Patent Publication Number: US-2022234462-A1

Title: Power transmission apparatus, and power transmission system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2021-10709, filed on Jan. 26, 2021, the entire disclosure of which is incorporated by reference herein. 
     FIELD 
     This application relates generally to a power transmission apparatus, and a power transmission system. 
     BACKGROUND 
     Attention has been paid to wireless power transmission technology that wirelessly transmits electric power. Since the wireless power transmission technology enables wireless transmission of electric power from a power transmission apparatus to a power receiving apparatus, it is expected that the wireless power transmission technology is applied to various products, for example, transport equipment such as an electric train or an electric vehicle, household electrical equipment, wireless communication equipment, and toys. In the wireless power transmission technology, a power transmission coil and a power receiving coil, which are coupled by magnetic flux, are used in order to transmit electric power. 
     In the meantime, if an object such as a living body or a metal piece is present near the power transmission coil, there is a possibility that various problems will arise. For example, when a living body is present near the power transmission coil, there is a possibility that the living body is exposed to an electromagnetic field occurring at the time of power transmission, and a health problem arises in the living body. Accordingly, there is a demand for an object detection apparatus that properly detects an object existing near the power transmission coil. 
     Unexamined Japanese Patent Application Publication No. 2014-57457 discloses a non-contact power supply system in which sensors that monitor a lateral surrounding of a power transmission coil are arranged around the power transmission coil in order to detect an entrance of a movable body into the lateral surrounding of the power transmission coil. Unexamined Japanese Patent Application Publication No. 2014-57457 discloses that a plurality of sensors is arranged such that a detection range of the sensor broadens toward the outside of the power transmission coil. 
     SUMMARY 
     However, the detection range of this sensor is narrow in a region near the sensor. Thus, in the arrangement of the sensors disclosed in Unexamined Japanese Patent Application Publication No. 2014-57457, a detection blind spot, which is a region where an object cannot be detected, occurs in a region along the outer edge of the power transmission coil. This being the case, there is a demand for technology which reduces the detection blind spot near the periphery of the power transmission coil. 
     The present disclosure has been made in consideration of the above problem, and the objective of the disclosure is to reduce a detection blind spot near a periphery of a power transmission coil, in the object detection involved in wireless power transmission. 
     In order to solve the above problem, a power transmission apparatus according to an embodiment of the present disclosure includes: 
     a power transmission coil unit including a power transmission coil formed such that a lead wire is spirally wound around a coil axis extending in a first direction, the power transmission coil unit wirelessly transmitting electric power to a power receiving apparatus; 
     a plurality of sensor modules each including a sensor and a controller, the sensor having a detection range of a first angle that is a detection angle spanning in an in-plane direction of a first plane orthogonal to the first direction, the controller being configured to control the sensor and generate output information based on a signal that the sensor outputs; and 
     a detector that determines presence or absence of an object, based on the output information, wherein 
     an outer edge of the power transmission coil unit, as viewed in the first direction, has a shape including a plurality of straight lines, 
     the plurality of sensors is disposed in a surrounding region that is, as viewed in the first direction, a region surrounding the power transmission coil unit along the outer edge of the power transmission coil unit, and 
     each of the plurality of sensors, as viewed in the first direction, is disposed such that a second angle that is an angle formed between a straight line overlapping the detection range, among the plurality of straight lines constituting the outer edge of the power transmission coil unit, and a center axis of the detection range is ½ or less of the first angle. 
     According to the above configuration, a detection blind spot near a periphery of a power transmission coil can be reduced in the object detection involved in wireless power transmission. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of this application can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG. 1  is a schematic configuration diagram of a power transmission system according to Embodiment 1; 
         FIG. 2  is a perspective view of a power transmission coil unit and a power receiving coil unit according to Embodiment 1; 
         FIG. 3  is a top view of a sensor module according to Embodiment 1; 
         FIG. 4  is a configuration diagram of an object detection apparatus according to Embodiment 1; 
         FIG. 5  is an explanatory diagram of a detection range of a sensor according to Embodiment 1; 
         FIG. 6  is an arrangement diagram of sensor modules according to Embodiment 1; 
         FIG. 7  is an explanatory diagram of an installation angle of the sensor module according to Embodiment 1; 
         FIG. 8  is an arrangement diagram of sensor modules according to Embodiment 2; 
         FIG. 9  is an explanatory diagram of an arrangement of a pair of sensor modules; 
         FIG. 10  is an arrangement diagram of sensor modules according to Embodiment 3; 
         FIG. 11  is an arrangement diagram of sensor modules according to Embodiment 4; and 
         FIG. 12  is an arrangement diagram of sensor modules according to Embodiment 5. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a power transmission system according to an embodiment of a technology relating to the present disclosure is described with reference to the accompanying drawings. Note that in the embodiment to be described below, the same structural parts are denoted by the same reference signs. In addition, the ratios in magnitude and the shapes of the structural elements illustrated in the drawings are not necessarily the same as the actual ones. 
     Embodiment 1 
     A power transmission system according the present embodiment is usable for charging secondary batteries of various apparatuses, for instance, an electric vehicle (EV), mobile equipment such as a smartphone, and industrial equipment. Hereinafter, a description is given of, by way of example, a case of charging a rechargeable battery of an EV by a power transmission system. 
       FIG. 1  is a schematic configuration diagram of a power transmission system  1000  that is used for charging a rechargeable battery  500  included in an electric vehicle  700 . The electric vehicle  700  runs by using, as a driving source, a motor that is driven by electric power that is charged in the rechargeable battery  500  such as a lithium ion battery or a lead storage battery. The electric vehicle  700  is an example of a movable body. 
     As illustrated in  FIG. 1 , the power transmission system  1000  is a system that wirelessly transmits electric power from a power transmission apparatus  200  to a power receiving apparatus  300  by magnetic coupling. The power transmission system  1000  includes a power transmission apparatus  200  that wirelessly transmits electric power of an alternating-current (AC) or direct-current (DC) commercial power source  400  to the electric vehicle  700 ; and a power receiving apparatus  300  that receives the electric power transmitted by the power transmission apparatus  200  and charges the rechargeable battery  500 . Note that in the description below, the commercial power source  400  is an AC power source. 
