DE102004025073A1 - Piezoelectric actuating element for fuel injector, has piezoelectric units with alternating piezoceramic layer stacks, internal electrode layer; no more than 50 stacks of piezoceramic layers - Google Patents

Abstract

The piezoelectric actuating element (1) has piezoelectric units (15) made with alternating stacks of a piezoceramic layer (151) and an internal electrode layer (153,154). The piezoelectric unit is formed by stacking no more than 50 layers of the piezoceramic layers and has a pair of external electrodes (5) with different potentials on their lateral surfaces.

Description

BACKGROUND OF THE INVENTION Field of the Invention

The The invention relates to a piezoelectric actuator and more particularly to a piezoelectric actuator, as the drive source of an injection device (injector) or the like is used.

Heretofore, the use of a piezoelectric device as a driving source of an injector, ie, a fuel injector of an internal combustion engine of a car has been proposed. Since the injector is repeatedly subjected to fuel atomization at extremely high speed for 10 ⁸ times, the piezoelectric device as the driving source is subjected to extremely severe use conditions. Therefore, not only excellent piezoelectric properties but also excellent durability for the piezoelectric device for the injector are required.

One stacked piezoelectric actuator (actuator) passing through alternately stacking a plurality of piezoelectric ceramic layers, experiencing an offset corresponding to an applied voltage, and internal electrode layers for supplying the applied voltage was shaped for Such a piezoelectric device is most desirable. This is because when the voltage is applied, that of the piezoelectric ceramic layers surrounding the internal electrode layers each offset in this piezoelectric actuator experienced and thus a great drive power is produced.

however occurs in piezoelectric actuators according to the state the technique has the problem on that within the actuator when applying the voltage a strong mechanical stress (stress) occurs, and that cracks occur in the actuator. Therefore It is difficult to piezoelectric actuators according to the state the technology for to operate for a long time and apply it to an injector, etc. imposed on the particularly severe conditions of use.

To the Solve this Problems according to the state The technique has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-230463 discloses a stacked piezoelectric actuator proposed in the unconnected end positions of internal Electrode layers and external electrodes in a stacking direction the internal electrode layers differ (are shifted). It it is believed that when the internal electrode layers are so are arranged, that their end positions deviate, which within of the actuator occurring mechanical stress can be alleviated.

If however, the above-described stacked piezoelectric actuator according to the state the technology for an injector, etc. is used in the harsh conditions of use be imposed, the stress (the mechanical stress) increases within the actuator because the end portions of the internal electrodes are offset, so that cracks occur. Consequently, the stacked piezoelectric actuator not enough in terms of durability. Another problem is that variations in the properties (characteristics) like electrostatic capacity and offset behavior become large.

SUMMARY THE INVENTION

in the With regard to the problems described above in the state of Technique, the invention is directed to a new piezoelectric actuator to provide that for Applications as with injectors is suitable and excellent Durability and excellent stability.

According to a first aspect, there is provided a piezoelectric actuator having piezoelectric units formed by alternately stacking a piezoelectric ceramic layer and an internal electrode layer, the piezoelectric unit being formed by stacking not more than 50 layers of the piezoelectric ceramic layers and a pair of external electrodes having different potentials at the side surfaces thereof, the internal electrode layers having exposed electrode portions exposed to the side surfaces of the piezoelectric units and the exposed electrode portions having one of the pair of external electrode layers a recessed portion as a recessed region of the internal electrode layer which is not extended to the side surface of the piezoelectric unit is partially connected in a peripheral portion of the piezoelectric unit, and the external electrode as a connection counterpart of the exposed electrode portions is changed alternately for each layer internal electrode layer, and a minimum width L, which is defined as a minimum value of a distance from the side surface of the piezoelectric unit at the recessed portion to an end portion of each internal electrode layer, and a variation width W, which is a difference between a maximum value and a the minimum value of the distance from the side surface of each piezoelectric unit at each recessed portion to each internal electrode layer is defined, in the cross section of the piezoelectric actuator in a stacking direction satisfies the following relationship (1): 0.1 mm ≤ L ≤ 1.0 mm, W ≤ 0.5 mm (1)

at the piezoelectric actuator according to the above described first embodiment of the invention meet the minimum width L of the reset Section and the variation width W is the relationship of the above Equation (1).

Therefore become variations in the surfaces the overlap sections the internal electrode layers (hereinafter referred to as "piezoelectrically active Region " are small within the piezoelectric unit, and the characteristics (Characteristics) such as the electrostatic capacity and the Offset amount can be stabilized become.

There furthermore, the minimum width L of the recessed portion and whose variation width W is limited as described above, will it be possible to prevent mechanical stress between the piezoelectric Ceramic layers (hereinafter referred to as "piezoelectric inactive region"), those at the back Section come into contact and not easily during the application of an electrical Voltage offset, and the above described concentrate piezoelectric active region, and also the Occurrence of cracks within the piezoelectric actuator to avoid. Therefore, the durability of the piezoelectric actuator be improved.

Farther the piezoelectric unit described above is passed through Stacking 50 or less layers of those described above produced piezoelectric ceramic layers. Because the number of layers the stacked piezoelectric units to not more than 50 is limited, the inside of the unit during the application of electrical Stress occurring stress (mechanical stress) are suppressed. Therefore, the occurrence of cracks that occur within the piezoelectric unit develop, be prevented.

As As described above, according to the first embodiment the invention provides a new piezoelectric actuator, that for an application as in an injection device (injector) suitable is outstanding in terms of durability and stable Features.

In addition to the first aspect, according to a second aspect of the invention, there is provided a piezoelectric actuator having piezoelectric units formed by alternately stacking a piezoelectric ceramic layer and an internal electrode layer, the piezoelectric unit stacking a pair of external electrodes having different potentials at the side surfaces thereof the internal electrode layer has exposed electrode portions exposed to the side surfaces of the piezoelectric units and connected to one of the pair of external electrode layers through the exposed electrode portions, and the external electrode is alternately changed for each layer as a connection counterpart of the exposed electrode portions; a recessed portion as a recess region of the internal electrode layer that does not face to the side surface of the p ieoelectric unit, partially formed in a peripheral portion of the internal electrode layer, and assuming that one of the pair of external electrodes is a first external electrode, the other is a second electrode, the internal electrode layer connected to the first external electrode a first internal electrode layer and the internal electrode layer connected to the second external electrode are a second internal electrode layer, the first and second internal electrode layers are constructed such that: the exposed electrode portion of the second internal electrode layer is not exposed in the portion of the piezoelectric unit on the the exposed electrode portion of the first internal electrode layer is exposed to overlap the exposed electrode portions of the first internal electrode layer with those of the second internal electrode layer to be avoided when the first and second internal electrode layers are viewed in perspective in the stacking direction, the area of either the first or the second internal electrode layers is larger than the area of the other internal electrode layer, and a length A of an outer circumference A and a length B of an outer circumference B satisfy the relationship B ≥ 0.5 × A, wherein the outer circumference A represents the outer periphery of a piezoelectric active region defined as a region in which the first internal electrode layer and the second internal electrode layer overlap each other and the outer periphery B represents a portion where the internal electrode layer having the larger area of the first and second internal electrode layers on the outer periphery A covers the outer of the outer periphery A when the first and second internal electrode layers are stacked in perspective be considered.

The functions and effects of the second embodiment of the present invention will be described below with reference to FIG 10 described.

10 shows a perspective view when the first internal electrode layers 153 and the second internal electrode layers 154 from the stacking direction in the piezoelectric actuator described above.

When the first internal electrode layers 153 and the second internal electrode layers 154 from the stacking direction into the piezoelectric actuator according to the second embodiment of the invention, their exposed electrode portions overlap 158 and 159 not each other.

Farther is the area of one of the first and second internal electrode layers is greater than the area the other, and the length A of the outer circumference A and the length B of the outer circumference B fulfill the relationship B ≥ 0.5 × A, where the outer circumference (Edge) A the outer circumference the piezoelectrically active region as the region in which the first internal electrode layer and the second internal electrode layer overlap each other, represents, and the outer circumference B represents the section in which that of the internal electrode layers with the larger area of the first and second internal electrode layers on the outer periphery A the outer of the outer circumference A covers when the first and second internal electrode layers can be seen from the stacking direction.

