DE102004007999A1 - Piezoelectric actuator for injector in IC engine of vehicle, has piezoelectric element units, each with stack of not more than 50 piezoelectric ceramic layers, and inactive bonded ceramic layers between electrode layers - Google Patents

Abstract

The piezoelectric actuator (1) has a piezoelectric unit element with piezoelectric element units (15) containing alternately stacked piezoelectric ceramic layers (151) and inner electrode layers (153,154) bonded to bond surfaces at the outermost sides to form bonded parts. Each piezoelectric element unit has a stack of not more than 50 piezoelectric ceramic layers. Bonded ceramic layers between 2 bounding inner electrode layers enclosing each bonded part are inactive.

Description

The invention relates to a piezoelectric Actuator used as a drive source for an injector, etc. becomes.

In the past, it has been proposed to use a piezoelectric element as a drive source for an injector (internal combustion engine injector) of an internal combustion engine of an automobile, etc. In particular, an injector repeatedly has to inject fuel at an extremely high speed at least 10 ⁸ times, so that an extremely hard state of use impacts the piezoelectric element as its drive source. Therefore, a piezoelectric element for an injector must not only have superior piezoelectric properties, but also superior durability.

As such a piezoelectric element becomes a stacked piezoelectric that consists of a variety of piezoelectric ceramic layers that are in accordance with the applied Shift voltage, and inner electrode layers to apply of tension, which are alternately stacked, is the most promising considered. This is because this stacked piezoelectric a great power source can result, since there is between the inner electrode layers lying piezoelectric ceramic layers move when they be supplied with voltage.

In general, the above can stacked piezoelectric by printing electrode structures or patterns on unfired ceramic plates using a conductive Paste material, overlaying tens or hundreds of them, and press bonding them, to make a stack, heating the stack to the binder to remove (degreasing), and then keep burning it become.

Furthermore, in the above stacked piezoelectric to a larger displacement of the stacked To get the piezoelectric, trials were performed to get the number stacked Increase layers. However, as the number of layers stacked increased, the problem was that not only stable production became difficult, but also when the stacked number reached nearly one hundred, the inner one Load generated when the piezoelectric element is operated becomes, so that easily Cracks appeared and the life span became shorter.

To address this problem in the prior art to solve, the method was proposed in which initially stack subunits are made from a variety of stacked together Unfired ceramic plates are made up of stacking subunits then be degreased to degreased units of the subunits manufacture, and then a variety of these degreased units stacked and burned to form a stacked piezoelectric the desired one Obtain number of layers stacked (see Japanese Unexamined Patent Publication (Kokai) No. 64-33980).

With the above stacked Piezoelectric, however, had the problem that the outermost layers of the stack subunits during the Printing the electrodes deformed and the bond surfaces of the Stack sub-units damaged were. There was also a big one Load in the stack subunits and there was a risk that in Inside the same cracks or breaks occur.

So it was stacked Piezoelectric heavy as a power source for a superior as explained above To use injector requiring durability.

The invention was made in view of these problems in the prior art and is said to address one in terms of Durability superior create piezoelectric actuator.

A first aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which is composed of piezoelectric ceramic layers and inner electrode layers alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of no more than 50 of the piezoelectric ceramic layers, and
bonded ceramic layers that lie between two adjacent inner electrode layers that enclose each bonded part between them are inactive.

The piezoelectric actuator of the first aspect of the invention, as explained above Piezoelectric unit element consisting of at least two piezoelectric Element units consist, each of which is made of piezoelectric ceramic layers and inner electrode layers that are alternately stacked and are bonded together.

Therefore, when there is tension is applied to the piezoelectric actuator, the piezoelectric Deform unit element, and drive power can be taken. Therefore, the above piezoelectric actuator can be used as a drive source for for Example an injector can be used.

Furthermore, in the above piezoelectric actuator each of the piezoelectric element units no longer from 50 stacked ceramic layers.

By the number of layers stacked each of the piezoelectric element units not larger than 50 is made, the one generated at the time of voltage application Suppressed load. Therefore it is possible the occurrence of cracks inside the piezoelectric element units at the time of applying voltage.

Furthermore, at the time of manufacture each batch of no more than 50 layers can be degreased separately. Therefore, the degreasing time is shortened and there is almost none finally binder remaining on the piezoelectric ceramic layers give. Therefore can the piezoelectric ceramic layers are sufficiently superior to their inherent ones show piezoelectric properties.

Furthermore, in the above piezoelectric actuator the bonded ceramic layers between two adjoining inner electrode layers are located enclose each bonded part between them, inactive.

Therefore, when there is tension is applied, even if the piezoelectric element units strongly deform the bonded in the piezoelectric unit element Ceramic layers that are formed even on the bonded parts are, do not deform positively, and become their extent of deformation be small.

Because of this, it is possible to prevent at the bond surfaces, to which the piezoelectric element units are bonded, when the piezoelectric actuator is manufactured, local damage occurs.

That way, it's in line with the first aspect of the invention possible one with regard to Durability superior Provide piezoelectric actuator.

A second aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which is composed of piezoelectric ceramic layers and inner electrode layers alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of no more than 50 piezoelectric ceramic layers, and
at each piezoelectric element unit, a parallelism value from one bond surface to another bond surface from the bond surfaces at both ends of the piezoelectric element unit is not higher than 0.1 mm.

With the piezoelectric actuator In the second aspect of the invention, the parallelism value of a bond surface is one other bond surface from the bond surfaces not at the two ends of each piezoelectric element unit higher than 0.1 mm.

Therefore, it is possible to prevent the occurrence of a local stress on the bond surfaces of the piezoelectric To prevent elemental units. Because of this, it is possible to get one damage to prevent the bonded parts and the durability of the improve piezoelectric actuator.

There is also the piezoelectric Actuator no longer consists of any piezoelectric element unit 50 stacked piezoelectric ceramic layers.

By the number of layers stacked each of the piezoelectric element units not larger than 50 is done in the same way as in the first Aspect of the invention generated at the time of voltage application Suppressed load. Therefore it is possible the occurrence of cracks inside the piezoelectric element units at the time of applying voltage. Furthermore, on the same manner as in the first aspect of the invention Time of making each stack from no more than 50 layers be degreased separately. Therefore, the degreasing time is shortened, and eventually there will be almost none give remaining binder to the piezoelectric ceramic layers.

A third aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which is composed of piezoelectric ceramic layers and inner electrode layers which are alternately stacked, bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of no more than 50 piezoelectric ceramic layers,
outermost ends in the stacking direction of the piezoelectric unit element have connecting elements with a modulus of elasticity greater than that of the piezoelectric element units, and
the piezoelectric unit element and the connection elements between them are provided with buffer units consisting of piezoelectric ceramic layers and inner electrode layers which are alternately stacked to buffer the internal load of the piezoelectric unit element.

The piezoelectric actuator of the third aspect of the invention has connecting elements with a Young's modulus or Young's modulus greater than that of the piezoelectric element units.

Therefore, it is possible to reduce the loss when a displacement of the piezoelectric actuator to external Transfer metal elements, etc. becomes.

They are also piezoelectric Unit element and the connecting elements between them with buffer units provided that of piezoelectric ceramic layers and inner Electrode layers, which are alternately stacked to to buffer the internal stress of the piezoelectric unit element.

Therefore, it is possible to prevent the appearance of cracks to prevent inside the piezoelectric actuator.

That is, when voltage on the piezoelectric Actuator is applied, the piezoelectric unit element expands in the stacking direction or expands and contracts in the Direction perpendicular to the stacking direction or contracts. On the other hand, the connecting elements will not deform. Therefore then when the piezoelectric unit element and the connecting elements would be directly connected the expansion and contraction of the piezoelectric unit element inhibited so that in As a result, the internal load would increase and there would be a risk of cracks occur.

By interposing buffer units between the piezoelectric element units and the connecting elements in this way it is possible to suppress the increase in internal stress and the occurrence of Suppress cracks. Therefore, the piezoelectric actuator is superior in durability.

It is noted that the extent of the shift using a laser displacement meter, one after the principle of electrostatic capacity working displacement meter, etc. can be measured.

A fourth aspect of the invention provides a piezoelectric actuator having a unit piezoelectric element composed of at least two unit piezoelectric elements, each of which is composed of piezoelectric ceramic layers and inner electrode layers which are alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of no more than 50 piezoelectric ceramic layers,
outermost ends in the stacking direction of the piezoelectric element element have connection elements with a modulus of elasticity greater than that of the piezoelectric element units, and
the piezoelectric unit element and the connecting elements between them are provided with dummy units which have a modulus of elasticity smaller than that of the connecting elements.

The piezoelectric actuator of the fourth aspect of the invention points in the same way as the third aspect of the invention connecting elements with a modulus of elasticity larger than that of the piezoelectric element units.

Therefore, it is the same way and Way as possible in the third aspect of the invention to reduce the loss, when a displacement of the piezoelectric actuator to external Transfer metal elements, etc. becomes.

