JP2004297042A - Piezoelectric actuator, its manufacturing method, and injector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator excellent in durability, its manufacturing method and its application to an injector for fuel injection. <P>SOLUTION: The piezoelectric actuator 1 comprises a housing case 20 with an elastic part 21 which expands and contracts elastically in the direction of an axis and a laminated piezoelectric element 10 put in the housing case. A case load applied to the laminate piezoelectric element 10 in the direction of the axis in which the elastic part 21 contracts is controlled so that it becomes zero or less than a tenth part of driving force generated by the laminated piezoelectric element 10 or less than 100 N on the basis of the elastic force of the elastic part 21 of the housing case 20 in the piezoelectric actuator 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric actuator using a laminated piezoelectric element and an injector for fuel injection incorporating the piezoelectric actuator.

Generally, when a multilayer piezoelectric element is operated in a no-load state, there is a possibility that delamination of a laminated ceramic layer or electrode layer may occur due to a driving force due to a piezoelectric effect of the multilayer piezoelectric element.
Therefore, when using the laminated piezoelectric element, it is necessary to apply a preload (set load) having a predetermined size or more for compressing the laminated piezoelectric element in the axial direction.

  Therefore, in a piezoelectric actuator in which a laminated piezoelectric element is accommodated in a case having an elastic portion made of a metal bellows or the like, the laminated piezoelectric element is placed in the case so that the elastic portion expands and deforms when the piezoelectric actuator alone is used. The element may be accommodated. That is, the preload is generated by the elastic force generated by the extension and deformation of the elastic portion of the case (see, for example, Patent Document 1).

JP-A-2002-26410 (paragraph number [0008] of the specification, FIG. 1)

However, the above-mentioned conventional piezoelectric actuator has the following problems. That is, there is a problem that a tensile stress is constantly applied to the above-mentioned expansion and contraction portion which has been elongated and deformed to generate an elastic force, and fatigue failure is likely to occur.
When a tensile stress is constantly applied to the expansion and contraction portion, the fatigue life tends to be short, and it is difficult to secure a sufficient product life of the entire piezoelectric actuator.

  The present invention has been made in view of such a conventional problem, and has as its object to provide a piezoelectric actuator having excellent durability, a method of manufacturing the same, and an injector for fuel injection incorporating the piezoelectric actuator.

According to a first aspect of the present invention, there is provided a piezoelectric actuator in which a multilayer piezoelectric element is housed in a housing case having an elastic portion that can elastically expand and contract in the axial direction.
Based on the elastic force of the expansion and contraction portion of the storage case, the case load acting on the multilayer piezoelectric element in the direction of compressing the multilayer piezoelectric element in the axial direction is 1/10 of the driving force generated by the multilayer piezoelectric element. The load is less than 100 N or less than 100 N.

  In the piezoelectric actuator according to the first aspect of the invention, based on the elastic force of the expansion and contraction portion, a case load acting on the laminated piezoelectric element from the storage case in a direction of compressing the laminated piezoelectric element in an axial direction thereof is reduced. The load is set to be less than 1/10 or less than 100N of the driving force generated by the laminated piezoelectric element.

  In other words, the extension deformation of the elastic portion is limited to a certain range so that the value of the case load falls within the load range.

Therefore, in the piezoelectric actuator, there is little possibility that an excessive tensile stress constantly acts on the expansion and contraction portion.
In other words, when 0.1% strain, which is the expansion and contraction displacement of a general multilayer piezoelectric element, is applied to the expansion and contraction section of the storage case, the tensile load of the expansion and contraction section when the multilayer piezoelectric element is set is increased by the above-described lamination. If the load is less than 1/10 or less than 100 N of the driving force generated by the piezoelectric element, the possibility of breakage due to fatigue caused by repeated operation of the laminated piezoelectric element in the expansion and contraction portion is extremely reduced.
Therefore, the expansion and contraction portion is less likely to be broken by fatigue, and the piezoelectric actuator can exhibit excellent performance for many years.
The multilayer piezoelectric element may be an element as a single ceramic laminate that exerts a piezoelectric effect, or a holding member that further protects an end face of the ceramic laminate, and a driving force due to the piezoelectric effect. An element including a driving force transmitting member or the like for transmitting to the outside may be used.

According to a second aspect of the present invention, there is provided an injector for fuel injection in which a storage case having an expansion and contraction portion that expands and contracts in an axial direction has a built-in piezoelectric actuator that houses a laminated piezoelectric element.
The injector is provided with an elastic member that applies an axial load to an operation surface on which the driving force of the piezoelectric actuator is applied,
The piezoelectric actuator is configured such that, when the piezoelectric actuator is used alone, a case load acting on the laminated piezoelectric element in a direction of compressing the laminated piezoelectric element in the axial direction is based on the elastic force of the elastic portion of the storage case. A fuel injection injector characterized in that the load is less than 1/10 or less than 100 N of the driving force generated by the piezoelectric element.

The fuel injector according to the second aspect of the invention includes the elastic member that applies an axial load to the operating surface of the piezoelectric actuator for driving the injector.
Therefore, in the injector, based on the elastic force of the expansion / contraction part, the preload obtained by combining the case load acting on the laminated piezoelectric element from the storage case in the axial direction of the laminated piezoelectric element and the load by the elastic member is applied to the laminated piezoelectric element. It can act on the element.
Therefore, in the injector, it is possible to suppress the elastic force to be generated in the expansion and contraction portion and the amount of extensional deformation thereof, and reduce the tensile stress constantly acting on the expansion and contraction portion.
Note that the term "single piezoelectric actuator alone" refers to the state of the piezoelectric actuator as a component which is not yet built in the injector.

Therefore, the injector according to the second aspect of the invention has a durability in which a sufficient preload is applied to the multilayer piezoelectric element, so that there is little trouble such as delamination, and there is little possibility of fatigue fracture occurring in the elastic part. It is excellent in performance and reliability.
Note that the elastic member disposed outside the piezoelectric actuator as described above can easily perform maintenance work such as replacement, and the excellent performance of the injector can be exhibited for a longer period of time.

