JP2001099859A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost and high-performance acceleration sensor little in variation, etc., which simplifies the constitution enough to enable the automation of assembling works and simplifies the detecting part of acceleration. SOLUTION: An insulative post 15a erected in the center of a cap plate 14 is inserted, positioned and fixed in the inner holes of a piezoelectric element 11 and a weight 21 annularly made of the same piezoelectric material, an electrode plane 11a of the piezoelectric element 11 is electrically bonded to a conductive film 12a of the weight 12, a conducting terminal 17 is soldered to the conductive film 12a to bond a conducting pin 21 which pierces the insulation post 15a to form a connector terminal 21 in a connector part 15b, the piezoelectric element 11 and the weight 12 are settled in a case 13 and the cap plate 14 is welded to seal it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration by converting vibration into an electric signal, and more particularly to a non-resonant type for use in a vehicle and the like for performing knocking control, airbag control, and the like. It relates to an acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, acceleration sensors that have been put into practical use are known which detect an applied acceleration by various methods such as an electromagnetic type, a piezoelectric type, and a semiconductor type. In the method, acceleration is detected by a voltage generated by a stress applied to the piezoelectric element.

[0003] As this kind of piezoelectric acceleration sensor,
For example, as shown in FIGS. 5 and 6, this acceleration sensor is formed in a donut shape and has an electrode 1 on one surface.
a is formed on one side of a disk-shaped metal vibration plate 3 which is electrically joined and supported by welding or the like to a support 2a erected on the case base 2 by welding or the like. Alternatively, the opposite side of the electrode 1a may be electrically bonded and fixed by an adhesive or the like.

In this piezoelectric element 1, a case base 2 has a screw portion 2b for fixing to an object to be measured such as an engine and is grounded together with a metal vibrator 3, while being electrically connected to an electrode 1a by wire bonding. The connected pins 5 face the outside in the connector portion 6a of the case cover 6 and serve as output terminals. The case cover 6 is fixed by inserting it into the case base 2 and caulking the end 2 c. By inserting the O-ring 7 between the end surfaces between the case cover 6 and the case base 2, highly reliable waterproofing is achieved. Fixed in structure.

In this acceleration sensor, a voltage is generated between the case substrate (earth) 2 and the pin (output terminal) 5 when the piezoelectric element 1 vibrates together with the vibration plate 3 by the applied vibration. A voltage is taken out as an output to detect acceleration (external vibration). For a constant acceleration, a high Q can be obtained near the resonance point f0 as shown in FIG. Since the frequency characteristics are flat in the region, a vibration output in the vicinity of the flat portion or f0 is used depending on the purpose of use.

In addition to the acceleration sensor having the structure shown in FIG. 5, there are various types such as a type that clamps the periphery of a piezoelectric element formed in a circular shape, a type that fixes a piezoelectric element formed in a rod-shaped vibrating body to a cantilever, and the like. There is also a type in which an impedance conversion circuit, an amplifier circuit, and the like are built in. Further, for example, the electrode 1a of the piezoelectric element 1 is divided into rings having different diameters, and is used for detection and self-diagnosis (for driving).
There is also a type that has a self-diagnosis function used as a self-diagnosis function.

[0007]

However, in such a conventional acceleration sensor, since the piezoelectric element 1 and the vibration plate 3 are integrated into a vibrating body, it is necessary to stably manufacture it with high accuracy. Difficulty, variations in dimensions, etc., cause variations in sensitivity, characteristics, etc., and make it difficult to reduce the defect rate. In particular, the variation width of f0 is important for a resonance type used near the resonance point. Therefore, a component with high dimensional accuracy and its assembly are required, which increases the cost. On the other hand, when the flat portion is used as a non-resonant type, the f0 is set to be high, so that the sensitivity is low and the configuration is complicated. Therefore, there is a problem that it is difficult to improve dimensional accuracy and reduce costs because it is not suitable for automatic assembly.

In order to solve the above-mentioned problems, the present invention makes it possible to automate the assembly by simplifying the structure and to simplify the acceleration detecting portion.
It is an object of the present invention to provide a low-cost, high-performance acceleration sensor with little variation or the like.

