JPH08327655A - Acceleration sensor - Google Patents

Abstract

PURPOSE: To obtain an acceleration sensor being employed in the air bag system for automobile in which both high resonance frequency and high sensitivity are satisfied. CONSTITUTION: A cantilever 1 provided with a hole 6 and rectangular notches 9a, 9b in the vicinity of border between a fixed area and a free area is secured to a moving body, e.g. an automobile, by means of screws and resistors 5a, 5b are printed in the area between the hole 6 and the notches 9a, 9b. According to this structure, concentration of stress due to curving on the outside of notches 9a, 9b is combined with superposed distribution of stress due to concentration of stress at the hole 6 and the notches 9a, 9b upon application of acceleration. Consequently, the stress is concentrated at high degree and high sensitivity can be attained even at high resonance frequency.

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 used in an air bag system of an automobile.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIGS.

In FIG. 6, the cantilever 1 is fixed to the moving body by means of through holes 2a and 2b by means of screws or the like (not shown) to form restraint regions 3a and 3b. Therefore, as shown in the figure, the cantilever 1 has a free region and a fixed region. A rectangular hole 6 is provided in the vicinity of the restraint regions 3a and 3b and the free region, and a strain resistance element as a strain resistance element is provided in the vicinity of the hole 6 near the boundary where the free region contacts the fixed region. Printing resistors 5a and 5b are formed. Then, as shown in FIG.
a and 5b are balance adjusting resistors 12a and 12b (see FIG. 5).
(Not shown) to form a bridge circuit and are electrically connected to the lead terminals 7 by the printed electrodes 4a to 4d.

The operation of the acceleration sensor having the above structure will be described below. The restraint regions 3a, 3
The movement of the automobile or the like is transmitted to the cantilever 1 by b, the free region is distorted by its own inertial force, and the strain is distributed so that the corners 8a and 8b are maximized due to the hole 6. Then, the resistance value changes according to the strain value distributed in the area where the printed resistors 5a and 5b are formed, and the change is taken out as an electric signal from the lead terminal 7 by the bridge circuit.

[0005]

However, the above conventional acceleration sensor has the following problems.

First, if the printed resistors 5a and 5b are provided at the peripheral portions without clearance, defects are likely to occur during manufacturing. Therefore, the corners 8a, which are the maximum points in the strain distribution,
The printed resistors 5a and 5b cannot be provided on 8b. Therefore, it is unavoidable to provide the printing resistors 5a and 5b in the region where the strain value is 25 to 30% lower than the maximum value.
Therefore, in order to increase the sensitivity in consideration of this loss, it is necessary to increase the weight of the free area of the cantilever 1 corresponding to the loss or reduce the rigidity of the free area. However, if the sensitivity is increased by this method, the resonance frequency is lowered, and it is difficult to achieve high sensitivity at the same time. In addition, there is a drawback that the strain generated in the corners 8a and 8b at the time of dropping becomes too high, and the impact fracture strength is small.

Secondly, the size of the printing resistors 5a and 5b needs to be a certain size or more in view of printing accuracy. Therefore, the printed resistors 5a and 5b change in accordance with the average value of the strain distribution in the region where the resistance is formed, but the difference between the maximum value and the minimum value of the strain distribution in this region is large, so the average The value becomes smaller and the loss becomes larger.

The present invention is intended to solve such a conventional problem, and an object thereof is to provide an acceleration sensor capable of concentrating strain on a strain resistance and achieving both high sensitivity and high resonance frequency. is there.

[0009]

In order to solve the above-mentioned problems, the acceleration sensor of the present invention comprises a cantilever having at least one hole and at least two notches, and has at least two restraint regions. According to this configuration, the strain resistance element is fixed to a moving body such as an automobile, and a strain resistance element is provided in a portion between the hole and the notch on the cantilever.

[0010]

With this structure, the strain distribution can be concentrated in the region sandwiched between the hole and the notch, and the difference between the maximum value and the minimum value of the strain in the region where the strain resistance element is formed can be reduced. Therefore, both high sensitivity and high resonance frequency can be compatible with each other, and as a result, impact fracture strength at the time of dropping can be improved.

[0011]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
Will be explained.

