Wireless power transfer coil and wireless power transfer system
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-27
- Publication Date
- 2026-08-13
Smart Images
Figure JP2026002612_13082026_PF_FP_ABST
Abstract
Description
WIRELESS POWER TRANSFER COIL AND WIRELESS POWER TRANSFER SYSTEMCross Reference
[0001] This application is based on Japanese Applications No. 2025-017272 filed on February 05, 2025 and No. 2025-154888 filed on September 18, 2025, the contents of which are incorporated herein by reference.
[0002] The present disclosure relates to a wireless power transfer coil and a wireless power transfer system.
[0003] In the related art, in a wireless power transfer system that supplies power from a power transmitter coil to a power receiver coil in a wireless manner, a technique for reducing a leakage magnetic field has been proposed.
[0004] For example, in the wireless power transfer system disclosed in Patent Literature 1, the power transmitter coil and the power receiver coil include a pair of coils provided in the horizontal direction adjacent to each other with a distance therebetween, sandwiching the front-to-rear direction of the vehicle. The pair of coils are configured such that the direction of the magnetic fields generated by a current is opposite to each other.
[0005] In the wireless power transfer device disclosed in Patent Literature 2, multiple cut units are provided at a constant pitch at positions corresponding to the center of the magnetic poles in the magnetic material yoke of multiple power transmitter coils on the ground side. The leakage magnetic flux of the power transmitter coil that transmits power to the power receiver coil is reduced by flowing a current through a cancel coil.
[0006] JP7564003BJP7275662B
[0007] In the related art, a ground-side power transmitter coil used for wireless power transfer while the vehicle travels generally had a magnetic material such as ferrite and a shield member provided on the rear surface. In this case, the distant leakage magnetic field (for example, 10 m ahead of the vehicle) tended to increase as the vehicle moves. However, when the power transmitter coil is an air-core coil provided with neither a magnetic material nor a shield member, the problem arises that the leakage magnetic field does not increase as the vehicle moves, but rather increases under conditions of maximum coupling. For example, reinforcing bars may be provided in the lower part of a road near a bridge, slightly away from the power transmitter coil, but when the power transmitter coil itself is an air-core coil, the effect is the same regardless of the presence or absence of nearby reinforcing bars.
[0008] The present invention has been conceived in view of such points, and the object is to provide a wireless power transfer coil that can suppress a distant leakage magnetic field even when the counterpart power transmitting-receiving coil is an air-core coil, and a wireless power transfer system using the same.
[0009] According to a first aspect of the present disclosure, a wireless power transfer coil is to be used for at least one of a power transmitter coil and a power receiver coil in a wireless power transfer system. The wireless power transfer system is configured to supply power from the power transmitter coil to the power receiver coil in a wireless manner. The wireless power transfer coil comprises: a core configured to induce a magnetic field of a coil. The core includes a plurality of low-magnetic resistance portions formed of a magnetic material and a high-magnetic resistance portion having a magnetic resistance, which is higher than a magnetic resistance of the low-magnetic resistance portion, and partially provided between the low-magnetic resistance portions. The low-magnetic resistance portions and the high-magnetic resistance portion are provided to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil.
[0010] The core includes a low-magnetic resistance portion formed of a magnetic material, and high-magnetic resistance portions that have higher magnetic resistance than the low-magnetic resistance portion and are partially provided between the low-magnetic resistance portions. The low-magnetic resistance portion and the high-magnetic resistance portions are provided so as to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil.
[0011] In a first aspect of the present invention, unlike a general coil where the core is formed of a single magnetic material, high-magnetic resistance portions are partially provided between the low-magnetic resistance portions, thus enabling the suppression of a distant leakage magnetic field even when the counterpart transmitting-receiving coil is an air-core coil.
[0012] By the way, as a trade-off of suppressing leakage magnetic fields, the efficiency of magnetic transmission decreases. For example, depending on leakage magnetic field tolerance standards by country or region, the disadvantage of decreased magnetic transmission efficiency may outweigh the advantage of leakage magnetic field suppression.
[0013] To address this issue, the wireless power transfer coil according to a second aspect of the present disclosure, a wireless power transfer coil is to be used for a power receiver coil in a wireless power transfer system. The wireless power transfer system is configured to supply power from a power transmitter coil on a ground side to the power receiver coil of a vehicle in a wireless manner while the vehicle travels. The wireless power transfer coil comprises: a core including a plurality of magnetic materials and configured to induce a magnetic field of a coil. The core is configured to switch between a first arrangement state in which the magnetic materials are arranged such that magnetic flux propagated along a traveling direction of the vehicle is relatively large and a second arrangement state in which the magnetic materials are arranged such that magnetic flux propagated along the traveling direction of the vehicle is relatively small. In the second arrangement state, the core is configured to include i) a plurality of low-magnetic resistance portions formed of the magnetic materials and ii) a high-magnetic resistance portion formed of an air gap, which has a magnetic resistance higher than a magnetic resistance of the low-magnetic resistance portion, and is partially provided between the low-magnetic resistance portions, to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil.
[0014] The core is configured to be switchable between a first arrangement state, in which multiple magnetic materials are arranged such that the magnetic flux propagated along the traveling direction of a vehicle is relatively large, and a second arrangement state, in which multiple magnetic materials are arranged such that the magnetic flux propagated along the traveling direction of the vehicle is relatively small.
[0015] In the second arrangement state, the core includes a low-magnetic resistance portion formed of a magnetic material, and a high-magnetic resistance portion (45) which is formed of an air gap having higher magnetic resistance than the low-magnetic resistance portion and is partially provided between the low-magnetic resistance portions. In the second arrangement state, the core suppresses a distant leakage magnetic field in the magnetic field generated by energizing the power transmitter coil.
[0016] In a second aspect of the present invention, the configuration of the core can be switched such that the magnitude of the magnetic flux propagated along the traveling direction of the vehicle changes depending on whether suppression of the leakage magnetic field or efficiency is prioritized. Therefore, specifications can be changed according to the situation.
