JPH11183515A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor which has excellent frequency characteristics, high precision, and high reliability. SOLUTION: This sensor is equipped with a case 20 as a fixed body which is fixed to a fitted body, a weight 3, a strain inducer 1 consisting of fixed area parts 2a, 2b, 2c, and 2d at least four places provided at the same periphery for fixation to the case 20 and a beam which extends toward the center of a circle to connect the weight 3, and an alloy thin-film resistance body as a detecting means which varies in electric characteristics according to variation in strain quantity generated in the beam owing to acceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an acceleration sensor used for vehicle control and the like.

[0002]

2. Description of the Related Art Conventionally, an acceleration sensor as shown in FIG. 8 has been proposed. 8, 101 is a cantilever, 102 is a strain resistance element, 103 is a weight, 104
Is a fixed area portion, 105 is a case, 106 is a connection terminal, 1
07 is a silicone oil.

The cantilever 101 has a fixed area 104
Is fixed to the case 105. A weight 103 is attached to a free end of the cantilever 101. Strain resistance elements 102 are adhered to the front and back of the cantilever 101 in the vicinity of the fixed region 104 to form a full bridge and are connected to the connection terminals 106. Silicone oil 1 is contained in case 105 to suppress resonance of cantilever 101.
07 are filled. When acceleration is applied to the vehicle, acceleration is also applied to the case 105 attached to the vehicle, but the weight 103 at the free end of the cantilever 101 tries to maintain the current position by inertia. Therefore, relative displacement between the weight 103 and the fixed area portion 104, that is, bending occurs. Due to this bending, a maximum distortion occurs near the fixed area portion 104 of the cantilever 101. This distortion is detected as a change in the resistance value by the distortion resistance element 102, and further transmitted to an electric circuit via the connection terminal 106 to obtain a signal corresponding to the acceleration.

[0004]

In the above prior art,
It is easy to increase the strain sensitivity because of the cantilever method, but there is a problem that the resonance frequency is inevitably too low to obtain necessary frequency characteristics. Therefore, the case 105 is filled with the silicone oil 107 to suppress resonance. However, the viscosity change of the silicone oil 107 due to the temperature is large and is greatly affected by the change. Further, a complicated means is required to reduce the influence, and there is a problem that the assemblability is deteriorated and the reliability is easily lowered.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a highly accurate and highly reliable acceleration sensor having good frequency characteristics.

[0006]

In order to solve this problem, an acceleration sensor according to the present invention comprises a fixed member fixed to an object to be mounted, a weight, and the same circumference for fixing to the fixed member. A flexure element comprising at least four fixed area portions provided and a beam extending toward the center of the circle and connecting the weights;
Detecting means for changing electrical characteristics in accordance with a change in the amount of strain generated in the beam due to acceleration. With this configuration, an acceleration sensor with good frequency characteristics, high accuracy and high reliability can be obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a fixed body fixed to an attached body, a weight, and at least one provided on the same circumference for fixing to the fixed body. A flexure element comprising four fixed area portions and a beam extending toward the center of the circle and connecting the weights; and a detecting means whose electric characteristics change in accordance with a change in the amount of strain generated in the beam due to acceleration. Therefore, there is an effect that the resonance frequency can be increased while securing the strain sensitivity comparable to that of the cantilever method.

According to a second aspect of the present invention, in the first aspect, the strain-generating body is made of any one of a ferritic stainless steel, a precipitation hardening stainless steel, and a 36Ni-12Cr alloy. It has the effect of increasing the strength of the body and increasing the impact resistance.

According to a third aspect of the present invention, in the first aspect of the invention, since the voids on the strain body are buried with a resin-based insulator, an insulating layer is further formed thereon by a thin film process. It has the effect of being able to form stably when formed.

According to a fourth aspect of the present invention, in the first aspect of the present invention, since a low distortion region is provided between the fixed region and the beam, the influence of uneven distortion near the fixed region is provided. Has the effect of being able to suppress the spread over the beam.

According to a fifth aspect of the present invention, in the first aspect of the present invention, since the widened portion is provided substantially at the center of the beam,
This has the effect that a high strain region due to stress concentration can be secured near the widened portion.

According to a sixth aspect of the present invention, in the first aspect of the present invention, at least one pair of detecting means are provided on both sides of the widened portion provided substantially at the center of the beam. A large change in electrical characteristics according to positive strain on one side and a large change in electrical characteristics according to negative strain on the other side can be formed on the same beam, and at the same time the resonance frequency can be increased. Have.

