JP2011249659A - Piezoelectric element, injector and fuel injection system comprising it - Google Patents

Abstract

Disclosed is a piezoelectric element in which the movement of a domain wall is not easily restricted, the response speed is high, the amount of displacement can be increased, the mechanical strength is sufficient, and the deterioration of characteristics can be suppressed.
A piezoelectric element includes a piezoelectric layer and an electrode layer provided so as to face each other through the piezoelectric layer, and oxygen vacancies are present in grain boundaries 12 between crystal grains 11 forming the piezoelectric layer. 10 is formed, and the oxygen vacancy 10 is located in the vicinity of the end of the domain wall 14 in the crystal particle 11. Thereby, the response speed of the piezoelectric element is increased, and the amount of displacement can be increased. Furthermore, it is possible to obtain a piezoelectric element that does not deteriorate in displacement even when continuously driven.
[Selection] Figure 2

Description

  The present invention relates to a piezoelectric element, an injection device using the piezoelectric element, and a fuel injection system. The 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.

  Conventionally, a piezoelectric element in which a piezoelectric layer is sandwiched between metal layers, and a stacked piezoelectric element including a stacked body in which a plurality of piezoelectric layers are stacked via a metal layer are known. In these piezoelectric elements, when an electric field is applied to the piezoelectric layer through the metal layer, displacement occurs due to deformation in which the crystal particles of the piezoelectric layer constituting the multilayer body expand and contract in the direction of the electric field.

  Here, as shown in FIGS. 7 (a), 7 (b) and 7 (c), there are a plurality of regions having different polarization axis directions in the crystal particle 11, and the polarization axis direction 13 of the domain. A domain wall 14 is formed at a boundary between different regions. That is, the domain wall 14 partitions a region where the polarization axes are aligned in a certain direction and a region where the polarization axes are aligned in a direction different from the direction of this region. 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, 12 is a grain boundary, 13 is the domain polarization axis 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. is there.

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

  However, when there are a plurality of regions having different polarization axis directions, it is rare that the direction in which the electric field is applied is aligned with all the polarization axis directions. Therefore, an electric field is applied in many regions of the crystal grains. Sometimes, the domain wall moves so that the ratio of the polarization axis direction to the electric field application direction increases. As a result, the region where the crystal grains of the piezoelectric layer extend is expanded and the piezoelectric element expands. Conversely, when the application of the electric field is released, the domain wall returns to the original position and the piezoelectric element contracts. Utilizing this phenomenon, the piezoelectric element is driven.

  Conventionally, since the crystal alignment at the grain boundary 12 is disturbed and the neutrality of the charge cannot be taken, the ions constituting the crystal grains in the vicinity of the grain boundary 12 move in a direction to compensate for the charge at the grain boundary 12 to neutralize the charge. Keep. Therefore, the polarization axis direction hardly changes near the grain boundary 12 when an electric field is applied. That is, the movement of the domain wall is constrained by the grain boundary 12 (see, for example, Patent Document 1).

JP 2005-191397

  In the 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 11 of the piezoelectric layer. Further, there is a problem that the displacement of the piezoelectric element is reduced because the movement of the domain wall 14 is restricted by the grain boundary 12 between the crystal grains 11 of the piezoelectric layer. In addition, there is a problem in that a portion constrained by continuous driving self-heats, cracks occur in the piezoelectric layer constituting the piezoelectric element, and the amount of displacement gradually decreases.

  The present invention has been devised to solve such problems, and its purpose is that the movement of the domain wall is less likely to be restrained, the response speed is high, and the amount of displacement can be increased. An object of the present invention is to provide a piezoelectric element that has sufficient strength and can suppress deterioration of characteristics.

  The piezoelectric element of the present invention includes a piezoelectric layer and an electrode layer provided so as to face each other with the piezoelectric layer interposed therebetween, and oxygen vacancies are formed at grain boundaries between crystal grains forming the piezoelectric layer. It is formed, and the oxygen vacancy is located in the vicinity of the end portion in the crystal grain.

  Further, in the piezoelectric element of the present invention, in the above configuration, the crystal particle having a region in which the directions of polarization axes coincide with each other and the crystal particle are adjacent to each other, and the domain wall in each adjacent crystal particle is The end portions are close to each other.

  The piezoelectric element of the present invention is characterized in that, in the above configuration, the domain walls in each of the adjacent crystal grains are substantially parallel.

  Moreover, the piezoelectric element of the present invention is characterized in that, in the above configuration, the oxygen vacancies are located between ends of the domain walls in the adjacent crystal grains. .

  The piezoelectric element of the present invention is characterized in that, in the above configuration, the domain wall is formed by a 90 ° domain.

  The piezoelectric element of the present invention is characterized in that, in the above configuration, the oxygen vacancy is located in the vicinity of the electrode layer.

  Moreover, the piezoelectric element of the present invention is characterized in that, in the above configuration, the piezoelectric element is a stacked piezoelectric element in which the piezoelectric layers and the electrode layers are alternately stacked.

  An injection device of the present invention includes a container having an ejection hole and any one of the above-described piezoelectric elements of the present invention, and the liquid stored in the container is ejected from the ejection hole by driving the piezoelectric element. It is characterized by this.

