WO2022201937A1

WO2022201937A1 - Magnet for detecting tire wear, tire wear sensor using magnet, and tire

Info

Publication number: WO2022201937A1
Application number: PCT/JP2022/005208
Authority: WO
Inventors: 学田村; 裕樹大野; 寿人小柴; 章伸小島; 徳男中村; 佑貴今井; 利恵黒澤; 貴史野口; 広人瀬戸川; 睦樹杉本
Original assignee: アルプスアルパイン株式会社; 住友ゴム工業株式会社
Priority date: 2021-03-25
Filing date: 2022-02-09
Publication date: 2022-09-29
Also published as: JPWO2022201937A1; JP7356619B2

Abstract

In a magnet 1 for detecting tire wear according to the present invention, the attraction of iron or the like due to the magnetism of a magnet exposed on the surface of a tread is suppressed, the magnet 1 for detecting tire wear being embedded in a tread 21 of a tire 2 and comprising a soft magnetic material layer 11 containing a soft magnetic material and a hard magnetic material layer 12 containing a hard magnetic material, wherein the magnet is magnetized in a Y-axis direction which is the layering direction of the soft magnetic material layer 11 and the hard magnetic material layer 12. Since the magnetism in the Y-axis direction emitted from a magnetic pole end 14 is reduced by the soft magnetic material layer 11, the attraction force that attracts iron or the like can be suppressed.

Description

Magnets for tire wear detection, tire wear sensors and tires using magnets

The present invention relates to a tire wear detection magnet embedded in a tire to detect tire wear, a tire wear sensor using a magnet, and a tire.

As tire wear progresses, grip performance when driving on a road surface and drainage performance for discharging water between the tire and the road surface when driving on a wet road surface deteriorate. Therefore, it is necessary for drivers and vehicle managers to visually inspect the worn state of the tread portion of the tire and replace the tire before the usage limit is exceeded in order to ensure safety. Visual inspection is performed by confirming the slip sign provided in the groove of the tire, but there is a risk of erroneously evaluating the state of wear. Moreover, since the inspection work is complicated, it is conceivable that some users do not perform the inspection. If the wear state of the tread portion is incorrectly evaluated or not evaluated, the tire exceeding the service limit may continue to be used, which is undesirable from the viewpoint of safety.
Therefore, a tire wear detection system has been proposed that measures the degree of wear of a tire by a method other than visual observation and detects that the performance of the tire has deteriorated. For example, in Patent Document 1, a magnetic sensor capable of detecting magnetism emitted by a tire wear detection magnet embedded in the tread portion of a tire is provided at a position facing the tire wear detection magnet on the inner surface of the tire. A tire wear sensor is described. This device detects the degree of tire wear by measuring changes in the magnetism of magnets that wear along with the tread.

JP 2019-203831 A

The tire wear sensor described in Patent Literature 1 measures the degree of wear of the tread portion based on changes in magnetism due to wear of magnets embedded in the tread portion. For this reason, the magnet is embedded in the tire so that one of the magnets is exposed on the surface of the tread portion so that it wears together with the tread portion. Therefore, there is a possibility that the tire may be damaged by an iron nail or the like attracted by the magnetism of the magnet exposed on the tread surface.
SUMMARY OF THE INVENTION An object of the present invention is to provide a tire wear detection magnet, a tire wear sensor using the same, and a tire that suppress the attraction of iron or the like by the magnetism of the magnet exposed on the surface of the tread portion.

A magnet for detecting tire wear according to one aspect of the present invention provided to solve the above problems is a magnet for detecting tire wear that is embedded in a tread portion of a tire, and includes a soft magnetic layer made of a soft magnetic material. and a hard magnetic layer made of a hard magnetic material, and is magnetized in the stacking direction of the soft magnetic layer and the hard magnetic layer.
By stacking the soft magnetic layer and the hard magnetic layer, magnetism from the hard magnetic layer is induced by the soft magnetic layer in a direction intersecting the lamination direction. The magnetism in the lamination direction can be made smaller than that of the magnet. Therefore, when the magnet is embedded so that the radial direction of the tire is aligned with the stacking direction, the attraction force that attracts iron or the like to the exposed surface of the tread portion can be suppressed.

