Abstract:
Disclosed is a vehicle guidance apparatus that can easily guide a vehicle in the vicinity of a power supply section to the power supply unit by guiding the vehicle along a path of travel to the power supply unit without employing image data. In this device, a power supply efficiency calculation unit calculates the power supply efficiency, which is the efficiency with which power is received from the power supply unit by the charging unit. An amount of change calculation unit calculates the amount of change of efficiency of power supply, which is the amount of change of efficiency of power supply calculated by the power supply efficiency calculation unit. A vehicle-side control unit displays on a display guidance to enable the vehicle to reach the power supply unit, based on the amount of change of efficiency of power supply calculated by the amount of change calculation unit.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a vehicle guidance apparatus that is mounted on a vehicle which receives power from a power supply section in a non-contact state and that guides the vehicle to the power supply section, and also to a vehicle guidance method. 
       BACKGROUND ART 
       [0002]    In a vehicle that runs using electricity stored in a storage battery of an electric vehicle or the like as a power source, the storage battery needs to be charged by using a power supply apparatus when the vehicle stops in a parking lot or the like. As a non-contact power supply apparatus of the related art, there is known a power supply apparatus in which a power supply section installed on the ground surface supplies power to a power receiving section mounted on the vehicle. The power supply section is installed on a road surface at a position where the vehicle stops such as a parking space or the like. Meanwhile, the power receiving section is installed on the bottom surface of the vehicle at a position facing the power supply section installed on the ground surface. 
         [0003]    In the non-contact charging system, when it is impossible to accurately match the positions of the power receiving section and the power supply section, a gap occurs in distance between the power receiving section and the power supply section. As a result, the charging efficiency is reduced or the leakage magnetic field or the unnecessary radiation occurs. Conventionally, as a method for improving the accuracy of position matching between the power receiving section and the power supply section, there is known a vehicle guidance apparatus that guides an accurate positional relation between the vehicle and the power supply apparatus by using images around the vehicle (for example, PTL 1). 
         [0004]    In PTL 1, the image data obtained by capturing images around a vehicle by a camera is combined so as to generate a combined image of an area including the vehicle, and the positional relation between the power supply section and the power receiving section is specified based on the measured power receiving efficiency. In PTL 1, when the combined image thus generated includes an image of the power supply section, the position of the power receiving section is displayed based on the specific positional relation between the positions of the power supply section and the power receiving section in the combined image. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1 
         Japanese Patent Application Laid-Open No. 2010-234878 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    However, in PTL 1, the power supply section in the image data needs to be identified, so that, a problem arises in that the power supply section in the image data cannot be identified when the power supply section is captured at a place distant from the power supply section. Further, in PTL 1, a problem also arises in that the power supply section in the image data cannot be identified even when the power supply section is captured at a place where the light is not sufficient at night. 
         [0008]    An object of the invention is to provide a vehicle guidance apparatus and a vehicle guidance method capable of easily guiding a vehicle approaching a power supply section to the power supply section even when the power supply section is captured at a position distant from the power supply section or the periphery of the vehicle is dark, by guiding an approach route with respect to the power supply section without using image data. 
       Solution to Problem 
       [0009]    A vehicle guidance apparatus according to an aspect of the present invention is an apparatus configured to be mounted on a vehicle that receives power from a power supply section in a non-contact state and to guide the vehicle to the power supply section, the vehicle guidance apparatus including: a power receiving section that receives power from the power supply section; a power supply efficiency calculation section that calculates a power supply efficiency that indicates how efficiently the power receiving section receives the power from the power supply section; a change amount calculation section that calculates a power supply efficiency change amount that is a change amount of the power supply efficiency calculated by the power supply efficiency calculation section; and a control section that causes an indication section to make indication for guiding the vehicle to the power supply section based on the power supply efficiency change amount calculated by the change amount calculation section. 
