Patent Publication Number: US-10763700-B2

Title: Power transmission device and power reception device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This a nonprovisional application claims priority to Japanese Patent Application No. 2017-130400 filed on Jul. 3, 2017 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     Field 
     The present disclosure relates to a power transmission device and a power reception device. 
     Description of the Background Art 
     Conventionally, a contactless charging system configured to contactlessly transmit electric power has been known. A contactless charging system includes a power transmission device and a power reception device. The power transmission device is configured to contactlessly transmit electric power to the power reception device (see Japanese Patent Laying-Open Nos. 2013-154815, 2013-146154, 2013-146148, 2013-110822, and 2013-126327). 
     For example, a vehicle charging pad disclosed in Japanese Patent National Publication No. 2016-526280 includes a first coil, a second coil and a modular ferrite block. 
     The first coil and the second coil are arranged in the modular ferrite block. The first coil and the second coil each are a multi-winding loop coil. The first coil and the second coil are arranged adjacent to each other. 
     The modular ferrite block is formed in a plate shape. The modular ferrite block includes a plurality of ferrite tiles. 
     SUMMARY 
     In the vehicle charging pad disclosed in Japanese Patent National Publication No. 2016-526280, when the above-mentioned vehicle charging pad receives electric power from a power transmission pad, a current flows through the first coil and the second coil of the vehicle changing pad, so that the vehicle charging pad receives electric power. 
     In the power reception device like the vehicle charging pad as described above, however, unless the shape and the arrangement of two coils are designed to improve the coupling coefficient, the power reception device tends to be increased in structure size since two coils are mounted therein. The same problem occurs also in the power transmission device. 
     The present disclosure has been made in light of the above-described problems. An object of the present disclosure is to provide a power transmission device and a power reception device that are improved in coupling coefficient and reduced in size. 
     A power transmission device according to the present disclosure includes: a first coil formed so as to surround a first winding axis extending in an up-down direction; and a second coil formed so as to surround a second winding axis extending in the up-down direction. The first coil and the second coil are configured such that a first current direction and a second current direction are opposite to each other during power transmission. In the first current direction, a current flowing through the first coil flows so as to be wound around the first winding axis, and in the second current direction, a current flowing through the second coil flows so as to be wound around the second winding axis. The first coil includes: a first adjacent portion located adjacent to the second coil; and a first spacer portion located on an opposite side of the first adjacent portion with respect to the first winding axis. The second coil includes: a second adjacent portion located adjacent to the first coil; and a second spacer portion located on an opposite side of the second adjacent portion with respect to the second winding axis. The first adjacent portion is located higher than the first spacer portion. 
     According to the above-described power transmission device, a magnetic flux is formed around the first coil and the second coil during power transmission. A magnetic flux is formed so as to surround each of the first spacer portion of the first coil and the second spacer portion ox the second coil. A magnetic flux is formed also around each of the first adjacent portion of the first coil and the second adjacent portion of the second coil. The first adjacent portion and the second adjacent-portion are located adjacent to each other. Thus, the magnetic flux formed around each of the first adjacent portion and the second adjacent portion is formed so as to extend over the first adjacent portion and the second adjacent portion. 
     The effective radius of the magnetic flux flowing so as to extend over the first adjacent portion and the second adjacent portion is larger than the effective radius of the magnetic flux flowing so as to surround the first spacer portion or the second spacer portion. 
     The magnetic flux flowing so as to extend over the first adjacent portion and the second adjacent portion is more likely to expand upward, with the result that this magnetic flux is more likely to reach the power reception device disposed above the power transmission device. 
     In the above-described power transmission device the first adjacent portion is located higher than the first spacer portion, and the second adjacent portion is located higher than the second spacer portion. 
     The first adjacent portion and the second adjacent portion are located closer to the power reception device than the first spacer portion and the second spacer portion are. Thus, the magnetic flux formed so as to extend over the first adjacent portion and the second adjacent portion (the magnetic firm from the power transmission device) is more likely to reach the power reception device. Accordingly, the coupling coefficient between the power transmission device and the power reception device can be increased. 
     The coupling coefficient between the power transmission device and the power reception device can be improved. Thus, even when the first coil and the second coil are reduced in size, electric power can be excellently transmitted to the power reception device, and the power transmission device can be reduced in size. 
     The foregoing and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram schematically showing a contactless charging system  1 . 
         FIG. 2  is a block diagram schematically showing contactless charging system  1 . 
         FIG. 3  is an exploded perspective view showing a power transmission device  3 . 
         FIG. 4  is a perspective view schematically showing a power transmission coil  23  and a ferrite plate  35 . 
         FIG. 5  is a perspective view schematically showing a first coil  50 . 
         FIG. 6  is a perspective view showing a second coil  51 . 
         FIG. 7  is a cross-sectional view taken along a line VII-VII in  FIG. 4 . 
         FIG. 8  is a plan view showing a power transmission coil  23 . 
         FIG. 9  is an exploded perspective view showing a power reception device  4 . 
         FIG. 10  is a perspective view schematically showing a power reception coil  16 . 
         FIG. 11  is a perspective view schematically showing a third coil  112 . 
         FIG. 12  is a perspective view schematically showing a fourth coil  113 . 
         FIG. 13  is a cross-sectional view showing a power reception coil  16  and a ferrite plate  104 . 
         FIG. 14  is a cross-sectional view schematically showing the state at the time when electric power is transmitted from power transmission device  3  to power reception device  4 . 
         FIG. 15  is a simulation result showing a magnetic flux distribution in power transmission device  3  and power reception device  4  during transmission and reception of electric power. 
         FIG. 16  is a cross-sectional view showing a power reception coil  16 A and a power transmission coil  23 A according to a comparative example. 
         FIG. 17  is a perspective view showing a part of a power transmission device  3 B according to the present second embodiment. 
         FIG. 18  is a perspective view schematically showing a ferrite plate  35 B. 
         FIG. 19  is a perspective view showing a power reception coil  16  and a ferrite plate in a power reception device  4 B. 
         FIG. 20  is a perspective view schematically showing a ferrite plate  104 B. 
         FIG. 21  is a cross-sectional view schematically showing the state where electric power is transmitted from power transmission device  3 B to power reception device  4 B. 
         FIG. 22  is a cross-sectional view showing the first modification of the ferrite plate. 
         FIG. 23  is a cross-sectional view showing the second modification of the ferrite plate. 
         FIG. 24  is a plan view showing a power transmission coil  23 C of a power transmission device  3 C. 
         FIG. 25  is a perspective view showing power transmission coil  23 C of power transmission device  3 C. 
         FIG. 26  is a plan view showing a power reception coil  16 C of a power reception device  4 C. 
         FIG. 27  is a perspective view showing power reception coil  160  of power reception device  4 C. 
