JP2011176114A - Laminated piezoelectric element and injection device including the same, as well as fuel injection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element which is free from cracks occurring at a border between an inactive area and an active area due to thermal stress, can be stably driven for a long time and is excellent in reliability. <P>SOLUTION: The laminated piezoelectric element 1 includes: an active area laminate 6 made of piezoelectric layers 3 and internal electrode layers 2; a columnar laminate 8 including an inactive area laminate 7 with the piezoelectric layers 3 laminated disposed at both ends in the lamination direction of the laminate 8; an external electrode layer 4 connected in the lamination direction on a pair of side faces of the laminate 8; and a coat layer 5 for covering the side face of the laminate 8 together with the external electrode layer 4 from the active area 6 to the inactive area 7. The coat layer 5 is thinner on a side face of the active area 6 than in a side face of the inactive area 7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to, for example, a driving element (piezoelectric actuator) using a piezoelectric body, a laminated piezoelectric element used as a sensor element or a circuit element, an injection device such as a fuel injection device of an automobile engine equipped with the piezoelectric element, and an automobile engine. The present invention relates to a fuel injection system.

  A conventional multilayer piezoelectric element includes, for example, a laminate in which piezoelectric layers and internal electrode layers are alternately laminated, and a pair that is bonded to each of a pair of side surfaces of the laminate and electrically connected to the internal electrode layer. The external electrode layer and a coating layer that covers the side surface of the laminated body are included (see, for example, Patent Document 1).

  Specifically, the internal electrode layers are laminated so that every other layer is alternately exposed on a pair of opposite side surfaces of the laminate, and alternately connected to a pair of external electrodes (positive external electrode and negative external electrode). ing. Here, piezoelectric layers are arranged at both ends in the stacking direction of the stacked body, and the stacked body can be divided into an active portion that is expanded and contracted by applying an internal voltage and an inactive portion that is not expanded and contracted at both ends. it can. The covering layer includes the end face of the internal electrode layer exposed on the side surface of the laminate and the surface of the external electrode layer, and is formed to have a uniform thickness from the active part to the inactive part.

  In such a conventional multilayer piezoelectric element, first, a conductive paste serving as an internal electrode layer is printed in a predetermined pattern on a ceramic green sheet containing a raw material for the piezoelectric layer. Next, a plurality of ceramic green sheets on which a conductive paste is printed are laminated to produce a laminated molded body, which is fired to obtain a laminated body. Thereafter, a pair of external electrodes is formed by applying and baking a conductive paste to be an external electrode on a pair of opposing side surfaces of the laminate, and then forming a coating layer by electrodeposition coating or dipping. Can do. (For example, see Patent Document 2).

Japanese Patent Laid-Open No. 2003-347621 Japanese Unexamined Patent Publication No. 7-7193

  Here, unlike an electronic component such as a capacitor, the multilayer piezoelectric element is self-heated to a high temperature because the piezoelectric layer constituting the active portion continuously undergoes a dimensional change during driving. On the other hand, the piezoelectric layer constituting the inactive portion does not change in size, and thus does not generate heat. Therefore, although there is a temperature increase due to heat transfer from the active part in the inactive part, a temperature difference occurs between the active part and the inactive part, and a thermal stress is generated due to this temperature difference. When the coating layer is not formed on the side surface of the laminate, heat is dissipated from the side surface of the laminate, so the thermal stress caused by the temperature difference between the active part and the inactive part is small, When the coating layer is formed with a uniform thickness, heat is not sufficiently dissipated, and thermal stress caused by a temperature difference between the active portion and the inactive portion increases. Therefore, there is a possibility that a crack may occur at the boundary between the inactive part and the active part in the laminate.

  The present invention has been devised in view of the above-described conventional problems, and suppresses thermal stress due to the temperature difference between the boundary between the inactive portion and the active portion to be small, and prevents cracks due to thermal stress from occurring for a long time. It is an object of the present invention to provide a laminated piezoelectric element having excellent reliability, an injection device including the same, and a fuel injection system.

  The multilayer piezoelectric element of the present invention is an active portion in which a plurality of piezoelectric layers and internal electrode layers are alternately stacked, and a plurality of piezoelectric layers disposed at both ends in the stacking direction of the active portion. A columnar stacked body having an active portion, a pair of external electrode layers that are respectively attached to a pair of side surfaces of the stacked body in the stacking direction, and the internal electrode layers are electrically connected alternately every other layer; A laminated piezoelectric element including a covering layer that covers a side surface of the multilayer body from the active portion to the inactive portion together with the external electrode layer, wherein the covering layer has a thickness greater than a thickness at a side surface of the inactive portion. It is characterized in that the thickness on the side surface of the active part is thin.

  The multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the coating layer is formed of a resin.

  Moreover, the multilayer piezoelectric element of the present invention is characterized in that, in the above-described configuration, the thickness of the active portion is smaller than the thickness of the inactive portion on all surfaces of the coating layer.

