JP4715097B2 - Piezoelectric actuator, method for manufacturing the same, and injector - Google Patents

Description

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

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

  Therefore, in a piezoelectric actuator in which a multilayer piezoelectric element is housed in a case having an expansion / contraction portion made of a metal bellows or the like, the multilayer piezoelectric element is formed in the case so that the expansion / contraction portion is deformed when the piezoelectric actuator is used alone. An element may be accommodated. That is, the preload is generated by the elastic force accompanying the expansion and deformation of the expansion / contraction part of the case (see, for example, Patent Document 1).

JP 2002-26410 (paragraph number “0008” in the specification, FIG. 1)

However, the above-described conventional piezoelectric actuator has the following problems. That is, there is a problem that a tensile stress is steadily applied to the expansion / contraction portion that is stretched and deformed to generate an elastic force, and fatigue failure is likely to occur.
If a tensile stress is constantly applied to the stretchable part, the fatigue life tends to be shortened, and it is difficult to ensure a sufficient product life as the whole piezoelectric actuator.

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

A first invention is a piezoelectric actuator for an injector built in an injector for fuel injection,
A storage case in the axial direction with an elastically stretchable stretch unit, Ri Na houses a laminated type piezoelectric elements,
During the piezoelectric actuator itself, tensile load acting on the expansion portion of the storage case, Ri load der less than 1/10 of the driving force generated by the zero or the stacked piezoelectric device,
The piezoelectric actuator is configured such that in a state where a preload is provided in the injector, a tensile load acting on the expansion / contraction portion is zero .

  In the piezoelectric actuator according to the first aspect of the invention, the case load acting in the axial compression direction from the storage case to the stacked piezoelectric element is based on the elastic force of the extendable portion. The load is set to be less than 1/10 of the driving force generated by the multilayer piezoelectric element or less than 100N.

  That is, the extension deformation of the expansion / contraction part is limited to a certain range so that the case load value falls within the load range.

For this reason, in the piezoelectric actuator, there is little possibility that an excessive tensile stress constantly acts on the stretchable portion.
That is, when 0.1% strain, which is the expansion / contraction displacement of a general multilayer piezoelectric element, is applied to the expansion / contraction part of the storage case, the tensile load of the expansion / contraction part when the multilayer piezoelectric element is set is If the load is less than 1/10 of the driving force generated by the piezoelectric element or less than 100 N, the possibility of breakage due to repeated fatigue of the laminated piezoelectric element of the stretchable part is extremely reduced.
Therefore, the expansion / contraction part is less likely to be damaged by fatigue, and the piezoelectric actuator can exhibit excellent performance for many years.
The multilayer piezoelectric element may be a single element of a ceramic laminate that exhibits a piezoelectric effect, or may be provided with a holding member for protecting the end surface of the ceramic laminate, or a driving force due to the piezoelectric effect. An element including a driving force transmission member for transmitting to the outside may be used.

According to a second aspect of the present invention, there is provided a fuel injection injector including a piezoelectric case in which a multilayer piezoelectric element is accommodated in a storage case having an expansion / contraction portion extending and contracting in an axial direction.
The injector includes an elastic member that applies an axial load to an operation surface on which the driving force of the piezoelectric actuator acts.
The piezoelectric actuator, at the time of the piezoelectric actuator itself, tensile load acting on the expansion portion of the storage case, Ri tensile load der less than 1/10 of the driving force generated by the zero or the stacked piezoelectric device,
In a state where a preload is provided in the injector, the fuel injection injector is characterized in that the tensile load acting on the expansion / contraction section is zero (claim 4).

The fuel injection injector according to the second aspect of the invention includes the elastic member that applies an axial load to the operation surface of the piezoelectric actuator for driving the injector.
Therefore, in the injector, a preload, which is a combination of a case load acting in the axial direction of the multilayer piezoelectric element from the storage case based on the elastic force of the expansion and contraction, and a load by the elastic member, is combined with the multilayer piezoelectric element. It can act on the element.
Therefore, in the injector, it is possible to suppress the elastic force to be generated at the expansion / contraction part and the amount of expansion / deformation thereof, and to reduce the tensile stress that constantly acts on the expansion / contraction part.
The term “only when the piezoelectric actuator is used” refers to the state of the piezoelectric actuator as a component that is not yet built in the injector.

Therefore, the injector according to the second aspect of the invention has a sufficient preload applied to the multilayer piezoelectric element, so that there are few troubles such as delamination, and there is little risk of fatigue failure occurring in the stretchable part. It is excellent in reliability and reliability.
The elastic member arranged outside the piezoelectric actuator as described above can easily perform maintenance work such as replacement, and can exhibit the excellent performance of the injector for a longer period of time.

