Fluid dynamic pressure bearing, pulley device, spindle motor, and blower device

Abstract

This fluid dynamic pressure bearing comprises a shaft, a sleeve, and a lubricant. An upper outer-peripheral surface and / or an upper inner-peripheral surface has an upper dynamic pressure fluid dynamic pressure bearing comprising upper dynamic pressure grooves that induce a fluid dynamic pressure in the lubricant during rotation. In a first upper dynamic pressure groove row, a plurality of upper dynamic pressure grooves, which are inclined to one side in a circumferential direction while proceeding upward in an axial direction, are arranged in the circumferential direction. A second upper dynamic pressure groove row is disposed adjacent to the first upper dynamic pressure groove row on the lower side in the axial direction, and a plurality of upper dynamic pressure grooves, which are inclined to the other side in the circumferential direction while proceeding upward in the axial direction, are arranged in the circumferential direction. A third upper dynamic pressure groove row is disposed adjacent to the second upper dynamic pressure groove row on the lower side in the axial direction, and a plurality of upper dynamic pressure grooves, which are inclined to the one side in the circumferential direction while proceeding upward in the axial direction, are arranged in the circumferential direction.

Description

Hydrodynamic bearing, pulley device, spindle motor, and blower device

[0001] The present invention relates to a hydrodynamic bearing, a pulley device, a spindle motor, and a blower device.

[0002] A conventional hydrodynamic bearing includes a shaft, a sleeve, and lubricating oil. The shaft is fixed along a central axis extending in the vertical direction. The sleeve has a through-hole into which the shaft is inserted and is supported by the shaft so as to be relatively rotatable. The lubricating oil is interposed between the shaft and the sleeve (see, for example, Patent Document 1).

[0003] German Patent Application Publication No. 102016008005

[0004] However, in the hydrodynamic bearing disclosed in Patent Document 1, the direction and magnitude of the hydrodynamic pressure induced in the lubricating oil are different when the sleeve is rotated in one circumferential direction with respect to the shaft and when it is rotated in the other circumferential direction. For this reason, the rotational performance of the sleeve with respect to the shaft may decrease.

[0005] An object of the present invention is to provide a hydrodynamic bearing capable of stabilizing the rotational performance for both-directional rotation of a sleeve with respect to a shaft, and a pulley device, a spindle motor, and a blower device including the same.

[0006] An exemplary fluid dynamic bearing of the present invention comprises a shaft, a sleeve, and a lubricating oil. The shaft is positioned along a central axis extending in the vertical direction. The sleeve has a through hole into which the shaft is inserted and is supported by the shaft so as to be rotatable relative to the shaft. The lubricating oil is interposed between the shaft and the sleeve. The shaft has an upper annular portion that protrudes radially outward from its outer circumferential surface and is positioned axially upward, and a lower annular portion that is positioned axially downward. The upper annular portion has an upper outer circumferential surface whose diameter increases with increasing axial direction toward upward. The lower annular portion has a lower outer circumferential surface whose diameter increases with increasing axial direction toward downward. The through hole has an upper inner circumferential surface and a lower inner circumferential surface. The upper inner circumferential surface is inclined away from the central axis with increasing axial direction toward upward, and faces the upper outer circumferential surface. The lower inner circumferential surface is inclined away from the central axis with increasing axial direction toward downward, and faces the lower outer circumferential surface. The sleeve has a communication hole that is positioned radially outward from the radially inner ends of the upper and lower inner circumferential surfaces and penetrates axially. The communication holes communicate with the minute gaps formed between the upper outer circumferential surface and the upper inner circumferential surface, and the minute gaps formed between the lower outer circumferential surface and the lower inner circumferential surface, allowing lubricating oil to circulate. At least one of the upper outer circumferential surface and the upper inner circumferential surface has an upper hydrodynamic bearing composed of upper hydrodynamic grooves that induce hydrodynamic fluid pressure in the lubricating oil when rotating. At least one of the lower outer circumferential surface and the lower inner circumferential surface has a lower hydrodynamic bearing composed of lower hydrodynamic grooves that induce hydrodynamic fluid pressure in the lubricating oil when rotating. The upper hydrodynamic bearing is composed of at least a first row of upper hydrodynamic grooves, a second row of upper hydrodynamic grooves, and a third row of upper hydrodynamic grooves. The first row of upper hydrodynamic grooves consists of multiple upper hydrodynamic grooves arranged circumferentially, inclined to one side in the circumferential direction as they move axially upward. The second row of upper hydrodynamic grooves is arranged adjacent to the first row of upper hydrodynamic grooves on the axially downward side, and consists of multiple upper hydrodynamic grooves arranged circumferentially, inclined to the other side in the circumferential direction as they move axially upward. The third upper hydrodynamic groove row is positioned adjacent to the axially lower side of the second upper hydrodynamic groove row, and consists of multiple upper hydrodynamic grooves arranged circumferentially, each inclined to one side in the circumferential direction as it extends axially upward. The lower hydrodynamic fluid hydrodynamic bearing consists of at least a first lower hydrodynamic groove row, a second lower hydrodynamic groove row, and a third lower hydrodynamic groove row. The first lower hydrodynamic groove row consists of multiple lower hydrodynamic grooves arranged circumferentially, each inclined to one side in the circumferential direction as it extends axially upward.The second row of lower dynamic pressure grooves is positioned adjacent to the first row of lower dynamic pressure grooves on the axially upper side, and consists of multiple lower dynamic pressure grooves arranged circumferentially, each inclined toward the other circumferential direction as it moves axially upward. The third row of lower dynamic pressure grooves is positioned adjacent to the second row of lower dynamic pressure grooves on the axially upper side, and consists of multiple lower dynamic pressure grooves arranged circumferentially, each inclined toward one circumferential direction as it moves axially upward.

[0007] According to exemplary aspects of the present invention, it is possible to provide a fluid dynamic bearing capable of stabilizing rotational performance with respect to bidirectional rotation of the sleeve relative to the shaft, as well as a pulley device, spindle motor, and blower device equipped therewith.

[0008] Figure 1 is a longitudinal cross-sectional view of a blower according to the first embodiment of the present invention. Figure 2 is a longitudinal cross-sectional view of a spindle motor according to the first embodiment of the present invention. Figure 3 is a longitudinal cross-sectional view showing an enlarged view of the fluid dynamic bearing of the spindle motor according to the first embodiment of the present invention. Figure 4 is a longitudinal cross-sectional view showing an enlarged view of a part of the sleeve of the spindle motor according to the first embodiment of the present invention. Figure 5 is a longitudinal cross-sectional view of a pulley device according to the second embodiment of the present invention.

[0009] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In this application, the direction parallel to the central axis J is referred to as the "axial direction," the direction perpendicular to the central axis J is referred to as the "radial direction," and the direction along the arc centered on the central axis J is referred to as the "circumferential direction." Furthermore, in this application, "parallel direction" also includes substantially parallel directions. Furthermore, in this application, "perpendicular direction" also includes substantially perpendicular directions.

[0010] Furthermore, in this application, the axial direction is defined as the vertical direction, and the stator 20 side is defined as the upper side relative to the base portion 72, and the shape and positional relationship of each part are described accordingly. However, this definition of the vertical direction is not intended to limit the orientation in which the spindle motor 10 and blower 1 according to the present invention are used.