     The power transmission apparatus  200  is an apparatus that wirelessly transmits electric power to the power receiving apparatus  300  by magnetic coupling. The power transmission apparatus  200  includes an object detection apparatus  100  that detects an object; a power transmission coil unit  210  that transmits AC power to the electric vehicle  700 ; and a power supply apparatus  220  that supplies AC power to the power transmission coil unit  210 . A detailed description of the object detection apparatus  100  is given later. 
       FIG. 2  illustrates a main part of the power transmission coil unit  210 , and a main part of the power receiving coil unit  310 . As illustrated in  FIG. 2 , the power transmission coil unit  210  includes a power transmission coil  211  that is supplied with AC power from the power supply apparatus  220  and induces an alternating magnetic flux  1 ; and a magnetic material plate  212  that passes magnetic force generated by the power transmission coil  211  and suppresses a loss of the magnetic force. The power transmission coil  211  is composed such that a lead wire is spirally wound around a coil axis  213  on the magnetic material plate  212 . The power transmission coil  211  and capacitors provided at both ends of the power transmission coil  211  constitute a resonance circuit, and an alternating magnetic flux  1  is induced by the flow of an AC current due to the application of an AC voltage. In  FIG. 2 , an axis in a vertically upward direction is a Z-axis, an axis orthogonal to the Z-axis is an X-axis, and an axis orthogonal to the Z-axis and X-axis is a Y-axis. 
     The magnetic material plate  212  has a plate shape with a hole formed in a central portion of the magnetic material plate  212 , and is formed of a magnetic material. The magnetic material plate  212  is, for example, a plate-shaped member formed of a ferrite that is a composite oxide of an iron oxide and a metal. Note that the magnetic material plate  212  may be composed of an aggregate of a plurality of magnetic material pieces, and the magnetic material pieces may be arranged in a frame shape, with an opening portion provided in a central portion of the arranged magnetic material pieces. 
     The power supply apparatus  220  includes a power factor improvement circuit that improves the power factor of the commercial AC power that is supplied by the commercial power source  400 ; and an inverter circuit that generates AC power which is supplied to the power transmission coil  211 . The power factor improvement circuit rectifies and boosts the AC power generated by the commercial power source  400 , and converts the AC power to DC power having a preset voltage value. The inverter circuit converts the DC power, which was generated by the conversion of electric power by the power factor improvement circuit, to AC power having a preset frequency. The power transmission apparatus  200  is fixed to, for example, the floor surface of a parking lot. 
     The power receiving apparatus  300  is an apparatus which wirelessly receives electric power from the power transmission apparatus  200  by magnetic coupling. The power receiving apparatus  300  includes a power receiving coil unit  310  that receives AC power transmitted by the power transmission apparatus  200 ; and a rectification circuit  320  that converts the AC power supplied from the power receiving coil unit  310  to DC power, and supplies the DC power to the rechargeable battery  500 . 
     As illustrated in  FIG. 2 , the power receiving coil unit  310  includes a power receiving coil  311  that induces electromotive force in accordance with a variation of the alternating magnetic flux  1  induced by the power transmission coil  211 ; and a magnetic material plate  312  that passes magnetic force generated by the power receiving coil  311  and suppresses a loss of the magnetic force. The power receiving coil  311  is composed such that a lead wire is spirally wound around a coil axis  313  on the magnetic material plate  312 . The power receiving coil  311  and capacitors provided at both ends of the power receiving coil  311  constitute a resonance circuit. 
     In the state in which the electric vehicle  700  is at rest in a preset position, the power receiving coil  311  is opposed to the power transmission coil  211 . If the power transmission coil  211  receives electric power from the power supply apparatus  220  and induces an alternating magnetic flux  1 , the alternating magnetic flux  1  is interlinked with the power receiving coil  311 , and thereby induced electromotive force is induced in the power receiving coil  311 . 
     The magnetic material plate  312  is plate-shaped member with a hole formed in a central portion of the magnetic material plate  312 , and is formed of a magnetic material. The magnetic material plate  312  is, for example, a plate-shaped member formed of a ferrite that is a composite oxide of an iron oxide and a metal. Note that the magnetic material plate  312  may be composed of an aggregate of a plurality of magnetic material pieces, and the magnetic material pieces may be arranged in a frame shape, with an opening portion provided in a central portion of the arranged magnetic material pieces. 
     The rectification circuit  320  rectifies the electromotive force induced in the power receiving coil  311 , and generates DC power. The DC power generated by the rectification circuit  320  is supplied to the rechargeable battery  500 . Note that the power receiving apparatus  300  may include, between the rectification circuit  320  and the rechargeable battery  500 , a charge circuit that converts the DC power supplied from the rectification circuit  320  to appropriate DC power for charging the rechargeable battery  500 . The power receiving apparatus  300  is fixed to, for example, the chassis of the electric vehicle  700 . 
     The object detection apparatus  100  is an apparatus that detects an object existing within a detection range. The detection range is a range in which an object can be detected. The detection range is a region near the power transmission coil unit  210  and the power receiving coil unit  310 . As objects that the object detection apparatus  100  detects, a living body and a metal piece are mainly conceivable. As living bodies, animal bodies of a dog, a cat and the like, as well as the human body, are conceivable. 
     If a living body exists within the detection range at the time of power transmission, there is a possibility that the living body is exposed to an electromagnetic field, and a health problem arises in the living body. In addition, if a metal piece exists within the detection range at the time of power transmission, there is a possibility that the metal piece adversely affects the power transmission, and generates heat. Thus, the object detection apparatus  100  detects an object existing within the detection range, and notifies a user that the object was detected. Upon receiving the notification, the user can move the object away from the detection range. 
     In the present embodiment, the object detection apparatus  100  includes a plurality of sensor modules  110 . The sensor module  110  is a unit in which components used for detecting an object are integrated in one housing. Specifically, as illustrated in  FIG. 3 , the sensor module  110  includes a sensor  120  that detects an object; a housing  160  that accommodates the sensor  120  and a detection board  170 ; and the detection board  170  that is connected to the sensor  120  by a cable  180 . In  FIG. 3 , for easier understanding, an illustration of a ceiling part of the housing  160  is omitted. In other words,  FIG. 3  is a top view of the sensor module  110  at a time when the ceiling portion of the housing  160  is removed. Note that the structures and functions of the plurality of sensor modules  110  are basically the same. 