Therefore, a variation in the area of the overlapping region of the two adjacent internal electrode layers becomes 153 and 154 (the piezoelectrically active region 150 indicated by the dotted line in 10 surrounded region) by a positional error, etc., when stacking the internal electrode layers 153 and 154 impaired. Therefore, the resulting piezoelectric actuator has excellent durability and also has stabilized properties such as electrostatic capacity and offset amount.

Farther have the internal electrode layers in the piezoelectric units exposed electrode portions on the side surfaces of the exposed to piezoelectric units. Furthermore, the first internal electrode layer and the second internal electrode layer such that when the first and second internal electrode layers perspective view in the stacking direction thereof, the exposed one Electrode portion of the second internal electrode layer not is exposed in the portion where the exposed electrode portion the first internal electrode layer is exposed to overlap the exposed electrode portions of the first internal electrode layer and to avoid that of the second electrode layer.

The is called, that both the exposed electrode sections of the first internal Electrode layer as well as those of the second internal electrode layer not to the same page surface the piezoelectric units are exposed. Accordingly, will it is possible an electrical short circuit due to a creeping discharge in the side surfaces to avoid the piezoelectric units.

SUMMARY THE DRAWINGS

The The invention will be described below with reference to the drawings. Show it:

1 an exploded perspective view of a piezoelectric actuator according to Example 1,

2 a sectional view taken along a line AA in 1 taken,

3 an enlarged sectional view of a portion in the vicinity of a coupling portion of the piezoelectric actuator according to 2 .

4 a perspective view of the state in which internal electrode layers are printed on a ceramic starting material according to Example 1,

5 a perspective view of a layering type, are stacked in the starting materials with the internal electrode layers according to Example 1,

6 a perspective view of the stacked body according to Example 1,

7 a perspective view of the piezoelectric unit according to Example 1,

8th 12 is a schematic diagram showing a pattern of arrangement of the internal electrode layers when the internal electrode layers of a pattern E6 are observed from the stacking direction of the piezoelectric units of Example 2;

9 FIG. 12 is a schematic diagram showing an arrangement pattern of the internal electrode layers when the internal electrode layers of a pattern E7 are viewed from the stacking direction of the piezoelectric units of Example 2; FIG.

10 FIG. 12 is a schematic diagram showing an arrangement pattern of internal electrode layers when the internal electrode layers of a pattern E8 are viewed from the stacking direction of the piezoelectric units of Example 3; FIG.

11 12 is a schematic diagram showing a pattern of arrangement of the internal electrode layers when the internal electrode layers of a pattern E9 are viewed from the stacking direction of the piezoelectric units of Example 3,

12 12 is a schematic diagram showing a pattern of arrangement of the internal electrode layers when the internal electrode layers of a pattern E10 are viewed from the stacking direction of the piezoelectric units of Example 3;

13 10 is an enlarged schematic view illustrating end portions of the internal electrode layers formed in the piezoelectric ceramic layers according to Example 4;

14 an enlarged schematic representation of the portion which is indicated by a dashed circle in 13 is limited

15 FIG. 15 is a graph showing the durability of the piezoelectric actuators (patterns E11 to E16) according to Example 4; FIG.

16 a graph illustrating the durability of the piezoelectric actuators (patterns E11a to E16a) according to Example 4,

17 FIG. 12 is a diagram illustrating the relationship of a boundary portion between an exposed electrode portion and a recessed portion and an external electrode when a pattern E17 is viewed from the side surface thereof according to Example 5; FIG.

18 12 is a set of schematic views showing the relationship between the exposed electrode portion of the internal electrode layer and the external electrode when the internal electrode layer of Example E17 is viewed from the stacking direction of the piezoelectric units of Example 5;

19 12 is a cross-sectional view illustrating a stacking direction of the piezoelectric units used for producing a pattern E18 according to Example 6;

20 12 is a cross-sectional view illustrating a stacking direction of the piezoelectric actuator according to a pattern E18 according to Example 6;

21 FIG. 6 is a graph showing the relationship between the stacking number of the piezoelectric ceramic layers and the stress in the piezoelectric unit. FIG.

22 the relationship between a variation width W of a recessed portion and the stress generated in the piezoelectric unit,

23 FIG. 4 is a graph showing the relationship between an electric field intensity of the outermost layer and an electric coercive field of the piezoelectric unit and a piezoelectric constant of the outermost layer; FIG.

24 FIG. 6 is a graph showing the relationship between a strength of the electric field of the piezoelectric unit and an offset amount. FIG.

25 a schematic view, in comparison, the internal electrode layers 153 and 154 and the piezoelectric active region 150 when using a relationship: B = O × A in accordance with Example 3,

26 a schematic view, in comparison, the internal electrode layers 153 and 154 and the piezoelectrically active region 150 using the relationship: B = 0.5 × A according to Example 3,

27 a graph showing the relationship between an outer circumference B / outer circumference A value and a variation in the characteristics of the piezoelectric actuator of Example 3, and FIG

28 a schematic view showing different combinations of a profile pattern of the internal electrode layers 153 and 154 illustrated in Example 3.

DESCRIPTION THE PREFERRED EMBODIMENTS

According to the above-described first aspect of the invention, the piezoelectric unit is manufactured by stacking not more than 50 layers of piezoelectric ceramic layers as described above. It shows 21 Results obtained by a simulation test show the relationship between the stacking number of the piezoelectric ceramic layers and the stress (mechanical stress) occurring within the piezoelectric unit. The simulation test was carried out by a piezoelectric analysis using a finite element method (FEM).

How out 21 As a result, the stress occurring within the unit generally becomes larger as the number of stacked piezoelectric ceramic layers increases. In particular, when the number exceeds 50, a large internal stress occurs when the voltage is applied. As a result, cracks are likely to occur inside the piezoelectric unit.

Further, in the cross section of the piezoelectric unit in the stacking direction, the minimum width L and the variation width W at the above-explained recessed portion satisfy the following equation (1): 0.1 mm ≤ L ≤ 1.0 mm, W ≤ 0.5 mm (1)

First, the minimum width L and the variation width W of the recessed portion are explained with reference to FIG 3 described.

3 shows an enlarged cross-sectional view in the stacking direction of the part of the piezoelectric actuator according to the invention, an example described later. As it is in 3 is shown, the piezoelectric actuator 1 piezoelectric units 15 each by alternately stacking piezoelectric ceramic layers 151 and internal electrode layers 153 and 154 getting produced.

A recessed section 155 as the area of each internal electrode layer 153 . 154 leading to the lateral surface of the piezoelectric unit 15 extends, that is, is reset by this, is partially around the internal electrode layer 153 . 154 formed at the stacking positions of these electrode layers.

The minimum width L of the recessed portion 155 may be determined by the minimum value of the distance from the side surface of the piezoelectric unit to the recessed portion 155 to the end portion of each internal electrode layer 153 . 154 in the cross section of the piezoelectric actuator in the stacking direction.

The variation width W of the recessed portion 155 can be determined by the difference between the maximum value and the minimum value of the distance from the side surface of the piezoelectric unit 15 at each recessed portion to the end portion of each internal electrode layer 153 . 154 in the cross section of the piezoelectric actuator 1 be expressed in the stacking direction. In the illustrated recessed portion, when the minimum width L of the recessed portion is less than 0.1 mm, the occurrence of cracks can not be effectively suppressed in some cases regardless of the variation width W.

If In contrast, the minimum width L exceeds 1.0 mm, the piezoelectrically active region becomes relatively small in comparison to the same physical structure and behavior of the piezoelectric Device, so that the offset generation force is likely reduced.

22 FIG. 12 shows the results obtained by the simulation test of the relationship between the variation width of the recessed portion and the stress occurring within the piezoelectric unit. The simulation test was carried out by a piezoelectric analysis using a finite element method like that according to FIG 21 executed.

How out 22 As is apparent, the stress occurring within the unit gradually increases as the variation width of the recessed portion increases. In particular, when the variation width exceeds 0.5 mm, a large internal stress occurs when the voltage is applied. As a result, cracks are likely to develop within the piezoelectric unit.