[0011] <First Embodiment> (1. Configuration of the Blower) An exemplary embodiment of the blower 1 of the present invention will be described. Figure 1 is a longitudinal cross-sectional view of the blower 1 according to the exemplary first embodiment of the present application. The blower 1 of this embodiment is a centrifugal fan and comprises a blade portion 60, a spindle motor 10, and a housing 70. The blower 1 draws air into the housing 70 along the central axis J through an intake port 73a. The drawn-in airflow is blown out in the circumferential direction from an outlet (not shown) formed on the radial outer surface of the housing 70 by the rotation of the spindle motor 10 equipped with the blade portion 60. In this embodiment, a centrifugal fan is used as an example of the blower 1, but the blower 1 is not limited to a centrifugal fan, and may be an axial flow fan, for example.

[0012] More specifically, the blade portion 60 is fixed to the spindle motor 10 via a cylindrical blade holder portion 50. The blade portion 60 is rotatable about a central axis J by the spindle motor 10. In this embodiment, the blade portion 60 is rotatable in both clockwise (Y2 direction) and counterclockwise (Y1 direction) directions about the central axis J when viewed from above.

[0013] The housing 70 houses the spindle motor 10 and the blade portion 60. The housing 70 has a cylindrical wall portion 71, a base portion 72, and a cover portion 73.

[0014] The cylindrical wall portion 71 covers the blade portion 60 from the radially outer side and has an outlet (not shown). The outlet is formed by a part of the cylindrical wall portion 71 opening radially outward. A cover portion 73 is positioned at the axial upper end of the cylindrical wall portion 71. The cover portion 73 covers the blade portion 60 from the axially upper side X1 and has an intake port 73a.

[0015] The spindle motor 10 is fixed to the base portion 72. The base portion 72 extends radially around the central axis J. The base portion 72 can be formed, for example, by resin molding, metal pressing, casting, etc.

[0016] (2. Configuration of the spindle motor) Figure 2 shows a longitudinal cross-sectional view of the spindle motor 10. The spindle motor 10 is an outer rotor type motor in which the rotor 30 rotates around the central axis J. The spindle motor 10 comprises a base portion 72, a stator 20, a rotor 30, and a fluid dynamic bearing 40.

[0017] The base portion 72 has a shaft insertion hole 72a that penetrates axially and is located on the central axis J. In this embodiment, the shaft insertion hole 72a penetrates the base portion 72 axially, but it does not have to penetrate. Furthermore, a substantially cylindrical holder portion 72b that protrudes axially is formed radially outward from the shaft insertion hole 72a. In this embodiment, the base portion 72 is part of the housing 70 and also part of the spindle motor 10, but the base portion 72 may be constructed from a separate component from the housing 70.

[0018] (2-1. Stator Configuration) The stator 20 has a stator core 21 and a plurality of coils 22. The stator core 21 surrounds the lower part of the shaft 41 and is fixed to the base portion 72. The stator core 21 is an annular laminated structure made of multiple stacked magnetic materials. The stator core 21 has a core back 21a and teeth 21b. The core back 21a is annular and is fitted to the outer circumferential surface of the holder portion 72b. Multiple teeth 21b protrude radially outward from the core back 21a.

[0019] The coil 22 is formed by a wire wound around each tooth 21b. The coil 22 is connected to a circuit board (not shown) via lead wires 22a.

[0020] (2-2. Rotor Configuration) The rotor 30 includes a hub member 31, a magnet 34, and a back iron 35. The hub member 31 includes a rotor cylindrical portion 32 and a magnet holding portion 33.

[0021] The rotor cylinder portion 32 extends axially, surrounding the sleeve 43, which will be described later. The rotor cylinder portion 32 is formed integrally with the sleeve 43. In this embodiment, the rotor cylinder portion 32 and the sleeve 43 are formed integrally, but they may be formed from separate components.

[0022] The magnet holder portion 33 is formed in a cylindrical shape, extending axially downward from the lower end of the rotor cylinder portion 32. In this embodiment, an annular magnet 34 is fixed to the inner circumferential surface of the magnet holder portion 33 via a back iron 35. Alternatively, the magnet 34 may be directly attached to the magnet holder portion 33 without using the back iron 35. The magnet 34 is positioned radially opposite the stator core 21. More specifically, the inner circumferential surface of the magnet 34 is the magnetic pole surface and is radially opposite the outer circumferential surfaces of the multiple teeth 21b of the stator core 21.

[0023] The outer circumferential surfaces of the magnet holder 33 and the rotor cylinder 32 are formed flush with each other, and the cylindrical blade holder 50 fits into them (see Figure 1). In this embodiment, the magnet holder 33 and the rotor cylinder 32 are formed flush with each other according to the shape of the blade holder 50, but they may not be formed flush and may have steps or other differences.

[0024] When drive current is supplied to the coil 22 of the spindle motor 10 via the circuit board, a radial magnetic flux is generated in the stator core 21. The magnetic field generated by the magnetic flux of the stator core 21 and the magnetic field generated by the magnet 34 act together to generate torque in the circumferential direction of the rotor 30. This torque causes the rotor 30 to rotate about the central axis J. The direction of rotation of the rotor 30 can be changed by changing the direction of the drive current supplied to the coil 22.

[0025] (2-3. Configuration of the fluid dynamic bearing) Figure 3 is an enlarged longitudinal cross-sectional view of the fluid dynamic bearing 40 of the spindle motor 10. The fluid dynamic bearing 40 in this embodiment is of the conical type and supports the rotor 30 so that it can rotate around the central axis J. In this embodiment, the fluid dynamic bearing 40 has a shaft 41, an upper annular portion 42a, a lower annular portion 42b, a sleeve 43, lubricating oil 44, and a sealing member 45.

[0026] The shaft 41 is a columnar member that extends along a central axis J that extends in the vertical direction. The lower end of the shaft 41 is press-fitted into the shaft insertion hole 72a. This fixes the shaft 41 to the base portion 72.

[0027] The shaft 41 has an upper annular portion 42a and a lower annular portion 42b. The upper annular portion 42a and the lower annular portion 42b protrude radially outward from the outer circumferential surface of the shaft 41. The upper annular portion 42a is positioned axially above the lower annular portion 42b. The lower annular portion 42b is positioned axially below the upper annular portion 42a.

[0028] In this embodiment, the upper annular portion 42a and the lower annular portion 42b are made of separate components from the shaft 41, but either the upper annular portion 42a or the lower annular portion 42b may be formed integrally with the shaft 41.

[0029] The upper annular portion 42a and the lower annular portion 42b are substantially conical in shape, and the upper and lower surfaces of the upper annular portion 42a and the lower annular portion 42b are formed to gradually decrease in diameter. Specifically, the upper annular portion 42a has an upper outer peripheral surface 421a whose diameter increases as it moves axially upward X1. The lower annular portion 42b has a lower outer peripheral surface 421b whose diameter increases as it moves axially downward X2.

[0030] Furthermore, the upper annular portion 42a has an upper annular portion communication hole 422a, and the lower annular portion 42b has a lower annular portion communication hole 422b (see Figure 3). The upper annular portion communication hole 422a is located radially inward from the upper outer peripheral surface 421a, extends along the upper outer peripheral surface 421a, and penetrates the upper annular portion 42a. The lower annular portion communication hole 422b is located radially inward from the lower outer peripheral surface 421b, extends along the lower outer peripheral surface 421b, and penetrates the lower annular portion 42b. Note that there may be one upper annular portion communication hole 422a and one lower annular portion communication hole 422b.

