阅读说明：本技术 油浴式轴承装置以及旋转机械 (Oil bath type bearing device and rotary machine ) 是由 横山真平 吉峰千寻 鴫原拓造 于 2020-01-22 设计创作，主要内容包括：一种油浴式轴承装置以及旋转机械,该油浴式轴承装置对绕轴线旋转的旋转轴(1)进行支承,所述油浴式轴承装置具备：多个轴瓦(51),它们沿着旋转轴(1)的外周面(1S)在周向上隔开间隔地排列；圆环状的承载圈(52),其从外周侧支承多个轴瓦(51),并且形成有供给润滑油的供油孔(52B)；以及外壳,其从外周侧覆盖承载圈(52),并且将润滑油保持于该外壳与旋转轴(1)之间,供油孔(52B)将承载圈(52)从外周侧贯通至内周侧,并且随着朝向针对轴线而言的径向内侧而朝向旋转轴(1)的旋转方向后方侧延伸。(An oil bath bearing device that supports a rotating shaft (1) that rotates around an axis, the oil bath bearing device comprising: a plurality of bearing bushes (51) arranged at intervals in the circumferential direction along the outer circumferential surface (1S) of the rotating shaft (1); an annular carrier ring (52) which supports the plurality of bearing shoes (51) from the outer peripheral side and in which an oil supply hole (52B) for supplying lubricating oil is formed; and a housing that covers the carrier ring (52) from the outer peripheral side and holds lubricating oil between the housing and the rotating shaft (1), wherein the oil supply hole (52B) penetrates the carrier ring (52) from the outer peripheral side to the inner peripheral side and extends toward the rear side in the rotation direction of the rotating shaft (1) as facing radially inward with respect to the axis.)

1. An oil bath bearing device for supporting a rotary shaft which rotates around an axis, wherein,

the oil bath bearing device is provided with:

a plurality of bearing bushes arranged at intervals in a circumferential direction along an outer circumferential surface of the rotary shaft;

an annular carrier ring that supports the plurality of bearing pads from the outer peripheral side and has an oil supply hole for supplying lubricating oil; and

a housing that covers the bearing ring from an outer peripheral side and holds lubricating oil between the housing and the rotating shaft,

the oil supply hole penetrates the carrier ring from the outer peripheral side to the inner peripheral side, and extends toward the rear side in the rotation direction of the rotary shaft as facing radially inward with respect to the axis.

2. The oil bath bearing device according to claim 1,

the oil bath bearing device further includes a constricted portion provided at an outlet-side end portion of the oil supply hole and having a smaller flow path cross-sectional area than other portions of the oil supply hole.

3. The oil bath bearing device according to claim 1,

an end surface of the bearing bush on the rotation direction front side extends toward the rotation direction rear side as facing radially inward.

4. The oil bath bearing device according to claim 1,

an end surface of the bearing bush on the rear side in the rotation direction extends toward the rear side in the rotation direction as facing radially inward.

5. The oil bath bearing device according to claim 1,

the oil supply hole is formed in plurality at intervals in the axial direction.

6. The oil bath bearing device according to claim 5,

among the plurality of oil supply holes, the hole diameter is larger as the oil supply hole is located at the center portion in the axial direction.

7. The oil bath bearing device according to any one of claims 1 to 6,

end surfaces of a pair of the adjacent bearing bushes which are opposed to each other in the circumferential direction are curved surfaces which are recessed in a direction away from each other.

8. A rotary machine, wherein,

the rotating machine is provided with:

a rotating shaft; and

the oil bath bearing device according to any one of claims 1 to 7, wherein the rotary shaft is rotatably supported.

Technical Field

The present invention relates to an oil bath bearing device and a rotary machine. The present application claims priority and incorporates the content therein against application No. 2019-028412, filed on 20/2/2019.

Background

In a rotary machine including a rotating shaft that rotates at a high speed, such as a compressor or a turbine, various bearing devices are provided to support a load while smoothly rotating the rotating shaft. As one of such bearing devices, a tilting pad bearing is cited. The tilting pad bearing comprises: a plurality of bearing pads provided along an outer circumferential surface of the rotary shaft; and a carrier ring covering the bearing pads from the outer peripheral side. The bearing is supported by a pointed pivot shaft on an inner peripheral surface of the carrier ring so as to be swingable (see, for example, patent document 1 below). In the bearing device of patent document 1, a nozzle for supplying lubricating oil is provided between the circumferentially adjacent bearing pads. This forms a film of lubricating oil between the bearing bush and the rotating shaft, and enables smooth rotation of the rotating shaft.