According to the first aspect of the invention, it is preferable that the following equation (2) is satisfied. 0.2 mm ≤ L ≤ 0.6 mm, W ≤ 0.3 mm (2)

The Functions and effects according to the first Embodiment of the invention can continue to be improved upon application of this relationship. It means that the above relationship is a variation of the areas of the piezoelectrically active one Range and also properties such as offset generation capability and the like of the piezoelectric element can stabilize. Since the during the Applying the electrical voltage generated internal mechanical Voltage can be suppressed, it becomes possible the probability reduce the generation of cracks in the piezoelectric units.

below a second embodiment of the invention is described.

According to the above described second embodiment of the invention fulfill the Length A the outer circumference A and the length B of the outer circumference B is the relationship: B ≥ 0.5 × A, where the outer circumference A the outer circumference represents a piezoelectrically active area as an area, in which the first internal electrode layer and the second internal Electrode layer overlap each other, and the outer circumference B illustrates a section in which one of the internal electrode layers with a larger area under the first and second internal electrode layers on the outer periphery A the outside the outer circumference A covers when the first and second internal electrode layers can be seen from the stacking direction.

When B <0.5 × A, it is likely that a variation of the area of the overlapping piezoelectric active region (represented by the broken line in FIG 10 limited region) is affected by a positioning error of the internal electrode layers in stacking, etc., and that the electrostatic capacitance and the displacement amount of the piezoelectric actuator can occasionally not be stabilized.

Farther it is preferable in the piezoelectric actuator that the relationship B ≥ 0.6 mm × A is satisfied. By applying this relationship, it becomes possible to have a variation in the area of the piezoelectric active region passing through a positional deviation during causing the starting of the internal electrode layers and other causes and also the properties such as the electrostatic capacity and the Offset amount of the piezoelectric actuator continue to stabilize.

Farther it is preferable that in the piezoelectric actuator the relationship B ≦ 0.75 × A is satisfied and that the exposed electrode portions of the first internal Electrode layer and those of the second internal electrode layer not in the same page surface the piezoelectric unit exposed. Since the relationship 0.6 × A ≦ B ≦ 0.75 × A is satisfied, can in this piezoelectric actuator stabilizes the properties of the piezoelectric actuator become. Furthermore, since the exposed electrode sections each are shaped so that they are not in the same side surface of the Piezoelectric units can expose the effects to avoid an electrical short circuit due to a creeping discharge and others will be further improved.

According to the first and second embodiments of the present invention, it is preferable the internal electrode layer indicates a variation or variance its outer edge and that the width D of the variation is within D ≦ 0.2 mm.

According to this embodiment Is it possible, To avoid stress (strain) on the outer circumference the internal electrode layer is concentrated, wherein also the Durability of the piezoelectric actuator further improved can be.

Hereinafter, the variation width D of the outer edge of the internal electrode layer will be explained with reference to FIG 13 and 14 described.

The internal electrode layer is formed, for example, by screen printing on a green sheet, which is converted into a piezoelectric ceramic layer after firing. 13 shows an enlarged view of the part of the internal electrode layer 154 on the piezoelectric ceramic layer 151 is shaped, and 14 shows an enlarged view of the part of the outer edge of the internal electrode layer 154 , in the 13 is shown (enlarged view of the by the dashed circle in 13 circled area).

As it is in 13 and 14 is the outer periphery of the screen-printed internal electrode layer 154 etc. is not linear, but shows a curved shape with some variation. As it is in 14 is shown, the width of a variation is around a centerline 199 as the center of the variation on the outer circumference of the internal electrode layer 154 the variation width D described above. That is, the variation width D is the degree of variation at the outer circumference of each internal electrode layer 154 represents.

If the variation width D is greater than 0.2 mm, a large occurs Internal stress (voltage) when applying the electrical voltage on, and it is likely that cracks within the piezoelectric Develop unity.

Farther For example, it is preferable that the external electrode completely cover the covers exposed electrode section.

According to this embodiment Is it possible, the variation of the coupling surface of the exposed electrode portion with the external electrode to thereby reduce offset transition characteristics. Furthermore you can adverse effects of the external environment the internal electrode layers are prevented.

Farther is preferable in the piezoelectric actuator that the distance from the boundary portion between the exposed electrode portion on the side surface the piezoelectric unit and the recessed portion to the on the side surface of the reset Section of the piezoelectric unit disposed external electrode at least 0.2 mm in terms of the shortest distance along the side surface the piezoelectric unit is.

When the distance from the boundary portion between the exposed electrode portion and the recessed portion to that arranged on the side surface of the recessed portion ex If the electrode is less than 0.2 mm, it is likely that a creeping discharge will occur on the surface of the piezoelectric actuator.

Farther it is preferable that the piezoelectric actuator by stacking a plurality of piezoelectric ones described above Units is constructed.

According to this embodiment can be a more elevated desired Offset amount by stacking of the piezoelectric units which are the predetermined ones Have offset amount.

Farther it is preferable that the outermost layer the piezoelectric units is active, that is, one activity having.

According to this embodiment Is it possible, the offset amount per unit length the piezoelectric actuator to increase in the stacking direction, This is constructed by stacking a plurality of piezoelectric units is, and the occurrence of cracks by reducing the internal to suppress mechanical stress those at the interface between the outermost layer as the outermost piezoelectric Layer and the internal drive layer occurs.

It It should be noted that the term "active" as used herein means that the field strength in the outermost layer while of the operation, the electrical coercive field in an inner section exceeds the piezoelectric unit.

This is further below with reference to 23 described.

23 FIG. 12 is a graph showing experimental results of the relationship between the electric field intensity of the piezoelectric unit piezoelectric unit for the piezoelectric unit and a piezoelectric constant of the piezoelectric unit. FIG.

In 23 The abscissa represents the electric field strength of the piezoelectric unit with respect to the electric coercive force of the piezoelectric unit {(field strength) / (electric coercive force)}, and the ordinate represents the piezoelectric constant of the piezoelectric unit.

How out 23 As is apparent, when the field strength of the outermost layer exceeds the coercive electric field of the piezoelectric unit, the piezoelectric constant of the outermost layer becomes larger. That is, this represents that the ceramic layer becomes active as the outermost layer.

Hereinafter, the coercive electric field (the electric coercive force) is explained with reference to FIG 24 described.

24 Fig. 10 is a graph describing the above-described electric coercive field (Ec). In 24 The abscissa represents the field strength supplied to the piezoelectric unit, and the ordinate represents the offset amount. It should be noted that in this graph, the same direction of the field strength as the polarization direction is positive (+), and a direction opposite to the polarization direction, is negative (-).

According to 24 is applied to the field strength of the piezoelectric unit from a point A as a starting point in the same direction as the polarization direction, and whose value is gradually increased. The amount of displacement of the piezoelectric unit increases with the increase of the field strength. It should be noted that the offset amount can be made by measuring the offset in the stacking direction when a predetermined voltage is applied and the offset unit length in the stacking direction is used as the offset amount. This offset amount can be measured by using a laser displacement meter and an electrostatic capacity displacement meter.

If then the field strength reaches a point B, the field strength is gradually reduced. The offset amount is reduced gradually at this time with a drop in field strength. The field strength is gradually and continuously in the direction opposite to the polarization direction set direction decreases, even after the field strength is zero (0) reached. The offset amount is reduced continue with decreasing field strength. When the field strength is one Reached point C, changes the amount of offset is abrupt, to increase. The absolute value of the field strength at this point is the electrical coercive field strength Ec referred to in the present invention.

To Reaching a point D, the field strength is increased again. The Reduced offset amount This time with the increase in field strength. If the field strength continues is increased in the polarization direction after reaching zero (0), it changes abruptly to a rise. Since the point B and the point C in some make are different, is the electrical coercive force when applying the electrical voltage in the Zuleitpolarisationsrichtung opposite set direction as Ec according to the present Invention defined.

It should be noted that, as it is in 24 is shown, when the field strength is further increased, the state finally reaches the state which is substantially the same as the point B, and thereafter exhibits a similar behavior.