[0031] The sleeve 43 has a through hole 431 into which the shaft 41 is inserted, extends axially, covers the outer circumferential surface of the shaft 41, and is cylindrical in shape.

[0032] The through hole 431 has an upper inner surface 431a, a middle inner surface 431c, and a lower inner surface 431b, in that order from top to bottom. The upper inner surface 431a is inclined away from the central axis J as it is directed upward in the axial direction X1, and forms a small gap S opposite the upper outer surface 421a. The lower inner surface 431b is inclined away from the central axis J as it is directed downward in the axial direction, and forms a small gap S opposite the lower outer surface 421b. The middle inner surface 431c is formed along the central axis J and faces the outer surface of the shaft 41.

[0033] Furthermore, the sleeve 43 has a communication hole 432 that penetrates in the axial direction. The communication hole 432 is located at one location in the circumferential direction, but there may be multiple locations. The communication hole 432 is located radially outward from the radially inward ends of the upper inner circumferential surface 431a and the lower inner circumferential surface 431b. In this embodiment, the communication hole 432 is located radially outward from the axially upper end X1 of the upper inner circumferential surface 431a and the axially lower end X2 of the lower inner circumferential surface 431b.

[0034] Furthermore, the communication hole 432 communicates with the minute gap S formed between the upper outer circumferential surface 421a and the upper inner circumferential surface 431a, and the minute gap S formed between the lower outer circumferential surface 421b and the lower inner circumferential surface 431b, allowing the lubricating oil 44 to circulate. This further suppresses the accumulation of air bubbles in the lubricating oil 44 in the minute gap S.

[0035] In this case, by positioning the communication hole 432 radially outward from the axial upper X1 end of the upper inner circumferential surface 431a and the axial lower X2 end of the lower inner circumferential surface 431b, the accumulation of air bubbles in the lubricating oil 44 in the communication hole 432 can be further suppressed. Furthermore, by circulating the lubricating oil 44 through the communication hole 432, the generation of differential pressure between the upper outer circumferential surface 421a and the upper inner circumferential surface 431a, between the lower outer circumferential surface 421b and the lower inner circumferential surface 431b, and between the outer circumferential surface of the shaft 41 and the middle inner circumferential surface 431c can be suppressed. As a result, the sleeve 43 is stably supported so as to be rotatable relative to the shaft 41.

[0036] Furthermore, the upper annular communication hole 422a communicates with the minute gap S formed between the upper outer circumferential surface 421a and the upper inner circumferential surface 431a, allowing the lubricating oil 44 to circulate. The lower annular communication hole 422b communicates with the minute gap S formed between the lower outer circumferential surface 421b and the lower inner circumferential surface 431b, allowing the lubricating oil 44 to circulate. By providing the upper annular communication hole 422a and the lower annular communication hole 422b, the accumulation of air bubbles in the lubricating oil 44 in the minute gap S can be further suppressed. In addition, the generation of differential pressure between the upper outer circumferential surface 421a and the upper inner circumferential surface 431a, between the lower outer circumferential surface 421b and the lower inner circumferential surface 431b, and between the outer circumferential surface of the shaft 41 and the middle inner circumferential surface 431c can be further suppressed.

[0037] The sealing member 45 extends radially inward from both axial ends of the sleeve 43, covering the opening end of the communication hole 432, the upper annular portion 42a, and the lower annular portion 42b from the axial outside, respectively. At this time, a seal taper is formed between the sealing member 45 and the upper annular portion 42a, with the diameter gradually decreasing toward the axial downward X2. On the other hand, a seal taper is formed between the sealing member 45 and the lower annular portion 42b, with the diameter gradually decreasing toward the axial upward X1. As a result, the lubricating oil 44 is retained within the bearing by forming an interface, and evaporation is suppressed.

[0038] Lubricating oil 44 preferably consists of an ester as its main component. Specifically, examples include polyol ester oils, diester oils, and monoester oils. Oils with esters as their main component are suitable as lubricating oil 44 for fluid dynamic bearings because they have excellent wear resistance, thermal stability, and fluidity.

[0039] (2-4. Configuration of Upper and Lower Dynamic Pressure Grooves) Figure 4 is a longitudinal cross-sectional view showing an enlarged portion of the sleeve 43. In Figure 4, the solid arrow B indicates the direction of the fluid dynamic pressure induced in the lubricating oil 44 when the sleeve 43 is rotated counterclockwise (one circumferential direction) Y1 relative to the shaft 41. The dashed arrow C indicates the direction of the fluid dynamic pressure induced in the lubricating oil 44 when the sleeve 43 is rotated clockwise (the other circumferential direction) Y2 relative to the shaft 41.

[0040] At least one of the upper outer circumferential surface 421a and the upper inner circumferential surface 431a has an upper dynamic pressure fluid dynamic bearing 47a composed of upper dynamic pressure grooves 461a, 462a, and 463a that induce fluid dynamic pressure in the lubricating oil 44 during rotation. At least one of the lower outer circumferential surface 421b and the lower inner circumferential surface 431b has a lower dynamic pressure fluid dynamic bearing 47b composed of lower dynamic pressure grooves 461b, 462b, and 463b that induce fluid dynamic pressure in the lubricating oil 44 during rotation.

[0041] In this embodiment, the upper dynamic pressure grooves 461a, 462a, and 463a are located on the upper inner circumferential surface 431a, and the lower dynamic pressure grooves 461b, 462b, and 463b are located on the lower inner circumferential surface 431b. Alternatively, the upper dynamic pressure grooves 461a, 462a, and 463a may be located on the upper outer circumferential surface 421a, and the lower dynamic pressure grooves 461b, 462b, and 463b may be located on the lower outer circumferential surface 421b.

[0042] More specifically, the upper hydrodynamic fluid bearing 47a is composed of at least a first upper hydrodynamic groove row 471a, a second upper hydrodynamic groove row 472a, and a third upper hydrodynamic groove row 473a. The first upper hydrodynamic groove row 471a consists of upper hydrodynamic grooves 461a arranged circumferentially, which are inclined toward one side Y1 in the circumferential direction as they move toward the axial upper side X1. The second upper hydrodynamic groove row 472a is located adjacent to the first upper hydrodynamic groove row 471a on the axial lower side X2, and consists of multiple upper hydrodynamic grooves 462a arranged circumferentially, which are inclined toward the other side Y2 in the circumferential direction as they move toward the axial upper side X1. The third upper hydrodynamic groove row 473a is located adjacent to the second upper hydrodynamic groove row 472a on the axial lower side X2, and consists of multiple upper hydrodynamic grooves 463a arranged circumferentially, which are inclined toward one side Y1 in the circumferential direction as they move toward the axial upper side X1.

[0043] The lower hydrodynamic bearing 47b is at least composed of a first lower hydrodynamic groove row 471b, a second lower hydrodynamic groove row 472b, and a third lower hydrodynamic groove row 473b. The first lower hydrodynamic groove row 471b has hydrodynamic grooves 461b that tilt in one circumferential direction Y1 as they go toward the upper side X1 in the axial direction arranged in the circumferential direction. The second lower hydrodynamic groove row 472b is arranged adjacent to the upper side X1 in the axial direction of the first lower hydrodynamic groove row 471b, and a plurality of hydrodynamic grooves 462b that tilt in the other circumferential direction Y2 as they go toward the upper side X1 in the axial direction are arranged in the circumferential direction. The third lower hydrodynamic groove row 473b is arranged adjacent to the upper side X1 in the axial direction of the second lower hydrodynamic groove row 472b, and a plurality of hydrodynamic grooves 463b that tilt in one circumferential direction Y1 as they go toward the upper side X1 in the axial direction are arranged in the circumferential direction.

