JP2010109057A - Stacked piezoelectric device, and injection apparatus and fuel injection system equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked piezoelectric device in which a displacement amount is stable even in a long time drive under qualifications of a high voltage and a high pressure. <P>SOLUTION: The stacked piezoelectric device 1 includes: an external electrode 9 which is bonded for a long time in the stacked direction to a side surface of a laminated body 7 constituted by alternately laminating piezoelectric substance layers 3 and inner electrode layers 5 and is electrically connected to the inner electrode layers 5; and a conductive connecting member 11 which is covered in the longitudinal direction on a front surface of the external electrode 9 and connects external lead wires, wherein in the conductive connecting member 11 there are formed slits 12 extending in a sense crossing in the stacked direction of the laminated body 7 over the thickness direction of the conductive connecting member 11. It is possible to make the stacked piezoelectric device 1 with an excellent durability by suppressing a peeling of the conductive connecting member 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laminated piezoelectric element used for a drive element (piezoelectric actuator), a sensor element or a circuit element using a piezoelectric body, for example. Examples of the driving element include a fuel injection device for an automobile engine, a liquid injection device such as a printing device for an ink jet printer, a precision positioning device such as a positioning device for 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.

  Conventionally, multilayer piezoelectric elements have been required to be able to ensure a large amount of displacement under a large pressure at the same time as miniaturization proceeds. For this reason, it is required that the multilayer piezoelectric element be used under severe conditions in which a higher voltage corresponding to a larger displacement amount is applied and continuous driving is performed for a long time.

When driving continuously for a long time under high voltage and high pressure conditions, with the driving of the multilayer piezoelectric element, the external electrode joined to the side surface of the multilayer body composed of the internal electrode layer and the piezoelectric body layer, In addition, since stress is applied to the conductive connection member attached to the surface of the external electrode for connecting the external lead wire, the conductive connection member may be peeled off from the external electrode. Therefore, for the purpose of relaxing the stress caused by the multilayer body so that the external electrode of the multilayer piezoelectric element does not break, for example, a slit-shaped stress relaxation portion is provided in the piezoelectric layer as disclosed in Patent Document 1. A multilayer piezoelectric element in which a porous layer as a target fracture layer is previously provided inside a piezoelectric layer, as disclosed in Japanese Patent Application Laid-Open No. 2004-133260, has been proposed. Furthermore, an external electrode having a structure in which a plurality of electrodes are combined has been proposed, for example, as disclosed in Patent Document 3, so that the external electrode can be driven even when it is broken by stress.
JP 2005-223013 A Special Table 2006-518934 JP 2006-128466 Gazette

  However, if only the stress applied to the conductive connection member by the piezoelectric layer during driving of the multilayer piezoelectric element is to be relaxed in order to prevent peeling of the conductive connection member, the external stress is applied to the multilayer piezoelectric element. In addition, even if the piezoelectric layer is deformed by stress, the portion restrained by the external electrode to which the conductive connection member is attached cannot be deformed, and the portion having no external electrode to which the conductive connection member is attached is present. Therefore, there is a problem that stress concentrates on the piezoelectric layer and cracks occur in the multilayer piezoelectric element laminate. Further, during the driving of the multilayer piezoelectric element, the conductive connection member is attached because the thermal expansion of the external electrode and the conductive connection member is different from the thermal expansion of the multilayer body due to self-heating caused by the drive. The stress is concentrated at the boundary between the part where there is no external electrode and the part where the conductive electrode is peeled off from the external electrode, or the conductive electrode is cracked and driven without supplying voltage to the internal electrode layer. There is a problem that decreases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a multilayer piezoelectric element having a stable displacement even when driven for a long time under high voltage and high pressure conditions.

  The multilayer piezoelectric element of the present invention has a multilayer body in which piezoelectric layers and internal electrode layers are alternately stacked, and is joined to the side surface of the multilayer body in the stacking direction so as to be electrically connected to the internal electrode layer. A laminated piezoelectric element comprising an external electrode and a conductive connecting member attached to the surface of the external electrode in the longitudinal direction and connecting an external lead wire, wherein the conductive connecting member has A slit extending in the thickness direction of the conductive connecting member extending in a direction intersecting with the stacking direction is formed.

  Moreover, the multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the slit extends in a direction perpendicular to the stacking direction of the multilayer body.

  In the multilayer piezoelectric element of the present invention, the slit has an end in the width direction of the conductive connecting member in the above configuration.

  Moreover, the multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the slit extends across both ends in the width direction of the conductive connecting member.

  The multilayer piezoelectric element of the present invention is characterized in that, in the above-described configuration, the slit overlaps a predetermined fracture layer set in the internal electrode layer or the piezoelectric layer of the multilayer body. is there.

  In the multilayer piezoelectric element of the present invention, in the above configuration, a plurality of the external lead wires are arranged in the stacking direction of the multilayer body, and the slit is between the external lead wires. It is a feature.

  In the multilayer piezoelectric element according to the present invention, the slit is separated from the external lead wire in the above configuration.

  The multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, at least a part of the slit follows the external lead wire.

  In addition, the multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, a part of the slit enters between the external lead wire and the external electrode.

