JP2001337101A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost, high-performance acceleration sensor which is very effective, particularly when using frequencies near a resonant frequency fo, by achieving reduction in spurious radiation resulting from antiresonance dips by a simple structure. SOLUTION: This acceleration sensor 10 detects accelerations applied by voltages produced in a piezoelectric element 13 according to the vibration of a vibrating plate 12, by welding to a column 11a of a fixed case 11 in the vibrating plate 12 having the piezoelectric element 13 affixed thereto, and then enclosing the vibrating plate in a vibration space V defined by both the fixed case and a connection case 16. Distances L1 and L2 between the opposite faces of vibration spaces V1 and V2 defined between the bottom faces of the fixed case 11 and the connection case 16 and the respective front and back faces of the vibrating plate 12 and the vibrating body 19 of the piezoelectric element 13 are each set, equal to or less than 0.1 times an inside diameter ϕA of each of the cases 11 and 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly, to an acceleration sensor in which a piezoelectric element is fixed to a vibration plate that vibrates in a closed space.

[0002]

2. Description of the Related Art Conventionally, acceleration sensors that have been put into practical use are known that detect acceleration applied by various methods such as an electromagnetic type, a piezoelectric type, and a semiconductor type. Some of them detect acceleration applied by bending of a piezoelectric element.
Such an acceleration sensor is frequently used especially for a vehicle, and detects acceleration required for knocking control, airbag control, and the like.

FIG. 9 shows an example of this type of piezoelectric acceleration sensor. In this acceleration sensor 100, a support 101a is erected integrally at the center of the bottom surface of a metal fixed side case 101 formed in a frame shape, and a metal disk formed on the support 101a as shown in FIG. The diaphragm 102 is welded and supported, and a piezoelectric element 103 formed in a donut shape is adhered to the upper surface of the diaphragm 102 so as to be coaxial. A detection electrode 104 is formed on the piezoelectric element 103 so as to be coaxial on both front and rear surfaces.
A vibration plate 102 is in conductive contact with one of the detection electrodes 104, and the other detection electrode 104 has a bowl-like shape connected to an external connector via a wire 105 connected by solder 105a such as wire bonding. It is connected to the connection pin 107 provided in the formed connection case 106 made of resin. Note that the fixed side case 101 and the connection side case 106 are
1c and 106c are fitted and caulked to house the vibration plate 102 and the piezoelectric element 103 in the vibration space to be defined, and the O-ring 108 is sandwiched between the open ends 101c and 106c to form the vibration space. Is assembled in a waterproof structure.

FIG. 11 shows a piezoelectric acceleration sensor of this type. This acceleration sensor 110 is configured such that a metal base 112 formed in a disc shape is welded to an open end portion 111c of a fixed metal case 111 formed in a frame shape, and a connection pin 107 connected to an external connector is formed thereon. A vibration space in which the vibration plate 102 and the piezoelectric element 103 are accommodated is defined by overlapping and caulking the provided disk-shaped connectors 116. The plate 102 has a support 112 a erected on the metal base 112 without providing a support on the fixed side case 111.
Is to be supported. Specifically, diaphragm 1
02 and the piezoelectric element 103 are both formed in a donut shape, and the connection pin 107 is penetrated into the support 112a of the metal base 112 while maintaining insulation by the resin material of the connector 116. The connection disk 115 is soldered to the detection electrode 104 of 103
By being fixedly provided by 15a, it supports so that vibration is possible. Note that this acceleration sensor 110
Now, the inner peripheral surface of the fixed side case 111 and the metal base 112
The vibration space is assembled in a waterproof structure by sandwiching an O-ring 118 between the diaphragm 10 and the outer peripheral surface of the diaphragm 10.
It is preferable that the rigidity of the connection disk 115 be as small as possible so as not to hinder the vibration of the piezoelectric element 103 or the piezoelectric element 103. However, instead of the connection disk 115, the diaphragm 102 is welded to the support 112 a and a wire is It is also possible to make the connection 105 electrically.

[0005] These acceleration sensors 100 and 110 are:
Male screw 1 provided on the lower surface side of fixed side cases 101 and 111
When a vibration of an object to be detected, such as an engine into which the first and second sensors 01b and 111b are screwed, is applied, a voltage generated in the piezoelectric element 103 in accordance with the vibration of the vibration plate 102 is applied to the fixed-side case 101,
11 and the metal base 112 as the ground,
Through the connection pin 107, and the acceleration can be detected.