         [0010]    A vehicle guidance method according to an aspect of the present invention is a method for a vehicle guidance apparatus configured to be mounted on a vehicle that receives power from a power supply section in a non-contact state and to guide the vehicle to the power supply section, the vehicle guidance method including: calculating a power supply efficiency that indicates how efficiently a power receiving section configured to receive power from the power supply section receives the power from the power supply section; calculating a power supply efficiency change amount that is a change amount of the power supply efficiency calculated in the calculating of the power supply efficiency; and controlling indication for guiding the vehicle to the power supply section based on the power supply efficiency change amount calculated in the calculating of the power supply efficiency change amount. 
       Advantageous Effects of Invention 
       [0011]    According to the present invention, guiding a vehicle using an approach route with respect to a power supply section without using image data makes it possible to easily guide the vehicle to the power supply section even when the vehicle approaches the power supply section from a place distant from the power supply section, or even when the periphery of the vehicle is dark. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a block diagram illustrating a configuration of a charging system of an embodiment of the present invention; 
           [0013]      FIG. 2  is a flowchart illustrating an operation of a vehicle guidance apparatus according to the embodiment of the present invention; 
           [0014]      FIG. 3  is a diagram illustrating a power supply efficiency of a power supply section of the embodiment of the present invention; 
           [0015]      FIG. 4  is a diagram illustrating approach route  1  with respect to the power supply section of the vehicle of the embodiment of the present invention; 
           [0016]      FIG. 5  is a diagram illustrating approach route  2  with respect to the power supply section of the vehicle of the embodiment of the present invention; 
           [0017]      FIG. 6  is a diagram illustrating approach route  3  with respect to the power supply section of the vehicle of the embodiment of the present invention; 
           [0018]      FIG. 7  is a diagram illustrating approach route  4  with respect to the power supply section of the vehicle of the embodiment of the present invention; 
           [0019]      FIG. 8  is a diagram illustrating a relationship between a positional mismatch between a power supply section and a power receiving section, and a power supply efficiency at each approach route of  FIG. 7 ; and 
           [0020]      FIG. 9  is a diagram illustrating a power supply efficiency change amount per unit moving distance for the power supply efficiency at each approach route acquired from  FIG. 8 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings. 
       Embodiment 
       [0022]      FIG. 1  is a block diagram illustrating a configuration of charging system  10  of the embodiment of the invention. 
         [0023]    Charging system  10  includes power supply apparatus  140  and vehicle  150 . 
         [0024]    Power supply apparatus  140  is installed on the ground or buried in the ground so that power supply section  143  is exposed from ground surface g. Power supply apparatus  140  is installed in, for example, a parking space, and supplies power to power receiving section  101  while facing power receiving section  101  of parked vehicle  150 . 
         [0025]    Vehicle  150  includes vehicle guidance apparatus  100  and storage battery  109 , and runs using the power accumulated in storage battery  109  as a power source. Vehicle  150  is, for example, an electric vehicle. 
         [0026]    Storage battery  109  accumulates the power supplied from power supply section  143  to power receiving section  101 . 
         [0027]    Vehicle guidance apparatus  100  guides vehicle  150  when vehicle  150  approaches power supply apparatus  140 . 
         [0028]    Furthermore,  FIG. 1  illustrates a positional relation between vehicle  150  and power supply apparatus  140  in a charging state, and vehicle guidance apparatus  100  guides vehicle  150  until the positional relation illustrated in  FIG. 1  is established. 
         [0029]    &lt;Configuration of Vehicle Guidance Apparatus&gt; 
         [0030]    Vehicle guidance apparatus  100  includes power receiving section  101 , vehicle-side communication section  102 , power supply efficiency calculation section  103 , vehicle information acquisition section  104 , change amount calculation section  105 , storage section  106 , vehicle-side control section  107 , and display section  108 . 
