JP6196134B2 - Multilayer piezoelectric element, injection device including the same, and fuel injection system - Google Patents

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 shown in FIG. 7, a multilayer piezoelectric element includes an active portion 93 in which a piezoelectric layer 91 and an internal electrode layer 92 are stacked, and an inactive portion 94 disposed at both ends of the active portion 93 in the stacking direction. Body 90, conductive bonding material 95 provided on the side surface of laminated body 90 from active portion 93 to inactive portion 94, and flat external electrode attached to the side surface of laminated body 90 via conductive bonding material 95 A configuration including a plate 96 is known. (See Patent Document 1).

JP 2005-223014 A

  Here, in the configuration of the multilayer piezoelectric element described in Patent Document 1, a crack generated in the internal electrode layer 92 develops inside the conductive bonding material 95 during driving, and the inside of the conductive bonding material 95 passes through the inside. There was a risk of spreading in a mesh shape. And when a crack spreads like this in the shape of a mesh, there is a possibility that the conductive bonding material becomes poor in conduction and sparks and cannot be driven.

  Further, even in the injection device and the fuel injection system provided with such a multilayer piezoelectric element, there is a possibility that the conductive bonding material in the multilayer piezoelectric element becomes poor in conduction, so that it cannot be stably driven for a long time. .

  The present invention has been devised in view of the above-mentioned problems, and its purpose is to suppress a network-like crack spreading inside a conductive bonding material, and to provide a laminated piezoelectric element that ensures conduction An injection device and a fuel injection system are provided.

The multilayer piezoelectric element of the present invention includes a laminate in which a piezoelectric layer and an internal electrode layer are laminated, an external electrode plate joined to a side surface of the laminate and electrically connected to the internal electrode layer, A conductive bonding material layer that joins an external electrode plate to a side surface of the laminate and electrically connects the internal electrode layer and the external electrode plate; when viewed in cross section perpendicular to the side of, the thickness of the conductive bonding material layer is a thinner than the thickness of the outer electrode plate is provided wherein a gap leading to the outside electrode plate from the side surface of the laminate The conductive bonding material layer has a void .

  In the multilayer piezoelectric element of the present invention, in the above configuration, when the conductive bonding material layer is viewed in a cross section perpendicular to the side surface of the stacked body, the gap is at least of the conductive bonding material layer. It is also characterized by being at one end.

  In the multilayer piezoelectric element of the present invention, in the above configuration, when the conductive bonding material layer is viewed in a cross section perpendicular to the side surface of the stacked body, the voids are at both ends of the conductive bonding material layer. It is also characterized by that.

  In the multilayer piezoelectric element of the present invention, a void is present in the conductive bonding material layer in the above configuration.

  In the multilayer piezoelectric element of the present invention, in the above configuration, an easily breakable layer having a structure in which cracks are more likely to occur in the multilayer body than the piezoelectric layer and the internal electrode layer due to expansion and contraction of the multilayer body. And the void is located at a position corresponding to the easily breakable layer.

  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.

  According to the multi-layer piezoelectric element of the present invention, since the thickness of the conductive bonding material layer is thinner than that of the external electrode plate, the stress applied to the conductive bonding material layer immediately after the start of driving increases, and the conductive bonding material layer In this case, the speed of crack growth is increased, and straight cracks immediately enter the thickness direction. Then, since the straight crack is immediately generated in the conductive bonding material layer, the stress applied to the conductive bonding material layer is released, and on the contrary, the stress is relaxed immediately after driving.

  Furthermore, since there is a gap between the external electrode plate and the laminate, it is possible to suppress cracks that enter a network.

  Therefore, the occurrence rate of sparks is reduced and the durability is excellent.

  Moreover, according to the injection device and the fuel injection system provided with the above-described multilayer piezoelectric element, the multilayer piezoelectric element has excellent durability, and can be driven stably for a long period of time.

