Patent Publication Number: US-2015061402-A1

Title: Power reception device, power transmission device and power transfer system

Description:
This nonprovisional application is based on Japanese Patent Application No. 2013-178104 filed on Aug. 29, 2013 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power reception device, a power transmission device and a power transfer system, and particularly to a power transfer system transferring electric power from a power transmission device to a power reception device in a contactless manner, and the power reception device and the power transmission device used therefor. 
     2. Description of the Background Art 
     Japanese Patent Laying-Open No. 2013-121258 discloses a contactless power transfer device transferring electric power in a contactless manner. This contactless power transfer device includes a power transmitter and a power receptor. Each of the power transmitter and the power receptor includes a plate-shaped ferrite core; a coil wound around the plate-shaped ferrite core in a spiral manner; and a capacitor (condenser) connected in parallel with the coil (see Japanese Patent Laying-Open No. 2013-121258). 
     The capacitor and other devices (for example, a cooler, a rectifier, a filter, and the like) electrically connected to the coil may be disposed near a coil unit formed of a core and a coil. When these devices are disposed around the coil unit, the power transmitter and the power receptor are increased in physical size. Furthermore, the electrical device disposed around the coil unit may be adversely influenced by the high-intensity electromagnetic field generated at the time of power transfer. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a power reception device, a power transmission device and a power transfer system that are configured to transfer electric power in a contactless manner, for allowing reduction in a physical size of each of the power reception device and the power transmission device and also allowing suppression of the influence of the electromagnetic field generated during power transfer upon an electrical device. 
     According to the present invention, a power reception device includes a coil through which electric power output from a power transmission device is received in a contactless manner; and a core around which the coil is wound. The core includes a plate-shaped first core unit and a plate-shaped second core unit disposed so as to face the first core unit at a distance from the first core unit. The coil is wound around the first core unit and the second core unit so as to extend over the first core unit and the second core unit. 
     Preferably, the power reception device further includes a device disposed in a space between the first core unit and the second core unit. 
     Further preferably, the device is an electrical device electrically connected to the coil. 
     Preferably, the distance between the first core unit and the second core unit is equal to or greater than a total value of a thickness of the first core unit and a thickness of the second core unit. 
     Preferably, the power reception device further includes a housing in which the coil and the core are housed, and a plurality of devices provided within the housing. 
     All of the plurality of devices are disposed in a space between the first core unit and the second core unit. 
     Preferably, the first core unit and the second core unit are plate-shaped members formed separately from each other. 
     Further preferably, the core is formed in a square tubular shape. The first core unit and the second core unit are opposing walls of the core formed in the square tubular shape. 
     Furthermore, according to the present invention, a power transmission device includes a coil through which electric power is transmitted to a power reception device in a contactless manner; and a core around which the coil is wound. The core includes a plate-shaped first core unit and a plate-shaped second core unit disposed so as to face the first core unit at a distance from the first core unit. The coil is wound around the first core unit and the second core unit so as to extend over the first core unit and the second core unit. 
     Preferably, the power transmission device further includes a device disposed in a space between the first core unit and the second core unit. 
     Further preferably, the device is an electrical device electrically connected to the coil. 
     Preferably, the distance between the first core unit and the second core unit is equal to or greater than a total value of a thickness of the first core unit and a thickness of the second core unit. 
     Preferably, the power transmission device further includes a housing in which the coil and the core are housed; and a plurality of devices provided within the housing. All of the plurality of devices are disposed in a space between the first core unit and the second core unit. 
     Preferably, the first core unit and the second core unit are plate-shaped members formed separately from each other. 
     Further preferably, the core is formed in a square tubular shape. The first core unit and the second core unit are opposing walls of the core formed in the square tubular shape. 
     Furthermore, according to the present invention, a power transfer system includes a power transmission device and a power reception device. The power transmission device includes a first coil through which electric power is transmitted to the power reception device in a contactless manner, and a first core around which the first coil is wound. The power reception device includes a second coil through which electric power output from the power transmission device is received in a contactless manner, and a second core around which the second coil is wound. The first core and the second core each include a plate-shaped first core unit, and a plate-shaped second core unit disposed so as to face the first core unit at a distance from the first core unit. The first coil and the second coil each are wound around the first core unit and the second core unit so as to extend over the first core unit and the second core unit. 
