JP2006066878A - Laminated piezoelectric element and injector using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element with a high electric reliability which excels in an operating reliability and a durability. <P>SOLUTION: A laminated piezoelectric element 1 is formed by providing a first side surface electrode 31 and a second side surface electrode 32 at side faces 101, 102 of a ceramic layered product 10 which is formed by alternately laying a piezoelectric layer 11, a first inner electrode 21 and a second inner electrode 22 in layers. At the side face 101 there is provided a first concave groove 41 in which an edge of the second inner electrode 22 is exposed to a bottom 410. At the side face 102 there is provided a second concave groove 42 in which an edge of the first inner electrode 21 is exposed to a bottom 420. The first concave groove 41 and the second concave groove 42 are filled with an insulating packing material 5 so as to cover edges of the second inner electrode 22 and the first inner electrode 21, respectively. On an external surface of the insulating packing material 5 there is formed a concave surface portion 50 which becomes inwardly depressed from the side faces 101, 102 of the ceramic layered product 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multilayer piezoelectric element having high operational reliability and a fuel injection injector using the multilayer piezoelectric element.

  Conventionally, for example, as a laminated piezoelectric element, a layered internal electrode has a structure in which an entire surface of the piezoelectric layer covers the entire surface of the piezoelectric layer, and a partial electrode in which the internal electrode leaves a portion that does not cover the piezoelectric layer There is a thing of structure. In general, in a laminated piezoelectric element having a full-surface electrode structure, displacement is easier to obtain than in a partial electrode structure, and there is less risk of stress concentration at the end of the internal electrode. Therefore, when a full-surface electrode structure is employed, a multilayer piezoelectric element having high displacement characteristics and high reliability can be realized.

  On the other hand, in the case of the full-surface electrode structure, the outer peripheral end of the layered internal electrode is exposed on the entire side surface of the multilayer piezoelectric element. For this reason, in this multilayer piezoelectric element having a full-surface electrode structure, each internal electrode must have an electrical insulation structure with the other side electrode while ensuring electrical contact with one side electrode. . When piezoelectric displacement is repeated for such a laminated piezoelectric element, a large stress repeatedly acts on the insulating structure between the side electrode and the internal electrode. For this reason, in the above-described insulating structure, structural ingenuity is required to maintain the insulation between the internal electrode and the side electrode over a long period of use. Conventionally, for example, an insulating structure in which a groove is provided on a side surface of a multilayer piezoelectric element and an insulating resin is filled in the groove has been proposed (for example, Patent Documents 1 to 5).

JP 2001-69771 A JP 2001-102647 A Japanese Patent Laid-Open No. 2002-111088 JP 2001-244513 A JP 2001-77436 A

  However, the conventional insulation structure has the following problems. That is, if the multilayer piezoelectric element is used for a long period of time, the side electrode peels off from the side surface of the ceramic laminate, and electrical connection with the internal electrode becomes insufficient. There is a problem that may occur. Due to such electrical troubles, the operational reliability and durability of the multilayer piezoelectric element have been reduced, and the product life has been shortened.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a laminated piezoelectric element having high electrical reliability, excellent operation reliability, and durability.

The first invention has a ceramic laminate in which a plurality of piezoelectric layers made of a piezoelectric material and a plurality of layered internal electrodes having conductivity are alternately laminated, and the first side is provided on a side surface of the ceramic laminate. A side electrode and a second side electrode are provided, and as the internal electrode, a first internal electrode conducting to the first side electrode and a second internal electrode conducting to the second side electrode are alternately arranged. In the laminated piezoelectric element,
The side surface provided with the first side electrode in the ceramic laminate is provided with a first groove portion, which is a groove in which an end portion of the second internal electrode is exposed at the bottom, while the second side electrode is provided. The side surface provided with a second groove portion that is a groove in which the end portion of the first internal electrode is exposed at the bottom,
The first concave groove portion and the second concave groove portion are filled with an insulating filler having electrical insulation so as to cover the end portion of the second internal electrode and the end portion of the first internal electrode, respectively.
A laminated surface characterized in that a concave portion recessed inward from a side surface of the ceramic laminate is formed on an outer surface of the insulating filler filled in the first concave groove portion and the second concave groove portion. A piezoelectric element (Claim 1).

  The multilayer piezoelectric element according to the first aspect of the present invention is formed on at least a part of the outer surface of the insulating filler filled in the first concave groove portion and the second concave groove portion from the side surface of the ceramic multilayer body inward. It has a concave surface that is recessed. If the concave portion is provided on the outer surface of the insulating filler as described above, in particular, the first side electrode and the second side electrode (hereinafter referred to as “side electrode” as appropriate) from the side surface of the ceramic laminate. It is possible to effectively suppress the stress acting to peel off.

  For example, when the side electrode is formed in contact with the concave surface portion, the stress acting on the side electrode from the thermally expanded insulating filler is applied to the inner side of the cross-sectional shape of the concave surface portion, ie, the circular arc It can be made to act toward the center direction. In this case, the component acting along the stacking direction in the stress is absorbed inside the side electrode. On the other hand, of the stress, the component acting in the radial direction of the multilayer piezoelectric element is a joint surface between the side electrode and the side surface of the ceramic laminate, and in the direction of pulling in the normal direction of the joint surface. Works. Here, in general, the bonding strength of the side electrodes is strong against the tensile force in the normal direction of the bonding surface, but is weak against the shearing force acting in the direction along the bonding surface. Therefore, as described above, when the side surface electrode is formed in contact with the concave surface portion, the shearing direction force that may act on the side surface electrode along the joint surface is provided by the concave surface portion. It can be effectively suppressed. As a result, it is possible to suppress the possibility that the side electrode peels off.

  Furthermore, for example, a concave portion may be provided in the insulating filler, and a gap may be provided between the recessed portion of the concave portion and the side electrode. Also in this case, the stress acting on the side electrode from the thermally expanded insulating filler can be suppressed. And if the stress itself which acts on the said side electrode from the said insulating filler is suppressed, the possibility that this side electrode will peel can be suppressed with high certainty.