[0017] The drawings described herein are intended to illustrate selected embodiments, do not depict all possible embodiments, and are not intended to limit the scope of the present disclosure.FIG. 1 is a block diagram showing the overall configuration of a wireless power transfer system during traveling.FIG. 2 is a diagram showing an example of the circuit configuration of a power transmitter circuit and a power receiver circuit.FIG. 3 is a top view of a wireless power transfer coil of a comparative example.FIG. 4 is a top view of a wireless power transfer coil of a first embodiment.FIG. 5 is a perspective view of the wireless power transfer coil of FIG. 4.FIG. 6 shows configuration examples 1 and 2 of the power transmitter coil.FIG. 7 is a diagram showing the effect of suppressing a distant leakage magnetic field according to the first embodiment.FIG. 8 is a diagram for illustrating a method for evaluating the distant leakage magnetic field.FIG. 9 is a diagram showing a leakage magnetic field generated from a power transmitter coil as a vehicle (power receiver coil) moves.FIG. 10 is a top view of a wireless power transfer coil according to a second embodiment.FIG. 11 is a top view of a wireless power transfer coil according to another embodiment 1.FIG. 12 is a top view of a wireless power transfer coil according to another embodiment 2.FIG. 13 is a top view of a wireless power transfer coil according to another embodiment 3.FIG. 14 is a top view of a wireless power transfer coil according to another embodiment 4.FIG. 15 is a top view of a wireless power transfer coil according to another embodiment 5A.FIG. 16 is a top view of a wireless power transfer coil according to another embodiment 5B.FIG. 17 is a top view of a wireless power transfer coil according to another embodiment 5C.FIG. 18 is a top view of a first arrangement state and a second arrangement state of a wireless power transfer coil (power receiver coil) according to a third embodiment.FIG. 19 is a side view (viewed in the direction of arrow XIX in FIG. 18) of a wireless power transfer coil (power receiver coil) of a fourth embodiment in a first arrangement state and a second arrangement state.FIG. 20 is a flowchart showing switching between the first arrangement state and the second arrangement state.
[0018] Multiple embodiments of a wireless power transfer coil will be described with reference to the drawings. In the multiple embodiments, substantially the same components are denoted by the same reference numerals, and a description of the same components will be omitted. A wireless power transfer coil is used for at least one of a power transmitter coil or a power receiver coil in a wireless power transfer system that supplies power from the power transmitter coil to the power receiver coil in a wireless manner. In the following description of the embodiment, a wireless power transfer coil used as a power receiver coil on a vehicle side in a wireless power transfer system while the vehicle travels will be mainly described.
[0019] A wireless power transfer system during traveling is desired as a means to solve the problem of electric vehicles running out of power. The system uses a magnetic field from a power transmitter coil provided on the ground to transmit power to a power receiver coil mounted on the vehicle. Among the magnetic fields generated by energizing the power transmitter coil, the magnetic field that does not interlink with the power receiver coil is called a "leakage magnetic field". There is a need to suppress a leakage magnetic field, taking into consideration the effects on other electronic devices and living bodies.
[0020] In the related art, a power transmitter coil was generally provided with a magnetic material such as ferrite and a shield member on the rear surface. In this case, the distant leakage magnetic field (for example, 10 m ahead of the vehicle) tended to increase as the vehicle moves. However, when the power transmitter coil is an air-core coil provided with neither a magnetic material nor a shield member, the problem arises that the leakage magnetic field does not increase as the vehicle moves, but rather increases under conditions of maximum coupling. Therefore, the wireless power transfer coil of the first and second embodiments and other embodiments 1 to 5 is intended to suppress a distant leakage magnetic field when used as a power receiver coil in a wireless power transfer system during traveling in which the power transmitter coil is an air-core coil.
[0021] However, the trade-off of suppressing the leakage magnetic field is that the efficiency of magnetic transmission decreases, and the disadvantage of the decreased efficiency may outweigh the advantage of suppressing the leakage magnetic field. Therefore, the wireless power transfer coil of the third and fourth embodiments is intended to enable the core configuration to be switched such that the magnitude of the magnetic flux propagating along the traveling direction of the vehicle changes depending on whether suppression of the leakage magnetic field or efficiency is prioritized.
[0022] (Wireless Power Transfer System during Traveling) The overall configuration of the wireless power transfer system during traveling and the circuit configuration related to the wireless power transfer will be outlined with reference to FIGS. 1 and 2. As shown in FIG. 1, the wireless power transfer system during traveling includes a power transfer system 100 on a road 105 side and a power receiving system 200 during traveling on the side of a vehicle 202. The wireless power transfer system during traveling is a system that can supply power from the power transfer system 100 during traveling to the vehicle 202 while the vehicle 202 travels. The vehicle 202 is an electric vehicle, including an electric vehicle and a hybrid vehicle. In FIG. 1, the x-axis direction indicates the traveling direction of the vehicle 202, the y-axis direction indicates the width direction of the vehicle 202, and the z-axis direction indicates the vertical direction from the ground side to the ceiling side. The same applies to the x, y, and z-axis directions in the following figures.
[0023] The power transfer system 100 during traveling on the road 105 side includes multiple power transmitter coils 140, multiple power transmitter circuits 130 that supply an AC voltage to each of the power transmitter coils 140, a power transfer circuit 110 that supplies a DC voltage to the multiple power transmitter circuits 130, and a power receiver coil position detection unit 120.
[0024] The multiple power transmitter coils 140 are installed along the direction in which the road 105 extends. The power transmitter circuit 130 is a circuit that converts the DC voltage supplied from the power transfer circuit 110 into a high-frequency AC voltage and applies the same to the power transmitter coil 140, and includes an inverter circuit, a filter circuit, and a resonant circuit (see FIG. 2). The power transfer circuit 110 is a circuit that supplies a DC voltage to the power transmitter circuit 130. For example, the power transfer circuit 110 is configured as an AC-DC converter circuit that rectifies an AC voltage supplied from a commercial power source and outputs a DC voltage.
