JP2014174075A - Piezoelectric element, pressure sensor, and method of increasing impact resistance strength of piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure detection element having high impact resistance.SOLUTION: A piezoelectric element includes a piezoelectric plate made of single crystal zinc oxide and the like and an insulation plate whose impact resistance strength is larger than the piezoelectric plate and that has conducting means on the surface thereof. The piezoelectric plate and insulation plate are laminated and bundled in parallel to the surface direction thereof.

Description

  The present invention relates to a piezoelectric element that detects pressure. More specifically, the present invention relates to a piezoelectric element having high impact resistance, a pressure sensor having high impact resistance, and a method for increasing the impact resistance of a piezoelectric element. This piezoelectric element is suitably used particularly for measuring the combustion pressure of an internal combustion engine such as an automobile.

  In recent years, in the automobile industry, various sensors are attached to an engine, and the operation of the engine is controlled based on data detected by the sensor. In particular, various improvements have been made to control the operation of the engine in order to improve running economy. An example is a lean combustion control system. In an engine employing this system, a pressure sensor using a piezoelectric material as a pressure detection element is incorporated in a cylinder, and the combustion pressure of the engine is directly measured (for example, Patent Documents 1 and 2).

  In a lean combustion control system, since the fuel gas concentration is burned in a lean state, preignition occurs more frequently than in a normal engine, and the combustion pressure at that time reaches several times the normal combustion pressure. . Therefore, the sensor for measuring the combustion pressure is also required to have a strength capable of withstanding the impact pressure generated during preignition, particularly a high impact strength of the piezoelectric element. However, the existing piezoelectric material does not have sufficient impact strength, and the piezoelectric material may be destroyed during preignition.

Patent Document 3 discloses a technique for improving heat resistance by changing the piezoelectric material from lead titanate to lithium niobate (LiNbO ₃ ).

  However, none of these patent documents mentions to increase the impact pressure resistance.

Patent Publication 2011-174882 Patent Publication 2000-277233 Patent Publication 5-172680

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric element having high impact resistance.

  The inventor has intensively studied to achieve the above object. The impact resistance strength of a piezoelectric element using a conventional piezoelectric material indicates a unique value of the material constituting the piezoelectric element. Therefore, it is conventionally considered that the impact resistance strength of the pressure detecting element cannot be changed except by changing the piezoelectric material.

  On the other hand, the present inventors surprisingly found that when a piezoelectric element is formed by stacking an insulating plate formed using an insulating material having an impact strength higher than that of the piezoelectric element on the piezoelectric element, the piezoelectric element is formed. It was discovered that the impact resistance strength of the device was greatly improved.

  The present invention has been completed based on the above discovery.

  The present invention for achieving the above object is described below.

[1] A piezoelectric element having a piezoelectric plate and an insulating plate having an impact resistance greater than that of the piezoelectric plate and having conductive means on its surface,
A piezoelectric element formed by laminating a piezoelectric plate and an insulating plate with the surface directions of the piezoelectric plate and the insulating plate being parallel.

[2] A piezoelectric plate and a first insulating plate having a larger impact resistance than the piezoelectric plate and having a conductive means on the surface thereof, with the surface directions of the piezoelectric plate and the first insulating plate being parallel to each other. Laminated laminates, and
A second insulating plate having a thickness of ± 5 μm with respect to the thickness of the laminated plate and having a greater impact strength than the piezoelectric plate;
A piezoelectric element formed by abutting surfaces in the thickness direction of the laminated plate and the second insulating plate.

[3] A piezoelectric plate and a third insulating plate having a thickness of ± 5 μm with respect to the thickness of the piezoelectric plate and having a higher impact strength than the piezoelectric plate, the piezoelectric plate and the third insulating plate Arrange the surface in the thickness direction with the plate,
Further, a piezoelectric element formed by laminating a fourth insulating plate that covers the upper surfaces of the piezoelectric plate and the third insulating plate and has a greater impact strength than the piezoelectric plate.

  [4] The piezoelectric element according to any one of [1] to [3], wherein the piezoelectric plate is made of single crystal zinc oxide, lithium niobate, lithium tantalate, or quartz.

  [5] The piezoelectric plate according to any one of [1] to [3], wherein the insulating plate is made of quartz glass, quartz, alumina, or diamond (however, when the piezoelectric plate is made of quartz, the insulating plate is quartz). element.