  As described above, in the multilayer piezoelectric element according to the first aspect of the present invention, by providing the concave surface portion, the possibility that the side surface electrode is peeled off from the side surface of the ceramic multilayer body is reduced. Therefore, in the multilayer piezoelectric element, the electrical connection between the first (2) internal electrode and the first (2) side electrode can be stably maintained, and the first (2) internal electrode and the first 2 (1) The electrical insulation with the side electrode can be maintained with high reliability over a long period of time.

  Therefore, in the multilayer piezoelectric element according to the first aspect of the present invention, the possibility that each side electrode peels from the side surface of the ceramic laminate is effectively suppressed, and the operational reliability and durability are remarkably improved.

A second invention is an injector configured to open and close a valve body using displacement of a piezoelectric actuator to perform fuel injection control.
The piezoelectric actuator is an injector comprising the multilayer piezoelectric element of the first invention (claim 10).

  The injector according to the second aspect of the present invention uses a piezoelectric actuator configured using the above-described excellent quality multilayer piezoelectric element. In this multilayer piezoelectric element, the side electrode is bonded to the side surface of the ceramic laminate with high durability. Therefore, even in an injector that is used in a harsh state under a high temperature atmosphere, it is possible to improve the durability by suppressing the occurrence of peeling of each side electrode during operation and improving the operation reliability of the entire injector. it can.

In the first aspect of the invention, it is preferable that the concave surface portion is formed so as to maintain a concave shape at a maximum temperature within a temperature range allowed for the multilayer piezoelectric element. ).
In this case, by maintaining the concave shape of the concave portion of the insulating filler over the entire allowable temperature range, there is a high degree of certainty that the side electrodes may peel off from the side surface of the ceramic laminate. Can be suppressed. Therefore, the operation reliability and durability of the multilayer piezoelectric element can be further improved.

The difference between the linear expansion coefficient of the piezoelectric layer and the linear expansion coefficient of the insulating filler is preferably 20 ppm / ° C. or more and 300 ppm / ° C. or less.
When the difference in linear expansion coefficient between the piezoelectric layer and the insulating filler is in the above range, the degree of deformation of the thermally expanded insulating filler is increased. Therefore, the stress acting on the side electrode from this insulating filler may be increased. Therefore, in this case, the function and effect of the first invention in which the possibility that the side electrode peels from the side surface of the ceramic laminate can be suppressed is particularly effective.

The insulating filler preferably contains at least one of silicon, polyimide, epoxy, or urethane.
In this case, the electrical insulation reliability of the multilayer piezoelectric element can be increased by using the insulating filler. Therefore, the electrical reliability of the entire multilayer piezoelectric element can be further improved.

The first side electrode and the second side electrode are preferably made of Sn-Ag paste.
The Sn—Ag paste has good electrical conductivity because it is metallicly bonded to the internal electrode, but has low adhesion to the multilayer piezoelectric element. Therefore, it may be weaker than other conductive materials against peeling due to thermal expansion of the insulating resin in the groove. Therefore, when the Sn-Ag paste is applied as each side electrode, the operational effect of the first invention is particularly effective. In addition, it replaces with Sn-Ag paste and the said side electrode can also be formed with the resin silver which made the resin material contain Ag, or solder.

Preferably, a gap is provided between the concave surface portion of the insulating filler and the first side electrode or the second side electrode.
In this case, stress acting on each side electrode from the thermally expanded insulating filler can be effectively suppressed by the gap provided between the concave surface portion and each side electrode. Therefore, in the multilayer piezoelectric element, it is possible to further suppress the possibility that each side electrode is peeled off from the side surface of the ceramic laminate.

Moreover, it is preferable that the width | variety of the said 1st groove part and the said 2nd groove part is 5 micrometers or more and 150 micrometers or less, and the hollow depth of the said concave surface part is 2 micrometers or more and 100 micrometers or less.
In this case, the concave shape of the concave portion can be maintained in a wide temperature range by setting the concave depth of the concave portion to the above range with respect to the width of each concave groove portion. Therefore, the multilayer piezoelectric element has a wide usable temperature range and is excellent in heat resistance, durability, and the like.

Moreover, it is preferable that the groove depth of the said 1st groove part and the said 2nd groove part is 10 micrometers or more and 400 micrometers or less (Claim 8).
In this case, the effective electrode area of the internal electrode that covers the piezoelectric layer is less decreased, and the good displacement characteristics of the multilayer piezoelectric element can be sufficiently maintained. If the groove depth exceeds 400 μm, the influence on the displacement characteristics may become obvious. On the other hand, if the groove depth is less than 10 μm, there is a risk that sufficient electrical insulation by the insulating filler cannot be secured.

Moreover, the non-concave surface part in which the said concave surface part is not formed exists in the outer surface of the said insulating filler with which the said 1st groove part and the said 2nd groove part were filled, Each said 1st groove part And, when the total length of each of the second concave grooves is A and the length of the non-concave portion is B, (AB) / A is preferably 0.3 or more. .
That is, the concave surface portion does not need to be formed in all parts of the outer surface of the insulating filler, and a portion in which the concave surface portion is not formed, that is, the non-concave surface portion is formed. May be.

When (A-B) / A is less than 0.3, there is a possibility that the effect of suppressing the possibility that the side electrodes are peeled off from the side surface of the ceramic laminate cannot be sufficiently obtained. Therefore, more preferably, the above (AB) / A is 0.6 or more.
In addition, said full length A is decided by each length of each said 1st ditch | groove part and each said 2nd ditch | groove part.