  The multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the external electrode has a second slit extending in a direction crossing the stacking direction of the stacked body and extending in the thickness direction of the external electrode. To do.

  In the multilayer piezoelectric element of the present invention, the second slit is connected to the slit of the conductive connection member in the above configuration.

  An ejection device according to the present invention includes a container having an ejection hole and any one of the multilayer piezoelectric elements according to the present invention, and fluid stored in the container is driven from the ejection hole by driving the multilayer piezoelectric element. It is characterized by being discharged.

  The fuel injection system of the present invention includes a common rail that stores high-pressure fuel, the injection device of the present invention 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 the injection And an injection control unit for supplying a drive signal to the apparatus.

  According to the multilayer piezoelectric element of the present invention, the slits are formed in the conductive connecting member, so that both ends of the conductive connecting member in the direction orthogonal to the stacking direction of the stacked body, that is, the side surface of the stacked body Since the slit formed in the conductive connection member can absorb the stress generated at the boundary between the part without the conductive connection member and the part with the conductive connection member, the conductive connection member peels from the external electrode, It can suppress that it peels from a laminated body with an external electrode, or a crack generate | occur | produces in a laminated body. In particular, even when stress is suddenly applied to the laminated body of the multilayer piezoelectric element, cracks are generated in the conductive connecting member starting from the slits to relieve the stress, thereby suppressing the occurrence of cracks in the laminated body, and Generation | occurrence | production of peeling of the electroconductive connection member from a body can be suppressed. Further, since the surface area of the conductive connecting member is increased by forming the slit, the self-heating generated in the laminated body during driving of the laminated piezoelectric element is caused to pass through the conductive connecting member from the laminated body. Can be effectively dissipated from the surface. As a result, even when driven for a long time under high voltage and high pressure conditions, it is possible to suppress the peeling of the conductive connecting member and the cracking of the laminated body, so the displacement amount of the laminated piezoelectric element can be stabilized. Can be made.

  In addition, according to the injection device of the present invention, the multilayer piezoelectric element of the present invention is provided as the multilayer piezoelectric element for discharging the fluid stored in the container from the ejection hole. Since it is possible to prevent the connection member from peeling off or cracks in the laminate, and to prevent problems due to self-heating of the laminate, the desired discharge from the fluid injection holes can be prevented. It can be performed stably over a long period of time.

  Furthermore, according to the fuel injection system of the present invention, since the injection device of the present invention is provided as a device for injecting the high-pressure fuel stored in the common rail, the desired injection of high-pressure fuel can be stably performed over a long period of time. Can do.

  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 perspective view showing an example of an embodiment of a laminated piezoelectric element of the present invention. FIGS. 2A and 2B are a side view and a cross-sectional view taken along line AA of an example of an embodiment of the multilayer piezoelectric element of the present invention, respectively.

  As shown in FIGS. 1 and 2, the multilayer piezoelectric element 1 of this example is bonded to the side surface of a multilayer body 7 in which piezoelectric layers 3 and internal electrode layers 5 are alternately stacked, and is bonded to the inside in the stacking direction. A laminate including an external electrode 9 electrically connected to the electrode layer 5 and a conductive connection member 11 connected to the surface of the external electrode 9 in the longitudinal direction for connecting an external lead wire (not shown). In the piezoelectric element 1, a slit extending in the thickness direction of the conductive connection member 11 (formed in the thickness direction of the conductive connection member 11) extends in the direction crossing the stacking direction of the multilayer body 7 in the conductive connection member 11. , Slits 12 reaching the external electrodes 9 are formed. 2 (a) and 2 (b), the same hatching is applied in both drawings except for the piezoelectric layer 3, and the same hatching is similarly applied in the following similar drawings.

  By forming the slit 12 in the conductive connecting member 11 in this way, a region that is locally deformed in the conductive connecting member 11 is formed around the slit 12, and stress applied to the conductive connecting member 11 is applied. Can be absorbed. In particular, even when stress is suddenly applied to the laminate 7, cracks are generated in the conductive connection member 11 starting from the slits 12 to relieve the stress, thereby suppressing the occurrence of cracks in the laminate 7, and Generation | occurrence | production of peeling of the electroconductive connection member 11 from the external electrode 9 or the laminated body 7 can be suppressed.

  Furthermore, since the surface area of the conductive connection member 11 is increased by the amount of the slit 12 formed by forming the slit 12 in the conductive connection member 11, it is generated in the multilayer body 7 during the driving of the multilayer piezoelectric element 1. The self-heat generated can be effectively dissipated from the surface of the conductive connection member 11 from the laminate 7 through the conductive electrode 11 via the external electrode 9. As a result, it is possible to suppress the peeling of the conductive connection member 11, the peeling of the external electrode 9, and the crack of the laminated body 7 even when driven for a long time under high voltage and high pressure conditions. The amount of displacement of the piezoelectric element 1 can be stabilized.

  Such a slit 12 preferably extends in a direction orthogonal to the stacking direction of the stacked body 7 (a direction orthogonal to the stacking direction and along the piezoelectric layer 3 and the internal electrode layer 5). This is because the slit 12 provided in the conductive connecting member 11 is easily deformed by changing the opening width in the direction in which the multilayer body 7 expands and contracts when the multilayer piezoelectric element 1 is driven. This is because the conductive connecting member 11 can be expanded and contracted together with the laminated body 7 by the deformation, and the stress relaxation effect can be effectively brought about.