     The sensor  120  is a sensor that detects an object existing within the detection range. As the sensor  120 , various types of sensors, such as a sensor that detects a reflective wave of a sound wave or an electromagnetic wave, and a sensor that detects an electromagnetic wave, can be adopted. For example, as the sensor  120 , an ultrasonic sensor, a millimeter-wave sensor, an X-band sensor, an infrared sensor, and a visible-light sensor can be adopted. In the present embodiment, the sensor  120  is an ultrasonic sensor that transmits an ultrasonic wave by a transmitter, and receives a reflective wave of the ultrasonic wave by a receiver. Hereinafter, the ultrasonic wave that the transmitter transmits is referred to as a transmission wave, where appropriate. 
     The sensor  120  includes a piezoelectric element and a housing that accommodates the piezoelectric element. The sensor  120  executes sensing in accordance with control by a controller  130 . The sensor  120  applies a voltage pulse, which is supplied from the controller  130 , to the piezoelectric element, and transmits a transmission wave that is an ultrasonic wave from the piezoelectric element. In addition, the sensor  120  supplies to the controller  130  a voltage signal indicative of a voltage generated in the piezoelectric element by a reflective wave of the transmission wave. 
     The sensor  120  includes a detection window  121  through which the transmission wave and the reflective wave pass. The detection window  121  is, for example, an opening portion in the housing of the sensor  120 , or a part in the housing of the sensor  120 , which is formed of a member that less easily attenuates a sound wave or an electromagnetic wave. The sensor  120  radiates a transmission wave from the detection window  121 , and receives a reflective wave through the detection window  121 . 
     The housing  160  accommodates the sensor  120  and the detection board  170 . The housing  160  is, for example, a box-shaped member including an opening portion  161  in a position opposed to the detection window  121  of the sensor  120 . The housing  160  includes an electromagnetic shielding member that covers at least a part of the sensor  120 . In the present embodiment, the electromagnetic shielding member covers at least a part of those portions of the sensor  120 , which are other than the detection window  121 . The electromagnetic shielding member is a member that suppresses the passage of electromagnetism, and is a member for suppressing the influence of magnetic flux by power transmission. The electromagnetic shielding member mainly functions to shield the sensor  120  from the influence of an electromagnetic field that the power transmission coil  211  generates. The electromagnetic shielding member is, for example, a member formed of aluminum. 
     The detection board  170  is a board on which components for executing various processes involved in the detection of an object are mounted. A central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a real time clock (RTC), an analog/digital (A/D) converter, a flash memory, a communication interface, and the like are mounted on the detection board  170 . The communication interface is a communication interface that supports, for example, well-known wired communication standards such as a universal serial bus (USB) (registered trademark) and Thunderbolt (registered trademark), or well-known wireless communication standards such as Wi-Fi (registered trademark), Bluetooth (registered trademark), long term evolution (LTE), 4th generation (4G), and 5th generation (5G). A controller  130 , a storage  140 , and a communicator  150 , which are described later, are implemented by these structural components mounted on the detection board  170 . 
     Next, referring to  FIG. 4 , a configuration of the object detection apparatus  100  is described. The object detection apparatus  100  includes a plurality of sensor modules  110 , and a detector  190 . Note that  FIG. 4  explicitly illustrates only one sensor module  110 . The sensor module  110  includes a sensor  120 , a controller  130 , a storage  140 , and a communicator  150 . The detector  190  includes a controller  191 , a storage  192 , a first communicator  193 , and a second communicator  194 . The detector  190  is provided outside the sensor module  110 . For example, the detector  190  is provided in the inside of the housing of the power transmission coil unit  210  or power supply apparatus  220 . 
     The controller  130  controls the operation of the entirety of the sensor module  110 . The controller  130  controls the sensor  120  according to an operation program stored in the storage  140 , and generates output information, based on a signal that the sensor  120  outputs. The controller  130  includes, for example, a CPU, a ROM, a RAM, an RTC, an A/D converter, and the like. 
     The controller  130  generates output information, based on a signal that the sensor  120  outputs. To begin with, the controller  130  drives the sensor  120  in accordance with control by the detector  190 . Specifically, the controller  130  supplies to the sensor  120  a voltage pulse for causing the sensor  120  to transmit a transmission wave of an amplitude and a frequency designated by parameters stored in the storage  140 . Based on the signal that the sensor  120  outputs, the controller  130  generates output information indicative of a detection result of the sensor  120 . Specifically, the controller  130  executes an A/D conversion process and a filtering process on an analog signal that the sensor  120  outputs, and specifies a distance from the sensor  120  to an object, and an amplitude of a reflective wave. 
     The controller  130  outputs the output information including a value indicative of the specified distance and a value indicative of the specified amplitude. The output information acquired by the controller  130  is stored in the storage  140 , where appropriate. In addition, the controller  130  transmits the acquired output information to the detector  190  via the communicator  150 . The controller  130  may transmit the output information to the detector  190  in accordance with a request by the detector  190 , or may transmit the output information to the detector  190 , responding to the acquisition of the output information. 
     The storage  140  stores operation programs and data, which are used for the controller  130  to execute various processes. For example, the storage  140  stores parameters for the sensor  120 . As the parameters, various kinds of parameters are conceivable. In the present embodiment, as the parameters, an amplitude of a transmission wave that is transmitted by the sensor  120 , and a frequency of a transmission wave that is transmitted by the sensor  120 , are adopted. In addition, the storage  140  stores data that the controller  130  generates or acquires by executing various processes. For example, the storage  140  stores output information acquired by the controller  130 . The storage  140  includes, for example, a flash memory. 
     The communicator  150  is a communication interface for communicating with the detector  190 . The communicator  150  includes a communication interface that supports a well-known wired communication standard, or includes a communication interface that supports a well-known wireless communication standard. 