According to a third aspect of the present invention, there is provided a cylindrical body having at least a portion formed with an elastic portion which elastically expands and contracts in an axial direction, and a driving mechanism for the laminated piezoelectric element which is provided at one end of the body. In a manufacturing method for manufacturing a piezoelectric actuator in which a stacked type piezoelectric element is housed in a storage case having a driving plate with a force acting thereon and a base is joined to the other end of the body.
An element forming step of manufacturing the laminated piezoelectric element,
A housing step of inserting the laminated piezoelectric element from the opening end of the storage case and disposing the laminated piezoelectric element at a predetermined position in the axial direction of the storage case,
A joining step of joining the base to an opening end of the storage case in a state where an axial end face of the base is in contact with a rear end face of the laminated piezoelectric element housed in the storage case. ,
In the housing step, in the housing case of the piezoelectric actuator, a case load acting in a direction of compressing the multilayer piezoelectric element in the axial direction is less than 1/10 of a driving force generated by the multilayer piezoelectric element or 100N. A method of manufacturing a piezoelectric actuator, wherein the stacked piezoelectric element is housed so that the load is less than (claim 8).

The accommodating step in the manufacturing method according to the third invention is characterized in that the case load acting on the laminated piezoelectric element in the piezoelectric actuator is less than 1/10 or less than 100N of a driving force generated by the laminated piezoelectric element. Perform so that it becomes a load.
For this reason, the piezoelectric actuator obtained by the above-described manufacturing method is one in which the elongation deformation generated in the elastic portion of the storage case is suppressed to a predetermined range.

In addition, by suppressing the tensile stress that constantly acts on the elastic portion, the possibility of fatigue fracture occurring in the elastic portion can be suppressed.
Therefore, according to the method for manufacturing a piezoelectric actuator, a highly reliable piezoelectric actuator having excellent durability can be manufactured.

In the first invention, the case load is preferably a load of less than 1/100 or less than 10 N of a driving force generated by the multilayer piezoelectric element (claim 2).
As a mounting accuracy when setting the multilayer piezoelectric element, a load that can be generally adjusted, that is, a tensile load of the expansion and contraction portion when setting the multilayer piezoelectric element is a driving force generated by the multilayer piezoelectric element. When the load is less than 1/100 of the force or less than 10N, there is a sufficient margin against the fatigue caused by the repeated operation of the laminated piezoelectric element in the elastic portion.
Further, it is preferable that the elastic portion does not undergo elongation deformation, and the case load is zero (claim 3).
In this case, the tensile stress that constantly acts on the expansion and contraction portion of the storage case can be set to zero, and the possibility of fatigue fracture occurring in the expansion and contraction portion can be suppressed, and the product life of the piezoelectric actuator can be further improved. .
Here, as a method of reducing the case load to zero, for example, there is a method of storing the multilayer piezoelectric element in the storage case so that the expansion and contraction of the expansion and contraction portion does not occur.

In the second aspect, the case load is preferably a load of less than 1/100 or less than 10 N of a driving force generated by the multilayer piezoelectric element (claim 5).
As a mounting accuracy when setting the multilayer piezoelectric element, a load that can be generally adjusted, that is, a tensile load of the expansion and contraction portion when setting the multilayer piezoelectric element is a driving force generated by the multilayer piezoelectric element. When the load is less than 1/100 of the force or less than 10N, there is a sufficient margin against the fatigue caused by the repeated operation of the laminated piezoelectric element in the elastic portion.
Further, it is preferable that, when the piezoelectric actuator is used alone, the expansion and contraction portion does not undergo any extensional deformation, and the case load is zero (claim 6).
In this case, with respect to the piezoelectric actuator incorporated in the injector, the deformation length of the expansion and contraction portion when the piezoelectric actuator is used alone can be set to zero, thereby suppressing the possibility of causing fatigue fracture in the expansion and contraction portion.
Therefore, the injector is less likely to cause fatigue failure in the expansion and contraction portion of the piezoelectric actuator, and can maintain excellent performance for a long period of time.

Further, in a state where the piezoelectric device is built in the injector and receives the urging force of the elastic member, the preload acting in the direction of compressing the multilayer piezoelectric element in the axial direction is one of the driving force generated by the multilayer piezoelectric element. It is preferably at least / 4 (claim 7).
In this case, a sufficient preload can be applied in the axial direction of the laminated piezoelectric element that generates a driving force for operating the injector.
Therefore, it is possible to suppress the tensile stress that constantly acts on the expansion and contraction portion, thereby prolonging the fatigue life and suppressing the occurrence of troubles such as delamination of the laminated piezoelectric element.

In the third aspect, it is preferable that the case load in the accommodation step is a load of less than 1/100 or less than 10 N of a driving force generated by the multilayer piezoelectric element (claim 9).
As a mounting accuracy when setting the multilayer piezoelectric element, a load that can be generally adjusted, that is, a tensile load of the expansion and contraction portion when setting the multilayer piezoelectric element is a driving force generated by the multilayer piezoelectric element. When the load is less than 1/100 of the force or less than 10N, there is a sufficient margin against the fatigue caused by the repeated operation of the laminated piezoelectric element in the elastic portion.
Further, in the housing step, a reference insertion of the laminated piezoelectric element into the housing case for realizing an extension deformation length of the expansion and contraction portion when an elastic force substantially corresponding to the predetermined case load is generated. Based on the position, the laminated piezoelectric element is inserted at a position where the laminated piezoelectric element is retracted in the reverse direction by the axial contraction length of the storage case generated in the joining step, and the laminated piezoelectric element is It is preferable to arrange them (claim 10).

In this case, in the accommodation step, the multilayer piezoelectric element is arranged at the attachment position determined in consideration of shrinkage that may occur in the accommodation case.
Therefore, in the piezoelectric actuator, the extension deformation amount of the expansion / contraction portion can be set to substantially match the design value.
Therefore, in the piezoelectric actuator manufactured by the manufacturing method, there is little possibility that the tensile stress constantly acting on the expansion and contraction portion becomes excessive, and there is little possibility that fatigue fracture occurs.