In such an acceleration sensor, as shown by a solid line in FIG. 12, the frequency characteristic with respect to the vibration at a constant acceleration can obtain a high Q near the resonance point f0, but becomes flat in the middle and low frequency regions. Therefore, generally, a flat portion or a vibration output near f0 is used according to the purpose of use, and the upper limit of the working band is substantially up to the vicinity of the resonance point fo. For example, when the vicinity of fo is used, a high Q is used in the same way as a filter, but there is an inconvenience that the Q is too high and even a slight fo shift cannot be detected. For this reason, generally, as shown in FIG. 13, a resistor [R] is connected in parallel with the piezoelectric element 3 and, as shown by a broken line in FIG.
Is appropriately reduced to eliminate the above-mentioned disadvantage. In terms of sensitivity, it has been experimentally found that the acceleration sensor 110 shown in FIG. 11 can achieve higher sensitivity than the acceleration sensor 100 shown in FIG. The metal base 112 is not a completely rigid body, and vibrates slightly but similarly to the vibration base 102 due to acceleration. It is thought that it functions so as to function and be amplified. An example of use of such an acceleration sensor is described in JP-A-58-142227.

The electrode formed on the piezoelectric element 103 may be divided into a small-diameter excitation electrode and a large-diameter detection electrode so as to be coaxially double, and may be formed via the excitation electrode. An external AC voltage is applied to the element 103 to vibrate the vibration plate 102 by the piezoelectric effect of the piezoelectric element 103, and the self-diagnosis of the function of the sensor and the presence or absence of a failure or the detection level of the detection level are determined from the output of the detection electrode caused by the vibration. Some of them can be calibrated.
Further, according to this conventional technique, a pillar 101 standing upright at the center is used.
The diaphragm 102 is supported by a and 112a, and there are various types such as a type in which a disk-shaped peripheral portion is clamped and a type in which a rod-shaped diaphragm is fixed to a cantilever. Also,
A printed circuit board on which electronic components such as an electric impedance converter, an amplifier, and a correction circuit are provided between the detection electrode 104 of the piezoelectric element 103 and the connection pin 107 is connected to a wire 105.
The fixed pins 101, 111, etc. also serve as grounds.
In addition to the single-terminal type, there is also a two-terminal type in which the ground is drawn to the output terminal.

[0008]

However, in such a conventional acceleration sensor, the vibration plate 102 and the piezoelectric element 103 usually have the frequency characteristic shown in FIG. 12 near the resonance point fo shown in FIG. However, depending on the size of the vibrating space of the diaphragm 102 and the piezoelectric element 103, an acoustic standing wave is generated, for example, as shown in FIG. When two resonances occur, a large anti-resonance (dip) that causes spurious due to a phase difference between the resonances may occur, which may cause deterioration of characteristics of the acceleration sensor. In addition, there are cases where acoustic resonance occurs in the vibration space, and in this case as well, a dip that becomes spurious occurs near fo and the like, resulting in characteristic deterioration.

[0009] Since the spurious components are generated acoustically, the generated frequency varies depending on the sound speed [u]. For example, if the temperature changes from 20 ° C to 120 ° C,
From the following equation, it can be seen that the sound speed [u] increases about 1.18 times. [U] = 331.45 + 0.607 · T (m / s) T: Temperature (° C.)

For this reason, a dip that does not occur at room temperature may occur at a high temperature, or on the contrary, as shown in FIG. 15, a large dip occurs at room temperature and becomes smaller at a high temperature. Since this spurious has not been elucidated, when designing an acceleration sensor, it is necessary to construct a vibration system having a desired resonance frequency fo and to repeat dimensional changes in accordance with the presence or absence of adverse effects of spurious. To design an acceleration sensor suitable for the object to be measured.

For this reason, there is a problem that it is difficult to design an acceleration sensor having various fos in a desired entire use band or a wide band so as to be able to be housed in a common case structure.

The present invention has been made to solve such a problem, and realizes the reduction of spurious generation due to antiresonant dip by a simple structure. It is an object of the present invention to provide a low-cost and high-performance acceleration sensor that can obtain a great effect when performing the operation.

[0013]

According to the acceleration sensor of the present invention, a piezoelectric element formed in a flat plate shape is fixed to one or both surfaces of a vibration plate, and the vibration deformation of the vibration plate according to an applied acceleration is provided. An acceleration sensor for detecting the acceleration by a voltage generated in the piezoelectric element, wherein the spatial distance between the piezoelectric element and the diaphragm in the vibration direction is set to 0 as the spatial distance between the piezoelectric element and the diaphragm in the plane direction. The piezoelectric element and the vibrating plate are housed in a case set to be equal to or less than .1 times.

