JP2001041972A - Acceleration detector - Google Patents

Abstract

(57) [Problem] To provide a small, low-cost, high-accuracy acceleration detection element which has a simple structure and can be easily and quickly mounted on a mounting board. SOLUTION: The piezoelectric device has a plate-shaped piezoelectric body 11 polarized in a plate thickness orthogonal direction perpendicular to the plate thickness direction, and electrodes 12 and 13 provided in a film shape on the surface of the piezoelectric body 11. The detection element has a unimorph structure for detecting the acceleration of the body 11 in the direction perpendicular to the plate thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an acceleration detecting element,
In particular, the present invention relates to a detection element using a piezoelectric effect, which is suitable for measuring or detecting acceleration in a vehicle or the like running by an internal combustion engine or an electric motor.

[0002]

2. Description of the Related Art Various types of conventional acceleration detecting elements such as an electromagnetic type, a piezoelectric type, and a semiconductor type are known. A piezoelectric type that obtains high detection sensitivity by utilizing conversion characteristics is often used. In addition, when measuring acceleration in a high frequency region, for example, in order to cope with a case where the sensor is used as an impact sensing sensor in an airbag system of an automobile, a bimorph structure is adopted to increase the output and increase the resonance of the detecting element. Higher frequencies are often used. With the rapid spread of airbag systems, acceleration sensors and airbag controllers themselves are required to be smaller, lower in cost, and more sophisticated, and the acceleration sensors detect collision acceleration with high accuracy. There is a need to.

As this type of acceleration sensor, there is, for example, one shown in FIGS.

In FIGS. 6 to 8, reference numeral 1 denotes a base unit, and a positioning pin 2 is provided at the center of the base unit 1.
The protrusions 2 having a are integrally formed in an electrically insulated state. Reference numeral 3 denotes a vibrator fixed to the protrusion 2 of the base unit 1 as shown in FIGS. 8 and 9, and a diaphragm 4 welded to the protrusion 2 using the upper welding electrode 2b and the lower welding electrode 2c. have. The vibrator 3 includes a vibrating plate 4 and piezoelectric ceramic elements 5 and 6 on both front and back surfaces thereof. The piezoelectric ceramic elements 5 and 6 have positive and negative annular electrodes 5a, 5b,
6a, 6b and positive and negative annular electrodes 5c, 5d for self-diagnosis.
6c and 6d are formed by baking or the like. The negative electrodes 5b and 5d of the piezoelectric ceramic element 5 and the positive electrodes 6a and 6c of the piezoelectric ceramic element 6 are opposed to each other, and the opposed electrodes are electrically connected. By doing so, the capacitance as a detection element is doubled. In addition, when bonding the element and the diaphragm, etc., the pyroelectric effect of the two piezoelectric elements 5 and 6 (absorption of thermal energy causes a change in spontaneous polarization,
Both electrodes are short-circuited so as to cancel out the phenomenon that charge is induced on the surface in proportion to the amount of change.

In this acceleration sensor, when the vibration plate 4 is deformed to be convex on one side and concave on the other side due to externally applied acceleration, one of the piezoelectric ceramic elements 5 and 6 is stretched and the other is expanded. Is compressed, the voltage generated by each piezoelectric ceramic element 5 or 6 is
a, 6b can be output to a signal processing circuit board 8 including a signal processing circuit via bonding wires 7a, 7b and the like.

The positive and negative annular electrodes 5c for self-diagnosis are provided.
The bonding wires 7c, 7 from the drive circuit 9 during 6d
When a voltage (for example, an AC voltage) is applied via d or the like, the vibrating plate 4 is bent (vibrated) by the piezoelectric ceramic elements 5 and 6, and the bending generates electric charges from the inner electrodes 5a and 6b. The output voltage is used as an output for self-diagnosis such as failure check and calibration.
Further, as shown in FIG. 10, an annular projection 4a is formed on the upper surface side of the diaphragm 4, and the piezoelectric ceramic element 5,
When the adhesive 6 is fixed to the vibration plate 4, the flow of the adhesive to the electrode side is prevented by the annular projection 4a.

