WO2022064956A1

WO2022064956A1 - Fluid dynamic pressure bearing device

Info

Publication number: WO2022064956A1
Application number: PCT/JP2021/031587
Authority: WO
Inventors: 大智加藤
Original assignee: Ntn株式会社
Priority date: 2020-09-24
Filing date: 2021-08-27
Publication date: 2022-03-31
Also published as: JP7467303B2; TW202219396A; JP2022053014A

Abstract

A fluid dynamic pressure bearing device 1 comprising a cylindrical bearing member 8, and an axis member 2 disposed on the inner circumference of the bearing member 8, wherein a radial dynamic pressure generation part 20 is formed on an inner circumference surface 8a of the bearing member 8 to generate dynamic pressure action of lubricating oil in a radial bearing gap. The radial dynamic pressure generation part 20 is configured with a plurality of polygon hill parts 21 provided at an interval along a circumferential direction Y, polygon groove parts 22 provided so as to surround the polygon hill parts 21, and circumferential groove parts 23 each coupling two polygon groove parts 22 adjacent to each other in the circumferential direction.

Description

Fluid dynamic bearing equipment

The present invention relates to a fluid dynamic bearing device.

As is well known, the fluid dynamic bearing device has features such as high speed rotation, high rotation accuracy and low noise. Therefore, the fluid dynamic bearing device is suitable as a bearing device for motors such as a spindle motor incorporated in a disk drive device such as an HDD, a fan motor incorporated in a PC or the like, or a polygon scanner motor incorporated in a laser beam printer. Used for.

For example, the hydrodynamic bearing device disclosed in Patent Document 1 below includes a cylindrical bearing sleeve (bearing member), a shaft member arranged on the inner circumference of the bearing member, and relative rotation between the bearing member and the shaft member. Along with this, the shaft member is moved in the radial direction by the dynamic pressure action of the radial bearing gap formed between the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft member and the fluid (for example, lubricating oil) generated in the radial bearing gap. It is provided with a radial bearing portion that supports non-contact with relative rotation. In this case, a dynamic pressure generating portion (radial dynamic pressure generating portion) is provided on either one of the two facing surfaces forming the radial bearing gap.

FIG. 6 shows a known radial dynamic pressure generating portion also described in FIG. 2 of Patent Document 1. The radial dynamic pressure generating portion 100 shown in the figure is provided on the inner peripheral surface of the bearing member 110 on the stationary side, and is inclined with respect to the axial direction and is provided at intervals in the circumferential direction. The upper dynamic pressure groove 101 of the above, a plurality of lower dynamic pressure grooves 102 inclined in the direction opposite to the upper dynamic pressure groove 101 and provided at intervals in the circumferential direction, and both

dynamic pressure grooves

101 and 102 are partitioned. It is composed of a convex hill portion (indicated by cross-hatching in the figure) 103, and the hill portion 103 is formed in a herringbone shape as a whole. Therefore, the convex hill portion 103 includes an inclined hill portion 104 provided between the dynamic pressure grooves adjacent to each other in the circumferential direction, and an annular hill portion 105 provided between the upper and lower

dynamic pressure grooves

101 and 102.

Japanese Unexamined Patent Publication No. 2011-196544

In order to generate dynamic pressure in the fluid in the radial bearing gap in the conventional radial dynamic pressure generating unit 100 shown in FIG. 6, the rotating shaft member 111 inserted in the inner circumference of the bearing member 110 rotates. Along with this, it is necessary to make the fluid in the radial bearing gap flow toward the annular hill 105 side along the dynamic pressure grooves 101 and 102 (see the black arrow in FIG. 6) and collide with the annular hill 105. Therefore, when the conventional radial dynamic pressure generation unit 100 is adopted, the rotation direction of the shaft member 111 is limited to one direction. Therefore, when assembling the fluid dynamic bearing device, it is necessary to pay attention to the posture of the bearing member 110, and there is a difficulty in the workability of the assembly work.