On the other hand, as another bearing device different from the tilting pad bearing, a bearing device called an oil bath type bearing device is also widely used. In this bearing device, a space between the housing and the rotating shaft is filled with lubricating oil. That is, the bearing pads are always immersed in the lubricating oil. The lubricating oil is supplied from an oil supply hole formed in the carrier ring into the housing through a space between the bearing pads. Then, the lubricating oil is mixed with the flowing lubricating oil (main flow) with the rotation of the rotating shaft. By mixing new lubricating oil, the temperature of the lubricating oil that has become high while flowing between the bearing and the rotating shaft can be reduced.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-109268

In the oil bath bearing device, the main flow of the lubricating oil that flows as the rotating shaft rotates is faster than the flow of the new lubricating oil supplied from the oil supply hole. Therefore, the newly supplied lubricating oil may be splashed by the main flow and the two may not be sufficiently mixed. As a result, the lubricating oil becomes high in temperature, and the load capacity of the bearing device may be affected.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object thereof is to provide an oil bath type bearing device and a rotary machine, in which the load capacity is improved by supplying lubricating oil more stably.

Means for solving the problems

According to a first aspect of the present invention, an oil bath bearing device for supporting a rotating shaft that rotates around an axis line, the oil bath bearing device comprising: a plurality of bearing bushes arranged at intervals in a circumferential direction along an outer circumferential surface of the rotary shaft; an annular carrier ring that supports the plurality of bearing pads from the outer peripheral side and has an oil supply hole for supplying lubricating oil; and a housing that covers the carrier ring from an outer peripheral side and holds lubricating oil between the housing and the rotating shaft, wherein the oil supply hole penetrates the carrier ring from the outer peripheral side to an inner peripheral side and extends toward a rear side in a rotation direction of the rotating shaft as facing radially inward with respect to the axis.

According to the above configuration, the oil supply hole extends toward the rear side in the rotation direction of the rotary shaft as it goes toward the radially inner side. Therefore, the new lubricating oil supplied through the oil supply hole flows in the direction opposite to the flow direction of the lubricating oil flowing along the outer peripheral surface of the rotating shaft (i.e., forward in the rotation direction). Thus, when new lubricating oil collides with existing lubricating oil, a vortex is formed in the space between the pads about the axial direction. By forming the swirl flow, the new lubricating oil and the existing lubricating oil can be sufficiently mixed.

According to a second aspect of the present invention, in the oil bath bearing device according to the first aspect, the oil bath bearing device may further include a constricted portion that is provided at an outlet-side end portion of the oil supply hole and has a smaller flow path cross-sectional area than other portions of the oil supply hole.

According to the above configuration, since the narrowed portion is provided at the outlet-side end portion of the oil supply hole, the flow velocity of the lubricating oil passing through the narrowed portion can be further increased. This makes it possible to more efficiently mix the newly supplied lubricating oil passing through the oil supply hole with the existing lubricating oil flowing along the outer peripheral surface of the rotating shaft.

According to a third aspect of the present invention, in the oil bath bearing device according to the first or second aspect, an end surface of the pad on the forward side in the rotation direction may extend toward the rearward side in the rotation direction as it goes toward the radially inner side.

According to the above configuration, the end surface of the pad on the front side in the rotation direction extends toward the rear side in the rotation direction as it goes toward the radially inner side. As a result, the new lubricating oil supplied through the oil supply hole more acutely collides with the fluid of the lubricating oil flowing along the outer peripheral surface of the rotating shaft, along the end surface toward the outer peripheral surface of the rotating shaft. This promotes the formation of a vortex, and enables more efficient mixing of new lubricating oil with existing lubricating oil.

According to a fourth aspect of the present invention, in the oil bath type bearing device according to any one of the first to third aspects, an end surface of the pad on the rear side in the rotation direction may extend toward the rear side in the rotation direction as it goes toward a radially inner side.

