JP2007288866A - Piezo actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure high airtightness in the case that a lead wire is connected to a piezoelectric stack. <P>SOLUTION: In the piezoelectric actuator where one end of the lead wire 3 is connected to the piezoelectric stack and the other end of the lead wire 3 is taken out of a casing 2, for a rubber bush 4, which performs sealing between the lead wire 3 and the casing 2, a core insertion hole 412 is made which abuts on the inserted core wire 31 of the lead wire 3. Then, the sealing between the rubber bush 4 and the lead wire 3 is made by the abutment between the core insertion hole 412 and the core wire 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezo actuator including a piezo stack in which a large number of piezo elements are stacked, and is particularly suitable for an injector of a fuel injection device.

  A conventional fuel injection device is configured to inject and supply high-pressure fuel stored in a common rail into a combustion chamber of each cylinder of an internal combustion engine via an injector. The injector includes a nozzle that opens and closes the nozzle hole with a needle and injects fuel when the valve is opened, and a piezo actuator that controls the opening and closing operation of the nozzle by controlling the pressure acting on the side of the needle opposite to the nozzle hole ( For example, see Patent Document 1).

  As is well known, a piezo actuator forms a piezo stack by laminating a large number of piezo elements while forming an insulating layer, and after connecting a lead electrode of a metal round bar to the piezo stack, the piezo stack is casing. It is stored in.

Here, the minimum plate thickness of the piezo element is several tens of μm, and a relatively high voltage is applied, so that an environment in which a short circuit between adjacent piezo elements is likely to occur is obtained. Therefore, a short circuit is easily generated when moisture enters the piezo actuator, and the piezo actuator is required to have particularly high airtightness. Therefore, glass hermetic has been applied between the electrode and the casing to achieve both insulation and airtightness.
JP 2002-257002 A

  However, taking into account the downsizing of the piezo actuator and the degree of freedom of electrode extraction, it is desirable that the electrode extraction from the piezo stack is a lead wire.

  As in the past, after connecting the lead electrode to the piezo stack and applying glass hermetic, it is also possible to connect the lead wire to the lead electrode, but in this case the cost of glass hermetic is high and the connection location is Decrease in reliability due to increase becomes a problem.

  In view of the above points, an object of the present invention is to ensure high airtightness when a lead wire is connected to a piezo stack.

  In the present invention, the piezo stack (1) is housed in the casing (2), one end of the lead wire (3) is connected to the piezo stack (1), and the other end of the lead wire (3) is outside the casing (2). The rubber bush (4), which is a piezoelectric actuator taken out in (2) and seals between the lead wire (3) and the casing (2), has a core wire insertion hole (412) into which the core wire (31) is inserted. The core wire insertion hole (412) has at least a part of an inner wall having a hole diameter with which the outer peripheral surface of the core wire (31) can come into contact.

  When the rubber bush (4) and the lead wire (3) are sealed by contact between the rubber bush (4) and the covering member (32) of the lead wire (3), the core wire (31) ) And the covering member (32), moisture enters the piezoelectric actuator. According to the present invention, the rubber bush (4) is brought into contact with the rubber bush (4) and the core wire (31). Since the seal between the lead wire (3) and the lead wire (3) is made, the intrusion of moisture from between the core wire (31) and the covering member (32) is prevented. Therefore, even when the lead wire (3) is connected to the piezo stack (1), high airtightness can be ensured.

  In this case, the rubber bush (4) can be provided with an annular protrusion (44) in the core wire insertion hole (412).

  If it does in this way, the surface pressure of the contact part of rubber bush (4) and core wire (31) will go up, and airtightness will improve.

  Further, the rubber bush (4) can be provided with an annular protrusion (45) at a portion that comes into contact with the casing (2).

  If it does in this way, the surface pressure of the contact part of rubber bush (4) and casing (2) will go up, and airtightness will improve.

  Further, the rubber bush (4) can be provided with a stepped portion (42) with which the end of the covering member (32) abuts on the end of the core wire insertion hole (412) on the outer side of the casing.

