JP2850576B2 - Multilayer piezoelectric actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Utility Model Publication No. 2-27755 and 89-9696 published technical bulletin issued by the Invention Association,
A piezoelectric actuator comprising a laminate formed by alternately laminating piezoelectric pellets having a constant thickness and internal electrode plates is disclosed.

[0003]

Conventionally, when a piezoelectric actuator is used by incorporating it into a fuel injection control device of an engine, for example, an applied voltage of 400
V to 1000 V, response speed 0.1 ms to 0.5 ms, ambient temperature −40 ° C. to 150 ° C., number of repeated operations 10 ⁹
It is required to be able to withstand severe use conditions.

[0004] Here, the aforementioned Japanese Utility Model Laid-Open No. 2-27755.
In the piezoelectric actuator disclosed in Japanese Unexamined Patent Application Publication No. 89-9696, published by the Japan Institute of Invention, the thickness of each piezoelectric pellet is constant. Accordingly, the temperature of both ends and the center of the laminated body that generates heat is different from each other in the axial direction. That is, the piezoelectric pellets at both ends of the laminate have high heat dissipation efficiency because one end face facing outward is in contact with the control member or the fixing member, and the piezoelectric pellets at the central portion are
Since both end faces are sandwiched between the piezoelectric pellets laminated on both sides, the heat radiation efficiency is lower than that of the piezoelectric pellets at both end parts. For this reason, a temperature gradient occurs in the axial direction of the laminate due to the difference in heat dissipation efficiency during driving, and the temperature of the piezoelectric pellets at the center is higher than that of the piezoelectric pellets at both ends, and the amount of displacement due to elongation due to the rise in temperature is reduced. It is larger than the piezoelectric pellets at both ends, the load is increased, and cracks are liable to occur, and the durability under the above-mentioned use conditions cannot be satisfied.

[0005] Therefore, the conventional piezoelectric actuator is premised on the necessity of cooling the temperature at the central portion in the axial direction of the laminate to the same temperature as the both ends at the time of driving, and the deterioration of the durability performance. The necessity of design and the degree of freedom in design are reduced accordingly. When the number and area of the laminated piezoelectric pellets are increased in order to satisfy the durability performance, the piezoelectric actuator is increased in size and the applied voltage at the time of driving needs to be increased. Costs increase.

An object of the present invention is to provide a laminated piezoelectric actuator which solves the above problems.

[0007]

According to the present invention, there is provided a laminated piezoelectric actuator comprising a plurality of piezoelectric pellets having metal electrodes on the front and back surfaces and a plurality of internal electrode plates alternately laminated. A piezoelectric actuator that is driven by applying a voltage in the axial direction of the laminate, wherein the plurality of piezoelectric pellets are:
It is characterized in that the piezoelectric constant (d ₃₃ ) is successively reduced along the arrangement direction from both ends in the axial direction of the laminate to the center in the axial direction.

In order to form the plurality of piezoelectric pellets such that the piezoelectric constant (d ₃₃ ) decreases sequentially along the direction of arrangement from both axial ends of the laminate to the central portion in the axial direction. For example, in a plurality of piezoelectric pellets,
Among the microstructures, polarization conditions, and the like, a configuration in which at least one is changed along the arrangement direction, or the microstructure,
A configuration in which two or all of the polarization conditions are changed along the arrangement direction can be used. In addition, as the configuration in which the microstructure of the plurality of piezoelectric pellets is changed, the piezoelectric constant (d ₃₃ ) is controlled by changing the crystal grain size and porosity of the piezoelectric pellets according to the raw material pulverizing method, conditions, and the like. A method can be used.

The composition in which the composition of the plurality of piezoelectric pellets is changed includes a method of adding Sr as an additive, and a method of adding Zr.
A method of controlling the piezoelectric constant (d ₃₃ ) can be used by, for example, changing the ratio of r and Ti. As a configuration in which the polarization conditions of the plurality of piezoelectric pellets are changed,
Applied voltage, by changing the ambient temperature, the piezoelectric constant (d ₃₃₎
Can be used.

[0010]

A plurality of piezoelectric pellets used in the laminated piezoelectric actuator of the present invention have voltage constants sequentially along the arrangement direction from both ends in the axial direction of the laminate to the center in the axial direction. It is characterized in that it is configured to be small. Therefore, when a voltage is applied to the plurality of piezoelectric pellets and driven, each of the piezoelectric pellets is displaced in accordance with the piezoelectric constant (d ₃₃ ) and the temperature generated by the driving.

