JP2002116221A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor that is suited for automation with a simple structure, and has high performance with a low price. SOLUTION: The sensor comprises a case 11 of a fixed side that encloses a vibrating plate 12 where a piezoelectric element 13 is fixed, which is welded at a column 11a on the center of a bottom plane, in a demarcated space, a metal base 15 that is welded to a cylindrical end part 11c of the case 11, and a connector 16, which is fixed by an extension part 11d of the outer edge of the open end of the case 11 that is caulked, covers with the base 15 with overlapping to the base 15. A connecting pin 17a of the connector 16 is grounded through the case 11 with face contacting a copper foil pattern 19a of a printed substrate 19 which is held between the connector 16 and the pin 17a to the base 15. On the other hand, a connecting pin 17b is connected by continuity through a contacting terminal 20 that is pressure contacted to a detecting electrode 14 of the element 13 by soldering to the substrate 19 which faces the inside from an opening 15a of the base 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an acceleration sensor, and more particularly, to an acceleration sensor for converting vibration into an electric signal and detecting an applied acceleration.

[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.

As a piezoelectric acceleration sensor of this type, there is, for example, a fixed center type sensor that fixes the vicinity of the center of a vibrating body (first conventional example) as shown in FIG. In this acceleration sensor 100, a support 101a is integrally erected at the center of the bottom surface of a metal fixed side case 101 formed in a frame shape, and as shown in FIG. In addition to supporting the metal vibration plate 102 formed on the supporting plate 101a by welding, the piezoelectric element 103 formed in a donut shape is coaxially bonded to the upper surface of the vibration plate 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 back surfaces.
The diaphragm 102 is formed in a bowl-like shape to be connected to an external connector via a wire 105 connected to the other detection electrode 104 by a solder 105a such as wire bonding. Connection pin 10 provided on connection side case 106 made of resin
7 is connected. The fixed-side case 101 and the connection-side case 106 are mutually open ends 101c and 106.
By fitting and caulking c, the diaphragm 102 and the piezoelectric element 103 are housed in the defined vibration space,
An O-ring 108 is sandwiched between the open ends 101c and 106c to assemble the vibration space into a waterproof structure.

FIG. 5 shows a piezoelectric acceleration sensor of this type (second conventional example).
In this acceleration sensor 110, a metal base 112 formed in a disc shape is welded to an open end portion 111c of a metal fixed side case 111 formed in a frame shape to cover the same, and an external connector is connected thereto. By overlapping and caulking the disc-shaped connector 116 provided with the connection pin 107, a vibration space for accommodating the vibration plate 102 and the piezoelectric element 103 is defined, and the piezoelectric element 103 is fixed. The provided vibration plate 102 is supported by a supporting column 112 a erected on a metal base 112 without providing a supporting column on the fixed side case 111.
Specifically, both the diaphragm 102 and the piezoelectric element 103 are formed in a donut shape, and
The metal base 112 while maintaining insulation by the resin material of
The connection disk 107 is fixedly connected to the connection pin 107 and the detection electrode 104 of the piezoelectric element 103 by the solder 115a and is electrically connected to the connection pin 107 and the detection electrode 104 of the piezoelectric element 103 so that the connection pin 107 is vibrated. Has become. In the acceleration sensor 110, the vibration space is assembled in a waterproof structure by sandwiching an O-ring 118 between the inner peripheral surface of the fixed side case 111 and the outer peripheral surface of the metal base 112. The connection disk 115 is a diaphragm 1
It is preferable to reduce the stiffness (stiffness) as much 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 the wire 105 is connected to the detection electrode 104. Can be electrically connected to each other.

[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 a detection target such as an engine into which the screw 01b or 111b is screwed is applied, a voltage generated in the piezoelectric element 103 according to the vibration of the diaphragm 102 is applied to the fixed case 101,
111 and the metal base 112 as ground,
4 through a connection pin 107, and the acceleration can be detected.

