JP2010147365A - Laminated piezoelectric element, and injection device and fuel injection system including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of a conventional laminated piezoelectric element wherein (1) movement of a domain wall is constrained by a grain boundary of a piezoelectric layer to reduce a response speed, (2) the displacement of the laminated piezoelectric element is reduced due to the constraint of the movement of the domain wall by the grain boundary of the piezoelectric layer, and (3) a part constrained by continuous drive generates heat by itself to cause a crack in the piezoelectric layer and the displacement is gradually reduced. <P>SOLUTION: This laminated piezoelectric element 1 includes a laminated body 7 with piezoelectric layers 3 and internal electrode layers 5 alternately laminated. In the piezoelectric layer 3, a domain wall 14 straddling over a plurality of crystal particles 11 is formed. By virtue of this structure, the response speed of the laminated piezoelectric element 1 is increased, and the displacement can be increased. The laminated piezoelectric element 1 never causing degradation of the displacement even when continuously driven can be provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  2. Description of the Related Art Conventionally, a multilayer piezoelectric element (hereinafter also referred to as an element) including a multilayer body in which a plurality of piezoelectric layers are stacked via an internal electrode layer, and a pair of external electrodes formed on the side surfaces of the multilayer body. Are known. This multilayer piezoelectric element has a structure in which a positive external electrode and a negative external electrode are formed on opposite side surfaces of a multilayer body, and internal electrode layers are alternately electrically connected to these external electrodes. A displacement is obtained in the stacking direction by applying a voltage to the piezoelectric layer between the internal electrode layers via the external electrode. This displacement is caused by deformation in which the crystal particles of the piezoelectric layer constituting the laminated body expand and contract in the voltage application direction.

  A plurality of regions having different polarization directions exist in crystal grains of the piezoelectric layer, and a domain wall is formed at a portion that becomes a boundary of the polarization region.

  When a voltage is applied to the crystal grains of the piezoelectric layer, a region where the polarization axis direction coincides with the voltage application direction extends. On the other hand, the region in which the polarization axis direction is 180 ° opposite to the voltage application direction is temporarily shrunk, but the voltage is applied in the polarization axis direction by applying a voltage that reverses the polarization axis (so-called coercive electric field). It changes to, and turns around and grows. Once reversed, the region extends when a voltage is applied unless a reverse coercive electric field is applied.

  However, when there are a plurality of regions having different polarization directions, it is rare that all the polarization directions are aligned in the direction in which the electric field is applied. For this reason, in many regions of the crystal grains, when a voltage is applied, the domain wall serving as the boundary of the polarization region moves so that the ratio of the polarization axis direction to the electric field application direction increases. As a result, the region in which the crystal grains of the piezoelectric layer extend is expanded and the element expands. Conversely, when the voltage application is canceled, the element shrinks by returning the domain wall to the original position. Utilizing this phenomenon, the stacked piezoelectric element is driven to expand and contract.

  Conventionally, as shown in FIGS. 7A to 7C, the domain wall 14 has been formed to relieve stress applied to each crystal particle 11, and to relieve stress from the adjacent crystal particle 11. In addition, the crystal grains 11 are discontinuous. Therefore, it is known that the movement of the domain wall 14 when an electric field is applied is restricted by the grain boundary 12 between the crystal grains 11 (see, for example, Patent Document 1).

In FIG. 7, (b) is an enlarged cross-sectional view enlarging a portion B of the cross-sectional view of the piezoelectric layer of (a), and (c) is a cross-sectional view showing an arrangement state of atoms with respect to (b). . In FIG. 7, 13 is a domain polarization direction, 15 is an oxygen ion, 16 is an A site ion of an ion such as barium or lead, and 17 is a B site ion of an ion such as titanium or zirconium.
JP 2005-191397

  In the multilayer piezoelectric element as described above, there is a problem that the response speed becomes slow because the movement of the domain wall 14 is restricted by the grain boundary 12 between the crystal grains of the piezoelectric layer.

  Further, there is a problem that the displacement amount of the multilayer piezoelectric element is reduced in response to the movement of the domain wall 14 being restricted by the grain boundary 12 between the crystal grains of the piezoelectric layer.

  In addition, there is a problem in that a portion constrained by continuous driving self-heats, a crack is generated in the piezoelectric layer, which is a piezoelectric ceramic constituting the multilayer piezoelectric element, and the amount of displacement gradually decreases.

  Accordingly, the present invention has been devised to solve the above-described problems, and the purpose of the present invention is to prevent the movement of the domain wall from being restrained, the response speed is high, and the displacement amount can be increased. An object of the present invention is to provide a laminated piezoelectric element that has sufficient mechanical strength and can suppress deterioration of characteristics, an injection device using the same, and a fuel injection system.

  The multilayer piezoelectric element of the present invention is a multilayer piezoelectric element including a multilayer body in which piezoelectric layers and internal electrode layers are alternately stacked, and the piezoelectric layer is a domain wall straddling a plurality of crystal particles. Is formed.

  In the multilayer piezoelectric element of the present invention, in the above configuration, a region where polarization axes are aligned exists in a portion where the adjacent crystal particles are in contact with each other in the region surrounded by the domain wall. Is.

  In the multilayer piezoelectric element of the present invention, in each of the above structures, the domain wall is characterized in that a portion straddling the adjacent crystal particles is formed in a straight line.

  In addition, the multilayer piezoelectric element of the present invention is characterized in that, in each of the above-described configurations, the crystal particles are mainly configured in a 90 ° domain.

  In the multilayer piezoelectric element of the present invention, the domain wall is formed in the piezoelectric layer between the adjacent internal electrode layers in each of the above configurations.

  In the multilayer piezoelectric element of the present invention, the domain wall is present in the vicinity of the end portion of the internal electrode layer in the piezoelectric layer in each of the above-described configurations.

  Further, the multilayer piezoelectric element of the present invention includes, in each of the above-described configurations, the multilayer body including a planned fracture layer that relieves stress by being fractured preferentially over the internal electrode layer during driving, The domain wall is formed in the vicinity of the predetermined fracture layer.

  In the multilayer piezoelectric element of the present invention, the domain wall is formed in the plurality of piezoelectric layers in each of the above configurations.

  In the multilayer piezoelectric element of the present invention, in each of the above structures, the piezoelectric layer has a lead element oxide component, and the lead element oxide component is located at a triple point between crystal grains. Is segregated.

