Centrifugal fan and fixing method

Abstract

A centrifugal fan (1) includes a first portion (9) provided on a rotor (5) and a second portion provided on a fan portion (3), wherein the second portion has a larger linear expansion coefficient than the first portion (9). The first portion (9) includes a top portion (22) and a first cylindrical portion (23), wherein the top portion (22) includes a plane (22a). The second portion includes: a main portion (34) located closer to the first axial direction (C1) than the top portion (22); a second cylindrical portion (35) including an inner cylindrical surface (35f) opposed to the outer cylindrical surface (23f) of the first cylindrical portion (23) with a gap (S); and an annular rib (38) and a plurality of auxiliary ribs (39) protruding from the main portion (34) toward the second axial direction (C2). Adhesive portions (40) formed of an adhesive are provided between the annular end surface (38a) of the annular rib (38) facing the plane (22a) and the plane (22a), and between the end surfaces (39a) of the plurality of auxiliary ribs (39) and the plane (22a).

Description

Technical Field

[0001] The present invention relates to a centrifugal fan and a method for fixing a fan part to a rotor of the centrifugal fan. Background Art

[0002] A centrifugal fan comprises a fan unit having multiple blades and a motor unit serving as a driving source for the fan unit. The fan unit draws fluid from near its center of rotation as it rotates and delivers it radially outward from the fan unit. Conventionally, a centrifugal fan employs a technique for securing the fan unit to the rotor of the motor unit, thereby rotating the rotor and fan unit together. For example, Patent Document 1 discloses a centrifugal fan in which the outer circumference of a metal rotor holder (rotor) provided on a motor (motor unit) is secured to the inner circumference of a blade support portion of a resin impeller (fan unit) using an adhesive.

[0003]

Prior technical literature

[0004] [Patent Literature]

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-116848 Summary of the Invention

[0006] [Problems to be solved by the invention]

[0007] However, when the outer circumferential surface of the rotor holder and the inner circumferential surface of the fan unit's blade support are bonded together, as in Patent Document 1, the center of gravity may shift due to thermal deformation, depending on the centrifugal fan's operating environment. Thermal deformation refers to dimensional changes in the fan unit and the fixing member (in Patent Document 1, the rotor holder) that secures the fan unit, respectively, due to the fan's ambient temperature and temperature fluctuations. The fan unit and the fixing member are often made of different materials. For example, in Patent Document 1, the fan unit may be made of resin, while the fixing member may be made of metal. Therefore, when the fan unit is made of a material with a larger linear expansion coefficient than the fixing member, the thermal deformation of the fan unit becomes greater than that of the fixing member, and the center of gravity of the fan unit relative to the fixing member may shift from its original position before thermal deformation. This shift in the center of gravity of the fan unit can adversely affect the fan's balance, potentially causing vibration and noise during operation. Therefore, to prevent the center of gravity of the fan unit from shifting relative to the fixing member, one approach is to modify the bonding point of the fan unit to the fixing member. However, in this case, ensuring bonding strength becomes a challenge.

[0008] The centrifugal fan and fixing method of the present invention were developed in response to such challenges. One of their objectives is to ensure the bonding strength of the fan unit to the rotor while suppressing the displacement of the center of gravity associated with thermal deformation. It should be noted that this objective is not limited to the present invention. Other objectives of the present invention include achieving effects derived from the various structures described in the specific embodiments below and not achievable with conventional techniques.

[0009]

Solutions to Solve the Problem

[0010] The disclosed centrifugal fan and fixing method can be implemented as the following embodiments (application examples) to solve at least a part of the above-mentioned problems.

[0011] A disclosed centrifugal fan comprises: a first portion provided on a rotor that rotates integrally with a shaft; and a second portion provided on a fan portion having a plurality of blades and fixed to the rotor, the second portion having a larger linear expansion coefficient than the first portion. The first portion comprises: a top portion extending radially outward from a first hole through which the shaft passes and having a flat surface oriented in a first axial direction of the shaft; and a first cylindrical portion extending from the radially outer end of the top portion in a second axial direction opposite to the first axial direction. The second portion includes: a main surface portion located closer to the first axial direction than the top surface portion and extending radially outward from a second hole portion through which the shaft passes; an annular rib portion projecting from the main surface portion in the second axial direction and having an annular end surface facing the plane; a plurality of auxiliary rib portions projecting from the main surface portion in the second axial direction and extending radially from the annular rib portion in the radial direction and having end surfaces facing the plane; and a cylindrical second cylindrical portion extending from the radially outer end portion of the main surface portion in the second axial direction and having an inner cylindrical surface facing the outer cylindrical surface of the first cylindrical portion with a gap therebetween. Adhesive portions formed of an adhesive are provided between the annular end surface of the annular rib portion and the plane, and between the end surfaces of each of the plurality of auxiliary rib portions and the plane.

[0012] The disclosed fixing method fixes a second portion to a first portion. The first portion is provided on a rotor of a motor unit having a rotor that rotates integrally with a shaft and a stator disposed opposite the rotor. The second portion is provided on a fan unit having multiple blades and having a larger linear expansion coefficient than the first portion. The first portion includes a top portion and a first cylindrical portion. The top portion extends radially outward from a first hole for passing the shaft and has a flat surface oriented in a first axial direction. The first cylindrical portion extends from a radially outward end of the top portion in a second axial direction opposite the first axial direction. The second part is provided with a main surface portion, an annular rib portion, a plurality of auxiliary rib portions, and a second cylindrical portion. The main surface portion extends radially outward from the second hole portion for the shaft to pass through, the annular rib portion protrudes from the main surface portion and has an annular end face. The plurality of auxiliary rib portions protrude from the main surface portion in the same direction as the annular rib portion and extend radially from the annular rib portion in the radial direction and have end faces facing in the same direction as the annular end face. The second cylindrical portion extends from the radially outer end portion of the main surface portion in the same direction as the annular rib portion. The fixing method comprises: a first step of applying an adhesive to the annular end face, or applying an adhesive to the following portion in the plane, wherein the portion refers to a portion in the plane that is opposite to the annular end face when the main portion of the second part is arranged at a position closer to the first axial side than the top portion of the first part; a second step of arranging the main portion of the second part at a position closer to the first axial side than the top portion of the first part, and making the annular end face and the end face opposite to the plane; and a third step of making the inner cylinder surface of the second cylinder portion and the outer cylinder surface of the first cylinder portion opposite to each other with a gap therebetween, and spreading the adhesive between the annular end face and the plane, and between the end face and the plane.