  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, since the coating layer is thinner on the side surface of the active part than on the side surface of the inactive part, the heat generated by the active part easily escapes and the temperature of the active part The rise can be suppressed. In addition, since the coating layer of the inactive part is thick, the heat transmitted from the active part to the inactive part is trapped and the temperature of the inactive part is likely to rise, so the temperature difference between the active part and the inactive part is small. Become. Therefore, the thermal stress at the boundary between the active part and the inactive part is reduced, and the generation of cracks can be suppressed.

  Further, since the coating layer in the active part is thin, the elastic modulus is lowered and the coating layer is easily stretched.

  Further, when the coating layer is formed of a resin, the resin is easily stretched, so that when the heated active part is stretched, the resin is thinned, heat is effectively dissipated, and the temperature rise of the active part can be suppressed. . On the other hand, the coating layer of the inactive part that does not stretch can maintain the thickness, and furthermore, since the thermal conductivity of the resin itself is low, heat is hardly dissipated, and the temperature difference between the active part and the inactive part becomes small, and the active part and The thermal stress at the boundary with the inactive part becomes smaller.

  The injection device of the present invention comprises a container having an injection hole and the multilayer piezoelectric element of the present invention, and the fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. Since the multilayer piezoelectric element having high reliability and durability is used, the injection device has high reliability and 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, since the highly reliable and durable injection device is used, the fuel injection system is highly reliable and durable.

1 is a partially transparent perspective view showing an example of an embodiment of a multilayer piezoelectric element of the present invention. FIG. 2 is an enlarged vertical cross-sectional view of a main part in which a vertical cross section of a portion where an external electrode layer and a coating layer of the multilayer piezoelectric element shown in FIG. 1 are formed is enlarged. (A)-(c) is a partially expanded longitudinal cross-sectional view which shows the other example about the coating layer in the multilayer piezoelectric element of this invention, respectively. It is sectional drawing which shows an example of embodiment about the injection apparatus of this invention. It is a block diagram which shows an example of embodiment about the fuel-injection system of this invention.

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

  FIG. 1 is a partially transparent perspective view showing an example of an embodiment of a multilayer piezoelectric element according to the present invention. FIG. 2 is a diagram in which an external electrode layer and a coating layer of the multilayer piezoelectric element shown in FIG. 1 are formed. It is the principal part expansion longitudinal cross-sectional view which expanded the longitudinal cross-section of the site | part.

  As shown in FIGS. 1 and 2, the multilayer piezoelectric element 1 of this example includes an active portion 6 in which a plurality of piezoelectric layers 3 and internal electrode layers 2 are alternately stacked, and both ends of the active portion in the stacking direction. A columnar laminated body 8 having an inactive portion 7 in which a plurality of arranged piezoelectric layers are laminated, and a pair of side surfaces of the laminated body 8 are respectively attached in a laminating direction, and the internal electrode layers 2 are formed every other layer. It includes a pair of external electrode layers 4 that are alternately electrically connected and a coating layer 5 that covers the side surface of the laminate 8 from the active portion 6 to the inactive portion 7 together with the external electrode layer 4. The thickness on the side surface of the active part 6 is smaller than the thickness on the side surface of the active part 7.

A laminated body 8 constituting the laminated piezoelectric element 1 is formed by alternately laminating piezoelectric layers 3 and internal electrode layers 2, and the internal electrode layer 2 is formed by alternately forming positive and negative electrodes every other layer. It is. The laminated body 8 is formed in a rectangular parallelepiped shape having a length of 0.5 to 10 mm, a width of 0.5 to 10 mm, and a height of 1 to 100 mm, for example. 1 is formed in a quadrangular prism shape, but is not limited to this shape, and may be, for example, a hexagonal prism shape or an octagonal prism shape. Furthermore, the diameter 0.5-10
A cylindrical shape with a height of about 1 to 100 mm may be used.

The piezoelectric layer 3 constituting the multilayer body 8 is a piezoelectric material mainly composed of, for example, lead zirconate titanate (Pb (Zr, Ti) O ₃ ) (hereinafter also referred to as PZT), barium titanate (BaTiO ₃ ), or the like. It is made of a ceramic material having properties. The piezoelectric layer 3 may be made of a ceramic having piezoelectricity, and has a high piezoelectric strain constant d33 (about 200 to 1000) so that the laminate 8 can be extended and contracted by a small input voltage. Is good. The thickness of the piezoelectric layer 3, that is, the interval between the internal electrode layers 2 is preferably about 3 μm to 0.25 mm. By setting it within this range, the stacked body 8 can be downsized, a high voltage can be applied, and a larger amount of displacement can be obtained in the stacked body 8.

