JP2007178195A - Pressure sensor and stress measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor simple in structure capable of realizing miniaturization without necessary of detecting out put on real time, and a method of pressure measuring using such a pressure sensor. <P>SOLUTION: The pressure measuring sensor 1 provided with magnetic powder 2 (e.g. Sm-Fe-N base powder or Nd-Fe-B base powder) and a filling member 3 to be filled with the magnetic powder 2 is used. The pressure sensor 1 is arranged on the pressure measuring part, after the object is subjected to the stress, the magnetic performance of the magnetic powder 2 (e.g. coercive force) is measured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pressure sensor and a stress measurement method using the pressure sensor.

Conventionally, various sensors such as a strain gauge are known as pressure-sensitive sensors for sensing stress (or strain).
Patent Document 1 discloses a stress measurement sensor including a wire made of an amorphous magnetic material and a coil for generating a magnetic field in the amorphous wire as a pressure-sensitive sensor for simplifying and downsizing the structure. Are listed.

On the other hand, an airbag for protecting an automobile driver from an impact at the time of a collision includes, for example, a mechanical sensor as a pressure-sensitive sensor for detecting the impact and an ignition pin when the impact is detected by the mechanical sensor. An all-mechanical sensor comprising a spring for actuating, for example, the above-described mechanical sensor, an element for converting an impact sensed by the mechanical sensor into an electric signal, and calculating the electric signal based on a predetermined condition, and igniting An electromechanical sensor including an output unit for outputting an ignition signal for operating a pin, an acceleration pickup (for example, a piezo element) that captures a deceleration of the vehicle as an electric signal, and the electric signal is predetermined There are roughly classified three types of electronic sensors that include an output unit for calculating the above-described conditions and outputting the ignition signal.
Japanese Patent Laid-Open No. 8-54297

  However, the known pressure-sensitive sensor can only detect when stress is actually applied, that is, the output must be detected in real time. I need it. Therefore, it is difficult to connect these known pressure-sensitive sensors to a measuring device at the time of stress measurement, such as measurement of stress applied to a test vehicle of a collision experiment or measurement of pressure in a cylinder of a vehicle engine. Not suitable for use.

In addition, the various known sensors used in airbags have the disadvantage that the structure is complicated, there are many components, and the sensor itself is large for any of the types described above.
Therefore, an object of the present invention is to provide a pressure sensor that has a simple structure, can be miniaturized, and does not need to detect an output in real time during stress measurement, and a stress measurement method using the pressure sensor. That is.

In order to achieve the above object, a pressure-sensitive sensor according to the present invention includes a magnetic powder having a nucleation type coercive force mechanism and a filling member filled with the magnetic powder.
A magnetic powder having a nucleation type (nucleation type) coercive force mechanism generates magnetization reversal nuclei when subjected to stress, and thus the maximum value of the received stress remains as a history. Therefore, in the pressure-sensitive sensor of the present invention, after receiving the stress, the magnetic powder is taken out from the filling member and the magnetic characteristics thereof are measured, or in a state where the magnetic powder is filled in the filling member. By measuring the magnetic properties of the magnetic powder for each filling member, the maximum stress received by the pressure sensor can be obtained.

Moreover, according to the pressure-sensitive sensor of the present invention, since it is composed of at least a magnetic powder having a nucleation type coercive force mechanism and a filling member filled with the magnetic powder, the structure of the pressure-sensitive sensor is Simplification and miniaturization can be realized.
In the pressure-sensitive sensor according to the present invention, a part of the filling member is opened, and the filling member includes a stress sensing unit that is provided in the opening and transmits stress from the outside to the magnetic powder. Also good.

In this case, it is possible to reliably detect stress from one direction applied to the stress sensing unit without damaging the magnetic powder having a nucleation type coercive force mechanism or a filling member filled with the magnetic powder. Can do.
In the pressure-sensitive sensor according to the present invention, it is preferable that the magnetic powder is an Sm—Fe—N-based powder or an Nd—Fe—B-based powder.

Further, the stress measurement method according to the present invention is a method in which the pressure sensitive sensor according to the present invention is installed at a stress measurement site of an object, and the magnetic property of the magnetic powder is measured after the object receives stress. It is characterized by.
According to the stress measurement method of the present invention, the maximum value of the stress received by the pressure sensor can be obtained based on the magnetic characteristics of the magnetic powder, that is, from the history of stress remaining in the magnetic powder.