Preferably, the soft magnetic layers and the hard magnetic layers are alternately stacked along the stacking direction, and the soft magnetic layers and the hard magnetic layers are paired.
Preferably, the thickness of the soft magnetic layer is smaller than the thickness of the hard magnetic layer.
With this configuration, the magnetism of the exposed surface of the magnet in the stacking direction can be reduced to suppress the attraction force to iron or the like, and the wear of the tire can be easily detected based on the change in magnetism accompanying the wear of the magnet.

One end in the stacking direction may be the hard magnetic layer.
One end in the magnetization direction may be the hard magnetic layer and the other end may be the soft magnetic layer.
By forming one end of the magnet as a hard magnetic layer, it is possible to efficiently detect the degree of wear of the magnet based on the change in magnetism on the one end side. Further, if the other end is formed of a soft magnetic layer, the intensity and range of magnetism on the other end side can be made smaller than those on the one end side.

It is preferable that a cross-sectional area of a cut surface orthogonal to the stacking direction increases from the one end toward the other end.
It is preferable that the cut surface has a circular shape.
Preferably, the hard magnetic layer is ferrite, and the soft magnetic layer is sendust.
With these configurations, it is possible to improve the correspondence between the degree of wear of the magnet and the change in magnetism while suppressing the attracting force of the exposed surface of the magnet to iron or the like.

The tire wear sensor of the present invention is arranged at a position facing the magnet of the present invention embedded in the tread portion of the tire and the magnet on the inner surface of the tire, and is capable of detecting magnetism emitted by the magnet. a magnetic sensor, wherein the magnetic sensor measures the magnetism in a direction intersecting the lamination direction of the magnets to measure the amount of wear of the tire.
By including the soft magnetic layer in the magnet, the magnetism from the hard magnetic layer can be induced in the direction intersecting the stacking direction, which is the magnetization direction. Therefore, by reducing the magnetism in the stacking direction and suppressing the attraction of iron or the like to the exposed surface of the magnet, by measuring the magnetism in the direction intersecting the stacking direction, which changes according to the degree of wear of the magnet, with a magnetic sensor. , tire wear can be measured.

The soft magnetic layers and the hard magnetic layers are alternately laminated along the lamination direction, the soft magnetic layers and the hard magnetic layers are paired, and the soft magnetic layers The thickness of the layer is preferably smaller than the thickness of the hard magnetic layer.
With this configuration, it is possible to reduce the magnetism in the stacking direction on the exposed surface of the magnet and increase the change in magnetism as the wear of the magnet progresses. Therefore, the exposed surface of the magnet can suppress the force of attracting iron or the like, and the degree of wear of the tire can be detected with high accuracy.

It is preferable that one end of the magnet in the stacking direction is the hard magnetic layer, the other end is the soft magnetic layer, and the one end is arranged to face the magnetic sensor.
By forming one end of the magnet as a hard magnetic layer, the degree of wear can be detected based on the change in magnetism on the one end side. Further, if the other end is formed of a soft magnetic layer, the intensity and range of magnetism on the other end side can be made smaller than those on the one end side.

It is preferable that the tire wear sensor has an induction member made of a magnetic material, and the magnetic detection section of the magnetic sensor is arranged between the induction member and the magnet.
Since the induction member guides the magnetism of the magnet, it is possible to more accurately measure the change in magnetism accompanying the progress of wear of the magnet.

Preferably, the magnetic sensor includes two magnetic detection units and detects the magnetism based on differential signals from the two magnetic detection units.
It is preferable that the two magnetic detection units are arranged at positions that are point-symmetrical with respect to the central point of the magnetism of the magnet when viewed from the lamination direction.
By using the differential signals from the two magnetic detection units, the influence of geomagnetism can be suppressed, and magnetism can be detected with high accuracy.

It is preferable that the cross-sectional area of the magnet perpendicular to the stacking direction increases from one end to the other end.
It is preferable that a cross section of the magnet perpendicular to the stacking direction has a circular shape.
With these configurations, it is possible to improve the correspondence relationship between the degree of wear of the magnet and the change in magnetism while suppressing the attracting force of the exposed surface of the magnet to iron or the like.

The tire of the present invention is characterized in that the magnet of the present invention is embedded in the tread portion.
By laminating the soft magnetic layer on the hard magnetic layer, it is possible to suppress the attraction of iron or the like to the magnet exposed on the surface of the tread portion.

