Coil unit

Abstract

The invention provides a coil unit. The coil unit is provided with a primary-side coil or a secondary-side coil that transmits or receives power by non-contact power transmission between the power transmission unit and the power reception unit, and a primary-side magnetic member or a secondary-side magnetic member that is disposed on the rear side of each coil. Each of the magnetic members is provided with: a primary-side first portion or a secondary-side first portion positioned further inward than an outer peripheral end portion of each of the coils in a direction orthogonal to an axial direction when viewed from the axial direction along the central axis; and a primary-side second portion or a secondary-side second portion protruding outward from each of the first portions than the outer peripheral end portion.

Description

Technical Field

[0001] The present invention relates to a coil unit. Background Art

[0002] In recent years, more and more people are conducting research and development related to charging and power supply in vehicles equipped with secondary batteries in order to ensure convenient, reliable, sustainable and advanced energy use, which contributes to energy efficiency.

[0003] Conventionally, in contactless power transmission systems that supply power to a vehicle from outside the vehicle through contactless power transmission, there is known a system having a back plate formed of a magnetic material for inducing magnetic flux around each coil on the power transmitting side and the power receiving side (for example, refer to the following patent document 1).

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 7232960 Summary of the invention

[0005] In the technology related to charging and power supply in a vehicle equipped with a secondary battery, in contactless power transmission, it is desired to reduce the magnetic flux (leakage magnetic flux) other than the main magnetic flux interlinked with each coil on the power transmission side and the power receiving side to improve the coupling coefficient. For example, as in the above-mentioned contactless power transmission system of the prior art, if the flat plate-shaped back plate formed of a magnetic material is only formed to a size that includes the coil when viewed from above, the following problem occurs: the appropriate induction of the magnetic flux is insufficient, and the core constant of the system as a whole cannot be improved.

[0006] The present invention is proposed in consideration of such a situation, and its purpose is to provide a coil unit that improves the core constant of the entire system and reduces leakage flux through appropriate induction of magnetic flux in contactless power transmission, and further contributes to energy efficiency.

[0007] In order to solve the above problems and achieve the above objects, the present invention adopts the following means.

[0008] (1): A coil unit according to one embodiment of the present invention comprises: a coil that transmits or receives electric power through contactless power transmission between a power transmitting section and a power receiving section; and a magnetic member that is arranged on the rear side of the coil when viewed from the other side when the power transmitting section and the power receiving section face each other, wherein the magnetic member comprises: a first portion that is located more inward than an outer peripheral end portion of the coil in an orthogonal direction to the axial direction when viewed from an axial direction along the central axis of the coil; and a second portion that protrudes outward from the first portion in the orthogonal direction than the outer peripheral end portion.

[0009] (2): In the above-mentioned solution (1), the first portion and the second portion may be in the form of an integral flat plate orthogonal to the axial direction.

[0010] (3): In the above-mentioned solution (1) or (2), the magnetic member may include a third portion, and the third portion may protrude from the first portion in the axial direction and be inserted into the hollow region of the coil.

[0011] (4): In the above scheme (3), the third part may also include: a frame-shaped wall portion, which protrudes from the periphery of the hole penetrating the first part along the axial direction and is arranged in the hollow area; and a cover portion, which closes the protruding side opening end of the wall portion.

[0012] According to the above solution (1), the magnetic component has a second portion that protrudes outward from the outer peripheral end of the coil, thereby allowing the leakage magnetic flux returning to the coil to expand outward, and the core constant (= effective magnetic path length / effective cross-sectional area) of the system as a whole can be improved. By improving the core constant, the directivity of the magnetic flux can be increased and the leakage magnetic flux to the surrounding can be reduced.

[0013] In the case of the above scheme (2), since the first part and the second part are integral flat plates orthogonal to the axial direction, the magnetic flux can be appropriately induced to reduce the leakage magnetic flux to the surroundings, compared with the case where the second part is bent toward the other side.

[0014] In the case of the above scheme (3), the magnetic member has a third portion inserted into the hollow core area of ​​the coil, thereby enabling the distribution of the main magnetic flux between the power transmission unit and the power reception unit to expand in the central portion in the direction orthogonal to the axial direction, thereby improving the core constant of the system as a whole. By improving the core constant, the main magnetic flux can be concentrated in the central portion, and the increase in the magnetic flux density in the outer direction orthogonal to the axial direction can be suppressed.