(Example 1)
This example is an example related to the multilayer piezoelectric element 1 that exhibits the piezoelectric effect. The contents will be described with reference to FIGS.
As shown in FIG. 1, the multilayer piezoelectric element 1 of this example is a ceramic in which a plurality of piezoelectric layers 11 made of a piezoelectric material and a plurality of layered internal electrodes 21 and 22 having conductivity are alternately stacked. The laminate 10 is provided, and the first side electrode 31 and the second side electrode 32 are provided on the side surfaces 101 and 102 of the ceramic laminate 10. As the internal electrodes 21 and 22, a first internal electrode conducting to the first side electrode 31 (hereinafter referred to as the first internal electrode 21 as appropriate) and a second internal electrode conducting to the second side electrode 32 (hereinafter referred to as “first internal electrode 21”). Are described as second internal electrodes 22 as appropriate).
The side surface 101 provided with the first side surface electrode 31 in the ceramic laminate 10 is provided with a first concave groove portion 41 that is a concave groove with the end portion of the second internal electrode 22 exposed at the bottom portion 410. The side surface 102 provided with the two side surface electrodes 32 is provided with a second groove portion 42 that is a groove in which the end portion of the first internal electrode 21 is exposed at the bottom portion 420.
As shown in FIG. 2, the first groove portion 41 and the second groove portion 42 are electrically insulating so as to cover the end portion of the second internal electrode 22 and the end portion of the first internal electrode 21, respectively. Filler 5 is filled. Here, on the outer surface of the insulating filler 5 filled in the first concave groove portion 41 and the second concave groove portion 42, a concave surface portion 50 that is recessed inward from the side surfaces 101 and 102 of the ceramic laminate 10 is formed. Yes.
This content will be described in detail below.

  As shown in FIG. 1, the multilayer piezoelectric element 1 of this example is an octagonal prism-shaped ceramic in which piezoelectric layers 11 that expand and contract in response to an applied voltage and internal electrodes 21 and 22 for supplying an applied voltage are alternately stacked. A laminate 10 is provided. The first side electrode 31 and the second side electrode 32 are provided on the pair of side surfaces 101 and 102, respectively, and a lead wire 7 for connecting an external electrode is connected to these. In this example, dummy layers 18 and 19 that do not produce a piezoelectric effect are provided on the upper and lower ends of the ceramic laminate 10 in the stacking direction. In addition to the above, the laminate shape may be a cylinder, a triangular prism, a quadrangular prism, or the like. Further, the side electrodes 31 and 32 need not face each other. Furthermore, the lead wire 7 may be not only the upper part of the laminate but also the lower part.

  As shown in FIGS. 1 and 2, the first internal electrode 21 has its end exposed on the side surface 101 and is in electrical contact with the first side electrode 31. On the other hand, on the side surface 102 facing the side surface 101, the first internal electrode 21 is exposed at the bottom 420 of the second concave groove portion 42 and is covered with the insulating filler 5 filled in the second concave groove portion 42. The second side electrode 32 is disposed outside the insulating filler 5.

  Similarly, the second internal electrode 22 has its end exposed on the side surface 102 and is in electrical contact with the second side electrode 32. On the other hand, on the side surface 101 facing the side surface 102, the second internal electrode 22 is exposed at the bottom 410 of the first concave groove portion 41 and is covered with the insulating filler 5 filled in the first concave groove portion 41. The first side electrode 31 is disposed outside the insulating filler 5.

  Further, as shown in FIGS. 2 and 9, each of the first and second groove portions 41 and 42 is provided such that the bottom surface formed by the bottom portions 410 and 420 is substantially parallel to the side surfaces 101 and 102. The depth D is about 100 μm. In addition, the groove width W of each of the first groove portions 41 and the second groove portions 42 is about 70 μm, and the thickness L is about 90% of the piezoelectric layer 11 having a thickness L = 80 μm. In addition, the 1st groove part 41 and the 2nd groove part 42 of this example are exhibiting cross-sectional substantially rectangular shape.

  Each first groove portion 41 and second groove portion 42 are filled with the insulating filler 5 as described above. In this example, the insulating filler 5 used was a resin material made of polyimide material dissolved in γ-butyllactone as a solvent. In this example, the content ratio of γ-butyl lactone as a solvent in 100% by weight of the insulating filler 5 was set to 50% by weight. In addition to the polyimide of this example, epoxy, silicon, urethane or the like can be used as the resin material constituting the insulating filler 5. Further, as the solvent constituting the insulating filler 5, N-methyl-2-pyrrolidone, butyl acetate, butyl cellosolve, etc. can be used in addition to γ-butyllactone of this example.

  Here, in this example, as shown in FIG. 2, the concave surface portion 50 is formed on the outer surface of the insulating filler 5 filled in the concave groove portions 41 and 42 (surface facing the outer peripheral side of the ceramic laminate 10). It is. In this example, the depth Dp of the concave surface portion 50 is set to 20 μm with respect to the groove width W = 70 μm in the stacking direction of the concave groove portions 41 and 42. The depth Dp = 20 μm of the concave surface portion 50 in this example is a depression of the concave surface portion 50 even if the insulating filler 5 is heated to 160 ° C. which is the maximum allowable temperature of the multilayer piezoelectric element 1 and thermally expands. The value is set so that the shape can be maintained to some extent (Dp> 0).

The first side electrode 31 and the second side electrode 32 were formed by heating the Sn—Ag paste applied to the side surfaces 101 and 102. The side electrodes 31 and 32 made of Sn—Ag paste have both bonding strength and flexibility, and can improve durability without deteriorating displacement characteristics. The side electrodes 31 and 32 may be formed of a conductive resin layer in which a conductive material is contained in a resin material having electrical insulation. For example, materials such as epoxy, silicon, polyimide, and urethane can be used as the resin material, and silver, Ni, copper, and the like can be contained as the conductive material. In addition, the side electrodes 31 and 32 can be formed of solder or the like.
The side electrodes 31 and 32 may be formed by laminating two materials. For example, as shown in FIG. 3, second side electrode layers 31 b and 32 b made of an epoxy resin added with a silver filler can be formed on the surfaces of the first side electrode layers 31 a and 32 a made of Sn—Ag paste. .