         [0031]    Power receiving section  101  is installed at the bottom portion of vehicle  150 , and faces power supply section  143  in a charging state. Power receiving section  101  receives power from power supply section  143  in a non-contact state in accordance with the control of vehicle-side control section  107 . Power receiving section  101  and power supply section  143  each include a built-in coil. Power supply section  143  supplies power to power receiving section  101  by electromagnetic induction (for example, an electromagnetic induction method, a magnetic resonance method, and the like). Furthermore, power receiving section  101  may receive power in accordance with the distance with respect to power supply section  143  even in a case where the power receiving section does not completely face power supply section  143 . That is, the power supplied from power supply section  143  to power receiving section  101  becomes greater as the power receiving section becomes closer to power supply section  143  (i.e., as the area of the portion facing power supply section  143  becomes greater). 
         [0032]    Vehicle-side communication section  102  generates a charge start signal or a charge stop signal in accordance with the control of vehicle-side control section  107 , and transmits the generated charge start signal or the generated charge stop signal to power-supply-side communication section  141 . Vehicle-side communication section  102  receives a reference value (a second reference value), which is transmitted from power supply section  143  to power receiving section  101 , from power-supply-side communication section  141  and outputs the received reference value to power supply efficiency calculation section  103 . Here, the reference value indicates the lower-limit value of the power to be transmitted to power receiving section  101  in a charging state and is set to, for example, a power value that makes the power supply efficiency equal to 70%. 
         [0033]    Power supply efficiency calculation section  103  calculates the efficiency of the power transmitted from power supply section  143  to power receiving section  101 . Specifically, power supply efficiency calculation section  103  acquires the actual measurement value of the power currently received by power receiving section  101 . Power supply efficiency calculation section  103  calculates the power supply efficiency as the ratio between the reference value and the actual measurement value of the power currently received by power receiving section  101 . Power supply efficiency calculation section  103  sequentially outputs the calculated power supply efficiency to change amount calculation section  105  and vehicle-side control section  107 . 
         [0034]    Vehicle information acquisition section  104  acquires vehicle information from a device of vehicle  150 , extracts vehicle speed information representing the speed of vehicle  150  in the vehicle information, and outputs the vehicle speed information to change amount calculation section  105  and vehicle-side control section  107 . Vehicle information acquisition section  104  acquires the vehicle speed information by, for example, a vehicle wheel speed sensor. 
         [0035]    Change amount calculation section  105  acquires power supply efficiency change amount Δk by using a plurality of power supply efficiencies. Then, when power supply efficiency change amount Δk is equal to or less than 0, change amount calculation section  105  outputs power supply efficiency change amount Δk to vehicle-side control section  107 . Meanwhile, when power supply efficiency change amount Δk is greater than 0, change amount calculation section  105  calculates the power supply efficiency by using the vehicle speed information and acquires the moving distance of vehicle  150  until the next power supply efficiency is calculated. Change amount calculation section  105  calculates power supply efficiency change amount Y per unit moving distance from the moving distance and the power supply efficiency change amount, and outputs the power supply efficiency change amount to vehicle-side control section  107 . 
         [0036]    Storage section  106  stores a lower-limit value of power supply efficiency change amount Y per unit distance of each of the power supply efficiencies in a table. Furthermore, the lower-limit value stored in the table is acquired in advance. The lower-limit value will be described later. 
         [0037]    Vehicle-side control section  107  controls power receiving section  101  and vehicle-side communication section  102  when receiving a charge request from the outside. 
         [0038]    Vehicle-side control section  107  determines that the approach route of vehicle  150  approaching power supply section  143  is wrong when power supply efficiency change amount Δk is equal to or less than 0. Further, vehicle-side control section  107  determines that the approach route of vehicle  150  approaching power supply section  143  is wrong when power supply efficiency change amount Y per unit moving distance input from change amount calculation section  105  is less than the lower-limit value of the power supply efficiency change amount of the table stored in storage section  106 . Then, vehicle-side control section  107  displays guidance for correcting the approach route on display section  108  when it is determined that the approach route is wrong. Meanwhile, vehicle-side control section  107  determines that the approach route is correct when power supply efficiency change amount Δk is greater than 0 and power supply efficiency change amount Y per unit moving distance is equal to or greater than the lower-limit value. Then, vehicle-side control section  107  displays a message that the approach route is correct on display section  108  when it is determined that the approach route is correct. Furthermore, vehicle-side control section  107  may perform a control so that the message is displayed only when the approach route is wrong without displaying the message when the approach route is correct. 
