Embedded structure of contactless power supply coil

Abstract

To provide an embedded structure of a contactless power supply coil that can suppress damage to the power supply coil while maintaining the function of a road surface.SOLUTION: An embedded structure 1 of a contactless power supply coil includes: a coil 10 to which power for contactless power supply is supplied; a pavement 20 including a recess 22 opening into an upper surface 21 that becomes a road surface for vehicles; and a resin part 30 formed in the recess 22 using polyurea, the coil 10 being embedded in the resin part 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an embedded structure for a coil for contactless power supply. [Background technology]

[0002] Patent Document 1 discloses a wireless power transfer coil that is buried in a concrete road surface. The coil in this document has a through-hole in its center. When this coil is buried in the road surface, the concrete above and below the coil is integrated via the concrete filled in the through-hole. This allows the concrete below the coil to support the load from above the coil via the concrete in the through-hole, preventing cracks from occurring in the concrete directly above the coil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-12377 Summary of the Invention [Problem to be solved by the invention]

[0004] As is well known, the power transmission efficiency in contactless power transfer increases as the distance between the power transfer coil and the power receiving coil decreases. Therefore, when considering power supply to vehicles such as electric vehicles via contactless power transfer, the closer the power transfer coil is to the road surface, the better. However, the road surface is directly affected by the load from the vehicle and fluctuations in temperature and humidity. In other words, the closer the power transfer coil is installed to the road surface, the more severe the environment it is exposed to.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a buried structure for a contactless power supply coil that can suppress damage to the power supply coil while maintaining the function of the road surface. [Means for solving the problem]

[0006] An embedded structure for a coil for contactless power supply according to one aspect of the present disclosure includes a coil to which power for contactless power supply is supplied, a pavement including a recess that opens onto the upper surface that becomes the road surface for vehicles, and a resin part formed in the recess using polyurea, and the coil is embedded in the resin part.

[0007] The coil may be spaced apart from the inner surface of the recess within the resin portion. The resin portion may have a surface formed as the road surface. The embedded structure may further include a magnetic material positioned between the coil and the bottom surface of the recess. The pavement may be formed of reinforced concrete including a plurality of reinforcing bars arranged in a grid pattern. Electrical insulation may be applied to the portions where one reinforcing bar of the plurality of reinforcing bars intersects with another reinforcing bar. The pavement may be formed as a paving slab from precast concrete. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a buried structure for a contactless power transfer coil that can suppress damage to the power transfer coil while maintaining the function of the road surface. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view illustrating an example of an embedded structure according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a top view of the embedded structure shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. [Figure 4] FIG. 4 is a partially enlarged view of FIG. [Figure 5A] 10 is a graph showing an example of changes in the electrical characteristics of a coil. [Figure 5B] 10 is a graph showing an example of changes in the electrical characteristics of a coil. [Figure 5C] 10 is a graph showing an example of changes in the electrical characteristics of a coil. [Figure 5D] 10 is a graph showing an example of changes in the electrical characteristics of a coil. [Figure 6A]FIG. 2 is a perspective view showing an example of a reinforcing bar embedded in a pavement. [Figure 6B] This is an enlarged view showing the area where two reinforcing bars intersect. [Figure 7] FIG. 1 is a perspective view of a specimen used in a durability test. [Figure 8] 10 is a graph showing the results of a durability test. [Figure 9A] FIG. 1 is a cross-sectional view showing a test specimen used in a submersion test. [Figure 9B] FIG. 1 is a diagram showing a measurement environment of a test specimen during a submersion test. [Figure 10A] 10 is a graph showing an example of changes in the electrical characteristics of a coil in a water immersion test. [Figure 10B] 10 is a graph showing an example of changes in the electrical characteristics of a coil in a water immersion test. DETAILED DESCRIPTION OF THE INVENTION

[0010] Several embodiments of the present disclosure will be described below. Note that common parts in each drawing are given the same reference numerals, and redundant explanations will be omitted. For convenience of explanation, mutually orthogonal X, Y, and Z directions are defined. The X and Y directions are parallel to the road surface on which a vehicle, such as an electric vehicle, travels. In this case, the Z direction is perpendicular to the road surface.

[0011] The coil according to this embodiment is a so-called power supply coil for contactlessly supplying power to a vehicle such as an electric car. This coil is embedded in, for example, a pavement that forms a road surface. The coil is connected to a power transmission device (not shown) that generates the desired power, and generates magnetic flux using the power supplied from the power transmission device. Meanwhile, a power receiving coil mounted on the vehicle generates power through electromagnetic induction of this magnetic flux. The generated power is used, for example, to charge the battery or drive the engine (electric motor).