[0013] Effects of the invention

[0014] According to the disclosed centrifugal fan and fixing method, it is possible to suppress the displacement of the center of gravity position due to thermal deformation while ensuring the bonding strength of the fan unit to the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is an axial cross-sectional view of the centrifugal fan according to the embodiment.

[0016] Figure 2 is Figure 1 A perspective view of a rotor yoke provided on a rotor of a motor portion of a centrifugal fan.

[0017] Figure 3 is Figure 1 An axial half-section view of a main board with blades provided on the fan portion of a centrifugal fan.

[0018] Figure 4 From the second axis Figure 3 A three-dimensional image of the motherboard with blades.

[0019] Figure 5 yes Figure 1 Magnified view of the X section.

[0020] Figure 6 From the radially outer side and the first axial side ( Figure 5 Observe in the direction of the arrow Y) Figure 1 A three-dimensional view of the middle plane portion and inclined portion of the rotor yoke in a centrifugal fan, and the annular rib portion and multiple auxiliary rib portions of the main plate with blades. DETAILED DESCRIPTION

[0021] A centrifugal fan and a fixing method according to an embodiment will be described with reference to the accompanying drawings. The embodiments described below are merely illustrative and are not intended to exclude various modifications or technical applications not explicitly described in the following embodiments. The various structures of this embodiment can be implemented with various modifications without departing from the scope of their main purpose.

[0022] [1. Structure]

[0023] Figure 1 FIG. 1 is an axial cross-sectional view of the centrifugal fan 1 of this embodiment. Figure 1 As shown, a centrifugal fan 1 includes a motor unit 2 serving as a drive source and a fan unit 3 driven by the motor unit 2. The centrifugal fan 1 is constructed, for example, by having the motor unit 2 and the fan unit 3 housed within a housing 10 that forms the outer contour of the centrifugal fan 1. The motor unit 2 includes a shaft 4, a rotor 5 that rotates integrally with the shaft 4, and a stator 6 disposed opposite the rotor 5. The fan unit 3 is mounted on one axial side of the shaft 4 (the first axial direction C1 side described later) relative to the rotor 5 of the motor unit 2 and is fixed to the rotor 5 with an adhesive, thereby rotating integrally with the shaft 4 and the rotor 5. The centrifugal fan 1 can be used, for example, as a ventilation fan mounted on a vehicle seat.

[0024] Hereinafter, the state in which the fan unit 3 is mounted and fixed to the rotor 5 of the motor unit 2 is referred to as the fixed state. In addition, the state before the fixed state is referred to as the pre-fixed state. The state in which the fan unit 3 is mounted on one side in the axial direction relative to the rotor 5 in the pre-fixed state (the fan unit 3 is placed on one side in the axial direction) is referred to as the mounted state, and the state in the pre-fixed state before the mounted state (the state in which the fan unit 3 and the rotor 5 are separated) is referred to as the pre-installed state. The centrifugal fan 1 is in the fixed state by the adhesive applied to the fan unit 3 in the pre-installed state being expanded (extended) and cured between the fan unit 3 and the rotor 5 when the mounted state is reached. The fan unit 3 utilizes the adhesive portion 40 (refer to Figure 5 and Figure 6 ) is bonded and fixed to the rotor 5, thereby rotating integrally with the shaft 4 and the rotor 5. In the following description, unless otherwise specified, it is assumed that the centrifugal fan 1 is in a fixed state.

[0025] Hereinafter, the direction in which the shaft 4 extends (the direction of the axis C of the shaft 4 ) is referred to as the axial direction. The direction in which the fan unit 3 is mounted relative to the motor unit 2 is referred to as the first axial direction C1, and the direction opposite to the first axial direction C1 is referred to as the second axial direction C2. Furthermore, the direction perpendicular to the axial direction and away from the axis C of the shaft 4 is referred to as the radially outward direction, while the direction in the same direction and toward the axis C is referred to as the radially inward direction. Unless otherwise specified, the term "radial direction" is simply used. The direction perpendicular to the axial direction and rotating about the axis C is referred to as the circumferential direction.

[0026] The motor unit 2 has the shaft 4, the rotor 5 and the stator 6 as described above. The motor unit 2 of this embodiment is an outer rotor type motor. Figure 1 As shown, the stator 6 is arranged radially inward of the rotor 5. The shaft 4 extends, for example, from a position closer to the second axial direction C2 than the stator 6 to a position closer to the first axial direction C1 than the fan unit 3. The end portion of the shaft 4 on the second axial direction C2 and the axial middle portion thereof can be rotatably supported by bearings 11. The bearings 11 are held by a cylindrical bearing holder 12 fixed to the housing 10.

[0027] The stator 6 includes an annular stator core 7 formed by stacking a plurality of identically shaped steel plates. A coil (not shown) wound around the stator core 7 via an insulator can be provided on the stator 6. The stator core 7 is fixed to the housing 10 in a non-rotatable manner by being fitted onto the bearing holder 12, with the stacking direction of the steel plates aligned with the axial direction at its center.

[0028] The rotor 5 includes a magnet 8 and a rotor yoke 9, which are arranged radially opposite to the stator core 7. The magnet 8 is formed, for example, from a long rectangular rubber magnet, joined at both ends to form a ring with an inner diameter larger than the outer diameter of the stator core 7. The magnet 8 is fixed to the rotor yoke 9 and is arranged radially outside the stator core 7, facing each other with a gap therebetween.

[0029] The rotor yoke 9 is a member that secures the magnet 8 against relative rotation with respect to the shaft 4 and prevents leakage of the magnet 8's magnetic flux lines. It is made, for example, of a magnetic steel plate (metal). The rotor yoke 9 has, for example, a bottomed cylindrical (cup-shaped) shape that opens in the second axial direction C2 and covers the stator 6 from the first axial direction C1. The rotor yoke 9 includes a first hole 21 for inserting the shaft 4, a cylindrical first portion 23 located radially outward of the stator core 7, and a top portion 22 connecting the first hole 21 and the first portion 23.

[0030] The first hole portion 21 is formed with a through hole 21h (see Figure 2 ) is formed into, for example, a cylindrical shape concentric with the axis C. The rotor yoke 9 is fixed to the shaft 4 so as not to rotate relative to the shaft 4 by inserting the shaft 4 into the through hole 21h and press-fitting the first hole portion 21 relative to the shaft 4.