The outermost layer The piezoelectric units can be used with different methods be treated to the outermost layer to put into the active state. A suitable method has a method of applying an electric voltage to the outermost layer to which normally no electrical voltage is applied. As a result, the outermost layer be converted into a piezoelectric active layer, if the electrical voltage is applied.

Farther it is preferable that the above-described piezoelectric Ceramic layer is formed of a PZT material.

According to this embodiment, it is possible to improve excellent properties of the PZT material, that is, generally, oxides having a perovskite structure of the Pb (Zr, Ti) O _{3 type} , thereby improving the performance of the piezoelectric actuator such as the injector.

at At least one of Ag, Pd, Cu, Ni, Au and Pt selected metal species be used in the generation of the internal electrode layer. The metal can be used alone or in combination.

In addition is it is preferable that the above-described piezoelectric Actuator for the injector is used.

According to this embodiment can excellent durability of the piezoelectric actuator be offered in the injector.

EXAMPLES

example 1

Hereinafter, a piezoelectric actuator according to the preferred embodiment of the invention with reference to 1 to 8th described.

As it is in 1 to 3 is shown, the piezoelectric actuator 1 according to this example piezoelectric units 15 by alternately stacking piezoelectric ceramic layers 151 and internal electrode layers 153 and 154 getting produced.

Each piezoelectric unit 15 is made by stacking not more than 50 layers of piezoelectric ceramic layers 151 and, as illustrated, has a few external electrodes 5 and 6 with different potentials on the side surface. Each of the internal electrode layers 153 and 154 has an exposed electrode portion 158 and 159 on the side of the piezoelectric unit 15 is exposed, and is over the exposed electrode portion 158 or 159 with one of the pair of external electrodes 5 and 6 connected. Furthermore, as illustrated, the external electrodes 5 and 6 as a connection counterpart of the exposed electrode portion 158 or 159 changed alternately for each shift.

Further, a recessed portion is a recess region in which each internal electrode layer 153 . 154 is recessed, that is not to the side surface of the piezoelectric unit 15 is performed, partially around each internal electrode layer 153 and 154 shaped.

As it is in 3 is shown in the cross section of the piezoelectric actuator 1 in the stacking direction, the minimum width L as the minimum value of the distance from the side surface of the piezo electrical unit 15 at each recessed section 155 to the end portion of each internal electrode layer 153 and 154 and the variation width W as the difference between the maximum value and the minimum value of the distance from the side surface of the piezoelectric unit 15 at each recessed section 155 to each internal electrode layer 153 and 154 the following relationship ( 1 ): 0.1 mm ≤ L ≤ 1.0 mm, W ≤ 0.5 mm (1)

The piezoelectric actuator 1 according to this example is described in detail with reference to 1 to 3 described.

As it is in 1 to 3 is shown, the piezoelectric actuator 1 according to this example, by stacking twenty (20) piezoelectric units 15 made to thereby coupling portions 13 to shape. Each piezoelectric unit 15 is by alternately stacking the piezoelectric ceramic layers 151 formed of the PZT material and the internal electrode layers 153 and 154 made of Ag and Pd. The number of stacking of the piezoelectric ceramic layers 151 as the piezoelectric devices in each piezoelectric unit 15 are active, is 20, although this is not shown in the drawings for ease of preparation of the drawings.

Each of the internal electrode layers 153 and 154 has the exposed electrode portion 158 and 159 on the side surface of the piezoelectric unit 15 exposed. At least part of the exposed electrode sections 158 and 159 are alternately electrically in the stacking direction with the external electrodes 5 and 6 connected to mutually different potentials, and so on the side surface of the piezoelectric unit 15 shaped them between the exposed electrode sections 158 and 150 are arranged. Therefore, adjacent ones are two internal electrode layers 153 and 154 within the piezoelectric actuator 1 connected to electrodes having mutually different potentials. According to the illustrated embodiment, the external electrodes are 5 and 6 formed from Ag, however, it is also possible to use Pd, Cu, Ni, Au or Pt, or at least one kind thereof except Ag.

The external electrodes 5 and 6 with mutually different potentials may have different shapes to each other, so that their polarities can be easily distinguished by the eye.

Furthermore, as it says in 2 and 3 is shown, each piezoelectric unit 15 the recessed sections 155 on, where the piezoelectric layers 151 come in mutual contact such that they do not on the side surfaces of the piezoelectric units 15 but the internal electrode layers 153 and 154 at the stacking positions of the internal electrode layers 153 and 154 are not available. As it is in 3 is shown, every reset section 155 essentially at the same level as each internal electrode layer 153 and 154 shaped, and the width of each recessed section 155 has a variation. The minimum width L of the recessed portion 155 and their variation width W satisfy the following relation (1) 0.1 mm ≤ L ≤ 1.0 mm, W ≤ 0.5 mm (1)

Hereinafter, the manufacturing method of the piezoelectric actuator according to this embodiment is explained with reference to FIG 4 to 7 described.

The piezoelectric actuator according to this embodiment can be measured using a starting material plate method (green Sheet method), which is generally conventional in the production a layered piezoelectric actuator is used. The starting material or the starting material plate (green sheet) is prepared in the manner described below.

First, be Lead oxide, zirconia, titania, niobium oxide, strontium carbonate powder and the like as main starting materials for the piezoelectric material dependent on from the desired Composition weighted by a known method. According to this embodiment the materials are prepared so that the final composition a so-called. PZT (lead zirconium titanate) is, where also the starting materials be mixed in a composition that richer by 1 to 2% in bleach than the stoichiometric Composition is, taking into account the evaporation of the lead. These starting materials are in one Mix mixer dry and then calcined at 800 to 950 ° C.

After that Distilled water and a dispersant are among the calcined Added powders to a slurry which is then wet pulverized using a medium mixer.

After this the result (the powder) is dried and degreased, becomes one Solvents a binder, a plasticizer, a dispersing agent, etc. are added, and the resulting mixture is mixed in a ball mill. The slurry will then defoamed in vacuo (de-foamed), and their viscosity is controlled while she with a stirrer in a vacuum equipment touched becomes.

After that gets the slurry in starting material (green sheet) having a predetermined thickness below Use of a scraper (doctor blade apparatus).

Then becomes the recovered source material either by a pressing device punched out or cut by a knife, around rectangular bodies with a predetermined size.

After that, as it is in 4 is shown, a silver / palladium paste (hereinafter referred to as Ag / Pd paste) having a ratio of silver to palladium of 7: 3, for example, on one of the surfaces of the molded starting material 7 screen printed. 4 shows an example of the starting material after printing the metal pattern. In so doing, this paste is prepared using a metal such as Ag, Pd, Cu, Ni, Au or Pt, or at least one kind of metal selected from these metals.

A pattern of Ag / Pd paste that is slightly smaller than the surface of the starting material 7 is formed on a substantially entire surface of the starting material to this as an internal electrode layer 153 ( 154 ) to use. An electrode-free section 75 , which free from the internal electrode 153 ( 154 ) is disposed on one of the opposite sides of the surfaces of the starting material. That is, the internal electrode layer 153 ( 154 ) does not reach one of the ends on the opposite sides of the starting material, but only reaches the other end. When forming the internal electrode layers 153 ( 154 ) becomes the desired starting material 7 (the desired starting material plate) 7 receive.

According to the illustrated embodiment, a predetermined stack number of starting materials 7 according to the required specification of the displacement amount of the piezoelectric actuator 1 prepared. A required number of raw material plates on which no internal electrode layers 153 ( 154 ) are also prepared.

Thereafter, the starting materials, each containing the internal electrode layers 153 ( 154 ) are stacked on it, as it is in 5 is shown. This will be the starting materials 7 stacked so that the electrodes have free sections 75 be alternately positioned on the left and on the right, as illustrated.

It should be noted that in 5 the internal electrode layers whose electrode-free portion is disposed on the left side as internal electrode layers 153 and the internal electrode layers whose electrode-free portion is disposed on the right side as internal electrode layers 154 are shown.

A stacked body (stacked body) 70 , which consists of a total of 30 layers of raw material plates, is made as in 6 is shown by twenty-one (21) plates of the starting material plates 7 on which internal electrode layers 153 and 154 are formed, stacked, followed by attaching starting material plates without internal electrode layers 153 and 154 on and under the stacked starting material plates 7 follows. It should be noted that in 6 the pile body 70 for ease of illustration is shown such that the stack number is omitted.

