Foreign body detection device

Abstract

The foreign matter detection device of the present invention comprises: a plurality of first detection coils (42-1 to 42-n) which are arranged to be electromagnetically coupled to each other between a transmitting coil (12) of a power transmission device (2) and a receiving coil (21) of a power receiving device (3) for transmitting power in a contactless manner, and together with a first capacitor, form a resonance circuit having a first resonance frequency; a plurality of second detection coils (44-1 to 44-m) which are arranged to be electromagnetically coupled to each other, and together with a second capacitor, form a resonance circuit having a second resonance frequency; a power supply circuit (41-1, 41-2) which supplies alternating current having a frequency at which the detection coil resonates to each detection coil; and a detection circuit (46-1, 46-2) which detects foreign matter mixed between the transmitting coil (12) and the receiving coil (21) based on the voltage of the alternating current transmitted via each detection coil.

Description

Technical Field

[0001] The present invention relates to a foreign object detection device for detecting foreign objects in a power transmission system for transmitting power in a contactless manner. Background Art

[0002] In the past, so-called contactless power supply (also called wireless power supply) technology that transmits power through space without passing through metal contacts, etc. has been studied. As one of such contactless power supply technologies, a method of supplying power by electromagnetic induction is known. In the method of supplying power by electromagnetic induction, electromagnetic coupling is performed by a coil on the primary side (transmission side or power supply side) (hereinafter referred to as a transmitting coil) and a coil on the secondary side (power receiving side) (hereinafter referred to as a receiving coil), and power is transmitted from the transmitting coil to the receiving coil.

[0003] In a power transmission system using such a contactless power supply technology, foreign matter such as metal may sometimes enter between the transmitting coil and the receiving coil. In such a case, the foreign matter may be inductively heated and catch fire during power transmission, or the device may fail due to the heat generated by the foreign matter. In addition, in such a power transmission system, the relative positional relationship between the transmitting coil and the receiving coil may change during power transmission, resulting in a change in the coupling degree between the transmitting coil and the receiving coil. Therefore, a technology for preventing failures caused by foreign matter mixed between the transmitting coil and the receiving coil even when the coupling degree between the transmitting coil and the receiving coil changes has been proposed (for example, refer to patent document 1). In this technology, even if the frequency of the alternating current supplied to the transmitting coil of the power transmission device of the contactless power supply device is changed within the entire specified frequency range, when the contactless power supply device does not perform a constant voltage output operation, the contactless power supply device determines that some foreign matter has been mixed between the transmitting coil and the receiving coil of the power receiving device, and stops supplying power to the transmitting coil.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-207764 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, when a very small foreign object is mixed between the transmitting coil and the receiving coil, the power transmission characteristics from the power transmitting device to the power receiving device do not change, and as a result, the foreign object mixed between the transmitting coil and the receiving coil may not be detected.

[0009] Therefore, an object of the present invention is to provide a foreign object detection device that can improve the accuracy of detecting foreign objects mixed between a transmission coil of a power transmission side device and a reception coil of a power reception side device.

[0010] Solutions to Solve Problems

[0011] As one embodiment of the present invention, a foreign object detection device is provided. The foreign object detection device comprises: a plurality of first detection coils, which are arranged on a substrate so as to be electromagnetically coupled to each other, and the substrate is arranged between a transmitting coil of a power transmission device and a receiving coil of a power receiving device for transmitting power in a contactless manner; a plurality of first capacitors, which respectively form a first resonant circuit having a first resonant frequency with each of the plurality of first detection coils; a plurality of second detection coils, which are arranged on the substrate so as to be electromagnetically coupled to each other; a plurality of second capacitors, which respectively form a second resonant circuit having a second resonant frequency different from the first resonant frequency with each of the plurality of second detection coils; and at least one power supply circuit for the plurality of first detection coils. The first input coil among the plurality of second detection coils is supplied with alternating current having a first frequency resonant with each first resonant circuit, and the second input coil among the plurality of second detection coils is supplied with alternating current having a second frequency resonant with each second resonant circuit; and the detection circuit detects a first voltage of the alternating current transmitted via the plurality of first detection coils from a first output coil different from the first input coil among the plurality of first detection coils, and detects a second voltage of the alternating current transmitted via the plurality of second detection coils from a second output coil different from the second input coil among the plurality of second detection coils, and detects foreign matter mixed between the transmitting coil and the receiving coil based on the detected first voltage or second voltage.

[0012] With such a configuration, the foreign object detection device of the present invention can improve the accuracy of detecting foreign objects mixed between the transmission coil of the power transmission side device and the reception coil of the power reception side device.

[0013] In the foreign matter detection device, the plurality of first detection coils and the plurality of second detection coils are preferably arranged alternately with each other when viewed in a normal direction of the substrate.

[0014] Thus, in the foreign object detection device, the foreign object mixed between the transmitting coil and the receiving coil is located near one of the plurality of first detection coils and the plurality of second detection coils, so that one of the first voltage or the second voltage changes to a degree sufficient to detect the foreign object due to the mixing of the foreign object. Therefore, the foreign object detection device can detect the foreign object with high accuracy regardless of the position of the mixed foreign object.

[0015] Furthermore, in the foreign object detection device, preferably, the first frequency is a frequency at which each second resonance circuit does not resonate, and the second frequency is a frequency at which each first resonance circuit does not resonate.

[0016] Thus, the alternating current with the first frequency does not affect each second resonant circuit, and conversely, the alternating current with the second frequency does not affect each first resonant circuit. Therefore, when a foreign object is located near one of the plurality of first detection coils, the first voltage changes to a degree sufficient to detect the foreign object. Similarly, when a foreign object is located near one of the plurality of second detection coils, the second voltage changes to a degree sufficient to detect the foreign object. Therefore, regardless of the position of the mixed foreign object, the foreign object detection device can detect the foreign object with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic configuration diagram of a power transmission system including a foreign object detection device according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of a foreign body detection device.

[0019] Figure 3 This is a schematic side cross-sectional view showing an example of the positional relationship between a substrate on which a foreign object detection device is provided and a transmission coil.

[0020] Figure 4 This is a schematic plan view showing an example of the arrangement of the detection coils included in the foreign object detection device.

[0021] Figure 5 1 is a circuit configuration diagram showing an example of a power supply circuit.

[0022] Figure 6 1 is a circuit configuration diagram showing an example of a detection circuit.

[0023] Figure 7 This is a diagram showing an example of the arrangement of the first detection coil and the second detection coil in a simulation showing a change in the frequency characteristic of the voltage detected by the detection circuit based on the presence or absence of foreign matter mixing.

[0024] Figure 8 This is a diagram showing an example of a simulation result showing a change in the frequency characteristic of the detection voltage of the detection circuit with respect to the alternating current transmitted between the first detection coils, depending on the presence or absence of foreign matter mixing.

[0025] Fig. 9 This is a diagram showing an example of a simulation result showing a change in the frequency characteristic of the detection voltage of the detection circuit with respect to the alternating current transmitted between the first detection coils, depending on the presence or absence of foreign matter mixing.

[0026] Fig.10 This is a diagram showing an example of a simulation result showing a change in the frequency characteristic of the detection voltage of the detection circuit with respect to the alternating current transmitted between the second detection coils, depending on the presence or absence of foreign matter mixing.

[0027] Fig.11 This is a diagram showing an example of a simulation result showing a change in the frequency characteristic of the detection voltage of the detection circuit with respect to the alternating current transmitted between the second detection coils, depending on the presence or absence of foreign matter mixing.

[0028] Fig.12 (a) and (b) are diagrams showing simulation results showing changes in the frequency characteristics of the detection voltage depending on the presence or absence of foreign matter in a comparative example.