         [0039]    Vehicle-side control section  107  determines whether it is a brake stepping timing based on the power supply efficiency received from power supply efficiency calculation section  103  and power supply efficiency change amount Y per unit moving distance received from change amount calculation section  105 . Specifically, when the power supply efficiency necessary for the charging operation is, for example, 70%, vehicle-side control section  107  acquires a subtraction value obtained by subtracting the current power supply efficiency from 70 and acquires the remaining distance to power supply section  143  by dividing the subtraction value by power supply efficiency change amount Y per unit moving distance. Then, vehicle-side control section  107  determines that it is the brake stepping timing when the remaining distance to power supply section  143  is less than a predetermined threshold value. When vehicle-side control section  107  determines that it is the brake stepping timing, the vehicle-side control section displays guidance for stopping vehicle  150  by a brake stepping operation on display section  108 . Here, the threshold value to be compared with the remaining distance to power supply section  143  is set to, for example, 1 meter. Furthermore, the specific control method in vehicle-side control section  107  will be described later. 
         [0040]    Display section  108  serves as an indication section that indicates a predetermined guidance. Specifically, display section  108  displays guidance for correcting the approach route, guidance for indicating a state where the approach route is correct, or guidance for stopping vehicle  150  by stepping on the brake in accordance with the control of vehicle-side control section  107 . 
         [0041]    &lt;Configuration of Power Supply Apparatus&gt; 
         [0042]    Power-supply-side communication section  141  receives a power supply start signal or a power supply stop signal transmitted from vehicle-side communication section  102 . Power-supply-side communication section  141  outputs the received power supply start signal or the received power supply stop signal to power-supply-side control section  142 . Power-supply-side communication section  141  indicates the reference value of the power transmitted from power supply section  143  to power receiving section  101  when power is supplied from power supply apparatus  140  to power receiving section  101 . 
         [0043]    When the power supply start signal is input from power-supply-side communication section  141 , power-supply-side control section  142  performs a control so that the power supply from power supply section  143  starts. When the power supply stop signal is input from power-supply-side communication section  141 , power-supply-side control section  142  performs a control so that the power supply from power supply section  143  stops. 
         [0044]    Power supply section  143  supplies power to power receiving section  101  facing thereto in accordance with the control of power-supply-side control section  142 . 
         [0045]    &lt;Operation of Vehicle Guidance Apparatus&gt; 
         [0046]      FIG. 2  is a flowchart illustrating an operation of vehicle guidance apparatus  100 .  FIG. 2  illustrates a case where the reference value of the power transmitted from power supply section  143  to power receiving section  101  is set to 70%. 
         [0047]    First, vehicle-side control section  107  determines whether there is a charge request from the outside (step ST 201 ). 
         [0048]    When there is no charge request (step ST 201 : NO), vehicle guidance apparatus  100  ends the process. 
         [0049]    Meanwhile, when there is a charge request (step ST 201 : YES), vehicle-side control section  107  starts the charging operation by controlling power receiving section  101  (step ST 202 ). 
         [0050]    Next, power supply efficiency calculation section  103  calculates the power supply efficiency (k 1 ) (step ST 203 ). 
         [0051]    Next, vehicle information acquisition section  104  acquires the vehicle speed information as the vehicle information (step ST 204 ). 
         [0052]    Next, vehicle-side control section  107  determines whether the vehicle speed is greater than 0 km/h (step ST 205 ). 
         [0053]    When the vehicle speed is equal to or less than 0 km/h (step ST 205 : NO), vehicle-side control section  107  determines whether vehicle  150  exists in a power suppliable area (step ST 206 ). That is, vehicle-side control section  107  determines whether the power supply efficiency at that time is equal to or greater than 70%. 
         [0054]    When vehicle  150  exists in the power suppliable area (step ST 206 : YES), vehicle guidance apparatus  100  ends the process. 