According to a seventh aspect of the present invention, in the first or the third aspect of the present invention, the detecting means includes a beam formed by the thin film process via the insulating layer formed on the strain body by the thin film process. Since it is an alloy thin film resistor formed thereon, it has an effect that temperature characteristics as an acceleration sensor are good.

According to an eighth aspect of the present invention, in the first aspect of the invention, at least two alloy thin film resistors having the same resistance increasing and decreasing directions are used, and the alloy thin film resistors are connected in series. In addition, since one side of the bridge circuit is configured, an effect that an optimal impedance can be secured as a bridge configuration is provided.

According to a ninth aspect of the present invention, in the first aspect of the present invention, an amplifier circuit for amplifying a signal from the detecting means and a filter circuit are provided. This has the effect that unnecessary frequency components can be easily removed.

According to a tenth aspect of the present invention, in the fourth aspect of the present invention, a terminal electrode for extracting a signal from the detecting means is provided between the fixed region and the low distortion region. Has the effect of minimizing the stress applied to the wire and ensuring the connection reliability.

According to an eleventh aspect of the present invention, in the first aspect of the present invention, a support plate is provided between the flexure element and the fixed body, the support plate being separated from the beam and the weight. It is possible to handle the distorted body after attaching it to the support plate in advance, not only has the effect of preventing inadvertent damage,
When the flexure element is fixed to the fixed body, deformation due to external force or the like can be prevented, and at the same time, the assembling property is improved.

According to a twelfth aspect of the present invention, in the first aspect, the magnetic flux generating means is attached to the fixed body so that the magnetic flux links with the non-magnetic and conductive weight. This has the effect of preventing the deterioration of the frequency characteristic due to the decrease in the resonance frequency, which occurs when higher sensitivity is achieved.

According to a thirteenth aspect of the present invention, in the twelfth aspect of the present invention, since the magnetic flux generating means comprises a magnet and a yoke for inducing the magnetic flux, energy is supplied from outside to generate the magnetic flux. There is no need to save power, and at the same time, the yoke has the effect of efficiently converging the magnetic flux to the weight.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a sectional view of a first embodiment of an acceleration sensor according to the present invention after assembly is completed. FIG. 2 is a plan view for explaining in detail the flexure element portion according to the first embodiment of the present invention. FIG. 3 is a sectional view of the flexure element according to the first embodiment of the present invention. FIG. 4 is a plan view for explaining in detail the positional relationship of the alloy thin-film resistors provided on the strain element according to the first embodiment of the present invention. FIG. 5 is a plan view for explaining the detailed positional relationship of the support plate according to the first embodiment of the present invention, and shows the strain generating body shown in FIG. 2 as viewed from the back. FIG. 6 is a block diagram of a bridge circuit for converting a change in resistance value into a signal voltage according to the first embodiment of the present invention.

1 to 6, reference numeral 1 denotes a ferritic stainless steel, a precipitation hardening stainless steel, or 36Ni-12.
This is a square plate-shaped flexure element made of a high-yield strength metallic material such as a Cr-based alloy. The periphery of this flexure element 1 is on the same circumference and has four fixed region portions 2a, 2b, 2c,
Four beams 6a, 6b, 6 extending toward the center of the circle with 2d
c, 6d. 3 is two cylindrical weights, 4
Are two beams 3a, 6b,
A fixing pin 5 connected to the front and back of 6c and 6d, a ring-shaped support plate 5 spot-welded to the fixing area portions 2a, 2b, 2c and 2d of the flexure element 1, and 20 a weight 3 capable of storing the weight 3 Is a case as a fixed body having a stepped portion at a part of the bottom so that only a predetermined amount of displacement is allowed, and is fixed to an attached body such as a vehicle. Reference numeral 21 denotes a stopper having a stepped portion capable of storing the weight 3 and circuit components and allowing the weight 3 to be displaced only by a predetermined amount. The support plate 5 and the stopper 21 are screwed to the case 20. Reference numeral 22 denotes terminal electrodes 12a, 12b, 12c, 12d, 12e, and 12 on the flexure element 1.
f, a flexible board for electrical connection with f; 23, a circuit board on which circuit components are mounted by being screwed to the stopper 21; 24, a terminal which is electrically connected to the circuit board 23 to take out an output signal; 25, a terminal 24 Only penetrates case 2
0 is the cover sealed.