According to the present invention, by using a magnet having a soft magnetic layer in addition to a hard magnetic layer, the magnetism of the exposed surface of the magnet in the tread portion of the tire can be reduced in the stacking direction. Therefore, the attraction of the exposed surface of the magnet to iron or the like is suppressed, and the risk of the tire being damaged by iron or the like can be reduced.

(a) Cross-sectional view schematically showing a configuration of a magnet for tire wear detection and a tire provided with the magnet, (b) Cross-sectional view showing an enlarged magnet (a) (b) Cross-sectional view schematically showing the configuration of a modification of the magnet Cross-sectional view schematically showing the configuration of a tire wear sensor provided with a magnet, (b) Cross-sectional view showing an enlarged tire wear sensor FIG. 3 is a plan view showing the positional relationship between the magnetic detector, the induction member, and the magnet in the tire wear sensor; (a) Graph showing the relationship between the height of the magnet and the output of the tire wear sensor using the magnet, (b) Graph showing the relationship between the height of the magnet and the attraction force (a) Graph showing simulation results of changes in magnet height and magnetic flux density on the side of the tire wear sensor, (b) Graph showing simulation results of changes in magnet height and magnetic flux density on the side exposed to the tire surface (a) Simulation result of the magnet of Comparative Example 2, (b) Simulation result of the magnet of Example 3 (a) Simulation result of the magnet of Comparative Example 3, (b) Simulation result of the magnet of Example 4

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The same numbers are assigned to the same members in each drawing, and the description thereof is omitted as appropriate.

<Magnet for tire wear detection>
FIG. 1(a) is a cross-sectional view schematically showing the structure of a magnet 1 for tire wear detection and a tire 2 provided with the magnet 1, and FIG. be.

The tire wear detection magnet 1 includes a soft magnetic layer 11 made of a soft magnetic material and a hard magnetic layer 12 made of a hard magnetic material. The magnet 1 is embedded in the tire 2 so that the lamination direction of the soft magnetic layer 11 and the hard magnetic layer 12 is aligned with the radial direction (Y-axis direction) of the tire 2 . The magnet 1 is magnetized in the stacking direction, and the magnetic pole ends 13 and 14 at both ends in the magnetization direction are composed of different magnetic poles.

The magnetism from the hard magnetic layer 12 is induced by the soft magnetic layer 11 in a direction deviating from the lamination direction in which the magnet 1 is magnetized. Therefore, the magnetism from the pole tip 14 of the magnet 1 in the stacking direction can be suppressed, and the force with which the pole tip 14 exposed on the surface of the tread portion 21 attracts iron or the like can be reduced.

The material forming the soft magnetic layer 11 is not particularly limited as long as it is a soft magnetic material. Examples include permalloy (Fe--Ni alloy), sendust (Fe--Si--Al alloy) which is another iron-based material, iron-based or non-ferrous amorphous magnetic alloy, and ferrite (soft ferrite). Among these exemplified materials, Sendust is preferable from the viewpoint of suppressing magnetism in the Y-axis direction from the pole tip 14 .

The hard magnetic layer 12 is not particularly limited as long as it is made of a hard magnetic material. Examples include ferrite (hard ferrite) containing iron oxide as a main component, alnico (Al--Ni--Co alloy), and samarium-cobalt. Among these exemplified materials, ferrite is preferable from the viewpoint of suppressing magnetism in the Y-axis direction from the pole tip 14 .

The pole tip 13 is one end on the center side of the tire 2 in the stacking direction of the magnet 1 and is composed of the hard magnetic layer 12 . The magnetic field generated by the magnet 1 spreads closer to the center of the tire 2 when the magnetic pole tip 13 is made of the hard magnetic layer 12 than when the magnetic pole tip 13 is made of the soft magnetic layer 11. be able to. Therefore, the magnetism of the magnet 1 can be detected more easily by the magnetic sensor 6 (see FIGS. 3A and 3B) arranged so as to face the pole tip 13 made of the hard magnetic layer 12. can be done.

The pole tip 14 is the other end on the surface side of the tread portion 21 in the lamination direction of the magnet 1 . The magnetism from the pole tip 14 is induced in the direction intersecting the stacking direction by the soft magnetic layer 11 provided adjacent to the hard magnetic layer 12, thereby reducing the magnetism in the stacking direction. Therefore, the force of attracting iron or the like to the pole tip 14 is smaller than that of a conventional magnet made only of a hard magnetic material.

