JP2002022762A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor of low cost and high performance reducing a spurious (dip by anti-resonance) failure with simple constitution. SOLUTION: This acceleration sensor is provided with lead wires 25a, 25b connected to an electrode 24a in the respective positions of an X-axis and a Y-axis almost orthogonal within the same plane almost orthogonal to a center axis passing almost the center of a plane of a vibrating plate 22. The electrode fitting positions of the lead wires 25a, 25b are set into such positions that an angle defined by straight lines connecting the center axis to the respective fitting positions of the lead wires is 90 deg..

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 converting vibration into an electric signal, and more particularly, it is mounted on an automobile or the like.
The present invention relates to an acceleration sensor capable of performing knocking control, airbag control, and the like.

[0002]

2. Description of the Related Art Generally, there are various types of acceleration sensors practically used, such as an electromagnetic type, a piezoelectric type, a semiconductor type and a capacitor type. Among them, a piezoelectric type acceleration sensor is shown in FIG. 9 will be described.

FIGS. 8 and 9 show a conventional acceleration sensor. In FIGS. 8 and 9, a screw portion 1a for fixing to a measurement object (engine or the like) is provided at a lower portion of a bottomed cylindrical metal case 1. FIG.
Are formed.

A support portion 1b is formed substantially at the center of the bottom surface of the metal case 1, and a diaphragm 2 made of metal or the like is fixed to the support portion 1b by welding or the like. A donut-shaped piezoelectric element 3 is fixed to the upper surface of the vibration plate 2 by bonding or the like, and electrodes 4a and 4b are attached to both surfaces of the piezoelectric element 3. Since the metal case 1 is electrically connected to the diaphragm 2 by welding or the like,
Generally, it is configured to serve as a ground for a subsequent electric circuit.

An output terminal 7 of a connector body 6 made of metal or the like is connected to an electrode 4a of the piezoelectric element 3 by a lead wire 5 (or wire bonding), and the lead wire 5 is output by solders 8a and 8b. It is fixed to the terminal 7 and the electrode 4a.

The connector body 6 is connected and fixed to the opening at the upper end of the metal case 1 by caulking 1c, and a waterproof process is performed by interposing an O-ring 9 at the connecting portion.

The one electrode 4b is electrically connected to the diaphragm 2 and the metal case 1.

Therefore, in this conventional example, the output terminal is of a one-terminal type in which the housing composed of the metal case 1 and the connector main body 6 also serves as ground. In addition,
There is also a two-terminal type using two output terminals other than the one-terminal type.

In an acceleration sensor having such a configuration, vibration (acceleration) applied to the acceleration sensor causes
The vibrating part composed of the vibration plate 3 and the piezoelectric element 2 vibrates and gives stress distortion to the piezoelectric element 3, so that electric charge [Q] is generated,
Depending on the capacitance [C] of the piezoelectric element 3, it can be taken out from the output terminal 7 as a generated voltage from [V] = Q / C.

FIG. 10 shows an example of a frequency characteristic with respect to the vibration (constant acceleration) of the acceleration sensor. As shown in FIG. 10, near the resonance point f ₀ has a high Q, but shows a flat characteristic in the middle and low ranges.

This acceleration sensor generally uses a vibration output in the vicinity of a flat portion or f ₀ depending on the purpose of use. For example, when using the vicinity of f ₀ , the high Q is used and the same as a filter is used. However, there is an inconvenience that detection may not be possible even if f ₀ is slightly shifted because Q is too high.

For this reason, a resistor (R) is generally connected in parallel with the piezoelectric element as shown in FIG. 11, and is used by being low-cut as shown in the characteristic example of the dashed line shown in FIG.

By using such a method, the Q can be appropriately reduced, so that the above-mentioned disadvantage can be solved (for a conventional example of such a low cut process, see Japanese Patent No. 1650633). . FIG. 12 shows an example of the measured characteristics near f _{0 at} this time.