     As described above, according to the present invention, a coil is wound around the plate-shaped first and second core units so as to extend over these first and second core units disposed so as to face each other at a distance from each other, thereby forming a low electromagnetic field region in the space between the first core unit and the second core unit. Thus, a capacitor and other devices can be housed in the space between the first core unit and the second core unit. Therefore, according to the present invention, the power transmission device and the power reception device can be reduced in physical size while the electrical device can be less influenced by the electromagnetic field generated at the time of power transfer. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an entire configuration diagram of a power transfer system according to the first embodiment of the present invention. 
         FIG. 2  is a plan view of a vehicle showing a planar arrangement of a power reception unit. 
         FIG. 3  is a diagram of an electrical circuit implementing contactless power transfer in the power transfer system shown in  FIG. 1 . 
         FIG. 4  is a perspective view of a coil unit of the power reception unit. 
         FIG. 5  is a cross-sectional view taken along an arrow line V-V in  FIG. 4 . 
         FIG. 6  is a diagram for illustrating an electromagnetic field formed at the time of power transfer from a power transmission unit to the power reception unit. 
         FIG. 7  is a diagram showing a change in a coupling coefficient in the case where a gap between the first core and the second core is changed in the coil unit. 
         FIG. 8  is a plan view of the power reception unit in the first embodiment. 
         FIG. 9  is a cross-sectional view taken along an arrow line XI-XI in  FIG. 8 . 
         FIG. 10  is a plan view of a power reception unit in the second embodiment. 
         FIG. 11  is a cross-sectional view of a coil unit of a power reception unit in the third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be hereinafter described in detail with reference to the accompanying drawings. In the following, although a plurality of embodiments will be described, it has been originally intended to combine the configurations described in each embodiment as appropriate in the present application. In the drawings, the same or corresponding components are designated by the same reference characters, and description thereof will not be repeated. 
     [First Embodiment] 
     (Configuration of Power Transfer System) 
       FIG. 1  is an entire configuration diagram of a power transfer system according to the first embodiment of the present invention. Referring to  FIG. 1 , this power transfer system includes a vehicle  10  and a power transmission device  20 . Vehicle  10  includes a power reception unit  100 , a rectifier circuit  200 , a power storage device  300 , a motive power generation device  400 , and a vehicle ECU (Electronic Control Unit)  500 . 
     Power reception unit  100  includes a coil through which electric power (alternating current) output from a power transmission unit  700  (described later) of power transmission device  20  is received in a contactless manner. Power reception unit  100  outputs the received electric power to rectifier circuit  200 . In this first embodiment, power transmission device  20  is provided on the surface of the ground or in the ground while power reception unit  100  is provided in the lower part of the vehicle body and closer to the forward part of the vehicle body. As shown in the plan view of the vehicle in  FIG. 2 , power reception unit  100  is provided approximately in the center of the vehicle body in the width direction thereof (a line C shows the center line of the vehicle body in  FIG. 2 ). 
     It is to be noted that the position of power reception unit  100  to be placed is not limited to the above. For example, power reception unit  100  may be disposed in the lower part of the vehicle body and closer to the rearward part of the vehicle body. If power transmission device  20  is provided above the vehicle, power reception unit  100  may be provided in the upper part of the vehicle body. The detailed configuration of power reception unit  100  will be described later. 
     Again referring to  FIG. 1 , rectifier circuit  200  rectifies the AC (alternating-current) power received by power reception unit  100  and outputs the rectified power to power storage device  300 . Although not shown in  FIG. 1 , a filter is provided between power reception unit  100  and rectifier circuit  200 . It is to be noted that this filter is not an indispensable component, but may be provided as required. 