  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 piezoelectric element of the present invention, oxygen vacancies are formed at the grain boundaries between crystal grains forming the piezoelectric layer, and the oxygen vacancies are located near the end of the domain wall. The movement of the domain wall is not constrained by the grain boundary, and the domain walls of adjacent crystal grains move in conjunction with the application of the electric field. Therefore, the moving speed and moving amount of the domain wall due to electric field application can be increased. Thereby, the response speed of the piezoelectric element is increased, and the amount of displacement can be increased. Further, since there is no region for restraining displacement, overheating of the driving 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 in the piezoelectric layer can be made small, thereby increasing the mechanical strength and the large displacement. It can be set as an element. As a result, it is possible to obtain a piezoelectric element that does not deteriorate in displacement even when continuously driven.

  Further, according to the ejecting apparatus of the present invention, since the piezoelectric element of the present invention is provided as a piezoelectric element for discharging the liquid stored in the container from the ejecting hole, the piezoelectric element has a large displacement amount and excellent durability. Therefore, it is possible to stably perform desired liquid ejection 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.

It is a perspective view which shows an example of embodiment of the piezoelectric element of this invention. (A), (b), and (c) are the schematic diagrams of the crystal grain and domain of a piezoelectric layer which respectively comprise the piezoelectric element shown in FIG. (A), (b), and (c) are schematic diagrams showing how the crystal grains and domains shown in FIG. 2 (a) undergo structural changes due to application of an electric field. FIG. 2 is a main part sectional view schematically showing an example of the vicinity of an end portion of an electrode layer 5 in a laminate 7 of a piezoelectric element 1 shown in FIG. 1. 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. (A), (b) and (c) are schematic diagrams of crystal grains and domains of a piezoelectric layer constituting a conventional piezoelectric element, respectively.

<Piezoelectric element>
Hereinafter, an example of an embodiment of a 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 piezoelectric element according to the present invention. FIGS. 2A, 2B, and 2C are piezoelectric bodies constituting the piezoelectric element 1 shown in FIG. FIG. 3 is a schematic diagram of crystal particles 11 and polarization domains in layer 3.

  The piezoelectric element 1 shown in FIG. 1 includes a laminated body 7 in which piezoelectric layers 3 and electrode layers 5 are alternately laminated, and an external body joined to the side surface of the laminated body 7 and electrically connected to the electrode layer 5. It is a multilayer piezoelectric element including an electrode 9. Although not illustrated, the piezoelectric element of the present invention is not limited to the stacked piezoelectric element shown in FIG. 1 as long as it includes the electrode layer 5 provided so as to face each other via the piezoelectric layer 3. .

In the piezoelectric element 1 of the present invention, as shown in FIGS. 2 (a), (b) and (c), oxygen vacancies are present in the grain boundaries 12 between the crystal grains 11 forming the piezoelectric layer 3. 10 is formed, and the oxygen vacancy 10 is located in the vicinity of the end of the domain wall 14 in the crystal particle 11. In FIG. 2, (b) is an enlarged view of a portion A shown in (a), and (c) is a cross-sectional view showing an arrangement state of atoms with respect to (b). In FIG. 2, 13 is the domain polarization axis 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.

Here, in the vicinity of the end portion, the distance from the end portion of the domain wall 14 is 1/8 or less of the outer peripheral distance of the crystal particle 11. This is the distance that the end of the domain wall 14 moves along the grain boundary 12. Preferably, the distance from the end of the domain wall 14 is 0.1 μm or less. This is because the strain of ions at the grain boundary easily propagates even in a weak electric field, and the domain wall 14 can be moved. These distances and the positions of the oxygen vacancies 10 are determined by a backscattered electron diffraction device (for example, NC5 manufactured by HKL), a wavelength dispersive X-ray analyzer (for example, JXA8100 manufactured by JEOL) or a transmission electron microscope (for example, JEOL). It can be measured by JEM-2010F).

  The ions constituting the crystal grains 11 in the vicinity of the grain boundaries 12 that are constrained in the direction to compensate the charges at the grain boundaries 12 in order to maintain the neutrality of the charges at the grain boundaries 12 are restrained by the charges at the grain boundaries 12. However, with the above configuration, when an electric field is applied to the piezoelectric element 1, the oxygen vacancies 10 in the grain boundaries 12 are ionized to generate charges that can be freely moved, so that the crystal grains 11 near the grain boundaries 12 are generated. The charge that binds the ions that make up the structure moves freely in the external electric field, and when polarized by applying an external electric field, the domain wall 14 moves freely without being constrained even near the grain boundary 12. become.

  In particular, when driving the piezoelectric element 1, since each of the crystal particles 11 constituting the piezoelectric layer 3 is deformed, a stress is applied between the crystal particles 11, so that a force constraining the movement of the domain wall 14 is applied. However, by providing an oxygen vacancy 10 in the vicinity of the end of the domain wall 14 at a position that intersects the electric field formed by applying a voltage to the electrode layer 5, the domain wall 14 in the direction of the electric field that drives the piezoelectric element 1 is provided. Therefore, the displacement response speed can be increased.