The predetermined case load of less than 1/10 or less than 100 N of the driving force generated by the laminated piezoelectric element includes zero.
When the predetermined case load is zero, the reference insertion position is shifted from a state where the working end face of the storage case and the tip end face of the multilayer piezoelectric element are in contact with no load. It is at an arbitrary position in the range up to the state where the gap is left.

  Further, the assembling position compresses the expansion and contraction portion by a length obtained by subtracting an extension deformation length of the expansion and contraction portion when an elastic force substantially corresponding to the predetermined case load is subtracted from the contraction length. It is preferable that the end of the multilayer piezoelectric element abuts on the drive plate in the storage case (claim 11).

In this case, the storage step can be easily and reliably performed by inserting the multilayer piezoelectric element to the back of the storage case in which the expansion and contraction portion is compressed in advance.
In the piezoelectric actuator, at least a part of the contraction length that may be generated in the joining step is offset by the free extension of the expansion and contraction portion, so that the distance between the end of the multilayer piezoelectric element and the working end surface is reduced. The above-mentioned predetermined case load can be applied to the above.

Further, the predetermined case load is zero, and the reference insertion position is a gap between the axial end of the multilayer piezoelectric element and the working end face of the storage case, the gap being equal to or more than the contracted length. Is preferably formed at the position where (a) is formed.
In this case, in the piezoelectric actuator, a gap can be formed between the multilayer piezoelectric element and the working end face. Therefore, the extension deformation generated in the elastic portion of the storage case can be reliably reduced to zero.
Therefore, it is possible to further suppress the possibility of fatigue fracture by setting the tensile stress constantly acting on the elastic portion to zero.

Preferably, the joining step is a step of welding the base to the opening end.
In this case, there is a high possibility that the storage case will shrink in the axial direction in the joining step, and the manufacturing method according to the third aspect of the invention is particularly effective.
In addition, as a welding method, there are methods such as laser welding, electron beam welding, and Tig welding.

(Example 1)
The piezoelectric actuator 1 of this example and a method of manufacturing the same will be described with reference to FIGS.
As shown in FIG. 1, the piezoelectric actuator 1 of this example is a piezoelectric actuator in which a laminated piezoelectric element 10 is housed in a housing case 20 having an elastic portion 21 that can elastically expand and contract in the axial direction.
In the piezoelectric actuator 1, the case load acting on the laminated piezoelectric element 10 in the direction of compressing the laminated piezoelectric element 10 in the axial direction thereof based on the elastic force of the elastic portion 21 of the storage case 20 is zero.
Hereinafter, this content will be described in detail.

As shown in FIG. 1, the laminated piezoelectric element 10 includes a holding member 12, a transmission member 13 and a holding member 12 on both end surfaces in a laminating direction of a ceramic laminated body 11 in which ceramic layers 111 and electrode layers 112 are alternately laminated. Is an element formed by bonding
The ceramic laminate 11 is formed by alternately stacking 50 to 700 layers of ceramic layers 111 having a thickness of 50 to 200 μm and electrode layers 112 having a thickness of 0.5 to 5 μm.

As shown in FIG. 3, the ceramic laminate 11 of the present example is a laminate having a partial electrode structure in which sheet pieces 521 made of ceramic and having electrode portions 503 and retaining portions 504 are laminated.
As shown in FIG. 4, a pair of side surfaces 115 that are parallel to the axial direction and face each other are arranged on the outer peripheral surface of the ceramic laminated body 11, and are substantially orthogonal to the laminating direction of the ceramic laminated body 11. The cross section to be taken has a substantially barrel shape.

  As shown in FIG. 1, side electrodes 116 are joined to the respective side surfaces 115. Each side electrode 116 is electrically connected to the electrode layer 112 including the electrode portion 503 that is exposed on every other side 115, and the electrode layer 112 electrically connected to one side electrode 116 is It is in a state of being electrically insulated from the other side electrode 116.

As shown in FIG. 1, the end of the side electrode 116 is electrically connected to an electrode terminal 117 disposed on the holding member 12 joined to the end face of the ceramic laminate 11.
When a base 30, which will be described later, is assembled to the laminated piezoelectric element 1, the pair of external electrodes 31 penetrating through the base 30 and the side electrodes 116 are electrically connected via the electrode terminals 117. It is configured as follows.
Note that the multilayer piezoelectric element 10 of the present example is configured to generate electric power by supplying power from the external electrode 31.

As shown in FIG. 1, the transmission member 13 on the other end face of the ceramic laminate 11 includes a joining portion 131 having substantially the same diameter as the ceramic laminate 11 and a rod portion 132 having a smaller diameter than the joining portion 131. It is a member having a substantially double cylindrical shape.
When the piezoelectric actuator 1 is used, the distal end surface of the rod portion 132 is configured to come into contact with a later-described working end surface 221 of the storage case 20.

As shown in FIG. 1, the storage case 20 is a substantially cup-shaped member having a cylindrical body 24 and a drive plate 22 serving as an operation surface 100 for transmitting the driving force of the piezoelectric actuator 1. .
An operating end surface 221 is formed on the rear surface of the driving plate 22 to be in contact with the distal end surface of the transmission member 13.

  As shown in FIG. 1, the body 24 has an elastic portion 21 made of a metal bellows formed near an end near the working end surface 22. The expandable portion 21 is arranged on the outer peripheral side of the rod portion 132 of the transmission member 13 of the laminated piezoelectric element 10 so as to be disposed with a predetermined gap from the outer peripheral surface of the rod portion 132. It is.

In the present embodiment, the drive plate 22 is laser-welded to an end of the storage case 20 on the side of the elastic portion 21.
The portion of the storage case 20 that contacts the drive plate 22 may be formed integrally with the body 24 by drawing or the like using a hydraulic press.

As shown in FIG. 1, the base 30 has a pair of external electrodes 31 penetratingly arranged in a substantially cylindrical member made of SUS304. The gap between the penetrated external electrode 31 and the base 30 is sealed by a hermetic seal 33 made of glass.
Further, an insertion portion 32 to be inserted into the body portion 24 of the storage case 20 is formed at an end of the base 30 on the storage case 20 side.