(A) is a schematic longitudinal cross-sectional view which shows an example of embodiment of the laminated piezoelectric element of this invention, (b) is a figure which shows an example of the cross section cut | disconnected by the AA line shown to (a). . It is a figure which shows the other example of the cross section cut | disconnected by the AA line shown to Fig.1 (a). It is a figure which shows the other example of the cross section cut | disconnected by the AA line shown to Fig.1 (a). It is a figure which shows the other example of the cross section cut | disconnected by the AA line shown to Fig.1 (a). 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. (A) is a schematic longitudinal cross-sectional view which shows an example of embodiment of the conventional lamination type piezoelectric element, (b) is a figure which shows an example of the cross section cut | disconnected by the AA line | wire shown to (a).

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

  FIG. 1A is a schematic longitudinal sectional view showing an example of an embodiment of the multilayer piezoelectric element of the present invention, and FIG. 1B is an example of a cross section taken along line AA shown in FIG. FIG.

  A laminated piezoelectric element 1 shown in FIG. 1 includes a laminated body 10 in which a piezoelectric layer 11 and an internal electrode layer 12 are laminated, and an external part joined to the side surface of the laminated body 10 and electrically connected to the internal electrode layer 12. An electrode plate 2 and a conductive bonding material layer 3 for bonding the external electrode plate 2 to the side surface of the laminate 10 and electrically connecting the internal electrode layer 12 and the external electrode plate 2, When the material layer 3 is viewed in a cross section perpendicular to the side surface of the laminate 10, the thickness of the conductive bonding material layer 3 is smaller than the thickness of the external electrode plate 2, and from the side surface of the laminate 10 to the external electrode plate 2. There is an air gap leading to it.

  A laminated body 10 constituting the laminated piezoelectric element 1 includes an active part 13 in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are laminated, and both ends in the lamination direction of the laminated body 1 positioned outside the active part 13. The laminated body 10 having the inactive portion 14 composed of the provided piezoelectric layer 11 has, for example, 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. Is formed.

The piezoelectric layer 11 constituting the laminated body 10 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 11 is, for example, 3 to 250 μm.

  The internal electrode layer 12 constituting the multilayer body 10 is formed by simultaneous firing with the ceramic forming the piezoelectric layer 2, and is alternately stacked with the piezoelectric layers 11 to sandwich the piezoelectric layers 11 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 11 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 alternately led out to a pair of opposite side surfaces of the stacked body 10, and a pair of conductive bonding material layers 3 provided on the side surfaces of the stacked body 10. And are electrically connected. The internal electrode layer 12 has a thickness of 0.1 to 5 μm, for example.

  As shown in FIG. 1A, the active portion 13 may be provided with an easy fracture layer 15 in addition to the piezoelectric layer 11 and the internal electrode layer 12. Here, the easy fracture layer 15 is a porous layer made of, for example, the same conductive material as that of the internal electrode layer 12 and formed such that the conductive material is scattered independently of each other. The easy rupture layer 15 is more easily ruptured than the piezoelectric layer 11 and the internal electrode layer 12, and this portion is intentionally generated when a crack is generated in the multilayer body 10 by driving the multilayer piezoelectric element 1 over a long period of time. Thus, cracks are generated in the inner electrode layer 12 so as not to hinder driving due to the breakage of the internal electrode layer 12.

  In addition, the external electrode plate 2 is bonded to the side surface of the laminate 10 via the conductive bonding material layer 3 and is electrically connected to the internal electrode layer 12. Specifically, the external electrode plates 2 are respectively provided on opposite side surfaces of the multilayer body 10 and are electrically connected to the internal electrode layer 12 by the conductive bonding material layer 3, and a part thereof is laminated. It extends in the stacking direction from one end face of the body 6. The pair of external electrode plates 2 is made of a metal flat plate such as copper, iron, stainless steel, phosphor bronze, etc., for example, having a width of 0.5 to 10 mm and a thickness greater than that of the conductive bonding material layer 3, for example, 0.1 The one formed to be -0.3 mm is used. The external electrode plate 2 is processed not only into a plate-shaped metal plate but also into, for example, a shape having a slit in the width direction or a mesh shape in order to obtain an effect of relieving stress caused by expansion and contraction of the laminate 1. A metal plate or the like can also be used.

