Coil unit, contactless power receiving device, and contactless power supply system

Abstract

To provide a coil unit (10) in which the depth of the bobbin groove can be made smaller than the thickness of the litz wire. [Solution] The coil unit (10) of the present invention is characterized by comprising a bobbin (11) having a coil-shaped groove (11a) and a Litz wire (12a) having a polygonal cross-section arranged in the groove (11a).

Description

Technical Field

[0001] The present invention relates to a coil unit, a non-contact power receiving device, and a non-contact power supply system.

Background Art

[0002] Conventionally, a coil unit having a bobbin with a spiral groove and a coil composed of a litz wire disposed in the spiral groove is known. For example, Patent Document 1 discloses a coil unit having a coil base (bobbin) with a spiral groove portion and a coil conductor (litz wire) held in the spiral groove portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] FIG. 1 schematically shows a cross-section of a litz wire 12a disposed in a groove of a bobbin 11 of a conventional coil unit as described above. As shown in FIG. 1, in the conventional coil unit, a litz wire 12a having a circular cross-section is disposed in the groove of the bobbin 11. The litz wire 12a is formed by multi-stage twisting of a plurality of enameled wires, and it is easy to perform multi-stage twisting when the cross-section is circular. Therefore, the cross-section of the litz wire 12a used for the coil is generally circular.

[0005] As shown in FIG. 1, in the conventional coil unit, in order to stably hold the litz wire 12a having a circular cross-section in the groove of the bobbin 11, it is necessary to make the depth of the groove equal to or greater than the thickness of the litz wire 12a. For this reason, the conventional coil unit has a problem that the thickness of the bobbin 11 becomes large and the weight of the coil unit becomes large.

[0006] The object of the present invention is to provide a coil unit that can make the depth of the bobbin groove smaller than the thickness of the Litz wire, and a contactless power receiving device and a contactless power supply system having the coil unit. [Means for solving the problem]

[0007] According to one aspect of the present invention for solving the above problems, A coil unit is provided, characterized by having a bobbin having a coil-shaped groove and a Litz wire having a polygonal cross-section arranged in the groove.

[0008] According to another aspect of the present invention for solving the above problems, A non-contact power receiving device is provided, characterized by having the above-described coil unit.

[0009] According to another aspect of the present invention for solving the above problems, A contactless power supply system is provided, characterized by having the above-mentioned contactless power receiving device. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a coil unit in which the depth of the groove in the bobbin can be made smaller than the thickness of the Litz wire, as well as a contactless power receiving device and a contactless power supply system having the coil unit. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a partially enlarged cross-sectional view of a conventional coil unit. [Figure 2] Figure 2A is a schematic diagram of a contactless power supply system, and Figure 2B is a diagram showing the inside of a contactless power receiving device. [Figure 3] Figure 3A is a partially enlarged cross-sectional view of the coil unit according to this embodiment, and Figure 3B is a partially enlarged cross-sectional view of the bobbin. [Modes for carrying out the invention]

[0012] The following describes a contactless power supply system and a contactless power receiving device according to one embodiment of the present invention. However, the embodiment shown below is merely illustrative, and the present invention is not limited thereto. The contactless power supply system and contactless power receiving device of the present invention are, for example, devices for charging batteries mounted on electric vehicles or plug-in hybrid vehicles in a contactless manner. In this specification, the "~" symbol indicating a numerical range includes both an upper and lower limit.

[0013] [Contactless power supply system] Figure 2A is a schematic diagram of a contactless power supply system 1 according to an embodiment. Figure 2B is a schematic diagram showing the internal structure of the contactless power receiving device 4 of the contactless power supply system 1 shown in Figure 2A. Figure 3A is a partially enlarged cross-sectional view of the coil unit 10 of the contactless power receiving device 4 shown in Figure 2B, showing the litz wire 12a of the coil 12 arranged in the groove 11a of the bobbin 11. Figure 3B is a partially enlarged cross-sectional view of the bobbin 11.

[0014] As shown in Figures 2A and 2B, the contactless power supply system 1 comprises a power source 2, a contactless power transmission device 3, a contactless power receiving device 4, and a battery 5. The contactless power receiving device 4 and the battery 5 are mounted in an electric vehicle 6.