In the case of the structure shown in FIG. The effect changes when progressing. If the soft magnetic layer 11 is provided near the pole tip 14 on the surface side of the tread portion 21, the effect at the start of use is enhanced. If the soft magnetic layer 11 is provided near the pole tip 13 on the inner surface 22 side of the tire 2, the effect of suppressing the magnetism in the stacking direction from the pole tip 14 when the wear of the magnet 1 progresses increases. If the soft magnetic layer 11 is used as the pole tip 13, the magnetism in the lamination direction can be suppressed until the hard magnetic layer 12 disappears. By providing the soft magnetic layer 11, the above two effects can be balanced.

The magnet 1 is formed by laminating a soft magnetic layer 11 and a hard magnetic layer 12 formed by dispersing particles (magnetic powder) of a soft magnetic material and a hard magnetic material in a polymer material. It is composed of magnets. It is embedded in the tread portion 21 in such a posture that its magnetization direction matches the radial direction (Y-axis direction) of the tire 2 . As the polymeric material, a rubber material having the same composition as the tread rubber composition used for the tread portion 21 is preferable.

The magnet 1 preferably has a magnetic flux density of 1 mT or more on the surface of the pole tip 13. From the viewpoint of preventing the magnetism of the magnet 1 from adversely affecting other electronic devices mounted on the vehicle, the surface magnetic flux density at the pole tip 13 of the magnet 1 is preferably 600 mT or less. The surface magnetic flux density at the pole tip 14 of the magnet 1 is preferably 60 mT or less from the viewpoint of preventing metal pieces such as iron nails falling on the road surface from being attracted while traveling on the road. The surface magnetic flux density is a value measured by directly contacting the magnetized surface of the magnet 1 with a Tesla meter.

FIGS. 2(a) and 2(b) are sectional views schematically showing

magnets

3 and 4 as modifications of the magnet 1 shown in FIG. 1(b). As shown in these figures, in both the

magnets

3 and 4, the soft magnetic layers 11 and the hard magnetic layers 12 are alternately laminated along the lamination direction in an unused (unworn) state. It has a laminated structure.

The

magnets

3 and 4 have the hard magnetic layer 12 at the magnetic pole tip 13 at one end in the stacking direction, and the soft magnetic layer 11 at the magnetic pole tip 14 at the other end. With this configuration, in the unused tire 2 (before the magnet 1 is worn), the magnetism in the stacking direction formed on the pole tip 14 side is suppressed compared to the pole tip 13 side, and an iron nail or the like is attracted to the pole tip 14. Therefore, the risk of the surface of the tread portion 21 being damaged or the tire 2 being punctured can be reduced.

As shown in FIGS. 2A and 2B, the soft magnetic layer 11 is preferably thinner than the hard magnetic layer 12 . By making the thickness L ₁₁ of the soft magnetic layer 11 smaller than the thickness L ₁₂ of the hard magnetic layer 12 , a magnetic path is easily formed in the soft magnetic layer 11 . Therefore, the soft magnetic layer 11 can easily induce the magnetism from the hard magnetic layer 12 in a direction other than the lamination direction. Therefore, in a state where the

magnets

3 and 4 are embedded in the tire 2 (see FIG. 1A), the magnetic flux density in the stacking direction from the pole tip 14 appearing on the surface of the tread portion 21 can be reduced. .

From the viewpoint of reducing the magnetic flux density in the stacking direction from the pole tip ₁₄ , the ratio _L11 / _L12 between the thickness _L11 and the thickness L12 is preferably 1/100 or more and less than 1/1. It is more preferably 10 or more and less than 1/2, and still more preferably 1/7 or more and less than 1/3.

From the same point of view, the thickness L ₁₁ of the soft magnetic layer 11 is preferably 0.05 mm or more and 1 mm or less, more preferably 0.1 mm or more and 0.5 mm or less, and even more preferably 0.15 mm or more and 0.3 mm or less. The thickness L ₁₂ of the hard magnetic layer 12 is preferably 0.1 mm or more and 5 mm or less, more preferably 0.3 mm or more and 3 mm or less, and even more preferably 0.5 mm or more and 2 mm or less.