  In this way, the stepped portion (42) functions as a positioning stopper for the lead wire (3). Therefore, the length of the exposed portion of the core wire (31) is controlled, and the core wire (31) is inserted into the core wire insertion hole (412) until the covering member (32) contacts the stepped portion (42). The welded portion length between the side electrode (14) and the core wire (31) of 1) can be managed, and the reliability of the welded portion can be improved.

  Moreover, a core wire (31) can be made into a single core wire. In this way, the problem in the case where the core wire (31) is a stranded wire, that is, the problem of moisture entering the piezo actuator through the gap between the wires does not occur, and high airtightness is reliably ensured. be able to.

  Further, the rubber bush (4) is disposed on one end side in the piezoelectric element stacking direction of the piezo stack (1), and a housing hole (221) for housing the rubber bush (4) is formed in the casing (2). A positioning surface (222) for preventing movement of the rubber bush (4) in the piezoelectric element stacking direction can be formed in the storage hole (221).

  In this way, rattling of the rubber bush (4) in the piezo element stacking direction is prevented. For this reason, wear of the seal portion due to relative movement between the rubber bush (4) and the core wire (31) is prevented, and the reliability of the seal portion is improved. Further, the welded portion is prevented from being damaged by the relative movement between the rubber bush (4) and the piezo stack (1), and the reliability of the welded portion is improved.

  Further, the rubber bush (4) is disposed on one end side of the piezo stack (1) in the piezo element stacking direction, and the lead wire (3) is guided between the rubber bush (4) and the piezo stack (1). A guide member (5) can be provided.

  When the rubber bush (4) and the guide member (5) are formed integrally, there are many undercuts and molding with a mold is not easy, but molding with a mold is easy by separating them. become.

  In addition, the code | symbol in the bracket | parenthesis of each means described in a claim and this column shows the correspondence with the specific means as described in embodiment mentioned later.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a sectional view of a piezo actuator according to a first embodiment of the present invention.

  The piezo actuator includes a casing 2 in which a piezo stack 1 that expands and contracts due to charge and discharge is stored. This casing 2 has a metal stepped cylindrical shape at one end side opening of a cylindrical cylindrical member 21 made of metal. The cap 22 is hermetically welded, and a metal thin diaphragm 23 is hermetically welded to the opening on the other end side of the cylindrical member 21. A metal rod 24 that transmits the displacement of the piezo stack 1 is hermetically welded to the center of the diaphragm 23. The rod 24 includes a truncated cone-shaped conical portion 241 and a columnar cylindrical portion 242. The conical portion 241 is disposed inside the casing 2, and the cylindrical portion 242 is inserted into a through hole formed at the center of the diaphragm 23 and protrudes outside the casing 2.

  The piezo stack 1 includes a laminate 11 in which a large number of piezo elements and internal electrodes are alternately laminated, and end plates 12 and 13 made of alumina are arranged at both ends of the piezo elements in the stacking direction (hereinafter referred to as the piezo element stacking direction). One end plate 12 is in contact with the cap 22 of the casing 2 and a rubber bush 4 described later, and the other end plate 13 is in contact with the conical portion 241 of the rod 24. A pair of side electrodes 14 is provided on the side surface of the multilayer body 11, and one of the two internal electrodes located on both sides of each piezo element is connected to one side electrode 14, and the other internal electrode is It is connected to the other side electrode 14.

  A pair of lead wires 3 is connected to the side electrode 14 of the piezo stack 1. The lead wire 3 has a core wire 31 covered with a covering member 32. The core wire 31 used in the present embodiment is a single core wire. A stepped columnar rubber bush 4 for sealing between the lead wire 3 and the cap 22 is inserted into the cap 22 of the casing 2. The lead wire 3 passes through the rubber bush 4 and is taken out of the casing 2 and connected to an external drive circuit (not shown). The rubber bush 4 is made of fluororubber having high heat resistance. In addition, an insulating member (not shown) is provided on the outer periphery of the laminate 11, the surface of the side electrode 14, and the connection portion between the side electrode 14 and the lead wire 3 in order to ensure insulation between the casing 2. Has been.

