JP4209076B2 - Acceleration sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an acceleration sensor that converts vibration into an electrical signal, and more particularly to an acceleration sensor that is mounted on an automobile or the like and can perform knocking control, airbag control, and the like.
[0002]
[Prior art]
In general, there are various types of acceleration sensors that are put into practical use, such as electromagnetic, piezoelectric, semiconductor, and capacitor types. As a characteristic method, the resonance frequency f _{0 of} sensitivity is set within a desired frequency range. There are a resonance type to be used and a non-resonance (flat) type to use a flat characteristic portion.
[0003]
Of these, a piezoelectric / resonant acceleration sensor will be described as an example with reference to FIGS.
[0004]
FIG. 8 is a diagram showing a conventional acceleration sensor. In FIG. 8, a screw portion 1 a for fixing to a measurement object (such as an engine) is formed at the bottom of a bottomed cylindrical metal case 1.
[0005]
A support portion 1b is formed at a substantially central portion 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 diaphragm 2 by adhesion or the like, and electrodes 4 a and 4 b are attached to both surfaces of the piezoelectric element 3. In addition, since the metal case 1 is electrically connected to the diaphragm 2 by welding or the like, the metal case 1 is generally configured to serve as a ground for a subsequent electric circuit.
[0006]
An output terminal 7 of a connector body 6 made of metal or the like is connected to the electrode 4a of the piezoelectric element 3 by a lead wire 5 (or wire bonding). The lead wire 5 is connected to the output terminal 7 by solder 8a and 8b. It is fixed to the electrode 4a.
[0007]
The connector main body 6 is connected and fixed to the upper end opening of the metal case 1 by caulking 1c, and a waterproofing process is performed by inserting a 0-ring 9 in this connecting portion.
[0008]
One electrode 4 b is electrically connected to the diaphragm 2 and the metal case 1. Therefore, in this conventional example, the output terminal is a one-terminal type in which the casing made up of the metal case 1 and the connector body 6 is also used as a ground. In addition to the one-terminal type, there are a two-terminal type using two output terminals.
[0009]
In the acceleration sensor having such a configuration, vibration (acceleration) applied to the acceleration sensor vibrates the vibration portion including the diaphragm 3 and the piezoelectric element 2 and applies stress strain to the piezoelectric element 3. [V] = Q / C so that the generated voltage can be taken out from the output terminal 7 by the capacitance [C] of the piezoelectric element 3.
[0010]
In general, the diaphragm 3 is often thin and has a disk shape for ease of resonance. The vibration amplitude is maximized near the outer peripheral edge of the diaphragm 3, but the stress distortion to the piezoelectric element 3 is expanded or contracted, and the vicinity of the fulcrum of the inner peripheral portion is considered to show the maximum value.
[0011]
FIG. 9 is a perspective view of the diaphragm 3 and the piezoelectric element 2, and the same parts as those in FIG.
[0012]
FIG. 10 shows an example of frequency characteristics with respect to vibration (constant acceleration) of this acceleration sensor. As shown in FIG. 10, the vicinity of the resonance point f ₀ has a high Q ₀ , but the middle / low range has a flat sensitivity V _0. Show properties. Depending on the purpose of use, it is common to use a vibration output near the flat portion or f ₀ .
[0013]
In the case of the resonance type using a resonance point, using a high Q ₀ at the resonance frequency f _0, corresponding to the f ₀ to a desired value.
[0014]
The resonance frequency f ₀ is generally shown below in the case of a circular diaphragm with a fixed center.
[0015]
f ₀ = α · t / R ² · {E / ρ (1-σ ² )} ^1/2
α: 0.172 t: thickness R: radius E: Young's modulus ρ: density σ: Poisson's ratio
For example, in the above, when Ni steel is used as the material of the diaphragm,
t = 0.4 (mm), R = 7 (mm),
E = 2 × 10 ¹¹ (N / m ² ), ρ = 7.8 × 10 ³ (kg / m ³ ),
σ = 0.28
Then, f _o = 7.41 (kHz).
[0017]
However, the _value of f ₀ of the actual diaphragm is slightly different because the piezoelectric element is added and averaged. Although the main body is determined by the diaphragm, it is slightly affected by the casing (case) and the like, so the actual resonance frequency f ₀ is determined by the overall average.
[0018]
From the above equation, it is generally understood that the plate thickness t and the radius R are appropriately selected and dealt with in order to obtain a desired resonance frequency f ₀ , and the influence of the radius R is particularly large. As a result of experimental confirmation, it is known that when the outer diameter of the disc-shaped diaphragm is changed, f _{0 of} about 1 to 2% / 0.1 mm changes in the same plate thickness.