  [6] A pressure sensor incorporating the piezoelectric element according to any one of [1] to [3].

  [7] A piezoelectric plate and an insulating plate having a greater impact strength than the piezoelectric plate and having a conductive means on the surface thereof are laminated and bundled with the surface directions of the piezoelectric plate and the insulating plate being parallel. A method for increasing the impact strength of a piezoelectric element.

[8] A piezoelectric plate and a first insulating plate having a greater impact strength than the piezoelectric plate and having a conductive means on the surface thereof, with the surface directions of the piezoelectric plate and the first insulating plate being parallel to each other. Laminated laminates, and
A second insulating plate having a thickness of ± 5 μm with respect to the thickness of the laminated plate and having a greater impact strength than the piezoelectric plate; and a thickness direction between the laminated plate and the second insulating plate. A method of increasing the impact strength of a piezoelectric element that is bundled by butting surfaces.

[9] A piezoelectric plate and a third insulating plate having a thickness of ± 5 μm with respect to the thickness of the piezoelectric plate and having a higher impact strength than the piezoelectric plate, the piezoelectric plate and the third insulating plate Arrange the surface in the thickness direction with the plate,
Furthermore, a method for increasing the impact strength of a piezoelectric element in which the upper surfaces of the piezoelectric plate and the third insulating plate are covered and a fourth insulating plate having a greater impact strength than the piezoelectric plate is laminated and bundled.

  Since the piezoelectric element of the present invention uses the piezoelectric plate and the insulating plate stacked, it has high impact strength and can be suitably used for measuring, for example, engine combustion pressure.

FIG. 1 is a side view showing an example of the piezoelectric element according to the first aspect of the present invention. FIG. 2 is a side view showing an example of the piezoelectric element according to the second aspect of the present invention. FIG. 3 is a side view showing an example of the piezoelectric element according to the third aspect of the present invention. FIG. 4 is a partially omitted side sectional view showing an example of a state in which the piezoelectric element of the present invention is incorporated in a sensor.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First aspect)
FIG. 1 shows an embodiment of a first piezoelectric element 100 of the present invention. In this example, the piezoelectric plate 2 and the insulating plate 4 are laminated and bundled with their plate surfaces parallel to each other. 6 is a conductive means such as a conductive film, which is an interface between the piezoelectric plate 2 and the insulating plate 4, a surface in the thickness direction of the insulating plate 4 (side surface in this figure), and a surface of the insulating plate 4 ( In this figure, it is formed on the upper surface). When the pressure is measured by incorporating this piezoelectric element into the sensor, the charge induced on the surface of the piezoelectric plate 2 is supplied to an electrode (not shown) through the conductive means 6.

  The conductive means 6 may be formed directly on the surface of the insulating plate 4. For example, a known method such as coating of a conductive metal thin film such as a conductive paste, gold, platinum, or copper can be used without limitation. Furthermore, a method of forming a jig by bending a metal plate into a U-shape and sandwiching an insulating plate in the jig can be exemplified.

  By being laminated in this way, the impact resistance of the piezoelectric element 100 is greatly improved.

  As the material of the piezoelectric plate 2, any known piezoelectric body exhibiting piezoelectricity can be used. Specific examples include lead zirconate titanate, lead titanate, barium titanate, lead magnesium niobium titanate, zinc oxide, aluminum nitride, crystal, lithium tantalate, lithium niobate, and polyfucca vinylidene. .

  Among these piezoelectric bodies, lithium tantalate, lithium niobate, and single crystal zinc oxide are preferable because of high heat resistance and large piezoelectricity, and single crystal zinc oxide is particularly preferable.

  The planar shape (in this embodiment, a rectangle) of the piezoelectric plate 2 is not particularly limited, and any shape such as a square, a rectangle, a polygon, an indefinite shape, a circle, an ellipse, or a rhombus can be adopted. The size of the piezoelectric plate is not particularly limited, but considering that it is incorporated in the sensor, the length and width are preferably 0.5 to 10 mm, more preferably 1 to 5 mm, and particularly preferably 1 to 3 mm.

  The thickness of the piezoelectric plate 2 is not particularly limited, but is preferably 0.1 to 5 mm, more preferably 0.3 to 2 mm in consideration of incorporation into the sensor.

  The insulating plate 4 is an electrical insulating plate having a greater impact strength than the piezoelectric plate. The insulation resistance is preferably 1.0E + 13 Ω · cm or more, and more preferably 1.0E + 14 Ω · cm or more, as a specific resistance.