[0015] In the case of the above-mentioned scheme (4), the third part which improves the coupling coefficient by being inserted into the hollow area of ​​the coil has a wall portion and a cover portion which closes the protruding side opening end of the wall portion, thereby suppressing the increase in weight compared to, for example, a case where the coil is not hollow. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a diagram showing a configuration of a contactless power transmission system including a coil unit according to an embodiment of the present invention.

[0017] Figure 2 It is a diagram showing the configuration of a power transmission unit and a power reception unit in the contactless power transfer system according to the embodiment of the present invention.

[0018] Figure 3It is a perspective view showing a primary-side coil and a primary-side magnetic member of a power transmitting device and a secondary-side coil and a secondary-side magnetic member of a power receiving device in a coil unit according to an embodiment of the present invention.

[0019] Figure 4 This is a diagram of a primary coil and a primary magnetic member of a power transmitting device and a secondary coil and a secondary magnetic member of a power receiving device in a coil unit according to an embodiment of the present invention as viewed from a direction perpendicular to the axial direction.

[0020] Figure 5 This is a diagram showing an example of a magnetic field (magnetic force field) in the coil unit according to the embodiment of the present invention as viewed from a direction perpendicular to the axial direction.

[0021] Figure 6 This is a contour diagram of an example of magnetic flux density distribution in the coil unit according to the embodiment of the present invention as viewed from a direction perpendicular to the axial direction.

[0022] Figure 7 This is a contour diagram of an example of magnetic flux density distribution in the coil unit according to the embodiment of the present invention as viewed from a direction perpendicular to the axial direction. DETAILED DESCRIPTION

[0023] Hereinafter, a coil unit according to an embodiment of the present invention will be described with reference to the drawings.

[0024] Figure 1 1 is a diagram showing a configuration of a contactless power transmission system 1 including a coil unit 20 according to the embodiment. Figure 2 1 is a diagram showing the configuration of the power transmission unit 8 and the power reception unit 15 in the contactless power transfer system 1 according to the embodiment.

[0025] Coil unit 20 of the embodiment constitutes a part of contactless power transmission system 1 for supplying power from outside of a moving body such as a vehicle to a moving body by contactless power transmission. The vehicle is, for example, an electric vehicle such as an electric automobile, a hybrid vehicle, or a fuel cell vehicle.

[0026] (Contactless power transmission system)

[0027] like Figure 1 and Figure 2 As shown, the contactless power transmission system 1 of the embodiment includes, for example, a power transmission device 2 provided on a travel path of a vehicle, and a drive control device 3 and a power receiving device 4 mounted on a mobile body such as a vehicle. It should be noted that the contactless power transmission system 1 of the embodiment may also include at least only components mounted on the mobile body (such as the drive control device 3 and the power receiving device 4) or components external to the mobile body (such as the power transmission device 2), and contactless power transmission may also be performed by combining the contactless power transmission system 1 with other components.

[0028] The power transmission device 2 includes, for example, a power supply unit 6, a power transmission power conversion unit 7, and a power transmission unit 8. The power transmission device 2 may include at least a plurality of power transmission units 8 in a predetermined coupling section such as a vehicle travel path.

[0029] The power supply unit 6 includes, for example, an AC power supply such as a commercial power supply, an AC-DC converter for converting AC power into DC power, and a capacitor for power smoothing. The power supply unit 6 converts AC power supplied from the AC power supply into DC power by the AC-DC converter.

[0030] The power transmission power conversion unit 7, for example, includes an inverter that converts DC power into AC power. The inverter of the power transmission power conversion unit 7, for example, includes a first bridge circuit formed by a plurality of switching elements and a rectifying element connected in a two-phase bridge, and a capacitor for voltage smoothing. Each switching element is, for example, a transistor such as a MOSFET (Metal Oxide Semi-conductor Field Effect Transistor) of SiC (Silicon Carbide). The plurality of switching elements are transistors of a high-side arm and a low-side arm that form a pair in each phase. The rectifying element is, for example, a return diode connected in parallel with each transistor. The capacitor for voltage smoothing is connected in parallel with the first bridge circuit.