         FIG. 28  is a cross-sectional view taken along a line XXVIII-XXVIII in  FIG. 26 . 
         FIG. 29  is a cross-sectional view taken along a line XXIX-XXIX in  FIG. 26 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIGS. 1 to 29 , a power transmission device and a power reception device according, to each of the present first to third embodiments will be hereinafter described. Among the configurations shown in  FIGS. 1 to 29 , the same or substantially the same configurations will be designated by the same reference characters, and the description thereof may not be repeated. 
     First Embodiment 
       FIG. 1  is a schematic diagram schematically showing a contactless charging system  1 . Contactless charging system  1  includes a power transmission device  3 , a vehicle  2 , a power supply  7 , and a converter  20 . 
     Power supply  7  is connected to converter  20 . Converter  20  includes an inverter and a converter. 
     Vehicle  2  includes a power reception device  4  and a power storage device  5 . In an example shown in  FIG. 1 , power storage device  5  is provided on the lower surface of a floor panel  6  of vehicle  2 . Power reception device  4  is provided on the lower surface of power storage device  5 . 
     Power reception device  4  includes a resonator  11  and equipment  10 . Resonator  11  includes a power reception coil  16  and a capacitor  17 . Capacitor  17  is connected in series to power reception coil  16 . Capacitor  17  and power reception coil  16  constitute an LC resonator. Resonator  11  has a Q value of 100 or more. Equipment  10  includes a rectifier  12  and a filter  14 . Rectifier  12  is connected to resonator  11 . Filter  14  is connected to rectifier  32  and power storage device  5 . Power storage device  5  serving as a battery or a capacitor is a chargeable and dischargeable device. 
     Power transmission device  3  includes a resonator  21  and a filter  24 . Resonator  21  includes a power transmission coil  23  and a capacitor  22 . Capacitor  22  is connected in series to power transmission coil  23 . Capacitor  22  and power transmission coil  23  constitute an LC resonator. Resonator  21  has a Q value of 100 or more. 
     Filter  24  is connected to resonator  21  and converter  20 . Filter  24  includes a plurality of coils and capacitors. Converter  20  is connected to power supply  7  and filter  24 . 
     The following is an explanation about the state where electric power is contactlessly transmitted from power transmission device  3  to power reception device  4  in contactless charging system  1  configured as described above. Converter  20  adjusts the frequency and the voltage of alternating-current (AC) power that is supplied from power supply  7 , and then supplies the adjusted AC power to filter  24 . 
     Filter  24  removes noise from the AC power supplied from converter  20 , and then supplies the resultant AC power to resonator  21 . When the AC power &amp; supplied to resonator  21 , an electromagnetic field is formed around power transmission coil  23 . The frequency of the AC power supplied to power transmission coil  23  is about several ten kHz to about one hundred and several ten kHz, or about 70 kHz or more aid about 100 kHz or less. 
     Power reception coil  16  receives electric power from the electromagnetic field formed around power transmission coil  23 . The frequency of the AC current flowing through power reception coil  16  during power reception is, for example, about several ten kHz to about one hundred and several ten kHz, and specifically, about 70 kHz or more: and about 100 kHz or less. Rectifier  12  converts the AC power supplied from resonator  11  into direct-current (DC) power, and supplies the converted DC power to filter  14 . Filter  14  removes noise from the DC power supplied from rectifier  12 , and supplies the resultant DC power to power storage device  5 . 
     Then, the configuration of power transmission device  3  will be hereinafter described with reference to  FIG. 3  and the like. 
       FIG. 3  is an exploded perspective view showing power transmission devices. Power transmission device  3  includes a case  30 , a substrate  33 , a metal plate  34 , a ferrite plate  35 , a filter  24 , a capacitor  22 , and a power transmission coil  23 . 
     Filter  24 , substrate  33 , capacitor  22 , metal plate  34 , ferrite plate  35 , and power transmission coil  23  are housed in case  30 . 
     Case  30  includes an upper cover  31  and a lower cover  32 . Upper cover  31  is disposed on the upper surface side of power transmission device  3 , and formed of resin. Upper cover  31  includes an upper wall  37  and a side wall  36 . Side wall  36  is formed so as to extend downward from tire outer peripheral edge of upper wall  37 . 
     Lower cover  32  is disposed on the ground side. Lower cover  32  is formed of metal such as aluminum or an aluminum alloy. 
     Lower cover  32  includes a bottom wall  41  and a side wall  40 . Side wall  40  is formed so as to extend upward from the outer peripheral edge of bottom wall  41 . 
     Substrate  33  is disposed on the upper surface side of bottom wall  41 . Substrate  33  is formed in a plate shape, and includes a lower surface  42  and an upper surface  43 . 
     Filter  24  is disposed on the lower surface  42  side of substrate  33 . Capacitor  22  is disposed on upper surface  43 . 
     Metal plate  34  is disposed on the upper surface  43  side of substrate  33 . Metal plate  34  is formed of a metal material such as aluminum or an aluminum alloy. Metal plate  34  is formed in a plate shape, and includes a lower surface  44  and an upper surface  45 . 
     Ferrite plate  35  is disposed on upper surface  45  of metal plate  34 . Ferrite plate  35  includes a divided ferrite plate  46  and a divided ferrite plate  47 . Divided ferrite plate  46  and divided ferrite plate  47  are provided so as to be arranged in the front-rear direction of vehicle  2  that is stopped above power transmission device  3 . 
     Divided ferrite plates  46  and  47  each are formed in a plate shape. Divided ferrite plate  46  includes an upper surface  61  and a lower surface  60 . Divided ferrite plate  47  includes a lower surface  62  and an upper surface  63 . 
     Power transmission coil  23  includes a first coil  50  and a second coil  51 . First coil  50  and second coil  51  are disposed to be arranged in the front-rear direction of vehicle  2  that is stopped above power transmission device  3 . First coil  50  is formed so as to surround a winding axis O 1  extending in the up-down direction. Second coil  51  is formed so as to surround a winding axis O 2  extending in the up-down direction. 
     First coil  50  and second coil  51  each are a spiral-shaped flat coil. Although first coil  50  and second coil  51  each are formed in an approximately rectangular shape, first coil  50  and second coil  51  each may be formed in various shapes. 
       FIG. 4  is a perspective view schematically showing a power transmission coil  23  and a ferrite plate  35 . First coil  50  is disposed on upper surface  61  of divided ferrite plate  46 . Second coil  51  is disposed on upper surface  63  of divided ferrite plate  4 . Power transmission coil  23  includes a connection line  53  that connects first coil  50  and second coil  51 . 
       FIG. 5  is a perspective view schematically showing first coil  50 . In  FIGS. 4 and 5 , first coil  50  includes an adjacent portion  71 , a spacer portion  72 , a connection portion  73 , a connection portion  74 , an inner peripheral end  75 , an outer peripheral end  77 , and a lead line  76 . 