A third invention is disposed with the expansion unit which expands and contracts elastically in the axial direction a cylindrical body portion formed at least in part, to one end of the body portion of the stacked piezoelectric device on the driving force is accommodating the stacked piezoelectric device in the storage case comprising a drive plate which acts, a method of manufacturing a piezoelectric actuator formed by joining the base to the other end of the body portion In
An element forming step for producing the laminated piezoelectric element;
An accommodating step of inserting the multilayer piezoelectric element from the opening end of the storage case and disposing the multilayer piezoelectric element at a predetermined position in the axial direction of the storage case;
A joining step of joining the base to the opening end of the storage case in a state where the axial end surface of the base is in contact with the rear end surface of the multilayer piezoelectric element housed in the storage case. ,
In the accommodating step, in the storage case of the piezoelectric actuator, as tensile load acting on the elastic portion becomes zero or 1/10 less than the load of the driving force generated in the stacked piezoelectric device, the laminate According to another aspect of the present invention, there is provided a method of manufacturing a piezoelectric actuator characterized by containing a piezoelectric element.

In the housing step in the manufacturing method of the third invention, the case load acting on the multilayer piezoelectric element in the piezoelectric actuator is less than 1/10 or less than 100 N of the driving force generated by the multilayer piezoelectric element. Carry out load.
For this reason, the piezoelectric actuator obtained by the manufacturing method suppresses expansion deformation generated in the expansion / contraction portion of the storage case within a predetermined range.

Then, by suppressing the tensile stress that constantly acts on the stretchable part, it is possible to suppress the possibility of causing fatigue failure in the stretchable part.
Therefore, according to the method for manufacturing a piezoelectric actuator, a piezoelectric actuator having excellent durability and high reliability can be manufactured.

In the first aspect of the invention, the tensile load acting on the expansion / contraction part is preferably a load less than 1/100 of the driving force generated by the multilayer piezoelectric element.
As the assembly accuracy at the time of setting the multilayer piezoelectric element, a load that can be adjusted in general, that is, the tensile load of the expansion / contraction part at the time of setting the multilayer piezoelectric element is the driving generated by the multilayer piezoelectric element. When the load is less than 1/100 of the force, there is a sufficient margin against fatigue due to repeated operation of the laminated piezoelectric element of the stretchable part.
Moreover, it is preferable that the said expansion-contraction part does not produce the expansion | extension deformation | transformation, and the tensile load which acts on the said expansion-contraction part is zero (Claim 3).
In this case, the tensile stress that constantly acts on the expansion / contraction part of the storage case is set to zero, the possibility of fatigue failure occurring in the expansion / contraction part can be suppressed, and the product life of the piezoelectric actuator can be further improved. .
Here, as a method of setting the case load to zero, for example, there is a method of accommodating the laminated piezoelectric element in the storage case so that the expansion / contraction part does not undergo expansion deformation.

In the above-described second invention, the tensile load acting on the stretching unit is preferably a load of less than 1/100 of the generated driving force of the stacked piezoelectric device (claim 5).
As the assembly accuracy at the time of setting the multilayer piezoelectric element, a load that can be adjusted in general, that is, the tensile load of the expansion / contraction part at the time of setting the multilayer piezoelectric element is the driving generated by the multilayer piezoelectric element. When the load is less than 1/100 of the force, there is a sufficient margin against fatigue due to repeated operation of the laminated piezoelectric element of the stretchable part.
In addition, when the piezoelectric actuator is used alone, the expansion / contraction part does not cause expansion deformation, and the tensile load acting on the expansion / contraction part is preferably zero (Claim 6).
In this case, with respect to the piezoelectric actuator built in the injector, the deformation length of the expansion / contraction portion when the piezoelectric actuator is a single unit can be set to zero, and the possibility of causing fatigue failure in the expansion / contraction portion can be suppressed.
Therefore, the injector is less likely to cause fatigue failure in the stretchable portion of the piezoelectric actuator, and can maintain excellent performance for a long period of time.

Further, the preload acting in the direction of compressing the laminated piezoelectric element in the axial direction in a state of being built in the injector and receiving the urging force of the elastic member is 1 of the driving force generated by the laminated piezoelectric element. / 4 or more is preferable (claim 7).
In this case, a sufficient preload can be applied in the axial direction of the multilayer piezoelectric element that generates a driving force for operating the injector.
Therefore, it is possible to suppress the possibility of causing troubles such as delamination of the multilayer piezoelectric element while suppressing the tensile stress that constantly acts on the expansion and contraction part and extending the fatigue life.

In the third aspect of the invention, it is preferable that the tensile load acting on the expansion / contraction portion in the housing step is a load less than 1/100 of the driving force generated by the multilayer piezoelectric element.
As the assembly accuracy at the time of setting the multilayer piezoelectric element, a load that can be adjusted in general, that is, the tensile load of the expansion / contraction part at the time of setting the multilayer piezoelectric element is the driving generated by the multilayer piezoelectric element. When the load is less than 1/100 of the force, there is a sufficient margin against fatigue due to repeated operation of the laminated piezoelectric element of the stretchable part.
Further, in the housing step, in the housing case of the stacked piezoelectric element for realizing the extension deformation length of the stretchable portion when generating an elastic force substantially coinciding with the tensile load acting on the stretchable portion. Based on the reference insertion position of the laminated type, the laminated type is located at the assembly position where the laminated piezoelectric element is retracted in the insertion reverse direction by the contraction length in the axial direction of the storage case generated in the joining step. It is preferable to arrange a piezoelectric element (claim 10).

