Abstract:
Disclosed is an electric vehicle which receives power from a road surface by means of a wireless connection, in which an optimal configuration of a repeater (which is a resonator) and a receiving coil relative to the vehicle body is clarified. A first coil configuring the repeater forms a first wireless connection with a receiver coil, and a second coil forms a second wireless connection with a transmitting coil. The first coil is proximally arranged below the receiving coil and is aligned with the receiving coil, which is on the top side of a vehicle underbody panel; the second coil is arranged on the bottom side of the vehicle underbody panel. A performance indicator k*Q of the path from the transmitting coil below the road surface to the receiving coil of the electric vehicle is increased.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electric vehicle, which is propelled by drive power from an electric motor that is energized by electric power from an electric storage device, and more particularly, to an electric vehicle which is capable of being charged wirelessly (contactlessly charged). 
       BACKGROUND ART 
       [0002]    Heretofore, electric vehicles have been known that travel based on a rotational torque transmitted to road wheels through a power transmitting mechanism from an electric motor that is energized by electric power from an electric storage device. Problems to be solved in order for such electric vehicles to find widespread use include the relatively small distance that such vehicles can travel with a single charging process performed on the electric storage device, lack of pervasive charging facilities, and long charging times, etc. 
         [0003]    Another concern in relation to electric vehicles is that, since electric accessories such as an air conditioner, etc., consume electric power, if the electric vehicle is involved in traffic congestion, then the distance that the electric vehicle can travel tends to be extremely reduced. 
         [0004]    Recently, a wired charging process has been proposed for charging the electric storage device on an electric vehicle through a charging cable that interconnects a charging plug on the electric vehicle and a charging stand or a home power supply. If the electric vehicle is to be charged on a daily basis, then it is highly tedious and time-consuming to connect and disconnect connectors on the charging cable. 
         [0005]    There have been demands for wireless charging, or stated otherwise, contactless charging, in order to eliminate the above tedious and time-consuming process. 
         [0006]    Japanese Laid-Open Patent Publication No. 2009-106136 discloses an electric vehicle (electrically-driven vehicle) that receives charging electric power contactlessly from a power supply outside of the electric vehicle according to a resonance process, which is used to charge an electric storage device in the electric vehicle. Japanese Laid-Open Patent Publication No. 2009-106136 states, in paragraphs [0015], [0033], etc., that a secondary self-resonant coil, which is an LC resonant coil having both ends thereof open, should preferably be disposed in a lower portion of the vehicle body. The patent publication also states ( FIG. 1 , paragraph [0034]) that a secondary coil (electric receiving coil) should preferably be disposed coaxially with respect to the secondary self-resonant coil (paragraph [0092],  FIG. 10 ), which is disposed in the lower portion of the vehicle body parallel to the electric vehicle. 
         [0007]    Wireless coupling (wireless electric transmission) according to a resonant process and wireless coupling according to an electromagnetic induction process are disclosed in “Second Section, Medium-Distance Electric Trans-mission Technology,” pages 27 through 31, of “EE TIMES Japan” published Oct. 9, 2009 by E2 Publishing Company (hereinafter referred to as “Non-Patent Document 1”), for example. 
         [0008]    Non-Patent Document 1 reveals that if ω represents an angular frequency, Rohm represents a resistive component, and Rrad represents a radiation resistive component, then a coil index Q concerning energy retained by the coil is expressed by the following equation (1). 
         [0000]        Q={ωL /(Rohm+Rrad)}  (1)
 
         [0009]    Non-Patent Document 1 also discloses that if the inductance of an electric transmitting coil is represented by Ls, the inductance of an electric receiving coil is represented by Lr, and the mutual inductance is represented by M, then the coupling strength k between the coils is expressed by the following equation (2). 
         [0000]        k=M /( Ls·Lr ) 1/2 =( M/√Ls·Lr )  (2)
 
         [0010]    Non-Patent Document 1 further discloses that a figure of merit concerning the electric power transmission efficiency of a wireless coupling is expressed as the product of the coupling strength k and the index Q, in accordance with the following equation (3). 