[0019]
[Problems to be solved by the invention]
However, such a conventional acceleration sensor has the following problems.
[0020]
A characteristic abnormality (spurious defect) is likely to occur near the resonance frequency f ₀ , leading to an increase in the defect rate, leading to a reduction in quality and an increase in cost.
[0021]
FIG. 11 shows an example of characteristics when only the vicinity of the resonance point is close-up. FIG. 11A shows a normal case, and FIG. 11B shows a case where there is a characteristic abnormality (spurious defect).
[0022]
Further, it was found by FEM analysis that the resonance type with the center fixed generally has a vibration mode as shown in FIG.
[0023]
In FIG. 12, (a) is a 1/2 vibration mode, (b) is a 1/1 vibration mode, and this vibration mode is used as the resonance frequency f ₀ . (C) is a 1/4 vibration mode.
[0024]
In general, the 1/2 vibration mode occurs in a fraction of f _{0, and} the 1/4 vibration mode generally occurs in the vicinity of f ₀ . If the vibration modes appear to be uniform evenly in the 1/2 vibration mode and the 1/4 vibration mode, the ± generated voltage should be uniform in the piezoelectric element 3 and the output should be zero. If this occurs, the output level will change due to the disturbance of the phase.
[0025]
In the case of the resonance type, as described above, characteristic abnormality (spurious failure) due to the 1/4 vibration mode becomes a problem. The cause of this is the size of the diaphragm / piezoelectric element, the nonuniformity of the support part, and the output extraction. The influence of a lead wire etc. can be considered.
[0026]
That is, as shown in FIG. 13, when assuming the X axis and the Y axis that are orthogonal to the vibration plate 3 and the piezoelectric element 2 when viewed from the upper surface, the respective axes are geometrically viewed to have similar shapes (one axis). Turned 90 ° and the same).
[0027]
FIG. 13 shows an example in which the lead wire 5 is soldered by going straight to the vicinity of the inner peripheral portion having little influence on the characteristics of the piezoelectric element 3.
[0028]
Even if the X-axis and Y-axis similar shapes are formed in this way, although some improvement is seen in the direction of suppressing the spurious dip, a complete improvement cannot be expected. Therefore, if the various factors as described above are eliminated, the characteristic abnormality (spurious defect) should not occur, but the actual condition is that a defect of about several percent to 10% occurs at a large level. .
[0029]
The present invention has been made to solve the conventional problems, and it is an object of the present invention to provide an excellent resonance type acceleration sensor that can easily reduce spurious defects and has high performance at a low price. To do.
[0030]
[Hand throws to solve problems]
An acceleration sensor according to a first aspect of the present invention includes a main body, a diaphragm fixed to a support portion provided at a substantially central portion of the main body, a donut-shaped piezoelectric element fixed to one or both surfaces of the diaphragm, A pair of electrodes provided on the front and back surfaces of the piezoelectric element, a closing member attached to the body so as to house the diaphragm and the piezoelectric element and close the body, and provided on the closing member. An acceleration sensor including an extraction means for extracting an output from the electrode, wherein the extraction means includes a plurality of connection members connected to one of the electrodes, and the connection member is a material rolling of the diaphragm fixedly connected to the front Symbol electrodes in the roll grain direction in accordance with the position of the inner peripheral portion substantially opposed to two places in the vicinity of the piezoelectric element of time, takes the output from the connector provided on said closure member through said connecting member out Shi Connecting angle of the connecting member with respect to the roll grain direction is set to a range of ± 15 °.
[0031]
With such a configuration, it is possible to reduce abnormal characteristics (spurious defects) due to the 1/4 vibration mode of the diaphragm and the piezoelectric element, and it is easy to assemble, reduces the number of parts, and is a low-cost, high-performance resonance type. An acceleration sensor can be obtained.
[0032]
In the acceleration sensor of the second invention, the connection angle of the connection member with respect to the roll direction is set in a range of ± 15 °.
[0033]
With such a configuration, it is possible to secure an allowable range capable of reducing characteristic abnormality (spurious defect).
[0034]
The acceleration sensor according to a third aspect of the invention is configured such that a recognition mark for recognizing a roll eye direction at the time of material rolling of the diaphragm is provided on the diaphragm.
[0035]
With such a configuration, even after the piezoelectric element is fixed by adhesion or the like, the roll mark direction at the time of rolling the diaphragm material can be confirmed by visually observing the recognition mark, and the roll mark direction can be recognized. It is possible to reliably prevent mistakes and the like and attach the connecting member to the electrode.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, description will be made based on embodiments of the present invention.