In this case, in the housing step, the laminated piezoelectric element is disposed at the assembly position determined in consideration of shrinkage that may occur in the housing case.
Therefore, in the piezoelectric actuator, it is possible to set the expansion deformation amount of the expansion / contraction part to substantially match the design value.
Therefore, in the piezoelectric actuator manufactured by the manufacturing method described above, there is little possibility that the tensile stress that constantly acts on the stretchable part will be excessive, and there is little possibility of causing fatigue failure.

The predetermined case load of less than 1/10 or less than 100 N of the driving force generated by the multilayer piezoelectric element includes zero.
When the predetermined case load is zero, the reference insertion position is determined from a state in which the working end surface of the storage case and the tip surface of the multilayer piezoelectric element are in contact with each other without load. It is at an arbitrary position in the range up to the state where a gap is left.

Further, the assembling position is equivalent to the length obtained by subtracting the extension deformation length of the expansion / contraction part when generating an elastic force substantially matching the tensile load acting on the expansion / contraction part from the contraction length. Preferably, the end of the multilayer piezoelectric element is in contact with the drive plate in the storage case compressed.

In this case, the housing step can be easily and reliably carried out by inserting the laminated piezoelectric element into the back of the housing case in which the stretchable portion is compressed in advance.
In the piezoelectric actuator, at least a part of the contraction length that may occur in the joining process is canceled by the free extension of the expansion / contraction part, and the gap between the end of the multilayer piezoelectric element and the working end surface The predetermined case load can be applied to the above.

The tensile load acting on the expansion / contraction part is zero, and the reference insertion position is the contraction length between the axial end of the multilayer piezoelectric element and the action end surface of the storage case. A position where the above gap is formed is preferred (claim 12).
In this case, in the piezoelectric actuator, a gap can be formed between the multilayer piezoelectric element and the working end surface. Therefore, it is possible to reliably eliminate the extension deformation generated in the expansion / contraction portion of the storage case.
Accordingly, it is possible to further suppress the possibility of fatigue failure by setting the tensile stress that constantly acts on the stretchable portion to zero.

Moreover, it is preferable that the said joining process is a process of welding the said base to the said opening edge part.
In this case, there is a high possibility that the storage case is contracted in the axial direction in the joining step, and the manufacturing method according to the third invention is particularly effective.
Examples of the welding method include laser welding, electron beam welding, and Tig welding.

Example 1
The piezoelectric actuator 1 of this example and its manufacturing method will be described with reference to FIGS.
As shown in FIG. 1, the piezoelectric actuator 1 of the present example is a piezoelectric actuator in which a laminated piezoelectric element 10 is accommodated in a storage case 20 having a stretchable portion 21 that can elastically expand and contract in the axial direction.
In the piezoelectric actuator 1, the case load acting in the axial compression direction on the stacked piezoelectric element 10 based on the elastic force of the expansion / contraction part 21 of the storage case 20 is zero.
This content will be described in detail below.

As shown in FIG. 1, the multilayer piezoelectric element 10 includes a holding member 12, a transmission member 13, and two end surfaces in the stacking direction of a ceramic laminate 11 in which ceramic layers 111 and electrode layers 112 are alternately stacked. It 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 this example is a laminate that exhibits a partial electrode structure in which sheet pieces 521 made of ceramic in which an electrode portion 503 and a holding portion 504 are formed 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 disposed on the outer peripheral surface of the ceramic laminate 11, and are substantially orthogonal to the lamination direction of the ceramic laminate 11. The cross section to be exhibited has a substantially barrel shape.

  Each side surface 115 is joined with a side electrode 116 as shown in FIG. Each side electrode 116 is electrically connected to the electrode layer 112 including the electrode portion 503 exposed on every other side 115, and the electrode layer 112 electrically connected to one side electrode 116 is: The other side electrode 116 is electrically insulated.

As shown in FIG. 1, the end portion of the side electrode 116 is electrically connected to the electrode terminal 117 disposed on the holding member 12 bonded to the end surface of the ceramic laminate 11.
When a base 30 to be described later is assembled to the multilayer 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 constituted as follows.
The laminated piezoelectric element 10 of this example is configured to generate a driving force by supplying electric power from the external electrode 31.

Further, as shown in FIG. 1, the transmission member 13 on the other end face of the ceramic laminate 11 includes a joint portion 131 having substantially the same diameter as the ceramic laminate 11 and a rod portion 132 having a smaller diameter than the joint portion 131. This 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 abut an action end surface 221 (to be described later) of the storage case 20.

As shown in FIG. 1, the storage case 20 is a substantially cup-shaped member having a cylindrical body portion 24 and a driving plate 22 that forms an operation surface 100 that transmits the driving force of the piezoelectric actuator 1. .
On the back surface of the drive plate 22, an action end surface 221 that abuts on the front end surface of the transmission member 13 is formed.