In FIG. 2, beams 6a, 6b, 6c, 6d
Are provided with widened portions 6e, 6f, 6g, 6h, respectively. Also, beams 6a, 6b, 6
c and 6d, the low strain region portions 7a,
7b, 7c, and 7d exist.

In FIG. 3, 1 is a strain body, 50 is a resin-based insulator in which voids on the surface of the strain body 1 are filled by CVD, and 8 is a resin-based insulator formed on the surface of the strain body 1. The insulating layer 9 is an insulating layer made of alumina formed by sputtering. The maximum height of the surface roughness corresponding to the depth of the void of the flexure element 1 is about 0.1 μm. The surface of the strain generating element 1 is coated with a resin-based insulator 50 by CVD so as to have a thickness corresponding to about 6 times or more of this value, and then planarized by polishing to obtain a resin-based insulator. At 50, the resin-based insulating layer 8 is completed at the same time as the portion in which the void is buried. By employing the high-strength flexure element 1 as described above,
It is also possible to increase the impact resistance.

In FIG. 4, insulating layers 8 and 9 as shown in FIG. A widened portion 6e is provided substantially at the center of the beam 6a of the strain generating element 1. Near the widened portion 6e, a comb-shaped alloy thin film resistor 11a made of NiCrAl is formed by sputtering. further,
On the opposite side of the widened portion 6e from the alloy thin film resistor 11a and near the low distortion region 7a, a comb-shaped alloy thin film resistor 11e made of NiCrAl is formed by sputtering. These alloy thin film resistors 11a and 11e are connected by electrodes. Next, Table 1 shows detailed assignments of each beam, each widened portion, and each alloy thin film resistor in FIG.

[0025]

[Table 1]

The alloy thin film resistors 11a, 11b, 11c,
11d, 11e, 11f, 11g, and 11h are connected to each other, and finally, the fixed region portions 2a, 2
b, 2c, 2d and the six terminal electrodes 12a, 1 formed between the low distortion region portions 7a, 7b, 7c, 7d, respectively.
2b, 12c, 12d, 12e, and 12f.
These terminal electrodes 12a, 12b, 12c, 12d, 1
2e and 12f are fixed region portions 2 where uneven fastening distortion remains.
In addition to avoiding the effects of a, 2b, 2c, and 2d, the stress generated in these parts is kept extremely small even when acceleration is applied, so that connection reliability is ensured.

In this embodiment, the six terminal electrodes 12a, 12b, 12c, 12d, 12e and 12f are connected to a circuit board 23 via a flexible board 22. The output subjected to signal processing by the circuit mounted on the circuit board 23 is guided to the outside of the cover 25 of the sensor by the terminal 24.

In FIG. 5, a support plate 5
Are installed, and the support plate 5 further includes beams 6a, 6b, 6c, 6
d and the weight 3, the strain-generating body 1 is attached to the support plate 5 in advance to prevent the damage from being inadvertently damaged. This has the effect of preventing deformation due to external force or the like when fixing the, and also improving the assemblability.

In this embodiment, when acceleration is applied to the vehicle, acceleration is simultaneously applied to the case 20 fixed to the vehicle, but the weights connected to the beams 6a, 6b, 6c, 6d on the flexure element 1 are also provided. Since the weight 3 is trying to maintain the current position by inertia, the weight 3 is displaced relative to the case 20. This displacement appears on the beam 6a shown in FIG. 4 as distortion having the opposite sign relationship between the weight 3 and the low distortion region 7a with the widened portion 6e as a boundary. Therefore, if the resistance value of the alloy thin film resistor 11a on the beam 6a increases, the resistance value of the alloy thin film resistor 11e decreases.
Similarly, each resistance value of the alloy thin film resistors 11b, 11c, 11d increases, and each resistance value of the alloy thin film resistors 11f, 11g, 11h decreases.

In this embodiment, the beams 6a, 6b, 6
The widened portions 6e, 6f, 6g, and 6h are provided in c and 6d, respectively, so that the widened portions 6e, 6f, 6g, and 6h serve as nodes at the time of deformation. Thereby, the beams 6a, 6
b, 6c, 6d, the low distortion region portions 7a, 7b, 7
A site where a large strain is generated near the c and 7d sides and near the widened portions 6e, 6f, 6g and 6h and on the side of the weight 3 (stress concentration site).
Can be provided. The alloy thin film resistors 11a, 11b, 11c,
Since 11d, 11e, 11f, 11g, and 11h are arranged, a large change in resistance value can be obtained. With this configuration, the resonance frequency of the beam is more than doubled (about 150 Hz) while obtaining a distortion amount (about 140 με / G) comparable to that of a cantilever. Thereby, sufficient frequency characteristics can be secured in the frequency range (0 to 25 Hz) required for vehicle control.