The conductive bonding material layer 3 is provided from the active portion 13 to the inactive portion 14 on the opposite side surfaces of the multilayer body 10, and the end portion of the internal electrode layer 12 led to the side surface of the multilayer body 10 and the external electrode plate 2. And are electrically connected. The pair of conductive bonding material layers 3 are 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.

  Here, when the conductive bonding material layer 3 is viewed in a cross section perpendicular to the side surface of the laminated body 10, the thickness of the conductive bonding material layer 3 is thinner than the external electrode plate 2, for example, 5 of the external electrode plate 2. It is formed to a thickness of ˜70%, specifically, a thickness of 5 to 70 μm.

  For example, as shown in FIG. 1B, the conductive bonding material layer 3 has a side surface of the laminated body 10 when the conductive bonding material layer 3 is viewed in a cross section perpendicular to the side surface of the laminated body 10. To the external electrode plate 2 is provided. In addition, seeing the conductive bonding material layer 3 in a cross section perpendicular to the side surface of the laminate 10 means that the cross section of the conductive bonding material layer 3 is viewed from the stacking direction (vertical direction in FIG. 1A). To do.

  The gap 4 is provided in the conductive bonding material layer 3 so as to extend in the stacking direction, and when the conductive bonding material layer 3 is viewed in a cross section perpendicular to the side surface of the stacked body 10. As shown in FIG. 1, the conductive bonding material layers 3 are arranged on both sides of the gap 4. The width L1 of the gap 4 provided inside the conductive bonding material layer 3 is set to a length of 2 to 40% of the width L2 of the external electrode plate 2, for example.

  Thus, by making the thickness of the conductive bonding material layer 3 thinner than that of the external electrode plate 2, the stress applied to the conductive bonding material layer 3 immediately after the start of driving increases, and cracks in the conductive bonding material layer 3 occur. The rate of progress of the cracks increases, and straight cracks immediately enter the thickness direction. Then, since the straight crack is immediately generated in the conductive bonding material layer 3, the stress applied to the conductive bonding material layer 3 is released, and the stress is relaxed after the driving. Furthermore, since there is a gap between the external electrode plate 2 and the laminated body 10, cracks that enter a mesh shape can be suppressed. Therefore, the occurrence rate of sparks is reduced, and a laminated piezoelectric element having excellent durability can be obtained.

  As shown in FIG. 2, it is desirable that the gap 4 is also present at one end of the conductive bonding material layer 3 when the conductive bonding material layer 3 is viewed in a cross section perpendicular to the side surface of the laminate 10. A large stress is applied at the portion between the widthwise end of the external electrode plate 2 and the laminated body 10, but the gap 4 is applied to the conductive bonding material layer 3 because the gap 4 is at one end of the conductive bonding material layer 3. Stress is more relaxed and durability is improved.

  Furthermore, as shown in FIG. 3, when the conductive bonding material layer 3 is viewed in a cross section perpendicular to the side surface of the laminated body 10, it is desirable that the voids 4 are also present at both ends of the conductive bonding material layer 3. By having the gap 4 at both ends, the stress applied to the conductive bonding material layer 3 is further relaxed and the durability is further improved.