The cantilever 1 is fixed to a moving body by means of through holes 2a and 2b by means of screws or the like (not shown), and the constrained regions 3a and 3 are formed.
b is formed. Therefore, a free region and a fixed region are formed in the cantilever 1 as shown in the figure. Then, a rectangular hole 6 and rectangular cutouts 9a, 9b are provided in the vicinity of the constrained areas 3a, 3b and the free area, and in a region sandwiched by the hole 6 and the cutouts 9a, 9b. Printed resistors 5a and 5b as strain resistance elements are formed near the boundary where the free region contacts the fixed region. Here, the side 6b of the hole 6 on the side of the fixed area is displaced from the sides 9c, 9d of the cutouts 9a, 9b by the amount of deviation Δd on the side of the fixed area. Also, the restraint regions 3a, 3b
The boundary is provided near the cutouts 9a and 9b.

The printing resistors 5a and 5b form a bridge circuit together with the balancing resistors 12a and 12b, as in the conventional example, and the lead terminals 7 are formed by the printing electrodes 4a to 4d.
Is electrically connected to.

The operation of the acceleration sensor configured as described above will be described. Due to the restraint regions 3a and 3b, the motion of the automobile or the like is transmitted to the cantilever beam 1, the free region is distorted by its own inertial force, and due to the hole 6 and the notches 9a and 9b, Distortion concentrates in the area sandwiched between. Then, the resistance value changes according to the strain value distributed in the area where the printed resistors 5a and 5b are formed, and the change is taken out as an electric signal from the lead terminal 7 by the bridge circuit.

Next, a series of effects of the shape relating to strain concentration will be briefly described. 4A and 4B show the deformed shape and the strain distribution of the cantilever in each shape when acceleration is applied to the acceleration sensor.

FIG. 4A (conventional example) and FIG. 4B (first)
Compared with the deformation of (a), by providing the cutouts 9a and 9b, the deformation at the time of applying an acceleration is such that the free region outside the cutouts 9a and 9b is curved as compared with the deformation of (a). ing. At this time, looking at this deformation in more detail, the curvature of the notches 9a and 9b in the vicinity of the corners 8c and 8d is the largest, and therefore the maximum strain region is also distributed in this vicinity.

Further, the hole 6 and the notches 9a, 9
Regarding the effect of stress concentration by b, since the boundary of the restraint region is close to the cutouts 9a, 9b, the stress is
Highly concentrated near the two points a and 8b, and the maximum strain increases. Therefore, if the side 6b of the hole and the notch 9a,
When the sides 9c and 9d of 9b are lined up on a line, the free region and the fixed region are also divided with this line as a boundary line, and high strain is concentrated in an extremely narrow region on the boundary line. Since the side 6b is displaced from the sides 9c and 9d by Δd toward the fixed area, the boundary becomes a band and the absolute value of the strain is slightly reduced, but a high strain is generated around the two points of the corners 8a and 8b. Are distributed over a relatively wide area.

Therefore, the maximum strain region is a superposition of the above two high strain regions, and the corner portions 8a and 8c and the corner portion 8 are formed.
A high strain region (strain region of 85% or more of the maximum value) is distributed along the line connecting b and 8d as shown in FIG. 4B.

As described above, according to the first embodiment, when acceleration is applied, the strain concentration due to the outward bending deformation of the cutouts 9a, 9b and the hole 6 and the cutout 9a are caused. , 9b, and the notch 9
Since a and 9b are close to the constraint regions 3a and 3b, the effect of further increasing the stress concentration and the superposition of the two concentration distributions cause the strain to be more highly concentrated, resulting in high resonance. It is possible to realize an acceleration sensor that achieves both high frequency and high sensitivity. Also, since the high strain area can be distributed in a relatively wide area,
An acceleration sensor with high impact fracture strength can be realized.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to FIG.

The cantilever 1 is fixed to the moving body by means of through holes 2a and 2b by means of screws or the like (not shown) so as to be restrained regions 3a and 3b.
b is formed. Therefore, a free region and a fixed region are formed in the cantilever 1 as shown in the figure. A hole 6 and a rectangular notch 9a, 9b formed in a substantially U shape are provided in the vicinity of the restraint regions 3a, 3b and the free region in a direction facing the free end 1a of the free region. ,
Printed resistors 5a and 5b as strain resistance elements are formed near the boundary between the free region and the fixed region in the region sandwiched by the hole 6 and the cutouts 9a and 9b. Here, the side 6b of the hole 6 on the side of the fixed area is displaced from the sides 9c, 9d of the cutouts 9a, 9b by the amount of deviation Δd on the side of the fixed area. Also, the restraint regions 3a, 3b
The boundary is provided near the cutouts 9a and 9b.

