WO2013179752A1 - Piezoelectric element for pressure sensor - Google Patents

Piezoelectric element for pressure sensor Download PDF

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Publication number
WO2013179752A1
WO2013179752A1 PCT/JP2013/059082 JP2013059082W WO2013179752A1 WO 2013179752 A1 WO2013179752 A1 WO 2013179752A1 JP 2013059082 W JP2013059082 W JP 2013059082W WO 2013179752 A1 WO2013179752 A1 WO 2013179752A1
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WO
WIPO (PCT)
Prior art keywords
main surface
piezoelectric element
electrode layer
peripheral edge
pressure sensor
Prior art date
Application number
PCT/JP2013/059082
Other languages
French (fr)
Japanese (ja)
Inventor
広章 中園
Original Assignee
京セラ株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 京セラ株式会社 filed Critical 京セラ株式会社
Priority to JP2014518317A priority Critical patent/JP5669985B2/en
Publication of WO2013179752A1 publication Critical patent/WO2013179752A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L23/00—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid
    • G01L23/26—Details or accessories
    • G01L23/32—Apparatus specially adapted for recording pressure changes measured by indicators
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L23/00—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid
    • G01L23/08—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid operated electrically
    • G01L23/10—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid operated electrically by pressure-sensitive members of the piezoelectric type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
    • F02P19/00—Incandescent ignition, e.g. during starting of internal combustion engines; Combination of incandescent and spark ignition
    • F02P19/02—Incandescent ignition, e.g. during starting of internal combustion engines; Combination of incandescent and spark ignition electric, e.g. layout of circuits of apparatus having glowing plugs
    • F02P19/028—Incandescent ignition, e.g. during starting of internal combustion engines; Combination of incandescent and spark ignition electric, e.g. layout of circuits of apparatus having glowing plugs the glow plug being combined with or used as a sensor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23Q—IGNITION; EXTINGUISHING-DEVICES
    • F23Q7/00—Incandescent ignition; Igniters using electrically-produced heat, e.g. lighters for cigarettes; Electrically-heated glowing plugs
    • F23Q7/001—Glowing plugs for internal-combustion engines
    • F23Q2007/002—Glowing plugs for internal-combustion engines with sensing means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23Q—IGNITION; EXTINGUISHING-DEVICES
    • F23Q7/00—Incandescent ignition; Igniters using electrically-produced heat, e.g. lighters for cigarettes; Electrically-heated glowing plugs

Definitions

  • the present invention relates to a piezoelectric element for a pressure sensor used for measuring a pressure in a combustion chamber of an internal combustion engine such as an automobile.
  • piezoelectric elements have been used as measuring means for various physical quantities such as pressure, force, and acceleration, and their application fields are diverse such as industrial, automotive, medical, and home appliances.
  • a piezoelectric element is used to reduce the combustion pressure in the combustion chamber in the cylinder of the diesel engine for the purpose of improving the emission of the diesel engine, reducing fuel consumption (fuel consumption rate), and reducing noise and vibration.
  • a combustion control system that measures and performs feedback control of the operation of a fuel injection device or an EGR (Exhaust Gas Recirculation) based on the measured combustion pressure information.
  • a glow plug with a pressure sensor has been proposed in which a pressure sensor having a piezoelectric element is mounted on the glow plug in order to accurately transmit the combustion pressure to the piezoelectric element without increasing the size of the entire engine.
  • the glow plug has a heater arranged in a combustion chamber or a sub-combustion chamber in a cylinder of a diesel engine, and the diesel engine is heated by heating the combustion chamber and the sub-combustion chamber with the heater before or at the start of the start. This assists the start-up.
  • a glow plug has been conventionally arranged in a cylinder head of a diesel engine.
  • Patent Document 1 discloses an example of a glow plug equipped with a pressure sensor.
  • FIG. 7 is a diagram for explaining a glow plug 100 with a pressure sensor (hereinafter, also simply referred to as a glow plug 100) disclosed in Patent Document 1, in which the vicinity of the piezoelectric element 101 provided in the glow plug 100 is enlarged. It shows.
  • the glow plug 100 includes a piezoelectric element 101, electrode plates 102 and 103 disposed so as to be in contact with the two main surfaces of the piezoelectric element 101 and sandwiching the piezoelectric element 101, and a pair of insulating substrates disposed on the outside thereof. 104 and 105 are provided. The upper main surface of the insulating substrate 105 is in contact with the fixing plate 117.
  • the piezoelectric element 101, the electrode plates 102 and 103, and the insulating substrates 104 and 105 are provided with through holes, and the insulating cylindrical member 112 is inserted into the through holes.
  • the piezoelectric element 101 and the electric wire 114 for supplying electric power to a heater (not shown) for heating the combustion chamber and the auxiliary combustion chamber are separated by a cylindrical member 112, and the piezoelectric element 101 and the electric wire 114 are electrically connected. Is insulated.
  • the glow plug 100 includes a transmission member 115 for transmitting a combustion pressure in a combustion chamber (not shown) disposed below the piezoelectric element 101 in FIG. 7 to the upper side in FIG.
  • both the upper main surface 101A and the lower main surface 101B are flat surfaces, and the upper main surface 101A and the lower main surface 101B are parallel to each other.
  • the present invention provides a first main surface having a circular first peripheral edge, a second main surface opposite to the first main surface, having a circular second peripheral edge, and the first A piezoelectric substrate having a circular through hole penetrating between one main surface and the second main surface, a first electrode layer bonded to the first main surface, and a second electrode bonded to the second main surface And a pressure sensor for outputting electric charges generated in the piezoelectric substrate by a load applied between the first main surface and the second main surface via the first electrode layer and the second electrode layer.
  • the first virtual plane including the first peripheral edge and the second virtual plane including the second peripheral edge are parallel to each other, and a central axis of the through hole is a center of the first peripheral edge.
  • the first main surface includes a protrusion concentrically with the first peripheral edge provided so as to surround the opening of the through hole, and the through hole in the cross section of the piezoelectric substrate including the central axis.
  • a cross-sectional line of the protrusion in each of the two partial regions arranged on both sides with respect to each other is an arc shape convex toward the outside of the piezoelectric substrate along a direction parallel to the central axis.
  • a piezoelectric element for a pressure sensor is provided.
  • the protrusion of each of the two partial regions arranged on both sides of the through hole in the cross section of the piezoelectric substrate including the central axis of the through hole is provided.
  • the cross-sectional line has a circular arc shape that protrudes toward the outside of the piezoelectric substrate along the direction parallel to the central axis, and even if the direction in which the pressure is applied changes slightly, the pressure is concentrated repeatedly on this protrusion. Therefore, it is possible to suppress variations in measurement results due to minute changes in the pressure direction.
  • FIG. 2 is a schematic perspective view of a piezoelectric substrate included in the piezoelectric element 1 shown in FIG. 1. It is sectional drawing which shows the state which attached the glow plug with a pressure sensor provided with the piezoelectric element shown in FIG. 1 to the engine head of a diesel engine. It is a schematic sectional drawing which expands and shows the pressure sensor part vicinity of the glow plug with a pressure sensor shown in FIG.
  • FIG. 4 is a diagram illustrating a state in which pressure is applied to the piezoelectric element in the glow plug with a pressure sensor illustrated in FIG.
  • FIG. 3 is a schematic cross-sectional view illustrating an enlarged vicinity of a first electrode layer of the piezoelectric element.
  • (A)-(c) is a schematic sectional drawing which shows other embodiment of the piezoelectric element of this invention, respectively. It is a schematic sectional drawing explaining the conventional glow plug with a pressure sensor.
  • FIG. 1 is a diagram for explaining a pressure sensor piezoelectric element 1 (hereinafter also simply referred to as a piezoelectric element 1), which is an embodiment of the pressure sensor piezoelectric element of the present invention.
  • FIG. 1B is a schematic sectional view of the piezoelectric element 1.
  • FIG. 2 is a schematic perspective view of the piezoelectric substrate 41 included in the piezoelectric element 1.
  • the piezoelectric element 1 has a first main surface 41A (see FIG. 1B) having a circular first peripheral edge 42 and a second main surface opposite to the first main surface 41A having a circular second peripheral edge 43.
  • a piezoelectric substrate 41 having a surface 41B (see FIG. 1B) and a circular through hole 44 penetrating between the first main surface 41A and the second main surface 41B, and joined to the first main surface 41A
  • the first electrode layer 51 and the second electrode layer 52 bonded to the second main surface 41B are provided.
  • the piezoelectric element 1 outputs, from the first electrode layer 51 and the second electrode layer 52, charges generated in the piezoelectric substrate 41 due to pressure applied between the first main surface 41A and the second main surface 41B.
  • the composition of the piezoelectric substrate 41 is not particularly limited, but piezoelectric ceramics such as a bismuth layered compound, aluminum nitride, zinc oxide, lead zirconate titanate (PZT), and lead titanate may be used.
  • a piezoelectric ceramic mainly composed of a bismuth layered compound having a high Curie temperature is used as the piezoelectric substrate 41.
  • a piezoelectric ceramic made of a bismuth layered compound is preferable in that it is easy to produce and is an oxide, so that it is highly reliable at high temperatures, has a high Curie temperature, and has high heat resistance.
  • the first electrode layer 51 and the second electrode layer 52 can use metals such as Ag, Au, Pt, Cu, and Ni.
  • the first electrode layer 51 and the second electrode layer 52 of the present embodiment are mainly composed of Ag which is relatively inexpensive and easy to manufacture and has excellent reliability.
  • the first virtual plane P1 including the first peripheral edge 42 (see FIG. 1B) and the second virtual plane P2 including the second peripheral edge 43 (see FIG. 1B) are parallel to each other, and the through hole 44 is provided.
  • the central axis S passes through the center 42c of the first peripheral edge 42 and the center 43c of the second peripheral edge 43, and is orthogonal to the first virtual plane P1 and the second virtual plane P2.
  • the piezoelectric substrate 41 is polarized along a direction parallel to the central axis S, and the piezoelectric substrate 41 is interposed between the first main surface 42 and the second main surface 43 along a direction parallel to the central axis S. Generates electric charge according to the applied pressure.
  • the first main surface 41A includes a protrusion 46A that is concentric with the first peripheral edge 42 provided so as to surround the opening 44a of the through hole 44.
  • the cross-sectional line of the protrusion 46A in each of the two partial regions 41 ⁇ (see FIG. 1B) and 41 ⁇ (see FIG. 1B) arranged on both sides of the through hole 44 is parallel to the central axis S. In this direction, the arc is convex toward the outside of the piezoelectric substrate 41.
  • the second main surface 41B is also provided so as to surround the opening 44b of the through hole 44.
  • the second main surface concentric with the second peripheral edge 43 is provided.
  • Two partial regions 41 ⁇ and 41 ⁇ which are provided with side protrusions 46B (hereinafter also simply referred to as protrusions 46B) and are arranged on both sides of the through hole 44 in the cross section of the piezoelectric substrate 41 including the central axis S.
  • the cross-sectional line of the protrusion 46B in each of these is a circular arc shape that protrudes toward the outside of the piezoelectric substrate 41 in a direction parallel to the central axis S.
  • the first electrode layer 51 is disposed only on the surface of the protrusion 46A of the first main surface 41A. Further, the surface 51A of the first electrode layer 51 opposite to the side bonded to the piezoelectric substrate 41 is parallel to the first virtual plane P1.
  • the first main surface 41A includes the first peripheral edge 42 and continues to the protrusion 46A.
  • the first main surface 41A includes the outer flat surface portion 47A that is flush with the first virtual plane P1 and the peripheral edge of the opening 44a of the through hole 44. 46A, the first virtual plane P1 and the flush inner plane portion 48A are provided.
  • the second electrode layer 52 is bonded only to the surface of the protrusion 46B of the second main surface 41B.
  • the surface 52B of the second electrode layer 52 opposite to the side bonded to the piezoelectric substrate 41 is parallel to the second virtual plane P2.
  • the second main surface 41B includes the second peripheral edge 43 and continues to the protrusion 46B, the outer flat surface part 47B flush with the second virtual plane P2, and the protrusion including the periphery of the opening 44b of the through hole 44. 46B, a second virtual plane P2 and a flush inner plane portion 48B are provided.
  • the outer diameter of the first main surface 41A and the second main surface 41B is, for example, about 3.5 mm to 20 mm, and extends from the surface 51A of the first electrode layer 51 to the surface 52B of the second electrode layer 52.
  • the length along the central axis S (that is, the height of the piezoelectric element 1) is about 0.5 mm to 18 mm.
  • the diameter of the through hole 44 is, for example, about 1 to 5.5 mm, and the thicknesses of the first electrode layer 51 and the second electrode layer 52 are, for example, about 2 to 200 ⁇ m.
  • the protrusion height of the protrusion 46A from the virtual plane P1 and the protrusion height of the protrusion 46B from the virtual plane P2 are both about 50 to 200 ⁇ m. Further, the length along the radial direction of the first peripheral edge 42 of the outer flat surface portion 47A and the inner flat surface portion 48A and the length along the radial direction of the second peripheral edge 43 of the outer flat surface portion 47B and the inner flat surface portion 48B are Is about 20 to 60 ⁇ m.