  Further, even when oxygen vacancies are formed inside the crystal particles 11 constituting the piezoelectric layer 3 and the movement of the domain wall 14 is restricted inside the crystal particles 11, it is formed by applying a voltage to the electrode layer 5. By providing the oxygen vacancy 10 in the vicinity of the end of the domain wall 14 that intersects the electric field, the domain wall 14 starts from the grain boundary 12 portion because the domain wall 14 near the grain boundary 12 can be easily moved. The domain wall 14 can move even in the region where the oxygen vacancies 10 inside the crystal particles 11 are present, and the amount of displacement can be increased.

The thickness of the piezoelectric layer 3 is preferably about 40 to 250 μm, and the thickness of the electrode layer 5 is preferably 1 to 20 μm. Thereby, the multilayer piezoelectric element can obtain a large displacement without distorting the piezoelectric element 1 due to internal stress. The particle size of the crystal particles 11 is preferably 0.1 to 50 μm. Thereby, the domain wall 14 can be provided in the crystal particle 11, and the oxygen vacancies inside the domain can be easily moved to the end portion of the domain wall by using the manufacturing method described later.

  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 are in the same direction, so that the polarization axis directions coincide with each other. Since the adjacent crystals of the domain wall 14 can move continuously, the moving speed of the domain wall 14 increases. That is, the response speed of displacement can be increased.

  Further, in the piezoelectric layer 3, there is a region where the directions of the polarization axes are coincident with each other between the adjacent crystal particles 11, and the ends of the domain walls 14 are close to each other. It is preferable. This is because the domain wall 14 moves continuously between the adjacent crystal particles 11 simultaneously with the application of the electric field, so that high-speed polarization is possible and the response speed of displacement can be increased.

Note that the proximity means 1/8 or less of the outer peripheral distance of the crystal particle 11. This is the distance that the end of the domain wall 14 moves along the grain boundary 12. Preferably, the distance from the end of the domain wall 14 is 0.1 μm or less. This is because the strain of ions at the grain boundary easily propagates even in a weak electric field, and the domain wall 14 can be moved.

  In addition, because the domain walls 14 in each adjacent crystal particle 11 are substantially parallel, the domain walls 14 move almost simultaneously between the adjacent crystal particles 11, so that high-speed polarization is possible, The response speed of displacement can be increased. Furthermore, since pre-processing such as polarization processing is not required and there is no residual stress due to polarization processing, the domain wall 14 stably moves between adjacent crystal grains 11 even in a long-term drive. This is because stable driving is realized. Further, the domain wall 14 with the oxygen vacancy 10 at the end is formed in a linear shape in a region straddling the adjacent crystal particles 11, so that when the domain wall 14 moves by applying an electric field, the displacement of ions is reduced. Since it is performed in a linear chain without being interrupted by the grain boundary 12, there is no distortion in the movement of the domain wall 14, and no stress is generated. Can be made extremely fast.

  In addition, since the oxygen vacancies 10 are positioned between the ends of the domain walls 14 in the adjacent crystal particles 11, the charge between the adjacent domain walls 14 can move freely. As shown in FIGS. 3A, 3B and 3C, the domain walls 14 of the adjacent crystal grains 11 can move continuously. In the piezoelectric layer 3 having such a domain structure, the binding force at the grain boundary 12 of the domain wall 14 having the oxygen vacancy 10 at the end is reduced, and oxygen with respect to the electric field applied to the piezoelectric layer 3 is reduced. The moving speed of the domain wall 14 having the holes 10 at the end is increased. That is, the response speed of displacement can be increased. Further, since there is no region for restraining displacement, overheating of the driving piezoelectric element 1 can be suppressed, and the piezoelectric element 1 having high durability can be obtained. Further, when the piezoelectric element 1 is driven and deformed, the vicinity of the grain boundary 12 is polarized and contributes to the deformation. Therefore, a highly durable piezoelectric element in which the amount of displacement does not change even when driven for a long time can be obtained.

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

  Further, it is preferable that the crystal particles 11 are mainly composed of 90 ° domains. When configured with a 90 ° domain, the domain wall 14 can be easily moved in a low electric field, so that the displacement response speed can be increased. Further, since there is no need to reverse the polarization, a high voltage polarization process is unnecessary, and the piezoelectric element 1 is not damaged at all by the high voltage, so that a highly durable piezoelectric element can be obtained.

  Further, when the oxygen vacancy 10 is formed in the vicinity of the electrode layer 5 as shown in FIG. 4, the electric field concentrates on the end of the electrode layer 5 to become a starting point for the movement of the domain wall 14, and simultaneously with the electric field application Since the movement of the domain wall 14 is started and the movement of the domain wall 14 is propagated toward the center of the piezoelectric layer 3 between the electrode layers 5 like a shogi, extremely stable high-speed driving is possible. In particular, it is preferably present in the vicinity 18 of the end portion of the electrode layer 5 in the piezoelectric layer 3. This is because the direction of polarization of the piezoelectric layer 3 is opposite to the electrode layer 5 in between, so that stress is concentrated most at the electrode layer end 18 in element driving, but the applied stress is relieved. When the crystal particles 11 near the end 18 of the electrode layer 5 are deformed, the domain wall 14 moves, so that the crystal particles 11 can be deformed. Therefore, when the oxygen vacancy 10 is formed in the vicinity 18 of the end of the electrode layer 5, the domain wall 14 can move at a high speed, so that the stress relaxation effect is enhanced and the element can be driven stably for a long time. .