[0031] The first cylindrical portion 23 is a portion for fixing the magnet 8. Figure 1 As shown in FIG. 1 , the stator core 7 is surrounded from the radially outer side. The first cylindrical portion 23 is, for example, cylindrical and concentric with the axis C and extends in the axial direction. Figure 2 and Figure 5 As shown, it has an inner cylindrical surface 23g facing radially inward (see Figure 5 ) and an outer cylindrical surface 23f facing radially outward. The diameter of the inner cylindrical surface 23g is set to be larger than the outer diameter of the stator core 7. The magnet 8 is fixed to the inner cylindrical surface 23g and is thereby fixed so as to be non-rotatable relative to the shaft 4.

[0032] like Figure 1 As shown, the top surface portion 22 is a portion that covers the magnet 8 and the stator 6 from the first axial direction C1 side. The top surface portion 22 is, for example, Figure 1 and Figure 2 As shown, the first hole portion 21 extends radially outward from the end portion on the second axial direction C2 side and connects to the end portion on the first axial direction C1 side of the first cylindrical portion 23. It should be noted that the term "extending toward..." herein is not limited to extending in a direction aligned with (parallel to) a reference direction (e.g., the radial direction) and also includes extending in a direction inclined relative to the reference direction. This also applies to the following description of "extending toward...".

[0033] The top surface portion 22 can be formed by combining a flat surface portion, a curved surface portion, a stepped surface portion, or a tapered surface portion. The top surface portion 22 shown here includes an inner flat surface portion 24, a stepped surface portion 25, an intermediate flat surface portion 26, an inclined surface portion 27, and an outer flat surface portion 28. These portions 24 to 28 are arranged in this order from the radial inside to the radial outside. The inner flat surface portion 24, the intermediate flat surface portion 26, the inclined surface portion 27, and the outer flat surface portion 28 are as follows: Figure 2 As shown, when viewed from the axial direction, each of them has an annular shape concentric with the axis C. The step portion 25 has a cylindrical shape concentric with the axis C and extends in the axial direction.

[0034] like Figure 1As shown, the inner flat portion 24 is connected to the second axial direction C2 side of the first hole portion 21 and extends radially outward. The step portion 25 is connected to the radially outward side of the inner flat portion 24 and extends radially outward in the second axial direction C2. The intermediate flat portion 26 is connected to the second axial direction C2 side of the step portion 25 and extends radially outward. The inclined portion 27 is connected to the radially outward side of the intermediate flat portion 26 and extends radially outward and in the second axial direction C2 (at an angle). The outer flat portion 28 is connected to the radially outward side of the inclined portion 27 and extends radially outward. The radially outward end of the outer flat portion 28 is connected to the end of the first cylindrical portion 23 on the first axial direction C1 side. The top portion 22 extends radially outward and in the second axial direction C2 from the first hole portion 21 as a whole through these portions 24-28. It should be noted that the term "connected" in this specification refers to the connection of two portions, not to the connection (adjacency) of two separate portions.

[0035] In this embodiment, the fan unit 3 is bonded and fixed to the rotor yoke 9. That is, the rotor yoke 9 corresponds to the "first portion" described in the technical proposal. The specific structure will be described later. Regarding the fan unit 3, the rib 36 provided on the fan unit 3 is bonded and fixed to the surface of the middle plane portion 26 of the top surface portion 22 facing the first axial direction C1 (see Figure 2 、 Figure 5 、 Figure 6 Hereinafter, this surface is referred to as the adhesive surface 22 a (flat surface).

[0036] The fan section 3 is an impeller that sends the fluid sucked in from the radial inside to the radial outside. Figure 3 As shown, the fan unit 3 includes a plurality of blades 31 standing in the axial direction. The blades 31 are arranged at equal intervals in the circumferential direction around the axis C. The fan unit 3 may be provided with a main plate 32 that supports the ends of the blades 31 on the second axial direction C2 side.

[0037] Fan unit 3 Figure 1 As shown, the fan unit 3 may include a bladed main plate 13 integrally formed with a plurality of blade portions 31 and a main plate portion 32, and a shroud 14. The fan unit 3 is configured, for example, by having the shroud 14 attached and fixed to the bladed main plate 13 on the first axial direction C1 side. The bladed main plate 13 and the shroud 14 are assembled, for example, by separately molding a resin having a larger linear expansion coefficient than that of the rotor yoke 9.

[0038] The shroud 14 is a plate fixed to the ends of the plurality of blades 31 on the first axial direction C1 side and is annular with air passage holes 14h for the suction air duct formed radially inward. The shroud 14 is fixed to the bladed main plate 13 by, for example, ultrasonic welding.

[0039] The bladed main plate 13 includes the blade portion 31 and the main plate portion 32. The main plate portion 32 of this embodiment is provided radially outward of the first cylindrical portion 23 of the rotor yoke 9. The main plate portion 32 is, for example, Figure 1 、 Figure 3 、 Figure 4 As shown, it has a flat plate shape with uniform axial dimensions (thickness, plate thickness), and is annular and concentric with the axis C when viewed from the axial direction.

[0040] The bladed main plate 13 further includes a second hole portion 33, a main surface portion 34, a second cylindrical portion 35, and a rib portion 36. These portions 33 to 36 are provided radially inward of the main plate portion 32. In this embodiment, these portions 33 to 36 correspond to the "second portion" described in the claims.

[0041] The second hole portion 33 is a hole portion for the shaft 4 to pass through. The second hole portion 33 is formed to form a through hole 33h (see Figure 3 and Figure 4 ) is formed, for example, into a cylindrical shape concentric with the axis C. The inner diameter of the second hole portion 33 is set, for example, to be equal to or slightly larger than the outer diameter of the shaft 4. It should be noted that the second hole portion 33 may or may not be fixed to the shaft 4.

[0042] The main surface portion 34 extends radially outward from the second hole portion 33. It has a plate-like shape with a dimension (thickness, plate thickness) that is approximately uniform in a direction perpendicular to the extension direction. When viewed axially, it forms an annular shape concentric with the axis C. For example, the main surface portion 34 extends radially outward (at an angle) from the second hole portion 33 toward the second axial direction C2, corresponding to the extension direction of the top surface portion 22 of the rotor yoke 9. It then connects to the radially inner side of the main plate portion 32. Thus, the main surface portion 34 covers the rotor yoke 9 from the first axial direction C1. Alternatively, the main surface portion 34 extends obliquely with respect to the axial direction, forming an arcuate shape that projects toward the first axial direction C1 when viewed radially. This main surface portion 34 facilitates the guidance of fluid drawn in from the first axial direction C1 toward the second axial direction C2 and radially outward along the extension direction of the main surface portion 34.