         [0000]        k·Q =( M/√Ls·Lr )·{ω Ls /(Rohm+Rrad)}  (3)
 
       SUMMARY OF INVENTION 
       [0011]    The self-resonant coil described in Japanese Laid-Open Patent Publication No. 2009-106136 is an LC resonant coil having both ends thereof open (unconnected). Since the C component (capacitive component) thereof varies significantly depending on how the LC resonant coil actually is installed on the vehicle, circuit and installation design are highly critical (subjected to large limitations). With respect to the layout of the self-resonant coil and the secondary coil (electric receiving coil) in the vehicle, the publication simply describes that the secondary coil (electric receiving coil) should preferably be disposed coaxially with respect to the self-resonant coil, which is disposed in a lower portion of the vehicle body parallel to the electric vehicle. 
         [0012]    The present invention has been made in view of the above problems and the disclosure of Non-Patent Document 1. It is an object of the present invention to provide an electric vehicle, which makes it possible to charge an electric storage device with high electric power transmission efficiency, even if there is a certain distance between the electric vehicle and the road surface, by clarifying the optimum layout of a relay (resonator) and an electric receiving coil on the electric vehicle for the purpose of increasing a figure of merit k·Q in a wireless charging process. 
         [0013]    According to the present invention, there is provided an electric vehicle propelled by drive power from an electric motor, which is energized by electric power from an electric storage device, comprising an electric receiving coil disposed above a vehicle underfloor panel, for supplying electric power to the electric storage device, and a relay for transmitting electric power from an electric transmitting coil disposed underneath a road surface to the electric receiving coil through at least one of an electromagnetic induction wireless coupling and a resonant wireless coupling. The relay comprises a first coil, a second coil, and a capacitor that jointly constitute a resonant circuit, the first coil and the electric receiving coil jointly constitute a first wireless coupling, the second coil and the electric transmitting coil jointly constitute a second wireless coupling, the first coil is disposed above the vehicle underfloor panel and beneath the electric receiving coil in close proximity thereto, in order to make the coupling strength k (k=M/√L 1 ·Lr, where L 1  represents an inductance of the first coil, Lr represents an inductance of the electric receiving coil, and M represents a mutual inductance) of the first wireless coupling greater than the coupling strength k of the second wireless coupling, and the second coil is disposed beneath the vehicle underfloor panel, and an index Q (particularly, an index Q=ωLs/r of the electric transmitting coil concerning energy retained thereby, where ω represents an angular frequency, Ls represents an inductance of the electric transmitting coil, and r represents a sum of a resistive component and a radiation resistive component of the electric transmitting coil) of the second wireless coupling concerning energy retained thereby is greater than an index Q of the first wireless coupling concerning energy retained thereby. 
         [0014]    According to the present invention, the index Q concerning energy retained between the electric transmitting coil underneath the road surface and the second coil of the relay, which forms the second wireless coupling in coaction with the electric transmitting coil, is increased, and the first coil of the relay and the electric receiving coil are disposed in close proximity to each other. Therefore, the coupling strength k is increased. Consequently, the figure of merit k·Q of the path from the electric transmitting coil underneath the road surface to the electric receiving coil of the electric vehicle  10  can also be increased. As a result, even if the electric vehicle and the road surface are distant from each other, the electric storage device can be charged with high electric power transmission efficiency through the relay. 
         [0015]    The electric receiving coil and the first coil may be aligned coaxially with each other for thereby increasing the coupling strength k. 
         [0016]    If the capacitor of the relay is disposed above the vehicle underfloor panel, then the capacitor, which is less durable than the coils, is disposed inside of the electric vehicle. Accordingly, selection of components is facilitated. 
         [0017]    According to the present invention, the electric vehicle, which receives electric power from the road surface through magnetic couplings, has a clarified optimum layout made up of the relay as a resonator and the electric receiving coil. As a result, the figure of merit of the path from the electric transmitting coil underneath the road surface to the electric receiving coil is increased. Therefore, even if the vehicle underfloor panel of the electric vehicle and the road surface are distant from each other, the electric storage device can be charged with high electric power transmission efficiency. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIGS. 1A ,  1 B, and  1 C are a side elevational view, a rear elevational view, and a plan view, respectively, showing transparently the layout of major vehicle-mounted components in an electric vehicle according to an embodiment of the present invention; 
           [0019]      FIG. 2  is a schematic block diagram showing the major vehicle-mounted components, interconnections therebetween, and pipes in the electric vehicle shown in  FIGS. 1A ,  1 B, and  1 C; 
           [0020]      FIG. 3  is a view showing an actual configuration of a relay; 
           [0021]      FIG. 4  is a circuit diagram of a wireless coupling electric transmitting and receiving system; and 
           [0022]      FIG. 5  is a schematic view showing an interlinked state of magnetic fluxes. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0023]    An electric vehicle according to an embodiment of the present invention will be described below with reference to the drawings. 