Then, as shown in FIG. 1, the piezoelectric actuator 1 of the present embodiment is formed by joining the storage case 20 and the base 30 by laser welding the insertion portion 32 inserted into the body portion 24.
In the piezoelectric actuator 1, the end of the base 30 on the side of the insertion portion 32 is brought into contact with the end of the holding member 12 of the multilayer piezoelectric element 10, so that the multilayer piezoelectric element 10 is accommodated in the storage case 20. The position is regulated.

Next, a method for manufacturing the piezoelectric actuator 1 of the present example will be described.
The step of manufacturing the piezoelectric actuator 1 includes an element forming step of manufacturing the multilayer piezoelectric element 10, inserting the multilayer piezoelectric element 10 from the opening end of the storage case 20, and inserting the multilayer piezoelectric element 10 into the storage case 20. The housing step of disposing the base 30 at the predetermined position in the axial direction of the base 30 and the opening of the storage case 20 in the state where the axial end surface of the base 30 is in contact with the rear end surface of the laminated piezoelectric element 10 disposed at the predetermined position. And a joining step of joining the base 30 to the end.

First, the above-described element forming step of manufacturing the multilayer piezoelectric element 10 will be described.
In producing the ceramic laminate 11 constituting the laminated piezoelectric element 10, a green sheet 500 (see FIG. 2) is produced in advance from a green sheet slurry that is a piezoelectric element material.
This slurry is obtained by adding a binder, a small amount of a plasticizer and a defoamer to a ceramic raw material such as lead zirconate titanate (PZT) to be a piezoelectric ceramic, and then dispersing the slurry in an organic solvent.

  In this example, the slurry was applied onto a carrier film (not shown) by a doctor blade method, to produce a green sheet 500 having a thickness of 40 to 250 μm. In addition, as a method of producing the green sheet 500 from the slurry, various methods other than the doctor blade method, such as an extrusion molding method, can be adopted.

Next, as shown in FIG. 2, an Ag-Pd paste, which is a conductive material, is applied by screen printing to a region to be the lamination surface 501 of the green sheet 500. Here, an Ag-Pd paste is applied except for one portion corresponding to the outer peripheral portion of the laminated surface 501, thereby forming an electrode print pattern 502 including an electrode portion 503 and a retaining portion 504 on the laminated surface 501.
Then, the slurry as an adhesive is applied to the entire surface of the laminated surface 501 to which the conductive material has been applied.

  Further, in this example, as shown in FIGS. 2 and 3, the arrangement of the retaining portions 504 in the sheet piece 521 is alternately switched every time the green sheet 500 is punched, as shown in FIG. Two types of electrode print patterns 502 having a mirror image relationship were formed.

Thereafter, as shown in FIG. 3, sheet pieces 521 having an electrode sheet pattern 502 are punched from the green sheet 500, and the punched sheet pieces 521 are sequentially laminated.
Here, as shown in the figure, sheet pieces 521 having two types of electrode print patterns 502 in a mirror image relationship are alternately laminated to produce an intermediate laminate (not shown), which is fired to form a ceramic laminate. The laminate 11 is manufactured.
In addition, in this example, the furnace was cooled after being held in a 1200 ° C. atmosphere for 2 hours to fire the intermediate laminate.

Then, the electrode portion 503 applied to the lamination surface 501 (FIG. 1) forms the respective electrode layers 112 in the ceramic laminate 11 as shown in FIG.
In the ceramic laminate 11, the electrode portions 503 of the other electrode layers 112 are exposed on the opposite side surfaces, and the electrode layers 112 exposing the electrode portions 503 on one side surface are on the other side surface. Then, the stay portion 504 is configured to be exposed.

As shown in FIG. 4, the ceramic laminated body 11 of this example is formed by flattening the side surface on which the electrode portion 503 and the retaining portion 504 appear every other layer in the laminating direction to form a pair of substantially planar side surfaces 115. It was done.
As shown in FIG. 1, the laminated piezoelectric element 10 of this embodiment is configured such that a side electrode 116 is joined to each side surface 115 of the ceramic laminated body 11 by a conductive adhesive and that the ceramic laminated body 11 is laminated in the laminating direction. The holding member 12 and the transmission member 13 are joined to both end surfaces.
In addition, an Ag-Pd paste, an Ag paste, an Au paste, a Cu paste, or the like can be used as the conductive adhesive.

Next, the accommodating step of accommodating the multilayer piezoelectric element 10 in the accommodating case 20 will be described.
In this step, as shown in FIG. 5, the base 30 is previously assembled to the end of the multilayer piezoelectric element 10 on the holding member 12 side.
In this example, the holding member 12 and the base 30 were brought into contact with each other by joining the electrode terminals 117 disposed on the holding member 12 and the external electrodes 31 of the base 30 by spot welding by laser irradiation. Both were assembled in the state.

As shown in FIG. 5, in storing the multilayer piezoelectric element 10 in the storage case 20, the distal end surface of the transmission member 13 of the multilayer piezoelectric element 10 contacts the working end surface 221 of the storage case 20 in advance, The reference insertion position of the laminated piezoelectric element 10 that does not cause the extension / deformation of the expansion / contraction portion 21 is calculated, and the axial contraction length of the storage case 20 that may occur in the joining process is experimentally calculated. .
Then, a position where the laminated piezoelectric element 10 was retracted in the reverse direction from the reference insertion position by the contraction length in the reverse direction was set as an assembling position, and the laminated piezoelectric element 10 was inserted and arranged at the assembling position.

In the joining step by laser welding of the present example described later, it is experimentally determined that the storage case 20 is contracted in the axial direction by about 70 μm.
Therefore, in this example, as shown in FIG. 6, the position where the gap G of 70 μm is formed between the working end face 221 of the storage case 20 and the end of the transmission member 13 of the multilayer piezoelectric element 10 is determined by the above-described assembly. Position.
Therefore, in the housing step of the present example, as shown in FIG.