[0031] The power transmission unit 8 transmits power by utilizing changes in high-frequency magnetic fields, for example, through magnetic field coupling such as magnetic field resonance or electromagnetic induction. Figure 2 As shown, the power transmission unit 8 includes, for example, a resonance circuit formed by a primary coil 8a, a primary resistor 8b, and a primary capacitor 8c connected in series. The power transmission unit 8 includes, for example, a sensor such as a current sensor for detecting a current It flowing through the resonance circuit.

[0032] For example, the power transmission device 2 controls the on (conduction) and off (isolation) switching of each switching element of the power transmission power conversion unit 7 according to a preset driving frequency or information on a required frequency received from the power receiving device 4, thereby transmitting power to the power receiving device 4 of a mobile body such as a vehicle.

[0033] like Figure 1 and Figure 2 As shown, the driving control device 3 of a mobile body such as a vehicle includes, for example, a power storage device 11, a power conversion unit 13, and a rotary electric machine 14. The power receiving device 4 of the mobile body includes, for example, a power receiving unit 15 and a received power conversion unit 16.

[0034] The power storage device 11 is connected to a power conversion unit 13 and a power receiving power conversion unit 16 described later. The power storage device 11 is charged by power transmitted in a non-contact manner from a power transmission device 2 outside a mobile body such as a vehicle. The power storage device 11 exchanges power with the rotating electric machine 14 via the power conversion unit 13.

[0035] The power storage device 11 includes a storage battery such as a lithium ion storage battery, a current sensor for detecting the current of the storage battery, and a voltage sensor for detecting the voltage of the storage battery.

[0036] The power conversion unit 13 is connected to the rotating electric machine 14. The power conversion unit 13 includes, for example, a power converter that converts DC power into AC power. The power converter includes, for example, a second element module and a capacitor for voltage smoothing.

[0037] The second element module, for example, includes a second bridge circuit formed by a plurality of switching elements and a rectifier element connected in a three-phase bridge. Each switching element is, for example, a transistor such as a SiC MOSFET. The plurality of switching elements are transistors of a high-side arm and a low-side arm that form a pair in each phase. The rectifier element is, for example, a return diode connected in parallel with each transistor. A capacitor for voltage smoothing is connected in parallel with the second bridge circuit.

[0038] The second element module controls the operation of the rotating electric machine 14 by transferring power. For example, when the rotating electric machine 14 is powered, the second element module converts the DC power input from the positive and negative DC terminals into three-phase AC power, and supplies the three-phase AC power from the three-phase AC terminals to the rotating electric machine 14. The second element module generates a rotational driving force by sequentially commutating the power supplied to the three-phase stator windings of the rotating electric machine 14.

[0039] The second element module converts three-phase AC power input from the three-phase stator winding into DC power by driving the switching elements of each phase to be turned on (conducted) and off (disconnected) in synchronization with the rotation of the rotating electric machine 14, for example, during the regeneration of the rotating electric machine 14. The second element module can supply the DC power converted from the three-phase AC power to the power storage device 11.

[0040] The rotating electric machine 14 is, for example, a three-phase AC brushless DC motor provided for driving a mobile body such as a vehicle. The rotating electric machine 14 includes a rotor having a permanent magnet for field excitation and a stator having a three-phase stator winding for generating a rotating magnetic field for rotating the rotor. The three-phase stator winding is connected to the three-phase AC terminal 13d of the power conversion unit 13.

[0041] The rotating electric machine 14 generates a rotational driving force by performing a power running operation using the electric power supplied from the electric power conversion unit 13. For example, when the rotating electric machine 14 can be connected to the wheels of the vehicle, it generates a driving force by performing a power running operation using the electric power supplied from the electric power conversion unit 13. The rotating electric machine 14 can also generate electric power by performing a regenerative operation using the rotational power input from the wheel side of the vehicle. When the rotating electric machine 14 can be connected to the internal combustion engine of the vehicle, it can also generate electricity using the power of the internal combustion engine.

[0042] The power receiving unit 15 is connected to the power receiving power conversion unit 16. The power receiving unit 15 receives power by utilizing the change of the high frequency magnetic field transmitted from the power transmitting unit 8 through magnetic field coupling such as magnetic field resonance or electromagnetic induction. Figure 2 As shown, the power receiving unit 15 includes, for example, a resonance circuit formed by a secondary coil 15a, a secondary resistor 15b, and a secondary capacitor 15c connected in series. The power receiving unit 15 includes, for example, a sensor such as a current sensor for detecting a current Ir flowing through the resonance circuit.