Next, a method for manufacturing the multilayer piezoelectric element 1 having the above configuration will be briefly described.
First, a piezoelectric layer firing step is performed in which a ceramic green sheet serving as a piezoelectric material is fired to obtain the piezoelectric layer 11.
In this example, a green sheet was produced as follows in order to employ PZT as the piezoelectric layer 11. First, powders such as lead oxide, zirconium oxide, titanium oxide, niobium oxide, and strontium carbonate, which are main raw materials of the piezoelectric material, are weighed so as to have a desired composition. In consideration of the evaporation of lead, the mixture is blended so as to be 1 to 2% richer than the stoichiometric ratio of the mixing ratio composition. This is dry-mixed in a mixer and then calcined at 800 to 950 ° C.

  Next, pure water and a dispersant are added to the calcined powder to form a slurry, which is wet pulverized by a pearl mill. After this pulverized product is dried and powdered and degreased, a solvent, a binder, a plasticizer, a dispersant and the like are added and mixed by a ball mill. Thereafter, this slurry is subjected to vacuum defoaming and viscosity adjustment while stirring with a stirrer in a vacuum apparatus.

  Next, the slurry is formed into a green sheet having a constant thickness by a doctor blade device. The collected green sheet was punched out with a press or cut with a cutting machine and formed into a 7 mm square. Of course, it is possible to form a rectangular, elliptical, barrel shape or the like according to the shape of the multilayer piezoelectric element 1 to be obtained.

Next, the green sheet is degreased and then fired to obtain the piezoelectric layer 11. The degreasing treatment was performed by holding the green sheet at a temperature of 400 to 700 ° C. for a predetermined time with an electric furnace. The firing process was performed by holding the green sheet at a temperature of 900 to 1200 ° C. for a predetermined time. Thus, in this example, the piezoelectric layer 11 having a thickness of 80 μm and mainly fired PZT, which is an oxide having a perovskite structure mainly of Pb (Zr, Ti) O ₃ , was formed separately for each layer. .

Next, as shown in FIG. 4, the laminated body production process which produces the laminated body formed by alternately laminating the obtained piezoelectric layer 11 and the electrode material 20 containing Cu was performed.
In this example, as the electrode material 20, a copper foil made of Cu having a purity of 99.9% and having a thickness of 5 μm was used. Further, as shown in FIG. 4, the shape of the copper foil was a 7 mm square and the same as that of the piezoelectric layer 11. And the piezoelectric layer 11 and the electrode material 20 were laminated | stacked alternately, and the laminated body was produced so that the lamination | stacking number of the piezoelectric layers 11 might be 250 layers. In addition, piezoelectric layers 11 serving as dummy layers were disposed on the upper and lower ends in the stacking direction of the stack.

Next, the laminate is placed in a furnace with a load of about 3 MPa applied from the lamination direction, and the atmosphere in the furnace is evacuated to a vacuum of 1 × 10 ⁻² Pa, and then the pressure in the furnace is set. N ₂ gas as an inert gas was introduced into the furnace so that was maintained at 10 Pa. And the heating joining process which joins the internal electrodes 21 and 22 which consist of the said electrode material 20, and the piezoelectric layer 11 was implemented by hold | maintaining for 10 minutes at the temperature of 960 degreeC.

As a result, as shown in FIG. 5, the substantially quadrangular prism-shaped ceramic laminate 10 having the four side surfaces 101 to 104 and having the internal electrodes 21 and 22 with the end portions exposed on the entire side surfaces is obtained.
Next, as shown in FIG. 6, the corner portion of the quadrangular prism shape is subjected to surface grinding, and four side surfaces 105 to 108 are newly provided to form the substantially octagonal prism-shaped ceramic laminate 10.

Next, as shown in FIG. 7, a groove was formed by irradiating a laser along the end portion of the second internal electrode 22 exposed on the side surface 101 of the ceramic laminate 10 to form the first concave groove portion 41. Similarly, a groove was formed by irradiating a laser along the end portion of the first internal electrode 21 exposed on the side surface 102 of the ceramic laminate 10 to form the second concave groove portion 42. In this example, a CO ₂ laser was used as the laser, and a method of irradiating while scanning using a galvano optical scanner was adopted. In addition, this groove processing can be performed using grinding with a grindstone, shot blasting, or the like instead of processing by laser irradiation. In addition, the cross-sectional shape of the 1st ditch | groove part 41 and the 2nd ditch | groove part 42 was taken as groove depth D = 100micrometer and groove | channel width W = 70micrometer (refer FIG. 2) as mentioned above.

  Next, as shown in FIG. 8, after the insulating filler 5 is supplied into the first concave groove portion 41 and the second concave groove portion 42 using a dispenser, the first concave groove portion 41 and the second concave portion 41 are drawn by vacuuming. The insulating filler 5 was filled in the concave groove portion 42 without any gap. Other filling methods such as screen printing and metal mask printing are also possible. Thereafter, the insulating filler 5 was heat-treated at a temperature of 200 ° C. for 60 minutes to thermally cure the insulating filler 5.

  In this example, the groove portions 41 and 42 are filled with the insulating filler 5 so that the concave portion 50 (FIG. 2) having a depth Dp = 20 μm is formed on the surface of the cured insulating filler 5. did. In this example, using the characteristics of the insulating filler 5 of this example that γ-butyl lactone as a solvent volatilizes during curing and causes about 20% cure shrinkage, the side surfaces 101 and 102 of the ceramic laminate 10, The insulating filler 5 before curing was filled so that the surfaces of the insulating filler 5 filled in the concave groove portions 41 and 42 were substantially flush with each other. Thereby, the concave surface portion 50 having a depth Dp = 20 μm was formed by curing shrinkage of the insulating filler 5 filled in the concave groove portions 41 and 42. In addition, as a method of adjusting Dp which is the amount of depressions from the side surfaces 101 and 102 of the ceramic laminate 10, a method of adjusting the filling amount when filling the insulating filler 5, or a predetermined filling amount There is a method of adjusting the content ratio of the solvent in the insulating filler 5.