  Next, in the bonding step, the base 30 that regulates the axial position of the multilayer piezoelectric element 10 is bonded to the storage case 20 while holding the mounting position of the multilayer piezoelectric element 10 with respect to the storage case 20. It is a process. In this example, the base 30 was joined to the storage case 20 by laser welding.

In the joining step, as described above, the housing case 20 is shrunk in the axial direction by about 70 μm due to the heat of welding.
At this time, as shown in FIG. 7, the gap G (see FIG. 6) provided between the working end face 22 and the end of the transmission member 13 in the accommodation step is reduced inside the accommodation case 20 as shown in FIG. 7. There are no gaps.
Here, when the contraction as designed occurs in the above-mentioned joining step, the working end face 22 and the end of the transmission member 13 come into contact with zero load, and the expansion and contraction section 21 of the storage case 20 undergoes elongation deformation. Will not occur.

As described above, in the present embodiment, the multilayer piezoelectric element is disposed at the mounting position determined in consideration of the contraction of the storage case that occurs in the bonding process.
Therefore, the extension deformation length of the elastic portion 21 in the piezoelectric actuator 1 can be appropriately set, and the tensile stress constantly acting on the elastic portion 21 can be suppressed.
Therefore, the piezoelectric actuator 1 of the present example is less likely to cause fatigue failure of the expansion and contraction portion 21 and can exhibit excellent performance over a long-term specification.

Note that the reference insertion position may be a position where a gap is formed between the working end surface 22 and the transmission member 13. In this case, as shown in FIG. 7, a gap can be formed between the working end face 22 and the multilayer piezoelectric element 10 in the manufactured piezoelectric actuator 1.
Therefore, even if a slight error occurs in the amount of contraction of the storage case 20 in the axial direction in the joining step, it is possible to reliably prevent the elastic portion 21 from being elongated.

Further, a predetermined case load for compressing the laminated piezoelectric element 10 built in the piezoelectric actuator 1 in the axial direction is set to be larger than zero within a range of less than 1/10 of the driving force generated by the laminated piezoelectric element 10 or less than 100N. You can also.
In this case, the reference insertion position is the insertion position of the multilayer piezoelectric element 10 when the elastic force due to the extension and deformation of the elastic portion 21 substantially matches the predetermined case load. And the position retracted in the insertion reverse direction from the reference insertion position by the contraction length in the joining step is the assembling position.

As shown in FIG. 8, an elastic part 21 is formed over the entire area of the body part 24 of the storage case 20 in the axial direction, and the laminated piezoelectric element 1 is disposed on the inner peripheral side of the elastic part 21. You can also.
In this case, stress acting per unit length of the elastic portion 21 can be dispersed to extend the fatigue life.

(Example 2)
This example is an example in which the method of performing the above-described storing step is changed based on Example 1.
In the piezoelectric actuator 1 of the present embodiment, the case load acting in the direction of compressing the laminated piezoelectric element 10 in the axial direction is larger than zero and less than 1/10 of the driving force generated by the laminated piezoelectric element 10 or A predetermined case load in a range of less than 100 N was set.

Then, as shown in FIG. 9, the housing step of this example is a step of assembling by bringing the end of the laminated piezoelectric element 10 in the insertion direction into contact with the working end face 221 of the housing case 20 which has been compressed in the axial direction in advance. It is.
In carrying out the housing step of the present example, in order to compress the laminated piezoelectric element 10 in the axial direction by a predetermined case load L1 and the axial contraction length L1 of the storage case 20 that may occur in the above-described joining step. A required extension deformation length L2 of the elastic portion 21 is obtained in advance.
In this example, the predetermined case load is set to be larger than zero in a range of less than 1/10 or less than 100 N of the driving force generated by the laminated piezoelectric element 10.

The length obtained by subtracting the extension deformation length from the contraction length is defined as the predetermined length P at which the expansion and contraction portion 21 is to be compressed. That is, P = L1−L2.
Therefore, in carrying out the housing process of this example, first, the housing case 20 is contracted in the axial direction by the predetermined length P.

In the accommodation step, the laminated piezoelectric element is inserted and arranged at a position where the transmitting member 13 of the laminated piezoelectric element 10 contacts the working end face 221 of the compressed storage case 20. Thereafter, when the joining step is performed, the storage case 20 contracts in the axial direction by the length L1 so as to substantially match the contracted length.
Thereafter, when the force compressing the storage case 20 is released, the storage case 20 is extended and returned by the predetermined length P.

Here, assuming that the original full length (inside) of the storage case 20 is L, the full length (inside) after performing the joining step is L-L1.
The total length (inside) of the compressed storage case 20 before the joining step is LP = L− (L1−L2). Before the joining step, the working end surface 221 of the storage case 20 and the end of the multilayer piezoelectric element 10 are in contact with each other, so that the contents of the storage case 20, that is, the total length of the multilayer piezoelectric element 10 is L-P. = L- (L1-L2).

Comparing the total length L-L1 of the storage case 20 after the joining step and the total length L-L1 + L2 of the multilayer piezoelectric element 10, the total length of the storage case 20 is shorter by L2.
Therefore, after the joining process, the elastic portion 21 of the storage case 20 is extended and deformed by L2.
The expansion and contraction portion 21 that has undergone elongation deformation by the amount of L2 acts on the multilayer piezoelectric element 10 in the direction of compressing the multilayered piezoelectric element 10 with the predetermined case load as originally designed.

Here, in this example, the mounting position of the multilayer piezoelectric element 10 in the storage case 20 is exactly the same as the mounting position calculated by the method described in the first embodiment.
In other words, in the present embodiment, the stacking step of bringing the end of the stacking type piezoelectric element 10 into contact with the working end face 221 of the housing case 20 which has been compressed to a predetermined length in advance is performed. This is an example in which the insertion arrangement of No. 10 is facilitated.
The other configuration and operation and effect are the same as those of the first embodiment.

(Example 3)
This example is an example of an injector incorporating the multilayer piezoelectric element of the first embodiment.
As shown in FIG. 10, the injector 6 of the present embodiment is a device that injects a high-pressure fuel of about 180 MPa stored in a common rail (not shown) into an engine cylinder.