  If the conductive connecting member 11 has a rectangular shape that is long in the vertical direction of the laminated body 7 like the external electrode 9, as shown in FIG. 1, it is orthogonal to the longitudinal direction along the laminated body 7 of the conductive connecting member 11. It is preferable to provide the slit 12 in the direction in which it is made. Further, if the conductive connecting member 11 is square, it is preferable to provide the slit 12 in a direction orthogonal to the side in the stacking direction of the stacked body 7. Further, the S-shaped or crank-shaped conductive connecting member 11 is also slit in a direction orthogonal to the longitudinal direction along the stacking direction of the laminate 7 when the entire conductive connecting member 11 is viewed. 12 is preferably provided.

  Further, as shown in FIGS. 3 (a) and 3 (b), respectively, a side view and a cross-sectional view taken along line AA of another embodiment of the multilayer piezoelectric element of the present invention, the slit 12 is a conductive connecting member. 11 is preferably at the end in the width direction, that is, one end of the slit 12 is preferably at the end (edge) in the width direction of the conductive connecting member 11. This is because when the multilayer piezoelectric element 1 is driven and the multilayer body 7 expands and contracts, the slit 12 can be more easily deformed at the end of the conductive connection member 11 where stress is likely to concentrate. This is because the stress of the member 11 can be effectively relaxed. Further, regarding the stress caused by the difference in thermal expansion of the conductive connecting member 11 with respect to the thermal expansion of the laminate 7 due to self-heating due to driving, this stress tends to concentrate on the end of the conductive connecting member 11. Therefore, when the outer peripheral distance (length along the outer periphery) of the end of the conductive connecting member 11 is increased by the slit 12, it can be effectively relaxed.

  In addition, as shown in FIGS. 4 (a) and 4 (b), respectively, a side view and a cross-sectional view taken along the line AA of the embodiment of the multilayer piezoelectric element of the present invention, the slit 12 has a conductive property. It is preferable that it extends between both ends of the connecting member 11 in the width direction. According to this, since the laminated piezoelectric element 1 is driven and the laminated body 7 is expanded and contracted, the opening width of the slit 12 provided in the conductive connecting member 11 is changed over the whole so that it can be easily deformed. As a result, the conductive connecting member 11 can be expanded and contracted together with the laminate 7, and the stress relaxation effect can be more effectively brought about.

  5 (a) and 5 (b), respectively, as shown in a side view and a cross-sectional view taken along the line AA of the embodiment of the laminated piezoelectric element of the present invention, the slit 12 is a laminated body. 7 is set in the internal electrode layer 5 or the piezoelectric layer 3, and the laminate 7 is preferentially broken in the laminate 7 over the other internal electrode layers 5 or piezoelectric layers 3 when the laminate 7 is driven. 7 is preferably overlapped with the planned fracture layer 13 that relieves the stress at 7. As described above, the laminate 7 is provided with the planned fracture layer 13 that relieves stress in the laminate 7 by being preferentially fractured in the laminate 7 over the other internal electrode layers 5 or the piezoelectric layers 3 during driving. In the laminated piezoelectric element 1, when the slit 12 is formed so as to overlap the planned fracture layer 13, the stress applied to the conductive connection member 11 is applied when the laminated piezoelectric element 1 is driven to expand and contract the laminated body 7. It can be transmitted to the planned fracture layer 13 through the slit 12, and the stress in the laminate 7 can be relaxed by breaking the planned fracture layer 13. As a result, even when the multilayer piezoelectric element 1 is used in an environment where a high load is applied for a long period of time, the piezoelectric body layer 3 is not subject to stress and cracks caused by the stress, and the laminated body 7 is expected to break. Stress relaxation that effectively generates cracks only in the fault 13 is possible, and the multilayer piezoelectric element 1 can be made highly durable. Furthermore, since the fracture can be started with respect to the planned fracture layer 13 from the position where the slit 12 of the conductive connecting member 11 is provided, when the planned fracture layer 13 is provided on the laminate 7, the fracture can be started from any position. It is possible to set whether it can be started, the layout design of the planned fracture layer 13 can be facilitated, and the multilayer piezoelectric element 1 excellent in mass productivity can be obtained.

  Further, as shown in FIGS. 6 (a) and 6 (b), respectively, a side view and a cross-sectional view taken along line AA of the embodiment of the multilayer piezoelectric element of the present invention, the external lead wire 14 is: It is preferable that a plurality of the stacked bodies 7 are arranged in the stacking direction, and the slits 12 are located between the plurality of external lead wires 14. According to this, since the external lead wire 14 can be firmly joined to the conductive auxiliary member 11, there is an effect that the external lead wire 14 is hardly peeled off.

  The external lead wires 14 are not shown in FIGS. 1 to 5, but in each example, one or a plurality of external lead wires 14 are arranged in the stacking direction of the laminate 7 as in the example shown in FIG. 6. It is embedded and connected to the conductive connecting member 11. The external lead wire 14 may be bonded to the surface of the conductive connecting member 11 and connected thereto. However, in order to achieve excellent durability, the external lead wire 14 is as shown in the example of FIG. It is preferably embedded in the conductive connection member 11.