Thereafter, the stack body 70 is heat-pressed, then is degreased at 400 to 700 ° C in an electric furnace, is fired at 900 to 1200 ° C and is then polished to a desired shape. According to this example, chamfering (C-chamfering) of 1 mm at the corners having a size of 7 mm ² and a thickness of the stacked body in the stacking direction is set to 1.8 mm. As a result, each raw material plate becomes 7 in the piezoelectric ceramic layer 151 converted, and becomes the reset section 155 formed on the electrode-free portion, in this way the piezoelectric unit 15 alternately stacked piezoelectric ceramic layers 151 and internal electrode layers 153 such as 154 has, as it is in 7 is shown. Although in 7 for simplicity, the number of stacked layers is not indicated, the piezoelectric unit 15 twenty (20) layers of the active piezoelectric layers as piezoelectric devices. Twenty ( 20 ) Piezoelectric units 15 are prepared in the process described above.

After the generation of the twenty (20) piezoelectric units 15 These are stacked to the piezoelectric actuator 1 according to 1 to 3 to obtain. The preparation is described below.

First, external electrodes are made of Ag 5 and 6 shaped so as to be the side surface of the piezoelectric units 15 pinch.

The external electrode 5 becomes at the position of each piezoelectric unit 15 shaped at which the internal electrode layer 153 with one of the poles exposed to connect to each internal electrode layer 153 manufacture.

The external electrode becomes at the position of each piezoelectric unit 15 shaped at which the internal electrode layer 153 with the other pole exposed to connect to each internal electrode layer 154 manufacture.

Thereafter, by applying a DC voltage across the external electrodes 5 and 6 to the internal electrode layers 153 and 154 the piezoelectric unit 15 with the external electrodes formed thereon 5 and 6 induces a polarization.

After that, as it is in 1 to 3 is shown, twenty (20) piezoelectric units 15 , which have been polarized as described above, via the coupling surface 156 (see. 7 ) are stacked one on top of the other about the piezoelectric actuator 1 according to 1 to 3 to create. The resulting piezoelectric actuator is referred to as "pattern E1".

In the piezoelectric actuator 1 as the pattern E1, the minimum width L of the recessed portion 155 was 0.3 mm, and the variation width W of the recessed portion 155 was 0.5 mm.

According to this Example will be other piezoelectric actuators in the same Way of making the pattern E1 with the proviso made such that the number of stacked piezoelectric ceramic layers, the minimum width L of the reset Section and its variation width W are changed. The resulting Products are called "patterns E2 to E5 "," patterns Es1 to Es4 "and" patterns C1 to C4 " Details of these patterns are summarized in Table 1.

To the generation of these patterns is applied to each of the patterns E1 to E5, the patterns Es1 to Es4 and the patterns C1 to C4 an electrical Voltage applied to the durability and stability of each Pattern according to the following Procedure to investigate.

beurteilt, Muster, die einen Kurzschluss in irgendeinem der zwischen 2 × 10⁸ mal bis 4 × 10⁸ mal ausgeführten Tests erfahren haben, werden als O beurteilt, und Muster, die einen oder mehrere Kurzschlüsse vor den 2 × 10⁸-ten Betrieb erfahren haben, werden als X beurteilt.First, ten (10) patterns of each of the patterns E1 to E5 and the patterns C1 to C4 are provided, and operating tests are carried out 4 × 10 ⁸ times by applying a positive drive voltage of 150 V without applying a negative electric voltage. The patterns are observed to determine whether or not a short circuit has been generated during operation of the patterns. Patterns that have not been short-circuited in each test are called

, patterns that have undergone a short circuit in any of the tests performed between 2 × 10 ⁸ times to 4 × 10 ⁸ times are judged to be O, and patterns that undergo one or more shorts before the 2 × 10 ^8th operation have, are judged as X.

The Results are summarized in Table 1.

Table 1

As is apparent from Table 1, the patterns E1 to E5 and the patterns Es1 to Es4 have not more than 50 piezoelectric ceramic layers, and the minimum width L and the variation width W of the recessed portion are within the range of 0.1 mm ≦ L ≦ 1.0 mm and W ≤ 0.5 mm respectively. The patterns E1 to E5 and the patterns Es1 to Es4 do not short-circuit during operation to 2 × 10 ⁸ times, and are excellent in durability and operational stability.

Specifically, the patterns Es1, Es3, and Es4 in which the minimum width L and the variation width W of the recessed portion are set to be in the range of 0.2 mm ≦ L ≦ 0.6 mm and W ≦ 0.3 mm, respectively, none Short circuit during operation up to the 4 × 10 ^8th time, and therefore show even more excellent durability and stability.

In the patterns E1 to E9 and the patterns Es1 to Es4, each piezoelectric unit 50 no more than 50 piezoelectric ceramic layers. Therefore, the occurrence of cracks within the piezoelectric unit can be effectively suppressed.

On the other hand, the patterns C1 and C2 have a larger number of piezoelectric units exceeding 50 layers. Further, in the patterns C3 and C4, the minimum width L and the variation width W of the recessed portion are each outside the range of 0.1 mm ≦ L ≦ 1.0 mm and W ≦ 0.5 mm. In the patterns C1 to C4, a short circuit occurs during operation to 2 × 10 ⁸ times in all patterns, so that durability and stability are not sufficient.

Example 2

This example is intended to produce two piezoelectric actuators 1 (hereinafter referred to as E6 and E7 patterns) by alternately stacking piezoelectric ceramic layers 151 and internal electrode layers 153 such as 154 as per 1 in the same manner as in Example 1 on the condition that the positional relationship and the shapes of the piezoelectric ceramic layers, the internal electrode layers and the external electrodes are changed.

8th and 9 each show an arrangement pattern of the internal electrode layers 153 and 154 with respect to the piezoelectric ceramic layers 151 and the external electrodes 5 and 6 in the piezoelectric actuators made according to this example.

The piezoelectric actuators according to this example, as in 1 and in the same manner as in Example 1 under the condition that the internal electrode layers 153 and 154 be formed such that the exposed electrode sections 158 and 159 the internal electrode layers 153 and 154 only at the connection portions with the external electrodes 5 and 6 are present, and the recessed section 155 the internal electrode layers 153 and 154 surrounded as it is in 8th and 9 is shown. The products made in this way are referred to as "E6 and E7" respectively.

In patterns E6 and E7 are the internal electrode layers 153 and 154 substantially in the same shape as the piezoelectric ceramic layer 151 however, its size is smaller than that of the ceramic layer 151 as it is in 8th and 9 is shown.

When the exposed electrode sections 158 and 159 completely with the external electrodes 5 and 6 As covered in the patterns E6 and E7, variation of the coupling areas with the external electrodes becomes small, offset transition characteristics can be stabilized, and piezoelectric actuators having higher stability can be obtained.

Example 3

This Example is a piezoelectric actuator according to the second Explain embodiment of the invention.

The piezoelectric actuator according to this example is the piezoelectric actuator 1 with the piezoelectric units 15 by alternately stacking the piezoelectric layers 151 and the internal electrode layers 153 such as 154 are shaped as described above with reference to 1 to 2 is described. Each of the piezoelectric units 15 has a pair of external electrodes 5 and 6 with mutually different potentials on the side surfaces.

The internal electrode layers 153 and 154 each have the exposed electrode sections 158 and 155 on, leading to the side surfaces of the piezoelectric unit 15 extend. The exposed electrode sections 158 and 159 are with one of the pair of external electrodes 5 and 6 connected, and the external electrodes 5 and 6 shift in layers.

10 shows the pattern-shaped internal electrode layers 153 and 154 when the piezoelectric actuator according to this example is viewed from the stacking direction.

As it is in 10 is shown is the recessed section 155 as a recess region of each internal electrode layer 153 and 154 from the side surface of the piezoelectric unit partially around each internal electrode layer 153 . 154 shaped.