  As shown in FIG. 1, the trunk portion 24 is formed by forming a stretchable portion 21 made of a metal bellows in the vicinity of an end portion close to the working end surface 22. And this expansion-contraction part 21 is comprised so that it may be arrange | positioned in the state which provided the predetermined clearance gap with the outer peripheral surface of this rod part 132 in the outer peripheral side of the rod part 132 of the transmission member 13 of the said laminated piezoelectric element 10. FIG. It is.

In this example, the drive plate 22 is laser welded to the end of the storage case 20 on the side of the stretchable part 21.
Note that the portion of the storage case 20 that contacts the drive plate 22 can be formed integrally with the body portion 24 by drawing or the like using a hydraulic press.

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

And the piezoelectric actuator 1 of this example joins the storage case 20 and the base 30 by laser-welding the insertion part 32 inserted in the trunk | drum 24, as shown in FIG.
In the piezoelectric actuator 1, the end of the base 30 on the insertion portion 32 side and the end of the holding member 12 of the multilayer piezoelectric element 10 are brought into contact with each other, thereby accommodating the multilayer piezoelectric element 10 in the storage case 20. The position is regulated.

Next, a method for manufacturing the piezoelectric actuator 1 of this example will be described.
The process of manufacturing the piezoelectric actuator 1 includes an element forming process for producing the multilayer piezoelectric element 10, a multilayer piezoelectric element 10 is inserted from the opening end of the storage case 20, and the multilayer piezoelectric element 10 is stored in the storage case 20. The housing case 20 is opened in a state in which the axial end surface of the base 30 is brought into 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 portion.

First, the element formation process for producing 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 slurry for a green sheet, which is a piezoelectric element material.
This slurry is obtained by adding a binder, a small amount of a plasticizer and an antifoaming agent to a ceramic raw material to be a piezoelectric ceramic such as lead zirconate titanate (PZT), and then dispersing it in an organic solvent.

  In this example, the slurry was applied on 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 | generating the green sheet 500 from a slurry, the extrusion method other various methods other than a doctor blade method can be taken.

Next, as shown in FIG. 2, Ag—Pd paste, which is a conductive material, is applied by screen printing to a region that becomes the laminated surface 501 in the green sheet 500. Here, the electrode printing pattern 502 including the electrode portion 503 and the holding portion 504 is formed on the laminated surface 501 by applying the Ag-Pd paste while leaving one place corresponding to the outer peripheral portion of the laminated surface 501.
Thereafter, the slurry as an adhesive is applied to the entire laminated surface 501 to which the conductive material is applied.

  In this example, as shown in FIG. 2 and FIG. 3, as shown in FIG. Two types of electrode print patterns 502 having a mirror image relationship were formed.

Thereafter, as shown in FIG. 3, the sheet pieces 521 having the electrode sheet pattern 502 are punched from the green sheet 500, and the punched sheet pieces 521 are sequentially stacked.
Here, as shown in the figure, an intermediate laminate (not shown) is produced by alternately laminating sheet pieces 521 having two kinds of electrode print patterns 502 having a mirror image relationship, and this is fired to produce a ceramic. The laminated body 11 is produced.
In this example, the intermediate laminate was baked by holding in an atmosphere of 1200 ° C. for 2 hours, and then furnace cooling was performed.

Then, the electrode portion 503 applied to the laminated surface 501 (FIG. 1) forms each electrode layer 112 that forms a layer in the ceramic laminate 11, as shown in FIG.
The ceramic laminate 11 exposes the electrode portions 503 of every other electrode layer 112 on the opposite side surface, and the electrode layer 112 that exposes the electrode portion 503 on one side surface has the other side surface. Then, it is comprised so that the holding | maintenance part 504 may be exposed.

In addition, as shown in FIG. 4, the ceramic laminated body 11 of this example planarizes the side surface where the electrode part 503 and the holding | maintenance part 504 appear every other layer of the lamination direction, and forms a pair of substantially planar side surfaces 115. It is a thing.
As shown in FIG. 1, the multilayer piezoelectric element 10 of this example joins side electrodes 116 to the respective side surfaces 115 of the ceramic multilayer body 11 with a conductive adhesive, and in the stacking direction of the ceramic multilayer body 11. The holding member 12 and the transmission member 13 are joined to both end faces.
As the conductive adhesive, an Ag—Pd paste, an Ag paste, an Au paste, a Cu paste, or the like can be used.

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

As shown in FIG. 5, when accommodating the multilayer piezoelectric element 10 in the storage case 20, the tip surface of the transmission member 13 of the multilayer piezoelectric element 10 comes into contact with the working end surface 221 of the storage case 20 in advance. The reference insertion position of the multilayer piezoelectric element 10 that does not cause expansion / deformation in the expansion / contraction part 21 is calculated, and the contraction length in the axial direction of the storage case 20 that can occur in the joining process is calculated experimentally. .
The position where the multilayer piezoelectric element 10 was retracted in the insertion reverse direction by the contraction length from the reference insertion position was defined as the assembly position, and the multilayer piezoelectric element 10 was inserted and disposed at the assembly position.