[0044] Also, between the third upper hydrodynamic groove row 473a and the third lower hydrodynamic groove row 473b in the axial direction, a blank region A where no hydrodynamic groove is formed is arranged. In the present embodiment, the blank region A is formed across the lower end portion of the upper inner peripheral surface 431a, the middle inner peripheral surface 431c, and the upper end portion of the lower inner peripheral surface 431b.

[0045] The upper hydrodynamic grooves 461a, 462a, 463a and the lower hydrodynamic grooves 461b, 462b, 463b induce hydrodynamic pressure in the lubricating oil 44 when the rotor 30 rotates. At this time, the hydrodynamic pressure is induced along the upper hydrodynamic grooves 461a, 462a, 463a and the lower hydrodynamic grooves 4, 61b, 462b, 463b respectively.

[0046] More specifically, as shown by the solid arrow B in FIG. 4, when the sleeve 43 is rotated in the counterclockwise direction (one circumferential direction) Y1 with respect to the shaft 41, the hydrodynamic pressure induced in the lubricating oil 44 by the first upper hydrodynamic groove row 471a acts in a direction approaching the boundary 48a between the first upper hydrodynamic groove row 471a and the second upper hydrodynamic groove row 472a along the upper hydrodynamic groove 461a. Also, the hydrodynamic pressure induced in the lubricating oil 44 by the second upper hydrodynamic groove row 472a acts in a direction approaching the boundary 48a along the upper hydrodynamic groove 462a. On the other hand, the hydrodynamic pressure induced in the lubricating oil 44 by the third upper hydrodynamic groove row, 473a acts in a direction away from the boundary 49a between the second upper hydrodynamic groove row 472a and the third upper hydrodynamic groove row 473a along the upper hydrodynamic groove 463a.

[0047] Also, the hydrodynamic pressure induced in the lubricating oil 44 by the third lower hydrodynamic groove row 473b acts in a direction approaching the boundary 49b between the second lower hydrodynamic groove row 472b and the third lower hydrodynamic groove row 473b along the lower hydrodynamic groove 463b. Further, the hydrodynamic pressure induced in the lubricating oil 44 by the second lower hydrodynamic groove row 472b acts in a direction approaching the boundary 49b along the lower hydrodynamic groove 462b. On the other hand, the hydrodynamic pressure induced in the lubricating oil 44 by the first lower hydrodynamic groove row 471b acts in a direction away from the boundary 48b between the first lower hydrodynamic groove row 471b and the second lower hydrodynamic groove row 472b along the lower hydrodynamic groove 461b.

[0048] Thus, when the sleeve 43 is rotated in the counterclockwise direction (one circumferential direction) Y1 with respect to the shaft 41, the hydrodynamic pressure induced in the lubricating oil 44 by the first upper hydrodynamic groove row 471a, the hydrodynamic pressure induced in the lubricating oil 44 by the second upper hydrodynamic groove row 472a, the hydrodynamic pressure induced in the lubricating oil 44 by the third lower hydrodynamic groove row 473b, and the hydrodynamic pressure induced in the lubricating oil 44 by the second lower hydrodynamic groove row 472b stably support the sleeve 43 so as to be relatively rotatable with respect to the shaft 41.

[0049] On the other hand, as shown by the dashed arrow C in FIG. 4, when the sleeve 43 is rotated in the clockwise direction (the other circumferential direction) Y2 with respect to the shaft 41, the hydrodynamic pressure induced in the lubricating oil 44 by the first upper hydrodynamic groove row 471a acts in a direction away from the boundary 48a. Further, the hydrodynamic pressure induced in the lubricating oil 44 by the second upper hydrodynamic groove row 472a acts in a direction approaching the boundary 49a between the second upper hydrodynamic groove row 472a and the third upper hydrodynamic groove row 473a along the upper hydrodynamic groove 462a. Also, the hydrodynamic pressure induced in the lubricating oil 44 by the third upper hydrodynamic groove row 473a acts in a direction approaching the boundary 49a along the upper hydrodynamic groove 463a.

[0050] Also, the hydrodynamic pressure induced in the lubricating oil 44 by the third lower hydrodynamic groove row 473b acts in a direction away from the boundary 49b between the second lower hydrodynamic groove row 472b and the third lower hydrodynamic groove row 473b along the lower hydrodynamic groove 463b. Further, the hydrodynamic pressure induced in the lubricating oil 44 by the second lower hydrodynamic groove row 472b acts in a direction approaching the boundary 48b between the first lower hydrodynamic groove row

[0051] As a result, when the sleeve 43 is rotated clockwise (in the other circumferential direction) Y2 relative to the shaft 41, the fluid dynamic pressure induced in the lubricating oil 44 at the second upper dynamic pressure groove row 472a, the fluid dynamic pressure induced in the lubricating oil 44 at the third upper dynamic pressure groove row 473a, the fluid dynamic pressure induced in the lubricating oil 44 at the second lower dynamic pressure groove row 472b, and the fluid dynamic pressure induced in the lubricating oil 44 at the first lower dynamic pressure groove row 471b allows the sleeve 43 to be stably supported so as to be rotatable relative to the shaft 41.

[0052] Therefore, even when the sleeve 43 is rotated relative to the shaft 41 in either the one Y1 or the other Y2 direction in the circumferential direction, the sleeve 43 is stably supported so as to be rotatable relative to the shaft 41. As a result, stable rotational performance can be obtained even when the sleeve 43 rotates at high speed relative to the shaft 41 in either the one Y1 or the other Y2 direction in the circumferential direction. Consequently, the generation of abnormal noise and vibration can be reduced. Furthermore, the difference between the rotational performance when the sleeve 43 rotates relative to the shaft 41 in the one Y1 direction in the circumferential direction and the rotational performance when the sleeve 43 rotates relative to the shaft 41 in the other Y2 direction in the circumferential direction can be reduced. Thus, a fluid dynamic bearing 40, a spindle motor 10, and a blower 1 equipped therewith can be provided that can stabilize the rotational performance of the sleeve 43 for rotation in both directions relative to the shaft 41.

[0053] In this case, by arranging the blank area A, the sleeve 43 is stably supported by the shaft 41 at two locations, the upper hydrodynamic bearing 47a and the lower hydrodynamic bearing 47b, allowing for relative rotation. This improves the bearing rigidity of the hydrodynamic bearing 40.

[0054] Furthermore, it is preferable that the inclination angle of the upper dynamic pressure groove 461a with respect to the central axis J when the first upper dynamic pressure groove row 471a is unfolded in the circumferential direction is the same as the inclination angle of the lower dynamic pressure groove 461b with respect to the central axis J when the first lower dynamic pressure groove row 471b is unfolded in the circumferential direction. Furthermore, it is preferable that the inclination angle of the upper dynamic pressure groove 462a with respect to the central axis J when the second upper dynamic pressure groove row 472a is unfolded in the circumferential direction is the same as the inclination angle of the lower dynamic pressure groove 462b with respect to the central axis J when the second lower dynamic pressure groove row 472b is unfolded in the circumferential direction. Furthermore, it is preferable that the inclination angle of the upper dynamic pressure groove 463a with respect to the central axis J when the third upper dynamic pressure groove row 473a is unfolded in the circumferential direction is the same as the inclination angle of the lower dynamic pressure groove 461b with respect to the central axis J when the third lower dynamic pressure groove row 473b is unfolded in the circumferential direction.

