Coil unit, wireless power transmission device, wireless power receiving device, and wireless power transmission system

A coil unit includes a coil configured by winding a conductive wire in a spiral shape, a magnetic body, and a base member disposed between the coil and the magnetic body, wherein the coil and the magnetic body are fixed to the base member.

BACKGROUND

The present disclosure relates to a coil unit, a wireless power transmission device, a wireless power receiving device, and a wireless power transmission system.

Priority is claimed on Japanese Patent Application No. 2018-070103, filed on Mar. 30 2018, the content of which is incorporated herein by reference.

A wireless power transmission technology is known. The wireless power transmission technology transmits electric power wirelessly using an electromagnetic induction mechanism between a primary (power transmission) coil and a secondary (power receiving) coil. The wireless power transmission technology uses linkage of an alternating magnetic flux generated in a power transmission-side coil to a power receiving-side coil.

In the wireless power transmission technology, reduction in thickness and size of a coil unit including a coil and a magnetic body is required. In the coil unit in the related art, a coil and a magnetic body are accommodated in an accommodating case (Japanese Unexamined Patent Application, First Publication No. 2017-84840, for example).

Japanese Unexamined Patent Application, First Publication No. 2017-84840 discloses a non-contact power transmission unit including a power transmission coil, a magnetic body, a base member and an accommodating case. In the non-contact power transmission unit disclosed in Japanese Unexamined Patent Application, First Publication No. 2017-84840, the accommodating case accommodates the magnetic body, the base member and the power transmission coil in sequence. The non-contact power transmission unit secures an interval between the power transmission coil and the magnetic body using a spacer region on the base member.

SUMMARY

In wireless power transmission, when a distance between a power transmission coil and a magnetic body is varied, since properties of the power transmission coil are varied, minimization of variation in properties of the power transmission coil is required simultaneously with reduction in thickness and size of a coil unit.

Incidentally, in the non-contact power transmission unit disclosed in Japanese Unexamined Patent Application, First Publication No. 2017-84840, the power transmission coil and the magnetic body are accommodated in the accommodating case, the magnetic body is fixed to the base member, and the power transmission coil is accommodated in a coil positioning groove section of the accommodating case and fixed by filler. Accordingly, in the non-contact power transmission unit disclosed in Japanese Unexamined Patent Application, First Publication No. 2017-84840, dispersion may easily occur in a distance between the power transmission coil and the magnetic body, properties of the power transmission coil may be varied, and power transmission performance may be decreased.

The present disclosure provides a coil unit capable of minimizing variation in properties of a power transmission coil due to generation of dispersion in a distance between a power transmission coil and a magnetic body, and a wireless power transmission device, a wireless power receiving device and a wireless power transmission system each including the coil unit.

A coil unit of the present disclosure includes a coil configured by winding a conductive wire in a spiral shape, a magnetic body, and a base member disposed between the coil and the magnetic body, wherein the coil and the magnetic body are fixed to the base member.

According to the present disclosure, it is possible to provide a coil unit capable of minimizing variation in properties of a power transmission coil due to generation of dispersion in a distance between a power transmission coil and a magnetic body, and a wireless power transmission device, a wireless power receiving device and a wireless power transmission system each including the coil unit.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings used in the following description, for the convenience of easy understanding of characteristics, characteristic parts may be enlarged, and dimensional ratios or the like between components may not necessarily be the same as actual ratios. Materials, dimensions, or the like, exemplified in the following description are merely examples. The present disclosure is not necessarily limited thereto and appropriate changes may be made without departing from the spirit of the present disclosure.

First, as an embodiment of the present disclosure, for example, a wireless power transmission system100shown inFIG. 1andFIG. 2will be described.FIG. 1is a configuration view showing an example of the wireless power transmission system100.FIG. 2is a circuit diagram showing a configuration of a power transmission coil unit203and a power receiving coil unit301of the wireless power transmission system100.

As shown inFIG. 1andFIG. 2, the wireless power transmission system100of the embodiment performs wireless charging of a battery (a secondary battery) mounted on an electric automobile EV. The electric automobile EV is an electrically driven vehicle (a moving body) that travels due to being driven by a motor using electric power charged into the battery. While the wireless power transmission system100is applied to the electric automobile EV in the embodiment, the wireless power transmission system may be applied to a moving body, a mobile device, or the like, other than the electric automobile EV, in another embodiment.

The wireless power transmission system100includes a wireless power transmission device200and a wireless power receiving device300. The wireless power transmission device200is installed on the ground G on the side of charging equipment. The wireless power receiving device300is mounted on the electric automobile EV.