Further, when the radial dynamic pressure generating portion 100 is adopted, the dynamic pressure is generated in the facing region of the annular hill portion 105 in the radial bearing gap (the pressure of the oil film in the facing region of the annular hill portion 105). Therefore, when the shaft member 111 rotates, the pressure (surface pressure) is intensively applied to the forming region of the annular hill portion 105 in the radial dynamic pressure generating portion 100. Therefore, there is also a problem that the wear of the annular hill portion 105 tends to progress.

Further, when the radial dynamic pressure generation unit 100 is adopted, a sufficient dynamic pressure effect cannot be obtained in a low rotation speed range such as when the fluid dynamic pressure bearing device is started and stopped, and the shaft member 111 is supported with high accuracy. The problem that it is difficult to do is also pointed out.

Therefore, the present invention collectively solves the above-mentioned various problems of the known radial dynamic pressure generator, whereby the fluid dynamic pressure has good assembly workability, durable life, and rotation accuracy in a low rotation speed range. The purpose is to realize a bearing device.

The present invention, which was devised to achieve the above object, is either a cylindrical bearing member, a shaft member arranged on the inner circumference of the bearing member, an inner peripheral surface of the bearing member, or an outer peripheral surface of the shaft member. A fluid dynamic bearing device provided on one side and provided with a radial dynamic pressure generating portion that generates a dynamic pressure action on the fluid in a radial bearing gap formed between the bearing member and the shaft member due to relative rotation. In the radial dynamic pressure generating portion, a plurality of polygonal hills provided at intervals along the circumferential direction, a polygonal groove provided so as to surround the polygonal hills, and a circumferential direction. It is characterized in that it is composed of a circumferential groove portion connecting two adjacent polygonal groove portions. The above-mentioned "fluid" is a concept that includes not only a liquid such as lubricating oil but also a gas such as air.

If the radial dynamic pressure generating portion has the above configuration, it can be handled regardless of whether the rotation direction of the shaft member (relative rotation direction of the bearing member and the shaft member) is the forward direction or the reverse direction. Therefore, when assembling the fluid dynamic pressure bearing device, it is not necessary to consider the mounting direction (posture) of the member (for example, the bearing member) provided with the radial dynamic pressure generating portion. This makes it possible to improve the workability of assembling the fluid dynamic bearing device.

The radial dynamic pressure generating portion adopted in the present invention is composed of a plurality of polygonal groove portions provided at intervals in the circumferential direction and a circumferential groove portion connecting two polygonal groove portions adjacent to each other in the circumferential direction. The fluid having an annular groove pattern and flowing along the groove pattern when the bearing member and the shaft member rotate relative to each other is a connection point between the grooves (a place where the flow direction of the fluid changes) or a place where a plurality of grooves meet. In, the pressure will be increased. That is, when the radial dynamic pressure generating portion according to the present invention is adopted, the place where the pressure of the fluid in the radial bearing gap increases (the place where the dynamic pressure is generated) is the conventional radial dynamic pressure generating portion 100 shown in FIG. It is not limited to a part of the radial bearing gap in the axial direction (opposing region of the annular hill 105) as in the case of adoption, but is dispersed in a plurality of axial directions of the radial bearing gap. As a result, it is possible to wear the radial dynamic pressure generation part (particularly the hill part) due to the concentrated surface pressure being applied to a part of the radial dynamic pressure generation part during the relative rotation of the bearing member and the shaft member. In addition to being able to prevent this, it is possible to obtain a sufficient dynamic pressure effect even in the low rotation speed range.

The radial dynamic pressure generating portion having the above configuration may be provided at only one place in the axial direction, or may be provided at a plurality of locations at intervals in the axial direction. If the radial dynamic pressure generating portions are provided at a plurality of positions in the axial direction, the bearing rigidity can be increased, which is advantageous in reducing the contact frequency between the bearing member and the shaft member during relative rotation. This is more advantageous in suppressing the wear of the bearing member and / or the shaft member, and in preventing the generation of abnormal noise due to the contact between the two.