That is, each of the piezoelectric pellets at the time of driving is displaced in proportion to the gradient of the piezoelectric constant (d ₃₃ ) gradually decreasing along the arrangement direction, and the both ends and the center of the laminated body in the axial direction are displaced. Is displaced in proportion to the temperature gradient that sequentially increases in the arrangement direction due to the difference in heat radiation efficiency. For this reason, each piezoelectric pellet is displaced in accordance with the voltage constant (d ₃₃ ) and the temperature having gradients in opposite directions along the arrangement direction. It will be constant.

Therefore, according to the laminated piezoelectric actuator of the present invention, the temperature of the piezoelectric pellets arranged at the central portion in the axial direction of the laminate is higher than that of the piezoelectric pellets at both ends due to the difference in heat radiation efficiency during driving. Even when the temperature rises, the amount of displacement due to elongation due to the rise in temperature does not become larger than that of the piezoelectric pellets at both ends, and no excessive load acts, so that cracks can be prevented and the driving durability of the laminated piezoelectric actuator can be prevented. The nature increases.

[0013] Further, it is not necessary to cool the temperature of the central portion in the axial direction of the laminate to the same temperature as the both ends during driving.
When designing a multilayer piezoelectric actuator, it is not necessary to assume the deterioration of the durability performance as in the past, and the design conditions for securing only the initial performance are sufficient, and the degree of freedom in design is increased. That is,
Since the rate of giving a margin to the initial performance is reduced,
The number and area of the stacked piezoelectric pellets can be reduced, and driving can be performed with a low applied voltage. As a result, effects such as a reduction in power consumption of the stacked piezoelectric actuator, a reduction in cost of the power supply, and a reduction in size can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the multilayer piezoelectric actuator of the present invention will be described below. Laminated piezoelectric actuator of this embodiment
As shown in FIG. 1, which is a perspective view, the rotor includes a laminated body 1 formed by alternately laminating a plurality of piezoelectric pellets 10 and a plurality of internal electrode plates 11.

The piezoelectric pellet 10 is made of PZT ceramics and has a diameter D1 of 2 as shown in FIG.
It has a disk shape of 0 mm and a thickness t ₁ of 0.5 mm. Then, on the front surface 101 and the back surface 102 of the piezoelectric pellet 10,
Silver is printed as an electrode as shown in FIG.
The baked metal electrodes 103 and 104 are formed. The piezoelectric pellets 10 are prepared in advance of 60 pieces, each of which has a piezoelectric constant [d
₃₃ (× 10 ⁻¹² m / v) (hereinafter referred to as “d _{33” in} the description) is arranged in the arrangement direction from both ends 1 a and 1 b in the axial direction P of the laminate 1 to the central portion 1 c in the axial direction P (FIG. 1)
.

The inner electrode plate 11 as shown in FIG. 4 showing a perspective in made of SUS, diameter D2 20 mm, the thickness t ₂ is 30μm disk-shaped. On the peripheral edge of the internal electrode plate 11, a substantially inverted L-shaped lead extracting tongue 110 is formed which extends horizontally outward in the radial direction and extends downward from the tip. 61 internal electrode plates 11 are prepared in advance.

In the embodiment, the 60 piezoelectric pellets 10 are used.
As shown in FIG. 8, the piezoelectric constant (d ₃₃ ) is set to 2 in order from the both ends 1 a and 1 b (up and down directions in FIG. 1) of the laminate 1 toward the center 1 c in the axial direction P as shown in FIG. The number of sheets (up to four in the top and bottom, hereinafter referred to as area a) is 522
(D ₃₃ ), the next three sheets (six in the upper and lower directions, hereinafter referred to as “area b”) are 515 (d ₃₃ ), and the next four sheets (eight in the upper and lower parts, hereinafter, are referred to as area b).
The area c is 500 (d ₃₃ ), and the next five sheets (upper and lower 1)
0 sheets (hereinafter, referred to as an area d) is 485 (d ₃₃ ) V, and the next seven sheets (a total of 14 upper and lower sheets, hereinafter, referred to as an area e) are 480.
(D ₃₃ ), the central 18 images (hereinafter referred to as region f) are 4
70 (d ₃₃ ) is obtained.