  The multilayer piezoelectric element of the present invention is characterized in that, in each of the above-described structures, the lead oxide component is an amorphous phase.

  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 the liquid stored in the container is driven by the multilayer piezoelectric element to form the ejection hole. It is characterized by being discharged from.

  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 fuel stored in the common rail, a pressure pump that supplies the high-pressure fuel to the common rail, and the injection device And an injection control unit for supplying a drive signal to the vehicle.

  According to the multilayer piezoelectric element of the present invention, the multilayer piezoelectric element includes a multilayer body in which piezoelectric layers and internal electrode layers are alternately stacked, and the piezoelectric layer is a domain straddling a plurality of crystal particles. Since the wall is formed, the movement of the domain wall is not constrained by the crystal grain boundary, and the domain wall of the adjacent crystal grain moves in conjunction with the application of the electric field. Therefore, the moving speed and moving amount of the domain wall due to the electric field can be increased. As a result, the response speed of the multilayer piezoelectric element is increased, and the amount of displacement can be increased.

  In addition, since the region for restraining the displacement is greatly reduced, overheating of the driving multilayer piezoelectric element can be suppressed, and a highly durable element can be obtained.

  Furthermore, since the amount of movement of the domain wall can be ensured even if the crystal particle diameter is kept small, the crystal particles of the piezoelectric layer can be made small, thereby increasing the mechanical strength and the large displacement amount. Type piezoelectric element. As a result, it is possible to obtain a laminated piezoelectric element in which the deterioration of the displacement amount is suppressed even when continuously driven.

  In the multilayer piezoelectric element of the present invention, in the above configuration, when there is a region where the polarization axes are aligned in a region where adjacent crystal particles are in contact with each other in the region surrounded by the domain wall, Since the movement of the wall continuously occurs in adjacent crystal grains, polarization at high speed is possible, and the response speed of displacement can be increased. In addition, pre-processing such as polarization treatment is not required, and there is no residual stress due to polarization treatment. Therefore, domain walls can stably exist between adjacent crystal grains even when driven for a long time. Drive is realized.

  Further, in the multilayer piezoelectric element of the present invention, in each of the above configurations, when the domain wall is formed in a linear shape so as to straddle adjacent crystal particles, the domain wall moves when the domain wall moves by applying an electric field. Displacement occurs linearly and continuously without being interrupted by grain boundaries. As a result, there is no distortion in the movement of the domain wall, and no stress is generated. Therefore, since the polarization is regularly performed simultaneously when an electric field is applied, the response speed of the displacement can be increased.

  Further, in the multilayer piezoelectric element of the present invention, in each of the above configurations, when the crystal grains are mainly composed of 90 ° domains, the domain wall can be easily moved in a low electric field. Speed can be increased. In addition, since there is no need to reverse the polarization as in the 180 ° domain, high voltage polarization processing is unnecessary, and no damage is caused by applying a high voltage to the multilayer piezoelectric element. Type piezoelectric element.

  In the multilayer piezoelectric element of the present invention, in each of the above configurations, when the domain wall is formed on the piezoelectric layer between the adjacent internal electrode layers, the piezoelectric body between the adjacent internal electrode layers is Since the region of the layer is a region that deforms when an electric field is applied to the multilayer piezoelectric element, the domain wall that moves across the plurality of crystal grains moves simultaneously with the application of the electric field. Can be driven at high speed. In particular, when a domain wall straddling a plurality of crystal grains is formed in the piezoelectric crystal grains in contact with the internal electrode layer, the electric field concentrates on the end portion of the internal electrode layer, so that the end portion is the origin of domain wall movement. Thus, the movement of the domain wall is started simultaneously with the voltage application. Accordingly, since the movement of the domain wall propagates like a shogi to the center of the piezoelectric layer between the internal electrode layers, extremely stable high-speed driving is possible.

  In the multilayer piezoelectric element of the present invention, in each of the above configurations, when the domain wall exists in the vicinity of the end portion of the internal electrode layer in the piezoelectric layer, the polarization direction of the piezoelectric layer is opposite to the internal electrode layer. Therefore, when the stacked piezoelectric element is driven, the stress is concentrated most at the end of the internal electrode layer, but when the crystal grains at the end of the internal electrode layer are deformed so as to relieve the stress. The movement of the domain wall facilitates the deformation of the crystal grains. As a result, when the domain wall straddling a plurality of crystal grains is formed at the end of the internal electrode layer, the domain wall can move at a high speed, so that the stress relaxation effect is enhanced and the multilayer piezoelectric element is stable for a long time. Can be driven.

  In the multilayer piezoelectric element of the present invention, in each of the above configurations, the multilayer body includes a planned fracture layer that relaxes stress by being preferentially fractured over the internal electrode layer during driving, and the domain wall is When the crack is generated in the planned rupture layer when the crack is generated in the planned rupture layer of the multilayer piezoelectric element being driven and the stress is relieved when it is formed in the vicinity of the planned rupture layer, When the domain wall of the crystal grain in the part where the crack has reached moves at high speed, the crystal grain can be deformed. As a result, the stress can be relaxed and the progress of cracks in the piezoelectric layer can be suppressed.

  In the multilayer piezoelectric element of the present invention, in each of the above configurations, when the domain wall is formed in a plurality of piezoelectric layers, the domain wall is added to the multilayer piezoelectric element generated when the multilayer piezoelectric element is driven. Since stress from all directions can be dispersed, the multilayer piezoelectric element can be made highly durable.

  In the multilayer piezoelectric element of the present invention, in each of the above structures, the piezoelectric layer has a lead element oxide component, and the lead element oxide component is segregated at a triple point between crystal grains. When the domain wall moves during the driving of the multilayer piezoelectric element, the domain wall cannot be moved with deformation of the crystal grains at the triple point where the oxide component of the lead element segregates. Acts as a stopper to prevent the domain wall from moving. As a result, when the drive voltage is turned on / off, the domain wall can move in the same region, and the stacked piezoelectric element can be made highly durable.

  In the multilayer piezoelectric element of the present invention, in each of the above structures, when the lead element oxide component is in an amorphous phase, the lattice vibration propagating the displacement of ions in the crystal grains disappears in the amorphous phase. Therefore, it becomes impossible to move the domain wall accompanied by the deformation of crystal grains at the triple point, and it works more effectively as a stopper so that the domain wall does not move indefinitely. As a result, when the drive voltage is turned on / off, the domain wall can be moved in the same region, and the stacked piezoelectric element can be made more durable.