     Power storage device  300  is a rechargeable DC (direct-current) power supply and is configured of a secondary battery such as a lithium-ion battery or a nickel-metal hydride battery, for example. The voltage of power storage device  300  is, for example, approximately 200V. Power storage device  300  stores electric power output from rectifier circuit  200 , and also stores the electric power generated by motive power generation device  400 . Then, power storage device  300  supplies the stored electric power to motive power generation device  400 . It is to be noted that a large capacity capacitor can also be employed as power storage device  300 . Although not particularly shown, a DC-DC converter adjusting the output voltage of rectifier circuit  200  may be provided between rectifier circuit  200  and power storage device  300 . 
     Motive power generation device  400  generates driving power for running of vehicle  10  using the electric power stored in power storage device  300 . Although not particularly shown, motive power generation device  400 , for example, includes an inverter receiving electric power from power storage device  300 , a motor driven by the inverter, driving wheels driven by the motor, and the like. In addition, motive power generation device  400  may also include a power generator for charging power storage device  300  and an engine capable of driving the power generator. 
     Vehicle ECU  500  includes a CPU (Central Processing Unit), a storage device, an input/output buffer, and the like (each of which is not shown). This vehicle ECU  500  inputs the signals from various sensors and outputs the control signal to each device while controlling each device in vehicle  10 . By way of example, vehicle ECU  500  performs running control of vehicle  10 , and charging control of power storage device  300 . It is to be noted that the above-described control is not limited to the process by software, but can be carried out by dedicated hardware (an electronic circuit). 
     Power transmission device  20  includes a power supply unit  600 , a power transmission unit  700  and a power supply ECU  800 . Power supply unit  600  receives electric power from an external power supply  900  such as a commercial system power supply, and generates AC power having a prescribed transmission frequency. Power supply unit  600  supplies the generated AC power to power transmission unit  700 . By way of example, power supply unit  600  includes a rectification unit rectifying the electric power from external power supply  900 , and a single-phase inverter generating AC power having a transmission frequency (each of which is not shown). It is to be noted that the rectification unit is not required when external power supply  900  is a DC power supply. The single-phase inverter is configured by a full-bridge circuit, for example. 
     Power transmission unit  700  includes a coil through which electric power is transmitted to power reception unit  100  of vehicle  10  in a contactless manner. Power transmission unit  700  receives the AC power having a transmission frequency from power supply unit  600 , and transmits the received AC power to power reception unit  100  of vehicle  10  in a contactless manner through the electromagnetic field generated around power transmission unit  700 . Although not shown in  FIG. 1 , a filter is provided between power supply unit  600  and power transmission unit  700 . This filter is not an indispensable component, but may be provided as required. 
     Power supply ECU  800  includes a CPU, a storage device, an input/output buffer, and the like (each of which is not shown). This Power supply ECU  800  inputs the signals from various sensors and outputs the control signal to each device while controlling each device in power transmission device  20 . By way of example, power supply ECU  800  carries out switching control of power supply unit  600  so as to cause power supply unit  600  (inverter) to generate AC power having a transmission frequency. It is to be noted that the above-described control is not limited to the process by software, but can be carried out by dedicated hardware (an electronic circuit). 
       FIG. 3  is a diagram of an electrical circuit implementing contactless power transfer in the power transfer system shown in  FIG. 1 . It is to be noted that the circuit configuration shown in this  FIG. 3  is merely by way of example, and the configuration for implementing contactless power transfer is not limited to the configuration in  FIG. 3 . 
     Referring to Fig,  3 , power reception unit  100  of vehicle  10  includes a coil unit  110  and a capacitor  120 . Coil unit  110  receives electric power from power transmission unit  700  of power transmission device  20  in a contactless manner, and outputs the received electric power to a filter  150 . Capacitor  120  is connected in series to coil unit  110  to form an LC resonance circuit together with coil unit  110 . Capacitor  120  is provided for adjusting the resonance frequency of power reception unit  100 . Capacitor  120  may be connected in parallel with coil unit  110 . It is to be noted that capacitor  120  does not have to be provided in the case where a desired resonance frequency can be obtained utilizing the stray capacitance of coil unit  110 . 