         [0024]      FIGS. 1A ,  1 B, and  1 C are a side elevational view, a rear elevational view, and a plan view, respectively, showing transparently the layout of major vehicle-mounted components in an electric vehicle  10  according to an embodiment of the present invention. 
         [0025]      FIG. 2  is a schematic block diagram showing the vehicle-mounted major components, interconnections therebetween, and pipes in the electric vehicle  10  shown in  FIGS. 1A ,  1 B, and  1 C. 
         [0026]    As shown in  FIGS. 1A ,  1 B, and  1 C, the electric vehicle  10  (vehicle) includes a high-voltage electric storage device  12  such as a lithium ion secondary battery, a capacitor, or the like. The electric storage device  12 , which has a thin shape in the form of a rectangular parallelepiped, extends from a position beneath the front seats along an underfloor panel (vehicle underfloor panel)  18  of a vehicle body  16  to a rear trunk  20 . 
         [0027]    A radiator  22  is disposed behind a front grill of the vehicle body  16 . An EWP (Electric Water Pump)  24  is disposed behind the radiator  22  and is offset therefrom in a transverse direction of the vehicle body  16  (see  FIG. 1C ). When the EWP  24  is actuated, a coolant flows through a pipe  31  (see  FIG. 2 ), which extends through the radiator  22  and an electric motor  30 . The coolant performs heat exchange in the radiator  22  and cools the electric motor  30 . 
         [0028]    A chamber  26 , which is defined in a front portion of the vehicle body  16  beneath the engine hood, houses therein a motor power mechanism  34 , which comprises an integral assembly of the electric motor  30  and a gearbox  32 . 
         [0029]    The electric motor  30  has an output shaft (not shown) connected to a gear train (not shown) in the gearbox  32 . The gear train causes a drive shaft (not shown) to rotate front road wheels  50 . The front road wheels  50  serve as drive wheels, whereas the rear road wheels  52  are driven wheels. 
         [0030]    Rotation of the front road wheels  50  is detected by a rotational speed sensor (not shown). An output signal from the rotational speed sensor is read into an ECU  58  as an output signal of a vehicle speed sensor  60  (see  FIG. 2 ), i.e., a vehicle speed V [km/h]. The ECU  58  includes a CPU, a ROM, and a RAM, and executes various programs stored in the ROM to carry out control processes in relation to all of the components mounted in the electric vehicle  10 , e.g., to perform a control process for charging and discharging the electric storage device  12 . 
         [0031]    As shown in  FIG. 1A , an inverter  36  and a VCU (Voltage Control Unit)  38  are disposed above the motor power mechanism  34 . 
         [0032]    A relay (resonator)  66  for transmitting and receiving electric power by way of a wireless coupling comprises a first coil capacitor unit  61 , which is disposed on an upper surface of the underfloor panel  18  and beneath a floor (not shown) of the vehicle, or within the engine compartment, and a second coil unit  62 , which is disposed on a lower surface of the underfloor panel  18 . The relay  66  is separately disposed vertically above and beneath the underfloor panel  18  of the vehicle body  16 . 
         [0033]    The second coil unit  62  and the first coil capacitor unit  61  are connected to each other by two electric wires  97  that extend through a small opening  96  defined in the vehicle underfloor panel  18  (see  FIGS. 1A and 2 ). 
         [0034]    The first coil capacitor unit  61  is disposed beneath an electric receiving device  40  in confronting relation thereto. A charger  44  is disposed above the electric receiving device  40 . The first coil capacitor unit  61  is disposed beneath a downverter  42  and parallel to the electric receiving device  40  and the charger  44 . 
         [0035]      FIG. 3  shows an actual configuration of the relay  66 . As described above with reference to  FIGS. 1A and 2 , the relay  66  includes the second coil unit  62 , which has a thin shape in the form of a rectangular parallelepiped, extending substantially fully underneath the vehicle underfloor panel  18  of the vehicle body  16 , and the first coil capacitor unit  61 , which is in the form of a rectangular parallelepiped disposed above the vehicle underfloor panel  18 . 