  Further, according to the ejection device of the present invention, the container having the ejection hole and any one of the multilayer piezoelectric elements of the present invention is provided, and the liquid stored in the container is ejected by driving the multilayer piezoelectric element. Since it is discharged from the hole, a large displacement amount and excellent durability can be obtained in the multilayer piezoelectric element, so that the desired liquid can be stably ejected over a long period of time.

  Further, according to the fuel injection system of the present invention, the common rail that stores high-pressure fuel, the injection device of the present invention that injects the fuel stored in the common rail, the pressure pump that supplies high-pressure fuel to the common rail, and the injection Since the injection control unit for supplying a drive signal to the apparatus is provided, the desired injection of the high-pressure fuel can be stably performed over a long period of time.

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

  FIG. 1 is a perspective view showing an example of an embodiment of a multilayer piezoelectric element of the present invention, and FIGS. 2A to 2C are piezoelectric layers constituting the multilayer piezoelectric element shown in FIG. It is sectional drawing which shows typically the crystal particle and polarization domain of.

  As shown in FIG. 1, the laminated piezoelectric element 1 of this example includes a laminated body 7 in which piezoelectric layers 3 and internal electrode layers 5 are alternately laminated, and an internal electrode joined to a side surface of the laminated body 7. And an external electrode 9 electrically connected to the layer 5. Then, as shown in FIGS. 2A to 2C, in the piezoelectric layer 3, domain walls 14 straddling a plurality of crystal particles 11 are formed.

  2, (b) is an enlarged cross-sectional view enlarging part A of the cross-sectional view of the piezoelectric layer of (a), and (c) is a cross-sectional view showing an arrangement state of atoms with respect to (b). . In FIG. 2, 12 is a grain boundary, 13 is a domain polarization direction, 15 is an oxygen ion, 16 is an A site ion of an ion such as barium or lead, and 17 is a B site ion of an ion such as titanium or zirconium. .

  With the above configuration, when an electric field is applied to the element 1, as shown in FIGS. 3A to 3C, the domain wall 14 straddling between adjacent crystal grains 11 can continuously move. In the piezoelectric layer 3 having such a domain structure, the binding force at the grain boundary 12 of the domain wall 14 straddling the plurality of crystal grains 11 is reduced, and the domain wall 14 against the electric field applied to the piezoelectric layer 3 is reduced. Increases movement speed. That is, the response speed of displacement can be increased.

  In FIGS. 3B and 3C, white arrows indicate the direction in which the electric field is applied.

  Moreover, since the area | region which restrains a displacement reduces significantly, overheating of the element 1 during a drive can be suppressed and it can be set as the element 1 with high durability.

  Further, when the element 1 is deformed by driving, the vicinity of the grain boundary 12 is polarized and contributes to the deformation, so that the vicinity of the grain boundary 12 does not become an ion pool due to defects such as oxygen vacancies. As a result, it is possible to obtain a highly durable element 1 in which the domain wall 14 is not restrained by ions segregated at the grain boundaries 12 and the displacement is not changed even after long-term driving.

  In particular, as shown in FIG. 2 (c), in the perovskite-type piezoelectric body, the arrangement of the B site ions 17 of the adjacent crystal particles 11 through the grain boundary 12 is in the same direction, so that the polarization directions coincide. Therefore, the movement of the domain wall 14 continuously occurs between the adjacent crystal grains 11 via the grain boundaries 12 when an electric field is applied. As a result, the moving speed of the domain wall 14 is increased. That is, the response speed of displacement can be increased.

  In addition, in the piezoelectric layer 3, it is preferable that a region where the polarization axes are aligned exists in a region where adjacent crystal particles 11 are in contact with each other in a region surrounded by the domain wall 14.

  With the above configuration, the movement of the domain wall 14 is continuously generated in the adjacent crystal particles 11 simultaneously with the application of the electric field. As a result, high-speed polarization is possible, and the response speed of displacement can be increased. Pre-processing such as polarization treatment is not required, and there is no residual stress caused by polarization treatment. Therefore, the domain wall 14 can stably exist between adjacent crystal grains 11 even if it is driven for a long time, and is stable. Drive is realized.

  In addition, it is preferable that the domain wall 14 straddling the plurality of crystal particles 11 is formed such that a portion straddling the adjacent crystal particles 11 is linear.

  With the above configuration, when the domain wall 14 moves during the application of an electric field, the displacement of ions is not interrupted by the grain boundary 12 but is linearly chained. As a result, since there is no distortion in the movement of the domain wall 14 and no stress is generated, the domain wall 14 is regularly and simultaneously polarized when an electric field is applied, and the response speed of displacement can be increased.

  The crystal particles 11 are preferably mainly composed of 90 ° domains.

  With the above configuration, the domain wall 14 can be easily moved with a low electric field, so that the displacement response speed can be increased. Further, since there is no need to reverse the polarization as in the 180 ° domain, a high-voltage polarization process is unnecessary. Therefore, since the element 1 is not damaged at all by the high voltage, the highly durable multilayer piezoelectric element 1 can be obtained.

  In this case, the ratio (content) of the crystal particles 11 composed of 90 ° domains is preferably 80% by volume or more, and more preferably, all of the 90 ° domains are composed of the domain walls 14. Can be more easily performed in a low electric field.

  The domain wall 14 is preferably formed in the piezoelectric layer 3 between the adjacent internal electrode layers 5.

  With the above configuration, the region of the piezoelectric layer 3 between the adjacent internal electrode layers 5 is a region that is deformed when an electric field is applied to the multilayer piezoelectric element 1. Since the wall 14 is formed, the domain wall 14 can move simultaneously with the application of the electric field, so that high-speed driving is possible. In particular, in the crystal particle 11 in contact with the internal electrode layer 5, when the domain wall 14 straddling the plurality of crystal particles 11 is formed, the electric field concentrates on the end of the internal electrode layer 5, so that the end becomes a domain The movement of the domain wall 14 is started simultaneously with the application of voltage. As a result, the movement of the domain wall 14 propagates toward the center of the piezoelectric layer 3 between the internal electrode layers 5 like a shogi, so that extremely stable high-speed driving is possible.