[0012] FIG. 1 is a perspective view showing an example of an embedded structure 1 for a coil 10 according to this embodiment. FIG. 2 is a top view of the embedded structure 1 shown in FIG. 1. FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. As shown in FIG. 1, the embedded structure 1 includes a coil 10, a pavement 20, and a resin part 30. Furthermore, as shown in FIG. 3, the coil 10 is embedded in the resin part 30 and is not exposed to the outside.

[0013] As described above, a power transmission device (not shown) is connected to coil 10, and power for contactless power supply output from the power transmission device is supplied to coil 10. The supplied power is AC power, and its frequency is, for example, on the order of kHz to MHz. Coil 10 is formed, for example, by winding litz wire 13. Litz wire 13 is an electric wire made by twisting together multiple enameled wires, and can suppress heat generation due to the skin effect when high-frequency power flows.

[0014] The coil 10 is formed by spirally winding the litz wire 13 on one plane (for example, the XY plane). The wound coil 10 is fixed to the mounting surface 12 inside the housing 11 with a predetermined fastening part after adjusting the spacing between adjacent litz wires 13. However, the electric wire constituting the coil 10 is not limited to the litz wire 13 described above, and may be, for example, a rectangular wire.

[0015] 2, the coil 10 has, for example, a rectangular shape extending in the X and Y directions. However, the overall shape of the coil 10 is not limited to a rectangle. For example, the coil 10 may be formed into a circular shape or another shape when viewed in the Z direction.

[0016] 2 and 3, the embedded structure 1 may further include a magnetic body 14. The magnetic body 14 contains, for example, ferrite, and is located between the coil 10 and the bottom surface 22b of the recess 22. The magnetic body 14 may be formed, for example, in the shape of a flat plate parallel to the coil 10 (i.e., parallel to the XY plane), or may have another shape. In either case, the provision of the magnetic body 14 increases the magnetic flux density generated by the coil 10, thereby improving transmission efficiency.

[0017] The pavement 20 according to this embodiment is a so-called pavement slab, and is made of precast concrete. That is, the pavement 20 is formed in advance in a factory or the like as a rectangular, plate-shaped concrete slab having a predetermined thickness. Because the pavement 20 is prefabricated, on-site work processes can be omitted, and construction time can be shortened. Furthermore, the shape can be easily changed, and there is a high degree of freedom in placement.

[0018] As shown in FIG. 1, the pavement 20 has an upper surface 21 and a recess 22 that opens into the upper surface 21. The upper surface 21 functions as a road surface (floor surface) on which vehicles run, stop, or park. Meanwhile, the recess 22 accommodates the coil 10 and is filled with a predetermined resin. In other words, the recess 22 forms an accommodation space for the coil 10 and the resin part 30. The cross-sectional shape of the recess 22 perpendicular to the Z direction has a shape and dimensions that allow the coil 10 (housing 11) to be accommodated. The depth of the recess 22 along the Z direction is set to a value that allows the coil 10 to be embedded in the resin part 30.

[0019] 3, the resin portion 30 is formed in the recess 22 using a predetermined resin. The resin portion 30 is formed by filling the recess 22 with a polyurethane resin and curing it while the coil 10 and the housing 11 are housed in the recess 22. In other words, the resin portion 30 fixes the coil 10 and the housing 11 to the recess 22 and protects them from external impacts and loads.

[0020] As described above, the recess 22 is deep enough to allow the coil 10 and the housing 11 to sink into the resin portion 30. Meanwhile, a predetermined resin is filled into the recess 22 until it reaches the upper surface 21 of the pavement 20, and then hardens. Therefore, the coil 10 and the housing 11 are embedded in the resin portion 30 and are not exposed to the outside.

[0021] The surface (top surface) 31 of the hardened resin part 30, together with the top surface 21 of the pavement 20, forms the road surface on which vehicles travel or park. Therefore, the specified resin that forms the resin part 30 is required to have physical properties that can withstand the load, friction, and impact of vehicles, etc., as well as temperature and humidity changes, and electrical properties that do not interfere with the AC magnetic flux generated by the coil 10.

[0022] In this embodiment, polyurea is used as a resin that satisfies these characteristics. Polyurea is a resin in which a curing agent, polyamine, is urea-bonded to a base resin, isocyanate. Polyurea has sufficient strength to function as a road surface and sufficient flexibility to resist cracking, and is used, for example, as a lining material to improve the strength of wall and floor surfaces. It is also known to have excellent waterproofing, abrasion resistance, and corrosion resistance.