     A voltage sensor  130  detects the voltage of power reception unit  100 , and outputs the detected value to vehicle ECU  500 . A current sensor  140  detects the current of power reception unit  100 , and outputs the detected value to vehicle ECU  500 . 
     Filter  150  is provided between power reception unit  100  and rectifier circuit  200 . Filter  150  suppresses the harmonic noise generated from rectifier circuit  200  during reception of electric power from power transmission device  20 . By way of example, filter  150  is formed of an LC filter including a capacitor connected in parallel with power reception unit  100  and a coil provided between one end of the connection node of the capacitor and rectifier circuit  200 . 
     A relay  210  is provided between rectifier circuit  200  and power storage device  300 . Relay  210  is turned on by vehicle ECU  500  while power storage device  300  is charged by power transmission device  20 . A system main relay (SMR)  310  is provided between power storage device  300  and motive power generation device  400 . SMR  310  is turned on by vehicle ECU  500  when startup of motive power generation device  400  is requested. 
     In addition, vehicle ECU  500  communicates with power transmission device  20  using a communication device  510  while power storage device  300  is charged by power transmission device  20 , and exchanges information about start/stop of charging, power receiving conditions of vehicle  10  and the like with power transmission device  20 . 
     In contrast, power transmission unit  700  of power transmission device  20  includes a coil unit  710  and a capacitor  720 . Coil unit  710  transmits electric power supplied from power supply unit  600  to power reception unit  100  of vehicle  10  in a contactless manner. Capacitor  720  is connected in series to coil unit  710  to form an LC resonance circuit together with coil unit  710 . Capacitor  720  is provided for adjusting the resonance frequency of power transmission unit  700 . Capacitor  720  may be connected in parallel with coil unit  710 . In addition, capacitor  720  does not have to be provided in the ease where a desired resonance frequency can be obtained utilizing the stray capacitance of coil unit  710 . 
     A filter  610  is provided between power supply unit  600  and power transmission unit  700 . Filter  610  suppresses the harmonic noise generated from power supply unit  600 . By way of example, filter  610  is formed of an LC filter including a capacitor connected in parallel with power supply unit  600  and a coil provided between one end of the connection node of the capacitor and power supply unit  600 . 
     In addition, at the time of power transmission to vehicle  10 , power supply ECU  800  communicates with vehicle  10  using communication device  810 , and exchanges information about start/stop of charging, power receiving conditions of vehicle  10  and the like with vehicle  10 . 
     Although not particularly shown, power transmission device  20  is also provided with a voltage sensor and a current sensor for detecting transmitted electric power. These voltage sensor and current sensor may be provided between filter  610  and power transmission unit  700 , or may be provided within power supply unit  600 . 
     In power transmission device  20 , AC power is supplied from power supply unit  600  through filter  610  to coil unit  710 . This causes energy (electric power) to be transferred from coil unit  710  to coil unit  110  through the electromagnetic field formed between coil unit  710  and coil unit  110  of vehicle  10 . The energy (electric power) transferred to coil unit  110  is supplied to power storage device  300  through filter  150  and rectifier circuit  200 . 
     As described above, coil unit  710  forms an LC resonance circuit together with capacitor  720  in power transmission unit  700  of power transmission device  20 . Also in power reception unit  100  of vehicle  10 , coil unit  110  forms an LC resonance circuit together with capacitor  120 . It is preferable that the difference between the resonance frequency of power transmission unit  700  and the natural frequency of power reception unit  100  is, for example, equal to or less than ±10% of the natural frequency of power transmission unit  700  or the natural frequency of power reception unit  100 . Then, coil unit  710  receives electric power from power supply unit  600 , and transmits the received electric power to power reception unit  100  of vehicle  10  in a contactless manner. Coil unit  110  of power reception unit  100  receives electric power from coil unit  710  of power transmission unit  700  in a contactless manner. 