  Note that the region 18 near the end of the electrode layer 5 is a region where the electric field concentrates and the distance from the end of the electrode layer 5 is 10 μm or less.

In addition, when the piezoelectric layer 3 and the electrode layer 5 are alternately stacked, the domain wall 14 can be moved simultaneously with the application of an electric field, so that high-speed driving is possible. In addition to not only relieving the stress caused by the lamination, the domain walls 14 having the oxygen vacancies 10 at the end portions are formed in the plurality of piezoelectric layers 3, so that they can be applied from all directions applied to the piezoelectric elements. Since stress can be dispersed, the piezoelectric element 1 can be made highly durable.

  Furthermore, the laminated body 7 includes a planned fracture layer 6 that relieves stress by being fractured preferentially over the electrode layer 5 when driven, and the domain wall 14 with the oxygen vacancy 10 at the end includes It is preferably formed in the vicinity of the fracture layer 6. This is because, when the crack is generated in the planned fracture layer 6 of the element being driven and the stress is relaxed, when the crack generated in the planned fracture layer 6 reaches the piezoelectric layer 3, the piezoelectric part of the crack has reached. When the domain wall 14 of the body crystal moves at a high speed, the crystal particles 11 can be deformed. As a result, the stress can be relaxed and the crack propagation to the piezoelectric layer 3 can be suppressed. Since the domain wall 14 moves in this manner, the crystal particles 11 can be deformed very easily. Therefore, even when the piezoelectric element 1 is used in an environment where a high load is applied for a long period of time, the piezoelectric layer 3, without causing a stress and a crack caused by the stress, it is possible to relax the stress by effectively generating a crack only in the expected fracture layer 6 of the laminate 7, and the piezoelectric element 1 has high durability. be able to.

  The planned fracture layer 6 in the laminate 7 forms, for example, a porous metal particle layer including a large number of independent metal particles in the laminate 7 separately from or in place of the electrode layer 5. Can be provided.

<Manufacturing method>
Next, a method for manufacturing the 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 calendar 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 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. When a laminated piezoelectric element is used, a plurality of ceramic green sheets on which the conductive paste is screen-printed are further laminated. And the laminated body 7 provided with the piezoelectric body layer 3 and the electrode layer 5 which were laminated | stacked alternately can be formed by baking as mentioned later.

At this time, if a porous metal particle layer including a large number of independent metal particles is formed as the planned fracture layer 6, for example, carbon powder is contained 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 including a large number of independent metal particles is formed as the planned fracture layer 6, the conductive paste of the porous metal particle layer to be the planned fracture layer 6 and other Diffusion of metal from the expected fracture layer 6 to the adjacent electrode layer 5 via the piezoelectric layer 3 by changing the metal component ratio with the conductive paste of the electrode layer 5 and utilizing the concentration difference during firing To make it porous. This method is preferable in terms of excellent mass productivity. In particular, when using a conductive paste mainly made of silver-palladium and making the silver concentration of the layer to be the expected fracture layer 6 higher than the silver concentration of the other electrode layers 5, the silver forms a liquid phase during firing. Since it is possible to easily move between the crystal particles 11 of the piezoelectric layer 3, it is possible to form the expected fracture layer 6 composed of a very uniform porous metal particle layer.

  Thereafter, the external electrode 9 is formed on the outer surface of the laminate 7 of the piezoelectric element 1 so as to obtain electrical continuity with the 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 oxygen vacancies 10 can be formed in the vicinity of the ends of the domain walls 14 in the crystal particles 11 in the piezoelectric layer 3 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 ion arrangement in the crystal structure is excellent in symmetry above the Curie point, and polarization itself does not occur. On the other hand, a crystal phase transformation occurs at the Curie point, and a structure extending in a uniaxial direction is formed. In the crystal particle 11, regions having different polarizations, that is, domains, and domain walls 14 are formed. Therefore, in order to provide the oxygen vacancy 10 in the vicinity of the end of the domain wall 14 in the crystal particle 11, the ion arrangement is matched between the crystal particles 11, and foreign matter and a grain boundary layer are generated at the grain boundary 12. It is necessary to form a piezoelectric body so as to eliminate it.

  In conventional sintering, there is an oxygen adsorption layer on the surface of the crystal particles 11 just before the sintering, and the crystal particles 11 are not joined together, but the large crystal particles 11 take in the small crystal particles 11, and finally the large crystals When the particles 11 come into contact with each other, they cannot take in each other and adhere to each other, so that the ionic arrangement of each crystal cannot be matched, the lattice becomes inconsistent, and the oxygen adsorption layer and the crystal component on the crystal surface An oxygen-excess grain boundary layer 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 deficient in the vicinity of the grain boundary 12, each domain wall 14 is formed in the direction of relaxing the stress applied to the crystal grain 11 for each crystal grain 11.

  Therefore, the following method was performed so that oxygen vacancies 10 were provided near the end of the domain wall 14 in the crystal grain 11 and other foreign matters and grain boundary layers were excluded from the crystal grain boundary 12.