  Examples of the material of the insulating plate 4 include quartz glass, Tempax glass, neoceram glass, Vycor glass, Pyrex (registered trademark) glass, crystal, silicon carbide, alumina, silicon nitride, zirconia, cordierite, and diamond. The

  The impact resistance of the insulating plate 4 is preferably 2 times or more, usually 2 to 20 times, more preferably 5 times or more the impact strength of the piezoelectric plate. A method for measuring the impact strength will be described later.

  When this piezoelectric element is incorporated in a sensor, pressure is applied from the vertical direction X to the piezoelectric plate surface.

  There is no restriction | limiting in particular as a form which bundles the piezoelectric plate 2 and the insulating board 4, Arbitrary bundling methods are employable.

  As a method of bundling the piezoelectric plate 2 and the insulating plate 4, there is an adhesion method using a conductive paste, a ceramic adhesive, or the like. Furthermore, there is a method of using a metal or ceramic frame and confining it inside.

  Alternatively, the piezoelectric plate 12 and the insulating plate 14 may be attached to a cured film of conductive paste.

  In the above example, the piezoelectric plate 2 and the insulating plate 4 are bundled to form a laminated structure. However, it is not necessary that the two are specifically fixed using some kind of bundling means. When used, for example, when assembled in a sensor, the piezoelectric plate 2 and the insulating plate 4 need only be maintained in the laminated structure shown in FIG. This also applies to the following embodiments.

  The piezoelectric element of the present invention is incorporated in a pressure sensor and used for pressure measurement. 4 is a partially omitted cross-sectional view showing an electrode portion of a pressure sensor in which the piezoelectric element 100 shown in FIG. 1 is incorporated. The structure of the pressure sensor itself is known.

  In FIG. 4, 400 is an electrode part of a pressure sensor. On the bottom wall of the bottomed cylindrical diaphragm 32, the lower electrode 34 is placed. On the upper surface of the lower electrode 34, the piezoelectric element 100 of the present invention in which the piezoelectric plate 2 and the insulating plate 4 are laminated and bundled is placed. An upper electrode 40 is further placed on the upper surface of the piezoelectric element 100.

(Second form)
FIG. 2 shows an example of a piezoelectric element 200 according to the second embodiment of the present invention. In this example, a piezoelectric plate 60 and a first insulating plate 62 are laminated in the thickness direction with their plate surfaces parallel to each other and bundled to form a laminated plate 64. Reference numeral 66 denotes conductive means made of a conductive film, which is an interface between the piezoelectric plate 60 and the first insulating plate 62, a surface in the thickness direction of the first insulating plate 62, and a surface of the first insulating plate 62 (in this figure). The upper surface). When this piezoelectric element is incorporated in the sensor, the charge induced in the piezoelectric plate 60 is supplied to the electrode through the conductive film 66.

  Reference numeral 68 denotes a second insulating plate having a thickness of ± 5 μm, preferably ± 3 μm, more preferably ± 2 μm with respect to the thickness of the laminated plate 64. The second insulating plate 68 and the laminated plate 64 are bundled by abutting the surfaces in the thickness direction. The thickness can be measured using a micrometer.

  Here, the piezoelectric plate, the (first or second) insulating plate, the conductive film, etc. have already been described.

(Third form)
FIG. 3 shows an example of a piezoelectric element 300 according to the third embodiment of the present invention. In this example, 12 is a piezoelectric plate and 14 is a third insulating plate. The third insulating plate 14 is preferably within a thickness of ± 5 μm, more preferably within ± 3 μm, and particularly preferably within 2 μm with respect to the thickness of the piezoelectric plate 12.

  The piezoelectric plate 12 and the third insulating plate 14 are disposed with their surfaces in the thickness direction abutting each other. Further, a fourth insulating plate 10 is laminated so as to cover one plate surface (the upper surface in the figure) of the piezoelectric plate 12 and the third insulating plate 14. Reference numeral 16 denotes a conductive means made of a conductive film or the like, which is an interface between the piezoelectric plate 12 and the fourth insulating plate 10, a surface in the thickness direction of the fourth insulating plate 10 (side surface in this figure), and It is formed on the surface of the fourth insulating plate 10 (the upper surface in the figure).