More specifically, in the piezoelectric element 103, a stress distortion occurs in the capacitance C between the detection electrodes 104 when the vibration plate 102 vibrates and deforms due to external vibration (acceleration). Since the charge Q is generated, a voltage V represented by the following equation can be taken out as the applied acceleration, and the vibration amplitude becomes maximum near the outer peripheral end of the vibration plate 102. Is the expansion or contraction, and it is considered that the vicinity of the fulcrum on the inner circumference shows the maximum value. V = Q / C

As shown in FIG. 6, the frequency characteristic with respect to the vibration at a constant acceleration has a high Q near the resonance point fo.
On the other hand, since the frequency characteristics become flat in the middle and low frequency regions, the acceleration sensor 100,
In general, a non-resonant type 110 using a flat portion of this frequency characteristic or a resonant type using a vibration output near a resonance frequency fo is selected according to a desired frequency range according to a purpose of use. It is designed to be used as
Practically, the upper limit of the used band is up to near the resonance point fo.

The resonance frequency fo can be generally expressed by the following equation in the case of a fixed center circular diaphragm 102: fo = α (t / R ² ) × [E / {ρ (1- σ ² )}] ^1/2 α: 0.172 (coefficient) t: plate thickness R: radius E: Young's modulus ρ: density σ: Poisson's ratio For example, when Ni steel is used as the material of the diaphragm 102, , The above parameters are as follows: t = 0.4 (mm) R = 7 (mm), E = 2 × 10 ¹¹ (N / m ² ) ρ = 7.8 × 10 ³ (k
g / m ³ ) σ = 0.28 The resonance frequency fo is fo = 7.41 (kHz).
The resonance frequency fo of the vibrating body mainly depends on the diaphragm 1
In practice, the resonance frequency fo is slightly affected by the case and the like because the value is slightly different due to the addition of the piezoelectric element 103 to the vibration plate 102. It will be determined by taking into account the overall average.

From the above, in order to obtain a desired resonance frequency fo, it is general that the thickness t and the radius R are appropriately selected and designed in the above equation. According to the results confirmed experimentally, when the outer diameter R of the diaphragm 102 is changed with the same thickness t, about 1-2% /
It has been found that the resonance frequency fo can be changed at about 0.1 mm. In terms of sensitivity, it has been experimentally found that the acceleration sensor 110 shown in FIG. 5 can achieve higher sensitivity than the acceleration sensor 100 shown in FIG. It is considered that the diaphragm 102 is configured in
Since the metal base 112 is not a completely rigid body and vibrates slightly but similarly to the diaphragm 102 due to acceleration,
This is probably because the vibration of the vibration plate 102 functions like a transformer and is amplified.

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 diaphragm 102 by the piezoelectric effect of the piezoelectric element 103, and the self-diagnosis or detection level of the sensor function based on the potential of the detection electrode caused by the vibration and the presence or absence of a failure. Some of them can be calibrated. Further, in this prior art, a pillar 10 standing upright in the center is used.
The diaphragm 102 is supported by 1a 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, the detection electrode 104 of the piezoelectric element 103 and the connection pin 107
And a printed circuit board on which electronic components such as an electric impedance converter, an amplifier, and a correction circuit are provided.
There is also a one-terminal type in which only the connection pin 107 is used for grounding in the fixed-side cases 101 and 111, and a two-terminal type in which the ground is drawn out to the output terminal. is there.

FIG. 7 shows a non-resonant piezoelectric acceleration sensor (third conventional example). The acceleration sensor 120 is of a compression type using a general piezoelectric element and a weight as a non-resonance type, and is formed in a substantially disk shape at an open end 121c of a metal fixed side case 121 formed in a frame shape. Connector 12 provided with connection pins 107 to be connected to an external connector.
6, the weight 122 and the piezoelectric element 123
As shown in FIG. 8, the piezoelectric element 123 formed in a donut shape and having the detection electrodes 124 formed on the front and back surfaces is formed into a cylindrical shape as shown in FIG. A weight 122 made of a material is placed on the fixed case 121, and a fixing screw 125 is screwed into a screw tap 121d drilled in the center of the bottom surface of the fixed side case 121 to be fixedly mounted.

In the acceleration sensor 120, the detection electrode 124 on the back surface of the piezoelectric element 123 is electrically connected to the fixed case 121, while the detection electrode 124 on the front surface is connected to the weight 12.
2 and L fixed by a fixing screw 125 so as to make conductive contact with the weight 122.
The connection pin 107 of the connector 126 is connected to the U-shaped connection terminal 127 via a wire 129 connected by solder 129a. Note that this acceleration sensor 1
20, the insulating tube 125 a and the insulating spacer 125 b are interposed between the weight 122 and the piezoelectric element 123 and the fixing screw 125, so that the fixed case 1
Short circuit between the connection pin 21 and the connection pin 107 is prevented. The open end 12 of the fixed case 121
1c and the outer periphery of the connector 126 between the O-ring 128
The space for accommodating the piezoelectric element 123 and the like is assembled in a waterproof structure.