According to the pressure sensor of the present invention, the structure can be simplified and the size can be reduced.
Further, according to the pressure sensor of the present invention, after the pressure sensor receives stress, the maximum value of the stress can be measured as a history remaining in the magnetic powder.
Further, according to the stress measurement method of the present invention, it is not necessary to detect the output in real time during the stress measurement, and the pressure sensor receives the stress from the history remaining in the magnetic powder after the pressure sensor receives the stress. Maximum stress can be obtained. Therefore, the stress measurement method of the present invention can be suitably used for applications where it is difficult to connect a measuring device to the pressure sensor during stress measurement.

FIG. 1 shows an embodiment of the pressure-sensitive sensor according to the present invention, in which (a) shows a perspective view and (b) shows a cross-sectional view.
In FIG. 1, the pressure sensor 1 includes a magnetic powder 2 having a nucleation type (nucleation type) coercive force mechanism, and a filling member 3 filled with the magnetic powder 2.
The magnetic powder 2 having a nucleation type coercive force mechanism is characterized in that it generates magnetization reversal nuclei when subjected to stress, and a history remains depending on the degree of the received stress. For example, Sm ₂ Sm—Fe—N based magnetic powder such as F ₁₇ N ₃ , for example, Nd—Fe—B based magnetic powder such as Nd ₂ Fe ₁₄ B, and the like can be mentioned.

In Sm-Fe-N magnetic powder and Nd-Fe-B magnetic powder, the change in magnetic properties due to the formation of magnetization reversal nuclei appears remarkably. Sensitivity and measurement accuracy can be improved. Further, from the viewpoint of difficulty in oxidation, Sm ₂ F ₁₇ N ₃ is particularly preferable among the magnetic powders exemplified above.
The particle diameter of the magnetic powder 2 thus obtained is not particularly limited, but is preferably a single domain particle size, specifically, for example, preferably 1 to 30 μm.

The usage amount of the magnetic powder 2 may be appropriately set according to, for example, the ability of the measuring device for measuring the magnetic properties of the magnetic powder 2, and if the usage amount capable of measuring the coercive force of the magnetic powder 2 is ensured. Good.
The filling member 3 is composed of a container for filling the magnetic powder 2. In this pressure-sensitive sensor 1, the filling member 3 is formed, for example, in a bottomed cylindrical shape with one side opened, A disc-shaped lid portion 4 is provided as a stress sensing portion so as to be closed.

The forming material of the filling member 3 and the lid 4 is appropriately selected according to the method for measuring the magnetic properties of the magnetic powder 2.
That is, for example, when the magnetic properties of the magnetic powder 2 are measured by taking the magnetic powder 2 out of the filling member 3, the forming material of the filling member 3 and the lid 4 is subjected to stress during stress measurement, It is sufficient that the magnetic powder 2 is filled with sufficient rigidity, and either a magnetic material or a nonmagnetic material can be used.

In this case, specific examples of the material for forming the filling member 3 and the lid 4 include various stainless steels, various carbon steels, various alloy steels, various cemented carbide materials (superhard alloy materials), and the like. .
On the other hand, when the magnetic properties of the magnetic powder 2 are measured in a state where the magnetic powder 2 is filled in the filling member 3, that is, when the magnetic properties of the magnetic powder 2 are measured together with the filling member 3, the filling member The material for forming the cover 3 and the lid 4 is required to be a non-magnetic material that has rigidity capable of maintaining the filled state of the magnetic powder 2 even when stress is applied during stress measurement.

Examples of such nonmagnetic materials include austenitic stainless steel (specifically, for example, SUS304, SUS301, SUS304L, SUS305, SUS316, etc.), nonmagnetic superhard materials, nonmagnetic metal materials, and the like. .
The thicknesses of the filling member 3 and the lid 4 are appropriately set according to the use of the pressure sensor 1 and the degree of stress to be measured, and are not particularly limited, but from the viewpoint of improving the accuracy of the pressure sensor 1, the stress It is preferable that the thickness is as thin as possible (that is, the minimum thickness calculated from the predicted stress) as long as it does not break during measurement.

  Specifically, the filling member 3 is, for example, by cutting a cylindrical (round bar) stainless steel into a predetermined length, and then digging the inside to a predetermined depth by cutting such as a lathe, Can be formed. The lid 4 can be formed by machining columnar (round bar) stainless steel into a disk shape corresponding to the inner diameter of the filling member 3 by machining.

And such a filling member 3 is filled with the magnetic powder 2. The filling of the magnetic powder 2 into the filling member 3 is not particularly limited. For example, after the inside of the filling member 3 is replaced with an inert gas (for example, argon gas (Ar), nitrogen gas (N ₂ ), etc.). The magnetic powder 2 described above is introduced from the opening of the filling member 3, and then the opening of the filling member 3 is closed by the lid 4. As a result, the magnetic powder 2 is sealed inside the filling member 3 filled with an inert gas, and oxidation of the magnetic powder 2 is prevented.