The magnet 4 having a shape (substantially frustum shape) in which the area of the cross section perpendicular to the stacking direction increases from the center of the tire 2 toward the outside has a greater effect on the magnetism from the pole tip 13 and the tire 2 than the magnet 3 with a uniform shape. high linearity with the degree of wear. Moreover, the magnet 4 has a high effect of suppressing magnetism in the stacking direction formed on the magnetic pole tip 14 side, and has the advantage of being easily embedded in the tire 2 . The shape of the magnet 4 is a truncated cone in which the width W in the X-axis direction of the cross section parallel to the Y-axis direction increases continuously from the pole tip 13 to the pole tip 14, and is orthogonal to the Y-axis, which is the magnetization direction. The cross-sectional area of the cut surface cut along the XZ plane increases continuously from the pole tip 13 toward the pole tip 14 . Although FIG. 2B shows a truncated cone with straight side surfaces, the side surfaces may be constricted inward or bulging outward.

The soft magnetic layers 11 and the hard magnetic layers 12 are alternately laminated along the stacking direction from the viewpoint of reducing the force that attracts iron or the like to the surface of the pole tip 14 . It is preferably paired with the body layer 12 . By alternately laminating the soft magnetic layers 11 and the hard magnetic layers 12 as a set, the soft magnetic layers 11 effectively direct the magnetism from the hard magnetic layers 12 in the direction crossing the magnetization direction. can be induced.

The total number of laminated layers of the soft magnetic layers 11 and the hard magnetic layers 12 is preferably 4 or more, more preferably 10 or more, and even more preferably 20 or more. The upper limit of the number of layers may be set to an appropriate number from the viewpoint of the length of the

magnets

3 and 4 in the stacking direction, the effect of suppressing the attractive force, and the manufacturing efficiency.

<Tire wear sensor>
FIG. 3(a) is a cross-sectional view schematically showing the configuration of a tire wear sensor 5 having a magnet 1, and FIG. 3(b) is a cross-sectional view showing the tire wear sensor 5 in an enlarged manner. As shown in the figure, the tire wear sensor 5 includes a tire wear detection magnet 1 and a magnetic sensor 6. The magnetic sensor 6 detects changes in the magnetism emitted by the magnet 1 and detects the wear amount of the tire 2. to measure

Since the magnet 1 embedded in the tread portion 21 of the tire 2 includes the soft magnetic layer 11 in addition to the hard magnetic layer 12 , the Y-axis direction from the pole tip 14 exposed on the surface of the tread portion 21 is magnetism can be reduced. The tire wear sensor 5 may be configured using the

magnets

3 and 4 shown in FIGS. 2(a) and 2(b) instead of the magnet 1.

The magnetic sensor 6 is arranged on the inner surface 22 of the tire 2 at a position facing the magnet 1 and capable of detecting the magnetism emitted by the magnet 1 . As the magnet 1 wears together with the tread portion 21 of the tire, the magnetism of the magnet 1 changes. The tire wear sensor 5 can detect the amount of wear of the tire 2 by detecting a change in magnetism accompanying wear of the tread portion 21 with the magnetic sensor 6 .

The magnetic sensor 6 detects magnetism in the X-axis direction that intersects the lamination direction (Y-axis direction) of the magnet 1 . The soft magnetic layer 11 reduces the magnetism in the Y-axis direction, which is the magnetization direction, of the magnetism from the magnet 1 . Therefore, the magnetic sensor 6 measures the magnetism in the X-axis direction perpendicular to the magnetization direction of the magnet 1, thereby improving the accuracy in measuring the wear amount of the tire 2. FIG.

The magnetic sensor 6 has an induction member 61 made of a magnetic material, and a magnetic detection part 62 is arranged between the induction member 61 and the magnet 1 . The configuration of the magnet 1 reduces the magnetism in the Y-axis direction from the magnetic pole tip 14 on the surface side of the tread portion 21 of the tire 2, and the arrangement position of the magnetic detection portion 62 is devised to improve the sensitivity of the magnetic sensor 6. can do.

As shown in FIGS. 3(a) and 3(b), the magnetic sensor 6 includes two magnetic detection units 62. Based on the differential signals from the two magnetic detection units 62, the magnetic field of the magnet 1 is detected. to detect. By using the difference output of the magnetism detected by the magnetism detector 62, the degree of wear of the tire 2 can be detected with high accuracy.