  First, when the ceramic green sheet to be the piezoelectric layer 3 is produced, as a calcined powder of piezoelectric ceramic, for example, PZT, a powder crystallized in a perovskite structure that exhibits piezoelectric characteristics, and a pyrochlore that does not exhibit piezoelectric characteristics. A raw material having a structure and a non-crystallized non-crystalline raw material are mixed with lead, titanium, and zirconium oxides. 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 in the perovskite structure as a nucleus.

  Then, in the reaction sintering process, the crystal grains 11 move in the grain boundary 12 during the sintering process so that the crystal grains 11 can be rotated during the sintering so as to align the ionic arrangement between the crystal grains 11 that have become. A liquid phase is formed. As the liquid phase component, it is preferable to utilize that the silver in the electrode layer 5 component becomes silver oxide during firing and becomes a liquid phase component composed of a piezoelectric material component. Since the excess oxygen component of the grain boundary 12 can be positively taken into the liquid phase, the silver ratio in the electrode layer is preferably 90% or more.

  In the part where the ionic arrangement between the crystal grains 11 became the same, diffusion of oxygen ions on the crystal surface became active due to oxygen defects, and a neck was formed from the grain boundary 12 part to grow into a giant particle. Thus, since the oxygen vacancies 10 in the grain boundaries 12 are taken into the crystal grains 11, the firing temperature is preferably 1000 ° C. or less so that excessive sintering does not proceed.

  Here, by using a metal paste having a different silver ratio depending on the position of the electrode layer 5 in the laminated body 7, the silver component in the liquid phase can have a concentration gradient, so that it penetrates the piezoelectric layer. A moving liquid phase can be formed. The crystal growth of the crystal particle 11 starts from the portion in contact with the electrode layer 5 by moving the liquid phase while performing reactive sintering in which the crystal particle 11 nucleates and sinters. As a result, particularly in the crystal particles 11 in contact with the electrode layer 5, the ionic arrangement can be matched while the excess oxygen between the adjacent crystal particles 11 is contained in the liquid phase. Further, in the cooling step of firing, the liquid phase silver component is taken into the electrode layer, the remaining component is taken in simultaneously with the piezoelectric crystal growth, and the remaining component is left at the triple point between the crystal grains 11. In PZT sintering, sintering in lead oxide vapor causes excessive lead components to be contained in the liquid phase and the progress of the sintering proceeds, leaving it at the triple point between the piezoelectric crystal particles 11. .

  In this way, in the portion sintered by matching the ionic arrangement between the adjacent crystal particles 11, the domain wall 14 straddling the adjacent crystal particles 11 is formed when the temperature becomes lower than the Curie point during cooling. At this time, unlike the grain boundary 12 which was in contact with the outside air during the sintering process, the inside of the crystal particle 11 is caused by oxygen defects due to stress from the outside of the particle 11 during the arrangement of ions, and when cooled below the Curie point Since it becomes a starting point of the strain, the domain wall 14 crosses the vicinity of the oxygen vacancy 10.

  When cooled to room temperature, a metal having a large thermal expansion coefficient such as silver is used for the electrode layer, so that the thermal expansion coefficient of the electrode layer is larger than the thermal expansion coefficient of the piezoelectric body. Since the layer contracts more than the piezoelectric body, the crystal particles 11 near the electrode layer are forcibly polarized in a direction perpendicular to the stacking direction. Since the polarization due to stress, not the polarization due to the electric field, occurs at the portion where the ionic arrangement between the crystal grains 11 coincided and sintered, the piezoelectric crystal grains 11 in contact with these crystal grains 11 are The entire piezoelectric layer is polarized in the same direction. On the other hand, the crystal particles 11 on the surface of the piezoelectric element that are not in contact with the electrode layer are polarized in various directions in order to compensate the charge of the piezoelectric element.

  Next, to move the oxygen vacancies 10 inside the crystal grains 11 to the grain boundaries 12 near the ends of the domain walls 14, the element surface after firing is polished and scraped off, and then at a temperature equal to or higher than the Curie point. Reheat and cool while rearranging the polarization direction. By doing so, stress of phase transformation is concentrated in the oxygen vacancies 10 at the time of rearrangement, so that the oxygen vacancies 10 are pushed out to the grain boundaries 12 so as to relax the stress.

  In addition, the surface of the device is treated by sandblasting before forming the external electrode, the electrode layer is shaved deeper than the surface of the device, and then the external electrode paste mainly composed of silver is printed and then fired. Simultaneously with electrode sintering, diffusion of the electrode layer to the outside of the element can be guided, so that the residual component of the liquid phase remaining in the vicinity of the electrode layer is also pulled out near the external electrode, and at the same time, between the adjacent crystal particles 11 Therefore, a region where the oxygen vacancies 10 are pushed out to the grain boundaries 12 extends throughout the device.