[0007]

However, in the above-mentioned conventional acceleration sensor, the piezoelectric ceramic elements 5 and 6 for detecting acceleration are attached to both surfaces of the vibration plate 4, and the vibration plate 4 and the piezoelectric ceramic element 5 are attached. , 6 are supported on the base unit 1 via the positioning projection 2, so that the structure of the detection element is not only complicated, but also bulky in the direction orthogonal to the detection direction, so that the size is small. It has been difficult to achieve cost reduction.

Moreover, the electrodes 5a, 6b and the electrodes 5b, 6
d and the mounting board 8 remote therefrom are bonded to the bonding wires 7a, 7b and 7c, 7d and the terminals 7e, 7d.
Since electrical connection was made via the gates f and 7g, not only the structure was complicated, but also the mounting process of the acceleration detecting element was complicated and time-consuming.

Accordingly, the present invention is to provide a small and low-cost acceleration detecting element which has a simple structure and can be easily and quickly mounted on a mounting substrate.

[0010]

According to a first aspect of the present invention, there is provided an acceleration detecting element comprising: a plate-shaped piezoelectric body polarized in a direction perpendicular to a thickness direction perpendicular to the thickness direction; An electrode provided in the form of a film on the surface of the piezoelectric body,
Wherein the charge generated according to the acceleration of the piezoelectric body in the direction perpendicular to the plate thickness is taken out from the electrode.
According to the present invention, the acceleration in the direction perpendicular to the thickness of the piezoelectric body is detected by the element having the unimorph structure. Therefore, a simple acceleration that simply forms a detection electrode on the surface of the piezoelectric body without providing a diaphragm or a base unit is provided. A detection element can be configured, and a mounting form in which the piezoelectric body is directly attached to a circuit board or the like can be adopted.

According to a second aspect of the present invention, there is provided an acceleration detecting element including a weight fixed to the piezoelectric body, the acceleration detecting element corresponding to an acceleration acting on the weight in a direction perpendicular to the thickness of the piezoelectric body. A force in a substantially shear direction is applied from the weight to the piezoelectric body. In the present invention,
By using the weight, the required force can be applied to the piezoelectric body under a wide range of operating conditions, the height dimension in the direction perpendicular to the detection direction can be reduced, and a highly sensitive acceleration detection element can be used. realizable.

According to a third aspect of the present invention, in the acceleration detecting element, the weight body is fixed to the detecting element;
It has a side surface forming a predetermined intersection angle with the fixed surface, and a signal extracting electrode is provided on the side surface of the weight. According to the present invention, it is possible to form an easily connectable signal extraction electrode having a sufficient area by using the side surface of the weight body, thereby facilitating mounting.

According to a fourth aspect of the present invention, in the acceleration detecting element, the piezoelectric body is formed of a piezoelectric ceramic element or a piezoelectric single crystal, and the piezoelectric ceramic element has a plate thickness. It is preferable that a plate-shaped piezoelectric body made of the piezoelectric single crystal that has been subjected to a polarization treatment in the orthogonal direction also produces the same piezoelectric effect.
When such an element is used, it is easy to form electrodes on the surface, and stable performance can be obtained.

According to a fifth aspect of the present invention, in the acceleration detecting element, the electrodes are detection electrodes of opposite polarities, which are arranged on both sides of the piezoelectric body in parallel with the fixed surface of the weight body. It is characterized by the following. In this case, by making the detection electrode face the plate thickness direction orthogonal to the polarization direction, even if a pyroelectric effect occurs on the piezoelectric body due to a temperature change, the pyroelectric charge generated on the electrode surface should be extremely small. Can be.

According to a sixth aspect of the present invention, the acceleration detecting element has a bottom plate having a thermal expansion coefficient substantially equal to that of the weight body. Therefore, it is possible to prevent a situation in which unnecessary stress is generated on the detection element side due to a difference in thermal expansion coefficient between the weight and the acceleration detection element, and the detection accuracy is reduced.