[0043] Figure 1 and Figure 2 The receiving power conversion unit 16 shown is connected to the power conversion unit 13. The receiving power conversion unit 16 includes a so-called full bridge less type (or bridgeless and totem pole type) power factor correction (PFC: Power Factor Correction) circuit that converts AC power into DC power. The so-called bridgeless PFC is a PFC that does not include a bridge rectifier composed of a plurality of diodes connected by a bridge, and the so-called totem pole PFC is a PFC that includes a pair of switching elements of the same conductivity type connected in series in the same direction (totem pole connection).

[0044] The receiving power conversion unit 16 includes, for example, a third bridge circuit formed by a plurality of switching elements and a rectifying element connected in a two-phase bridge and a capacitor for voltage smoothing. Each switching element is, for example, a transistor such as SiC MOSFET. The plurality of switching elements are transistors of a high-side arm and a low-side arm that form a pair in each phase. The rectifying element is, for example, a return diode connected in parallel with each transistor. The capacitor for voltage smoothing is connected in parallel with the third bridge circuit.

[0045] For example, the power receiving device 4 including the power receiving unit 15 and the power receiving power conversion unit 16 controls the switching of each switching element of the power receiving power conversion unit 16 to be turned on (conducted) and off (isolated) based on the information of the frequency of power transmission performed by the power transmitting device 2, thereby receiving the power transmitted from the power transmitting device 2.

[0046] (Coil unit)

[0047] The coil unit 20 according to the embodiment constitutes at least one of the power transmission unit 8 and the power reception unit 15 , for example.

[0048] Hereinafter, as the coil unit 20 according to the embodiment, for example, a power transmission-side coil unit 20 a constituting the power transmission unit 8 and a power reception-side coil unit 20 b constituting the power reception unit 15 will be described.

[0049] Figure 3 It is a perspective view showing the primary coil 8 a and the primary magnetic member 30 of the power transmitting device 2 and the secondary coil 15 a and the secondary magnetic member 40 of the power receiving device 4 in the coil unit 20 according to the embodiment.

[0050] Figure 4 The diagram shows the primary coil 8 a and the primary magnetic member 30 of the power transmitting device 2 and the secondary coil 15 a and the secondary magnetic member 40 of the power receiving device 4 in the coil unit 20 according to the embodiment as viewed from a direction perpendicular to the axial direction.

[0051] like Figure 3 and Figure 4 As shown, the power transmission coil unit 20a (20) of the embodiment includes, for example, a primary coil 8a and a primary magnetic member 30. The power reception coil unit 20b (20) of the embodiment includes, for example, a secondary coil 15a and a secondary magnetic member 40.

[0052] The primary coil 8a and the secondary coil 15a each have an outer shape of, for example, a rectangular spiral shape.

[0053] The outer shape of each of the primary side magnetic member 30 and the secondary side magnetic member 40 is formed into a rectangular flat plate with a box-shaped convex portion, for example. The primary side magnetic member 30 and the secondary side magnetic member 40 are respectively formed of a magnetic material with a relatively large magnetic permeability, such as a non-directional (isotropic) magnetic material such as ferrite, or an electromagnetic steel plate such as a silicon steel plate, or a directional (anisotropic) magnetic material such as a soft magnetic material such as a nanocrystalline soft magnetic material. For example, when the power transmission unit 8 faces the power reception unit 15, the primary side magnetic member 30 is arranged on the rear side of the primary side coil 8a when viewed from the power reception unit 15 side. For example, when the power transmission unit 8 faces the power reception unit 15, the secondary side magnetic member 40 is arranged on the rear side of the secondary side coil 15a when viewed from the power transmission unit 8 side.

[0054] The primary magnetic member 30 includes, for example, a primary first portion 31 , a primary second portion 32 , and a primary third portion 33 .

[0055] The outer shapes of the primary-side first portion 31 and the primary-side second portion 32 are, for example, integral flat plate shapes that are orthogonal to the axial direction along the central axis O of the primary-side coil 8 a .