[0029] Fig.13 This is a circuit configuration diagram of a power supply circuit according to a modified example. DETAILED DESCRIPTION

[0030] Below, while referring to the attached Figure 1A foreign object detection device according to an embodiment of the present invention is described. The foreign object detection device has a substrate disposed between a transmitting coil of a power transmission side device (hereinafter referred to as simply a power transmission device) and a receiving coil of a power receiving side device (hereinafter referred to as simply a power receiving device) in a power transmission system that transmits power by contactless transmission, and has a plurality of first detection coils formed on the substrate and disposed so as to be electromagnetically coupled to each other, and a plurality of second detection coils disposed so as to be electromagnetically coupled to each other. Each of the plurality of first detection coils constitutes a first resonant circuit together with a first capacitor connected to the first detection coil. Furthermore, each of the first resonant circuits has a first resonant frequency that is different from the frequency of the power supplied to the transmitting coil of the power transmission device (hereinafter referred to as a transmission frequency for convenience of description) and that does not resonate in either the resonant circuit including the transmitting coil (when the resonant circuit is provided on the power transmission side) or the resonant circuit including the receiving coil. Similarly, each of the plurality of second detection coils constitutes a second resonant circuit together with a second capacitor connected to the second detection coil. Furthermore, each of the second resonant circuits has a second resonant frequency that is different from the transmission frequency and the first frequency and that does not resonate with either the resonant circuit including the transmitting coil or the resonant circuit including the receiving coil. The foreign object detection device supplies an alternating current having a first frequency that each of the first resonant circuits can resonate with to a first input coil that is one of the plurality of first detection coils, and detects a first voltage output from a first output coil that is another of the plurality of first detection coils. Similarly, the foreign object detection device supplies an alternating current having a second frequency that each of the second resonant circuits can resonate with to a second input coil that is one of the plurality of second detection coils, and detects a second voltage output from a second output coil that is another of the plurality of second detection coils.

[0031] If a conductive foreign object such as metal is mixed between the transmitting coil and the receiving coil, the resonance characteristic of one of the plurality of first resonant circuits or the plurality of second resonant circuits changes, and as a result, at least one of the detected first voltage and the second voltage changes. In particular, even if the foreign object is mixed in a position where the resonance characteristic changes less in any of the plurality of first resonant circuits, the resonance characteristic of one of the plurality of second resonant circuits changes relatively greatly, and conversely, even if the foreign object is mixed in a position where the resonance characteristic changes less in any of the plurality of second resonant circuits, the resonance characteristic of one of the plurality of first resonant circuits changes relatively greatly. As a result, if the foreign object is mixed, at least one of the first voltage and the second voltage changes greatly.

[0032] Therefore, the foreign object detection device monitors the first voltage and the second voltage to be detected, and if at least one of the first voltage and the second voltage deviates from a predetermined reference range corresponding to the case where no foreign object is mixed, it is determined that a foreign object is mixed between the transmitting coil and the receiving coil. Therefore, the foreign object detection device can detect the foreign object with high accuracy regardless of the position of the foreign object mixed between the transmitting coil and the receiving coil.

[0033] Figure 1 FIG. 1 is a schematic diagram of a power transmission system including a foreign object detection device according to an embodiment of the present invention. Figure 1 As shown in FIG. 1 , a power transmission system 1 includes a power transmission device 2, a power receiving device 3, and a foreign object detection device 4. The power transmission device 2 and the power receiving device 3 constitute a contactless power supply device, and power is transmitted from the power transmission device 2 to the power receiving device 3 via space in a contactless manner. The power transmission device 2 includes a power supply circuit 11 and a transmission coil 12. On the other hand, the power receiving device 3 includes a receiving coil 21, a resonant capacitor 22, and a power receiving circuit 23. The power transmission system 1 can be set as a contactless power supply device of, for example, a so-called primary series and secondary series resonant capacitor method (SS method) or a primary series and secondary parallel resonant capacitor method (SP method). Alternatively, the power transmission system 1 can also be a contactless power supply device of a method (NS method) in which the resonance on the primary side is not used, and the receiving coil and the resonant capacitor on the secondary side are in a series resonant method, or a contactless power supply device of a method (NP method) in which the resonance on the primary side is not used, and the receiving coil and the resonant capacitor on the secondary side are in a parallel resonant method.

[0034] First, the power transmission device 2 will be described.

[0035] The power supply circuit 11 supplies AC power to the transmitting coil 12. For this purpose, for example, the power supply circuit 11 has a DC power supply that supplies DC power, an inverter circuit that converts the DC power supplied from the DC power supply into AC power and supplies it to the transmitting coil 12, and a control circuit that controls the inverter circuit. The inverter circuit may be a full-bridge inverter in which four switching elements (for example, MOSFETs) are connected in a full-bridge shape, or a half-bridge inverter in which two switching elements are connected in a half-bridge shape. The control circuit controls the switching of the on / off of each switching element of the inverter circuit so that the frequency of the AC power supplied to the transmitting coil 12 is a specified frequency (for example, the frequency of the resonance of the resonant circuit of the power receiving device 3). The power supply circuit 11 may also have a DC-DC converter between the DC power supply and the inverter circuit. Alternatively, the power supply circuit 11 may include a rectifier circuit connected to the AC power supply to rectify the AC power from the AC power supply, and a power factor improvement circuit connected to the rectifier circuit to convert the pulsating current power output from the rectifier circuit into DC power, instead of the DC power supply. In this case, for example, in order to ensure that the voltage of the power received by the power receiving device 3 is constant, the control circuit may control the power factor improvement circuit to adjust the voltage of the DC power supplied to the inverter circuit.

[0036] The transmitting coil 12 transmits the AC power supplied from the power supply circuit 11 to the receiving coil 21 of the power receiving device 3 through space. Furthermore, the power transmission device 2 may include a capacitor connected in series with the transmitting coil 12 between the transmitting coil 12 and the inverter circuit of the power supply circuit 11. The capacitor may be a capacitor for cutting off the DC power, or a capacitor for forming a resonant circuit that resonates with the transmitting coil 12 at the frequency of the AC power supplied to the transmitting coil 12.

[0037] Furthermore, the power transmission device 2 may also include a communicator that receives a signal indicating the power receiving status of the power receiving device 3. In this case, the control circuit of the power supply circuit 11 may also change the switching timing of the on / off of each switching element of the inverter circuit according to the power receiving status, thereby changing the frequency of the AC power supplied to the transmission coil 12.

[0038] Moreover, if a signal is received from the foreign object detection device 4 indicating that a foreign object has been detected mixed between the transmitting coil 12 and the receiving coil 21, the control circuit of the power supply circuit 11 can also turn off the switching elements of the inverter to stop the power supply from the power supply circuit 11 to the transmitting coil 12.

[0039] Next, the power receiving device 3 will be described.

[0040] The receiving coil 21 and the resonant capacitor 22 together form a resonant circuit, and receive power from the transmitting coil 12 by resonating with the AC current flowing in the transmitting coil 12 of the power transmission device 2. For this purpose, the resonant capacitor 22 may be connected in series with the receiving coil 21, or may be connected in parallel with the receiving coil 21. Then, the AC power output from the resonant circuit formed by the receiving coil 21 and the resonant capacitor 22 is output to the power receiving circuit 23. In addition, the number of turns of the receiving coil 21 and the number of turns of the transmitting coil 12 may be the same, or may be different from each other.

[0041] The power receiving circuit 23 converts the AC power from the resonance circuit formed by the receiving coil 21 and the resonance capacitor 22 into DC power, and outputs the DC power to a load circuit (not shown) connected to the power receiving circuit 23. To this end, the power receiving circuit 23 has, for example, a full-wave rectifier circuit that converts the AC power from the resonance circuit into pulsating current power, and a smoothing capacitor for smoothing the pulsating current power output from the full-wave rectifier circuit and outputting it to the load circuit. In addition, the power receiving circuit 23 may also have a voltmeter for measuring the voltage output to the load circuit, a communicator for transmitting a signal indicating the power receiving status such as the voltage measured by the voltmeter to the power transmission device 2, a switch element for switching the connection or disconnection between the load circuit and the power receiving circuit 23, and a control circuit for controlling the switching of the switch element on / off, etc.