On the other hand, FIG. 13 shows another shape of the acceleration sensor. In FIG. 13, a part different from the acceleration sensor of FIG. Is provided near the center of the metal base 11 fixed by welding or the like.
The connection method between the electrode 4a and the output terminal 13 of the connector main body 12 is different. The output terminal 13 penetrates the inside of the support portion 11a, and is soldered to the electrode 4a through the connection terminal 14 provided at the tip end thereof. It is a connected point.

It is desirable that the connection terminals 14 have as small a stiffness as possible in order to avoid the influence on the diaphragm 2.

As a method of taking out the output, it is a matter of course that the output may be taken out by wiring with a lead wire or the like instead of the configuration shown in FIG.

Although this acceleration sensor operates in the same manner as the acceleration sensor shown in FIG. 8, it is experimentally considered that the acceleration sensor can achieve higher sensitivity in consideration of sensitivity. I know.

This is because the diaphragm 2 is formed on the metal base 11, and the metal base 11 is not a completely rigid body, and vibrates slightly by acceleration as in the case of the diaphragm. This is considered to be a function of amplifying the vibration of a transformer.

[0019]

However, the above-described acceleration sensor has the following problems. As in the characteristic example in the vicinity of the resonance frequency f ₀ shown in FIG. 14 depending on the shape-soldered method such as the lead wire 5 or the connection terminals 14 for taking out the output, the anti-resonance to be spurious in f ₀ near ( (Dip) occurs, resulting in characteristic deterioration. Therefore, the lead wire 5 or the connection terminal 14
It can be said that it is preferable that the fixed point of the center is smaller than the center where the influence is small. In the case where a part of the diaphragm 3 is trimmed and cut (indicated by reference numeral 16) as shown in FIG. 15 for adjusting (up) the f ₀ value, if the number of cuts and the trimming cut amount increase, the characteristic example of FIG. In the same manner as described above, characteristic deterioration occurs. Also,
sometimes it occurs similarly characteristic deterioration even when adding the damping resistance of the large potting agent in the vicinity of the outer peripheral portion of the diaphragm 2 to lower adjusting the f _0.

[0020] The present invention has been made to solve such a problem, there is a large effect when using the vicinity of the resonance frequency f _0, a defect (dip by anti-resonance) spurious with a simple configuration It is an object of the present invention to provide a low-cost, high-performance acceleration sensor that can be reduced.

[0021]

According to a first aspect of the present invention, there is provided an acceleration sensor, comprising: a main body; a flat diaphragm fixed to a support provided substantially at the center of the main body; A flat plate-like piezoelectric element fixed to both surfaces, a pair of electrodes provided on the front and back surfaces of the piezoelectric element, a closing member attached to the main body so as to close the main body, and a main body or a closing member. An acceleration sensor provided on at least one of the electrodes, and an extraction unit for extracting an output from the pair of electrodes, wherein the extraction unit has a plurality of connection members connected to one of the electrodes; The position at which the member is attached to the electrode has an angle formed by a straight line connecting the central axis and each of the take-out means attaching positions in a plane substantially perpendicular to a central axis passing substantially the center of the diaphragm plane. ° and Configured so that.

[0022] With this configuration, the connecting member only by devising the mounting position with respect to the electrode, generating as outputs cancel the generation voltage of the reverse-phase halves in 1/4 mode existing near the resonance frequency f ₀ The spurious (dip due to anti-resonance) defect can be reduced with a simple configuration. As a result,
A low-cost and high-performance acceleration sensor can be obtained.

In the acceleration sensor according to the second aspect of the invention, an adhesive is applied to at least one of the electrodes or the diaphragm, and the application position of the adhesive is substantially perpendicular to a central axis passing through a substantially center of the plane of the diaphragm. The angle formed by a straight line connecting the central axis and the respective mounting positions of the take-out means in a plane is 90 °.
It is configured so that

With such a configuration, it is possible to reduce spurious (dip due to anti-resonance) with a simple configuration while adjusting the resonance frequency f ₀ .