FIG. 4 is a plan view schematically showing the positional relationship between the magnet 1, the magnetic detection portion 62 of the magnetic sensor 6, and the guide member 61 in the tire wear sensor 5 of FIGS. 3(a) and 3(b). It is a diagram. This figure schematically shows the positional relationship viewed from the Y-axis direction, which is the magnetization direction of the magnet 1 . As shown in the figure and FIG. 3(b), the magnetic detector 62 is arranged between the magnet 1 and the guide member 61. As shown in FIG. Moreover, the magnetic detection part 62 is arranged so as to have a portion positioned outside the outer shell of the magnet 1 when viewed from the magnetization direction. With this configuration, the tire wear sensor 5 can accurately measure changes in magnetism in the X-axis direction as the degree of wear of the tire 2 progresses. This is because the magnetic field generated by the magnet 1 is induced from the magnet 1 to the induction member 61, so the magnetic field induced from the magnet 1 to the induction member 61, that is, the magnetic field at the location where the magnetic detection unit 62 is arranged has a high magnetic flux density. It is because In addition, since the guiding member 61 is arranged at a position away from the magnet 1 in the X direction, the magnetism of the magnetic field at the location where the magnetic detection unit 62 is arranged is the X-axis direction detectable by the magnetic detection unit 62. This is because it always contains the components of

The two magnetic detection parts 62 are arranged at points symmetrical with respect to the central point of the magnetism from the magnet 1 , that is, the central axis of the magnet 1 when viewed from the magnetization direction of the magnet 1 . The two magnetic detectors 62 and the two guide members 61 are positioned on a straight line L parallel to the X-axis connecting their centers. The two magnetic detection units 62 are arranged point-symmetrically with respect to the center point O of the cross-sectional circle obtained by cutting the magnet 1 along the XZ plane. The two guide members 61 are also arranged symmetrically with respect to the center point O. As shown in FIG.

With the above-described configuration, the emitted magnetism Ma of the magnet 1 detected by one magnetic detector 62 and the emitted magnetism Mb of the magnet 1 detected by the other magnetic detector 62 have the same magnetic flux density and magnetic direction. is reversed. Therefore, wear of the tire 2 can be detected based on only one of the emitted magnetism Ma and Mb detected by the two magnetic detectors 62, so the redundancy of the tire wear sensor 5 is improved.

In addition, the external magnetism that becomes noise in the measurement of magnetism by the tire wear sensor 5 has the same effect on the two magnetism detection units 62 . Therefore, by using the output difference (difference, differential signal) from the two magnetic detectors 62, the components of the external magnetic field are canceled and the influence of the external magnetism can be removed. Since the outputs from the two magnetic detectors 62 have opposite magnetic directions, by using the difference between the two outputs, the magnitude of the output from one magnetic detector 62 can be doubled while eliminating the influence of noise. gives the output of Therefore, by using the difference in the output of the magnetism detecting section 62, the influence of noise such as external magnetism can be removed and the output can be increased, so that the degree of wear of the tire 2 can be measured with high accuracy.

The magnet 1 is configured to have a magnetic flux density of 0.05 mT or more at the measurement position where the magnetic detectors 62 are arranged in order to reliably measure the magnetic flux density with the two magnetic detectors 62 without being affected by the geomagnetism. and more preferably configured to have a magnetic flux density of 0.5 mT or more.

The embodiments disclosed in this specification are illustrative in all respects and are not limited to these embodiments. The scope of the present invention is indicated by the scope of the claims rather than the description of the above-described embodiments, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

<Example 1>
Using a truncated cone-shaped magnet (see FIG. 2(b)) having the following shape, the X-axis direction (FIG. 3(a), 3(b)), and changes in the magnetic attraction force (magnetic flux density in the Y-axis direction) to the iron on the bottom surface side were measured.
Initial shape: Upper bottom diameter 16 mm, lower bottom diameter 24 mm, height 18 mm, 1 mm thick soft magnetic layer and 1 mm thick hard magnetic layer are alternately laminated (18 layers).
Soft magnetic layer: permalloy Hard magnetic layer: ferrite (hard ferrite)

<Example 2>
Regarding the shape of the magnet, the same magnet as in Example 1 was used except that the diameter of the upper bottom surface was changed from 16 mm to 22 mm. The change in adsorption force for iron was measured.

<Comparative Example 1>
A truncated conical magnet similar to that of Example 1 was formed using only the hard magnetic layer, and changes in the output of the magnetic sensor and the adsorption force on the bottom surface side were measured as the wear progressed from the bottom surface side.