One of the above members (bearing member or shaft member) having a radial dynamic pressure generating portion can be formed of a porous body such as a sintered metal or a porous resin. Since this type of porous body is excellent in processability, it is advantageous in improving the shape accuracy of the radial dynamic pressure generating portion. Further, since the porous body can hold the fluid in its internal pores, it is advantageous in preventing the amount of fluid to be interposed in the radial bearing gap from being insufficient. At this time, if the surface opening ratio of the polygonal groove portion and the circumferential groove portion is made larger than the surface opening ratio of the polygonal hill portion, the fluid held in the internal pores is positively applied to the polygonal groove portion and the circumferential groove portion. Since the polygonal groove portion and the circumferential groove portion can be filled with abundant fluid, the desired bearing performance can be stably exhibited.

The fluid dynamic bearing device according to the present invention described above can be suitably used as a bearing device for various motors such as a fan motor, a spindle motor and a polygon scanner motor.

Based on the above, according to the present invention, various problems of the conventional radial dynamic pressure generating unit 100 shown in FIG. 6 can be collectively solved, so that assembly workability, durable life, and rotation in a low rotation speed range can be solved. It is possible to realize a fluid dynamic bearing device with good accuracy (bearing performance).

It is a figure which shows an example of a fan motor conceptually. It is a schematic sectional drawing of the fluid dynamic pressure bearing apparatus which concerns on one Embodiment of this invention. It is a partially developed plan view of the inner peripheral surface of the bearing member shown in FIG. It is a figure explaining the distribution mode of the lubricating oil when the shaft member rotates in the forward direction. It is a figure explaining the flow mode of the lubricating oil when the shaft member rotates in the reverse direction. It is a figure which shows the deformation example of the radial dynamic pressure generation part schematically. It is a figure which shows the deformation example of the radial dynamic pressure generation part schematically. It is a figure which shows the deformation example of the radial dynamic pressure generation part schematically. It is a vertical sectional view of the bearing member in which the conventional radial dynamic pressure generation part was formed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 conceptually shows an example of a fan motor incorporating a fluid dynamic bearing device 1 according to an embodiment of the present invention, and more specifically, a shaft rotation type fluid dynamic bearing device 1. The fan motor shown in the figure comprises a fluid dynamic bearing device 1, a motor base 6 constituting the stationary side of the motor, a stator coil 5 fixed to the motor base 6, and a fan (rotating side of the motor). A rotor 3 having a blade) and a rotor magnet 4 fixed to the rotor 3 and facing the stator coil 5 via a radial gap are provided. The fluid dynamic pressure bearing device 1 is fixed to the inner circumference of the motor base 6, and the rotor 3 is fixed to the shaft member 2 of the fluid dynamic pressure bearing device 1. In the fan motor configured in this way, when the stator coil 5 is energized, the rotor magnet 4 is rotated by the electromagnetic force between the stator coil 5 and the rotor magnet 4, and the shaft member 2 and the rotor 3 are integrated accordingly. Rotate.

When the shaft member 2 rotates, wind is sent upward or downward in the figure depending on the form of the blades provided on the rotor 3. Therefore, when the shaft member 2 is rotated, a downward or upward thrust force acts on the shaft member 2 as a reaction force of this blowing action. A magnetic force (repulsive force) in a direction that cancels this thrust is applied between the stator coil 5 and the rotor magnet 4, and the thrust load generated by the difference between the thrust and the magnitude of the magnetic force is the fluid dynamic bearing device 1. It is supported by the thrust bearing portion T of. The magnetic force in the direction of canceling the thrust can be generated, for example, by arranging the stator coil 5 and the rotor magnet 4 so as to be displaced in the axial direction (detailed illustration is omitted). Further, when the shaft member 2 is rotated, a radial load acts on the shaft member 2. This radial load is supported by the radial bearing portions R1 and R2 of the fluid dynamic bearing device 1.

FIG. 2 shows an enlarged view of the fluid dynamic bearing device 1 shown in FIG. In the following, for convenience of explanation, the lower side of the paper surface of FIG. 2 is referred to as “lower side” and the upper side of the paper surface of FIG. 2 is referred to as “upper side”, but the usage posture of the fluid dynamic bearing device 1 is not limited.