[0042] Next, the foreign object detection device 4 of this embodiment is described. The foreign object detection device 4 is arranged between the transmitting coil 12 and the receiving coil 21 when the power transmission device 2 and the power receiving device 3 are in a positional relationship where power transmission is possible, that is, when the transmitting coil 12 and the receiving coil 21 are in a positional relationship where electromagnetic coupling is possible. Furthermore, the foreign object detection device 4 detects conductive foreign objects such as metal mixed between the transmitting coil 12 and the receiving coil 21.

[0043] Figure 2 It is a schematic structural diagram of the foreign matter detection device 4. Figure 3 1 is a schematic side cross-sectional view showing an example of the positional relationship between the substrate on which the foreign object detection device 4 is installed and the transmission coil 12. Figure 4 It is a schematic plan view showing an example of the arrangement of the detection coils included in the foreign object detection device 4 .

[0044] like Figure 2As shown in , the foreign object detection device 4 includes two power supply circuits 41-1 and 41-2, a plurality of first detection coils 42-1 to 42-n (n is an integer greater than or equal to 2), a plurality of first capacitors 43-1 to 43-n, a plurality of second detection coils 44-1 to 44-m (m is an integer greater than or equal to 2), a plurality of second capacitors 45-1 to 45-m, and a detection circuit 46. In the present embodiment, the detection circuit 46 includes two detection circuits 46-1 and 46-2. These elements included in the foreign object detection device 4 are provided on a substrate 47 located between the transmission coil 12 and the reception coil 21 in a positional relationship where the transmission coil 12 and the reception coil 21 can be electromagnetically coupled. In the present embodiment, the substrate 47 is mounted in the power transmission device 2. Then, signals indicating the foreign object detection results from the detection circuits 46-1 and 46-2 are output to the power supply circuit 11 of the power transmission device 2.

[0045] Next, the details of the power supply circuits 41-1 and 41-2 are described. In this embodiment, it can be assumed that the power supply circuits 41-1 and 41-2 are the same except that the frequencies of the supplied AC power are different from each other. Therefore, the power supply circuit 41-1 is mainly described below, and the power supply circuit 41-2 is described in terms of differences from the power supply circuit 41-1.

[0046] Figure 5 4 is a circuit diagram showing an example of the power supply circuit 41 - 1 . The power supply circuit 41 - 1 includes, for example, a DC power supply 51 for supplying DC power, a power supply coil 52 , a capacitor 53 , an inverter circuit 54 , and a control circuit 55 for controlling the inverter circuit 54 .

[0047] One end of the power supply coil 52 is connected to the inverter circuit 54 via the capacitor 53, and the other end is grounded. Moreover, the power supply coil 52 is configured to be electromagnetically coupled with the first input coil (in the present embodiment, the detection coil 42-1) which is one of the plurality of first detection coils 42-1 to 42-n, and the AC power supplied from the inverter circuit 54 is supplied to the first input coil. Furthermore, the connection order of the power supply coil 52 and the capacitor 53 can also be reversed. Furthermore, for the power supply circuit 41-2, the power supply coil 52 is configured to be electromagnetically coupled with the second input coil (in the present embodiment, the detection coil 44-1) which is one of the plurality of second detection coils 44-1 to 44-m, and the AC power supplied from the inverter circuit 54 is supplied to the second input coil.

[0048] The inverter circuit 54 converts the DC power supplied from the DC power supply 51 into AC power and supplies it to the power supply coil 52. In this example, the inverter circuit 54 is configured as a half-bridge inverter in which two switching elements (for example, MOSFET) are connected in a half-bridge shape, but the inverter circuit 54 may be a full-bridge inverter in which four switching elements are connected in a full-bridge shape. The control circuit 55 controls the switching of the on / off of each switching element of the inverter circuit so that the frequency of the AC power supplied to the power supply coil 52 becomes the first frequency that can resonate with the first resonant circuit having the first resonant frequency composed of the first detection coil 42-i (i=1, 2, ..., n) and the first capacitor 43-i. That is, the first frequency can be any frequency as long as the supplied AC power can propagate in each first detection coil, and for example, it can be set to the first resonant frequency itself. In addition, for the power supply circuit 41-2, the control circuit 55 controls the switching of the on / off of each switching element of the inverter circuit so that the frequency of the AC power supplied to the power supply coil 52 becomes the second frequency that can be resonated by the second resonance circuit having the second resonance frequency composed of the second detection coil 44-i (i=1, 2, ..., m) and the second capacitor 45-i. That is, the second frequency can be any frequency that the supplied AC power can propagate in each second detection coil, for example, it can be set to the second resonance frequency itself.

[0049] As described above, with respect to the power supply circuit 41-1, it is preferable that the first frequency of the alternating current supplied from the power supply circuit 41-1 to the first input coil via the power supply coil 52 is different from the transmission frequency of the alternating current supplied to the transmission coil 12 of the power transmission device 2, and is set to a frequency at which neither the resonant circuit including the transmission coil 12 nor the resonant circuit including the reception coil 21 resonates. Moreover, with respect to the power supply circuit 41-2, it is preferable that the second frequency of the alternating current supplied from the power supply circuit 41-2 to the second input coil via the power supply coil 52 is different from the transmission frequency, and is set to a frequency at which neither the resonant circuit including the transmission coil 12 nor the resonant circuit including the reception coil 21 resonates. Furthermore, it is preferable that the first frequency and the second frequency are different from each other, the first frequency is a frequency at which each second resonant circuit does not resonate, and the second frequency is a frequency at which each first resonant circuit does not resonate.

[0050] For example, the first frequency of the AC power supplied by the power supply circuit 41-1 and the second frequency of the AC power supplied by the power supply circuit 41-2 can be set to a frequency higher than the transmission frequency (for example, 85 kHz or 150 kHz), for example, 13.56 MHz, 27.12 MHz, or 40.68 MHz belonging to the ISM band. Furthermore, the first frequency can be set to 13.56 MHz, and the second frequency can be set to 27.12 MHz. Thus, the AC power supplied from the power supply circuit 41-1 and the AC power supplied from the power supply circuit 41-2 are prevented from affecting the power transmission from the power transmission device 2 to the power receiving device 3. In addition, by setting the first frequency and the second frequency in this way, the inductance of each of the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m of the foreign object detection device 4 can be relatively reduced, so that the size of each detection coil can be easily made smaller than the size of the transmission coil 12.

[0051] Furthermore, since the first frequency and the second frequency are different, the first frequency is a frequency at which each second resonance circuit does not resonate, and the second frequency is a frequency at which each first resonance circuit does not resonate, even if the resonance characteristic of any one of the first resonance circuits does not change much due to foreign matter, the resonance characteristic of one of the second resonance circuits changes relatively greatly due to foreign matter. Conversely, even if the resonance characteristic of any one of the second resonance circuits does not change much due to foreign matter, the resonance characteristic of one of the first resonance circuits changes relatively greatly due to foreign matter. Therefore, the detection accuracy of foreign matter is improved.