  FIG. 2 is an exploded cross-sectional view showing the lead wire 3, the rubber bush 4, and the cap 22 of the casing 2. As shown in FIG.

  As shown in FIG. 2, the rubber bush 4 has a pair of insertion holes 41 into which the lead wires 3 are inserted. The insertion hole 41 includes three insertion hole portions 411 to 413 and communicates the inside and the outside of the casing 2.

The cylindrical first insertion hole 411 located on the outermost side of the casing is in contact with the outer peripheral surface of the covering member 32 by inserting the core wire 31 and the covering member 32. Only the core wire 31 is inserted into the cylindrical second insertion hole portion 412 located at the intermediate portion, and comes into contact with the outer peripheral surface of the core wire 31. More specifically, the outer peripheral surface of the core wire 31 contacts the inner wall surface of the second insertion hole 412 over the entire periphery. The second insertion hole 412 corresponds to the core wire insertion hole of the present invention.

The third insertion hole 413 located on the innermost side of the casing expands the distance between the tip ends of the pair of core wires 31 (that is, the ends on the inner side of the casing) to the same size as the distance between the pair of side electrodes 14. It has a function and spreads outward as it goes from the casing outer side to the inner side.

The first insertion hole 411 and the second insertion hole 412 are arranged coaxially. In the free state, the inner diameter of the first insertion hole 411 is set larger than the inner diameter of the second insertion hole 412. More specifically, in the free state, the inner diameter of the first insertion hole 411 is larger than the outer diameter of the covering member 32, and the inner diameter of the second insertion hole 412 is smaller than the outer diameter of the core wire 31. Therefore, there is a step 42 at the boundary between the first insertion hole 411 and the second insertion hole 412, and the end of the covering member 32 can come into contact with the step 42. Further, on the outer peripheral surface of the rubber bush 4, an outer peripheral end surface 43 that is orthogonal to the axis of the rubber bush 4 is formed in an intermediate portion in the axial direction of the rubber bush 4. Further, the inner diameter of the second insertion hole 412 is smaller than the inner diameter of the third insertion hole 413.

  The cap 22 of the casing 2 has a stepped cylindrical storage hole 221 in which the rubber bush 4 is stored. An inner peripheral end face 222 that is orthogonal to the axis of the cap 22 is formed in the storage hole 221 at an intermediate portion in the axial direction of the cap 22. As shown in FIG. 1, when the assembly of the piezo actuator is completed, the outer peripheral end surface 43 of the rubber bush 4 abuts on the inner peripheral end surface 222 of the cap 22 to move the rubber bush 4 in the piezo element stacking direction. It comes to stop. The inner peripheral end surface 222 of the cap 22 corresponds to the positioning surface of the present invention.

  Next, assembly of the piezo actuator will be described. FIG. 3 is a cross-sectional view showing the piezo actuator disassembled into a piezo stack 1, an assembly such as a lead wire 3, and an assembly such as a cylindrical member 21.

  First, as shown in FIG. 3, a piezo stack 1, an assembly such as a lead wire 3, and an assembly such as a cylindrical member 21 are prepared.

  The assembly of the lead wires 3 and the like is manufactured as follows. Unnecessary portions of the covering member 32 of the lead wire 3 are peeled off, and the lead wire 3 is inserted into the insertion hole 41 from the first insertion hole 411 side of the rubber bush 4. In the process of inserting the lead wire 3 into the insertion hole 41, the core wire 31 is guided by the third insertion hole 413 and spreads outward. At this time, since the inner diameter of the third insertion hole 413 is larger than that of the second insertion hole 412, the core wire 31 can be easily taken out. Further, by inserting the lead wire 3 into the insertion hole 41, the inner peripheral surface of the second insertion hole portion 412 and the core wire 31 are brought into close contact with each other, thereby ensuring airtightness. Thereafter, the cap 22 of the casing 2 is put on the rubber bush 4 through which the lead wire 3 has passed. Thereby, airtightness between the rubber bush 4 and the cap 22 is performed.