     The detector  190  determines the presence or absence of an object, based on the output information acquired from the sensor module  110 . The controller  191  controls the operation of the entirety of the detector  190 . The controller  191  acquires output information from the sensor module  110  according to an operation program stored in the storage  192 , and detects an object, based on the output information. The controller  191  includes, for example, a CPU, a ROM, a RAM, an RTC, an A/D converter, and the like. 
     Specifically, the controller  191  transmits the parameters stored in the storage  192  to the sensor module  110  via the first communicator  193 . In addition, the controller  191  instructs the sensor module  110  to detect an object, via the first communicator  193 . For example, the controller  191  instructs the sensor module  110  to detect an object, at a time of powering on the object detection apparatus  100 , or at a time of receiving an instruction from the power transmission coil unit  210  or the power supply apparatus  220 . The controller  191  acquires the output information from the sensor module  110  via the first communicator  193 . 
     The controller  191  determines the presence or absence of an object, based on the acquired output information. The controller  191  executes various notification processes in accordance with the determination result. For example, when an object was successively detected a predetermined number of times, the controller  191  makes notification indicating the presence of an object. Note that the destination of notification is the power transmission coil unit  210 , the power supply apparatus  220 , a terminal apparatus (not shown), or the like. 
     The storage  192  stores operation programs and data, which are used for the controller  191  to execute various processes. For example, the storage  192  stores parameters for the sensor  120 . In addition, the storage  192  stores data that the controller  191  generates or acquires by executing various processes. For example, the storage  192  stores output information acquired by the controller  191 . The storage  192  includes, for example, a flash memory. 
     The first communicator  193  is a communication interface for communicating with the sensor module  110 . The first communicator  193  includes a communication interface that supports a well-known wired communication standard, or includes a communication interface that supports a well-known wireless communication standard. The second communicator  194  is a communication interface for communicating with the power transmission coil unit  210 , the power supply apparatus  220 , an external terminal apparatus (not shown), and the like. The second communicator  194  includes a communication interface that supports a well-known wired communication standard, or includes a communication interface that supports a well-known wireless communication standard. 
     Next, referring to  FIG. 5 , a detection range  115  of the sensor  120  included in the sensor module  110  is described.  FIG. 5  is a diagram illustrating the detection range  115  of the sensor  120  in a case where the sensor module  110  is disposed such that a detection direction of the sensor  120  is directed toward a positive direction of the X-axis. 
     A plane  10  is a plane orthogonal to the Z-axis, and is a plane on which the sensor module  110  is disposed. A plane  20  is a plane orthogonal to the Z-axis, and a plane including a center axis  117  of the detection range  115 . An object  30 A is an object disposed in such a position that the sensor  120  can detect the object  30 A. An object  30 B is an object disposed in such a position that the sensor  120  cannot detect the object  30 B. Hereinafter, the object  30 A and the object  30 B are comprehensively referred to as an object  30  where appropriate. 
     The detection range  115  is a range within which the sensor  120  can detect the object  30 . A non-detection range  116  is a range within which the sensor  120  can hardly detect the object  30 . The non-detection range  116  is a range corresponding to a region, the distance of which from the sensor  120  is a minimum detectable distance or less. The non-detection range  116  is a range corresponding to a first region that becomes broader as a distance from a vertex, which is set at the position of the sensor  120 , becomes greater. The detection range  115  is a range corresponding to a region that is defined by excluding the first region from a second region that includes the first region and becomes broader as a distance from a vertex, which is set at the position of the sensor  120 , becomes greater. The center axis  117  is a center axis of the detection range  115 . θ 1  is a detection angle spanning in an in-plane direction of a plane that is orthogonal to the Y-axis and includes the center axis  117 . In the present embodiment, θ 1  is 90 degrees. 
     The sensor  120  can detect an object  30 , which is disposed at a position that is neither excessively close to nor excessively far from the sensor  120 , among objects  30  existing in an extending direction of the center axis  117 , as viewed from the sensor  120 . Specifically, the sensor  120  can detect the object  30 A disposed within the detection range  115  that is neither excessively close to nor excessively far from the sensor  120 . On the other hand, the sensor  120  cannot detect the object  30 B disposed in the non-detection range  116  that is excessively close to the sensor  120 . In this manner, the sensor  120  can detect neither the object  30  disposed at an excessively far position, nor the object  30  disposed at an excessively close position. 
     Next, referring to  FIG. 6  and  FIG. 7 , installation positions and installation angles of the sensor modules  110  is described.  FIG. 6  is an arrangement diagram of four sensor modules  110  included in the object detection apparatus  100 .  FIG. 7  is an explanatory diagram of an installation angle of the sensor module  110 . As illustrated in  FIG. 6 , the object detection apparatus  100  includes four sensor modules  110 , namely a sensor module  110 A, a sensor module  110 B, a sensor module  110 C, and a sensor module  110 D. The sensor module  110  is a general term for the sensor module  110 A, sensor module  110 B, sensor module  110 C, and sensor module  110 D. 
     To begin with, the sensor  120  included in the sensor module  110  has a detection range  115  of a first angle that is a detection angle spanning in the in-plane direction of a first plane orthogonal to a first direction. The first direction is an extending direction of the coil axis  213  of the power transmission coil  211 . In the present embodiment, the first direction is an extending direction of the Z-axis, and the first plane is the plane  20 . In  FIG. 7 , θ 2  is a detection angle spanning in the in-plane direction of the first plane. In the present embodiment, the first angle that is the detection angle is 90 degrees. 
     The sensor  120  included in the sensor module  110 A has a detection range  115 A and a non-detection range  116 A. The sensor  120  included in the sensor module  110 B has a detection range  115 B and a non-detection range  116 B. The sensor  120  included in the sensor module  110 C has a detection range  115 C and a non-detection range  116 C. The sensor  120  included in the sensor module  110 D has a detection range  115 D and a non-detection range  116 D. The detection range  115  is a general term for the detection range  115 A, detection range  115 B, detection range  115 C and detection range  115 D. The non-detection range  116  is a general term for the non-detection range  116 A, non-detection range  116 B, non-detection range  116 C and non-detection range  116 D. 