For this reason, the acceleration sensor 120 uses the fixed-side case 121 as the ground of the electric circuit and the piezoelectric element 1.
It is constructed so that the output of 23 can be taken out via the weight 122 and the connection terminal 107, and vibration of a detection target such as an engine into which a male screw 121b provided on the lower surface side of the fixed side case 121 is screwed is applied. Sometimes, a load (compression force) corresponding to the vibration is applied to the piezoelectric element 123 from the weight 122, so that the piezoelectric element 12
3 is taken out through the connection pin 107 and its acceleration can be detected. Note that the acceleration sensor 120 has a vibration (constant acceleration)
6, the frequency characteristics as shown in FIG. 6 are shown as in the case of the acceleration sensors 100 and 110 described above. However, depending on the assembly conditions, the resonance point fo may not appear so as to be recognizable. Piezoelectric element 123 and weight 12
It is considered that when the center of No. 2 is pressed by the fixing screw 125, it vibrates in a high frequency region (has a resonance point) due to a slight weak pressing force near the outer peripheral portion. For this reason, in order to increase the resonance point fo, considerably high precision and contrivance are required for the torque force of the fixing screw 125 and the processing of the contact surface.

In the non-resonant type acceleration sensor 120, the resonance frequency fo is set to 20 kHz.
The sensitivity Vo of the flat portion can be utilized by setting the acceleration sensor 120 out of the use band above the vicinity.
The basic operating principle is that when the acceleration G is applied to the weight 122 having the mass m, the stress strain F is applied to the piezoelectric element 123 and the output voltage Vo is obtained as shown by the following equation. F = m × G Vo ≒ α × F × t / S α: proportional coefficient such as piezoelectric constant S: electrode area of detection electrode 124 of piezoelectric element 123 t: plate thickness of piezoelectric element 123

From the above, in order to increase the sensitivity of the acceleration sensor 120, the weight is increased, and the t / S of the piezoelectric element 123 is increased (however, the capacity is limited to some extent from a desired capacity and the like).

Although it is possible to take measures such as the above, it can be seen that the size is inevitably increased (especially in the height direction) in order to increase the sensitivity.

In the acceleration sensor 120, the connection pins 107 and the weights 122 are formed by using gold-plated contact terminals or the like without using lead wires such as the wires 129.
The (connecting terminal 127) may be conductively connected, and is not limited to a one-terminal type in which the fixed side case 121 is grounded and only the connecting pin 107 is used, but may be a two-terminal type using two output terminals. A printed circuit board may be built in which an impedance conversion circuit, an amplifier circuit, and a circuit for connecting a disconnection detection resistor in parallel with the piezoelectric element 123 may be incorporated. For example, the electrode 124 of the piezoelectric element 123 may be divided and detected. And a self-diagnosis type having a self-diagnosis function. Further, the fixed side case may be made of a resin material or the like without being made of metal.

[0018]

However, in the first conventional example, the connection pin 107 of the connector 106 and the detection electrode 104 is required to take out the output from the piezoelectric element 103.
Must be connected by soldering the wire 105 or the like by wire bonding or the like, which makes it difficult to automate the assembly and is not suitable for cost reduction.

Further, in the second conventional example, it is possible to automate assembly by eliminating the need for wire connection,
Although the sensitivity can be made higher than that of the first conventional example, in particular,
In a high-frequency region exceeding 0 kHz, it is considered that the vibration is not transmitted as acceleration but inside the housing such as the case 111 as vibration transmission, so that it is easily affected by phase characteristics and the like when transmitting inside the housing. Further, since the metal base 112 is not a completely rigid body but caulks and fixes the open end 111c of the fixed side case 111 via the connector 116, the metal base 112 is loosened with the resin-made connector 116 at a high temperature. It is considered that the temperature characteristics are degraded due to the influence of the vibration of the magnetic field. From this, the connection pin 107
There is a problem that vibration noise via an external connector connected to the connector 116 is transmitted to the vibration plate 102 via the metal base 112 and may become large vibration noise which hinders the accuracy of acceleration detection.

