JP3944931B2 - Piezo actuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pressurizing structure of a piezo actuator that expands by an applied voltage.
[0002]
[Prior art]
2. Description of the Related Art Some fuel injection valves and the like provided in automobile engines include a piezo actuator in which piezo elements that expand according to an applied voltage are stacked, and a needle (valve element) is opened through the piezo actuator. By driving the needle with a piezo actuator, the high-speed response of the fuel injection valve is enhanced, and the injectable range for accommodating high output can be expanded. In addition, a small amount of fuel can be stably injected, and fuel consumption can be reduced.
[0003]
Conventionally, there is a piezoelectric actuator of this type as shown in FIG. 4, for example (see Japanese Patent Application Laid-Open No. 7-193295).
[0004]
This will be described. The laminated piezoelectric actuator 71 has end plates 72 and 73 attached to both ends thereof, and a cylindrical spring 74 that compresses the piezoelectric actuator 71 via the end plates 72 and 73 is provided. The piezoelectric actuator 71 is applied with a pressure of 20 to 30% of the normal operating force via the cylindrical spring 74, so that stable operability is ensured.
[0005]
When the piezo actuator 71 is manufactured, the cylindrical spring 74 is joined to the end plates 72 and 73 by welding while being heated to a predetermined temperature. When the cylindrical spring 74 is lowered to room temperature after welding, a predetermined pressurized load is applied to the piezo actuator 71 due to a difference in thermal expansion.
[0006]
[Problems to be solved by the invention]
However, since the conventional cylindrical spring 74 has a structure that generates a pressurized load using a difference in thermal expansion, there is a problem that the pressurized load is likely to vary.
[0007]
In addition, since the pressurizing load applied by the cylindrical spring 74 is greatly changed by the temperature change of the piezo actuator 71, there is a problem that the operation characteristics of the piezo actuator 71 are not stable.
[0008]
In particular, when such a piezo actuator is applied to a device that is used in a high temperature environment such as a fuel injection valve provided in an automobile engine, the pressurized load is reduced at a high temperature, and the stable operation of the piezo actuator becomes even more difficult. It is.
[0009]
To cope with this, it is conceivable to increase the temperature when welding the cylindrical spring 74 to each of the end plates 72 and 73 to about 300 ° C. This will overheat the piezo actuator 71, in this case There is a possibility of causing peeling of an adhesive or the like used when laminating a plurality of piezoelectric elements.
[0010]
The present invention has been made in view of the above problems, and an object thereof is to apply a pressurized load to a piezo actuator without difficulty.
[0011]
[Means for Solving the Problems]
The piezo actuator according to claim 1, wherein a plurality of stacked piezo elements extending by an applied voltage , a pair of end plates joined to both ends of the stacked piezo elements, and the stacked piezo elements A coil spring that is arranged so as to wrap around the outer periphery and pressurizes the piezo element in the compression direction via each end plate, an annular spring case connected to one end of the coil spring, and a cylindrical shape in which the spring case is screwed An actuator guide having a guide portion and a bottom portion that applies an axial load of the coil spring to the one end plate; a recess formed in one of the bottom portion of the actuator guide and the end plate; and the recess portion And when the load of the coil spring is applied to the end plate via the spring case and the actuator guide is rotated. Serial twisting load in the rotational direction to the piezoelectric element is intended to comprise a ball to prevent the occurrence.
[0012]
According to a second aspect of the present invention, in the piezoelectric actuator according to the first aspect, the piezoelectric actuator includes a gas chamber in which the piezoelectric elements stacked inside the coil spring are accommodated .
[0013]
According to a third aspect of the present invention, the piezoelectric actuator according to the second aspect of the present invention includes a cylindrical bellows that partitions the gas chamber .
[0014]
According to a fourth aspect of the present invention, there is provided the piezoelectric actuator according to the second aspect, wherein the gas chamber is defined and a bottomed cylindrical member slidably fitted to the actuator guide, the actuator guide, An O-ring for sealing the gas chamber interposed in the fitting portion with the bottomed cylindrical member is provided .