[0023] FIG. 4 is a partially enlarged view of FIG. 3. For ease of explanation, hatching indicating the resin portion 30 is omitted in FIG. 4. As shown in FIG. 4, the housing 11 includes a bottom plate 15, a middle plate 16, and a top plate 17. These are stacked in the Z direction in the order shown and fixed to each other using known fasteners. The bottom plate 15 has a recess 15a for accommodating the magnetic body 14. The depth of the recess 15a along the Z direction is equal to the thickness of the magnetic body 14. The middle plate 16 has a groove 16a for accommodating the coil 10. By accommodating the coil 10 in the groove 16a, the spacing of the litz wire 13 between turns becomes approximately constant, suppressing excessive variation in this spacing. In other words, compared to when the litz wire 13 is simply bundled, variation in the electrical characteristics of the coil 10, such as transmission characteristics, can be suppressed. The top plate 17 is placed on the middle plate 16 and closes the opening of the groove 16a.

[0024] As shown in Fig. 4, the coil 10 may be spaced apart from the inner surface 22a of the recess 22 in the resin part 30. For example, the coil 10 may be spaced apart from the bottom surface 22b, which is part of the inner surface 22a, via the housing 11. Moisture from the constituent materials of the concrete (cement, coarse aggregate, fine aggregate, water, etc.) or from the environment, such as rainfall, may affect the transmission characteristics of the coil 10. Therefore, by separating the coil 10 from the concrete pavement 20, it is possible to prevent deterioration of the transmission characteristics.

[0025] The electrical characteristics of the coil 10 can be evaluated using a vector network analyzer (VNA). The VNA measures S-parameters using the coil 10 to be evaluated and a receiving coil (not shown). By performing a well-known conversion process on these S-parameters, the resistance, Q-factor, transmission efficiency, and output power of the coil 10 can be obtained. In the evaluation tests described below, the coil 10 and receiving coil were pre-adjusted using a resonant capacitor to have a resonant frequency of 85 kHz. The output power was calculated by converting the input voltage to 600 V. The distance between the coil 10 and the receiving coil (i.e., the transmission distance) was, for example, 170 mm. In each evaluation test, a pavement 20 with two layers of reinforcing bars 23 embedded in it was used, and the distance between the coil 10 and the upper layer of reinforcing bars 23 in the Z direction was kept constant. The frequency setting of 85 kHz is within the frequency band that is being considered by the Society of Automotive Engineers (SAE) for in-motion power transfer. The 600V input voltage setting is based on the SAE standard for DC power supply voltage, level 3.

[0026] 5A to 5D are graphs showing an example of changes in the electrical characteristics of the coil 10 depending on the position of the coil 10 within the resin part 30. Specifically, each figure shows a comparison result between a case in which the coil 10 is placed on the bottom surface 22b of the recess 22 (Case 1) and a case in which a part of the resin part 30 is provided between the coil 10 and the bottom surface 22b of the recess 22 (Case 2). Note that the distance between the coil 10 and the bottom surface 22b in Case 2 is 22.5 mm.

[0027] As shown in FIG. 5A, the resistance value of coil 10 in Case 2 is reduced by approximately 20% compared to Case 1. On the other hand, as shown in FIG. 5B, the Q value of coil 10 in Case 2 is increased by 23% compared to Case 1. Furthermore, as shown in FIG. 5C, the transmission efficiency in Case 2 is increased by 0.8% compared to Case 1, and as shown in FIG. 5D, the output power in Case 2 is increased by 10%. As these results show, the transmission characteristics of coil 10 can be improved by separating coil 10 from concrete.

[0028] FIG. 6A is a perspective view showing an example of reinforcing bars 23 embedded in a pavement 20. As shown in FIG. 6A, the pavement 20 may be formed of reinforced concrete containing a plurality of reinforcing bars 23. In this case, some of the plurality of reinforcing bars 23 extend in the Y direction and are arranged at a predetermined interval (pitch) in the X direction. The remaining portions of the plurality of reinforcing bars 23 extend in the X direction and are arranged at a predetermined interval (pitch) in the Y direction. In other words, the plurality of reinforcing bars 23 are arranged in a lattice pattern. Note that the layers of reinforcing bars 23 that make up the lattice may be arranged at intervals in the Z direction. Forming the pavement 20 from reinforced concrete significantly improves mechanical strength. Furthermore, the occurrence of cracks is suppressed, thereby increasing durability.

