JPH10313578A - Piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength of each terminal as a whole, to prevent fracture against external force, for example, vibration, and at the same time to facilitate connecting work, by alternately laminating a plate-shaped piezoelectric element and an electrode plate, and by connecting the terminals being radially extended and provided from each electrode plate to interconnecting longerons. SOLUTION: An actuator 12 is cylindrically formed by laminating a plurality of disk-shaped piezoelectric elements and positive and negative electrodes alternately, and an end plate 15 and a piston 18 are provided at the end part of a back side and a tip side, respectively. A pair of terminals is provided on the electrode plate of the positive electrode toward outside with an interval of 180 deg.. Also, a pair of terminals is provided on the electrode plate of the negative electrode and are directed with an interval of 90 deg. each other. A longeron 32 consisting of a U-shaped conductive material is mounted to each terminal line, a groove part 32a is formed in axial direction on the outer surface of the longeron, and the longeron 32 is electrically connected to each terminal, for example, by soldering, thus continuing conduction to the other electrodes and elements even when one portion of the terminal is broken and damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of a piezo actuator used for a fuel injection valve or the like.

[0002]

2. Description of the Related Art A fuel injection valve applied to an in-cylinder fuel injection type spark ignition type internal combustion engine is required to have high responsiveness and high opening / closing accuracy. As a fuel injection valve that meets such a demand, a fuel injection valve that controls the opening and closing of a needle valve by supplying a signal current to a piezo actuator to expand and contract the needle valve is known.

A piezo actuator is formed by laminating a large number of disk-shaped piezo elements and positive and negative electrode plates alternately, and performs expansion and contraction displacement by controlling energization via terminals extending from the electrode plates. (Japanese Unexamined Patent Publication No.
No. 121791).

[0004]

In a conventional piezo actuator, a terminal extended from an electrode plate is sequentially connected by soldering to a terminal adjacent to each other between a positive electrode and a negative electrode.
All the piezo elements are energized by lead wires connected to terminals located at the ends.

However, for this reason, if the connecting portion of the terminal is peeled off or the terminal is broken even in one place, there arises a problem that it becomes impossible to supply current to the electrodes and elements thereafter. Normally, a plurality of terminals are provided for each electrode. Therefore, even if one of the terminals is broken, current does not necessarily stop immediately.However, in the case of a piezo actuator, the expansion / contraction operation due to the displacement, distortion of the electrode plate, In addition, vibrations and the like act, so that the terminals are easily broken.Moreover, there are many connection points between the terminals,
It can be said that there is much room for improvement in order to obtain reliable reliability.

[0006]

According to a first aspect of the present invention, in an actuator in which plate-shaped piezo elements and electrode plates are alternately stacked, terminals extending radially from each electrode plate are connected to each other. A longitudinal member is provided, and electric current is applied to each electrode plate via the longitudinal member.

According to a second aspect of the present invention, the terminal of the present invention has an arm extending radially from the electrode plate and a projection extending from the tip of the arm in a direction substantially perpendicular to the arm.
The longitudinal member has a groove in which the arm is fitted, and a terminal protrusion is joined to the surface of the longitudinal member in a state where the terminal of each electrode plate is inserted into the groove.

According to a third aspect of the present invention, the longitudinal member according to the above aspect of the invention has a configuration in which legs are provided on an outer peripheral surface of the piezo element in a state of being insulated.

According to a fourth aspect of the present invention, the height of the leg is set to 1.5% or more of the entire length of the actuator.

According to a fifth aspect of the present invention, the longitudinal member is formed of an elastic member that can expand and contract along the direction of displacement of the piezo element.

According to a sixth aspect of the present invention, there is provided the electrode plate of the above invention,
It is assumed that the terminal has a plurality of sets of terminals alternately protruding along the circumferential direction of the piezo element.

According to a seventh aspect of the present invention, in the above-mentioned invention, the positive and negative electrodes each have two terminals at 180 intervals on the circumference, and the positive and negative electrodes are 90 degrees apart from each other on the circumference. It is assumed that they are arranged in.

According to an eighth aspect of the present invention, in the above invention, a cylindrical member surrounding the piezo element and holding each of the longitudinal members of the positive and negative electrodes is formed of an insulator, and a metal film is formed around the insulator. It shall be formed.

According to a ninth aspect of the present invention, the cylindrical member has one end fixed to an end plate provided at an end of the actuator.