The print resistors 5a and 5b form a bridge circuit together with the balance adjustment resistors 12a and 12b as in the conventional example, and the lead terminals 7 are formed by the print electrodes 4a to 4d.
Is electrically connected to.

The operation of the acceleration sensor configured as described above will be described. Due to the restraint regions 3a and 3b, the motion of the automobile or the like is transmitted to the cantilever beam 1, the free region is distorted by its own inertial force, and due to the hole 6 and the notches 9a and 9b, Distortion concentrates in the area sandwiched between. Further, the tongue-shaped body 6a protruding into the hole 6 narrows the region where strain is concentrated, and the strain distribution density is increased. Then, the resistance value changes according to the strain value distributed in the area where the printed resistors 5a and 5b are formed, and the change is taken out as an electric signal from the lead terminal 7 by the bridge circuit.

Next, a series of effects of the shape relating to strain concentration will be briefly described. 4A and 4C show the deformed shape and strain distribution of the cantilever in each shape when acceleration is applied to the acceleration sensor.

FIG. 4A (conventional example) and FIG. 4C (second)
Comparing the example, compared to the deformation of (a), by providing the notch, the deformation at the time of applying the acceleration is deformed so that the free region outside the notches 9a and 9b is curved. At this time, looking at this deformation in more detail, the curvature of the notches 9a and 9b in the vicinity of the corners 8c and 8d is the largest, and therefore the maximum strain region is also distributed in this vicinity.

Further, the hole 6 and the notches 9a, 9
Regarding the effect of stress concentration by b, since the boundary of the restraint region is close to the cutouts 9a, 9b, the stress is
Highly concentrated near the two points a and 8b, and the maximum strain increases. Therefore, if the side 6b of the hole and the notch 9a,
When the sides 9c and 9d of 9b are lined up on a line, the free region and the fixed region are also divided with this line as a boundary line, and high strain is concentrated in an extremely narrow region on the boundary line. Since the side 6b is displaced from the sides 9c and 9d by Δd toward the fixed area, the boundary becomes a band and the absolute value of the strain is slightly reduced, but a high strain is generated around the two points of the corners 8a and 8b. Are distributed over a relatively wide area.

Therefore, the maximum strain region is a superposition of the above two high strain regions, and the corner portions 8a and 8c and the corner portion 8 are formed.
A high strain region (strain region of 85% or more of the maximum value) is distributed along the line connecting b and 8d as shown in FIG. 4C.

Moreover, since the tongue-shaped member 6a at the center of the hole 6 increases the rigidity, the deformation of the center is suppressed. Therefore, stress concentration occurs due to narrowing of the strainable region, and the absolute value of strain in the region sandwiched between the hole 6 and the cutouts 9a and 9b increases, resulting in a high strain region (maximum value). Area of 85% or more of the strain area).

As described above, according to the second embodiment, when acceleration is applied, the strain concentration due to the outward bending deformation of the cutouts 9a, 9b and the hole 6 and the cutout 9a are caused. , 9b, and the notch 9
Since a and 9b are close to the restraint regions 3a and 3b, the effect of further increasing the stress concentration and the superposition of the two concentration distributions and the central tongue 6a of the hole 6 are provided. Since the strain is concentrated more highly by narrowing the overlapping strain distribution region, it is possible to realize an acceleration sensor having both high resonance frequency and high sensitivity. Further, since the high strain area can be distributed over a wide area, an acceleration sensor having high impact fracture strength can be realized.

(Third Embodiment) Next, a third embodiment will be described with reference to FIG.