They are also piezoelectric Unit element and the connecting elements between themselves with dummy or blind units with a modulus of elasticity smaller than that of Provide fasteners.

Therefore, it is possible to increase the inner Suppress stress at the time of application of voltage, and to suppress the occurrence of cracks.

That is, as explained above when voltage is applied to the piezoelectric actuator, it expands the piezoelectric unit element in the stacking direction or expands and contracts in the direction perpendicular to that Stack direction or contracts. At that time, if the modulus of elasticity the connecting elements would be larger than that modulus of elasticity of the piezoelectric unit element, the expansion and the contraction of the piezoelectric unit element inhibited, so that as a result the internal burden would increase and there is a danger that cracks occur.

By inserting blind units with a modulus of elasticity smaller than that of the connecting elements between the connecting elements and the piezoelectric unit element in this way Is it possible, suppress the increase in internal stress, and the occurrence of Suppress cracks. Therefore, the piezoelectric actuator is superior in durability.

A fifth aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which is composed of piezoelectric ceramic layers and inner electrode layers which are alternately stacked, bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of at least six piezoelectric ceramic layers, and
bonded ceramic layers that lie between two adjacent inner electrode layers that enclose each bonded part between them are inactive.

With the piezoelectric actuator the fifth Aspects of the invention are in the same manner as in the third aspect of the invention is the bonded ceramic layers that lie between two adjacent electrode layers that enclose each bonded part between them, inactive.

Therefore, when there is tension is created in the same way as in the first aspect of the invention, even if the piezoelectric element units strongly deform the bonded in the piezoelectric unit element Ceramic layers that are formed even on the bonded parts are, do not deform positively, and become their extent of deformation be small. Because of this, it is possible to prevent a local damage on the bond surfaces occurs on which the piezoelectric element units are bonded are when the piezoelectric actuator is manufactured.

There is also the fifth aspect of the invention each piezoelectric element unit from at least six piezoelectric ceramic layers. If the number of stacked Layers of each piezoelectric element unit is six or larger, will the extent of Displacement of the bonded ceramic layers become large, and easily becomes one local damage on the bond surfaces occur. In the fifth Aspects of the invention, however, as explained above, the bonded ceramic layers become inactive so that it is possible for an occurrence to occur damage on the bond surfaces to suppress. This means, that then if six or more piezoelectric ceramic layers like that fifth Aspect of the invention are present, the effect of suppressing the Occurrence of damage, which is obtained by rendering the bonded ceramic layers inactive is becoming stronger can be obtained remarkably.

The other effects are similar to those of the first aspect of the invention.

A sixth aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which consists of piezoelectric ceramic layers and inner electrode layers alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of at least six piezoelectric ceramic layers, and
at each piezoelectric element unit, a parallelism value from one bond surface to another bond surface from the bond surfaces at both ends of the piezoelectric element unit is not higher than 0.1 mm.

With the piezoelectric actuator of the sixth aspect of the invention is in the same way as in the second aspect of the invention, the parallelism value is one bonding surface to another bond surface from the bond surfaces at both ends of each piezoelectric element unit not higher than 0.1 mm.

Therefore, it is in the same way and Way as in the second aspect of the invention, possible Occurrence of local stress on the bond surfaces of the to prevent piezoelectric element units. Because of that Is it possible, damage to prevent the bonded parts and the durability of the improve piezoelectric actuator.

In the sixth aspect of the invention each piezoelectric element unit consists of at least six piezoelectric ceramic layers. If the number of stacked Layers of each piezoelectric element unit is six or larger, will the extent of Deformation of the bonded ceramic layers becomes large and easily a local damage on the bonded surfaces occur. In the sixth aspect of the invention, however, is how explained above was the parallelism value a bond surface to another bond surface from the bond surfaces not at the two ends of each piezoelectric element unit higher than 0.1 mm so that it possible is the occurrence of damage on the bond surfaces to suppress. This means, that then if six or more piezoelectric ceramic layers like that sixth aspect of the invention, the effect of suppressing the Occurrence of damage, that by not higher making the parallelism value of the bond surfaces than 0.1 mm is obtained, stronger can be obtained remarkably.

The other effects are similar to those of the second aspect of the invention.

A seventh aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which is composed of piezoelectric ceramic layers and inner electrode layers alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of at least six piezoelectric ceramic layers,
outermost ends in the stacking direction of the piezoelectric element element have connection elements with a modulus of elasticity greater than that of the piezoelectric element units, and
the piezoelectric unit element and the connection elements between them are provided with buffer units consisting of piezoelectric ceramic layers and inner electrode layers which are alternately stacked to buffer the internal load of the piezoelectric unit element.

The piezoelectric actuator of the seventh aspect of the invention points in the same way as in the third aspect of the invention, connection or Connecting elements with a modulus of elasticity greater than that of the piezoelectric Element units.

Therefore, it is in the same way and Way as in the third aspect of the invention, possible Reduce loss when a shift of the piezoelectric Actuator is transferred to external metal elements, etc.

Furthermore, in the same way and Way as in the third aspect of the invention, the piezoelectric unit element and provide the connecting elements between them with buffer units, that of piezoelectric ceramic layers and inner electrode layers consist of, which are alternately stacked to the internal load buffer the piezoelectric unit element.

Therefore, it is in the same way and Way as in the third aspect of the invention, possible that Occurrence of cracks inside the piezoelectric actuator to prevent.

In the seventh aspect of the invention each piezoelectric element unit consists of at least six piezoelectric ceramic layers. If the number of stacked Layers of each piezoelectric element unit six or more is the extent of Displacement of the ceramic layers on the outermost sides of each piezoelectric Element unit in the stacking direction, that is, the outermost ceramic layers, become large. Therefore then when the piezoelectric unit element with for example another element, such as a connecting element, would be bonded there is a risk that a local damage on the bond surfaces occurs. However, in the seventh aspect of the invention are as above explained has been interposed, so that it is possible to indicate the occurrence of damage the bond surfaces to suppress and to improve the durability of the piezoelectric actuator.

The other effects are similar to those of the third aspect of the invention.

An eighth aspect of the invention provides a piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each composed of piezoelectric ceramic layers and inner electrode layers alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts, characterized in that
each piezoelectric element unit consists of a stack of at least six piezoelectric ceramic layers,
outermost ends in the stacking direction of the piezoelectric element element have connection elements with a modulus of elasticity greater than that of the piezoelectric element units, and
the piezoelectric unit element and the connecting elements between them are provided with dummy units which have a modulus of elasticity greater than that of the connecting elements.

The piezoelectric actuator of the eighth aspect of the invention, in the same manner as that of the fourth aspect of the invention, connecting elements with a modulus of elasticity larger than the piezoelectric element units.

Therefore, it is in the same way and Way as in the fourth aspect of the invention, possible Reduce loss when a shift of the piezoelectric Actuator is transferred to external metal elements, etc.

Furthermore, in the same way and Way as in the fourth aspect of the invention, the piezoelectric Unit element and the connecting elements between them with dummy units with a modulus of elasticity provided smaller than the connecting elements.

Therefore, it is in the same way and Way as in the fourth aspect of the invention, possible Increase in internal stress at the time voltage is applied to suppress, and possible to suppress the occurrence of cracks.

In the eighth aspect of the invention each piezoelectric element unit consists of at least six piezoelectric ceramic layers. If the number of stacked Layers of each piezoelectric element unit is six or larger, will the extent of Displacement of the ceramic layers on the outermost sides of each piezoelectric Element unit in the stacking direction, that is, the outermost ceramic layers, become large. Therefore then when the piezoelectric unit element with for example another element, such as a connecting element, is bonded, there is a risk of local damage the bond surfaces occurs. However, in the eighth aspect of the invention are as above explained has been interposed, so that it is possible to prevent the occurrence of a damage on the bond surfaces to suppress and to improve the durability of the piezoelectric actuator.

The other effects are similar to those of the fourth aspect of the invention.