According to this configuration, the diaphragm and the piezoelectric element respond to the applied acceleration in a vibration space in which the distance between the opposing surfaces is set to 0.1 times or less than the interval in the planar direction such as the inner diameter of the case. Vibration, it is possible to prevent acoustic standing waves inside the case, and also to reduce the internal space, so that the acoustic resonance frequency is outside the upper limit of the use band, The occurrence of anti-resonance dips can be reduced. Therefore, it is possible to realize the common use of the case, which only requires designing the outer shapes of the diaphragm and the piezoelectric element so as to be able to be housed in the vibration space, and it is possible to prevent the occurrence of spurious components with a simple structure. In addition, a high-performance acceleration sensor that can obtain a great effect when the vicinity of the resonance frequency fo is used can be manufactured at low cost. Note that the gap between the outer surface of the vibration plate and the piezoelectric element and the inner surface of the case may be set to be small as usual so as not to hinder the vibration of the vibration plate and the piezoelectric element.

Here, the acceleration sensor according to the present invention comprises:
The vibrating plate is formed in a disk shape and the piezoelectric element is formed in a donut shape, and a central portion of the vibrating plate on which the piezoelectric element is fixed is supported by a column standing on a fixed side case of the case. On the other hand, a connection terminal electrically connected to the electrode of the piezoelectric element is provided on a connection side case of the case, and the fixed side case and the end of the connection side case are fitted to each other to form the fixed side. The vibration of the piezoelectric element and the vibration plate, wherein the distance between the opposing surfaces of the case with respect to the vibration plate and the distance between the opposing surfaces of the connection side case with the piezoelectric element are set to be 0.1 times or less the inner diameter of the case. It can be a composition that defines space,

Further, the vibration plate and the piezoelectric element are formed in a donut shape, and a connection terminal for electrically connecting a central portion of the vibration plate on which the piezoelectric element is fixed to an electrode of the piezoelectric element is provided. Arranged and connected to an external connector, supported by a column erected on the connection side case of the case,
By fitting the fixed-side case and the end of the connection-side case together, the distance between the facing surfaces of the fixed-side case with respect to the piezoelectric element and the distance between the facing surfaces of the connection-side case with respect to the diaphragm are determined by the inner diameter of the case. It is possible to adopt a configuration that defines a vibration space of the piezoelectric element and the vibration plate set to be 0.1 times or less of the following.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 7 are views showing a first embodiment of the acceleration sensor according to the present invention.

First, the structure of the acceleration sensor will be described.
In FIG. 1, an acceleration sensor 10 is a fixed side case 1.
1, a vibration plate 12, a piezoelectric element 13, and a connection side case 1.
6 and an O-ring 18 are assembled. As in the prior art shown in FIG. 9, a donut shape is formed on the disk-shaped metal diaphragm 12 and detected on the front and back surfaces. The piezoelectric element 13 on which the electrode 14 is formed is adhered so as to be coaxial, so that, for example, when vibration of a detection target such as an engine is applied, the piezoelectric element 13 is subjected to stress distortion given through the diaphragm 12. A charge [Q] is generated in the piezoelectric element 13, a voltage [V] having a magnitude represented by the following expression that is generated according to the capacitance [C] of the piezoelectric element 13 is taken out, and the applied acceleration is detected. I have. [V] = Q / C

The fixed case 11 is formed of a metal material in the shape of a bottomed cylindrical frame having a circular bottom surface, and a diaphragm 12 having a piezoelectric element 13 fixed on one surface is welded to the center of the bottom surface. A support post 11a is integrally formed so as to support the screw, and a male screw 1 screwed and fixed to a screw hole provided in a detection target such as an engine on the lower surface side.
1b is provided.

The connection side case 16 is formed of a resin material in the shape of a bottomed cylindrical frame having substantially the same diameter as the fixed side case 11, and an external connector having a connection pin 17 passing through the center of the bottom surface as a center can be connected. The connector portion 16a is integrally formed so as to be located on the back side of the fixed side case 11. The connection pin 17 is connected to the detection electrode 1 of the piezoelectric element 13.
4, a wire 15 electrically conductively fixed by wire bonding or the like is connected by solder 15a, so that the piezoelectric [V] generated in the piezoelectric element 13 can be taken out.