In order to ensure such sealing, the gap between the inner peripheral surface of the filling member 3 and the outer peripheral surface of the lid portion 4 is sealed at the opening of the filling member 3. A sealing member such as an O-ring can also be provided.
Further, when the magnetic powder 2 that is not easily oxidized, such as Sm ₂ F ₁₇ N ₃ , is used as the magnetic powder 2 and the time from the production of the pressure sensor 1 to the end of the stress measurement is short. For example, the above-described magnetic powder 2 may be introduced as it is from the opening of the filling member 3 and then the opening of the filling member 3 may be closed by the lid 4.

  The shape of the filling member 3 is not limited to the cylindrical shape shown in FIG. 1, and can be set as appropriate according to the application of the pressure sensor 1. From the viewpoint of improving the accuracy of the pressure-sensitive sensor 1 (in other words, the stress received by the pressure-sensitive sensor 1 directly acts on the change in the magnetic properties of the magnetic powder 2 (formation of magnetization reversal nuclei)). In order to achieve this, a simple shape is preferable, and specific examples include a prismatic shape and a spherical shape in addition to the above-described cylindrical shape.

In the stress measurement method described later, when the magnetic characteristics of the magnetic powder 2 are measured while the magnetic powder 2 is filled in the filling member 3, the magnetic powder 2 is simply sealed in the filling member 3. Therefore, the lid 4 may not be provided.
The pressure sensor 1 manufactured in this way has a simple structure and can be downsized.

Furthermore, the pressure sensor 1 can measure the value of the maximum stress as a history remaining in the magnetic powder 2 after receiving the stress. Therefore, the pressure sensor 1 can be used for various stress measurements.
Next, an embodiment of the stress measurement method of the present invention using the pressure sensor 1 described above will be described.

In this method, first, the pressure-sensitive sensor 1 is disposed on a stress measurement object, preferably in a part of the object that receives stress from the outside. The direction of the pressure-sensitive sensor 1 is not particularly limited, but it is preferable to dispose the lid portion 4 of the filling member 3 in a direction in which stress is applied.
If arranged in this way, stress from one direction applied to the lid 4 can be reliably detected without damaging the magnetic powder 2 and the filling member 3.

  For example, in a vehicle collision experiment, when measuring stress applied to an experimental vehicle, the pressure sensor 1 is attached to the experimental vehicle that is a measurement target. More specifically, for example, in the full-wrap frontal collision test and the offset frontal collision test, the pressure-sensitive sensor 1 is provided, for example, on a vehicle hood, windshield, dashboard, a dummy doll on a driver seat or a passenger seat, In the collision test, it is attached to a door on the driver's seat or the passenger's seat, a dummy doll on the driver's seat or the passenger's seat, etc., for example, in a head impactor in the pedestrian head protection performance test.

Moreover, the attachment of the pressure sensor 1 includes, for example, attachment using an adhesive tape or the like, adhesion using an adhesive, and the like.
After the pressure-sensitive sensor 1 is arranged, stress is applied to the object for stress measurement from the outside.
The external stress is applied, for example, by causing the vehicle to make a frontal collision against the barrier in a full-wrap frontal collision test. In the offset frontal collision test, it is applied by causing the vehicle to collide so that a part of the driver's seat side of the vehicle collides with the barrier. In the side collision test, it is added by causing the vehicle to collide with the door on the driver's seat or passenger's seat. In the pedestrian head protection performance test, the head impactor is added to the vehicle bonnet or the like.

Next, after the pressure-sensitive sensor 1 receives stress, the magnetic powder 2 is taken out of the filling member 3 or is measured while the filling member 3 is filled with the magnetic powder 2. Is calculated from the history remaining in the magnetic powder 2.
Since the magnetic characteristics of the magnetic powder 2 change according to a specific function according to the received stress, the maximum stress received by the pressure-sensitive sensor 1 can be obtained by measuring this.

Specific examples of the magnetic characteristics of the magnetic powder 2 include magnetization characteristics such as the coercive force (Oe or kA / m) of the magnetic powder 2.
Further, the magnetic properties of the magnetic powder 2 are, for example, the magnetic powder 2 taken out from the filling member 3 or the filling member 3 filled with the magnetic powder 2, for example, a vibrating sample magnetometer (VSM), It can be measured using a magnetization characteristic measuring device such as a BH tracer or a magnetic detection circuit such as a Gauss meter.

