JP2005129871A - Multilayer piezoelectric element and jetting apparatus using the same - Google Patents

Abstract

Disclosed is a multilayer piezoelectric element and jetting that have small variations in displacement even when used under a high electric field and high pressure, and have little change in displacement even when continuously driven for a long period of time, and are excellent in reliability and durability. An object is to provide an apparatus.
And a pair of external electrodes in which the internal electrodes are alternately connected to every other layer on a side surface of the multilayer body. In a multilayer piezoelectric element that is driven by applying an electric field to an external electrode, a pillar made of ceramic is provided that connects the opposing piezoelectric bodies through the internal electrode and sandwiching the internal electrode.
[Selection] Figure 2

Description

  The present invention relates to a laminated piezoelectric element and an injection device, for example, a fuel injection device for an automobile engine, a liquid injection device such as an inkjet, a drive element mounted on a precision positioning device such as an optical device, a vibration prevention device, and the like, and a combustion Sensor elements mounted on pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., and circuit elements mounted on piezoelectric gyros, piezoelectric switches, piezoelectric transformers, piezoelectric breakers, etc. The present invention relates to a stacked piezoelectric element and a jetting device used.

  Conventionally, as a multilayer piezoelectric element, a multilayer piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately stacked is known. Multilayer piezoelectric actuators are classified into two types: the simultaneous firing type and the stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Since the multilayer piezoelectric actuator of the type is advantageous for thinning, its superiority is being shown.

  FIG. 5 shows a conventional laminated piezoelectric actuator. In this laminated piezoelectric actuator, piezoelectric bodies 51 and internal electrodes 52 are alternately laminated to form a laminated body 53, which is formed on both end surfaces in the laminating direction. An inactive layer 55 is laminated. One end portion of the internal electrode 52 is alternately exposed on the side surface of the multilayer body 53, and the external electrode 70 is formed on the side surface of the multilayer body 53 where the end portion of the internal electrode 52 is exposed. . The other end of the internal electrode 52 is covered with an insulator 61 and insulated from the external electrode 70.

  A co-fired multilayer piezoelectric actuator is a ceramic green sheet consisting of a calcined powder of piezoelectric material and an organic binder, with a predetermined number of layers printed with internal electrode paste in which a binder is added to silver-palladium powder. The laminated body obtained in this manner was degreased at a predetermined temperature and then baked to obtain a laminated body.

  Since the conventional piezoelectric body required a temperature of 1200 to 1300 ° C. as a firing temperature, silver-palladium having a high ratio of expensive palladium was used as the internal electrode. However, recently, a technique for low-temperature firing has progressed, and a piezoelectric body that can be fired at a temperature of about 1100 ° C. has been developed. Even in this case, considering the melting point of the internal electrode, the silver ratio is 70 wt% and the palladium ratio is 30 Weight percent silver-palladium was required.

  In addition, since the internal electrode is a metal, the bonding force with the piezoelectric body is weak, and when the internal electrode and the piezoelectric body are cracked due to the generation of internal stress due to the difference in thermal expansion, There was also a problem of destruction. In order to solve this problem, for example, Patent Document 1 discloses a method in which ceramic powder is mixed with an internal electrode to increase the bonding strength between the piezoelectric body and the internal electrode.

By the way, in recent years, in order to ensure a large displacement under a large pressure with a small piezoelectric actuator, a higher electric field is applied to continuously drive for a long time.
JP-A-4-299588

  However, the conventional multilayer piezoelectric actuator has a problem that since the internal electrode 52 portion is softer than the piezoelectric body 51, a part of the displacement generated in the piezoelectric body 51 is absorbed, and the variation in displacement becomes large. There is also a problem in durability, and there is also a problem that the variation of the displacement amount becomes large after repeated use for a long time. These problems cannot be solved even by a method of improving the bonding strength between the internal electrode 52 and the piezoelectric body 51 by mixing ceramic powder in the internal electrode 52 as shown in Patent Document 1 above.

  That is, as in recent years, in order to reduce the size of the actuator and ensure a large amount of displacement under a large pressure, a higher electric field is applied and the actuator is continuously driven for a long time. The variation in the displacement of this is a problem. Furthermore, a change in the displacement amount during a long operation is also a problem.

  Therefore, the present invention provides a multilayer piezoelectric element that is small in variation in displacement even when used under a high electric field and high pressure, and has little change in displacement even when continuously driven for a long period of time, and has excellent reliability and durability. And an injection device.

  The laminated piezoelectric element of the present invention has a laminated body in which piezoelectric bodies and internal electrodes are alternately laminated, and a pair of external electrodes in which the internal electrodes are alternately connected to the side surfaces of the laminated body every other layer. In the multilayer piezoelectric element that is driven by applying an electric field to the external electrode, there is provided a column that penetrates the internal electrode and connects the opposing piezoelectric bodies with the internal electrode interposed therebetween.

  The multilayer piezoelectric element according to the present invention is characterized in that the number of joints between the pillar and the piezoelectric body is 50% or more of the maximum diameter of the pillar and occupies 30% or more of the whole.

  The multilayer piezoelectric element of the present invention is characterized in that the average value of the minimum diameters of the columns is 0.2 μm or more.

