JPWO2010110291A1 - Multilayer piezoelectric element, injection device using the same, and fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer piezoelectric element having improved durability by dispersing and reducing stress generated at a boundary portion between an active region and an inactive region in the entire laminated body. SOLUTION: A laminated piezoelectric element 1 is bonded to a laminated body 5 in which a plurality of piezoelectric layers 2 and internal electrode layers 3a and 3b are alternately laminated, and a pair of side surfaces opposed to each other, and each is internally connected. In the laminated piezoelectric element 1 including the external electrodes 4a and 4b to which the first set (3a) and the second set (3b) of the electrode layers 3a and 3b are connected, the internal electrode layer 3a of the first set includes The connected first external electrode 4a and the second set of internal electrode layers 3b are insulated to form an inactive region A2, and the first external electrode 4a and the second external electrode A2 in the inactive region A2 are insulated. The width w between the set of internal electrode layers 3b is smaller at the end than the central portion of the stacked body 5 in the stacking direction. [Selection] Figure 1

Description

  The present invention relates to a laminated piezoelectric element used for, for example, a drive element (piezoelectric actuator), a sensor element, a circuit element, and the like, an injection device using the same, and a fuel injection system.

  Conventionally, multilayer electronic components such as multilayer piezoelectric elements have a multilayer molded body in which a conductive paste serving as an internal electrode layer is printed on a ceramic green sheet, and a plurality of ceramic green sheets coated with the conductive paste are stacked. Is produced by firing the laminated molded body to produce a fired laminated body, and subjecting the laminated body to processing such as grinding.

  Every other internal electrode layer is connected to positive and negative external electrodes. The part where the internal electrode layer connected to the positive external electrode and the adjacent internal electrode layer connected to the negative external electrode overlap in the stacking direction of the laminate is the active region, and the part that does not overlap is inactive It becomes an area. The active region is a portion where the piezoelectric layer sandwiched between the internal electrode layer connected to the positive external electrode and the internal electrode layer adjacent to the negative external electrode is driven to expand and contract. The inactive region is a portion where the piezoelectric layer sandwiched between the internal electrode layer connected to the positive external electrode and the adjacent internal electrode layer connected to the negative external electrode is not stretched and driven.

  Conventionally, in the laminated body, the area of the inactive region is almost constant, and stress is concentrated on the boundary portion between the active region and the inactive region. Therefore, it has been proposed to improve the durability characteristics of the multilayer piezoelectric element by defining the arrangement permutation of the inactive regions (see Patent Document 1 below).

In Patent Document 1, in a laminated element in which a large number of thin plates each having an internal electrode formed on the surface of an electrostrictive / piezoelectric material are stacked and each internal electrode is alternately connected by a pair of external electrodes, the thin plate is It has an electrodeless portion for preventing conduction between the internal electrode formed on one side and the external electrode on one side, and the electrodeless portion has n types with different widths (where n is an integer of 2 or more, W ₁ <W ₂ <... <W _n ) and the width of the thin plate depends on the width of the electrodeless portion..., W ₁ , W ₂ ,. A stacked electrostrictive / piezoelectric element stacked in the order of _{n 1} , W _n ,..., W ₂ , W ₁ , W ₂ ,.

  That is, the multilayer electrostrictive / piezoelectric element of Patent Document 1 is formed such that the width of the electrodeless portion changes in a wave shape in the stacking direction.

  With the above configuration, the electric field strength distribution at the end portion of the element changes gradually in steps, and the internal stress can be dispersed. Therefore, the breakage due to stress strain can be prevented. Further, since the electric field strength distribution becomes gentle, dielectric breakdown can be prevented. As a result, the multilayer electrostrictive / piezoelectric element can be driven at a high voltage, so that even a small element can generate a large displacement.

Japanese Patent No. 2645628

  However, in recent years, the multilayer piezoelectric element has been required to be able to be driven continuously for a long time under high voltage and high pressure, and further improvement in durability is desired.

  For example, the laminated electrostrictive / piezoelectric element of Patent Document 1 is formed so that the width of the electrodeless portion changes in a wave shape in the laminating direction, so that the stress strain periodically increases in the laminating direction. This causes a problem that breakage or the like is likely to occur at a portion where stress strain increases.

  Therefore, the present invention has been devised in view of the above-mentioned conventional problems, and its purpose is to disperse and reduce the stress generated at the boundary between the active region and the inactive region over the entire laminate. Another object of the present invention is to provide a laminated piezoelectric element with improved durability, an injection device using the same, and a fuel injection system.