The VSM is preferably used when the magnetic powder 2 is taken out from the filling member 3 and measured, the BH tracer is preferably used when the magnetic powder 2 is measured together with the filling member 3, and the gauss meter measures in real time. It is preferably used in some cases.
Further, the magnetic characteristics measured by these measurements, for example, the coercive force, can be converted into the maximum stress received from a calibration curve such as a correlation diagram of coercive force-stress characteristics prepared in advance.

As described above, the pressure sensor 1 shown in FIG. 1 can calculate the maximum stress applied from the outside to the pressure sensor 1 from the history remaining in the magnetic powder 2. There is no need to connect to measuring equipment and there is no need to measure in real time.
Therefore, the pressure-sensitive sensor 1 shown in FIG. 1 includes, for example, the measurement of the pressure in the cylinder of the engine and the pressure sensor 1 such as a closed space or a rotating object in addition to the above-described vehicle collision experiment. And it can use for the stress measurement about the target object with which connection with the measuring device of the magnetic characteristic of magnetic powder 2 is difficult.

Moreover, the pressure sensor 1 shown in FIG. 1 can also measure the stress applied to the pressure sensor 1 in real time by connecting with the filling member 3 and a measuring device.
Therefore, the pressure-sensitive sensor 1 shown in FIG. 1 can be used for applications such as a strain gauge substitute and a crustal deformation measuring device, for example.
Next, an example in which the pressure sensor of the present invention is applied to an airbag system will be described.

FIG. 2 is a schematic configuration diagram of a pressure-sensitive sensor 5 according to another embodiment of the present invention and an airbag system using the pressure-sensitive sensor 5.
In FIG. 2, this pressure-sensitive sensor 5 includes a magnetic powder 2 having the above-described nucleation type coercive force mechanism, a filling member 6 that is partially provided with an open portion and is filled with the magnetic powder 2; And a stress sensing unit 7 provided at the opening of the filling member 6.

  Further, a measuring device 10 for measuring the magnetic characteristics of the magnetic powder 2 is connected to the filling member 6 of the pressure sensor 5, and the measuring device 10 is added to the pressure sensor 5 from the outside. A control unit 11 comprising a constant current diode for inflating the airbag 12 when the stress is compared with a preset threshold for the stress and the stress reaches a preset threshold, It is connected.

The filling member 6 includes a large-diameter portion 6a facing the open portion, and a small-diameter portion 6b formed continuously from the large-diameter portion 6a and filled with the magnetic powder 2.
The stress sensing portion 7 is formed in a substantially T-shaped cross section that matches the large diameter portion 6a and the small diameter portion 6b of the filling member 6, and is fitted to the flange portion 7a that fits the large diameter portion 6a and the small diameter portion 6b. Shaft portion 7b.

The stress sensing unit 7 is supported so as to be able to advance and retreat with respect to the filling member 6, and when the flange portion 7 a of the stress sensing unit 7 slides on the large diameter portion 6 a of the filling member 6, the stress sensing unit 7. The forward and backward movement of the shaft portion 7b with respect to the small diameter portion 6b of the filling member 6 is guided.
As the measuring device 10, a Gauss meter is used among the measuring devices described above. In the pressure-sensitive sensor 5 shown in FIG. 2, the magnetic characteristics of the magnetic powder 2 can be measured in real time by using a gauss meter.

  The pressure-sensitive sensor 5 is attached to the vehicle, and when the vehicle collides during traveling, the flange portion 7a of the stress sensing unit 7 receives stress due to the collision. Further, when the flange portion 7 a receives stress due to collision, the stress sensing portion 7 advances with respect to the filling member 6, and the shaft portion 7 b presses the magnetic powder 2 filled in the small diameter portion 6 a of the filling member 6. To do. Thereby, the magnetic characteristic of the magnetic powder 2 changes according to the stress received by the flange part 7a.

The measuring device 10 connected to the filling member 6 detects a change in the magnetic characteristics of the magnetic powder 2 and inputs the change to the control unit 11.
Next, the control unit 11 calculates the magnitude of the stress received at the flange portion 7a based on the change in the magnetic characteristics of the magnetic powder 2, and when the stress reaches a preset threshold, for example, ignition of an airbag The device is ignited and the airbag 12 is inflated.

In order to improve the measurement accuracy of the stress, the shaft portion 7b of the stress sensing unit 7 is disposed along the stress sensing direction (the direction of receiving an impact at the time of collision), and the flange portion 7a is arranged in the sensing direction. It is arranged vertically with respect to it.
The pressure-sensitive sensor 5 shown in FIG. 2 has a simple structure and can be downsized. Therefore, according to the airbag system shown in FIG. 2, the sensor can be simplified and downsized.