[0055] As a result, even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or the other Y2, the sleeve 43 is supported more stably and rotatably relative to the shaft 41.

[0056] Furthermore, in this embodiment, the number of upper dynamic pressure grooves 461a constituting the first upper dynamic pressure groove row 471a is large, followed by the number of upper dynamic pressure grooves 462a constituting the second upper dynamic pressure groove row 472a, and then the number of upper dynamic pressure grooves 463a constituting the third upper dynamic pressure groove row 473a.

[0057] As a result, even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or Y2, the lubricating oil 44 can be pumped into the bearing center, thus suppressing negative pressure inside the bearing. Furthermore, by using different combinations of the number of dynamic pressure grooves constituting the first upper dynamic pressure groove row 471a, the number of dynamic pressure grooves constituting the second upper dynamic pressure groove row 472a, and the number of dynamic pressure grooves constituting the third upper dynamic pressure groove row 473a, it is possible to suppress noise of a specific frequency corresponding to the number of dynamic pressure grooves during rotation. Therefore, the sleeve 43 is stably supported on the shaft 41 while remaining rotatable relative to it.

[0058] In this case, it is preferable that the number of upper dynamic pressure grooves 461a constituting the first upper dynamic pressure groove row 471a is two or more greater than the number of upper dynamic pressure grooves 462a constituting the second upper dynamic pressure groove row 472a, and the number of upper dynamic pressure grooves 462a constituting the second upper dynamic pressure groove row 472a is two or more greater than the number of upper dynamic pressure grooves 463a constituting the third upper dynamic pressure groove row 473a. For example, the number of upper dynamic pressure grooves 461a is 20, the number of upper dynamic pressure grooves 462a is 17, and the number of upper dynamic pressure grooves 463a is 14.

[0059] As a result, even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or Y2, the lubricating oil 44 can be pumped into the bearing center, thus suppressing negative pressure inside the bearing. Furthermore, by using different combinations of the number of dynamic pressure grooves constituting the first upper dynamic pressure groove row 471a, the number of dynamic pressure grooves constituting the second upper dynamic pressure groove row 472a, and the number of dynamic pressure grooves constituting the third upper dynamic pressure groove row 473a, it is possible to suppress noise of a specific frequency corresponding to the number of dynamic pressure grooves during rotation. Therefore, the sleeve 43 is stably supported on the shaft 41 while remaining rotatable relative to it.

[0060] Furthermore, it is preferable that the number of upper dynamic pressure grooves 461a constituting the first upper dynamic pressure groove row 471a, the number of upper dynamic pressure grooves 462a constituting the second upper dynamic pressure groove row 472a, and the number of upper dynamic pressure grooves 463a constituting the third upper dynamic pressure groove row 473a are all prime numbers. For example, the number of upper dynamic pressure grooves 461a may be 19, the number of upper dynamic pressure grooves 462a may be 17, and the number of upper dynamic pressure grooves 463a may be 13. Alternatively, the number of upper dynamic pressure grooves 461a may be 23, the number of upper dynamic pressure grooves 462a may be 19, and the number of upper dynamic pressure grooves 463a may be 17.

[0061] As a result, even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or Y2, the lubricating oil 44 can be pumped into the bearing center, thus suppressing negative pressure inside the bearing. Furthermore, by using different prime number combinations for the number of dynamic pressure grooves constituting the first upper dynamic pressure groove row 471a, the second upper dynamic pressure groove row 472a, and the third upper dynamic pressure groove row 473a, noise of a specific frequency corresponding to the number of dynamic pressure grooves can be suppressed during rotation. More specifically, noise of the frequency component of the least common divisor of the number of dynamic pressure grooves in the first upper dynamic pressure groove row 471a, the second upper dynamic pressure groove row 472a, and the third upper dynamic pressure groove row 473a can be suppressed. Therefore, the sleeve 43 is stably supported by the shaft 41 so as to be rotatable relative to it.

[0062] Furthermore, it is preferable that the number of lower dynamic pressure grooves 461b constituting the first lower dynamic pressure groove row 471b is the same as the number of upper dynamic pressure grooves 461a constituting the first upper dynamic pressure groove row 471a. Furthermore, it is preferable that the number of lower dynamic pressure grooves 462b constituting the second lower dynamic pressure groove row 472b is the same as the number of upper dynamic pressure grooves 462a constituting the second upper dynamic pressure groove row 472a. Furthermore, it is preferable that the number of lower dynamic pressure grooves 463b constituting the third lower dynamic pressure groove row 473b is the same as the number of upper dynamic pressure grooves 463a constituting the third upper dynamic pressure groove row 473a.

[0063] As a result, even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or the other Y2, the sleeve 43 is supported more stably and rotatably relative to the shaft 41.

[0064] Furthermore, the axial width of the first upper dynamic pressure groove row 471a, the axial width of the second upper dynamic pressure groove row 472a, the axial width of the third upper dynamic pressure groove row 473a, the axial width of the first lower dynamic pressure groove row 471b, the axial width of the second lower dynamic pressure groove row 472b, and the axial width of the third lower dynamic pressure groove row 473b are all the same.

[0065] As a result, even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or Y2, the generation of negative pressure due to the dynamic pressure difference in the upper hydrodynamic bearing 47a and the lower hydrodynamic bearing 47b can be suppressed, and the sleeve 43 is stably supported on the shaft 41 in a relative rotational manner.

[0066] Furthermore, the axial width between the boundary 48a between the first upper dynamic pressure groove row 471a and the second upper dynamic pressure groove row 472a and the boundary 49b between the second lower dynamic pressure groove row 472b and the third lower dynamic pressure groove row 473b is the same as the axial width between the boundary 49a between the second upper dynamic pressure groove row 472a and the third upper dynamic pressure groove row 473a and the boundary 48b between the first lower dynamic pressure groove row 471b and the second lower dynamic pressure groove row 472b.

[0067] This reduces the difference between the bearing rigidity when the sleeve 43 rotates in one circumferential direction Y1 relative to the shaft 41 and the bearing rigidity when the sleeve 43 rotates in the other circumferential direction Y2 relative to the shaft 41. Therefore, the distance between bearings can be kept constant in either direction of rotation, and the difference in rotational performance in each direction of rotation can be reduced.

[0068] Furthermore, when the first upper dynamic pressure groove row 471a, the second upper dynamic pressure groove row 472a, and the third upper dynamic pressure groove row 473a are unfolded in the circumferential direction, the upper dynamic pressure grooves 461a, 462a, and 463a are preferably point-symmetrical with respect to the lower dynamic pressure grooves 461b, 462b, and 463b when the first lower dynamic pressure groove row 471b, the second lower dynamic pressure groove row 472b, and the third lower dynamic pressure groove row 473b are unfolded in the circumferential direction, with respect to the midpoint P. The midpoint P is located midway between the axial lower end (the axial lower X2 end) of the upper dynamic pressure fluid bearing 47a and the axial upper end (the axial upper X1 end) of the lower dynamic pressure fluid bearing 47b on the central axis J.

[0069] As a result, regardless of whether the sleeve 43 is rotated relative to the shaft 41 in one direction Y1 or the other Y2 in the circumferential direction, the sleeve 43 is stably supported by the shaft 41, allowing for relative rotation. Furthermore, the difference between the rotational performance when the sleeve 43 rotates relative to the shaft 41 in one direction Y1 and the rotational performance when the sleeve 43 rotates relative to the shaft 41 in the other direction Y2 in the circumferential direction can be further reduced.