[0043] It should be noted that if Figure 1 and Figure 3 As shown, the ends of the plurality of blade portions 31 on the second axial direction C2 side may be connected not only to the main plate portion 32 but also to the main surface portion 34. In other words, the main surface portion 34 may share the function of the main plate portion 32 (the function of supporting the ends of the plurality of blade portions 31 on the second axial direction C2 side) with the main plate portion 32. The thickness of the main surface portion 34 is preferably the same as that of the main plate portion 32.

[0044] The second cylindrical portion 35 is a cylindrical portion extending from the radially outer end portion of the main surface portion 34 (ie, the boundary position between the main plate portion 32 and the main surface portion 34) in the second axial direction C2. Figure 4 As shown in FIG, the inner cylindrical surface 35f facing radially inward and the outer cylindrical surface facing radially outward are cylindrical in shape with the same diameter in the axial direction and are concentric with the axis C. The second cylindrical portion 35 is as shown in FIG. Figure 1 As shown in FIG. 1 , the second cylindrical portion 35 extends to a position overlapping with the first cylindrical portion 23 of the rotor yoke 9 when viewed from the radial direction, and surrounds the first cylindrical portion 23 of the rotor yoke 9 from the radial outside. The inner cylindrical surface 35f of the second cylindrical portion 35 is as shown in FIG. Figure 5 As shown, it faces the outer cylindrical surface 23f of the first cylindrical portion 23.

[0045] like Figure 1 、 Figure 3 and Figure 4 As shown, the radially inner portion of the main plate portion 32 of the bladed main plate 13 is formed into a bottomed cylindrical (cup-shaped) shape open in the second axial direction C2 by the second hole portion 33, main surface portion 34, and second cylindrical portion 35. Hereinafter, these portions 33-35 are collectively referred to as the cup portion 37.

[0046] The rib 36 is provided to protrude from the main surface portion 34 in the second axial direction C2 and is a portion that reinforces the main surface portion 34. In this embodiment, as described above, the rib 36 is bonded and fixed to the bonding surface 22a of the rotor yoke 9. Therefore, the rib 36 is arranged at a position where at least a portion thereof overlaps with at least a portion of the bonding surface 22a when viewed from the axial direction. The rib 36 is preferably as follows: Figure 1 As shown, it is provided at a position spaced radially inward from the second cylindrical portion 35 and radially outward from the second hole portion 33 .

[0047] Here, if the bladed main plate 13 (fan unit 3) having the cup portion 37 is made of a material having a larger linear expansion coefficient than the rotor yoke 9 to which it is fixed, the fan unit 3 may thermally deform significantly compared to the rotor yoke 9 when exposed to an environment with drastic temperature fluctuations. The inventors of the present invention have discovered that the thermal deformation of the cup portion 37 has characteristics such that the second cylindrical portion 35 deforms in a manner that reduces in diameter with the boundary between the main surface portion 34 and the second cylindrical portion 35 as a base point, and that the main surface portion 34 deforms in a manner that rises toward the first axial direction C1.

[0048] Furthermore, it was discovered that the latter of these deformation characteristics (i.e., upward deformation of the main surface portion 34) is caused by a shift in the center of gravity of the fan unit 3. Furthermore, the following insight was obtained: in conventional centrifugal fans in which an adhesive is provided between the rotor cylinder and the fan cylinder, even if the fan cylinder were to undergo diameter reduction deformation due to temperature changes, this deformation would be inhibited by the adhesive, and this deformation would instead result in upward deformation of the fan top surface portion and the cylinder by the amount of the inhibition of deformation (the amount of upward deformation would be greater than in a case where deformation of the cylinder was not inhibited).

[0049] Therefore, in the centrifugal fan 1 of the present invention, Figure 5 As shown, a gap S is provided between the first cylindrical portion 23 and the second cylindrical portion 35. Even if the second cylindrical portion 35 is deformed by shrinking, it will not hinder it. In addition, in order to leave space for this gap S, the bonding position is changed, and the top surface portion 22 and the rib portion 36 are bonded and fixed. As a result, the shrinking deformation of the second cylindrical portion 35 is allowed, so it will not be replaced by the floating deformation of the main surface portion 34. The situation in which the force of the shrinking deformation of the second cylindrical portion 35 is converted into the force of deforming the main surface portion 34 is suppressed. Therefore, the floating deformation of the main surface portion 34 is suppressed, and the displacement of the center of gravity of the fan portion 3 is suppressed.

[0050] The gap S is a cylindrical space (gap) with a small radial dimension formed between the outer cylindrical surface 23f of the first cylindrical portion 23 and the inner cylindrical surface 35f of the second cylindrical portion 35. The radial dimension of the gap S is set to a size such that the second cylindrical portion 35 does not contact the first cylindrical portion 23 even when the second cylindrical portion 35 is deformed by reducing its diameter. The diameter of the inner cylindrical surface 35f of the second cylindrical portion 35 is set to a size that can form such a gap S between it and the outer cylindrical surface 23f of the first cylindrical portion 23.

[0051] In this embodiment, the portion forming the boundary position between the plate-shaped main surface portion 34 and the second cylindrical portion 35 having the same diameter in the axial direction is as shown in FIG. Figure 5 As shown, the wall thickness of the fan section 35a can be relatively thick compared to the rest of the main bladed plate 13. It should be noted that the term "thick wall" here refers to the convergence of the various components that make up the fan section 3, resulting in the convergence of the wall (resin) of the fan section 3. This portion will be referred to as the "thick wall portion 35a" below.

[0052] In this embodiment, as described above, the ends of the plurality of blade portions 31 on the second axial direction C2 side are connected to the main surface portion 34, and the radially inner end of the main plate portion 32 is connected to the radially outer end of the main surface portion 34. Figure 3 As shown, the thickness of the thick portion 35 a can be further increased at the location where the root portion of the blade portion 31 in the second axial direction C2 and the root portion of the main plate portion 32 on the radially inner side converge.