In the acceleration sensor according to a third aspect of the present invention, a deformable metal base having a supporting portion is provided on one of the main body and the closing member, and the diaphragm is fixed to the supporting portion of the metal base. It is configured as follows.

With such a configuration, since the diaphragm is fixed on the deformable metal base, the metal base is vibrated by acceleration in the same manner as the diaphragm to amplify the vibration of the diaphragm like a transformer. And the sensitivity of the acceleration sensor can be improved.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is an explanation based on an embodiment of the present invention.

FIGS. 1 to 3 show a first embodiment of an acceleration sensor according to the present invention. This acceleration sensor can be applied to a vehicle which performs knocking control, airbag control and the like by being applied to an automobile. it can.

First, the configuration will be described. 1 and 2, a screw portion 21a for fixing to a measured object (engine or the like) is formed at a lower portion of a bottomed cylindrical metal case (main body) 21.

A support portion 21b is formed substantially at the center of the bottom surface of the metal case 21, and a diaphragm 22 made of metal or the like is fixed to the support portion 21b by bonding or the like. A donut-shaped piezoelectric element 23 is fixed to the upper surface of the vibration plate 22 by welding or the like, and electrodes 24a and 24b are attached to both surfaces of the piezoelectric element 23. In addition, metal case
Since 21 is electrically connected to the diaphragm 22 by welding or the like,
Generally, it is configured to serve as a ground for a subsequent electric circuit.

An output terminal 27 of a connector body (closing member) 26 made of metal or the like is connected to the electrode 24a of the piezoelectric element 23 via a pair of lead wires (connection members) 25a and 25b. 25a and 25b are fixed to the output terminal 27 and the electrode 24a by solders 28a and 28b, respectively. In addition,
Wire bonding may be used instead of the lead wire.

The connector main body 26 is connected and fixed to the upper end opening of the metal case 21 by caulking 21c, and a waterproof process is performed by interposing an O-ring 29 at the connecting portion.

The one electrode 24b is electrically connected to the diaphragm 22 and the metal case 21.

Therefore, in this conventional example, the output terminal is of a one-terminal type in which the housing composed of the metal case 21 and the connector body 26 also serves as ground. In addition,
There is also a two-terminal type using two output terminals other than the one-terminal type.

In this embodiment, the metal case 21, the diaphragm 22, the lead wires 25a and 25b, the output terminal 27, and the connector main body 26 constitute a take-out means for taking out the output from the pair of electrodes 24a and 24b. .

On the other hand, in this embodiment, two lead wires 25
a and 25b are attached to the electrode 24a.
a and 25b are straight lines connecting the center axis of the diaphragm 22 and the mounting positions of the respective lead wires in the same plane substantially orthogonal to the center axis passing substantially the center of the plane of the diaphragm 22 as shown in FIG. The angle is 90 degrees.

It is to be noted that the lead wire can be connected not only at two places but also at many points. However, it is disadvantageous in terms of cost and causes a large variation, so that two places are preferable.

Next, the reason why the leads 25a and 25b are attached as described above will be described.

As a result of the analysis, there are a plurality of modes other than the desired fundamental mode as the vibration eigenvalue when the diaphragm and the piezoelectric element are fixed at the center, and there is a quarter mode near f _0. Do you get it.

FIG. 3 shows an example of the vibration mode. FIG.
Represents the 1/1 mode at the point f ₀ , and FIG. It is considered that the frequency of the 1/4 mode is determined by the dimensions of the diaphragm 22 and the piezoelectric element 23. Of course,
A diaphragm 2 for separating the 1/4 mode from the f ₀ point as much as possible
It may also suitably of such second dimension conditions, in order to reduce the influence of spurious, must be outside _{f 0 ± 1~1.5 (kHz),} f 0 · sensitivity, which is another characteristic conditions From Q and the like, it can be said that such a configuration is often impossible.