  The width L3 of the gap 4 provided at one end of the conductive bonding material layer 3 and the width L4 of the gap 4 provided at both ends of the conductive bonding material layer 3 are 2 to 20% of the width L2 of the external electrode plate 2. Set to the length of

Further, as shown in FIG. 4, it is desirable that a void 31 is present in the conductive bonding material layer 3. Note that the voids 31 mentioned here do not extend in the laminating direction of the conductive bonding material layer 3 while the voids 4 are provided extending in the laminating direction. The layer 3 is, for example, approximately spherical in size so as not to penetrate in the thickness direction of the layer 3. It is desirable that such voids 31 are appropriately dispersed in the conductive bonding material layer 3. Since the void 31 is present in the conductive bonding material layer 3, the stress applied to the conductive bonding material layer 3 is further relaxed, so that the durability is further improved. The void diameter when the void 31 is spherical is, for example, 1 to 15 μm, and the void 3 with respect to the entire area when the conductive bonding material layer 3 is viewed in a cross section.
The area ratio of 1 is preferably 20% or less from the viewpoint of relaxing stress while maintaining electrical conductivity.

  The void 31 may be provided in any part of the conductive bonding material layer 3 in the stacking direction. However, as shown in FIG. When the easily breakable layer 15 having a structure in which cracks are more likely to occur than the internal electrode layer 12 is provided, the void 31 is desirably located at a position corresponding to the easily breakable layer 15. Since the void 31 in the conductive bonding material layer 3 is in a position corresponding to the easy breakage layer 15, the crack that has developed from the easy breakage layer 15 stops at the void 31, and the conductive bonding material layer 3 Since the number of cracks can be reduced, durability is further improved.

  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 11 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 12 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 12 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 The active part 13 provided with the piezoelectric body layers 11 and the internal electrode layers 12 that are alternately laminated is manufactured by performing a grinding process so as to have a shape. The inactive portion 14 is produced by laminating sheets that are not coated with the conductive paste that becomes the internal electrode layer 12. The laminated body 10 is manufactured by combining the active part 13 and the inactive part 14.

  Here, when providing the easy fracture layer 15, the conductive paste used as the easy fracture layer 15 is produced. The conductive paste to be the easily breakable layer 15 is produced by adding and mixing a binder and a plasticizer to a metal powder of silver-palladium alloy in the same manner as the conductive paste to be the internal electrode layer 12. At this time, the adhesion strength can be made lower than that of the internal electrode layer by mixing a resinous bead in the binder or changing the ratio of the silver-palladium alloy. This conductive paste is applied onto the above ceramic green sheet using a screen printing method. What is necessary is just to arrange | position to the desired position, when manufacturing the laminated body 10 with the ceramic green sheet on which this electrically conductive paste was printed.

  The laminate 10 is not limited to the one produced by the above manufacturing method, and any laminate 10 can be produced as long as the laminate 10 formed by laminating a plurality of piezoelectric layers 11 and internal electrode layers 12 can be produced. It may be produced by a manufacturing method.

  Next, the external electrode plate 2 is connected to the side surface of the laminate 10 via the conductive bonding material layer 3 and fixed.

The conductive bonding material layer 3 is formed to a thickness of 5 to 70 μm using an adhesive made of an epoxy resin or a polyimide resin containing a metal powder having good conductivity such as Ag powder or Cu powder. It can be formed by controlling to a predetermined thickness and width by screen printing or dispensing method.

  In the case of screen printing, in order to provide the gap 4, there may be mentioned a method of printing by providing a pattern with a predetermined hole on the screen printing plate making. Further, in the case of the dispensing method, in order to provide the gap 4, there is a method in which a needle diameter that is suitable for the width to be applied is used, and it is dispensed only where it is desired to be applied without being applied to the place where the gap is provided. Moreover, when producing a void, the adhesive agent to be used is stirred, air bubbles are created in the adhesive agent, and it is degassed by vacuum. Here, the bubbles remaining in the adhesive can be controlled by changing the vacuum defoaming time, and if it is dispensed as it is, it can be applied in a bubble-containing state. Furthermore, in order to create a void at a specific part such as the position corresponding to the easy-breaking layer, an adhesive containing bubbles is applied only to that part, and an adhesive without bubbles is applied to other parts. It may be applied separately.