[0017]
Operation and effect of the invention
In the first aspect of the present invention, the piezo actuator expands instantaneously when a voltage is applied to each piezo element and charges are stored, and contracts instantaneously by cutting off the voltage and short-circuiting both terminals.
[0018]
A piezoelectric actuator is applied with a predetermined compressive load in the axial direction with respect to a normal operating force via a coil spring. The coil spring in which the wire is wound in a coil shape has a small unbalance load applied in the radial direction of each piezo element, and ensures stable operability of the piezo actuator.
[0019]
A coil spring in which a wire is wound in a coil shape has a structure in which the wire is greatly elastically deformed according to the distance between both ends of the laminated piezo elements, so that the piezoelectric spring can be used without being affected by the processing accuracy and assembly accuracy of the coil spring. The applied pressure load can be managed with high accuracy.
[0020]
In addition, a change in the pressurizing load due to a difference in thermal expansion between the coil spring and each piezoelectric element is small, and a change in the pressurizing load due to a temperature change is suppressed, so that stable operability of the piezoelectric actuator is ensured.
[0021]
Co Irubane is relatively rotated with respect to the piezoelectric actuator via a ball with its expansion, without twisting load is applied to the piezoelectric element from the coil spring, stable operating properties of the piezoelectric actuator is obtained.
[0022]
By changing the screwing position relative to the actuator guide bar Nekesu, the coil spring can be adjusted easily compressive load of the coil spring to be applied to the piezoelectric actuator, productivity, improvement of maintainability achieved.
[0023]
In the second aspect of the present invention, the gas chamber in which the piezo element is accommodated is defined, so that dew condensation due to a temperature change of the piezo actuator can be prevented from occurring in each piezo element.
[0024]
By disposing the gas chamber inside the coil spring, an increase in size of the piezo actuator can be avoided.
[0025]
In the invention according to claim 3 , the bellows expands and contracts with expansion and contraction of each piezoelectric element, and the sealing performance of the gas chamber is ensured.
[0026]
In the invention according to claim 4 , the actuator guide and the bottomed cylindrical member slide with the expansion and contraction of each piezo element, and the sealing performance of the gas chamber is ensured through an O-ring interposed therebetween. Is done.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0028]
As shown in FIG. 1, the piezo actuator 1 includes a plurality of disk-shaped piezo elements 13 stacked on both sides of a disk-shaped internal electrode plate and fixed with an adhesive. Each piezo element increases its thickness instantly when voltage is applied through the internal electrode plates and charges are stored, and the thickness decreases instantaneously by cutting off the voltage and shorting both internal electrode plates. It has become.
[0029]
Between the piezo elements 13, negative internal electrode plates and positive internal electrode plates are alternately stacked. The negative-side internal electrode plate and the positive-side internal electrode plate are coupled to the respective strip-shaped external electrodes provided on the side surfaces of the laminated piezoelectric elements 13 and connected to the drive circuit via lead wires. Yes.
[0030]
A pair of end plates 2 and 3 are provided at both ends of each piezo element 13 stacked in a columnar shape. Each end plate 2 and 3 is bonded to the piezo element 13 via an internal electrode plate.
[0031]
A coil spring 4 is provided to pressurize each piezoelectric element 13 stacked in a columnar shape in the compression direction. A pair of spring cases 6 and 5 are attached to both ends of the coil spring 4. The coil springs 4 are interposed between the spring cases 6 and 5 in an extended state, and the piezoelectric elements 13 stacked between the spring cases 6 and 5 via the end plate 2.3 are sandwiched.
[0032]
An actuator guide 7 is provided between the upper spring case 6 and the upper end plate 2. The actuator guide 7 is formed in a bottomed cylindrical shape, and has a disc-shaped bottom portion 21 on which the upper end plate 2 is seated, and a guide portion 22 that extends from the bottom portion 21 in a cylindrical shape. A screw portion 9 is carved on the outer periphery of the guide portion 22, and the annular upper spring case 6 is screwed into the screw portion 9. Thereby, the spring support part 6b formed in the spring case 66 can hold | maintain the upper part of the coil spring 4 in arbitrary positions. Similarly, by accommodating the end plate 3 in the bottomed cylindrical spring case 5, the spring support portion 55 holds the lower end of the coil spring 4.