  Further, the slit 12 is preferably separated from the external lead wire 14. According to this, since the slit 12 is separated from the external lead wire 14, the stress in the multilayer body 7 due to the driving of the multilayer piezoelectric element 1 is not directly applied to the external lead wire 14, so that the external lead wire 14 is connected. The conductive auxiliary member 11 thus made can bring about an effect that it is difficult to peel off from the external electrode 9.

  Further, as shown in FIGS. 7A and 7B, respectively, a side view and a cross-sectional view taken along line AA of the embodiment of the multilayer piezoelectric element of the present invention, the slit 12 has at least one slit. It is preferable that the portion is attached to the external lead wire 14. According to this, even if stress is applied to the external lead wire 14, the stress on the conductive connection member 11 can be relaxed by the slit 12 being deformed and widened. A mitigating effect can be brought about.

  8A and 8B, at least a part of the slit 12, as shown in a side view and a cross-sectional view taken along line AA of another embodiment of the multilayer piezoelectric element of the present invention. However, it is preferable to enter between the external lead wire 14 and the external electrode 9. According to this, even if stress is applied to the external lead wire 14, the stress on the conductive connection member 11 can be relaxed by the slit 12 being deformed and widened. A mitigating effect can be brought about.

  Further, as shown in FIGS. 9 (a) and 9 (b), respectively, a side view and a cross-sectional view taken along line AA of the embodiment of the multilayer piezoelectric element of the present invention, There is preferably a second slit (slit) 10 extending in the thickness direction of the external electrode 9 extending in a direction intersecting with the stacking direction of the body 7. According to this, the second slit 10 is deformed so that the width in the stacking direction is changed when the stacked body 7 is driven, thereby providing an effect of relaxing the stress generated in the external electrode 9.

  Furthermore, as shown in FIGS. 10 (a) and 10 (b), respectively, a side view and a cross-sectional view taken along the line AA of the embodiment of the multilayer piezoelectric element of the present invention, The second slit 10 is preferably connected to the slit 12 of the conductive connecting member 11 (overlapping in the stacking direction of the external electrode 9 and the conductive connecting member 11). According to this, the second slit 10 of the external electrode 9 has an effect of relaxing the stress generated in the external electrode 9, and the slit 12 of the conductive connecting member 11 is generated in the conductive connecting member 11 at the same location. Since the effect of relaxing the stress can be brought about, both the external electrode 9 and the conductive connecting member 11 can bring about the effect that it is difficult to peel off from the laminate 7.

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

First, a ceramic green sheet to be the piezoelectric layer 3 is produced. Specifically, a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer are mixed to prepare a slurry. And a ceramic green sheet is produced by using tape molding methods, such as a doctor blade method and a calender roll method, for this slurry. The piezoelectric ceramic may be any piezoelectric ceramic, and for example, a perovskite oxide made of PbZrO ₃ —PbTiO ₃ or the like can be used. As the plasticizer, DBP (dibutyl phthalate), DOP (dioctyl phthalate), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 5 is produced. Specifically, a conductive paste is produced by adding and mixing a binder, a plasticizer, and the like to a metal powder such as silver-palladium. This conductive paste is printed on the ceramic green sheet in a predetermined pattern using a screen printing method. Further, a plurality of ceramic green sheets on which the conductive paste is screen-printed are stacked. And the laminated body 7 provided with the piezoelectric material layer 3 and the internal electrode layer 5 which were laminated | stacked alternately can be formed by baking as mentioned later.

  At this time, for example, when forming a porous metal particle layer including a large number of independent metal particles as the expected fracture layer 13, carbon powder is included in the conductive paste, and the carbon powder is baked during firing. There is a method of eliminating the ink, pattern printing so as to form a dot pattern when the conductive paste is printed, or performing dry ice blasting after the conductive paste is printed and dried to roughen the printed surface. In addition, if the porous metal particle layer containing a large number of independent metal particles is formed as the planned fracture layer 13, the conductive paste of the porous metal particle layer to be the planned fracture layer 13 and other By changing the metal component ratio of the internal electrode layer 5 to the conductive paste and utilizing the difference in concentration during firing, the metal is transferred from the expected fracture layer 13 to the adjacent internal electrode layer 5 via the piezoelectric layer 3. It can be made porous by diffusing. This method is preferable in terms of excellent mass productivity. In particular, when a conductive paste mainly made of silver-palladium is used and the silver concentration of the layer to be the expected fracture layer 13 is made higher than the silver concentration of the other internal electrode layers 5, the silver forms a liquid phase during firing. At the same time, since it can easily move between the piezoelectric particles of the piezoelectric layer 3, it is possible to form the expected fracture layer 13 made of a very uniform porous metal particle layer.

  Thereafter, the external electrode 9 is formed on the outer surface of the multilayer body 7 of the multilayer piezoelectric element 1 so as to obtain conduction with the internal electrode layer 5 whose end is exposed. The external electrode 9 can be obtained by adding a binder to silver powder and glass powder to produce a silver glass conductive paste, printing this on the side surface of the laminate 7, drying and adhering, or baking.