  Here, the length L1 (see FIG. 2) of the exposed portion of the core wire 31 is managed, and the lead wire 3 is inserted to a position where the end portion of the covering member 32 abuts on the stepped portion 42, whereby the insertion hole of the core wire 31 is inserted. The protrusion length L2 from 41, and by extension, the welded portion length between the side electrode 14 and the core wire 31 can be managed.

  On the other hand, the cylindrical member 21, the diaphragm 23, and the rod 24 are integrated by welding to produce an aggregate such as the cylindrical member 21.

  After preparing the piezo stack 1, the assembly of the lead wires 3, and the assembly of the cylindrical member 21, they are assembled. First, an assembly such as the lead wire 3 is disposed on the end face of the piezo stack 1, and the lead wire 3 is welded to the side electrode 14. Thereafter, the piezo stack 1 is inserted into an assembly such as the cylindrical member 21, the cap 22 is inserted into the opening of the cylindrical member 21, and the cap 22 and the cylindrical member 21 are welded. Thereby, the piezo actuator shown in FIG. 1 is completed.

  In the present embodiment, the inner peripheral surface of the second insertion hole 412 of the rubber bush 4 and the core wire 31 of the lead wire 3 are brought into close contact with each other, and a seal is formed between the rubber bush 4 and the lead wire 3. Therefore, even when the lead wire 3 is connected to the side electrode 14 of the piezo stack 1, high airtightness can be ensured.

  Further, since the step portion 42 of the rubber bush 4 functions as a positioning stopper for the lead wire 3, the protruding length L <b> 2 of the core wire 31 from the insertion hole 41, and the welded portion length between the side electrode 14 and the core wire 31 is managed. And the reliability of the welded portion can be improved.

  In addition, the inner peripheral end surface 222 of the housing hole 221 formed in the cap 22 of the casing 2 prevents the rubber bush 4 from rattling in the piezoelectric element stacking direction. For this reason, wear of the seal portion due to relative movement between the rubber bush 4 and the core wire 31 is prevented, and the reliability of the seal portion is improved. Further, damage to the welded portion between the side electrode 14 and the lead wire 3 due to relative movement between the rubber bush 4 and the piezo stack 1 is prevented, and the reliability of the welded portion is improved.

(Second Embodiment)
A second embodiment of the present invention will be described. 4 is a cross-sectional view of the rubber bush in the piezo actuator according to the second embodiment, FIG. 5 is an enlarged cross-sectional view of part A in FIG. 4, and FIG. It is. In addition, the same code | symbol is attached | subjected to the same or equivalent part as 1st Embodiment, and the description is abbreviate | omitted.

  As shown in FIGS. 4 and 5, two annularly continuous protrusions 44 are formed on the inner peripheral surface of the second insertion hole portion 412 in the insertion hole 41 of the rubber bush 4. Further, the inner diameter of the tip of the protrusion 44 in the free state is set to be smaller than the outer diameter of the core wire 31 of the lead wire 3. Therefore, as shown in FIG. 6, when the lead wire 3 is inserted into the insertion hole 41, the tip of the protrusion 44 is elastically deformed and closely adheres to the core wire 31, and the surface pressure at the contact portion between the protrusion 44 and the core wire 31 increases. Airtightness is improved.

(Third embodiment)
A third embodiment of the present invention will be described. 7 is a cross-sectional view of the rubber bush in the piezo actuator according to the third embodiment, FIG. 8 is an enlarged cross-sectional view of a portion B in FIG. 7, and FIG. FIG. In addition, the same code | symbol is attached | subjected to the same or equivalent part as 1st Embodiment, and the description is abbreviate | omitted.

  As shown in FIGS. 7 and 8, two annular protrusions 45 are formed on the outer peripheral surface of the rubber bush 4 at the portion inserted into the storage hole 221 of the cap 22. Further, the outer diameter of the tip of the protrusion 45 in the free state is set to be larger than the inner diameter of the storage hole 221 of the cap 22. Therefore, as shown in FIG. 9, when the cap 22 is attached to the rubber bush 4, the tip of the protrusion 45 is elastically deformed and closely contacts the inner peripheral surface of the storage hole 221, and the protrusion 45 and the inner peripheral surface of the storage hole 221 The surface pressure of the contact portion is increased and the airtightness is improved.