  The multilayer piezoelectric element of the present invention is characterized in that 5 to 150 columns are present per 1 mm.

The multilayer piezoelectric element of the present invention is characterized in that the difference in thermal expansion between the column and the piezoelectric body is 3 × 10 ⁻⁵ / ° C. or less.

  In the multilayer piezoelectric element of the present invention, the column is made of the same material as the piezoelectric body.

  In the multilayer piezoelectric element of the present invention, the metal composition in the internal electrode is mainly composed of a Group VIII metal and / or a Group Ib metal.

  In the multilayer piezoelectric element of the present invention, when the content of the Group VIII metal in the internal electrode is M1 (wt%) and the content of the Group Ib metal is M2 (wt%), 0.001 ≦ M1 ≦ 15, 85 ≦ M2 ≦ 99.999, M1 + M2 = 100 is satisfied.

  In the multilayer piezoelectric element of the present invention, the group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the group Ib metal is at least one of Cu, Ag, and Au. It is one or more types.

  In the multilayer piezoelectric element of the present invention, the group VIII metal is at least one of Pt and Pd, and the group Ib metal is at least one of Ag and Au.

  In the multilayer piezoelectric element of the present invention, the group VIII metal is Ni and the group Ib metal is Cu.

  In the multilayer piezoelectric element of the present invention, the piezoelectric body contains a perovskite oxide as a main component.

In the multilayer piezoelectric element of the present invention, the piezoelectric body is mainly composed of a perovskite oxide made of PbZrO ₃ —PbTiO ₃ .

  In the multilayer piezoelectric element of the present invention, the internal electrodes whose ends are exposed on the side surfaces of the multilayer body and the internal electrodes whose ends are not exposed are alternately configured, and the ends are exposed. A groove is formed in a portion of the piezoelectric body between the internal electrode and the external electrode that is not, and the groove is filled with an insulator having a Young's modulus lower than that of the piezoelectric body.

  In addition, the injection device of the present invention includes a storage container having an injection hole, the stacked piezoelectric element stored in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. It is characterized by comprising.

  Thus, according to the multilayer piezoelectric element of the present invention, it has a multilayer body in which piezoelectric bodies and internal electrodes are alternately stacked, and the internal electrodes are alternately connected to the side surfaces of the multilayer body every other layer. In a laminated piezoelectric element that includes a pair of external electrodes that are driven by applying an electric field to the external electrodes, by providing columns that penetrate the internal electrodes and connect the opposing piezoelectric bodies with the internal electrodes sandwiched therebetween, In addition, it is possible to provide a highly reliable and highly durable piezoelectric actuator in which the variation in the amount of displacement can be reduced, and the change in the amount of displacement is small even after a long continuous operation.

  Furthermore, since the variation of the displacement of the multilayer piezoelectric element is small and the change in the displacement is small even when continuously driven, it is possible to provide an injection device with excellent durability and high reliability.

  FIG. 1 shows an embodiment of a multilayer piezoelectric actuator comprising the multilayer piezoelectric element of the present invention, wherein (a) is a perspective view and (b) is a side view. FIG. 2 is a cross-sectional view of the internal electrode 2 portion.

  As shown in FIG. 1, the multilayer piezoelectric actuator comprising the multilayer piezoelectric element of the present invention is formed on the side surface of a quadrangular prism-shaped multilayer body 10 in which a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are alternately laminated. The inner electrode 2 is covered with the insulator 3 every other end, and the end of the inner electrode 2 not covered with the insulator 3 is made of a conductive material mainly composed of silver and glass, and is three-dimensional. An external electrode 4 made of a porous conductor having a mesh structure is joined, and a lead wire 6 is connected and fixed to each external electrode 4. The laminated body does not necessarily have to be a square column, and various shapes such as a cylinder and a polygonal column are conceivable.

  An internal electrode 2 is disposed between the piezoelectric bodies 1, and the internal electrode 2 is formed of a metal material such as silver-palladium, and a predetermined voltage is applied to each piezoelectric body 1. Has a function of causing displacement due to the inverse piezoelectric effect.

  In contrast, since the inactive layer 9 is a layer of a plurality of piezoelectric bodies 1 on which the internal electrode 2 is not disposed, no displacement occurs even when a voltage is applied.

  In addition, external electrodes 4 are joined to the opposite side surfaces of the laminated body 10, and the laminated internal electrodes 2 are electrically connected to every other layer so that they are connected to each other. A voltage necessary for displacing the piezoelectric body 1 by the inverse piezoelectric effect can be commonly supplied to the internal electrodes 2.

  Furthermore, since the lead wire 6 is connected and fixed to the external electrode 4 with solder or the like, the external electrode 4 can be connected to an external voltage supply unit.

  In the multilayer piezoelectric actuator of the present invention, as shown in FIG. 2, a plurality of pillars 20 are provided to connect the opposing piezoelectric bodies 1 through the internal electrode 2. Thus, by forming the pillars 20 with a hard material such as ceramic between the piezoelectric bodies 1, the rigidity of the internal electrode 2 is improved, and the amount of displacement that occurs in the internal electrode 2 is reduced. The amount stabilizes. As a result, variation in the amount of displacement of each product is reduced, and reliability can be improved. In addition, the change in displacement after a long period of use is reduced, and durability can be improved.