  In order to provide the second slit 10 in the external electrode 9, a method of pattern printing so as to form the second slit 10 when the silver glass conductive paste is printed is most mass-produced. In addition, a method of etching the pattern of the second slit 12 after forming the external electrode 9, a method of performing sandblasting or dry ice blasting with a metal mask provided with a pattern of the shape of the second slit 10, Alternatively, there is a method of dicing using a diamond disk.

  Next, the conductive connection member 11 is attached to the surface of the external electrode 9 in the longitudinal direction. The conductive connecting member 11 is attached in the longitudinal direction by applying a conductive bonding agent such as solder or conductive adhesive to the surface of the external electrode 9 by applying it in accordance with the shape of the external electrode 9. Then, using this conductive connecting member 11, a lead wire made of a metal wire, an external lead wire 14 made of a metal mesh, a mesh-like metal plate, or the like is joined and fixed to the surface of the external electrode 9.

  Here, the material of the external lead wire 14 is preferably a metal or an alloy such as silver, nickel, copper, phosphor bronze, iron, and stainless steel. Further, the surface of the external lead wire 14 may be plated with silver, nickel, or the like. The external lead wire 14 may be connected over the entire stacking direction of the external electrode 9 by the conductive connection member 11 or may be connected to a partial region of the external electrode 9.

  Then, in order to provide the slit 12 in the conductive connection member 11, a method of etching after forming the conductive connection member 11, as in the method of providing the second slit 12 in the external electrode 9, a pattern of the shape of the slit 12 There are a method of carrying out sand blasting or dry ice blasting with a metal mask provided with a metal mask, or a method of dicing using a diamond disk.

  Next, the laminate 7 in which the conductive connection member 11 is formed and the external lead wire 14 is connected is immersed in a resin solution containing an exterior resin made of silicone rubber. Then, the silicone resin solution is vacuum degassed to bring the silicone resin into close contact with the concavo-convex portions on the outer peripheral side surface of the laminate 7, and then the laminate 7 is pulled up from the silicone resin solution. Thereby, the silicone resin as the exterior resin is coated on the side surface of the laminate 7 on which the conductive connecting member 11 having the slits 12 is formed.

  Thereafter, a direct current electric field of 0.1 to 3 kV / mm is applied to the piezoelectric layer 3 from the pair of external electrodes 9 through the external lead wires 14 and the conductive connection member 11 by the internal electrode layer 5, and the piezoelectric layers of the laminate 7. By polarizing 3, the laminated piezoelectric element 1 of this example is completed. Then, the external lead wire 14 is connected to an external voltage supply unit (not shown), and a voltage is applied to the piezoelectric layer 3 by the internal electrode layer 5 via the external lead wire 14, the conductive connection member 11 and the external electrode 9. By applying, each piezoelectric layer 3 can be largely displaced by the inverse piezoelectric effect. Thereby, for example, it is possible to function as an automobile fuel injection valve mechanism for injecting and supplying fuel to the engine.

  Next, an example of an embodiment of a fluid ejection device as the ejection device of the present invention will be described. FIG. 11 is a schematic cross-sectional view showing an example of an embodiment of an injection device of the present invention.

  As shown in FIG. 11, in the injection device 21 of this example, the multilayer piezoelectric element 1 of the present invention represented by the example of the above embodiment is accommodated in a container 25 having an injection hole 23 at one end. Yes.

  A needle valve 27 that can open and close the injection hole 23 is disposed in the container 25. A fluid passage 29 is arranged in the injection hole 23 so that it can communicate with the movement of the needle valve 27. The fluid passage 29 is connected to an external fluid supply source, and is constantly supplied with, for example, a liquid that is a fluid at a high pressure. Therefore, when the needle valve 27 opens the injection hole 23 by driving the multilayer piezoelectric element 1, the fluid supplied to the fluid passage 29 is transferred to the outside of the injection hole 23 or a container adjacent to the injection hole 23, for example, an internal combustion engine. A fuel chamber (not shown) is configured to be discharged from the injection hole 23 and injected.

  The upper end of the needle valve 27 has a large inner diameter, and a cylinder 31 formed in the container 25 and a slidable piston 33 are disposed in that portion. In the container 25, the multilayer piezoelectric element 1 of the present invention is accommodated.

  In such an injection device 21, when the multilayer piezoelectric element 1 functioning as a piezoelectric actuator is applied with a voltage and extended, the piston 33 is pressed, the needle valve 27 closes the injection hole 23, and the supply of fluid is stopped. The When the application of voltage is stopped, the laminated piezoelectric element 1 contracts, the disc spring 35 pushes back the piston 33, the fluid passage 29 is opened, the injection hole 23 communicates with the fluid passage 29, and the injection hole The fluid is ejected from 23.

  The fluid ejection operation is to apply a voltage to the multilayer piezoelectric element 1 to open the fluid passage 29 and discharge the fluid from the ejection hole 23, and to stop applying the voltage to close the fluid passage 29. Thus, the discharge of the fluid may be stopped.

  The injection device 21 of the present invention includes a container 25 having an injection hole 23 and the multilayer piezoelectric element 1 of the present invention, and the fluid filled in the container 25 is ejected by driving the multilayer piezoelectric element 1. It may be configured to discharge from 23. That is, the multilayer piezoelectric element 1 does not necessarily have to be inside the container 25, and the pressure for supplying and stopping the fluid to the injection hole 23 is applied to the inside of the container 25 by driving the multilayer piezoelectric element 1. It suffices to be configured. In addition, the fluid including the liquid is not only supplied to the injection hole 23 through the fluid passage 29, but also provided in the container 25 with a portion for temporarily storing the fluid in an appropriate place in the container 25. The filled fluid may be discharged from the injection hole 23.