In order to make such a setting, the microstructure of a total of 60 piezoelectric pellets 10 alternately stacked together with the total of 61 internal electrode plates 11 was changed in the arrangement direction. That is, the crystal grain size (μm) of each piezoelectric pellet 10 is such that, when driven under the conditions described later, the central portion 1c in the axial direction P is moved from both ends 1a and 1b in the axial direction P in units of 2 to 18 pieces. 11 areas a, b,
In order to obtain the piezoelectric constant (d ₃₃ ) of the above value for each of c, d, e, and f, 5 μm in the area a, 4 μm in the area b, 3.5 μm in the area c, 3 μm in the area d, and 2 μm in the area e. .
It was set to 5 μm and 2 μm in the region f (see FIG. 18).

Each of the regions a, b, c, d, e, f
The grounds for setting the piezoelectric constant (d ₃₃ ) of the piezoelectric pellet 10 for each time as described above will be described below. For example, a laminated piezoelectric actuator in which a total of 60 piezoelectric pellets 10 are laminated is applied with an applied voltage of 600 V (pulse) and a response speed of 0.2.
ms, frequency 100 Hz, pressure 20 MPa, an atmospheric temperature 135 ° C., the results of the temperature distribution of the laminate 1 was calculated by FEM (finite element method) analysis at the time of driving in the driving conditions of the repeated actuation number ¹⁰⁸ times in FIG. 7 Show.

According to this, the temperature distribution of the laminated body 1 is such that the diameter (diameter) of the area f corresponding to the central part 1c of the laminated body 1 among the eleven areas a, b, c, d, e, f (Center side)
Temperature of 112 ° C and external temperature (peripheral surface side) of 105 ° C
Is 7 ° C., but outside the region f (on the peripheral surface side).
Temperature of 105 ° C. and temperature (outer surface side) outside the area a 8
A temperature difference from 0 ° C. is achieved as high as 25 ° C. The displacement (μm, the same applies hereinafter) of each of the piezoelectric pellets 10 during driving is substantially proportional to the temperature as shown by the solid line in FIG. 9 corresponding to the temperature distribution in FIG. Therefore, in order to eliminate the stress concentration in the region f corresponding to the central portion 1c of the laminated body 1, it is necessary to uniformly displace each piezoelectric pellet 10, but the current total displacement (the displacement of each piezoelectric pellet 10) is required. In order to secure the sum of ≒ 43 μm), an average value (43 μm ÷ 60 pieces of the piezoelectric pellets 10 stacked) requires a displacement of 0.7 μm / sheet (see broken line in FIG. 9). Therefore, in the present embodiment, a piezoelectric constant (d ₃₃ ) of a value suitable for displacing 0.7 μm / sheet was estimated (formula 1 below).
reference).

As a calculation method, for example, if the multilayer piezoelectric actuator is driven under the above-mentioned driving conditions [the value of the piezoelectric constant is 500 (d ₃₃ )], the temperature of the piezoelectric pellet 10 in the region a is , 80 ° C. (see FIG. 7), and the displacement amount is 0.67 μm / sheet (see FIG. 9).
Solid line). To make it 0.7 μm / sheet, as in the following (Equation 1)

Hereinafter, similarly to the above case, an average value of 0.7 μm / sheet displacement for each temperature of each piezoelectric pellet 10 in each of the regions b, c, d, e, and f shown in FIG. 7 (see the broken line in FIG. 9). the) piezoelectric constant of suitable value to be (d _33), wherein (by substituting the amount of displacement of the piezoelectric pellet 10 corresponding to the temperature distribution of FIG. 7 in the denominator of equation 1) to (see the solid line in FIG. 9) estimates Then, 515 (d ₃₃ ) in the area b, 500 (d ₃₃ ) in the area c, 485 (d ₃₃ ) in the area d, 480 (d ₃₃ ) in the area e,
In the area f, it is 470 (d ₃₃ ).

For this reason, according to the multilayer piezoelectric actuator of the present embodiment, each region a, b, c, d, e,
Each of the piezoelectric pellets 10 corresponding to f is configured as described above. The 60 piezoelectric pellets 10 and the 61 internal electrode plates 11 are alternately stacked as shown in FIG. 5 and stacked in 60 layers. Also, each internal electrode plate 11
As shown in FIG. 6, the tongues 110 are connected together.
A cathode lead line 111 and an anode lead line 112 respectively connected to the tongue-shaped piece 110 are formed at two points on the circumference of the laminated body 1 shown in FIG. The laminate 1 is formed. And both ends 1 of the laminate 1
On a and 1b, an unillustrated insulating plate and a steel shim are laminated.
Further, a protective layer 2 is formed on the laminate 1 to cover the outer peripheral surface 12 excluding the insulating plate and the steel shim (not shown).

