JPH0763782A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To provide a highly reliable acceleration sensor which has a simple structure, can be easily assembled, and can be manufactured at a low cost. CONSTITUTION:An acceleration sensor is provided with a metallic elastic plate 2, a pair of piezoelectric elements 3a and 3b which are joined to both end faces of the plate 2 in a state where their polarizing axis directions are counterposed to each other, and a through bolt 6 which passes through the plate 2 and elements 3a and 3b in an insulating state. Since the sensor is constituted in such a way, the structure of the sensor is simplified and the sensor can be easily assembled. Therefore, the manufacturing cost of the sensor can be reduced and the sensitivity of the sensor can be easily adjusted. In addition, the reliability of the sensor is improved and the sensor is not affected by temperature changes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
More specifically, the present invention relates to an acceleration sensor suitable for an airbag that is attached to a driver's seat of a vehicle.

[0002]

2. Description of the Related Art As this type of acceleration sensor, both a mechanical acceleration sensor and an electric acceleration sensor have been put into practical use.

The mechanical acceleration sensor is called a roller mite type or a spring mass type and is configured as a mechanical switch utilizing the elasticity of a leaf spring or a metal plate, and the elasticity of the leaf spring or the like changes with time. Therefore, there is a problem that sensitivity adjustment is difficult.

On the other hand, FIG. 9 shows an electric acceleration sensor.
As shown in FIG.
2 is attached, and the lead wire 3 is attached to the piezo elements 31 and 32.
There is known one in which mechanical shocks acting on the piezo elements 31, 32 are connected to each other by converting them into electric signals, and the electric signals are taken out by the lead wires 33, 34 (Japanese Patent Laid-Open No. Sho 63-63). -195573). In addition, in FIG.
Is a fixing member.

However, in the case of this electric acceleration sensor, there is a problem that the piezoelectric elements 31 and 32 are separated from the metal plate 30 and destroyed due to the mechanical shock acting on the piezoelectric elements 31 and 32. For this reason, it has been attempted to store the metal plate 30 and the piezo elements 31, 32 in a container (not shown) and add silicon oil to prevent mechanical resonance. However, in this case, the structure becomes complicated and the assembly is troublesome. However, there is a problem that the manufacturing cost also rises.

In addition, as an electric acceleration sensor, there is also known one which utilizes the piezoresistive effect of a piezoresistive element incorporated in a semiconductor (silicon chip), but in this case, there are many connection points and the temperature is high. There is a problem that the drift is caused by the change and the reliability is poor.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a simplified structure, facilitates assembly, reduces manufacturing cost, and facilitates sensitivity adjustment. The object of the present invention is to provide an acceleration sensor that can improve reliability.

[0008]

An acceleration sensor according to the present invention includes a metal elastic plate, a pair of piezoelectric elements bonded to both surfaces of the metal elastic plate in a state where polarization axis directions face each other, the metal elastic plate and the pair. Of the piezoelectric element of FIG.

The metal elastic plate and the pair of piezoelectric elements are attached to an object to be attached using the through bolts.

[0010]

According to the acceleration sensor having the above-described structure, the pair of piezoelectric elements are bonded to both surfaces of the metal elastic plate with the polarization axis directions facing each other, and the metal elastic plate and the pair of piezoelectric elements are penetrated in an insulated state. Since the structure can be configured by simply disposing the bolts through, the structure is simplified, the assembling can be facilitated, the manufacturing cost can be reduced, and the sensitivity can be easily adjusted.

Further, the acceleration can be detected by utilizing the difference in the polarization axis direction of the pair of piezoelectric elements, and since no semiconductor or the like is used, the number of connection points is small and the reliability can be improved.
It is possible to reduce drift due to temperature change and temperature drift at no load due to thermal stress.

Furthermore, since the metal elastic plate and the pair of piezoelectric elements are attached to the object to be attached by using the through bolts, it is not necessary to prepare a separate component for attachment, and the attachment to the object to be attached is performed. Is extremely simple.

[0013]

EXAMPLES Examples of the present invention will be described in detail below.

The acceleration sensor 1 shown in FIGS. 1 and 2 has a metal elastic plate 2 having a circular hole at one end and a mass body 8 fixed at the other end, and both surfaces of the metal elastic plate 2 are polarized in advance. A pair of piezoelectric elements 3a, 3b joined in a state in which the processed polarization axes are opposed to each other and the circular holes provided in each are concentric with the circular holes of the metal elastic plate 2 to form the through holes 4.
A hollow through bolt 6 penetrating the through hole 4 formed by the metal elastic plate 2 and the pair of piezoelectric elements 3a, 3b in a state of being insulated by an insulating sleeve 5, and a lead wire mounting protrusion. Metal terminal plates 7a and 7b that are provided with pieces 7c and 7d and are fitted into the insulating sleeve 5 and are in contact with the pair of piezoelectric elements 3a and 3b, respectively, and the metal terminal plate 7
a pair of insulating plates 9a and 9b fitted to the through bolts 6 from the outside of a and 7b, and a pair of washers 10a and 1a fitted to the through bolts 6 from the outside of the insulating plates 9a and 9b, respectively.
0b and a pair of nuts 11a and 11b screwed into the through bolt 6 from the outside of the washers 10a and 10b, respectively.