[0037]
FIGS. 1-6 is a figure which shows 1st Embodiment of the acceleration sensor based on this invention, This acceleration sensor can be applied to what is applied to a motor vehicle and performs knocking control, airbag control, etc. FIG.
[0038]
First, the configuration will be described. 1 and 2, a screw portion 21a for fixing to a measurement object (engine or the like) is formed at the bottom of a bottomed cylindrical metal case (main body) 21.
[0039]
A support portion 21b is formed at a substantially central portion 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 diaphragm 22 by welding or the like, and electrodes 24 a and 24 b are attached to both surfaces of the piezoelectric element 23. Since the metal case 21 is electrically connected to the diaphragm 22 by welding or the like, the metal case 21 is generally configured to serve as a ground for the subsequent electrical circuit.
[0040]
An output terminal 27 of a connector main 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 (connecting members) 25a and 25b, and the lead wires 25a and 25b are connected. Are fixed to the output terminal 27 and the electrode 24a by solders 28a and 28b, respectively. Note that wire bonding may be used instead of the lead wires.
[0041]
The connector main body 26 is connected and fixed to the upper end opening of the metal case 21 by caulking 21c, and a waterproofing process is performed by inserting an O-ring 29 in the connecting portion.
[0042]
One electrode 24 b is electrically connected to the diaphragm 22 and the metal case 21.
[0043]
Therefore, in this conventional example, the output terminal is a one-terminal type in which the casing made up of the metal case 21 and the connector body 26 is also used as the ground. In addition to the one-terminal type, there are a two-terminal type using two output terminals.
[0044]
In the present 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 takeout means for taking out the output from the pair of electrodes 24a and 24b.
[0045]
In this embodiment, the difference from the conventional example is that the output lead wires 25a and 25b from the electrode 24a of the piezoelectric element 23 are substantially aligned with the roll direction X when the diaphragm 22 is rolled, as shown in FIG. Therefore, the piezoelectric element 23 is connected and fixed by solders 28a, 28b, etc. at two positions substantially opposite to the vicinity of the inner peripheral portion of the piezoelectric element 23.
[0046]
Next, this point will be described in detail.
[0047]
Although the X-axis / Y-axis similar shape shown in FIG. 13 shown in the conventional example is slightly improved (in the direction of pressing the dip), a complete improvement cannot be expected. We have confirmed this by experiment to investigate the cause, and will be described next.
[0048]
As a current situation, it has been found that when the lead wires 25a, 25b made of solder 28b or the like are connected to two substantially opposed positions, the superiority or inferiority of the occurrence appears depending on the mounting direction.
[0049]
From this result, the following can be inferred.
[0050]
(1) There is a relationship between the warp of the diaphragm 22 and the connection position.
[0051]
{Circle around (2)} In the case of a thin diaphragm, in general, there are many ½ half warpages for a center line that tends to induce a ½ vibration mode.
[0052]
(3) Therefore, in the warped state of (2), the lead wires 25a, 25b made of solder 28b or the like are connected to two positions substantially opposite in the random direction, and this load induces a 1/4 vibration mode. Is n’t it?
[0053]
Although the influence of the warp of the piezoelectric element 23 can be considered, since the warp is smaller than that of the diaphragm 22 and the influence on the resonance is also smaller than that of the diaphragm 22, it is considered that the anti-spurious effect is also small.
[0054]
Therefore, the main factor is considered to be the warpage of the diaphragm 22.
[0055]
FIG. 3 is a result of an experiment confirmed by changing the angle at which the lead wires 25a and 25b are connected by solder 28ba or the like at two substantially opposed positions with reference to the roll direction X when the diaphragm 22 is rolled. The figure shows the relationship between the roll angle and the spurious rate.
[0056]
FIG. 4 is a characteristic example showing a determination level of small to large spurious in FIG.
[0057]
The average value in FIG. 3 is a reference value obtained by estimating the case where the average value is randomly added in all directions by the following formula.
[0058]
Average value = (0 ° + 30 ° × 2 + 60 ° × 2 + 90 °) / 6
[0059]
As the influence level of small to large spurious, as is apparent from the characteristics of the judgment level, it is a large level that is harmful in the actual use state, and it is necessary to reduce the occurrence rate.
[0060]
The following results were found from the results.
(1) There is a difference in spurious incidence depending on the angle with respect to the roll, and the minimum is the 0 ° direction. The maximum is in the 90 ° direction.
(2) Compared with other directions, the 0 ° direction is reduced in all levels of small to large spurious.