In the fluid dynamic bearing device 1 shown in FIG. 2, the shaft member 2 constituting the rotating side, the housing 7 constituting the stationary side, the bearing member 8 and the sealing member 9, and the fluid filled in the internal space of the housing 7 are used. It is a so-called shaft rotation type fluid dynamic bearing device equipped with the lubricating oil (not shown). The lubricating oil may be filled so as to fill the entire internal space of the housing 7, or may be filled in a part of the internal space of the housing 7. Even in the latter case, at least the outer peripheral surface of the shaft member 2 is filled. The radial gap (radial bearing gap between the radial bearing portions R1 and R2) between 2a and the inner peripheral surface 8a of the bearing member 8 and the bottom space 10 accommodating the thrust bearing portion T are filled with lubricating oil.

The shaft member 2 is formed of, for example, a metal material such as stainless steel, its outer peripheral surface 2a is formed on a smooth cylindrical surface without unevenness, and its lower end surface 2b is formed on a convex spherical surface. A rotor 3 having blades (see FIG. 1) is fixed to the upper end of the shaft member 2.

The housing 7 is provided on the inner circumference of the boundary between the cylindrical cylinder portion 7a, the bottom portion 7b that closes the lower end opening of the cylinder portion 7a, and the cylinder portion 7a and the bottom portion 7b, using a soft metal material such as brass or a resin material. It is formed in the shape of a bottomed cylinder having a stepped portion 7c integrally. The inner bottom surface (upper end surface of the bottom portion 7b) 7b1 of the housing 7 of the present embodiment forms a thrust bearing portion T that contacts and supports the shaft member 2 in the thrust direction during operation of the fluid dynamic bearing device 1. Therefore, although not shown, a plate-shaped member (thrust plate) made of a material having better wear resistance than the housing 7 is arranged on the bottom portion 7b of the housing 7, and the shaft member 2 is formed by this thrust plate. It may be contact-supported.

The seal member 9 is formed of a metal material or a resin material in a cylindrical shape, and is fixed to the inner circumference of the upper end portion of the tubular portion 7a of the housing 7 by an appropriate means. The inner peripheral surface 9a of the seal member 9 forms a seal gap S with the outer peripheral surface 2a of the opposing shaft member 2. The gap width of the seal gap S is set to be larger than the gap width of the radial gap (radial bearing gap) formed between the outer peripheral surface 2a of the shaft member 2 and the inner peripheral surface 8a of the bearing member 8.

The bearing member 8 of the present embodiment is formed in a cylindrical shape with a porous body having innumerable internal pores (porous structure), for example, a porous body of a sintered metal containing iron and copper as main components, and the internal pores thereof. Is impregnated with lubricating oil. As the bearing member 8, a material formed of a porous body other than the sintered metal (for example, a porous resin) or a non-porous material such as a solid soft metal material or a resin material is used. Is also good.

The bearing member 8 of the present embodiment is fixed to the inner circumference of the housing 7 in a state where the lower end surface 8b is in contact with the upper end surface 7c1 of the step portion 7c of the housing 7. The bearing member 8 can be fixed to the housing 7 by press-fitting, bonding, or press-fitting (combined use of press-fitting and bonding), but in the present embodiment, the bearing member is formed by the sealing member 9 and the step portion 7c of the housing 7. The bearing member 8 is fixed to the inner circumference of the housing 7 by sandwiching the 8 from both sides in the axial direction. If such a fixing method is adopted, the bearing member 8 can be fixed to the housing 7 at the same time as fixing the seal member 9 to the housing 7, so that the time and effort required for assembling the members can be reduced. can. Further, for example, when the bearing member 8 is press-fitted into the inner circumference of the tubular portion 7a of the housing 7 with a large tightening margin, the deformation of the bearing member 8 due to the press-fitting spreads to the inner peripheral surface 8a of the bearing member 8 and the radial bearing gap is formed. The width accuracy and, by extension, the bearing performance of the radial bearing portions R1 and R2 may be adversely affected. The above-mentioned fixing method adopted in the present embodiment can prevent such a problem from occurring as much as possible.