According to the above configuration, the end surface of the pad on the rear side in the rotational direction extends toward the rear side in the rotational direction as it goes toward the radially inner side. As a result, the new lubricating oil supplied through the oil supply hole more acutely collides with the fluid of the lubricating oil flowing along the outer peripheral surface of the rotating shaft, along the end surface toward the outer peripheral surface of the rotating shaft. This promotes the formation of a vortex, and enables more efficient mixing of new lubricating oil with existing lubricating oil.

According to a fifth aspect of the present invention, in the oil bath bearing device according to any one of the first to fourth aspects, a plurality of the oil supply holes may be formed at intervals in the axial direction.

According to the above configuration, since the plurality of oil supply holes are formed at intervals in the axial direction, the lubricating oil can be stably supplied over the entire axial region.

According to a sixth aspect of the present invention, in the oil bath bearing device according to the fifth aspect, among the plurality of oil supply holes, the diameter of the hole may be increased as the oil supply hole is located at the center in the axial direction.

Here, the closer to the center of the bearing pad in the axial direction, the higher the pressure generated by the load of the rotating shaft, and therefore the higher the flow velocity of the lubricating oil. According to the above configuration, the diameter of the hole is larger in the center portion of the plurality of oil supply holes in the axial direction. Therefore, more lubricant can be supplied from the oil supply hole in the center portion. As a result, the rotating shaft can be supported more stably.

According to a seventh aspect of the present invention, in the oil bath type bearing device according to any one of the first to sixth aspects, end surfaces of a pair of the bushes that are adjacent to each other in the circumferential direction that face each other may be curved surfaces that are recessed in a direction away from each other.

According to the above configuration, the end surfaces of the adjacent bushes are curved surfaces that are recessed in the direction away from each other. This allows the lubricating oil to flow along the curved surface, thereby more smoothly forming a vortex. As a result, the new lubricating oil supplied through the oil supply hole and the lubricating oil flowing along the outer peripheral surface of the rotating shaft can be mixed more efficiently.

According to an eighth aspect of the present invention, a rotary machine includes: the rotating shaft; and an oil bath bearing device according to any one of the first to seventh aspects, wherein the rotary shaft is rotatably supported.

According to the above configuration, a rotary machine that can be operated more stably can be provided.

Effects of the invention

According to the present invention, it is possible to provide an oil bath bearing device and a rotary machine in which the load capacity is improved by supplying a lubricating oil more stably.

Drawings

Fig. 1 is a sectional view showing a configuration of a rotary machine according to a first embodiment of the present invention.

Fig. 2 is a sectional view showing the structure of a bearing device according to a first embodiment of the present invention.

Fig. 3 is an enlarged sectional view of a main part of a bearing device according to a first embodiment of the present invention.

Fig. 4 is a diagram showing a structure of an oil supply hole of a bearing device according to a second embodiment of the present invention.

Fig. 5 is an enlarged sectional view of a main part of a bearing device according to a third embodiment of the present invention.

Fig. 6 is an enlarged cross-sectional view of a main part of a bearing device according to a fourth embodiment of the present invention.

Fig. 7 is an enlarged cross-sectional view of a main part of a bearing device according to a fifth embodiment of the present invention.

Fig. 8 is a main part enlarged sectional view showing a modification of the bearing device according to the fifth embodiment of the present invention.

Description of reference numerals:

a rotating shaft;

1s.. the outer peripheral surface;

a flow path;

a housing;

an impeller;

journal bearings (oil bath bearing arrangement);

a bearing shell;

51C, 251℃. bearing shell end faces;

a front side end face;

a rear side end face;

a load ring;

52a.

An oil supply hole;

53.. a bearing housing;

a first oil supply hole;

a second oil supply hole;

a lubricant supply;

a can;

supply piping;

a pump;

a thrust bearing;

air suction port;

an exhaust port;

a disc;

a leaf;

a cover;

a rotating blade;

100.. a centrifugal compressor;

an axis;

s. narrowing;

t1.. outlet side end;

t2.. inlet side end;

v. space;

eddy currents.

Detailed Description

[ first embodiment ]

A first embodiment of the present invention will be described with reference to fig. 1 to 3. As shown in fig. 1, a centrifugal compressor 100 as a rotary machine according to the present embodiment includes a rotary shaft 1 that rotates around an axis, a casing 3 that covers the periphery of the rotary shaft 1 to form a flow path 2, a plurality of impellers 4 provided on the rotary shaft 1, and a journal bearing 5 (oil bath bearing device).