(3) Further, when the spurious level is large, there is an effect that the direction can be about 0.57 times as large as the estimated average value when randomly attached.
[0061]
From the above results, when connecting the lead wires 25a, 25b with solder 28b or the like at two substantially opposed positions, the optimum position is the position in the roll direction X (angle 0 °) when the diaphragm 22 is rolled. It was confirmed that there was. Further, the worst position where the occurrence of spurious becomes large can be said to be an orthogonal position with an angle of ± 90 °.
[0062]
From the experimental results, it can be inferred from FIG. 2 that there is not much difference in the effect if the allowable range of the connection angle of the lead wires 25a, 25b with respect to the roll direction X is within about ± 10 ± 15 °.
[0063]
Further, as a result of investigating the warpage of the diaphragm 22, as shown in FIG. 5, a half half warp 32 having a roll line direction X as a center line was confirmed. In the figure, (a) is a top view, (b) is a side view, and 33 is a roll.
[0064]
In addition, it is also found that if the diaphragm 22 having a small warp is fixed to the support portion 21b by welding or the like, as a result, a half warp 32 of 1/2 with the roll direction X as the center line is likely to occur as described above. It was. Therefore, it is considered that even when flattening processing for flattening is performed by press working, warping of the material itself occurs due to application of thermal strain or the like during welding fixation.
[0065]
Considering the cause of this warp 33, it is not an internal strain at the time of material rolling because of its directionality (rolling strain is considered to be the roll direction and the perpendicular direction), and as shown in FIG. This is considered to be a slitter processing distortion when creating the width hoop material 31.
[0066]
Therefore, a measure to reduce the slitter distortion 33 as much as possible is conceivable. However, since the relationship between the material yield and the like is largely caused, an increase in cost cannot be avoided, so it cannot be said that it is an optimum measure.
[0067]
Therefore, as described above, the connection of the lead wires 25a, 25b is substantially matched with the position in the roll stitch direction X at the time of rolling of the diaphragm 22, so that spurious defects can be easily greatly improved and can be said to be an optimum countermeasure method. .
[0068]
As described above, in the present embodiment, the lead wires 25a and 25b are connected to the electrode 24a at two positions substantially opposite to the vicinity of the inner peripheral portion of the piezoelectric element 23 in accordance with the roll direction X when the diaphragm 22 is rolled. Since the output is taken out from the output terminal 27 provided in the connector 26 through the lead wire 24a, the characteristic abnormality (spurious defect) due to the 1/4 vibration mode of the diaphragm 22 and the piezoelectric element 23 can be reduced. In addition, it is possible to obtain a high-performance resonance type acceleration sensor that is easy to assemble, reduces the number of parts, and is low in cost.
[0069]
In this embodiment, it seems that two lead wires 25a and 25b are required. However, actually, one lead wire is folded in half, and the vicinity of the center is soldered to the output terminal 27 of the connector 26 by soldering 25a and 25b. Since they are connected, there is not much difference in parts materials.
[0070]
In this embodiment, the acceleration sensor does not have an electric circuit or the like, but there is an acceleration conversion circuit, an amplifier circuit, or the like. Further, for example, the electrodes 24a and 24b of the piezoelectric element 23 may be divided and a self-diagnosis function configured for detection and self-diagnosis may be added.
[0071]
Although the acceleration sensor is described in the present embodiment, if a sound wave introduction hole or a radiation hole is configured instead of a sealed structure, it has a function as an acoustic transducer such as a microphone or a speaker, and its application is also possible. Conceivable. Therefore, it goes without saying that the application to such a converter is the same as the gist of the present invention.
[0072]
FIG. 7 is a view showing a second embodiment of the acceleration sensor according to the present invention. The same reference numerals are given to the same components as those in the first embodiment, and the description will be omitted.
[0073]
In FIG. 7, a recognition mark 41a is provided in the vicinity of the outer peripheral portion of the diaphragm 22 so that the roll direction X at the time of rolling the diaphragm 22 can be easily recognized even after the piezoelectric element 23 is fixed with an adhesive or the like. Is. In addition, the figure (a) is a top view, (b) is the elements on larger scale of star hit 41b.
[0074]
In this embodiment, a minute star striking of several μm in height for facilitating electrical connection with the electrode 24a of the piezoelectric element 23 on the surface of the diaphragm 22 is formed on the diaphragm surface by processing such as pressing. In this example, the recognition mark 41a is obtained by eliminating a part of the star hit 41b (refer to Japanese Patent Publication No. 7-78448 for details of the star hit).