A pressure-sensitive sensor 1 according to the embodiment shown in FIG. 1 was produced, and the change in the coercive force of the magnetic powder 2 with respect to the stress applied to the magnetic powder 2 having a nucleation type coercive force mechanism was measured.
As the magnetic powder 2 having a nucleation type coercive force mechanism, Sm ₂ Fe ₁₇ N ₃ magnetic powder (average particle size 2.5 μm) was used. It was 525.2 kA / m when the coercive force of the magnetic powder 2 was measured with the vibrating sample magnetometer (VSM). The coercive force at this time was set as an initial value.

In addition, a cylindrical member (diameter 20 mm) of a super hard material (WC; tungsten carbide) is ground with a lathe to form a hollow portion having an inner diameter of 3 mm. Used a super hard material (WC) having a disk shape (diameter 3 mm, length 10 mm).
The pressure-sensitive sensor 1 was produced by putting 0.5 g of the magnetic powder 2 into the hollow portion of the bottomed substantially cylindrical filling member 3 and sealing it with the lid portion 4.

Next, the pressure-sensitive sensor 1 was fixed to the tip of a carriage having a weight of 20 kg with an epoxy adhesive, and the carriage was made to collide with a steel plate barrier (rigid barrier) at a speed of 5 km / h. The collision mode was a so-called frontal collision, and was set so that the stress at the time of collision was applied in a direction perpendicular to the axial direction of the filling member 3.
After the collision, the magnetic powder 2 in the pressure sensor 1 was taken out, and its coercive force was measured by VSM.

Thereafter, the stress (MPa) applied to the pressure sensor 1 was obtained from the measured coercivity of the magnetic powder 2 based on the calibration curve shown in FIG.
As a result, the coercive force measured by VSM was 496.8 kA / m. Therefore, when the corresponding stress was read from the calibration curve, the applied stress was 215 MPa. Moreover, it turned out that the impact force is 6080 kN by applying the cross-sectional area of the filling member 6 to this.

The calibration curve shown in FIG. 3 can be created from the coercive force-stress characteristics measured in advance. Specifically, the applied stress (horizontal axis) is x and the coercive force (longitudinal) by regression calculation. When the axis is y, the following equation (1) is obtained.
y = -2 × 10 ⁻⁷ x ³ + 2 × 10 ⁻⁴ x ² −0.1739x + 525.19 (1)
Moreover, the electron micrograph in the initial state (state before stress is applied) of the magnetic powder 2 is shown in FIG. 4A, and the electron micrograph when stress (215 MPa) is applied to the magnetic powder 2 is shown. This is shown in 4 (b).

4 (a) and FIG. 4 (b), when the magnetic powder 2 receives stress, the magnetic powder 2 is damaged, such as cracks 20 and surface roughness (scratches) 21 occur. I understand that I am receiving it. In addition, when the magnetic powder 2 receives stress, magnetization reversal nuclei are formed in the magnetic powder 2, and the magnetic characteristics of the magnetic powder 2 change as shown in FIG.
The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

It is a figure which shows one Embodiment which concerns on the pressure sensor of this invention, Comprising: (a) shows a perspective view, (b) shows sectional drawing. It is a block diagram which shows other embodiment which concerns on the pressure-sensitive sensor of this invention, and the structural example of an airbag system using the same. It is a graph which shows the relationship between the stress provided to magnetic powder, and the coercive force of magnetic powder. It is an electron micrograph of magnetic powder, (a) shows the state before giving stress to magnetic powder, and (b) shows the state after giving stress to magnetic powder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressure sensor 2 Magnetic powder 3 Filling member 5 Pressure sensitive sensor 6 Filling member 7 Force sensing part

Claims (4)

  A pressure-sensitive sensor comprising a magnetic powder having a nucleation type coercive force mechanism and a filling member filled with the magnetic powder.   2. The filling member according to claim 1, wherein a part of the filling member is open, and is provided in the open part, and includes a stress sensing part for transmitting external stress to the magnetic powder. The pressure-sensitive sensor described in 1.   The pressure-sensitive sensor according to claim 1, wherein the magnetic powder is Sm—Fe—N-based powder or Nd—Fe—B-based powder.   The pressure sensitive sensor according to any one of claims 1 to 3 is installed at a stress measurement site of an object, and the magnetic property of the magnetic powder is measured after the object receives stress. A stress measurement method.