     Here, an outer edge of the power transmission coil unit  210 , as viewed in the first direction, has a shape including a plurality of straight lines  216 . Note that the outer edge of the power transmission coil unit  210  is substantially an outer edge of a housing  214  that the power transmission coil unit  210  includes. In the present embodiment, the outer edge of the power transmission coil unit  210 , as viewed in the first direction, is referred to simply as the outer edge of the power transmission coil unit  210  where appropriate. 
     Here, the power transmission coil unit  210 , as viewed in the first direction, has a substantially polygonal shape. Specifically, the power transmission coil unit  210 , as viewed in the first direction, has a substantially quadrangular shape. Accordingly, the outer edge of the power transmission coil unit  210  has a shape including four straight lines  216 , namely a straight line  216 A, a straight line  216 B, a straight line  216 C and a straight line  216 D. Note that the straight line  216  is a general term for the straight line  216 A, straight line  216 B, straight line  216 C, and straight line  216 D. In addition, in the present embodiment, the straight line is a concept including a line segment. 
     Here, the plurality of sensors  120  is disposed in a surrounding region  215 . The surrounding region  215 , as viewed in the first direction, is a region surrounding the power transmission coil unit  210  along the outer edge of the power transmission coil unit  210 . The surrounding region  215 , as viewed in the first direction, is a strip-shaped region near the periphery of the power transmission coil unit  210 . In addition, in the present embodiment, the plurality of sensors  120  is disposed at the vertices of the substantially polygonal shape. In other words, in the present embodiment, the four sensors  120  are disposed near the four vertices of the quadrangle representing the power transmission coil unit  210  in the surrounding region  215 . 
     Specifically, the sensor  120  included in the sensor module  110 A is disposed at a position close to one end of the straight line  216 A and one end of the straight line  216 B in the surrounding region  215 . In addition, the sensor  120  included in the sensor module  110 B is disposed at a position close to the other end of the straight line  216 B and one end of the straight line  216 C in the surrounding region  215 . The sensor  120  included in the sensor module  110 C is disposed at a position close to the other end of the straight line  216 C and one end of the straight line  216 D in the surrounding region  215 . The sensor  120  included in the sensor module  110 D is disposed at a position close to the other end of the straight line  216 D and the other end of the straight line  216 A in the surrounding region  215 . 
     Here, each of the plurality of sensors  120 , as viewed in the first direction, is disposed such that an angle formed between the plurality of straight lines  216  overlapping the detection range  115 , among the straight lines  216  constituting the outer edge of the power transmission coil unit  210 , and the center axis  117  of the detection range  115  is ½ or less of the first angle. In the example illustrated in  FIG. 7 , the straight line  216  overlapping the detection range  115  of the sensor  120  included in the sensor module  110 A, among the four straight lines  216 , is the straight line  216 A. In addition, the angle formed between the straight line  216 A and the center axis  117  of the detection range  115  is θ 3 . Besides, the first angle that is the detection angle is θ 2 . Accordingly, each of the plurality of sensors  120  is disposed such that θ 3  is ½ or less of θ 2 . 
     In the present embodiment, each of the plurality of sensors  120 , as viewed in the first direction, is disposed such that the second angle is ½ of the first angle. Accordingly, each of the plurality of sensors  120  is disposed such that θ 3  is ½ of θ 2 . Specifically, the sensor  120  included in the sensor module  110 A is disposed such that an end portion of the detection range  115  is positioned along the straight line  216 A. In addition, the sensor  120  included in the sensor module  110 B is disposed such that an end portion of the detection range  115  is positioned along the straight line  216 B. Further, the sensor  120  included in the sensor module  110 C is disposed such that an end portion of the detection range  115  is positioned along the straight line  216 C. Besides, the sensor  120  included in the sensor module  110 D is disposed such that an end portion of the detection range  115  is positioned along the straight line  216 D. 
     As described above, in the present embodiment, each of the plurality of sensors  120 , as viewed in the first direction, is disposed in the surrounding region  215  such that the second angle is ½ or less of the first angle. Specifically, in the present embodiment, most of the region near the outer edge of the power transmission coil unit  210  is included in the detection range  115  of the sensor  120 . Thus, according to the present embodiment, the detection blind spot near the periphery of the power transmission coil  211  can be reduced. 
     In particular, in the present embodiment, each of the plurality of sensors  120 , as viewed in the first direction, is disposed in the surrounding region  215  such that the second angle is ½ of the first angle. Specifically, in the present embodiment, one end of the detection range  115  of the sensor  120  overlaps the straight line  216  forming the outer edge of the power transmission coil unit  210 . Thus, according to the present embodiment, while the broad detection range  115  is being secured, the detection blind spot near the periphery of the power transmission coil  211  can be reduced. 
     Furthermore, in the present embodiment, the power transmission coil unit  210 , as viewed in the first direction, has a substantially polygonal shape, and the plurality of sensors  120  is disposed at the vertices of the substantially polygonal shape. In other words, in the present embodiment, the detection range  115  of the sensor  120  disposed at a certain vertex includes a region along a side having one end at this vertex. Thus, according to the present embodiment, the detection blind angle near the periphery of the power transmission coil  211  can be efficiently reduced by a small number of sensors  120 . 
     Embodiment 2 
     In Embodiment 1, the example was described in which the detection ranges of the plurality of sensors  120  do not largely overlap. In the present embodiment, an example is described in which the detection ranges of the plurality of sensors  120  largely overlap. Note that the description of the same configuration and process as in Embodiment 1 is omitted or simplified. 
       FIG. 8  is an arrangement diagram of eight sensor modules  110  included in the object detection apparatus  100  according to the present embodiment. In the present embodiment, a plurality of sensors  120  comprises four pairs of sensors  120  having mutually overlapping detection ranges  115 . Each of the four pairs of sensors  120  is two sensors  120  disposed at both ends of each of the four sides constituting the outer edge of the power transmission coil unit  210 . 
     Specifically, the sensor  120  included in the sensor module  110 A disposed at one end of the side corresponding to the straight line  216 A and a sensor  120  included in a sensor module  110 E disposed at the other end of the side corresponding to the straight line  216 A are one pair of sensors  120 . In addition, the sensor  120  included in the sensor module  110 B disposed at one end of the side corresponding to the straight line  216 B and a sensor  120  included in a sensor module  110 F disposed at the other end of the side corresponding to the straight line  216 B are one pair of sensors  120 . 