In addition, it is experimentally calculated | required that the shrinkage | contraction of the axial direction of about 70 micrometers arises about the storage case 20 in the joining process by the laser welding of this example mentioned later.
Therefore, in this example, as shown in FIG. 6, the position where the gap G of 70 μm is formed between the working end surface 221 of the storage case 20 and the end of the transmission member 13 of the multilayer piezoelectric element 10 is the above assembly. Position.
Therefore, in the housing process of this example, as shown in FIG. 6, the multilayer piezoelectric element 10 is housed and arranged at the assembly position.

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

In the joining step, as described above, axial shrinkage of about 70 μm occurs in the storage case 20 due to the heat of welding.
At this time, inside the storage case 20, as shown in FIG. 7, the gap G (see FIG. 6) provided between the working end surface 22 and the end of the transmission member 13 in the storage step is narrowed. The gap disappears.
Here, when shrinkage as designed occurs in the joining process, the working end face 22 and the end of the transmission member 13 come into contact with zero load, and the expansion / contraction part 21 of the storage case 20 is stretched and deformed. It does not occur.

Thus, in this example, the laminated piezoelectric element is disposed at the assembly position determined in consideration of the shrinkage of the storage case that occurs in the joining step.
Therefore, the extension deformation length of the expansion / contraction part 21 in the piezoelectric actuator 1 can be set appropriately, and the tensile stress that constantly acts on the expansion / contraction part 21 can be suppressed.
Therefore, the piezoelectric actuator 1 of the present example is less likely to cause fatigue failure of the stretchable part 21, and can exhibit excellent performance over a long term specification.

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, in the manufactured piezoelectric actuator 1, a gap can be formed between the working end surface 22 and the laminated piezoelectric element 10.
Therefore, even if a slight error occurs in the amount of contraction in the axial direction of the storage case 20 in the joining step, the expansion / contraction part 21 can be reliably prevented from being stretched and deformed.

Further, a predetermined case load for axially compressing the laminated piezoelectric element 10 built in the piezoelectric actuator 1 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 expansion and deformation of the expansion / contraction part 21 substantially coincides with the predetermined case load. Then, a position retracted from the reference insertion position by the contraction length in the joining step in the insertion reverse direction is the assembly position.

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

(Example 2)
This example is an example in which the method for carrying out the housing step is changed based on the first embodiment.
In the piezoelectric actuator 1 of this example, the case load acting in the axial compression direction of the multilayer piezoelectric element 10 is less than 1/10 of the driving force generated by the multilayer piezoelectric element 10 greater than zero or A predetermined case load in the range of less than 100N was set.

And the accommodation process of this example is a process of assembling | attaching by making the edge part of the insertion direction of the laminated piezoelectric element 10 contact | abut to the action | operation end surface 221 of the storage case 20 compressed in the axial direction previously, as shown in FIG. It is.
In carrying out the housing step of this example, in order to compress the laminated piezoelectric element 10 in the axial direction in advance by the axial contraction length L1 of the housing case 20 that may occur in the joining step and a predetermined case load. The required extension deformation length L2 of the stretchable part 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 of the driving force generated by the multilayer piezoelectric element 10 or less than 100N.

The length obtained by subtracting the extension deformation length from the contraction length is defined as the predetermined length P to which the expansion / contraction part 21 is to be compressed. That is, P = L1-L2.
Therefore, in carrying out the housing step of this example, first, the housing case 20 is shrunk in the axial direction by the predetermined length P.

In the housing step, the laminated piezoelectric element is inserted and disposed at a position where the transmission member 13 of the laminated piezoelectric element 10 contacts the action end surface 221 of the compressed storage case 20. Thereafter, when the joining step is performed, the storage case 20 contracts in the axial direction by a length L1 substantially in agreement with the contraction length.
Thereafter, when the force that has compressed the storage case 20 is released, the storage case 20 expands and returns by the predetermined length P.

Here, when the original full length (inner side) of the storage case 20 is L, the full length (inner side) after execution of the joining step is L-L1.
The total length (inner side) of the compressed storage case 20 before the joining step is L−P = L− (L1−L2). Before the joining process, the working end surface 221 of the storage case 20 and the end of the multilayer piezoelectric element 10 are brought into contact with each other. Therefore, the contents of the storage case 20, that is, the total length of the multilayer piezoelectric element 10 is LP. = L- (L1-L2).

When the total length L-L1 after the joining process of the storage case 20 is compared with 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 step, the expansion / contraction part 21 of the storage case 20 is extended and deformed by L2.
The expansion / contraction part 21 that has undergone expansion deformation by L2 acts on the predetermined case load as in the original design in the direction in which the multilayer piezoelectric element 10 is compressed.

Here, in this example, the assembly position of the multilayer piezoelectric element 10 in the storage case 20 is exactly the same as the assembly position calculated by the method shown in the first embodiment.
That is, in this example, the stacked piezoelectric element at the assembly position is brought into contact with the working end surface 221 of the storage case 20 compressed in advance to a predetermined length by the storing step of bringing the end of the stacked piezoelectric element 10 into contact. This is an example in which the insertion arrangement of 10 is facilitated.
Other configurations and operational effects are the same as those in 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 this example is a device that injects approximately 180 MPa of high-pressure fuel stored in a common rail (not shown) into the engine cylinder.