Further, in the third embodiment, since the number of parts is large and the structure is complicated, it is not suitable for automation. Further, as described above, the piezoelectric element 123 and the weight 122 are fixed. Fixed side case 121
Since it is necessary to closely contact the bottom of the
The torque must be strictly controlled, and high surface processing accuracy and the like are required. This is not suitable for cost reduction, and the external shape is particularly large in the height direction. Furthermore, there is a possibility that the fixing screw 127 and the like may be loosened, and it is difficult to obtain high reliability.

The present invention has been made to solve the above-mentioned conventional problems. As a characteristic method, a non-resonant type using a flat characteristic portion in a frequency characteristic has a simple structure, is suitable for automation, and has a low cost. It is an object of the present invention to provide an excellent acceleration sensor having high performance at a high speed.

[0022]

According to the acceleration sensor of the present invention, a piezoelectric element is fixed to a vibration plate, and an acceleration applied to the vibration plate by a voltage generated in the piezoelectric element due to vibration deformation of the vibration plate. An acceleration sensor for detecting the vibration, wherein a case for accommodating the vibration plate on which the piezoelectric element is fixed is formed in a frame shape so as to define a space for accommodating the vibration plate and the piezoelectric element so as to vibrate. A case member that supports the vibrating plate and the piezoelectric element so as to be able to vibrate on a column formed on the bottom surface and a connection terminal electrically connected to an electrode of the piezoelectric element and connected to an external connector is provided. A closing member that is disposed and closes a receiving opening of the case member, and the closing member holds a printed circuit board that connects the connection terminal and the electrode of the piezoelectric element to conduct electricity. It has formed.

According to this configuration, the weight is placed on the piezoelectric element, so that the number of parts increases and automation is difficult, and the assembly accuracy is strict and the size is increased (third conventional example). The vibration plate and the piezoelectric element are supported on the side of the member having the shape of the lid, so that a type (second conventional example) inferior in temperature characteristics or the like is adopted. (A first conventional example) is adopted in which the support is provided on the bottom of a case member formed in a frame shape so as to define a frame so as to be able to vibrate, but the electrodes of the piezoelectric element are formed by wire bonding or the like. Instead, it is conductively connected to the connection terminal connected to the external connector via the printed circuit board, so that a structure that can easily automate assembly can be achieved, and low-cost and high-performance acceleration It is possible to provide a sensor.

In the acceleration sensor according to the present invention, the case member and the vibration plate are formed of a conductive material and one electrode of the piezoelectric element is fixed in a conductive state, while the closing member is formed of the case member. A base member made of a conductive material that is welded to a frame-shaped end portion of the base member and that closes the receiving port; and the connection terminal is disposed outside the base member so that the external connector can be connected to the base member. A connector member made of an insulating material fixed to the frame-shaped end of the case member, wherein the closing member secures an insulating state and connects the connection terminal of the connector member to the other electrode of the piezoelectric element. With this configuration, the closing member is not only integrally formed of a resin material or the like, but also connected to the base member and the connector as in the second conventional example described above. It can be constituted by a member. In the connector member, two terminals for ground and output are provided as the connection terminals.
By having a configuration in which the connection terminal for ground is connected to the printed circuit board and a pattern for contacting and connecting to the base member is formed, a two-terminal type can be obtained at low cost.

Further, the acceleration sensor of the present invention
The printed circuit board has a configuration in which a contact terminal that is electrically connected to the connection terminal and that is in contact with an electrode of the piezoelectric element is provided, so that the piezoelectric element has a simple configuration that can be easily automated. In addition, since the printed circuit board has a configuration in which a signal processing circuit of an acceleration sensor is formed, a small-sized acceleration sensor having better performance can be obtained.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 and 2 are views showing an embodiment of the acceleration sensor according to the present invention.