Further, in the polarization treatment, an electric field is applied after heating to a temperature above the Curie point, and cooling is performed to a temperature below the Curie point while applying a polarization voltage. At this time, the temperature is maintained for 10 minutes or more while applying a voltage at the Curie point where the formation of the domain wall 14 starts, and when the cooling is performed with a temperature gradient slower than 100 ° C./hour, the piezoelectric crystal particles 11 Since polarization can be performed without applying an abrupt stress, the oxygen vacancies 10 can be pushed out to the grain boundaries 12 in the crystal grains 11 between the electrode layers, and as a result, the grain boundaries 12 between the crystal grains 11 forming the piezoelectric layer. In this case, oxygen vacancies 10 are formed, and the oxygen vacancies 10 can be formed near the ends of the domain walls 14 in the crystal grains 11.

  In the polarization treatment, the oxygen concentration is made lower 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 low. As a result, the movement of the oxygen vacancies 10 can be activated, so that the oxygen vacancies 10 are formed at the grain boundaries 12 between the crystal grains 11 forming the piezoelectric layer. It can be formed near the end of the inner domain wall 14. By reducing the oxygen concentration to less than half of the atmosphere, oxygen vacancies 10 are formed at the grain boundaries 12 between the crystal grains 11 forming the piezoelectric layer in the piezoelectric layer near the element surface and the electrode layer, Oxygen vacancies 10 can be formed near the ends of the domain walls 14 in the crystal particles 11.

  In particular, when the porous metal particle layer containing a large number of independent metal particles is mass-produced as the planned fracture layer 6, the conductive paste of the porous metal particle layer that becomes the planned fracture layer 6 and other electrode layers The metal component ratio with the conductive paste of 5 is changed, and the metal is diffused from the planned fracture layer 6 to the adjacent electrode layer 5 through the piezoelectric layer 3 by utilizing the concentration difference during firing. Since the liquid phase that moves through the piezoelectric layer can be formed in the same manner, the liquid phase can be reduced by performing reactive sintering in which crystal grains grow and sinter. By moving, the crystal growth of the piezoelectric crystal particles starts from the metal particles of the porous metal layer and the electrode layer next to the porous metal layer. As a result, in the crystal particles 11 in the vicinity of the planned fracture layer 6, the ionic arrangement can be made to coincide while the excess oxygen between the adjacent crystal particles is contained in the liquid phase, and the domains straddling the plurality of crystal particles 11 can be matched. The wall 14 can be formed at the same time.

  The method of forming the domain wall 14 straddling the crystal particles 11 is not limited to the example of the above embodiment, and for example, for the purpose of controlling the reaction sintering speed and the liquid phase movement speed, firing is performed. Various changes may be made without departing from the gist of the present invention, such as changing the oxygen concentration in the atmosphere for each temperature range of firing.

  Next, a lead wire made of a metal wire, a conductive member made of a metal mesh or a mesh-like metal plate, etc. are joined and fixed to the surface of the external electrode 9 using a bonding material such as solder or conductive adhesive. To do. Here, the material of the conductive member is preferably a metal or alloy such as silver, nickel, copper, phosphor bronze, iron, and stainless steel. The surface of the conductive member may be plated with silver or nickel.

  Note that the conductive member may be bonded over the entire stacking direction of the external electrodes 9 or may be bonded to a part of the external electrodes 9.

  Next, the laminate 7 on which the external electrode 9 is formed 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 is coated on the side surface of the laminate 7 on which the external electrode 9 is formed.

Thereafter, a direct current voltage of 0.1 to 3 kV / mm is applied to the piezoelectric layer 3 from the pair of external electrodes 9 through the electrode layer 5 through a conductive member connected to the external electrode 9 to polarize the piezoelectric layer 3 of the laminate 7. Thus, the piezoelectric element 1 of this example is completed. Then, the conductive member is connected to an external voltage supply unit, and an electric field is applied to the piezoelectric layer 3 by the electrode layer 5 via the conductive member and the external electrode 9, whereby each piezoelectric layer 3 is greatly increased by the inverse piezoelectric effect. Can be displaced. 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. 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 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.

  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. Accordingly, when the needle valve 25 opens the injection hole 21 by driving the piezoelectric element 1, the fluid supplied to the fluid passage 27 is outside the injection hole 21 or a container adjacent to the injection hole 21, for example, a fuel chamber of an internal combustion engine. (Not shown) is configured to be discharged and injected from the injection hole 21.

  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 contact with the upper end portion. And in the container 23, the piezoelectric element 1 of this invention is accommodated.

  In such an injection device 19, when the piezoelectric element 1 functioning as a piezoelectric actuator is applied with a voltage and extended, the piston 31 is pressed, the needle valve 25 closes the injection hole 21, and the supply of fluid is stopped. When the voltage application is stopped, the piezoelectric element 1 contracts, and the disc spring 33 pushes back the piston 31 to open the fluid passage 27, and the injection hole 21 communicates with the fluid passage 27, Fluid injection is performed.

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

  The injection device 19 of the present invention includes a container 23 having an injection hole 21 and the piezoelectric element 1 of the present invention, and causes the fluid filled in the container 23 to be discharged from the injection hole 21 by driving the piezoelectric element 1. It may be configured as follows. That is, the piezoelectric element 1 does not necessarily have to be inside the container 23, and is configured such that a pressure for supplying and stopping fluid to the injection hole 21 is applied to the inside of the container 23 by driving the piezoelectric element 1. Just do it. 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 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 19 of the present invention 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 invention that employs the piezoelectric element 1 of the present invention is used in an internal combustion engine, fuel can be injected more accurately into the combustion chamber of the internal combustion engine such as the engine over a longer period of time than in a conventional injection device. Can do.