[0016]

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 5 show an embodiment of an acceleration detecting element according to the present invention. FIG. 1 (a) and FIG. 1 (b)
In the figure, reference numeral 10 denotes a unimorph acceleration detecting element (hereinafter, simply referred to as a detecting element) mounted on a mounting substrate 20. The detecting element 10 has a plate-shaped piezoelectric body 11 and a flat surface on the surface of the piezoelectric body 11. It has an upper surface side detection electrode 12 and a lower surface side detection electrode 13 provided in a film shape.

The piezoelectric body 11 is previously subjected to a polarization process in a direction perpendicular to the plate thickness direction (the direction of arrow P in FIG. 1A), and is made of, for example, a piezoelectric ceramic element. This piezoelectric body 11 has the property that it undergoes expansion and contraction in an electric field in the polarization direction, but generates shear strain in the electric field in the plate thickness direction such that the upper and lower surfaces are shifted in opposite directions. When a corresponding shear stress is generated by an external force directed toward the left and right directions in ()), a voltage corresponding to the shear stress is generated between the detection electrodes 12 and 13 on both sides. The piezoelectric body 11 is not limited to the piezoelectric ceramic element, but may be made of quartz or a piezoelectric single crystal capable of performing the same function.

Upper detection electrode 12 and lower detection electrode 13
Are formed on the surface of the piezoelectric body 11 by vapor deposition or plating, and are disposed on both sides of the piezoelectric body 11. The lower detection electrode 13 has a polarity opposite to that of the upper detection electrode 12, and the lower detection electrode 13 is electrically connected to the plus electrode 21 of the mounting substrate 20 (see FIG. 2). The detection element 10 is directly mounted on the top, and is fixed to the mounting board 20 by, for example, a conductive adhesive 16.

Reference numeral 14 denotes a weight fixed to the detection element 10. The weight 14 has a fixed surface 14 a fixed to the detection element 10 with an adhesive 17, and a predetermined intersection angle with the fixed surface 14 a. (A substantially right angle). This weight 14 is
When the piezoelectric body 11 is accelerated in a direction perpendicular to the thickness of the piezoelectric body 11 (the left-right direction in FIG. 1B), a force in a substantially shear direction corresponding to the acceleration and the mass of the weight body 14 is applied to the detection element 10. be able to.

The detection element 10 is provided with a bottom plate 23 facing the lower detection electrode 13 of the detection element 10. The bottom plate 23 is connected to the positive electrode 21 of the mounting board 20. I have. Further, the weight 14 is made of the same material as the bottom plate 23 or a material having a thermal expansion coefficient close thereto, so as to enhance the sensor sensitivity. Of course, the electrode arrangement of the detection element 10 can be directly attached to the mounting substrate 20 without the dedicated bottom plate 23. Needless to say, the conductive adhesives 16 and 17 may be solder or the like.

On the other hand, on the side surface 14b of the weight 14, a signal extraction electrode 15 formed in a film shape by vapor deposition or plating is provided. The signal extraction electrode 15 is electrically connected to the upper surface side detection electrode 12 by a conductive adhesive 17 and is fixed to the negative electrode 22 of the mounting board 20 by a conductive adhesive or solder 18. . Reference numeral 19 denotes an insulating adhesive applied and solidified between the side end face of the detection element 10 and the mounting board 20 so as to cover the end face of the lower detection electrode 13 exposed from the side end face of the detection element 10.

As shown in FIGS. 3 and 4, the detecting element
10 and the mounting substrate 20 include a sensor base 31a and a sealing cap.
It is housed in a shield case 31 composed of 31b, and is configured as a sensor unit 30 having a signal processing board 25 and lead pins 32, 33, 34, and 35 for sensor output, ground, power supply, and capacity check, The mounting direction is defined so that the weight 14 receives acceleration toward the plate surface (upper surface, lower surface) of the piezoelectric body 11 in a state where the detection element 10 is mounted on the mounting board 20. Although the signal processing board 25 does not show a detailed circuit configuration, an impedance conversion circuit,
It is configured to include an output amplifier circuit, a filtering circuit, a temperature compensation circuit, and the like.