         [0036]    The second coil unit  62  has a second coil  72  made of multiple turns of a thermal-fusion electric wire along four inner wall surfaces (side surfaces of the rectangular parallelepiped) thereof. The second coil unit  62  is entirely encased within a resin molding, which also has a thin shape in the form of a rectangular parallelepiped, for fixing the second coil  72  in position and securing the second coil  72  to the lower surface of the underfloor panel  18 . 
         [0037]    The height of the wall surfaces of the second coil unit  62  (the height along the Y direction in  FIG. 1A ) is small. The second coil unit  62  has a given number of turns and defines a large second closed-path area A 2  as a spatial area. If the second coil  72  is considered as a finite-length solenoid, then it is understandable that the inductance of the second coil  72  of the relay  66  can be increased. 
         [0038]    The first coil capacitor unit  61  includes a first coil  71 , which also has a thin shape in the form of a rectangular parallelepiped, similar to the second coil  72 . The first coil  71  comprises multiple turns of thermal-fusion electric wire along four inner wall surfaces of the rectangular parallelepiped shape thereof. The first coil capacitor unit  61  is encased within a resin molding for securing the first coil  71  to the underfloor panel  18 . 
         [0039]    With the electric vehicle  10  according to the present embodiment, the second closed-path area A 2 , which is defined by the second coil  72  as a central area that is free of electric wires, is greater than a first closed-path area A 1 , which is defined by the first coil  71  as a central area that is free of electric wires. The first coil  71  is axially aligned with an electric receiving coil  81  of the electric receiving device  40 , and is disposed in close confronting relation to the electric receiving coil  81  (see  FIGS. 1A and 1C ). 
         [0040]    As shown in  FIG. 3 , the first coil capacitor unit comprises a series-connected circuit made up of the first coil  71  and two capacitors  64 . The two capacitors  64  may be combined into a single capacitor. 
         [0041]    As described above, the first coil capacitor unit  61  and the second coil unit  62  are connected to each other by the two electric wires  97 , which extend through the small opening  96  defined in the vehicle underfloor panel  18 , such that the first and second coils  71 ,  72  and the capacitors  64  make up a closed resonant circuit. 
         [0042]    If the series-connected capacitors  64  have a combined capacitance C and the first and second coils  71 ,  72  have a combined inductance L, then the relay  66 , which acts as a resonator, has a resonant frequency f 0  of 1/2π√LC (f 0 =1/2π√LC). 
         [0043]      FIG. 4  is a circuit diagram of a wireless coupling electric transmitting and receiving system  200 . As shown in  FIG. 4 , the wireless coupling electric transmitting and receiving system  200  comprises a road infra-unit  112  (vehicle-bearing infra-unit) disposed underneath a road surface  104  (see  FIG. 2 ), and a vehicular electric receiver  110  disposed in a lower portion of the vehicle body  16  of the electric vehicle  10 . 
         [0044]    The vehicular electric receiver  110  includes the relay  66  and the electric receiving device  40 . 
         [0045]    The road infra-unit  112  comprises a high-frequency power supply  100  having the above resonant frequency f 0 , e.g., a frequency of about f 0 =10 [MHz], a signal characteristic impedance  103 , an electric transmitting device  80 , and a coaxial cable  114  having a characteristic impedance Zo, and which interconnects the high-frequency power supply  100 , the signal characteristic impedance  103 , and the electric transmitting device  80 . 
         [0046]    The electric transmitting device  80  comprises a terminating resistor  86  and a resonator  102  including a capacitor  92  and an electric transmitting coil  82 . The resonator  102  has a resonant frequency that is equal to the resonant frequency f 0 . 
         [0047]    As described above with reference to  FIGS. 2 and 3 , the relay  66  of the vehicular electric receiver  110  is constructed as a relay (having the resonant frequency f 0 ), which is made up of the first coil  71 , the second coil  72 , and the capacitors  64 . 
         [0048]    The electric receiving device  40  of the vehicular electric receiver  110  comprises a resonator  101  (resonator) with the resonant frequency f 0 , which includes the electric receiving coil  81  and a capacitor  91 , a damping resistor  84 , and a rectifier  43  for supplying a DC voltage to the charger  44 . 