[0015] In the contactless power supply system 1, an alternating current supplied from the power source 2 is supplied to the contactless power transmission device 3 via cable 3a, generating a magnetic field. The generated magnetic field acts on the contactless power receiving device 4 of the electric vehicle 6 shown in Figure 2B, generating an electric current. The generated current charges the battery 5, which is electrically connected to the contactless power receiving device 4 via cable 4a.

[0016] Specifically, the magnetic field generated by the non-contact power transmission device 3 acts on the coil 12 disposed on the bobbin 11 of the coil unit 10 included in the non-contact power reception device 4 as shown in FIG. 2B, and a current is generated in the coil 12. The current generated in the coil 12 is used to charge the battery 5 as described above.

[0017] FIG. 3A is a partially enlarged cross-sectional view of the coil unit 10 as described above. FIG. 3B is a view showing only the bobbin 11 of FIG. 3A. As shown in FIGS. 3A and 3B, the cross-section of the litz wire 12a disposed in the groove 11a of the bobbin 11 is polygonal (for example, rectangular). Thereby, the contact area between the litz wire 12a and the surface of the groove 11a of the bobbin 11 becomes larger than that of the litz wire 12a having a circular cross-section, and the litz wire 12a is more likely to be stably held in the groove 11a. When the litz wire 12a is stably held in the groove 11a, the electrical characteristics (resonance frequency) of the coil 12 also become stable. Details thereof will be described later while showing examples. As shown in FIG. 3A, the litz wire 12a is formed by twisting a plurality of enameled wires 12e.

[0018] Hereinafter, details of each component will be described.

[0019] (Power supply) The power supply 2 supplies electrical energy to the non-contact power transmission device 3. In the present embodiment, the power supply 2 is an AC power supply, and the current supplied to the circuit is an alternating current. In the present embodiment, the power supply 2 is disposed on the ground and is electrically connected to the non-contact power transmission device 3 via a cable 3a. The power supply 2 preferably supplies a current having a resonance frequency of the coil 12. Generally, since the resonance frequency of the coil 12 for non-contact power supply of the electric vehicle 6 is 85 kHz, the power supply 2 preferably can supply a current having a frequency of 85 kHz.

[0020] (Non-contact power transmission device) The non-contact power transmission device 3 includes a coil 12 and a capacitor 13. The coil 12 and the capacitor 13 are preferably configured such that the resonance frequency is 85 kHz. The configuration of the non-contact power transmission device 3 may be the same as the configuration of the non-contact power reception device 4.

[0021] (Non-contact power receiving device) As shown in FIG. 2B, the non-contact power receiving device 4 includes a coil unit 10, a capacitor 13, and a housing 14.

[0022] 〈Coil unit〉 As shown in FIGS. 2B and 3A, the coil unit 10 includes a bobbin 11 and a coil 12 disposed on the bobbin 11. The coil 12 is formed by winding a litz wire 12a. The litz wire 12a is formed by twisting a plurality of enameled wires 12e.

[0023] The overall shape of the coil 12 may be appropriately designed based on the required electrical characteristics. For example, the overall shape such as the size of the spiral and the number of turns of the coil 12 is appropriately designed based on the required electrical characteristics. In the present embodiment, the overall shape of the coil 12 is a planar spiral shape and an angular ring shape.

[0024] Specifically, it is preferable that the shape of the coil 12 is adjusted together with the capacitance of the capacitor 13 so that the resonance frequency of the coil 12 becomes 85 kHz, which is the resonance frequency for non-contact power feeding.

[0025] The litz wire 12a of the coil 12 is not particularly limited as long as its cross section is polygonal as shown in FIG. 3A. Here, the "polygonal shape" is a shape having a flat portion and a corner portion configured to increase the area that can contact the inner surface of the groove 11a as compared with the "circular" cross section disposed in the groove 11a as shown in FIG. 1. Note that, as shown in FIG. 3A, the corners may be rounded or may not be rounded. Examples of the "polygonal shape" include a square, a rectangle, an octagon, a rounded square, a rounded rectangle, and a rounded octagon.