The fixed-side case 11 and the connection-side case 16 are provided with cylindrical end portions 11c, 16 which abut each other.
c and the vibration plate 12 and the piezoelectric element 13
V (V1, V
2), and has a cylindrical end 11c.
O-ring 18 between large-diameter wall portion 11d and small-diameter wall portion 11e.
Is set, and the large-diameter wall portion 11 of the fixed side case 11 is fitted so as to sandwich the cylindrical end portion 16c.
By caulking d so as to press the corner of the connection side case 16, the vibration space V is assembled into a waterproof structure.

The vibration space V (V1, V2) defined inside the fixed case 11 and the connection case 16 is
The inner peripheral wall surfaces of the fixed side case 11 and the connection side case 16 are formed with an inner diameter φA (φA1, φA
2), the thickness D of the vibration plate 12 and the piezoelectric element 13, the distance L1 between opposing surfaces from the lower surface of the vibration plate 12 to the bottom surface of the fixed case 11, and the thickness of the connection case from the upper surface of the piezoelectric element 13. When setting the distance between the bottom surfaces of the fixed case 11 and the connection case 16 to which the distance L2 between the opposed surfaces to the bottom surface of the fixed case 16 is added, the distance between the opposed surfaces of the fixed case 11 and the connection case 16 is set. L1 and L2 are set to be 0.1 times or less the inner diameter φA of the inner peripheral wall surface. Therefore, the vibration space V defined by the fixed-side case 11 and the connection-side case 16 is set to be thin, in which the spatial distance L in the vibration direction of the vibration plate 12 and the piezoelectric element 13 is narrower than in the related art.

Next, the dimensional design of the acceleration sensor 10 will be described. As shown in FIG. 2, the acceleration sensor 10 includes a vibration plate 12 and a vibrating body 19 of the piezoelectric element 13 in a vibration space V (V1, V2) defined inside the fixed side case 11 and the connection side case 16. It can be modeled as being mounted so that it can be oscillated. The acoustic standing wave generated in the vibration space V is generated when a sound source is basically present between a closed wall or a housing having a tubular configuration with one end opened, and the maximum amplitude of the sound source is obtained. The part tends to be the maximum point of the wavelength, and the method of generation changes due to the asymmetry of the wall surface material and shape. Since [fc] is approximately represented by the following equation, it can be seen that it occurs at an integral multiple of this fc, and that this fc is proportional to the sound speed [u]. [Fc] = u / λ u: sound velocity (m / s) λ: wavelength (m)

From the above, the standing wave generated in the acceleration sensor 10 is basically a frequency at which the distance b is λ / 2 when between the closed walls, and λ / 4 when at the open end.
The frequency becomes That is, the frequency [fc] of the standing wave generated in the acceleration sensor 10 is expressed by the following equations. In addition, even in the case between the closed walls, when the material of one wall is a material having a strong sound absorbing property, it is not λ / 2 but λ /
May be 4. In case of between closed walls [fc] = u / (2 × b) In case of open end [fc] = u / (4 × b)

When the vibration space V is simply defined as described above, the standing wave is basically generated easily as shown in FIG. However, in the acceleration sensor 10, the frequency [fc] generated by the standing wave is outside the desired use band (generally outside the upper limit), or the generation itself is suppressed by an effect such as acoustic resistance. To be designed.

For example, since the general use band of the acceleration sensor is fo = 20 (kHz) or less, the frequency of the standing wave may be set to 20 (kHz) or more. Here, in order to prevent standing waves in the height L direction (vibration direction) of the vibration space V in FIG. 2 by acoustic resistance or the like described later, it is first necessary to add a sound absorbing material or the like in the vibration space V. It is conceivable, but it is not suitable because the structure is complicated, so that the generation frequency [fc] due to the standing wave is considered to be outside the usable band.

When the standing wave in the L direction is considered, the lowest frequency is the frequency at which L is λ / 2, but if the material is close to the open end structure, the frequency is λ / 4. Therefore, from the above equation, u = 343.59
(M), fc = 20 (kHz) and the L dimension is obtained as follows. This size is a realistic size, and the standing wave in the L direction can be relatively easily prevented. For λ / 2 L ≦ 8.59 (mm) For λ / 4 L ≦ 4.29 (mm)

On the other hand, regarding the standing wave in the diameter φA direction of the vibration space V, for example, considering the lower limit of the use band of the resonance type, the resonance frequency fo is about 6 to 7 (kHz), and fo is Since the thickness, radius (outer diameter), material, and the like of the vibrating body 19 are determined, the radial dimension φA of the vibration space V in which the vibrating body 19 is vibrated is naturally determined. Under the following conditions, about fo = 7.095 (k
Hz).