[0025] The power receiver coil position detection unit 120 detects the position of a power receiver coil 240 mounted on the vehicle 202. The power receiver coil position detection unit 120 may, for example, detect the position of the power receiver coil 240 from the magnitude of the transmitted power or transmitted current in the multiple power transmitter circuits 130, or may detect the position of the power receiver coil 240 by using wireless communication with the vehicle 202 or a position sensor that detects the position of the vehicle 202. The multiple power transmitter circuits 130 transmit power by using one or more power transmitter coils 140 that are close to the power receiver coil 240, depending on the position of the power receiver coil 240 detected by the power receiver coil position detection unit 120.
[0026] The vehicle 202 includes a main battery 210, an auxiliary battery 215, a control device 220, a power receiver circuit 230, a power receiver coil 240, a DC-DC converter circuit 260, an inverter circuit 270, a motor generator 280, and an auxiliary device 290. The power receiver coil 240 is connected to the power receiver circuit 230. The output end of the power receiver circuit 230 is connected to the main battery 210, the high-voltage side of the DC / DC converter circuit 260, and the inverter circuit 270. The auxiliary battery 215 and the auxiliary device 290 are connected to the low-voltage side of the DC / DC converter circuit 260. The motor generator (MG in the figure) 280 is connected to the inverter circuit 270.
[0027] The power receiver coil 240 is a device that generates an induced electromotive force by electromagnetic induction between the power receiver coil 240 and the power transmitter coil 140. The power receiver circuit 230 includes a rectifier (see FIG. 2) that converts the AC voltage output from the power receiver coil 240 into a DC voltage. The power receiver circuit 230 may include a DC / DC converter circuit that converts the DC voltage output by the rectifier into a voltage suitable for charging the main battery 210. The DC voltage output from the power receiver circuit 230 can be used to charge the main battery 210 and drive the motor generator 280 via the inverter circuit 270. The DC voltage output from the power receiver circuit 230 is stepped down by the DC / DC converter circuit 260 and can be used to charge the auxiliary battery 215 and drive the auxiliary device 290.
[0028] The main battery 210 is a secondary battery that outputs a DC voltage of several hundred volts. The motor generator 280 is a three-phase AC motor that generates a driving force for the vehicle 202. When the motor generator 280 operates in a power operation, the inverter circuit 270 converts the DC voltage of the main battery 210 into a three-phase AC voltage and supplies the same to the motor generator 280. When the motor generator 280 is in a regenerative operation during deceleration of the vehicle 202, the inverter circuit 270 converts the three-phase AC voltage output by the motor generator 280 into a DC voltage and supplies the same to the main battery 210.
[0029] The DC / DC converter circuit 260 steps down the DC voltage of several hundred volts of the main battery 210 to several volts to several tens of volts, and supplies the stepped-down voltage to the auxiliary battery 215 and the auxiliary device 290. The auxiliary device 290 includes peripheral devices such as an air conditioner, an electric power steering device, headlights, blinkers, wipers, and various accessories of the vehicle 202.
[0030] The control device 220 transmits and receives signals to and from the main battery 210, the inverter circuit 270, the motor generator 280, the DC / DC converter circuit 260, the auxiliary battery 215, the auxiliary device 290, and the like, and controls each part within the vehicle 202. When receiving wireless power transfer during traveling, the control device 220 controls the power receiver circuit 230 to receive power.
[0031] FIG. 2 shows an example of the circuit configuration of the power transmitter circuit 130 and the power receiver circuit 230. In FIG. 2, the power transfer circuit 110 that outputs DC power is schematically represented by a battery symbol. The power transmitter circuit 130 includes an inverter circuit 132, a filter circuit 134, and a resonant circuit 136. The inverter circuit 132 converts the DC voltage supplied from the power transfer circuit 110 into a high-frequency AC voltage by, for example, switching operations of four H-bridge connected transistors.
[0032] The filter circuit 134 includes, for example, an inductor and a capacitor, and blocks unnecessary high-frequency components contained in the AC voltage output by the inverter circuit 132. The resonant circuit 136 is configured by connecting, for example, the power transmitter coil 140 and a capacitor C1 in series. However, the resonant circuit is not limited to this configuration, and may have a configuration in which the power transmitter coil 140 and the capacitor C1 are connected in parallel, or may have other configurations.
[0033] The power receiver circuit 230 includes a resonant circuit 236, a filter circuit 234, and a rectifier 232. The resonant circuit 236 is configured by connecting, for example, the power receiver coil 240 and a capacitor C2 in series. However, the resonant circuit is not limited to this configuration, and may have a configuration in which the power receiver coil 240 and the capacitor C2 are connected in parallel, or may have other configurations. The filter circuit 234 has a configuration similar to that of the filter circuit 134 of the power transmitter circuit 130, and blocks unnecessary high-frequency components. The rectifier 232 has a configuration similar to that of the inverter circuit 132 of the power transmitter circuit 130, and converts AC voltage into DC voltage to supply to the main battery 210.
[0034] As shown in parentheses, in the third and fourth embodiments, a switching control unit 251 and a drive mechanism 252 are provided outside the power receiver coil 240 as a configuration for switching the arrangement state of the multiple magnetic materials in the power receiver coil 240. The switching of the arrangement of the magnetic materials will be described later.
[0035] In FIG. 2, the power transmitter coil 140 is included in the resonant circuit 136, which is a part of the power transmitter circuit 130, but for the sake of convenience, in FIG. 1, the "power transmitter circuit of the portion excluding the power transmitter coil" is illustrated as the power transmitter circuit 130, and the corresponding parts of the specification are also described in accordance with the description in FIG. 1. Similarly, in FIG. 2, the power receiver coil 240 is included in the resonant circuit 236, which is a part of the power receiver circuit 230, but for the sake of convenience in FIG. 1, the "power receiver circuit of the portion excluding the power receiver coil" is illustrated as the power receiver circuit 230, and the corresponding parts of the specification are also described in accordance with the description in FIG. 1.
[0036] (First Embodiment) Next, with reference to FIGS. 3 to 5, the configuration of a wireless power transfer coil 401 of a first embodiment will be described in comparison with a wireless power transfer coil 409 of a comparative example. These wireless power transfer coils 401 and 409 are used as power receiver coils 240 on the vehicle side. FIG. 3 of the comparative example and FIG. 4 of the first embodiment are top views viewed from below with a coil unit 41 facing downward (toward the ground) and a core 440 and a shield member 48 provided on the rear surface of the coil unit 41 facing upward (toward the vehicle floor). FIG. 5 is a perspective view of the wireless power transfer coil 401 of the first embodiment, viewed obliquely from below.