FIG. 5(a) is a graph showing the relationship between the height (thickness) of a tire wear detection magnet and the output of a tire wear sensor using the tire wear detection magnet, and FIG. 3 is a graph showing the relationship between the height (thickness) of a magnet for tire wear detection and the attraction force. The measured values in FIGS. 5(a) and 5(b) are both shown as a ratio (%) to the initial sensor output and adsorption force (100%) in Comparative Example 1.

As shown in FIG. 5(a), when the magnets of Examples 1 and 2 are used, the sensor output changes linearly with the progress of wear, similarly to when the magnet of Comparative Example 1 is used. did. That is, even when using a magnet in which soft magnetic layers and hard magnetic layers are alternately laminated, the linearity between the progress of wear and the sensor output is similar to the case where a magnet consisting of only hard magnetic layers is used. was good.

On the other hand, as shown in FIG. 5(b), in the magnets of Examples 1 and 2, the attraction force of the lower bottom surface exposed on the surface of the tread portion of the tire was smaller than that of Comparative Example 1. That is, the attracting force of the magnet in which the soft magnetic layer and the hard magnetic layer are alternately laminated was suppressed to 50% or less of the initial value of the magnet composed only of the hard magnetic layer. From these results, it was found that the provision of the soft magnetic layer reduces the magnetism in the perpendicular direction of the exposed surface of the magnet, thereby reducing the attractive force for attracting iron and the like.

<Example 3>
Using a truncated cone-shaped magnet (see FIG. 2(b)) having the following shape, the X-axis direction (FIG. 3(a), 3(b)), the output of the magnetic sensor and the change in the adsorption force on the bottom surface side were measured.
Initial shape: 15 layers of soft magnetic layers with an upper bottom diameter of 16 mm, a lower bottom diameter of 28 mm, a height of 18 mm, and a thickness of 1 mm and a hard magnetic layer with a thickness of 0.2 mm are alternately laminated (number of layers) 30)
Soft magnetic layer: Sendust Hard magnetic layer: Ferrite (hard ferrite)

<Comparative Example 2>
A truncated conical magnet similar to that of Example 3 was formed using only the hard magnetic layer, and changes in the output of the magnetic sensor and the attractive force on the bottom surface side were measured as the wear progressed from the bottom surface side.

FIG. 6(a) is a graph showing simulation results of changes in magnetic flux density on the sensor side with changes in the height (thickness) of the magnet, and FIG. 2 is a graph showing simulation results of changes in magnetic flux density at the other end (on the tread surface side of the tire). The measured values obtained by simulation in these graphs are shown as a ratio (%) to the initial value (100%) of Comparative Example 2, as in FIGS. 5(a) and 5(b).

From the simulation results shown in FIGS. 6A and 6B, similarly to the measurement results shown in FIGS. At the same time, it was shown that the magnetic flux density of the lower bottom surface appearing on the tread surface can be suppressed, and the adsorption force that attracts iron or the like can be reduced.

　Figures 7(a) and 7(b) are simulation results of the magnetism generated in the magnet, and the arrows shown in each figure indicate the direction of the magnetism. FIG. 7(a) shows the magnetism simulation results for the magnet of Comparative Example 2 consisting of only hard magnetic layers, and FIG. FIG. 10 is a simulation result of magnetism in the magnet of Example 3. FIG. In the magnet of Comparative Example 2, which consists of only hard magnetic layers, only magnetism parallel to the Y-axis direction, which is the direction of magnetization, is generated as shown in FIG. 7(a). On the other hand, in the magnet of Example 3 in which the soft magnetic layers and the hard magnetic layers are alternately laminated, as shown in FIG. It has been shown that the magnetism is induced in the cross-direction.

<Example 4>
Magnetism in a cylindrical magnet (see FIG. 2(a)) with the following shape was simulated.
Initial shape: 13 soft magnetic layers with a bottom diameter of 18 mm, a height of 18 mm, and a thickness of 1 mm and hard magnetic layers with a thickness of 0.2 mm are alternately laminated (26 layers).
Soft magnetic layer: Sendust Hard magnetic layer: Ferrite (hard ferrite)

<Comparative Example 3>
Magnetism was simulated in the same magnet as in Example 4, except that it consisted of only a hard magnetic layer.

FIG. 8(a) shows the magnetism simulation results for the magnet of Comparative Example 3 consisting of only hard magnetic layers, and FIG. FIG. 10 is a simulation result of magnetism in the magnet of Example 4. FIG. 8(a) and 8(b) schematically show the positional relationship between the magnetism of the magnet and the magnetic sensor 6 obtained by simulation.