  As shown in FIG. 10, the injector 6 is formed by assembling a housing 50 in which the piezoelectric actuator 1 according to the first embodiment is accommodated and a nozzle housing 60 in which an injection nozzle portion 61 including an injection nozzle 65 is formed.

  As shown in FIG. 10, the housing 50 having a substantially cylindrical outer shape has a recess 51 that is eccentric from the center axis and has a substantially circular cross section that is perforated from an end surface on the connector 70 side, and is substantially coaxial with the recess 51. A first cylinder 53 having a substantially circular cross section drilled from an end surface on the nozzle housing 60 side, and a fuel supply passage 52 drilled from the same end surface 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 that is drilled substantially coaxially from the bottom of the recess 51. In this example, the communication hole 54 is formed with a smaller diameter than the recess 51 and the first cylinder 53. The fuel supply passage 52 opens to a joint portion 520 provided at the 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 accommodated in the joint portion 520. It is.
Further, the joint portion 580 formed on the rear end side of the housing 50 has a drain passage 58 communicating with a three-way valve 62 described later, and a fuel outlet pipe 585 for discharging fuel is provided in the drain passage 58. It is connected.

The housing 50 has the piezoelectric actuator 1 in the recess 51 as shown in FIG. A first plunger 530 is accommodated in the first cylinder 53. The first plunger 530 has a body portion 531 that slides in the first cylinder 53 and a shaft portion 532 that passes through the communication hole 54.
The end surface of the shaft portion 532 is in contact with the drive plate 22 as the 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 having a diameter larger than that of the coil spring 552 in the vicinity of the end portion on the piezoelectric actuator 1 side. The urging rod 553 is pressed toward the piezoelectric actuator 1 by the urging force that the coil spring 552 acts on the seat portion 554.

  The spring seat 551 is configured to be engaged with a shelf portion extending from the recess 51 to the communication hole 54 to restrict the position of one end portion of the coil spring 552 in the axial direction. A through hole through which the urging rod 553 is inserted is formed in the central portion of the spring seat 551.

In the drive transmission unit 55 of this example, the static compressive load acting on the operating surface 100 of the piezoelectric actuator 1 from the biasing rod 553 is set to 1/4 or more of the driving force generated by the multilayer piezoelectric element 10. It is.
On the other hand, when the piezoelectric actuator 1 is used alone, the case load acting on the multilayer piezoelectric element 1 is zero.
Therefore, a preload more than ¼ of the driving force generated by the multilayer piezoelectric element 10 acts in the axial direction on the multilayer piezoelectric element 10 of the piezoelectric actuator 1 incorporated in the injector 6.

  Further, the injector 6 is laminated via an external electrode 31 (see FIG. 1) penetrating the base 30 by applying a predetermined voltage to a pair of electrodes (not shown) accommodated in the connector 70. 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 that is coaxially drilled from the end surface on the housing 50 side, a three-way valve 62 that communicates with the fuel supply passage 52 or the drain passage 58, and an injection nozzle portion 61. have.
A second cylinder 63 is formed so as to communicate with the first cylinder 53 when the nozzle housing 60 is assembled to the housing 50. In the second cylinder 63, a second plunger 630 is slidably accommodated.
Accordingly, one pressure chamber 506 is formed between the first plunger 530 and the second plunger 630 from the first cylinder 53 to the second cylinder 63.

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 by following the first plunger 530.
Here, the second cylinder 63 is formed with a smaller 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 act by the stroke of the second plunger 630 in the direction of the nozzle housing 60 to communicate the drain passage 58 and the back pressure chamber 610.

Further, when the second plunger 630 is positioned on the housing 50 side, the valve body is configured to allow the fuel supply passage 52 and the back pressure chamber 610 to communicate with each other.
That is, the back pressure chamber 610 of the injector 6 of this example is normally maintained at a high pressure by introducing high-pressure fuel, and the back pressure chamber 610 and the drain are discharged by the stroke of the second plunger 630 toward the nozzle housing 60 side. The back pressure chamber 610 is configured to be depressurized by communication with the passage 58.

  As shown in FIG. 10, the injection nozzle section 61 includes an injection nozzle 65 disposed on the tip end side 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 that is drilled coaxially with the axis. The needle hole 650 is opened at the tip of the injection nozzle 65 as an injection hole for injecting 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 so that a step portion 616 whose diameter changes is located in the fuel reservoir 612. Further, the nozzle needle 615 is configured such that the nozzle hole at the tip of the injection nozzle 65 can be opened and closed by a spherical tip 613.

  Further, as shown in FIG. 10, a back pressure chamber 610 communicating with the three-way valve 62 is formed on the other end side of the nozzle needle 615. A 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 is configured to act on the step portion 616 of the nozzle needle 615 with a pressure in a direction in which the nozzle needle 615 is retracted toward the housing 50 side.

