JPS61259174A - Dynamic quantity sensor - Google Patents

Abstract

PURPOSE:To prevent the effect of external force from exerting on a diaphragm even if strain is generated in a housing, by mounting the diaphragm to a frame through a support member and supporting said frame on a sufficient small point in an enclosure. CONSTITUTION:In a sensor wherein a diaphragm 1 equipped with a strain- electric energy converter element is received in an enclosure 7 to detect dynamic quantity, the diaphragm 1 is mounted to frames 2, 3 through a support member 4. This frame 2 is mounted to the housing 7 on one point such as a protruded part sufficiently smaller than the area of said frame 2. By this method, because the diaphragm 1 receives no external force even if said external force is applied to the enclosure 7 and strain is generated, the generation of detection noise can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a mechanical quantity sensor using a strain-to-electrical quantity conversion element, such as a piezoelectric element, and particularly to a mechanical quantity sensor suitable as an acceleration sensor for a vehicle.

[Prior art]

As an acceleration sensor using a piezoelectric element, there is one shown in, for example, Japanese Patent Publication No. 1982-23223.

FIG. 4 is a cross-sectional view of the overall structure of the above acceleration sensor and a plan view of the piezoelectric element.

In FIG. 4, a piezoelectric element 50 is made by laminating two disc-shaped piezoelectric ceramics, and a "U"-shaped slit 51 is formed near the center by laser processing, and a The portions are adapted to form a cantilever beam 52.

The periphery of the disk-shaped piezoelectric element 50 as described above is enclosed in a housing 53.
By fixing it with a member 54, the cantilever beam 52 functions as a deflection vibrator.

In addition, 56 is an electronic circuit board, and various electronic components 57
is mounted on the housing 53 by a member 55.

Furthermore, a lead wire 58 is provided to connect the cantilever 52 portion of the piezoelectric element 50 and a detection electronic circuit formed on the electronic circuit board 56.

[Problem that the invention seeks to solve]

In the conventional acceleration sensor using a piezoelectric element as described above, the piezoelectric element 50 that detects acceleration is directly fixed to the housing 53, so an external force is applied to the housing 53 and There is a problem in that when distortion occurs, it directly deforms the piezoelectric element 50, and the distortion of the housing 53 directly becomes noise and is superimposed on the detection signal.

It is also possible to support the piezoelectric element in the housing 53 via an elastic body, but if the distortion of the housing 53 is large,
Sufficient strain absorption cannot be expected with the above-mentioned elastic body alone.

The present invention aims to solve the problems of the prior art as described above.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a diaphragm equipped with a strain-to-electricity conversion element is attached to a frame via a support member, and the frame is supported inside the casing at a point that is sufficiently smaller than the area of the diaphragm. It is configured as follows.

With the above configuration, even if the casing is distorted by external force, there is no possibility that the distortion will affect the diaphragm.

[Embodiments of the invention]

FIG. 1 is a sectional view of one embodiment of the present invention.

In Fig. 1, 1 is a piezoelectric diaphragm (details will be described later);
Reference numerals 2 and 3 denote frames, and the piezoelectric diaphragm 1 is supported by combining 2 and 3.

Further, 4 is a support member made of an elastic material, and 5 is a convex portion provided on the lower surface of the frame 2. Further, 6 is a ventilation hole provided in the frame 2, 7 is a closed type casing, 8 is a mounting part, and 9 is a board.

In the device shown in FIG. 1, frames 2 and 3 supporting a piezoelectric diaphragm 1 are attached to a casing 7 by adhesion only by a small-area convex portion 5 provided on the lower surface of the frame 2.

Further, the housing 7 is attached to the substrate 9 via the attachment portion 8 by screwing or the like.

Next, FIG. 3 is a front view and a sectional view taken along the line AA' of one embodiment of the piezoelectric diaphragm 1 and the support member 4.

In FIG. 3, piezoelectric elements 11 and 12 are bonded to both surfaces of a thin metal plate 10 using an adhesive such as epoxy resin.

The piezoelectric elements 11 and 12 are smaller in area than the thin metal plate 10, and the thin metal plate 10 is exposed around the piezoelectric diaphragm 1.

Since piezoelectric elements generate voltage in response to temperature changes due to their pyroelectric properties, the pyroelectric output can be removed by bonding two piezoelectric elements so that they have opposite output characteristics as described above. There is.

Further, the metal thin plate 10 needs to have the same thermal expansion value as the piezoelectric element 11.12 as much as possible. Therefore, for example, when P, Z, and T are used as the piezoelectric element 11.12, the thermal expansion coefficient A Ni-Fe alloy with a similar value is used.