[0009]

Means for Solving the Problems A first method for solving the above problems is described below.
The present invention provides an acceleration sensor comprising a piezoelectric element which is polarized in a thickness direction between two electrode planes with both opposing planes as electrode planes, and detects acceleration by a voltage generated between the electrode planes. A weight member functioning as a weight is joined to one of the electrode surfaces, and the weight member is formed of a conductive material, or the weight member is formed of a material having an expansion coefficient equivalent to that of the piezoelectric element, and a conductive film is formed on the outer surface. Forming an electrically conductive surface on which the electrode surface of the piezoelectric element is drawn out on the opposite side of the joint surface of the weight member by electrically bonding the electrode surface of the piezoelectric element to the weight member. It is a feature.

In the present invention, a weight member is joined to one electrode surface of the piezoelectric element, and a stress (load) by the weight member according to the applied acceleration (vibration) is applied to the piezoelectric element. It is possible to detect a voltage generated between the electrode surfaces of the piezoelectric element between the electrode surface of the piezoelectric element and the conductive surface of the weight member sandwiching the joint surface. Therefore, a large voltage can be generated between the electrode surfaces of the piezoelectric element with respect to the applied acceleration, and the applied acceleration can be detected with high sensitivity. Further, by manufacturing the weight member with a material having an expansion coefficient equivalent to that of the piezoelectric element, for example, the same piezoelectric material, the conductive film of the weight member and the electrode surface of the piezoelectric element can be electrically connected with each other with a small influence of environmental changes. Can be joined.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, there is provided an acceleration sensor in which the donut-shaped piezoelectric element is hermetically sealed inside a case, wherein the weight member is It is formed in a donut shape having substantially the same inner diameter as the piezoelectric element and is joined to one electrode surface of the piezoelectric element, and is fixed to the case main body to form a cap plate that defines the interior space. An electrode surface is electrically joined, an insulating column for positioning the piezoelectric element and the weight member through the cap plate, through the donut-shaped inner hole, and one end side penetrated into the insulating column and having the weight attached thereto. A conductive pin electrically connected to the conductive surface of the member and having the other end exposed to the outside of the case and serving as a connector terminal; and connecting the cap plate and the conductive pin. It is characterized in that for detecting the voltage generated between the electrode surface of the piezoelectric element by pins.

According to the present invention, the piezoelectric element and the weight member are formed in a donut shape, and can be easily positioned and fixed in the case simply by inserting the insulating column of the cap plate into the inner hole. One end of the conductive pin in the insulating pillar is electrically connected to the conductive surface of the weight member and the other end (connector terminal) is exposed to the outside, while the electrode surface of the piezoelectric element opposite to the weight member is Since it is electrically connected to the cap plate, the electrode surface of the piezoelectric element can be drawn out to the cap plate and the connector terminal, and the electrical connection structure of the acceleration sensor can be arranged on the same side. Therefore, the assembly structure and the mounting structure of the acceleration sensor can be simplified.

According to a third aspect of the present invention, in addition to the configuration of the second aspect, the other electrode surface of the piezoelectric element joined to the cap plate is indirectly connected to the other electrode surface via the cap plate. Alternatively, a connector terminal is provided which is directly electrically connected without being interposed through the cap plate and is exposed outside the case.

According to the present invention, since both electrode surfaces of the piezoelectric element are electrically connected to the connector terminals exposed outside the case, an output terminal (connector terminal) from the electrode surface of the piezoelectric element is provided.
Can be located on the same side. Therefore, the acceleration sensor can be easily connected to an external electric circuit.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 3 show a first example of an acceleration sensor according to the present invention.
It is a figure showing an embodiment.

First, the configuration will be described. 1 to 3, an acceleration sensor 10 has a detection element formed by bonding a weight member 12 on a piezoelectric element 11 with a conductive adhesive or the like.
The piezoelectric element 1 and the weight member 12 are hermetically sealed inside a case 13 and the piezoelectric element 1 is mounted with the weight member 12 mounted thereon.
1 is measured as the potential between the connector terminal 21 and the ground, and the acceleration is detected. Note that case 13
Is mounted and fixed to an object to be measured such as an engine by a screw portion 13a.