One of the pair of external electrodes is referred to as a "first external electrode 5 "and the other external electrode is referred to as a" second external electrode 6 The one with the first external electrode 5 connected internal electrode layer is called "first internal electrode layer 153 "and with the second external electrode 6 connected internal electrode layer is called "second internal electrode layer 154 ' designated. According to this example, the first and second internal electrode layers 153 and 154 such an arrangement that the second internal electrode layer 154 on the side surface where the first internal electrode layer 153 is exposed, not exposed, to overlap the exposed electrode sections 158 and 159 to avoid when the first and second internal electrode layers 153 and 154 from the stacking direction.

The area of one of the first and second internal electrode layers 153 and 154 is larger than the area of the other internal electrode layer. It should be noted that according to this example, the larger area internal electrode layer is the second internal electrode layer 154 is, and that one with the smaller area the first internal electrode layer 153 is how it is in 10 is shown.

When the first and second internal electrode layers 153 and 154 from the stacking direction, becomes the outer circumference (circumference) of the piezoelectric active region 150 in which the first and second internal electrode layers 153 and 154 overlap each other, referred to as "outer circumference A". In this outer circumference A, the portion formed with the larger-area internal electrode layer (the second internal electrode layer 154 ) of the first and second internal electrode layers 153 and 154 to the outside of the outer edge A is called "outer circumference B". Then, the length A of the outer edge A and the length B of the outer edge B satisfy the relationship: B ≥ 0.5 × A.

The manufacturing method of the piezoelectric actuator 1 according to this example, the same as that according to Example 1 except that the shapes of the internal electrode layers 153 and 154 are changed, as is in 10 is shown. The resulting actuator is referred to as "pattern E8".

According to Example 8, the first internal electrode layer 153 and the second internal electrode layer 154 shaped such that the overlapping portion of the first and second internal electrode layers 153 and 154 (the region surrounded by the dashed line and crossed by oblique lines), that is, the piezoelectrically active region 150 , which is active as the piezoelectric device, becomes substantially square.

When the first and second internal electrode layers 153 and 154 from the stacking direction, assuming that the outer circumference of the piezoelectrically active region 150 is referred to as "outer circumference A", and in this outer circumference A, the portion connected to the larger-area internal electrode layer (the second internal electrode layer 154 ) of the first and second internal electrode layers 153 and 154 to the outside of the outer edge A covered portion is referred to as "outer circumference B", the length A of the outer edge A and the length B of the outer edge B, the relationship B ≥ 0.5 × A.

It should be noted that 10 such as 11 and 12 As will be referred to later, the arrangement of the patterned first and second internal electrode layers relative to the piezoelectric ceramic layers and the external electrode layers will be exhibited when the first and second internal electrode layers are viewed from the stacking direction. In each drawing, an arrow represents the outer circumference B. Although this arrow is actually the outer circumference A (indicated by the dotted or dashed line in FIG 10 overlapped portion), this is slightly shifted for ease of illustration.

According to this example, in addition to the production of the pattern E8, piezoelectric actuators having different patterns of the internal electrode layers are compared with those of the pattern E8 as in FIG 11 and 12 shown and are referred to as "pattern E9" ( 11 ) and "sample E10" ( 12 ) designated. The patterns E9 and E10 are the same as the pattern E8 on the condition that the patterns of the internal electrode layers are changed.

In the patterns E8 to E10 is the second internal electrode layer 154 not free on the side surface where the first internal electrode layer 153 exposed so that the exposed electrode sections 158 the first and second internal electrode layers 153 and 154 do not overlap each other as it is in 10 to 12 is shown.

Farther fulfill in the patterns E8 to E10 the length A of the outer edge A and the length B of the outer edge B is the relationship: B ≥ 0.5 × A.

When Result can the piezoelectric actuators the pattern E8 to E10 the occurrence of a creeping discharge at their side surfaces avoid.

Furthermore, a variation in the area of the piezoelectric active region becomes 150 (which is surrounded by the dashed line and by diagonal lines in 10 to 12 dashed area) as the area in which two internal electrode layers 153 and 154 overlap each other, not easily affected by positioning errors when the internal electrode layers 153 and 154 be stacked. Therefore, the piezoelectric actuators of the patterns E8 to E10 have excellent durability and extremely high stability of properties such as electrostatic capacitance and displacement amount.

Furthermore, when the internal electrode layers 153 and 154 are formed such that one of these internal electrode layers has a larger surface area and an outer circumference A of the piezoelectric active region 150 the relationship outer circumference B = 0.5 × A satisfies useful effects such as the blocking of negative deterioration, for example, a positioning deviation during stacking of the internal electrode layers 153 and 154 , That is, for example, that compared to the piezoelectric actuator having the internal electrode layers 153 and 154 With substantially the same structure, it becomes possible to reduce the adverse effects such as positioning deviation during stacking to about half or less in this piezoelectric actuator.

For example, if the internal electrode layers 153 and 154 are formed substantially with the same structure, as in 25 is shown, the area of the piezoelectric active region 150 substantially reduced if stacking deviation of the internal electrode layer 154 with respect to the internal electrode layer 153 is effected. It should be noted that in 25 (a) the illustrated piezoelectrically active region 150 is in ideal stacking conditions, and therefore there is no stacking deviation between the internal electrode layers 153 and 154 gives. Continue to show 25 (b) and 26 (c) the piezoelectrically active areas 150 with varied areas resulting from a positional deviation on both sides of the direction (side a + and side a-) of the direction of the diagonal a in the internal electrode layers 153 and 154 with the essentially square construction.

In contrast, shows 26 the arrangement of the internal electrode layers 153 and 154 in which one of these internal electrode layers, ie the internal electrode layer 153 , has a larger area and it has the relationship outer circumference B = 0.5 × A with respect to the outer circumference A of the piezoelectric active region 150 met, along with a variation of the area of the piezoelectrically active region 150 which is caused by a stack deviation. It should be noted that in 26 (a) the illustrated piezoelectrically active region 150 is in an ideal stacking condition, and therefore there is no stacking deviation between the internal electrode layers 153 and 154 gives. In the illustrated stacking conditions, the internal electrode layers are 153 and 154 are stacked with the substantially square structure with superimposition of two sides and one corner thereof. Continue to show 26 (b) and 26 (c) a variation of the area of the piezoelectrically active areas 150 which is caused when a positional deviation in both direction sides (side a + and side a-) of the direction of the diagonal a in the internal electrode layers 153 and 154 is effected with the substantially square structure.

As it is in 26 (b) is shown, when a stack deviation in a direction of the diagonal a, ie in the direction a +, in the internal electrode layer 154 caused the area of the piezoelectrically active region 150 as with the above with reference to 25 described piezoelectrically active region 150 is reduced. However, as it is in 26 (c) shown is the area of the piezoelectrically active region 150 does not vary, even if a stack deviation in the other direction of the diagonal a, ie the direction a- in the internal electrode layer 154 is caused.

That is, if one of the internal electrode layers 153 and 154 is designed to have a larger area, and the internal electrode layers 153 and 154 are shaped so as to satisfy the relationship: outer circumference B = 0.5 × A as described above, the direction of the stack deviation which can cause variation of the piezoelectric active region can be controlled only in one signal direction. It can namely, in contrast to the internal electrode layers 153 and 154 with the substantially same structure according to 25 the likelihood of reducing the piezoelectric active region due to stack deviation is reduced to about one half or less.

Further shows 27 a graph showing a relationship between the value of (outer circumference B / outer circumference A) of the piezoelectric active region 150 and shows a variation in the characteristics of the piezoelectric actuator that results in stacking between the internal electrode layers 153 and 154 caused. In 27 the value of (outer circumference B / outer circumference A) is plotted on the abscissa, and the variation of the properties is plotted on the ordinate. It should be noted that the variation of the properties (%) by dividing the characteristics (electrostatic capacity) of the actuator in which a stack deviation was caused was calculated by the corresponding characteristics of the actuator in which no stack deviation was caused. Furthermore, the letters (A) to (F) correspond to 27 the letters (A) to (F) according to 28 in which different combinations of the profile patterns of the internal electrode layers 153 and 154 are each shown. As it is in 28 (A) to 28 (F) are shown are the internal electrode layers 153 and 154 stacked with different combinations of tread patterns. In the 28 (A) to 28 (F) the left side shows a station wagon nation of the internal electrode layers 153 and 154 under ideal stacking conditions, whereas the right side is a combination of the internal electrode layers 153 and 154 with a stack deviation points.