<Support 11a of Fixed Side Case 11> Diameter: φ4.3 (mm)

<Vibration plate 12> Outer diameter / inner diameter: φ21.6 / 3.1 (mm) Plate thickness: 0.4 (mm) Young's modulus E = 2 × 10 ¹¹ (N / m ² ) Density ρ = 7 0.8 × 10 ³ (kg / m ³ ) Poisson's ratio σ = 0.28

<Piezoelectric element 13> Outer diameter / inner diameter: φ15.8 / 3.1 (mm) Plate thickness: 0.38 (mm) Young's modulus E = 6.3 × 10 ¹⁰ (N / m ² ) Density ρ = 7.65 × 10 ³ (kg / m ³ ) Poisson's ratio σ = 0.34

Under the condition of the vibrating body 19, in order to prevent the appearance of the acceleration sensor 10 from becoming large, the inner peripheral wall surfaces of the fixed case 11 and the connection case 16 have an inner diameter φA of about 23 (mm). (Resonant frequency f
In the case of o, the outer diameter is reduced by reducing the plate thickness D of the vibrating body 19 or the like, and the vibration is designed to be within the inner diameter φA), and the frequency of the standing wave is from λ / 2 to about fc = 7.47
(KHz), which indicates that there is a possibility that a standing wave may be generated in the used band. (In the case of a standing wave of λ / 4, fc is inevitable from the configuration in comparison with the case of a standing wave of λ / 2. Slightly higher). With the outer diameter of the vibrating body 19, the inner peripheral wall surfaces of the fixed case 11 and the connection case 16 have an inner diameter φA =
Since it cannot be made smaller than 23 (mm), in order to prevent the standing wave from being generated in the vibration space V, it is not possible to take the method of bringing the frequency fc of the standing wave out of the used band. Understand.

Therefore, in order to prevent the standing wave from occurring in the direction of the inner diameter φA, it is necessary to consider a method of increasing the acoustic resistance in the vibration space V. To increase the acoustic resistance without adding a sound absorbing material or the like in the vibration space V so as not to complicate the structure, the viscosity (friction) which is a property of air is used.
It is conceivable to use resistance.

For example, the acoustic resistance [γ] of a rectangular parallelepiped air layer
Is generally expressed by the following equation, which shows that it is effective to reduce the dimension of the height h of the air layer to increase the acoustic resistance [γ]. This measure can be said to be an optimal method since it also leads to prevention of generation of a standing wave in the L direction. [Γ] = 12 × μ × d / (w × h ³ ) μ: viscous resistance of air d: length of air layer w: width of air layer h: height of air layer

For this reason, as to the distances L1 and L2 between the opposing surfaces from the bottom surfaces of the fixed case 11 and the connection case 16 to the front and back surfaces of the vibrating body 19, values that do not generate standing waves are experimentally obtained. It has been found that it is desirable to configure the distances L1 and L2 between the facing surfaces to be about 0.1 times or less the inner diameter φA of the inner peripheral wall surfaces of the fixed case 11 and the connection case 16. Although it is considered that it depends on the presence or absence of the support 11a, the vibration space V2 (distance L2) between the connection case 16 and the bottom surface is closer to the vibration space V1 (distance L1) between the fixed case 11 and the bottom surface. Is particularly important because it has a greater effect on the generation of standing waves.

It is preferable that the lower limit of the distances L1 and L2 between the opposing surfaces is a value that can secure the vibration allowance of the diaphragm 12.

As described above, when the inner diameter φA is 23 (mm), the distance L1 and L2 ≦ 2.3 (mm) between the opposing surfaces is satisfied. When the inner diameter φ is 19 (mm), the distance L between the opposing surfaces is L.
1, L2 ≦ 1.9 (mm), and when compared with the result of the standing wave in the L direction, depending on the thickness D of the vibrating body 19, except for λ / 4 at the open end, The result in the direction of the inner diameter φA is determined preferentially at the time of dimension setting.