The piezoelectric element 11 is formed by forming a piezoelectric material such as single crystal or ceramic into a donut shape, and forming electrodes 11a on both opposing planes by plating or vapor deposition, and applying a voltage between the electrodes 11a. By doing
Polarization (electric axis) is given in the direction (thickness direction) of the arrow shown in FIG. 1 perpendicular to the electrode surface 11a. Needless to say, the polarization direction of the piezoelectric element 11 may be opposite to the direction shown in FIG.

The weight member 12 is formed of a metal material (conductive material) in the form of a donut having the same inner diameter and outer diameter as the piezoelectric element 11 or a piezoelectric material equivalent to the piezoelectric element 11 having the same inner diameter and outer diameter. By forming a conductive film 12a by plating or vapor deposition on the entire outer surface including both opposing surfaces thereof so as to be electrically connected to the electrode surface 11a of the piezoelectric element 11, Has become. The weight member 12 is bonded to the piezoelectric element 11 with an adhesive or the like to be conductively fixed (electrically bonded).
Therefore, it is desirable that the piezoelectric element 11 be made of a material having the same linear expansion coefficient or the like as that of the piezoelectric element 11, preferably the same piezoelectric material, so that the influence of the environment such as temperature is at least equal to that of the piezoelectric element 11. Hereinafter, a case will be described in which the weight member 12 is made of the same piezoelectric material as the piezoelectric element 11 and the conductive surface on the upper surface thereof is a conductive film 12a.

The case 13 is provided with a cap plate 1 on the cylindrical edge opposite to the screw portion 13a to be attached and fixed to the object to be measured.
The space for accommodating the piezoelectric element 11 and the weight member 12 is sealed by welding or the like.

The cap plate 14 is made of a conductive material, and has an insulating member 15 fitted in the center thereof. The insulating member 15 is provided upright in the storage space of the case 13 to hold the piezoelectric element 11 and the weight member 12 together. Insulating column 15 that functions as a positioning member for a detection element by being inserted into the inner hole
a, and a connector 15b for mounting a connector from an external electric circuit on the opposite side (outside of the case 13).

For this reason, the cap plate 14 is provided on the electrode surface 1 of the piezoelectric element 11 in which the insulating pillar 15a is inserted into the inner hole.
1a is adhered by an adhesive or the like so as to be conductively fixed (electrically bonded), and inside the insulating pillar 15a, a conductive film (conductive surface) 12a of the weight member 12 is soldered to one end side.
6, the conductive terminal 17 is joined, and the conductive pin 21 which functions as the connector terminal 21 and whose other end is located in the connector portion 15b is penetrated. In the present embodiment, the conductive pin 21 and the conductive film 12a of the weight member 12 are electrically connected to each other by soldering the conductive terminal 17, but it is needless to say that the bonding method is not limited to this. Nor.

Next, the operation will be described. As described above, in the acceleration sensor 10, the weight member 12 is placed on the piezoelectric element 11 and the conductive film 12a of the weight member 12 is electrically joined to the electrode surface 11a of the piezoelectric element 11. For example, when acceleration such as vibration is applied from a measurement object such as an engine attached by the screw portion 13a of the case 13, a stress (load) by the weight member 12 proportional to the acceleration (vibration) is applied to the piezoelectric element. The piezoelectric element 11 generates a piezoelectric force corresponding to the stress between the electrode surfaces 11a of the piezoelectric element 11 so that, for example, the cap plate 1
4 is grounded, measurement is made at the connector terminal (conductive pin) 21 via the conductive film 12a of the weight member 12, and the applied acceleration can be detected.

At this time, the voltage (piezoelectric) V generated in the piezoelectric element 11 is as follows: G: acceleration F: stress due to acceleration g33: piezoelectric constant T: plate thickness of piezoelectric element S: area of piezoelectric element m: weight of weight member L: thickness of the weight member ρ: density of the weight member, V = F · g33 · T / S, and F = m · G =
Since ρ · S · L · G, V = ρ · L · G · g33
-It becomes T.