The cantilever 1 is fixed to the moving body by means of through holes 2a and 2b with screws or the like (not shown), and the restraining regions 3a and 3 are provided.
b is formed. Therefore, a free region and a fixed region are formed in the cantilever 1 as shown in the figure. A hole 6 and a notch 11a, 11b, which are formed in a substantially U-shape, are provided near the restraint regions 3a, 3b and the free region in a direction facing the free end of the free region. Printed resistors 5a and 5b as strain resistance elements are formed near the boundary where the free region contacts the fixed region in a region sandwiched by 6 and the cutouts 11a and 11b. here,
The side 6b of the hole 6 on the side of the fixed region is provided with the cutout 11
Similar to the second embodiment, a and 11b are shifted toward the fixed area by Δd. Also, the restraint regions 3a, 3b
The boundary is provided near the cutouts 11a and 11b. The printed resistors 5a and 5b form a bridge circuit together with the balance adjusting resistors 12a and 12b as in the second embodiment, and are electrically connected to the lead terminal 7 by the printed electrodes 4a to 4d.

The above is the same as the configuration of the second embodiment.
The following two points are different from the configuration of the second embodiment.

One is the shape of the cutouts 11a and 11b. The notches 11a and 11b have a rectangular shape in which the corners on the fixed region side (corresponding to the corners 8a and 8b in FIG. 2) are left so as not to be cut off. Further, of the two vertices of the side generated by not cutting off, 10b and 10d are near the center lines of the constraint regions 3a and 3b, respectively. Further, regarding the vertices 10a and 10c, when the width when the corners 8a and 8b of the cutouts 9a and 9b are cut off is W, the remaining width when not cut off is at a position of 1/2 or more of W. .

Another point different from the second embodiment is the shape of the free area. The shape of the free region is a shape that tapers toward the free end.

The operation of the configuration of the third embodiment is basically the same as that of the second embodiment. That is,
When acceleration is applied, as described in the second embodiment, the strain concentration due to the bending deformation of the free region outside the cutouts 11a and 11b, the hole 6, and the cutouts 11a and 11b are concentrated. By superimposing the strain distributions due to the stress concentration and further narrowing the superposition strain distribution region by the central tongue 6a of the hole 6,
Distortion is more highly concentrated, and even at high resonance frequencies,
High sensitivity is realized.

Next, a peculiar operation in the configuration of the third embodiment will be described with reference to FIGS. 5 (a) and 5 (b).

FIGS. 5A and 5B are strain distributions in the vicinity of the cutout portion when acceleration is applied. Looking at the strain distribution in more detail in FIG. 5A, the outside of the line connecting the center of the corner 8a and the center of the through hole 2a hardly distorts when acceleration is applied, and can be regarded as a substantially constrained region. for that reason,
Since the maximum strain region is usually generated in the vicinity of the restraint region, it is distributed so as to be applied to the corner portion 8a as shown in the figure. However, at the time of a drop impact, in addition to the tensile strain / compressive strain on the front surface / rear surface, the shear strain generated on the side surface becomes the maximum at this corner portion 8a, which easily becomes the starting point of cracks, and the maximum strain region is added to the corner portion 8a. With such a shape of FIG. 5A, cracks are likely to occur. On the other hand, FIG.
In (b), the notch 11a has a rectangular shape in which the corner on the fixed region side is not cut off, and the remaining width when one of the two vertices of the side that is not cut off is cut off is 1/2. The corner portion 10a described above is used, and the other is a point 10b near the center line of the restraint region. The influence of the position of the corner portion 10a is complicated because the respective shape factors interfere with each other, but the result of examination using both the trial examination and the structural analysis shows that the width W of the cutout portion 11a is different. When the remaining width when not cut off is 1/2 W, the area of the high strain region becomes maximum, and even if it is more than that, the region area remains almost unchanged. At this time, the cantilever 1 is deformed on the line connecting the center of the corner 10a and the center of the through hole 2a and in the vicinity of the constrained region to have the highest curvature.
However, since the corner 10b located at the end of the free region is near the center line of the restraint region and is the closest to the restraint region, the displacement is restrained. Therefore, the corner 10a and the center of the through hole 2a are The region surrounded by the connecting line, the line connecting the corners 10a and 10b, and the boundary line of the constrained region is a free region but is substantially a constrained region. Therefore, the maximum strain region can be narrowed inward of the corner 10b.

Therefore, one is the strain concentration due to the narrowing of the region, and the higher sensitivity can be realized in combination with the strain concentration effect in the second embodiment.