The internal electrode layer 2 is made of, for example, silver having a low electrical resistance and easy handling, or a metal containing a silver-based alloy such as a silver-palladium alloy, a silver-platinum alloy, or a silver-gold alloy, or a ceramic. It is made of such an inorganic material (a sintered body of silver and barium titanate). In addition, having silver as a main component means that the silver content is maximum. The internal electrode layer 2 is not formed on the entire main surface of the piezoelectric layer 3 and has a so-called partial electrode structure having a non-formed portion on the side opposite to the side connected to the external electrode layer 4. Yes. The plurality of internal electrode layers 2 of the partial electrode structure are arranged so as to be exposed at opposite side surfaces of the laminated body 8 every other layer, and are alternately electrically connected to the pair of external electrode layers 4 every other layer. . In FIG. 1, the internal electrode layer 2 serving as a positive electrode is exposed on one of a pair of side surfaces facing each other, and the internal electrode layer 2 serving as a negative electrode is exposed on the other side. Both electrodes of the negative electrode are exposed.

  A pair of external electrode layers 4 in which the internal electrode layers 2 are alternately electrically connected every other layer are respectively deposited in a stacking direction on a pair of opposite side surfaces of the stacked body 8 (in FIGS. 1 and 2). One external electrode layer is not shown). Similar to the internal electrode layer 2, the external electrode layer 4 is made of silver or a metal containing a silver-based alloy such as a silver-palladium alloy, a silver-platinum alloy, or a silver-gold alloy, or silver and glass. It is made of a material (a sintered body of silver and glass). Each external electrode layer 4 (the external electrode layer 4 electrically connected to the internal electrode layer 2 serving as the positive electrode and the external electrode layer 4 electrically connected to the internal electrode layer 2 serving as the negative electrode) is externally connected. A lead member (not shown) is attached by solder or the like. Then, by applying a predetermined voltage between the upper and lower internal electrode layers 2 through the pair of external electrode layers 4, each piezoelectric layer 3 constituting the active portion 6 is displaced by the inverse piezoelectric effect. ing. The pair of external electrode layers 4 is not limited to the pair of side surfaces facing each other, and may be formed on two adjacent side surfaces of the stacked body 8. In this case, the side surfaces on which the external electrode layer 4 is formed The internal electrode layer 2 may be formed so that one of the positive electrode and the negative electrode of the internal electrode layer 2 is exposed.

  Here, the laminated body 8 includes an active portion 6 that is extended and driven in which a plurality of piezoelectric layers 3 and internal electrode layers 2 are alternately stacked, and the piezoelectric layer 3 that is disposed at both ends of the active portion 6 in the stacking direction. And an inactive portion 7 that is not stretched and driven. Since the internal electrode layer 2 is not disposed in the inactive portion 7, no displacement (stretching) occurs in the inactive portion 7 even when a voltage is applied to the stacked body 8.

  On the side surface of the laminate 8, a coating layer 5 that covers the active portion 6 and the inactive portion 7 together with the external electrode layer 4 is formed.

  Specifically, the coating layer 5 is formed on the active portion 6 and is formed from the boundary between the active portion 6 and the inactive portion 7 to a region that enters the inactive portion 7. The formation from the boundary between the active portion 6 and the inactive portion 7 to the region entering the inactive portion 7 means that at least the thickness of the piezoelectric layer 3 in the active portion 6 (the interval between the internal electrode layers 2). ) As long as it is formed up to the above distance, which means that it does not necessarily have to be formed in the entire area of the inactive portion 7. For example, the distance may be 3 μm or more, preferably 0.1 mm or more, and more preferably 0.2 mm or more. If the distance is formed up to the region, the thermal stress at the boundary between the active portion 6 and the inactive portion 7 is sufficient. Can be reduced.

  Further, since the external electrode layer 4 is formed from the active portion 6 to the inactive portion 7, the coating layer 5 is also formed on the surface of the external electrode layer 4. Here, since an external lead member (not shown) is electrically connected to the external electrode layer 4 as described later, a part for electrically connecting the external lead member (not shown). Thus, the coating layer 5 is formed on the surface of the external electrode layer 4.

And it is important that the coating layer 5 has a smaller thickness on the side surface of the active portion 6 than on the side surface of the inactive portion 7. With this configuration, the self-generated heat can easily escape and the temperature rise of the active portion 6 can be suppressed. Further, since the coating layer 5 of the inactive part 7 is thick, the heat transmitted from the active part 6 to the inactive part 7 is trapped, and the temperature of the inactive part 7 is likely to rise. The temperature difference from 7 is reduced. Therefore, the thermal stress at the boundary between the active part 6 and the inactive part 7 is reduced, and cracks can be suppressed.

  Furthermore, since the coating layer 5 in the active part 6 is thin, the elastic modulus is low and the restraint of the active part becomes small, so that it becomes easy to stretch.

  Examples of the formation of the coating layer 5 include screen printing, dipping, aerosol deposition, chemical vapor deposition, and physical vapor deposition (sputtering).