  Further, as shown in FIG. 2, the number of columns 20 in which the diameter B of the joint portion 22 between the columns 20 and the piezoelectric body 1 is 50% or more of the maximum diameter A of the columns 20 occupies 30% or more of the whole. Is preferred. This is because the number of the columns 20 such that the diameter B of the joint portion 22 between the columns 20 and the piezoelectric body 1 is 50% or more of the maximum diameter A of the columns 20 occupies 30% or more. This is because the strength of No. 1 increases and the rigidity also increases, so that the amount of displacement occurring in the internal electrode 2 is less absorbed and the amount of displacement is stabilized. As a result, variation in the amount of displacement of each product is reduced, and reliability can be improved. In addition, the change in displacement after a long period of use is reduced, and durability can be improved. For the same reason, it is more preferable that the number of columns 20 in which the diameter B of the joint portion 22 between the columns 20 and the piezoelectric body 1 is 50% or more of the maximum diameter A of the columns 20 is 50% or more.

  Here, the measurement method will be described. As shown in FIG. 2, a length of about 1 mm is measured in a cross-sectional photograph of the vicinity of the internal electrode 2 of the multilayer piezoelectric element, and the diameter B of the joint portion between the maximum diameter A and the piezoelectric body 1 for each column 20 is measured. B / A) × 100 was calculated and the ratio of the maximum diameter A of the column 20 and the diameter B of the joint portion 22 between the column 20 and the piezoelectric body 1 was determined for each column 20. Then, it was calculated what percentage of the number of those whose value was 50% or more was measured. Such a thing was performed 10 places and the average was taken and expressed as a numerical value.

  Moreover, in this invention, it is preferable that the average value of the minimum diameter of the pillar 20 is 0.2 micrometer or more. Furthermore, it is more preferable that it is 0.3 micrometer or more. By doing in this way, since the strength of the pillar 20 becomes large and it becomes difficult to break down, variation in the amount of displacement is reduced, change in the amount of displacement after continuous use is also reduced, and reliability and durability are improved.

  In the multilayer piezoelectric element of the present invention, it is preferable that 5 to 150 columns 20 per 1 mm exist in the cross section in the vicinity of the internal electrode 2. Moreover, it is more preferable that 10-100 exists. This is because by setting the number of pillars 20 as described above, the rigidity can be increased, and a laminated piezoelectric element having a small variation in displacement and excellent reliability can be obtained. When the number of pillars 20 is less than 5, the above effect is reduced. On the other hand, when the number of pillars 20 is more than 100, the resistance of the internal electrode 2 is increased, and the function as an electrode is degraded, for example, the electrode is heated.

Furthermore, it is preferable that the thermal expansion difference between the column 20 and the piezoelectric body 1 is 3 × 10 ⁻⁵ / ° C. or less, particularly 2 × 10 ⁻⁵ / ° C. As a result, the internal stress between the piezoelectric body 1 and the column 20 is reduced, the bonding strength at the interface is increased, and the durability can be improved. In the case where the thermal expansion difference is 3 × 10 ⁻⁵ / ° C. or less, when PZT is used for the piezoelectric body 1, the material of the pillar 20 is PZT, Al ₂ O ₃ , ZrO ₂ , TiO ₂ , SiO ₂ or the like. Can be used.

  Furthermore, it is preferable that the pillar 20 is made of the same material as that of the piezoelectric body 1. Thereby, the internal stress generated between the column 20 and the piezoelectric body 1 is further reduced, the bonding strength at the interface is increased, and the durability can be improved.

  The column 20 is formed by mixing powder of the material forming the column 20 in the internal electrode 2 in advance in the manufacturing process, and holding at least once at a temperature of 80% or more of the maximum firing temperature during the temperature rise. Is achieved by doing That is, unlike conventional firing, after degreasing, the powder of the material forming the pillar 20 mixed with the internal electrode 2 is affected by the surrounding metal composition by holding once at 80% or more of the maximum firing temperature. In this way, it becomes a state in which grain growth is likely to occur, and the piezoelectric elements 1 that face each other with the internal electrode 2 sandwiched between the internal electrodes 2 by connecting the piezoelectric bodies 1 that face the grain growth by firing at the maximum firing temperature. A pillar 20 connecting the body 1 can be formed. The addition amount of the material powder of the pillar 20 added to the internal electrode 2 is suitably 5 to 40% by weight. If the amount exceeds 40% by weight, the resistance of the electrode increases excessively, and there is a possibility of heating. If the amount is less than 5% by weight, the columns cannot be provided sufficiently, and the effect of improving the rigidity of the internal electrode is reduced. Reliability and durability cannot be sufficiently improved.

  The metal composition in the internal electrode 2 of the present invention is preferably composed of a Group VIII metal and a Group Ib metal. Since the metal composition has heat resistance, the piezoelectric body 1 and the internal electrode 2 can be fired simultaneously.

  When the metal composition in the internal electrode 2 of the present invention has a group VIII metal content of M1 (wt%) and a group Ib metal content of M2 (wt%), 0.001 ≦ M1 ≦ 15 , 85 ≦ M2 ≦ 99.999 and M1 + M2 = 100 are preferably used as a main component.