  In the present invention, the fluid includes various liquid materials (such as conductive paste) and gas, as well as liquid such as fuel or ink. By using the ejection device 21 of the present invention for these fluids, the fluid flow rate and ejection timing can be stably controlled over a long period of time.

  When the injection device 21 of the present invention that employs the multilayer piezoelectric element 1 of the present invention is used in an internal combustion engine, fuel can be injected into a combustion chamber of an internal combustion engine such as an engine more accurately over a longer period than a conventional injection device. Can be made.

  Next, the example of embodiment of the fuel-injection system of this invention is demonstrated. FIG. 12 is a schematic diagram showing an example of an embodiment of a fuel injection system of the present invention.

  As shown in FIG. 12, the fuel injection system 41 of this example includes a common rail 43 that stores high-pressure fuel, a plurality of injection devices 21 of the present invention that inject the high-pressure fuel stored in the common rail 43, and a high pressure on the common rail 43. A pressure pump 45 for supplying fuel and an injection control unit 47 for supplying a drive signal to the injection device 21 are provided.

  The injection control unit 47 controls the amount and timing of high-pressure fuel injection based on external information or an external signal. For example, in the case of the injection control unit 47 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 45 serves to supply fluid fuel from the fluid tank 49 to the common rail 43 at a high pressure. For example, in the case of an engine fuel injection system 41, fluid fuel is fed into the common rail 43 at a high pressure of about 1000 to 2000 atmospheres, preferably about 1500 to 1700 atmospheres.

  In the common rail 43, the high-pressure fuel sent from the pressure pump 45 is stored and appropriately sent to the injection device 21 in accordance with the driving of the multilayer piezoelectric element 1. As described above, the injection device 21 discharges (injects) high-pressure fuel, which is a predetermined amount of fluid, from the injection hole 23 to the outside of the injection hole 23 or a container adjacent to the injection hole 23 at high pressure. For example, when the target for injecting and supplying fuel is an engine, high-pressure fuel, which is a fluid, is injected from the injection hole 23 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. Further, the present invention relates to a multilayer piezoelectric element, but is not limited to the above-described embodiment, and may be used for, for example, a printing device of an ink jet printer or a pressure sensor. Any multilayer piezoelectric element using piezoelectric characteristics can be implemented with the same configuration.

  An example of the multilayer piezoelectric element of the present invention was produced as follows.

  First, a slurry is prepared by mixing a binder powder and a plasticizer with a raw material powder mainly composed of lead zirconate titanate (PZT) powder with an average particle size of 0.4 μm, and a ceramic green sheet with a thickness of 150 μm is prepared by the doctor blade method. did.

  Next, a conductive paste A obtained by adding a binder to a raw material powder containing silver-palladium alloy powder having a metal composition of Ag 95 mass% -Pd 5 mass%, and a raw material containing silver powder having a metal composition of Ag 100 mass% A conductive paste B was prepared by adding a binder to the powder.

  Then, the conductive paste A was printed on one side of the ceramic green sheet with a pattern of the internal electrode layer 5 so as to have a thickness of 30 μm by screen printing. And each green ceramic sheet on which conductive paste A was printed was laminated to produce a green laminate. As for the number of laminated layers, the number of internal electrode layers 5 is laminated to be 300, and only 20 ceramic green sheets on which no conductive paste is printed are provided at both ends in the lamination direction of the green laminate. Laminated to make sample numbers 1-10.

  Next, in order to provide a low-rigidity metal layer made of isolated metal particles as the expected fracture layer 13, in the sample numbers 5 to 10, the internal electrode layers 5 located at the 50th and 250th positions in the stacking direction are made conductive. Printing was performed using paste B.

  Next, the raw laminate of each sample number was subjected to binder removal treatment at a predetermined temperature, and then fired at 800 to 1000 ° C. to obtain a laminate 7. Here, in Sample Nos. 5 to 10, since the silver of the electrode component of the layer using the conductive paste B diffused into the adjacent metal layer having a low silver concentration during firing, the layer using the conductive paste B A planned fracture layer 13 which is a low-rigidity metal layer made of isolated metal particles was formed.

  And after processing to the laminated body 7 of each sample number to a desired dimension, as shown in Table 1, sample numbers 9 and 10 have external electrodes 9 respectively so that the second slit 10 can be formed. Formed. First, a conductive paste C for the external electrode 9 was prepared by adding and mixing a binder, a plasticizer, glass powder, and the like to metal powder containing silver as a main component. This conductive paste C was printed in a rectangular pattern extending in the stacking direction of the multilayer body 7 by screen printing or the like at a location where the rectangular side surface of the multilayer body 7 was to be formed. Thereafter, the external electrode 9 was formed by baking at 600 to 800 ° C. At this time, the external electrode 9 is formed on the side surface of the multilayer body 7 in the longitudinal direction in the laminating direction, and the second slit 10 is a predetermined fracture layer that is the internal electrode layer 5 located at the 50th and 250th positions in the laminating direction. At a position overlapping 13, the width (width in the stacking direction) × length (the length in the direction orthogonal to the stacking direction) was set to a size of 0.5 mm × 3 mm in a direction orthogonal to the stacking direction.