[0052] Refer again Figure 3 and Figure 4, each of the plurality of first detection coils 42-1 to 42-n is configured as a wiring pattern of a conductor such as metal provided on a substrate 47. Furthermore, the first detection coils 42-i (i=1, 2, ..., n) and the corresponding first capacitors 43-i are connected to each other to form a first resonant circuit respectively. Preferably, the inductance of the first detection coil 42-i and the electrostatic capacitance of the first capacitor 43-i are set so that the first resonant frequency of the first resonant circuit formed by the first detection coil and the first capacitor becomes a frequency that does not resonate at the transmission frequency of the alternating current supplied to the transmitting coil 12. Thus, each first resonant circuit does not resonate with respect to the alternating current transmitted from the power transmission device 2 to the power receiving device 3, so that the foreign object detection device 4 can prevent the alternating current transmitted from the power transmission device 2 to the power receiving device 3 from affecting the detection of foreign objects. Furthermore, it is preferred that the inductance of the first detection coil 42-i and the electrostatic capacitance of the first capacitor 43-i are set so that each first resonant circuit resonates at the first frequency of the alternating current supplied from the power supply circuit 41-1. Thus, the loss before the alternating current supplied from the power supply circuit 41-1 reaches the detection circuit 46-1 is suppressed, so that the foreign object detection device 4 can suppress the decrease in the detection accuracy of the foreign object. As described above, as long as the alternating current supplied from the power supply circuit 41-1 propagates through each first resonant circuit and reaches the detection circuit 46-1, the first resonant frequency and the first frequency may not be consistent.

[0053] Similarly, each of the plurality of second detection coils 44-1 to 44-m is formed as a wiring pattern formed of a conductor such as metal and provided on the substrate 47. Furthermore, the second detection coils 44-i (i=1, 2, ..., m) and the corresponding second capacitors 45-i are connected to each other to form a second resonant circuit respectively. Preferably, the inductance of the second detection coil 44-i and the electrostatic capacitance of the second capacitor 45-i are set so that the second resonant frequency of the second resonant circuit formed by the second detection coil and the second capacitor is a frequency that does not resonate at the transmission frequency of the alternating current supplied to the transmitting coil 12. Thus, each second resonant circuit does not resonate with respect to the alternating current transmitted from the power transmission device 2 to the power receiving device 3, so that the foreign object detection device 4 can prevent the alternating current transmitted from the power transmission device 2 to the power receiving device 3 from affecting the detection of foreign objects. Furthermore, it is preferred that the inductance of the second detection coil 44-i and the electrostatic capacitance of the second capacitor 45-i are set so that each second resonant circuit resonates at the second frequency of the alternating current supplied from the power supply circuit 41-2. As a result, the loss before the alternating current supplied from the power supply circuit 41-2 reaches the detection circuit 46-2 is suppressed, so that the foreign object detection device 4 can suppress the decrease in the detection accuracy of the foreign object. As described above, as long as the alternating current supplied from the power supply circuit 41-2 propagates through each second resonant circuit and reaches the detection circuit 46-2, the second resonant frequency and the second frequency may not be consistent.

[0054] In addition, each of the plurality of first detection coils 42-1 to 42-n is arranged on one surface of the substrate 47 (for example, the surface facing the receiving coil 21, hereinafter referred to as the surface for convenience) so as not to be in electrical contact with each other and to be electromagnetically coupled with each other. For example, each of the plurality of first detection coils 42-1 to 42-n is arranged on the surface of the substrate 47 so as to be directly electromagnetically coupled with one or more of the other first detection coils among the plurality of first detection coils. Furthermore, the power supply circuit 41-1 and the detection circuit 46-1 are also arranged on the surface of the substrate 47. Therefore, the alternating current supplied from the power supply circuit 41-1 resonates with the corresponding first capacitor through each first detection coil, and the alternating current is transmitted to the detection circuit 46-1.

[0055] Similarly, each of the plurality of second detection coils 44-1 to 44-m is arranged on the other side of the substrate 47 (for example, the side facing the transmission coil 12, hereinafter referred to as the back side for convenience) so as not to be in electrical contact with each other and to be electromagnetically coupled with each other. For example, each of the plurality of second detection coils 44-1 to 44-n is arranged on the back side of the substrate 47 so as to be directly electromagnetically coupled with one or more of the other second detection coils among the plurality of second detection coils. Moreover, the power supply circuit 41-2 and the detection circuit 46-2 are also arranged on the back side of the substrate 47. Therefore, each second detection coil resonates with the corresponding second capacitor for the alternating current supplied from the power supply circuit 41-2, and the alternating current is transmitted to the detection circuit 46-2.

[0056] Furthermore, with Figure 4 Contrary to the example shown, the power supply circuit 41-1, the plurality of first detection coils 42-1 to 42-n, and the detection circuit 46-1 may be arranged on the back surface of the substrate 47, and the power supply circuit 41-2, the plurality of second detection coils 44-1 to 44-m, and the detection circuit 46-2 may be arranged on the surface of the substrate 47. In addition, the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m may be arranged on the same surface of the substrate 47.

[0057] The substrate 47 is arranged so that the central axis direction of the transmission coil 12 is substantially parallel to the normal direction of the substrate 47. The plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m are arranged so as to cover the entire transmission coil 12 when the transmission coil 12 is viewed from the central axis direction.

[0058] Furthermore, the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m are alternately arranged when viewed from the normal direction of the substrate 47. Thus, even if the foreign matter mixed between the transmission coil 12 and the reception coil 21 is located outside any winding of the first detection coil, it is located inside any winding of the second detection coil. Therefore, one of the second detection coils is greatly affected by the foreign matter, so that even if the first voltage does not change much, the second voltage changes greatly. Conversely, even if the foreign matter is located outside any winding of the second detection coil, it is located inside any winding of the first detection coil. Therefore, one of the first detection coils is greatly affected by the foreign matter, so that even if the second voltage does not change much, the first voltage changes greatly. In this way, at least one of the first voltage and the second voltage changes greatly regardless of the position of the mixed foreign matter, so the foreign matter detection device 4 can detect the foreign matter with high accuracy.

[0059] Furthermore, in Figure 4 In the example shown, each of the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m is formed in a substantially circular shape, but the shape of each detection coil is not limited to a circular shape, and may be, for example, an elliptical shape or a rectangular shape. In addition, the shapes and sizes of each of the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m may be the same as each other, or may be different from each other. Moreover, it is preferable that the size of each of the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m as viewed from the central axis direction of the transmission coil 12 is smaller than the size of the transmission coil 12. Thus, even when a foreign object smaller than the transmission coil 12 is mixed between the transmission coil 12 and the reception coil 21, one of the plurality of first detection coils 42-1 to 42-n and the plurality of second detection coils 44-1 to 44-m is easily affected by the foreign object, so that the foreign object detection device 4 can detect such a small foreign object with high accuracy.

[0060] Next, the detection circuits 46 - 1 and 46 - 2 will be described.

[0061] The detection circuit 46-1 detects a first voltage of the alternating current transmitted via the plurality of first detection coils 42-1 to 42-n, and detects a foreign object mixed between the transmitting coil 12 and the receiving coil 21 based on the detected first voltage. Similarly, the detection circuit 46-2 detects a second voltage of the alternating current transmitted via the plurality of second detection coils 44-1 to 44-m, and detects a foreign object mixed between the transmitting coil 12 and the receiving coil 21 based on the detected second voltage.

[0062] In this embodiment, the detection circuit 46-1 and the detection circuit 46-2 can be configured to have the same structure, so the detection circuit 46-1 is described below. In the following description, regarding the circuit 46-2, the first detection coil is read as the second detection coil, the power supply circuit 41-1 is read as the power supply circuit 41-2, and the first voltage is read as the second voltage.

