as shown in FIG. 4, the plurality of voids 7 are preferably distributed unevenly toward the side surface of the laminate 4. Since the plurality of voids 7 are unevenly distributed on the side surface side of the stacked body 4 that is easily deformed by driving, stress can be absorbed more and migration can be suppressed. The plurality of voids 7 are not present on the surface side of the ceramic coat layer 6, and the present invention is not limited to the configuration in which the voids 7 are present only on the side surface of the laminate 4. It may be larger than the abundance ratio on the surface side. However, when there are no plural voids 7 on the surface side of the ceramic coat layer 6, metal ions may be used even when the voids 7 communicate with each other. Thus, it is possible to reliably prevent moisture from entering from the outside which accelerates the diffusion of water.

  Note that the plurality of voids 7 are distributed in the ceramic coat layer 6 so as to be biased toward the side surface of the multilayer body 4. This is because the cross section of the multilayer piezoelectric element 1 is measured with an electron microscope such as a scanning electron microscope (SEM). The number of metal particles included in the distance from the side surface of the laminate 4 in the ceramic coat layer 6 to one third of the thickness when observed with a metal microscope, and the thickness of the ceramic coat layer 6 from the surface side to 3 minutes. It can be determined by measuring the number of metal particles included in the distance up to 1 and confirming that there are many voids on the side surface of the laminate 4.

  The plurality of voids 7 are preferably located on the side of the piezoelectric layer 2 as shown in FIG. Since the piezoelectric layer 2 expands and contracts by driving the stacked piezoelectric element 1, the plurality of voids 7 are located on the side of the piezoelectric layer 2 that is most driven and deformed, so that stress can be absorbed effectively, and migration. Can be suppressed.

The plurality of voids 7 are preferably dispersed so as not to communicate with each other along the thickness direction of the ceramic coat layer 6. According to this structure, it can suppress that the water | moisture content in external air penetrate | invades into the several void 7, and can suppress that the spreading | diffusion of a metal ion is accelerated. Further, since the inner surface of the void 7 is negatively charged by oxygen vacancy ions caused by oxygen defects, a plurality of voids 7 are dispersed, so that metal ions (for example, Ag ions) are dispersed.
Becomes trapped by the void 7. Therefore, migration can be suppressed and the multilayer piezoelectric element 1 can be driven stably for a long period of time.

Then, a lead member 8 as shown in FIG. 5 is connected and fixed to the metallized layer 5 with solder, a conductive adhesive or the like, and a DC electric field of 0.1 to 3 kV / mm is applied from the lead member 8 to constitute the laminate 4. By polarizing the piezoelectric layer 2, the entire multilayer piezoelectric element 1 can be polarized.

  The laminated piezoelectric element 1 is formed by connecting a metallized layer 5 and an external power source via a lead member 8 as shown in FIG. 2 can be greatly displaced by the inverse piezoelectric effect. Although not shown in the drawing, an external electrode such as a flat plate shape or a wire mesh-like longitudinal cross-sectional shape is disposed on the metallized layer 5 so as to cover the metallized layer 5 via a conductive bonding material, and a lead member is provided on the external electrode. 8 may be joined.

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

First, a piezoelectric 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. Then, a piezoelectric ceramic green sheet is produced using this ceramic slurry by using a tape molding method such as a doctor blade method or 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 (PZT: PbZrO ₃ —PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, an internal electrode conductive paste to be the internal electrode 3 is prepared. Specifically, an internal electrode conductive paste is prepared by adding and mixing a binder and a plasticizer to a metal powder of a silver-palladium alloy. Note that silver powder and palladium powder may be mixed instead of the silver-palladium alloy.

  Next, the internal electrode conductive paste is applied to the piezoelectric ceramic green sheet in the pattern of the internal electrode 3 by, for example, a screen printing method.

  Next, a predetermined number of piezoelectric ceramic green sheets coated with the internal electrode conductive paste are laminated.

And after performing a binder removal process to this at predetermined | prescribed temperature, it bakes at the temperature of 900-1200 degreeC.

  Next, the laminated body obtained by firing is subjected to a grinding process on a side surface so as to have a predetermined shape using a surface grinder or the like. Thereby, the laminated body 4 in which the piezoelectric layers 2 and the internal electrodes 3 are alternately laminated is obtained.

Next, for example, after applying the ink for the ceramic coat layer for forming the ceramic coat layer 6 to the region where the end faces of both the positive electrode and the negative electrode 3 are exposed on the side surface of the laminate 4 by dipping or screen printing, 900 Baking at ˜1200 ° C. to form a ceramic coat layer on the side surface of the laminate 4. At this time, the ceramic coat layer ink is not applied to the formation surface of the metallized layer 5 or only the edge is applied. The ceramic powder contained in the ceramic coat layer ink is preferably a calcined powder of piezoelectric ceramic, and more preferably a ceramic powder having the same composition as that of the piezoelectric layer 2.