[0070] <Second Embodiment> Next, a second embodiment of the present invention will be described. Figure 5 is a longitudinal cross-sectional view of the pulley device 100 of the second embodiment. For convenience of explanation, the same reference numerals are used for parts that are the same as those for the fluid dynamic bearing 40 of the first embodiment shown in Figures 1 to 4 above. The pulley device 100 of the second embodiment comprises a fluid dynamic bearing 40 and a disc portion 90. The disc portion 90 is formed in a cylindrical shape and is positioned radially outward of the sleeve 43. A groove portion 91 is formed on the outer circumferential surface of the disc portion 90, recessed radially inward and extending circumferentially. The groove portion 91 receives a linear member (not shown). Other parts are the same as in the first embodiment.

[0071] Furthermore, the shaft 41 protrudes axially outward from the sleeve 43 and has a shaft recess 41a. The shaft recess 41a is recessed from at least one end face in the axial direction of the shaft 41 toward the center. In this embodiment, the shaft recess 41a is formed on both end faces in the axial direction of the shaft 41.

[0072] For example, the shaft recess 41a has a threaded portion 41b formed on its inner circumferential surface, into which a screw (not shown) is screwed. One end of the shaft 41 in the axial direction is fixed via the screw, and the linear member is received by the groove 91 of the disc portion 90. As the disc portion 90 rotates, the linear member received by the groove 91 can be smoothly guided without twisting. Furthermore, by using the fluid dynamic bearing 40 of this embodiment in the pulley device 100, stable rotational performance can be obtained even when the sleeve 43 rotates at high speed in one Y1 or the other Y2 direction in the circumferential direction relative to the shaft 41. At this time, the generation of abnormal noise and vibration of the pulley device 100 can be reduced.

[0073] Furthermore, the disc portion 90 can be applied to a spool. For example, instead of grooves 91, annular flange portions (not shown) protruding radially outward from both axial ends are formed on the outer circumferential surface of the disc portion 90. By fixing one end of a linear member to the disc portion 90 and rotating the disc portion 90, the winding and unwinding operations of the linear member can be performed efficiently. This also allows the pulley device 100 to be used as a winding device.

[0074] <Other> The above embodiments are merely illustrative examples of the present invention. The configuration of the embodiments may be modified as appropriate without exceeding the technical spirit of the present invention. Furthermore, the embodiments may be combined to the extent possible. In this embodiment, the upper dynamic fluid dynamic bearing 47a is composed of three rows of upper dynamic grooves: a first upper dynamic groove row 471a, a second upper dynamic groove row 472a, and a third upper dynamic groove row 473a. However, additional upper dynamic groove rows may be added to make it four or more rows.

[0075] Similarly, the lower hydrodynamic bearing 47b is composed of three rows of grooves: a first row of grooves 471b, a second row of grooves 472b, and a third row of grooves 473b. However, additional rows of grooves may be added to make it four or more rows in total.

[0076] In this case, it is preferable that the upper hydrodynamic bearing 47a and the lower hydrodynamic bearing 47b have a point-symmetric shape with respect to the midpoint P. This ensures that even when the sleeve 43 is rotated relative to the shaft 41 in either the circumferential direction Y1 or Y2, the sleeve 43 is stably supported by the shaft 41 in a way that allows for relative rotation.

[0077] <Note> As described above, a fluid dynamic bearing (40) according to one aspect of the present disclosure comprises a shaft (41) arranged along a central axis (J) extending in the vertical direction, a sleeve (43) having a through hole (431) into which the shaft is inserted and supported by the shaft so as to be rotatable relative to the sleeve, and a lubricating oil (44) interposed between the shaft and the sleeve, wherein the shaft has an upper annular portion (42a) that protrudes radially outward from its outer circumferential surface and is located on the axially upper side, and a lower annular portion (42b) that is located on the axially lower side, and the diameter of the upper annular portion increases as it moves axially upward The upper outer circumferential surface (421a) is larger, the lower annular portion has a lower outer circumferential surface (421b) whose diameter increases as it is directed downward in the axial direction, the through hole has an upper inner circumferential surface (431a) that is inclined in a direction away from the central axis as it is directed upward in the axial direction (X1) and facing the upper outer circumferential surface, and a lower inner circumferential surface (431b) that is inclined in a direction away from the central axis as it is directed downward in the axial direction (X2) and facing the lower outer circumferential surface, the sleeve has a communication hole (432) that is radially outward from the radially inward ends of the upper inner circumferential surface and the lower inner circumferential surface and penetrates in the axial direction The communication hole communicates with a minute gap (S) formed between the upper outer circumferential surface and the upper inner circumferential surface and a minute gap (S) formed between the lower outer circumferential surface and the lower inner circumferential surface, through which the lubricating oil circulates, and at least one of the upper outer circumferential surface and the upper inner circumferential surface has an upper dynamic pressure fluid dynamic bearing (47a) composed of upper dynamic pressure grooves (461a, 462a, 463a) that induce fluid dynamic pressure in the lubricating oil when rotating, and at least one of the lower outer circumferential surface and the lower inner circumferential surface has a lower dynamic pressure flow groove (461b, 462b, 463b) that induce fluid dynamic pressure in the lubricating oil when rotating The upper hydrodynamic bearing has a body hydrodynamic bearing (47b), and the upper hydrodynamic fluid hydrodynamic bearing is composed of at least: a first upper hydrodynamic groove row (471a) in which a plurality of upper hydrodynamic grooves are arranged in the circumferential direction and are inclined to one side in the circumferential direction as they are directed upward in the axial direction; a second upper hydrodynamic groove row (472a) arranged adjacent to the axially lower side of the first upper hydrodynamic groove row, in which a plurality of upper hydrodynamic grooves are arranged in the circumferential direction and are inclined to the other side in the circumferential direction as they are directed upward in the axial direction; and a third upper hydrodynamic groove row (473a) arranged adjacent to the axially lower side of the second upper hydrodynamic groove row, in which a plurality of upper hydrodynamic grooves are arranged in the circumferential direction and are inclined to one side in the circumferential direction as they are directed upward in the axial direction.The lower hydrodynamic bearing is at least composed of: a first row of lower hydrodynamic grooves (471b) having multiple lower hydrodynamic grooves arranged circumferentially, each inclined to one side in the circumferential direction as it extends axially upward; a second row of lower hydrodynamic grooves (472b) positioned adjacent to the first row of lower hydrodynamic grooves on the axially upward side, each having multiple lower hydrodynamic grooves arranged circumferentially, each inclined to the other side in the circumferential direction as it extends axially upward; and a third row of lower hydrodynamic grooves (473b) positioned adjacent to the second row of lower hydrodynamic grooves on the axially upward side, each having multiple lower hydrodynamic grooves arranged circumferentially, each inclined to one side in the circumferential direction as it extends axially upward (first configuration).