[0037] However, when mounted on a vehicle, the coil unit 41 is provided facing downward so as to face the road. Therefore, the front side of the paper in FIGS. 3 and 4 corresponds to the ground side in the z-axis direction (indicated by the x mark). The left and right directions in FIGS. 3 and 4 correspond to the front-to-rear direction of the vehicle (x-axis direction), and the vertical direction in FIGS. 3 and 4 corresponds to the width direction of the vehicle (y-axis direction). The same applies to FIGS. 10 to 14.
[0038] In the wireless power transfer coil 409 of the comparative example shown in FIG. 3, the core 440 for inducing the magnetic field of the coil unit 41 is provided on the rear side of the coil unit 41. In the comparative example, the entire core 440 is made of a uniform magnetic material (that is, low-magnetic resistance portion) 44. The magnetic material 44 may be, for example, a soft magnetic material such as ferrite. The shield member 48 that shields the magnetic field generated by the coil unit 41 is provided on the rear side of the core 440. The shield member 48 is formed of a metal plate such as aluminum. In this configuration, the base plate also serves as the shield member 48, but the shield member 48 may be provided separately from the base plate.
[0039] In contrast, in the wireless power transfer coil 401 of the first embodiment shown in FIG. 4, the core 440 provided on the rear side of the coil unit 41 includes the magnetic material 44 and an air gap 45. The air gaps 45 are partially provided between the magnetic materials 44 and divide the magnetic materials 44 in the x-axis direction.
[0040] The air present in the air gap 45 has a high magnetic resistance with respect to the magnetic material 44 such as ferrite. Therefore, in general terms, the magnetic material 44 with a relatively low magnetic resistance can be called a "low-magnetic resistance portion," and the air gap 45 with a relatively high magnetic resistance can be called a "high-magnetic resistance portion". That is, in the wireless power transfer coil 401, the core 440 includes the magnetic material 44 as a "low-magnetic resistance portion" and the air gap 45 as a "high-magnetic resistance portion". In the first embodiment, the high-magnetic resistance portion is formed of the air gap 45.
[0041] As shown in FIG. 5, an imaginary plane Sφ is assumed through which a magnetic flux φ passes when the coil unit 41 is energized. The imaginary plane Sφ is parallel to the x-axis direction. The air gap 45 extends in a direction (y-axis direction) perpendicular to the imaginary plane Sφ through which the magnetic flux φ passes. By using the wireless power transfer coil 401 having the air gap 45 provided in this manner as the power receiver coil 240, it is possible to suppress the distant leakage magnetic field from the power transmitter coil 140. That is, the magnetic material 44, which is a low-magnetic resistance portion, and the air gap 45, which is a high-magnetic resistance portion, are provided to suppress the distant leakage magnetic field.
[0042] Next, a configuration example of the ground-side power transmitter coil 140 will be described. A coil that is provided with neither a magnetic material such as ferrite that induces the magnetic field of the coil nor a shield member that shields the magnetic field of the coil, is called an "air-core coil". As a main example in which the effect of suppressing the distant leakage magnetic field by the wireless power transfer coil 401 of the first embodiment is particularly exerted, it is assumed that the power transmitter coil 140 is an air-core coil.
[0043] In a configuration example 1 shown in the upper part of FIG. 6, two adjacent coil units 141 and 142 form one set, and a winding W is wound in an eight-shape. That is, the winding W is wound so that the winding direction of the first coil unit 141 and the winding direction of the second coil unit 142 are opposite to each other.
[0044] In a configuration example 2 shown in the lower part of FIG. 6, two adjacent coil units 141 and 142 are each wound independently with the winding W such that the winding direction of the first coil unit 141 and the winding direction of the second coil unit 142 are opposite to each other.
[0045] In each of the configuration examples 1 and 2 of the power transmitter coil 140, the number of turns is determined according to the design. The configuration example 1 and the configuration example 2 may be combined as appropriate.
[0046] Next, performance evaluation of the wireless power transfer coil 409 (without an air gap) of the comparative example and the wireless power transfer coil 401 (with an air gap) of the first embodiment will be described. The comparative example and the first embodiment have the same power transfer and efficiency. As shown in FIG. 7, when comparing the leakage magnetic field at a point 10 m away from the power transmitter coil 140, the leakage magnetic field was suppressed more effectively in the first embodiment than in the comparative example.
[0047] In this way, the wireless power transfer coil 401 of the first embodiment, which is provided with the air gap 45 extending in a direction (y-axis direction) perpendicular to the imaginary plane Sφ through which the magnetic flux φ passes, has little effect on power transfer performance and can suppress magnetic flux propagation in the direction (x-axis direction) of the imaginary plane Sφ through which the magnetic flux φ passes. Therefore, it is possible to suppress the distant leakage magnetic field.
[0048] The evaluation method and evaluation results of the distant leakage magnetic field will be described with reference to FIGS. 8 and 9. As shown in FIG. 8, a leakage evaluation loop antenna 108 is installed 10 m away from one ground-side power transmitter coil 140. The vehicle moves forward from an initial position A where the positions of the power receiver coil 240 and the power transmitter coil 140 are aligned. The length of the power receiver coil 240 in the front-to-rear direction of the vehicle is defined as L, and a position (L / 2) forward from the initial position A is defined as a position B. The leakage magnetic field generated from the power transmitter coil 140 as the vehicle moves from position A to position B is evaluated when the wireless power transfer coil 409 of the comparative example is used in the power receiver coil 240 of the vehicle and when the wireless power transfer coil 401 of the first embodiment was used.
[0049] FIG. 9 shows the change in the "leakage magnetic field (radiated magnetic field) generated from the power transmitter coil" with respect to the vehicle position in the range from position A to position B, with the radiated magnetic field of the comparative example at the position A set as 1 (reference). In the comparative example, the radiated magnetic field from the ground varies in the range from less than 0.6 to more than 1.1.