First, the structure of the acceleration sensor will be described.
1 and 2, the acceleration sensor 10 includes a fixed-side case (case member) 11, a diaphragm 12, a piezoelectric element 13, a metal base (base member) 15, a connection connector (connector member) 16, , And an O-ring 18. Similar to the first and second prior art examples shown in FIGS. 3 and 5, the upper surface of the doughnut-shaped metal diaphragm 12 has substantially the same inner diameter. The piezoelectric element 13 formed by processing a piezoelectric element material such as ceramic into a donut shape and forming the detection electrodes 14 on the front and back surfaces is adhered by an adhesive or the like so as to be coaxial. Accordingly, for example, when a vibration of a detection target such as an engine is applied, electric charge Q is generated in the piezoelectric element 13 due to stress distortion applied through the diaphragm 12, and the capacitance C of the piezoelectric element 13 is increased.
A voltage V having a magnitude represented by the following equation generated according to
The applied acceleration can be detected. That is,
The acceleration sensor 10 has a basic structure similar to that of the first and second conventional examples and is constructed to have a configuration using a fixed center vibrator, and is basically a resonance type. By using the external configuration, the sensitivity Vo of the flat portion is used like a non-resonant type. V = Q / C

The fixed side case 11 is formed of a metal material in the shape of a bottomed cylindrical frame having a circular bottom surface formed at a depth capable of accommodating both the vibration plate 12 and the piezoelectric element 13. 2 Unlike the conventional example, similar to the first conventional example, a column 11a for supporting the diaphragm 12 and the piezoelectric element 13 is erected at the center of the bottom surface, and the lower surface thereof is used as a detection target such as an engine. A male screw 11b that is screwed into the provided screw hole and fixed is provided. The support 11a of the fixed side case 11, the diaphragm 12 and the hole at the center of the piezoelectric element 13 are formed for the purpose of determining the center at the time of assembling work. It is possible to do.

As in the first conventional example, the fixed side case 11 is fixed to a support 11a standing at the center of the bottom surface by welding the diaphragm 12 and the piezoelectric element 13, for example.
Similarly to the conventional example, a metal base 15 made of a metal disk having substantially the same diameter is fixed on the open end face 11c by full circumference welding (may be partially welded) 11e.
On the metal base 15, a connector portion 1 capable of connecting and fixing an external connector to a substantially equivalent disk-shaped disk portion 16a.
6b is a connector 1 made by integral molding of a resin material
6, the extension portion 11d of the outer edge of the open end is crimped, and the upper surface of the disk portion 16a is pressed down and fixed, thereby closing the cover of the storage opening for storing the vibration plate 12 and the piezoelectric element 13 (closed). ) A vibration space is defined. Therefore, the metal base 15 and the connector 16 can be fixed to the fixed side case 11 by an automatic machine, and the assembly can be easily automated. O-ring 18
Is sandwiched between the inner surface of the open end extension 11d of the fixed case 11 and the outer surface of the metal base 15 to ensure waterproofness of the vibration space in which the vibration plate 12 and the piezoelectric element 13 are housed. Note that the metal base 15 employs a configuration in which the fixed-side case 11 is reliably closed by welding. However, even if the metal base 15 is simply brought into surface contact with the open end face 11c and pressed by the connector 16 by caulking the extension 11d. It goes without saying that it is good.

Unlike the second conventional example, the metal base 15 is formed in a donut shape without providing a support for the vibration plate 12 and the piezoelectric element 13, and an opening (path) 15a is formed in the center. The fixed side case 11 and the metal base 15 are provided in the connector portion 16 b of the connector 16.
Connection pin (ground connection terminal) for ground connection via
Connection pin (output connection terminal) 1 for conducting connection between the external connector 17a and the detection electrode 14 of the piezoelectric element 13
7b. Therefore, in order to achieve non-resonance in a desired use band, the resonance point fo needs to be set high. On the other hand, by fixing the vibrator to the metal base 15 side, The resonance frequency of the vibrating body is not averaged by the low resonance frequency of the housing such as the metal base 11 and the metal base 15, so that it becomes impossible to raise the resonance point fo, and the desired use band can be easily obtained. Can be made non-resonant.

The metal base 15 and the connector 16
Can be positioned with respect to each other by inserting the positioning pins 15c into the positioning holes 16c and joining them at a plurality of locations.
The positioning pin 15c is inserted into the positioning hole 19c between the
The printed circuit board 19 having the copper foil patterns 19a formed on both sides (or one side) is positioned so as to face the inside (storage space) below the connector portion 16b and above the piezoelectric element 13 by the opening 15a. It is designed to hold the position. Therefore, the diaphragm 12 and the piezoelectric element 13
Together with the fixed side case 11 on which the metal base 1 is fixed.
5, the connector 16 and the printed circuit board 19 are integrated by positioning and fixing, so that they can be handled as one component.

