JPH06201723A - Acceleration sensor and air bag system by using this - Google Patents

Abstract

PURPOSE:To provide a highly reliable acceleration sensor having also a self- diagnostic function at the same time by deterioration of detecting accuracy in a low frequency area in the acceleration sensor to detect acceleration of a moving body while being mounted on the moving body. CONSTITUTION:An acceleration sensor is composed of a magnetic substance 2 installed in a case 1 fixed to a moving body so as to be capable of relative displacement, a glass enamel covering layer 3 arranged on this magnetic substance 2, a distortion resistance element 4 formed directly on this, a driving coil 5 arranged oppositely in a relative displacement possible part on the free end side of the magnetic substance 2 and the input, terminals 6a and 6b. Deterioration of detecting accuracy is by arranging the distortion resistance element 4 on the magnetic substance 2, and self-diagnosis becomes possible by the driving coil 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration and an airbag system using the acceleration sensor.

[0002]

2. Description of the Related Art A conventional acceleration sensor will be described with reference to FIGS. As shown in the figure, 11 is a cylindrical case made of metal or conductive resin, and the central portion of the circular vibrator 12 is fixed to the central protruding portion 11a of the case 11 by fixing means. The outer peripheral end of the vibrator 12 is a free end, and the vibrator 12 is flexibly deformed, so that the vibrator 12 can be displaced relative to the case 11. One surface of the piezoelectric element 13 is surface-bonded to the vibrator 12, and the piezoelectric element 1
On the other side of 3, the thin plate electrode 1 made of silver
4, the acceleration sensor 15 is configured by being attached.

As shown in FIG. 10, this electrode 14 is formed by being divided into four pieces.
The fourth electrodes 14a to 14d are insulated from each other, but the output line 1 is connected to the first electrode 14a and the third electrode 14c.
6, 19 are connected, and the input lines 17, 18 are connected to the second electrode 14b and the fourth electrode 14d. Also,
The output lines 16 and 19 are connected to one and connected to the output terminal 20,
The input lines 17 and 18 are connected to each other and connected to the drive input terminal 21.

Next, the operation of the above prior art will be described. When acceleration is generated in a moving body (not shown) to which the case 11 is fixed, the vibrator 12 is relatively displaced with respect to the case 11, and the piezoelectric element 13 is distorted.
A voltage proportional to the acceleration is output from the output terminal 20 through the output lines 16 and 19 from the electrodes 14a and 14c.

On the other hand, in diagnosing whether the acceleration sensor 15 operates normally, a separate pulse signal is input to the second and fourth electrodes 14b and 14d of the acceleration sensor 15 via the drive input terminal 21, and at this time, , Piezoelectric element 13
To the output lines 16 and 19 from the electrodes 14a and 14c.
The output is output from the output terminal 20 via the output terminal 20 to diagnose whether the acceleration sensor 15 normally operates.

[0006]

However, in the above-mentioned conventional acceleration sensor, it is impossible in principle to extract an output from direct current to the piezoelectric element 13, the output level is low even in a low frequency region, and the pyroelectricity is low. Since the output voltage is likely to be buried due to the phenomenon, there is a problem that it is difficult to suppress deterioration of acceleration detection accuracy in the low frequency region.

Further, since the piezoelectric element is usually a brittle material, it is weak against impact and cannot be used as a vibrator alone. Therefore, in many cases, an adhesive is applied to another vibrator 12 made of a metal elastic body or the like. However, the structure is complicated, the number of assembling steps is increased, and there is a problem in cost. In addition, the heat resistance has a problem because of the structure including adhesion.

The present invention is intended to solve such a conventional problem and is inexpensive and highly reliable with a simple structure having strong impact resistance capable of sufficiently accurately detecting acceleration even in a low frequency range. It is an object of the present invention to provide an acceleration sensor of.

[0009]

In order to solve the above-mentioned problems, an acceleration sensor of the present invention includes a magnetic body made of a flat plate-shaped metal elastic body which is attached to a case fixed to a moving body so as to be relatively displaceable, It is composed of a glass holo coating layer provided on the magnetic body, a strain resistance element directly formed on the glass holo coating layer, and a drive coil arranged to face the relative displaceable portion of the magnetic body. .