[0026] In this embodiment, the cross-section of the Litz wire 12a, as shown in Figures 3A and 3B, has a flat bottom portion 12b corresponding to the flat bottom surface 11b of the groove 11a, two flat side portions 12c corresponding to the flat wall surfaces 11c of the groove 11a, and a flat top portion 12d parallel to the bottom surface 11b of the groove 11a. Note that the wall surface 11c of the groove 11a is perpendicular to the bottom surface 11b of the groove 11a. Accordingly, the flat side portions 12c of the Litz wire 12a are perpendicular to the flat bottom portion 12b of the Litz wire 12a. Furthermore, the cross-section of the Litz wire 12a has a rounded corner between two flat sections. In this embodiment, the rectangular shape of the cross-section of the Litz wire 12a is approximately rectangular (rounded rectangle). The width of the cross-section of the Litz wire 12a is, for example, 2 mm to 20 mm, and the height is 2 mm to 20 mm.

[0027] The cross-sectional shape of each of the multiple enameled wires constituting the Litz wire 12a is not particularly limited. Examples of enameled wire cross-sectional shapes include circular and rectangular shapes.

[0028] Figure 3B shows only the bobbin 11 from Figure 3A. As shown in Figure 3B, the bobbin 11 has a groove 11a in which the Litz wire 12a is placed. The overall shape of the groove 11a can be appropriately designed to match the shape of the coil 12. In this embodiment, the overall shape of the groove 11a is coil-shaped to match the coil, and more specifically, it is a spiral shape formed in a planar manner. Also in this embodiment, the groove 11a is formed in a spiral shape on the main surface of the plate-shaped bobbin 11. The material of the bobbin 11 is, for example, polypropylene or polyphenylene sulfide. The depth of the groove 11a is approximately uniform to match the height of the coil 12 (height of the Litz wire 12a), which is approximately constant.

[0029] The shallower the groove 11a, the lower the height of the groove wall, which allows for a lighter bobbin 11. As a result, the coil unit 10, the contactless power receiving device 4, and the electric vehicle 6 can also be made lighter. From this viewpoint, as shown in Figure 3A, when the depth of the groove 11a (height of the groove wall) is a and the height of the Litz wire 12a is A, it is preferable that a / A is less than 1, preferably 0.7 or less, and more preferably 0.5 or less. In the coil unit 10 according to this embodiment, since the cross-sectional shape of the Litz wire 12a is polygonal (for example, rectangular), even if the depth of the groove 11a (height of the groove wall) a is smaller than the height A of the Litz wire 12a, the Litz wire 12a can be stably held in the groove 11a. On the other hand, if the groove 11a is too shallow, it becomes difficult to stably hold the Litz wire 12a, which may adversely affect the electrical characteristics of the coil. From this viewpoint, it is preferable that a / A is 0.3 or greater.

[0030] The width of the Litz wire 12a is preferably slightly smaller than or the same as the width of the groove 11a. This makes it easier for the coil 12 to fit and be fixed into the groove 11a.

[0031] Capacitor Capacitor 13 is electrically connected to coil 12 and, together with coil 12, constitutes a resonant circuit of the contactless power receiving device 4, generating a resonant phenomenon for contactless power supply. The resonant frequency of the resonant circuit is determined mainly by the inductance of coil 12 and the capacitance of capacitor 13. Therefore, the capacitance of capacitor 13 is set to approach the desired frequency of the contactless power receiving device 4 (e.g., 85 kHz). Capacitor 13 may be connected in parallel or in series with coil 12. In this embodiment, capacitor 13 is arranged in series with coil 12. That is, capacitor 13 is placed between one end of coil 12 and one of the two cables 4a.

[0032] <housing> The housing 14 houses the coil unit 10 and the capacitor 13. Preferably, the housing 14 can protect the housed coil unit 10 and capacitor 13 from the external environment. In this embodiment, the housing 14 is located inside the electric vehicle 6. The material of the housing 14 is not particularly limited as long as it adequately protects the coil 12 and capacitor 13. The material of the housing 14 may be the same as the material of the bobbin 11.

[0033] (cable) In this embodiment, two cables 4a are arranged between the contactless power receiving device 4 and the battery 5. Specifically, one end of each of the two cables 4a is electrically connected to the battery 5, and the other end is connected to a capacitor 13 that is electrically connected to the coil 12.