How out 27 As a result, as the value of (outer circumference B / outer circumference A) increases, a variation of the properties can be effectively blocked. In particular, if the value of (outer circumference B / outer circumference A) is increased to 0.6 or more, that is, if the equation: B ≥ 0.6 × A is satisfied, the variation of the characteristics can be made to 5% or be reduced less. Further, if the value of (outer circumference B / outer circumference A) is set in the range of not less than 0.6 to not more than 0.75, whereby the relationship 0.6 × A ≦ B ≦ 0.75 × A is satisfied and the first internal electrode layer 153 and the second internal electrode layer 154 are constructed such that the exposed electrode portions of each of the first and second internal electrode layers 153 and 154 are not exposed on the same side surface of the piezoelectric unit, it becomes possible to further enhance the effects of avoiding the electric shorting due to creeping discharge, thereby more effectively blocking a variation in the characteristics.

Example 4

This Example is intended to explain a piezoelectric actuator, the a variation on the outer circumference having the internal electrode layer.

The piezoelectric actuator according to this example can be produced by the green sheet method in the same manner as in Example 1. The shape of the internal electrode layer formed in the piezoelectric ceramic layer is the same as the shape of the pattern E6 of Example 2 (see FIG. 8th ).

six (6) piezoelectric actuators are screen printed by changing the minimum width L and the variation width W of the recessed portion in the same Way as example 1 produced. The resulting patterns are called "patterns E11 to E16". The minimum width L and the variation width W of each pattern is shown in the table below 2 summarized.

Farther become six (6) piezoelectric actuators in the same Way as the patterns E11 to E16 produced under the condition that the size of the sieve grid (screen mesh) to form the internal electrode layers on the Starting material plate of the piezoelectric ceramic layer in the starting material plate method changed is. The resulting patterns are referred to as "patterns E11a to E16a".

As it is in 13 and 14 is the outer edge of each internal electrode layer 154 not linear, but has a waveform with some variation in each of the patterns E11 to E16 and the patterns E11a to E16a. When the width of the variation, that is, the variation width D is measured, it is 0.2 mm in all patterns E11 to E16, and is 0.4 mm in all the patterns E11a to E16a.

The Measurement of the variation of the outer edge the internal electrode layer is defined by a dimensional dimension using SEM photographs (SEM = scanning electron microscope, Scanning Electron Microscope).

table Fig. 2 shows the details of the patterns E11 to E16 and the pattern E11a to E16a.

beurteilt, Muster, die in irgendeinem Test zwischen dem 2 × 10⁸-ten Test und dem 4 × 10⁸-ten Test einen Kurzschluss erfahren, werden als O beurteilt, und Muster, die einen oder mehrere Kurzschlüsse vor den 2 × 10⁸-ten Betrieb erfahren, werden als X beurteilt. Die Ergebnisse sind in Tabelle 2 zusammengefasst.According to this example, the 4 x 10 ⁸ operation tests of the patterns E11 to E16 and the patterns E11a to E16a were performed by applying an electric voltage to each pattern in the same manner as in the example. The patterns were observed to determine whether shorts were generated during operation of the pattern or not. Patterns that have not been short-circuited in each test are called

For example, samples that short-circuit in any test between the 2 × 10 ^8th test and the 4 × 10 ⁸ th test are judged to be O, and patterns that cause one or more shorts to occur before the 2 × 10 ^{8 test} . experienced operations are assessed as X. The results are summarized in Table 2.

Table 2

As is apparent from Table 2, none of the patterns E11 to E16 and the patterns E11a to E16a showed a short circuit to the 2.0 x 10 ^8th execution of the operation, and therefore they have a high durability.

However, a short circuit occurred between the 2 × 10 ^8th and the 4 × 10 ^8th operation in the patterns E11a and E13a to E16a.

In contrast, the patterns E11, and E13 to E16 having the same minimum width L and the same variation width W as the patterns E11a and E13a to E16a but having different variation widths D do not show a short circuit up to the 4 × 10 ^8th embodiment of operation and have a higher durability.

For further investigation of these results, the results of Table 2 in 15 and 16 applied. 15 Fig. 12 shows the results of the patterns E11 to E16 in which the variation width D of the internal electrode layers is 0.2 mm.

16 Fig. 12 shows the results of the patterns E11a to E16a in which the variation width D of the internal electrode layer is 0.4 mm.

die Muster darstellt, die keinen Kurzschluss erfahren haben, O die Muster darstellt, bei denen ein Kurzschluss zwischen der 2 × 10⁸-ten Ausführung bis zu der 4 × 10⁸-ten Ausführung des Tests darstellt, und stellt X die Muster dar, die vor der 2 × 10⁸-ten Ausführung einen oder mehrere Kurzschlüsse erfahren haben.In 15 and 16 The abscissa represents the minimum width L of the recessed portion, and the ordinate represents the variation width W of the recessed portion. It should be noted that in FIG 15 and 16

represents the patterns that have not been shorted, O represents the patterns in which a short circuit between the 2 × 10 ^8th embodiment up to the 4 × 10 ^8th execution of the test represents, and X represents the patterns that represent have experienced one or more short circuits before the 2 × 10 ⁸ -th execution.

How out 15 and 16 5, the piezoelectric actuators according to this example (patterns E11 to E16 and patterns E11a to E16a) do not short-circuit even in the high number of operation passes of 2 × 10 ^8, and have excellent durability when the minimum width L of the reset Section and its variation width W within the by the dashed lines in 15 and 16 surrounded areas falls.

How, however, out 16 3, E11a and E13a to E16a undergo short circuits before the number of times of operation is increased to 4 × 10 ⁸ times.

In contrast, learn how it looks 15 ⁸ , the patterns E11, E14 and E15 do not short-circuit even to the 4 × 10 ^8th operation, since they have the same minimum width L and the same variation width W of the recessed portion as in the patterns E11a, E14a and E15a, but a variation width D of the internal electrode layer of 0.2 mm.

As From the foregoing, the durability of the piezoelectric can actuators by further holding the variation width D of the internal electrode layers be improved within 0.2 mm.

Example 5

This Example is intended to explain a piezoelectric actuator, in the distance from a boundary section between the exposed Electrode section and the reset Section of the piezoelectric unit to that on the side surface of piezoelectric unit disposed on the side of the recessed portion external electrode to at least 0.2 mm as the shortest distance along the side surface the piezoelectric unit is set.

As it is in 17 and 18 is shown in the 1 shown piezoelectric actuator 1 by arranging the internal electrode layers 153 and 154 and the external electrodes 5 and 6 on the resulting piezoelectric actuator made such that the distance c from the boundary portion 8th between the exposed electrode portion 159 that does not work with the external electrodes 5 and 6 connected and the recessed section 155 to the on the side surfaces of the piezoelectric unit 15 arranged external electrodes 5 and 6 on the side of the reset section 15 at least 0.2 mm as the shortest distance along the side surface of the piezoelectric unit 15 is the remainder of the construction the same as in the sample E8 of Example 3. This pattern is called "Pattern E17".

17 partially shows the side surface of the piezoelectric unit 15 in the piezoelectric actuator as pattern E17, and 18 shows the arrangement pattern of the internal electrode layers 153 and 154 with respect to the piezoelectric ceramic layer 151 and the external electrodes 5 and 6 in the pattern E17.

In the pattern E17, the internal electrode layer 153 connected to one of the external electrodes 5 is connected, no exposed electrode portion 158 except at the section where it connects to the external electrode 5 connected as it is in 18 is shown.

The internal electrode layer 154 connected to the other external electrode 6 is connected, has the exposed electrode sections 159 at portions other than the side surfaces on which the external electrodes 5 and 6 are shaped.

Therefore, as it is in 17 and 18 shown on a side surface other than the side surfaces on which the external electrodes 5 and 6 are exposed internal electrode layer, the internal electrode layer 154 connected to the external electrode 6 connected is.