Therefore, if g33 and ρ are fixed,
When the thicknesses T and L of the piezoelectric element 11 and the weight member 12 are larger, the voltage V generated in the piezoelectric element 11 can be increased, and the applied acceleration can be detected with high sensitivity.

The piezoelectric element 11 and the weight member 12 of the acceleration sensor 10 can be easily positioned and fixed simply by inserting the insulating column 15a of the cap plate 14 into the donut-shaped inner hole. The surface 11 a is joined to the cap plate 14 and the conductive film 12 a of the weight member 12, and the conductive film 12 a is
a can be pulled out only by soldering and joining to the conductive pin 21 in the conductive pin 21 via the conductive terminal 17. Thereafter, the case 13 is covered with the cap plate 1 on the cylindrical edge.
It is possible to assemble it into a sealed interior simply by welding 4 or the like. The acceleration sensor 10 can be mounted on an object to be measured such as an engine by simply attaching the screw portion 13a of the case 13 to the object to be measured, connecting a connector from an electric circuit to the connector portion 15b, and grounding the cap plate 14 to ground. The applied acceleration can be detected.

As described above, in the present embodiment, the stress (load) of the weight member 12 according to the applied acceleration is reduced by placing the electrically connected weight member 12 on the piezoelectric element 11 of the acceleration sensor 10. The applied acceleration can be applied to the piezoelectric element 11, and the applied acceleration can be detected with high sensitivity by the voltage generated between the electrode surfaces 11a of the piezoelectric element 11 measured via the conductive film 12a of the weight member 12.

The acceleration sensor 10 includes a doughnut-shaped piezoelectric element 11 and a weight member 12 on which a cap plate 1 is attached.
4 is inserted and positioned and bonded and fixed, and the conductive pin 21 in the insulating column 15a and the conductive film 12a of the weight member 12 are soldered via the conductive terminal 17, and then the case 13 is removed. It can be assembled simply by welding to the cap plate 14, and the voltage generated between the electrode surfaces 11 a of the piezoelectric element 11 can be reduced by the simple configuration by the cap plate 14 and the connector terminals (conductive pins) 21 in the connector portion 15 b. Can be measured.

Therefore, the assembling structure and the mounting structure of the acceleration sensor 10 can be simplified, the assembly can be automated, the cost can be reduced, and the acceleration can be detected with high sensitivity by reducing the dimensional variation. can do.

FIG. 4 shows a second embodiment of the acceleration sensor according to the present invention. In addition, since the present embodiment is configured substantially in the same manner as the above-described embodiment, the same components are denoted by the same reference numerals, and the characteristic portions will be described.

In FIG. 4, reference numeral 31 denotes a connector terminal. The connector terminal 31 is fixed to the cap plate 14 by welding or the like so as to be conductive, and the connector terminal 31 is exposed together with the connector terminal 21 in the connector portion 15b. Thus, a connector can be connected to an external electric circuit.

Therefore, the electrode surface 11a of the piezoelectric element 11
Both output terminals can be arranged in the same connector section 15b as the connector terminals 21 and 31, and can be easily connected to an external electric circuit, and wiring and noise countermeasures can be facilitated. .

As described above, in this embodiment, in addition to the functions and effects of the above-described embodiment, a two-terminal acceleration sensor 10 can be provided, and the circuit to be connected can be simplified to facilitate the design. it can.

In this embodiment, the connector terminals 31
Is bonded to the cap plate 14, but it goes without saying that the cap plate 14 may be integrally formed with the insulating member 15 using an insulating material and directly bonded to the electrode surface 11a of the piezoelectric element 11. .

In the above-described embodiment, the piezoelectric element 1
Although the case of one is described, a plurality of sheets may be stacked to form a laminated structure. In this case, the piezoelectric elements may be electrically connected to each other to be configured in the same manner as in the present embodiment.