  Specifically, in order to form the thickness on the side surface of the inactive portion 7 thicker than the side surface of the active portion 6, in the case of the screen printing method or dipping method, the coating layer is once applied from the active portion 6 to the inactive portion 7. After forming the coating layer 5, only the inactive portion 7 is selectively formed on the coating layer 5 to further form the coating layer 5. Further, in this case, since a paste in which the component constituting the coating layer is diluted with a solvent or the like is used, the paste having a higher content of the component constituting the coating layer is applied to the inactive portion 7 to be inactive. The thickness of the coating layer 5 in the part 7 can also be increased.

  In the case of an aerosol deposition method, a chemical vapor deposition method or a physical vapor deposition method (sputtering method), a method of forming the coating layer 5 of the inactive portion 7 in two stages may be used. The formation time may be lengthened.

Here, the coating thickness of the active part 6 is preferably 1 μm to 1 mm. If the thickness is less than 1 μm, the insulating function tends to be reduced, and if the thickness exceeds 1 mm, the heat dissipation of the active part 6 tends to be insufficient, and the temperature of the active part 6 becomes high and the inactive part is increased. This is because the thermal stress due to the temperature difference from 7 may increase. Preferably, 3 μm to 0.5 mm,
More preferably, it is 10 μm to 0.1 mm.

On the other hand, the coating thickness of the inactive portion 7 is preferably 3 μm to 1.5 mm on the premise that the coating thickness of the active portion 6 is thicker. If the thickness is less than 3 μm, the heat of the inactive part 7 is dissipated, the temperature of the inactive part 7 does not increase, and the thermal stress due to the temperature difference from the active part 6 tends to increase. If the thickness exceeds 1.5 mm, heat is not easily dissipated, so there is no effect on thermal stress, but its formation becomes difficult. Preferably, 5 μm to 1.0 mm, more preferably 15
It is μm to 0.15 mm.

  The coating thickness of the coating layer 5 is obtained by subtracting the thickness before forming the coating layer 5 from the thickness of the coating layer 5 formed directly on the side surface of the laminate 8 or on the surface of the external electrode layer 4 at the time of manufacture. It is possible to measure, and in a manufactured product, a cut section can be measured with a tool microscope or a scanning electron microscope (SEM). Here, for example, when the coating thickness of the region directly formed on the side surface of the laminate 8 in the coating layer 5 and the region on the surface of the external electrode layer 4 are the same, a step is formed by the thickness of the external electrode layer 4. .

  Here, if the coating layer 5 is formed on at least one of the side surfaces of the laminate 8, the thermal stress at the boundary between the active portion 6 and the inactive portion 7 is reduced, and the generation of cracks is suppressed. However, it is preferable that the thickness of the active portion 6 is thinner than the thickness of the inactive portion 7 on all the side surfaces of the stacked body 8. Therefore, the thermal stress at the boundary between the active part and the inactive part can be further reduced.

The material of the covering layer 5 is preferably an insulator such as an inorganic material (ceramics or glass) or an organic material (resin), and is particularly preferably a resin. Since the resin easily expands and contracts, the coating layer 5 is formed of a resin, so that when the heated active part 6 is stretched, the resin becomes thin and heat can be effectively dissipated, and the temperature of the active part 6 increases. Can be suppressed. On the other hand, the coating layer 5 of the inactive part 7 that does not stretch can maintain its thickness, and since the heat conduction of the resin itself is low and the heat is not easily dissipated, the temperature difference between the active part 6 and the inactive part 7 is reduced. The thermal stress at the boundary between the active portion 6 and the inactive portion 7 is reduced, and cracks are less likely to occur.

  Examples of the resin include those having low Young's modulus and low thermal conductivity such as silicone resin, epoxy resin, acrylic resin, urethane resin, and fluororesin.

  Moreover, the shape of the coating layer 5 is not limited to the configuration in which the thickness changes abruptly in the vicinity of the boundary between the active portion 6 and the inactive portion 7 as shown in FIG. Various configurations can be adopted.

  FIG. 3A shows that the thickness of the coating layer 5 gradually increases from the active portion 6 to the inactive portion 7 in the stacking direction of the columnar laminate 8, in other words, from a region where heat is generated to a region where heat is not generated. In this configuration, heat dissipation can be gradually improved toward the center of the active portion 6, and the thermal stress at the boundary between the active portion 6 and the inactive portion 7 can be reduced. can do.

  The covering layer 5 shown in FIG. 3A is formed so that the thickness gradually increases starting from the center of the laminated body 8 (active part 6). For example, most of the active portion 6 is formed to have a thickness of 1 μm to 1 mm, and the thickness of the piezoelectric layer 3 (between the internal electrode layers 2) from the boundary between the active portion 6 and the inactive portion 7. Starting from a point having a distance greater than or equal to the distance, for example, 3 μm to 1 mm in the region of the active portion 6, the thickness may gradually increase from this point, preferably 0.01 to 0.5 mm, more preferably May start from a point of 0.05 to 0.2 mm.

  FIG. 3B shows that the thickness of the coating layer 5 increases stepwise from the active portion 6 to the inactive portion 7 in the stacking direction of the stacked body 8, and according to this configuration, the active portion 6 The heat dissipating property can be improved stepwise toward the center of the substrate, and the thermal stress at the boundary between the active portion 6 and the inactive portion 7 can be reduced.