  Further, as shown in FIG. 4, the domain wall 14 straddling the plurality of crystal grains 11 is preferably present in the vicinity 18 of the end portion of the internal electrode layer 5 in the piezoelectric layer 3.

  With the above configuration, since the polarization direction of the piezoelectric layer 3 is opposite to the internal electrode layer 5, the stress is most concentrated in the vicinity 18 of the end portion of the internal electrode layer 5 when the element 1 is driven. The crystal particles 11 can be deformed by moving the domain wall 14 when the crystal particles 11 in the vicinity of the end 18 of the internal electrode layer 5 are deformed so as to relieve the applied stress. Therefore, if the domain wall 14 straddling the plurality of crystal grains 11 is formed in the vicinity 18 of the end portion of the internal electrode layer 5, the domain wall 14 can move at a high speed, so that the stress relaxation effect is enhanced and stable for a long time. The element 1 can be driven.

  In this case, the vicinity 18 of the end portion of the internal electrode layer 5 is a region having about 5 to 20 crystal particles 11 from the end portion of the internal electrode layer 5.

  Furthermore, the laminated body 7 includes a planned fracture layer 6 that relieves stress by being fractured preferentially over the internal electrode layer 5 during driving, and the domain wall 14 straddling the plurality of crystal grains 11 has the planned fracture. It is preferably formed in the vicinity of the fault 6.

  According to the above configuration, when the crack is generated in the planned fracture layer 6 of the driving element 1 to relieve the stress, the crack reaches when the crack generated in the planned fracture layer 6 reaches the piezoelectric layer 3. When the domain wall 14 of the crystal particle 11 moves at a high speed, the crystal particle 11 can be deformed. As a result, the stress can be relaxed and the crack propagation to the piezoelectric layer 3 can be suppressed. As described above, the movement of the domain wall 14 makes it possible to deform the crystal particles 11 very easily. Accordingly, even when the multilayer piezoelectric element 1 is used in a state where a high load is applied for a long period of time, the piezoelectric layer 3 does not generate stress and cracks due to the stress, and the planned fracture layer 6 of the multilayer body 7 is not generated. Thus, cracks can be effectively generated to effectively relieve stress, and the multi-layer piezoelectric element 1 can be made highly durable.

  The planned fracture layer 6 in the laminate 7 is, for example, a porous metal particle layer containing a large number of independent metal particles in the laminate 7 separately from the internal electrode layer 5 or instead of the internal electrode layer 5. It can be provided by forming.

  The domain walls 14 straddling the plurality of crystal grains 11 are preferably formed in the plurality of piezoelectric layers 3.

  With the above configuration, stress from all directions applied to the multilayer piezoelectric element 1 can be dispersed, so that the multilayer piezoelectric element 1 can have high durability.

  The piezoelectric layer 3 preferably has an oxide component of lead element, and the oxide component of the lead element is preferably segregated at a triple point between the crystal particles 11.

  With the above configuration, when the domain wall 14 moves during driving, the domain wall 14 accompanying the deformation of the crystal particles 11 cannot move at the triple point where the oxide component of the lead element segregates. Acts as a stopper to prevent 14 from moving. Thereby, when the drive voltage is turned on / off, the domain wall 14 is moved in the same region, and the stacked piezoelectric element 1 can be made highly durable.

  Moreover, it is preferable that the oxide component of lead element is an amorphous phase.

  With the above configuration, the lattice vibration propagating the displacement of the ions in the crystal particles 11 disappears in the amorphous phase, so that the domain wall 14 with the deformation of the crystal particles 11 cannot be moved at the triple point, and the limit is limited. It acts as a stopper to prevent the domain wall 14 from moving. Accordingly, when the drive voltage is turned on / off, the domain wall 14 is moved in the same region, and the stacked piezoelectric element 1 can be made highly durable.

<Manufacturing method of multilayer piezoelectric element>
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 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, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 5 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder, a plasticizer, and the like to a metal powder made of silver-palladium alloy or the like. 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 6, carbon powder is contained in the conductive paste, and the carbon powder disappears during firing. There are also methods of pattern printing so that a dot pattern is formed during printing of the conductive paste, or dry-ice blasting after the conductive paste is printed and dried to roughen the printed surface.

  Further, when a plurality of porous metal particle layers including a large number of independent metal particles are collectively formed as the planned rupture layer 6, a conductive paste for forming a porous metal particle layer that becomes the planned rupture layer 6. And other metal electrode ratios with the conductive paste for forming the internal electrode layer 5, and utilizing the difference in concentration during firing, from the expected fracture layer 6 through the piezoelectric layer 3. A porous metal particle layer can be formed by diffusing a metal into the adjacent internal electrode layer 5. This method is preferable in terms of excellent mass productivity. In particular, using a conductive paste mainly containing silver-palladium, the silver concentration of the conductive paste layer to be the expected fracture layer 6 is set to be higher than the silver concentration of the conductive paste layers to be the other internal electrode layers 5. When it is increased, silver forms a liquid phase during firing and can easily move between the crystal grains 11 of the piezoelectric layer 3. Accordingly, it is possible to form the planned fracture layer 6 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.

  Here, how the domain wall 14 straddling a plurality of crystal particles 11 can be formed will be described in order.

  First, the domain wall 14 is formed in the crystal particles 11 when the temperature of the piezoelectric body becomes equal to or lower than the Curie point when the piezoelectric body sintered by firing is cooled. This is because the ionic arrangement in the crystal particle 11 is excellent in symmetry above the Curie point, and polarization itself does not occur, whereas the phase transformation of the crystal particle 11 occurs at the Curie point and becomes a structure extending in a uniaxial direction. Regions or domains having different polarizations are formed in the particles 11 and domain walls 14 are formed. Therefore, in order to form the domain wall 14 across the plurality of crystal particles 11, the ionic arrangement is consistent between the crystal particles 11, and the generation of a foreign substance or a grain boundary layer at the grain boundary 12 is excluded. It is necessary to form a body.

  In the conventional sintering, there is an oxygen adsorption layer on the surface of the crystal particles 11 just before sintering, and the crystal particles 11 are not joined to each other, but the large crystal particles 11 take in the small crystal particles 11 and finally the large particles When the crystal particles 11 come into contact with each other, they cannot be taken into each other and adhere to each other, so that the ion arrangement of the crystal particles 11 cannot be matched. Accordingly, the crystal lattice becomes mismatched, and an oxygen-excess grain boundary layer composed of the oxygen adsorption layer and the crystal component on the surface of the crystal particle 11 is formed. As a result, in the perovskite structure, which is a typical piezoelectric structure, B site ions are lost in the vicinity of the grain boundary 12 in order to compensate for the charge with the grain boundary 12 in which oxygen is excessive. Since the B site ions that cause polarization are missing in the vicinity of the grain boundary 12, each domain wall 14 is formed in the direction of relaxing the stress applied to each crystal grain 11.