[0056] For example, the primary-side first portion 31 is arranged inward of the outer peripheral end portion 8ae of the primary-side coil 8a in a direction perpendicular to the axial direction when viewed in the axial direction along the central axis O of the primary-side coil 8a.

[0057] For example, when viewed in the axial direction along the central axis O of the primary coil 8a, the primary second portion 32 protrudes outward from the primary first portion 31 by a predetermined first length L1 in a direction perpendicular to the axial direction beyond the outer peripheral end portion 8ae.

[0058] The primary third portion 33 protrudes axially from the center of the primary first portion 31 and is inserted into the air core region 8ac of the primary coil 8a. The protruding height of the primary third portion 33 is set according to the axial thickness of the primary coil 8a.

[0059] The primary-side third site 33 includes, for example, a primary-side wall portion 33 a and a primary-side cover portion 33 b .

[0060] The primary side wall portion 33a has a frame shape protruding from the periphery of the hole 31a penetrating the primary side first portion 31 in the axial direction and arranged in the hollow region 8ac of the primary side coil 8a. The primary side cover portion 33b has a flat plate shape that closes the protruding side opening end of the primary side wall portion 33a.

[0061] The secondary magnetic member 40 includes, for example, a secondary first portion 41 , a secondary second portion 42 , and a secondary third portion 43 .

[0062] The outer shapes of the secondary-side first portion 41 and the secondary-side second portion 42 are, for example, integral flat plate shapes that are orthogonal to the axial direction along the central axis O of the secondary-side coil 15 a .

[0063] For example, the secondary first portion 41 is arranged inward of the outer peripheral end 15ae of the secondary coil 15a in a direction perpendicular to the axial direction when viewed in the axial direction along the central axis O of the secondary coil 15a.

[0064] For example, when viewed in the axial direction along the central axis O of the secondary coil 15 a , the secondary second portion 42 protrudes outward from the secondary first portion 41 by a predetermined second length L2 in the direction orthogonal to the axial direction beyond the outer peripheral end portion 15 ae.

[0065] The secondary side third portion 43 protrudes in the axial direction from the central portion of the secondary side first portion 41 and is inserted into the hollow region 15ac of the secondary side coil 15a. The protruding height of the secondary side third portion 43 is set, for example, according to the thickness of the paving material such as concrete or asphalt to which the power transmission unit 8 is fixed on the running road of the vehicle, etc.

[0066] The secondary-side third site 43 includes, for example, a secondary-side wall portion 43 a and a secondary-side cover portion 43 b .

[0067] The outer shape of the secondary wall portion 43a is, for example, a frame-like shape that protrudes from the periphery of a hole 41a that penetrates the secondary first site 41 in the axial direction and is arranged in the air-core region 15ac of the secondary coil 15a.

[0068] The outer shape of the secondary side cover portion 43 b is, for example, a flat plate shape that closes the protruding side opening end of the secondary side wall portion 43 a .

[0069] For example, when the outer peripheries of the primary coil 8a and the secondary coil 15a are the same in size (eg, width L3 in a direction perpendicular to the axial direction), the predetermined first length L1 is greater than the predetermined second length L2 by a predetermined length ΔL.

[0070] Figure 5 This is a diagram showing an example of a magnetic field (magnetic force field) in coil unit 20 according to the embodiment as viewed from a direction perpendicular to the axial direction.

[0071] like Figure 5 As shown, the following can be confirmed: the primary side magnetic component 30 and the secondary side magnetic component 40 have a primary side second portion 32 and a secondary side second portion 42, whereby the distribution of the leakage magnetic flux Fa that does not interlink with the primary side coil 8a and the secondary side coil 15a and returns to each coil 8a, 15a (especially the primary side coil 8a, etc.) expands laterally (outward in the orthogonal direction to the axial direction).

[0072] The following can be confirmed: the primary side magnetic member 30 and the secondary side magnetic member 40 have a primary side third portion 33 and a secondary side third portion 43, whereby the distribution of the main magnetic flux Fb interlinked with the primary side coil 8a and the secondary side coil 15a expands in the central part in a direction orthogonal to the axial direction.

[0073] It was confirmed that the magnetic flux density distribution becomes thinner between the primary coil 8a and the secondary coil 15a, thereby increasing the core constant (=effective magnetic path length / effective cross-sectional area), increasing the directivity of the magnetic flux, and reducing the leakage flux to the surroundings.