  As shown in FIG. 10, the injector 6 is configured by assembling a housing 50 in which the piezoelectric actuator 1 of the first embodiment is housed and a nozzle housing 60 having an injection nozzle portion 61 including an injection nozzle 65.

  As shown in FIG. 10, the housing 50 having a substantially cylindrical outer shape is provided with a concave portion 51 having a substantially circular cross section which is eccentric from the central axis and is bored from the end face on the connector 70 side, and is substantially coaxial with the concave portion 51. A first cylinder 53 having a substantially circular cross-section perforated from the end face on the nozzle housing 60 side, and a fuel supply passage 52 perforated from the same end face adjacent to the first cylinder 53 and the recess 51. ing.

As shown in FIG. 10, the recess 51 and the first cylinder 53 communicate with each other through a communication hole 54 formed substantially coaxially from the bottom of the recess 51. In this example, the communication hole 54 is formed to have a smaller diameter than the concave portion 51 and the first cylinder 53. The fuel supply passage 52 opens at a joint 520 provided at an end of the housing 50 on the connector 70 side, and is connected to a common rail (not shown) via a fuel introduction pipe 525 housed in the joint 520. It is.
Further, a joint portion 580 formed on the rear end side of the housing 50 is provided with a drain passage 58 communicating with a three-way valve 62 described later, and the drain passage 58 is provided with a fuel outlet pipe 585 for discharging fuel. It is connected.

The housing 50 has the piezoelectric actuator 1 in the concave portion 51 as shown in FIG. A first plunger 530 is housed in the first cylinder 53. The first plunger 530 has a body 531 that slides in the first cylinder 53 and a shaft 532 that penetrates the communication hole 54.
The end surface of the shaft portion 532 is in contact with the drive plate 22 as an operation surface of the piezoelectric actuator 1 via the drive transmission unit 55.

  The drive transmission unit 55 includes an urging rod 553 that contacts the first plunger 530 and the piezoelectric actuator 1 at both ends in the axial direction, a coil spring 552 that urges the urging rod 553 toward the piezoelectric actuator 1, and a spring. And a sheet 551.

  The urging rod 553 has a sheet portion 554 larger in diameter than the coil spring 552 near the end on the piezoelectric actuator 1 side. The urging rod 553 is pressed toward the piezoelectric actuator 1 by the urging force of the coil spring 552 acting on the seat portion 554.

  The spring seat 551 is configured to engage with a shelf extending from the recess 51 to the communication hole 54 to regulate the axial position of one end of the coil spring 552. A through hole is formed in the center of the spring seat 551 to allow the urging rod 553 to pass therethrough.

In the drive transmission unit 55 of this example, the static compressive load acting on the operation surface 100 of the piezoelectric actuator 1 from the urging rod 553 is set to be equal to or more than １ ／ of the driving force generated by the laminated piezoelectric element 10. I have.
On the other hand, when the piezoelectric actuator 1 is used alone, the case load acting on the multilayer piezoelectric element 1 is set to zero.
Therefore, a preload equal to or more than ４ of the driving force generated by the laminated piezoelectric element 10 acts on the laminated piezoelectric element 10 of the piezoelectric actuator 1 built in the injector 6 in the axial direction.

  The injector 6 is laminated via the external electrodes 31 (see FIG. 1) penetrating through the base 30 by applying a predetermined voltage to a pair of electrodes (not shown) accommodated in the connector 70. It is configured such that a voltage can be applied to each ceramic layer 111 of the piezoelectric element 1.

As shown in FIG. 10, the nozzle housing 60 includes a second cylinder 63 coaxially drilled from the end face on the housing 50 side, a three-way valve 62 communicating with the fuel supply passage 52 or the drain passage 58, and an injection nozzle portion 61. have.
When the nozzle housing 60 is assembled to the housing 50, a second cylinder 63 is formed so as to communicate with the first cylinder 53. A second plunger 630 is slidably housed in the second cylinder 63.
Therefore, one pressure chamber 506 is formed between the first cylinder 53 and the second cylinder 63 between the first plunger 530 and the second plunger 630.

In this example, as shown in FIG. 10, the pressure chamber 506 is filled with a working fluid, and the second plunger 630 can be stroked following the first plunger 530.
Here, the second cylinder 63 is formed smaller in diameter than the first cylinder 53. Therefore, the injector 6 is configured such that the stroke of the first plunger 530 can be amplified and the second plunger 630 can be stroked.

  As shown in FIG. 10, the three-way valve 62 has a valve body (not shown) for selectively communicating the fuel supply passage 52 or the drain passage 58 with a back pressure chamber 610 described later. This valve element is configured to operate by a stroke of the second plunger 630 in the direction toward the nozzle housing 60, thereby allowing the drain passage 58 to communicate with the back pressure chamber 610.

When the second plunger 630 is located on the housing 50 side, the valve body is configured to allow the fuel supply passage 52 to communicate with the back pressure chamber 610.
That is, the back pressure chamber 610 of the injector 6 of the present embodiment is usually maintained at a high pressure by introducing high-pressure fuel, and the back pressure chamber 610 and the drain are moved by a stroke of the second plunger 630 toward the nozzle housing 60 side. The pressure in the back pressure chamber 610 is reduced by communication with the passage 58.

  As shown in FIG. 10, the injection nozzle portion 61 includes an injection nozzle 65 disposed at the tip end of the nozzle housing 60, a nozzle needle 615 that opens and closes the injection nozzle 65, and a fuel reservoir 612 that stores fuel to be injected. have.

As shown in FIG. 10, the injection nozzle 65 has a needle hole 650 formed coaxially with the axis. The needle hole 650 is opened at the tip of the injection nozzle 65 as an injection hole for ejecting fuel.
The nozzle needle 615 has a two-stage substantially cylindrical shape with a small diameter in the tip direction, and is accommodated in the needle hole 650 such that a step 616 having a variable diameter is located in the fuel reservoir 612. Further, the nozzle needle 615 is configured so that the injection hole at the tip of the injection nozzle 65 can be opened and closed by the spherical tip 613.