  The thickness of the fourth insulating plate 10 is not particularly limited, but practically the same thickness as that of the third insulating plate 14 is preferable. Other materials are described in the first embodiment.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Impact resistance testing Currently, no suitable device is available on the market for performing impact resistance testing of piezoelectric materials. Therefore, the present inventors conducted an impact resistance test using an acceleration impact test apparatus SM-110-MP (manufactured by Air Brown) of Miyagi Prefectural Industrial Technology Center.

  The impact resistance test method is described below. First, a test jig was attached to an impact test apparatus, and a sample (piezoelectric element) was attached to the jig. The dropping speed of the jig attached to the impact test apparatus was set to a predetermined value. The jig was dropped and collided with the base of the test apparatus. The impact was given to the sample by this collision. Then, the presence or absence of the crack of a sample was observed visually.

On the other hand, the acceleration of the gravity sensor attached to the jig was read. Using this acceleration, the impact load was calculated from the following equation. The jig weight was 1.07066 kg.

Impact load (N) = acceleration (m / s ² ) x jig weight (Kg) x 9.80665

The impact strength (MPa) per unit area was calculated by dividing the calculated impact load by the sample area (mm ² ).

Example 1
A piezoelectric element of the first form shown in FIG. 1 was manufactured. A single plate of zinc oxide (ZnO) having dimensions of 10 × 10 × 0.5 mm manufactured by Tokyo Denki Co., Ltd. was cut into a size of 2 mm × 2 mm × 0.5 mm (thickness) to produce a piezoelectric plate. On the other hand, the insulating board of the same dimension was manufactured using quartz glass. Piezoelectric elements were manufactured by inserting these piezoelectric plates and insulating plates into a cylindrical guide made of super engineering plastic PPSGF40 (40% glass fiber reinforced polyphenylene sulfide) and laminating them. Similarly, a total of 10 piezoelectric elements were manufactured.

  In this example, since the main purpose was to obtain the result of the impact resistance test, the conductive film was not formed.

  These piezoelectric elements were subjected to an impact resistance test using the accelerated impact test apparatus. The obtained impact strength without breaking was 640 MPa.

Comparative Example 1
A piezoelectric element of 2 mm × 2 mm × 0.5 mm (thickness) was manufactured using the same single crystal as the single crystal of zinc oxide used in Example 1 as the piezoelectric material.

  In the same manner as in Example 1, an impact resistance test of this piezoelectric element was performed. The obtained non-breaking impact strength was 130 MPa.

Example 2
A piezoelectric element of the second form shown in FIG. 2 was manufactured. First, a 1 mm × 1 mm × 0.5 mm (thickness) piezoelectric plate 60 was manufactured using a single crystal of zinc oxide (ZnO). On the other hand, the 1st insulating board 62 of the same dimension was manufactured using quartz glass. These piezoelectric plates and insulating plates were laminated with insulating plates in a cylindrical guide made of super engineering plastic PPSGF 40 to produce a laminated plate 64.

A second insulating plate 68 of 1 mm × 1 mm × 1 mm (thickness) was made of quartz glass.
The second insulating plate 68 was inserted into the cylindrical guide so that the thickness surface of the laminated plate 64 and the thickness surface of the second insulating plate 68 were abutted to manufacture a piezoelectric element. A total of ten piezoelectric elements were manufactured. The difference between the thickness of the laminated plate and the thickness of the second insulating plate was all within 5 μm.

  In this embodiment, since the main purpose was to obtain the result of the impact resistance test, the conductive means 66 was not formed.

  These piezoelectric elements were subjected to an impact resistance test using the accelerated impact test apparatus. The obtained non-breaking impact strength was 600 MPa.

Comparative Example 2
A piezoelectric element similar to that of Example 2 was manufactured, except that a laminated plate having a thickness of 10 μm smaller than that of the second insulating plate 68 was used. In this case, in the impact resistance test, the impact strength without breaking was as high as 550 MPa, but the sensor sensitivity was lowered.

Example 3
A piezoelectric element of the third form shown in FIG. 3 was manufactured. First, a 1 mm × 1 mm × 0.5 mm (thickness) piezoelectric plate 12 was manufactured using a single crystal of zinc oxide (ZnO). On the other hand, the 3rd insulating board 14 of the same dimension was manufactured using quartz glass. The piezoelectric plate 12 and the insulating plate 14 were placed in a cylindrical guide made of super engineering plastic PPSGF 40 with their thickness surfaces facing each other.