  The laminated piezoelectric element of the present invention is bonded to a laminated body in which a plurality of piezoelectric layers and internal electrode layers are alternately laminated, and a pair of opposite side surfaces of the laminated body. In a multilayer piezoelectric element including a set and an external electrode connected to a second set, the first external electrode connected to the first set of internal electrode layers and the second set of internal electrode layers Between the first external electrode and the second set of internal electrode layers in the inactive region is in the stacking direction of the stacked body. It is smaller at the end than at the center.

  In the multilayer piezoelectric element of the present invention, in the above configuration, the width between the first external electrode and the second set of internal electrode layers in the inactive region is the stacking direction of the multilayer body. It is characterized in that it is smaller at both end portions than the central portion.

  In the multilayer piezoelectric element of the present invention, in the configuration described above, the edge shape of the second set of internal electrode layers facing the first external electrode is the first in the center rather than on both sides. The arc shape is far from the external electrode.

  In the multilayer piezoelectric element of the present invention, in the above configuration, the width between the first external electrode and the second set of internal electrode layers in the inactive region is the stacking direction of the multilayer body. It is characterized in that it gradually decreases from the central part side toward the end at the end part.

  In the multilayer piezoelectric element of the present invention, in the above configuration, the piezoelectric layer is thicker at the end than the center in the stacking direction of the stacked body, and the interval between the internal electrode layers is It is characterized by widening.

  In the multilayer piezoelectric element of the present invention, in the configuration described above, the non-connection between the second external electrode to which the second set of internal electrode layers is connected and the first set of internal electrode layers is provided. The width of the active region is also smaller at the end than the central portion in the stacking direction of the stacked body.

  An ejection device according to the present invention includes a container having an ejection hole and the multilayer piezoelectric element according to the present invention, and fluid stored in the container is discharged from the ejection hole by driving the multilayer 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 the high-pressure fuel stored in the common rail, a pressure pump that supplies the high-pressure fuel to the common rail, and the injection And an injection control unit for supplying a drive signal to the apparatus.

  According to the multilayer piezoelectric element of the present invention, the multilayer body in which a plurality of piezoelectric layers and internal electrode layers are alternately stacked and the pair of opposite side surfaces of the multilayer body are joined to each other, In a stacked piezoelectric element including an external electrode to which the set and the second set are connected, between the first external electrode to which the first set of internal electrode layers is connected and the second set of internal electrode layers Is insulated and becomes an inactive region, and the width between the first external electrode and the second set of internal electrode layers in the inactive region is closer to the end than the central portion in the stacking direction of the stacked body. Since it is small, the stress generated at the boundary portion between the active region and the inactive region is dispersed and reduced from the center portion to the end portion of the laminate, thereby improving the durability. That is, the stress generated at the boundary between the active region and the inactive region is dispersed because the overlapping positions of the second set of internal electrode layers are not aligned in a plan view. As a result, the durability of the multilayer piezoelectric element is reduced. Will improve. In addition, since the area of the internal electrode layer at the end of the multilayer body increases, the volume of the piezoelectric layer that expands and contracts with respect to a constant driving power at the end of the multilayer body increases. The stress is more dispersed. As a result, damage such as cracks is less likely to occur in the laminate, and durability is improved.

  In the multilayer piezoelectric element of the present invention, the width between the first external electrode and the second set of internal electrode layers in the inactive region is at both ends of the stacked body in the stacking direction. When it is small, stress can be dispersed and reduced throughout the laminate.

  In the multilayer piezoelectric element of the present invention, the shape of the edge of the second set of internal electrode layers facing the first external electrode is an arc shape that is farther from the first external electrode in the center than on both sides. In some cases, there is no portion where stress concentrates at the boundary between the active region and the inactive region, so that the stress is further dispersed and the piezoelectric layer is less likely to be damaged such as cracks, and durability is improved.

  In the multilayer piezoelectric element of the present invention, the width between the first external electrode and the second set of internal electrode layers in the inactive region is such that the end of the multilayer body in the stacking direction extends from the center side. When the thickness gradually decreases toward the end, the durability is further improved by further dispersing and reducing the stress from the center to the end at the end in the stacking direction of the stack.

  Further, in the multilayer piezoelectric element of the present invention, when the thickness of the piezoelectric layer is thicker at the end than the central portion in the stacking direction of the multilayer body, and the distance between the internal electrode layers is wide, the stress is The amount of strain per layer is reduced at the end portion in the stacking direction of the stacked body, which increases the stress relaxation effect and improves the durability.

  The laminated piezoelectric element according to the present invention also has a width of the inactive region between the second external electrode connected to the second set of internal electrode layers and the first set of internal electrode layers. At the end of the stack in the stacking direction at the boundary between the active region and the inactive region on both the first external electrode side and the second external electrode side of the stack. The generated stress can be more dispersed and reduced from the center to the end of the laminate. Therefore, a laminated piezoelectric element with improved durability can be obtained.