  The ink for the ceramic coat layer, for example, disperses the powder agglomeration by dispersing the ceramic powder in a solution of solvent, dispersant, plasticizer, and binder, and then passing the three rolls several times. At the same time, it is produced by dispersing the powder.

  In dipping, the exposed surface of both ends of the internal electrode 3 of the laminate 4 is dipped in the ink for the ceramic coat layer, pulled up, and dried to form a raw ceramic coat layer. The thickness of the ceramic coat layer can be controlled by controlling the viscosity and pulling speed of the ink.

  Further, in screen printing, the same size as the surface where both end faces of the internal electrode 3 of the laminate 4 are exposed, or a slightly larger mesh is formed to prepare a plate, and ink is placed on the plate. The raw ceramic coat layer is formed by printing the ceramic coat layer ink on the surface of the laminate 4 where both surfaces of the internal electrode 3 are exposed with a squeegee and drying. The thickness of the ceramic coat layer can be controlled by the viscosity of the ink for the ceramic coat layer, the thickness of the mesh, the moving speed of the squeegee, and the like.

  In order to form the void 7 in the ceramic coat layer 6, the ceramic coat layer ink in which the amount of binder such as acrylic or butyral which is easily voided is increased, or the acrylic beads having a predetermined size are added. What is necessary is just to produce the ink for coat layers. A ceramic coat layer ink having a large amount of binder has a lower density after printing than a normal ceramic coat layer ink, so that voids are easily formed during firing. Also, the ceramic coat layer ink mixed with acrylic beads forms voids when the acrylic beads are decomposed during firing.

  In order to provide the voids 7 in such a manner that the voids 7 are unevenly distributed on the side surface, for example, two types of inks for ceramic coat layers are prepared. A ceramic that is easy to form voids by making normal ink in the first type (first ink) and increasing the amount of binder in the second type (second ink) or adding acrylic beads of a predetermined size A coating layer ink is prepared. Then, the second ink may be applied to the first layer, the first ink may be applied to the second layer, and sintered.

  In order to provide a void on the side of the piezoelectric layer 2, for example, when the ceramic coat layer 6 is sintered, the vicinity of the internal electrode 3 may be sintered first. Becomes dense, the sides of the piezoelectric layer 2 become rough, and voids are provided. For example, in order to sinter the vicinity of the internal electrode 3 first, the ceramic coat layer 6 is held at a temperature lower by 100 to 200 ° C. than the temperature at which the ceramic coat layer 6 sinters for 1 to 5 hours, and then the ceramic coat layer 6 is sintered. What is necessary is just to raise temperature. By doing so, the components of the internal electrode 3 can diffuse into the ceramic coat layer 6 and the vicinity of the internal electrode 3 can be sintered first. As another method of providing a void on the side of the piezoelectric layer 2, the first ink is printed on the side of the internal electrode 3 and the vicinity thereof, and the second ink is printed on the other areas. May be.

  Sintering of the ceramic coat layer ink is performed by applying the ceramic coat layer ink to the raw laminate and then simultaneously firing it, or by applying the ceramic coat layer ink to the sintered laminate. After that, any of the methods of firing again is possible.

Thereafter, a pair of metallized layers 5 in which the internal electrodes 3 are electrically connected are formed on the side surfaces of the laminate 4. In this case, first, a silver glass-containing conductive paste is prepared by adding a binder to silver particles and glass powder, and this is printed on the side surface of the laminate 4 by a screen printing method.
A baking process is performed at a temperature of about 00 ° C. Thereby, the metallized layer 5 is formed, and the laminated piezoelectric element 1 is completed.

The lead member 8 is connected and fixed to the pair of metallized layers 5 with solder, conductive adhesive or the like, and then a direct current electric field of 0.1 to 3 kV / mm is applied from the lead members 8 respectively connected to the pair of metallized layers 5. When the piezoelectric layer 2 constituting the multilayer body 4 is polarized, the entire multilayer piezoelectric element 1 is polarized. The multilayer piezoelectric element 1 connects the metallized layer 5 and an external power source via a lead member 8 and applies a driving voltage to the piezoelectric layer 2, thereby causing each piezoelectric layer 2 to have an inverse piezoelectric effect. It can be displaced greatly.

  The laminated piezoelectric element of the present embodiment is used as, for example, a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precision positioning device such as an optical device, or the like.

  Next, an example of an embodiment of the piezoelectric actuator of the present invention will be described.