  • the piezoelectric element 1 is mounted and used, for example, in a pressure sensor that measures the temperature in the combustion chamber of a diesel engine.
  • a pressure sensor that measures the temperature in the combustion chamber of a diesel engine.
  • an embodiment of a pressure sensor including the piezoelectric element 1 will be described, and the function of the piezoelectric element 1 will be described.
  • FIG. 3 is a view for explaining a glow plug 10 with a pressure sensor (hereinafter also simply referred to as a glow plug 10) including the piezoelectric element 1, and a cross-sectional view showing a state in which the glow plug 10 is attached to an engine head 110 of a diesel engine. It is.
  • a through hole 11 that communicates with the combustion chamber 12 in the engine head 110 is provided.
  • a threaded portion 14 is provided near the upper end of FIG. 3 on the inner surface of the through hole 11, and the taper is reduced in diameter near the lower end of FIG. 3 as it approaches the lower side of FIG. 3.
  • a stepped portion 13 is provided.
  • the glow plug 10 includes a housing 2, a transmission member 3, a seal member 8, a heating element 26, an electric wire 27, and a pressure sensor unit (pressure sensor) 6 including the piezoelectric element 1.
  • the housing 2 is mounted with the insertion portion 29 inserted into the through hole 11 of the engine head 110 and the piezoelectric element 1 disposed outside the engine head 110 (opposite to the combustion chamber 12, that is, on the upper side in FIG. 3).
  • the insertion portion 29 of the housing 2 has a substantially cylindrical shape having a hollow portion 21 having a circular cross section, and a lower end (side closer to the combustion chamber 12) of FIG. 3 has a tapered portion 13 of the engine head 110.
  • adheres is provided.
  • a screw portion 23 that is screwed with the screw portion 14 of the through hole 11 is provided.
  • the housing 2 and the engine head 110 are brought into close contact with each other by the taper portion 22 of the housing 2 and the taper portion 13 of the engine head 110 by an axial force generated by the screwing of the screw portion 14 and the screw portion 23. Is prevented from leaking into the gap between the inner periphery of the through hole 11 of the engine head 110 and the outer periphery of the housing 2.
  • a transmission member 3 made of a heat-resistant metal such as stainless steel, which extends from the upper side to the lower side in FIG.
  • the transmission member 3 is provided with a hollow portion 33 having a circular cross section extending in the vertical direction in FIG.
  • the transmission member 3 is joined and held with the seal member 8, and is held so as to be movable along the vertical direction in FIG.
  • the seal member 8 is made of a metal such as stainless steel, and is hermetically fixed to the front end of the housing 2 and the pressure receiving portion 31 of the transmission member 3 by laser welding or the like, so that the combustion gas in the combustion chamber 12 is a hollow portion of the housing 3. Intrusion into 21 is prevented.
  • the seal member 8 has a bellows shape and can be deformed along the vertical direction in FIG. When the seal member 8 is deformed along the vertical direction in FIG. 3, the position of the transmission member 3 can be changed along the vertical direction in FIG. 3.
  • the through-hole 11 of the engine head 110, the hollow portion 21 of the housing 2, and the hollow portion 33 of the transmission member 3 are arranged so that their central axes (axis indicated by the central axis S in FIG. 3) coincide with each other.
  • the hollow portion 33 of the transmission member 3 is closed at the lower end portion, and the lower end portion of the transmission member 3 is exposed as the pressure receiving portion 31 in the combustion chamber 12.
  • a disc-shaped flange 32 disposed on the mounting portion 25 of the housing 2 is provided, and the upper side of the hollow portion 33 is open.
  • the upper main surface 32A of the flange portion 32 is a plane perpendicular to the central axis S.
  • a heating element 26 is disposed in the vicinity of the lower end of the hollow portion 33 of the transmission member 3 (that is, in the vicinity of the pressure receiving portion 31), and an electric wire 27 for supplying electric power to the heating element 26 is transmitted.
  • the electric wire 27 is connected to the heating element 26 through the opening on the upper side of the member 3 and inserted into the hollow portion 33.
  • the heating element 26 is made of, for example, a known nichrome wire, and generates heat when a current flows through the electric wire 27.
  • the glow plug 10 in which the heating element 26 and the electric wire 27 are arranged on the transmission member 3 has a function of warming the combustion chamber 12 of the engine head 110 when the diesel engine is started at a low temperature, for example.
  • the piezoelectric element 1 of the pressure sensor unit 6 can measure the pressure (combustion pressure) in the combustion chamber 12.
  • the glow plug 10 of the present embodiment not only warms the combustion chamber but also has a function of measuring the pressure in the combustion chamber 12.
  • FIG. 4 is an enlarged schematic cross-sectional view showing the vicinity of the pressure sensor portion 6 of the glow plug 10 shown in FIG.
  • the pressure sensor unit 6 includes a piezoelectric element 1, an electrode plate 62 and an electrode plate 63 for extracting an electric signal output from the piezoelectric element 1, a pair of insulating substrates 64 and 65 that sandwich the electrode plate 62 and the electrode plate 63, The fixed substrate 7 is included.
  • the fixed substrate 7 has a screw portion 71 on the side surface, and the screw portion 71 on the side surface is screwed to a screw portion 76 provided on the inner peripheral surface of the mounting portion 25, so that the fixed substrate 7 is fixed to the housing 2. Yes.
  • the lower main surface 7B of the fixed substrate 7 is disposed in parallel with the upper main surface 32A of the flange portion 32.
  • the upper main surface 64A of the insulating substrate 64 is in contact with the lower main surface 7B of the fixed substrate 7, and the upper main surface 62A of the electrode plate 62 is in contact with the lower main surface 64B of the insulating substrate 64.
  • the lower main surface 65B of the insulating substrate 65 is in contact with the upper main surface 32A of the flange 32, and the lower main surface 63B of the electrode plate 63 is in contact with the upper main surface 65A of the insulating substrate 65.
  • the upper main surface 65A and the lower main surface 65B of the insulating substrate 65 are both parallel, and the piezoelectric element 1 is disposed between the lower main surface 62B and the upper main surface 63A that are parallel to each other.
  • the fixed substrate 7, the insulating substrate 64, the electrode plate 62, the electrode plate 63, and the insulating substrate 65 are all provided with through holes, and these through holes are connected to the through holes 44 of the piezoelectric element 1.
  • a cylindrical insulator 72 is inserted into the hole portion where the through holes are continuous. The insulator 72 sets the relative positions of the fixed substrate 7, the insulating substrate 64, the electrode plate 62, the electrode plate 63, the insulating substrate 65 and the piezoelectric element 1, and ensures insulation between the electric wire 27 and these members. ing.
  • a preliminary pressure in a direction of compressing the piezoelectric element 1 along the vertical direction in the figure is applied in advance to the piezoelectric element 1 by screwing the fixed substrate 7.
  • the pressure receiving portion 31 of the transmission member 3 receives the pressure in the combustion chamber 12 of the engine head 110, so that the pressure is transferred to the pressure via the transmission member 3. It is transmitted to the piezoelectric element 1 of the sensor unit 6. That is, the pressure applied to the pressure receiving portion 31 is transmitted through the flange portion 32 of the transmission member 3, the insulating substrate 65, and the electrode plate 63 so as to push the piezoelectric element 1 upward from the lower side in FIGS.
  • the upper side of the piezoelectric element 1 in FIGS. 3 and 4 is fixed in the vertical direction by the fixed substrate 7, and the piezoelectric element 1 is placed in the combustion chamber 12 in the direction of compressing the piezoelectric element 1 along the vertical direction. Pressure is applied.
  • the cross-sectional line of the protrusion 46A in each of the two partial regions 41 ⁇ and 41 ⁇ disposed on both sides of the through hole 44 of the piezoelectric substrate 41 is The arcuate shape is convex toward the outside of the piezoelectric substrate 41 in a direction parallel to the central axis S.
  • FIG. 5 is a diagram showing a state in which pressure is applied to the piezoelectric element 1 in the glow plug 10 shown in FIG. 3, and is a schematic sectional view showing the vicinity of the first electrode layer 51 of the piezoelectric element 1 in an enlarged manner. is there.
  • the electrode layer 51 is a metal layer made of Ag, has a relatively high spreadability, and is deformed so as to be spread by the electrode plate 62 and the piezoelectric substrate 41 by the pressure applied via the transmission member 3.
  • a reaction force from the electrode plate 62 is applied to the piezoelectric substrate 41.
  • the cross-sectional line of the protrusion 46A of the piezoelectric substrate 41 has an arc shape that is convex toward the outside of the piezoelectric substrate 41, and the reaction force from the electrode plate 62 is applied to the top of the protrusion 46A. It will be concentrated. For this reason, when pressure is repeatedly applied, even if the direction in which the pressure is applied changes slightly, the pressure is repeatedly concentrated on the top. That is, in the piezoelectric element 1 of the present embodiment, even when the direction in which the pressure is applied changes slightly, the pressure in the direction substantially parallel to the central axis S passes through the vicinity of the top of the protrusion 46A as shown in FIG. Applied repeatedly.
  • the piezoelectric element 1 of the present embodiment can reduce such a variation in pressure distribution, and can repeatedly measure the pressure in the combustion chamber 12 with high reproducibility and high accuracy.
  • the cross-sectional line of the protrusion 46B is formed in an arc shape that protrudes toward the outside of the piezoelectric substrate 41 along the direction parallel to the central axis S on the second main surface 41B side. ing.
  • the piezoelectric element 1 of the present embodiment is made of a bismuth layered compound and has a high Curie temperature and can be used even at a relatively high temperature.
  • the ratio of output voltage magnitude is relatively low. For this reason, when using a piezoelectric element whose main component is a bismuth layered compound, it is preferable to reduce as much as possible the noise component that occurs with changes in the stress distribution of the piezoelectric element.
  • the piezoelectric element 1 includes a bismuth layered compound as a main component and can be used in a high temperature environment such as an engine, and noise due to variations in stress distribution in the piezoelectric substrate 41 due to a minute change in the pressure application direction. There are few ingredients.
  • the piezoelectric element 1 is preferably used as a pressure sensor for measuring pressure in a relatively high temperature environment, such as a pressure sensor mounted on a glow plug.
  • the first electrode layer 51 is bonded only to the surface of the protrusion 46A of the first main surface 41A. As shown in FIG. 5, even when the first electrode layer 51 is deformed and spread out, the first electrode layer 51 hardly protrudes to the side surface of the piezoelectric substrate 41.
  • the second electrode layer 52 is bonded only to the surface of the protrusion 46B of the second main surface 41B, the second electrode layer 52 is deformed and spread when pressure is applied. However, the second electrode layer 52 tends to stay in the range of the protrusion 46B, and hardly protrudes to the side surface of the piezoelectric substrate 41.
  • the surface 51A (upper surface in FIG. 3) opposite to the side bonded to the piezoelectric substrate 41 of the first electrode layer 51 is parallel to the first virtual plane P1. Therefore, the surface 51A of the first electrode layer 51 can contact the electrode plate 62 with a relatively large area. For example, if the surface 51A of the first electrode layer 51 is a surface having an arcuate cross section along the protrusion 46A, the first electrode layer 51 and the electrode plate 62 are partially separated particularly when the piezoelectric substrate 41 is inclined. In this case, the voltage generated in the piezoelectric substrate 41 may not be measured with high accuracy. On the other hand, as shown in FIG.
  • the piezoelectric element 1 of the present embodiment has a surface 51A (the upper surface in FIG. 3) opposite to the side of the first electrode layer 51 bonded to the piezoelectric substrate 41. ) Is parallel to the first virtual plane P1, and even when the piezoelectric substrate 41 is slightly inclined as shown in FIG. 5, the first electrode layer 51 is deformed according to the pressure, Since a relatively wide contact area with the electrode plate 62 can be ensured, the voltage generated in the piezoelectric substrate 41 can be repeatedly measured with high accuracy.
  • the surface 51B (the lower surface in FIG. 3) opposite to the side of the second electrode layer 52 bonded to the piezoelectric substrate 41 is the second virtual plane P2.
  • the surface 52B of the second electrode layer 52 ensures a relatively wide contact area with the electrode plate 63.
  • the first main surface 41A includes an outer flat surface portion 47A that is flush with the first virtual plane P1 and that includes the first peripheral edge 42 and continues to the protrusion 46A.
  • the first imaginary plane P1 and the inner plane portion 48A that are flush with the protrusion 46A including the periphery of the opening 44a of the through hole 44 are provided.
  • the spread of the first electrode layer 51 is blocked by the outer flat surface portion 47A.
  • the second main surface 41B includes the second peripheral edge 43 and continues to the protrusion 46B.
  • the second main surface 41B protrudes including the outer flat part 47B flush with the second virtual plane P2 and the periphery of the opening 44a of the through hole 44.