The invention is set out below Reference to the drawing in more detail described. Show it:

1 a disassembled explanatory view of a piezoelectric actuator according to an example 1;

2 a sectional view in which the piezoelectric actuator according to Example 1 is cut in a plane parallel to its stacking direction in slices;

3 an enlarged view showing the state near a bonded part of the in 2 piezoelectric actuator shown;

4 an explanatory view of the state of printing an inner electrode layer on a green ceramic plate according to Example 1;

5 an explanatory view of the state of stacking green sheets formed with inner electrode layers according to Example 1;

6 an explanatory view of a stack according to Example 1;

7 a perspective explanatory view showing a piezoelectric element unit according to Example 1;

8th 11 is an explanatory view related to the parallelism value of the bond surfaces of a piezoelectric element unit according to Example 1;

9 a first explanatory view showing the stacked state of piezoelectric ceramic layers in a buffer unit according to Example 1;

10 a second explanatory view showing the stacked state of piezoelectric ceramic layers in a buffer unit according to Example 1;

11 a third explanatory view showing the stacked state of piezoelectric ceramic layers in a buffer unit according to Example 1;

12 a fourth explanatory view showing the stacked state of piezoelectric ceramic layers in a buffer unit according to Example 1;

13 11 is an explanatory view showing the state near a bonded part of a piezoelectric actuator according to Example 1 with resin insulation layers on the bonded parts;

14 (A) and (B) each is an explanatory view showing the shapes of inner electrode layers formed on piezoelectric ceramic layers according to Example 1;

15 (A) and (B) each is an explanatory view showing inner electrode layers of a full electrode structure formed on piezoelectric ceramic layers according to Example 1;

16 11 is an explanatory sectional view showing the state near a bonded part of a piezoelectric actuator with inner electrode layers of full electrode structures according to Example 1;

17 Fig. 11 is an explanatory view showing the state near a bonded part of a piezoelectric actuator where two adjacent inner electrode layers sandwiching a bonded part between them are connected to electrodes of the same polarity according to Example 2;

18 a partially enlarged view of a bonded part of a piezoelectric element unit according to Example 2;

19 11 is an enlarged explanatory view showing the state near a bonded part of a piezoelectric actuator according to an example 3 configured to increase the thicknesses of the outermost ceramic layers;

20 a perspective explanatory view showing piezoelectric element units according to Example 3;

21 Fig. 11 is an explanatory view showing the relationship between the number of layers of piezoelectric ceramic layers stacked and the stress occurring within a piezoelectric element unit;

22 11 is an explanatory view showing the relationship between the electric field strength of bonded ceramic layers with respect to the coercive electric field of the unit piezoelectric element and a piezoelectric constant of the bonded ceramic layers;

23 an explanatory view showing the relationship between the electric field strength and the amount of displacement of the unit piezoelectric element; and

24 11 is an explanatory view showing the relationship between the parallelism value of the bond surfaces of a piezoelectric element unit and an internal load.

The invention is by reference to the preferred embodiments closer to it described. However, it is noted that the invention does not apply to this embodiments limited is.

In the above first to fourth Aspects of the invention existed in any piezoelectric element unit from no more than 50 stacked piezoelectric ceramic layers.

Here are the results of finding the relationship between the number of stacked layers of the piezoelectric ceramic layers and that inside of a piezoelectric element unit by Si mulation in 21 shown.

The simulation was done by a piezoelectric Analysis performed using the finite element method.

As in 21 is shown, the greater the number of layers stacked, the greater the stress generated in the unit. In particular, with over 50 layers, a large internal stress is generated at the time voltage is applied. As a result, there is a fear that cracks or breaks occur in the piezoelectric element unit.

Furthermore, in the fifth to eighth aspects of the invention each piezoelectric element unit at least six stacked piezoelectric ceramic layers.

If the number of layers stacked of the piezoelectric ceramic layers is less than six the extent of Deformation or deformation per piezoelectric element unit smaller. So it would be around a sufficient displacement generating piezoelectric To get the actuator, necessary a larger number of piezoelectric To bond element units. This would not only cause the overall length to decrease the bonding increases, but would also result in the fact that Thickness in the stacking direction per piezoelectric element unit becomes smaller, handling becomes more difficult, the production process becomes more laborious, and production costs would also increase.

Next, the piezoelectric Element units are bonded using an adhesive. As such Binder can for example a silicone-based, an epoxy-based, a urethane-based, a Polyimide-based, or another adhesive can be used.

Furthermore, it is in the first aspect and in the fifth Aspect of the invention preferred that the two be contiguous inner electrode layers that have a bonded portion between them to lock myself in, be connected to external electrodes of different potentials and that the electric field strength (Field intensity) of bonded ceramic layers is not larger than the coercive electric field of the piezoelectric element units.

In this case, the bonded ceramic layers can be made essentially inactive.

Here are the results of finding the relationship between the electric field strength of bonded ceramic layers with respect to the coercive electric field of the piezoelectric element units and the piezoelectric constant of the bonded ceramic layers by experiments in FIG 22 shown.

In the figure, the abscissa shows the electric field strength of the bonded ceramic layers in relation to the coercive electrical Field of the piezoelectric unit element [(electrical field strength of bonded ceramic layers) / (coercive electric field of the piezoelectric unit element)], while the Ordinate the piezoelectric constant of the bonded ceramic layers shows.

How out 22 As can be seen, when the electric field strength of the bonded ceramic layers exceeds the coercive electric field of the piezoelectric unit element, the piezoelectric constant of the bonded ceramic layers will become larger. This means that this shows that the ceramic layers become active. Furthermore, in this case, the bonding surfaces of the piezoelectric element units are easily damaged at the time of operation.

Furthermore, the electric field strength is bonded ceramic layers stronger preferably not more than 0.8 times the coercive electrical Field of the piezoelectric unit element.

In this case, how 22 it can be seen that the piezoelectric constant of the bonded ceramic layers become almost zero, and the bonded ceramic layers will become inactive in their state.

Next up is the coercive electrical field explained.

23 Fig. 3 is an explanatory view of the coercive electric field (Ec). The figure shows the electric field strength applied to the unit piezoelectric element on the abscissa and the amount of displacement on the ordinate. It is noted that the electric field strength is given as a plus (+) for the same direction as the polarization direction and as a minus (-) for the direction opposite to the polarization direction.

Furthermore, starting at the point A first the electric field strength to the piezoelectric unit element in the same direction as polarization direction and slowly increased in value. Along with this, the amount of displacement of the piezoelectric increases Unit elements too. It is noted that the amount of shift by measurement the shift in the stack direction when creating a constant Tension and use the shift per unit length in the stacking direction at that time as the extent of Displacement can be determined. This amount of shift can be under Use of a laser displacement meter, one based on the electrostatic capacitance principle working displacement meter, etc. can be measured.

Next, after the electric field strength reaches point B, the electric field strength is slowly decreased. This time, the amount of the shift drops along with the drop in the electric field strength. Even after the electric field strength becomes 0, the electric field strength is slowly reduced in the direction opposite to the polarization direction. This coincides with the extent of Shift further down. Further, when the electric field strength reaches the point C, the amount of the shift suddenly increases. The absolute value of the electric field strength at this point is the coercive electric field in the present invention.

Next, if the electric field strength reached point D, the electric field strength increased again. Together with this falls this time the extent of Shift from. It also begins when the electric field strength becomes 0 and the electric field strength is further increased in the direction of polarization, the amount of shift suddenly increase. Because between point D and point C different Cases exist according to the invention, the coercive electric field when voltage in the direction of polarization opposite direction is made to Ec.

It is noted that as in 23 shown by subsequently further increasing the electric field strength, a state is reached which is essentially the same as that at point B, and then a similar behavior is subsequently repeated.

If the electric field strength of the bonded ceramic layers is larger as the coercive electric field of the piezoelectric unit element, there is a risk; that the bonded ceramic layers shift and the bond surfaces to Damage time of voltage application.

Next, two are preferred contiguous inner electrode layers that bond one Include part between them connected to external electrodes of different potentials, is an electric field strength bonded ceramic layers larger than a coercive electric field of the piezoelectric element units, and a bonded part has a resin insulation layer.

In this case it allows the resin insulation layer, the actual electric field strength, the is applied to the bonded ceramic layers, smaller than that to make coercive electric field. Therefore, it is easily possible to make bonded ceramic layers inactive.

The resin insulation layer can be, like explained above by bonding the piezoelectric element units by means of for example a silicone-based, an epoxy-based, a Urethane-based, a polyimide-based, or another Glue are generated.

Next, two are preferred contiguous inner electrode layers that bond one Include part between them connected to external electrodes of substantially the same potential.

In this case, too, if the bonded ceramic layers are damaged, possible short circuits on the to prevent bonded parts. Furthermore, it is easy in this case possible, to make the bonded ceramic layers inactive in their state.

Also preferred are bonded to one Part of bond surfaces the piezoelectric element units partly in direct contact, and the bonded part has a resin layer.

In this case it is possible to Loss of displacement and force generated on the bonded part to reduce. The resin insulation layer can be made by bonding the piezoelectric Element units using, for example, a silicone-based one Epoxy-based, a urethane-based, a polyimide-based, or another adhesive.

Next is in the sixth Aspect of the invention and the sixth aspect of the invention a parallelism value bonding surface to another bond surface from the bond surfaces at both ends of the piezoelectric element unit not higher than 0.1 mm.

Here, the relationship between the parallelism value of bond surfaces and the stress generated near the surfaces (bonded part) of the piezoelectric element unit is in 24 shown. The figure shows the parallelism value of the bond surfaces on the abscissa and the stress generated on the ordinate near the surfaces (bonded part) of the piezoelectric element unit.

As in 24 is shown, as the parallelism value of the bond surfaces becomes larger, the stress occurring near the surfaces (bonded part) of the piezoelectric element unit becomes larger.

As can be seen from the figure becomes when the parallelism value of the bond surfaces not higher than 0.1 mm, the load occurring in the units is extremely small. Therefore it is possible damage on the bond surfaces prevent further.

It is noted that the parallelism value is in agreement can be measured using the method defined in JIS-B0621-1984 can.