[0050] On the other hand, when the wireless power transfer coil 401 of the first embodiment is used, the radiated magnetic field from the ground gradually increases from about 0.4 at the position A to about 0.7 at the position B. That is, the radiated magnetic field becomes stronger as the vehicle approaches the loop antenna 108, but in the first embodiment, the radiated magnetic field from the ground is smaller overall than in the comparative example. The air gap 45 is provided at a position where the radiated magnetic field from the ground does not change, so the current value and the like related to the power transfer do not change.
[0051] As described above, the wireless power transfer coil 401 of the first embodiment can suppress magnetic flux propagation in the x-axis direction and suppress radiation from the ground side by providing the air gap 45 that divides the magnetic material 44, which is the low-magnetic resistance portion, in the x-axis direction. Therefore, when applied to the power receiver coil 240 of a wireless power transfer system during traveling, it is possible to suppress the distant leakage magnetic field even when the ground-side power transmitter coil 140 is an air-core coil.
[0052] (Second Embodiment) A wireless power transfer coil 402 according to a second embodiment will be described with reference to FIG. 10. In the second embodiment, the high-magnetic resistance portion 46 is magnetically saturated or is formed of a non-magnetic material such as aluminum. For example, thin ferrite is prone to magnetic saturation due to the magnetic field generated by energizing the coil unit 41. A magnetically saturated material has a non-permeability close to 1 and is used as a "high-magnetic resistance portion".
[0053] Non-magnetic materials such as aluminum have a non-permeability close to 1. Since air is also a non-magnetic material, the air gap 45 of the first embodiment can be broadly interpreted as being included in the "high-magnetic resistance portion 46" defined in the second embodiment.
[0054] The disposition of the high-magnetic resistance portions 46 shown in FIG. 10 is similar to the disposition of the air gaps 45 in the first embodiment shown in FIG. 4. In other words, the high-magnetic resistance portion 46, which is magnetically saturated or made of a non-magnetic material, extends in a direction (y-axis direction) perpendicular to the imaginary plane Sφ through which the magnetic flux φ passes, and divides the magnetic material 44 into two parts. As a result, the wireless power transfer coil 402 of the second embodiment also achieves the same effects as the wireless power transfer coil 401 of the first embodiment.
[0055] (Other Embodiments Corresponding to First and Second Embodiments) (a) FIGS. 11 to 17 show the configurations of wireless power transfer coils 403 to 407C of other embodiments 1 to 5C, which differ from the first embodiment in the disposition of the air gaps 45 or the configuration of the coil unit. In each of the embodiments shown in FIGS. 11 to 17, the air gap 45 may be replaced with the high-magnetic resistance portion 46 formed of a magnetically saturated or non-magnetic material, as in the second embodiment. Taking the first and second embodiments and the other embodiments 1 to 5C into consideration, it can be said that it is preferable that "at least a part of the high-magnetic resistance portion extends in a direction intersecting an imaginary plane through which the magnetic flux passes".
[0056] In the wireless power transfer coil 403 shown in FIG. 11, the air gap 45 has a part extending in the y-axis direction and a part extending in the x-axis direction provided in a cross shape, dividing the magnetic material 44 into four parts. This configuration can suppress the distant leakage magnetic field in the vehicle traveling direction (x-axis direction) in the power transfer during traveling, and can also suppress the distant leakage magnetic field in the vehicle width direction (y-axis direction). In the example of FIG. 11, the air gaps 45 may be provided at two or more positions in both the x-axis direction and the z-axis direction to divide the magnetic material 44 into a greater number of parts.
[0057] In the wireless power transfer coil 404 shown in FIG. 12, the air gap 45 has a part extending in the y-axis direction and a part extending in the x-axis direction provided in a crank shape. In detail, the parts extending in the y-axis direction are provided at different positions in the x-axis direction on one side (upper side of the figure) and the other side (lower side of the figure) relative to the center of the y-axis direction, and the parts are connected by a part extending in the x-axis direction. Even with the crank-shaped air gap 45, as with the linear air gap 45, the magnetic flux propagation in the x-axis direction can be suppressed by dividing the magnetic material 44 into two parts. As this modification example, the air gap 45 may be formed to extend in a direction oblique to the x-axis direction, that is, in a direction obliquely intersecting the imaginary plane Sφ through which the magnetic flux φ passes.
[0058] In the wireless power transfer coil 405 shown in FIG. 13, the air gaps 45 extending in the y-axis direction are provided at two positions at a predetermined interval in the x-axis direction, dividing the magnetic material 44 into three parts. This configuration also makes it possible to suppress magnetic flux propagation in the x-axis direction and to suppress the distant leakage magnetic field.
[0059] In the wireless power transfer coil 406 shown in FIG. 14, the air gaps 45 extending in the y-axis direction are formed intermittently. The magnetic material 44 is not completely divided into two parts by the air gap 45, but is connected via one or more relatively narrow connection units 446. This configuration cannot completely block the magnetic flux passing through the connection unit 446, but can suppress most of the magnetic flux propagation in the x-axis direction and suppress the distant leakage magnetic field to some extent.
[0060] Each of the wireless power transfer coils shown in FIGS. 4 and 10 to 14 is configured with one coil unit 41 that is a circular coil. In contrast, in wireless power transfer coils 407A, 407B, and 407C shown in FIGS. 15 to 17, multiple circular coils are provided to partially overlap each other or in parallel.
[0061] In detail, the wireless power transfer coil 407A shown in FIG. 15 is a two-phase circular coil in which two coil units 411 and 412 are provided to partially overlap each other. The wireless power transfer coil 407B shown in FIG. 16 is a three-phase circular coil in which three coil units 411, 412, and 413 are provided to partially overlap one another. The wireless power transfer coil 407C shown in FIG. 17 is a DD coil in which two coil units 411 and 412 are provided in parallel.
[0062] (b) The wireless power transfer coil of the first and second embodiments is not limited to wireless power transfer while the vehicle travels, and may be used for wireless power transfer during parked, or for wireless power transfer to a device other than a vehicle.