The wireless power transmission device200includes a conversion circuit201, a power transmission circuit202, and the power transmission coil unit203. The wireless power receiving device300includes the power receiving coil unit301and a rectification smoothing circuit303. Further, a load Vload is disposed outside the wireless power receiving device300.

The conversion circuit201functions as an AC/DC power supply electrically connected to an external commercial power supply P and configured to convert an alternating current voltage input from the commercial power supply P into a desired direct current voltage. The conversion circuit201is electrically connected to the power transmission circuit202. The conversion circuit201supplies the converted direct current voltage to the power transmission circuit202.

For the conversion circuit201, any configuration may be used as long as a direct current voltage is output to the power transmission circuit202and the configuration is not particularly limited. As the conversion circuit201, a conversion circuit obtained by combining a rectifying circuit configured to rectify an alternating current voltage and convert the alternating current voltage into a direct current voltage and a power factor correction (PFC) circuit configured to improve a power factor; a conversion circuit obtained by combining a rectifying circuit and a switching circuit such as a switching converter or the like, or the like, may be exemplified.

The power transmission circuit202converts a direct current voltage supplied from the conversion circuit201into an alternating current voltage. As the power transmission circuit202, a switching circuit or the like to which a plurality of switching elements are bridge-connected may be exemplified. The power transmission circuit202is electrically connected to the power transmission coil unit203. The power transmission circuit202supplies an alternating current voltage having a driving frequency controlled on the basis of a resonance frequency of a first LC resonance circuit, which will be described below, included in the power transmission coil unit203, to the power transmission coil unit203.

The power transmission coil unit203includes a first LC resonance circuit, a base member (not shown) and a magnetic body (not shown). The base member (not shown) and the magnetic body (not shown) will be described later in detail in the section for the “<Coil unit>,” which will be described below.

The first LC resonance circuit includes a power transmission coil L1and a power transmission-side capacitor C1. When a resonance frequency of the first LC resonance circuit approaches (including also “coincides with”) a resonance frequency on the side of the power receiving coil unit301, magnetic resonance type wireless power transmission becomes possible. In addition, in another embodiment, the power transmission coil unit may not include an LC resonance circuit. That is, in another embodiment, the power transmission coil unit may not include a power transmission-side capacitor.

In the power transmission coil unit203of the embodiment, a reactor Ls is configured to be inserted in series with the power transmission-side capacitor C1. In the case of this configuration, an imaginary part of an impedance of a wireless power transmission network constituted by the power transmission coil unit203, the power receiving coil unit301, the rectification smoothing circuit303and the load Vload is easily controlled such that it becomes positive. The reactor Ls has an impedance which is higher than a frequency component that is sufficiently higher than a resonance frequency on the side of the power transmission coil unit203. Accordingly, the reactor Ls can function as a filter configured to remove a high frequency component.

The power transmission coil L1is constituted by a coil for wireless power transmission. The power transmission coil L1of the embodiment is installed on the ground G or buried in the ground G to face a floor bottom of the electric automobile EV. Further, in the embodiment, a configuration in which the power transmission coil L1(the power transmission coil unit203) is installed on the ground G together with the conversion circuit201may be provided.

The power transmission-side capacitor C1has a function of adjusting a resonance frequency. While the power transmission-side capacitor C1of the embodiment is constituted by a first capacitor C11serially connected to the power transmission coil L1and a second capacitor C12connected in parallel with the power transmission coil L1, the power transmission-side capacitor C1is not limited to such a configuration. For example, the power transmission-side capacitor C1may be constituted by only the first capacitor C11serially connected to the power transmission coil L1.

The power receiving coil unit301includes a second LC resonance circuit, a base member (not shown) and a magnetic body (not shown). The base member (not shown) and the magnetic body (not shown) will be described in detail in the section for the “<Coil unit>,” which will be described below.

The second LC resonance circuit includes a power receiving coil L2and a power receiving-side capacitor C2. When a resonance frequency of the second LC resonance circuit approaches (including also “coincides with”) a resonance frequency on the side of the power transmission coil unit203, magnetic resonance type wireless power transmission becomes possible. In addition, in another embodiment, the power receiving coil unit may not include an LC resonance circuit. That is, in another embodiment, the power receiving coil unit may not include a power receiving-side capacitor.

In the power receiving coil unit301of the embodiment, a reactor Lr is configured to be inserted in series with the power receiving-side capacitor C2. In the case of the configuration, the reactor Lr has an impedance higher than a frequency component that is sufficiently higher than a resonance frequency on the side of the power receiving coil unit301. Accordingly, the reactor Lr functions as a filter configured to remove a high frequency component.