FIG. 3 shows a partially developed plan view of the inner peripheral surface 8a of the bearing member 8. As shown in the figure, the inner peripheral surface 8a of the bearing member 8 is provided with radial bearing surfaces that form a radial bearing gap between the inner peripheral surface 8a and the outer peripheral surface 2a of the opposing shaft member 2 at two locations that are vertically separated from each other. ing. Each of the two radial bearing surfaces is provided with a radial dynamic pressure generating portion 20 for generating a dynamic pressure action on the lubricating oil interposed in the radial bearing gap.

Each radial dynamic pressure generating portion 20 includes a plurality of polygonal hill portions 21 provided at intervals along the circumferential direction Y, and polygonal groove portions 22 provided so as to surround the polygonal hill portions 21. , It is composed of a circumferential groove portion 23 extending in the circumferential direction Y and connecting two polygonal groove portions 22 adjacent to each other in the circumferential direction Y. The polygonal hill portion 21 in the illustrated example is an octagonal hill portion (convex portion) in a plan view. Therefore, the polygonal groove portion 22 provided so as to surround the polygonal hill portion 21 is configured by connecting eight grooves in an octagonal shape. The polygonal hill portion 21 (and the polygonal groove portion 22 surrounding the polygonal hill portion 21) in the illustrated example has a line-symmetrical shape (left-right symmetric shape) centered on a straight line extending in the axial direction X and a circumferential direction Y. It is an axisymmetric shape (vertical symmetry shape) centered on a straight line extending to.

In the fluid dynamic pressure bearing device 1 having the above configuration, when the shaft member 2 rotates, the inner peripheral surface 8a of the bearing member 8 (two radial dynamic pressure generating portions 20 provided at intervals in the axial direction) and A radial bearing gap is formed between the shaft member 2 and the outer peripheral surface 2a facing the shaft member 2. Further, in the present embodiment in which the bearing member 8 is made of a porous body of sintered metal, when the shaft member 2 rotates, the lubricating oil impregnated in the internal pores of the bearing member 8 rotates the shaft member 2. Due to the generation of pressure (negative pressure) and the thermal expansion of the lubricating oil due to the temperature rise, the bearing member 8 seeps out one after another through the surface opening of the bearing member 8 and is drawn into the radial bearing gap. The lubricating oil previously interposed in the radial bearing gap and the lubricating oil exuded from the bearing member 8 and drawn into the radial bearing gap form an oil film, and the pressure of this oil film is increased by the dynamic pressure action of the radial dynamic pressure generating portion 20. Be done. As a result, the radial bearing portions R1 and R2 that rotatably and non-contactly support the shaft member 2 in the radial direction are formed at two positions separated from each other in the vertical direction.

At the same time, a thrust bearing portion T that supports the shaft member 2 in contact (point contact) in the thrust direction is formed. As described above, in the present embodiment, an external force (magnetic force) for pressing the shaft member 2 downward is applied to the shaft member 2. Therefore, even when the pressure in the bottom space 10 increases with the rotation of the shaft member 2, it is possible to prevent the shaft member 2 from overfloating as much as possible. The external force does not necessarily have to be applied, and may be applied as needed.

In the fluid dynamic pressure bearing device 1 described above, the radial dynamic pressure generating portion 20 has a plurality of polygonal hill portions 21 provided at intervals along the circumferential direction Y, and the polygonal hill portions 21. It is composed of a polygonal groove portion 22 provided so as to surround it, and a circumferential groove portion 23 connecting two polygonal groove portions 22 adjacent to each other in the circumferential direction. In this case, there are cases where the shaft member 2 rotates in the direction (forward direction) shown in FIG. 4A and cases where the shaft member rotates in the direction (reverse direction) shown in FIG. 4B, and lubrication interposed in the radial bearing gap. Although the oil flows in the opposite directions, there is no difference in the flow of the lubricating oil (the flow of the lubricating oil along the groove pattern including the polygonal groove 22 and the circumferential groove 23). Therefore, regardless of whether the rotation direction of the shaft member 2 is in the forward direction or the reverse direction, the radial bearing portions R1 and R2 capable of appropriately increasing the oil film pressure formed in the radial bearing gap and exhibiting the desired bearing performance can be provided. Can be formed. This eliminates the need to consider the mounting direction (attitude) of the member (here, the bearing member 8) provided with the radial dynamic pressure generating portion 20 when assembling the fluid dynamic pressure bearing device 1. The assembly workability of 1 can be improved.