     Besides, the sensor  120  included in the sensor module  110 C disposed at one end of the side corresponding to the straight line  216 C and a sensor  120  included in a sensor module  110 G disposed at the other end of the side corresponding to the straight line  216 C are one pair of sensors  120 . In addition, the sensor  120  included in the sensor module  110 D disposed at one end of the side corresponding to the straight line  216 D and a sensor  120  included in a sensor module  110 H disposed at the other end of the side corresponding to the straight line  216 D are one pair of sensors  120 . 
     The eight sensors  120  are disposed in the surrounding region  215  that is, as viewed in the first direction, a region surrounding the power transmission coil unit  210  along the outer edge of the power transmission coil unit  210 . In addition, each of the eight sensors  120 , as viewed in the first direction, is disposed such that the second angle is ½ of the first angle. Besides, the power transmission coil unit  210 , as viewed in the first direction, has a substantially quadrangular shape. The eight sensors  120  are disposed two by two at the four vertices of the substantially quadrangular shape. 
     Note that two sensors  120  disposed at one vertex are preferably disposed not to interfere with each other&#39;s sensing. For example, the two sensors  120  disposed at one vertex may be situated at different positions in the Z-axis direction. Alternatively, the two sensors  120  disposed at one vertex may be situated at the same position in the Z-axis direction, if the two sensors  120  do not interfere with each other&#39;s sensing. 
     Here, a plurality of pairs of the sensors  120  is disposed such that the detection range  115  of one sensor  120  includes at least a part of the other sensor  120 , and that the detection range  115  of the other sensor  120  includes at least a part of the one sensor  120 . Hereinafter, referring to  FIG. 9 , a description is given of the arrangement of one pair of sensors  120  including the sensor  120 , which the sensor module  110 A includes, and the sensor  120 , which the sensor module  110 E includes. 
     The sensor  120  included in the sensor module  110 A is disposed near one end of a side including the straight line  216 A. The detection range  115 A is the detection range  115  of the sensor  120  included in the sensor module  110 A. The non-detection range  116 A is the non-detection range  116  of the sensor  120  included in the sensor module  110 A. A center axis  117 A is the center axis of the detection range  115 A. θ 2   a  is a detection angle spanning in the in-plane direction of the first plane in the detection range  115 A. θ 3   a  is an angle formed between the straight line  216 A and the center axis  117 A. The sensor  120  included in the sensor module  110 A is disposed such that θ 3   a  is ½ of θ 2   a.    
     The sensor  120  included in the sensor module  110 E is disposed near the other end of the side including the straight line  216 A. A detection range  115 E is the detection range  115  of the sensor  120  included in the sensor module  110 E. A non-detection range  116 E is the non-detection range  116  of the sensor  120  included in the sensor module  110 E. A center axis  117 E is the center axis of the detection range  115 E. θ 2   e  is a detection angle spanning in the in-plane direction of the first plane in the detection range  115 E. θ 3   e  is an angle formed between the straight line  216 A and the center axis  117 E. The sensor  120  included in the sensor module  110 E is disposed such that θ 3   e  is ½ of θ 2   e.    
     Here, the detection range  115 A includes at least a part of the sensor  120  included in the sensor module  110 E, and the detection range  115 E includes at least a part of the sensor  120  included in the sensor module  110 A. Thus, the detection range  115 A and the detection range  115 E, as viewed in the first direction, largely overlap in the vicinity of the straight line  216 A. In addition, in the present embodiment, the entirety of the non-detection range  116 E, as viewed in the first direction, overlaps the detection range  115 A, and the entirety of the non-detection range  116 A, as viewed in the first direction, overlaps the detection range  115 E. Accordingly, no detection blind spot exists in the vicinity of the straight line  216 A. 
     In addition, the detection range  115 B includes at least a part of the sensor  120  included in the sensor module  110 F, and the detection range  115 F includes at least a part of the sensor  120  included in the sensor module  110 B. Thus, the detection range  115 B and the detection range  115 F, as viewed in the first direction, largely overlap in the vicinity of the straight line  216 B. In addition, in the present embodiment, the entirety of the non-detection range  116 F, as viewed in the first direction, overlaps the detection range  115 B, and the entirety of the non-detection range  116 B, as viewed in the first direction, overlaps the detection range  115 F. Accordingly, no detection blind spot exists in the vicinity of the straight line  216 B. 
     Furthermore, the detection range  115 C includes at least a part of the sensor  120  included in the sensor module  110 G, and the detection range  115 G includes at least a part of the sensor  120  included in the sensor module  110 C. Thus, the detection range  115 C and the detection range  115 G, as viewed in the first direction, largely overlap in the vicinity of the straight line  216 C. In addition, in the present embodiment, the entirety of the non-detection range  116 G, as viewed in the first direction, overlaps the detection range  115 C, and the entirety of the non-detection range  116 C, as viewed in the first direction, overlaps the detection range  115 G. Accordingly, no detection blind spot exists in the vicinity of the straight line  216 C. 
     Besides, the detection range  115 D includes at least a part of the sensor  120  included in the sensor module  110 H, and the detection range  115 H includes at least a part of the sensor  120  included in the sensor module  110 D. Thus, the detection range  115 D and the detection range  115 H, as viewed in the first direction, largely overlap in the vicinity of the straight line  216 D. In addition, in the present embodiment, the entirety of the non-detection range  116 H, as viewed in the first direction, overlaps the detection range  115 D, and the entirety of the non-detection range  116 D, as viewed in the first direction, overlaps the detection range  115 H. Accordingly, no detection blind spot exists in the vicinity of the straight line  216 D. 
     In this manner, no detection blind spot exists in the vicinity of the straight line  216 A, straight line  216 B, straight line  216 C or straight line  216 D. In other words, in the present embodiment, each of all regions included in the surrounding region  215  is included in the detection range  115  of any one of the plurality of sensors  120 . 