         [0055]    Meanwhile, when vehicle  150  does not exist in the power suppliable area (step ST 206 : NO), vehicle-side control section  107  controls display section  108  so that a parking position correction guidance is performed (step ST 207 ), and then returns the process to step ST 203 . 
         [0056]    Further, in step ST 205 , when the vehicle speed information is greater than 0 km/h (step ST 205 : YES), power supply efficiency calculation section  103  measures the power supply efficiency (k 2 ) again. Further, change amount calculation section  105  acquires power supply efficiency change amount Δk by calculation (Δk=k 2 −k 1 ), and acquires moving distance X of vehicle  150  when power supply efficiency change amount Δk is acquired (step ST 208 ). That is, change amount calculation section  105  acquires moving distance X of vehicle  150  until power supply efficiency k 2  is calculated in step ST 207  after power supply efficiency k 1  is calculated in step ST 203 . Specifically, change amount calculation section  105  acquires moving distance X by multiplying time t until power supply efficiency k 2  is calculated after the calculation of power supply efficiency k 1  by average value A of the vehicle speed of the vehicle speed information in time t (X=A*t). 
         [0057]    Next, change amount calculation section  105  determines whether power supply efficiency change amount Δk is equal to or greater than 0 (step ST 209 ). 
         [0058]    When power supply efficiency change amount Δk is less than 0 (does not increase) (step ST 209 : NO), vehicle-side control section  107  controls display section  108  so as to display guidance for correcting the approach route of vehicle  150  approaching power supply section  143  (step ST 210 ). 
         [0059]    Meanwhile, when power supply efficiency change amount Δk is equal to or greater than 0 (increases) (step ST 209 : YES), change amount calculation section  105  acquires power supply efficiency change amount Y per unit moving distance (Y=Δk/X) (step ST 211 ). 
         [0060]    Next, vehicle-side control section  107  determines whether power supply efficiency change amount Y per unit moving distance is equal to or greater than the lower-limit value of the power supply efficiency at that time by referring to the table stored in storage section  106  (step ST 212 ). 
         [0061]    When power supply efficiency change amount Y per unit moving distance is less than the lower-limit value (step ST 212 : NO), vehicle  150  approaching power supply section  143  is shifted from the approach route, and hence vehicle-side control section  107  controls display section  108  so as to display guidance for correcting the approach route (step ST 213 ). 
         [0062]    Meanwhile, when power supply efficiency change amount Y per unit moving distance is equal to or greater than the lower-limit value (step ST 212 : YES), vehicle-side control section  107  determines whether it is the brake stepping timing ((70−k 2 )/Y&lt;1[m]?) (step ST 214 ). 
         [0063]    When it is not the brake stepping timing (step ST 214 : NO), vehicle-side control section  107  controls display section  108  so as to display a message that the approach route is correct (step ST 215 ), and vehicle guidance apparatus  100  returns the process to step ST 203 . 
         [0064]    Meanwhile, when it is the brake stepping timing (step ST 214 : YES), vehicle-side control section  107  controls display section  108  so as to display guidance for stopping vehicle  150  by stepping on the brake (step ST 216 ), and vehicle guidance apparatus  100  returns the process to step ST 203 . 
         [0065]    &lt;Power Supply Efficiency at Power Supply Section&gt; 
         [0066]      FIG. 3  is a diagram illustrating the power supply efficiency at power supply section  143 . 
         [0067]    In  FIG. 3 , power supply section  143  has a circular shape in the top view, and power supply efficiencies R 1 , R 2 , and R 3  (R 1 &gt;R 2 &gt;R 3 ) which are concentrically provided from the center of the circular circle decrease as it comes closer to the outer periphery of the circular circle. For example, R 1  is 80%, R 2  is 75%, and R 3  is 70%. 