     Adjacent portion  71  is located adjacent to second coil  51 . Spacer portion  72  is located on the opposite side of adjacent portion  71  with respect to winding axis O 1 . Connection portion  73  connects one end of adjacent portion  71  and one end of spacer portion  72 . Connection portion  74  connects the other end of adjacent portion  71  and the other end of spacer portion  72 . 
     One end of adjacent portion  71  is formed so as to extend upward from the end of connection portion  73 . The other end of adjacent portion  71  is formed so as to extend upward from the end of connection portion  74 . Adjacent portion  71  extends from its one end to its other end in a linear shape. In an example shown in  FIG. 5  and the like, adjacent portion  71  and spacer portion  72  are formed so as to extend in the right-left direction of vehicle  2 . Connection portions  73  and  74  are also formed in a linear shape so as to extend in the front-rear direction of vehicle  2 . 
     Spacer portion  72  and connection portions  73  and  74  are disposed on upper surface  61  of divided ferrite plate  46 . Thus, adjacent portion  71  is located higher than spacer portion  72 . Specifically, adjacent portion  71  is located higher than spacer portion  72  and connection portions  73  and  74 . 
     Inner peripheral end  75  is located on the inner periphery of first coil  50 . Outer peripheral end  77  is located on the outer periphery of first coil  50 . Lead line  16  is connected to inner peripheral end  75 . Connection line  53  is connected to outer peripheral end  77 . 
     First coil  50  configured as described above is formed by winding a coil wire  70  so as to surround winding axis O 1 . Specifically, first coil  50  is formed so as to be reduced in distance from winding axis O 1  from outer peripheral end  77  toward inner peripheral end  75  every winding of coil wire  70 . 
     Thus, first coil  50  extends in the direction of leftward rotation (in the counter-clockwise direction) from outer peripheral end  77  toward inner peripheral end  75 . 
     Load line  76  connected to inner peripheral end  75  is pulled out to the outside through a gap between adjacent portion  71  and divided ferrite plate  46 . 
       FIG. 6  is a perspective view showing second coil  51 . Second coil  51  includes an adjacent portion  81 , a spacer portion  82 , a connection portion  83 , a connection portion  84 , an inner peripheral end  85 , an outer peripheral end  87 , and a lead portion  86 . 
     Adjacent portion  81  is located adjacent to first coil  50 . Specifically, adjacent portion  81  is located adjacent to adjacent portion  71  of first coil  50 . Spacer portion  82  is located on the opposite side of adjacent portion  81  with respect to winding axis O 2 . Connection portion  83  connects one end of adjacent portion  81  and one end of spacer portion  82 . Connection portion  84  connects the other end of adjacent portion  81  and the other end of spacer portion  82 . 
     One end of adjacent portion  81  is formed so as to extend upward from the end of connection portion  83 . The other end of adjacent portion  81  is formed so as to extend upward front the end of connection portion  84 . Also, adjacent portion  81  extends from its one end to its other end in a linear shape. Adjacent portion  81  and adjacent portion  71  are formed so as to extend in the same direction. 
     In an example shown in  FIG. 6  and the like, adjacent portion  81  and spacer portion  82  are formed so as to extend in the right-left direction of vehicle  2 . Connection portions  83  and  84  are also formed in a linear shape so as to extend in the front-rear direction of vehicle  2 . 
     Spacer portion  82  and connection portions  83  and  84  are disposed on upper surface  63  of divided ferrite plate  47 . Thus, adjacent portion  81  is located higher than spacer portion  82 . Specifically, adjacent portion  81  is located higher than spacer portion  82  and connection portions  83  and  84 . 
     Inner peripheral end  85  is located on the inner periphery of second coil  51 . Outer peripheral end  87  is located on the outer periphery of second coil  51 . 
     Second coil  51  configured as described above is formed by winding a coil wire  80  so as to surround winding axis O 2 . Specifically, second coil  51  is formed to be reduced in distance: from winding axis O 2  from outer peripheral end  87  toward inner peripheral end  85  every winding of coil wire  80 . 
     Thus, second coil  51  extends in the direction of right ward rotation (in the clockwise direction) from outer peripheral end  87  toward inner peripheral end  85 . 
     Lead portion  86  is connected to outer peripheral end  87 . Connection line  53  is connected to inner peripheral end  85 . 
       FIG. 7  is a cross-sectional view taken along a line VII-VII in  FIG. 4 . Adjacent portion  71  of first coil  50  is located higher than the upper end of spacer portion  72 . Similarly, adjacent portion  81  of second coil  51  is located higher than the upper end of spacer portion  82 . 
       FIG. 8  is a plan view showing power transmission coil  23 . Lead portion  86  of second coil  51  is connected to capacitor  22 , and lead line  76  is connected to filter  24 . 
     During power transmission, the frequency of the AC current flowing through power transmission coil  23  is about 70 kHz or more and about 100 kHz or less. The wavelength of the AC current of this frequency is several hundred meters. On the other hand, the total length of coil wires  70  and  80  and connection line  53  that constitute power transmission coil  23  is about several meters to about a dozen or more meters. 
     There is almost no current phase difference inside power transmission coil  23 . Thus, for example, when a current flows through lead portion  86  in a current direction A, a current flows through lead line  76  in current direction A. 
     When the current flows through lead portion  86  in current direction A, the current direction in which an AC current flowing through second coil  51  flows so as to be wound around winding axis O 2  (the second current direction) is the direction of rightward rotation (the clockwise direction). On the other hand, the current direction in which an AC current flowing through first coil  50  flows so as to be wound around winding axis O 2  (the first current direction) is the direction of leftward direction (the counter-clockwise direction). 
     Furthermore, when a current flows through lead portion  86  in a current direction B, the current direction in which an AC current flowing through second coil  51  flows so as to fee wound around winding axis O 2  (the second current direction) is the direction of leftward rotation (the counter-clockwise direction). On the other hand, the current direction in which an AC current flowing through first coil  50  flows so as to be wound around winding axis O 2  (the first current direction) is the direction of rightward direction (the clockwise direction). 
     In this way, power transmission coil  23  according to the present first embodiment is formed such that, during power transmission, the current direction in which a current flowing through first coil  50  flows so as to be wound around winding axis O 1  is opposite to the current direction in which a current flowing through second coil  51  flows so as to be wound around winding axis O 2 . 
     Then, the configuration of power reception device  4  will be hereinafter described with reference to  FIG. 9  and the like.  FIG. 9  is an exploded perspective view showing power reception device  4 . 
     Power reception device  4  includes a case  100 , a power reception coil  16 , a ferrite plate  104 , a metal plate  105 , a capacitor  11 , a filter  14 , a substrate  106 , and a rectifier  12 . 