  Next, Sn-Ag paste is printed on the side surfaces 101 and 102 of the ceramic laminate (in this example, printed by a metal mask method), and then held at a temperature of 260 ° C. and a pressure of 3 MPa for 120 minutes. And heat cured. As a result, as shown in FIGS. 1 and 9, electrical conduction is ensured between the first side electrode 31 and each first internal electrode 21 on the side surface 101, and each of the second side electrode 32 and each side on the side surface 102. Electrical continuity with the second internal electrode 22 was ensured. The side electrodes 31 and 32 can be formed of solder, an epoxy resin added with a silver filler, or the like in addition to the Sn—Ag paste of this example. The multilayer piezoelectric element of this example shown in FIG. 1 is obtained by joining the lead wire 7 to the first side surface electrode 31 and the second side surface electrode 32 using an epoxy resin added with a silver filler.

Next, the function and effect of the multilayer piezoelectric element 1 of this example will be described.
As described above, the multilayer piezoelectric element 1 of the present example has an inner surface from the side surfaces 101 and 102 of the ceramic laminate 10 on the outer surface of the insulating filler 5 filled in the first concave groove portion 41 and the second concave groove portion 42. A concave surface portion 50 that is recessed is formed. In particular, in this example, the concave surface portion 50 is configured to maintain its concave shape (a shape where Dp> 0) even at 160 ° C., which is the maximum allowable temperature of the multilayer piezoelectric element 1. .

  Here, when the insulating filler 5 is thermally expanded, stress acts on the first side electrode 31 or the second side electrode 32 from the insulating filler 5. In general, the bonding strength of the side electrodes 31 and 32 is strong against the tensile force in the normal direction of the side surfaces 101 and 102 that are the bonding surfaces, but the shearing force acting in the direction along the side surfaces 101 and 102. Weak against.

  In this example, by providing the concave surface portion 50 on the outer surface of the insulating filler 5, as shown in FIG. 10, the insulating filler 5 is thermally expanded from the initial state (state indicated by the solid line L1) (broken line L2). The stress acting on the side surface electrodes 31 and 32 when deformed to the inner side of the cross-sectional shape of the concave portion 50 as shown by the arrows in the figure, that is, toward the center of the arc. Act. Therefore, the shear direction component acting along the stacking direction among the stress is absorbed inside the side electrodes 31 and 32. On the other hand, the component that acts in the radial direction of the multilayer piezoelectric element 1 in the stress is the joint surface between the side electrodes 31 and 32 and the side surfaces 101 and 102 of the ceramic laminate 10. Acts in the direction of pulling in the linear direction.

  As described above, in the insulating filler 5 of the multilayer piezoelectric element 1 of the present example, the concave surface portion 50 is provided on the outer surface thereof, so that the side electrodes 31 and 32 are arranged along the side surfaces 101 and 102. The acting shear force is suppressed. Therefore, there is little possibility that the side electrodes 31 and 32 are peeled off from the side surfaces 101 and 102 of the ceramic laminate 10.

  Here, for comparison, a problem that may occur when the outer surface of the insulating filler 5 is formed substantially flush with the side surfaces 101 and 102 of the ceramic laminate 10 will be described. As shown in FIG. 11, when the outer surface of the insulating filler 5 is substantially flush with the side surfaces 101 and 102 of the ceramic laminate 10, the insulating filler 5 is in its initial state (state indicated by the solid line L1) due to thermal expansion. ) To a thermally expanded state (state indicated by a broken line L2), stress acts on the side electrodes 31 and 32 as indicated by arrows in the figure. That is, stress acts in a radial direction from a convex curved surface (surface indicated by a broken line L2) formed by thermal expansion of the insulating filler 5. Here, components in the shearing direction generated along the side surfaces 101 and 102 of the ceramic laminate 10 are not absorbed inside the side electrodes 31 and 32. The force of the component in the shear direction acts directly on the joint surface between the side electrodes 31 and 32 and the side surfaces 101 and 102 of the ceramic laminate 10. Therefore, in this case, when the thermal cycle is applied to the insulating filler 5 over a long period of use, the side electrodes 31 and 32 may be separated from the side surfaces 101 and 102 of the ceramic laminate 10.

In contrast, in the multilayer piezoelectric element 1 of this example, as described above, the side electrodes 31 and 32 are less likely to peel from the side surfaces 101 and 102 of the ceramic laminate 10. Therefore, the electrical connection between the internal electrode 21 (22) and the side electrode 31 (32) can be stably maintained, and the electrical connection between the internal electrode 21 (22) and the side electrode 32 (31). It is possible to maintain a reliable insulation over a long period of time.
Therefore, for example, even if the thermal cycle is repeatedly applied to the multilayer piezoelectric element 1, the side electrodes 31, 32 formed on the side surfaces 101, 102 of the ceramic laminate 10 can be maintained in a good state. Thereby, the multilayer piezoelectric element 1 has higher electrical reliability between the side electrode 31 (32) and the internal electrode 21 (22) than in the past.

  Furthermore, the groove width W of the first groove portion 41 and the second groove portion 42 is set to 90% of the thickness L of the piezoelectric layer 11 as described above. For this reason, it is possible to suppress the possibility that excessive internal stress or the like is generated in the insulating filler 5 in accordance with the piezoelectric displacement of the multilayer piezoelectric element 1, and it is possible to further enhance the effect of suppressing problems such as cracks and peeling. In addition, as an internal electrode, it may replace with copper of this example and may form the internal electrode containing silver or a silver-palladium alloy.

In addition to the curved concave shape of the present example, the concave surface portion 50 can be formed in various shapes such as a triangular shape (FIG. 12) and a trapezoidal shape (FIG. 13). Furthermore, the concave surface portion 50 may have a symmetrical shape in the stacking direction or an asymmetric shape (FIGS. 14 and 15).
In addition to the rectangular shape of the present example, the concave groove portions 41 and 42 can have various shapes such as a triangular shape (FIG. 16), a trapezoidal shape (FIG. 17), and a polygonal shape (FIG. 18). . Furthermore, the concave groove portions 41 and 42 may have a symmetrical shape in the stacking direction or an asymmetric shape (FIG. 19).