The radial dynamic pressure generating portion 20 of the present embodiment is composed of a plurality of polygonal groove portions 22 provided at intervals in the circumferential direction Y and a circumferential groove portion 23 connecting adjacent polygonal groove portions 22 in the circumferential direction Y. The lubricating oil having a band-shaped groove pattern configured and flowing along the groove pattern when the shaft member 2 is rotated is a connection point between the grooves (flow of lubricating oil) indicated by reference numeral A in FIGS. 4A and 4B. The pressure is increased at the place where the direction changes) and the place where the two grooves meet (the place where the lubricating oil flowing along the groove pattern joins) indicated by the reference numeral B in FIGS. 4A and 4B.

That is, when the radial dynamic pressure generating section 20 of the present embodiment is adopted, the conventional radial dynamic pressure generating section 100 shown in FIG. 6 is adopted as the location where the oil film pressure increases (the location where the dynamic pressure is generated) in the radial bearing gap. It is not limited to a partial axial region (opposing region of the annular hill 105) of the radial bearing gap as in the case of the above, but is dispersed in a plurality of axial directions of the radial bearing gap. In addition to this, the axial width of the polygonal hill portion 21 constituting the radial dynamic pressure generating portion 20 can be made larger than the axial width of the annular hill portion 105 constituting the conventional radial dynamic pressure generating portion 100. .. As a result, the radial dynamic pressure generating portion 20 (particularly the polygonal hill portion 21 as a hill portion) is caused by the concentrated surface pressure being applied to a part of the radial dynamic pressure generating portion 20 when the shaft member 2 is rotated. In addition to being able to prevent wear as much as possible, it is possible to obtain a sufficient dynamic pressure effect even in the low rotation speed range.

Further, in the present embodiment, the bearing member 8 on which the radial dynamic pressure generating portion 20 is formed is formed of a porous body of sintered metal. Since this type of porous body is excellent in workability, it is advantageous in improving the shape accuracy of the radial dynamic pressure generating portion 20 and further in improving the bearing performance of the radial bearing portions R1 and R2. Further, since the bearing member 8 made of a porous body can hold the lubricating oil in the internal pores thereof, it is possible to prevent the amount of the lubricating oil to be interposed in the radial bearing gap from being insufficient. From this point as well, the bearing performance of the radial bearing portions R1 and R2 can be improved.

In the present embodiment in which the bearing member 8 having the radial dynamic pressure generating portion 20 is formed of a porous body (a porous body of sintered metal), the surface opening ratios of the polygonal groove portion 22 and the circumferential groove portion 22 are formed. Is preferably larger than the surface aperture ratio of the polygonal hill portion 21. By doing so, the lubricating oil held in the internal pores of the bearing member 8 is positively supplied to the polygonal groove portion 22 and the circumferential groove portion 23, and the polygonal groove portion 22 and the circumferential groove portion 23 are provided with abundant lubricating oil. Since it can be satisfied, it is advantageous in stably exhibiting the bearing performance of the radial bearing portions R1 and R2.

Although the fluid dynamic pressure bearing device 1 according to the embodiment of the present invention has been described above, various changes can be made to the fluid dynamic pressure bearing device 1 without departing from the gist of the present invention.