Below, operation | movement of the injector 6 of this example applied to the common rail injection system of the diesel engine which is not shown in figure is demonstrated.
In order to operate the injector 6 and inject fuel at a high pressure 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 in contact with the operating 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 voltage.

  And the 1st plunger 530 which contact | abutted to the urging | biasing rod 553 and stroked moves the inside of the 1st cylinder 53 to the nozzle housing 60 side. As the volume in 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. 2 The plunger 630 is moved toward the injection nozzle 65 side.

  Due to 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 body, the passage from the fuel supply passage 52 to the back pressure chamber 610 is blocked, 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 inside of the back pressure chamber 610 is decompressed.

The pressure difference generated between the back pressure chamber 610 and the fuel reservoir 612 as the pressure in the back pressure chamber 610 decreases generates a force that pushes up the nozzle needle 615 toward the housing 50 as shown in FIG. As the nozzle needle 615 moves toward the housing 50, the nozzle hole at the tip of the injection nozzle 615 that has been closed by the tip 613 of the nozzle needle 615 opens. When the injection hole is opened, the high-pressure fuel in the fuel reservoir 612 is injected into the engine cylinder.
In this example, an engine ECU (not shown) that controls the engine controls the injector 6 attached to each engine cylinder, and the fuel is repeatedly injected as described above at an appropriate timing.

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 this example, there is little possibility of causing troubles such as delamination of the multilayer piezoelectric element 10 inside the piezoelectric actuator 1.

And relatively, in the injector 6 of this example, the said case load which needs to be generated in the expansion-contraction part 21 of the storage case 20 can be suppressed. In this example, the case load is zero.
Therefore, in the piezoelectric actuator 1 of the present example, the tensile stress that constantly acts on the stretchable part 21 can be made zero, and there is little risk of fatigue failure occurring in the stretchable part 21.
Other configurations and operational effects are the same as those in the first embodiment.

Example 4
This example is an example in which the fatigue life of the expansion / contraction part of the storage case was examined for the piezoelectric actuator of the injector of Example 3.
In this example, the relationship between the magnitude of the elastic force due to the expansion and contraction of the expansion / contraction portion and the fatigue life when the piezoelectric actuator was used alone was examined. Here, the elastic force due to the expansion and contraction of the expansion / contraction part substantially coincides with 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 when the piezoelectric actuator is a single unit (set load)) acting on the multilayer piezoelectric element of the piezoelectric actuator and the failure probability of 50% or less when operated 2 × 109 times are shown. The relationship with the operation amplitude (μm) of the piezoelectric actuator for maintaining the above was obtained.
In the figure, the horizontal axis indicates the case load ratio (the ratio of the case load to the driving force 1000 N generated by the multilayer piezoelectric element) acting on the multilayer piezoelectric element, and the vertical axis defines the operation amplitude of the piezoelectric actuator. is doing.
An area in which the failure probability of 50% or less at the time of 2 × 109 operations, which is a design target, can be realized is shown as a hatched area.
Here, the failure probability at the time of operating 2 × 109 times is the proportion of individuals that have failed in the mother set when the piezoelectric actuator of a sufficient population is operated 2 × 109 times respectively.

Here, the area of the negative portion at the left end of the horizontal axis shows a state where a gap is formed between the end of the laminated piezoelectric element and the working end surface of the storage case when the piezoelectric actuator is a single unit. In other words, it originally indicates a region where the case load of the multilayer piezoelectric element is zero.
Therefore, in this example, for the sake of convenience, in order to quantify and express the size of the gap, the load required for compression until the working end surface and the end of the multilayer piezoelectric element come into contact with each other is expressed as a negative load. expressing.

According to the figure, in order to achieve both a total length ratio of 0.1%, which is a general operation amplitude of a multilayer piezoelectric element, and a failure probability of 50% when operated 2 × 109 times, It can be seen that the case load ratio should be 1/10 or less. The reason for this can be considered as follows.
That is, if the case load is reduced, the stretchable deformation length of the stretchable part can be set short, and the tensile force acting on the stretchable part can be suppressed. And in the expansion-contraction part which suppressed the tensile force, it is possible to suppress a possibility that fatigue failure will occur.
Other configurations and operational effects are the same as in the third embodiment.

FIG. 3 is a cross-sectional view illustrating the structure of the piezoelectric actuator in the first embodiment. FIG. 3 is an explanatory diagram illustrating a printing procedure for an electrode print pattern in the first embodiment. FIG. 3 is an explanatory diagram showing a procedure for laminating ceramic laminates in Example 1. Sectional drawing which shows the laminated structure of the ceramic laminated body in Example 1. FIG. Explanatory drawing which shows the accommodation process in Example 1. FIG. Explanatory drawing which shows the assembly | attachment structure by the accommodation process in Example 1. FIG. Sectional drawing which shows the structure of the other piezoelectric actuator in Example 1. FIG. Sectional drawing which shows the structure of the other piezoelectric actuator in Example 1. FIG. Explanatory drawing which shows the assembly | attachment procedure in the accommodation process in Example 2. FIG. Sectional drawing which shows the structure of the injector which incorporated the piezoelectric actuator in Example 3. FIG. 10 is a graph showing the relationship between case load and amplitude of a multilayer piezoelectric element in Example 4.