For example, under the following conditions, about f ₀ = 7.095
(KHz), and the 1/4 mode is about 1.11 times f ₀
It is 7.87 (kHz). [Conditions] Diameter of support part 21b φ4.3 (mm) Diameter / inner diameter of diaphragm 22 φ21.6 / 3.1 (mm) Thickness of diaphragm 22 0.4 (mm) Diameter / inner diameter of piezoelectric element 23 φ15. 8 / 3.1 (mm) The thickness of the piezoelectric element 23 is 0.38 (mm). E: Young's modulus ρ: Density, C: Poisson's ratio are as follows.

<Vibration plate> E = 2 × 10 ¹¹ (N / m ² ) ρ = 7.8 × 10 ³ (kg / m ³ ) σ = 0.28 <Piezoelectric element>

E = 6.3 × 10 ¹⁰ (N / m ² ) ρ = 7.65 × 10 ³ (kg / m ³ ) σ = 0.34

In the case of the following condition, about f ₀ = 13.132
A (kHz), about 1/4 mode is about 1.01 times the f ₀
It is 13.328 (kHz). Diameter of support part 21b φ4.3 (mm) Outer diameter / inner diameter of diaphragm 22 16.96 / 3.1 (mm) Thickness of diaphragm 22 0.5 (mm) Outer diameter / inner diameter of piezoelectric element 23 12.0 / 3.1 (Mm) Thickness of piezoelectric element 23 0.45 (mm)

In such a configuration, 1/1 of the f ₀ point
In the mode, the vibrating plate vibrates in the same direction in the entire circumferential direction. As a result, an output is obtained from the stress on the piezoelectric element 23.
However, in the 1/4 mode, the phases in the vibration direction are reversed by half, so that in the case of the uniform 1/4 mode, the generated voltages do not appear as cancellation outputs.

[0046] Thus, taking the mechanical configuration disturbing the uniform mode, cause the occurrence of the spurious caused the phase difference between the 1/1 mode f ₀ points. Also, the method of connecting the lead wire to the electrode at one place as in the conventional example is as follows.
Depending on the amount of solder for connection, the connection position, and the like, spurious components may be caused.

In the present embodiment, in order to solve such a problem, the two lead wires 25a and 25b are substantially perpendicular to a central axis passing through substantially the center of the plane of the diaphragm 22 in a plane substantially perpendicular to the center axis. The electrodes 24a are connected at the respective positions of the X axis and the Y axis, and the mounting position of the lead wires 25a and 25b is 90 degrees with respect to the straight line connecting the center axis of the diaphragm 22 and the mounting position of each lead wire. ° (that is, a position where the shape of the diaphragm 22 in the X-axis and the Y-axis is geometrically similar), so that in the 1/4 mode, half of the generated voltage of opposite phase is generated. It is possible to cancel each other out and make it hard to generate as an output.

As a result, spurious (dip due to anti-resonance) defects can be reduced with a simple configuration, and a low-cost and high-performance acceleration sensor can be obtained.

The present embodiment is a center fixed type having a support portion 21b at the center of the main body case 21, but a type in which a peripheral portion is clamped in a circular shape, in which a rod-shaped diaphragm is fixed to a cantilever. There may be.

In the present embodiment, the acceleration sensor does not have an electric circuit or the like, but may include an impedance conversion circuit or an amplifier circuit. Also, for example, the electrodes 24a and 24b of the piezoelectric element 23 may be divided to add a self-diagnosis function configured for detection and self-diagnosis.

[0051] Further, it is also possible to diaphragm 22 of the present embodiment is applied f ₀ adjustment of box coating agent (adhesive) to obtain the same effect. Also in this case, the botting agent is applied to the outer peripheral portion of the diaphragm in a plane substantially orthogonal to the central axis passing through the substantially center of the diaphragm 22 plane, and the application position of the botting agent is What is necessary is just to set it to the position where the angle formed by the straight line connecting the center axis and the mounting position of each lead wire is 90 °.

It is to be noted that the spurious cannot be reduced unless the above conditions are strictly adhered to as in the present embodiment. This depends on how much each component has an influence, and it is needless to say that it is not necessary to take measures when the influence is small.