[0015]

According to the first and second aspects of the present invention, a large number of electrode plates arranged in the direction of expansion and contraction of the actuator have their terminals connected to the longitudinal members instead of adjacent ones. Therefore, even if some of the terminals are broken, the current to other electrodes and elements is not interrupted, and each terminal is held in common by a longitudinal member. Therefore, the strength of the terminal is improved as a whole, and the terminal is hardly damaged by external force such as vibration.
As a result, the reliability of the piezo actuator becomes extremely high.

According to the second aspect of the present invention, the terminal projection is exposed on the outer surface of the longitudinal member through the groove of the longitudinal member, so that the operation for connecting the terminal and the longitudinal member by soldering or the like is easy. And excellent productivity can be obtained.

According to the third aspect of the present invention, since the longitudinal member is fitted to each electrode terminal in a state of being mounted on the outside of the piezo element by its leg, the work when connecting the terminal and the longitudinal member is performed. The performance is further improved.

According to the fourth aspect of the present invention, the height of the leg portion of the longitudinal member is set to be 1.5% or more of the actuator length, so that the direction of distortion of the electrode terminal when the actuator expands and contracts. Is sufficiently secured, thereby making it possible to more reliably prevent the terminal from being damaged.

According to the fifth aspect of the present invention, since the longitudinal member can expand and contract along the direction of displacement of the piezo element, the connection portion with the terminal is also easily displaced with the displacement of the element. The terminal can be prevented from being subjected to excessive force and its durability can be improved.

According to the invention of claim 6 or claim 7,
Since the terminals of the positive and negative electrodes are located at a plurality of locations alternately around the piezo element, external force such as strong vibration or inertia force acts on the piezo element from the side and deforms in one direction. Even if one of the terminals is damaged, the power supply is ensured by the terminal on the other side, so that the reliability against vibration and the like is further improved.

According to the invention of claim 8, the strength of the longitudinal member is improved by being held by the cylindrical member, and noise from the element and the electrode is radiated to the outside by the metal film covering the outer periphery of the cylindrical member. Can be prevented.

According to the ninth aspect of the present invention, one end of the cylindrical member is fixed to the end plate at the end of the actuator, so that the holding strength of the cylindrical member is ensured and the durability is higher. be able to.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a fuel injection valve 1 to which a piezo actuator as a first embodiment is applied.
1 shows a schematic cross-sectional structure.

In the fuel injection valve 1, an actuator 12 is housed inside a cylindrical main body 11, and the main body 1
A nozzle body 14 in which a needle valve 13 is housed is provided at the front end of the nozzle body 1.

As will be described later in detail, the actuator 12 is formed in a columnar shape by laminating a number of thin plate-shaped piezo elements. The end plate 15 provided at the rear end thereof is
Positioned via a ball 17 with respect to a cap 16 fitted to the main body 11. A piston 18 is provided on the distal end side, and the piston 18 is fitted in a cylinder portion 19 formed in the main body via a seal ring 20 in an oil-tight and slidable manner.

A pressure chamber 21 is defined in front of the piston 18 and between the cylinder section 19 and the piston 18 is urged rearward by the tension of a disc spring 22 housed in the pressure chamber 21. ing.

A needle valve 13 for opening and closing a nozzle hole 23 opened at the tip of the nozzle body 14 is housed therein. The needle valve 13 has a large-diameter piston portion 24 at its base end, and the piston portion 24 is slidably held along a cylinder portion 25 formed on the inner periphery of the holder. A coil spring 27 is interposed in a pressure chamber 26 defined behind the piston portion 24, and the needle valve 13 is urged in a valve closing direction by the tension of the spring 27.

The space inside the nozzle body 14 ahead of the piston portion 24 is a fuel chamber 28, and this fuel chamber 2
The fuel 8 is supplied with fuel adjusted to a predetermined pressure through a fuel passage 31 connected to a fuel supply port 29. The rear pressure chamber 26 communicates with the rear pressure chamber 21 via a passage 30.

In this fuel injection valve, a fuel injection amount is determined by a fuel injection control circuit (not shown) using, for example, the rotation speed of the internal combustion engine and the intake air amount as parameters, and an injection signal having a pulse width corresponding to the fuel injection amount is determined. Is applied to the actuator 12 to perform fuel injection.

The details of the operation of the fuel injection valve 1 when such an injection signal is input are as follows. First, in the fuel injection valve 1, the actuator 12 is in an extended state during non-injection, and the volume of the pressure chamber 21 is kept small. The pressure of the fuel supplied to the fuel chamber 28 also acts on the pressure chambers 26 and 21 via the sliding gap between the needle valve piston portion 24 and the cylinder portion 25.
, The needle valve 13 is held closed by the tension of the spring 27.