[0034] (effect) In this embodiment, the coil unit 10 has a polygonal cross-section for the litz wire 12a of the coil 12, which is positioned in the groove 11a of the bobbin 11. This makes it easier for the litz wire 12a to be held stably in the groove 11a of the bobbin 11. Furthermore, because the litz wire 12a is held stably, the bobbin 11 can be made lighter by making the groove 11a shallower, and as a result, the coil unit 10, the contactless power receiving device 4, and the electric vehicle 6 can be made lighter. [Examples]

[0035] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0036] Coil units for samples 1-6 were manufactured, and their respective coil characteristics (impact on resonant frequency) were evaluated.

[0037] The coil units of Samples 1-4 had a rectangular cross-section for the litz wire, and the depth of the bobbin groove was varied so that the a / A ratio was 0.66, 0.50, 0.33, and 0.10 respectively (see Figure 3A). Each litz wire in the coil units of Samples 1-4 was made by twisting together several thousand enameled wires (round wires) to form a rectangular cross-section. In addition, the height A of the litz wire used in the coil units of Samples 1-4 ranged from 2 mm to 20 mm (see Figure 3A).

[0038] On the other hand, the coil units of samples 5 and 6 had a circular cross-section for the litz wire, and the depth of the bobbin groove was varied so that a / A was 1.00 and 0.50, respectively. In addition, each litz wire in the coil units of samples 5 and 6 had several thousand enameled wires (round wires), and the height A of the litz wire in the coil units of samples 5 and 6 was set to 2 mm to 20 mm.

[0039] The effect of the coil units of samples 1-6 described above on the resonant frequency was investigated. The effect on the resonant frequency was measured using the capacitor capacitance at which the resonant frequency is 85 kHz when a / A is 1 as a reference, and the resonant frequency when the coil characteristics (inductance) changed was measured. Table 1 below shows the parameters for each sample and their effect on the resonant frequency. Table 1 also shows the bobbin weight reduction rate when a / A is less than or equal to 1, as in each sample, with the bobbin mass when a / A is 1 as the baseline. That is, weight reduction rate (%) = [1 - {(bobbin mass for each sample) / (bobbin mass when a / A is 1)}] × 100.

[0040] [Table 1]

[0041] As can be seen from Table 1, when the cross-section of the Litz wire is circular, the resonant frequency changed significantly when a / A was less than 1 (Sample 6). This is thought to be because the Litz wire partially came out of the bobbin groove, disrupting the shape of the coil. On the other hand, when the cross-section of the Litz wire was polygonal (rectangular), the resonant frequency hardly changed even when a / A was less than 1 (Samples 1-3). This is thought to be because the Litz wire is held stably even with shallow bobbin grooves, and the coil shape is stable. Specifically, comparing sample 2 and sample 6, both of which have an a / A ratio of 0.50, sample 2 showed a smaller change in resonant frequency. Thus, by making the cross-section of the litz wire polygonal, the litz wire can be stably fixed even with shallow grooves, thus allowing for a lighter bobbin.

[0042] On the other hand, comparing samples 1 to 4, sample 4, where a / A is less than 0.3, showed a larger change in resonant frequency. Therefore, it is preferable that a / A be 0.3 or higher. [Industrial applicability]

[0043] The coil unit, contactless power receiving device, and contactless power supply system of the present invention are useful, for example, for contactless power supply in automobiles. [Explanation of Symbols]

[0044] 1. Contactless power supply system 2 power supply 3. Contactless power transmission device 3a, 4a cable 4. Contactless power receiving device 5 batteries 6 Electric vehicles 10 Coil Units 11 bobbins 11a Groove 11b Bottom 11c Wall 12 coils 12a Litz Line 12b, 12c, 12d flat part 12e Enameled wire 13 Capacitors

Claims

1. A coil unit characterized by comprising a bobbin having a coil-shaped groove and a Litz wire having a polygonal cross-section arranged in the groove.

2. A coil unit according to claim 1, characterized in that the bottom surface of the groove is flat.

3. A coil unit according to claim 1, characterized in that, in the cross-section of the groove in which the Litz wire is arranged, when the depth of the groove is a and the height of the Litz wire is A, a / A is 0.3 or more and less than 1.

4. A coil unit according to claim 3, characterized in that the a / A ratio is 0.3 or more and 0.7 or less.

5. A coil unit according to claim 1, characterized in that the coil unit is a coil unit used for contactless power reception.

6. A non-contact power receiving device characterized by having the coil unit described in claim 5.

7. A contactless power supply system characterized by having the contactless power receiving device described in claim 6.

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