In FIG. 3B, a thickness step is first formed at the boundary between the active portion 6 and the inactive portion 7 and further enters the region of the active portion 6 from the boundary between the active portion 6 and the inactive portion 7. A step is formed at this point, but the point that enters the region of the active portion 6 from the boundary between the active portion 6 and the inactive portion 7 is that the piezoelectric body from the boundary between the active portion 6 and the inactive portion 7. The point of the distance more than the thickness of the layer 3 (space | interval between the internal electrode layers 2), for example, the point which entered 3 micrometers-1 mm, for example, Preferably it is 0.01-0.5 m
m, more preferably a point of 0.05 to 0.2 mm. At this time, the thickness of the step (height of the step) may be 3 μm or more, preferably 0.01 mm, more preferably 0.05 mm or more. The number of steps (the number of steps) is preferably about 2 to 5 steps including the step at the boundary between the active portion 6 and the inactive portion 7.

  Further, FIG. 3C shows that the thickness of the coating layer 5 formed on the inactive portion 7 is larger than the average value of the thickness of the coating layer 5 formed on the active portion 6 when the thickness of the coating layer 5 varies. The average value of thickness is larger. Here, the difference between the average value of the thickness of the coating layer 5 in the inactive part 7 and the average value of the thickness of the coating layer 5 in the active part 6 is 2 μm or more, preferably 5 μm or more.

Here, the average value of the thickness of the coating layer 5 formed on the active portion 6 was measured at intervals of 0.1 mm using a surface roughness meter in the region from the boundary between the active portion 6 and the inactive portion 7 to 1 mm. The average value of the thickness of the coating layer 5 formed on the inactive portion 7 is the active portion 6 and the inactive portion 7.
From the boundary between the active part 6 and the inactive part 7 when the coating layer 5 is not formed up to 1 mm from the boundary between the active part 6 and the inactive part 7 It is the average value of the values measured at intervals of 0.1 mm using a surface roughness meter for all regions up to the end).
In the area to be measured, 5 points with high peaks and 5 points with low valleys are selected within the standard length according to the ten-point average roughness Rzjis (Rz in the old standard) in Japanese Industrial Standard JIS B 0601. An average value may be selected.

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

First, a ceramic green sheet to be the piezoelectric layer 3 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. The piezoelectric ceramic is not particularly limited as long as it has piezoelectric characteristics. For example, a perovskite oxide made of PbZrO ₃ —PbTiO ₃ or the like can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, using this ceramic slurry, a ceramic green sheet is produced by a tape molding method such as a doctor blade method or a calender roll method.

  Next, a conductive paste to be the internal electrode layer 2 is produced. For example, a conductive paste is prepared by adding and mixing a binder, a plasticizer, and the like to a metal powder made of silver-palladium alloy or the like. This conductive paste is printed on the ceramic green sheet in a predetermined pattern by a screen printing method. Further, a plurality of ceramic green sheets screen-printed with this conductive paste are laminated to produce a laminated molded body. And the laminated body 8 by which the piezoelectric body layer 3 and the internal electrode layer 2 were laminated | stacked alternately is produced by baking this laminated molded object.

  Thereafter, the external electrode layer 4 is formed so as to obtain electrical continuity with the internal electrode layer 2 whose end is exposed on the outer surface of the multilayer body 8 of the multilayer piezoelectric element 1. This external electrode layer 4 is prepared by adding a binder to silver powder and glass powder to produce a silver glass-containing conductive paste, printing this on the side surface of the laminate 8 by a screen printing method, etc., and then drying and adhering. Alternatively, it can be formed by baking.

  Next, the coating layer 5 is formed on the side surface of the laminate 8. The formation method of the covering layer 5 may be changed depending on the shape of the columnar laminate 8. For example, a prismatic shape can be easily formed by printing on the side surface of the laminate 8 by a screen printing method and then bonding or baking after drying. The cylindrical shape is easy to form by dipping.

  For example, screen printing is performed with a coating material whose viscosity is adjusted by adding an organic solvent to the resin. In particular, in the inactive portion, screen printing is repeated to form a multilayer so that the thickness is thicker than that of the active portion. The forming method is not limited to screen printing, and the laminate 8 on which the external electrode layer 4 is formed may be immersed in a covering material. Further, by masking the active portion to be thinly formed, a coating layer in which the thickness of the inactive portion is larger than the thickness of the active portion can be formed. Alternatively, film formation by sputtering, electrodeposition formation, chemical vapor deposition, or physical vapor deposition may be used.

Specifically, the coating material is obtained by adjusting the viscosity by adding an organic solvent to a resin such as a silicone resin, an epoxy resin, an acrylic resin, a urethane resin, or a fluororesin. For example, it is prepared by adding a predetermined amount of several% to several tens% of an organic solvent to an epoxy resin containing a bisphenol A type component and mixing the mixture uniformly to adjust the viscosity. Examples of the organic solvent include alcohol, benzene, ether compounds, and petroleum naphtha. In addition, you may mix the filler component of inorganic materials, such as glass and ceramics.