The housing 3 is cylindrical and extends along the axis O. The rotary shaft 1 extends along the axis O so as to penetrate the inside of the housing 3. Journal bearings 5 and thrust bearings 6 are provided at both ends of the housing 3 in the axis O direction, respectively. The rotary shaft 1 is supported by the journal bearing 5 and the thrust bearing 6 so as to be rotatable about the axis O. The structure of the journal bearing 5 will be described later.

An intake port 7 for taking in air as the working fluid G from the outside is provided on one side of the housing 3 in the axis O direction. Further, an exhaust port 8 for discharging the working fluid G compressed inside the housing 3 is provided on the other side of the housing 3 in the axis O direction.

An internal space (flow path 2) is formed inside the casing 3, the internal space communicating the intake port 7 and the exhaust port 8 and repeatedly reducing and expanding in diameter. In the following description, the side of the flow path 2 where the inlet port 7 is located is referred to as the upstream side, and the side where the outlet port 8 is located is referred to as the downstream side.

A plurality of (6) impellers 4 are provided on the outer peripheral surface of the rotary shaft 1 at intervals along the axis O direction. Each impeller 4 has a disk 41 having a substantially circular cross section when viewed in the direction of the axis O, a plurality of blades 42 provided on the upstream side surface of the disk 41, and a cover 43 covering the plurality of blades 42 from the upstream side.

In the present embodiment, one flow path 2 is formed for each impeller 4 (each compression stage). That is, in the centrifugal compressor 100, five flow paths 2 are formed so as to be continuous from the upstream side to the downstream side in correspondence to five impellers 4 except for the impeller 4 at the last stage. In addition, a plurality of turning vanes 50 for guiding the flow of the fluid are provided in each flow path 2. The rotary blades 50 extend radially about the axis O.

Next, the structure of the journal bearing 5 will be described with reference to fig. 2 and 3. As shown in fig. 2, the journal bearing 5 includes a plurality of (5) bearing pads 51, a carrier ring 52, a bearing housing 53 (casing), and a lubricant supply portion 54.

The plurality of bushes 51 are arranged at intervals in the circumferential direction along the outer circumferential surface 1S of the rotary shaft 1. Each of the bushes 51 has an arc shape with the axis O as the center. The inner circumferential surface (sliding surface 51A) of the bearing bush 51 faces the outer circumferential surface 1S of the rotary shaft 1 with a gap in the radial direction. The sliding surface 51A has an arc shape with the axis O as the center. The surface (bearing surface 51B) of the bush 51 facing the outer peripheral side is arc-shaped with the axis O as the center, similarly to the sliding surface 51A.

A space V spreading in the circumferential direction is formed between the circumferential end surfaces (bush end surfaces 51C) of the pair of bushes 51 adjacent to each other. The lubricating oil is supplied to the space V through an oil supply hole described later.

A carrier ring 52 is provided on the outer peripheral side of the bush 51. The carrier ring 52 has an annular shape centered on the axis O. A pivot shaft P for supporting the bearing bush 51 is provided on the inner peripheral surface of the carrier ring 52 (carrier ring inner peripheral surface 52A). The pivot axis P is provided one for each bearing bush 51. The pivot shaft P is pointed and protrudes radially inward from the inner peripheral surface 52A of the carrier ring. The top of the pivot axis P is in point contact with the bearing surface 51B of the bearing bush 51. The bearing bush 51 can swing three-dimensionally about the top of the pivot shaft P as a fulcrum.

Further, the carrier ring 52 is formed with an oil supply hole 52B for guiding the lubricant oil supplied from a lubricant oil supply portion 54, which will be described later, to the inner peripheral side of the carrier ring 52. The oil supply hole 52B is a hole that penetrates the carrier ring 52 from the inner peripheral side to the outer peripheral side. The oil supply hole 52B is provided at a position corresponding to the space V in the circumferential direction. That is, in the present embodiment, five oil supply holes 52B are formed. The structure of the oil supply hole 52B will be described later.

A bearing housing 53 is provided on the outer peripheral side of the carrier ring 52. The bearing housing 53 is provided for covering the bearing shoes 51 and the carrier ring 52 from the outer peripheral side, and holds lubricating oil between it and the outer peripheral surface 1S of the rotating shaft 1. That is, the journal bearing 5 of the present embodiment is an oil bath type bearing device, and the space on the inner peripheral side of the bearing housing 53 is filled with the lubricating oil.