Referring to the acoustic resonance frequency of the vibration space V, first, as shown in FIG. 3, a sectional view for explaining the acoustic resonance (Helmholtz resonance tube) frequency fh will be discussed. When the air chamber R has the area s and the pore H having the length da is formed, when resonance occurs by the air chamber R and the pore H, the resonance frequency [fh] is expressed by the following equation. [Fh] due to this acoustic resonance also has a sound velocity [u]
It turns out that it is proportional to. fh = (1 / 2π) × (So / mo) ^1/2 = (u / 2π) × (s / (da × v)) ^1/2 So: Stiffness of air mo: Mass of air ρ: Density of air So = ρ × u ² / v mo = ρ × da / s

When the vibration space V of the acceleration sensor 10 is applied to this acoustic resonance example, it can be modeled as shown in FIG. 4, where mo is the outer peripheral surface of the vibrating body 19 and the case 1
This is a mass between the inner peripheral wall surfaces (inner diameter φA) of the first and the second 16 and when the gap η is reduced to some extent, the acoustic resistance ro cannot be ignored. When measured, the gap η was about 0.3
(Mm) or less, it was confirmed that no acoustic resonance occurred. In the vibration spaces V1 and V2 defined by the fixed-side case 11 and the connection-side case 16, different air stiffnesses So1 and So are provided.
It will take a value of 2.

A model of the vibration space V of the acceleration sensor 10 can be represented by an equivalent circuit shown in FIG. 5. From this equivalent circuit, it seems that acoustic resonance occurs at two frequencies. Was confirmed. Although the reason for this is not clear, the calculated value roughly coincides with the case where the air stiffness So1 and So2 are connected in parallel.

However, from the above equation of the frequency [fh] of the acoustic resonance, the control based on the area s of the pore H and the length da is determined from the dimensions of the vibrating body 19 and the inner diameter φA of the inner peripheral wall surfaces of the cases 11 and 16. Therefore, it can be said that it is determined by the desired resonance frequency [fo].
It is not suitable to obtain a desired resonance frequency [fo] by changing the outer diameter dimension of the vibrating body 19 by sharing the elements 1 and 16.

From this, the frequency [fh] of the acoustic resonance
Is easily controlled by the volume v of the air chamber R. It can be seen that the volume v needs to be reduced as much as possible in order to increase the frequency [fh] to outside the upper limit of the use band.

Therefore, it is optimal to make the distances L1 and L2 between the opposing surfaces between the fixed case 11 and the vibrating body 19 of the connection case 16 small as in the case of the standing wave countermeasure. In the same manner, it was found that the distances L1 and L2 between the facing surfaces need to be about 0.1 times or less the inner diameter φA of the inner peripheral wall surfaces of the cases 11 and 16.

In the case of acoustic resonance, the fixed case 1
1 and the parallel connection of the vibration spaces V1 and V2 defined by the connection-side case 16 and the vibrating body 19, it is not necessary to completely reduce the distances L1 and L2 between the opposing surfaces. , The distance L1 between the facing surfaces,
It is considered that one side of L2 may be positively reduced.
However, in this case, it was confirmed by actual measurement that one side of the distances L1 and L2 between the opposing surfaces needs to be reduced to about 0.05 times or less the inner diameter φA of the inner peripheral wall surfaces of the cases 11 and 16.

Therefore, when the cases 11 and 16 are commonly used to cope with a wide desired band only by changing mainly the outer diameter of the vibrating body 19, the upper limit resonance frequency [f
o], the vibration spaces V1 and V2 defined by the fixed-side case 11, the connection-side case 16, and the vibrating body 19 may be configured to be narrow so that acoustic resonance does not occur in the use band.

For example, the relatively small vibration spaces V1, V2
In the case of, as shown in the graph of FIG.
When the gap η is changed by changing the inner diameter φA of the cases 11 and 16 at 9 (the same outer diameter), the change in the resonance frequency [fh] with respect to the constant resonance frequency [fo]
It can be seen that when the gap η becomes large to some extent, the resonance frequency [fh] becomes saturated, which is equivalent to the resonance frequency [fh].
Can also be inferred from the changes in s and v in the above equation showing From this result, it can be seen that when there is a certain gap η, the resonance frequency [fh] is substantially determined by the outer diameter of the vibrating body 19.

When the gap η is changed by changing the outer diameter of the vibrating body 19 at the same inner diameter φA of the cases 11 and 16, as shown in a similar graph of FIG. 7, the resonance frequency [fo ] And the resonance frequency [fh] change linearly with different gradients, so that the vibration spaces V1, V
2 is set to be small and the resonance frequency [fh] is set higher than the resonance frequency [fo].