         [0068]    &lt;Specific Control Example of Vehicle-Side Control Section&gt; 
         [0069]      FIG. 4  is a diagram illustrating approach route  1  with respect to the power supply section of vehicle  150 .  FIG. 5  is a diagram illustrating approach route  2  with respect to the power supply section of vehicle  150 .  FIG. 6  is a diagram illustrating approach route  3  with respect to the power supply section of vehicle  150 .  FIG. 7  is a diagram illustrating approach route  4  with respect to the power supply section of vehicle  150 .  FIG. 8  is a diagram illustrating a relationship between the positional mismatch between power supply section  143  and power receiving section  101 , and the power supply efficiency in each approach route of  FIG. 7 .  FIG. 9  is a diagram illustrating the power supply efficiency change amount per unit moving distance of each of the power supply efficiencies at each approach route obtained from  FIG. 8 . 
         [0070]    In  FIG. 8 , the positional deviation [m] of the horizontal axis indicates the distance between the center of power receiving section  101  and the center of power supply section  143  in the front to rear direction. Specifically, in the case of approach route  1  of  FIG. 4 , the positional mismatch of  FIG. 8  is distance r 1  of  FIG. 4 . In the case of approach route  2  of  FIG. 5 , the positional mismatch of  FIG. 8  is distance r 2  of  FIG. 5 . In the case of approach route  3  of  FIG. 6 , the positional deviation of  FIG. 8  is distance r 3  of  FIG. 6 . In the case of approach route  4  of  FIG. 7 , the positional mismatch of  FIG. 8  is distance r 4  of  FIG. 7 . 
         [0071]      FIGS. 4 and 6  illustrate a case where vehicle  150  succeeds in approaching with respect to power supply section  143 . That is,  FIGS. 4 and 6  illustrate a case where power receiving section  101  and power supply section  143  face each other in the state illustrated in  FIG. 1 .  FIG. 5  illustrates a case where vehicle  150  fails in approaching with respect to power supply section  143 .  FIG. 7  illustrates a case where vehicle  150  finally fails in approaching with respect to power supply section  143  since vehicle  150  changes the advancing direction while approaching power supply section  143 . 
         [0072]    In  FIG. 8 , in the case of approach route  1 , since the vehicle accurately follows the correct approach route as indicated by curve # 801 , the power supply efficiency of the power receiving section exceeds 70% even when the positions of power supply section  143  and power receiving section  101  do not accurately match each other. In the case of approach route  2 , since the vehicle always follows a route shifted from the correct approach route as indicated by curve # 802 , power may not be supplied to the vehicle, and the power supply efficiency does not exceed 70%. In the case of approach route  3 , since the vehicle substantially follows the correct approach route as indicated by curve # 803 , the power supply efficiency finally becomes 70%. In the case of approach route  4 , since the vehicle is largely shifted from the correct approach route in the course of the route as indicated by curve # 804 , the power supply efficiency is finally less than 70%. Furthermore, the reason why the value of approach route  3  of  FIG. 8  has a peak value at the power supply efficiency of 40% is that the gradient in the vicinity of the power supply efficiency of 40% at curve # 803  of approach route  3  illustrated in  FIG. 8  is the steepest. 
         [0073]    From the description above, approach route  3  of  FIG. 6  illustrates the limit of the success in which vehicle  150  approaches power supply section  143 . Accordingly, each value (the first reference value) of the power supply efficiency change amount per unit moving distance for each of the power supply efficiencies in approach route  3  of  FIG. 9  becomes the lower-limit value of each of the power supply efficiencies written in the table stored in storage section  106 . 
         [0074]    For example, the lower-limit value of the power supply efficiency of 30% is 7 [%/m] from  FIG. 9 . Since the power supply efficiency change amount per unit moving distance of the power supply efficiency of 30% of each of approach routes  1  and  4  is 8 [%/m] and is equal to or greater than the lower-limit value, vehicle-side control section  107  controls display section  108  so as to display a message that the approach route is correct. 
         [0075]    Meanwhile, since the power supply efficiency change amount per unit moving distance of the power supply efficiency of 30% of approach route  2  is 6.5 [%/m] and is less than the lower-limit value, vehicle-side control section  107  controls display section  108  so as to display guidance for correcting the approach route. Further, the lower-limit value of the power supply efficiency of 70% is 0 [%/m]. Since the power supply efficiency change amount per unit moving distance of the power supply efficiency of 70% of approach route  4  is −3.5 [%/m] and is less than the lower-limit value, vehicle-side control section  107  controls display section  108  so as to display guidance for correcting the approach route. 