A lubricant oil supply portion 54 is connected to the bearing housing 53. The lubricant oil supply unit 54 includes a tank 54A for storing lubricant oil, a supply pipe 54B for connecting the tank 54A and the bearing housing 53, and a pump 54C provided in the supply pipe 54B. By driving the pump 54C, the lubricant in the tank 54A is pressure-fed into the bearing housing 53 through the supply pipe 54B.

The lubricating oil pressure-fed into the bearing housing 53 reaches the space V between the bearing bushes 51 through the oil supply hole 52B formed in the carrier ring 52. In this space V, the new lubricating oil supplied from the oil supply hole 52B is mixed with the fluid (main flow) of the lubricating oil flowing along the outer peripheral surface 1S of the rotating shaft 1. By mixing new lubricating oil, the temperature of the lubricating oil that has become high while flowing between the bearing bush 51 and the rotary shaft 1 can be reduced. However, depending on the rotation speed of the rotating shaft 1, the difference in the speed of the fluid between the main flow and the new lubricating oil may become excessively large, and the two may not be sufficiently mixed. As a result, the lubricating oil becomes high in temperature, and the load capacity of the journal bearing 5 may be affected.

Therefore, in the present embodiment, the oil supply hole 52B has a structure as shown in fig. 3. As shown in the drawing, the oil supply hole 52B extends obliquely with respect to the radial direction of the axis O. More specifically, the oil supply hole 52B extends toward the rear side in the rotation direction of the rotary shaft 1 as facing radially inward with respect to the axis O. Thereby, the lubricating oil flowing into the space V through the oil supply hole 52B collides with the fluid (main flow M) of the lubricating oil flowing along the outer peripheral surface 1S of the rotating shaft 1 at an acute angle. As a result, as shown in fig. 3, in the space V, a vortex X of the lubricating oil is formed by the main flow M and the new fluid of the lubricating oil. The main flow M is mixed with new lubricating oil by the swirl X.

As described above, according to the configuration of the present embodiment, the oil supply hole 52B extends toward the rear side in the rotation direction of the rotary shaft 1 as it goes toward the radially inner side. Therefore, the new flow of the lubricating oil supplied through the oil supply hole 52B faces the flow direction of the lubricating oil flowing along the outer peripheral surface 1S of the rotary shaft 1 (i.e., the forward direction in the rotational direction). Thus, when new lubricating oil collides with existing lubricating oil, a vortex X centered on the axis O direction is formed in the space V between the bearing pads 51. By forming the vortex X, the new lubricating oil and the existing lubricating oil (main flow M) can be sufficiently mixed. As a result, the temperature of the main flow M of the lubricating oil can be reduced, and the load capacity of the journal bearing 5 can be maintained/improved.

The first embodiment of the present invention has been described above. In addition, various changes and modifications can be made to the above-described structure without departing from the scope of the present invention. For example, in the above embodiment, an example in which five bearing shoes 51 are provided is explained. However, the number of the bearing bushes 51 may be four or less or six or more. In the above embodiment, an example in which one oil supply hole 52B is formed in each of the spaces V between the bearing bushes 51 has been described. However, the oil supply hole 52B may be formed in a region corresponding to only a part of the space V.

[ second embodiment ]

Next, a second embodiment of the present invention will be described with reference to fig. 4. The same components as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. As shown in fig. 4, in the present embodiment, a plurality of (3) oil supply holes 52B are formed for each space V. The oil supply holes 52B are arranged at intervals in the axis O direction. Of the plurality of oil supply holes 52B, the first oil supply hole 521B located at the center in the axis O direction is set to have a larger opening diameter than the other oil supply holes 52B (second oil supply holes 522B).

According to the above configuration, since the plurality of oil supply holes 52B are formed at intervals in the axis O direction, the lubricant can be stably supplied to the bearing bush 51 over the entire area in the axis O direction.

Here, the closer to the center portion of the bearing bush 51 in the axis O direction, the higher the pressure generated by the load of the rotary shaft 1, and therefore the higher the flow velocity of the lubricating oil. According to the above configuration, the diameter of the hole of the plurality of oil supply holes 52B increases as the oil supply hole becomes the center portion in the axis O direction. Therefore, more lubricant can be supplied from the oil supply hole 52B (first oil supply hole 521B) in the central portion. As a result, the rotary shaft 1 can be supported more stably.