[0010]

According to the present invention described above, when acceleration occurs in the moving body, the magnetic body is displaced relative to the case and the strain resistance element is distorted, so that a voltage proportional to the acceleration is output. Acceleration can be detected. In addition, since the output due to the strain resistance effect does not depend on the frequency even in the low frequency range, the detection accuracy does not decrease, and an alternating magnetic field is generated by applying an alternating voltage to the drive coil, which causes the magnetic body to flex and vibrate, causing distortion. It is possible to diagnose whether or not the device normally operates by detecting the output due to the distortion of the resistance element.

[0011]

【Example】

(Embodiment 1) One embodiment of the acceleration sensor of the present invention is shown in FIGS.
This will be described with reference to FIG. 2 is a case 1 fixed to a moving body
It is a magnetic body made of a flat plate-like metal elastic body attached to the cantilever type so as to be relatively displaceable, and the magnetic body 2 has a glass holo coating layer 3 having an interdiffusion layer sandwiched at the boundary surface.
The strain resistance element 4 is directly formed by printing on the glass hollow coating layer 3 by a screen printing method or the like, and then firing. The case 1 side of the relative displaceable portion of the magnetic body 2 on the free end side. Is provided with a drive coil 5 and its input terminals 6a and 6b which are arranged to face each other. Further, as shown in FIG. 2, the strain resistance element 4 is divided into two, 4a and 4b, which form a bridge circuit as shown in FIG. 7 is a constant voltage source, and 8 and 9 are fixed resistors.

The operation of the above embodiment will now be described. When acceleration is generated in the moving body, the magnetic body 2 is displaced relative to the case 1 and the strain resistance element 4a,
4b is distorted and its resistance value changes. At this time, the bridge circuit shown in FIG. 2 outputs the output corresponding to the change in the resistance value from the output terminals 10a and 10b.

The input terminal 6a of the drive coil 5 is
An alternating magnetic field is generated by applying an alternating voltage to 6b,
As a result, the magnetic body 2 is flexurally vibrated, and the output caused by the strain resistance elements 4a and 4b being distorted is output from the output terminal 1.
It is also possible to detect from 0a and 10b to diagnose whether or not it operates normally.

As described above, according to the above-described embodiment, since the acceleration is detected by the strain resistance effect, the output does not depend on the frequency even in the low frequency range, so that the detection accuracy does not change.

In the above embodiment, the two-gauge method in which two strain resistance elements 4a and 4b are formed on one surface of the magnetic body 2 is used, but two strain resistance elements are further formed on the other surface. In addition, high linearity can be obtained and detection accuracy can be improved by adopting the 4-gauge method in which a bridge is configured with these four elements.

Further, in this embodiment, since the interdiffusion layer is present at the boundary surface between the magnetic body 2 and the glass holo coating layer 3, the adhesiveness is high, and the glass holo coating layer 3 and the strain resistance element 4 are also strongly adhesive, so that the heat resistance is high. It has a highly reliable structure.

Further, the magnetic body 2 is made of a metal elastic body and is excellent in impact resistance. Therefore, since a structure for reinforcement is not required, the magnetic body 2 has a cantilever structure as shown in the embodiment. It is a simple and low-cost structure with excellent mass productivity.

(Embodiment 2) Next, a second embodiment will be described with reference to FIG.
This will be described with reference to (a) and (b). In FIG. 4, FIG.
The difference from the first embodiment shown in FIG.
, The position of the strain resistance element 4, and the restraint portion. As shown in FIG. 4, the cantilevered magnetic body 2 is arranged at equal intervals with respect to the center of the glass holo coating layer 3 in the longitudinal direction (hereinafter referred to as “width”) and in parallel with the widthwise direction of the magnetic body 2. Holes 2a, 2
b is provided, and the hole 2 is provided between the holes 2a and 2b.
Strain resistance elements 4c and 4d are formed at positions between the broken lines l and l'connecting the edges of a and 2b. The glass holo coating layer 3 is held by fixing two portions apart from the vicinity of the holes 2a and 2b with screws (shown by hatched portions in the figure).