Furthermore, the piezoelectric Actuators of the third aspect of the invention, the fourth aspect of the Invention, the seventh aspect of the invention, and the eighth aspect the invention connection or connecting elements with a Young's module or elastic modulus larger than that of the piezoelectric element units as described above has been.

As such fasteners exist for example those made of aluminum oxide, silicon carbide, aluminum nitride, Boron nitride, etc. are made.

The modulus of elasticity can be measured using the method defined in JIS-R1602-1995. However, if the specified test specimen form cannot be obtained or manufactured, it is possible to un Using a sample obtained by cutting a connector and a piezoelectric element unit to the same shape and comparing them, to perform a test similar to the JIS standard.

Furthermore, the piezoelectric Actuators of the third aspect of the invention and the seventh aspect the invention, the piezoelectric unit element and connecting elements between them with buffer units made of piezoelectric Ceramic layers and inner electrode layers are made up alternately are stacked to the internal stress of the piezoelectric unit element buffering.

The piezoelectric ceramic layers of the buffer units can using materials similar to those of piezoelectric Ceramic layers made in the piezoelectric element units become.

Each buffer unit consists of piezoelectric ones Ceramic layers and inner electrode layers, in the same way and way like the piezoelectric element units. As a certain Process for buffering the internal stress in the piezoelectric Unit element it is possible the thicknesses of the piezoelectric ceramic layers in the buffer units larger than that of the piezoelectric ceramic layers in the piezoelectric To make elemental units. It is also possible to use piezoelectric materials with smaller piezoelectric constants than that of the piezoelectric To use element units to make the buffer units or the voltage applied to the buffer units versus the voltage applied to the piezoelectric element units to reduce.

It is also possible to use the buffer units and the piezoelectric unit element by means of a resin binder to bond. The force of a resin binder is smaller, so that too in this case the effect of the interposition of the buffer units can be obtained sufficiently.

Next is the modulus of elasticity of the connecting elements at least twice the elastic modulus of the piezoelectric element units.

If the modulus of elasticity the connecting elements is less than twice the elastic modulus of the piezoelectric element units, it could be when the shift of the piezoelectric actuator is transmitted to the outside, become impossible the loss of displacement and generated force between the piezoelectric Actuator and the outside Reduce metal element etc. sufficiently.

Next, the extent of the shift is preferred per unit length a buffer unit smaller than the amount of displacement per unit length of piezoelectric element unit on the connector side and substantially the same as the amount of displacement per unit length of the piezoelectric Unit elements on the piezoelectric unit element side.

In this case it is possible that Occurrence of cracks or breaks prevent more effectively inside the piezoelectric actuator.

As a certain means of doing of extent the displacement per unit length a buffer unit smaller than that of the piezoelectric element unit on the side of the connecting element and essentially to the same like that of the piezoelectric unit element on the side of the For example, piezoelectric unit elements are as follows Method.

This means that this can be achieved be that the Thicknesses of the piezoelectric ceramic layers inside the buffer unit to substantially the same thickness as that of the piezoelectric Ceramic layer of the piezoelectric unit element on the side of the piezoelectric unit element, and larger than that of the piezoelectric ceramic layers of the piezoelectric Element units are made on the side of the connecting element.

Furthermore, this can be considered another Procedure while the manufacture of the buffer unit by using a piezoelectric Material with a smaller piezoelectric constant than that of the piezoelectric ceramic layers of the piezoelectric element units for the piezoelectric ceramic layers of the connecting element side and Using a piezoelectric material with a piezoelectric constant substantially the same as that of the piezoelectric ceramic layers of the piezoelectric element units for the piezoelectric ceramic layers the side of the piezoelectric unit element to the buffer units to manufacture, to be realized. Furthermore, this can be done by reducing the applied to the side of the connecting element of the buffer unit Tension towards that applied to the side of the piezoelectric unit element Tension can be realized.

Furthermore, in the fourth aspect of the invention and in the eighth aspect of the invention the piezoelectric Unit element and connecting elements between them with dummy units with a modulus of elasticity smaller than that of the connecting elements.

The modulus of elasticity can be measured using the method defined in JIS-R1602-1995. However, if the specified test specimen shape cannot be obtained, it is possible to perform a test similar to the JIS standard by using a specimen obtained by cutting a connector and a dummy unit to the same shape and comparing them to lead.

It is also possible to use the dummy units and the piezoelectric unit element by means of a resin binder bonding. The force of a resin binder is smaller, so that too in this case the effect of the interposition of the blind units can be obtained sufficiently.

Furthermore, the piezoelectric unit element and the connecting elements both buffer units and dummy units have, which are placed between them. In this case Piezoelectric unit element, the buffer units, the dummy units and the connection members are bonded by the above resin binder.

The modulus of elasticity is preferably of the connecting elements at least twice the elastic modulus of the piezoelectric element units and dummy units.

If the modulus of elasticity the connecting elements is less than twice the elastic modulus of the piezoelectric element units and dummy units, it could then when the displacement of the piezoelectric actuator is after transmitted outside becomes impossible the loss of displacement and force generated between the piezoelectric actuator and the external metal element etc. to reduce sufficiently.

Each blind unit is preferably present made of a ceramic material that is the same as that of a piezoelectric Ceramic layer of the piezoelectric element units.

In this case, it won't just easy to manufacture the blind units, but also the modulus of elasticity of the dummy units is substantially the same as that of the piezoelectric ones Elemental units are made so that even if there are cracks in the blind units starting from the side of the connecting element occur, possible is effective the progression of the cracks to the piezoelectric To prevent elemental units.

The blind units are preferred and the piezoelectric unit element between them with buffer units provided that of piezoelectric ceramic layers and inner There are electrode layers that are alternately stacked to buffer the internal stress of the piezoelectric unit element, and is the extent of Displacement per unit length a buffer unit smaller than the amount of displacement per unit length of piezoelectric element unit on the side of the dummy unit and substantially the same as the amount of displacement per unit length of piezoelectric unit elements on the side of the piezoelectric Unit element.

In this case it is possible that Occurrence of cracks inside the piezoelectric actuator more effectively to prevent.

As a certain means of doing of extent the displacement per unit length a buffer unit smaller than that of the piezoelectric element unit on the side of the dummy element and essentially to the same like that of the piezoelectric unit element on the side of the For example, piezoelectric unit elements are as follows Method.

This means that this can be achieved be that the Thicknesses of the piezoelectric ceramic layers inside the buffer unit to substantially the same thickness as that of the piezoelectric Ceramic layer of the piezoelectric unit element on the side of the piezoelectric unit element, and larger than that of a piezoelectric ceramic layer of a piezoelectric Element unit are made on the side of the blind unit.

Furthermore, this can be considered another Procedure while the manufacture of the buffer unit by using a piezoelectric Material with a smaller piezoelectric constant than that of the piezoelectric ceramic layers of the piezoelectric element units for the piezoelectric ceramic layers on the side of the dummy unit and Use a piezoelectric material with a piezoelectric Constants are substantially the same as those of the piezoelectric ceramic layers of the piezoelectric element units for the piezoelectric ceramic layers the side of the piezoelectric unit element to the buffer units to manufacture, to be realized. Furthermore, this can be done by reducing the voltage applied to the side of the dummy unit of the buffer unit across from that applied to the side of the piezoelectric unit element Tension can be realized.

Furthermore, in the third and the fourth aspect of the invention does not prefer any buffer unit from more than 50 stacked piezoelectric ceramic layers, and are the ceramic layers on the outermost sides of the buffer unit in the stacking direction, that is the outermost Ceramic layers, inactive.

As in the case of a piezoelectric element unit, the load occurring in a buffer unit becomes greater the greater the number of layers of the piezoelectric ceramic layers stacked. In particular, with more than 50 layers, a large internal stress is generated at the time of applying voltage, so that there is a risk that cracks occur in the piezoelectric element unit. Furthermore, when the ceramic layers on the outermost sides of each buffer unit in the stacking direction, that is, the outermost ceramic layers, are not inactive, that is, active, at the time of the application of voltage, there is a danger that the ceramic layers that are adjacent between two inner electrode layer are positive that deform each bonded part between them, and there is a risk that the bonded parts between the buffer units and the piezoelectric element units, connecting elements or dummy units are damaged.

Furthermore, in the seventh and the eighth aspect of the invention prefers each buffer unit from at least six stacked piezoelectric ceramic layers, and are the ceramic layers on the outermost sides of the buffer unit in the stacking direction, that is the outermost Ceramic layers, inactive.

If the number of layers stacked of the piezoelectric ceramic layers in a buffer unit smaller is six, the thickness in the stacking direction per buffer unit small, so the Handling becomes more difficult, the production process becomes more laborious, and there is also a risk that the Production costs increase. Furthermore, if there is currently the voltage on the ceramic layers on the outermost sides each buffer unit in the stacking direction, that is, the outermost Ceramic layers, are not inactive, that is, are active, the risk that itself the ceramic layers that are adjacent between the two inner electrode layers that lie between each bonded part to lock myself in, deform positively, and there is a risk that the bonded parts between the buffer units and the piezoelectric element units, Fasteners or dummy units are damaged.