     Power reception coil  16 , ferrite plate  104 , metal plats  105 , filter  14 , substrate  106 , capacitor  17 , and rectifier  12  are housed in case  100 . 
     Case  100  includes an upper cover  101  and a lower cover  102 . Upper cover  101  and lower cover  102  each are formed of resin. 
     Upper cover  101  includes an upper wall  108  and a side wall  107 . Side wall  107  is formed so as to extend downward from the outer peripheral edge of upper wall  108 . 
     Lower cover  102  includes a bottom wall  111  and a side wall  110 . Side wall  110  is formed so as to extend upward from the outer peripheral edge of bottom wall  111 . 
     Power reception coil  16  is disposed on the upper surface of bottom wall  111 . Power reception coil  16  includes a third coil  112  and a fourth coil  113 . Third coil  112  is formed so as to surround a winding axis O 3  extending in the up-down direction. Fourth coil  113  is formed so as to surround a winding axis O 4  extending in the up-down direction. Third coil  112  and fourth coil  113  are disposed so as to be arranged in the front-rear direction of vehicle  2 . 
     Each of third coil  112  and fourth coil  113  is a spiral-shaped flat coil. Although third coil  112  and fourth coil  113  each are formed in an approximately rectangular shape, third coil  112  and fourth coil  113  each may be formed in various shapes. 
     Ferrite plate  104  is disposed on the upper surface side of power reception coil  16 . Ferrite plate  104  includes a divided ferrite plate  114  and a divided ferrite plate  115 . 
     Divided ferrite plate  114  and  115  are disposed so as to be arranged in the front-rear direction of vehicle  2 . Divided ferrite plates  114  and  115  each are formed in a plate shape. Divided ferrite plate  114  include a lower surface  120  and an upper surface  121 . Divided ferrite plate  115  includes a lower surface  123  and an upper surface  124 . 
     Third coil  112  is disposed on lower surface  120  of divided ferrite plate  114 . Fourth coil  113  is disposed on lower surface  123  of divided ferrite plate  115 . 
     Metal plate  105  is disposed on the upper surface side of ferrite plate  104 . Metal plate  105  is formed of a metal material such as aluminum or an aluminum alloy. Metal plate  105  is formed in a plate shape and includes a lower surface  125  and an upper surface  126 . 
     Substrate  106  is disposed on the upper surface  126  side of metal plate  105 . Substrate  106  is formed in a plate shape, and includes a lower surface  128  and an upper surface  129 . Filter  14  and capacitor  17  are disposed on lower surface  128  of substrate  106 . Filter  14  includes a capacitor  130  and a coil  131 . Capacitor  130  and coil  131  are disposed on lower surface  128  of substrate  106 . Rectifier  12  is disposed on upper surface  129  of substrate  106 . 
     Upper cover  101  is disposed on the upper surface  129  side of substrate  106 . Upper cover  101  is disposed on the lower surface of power storage device  5  shown in  FIG. 1 . 
       FIG. 10  is a perspective view schematically showing power reception coil  16 . Power reception coil  16  includes a connection line  116  that connects third coil  112  and fourth coil  113 . 
       FIG. 11  is a perspective view schematically showing third coil  112 . As shown in  FIGS. 10 and 11 , third coil  112  includes an adjacent portion  141 , a spacer portion  142 , a connection portion  143 , a connection portion  144 , an inner peripheral end  145 , an outer peripheral end  147 , and a lead line  146 . 
     Adjacent portion  141  is located adjacent to fourth coil  113 . Spacer portion  142  is located on the opposite side of adjacent portion  141  with respect to winding axis O 3 . Connection portion  143  connects one end of adjacent portion  141  and one end of spacer portion  142 . Connection portion  144  connects the other end of adjacent portion  141  and the other end of spacer portion  142 . 
     One end of adjacent portion  141  is formed so as to extend downward from the end of connection portion  143 . The other end of adjacent portion  141  is formed so as to extend downward from the end of connection portion  144 . Adjacent portion  141  is formed so as to extend from its one end toward its other end in a linear shape. 
     In an example shown in  FIG. 11  and the like, adjacent portion  141  and spacer portion  142  are formed so as to extend in the right-left direction of the vehicle. Connection portions  143  and  144  are formed so as to extend in the front-rear direction of vehicle  2 . 
     Adjacent portion  141  is located lower than spacer portion  142 . Spacer portion  142  and connection portions  144  and  143  are disposed on lower surface  120  of divided ferrite plate  114 . 
     Inner peripheral end  145  is located on the inner periphery of third coil  112 . Outer peripheral end  14  is located on the outer periphery of third coil  112 . Lead line  146  is connected to inner peripheral end  145 , and pulled out to the outside from between adjacent portion  141  and divided ferrite plate  114 . Connection line  116  is connected to outer peripheral end  147 . 
     Third coil  112  configured as described above is formed by winding a coil wire  140  around winding axis O 3 . Specifically, third coil  112  is formed to be closer to winding axis O 3  from outer peripheral end  147  toward inner peripheral end  145  every winding of coil wire  140 . 
     Coil wire  140  is formed so as to extend in the direction of leftward rotation (in the counter-clockwise direction) around winding axis O 3  from outer peripheral end  147  toward inner peripheral end  145 . 
       FIG. 12  is a perspective view schematically showing fourth coil  113 . Fourth coil  113  includes an adjacent portion  151 , a spacer portion  152 , a connection portion  153 , a connection portion  154 , an inner peripheral end  155 , an outer peripheral end  158 , and a lead line  156 . 
     Adjacent portion  151  is located adjacent to third coil  112 . Specifically, adjacent portion  151  is located adjacent to adjacent portion  141  of third coil  112 . Adjacent portion  151  is located on the opposite side of spacer portion  152  with respect to winding axis O 4 . Connection portion  153  connects one end of adjacent portion  151  and one end of spacer portion  152 . Connection portion  153  connects the other end of adjacent portion  151  and the other end of spacer portion  152 . 
     One end of adjacent portion  151  is formed so as to extend downward from the end of connection portion  153 . The other end of adjacent portion  351  is formed so as to extend downward from the end of connection portion  154 . Adjacent portion  151  is located lower than spacer portion  152 . 
     Fourth coil  113  configured as described above is formed by winding a coil wire  150  so as to extend around winding axis O 4  in the direction of rightward rotation (in the clockwise direction) from outer peripheral end  158  toward inner peripheral end  155 . 
       FIG. 13  is a cross-sectional view showing a power reception coil  16  and a ferrite plate  104 . In third coil  112 , adjacent portion  141  is located lower than the lower end of spacer portion  142 . In fourth coil  113 , adjacent portion  151  is located lower than spacer portion  152 . 
     When power reception device  4  configured as described above receives electric power from power transmission device  3 , an AC current flows through power reception coil  16 . 