  On the other end side of the nozzle needle 615, a back pressure chamber 610 communicating with the three-way valve 62 is formed as shown in FIG. The spring 618 disposed in the back pressure chamber 610 is configured to urge the nozzle needle 615 in a direction to close the injection hole at the tip of the injection nozzle 65.

  Further, as shown in FIG. 10, a fuel supply passage 52 for supplying high-pressure fuel is communicated with a fuel reservoir 612 having a substantially circular cross section formed on the outer periphery of the step portion 616 of the nozzle needle 615. The high-pressure fuel in the fuel reservoir 612 acts on the step 616 of the nozzle needle 615 in such a way that the pressure in the direction of retracting the nozzle needle 615 toward the housing 50 is applied.

Hereinafter, the operation of the injector 6 of the present example applied to a diesel engine common rail injection system (not shown) will be described.
In order to operate the injector 6 and inject a high-pressure fuel of 180 MPa from the injection nozzle 65 into the engine cylinder, a predetermined voltage is applied to the piezoelectric actuator 1 as shown in FIG.
The urging rod 553 of the drive transmission unit 55 abutting on the operation surface 100 of the piezoelectric actuator 1 is caused to stroke toward the first plunger 530 by the extension of the piezoelectric actuator 1 due to the application of the voltage.

  Then, the first plunger 530 that has made a stroke in contact with the urging rod 553 moves inside the first cylinder 53 toward the nozzle housing 60. As the volume of the first cylinder 53 is reduced by the movement of the first plunger 530, the working fluid in the pressure chamber 506 flows into the second cylinder 63 and increases the volume in the second cylinder 63. The two plungers 630 are moved toward the injection nozzle 65 side.

  By the stroke of the second plunger 630, the valve body of the three-way valve 62 is pushed down toward the injection nozzle 65 as shown in FIG. By pushing down the valve element, the passage from the fuel supply passage 52 to the back pressure chamber 610 is shut off, and instead, the passage from the drain passage 58 to the back pressure chamber 610 is communicated. Then, the fuel filled in the back pressure chamber 610 is discharged to the outside from the fuel outlet pipe 585 through the drain passage 58, and the pressure in the back pressure chamber 610 is reduced.

The pressure difference generated between the back pressure chamber 610 and the fuel reservoir 612 due to the decrease in the pressure of the back pressure chamber 610 generates a force for pushing the nozzle needle 615 toward the housing 50 as shown in FIG. Then, as the nozzle needle 615 moves toward the housing 50, the injection hole at the tip of the injection nozzle 615 closed by the tip 613 of the nozzle needle 615 is opened. Then, when the injection hole is opened, the high-pressure fuel in the fuel reservoir 612 is injected into the engine cylinder.
In this example, the injectors 6 attached to the respective engine cylinders were controlled by an engine ECU (not shown) for controlling the engine, and the fuel injection was repeatedly performed at an appropriate timing as described above.

As described above, the injector 6 including the coil spring 552 that compresses the built-in piezoelectric actuator 1 in the axial direction can apply an appropriate preload to the laminated piezoelectric element 10 inside the piezoelectric actuator 1.
Therefore, in the injector 6 of the present example, there is little possibility that trouble such as delamination of the multilayer piezoelectric element 10 occurs inside the piezoelectric actuator 1.

And relatively, in the injector 6 of the present example, the above-mentioned case load that needs to be generated in the elastic portion 21 of the storage case 20 can be suppressed. In this example, the case load is set to zero.
Therefore, in the piezoelectric actuator 1 of this example, the tensile stress constantly acting on the elastic portion 21 can be reduced to zero, and the possibility that fatigue fracture occurs in the elastic portion 21 is reduced.
The other configuration and operation and effect are the same as those of the first embodiment.

(Example 4)
This example is an example of examining the fatigue life of the expansion and contraction portion of the storage case for the piezoelectric actuator of the injector according to the third embodiment.
In the present example, the relationship between the magnitude of the elastic force due to the extension deformation of the expansion and contraction portion when the piezoelectric actuator is used alone and the fatigue life was examined. Here, the elastic force due to the extension deformation of the expansion and contraction portion substantially matches the case load acting in the direction of compressing the laminated piezoelectric element built in the piezoelectric actuator in the axial direction.

Therefore, as shown in FIG. 11, the case load (preload (set load) when the piezoelectric actuator is used alone) acting on the laminated piezoelectric element of the piezoelectric actuator and the failure probability of 50% or less when the actuator is operated 2 × 109 times. The relationship with the operating amplitude (μm) of the piezoelectric actuator for maintaining the value was obtained.
In the drawing, the horizontal axis indicates the case load ratio acting on the multilayer piezoelectric element (the ratio of the case load to the driving force 1000N generated by the multilayer piezoelectric element), and the vertical axis indicates the operating amplitude of the piezoelectric actuator. are doing.
An area in which the design target, that is, a failure probability of 50% or less at the time of 2 × 109 operations, is shown as a hatched area.
Here, the failure probability at the time of 2 × 109 operations is the ratio of individuals having a failure to the mother set when the piezoelectric actuators of a sufficient population are operated 2 × 109 times, respectively.

Here, a minus region at the left end of the horizontal axis shows a state in which a gap is formed between the end of the multilayer piezoelectric element and the working end surface of the storage case when the piezoelectric actuator is used alone. In other words, it essentially indicates a region where the case load of the laminated piezoelectric element is zero.
Therefore, in this example, in order to quantify and express the size of the gap for convenience, the load required to compress until the working end face and the end of the multilayer piezoelectric element are brought into contact with each other is defined as a minus load. expressing.

According to the figure, in order to achieve both the overall operation ratio of 0.1%, which is a general operation amplitude of the multilayer piezoelectric element, and the failure probability of 50% at the time of 2 × 109 operations, it is necessary to use the multilayer piezoelectric element. It is understood that the case load ratio should be set to 1/10 or less. The reason can be considered as follows.
That is, if the case load is reduced, the length of the extension deformation of the elastic portion can be set short, and the pulling force acting on the elastic portion can be suppressed. And in the elastic | stretch part which suppressed the pulling force, it is possible to suppress the possibility that fatigue fracture may arise.
The other configuration and operation and effect are the same as those of the third embodiment.

