Magnetic marker

Abstract

To provide a magnetic marker that is highly likely to maintain its function even when pavement is damaged.SOLUTION: A magnetic marker 1 disposed on a road 3 for use in driving support of a vehicle is a columnar magnet that has a shape where the uniformity of stress in response to an external force is impaired and stress is concentrated at a location, and is easy to break and separate into multiple small pieces due to concentration of stress. When pavement damage occurs around magnetic marker 1, by separating some of the small pieces, there is a possibility that some of the remaining pieces will remain on the road side and maintain magnetic performance.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetic marker disposed on a road to assist in the operation of a vehicle.

Background Art

[0002] Conventionally, a magnetic marker detection system for vehicles using magnetic markers disposed on a road has been known (see, for example, Patent Document 1). Such a magnetic marker detection system targets a vehicle equipped with a magnetic sensor. By the vehicle detecting magnetic markers disposed along a lane, various driving supports such as automatic steering control and lane departure warning are realized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the paving of the road deteriorates, the magnetic marker may fall off the road, and there is a risk that the function of the magnetic marker will be lost all at once.

[0005] The present invention has been made in view of the above conventional problems, and aims to provide a magnetic marker that has a high possibility of maintaining the function of the magnetic marker even when the paving is damaged.

Means for Solving the Problems

[0006] The present invention is a magnetic marker disposed on a road for use in assisting the operation of a vehicle, where the magnetic marker is a columnar magnet having a shape in which the uniformity of stress according to an externally acting force is impaired and a location where stress is concentrated occurs.

[0007] The magnetic marker of the present invention is configured to create areas where stress concentrates. Compared to magnetic markers where the stress is uniform when an external force is applied, this magnetic marker is more prone to fracture due to stress concentration. For example, when the magnetic marker of the present invention falls off a road, it is more likely to break into multiple small pieces, reducing the risk of the entire marker falling off the road immediately. The magnetic marker of the present invention has the excellent characteristic of being highly likely to maintain some degree of magnetic performance even when a situation occurs in which it falls off a road. [Brief explanation of the drawing]

[0008] [Figure 1] An explanatory diagram showing magnetic markers installed on a road in Example 1. [Figure 2] A perspective view showing the first magnetic marker in Example 1. [Figure 3] Cross-sectional view of the first magnetic marker in Example 1 (viewed along line AA in Figure 2). [Figure 4] An explanatory diagram showing the other magnet sheet constituting the first magnet sheet in Example 1. [Figure 5] A perspective view of the second magnetic marker in Example 1. [Figure 6] Cross-sectional view of the second magnetic marker in Example 1 (viewed along the line BB in Figure 5). [Figure 7] An explanatory diagram showing another second magnetic marker in Example 1. [Figure 8] A perspective view showing the third magnetic marker in Example 1. [Figure 9] A perspective view showing another third magnetic marker in Example 1. [Figure 10] Diagram illustrating the marker rod in Example 2. [Figure 11] An explanatory diagram showing how magnetic markers are cut from marker rods in Example 2. [Figure 12(a)] An explanatory diagram of the state in which the tip of the marker rod is inserted into the housing hole in Example 2. [Figure 12(b)]A diagram illustrating the first step in the procedure for separating the magnetic marker at the tip of the marker rod in Example 2. [Figure 12(c)] A diagram illustrating the second step in the procedure for separating the magnetic marker at the tip of the marker rod in Example 2. [Figure 12(d)] A diagram illustrating the procedure for detaching the magnetic marker from the tip of the marker rod and placing it in the housing hole in Example 2. [Modes for carrying out the invention]

[0009] (Example 1) This example shows a magnetic marker 1 that is positioned on road 3 so as to be detectable by a magnetic sensor (not shown) attached to the vehicle, and is used to assist the driver's operation of the vehicle or to enable vehicle-side control for autonomous driving that does not depend on the driver's operation. This will be explained with reference to Figures 1 to 9.

[0010] The magnetic marker 1 in this example is an embedded type magnetic marker, and is installed (embedded) in a housing hole 30 with a depth of 30 mm provided in the road surface 3S. The magnetic marker 1 has a columnar shape with a diameter of 30 mm and a height of 20 mm. Since the height of the magnetic marker 1 is 20 mm relative to the depth of the housing hole 30 mm, the upper surface of the magnetic marker 1 placed in the housing hole 30 is set back about 10 mm from the road surface. After the magnetic marker 1 is housed in the housing hole 30, a polymer material such as asphalt or resin material is filled into the hole 30. As a result, a cover 31 made of asphalt or resin material is formed on the upper side of the magnetic marker 1.