[0075]
In the present embodiment, the recognition marks 41a are formed at two positions according to the roll stitch direction X, but the number is not specified separately, and may be one.
[0076]
Therefore, the processing of the recognition mark 41a as described above can be added without any influence on characteristic change and cost increase.
[0077]
Various recognition marks can be considered in addition to the present embodiment. However, if the purpose is the same, it can be said that the same as the gist of the present invention.
[0078]
As described above, in this embodiment, the recognition mark 41a for recognizing the roll eye direction X at the time of rolling the material of the diaphragm 22 is provided in the vicinity of the outer peripheral portion of the diaphragm 22, so that the piezoelectric element 23 is fixed by an adhesive or the like. Even after, the roll mark direction X at the time of rolling the diaphragm 22 can be confirmed by visually observing the recognition mark 41a, and it is possible to surely prevent the recognition error of the roll roll direction X from occurring. Thus, the lead wires 25a and 25b can be attached to the electrode 24a.
[0079]
In each of the above embodiments, the output output from the electrode 24a of the piezoelectric element 23 is taken out by connecting and fixing the lead wire 25a or the like by soldering 28b or the like, but other contact terminal pins are used instead of the lead wire 25a or the like. The connection point may be taken out as long as it is within the scope of the present invention.
[0080]
Even if the basic structure of the acceleration sensor is different, as described above, the present invention relates to a method for extracting output from the diaphragm / piezoelectric element, and the output extraction position is the same as that of the present invention. If it exists, it can be said that it is the same as the gist of the present invention.
[0081]
【The invention's effect】
According to the present invention, characteristic abnormality (spurious failure) due to the 1/4 vibration mode of the diaphragm and the piezoelectric element can be reduced, the assembly is simple, the number of parts is reduced, and the low-cost and high-performance resonance type. An 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 diagram showing a partially enlarged top view of a diaphragm / piezoelectric element portion of the first embodiment. FIG. 4 is a diagram showing an experimental result of a relationship between an angle with respect to a roll eye and a spurious incidence according to a difference in lead wire connection position in the first embodiment. FIG. 4 is a characteristic example showing a small to large determination level of spurious in the first embodiment. FIGS. 5A and 5B are diagrams showing the diaphragm according to the first embodiment, wherein FIG. 5A is a top view and FIG. 6B is a side view. FIG. 6 is a view of the diaphragm material according to the first embodiment after slitting. FIG. 7 is a diagram showing a first embodiment of an acceleration sensor according to the present invention, FIG. 7A is a top view of the diaphragm, and FIG. 7B is a star hitting portion formed on the diaphragm. FIG. 8 is a sectional view of a conventional acceleration sensor. FIG. 9 is a conventional diaphragm / piezoelectric element. FIG. 10 is a diagram showing a conventional frequency characteristic. FIG. 11 is a characteristic in the case where only the vicinity of a conventional resonance point is close-up. (A) is normal, and (b) is a characteristic. FIG. 12 is a diagram showing an FEM analysis result of a vibration mode in a conventional resonance type. FIG. 13 is a diagram showing a partially enlarged top view of a conventional diaphragm / piezoelectric element section. [Explanation of symbols]
21 Metal case (main body, removal means)
21b Support section
22 Diaphragm (extraction means)
23 Piezoelectric element
24a, 24b electrode
25a, 25b Lead wire (connecting member, extraction means)
26 Connector body (blocking member)
27 Output terminal (extraction means)
33 roll eyes
41a Recognition mark X Roll eye direction

Claims (2)

A main body, a diaphragm fixed to a support provided at a substantially central portion of the main body, a donut-shaped piezoelectric element fixed to one or both surfaces of the diaphragm, and provided on the front and back surfaces of the piezoelectric element A pair of electrodes, a closing member attached to the main body so as to store the diaphragm and the piezoelectric element and close the main body, and a take-out means provided on the closing member for taking out the output from the pair of electrodes An acceleration sensor comprising:
The take-out means has a plurality of connecting members connected to one of the electrodes, and the connecting members are arranged in the vicinity of the inner peripheral portion of the piezoelectric element in accordance with the roll direction when the diaphragm is rolled. fixedly connected to the front Symbol electrodes at positions opposed to two positions,
Wherein to eject the output from the connector provided on the closure member through before Symbol connecting member,
An acceleration sensor, wherein a connection angle of the connection member with respect to the roll eye direction is set in a range of ± 15 ° . The acceleration sensor according to claim 1, wherein a recognition mark for recognizing a roll eye direction during material rolling of the diaphragm is provided on the diaphragm .

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