  Next, the 4th insulating board 10 of 1 mm x 1 mm x 0.5 mm (thickness) was manufactured with quartz glass.

  The fourth insulating plate 10 was laminated on the upper surfaces of the piezoelectric plate 12 and the third insulating plate 14 placed as described above to manufacture a piezoelectric element. A total of ten piezoelectric elements were manufactured. The difference between the thickness of the piezoelectric plate and the thickness of the third insulating plate was all within 5 μm.

  In this example, since the main purpose was to obtain the result of the impact resistance test, the conductive film was not formed.

  These piezoelectric elements were subjected to an impact resistance test using the accelerated impact test apparatus. The obtained impact strength without breaking was 550 MPa.

Comparative Example 3
A piezoelectric element similar to that of Example 3 was manufactured, except that a piezoelectric plate having a thickness of 10 μm smaller than the thickness of the third insulating plate was used. In this case, in the impact resistance test, the impact strength without breaking was as high as 550 MPa, but the sensor sensitivity was lowered.

100, 200, 300 Piezoelectric elements 2, 12, 60 Piezoelectric plate 4 Insulating plate 10 Fourth insulating plate 14 Third insulating plate 16 Conducting means 32 Diaphragm 34 Lower electrode 40 Upper electrode 62 First insulating plate 64 Laminated plates 6, 66 Conducting means 68 second insulating plate

Claims (9)

A piezoelectric element having a piezoelectric plate and an insulating plate having a larger impact resistance than the piezoelectric plate and having a conductive means on its surface,
A piezoelectric element formed by laminating a piezoelectric plate and an insulating plate with the surface directions of the piezoelectric plate and the insulating plate being parallel. A piezoelectric plate and a first insulating plate having a greater impact strength than the piezoelectric plate and having a conductive means on the surface are laminated with the surface directions of the piezoelectric plate and the first insulating plate being parallel to each other. A laminated board,
A second insulating plate having a thickness of ± 5 μm with respect to the thickness of the laminated plate and having a greater impact strength than the piezoelectric plate; and a thickness direction between the laminated plate and the second insulating plate. Piezoelectric elements made by butting surfaces. A piezoelectric plate, and a third insulating plate having a thickness of ± 5 μm with respect to the thickness of the piezoelectric plate and having a greater impact resistance than the piezoelectric plate, the piezoelectric plate and the third insulating plate Arrange the surfaces in the thickness direction to face each other,
Further, a piezoelectric element formed by laminating a fourth insulating plate that covers the upper surfaces of the piezoelectric plate and the third insulating plate and has a greater impact strength than the piezoelectric plate. The piezoelectric element according to any one of claims 1 to 3, wherein the piezoelectric plate is made of single crystal zinc oxide, lithium niobate, lithium tantalate, or quartz. The piezoelectric element according to any one of claims 1 to 3, wherein the insulating plate is made of quartz glass, quartz, alumina, or diamond (provided that the piezoelectric plate is made of quartz, excluding the case where the insulating plate is quartz). A pressure sensor incorporating the piezoelectric element according to claim 1. A piezoelectric element in which a piezoelectric plate and an insulating plate having impact resistance greater than that of the piezoelectric plate and having a conductive means on the surface thereof are stacked and bundled with the surface directions of the piezoelectric plate and the insulating plate being parallel. Method to increase impact strength. A piezoelectric plate and a first insulating plate having a greater impact strength than the piezoelectric plate and having a conductive means on the surface are laminated with the surface directions of the piezoelectric plate and the first insulating plate being parallel to each other. A laminated board,
A second insulating plate having a thickness of ± 5 μm with respect to the thickness of the laminated plate and having a greater impact strength than the piezoelectric plate; and a thickness direction between the laminated plate and the second insulating plate. A method of increasing the impact strength of a piezoelectric element that is bundled by butting surfaces. A piezoelectric plate, and a third insulating plate having a thickness of ± 5 μm with respect to the thickness of the piezoelectric plate and having a greater impact resistance than the piezoelectric plate, the piezoelectric plate and the third insulating plate Arrange the surfaces in the thickness direction to face each other,
Furthermore, a method for increasing the impact strength of a piezoelectric element in which the upper surfaces of the piezoelectric plate and the third insulating plate are covered and a fourth insulating plate having a greater impact strength than the piezoelectric plate is laminated and bundled.

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