The power receiving coil L2is constituted by a coil for wireless power transmission. The power receiving coil L2of the embodiment is installed on the floor bottom of the electric automobile EV to face the power transmission coil L1installed on the ground G or buried in the ground G.

The power receiving-side capacitor C2has a function of adjusting a resonance frequency. While the power receiving-side capacitor C2of the embodiment is constituted by a third capacitor C21serially connected to the power receiving coil L2and a fourth capacitor C22connected in parallel with the power receiving coil L2, the power receiving-side capacitor C2is not limited to such a configuration. For example, the power receiving-side capacitor C2may be constituted by only the third capacitor C21serially connected to the power receiving coil L2.

The rectification smoothing circuit303is electrically connected to the power receiving coil unit301, and rectifies an alternating current voltage supplied from the power receiving coil L2and converts the alternating current voltage into a direct current voltage. As the rectification smoothing circuit303, a half wave rectification smoothing circuit constituted by a switching element or a diode and a smoothing capacitor; a full wave rectification smoothing circuit constituted by four switching elements or diodes, which are bridge-connected, and a smoothing capacitor, or the like, may be exemplified. The rectification smoothing circuit303is electrically connected to the load Vload. The rectification smoothing circuit303supplies the converted direct current power to the load Vload. Further, in the wireless power receiving device300, a configuration in which a charging circuit is installed between the rectification smoothing circuit303and the load Vload may be provided.

The load Vload is connected between output terminals of the rectification smoothing circuit303and a direct current voltage is supplied from the rectification smoothing circuit303. As the load Vload, a battery, a motor, or the like, mounted on the above-mentioned electric automobile EV may be exemplified.

The load Vload can be regarded as a resistance load having an equivalent resistance value that varies over time according to a demand state (a storage state or a consumption state) of electric power. Further, power consumption in the rectification smoothing circuit303is sufficiently smaller than power consumption in the load Vload.

In the power transmission system100including the above-mentioned configuration, electric power can be transmitted wirelessly from the wireless power transmission device200to the wireless power receiving device300according to a magnetic resonance method using a resonance (resound) phenomenon between the power transmission coil unit203and the power receiving coil unit301. That is, in the magnetic resonance method, resonance frequencies between the two coil units203and301can approach (also including “coincide with”) each other, the high frequency current and voltage in the vicinity of the resonance frequency can be applied to the power transmission coil unit203, and electric power can be transmitted (supplied) wirelessly to the power receiving coil unit301that electromagnetically resonates (resounds). Further, the wireless power transmission device200and the wireless power receiving device300may include a communication circuit configured to perform communication between the wireless power transmission device200and the wireless power receiving device300.

Accordingly, in the power transmission system100of the embodiment, wireless charging of the battery mounted on the electric automobile EV can be performed while electric power supplied from the charging equipment side is transmitted wirelessly to the electric automobile EV with no connection to a charging cable.

Next, as a coil unit of the embodiment, a coil unit1shown inFIG. 3toFIG. 6will be described.FIG. 3is a perspective view of a cutaway model for explaining a configuration of the coil unit1.FIG. 4is a plan view of the coil unit1.FIG. 5is a plan view of the coil unit1.FIG. 6is a cross-sectional view of the coil unit1taken along line A-A shown inFIG. 4.

As shown inFIG. 3toFIG. 6, the coil unit1includes a base member11, a coil12and a magnetic body13. In the coil unit1, the magnetic body13is constituted by a plurality of (in the embodiment, four) magnetic body pieces21. The magnetic body pieces21will be described. In the coil unit1, the base member11, the coil12and the magnetic body13are accommodated in a housing (not shown). Further, the coil unit1may further include a capacitor. When the coil unit1includes a capacitor, the capacitor is not particularly limited.

The base member11is disposed between the coil12and the magnetic body pieces21. The base member11has a first surface11aand a second surface11b. The first surface11aand the second surface11bface each other and are parallel to each other. Then, a distance between the first surface11aand the second surface11b, i.e., a thickness D of the base member11is constant. While the thickness D of the base member is not particularly limited, the thickness D may be, for example, 0.5 to 5.0 mm.

The base member11is constituted by an insulating member. While the insulating member is not particularly limited, the insulating member may be exemplified as being of glass, a resin, or the like. However, a resin is preferably used for the insulating member. As a specific example of the resin, an acrylonitrile-butadiene-styrene copolymer resin (an ABS resin), a polybutylene terephthalate resin (a PBT resin), a polyphenylene sulfide resin (a PPS resin), or the like, may be exemplified.