(Example 2)
This example is an example in which the durability D was examined by changing the depth Dp of the concave surface portion of each concave groove portion in the multilayer piezoelectric element 1 of the first embodiment. This will be described with reference to FIGS. 20 and 21. FIG.
In this example, the electrical contact resistance between the side electrode and the internal electrode is measured after 500 cycles of a cooling cycle of −40 ° C. to 160 ° C. with a cycle time of 60 min for each laminated piezoelectric element. did.

  The result is shown in FIG. In the figure, the horizontal axis defines the depression amount Dp of the concave surface portion, and the vertical axis defines the resistance value which is the electrical contact resistance between the internal electrode and the side electrode. As can be seen from the figure, when the amount of depression Dp of the concave surface portion exceeds zero, the resistance value decreases. That is, the durability and reliability of the electrical contact portion between the side electrode and the internal electrode can be improved by making Dp larger than zero and providing the concave portion on the surface of the insulating filler. In particular, in the region where Dp exceeds zero and reaches about 4 μm, the effect that the durability of the contact portion between the side electrode and the internal electrode is improved as Dp exceeds zero and increases. Then, the inflection point A is reached at Dp = about 4 μm, and in the region where Dp = about 4 μm or more, even if Dp is increased, the durability of the contact portion between the side electrode and the internal electrode is cumulatively increased. Is fading.

  In this example, it was further investigated how the position of the inflection point A changes with respect to the groove depth D of the concave groove portion. The result is shown in FIG. In the figure, the groove depth D of the recessed groove portion is defined on the horizontal axis, and the indentation amount Dp at the inflection point A corresponding to the groove depth D is defined on the vertical axis. As is known from the figure, the relationship between the groove depth D of the concave groove portion and the depression amount Dp at the inflection point A is an approximate straight line B (Dotted line in the figure) representing Dp = (5% / 100%) × D. It can be approximated by Therefore, if the size of the recess amount Dp of the concave surface portion is set to about 5% or more of the groove depth D of the concave groove portion, the effect of enhancing the durability of the electrical contact portion between the internal electrode and the side electrode. Can be brought close to the maximum.

On the other hand, if the recess amount Dp of the concave surface portion is excessive with respect to the groove depth D of the concave groove portion, the amount of the insulating filler covering the outer peripheral end portion of the internal electrode may not be sufficient. Therefore, the effect of enhancing the durability of the electrical contact portion between the internal electrode and the side electrode, and the effect of ensuring the electrical insulation by covering the outer peripheral end of the internal electrode with the insulating filler. In order to achieve both at a high level, it is preferable to set the size of the recess amount Dp of the concave surface portion to approximately 5% to 90% of the groove depth D of the concave groove portion.
Other configurations and operational effects are the same as those in the first embodiment.

(Example 3)
This example is an example in which a gap is provided between the insulating filler and the side electrode based on the multilayer piezoelectric element 1 of the first embodiment. The contents will be described with reference to FIGS.
In this example, as shown in FIG. 22, a gap 505 is formed between the side electrode 31 (32) and the concave portion 50 of the insulating filler 5 by forming the contact surface on the ceramic laminate 10 side substantially flat. It is provided.

  In this example, as shown in the figure, the viscosity of the Sn-Ag paste applied to the side surface 101 (102) of the ceramic laminate 10 is set high so that the gap between the concave portion 50 and the side electrode 31 (32) is set. A gap 505 was formed. That is, when the viscosity of the Sn-Ag paste forming the side electrode 31 (32) is increased, it becomes difficult to enter the recess formed by the concave portion 50 of the insulating filler 5, and along the side surface 101 (102) of the ceramic laminate 10. Thus, the side electrode 31 (32) is formed. Thereby, the clearance gap 505 can be vacated between the concave surface part 50 and the side surface electrode 31 (32).

Instead of the method of providing the gap 505 by controlling the viscosity of the electrode material forming the side electrode 31 (32), the gap 505 is controlled by controlling the heat treatment temperature when forming the side electrode 31 (32). Can also be formed. In general, the electrode material for forming the side electrode 31 (32) has a viscosity characteristic that once heated, the viscosity is lowered and then the viscosity is increased. The gap 505 can be formed by increasing the viscosity when the electrode material is cured by appropriately setting the heating profile during the heat treatment so that the viscosity characteristics can be positively utilized.
Furthermore, various shapes can be employed for the groove shape of the concave groove portion 41 (42) and the formation shape of the concave surface portion 50, as in the first embodiment.

  FIG. 23 shows the result of the same thermal cycle test as in Example 2 for the multilayer piezoelectric element of this example. That is, in the figure, the relationship between the gap amount Dp of the concave surface portion 50 and the magnitude of the electrical contact resistance between the side electrode 31 (32) and the internal electrode 21 (22) after the cooling and heating cycle is shown. In the figure, the vertical axis defines the resistance value between the side electrode 31 (32) and the internal electrode 21 (22), and the horizontal axis defines the gap amount Dp of the concave portion 50.

As is known from FIG. 23, when the gap amount Dp of the concave portion 50 exceeds zero, the resistance value is reduced. That is, by providing Dp to be larger than zero and providing the concave portion 50 on the surface of the insulating filler 5, durability and reliability of the electrical contact portion between the side electrode 31 (32) and the internal electrode 21 (22) are provided. Can be improved. In particular, in the region where Dp exceeds zero and reaches about 1 μm, the effect of improving the durability of the contact portion between the side electrode and the internal electrode is remarkable as Dp increases beyond zero. Then, the inflection point A is reached at Dp = about 1 μm, and in the region where Dp = about 1 μm or more, as Dp is increased, the durability of the contact portion between the side electrode and the internal electrode is cumulatively increased. Slightly faded.
Other configurations and operational effects are the same as those in the first embodiment.