The copper foil pattern 19 of the printed circuit board 19
a comes into surface contact with the metal base 15, and the connection pin 1 of the connector 16 in the opening 15 a of the metal base 15.
While a system is formed in which 7a is connected by solder 19a, a connection pin 17b is connected to the metal base 15 by solder 19a while facing the opening 15a while maintaining a non-contact state. A system is formed in which a contact terminal 20 for press-contacting the detection electrode 14 is soldered. Therefore, the piezoelectric V generated in the piezoelectric element 13 due to the vibration of the vibration plate 12 can be taken out to the outside via the contact terminals 20, the printed circuit board 19, and the connection pins 17b. The contact terminals 20
Is not limited to the pressure contact connection, but may adopt other various shapes and connection methods.
Needless to say, the configuration of the present embodiment is suitable for automation, although it is needless to say that the connection may be made to be conductive. The printed circuit board 19 may have a circuit configuration in which an impedance conversion circuit, an amplifier circuit, or a disconnection detection resistor r is connected to the copper foil pattern 19a by soldering so as to be in parallel with the piezoelectric element 13. Further, the present embodiment is a two-terminal type in which connection pins 17a and 17b are arranged on the connector 16 as connection terminals. However, in the case of a one-terminal type in which the grounding is not particularly provided, the metal base 15 and the printed board are used. 19
No connection is needed.

Next, the dimensional design of the acceleration sensor 10 will be described. First, in order to set the resonance frequency fo of the vibrating body composed of the vibration plate 12 and the piezoelectric element 13 high, the resonance frequency fo can be expressed by the following equation, as can be seen from the calculation equation of the resonance frequency fo described in the related art. In the case where the radius R of the vibrating body is the same, the thicker the plate thickness t, the higher the resonance point fo can be. fo ≒ α '× (t / R ² ) α': proportional coefficient

However, it is not necessarily the case that the plate thickness t is large, and the resonance point fo has a maximum point, and it has been experimentally confirmed that an appropriate relationship exists. In other words, since the resonance point fo must be high and the sensitivity Vo must be high, it has been found that the conditions for this are generally as follows. R1 / t1 = radius of diaphragm 12 / thickness t of diaphragm 12 ≒ about 3.3 R2 / R1 = radius of piezoelectric element 13 / radius of diaphragm 12 前後 about 0.5 t1 / t2 = of diaphragm 12 Thickness / thickness of piezoelectric element 13 前後 1

Here, the sensitivity Vo is expressed by the following equation, and it is understood that it is more advantageous that the radius R of the vibrator is larger, and the resonance point f
This is in conflict with the relationship of o. Vo ≒ α '× R ²

From the above, it is considered that the size of the vibrating body is considerably large and heavy under the above conditions. When the vibrating body is formed on the metal base 15 as in the second conventional example, It can be seen that the metal base 15 vibrates greatly and the average resonance frequency fo decreases, so that it is impossible to achieve non-resonance. For this reason, in consideration of an optimum structure for increasing the radius R1 of the diaphragm 12, in the configuration of the first conventional example, the connector serving as the lid of the fixed side case 11 is inevitably thick on the side surface because of the resin material. This is not the optimal configuration. On the other hand, in the present embodiment, since the peripheral edge of the diaphragm 12 faces the side surface of the metal fixed side case 11 that can be made thin in strength, the side surface of the fixed side case 11 is made thin. The acceleration sensor 10
The radius R1 of the diaphragm 12 can be maximized without increasing the overall size, which is an optimal structure.

As described above, in this embodiment, the vibrating body composed of the vibration plate 12 and the piezoelectric element 13 is supported by the support 11a standing on the bottom surface of the fixed side case 11, and the fixed side case 11 is Is closed by a lid with a metal base 15 and a connector that does not support the connector 16, while the connection pins 17a and 17b of the connector 16 are
The printed circuit board 19 is connected to the ground and the output via a printed circuit board 19 which is held between the metal base 15 and the opening 15a, and the printed circuit board 19 presses the contact terminal 20 to the detection electrode 14 of the piezoelectric element 13 by pressure. And the conductive connection is made, the detection electrode 14 of the piezoelectric element 13 is
There is no need to solder a wire to the
As with the type in which a weight is placed on top of 3, the number of parts increases, automation becomes difficult, assembly precision is strict, and the size is not increased. Unlike the type in which the vibration plate 12 and the piezoelectric element 13 are supported by 15, the temperature characteristics and the like do not decrease. Therefore, it is possible to provide a high-performance acceleration sensor 10 that can be easily assembled and manufactured at low cost.