The lead wires 13 and 14 are formed by twisting thin wires made of, for example, tin-plated mild steel, and their surfaces are coated with a polyurethane material for durability.

Connect one end of the above lead wire 13.14 to the piezoelectric element 11.12.
The entire soldered joint is covered with a cushioning material (elastic material) such as polyurethane.

Further, after the lead wires 13 and 14 are given a predetermined play by bending or the like, the middle portion thereof is fixed to a part of the thin metal plate 10 around the piezoelectric diaphragm using a cushioning material 16, 18 such as polyurethane. There is.

Further, reference numeral 19 denotes a small hole serving as an air passage, and is provided so that both the front and back surfaces of the piezoelectric diaphragm 1 are communicated with each other.

Next, the support member 4 is made of, for example, a synthetic resin such as polyurethane, and is formed in a shape that covers both the front and back surfaces of the outer peripheral portion of the piezoelectric diaphragm with a predetermined width and thickness.

The piezoelectric diaphragm 1 and the supporting member 4 formed as described above are fitted into the frames 2 and 3 shown in FIG. Attach to the frame.

Next, the effect will be explained.

A mechanical quantity such as acceleration applied from the outside acts on the piezoelectric diaphragm 1 via the housing 7 and the frames 2 and 3, and the piezoelectric diaphragm 1 undergoes a deformation amount proportional to the applied mechanical quantity.
cause to occur.

By detecting this amount of deformation using the piezoelectric elements 11 and 12, the applied mechanical quantity is converted into an electrical quantity and output.

Also, when installing the above-mentioned casing, external force acts on portion 8.

Even if the casing 7 is distorted, the casing 7 and the frame 2 are supported at one point via the small-area convex portion 5.
Distortion that would cause deformation of the piezoelectric diaphragm 1 due to distortion of the housing 7 does not occur. Therefore, even if distortion occurs in the housing 7, there is no possibility that noise will be superimposed on the detection output.

Next, FIG. 2 is a diagram showing a second embodiment of the present invention.
The same reference numerals as in the figure indicate the same thing.

In FIG. 2, 20 is a hollow cylindrical spacer.

21 is a bolt, and 22 is a nut.

In the embodiment shown in FIG.
The case is shown in which it is attached to the housing 7 using a nut 22. Other configurations, functions, etc. are the same as those in FIG. 1 above.

Next, in the embodiment of FIGS. 1 and 2, frame 2
The ventilation holes 6 provided in the will be explained.

In the structure of the embodiment shown in FIGS. 1 and 2, the frame 2 and the piezoelectric diaphragm 1 form a sealed chamber.

Therefore, when the air in the sealed chamber expands or contracts due to a change in temperature or the like, pressure is applied to the piezoelectric diaphragm 1, which causes noise to be generated in the detection output.

In order to solve the above problem, a vent hole 6 is provided so that the pressure on both the front and back sides of the piezoelectric diaphragm 1 is always the same.

Incidentally, as shown in FIG. 3, the same effect as the ventilation hole 6 can be obtained even if the piezoelectric diaphragm 1 is provided with a small hole 19 that communicates with both the front and back surfaces thereof.

〔Effect of the invention〕

As explained above, in the present invention, a diaphragm equipped with a strain-to-electricity conversion element is attached to a frame via a support member, and the frame is supported inside the casing at a point that is sufficiently smaller than the area of the diaphragm. Therefore, even if the casing is distorted due to the application of an external force, it will not affect the distortion-to-electrical quantity conversion element, which is an excellent feature that eliminates the risk of noise occurring in the detection output. Effects can be obtained.

[Brief explanation of the drawing]

1 and 2 are sectional views of embodiments of the present invention, respectively;
FIG. 3 is a front view and a sectional view of an embodiment of a piezoelectric diaphragm, and FIG. 4 is a sectional view of an example of a conventional device and a front view of a piezoelectric element. Explanation of symbols> 1... Piezoelectric diaphragm 2, 3... Frame 4.
・Support member 5 ・Protrusion 6 ・Vent hole
7... Housing 8... Mounting part 9
... Board 20 ... Spacer 21 ... Bolt 22 ... Natsuto Patent Attorney Junnosuke Nakamura 1-1 Figure 2 Figure 5j-3 Figure 19 --- -1 Hole

Claims (1)

[Claims] A mechanical quantity sensor in which a diaphragm equipped with a strain-electrical quantity conversion element is mounted inside a housing, and a mechanical quantity applied to the diaphragm from the outside via the housing is detected by the strain-electrical quantity conversion element, A mechanical quantity sensor characterized in that the diaphragm is attached to a frame via a support member, and the frame is supported inside the housing at a point that is sufficiently smaller than the area of the frame.