  When a conductive paste using silver powder is applied to the entire surface of the external electrode 9 of each sample number as a conductive connection member 11 and cured and applied, the diameter of the conductive connection member 11 is reduced. An external lead wire 14 made of a 0.5 mm metal wire was buried and connected. Then, after forming the conductive connection member 11, a metal mask provided with a pattern having the shape of the slit 12 was placed thereon, and the slit 12 was processed by sandblasting. The slit 12 was formed as follows for each sample number.

  In sample number 1, the slit 12 was not formed as a comparative example of the present invention. In sample number 2, the conductive connecting member 11 at a position overlapping the 50th and 250th internal electrode layers 5 in the stacking direction of the stacked body 7 is provided with a slit 12 having a width of 0.5 mm and a length of 1 mm in a direction perpendicular to the stacking direction. Was formed so as to fit in the conductive connecting member 11. In sample number 3, the conductive connecting member 11 on the internal electrode layer 5 at the same position as the sample number 2 is provided with a slit 12 having a width of 0.5 mm and a length of 1 mm in the direction perpendicular to the stacking direction, and one end of the external connection electrode It was formed to reach the end of 9. In sample number 4, a slit 12 having a width of 0.5 mm and a length of 3 mm is formed from the end of the external electrode 9 in the direction perpendicular to the stacking direction in the conductive connecting member 11 on the internal electrode layer 5 at the same position as the sample number 2. It was formed to reach the end. In the sample numbers 5 to 8, the conductive connecting member 11 has a width of 0.5 mm × a length of 3 mm in a direction perpendicular to the stacking direction so as to overlap the 50th and 250th planned fracture layers 13 in the stacking direction of the stacked body 7. The slit 12 was formed so as to reach the end of the external electrode 9. In Sample No. 9, the slit 12 was not provided in the conductive connecting member 11. In Sample No. 10, the external electrode 9 and the conductive connecting member 13 are overlapped with the external electrode 9 and the conductive connecting member 13 so as to overlap the 50th and 250th planned fracture layers 13 in the stacking direction, with a width 0.5 mm × length 3 mm. The slits 12 having a width of 0.5 mm and a length of 3 mm were formed so as to extend from the end of the external electrode 9 to the end.

  And the laminated body 7 which formed the external electrode 9 and adhered the electroconductive connection member 11 was immersed in the resin solution containing the exterior resin which consists of silicone rubber. Then, the silicone resin solution is vacuum degassed to bring the silicone resin into close contact with the irregularities on the outer peripheral side surface of the laminate 7, and then the laminate 7 is pulled up from the silicone resin solution to be externally attached to the side surface of the laminate 7. A silicone resin was formed as the resin.

  Driving evaluation was performed using each sample thus produced. As drive evaluation, high-speed response evaluation and durability evaluation were performed. First, a polarization process is performed by applying a 3 kV / mm direct current electric field from the internal electrode layer 5 to the piezoelectric layer 3 through the external lead wire 14, the conductive connecting member 11 and the external electrode 9 for 15 minutes. A piezoelectric actuator using No. 1 was produced. A DC voltage of 170 V was applied to the obtained piezoelectric actuator, and the amount of displacement in the initial state was measured.

For high-speed response evaluation, an AC voltage of 0 to +170 V at room temperature was applied to each piezoelectric actuator with the frequency gradually increased from 150 Hz. For durability evaluation, an AC voltage of 0 to +170 V was applied to each piezoelectric actuator at a frequency of 150 Hz at room temperature, and a test was continuously performed up to 1 × 10 ⁹ times. The production conditions for each of these samples are shown in Table 1, and the test results are shown in Table 2.

  As shown in Tables 1 and 2, only the sample number 1 of the comparative example in which the slit 12 is not formed in the conductive connecting member 11, the piezoelectric actuator generates a beat sound when the frequency of the applied voltage exceeds 1 kHz. Was recognized. This is indicated by “occurrence” in the column of the occurrence of a beat sound in Table 2. This is because, in the laminated piezoelectric element of sample number 1, since the laminated body 7 is constrained by the conductive connecting member 11, when local heat is generated between the internal electrode layers 5 with driving, the piezoelectric body It is considered that the displacement speed for each layer 3 is disturbed, and the displacement cannot follow the frequency of the applied AC voltage.

  In order to confirm the drive frequency, the pulse waveform of the drive signal of sample number 1 was confirmed using an oscilloscope DL1640L manufactured by Yokogawa Electric Corporation, and harmonic noise was confirmed at a location corresponding to an integer multiple of the drive frequency. It was done. This is indicated by “occurrence” in the noise column of the harmonic component in Table 2.

As a result of the durability evaluation, in the sample number 1 of the comparative example, the displacement amount after the durability evaluation test (displacement amount after 1 × 10 ⁹ cycles) is 5 μm, which is compared with that before the durability evaluation test. Nearly 90% ({(45-5) / 45} × 100 = 88.9 (%)) was decreased. In the piezoelectric actuator of sample number 1, peeling was observed in a part of the conductive connecting member 11 and a part of the external electrode 9 after continuous driving (1 × 10 ⁹ times). Cracks were observed in some of the areas.