As described above, in the present embodiment, the vibration plate 12 and the piezoelectric element 13 are provided with the distance L between the opposing surfaces of the vibration spaces V1 and V2 defined between the bottom surfaces of the cases 11 and 16.
1, L2 is the inner diameter φ of the cases 11, 16 in the plane direction.
By setting it to 0.1 times or less of A, it is possible to prevent generation of an acoustic standing wave in the vibration space V, and by reducing the vibration space V,
The acoustic resonance frequency [fh] can be configured to be outside the upper limit of the use band. Therefore, the generation of spurious due to the anti-resonance dip, which was difficult to prevent by the dimension setting of the conventional technology, can be prevented by a simple configuration that can be manufactured at low cost. Further, even if the cases 11 and 16 that define the vibration space V are shared, the occurrence of spurious is prevented only by changing the outer diameter of the vibration plate 12 and the piezoelectric element 13 housed in the vibration space V. In particular, a large effect can be obtained when the vicinity of the resonance frequency fo is used.

Next, FIG. 8 is a view showing a second embodiment of the acceleration sensor according to the present invention. In addition, in this embodiment, since it is comprised similarly to the above-mentioned embodiment, the same code | symbol is attached | subjected to the same structure, and a characteristic part is demonstrated.

In FIG. 8, an acceleration sensor 20 includes a diaphragm 12 and a piezoelectric element 13, and replaces the fixed case 11, the connection case 16, and the O-ring 18 in the above embodiment with a fixed case. 21, metal base 2
2, a connector 26, and an O-ring 28, and a piezoelectric element 1 having a detection electrode 14 formed on a diaphragm 12 as in the prior art shown in FIG.
3 and the vibration of the detection target such as the engine
The piezoelectric element is taken out as piezoelectric [V] generated by stress strain applied to the piezoelectric element 13 via the second element 2, and the applied acceleration is detected.

The fixed case 21 is, as in the prior art,
A pillar provided at the center of the bottom surface is made of a metal material in a cylindrical frame shape deeper than the fixed side case 11 in the above-described embodiment, and a screw provided on a lower surface of the detection target such as an engine. A male screw 21b screwed into the hole and fixed is provided. The metal base 22 includes a support column 22 a that is welded to the diaphragm 12 on the opposite side of the piezoelectric element 13.
Is formed in a disk shape having substantially the same diameter as the fixed side case 21 erected at the center.
The connection pin 17 penetrating through the center of the a and the disk portion 26b is formed of a resin material so as to be electrically insulated from the metal base 22 or the like. This acceleration sensor 20
The metal base 22 and the connector 26 constitute a connection side case. The metal base 22 is welded on the open end face 21 c of the fixed side case 21, and the connector 2
6 and press the upper surface of the corner portion of the connector 26 by caulking the extension portion 21d of the outer edge of the open end, so that the diaphragm 12
And a vibration space V in which the piezoelectric element 13 is accommodated.
The O-ring 28 is sandwiched between the inner surface of the open end extension 21 d of the fixed case 21 and the outer surface of the metal base 22 to ensure waterproofness.

On the other hand, the diaphragm 12 and the piezoelectric element 13
The connection disk 25 is conductively fixed to the connection pin 17 of the connector 26 and the detection electrode 14 of the piezoelectric element 13 which are formed in a donut shape and pass through the support 22a of the metal base 22 passing through the center thereof by the solder 25a. By
The support 22a is allowed to vibrate.

In the acceleration sensor 20, since the connection disk 25 protrudes from the upper surface of the piezoelectric element 13 toward the bottom surface of the fixed case 21, the vibration plate 12 and the vibration body 19 of the piezoelectric element 13 in the vibration space V In order to set the distances L1 and L2 between the facing surfaces in the same manner as in the above-described embodiment,
A recess 21 e is formed in the center of the bottom surface of the fixed case 21.

Therefore, in this acceleration sensor 20,
In the vibration space V in which the vibration plate 12 and the piezoelectric element 13 are accommodated so as to vibrate, a vibration space V1 is defined between the metal base 22 and the vibration body 19, and the vibration space V between the fixed case 11 and the vibration body 19 is formed. A vibration space V1 is defined therebetween, and the distances L1 and L2 between the opposing surfaces are set to be equal to or less than 0.1 times the inner diameter φA of the inner peripheral wall surface of the fixed case 21.

That is, even with this acceleration sensor 20,
The dimensions may be designed in the same manner as the acceleration sensor 10 of the above-described embodiment, and the vibration space V, which is the vibration direction of the vibration plate 12 and the piezoelectric element 13, is set to be thin with the L direction narrowed.
The generation of standing waves in the L direction and the inner diameter φA direction can be effectively prevented.
And the connector 26 can be shared.