[0011] The cross-sectional structure of road 3 paved with asphalt, etc., is not shown in the diagram, but roughly consists of three layers: a subgrade made of compacted soil, a base course made of granular materials such as crushed stone or crushed stone run, and a surface layer made of a heated asphalt mixture. The heated asphalt mixture is an asphalt mixture in which coarse aggregate 331, fine aggregate 332, filler, and asphalt are mixed while heated. The thickness of the surface layer is, for example, about 10 cm.

[0012] The coarse aggregate 331 is, for example, crushed stone with a particle size of 2.5 to 5 mm. The fine aggregate 332 is, for example, an aggregate that passes through a 2.36 mm sieve and remains on a 0.075 mm sieve. The fine aggregate 332 is, for example, sand with a particle size of 0.075 to 2.36 mm. The filler, not shown in the figure, is a mineral powder that passes through a 0.075 mm sieve. The filler is, for example, stone powder made by pulverizing limestone.

[0013] In the paving of roads, damage such as potholes is inevitable over time. A pothole is a hole that occurs when a part of the surface layer made of a hot asphalt mixture peels off from the road surface. A pothole is caused, for example, by the damage of the connection structure between the coarse aggregates 331 in the hot asphalt mixture forming the surface layer.

[0014] The magnetic marker 1 (Fig. 1) is a columnar permanent magnet with a diameter of 30 mm and a height of 20 mm. The magnet forming the magnetic marker 1 is an isotropic ferrite plastic magnet in which magnetic powder of iron oxide, which is a magnetic material, is dispersed in a polymer material as a base material. This magnet has magnetic properties of maximum energy product (BHmax) = 12 kJ / cubic m. Examples of the polymer material forming the magnet include asphalt, rubber, PPS (Poly Phenylene Sulfide), nylon 66, nylon 12, etc.

[0015] Since the isotropic ferrite plastic magnet has a magnetic material of iron oxide, it is resistant to corrosion and does not need to be housed in a metal case or the like. Therefore, the magnetic marker 1 in this example may be the magnet itself. A coating layer may be provided on the outer peripheral surface of the magnet as appropriate if necessary. The magnetic marker 1 can be directly housed in the housing hole 30 provided in the road surface 3S.

[0016] The magnetic marker 1 is a magnet with a magnetic flux density on the surface of 45 mT (millitesla) and a magnetic flux density reaching about 8 μT at a height of 250 mm. Note that the height of 250 mm is an example of the height corresponding to the upper limit in the assumed range of the mounting height of the magnetic sensor in a vehicle.

[0017] The magnetic marker 1 in this example is characterized by being a columnar permanent magnet with a shape that impairs the uniformity of stress in response to externally applied forces, resulting in areas where stress concentrates. Because stress concentration occurs, this magnetic marker 1 is more prone to fracture and easily separates into multiple small pieces compared to a magnetic marker in which stress is distributed uniformly when an external force is applied.

[0018] Generally, stress concentration in an object tends to occur at points where the cross-sectional area changes abruptly. When an external force is applied, stress concentrates, making it easier for excessive stress exceeding the material strength of the object's constituent materials to occur. Naturally, an object with points of stress concentration is more prone to fracture than an object where there are no points of abrupt change in cross-sectional area, and stress is generated uniformly when an external force is applied, thus suppressing the maximum stress value.

[0019] If the magnetic marker remained intact when it rolled onto the road surface 3S, and the magnetic marker 1 detached from the road as a whole in response to the formation of potholes, the magnetic function of the magnetic marker 1 would be lost all at once. However, with the magnetic marker 1 in this example, which has a structure that allows it to be separated into multiple small pieces, it is possible that a portion can be separated in response to the expansion of potholes, while the remaining portion can remain on the road. Therefore, the magnetic marker 1 is highly likely to be able to maintain its magnetic function to some extent.

[0020] Thus, the magnetic marker 1 in this example is a magnetic marker with excellent properties that reduce the risk of the magnetic marker's function of exerting magnetism on its surroundings being suddenly lost. In this example, several types of magnetic markers 1 with such properties are illustrated.