The other is that, as described in the second embodiment, the maximum strain region is not applied to the corner portion 10b, which is likely to be the starting point of crack generation, so that the shape of the crack is low.

Since the free region is tapered toward the free end 1a, the weight distribution becomes lighter toward the free end, and the distance between the center of gravity of the free region and the fixed region becomes shorter, so that the resonance frequency is high. Has become.

As described above, according to the third embodiment, the notches 11a and 11b have a rectangular shape in which the corners on the fixed region side are left without being cut off, and have corners 10a and 10b as vertices. By adopting the shape, in addition to achieving high sensitivity at a higher resonance frequency than the second embodiment, it is possible to improve impact fracture strength such as dropping.

In the first to third embodiments,
When the detection unit is composed of the metal core substrate and the printing resistor directly formed on the metal core substrate, the detection unit can be easily realized by planar processing, and thus a low-cost sensor can be realized.

In the first to third embodiments,
The balance print resistors 12a and 12b are replaced with the print resistors 5a and 5
It is composed of a print resistor formed on the back surface of the surface on which b is formed, a print electrode is formed similarly to the front surface, and the lead terminal 7 is a clip terminal, so that the four resistances are electrically connected. A bridge circuit may be configured by connecting them.

[0044]

As described above, according to the present invention, a cantilever having at least one hole and at least two cutouts is provided relative to a moving body such as an automobile by at least two restraint regions. By fixing and providing a strain resistance element in the part sandwiched between the hole and the notch on the cantilever, it is possible to achieve both high sensitivity and high resonance frequency, and breaking strength. It is intended to realize an excellent acceleration sensor with high efficiency.

[Brief description of drawings]

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

FIG. 2 is a front view of an acceleration sensor according to a second embodiment of the present invention.

FIG. 3 is a front view of an acceleration sensor according to a third embodiment of the present invention.

FIG. 4 is an operation explanatory view of the acceleration sensor of the present invention and the conventional acceleration sensor.

FIG. 5 is an operation explanatory diagram of the acceleration sensor according to the third embodiment of the present invention.

FIG. 6 is a front view of a conventional acceleration sensor.

FIG. 7 is a connection diagram of a bridge circuit in a conventional acceleration sensor.

[Explanation of symbols]

 1 cantilever 2a, 2b through hole 3a, 3b constrained region 4a, 4b, 4c, 4d printed electrode 5a, 5b printing resistor 6 hole portion 7 lead terminal 8a, 8b, 8c, 8d corner portion 9a, 9b, 11a, 11b Notch parts 10a, 10b, 10c, 10d Vertices

Claims (8)

[Claims] 1. A fixed region whose displacement is substantially restrained by at least two restraint regions fixed to a moving body, a free region displaceable relative to the moving body, the restraint region and the free region. And a cantilever having at least one hole and at least two rectangular notches near the hole, and a strain resistance provided in a portion sandwiched between the hole and the notch of the cantilever. An acceleration sensor comprising an element and a lead terminal attached to a fixed region so as to be electrically connected to the strain resistance element. 2. The acceleration sensor according to claim 1, wherein the hole has a substantially U shape in a direction facing the free end of the free region. 3. The acceleration sensor according to claim 2, wherein the boundary of the constrained region and the notch are close to each other. 4. When the hole has a substantially U-shape in a direction facing the free end of the free area, the position of the side of the hole on the fixed area side is closer to the fixed area than the cutout. The acceleration sensor according to claim 3, wherein the acceleration sensor is shifted. 5. The restraint region has two cutouts in the vicinity of the free region in parallel with the restraint region, and has a rectangular shape with at least the corners on the fixed region side. The acceleration sensor according to any one of claims 1 to 4, which is characterized in that. 6. The acceleration sensor according to claim 5, wherein the free region has a tapered shape toward the free end. 7. The notch has a rectangular shape in which a corner is left on the fixed area side, and one of two vertices of a side left with a corner is a point near the center of the constraint area, and The acceleration sensor according to claim 6, wherein one of the points has a remaining width of 1/2 or more when a corner is left. 8. The acceleration sensor according to claim 1, wherein the detection unit includes a metal core substrate and a strain resistance element directly formed on the metal core substrate.