Furthermore, in the seventh and According to the eighth aspect of the invention, each buffer unit does not prefer more than 50 stacked piezoelectric ceramic layers.

If the number of piezoelectric Ceramic layers in a buffer unit exceeds 50, is on the same Way as in a piezoelectric element unit internal stress occurring in the buffer unit increases and becomes a great inner one at the time of applying tension Load are generated so that the There is a risk of cracks occur in the piezoelectric element unit.

Next, each is preferred Piezoelectric element unit made up of not more than 50 stacked together piezoelectric ceramic layers.

As explained above becomes when the number of stacked layers of the piezoelectric ceramic layers in a piezoelectric element unit exceeds 50, a large inner one Stress occurs at the time voltage is applied and persists consequently the risk of cracks occur in the piezoelectric element unit.

Next it will be in the first to eighth aspects of the invention preferred that the thicknesses of the ceramic layers at the extreme Sides of the piezoelectric element units in the stacking direction, this means the outermost Ceramic layers, at least the thickness of one between inner electrode layers ceramic layer placed in the piezoelectric element units, this means a drive ceramic layer.

In this case it is possible that Extent of Deformation of the outermost Suppress ceramic layers, so that it possible is damage of the bond surfaces to suppress the piezoelectric element units further.

Furthermore, according to the invention, there is any piezoelectric Ceramic layer preferably made of a PZT-based material.

In this case, it is possible to make good use of the superior property of the above PZT material [generic name for an oxide of a Pb (Zr, Ti) O ₃ based perovskite structure] as a piezoelectric in order to perform as an actuator of an injector etc. to improve.

As the inner electrode layer Is it possible, to use a metal containing at least one of Ag, Pd, Pt, Cu and includes Ni or an alloy thereof.

Furthermore, the above piezoelectric Actuators preferred for Injectors or injectors used.

In this case, the superior Durability of the piezoelectric actuators shown sufficiently become.

The invention is by reference further described on their examples. However, it is noted that the Invention is not limited to these examples.

example 1

Next, the piezoelectric actuator according to an embodiment of the invention using the 1 to 16 explained.

The piezoelectric actuator 1 this example consists of at least two piezoelectric element units 15 each made of piezoelectric ceramic layers 151 and inner electrode layers 153 and 154 that are alternately stacked as in 7 and on the surfaces on the outermost sides in the stacking direction, that is, the bond surfaces 155 , are bonded to the bonded parts as in 1 to 3 shown to generate. Each piezoelectric element unit 15 consists of no more than 50 of the stacked piezoelectric ceramic layers 151 , The bonded ceramic layers 115 which are between two adjacent inner electrode layers 153 and 154 lying and on both sides of a bonded part 13 are inactive.

Next, a piezoelectric actuator of this example is made using the 1 to 3 explained in detail.

As in the 1 to 3 is shown, the piezoelectric actuator (sample E1) 1 of the present example, a bonded piezoelectric unit element 11 on that from 20 piezoelectric element units 15 consists of bonded parts 13 are bonded. Each piezoelectric element unit 15 consists of alternately stacked piezoelectric ceramic layers 151 , which consist of a PZT-based material, and inner electrode layers 153 and 154 consisting of Ag and Pd. For the sake of convenience in creating the figures, the figures do not show the details but the number of stacked layers of the active piezoelectric ceramic layers 151 that act as piezoelectric elements in each piezoelectric element unit 15 to 20 serve.

Each of the electrode layers 153 and 154 is designed so that it has only one side surface of the piezoelectric ceramic layers 151 reached. Furthermore, the side surfaces of each piezoelectric element unit 15 with external electrodes 5 and 6 provided, which consist of Ag and are connected to external power sources with different potentials that they are on both sides of the same. On the side surfaces of each piezoelectric element unit 15 are the inner electrode layers 153 and 154 alternately electrically with the external electrodes 5 and 6 connected in the stacking direction. Therefore, there are two adjacent inner electrode layers in the piezoelectric actuator 153 and 154 connected to external electrodes with different potentials.

Furthermore, as in 1 and 2 is shown, the piezoelectric actuator 1 In this example, fasteners made from alumina 5 with a larger modulus of elasticity than the piezoelectric element units 15 at the extreme ends of the piezoelectric unit element 11 in the stacking direction.

The piezoelectric unit element 11 and fasteners 4 have buffer units 2 placed between them for buffering the internal load on the piezoelectric unit element 11 and non-powered dummy units 3 with a modulus of elasticity smaller than that of the connecting elements. The buffer units 2 and the blind units 3 consist of a PZT-based material, which is the same as that of the piezoelectric ceramic layers 151 of the piezoelectric element units 15 ,

Each buffer unit 2 consists, as in 1 . 2 and 9 is shown, made of piezoelectric ceramic layers 151 and inner electrode layers 253 and 254 , In each buffer unit is the thickness of a piezoelectric ceramic layer active as a piezoelectric element 251 essentially the same as that of a piezoelectric ceramic layer 151 in a piezoelectric element unit 15 on the side of the piezoelectric unit element 11 , and is larger than that of a piezoelectric ceramic layer 151 in a piezoelectric element unit 15 on the connector side. Each buffer unit also has 2 external electrodes 5 and 6 on the side surfaces of the buffer unit in the same manner as in a piezoelectric element unit 15 enclose between themselves. These external electrodes 5 and 6 are with the inner electrode layers 253 and 254 connected.

Furthermore, as in 1 and 2 each blind unit is shown 3 made of piezoelectric ceramic layers similar to the piezoelectric ceramic layers 151 in a piezoelectric element unit 15 and the piezoelectric ceramic layers 251 in a buffer unit 2 , but has no inner electrode layers like a piezoelectric element unit 15 and a buffer unit 2 on.

Next, the method of manufacturing a piezoelectric actuator according to this example is described using the 1 to 9 explained.

The piezoelectric actuator of this example can be produced using the widely used green sheet method. The unfired plates are prepared as follows:
That is, first of all, a known method is used to weigh powder of zinc oxide, zirconium oxide, titanium oxide, niobium oxide, strontium carbonate, etc., which are the main ingredients of the piezoelectric material, to obtain a desired composition. In this example this is done so that the final composition becomes PZT (lead zirconate titanate). Furthermore, taking lead evaporation into account, the materials are prepared to be 1 to 2% richer than the stoichiometric ratio of the composition. These materials are mixed dry using a mixer and then calcined at 800 to 950 ° C.

Next is the calcined Pure water powder and a dispersant added to one To produce porridge, and is then pulverized wet using a ball mill. The pulverized material is then dried, degreased, with a solvent, a binder, a plasticizer, a dispersant, etc. and by means of a ball mill mixed. Next will this porridge while he using a stirrer touched is extracted under vacuum, and this is with respect to the viscosity set.

Next, the porridge becomes unbaked using a doctor blade or scraper system th plate of a constant thickness.

The resulting unfired plate is punched using a press or cut using a cutter, around rectangular Obtain plates of predetermined sizes.

Next, for example, as in 4 a silver and palladium paste with a silver / palladium ratio of 7/3 (hereinafter abbreviated as "Ag / Pd paste") is used to pattern or pattern a surface of each of the molded green sheets 7 to print using screen or screen printing. 4 shows an example of a green sheet after printing an electrode structure.

The surface of each green plate 7 is formed over its entire surface with a structure that is slightly smaller than it. This is called the inner electrode layer 153 ( 154 ) used. One of two opposite sides of the surface of the green sheet 7 is with a part not designed 75 provided on which the inner electrode layer 153 ( 154 ) is not trained. That is, the inner electrode layer 153 ( 154 ) is arranged so that it has an end of one of two opposite sides of the unfired plate 7 (the portion corresponding to the side surface of the piezoelectric actuator) is not reached while the inner electrode layer 153 ( 154 ) reaches the end of the other opposite side.

A predetermined number of green sheets 7 that with this inner electrode layer 153 are formed, based on the required specification of the amount of displacement of the piezoelectric unit element 11 and the buffer units 2 prepared. Furthermore, the necessary number of unfired plates 7 that don't have inner electrode layers 153 ( 154 ) are printed, prepared.

Next, these unfired plates 7 as in 5 shown stacked. At this time, they are stacked so that the unshaped or non-formed ends 75 can be positioned alternately on the left side and the right side in the figure.

Twenty-one ( 21 ) unfired plates with inner electrode layers 153 ( 154 ) are stacked together in this way, then unfired plates that do not have inner electrode layers 153 ( 154 ) are formed, superimposed on the top and bottom to form a stack 70 to produce, which consists of a total of 30 unfired plates, as in 6 is shown. It is noted that 6 shows a stack in which certain stacked layers are omitted for the convenience of creating the figure.