  FIG. 5 is a schematic sectional view showing an example of the embodiment of the piezoelectric actuator of the present invention. The piezoelectric actuator 11 of the example shown in FIG. 5 is obtained by housing the multilayer piezoelectric element 1 in a case 13. .

  Specifically, the case 13 includes a case main body 15 whose upper end is closed and whose lower end is open, and a lid member 17 attached to the case main body 15 so as to close the opening of the case main body 15. The laminated piezoelectric element 1 is enclosed and accommodated in the case 13 together with, for example, an inert gas so that both end faces of the element 1 are brought into contact with the upper and lower inner walls of the case 13, respectively.

  The case body 15 and the lid member 17 are made of a metal material such as SUS304 or SUS316L.

  The case main body 15 is a cylindrical body whose upper end is closed and whose lower end is opened, and has, for example, a bellows (bellows) shape so as to be extendable in the stacking direction of the stack 4. The lid member 17 is formed, for example, in a plate shape so as to close the opening of the case body 15, and is welded to the case body 15 at the lower end by laser welding or the like. The lid member 17 has two through holes into which the lead member 8 can be inserted. The lead member 8 is inserted into the through hole to electrically connect the metallized layer 5 to the outside. The gap between the through holes is filled with soft glass or the like to fix the lead member 8 and prevent intrusion of outside air.

  According to the piezoelectric actuator 11 of this example, it can be driven stably for a long period of time.

  Next, the example of embodiment of the injection device of the present invention is explained.

  FIG. 6 is a schematic sectional view showing an example of the embodiment of the injection device of the present invention. The injection device 19 of the example shown in FIG. 6 is disposed inside a storage container (container) 23 having an injection hole 21 at one end. The laminated piezoelectric element 1 of the above example is accommodated.

  A needle valve 25 that can open and close the injection hole 21 is disposed in the storage container 23. 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 the outside or an adjacent container, for example, a fuel chamber (not shown) of the internal combustion engine. It is configured.

  The upper end of the needle valve 25 has a large inner diameter, and is a piston 31 that can slide 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 of this example includes a container 23 having an injection hole 21 and the multilayer piezoelectric element 1 of the above example, and the fluid filled in the container 23 is ejected by driving the multilayer piezoelectric element 1. It may be configured to discharge from the 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 ejection device 19 of this example, the fluid includes various liquids and gases such as a conductive paste in addition to fuel, ink, and the like. By using the ejection device 19 of this example, 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 this example that employs the multilayer piezoelectric element 1 of the above example is used for an internal combustion engine, the fuel is accurately injected into the combustion chamber of the internal combustion engine such as an engine over a longer period than the conventional injection device. Can be made.

  Next, the example of embodiment of the fuel-injection system of this invention is demonstrated.

  FIG. 7 is a schematic diagram showing an example of an embodiment of the fuel injection system of the present invention. The fuel injection system 35 shown in FIG. 7 includes a common rail 37 that stores high-pressure fuel as a high-pressure fluid, and the common rail 37. A plurality of the injection devices 19 in the above example for injecting the high-pressure fluid stored in the pressure, a pressure pump 39 for supplying the high-pressure fluid to the common rail 37, and an injection control unit 41 for supplying a drive signal to the injection device 19. .

  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 fuel injection system 35 of this example 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 about 1000 to 2000 atmospheres (about 101 MPa to about 203 MPa), preferably about 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.

  According to the fuel injection system 35 of this example, desired injection of high-pressure fuel can be stably performed over a long period of time.

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 metallized layer 5 in the multilayer piezoelectric element 1 is formed on each of two opposing side surfaces of the multilayer body 4 in the above example, but the two metallized layers 5 are formed on adjacent side surfaces of the multilayer body 4. Alternatively, they may be formed on the same side surface of the laminate 4. Moreover, the cross-sectional shape in the direction orthogonal to the stacking direction of the stacked body 4 is not limited to the quadrangular shape which is 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 this example 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 piezoelectric circuit element include a piezoelectric gyro, a piezoelectric switch, a piezoelectric transformer, and a piezoelectric breaker.

  A piezoelectric actuator comprising the multilayer piezoelectric element of the present invention was produced as follows.

First, a ceramic slurry is 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. A ceramic green sheet to be a piezoelectric layer having a thickness of 150 μm was produced.

On one side of this ceramic green sheet, a ceramic green sheet obtained by printing a conductive paste to be an internal electrode made by adding a binder to a silver-palladium alloy (95% by mass of silver—5% by weight of palladium) by screen printing is used. Sheets were laminated to produce a laminated molded body.

Next, a piezoelectric ceramic green sheet 300 printed with a conductive paste to be an internal electrode
A total of 15 piezoelectric ceramic green sheets on which conductive paste to be internal electrodes are not printed are laminated on the upper and lower layers with the sheet as the center.