     Although not particularly shown, in power transmission device  20 , an isolation transformer may be provided between power transmission unit  700  and power supply unit  600  (for example, between power transmission unit  700  and filter  610 ). Furthermore, also in vehicle  10 , an isolation transformer may be provided between power reception unit  100  and rectifier circuit  200  (for example, between power reception unit  100  and filter  150 ). 
     (Configuration of Coil Unit) 
       FIG. 4  is a perspective view of coil unit  110  of power reception unit  100 .  FIG. 5  is a cross-sectional view taken along an arrow line V-V in  FIG. 4 . Coil unit  710  of power transmission unit  700  is also similar in configuration to coil unit  110 . In these  FIGS. 4 and 5 , the configuration of coil unit  110  will be representatively described. Since the description of the configuration of coil unit  710  is the same as that of coil unit  110  described below, the description thereof will not be repeated. In the figures, “X” indicates the direction in which the vehicle moves forward, “Y” indicates the leftward direction of the vehicle, and “Z” indicates the upward direction of the vehicle. In addition, “Y” may indicate the direction in which vehicle moves forward, and “X” may indicate the rightward direction of the vehicle. 
     Referring to  FIGS. 4 and 5 , coil unit  110  includes a core  113  and a coil.  114 . Core  113  is formed of a first core  111  and a second core  112 . First core  111  and second core  112  each are formed of a magnetic material, and representatively formed of ferrite, but may be formed of a magnetic material other than ferrite. Each of first core  111  and second core  112  is formed in a shape of a plate having a thickness D, for example, and has a rectangular shape as seen in a plan view along the Z-axis direction. 
     First core  111  is disposed so as to extend along the X-Y plane. Second core  112  is provided above first core  111  in the vehicle body (in the Z-axis positive direction) and disposed so as to face first core  111  while leaving a gap AG from first core  111 . 
     Coil  114  is electrically connected to capacitor  120  and filter  150  (not shown). Coil  114  is spirally wound around first core  111  and second core  112  about the X-axis direction as an axis around which coil  114  is wound, such that coil  114  extends over first core  111  and second core  112 . In other words, coil  114  does not exist in the space between first core  111  and second core  112 , but is wound so as to extend over first core  111  and second core  112  at the end faces of these first core  111  and second core  112  in the Y-axis direction, 
     In addition, while  FIG. 4  does not describe each winding of coil  114  in detail, coil  114  is specifically formed in a spiral shape so as to surround first core  111  and second core  112  and extend in the X-axis direction, as coil  114  is wound from one end to the other end. Furthermore, although not shown, coil unit  110  is housed in the housing (case). 
       FIG. 6  is a diagram for illustrating an electromagnetic field formed at the time of power transfer from power transmission unit  700  to power reception unit  100 . Referring to  FIG. 6 , coil unit  710  of power transmission unit  700  includes a first core  711 , a second core  712  and a coil  714 . 
     When a current is supplied to coil  714  of coil unit  710 , an electromagnetic field of high intensity is formed inside first core  711  and second core  712  each formed of a magnetic material. Accordingly, an electromagnetic field oscillating with a transmission frequency is formed between coil unit  110  of power reception unit  100  and each of first core  711  and second core  712 , thereby forming an electromagnetic field of high intensity inside first core  111  and second core  112  each formed of a magnetic material. This induces a current in coil  114  and electric power is extracted from coil  114 . 
     In this way, in coil unit  110 , an electromagnetic field of high intensity is formed inside first core  111  and second core  112  while the intensity of the electromagnetic field in the space between first core  111  and second core  112  is relatively low. Similarly, in coil unit  710 , an electromagnetic field of high intensity is formed inside first core  711  and second core  712 , while the intensity of the electromagnetic field in the space between first core  711  and second core  712  is relatively low. Thus, according to this first embodiment, a device such as a capacitor is disposed in a region of power reception unit  100  that is formed between first core  111  and second core  112  of coil unit  110 , and also in a region of power transmission unit  700  that is formed between first core  711  and second core  712  of coil unit  710 , as described later. Consequently, the space between the first core and the second core is used as a place in which a device such as a capacitor is arranged, so that each of power reception unit  100  and power transmission unit  700  can be reduced in physical size while the electrical device can be less influenced by the electromagnetic field generated during power transfer from power transmission unit  700  to power reception unit  100 . 