  The external electrode plate 2 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 0.1 to 0.3 mm, for example. Here, to form the external electrode plate 8 with a slit or a mesh shape in the width direction, for example, the external electrode plate 2 is formed by punching with a punching die or a laser. A method such as processing may be used, and a bending mold is preferably used to obtain a curved or bent shape.

  Thereafter, a direct current electric field of 0.1 to 3 kV / mm is applied to the external electrode plate 2 to polarize the piezoelectric layer 11 constituting the multilayer body 10, thereby completing the multilayer piezoelectric element 1. The laminated piezoelectric element 1 is connected to an external power source via the external electrode plate 2 and applies a voltage to the piezoelectric layer 11 so that each piezoelectric layer 11 can be largely displaced by the inverse piezoelectric effect. it can. 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. 5 is a schematic sectional view showing an example of the embodiment of the injection device of the present invention.

  As shown in FIG. 5, in the injection device 19 of this example, the multilayer piezoelectric element 1 of the above example is stored inside 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. 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 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.

  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. You may be comprised so that it may discharge from the hole 21. FIG. 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 injection device 19 of the present example, the fluid includes various liquids and gases such as 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 the present example employing 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 of time compared to the conventional injection device. Can be made.

  Next, the example of embodiment of the fuel-injection system of this invention is demonstrated. FIG. 6 is a schematic view showing an example of an embodiment of the fuel injection system of the present invention.

  As shown in FIG. 6, the fuel injection system 35 of this example includes a common rail 37 that stores high-pressure fuel as a high-pressure fluid, and a plurality of injection devices 19 of the above-described examples that inject the high-pressure fluid stored in the common rail 37. A pressure pump 39 for supplying a high-pressure fluid to the common rail 37 and an injection control unit 41 for supplying 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 fuel injection system 35 of this example is used for engine fuel injection, the amount and timing of fuel injection can be controlled while sensing the state of 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 an engine fuel injection system 35, fluid fuel is fed into the common rail 37 at a high pressure of 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.

  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.

  Examples of the present invention will be described.

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 baked at 980-1100 degreeC, it ground to the predetermined shape using the surface grinder, and obtained the 5 mm square laminated body.

  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 laminate by dispensing, and the external electrode plate was connected to the surface of the laminate and fixed.

  Here, as the sample 1, a multilayer piezoelectric element was manufactured using an external electrode plate having a thickness of 0.1 mm and a width of 4.0 mm made of phosphor bronze having a cross section shown in FIG. A conductive bonding material made of silver polyimide is applied between the side surface of the active portion and the external electrode plate so as to form a conductive bonding material layer, and has a structure with a thickness of 0.03 mm. Yes. Specifically, the width of the conductive bonding material discharged from the nozzle diameter of the dispenser is set to 1.5 mm so as to have the cross section shown in FIG. . Here, the conductive bonding material was provided in two places with a width of 1.5 mm, and the gap was set to a width of 1.0 mm.

  Further, as Sample 2, a multilayer piezoelectric element was fabricated using an external electrode plate made of phosphor bronze having a cross section shown in FIG. 2 and having a thickness of 0.1 mm and a width of 4.0 mm. Specifically, the conductive bonding material was applied in two portions so as to provide a gap with a dispenser. Further, an external electrode plate is provided so as to provide a gap on one end side. Here, the conductive bonding material was provided at two places with a thickness of 0.03 mm and a width of 1.5 mm, and the gap was provided at two places with a width of 0.5 mm.

  Further, as Sample 3, a multilayer piezoelectric element was manufactured using an external electrode plate made of phosphor bronze having a cross section shown in FIG. 3 and having a thickness of 0.1 mm and a width of 4.0 mm. Specifically, the conductive bonding material was applied in two portions so as to provide a gap with a dispenser. In addition, a conductive bonding material is thinly applied so as to provide a gap at both ends, and an external electrode plate is installed. Here, the conductive bonding material was provided at two places with a thickness of 0.03 mm and a width of 1.5 mm, and the gap was provided at three places with a width of 0.33 mm.

