JP2001208766A - Acceleration detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration detector which can act surely. SOLUTION: This acceleration detector 1 is manufactured by a micro- machining technique. The detector 1 is provided with a fixed electrode 13 and a plurality of mobile electrodes 15a-15k having different lengths. The fixed electrode 13 is composed of a thin film permanent magnet. The mobile electrodes 15a-15k are made of a ferromagnetic material and formed in cantilevers. When an automobile is accelerated, the electrodes 15a-15k move to the fixed electrode 13 side. Since the electrodes 15a-15k have different lengths, the acceleration applied to the electrodes 15a-15k when the electrodes 15a-15k are attracted to the fixed electrode 13 are different from each other. Consequently, the recording of the maximum acceleration and switching operations can be performed without requiring power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration detecting device mounted on a vehicle such as an automobile.

[0002]

2. Description of the Related Art Conventionally, a vehicle such as an automobile is equipped with an acceleration detecting device. The applications of this acceleration detecting device are, for example, the following two. One is to record the maximum acceleration for accident analysis. The other is a switch for activating a safety device such as an airbag.

[0003] A conventional acceleration detecting device detects acceleration based on a change in capacitance. However, according to this, when a disconnection or the like occurs between the acceleration detection device and the power supply that operates the acceleration detection device in the event of an accident, the acceleration detection device does not operate, so that acceleration recording and switch operation are performed. There is a problem that you can not.

[0004] It is an object of the present invention to provide an acceleration detecting device capable of operating reliably and recording.

[0005]

SUMMARY OF THE INVENTION The present invention is an apparatus for detecting the acceleration of an object, comprising a movable part and a fixed part,
The movable part and the fixed part are manufactured by a micromachining technique, and at least one of the movable part and the fixed part has a permanent magnet, and the movable part is fixed to the fixed part with a predetermined part. The movable portion is movable toward the fixed portion, and when the acceleration of the object is equal to or greater than a predetermined value, the movable portion is moved by the magnetic force of the permanent magnet. And is adsorbed.

In the acceleration detecting device according to the present invention, as the acceleration of the object increases, the distance between the movable portion and the fixed portion decreases, and when the acceleration of the object is equal to or greater than a predetermined value, the movable portion is moved by the magnetic force of the permanent magnet. Adsorbs to the fixed part. The acceleration detecting device of the present invention detects the acceleration by the suction. Therefore, since the acceleration detection device of the present invention operates without a power supply, even if a peripheral device such as a power supply fails in an accident, the acceleration can be reliably detected.

Further, the movable part and the fixed part provided in the acceleration detecting device of the present invention are manufactured by a micromachining technology. Micromachining is a method of precisely processing a three-dimensional structure having fine dimensions. Therefore, according to the present invention, the acceleration detection device can be downsized.

The movable portion of the acceleration detecting device of the present invention includes, for example, a beam such as a cantilever beam or a fixed beam.
In the case where a beam is used as the movable portion, the movable portion is attracted to the fixed portion when the attraction force by the permanent magnet is larger than the restoring force of the movable portion displaced by acceleration to return to the original position. By changing the dimensions (length, width, thickness) of the movable part, the magnetic force of the permanent magnet, the distance between the movable part and the fixed part at rest, and the like, the value of the detected acceleration can be made different.

In the acceleration detecting device according to the present invention, at least one of the movable part and the fixed part may have a permanent magnet. In a configuration in which one of the movable portion and the fixed portion has a permanent magnet, and the other includes a material that is attractable to a magnet such as a ferromagnetic material, both the movable portion and the fixed portion have a permanent magnet. Since the magnetic force is weaker than the configuration, the attracted state can be easily released. This is advantageous when the acceleration detection device is reused. On the other hand, the configuration in which both the movable portion and the fixed portion have the permanent magnet has a stronger magnetic force than the configuration in which only one has the permanent magnet, so that the acceleration can be more reliably recorded.