[0021] (First magnetic marker) The first magnetic marker 1 is the magnetic marker shown in Figures 2 and 3. Figure 2 is a perspective view showing the external appearance of the magnetic marker 1. Figure 3 is a cross-sectional view showing the structure of the cross section including the central axis of the columnar shape. The cross section in the same figure is the cross section of line AA in Figure 2. The first magnetic marker 1 is made by first creating an intermediate processed product (not shown) by forming an isotropic ferrite plastic magnet, which is a permanent magnet, into a columnar shape, and then slitting the outer surface thereof.

[0022] In this slitting process, for example, multiple annular slits 101 perpendicular to the axial direction of the columnar material are created at regular intervals, for example, by laser processing. The width of one example of a groove slit 101 is very small, for example, 0.1 to 0.2 mm. The inner diameter of the annular slit 101 is, for example, 5 mm. In this magnetic marker 1, the presence of the slits 101 creates points where the cross-sectional area perpendicular to the axial direction changes abruptly in the axial direction, and these points become areas of stress concentration.

[0023] As shown in Figure 3, the magnetic marker 1 has a structure in which multiple magnetic sheets, each partitioned by an annular slit 101, are stacked. In this magnetic marker 1, stress concentration occurs at the slit 101, making it prone to cracking. The magnetic marker 1 is easily fractured by the cracks in the slit 101, i.e., by the expansion of the gaps, and separates into multiple small pieces. Because the magnetic marker 1 is easily fractured due to the presence of the slit 101, the force required to separate it into multiple small pieces is smaller compared to the intermediate processed product.

[0024] Furthermore, the slit 101 (Figure 3) may be filled with powder or the like of a soft magnetic material. Examples of soft magnetic materials include iron, silicon iron, and permalloy. The soft magnetic material used for filling should be of lower strength and more easily broken than the magnet forming the magnetic marker 1. Instead of a soft magnetic material, a polymer material such as a resin material may be used for filling. Because soft magnetic materials have high magnetic permeability, they can suppress the decrease in magnetic performance caused by the presence of the slit 101. In this example, if the gap is about 0.1 to 0.2 mm, the decrease in magnetic performance will not be a major problem. When the gap becomes larger and the decrease in magnetic performance becomes greater, the effectiveness of the soft magnetic material filled in the slit 101 becomes more apparent. It is also possible to apply a resin coating to the outer surface where the slit 101 is provided.

[0025] It is also acceptable not to cover the opening of the slit 101 that opens on the outer surface of the magnetic marker 1. In this case, the freezing of moisture that has entered the slit 101 can promote rupture triggered by the slit 101. If the magnetic marker 1 has already ruptured, a portion of it can be immediately separated as the pothole expands. Furthermore, it is also acceptable to fill the slit 101 with a porous material such as foamed resin. In this case, the intrusion of moisture can be promoted by drawing moisture into the slit 101 through capillary action.

[0026] Alternatively, for example, a magnetic marker 1 similar to those in Figures 2 and 3 can be obtained by stacking and joining together magnetic sheets 11, as shown in Figure 4, which are disc-shaped and have a thicker inner circumference than outer circumference, in the axial direction. Or, although not shown in the illustration, a magnetic marker with the same shape as the magnetic markers in Figures 2 and 3 can be obtained by alternately stacking and joining discs of a certain thickness and discs of a small diameter.

[0027] If an adhesive or tack material that does not harden over time is used as the bonding material for joining the magnet sheets 11 in Figure 4, the adjacent magnet sheets 11 will be more easily separated via the bonding layer. Alternatively, an adhesive material that hardens but is prone to fracture of the bonding layer may be used. If the bonding layer fractures, cracks will form between the adjacent magnet sheets, causing them to break and making it easier for the magnetic marker 1 to separate into multiple small pieces.

[0028] Adhesive materials, in the narrow sense, are liquid before use and solidify over time. Sticky materials, on the other hand, possess properties of both liquid and solid, and are semi-solid and viscous. It can also be argued that the broader concept of adhesive materials encompasses both adhesive materials in the narrow sense and sticky materials in general.

[0029] As adhesive or bonding materials, it is also possible to use adhesive materials that have relatively high strength immediately after joining, but whose bonding strength gradually decreases over time. Alternatively, it is also possible to use disassemblable adhesive or bonding material that has some kind of disassembly factor and whose bonding strength decreases or peels off when disassembly operations are performed to activate the disassembly factor.