FIG. 2 is a cross-sectional view illustrating the structure of the piezoelectric actuator according to the first embodiment. FIG. 3 is an explanatory diagram illustrating a printing procedure of an electrode printing pattern in the first embodiment. FIG. 3 is an explanatory view showing a lamination procedure of the ceramic laminate in the first embodiment. FIG. 3 is a cross-sectional view illustrating a laminated structure of the ceramic laminated body according to the first embodiment. FIG. 4 is an explanatory view showing a housing step in the first embodiment. FIG. 4 is an explanatory diagram illustrating an assembling structure in a housing process according to the first embodiment. FIG. 4 is a cross-sectional view illustrating another structure of the piezoelectric actuator according to the first embodiment. FIG. 4 is a cross-sectional view illustrating another structure of the piezoelectric actuator according to the first embodiment. FIG. 11 is an explanatory diagram illustrating an assembling procedure in a housing process according to the second embodiment. FIG. 13 is a cross-sectional view illustrating a structure of an injector including a piezoelectric actuator according to a third embodiment. 13 is a graph showing the relationship between the case load and the amplitude of the multilayer piezoelectric element in Example 4.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 10 Multilayer type piezoelectric element 11 Ceramic laminated body 12 Holding member 13 Transmission member 20 Storage case 21 Elastic part 24 Trunk part 30 Base 31 External electrode 6 Injector

Claims (13)

In a piezoelectric actuator that houses a laminated piezoelectric element in a storage case having an elastic portion that can elastically expand and contract in the axial direction,
Based on the elastic force of the expansion and contraction portion of the storage case, the case load acting on the multilayer piezoelectric element in the direction of compressing the multilayer piezoelectric element in the axial direction is 1/10 of the driving force generated by the multilayer piezoelectric element. A load of less than 100 N.   2. The piezoelectric actuator according to claim 1, wherein the case load is a load of less than 1/100 or less than 10N of a driving force generated by the laminated piezoelectric element.   3. The piezoelectric actuator according to claim 1, wherein the expansion and contraction portion does not undergo extensional deformation, and the case load is zero. 4. In a fuel injector having a built-in piezoelectric actuator containing a laminated piezoelectric element in a storage case having an elastic portion that expands and contracts in the axial direction,
The injector is provided with an elastic member that applies an axial load to an operation surface on which the driving force of the piezoelectric actuator is applied,
The piezoelectric actuator is configured such that, when the piezoelectric actuator is used alone, a case load acting on the laminated piezoelectric element in a direction of compressing the laminated piezoelectric element in the axial direction is based on the elastic force of the elastic portion of the storage case. An injector for fuel injection, wherein the load is less than 1/10 or less than 100 N of the driving force generated by the piezoelectric element.   5. The injector according to claim 4, wherein the case load is a load of less than 1/100 or less than 10N of a driving force generated by the laminated piezoelectric element.   6. The injector according to claim 4, wherein the expansion and contraction portion does not undergo any extensional deformation when the piezoelectric actuator is used alone, and the case load is zero.   The preload according to any one of claims 4 to 6, wherein the preload that is built in the injector and that acts in a direction of compressing the laminated piezoelectric element in an axial direction in a state where the biasing force is exerted by the elastic member is a lamination. An injector for fuel injection, wherein the driving force is at least 1/4 of the driving force generated by the piezoelectric element. A cylindrical body formed at least in part with a telescopic part that elastically expands and contracts in the axial direction, and a drive plate disposed at one end of the body and on which the driving force of the laminated piezoelectric element acts In a manufacturing method for manufacturing a piezoelectric actuator in which a stacked type piezoelectric element is housed in a storage case having a base and joined to a base at the other end of the body,
An element forming step of manufacturing the laminated piezoelectric element,
A housing step of inserting the laminated piezoelectric element from the opening end of the storage case and disposing the laminated piezoelectric element at a predetermined position in the axial direction of the storage case,
A joining step of joining the base to an opening end of the storage case in a state where an axial end face of the base is in contact with a rear end face of the laminated piezoelectric element housed in the storage case. ,
In the housing step, in the housing case of the piezoelectric actuator, a case load acting in a direction of compressing the multilayer piezoelectric element in the axial direction is less than 1/10 of a driving force generated by the multilayer piezoelectric element or 100N. A method of manufacturing a piezoelectric actuator, wherein the stacked piezoelectric element is housed so as to have a load of less than.   9. The method according to claim 8, wherein the case load in the housing step is a load of less than 1/100 or less than 10N of a driving force generated by the multilayer piezoelectric element.   The storage case of the multilayer piezoelectric element according to claim 8 or 9, wherein in the storage step, the extension deformation length of the expansion and contraction portion when an elastic force substantially corresponding to the predetermined case load is generated. On the basis of the reference insertion position in the assembling position, which is a position in which the laminated piezoelectric element is retracted in the insertion reverse direction by an axial contraction length of the storage case generated in the joining step, A method for manufacturing a piezoelectric actuator, comprising disposing a laminated piezoelectric element.   11. The expansion / contraction part according to claim 10, wherein the assembling position is a length obtained by subtracting an extension deformation length of the expansion / contraction part from the contraction length when an elastic force substantially corresponding to the predetermined case load is generated. A method of manufacturing the piezoelectric actuator, wherein the end of the multilayer piezoelectric element is in contact with the driving plate in the storage case in which the piezoelectric actuator is compressed.   11. The contracted length according to claim 10, wherein the predetermined case load is zero, and the reference insertion position is defined between an axial end of the multilayer piezoelectric element and the working end face of the storage case. A method for manufacturing a piezoelectric actuator, comprising: a position where the above gap is formed.   The method according to any one of claims 8 to 12, wherein the joining step is a step of welding the base to the opening end.

Images