  According to the injection device of the present invention, the container having the injection hole and the multilayer piezoelectric element of the present invention are provided, and the fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. Therefore, since the multilayer piezoelectric element having improved durability is provided, the injection device has improved durability.

  The fuel injection system of the present invention includes a common rail that stores high-pressure fuel, the above-described injection device of the present invention that injects high-pressure fuel stored in the common rail, a pressure pump that supplies high-pressure fuel to the common rail, and a drive signal to the injection device. Since the injection control unit is provided, the fuel injection system with improved durability is provided because the injection device with improved durability is provided.

It is a perspective view which shows an example of embodiment about the lamination type piezoelectric element of this invention. It is a perspective view which shows the other example of embodiment about the lamination type piezoelectric element of this invention. It is a top view which shows an example of embodiment about the 2nd set of internal electrode in the lamination type piezoelectric element of this invention. It is a perspective view which shows the other example of embodiment about the lamination type piezoelectric element of this invention. It is a perspective view which shows the other example of embodiment about the lamination type piezoelectric element of this invention. It is a schematic sectional drawing which shows an example of embodiment about the injection apparatus of this invention. It is a schematic block diagram which shows an example of embodiment about the fuel-injection system of this invention.

  Hereinafter, an example of an embodiment of the multilayer piezoelectric element of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing a laminated piezoelectric element (hereinafter also referred to as element) 1 of the present embodiment. The laminated piezoelectric element 1 has a laminated body 5 in which a plurality of piezoelectric layers 2 and internal electrode layers 3a and 3b are alternately laminated. A pair of external electrodes 4 a and 4 b are formed on the side surface of the multilayer body 5. The stacked body 5 includes a facing portion 6 that the internal electrode layers 3a and 3b face each other, and a non-facing portion 7 that is positioned on both ends in the stacking direction with respect to the facing portion 6.

  The facing portion 6 is an active portion that the piezoelectric layer 2 is driven to expand and contract, and the non-facing portion 7 is an inactive portion that the piezoelectric layer 2 is not expanded and driven.

  The laminated piezoelectric element 1 according to the present embodiment is bonded to a laminated body 5 in which a plurality of piezoelectric layers 2 and internal electrode layers 3 a and 3 b are alternately laminated, and a pair of side surfaces facing the laminated body 5. In the multilayer piezoelectric element 1 including the external electrodes 4a and 4b to which the first set (3a) and the second set (3b) of the internal electrode layers 3a and 3b are respectively connected, the first set of internal electrodes The first external electrode 4a to which the layer 3a is connected and the second set of internal electrode layers 3b are insulated to form an inactive region A2, and the first external electrode 4a in the inactive region A2 The width w between the second set of internal electrode layers 3 b is smaller at the end than the central portion of the stacked body 5 in the stacking direction.

  With the above configuration, the stress generated at the boundary between the active region and the inactive region is dispersed and reduced from the center portion to the end portion of the laminate, thereby improving durability. That is, the stress generated at the boundary between the active region and the inactive region is dispersed because the overlapping positions of the second set of internal electrode layers are not aligned in a plan view. As a result, the durability of the multilayer piezoelectric element is reduced. Will improve. In addition, since the area of the internal electrode layer at the end of the multilayer body increases, the volume of the piezoelectric layer that expands and contracts with respect to a constant driving power at the end of the multilayer body increases. The stress is more dispersed. As a result, damage such as cracks is less likely to occur in the laminate, and durability is improved.

  In the multilayer piezoelectric element 1 of the present embodiment, the central portion in the stacking direction of the multilayer body 5 means a central portion having a length of about 10% to 30% of the total length of the multilayer body 5 in the stacking direction. The end portion in the stacking direction of the stacked body 5 means an end portion having a length of about 5% to 10% of the total length of the stacked body 5 in the stacking direction.

  The ratio in which the width w between the first external electrode 4a and the second set of internal electrode layers 3b in the inactive region A2 is smaller at the end than the center in the stacking direction of the stacked body 5 is 5% It is preferable to decrease by ~ 10%. By setting it within this range, the stress generated at the boundary between the active region and the inactive region can be dispersed and reduced from the center to the end of the laminate, and the rate of change in the width w is large. It is possible to suppress the problem that the displacement direction becomes unstable due to being too much.

  Further, the rate of change of the width w may be constant, but may change in the stacking direction of the stacked body 5. For example, the width w is constant (the rate of change of the width w is 0) in the central portion having a length of about 10% to 30% of the total length of the stacked body 5 in the stacking direction. The ratio of the change of the width w may be constant from the center to the end, and the width w may be gradually reduced. In this case, the direction of displacement in the stacked body 5 is stable, and a portion where the amount of displacement changes rapidly is unlikely to occur.