The second embodiment of the present invention has been described above. In addition, various changes and modifications can be made to the above-described structure without departing from the scope of the present invention. For example, in the second embodiment, an example in which three oil supply holes 52B are formed in the axis O direction is described. However, the number of the oil supply holes 52B is not limited to the above, and may be four or more.

[ third embodiment ]

Next, a third embodiment of the present invention will be described with reference to fig. 5. The same components as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. As shown in fig. 5, in the present embodiment, a narrowed portion S is provided at the outlet-side end T1 of the oil supply hole 52B. In the narrowed portion S, the flow path cross-sectional area is smaller than the other portion in the oil supply hole 52B. That is, the opening diameter of the outlet-side end T1 is smaller than the opening diameter of the inlet-side end T2.

According to the above configuration, since the narrowed portion S is provided at the outlet-side end T1 of the oil supply hole 52B, the flow velocity of the lubricating oil passing through the narrowed portion S can be further increased. This further increases the swirling flow velocity of the vortex X formed in the space V, and the lubricating oil newly supplied through the oil supply hole 52B and the conventional lubricating oil flowing along the outer circumferential surface 1S of the rotary shaft 1 can be mixed more efficiently.

The third embodiment of the present invention has been described above. In addition, various changes and modifications can be made to the above-described structure without departing from the scope of the present invention. For example, a combination of the structure of the second embodiment and the structure of the third embodiment may be adopted.

[ fourth embodiment ]

Next, a fourth embodiment of the present invention will be described with reference to fig. 6. The same components as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. As shown in fig. 6, the present embodiment differs from the above-described embodiments in the shape of the end surface (the bush end surface 251C) of the bush 51 in the circumferential direction. Specifically, the bush end face 251C forms a curved surface recessed in the circumferential direction. That is, in the pair of shoes 51 adjacent to each other, the respective shoe end surfaces 251C are recessed in a curved surface shape in a direction away from each other.

According to the above configuration, the end surfaces (the bush end surfaces 251C) of the mutually adjacent bushes 51 form curved surfaces that are recessed in the direction away from each other. This causes the lubricating oil to flow along the curved surface, thereby more smoothly forming the vortex X. As a result, the new lubricating oil supplied through the oil supply hole 52B and the lubricating oil flowing along the outer peripheral surface of the rotating shaft can be mixed more efficiently.

The fourth embodiment of the present invention has been described above. In addition, various changes and modifications can be made to the above-described structure without departing from the scope of the present invention. For example, a combination of the structure of the fourth embodiment and the structures of the second and third embodiments described above may be employed.

[ fifth embodiment ]

Next, a fifth embodiment of the present invention will be described with reference to fig. 7. The same components as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. As shown in fig. 7, in the present embodiment, of the shoe end surfaces 51C of the shoes 51, the end surface on the front side in the rotation direction (the front side end surface 51F) extends obliquely with respect to the radial direction of the axis O. That is, the front side end surface 51F extends toward the rear side in the rotation direction as it goes toward the radially inner side.

According to the above configuration, the end surface (front side end surface 51F) of the bush 51 on the front side in the rotation direction extends toward the rear side in the rotation direction as it goes toward the inside in the radial direction. As a result, the new lubricating oil supplied through the oil supply hole 52B collides with the fluid of the lubricating oil flowing along the outer peripheral surface 1S of the rotating shaft 1 at a more acute angle along the front side end surface 51F toward the outer peripheral surface 1S of the rotating shaft 1. This promotes formation of the vortex X, and enables efficient mixing of new lubricating oil with existing lubricating oil.

The fifth embodiment of the present invention has been described above. In addition, various changes and modifications can be made to the above-described structure without departing from the scope of the present invention. For example, as shown in fig. 8, an end surface on the rear side in the rotational direction (rear side end surface 51R) may extend obliquely with respect to the radial direction instead of the front side end surface 51F of the bush 51. That is, the rear side end surface 51R extends toward the rear side in the rotation direction as it goes toward the radially inner side. With this structure, the formation of the eddy current X can be promoted. Further, a combination of the front-side end surface 51F and the rear-side end surface 51R may be employed. In addition, the configurations of the second to fourth embodiments described above may be appropriately selected and combined with the configuration of the fifth embodiment.