[0030] For example, the adhesive material may have a disintegration factor in the form of gas generation at the adhesive interface, and may lose its bonding strength through a disintegration operation such as ultraviolet irradiation. This adhesive material is used, for example, as the adhesive material for ultraviolet-release tapes called dicing tapes in semiconductor processes. For example, the adhesive material may be one containing a water-absorbing resin, which has a disintegration factor in the form of expansion of the water-absorbing resin, and whose bonding strength decreases through a disintegration operation such as water immersion. For example, the adhesive material may be one containing thermally expandable microcapsules, which has a disintegration factor in the form of expansion of microcapsules, and whose bonding strength decreases with heating. For example, the adhesive material may be a thermosetting / thermoplastic adhesive material, which has a disintegration factor in the form of softening / melting, and whose bonding strength decreases with a disintegration operation such as heating. For example, the adhesive material may have a disintegration factor in the form of brittleness of the adhesive material, and may become brittle and lose bonding strength due to heating or ultraviolet irradiation. For example, the adhesive material may be a hydrolyzable adhesive or adhesive material, which has a disintegration factor in the form of hydrolysis, and whose bonding strength decreases with a disintegration operation such as the supply of moisture. The adhesive material may be a moisture-absorbing release adhesive material, which has a disintegration factor in the form of moisture absorption and softening / melting, and whose bonding strength decreases with hot water immersion. For example, it may be an electromagnetic induction thermoplastic adhesive material that possesses a decomposition factor of softening and melting, and whose bonding strength decreases with electromagnetic induction heating. For example, it may be an easily peelable adhesive material that possesses a decomposition factor of mechanical fracture, and whose bonding strength decreases with a decomposition operation such as applying a vertical load. For example, it may be an adhesive material that possesses a decomposition factor of mechanical fracture, and whose bonding strength decreases with a decomposition operation such as applying a shear load.

[0031] Furthermore, for example, biodegradable adhesives or bonding materials can be used. By using biodegradable adhesives that decompose in nature, the bonding strength of the magnetic marker 1 can be gradually reduced after it is embedded. Moreover, if biodegradable adhesives are used, the disposal of the magnetic marker 1 becomes easier, and the cost of disposing of the magnetic marker 1 can be reduced.

[0032] After placing the magnetic marker 1 in the containment hole 30 (see Figure 1), filling the containment hole 30 with a polymer material such as asphalt or resin material allows the shape of the magnetic marker 1 to be maintained by the polymer material. Therefore, even if the bonding strength of the bonding layer is lost over time, as long as the magnetic marker 1 remains in the containment hole 30, the magnetic marker 1 can be maintained as a single unit without separating into multiple small pieces.

[0033] (Second magnetic marker) The second magnetic marker 1 is the magnetic marker shown in Figures 5 and 6. Figure 5 is a perspective view showing the external appearance of the magnetic marker 1. Figure 6 is a cross-sectional view of the magnetic marker 1 perpendicular to the axial direction. The cross-section in the same figure is a cross-sectional view of the cross-section taken along the BB line in Figure 5. In this magnetic marker 1, multiple radial transverse holes 102 (an example of holes) are drilled intersecting the central axis. This magnetic marker 1 is made, for example, by creating an intermediate product from which an isotropic ferrite plastic magnet has been formed into a columnar shape, and then providing numerous radially penetrating transverse holes 102.

[0034] The lateral holes 102 are, for example, fine holes with a diameter of about 0.5 to 1.0 mm, created by laser processing. The lateral holes 102 intersect the central axis of the cylindrical magnetic marker 1 and penetrate radially. The lateral holes 102 are located along nine cross-sections (hereinafter referred to as the lateral hole 102 formation surfaces) of the magnetic marker 1 at 2 mm intervals in the axial direction. The formation surfaces at both ends are each located 1 mm away in the axial direction from the end face of the magnetic marker 1. On each formation surface of the magnetic marker 1, for example, multiple lateral holes 102 are drilled in the circumferential direction at 16 equally spaced divisions (equally spaced at an angle of 22.5 degrees) (see Figure 6).