[0053] By forming such a thick portion 35a, the aforementioned thermal deformation characteristics of the cup portion 37 in the fan unit 3 are more readily manifested. However, the clearance S allows the second cylindrical portion 35 to deform in diameter starting from the thick portion 35a, thereby suppressing deformation of the main surface portion 34. It should be noted that in this embodiment, the aforementioned rib 36 can also be alternatively stated as being provided at a position separated from the second cylindrical portion 35, that is, at a position separated from the thick portion 35a.

[0054] Furthermore, the centrifugal fan 1 of the present invention is provided with a structure for improving the bonding strength of the fan portion 3 with respect to the rotor yoke 9. Specifically, Figure 4 and Figure 5 As shown, an annular rib 38 and a plurality of auxiliary ribs 39 are provided as the rib 36, which are protruded from the main surface portion 34 toward the second axial direction C2. In the centrifugal fan 1, the adhesive applied to the annular end surface 38a on the second axial direction C2 side of the annular rib 38 expands when it becomes the installed state, so that the adhesive is not only spread between the annular end surface 38a and the bonding surface 22a, but also between the end surface 39a on the second axial direction C2 side of the plurality of auxiliary ribs 39 and the bonding surface 22a. In other words, the adhesive applied to the annular end surface 38a of the annular rib 38 expands when it becomes the installed state, thereby also showing that the adhesive is in close contact with the annular rib 38 and the plurality of auxiliary ribs 39. The centrifugal fan 1 utilizes the bonding portion 40 (refer to Figure 5 ) The rib 36 is fixed to the bonding surface 22 a to ensure the bonding strength of the fan unit 3 relative to the rotor yoke 9.

[0055] The annular rib 38 is a portion that protrudes from the main surface portion 34 toward the second axial direction C2 and has an annular end surface 38a facing the second axial direction C2. The annular end surface 38a is an annular plane that surrounds the axis C when viewed from the second axial direction C2 and faces the bonding surface 22a. Figure 4 As shown, it may be cylindrical having an annular end surface 38a that is concentric with the axis C, an inner peripheral surface 38b that faces radially inward, and an outer peripheral surface 38c that faces radially outward.

[0056] The plurality of auxiliary ribs 39 are portions that protrude from the main surface portion 34 in the same direction as the annular rib 38 (i.e., the second axial direction C2) and extend radially from the annular rib 38 in the radial direction. In this embodiment, the plurality of auxiliary ribs 39 are arranged on the radially outer side of the annular rib 38 and extend radially from the annular rib 38 to the radially outer side. The plurality of auxiliary ribs 39 are all of the same shape and can be separated from each other in the circumferential direction and arranged at equal intervals. Here, the twelve auxiliary ribs 39 of the same shape are separated from each other in the radially outer side of the annular rib 38 and arranged at equal intervals. It should be noted that in Figure 4In FIG. 1 , only one auxiliary rib 39 among the twelve auxiliary ribs 39 is denoted by a reference numeral.

[0057] Each auxiliary rib 39 has an end face 39a facing the second axial direction C2. Each end face 39a is opposite to the bonding surface 22a. Each auxiliary rib 39 is, for example, in the shape of a roughly triangular prism having a rectangular end face 39a and a pair of triangular side faces 39d facing opposite directions in the circumferential direction. Hereinafter, the end face 39a is also referred to as the rectangular end face 39a. Each auxiliary rib 39 is as follows Figure 4 and Figure 5 As shown, it extends in the axial direction to the same position as the annular rib 38. The annular end surface 38a of the annular rib 38 and the rectangular end surface 39a of each auxiliary rib 39 thus form a mutually continuous plane (a plane orthogonal to the axial direction).

[0058] It should be noted that the circumferential width of the auxiliary rib 39 is preferably set to be equal to the radial width of the annular rib 38. The radial width of the annular rib 38 and the circumferential width of the auxiliary rib 39 are further preferably set to ensure a bonding area sufficient to achieve a bonding strength that meets the specifications of the centrifugal fan 1. They are preferably set slightly larger than the thickness of the main surface portion 34 and the main plate portion 32. This prevents deformation of the bladed main plate 13 caused by differences in curing time due to differences in resin volume during molding.

[0059] Some of the auxiliary ribs 39 among the plurality of auxiliary ribs 39 may be as follows Figure 3 and Figure 4 As shown in FIG. 3 , a convex portion 50 is provided that protrudes from the rectangular end surface 39a toward the second axial direction C2. The convex portion 50 is provided to form a space (gap) between the annular end surface 38a and the adhesive surface 22a, and between the rectangular end surface 39a and the adhesive surface 22a. Figure 6 As shown, in the mounted state, the protrusions 50 abut (rest against) the bonding surface 22a. The number of protrusions 50 is preferably three or more. In this case, the three or more protrusions 50 are preferably spaced apart from each other in the circumferential direction and arranged at equal intervals, and are preferably set so that the protrusion amounts relative to the rectangular end surface 39a are the same.

[0060] Here, if Figure 4 As shown, every third of the twelve auxiliary ribs 39 is provided with a protrusion 50. These protrusions 50 abut against the bonding surface 22a of the rotor yoke 9, aligning the annular end surface 38a and the rectangular end surface 39a parallel to the bonding surface 22a. Consequently, the axial width of the gaps (spaces) formed between the annular end surface 38a and the bonding surface 22a, and between the rectangular end surface 39a and the bonding surface 22a, is uniform, improving the bonding balance of the fan unit 3 to the rotor 5.

[0061] It should be noted that the amount of projection of the convex portion 50 relative to the rectangular end surface 39a is preferably set to be equivalent to the optimal film thickness of the adhesive. The optimal film thickness herein refers to the film thickness at which the adhesive exhibits a bond strength sufficient to withstand the loads expected during use as the centrifugal fan 1. For example, the relationship between film thickness and bond strength can be verified through experimental simulations, etc., for adhesives that meet the specifications of the centrifugal fan 1, and the optimal film thickness can be determined based on the verification results.

[0062] As described above, the adhesive applied to the annular end surface 38a before installation expands and solidifies during installation to form the adhesive portion 40. The adhesive portion 40 is provided at least between the annular end surface 38a and the adhesive surface 22a, and between the rectangular end surface 39a and the adhesive surface 22a.

