JP2008192807A - Laminated piezoelectric actuator element and laminated piezoelectric actuator - Google Patents

Abstract

A laminated piezoelectric actuator element and a laminated type capable of relaxing driving stress at a boundary portion between a polarization region and a non-polarization region as compared with the prior art and capable of improving durability as compared with the prior art. A piezoelectric actuator is provided.
SOLUTION: The tip portions 30 and 40 of internal electrodes 3 and 4 formed so as to sandwich a piezoelectric layer 2 are formed to have an uneven shape when projected from the stacking direction. The uneven shape is regularly formed in a wave shape and has no corners.
[Selection] Figure 2

Description

  The present invention relates to a multilayer piezoelectric actuator element and a multilayer piezoelectric actuator, and more particularly to a multilayer piezoelectric actuator element and a multilayer piezoelectric actuator suitable as a drive source for a fuel injection injector or the like.

  In recent years, a multilayer piezoelectric actuator element using a piezoelectric element in which a plurality of piezoelectric layers extending in response to an applied voltage and a plurality of internal electrodes for supplying an applied voltage are alternately stacked has been developed and put into practical use. Yes. In such a laminated piezoelectric actuator element, a portion of the piezoelectric layer sandwiched between the internal electrodes is a polarization region, and a portion not sandwiched between the internal electrodes is a non-polarization region. For this reason, the displacement distribution changes greatly at the boundary portion between the polarization region and the non-polarization region, and stress concentrates on this portion. Due to this stress concentration, the possibility of cracking increases when driven for a long period of time, resulting in a decrease in durability. For this reason, a multilayer piezoelectric actuator element in which the tip position of the internal electrode is shifted in the overlapping direction of the internal electrodes is known (see, for example, Patent Document 1).

Further, the minimum width L that is the minimum distance of the region (back portion) from the end of the piezoelectric layer to the tip of the internal electrode, and the variation width W that is the difference between the maximum and minimum of this distance,
0.1 mm ≦ L ≦ 1.0 mm, W ≦ 0.5 mm
In addition, a technique for reducing the above-described stress concentration by setting the number of stacked layers to 50 or less is also known (for example, see Patent Document 2).
JP 2001-230463 A JP 2005-5680

  As described above, in the multilayer piezoelectric actuator element and the multilayer piezoelectric actuator, a technique for relaxing stress during driving at the boundary portion between the polarization region and the non-polarization region has been conventionally proposed. However, further stress relaxation can be realized, and further improvement in durability is required compared to the conventional case.

  The present invention has been made in response to such a conventional situation, and can reduce the stress at the time of driving at the boundary portion between the polarization region and the non-polarization region as compared with the conventional case, and is more durable than the conventional case. It is an object of the present invention to provide a laminated piezoelectric actuator element and a laminated piezoelectric actuator that can be improved.

  The multilayer piezoelectric actuator element of the present invention is a multilayer body formed by alternately laminating a plurality of piezoelectric layers and internal electrodes, one side of which is exposed on the side surface of the multilayer body and the other side is the multilayer body. A laminate in which the internal electrodes that are not exposed on the side surfaces of the body and the internal electrodes in which the other side is exposed on the side surfaces of the laminate and the side electrodes that are not exposed on the side surfaces of the laminate are alternately laminated; In the laminated piezoelectric actuator element, at least some of the internal electrodes have irregular shapes regularly arranged when the side sides not exposed to the side surfaces of the laminated body are projected from the laminating direction. To do.

  In the multilayer piezoelectric actuator element of the present invention configured as described above, the side electrode (tip portion) that is not exposed on the side surface of the laminate of at least some of the internal electrodes, that is, the internal electrode serving as the boundary between the polarization region and the non-polarization region By making the side edges of the layers into a regular concavo-convex shape instead of a linear shape, the stress applied to the laminate can be dispersed in the cross section (the surface on which the internal electrodes are formed). As a result, the stress at the time of driving at the boundary between the polarization region and the non-polarization region can be relaxed compared to the conventional case, and the durability can be improved as compared with the conventional case.

  As described above, when the side (tip portion) that is not exposed on the side surface of the laminate of the internal electrodes is a regular uneven shape, it is preferable to have a shape that does not have a corner such as a sine curve, For example, a shape having corners such as a triangular wave shape may be used. Further, the regular uneven shape may be the same for all the internal electrodes, or may be different. When the regular concavo-convex shape varies depending on the internal electrodes, the concavo-convex shape of the internal electrode can also be varied, but the concavo-convex shape of the same-polar internal electrode exposed on the same side surface of the laminate is projected from the lamination direction It is sometimes preferable that the concave and convex portions are arranged so as to be shifted in the direction perpendicular to the amplitude direction. With such a configuration, the stress applied to the laminate can be dispersed in the transverse section (surface on which the internal electrodes are formed) and in the longitudinal section direction (stacking direction), and the polarization region as a whole The driving stress at the boundary with the non-polarized region can be relaxed three-dimensionally.