Next, after cutting the laminated molded body with a dicing saw machine so as to have a predetermined size, the laminated molded body was dried and fired to produce a laminated body. Firing was carried out at 1000 ° C. for 200 minutes after holding the temperature of 800 ° C. for 90 minutes. The laminate has a rectangular parallelepiped shape, and its size is 5 m at the end face.
m, width 5 mm, and height 40 mm. After firing, the laminate was flattened, and then the laminate was washed with acetone and dried. Thereafter, the laminate was heat-treated at 750 ° C. for 120 minutes.

Next, an ink for a ceramic coating layer is prepared by adding a butyral binder and a dibutyl phthalate plasticizer to lead zirconate titanate, and the amount of binder in the first layer is 100 parts by weight of lead zirconate titanate. The ceramic coating layer ink added by 75 parts by mass
Printed on the side of the laminate where both electrodes of the internal electrode are exposed by screen printing so that the thickness is 10μm, and the second layer has a binder amount of 50 mass by external addition to 100 parts by mass of lead zirconate titanate. The ceramic coat layer ink added in part was printed on the first layer on the side of the laminate where both electrodes of the internal electrode layer were exposed. Thereafter, firing was performed at 1000 ° C. to form a ceramic coat layer having a plurality of voids distributed unevenly on the side surface side of the laminate.

Next, silver glass paste prepared by adding glass, binder and plasticizer to silver powder is printed on the side of the laminate with the pattern of metallized layer, dried and baked at 700 ° C,
A metallized layer was formed. Then, an external electrode was formed on the metallized layer and connected and fixed to the lead member using solder.

  By the above method, a laminated piezoelectric element as an example of the present invention was produced.

  As a comparative example, a laminated piezoelectric element provided with a ceramic coat layer formed of the above-mentioned second layer material as a coating layer was produced.

  Then, the two lead pins of these laminated piezoelectric elements were connected, and a 3 kV / mm direct current electric field was applied for 15 minutes for polarization treatment, thereby producing the piezoelectric actuator of the embodiment of the present invention and the piezoelectric actuator of the comparative example. .

When a DC voltage of 170 V was applied to the manufactured piezoelectric actuator, displacement amounts were obtained in the stacking direction in all piezoelectric actuators.

Furthermore, a high-temperature continuous drive test was continuously performed on these piezoelectric actuators under a 150 ° C. environment in which a DC voltage of 250 V was continuously applied.

  As a result, the piezoelectric actuator of the embodiment of the present invention showed no abnormality in the ceramic coat layer after the high temperature continuous driving test after 2000 hours.

On the other hand, the operation of the comparative piezoelectric actuator stopped after 153 hours of continuous driving. When the failure source of the piezoelectric actuator of the comparative example was confirmed, a grain boundary defect was generated in the ceramic coat layer, and migration occurred from the progressed portion of the defect, and the spark was stopped.

  From the above, it can be seen that the multilayer piezoelectric element of the present invention can suppress the development of grain boundary defects in the ceramic coat layer by the void absorbing stress due to expansion and contraction and vibration of the multilayer body.

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 2 ... Piezoelectric layer 3 ... Internal electrode 4 ... Laminated body 5 ... Metallized layer 6 ... Ceramic coat layer 7 ... Void 8 ... Lead Element
11 ... Piezoelectric actuator
13 ... Case
15 ... Case body
17 ... Cover member
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 (8)

  A laminated body in which a plurality of piezoelectric layers and internal electrodes having a positive electrode and a negative electrode are laminated, and a part of an end surface of the internal electrode reaches the side surface, and the laminated body so as to be electrically connected to the internal electrodes A pair of metallized layers deposited on the side surfaces of the laminate, and at least a portion where the pair of metallized layers does not exist, and are deposited on the side surfaces of the laminated body so as to cover the end surfaces of both the positive electrode and the negative electrode. And a ceramic coat layer, wherein the ceramic coat layer has a plurality of voids.   The multilayer piezoelectric element according to claim 1, wherein the plurality of voids are unevenly distributed toward the side surface.   The multilayer piezoelectric element according to claim 1, wherein the plurality of voids are located on a side of the piezoelectric layer.   The multilayer piezoelectric element according to claim 1, wherein the plurality of voids are dispersed so as not to communicate with each other along a thickness direction of the ceramic coat layer.   The multilayer piezoelectric element according to claim 1, wherein the ceramic coat layer is made of a piezoelectric body.   A piezoelectric actuator comprising: the multilayer piezoelectric element according to claim 1; and a case for housing the multilayer piezoelectric element therein.   A container having an injection hole and the multilayer piezoelectric element according to claim 1, wherein fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. Injection device.   A common rail for storing high-pressure fuel, an injection device according to claim 7 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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