[0078] Furthermore, in the first configuration described above, the inclination angle of the upper hydrodynamic grooves with respect to the central axis when the first upper hydrodynamic groove row is unfolded in the circumferential direction is the same as the inclination angle of the lower hydrodynamic grooves with respect to the central axis when the first lower hydrodynamic groove row is unfolded in the circumferential direction; the inclination angle of the upper hydrodynamic grooves with respect to the central axis when the second upper hydrodynamic groove row is unfolded in the circumferential direction is the same as the inclination angle of the lower hydrodynamic grooves with respect to the central axis when the second lower hydrodynamic groove row is unfolded in the circumferential direction; and the inclination angle of the upper hydrodynamic grooves with respect to the central axis when the third upper hydrodynamic groove row is unfolded in the circumferential direction is the same as the inclination angle of the lower hydrodynamic grooves with respect to the central axis when the third lower hydrodynamic groove row is unfolded in the circumferential direction (second configuration).

[0079] Furthermore, in the first or second configuration described above, the number of upper dynamic pressure grooves constituting the first upper dynamic pressure groove row, the number of upper dynamic pressure grooves constituting the second upper dynamic pressure groove row, and the number of upper dynamic pressure grooves constituting the third upper dynamic pressure groove row may be set in increasing order (third configuration).

[0080] Furthermore, in any of the first to third configurations described above, the number of upper dynamic pressure grooves constituting the first upper dynamic pressure groove row may be two or more greater than the number of upper dynamic pressure grooves constituting the second upper dynamic pressure groove row, and the number of upper dynamic pressure grooves constituting the second upper dynamic pressure groove row may be two or more greater than the number of upper dynamic pressure grooves constituting the third upper dynamic pressure groove row (fourth configuration).

[0081] Furthermore, in any of the first to fourth configurations described above, the number of upper dynamic pressure grooves constituting the first upper dynamic pressure groove row, the number of upper dynamic pressure grooves constituting the second upper dynamic pressure groove row, and the number of upper dynamic pressure grooves constituting the third upper dynamic pressure groove row may each be prime numbers (fifth configuration).

[0082] Furthermore, in any of the first to fifth configurations described above, the number of lower dynamic pressure grooves constituting the first lower dynamic pressure groove row is the same as the number of upper dynamic pressure grooves constituting the first upper dynamic pressure groove row, the number of lower dynamic pressure grooves constituting the second lower dynamic pressure groove row is the same as the number of upper dynamic pressure grooves constituting the second upper dynamic pressure groove row, and the number of lower dynamic pressure grooves constituting the third lower dynamic pressure groove row is the same as the number of upper dynamic pressure grooves constituting the third upper dynamic pressure groove row (sixth configuration).

[0083] Furthermore, in any of the first to sixth configurations described above, the axial width of the first upper dynamic pressure groove row, the axial width of the second upper dynamic pressure groove row, the axial width of the third upper dynamic pressure groove row, the axial width of the first lower dynamic pressure groove row, the axial width of the second lower dynamic pressure groove row, and the axial width of the third lower dynamic pressure groove row may be the same (seventh configuration).

[0084] Furthermore, in any of the first to seventh configurations described above, the axial width between the boundary between the first upper dynamic pressure groove row and the second upper dynamic pressure groove row and the boundary between the second lower dynamic pressure groove row and the third lower dynamic pressure groove row may be the same as the axial width between the boundary between the second upper dynamic pressure groove row and the third upper dynamic pressure groove row and the boundary between the first lower dynamic pressure groove row and the second lower dynamic pressure groove row (eighth configuration).

[0085] Furthermore, in any of the first to eighth configurations described above, the upper dynamic pressure grooves when the first upper dynamic pressure groove row, the second upper dynamic pressure groove row, and the third upper dynamic pressure groove row are unfolded in the circumferential direction may be configured to have a point-symmetric shape with respect to the lower dynamic pressure grooves when the first lower dynamic pressure groove row, the second lower dynamic pressure groove row, and the third lower dynamic pressure groove row are unfolded in the circumferential direction, with respect to the midpoint (P) on the central axis which is midway between the axially lower end of the upper dynamic pressure fluid hydrodynamic bearing and the axially upper end of the lower dynamic pressure fluid hydrodynamic bearing (the ninth configuration).

[0086] Furthermore, in any of the first to ninth configurations described above, the communication hole may be positioned radially outward from the axial upper end of the upper inner circumferential surface and the axial lower end of the lower inner circumferential surface (the tenth configuration).

[0087] Furthermore, in any of the first to tenth configurations described above, the upper annular portion may be configured such that it is radially inward from the upper outer circumferential surface and has an upper annular portion communication hole (422a) that extends along and penetrates the upper outer circumferential surface, and the lower annular portion may be configured such that it is radially inward from the lower outer circumferential surface and has a lower annular portion communication hole (422b) that extends along and penetrates the lower outer circumferential surface (the eleventh configuration).

[0088] Furthermore, in any of the first to eleventh configurations described above, a blank region (A) in which the upper and lower dynamic pressure grooves are not formed may be located between the axial direction of the third upper dynamic pressure groove row and the third lower dynamic pressure groove row (the twelfth configuration).

[0089] Furthermore, in any of the first to twelfth configurations described above, the shaft may protrude axially outward from the sleeve, and the shaft may have a shaft recess (41a) that is recessed from at least one end face in the axial direction toward the center (the thirteenth configuration).

[0090] Furthermore, a pulley device (100) according to one aspect of the present disclosure comprises a fluid dynamic bearing having any of the first to thirteen configurations described above, and a disc portion (90) arranged radially outward of the sleeve (fourteenth configuration).

[0091] Furthermore, a spindle motor (10) according to one aspect of the present disclosure includes a fluid dynamic bearing having any of the first to thirteenth configurations described above (fifth configuration).

[0092] Furthermore, a blower (1) according to one aspect of the present disclosure comprises a spindle motor having the configuration of the 15th configuration described above, and a blade portion 60 that can rotate about the central axis by the spindle motor (16th configuration).

[0093] According to the present invention, for example, it can be used in a blower or a pulley system.

[0094] 1 Blower 10 Spindle motor 20 Stator 21 Stator core 21a Core back 21b Teeth 22 Coil 22a Lead wire 30 Rotor 31 Hub member 32 Rotor cylinder 33 Magnet holder 34 Magnet 35 Back iron 40 Fluid dynamic bearing 41 Shaft 41a Shaft recess 41b Threaded part 42a Upper annular part 42b Lower annular part 43 Sleeve 44 Lubricating oil 45 Seal member 46a Upper dynamic groove 47a Upper fluid dynamic bearing 47b Lower fluid dynamic bearing 48a, 48b, 49a, 49b Boundary 50 Blade holder 60 Blade part 70 Housing 71 Cylinder wall part 72 Base part 72a Shaft insertion hole 72b Holder part 73 Cover part 73a Exhaust port 90 Disc part 91 Groove part 100 Pulley device 421a Upper outer peripheral surface 421b Lower outer peripheral surface 422a Upper annular part communication hole 422b Lower annular part communication hole 431 Through hole 431a Upper inner peripheral surface 431b Lower inner peripheral surface 431c Middle inner peripheral surface 432 Communication holes 461a, 462a, 463a Upper dynamic pressure groove 461b, 462b, 463b Lower dynamic pressure groove 471a First row of upper dynamic pressure grooves 471b First row of lower dynamic pressure grooves 472a Second row of upper dynamic pressure grooves 472b Second row of lower dynamic pressure grooves 473a Third row of upper dynamic pressure grooves 473b Third row of lower dynamic pressure grooves A Blank area B Solid arrow C, dashed arrow J, central axis, P midpoint, S minute gap, X1 upper axial side, X2 lower axial side, Y1 one circumferential direction (counterclockwise), Y2 the other circumferential direction (clockwise)