  The reason why the composition ratio of the main component of the metal component constituting the internal electrode 2 of the present invention is limited to the above range is as follows. That is, M1 is set to 0.001 or more and 15 or less when the internal metal M2 element migrates into the piezoelectric body when it is less than 0.001, and when it exceeds 15, the specific resistance of the internal electrode 2 increases, and the laminated type This is because, when the piezoelectric element is continuously driven, the internal electrode 2 portion generates heat, and the electrode and porcelain interface deteriorates, thereby causing delamination during driving. In particular, M1 is preferably 0.1 or more and 10 or less in terms of preventing delamination and improving the durability of the multilayer piezoelectric element. Moreover, when it is excellent in heat conduction and needs higher durability, 0.5 or more and 9.5 or less are more preferable. Moreover, when higher durability is calculated | required, 2-8 is more preferable.

  Also, the reason why M2 is set to 85 or more and 99.999 or less is that when 99.999 is exceeded, the internal metal M2 element migrates into the piezoelectric body 1, and when it is less than 85, the specific resistance of the internal electrode 2 increases. This is because when the laminated piezoelectric element is continuously driven, the internal electrode 2 portion generates heat, and the electrode and porcelain interface deteriorates, thereby causing delamination during driving. In particular, M2 is preferably 90 or more and 99.9 from the viewpoint of improving the durability of the multilayer piezoelectric element. Moreover, when higher durability is required, 90.5 or more and 99.5 or less are more preferable. Moreover, when higher durability is calculated | required, 92-98 is further more preferable.

  These M1 and M2 indicating the weight% of the metal component in the internal electrode 2 can be specified by an analysis method such as EPMA (Electron Probe Micro Analysis) method.

  The metal component in the internal electrode 2 of the present invention is such that the Group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the Group Ib metal is Cu, Ag, or Au. Of these, at least one is preferable. This is because the metal composition has excellent mass productivity in recent alloy powder synthesis techniques.

  More preferably, the metal component in the internal electrode 2 is a group VIII metal of at least one of Pt and Pd, and a group Ib metal of at least one of Ag and Au. As a result, an electrode having excellent heat resistance can be formed, and the specific resistance of the internal electrode 2 can be reduced, so that heat generation in the internal electrode 2 portion can be suppressed even when continuously driven. Furthermore, it is preferable that the metal component contained in the internal electrode 2 is mainly composed of Ag, which is a group Ib metal, and contains at least one of Pt and Pd, which are group VIII metals.

  Furthermore, as for the metal component in the said internal electrode 2, it is more preferable that a VIII group metal is Ni and a Ib group metal is Cu. This is because an electrode having excellent oxidation resistance can be formed, and even when continuously driven, the resistance of the internal electrode 2 is hardly deteriorated and durability can be improved.

Moreover, it is preferable that the piezoelectric body 1 of the present invention contains a perovskite oxide as a main component. For example, when formed of a perovskite-type piezoelectric ceramic material typified by barium titanate (BaTiO ₃ ), the amount of displacement can be increased because the piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristics is high. Furthermore, the piezoelectric body and the internal electrode can be fired simultaneously while functioning as an excellent piezoelectric element.

Moreover, it is preferable that the piezoelectric body of the present invention contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component.

Accordingly, in such a multilayer piezoelectric element can further because of high piezoelectric strain constant d _33, a large amount of displacement.

  In addition, the internal electrodes whose end portions are exposed on the side surfaces of the multilayer piezoelectric element of the present invention and the internal electrodes whose end portions are not exposed are alternately configured, and between the internal electrodes and the external electrodes whose end portions are not exposed. It is preferable that a groove is formed in the piezoelectric body portion, and an insulator having a Young's modulus lower than that of the piezoelectric body is formed in the groove.

  Thereby, in such a multilayer piezoelectric element, stress generated by displacement during driving can be relieved, so that heat generation of the internal electrode portion can be suppressed even when continuously driven.

  Further, as shown in FIG. 3, the external electrode 4 is preferably made of a porous conductor having a three-dimensional network structure. If the external electrode 4 is not composed of a porous conductor having a three-dimensional network structure, the external electrode 4 does not have flexibility and cannot follow the expansion and contraction of the laminated piezoelectric actuator. A contact failure between the external electrode 4 and the internal electrode 2 may occur. Here, the three-dimensional network structure does not mean a state in which a so-called spherical void exists in the external electrode 4, but the conductive material powder and the glass powder constituting the external electrode 4 are baked at a relatively low temperature. For this reason, voids exist in a state of being connected to some extent without completing the sintering, suggesting a state in which the conductive material powder and the glass powder constituting the external electrode 4 are three-dimensionally connected and joined.

  Alternatively, the porosity in the external electrode 4 is desirably 30 to 70% by volume. Here, the porosity is the ratio of the voids 4 a in the external electrode 4. This is because if the porosity in the external electrode 4 is smaller than 30% by volume, the external electrode 4 cannot withstand the stress generated by the expansion and contraction of the multilayer piezoelectric actuator, and the external electrode 4 may be disconnected. In addition, when the porosity in the external electrode 4 exceeds 70% by volume, the resistance value of the external electrode 4 increases, and thus when the large current is passed, the external electrode 4 may cause local heat generation and break. There is.