When a drive signal in the compression direction is applied from this state, the actuator 12 and the piston 19 contract immediately to the desired position, so that the pressure chamber 21 expands its volume and reduces the pressure. . This pressure drop is immediately transmitted to the pressure chamber 26 behind the needle valve via the passage 30. At this time, the sliding gap between the needle valve piston portion 24 and the cylinder portion 25 acts as an orifice. The pressure change in the fuel chamber 28 is delayed with respect to the pressure drop, and the fuel chamber 28 becomes relatively high in pressure. Based on the pressure difference between the front and rear of the piston portion 24, the needle valve 13
7, the lift operation is performed in the rearward direction to open the injection hole 23 to perform the fuel injection.

When the actuator 12 is extended again after a time determined in accordance with the required fuel injection amount at that time, the pressure in the pressure chambers 21 and 26 rises, so that the needle valve 13 moves in the valve closing direction. Then, the fuel injection ends. The closed state of the needle valve 13 during non-injection is maintained by the pressure equilibrium state before and after the piston 24 as described above.

By the way, in such a fuel injection valve 1, as described above, if an electrode of the actuator 12 is damaged by vibration or the like and an element that does not operate partially occurs, the amount of expansion / contraction displacement is reduced by that amount. The fuel injection amount corresponding to the injection signal cannot be obtained. An object of the present invention is to obtain a piezo actuator which does not cause a malfunction due to such damage of the electrode, and a specific configuration example for that is as shown in FIG.

2 or 3, the actuator 12 has a structure in which a large number of disk-shaped piezo elements and positive and negative electrodes are alternately stacked. A pair of terminals 12A is provided on the negative electrode plate, and a pair of terminals 12B is provided on the negative electrode plate, and the positive and negative terminals 12A and 12B are oriented so as to be 90 degrees apart from each other.

A longitudinal member 32 made of a conductive material having a substantially U-shaped cross section is attached to each terminal row so as to interconnect a large number of terminals 12A or 12B arranged in the axial direction of the actuator 12. Can be Longitudinal member 32
A slit-shaped groove 32a is formed in the outer surface of the vertical direction, and the longitudinal member 32 and the terminal 12A or the terminal 12B are electrically connected by soldering or the like through the groove 32a.

According to such a configuration, in the electrode plates arranged in a large number in the direction of expansion and contraction of the actuator 12, the respective terminals 12A or 12B are connected to the longitudinal member 32 instead of adjacent ones. Therefore, even if a part of a large number of terminals is broken, the power supply to the other electrodes and elements is not interrupted, and each terminal 12A or 12B
Is held in common, so that the strength of the terminal is improved as a whole, and the terminal is hardly damaged by external force such as vibration.

The longitudinal member 32 may be formed of an elastic material having high elasticity, and its end may be fixed to the end plate 15 or the piston 18 so as to expand and contract together with the actuator 12. Vertical member 32 and terminal 12A
Alternatively, since the connection portion with 12B is also displaced in the axial direction together with the element, the possibility of causing a problem such as terminal breakage is further reduced.

Also, in this embodiment, since the terminals 12A and 12B of the positive and negative electrodes are provided at a plurality of locations so as to be alternately located around the piezo element, an external force such as strong vibration or an inertial force is applied to the actuator 12. Acts from the side and deforms in one direction, so that even if the terminal on either side is damaged, energization is ensured by the terminal on the other side, further improving the reliability against vibration etc. I do.

FIGS. 4 and 5 show a second embodiment of the present invention. As shown in the figure, a protrusion 12p is provided on both sides of the distal end of the terminal 12A or 12B to form a substantially T-shape, and a second groove 32b in which the protrusion 12p fits is formed by a longitudinal member. 32 is formed so as to open outward.

The longitudinal member 32 is formed with a leg 32c so as to be seated on the outer peripheral surface of the element. The leg 32c is electrically insulated so as not to short-circuit the element and the electrode plate.
This means that the entire longitudinal member 32 or the leg 32c is formed of an electrical insulator and only the connection portion between the terminals 12A and 12B is formed of metal, or an insulator is interposed between the leg 32c and the element surface. This ensures an insulating state.

As shown in FIG. 4, the grooves 32a and 32b are open at one end of the longitudinal member 32. The longitudinal member 32 is inserted into each terminal row through this opening, and then the grooves 32b are formed. By soldering the terminal protrusions 12p to the upper surface, the vertical connection member 32 and the respective terminals 12A or 12B are electrically connected.

As described above, according to this embodiment, the terminal protrusion 12 is formed through the grooves 32a and 32b of the longitudinal member 32.
Since p is exposed on the outer surface of the longitudinal member 32, the terminal 12
The work when connecting A, 12B and the longitudinal member 32 by soldering or the like is easy, and excellent productivity is obtained.