On the other hand, in the piezoelectric actuators of sample numbers 2 to 10 which are the embodiments of the present invention, the conductive connecting member 11 is peeled off, the external electrode 9 is peeled off, and the laminate 7 after continuous driving (1 × 10 ⁹ times). Cracks in the laminated part were not confirmed. In addition, the decrease in the displacement after the durability evaluation test (displacement after 1 × 10 ⁹ cycles) is 8 μm or less, and the decrease in the displacement is 18% or less (maximum sample). In number 2, it was suppressed to {(45−37) / 45} × 100 = 17.8 (%)). In particular, in the piezoelectric actuators of sample numbers 5 to 8, since the slit 12 is formed so as to overlap the planned fracture layer 13, the stress applied to the conductive connecting member 11 is applied to the slit 12 when the laminate 7 expands and contracts. Since the stress in the laminate 7 can be relieved by breaking the planned fracture layer 13, the displacement is reduced by 6% even after 1 × 10 ⁹ cycles. It was found to have a very high durability, being 10% or less. Further, in the piezoelectric actuator of sample number 10, the second slit 10 of the external electrode 9 has an effect of relieving the stress generated in the external electrode 9, and is further made conductive by the slit 12 of the conductive connecting member 11 at the same location. Since the stress generated in the connecting member 11 could be relaxed, there was almost no decrease in displacement even after 1 × 10 ⁹ cycles, the decrease was 1 μm, and the rate of change was as small as 2.1%. It was found to have sex.

  In addition, after the durability evaluation test, it was confirmed that the laminated piezoelectric elements of sample numbers 5 to 10 had cracks in the expected fracture layer 13. This is because the stress is concentrated at the position where the slit 12 is provided in the conductive connecting member 11 or at the position where the second slit 10 is provided in the external electrode 9 so that they are formed so as to overlap with each other. The stress was transmitted to 13 and the fracture was started. From this, it was confirmed that by providing the slit 12 in the conductive connecting member 11, the expected fracture layer 13 was preferentially fractured and the stress in the laminate 7 was relaxed.

It is a perspective view which shows an example of embodiment of the lamination type piezoelectric element of this invention. (A) is a side view which shows an example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the other example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. (A) is a side view which shows the further another example of embodiment of the lamination type piezoelectric element of this invention, (b) is the AA sectional view taken on the line. 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 3 ... Piezoelectric layer 5 ... Internal electrode layer 7 ... Laminated body 9 ... External electrode
10 ... Second slit
11 ... Conductive connection member
12 ... Slit
13 ... Scheduled fracture layer
14 ... External lead wire
21 ... Injection device
23 ・ ・ ・ Injection hole
25 ・ ・ ・ Container
27 ... Needle valve
29 ・ ・ ・ Fluid passage
31 ... Cylinder
33 ... Piston
35 ... Belleville spring
41 ... Fuel injection system
43 ... Common rail
45 ... Pressure pump
47 ・ ・ ・ Injection control unit
49 ... Fuel tank

Claims (13)

  A laminate in which piezoelectric layers and internal electrode layers are alternately laminated; an external electrode that is joined to a side surface of the laminate in the laminating direction and is electrically connected to the internal electrode layer; and a surface of the external electrode A laminated piezoelectric element including a conductive connecting member that is attached in the longitudinal direction to connect an external lead wire, and extends to the conductive connecting member in a direction crossing the stacking direction of the laminate. A laminated piezoelectric element having a slit extending in a thickness direction of the conductive connecting member.   The multilayer piezoelectric element according to claim 1, wherein the slit extends in a direction orthogonal to the stacking direction of the multilayer body.   The multilayer piezoelectric element according to claim 1, wherein the slit reaches an end in the width direction of the conductive connecting member.   The multilayer piezoelectric element according to claim 3, wherein the slit extends between both ends in the width direction of the conductive connecting member.   The slit is overlapped with a planned rupture layer that is set in the internal electrode layer or the piezoelectric layer of the multilayer body and is preferentially ruptured during driving to relieve stress. The multilayer piezoelectric element according to claim 2.   2. The multilayer piezoelectric element according to claim 1, wherein a plurality of the external lead wires are arranged in a stacking direction of the multilayer body, and the slit is between the external lead wires.   The multilayer piezoelectric element according to claim 6, wherein the slit is separated from the external lead wire.   The multilayer piezoelectric element according to claim 6, wherein at least a part of the slit follows the external lead wire.   The multilayer piezoelectric element according to claim 8, wherein a part of the slit enters between the external lead wire and the external electrode.   2. The multilayer piezoelectric element according to claim 1, wherein the external electrode has a second slit extending in a direction intersecting with the stacking direction of the multilayer body and extending in the thickness direction of the external electrode.   The multilayer piezoelectric element according to claim 10, wherein the second slit is connected to the slit of the conductive connection member.   A container having an injection hole and the multilayer piezoelectric element according to any one of claims 1 to 11, wherein fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. An injection device.   A common rail that stores high-pressure fuel, the injection device according to claim 12 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.

Images