[0063] In this embodiment, the bonding portion 40 is as follows Figure 5 and Figure 6 As shown, adhesive portions 40 are provided not only between the annular end surface 38a and the bonding surface 22a, and between the rectangular end surface 39a and the bonding surface 22a, but also on the radially inner side of the annular rib 38, the radially outer side of the annular rib 38, and on both circumferential sides of the auxiliary rib 39. Specifically, the applied adhesive extends from the bonding surface 22a across the inner circumferential surface 38b of the annular rib 38, the outer circumferential surface 38c of the annular rib 38, and the pair of side surfaces 39d of the auxiliary rib 39, providing adhesive portions 40 at these locations as well. This ensures that not only the annular end surface 38a and the rectangular end surface 39a are bonded and fixed to the bonding surface 22a, but also the inner circumferential surface 38b, outer circumferential surface 38c, and side surfaces 39d are bonded and fixed to the bonding surface 22a. This further enhances the bonding strength of the fan unit 3 to the rotor 5. In particular, the bonding strength along the circumferential direction (i.e., the direction of rotation of the fan unit 3) is further enhanced.

[0064] It should be noted that, in order to form such an adhesive portion 40, it is preferable to apply an amount of adhesive to the annular end surface 38a before mounting that is greater than the volume of the gap formed between the bonding surface 22a and the annular end surface 38a in the mounted state. It is further preferable to apply an amount of adhesive to the annular end surface 38a before mounting that is greater than the volume of the gap formed between the bonding surface 22a and the annular end surface 38a, and between the bonding surface 22a and the rectangular end surface 39a in the mounted state (hereinafter referred to as "excessive amount").

[0065] [2. Fixing method]

[0066] Hereinafter, a method (fixing step) of fixing the fan unit 3 (bladed main plate 13 ) of the centrifugal fan 1 to the rotor 5 (rotor yoke 9 ) will be described. This fixing method includes three steps: a first step, a second step, and a third step.

[0067] First, in the first step, adhesive is applied to the annular end surface 38a of the bladed main plate 13 before installation. Specifically, the first step involves applying adhesive to the annular end surface 38a. In the first step, an excessive amount of adhesive is uniformly applied to the entire annular end surface 38a, for example.

[0068] Next, in the second step, the bladed main plate 13, in its pre-mounted state, is positioned concentrically with the rotor yoke 9 and positioned closer to the rotor yoke 9 in the first axial direction C1. Specifically, the main surface portion 34 is positioned concentrically with the top surface portion 22 and closer to the top surface portion 22 in the first axial direction C1. This positions the annular end surface 38a and the rectangular end surface 39a opposite the bonding surface 22a. In other words, the second step positions the main surface portion 34 of the bladed main plate 13 closer to the top surface portion 22 in the first axial direction C1 than the rotor yoke 9, with the annular end surface 38a and the rectangular end surface 39a facing the bonding surface 22a.

[0069] In the second step, the end portion of the shaft 4 on the first axial direction C1 side is inserted into the second hole 33 of the bladed main plate 13 , for example, with the rotor yoke 9 press-fitted.

[0070] In the subsequent third step, the bladed main plate 13 is placed on the first axial direction C1 side of the rotor yoke 9. The bladed main plate 13 is pressed toward the second axial direction C2 side until the protrusion 50 abuts the adhesive surface 22a, thereby being placed on the first axial direction C1 side of the rotor yoke 9. The centrifugal fan 1 is thus assembled.

[0071] The bladed main plate 13 is placed on the rotor yoke 9, so that the second cylindrical portion 35 is arranged at a position surrounding the first cylindrical portion 23 from the radial outside. Figure 5 As shown, the inner cylindrical surface 35f of the second cylindrical portion 35 and the outer cylindrical surface 23f of the first cylindrical portion 23 are positioned opposite each other with a gap S therebetween. Furthermore, the adhesive applied to the annular end surface 38a by placing the bladed main plate 13 on the rotor yoke 9 is not contained in the gap between the annular end surface 38a and the bonding surface 22a, but rather spreads (expands) not only between the annular end surface 38a and the bonding surface 22a, but also between the rectangular end surface 39a and the bonding surface 22a. In other words, the third step can be said to be a step of placing the inner cylindrical surface 35f of the second cylindrical portion 35 and the outer cylindrical surface 23f of the first cylindrical portion 23 opposite each other with a gap S therebetween, and spreading the adhesive between the annular end surface 38a and the bonding surface 22a, and between the rectangular end surface 39a and the bonding surface 22a.

[0072] When an excessive amount of adhesive is applied to the annular end surface 38a, the adhesive also spreads (expands) radially inwardly of the annular rib 38, radially outwardly of the annular rib 38, and circumferentially on both sides of the auxiliary rib 39. Figure 5 and Figure 6 As shown, the adhesive spread on each surface also contacts the inner peripheral surface 38b, the outer peripheral surface 38c, and the side surface 39d. The adhesive spread on each surface solidifies over time, and thus all become the above-mentioned bonding portion 40. In addition, the centrifugal fan 1 is fixed by the curing of the adhesive.

[0073] It should be noted that the shroud 14 can be secured to the bladed main plate 13 before or after the first, second, and third steps. The stator 6 can be secured to the bearing holder 12 and the shaft 4 can be installed before or after the first, second, and third steps. The shaft 4 can also be inserted into the first and second holes 21 and 33 after the first, second, and third steps.

[0074] [3. Action, effect]

[0075] (1) In the centrifugal fan 1 described above, a gap S is formed between the outer cylindrical surface 23f of the first cylindrical portion 23 and the inner cylindrical surface 35f of the second cylindrical portion 35. Thus, even when the centrifugal fan 1 is used in an environment subject to significant temperature fluctuations, the diameter reduction deformation of the second cylindrical portion 35 caused by the temperature fluctuations is permitted. This prevents the main surface portion 34 from floating upward due to the obstruction of the diameter reduction deformation of the second cylindrical portion 35. Consequently, the center of gravity of the fan unit 3 can be prevented from shifting.