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

FIG. 6 is a schematic view showing an example of an embodiment of the fuel injection system of the present invention. As shown in FIG. 6, the fuel injection system 35 of this example includes a common rail 37 that stores high-pressure fuel, a plurality of injection devices 19 of the present invention that inject high-pressure fuel stored in the common rail 37, and a high pressure to the common rail 37. A pressure pump 39 for supplying fuel and an injection control unit 41 for supplying a drive signal to the injection device 19 are provided.

The injection control unit 41 controls the amount and timing of high-pressure fluid injection based on external information or an external signal. For example, 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 supplies fuel from the fuel tank 43 to about 101 MPa to 203 MPa (1000 to 2000 atmospheres), preferably about 152 MPa.
It serves to supply the common rail 37 at a high pressure of about 172 MPa (1500-1700) atmospheric pressure. 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. Further, the present invention relates to a piezoelectric element, an injection device, and a fuel injection system, but is not limited to the above-described embodiments, and is used for, for example, a printing device of an ink jet printer or a pressure sensor. Even if it is a thing, if it is a laminated type piezoelectric element using a piezoelectric characteristic, it can be implemented by the same structure.

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

First, calcined at 1200 ° C, and then pulverized to an average particle size of 0.4 µm lead zirconate titanate (
A slurry in which a binder and a plasticizer are mixed with a raw material powder mainly composed of (PZT) powder was prepared, and a ceramic green sheet A having a thickness of 150 μm was prepared by a doctor blade method.

Next, after calcining at 1200 ° C., lead zirconate titanate with an average particle diameter of 0.4 μm (
PZT) 50% by mass of a raw material powder consisting mainly of powder and calcined at 700 ° C. and then pulverized to an average particle size of 0.4 μm (PZT powder comprising titanium oxide, zirconium oxide, lead oxide and pyrochlore phase) A slurry in which a binder and a plasticizer are mixed by blending 50% by mass of a raw material powder composed mainly of a glass layer with a PZT composition) and a ceramic green sheet B having a thickness of 150 μm is produced by a doctor blade method. did.

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 obtained by adding a binder to a raw material powder containing palladium alloy powder and a conductive paste C obtained by adding a binder 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 surface of the ceramic green sheet with a pattern of an 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 layers, the electrode layers 5 are stacked so that the number is 300, and only 20 ceramic green sheets on which no conductive paste is printed are stacked at both ends in the stacking direction of the green laminate. Sample numbers 1 to 3 were used.

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

  Sample Nos. 2 and 3 were produced by using ceramic green sheets B, using conductive paste A and conductive paste B, and alternately laminating conductive paste A and conductive paste B.

  Sample Nos. 4 and 5 are made of ceramic green sheet B, conductive paste A and conductive paste B, and conductive paste A and conductive paste B are alternately laminated, 6, in order to provide a low-rigidity metal layer made of isolated metal particles, the conductive paste C is used for the electrode layers 5 located at the 50th, 150th and 250th positions in the stacking direction in the sample numbers 4 and 5. Printed.

  Next, the raw laminate of each sample number was subjected to binder removal treatment at a predetermined temperature, and then fired at 950 ° 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 the sample numbers 2 to 5, the electrode component silver of the layer using the conductive paste diffuses into the adjacent metal layer having a low silver concentration during firing. In particular, the layer using the conductive paste C has a higher concentration of silver in the base than the other pastes, so that the diffusion becomes remarkable, and the expected fracture layer 6 which is a low-rigidity metal layer made of isolated metal particles is formed. .

Then, the laminated body 7 of each sample number is polished to a desired size, and after polishing, blasted to polish the electrode layer exposed on the surface so that it is more concave than the piezoelectric surface height. I made it. Thereafter, external electrodes 9 were respectively formed. First, a conductive paste for the external electrode 9 was prepared by adding and mixing a binder, a plasticizer, glass powder and the like to a metal powder containing silver as a main component. This conductive paste was pattern-printed by screen printing or the like on the side surface of the laminate 7 where the external electrodes 9 were to be formed, and then fired at 600 to 800 ° C. The cooling process of firing is performed in a synthetic air stream of 20% oxygen and 80% nitrogen. In cooling, the oxygen concentration is gradually reduced to 15% by adding nitrogen gas to the synthetic air at a cooling rate of 200 ° C / hour. The external electrode 9 was formed while diluting.

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

In this way, two sample piezoelectric elements were prepared, and one of them observed the domain wall 14 with a transmission electron microscope. 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 piezoelectric element 1 to measure an initial displacement amount as a piezoelectric actuator.

As for the displacement speed, as a high-speed response evaluation, each piezoelectric element 1 has 0 to +170 V at room temperature.
The alternating voltage of the voltage was applied by gradually increasing the frequency from 150 Hz. The durability evaluation, by applying an AC voltage of a voltage of 0 to + 170 V at room temperature in each of the piezoelectric elements 1 at a frequency of 150 Hz, subjected to the test was continuously driven up to 1 × 10 ⁹ times, until 1 × 10 ⁹ times After continuous driving, high-speed response evaluation was performed by applying an AC voltage of 0 to +170 V at room temperature with the frequency gradually increased from 150 Hz.