In the coil unit1, the base member11has a form of a bobbin. This bobbin is a part configured to allow a conductive wire16of the coil12to be wound neatly and hold a shape of the conductive wire16of the coil12.

The base member11has a first accommodating section14and a second accommodating section15.

The first accommodating section14accommodates the coil12. The first accommodating section14is provided on the first surface11aof the base member11. The first accommodating section14has a partition wall17configured to be a boundary between lines of the conductive wire16of the coil12. Since the partition wall17can minimize fluctuation of a position of the conductive wire16for each winding, variation in properties of the power transmission coil can be further minimized.

The partition wall17is provided on the first surface11a. A height of the partition wall17is not particularly limited. However, the height of the partition wall17is preferably greater than a diameter of the conductive wire16and preferably 1.2 times or less than a diameter of the conductive wire16. When the height of the partition wall17is greater than the diameter of the conductive wire16, contact between the coil12and other members is easily prevented when an external force such as vibration, impact, or the like, is applied to the coil unit1. In addition, when the height of the partition wall17is 1.2 times or less than the diameter of the conductive wire16, the coil unit1can be further reduced in thickness. For this reason, when the height of the partition wall17is greater than the diameter of the conductive wire16and 1.2 times or less the diameter of the conductive wire16, both of reduction in thickness of the coil unit1and prevention of contact between the coil12and other members can be achieved.

Further, when an influence to the coil unit1due to an external force such as vibration, impact, or the like, is small, the height of the partition wall17is preferably the diameter or less of the conductive wire16. Accordingly, the coil unit1can be further reduced in thickness.

The second accommodating section15accommodates the magnetic body pieces21. The second accommodating section15is provided on the second surface11bof the base member11. The second accommodating section15is formed in a square shape and incised toward the first surface11awith the second surface11bas a reference surface. That is, an incised portion configured to accommodate the magnetic body pieces21is formed in the second accommodating section15. Accordingly, the coil unit1can be further reduced in thickness.

An incision depth of the second accommodating section15is not particularly limited. However, the incision depth is preferably greater than the thickness of the magnetic body pieces21or 1.2 times or less the thickness of the magnetic body pieces21. In the case in which the incision depth is greater than the thickness of the magnetic body pieces21, a contact between the magnetic body pieces21and another member is easily prevented when an external force such as vibrations, an impact, or the like, is applied to the coil unit1. In addition, when the incision depth is 1.2 times or less than the thickness of the magnetic body pieces21, the coil unit1can be further reduced in thickness. For this reason, when the incision depth is greater than the thickness of the magnetic body pieces21and 1.2 times or less than the thickness of the magnetic body pieces21, both of reduction in thickness of the coil unit1and prevention of a contact between the magnetic body pieces21and another member can be achieved. Further, the incision depth is measured using the second surface11bas a reference surface.

Further, when an influence on the coil unit1due to an external force such as vibrations, an impact, or the like, is small, the incision depth is preferably the thickness or less of the magnetic body pieces21. Accordingly, the coil unit1can be further reduced in thickness.

In the embodiment, the second accommodating section15is divided into a plurality of (four) regions. In this way, in the coil unit1, the plurality of magnetic body pieces21are divided into a plurality of second accommodating sections15. Accordingly, a deviation in size of gaps formed in the second accommodating section15due to dimensional variation of the magnetic body pieces21can be minimized, and variation in properties of the power transmission coil can be further minimized.

Specifically, for example, in the case in which there is one second accommodating section15, when magnetic body pieces are filled into and accommodated in the second accommodating section15from ends thereof, gaps may occur in portions of the second accommodating section15. Accordingly, the magnetic symmetry breaks down, and variation in properties of the power transmission coil readily occurs. Meanwhile, in the case in which a plurality of second accommodating sections15are provided, when the plurality of magnetic body pieces21are filled into and accommodated in the second accommodating sections15from ends thereof, respectively, while gaps occur in portions of the second accommodating sections15, symmetry can be provided in the gaps between the second accommodating sections15. Accordingly, magnetic symmetry cannot be easily collapsed in the power transmission coil as a whole, and variation in properties of the power transmission coil can be further minimized.

The coil12has a winding section18, a first wiring section19and a second wiring section20.

The winding section18is a portion configured by winding the conductive wire16in a spiral shape. The conductive wire16may be a Litz wire including, for example, copper, aluminum, or the like.

The first wiring section19is a portion in which the conductive wire16extends from an end portion (a first end portion of the coil12) on an inner circumferential side of the winding section18toward the circumferential inside of the winding section18.

The second wiring section20is a portion in which the conductive wire16extends from an end portion (a second end portion of the coil12) on an outer circumferential side of the winding section18toward the circumferential outside.