  • the second virtual plane P2 and the inner plane plane 48B that are flush with the portion 46B are provided. Even when the second electrode layer is deformed and spread by the outer flat portion 47B and the inner flat portion 48B (not shown), the spread of the second electrode layer 52 due to the deformation is blocked. The sagging of the second electrode layer 52 on the side surface of the piezoelectric substrate 41 is suppressed.
  • Such a piezoelectric element 1 can be manufactured as follows, for example. SrCO 3 powder purity of 99.9% or more as a starting material, BaCO 3 powder, the Bi 2 O 3 powder and TiO 2 powder, the composition formula Bi 4 Ti 3 O 12 ⁇ 0.47 (Sr 0.5 Ba 0.5 Weigh so that the ratio is TiO 3 ).
  • MnO 2 powder 0.5 parts by mass is weighed and mixed with 100 parts by mass of this main component, and a 500 ml resin pot with 99.9% purity ZrO 2 balls and water or isopropyl alcohol (IPA). The resin pot is placed on a turntable and mixed for 16 hours.
  • IPA isopropyl alcohol
  • the slurry after mixing was dried in the air, passed through # 40 mesh, and then calcined by holding at 950 ° C. for 3 hours in the air, and this synthetic powder was mixed with ZrO 2 balls having a purity of 99.9% and water.
  • this synthetic powder was mixed with ZrO 2 balls having a purity of 99.9% and water.
  • it is put into a 500 ml resin pot together with isopropyl alcohol (IPA), and the resin pot is placed on a rotating table and pulverized for 20 hours.
  • IPA isopropyl alcohol
  • An appropriate amount of an organic binder is added to the pulverized powder to form granules, and the granules are formed by, for example, a uniaxial pressure molding method to obtain a generated shape having a shape corresponding to the piezoelectric substrate 41.
  • firing is performed at about 1150 ° C. for 3 hours in an air atmosphere to obtain the piezoelectric substrate 41.
  • a so-called Ag paste is printed (applied) on the first main surface 41A and the second main surface 41B of the piezoelectric substrate 41 by using a printing machine, and the whole is baked to form the first main surface 41A and the second main surface 41B. Electrode layers (first electrode layer 51 and second electrode layer 52) containing Ag as a main component are formed on the surface 41B. At this time, the Ag paste is printed (applied) only on the protrusion 46A for the first main surface 41A, and is printed (applied) only on the protrusion 46B for the second main surface 41B.
  • the surface of the Ag electrode formed by firing is polished to form the first electrode layer 51 and the second electrode layer 52, and then the first electrode layer 51 and A predetermined voltage is applied between the second electrode layer 52 and the polarization process is performed.
  • the piezoelectric element 1 of this embodiment can be formed in this way.
  • FIGS. 6A to 6C are schematic sectional views showing other embodiments of the piezoelectric element of the present invention.
  • the configuration corresponding to the piezoelectric element 1 is indicated using the same reference numerals as in FIGS.
  • the first main surface 41A and the second main surface 41B do not include the outer flat surface portion or the inner flat surface portion, and only the convex portion 46A is the first.
  • the main surface 41A may be configured, and similarly, the second main surface 41B may be configured by only the convex portion 46B.
  • the surface 51A of the first electrode layer 51A and the surface 52B of the second electrode layer 52 are shaped along the surfaces of the protrusions 46A and the protrusions 46B. May be.
  • the surface 51A of the first electrode layer 51A is preferably parallel to the first virtual plane P1 and the second electrode layer 52 in that the contact area with the electrode plate 62 and the electrode plate 63 is relatively large.
  • the surface 52B is preferably parallel to the second virtual plane P2.
  • the piezoelectric substrate 41 may be provided with a protrusion 46A only on the first main surface 41A, for example, and the second main surface 41B side may be a flat surface. Also in this case, on the first main surface 11 ⁇ / b> A side, the pressure application direction is deviated, so that the position of the portion where the pressure is concentrated is suppressed from varying, but the first main surface can be more reliably suppressed.
  • the side opposite to the combustion chamber 12 is the first main surface 41A and the combustion chamber 12 side is the second main surface 41B.
  • the first main surface 41A and the second main surface 41B are The positional relationship with respect to the combustion chamber 12 is not particularly distinguished.
  • the combustion chamber 12 side may be the first main surface 41A, and the protrusion 41A may be provided only on the first main surface 41A on the combustion chamber 12 side.
  • the pressure sensor piezoelectric element of the present invention is not limited to the above-described embodiment, and various modifications and changes may be made without departing from the scope of the present invention.

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Abstract

[Problem] To suppress variations in measurement result, which are caused by minute changes in the direction of pressure. [Solution] The sectional line of a protrusion (46A) in each of two partial regions (41α, 41β) disposed on both sides of a through-hole (11) in the section of a piezoelectric substrate (41) including the central axis (S) of the through-hole (11) is formed in an arc shape protruding to the outside of the piezoelectric substrate (41) along a direction parallel to the central axis (S), and even when the direction in which pressure is applied slightly changes, the pressure is repeatedly applied concentratedly to the top of the protrusion (46A).

Description

圧力センサー用圧電素子Piezoelectric element for pressure sensor
　本発明は、例えば自動車等の内燃機関エンジンの燃焼室内の圧力等を計測するために用いる圧力センサー用圧電素子に関する。 The present invention relates to a piezoelectric element for a pressure sensor used for measuring a pressure in a combustion chamber of an internal combustion engine such as an automobile.
　従来より、圧電素子は圧力、力、加速度など様々な物理量の計測手段として用いられており、その応用分野も産業用、自動車用、医療用、および家電用等多岐にわたっている。 Conventionally, piezoelectric elements have been used as measuring means for various physical quantities such as pressure, force, and acceleration, and their application fields are diverse such as industrial, automotive, medical, and home appliances.
　例えば、自動車のディーゼルエンジンにおいて、ディーゼルエンジンのエミッションの改善や燃費（燃料消費率）の低減、騒音や振動の低減を目的として、ディーゼルエンジンのシリンダ内の燃焼室の燃焼圧を圧電素子を用いて計測し、計測した燃焼圧情報に基き、燃料噴射装置やＥＧＲ（Exhaust Gas Recirculation：排出ガス再循環装置）の動作をフィードバック制御する燃焼制御システムが提案されている。 For example, in a diesel engine of an automobile, a piezoelectric element is used to reduce the combustion pressure in the combustion chamber in the cylinder of the diesel engine for the purpose of improving the emission of the diesel engine, reducing fuel consumption (fuel consumption rate), and reducing noise and vibration. There has been proposed a combustion control system that measures and performs feedback control of the operation of a fuel injection device or an EGR (Exhaust Gas Recirculation) based on the measured combustion pressure information.
　ディーゼルエンジンの燃焼圧を圧電素子を用いて計測するには、圧電素子に燃焼圧を伝える必要がある。そこで、エンジン全体を大型化することなく、燃焼圧を正確に圧電素子に伝えるために、圧電素子を備えた圧力センサーをグロープラグに搭載した圧力センサー付きグロープラグが提案されている。 In order to measure the combustion pressure of a diesel engine using a piezoelectric element, it is necessary to transmit the combustion pressure to the piezoelectric element. Accordingly, a glow plug with a pressure sensor has been proposed in which a pressure sensor having a piezoelectric element is mounted on the glow plug in order to accurately transmit the combustion pressure to the piezoelectric element without increasing the size of the entire engine.
　グロープラグは、ディーゼルエンジンのシリンダ内の燃焼室もしくは副燃焼室内に配置されるヒータを備えており、始動開始前や始動時に、このヒーターで燃焼室や副燃焼室を加熱することにより、ディーゼルエンジンの始動を補助するものである。このようなグロープラグは、従来からディーゼルエンジンのシリンダヘッドに配置されており、このグロープラグに圧電素子を有する圧力センサーを併設することで、エンジン全体を大型化することなく燃焼圧を圧電素子に伝え、ディーゼルエンジンの燃焼圧を計測することができる。 The glow plug has a heater arranged in a combustion chamber or a sub-combustion chamber in a cylinder of a diesel engine, and the diesel engine is heated by heating the combustion chamber and the sub-combustion chamber with the heater before or at the start of the start. This assists the start-up. Such a glow plug has been conventionally arranged in a cylinder head of a diesel engine. By attaching a pressure sensor having a piezoelectric element to the glow plug, the combustion pressure can be converted into a piezoelectric element without increasing the size of the entire engine. It is possible to measure the combustion pressure of a diesel engine.
　例えば下記特許文献１には、圧力センサーが搭載されたグロープラグの一例が開示されている。 For example, Patent Document 1 below discloses an example of a glow plug equipped with a pressure sensor.
　図７は、特許文献１に開示されている圧力センサー付きグロープラグ１００（以降、単にグロープラグ１００ともいう）について説明する図であり、グロープラグ１００に備えられた圧電素子１０１の近傍を拡大して示している。グロープラグ１００には、圧電素子１０１、圧電素子１０１の２つの主面と当接してこの圧電素子１０１を挟むように配置された電極板１０２および１０３、さらにその外側に配置された一対の絶縁基板１０４および１０５を備えている。絶縁基板１０５の上側主面は固定板１１７と当接している。圧電素子１０１、電極板１０２および１０３、さらに絶縁基板１０４および１０５には貫通孔が設けられており、この貫通孔に絶縁性円柱部材１１２が挿着されている。圧電素子１０１と、燃焼室や副燃焼室を加熱するための図示しないヒーターに電力を供給するための電線１１４とは、円柱部材１１２によって隔てられており、圧電素子１０１と電線１１４とは電気的に絶縁されている。グロープラグ１００は、圧電素子１０１よりも図７の下側に配置された図示しない燃焼室内の燃焼圧を図７中の上側に伝達するための伝達部材１１５を備えている。この伝達部材１１５と固定部材７との間に挟まれるように配置された圧電素子１０１には、この伝達部材１１５から燃焼圧が伝達される。圧電素子１０１は、上側主面１０１Ａおよび下側主面１０１Ｂの双方が平坦な面であり、これら上側主面１０１Ａと下側主面１０１Ｂとは平行とされている。 FIG. 7 is a diagram for explaining a glow plug 100 with a pressure sensor (hereinafter, also simply referred to as a glow plug 100) disclosed in Patent Document 1, in which the vicinity of the piezoelectric element 101 provided in the glow plug 100 is enlarged. It shows. The glow plug 100 includes a piezoelectric element 101, electrode plates 102 and 103 disposed so as to be in contact with the two main surfaces of the piezoelectric element 101 and sandwiching the piezoelectric element 101, and a pair of insulating substrates disposed on the outside thereof. 104 and 105 are provided. The upper main surface of the insulating substrate 105 is in contact with the fixing plate 117. The piezoelectric element 101, the electrode plates 102 and 103, and the insulating substrates 104 and 105 are provided with through holes, and the insulating cylindrical member 112 is inserted into the through holes. The piezoelectric element 101 and the electric wire 114 for supplying electric power to a heater (not shown) for heating the combustion chamber and the auxiliary combustion chamber are separated by a cylindrical member 112, and the piezoelectric element 101 and the electric wire 114 are electrically connected. Is insulated. The glow plug 100 includes a transmission member 115 for transmitting a combustion pressure in a combustion chamber (not shown) disposed below the piezoelectric element 101 in FIG. 7 to the upper side in FIG. The combustion pressure is transmitted from the transmission member 115 to the piezoelectric element 101 disposed so as to be sandwiched between the transmission member 115 and the fixing member 7. In the piezoelectric element 101, both the upper main surface 101A and the lower main surface 101B are flat surfaces, and the upper main surface 101A and the lower main surface 101B are parallel to each other.
特開２００８－２８０９号公報JP 2008-2809 A
　図７に示す例のように、圧電素子１０１の２つの主面１０１Ａおよび１０１Ｂがいずれも平坦な場合は、上側主面１０１Ａおよび下側主面１０１Ｂに対して、精度良く垂直に圧力が印加されると、上側主面１０１Ａおよび下側主面１０１Ｂ全体に均等に分散するように圧力がかかる。しなしながら、伝達部材１１５から印加される圧力の方向が微小に変化した場合には、圧力が集中してかかる部位が、この圧力の方向の微小変化に伴って不規則に変化してしまう。圧力が集中してかかる部位が変化すると、圧電素子１０１内の応力分布も変化し、圧電素子１０１において発生する電荷量も変化する。特許文献１に開示されているグロープラグ１００では、圧電素子１０１に対して伝達部材１１５から同じ大きさの燃焼圧がかかった場合でも、圧力がかかる方向の微小な変化や、圧電素子１０１と電極板１０２および電極板１０３との接触状態の変化に伴い、出力される電圧が変化してしまうといった課題があった。すなわち、特許文献１に記載されている従来の圧力センサー用圧電素子１０１は、圧電素子１０１にかかる圧力の方向が微小に変化した際に、圧電素子１０１から出力される電圧がばらついてしまうといった課題があった。 When the two main surfaces 101A and 101B of the piezoelectric element 101 are both flat as in the example shown in FIG. 7, pressure is applied vertically with high accuracy to the upper main surface 101A and the lower main surface 101B. Then, pressure is applied so that the upper main surface 101A and the lower main surface 101B are uniformly distributed. However, when the direction of the pressure applied from the transmission member 115 is slightly changed, the portion where the pressure is concentrated is irregularly changed along with the minute change in the direction of the pressure. When the pressure is concentrated and the portion changes, the stress distribution in the piezoelectric element 101 also changes, and the amount of charge generated in the piezoelectric element 101 also changes. In the glow plug 100 disclosed in Patent Document 1, even when a combustion pressure of the same magnitude is applied to the piezoelectric element 101 from the transmission member 115, a slight change in the direction in which the pressure is applied, or the piezoelectric element 101 and the electrode There is a problem in that the output voltage changes with the change in the contact state between the plate 102 and the electrode plate 103. That is, the conventional pressure sensor piezoelectric element 101 described in Patent Document 1 has a problem in that the voltage output from the piezoelectric element 101 varies when the direction of pressure applied to the piezoelectric element 101 changes slightly. was there.