Next is the stack 70 hot press bonded, then degreased using an electric furnace at a temperature of 400 to 700 ° C, fired at a temperature of 900 to 1200 ° C, and then ground to a desired shape. Because of this, the unfired ceramic plates 7 to piezoelectric ceramic layers 151 , and becomes a piezoelectric element unit 15 made of piezoelectric ceramic layers 151 and inner electrode layers 153 and 154 that are alternately stacked as in 7 get shown. This piezoelectric element unit 15 has 20 piezoelectric ceramic layers that are active as piezoelectric elements. The same routine as above is followed for 20 such piezoelectric element units 15 prepare.

The parallelism value of the bond surfaces 155 each of the piezoelectric element units 15 was measured in accordance with the method specified in JIS-B0621-1984, whereupon, as shown in Table 1 mentioned later, the parallelism value was less than 0.05 mm.

Here is the parallelism value of the bond surfaces of a piezoelectric element unit 15 under the use of 8th explained. 8th Fig. 12 is a view of a piezoelectric element unit seen from a side surface.

As shown in the figure, the two ends form the piezoelectric element unit 15 two bond surfaces in the stacking direction 155a and 155b which serve as bonding surfaces for bonding with other piezoelectric element units. The parallelism value of these bond surfaces is the parallelism value of a bond surface 155a (or 155b ) in relation to another bond surface 155b (or 155a ) from the two bond surfaces 155a and 155b at both ends of the piezoelectric element unit 15 in the stacking direction. That means in 8th becomes when a line is substantially parallel to a bond surface 155b is referred to as line A through the on the other bond surface 155a the most protruding portion and the line parallel to line A is referred to as line A1, and by the line on the bond surface 155a is referred to as the line A2 by the most receding section and the line parallel to the line A, the distance X between the lines A1 and A2 to the parallelism value.

Next, sets of 19 green sheets stacked with internal electrode layers similar to those formed in the manufacture of the above piezoelectric element units were stacked to produce stacks for buffer units. In each buffer unit stack, green sheets, which were not formed with inner electrode layers, were interposed for the part of two layers on the side forming the connection element side after the piezoelectric actuator was assembled sets to make the thickness of the side of the connection member twice that of a piezoelectric ceramic layer of a piezoelectric element unit. In addition, green sheets not formed with inner electrode layers were further stacked on the outermost side of the connector side.

Next, these stacks of buffer units were hot press bonded, degreased, and then fired, in the same manner as the above, around buffer units 2 as in 8th shown to manufacture.

Next, sets of 20 green sheets that were not formed with inner electrode layers were stacked to make stacks for dummy units. These stacks of dummy units were then hot press bonded, degreased, and then fired, in the same manner as the above, around dummy units 3 to obtain.

Furthermore, connecting elements 4 made by machining sintered alumina blocks to the desired shapes.

Next, the piezoelectric element units thus manufactured 15 , the buffer units 2 who have favourited Blind Units 3 and the fasteners 4 stacked to one in the 1 to 3 Piezoelectric actuator shown in the following manner.

In detail, external electrodes made of Ag were initially used 5 and 6 so generated that these side surfaces of the piezoelectric element units 15 and the buffer units 2 locked between them.

The external electrodes 5 are at the positions of the piezoelectric element units 15 and the buffer units 2 formed on which the inner electrode layers 153 or inner electrode layers 253 one of the polarities is exposed and the inner electrode layers 153 or inner electrode layers 253 connect conductively.

The external electrodes 6 are formed at the positions where the inner electrode layers 154 or inner electrode layers 254 the other of the polarities are exposed and the inner electrode layers 154 or inner electrode layers 254 connect conductively.

Next are the inner electrode layers 153 and 154 of the piezoelectric element units 15 and the inner electrode layers 154 and 254 the buffer layers, which are formed with the external electrodes, with a DC voltage from the external electrodes 5 and 6 supplied for polarization.

Next, as in the 1 to 3 is shown 20 of the thus polarized piezoelectric element units 15 on the bond surfaces 155 stacked, become buffer units 2 Stacked at both ends, blind units are again 2 stacked at both ends, and become fasteners again 4 stacked at both ends. At that time, as in 3 is shown, this is stacked so that the two adjacent inner electrode layers 153 and 154 that each bonded part 13 enclose between them, reach opposite side surfaces.

In this way, a piezoelectric actuator 1 like in the 1 to 3 shown manufactured. This was used as the sample E1.

With the piezoelectric actuator 1 sample E1 was the electric field strength of the bonded ceramic layers 115 essentially 0. That is, it was below the coercive electric field of the piezoelectric unit element. The electric field strength of the bonded ceramic layers and the coercive electric field of the unit piezoelectric element were calculated by the above methods.

Furthermore, a piezoelectric actuator was used in this example 1 by bonding the above piezoelectric element units 15 using a silicone-based resin binder and forming a resin insulation layer 135 on each bonded part 13 as in 13 shown. This was referred to as Sample E2.

Sample E2 is the same as Sample E1 except that it has a resin insulation layer 135 on each bonded part 13 having.

Furthermore, in this example piezoelectric actuators using the same procedure as for the sample E1 manufactured, but the number of stacked layers of piezoelectric Ceramic layers in the piezoelectric element units as piezoelectric ceramic layers are active, the presence of resin insulation layers, the parallelism value of the bond surfaces of the piezoelectric element units, or the presence of dummy units and buffer units have been changed. These were referred to as samples E3 to E19. Details are in the later shown Table 1 shown.

Next up was tension on the Samples E1 through E19 and sample C1 applied to the durability of the samples as explained above to investigate.

First, 10 pieces of each of samples E1 to E19 and sample C1 were prepared. These were driven by a positive voltage without applying a negative voltage for 2 × 10 ⁸ cycle operation tests. The number of pieces that were short-circuited during operation was counted. The samples were rated "good" when there were no shorts, "useful" when shorts occurred in some, and "bad" when shorts occurred in all. Furthermore, the number of Be operations until short circuits occurred, measured for samples E2 and E7 to E12.

The results are in Table 1 shown.

As can be seen from Table 1, samples E1 to E19 meet at least one of the requirements that the electric field strength of the bonded ceramic layers with respect to the coercive electric field of the piezoelectric element units is not greater than 1.0 and the bonded ceramic layers inactive that there are resin insulation layers and that the bonded ceramic layers are inactive, that the parallelism value of the bond surfaces is not greater than 0.1, that there are buffer units for buffering the internal stress of the piezoelectric unit elements, and that dummy units have a smaller elastic modulus than that of the connection elements available. Furthermore, these piezoelectric actuators can work at least 2 × 10 ⁸ times almost without short circuits and were therefore superior in terms of durability. Therefore, they are particularly suitable for applications such as injectors.

On the other hand, as shown in Table 1, the sample C1, which did not meet any of the above conditions, suffered short-circuits in all of the 10 pieces during operation for 2 × 10 ⁸ Ma1.

In addition, samples E1 to E14 and samples E17 to E19 each piezoelectric element unit from no more than 50 piezoelectric ceramic layers. Therefore could be a stress occurring at the time of applying voltage repressed and could be the occurrence of cracks in the piezoelectric Element units are effectively suppressed.

In addition, samples E1 to E17 and the sample E19 the piezoelectric element unit from at least six piezoelectric ceramic layers. If the number of stacked Layers of the piezoelectric element unit is six or more the extent of Deformation of the bonded ceramic layers or the ceramic layers at the extreme Sides of the piezoelectric element unit in the stacking direction, this means at the extreme Ceramic layers, bigger. Therefore there is a risk that a local damage on the bonded surfaces the piezoelectric element units or the bonded surface of the piezoelectric unit elements with another element such as for example, a connecting element occurs.

For samples E1 to E17 and However, sample E19 is at least one of the requirements from the conditions that the electric field strength of the bonded ceramic layers in relation to the coercive electrical Field of piezoelectric element units is not larger than 1.0 and the bonded ceramic layers are inactive that resin insulation layers are present and the bonded ceramic layers are inactive, that the parallelism value of the bond surfaces not bigger than 0.1 is that buffer units for buffering the internal stress of the piezoelectric unit elements are present, and that blind units with a smaller modulus of elasticity than that of the connecting elements are met. Therefore can damage on the bonded surfaces repressed and is superior to durability, as in the table 1 is shown.

Furthermore, as can be seen in Table 1 is when the sample E1, the sample E7, the sample E10 and the sample E11 are compared, under otherwise the same conditions, the smallest number of operations without short circuits all the way bigger and the smaller the parallelism value, the better the durability.

Furthermore, the piezoelectric actuators of samples E1 to E8, sample E10, sample E11 and samples E13 to E19 had buffer units. As in 9 each buffer unit is shown 9 a piezoelectric ceramic layer 251 with a thickness substantially equal to that of a piezoelectric ceramic layer in a piezoelectric element unit on the side of the piezoelectric unit element 11 , and has a piezoelectric ceramic layer twice as thick as a piezoelectric ceramic layer in a piezoelectric element unit on the connector side 4 ,

Therefore, the amount of shift per unit length of the buffer unit 2 smaller than the amount of displacement per unit length of a piezoelectric element unit on the connector side and substantially the same as the amount of displacement per unit length of the piezoelectric unit element on the piezoelectric unit element side. Therefore, it is possible to more effectively prevent cracks from occurring on the inside of the piezoelectric actuator.