The coil12may also be used as the power transmission coil L1or the power receiving coil L2.

The magnetic body piece21is a plate-shaped member having a square-shaped surface. The square-shaped surface of the magnetic body piece21is smaller than a surface of the second accommodating section15configured to accommodate the magnetic body pieces21. A face of the square-shaped surface of the magnetic body piece21is coated with a first potting resin (not shown), which will be described below, and fixed to an accommodating surface of the second accommodating section15. The accommodating surface of the second accommodating section15is a surface of the second accommodating section15configured to accommodate the magnetic body pieces21.

The magnetic body pieces21are constituted of ferrite, as an example. Coupling between the coils can be increased via the magnetic body pieces21.

The magnetic body pieces21are fixed to the base member11using a first potting resin (not shown) in the second accommodating section15. The first potting resin fixes the magnetic body pieces21to the accommodating surface of the second accommodating section15by coating the faces of the square-shaped surfaces of the magnetic body pieces21. Accordingly, even when the magnetic body pieces21are separated due an impact or the like, scattering of the divided magnetic body pieces21can be prevented.

The first potting resin is not particularly limited. However, a thermosetting resin is preferable as the first potting resin. As a specific example of the thermosetting resin, an acryl resin, a phenol resin, a polyester resin, an epoxy resin, a thermosetting polyimide, a silicone resin, a polyurethane resin, or the like, may be exemplified. The thermoplastic resin is not limited to these examples.

In manufacture with a magnetic material such as conventional ferrite or the like, because of undergoing a process such as baking or the like, dimensional errors easily occur, and variation in properties of the power transmission coil may occur due to dimensional errors in a magnetic body. On the other hand, the coil unit1is less susceptible to dimensional errors in the magnetic body due to disposing the plurality of magnetic body pieces21in the plurality of second accommodating sections15by separating them. In addition, deviations in gaps formed in the second accommodating section15due to a dimensional variation of the magnetic body pieces21can be minimized. As a result, variation in properties of the power transmission coil can be further minimized.

While the example in which the first accommodating section14has the partition wall17has been described exemplarily in the coil unit1of the embodiment, the partition wall17may be omitted in another variant. In this case, a coil configured by winding the conductive wire16in a spiral shape is accommodated in the first accommodating section14. In addition, the first accommodating section14may have a shape engraved toward the second surface11busing the first surface11aas a reference surface.

While the example in which the second accommodating section15is formed to be engraved toward the first surface11ahas been described exemplarily in the coil unit1of the embodiment, another variant may have a configuration in which the second accommodating section15includes a protrusion configured to accommodate a magnetic body. In this case, the protrusion is provided on the second surface11busing a direction from the first surface11atoward the second surface11bas a height direction of the protrusion.

While the example in which the magnetic body13is configured by disposing the plurality of magnetic body pieces21to be arranged in the plurality of second accommodating sections15as a whole has been described exemplarily in the coil unit1of the embodiment, another variant may have a configuration in which the coil unit1includes one magnetic body.

In the coil unit of the embodiment as described above, since the coil and the magnetic body are fixed to the base member disposed between the coil and the magnetic body, the base member can hold the coil and the magnetic body integrally. Further, in the coil unit of the embodiment, a thickness of the base member is constant. As described above, variation cannot easily occur in the distance between the coil and the magnetic body during actual manufacture, and variation in properties of the coil is minimized.

When the coil and the magnetic body are fixed to the base member in this way, among causes of the variation in distance between the coil and the magnetic body that easily occur in a manufacturing site, causes other than the variation in thickness of the base member can be minimized.

FIG. 7is a plan view of a coil unit2according to another embodiment. In the following description, components having the same or similar functions to the components of the coil unit2and the components of the coil unit1are designated by the same reference numerals. Descriptions of components that duplicate those of the coil unit2and the coil unit1will be omitted.

In the coil unit2, a part of a section (the winding section18) in which the conductive wire of coil12is wound in a spiral shape is fixed to the base member11by a second potting resin22. When the part of the winding section18is fixed by the second potting resin22in this way, the coil12can be fixed to the base member11while an increase in weight of the coil unit2due to the second potting resin22is minimized.

The second potting resin is not particularly limited. However, a thermosetting resin is preferable as the second potting resin. A specific example of the thermosetting resin is the same as the resin exemplified as the preferable specific example of the first potting resin. The second potting resin may be the same as or may be different from the first potting resin.

Even in the coil unit2, since the same effects as those of the coil unit1are obtained, variation in properties of the coil is minimized, and an increase in thickness of the coil unit is minimized.

EXPLANATION OF REFERENCES