[0063] (c) The wireless power transfer coil of the first and second embodiments is not limited to being applied to the power receiver coil 240, but may also be applied to the power transmitter coil 140. For example, in a wireless power transfer system in which the power receiver coil 240 is an air-core coil, applying the wireless power transfer coil of the first or second embodiment to the power transmitter coil 140 is effective in suppressing the distant leakage magnetic field.
[0064] In the wireless power transfer system which is assumed to be the main application target of the present invention, one of the power transmitter coil 140 or the power receiver coil 240 is an air-core coil, and the other of the power transmitter coil 140 or the power receiver coil 240 is formed of the wireless power transfer coil of the first or second embodiment. However, in a wireless power transfer system in which both the power transmitter coil 140 and the power receiver coil 240 have a magnetic material or a shield member, at least one of the power transmitter coil 140 and the power receiver coil 240 may be configured as the wireless power transfer coil of the first or second embodiment.
[0065] (Third and Fourth Embodiments) Next, wireless power transfer coils 50 and 60 according to third and fourth embodiments will be described with reference to FIGS. 18 to 20. The wireless power transfer coils 50 and 60 of the third and fourth embodiments are assumed to be used for the power receiver coil 240 in a wireless power transfer system that supplies power from the power transmitter coil 140 on a ground side to the power receiver coil 240 of the vehicle in a wireless manner while the vehicle travels.
[0066] As described above, the trade-off of suppressing the leakage magnetic field is the reduction in the efficiency of magnetic transmission. Even when the leakage magnetic field is at the same level, there may be cases where suppression is required or permitted depending on the standards of the country or region. When the leakage magnetic field is always suppressed even when the suppression is permitted, the disadvantage of reduced efficiency may outweigh the advantage of suppressing the leakage magnetic field. Therefore, the wireless power transfer coils 50 and 60 are configured such that the first arrangement state and the second arrangement state of the core 440 can be switched so that the magnitude of the magnetic flux propagated along the traveling direction of the vehicle changes depending on whether suppression of the leakage magnetic field or efficiency is prioritized.
[0067] The wireless power transfer coils 50 and 60 are provided with the "core 440 composed of multiple magnetic materials 44 and inducing the magnetic field of the coil". In the first arrangement state, the multiple magnetic materials 44 are arranged so that the magnetic flux propagating in the traveling direction of the vehicle is relatively large. In the second arrangement state, the multiple magnetic materials are arranged so that the magnetic flux propagating in the traveling direction of the vehicle is relatively small. The core 440 in the second arrangement state has the same configuration as the wireless power transfer coils 401 to 407C in the first embodiment.
[0068] In other words, in the second arrangement state, the core 440 includes a "low-magnetic resistance portion" formed of the magnetic material 44 and a "high-magnetic resistance portion" composed of the air gap 45 having a higher magnetic resistance than the low-magnetic resistance portion. The high-magnetic resistance portions are partially provided between the low-magnetic resistance portions. This configuration suppresses the distant leakage magnetic field in the magnetic field generated by energizing the power transmitter coil 140.
[0069] As shown in FIG. 2, the vehicle 202 is provided with the switching control unit 251 and the drive mechanism 252. The switching control unit 251 determines whether to prioritize suppression of the leakage magnetic field or efficiency based on information about the power transmitter coil 140 on the ground side, and selects the first arrangement state or the second arrangement state as the arrangement state to be taken. When the selected arrangement state is different from the current arrangement state, the switching control unit 251 instructs the drive mechanism 252 to switch the arrangement state of the multiple magnetic materials 44.
[0070] A specific arrangement for switching the arrangement state will be described with reference to FIGS. 18 and 19. The state shown in the figure is considered to be a state in which the amount of change in the magnetic resistance is 100%. However, the amount of change in the magnetic resistance is not limited to 100% and may be set to any intermediate value less than 100%. For example, by adjusting the magnetic resistance according to the type and output of the power transmitter coil 140, the self-inductance of the power receiver coil 240 and the mutual inductance with the power transmitter coil 140 can be adjusted.
[0071] FIG. 18 shows a top view of the wireless power transfer coil 50 according to the third embodiment. In the wireless power transfer coil 50, the core 440 is formed of the multiple magnetic materials 44 each having a substantially rectangular shape in a top view. Each magnetic material 44 can be rotated by the drive mechanism 252 around the z-axis as a rotation axis. When the wireless power transfer coil 50 is rotationally driven by the drive mechanism 252, the arrangement state of the multiple magnetic materials 44 is switched as follows.
[0072] In the first arrangement state, the longitudinal direction of each magnetic material 44 is aligned along the x-axis direction, that is, the traveling direction of the vehicle. Therefore, the gap between the magnetic materials 44 adjacent to each other in the x-axis direction becomes smaller, and the magnetic flux propagating in the traveling direction of the vehicle becomes relatively larger. Accordingly, the efficiency of magnetic flux transmission is improved.
[0073] In the second arrangement state, the longitudinal direction of each magnetic material 44 is arranged in a direction intersecting the traveling direction of the vehicle, in accordance with the rotation angle that correlates with the amount of change in the magnetic resistance. In particular, when the amount of change in the magnetic resistance is 100%, each magnetic material 44 is rotated by 90 degrees and aligned so that the longitudinal direction thereof is along the y-axis direction, that is, a direction perpendicular to the traveling direction of the vehicle. The magnetic material 44 arranged in the y-axis direction forms a low-magnetic resistance portion. Between adjacent magnetic materials 44 in the x-axis direction, the air gaps 45 are partially provided as high and low-magnetic resistance portions. Therefore, in the second arrangement state, the magnetic flux propagating in the traveling direction of the vehicle is relatively small. Therefore, the distant leakage magnetic field in the magnetic field generated by energizing the power transmitter coil 140 is suppressed. For example, the peak of the leakage magnetic field may be suppressed by rotating only the magnetic material 44 at the position of the coil unit 41 where the power is large to partially change the magnetic resistance.
[0074] FIG. 19 shows a side view of the wireless power transfer coil 60 according to the fourth embodiment. In the wireless power transfer coil 60, the coil unit 41 around which a conductive wire is wound and the core 440 are stacked in the z-axis direction, that is, the vertical direction. The core 440 has multiple rows (for example, four rows) of magnetic material 44 arranged along the traveling direction of the vehicle.