[0029] FIG. 6B is an enlarged view showing a portion P where two reinforcing bars 23 intersect. As shown in FIG. 6B, the portion P where one reinforcing bar 23A and another reinforcing bar 23B intersect among the multiple reinforcing bars 23 may be electrically insulated. That is, the reinforcing bars 23A and 23B may be electrically insulated from each other. To achieve this electrical insulation, for example, as shown in FIG. 6B, a highly electrically insulating resin tape 24 is wrapped around at least one of the reinforcing bars 23A and 23B. This positions the tape 24 between the reinforcing bars 23A and 23B, separating the reinforcing bars 23A and 23B from each other. This insulation reduces the impact of the electrically connected multiple reinforcing bars 23 on the electrical characteristics of the coil 10, thereby preventing deterioration of the transmission performance of the coil 10.

[0030] Next, we will explain the test results regarding the physical properties of the buried structure 1. As described below, in order to evaluate the physical properties of the buried structure 1, a durability test was conducted on a specimen 50 that imitated the buried structure 1. Specifically, a wheel tracking (WT) test was conducted on the specimen 50 as the durability test.

[0031] FIG. 7 is a perspective view of a specimen 50 used in a durability test. As shown in FIG. 7, the specimen 50 has a flat plate 51 as a base and a resin plate 52 formed on the flat plate 51. The flat plate 51 is a rectangular plate made of concrete and has a thickness of 50 mm. The length of the flat plate 51 along the X and Y directions is 300 mm. On the other hand, the resin plate 52 is a rectangular plate made of polyurea and has a thickness of 30 mm. The length of the resin plate 52 along the X and Y directions is 300 mm, the same as the flat plate 51.

[0032] Seven litz wires 13 are embedded in the resin plate 52, with the same number of turns as the coil 10. The litz wires 13 extend in the Y direction at intervals in the X direction and are embedded in the resin plate 52. The intervals in the X direction are the same as the intervals between the litz wires 13 in the coil 10. The litz wires 13 are not exposed on the top surface 50a, which simulates the road surface, but are drawn out from the side surface 50b of the test piece 50. The litz wires 13 are also positioned at the center of the resin plate 52 in the Z direction, and their outer diameter is 9 mm. Therefore, the litz wires 13 are approximately 10 mm away from both the top surface 50a and the boundary surface 53 between the resin plate 52 and the flat plate 51.

[0033] The specific specifications for this test are as follows: Running method: Crank type Load: 686±10N (ground pressure: 0.69MPa) Loading method: Load plate Running wheels: φ200mm, width 50mm, thickness 15mm (solid tires) Number of runs: 42 runs / min Travel distance: 230±10mm In this test, a tire (solid tire) 60 of a WT tester is run in the X direction on the upper surface 50a of the specimen 50, and the resistance value of each litz wire 13 is measured every time the tire 60 reaches 10,000 runs. A similar measurement is also performed when the tire 60 is run in the Y direction on the upper surface 50a of the specimen 50. That is, in the former test, the tire 60 runs in a direction (X direction) perpendicular to the longitudinal direction of the litz wire 13. On the other hand, in the latter test, the tire 60 runs in a direction (Y direction) parallel to the longitudinal direction of the litz wire 13.

[0034] Fig. 8 is a graph showing the results of the durability test (WT test) described above. For comparison, a test specimen was prepared in which the resin plate 52 was replaced with high-toughness mortar, and the test described above was carried out. However, the tire 60 (see Fig. 7) was run in the X direction on the high-toughness mortar test specimen.

[0035] As shown in Figure 8, each specimen was subjected to 200,000 loads. If the litz wire 13 was damaged by this load, the resistance value of the litz wire 13 would increase. However, as shown in Figure 8, the resistance value of the litz wire 13 embedded in the resin plate 52 fluctuates within a certain range, but does not show a significant increase. This trend is similar to the trend in the resistance value of the litz wire 13 embedded in high-toughness mortar. In other words, this test result shows that the polyurethane resin plate 52, like high-toughness mortar, is significantly less likely to damage the litz wire 13 embedded in the resin plate 52.

[0036] Furthermore, in this test, each time the resistance value was measured, the upper surface 50a was visually observed to check for the presence or absence of ruts or cracks. According to the results of this inspection, no damage such as ruts or cracks was found on the upper surface 50a of the test specimen 50 on which the polyurethane resin plate 52 was formed. This was also true for the test specimen in which the resin plate 52 was replaced with high-toughness mortar. In other words, this result indicates that the polyurethane resin plate 52, like the high-toughness mortar, has high resistance (i.e., mechanical strength) to the load, friction, and impact of vehicles, etc.