[0033]
A concave portion 24 recessed on a cone is formed at the center portion of the upper end plate 2 so as to face the bottom portion 21 of the actuator guide 7, and a ball 8 made of a hard material such as a steel ball is formed between the concave portion 24 and the actuator guide 7. Is installed. Note that the recess 24 can be formed on the bottom 21 side.
[0034]
The upper and lower end plates 2, 3, the spring cases 6, 5, the coil spring 4, the actuator guide 7, and the ball 8 constituting the piezo actuator 5 are arranged coaxially with the piezo elements 13 stacked in a cylindrical shape. The
[0035]
The operation will be described next.
[0036]
The piezo actuator 1 expands when a voltage is applied to each piezo element 13 and contracts when the voltage is cut off.
[0037]
The piezoelectric actuator 1 is applied with a predetermined proportion of compressive load in the axial direction with respect to the normal operating force via the coil spring 4. The coil spring 4 in which the wire is wound in a coil shape has a small unbalance load applied in the radial direction of each piezo element 13, and stable operability of the piezo actuator 1 is ensured.
[0038]
The coil spring 4 in which the wire is wound in the shape of a coil has a structure in which the wire is greatly elastically deformed according to the distance between the spring cases 6 and 5, so that the piezoelectric actuator 1 is not affected by the processing accuracy and assembly accuracy of the coil spring 4. It is possible to manage the pressurizing load applied to the head with high accuracy.
[0039]
Further, the change in the pressurization load due to the difference in thermal expansion between the coil spring 4 and each piezoelectric element 13 is small, and the change in the pressurization load due to the temperature change is suppressed, and the operation characteristics of the piezoelectric actuator 1 are stabilized.
[0040]
By changing the screwing position of the upper spring case 6 with respect to the actuator guide 7, the compression load of the coil spring 4 applied to the piezo actuator 1 by the coil spring 4 can be easily adjusted, and the productivity and maintainability can be improved.
[0041]
Since the ball 8 is interposed between the actuator guide 7 and the end plate 2 at this time, the spring case 6 and the actuator guide 7 are screwed together without rotating the coil spring 4 by rotating the actuator guide 7. The position can be changed.
[0042]
Furthermore, it is not necessary to heat the piezo actuator 1 when the coil spring 4 is assembled, and peeling of the adhesive or the like can be avoided.
[0043]
Since the coil spring 4 is disposed so as to wrap around the outer periphery of each piezo element 13, the piezo actuator 5 can be made compact.
[0044]
As the coil spring 4 expands and contracts, the coil spring 4 rotates relative to the piezo actuator 1 via the ball 8, and a torsional load is not applied to each piezo element 13 from the coil spring 4, so that stable operability of the piezo actuator 1 is obtained.
[0045]
Next, the embodiment shown in FIG. 2 will be described. In addition, the same code | symbol is attached | subjected to a corresponding part with FIG.
[0046]
A gas chamber 14 for housing each piezoelectric element 13 stacked inside the coil spring 4 is provided.
[0047]
The gas chamber 14 is defined by a pair of actuator guides 7 and 10 and a bellows 15 or the like. Nitrogen gas is sealed in the gas chamber 14.
[0048]
The upper actuator guide 7 is formed in a bottomed cylindrical shape, and has a disc-shaped bottom portion 21 on which the upper end plate 2 is seated, and a guide portion 22 that extends from the bottom portion 21 in a cylindrical shape. A screw portion 9 is carved on the outer periphery of the guide portion 22, and the annular upper spring case 6 is screwed into the screw portion 9.
[0049]
The lower actuator guide 10 is formed in a cylindrical shape, and the lower end thereof is seated on the lower spring case 5 via the O-ring 16.