Next, the operation of this embodiment will be described.
When an acceleration is applied, the free end of the magnetic body 2 is displaced relative to the case 1. At this time, the magnetic body 2 bends with the portions where the holes 2a and 2b are provided, particularly the broken line 1 as the fixed end. The structure is such that it is hardly affected by the positional accuracy of holding the glass holo coating layer 3. On the other hand, Example 1
, The edge of the shaded area shown in FIG.
If this edge is not accurately restrained, there is a demerit that sensitivity will vary. Further, since the width of the magnetic body between the holes 2a and 2b is smaller than the width of the tip portion, even if the length of the magnetic body is shortened with respect to the first embodiment due to the stress concentration effect, the same degree is obtained. There is an effect that the sensitivity of can be taken.

Further, since the magnetic bodies 2a and 2b can be made shorter in length as compared with the first embodiment, the resonance frequency can be set high,
This has the effect of reducing the influence of the resonance of the magnetic bodies 2a and 2b on the traceability.

In contrast to the first embodiment, in the second embodiment, when lateral acceleration is applied, both ends of the hole portions 2a and 2b serve as bars, and since the intervals between the bars are wide, a large repulsive moment is generated and strain occurs. Becomes small, and it becomes easy to give directivity to the acceleration sensitive direction.

(Third Embodiment) Next, a third embodiment will be described with reference to FIG. The difference from the first and second embodiments is that
In this embodiment, one hole 2c is provided along the root at the center of the width, and strain resistance elements 4e and 4f are formed at both ends of the hole 2c. The holding of the glass holo coating layer 3 is the same as in the second embodiment.

Next, the operation of this embodiment will be described.
The magnetic body 2c bends when an acceleration is applied, but at this time, the structure is less affected by the positional accuracy of holding the portion provided in the hole 2c. In addition, the strain resistance elements 4e and 4f
Since the width of the magnetic body 2c in the portion provided with is smaller than the width of the tip portion, there is an effect that the strain sensitivity is increased by the stress concentration effect.

Further, as in the second embodiment, compared to the first embodiment, both ends of the hole 2c are crosspieces, and the intervals between the crosspieces are wide, so that it is easy to give directivity in the acceleration sensitive direction.

(Fourth Embodiment) Next, a fourth embodiment will be described with reference to FIG.
This will be described with reference to (a) and (b). The difference from the first to third embodiments is that a glass holo, which is a holo layer on the surface opposite to the surface on which the strain resistance elements 4c and 4d are formed, in the portion where the holes 2a and 2b are provided. It has a structure in which the coating layer 30 is removed.

The operation of this embodiment is almost the same as that of the second embodiment, but the stress concentration effect is enhanced and the strain sensitivity (the amount of strain generated per unit acceleration) is increased because the holo layer is removed. There is an advantage.

However, since the resonance frequency also decreases slightly at the same time, this shape is preferable when the strain sensitivity is prioritized in consideration of the balance with the strain sensitivity.

(Fifth Embodiment) Next, a fifth embodiment will be described with reference to FIG.
Shown in (a) and (b). Except for the glass holo layer 30 from which the holo layer is removed, it is the same as the third embodiment, and the effect is the same as in the fourth embodiment.

Next, FIG. 8 shows an application example in which the sensor of the above-mentioned embodiment is mounted in an air bag system for a vehicle.

In the figure, 1 to 10a, 10b
The description up to this point is omitted because it corresponds to the above-described embodiment, 22 is an amplifier circuit, 23 is a signal processing circuit, and 24 is a signal processing circuit.
Is a detonator, 25 is a mechanical acceleration sensor for preventing accidents having contacts intervening in the ignition circuit, 26 is a fail-safe relay, 27 is a diagnostic pulse generator, 28 is a diagnostic circuit, 29
Is an alarm.

Next, the operation of the above application example will be described. When the vehicle collides, the magnetic body 2 is bent and the strain resistance elements 4a and 4b are distorted, and the resulting output is the output terminal 10
It is output from a and 10b. The output is amplified by the amplifier circuit 22 and input to the signal processing circuit 23. Here, when the input voltage becomes equal to or higher than the set voltage, an ignition signal is output to the detonator 24 and the airbag operates.