Next, a durability driving test was performed on the laminated piezoelectric actuator of the embodiment formed as described above under the following conditions. That is, in the multilayer piezoelectric actuator of the present embodiment, each region a, b, c, d, e,
The piezoelectric constants 522 and 51 for each of the piezoelectric pellets 10 for each f are sequentially reduced in the arrangement direction.
5, 500, 485, 480, 470 (d ₃₃ ), applied voltage 600 V (pulse), response speed 0.2 ms, frequency 1
The device was driven under the driving conditions of 00 Hz, a pressure of 20 MPa, an ambient temperature of 135 ° C., and a number of repetition operations of 3 × 10 ⁸ .

As a result, the laminated body 1 has a temperature gradient in which the temperature distribution in the axial direction is gradually increased along the arrangement direction with driving, and the temperature of the region f becomes higher than the temperature of the region a. Also, the gradient of the piezoelectric constant (d ₃₃ ) value with respect to each of the piezoelectric pellets 10 for each of the regions a, b, c, d, e, and f is inversely sequentially along the arrangement direction as shown by the solid line in FIG. Since the temperature is reduced, the elongation of each piezoelectric pellet 10 due to the temperature distribution is corrected so as to be substantially constant. Therefore, the amount of displacement of each piezoelectric pellet 10 becomes 0.7 μm, which is substantially averaged as shown by the broken line in FIG. 9, and the amount of displacement of the region f of the central portion 1 c is The displacement amount is the same as the displacement amount of the region a at both ends 1a and 1b.

Therefore, according to the multilayer piezoelectric actuator of the present embodiment, when the piezoelectric actuator is driven, the characteristic changes of the regions a and f of the multilayer body 1 and the regions a, b, c, d, e, and f, that is, Variations in displacement amount (deterioration in displacement performance) can be reduced. In addition, the load does not increase only on the piezoelectric pellets 10 in the region f.
No concentration of cracks was observed at 0. It should be noted that this is because the heat resistance (T
This is because c) and the bending strength (σ _b ) increase as the displacement amount decreases, as shown in FIGS. 11 and 12, and as in the laminated piezoelectric actuator of the present embodiment, during driving, piezoelectric pellets 10 of the most piezoelectric constant (d _{3 3)} value of the piezoelectric pellets 10 of the temperature rises region f is the area f
It is considered effective to have a gradient that is smaller than the piezoelectric constant (d ₃₃ ) value of the piezoelectric pellet 10 in the region a where the temperature is lower than the temperature.

(Comparative Example) In order to confirm the effect of the laminated piezoelectric actuator of the embodiment, the present inventor used a piezoelectric actuator disclosed in 89-9696 published technical report issued by the Japan Institute of Invention as a comparative example. A durability driving test was performed. The driving conditions were as follows.
0 (d _33), the voltage value 600V (pulse) to be applied, the response speed 0.2 ms, frequency 100 Hz, pressure 20MP
a, Cracks were generated in 30% of the piezoelectric pellets when driven at an ambient temperature of 135 ° C. and 10 ⁸ repetitions, and cracks were generated in all the piezoelectric pellets when driven 3 × 10 ⁸ times. (See FIG. 12), the displacement performance retention rate is reduced to 50%, and the displacement characteristics are greatly deteriorated (see FIG. 13). Therefore, the durability performance is not sufficient.

Further, the inventor of the present invention has investigated the location of the occurrence of cracks in the piezoelectric pellet in the piezoelectric actuator after being driven at the above-mentioned number of repetitive operations of 10 ⁸ .
It turned out that it concentrated on the piezoelectric pellet of the center part of a laminated body (refer FIG. 15). 3 × 10
It was found that the piezoelectric pellet at the center after being driven ^eight times had a higher crack generation rate than the piezoelectric pellets at both ends. This is because, as described above, the central portion in the axial direction of the piezoelectric actuator is sandwiched between both ends, so that the heat radiation efficiency is lower than that of both ends, and the temperature increases by that much, so that the central portion of the laminated body becomes higher. It is considered that stress concentration occurs in The reason for this is that the displacement performance of the piezoelectric pellet generally increases in proportion to the temperature below the Curie temperature (see FIG. 14). Therefore, when the piezoelectric pellet is driven with the same piezoelectric constant (d ₃₃ ), It is known that the higher the temperature due to heat generation, the larger the displacement, the larger the load, and the sooner the characteristics deteriorate.