  Therefore, the following method is performed so that the ionic arrangements between the adjacent crystal grains 11 are made to coincide with each other and foreign substances and grain boundary layers are prevented from being generated at the grain boundaries 12.

  First, when the ceramic green sheet to be the piezoelectric layer 3 is manufactured, if the calcined powder of the piezoelectric ceramic is, for example, lead zirconate titanate (PZT), the powder crystallized into a perovskite structure that exhibits piezoelectric characteristics Then, a powder crystallized in a pyrochlore structure that does not exhibit piezoelectric characteristics, a non-crystallized amorphous powder, and a powder of each of lead, titanium, and zirconium oxides are used as raw materials. As a result, when the firing temperature rises and the sintering proceeds, reactive sintering is performed in which the crystal particles 11 grow and sinter using the powder crystallized into a perovskite structure as a nucleus.

  Then, in the reaction sintering process, in order to match the ionic arrangement between the adjacent crystal particles 11, the crystal particles 11 are rotated during the sintering, and the alignment with the adjacent crystal particles 11 is performed. During the setting process, a liquid phase is formed to move through the grain boundary 12 and cause particle growth. As the liquid phase component, it is preferable to utilize the fact that silver in the component of the internal electrode layer 5 becomes silver oxide during firing, and becomes a piezoelectric material component and a liquid phase component. Therefore, it is preferable that the silver ratio in the internal electrode layer 5 is 90% by mass or more.

  The firing temperature is preferably 1000 ° C. or less. If the temperature exceeds 1000 ° C., oxygen vacancies in the grain boundary 12 are likely to be formed unless the oxygen partial pressure of the atmospheric gas during reaction sintering is set to be greater than that in the atmosphere. Even in the matched portions, oxygen ions diffuse on the surface of the crystal grains 11 due to oxygen defects. As a result, the neck grows from the grain boundary 12 portion to grow into a giant particle, and the domain wall 14 straddling the plurality of crystal particles 11 disappears.

  Here, by using a conductive paste having a different silver ratio depending on the position of the internal electrode layer 5 in the laminate 7, the silver component in the liquid phase can have a concentration gradient. As a result, a liquid phase that moves through the piezoelectric layer 3 can be formed. The crystal growth of the crystal particle 11 starts from the portion in contact with the internal electrode layer 5 by moving the liquid phase while performing reactive sintering in which the crystal particle 11 grows and sinters. As a result, particularly in the crystal particles 11 in contact with the internal electrode layer 5, the ionic arrangement can be matched between the adjacent crystal particles 11.

  Further, in the cooling stage of firing, the liquid phase silver component is taken into the internal electrode layer 5, the remaining component is taken in simultaneously with the growth of the crystal particles 11, and the remaining component is at the triple point between the crystal particles 11. Left behind. In the sintering of PZT, by sintering in the vapor of lead oxide, an excessive lead component is contained in the liquid phase and the progress of the sintering proceeds, so that it is left at the triple point between the crystal grains 11.

  As described above, in the portion where the ionic arrangement is matched between the adjacent crystal particles 11 and sintered, the domain wall 14 straddling the existing crystal particle 11 is formed when the temperature becomes below the Curie point during cooling. Furthermore, by including a metal having a large thermal expansion coefficient, such as silver, in the internal electrode layer 5, the thermal expansion coefficient of the internal electrode layer 5 becomes larger than the thermal expansion coefficient of the piezoelectric layer 3. As a result, the internal electrode layer 5 contracts more than the piezoelectric layer 3 in the cooling process after firing, so that the crystal particles 11 near the internal electrode layer 5 are forcibly polarized in a direction perpendicular to the stacking direction. . Instead of polarization due to an electric field, polarization due to stress occurs at a portion where the ionic arrangement is matched between the adjacent crystal grains 11 and sintered. Therefore, the other crystal particles 11 in contact with these crystal particles 11 are polarized in the same direction throughout the piezoelectric layer 3. On the other hand, the crystal grains 11 on the surface of the element 1 that are not in contact with the internal electrode layer 5 are polarized in various directions in order to compensate the charge of the element 1.

  Therefore, in order to form the domain wall 14 straddling the plurality of crystal grains 11 on the surface of the element 1, the surface of the fired element 1 is polished and scraped off, and then reheated to a temperature equal to or higher than the Curie point. , Rearrange the polarization direction.

  In order to expand the region where the domain wall 14 across the crystal particle 11 is formed over the entire element 1, the surface of the element 1 is subjected to a treatment such as sand blasting before the external electrode 9 is formed, and the internal electrode layer 5 is formed into the element 1. After cutting deeper than the surface, a conductive paste for forming the external electrode 9 mainly composed of silver is printed and then fired. Thereby, the diffusion of the metal component in the internal electrode layer 5 to the outside of the element 1 can be guided simultaneously with the sintering of the external electrode 9, and the liquid phase residual component remaining in the vicinity of the internal electrode layer 5 is also the external electrode 9. The force of contact between the crystal grains 11 that has been pulled out in the vicinity is increased, and the region where the domain wall 14 is formed across the crystal grains 11 is spread over the entire device 1.

  Further, in the polarization treatment, an electric field is applied after heating to a temperature equal to or higher than the Curie point, and cooling is performed to a temperature equal to or lower than the Curie point while applying a voltage for polarization. At this time, at the Curie point where the formation of the domain wall 14 is started, the temperature is maintained for 10 minutes or more while applying a voltage, and when the cooling is performed at a temperature gradient slower than 100 ° C./hour, Polarization can be performed without applying stress. As a result, in the piezoelectric layer 3 between the internal electrode layers 5, the domain wall 14 straddling the plurality of crystal particles 11 can be formed.