(Example 4)
This example is an example in which a non-concave surface portion is formed on a part of the outer surface of the insulating filler filled in each concave groove portion based on the multilayer piezoelectric element 1 of the first embodiment. The contents will be described with reference to FIGS.
In this example, as shown in FIG. 24 and FIG. 25, a non-concave surface portion 51 which is a portion where the concave surface portion 50 is not formed on a part of the outer surface of the insulating filler 5 filled in the concave groove portions 41 and 42. Is provided. Here, the non-concave surface portion 51 is a portion in which the outer surface of the insulating filler 5 filled in the groove portions 41 and 42 is formed to protrude outward from the side surfaces 101 and 102 of the ceramic laminate 10 (FIG. 26). To FIG. 28), or a portion (FIG. 29) formed along the side surfaces 101 and 102 of the ceramic laminate 10.

  For example, in the case of a complicated shape as shown in FIGS. 30 and 31, the insulating filler 5 protrudes outward with the area S of the portion recessed inward with respect to the side surfaces 101 and 102 of the ceramic laminate 10. The area T of the portion is compared, and if S> T, it can be determined as a concave surface portion, and if S ≦ T, it can be determined as a non-concave surface portion. In addition, when there are a plurality of portions recessed inward or protruding outward, the area S or the area T is obtained by the sum of the areas of the respective portions. For example, in FIG. 30, S = s1 and T = t1 + t2. In FIG. 31, S = s2 + s3 and T = t3.

As shown in FIG. 25, the non-concave surface 51 has a total length A in each first concave groove portion 41 and each second concave groove portion 42, and a length of a portion where the non-concave surface portion 51 is formed as B. (AB) / A is formed to be 0.3 or more. In the case where a plurality of non-concave portions 51 are formed, the sum of the lengths of the portions is B. For example, in FIG. 25, B = b1 + b2. In addition, said full length A is decided by each length of the 1st ditch | groove part 41 and the 2nd ditch | groove part 42 to form.
Further, in this example, the ceramic laminate 10 having a quadrangular prism shape was used (see FIG. 5).
Other configurations are the same as those in the first embodiment.

In this case, as in the first embodiment, by providing the concave surface portion 50 on the outer surface of the insulating filler 5, there is a risk that the side electrodes 31, 32 may be peeled off from the side surfaces 101, 102 of the ceramic laminate 10. Can be suppressed.
Further, in order to obtain the above effect more sufficiently and reliably, the concave surface portion 50 may be formed so that the above (AB) / A is 0.6 or more.
The other functions and effects are the same as those of the first embodiment.

(Example 5)
In this example, the laminated piezoelectric element 1 of Example 1 or Example 2 is used as the piezoelectric actuator of the injector 6.
The injector 6 of this example is applied to a common rail injection system of a diesel engine as shown in FIG.
As shown in the figure, the injector 6 includes an upper housing 62 in which the laminated piezoelectric element 1 serving as a drive unit is accommodated, and a lower housing 63 that is fixed to the lower end of the injector 6 and has an injection nozzle portion 64 formed therein. have.

  The upper housing 62 has a substantially cylindrical shape, and the laminated piezoelectric element 1 is inserted and fixed in a vertical hole 621 that is eccentric with respect to the central axis. A high-pressure fuel passage 622 is provided in parallel to the side of the vertical hole 621, and an upper end portion thereof communicates with an external common rail (not shown) through a fuel introduction pipe 623 protruding to the upper side of the upper housing 62. .

  A fuel lead-out pipe 625 communicating with the drain passage 624 protrudes from the upper portion of the upper housing 62, and the fuel flowing out from the fuel lead-out pipe 625 is returned to the fuel tank (not shown). The drain passage 624 passes through a gap 60 between the vertical hole 621 and the drive unit (piezoelectric element) 1, and further, a three-way valve, which will be described later, by a passage (not shown) extending downward from the gap 60 in the upper and lower housings 62 and 63. 651 communicates.

  The injection nozzle section 64 has a nozzle needle 641 that slides in the vertical direction in the piston body 631, and an injection hole 643 that is opened and closed by the nozzle needle 641 and injects high-pressure fuel supplied from a fuel reservoir 642 into each cylinder of the engine. I have. The fuel reservoir 642 is provided around the middle portion of the nozzle needle 641, and the lower end portion of the high-pressure fuel passage 622 is opened here. The nozzle needle 641 receives the fuel pressure in the valve opening direction from the fuel reservoir 642 and receives the fuel pressure in the valve closing direction from the back pressure chamber 644 provided facing the upper end surface, and the pressure in the back pressure chamber 644 is reduced. When lowered, the nozzle needle 641 is lifted, the nozzle hole 643 is opened, and fuel is injected.

  The pressure in the back pressure chamber 644 is increased or decreased by the three-way valve 651. The three-way valve 651 is configured to selectively communicate with the back pressure chamber 644 and the high pressure fuel passage 622 or the drain passage 624. Here, a ball-shaped valve body that opens and closes a port communicating with the high-pressure fuel passage 622 or the drain passage 624 is provided. The valve body is driven by the drive unit 1 through a large-diameter piston 652, a hydraulic chamber 653, and a small-diameter piston 654 disposed below the valve body.

In this example, the multilayer piezoelectric element 1 shown in the first embodiment is used as a drive source in the injector 6 having the above-described configuration. As described above, this multilayer piezoelectric element 1 has a high reliability of the insulating structure between the internal electrodes 21 and 22 and the side electrodes 31 and 32 and is extremely excellent in durability. Therefore, even in the injector 6 used in a harsh state under a high-temperature atmosphere, the occurrence of cracks during operation can be suppressed, durability can be improved, and the performance and reliability of the injector 6 as a whole are improved. Can be achieved.
Other configurations and operational effects are the same as those in the first or second embodiment.