(Fourth embodiment)
A fourth embodiment of the present invention will be described. FIG. 10 is a sectional view of a piezo actuator according to the fourth embodiment. In addition, the same code | symbol is attached | subjected to the same or equivalent part as 1st Embodiment, and the description is abbreviate | omitted.

  In the first embodiment, the third insertion hole 413 for guiding the core wire 31 is formed in the rubber bush 4. However, in the present embodiment, the third insertion hole 413 is formed in a member different from the rubber bush 4. ing.

  That is, as shown in FIG. 10, the third insertion hole 413 is formed in the resin guide member 5 that is separate from the rubber bush 4. The guide member 5 is inserted into the cap 22 of the casing 2 and disposed between the rubber bush 4 and the piezo stack 1.

  When the third insertion hole 413 is also formed in the rubber bush 4, there are many undercuts and molding with a mold is not easy, but the third insertion hole 413 is not formed in the guide member 5 separately from the rubber bush 4. Forming the rubber bush 4 by a mold becomes easy.

(Other embodiments)
The piezo actuator of each of the above embodiments can be applied to an injector of a fuel injection device and can also be applied to other devices.

1 is a cross-sectional view of a piezo actuator according to a first embodiment of the present invention. It is sectional drawing which decomposes | disassembles and shows the lead wire, rubber bush, and cap of FIG. It is sectional drawing which decomposes | disassembles and shows the piezoelectric actuator of FIG. It is sectional drawing of the rubber bush in the piezoelectric actuator which concerns on 2nd Embodiment of this invention. It is an expanded sectional view of the A section of FIG. It is sectional drawing which shows the state which mounted | wore the rubber bush of FIG. 4 with the lead wire. It is sectional drawing of the rubber bush in the piezoelectric actuator which concerns on 3rd Embodiment of this invention. It is an expanded sectional view of the B section of FIG. It is sectional drawing which shows the state which attached the cap of the casing to the rubber bush of FIG. It is sectional drawing of the piezoelectric actuator which concerns on 4th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piezo stack, 2 ... Casing, 3 ... Lead wire, 4 ... Rubber bush, 31 ... Core wire, 32 ... Cover member, 412 ... 2nd insertion hole part (core wire insertion hole).

Claims (7)

A piezo stack (1) in which a large number of piezo elements are stacked is housed in a casing (2), and one end of a lead wire (3) having a core wire (31) covered with a covering member (32) is attached to the piezo stack (1). A piezoelectric actuator connected and having the other end of the lead wire (3) taken out of the casing (2),
A rubber bush (4) for sealing between the lead wire (3) and the casing (2);
The rubber bush (4) has a core wire insertion hole (412) into which the core wire (31) is inserted,
The core wire insertion hole (412) has at least a part of an inner wall having a hole diameter with which the outer peripheral surface of the core wire (31) can contact. The piezoelectric actuator according to claim 1, wherein the rubber bush (4) includes an annular protrusion (44) on an inner peripheral surface of the core wire insertion hole (412). The piezo actuator according to claim 1 or 2, wherein the rubber bush (4) includes an annular protrusion (45) at a portion in contact with the casing (2). The said rubber bush (4) is provided with the level | step-difference part (42) with which the edge part of the said covering member (32) contact | abuts at the edge part of the casing outer side in the said core wire insertion hole (412). The piezo actuator according to any one of 1 to 3. The piezoelectric actuator according to any one of claims 1 to 4, wherein the core wire (31) is a single core wire. The rubber bush (4) is disposed on one end side of the piezo stack (1) in the piezo element stacking direction,
The casing (2) is formed with a storage hole (221) in which the rubber bush (4) is stored,
The positioning hole (222) for preventing the movement of the rubber bush (4) in the piezoelectric element stacking direction is formed in the storage hole (221). Piezo actuator described in 1. The rubber bush (4) is disposed on one end side of the piezo stack (1) in the piezo element stacking direction,
The guide member (5) for guiding the lead wire (3) is provided between the rubber bush (4) and the piezo stack (1). The piezo actuator according to any one of the above.

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