In the present embodiment, the piezoelectric element and the weight have a donut shape having substantially the same inner and outer diameters. However, the present invention is not limited to this. For example, it is conceivable to configure the outer diameter of the weight larger than the outer diameter of the element in order to further improve the sensitivity.

[0036]

According to the present invention, the weight member is electrically joined to and overlapped with the piezoelectric element, so that the load of the weight member according to the applied acceleration (vibration) is applied to the piezoelectric element.
The voltage generated between the electrode surfaces of the piezoelectric element can be detected via the weight member, and the acceleration can be detected with high sensitivity. Further, by using the same piezoelectric material as the piezoelectric element for the weight member, for example, the influence on the bonding surface due to environmental changes such as temperature can be reduced, and the reliability can be improved.

The piezoelectric element and the weight member are positioned and fixed by the insulating columns of the cap plate of the case, and the piezoelectric element is electrically connected to the cap plate.
Assembling the acceleration sensor by using the conductive pins in the insulating pillar electrically connected to the conductive surface of the weight member as connector terminals, and also electrically connecting the connector terminals to the cap plate side of the piezoelectric element. The structure and the mounting structure can be simplified, the assembly can be automated, and the portion for detecting the acceleration can be made a simple configuration to reduce variations and the like.

Therefore, a low-cost and high-performance acceleration sensor can be provided.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of an acceleration sensor according to the present invention, and is a longitudinal sectional view showing an entire configuration thereof.

FIG. 2 is a view showing the piezoelectric element and a weight member;
(A) is its top view, (b) is its side view.

FIG. 3 is a view showing the piezoelectric element and a weight member, and is an assembly perspective view thereof.

FIG. 4 is a view showing a second embodiment of the acceleration sensor according to the present invention, and is a longitudinal sectional view showing the entire configuration thereof.

FIG. 5 is a view for explaining the prior art, and is a longitudinal sectional view showing the entire configuration thereof.

FIG. 6 is a perspective view showing an assembled state of the piezoelectric element.

FIG. 7 is a graph illustrating the characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Acceleration sensor 11 Piezoelectric element 11a Electrode surface 12 Weight member 12a Conductive film 13 Case 13a Screw part 14 Cap plate 15 Insulating member 15a Insulating pillar 15b Connector part 17 Conducting terminal 21 Conducting pin (connector terminal) 31 Connector terminal

Claims (3)

[Claims] 1. An acceleration sensor, comprising: a piezoelectric element polarized in a thickness direction between two electrode planes with both opposing planes as electrode planes, and detecting acceleration by a voltage generated between the electrode planes. A weight member functioning as a weight is joined to one of the electrode surfaces, and the weight member is formed of a conductive material, or the weight member is formed of a material having an expansion coefficient equivalent to that of the piezoelectric element, and the outer surface is electrically conductive. By forming a film, the electrode surface of the piezoelectric element is electrically connected to the weight member, and a conductive surface from which the electrode surface of the piezoelectric element is drawn is formed on the opposite side of the bonding surface of the weight member. An acceleration sensor characterized by the above-mentioned. 2. An acceleration sensor in which a donut-shaped piezoelectric element is hermetically sealed inside a case, wherein the weight member is formed in a donut shape having substantially the same inner diameter as the piezoelectric element. The other electrode surface of the piezoelectric element is electrically joined to a cap plate that defines the interior space by being fixed to the case main body and is fixed to the case main body. An insulating column that is inserted into the hole to position the piezoelectric element and the weight member, and that is penetrated into the insulating column and has one end electrically connected to the conductive surface of the weight member and the other end outside the case; A conductive pin exposed to the connector terminal and exposed to the
The acceleration sensor according to claim 1, wherein a voltage generated between electrode surfaces of the piezoelectric element is detected by the cap plate and a connector terminal of the conduction pin. 3. The piezoelectric element, which is electrically connected to the other electrode surface of the piezoelectric element bonded to the cap plate indirectly via the cap plate or directly without passing through the cap plate. 3. The acceleration sensor according to claim 2, wherein a connector terminal exposed outside the case is provided.