  Further, the rate of change of the width w is constant at the center of the laminate 5 in the stacking direction, and the rate of change of the width w gradually increases from the center to the end of the stack 5 in the stacking direction. Also good. In this case, there is an effect that the stress relaxation effect at the end portion is increased and the durability is improved.

  Further, the width w may be changed stepwise from the center portion to the end portion in the stacking direction of the stacked body 5 so that the portions where the width w is constant and the changing portions are alternately arranged.

  Further, as shown in FIG. 2, the multilayer piezoelectric element 1 of the present embodiment has a width w between the first external electrode 4a and the second set of internal electrode layers 3b in the inactive region A2. It is preferable that both end portions are smaller than the central portion in the stacking direction of the stacked body 5. With this configuration, it is possible to disperse and reduce stress over the entire laminate 5.

  In this case, the method of changing the width w from the central portion of the stacked body 5 in the stacking direction to one end, and the method of changing the width w of the stack 5 from the central portion in the stacking direction to the other end Are preferably the same. With this configuration, the stress distribution in the stacking direction of the stacked body 5 becomes symmetrical, and no bias is generated, so that the durability of the stacked piezoelectric element 1 is further improved.

  Further, the rate of change of the width w may be constant, but may change in the stacking direction of the stacked body 5. For example, the width w is constant (the rate of change in the width w is 0) in the central portion having a length of about 5% to 20% of the total length of the stacked body 5 in the stacking direction. The rate of change of the width w may be constant from the center to both ends, and the width w may be gradually reduced. In this case, the direction of displacement in the stacked body 5 is stable, and a portion where the amount of displacement changes rapidly is unlikely to occur.

  In addition, the rate of change of the width w is constant at the center portion in the stacking direction of the stacked body 5, and the rate of change of the width w gradually increases from the center portion in the stacking direction of the stack 5 to both ends. There may be. In this case, there is an effect that the stress relaxation effect at the end portion is increased and the durability is improved.

  Moreover, the width w may be changed stepwise from the center in the stacking direction of the stacked body 5 to both ends so that the portions with a constant width w and the portions with the width w are alternated. Good.

  Further, as shown in FIG. 3, the multilayer piezoelectric element of the present embodiment is such that the edge shape of the second set of internal electrode layers 3b facing the first external electrode 4a is centered more than both sides. It is preferable that the arc shape is far from the first external electrode 4a. With this configuration, there is no portion where stress is concentrated at the boundary between the active region A1 and the inactive region A2, and therefore, the stress is further dispersed, and the piezoelectric layer 2 is less likely to be damaged such as cracks, resulting in durability. improves.

  In this case, when the arc shape is a smooth curved shape such as an arc shape having a constant radius of curvature or an elliptical arc shape, it is more effective that stress is concentrated at the boundary portion between the active region A1 and the inactive region A2. This is preferable because it can be suppressed. When the arc shape is an arc shape having a constant radius of curvature, the radius of curvature (R) is more preferably about 10 mm to 100 mm. By setting it within this range, it is possible to more effectively suppress stress concentration at the boundary between the active region A1 and the inactive region A2, and the shape of the edge of the second set of internal electrode layers 3b. It can be suppressed that the effect of the stress dispersion is lowered due to the fact that the film approaches a straight line.

  Moreover, the arc shape may connect the plurality of straight portions to form an arc shape as a whole. In this case, the portion where the straight portions are connected to each other has a bent shape, and stress tends to concentrate on the bent portion, but if the angle of bending is sufficiently large to be about 45 ° or more, the concentration of stress is suppressed. Can be preferred.

  In the multilayer piezoelectric element 1 of the present embodiment, the width w between the first external electrode 4a and the second set of internal electrode layers 3b in the inactive region A2 is set in the stacking direction of the stacked body 5. It is preferable that the end portion gradually decreases from the center side toward the end. With this configuration, the durability is further improved by further dispersing and reducing the stress from the center side to the end at the end in the stacking direction of the stacked body 5.

  In this case, the end portion of the stacked body 5 that is gradually reduced from the center side toward the end at the end portion in the stacking direction has a length of about 5% to 40% of the total length of the stacked body 5 in the stacking direction. It is preferable that it is an edge part. By setting it within this range, the effect of dispersing and reducing the stress from the center side to the end at the end in the stacking direction of the stacked body 5 becomes higher.

  Further, the width w gradually decreases from the central portion side toward the end at the end portion of the stacked body 5 in the stacking direction. In this case, the change rate of the width w is substantially constant. As a result, the width w changes smoothly so as to gradually decrease. The change rate of the width w is preferably 1% or less. By setting it within this range, the effect of dispersing and reducing the stress from the center side to the end at the end of the stack 5 in the stacking direction is further enhanced.