The magnetic sensor 6 has two magnetic detection portions 62, each of which is provided outside the center of the magnet. It also has a guide member 61 that guides the magnetism from the magnet. Therefore, the magnetic direction oblique to the Y-axis has little effect on the detection result of the magnetic detection unit 62 . On the other hand, the attraction force with which the pole tip 14 exposed on the tread portion 21 of the magnet 1 attracts iron or the like is proportional to the magnitude of magnetism in the Y-axis direction. It is thought that the magnetism in the Y-axis direction decreased because the direction of magnetism was induced in the direction crossing the Y-axis by the soft magnetic layer 11 (see FIG. 1), and the attractive force of the pole tip 14 decreased. .

As described above, the present invention can be applied to a magnet for detecting tire wear, a tire wear sensor, and a tire that can measure the wear state of a tire without visual inspection.

1, 3, 4: magnet 2: tire 5: tire wear sensor 6: magnetic sensor 11: soft magnetic layer 12: hard magnetic layer 13, 14: pole tip 21: tread portion 22: inner surface 61: guide member 62 : Magnetic detection portions L ₁₁ , L ₁₂ : Thicknesses Ma, Mb: Emitted magnetism O : Center point W : Width L : Straight line parallel to X-axis

Claims

In the tire wear detection magnet embedded in the tread of the tire,
A soft magnetic layer made of a soft magnetic material and a hard magnetic layer made of a hard magnetic material,
A magnet for detecting wear of a tire, wherein the magnet is magnetized in a lamination direction of the soft magnetic layer and the hard magnetic layer.
The soft magnetic layers and the hard magnetic layers are alternately laminated along the lamination direction,
The soft magnetic layer and the hard magnetic layer are paired,
The magnet for tire wear detection according to claim 1.
the thickness of the soft magnetic layer is smaller than the thickness of the hard magnetic layer;
The magnet for tire wear detection according to claim 1 or 2.
One end in the stacking direction is the hard magnetic layer,
The magnet for tire wear detection according to claim 1 or 2.
One end in the stacking direction is the hard magnetic layer, and the other end is the soft magnetic layer.
The magnet for tire wear detection according to claim 1 or 2.
The cross-sectional area of the cut surface perpendicular to the stacking direction increases from the one end toward the other end.
The magnet for tire wear detection according to claim 5.
The shape of the cut surface is circular,
The magnet for tire wear detection according to claim 6.
The hard magnetic layer is ferrite, and the soft magnetic layer is sendust.
The magnet for tire wear detection according to claim 1 or 2.
a magnet according to claim 1 embedded in the tread portion of the tire;
a magnetic sensor arranged at a position facing the magnet on the inner surface of the tire and capable of detecting the magnetism emitted by the magnet,
A tire wear sensor, wherein the magnetic sensor measures the magnetism in a direction intersecting with the stacking direction of the magnets to measure the amount of wear of the tire.
The soft magnetic layers and the hard magnetic layers are alternately laminated along the lamination direction,
The soft magnetic layer and the hard magnetic layer are paired,
the thickness of the soft magnetic layer is smaller than the thickness of the hard magnetic layer;
A tire wear sensor according to claim 9 .
one end of the magnet in the stacking direction is the hard magnetic layer and the other end is the soft magnetic layer;
The one end is arranged to face the magnetic sensor,
A tire wear sensor according to claim 9 .
Having an induction member made of a magnetic material,
The magnetic detection unit of the magnetic sensor is arranged between the induction member and the magnet,
A tire wear sensor according to claim 9 .
The magnetic sensor includes two magnetic detection units,
detecting the magnetism based on differential signals from the two magnetic detection units;
A tire wear sensor according to claim 9 .
The two magnetic detection units are arranged at points symmetrical with respect to the center point of the magnetism of the magnet when viewed from the stacking direction,
14. The tire wear sensor of claim 13.
The cross-sectional area of the cross-section perpendicular to the stacking direction of the magnet increases from one end to the other end,
A tire wear sensor according to claim 9 .
The shape of the cross section of the magnet perpendicular to the stacking direction is circular.
A tire wear sensor according to claim 9 .
A tire, wherein the magnet according to claim 1 is embedded in the tread portion.