When the piezoelectric actuator after the endurance driving test was disassembled and the state of occurrence of cracks in the removed piezoelectric pellets was investigated, micro-shaped cracks were generated in the piezoelectric pellets at both ends (see FIG. 16). It was found that a spider web-like crack was generated in the central piezoelectric pellet (see FIG. 17). The above-described conventional piezoelectric actuators were all the same when the piezoelectric constant (d ₃₃ ) at the time of driving acting on each piezoelectric pellet and the characteristics of each piezoelectric pellet were examined. It can be estimated that the displacement at the central part in the direction is large, the characteristics deteriorate quickly, and the crack occurrence probability is high.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a cross section of a part of a laminated piezoelectric actuator used in a driving method according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a piezoelectric pellet in FIG.

FIG. 3 is a side view showing the piezoelectric pellet in FIG.

FIG. 4 is a perspective view showing an internal electrode plate in FIG. 1;

FIG. 5 is a perspective view showing a state in which the piezoelectric pellets and the internal electrode plates shown in FIGS. 2 and 4 are stacked.

FIG. 6 is an enlarged cross-sectional view showing a part of the laminate in FIG.

FIG. 7 is an explanatory diagram showing a temperature (C °) distribution of each of the piezoelectric pellets forming the laminated body when the laminated piezoelectric actuator is driven.

FIG. 8 is an explanatory diagram showing the number of piezoelectric pellets on the vertical axis and the piezoelectric constant (d ₃₃ ) required for each piezoelectric pellet to be displaced by 0.7 μm at 600 V on the horizontal axis.

FIG. 9 is an explanatory diagram showing the number of piezoelectric pellets on the vertical axis and the displacement (μm) of the piezoelectric pellets on the horizontal axis.

FIG. 10 shows the displacement scale (d ₃₃ ) of the piezoelectric pellet on the vertical axis.
It is explanatory drawing which shows a heat resistance scale (Tc) number on a horizontal axis.

FIG. 11 shows the displacement scale (d) of the piezoelectric pellet on the vertical axis.₃₃),
The transverse axis shows the bending strength (σ _bFIG.

FIG. 12 is an explanatory diagram showing the crack occurrence rate (%) of the piezoelectric pellets on the vertical axis and the number of repetitive operations of the laminated piezoelectric actuator on the horizontal axis.

FIG. 13 is an explanatory diagram showing the displacement performance retention rate (%) of the piezoelectric pellets on the vertical axis and the number of repetitive operations of the laminated piezoelectric actuator on the horizontal axis.

FIG. 14 shows the displacement (μm) of one piezoelectric pellet on the vertical axis,
It is explanatory drawing which shows the temperature (C degrees) of a piezoelectric pellet on a horizontal axis.

FIG. 15 is a perspective view showing a crack generation portion of each of the piezoelectric pellets forming the laminate when the multilayer piezoelectric actuator is driven.

FIG. 16 is a perspective view showing a state in which micro cracks have occurred in FIG. 15;

FIG. 17 is a perspective view showing a state of occurrence of a spider web-like crack in FIG. 15;

FIG. 18 is an explanatory diagram showing the piezoelectric constant (d ₃₃ ) on the vertical axis and the crystal grain size (μm) on the horizontal axis.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laminated body 10 ... Piezoelectric pellet 11 ...
Internal electrode plate

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 41/083

Claims (1)

(57) [Claims] 1. A laminate formed by alternately laminating a plurality of piezoelectric pellets having metal electrodes on a front surface and a back surface, and a plurality of internal electrode plates, wherein the laminate is formed in an axial direction of the laminate. A piezoelectric actuator driven by applying a voltage to the laminated body, wherein the plurality of piezoelectric pellets are arranged along a direction of arrangement from both axial end portions of the laminate to a central portion in the axial direction. multilayer piezoelectric actuator, characterized in that the constant (d ₃₃₎ is configured to gradually decrease - data