As explained above, in this example, as in 9 use of a buffer unit with twice the thickness of the piezoelectric ceramic layer 251 made on the side of the connecting element. In addition, it is also possible to use a buffer unit 2 to use with piezoelectric ceramic layers 251 like in the 10 to 12 shown is configured.

That is, the in 10 shown buffer unit 2 has a piezoelectric ceramic layer 251 with a thickness substantially equal to that of a piezoelectric ceramic layer in a piezoelectric element unit on the side of the piezoelectric unit element and increases the thicknesses of two of the piezoelectric ceramic layers 251 , which are active as piezoelectric elements on the connection element side, above the piezoelectric unit element side. Further, among these two layers, the layer on the outermost side on the connecting element side is made twice the thickness of the piezoelectric ceramic layer on the unit piezoelectric element side, while the other one is 1.5 times the thickness of the piezoelectric ceramic layer on the side Side of the piezo electrical unit elements is configured.

Furthermore, in 11 shown buffer unit 2 a piezoelectric ceramic layer 251 with a thickness substantially equal to that of a piezoelectric ceramic layer in a piezoelectric element unit on the side of the piezoelectric unit element, and has a piezoelectric ceramic layer 251 which is inactive as a piezoelectric element and has a thickness larger than that of the piezoelectric ceramic layer on the side of the piezoelectric unit element on the side of the connecting element.

Furthermore, in 12 shown buffer unit 2 a piezoelectric ceramic layer 251 having a thickness substantially equal to that of a piezoelectric ceramic layer in a piezoelectric element unit on the side of the piezoelectric unit element increases the thickness of two of the piezoelectric ceramic layers 251 , which are active as piezoelectric elements, on the side of the connecting element, to twice the thickness of the piezoelectric ceramic layer 251 on the side of the piezoelectric unit element, and has a piezoelectric ceramic layer 251 which is inactive as a piezoelectric element and has a thickness larger than that of the piezoelectric ceramic layer on the side of the unit piezoelectric element on the connecting element side on the outermost side of the connecting element side.

The shapes of piezoelectric ceramic layers 151 and that on the piezoelectric ceramic layers 151 trained inner electrode layers 153 and 154 in the piezoelectric actuator 1 of this example are in the 14 (A) and (B) shown.

As in 14 has a piezoelectric ceramic layer 151 four bevelled corners 159 and has an essentially hexagonal cross-sectional shape. The one on a piezoelectric ceramic layer 151 trained inner electrode layers 153 and 154 do not reach one end on the formed two opposite sides, as a result of which parts are not designed 75 be generated. The other end and the ends of the opposite sides that are not connected to the external electrodes 5 and 6 are formed, have exposed electrode parts 157 and 158 on which the inner electrode layer 153 and the inner electrode layer 154 exposed.

In this example there were inner electrode layers 153 and 154 the in 14 forms shown, however, the inner electrode layers 153 and 154 generated with changes in shape. Furthermore, the piezoelectric actuators of this example (samples E1 to E12) do not depend on the shapes of the piezoelectric ceramic layers and can lead to similar effects even if they are changed.

Furthermore, in this example, inner electrode layers of so-called "partial electrode structures" were produced in such a way that non-designed parts were formed on the piezoelectric ceramic layers as explained above; however, it is like in the 15 (A) and (B) shown also possible inner electrode layers 152 so-called "full electrode structures" so that the entire surfaces of the piezoelectric ceramic layers 151 be covered.

In this case, an insulation element 8th on one of the parts where the inner electrode layer connects to the external electrode 5 and the external electrode 6 connects to allow two adjacent inner electrode layers 152 in a piezoelectric element unit alternating with external electrodes 5 and 6 different potentials are connected in the same manner as in the case of the inner electrode layers of the above sub-electrode structures.

Here is 16 a sectional view of the area near a bonded part 13 of a piezoelectric actuator 1 with inner electrode layers 152 of full electrode structures.

As in 16 each inner electrode layer is shown 152 an insulation element 8th on one of the with the external electrode 5 and the external electrode 6 connecting parts so that only the external electrode 5 or the external electrode 6 is connected to it.

This isolation element 8th disconnects the electrical connection between the external electrode 5 or 6 and the inner electrode layer 152 , Therefore, two adjacent inner electrode layers 152 in a piezoelectric element unit 15 with an external electrode 5 and an external electrode 6 different potentials connected. As a result, it is possible to obtain effects similar to a piezoelectric actuator with inner electrode layers of partial electrode structures as explained above.

Example 2

This example is an example the manufacture of a piezoelectric actuator in which two contiguous inner electrode layers that bond one Include part between them connected to electrodes of substantially the same potential are.

In the piezoelectric actuator of this example, as in 17 is shown, two adjacent inner electrode layers 154 that have a bonded part 13 enclose between themselves with Electrodes connected of substantially the same potential. The rest of the configuration is the same as that of Sample E1 of Example 1.

When manufacturing a piezoelectric actuator 1 In this example, 20 piezoelectric element units were first made in the same manner as in Example 1 15 as in 7 shown prepared.

Furthermore, in the same way and As for sample E1 of Example 1, buffer units, dummy units and connecting elements prepared.

Next, the piezoelectric element units and the buffer units with external electrodes 5 and 6 were provided in the same manner as the sample E1 of Example 1, and were further in the same manner as the sample 1 polarized from Example 1. Next were 20 with external electrodes 5 and 6 provided piezoelectric element units 15 were stacked on their bonding surfaces, and then buffer units, dummy units, and connectors were stacked at both ends in the same manner as in the sample E1 of Example 1. At this time, the piezoelectric element units as in FIG 17 shown stacked so that the two adjacent inner electrode layers 153 which is the bonded part 13 between them, reached the same side surface. The piezoelectric element units 15 were bonded using a silicone-based resin binder.

In this way, a piezoelectric actuator 1 manufactured.

With the piezoelectric actuator 1 of this example are as in 17 is shown, the two adjacent inner electrode layers 154 which is the bonded part 13 between them, with the same external electrode 6 connected.

Therefore, when voltage is applied, the same electric field is applied to the two adjacent inner electrode layers 154 that each bonded part 13 enclose between themselves.

Therefore, the bonded ceramic layers shift 115 not too much at the time of voltage application and are inactive in their state. Furthermore, in this case, it is possible to prevent short circuits on the bonded parts 13 occur, even if the bonded ceramic layers 115 to be damaged.

Furthermore, as in 18 is shown on the bonded parts 13 the bond surfaces of the piezoelectric element units 15 partially in direct contact, and became resin layers 138 on the bonded parts 13 educated. Therefore, it is possible to reduce the loss of displacement on the bonded parts and the loss of stress caused. Note that in this example, the resin layers 138 using a silicone-based binder, i.e., an electrically insulating binder, but in the present example, as explained above, it is because the two adjacent inner electrode layers 154 that each bonded part 13 between them, connected to electrodes of substantially the same potential, not necessarily required to use a binder with an electrical insulation property.

Example 3

This example is an example the manufacture of a piezoelectric actuator that is configured that the Thickness of the extreme Ceramic layers of the piezoelectric element units become larger than the thicknesses of the drive ceramic layers.

In the piezoelectric actuator of this example, as in 19 the thicknesses of the ceramic layers on the outermost sides of the piezoelectric element units 15 in the stacking direction, that is, the outermost ceramic layers 156 , greater than the thicknesses of the ceramic layers lying between the inner electrodes in the piezoelectric element units, that is to say the drive ceramic layers 151 , The rest of the configuration is similar to that of Sample E1 of Example 1.

When manufacturing the piezoelectric actuator of this example, 20 piezoelectric element units were first made in the same manner as in Example 1 15 prepared. At the time, in this example, as in 20 shown piezoelectric element units 15 with thicknesses of the outermost ceramic layers 156 greater than the thickness of the drive ceramic layers 151 in the piezoelectric element units 15 prepared.

Next were on the same Mode as for sample E1 of example 1 buffer units, blind units and connecting elements prepared.

Next, the piezoelectric element units and the buffer units were provided with external electrodes in the same manner as in the sample E1 of Example 1 and polarized in the same manner as in the sample E1 of Example 1. Next, 20 piezoelectric element units provided with external electrodes 15 stacked on their bond surfaces, and were stacked at both ends in the same manner as in Sample E1 of Example 1, buffer units, dummy units, and connectors. In this way, a piezoelectric actuator was manufactured.

In the piezoelectric actuator of this example, as in 19 is shown the thicknesses of the outermost ceramic layers 156 greater than the thickness of the drive ceramic layers 151 , Therefore, it is possible to suppress the amount of deformation of the outermost ceramic layers and possible damage to the bonding surfaces of the piezoelectric element units 15 to suppress further.