  Further, another multilayer piezoelectric actuator element of the present invention is a multilayer body in which a plurality of piezoelectric layers and internal electrodes are alternately stacked, one side of which is exposed on the side surface of the multilayer body and the other side. The internal electrodes whose sides are not exposed on the side surfaces of the stacked body and the internal electrodes whose other side is exposed on the side surfaces of the stacked body and whose one side is not exposed on the side surfaces of the stacked body are alternately stacked. In the multilayer piezoelectric actuator element including the multilayer body, at least a part of the internal electrodes has a concave and convex shape having no corners when the side that is not exposed to the side surface of the multilayer body is projected from the stacking direction. It is characterized by.

  In the multilayer piezoelectric actuator element of the present invention configured as described above, the side electrode (tip portion) that is not exposed on the side surface of the laminate of at least some of the internal electrodes, that is, the internal electrode serving as the boundary between the polarization region and the non-polarization region By making the side sides of this layer into a concavo-convex shape having no corners instead of a straight line, the stress applied to the laminate can be dispersed in the cross section (the surface on which the internal electrodes are formed). As a result, the stress at the time of driving at the boundary between the polarization region and the non-polarization region can be relaxed compared to the conventional case, and the durability can be improved as compared with the conventional case.

  According to the present invention, the multilayer piezoelectric actuator element capable of relaxing the driving stress at the boundary between the polarization region and the non-polarization region as compared with the prior art and improving the durability as compared with the prior art. In addition, a multilayer piezoelectric actuator can be provided.

  Hereinafter, details of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an overall schematic configuration of a multilayer piezoelectric actuator element according to an embodiment of the present invention. As shown in FIG. 1, a multilayer piezoelectric actuator element 1 includes a plurality of piezoelectric layers 2 made of piezoelectric ceramic, for example, lead zirconate titanate (PZT), and a plurality of conductive internal electrodes (internal electrode layers). The laminate 5 is formed by alternately laminating a plurality of layers 3 and 4.

  The internal electrodes 3 and 4 are alternately arranged in the stacking direction, and the piezoelectric layer 2 is sandwiched between the internal electrode 3 and the internal electrode 4. These internal electrodes 3 are used as electrodes having the same polarity (for example, positive electrode), and the internal electrodes 4 are used as electrodes having the same polarity (for example, negative electrode).

  The internal electrode 3 is formed up to its end so that one side is exposed on one side surface (the left side surface in FIG. 1) of the multilayer body 5, and the tip which is the other side of the internal electrode 3 The portion 30 is formed from the other side surface (the right side surface in FIG. 1) of the laminated body 5 to a predetermined distance and is not exposed to the other side surface of the laminated body 5. On the other hand, the internal electrode 4 is formed up to its end so that the other side is exposed on the other side surface (the right side surface in FIG. 1) of the multilayer body 5. A certain tip portion 40 is formed from the one side surface (the left side surface in FIG. 1) of the laminated body 5 to a predetermined distance and is not exposed to one side surface of the laminated body 5. By configuring the internal electrodes 3 and 4 in this way, the internal electrodes 3 and 4 having different polarities are not electrically short-circuited.

  A pair of external electrodes 6 and 7 are provided on the outside of the multilayer body 5. These external electrodes 6 and 7 are electrically connected to the internal electrodes 3 and 4 via exterior electrodes 8 and 9 and solder layers 10 and 11 formed on the side surfaces of the laminate. Further, the external electrodes 6 and 7 are made of a conductive member, for example, in a mesh shape, and can be deformed according to the expansion and contraction of the laminate 5. For example, lead wires 12 and 13 are provided on these external electrodes 6 and 7 as terminals for electrical connection to the outside.

  The tip portions 30 and 40 of the internal electrodes 3 and 4 are formed to have a concavo-convex shape when projected from the stacking direction as shown in an enlarged view in FIG. The uneven shape is regularly formed in a wave shape (sine curve shape) and has no corners. Moreover, when the laminated body 5 is about 5 mm square and 6 mm square, for example, the amplitude of the concavo-convex shape is about 0.5 mm or more, for example. As described above, the tip portions 30 and 40 of the internal electrodes 3 and 4, that is, the side portions of the internal electrode that are the boundary between the polarization region and the non-polarization region are not linear but regular irregular shapes. The stress applied to the laminated body 5 can be dispersed in the cross section (the surface on which the internal electrodes 3 and 4 are formed). In addition, although it is preferable to form such uneven | corrugated shape in all the internal electrodes 3 and 4 in the laminated body 5, it does not necessarily need to be all and it forms in only some internal electrodes 3 and 4. Also good. When the uneven shape is formed only on some of the internal electrodes 3, 4, it is preferable to form the uneven shape on the number of internal electrodes 3, 4 which is about 50% or more of the total number of internal electrodes 3, 4. Furthermore, it is preferable that the number of internal electrodes 3 having an uneven shape among the same-polarity internal electrodes and the number of internal electrodes 4 having an uneven shape among the other internal electrodes of the same polarity are the same. .