  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, in the piezoelectric element of sample number 1, the domain wall 14 is formed in each direction for each of the plurality of crystal grains 11, so that the movement of the domain wall 14 is restricted by the crystal grain boundary 12 of the piezoelectric layer. It is considered that the problem that the response speed becomes slow occurs, the displacement speed of each piezoelectric layer is disturbed, and the beat cannot be 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 harmonic noise was confirmed at a location corresponding to an integer multiple of the drive frequency. It was done. Regarding this, in Table 1, “present” is shown in the column of noise generation of harmonic components.

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 nearly 90% compared with that before the durability evaluation test. ({(45-5) / 45} × 100 = 88.9). Further, in the piezoelectric actuator of sample number 1, peeling was observed on the external electrode 9 after continuous driving (1 × 10 ⁹ times), and peeling was observed on a part of the laminated portion in the laminated body 7.

With respect to this sample number 1, after continuously driving, an AC voltage of 0 to +170 V was applied again at room temperature by gradually increasing the frequency from 150 Hz, and as a result of performing high-speed response evaluation, the frequency exceeded 100 Hz. Occasionally a roaring sound was observed. This is presumably because, in the piezoelectric element of sample number 1, peeling occurred between the piezoelectric body and the electrode layer, 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 harmonic noise was confirmed at a location corresponding to an integer multiple of the drive frequency. It was done. Regarding this, in Table 1, “present” is shown in the column of noise generation of harmonic components.

On the other hand, in the piezoelectric actuators of sample numbers 2 to 5 which are the examples of the present invention, the peeling of the external electrode 9 and the peeling of the laminated portion in the laminated body 7 were confirmed after continuous driving (1 × 10 ⁹ times). Was not. Further, 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) / 52} × 100) compared with that before the durability evaluation test.
= 5.7). In particular, in the piezoelectric actuators of sample numbers 4 and 5, 1 × 10 ⁹
It was found that the displacement amount was not lowered even after the rotation, and the durability was very high.

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

  Furthermore, when a thermocouple was attached to the central portion of the piezoelectric element and the maximum temperature of the driving piezoelectric element was measured, as shown in Table 1, it was confirmed that an increase in heat generation at the central portion of the element could be suppressed. From these facts, since the oxygen vacancy 10 is formed in the grain boundary 12 near the end of the domain wall 14 of the crystal grain forming the piezoelectric layer 5, there is no region for restraining displacement, and the element being driven It is thought that the overheating of was able to be suppressed. As a result, a highly durable piezoelectric element could be obtained.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric element 3 ... Piezoelectric layer 5 ... Electrode layer 6 ... Planned fracture | rupture layer 7 ... Laminated body 9 ... External electrode
10 ... Oxygen vacancies
11 ... Crystal particles
12 ... grain boundaries
13 ... Domain polarization axis direction
14 ... Domain wall
15 ... Oxygen ions
16 ... A Site Ion
17 ・ ・ ・ B site ion
18 ・ ・ ・ Near electrode layer edge
19 ... Injection device
21 ... Injection hole
23 ・ ・ ・ Storage container (container)
25 ... Needle valve
27 ... Fluid passage
29 ... Cylinder
31 ... Piston
33 ・ ・ ・ Belleville spring
35 ... Fuel injection system
37 ... Common rail
39 ・ ・ ・ Pressure pump
41 ... Injection control unit
43 ... Fuel tank

Claims (9)

  A piezoelectric layer and an electrode layer provided so as to face each other with the piezoelectric layer interposed therebetween, and oxygen vacancies are formed at grain boundaries between crystal grains forming the piezoelectric layer, and the oxygen layer A piezoelectric element characterized in that vacancies are located in the vicinity of an end of a domain wall in the crystal grain.   The crystal grains having a region in which directions of polarization axes coincide with each other, and the crystal grains are adjacent to each other, and ends of the domain walls in the adjacent crystal grains are close to each other. Item 2. The piezoelectric element according to Item 1.   The piezoelectric element according to claim 2, wherein the domain walls in each of the adjacent crystal grains are substantially parallel.   4. The piezoelectric element according to claim 2, wherein the oxygen vacancies are located between ends of the domain walls in the adjacent crystal grains. 5.   The piezoelectric element according to claim 1, wherein the domain wall is formed of a 90 ° domain.   2. The piezoelectric element according to claim 1, wherein the oxygen vacancy is located in the vicinity of the electrode layer.   The piezoelectric element according to claim 1, wherein the piezoelectric element is a stacked piezoelectric element in which the piezoelectric layers and the electrode layers are alternately stacked.   An ejection device comprising: a container having ejection holes; and the piezoelectric element according to any one of claims 1 to 7, wherein liquid filled in the container is ejected from the ejection holes by driving the piezoelectric element. .   9. A common rail that stores high-pressure fuel; an injection device according to claim 8 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 that provides the injection device A fuel injection system comprising an injection control unit.

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