[0076] Furthermore, in the centrifugal fan 1 described above, an annular rib 38 and a plurality of auxiliary ribs 39 are provided as ribs 36 for adhesively securing to the rotor yoke 9, in place of the second cylindrical portion 35. Furthermore, in the centrifugal fan 1 described above, an adhesive bonding portion 40 is interposed not only between the annular end surface 38a and the bonding surface 22a, but also between each of the rectangular end surfaces 39a of the plurality of auxiliary ribs 39 and the bonding surface 22a. This allows the fan unit 3 to be secured to the rotor yoke 9 with a higher bonding strength than would be achieved by simply bonding the annular end surface 38a to the bonding surface 22a. Furthermore, providing a plurality of auxiliary ribs 39 radially extending from the annular rib 38 ensures a greater bonding area, compared to simply increasing the radial width of the annular end surface 38a to expand the bonding area. This also contributes to reduced material costs and weight reduction. Furthermore, when the fan unit 3 is made of resin, deformation caused by differences in curing time due to differences in the amount of resin can be suppressed. Therefore, according to the centrifugal fan 1 described above, it is possible to effectively suppress the displacement of the center of gravity caused by thermal deformation while ensuring the bonding strength of the fan unit 3 to the rotor 5. Furthermore, the auxiliary ribs 39 are radially extended radially outward from the annular rib 38, thereby improving the fluidity of the resin during molding, and improving the finishing accuracy of the fan unit 3, such as flatness and parallelism.

[0077] (2) If the bonding portion 40 is provided not only between the bonding surface 22a and the annular end surface 38a and between the bonding surface 22a and the rectangular end surface 39a, but also across the inner circumferential surface 38b and outer circumferential surface 38c of the annular rib 38, and the side surface 39d of the auxiliary rib 39, the bonding strength of the fan unit 3 to the rotor 5 can be further improved. In particular, the bonding strength in the circumferential direction (i.e., the rotational direction of the fan unit 3) can be further improved.

[0078] (3) When the main surface portion 34 extends radially outward from the second hole portion 33 and toward the second axial direction C2, fluid drawn in from the first axial direction C1 can be smoothly pushed outward in the second axial direction C2 and radially outward along the main surface portion 34. Consequently, the air supply efficiency of the fan unit 3 can be improved. Furthermore, the formation of vortices in the radially inner side of the fan unit 3 can be suppressed, thereby also achieving noise reduction of the fan unit 3.

[0079] (4) When the main surface portion 34 extends radially outward from the second hole portion 33 and toward the second axial direction C2, if the auxiliary rib 39 is provided radially outward of the annular rib 38 rather than radially inward of the annular rib 38, the amount of protrusion of the auxiliary rib 39 relative to the main surface portion 34 can be suppressed. In addition, when the main plate 13 with blades is made of resin, by suppressing the amount of protrusion of the auxiliary rib 39, deformation of the shape caused by the difference in curing time due to the difference in the amount of resin during molding can be suppressed.

[0080] (5) If the rib 36, which is composed of the annular rib 38 and the plurality of auxiliary ribs 39, is provided at a position radially separated from the second cylindrical portion 35, it is possible to prevent the rib 36, which is fixed to the bonding surface 22a, from hindering the diameter-reducing deformation of the second cylindrical portion 35. This prevents the force of the diameter-reducing deformation of the second cylindrical portion 35 from being replaced by the upward deformation of the main surface portion 34, thereby effectively preventing the center of gravity of the fan portion 3 from shifting.

[0081] (6) If the rib 36 is radially spaced from the second hole 33, the amount of protrusion of the rib 36 relative to the main surface portion 34, which extends radially outward and in the second axial direction C2, can be reduced. Consequently, the formability of the bladed main plate 13, which includes the second hole 33, the main surface portion 34, the second cylindrical portion 35, and the rib 36, can be improved. Furthermore, when the annular rib 38 is spaced from the second hole 33, the area of ​​the annular end surface 38a of the annular rib 38 is increased. This increases the bonding area and improves the bonding strength.

[0082] (7) When the bladed main plate 13 is made of resin, the bladed main plate 13 having the second hole portion 33, the main surface portion 34, the second cylindrical portion 35, and the rib portion 36 can be easily molded using a resin having a higher moldability than metal. Furthermore, since the rotor yoke 9 is made of metal, which is less susceptible to thermal deformation than resin, thermal deformation of the rotor yoke 9 due to temperature changes can be suppressed. Consequently, displacement of the center of gravity of the fan unit 3 can be more effectively suppressed.

[0083] (8) In the above-described fixing method, the bladed main plate 13 is fixed to the rotor yoke 9 simply by applying adhesive only to the annular end surface 38a (first step), positioning the bladed main plate 13 opposite the rotor yoke 9 (second step), and placing the bladed main plate 13 on the rotor yoke 9 (third step). Therefore, a centrifugal fan 1 can be constructed by a simple method in which the center of gravity of the fan unit 3 is less likely to shift and the bonding strength is maintained.

[0084] [4. Others]

[0085] The structure of the centrifugal fan 1 described above is an example and is not limited to the above structure. The fixing method described above is also an example and is not limited to the above method. In the first step, adhesive may be applied to the rotor yoke 9. More specifically, in the first step, adhesive may be applied to the portion of the bonding surface 22a of the rotor yoke 9 that faces the annular end surface 38a when the main surface portion 34 is positioned closer to the first axial direction C1 than the top surface portion 22.

[0086] The top surface portion 22 of the rotor yoke 9 does not need to extend radially outward and toward the second axial direction C2. For example, it may simply extend radially outward (perpendicular to the axial direction) from the first hole portion 21. The top surface portion 22 does not need to include multiple portions 24-28 extending in different directions.

[0087] The first cylindrical portion 23 only needs to extend from at least the radially outer end of the top surface portion 22 in the second axial direction C2 and need not be a portion that fixes the magnet 8 or a portion that radially surrounds the stator core 7. That is, in the centrifugal fan 1 described above, the rotor yoke 9 is provided as the "first portion" described in the technical solution, but the "first portion" described in the technical solution does not need to be the rotor yoke 9.

[0088] The rotor 5 may also be provided with a portion (component) corresponding to the "first portion" described in the claims, separate from the rotor yoke 9. This portion need not be cup-shaped like the rotor yoke 9. Furthermore, the "first portion" described in the claims need only be made of a material with a lower linear expansion coefficient than the "second portion" described in the claims, and need not be made of metal. It should be noted that the motor unit 2 may also be an inner rotor type motor.

[0089] The annular end surface 38a may be annular, extending at least around the axis C, and may, for example, have a polygonal shape when viewed axially. The plurality of auxiliary ribs 39 do not all have the same shape and may extend radially inward from the annular rib 38. The number of auxiliary ribs 39 is not limited to twelve; two or more (or more) may suffice. The end surface 39a of the auxiliary rib 39 does not need to be rectangular. The protrusion 50 provided on the auxiliary rib 39 may also be omitted.