         [0049]    While the electric vehicle  10  is held at rest in an electric transmitting and receiving mode, the electric vehicle  10  is positioned on the road surface  104  such that the closed-path area of the electric transmitting coil  82  of the electric transmitting device  80  and the closed-path area of the second coil  72  of the relay  66  confront each other and preferably are aligned coaxially with each other. If a succession of road infra-units  112  are provided underneath the road surface  104 , then the electric vehicle  10  can also operate in an electric transmitting and receiving mode when the electric transmitting coil  82  and the second coil  72  confront each other during times that the electric vehicle  10  is traveling. 
         [0050]    The first coil  71  of the relay  66  and the electric receiving coil  81  of the electric receiving device  40  are aligned coaxially with each other, have essentially the same diameter as each other, have as large a closed-path area as possible, and are disposed in close proximity to each other. Therefore, the first coil  71  and the electric receiving coil  81  have a large coupling strength k therebetween, i.e., k=M(L 1 ·Lr) 1/2 =M√L 1 ·Lr, where L 1  represents the inductance of the first coil  71 , Lr represents the inductance of the electric receiving coil  81 , and M represents the mutual inductance. 
         [0051]    Operations of the electric vehicle  10 , which incorporates the wireless coupling electric transmitting and receiving system  200  constructed basically as described above, will be described below with reference to  FIG. 5 , which shows an interlinked state of magnetic fluxes. 
         [0052]    The electric storage device  12  is charged while the electric vehicle  10  is traveling on a road in which a succession of electric transmitting devices  80  of road infra-units  112  are disposed below and near the road surface (road surface)  104 . 
         [0053]    The electric storage device  12  also is charged when the electric transmitting coil  82  of the electric transmitting device  80  and the second coil  72  of the relay  66  are disposed in confronting relation to each other, and preferably in coaxial alignment with each other, with the relay  66  being positioned directly above the electric transmitting device  80  while the electric vehicle  10  is held at rest. 
         [0054]    The road infra-unit  112  may be installed in a public or private parking space. Therefore, while the electric vehicle  10  is parked or stopped in such a public or private parking space, which is equipped with the electric transmitting device  80  of the road infra-unit  112 , the electric storage device  12  on the electric vehicle  10  can be charged when the electric transmitting coil  82  of the electric transmitting device  80  and the second coil  72  of the relay  66  are disposed in confronting relation and in coaxial alignment with each other. 
         [0055]    When the high-frequency power supply  100  is energized for charging, high-frequency electric power from the high-frequency power supply  100  is supplied through the coaxial cable  114  to the electric transmitting device  80 . When the resonator  102  of the electric transmitting device  80  is excited by high-frequency electric power, a large resonant current flows with a large inductance into the resonator  102 , which includes the capacitor  92  and the electric transmitting coil  82 , thereby generating lines  122  of magnetic flux (see  FIG. 5 ) and retaining resonant energy. 
         [0056]    As shown in  FIG. 4 , the relay  66  is excited by a second wireless coupling  402 , which comprises at least one of a wireless coupling  202  according to an electromagnetic induction process and a wireless coupling  302  according to a resonant process, based on the lines  122  of magnetic flux. At this time, high-frequency electric power is transmitted from the resonator  102  of the electric transmitting device  80  underneath the road surface  104 , and the high-frequency electric power is received by the relay  66  of the vehicular electric receiver  110 . 
         [0057]      FIG. 5  schematically illustrates the manner in which the electric transmitting coil  82  and the second coil  72  are coupled to each other through the lines  122  of magnetic flux. 
         [0058]    Since the electric transmitting coil  82  of the electric transmitting device  80 , which is disposed underneath the road surface  104 , and the second coil  72  of the relay  66 , which is disposed on the vehicle underfloor panel outside of the vehicle body  16 , are spaced from each other by a relatively large distance and have a small mutual inductance, the coupling strength k therebetween is small. However, since the respective inductances of the electric transmitting coil  82  and the second coil  72  are large, the index Q=ωLs/r (in particular, the index of energy retained by the electric transmitting coil  82 , where ω represents an angular frequency, Ls represents the inductance of the electric transmitting coil  82 , and r represents the sum of a resistive component and a radiation resistive component of the electric transmitting coil  82 ) is large. Inasmuch as the respective retained energies are large, the efficiency at which electric power is transmitted from the electric transmitting device  80  to the relay  66  is increased. The indexes Q of the second coil  72  and the first coil  71  of the relay  66  (the inductance value of the second coil  72 &gt;the inductance value of the first coil  71 ) also are required to be large. In other words, it is necessary to increase inductive components and to reduce resistive components as much as possible in order to maximize retained energies and to minimize electric power losses caused by the resistive components when high-frequency current flows through the relay  66 . 