  When an external lead member (not shown) for electrically connecting the external electrode layer 4 to an external circuit is joined to the external electrode layer 4 after the formation of the coating layer, the location where the external lead member is attached is masked. Then, after the coating layer 5 is formed, it is joined to the masked place by soldering or welding. In this case, the coating layer 5 is preferably formed by screen printing or dipping. When the coating layer 5 is formed after the external lead member is bonded to the external electrode layer 4, the coating layer is formed by a dipping method, a sputtering method, an electrodeposition formation method, a chemical vapor phase method, or a physical method. Film formation by a vapor phase method is preferred.

Thereafter, a direct current electric field of 0.1 to 3 kV / mm is applied from the pair of external electrode layers 4 to the piezoelectric layer 3 between the internal electrode layers 2 through an external lead member electrically connected to the external electrode layer 4. By laminating the piezoelectric layer 3 of the laminated body 8, the laminated piezoelectric element 1 is completed.

  Then, by electrically connecting a power source for supplying external driving power to the external lead member and applying a voltage to the piezoelectric layer 3 between the internal electrode layers 2 via the external electrode layer 4, each piezoelectric body The layer 3 can be greatly displaced by the inverse piezoelectric effect. This makes it possible to function as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  Next, an example of an embodiment of a fluid ejection device as the ejection device of the present invention will be described. FIG. 4 is a schematic cross-sectional view showing an example of an embodiment of the injection device of the present invention.

  As shown in FIG. 4, the injection device 19 of the present embodiment includes a container 23 having an injection hole 21 and the laminated piezoelectric element 1 of the present embodiment, and the fluid stored in the container 23 is stored in the container 23. In this configuration, the multilayer piezoelectric element 1 is ejected from the injection hole 21 by driving.

  With this configuration, since the multilayer piezoelectric element 1 with high reliability and durability is used, the injection device 19 with high reliability and durability is obtained.

  In the injection device 19 of the present embodiment, the multilayer piezoelectric element 1 of the present invention represented by the example of the above embodiment is housed in a container 23 having an injection hole 21 at one end. A needle valve 25 that can open and close the injection hole 21 is disposed in the container 23. A fluid passage 27 is disposed in the injection hole 21 so that it can communicate with the movement of the needle valve 25. The fluid passage 27 is connected to an external fluid supply source, and the fluid passage 27 is always supplied with a high-pressure fluid such as a liquid. Therefore, when the needle valve 25 opens the injection hole 21 by driving the multilayer piezoelectric element 1, the fluid supplied to the fluid passage 27 is transferred to the outside of the injection hole 21 or a container adjacent to the injection hole 21, such as an internal combustion engine. A fuel chamber (not shown) is discharged from the injection hole 21 and injected.

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

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

  The fluid ejection operation is performed by applying a voltage to the multilayer piezoelectric element 1 to open the fluid flow path 27 to discharge the fluid from the ejection holes 21 and stopping the application of the voltage. May be closed to stop the discharge of fluid.

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

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

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

  Next, the example of embodiment of the fuel-injection system of this invention is demonstrated. FIG. 5 is a schematic block diagram showing an example of an embodiment of the fuel injection system of the present invention.

  As shown in FIG. 5, the fuel injection system 35 of the present embodiment includes a common rail 37 that stores high-pressure fuel, and a plurality of injection devices 19 of the present embodiment that inject high-pressure fuel stored in the common rail 37. A pressure pump 39 that supplies high-pressure fuel to the common rail 37 and an injection control unit 41 that supplies a drive signal to the injection device 19 are provided.

  The injection control unit 41 controls the amount and timing of high-pressure fuel injection based on external information or an external signal. For example, in the case of the injection control unit 41 used for fuel injection of the engine, the amount and timing of fuel injection can be controlled while sensing the condition in the combustion chamber of the engine with a sensor or the like.

The pressure pump 39 serves to supply fluid fuel from the fuel tank 43 to the common rail 37 at a high pressure. For example, in the case of the engine fuel injection system 35, 1000 to 2000 atmospheres (about 101M)
Pa to about 203 MPa), preferably 1500 to 1700 atmospheres (about 152 MPa to about 172 MPa)
The fluid fuel is fed into the common rail 37 at a high pressure.

  The common rail 37 stores the high-pressure fuel sent from the pressure pump 39 and appropriately sends it to the injection device 19 in accordance with the driving of the multilayer piezoelectric element 1. As described above, the injection device 19 discharges and injects high-pressure fuel, which is a predetermined amount of fluid, from the injection hole 21 to the outside or a container adjacent to the injection hole 21 from the injection hole 21 of the injection device 19 at high pressure. For example, when the target for injecting and supplying high-pressure fuel is an engine, high-pressure fuel that is a fluid is injected into the combustion chamber of the engine in a mist form from the injection hole 21.