Further, a portion where a large strain is generated (stress concentrated portion) near the widened portions 6e, 6f, 6g, 6h and on the side of the weight 3.
Can be provided, so that it is possible to avoid a portion where uneven distortion remains, such as the vicinity where the weight 3 is fixed. Similarly, the presence of the low distortion regions 7a, 7b, 7c, and 7d allows the fixed regions 2a, 2b, and 2 to retain uneven distortion.
The alloy thin film resistors 11e, 11f, 11g and 11h can be arranged on the beams 6a, 6b, 6c and 6d while avoiding the influence of c and 2d.

In FIG. 6, eight alloy thin film resistors 11
a, 11b, 11c, 11d, 11e, 11f, 11
g and 11h constitute a full bridge. In addition, since one side of the bridge is formed by combining two resistors having the same resistance increasing and decreasing tendency like the alloy thin film resistors 11a and 11b, an optimum impedance can be secured. Further, the opposite sides of the bridge are constituted by alloy thin film resistors 11c and 11d, the alloy thin film resistors 11a and 11e are respectively connected to a power source, and the alloy thin film resistors 11c and 11h are respectively connected to ground. The connection point between the alloy thin film resistors 11b and 11g and the connection point between the alloy thin film resistors 11d and 11f are respectively connected to the amplifier 60.
The signal is differentially amplified to a desired magnitude, and an unnecessary signal is attenuated by the filter circuit 70 to obtain an output.

The alloy thin film resistors 11a, 11b, 11c, 11d, 11e,
11f, 11g, and 11h have very small temperature coefficients of resistance, so that when driven at a power supply voltage of 5 V, the temperature drift is ± 3.
% FS can be suppressed. Further, the alloy thin film resistors 11a, 11b, 11c, 11d, 11e, 11
Between the fact that the temperature coefficients of resistance f, 11g and 11h are extremely small and that a large amount of distortion can be secured, the amplification circuit 6
It is also possible to keep the gain of 0 within 400 times.

In the present embodiment, since the flexure element 1 made of a metal material having high proof stress is used, a relatively large displacement is allowed to secure a predetermined amount of distortion. Therefore,
The gap between the case 20 and the weight 3 and the gap between the stopper 21 and the weight 3 can be optimized in consideration of the assembly tolerance of each component. In this configuration, any gap can be secured to 0.3 mm or more. Also, case 20
Since the displacement of the weight 3 can be restricted by the stopper 21 and the stopper 21, it is possible to prevent damage due to an impact such as dropping.

In the present embodiment, the alloy thin film resistors 11a, 11b, 11
Although examples using c, 11d, 11e, 11f, 11g, and 11h have been described, various types such as a piezoresistor, a piezoelectric, and a magnetic material made of a semiconductor whose electrical characteristics change are not necessarily specified. Things are possible.

(Embodiment 2) FIG. 7 is a sectional view of an acceleration sensor according to a second embodiment of the present invention after assembly is completed. 7, the same components as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different portions will be described in detail. In FIG. 7, reference numeral 3 denotes a nonmagnetic and conductive weight such as copper or aluminum; 30 denotes a magnet as a rectangular parallelepiped magnetic flux generating means having N and S poles attached to the bottom of the case 20; Is a yoke made of an iron-based magnetic material housed in the case 20 and bonded to the magnet 30.

The magnetic flux emitted from the magnet 30 is applied to the yoke 31
a, 31b, and are linked to the weight 3. Therefore,
When an acceleration is applied and the non-magnetic and conductive weight 3 moves in the interlinkage magnetic flux, an eddy current is generated, which functions as a vibration damping action. The temperature characteristic of this vibration damping function basically depends on the magnet 30 and the yoke 3
Since it is determined by the temperature characteristics of the magnetic characteristics of 1a and 31b and the temperature characteristics of the conductivity of the weight 3, it is extremely good as compared with the case using the silicone oil 107 described in the conventional example.