     In the present embodiment, the plurality of tpairs of the sensors  120  that the detection ranges  115  overlap each other, is disposed such that the detection range of one sensor  120  includes at least a part of the other sensor  120 , and that the detection range of the other sensor  120  includes at least a part of the one sensor  120 . Thus, according to the present embodiment, the detection blind spot near the periphery of the power transmission coil  211  can further be reduced. 
     Additionally, according to the present embodiment, the object  30  disposed in a detection range where the detection ranges  115  overlap each other can exactly be detected. Moreover, according to the present embodiment, even when one of the paired sensors  120  is unable to perform detection because of damage or adhesion of contamination, the detection function can be maintained in regard to the overlapping detection range. 
     Additionally, according to the present embodiment, each of all regions included in the surrounding region  215  is included in the detection range  115  of any one of the plurality of sensors  120 . Thus, according to the present embodiment, the detection blind spot near the periphery of the power transmission coil  211  can further be reduced. 
     Embodiment 3 
     In Embodiments 1 and 2, the example was described in which the power transmission coil unit  210 , as viewed in the first direction, has the substantially quadrangular shape. In the present embodiment, an example is described in which a power transmission coil unit  210 A, as viewed in the first direction, has a substantially hexagonal shape. Note that the description of the same configuration and process as in Embodiments 1 and 2 is omitted or simplified. 
       FIG. 10  is an arrangement diagram of six sensor modules  110  included in the object detection apparatus  100  according to the present embodiment. In the present embodiment, an outer edge of the power transmission coil unit  210 A, as viewed in the first direction, has a substantially hexagonal shape. The outer edge of the power transmission coil unit  210 A is substantially an outer edge of a housing  214 A that the power transmission coil unit  210 A includes. The substantially hexagonal shape includes six sides, which comprise a side including a straight line  216 A, a side including a straight line  216 B, a side including a straight line  216 C, a side including a straight line  216 D, a side including a straight line  216 E and a side including a straight line  216 F, and six vertices that are each connected to two corresponding sides among these six sides. 
     The sensor module  110 A is disposed near the vertex connected to the side including the straight line  216 A and the side including the straight line  216 B. The sensor module  110 B is disposed near the vertex connected to the side including the straight line  216 B and the side including the straight line  216 C. The sensor module  110 C is disposed near the vertex connected to the side including the straight line  216 C and the side including the straight line  216 D. The sensor module  110 D is disposed near the vertex connected to the side including the straight line  216 D and the side including the straight line  216 E. The sensor module  110 E is disposed near the vertex connected to the side including the straight line  216 E and the side including the straight line  216 F. The sensor module  110 F is disposed near the vertex connected to the side including the straight line  216 F and the side including the straight line  216 A. 
     The six sensors  120  are disposed in a surrounding region  215 A that is, as viewed in the first direction, a region surrounding the power transmission coil unit  210 A along the outer edge of the power transmission coil unit  210 A. In addition, each of the six sensors  120 , as viewed in the first direction, is disposed such that the second angle is ½ of the first angle. 
     In the present embodiment, each of the plurality of sensors  120 , as viewed in the first direction, is disposed in the surrounding region  215 A such that the second angle is ½ of the first angle. Thus, according to the present embodiment, while the broad detection range  115  is being secured, the detection blind spot near the periphery of the power transmission coil  211  can be reduced. 
     Furthermore, in the present embodiment, the power transmission coil unit  210 A, as viewed in the first direction, has a substantially polygonal shape, and the sensors  120  are disposed at the vertices of the substantially polygonal shape. Thus, according to the present embodiment, the detection blind angle near the periphery of the power transmission coil  211  can be efficiently reduced by a small number of sensors  120 . 
     Embodiment 4 
     In Embodiment 1, the example was described in which each of the plurality of sensors  120 , as viewed in the first direction, is disposed in the surrounding region  215  such that the second angle is ½ of the first angle. In the present embodiment, an example is described in which each of the plurality of sensors  120 , as viewed in the first direction, is disposed in the surrounding region  215  such that the second angle is less than ½ of the first angle. Note that the description of the same configuration and process as in Embodiments 1 to 3 is omitted or simplified. 
       FIG. 11  is an arrangement diagram of four sensor modules  110  included in the object detection apparatus  100  according to the present embodiment. In the present embodiment, too, the four sensors  120  are disposed near the four vertices of the quadrangle representing the power transmission coil unit  210  in the surrounding region  215 . θ 2  is a detection angle spanning in the in-plane direction of the first plane. In the present embodiment, the first angle that is the detection angle is 90 degrees. θ 4  is an angle formed between the straight line  216  overlapping the detection range  115 , as viewed in the first direction, among the four straight lines  216 , and the center axis  117  of the detection range  115 . In the present embodiment, each of the plurality of sensors  120  is disposed such that θ 4  is less than ½ of θ 2 . 
     Specifically, the sensor  120  included in the sensor module  110 A is disposed such that an end portion of the detection range  115  is located more on the center side of the power transmission coil unit  210  than the straight line  216 A. In addition, the sensor  120  included in the sensor module  110 B is disposed such that an end portion of the detection range  115  is located more on the center side of the power transmission coil unit  210  than the straight line  216 B. Further, the sensor  120  included in the sensor module  110 C is disposed such that an end portion of the detection range  115  is located more on the center side of the power transmission coil unit  210  than the straight line  216 C. Besides, the sensor  120  included in the sensor module  110 D is disposed such that an end portion of the detection range  115  is located more on the center side of the power transmission coil unit  210  than the straight line  216 D. 
     Additionally, in the present embodiment, the entirety of the non-detection range  116  of a certain sensor  120  is included in the detection range  115  of another sensor  120 . Specifically, the entirety of the non-detection range  116  of the sensor  120  included in the sensor module  110 A is included in the detection range  115 B of the sensor  120  included in the sensor module  110 B. In addition, the entirety of the non-detection range  116  of the sensor  120  included in the sensor module  110 B is included in the detection range  115 C of the sensor  120  included in the sensor module  110 C. 
     Besides, the entirety of the non-detection range  116  of the sensor  120  included in the sensor module  110 C is included in the detection range  115 D of the sensor  120  included in the sensor module  110 D. In addition, the entirety of the non-detection range  116  of the sensor  120  included in the sensor module  110 D is included in the detection range  115 A of the sensor  120  included in the sensor module  110 A. As a result, in the present embodiment, each of all regions included in the surrounding region  215  is included in the detection range  115  of any one of the plurality of sensors  120 . 