　上記課題を解決するために本発明は、円形状の第１周縁を有する第１主面、円形状の第２周縁を有する、前記第１主面と反対側の第２主面、および前記第１主面と前記第２主面との間を貫通した円形状の貫通孔を備える圧電基体と、前記第１主面に接合した第１電極層と、前記第２主面に接合した第２電極層とを備え、前記第１主面と前記第２主面との間に加わる荷重によって前記圧電基体に生じる電荷を前記第１電極層および前記第２電極層を介して出力する圧力センサー用圧電素子であって、前記第１周縁を含む第１仮想平面と、前記第２周縁を含む前記第２仮想平面とはそれぞれ平行であり、前記貫通孔の中心軸は、前記第１周縁の中心と前記第２周縁の中心とを通って前記第１仮想平面および前記第２仮想平面に直交しており、前記第１主面は、前記貫通孔の開口を囲むように設けられた、前記第１周縁と同心円状の突部を備えており、前記中心軸を含む前記圧電基体の断面のうち、前記貫通孔を挟んで両側に配置された２つの部分領域のそれぞれにおける前記突部の断面線が、前記中心軸に平行な方向に沿って前記圧電基体の外側に向けて凸な円弧状であることを特徴する圧力センサー用圧電素子を提供する。 In order to solve the above-described problems, the present invention provides a first main surface having a circular first peripheral edge, a second main surface opposite to the first main surface, having a circular second peripheral edge, and the first A piezoelectric substrate having a circular through hole penetrating between one main surface and the second main surface, a first electrode layer bonded to the first main surface, and a second electrode bonded to the second main surface And a pressure sensor for outputting electric charges generated in the piezoelectric substrate by a load applied between the first main surface and the second main surface via the first electrode layer and the second electrode layer. The first virtual plane including the first peripheral edge and the second virtual plane including the second peripheral edge are parallel to each other, and a central axis of the through hole is a center of the first peripheral edge. Passing through the center of the second peripheral edge and perpendicular to the first virtual plane and the second virtual plane, The first main surface includes a protrusion concentrically with the first peripheral edge provided so as to surround the opening of the through hole, and the through hole in the cross section of the piezoelectric substrate including the central axis. A cross-sectional line of the protrusion in each of the two partial regions arranged on both sides with respect to each other is an arc shape convex toward the outside of the piezoelectric substrate along a direction parallel to the central axis. A piezoelectric element for a pressure sensor is provided.
　本発明では、円形状の第１周縁を有する第１主面、円形状の第２周縁を有する第２主面、および前記第１主面と前記第２主面との間を貫通した円形状の貫通孔を備える圧電基体を備える圧力センサー用圧電素子において、貫通孔の中心軸を含む圧電基体の断面のうち、貫通孔を挟んで両側に配置された２つの部分領域のそれぞれにおける突部の断面線を、中心軸に平行な方向に沿って圧電基体の外側に向けて凸な円弧状としており、圧力が印加される方向が微小に変化したとしても、この突部に繰り返し集中して圧力がかかるので、圧力方向の微小変化に伴う計測結果のばらつきを抑制することができる。 In the present invention, a first main surface having a circular first peripheral edge, a second main surface having a circular second peripheral edge, and a circular shape penetrating between the first main surface and the second main surface. In the piezoelectric element for a pressure sensor including the piezoelectric substrate including the through hole, the protrusion of each of the two partial regions arranged on both sides of the through hole in the cross section of the piezoelectric substrate including the central axis of the through hole is provided. The cross-sectional line has a circular arc shape that protrudes toward the outside of the piezoelectric substrate along the direction parallel to the central axis, and even if the direction in which the pressure is applied changes slightly, the pressure is concentrated repeatedly on this protrusion. Therefore, it is possible to suppress variations in measurement results due to minute changes in the pressure direction.
本発明の圧力センサー用圧電素子の一実施形態について説明する図であり、（ａ）は概略斜視図、（ｂ）は概略断面図である。It is a figure explaining one Embodiment of the piezoelectric element for pressure sensors of this invention, (a) is a schematic perspective view, (b) is a schematic sectional drawing. 図１に示す圧電素子１が備える圧電基体の概略斜視図である。FIG. 2 is a schematic perspective view of a piezoelectric substrate included in the piezoelectric element 1 shown in FIG. 1. 図１に示す圧電素子を備える圧力センサー付きグロープラグを、ディーゼルエンジンのエンジンヘッドに取り付けた状態を示す断面図である。It is sectional drawing which shows the state which attached the glow plug with a pressure sensor provided with the piezoelectric element shown in FIG. 1 to the engine head of a diesel engine. 図３に示す圧力センサー付きグロープラグの、圧力センサー部近傍を拡大して示す概略断面図である。It is a schematic sectional drawing which expands and shows the pressure sensor part vicinity of the glow plug with a pressure sensor shown in FIG. 図３に示す圧力センサー付きグロープラグにおいて、圧電素子に対し圧力が印加された状態を示す図であり、圧電素子の第１電極層近傍を拡大して示す概略断面図である。FIG. 4 is a diagram illustrating a state in which pressure is applied to the piezoelectric element in the glow plug with a pressure sensor illustrated in FIG. 3, and is a schematic cross-sectional view illustrating an enlarged vicinity of a first electrode layer of the piezoelectric element. （ａ）～（ｃ）はそれぞれ、本発明の圧電素子の他の実施形態を示す概略断面図である。(A)-(c) is a schematic sectional drawing which shows other embodiment of the piezoelectric element of this invention, respectively. 従来の圧力センサー付きグロープラグについて説明する概略断面図である。It is a schematic sectional drawing explaining the conventional glow plug with a pressure sensor.
　本発明の圧力センサー用圧電素子の実施形態について、図面を参照して説明する。 Embodiments of the piezoelectric element for pressure sensor of the present invention will be described with reference to the drawings.
　図１は、本発明の圧力センサー用圧電素子の一実施形態である圧力センサー用圧電素子１（以降、単に圧電素子１ともいう）について説明する図であり、図１（ａ）は圧電素子１の概略斜視図、図１（ｂ）は圧電素子１の概略断面図である。図２は圧電素子１が備える圧電基体４１の概略斜視図である。 FIG. 1 is a diagram for explaining a pressure sensor piezoelectric element 1 (hereinafter also simply referred to as a piezoelectric element 1), which is an embodiment of the pressure sensor piezoelectric element of the present invention. FIG. 1B is a schematic sectional view of the piezoelectric element 1. FIG. 2 is a schematic perspective view of the piezoelectric substrate 41 included in the piezoelectric element 1.
　圧電素子１は、円形状の第１周縁４２を有する第１主面４１Ａ（図１（ｂ）参照）、円形状の第２周縁４３を有する、第１主面４１Ａと反対側の第２主面４１Ｂ（図１（ｂ）参照）、および第１主面４１Ａと第２主面４１Ｂとの間を貫通した円形状の貫通孔４４を備える圧電基体４１と、第１主面４１Ａに接合した第１電極層５１と、第２主面４１Ｂに接合した第２電極層５２とを備える。圧電素子１は、第１主面４１Ａと第２主面４１Ｂとの間に加わる圧力によって圧電基体４１に生じる電荷を、第１電極層５１および第２電極層５２から出力する。 The piezoelectric element 1 has a first main surface 41A (see FIG. 1B) having a circular first peripheral edge 42 and a second main surface opposite to the first main surface 41A having a circular second peripheral edge 43. A piezoelectric substrate 41 having a surface 41B (see FIG. 1B) and a circular through hole 44 penetrating between the first main surface 41A and the second main surface 41B, and joined to the first main surface 41A The first electrode layer 51 and the second electrode layer 52 bonded to the second main surface 41B are provided. The piezoelectric element 1 outputs, from the first electrode layer 51 and the second electrode layer 52, charges generated in the piezoelectric substrate 41 due to pressure applied between the first main surface 41A and the second main surface 41B.
　圧電基体４１の組成は特に限定されないが、ビスマス層状化合物、窒化アルミニウム、酸化亜鉛、チタン酸ジルコン酸鉛（ＰＺＴ）およびチタン酸鉛などの圧電磁器を使用すればよい。本実施形態では、高いキュリー温度を有するビスマス層状化合物を主成分とする圧電磁器を圧電基体４１として用いている。ビスマス層状化合物からなる圧電磁器は、作製が容易であり、酸化物であるため高温での信頼性が高く、高いキュリー温度を有し耐熱性も高い点で好ましい。 The composition of the piezoelectric substrate 41 is not particularly limited, but piezoelectric ceramics such as a bismuth layered compound, aluminum nitride, zinc oxide, lead zirconate titanate (PZT), and lead titanate may be used. In the present embodiment, a piezoelectric ceramic mainly composed of a bismuth layered compound having a high Curie temperature is used as the piezoelectric substrate 41. A piezoelectric ceramic made of a bismuth layered compound is preferable in that it is easy to produce and is an oxide, so that it is highly reliable at high temperatures, has a high Curie temperature, and has high heat resistance.
　第１電極層５１および第２電極層５２は、Ａｇ、Ａｕ、Ｐｔ、Ｃｕ、Ｎｉ等の金属を用いることができる。本実施形態の第１電極層５１および第２電極層５２は、比較的低価格で作製が容易であるとともに信頼性に優れるＡｇを主成分としている。第１周縁４２を含む第１仮想平面Ｐ１（図１（ｂ）参照）と、第２周縁４３（図１（ｂ）参照）を含む第２仮想平面Ｐ２とはそれぞれ平行であり、貫通孔４４の中心軸Ｓは、第１周縁４２の中心４２ｃと第２周縁４３の中心４３ｃとを通って、第１仮想平面Ｐ１および第２仮想平面Ｐ２に直交している。圧電基体４１は、中心軸Ｓに平行な方向に沿って分極されており、圧電基体４１は、中心軸Ｓに平行な方向に沿って第１主面４２と第２主面４３との間に加わる圧力に応じた電荷を発生する。 The first electrode layer 51 and the second electrode layer 52 can use metals such as Ag, Au, Pt, Cu, and Ni. The first electrode layer 51 and the second electrode layer 52 of the present embodiment are mainly composed of Ag which is relatively inexpensive and easy to manufacture and has excellent reliability. The first virtual plane P1 including the first peripheral edge 42 (see FIG. 1B) and the second virtual plane P2 including the second peripheral edge 43 (see FIG. 1B) are parallel to each other, and the through hole 44 is provided. The central axis S passes through the center 42c of the first peripheral edge 42 and the center 43c of the second peripheral edge 43, and is orthogonal to the first virtual plane P1 and the second virtual plane P2. The piezoelectric substrate 41 is polarized along a direction parallel to the central axis S, and the piezoelectric substrate 41 is interposed between the first main surface 42 and the second main surface 43 along a direction parallel to the central axis S. Generates electric charge according to the applied pressure.
　第１主面４１Ａは、貫通孔４４の開口４４ａを囲むように設けられた、第１周縁４２と同心円状の突部４６Ａを備えており、中心軸Ｓを含む圧電基体４１の断面のうち、貫通孔４４を挟んで両側に配置された２つの部分領域４１α（図１（ｂ）参照）および４１β（図１（ｂ）参照）のそれぞれにおける突部４６Ａの断面線が、中心軸Ｓに平行な方向に圧電基体４１の外側に向けて凸な円弧状とされている。 The first main surface 41A includes a protrusion 46A that is concentric with the first peripheral edge 42 provided so as to surround the opening 44a of the through hole 44. Of the cross section of the piezoelectric substrate 41 including the central axis S, The cross-sectional line of the protrusion 46A in each of the two partial regions 41α (see FIG. 1B) and 41β (see FIG. 1B) arranged on both sides of the through hole 44 is parallel to the central axis S. In this direction, the arc is convex toward the outside of the piezoelectric substrate 41.
　本実施形態の圧電素子１では、第１主面４１Ａに加えて第２主面４１Ｂも、貫通孔４４の開口４４ｂを囲むように設けられた、第２周縁４３と同心円状の第２主面側突部４６Ｂ（以降、単に突部４６Ｂともいう）を備えており、中心軸Ｓを含む圧電基体４１の断面のうち、貫通孔４４を挟んで両側に配置された２つの部分領域４１αおよび４１βのそれぞれにおける突部４６Ｂの断面線が、中心軸Ｓに平行な方向に圧電基体４１の外側に向けて凸な円弧状とされている。 In the piezoelectric element 1 of the present embodiment, in addition to the first main surface 41A, the second main surface 41B is also provided so as to surround the opening 44b of the through hole 44. The second main surface concentric with the second peripheral edge 43 is provided. Two partial regions 41α and 41β which are provided with side protrusions 46B (hereinafter also simply referred to as protrusions 46B) and are arranged on both sides of the through hole 44 in the cross section of the piezoelectric substrate 41 including the central axis S. The cross-sectional line of the protrusion 46B in each of these is a circular arc shape that protrudes toward the outside of the piezoelectric substrate 41 in a direction parallel to the central axis S.
　圧電素子１では、第１電極層５１は、第１主面４１Ａの突部４６Ａの表面のみに配置されている。また、第１電極層５１の圧電基体４１に接合した側と反対側の表面５１Ａは、第１仮想平面Ｐ１と平行である。また、第１主面４１Ａは、第１周縁４２を含んで突部４６Ａに連なる、第１仮想平面Ｐ１と面一な外側平面部４７Ａと、貫通孔４４の開口４４ａの周縁を含んで突部４６Ａに連なる、第１仮想平面Ｐ１と面一な内側平面部４８Ａとを備えている。 In the piezoelectric element 1, the first electrode layer 51 is disposed only on the surface of the protrusion 46A of the first main surface 41A. Further, the surface 51A of the first electrode layer 51 opposite to the side bonded to the piezoelectric substrate 41 is parallel to the first virtual plane P1. The first main surface 41A includes the first peripheral edge 42 and continues to the protrusion 46A. The first main surface 41A includes the outer flat surface portion 47A that is flush with the first virtual plane P1 and the peripheral edge of the opening 44a of the through hole 44. 46A, the first virtual plane P1 and the flush inner plane portion 48A are provided.
　第２主面４１Ｂの側も同様に、第２電極層５２は、第２主面４１Ｂの突部４６Ｂの表面のみに接合している。また、第２電極層５２の圧電基体４１に接合した側と反対側の表面５２Ｂは、第２仮想平面Ｐ２と平行である。また、第２主面４１Ｂは、第２周縁４３を含んで突部４６Ｂに連なる、第２仮想平面Ｐ２と面一な外側平面部４７Ｂと、貫通孔４４の開口４４ｂの周縁を含んで突部４６Ｂに連なる、第２仮想平面Ｐ２と面一な内側平面部４８Ｂとを備えている。 Similarly, on the second main surface 41B side, the second electrode layer 52 is bonded only to the surface of the protrusion 46B of the second main surface 41B. The surface 52B of the second electrode layer 52 opposite to the side bonded to the piezoelectric substrate 41 is parallel to the second virtual plane P2. Further, the second main surface 41B includes the second peripheral edge 43 and continues to the protrusion 46B, the outer flat surface part 47B flush with the second virtual plane P2, and the protrusion including the periphery of the opening 44b of the through hole 44. 46B, a second virtual plane P2 and a flush inner plane portion 48B are provided.
　本実施形態では、第１主面４１Ａおよび第２主面４１Ｂの外径は、例えば３．５ｍｍ～２０ｍｍ程度であり、第１電極層５１の表面５１Ａから第２電極層５２の表面５２Ｂまでの中心軸Ｓに沿った長さ（すなわち、圧電素子１の高さ）は、０．５ｍｍ～１８ｍｍ程度である。また、貫通孔４４の直径は、例えば１～５．５ｍｍ程度であり、第１電極層５１および第２電極層５２の厚みは、例えば２～２００μｍ程度である。突部４６Ａの仮想平面Ｐ１からの突出高さ、および突部４６Ｂの仮想平面Ｐ２からの突出高さは、いずれも５０～２００μm程度である。また、外側平面部４７Ａおよび内側平面部４８Ａの第１周縁４２の径方向に沿った長さ、外側平面部４７Ｂおよび内側平面部４８Ｂの第２周縁４３の径方向に沿った長さは、いずれも２０～６０μｍ程度である。 In the present embodiment, the outer diameter of the first main surface 41A and the second main surface 41B is, for example, about 3.5 mm to 20 mm, and extends from the surface 51A of the first electrode layer 51 to the surface 52B of the second electrode layer 52. The length along the central axis S (that is, the height of the piezoelectric element 1) is about 0.5 mm to 18 mm. The diameter of the through hole 44 is, for example, about 1 to 5.5 mm, and the thicknesses of the first electrode layer 51 and the second electrode layer 52 are, for example, about 2 to 200 μm. The protrusion height of the protrusion 46A from the virtual plane P1 and the protrusion height of the protrusion 46B from the virtual plane P2 are both about 50 to 200 μm. Further, the length along the radial direction of the first peripheral edge 42 of the outer flat surface portion 47A and the inner flat surface portion 48A and the length along the radial direction of the second peripheral edge 43 of the outer flat surface portion 47B and the inner flat surface portion 48B are Is about 20 to 60 μm.
　圧電素子１は、例えばディーゼルエンジンの燃焼室内の温度を測定する圧力センサーに搭載されて用いられる。以下、圧電素子１を備えて構成される圧力センサーの一実施形態について説明するとともに、圧電素子１の機能について説明する。 The piezoelectric element 1 is mounted and used, for example, in a pressure sensor that measures the temperature in the combustion chamber of a diesel engine. Hereinafter, an embodiment of a pressure sensor including the piezoelectric element 1 will be described, and the function of the piezoelectric element 1 will be described.
　図３は、圧電素子１を備える圧力センサー付きグロープラグ１０（以降、単にグロープラグ１０ともいう）について説明する図であり、グロープラグ１０をディーゼルエンジンのエンジンヘッド１１０に取り付けた状態を示す断面図である。 FIG. 3 is a view for explaining a glow plug 10 with a pressure sensor (hereinafter also simply referred to as a glow plug 10) including the piezoelectric element 1, and a cross-sectional view showing a state in which the glow plug 10 is attached to an engine head 110 of a diesel engine. It is.
　ディーゼルエンジンのエンジンヘッド１１０には、エンジンヘッド１１０内の燃焼室１２に通じる貫通孔１１が設けられている。貫通孔１１の内面には、図３の上側の端部近傍にねじ部１４が設けられており、図３の下側の端部近傍に、図３の下側に近づくにしたがって縮径したテーパー状の段部１３が設けられている。 In the engine head 110 of the diesel engine, a through hole 11 that communicates with the combustion chamber 12 in the engine head 110 is provided. A threaded portion 14 is provided near the upper end of FIG. 3 on the inner surface of the through hole 11, and the taper is reduced in diameter near the lower end of FIG. 3 as it approaches the lower side of FIG. 3. A stepped portion 13 is provided.
　グロープラグ１０は、ハウジング２と、伝達部材３と、シール部材８と、発熱体２６と電線２７と、圧電素子１を備えて構成された圧力センサー部（圧力センサー）６とを備えている。 The glow plug 10 includes a housing 2, a transmission member 3, a seal member 8, a heating element 26, an electric wire 27, and a pressure sensor unit (pressure sensor) 6 including the piezoelectric element 1.
　ハウジング２は、エンジンヘッド１１０の貫通孔１１内に挿入された挿入部２９と、エンジンヘッド１１０の外側（燃焼室１２と反対、すなわち図３における上側）に配置された、圧電素子１が搭載された搭載部２５とを有する。ハウジング２の挿入部２９は、断面が円形状の中空部２１を有する略円筒形状であり、図３の下側（燃焼室１２に近い側）の先端部は、エンジンヘッド１１０のテーパ部１３と密着するテーパ部２２が設けられている。また、挿入部２９の図３の上側端部の外周には、貫通孔１１のねじ部１４と螺合するねじ部２３が設けられている。 The housing 2 is mounted with the insertion portion 29 inserted into the through hole 11 of the engine head 110 and the piezoelectric element 1 disposed outside the engine head 110 (opposite to the combustion chamber 12, that is, on the upper side in FIG. 3). Mounting portion 25. The insertion portion 29 of the housing 2 has a substantially cylindrical shape having a hollow portion 21 having a circular cross section, and a lower end (side closer to the combustion chamber 12) of FIG. 3 has a tapered portion 13 of the engine head 110. The taper part 22 which closely_contact | adheres is provided. Further, on the outer periphery of the upper end portion of the insertion portion 29 in FIG. 3, a screw portion 23 that is screwed with the screw portion 14 of the through hole 11 is provided.
　ハウジング２とエンジンヘッド１１０とは、ねじ部１４とねじ部２３との螺合による軸力によって、ハウジング２のテーパ部２２とエンジンヘッド１１０のテーパ部１３とが押し合わされて密着し、燃焼室１２で発生する高圧の燃焼ガスが、エンジンヘッド１１０の貫通孔１１の内周とハウジング２の外周との間隙に漏れないようになっている。 The housing 2 and the engine head 110 are brought into close contact with each other by the taper portion 22 of the housing 2 and the taper portion 13 of the engine head 110 by an axial force generated by the screwing of the screw portion 14 and the screw portion 23. Is prevented from leaking into the gap between the inner periphery of the through hole 11 of the engine head 110 and the outer periphery of the housing 2.
　ハウジング２の中空部２１内には、図３中の上側から下側に延びる、ステンレス等の耐熱金属からなる伝達部材３が配置されている。伝達部材３は、図３における上下方向に沿って延びた、断面が円形状の中空部３３が設けられている。伝達部材３は、シール部材８と接合して保持され、図３における上下方向に沿って移動可能に保持されている。 In the hollow portion 21 of the housing 2, a transmission member 3 made of a heat-resistant metal such as stainless steel, which extends from the upper side to the lower side in FIG. The transmission member 3 is provided with a hollow portion 33 having a circular cross section extending in the vertical direction in FIG. The transmission member 3 is joined and held with the seal member 8, and is held so as to be movable along the vertical direction in FIG.
　シール部材８は、ステンレス等の金属からなり、ハウジング２の先端と伝達部材３の受圧部３１とにレーザ溶接等によって気密に固定されており、燃焼室１２内の燃焼ガスがハウジング３の中空部２１内に侵入するのを防止している。シール部材８は蛇腹状であり図３における上下方向に沿って変形することができる。シール部材８が図３における上下方向に沿って変形することで、伝達部材３は図３における上下方向に沿って位置変動することができる。 The seal member 8 is made of a metal such as stainless steel, and is hermetically fixed to the front end of the housing 2 and the pressure receiving portion 31 of the transmission member 3 by laser welding or the like, so that the combustion gas in the combustion chamber 12 is a hollow portion of the housing 3. Intrusion into 21 is prevented. The seal member 8 has a bellows shape and can be deformed along the vertical direction in FIG. When the seal member 8 is deformed along the vertical direction in FIG. 3, the position of the transmission member 3 can be changed along the vertical direction in FIG. 3.
　エンジンヘッド１１０の貫通孔１１、ハウジング２の中空部２１、伝達部材３の中空部３３は、それぞれの中心軸（図３に中心軸Ｓで示す軸）が一致するように配置されている。伝達部材３の中空部３３は下側端部で閉塞されており、伝達部材３の下側の先端部が受圧部３１として燃焼室１２内に露出している。伝達部材３の上側の端部には、ハウジング２の搭載部２５に配置される円盤状の鍔部３２が設けられており、中空部３３の上側は開放されている。鍔部３２の上方主面３２Ａは、中心軸Sに対して垂直な平面となっている。 The through-hole 11 of the engine head 110, the hollow portion 21 of the housing 2, and the hollow portion 33 of the transmission member 3 are arranged so that their central axes (axis indicated by the central axis S in FIG. 3) coincide with each other. The hollow portion 33 of the transmission member 3 is closed at the lower end portion, and the lower end portion of the transmission member 3 is exposed as the pressure receiving portion 31 in the combustion chamber 12. At the upper end of the transmission member 3, a disc-shaped flange 32 disposed on the mounting portion 25 of the housing 2 is provided, and the upper side of the hollow portion 33 is open. The upper main surface 32A of the flange portion 32 is a plane perpendicular to the central axis S.
　また、伝達部材３の中空部３３の下側端部近傍（すなわち、受圧部３１近傍）には発熱体２６が配置されており、この発熱体２６に電力を供給するための電線２７が、伝達部材３の上側の開口を通じて中空部３３内に挿通され、電線２７が発熱体２６と接続されている。 In addition, a heating element 26 is disposed in the vicinity of the lower end of the hollow portion 33 of the transmission member 3 (that is, in the vicinity of the pressure receiving portion 31), and an electric wire 27 for supplying electric power to the heating element 26 is transmitted. The electric wire 27 is connected to the heating element 26 through the opening on the upper side of the member 3 and inserted into the hollow portion 33.
　発熱体２６は、例えば公知のニクロム線等からなり、電線２７を介して電流が流れることで発熱する。発熱体２６が発熱することで、エンジンヘッド１１０の燃焼室１２内が加熱され、燃焼室１２内の温度が上昇する。これら発熱体２６と電線２７が伝達部材３に配置されたグロープラグ１０は、例えばディーゼルエンジンの低温始動時に、エンジンヘッド１１０の燃焼室１２内を暖める機能を有する。圧力センサー部６の圧電素子１は燃焼室１２内の圧力（燃焼圧）の大きさを計測することができる。本実施形態のグロープラグ１０は、燃焼室を暖めるのみでなく、燃焼室１２内の圧力を計測する機能も有する。 The heating element 26 is made of, for example, a known nichrome wire, and generates heat when a current flows through the electric wire 27. When the heating element 26 generates heat, the inside of the combustion chamber 12 of the engine head 110 is heated, and the temperature in the combustion chamber 12 rises. The glow plug 10 in which the heating element 26 and the electric wire 27 are arranged on the transmission member 3 has a function of warming the combustion chamber 12 of the engine head 110 when the diesel engine is started at a low temperature, for example. The piezoelectric element 1 of the pressure sensor unit 6 can measure the pressure (combustion pressure) in the combustion chamber 12. The glow plug 10 of the present embodiment not only warms the combustion chamber but also has a function of measuring the pressure in the combustion chamber 12.
　図４は、図３に示すグロープラグ１０の、圧力センサー部６近傍を拡大して示す概略断面図である。圧力センサー部６は、圧電素子１、圧電素子１から出力される電気信号を取り出すための電極板６２および電極板６３、電極板６２および電極板６３を挟む一対の絶縁基板６４および絶縁基板６５、ならびに固定基板７を有して構成されている。 FIG. 4 is an enlarged schematic cross-sectional view showing the vicinity of the pressure sensor portion 6 of the glow plug 10 shown in FIG. The pressure sensor unit 6 includes a piezoelectric element 1, an electrode plate 62 and an electrode plate 63 for extracting an electric signal output from the piezoelectric element 1, a pair of insulating substrates 64 and 65 that sandwich the electrode plate 62 and the electrode plate 63, The fixed substrate 7 is included.
　固定基板７は側面にねじ部７１を有し、この側面のねじ部７１が、搭載部２５の内周面に設けられたねじ部７６に螺合され、固定基板７がハウジング２に固定されている。固定基板７の下方主面７Ｂは、鍔部３２の上方主面３２Ａと平行に配置されている。 The fixed substrate 7 has a screw portion 71 on the side surface, and the screw portion 71 on the side surface is screwed to a screw portion 76 provided on the inner peripheral surface of the mounting portion 25, so that the fixed substrate 7 is fixed to the housing 2. Yes. The lower main surface 7B of the fixed substrate 7 is disposed in parallel with the upper main surface 32A of the flange portion 32.
　固定基板７の下方主面７Ｂに、絶縁基板６４の上方主面６４Ａが当接し、絶縁基板６４の下方主面６４Ｂに、電極板６２の上方主面６２Ａが当接している。 The upper main surface 64A of the insulating substrate 64 is in contact with the lower main surface 7B of the fixed substrate 7, and the upper main surface 62A of the electrode plate 62 is in contact with the lower main surface 64B of the insulating substrate 64.
　鍔部３２の上方主面３２Ａには、絶縁基板６５の下方主面６５Ｂが当接し、絶縁基板６５の上方主面６５Ａには、電極板６３の下方主面６３Ｂが当接している。 The lower main surface 65B of the insulating substrate 65 is in contact with the upper main surface 32A of the flange 32, and the lower main surface 63B of the electrode plate 63 is in contact with the upper main surface 65A of the insulating substrate 65.
　固定基板７の下方主面７Ｂ、絶縁基板６４の上方主面６４Ａおよび下方主面６４Ｂ、電極板６２の上方主面６２Ａおよび下方主面６２Ｂ、電極板６３の上方主面６３Ａおよび下方主面６３Ｂ、絶縁基板６５の上方主面６５Ａおよび下方主面６５Ｂはいずれも平行となっており、互いに平行な下方主面６２Ｂと上方主面６３Ａとの間に、圧電素子１が配置されている。 Lower main surface 7B of fixed substrate 7, upper main surface 64A and lower main surface 64B of insulating substrate 64, upper main surface 62A and lower main surface 62B of electrode plate 62, upper main surface 63A and lower main surface 63B of electrode plate 63 The upper main surface 65A and the lower main surface 65B of the insulating substrate 65 are both parallel, and the piezoelectric element 1 is disposed between the lower main surface 62B and the upper main surface 63A that are parallel to each other.
　また、固定基板７、絶縁基板６４、電極板６２、電極板６３および絶縁基板６５には、いずれも貫通孔が設けられており、これら貫通孔は、圧電素子１の貫通孔４４に連なり、これら貫通孔が連なった孔部に、円筒状の絶縁体７２が挿入されている。この絶縁体７２によって、固定基板７、絶縁基板６４、電極板６２、電極板６３、絶縁基板６５および圧電素子１の相対位置が設定されるとともに、電線２７とこれら各部材との絶縁を確保している。 The fixed substrate 7, the insulating substrate 64, the electrode plate 62, the electrode plate 63, and the insulating substrate 65 are all provided with through holes, and these through holes are connected to the through holes 44 of the piezoelectric element 1. A cylindrical insulator 72 is inserted into the hole portion where the through holes are continuous. The insulator 72 sets the relative positions of the fixed substrate 7, the insulating substrate 64, the electrode plate 62, the electrode plate 63, the insulating substrate 65 and the piezoelectric element 1, and ensures insulation between the electric wire 27 and these members. ing.
　なお、圧電素子１には、固定基板７がねじ込まれることで、図中の上下方向に沿って圧電素子１を圧縮する方向の予備圧力が予め印加されている。 Note that a preliminary pressure in a direction of compressing the piezoelectric element 1 along the vertical direction in the figure is applied in advance to the piezoelectric element 1 by screwing the fixed substrate 7.
　ディーゼルエンジンのエンジンヘッド１１０に取り付けられたグロープラグ１０では、伝達部材３の受圧部３１が、エンジンヘッド１１０の燃焼室１２内の圧力を受けることで、この圧力が伝達部材３を介して、圧力センサー部６の圧電素子１に伝わる。すなわち、受圧部３１にかかった圧力は、伝達部材３の鍔部３２、絶縁基板６５および電極板６３を介して、圧電素子１を図３および図４の下側から上側に押し上げるように伝わる。圧電素子１の図３および図４の上側は、固定基板７によって上下方向の位置が固定されており、圧電素子１には、上下方向に沿って圧電素子１を圧縮する方向に燃焼室１２内の圧力が加わる。 In the glow plug 10 attached to the engine head 110 of the diesel engine, the pressure receiving portion 31 of the transmission member 3 receives the pressure in the combustion chamber 12 of the engine head 110, so that the pressure is transferred to the pressure via the transmission member 3. It is transmitted to the piezoelectric element 1 of the sensor unit 6. That is, the pressure applied to the pressure receiving portion 31 is transmitted through the flange portion 32 of the transmission member 3, the insulating substrate 65, and the electrode plate 63 so as to push the piezoelectric element 1 upward from the lower side in FIGS. The upper side of the piezoelectric element 1 in FIGS. 3 and 4 is fixed in the vertical direction by the fixed substrate 7, and the piezoelectric element 1 is placed in the combustion chamber 12 in the direction of compressing the piezoelectric element 1 along the vertical direction. Pressure is applied.
　図１に示すように、本実施形態の圧電素子１は、圧電基体４１の、貫通孔４４を挟んで両側に配置された２つの部分領域４１αおよび４１βのそれぞれにおける突部４６Ａの断面線が、中心軸Ｓに平行な方向に圧電基体４１の外側に向けて凸な円弧状とされている。これにより、伝達部材３から印加される圧力の方向が微小に変化した場合であっても、圧力が集中してかかる部位が大きく変動することを抑制して、圧電素子４１内の応力分布の変化を抑制し、圧電素子４１における、圧力方向の微小変化に伴う発生電圧の変化を抑制する。 As shown in FIG. 1, in the piezoelectric element 1 of the present embodiment, the cross-sectional line of the protrusion 46A in each of the two partial regions 41α and 41β disposed on both sides of the through hole 44 of the piezoelectric substrate 41 is The arcuate shape is convex toward the outside of the piezoelectric substrate 41 in a direction parallel to the central axis S. As a result, even if the direction of the pressure applied from the transmission member 3 changes minutely, it is possible to suppress the concentration of the pressure and greatly change the portion, and the stress distribution in the piezoelectric element 41 changes. And the change in the generated voltage accompanying the minute change in the pressure direction in the piezoelectric element 41 is suppressed.
　図５は、図３に示すグロープラグ１０において、圧電素子１に対して圧力が印加された状態を示す図であり、圧電素子１の第１電極層５１近傍を拡大して示す概略断面図である。図５に示すように、圧電素子１に伝達部材３（図５では図示せず）を介して圧力が加わった場合に、圧電素子１は電極層５１が電極板６２に押し付けられるように上昇する。電極層５１はＡｇからなる金属層であり、比較的高い展延性を有しており、伝達部材３を介して加わる圧力によって、電極板６２と圧電基体４１とによって押し広げられるように変形していくとともに、電極板６２からの反力が圧電基体４１にかかる。 FIG. 5 is a diagram showing a state in which pressure is applied to the piezoelectric element 1 in the glow plug 10 shown in FIG. 3, and is a schematic sectional view showing the vicinity of the first electrode layer 51 of the piezoelectric element 1 in an enlarged manner. is there. As shown in FIG. 5, when pressure is applied to the piezoelectric element 1 via the transmission member 3 (not shown in FIG. 5), the piezoelectric element 1 rises so that the electrode layer 51 is pressed against the electrode plate 62. . The electrode layer 51 is a metal layer made of Ag, has a relatively high spreadability, and is deformed so as to be spread by the electrode plate 62 and the piezoelectric substrate 41 by the pressure applied via the transmission member 3. At the same time, a reaction force from the electrode plate 62 is applied to the piezoelectric substrate 41.
　本実施形態では、圧電基体４１の突部４６Ａの断面線が、圧電基体４１の外側に向けて凸な円弧状とされており、電極板６２からの反力が、この突部４６Ａの頂部に集中してかかることになる。このため、繰り返し圧力がかかった場合に、圧力が印加される方向が微小に変化したとしても、この頂部に圧力が繰り返し集中してかかることになる。すなわち、本実施形態の圧電素子１では、圧力が加わる方向が微小に変化した場合も、図５に示すように、突部４６Ａの頂部近傍を通り、中心軸Ｓにほぼ平行な方向の圧力が繰り返し印加される。 In the present embodiment, the cross-sectional line of the protrusion 46A of the piezoelectric substrate 41 has an arc shape that is convex toward the outside of the piezoelectric substrate 41, and the reaction force from the electrode plate 62 is applied to the top of the protrusion 46A. It will be concentrated. For this reason, when pressure is repeatedly applied, even if the direction in which the pressure is applied changes slightly, the pressure is repeatedly concentrated on the top. That is, in the piezoelectric element 1 of the present embodiment, even when the direction in which the pressure is applied changes slightly, the pressure in the direction substantially parallel to the central axis S passes through the vicinity of the top of the protrusion 46A as shown in FIG. Applied repeatedly.
　一方、圧電基体４１の一方主面４１Ａが、突部４６Ａを有さず平坦な場合は、圧力が印加される方向が微小に変化すると、圧力が集中してかかる部位が変化し、圧電基体４１における圧力分布が、圧力が印加されるたびに変化してしまう。本実施形態の圧電素子１は、このような圧力分布のばらつきを低減し、燃焼室１２内の圧力を繰り返し再現性よく高精度に計測することができる。 On the other hand, when the one main surface 41A of the piezoelectric base 41 is flat without the protrusion 46A, when the direction in which the pressure is applied changes slightly, the portion where the pressure is concentrated changes and the piezoelectric base 41 changes. The pressure distribution changes at every time pressure is applied. The piezoelectric element 1 of the present embodiment can reduce such a variation in pressure distribution, and can repeatedly measure the pressure in the combustion chamber 12 with high reproducibility and high accuracy.
　本実施形態の圧電素子１は、第２主面４１Ｂの側でも、突部４６Ｂの断面線が、中心軸Ｓに平行な方向に沿って圧電基体４１の外側に向けて凸な円弧状とされている。これにより、伝達部材３側から繰り返し圧力がかかった場合に、圧力が印加される方向が微小に変化したとしても、突部４６Ｂの頂部に圧力が繰り返し集中してかかるので、高精度に燃焼室１２内の圧力を計測することができる。 In the piezoelectric element 1 of the present embodiment, the cross-sectional line of the protrusion 46B is formed in an arc shape that protrudes toward the outside of the piezoelectric substrate 41 along the direction parallel to the central axis S on the second main surface 41B side. ing. As a result, even when the pressure is repeatedly applied from the transmission member 3 side, even if the direction in which the pressure is applied changes slightly, the pressure is repeatedly concentrated on the top of the protrusion 46B, so the combustion chamber is highly accurate. The pressure in 12 can be measured.
　本実施形態の圧電素子１はビスマス層状化合物からなり、高いキュリー温度を有し比較的高温でも使用可能となっているが、いわゆるＰＺＴ系の圧電素子と比較すると、入力される圧力の大きさに対する出力電圧の大きさの割合（いわゆる感度）が比較的低い。このため、ビスマス層状化合物を主成分とする圧電素子を使用する場合は、圧電素子の応力分布の変化に伴って発生するノイズ成分をなるべく低減しておくことが好ましい。本実施形態の圧電素子１は、ビスマス層状化合物を主成分としており、エンジン等の高温環境下で使用できるとともに、圧力の印加方向の微小な変化に伴う圧電基体４１内の応力分布のばらつきによるノイズ成分が少ない。圧電素子１は、例えばグロープラグに搭載される圧力センサーなど、比較的高温環境下の圧力を計測するための圧力センサーに好適に用いられる。 The piezoelectric element 1 of the present embodiment is made of a bismuth layered compound and has a high Curie temperature and can be used even at a relatively high temperature. However, compared with a so-called PZT-based piezoelectric element, The ratio of output voltage magnitude (so-called sensitivity) is relatively low. For this reason, when using a piezoelectric element whose main component is a bismuth layered compound, it is preferable to reduce as much as possible the noise component that occurs with changes in the stress distribution of the piezoelectric element. The piezoelectric element 1 according to the present embodiment includes a bismuth layered compound as a main component and can be used in a high temperature environment such as an engine, and noise due to variations in stress distribution in the piezoelectric substrate 41 due to a minute change in the pressure application direction. There are few ingredients. The piezoelectric element 1 is preferably used as a pressure sensor for measuring pressure in a relatively high temperature environment, such as a pressure sensor mounted on a glow plug.
　また、圧電素子１は図１（ｂ）に示すように、第１電極層５１が、第１主面４１Ａの突部４６Ａの表面のみに接合しているので、圧力が印加された際、図５に示すように第１電極層５１が変形して押し広げられた場合も、第１電極層５１が、圧電基体４１の側面まではみ出すことが少ない。同様に、第２電極層５２が、第２主面４１Ｂの突部４６Ｂの表面のみに接合しているので、圧力が印加された際に第２電極層５２が変形して押し広げられた場合も、第２電極層５２が突部４６Ｂの範囲に留まりやすく、圧電基体４１の側面まではみ出すことが少ない。 Further, as shown in FIG. 1B, in the piezoelectric element 1, the first electrode layer 51 is bonded only to the surface of the protrusion 46A of the first main surface 41A. As shown in FIG. 5, even when the first electrode layer 51 is deformed and spread out, the first electrode layer 51 hardly protrudes to the side surface of the piezoelectric substrate 41. Similarly, since the second electrode layer 52 is bonded only to the surface of the protrusion 46B of the second main surface 41B, the second electrode layer 52 is deformed and spread when pressure is applied. However, the second electrode layer 52 tends to stay in the range of the protrusion 46B, and hardly protrudes to the side surface of the piezoelectric substrate 41.
　また図１（ｂ）に示すように、第１電極層５１の圧電基体４１に接合した側と反対側の表面５１Ａ（図３中の上側の表面）は、第１仮想平面Ｐ１と平行となっているので、第１電極層５１の表面５１Ａは、電極板６２と比較的広い面積で接触することができる。例えば、第１電極層５１の表面５１Ａが、突部４６Ａに沿って断面が円弧状の表面であると、特に圧電基体４１が傾いた場合、第１電極層５１と電極板６２とが部分的に大きく離れることもあり、この場合、圧電基体４１において発生した電圧を、高精度に計測できない場合もある。これに対し、本実施形態の圧電素子１は、図１（ｂ）に示すように、第１電極層５１の圧電基体４１に接合した側と反対側の表面５１Ａ（図３中の上側の表面）は、第１仮想平面Ｐ１と平行であり、図５に示すように圧電基体４１が多少傾いた場合も、第１電極層５１が圧力に応じて変形することで、第１電極層５１と電極板６２とが比較的広い接触面積を確保することができるので、圧電基体４１における発生電圧を繰り返し高精度に計測することができる。同様に、図１（ｂ）に示すように、第２電極層５２の圧電基体４１に接合した側と反対側の表面５１Ｂ（図３中の下側の表面）は、第２仮想平面Ｐ２と平行であり、第２電極層５２の表面５２Ｂは電極板６３と比較的広い接触面積を確保している。 As shown in FIG. 1B, the surface 51A (upper surface in FIG. 3) opposite to the side bonded to the piezoelectric substrate 41 of the first electrode layer 51 is parallel to the first virtual plane P1. Therefore, the surface 51A of the first electrode layer 51 can contact the electrode plate 62 with a relatively large area. For example, if the surface 51A of the first electrode layer 51 is a surface having an arcuate cross section along the protrusion 46A, the first electrode layer 51 and the electrode plate 62 are partially separated particularly when the piezoelectric substrate 41 is inclined. In this case, the voltage generated in the piezoelectric substrate 41 may not be measured with high accuracy. On the other hand, as shown in FIG. 1B, the piezoelectric element 1 of the present embodiment has a surface 51A (the upper surface in FIG. 3) opposite to the side of the first electrode layer 51 bonded to the piezoelectric substrate 41. ) Is parallel to the first virtual plane P1, and even when the piezoelectric substrate 41 is slightly inclined as shown in FIG. 5, the first electrode layer 51 is deformed according to the pressure, Since a relatively wide contact area with the electrode plate 62 can be ensured, the voltage generated in the piezoelectric substrate 41 can be repeatedly measured with high accuracy. Similarly, as shown in FIG. 1B, the surface 51B (the lower surface in FIG. 3) opposite to the side of the second electrode layer 52 bonded to the piezoelectric substrate 41 is the second virtual plane P2. The surface 52B of the second electrode layer 52 ensures a relatively wide contact area with the electrode plate 63.
　また、図１（ａ）および（ｂ）に示すように、第１主面４１Ａは、第１周縁４２を含んで突部４６Ａに連なる、第１仮想平面Ｐ１と面一な外側平面部４７Ａと、貫通孔４４の開口４４ａの周縁を含んで突部４６Ａに連なる、第１仮想平面Ｐ１と面一な内側平面部４８Ａとを備えている。このような外側平面部４７Ａと内側平面部４８Ａとを有することで、例えば図５に示すように、圧力が印加された際に第１電極層５１が変形して押し広げられた場合でも、これら外側平面部４７Ａや内側平面部４８Ａによって第１電極層５１の広がりが堰き止められ、圧電基体４１の側面への電極のたれ等が抑制される。図５では、第１電極層５１の広がりが、外側平面部４７Ａによって堰き止められている。同様に、第２主面４１Ｂが、第２周縁４３を含んで突部４６Ｂに連なる、第２仮想平面Ｐ２と面一な外側平面部４７Ｂと、貫通孔４４の開口４４ａの周縁を含んで突部４６Ｂに連なる、第２仮想平面Ｐ２と面一な内側平面部４８Ｂとを備えている。このような外側平面部４７Ｂと内側平面部４８Ｂとにより、仮に第２電極層が変形して押し広げられた場合も（図示せず）、変形による第２電極層５２の広がりが堰き止められ、圧電基体４１の側面への第２電極層５２のたれ等が抑制される。 Further, as shown in FIGS. 1A and 1B, the first main surface 41A includes an outer flat surface portion 47A that is flush with the first virtual plane P1 and that includes the first peripheral edge 42 and continues to the protrusion 46A. The first imaginary plane P1 and the inner plane portion 48A that are flush with the protrusion 46A including the periphery of the opening 44a of the through hole 44 are provided. By having such an outer plane portion 47A and an inner plane portion 48A, even when the first electrode layer 51 is deformed and spread when a pressure is applied, for example, as shown in FIG. The spread of the first electrode layer 51 is blocked by the outer plane portion 47A and the inner plane portion 48A, and the sagging of the electrode on the side surface of the piezoelectric substrate 41 is suppressed. In FIG. 5, the spread of the first electrode layer 51 is blocked by the outer flat surface portion 47A. Similarly, the second main surface 41B includes the second peripheral edge 43 and continues to the protrusion 46B. The second main surface 41B protrudes including the outer flat part 47B flush with the second virtual plane P2 and the periphery of the opening 44a of the through hole 44. The second virtual plane P2 and the inner plane plane 48B that are flush with the portion 46B are provided. Even when the second electrode layer is deformed and spread by the outer flat portion 47B and the inner flat portion 48B (not shown), the spread of the second electrode layer 52 due to the deformation is blocked. The sagging of the second electrode layer 52 on the side surface of the piezoelectric substrate 41 is suppressed.
　このような圧電素子１は、例えば以下のように作製することができる。出発原料として純度９９．９％以上のＳｒＣＯ３粉末、ＢａＣＯ３粉末、Ｂｉ２Ｏ３粉末およびＴｉＯ２粉末を、組成式Ｂｉ４Ｔｉ３Ｏ１２・０．４７（Ｓｒ０．５Ｂａ０．５ＴｉＯ３）の比率となるように秤量する。 Such a piezoelectric element 1 can be manufactured as follows, for example. SrCO 3 powder purity of 99.9% or more as a starting material, BaCO 3 powder, the Bi 2 O 3 powder and TiO 2 powder, the composition formula Bi 4 Ti 3 O 12 · 0.47 (Sr 0.5 Ba 0.5 Weigh so that the ratio is TiO 3 ).
　この主成分１００質量部に対して、０．５質量部のＭｎＯ２粉末を秤量して混合し、純度９９．９％のＺｒＯ２ボールと、水あるいはイソプロピルアルコール（ＩＰＡ）とともに５００ｍｌの樹脂製ポットに投入し、その樹脂製ポットを回転台に置き、１６時間混合する。 0.5 parts by mass of MnO 2 powder is weighed and mixed with 100 parts by mass of this main component, and a 500 ml resin pot with 99.9% purity ZrO 2 balls and water or isopropyl alcohol (IPA). The resin pot is placed on a turntable and mixed for 16 hours.
　混合後のスラリーを大気中で乾燥した後、＃４０メッシュを通し、その後、大気中で９５０℃に３時間保持して仮焼し、この合成粉末を純度９９．９％のＺｒＯ２ボールと水あるいはイソプロピルアルコール（ＩＰＡ）とともに５００ｍｌの樹脂製ポットに投入し、その樹脂製ポットを回転台に置き２０時間粉砕する。 The slurry after mixing was dried in the air, passed through # 40 mesh, and then calcined by holding at 950 ° C. for 3 hours in the air, and this synthetic powder was mixed with ZrO 2 balls having a purity of 99.9% and water. Alternatively, it is put into a 500 ml resin pot together with isopropyl alcohol (IPA), and the resin pot is placed on a rotating table and pulverized for 20 hours.
　この粉砕した粉末に適量の有機バインダを添加して顆粒を造粒し、この顆粒を例えば一軸加圧成型法により成形し、圧電基体４１に対応する形状の生成形体を得る。この生成形体について脱バインダ処理を行なった後に、大気雰囲気中にて約１１５０℃で３時間かけて焼成を行ない、圧電基体４１を得る。 An appropriate amount of an organic binder is added to the pulverized powder to form granules, and the granules are formed by, for example, a uniaxial pressure molding method to obtain a generated shape having a shape corresponding to the piezoelectric substrate 41. After performing the binder removal processing on the generated shaped body, firing is performed at about 1150 ° C. for 3 hours in an air atmosphere to obtain the piezoelectric substrate 41.
　次に、圧電基体４１の第１主面４１Ａおよび第２主面４１Ｂに、印刷機を用いて、いわゆるＡｇペーストを印刷（塗布）して全体を焼成し、第１主面４１Ａおよび第２主面４１Ｂに、Ａｇを主成分とする電極層（第１電極層５１および第２電極層５２）を形成する。この際Ａｇペーストは、第１主面４１Ａについては突部４６Ａのみに印刷（塗布）し、第２主面４１Ｂについては突部４６Ｂのみに印刷（塗布）する。 Next, a so-called Ag paste is printed (applied) on the first main surface 41A and the second main surface 41B of the piezoelectric substrate 41 by using a printing machine, and the whole is baked to form the first main surface 41A and the second main surface 41B. Electrode layers (first electrode layer 51 and second electrode layer 52) containing Ag as a main component are formed on the surface 41B. At this time, the Ag paste is printed (applied) only on the protrusion 46A for the first main surface 41A, and is printed (applied) only on the protrusion 46B for the second main surface 41B.
　印刷したＡｇペーストを焼成した後、必要に応じて、焼成によって形成されたＡｇ電極の表面を研磨して、第１電極層５１および第２電極層５２を形成した後、第１電極層５１と第２電極層５２との間に所定の電圧を印加して分極処理を行なう。本実施形態の圧電素子１は、このようにして形成することができる。 After firing the printed Ag paste, if necessary, the surface of the Ag electrode formed by firing is polished to form the first electrode layer 51 and the second electrode layer 52, and then the first electrode layer 51 and A predetermined voltage is applied between the second electrode layer 52 and the polarization process is performed. The piezoelectric element 1 of this embodiment can be formed in this way.