     In  FIG. 10 , the total length, of the coil wire of third coil  112 , the coil wire of fourth coil  113 , and connection line  116  is about several meters to about a dozen or more meters. 
     On the other band, the frequency of the AC current received by power reception coil  16  is about several ten kHz to about one hundred and several ten kHz, and the wavelength of the current is about several hundred meters. 
     Accordingly, when a current flows through lead line  156  of fourth coil  113  in a current direction C, a current flows through lead line  146  of third coil  112  in current direction C. 
     In  FIG. 12 , when the current flows through lead line  156  in current direction C, the current direction in which the current flowing through fourth coil  113  winds around winding axis O 4  (the fourth current direction) is the direction of rightward rotation (the counter-clockwise direction). Similarly, the current direction in which the current flowing through third coil  112  winds around winding axis O 3  (the third current direction) is the direction of leftward rotation (the clockwise direction). 
     In this way, power reception coil  16  is also formed such that, during power reception, the current direction in which the current flows through third coil  112  (the third current direction) and the current direction in which the current flows through fourth coil  113  (the fourth current direction) are opposite to each other. 
       FIG. 14  is a cross-sectional view schematically showing the state at the time when electric power is transmitted from power transmission device  3  to power reception device  4 . 
     During power transmission, an AC current flows through power transmission coil  23 . When the AC current flows through power transmission coil  23 , a magnetic flux is formed around first coil  50  and second coil  51 . 
     For example, a magnetic flux MF 1  is formed in the vicinity of adjacent portion  71 , and a magnetic flux MF 6  and a magnetic flux MF 7  are formed around spacer portion  72 . A magnetic flux MF 2  is formed in the vicinity around adjacent portion  81 , and a magnetic flux MF 8  and a magnetic flux MF 9  are formed around spacer portion  82 . 
     In this case, the current direction in which a current flows through first coil  50  and the current direction in which a current flows through second coil  51  are opposite to each other. 
     Accordingly, the magnetic flux formed around adjacent portion  71  and the magnetic flux formed around adjacent portion  81  are more likely to be coupled. Thus, a magnetic flux MF 3  formed so as to extend over adjacent portion  71  and adjacent portion  81  is more likely to be formed. 
     In this ease, a width W 1  between the inner peripheral edge of adjacent portion  71  and the inner peripheral edge of adjacent portion  81  is larger than a width W 2  of spacer portion  72  or a width W 3  of spacer portion  82 . 
     Accordingly, the effective radius of the magnetic flux formed so as to extend over adjacent portion  71  and adjacent portion  81  is longer than the effective radius of the magnetic flux formed so as to surround each of spacer portions  72  and  82 . 
     Thus, the magnetic flux formed so as to extend over adjacent portion  71  and adjacent portion  81  is more likely to be distributed so as to expand upward. Thus, magnetic fluxes such as magnetic flux MF 4  and magnetic flux MF 5  are more likely to be formed. Consequently, a magnetic flux such as magnetic flux MF 5  interlinked with power reception coil  16  is more likely to be generated. 
     Particularly in power transmission device  3  according to the present first embodiment, adjacent portion  71  and adjacent portion  81  are located at higher positions. Consequently, the magnetic flux formed so as to extend over adjacent portion  71  and adjacent portion  81  is more likely to be distributed upward, and also, more likely to be interlinked with power reception coil  16 . 
     Thus, in power transmission device  3  according to the present first embodiment the coupling coefficient between power transmission device  3  and power reception device  4  can be improved. 
     Adjacent portions  141  and  151  of power reception coil  16  are located lower than spacer portions  142  and  152 . Accordingly, adjacent portions  141  and  151  are more likely to be interlinked with the magnetic flux formed so as to extend over adjacent portion  71  and adjacent portion  81 . Also, in power transmission coil  23 , width W 2  of spacer portion  72  and width W 3  of spacer portions  82  are small, so that magnetic fluxes MF 6  and MF 7  formed around spacer portion  72  are less likely to expand upward. Consequently, like magnetic fluxes MF 6  and MF 7 , the magnetic flux formed around spacer portion  72  is formed so as to surround spacer portion  72 . Similarly, the magnetic flux formed around spacer portion  82  is also formed so as to surround spacer portion  82 . 
     When the magnetic flux from power transmission coil  23  is interlinked with power reception coil  16 , an AC current flows through power reception coil  16 . When the AC current flows through power reception coil  16 , a magnetic flux is formed also around power reception coil  16 . 
     Since adjacent portion  141  and adjacent portion  151  are arranged so as to be located adjacent to each other, a magnetic flux is formed so as to extend over adjacent portion  141  and adjacent portion  151 . Furthermore, magnetic fluxes MF 10  and MF 11  are formed so as to surround spacer portion  142  while magnetic fluxes MF 12  and MF 13  are formed so as to surround spacer portion  152 . 
     The distance between the inner peripheral edge of adjacent portion  141  and the inner peripheral edge of adjacent portion  151  is larger than the width of each of spacer portions  142  and  152 . Thus, the magnetic flux formed so as to extend over adjacent portion  141  and adjacent portion  151  is more likely to expand downward so as to be interlinked with power transmission coil  23 . 
     Particularly, since adjacent portions  141  and  151  are located, lower than spacer portions  142  and  152 , the magnetic flux formed so as to extend over adjacent portions  141  and  151  is more likely to be interlinked with power transmission coil  23 . Thereby, the coupling coefficient between power reception device  4  and power storage device  5  is improved. 
     In this way, according to power reception device  4  in the present first embodiment, the magnetic flux from power transmission device  3  is readily captured, so that the coupling coefficient between power transmission device  3  and power reception device  4  can be improved. 
       FIG. 15  is a simulation result showing the magnetic flux distribution in power transmission device  3  and power reception device  4  during transmission and reception of electric power. In the simulation, electromagnetic field analysis software such as JMAG (registered trademark) was used. As apparent also from this  FIG. 15 , it turns out that many magnetic fluxes are interlinked between adjacent portions  71 ,  81  of power transmission coil  23  and adjacent portions  141 ,  151  of power reception coil  16 . 
       FIG. 16  is a cross-sectional view showing a power reception coil  16 A and a power transmission coil  23 A according to a comparative example. Power transmission coil  23 A includes a first coil  50 A and a second coil  51 A. First coil  50 A includes an adjacent portion  71 A and a spacer portion  72 A that are located coplanar with each other. Second coil  51 A includes an adjacent portion  81 A and a spacer portion  82 A that are located coplanar with each other. 
     Similarly, power reception coil  16 A includes a third coil  112 A and a fourth coil  113 A. Third coil  112 A includes a spacer portion  142 A and an adjacent portion  141 A that are located coplanar with each other. 