Each of the electrode terminals 12A or 1A is placed in a state where the longitudinal member 32 rides on the outer periphery of the element by its leg 32c.
2B, it is not necessary to hold the longitudinal member 32 at the time of connection work, so that workability is further improved.

According to the findings of the present applicant, in each of the above embodiments, the height of the terminal 12A or 12B protruding from the element surface or the height CL of the longitudinal member leg 32c (see FIG. 5). 1.5% of the total length of the actuator 12
By making the length longer, a sufficient amount of deformation of the terminal in the strain direction when the actuator 12 expands and contracts is ensured, so that the damage can be more reliably prevented.

FIGS. 6 to 8 show a third embodiment of the present invention. This is achieved by using a cylindrical member 33 provided with a fitting groove 33a into which four longitudinal members 32 arranged around the actuator 12 are fitted as in the case of FIG.
Is surrounded. The cylindrical member 33 is formed of an electrical insulator in order to prevent a short circuit between the adjacent longitudinal members 32, and a metal film 33b is formed on an outer peripheral surface thereof. One end of the cylindrical member 33 is fixed to the end plate 15.

According to this embodiment, the strength of the longitudinal member 32 is improved by being held in the fitting groove 33a of the cylindrical member 33, and the element and the element are formed by the metal film 33b covering the outer periphery of the cylindrical member 33. It is possible to prevent noise from being emitted from the electrodes to the outside. In addition, with the configuration in which one end of the cylindrical member 33 is fixed to the end plate 15, the holding strength of the cylindrical member 33 is ensured, and the durability can be further increased.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a fuel injection valve to which a piezo actuator according to a first embodiment of the present invention is applied.

FIG. 2 is a side view of the piezo actuator of the embodiment.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a perspective view of a main part of a piezo actuator according to a second embodiment of the present invention.

FIG. 5 is a front sectional view of the same.

FIG. 6 is a side sectional view of a Piazo actuator according to a third embodiment of the present invention.

FIG. 7 is a sectional view taken along line BB of FIG. 6;

8 is an enlarged view of a portion C in FIG. 7;

[Explanation of symbols]

 Reference Signs List 1 fuel injection valve 11 body of fuel injection valve 12 actuator 12A, 12B terminal 12p terminal protrusion 13 needle valve 14 nozzle body 15 end plate 16 cap 17 ball 18 piston 19 cylinder portion 20 seal ring 21 pressure chamber 22 disc spring 23 jet Hole 24 Piston part 25 Cylinder part 26 Pressure chamber 27 Coil spring 28 Fuel chamber 29 Fuel supply port 30 Passage 32 Longitudinal member 32a, 32b Groove part 32c Leg 33 Cylindrical member 33a Fitting groove 33b Metal film

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Fukuda Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa

Claims (9)

[Claims] 1. An actuator in which plate-shaped piezo elements and electrode plates are alternately stacked, a vertical member is provided for interconnecting terminals extending radially from each electrode plate, and the vertical member is provided with a vertical member. A piezoelectric actuator characterized in that a current is supplied to each electrode plate through the piezo actuator. 2. The terminal has an arm extending radially from the electrode plate and a projection extending from the tip of the arm in a direction substantially perpendicular to the arm, and the longitudinal member is fitted with the arm. 2. The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator has a configuration in which a terminal protruding portion is joined to a surface side of the longitudinal member in a state where a terminal of each electrode plate is inserted into the groove portion. 3. 3. The longitudinal member has a leg portion which is seated in an insulating state on an outer peripheral surface of the piezo element.
A piezo actuator according to claim 1. 4. The height of the leg is set to 1.1 of the total length of the actuator.
The piezo actuator according to claim 3, wherein the piezo actuator is set to 5% or more. 5. The piezo actuator according to claim 1, wherein the longitudinal member is formed of an elastic member that can expand and contract along the direction of displacement of the piezo element. 6. The piezo actuator according to claim 1, wherein the electrode plate has a plurality of sets of terminals alternately protruding along a circumferential direction of the piezo element. 7. The positive and negative electrodes each have two terminals at 180 intervals on the circumference, and the positive and negative electrodes are arranged at 90 degrees on the circumference. 5. The piezo actuator according to 4. 8. A cylindrical member surrounding the piezo element and holding each longitudinal member of the positive and negative electrodes is formed of an insulator, and a metal film is formed on an outer peripheral surface of the cylindrical member. The piezo actuator according to claim 1. 9. The piezo actuator according to claim 8, wherein one end of the cylindrical member is fixed to an end plate provided at an end of the actuator.