[0035] Furthermore, the number of forming surfaces may be more than nine, or fewer. The forming surfaces may be spaced unevenly. Also, the circumferential spacing of the transverse holes 102 on the forming surfaces may be finer than 16 divisions, or coarser. The circumferential spacing of the transverse holes 102 may be spaced unevenly.

[0036] The magnetic marker 1 in Figures 5 and 6 has a structure that is prone to cracking at the forming surface of the lateral hole 102, which is an example of a gap, and can be separated into multiple small pieces. This magnetic marker 1 is a magnetic marker in which magnet sheets are stacked with the forming surface of the lateral hole 102 in between. In this magnetic marker 1, the strength is reduced due to the presence of the forming surface of the lateral hole 102. In the magnetic marker 1, adjacent small pieces separate through the forming surface as the lateral hole 102, which is a gap, expands. Due to the presence of the forming surface with the lateral hole 102, this magnetic marker 1 is more prone to fracture and separation into small pieces than the intermediate processed product described above. In the magnetic marker 1 in Figures 5 and 6, at the forming surface in the axial direction, the cross-sectional area perpendicular to the axial direction decreases sharply, creating a point where stress concentrates.

[0037] Furthermore, it is also possible to fill the inside of the horizontal hole 102 with a soft magnetic material. The soft magnetic material should preferably have lower strength than the magnet forming the magnetic marker 1 and be easily broken. Instead of the soft magnetic material, a polymer material such as a resin material may be used to fill the hole. It is also possible to provide a coating of resin material on the outer surface through which the lateral hole 102 opens.

[0038] As shown in Figure 7, it is also possible to provide vertical holes 103 that penetrate axially instead of horizontal holes 102. For example, multiple vertical holes 103 are formed along a plane containing the central axis of the magnetic marker 1. In the magnetic marker 1, the plane along which the vertical holes 103 are formed is provided at equal intervals of 45 degrees in the circumferential direction. At the end face of the magnetic marker 1, the openings of the vertical holes 103 are arranged radially. In the magnetic marker 1 shown in the figure, columnar regions with a sector-shaped cross-section are formed, demarcated by the formation surfaces of the vertical holes 103 (the planes mentioned above), which constitute an example of a gap. In the magnetic marker 1 shown in Figure 7, there are places where the cross-sectional area of ​​the plane containing the central axis decreases sharply at the plane in which the vertical holes 103 are formed in the circumferential direction, resulting in areas where stress is concentrated.

[0039] In addition to the horizontal holes 102 (Figures 5 and 6), vertical holes 103 (an example of a hole; see Figure 7) may also be provided. In this example, through holes are shown as the horizontal holes 102 and vertical holes 103, but closed-end holes that do not penetrate are also acceptable. A magnetic marker with holes forming an example of a gap has reduced strength due to the presence of the holes and is prone to breakage. This magnetic marker has a structure that can be separated into multiple small pieces by breakage. The handling of the openings of the horizontal hole 102 and the vertical hole 103 is the same as in the case of the slit 101 in the first magnetic marker 1. They may be left open to the outside.

[0040] (Third magnetic marker) The magnetic marker 1 in Figure 8 is a magnetic marker with radial slits 131 that divide it into multiple columnar magnetic regions 13 with a fan-shaped cross-section. The slits 131 are formed along a plane defined by the radial and axial directions, and are formed to avoid the central part 1C of the magnetic marker 1 in the radial direction. Therefore, the multiple fan-shaped magnetic regions 13 are interconnected via a central part 1C, similar to the core of a pineapple.

[0041] In this magnetic marker 1, the fan-shaped magnetic regions 13 are connected only to the central part 1C, and adjacent magnetic regions 13 in the circumferential direction are adjacent via slits 131 and are not connected to each other. In other words, in the magnetic marker 1 of Figure 8, due to the presence of slits 131, there are places where the radial cross-sectional area including the central axis changes abruptly in the circumferential direction, and stress concentrates at these locations.

[0042] Alternatively, a magnetic rod corresponding to the central part 1C of the aforementioned magnetic marker may be prepared, and a magnetic piece forming a magnetic region 13 may be attached to the magnetic rod to form a magnetic marker similar to the magnetic marker 1 in Figure 8. The slit 131 may be filled with a soft magnetic material. The soft magnetic material should be of a type that is weaker and more easily broken than the magnet forming the magnetic marker 1. A polymer material such as a resin material may be used instead of the soft magnetic material. The outer surface through which the slit 131 opens may also be coated with a resin material.