     Fourth coil  113 A includes an adjacent portion  151 A and a spacer portion  152 A that are located coplanar with each other. 
     Also when electric power is transmitted to power reception coil  16 A from power transmission coil  23 A configured as described above, an AC current is supplied to power transmission coil  23 A. Adjacent portions  71 A and  81 A are located lower than adjacent portions  71  and  81  shown in  FIG. 14 . 
     Accordingly, the magnetic flux formed around adjacent portions  71 A and  81 A is less likely to be interlinked with power reception coil  16 A. 
     Similarly, adjacent portions  141 A and  151 A of power reception coil  16 A are located higher than adjacent portions  141  and  151  of power reception coil  16 . Accordingly, power reception coil  16 A is less likely to capture the magnetic flux as compared with power reception coil  16 . 
     In other words, it turns out that the coupling coefficient can be Improved more, in power transmission device  3  and power reception device  4  according to the present first embodiment than in power transmission device  3 A and power reception device  4 A according to the comparative example. 
     Since the coupling coefficient can be improved more in power transmission device  3  than in power transmission device  3 A, power transmission coil  23  of power transmission device  3  can be formed smaller in size than power transmission coil  23 A of power transmission device  3 A. Thereby, power transmission device  3  can be formed smaller in structure size than power transmission device  3 A. 
     Similarly, according to power reception device  4  in the present first embodiment, power reception coil  16  can be formed smaller in size than power reception coil  16 A, so that power reception device  4  can be formed smaller in structure size than power reception device  4 A. 
     Second Embodiment 
     Then, a power transmission device  38  and a power reception device  4 B according to the second embodiment will be hereinafter described with reference to  FIG. 17  and the like. 
       FIG. 17  is a perspective view showing a part of power transmission device  3 B according to the present second embodiment. Power transmission device  3 B includes a power transmission coil  23  and a ferrite plate  35 B. 
     Power transmission coil  23  of power transmission device  3 B according to the present second embodiment has the same shape as that of power transmission coil  23  in the first embodiment. 
       FIG. 18  is a perspective view schematically showing ferrite plate  35 B. Ferrite plate  35 B includes a divided ferrite plate  46 B and a divided ferrite plate  47 B. Divided ferrite plate  46 B includes a plate portion  200  and a protruding portion  201 . Plate portion  200  is formed in a plate shape. 
     Protruding portion  201  is formed on the upper surface of plate portion  200 . Protruding portion  201  includes a divided protruding portion  202  and a divided protruding portion  203 . Each of divided protruding portions  202  and  203  is formed so as to protrude upward from the upper surface of plate portion  200 . There is a gap formed between divided protruding portion  202  and divided protruding portion  203 . 
     As shown in  FIGS. 17 and 18 , first coil  50  is disposed on an upper surface  61  of ferrite plats  35 B. Spacer portion  72  and connection portions  73  and  74  are disposed on the upper surface of plate portion  200 . Adjacent portion  71  is disposed on the upper surface of protruding portion  201 . Specifically, adjacent portion  71  is disposed on the upper surfaces of divided protruding portion  202  and divided protruding portion  203 . Lead line  76  is disposed so as to extend through the gap between divided protruding portion  202  and divided protruding portion  203 . 
     In divided ferrite plate  46 B, a portion that faces spacer portion  72  (the first facing portion) is an upper surface of plate portion  200 . In divided ferrite plate  40 B, a portion that faces adjacent portion  71  (the second facing portion) is: divided protruding portion  202  and divided protruding portion  203 ; and a portion of plate portion  200  that is located between divided protruding portions  202  and  203 . 
     As apparent also from  FIG. 18  at least a part of the portion of divided ferrite plate  46 B that faces adjacent portion  71  is formed thicker than the portion of divided ferrite plate  46 B that faces spacer portion  72 . Specifically, the portion of ferrite plate  35 B on which protruding portion  201  is located is thicker than plate portion  200 . 
     Second coil  51  is disposed on upper surface  63  of divided ferrite plate  47 B. Divided ferrite plate  47 B includes a plate portion  210  and a protruding portion  211 . Plate portion  210  is formed in a plate shape. Protruding portion  211  is formed on the upper surface of plate portion  210 . Protruding portion  211  includes a divided protruding portion  212  and a divided protruding portion  213 . There is a gap formed also between divided protruding portion  212  and divided protruding portion  213 . A connection line  53  is disposed so as to pass through this gap. 
     Adjacent portion  81  is disposed on the upper surface of protruding portion  211 . Specifically, adjacent portion  81  is disposed on the upper surface ox protruding portion  211 . Also, spacer portion  82  and connection portions  83  and  84  are disposed on the upper surface of plate portion  210 . 
     As apparent also from  FIG. 18 , at least a part of the portion of divided ferrite plate  47 B that faces adjacent portion  81  is formed thicker than the portion of divided ferrite plate  47 B that faces spacer portion  82 . 
       FIG. 19  is a perspective view showing a power reception coil  16  and a ferrite plate  104 B in power reception device  4 B.  FIG. 20  is a perspective view schematically showing ferrite plate  104 B. Ferrite plate  104 B includes a divided ferrite plate  114 B and a divided ferrite plate  115 B. 
     Divided ferrite plate  114 B includes a plate portion  220  and a protruding portion  221 . Protruding portion  221  is formed on the lower surface of plate portion  220 . Protruding portion  221  includes a divided protruding portion  222  and a divided protruding portion  223 . Between divided protruding portion  222  and divided protruding portion  223 , there is a gap through which connection line  116  is disposed. 
     Adjacent portion  141  of third coil  112  is disposed on the lower surface of protruding portion  221 . Spacer portion  142  and connection portions  143  and  144  are disposed on the lower surface of plate portion  220 . 
     As apparent from  FIG. 20 , at least a part of the portion of divided ferrite plate  1148  that faces adjacent portion  141  is thicker than the portion of divided ferrite plate  114 B that races spacer portion  142 . 
     Divided ferrite plate  115 B includes a plate portion  230  and a protruding portion  231 . Protruding portion  231  is formed on the lower surface of plate portion  230  so as to protrude downward from the lower surface of plate portion  230 . 
     Protruding portion  231  includes a divided protruding portion  232  and a divided protruding portion  233 . Between divided protruding portion  232  and divided protruding portion  233 , there is a gap through which connection line  116  passes. 
     Adjacent portion  151  of fourth coil  113  is disposed on the lower surface of protruding portion  231 . Spacer portion  152  and connection portions  153  and  154  are disposed on the lower surface of plate portion  230 . 
     At least a part of the portion of divided ferrite plate  115 B that faces adjacent portion  151  is thicker than the portion of di vided ferrite plate  115 B that faces spacer portion  152 . 
