Coil unit, power transmission device, external power feeding apparatus, and vehicle charging system

1. A coil unit comprising:

a resonant coil establishing an electromagnetic field resonant coupling with an externally provided external resonant coil,

said resonant coil including an outer side coil extending along a circumference of a first winding center and centered at about said first winding center, and an extension extending from said outer side coil into a region surrounded by said outer side coil,

said resonant coil, which is formed such that an anti-node of the resonant coil that is an area of an anti-node of AC current flowing through said resonant coil, is located at said extension when the electromagnetic field resonant coupling is established between said external resonant coil and said resonant coil.

2. The coil unit according to claim 1 , wherein

said resonant coil includes an inner side coil formed in a loop, whose direction of a magnetic field developed by a flow of current is identical to the direction of the magnetic field developed by said outer side coil, and

said extension is said inner side coil.

3. The coil unit according to claim 2 , wherein

a plurality of said inner side coils are provided spaced apart along said outer side coil, and

said anti-node is located at one of said plurality of inner side coils.

4. The coil unit according to claim 2 , wherein

said inner side coil extends along a circumference of a second winding center,

said second winding center is located at a position distant from said first winding center, and

said resonant coil is formed such that said anti-node is located closer to said first winding center than said second winding center.

5. The coil unit according to claim 1 , wherein said resonant coil includes a first end and a second end,

further comprising a capacitor connected to said first and second ends,

wherein said anti-node is located at a middle of a conductor wire constituting said resonant coil in a length direction from one end to the other end of the conductor wire.

6. The coil unit according to claim 5 , wherein

said resonant coil includes an inner side coil formed in a loop, whose direction of a magnetic field developed by a flow of current is identical to the direction of the magnetic field developed by said outer side coil,

a plurality of said inner side coils are provided spaced apart along said outer side coil, and

said plurality of the inner side coils include a first inner side coil where the anti-node of said resonant coil is located, and a second inner side coil including said first end and second end, and to which said capacitor is connected.

7. The coil unit according to claim 5 , wherein

said resonant coil and said capacitor constitute a resonant circuit, and

said anti-node is located at a middle of a current path of said resonant circuit.

8. The coil unit according to claim 1 , further comprising an electromagnetic induction coil coupled with said resonant coil in an electromagnetic induction manner.

9. A vehicle including the coil unit defined in claim 1 , wherein a distance between the anti-node of said resonant coil and the center of said vehicle is smaller than the distance between said first winding center and the center of said vehicle.

10. An external power feeding apparatus comprising the coil unit defined in claim 1 .

11. A vehicle power charging system comprising:

a vehicle including a coil unit, the coil unit including a resonant coil establishing an electromagnetic field resonant coupling with an external resonant coil provided externally to said vehicle,

said resonant coil including an outer side coil extending along a circumference of a first winding center and centered at about said first winding center, and an extension extending from said outer side coil into a region surrounded by said outer side coil,

said resonant coil, which is formed such that an anti-node of the resonant coil that is an area of an anti-node of AC current flowing through said resonant coil, is located at said extension when the electromagnetic field resonant coupling is established between said external resonant coil and said resonant coil, wherein a distance between the anti-node of said resonant coil and a center of said vehicle is smaller than a distance between said first winding center and the center of said vehicle, and

an external power feeding apparatus including the coil unit.