[0063] In the present embodiment, the AC power transmitted from the power transmission device 2 to the power receiving device 3 does not affect the transmission of the AC power from the power supply circuit 41-1 to the detection circuit 46-1 via the plurality of first detection coils 42-1 to 42-n. On the other hand, if a foreign object is mixed between the transmission coil 12 and the reception coil 21, the resonance characteristics of one of the plurality of first detection coils 42-1 to 42-n will change due to the foreign object, and the transmission of the AC power from the power supply circuit 41-1 to the detection circuit 46-1 will be affected. In particular, when the foreign object is located near one of the first detection coils, for example, when the foreign object is located inside the winding of one of the first detection coils when viewed from the normal direction of the substrate 47, the influence is significant. As a result, the first voltage detected by the detection circuit 46-1 changes. For example, due to the supplied AC power, if a metal approaches one of the first detection coils through which the current flows, an eddy current is generated in the metal due to the magnetic flux generated near the first detection coil by the current, and a loss is generated. In addition, the inductance of the first detection coil decreases due to the magnetic flux caused by the generated eddy current. In particular, when the metal is a magnetic body, although the change in inductance is small, sometimes only the loss is relatively large. As a result of this, the resonance characteristics of the first resonance circuit including the first detection coil change. Therefore, the detection circuit 46-1 determines whether the detected first voltage is included in the prescribed reference range, and in the case of deviation from the prescribed reference range, it is determined that a foreign object is mixed between the transmission coil 12 and the receiving coil 21. Furthermore, as the prescribed reference range, only the lower limit value can be set, or both the upper limit value and the lower limit value can be set. In the case of setting only the lower limit value, when the detected first voltage is lower than the lower limit value, it is determined that the detected first voltage deviates from the prescribed reference range. In addition, in the case of setting both the upper limit value and the lower limit value, when the detected first voltage is lower than the lower limit value, or higher than the upper limit value, it is determined that the detected first voltage deviates from the prescribed reference range.

[0064] Furthermore, in this example, the number of detection circuits 46 - 1 included in the foreign object detection device 4 is one, but the invention is not limited thereto, and the foreign object detection device 4 may include two or more detection circuits 46 - 1. Figure 4In the array of the plurality of first detection coils 42-1 to 42-n, the upper right end and the lower left end are not so functional as the transmission path of the alternating current from the power supply circuit 41-1 to the detection circuit 46-1. Therefore, the detection circuit 46-1 may be added to one or both of the upper right end and the lower left end of the array of the plurality of detection coils 42-1 to 42-n. Thus, the foreign object detection device 4 can detect foreign objects with high accuracy in a wider range. Similarly, the foreign object detection device 4 may also have two or more detection circuits 46-2.

[0065] Figure 6 Detection circuit 46-1 is a circuit diagram showing an example of a detection circuit 46-1. Detection circuit 46-1 includes a resonant circuit 63 including a receiving coil 61 and a resonant capacitor 62, a high-pass filter 64, an amplifier 65, a half-wave rectifier circuit 66, a low-pass filter 67, a voltage detection circuit 68, and a determination circuit 69. The circuit configuration of detection circuit 46-1 is not limited to Figure 6 The circuit configuration shown may be any of various circuits that detect the first voltage of the alternating current transmitted by each first detection coil and can determine whether the detected first voltage deviates from a predetermined reference range.

[0066] The resonant circuit 63 detects the alternating current supplied from the power supply circuit 41-1 and transmitted via the plurality of first detection coils 42-1 to 42-n. To this end, the receiving coil 61 of the resonant circuit 63 is configured to be electromagnetically coupled directly (i.e., not via other first detection coils) to an output coil (in the present embodiment, the first detection coil 42-n) other than the input coil supplied with alternating current from the power supply circuit 41-1 among the plurality of first detection coils 42-1 to 42-n. Furthermore, the inductance of the receiving coil 61 and the electrostatic capacitance of the resonant capacitor 62 are set so that the resonant circuit 63 resonates with the alternating current supplied from the power supply circuit 41-1. Furthermore, in Figure 6 In FIG. 6 , two resonant capacitors 62 are shown to be connected in parallel with the receiving coil 61 , but the number of resonant capacitors 62 included in the resonant circuit 63 is not limited to two, and may be one or more than three. In addition, the receiving coil 61 and the resonant capacitor 62 may be connected in series.

[0067] Furthermore, it is preferable that the receiving coil 61 and the electromagnetically coupled output coil (detection coil 42-n) are detection coils that are not directly electromagnetically coupled to the input coil (first detection coil 42-1) that supplies the alternating current from the power supply circuit 41-1, such that the alternating current supplied from the power supply circuit 41-1 is transmitted to the receiving coil 61 via all of the plurality of first detection coils 42-1 to 42-n. In this embodiment, Figure 4 As shown, the output coil is located at the end portion opposite to the end portion on the side where the input coil is located.

[0068] The high-pass filter 64 is connected between the resonance circuit 63 and the amplifier 65, and attenuates the noise component having a frequency lower than the frequency of the AC power supplied from the power supply circuit 41-1 in the AC power received by the resonance circuit 63. The amplifier 65 is connected between the high-pass filter 64 and the half-wave rectifier circuit 66, and amplifies the AC power output from the high-pass filter 64.

[0069] The half-wave rectifier circuit 66 is connected between the amplifier 65 and the low-pass filter 67, and performs half-wave rectification on the amplified alternating current output from the amplifier 65 and converts it into pulsating current power. The low-pass filter 67 is connected between the half-wave rectifier circuit 66 and the voltage detection circuit 68, and smoothes the pulsating current power output from the half-wave rectifier circuit 66 and converts it into direct current.

[0070] The voltage detection circuit 68 is connected to the low-pass filter 67, and detects the voltage of the DC power output from the low-pass filter 67 (i.e., the first voltage). Then, the determination circuit 69 determines whether the detected first voltage is included in the prescribed reference range. When the detected first voltage is included in the prescribed reference range, the determination circuit 69 does not detect the foreign matter between the transmitting coil 12 and the receiving coil 21. On the other hand, if the detected first voltage deviates from the prescribed reference range, the determination circuit 69 determines that there is a foreign matter mixed between the transmitting coil 12 and the receiving coil 21. Then, the determination circuit 69 outputs a signal indicating the detection result of the foreign matter to the power supply circuit 11 of the power transmission device 2. Furthermore, the voltage detection circuit 68 can be set to any circuit of a voltage detection circuit for detecting a DC voltage. In addition, the determination circuit 69 can be set to any circuit of various circuits that compare the detected first voltage with the prescribed reference range and output a signal corresponding to the comparison result.

[0071] Therefore, when the determination circuit 69 of at least one of the detection circuits 46 - 1 and 46 - 2 determines that there is a foreign object mixed between the transmission coil 12 and the reception coil 21 , the foreign object detection device 4 detects the foreign object mixed between the transmission coil 12 and the reception coil 21 .

[0072] Figure 7 The diagram shows an example of the arrangement of the first detection coil and the second detection coil in a simulation showing changes in the frequency characteristics of the voltage detected by the detection circuits 46 - 1 and 46 - 2 (hereinafter, sometimes simply referred to as the detection voltage) depending on the presence or absence of foreign matter. Figure 8 and Fig. 9Each of them is a diagram showing an example of a simulation result showing a change in the frequency characteristic of the first voltage (hereinafter, for convenience, referred to as the first detection voltage) detected by the detection circuit 46-1 based on the presence or absence of foreign matter mixing. Fig.10 and Fig.11 1 and 2 are diagrams showing an example of simulation results showing changes in the frequency characteristics of the second voltage (hereinafter, for convenience, referred to as the second detection voltage) detected by the detection circuit 46-2 depending on whether or not foreign matter is mixed. In this simulation, for simplicity, Figure 7 As shown, the number of the first detection coils and the number of the second detection coils are set to 3 (i.e., m=n=3), and it is assumed that the first detection coils 42-1 to 42-3 and the second detection coils 44-1 to 44-3 are alternately arranged in a row between the power supply circuits 41-1, 41-2 and the detection circuits 46-1, 46-2. In addition, it is assumed that the first detection coils 42-1 to 42-3 are arranged on the surface of the substrate 47, while the second detection coils 44-1 to 44-3 are arranged on the back side of the substrate 47. Moreover, in this simulation, the inductance L of each detection coil is set to 50nH, the electrostatic capacitance C1 of the first capacitors 43-1 to 43-3 constituting the first resonant circuit with each first detection coil 42-1 to 4-3 is set to 2.755nF, and the electrostatic capacitance C2 of the second capacitors 45-1 to 45-3 constituting the second resonant circuit with each second detection coil 44-1 to 44-3 is set to C1 / 4. In addition, the resistance R of the resonant circuit constituted by each detection coil and the corresponding capacitor is set to 0.1Ω. That is, the first resonant frequency of each first resonant circuit is 13.56MHz, and the second resonant frequency of each second resonant circuit is 27.12MHz. In addition, the coupling degree between two adjacent first detection coils and the coupling degree between two adjacent second detection coils are set to 0.01 respectively. In addition, the coupling degree between the first detection coil 42-1 and the first detection coil 42-3, and the coupling degree between the second detection coil 44-1 and the second detection coil 44-3 are respectively set to 0.0001. In addition, in this simulation, it is assumed that a foreign object is mixed in the vicinity of a certain detection coil, for example, at a position corresponding to the inner side of the winding of a certain detection coil, and as a result, the inductance of the detection coil near the foreign object or the resistance value of the resonant circuit including the detection coil changes.