       FIG. 21  is a cross-sectional view schematically showing the state where electric power is transmitted from power transmission device  3 B to power reception device  4 B. The magnetic flux formed around, adjacent portion  71  and the magnetic flux formed around adjacent portion  81  are more likely to be coupled with each other. Thus, the most, part of the magnetic flux formed around adjacent portion  71  by a current flowing through adjacent portion  71  and the most part of the magnetic flux formed around adjacent portion  81  by a current flowing through adjacent portion  81  are formed so as to extend over adjacent portion  71  and adjacent portion  81 . 
     The amount of the magnetic flux flowing so as to extend over adjacent portion  71  and adjacent portion  81  is greater than the amount of the magnetic flux formed around spacer portion  72 . Similarly, the amount of the magnetic flux flowing so as to extend over adjacent portion  71  and adjacent portion  81  is greater than the amount of the magnetic flux formed around spacer portion  82 . 
     The magnetic flux flowing so as to extend over adjacent portion  71  and adjacent portion  81  flows through the portion of ferrite plate  35 B that faces adjacent portions  71  and  81 . Furthermore, the magnetic flux flowing so as to surround only adjacent portion  71  also flows through the portion of ferrite plate  35 B that faces adjacent portion  71 . The magnetic flux flowing so as to surround only adjacent portion  81  also flows through the portion of ferrite plate  35 B that faces adjacent portion  81 . 
     The magnetic flux formed around each of spacer portions  72  and  82  flows through the portion of ferrite plate  35 B that faces each of spacer portions  72  and  82 . 
     Thus, the amount of the magnetic flux flowing through the portion of ferrite plate  35 B that faces each of adjacent portions  71  and  81  is greater than the amount of the magnetic flux flowing through the portion of ferrite plate  35 B that faces each of spacer portions  72  and  82 . 
     In power transmission device  3 B according to the present second embodiment, the portion of ferrite plate  35 B that faces each of adjacent portions  71  and  81  is thicker than the portion of ferrite plate  35 B that faces each of spacer portions  72  and  82 . 
     Thus, local temperature rise Inside ferrite plate  35 B can be suppressed. 
     In power transmission device  3 A of the comparative example shown in  FIG. 16 , ferrite plate  35  is formed in a plate shape. Accordingly, the portion of ferrite plate  35  that feces each of adjacent portions  71 A and  81 A is identical in thickness to the portion of ferrite plate  35  that faces each of spacer portions  72 A and  82 A. 
     On the other hand, the amount of the magnetic flux flowing through the portion of ferrite plate  35  that faces each of adjacent portions  71 A and  81 A is greater than the amount of the magnetic flux flowing through the portion of ferrite plate  35  that faces each of spacer portions  72 A and  82 A. 
     Accordingly, the portion of ferrite plate  35  that feces each of adjacent portions  71 A and  81 A is higher in temperature than the portion of ferrite plate  35  that faces each of spacer portions  72 A and  82 A. 
     Consequently, the portion of ferrite plate  35  that faces each of adjacent portions  71 A and  81 A expands more than the portion of ferrite plate  35  that faces each of spacer portions  72 A and  82 A. Consequently, thermal stress occurs in the portion of fertile plate  35  that feces each of adjacent portions  71  and  81 . 
     Generally, as the internal stress Inside ferrite increases, the magnetic resistance increases. As the magnetic resistance increases, the amount of heat generated upon passage of a magnetic flux also increases. 
     Thus, the portion of ferrite plate  35  that feces each of adjacent portions  71 A and  81 A is more likely to be increased in temperature. 
     On the other hand, in power transmission device  3 B according to the present second embodiment, the adverse effect as described above can be suppressed. 
     In  FIG. 21 , power reception device  4 B receives electric power from power transmission device  3 B. In this case, an AC current occurs in power reception coil  16 , and a magnetic flux is formed around power reception coil  16 . 
     Also in power reception coil  16 , the most part of the magnetic flux formed around adjacent portion  141  and the most part of the magnetic flux formed around adjacent portion  151  join together, and then, flow so as to extend over adjacent portion  141  and adjacent portion  151 . 
     The amount of the magnetic flux flowing so as to extend over adjacent portion  141  and adjacent portion  151  is greater than the amount of the magnetic flux formed around each of spacer portions  142  and  152 . 
     Accordingly, the amount of the magnetic flux flowing through the portion of ferrite plate  104 B that faces each of adjacent portions  141  and  151  is greater than the amount of the magnetic flux flowing through the portion of ferrite plate  104 B that faces each of spacer portions  142  and  152 . The portion of ferrite plate  104 B that faces each of adjacent portions  141  and  151  is thicker than, the portion of ferrite plate  104 B that faces each of spacer portions  142  and  152 . 
     Thus, local temperature rise in ferrite plate  104 B can also be suppressed. 
     In the above-described first embodiment, ferrite plate  35  is divided into divided ferrite plates  46  and  47 . In the above-described second embodiment, ferrite plate  35 B is divided into divided ferrite plates  46 B and  47 B. However, divided ferrite plates  46  and  47  may be integrally formed, and also, divided ferrite plates  46 B and  47 B may be integrally formed. 
       FIG. 22  is a cross-sectional view showing the first modification of the ferrite plate. A ferrite plate  250  includes a plate portion  252  and a protruding portion  251 . Adjacent portions  71  and  81  of power transmission coil  23  are disposed on the upper surface of protruding portion  251 . 
     In this ferrite plate  250 , it becomes possible to reduce the distance by which the magnetic flux flowing so as to extend over adjacent portions  71  and  81  passes through the air. Thus, the amount of the magnetic flux flowing so as to extend over adjacent portions  71  and  81  can be increased. Thereby, the coupling coefficient between power reception device  4  and power transmission device  3  can be improved. 
     The configuration of ferrite plate  250  is applicable also to the ferrite plate of power reception device  4 . 
       FIG. 23  is a cross-sectional view showing the second modification of the ferrite plate. Ferrite plate  250 A includes a plate portion  252 A and a protruding portion  253 A. Protruding portion  253 A is formed so as to protrude upward from the upper surface of plate portion  252 A and also protrude downward. 
     Furthermore, protruding portion  253 A is formed so as to be increased in thickness toward the center portion of protruding portion  253 A in the width direction. 
     During power transmission, a large amount of magnetic flux flows through protruding portion  253 A. Particularly in this case, the largest amount of magnetic flux flows through the center portion of protruding portion  253 A. 
     When ferrite plate  250 A is formed so as to be increased in thickness of the center portion of protruding portion  253 A in the width direction, local temperature rise also inside protruding portion  253 A can be suppressed. 
     Third Embodiment 
     Referring to  FIG. 24  and the like, a power transmission device  3 C and a power reception device  4 C according to the present third embodiment will be hereinafter described. 