  In addition, the width w may be constant in the central portion of the stacked body 5 in the stacking direction, or the width w may decrease from the center toward the end portion in the central portion.

  In the multilayer piezoelectric element 1 of the present embodiment, the piezoelectric layer 2 is thicker at the end than the central portion of the multilayer body 5 in the stacking direction, and the distance between the internal electrode layers 3a and 3b is increased. Is preferably wide. With this configuration, the volume of the inactive region A2 is also increased at the end of the stacked body 5 in the stacking direction, so that the stress relaxation effect at the end is increased and the durability is improved. In this case, the interval (D2) between the internal electrode layers 3a and 3b at the end portion in the stacking direction of the multilayer body 5 with respect to the interval (D1) between the internal electrode layers 3a and 3b in the center portion in the stacking direction of the stacked body 5. ) Is more preferably widened so that D2 / D1 = about 1.1 to 3. By making it within this range, the stress relaxation effect at the end in the stacking direction of the stacked body 5 is increased, and the stretch driveability due to the enlargement of the stacked body 5 due to the excessively large D2 is reduced. Can be suppressed.

  Further, as shown in FIGS. 4 and 5, the multilayer piezoelectric element 1 of the present embodiment includes a second external electrode 4b to which the second set of internal electrode layers 3b are connected and the interior of the first set. It is preferable that the width w1 of the inactive region A3 between the electrode layer 3a is also smaller at the end than the central portion of the stacked body 5 in the stacking direction. With this configuration, on both the first external electrode 4a side and the second external electrode 4b side of the multilayer body 5, the stress generated at the boundary between the active region A1 and the inactive regions A2 and A3 is laminated body. 5 can be further dispersed and reduced from the center to the end. Therefore, the laminated piezoelectric element 1 with improved durability can be obtained.

  In this case, the method of changing the width w of the inactive region A2 in the stacking direction on the first external electrode 4a side of the stacked body 5 and the stacking direction on the second external electrode 4b side of the stacked body 5 are described. More preferably, the way of changing the width w1 of the inactive region A3 is the same. Thereby, stress can be similarly distributed between the first external electrode 4a side and the second external electrode 4b side of the multilayer body 5, and there is no place where the stress is concentrated or biased. Durability is further improved.

  Next, a method for manufacturing the multilayer piezoelectric element 1 of the present embodiment will be described. First, for example, lead zirconate titanate (PZT) powder, a binder made of an acrylic or butyral organic polymer, and a plasticizer such as DBP (dibutyl phthalate) or DOP (dioctyl phthalate) are mixed. To prepare a slurry.

  Next, the obtained slurry is formed into a ceramic green sheet using a tape forming method such as a doctor blade method or a calender roll method.

  Next, a conductive paste to be the internal electrode layers 3a and 3b is produced. This conductive paste is obtained by adding and mixing a binder, a plasticizer and the like to a metal powder mainly composed of a silver-palladium alloy. This conductive paste is printed on the pattern of the internal electrode layers 3a and 3b on one side of the ceramic green sheet by screen printing or the like. At this time, the area of the pattern of the conductive paste is increased toward the end of the laminate 5.

  Next, the ceramic green sheet on which the conductive paste is printed is laminated so as to be, for example, the laminated body 5 having the configuration shown in FIG. 1 and dried to obtain a laminated molded body. A plurality of ceramic green sheets for the non-facing portion 7 on which the conductive paste is not printed are laminated on both end sides in the stacking direction of the stacked molded body. In addition, you may cut | judge a laminated molded object along a lamination direction as needed, and may make it a desired shape.

  Next, after delaminating the laminated molded body at a predetermined temperature, the laminated body 5 is obtained by firing at 900 to 1150 ° C. You may grind the side surface of the laminated body 5 as needed. Further, both sides of the laminate 5 are polished by deforming and firing so that the entire side surface of the laminate 5 is slightly arcuately curved at the time of firing, and then polishing the sides of the laminate 5 in a flat shape. It is also possible to make the partial electrode portion smaller.

  Next, external electrodes 4 a and 4 b are formed on the side surfaces of the multilayer body 5. The external electrodes 4a and 4b are prepared by adding a binder, a plasticizer, glass powder or the like to a metal powder mainly composed of silver to produce a conductive paste, and applying the conductive paste to the side surface of the laminate 5 by a screen printing method or the like. It can be formed by printing and baking at 600 to 800 ° C. Furthermore, a conductive auxiliary member made of a conductive adhesive in which a mesh-like body made of metal or a mesh-like metal plate is embedded on the outer surfaces of the external electrodes 4a and 4b may be formed. A mesh-like body made of metal is a braided metal wire, and a mesh-like metal plate is a metal plate in which a large number of through holes are formed in a mesh shape.