  In the polarization treatment, the oxygen gas concentration is made higher than the oxygen partial pressure during sintering, and then heated to a temperature above the Curie point, and cooled to a temperature below the Curie point while keeping the oxygen concentration high. This can suppress the movement of oxygen ions that disturb the ion arrangement between adjacent crystal grains. As a result, the domain wall 14 straddling the plurality of crystal particles 11 can be formed for the crystal particles 11 between the internal electrode layers 5. Therefore, it is preferable to increase the oxygen gas concentration more than twice as much as the oxygen partial pressure during sintering. A straddling domain wall 14 can be formed.

  In particular, when a plurality of porous metal particle layers including a large number of independent metal particles are collectively formed as the planned fracture layer 6, for example, a conductive paste that becomes a porous metal particle layer as the planned fracture layer 6, The internal components adjacent to each other from the planned fracture layer 6 through the piezoelectric layer 3 by changing the metal component ratio with the conductive paste to be the other internal electrode layer 5 and utilizing the concentration difference of the metal component during firing. A porous metal particle layer is formed by diffusing metal into the electrode layer 5. In this case, a liquid phase that moves through the piezoelectric layer 3 can be formed. Therefore, by performing reactive sintering in which the crystal particles 11 nucleate and sinter, and moving the liquid phase, Crystal growth of the particles 11 starts from the metal particles of the porous metal particle layer and the internal electrode layer 5 adjacent to the porous metal particle layer. As a result, in the crystal particles 11 in the vicinity of the expected fracture layer 6, the ion arrangement can be matched between the adjacent crystal particles 11, and the domain wall 14 straddling the plurality of crystal particles 11 can be formed.

  Note that the method of forming the domain wall 14 straddling the crystal particles 11 is not limited to the above example. For example, for the purpose of controlling the rate of reaction sintering and the moving speed of the liquid phase, oxygen in the firing atmosphere A method of changing the gas concentration for each temperature range of firing can be adopted, and various changes can be made without departing from the scope of the present invention.

  Next, a lead member made of a metal wire, a conductive member made of a metal mesh or a mesh-like metal plate, etc. is joined and connected to the surface of the external electrode 9 using a conductive bonding material such as solder or a conductive adhesive. Fix it. The material of the conductive member is preferably a metal or alloy such as silver, nickel, copper, phosphor bronze, iron or stainless steel. A plating layer made of silver, nickel, or the like may be formed on the surface of the conductive member.

  The conductive member may be bonded over the entire outer surface of the external electrode 9 in the stacking direction, or may be bonded to a part of the outer surface of the external electrode 9.

  Next, the laminate 7 on which the external electrode 9 is formed is immersed in a resin solution containing a silicone resin that serves as an exterior resin. Then, the resin solution is vacuum degassed to bring the silicone resin into close contact with the uneven portions on the outer peripheral side surface of the laminate 7, and then the laminate 7 is pulled up from the resin solution. Thereby, the silicone resin layer is coated on the side surface of the laminate 7 on which the external electrode 9 is formed.

  Thereafter, a direct current electric field of 0.1 to 3 kV / mm is applied from the pair of external electrodes 9 to the piezoelectric layer 3 through the conductive member connected to the external electrode 9 by the internal electrode layer 5. By polarizing, the laminated piezoelectric element 1 of this example is completed. Then, the conductive member is connected to an external voltage supply source, and a voltage is applied to the piezoelectric layer 3 by the internal electrode layer 5 via the conductive member and the external electrode 9, thereby causing each piezoelectric layer 3 to have an inverse piezoelectric effect. It can be displaced greatly. Thereby, for example, it is possible to function as a fuel injection valve mechanism or the like for an automobile for 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. 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 present invention represented by the example of the above embodiment is accommodated in a container 23 having an injection hole 21 at one end. Yes.

  A needle valve 25 that can open and close the injection hole 21 is disposed in the container 23. A fluid passage 27 is disposed in the injection hole 21 so that it can communicate with the movement of the needle valve 25. The fluid passage 27 is connected to an external fluid supply source, and is supplied with, for example, a liquid that is a fluid at a high pressure at all times. Therefore, when the needle valve 25 opens the injection hole 21 by driving the multilayer piezoelectric element 1, the fluid supplied to the fluid passage 27 is transferred to the outside of the injection hole 21 or a container adjacent to the injection hole 21, such as an internal combustion engine. The fuel is discharged from the injection hole 21 and injected into a fuel chamber (not shown).

  The upper end portion of the needle valve 25 has a large inner diameter, and a cylinder 29 formed in the container 23 and a slidable piston 31 are disposed in that portion. In the container 23, the multilayer piezoelectric element 1 of the present embodiment is accommodated.

  In such an injection device 19, when the multilayer piezoelectric element 1 that functions as a piezoelectric actuator is extended by applying a voltage, the piston 31 is pressed, the needle valve 25 closes the injection hole 21, and the supply of fluid is stopped. The When the application of voltage is stopped, the multilayer piezoelectric element 1 contracts, and the disc spring 33 pushes back the piston 31 to open the fluid passage 27, so that the injection hole 21 communicates with the fluid passage 27 and the injection hole. The fluid is ejected from 21.

  The fluid ejection operation is to apply a voltage to the multilayer piezoelectric element 1 to open the fluid passage 27 to discharge the fluid from the ejection hole 21 and to close the fluid passage 27 by stopping the voltage application. Thus, the discharge of the fluid may be stopped.

  The injection device 19 according to the present embodiment includes a container 23 having an injection hole 21 and the multilayer piezoelectric element 1 according to the present embodiment, and the fluid filled in the container 23 is used for the multilayer piezoelectric element 1. It may be configured to discharge from the injection hole 21 by driving. That is, the multilayer piezoelectric element 1 does not necessarily have to be inside the container 23, and the pressure for supplying and stopping the fluid to the injection hole 21 is applied to the inside of the container 23 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 21 through the fluid passage 27, but also provided in the container 23 with a portion for temporarily storing the fluid in an appropriate place in the container 23. The filled fluid may be discharged from the ejection hole 21.

  In the present embodiment, the fluid includes various liquid materials (such as conductive paste) and gas in addition to liquids such as fuel or ink. By using the ejection device 19 of the present embodiment for these fluids, the fluid flow rate and ejection timing can be stably controlled over a long period of time.

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

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

  FIG. 6 is a schematic block diagram 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, a plurality of injection devices 19 of the present embodiment that inject high-pressure fuel stored in the common rail 37, and a common rail 37. A pressure pump 39 for supplying high-pressure fuel to the injection device 19 and an injection control unit 41 for supplying a drive signal to the injection device 19.