Note that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention. For example, the present invention relates to a multilayer piezoelectric element, an injection device, and a fuel injection system, but is not limited to the above-described embodiment, and for example, the multilayer piezoelectric element of the present invention is used. It may be a printing device of an ink jet printer, a pressure sensor, or the like, and can be applied to various products with the same configuration as long as it uses a laminated piezoelectric element utilizing piezoelectric characteristics.

  The laminated piezoelectric element according to the present invention includes a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precision positioning device such as an optical device, a drive element (piezoelectric actuator) mounted on a vibration prevention device, a combustion pressure, etc. Sensor elements mounted on 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. Can be used.

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

A piezoelectric actuator comprising the multilayer piezoelectric element of the present invention was produced as follows. First, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) having an average particle size of 0.4 μm, a binder, and a plasticizer. A ceramic green sheet having a piezoelectric layer having a thickness of 140 μm was prepared by the method.

  Next, 300 ceramic green sheets formed by screen printing are laminated on one side of this ceramic green sheet with a conductive paste in which a binder is added to a silver-palladium alloy (silver 70% by mass—palladium 30% by weight). Baked. In the firing, the temperature was once maintained at 800 ° C. in a firing furnace, and then the temperature was raised to 1000 ° C. to perform firing. And it grind | polished in the rectangular parallelepiped shape whose length of planar view is a square of 8 mm x 8 mm and length is 100 mm.

Next, a binder is added to a mixture of 80% by mass of flaky silver powder having an average particle diameter of 2 μm and an amorphous glass powder having a balance of silicon having an average particle diameter of 2 μm as a main component and a softening point of 640 ° C. A mixed silver glass-containing conductive paste was prepared. This silver glass-containing conductive paste was screen-printed on a pair of side surfaces of the laminate, and then baked to form an external electrode layer having a width of 2 mm and a thickness of 30 μm. An external lead member is joined to one end side of the external electrode layer later, and this one end side is formed with a length of 3 mm longer at the inactive portion than the other end side.

  Next, a coating layer was formed.

  In Sample No. 1, the coating thickness of the coating layer was set to be thicker in the active part than in the inactive part. Specifically, a coating material containing an epoxy resin was prepared, screen-printed from the active part to the inactive part, and dried and cured to form a coating layer having a thickness of 0.1 mm.

The covering material was 25% by weight of alcohol, 3% by weight of benzene with respect to 10% by weight of inorganic oxide containing titania and 90% by weight of bisphenol A type epoxy resin (total 100 parts by weight).
An organic solvent consisting of 25% by mass of an ether compound and the balance of petroleum naphtha is added as an external additive and mixed uniformly, and the viscosity is adjusted to 20 Pa · s.

  Here, the inactive portion has a length of 6 mm, and the formation region in the inactive portion of the coating layer was a region from the boundary between the active portion and the inactive portion to 2 mm. At this time, the connection end side of the external electrode layer with the external lead member was exposed 3 mm to form a coating layer.

Further, the paste was screen-printed again only on the active part, and then dried and cured, so that the thickness of the coating layer of the active part was 0.2 mm. The thickness of the coating layer is measured in advance with a surface roughness meter when the side surface of the laminate is formed and when the external electrode layer is formed, and the thickness measured in advance from the thickness after the coating layer is formed. It is the deduction.

  In Sample No. 2, the coating thickness of the coating layer was matched between the active part and the inactive part. Specifically, a coating material containing the same epoxy resin as Sample No. 1 was prepared, screen-printed from the active part to the inactive part, dried and cured to form a coating layer having a thickness of 0.1 mm.

  As in the case of sample number 1, the formation region in the inactive portion of the coating layer is a region from the boundary between the active portion and the inactive portion to 2 mm, and the connection end side of the external electrode layer to the external lead member is 3 mm. A coating layer was formed by exposure.

  Moreover, the coating thickness of sample numbers 3 to 5 was such that the inactive part was thicker than the active part.

Sample No. 3 produced a coating material containing the same epoxy resin as Sample No. 1, screen printed from the active part to the inactive part, dried and cured to form a coating layer having a thickness of 0.1 mm. Further, the paste was screen-printed again only on the inactive part, and then dried and cured, so that the thickness of the coating layer on the inactive part was 0.2 mm.

  As in the case of sample number 1, the formation region in the inactive portion of the coating layer is a region from the boundary between the active portion and the inactive portion to 2 mm, and the connection end side of the external electrode layer to the external lead member is 3 mm. A coating layer was formed by exposure.

  Sample No. 4 produced a coating material containing the same epoxy resin as Sample No. 1, screen printed from the active part to the inactive part, dried and cured to form a 0.05 mm thick coating layer . Further, the paste was screen-printed again only on the inactive portion, and then dried and cured, so that the thickness of the coating layer on the inactive portion was 0.1 mm.