  Then, after connecting the lead wires to the external electrodes 4a and 4b with solder or the like, the exterior resin made of silicone rubber or the like is coated on the side surface of the laminate 5 including the external electrodes 4a and 4b using a technique such as dipping. Thus, the multilayer piezoelectric element 1 is obtained.

  FIG. 6 is a schematic cross-sectional view showing the injection device of the present embodiment. As shown in FIG. 6, in the injection device 25 of the present embodiment, the multilayer piezoelectric element 1 of the above-described embodiment is stored in a storage container 29 having an injection hole 27 at one end. A needle valve 31 that can open and close the injection hole 27 is disposed in the storage container 29. A fuel passage 33 is disposed in the injection hole 27 so as to be communicable in accordance with the movement of the needle valve 31. The fuel passage 33 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 33 at a constant high pressure. Therefore, when the needle valve 31 opens the injection hole 27, the fuel supplied to the fuel passage 33 is injected into a fuel chamber of an internal combustion engine (not shown) at a constant high pressure.

  The upper end of the needle valve 31 has a large inner diameter, and a cylinder 37 formed in the storage container 29 and a piston 37 that can slide are disposed. And in the storage container 29, the piezoelectric actuator provided with the said laminated piezoelectric element 1 is accommodated.

  In such an injection device 25, when the piezoelectric actuator is extended by applying a voltage, the piston 35 is pressed, the needle valve 31 closes the injection hole 27, and the supply of fuel is stopped. When the application of voltage is stopped, the piezoelectric actuator contracts, the disc spring 39 pushes back the piston 37, and the injection hole 27 communicates with the fuel passage 33 so that fuel is injected.

  The injection device 25 according to the present embodiment includes a container having the injection hole 27 and the multilayer piezoelectric element 1, and the liquid filled in the container is discharged from the injection hole 27 by driving the multilayer piezoelectric element 1. You may be comprised so that it may make. That is, the element 1 does not necessarily have to be inside the container, and it is sufficient that the multilayer piezoelectric element 1 is driven so that pressure is applied to the inside of the container. In the present embodiment, the liquid includes various liquid fluids (such as conductive paste) in addition to fuel and ink.

  FIG. 7 is a schematic block diagram showing the fuel injection system of the present embodiment. As shown in FIG. 7, the fuel injection system 41 of the present embodiment includes a common rail 43 that stores high-pressure fuel, a plurality of injection devices 25 that inject fuel stored in the common rail 43, and high-pressure fuel in the common rail 43. And a pressure control unit 47 for supplying a drive signal to the spray device 25.

  The injection control unit 47 controls the amount and timing of fuel injection while sensing the state in the combustion chamber of the engine with a sensor or the like. The pressure pump 45 plays a role of sending fuel from the fuel tank 49 to the common rail 43 at a pressure of about 1000 to 2000 atmospheres (about 101 MPa to about 203 MPa), preferably about 1500 to 1700 atmospheres (about 152 MPa to about 172 MPa). In the common rail 43, the fuel sent from the pressure pump 45 is stored and sent to the injection device 25 as appropriate. As described above, the injection device 25 injects a small amount of fuel into the combustion chamber from the injection hole 27 in the form of a mist.

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

  First, a slurry was prepared by mixing a calcined powder of a PZT main component piezoelectric ceramic, a binder made of an organic polymer, and a plasticizer, and a ceramic green sheet having a thickness of 150 μm was prepared by a slip casting method.

  Next, on one side of the ceramic green sheet, the silver content is 70% by mass and the palladium content is 30% by mass, and the silver-palladium alloy powder is contained in 100 parts by mass. A conductive paste containing 30 parts by mass of piezoelectric ceramic was printed as a desired pattern shape to a thickness of 5 μm by screen printing.

  Next, after the conductive paste layer was dried, 100 ceramic green sheets coated with the conductive paste layer were laminated to produce a primary laminated molded body. Furthermore, 10 ceramic green sheets not coated with conductive paste were laminated on the upper end portion in the laminating direction of the primary laminated molded body, and 20 ceramic green sheets were laminated on the lower end portion to produce a laminated molded body.

  Next, this laminated molded body was pressurized while being heated at 100 ° C. to integrate the ceramic green sheets of the laminated molded body.

  Next, after cutting the laminated molded body into a quadrangular prism having a cross section of 8 mm × 8 mm and a length of 18 mm, the binder is removed at 800 ° C. for 10 hours, and the laminated molded body is fired at 1130 ° C. for 2 hours. As a result, a laminate was obtained. The firing pot used at the time of firing was an MgO bowl having a closed structure, and ceramic powder having the same composition as the ceramic contained in the multilayer molded body and the multilayer molded body was placed in the bowl and fired. Further, the thickness of the piezoelectric layer in the laminate was 100 μm.