  The injection control unit 41 controls the amount and timing of high-pressure fluid injection based on information or signals from the outside. For example, the amount and timing of fuel injection are controlled while sensing the condition in the combustion chamber of the engine with a sensor or the like. The pressure pump 39 serves to supply the fuel from the fuel tank 43 to the common rail 37 at a high pressure of about 101 MPa to 203 MPa (1000 to 2000 atmospheres), preferably about 152 MPa to 172 MPa (1500 to 1700 atmospheres). 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 injection device 19 injects a predetermined amount of high-pressure fuel from the injection hole 21 into the outside or an adjacent container, for example, the combustion chamber of the engine in the form of a mist.

  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. In addition, the present invention relates to a multilayer piezoelectric element, an injection device, and a fuel injection system, but is not limited to the above-described embodiment, for example, a printing device of an ink jet printer, a pressure sensor, or the like Even if it is what is used for, if it is a lamination type piezoelectric element using a piezoelectric characteristic, it can implement with the same structure.

  Examples of the multilayer piezoelectric element of the present invention will be described below.

  The multilayer piezoelectric element of this example was manufactured as follows.

  First, a slurry in which a binder and a plasticizer were mixed with raw material powder mainly composed of lead zirconate titanate (PZT) powder having an average particle diameter of 0.4 μm after calcining at 1200 ° C. was prepared. Using the slurry, a ceramic green sheet A having a thickness of 150 μm was prepared by a doctor blade method.

  Next, it is calcined at 1200 ° C and then pulverized to have an average particle size of 0.4 µm, and the raw material powder is 50% by mass of lead zirconate titanate (PZT) powder. 50% by mass of a raw material powder whose main component is another powder having an average particle size of 0.4 μm (a PZT composition composed of titanium oxide, zirconium oxide, lead oxide and pyrochlore phase and a glass phase). A slurry was prepared by blending and mixing a binder and a plasticizer. Using the slurry, a ceramic green sheet B having a thickness of 150 μm was prepared by a doctor blade method.

  Next, conductive paste A in which a binder is added to a raw material powder containing silver-palladium alloy powder having a metal composition of Ag 95% by mass-Pd 5% by mass, and silver 96% by mass Ag-96% by mass-Pd 4% by mass. A conductive paste B in which a binder was added to a raw material powder containing palladium alloy powder and a conductive paste C in which a binder was added to a raw material powder containing silver powder having a metal composition of Ag 100% by mass were prepared.

  Then, a conductive paste was printed on one side of the ceramic green sheet with a pattern of the internal electrode layer so as to have a thickness of 30 μm by screen printing. And each green sheet on which the conductive paste 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. The green laminates were prepared by stacking five types (sample numbers 1 to 5).

  Sample No. 1 was made of ceramic green sheet A and conductive paste A.

  Sample Nos. 2 and 3 were made so that the layers of the conductive paste A and the conductive paste B were alternately laminated using the ceramic green sheet B, the conductive paste A, and the conductive paste B. Produced.

  Sample Nos. 4 and 5 use the ceramic green sheet B, the conductive paste A, and the conductive paste B so that the layers of the conductive paste A and the layers of the conductive paste B are alternately stacked. At the same time, in order to provide a porous metal particle layer made of isolated metal particles as the expected fracture layer 6, layers of the conductive paste C were printed at the 50th, 150th and 250th positions from the bottom in the stacking direction.

  Next, the raw laminate of each sample number was subjected to a binder removal treatment at a predetermined temperature, and then fired at 800 to 1000 ° C. to obtain a laminate 7. The cooling rate of firing was 100 ° C./hour for sample numbers 1, 2, and 4, and 200 ° C./hour for sample numbers 3 and 5.

  Here, in sample numbers 2 to 5, silver, which is a metal component of the conductive paste layer, diffuses into the adjacent conductive paste layer having a low silver concentration during firing. In particular, the conductive paste C layer has a higher silver concentration than the other conductive pastes, so that the diffusion becomes remarkable, and the expected fracture layer 6 composed of a porous metal particle layer composed of isolated metal particles is formed. .

  Then, the laminated body 7 of each sample number is subjected to a polishing process so as to have a desired dimension, blasted after the polishing process, and the end of the internal electrode layer 5 exposed on the surface is polished, and the end Is recessed from the surface of the piezoelectric layer 3.

  Next, the external electrode 9 was formed. First, a conductive paste for forming 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 was subjected to pattern printing by screen printing or the like on the portion of the laminate 7 where the external electrodes 9 on the two side surfaces facing each other were formed, and then fired at 600 to 800 ° C. The cooling process of firing was performed in a stream of synthetic air with 20% oxygen gas and 80% nitrogen gas, and the external electrode 9 was formed at a cooling rate of 200 ° C./hour.

  Next, a lead wire is connected to the external electrode 9, and a 3 kV / mm DC electric field is applied to the piezoelectric layer 3 from the positive and negative external electrodes 9 through the lead wire while heating at 300 ° C. for 15 minutes for polarization. The sample was processed and cooled at a rate of 200 ° C./hour to produce each sample of the multilayer piezoelectric element 1.

  In this way, two laminated piezoelectric elements 1 were produced for each sample, and the domain wall 14 was observed with a transmission electron microscope (TEM) for each of the laminated piezoelectric elements 1. Drive evaluation was performed using the remaining one.

  As drive evaluation, high-speed response evaluation and durability evaluation were performed. A DC voltage of 170 V was applied to the obtained multilayer piezoelectric element 1 to measure an initial displacement amount as a piezoelectric actuator.

  As for the presence or absence of beat noise due to the disturbance of the displacement speed as a high-speed response evaluation, an AC voltage of 0V to + 170V is gradually applied from 150 Hz to each laminated piezoelectric element 1 at a room temperature. It was measured.

As the durability evaluation, a test was performed in which each laminated piezoelectric element 1 was continuously driven up to 1 × 10 ⁹ times by applying an AC voltage of 0 V to +170 V at a frequency of 150 Hz at room temperature. Furthermore, after continuously driving up to 1 × 10 ⁹ times, an AC voltage of 0 V to +170 V is applied again at room temperature by gradually increasing the frequency from 150 Hz to evaluate high-speed response (evaluation of the presence or absence of beat sound) ).

  The results of these tests are shown in Tables 1 and 2 together with the observation results of the domain wall 14.