[0073] exist Figure 8 to Figure 11 In FIG. 1 , the horizontal axis represents the frequency, and the vertical axis represents the detection voltage. Figure 8The curve 801 in shows the frequency characteristics of the first detection voltage when there is no foreign matter between the transmitting coil 12 and the receiving coil 21. The curve 802 shows the frequency characteristics of the first detection voltage when it is assumed that the inductance of the first detection coil 42-1 decreases by 10% due to the mixing of foreign matter in the vicinity of the first detection coil 42-1 (for example, in the winding of the first detection coil 42-1). In addition, the curve 803 shows the frequency characteristics of the first detection voltage when it is assumed that the inductance of the second detection coil 44-1 decreases by 10% due to the mixing of foreign matter in the vicinity of the second detection coil 44-1. Furthermore, the curve 804 shows the frequency characteristics of the first detection voltage when it is assumed that the inductance of the first detection coil 42-2 decreases by 10% due to the mixing of foreign matter in the vicinity of the first detection coil 42-2. Furthermore, a curve 805 shows the frequency characteristics of the first detection voltage when it is assumed that the inductance of the first detection coil 42 - 3 decreases by 10% due to foreign matter being mixed in the vicinity of the first detection coil 42 - 3 .

[0074] As shown in curves 801, 802, 804, and 805, it can be seen that the frequency characteristics of the first detection voltage when a foreign object is mixed in the vicinity of one of the first detection coils 42-1 to 42-3, which is assumed to be between the transmitting coil 12 and the receiving coil 21, are lower than the frequency characteristics of the first detection voltage when there is no such foreign object. In particular, when an alternating current having a frequency equal to the first resonant frequency (13.56 MHz) of each first resonant circuit is supplied from the power supply circuit 41-1, the voltage changes significantly. Therefore, it can be seen that by investigating the first detection voltage, the foreign object detection device 4 can detect a foreign object mixed in the vicinity of one of the first detection coils 42-1 to 42-3 between the transmitting coil 12 and the receiving coil 21.

[0075] On the other hand, as shown in the curve 803, it can be seen that when it is assumed that a foreign object is mixed between the transmitting coil 12 and the receiving coil 21 and near the second detection coil 44-1, that is, when it is assumed that the foreign object is located outside the winding of each first detection coil, the frequency characteristic of the first detection voltage is almost the same as the frequency characteristic of the first detection voltage when there is no such foreign object. Therefore, it can be seen that when a foreign object is mixed near one of the second detection coils 44-1 to 44-3, even if the first detection voltage is checked, there is a risk that the foreign object detection device 4 cannot detect the foreign object mixed at such a position.

[0076] Fig. 9The curve 901 in FIG. 1 shows the frequency characteristics of the first detection voltage when there is no foreign matter between the transmission coil 12 and the reception coil 21. The curve 902 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the first detection coil 42-1 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the first detection coil 42-1. In addition, the curve 903 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the second detection coil 44-1 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the second detection coil 44-1. In addition, the curve 904 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the first detection coil 42-2 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the first detection coil 42-2. In addition, the curve 905 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the first detection coil 42-3 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the first detection coil 42-3.

[0077] As shown in curves 901, 902, 904, and 905, it can be seen that in this case, the frequency characteristics of the first detection voltage when a foreign object is mixed in the vicinity of one of the first detection coils 42-1 to 42-3 between the transmitting coil 12 and the receiving coil 21 are also reduced compared to the frequency characteristics of the first detection voltage when there is no such foreign object. In particular, when an alternating current having a frequency equal to the first resonant frequency (13.56 MHz) is supplied from the power supply circuit 41-1, the voltage changes significantly. Therefore, it can be seen that in this case, by investigating the first detection voltage, the foreign object detection device 4 can also detect a foreign object mixed in the vicinity of one of the first detection coils 42-1 to 42-3 between the transmitting coil 12 and the receiving coil 21.

[0078] On the other hand, as shown in the curve 903, it can be seen that the frequency characteristics of the first detection voltage when a foreign object is mixed in the vicinity of the second detection coil 44-1 between the transmission coil 12 and the reception coil 21 are almost the same as the frequency characteristics of the first detection voltage when there is no such foreign object. Therefore, when a foreign object is mixed in the vicinity of one of the second detection coils 44-1 to 44-3, there is a risk that the foreign object detection device 4 cannot detect the foreign object mixed in at such a position even if the first detection voltage is checked.

[0079] Fig.10The curve 1001 in represents the frequency characteristic of the second detection voltage when there is no foreign matter between the transmitting coil 12 and the receiving coil 21. The curve 1002 represents the frequency characteristic of the second detection voltage when it is assumed that the inductance of the second detection coil 44-1 is reduced by 10% due to the mixing of foreign matter in the vicinity of the second detection coil 44-1 (for example, in the winding of the second detection coil 44-1). In addition, the curve 1003 represents the frequency characteristic of the second detection voltage when it is assumed that the inductance of the second detection coil 44-2 is reduced by 10% due to the mixing of foreign matter in the vicinity of the second detection coil 44-2. Moreover, the curve 1004 represents the frequency characteristic of the second detection voltage when it is assumed that the inductance of the second detection coil 44-3 is reduced by 10% due to the mixing of foreign matter in the vicinity of the second detection coil 44-3.

[0080] As shown in curves 1001 to 1004, it can be seen that the frequency characteristics of the second detection voltage in the case where a foreign object is mixed between the transmitting coil 12 and the receiving coil 21 and near one of the second detection coils 44-1 to 44-3 are lower than the frequency characteristics of the second detection voltage in the case where there is no such foreign object. In particular, when an alternating current having a frequency equal to the second resonant frequency (27.12 MHz) of each second resonant circuit is supplied from the power supply circuit 41-2, the voltage changes significantly. Therefore, it can be seen that by investigating the second detection voltage, the foreign object detection device 4 can detect a foreign object mixed between the transmitting coil 12 and the receiving coil 21 and near one of the second detection coils 44-1 to 44-3.

[0081] Fig.11 The curve 1101 in shows the frequency characteristics of the second detection voltage when there is no foreign matter between the transmitting coil 12 and the receiving coil 21. The curve 1102 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the second detection coil 44-1 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the second detection coil 44-1. In addition, the curve 1103 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the second detection coil 44-2 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the second detection coil 44-2. And, the curve 1104 shows the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the second detection coil 44-3 is tripled due to the loss caused by the foreign matter mixed in the vicinity of the second detection coil 44-3.