[0050]
The bellows 15 is formed in a cylindrical shape whose cross section is bent in a bellows shape, and is interposed between the actuator guides 7 and 10 in a compressed state.
[0051]
The operation will be described next.
[0052]
By filling the gas chamber 14 with nitrogen gas, it is possible to prevent dew condensation due to a temperature change of the piezo actuator 1 from occurring in each piezo element 13.
[0053]
The bellows 15 expands and contracts with the expansion and contraction of each piezo element 13, and the O-ring 16 is pressed against the lower spring case 5 by the elastic restoring force of the bellows 15, and the sealing performance of the gas chamber 14 is ensured.
[0054]
Further, since the gas chamber 14 is disposed inside the coil spring 4, an increase in size of the piezo actuator 1 can be avoided.
[0055]
Next, the embodiment shown in FIG. 3 will be described. In addition, the same code | symbol is attached | subjected to a corresponding part with FIG.
[0056]
A gas chamber 14 for housing each piezoelectric element 13 stacked inside the coil spring 4 is provided.
[0057]
The gas chamber 14 is defined by a pair of actuator guides 7, 10 and the like. Nitrogen gas is sealed in the gas chamber 14.
[0058]
The upper actuator guide 7 is formed in a bottomed cylindrical shape, and has a disk-shaped bottom portion 21 on which the upper end plate 2 is seated, and a guide portion 22 that extends from the bottom portion 21 in a cylindrical shape. A screw portion 9 is carved on the outer periphery of the guide portion 22, and the annular upper spring case 6 is screwed into the screw portion 9.
[0059]
The lower actuator guide 10 is formed in a cylindrical shape, and its lower end is coupled to the lower end plate 3 by welding.
[0060]
The lower actuator guide 10 is fitted to the outside of the cylindrical portion 22 of the upper actuator guide 7, and an O-ring 17 is interposed therebetween.
[0061]
The operation will be described next.
[0062]
Also in this case, the gas chamber 14 is filled with nitrogen gas, so that dew condensation due to a temperature change of the piezo actuator 1 can be prevented from occurring in each piezo element 13.
[0063]
As each piezo element 13 expands and contracts, the actuator guides 7 and 10 slide, and the gas chamber 14 is secured through an O-ring 17 interposed therebetween.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a piezoelectric actuator showing an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a piezo actuator showing another embodiment.
FIG. 3 is a cross-sectional view of a piezo actuator showing still another embodiment.
FIG. 4 is a cross-sectional view of a piezo actuator showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piezo actuator 2 End plate 3 End plate 4 Coil spring 5 Spring case 6 Spring case 7 Actuator guide 8 Ball 9 Screw part 10 Actuator guide 13 Piezo element 14 Gas chamber 15 Bellows 16 O ring 17 O ring 21 Bottom part 22 Guide part 24 Recessed part

Claims (4)

A plurality of stacked piezo elements stretched by an applied voltage;
A pair of end plates joined to both ends of the laminated piezo elements;
A coil spring which is arranged so as to wrap around the outer periphery of the stacked piezo elements and pressurizes the piezo elements in the compression direction via the end plates;
An annular spring case connected to one end of the coil spring;
An actuator guide having a cylindrical guide portion into which the spring case is screwed and a bottom portion that applies an axial load of the coil spring to the one end plate;
A recess formed in one of the bottom of the actuator guide and the end plate;
The coil spring is housed in the concave portion and applies a load of the coil spring to the end plate via the spring case, and prevents a torsional load in the rotation direction from being generated in the piezoelectric element when the actuator guide is rotated. With the ball,
A piezo actuator characterized by comprising: A gas chamber is provided in which each piezoelectric element stacked inside the coil spring is accommodated.
The piezo actuator according to claim 1. A cylindrical bellows that partitions the gas chamber is provided.
The piezo actuator according to claim 2. A bottomed cylindrical member that divides the gas chamber and is slidably fitted to the actuator guide;
  An O-ring for sealing the gas chamber interposed in a fitting portion between the actuator guide and the bottomed cylindrical member;
The piezo actuator according to claim 2, further comprising:

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