         [0059]    A process of transmitting and receiving electric power between the relay  66  and the electric receiving device  40  will be described below. Interlinking lines  121  of magnetic flux between the first coil  71  of the relay  66  disposed above the vehicle underfloor panel  18  (i.e., inside the vehicle body  16 ) and the electric receiving coil  81  of the electric receiving device  40  provide a large coupling strength k, i.e., k=M(L 1 ·Lr) 1/2 =M√L 1 ·Lr where L 1  represents the inductance of the first coil  71 , Lr represents the inductance of the electric receiving coil  81 , and M represents the mutual inductance, because the first coil  71  and the electric receiving coil  81  are positioned in close proximity to each other. As a result, due to the high mutual inductance therebetween, the first coil  71  and the electric receiving coil  81  are coupled to each other highly efficiently by an electromagnetic induction wireless coupling  201  based on the lines  121  of magnetic flux. Furthermore, the relay  66  and the resonator  101  of the electric receiving device  40  are coupled to each other by a resonance wireless coupling  301 . In other words, the relay  66  and the resonator  101  are coupled to each other by the first wireless coupling  401 , which comprises at least one of the electromagnetic induction wireless coupling  201  and the resonance wireless coupling  301 . 
         [0060]    Since the indexes Q of the second coil  72  and the first coil  71  of the relay  66 , which function as electric transmitting coils, are high, the resonance wireless coupling  301  is capable of transmitting electric power highly efficiently. 
         [0061]    Therefore, electric power is transmitted from the relay  66  to the electric receiving device  40  by the first wireless coupling  401 , which comprises at least one of the electromagnetic induction wireless coupling  201  based on the lines  121  of magnetic flux and the resonance wireless coupling  301 , and the electric power is received by the electric receiving device  40 . 
         [0062]    Since the figure of merit k·Q of the relay  66  is large, the overall electric power transmission efficiency at which electric power is transmitted from the electric transmitting device  80  underneath the road surface  104 , through the relay  66  outside of the vehicle body  16 , and to the electric receiving device  40  within the vehicle body  16  is kept high. 
         [0063]    A voltage developed across the resonator  101  of the electric receiving device  40  is applied through the resistor  84  to the rectifier  43 , which converts the voltage into a DC voltage. The DC voltage then is applied to the charger  44 , which charges the electric storage device  12 . If necessary, a DC/DC booster converter may be connected to an input side of the charger  44 . 
         [0064]    While the electric vehicle  10  is traveling, a high DC voltage, which is output from the charged electric storage device  12 , is converted by the VCU  38  into a higher DC voltage, which is converted by the inverter  36  into a three-phase AC drive signal to energize the electric motor  30 . Rotational torque (rotation) generated by the electric motor  30  is transmitted through the gearbox  32  and a drive shaft to the front road wheels  50 , thereby propelling the electric vehicle  10 . Regenerative electric power generated by the electric motor  30  is supplied through the VCU  38  in order to charge the electric storage device  12 . 
         [0065]    The high DC voltage from the charged electric storage device  12  is converted by the downverter  42  into a lower DC voltage, which is supplied to the EWP  24 . The EWP  24  circulates a coolant for carrying out heat exchange for cooling the electric motor  30  through the radiator  22 . The gearbox  32  is cooled by oil that is splashed up by rotation of the electric motor  30 . The oil is cooled by a pipe inside the electric motor  30  through which the coolant flows. 
         [0066]    As described above, the electric vehicle  10  according to the present embodiment is propelled by drive power from the electric motor  30 , which is energized by electric power from the electric storage device  12 . 
         [0067]    The electric vehicle  10  includes the electric receiving coil  81 , which is disposed above the vehicle underfloor panel  18  for supplying electric power to the electric storage device  12 , and the relay  66  for transmitting electric power from the electric transmitting coil  82 , which is disposed underneath the road surface  104 , to the electric receiving coil  81  through the second wireless coupling  402  and the first wireless coupling  401 . The second wireless coupling  402  and the first wireless coupling  401  each comprise at least one of an electromagnetic induction wireless coupling and a resonant wireless coupling. 