In the present embodiment, a case in which the diaphragm 12 and the piezoelectric element 13 are housed in a closed type case will be described. However, the present invention is not limited to this. Although not described, the present invention can also be applied to a device that can also be configured as an acoustic transducer such as an ultrasonic wave by forming a ventilation hole or the like on the case side.

[0039]

As described above, according to the present invention, the support plate is erected on the bottom surface of the case member formed in a frame shape so as to define the receiving space together with the closing member, and the diaphragm and the piezoelectric element are formed. Vibration is supported, and the electrodes of the piezoelectric element are conductively connected to the connection terminals connected to the external connector via the printed circuit board, so that the assembly is simple and the number of parts is small, so that assembly can be relatively easily automated. It is possible to provide a low-cost, high-performance, and excellent acceleration sensor that can be used.

[Brief description of the drawings]

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

FIG. 2 is an exploded perspective view thereof.

FIG. 3 is a longitudinal sectional view showing the first prior art.

FIG. 4 is a perspective view showing a main part thereof.

FIG. 5 is a longitudinal sectional view showing the second prior art.

FIG. 6 is a graph showing its frequency characteristics.

FIG. 7 is a longitudinal sectional view showing the third conventional technique.

FIG. 8 is a perspective view showing the main part.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Acceleration sensor 11 Fixed side case 11a Support column 12 Vibration plate 13 Piezoelectric element 14 Detection electrode 15 Metal base 15a Opening 16 Connector 17a Connection pin 17b Connection pin 18 O-ring 19 Printed circuit board 20 Contact terminal

Claims (5)

[Claims] 1. An acceleration sensor, wherein a piezoelectric element is fixed to a diaphragm, and the acceleration sensor detects acceleration applied to the diaphragm by a voltage generated in the piezoelectric element due to vibration deformation of the diaphragm. A case for housing the vibration plate on which the element is fixed is formed in a frame shape so as to define a space for accommodating the vibration plate and the piezoelectric element so as to be able to vibrate, and a column standing on the bottom surface. A case member for vibratingly supporting the vibration plate and the piezoelectric element, a connection terminal electrically connected to an electrode of the piezoelectric element and connected to an external connector, and housing the case member An acceleration sensor, comprising: a closing member that closes a mouth, wherein the closing member holds a printed circuit board that connects the connection terminal and the electrode of the piezoelectric element to conduct electricity. 2. The method according to claim 1, wherein the case member and the vibration plate are formed of a conductive material to fix one electrode of the piezoelectric element in a conductive state, and the closing member is provided at a frame-shaped end of the case member. A base member made of a conductive material that is welded to close the receiving port, and a frame-shaped end of the case member that is provided outside the base member and is provided with the connection terminal so that the external connector can be connected to the base member; A connector member made of an insulating material fixed to the portion, wherein the closing member forms a path for conducting the connection terminal of the connector member to the other electrode of the piezoelectric element while ensuring an insulating state. The acceleration sensor according to claim 1, wherein: 3. The case member and the diaphragm are formed of a conductive material to fix one electrode of the piezoelectric element in a conductive state, and the closing member serves as the connection terminal for grounding and output. A connector member made of an insulating material to which the two terminals are disposed and to which the external connector is connected; and a connector member fixedly connected to the case member in a conductive state to close the receiving port and secure the insulating state. A base member made of a conductive material that forms a path for conducting two terminals provided as the connection terminals of the connector member to the respective electrodes of the piezoelectric element. The acceleration sensor according to claim 1, wherein a pattern for connecting a connection terminal and contacting and connecting to the base member is formed. 4. The printed circuit board according to claim 1, further comprising a contact terminal electrically connected to the connection terminal and connected to an electrode of the piezoelectric element. Acceleration sensor as described. 5. The acceleration sensor according to claim 1, wherein a signal processing circuit of the acceleration sensor is formed on the printed circuit board.