　図６（ａ）～（ｃ）はそれぞれ、本発明の圧電素子の他の実施形態を示す概略断面図である。図６の各実施形態では、圧電素子１に対応する構成については、図１～図５と同じ符号を使って示している。本発明の圧電素子は、図６（ａ）に示す実施形態のように、第１主面４１Ａや第２主面４１Ｂが外側平面部や内側平面部を備えず、凸部４６Ａのみが第１主面４１Ａを構成してもよく、同様に凸部４６Ｂのみで第２主面４１Ｂを構成してもよい。ただし、第１電極層５１や第２電極層５２の変形に伴う、これら電極層の圧電基体４１からのはみ出しを抑制する点で、また、第１電極層５１や第２電極層５２の形成時におけるＡｇペーストのはみ出しを抑制する点で、外側平面部４７Ａおよび４７Ｂや、内側平面部４８Ａおよび４８Ｂを有することが好ましい。 FIGS. 6A to 6C are schematic sectional views showing other embodiments of the piezoelectric element of the present invention. In each embodiment of FIG. 6, the configuration corresponding to the piezoelectric element 1 is indicated using the same reference numerals as in FIGS. In the piezoelectric element of the present invention, as in the embodiment shown in FIG. 6A, the first main surface 41A and the second main surface 41B do not include the outer flat surface portion or the inner flat surface portion, and only the convex portion 46A is the first. The main surface 41A may be configured, and similarly, the second main surface 41B may be configured by only the convex portion 46B. However, in the point which suppresses the protrusion of these electrode layers from the piezoelectric base | substrate 41 accompanying the deformation | transformation of the 1st electrode layer 51 or the 2nd electrode layer 52, and the time of formation of the 1st electrode layer 51 and the 2nd electrode layer 52 It is preferable to have the outer plane portions 47A and 47B and the inner plane portions 48A and 48B in terms of suppressing the protrusion of the Ag paste.
　また、図６（ｂ）に示す実施形態のように、第１電極層５１Ａの表面５１Ａおよび第２電極層５２の表面５２Ｂが、突部４６Ａや突部４６Ｂの表面に沿った形状となっていてもよい。ただし、電極板６２や電極板６３との接触面積を比較的大きくしておく点で、第１電極層５１Ａの表面５１Ａは第１仮想平面Ｐ１に平行であることが好ましく、第２電極層５２の表面５２Ｂは第２仮想平面Ｐ２に平行であることが好ましい。 Further, as in the embodiment shown in FIG. 6B, the surface 51A of the first electrode layer 51A and the surface 52B of the second electrode layer 52 are shaped along the surfaces of the protrusions 46A and the protrusions 46B. May be. However, the surface 51A of the first electrode layer 51A is preferably parallel to the first virtual plane P1 and the second electrode layer 52 in that the contact area with the electrode plate 62 and the electrode plate 63 is relatively large. The surface 52B is preferably parallel to the second virtual plane P2.
　また、図５（ｃ）に示すように、圧電基体４１は、例えば第１主面４１Ａのみに突部４６Ａを設け、第２主面４１Ｂの側は平坦面としてもよい。この場合も、第１主面１１Ａの側において、圧力印加方向がずれることにより、圧力が集中する部分の位置がばらつくことが抑制されるが、ばらつきをより確実に抑えるには、第１主面４１Ａに加えて、第２主面４２Ｂにも突部４６Ｂを設けることが好ましい。 Further, as shown in FIG. 5C, the piezoelectric substrate 41 may be provided with a protrusion 46A only on the first main surface 41A, for example, and the second main surface 41B side may be a flat surface. Also in this case, on the first main surface 11 </ b> A side, the pressure application direction is deviated, so that the position of the portion where the pressure is concentrated is suppressed from varying, but the first main surface can be more reliably suppressed. In addition to 41A, it is preferable to provide a protrusion 46B on the second main surface 42B.
　なお、以上の実施形態では、燃焼室１２と反対の側を第１主面４１Ａとし、燃焼室１２の側を第２主面４１Ｂとしているが、第１主面４１Ａと第２主面４１Ｂとの燃焼室１２に対する位置関係は特に区別されない。例えば燃焼室１２の側を第１主面４１Ａとし、この燃焼室１２の側の第１主面４１Ａのみに突部４１Ａを設けても構わない。 In the above embodiment, the side opposite to the combustion chamber 12 is the first main surface 41A and the combustion chamber 12 side is the second main surface 41B. However, the first main surface 41A and the second main surface 41B are The positional relationship with respect to the combustion chamber 12 is not particularly distinguished. For example, the combustion chamber 12 side may be the first main surface 41A, and the protrusion 41A may be provided only on the first main surface 41A on the combustion chamber 12 side.
　本発明の圧力センサー用圧電素子は、上記の実施形態に限定されるものでなく、本発明の要旨を逸脱しない範囲において、各種の改良および変更を行なってもよいのはもちろんである。 The pressure sensor piezoelectric element of the present invention is not limited to the above-described embodiment, and various modifications and changes may be made without departing from the scope of the present invention.
１　圧電素子
２　ハウジング
３　伝達部材
６　圧力センサー部（圧力センサー）
８　シール部材
１０　グロープラグ
２６　発熱体
２７　電線
４１　圧電基体
４１Ａ　第１主面
４１α、４１β　部分領域
４２　第１周縁
４１Ｂ　第２主面
４３　第２周縁
４４　貫通孔
４４ａ　開口
４６Ａ、４６Ｂ　突部
４７Ａ、４８Ａ　外側平面部
４７Ｂ、４８Ｂ　内側平面部
５１　第１電極層
５２　第２電極層
Ｐ１　第１仮想平面
Ｐ２　第２仮想平面
Ｓ　中心軸 DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2 Housing 3 Transmission member 6 Pressure sensor part (pressure sensor)
8 Seal member 10 Glow plug 26 Heating element 27 Electric wire 41 Piezoelectric base 41A First main surface 41α, 41β Partial region 42 First peripheral edge 41B Second main surface 43 Second peripheral edge 44 Through hole 44a Opening 46A, 46B Protrusions 47A, 48A Outer plane portion 47B, 48B Inner plane portion 51 First electrode layer 52 Second electrode layer P1 First virtual plane P2 Second virtual plane S Central axis

Claims (8)

  1. 　円形状の第１周縁を有する第１主面、円形状の第２周縁を有する、前記第１主面と反対側の第２主面、および前記第１主面と前記第２主面との間を貫通した円形状の貫通孔を備える圧電基体と、
    前記第１主面に接合した第１電極層と、
    前記第２主面に接合した第２電極層とを備え、
    前記第１主面と前記第２主面との間に加わる荷重によって前記圧電基体に生じる電荷を前記第１電極層および前記第２電極層を介して出力する圧力センサー用圧電素子であって、
    前記第１周縁を含む第１仮想平面と、前記第２周縁を含む前記第２仮想平面とはそれぞれ平行であり、
    前記貫通孔の中心軸は、前記第１周縁の中心と前記第２周縁の中心とを通って前記第１仮想平面および前記第２仮想平面に直交しており、
    前記第１主面は、前記貫通孔の開口を囲むように設けられた、前記第１周縁と同心円状の突部を備えており、
    前記中心軸を含む前記圧電基体の断面のうち、前記貫通孔を挟んで両側に配置された２つの部分領域のそれぞれにおける前記突部の断面線が、前記中心軸に平行な方向に前記圧電基体の外側に向けて凸な円弧状であることを特徴する圧力センサー用圧電素子。     A first main surface having a circular first peripheral edge, a second main surface opposite to the first main surface having a circular second peripheral edge, and the first main surface and the second main surface A piezoelectric substrate having a circular through-hole penetrating between;
    A first electrode layer bonded to the first main surface;
    A second electrode layer bonded to the second main surface,
    A pressure sensor piezoelectric element that outputs charges generated in the piezoelectric substrate by a load applied between the first main surface and the second main surface via the first electrode layer and the second electrode layer;
    The first virtual plane including the first peripheral edge and the second virtual plane including the second peripheral edge are parallel to each other,
    A center axis of the through hole passes through the center of the first peripheral edge and the center of the second peripheral edge and is orthogonal to the first virtual plane and the second virtual plane,
    The first main surface includes a protrusion that is concentric with the first peripheral edge and is provided so as to surround the opening of the through hole.
    Of the cross-section of the piezoelectric substrate including the central axis, the cross-sectional lines of the protrusions in each of two partial regions arranged on both sides of the through-hole are in a direction parallel to the central axis. A piezoelectric element for a pressure sensor, characterized by having an arc shape convex toward the outside.
  2. 　前記第１電極層は、前記第１主面の前記突部の表面のみに接合していることを特徴とする請求項１記載の圧力センサー用圧電素子。 2. The piezoelectric element for a pressure sensor according to claim 1, wherein the first electrode layer is bonded only to the surface of the protrusion of the first main surface.
  3. 　前記第１電極層の前記圧電基体に接合した側と反対側の表面は、前記第１仮想平面と平行であることを特徴とする請求項１または２記載の圧力センサー用圧電素子。 3. The piezoelectric element for a pressure sensor according to claim 1, wherein a surface of the first electrode layer opposite to a side bonded to the piezoelectric substrate is parallel to the first virtual plane.
  4. 　前記第１主面は、前記第１周縁を含んで前記突部に連なる、前記第１仮想平面と面一な外側平面部と、前記貫通孔の前記開口の周縁を含んで前記突部に連なる、前記第１仮想平面と面一な内側平面部とを備えることを特徴する請求項１～３のいずれかに記載の圧力センサー用圧電素子。 The first main surface includes the first peripheral edge and continues to the protrusion, and includes the outer plane portion that is flush with the first virtual plane, and the peripheral edge of the opening of the through hole and continues to the protrusion. The pressure sensor piezoelectric element according to any one of claims 1 to 3, further comprising an inner plane portion that is flush with the first virtual plane.
  5. 　前記第２主面は、前記貫通孔の開口を囲むように設けられた、前記第２周縁と同心円状の第２主面側突部を備えており、
    前記中心軸を含む前記圧電基体の断面のうち、前記貫通孔を挟んで両側に配置された２つの部分領域のそれぞれにおける前記第２主面側突部の断面線が、前記中心軸に平行な方向に前記圧電基体の外側に向けて凸な円弧状であることを特徴する請求項１～４のいずれかに記載の圧力センサー用圧電素子。     The second main surface includes a second main surface side protrusion that is concentric with the second peripheral edge and is provided so as to surround the opening of the through hole.
    Of the cross-section of the piezoelectric substrate including the central axis, cross-sectional lines of the second principal surface side protrusions in each of the two partial regions disposed on both sides of the through hole are parallel to the central axis. The pressure sensor piezoelectric element according to any one of claims 1 to 4, wherein the piezoelectric element has a circular arc shape projecting in a direction toward the outside of the piezoelectric substrate.
  6. 　前記第２電極層は、前記第２主面側突部の表面のみに接合していることを特徴とする請求項５記載の圧力センサー用圧電素子。 The piezoelectric element for a pressure sensor according to claim 5, wherein the second electrode layer is bonded only to the surface of the second main surface side protrusion.
  7. 　前記第２電極層の前記圧電基体に接合した側と反対側の表面は、前記第２仮想平面と平行であることを特徴とする請求項５または６記載の圧力センサー用圧電素子。 The pressure sensor piezoelectric element according to claim 5 or 6, wherein the surface of the second electrode layer opposite to the side bonded to the piezoelectric substrate is parallel to the second virtual plane.
  8. 　前記第２主面は、前記第２周縁を含んで前記第２主面側突部に連なる、前記第２仮想平面と面一な外側平面部と、前記貫通孔の前記開口の周縁を含んで前記突部に連なる、前記第１仮想平面と面一な内側平面部とを備えることを特徴する請求項５～７のいずれかに記載の圧力センサー用圧電素子。 The second main surface includes the outer peripheral plane portion that is flush with the second virtual plane and includes the second peripheral edge and includes the peripheral edge of the opening of the through hole. The piezoelectric element for a pressure sensor according to any one of claims 5 to 7, further comprising an inner plane portion that is flush with the first virtual plane and that is continuous with the protrusion.
PCT/JP2013/059082 2012-05-31 2013-03-27 Piezoelectric element for pressure sensor WO2013179752A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6242345Y2 (en) * 1982-06-21 1987-10-30
JPS6347249U (en) * 1986-09-12 1988-03-30
JP2006300046A (en) * 2004-08-05 2006-11-02 Ngk Spark Plug Co Ltd Glow plug with combustion pressure detecting function

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6242345Y2 (en) * 1982-06-21 1987-10-30
JPS6347249U (en) * 1986-09-12 1988-03-30
JP2006300046A (en) * 2004-08-05 2006-11-02 Ngk Spark Plug Co Ltd Glow plug with combustion pressure detecting function

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