  The uneven shape is not limited to the wave shape (sine curve shape) as shown in FIG. 2, and various modifications can be made. For example, as shown in FIG. 3, it is good also as a triangular wave form (shape which arranged the triangular unevenness | corrugation). Moreover, as shown in FIG. 4, it is good also as a shape which changed the amplitude of the wavy uneven | corrugated shape periodically. In addition, the above-described regular uneven shape is not limited to the same uneven shape arranged, but as shown in FIG. 4, a shape in which the amplitude is regularly changed or a shape in which the period is regularly changed Including a line-symmetric shape or the like that is intentionally changed in shape. 2 to 4 show an example in which the period of the concavo-convex shape is relatively short and has a large number of concavo-convex shapes, the concavo-convex shape may have a long period, and has at least about two or more sets of concavo-convex shapes. Anything is acceptable. Furthermore, the internal electrodes 3 and 4 having different uneven shapes may exist in one laminated body 5.

  Further, as shown in FIG. 5, when the same-polarity internal electrodes 3, 3 or the internal electrodes 4, 4 are projected from the stacking direction, the concave portion and the convex portion of the tip portion 30 or the tip portion 40 are projected. You may arrange | position so that a part may be in the state shifted | deviated to the orthogonal | vertical direction with respect to the amplitude direction. Furthermore, it is preferable to arrange the concavo-convex shape so as to be in a state in which the concavo-convex shape is shifted by a half cycle, and the concave and convex portions and the convex and concave portions are overlapped. And it is more preferable that the same polarity internal electrodes 3 and 3 or the internal electrodes 4 and 4 with which the recessed part and the convex part shifted | deviated adjoin. With such a configuration, the stress applied to the stacked body 5 can be dispersed in the transverse section (the surface on which the internal electrodes 3 and 4 are formed) and can be dispersed in the longitudinal section direction (stacking direction). Stress can be relaxed dimensionally.

  As described above, in the multilayer piezoelectric actuator element 1 of this embodiment, the driving stress at the boundary portion between the polarization region and the non-polarization region can be relaxed as compared with the conventional case, and the durability is improved as compared with the conventional case. Can be achieved.

  Next, an example of a method for manufacturing the multilayer piezoelectric actuator element 1 will be described. First, the prepared composition PZT mixed powder is heat-treated at a temperature of 600 to 1000 ° C. for about 1 to 10 hours to prepare a calcined powder.

  Next, calcined powder, polyvinyl butyral resin, DOP (di-2-ethylhexyl phthalate) and solvent (MEK + toluene) are mixed and pulverized, and a sheet is prepared by the doctor blade method, which is suitable for processing. Cut to a predetermined size.

  In addition, ethyl cellulose, butyl carbitol or terpineol is added and mixed in advance with AgPd powder to prepare a conductive paste.

  On the obtained sheet, the conductive paste is patterned by screen printing using a mask having a concavo-convex pattern to form an internal electrode having a regular concavo-convex shape on the tip side that is not connected to the external electrode. At this time, when the concavo-convex shape of the adjacent electrode of the same polarity is shifted by a half cycle, printing is performed by facilitating another mask or by shifting the position of the mask by one concave or convex.

Next, a temporary press-bonded body in which about 10 to 30 sheets on which a predetermined pattern is formed is laminated (60 ° C.-100 kg / cm ² ) is produced.

Next, a necessary number of the above-mentioned temporary press-bonded bodies are stacked, and main press-bonding (40 to 70 ° C.-100 to 1000 kg / cm ² ) is performed to produce a laminate, and a columnar piece is cut out.

  Next, after degreasing the cut-out columnar piece, it is fired at 1000 to 1200 ° C., and surface grinding is performed to make the fired body have a predetermined size.

  Then, a silver-based paste is printed on the side surface of the columnar piece having a predetermined size and baked at 600 to 800 ° C. Thereafter, a lead wire or the like is fixed on the silver with solder as necessary, and a voltage of 1 to 3 kV / mm is applied via the lead wire to perform polarization.