As described above, in the present embodiment, the functions and effects of the above-described embodiment can be similarly obtained.

In the embodiment described above, the vibrating body 19
The case where the plate thickness D is relatively small will be described, but the present invention can be applied to a case where the plate thickness D is set to be large depending on the resonance frequency [fo]. Further, the diaphragm 12 of the vibrating body 19
When there is a large difference between the outer diameter of the piezoelectric element 13 and the outer diameter of the piezoelectric element 13, it is difficult to determine the reference of the distances L1 and L2 between the opposing surfaces. It is considered that it should be determined in consideration of
A1 and φA2 may be similarly considered.

[0058]

As described above, according to the present invention, the diaphragm can be accommodated in the vibration space in the case in which the distance between the opposed surfaces is set to 0.1 times or less with respect to the interval in the plane direction. By simply designing the outer shape of the piezoelectric element, it is possible to prevent acoustic standing waves inside the case and reduce the vibration space so that the acoustic resonance frequency is outside the upper limit of the operating band. The generation of spurious due to the resonance dip can be reduced. Therefore, a common case can be used, and an acceleration sensor having high performance at low cost 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 the entire configuration thereof.

FIG. 2 is a cross-sectional model diagram for explaining generation of the acoustic standing wave.

FIG. 3 is a conceptual cross-sectional view illustrating generation of the acoustic resonance.

FIG. 4 is a cross-sectional model diagram illustrating the generation of the acoustic resonance.

FIG. 5 is a schematic equivalent circuit diagram in the model of FIG. 4;

FIG. 6 is a graph showing a change in frequency when the vibrating body is fixed.

FIG. 7 is a graph showing a change in frequency when the inner diameter is fixed.

FIG. 8 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. 9 is a longitudinal sectional view showing the prior art.

FIG. 10 is a perspective view showing the vibrating body.

FIG. 11 is a longitudinal sectional view showing a conventional technique different from that of FIG. 9;

FIG. 12 is a graph showing an example of the frequency characteristic.

FIG. 13 is a circuit diagram showing an example of its use.

FIG. 14 is a graph showing characteristics near the resonance frequency fo.

FIG. 15 is a graph showing characteristics near a resonance frequency fo for explaining the problem.

[Explanation of symbols]

 10, 20 Acceleration sensor 11, 21 Fixed side case 11a, 22a Column 11c Cylindrical end 12 Vibration plate 13 Piezoelectric element 14 Detection electrode 16 Connection side case 17 Connection pin 19 Vibration body 21c Open end face 22 Metal base 26 Connector φA, φA1 , ΦA2 Inner diameter L1, L2 Distance between opposing surfaces V, V1, V2 Vibration space

Claims (3)

[Claims] An acceleration for fixing a piezoelectric element formed in a flat plate shape to a vibration plate and detecting the acceleration by a voltage generated in the piezoelectric element due to vibration deformation of the vibration plate according to the applied acceleration. A sensor, wherein the spatial distance in the vibration direction of the piezoelectric element and the diaphragm is set to be 0.1 times or less the spatial distance in the planar direction of the piezoelectric element and the diaphragm, An acceleration sensor including a piezoelectric element and the vibration plate. 2. The vibration plate is formed in a disk shape and the piezoelectric element is formed in a donut shape, and a central portion of the vibration plate on which the piezoelectric element is fixed is erected on a fixed side case of the case. A connection terminal electrically connected to the electrode of the piezoelectric element is provided on the connection side case of the case, and an end of the fixed side case and the end of the connection side case are fitted. According to the piezoelectric element, the distance between the opposing surfaces of the fixed side case with respect to the diaphragm and the distance between the opposing surfaces of the connection side case with respect to the piezoelectric element are set to be 0.1 times or less the inner diameter of the case. The acceleration sensor according to claim 1, wherein a vibration space of the diaphragm is defined. 3. A connection terminal for electrically connecting a central portion of the diaphragm on which the piezoelectric element is fixed to an electrode of the piezoelectric element, wherein the diaphragm and the piezoelectric element are formed in a donut shape. Arranged and connected to an external connector, the case is supported by uprights erected on a connection side case of the case, and the fixed side case and the end of the connection side case are fitted to each other, whereby the piezoelectric of the fixed side case is fitted. The vibration space of the piezoelectric element and the vibration plate is set such that the distance between the opposing surfaces with respect to the element and the distance between the opposing surfaces of the connection side case with respect to the vibration plate are set to be 0.1 times or less the inner diameter of the case. The acceleration sensor according to claim 1, wherein: