JPH04289459A - Piezoelectric acceleration sensor - Google Patents

Abstract

PURPOSE:To facilitate the preparation of a piezoelectric acceleration sensor by simplifying the structure of the piezoelectric element of said acceleration sensor, to provide the piezoelectric element in a both-end support structure to enhance the vibration resistance and impact resistance thereof and to facilitate the temp. compensation due to temp. compensation circuit. CONSTITUTION:A piezoelectric element 2 is formed by alternately laminating piezoelectric ceramic thin plate layers 4a, 4b and three electrode layers 5a, 5b, 5c to achieve structural simplification. Both ends of the piezoelectric element are respectively supported by two supports 3a, 3b. By this constitution, the force applied to the piezoelectric element 2 is dispersed when said element receives an impact. Further, two piezoelectric ceramics thin plate layers 4a, 4b different in the temp. characteristics of a quality coefficient are combined to linearly change the sensor output to a temp. change.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric acceleration sensor that electrically detects shocks, vibrations, etc. acting on an object using a piezoelectric element, and particularly relates to a piezoelectric acceleration sensor having a simple structure.

0002

[Prior Art] In recent years, especially in vehicles such as automobiles,
High safety and comfort as well as stable driving performance and maneuverability are required, and in order to meet these demands, passenger protection devices such as airbag systems to protect passengers in the event of a collision, or ride comfort. Electronically controlled suspension systems and the like have been developed to improve the stability of driving and steering, and at the same time, the need for acceleration sensors is increasing.

Such acceleration sensors are of various types, such as piezoelectric type, electrodynamic type, photoelectric type, and servo type, depending on their operating principles and configurations. Among these, piezoelectric acceleration sensors utilize the fact that when a piezoelectric element is distorted by the action of an external force, it generates an amount of charge proportional to the external force.The piezoelectric acceleration sensor has a simple structure, and is compact, lightweight, and robust. Therefore, it is widely used.

By the way, as a conventional piezoelectric acceleration sensor having a cantilever structure, there is one disclosed in, for example, Japanese Patent Laid-Open No. 62-24154. In this method, a piezoelectric element is formed by fixing a reinforcing metal plate between a pair of piezoelectric element plates made of ceramics or polymeric substances and covered with electrodes on both sides, and is directly or indirectly attached to the object to be measured using a fixing part. This is a configuration that supports this.

In such a configuration, when acceleration is applied to the object to be measured, an inertial force corresponding to the acceleration acts on the piezoelectric element as an external force F, and the piezoelectric element itself bends due to the stress, causing distortion in its longitudinal direction. occurs. As this strain occurs, a charge is generated on the electrode surface of the piezoelectric element which has been polarized in advance, and the charge Q is supplied as a voltage V to an external measuring device via a lead wire and read as acceleration.

[0006] Here, the external force F applied to the acceleration sensor is
The relationship with the charge Q generated in the piezoelectric element is expressed by the following equation I.

Q=d・F
...(I) (where d is a piezoelectric strain coefficient) Further, the relationship between the charge Q generated in the piezoelectric element and the voltage V supplied to the measuring device is expressed by the following equation II.

[0008]V=Q/C
...(II) However, C is a capacitance that determines the electrical characteristics of the piezoelectric element and is a temperature-dependent value, and the dielectric constant is εr,
If the electrode area of the piezoelectric element is S and the inter-electrode thickness is d, then the capacitance C, the dielectric constant εr, the electrode area S and the inter-electrode thickness d
The relationship is as shown in the following equation III. C=εr S/d...
(III) By the way, one of the factors that affects the voltage V is the quality factor. This is, for example, an alternating electric field E with an angular frequency ω
When applied to a dielectric, the electric displacement D also vibrates at the same angular frequency, but since the speed at which polarization occurs is finite, the phase of the electric displacement D lags behind the phase of the applied electric field. If the delay angle is δ, then ω=π during one period of the alternating electric field
An energy loss of ED sin δ occurs.

Electrical displacement D=εε0E where E: external electric field, ε0: relative permittivity of vacuum, ε: relative permittivity.

[0010] In the case of no loss, ε is a real number, but in the case of loss, it becomes a complex number, which is called a complex dielectric constant. If we set this as ε=ε′−jε″, tanδ
= ε″/ε′.The energy loss is ω=πε
′ε0E2tanδ. ε″ or tanδ is used as the characteristic value of dielectric loss. Here, Q=1/tanδ
is called the quality factor and is one of the characteristic values of dielectric materials.

[0011]

[Problems to be Solved by the Invention] By the way, one of the requirements for automobile parts, for example, is that the manufacturing cost be low. One desirable method for reducing costs is to simplify the product structure, thereby reducing the number of component parts and simplifying the manufacturing process, resulting in lower costs. However, conventional piezoelectric elements have a complex structure, and the complexity of the product structure not only increases manufacturing costs, but also makes it difficult to evaluate reliability due to the large number of component parts, making it susceptible to deterioration and deterioration. Since the constituent members cannot be removed, this also poses a problem in that it is difficult to improve durability.

[0012] Furthermore, piezoelectric acceleration sensors used in automobile airbag systems, for example, are constantly subjected to vibrations and shocks while the car is running, and the piezoelectric elements constituting the acceleration sensor must be resistant to vibrations and shocks. However, conventional ones have had the problem of not necessarily having sufficient durability against vibrations and shocks.

Furthermore, piezoelectric acceleration sensors used, for example, in automobile airbag systems usually have a wide operating temperature range of -40°C to 100°C. It is known that in piezoelectric materials such as piezoelectric ceramics, the amount of charge generated by the action of external force is affected by temperature. Therefore, when applied as an acceleration sensor, changes in output (generated charge amount) due to temperature are often compensated for through a temperature compensation circuit.

However, if the output of the acceleration sensor changes linearly with temperature, the objective is achieved by combining a temperature compensation circuit that shows a constant slope with respect to temperature, but the output of the acceleration sensor changes linearly with temperature. This is extremely difficult to compensate for when it varies curvilinearly with temperature. For example, when the quality factor decreases on the high temperature side of the operating temperature range (FIG. 12), the output as an acceleration sensor also decreases in the same temperature range (FIG. 13). Further, when the quality factor shows a large concave shape in the middle of the operating temperature range (FIG. 14), the output as an acceleration sensor also shows a large concave shape (FIG. 15). On the other hand, if the quality factor changes linearly with temperature (FIG. 10), the output as an acceleration sensor also changes linearly with temperature (FIG. 11).

The present invention has been made in view of the above circumstances, and provides a piezoelectric acceleration sensor that has a simple structure, excellent durability, excellent vibration resistance and shock resistance, and can easily perform temperature compensation. is intended to provide.

[0016]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a piezoelectric type acceleration device having a piezoelectric element that generates distortion when subjected to acceleration and senses acceleration from the amount of charge generated in response to the distortion. In the sensor, the piezoelectric element
It is formed by laminating a plurality of thin plate-like piezoelectric substances and a plurality of thin film-like electrode materials.

[0017]

[Operation] Since the piezoelectric element is formed by laminating a plurality of thin plate-like piezoelectric substances and a plurality of thin film-like electrode materials, the structure is simple and the number of manufacturing steps is reduced.

[0018]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

FIG. 16 is a sectional view of a piezoelectric acceleration sensor according to the first embodiment of the present invention, in which 1 is a piezoelectric acceleration sensor, and a piezoelectric element 2 and a support for supporting the piezoelectric element 2 are shown. 3a, 3b, a base portion 6, and a metal case 7.

As shown in FIG. 20, the piezoelectric element 2 includes a pair of thin plate-shaped piezoelectric ceramic layers (piezoelectric material) 4a and 4b.
and electrode layers (electrode materials) 5a, 5b, and 5c. Examples of piezoelectric substances include the following substances.

The piezoelectric ceramic layers 4a and 4b have the same shape. The piezoelectric ceramic layers 4a and 4b have a rectangular shape. The piezoelectric element 2 is formed by alternately bonding piezoelectric ceramic layers 4a, 4b and thin film electrode layers 5a, 5b, 5c made of platinum, palladium, silver, nickel, or an alloy thereof.
is formed. This piezoelectric element 2 has a thickness of, for example, 0.1 to
0.6mm, preferably 0.15-0.3mm, width 1
．． 0-5.0 mm, preferably 1.8-3.5 mm, length 6.0-15.0 mm, preferably 7.9-8.6
It is mm.

In the piezoelectric element shown in FIG. 17, one end of the electrode layer 5a bonded to the piezoelectric ceramic layer 4a is shown in FIG.
As shown in FIG. 2, the piezoelectric ceramic layer 4a is cut out and one end portion of the piezoelectric ceramic layer 4a is exposed. FIG. 18 is a sectional view of the piezoelectric element 2 seen from the opposite direction of FIG. 16, and one end of the electrode layer 5c bonded to the piezoelectric ceramic layer 4b is also cut away as shown in FIG. One end is exposed. As shown in FIG. 20, the position of the notch of the electrode layer 5a is asymmetrical with respect to the notch of the electrode layer 5c in plan view. FIG. 19 is a cross-sectional view taken along the line B-B in FIG. 17, in which both ends of the electrode layer 5b are cut out, and the piezoelectric ceramic layer 4
Both ends of b are exposed.

The piezoelectric element 2 has a both-end support structure in which both ends in the longitudinal direction are supported by supports 3a and 3b passing through the base portion 6 via a sealed insulator 8 such as glass. One end of the supports 3a, 3b is formed into a bifurcated shape, one end of the support 3a is connected to the electrode 5a, and one end of the support 3b is connected to the electrode 5a.
One end of each is connected to the electrode 5c, and the support 3
The other ends of a and 3b extend outward through the base portion 6 via an insulator 8, and are connected to a temperature compensation circuit (not shown). Each of the supports 3a and 3b also has the function of acting as an electrode terminal and transmitting the charge from each electrode as an output.

The supports 3a, 3b and the electrode layers 5a, 5c may be connected by soldering, adhesion with a conductive adhesive, or by insertion (
This is done by methods such as press-fitting. When the electrode layers 5a and 5c have no notches and both sides of the bifurcated supports 3a and 3b contact the electrode layers 5a and 5c, the charges generated on both sides of the piezoelectric element 2 are neutralized and cancel each other out. For storage purposes, a portion of the electrode layers 5a and 5c is cut out on one side.

The thin film electrode layer 5b between the piezoelectric ceramic layers 4a, 4b is in contact with the supports 3a, 3b, or by applying a conductive adhesive or the like between the electrode layer 5a (5c) and the support 3a (3b). When placed in between, the conductive adhesive and electrode layer 5b protrude
Both ends are cut out to prevent contact. A temperature compensation circuit (not shown) is composed of a circuit whose purpose is impedance conversion, output amplification, and temperature compensation. Furthermore, the piezoelectric element 2 is fixed to a metal case 7 by resistance welding, soldering, pressure welding, etc. to a flat metal base part 6.
The device is housed in a vacuum or in an inert gas atmosphere such as N2. The atmosphere inside the metal case 7 may be dry air or may be a liquid such as silicone oil. The principle of detection operation is the same as the conventional one described above, except that the cantilever structure has been changed to a structure supported at both ends, and the reinforcing metal plate and the like have been eliminated accordingly.

It goes without saying that the above configuration can also be applied to a piezoelectric acceleration sensor that does not have a temperature compensation circuit.

The novel points different from conventional piezoelectric acceleration sensors are a plurality of piezoelectric ceramic layers 4a and 4b made of thin plate-like piezoelectric materials and a plurality of electrode layers 5a made of a plurality of thin film-like electrode materials.
, 5b, and 5c are alternately stacked. Here, the piezoelectric element 2 is manufactured by a method described later.

The piezoelectric element 2 of this embodiment has a simpler structure than the conventional one, so it is easier to manufacture, and at the same time, since the number of constituent members of the piezoelectric element 2 is reduced, for example, temperature,
It is possible to reduce the use of materials that are sensitive to humidity and the like. In other words, in conventional piezoelectric elements, a reinforcing metal plate is bonded to a ceramic plate using adhesive to give it enough strength to withstand impact, but the linear expansion coefficient of the metal plate and adhesive is different from that of ceramic. In many cases, in an environment where the temperature changes, thermal stress may be generated and fatigue damage may occur, and the adhesive may deteriorate due to moisture absorption.However, in this embodiment, the piezoelectric ceramic layers 4a and 4b are Since the electrode layer 5b connecting the two is very thin and has a small coefficient of linear expansion, the above-mentioned problem does not occur. In addition, the two supports 3a and 3b are used to absorb the weight of the piezoelectric element 2 at two places (both ends), and when an impact is applied to the base part 6, which is the fixed base of the piezoelectric element 2, the force is absorbed by the support. It is distributed and transmitted to both bodies 3a and 3b. For this reason, the impact force is less likely to concentrate in one place on the piezoelectric element 2 and lead to damage, and it is also possible to prevent the impact force from being concentrated in one place on the piezoelectric element 2, resulting in damage. It is impossible to imagine a case where only stress acts, and the impact resistance is improved.

The method for manufacturing the piezoelectric element 2 of this embodiment is as follows.

A conductive ink layer is laminated by a screen printing method on one side of a piezoelectric ceramic sheet formed by a doctor blade method and dried, and a plurality of sheets are stacked so that the conductive ink layers do not face each other. On the surface on which the conductive ink layer is not laminated, a separately prepared sheet with conductive ink layers printed on both sides using a screen printing method is stacked, and hot pressed to bond with heat to form a plurality of piezoelectric ceramic layers and one or more layers. It is completed in 10 steps: creating a laminate consisting of a plurality of intermediate electrode layers, degreasing and firing it to obtain a sintered body of the laminate, subjecting it to polarization treatment, and cutting it into the final size of the device.

A second embodiment of the present invention is shown in FIGS. 21 to 26. This embodiment differs from the first embodiment described above only in the configuration of the piezoelectric element 12.

As shown in FIG. 26, the piezoelectric element 12 includes a pair of thin plate-shaped piezoelectric ceramic layers (piezoelectric material) 4a, 4.
b, and electrode layers (electrode materials) 15a, 15b, 15c, 1
5d and an adhesive layer 9. Other effects etc. are the first
The piezoelectric element 12 is used here because it is exactly the same as the embodiment of
Only the parts that are different from the piezoelectric element 2 will be explained.

The piezoelectric ceramic layer 4a has thin plate-shaped electrode layers 15a and 15b bonded to both sides, and the piezoelectric ceramic layer 4b has thin plate-shaped electrode layers 15c and 15d bonded to both sides thereof.
are joined. The piezoelectric ceramic layers 4a and 4b, to which the two electrode layers are bonded, are bonded together using an adhesive layer 9 or the like to form a piezoelectric element 12. Thin plate-like electrode layers 15b and 15
Although the electrode layers 15b and 15d are in contact with each other through the adhesive layer 9, the electrode layers 15b and 15d are electrically connected because they are bonded under pressure during bonding. 21, 23, 24, 25, the electrode layer 15a,
The shapes of 15b, 15c, and 15d are shown. The contact surfaces of these electrode layers with the supports 3a and 3b are shaped so that charges can be extracted from only one side of the piezoelectric element 12, as in the first embodiment. The thin plate-shaped electrode layers 15b and 15d have a rectangular portion and some overhanging portions 15b1 and 15d1. This is for the purpose of increasing the capacitance and for supporting 3
This shape was adopted to prevent contact with the thin electrode layers 15b and 15d even if the conductive adhesive 9 is applied across both sides of the piezoelectric ceramic layers 4a and 4b.

The reason for not providing an overhanging portion on the opposite side of the overhanging portions 15b1 and 15d1 is that the thin plate-like electrode layers (15a and 15b, 15c and 1
This is designed to prevent the capacitance from changing even if a positional shift occurs between 5d and 5d).

The method for manufacturing the piezoelectric element 12 of the second embodiment described above is as follows.

After making the slip, the sheet formed by the doctor blade method is cut, dried, degreased, and fired to form a thin plate-like sintered body, which is surface ground to expose both sides, and electrode material paste is applied to both sides. The process consisted of 11 steps: screen printing, baking, polarizing, bonding the two sheets with adhesive, and cutting to the final size of the device. Note that the surface grinding step can be omitted depending on the completion of the sintered body.

A third embodiment of the present invention is shown in FIGS. 27 to 33. This embodiment differs from the second embodiment only in the structure of the piezoelectric element 22.

As shown in FIG. 33, the piezoelectric element 22 includes a pair of thin plate-shaped piezoelectric ceramic layers (piezoelectric material) 24a,
24b, and electrode layers (electrode materials) 25a, 25b, 25c
, 25d, the reinforcing metal plate 19, and the adhesive layer 29a, 2
9b.

The piezoelectric ceramic layer 4a has thin plate-shaped electrode layers 25a and 25b bonded to both sides thereof, and the piezoelectric ceramic layer 4b has thin plate-shaped electrode layers 25c and 25d bonded to both sides thereof.
are joined. These two electrode layers 25a, 25
Piezoelectric ceramic layer 4a to which b, 25c, and 25d are joined
, 4b, and the reinforcing metal plate 19 is sandwiched between them and bonded with adhesive layers 29a and 29b, respectively. An electrode layer 25b,
Electrical continuity between the reinforcing metal plate 19 and the electrode layer 25d is established through the second
is kept similar to the example.

FIGS. 31 and 32 show specific examples of reinforcing metal plates 19, 19' having different shapes.

The method for manufacturing the piezoelectric element of the third embodiment is as follows.
This embodiment is almost the same as the embodiment described above, and differs only in the process of sandwiching the reinforcing metal plate between the two polarized sheets and bonding them together with an adhesive.

[Table 1]

Furthermore, in the past, temperature compensation using a temperature compensation circuit (not shown) was sometimes difficult due to temperature changes in the quality factor; however, piezoelectric ceramic thin plate layers ( Temperature compensation can be realized by the temperature compensation circuit by adjusting the combination of the sheets or thin plates 4a and 4b of the sintered body to adjust the change in sensitivity to temperature changes or to linearly change the sensor output. For example, a plurality of sheets or sintered thin plates made of a piezoelectric ceramic material whose quality factor decreases as the temperature increases as shown in FIG. 4 and a piezoelectric ceramic material whose quality factor decreases as the temperature increases as shown in FIG. As shown in FIG. 6, the rate at which the quality factor decreases as the temperature increases can be adjusted to a desired rate. In addition, sheets or thin plates of sintered bodies made of piezoelectric ceramic materials whose quality coefficient rapidly decreases at high temperatures as shown in Figure 7 and piezoelectric ceramic materials whose quality coefficient rapidly decreases at high temperatures as shown in Figure 8 are used. By combining a plurality of sheets, it is possible to adjust the quality factor so that it changes linearly with respect to temperature changes as shown in FIG.

FIGS. 1 to 3 show a fourth embodiment of the present invention in which the shapes of supports 13a and 13b for supporting a piezoelectric element 32 are changed. In the figure, 35a to 35c are electrode layers.

FIG. 34 shows, as a fifth embodiment of the present invention,
An embodiment in which the shapes of the supports 23a and 23b that support the piezoelectric elements are changed is shown, and FIG. 35 is a top view of this embodiment. The main sensitivity direction in this case is the vertical direction in FIG. In the figure, 23a and 23b are supports that hold both ends of the piezoelectric element.

FIG. 36 shows a sixth embodiment of the present invention, and FIG. 37 is a top view of this. In the figure, 33a, 33
b is a support having no curved portion.

FIG. 38 shows a seventh embodiment of the present invention,
FIG. 39 is a view of this from above. In the figure, 43a
, 43b is a support bent into a hook shape. FIG. 40 shows an eighth embodiment of the present invention, and FIG. 41 shows this from above.
FIG. 42 is a view seen from the right direction. 53a1, 53 in the figure
a2, 53b1, and 53b2 are supports of a type that clamp both ends of the element, respectively.

[0047]

As described above, according to the piezoelectric acceleration sensor of the present invention, the piezoelectric element is formed by laminating a plurality of thin plate-like piezoelectric substances and a plurality of thin film-like electrode materials, and the structure is simple. Therefore, the number of manufacturing steps is reduced, manufacturing becomes easier, and costs can be reduced. Also,
Durability is further improved when a reinforcing metal plate is not used.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a piezoelectric acceleration sensor according to a fourth embodiment of the present invention.

[Fig. 2] Cross-sectional view taken along line II-II in Fig. 1

[Figure 3] Fourth
A cross-sectional view of a piezoelectric element according to an example of

[Fig. 4] Curve diagram showing the relationship between quality factor and temperature according to the first embodiment

[Fig. 5] Curve diagram showing the relationship between quality factor and temperature according to the first embodiment

[Fig. 6] Curve diagram showing the relationship between quality factor and temperature according to the first embodiment

[Figure 7] Curve diagram showing the relationship between quality factor and temperature according to another example

[Figure 8] Curve diagram showing the relationship between quality factor and temperature according to another example

[Figure 9] Curve diagram showing the relationship between quality factor and temperature according to another example

[Figure 10] Curve diagram showing the relationship between quality factor and temperature

[Figure 1
1] Curve diagram showing the relationship between output voltage and temperature

[Figure 12] Curve diagram showing the relationship between quality factor and temperature

[Figure 13] Curve diagram showing the relationship between output voltage and temperature

[Figure 14] Curve diagram showing the relationship between quality factor and temperature

[Figure 15] Curve diagram showing the relationship between output voltage and temperature

FIG. 16 is a vertical cross-sectional view of a piezoelectric acceleration sensor according to the first embodiment of the present invention.

[Fig. 17] Cross-sectional view taken along line A-A in Fig. 16

[Fig. 18] Vertical cross-sectional view of the sensor shown in Fig. 16 viewed from the opposite direction.

[Fig. 19] A diagram of the piezoelectric element portion in the cross section taken along the line B-B in Fig. 17.

FIG. 20 is a cross-sectional view of the piezoelectric element according to the first example.

[Figure 2
1] Vertical cross-sectional view of a piezoelectric acceleration sensor according to a second embodiment of the present invention

[Fig. 22] Cross-sectional view taken along line A-A in Fig. 21

[Figure 23] Longitudinal cross-sectional view of the sensor in Figure 21 viewed from the opposite direction.

[Fig. 24] A diagram of the piezoelectric element portion in the cross section taken along the line BB in Fig. 22.

[Fig. 25] A diagram of the piezoelectric element portion in the cross section taken along the line C-C in Fig. 22.

FIG. 26 is a cross-sectional view of a piezoelectric element according to a second embodiment.

[Figure 2
7] Vertical cross-sectional view of a piezoelectric acceleration sensor according to a third embodiment of the present invention

[Fig. 28] Cross-sectional view taken along line A-A in Fig. 27

[Fig. 29] Vertical cross-sectional view of the sensor shown in Fig. 27 viewed from the opposite direction.

[Fig. 30] A diagram of the piezoelectric element portion in the cross section taken along the line BB in Fig. 28.

FIG. 31 is a diagram showing the shape of a reinforcing metal plate according to the third embodiment.

FIG. 32 is a diagram showing another shape of the reinforcing metal plate according to the third embodiment.

[Fig. 33] Cross-sectional view of a piezoelectric element according to a third example

[Figure 34
]A vertical cross-sectional view showing a support structure for a piezoelectric element according to a fifth embodiment of the present invention.

[Figure 35] View of the piezoelectric element in Figure 34 from above

[Figure 36
]A vertical cross-sectional view showing a support structure for a piezoelectric element according to a sixth embodiment of the present invention.

[Figure 37] View of the piezoelectric element in Figure 36 from above

[Figure 38
]A vertical cross-sectional view showing a support structure for a piezoelectric element according to a seventh embodiment of the present invention.

[Figure 39] View of the piezoelectric element in Figure 38 from above

[Figure 40
]A vertical cross-sectional view showing a support structure for a piezoelectric element according to an eighth embodiment of the present invention.

[Figure 41] View of the piezoelectric element in Figure 40 viewed from above

[Figure 42
] View of the piezoelectric element in Figure 40 from the right side

[Explanation of symbols]

2 Piezoelectric element 3a, 3b Support body

Claims (1)

[Claims] 1. A piezoelectric acceleration sensor having a piezoelectric element that generates strain when subjected to acceleration and senses acceleration from the amount of charge generated in response to the strain, the piezoelectric element comprising a plurality of thin plate-like piezoelectric elements. A piezoelectric acceleration sensor characterized by being formed by laminating a substance and a plurality of thin film electrode materials.