[0075] The front and rear rows of magnetic material corresponding to the front and rear sides of the coil unit 41 in the x-axis direction are defined as immovable magnetic material 44S. The magnetic material in the middle row corresponding to the hollow unit of the coil unit 41 in the x-axis direction is defined as a movable magnetic material 44M. The movable magnetic material 44M corresponds to "a specific row of magnetic material that is a part of multiple rows". Each movable magnetic material 44M can be moved up and down in the z-axis direction by the drive mechanism 252 that utilizes, for example, electromagnetic force. By being driven up and down by the drive mechanism 252, the arrangement state of multiple movable magnetic material 44M of the wireless power transfer coil 60 is switched as follows.
[0076] In both the first arrangement state and the second arrangement state, the immovable magnetic material 44S forms a low-magnetic resistance portion. In the first arrangement state, the distance between the coil unit 41 and the movable magnetic material 44M is relatively short. Therefore, the movable magnetic material 44M also forms a low-magnetic resistance portion, and the magnetic flux propagating in the traveling direction of the vehicle becomes relatively large. Accordingly, the efficiency of magnetic flux transmission is improved.
[0077] In the second arrangement state, the movable magnetic material 44M is lifted so that the distance from the coil unit 41 becomes relatively large in accordance with the lift amount that correlates with the amount of change in the magnetic resistance. In particular, when the amount of change in the magnetic resistance is 100%, the movable magnetic material 44M is lifted to the full stroke position. As a result, the air gaps 45, which are high and low-magnetic resistance portions, are partially provided between the front and rear immovable magnetic materials 44S. Therefore, in the second arrangement state, the magnetic flux propagating in the traveling direction of the vehicle is relatively small. Therefore, the distant leakage magnetic field in the magnetic field generated by energizing the power transmitter coil 140 is suppressed.
[0078] The switching between the first arrangement state and the second arrangement state will be described with reference to the flowchart in FIG. 20. The symbol "S" in the flowchart means a step. In S1, the switching control unit 251 determines the priority between leakage magnetic field suppression and efficiency of magnetic transmission. When it is determined that efficiency is prioritized over suppression of the leakage magnetic field, the first arrangement state is selected as the arrangement state to be taken in S2. On the other hand, when it is determined that suppression of the leakage magnetic field prioritized over efficiency, the second arrangement state is selected as the arrangement state to be taken in S3. In S4, the switching control unit 251 sets the amount of change in the magnetic resistance based on information about the power transmitter coil 140 on the ground side, for example.
[0079] In S5, the switching control unit 251 determines whether the selected arrangement state is different from or the same as the current arrangement state. When the selected arrangement state is the same as the current arrangement state, the drive mechanism 252 is not actuated and the current arrangement state is maintained. When the selected arrangement state is different from the current arrangement state, the switching control unit 251 instructs the drive mechanism 252 to perform rotational driving or up and down driving, thereby switching the arrangement state.
[0080] As described above, in the third and fourth embodiments, the arrangement of the magnetic material 44 in the configuration of the core 440 can be switched so that the magnitude of the magnetic flux propagating along the traveling direction of the vehicle changes depending on whether suppression of the leakage magnetic field or efficiency is prioritized. Therefore, specifications can be changed according to the situation.
[0081] The same effect can also be obtained in a wireless power transfer system during traveling in which the power receiver coil 240 is configured with the wireless power transfer coils 50 and 60 of the third and fourth embodiments. As in the first and second embodiments, when the power transmitter coil 140 in this wireless power transfer system during traveling is an air-core coil, the effect of suppressing the distant leakage magnetic field in the second arrangement state is particularly exerted.
[0082] The present invention is not limited to the above embodiments, and may be implemented in various configurations without departing from the spirit of the invention.
[0083] While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. To the contrary, the present disclosure is intended to cover various modification and equivalent arrangements. Furthermore, although various combinations and modes are described in the present disclosure, the scope and idea of the present disclosure further include other combinations and modes including only one element, more elements, or less elements in these.
[0084] (Disclosure of technical idea) This description discloses multiple technical ideas described in multiple items listed below. Some items may be written in a multiple dependent form with subsequent items referring to the preceding item as an alternative. Some items may be written in a multiple dependent form referring to another multiple dependent form. These items written in a multiple dependent form define multiple technical ideas.