         [0068]    The relay  66  includes a resonant circuit made up of the first coil  71 , the second coil  72 , and the capacitors  64 . The first coil  71  and the electric receiving coil  81  jointly constitute the first wireless coupling  401 , and the second coil  72  and the electric transmitting coil  82  jointly constitute the second wireless coupling  402 . 
         [0069]    In order to increase the coupling strength k (k=M/√L 1 ·Lr) of the first wireless coupling  401  and the coupling strength k (k=M′/√Ls·L 2 ) of the second wireless coupling  402 , the first coil  71  is disposed above the vehicle underfloor panel  18  and beneath the electric receiving coil  81 . 
         [0070]    The second coil  72  is disposed beneath the lower surface of the vehicle underfloor panel  18 . The index Q of the second wireless coupling  402  concerning energy retained thereby (in particular, the index Q=ωLs/r of the electric transmitting coil  82  concerning energy retained thereby, where ω represents an angular frequency, Ls represents the inductance of the electric transmitting coil  82 , and r represents the sum of a resistive component and a radiation resistive component of the electric transmitting coil  82 ) is higher than the index Q of the first wireless coupling  401  concerning energy retained thereby (in particular, the index Q=ω(L 2 +L 1 )/r of the second coil  72  and the first coil  71  on the transmission side concerning energy retained thereby). 
         [0071]    According to the present embodiment, since the index Q of the electric transmitting coil  82  underneath the road surface  104  and the second coil  72  of the relay  66  of the second wireless coupling  402  concerning energy retained therebetween is increased, and the first coil  71  of the relay  66  and the electric receiving coil  81  of the electric receiving device  40  are positioned in close proximity to each other, the coupling strength k is increased. As a result, even if the electric vehicle  10  and the road surface  104  are distant from each other, the electric storage device  12  can be charged through the relay  66  with high electric power transmission efficiency. Consequently, the figure of merit k·Q of the path from the electric transmitting coil  82  underneath the road surface  104  to the electric receiving coil  81  of the electric vehicle  10  can be increased. 
         [0072]    Since the electric receiving coil  81  and the first coil are aligned coaxially with each other, the coupling strength k is increased. 
         [0073]    In order to increase the coupling strength k of the first wireless coupling  401 , the first coil  71  is disposed above the vehicle underfloor panel  18  and below the electric receiving coil  81  in close coaxial alignment with the electric receiving coil  81 . In order to increase the index Q of the resonant circuit of the second wireless coupling  402 , the second coil  72  is disposed underneath the vehicle underfloor panel  18 , while additionally, the closed-path area A 2  defined by the second coil  72  is greater than the closed-path area A 1  defined by the first coil  71 . 
         [0074]    The wireless coupling electric transmitting and receiving system  200 , which is incorporated in the electric vehicle  10 , is constructed as described above. Since the inductance of the second coil  72  is increased, the index Q of the relay  66  is increased. Furthermore, since the first coil  71  and the electric receiving coil  81  are disposed in proximity to each other, the coupling strength k is increased. As a consequence, the figure of merit k·Q, which contributes to the wireless coupling between the electric transmitting device  80  and the electric receiving device  40 , is increased. 
         [0075]    Inasmuch as the capacitors  64  of the relay  66  are disposed above the vehicle underfloor panel  18 , capacitors, which are less durable than coils, are disposed within the vehicle. Accordingly, the selection of components is facilitated. 
         [0076]    According to the present embodiment, the electric vehicle  10 , which receives electric power from the road surface  104  through the wireless couplings  402 ,  401 , has a clarified optimum layout of the relay  66  as a resonator and the electric receiving coil  81 . As a result, the figure of merit k·Q is increased. Even if the vehicle underfloor panel  18  of the electric vehicle  10  and the road surface  104  are distant from each other, the electric storage device  12  can be charged through the relay  66  with high electric power transmission efficiency. 
         [0077]    The present invention is not limited to the above embodiment. The present invention also is applicable to a hybrid vehicle including an electric motor and an engine in combination. Various other arrangements can also be adopted based on the descriptive content of the present invention.