  As in the case of sample number 1, the formation region in the inactive portion of the coating layer is a region from the boundary between the active portion and the inactive portion to 2 mm, and the connection end side of the external electrode layer to the external lead member is 3 mm. A coating layer was formed by exposure.

Sample No. 5 is 10% by mass of inorganic oxide containing titania and 90% by mass of bisphenol A type epoxy resin (100 parts by mass in total), 25% by mass of alcohol, 3% by mass of benzene, 25% by mass of ether compound, and the balance 1% by weight of an organic solvent consisting of petroleum naphtha was added externally and mixed uniformly to produce a coating material with a viscosity adjusted to 100 Pa · s, and the outer leads of the laminate and external leads of the external electrode layer Masking was performed to expose 3 mm of the connecting end side with the member, the entire laminate was impregnated and dipped, and then dried and cured to form a coating layer having a thickness of 0.5 mm. Further, masking is performed to expose the active portion and 3 mm of the external electrode layer connected to the external lead member, impregnation of the entire laminate, dipping, drying and curing, and 1 mm of the coating layer of the inactive portion. It was set as the thickness.

  Thereafter, an external lead member is solder welded to the exposed end portions of the external electrode layers of the positive electrode and the negative electrode, and a 3 kV / mm DC electric field is applied through the external lead member for 15 minutes to perform polarization treatment. A piezoelectric actuator using a laminated piezoelectric element having the structure shown in the drawing was produced.

When a DC voltage of 170 V was applied to the obtained multilayer piezoelectric element, a displacement amount was obtained in the lamination direction in all piezoelectric actuators.

Further, an AC voltage of 0V to + 200V to the piezoelectric actuator at room temperature was applied at a frequency of 60 Hz, 1 × 10 ⁸ times continuously driven by displacement of the rate of change after (reduction ratio), 1 × 10 ⁸ consecutive drive The number of fractures of the multilayer piezoelectric element and the number of cracks generated were measured for 100 multilayer piezoelectric elements after the above. The results are shown in Table 1.

  The change rate of the displacement amount of the laminated piezoelectric element was measured with a laser displacement device (product name “Laser Doppler Vibrometer LV-1710” manufactured by Ono Sokki Co., Ltd.). Further, the side surface of the multilayer piezoelectric element was polished, and the number of cracks was observed with a scanning electron microscope (SEM) to check whether there was any crack at the boundary between the inactive portion and the active portion.

From Table 1, the laminated piezoelectric element of Sample No. 1 (Comparative Example) in which the active part is thicker than the inactive part has a displacement change rate of 35% after 1 × 10 ⁸ continuous driving. The number of cracks generated in 100 multilayer piezoelectric elements was 90, and the average frequency of cracks per multilayer piezoelectric element was 0.9, which was very high.

In addition, the laminated piezoelectric element of sample number 2 (comparative example) in which the active layer and the inactive part have the same thickness is formed, and the displacement change rate after continuous driving 1 × 10 ⁸ times is as large as 20%. The number of cracks generated in 100 multilayer piezoelectric elements was 50, and the average frequency of cracks per multilayer piezoelectric element was 0.5, which was high.

On the other hand, in Sample Nos. 3 to 5 which are examples of the present invention, the change in displacement amount is as small as 8% or less even after continuous driving 1 × 10 ⁸ times. Cracks did not occur.

1: Laminated piezoelectric element 2: Internal electrode layer 3: Piezoelectric layer 4: External electrode layer 5: Cover layer 6: Active part 7: Inactive part 8: Laminated body 19: Injecting device 21: Injecting hole 23: Container 25 : Needle valve 27: Fluid passage 29: Cylinder 31: Piston 33: Belleville spring 35: Fuel injection system 37: Common rail 39: Pressure pump 41: Injection control unit 43: Fuel tank

Claims (5)

A columnar laminate having an active portion in which a plurality of piezoelectric layers and internal electrode layers are alternately laminated, and an inactive portion in which a plurality of piezoelectric layers are arranged at both ends of the active portion in the lamination direction; A pair of external electrode layers that are respectively deposited in a stacking direction on a pair of side surfaces of the multilayer body and in which the internal electrode layers are alternately electrically connected every other layer; and a side surface of the multilayer body from the active portion A laminated piezoelectric element including a coating layer covering the inactive portion together with the external electrode layer,
The multilayer piezoelectric element, wherein the covering layer has a thickness on a side surface of the active portion that is smaller than a thickness on a side surface of the inactive portion.   The multilayer piezoelectric element according to claim 1, wherein the coating layer is made of a resin.   3. The multilayer piezoelectric element according to claim 1, wherein the coating layer has a thickness of the active portion that is thinner than a thickness of the inactive portion on all surfaces. 4.   A container having an injection hole and the multilayer piezoelectric element according to claim 1, wherein fluid stored in the container is discharged from the injection hole by driving the multilayer piezoelectric element. Injection device.   5. A common rail for storing high-pressure fuel; an injection device according to claim 4 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.

Images