       FIG. 24  is a plan view showing a power transmission coil  23 C of power transmission device  3 C.  FIG. 25  is a perspective view showing power transmission coil  23 C of power transmission device  3 C. Power transmission coil  23 C includes a first coil  50  and a second coil  51 . First coil  50  includes an adjacent portion  71 , a spacer portion  72 , and connection portions  73  and  74 . 
     Adjacent portion  71  includes a recess portion  78 . Recess portion  78  is formed so as to be away from adjacent portion  81  of second coil  51 . 
     Recess portion  78  is formed in the center portion of adjacent portion  71  in the direction in which adjacent portion  71  extends. In examples shown in  FIGS. 24 and 25 , adjacent portion  71  is formed so as to be away from second coil  51  from the end of adjacent portion  71  toward the center portion thereof. 
     Adjacent portion  81  of second coil  51  also includes a recess portion  88 . Recess portion  88  is formed so as to be away from first coil  50 . Recess portion  88  is formed in the center portion of adjacent portion  81  in the direction in which adjacent portion  81  extends. 
     In the examples shown in  FIGS. 24 and 25 , adjacent portion  81  is formed so as to be away from first coil  50  from the end of adjacent portion  81  toward the center portion thereof. Recess portion  88  and recess portion  78  are formed so as to face each other. 
       FIG. 26  is a plan view showing a power reception coil  16 C of a power reception device  4 C.  FIG. 27  is a perspective view showing power reception coil  16 C of power reception device  4 C. 
     In  FIGS. 26 and 27 , third coil  112  includes an adjacent portion  141 . Adjacent portion  141  includes a recess portion  148 . Recess portion  148  is formed so as to be away from adjacent portion  151  of fourth coil  113 . 
     Recess portion  148  is formed in the center portion of adjacent portion  141  in the direction in which adjacent portion  141  extends. From the end of adjacent portion  141  toward the center portion thereof; adjacent portion  141  is formed so as to be away from fourth coil  113 . 
     Fourth coil  113  includes an adjacent portion  151 . Adjacent portion  151  includes a recess portion  159 . Recess portion  159  is formed so as to be away from adjacent portion  141  of third coil  112 . Recess portion  159  is formed in the center portion of adjacent portion  151  in the direction in which adjacent portion  151  extends. From the end of adjacent portion  151  toward the center portion thereof, adjacent portion  151  is formed so as to be away from adjacent portion  141 . Recess portion  148  and recess portion  159  are formed so as to face each other. 
       FIG. 28  is a cross-sectional view taken along a line XXVIII-XXVIII in  FIG. 26 .  FIG. 29  is a cross-sectional view taken along a line XXIX-XXIX in  FIG. 26 . 
     As shown in  FIGS. 28 and 29 , power transmission device  3 C and power reception device  4 C according to the present third embodiment include a ferrite plate  35 B and a ferrite plate  104 B, respectively, according to the second embodiment. Then, as shown in  FIGS. 28 and 29 , the distance between adjacent portion  71  and adjacent portion  81  becomes longest between recess portion  78  and recess portion  88 . 
     Thus, it becomes possible to reduce the amount of the magnetic flux that flows through the portion of ferrite plate  35 B that faces each of recess portion  78  and recess portion  88 , so that temperature rise in protruding portions  201  and  211  can be suppressed. 
     The distance between adjacent portion  141  and adjacent portion  151  becomes longest between recess portion  148  and recess portion  159 . Accordingly, the amount of the magnetic flux flowing so as to extend over recess portion  148  and recess portion  159  can be reduced. 
     Consequently, it becomes possible to suppress an increase in amount of the magnetic flux that flows through the portion of ferrite plate  104 B that faces recess portion  148  and recess portion  159 , so that temperature rise in protruding portions  221  and  231  can be suppressed. Also in the present third embodiment, in the state where power reception device  4 C and power transmission device  3 C face each other, recess portions  148  and  159  face recess portions  78  and  88 , respectively, in the up-down direction. Thereby, it becomes possible to suppress an excessive increase in amount of the magnetic flux flowing through recess portions  148  and  159  and also through recess portions  78  and  88 . Thus, for example, it becomes possible to suppress an increase in difference between the coupling coefficient (Kmax) at the time when power transmission device  3 C and power reception device  4 C are misaligned from each other in the front-rear direction or in the right-left direction; and the coupling coefficient at the time when power reception device  4 C and power transmission device  3 C face each other. 
     In the above-described third embodiment, as shown in  FIGS. 28 and 29 , in power transmission device  3 C, it is not indispensable to employ a ferrite plate having protruding portions  201  and  211  formed thereon, but a plate-shaped ferrite plate not having protruding portions  201  and  211  formed thereon may be employed. Also, a protruding portion  253  having an upward ridge shape shown in  FIG. 23  may be formed on a plate-shaped ferrite plate. Similarly, in power reception device  4 C, it is not indispensable to employ ferrite plate  104 B having protruding portions  221  and  231  formed thereon, but a plate-shaped ferrite plate not having protruding portions  221  and  231  formed thereon may be employed. Also, a protruding portion having an upward ridge shape may be formed on the upper surface side of a plate-shaped ferrite plate. 
     The present first to third embodiments have been described above. In the above-described first to third embodiments, an explanation has been given with regard to an example in which first coil  50  and second coil  51  are connected in series in power transmission coil  23 , but first coil  50  may be connected to filter  24  and capacitor  22  while second coil  51  may be connected to filter  24  and capacitor  22 . 
     Even when each of first coil  50  and second coil  51  is connected as described above, the current direction in which the current flows through first coil  50  and the current direction in which the current flows through second coil  51  become opposite to each other during power transmission. 
     Also in power reception coil  16 , third coil  112  may be connected to rectifier  12  and capacitor  17  while fourth coil  113  may be connected to rectifier  12  and capacitor  17 . 
     In the above-described first to third embodiments, power transmission coil  23  includes adjacent portion  71  and adjacent portion  81 . Also, adjacent portion  71  and adjacent portion  81  each are located higher than spacer portion  72  and spacer portion  82 . On the other hand, at least one of adjacent portions  71  and  81  may be located higher than spacer portions  72  and  82 . 
     Similarly, also in power reception, coil  16 , at least one of adjacent portions  141  and  151  may be located lower than spacer portions  142  and  152 . 
     In the above-described first to third embodiments, third coil  112  and fourth coil  113  are disposed so as to be arranged in the front-rear direction of vehicle  2 . On the other hand, third coil  112  and fourth coil  113  may be disposed so as to be arranged in the width direction of vehicle  2 . Similarly, in the above-described first to third embodiments, first coil  50  and second coil  51  are disposed so as to be arranged in the front-rear direction of vehicle  2  that is stopped. On the other hand, first coil  50  and second coil  51  may be disposed so as to be arranged in the width direction of vehicle  2  that is stopped. 
     Although the embodiments of the present disclosure have been described as above, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.