A piezoelectric actuator has thus been described above 1 described with a piezoelectric unit element 11 , which consists of at least two piezoelectric element units 15 consists of each of alternately stacked piezoelectric ceramic layers 151 and inner electrode layers 153 and 154 exists, which are bonded on their outermost bond surfaces in the stacking direction and bonded parts 13 form. Each piezoelectric element unit 15 consists of no more than 50 stacked piezoelectric ceramic layers 151 , Bonded ceramic layers 115 between two adjacent inner electrode layers 153 and 154 over a bonded part 13 are inactive.

Claims (33)

Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and on bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of no more than 50 piezoelectric Ceramic layers, and bonded ceramic layers that lie between two adjacent inner electrode layers that enclose each bonded part between them, are inactive. Piezoelectric actuator according to claim 1, characterized characterized that two contiguous inner electrode layers that bond one Include part between them are connected to external electrodes of different potentials, and an electric field strength bonded ceramic layers is no larger than a coercive electric field of the piezoelectric element units. Piezoelectric actuator according to claim 1, characterized characterized that two contiguous inner electrode layers that bond one Include part between them are connected to external electrodes of different potentials, an electric field strength bonded ceramic layers is larger as a coercive electric field of the piezoelectric element units, and the bonded part has a resin insulation layer. Piezoelectric actuator according to claim 1, characterized characterized that two contiguous inner electrode layers that bond one Include part between them with external electrodes of essentially the same potential are connected. Piezoelectric actuator according to claim 4, characterized characterized that at a bonded part of bond surfaces of the piezoelectric element units partially in direct contact and the bonded part has a resin layer. Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and on bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of no more than 50 piezoelectric Ceramic layers, and on each piezoelectric element unit a parallelism value from a bond surface to another bond surface from the bond surfaces at both ends of the piezoelectric element unit not higher than Is 0.1 mm. A piezoelectric actuator having a piezoelectric unit element composed of at least two piezoelectric element units, each of which is composed of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and bonded to bonding surfaces on the outermost sides in the stacking direction to form bonded parts that each piezoelectric element unit is composed of a stack of not more than 50 piezoelectric ceramic layers, outermost ends in the stacking direction of the piezoelectric unit element have connecting elements with a modulus of elasticity larger than that of the piezoelectric element units, and the piezoelectric unit element and the connection elements between them are provided with buffer units consisting of piezoelectric ceramic layers and inner electrode layers which are alternately stacked to buffer the internal load of the piezoelectric unit element. Piezoelectric actuator according to claim 7, characterized characterized in that the modulus of elasticity of the connecting elements at least twice the elastic modulus of the piezoelectric element units. Piezoelectric actuator according to claim 7 or 8, characterized in that a Extent of Displacement per unit length of a buffer unit is smaller than an amount of shift per unit length of piezoelectric element unit on the connecting element side, and is essentially the same as the amount of displacement per unit length of Piezoelectric unit elements on the side of the piezoelectric Unit element. Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which alternately stacked on Bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of no more than 50 piezoelectric Ceramic layers, extreme ends connecting elements in the stacking direction of the piezoelectric unit element with a modulus of elasticity larger than that of the piezoelectric element units, and the piezoelectric unit element and the connecting elements between are provided with blind units that have a modulus of elasticity have smaller than that of the connecting elements. Piezoelectric actuator according to claim 10, characterized characterized in that the modulus of elasticity of the connecting elements at least twice the elastic modulus of the piezoelectric element units and the dummy units. Piezoelectric actuator according to claim 10 or 11, characterized in that each Blind unit made of a ceramic material that is the same is like that of a piezoelectric ceramic layer of the piezoelectric Element units. Piezoelectric actuator according to claim 12, characterized characterized that the Dummy units and the piezoelectric unit element between are provided with buffer units made of piezoelectric Ceramic layers and inner electrode layers are made up alternately are stacked to the internal stress of the piezoelectric unit element buffer, and that a Extent of Displacement per unit length of a buffer unit is smaller than an amount of shift per unit length of piezoelectric element unit on the side of the dummy unit, and is essentially the same as the amount of displacement per unit length of Piezoelectric unit elements on the side of the piezoelectric Unit element. Piezoelectric actuator according to one of claims 7 to 9 or 13, characterized in that each buffer unit does not consist of there are more than 50 piezoelectric ceramic layers stacked together and that the Ceramic layers on the outermost Sides of the buffer unit in the stacking direction, that is, the outermost Ceramic layers are inactive. Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and on bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of at least six piezoelectric Ceramic layers, and bonded ceramic layers that lie between two adjacent inner electrode layers that enclose each bonded part between them, are inactive. Piezoelectric actuator according to claim 15, characterized characterized that two contiguous inner electrode layers that bond one Include part between them are connected to external electrodes of different potentials, and an electric field strength bonded ceramic layers is no larger than a coercive electric field of the piezoelectric element units. Piezoelectric actuator according to claim 15, characterized characterized that two contiguous inner electrode layers that bond one Include part between them are connected to external electrodes of different potentials, an electric field strength bonded ceramic layers is larger as a coercive electric field of the piezoelectric element units, and the bonded part has a resin insulation layer. Piezoelectric actuator according to claim 15, characterized characterized that two contiguous inner electrode layers that bond one Include part between them with external electrodes of essentially the same potential are connected. Piezoelectric actuator according to claim 18, characterized characterized that at the bonded part bond surfaces of the piezoelectric element units partially in direct contact and the bonded part has a resin layer. Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and on bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of at least six piezoelectric Ceramic layers, and on each piezoelectric element unit a parallelism value from a bond surface to another bond surface from the bond surfaces at both ends of the piezoelectric element unit not higher than Is 0.1 mm. Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and on bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of at least six piezoelectric Ceramic layers, extreme ends connecting elements in the stacking direction of the piezoelectric unit element with a modulus of elasticity larger than that of the piezoelectric element units, and the piezoelectric unit element and the connecting elements between are provided with buffer units made of piezoelectric Ceramic layers and inner electrode layers are made up alternately are stacked to the internal stress of the piezoelectric unit element buffering. Piezoelectric actuator according to claim 21, characterized characterized in that the modulus of elasticity of the connecting elements at least twice the elastic modulus of the piezoelectric element units. Piezoelectric actuator according to claim 21 or 22, characterized in that a Extent of the shift per unit length of a buffer unit is smaller than an amount of shift per unit length of piezoelectric element unit on the connecting element side, and is essentially the same as the amount of displacement per unit length of Piezoelectric unit elements on the side of the piezoelectric Unit element. Piezoelectric actuator with a piezoelectric Unit element consisting of at least two piezoelectric element units consists of each of piezoelectric ceramic layers and inner electrode layers, which are alternately stacked and on bond surfaces at the extreme Sides are bonded in the stacking direction to bond parts form, characterized in that any piezoelectric Element unit from a stack of at least six piezoelectric Ceramic layers, extreme ends connecting elements in the stacking direction of the piezoelectric unit element with a modulus of elasticity larger than that of the piezoelectric element units, and the piezoelectric unit element and the connecting elements between are provided with blind units that have a modulus of elasticity larger than that of the fasteners. Piezoelectric actuator according to claim 24, characterized characterized in that the modulus of elasticity of the connecting elements at least twice the elastic modulus of the piezoelectric element units and the dummy units. Piezoelectric actuator according to claim 24 or 25, characterized in that each Blind unit made of a ceramic material that is the same is like that of a piezoelectric ceramic layer of the piezoelectric Element units. Piezoelectric actuator according to claim 26, characterized characterized that the Dummy units and the piezoelectric unit element between are provided with buffer units made of piezoelectric Ceramic layers and inner electrode layers are made up alternately are stacked to the internal stress of the piezoelectric unit element buffer, and that a Extent of Displacement per unit length of a buffer unit is smaller than an amount of shift per unit length of piezoelectric element unit on the side of the dummy unit, and is essentially the same as the amount of displacement per unit length of Piezoelectric unit elements on the side of the piezoelectric Unit element. Piezoelectric actuator according to one of claims 21 to 23 or 27, characterized in that each buffer unit consists of at least six piezoelectric ceramic layers, which are stacked together, and that the Ceramic layers on the outermost Sides of the buffer unit in the stacking direction, that is, the outermost Ceramic layers are inactive. Piezoelectric actuator according to one of claims 21 to 23, 27 or 28, characterized in that each buffer unit does not consist of more from 50 stacked piezoelectric ceramic layers consists. Piezoelectric actuator according to one of claims 15 to 29, characterized in that each piezoelectric Element unit made of no more than 50 piezoelectric stacked together Ceramic layers exist. Piezoelectric actuator according to one of claims 1 to 30, characterized in that thicknesses of Ceramic layers on the outermost Sides in the stacking direction in each piezoelectric element unit, this means the outermost Ceramic layers, at least the thickness of a ceramic layer that between inner electrode layers in the piezoelectric element unit, this means a drive ceramic layer. Piezoelectric actuator according to one of claims 1 to 31, characterized in that each piezoelectric ceramic layer made of a PZT-based material consists. Piezoelectric actuator according to one of claims 1 to 32, characterized in that the piezoelectric actuator for an injector is used.