[0074] Figure 6 This is a contour diagram of an example of magnetic flux density distribution in coil unit 20 according to the embodiment as viewed from a direction perpendicular to the axial direction. Figure 7 This is a contour diagram of an example of magnetic flux density distribution in coil unit 20 according to the embodiment as viewed from a direction perpendicular to the axial direction.

[0075] like Figure 6 and Figure 7As shown, the following can be confirmed: the primary side magnetic component 30 and the secondary side magnetic component 40 have a primary side second portion 32 and a secondary side second portion 42 and a primary side third portion 33 and a secondary side third portion 43, whereby the main magnetic flux is concentrated in the central portion and the increase in the magnetic flux density to the outside in the orthogonal direction to the axial direction is suppressed.

[0076] As described above, according to the coil unit 20 of the embodiment, each magnetic member 30, 40 has each second portion 32, 42 protruding outward from the outer peripheral end 8ae, 15ae of each coil 8a, 15a, thereby enabling the leakage flux returning to each coil 8a, 15a to expand outward, and improving the core constant of the system as a whole. By improving the core constant, the directivity of the magnetic flux can be increased, and the leakage flux to the surrounding can be reduced.

[0077] Each first portion 31, 41 and each second portion 32, 42 is an integral flat plate orthogonal to the axial direction, thereby being able to appropriately induce magnetic flux so as to reduce leakage magnetic flux to the surroundings, compared with a case where each second portion 32, 42 is bent toward the other side (the power transmitting unit 8 side or the power receiving unit 15 side), for example.

[0078] Each magnetic member 30, 40 has each third portion 33, 43 inserted into the hollow core area 8ac, 15ac of each coil 8a, 15a, thereby enabling the distribution of the main magnetic flux between the power transmission unit 8 and the power reception unit 15 to expand in the central portion in the orthogonal direction to the axial direction, thereby improving the core constant of the system as a whole. By improving the core constant, the main magnetic flux can be concentrated in the central portion, and the increase in the magnetic flux density in the outer direction orthogonal to the axial direction can be suppressed.

[0079] The third parts 33 and 43 that improve the coupling coefficient by being inserted into the hollow areas 8ac and 15ac include wall parts 33a and 43a and cover parts 33b and 43b that close the protruding side opening ends of the wall parts 33a and 43a, thereby suppressing the increase in weight compared with, for example, the case where the part is not hollow.

[0080] (Variation Example)

[0081] In the above embodiment, the prescribed first length L1 of the primary side second portion 32 is greater than the prescribed second length L2 of the secondary side second portion 42 by a prescribed length ΔL, but the present invention is not limited thereto. In terms of reducing the leakage magnetic flux, it is preferred that the primary side second portion 32 on the power transmission side is formed relatively large, but the prescribed first length L1 and the prescribed second length L2 may be the same, and the prescribed second length L2 may be greater than the prescribed first length L1.

[0082] The embodiments of the present invention are provided as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the scope of the main purpose of the invention. These embodiments and their variations are included in the scope and main purpose of the invention, and are also included in the invention described in the technical solution and its equivalent scope.

Claims

1. A coil unit, wherein: The coil unit comprises: a coil for transmitting or receiving electric power by contactless electric power transmission between a power transmitting unit and a power receiving unit; and a magnetic member disposed on the rear side of the coil when viewed from the other side when the power transmission unit and the power reception unit face each other; The magnetic component comprises: a first portion, when viewed in an axial direction along the central axis of the coil, located inwardly of an outer peripheral end of the coil in a direction orthogonal to the axial direction; as well as The second portion protrudes outward from the first portion in the orthogonal direction relative to the outer peripheral end portion.

2. The coil unit according to claim 1, wherein: The first portion and the second portion are in the shape of an integrated flat plate that is perpendicular to the axial direction.

3. The coil unit according to claim 1 or 2, wherein: The magnetic member includes a third portion that protrudes from the first portion in the axial direction and is inserted into a hollow region of the coil.

4. The coil unit according to claim 3, wherein: The third part has: a frame-shaped wall portion protruding from the periphery of a hole penetrating the first portion in the axial direction and arranged in the hollow region; and A cover portion closes the protruding side opening end of the wall portion.

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