The acceleration detecting device according to the present invention can have the following configuration. That is, there are a plurality of the movable parts,
The predetermined value of the acceleration at which the movable part is attracted to the fixed part is:
Each is different. According to this configuration, since a plurality of acceleration values can be detected, for example, the maximum acceleration can be detected by examining up to which movable portion is attracted to the fixed portion. In addition, the number of movable parts of the acceleration detecting device of the present invention may be one. In this case, only one kind of acceleration value can be detected.

The acceleration detecting device according to the present invention can have the following configuration. That is, the movable part and the fixed part have conductivity, and the movable part and the fixed part constitute an electric circuit switch. According to this configuration, since the acceleration detecting device is an electric circuit switch,
With this switch, for example, a safety device such as an airbag can be operated. When the acceleration detection device of the present invention is used as an acceleration recording device and is not used as an electric circuit switch, the movable portion and the fixed portion need not have conductivity.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the acceleration detecting device according to the present invention will be described.

[Structure of this Embodiment] First, the structure of the acceleration detecting device of this embodiment will be described with reference to FIGS. FIG. 1 is a plan view of the acceleration detection device 1 of the present embodiment. FIG. 2 shows the acceleration detection device 1 shown in FIG.
It is sectional drawing cut | disconnected along A2 line. The acceleration detection device 1 is manufactured by a micro-machining technology and is small. The acceleration detection device 1 includes a silicon substrate 11, a fixed electrode 13, and movable electrodes 15a to 15k.

On the silicon substrate 11, a silicon oxide film 17 is located. The fixed electrode 13 and the movable electrodes 15a to 15k are patterned on the silicon oxide film 17.

The fixed electrode 13 is a permanent magnet, for example, a thin film magnet such as CoPt or SmCo. The fixed electrode 13 is provided with a terminal 19.

The movable electrodes 15a to 15k are, for example, N
It is made of a non-magnet ferromagnetic material such as i, Fe, Co, or NiFe alloy. The movable electrodes 15 a to 15 k are provided with a predetermined distance d (for example, 10 μm) from the fixed electrode 13. This distance d means the distance between the movable electrodes 15a to 15k and the fixed electrode 13 when the object whose acceleration is to be detected is stationary. The movable electrodes 15a to 15k have a cantilever shape, and have different lengths. Specifically, it is as follows.

Movable electrode 15a: 220 μm Movable electrode 15 b: 200 μm Movable electrode 15 c: 180 μm Movable electrode 15 d: 160 μm Movable electrode 15 e: 140 μm Movable electrode 15 f: 120 μm Movable electrode 15 g: 100 μm Movable electrode 15 h: 80 μm Movable electrode 15 i: 60 μm Movable electrode 15j: 40 μm Movable electrode 15 k: 20 μm The width of the movable electrodes 15 a to 15 k is the same (for example, 10 μm), and the thickness of the movable electrodes 15 a to 15 k is the same (for example, 2 μm). The fixed ends of the movable electrodes 15a to 15k are connected to the terminals 21a to 21a, respectively.
21k is provided.

Next, the mechanism of detecting acceleration by the acceleration detecting device 1 of the present embodiment will be described based on the relationship between the attraction force of the magnet and the restoring force of the cantilever. The magnet corresponds to the fixed electrode. The cantilever beam corresponds to the movable electrode. FIG. 3 is a graph showing the relationship between the magnet attraction force F ₁ and the gap distance D, and the relationship between the cantilever restoring force F ₂ and the gap distance D. The attraction force F ₁ , the restoring force F ₂ , and the gap distance D are respectively as follows.

The suction force ^{_{F 1 = S 0 B 2 /}} 2μ 0 S 0: adsorption area B: magnetic flux density of the adsorption portion mu _0: permeability of vacuum restoring force F ₂ = -KX K: spring constant X of the cantilever : cantilever displacement amount gap distance D = D ₀ -X D _0: when the object of the stationary (i.e., when not in a state of acceleration) as the distance gap distance D between the cantilever and the magnet in a small, cantilever Is close to the magnet. As can be seen from FIG. 3, the gap distance D is equal to or less than the suction point X _1, the suction force F ₁ becomes the restoring force F ₂ or more, the cantilever is to adsorb to the magnet.
In the present embodiment, the acceleration is detected by this suction. That is, when the movable electrodes 15a to 15k are displaced by acceleration, a restoring force is applied to the movable electrodes 15a to 15 to return to the original state. The adsorption force of the fixed electrode 13 is
The movable electrodes 15a to 15k are attracted to the fixed electrode 13 when the restoring force is exceeded. The acceleration detection device 1 detects a desired acceleration by the suction.