[0085] (Technical idea 1) A wireless power transfer coil is to be used for at least one of a power transmitter coil (140) and a power receiver coil (240) in a wireless power transfer system. The wireless power transfer system is configured to supply power from the power transmitter coil to the power receiver coil in a wireless manner. The wireless power transfer coil includes: a core (440) configured to induce a magnetic field of a coil. The core includes a plurality of low-magnetic resistance portions (44) formed of a magnetic material and a high-magnetic resistance portion (45, 46) having a magnetic resistance, which is higher than a magnetic resistance of the low-magnetic resistance portion, and partially provided between the low-magnetic resistance portions. The low-magnetic resistance portions and the high-magnetic resistance portion are provided to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil. (Technical idea 2) The wireless power transfer coil according to technical idea 1, in which the high-magnetic resistance portion (46) is magnetically saturated or formed of a non-magnetic material. (Technical idea 3) The wireless power transfer coil according to technical idea 1, in which the high-magnetic resistance portion (45) is formed of an air gap. (Technical idea 4) The wireless power transfer coil according to any one of technical ideas 1 to 3, in which at least a part of the high-magnetic resistance portion extends in a direction that intersects an imaginary plane through which magnetic flux passes. (Technical idea 5) The wireless power transfer system configured to supply power from the power transmitter coil (140) to the power receiver coil (240) in a wireless manner, in which one of the power transmitter coil and the power receiver coil is an air-core coil provided with neither a magnetic material, which is configured to induce a magnetic field of a coil, nor a shield member, which is configured to shield the magnetic field of the coil, and an other of the power transmitter coil and the power receiver coil is the wireless power transfer coil according to any one of technical ideas 1 to 4. (Technical idea 6) A wireless power transfer coil is to be used for a power receiver coil (240) in a wireless power transfer system. The wireless power transfer system is configured to supply power from a power transmitter coil (140) on a ground side to the power receiver coil of a vehicle in a wireless manner while the vehicle travels. The wireless power transfer coil includes: a core (440) including a plurality of magnetic materials (44) and configured to induce a magnetic field of a coil, in which the core is configured to switch between a first arrangement state in which the magnetic materials are arranged such that magnetic flux propagated along a traveling direction of the vehicle is relatively large and a second arrangement state in which the magnetic materials are arranged such that magnetic flux propagated along the traveling direction of the vehicle is relatively small. In the second arrangement state, the core is configured to include i) a plurality of low-magnetic resistance portions formed of the magnetic materials and ii) a high-magnetic resistance portion (45) formed of an air gap, which has a magnetic resistance higher than a magnetic resistance of the low-magnetic resistance portion, and is partially provided between the low-magnetic resistance portions, to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil. (Technical idea 7) The wireless power transfer coil according to technical idea 6, in which the core is formed of the magnetic materials each having a substantially rectangular shape in a top view, and an arrangement state of the magnetic materials is configured to be switched by being rotationally driven by an external drive mechanism (252) such that in the first arrangement state, a longitudinal direction of each of the magnetic materials is arranged along the traveling direction of the vehicle, and in the second arrangement state, the longitudinal direction of each of the magnetic materials is arranged along a direction that intersects the traveling direction of the vehicle. (Technical idea 8) The wireless power transfer coil according to technical idea 6, in which a coil unit (41), which includes a conductive wire that is wound, and the core, in which a plurality of rows of magnetic materials are arranged along the traveling direction of the vehicle, are stacked in a vertical direction, and in a specific row of the magnetic materials, which is a part of the rows, an arrangement state of the magnetic materials is configured to be switched by being driven up and down by an external drive mechanism (252) such that in the first arrangement state, a distance between the coil unit and the magnetic materials is relatively close, and in the second arrangement state, the distance between the coil unit and the magnetic materials is relatively far. (Technical idea 9) The wireless power transfer system configured to supply power from the power transmitter coil (140) on the ground side to the power receiver coil (240) of the vehicle in a wireless manner while the vehicle travels, in which the power receiver coil is the wireless power transfer coil according to any one of technical ideas 6 to 8.
Claims
1. A wireless power transfer coil to be used for at least one of a power transmitter coil (140) and a power receiver coil (240) in a wireless power transfer system, the wireless power transfer system configured to supply power from the power transmitter coil to the power receiver coil in a wireless manner, the wireless power transfer coil comprising: a core (440) configured to induce a magnetic field of a coil, wherein the core includes a plurality of low-magnetic resistance portions (44) formed of a magnetic material and a high-magnetic resistance portion (45, 46) having a magnetic resistance, which is higher than a magnetic resistance of the low-magnetic resistance portion, and partially provided between the low-magnetic resistance portions, and the low-magnetic resistance portions and the high-magnetic resistance portion are provided to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil.
2. The wireless power transfer coil according to claim 1, wherein the high-magnetic resistance portion (46) is magnetically saturated or formed of a non-magnetic material.
3. The wireless power transfer coil according to claim 1, wherein the high-magnetic resistance portion (45) is formed of an air gap.
4. The wireless power transfer coil according to claim 1, wherein at least a part of the high-magnetic resistance portion extends in a direction that intersects an imaginary plane through which magnetic flux passes.
5. The wireless power transfer system configured to supply power from the power transmitter coil (140) to the power receiver coil (240) in a wireless manner, wherein one of the power transmitter coil and the power receiver coil is an air-core coil provided with neither a magnetic material, which is configured to induce a magnetic field of a coil, nor a shield member, which is configured to shield the magnetic field of the coil, and an other of the power transmitter coil and the power receiver coil is the wireless power transfer coil according to any one of claims 1 to 4.
6. A wireless power transfer coil to be used for a power receiver coil (240) in a wireless power transfer system, the wireless power transfer system configured to supply power from a power transmitter coil (140) on a ground side to the power receiver coil of a vehicle in a wireless manner while the vehicle travels, the wireless power transfer coil comprising: a core (440) including a plurality of magnetic materials (44) and configured to induce a magnetic field of a coil, wherein the core is configured to switch between a first arrangement state in which the magnetic materials are arranged such that magnetic flux propagated along a traveling direction of the vehicle is relatively large and a second arrangement state in which the magnetic materials are arranged such that magnetic flux propagated along the traveling direction of the vehicle is relatively small, and in the second arrangement state, the core is configured to include i) a plurality of low-magnetic resistance portions formed of the magnetic materials and ii) a high-magnetic resistance portion (45) formed of an air gap, which has a magnetic resistance higher than a magnetic resistance of the low-magnetic resistance portion, and is partially provided between the low-magnetic resistance portions, to suppress a distant leakage magnetic field in a magnetic field generated by energizing the power transmitter coil.
7. The wireless power transfer coil according to claim 6, wherein the core is formed of the magnetic materials each having a substantially rectangular shape in a top view, and an arrangement state of the magnetic materials is configured to be switched by being rotationally driven by an external drive mechanism (252), such that in the first arrangement state, a longitudinal direction of each of the magnetic materials is arranged along the traveling direction of the vehicle, and in the second arrangement state, the longitudinal direction of each of the magnetic materials is arranged along a direction that intersects the traveling direction of the vehicle.
8. The wireless power transfer coil according to claim 6, wherein a coil unit (41), which includes a conductive wire that is wound, and the core, in which a plurality of rows of magnetic materials are arranged along the traveling direction of the vehicle, are stacked in a vertical direction, and in a specific row of the magnetic materials, which is a part of the rows, an arrangement state of the magnetic materials is configured to be switched by being driven up and down by an external drive mechanism (252), such that in the first arrangement state, a distance between the coil unit and the magnetic materials is relatively close, and in the second arrangement state, the distance between the coil unit and the magnetic materials is relatively far.
9. The wireless power transfer system configured to supply power from the power transmitter coil (140) on the ground side to the power receiver coil (240) of the vehicle in a wireless manner while the vehicle travels, wherein the power receiver coil is the wireless power transfer coil according to any one of claims 6 to 8.