[0043] Furthermore, as shown in Figure 9, a region with a shape similar to the magnetic region 13 in Figure 8 can be sliced ​​into multiple sections by multiple slits 132, dividing it into multiple magnetic regions 135. In the columnar magnetic marker 1 as a whole, the slits 132 form an annular shape, leaving the central part 1C untouched. The fan-shaped magnetic regions 135, resembling a slice of pizza, are connected to and held by the central part 1C.

[0044] As described above, the magnetic marker 1 in this example is a columnar permanent magnet with a shape that impairs the uniformity of stress in response to externally applied forces, resulting in areas where stress concentrates. In this magnetic marker 1, the paving material that makes up the pavement to be constructed is more Easily breakable Points where stress concentrates are provided in such a way. With this magnetic marker 1, when the pavement is damaged and a pothole occurs, stress concentration occurs in proportion to the expansion of the pothole, making it easier to fracture and potentially allowing a portion to be separated. Therefore, even if a pothole occurs nearby, there is a high possibility that a portion of the magnetic marker 1 will remain on the road side, and the magnetic function of the magnetic marker 1 may be maintained to some extent.

[0045] Furthermore, while the coarse aggregate 331 forming the surface layer of the pavement has a particle size of, for example, 2.5 to 5 mm, the magnetic marker 1 has a diameter of 30 mm and a height of 20 mm. If the magnetic marker were to be a single unit, when a pothole occurs, there is a possibility that a magnetic marker larger than the coarse aggregate 331 could roll onto the road surface. On the other hand, with the magnetic marker 1 in this example, which has a structure that allows it to be separated into multiple small pieces, there is less risk of it rolling onto the road surface as a single unit. Because this magnetic marker 1 can be separated into multiple small pieces, it will only roll onto the road surface as small pieces that are equivalent in size to, or even smaller than, the coarse aggregate 331.

[0046] In this example, a columnar magnetic marker with a circular cross-section is used as an illustration. However, the cross-sectional shape is not limited to a circle. Columnar magnetic markers with triangular, square, pentagonal, or other cross-sectional shapes are also acceptable.

[0047] (Example 2) This example demonstrates a configuration that utilizes a structure that can be separated into multiple small pieces, allowing multiple magnetic markers to be handled as a single unit. This example relates to a marker rod 1R in which multiple magnetic markers 1 from Example 1 are connected. This will be explained using Figures 10 to 12(d).

[0048] The marker rod 1R (Figure 10) has a connecting surface 100 that connects two magnetic markers 1 in the axial direction, and is composed of multiple magnetic markers 1 as a whole. The connecting strength of the two magnetic markers 1 at the connecting surface 100 is set to be less than the strength required to separate the individual magnetic markers 1 into small pieces.

[0049] For example, as shown in Figure 11, if the marker rod 1R is placed on the workbench 105 so that its tip protrudes from the edge, and a force perpendicular to its tip is applied, the connecting surface 100 becomes the cutting surface, and the magnetic marker 1 can be cut out from the marker rod 1R. If the amount the tip protrudes from the edge of the workbench 105 is set to slightly exceed the height (total length) of the magnetic marker 1, the magnetic markers 1 can be cut out one by one efficiently.

[0050] Alternatively, a marker rod 1R can be used to house one magnetic marker 1 in each housing hole 30, as shown in Figures 12(a) to 12(d). With the tip of the marker rod 1R inserted into the housing hole 30, which has a diameter of 38 mm and a depth of 30 mm, for example, by about 13 to 18 mm (less than the height dimension of the magnetic marker 1) (Figure 12(a)), one magnetic marker 1 can be easily separated by rotating the rear end of the marker rod 1R (Figure 12(b)) (Figure 12(c)). The magnetic marker 1 separated from the marker rod 1R in this way falls to the bottom of the housing hole 30 due to its own weight and is housed there (Figure 12(d)).

[0051] For example, in the case of the second magnetic marker 1 in Example 1, it is preferable to drill a lateral hole (reference numeral 102 in Figure 5) similar to the lateral hole in the connecting surface 100. While the lateral hole in this magnetic marker 1 is formed with 16 divisions in the circumferential direction, it is preferable to form the lateral hole in the connecting surface 100 with a larger number of divisions, such as 32 divisions in the circumferential direction. In this case, the strength of the connecting surface 100 can be reduced compared to the surface where the lateral hole is formed in the magnetic marker 1.