Further, with the configuration described in the present embodiment, it is possible to prevent the deterioration of the frequency characteristic due to the decrease of the resonance frequency which occurs when the sensitivity is further improved. That is, it is possible to achieve a higher frequency characteristic band. Further, since the magnets 30 and the yokes 31a and 31b for inducing the magnetic flux are used as the magnetic flux generating means, there is no need to supply energy from the outside to generate the magnetic flux, and power can be saved. At the same time, the yokes 31a and 31b have the effect of efficiently converging the magnetic flux to the weight 3.
Needless to say, even if an electromagnet is used as the magnetic flux generating means, a braking force due to eddy current can be obtained.

[0039]

As described above, according to the present invention, there are provided a fixed body fixed to an attached body, a weight, and at least four fixing area portions provided on the same circumference for fixing to the fixed body. A flexure element comprising a beam extending toward the center of gravity and a beam connecting the weight, and a detecting means whose electric characteristics change in accordance with a change in the amount of strain generated in the beam due to acceleration. An acceleration sensor with good characteristics, high accuracy and high reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the present invention after assembly is completed.

FIG. 2 is a plan view for explaining a flexure element in the present embodiment in detail.

FIG. 3 is a cross-sectional view of a strain body according to the present embodiment.

FIG. 4 is a plan view illustrating a positional relationship of an alloy thin-film resistor provided on a strain body in the present embodiment in detail.

FIG. 5 is a plan view illustrating a detailed positional relationship of a support plate in the present embodiment.

FIG. 6 is a block diagram of a bridge circuit for converting a change in resistance value into a signal voltage according to the embodiment;

FIG. 7 is a sectional view of the second embodiment of the present invention after assembly is completed.

FIG. 8 is a cross-sectional view of a conventional acceleration sensor after assembly is completed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Flexure body 2a, 2b, 2c, 2d Fixed area part 3 Weight 4 Fixed pin 5 Support plate 6a, 6b, 6c, 6d Beam 6e, 6f, 6g, 6h Widening part 7a, 7b, 7c, 7d Low distortion area part 8, 9 insulating layers 11a, 11b, 11c, 11d, 11e, 11f, 1
1g, 11h Alloy thin film resistor 12a, 12b, 12c, 12d, 12e, 12f Terminal electrode 20 Case 21 Stopper 22 Flexible board 23 Circuit board 24 Terminal 25 Cover 30 Magnet 31a, 31b Yoke 50 Insulator 60 Amplifying circuit 70 Filter circuit

Claims (13)

[Claims] 1. A fixed body fixed to an attached body, a weight, and at least four fixed area portions provided on the same circumference for fixing to the fixed body and extending toward the center of the circle. An acceleration sensor comprising: a flexure element composed of a beam connecting a weight; and a detection unit whose electrical characteristics change in accordance with a change in the amount of strain generated in the beam due to acceleration. 2. The acceleration sensor according to claim 1, wherein the strain element is made of one of ferrite stainless steel, precipitation hardening stainless steel, and 36Ni-12Cr alloy. 3. The acceleration sensor according to claim 1, wherein a void on the strain body is buried with a resin-based insulator. 4. The acceleration sensor according to claim 1, wherein a low distortion region is provided between the fixed region and the beam. 5. The acceleration sensor according to claim 1, wherein a widened portion is provided substantially at the center of the beam. 6. At least one pair of detection means is provided on both sides of a widened portion provided substantially at the center of the beam.
2. The acceleration sensor according to 1. 7. The method according to claim 1, wherein the detecting means is an alloy thin film resistor formed on the beam by a thin film process via an insulating layer formed on the strain body by a thin film process. The acceleration sensor as described in the above. 8. The bridge circuit according to claim 7, wherein at least two alloy thin-film resistors having the same resistance increasing and decreasing directions are used, and the alloy thin-film resistors are connected in series to constitute one side of a bridge circuit. Acceleration sensor. 9. The acceleration sensor according to claim 1, further comprising an amplification circuit for amplifying a signal from the detection means and a filter circuit. 10. The acceleration sensor according to claim 4, wherein a terminal electrode for extracting a signal from the detection means is provided between the fixed region and the low distortion region. 11. The acceleration sensor according to claim 1, wherein a support plate separated from the beam and the weight is provided between the strain body and the fixed body. 12. The acceleration sensor according to claim 1, wherein the magnetic flux generating means is attached to the fixed body so that the magnetic flux links to the non-magnetic and conductive weight. 13. The acceleration sensor according to claim 12, wherein the magnetic flux generating means comprises a magnet and a yoke for inducing a magnetic flux.