The diagnostic pulse generator 27 is configured to generate a diagnostic pulse when the vehicle is cranked while the vehicle is stopped from the vehicle speed signal, the cranking signal, and the parking brake signal, for example, when the scooter of the ignition key is started. A magnetic field is generated by the drive coil 5 by the input of the diagnostic pulse to the input terminals 6a, 6b, and thereby the magnetic body 2 is flexibly vibrated, whereby the strain resistance elements 4a, 4b.
b is distorted, and the resulting output is output from the output terminals 10a and 10b. The output is input to the diagnostic circuit 28,
If an input voltage equal to or higher than the set voltage is detected, it is determined that there is no failure. If not detected, it is determined that there is a failure, the fail-safe relay 26 is turned off, and the alarm 29 is activated to notify the driver of the abnormality.

Since the diagnostic pulse is generated because the vehicle is stopped and the contact point of the mechanical acceleration sensor 25 is off, no ignition signal is applied to the detonator 24.

As described above, according to the above-mentioned embodiment, since the vibrating device for checking whether or not the sensor operates normally is not necessary and the sensor does not have to be removed from the vehicle, the sensor diagnosis can be performed easily. Therefore, there is an advantage that the sensor can always be maintained in a normal state.

The acceleration sensor of FIGS. 1 to 3 including the amplifier circuit of FIG. 4 can be treated as an acceleration sensor to simplify the circuit of the airbag system.

[0036]

As is apparent from the above-described embodiment, the present invention can detect acceleration even in a low frequency range with high accuracy because a strain resistance element provided on a magnetic body detects acceleration, and drives the magnetic body. It is also possible to have a self-diagnosis function to diagnose whether it operates normally by vibrating with a coil and detecting the output due to distortion of the strain resistance element, and always check whether the acceleration sensor is in a normal state at all times. Moreover, since the strain resistance element is formed directly on the magnetic body, it has excellent heat resistance and reliability. Furthermore, the material of the magnetic body is a metal elastic body with high impact resistance, so it is structurally simple and low in structure. It has an effect that a structure excellent in cost mass productivity can be obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a plan view of a magnetic body, which is the main part of the same.

FIG. 3 is a circuit diagram of the main part of the same.

FIG. 4A is a plan view of a magnetic body according to a second embodiment of the present invention, and FIG.

FIG. 5 is a plan view of a magnetic body according to a third embodiment of the invention.

FIG. 6A is a plan view of a magnetic body according to a fourth embodiment of the present invention. FIG. 6B is a side view of the same.

FIG. 7A is a plan view of a magnetic body according to a fifth embodiment of the present invention. FIG. 7B is a side view of the same.

FIG. 8 is a circuit block diagram of an application example in which the sensor of the present invention is applied to a vehicle airbag system.

FIG. 9 is a side sectional view of a conventional acceleration sensor.

FIG. 10 is a circuit diagram of the main part of the same.

[Explanation of symbols]

 1 Case 2 Magnetic Material 3 Glass Holo Cover Layer 4 Strain Resistance Element 4a Strain Resistance Element 4b Strain Resistance Element 5 Drive Coil 6a Drive Coil Input Terminal 6b Drive Coil Input Terminal 7 Constant Voltage Source 8 Fixed Resistance 9 Fixed Resistance 10a Output Terminal 10b Output terminal

Front page continuation (72) Inventor Shinjiro Ueda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A magnetic body made of a metal elastic body attached to a case fixed to a moving body so as to be capable of relative displacement, a glass holo coating layer provided on the magnetic body, and directly formed on the glass holo coating layer. And a drive coil that is disposed so as to face the relative displaceable portion of the magnetic body and that exerts a magnetic force on the magnetic body by applying a voltage. 2. The glass holo coating layer is provided with a hole portion provided in the vicinity of the glass holo coating layer so as not to contact both end surfaces in the longitudinal direction of the glass holo coating layer, and two strain resistance elements provided between the hole portions. The acceleration sensor described. 3. The strain resistance element provided on the glass holo coating layer in the vicinity of the glass holo coating layer not in contact with both end surfaces in the longitudinal direction of the glass holo coating layer, and a hole portion provided between the strain resistance elements. Acceleration sensor. 4. The acceleration sensor according to claim 2, wherein the glass holo coating layer on the surface opposite to the strain resistance element provided on the glass holo coating layer is removed. 5. The airbag system according to claim 1, wherein the airbag system is mounted on a vehicle and operates by detecting an impact received by the vehicle in a collision or the like.