  As shown in Tables 1 and 2, only Sample No. 1 was observed to generate a roar when the frequency exceeded 1 kHz. This is because the domain wall 14 is formed in each of the plurality of crystal grains 11 in different directions in the multilayer piezoelectric element 1 of sample number 1, and therefore the domain wall 14 is moved by the grain boundary 12 of the piezoelectric layer 3. It is considered that the response speed becomes slow due to restraint, the displacement speed of each piezoelectric layer 3 is disturbed, and the beat sound is generated because 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 harmonics were found at locations corresponding to an integral multiple of the drive frequency. A component (noise) was confirmed.

In addition, as a result of the durability evaluation, in Sample No. 1, the displacement amount after the durability evaluation test (displacement amount after 1 × 10 ⁹ times) is 5 μm, which is close to 90% compared to before the durability evaluation test (( (45-5) / 45) × 100 = 88.9%). Further, in the piezoelectric actuator of sample number 1, peeling occurred in the external electrode 9 after continuous driving (1 × 10 ⁹ times), and peeling also occurred in a part of the laminated portion in the laminated body 7.

For this sample No. 1, as a durability evaluation, after continuous driving (1 × 10 ⁹ times), an AC voltage of 0 V to +170 V was applied again at room temperature by gradually increasing the frequency from 150 Hz to 1 kHz, and high speed was applied. Responsiveness evaluation was performed. As a result, generation of a roaring sound was observed when the frequency exceeded 100 Hz. This is presumably because, in the multilayered piezoelectric element 1 of sample number 1, peeling occurred between the piezoelectric layer 3 and the internal electrode layer 5, and thus a beat sound like a piezoelectric buzzer was generated.

  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 harmonics were found at locations corresponding to an integral multiple of the drive frequency. A component (noise) was confirmed.

On the other hand, in the piezoelectric actuators of sample numbers 2 to 5 which are embodiments of the present invention, peeling of the external electrode 9 and peeling of the laminated portion in the laminated body 7 were confirmed after continuous driving (1 × 10 ⁹ times). There wasn't.

The decrease in the displacement after the durability evaluation test is 3 μm or less, and the decrease in the displacement is 6% or less (((55−52) / 55) × 100 = 5.5). In particular, the piezoelectric actuators of Sample Nos. 4 and 5 were found to have very high durability because no decrease in displacement was confirmed even after 1 × 10 ⁹ cycles.

  In addition, after the durability evaluation test, the laminated piezoelectric element 1 of sample numbers 4 and 5 had cracks in the planned fracture layer 6. It was confirmed that the planned fracture layer 6 was preferentially fractured and the stress in the laminate 7 was relaxed.

  Further, when a thermocouple was attached to the central portion of all the multilayer piezoelectric elements 1 and the maximum temperature of the multilayer piezoelectric element 1 being driven was measured, as shown in Table 1, the center of the multilayer piezoelectric element 1 was measured. It was confirmed that the increase in heat generation in the area could be suppressed. Thus, it is considered that the domain wall 14 straddling the plurality of crystal grains 11 is formed, so that there is no region for restraining displacement, and overheating of the multilayer piezoelectric element 1 during driving can be suppressed. As a result, a highly durable multilayer piezoelectric element 1 was obtained.

It is a perspective view which shows an example of embodiment of the lamination type piezoelectric element of this invention. (A)-(c) is a typical expanded sectional view of the crystal grain and domain wall in the piezoelectric material layer which respectively comprise the lamination type piezoelectric element of FIG. (A)-(c) is a typical expanded sectional view similar to Fig.2 (a) which shows a mode that a crystal grain and a domain wall each change a structure by voltage application. FIG. 2 is a schematic cross-sectional view showing the vicinity of an end portion of an internal electrode layer in the multilayer body of the multilayer piezoelectric element in FIG. 1. 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)-(c) is a typical expanded sectional view of the crystal grain and domain wall in the piezoelectric material layer which respectively comprises the conventional laminated piezoelectric element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 3 ... Piezoelectric layer 5 ... Internal electrode layer 6 ... Planned fracture layer 7 ... Laminated body 9 ... External electrode
11 ... Crystal particles
12 ... grain boundaries
13 ... Domain polarization direction
14 ... Domain wall
18 ... Near the edge of the internal electrode layer
19 ... Injection device
21 ... Injection hole
23 ・ ・ ・ Storage container
35 ... Fuel injection system
37 ... Common rail
39 ・ ・ ・ Pressure pump
41 ... Injection control unit

Claims (12)

  A multilayer piezoelectric element including a multilayer body in which piezoelectric layers and internal electrode layers are alternately stacked, wherein the piezoelectric layer is formed with a domain wall straddling a plurality of crystal grains. Laminated piezoelectric element.   2. The multilayer piezoelectric element according to claim 1, wherein the piezoelectric layer has a region where polarization axes are aligned at a portion where the adjacent crystal particles are in contact with each other in a region surrounded by the domain wall. element.   3. The multilayer piezoelectric element according to claim 1, wherein the domain wall is formed so that a portion straddling the adjacent crystal grains is formed linearly. 4.   The multilayer piezoelectric element according to any one of claims 1 to 3, wherein the crystal grains are mainly composed of a 90 ° domain.   5. The multilayer piezoelectric element according to claim 1, wherein the domain wall is formed in the piezoelectric layer between the adjacent internal electrode layers. 6.   The multilayer piezoelectric element according to claim 1, wherein the domain wall is present in the vicinity of an end portion of the internal electrode layer in the piezoelectric layer.   The laminate includes a planned fracture layer that relaxes stress by being preferentially fractured over the internal electrode layer when driven, and the domain wall is formed in the vicinity of the planned fracture layer The multilayer piezoelectric element according to any one of claims 1 to 6, wherein:   The multilayer piezoelectric element according to claim 1, wherein the domain wall is formed in a plurality of the piezoelectric layers.   The piezoelectric body layer has an oxide component of lead element, and the oxide component of the lead element is segregated at a triple point portion between crystal grains. The multilayer piezoelectric element according to any one of 8.   The multilayer piezoelectric element according to claim 9, wherein the oxide component of the lead element is an amorphous phase.   A container having an ejection hole and the multilayer piezoelectric element according to any one of claims 1 to 10, wherein the liquid filled in the container is discharged from the ejection hole by driving the multilayer piezoelectric element. An injection device.   A common rail for storing high-pressure fuel, an injection device according to claim 11 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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