[0037] Next, the effect of moisture on the buried structure 1 will be described. FIG. 9A is a cross-sectional view showing specimen 1A of the buried structure 1 used in the submersion test. FIG. 9B is a diagram showing the measurement environment of specimens 1A and 1B during the submersion test. In specimen 1A, coil 10 is housed in housing 11 and embedded in resin part 30. A portion of resin part 30 with a thickness of 10 mm is interposed between housing 11 and bottom surface 22b of recess 22. In contrast, coil 10 in specimen 1B is embedded directly in resin part 30. The distance between coil 10 and bottom surface 22b in specimen 1B was 10 mm. In both specimens 1A and 1B, two layers of reinforcing bars 23 were installed in pavement 20. In other words, both specimens 1A and 1B are pavement slabs made of reinforced concrete.

[0038] 10A and 10B are graphs showing an example of the change in the electrical characteristics of the coil 10 during a submersion test. In the submersion test, the test specimens 1A and 1B were submerged in a pool 70 filled with water for one week, and then allowed to dry for one week. The resistance and Q value of the coil 10 were measured at several times during this period. The pool 70 was placed on a wooden (laminated wood) base 71, and metal that could affect the EVA measurement was isolated from the surroundings of the test specimens 1A and 1B.

[0039] The graph in Figure 10A shows an example of the change in the resistance value of the coil 10 embedded in the test specimen 1A. Meanwhile, the graph in Figure 10B shows an example of the change in the Q value of the coil 10 embedded in the test specimen 1A. Both the resistance value and the Q value were measured at five different times: before the test specimen 1A was submerged, immediately after the submersion, one week after the submersion, after the submersion, and one week after the submersion. As shown in these graphs, the resistance value deteriorates by about 5% while the test specimen 1A is submerged, but remains almost constant while the submersion is complete. Furthermore, the resistance value gradually recovers immediately after the test specimen 1A is removed from the pool. A similar trend can be seen in the change in the Q value shown in Figure 10B. That is, the Q value of the test specimen 1A while submerged decreases by 6.9% compared to the value before the submersion. These trends were also observed for the test specimen 1B.

[0040] As described above, although some changes due to moisture adhering to the surface of the test specimen 1A (1B) were observed, no significant changes were observed in the results of the transmission characteristics measurements, which were conducted in conjunction with the measurements of the resistance value and Q value. Therefore, it is believed that moisture has no effect on the polyurea resin portion 30, and that the polyurea has sufficient waterproofing properties for the coil 10. In other words, the buried structure 1 according to this embodiment can adequately withstand humid environments such as rainy weather.

[0041] It should be noted that the above-described embodiments are merely examples for facilitating understanding of the invention, and the technical scope of the invention includes various modifications, changes, alternative technologies, etc. that can be easily derived therefrom.

[0042] For example, the housing 11 may be omitted. In this case, the recess 22 (resin portion 30) accommodates the coil 10 and a restraining part such as a band that maintains the shape of the coil 10. Furthermore, the coil 10 may be buried in a recess in a road surface that has been paved (constructed) on-site with asphalt or concrete. In this case, the coil 10 is also secured to the road surface while being protected by the polyurethane resin portion 30. [Explanation of symbols]

[0043] 1 Buried structure 10 coils 14 Magnetic material 20 Pavement 21 Top side 22 recess 23 Reinforced concrete 30 Resin part

Claims

1. a coil to which power for contactless power transfer is supplied; a pavement including a recessed portion that opens onto an upper surface that serves as a road surface for vehicles; a resin portion formed in the recess by polyurea; Equipped with The coil is embedded in the resin portion. Embedded structure of a coil for contactless power supply.

2. The resin portion has a surface that is formed as the road surface. The embedded structure for a contactless power supply coil according to claim 1 .

3. The coil is spaced apart from the inner surface of the recess within the resin portion. The embedded structure for a contactless power supply coil according to claim 1 .

4. Further, a magnetic body is provided between the coil and the bottom surface of the recess. The embedded structure for a contactless power supply coil according to claim 1 .

5. The pavement is formed of reinforced concrete including a plurality of reinforcing bars arranged in a grid pattern. The embedded structure for a contactless power supply coil according to claim 1 .

6. The portion where one reinforcing bar intersects with another reinforcing bar is electrically insulated. The embedding structure of a contactless power supply coil according to claim 5 .

7. The pavement is formed as a paving slab using precast concrete. The embedded structure for a contactless power supply coil according to any one of claims 1 to 6.

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