  Further, as the sample 4, a multilayer piezoelectric element was manufactured using an external electrode plate made of phosphor bronze having a cross section shown in FIG. Specifically, the conductive bonding material was applied in two portions so as to provide a gap with a dispenser. At this time, air was previously injected into the conductive bonding material, and a void having a diameter of 0.005 to 0.01 mm was intentionally provided in the applied conductive bonding material. Here, the conductive bonding material was provided at two places with a thickness of 0.03 mm and a width of 1.5 mm, and the gap was provided at three places with a width of 0.33 mm.

  Also, as the sample 5, a multilayer piezoelectric element was manufactured using an external electrode plate made of phosphor bronze having a cross section shown in FIG. Specifically, the conductive bonding material was applied in two portions so as to provide a gap with a dispenser. Further, a conductive bonding material into which air was previously injected was applied on the easily breakable layer, and a void of 0.005 to 0.01 mm was intentionally provided on the easily breakable layer. Here, the conductive bonding material was provided at two places with a thickness of 0.03 mm and a width of 1.5 mm, and the gap was provided at three places with a width of 0.33 mm.

  As a comparative example, a laminated piezoelectric element (sample 6) using an external electrode plate having a cross section shown in FIG. 6 was also produced. Here, the external electrode plate having a thickness of 0.1 mm and a width of 4.0 mm was used, and the conductive bonding material was provided with a thickness of 0.2 mm and a width of 4 mm.

  These laminated piezoelectric elements were subjected to polarization treatment by applying a 3 kV / mm direct current electric field to the external electrode plate 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.

  Furthermore, 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% and continuously driven.

As a result, the laminated piezoelectric element of Sample 6 as a comparative example peeled off the external electrode plate after 1 × 10 ⁴ continuous driving, and stopped driving after 1 × 10 ⁵ times.

On the other hand, the laminated piezoelectric elements of Sample 1, Sample 2 and Sample 3, which are examples of the present invention, are driven without peeling of the external electrode plate even after continuous driving 1 × 10 ⁷ times. Was.

  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 10 ... Laminated body 11 ... Piezoelectric layer 12 ... Internal electrode layer 13 ... Active layer 14 ... Inactive layer 15 ... Easily fractured layer 2. ..External electrode plate 3 ... conductive bonding material layer 31 ... void 4 ... void

Claims (6)

A laminate in which a piezoelectric layer and an internal electrode layer are laminated, an external electrode plate joined to a side surface of the laminate and electrically connected to the internal electrode layer, and the external electrode plate on the side surface of the laminate A conductive bonding material layer electrically connected to the internal electrode layer and the external electrode plate, and the conductive bonding material layer is seen in a cross section perpendicular to the side surface of the laminate. When the thickness of the conductive bonding material layer is thinner than the thickness of the external electrode plate, a gap is provided from the side surface of the laminate to the external electrode plate ,
A laminated piezoelectric element comprising a void in the conductive bonding material layer .   2. The multilayer mold according to claim 1, wherein the gap is also at one end of the conductive bonding material layer when the conductive bonding material layer is viewed in a cross section perpendicular to a side surface of the stacked body. Piezoelectric element.   2. The multilayer mold according to claim 1, wherein the gap is also present at both ends of the conductive bonding material layer when the conductive bonding material layer is viewed in a cross section perpendicular to a side surface of the stacked body. Piezoelectric element. An easily breakable layer having a structure in which cracks are more likely to occur than the piezoelectric layer and the internal electrode layer due to expansion and contraction of the laminate is provided inside the laminate, and the void is located at a position corresponding to the easily breakable layer. The multilayer piezoelectric element according to any one of claims 1 to 3, wherein the multilayer piezoelectric element is provided. A container having an injection hole and the multilayer piezoelectric element according to any one of claims 1 to 4 , wherein fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. An injection device. 6. A common rail for storing high-pressure fuel, an injection device according to claim 5 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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