For example, in the embodiment described above, the radial dynamic pressure generating portions 20 for forming the radial bearing portion made of the dynamic pressure bearing are arranged at two positions in the axial direction at intervals, but the radial dynamic pressure generating portion 20 is arranged. May be provided at only one place in the axial direction, or may be arranged at three or more places in the axial direction at intervals. In short, the present invention is also applied to a fluid dynamic bearing device 1 in which a radial bearing portion is provided at only one position in the axial direction and a fluid dynamic pressure bearing device 1 in which a radial bearing portion is provided at three or more positions in the axial direction. be able to. Further, the radial dynamic pressure generating portion 20 may be provided on either one of the two facing surfaces (inner peripheral surface 8a of the bearing member 8 and outer peripheral surface 2a of the shaft member 2) forming the radial bearing gap. Therefore, the radial dynamic pressure generating portion 20 may be provided on the outer peripheral surface 2a of the shaft member 2 instead of the inner peripheral surface 8a of the bearing member 8.

Further, in the radial dynamic pressure generating portion 20 described above, the polygonal hill portion 21 (and the polygonal groove portion 22) having an octagonal shape in a plan view is adopted, but the polygonal hill portion 21 (and the polygonal groove portion 22) are adopted. 22) may be formed into a polygonal shape other than an octagon, such as a quadrangular shape as shown in FIG. 5A, a pentagonal shape as shown in FIG. 5B, and a hexagonal shape as shown in FIG. 5C.

The polygonal groove portion 22 provided so as to surround the polygonal hill portion 21 functions as an oil passage through which the lubricating oil interposed in the radial bearing gap flows when the shaft member 2 rotates. Therefore, in the triangular polygonal groove portion 22 in which at least two acute-angled portions are formed on the oil passage, the lubricating oil cannot smoothly flow when the shaft member 2 rotates, and the bearing of the radial bearing portion. Performance may be adversely affected. Therefore, it is preferable that the polygonal hill portion 21 (and the polygonal groove portion 22) is formed in a polygonal shape having four or more corner portions.

Further, in the embodiment described above, the two polygonal groove portions 22 adjacent to each other in the circumferential direction Y are connected by one circumferential groove portion 23, but the two polygonal groove portions adjacent to each other in the circumferential direction Y are connected. 22 may be connected by two or more circumferential groove portions 23 parallel to each other.

Further, in the fluid dynamic bearing device 1 described above, the shaft member 2 is on the rotating side and the bearing member 8 is on the stationary side, but the shaft member 2 constitutes the stationary side and the bearing member 8 is on the rotating side. It may be configured. That is, the present invention can be applied not only to the so-called shaft rotation type fluid dynamic pressure bearing device 1 but also to the so-called shaft fixed type fluid dynamic pressure bearing device 1.

1 Fluid dynamic bearing device 2 Shaft member 8 Bearing member 20 Radial dynamic pressure generation part 21 Polygonal hill part 22 Polygonal groove part 23 Circumferential groove part R1, R2 Radial bearing part T Thrust bearing part X Axial direction Y Circumferential direction

Claims

A cylindrical bearing member, a shaft member arranged on the inner circumference of the bearing member, and the bearing member and the shaft member provided on either the inner peripheral surface of the bearing member or the outer peripheral surface of the shaft member. In a fluid dynamic bearing device provided with a radial dynamic pressure generating portion that generates a dynamic pressure action on the fluid in the radial bearing gap formed between the two in accordance with the relative rotation of the bearing.
The radial dynamic pressure generating portion has a plurality of polygonal hills provided at intervals along the circumferential direction, a polygonal groove provided so as to surround the polygonal hill, and a circumferential groove. A fluid dynamic pressure bearing device comprising a circumferential groove portion connecting two adjacent polygonal groove portions.
The fluid dynamic pressure bearing device according to claim 1, wherein a plurality of the radial dynamic pressure portions are provided at intervals in the axial direction.
One of the members having the radial dynamic pressure generating portion is made of a porous body.
The fluid dynamic bearing device according to claim 1 or 2, wherein the surface opening ratio of the polygonal groove portion and the circumferential groove portion is larger than the surface opening ratio of the polygonal hill portion.