When the detection element 10 is mounted, first, the lower detection electrode 13 is connected to the positive electrode 21 with a conductive adhesive or solder and fixed to the mounting board 20. An insulating adhesive 19 is applied between the side end surface of the detection element 10 and the mounting board 20 so as to cover the end surface of the lower detection electrode 13 exposed from the substrate. Next, the fixing surface 14 of the weight 14
a is adhered and fixed to the upper detection electrode 12 of the detection element 10 with an adhesive 17, and the signal extraction electrode 15 on the side surface 14 b of the weight 14 is connected to the upper detection electrode 12.
Next, the signal extracting electrode 15 is bonded and fixed to the negative electrode 22 of the mounting board 20 with a conductive adhesive or solder 18.

In the acceleration sensor configured as described above, when detecting acceleration, the weight 14 is accelerated in the direction of arrow A so as to move from the position shown by the solid line in FIG. A force corresponding to the mass and the acceleration is applied to the detection element 10. At this time, since a shear strain is generated in the detection element 10, a voltage is generated between the detection electrodes 12 and 13 of the detection element 10 having a unimorph structure, and a voltage signal according to the acceleration is processed by the signal processing board 25, and the sensor is processed. The output is obtained.

In the present embodiment, a simple detection element 10 can be formed by simply forming the detection electrodes 12 and 13 on the surface of the piezoelectric body 11, and a mounting form in which the piezoelectric body 11 is directly mounted on the mounting board 20 or the like is provided. A small, low-cost acceleration sensor that can be adopted can be realized.

In addition, there is no need to attach to a diaphragm or a base unit such as a bimorph structure detection element,
It is possible to reduce the height (reduce the height). In addition, it is not necessary to perform a troublesome connection such as wire bonding as in the related art, and when forming the detection element 10, a plurality of sets of piezoelectric materials having a size corresponding to a plurality of piezoelectric bodies 11 are formed by vapor deposition or plating. To form a piezoelectric unit that can take a large number of detection elements 10 by forming electrodes of the same or performing a partial peeling treatment of the vapor deposition film or plating film, and cut out the detection element 10 from this can do. Therefore,
The manufacturing process can be greatly simplified and costs can be reduced.

Further, in the present embodiment, by using the weight 14, a required force can be applied to the piezoelectric body 11 under a wide range of use conditions to generate a shear strain. The height dimension in the direction can be reduced, and a highly sensitive acceleration sensor can be realized.
Further, the extraction electrode 15 having a sufficient area and easy connection can be formed by using the side surface 14b of the weight 14, so that the mounting operation can be facilitated. In addition, since the electrodes 12 and 13 are disposed opposite to both surfaces of the piezoelectric body 11 in a direction perpendicular to the polarization direction and parallel to the fixing surface 14a of the weight 14, unnecessary charges due to the pyroelectric effect of the piezoelectric body 11 are removed. The surface can be made very small, and the sensor sensitivity can be increased.

In the above-described embodiment, the detection electrodes 12 and 13 of the detection element 10 are provided on both surfaces of the piezoelectric body 11. However, for example, a structure is adopted in which the ends of the electrodes on the upper surface are wrapped around to the lower surface and the mounting is performed. It is also possible to adopt a mounting form in which it is directly attached to the positive and negative electrodes disposed to face the substrate side.

[0030]

According to the acceleration detecting element of the present invention, since the acceleration in the direction perpendicular to the thickness of the piezoelectric body is detected as a unimorph structure, a simple detection electrode is formed on the surface of the piezoelectric body. The height dimension in the direction orthogonal to the detection direction can be reduced by adopting a mounting mode in which the piezoelectric body is directly mounted on a mounting board or the like.
As a result, a small-sized and low-cost acceleration sensor can be provided.