[0090] The main surface portion 34 of the fan portion 3 may not be a surface portion extending from the second hole portion 33 toward the radially outer side and the second axial direction C2. For example, it may be a surface portion extending simply from the second hole portion 33 toward the radially outer side (perpendicular to the axial direction). The second cylindrical portion 35 may be a cylindrical shape that extends from at least the radially outer end portion of the main surface portion 34 toward the second axial direction C2 and has an inner cylindrical surface 35f that is opposed to the outer cylindrical surface 23f of the first cylindrical portion 23 with a gap S between them. It may not be a cylindrical shape. For example, the second cylindrical portion 35 may be a cylindrical shape having a polygonal shape when viewed from the axial direction. Similarly, the first cylindrical portion 23 may be a cylindrical shape having a polygonal shape when viewed from the axial direction.

[0091] The second hole portion 33, main surface portion 34, second cylindrical portion 35, and rib portion 36 may be provided at least in the fan unit 3 having the plurality of blades 31. Alternatively, they may be separate components from the main plate 13 with blades. In other words, the "second portion" described in the technical proposal need not be part of the main plate 13 with blades. Furthermore, the shroud 14 of the fan unit 3 may be omitted, and the blades 31 and main plate 32 may not be integrally formed as part of the main plate 13 with blades.

[0092] The "second portion" described in the claims need only be composed of a material having a larger linear expansion coefficient than the "first portion" described in the claims and need not be made of resin. The "first portion" and "second portion" described in the claims may both be made of resin or metal as long as the relationship between the linear expansion coefficients is satisfied.

[0093] [Description of Reference Numerals]

[0094] 1 centrifugal fan

[0095] 2 Motor

[0096] 3 Fan unit

[0097] 4-axis

[0098] 5 rotor

[0099] 21 First hole

[0100] 22 Top face

[0101] 22a Bonding surface (flat surface)

[0102] 23 First tube

[0103] 23f outer cylinder surface

[0104] 31 blade

[0105] 33 Second hole

[0106] 34 Main face

[0107] 35 Second tube

[0108] 35f inner cylinder surface

[0109] 38 Annular ribs

[0110] 38a Annular end face

[0111] 38b inner circumference

[0112] 38c outer surface

[0113] 39 Auxiliary ribs

[0114] 39a Rectangular end face (end face)

[0115] 39d side view

[0116] 40 bonding part

[0117] C1 First Axis

[0118] C2 Second Axis

[0119] S gap.

Claims

1. A centrifugal fan, characterized in that: The centrifugal fan has: A first portion is provided on a rotor that rotates integrally with the shaft; and The second portion is provided in a fan portion having a plurality of blades and fixed to the rotor, and has a larger linear expansion coefficient than the first portion. The first part has: a top surface portion extending from a first hole portion through which the shaft passes toward a radially outer side of the shaft and having a flat surface facing a first axial direction of the shaft; and a cylindrical first cylindrical portion extending from the radially outer end portion of the top surface portion in a second axial direction opposite to the first axial direction, The second part has: a main surface portion located closer to the first axial direction than the top surface portion and extending from the second hole portion through which the shaft passes toward the radially outer side; an annular rib portion protruding from the main surface portion toward the second axial direction and having an annular end surface facing the plane; a plurality of auxiliary ribs projecting from the main surface portion toward the second axial direction and extending radially from the annular rib portion in the radial direction, and having end surfaces facing the plane; and a cylindrical second cylindrical portion extending from the radially outer end of the main surface portion toward the second axial direction and having an inner cylindrical surface opposed to the outer cylindrical surface of the first cylindrical portion with a gap therebetween; Adhesive portions formed of an adhesive are provided between the annular end surface of the annular rib and the flat surface, and between the end surfaces of each of the plurality of auxiliary ribs and the flat surface.

2. The centrifugal fan according to claim 1, wherein: The bonding portion is provided across the inner peripheral surface of the annular rib, the outer peripheral surface of the annular rib, and the side surfaces of the auxiliary ribs facing the circumferential direction of the shaft.

3. The centrifugal fan according to claim 1, wherein: The main surface portion extends from the second hole portion toward the radially outer side and the second axial direction side.

4. The centrifugal fan according to claim 3, wherein: The plurality of auxiliary ribs extend radially from the annular rib toward the radially outer side.

5. The centrifugal fan according to claim 3 or 4, characterized in that: The annular rib and the plurality of auxiliary ribs are provided at positions spaced apart from the second cylindrical portion in the radial direction.

6. The centrifugal fan according to claim 5, characterized in that: The annular rib and the plurality of auxiliary ribs are provided at positions spaced apart from the second hole portion in the radial direction.

7. The centrifugal fan according to claim 1, wherein: The first part is a metal product, The second part is a resin product.

8. A fixing method comprising fixing a second part to a first part, wherein the first part is provided in a rotor of a motor unit having a rotor that rotates integrally with a shaft and a stator disposed opposite the rotor, and the second part is provided in a fan unit having a plurality of blades and having a larger linear expansion coefficient than the first part, characterized in that: The first portion is provided with a top portion and a first cylindrical portion. The top portion extends radially outward from the first hole portion for the shaft to pass through and has a flat surface facing a first axial direction. The first cylindrical portion extends from a radially outer end portion of the top portion toward a second axial direction opposite to the first axial direction. The second portion is provided with a main surface portion, an annular rib portion, a plurality of auxiliary rib portions, and a second cylindrical portion, the main surface portion extending radially outward from the second hole portion for the shaft to pass through, the annular rib portion protruding from the main surface portion and having an annular annular end face, the plurality of auxiliary rib portions protruding from the main surface portion in the same direction as the annular rib portion and extending radially from the annular rib portion in the radial direction and having end faces facing the same direction as the annular end face, and the second cylindrical portion extending from the radially outer end portion of the main surface portion in the same direction as the annular rib portion, The fixing method comprises: A first step is to apply an adhesive to the annular end surface, or to a portion of the plane that faces the annular end surface when the main surface portion of the second portion is positioned closer to the first axial side than the top surface portion of the first portion. a second step of arranging the main surface portion of the second portion closer to the first axial side than the top surface portion of the first portion, and placing the annular end surface and the end surface opposite to the plane; as well as In the third step, the inner cylindrical surface of the second cylindrical portion and the outer cylindrical surface of the first cylindrical portion are opposed to each other with a gap therebetween, and the adhesive is spread between the annular end surface and the flat surface, and between the end surface and the flat surface.

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