[0082] As shown in curves 1101 to 1104, it can be seen that in this case, the frequency characteristics of the second detection voltage when a foreign object is mixed in the vicinity of one of the second detection coils 44-1 to 44-3 between the transmitting coil 12 and the receiving coil 21 are lower than the frequency characteristics of the first detection voltage when there is no such foreign object. In particular, when an alternating current having a frequency equal to the second resonant frequency (27.12 MHz) is supplied from the power supply circuit 41-2, the voltage changes significantly. Therefore, it can be seen that by investigating the second detection voltage, the foreign object detection device 4 can detect foreign objects mixed in the vicinity of one of the second detection coils 44-1 to 44-3 between the transmitting coil 12 and the receiving coil 21.

[0083] Therefore, it can be seen that the foreign object detection device 4 can detect foreign objects even when foreign objects are mixed in the vicinity of one of the first detection coils 42 - 1 to 42 - 3 and the second detection coils 44 - 1 to 44 - 3 by checking both the first detection voltage and the second detection voltage.

[0084] Furthermore, it is also possible to arrange each detection coil among the multiple detection coils of the foreign object detection device closely so that the adjacent detection coils partially overlap each other when viewed from the normal direction of the substrate, and to arrange each detection coil so that it resonates with the same resonant frequency, and to supply alternating current with the resonant frequency from a power supply circuit. However, if each detection coil is arranged in this way, the variation of the magnetic flux generated by the supplied alternating current between the detection coils becomes larger. As a result, the variation of the detection voltage based on the presence or absence of foreign objects near the detection coil is also reduced due to the detection coil.

[0085] Fig.12 (a) and Fig.12 (b) is a diagram showing the simulation results of the change in the frequency characteristics of the detection voltage based on the presence or absence of foreign matter in the comparative example in which the detection coils adjacent to each other are arranged closely so as to partially overlap. Fig.12 As shown in (a), the number of detection coils 42-1 to 42-n of the foreign matter detection device of the comparative example is set to 3 (i.e., n=3), and it is assumed that these detection coils 42-1 to 42-3 are arranged in a row between the power supply circuit and the detection circuit. Then, it is assumed that the detection coils 42-1 and 42-3 are arranged on the surface of the substrate 47, and on the other hand, the detection coil 42-2 is arranged on the back side of the substrate 47. In addition, in this simulation, it is assumed that the values ​​of the parameters of each circuit element are the same as Figure 7 to Figure 11The values ​​of the parameters used in the simulation shown are the same. That is, the resonant frequency of the resonant circuit composed of each detection coil and the corresponding capacitor is set to 13.56 MHz. Among them, the coupling degree between the detection coil 42-1 and the detection coil 42-2, and the coupling degree between the detection coil 42-2 and the detection coil 42-3 are set to 0.1, and the coupling degree between the detection coil 42-1 and the detection coil 42-3 is set to 0.01.

[0086] exist Fig.12 In (b), the horizontal axis represents frequency and the vertical axis represents detection voltage. Curve 1201 represents the frequency characteristics of the detection voltage when there is no foreign matter between the transmission coil 12 and the reception coil 21. Curve 1202 represents the frequency characteristics of the detection voltage when it is assumed that the inductance of the detection coil 42-1 decreases by 10% due to the presence of foreign matter in the vicinity of the detection coil 42-1. In addition, curve 1203 represents the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonant circuit including the detection coil 42-1 increases by three times due to the loss caused by the presence of foreign matter in the vicinity of the detection coil 42-1. Similarly, curve 1204 represents the frequency characteristics of the detection voltage when it is assumed that the inductance of the detection coil 42-2 decreases by 10% due to the presence of foreign matter in the vicinity of the detection coil 42-2. In addition, curve 1205 represents the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonant circuit including the detection coil 42-2 increases by three times due to the loss caused by the presence of foreign matter in the vicinity of the detection coil 42-2. Furthermore, curve 1206 represents the frequency characteristics of the detection voltage when it is assumed that the inductance of the detection coil 42-3 decreases by 10% due to the mixing of foreign matter near the detection coil 42-3. Furthermore, curve 1207 represents the frequency characteristics of the detection voltage when it is assumed that the resistance of the resonance circuit including the detection coil 42-3 increases by 3 times due to the loss caused by the mixing of foreign matter near the detection coil 42-3.

[0087] As shown in curves 1201 to 1207, in this comparative example, it can be seen that the frequency characteristics of the detection voltage in the case where a foreign object is mixed in the vicinity of the detection coil 42-1 or the detection coil 42-3 vary greatly compared to the frequency characteristics of the detection voltage in the case where no foreign object is mixed. On the other hand, it can be seen that the frequency characteristics of the detection voltage in the case where a foreign object is mixed in the vicinity of the detection coil 42-2 vary almost unchanged compared to the frequency characteristics of the detection voltage in the case where no foreign object is mixed. In particular, when the power supply circuit supplies an alternating current having the resonant frequency of each resonant circuit, that is, a frequency of 13.56 MHz, the detection voltage hardly changes due to the presence or absence of foreign matter. It can be seen from this that, compared to the comparative example in which adjacent detection coils are closely arranged and alternating current of the same frequency is supplied to each detection coil, the foreign matter detection device 4 based on this embodiment can detect the foreign matter with high accuracy regardless of the position of the mixed foreign matter.

[0088] As described above, the foreign object detection device includes a first detection coil that is arranged between a transmitting coil and a receiving coil and can be electromagnetically coupled to each other when the power transmission device and the power receiving device are in a positional relationship in which power can be transmitted from the power transmission device to the power receiving device, and a plurality of second detection coils that are arranged to be electromagnetically coupled to each other. In addition, the first resonance circuit including the first detection coil has a first resonance frequency, and on the other hand, the second resonance circuit including the second detection coil has a second resonance frequency different from the first resonance frequency. In addition, the foreign object detection device detects a first voltage generated by an alternating current supplied to one of the plurality of first detection coils and transmitted in the plurality of first detection coils through a detection circuit. Similarly, the foreign object detection device detects a second voltage generated by an alternating current supplied to one of the plurality of second detection coils and transmitted in the plurality of second detection coils through a detection circuit. In addition, when at least one of the detected first voltage and the second voltage deviates from a predetermined reference range, the foreign object detection device determines that a foreign object has been mixed between the transmitting coil and the receiving coil. Therefore, even if a foreign object smaller than the transmitting coil and the receiving coil is mixed, the foreign object detection device can detect the foreign object with high accuracy. Moreover, no matter which detection coil the mixed foreign object is located near, the foreign object detection device can detect the foreign object with high accuracy. Moreover, the foreign object detection device uses an alternating current different from the alternating current transmitted from the power transmission device to the power receiving device to detect foreign objects, so it is possible to detect foreign objects without being affected by the power transmission from the power transmission device to the power receiving device.

[0089] Furthermore, according to a variation example, the foreign object detection device 4 has a power supply circuit 41, which can also supply alternating current with a first frequency to a first input coil among a plurality of first detection coils, and at the same time supply alternating current with a second frequency to a second input coil among a plurality of second detection coils.

[0090] Fig.13 4 is a circuit diagram of a power supply circuit 41 according to this modification. The power supply circuit 41 includes, for example, a DC power supply 51 for supplying DC power, a power supply coil 52, two capacitors 53-1 and 53-2, an inverter circuit 54, a switching element 56, and a control circuit 55. Figure 5 Compared with the power supply circuit 41 - 1 shown in the figure, the power supply circuit 41 according to this modification example is different in that it has two capacitors 53 - 1 and 53 - 2 and a switch element 56 , and in that part of the control is performed by a control circuit 55 . Therefore, these different aspects and related parts are described below.