Next, an example of setting the acceleration to be detected will be described. When the movable electrode is in the state of acceleration a, the displacement amount of the tip of the movable electrode is x. This relationship can be expressed as follows.

Ma = -kx m: mass of the movable electrode k: spring constant of the movable electrode As described above, when the gap distance becomes equal to or less than the suction point, the movable electrode is attracted to the fixed electrode. _{In the case of 1} , the gap distance may be set to be equal to or less than the suction point. Then, the mass of the movable electrode m = ρlwt
(Ρ is the density of the movable electrode, l is the length of the movable electrode, w is the width of the movable electrode, and t is the thickness of the movable electrode). Further, the spring constant of the movable electrode is k = Etw ³ / l ³ (E is the Young's modulus of the movable electrode). Therefore, by adjusting the length l of the movable electrode, the width w of the movable electrode, or the thickness t of the movable electrode,
Desired can detect acceleration a _1. This will be specifically described with an example in which the length l of the movable electrode is changed.

FIG. 4 is a graph showing the relationship between the length of the movable electrode and the detectable acceleration. As can be seen from this graph, the detectable acceleration decreases as the length of the movable electrode increases, and the detectable acceleration increases as the length of the movable electrode decreases. In this embodiment,
As shown in FIG. 1, the value of the detected acceleration is changed by changing the length of each of the movable electrodes 15a to 15k.

[Use of this Embodiment] The use of the acceleration detecting device 1 will be described. The applications of the acceleration detection device 1 are a device for recording the maximum acceleration for accident analysis and a switch for activating a safety device such as an airbag. First, the recording of the maximum acceleration will be described with reference to FIG. According to the acceleration detection device 1, the length of the movable electrode 15a is the longest, and then gradually shortens, and the length of the movable electrode 15k is the shortest. Therefore, the movable electrode 1
The value of the acceleration required for causing the fixed electrode 13 to attract 5a is the smallest, and the value of the acceleration required for causing the movable electrode 15k to be attracted to the fixed electrode 13 is the largest. Therefore, the maximum acceleration can be determined by checking which movable electrode is attracted.

Next, the switching operation will be described with reference to FIGS.
This will be described with reference to FIG. As shown in FIG. 1, a wiring 23 is connected to a terminal 21d of the movable electrode 15d of the acceleration detection device 1. Further, a wiring 25 is connected to the terminal 19 of the fixed electrode 13. The wirings 23 and 25 are connected to the airbag deployment signal generating circuit 31 shown in FIG. The airbag deployment signal generation circuit 31 is connected to the airbag deployment device 32. Here, the movable electrode 15
The acceleration detected by d is 5 g (g is gravitational acceleration). This is a collision acceleration at which the driver and the passenger are in a dangerous state. Therefore, for example, when the collision acceleration occurs in a vehicle due to a vehicle collision accident, the movable electrode 15 d is attracted to the fixed electrode 13. As a result, the switch is turned on, an airbag deployment signal is generated in the airbag deployment signal generation circuit 31, and this signal is transmitted to the airbag deployment device 32 to deploy the airbag.

As described above, since the acceleration detecting device 1 according to the present embodiment operates without a power supply, even if a peripheral device such as a power supply fails in the event of an accident, it is possible to reliably record the maximum acceleration and air. Switch operation for back deployment can be performed.