  The multilayer piezoelectric actuator element 1 is manufactured by the manufacturing process as described above. FIG. 6 shows a configuration of a multilayer piezoelectric actuator 100 including the multilayer piezoelectric actuator element 1 having the above configuration. The multilayer piezoelectric actuator 100 includes a multilayer piezoelectric actuator element 1 and a case 101 that houses the multilayer piezoelectric actuator element 1.

  One end face (upper end face in FIG. 6) of the multilayer piezoelectric actuator element 1 in the expansion / contraction direction (stacking direction of the multilayer body 5) is engaged with the back cover 102 of the case 101. Further, a push rod 103 is connected to the other end surface (lower end surface in FIG. 6) in the expansion / contraction direction of the multilayer piezoelectric actuator element 1, and this push rod 103 is connected to the case 101 via a leaf spring 104. The front lid 105 is locked. The tip of the push rod 103 is disposed so as to protrude from an opening 106 provided in the front lid 105. Further, the lead wires 12 and 13 of the multilayer piezoelectric actuator element 1 are fixed to the case 101 and the back cover 102 via a sleeve 107.

  In the multilayer actuator 100 having the above-described configuration, a high voltage is applied from a drive circuit (not shown) via the lead wires 12 and 13, whereby the multilayer piezoelectric actuator element 1 expands and contracts in the vertical direction on the order of, for example, several tens of micrometers. . This expansion and contraction is transmitted as a displacement to an injector valve (not shown) or the like via the push rod 103. At this time, as described above, the stress at the boundary between the polarization region and the non-polarization region of the multilayer piezoelectric actuator element 1 can be relaxed, and the durability can be improved as compared with the conventional case.

  While the present invention has been described in detail based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the case where the shape of the tip portions 30 and 40 of the internal electrodes 3 and 4 is a regular concavo-convex shape has been described. However, this concavo-convex shape is regular as long as it has no corners. It is good also as a shape which is not. The uneven shape is not limited to the tip portions 30 and 40 of the internal electrodes 3 and 4, and may be provided anywhere as long as it is a portion of the internal electrode that is not exposed on the side surface of the laminate.

The figure which shows typically the cross-sectional structure of the lamination type piezoelectric actuator element of one Embodiment of this invention. FIG. 2 is an enlarged view showing a main part configuration of internal electrodes of the multilayer piezoelectric actuator element of FIG. FIG. 2 is a diagram showing an example of another internal electrode of the multilayer piezoelectric actuator element of FIG. FIG. 2 is a diagram showing an example of another internal electrode of the multilayer piezoelectric actuator element of FIG. FIG. 2 is a diagram showing an example of another internal electrode of the multilayer piezoelectric actuator element of FIG. The figure which shows typically the cross-sectional structure of the laminated piezoelectric actuator of one Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric actuator element, 2 ... Piezoelectric layer, 3, 4 ... Internal electrode, 5 ... Laminated body, 6, 7 ... External electrode, 8, 9 ... Exterior electrode, 10, 11 ... Solder layer, 12, 13 ... Lead wire.

Claims (5)

A laminated body formed by alternately laminating a plurality of piezoelectric layers and internal electrodes, wherein one side is exposed on a side surface of the laminated body and the other side is not exposed on a side surface of the laminated body; In the stacked piezoelectric actuator element comprising a stacked body in which the other side is exposed on the side surface of the stacked body and the one side is alternately stacked with the internal electrodes not exposed on the side surface of the stacked body,
At least a part of the internal electrodes has a concavo-convex shape regularly arranged when a side that is not exposed on the side surface of the multilayer body is projected from the laminating direction. The multilayer piezoelectric actuator element according to claim 1,
The multilayer piezoelectric actuator element, wherein the uneven shape has no corners. The multilayer piezoelectric actuator element according to claim 1 or 2,
The concave and convex shapes of the internal electrodes exposed on the same side surface of the multilayer body are arranged so that the concave portions and the convex portions are shifted in a direction perpendicular to the amplitude direction when projected from the stacking direction. Multilayer piezoelectric actuator element. A laminated body formed by alternately laminating a plurality of piezoelectric layers and internal electrodes, wherein one side is exposed on a side surface of the laminated body and the other side is not exposed on a side surface of the laminated body; In the stacked piezoelectric actuator element comprising a stacked body in which the other side is exposed on the side surface of the stacked body and the one side is alternately stacked with the internal electrodes not exposed on the side surface of the stacked body,
At least some of the internal electrodes have a concavo-convex shape that does not have corners when projected from the stacking direction on the side that is not exposed on the side surface of the stacked body. The laminated piezoelectric actuator element according to any one of claims 1 to 4,
A multilayer piezoelectric actuator comprising a case for housing the multilayer piezoelectric actuator element.

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