       FIG. 7  is a diagram showing a change in a coupling coefficient κ in the case where a gap AG between the first core and the second core is changed in the coil unit. In this case, the size of gap AG is set to be the same in power transmission unit  700  and power reception unit  100  (changed by the same amount). Furthermore, as a comparative example, the figure also shows a change in coupling coefficient x at the time when a thickness TT is changed in the case where the core is formed of one core having thickness TT ( FIG. 5 ). 
     Referring to  FIG. 7 , the horizontal axis shows the sum of gap AG, the thickness of the first core and the thickness of the second core (in the comparative example, the horizontal axis shows thickness TT of the core). The vertical axis shows coupling coefficient K. A line Li shows a change in coupling coefficient κ in this first embodiment while a line L 2  shows a change in coupling coefficient κ in the comparative example. It is to be noted that “efficiency 90%” shows a line obtained when the efficiency of power transfer from the power transmission unit to the power reception unit is 90% while “efficiency 95%” shows a line obtained when the efficiency of power transfer from the power transmission unit to the power reception unit is 95%. 
     As shown in the figure, even if the core is formed of the first core and the second core each formed in a shape of a plate, and gap AG is provided between the first core and the second core, a significant decrease in each of the coupling coefficient and the power transfer efficiency is not observed, as compared with the case of the conventional-type core shown in the comparative example. By way of example, even if gap AG is set to be equal to or greater than a total value of the thickness of the first core and the thickness of the second core, a significant decrease in each of the coupling coefficient and the power transfer efficiency is not observed. Even if gap AG is increased at least to approximately  4  times as the total value of the thickness of the first core and the thickness of the second core, a significant decrease in each of the coupling coefficient and the power transfer efficiency is not observed. 
       FIG. 8  is a plan view of power reception unit  100  in this first embodiment.  FIG. 9  is a cross-sectional view taken along an arrow line XI-XI in  FIG. 8 . Power transmission unit  700  is also similar in configuration to power reception unit  100 . Also in these  FIGS. 8 and 9 , the configuration of power reception unit  100  will be representatively described. Since the description of the configuration of power transmission unit  700  is the same as that of power reception unit  100  described below, the description thereof will not be repeated. 
     Referring to  FIGS. 8 and 9 , capacitor  120  is disposed in a region formed between first core  111  and second core  112 . As described above, since the electromagnetic field intensity of the space between first core  111  and second core  112  is relatively low, capacitor  120  is to be disposed in this region. Consequently, power reception unit  100  is reduced in physical size while capacitor  120  is less influenced by the electromagnetic field generated during power transfer from power transmission unit  700  to power reception unit  100 . 
     In addition, a power line  121  has one end connected to one end of coil  114  and the other end (not shown) connected to filter  150  ( FIG. 3 ). A power line  122  has one end connected to the other end of coil  114  and the other end connected to one end of capacitor  120 . A power line  123  has one end connected to the other end of capacitor  120  and the other end (not shown) connected to filter  150 . Power lines  121  and  123  are extended from power reception unit  100  while being located in proximity to each other. This allows easy wiring between power reception unit  100  and filter  150 . 
     It is preferable that capacitor  120  is formed relatively thin in consideration of the fact that it is disposed in a region formed between first core  111  and second core  112 . By way of example, capacitor  120  is formed of a substrate, a wiring circuit formed on the surface of the substrate, and a plurality of ceramic condensers provided on the wiring circuit. By such a configuration, capacitor  120  can also be formed thin so as to have a thickness of about several millimeters, and therefore, can be disposed in a region formed between first core  111  and second core  112 . Furthermore, when a strong electromagnetic field is applied to the capacitor having such a configuration, the wiring circuit may be raised in temperature. In this first embodiment, however, since capacitor  120  is disposed in a region of a low electromagnetic field formed between first core  111  and second core  112 , there occurs no such a problem that the wiring circuit is raised in temperature. In addition, when a relatively larger gap AG is provided between first core  111  and second core  112 , capacitor  120  is not necessarily limited to the configuration as described above. 