     In the present embodiment, each of the plurality of sensors  120 , as viewed in the first direction, is disposed in the surrounding region  215  such that the second angle is less than ½ of the first angle. Specifically, in the present embodiment, an end portion of the detection range  115  of the sensor  120  is located more on the center side of the power transmission coil unit  210  than the straight line  216  that constitutes the outer edge of the power transmission coil unit  210 . Thus, according to the present embodiment, the detection blind spot near the periphery of the power transmission coil  211  can be reduced. 
     Furthermore, in the present embodiment, the power transmission coil unit  210 , as viewed in the first direction, has a substantially polygonal shape, and the plurality of sensors  120  is disposed at the vertices of the substantially polygonal shape. Thus, according to the present embodiment, the detection blind angle near the periphery of the power transmission coil  211  can be efficiently reduced by a small number of sensors  120 . 
     Additionally, in the present embodiment, each of all regions included in the surrounding region  215  is included in the detection range  115  of any one of the plurality of sensors  120 . Thus, according to the present embodiment, the detection blind angle near the periphery of the power transmission coil  211  can further be reduced. 
     Embodiment 5 
     In Embodiment 1, the example was described in which the plurality of sensor modules  110  and the power transmission coil unit  210  are separately disposed. In the present embodiment, an example is described in which the plurality of sensor modules  110  is provided as one body with the power transmission coil unit  210 . Note that the description of the same configuration and process as in Embodiment 1 is omitted or simplified. 
       FIG. 12  is an arrangement diagram of sensor modules  110  according to the present embodiment. In the present embodiment, a power transmission coil unit  210 B includes a housing  214 B that accommodates the power transmission coil  211 , and the plurality of sensor modules  110  is accommodated in the housing  214 B that the power transmission coil unit  210 B includes. Specifically, in the present embodiment, four sensor modules  110  are assembled in the inside of the housing  214 B of the power transmission coil unit  210 B. 
     Specifically, the housing  214 B includes a storing portion  217 A that stores the sensor module  110 A, a storing portion  217 B that stores the sensor module  110 B, a storing portion  217 C that stores the sensor module  110 C, and a storing portion  217 D that stores the sensor module  110 D. The housing  214 B has a substantially quadrangular shape in plan view, and includes the storing portion  217 A, storing portion  217 B, storing portion  217 C and storing portion  217 D at the four corners thereof. 
     In the present embodiment, the housing  214 B functions as a housing of the four sensor modules  110 , and the four sensor modules  110  do not include housings  160 . Note that opening portions are provided in those parts of the housing  214 B, which are opposed to the detection windows  121 . The storing portion  217  is a general term for the storing portion  217 A, storing portion  217 B, storing portion  217 C and storing portion  217 D. 
     In the present embodiment, too, each of the plurality of sensors  120 , as viewed in the first direction, is disposed in a surrounding region  215 B such that the second angle is ½ of the first angle. Thus, according to the present embodiment, while the broad detection range  115  is being secured, the detection blind spot near the periphery of the power transmission coil  211  can be reduced. 
     In addition, in the present embodiment, the power transmission coil unit  210 , as viewed in the first direction, has a substantially polygonal shape, and the plurality of sensors  120  is disposed at the vertices of the substantially polygonal shape. Thus, according to the present embodiment, the detection blind angle near the periphery of the power transmission coil  211  can be efficiently reduced by a small number of sensors  120 . 
     Furthermore, in the present embodiment, a plurality of sensor modules  110  is accommodated in the housing  214 B that the power transmission coil unit  210 B includes. Thus, according to the present embodiment, the time and labor for arranging the plurality of sensor modules  110  can be reduced. 
     (Modifications) 
     While the embodiments of the present disclosure have been described above, modifications and applications in various modes can be made in implementing the present disclosure. In the present disclosure, which part of the structures, functions and operations described in the above embodiments is to be adopted is discretionary. In addition, in the present disclosure, besides the above-described structures, functions and operations, other structures, functions and operations may be adopted. The above-described embodiments may freely be combined as appropriate. The number of structural elements described in the embodiments can be adjusted as appropriate. Furthermore, needless to say, the materials, sizes, electrical characteristics, and the like, which can be adopted in the present disclosure, are not limited to those in the above-described embodiments. 
     In Embodiment 1, the example was described in which the outer shape of the power transmission coil unit  210 , as viewed in the first direction, is the quadrangle, and the number of sensors  120  is four. The outer shape of the power transmission coil unit  210  may be a triangle, and the number of sensors  120  may be three. In addition, the outer shape of the power transmission coil unit  210  may be a polygon having five or more vertices, and the number of sensors  120  may be the same as the number of vertices. Besides, the outer shape of the power transmission coil unit  210 , as viewed in the first direction, may not be a polygon. For example, as the outer shape of the power transmission coil unit  210  as viewed in the first direction, various shapes including straight lines and curves may be adopted. 
     In Embodiment 1, the example was described in which the ultrasonic sensor was adopted as the sensor  120  that is used for detecting the object  30 . Various types of sensors can be adopted as the sensor  120 . For example, as the sensor  120 , a millimeter-wave sensor, an X-band sensor, an infrared sensor, and a visible-light sensor can be adopted. In addition, in Embodiment 1, the example was described in which the first angle that is the detection angle spanning in the in-plane direction of the first plane orthogonal to the first direction is 90 degrees. The first angle may be an angle less than 90 degrees, or may be an angle greater than 90 degrees. 
     By applying the operation program, which defines the operation of the object detection apparatus  100  according to the present disclosure, to a computer such as an existing personal computer or information terminal apparatus, this computer can be caused to function as the object detection apparatus  100  according to the present disclosure. In addition, a method of distributing the program may be freely chosen, and the program may be distributed by being stored in a non-transitory computer-readable recording medium such as a compact disk ROM (CD-ROM), a digital versatile disk (DVD), a magneto-optical disk (MO) or a memory card, or may be distributed via a communication network such as the Internet. 
     The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.