  Next, the four side surfaces of the laminate were polished by a thickness of 0.2 mm using a surface grinder.

  Next, in two opposite side surfaces of the multilayer body, every other layer of the piezoelectric layer has a depth so as to alternate with the end surface of the piezoelectric layer including the end surface of the internal electrode layer on the two side surfaces of the multilayer body. A groove having a thickness of 200 μm and a width in the stacking direction of 75 μm was formed. These grooves were filled with silicone rubber to form an insulator made of silicone rubber, and the ends of the internal electrode layer were exposed on the two side surfaces of the laminate. That is, the end portion of the first set of internal electrode layers is exposed on the side surface of the first external electrode side laminate, and the end portion of the second set of internal electrode layers is the second external electrode side laminate. I was exposed to the side of the.

  Next, a conductive adhesive containing silver and polyimide resin is applied to the two side surfaces of the laminate, and a mesh-like body made of stainless steel is embedded in the conductive adhesive and heated to 200 ° C. in this state. The first and second external electrodes were formed by curing the conductive adhesive.

  Next, the lead wires were connected to the positive external electrode (first external electrode) and the negative external electrode (second external electrode) with solder, respectively, and the surface of the multilayer piezoelectric element was washed with alcohol. . Thereafter, the laminate was subjected to a surface treatment with a primer to improve the adhesion of the exterior resin, and then the exterior resin made of silicone rubber was coated on the surface of the laminate by a dipping method to produce a multilayer piezoelectric element.

  Finally, a polarization voltage of 1 kV was applied to the multilayer piezoelectric element, and the entire piezoelectric body layer of the multilayer piezoelectric element was subjected to polarization treatment to obtain the multilayer piezoelectric element of the present invention.

  At this time, five types of stacked piezoelectric elements were produced in which the internal electrode layers in the stack had five types as shown in Table 1.

  The laminated piezoelectric element of sample number 1 has the structure shown in FIG. 1, and the width between the first external electrode and the second set of internal electrode layers in the inactive region is the stacking direction of the stacked body. This is a configuration that is smaller at one end than at the center. In this case, the central portion in the stacking direction of the stacked body is a central portion having a length of 10% of the total length (15 mm) in the stacking direction of the stacked body, and the end portion in the stacking direction of the stacked body is the stack of the stacked body. An end having a length of 5% of the total length in the direction. Further, the rate at which the width between the first external electrode and the second set of internal electrode layers in the inactive region becomes smaller at the end than the central portion in the stacking direction of the stacked body is decreased by 1%. I did it.

  The laminated piezoelectric element of sample number 2 has the configuration shown in FIG. 2, and the width between the first external electrode and the second set of internal electrode layers in the inactive region is the stacking direction of the stacked body. It is the structure which is smaller at both ends than the central part. In this case, the central portion in the stacking direction of the stacked body is a central portion having a length of 10% of the total length (15 mm) in the stacking direction of the stacked body, and the end portion in the stacking direction of the stacked body is the stack of the stacked body. An end having a length of 5% of the total length in the direction. Further, the rate at which the width between the first external electrode and the second set of internal electrode layers in the inactive region becomes smaller at both ends than the central portion in the stacking direction of the stacked body is 1% each. I tried to make it smaller.

  The laminated piezoelectric element of sample number 3 has the structure shown in FIGS. 1 and 3, and the width between the first external electrode and the second set of internal electrode layers in the inactive region is the laminated body. The edge shape of the second set of internal electrode layers facing the first external electrode is smaller at the one end than the central portion in the stacking direction, and the shape of the edge of the second set of internal electrodes is the first at the center rather than the both sides. It is the structure which is an arc shape far from the external electrode. In this case, the central portion in the stacking direction of the stacked body is a central portion having a length of 10% of the total length (15 mm) in the stacking direction of the stacked body, and the end portion in the stacking direction of the stacked body is the stack of the stacked body. An end having a length of 5% of the total length in the direction. Further, the rate at which the width between the first external electrode and the second set of internal electrode layers in the inactive region becomes smaller at the end than the central portion in the stacking direction of the stacked body is decreased by 1%. I did it. At this time, the width between the first external electrode and the second set of internal electrode layers was the width between the first external electrode and the arc-shaped intermediate portion. The arc shape is an arc shape having a constant radius of curvature, and the radius of curvature is 30 mm.