Therefore, it can be said that the gist of the present invention is the same as long as there is at least one configuration as in the present embodiment. Further, in the present embodiment, the acceleration sensor is described. However, if an acoustic wave introduction hole or a radiation hole is formed instead of a hermetically sealed structure, it also has a function as an acoustic transducer such as a microphone or a speaker, and its application is also Conceivable. Therefore, it goes without saying that the application to such a converter is the same as the gist of the present invention.

FIGS. 4 to 6 are views showing a second embodiment of the acceleration sensor according to the present invention.

First, the configuration will be described. In FIG. 4, a screw portion 31a for fixing to an object to be measured (such as an engine) is formed at a lower portion of a bottomed cylindrical metal case (main body) 31.

A connector body 32 made of resin is fixed to the metal case 31 by a caulking portion 31b. A deformable metal base 33 is fixed to a lower portion of the connector body 32 by welding. It is closed by 32 and a metal base 33. In the present embodiment, the connector main body 32 and the metal base 33 constitute a closing member, and the connector main body 32 penetrates a support portion 33a provided at a substantially central portion of the metal base 33.

A diaphragm 34 made of metal or the like is fixed to the support portion 33a of the metal base 33 by bonding or the like.
A donut-shaped piezoelectric element 35 is fixed to the upper surface of the diaphragm 34 by welding or the like, and electrodes are provided on both surfaces of the piezoelectric element 35.
36a and 36b are attached.

The output terminal 37 of the connector main body 32 passes through the support portion 33a, and the distal end thereof is connected to the metal case 31 and the connector main body 32.
It is exposed to the space between. At the tip of the output terminal 37, a connection terminal (connection member) 38 is provided. As shown in FIG.
The position is fixed at a position where the angle formed by a straight line connecting the central axis of the diaphragm 34 and the fixing position of each solder is 90 °. For this reason, the electrodes
The output from 36a can be taken out to output terminal 37 via connection terminal 38.

The output terminal 37 is also fixed to the connection terminal 38 by solder 39. Note that, in the present embodiment, the connection terminal 38, the diaphragm 34, and the output terminal 37 constitute an extraction unit. Reference numeral 40 denotes a metal case 31 and a connector body.
O-ring sealing 32.

In this embodiment, the connection terminal 38 is an electrode
The solder 39a is fixed to the solder 39a at two places, and the fixed place is set at a position where the angle formed by a straight line connecting the central axis and the respective solder fixing position is 90 °.
The same effect as that of the embodiment can be obtained.

In the present embodiment, since the diaphragm 34 is fixed on the deformable metal base 33, the metal base 33 is vibrated by acceleration in the same manner as the diaphragm 34, so that the vibration of the diaphragm 34 is like a transformer. It can be amplified, and the sensitivity of the acceleration sensor can be improved.

In this embodiment, two portions of the connection terminal 38 are connected to the electrode 36a. However, the present invention is not limited to this, and four portions of the connection terminal 38 are connected to the electrodes 36a by solder 41 as shown in FIG.
a. Even in this case, the connection terminal 38
Needless to say, the fixing point is set at a position where the angle formed by the straight line connecting the central axis of the diaphragm 34 and the connection terminal fixing position is 90 °.

The diaphragm in each of the above embodiments may be configured as shown in FIG. That is, as shown in FIG. 7A, trimming cutting is performed on two portions of the outer periphery of the diaphragm 51 in the X-axis direction and the Y-axis direction (the cut portion is denoted by reference numeral 52).
a, 52b), trimming and cutting the four peripheral portions of the diaphragm 51 in the X-axis direction and the Y-axis direction (cut portions are denoted by reference numerals 53a to 53d), and a center passing substantially through the center of the plane of the diaphragm 51 A lead wire or an output terminal (not shown) is connected to the electrode at each of the X-axis and the Y-axis that are substantially orthogonal to each other in the same plane that is substantially orthogonal to the axis. The angle formed by the straight line connecting the center axis of the lead and the mounting position of each lead wire or output terminal is 9
The same effect can be obtained by setting the position at 0 °.