         [0076]    Furthermore, the value of “−3.5” acquired when the power supply efficiency of approach route  4  is greater than 70% and the power supply efficiency is 70% means that vehicle  150  passes by power supply section  143  and is distant from power supply section  143 . 
         [0077]    &lt;Effect of Embodiment&gt; 
         [0078]    According to the embodiment, since the positional relation between the power receiving section and the power supply section may be specified without using the image data, the vehicle that approaches the power supply section from a place distant from the power supply section can be easily guided to the power supply section. 
         [0079]    Further, according to the embodiment, since there is no need to install a guiding camera, the manufacturing cost of the system can be reduced. 
         [0080]    Further, according to the embodiment, since an instruction of stopping the vehicle by stepping on the brake is displayed, it is possible to accurately match the positions of the power receiving section and the power supply section. 
         [0081]    Further, according to the embodiment, since the vehicle is guided by using the power supply efficiency, it is possible to determine whether the power supply efficiency is sufficient for the charging operation while guiding the vehicle. Accordingly, even when a slight positional mismatch occurs in the position matching between the power receiving section and the power supply section, the vehicle may be charged while the vehicle is stopped at a position where a sufficient power supply efficiency can be obtained. Thus, it is possible to reduce the burden on the driver of the vehicle due to the precise position matching between the power receiving section and the power supply section. 
         [0082]    &lt;Variations of Embodiment&gt; 
         [0083]    In the embodiment, moving distance X of vehicle  150  is acquired from the vehicle speed information, but the invention is not limited thereto. For example, moving distance X of vehicle  150  may be directly acquired. 
         [0084]    Further, in the embodiment, the reference value of the power transmitted from power supply section  143  to power receiving section  101  is received from power supply apparatus  140 , but the invention is not limited to this case. For example, the reference value may be stored in advance in vehicle  150  and the reference value may be arbitrarily set by a user. 
         [0085]    Further, in the embodiment, the guidance of vehicle  150  approaching power supply section  143  is performed on a display, but the invention is not limited to this case. For example, the guidance of vehicle  150  approaching power supply section  143  may be performed by any method using a sound or the like. 
         [0086]    Further, in the embodiment, an instruction of stopping vehicle  150  by stepping on the brake is displayed, but the invention is not limited thereto. For example, an instruction of stopping vehicle  150  by stepping on the brake may not be displayed. In this case, the driver of vehicle  150  stops vehicle  150  by appropriately stepping on the brake while viewing the guidance of the power supply efficiency or the approach route. 
         [0087]    Further, in the embodiment, the guidance is performed when vehicle  150  moves backward and approaches the power supply section, but the invention is not limited thereto. For example, the guidance may be performed when vehicle  150  moves forward and approaches the power supply section. 
         [0088]    Further, in the embodiment, the guidance for correcting the approach route or indicating the correct approach route is displayed on display section  108 , but the invention is not limited thereto. For example, the guidance may be performed by a method using a sound or the like other than a display. 
         [0089]    The disclosure of Japanese Patent Application No. 2011-266924, filed on Dec. 6, 2011, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0090]    The vehicle guidance apparatus and the vehicle guidance method according to the present invention are suitable for use as an apparatus is mounted on a vehicle which receives power from a power supply section in a non-contact state and that guides the vehicle to the power supply section, and as a method for the apparatus. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  Charging system 
           100  Vehicle guidance apparatus 
           101  Power receiving section 
           102  Vehicle-side communication section 
           103  Power supply efficiency calculation section 
           104  Vehicle information acquisition section 
           105  Change amount calculation section 
           106  Storage section 
           107  Vehicle-side control section 
           108  Display section 
           109  Storage battery 
           140  Power supply apparatus 
           141  Power-supply-side communication section 
           142  Power-supply-side control section 
           143  Power supply section 
           150  Vehicle