[0091] The two capacitors 53-1 and 53-2 are connected in parallel to each other and are controlled in series with respect to the power supply coil 52. In addition, the capacitor 53-2 and the switching element 56 are connected in series. In addition, the switching element 56 can be set as, for example, a MOSFET or a relay. That is, when the switching element 56 is turned off, the capacitor 53-1 of the two capacitors 53-1 and 53-2 forms a resonance circuit together with the power supply coil 52, and on the other hand, when the switching element 56 is turned on, the two capacitors 53-1 and 53-2 each form a resonance circuit together with the power supply coil 52. The electrostatic capacitance of the capacitor 53-1 is set so that, for example, the resonance frequency of the resonance circuit composed of the power supply coil 52 and the capacitor 53-1 is the second frequency of the alternating current supplied to the second input coil including the second detection coil. In addition, the electrostatic capacitance of the capacitor 53-2 is set so that, for example, the resonance frequency of the resonance circuit composed of the power supply coil 52 and the two capacitors 53-1 and 53-2 is the first frequency of the alternating current supplied to the first input coil.

[0092] Furthermore, the power supply coil 52 is disposed so as to be electromagnetically coupled to each of the first input coils among the plurality of first detection coils and each of the second input coils among the plurality of second detection coils.

[0093] The control circuit 55 switches the switching element 56 on / off for each predetermined cycle (a cycle longer than the cycle corresponding to the first frequency and the cycle corresponding to the second frequency). Then, the control circuit 55 controls the switching of the switching elements of the inverter circuit 54 so that the frequency of the AC power supplied to the power supply coil 52 is the first frequency during the period when the switching element 56 is on. In addition, the control circuit 55 controls the switching of the switching elements of the inverter circuit 54 so that the frequency of the AC power supplied to the power supply coil 52 is the second frequency during the period when the switching element 56 is off. Thus, the power supply circuit 41 can switch between supplying the AC power having the first frequency to the first input coil and supplying the AC power having the second frequency to the second input coil for each predetermined cycle.

[0094] According to another modified example, the foreign object detection device 4 can also be installed in the power receiving device 3. In this case, the power receiving device 3 can also have a switch element (not shown) connected in parallel with the receiving coil 21 to switch whether to short-circuit the two ends of the receiving coil 21, and a control circuit (not shown) for switching the switch element on or off. Then, the signal indicating the detection result of the foreign object from the detection circuit 46-1, 46-2 is output to the control circuit of the power receiving device 3. When one of the signals indicates that a foreign object is detected between the transmitting coil 12 and the receiving coil 21, the control circuit turns on the switch element to short-circuit the two ends of the receiving coil 21. As a result, the power transmission from the power transmission device 2 to the power receiving device 3 is interrupted, preventing the occurrence of a malfunction caused by the mixed foreign object.

[0095] Furthermore, when the power transmission device 2 and the power receiving device 3 each have a communicator (not shown) for mutual communication, the control circuit of the power receiving device 3 may send a signal instructing to stop power transmission to the power transmission device 2 via the communicator when one of the signals received from the detection circuits 46-1 and 46-2 of the foreign object detection device 4 indicates that a foreign object mixed between the transmission coil 12 and the reception coil 21 has been detected. Then, when the control circuit of the power supply circuit 11 of the power transmission device 2 receives the signal instructing to stop power transmission via the communicator, the power supply circuit 11 may stop the power supply to the transmission coil 12.

[0096] Furthermore, the foreign object detection device 4 may be installed in each of the power transmission device 2 and the power reception device 3. That is, two foreign object detection devices 4 may be arranged between the transmission coil 12 and the reception coil 21.

[0097] Moreover, according to another modified example, the foreign matter detection device 4 may also include a removal mechanism (not shown) for removing foreign matter mixed between the transmitting coil 12 and the receiving coil 21. In this case, if one of the detection circuits 46-1 and 46-2 detects foreign matter mixed between the transmitting coil 12 and the receiving coil 21, the removal mechanism may be operated to remove the foreign matter. Furthermore, such a removal mechanism may be, for example, a wiper that wipes the surface of the housing of the power transmission device 2 opposite to the power receiving device 3, or the surface of the housing of the power receiving device 3 opposite to the power transmission device 2, or an air gun that sprays air between the power transmission device 2 and the power receiving device 3 to remove foreign matter. Thus, even when a foreign matter is detected, the foreign matter detection device 4 can prevent the power transmission device 2 or the power receiving device 3 from malfunctioning due to ignition or heating of the foreign matter, and can continue to transmit power from the power transmission device 2 to the power receiving device 3.

[0098] Thus, those skilled in the art can make various modifications according to the embodiments within the scope of the present invention.

[0099] Description of symbols

[0100] 1 Power transmission system

[0101] 2 Power transmission device

[0102] 11 Power supply circuit

[0103] 12 Transmitter Coil

[0104] 3 Power receiving device

[0105] 21 Receiving coil

[0106] 22 Resonant capacitor

[0107] 23 Power receiving circuit

[0108] 4 Foreign matter detection device

[0109] 41, 41-1, 41-2 Power supply circuit

[0110] 42-1~42-n 1st detection coil

[0111] 43-1~43-n Capacitor No. 1

[0112] 44-1~44-n Second detection coil

[0113] 45-1~45-n Second capacitor

[0114] 46, 46-1, 46-2 Detection circuit

[0115] 47 substrate

[0116] 51 DC power supply

[0117] 52 Power supply coil

[0118] 53, 53-1, 53-2 Capacitor

[0119] 54 Inverter Circuit

[0120] 55 Control Circuit

[0121] 56 Switching elements

[0122] 61 Receiving coil

[0123] 62 Resonant capacitor

[0124] 63 Resonance Circuit

[0125] 64 High pass filter

[0126] 65 Amplifier

[0127] 66 Half-wave rectifier circuit

[0128] 67 Low pass filter

[0129] 68 Voltage detection circuit

[0130] 69 Decision circuit

Claims

1. A foreign body detection device, comprising: A plurality of first detection coils are arranged on a substrate so as to be electromagnetically coupled to each other, the substrate being arranged between a transmitting coil of a power transmission device and a receiving coil of a power receiving device for transmitting power in a contactless manner; a plurality of first capacitors, for each of the plurality of first detection coils, forming a first resonance circuit having a first resonance frequency together with the first detection coil; A plurality of second detection coils are arranged on the substrate so as to be electromagnetically coupled to each other; a plurality of second capacitors, for each of the plurality of second detection coils, forming a second resonance circuit having a second resonance frequency different from the first resonance frequency together with the second detection coil; at least one power supply circuit for supplying an alternating current having a first frequency at which each of the first resonant circuits can resonate to a first input coil among the plurality of first detection coils, and for supplying an alternating current having a second frequency at which each of the second resonant circuits can resonate to a second input coil among the plurality of second detection coils; as well as a detection circuit that detects a first voltage of the alternating current transmitted via the plurality of first detection coils from a first output coil different from the first input coil among the plurality of first detection coils, and detects a second voltage of the alternating current transmitted via the plurality of second detection coils from a second output coil different from the second input coil among the plurality of second detection coils, and detects a foreign object mixed between the transmitting coil and the receiving coil based on the detected first voltage or the second voltage, When viewed from the normal direction of the substrate, the plurality of first detection coils and the plurality of second detection coils are alternately arranged. The first detection coils and the second detection coils adjacent to each other among the plurality of first detection coils and the plurality of second detection coils are arranged so as to partially overlap each other when viewed from a normal direction of the substrate. The first detection coils adjacent to each other among the plurality of first detection coils are arranged so as not to overlap each other when viewed from the normal direction of the substrate, and The second detection coils adjacent to each other among the plurality of second detection coils are arranged so as not to overlap each other when viewed from a normal direction of the substrate.

2. The foreign body detection device according to claim 1, The first frequency is a frequency at which each of the second resonant circuits does not resonate, and the second frequency is a frequency at which each of the first resonant circuits does not resonate.

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