[0052] It should be noted that suppressing the strength of the connecting surface 100 is not an essential configuration. It is advisable to use a jig or similar device to cut out the magnetic markers 1 one by one from the marker rod 1R. By using a jig or similar device, the magnetic markers 1 can be efficiently cut out from the marker rod 1R, which has a substantially constant fracture strength in the axial direction. The other components and effects are the same as in Example 1.

[0053] Although specific examples of the present invention have been described in detail as shown in the examples above, these examples only disclose an example of the technology covered by the claims. Needless to say, the claims should not be interpreted restrictively based on the configuration or numerical values ​​of the specific examples. The claims encompass technologies obtained by various modifications, changes, or combinations of the above examples using prior art or the knowledge of those skilled in the art. [Explanation of symbols]

[0054] 1 Magnetic marker 1R Marker Stick 100 connection plane 101 Slit (groove, gap) 102 Horizontal holes (holes, gaps) 103 Vertical hole (hole, gap) 11 Magnetic Sheet 13, 135 Magnetic Area 131, 132 Slits 3 road 3S road surface 30 Intake holes 331 Coarse aggregate 332 Fine aggregate

Claims

1. A magnetic marker installed on a road for use in assisting vehicle driving, The magnetic marker is a columnar magnet having a shape that impairs the uniformity of stress in response to externally applied forces, resulting in areas where stress concentrates. The locations where the aforementioned stress is concentrated are provided by drilling slit-shaped grooves or holes on the outer surface of the columnar magnet. A magnetic marker in which the groove or hole is filled with powder or porous material of a soft magnetic material.

2. The magnetic marker according to claim 1, wherein the slit-shaped groove along the cross section perpendicular to the axial direction of the columnar magnet forms an annular shape surrounding the center, and a plurality of such grooves are provided in parallel along the axial direction.

3. A magnetic marker installed on a road for use in assisting vehicle driving, The magnetic marker is a columnar magnet having a shape that impairs the uniformity of stress in response to externally applied forces, resulting in areas where stress concentrates. A magnetic marker in which the location where the stress is concentrated is formed by drilling a hole along a cross-section perpendicular to the axial direction of the columnar magnet on the outer surface of the columnar magnet, thereby reducing the area of ​​the cross-section perpendicular to the axial direction.

4. A magnetic marker installed on a road for use in assisting vehicle driving, The magnetic marker is a columnar magnet having a shape that impairs the uniformity of stress in response to externally applied forces, resulting in areas where stress concentrates. The columnar magnet is made by laminating disc-shaped magnet sheets, the inner circumference of which is thicker than the outer circumference, and on the outer surface of the columnar magnet, there are slit-shaped grooves opening along the cross section perpendicular to the axial direction of the columnar magnet, forming gaps between adjacent disc-shaped magnet sheets. A magnetic marker in which the stress concentration points are formed in areas where the area of ​​the cross-section perpendicular to the axial direction is reduced by the slit-shaped grooves that form gaps between adjacent disc-shaped magnetic sheets.

5. A magnetic marker installed on a road for use in assisting vehicle driving, The magnetic marker is a columnar magnet having a shape that impairs the uniformity of stress in response to externally applied forces, resulting in areas where stress concentrates. The location where the stress is concentrated is provided by drilling a slit-shaped groove or hole on the outer surface of the columnar magnet. A magnetic marker in which the groove or hole is formed along a cross-section in the axial direction of the columnar magnet, and the location where stress is concentrated is formed in a location where the area of ​​the cross-section in the axial direction is reduced by the groove or hole.

6. The magnetic marker according to claim 5, wherein the cross-section is a plane including the central axis of the columnar magnet, and a plurality of such cross-sections are provided in the circumferential direction so as to intersect at the central axis, and the grooves formed in each cross-section are formed so as to avoid the central part including the central axis, so as not to divide the columnar magnet.

7. The magnetic marker according to any one of claims 1 to 6, wherein the magnetic marker is embedded in the pavement of a road, and the location of stress concentration is provided such that it is more prone to fracture than the pavement material making up the pavement to be constructed.

8. A magnetic marker in which the columnar magnet is a permanent magnet in which iron oxide magnetic powder is dispersed in a substrate made of a polymer material.

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