Further, in the acceleration detecting element of the present invention, by using the weight, a required force can be applied to the piezoelectric body under a wide range of use conditions, and a highly sensitive acceleration sensor can be realized. Furthermore, a signal extraction electrode having a sufficient area and easy connection can be formed by using the side surface of the weight body, and mounting can be facilitated. In addition, if the opposite polarity detection electrodes are disposed on both sides of the piezoelectric body, the influence of the pyroelectric effect of the piezoelectric body can be extremely reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an acceleration sensor according to an embodiment of an acceleration detecting element of the present invention, wherein FIG.
(B) is a sectional view taken along the line B1-B1 in (a).

FIG. 2 is a perspective view of a main part of the acceleration sensor shown in FIG.

FIG. 3 is a perspective view showing the inside of a shield case of the acceleration sensor according to the embodiment;

FIG. 4 is a perspective view showing a circuit board of the acceleration sensor according to one embodiment, wherein FIG.
(B) shows the signal processing board.

FIG. 5 is an operation explanatory diagram of the acceleration sensor according to the embodiment;

FIG. 6 is a plan view around a detection element of a conventional acceleration sensor.

7A is a cross-sectional view illustrating a configuration around a detection element of a conventional acceleration sensor, and FIG. 7B is a cross-sectional view illustrating a connection portion of the conventional detection element by wire bonding.

FIG. 8 is a configuration diagram showing a vibrator, a detection unit, and a self-diagnosis unit of a conventional acceleration sensor.

FIG. 9 is an exploded perspective view illustrating a structure of bonding a vibrator of a conventional acceleration sensor.

FIG. 10 is a diagram showing a diaphragm of a conventional acceleration sensor.
(A) is a plan view thereof, and (b) is a sectional view taken along the line B2-B2 in (a).

[Explanation of symbols]

 10 Detection element (acceleration detection element) 11 Piezoelectric body 12 Upper side detection electrode (electrode) 13 Lower side detection electrode (electrode) 14 Plumb 14a Fixed surface 14b Side surface 15 Signal extraction electrode 20 Mounting board 21 Positive side electrode 22 Minus side Electrode 23 Bottom plate 25 Signal processing board 30 Sensor unit 31 Shield case 32, 33, 34, 35 Lead pin

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Baba 3-3-1 Tsunashima Higashi, Kohoku-ku, Yokohama, Kanagawa Prefecture Inside Matsushita Communication Industrial Co., Ltd. Matsushita Communication Industrial Co., Ltd. (72) Inventor Toru Fukuda 4-3-1 Tsunashima Higashi, Kohoku-ku, Yokohama, Kanagawa

Claims (6)

[Claims] 1. A piezoelectric device comprising: a plate-shaped piezoelectric body polarized in a plate thickness orthogonal direction orthogonal to a plate thickness direction; and an electrode provided in a film shape on a surface of the piezoelectric body. An acceleration detecting element having a unimorph structure, wherein generated electric charges corresponding to the acceleration in the direction perpendicular to the plate thickness are taken out from the electrodes. 2. A weight fixed to the piezoelectric body, wherein a force in a substantially shearing direction according to an acceleration acting on the weight in a direction perpendicular to the plate thickness of the piezoelectric body is generated from the weight. The acceleration detecting element according to claim 1, wherein the acceleration detecting element is applied to the piezoelectric body. 3. The weight body has a fixed surface fixed to the piezoelectric body, and a side surface forming a predetermined intersection angle with the fixed surface, and a signal extracting electrode is provided on the side surface of the weight body. The acceleration detecting element according to claim 2, wherein the acceleration detecting element is provided. 4. The acceleration detecting element according to claim 1, wherein said piezoelectric body is made of a piezoelectric ceramic element or a piezoelectric single crystal. 5. The detection electrode according to claim 3, wherein said electrodes are detection electrodes of opposite polarities, which are disposed opposite to both surfaces of said piezoelectric body in parallel with said fixed surface of said weight. Acceleration detection element. 6. The acceleration detecting element according to claim 2, further comprising a bottom plate having substantially the same thermal expansion coefficient as that of said weight.