  In the laminated piezoelectric element of sample number 4, the width between the first external electrode and the second set of internal electrode layers in the inactive region is from the center to the end at the end in the stacking direction of the stack. It is the structure which becomes small gradually. In this case, the end portion in the stacking direction of the stacked body is an end portion having a length of 5% of the total length in the stacking direction of the stacked body. The ratio of the change in width between the first external electrode and the second set of internal electrode layers is constant at 1%. Further, in the central portion in the stacking direction of the stacked body, the width between the first external electrode and the second set of internal electrode layers is constant at 1 mm.

  The multilayer piezoelectric element of sample number 5 is the multilayer piezoelectric element of sample number 1 having the configuration shown in FIG. 1, and the thickness of the piezoelectric layer is thicker at the end than the center in the stacking direction of the multilayer body. In other words, the interval between the internal electrode layers is wide. The ratio of the distance between the internal electrode layers (D2 = 240 μm) at the end in the stacking direction of the stacked body to the distance between the internal electrode layers (D1 = 120 μm) at the center in the stacking direction of the stacked body is D2 / D1 = 2.

  As a result of applying a DC voltage of 200 V to each of these laminated piezoelectric elements, a displacement of 10 μm was obtained for each laminated piezoelectric element due to expansion and contraction driving.

Further, an AC electric field of 0 V to +200 V was applied to these multilayer piezoelectric elements at a frequency of 200 Hz, and a driving test was performed at 150 ° C. In the driving test, the displacement after continuously driving the laminated piezoelectric element for 1 × 10 ⁹ cycles was measured, and the change from the initial displacement was examined. At this time, an absolute value of the change amount of 0.5 μm or less was regarded as no abnormality.

  The displacement is measured by fixing the sample on a vibration isolation table, attaching an aluminum foil on the upper surface of the sample, and measuring at three locations at the center and both ends of the element with a laser displacement meter. The average value of the displacement amounts was defined as the displacement amount of the multilayer piezoelectric element.

From Table 1, the laminated piezoelectric element of Sample No. 1 changed (increased) 0.4 μm in the displacement after 1 × 10 ⁹ cycles of continuous driving with respect to the initial displacement, but no abnormality was observed.

In the laminated piezoelectric elements of Sample Nos. 2 to 5, the displacement after continuous driving of 1 × 10 ⁹ cycles did not change with respect to the initial displacement.

  The present invention is not limited to the above-described embodiment and examples, and various modifications may be made without departing from the scope of the present invention. For example, the non-opposing portion of the laminate is a portion where the internal electrode layer contributing to driving at the time of voltage application is not facing, that is, a portion that does not drive itself, but the non-facing portion includes a metal layer or the like. Good.

1: laminated piezoelectric element 2: piezoelectric layer 3a: first set of internal electrode layers 3b: second set of internal electrode layers 4a: first external electrode 4b: second external electrode 5: laminated body 6 : Opposite part of laminate 7: Non-opposite part of laminate

Claims (8)

  A laminated body in which a plurality of piezoelectric layers and internal electrode layers are alternately laminated, and a pair of opposed side surfaces of the laminated body are joined to each other, and the first set and the second set of the internal electrode layers are connected to each other. In the laminated piezoelectric element including the external electrode, the first external electrode connected to the first set of internal electrode layers and the second set of internal electrode layers are insulated and inactive. The width between the first external electrode and the second set of internal electrode layers in the inactive region is smaller at the end than the central portion in the stacking direction of the stacked body. A laminated piezoelectric element characterized by comprising:   The width between the first external electrode and the second set of internal electrode layers in the inactive region is smaller at both ends than the central portion in the stacking direction of the stacked body. The multilayer piezoelectric element according to claim 1, wherein   The shape of the edge of the second set of internal electrode layers facing the first external electrode is an arc shape that is farther from the first external electrode in the center than on both sides. The laminated piezoelectric element according to 1.   The width between the first external electrode and the second set of internal electrode layers in the inactive region is gradually reduced from the central side toward the end at the end in the stacking direction of the stacked body. The multilayer piezoelectric element according to claim 1, wherein:   2. The laminate according to claim 1, wherein a thickness of the piezoelectric layer is thicker at an end portion than a center portion in a stacking direction of the laminate, and a gap between the internal electrode layers is widened. Type piezoelectric element.   The width of the inactive region between the second external electrode to which the second set of internal electrode layers are connected and the first set of internal electrode layers is also greater than the central portion in the stacking direction of the stacked body. The laminated piezoelectric element according to claim 1, wherein the laminated piezoelectric element is also small at the end.   A container having an injection hole and the multilayer piezoelectric element according to any one of claims 1 to 6, wherein fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. An injection device.   A common rail for storing high-pressure fuel, an injection device according to claim 7 for injecting the high-pressure fuel stored in the common rail, a pressure pump for supplying the high-pressure fuel to the common rail, and a drive signal for the injection device A fuel injection system comprising an injection control unit.

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