[Modification of the Embodiment] A modification of the embodiment will be described. The acceleration detection device 3 shown in FIG. 6 is a modified example of the acceleration detection device 1 shown in FIG. According to this,
The airbag can be prevented from being accidentally deployed. First, the structure of the acceleration detection device 3 will be described. Parts having the same functions as the acceleration detection device 1 shown in FIG.
The same reference numerals are given. The parts of the acceleration detection device 3 that are different from those of the acceleration detection device 1 will be described, and descriptions of the same portions will be omitted. In the acceleration detection device 3, the movable electrode 15f
The wiring 27 is connected to the terminal 21f of the fixed electrode 13 and the wiring 29 is connected to the terminal 19 of the fixed electrode 13. The wiring 29
May be shared with the wiring 25. The movable electrode 15f is
At an acceleration of 7 g, it is attracted to the fixed electrode 13.

The acceleration detecting device 3 is a switch of a mechanism for deploying the airbag shown in FIG. That is,
Wirings 23, 25, 27 of the acceleration detection device 3 shown in FIG.
Reference numeral 29 is connected to the collision acceleration determination circuit 33 shown in FIG. The collision acceleration determination circuit 33 is connected to the airbag deployment signal generation circuit 31. The airbag deployment signal generation circuit 31 is connected to the airbag deployment device 32.

Next, the operation of the modification of this embodiment will be described. The acceleration at which the airbag should be deployed also occurs when an impact is applied to the steering wheel or when the vehicle gets over a hole or bump on a road while traveling. At this time, if the airbag is deployed, the driver or the passenger may be injured. In the modified example of the present embodiment, the operation as described below prevents the malfunction of the airbag deployment. An initial acceleration a1 (for example, a relatively small acceleration at which a bumper or the like is crushed) peculiar to the collision is detected by the movable electrode 15d, and an acceleration a2 at which the airbag should be deployed (for example, an acceleration at which the body of the car is crushed) is movable. Electrode 15f
To detect. The collision acceleration determination circuit 33 determines the timing at which the airbag should be deployed based on the existence of the two accelerations and the temporal relationship, and sends the signal to the airbag deployment signal generation circuit 31. This prevents a malfunction of the airbag deployment.

[Brief description of the drawings]

FIG. 1 is a plan view of an acceleration detection device 1 according to an embodiment.

FIG. 2 is a cross-sectional view of the acceleration detection device 1 shown in FIG. 1 taken along line A1-A2.

FIG. 3 is a graph showing a relationship between a magnet attracting force F ₁ and a gap distance D, and a relationship between a cantilever restoring force F ₂ and a gap distance D.

FIG. 4 is a graph showing a relationship between the length of a movable electrode and a detectable acceleration.

FIG. 5 is a block diagram of a mechanism applied to the present embodiment for deploying an airbag.

FIG. 6 is an acceleration detection device 3 according to a modification of the present embodiment.
FIG.

FIG. 7 is a block diagram of a mechanism for deploying an airbag applied to a modification of the embodiment.

[Explanation of symbols]

 1, 3 acceleration detecting device 11 silicon substrate 13 fixed electrode 15a to 15k movable electrode 17 silicon oxide film 19 terminal 21a to 21k terminal 23, 25, 27, 29 wiring

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01H 59/00 G01P 15/00 DF (72) Inventor Hiroshi Nonomura Okumachi, Nagakute-cho, Aichi-gun, Aichi Prefecture 41 No. 1 Toyota Central Research Laboratory Co., Ltd. F term (reference) 3D054 EE04 FF13 FF17 5G056 BE51 BF01

Claims (3)

[Claims] 1. An apparatus for detecting an acceleration of an object, comprising: a movable portion and a fixed portion, wherein the movable portion and the fixed portion are manufactured by a micromachining technique; At least one of the sections has a permanent magnet; the movable section is disposed at a predetermined distance from the fixed section; the movable section is movable toward the fixed section; An acceleration detecting device, wherein when the acceleration of an object is equal to or more than a predetermined value, the movable portion is attracted to the fixed portion by the magnetic force of the permanent magnet. 2. The method according to claim 1, wherein the movable portion includes a plurality of movable portions, and a predetermined value of an acceleration at which the movable portion is attracted to the fixed portion is:
Different acceleration detectors. 3. The acceleration detection device according to claim 1, wherein the movable part and the fixed part have conductivity, and the movable part and the fixed part constitute an electric circuit switch.