Explanation of symbols

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

Claims (13)

A piezoelectric actuator for an injector built in an injector for fuel injection,
A storage case in the axial direction with an elastically stretchable stretch unit, Ri Na houses a laminated type piezoelectric elements,
During the piezoelectric actuator itself, tensile load acting on the expansion portion of the storage case, Ri load der less than 1/10 of the driving force generated by the zero or the stacked piezoelectric device,
A piezoelectric actuator characterized in that in a state of being built in the injector and given a preload, a tensile load acting on the expansion / contraction section is zero . In claim 1, the tensile load acting on the stretching unit, a piezoelectric actuator, which is a load of less than 1/100 of the driving force generated in the stacked piezoelectric device. 3. The piezoelectric actuator according to claim 1, wherein the expansion / contraction portion is not stretch-deformed and a tensile load acting on the expansion / contraction portion is zero. In a fuel injection injector having a built-in piezoelectric actuator that houses a laminated piezoelectric element in a storage case having an expansion / contraction part that expands and contracts in the axial direction,
The injector includes an elastic member that applies an axial load to an operation surface on which the driving force of the piezoelectric actuator acts.
The piezoelectric actuator, at the time of the piezoelectric actuator itself, tensile load acting on the expansion portion of the storage case, Ri tensile load der less than 1/10 of the driving force generated by the zero or the stacked piezoelectric device,
An injector for fuel injection, wherein a tensile load acting on the expansion / contraction part is zero in a state of being built in the injector and applied with a preload . In claim 4, the tensile load acting on the elastic part, an injector for fuel injection, which is a load of less than 1/100 of the driving force generated in the stacked piezoelectric device. 6. The injector for fuel injection according to claim 4, wherein when the piezoelectric actuator is a single unit, the expansion / contraction part is not deformed and the tensile load acting on the expansion / contraction part is zero.   The preload acting in any one of claims 4 to 6, wherein the preload, which is built in the injector and receives the urging force of the elastic member, acts in the axial compression direction of the multilayer piezoelectric element. An injector for fuel injection, wherein the injector is 1/4 or more of the driving force generated by the piezoelectric element. A piezoelectric actuator for an injector according to any one of claims 1 to 3, a tubular body portion formed at least in part the expansion unit which expands and contracts elastically in the axial direction, the barrel portion one is disposed on an end portion on which accommodates the laminated piezoelectric device in the housing case to which the driving force of the stacked piezoelectric device is a drive plate which acts, the other end of the barrel of the In a manufacturing method for manufacturing a piezoelectric actuator formed by joining a base to a part,
An element forming step for producing the laminated piezoelectric element;
An accommodating step of inserting the multilayer piezoelectric element from the opening end of the storage case and disposing the multilayer piezoelectric element at a predetermined position in the axial direction of the storage case;
A joining step of joining the base to the opening end of the storage case in a state where the axial end surface of the base is in contact with the rear end surface of the multilayer piezoelectric element housed in the storage case. ,
In the accommodating step, in the storage case of the piezoelectric actuator, as tensile load acting on the elastic portion becomes zero or 1/10 less than the load of the driving force generated in the stacked piezoelectric device, the laminate A piezoelectric actuator manufacturing method characterized by containing a piezoelectric element. 9. The method of manufacturing a piezoelectric actuator according to claim 8, wherein the tensile load acting on the expansion / contraction portion in the housing step is a load less than 1/100 of the driving force generated by the multilayer piezoelectric element. The multilayer piezoelectric element according to claim 8 or 9, wherein, in the housing step, the stretchable piezoelectric element for realizing an extension deformation length of the expansion / contraction portion when an elastic force substantially corresponding to a tensile load acting on the expansion / contraction portion is generated. Based on the reference insertion position in the storage case, the assembly position is a position where the stacked piezoelectric element is retracted in the insertion reverse direction by the contraction length in the axial direction of the storage case generated in the joining step. A method of manufacturing a piezoelectric actuator, comprising: arranging the laminated piezoelectric element. In claim 10, the assembly position is the length obtained by subtracting the extension deformation length of the extension / contraction part when generating an elastic force substantially corresponding to the tensile load acting on the extension / contraction part from the contraction length, A method of manufacturing a piezoelectric actuator, characterized in that the end of the laminated piezoelectric element is in contact with the drive plate in the storage case in which the expansion / contraction part is compressed. In Claim 10, the tensile load which acts on the expansion-contraction part is zero, and the reference insertion position is between the end part in the axial direction of the multilayer piezoelectric element and the action end surface of the storage case. A method for manufacturing a piezoelectric actuator, wherein the gap is a position where a gap longer than the contraction length is formed.   13. The method of manufacturing a piezoelectric actuator according to claim 8, wherein the joining step is a step of welding the base to the opening end.

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