In each of the above embodiments, the piezoelectric element is mounted on one side of the diaphragm, but may be mounted on both sides.

[0065]

According to the present invention, the connecting member only by devising the mounting position with respect to the electrodes, the output cancel each other generated voltage having a phase opposite to that of the halves in the 1/4 mode existing near the resonance frequency f ₀ The spurious (dip due to anti-resonance) defect can be reduced with a simple configuration. As a result, a low-cost and high-performance acceleration sensor can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an acceleration sensor according to the present invention, and is a cross-sectional view thereof.

FIG. 2 is a top view of a vibration plate and a piezoelectric element to which a lead wire according to the first embodiment is attached.

FIG. 3A shows 1/1 of the resonance frequency f ₀ of the first embodiment.
FIG. 4B is a model diagram illustrating one mode, and FIG. 4B is a model diagram illustrating a モ ー ド mode.

FIG. 4 is a sectional view showing a second embodiment of the acceleration sensor according to the present invention.

FIG. 5 is a top view of a vibration plate and a piezoelectric element portion of a second embodiment when there are two connection terminals.

FIG. 6 is a top view of a vibration plate and a piezoelectric element portion of the second embodiment when there are four connection terminals.

FIG. 7A is a top view of a vibration plate and a piezoelectric element portion common to each embodiment when trimming cuts are two places,
(B) is a top view of the vibration plate and the piezoelectric element portion common to each embodiment when there are four trimming cuts.

FIG. 8 is a sectional view of a conventional acceleration sensor.

FIG. 9 is a perspective view of a conventional diaphragm and a piezoelectric element.

FIG. 10 is a diagram illustrating a conventional frequency characteristic.

FIG. 11 is a circuit diagram for low cut.

FIG. 12 is a diagram illustrating a measurement example of a conventional frequency characteristic.

FIG. 13 is a cross-sectional view showing another shape of the conventional acceleration sensor.

FIG. 14 is a characteristic diagram showing a conventional spurious defect.

FIG. 15 is a top view of a conventional trimmed vibration plate and a piezoelectric element portion.

[Explanation of symbols]

 21 Metal case (main body, take-out means) 21b Support 22, 41 Vibration plate (take-out means) 23 Piezoelectric elements 24a, 24b Electrodes 25a, 25b Lead wire (connecting member, take-out means) 26 Connector body (obstruction member) 27 Output terminal (Take-out means) 31 Metal case (body) 32 Connector body (obstruction member) 33 Metal base (obstruction member) 33a Supporting part 34 Vibrating plate (take-out means) 35 Piezoelectric elements 36a, 36b Electrode 37 Output terminal (take-out means) 38 Connection Terminals (connection members, extraction means)

Claims (3)

[Claims] A main body, a flat plate-shaped diaphragm fixed to a support provided substantially at the center of the main body, a flat plate-shaped piezoelectric element fixed to one or both sides of the diaphragm, A pair of electrodes provided on the front and back surfaces of the piezoelectric element, and a closing member attached to the main body so as to close the main body,
Provided on at least one of the main body or the closing member,
An acceleration sensor comprising: a takeout unit that takes out an output from the pair of electrodes, wherein the takeout unit has a plurality of connection members connected to one of the electrodes, and connects the connection member to the electrode. The mounting position is a position at which an angle formed by a straight line connecting the central axis and the respective mounting means mounting positions is 90 ° in a plane substantially orthogonal to a central axis passing through a substantially center of the diaphragm plane. An acceleration sensor characterized in that: 2. An adhesive is applied to at least one of the electrodes or the diaphragm, and the adhesive is applied to the central axis in a plane substantially orthogonal to a central axis passing through a substantially center of the plane of the diaphragm. 2. The acceleration sensor according to claim 1, wherein an angle formed by a straight line connecting the position and each of the take-out means mounting positions is 90 °. 3. A metal base having a supporting portion and being deformable is provided on one of the main body and the closing member, and the diaphragm is fixed to the supporting portion of the metal base. Item 3. The acceleration sensor according to item 1 or 2.