FIG. 3 is an explanatory diagram showing the structure of a multilayer piezoelectric element in Example 1. FIG. 3 is an explanatory view showing a peripheral structure of a concave surface portion of an insulating filler in Example 1. FIG. 3 is an explanatory diagram showing another structure of the multilayer piezoelectric element in Example 1. FIG. 3 is an explanatory diagram showing a stacking order of ceramic laminates in Example 1. FIG. 3 is an explanatory diagram showing a quadrangular prism-shaped ceramic laminate in Example 1. FIG. 3 is an explanatory diagram showing an octagonal prism-shaped ceramic laminate in Example 1. Explanatory drawing which shows the state which formed the 1st ditch | groove part and the 2nd ditch | groove part in Example 1. FIG. Explanatory drawing which shows the state which filled the insulating filler in the 1st ditch | groove part and the 2nd ditch | groove part in Example 1. FIG. FIG. 3 is an explanatory diagram illustrating a cross section orthogonal to the stacking direction of the stacked piezoelectric elements in Example 1. FIG. 3 is an explanatory diagram showing stress acting on a side electrode due to thermal expansion of an insulating filler in Example 1. FIG. 3 is an explanatory diagram showing stress acting on a side electrode due to thermal expansion of an insulating filler according to a comparative example in Example 1. Explanatory drawing which shows the shape of the other concave-surface part in Example 1. FIG. Explanatory drawing which shows the shape of the other concave-surface part in Example 1. FIG. Explanatory drawing which shows the shape of the other concave-surface part in Example 1. FIG. Explanatory drawing which shows the shape of the other concave-surface part in Example 1. FIG. Explanatory drawing which shows the shape of the other groove part in Example 1. FIG. Explanatory drawing which shows the shape of the other groove part in Example 1. FIG. Explanatory drawing which shows the shape of the other groove part in Example 1. FIG. Explanatory drawing which shows the shape of the other groove part in Example 1. FIG. The graph which shows the relationship between the hollow amount Dp after resistance test implementation by a thermal cycle in Example 2, and resistance value. The graph which shows the relationship between the groove depth D and the amount of depressions Dp in Example 2. FIG. Explanatory drawing which shows the periphery structure of the concave surface part of an insulating filler in Example 3. FIG. The graph which shows the relationship between the hollow amount Dp and resistance value after the reliability test implementation by a thermal cycle in Example 3. FIG. Explanatory drawing which shows the structure of the ceramic laminated body in Example 4. FIG. Explanatory drawing which shows the structure of the side surface of the ceramic laminated body in Example 4. FIG. Explanatory drawing which shows the non-concave surface part of the insulating filler in Example 4. FIG. Explanatory drawing which shows the non-concave surface part of the insulating filler in Example 4. FIG. Explanatory drawing which shows the non-concave surface part of the insulating filler in Example 4. FIG. Explanatory drawing which shows the non-concave surface part of the insulating filler in Example 4. FIG. Explanatory drawing which shows the judgment method of the concave part or non-concave part of an insulating filler in Example 4. FIG. Explanatory drawing which shows the judgment method of the concave part or non-concave part of an insulating filler in Example 4. FIG. Explanatory drawing which shows the cross-section of an injector in Example 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer piezoelectric element 10 Ceramic laminated body 101, 102 Side surface (side surface of ceramic laminated body)
11 Piezoelectric layer 21 First internal electrode (internal electrode)
22 Second internal electrode (internal electrode)
31 First side electrode (side electrode)
32 Second side electrode (side electrode)
41 1st groove part (concave groove part)
42 Second concave groove (concave groove)
410, 420 Bottom 5 Insulating filler 50 Concave surface 51 Non-concave surface 505 Clearance 6 Injector

Claims (10)

A ceramic laminated body in which a plurality of piezoelectric layers made of a piezoelectric material and a plurality of layered internal electrodes having conductivity are alternately laminated, and a first side surface electrode and a second side surface are formed on side surfaces of the ceramic laminated body. An electrode is provided, and as the internal electrode, a laminated piezoelectric element in which a first internal electrode conducting to the first side electrode and a second internal electrode conducting to the second side electrode are alternately arranged In
The side surface provided with the first side electrode in the ceramic laminate is provided with a first groove portion, which is a groove in which an end portion of the second internal electrode is exposed at the bottom, while the second side electrode is provided. The side surface provided with a second groove portion that is a groove in which the end portion of the first internal electrode is exposed at the bottom,
The first concave groove portion and the second concave groove portion are filled with an insulating filler having electrical insulation so as to cover the end portion of the second internal electrode and the end portion of the first internal electrode, respectively.
A laminated surface characterized in that a concave portion recessed inward from a side surface of the ceramic laminate is formed on an outer surface of the insulating filler filled in the first concave groove portion and the second concave groove portion. Type piezoelectric element.   2. The multilayer piezoelectric element according to claim 1, wherein the concave surface portion is formed so as to maintain a hollow shape at a maximum temperature within a temperature range allowed for the multilayer piezoelectric element. .   3. The multilayer piezoelectric element according to claim 1, wherein a difference between a linear expansion coefficient of the piezoelectric layer and a linear expansion coefficient of the insulating filler is 20 ppm / ° C. or more and 300 ppm / ° C. or less.   The multilayer piezoelectric element according to claim 1, wherein the insulating filler contains at least one of silicon, polyimide, epoxy, or urethane.   5. The multilayer piezoelectric element according to claim 1, wherein the first side electrode and the second side electrode are made of Sn—Ag paste.   The laminate according to any one of claims 1 to 5, wherein a gap is provided between the concave surface portion of the insulating filler and the first side electrode or the second side electrode. Type piezoelectric element.   7. The width of the first groove portion and the second groove portion is 5 μm or more and 150 μm or less, and the depth of the recess portion is 2 μm or more and 100 μm or less. A laminated piezoelectric element characterized by the above.   8. The multilayer piezoelectric element according to claim 1, wherein groove depths of the first concave groove portion and the second concave groove portion are not less than 10 μm and not more than 400 μm.   9. The non-concave portion in which the concave portion is not formed on the outer surface of the insulating filler filled in the first concave groove portion and the second concave groove portion according to claim 1. When the total length of each of the first and second concave groove portions is A and the length of the non-concave surface portion is B, (AB) / A is 0.3 or more. A laminated piezoelectric element, characterized in that: In an injector configured to open and close the valve body using the displacement of the piezoelectric actuator and perform fuel injection control,
The injector according to any one of claims 1 to 9, wherein the piezoelectric actuator comprises the multilayer piezoelectric element according to any one of claims 1 to 9.

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