Further, in the pattern E17, the distance c from the boundary portion 8th between the exposed electrode portion 159 that does not work with the external electrodes 5 and 6 connected and the recessed section 155 to the on the side surface of the piezoelectric unit 15 arranged electrode 5 at least 0.2 mm as the shortest distance along the side surface of the piezoelectric unit 15 ,

Thus, it becomes possible to effectively prevent the occurrence of creeping discharge on the side surfaces of the piezoelectric actuator when the internal electrode layers 153 and 154 and the external electrode layers 5 and 6 arranged as described above.

Example 6

This Example is the production of a piezoelectric actuator explain, where the outermost layer the piezoelectric unit has activity.

First, as it is in 19 is shown, the piezoelectric unit 15 similar to that prepared according to Example 1. The piezoelectric unit 15 is made by alternately stacking piezoelectric ceramic layers 151 and internal electrode layers 153 and 154 produced. An internal electrode layer becomes on the surface of the outermost layer 152 the piezoelectric ceramic layers 151 in the piezoelectric unit 15 shaped.

After that, two external electrodes 5 and 6 formed with different potentials such that they are the side surfaces of the piezoelectric unit 15 between them as it is in 20 is shown. The external electrode 5 is electrically connected to the internal electrode layer 153 connected, and the external electrode 6 is electrically connected to the internal electrode layer 154 connected.

Furthermore, the external electrode 5 a main body section 51 attached to the side surface of the piezoelectric actuator 1 is arranged, and a branching section 53 shaped to be substantially perpendicular to the main body portion 51 extends and the outermost layer 152 the piezoelectric unit 15 covered.

After that, the piezoelectric units become 15 stacked up so that when the branching sections 53 the external electrodes 5 overlap each other, and the main body sections 51 the external electrodes 5 and the external electrodes 6 be positioned on the same side surface after stacking to obtain the piezoelectric actuator. The resulting actuator is referred to as "pattern E18".

In the pattern E18 are the branch portions 53 the external electrodes 5 between piezoelectric units 15 arranged as it is in 20 is shown.

In the resulting piezoelectric actuator, the outermost layer undergoes 152 every piezoelectric unit 15 also an offset when an electrical voltage is applied, and becomes piezoelectrically active. As a result, the amount of displacement per unit length of the piezoelectric actuator in the stacking direction can be increased, and thus the piezoelectric actuator can exhibit a larger driving force.

As described above, a piezoelectric actuator (FIG. 1 ) piezoelectric units ( 15 ), each by alternately stacking a piezoelectric ceramic layer ( 151 ) and an internal electrode layer ( 153 or 154 ) are made. The piezoelectric unit ( 15 ) is by stacking not more than 50 piezoelectric ceramic layers ( 151 ) educated. The piezoelectric unit ( 15 ) has on its side surfaces a few external electrodes ( 5 . 6 ) with different potentials. The internal electrode layer ( 153 . 154 ) has an exposed electrode portion ( 158 . 159 ) located on the side surfaces of the piezoelectric unit ( 15 ) is exposed. The internal electrode layer is over the exposed electrode portion ( 158 . 159 ) with one of the pair of external electrodes ( 5 . 6 ), and the connection counterpart of the exposed electrode portion is alternately changed for each layer. A reset section ( 155 ) as a recess region of the internal electrode layer ( 153 . 154 ) that do not interfere with the side surface of the piezoelectric unit ( 15 ) is partially in an edge portion of the internal electrode layer (FIG. 153 . 154 ) shaped. A minimum width (L) of the recessed portion ( 155 ) and their variation width (W) satisfy the relationship 0.1 mm ≦ L ≦ 1.0 mm and W ≦ 0.5 mm.

Claims (12)

A piezoelectric actuator having piezoelectric units formed by alternately stacking a piezoelectric ceramic layer and an internal electrode layer, the piezoelectric unit being formed by stacking not more than 50 layers of the piezoelectric ceramic layers and having a pair of external electrodes having different potentials on the side surfaces thereof; the internal electrode layers has exposed electrode portions exposed to the side surfaces of the piezoelectric units and connected to one of the pair of external electrode layers through the exposed electrode portions, and a recessed one alternating as a connection counterpart of the exposed electrode portions for each layer Portion as a recess region of the internal electrode layer which is not to the side surface of the piezoelectric Ein and a minimum width L, which is defined as a minimum value of a distance from the side surface of the piezoelectric unit at the recessed portion to an end portion of each internal electrode layer, and a variation width W, which is defined as the difference between a maximum value and a minimum value of the distance from the side surface of each piezoelectric unit at each recessed portion to each internal electrode layer in the cross section of the piezoelectric actuator in a stacking direction satisfies the following relationship (1): 0.1 mm ≤ L ≤ 1.0 mm, W ≤ 0.5 mm (1) A piezoelectric actuator according to claim 1, wherein the minimum width L and the variation width W satisfy the following relationship (2): 0.2 mm ≤ L ≤ 0.6 mm, W ≤ 0.3 mm (2) Piezoelectric actuator with piezoelectric Units created by alternately stacking a piezoelectric Ceramic layer and an internal electrode layer produced be, where the piezoelectric unit by stacking Pair of external electrodes with different potentials at their side surfaces having, the internal electrode layers have exposed electrode sections that faces the side surfaces of the piezoelectric Units are exposed and through the exposed electrode sections connected to one of the pair of external electrode layers and the external electrode as a connection counterpart of the exposed ones Alternating electrode sections for each layer, one recessed Portion as a recess region of the internal electrode layer, not to the page surface the piezoelectric unit is extended, partially in one Edge portion of the internal electrode layer is formed, and under Assuming that one of the pair of external electrodes has a first external electrode is, the other is a second electrode, the internal electrode layer connected to the first external electrode first internal electrode layer and with the second external Electrode connected internal electrode layer a second internal Electrode layer, the first and second internal electrode layers such are built that the exposed electrode portion of the second internal electrode layer not in the portion of the piezoelectric Unit is exposed, on which the exposed electrode section the first internal electrode layer is exposed to overlap the exposed electrode portions of the first internal electrode layer to avoid with those of the second internal electrode layer, when the first and second internal electrode layers are in perspective be viewed in the stacking direction, the area of either the first or the second internal electrode layers larger than the area of the other internal electrode layer is, and a length A of an outer circumference A and a length B of an outer circumference B satisfy the relationship B ≥ 0.5 × A, where the outer circumference A the outer circumference represents a piezoelectrically active region that defines as a region in which the first internal electrode layer and the second internal one Electrode layer overlap each other, and the outer circumference B represents a section in which the internal electrode layer with the larger area of the first and second internal electrode layers on the outer periphery A the outer of the outer circumference A covers when the first and second internal electrode layers be considered in perspective in the stacking direction. A piezoelectric actuator according to claim 3, wherein the length A of the outer circumference A and the length B of the outer circumference B satisfy the relationship B ≥ 0.6 × A. Piezoelectric actuator according to claim 4, where the length A of the outer circumference A and the length B of the outer circumference B satisfy the relationship B ≤ 0.75 × A, and the exposed electrode portions of the first internal electrode layer and the exposed electrode portions of the second internal Electrode layer not on the same side surface of the exposed piezoelectric unit. Piezoelectric actuator according to one of claims 1-5, wherein the internal electrode layer is a variation on an outer edge the internal electrode layer, and a variation width D as D ≤ 0.2 mm is defined. Piezoelectric actuator according to one of claims 1 to 6, wherein the external electrode completely the exposed electrode sections covers. Piezoelectric actuator according to one of claims 1 to 7, being a distance from a boundary between the exposed Electrode section and the reset Section on the page surface the piezoelectric unit to the external electrode, on the page surface the piezoelectric unit is arranged on the side of the reset Section is at least 0.2 mm, which as shortest Distance along the side surface the piezoelectric unit is measured. Piezoelectric actuator according to one of claims 1 to 8, with a plurality of stacked piezoelectric units. Piezoelectric actuator according to claim 9, the outermost layer the stacked piezoelectric units has an activity. Piezoelectric actuator according to one of claims 1 to 10, wherein the piezoelectric ceramic layer of a PZT material is formed. Piezoelectric actuator according to one of claims 1 to 11, wherein the piezoelectric actuator for an injection device is used.