     Although power transmission unit  700  is not particularly shown, capacitor  720  ( FIG. 3 ) is disposed in a region formed between first core  711  and second core  712 . Consequently, power transmission unit  700  is reduced in physical size while capacitor  720  is less influenced by the electromagnetic field generated during power transfer from power transmission unit  700  to power reception unit  100 . 
     As described above, according to this first embodiment, in power reception unit  100  of vehicle  10 , coil  114  is wound around plate-shaped first core  111  and second core  112  so as to extend over these first core  111  and second core  112  disposed to face each other at a distance from each other, thereby forming a region of a low electromagnetic field in the space between first core  111  and second core  112 . Then, capacitor  120  is housed in the space between first core  111  and second core  112 . Therefore, according to this first embodiment, power reception unit  100  can be reduced in physical size while capacitor  120  can be less influenced by the electromagnetic field generated during power transfer. 
     Furthermore, according to this first embodiment, also in power transmission unit  700  of power transmission device  20 , coil  714  is wound around plate-shaped first core  711  and second core  712  so as to extend over these first core  712  and second core  712  disposed to face each other at a distance from each other, thereby forming a region of a low electromagnetic field in the space between first core  711  and second core  712 . Then, capacitor  720  is housed in the space between first core  711  and second core  712 . Therefore, according to this first embodiment, power transmission unit  700  can be reduced in physical size while capacitor  720  can be less influenced by the electromagnetic field generated during power transfer. 
     [Second Embodiment] 
     In the second embodiment, not only a capacitor but also other devices are housed within a case in which the coil unit is housed. Then, devices other than the capacitor are also arranged together with the capacitor in the region formed between the first core and the second core. 
     The entire configuration and the electrical circuit configuration of the power transfer system in the second embodiment are the same as those in the above-described first embodiment. 
       FIG. 10  is a plan view of a power reception unit in the second embodiment. The power transmission unit of power transmission device  20  is also similar in configuration to the power reception unit. In this  FIG. 10 , the configuration of the power reception unit will be representatively described. Since the detailed description of the configuration of the power transmission unit is the same as that of the power reception unit described below, the description thereof will not be repeated. 
     Referring to  FIG. 10 , in a power reception unit  100 A in the second embodiment, coil unit  110  is housed in a case (housing)  180 . In addition to capacitor  120 , case  180  further houses a voltage sensor  130 , a current sensor  140 , a filter  150 , a cooling device  160 , and other devices  170 . All of the devices housed in case  180  are arranged between first core  111  and second core  112  that form core  113 . In this way, each of the devices housed in case  180  is arranged in the region between first core  111  and second core  112 , so that power reception unit  100 A can be reduced in physical size. Furthermore, since coil unit  110  can be arranged bilaterally symmetrically in the X-axis direction within case  180 , power reception unit  100 A and the power transmission unit of power transmission device  20  can be readily aligned with each other at the time of parking. 
     It is to be noted that various devices that may be housed in case  180  are collectively indicated as devices  170 . For example, devices  170  may include rectifier circuit  200  ( FIG. 3 ). Alternatively, devices  170  may also include relay  210 , a fuse, a cooling duct, and the like. Furthermore, although capacitor  120  and rectifier circuit  200  are electrically connected to coil  114 , the devices arranged between first core  111  and second core  112  are not limited to those electrically connected to coil  114 , but may also include voltage sensor  130 , current sensor  140 , cooling device  160 , and the like. 
     It is to be noted that the devices housed in case  180  and arranged between first core  111  and second core  112  are not limited to those described above, but may be a part of the above-described devices, or may also include still other devices. Furthermore, although it is preferable that all of the devices housed in case  180  are arranged between first core  111  and second core  112 , all of the devices housed in case  180  are not necessarily arranged between first core  111  and second core  112 . 