Here, the principle of the acceleration sensor 1 will be described with reference to FIGS.

As shown in FIG. 3, two plate-shaped piezoelectric elements 23, which are pre-polarized, are prepared, and each piezoelectric element 23 is formed as shown in FIG.
As shown in, the metal elastic plate 22 having the mass body 24 fixed to the ends is bonded to both surfaces in a state where the polarization axis directions face each other.

Then, as shown in FIG. 5, each piezoelectric element 23
The output electrodes 25, 26 are attached to the
Lead wires 27 and 28 are connected to 26.

When a large impact (acceleration) is applied to the mass body 24, the metal elastic plate 2 is passed through the mass body 24.
2 is curved as shown in FIG. 5, whereby an extension force acts on one piezoelectric element 23 and a compression force acts on the other piezoelectric element 23, and charges of opposite polarities are applied to both piezoelectric elements. Occurs, and a potential difference V is generated between the ends of the lead wires 27 and 28 according to the impact acting on the mass body 24.

The acceleration sensor 1 of this embodiment is based on such a principle.

According to the acceleration sensor 1 having the above structure,
A pair of piezoelectric elements 3a and 3b are joined to both surfaces of the metal elastic plate 2 so that their polarization axis directions face each other, and the through bolt 6 is insulated from the metal elastic plate 2 and the pair of piezoelectric elements 3a and 3b.
Since it can be configured by arranging through, it is possible to simplify the structure, facilitate the assembly and reduce the manufacturing cost,
In addition, sensitivity adjustment becomes easy.

Further, since the acceleration can be detected by utilizing the difference in the polarization axis directions of the pair of piezoelectric elements 3a and 3b, since no semiconductor or the like is used, the drift due to the temperature change and the temperature drift at the time of no load due to the thermal stress are caused. Can be reduced.

Further, according to the acceleration sensor 1, since the potential difference V depending on the impact generated on the piezoelectric elements 3a and 3b can be taken out from the metal terminal plates 7a and 7b, soldering is not required, and the number of connection points is small and the reliability is low. Can be improved.

Next, an example of mounting the acceleration sensor 1 on a mounting object will be described with reference to FIGS. 6 to 8.

As shown in FIGS. 6 and 7, the through bolt 6 of the acceleration sensor 1 is inserted into the casing 15 having a rectangular parallelepiped shape.
Are assembled so that both ends thereof are exposed to the outside, and lead wires 16a and 16b are connected to the metal terminal plates 7a and 7b, respectively, and these lead wires 16a and 16b are connected to the casing 15.
To the side of.

Then, as shown in FIG. 8, for example, one end portion of the through bolt 6 exposed from the casing 15 is screwed into a screw portion provided on a mounting object 18 such as a vehicle body of an automobile or a handle portion, and the casing is screwed. The casing 15 can be easily attached to the attachment target 18 by screwing the nut 19 into the other end of the penetrating bolt 6 exposed from the screw 15.

As a result, a separate mounting bolt,
Since it is not necessary to prepare parts such as nuts, the attachment to the attachment object 18 becomes extremely simple.

The present invention is not limited to the above-described embodiments, but various modifications can be made within the scope of the gist thereof.

[0028]

According to the present invention described above in detail, a pair of piezoelectric elements are bonded to both surfaces of a metal elastic plate, and a through bolt is arranged to penetrate the metal elastic plate and the pair of piezoelectric elements in an insulated state. It is possible to provide an acceleration sensor having a simplified structure, facilitating assembly, and reducing manufacturing cost, facilitating sensitivity adjustment, having high reliability, and being unaffected by temperature changes.

Further, since the metal elastic plate and the pair of piezoelectric elements can be attached to the object to be attached by using the through bolts, it is not necessary to prepare a separate component for attachment, and the attachment to the object to be attached is extremely easy. It is possible to provide a simple acceleration sensor.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an acceleration sensor of the present invention.

FIG. 2 is an exploded perspective view of the acceleration sensor according to the present embodiment.

FIG. 3 is an explanatory view of the principle of the acceleration sensor of this embodiment.

FIG. 4 is a diagram showing a polarization state of a piezoelectric element in the acceleration sensor of this embodiment.

FIG. 5 is a diagram showing a polarization state of a piezoelectric element in the acceleration sensor of this embodiment.

FIG. 6 is a plan view showing a state in which the acceleration sensor of this embodiment is incorporated in a casing.

FIG. 7 is a front view showing a state in which the acceleration sensor of this embodiment is incorporated in a casing.

FIG. 8 is an explanatory diagram showing a mounting example of a casing incorporating the acceleration sensor of the present embodiment to a mounting target.

FIG. 9 is a perspective view showing an example of a conventional acceleration sensor.

[Explanation of symbols]

 1 Acceleration sensor 2 Metal elastic plates 3a, 3b Piezoelectric element 6 Penetration bolt 8 Mass body 15 Casing

Claims (2)

[Claims] 1. A metal elastic plate, a pair of piezoelectric elements joined to both surfaces of the metal elastic plate in a state where polarization axis directions face each other, and a through-hole disposed in an insulating state with respect to the metal elastic plate and the pair of piezoelectric elements. An acceleration sensor having a through bolt. 2. The acceleration sensor according to claim 1, wherein the metal elastic plate and the pair of piezoelectric elements are attached to an attachment target by using the through bolt.