  Furthermore, it is desirable that a glass rich layer is formed on the surface layer portion of the external electrode 4 on the piezoelectric body 1 side. This is because, if the glass-rich layer is not present, it is difficult to bond the glass component in the external electrode 4, so that there is a possibility that the external electrode 4 cannot easily be firmly bonded to the piezoelectric body 1.

  In addition, the softening point (° C.) of the glass constituting the external electrode 4 is desirably 4/5 or less of the melting point (° C.) of the conductive material constituting the internal electrode 2. When the softening point of the glass constituting the external electrode 4 exceeds 4/5 of the melting point of the conductive material constituting the internal electrode 2, the softening point of the glass constituting the external electrode 4 and the internal electrode 2 are constituted. Since the melting point of the conductive material becomes the same temperature, the temperature at which the external electrode 4 is baked inevitably approaches the melting point that constitutes the internal electrode 2. The conductive material aggregates to prevent diffusion bonding, and the baking temperature cannot be set to a temperature sufficient to soften the glass component of the external electrode 4, so that sufficient bonding strength with the softened glass cannot be obtained. There is a case.

  Furthermore, it is desirable that the glass constituting the external electrode 4 be amorphous. This is because, in crystalline glass, the external electrode 4 cannot absorb the stress generated by the expansion and contraction of the laminated piezoelectric actuator, so that cracks and the like may occur.

  Furthermore, it is desirable that the thickness of the external electrode 4 is thinner than the thickness of the piezoelectric body 1. This is because when the thickness of the external electrode 4 is larger than the thickness of the piezoelectric body 1, the strength of the external electrode 4 increases, so that the load on the joint between the external electrode 4 and the internal electrode 2 when the laminate 10 expands and contracts. May increase and contact failure may occur.

  Furthermore, it is desirable to provide a conductive auxiliary member 7 made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded on the outer surface of the external electrode 4. If the conductive auxiliary member 7 is not provided on the outer surface of the external electrode 4, when the laminate 10 is driven by passing a large current, the external electrode 4 cannot withstand the large current and locally generates heat, which may cause disconnection. There is sex.

  Further, if a mesh or a mesh-like metal plate is not used on the outer surface of the external electrode 4, the stress due to the expansion and contraction of the multilayer body 10 directly acts on the external electrode 4, so that the external electrode 4 is laminated due to fatigue during driving. There is a possibility that it will be easy to peel off from the side surface.

  Furthermore, it is desirable that the conductive adhesive is made of a polyimide resin in which conductive particles are dispersed. This is because the conductive adhesive maintains a high adhesive strength by using a polyimide resin having a relatively high heat resistance even when the laminate 10 is driven at a high temperature by using the polyimide resin. Cheap.

  Furthermore, it is desirable that the conductive particles are silver powder. This makes it easy to suppress local heat generation in the conductive adhesive by using silver powder having a relatively low resistance value for the conductive particles.

  In addition, the multilayer piezoelectric element of the present invention is preferably composed of a single plate or one or more layers. As a result, the pressure applied to the element can be converted into a voltage, or the element can be displaced by applying a voltage to the element. Therefore, even if an unexpected stress is applied during element driving, the stress is reduced. Since the stress can be relieved by dispersing and converting the voltage, a highly reliable piezoelectric actuator having excellent durability can be provided.

  Further, FIG. 4 shows an ejection device using the laminated piezoelectric element of the present invention, and a storage container 31 having an injection hole 33, a piezoelectric actuator 43 stored in the storage container 31, and a piezoelectric actuator of this piezoelectric actuator. A valve 35 for ejecting liquid from the ejection hole 33 by driving is provided.

  A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate. The fuel passage 37 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 37 at a constant high pressure. Accordingly, when the valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is formed to be injected into a fuel chamber (not shown) of the internal combustion engine at a constant high pressure.

  Further, the upper end portion of the valve 35 has a large diameter, and serves as a piston 41 slidable with a cylinder 39 formed in the storage container 31.

  In such an injection device, when the piezoelectric actuator 43 is extended by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. When the application of voltage is stopped, the piezoelectric actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 so that fuel is injected.

  As a result, in the injection device, as described above, even if the multilayer piezoelectric element is continuously driven, the desired displacement amount does not change effectively, so that the device does not malfunction and has excellent durability. A highly reliable injection device can be provided.

  A method for manufacturing the multilayer piezoelectric element of the present invention will be described below.

In the multilayer piezoelectric element of the present invention, first, the multilayer body 10 is produced. A laminated body 10 formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 includes, for example, a calcined powder of a piezoelectric ceramic such as a perovskite oxide made of PbZrO ₃ —PbTiO ₃ , an acrylic type, A binder made of an organic polymer such as butyral is mixed with a plasticizer such as DBP (dioctyl phthalate) or DOP (dibutyl phthalate) to prepare a slurry. A ceramic green sheet to be the piezoelectric body 1 is produced by a tape molding method such as the above method.

Next, for example, a metal powder constituting an internal electrode such as silver-palladium or the like as a material of the pillar 20 and a ceramic powder such as PZT, Al ₂ O ₃ , ZrO ₂ , TiO ₂ , or SiO ₂ as one or more binders, A conductive paste is prepared by adding and mixing a plasticizer and the like, and this is printed on the upper surface of each green sheet to a thickness of 1 to 40 μm by screen printing or the like.

  Then, after laminating a plurality of green sheets each having a conductive paste printed on the upper surface, the binder is debindered at a predetermined temperature, and once held at a temperature of 80% or more of the maximum temperature, the maximum temperature is reached. Firing is performed at 900 to 1200 ° C. The holding time at 80% or more of the maximum temperature is preferably longer than 0.25 h. Further, two or more steps may be provided. For example, the holding may be performed at 80% and 90% of the maximum holding temperature and heated in a multistage pattern. In order to promote the growth of the pillars, it is necessary to hold once at 80% or more of the maximum holding temperature. Thereby, the opposing piezoelectric bodies can be firmly coupled. The reason why the temperature is limited to 900 ° C. or more and 1200 ° C. or less is that a dense piezoelectric body cannot be manufactured at a temperature lower than 900 ° C., and if it exceeds 1200 ° C., the shrinkage between the contraction of the electrode and the contraction of the piezoelectric body during firing This is because the stress increases, and cracks occur during continuous driving.

  Moreover, it is preferable that the composition shift in the electrode is 5% or less before and after firing. Thereby, it can suppress that an electrode becomes hard. Thereby, the laminated body 10 is produced.

  Thereafter, the internal electrodes whose end portions are exposed on the side surfaces of the multilayer piezoelectric element and the internal electrodes 2 whose end portions are not exposed are alternately configured, and the internal electrodes 2 and the external electrodes 4 whose end portions are not exposed are alternately formed. When a groove is formed in the piezoelectric body 1 and an insulator having a Young's modulus lower than that of the piezoelectric body 1, such as a resin or rubber, is formed in the groove, the columnar laminate 10 is formed by an internal dicing device or the like. Grooves 3 are formed every other layer on the side surface.

  The conductive material constituting the external electrode 4 is preferably silver having a low Young's modulus or an alloy containing silver as a main component from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator.

A binder is added to the glass powder to produce a silver glass conductive paste, which is formed into a sheet and dried (the solvent is scattered), and the raw density of the sheet is controlled to 6 to 9 g / cm ^3. The sheet is transferred to the external electrode forming surface of the columnar laminate 10, and is at a temperature higher than the softening point of glass, at a temperature not higher than the melting point of silver (965 ° C.), and not higher than 4/5 of the firing temperature (° C.). By baking at a temperature, the binder component in the sheet produced using the silver glass conductive paste is scattered and disappeared, and the external electrode 4 made of a porous conductor having a three-dimensional network structure can be formed.

  The baking temperature of the silver glass conductive paste effectively forms a neck portion, diffuses and joins silver in the silver glass conductive paste and the internal electrode 2, and effectively creates voids in the external electrode 4. 550-700 degreeC is desirable from the point that it is made to remain, and also the external electrode 4 and the laminated body 10 side surface are joined partially. The softening point of the glass component in the silver glass conductive paste is preferably 500 to 700 ° C.

  When the baking temperature is higher than 700 ° C., the sintering of the silver powder of the silver glass conductive paste proceeds so much that a porous conductor having an effective three-dimensional network structure cannot be formed, and the external electrode 4 Becomes too dense, and as a result, the Young's modulus of the external electrode 4 becomes too high to absorb the stress during driving sufficiently, and the external electrode 4 may be disconnected. Preferably, baking should be performed at a temperature within 1.2 times the softening point of the glass.

  On the other hand, when the baking temperature is lower than 550 ° C., the diffusion electrode is not sufficiently bonded between the end portion of the internal electrode 2 and the external electrode 4, so that the neck portion is not formed, and the internal electrode 2 and the external electrode are not driven. There is a possibility of causing a spark between the electrodes 4.

  Note that the thickness of the silver glass conductive paste sheet is preferably thinner than the thickness of the piezoelectric body 1. More preferably, it is 50 μm or less from the viewpoint of following the expansion and contraction of the actuator.

  Next, the laminated body 10 on which the external electrode 4 is formed is immersed in a silicone rubber solution, and the silicone rubber solution is vacuum degassed to fill the groove of the laminated body 10 with silicone rubber. The laminated body 10 is pulled up, and silicone rubber is coated on the side surface of the laminated body 10. Thereafter, the silicone rubber filled in the groove and coated on the side surface of the laminate 10 is cured.

  Thereafter, a lead wire is connected to the external electrode 4 to complete the multilayer piezoelectric element of the present invention.

  Then, a direct current voltage of 0.1 to 3 kV / mm is applied to the pair of external electrodes 4 via the lead wires, and the laminated body 4 is subjected to polarization treatment, thereby completing a laminated piezoelectric actuator as a product. Is connected to an external voltage supply unit, and a voltage is applied to the internal electrode 2 via the lead wire and the external electrode 4, the piezoelectric bodies 1 are greatly displaced by the inverse piezoelectric effect, thereby supplying fuel to the engine, for example. It functions as a fuel injection valve for automobiles that supply fuel.

  The laminated piezoelectric element configured as described above increases the rigidity of the internal electrode 2 and improves the bonding strength, so that the amount of displacement absorbed by the internal electrode is reduced, and even when continuously driven, Since delamination does not occur, the amount of displacement does not change effectively. Therefore, a highly reliable piezoelectric actuator can be provided without malfunctioning the device.

  The multilayer piezoelectric element of the present invention is not limited to these, and various modifications can be made without departing from the gist of the present invention.

  Moreover, although the example which formed the external electrode 4 in the side surface which the columnar laminated body 10 opposes was demonstrated in the said example, in this invention, you may form a pair of external electrode in the side surface provided adjacently, for example.

  Further, the present invention relates to a multilayer piezoelectric element and an injection device, but is not limited to the above-described embodiments. For example, a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, an optical device, etc. Drive elements mounted on precision positioning devices and vibration prevention devices, as well as sensor elements mounted on combustion pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensors, yaw rate sensors, and piezoelectric gyroscopes Needless to say, even a circuit element other than a circuit element mounted on a piezoelectric switch, a piezoelectric transformer, a piezoelectric breaker, or the like can be used as long as the element uses piezoelectric characteristics.

Example A multilayer piezoelectric actuator comprising the multilayer piezoelectric element of the present invention was produced as follows.

First, a columnar laminate was produced. The piezoelectric body is formed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) having a thickness of 150 μm, and the internal electrodes are formed with a thickness of 3 μm. The number of stacked piezoelectric bodies and internal electrodes is 300 layers. did. As the internal electrode, a mixture of metal (for example, 90Ag-10Pd) as shown in Table 1 and powder such as ceramic was used. The particle diameter of a powder such as ceramic was 1.5 μm or less, and particles having an aspect ratio of 3 or less were used. Thereafter, the laminate was degreased at 400 to 700 ° C., held at 850 ° C. for 20 minutes, and then held at 1000 ° C. to obtain a sintered body. When the metal composition of the internal electrode was Ni, the laminate was degreased at 400 to 700 ° C., held at 1050 ° C. for 20 minutes, and then held at 1200 ° C. to obtain a sintered body.

  Thereafter, a groove having a depth of 50 μm and a width of 50 μm was formed at every other end of the internal electrode on the side surface of the columnar laminate by a dicing apparatus.

Next, a mixture of 90% by volume of flaky silver powder having an average particle diameter of 2 μm and 10% by volume of amorphous glass powder having a remaining softening point of 640 ° C. mainly composed of silicon having an average particle diameter of 2 μm. In addition, 8 parts by mass of the binder was added to 100 parts by mass of the total weight of the silver powder and the glass powder, and mixed sufficiently to prepare a silver glass conductive paste. The silver glass conductive paste thus produced was formed on a release film by screen printing, dried and then peeled off from the release film to obtain a sheet of silver glass conductive paste. The raw density of this sheet was measured by the Archimedes method and found to be 6.5 g / cm ³ .

  Next, the silver glass paste sheet was transferred to the external electrode surface of the columnar laminate, and baked at 650 ° C. for 30 minutes to form an external electrode made of a porous conductor having a three-dimensional network structure. The porosity of the external electrode at this time was 40% when a cross-sectional photograph of the external electrode was measured using an image analyzer.

  Thereafter, a lead wire is connected to the external electrode, a 3 kV / mm DC electric field is applied to the positive electrode and the negative external electrode via the lead wire for 15 minutes to perform polarization treatment, and the laminated piezoelectric element as shown in FIG. A multilayer piezoelectric actuator made of

  A DC voltage of 170 V was applied to the obtained multilayer piezoelectric actuator composed of the multilayer piezoelectric element, the displacement amount in each sample was measured, and the variation was calculated and shown in Table 1. Further, a driving test was performed by applying an AC voltage of 0 to +170 V at a room temperature to a multilayer piezoelectric actuator composed of the multilayer piezoelectric element at a frequency of 150 Hz.

A DC voltage of 170 V is applied to the laminated piezoelectric actuator composed of laminated piezoelectric elements that have been driven 1 × 10 ⁹ times, the amount of displacement in each sample is measured, and the change in the amount of displacement before and after the driving test is measured. Calculated. In the calculation, the displacement amount before the driving test was used as a numerator, the displacement amount after the driving test was used as a denominator, and this was multiplied by 100 and expressed in%.

  In addition, the diameter and the number of the pillars that penetrate the internal electrodes and connect the piezoelectric bodies were measured as follows.

  As for the ratio of the columns where the joint portion is 50% or more of the maximum diameter, a length of 1 mm is measured in a cross-sectional photograph near the internal electrode 2 of the multilayer piezoelectric element as shown in FIG. The diameter B of the joint portion 22 between the pillar 20 and the piezoelectric body 1 is measured, and the calculation of (B / A) × 100 is performed, and the maximum diameter A of the pillar 20 and the joint portion 22 between the pillar 20 and the piezoelectric body 1 are calculated. The ratio of the diameter B was determined. Then, it was calculated how many percent of the measured values had a value of 50% or more. Such a thing was performed 10 places and the average was taken and expressed as a numerical value. The minimum diameter of the column was measured by the same measurement as described above. Moreover, the measurement was performed at 10 places.

Table 1 shows the above results, the material of the internal electrode, the difference in thermal expansion between the piezoelectric body and the column, and the like.

  Sample No. of the product of the present invention provided with a pillar that penetrates the internal electrode and connects the opposing piezoelectric bodies across the internal electrode. In Nos. 1 to 25, the initial displacement variation was 10% or less, which was smaller than that of the comparative example (No. 26). Moreover, the change of the displacement amount after the continuous durability test was as small as 5% or less, and it was found that the reliability and durability were excellent as compared with the comparative example.

  In particular, sample no. In Nos. 2 to 25, it was found that the variation in the initial displacement amount was 8% or less and the change in the displacement amount after the continuous durability test was 4% or less, which further improved reliability and durability.

  Furthermore, Sample No. in which the number of columns having a joint portion of 50% or more of the maximum diameter is 50% or more and the average value of the minimum diameter of the columns is 0.2 μm. 3 to 5 and 7 to 25 were found to have an even smaller initial variation of 7% or less and further improved reliability.

  On the other hand, Sample No. which is not provided with a column which is outside the scope of the present invention. No. 26 had a poor initial displacement variation of 20%, and the displacement change after the continuous durability test was also 10%, which was inferior to the product of the present invention in terms of reliability and durability.

  The multilayer piezoelectric element of the present invention can be used for a piezoelectric transformer. In addition, the multilayer piezoelectric element of the present invention can be used in multilayer piezoelectric actuators used in fuel injectors for automobiles, ink jet printer ink ejectors, precision positioning devices such as optical devices, vibration preventing drive elements, and the like. Furthermore, it is mounted on sensor elements mounted on combustion pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., and piezoelectric gyros, piezoelectric switches, piezoelectric transformers, piezoelectric breakers, etc. It can be used for a laminated piezoelectric element used for a circuit element.

The laminated piezoelectric element of this invention is shown, (a) is a perspective view, (b) is a side view. It is sectional drawing which shows a part of laminated piezoelectric element of this invention. 2A and 2B show a laminated piezoelectric element in which a conductive auxiliary member is formed on the outer surface of an external electrode. FIG. 1A is a perspective view, and FIG. It is sectional drawing which shows the injection apparatus of this invention. It is a side view of a conventional multilayer piezoelectric actuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 2 ... Internal electrode 3 ... Insulator 4 ... External electrode 6 ... Lead wire 7 ... Conductive auxiliary member 9 ... Inactive layer 10 ... Lamination | stacking Body 20 ··· Column 22 ··· Joint portion 31 of column and piezoelectric body ··· Storage container 33 ··· Injection hole 35 ··· Valve 43 ··· Piezoelectric actuator

Claims (15)

A laminated body in which piezoelectric bodies and internal electrodes are alternately laminated; and a pair of external electrodes in which the internal electrodes are alternately connected on every other side of the laminated body. A laminated piezoelectric element driven by applying a layer, wherein a pillar is provided through the internal electrode to connect the opposing piezoelectric bodies with the internal electrode interposed therebetween. 2. The multilayer piezoelectric element according to claim 1, wherein the number of the joints between the pillars and the piezoelectric body is 50% or more of the maximum diameter of the pillars occupies 30% or more. The multilayer piezoelectric element according to claim 1 or 2, wherein an average value of minimum diameters of the pillars is 0.2 µm or more. 4. The multilayer piezoelectric element according to claim 1, wherein there are 5 to 150 columns per mm. ^5. The multilayer piezoelectric element according to claim 1, wherein a difference in thermal expansion between the column and the piezoelectric body is 3 × 10 ⁻⁵ / ° C. or less. 6. The stacked piezoelectric element according to claim 1, wherein the pillar is made of the same material as that of the piezoelectric body. 7. The multilayer piezoelectric element according to claim 1, wherein the metal composition in the internal electrode contains a Group VIII metal and / or a Group Ib metal as a main component. When the content of the Group VIII metal in the internal electrode is M1 (wt%) and the content of the Group Ib metal is M2 (wt%), 0.001 ≦ M1 ≦ 15, 85 ≦ M2 ≦ 99.999, The multilayer piezoelectric element according to claim 7, wherein M1 + M2 = 100 is satisfied. The group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the group Ib metal is at least one of Cu, Ag, and Au. The multilayer piezoelectric element according to any one of 7 to 8. The laminated piezoelectric material according to any one of claims 7 to 9, wherein the Group VIII metal is at least one of Pt and Pd, and the Group Ib metal is at least one of Ag and Au. element. The multilayer piezoelectric element according to claim 7, wherein the group VIII metal is Ni and the group lb metal is Cu. The multilayer piezoelectric element according to claim 1, wherein the piezoelectric body contains a perovskite oxide as a main component. 13. The multilayer piezoelectric element according to claim 12, wherein the piezoelectric body contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component. The internal electrode whose end is exposed on the side surface of the laminate and the internal electrode whose end is not exposed are alternately configured, and the piezoelectric element between the internal electrode and the external electrode where the end is not exposed. 14. The multilayer piezoelectric element according to claim 1, wherein a groove is formed in a body portion, and the groove is filled with an insulator having a Young's modulus lower than that of the piezoelectric body. A storage container having an injection hole, the laminated piezoelectric element according to any one of claims 1 to 14 accommodated in the storage container, and liquid is ejected from the injection hole by driving the multilayer piezoelectric element. An injection device comprising a valve.

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