     Although not particularly shown, also in the power transmission unit of power transmission device  20 , coil unit  710  is housed in the case, and all of the devices housed in the case are arranged between first core  711  and second core  712 . In addition to capacitor  720 , for example, such devices may include filter  610  ( FIG. 3 ), a voltage sensor, a current sensor, a cooling device, a cooling duct, a relay, a fuse, and the like. Although it is preferable that all of the devices housed in the case are arranged between first core  711  and second core  712 , all of the devices housed in the case are not necessarily arranged between first core  711  and second core  712 . 
     As described above, according to this second embodiment, since various devices housed in the case are housed in the space between the first core and the second core, the power reception unit and the power transmission unit each can be reduced in physical size. Furthermore, all of the devices housed in the case are housed in the space between the first core and the second core, thereby eliminating the need to ensure the space around the coil unit for allowing each device to be arranged therein. Accordingly, the coil unit can be arranged bilaterally symmetrically in the X-axis direction. Therefore, according to this second embodiment, alignment between the power transmission unit and the power reception unit (alignment of vehicle  10  with power transmission device  20 ) can be readily achieved. 
     [Third Embodiment] 
     In the first and second embodiments, the core of the coil unit is formed of the plate-shaped first and second cores disposed so as to face each other at a distance from each other. In contrast, in this third embodiment, the core of the coil unit is formed of a core in a square tubular shape. 
     The entire configuration and the electrical circuit configuration of the power transfer system in this third embodiment are the same as those in the above-described first and second embodiments. 
       FIG. 11  is a cross-sectional view of a coil unit of a power reception unit in the third embodiment. This cross-sectional view corresponds to the cross-sectional view shown in  FIG. 5 . In addition, the coil unit of the power transmission unit is also similar in configuration to the coil unit of the power reception unit, In this  FIG. 11 , the configuration of the coil unit of the power reception unit will be representatively described. Since the detailed description of the configuration of the coil unit in the power transmission unit is the same as that of the coil unit in the power reception unit described below, the description thereof will not be repeated. 
     Referring to  FIG. 11 , a coil unit  110 A includes a first core  111 A, a second core  112 A and a coil  114 . First core  111 A has edge portions at its both ends in the Y-axis direction that extend in the Z-axis positive direction in the configuration of the plate-shaped first core  111  shown in  FIG. 5 . Second core  112 A has edge portions at its both ends in the Y-axis direction that extend in the Z-axis negative direction in the configuration of the plate-shaped second core  112  shown in  FIG. 5 . Thus, the above-described edge portions of first core  111  A and the above-described edge portions of second core  112 A form sidewalls  116  and  117 . In other words, first core  111 A and second core  112 A form a core in a square tubular shape having an inner space. 
     Also according to such a configuration, the intensity of the electromagnetic field is relatively lower in the region between the plate-shaped portion of first core  111 A and the plate-shaped portion of second core  112 A, that is, the region surrounded by first core  111 A and second core  112 A, as in the first and second embodiments. 
     Thus, in this third embodiment, capacitor  120  and other devices are housed (not shown) in the inner space of the square-tubular core formed by first core  111 A and second core  112 A. The devices housed within the square-tubular core are the same as those in the first and second embodiments. 
     Although the core in a square tubular shape is formed by first core  111 A and second core  112 A in the above description, the core in a square tubular shape may be integrally formed without using separate first core  111 A and second core  112 A. In addition, the core in a square tubular shape is formed by separate first core  111 A and second core  112 A, so that the core can be readily manufactured while the installability can be improved at the time when the devices are housed within the core in a square tubular shape. 
     Although not particularly shown, the coil unit in the power transmission unit of power transmission device  20  may also be formed by a core in a square tubular shape, as with coil unit  110 A described above. Also, capacitor  720  and other devices may be housed in the inner space of the square-tubular core. 
     According to this third embodiment, the core is formed in a square tubular shape, thereby allowing improvement in the strength of the core while achieving the effect similar to those in the first and second embodiments. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.