Claims

1. A shaft arranged along a central axis extending in the vertical direction; a sleeve having a through hole into which the shaft is inserted and supported by the shaft so as to be rotatable relative to the shaft; and a lubricating oil interposed between the shaft and the sleeve, wherein the shaft has an upper annular portion that protrudes radially outward from its outer circumferential surface and is located on the axially upper side, and a lower annular portion that is located on the axially lower side, the upper annular portion has an upper outer circumferential surface whose diameter increases as it is directed axially upward, the lower annular portion has a lower outer circumferential surface whose diameter increases as it is directed axially downward, the through hole has an upper inner circumferential surface that is inclined in a direction away from the central axis as it is directed axially upward and facing the upper outer circumferential surface, and a lower inner circumferential surface that is inclined in a direction away from the central axis as it is directed axially downward and facing the lower outer circumferential surface, the sleeve has a communication hole that is located radially outward from the radially inner ends of the upper inner circumferential surface and the lower inner circumferential surface and penetrates through in the axial direction. The communication hole communicates with a minute gap formed between the upper outer surface and the upper inner surface and a minute gap formed between the lower outer surface and the lower inner surface, and the lubricating oil circulates through it. At least one of the upper outer surface and the upper inner surface has an upper dynamic pressure fluid dynamic bearing composed of an upper dynamic pressure groove that induces fluid dynamic pressure in the lubricating oil when it rotates. At least one of the lower outer surface and the lower inner surface has a lower dynamic pressure fluid dynamic bearing composed of a lower dynamic pressure groove that induces fluid dynamic pressure in the lubricating oil when it rotates. The upper dynamic pressure fluid dynamic bearing comprises a first row of upper dynamic pressure grooves arranged circumferentially, each of which is inclined to one side in the circumferential direction as it moves axially upward, and a second row of upper dynamic pressure grooves arranged circumferentially, each of which is inclined to the other side in the circumferential direction as it moves axially upward. The lower hydrodynamic bearing comprises at least a third upper hydrodynamic groove row, which is arranged adjacent to the axially lower side of the second upper hydrodynamic groove row and has multiple upper hydrodynamic grooves arranged in the circumferential direction, each of which is inclined to one side in the circumferential direction as it extends axially upward, and a first lower hydrodynamic groove row, which has multiple lower hydrodynamic grooves arranged in the circumferential direction, each of which is inclined to one side in the circumferential direction as it extends axially upward,A fluid dynamic bearing comprising at least: a second row of lower dynamic grooves arranged adjacent to the axially upper side of the first row of lower dynamic grooves, each having a plurality of lower dynamic grooves arranged circumferentially that are inclined to the other circumferential direction as they move axially upward; and a third row of lower dynamic grooves arranged adjacent to the axially upper side of the second row of lower dynamic grooves, each having a plurality of lower dynamic grooves arranged circumferentially that are inclined to one circumferential direction as they move axially upward.

2. The fluid dynamic bearing according to claim 1, wherein when the first row of upper dynamic grooves is unfolded in the circumferential direction, the inclination angle of the upper dynamic grooves with respect to the central axis is the same as the inclination angle of the lower dynamic grooves with respect to the central axis when the first row of lower dynamic grooves is unfolded in the circumferential direction, the inclination angle of the upper dynamic grooves with respect to the central axis when the second row of upper dynamic grooves is unfolded in the circumferential direction, the inclination angle of the lower dynamic grooves with respect to the central axis when the second row of lower dynamic grooves is unfolded in the circumferential direction, and the inclination angle of the upper dynamic grooves with respect to the central axis when the third row of upper dynamic grooves is unfolded in the circumferential direction, the inclination angle of the upper dynamic grooves with respect to the central axis is the same as the inclination angle of the lower dynamic grooves with respect to the central axis when the third row of lower dynamic grooves is unfolded in the circumferential direction.

3. A fluid dynamic bearing according to claim 1 or claim 2, wherein the number of upper dynamic grooves constituting the first upper dynamic groove row, the number of upper dynamic grooves constituting the second upper dynamic groove row, and the number of upper dynamic grooves constituting the third upper dynamic groove row are in increasing order.

4. The fluid dynamic bearing according to claim 3, wherein the number of upper dynamic grooves constituting the first upper dynamic groove row is two or more than the number of upper dynamic grooves constituting the second upper dynamic groove row, and the number of upper dynamic grooves constituting the second upper dynamic groove row is two or more than the number of upper dynamic grooves constituting the third upper dynamic groove row.

5. The fluid dynamic bearing according to claim 4, wherein the number of upper dynamic grooves constituting the first upper dynamic groove row, the number of upper dynamic grooves constituting the second upper dynamic groove row, and the number of upper dynamic grooves constituting the third upper dynamic groove row are all prime numbers.

6. The fluid dynamic bearing according to claim 3, wherein the number of lower dynamic grooves constituting the first lower dynamic groove row is the same as the number of upper dynamic grooves constituting the first upper dynamic groove row, the number of lower dynamic grooves constituting the second lower dynamic groove row is the same as the number of upper dynamic grooves constituting the second upper dynamic groove row, and the number of lower dynamic grooves constituting the third lower dynamic groove row is the same as the number of upper dynamic grooves constituting the third upper dynamic groove row.

7. The fluid dynamic bearing according to claim 1 or 2, wherein the axial width of the first upper dynamic groove row, the axial width of the second upper dynamic groove row, the axial width of the third upper dynamic groove row, the axial width of the first lower dynamic groove row, the axial width of the second lower dynamic groove row, and the axial width of the third lower dynamic groove row are all the same.

8. The fluid dynamic bearing according to claim 1 or 2, wherein the axial width between the boundary between the first upper dynamic groove row and the second upper dynamic groove row and the boundary between the second lower dynamic groove row and the third lower dynamic groove row is the same as the axial width between the boundary between the second upper dynamic groove row and the third upper dynamic groove row and the boundary between the first lower dynamic groove row and the second lower dynamic groove row.

9. The fluid dynamic bearing according to claim 1 or 2, wherein when the first upper dynamic groove row, the second upper dynamic groove row, and the third upper dynamic groove row are unfolded in the circumferential direction, the upper dynamic grooves are point-symmetric with respect to the lower dynamic grooves when the first lower dynamic groove row, the second lower dynamic groove row, and the third lower dynamic groove row are unfolded in the circumferential direction, with respect to the midpoint on the central axis which is midway between the axially lower end of the upper fluid dynamic bearing and the axially upper end of the lower fluid dynamic bearing.

10. The fluid dynamic bearing according to claim 1 or 2, wherein the communication hole is positioned radially outward from the axially upper end of the upper inner circumferential surface and the axially lower end of the lower inner circumferential surface.

11. The fluid dynamic bearing according to claim 1 or 2, wherein the upper annular portion is located radially inward from the upper outer circumferential surface and has an upper annular portion communication hole that extends along and penetrates the upper outer circumferential surface, and the lower annular portion is located radially inward from the lower outer circumferential surface and has a lower annular portion communication hole that extends along and penetrates the lower outer circumferential surface.

12. The fluid dynamic bearing according to claim 1 or claim 2, wherein a blank region in which the upper dynamic grooves and the lower dynamic grooves are not formed is disposed between the axial direction of the third upper dynamic groove row and the third lower dynamic groove row.

13. The fluid dynamic bearing according to claim 1 or 2, wherein the shaft protrudes axially outward from the sleeve, and the shaft has a shaft recess that is recessed from at least one end face in the axial direction toward the center.

14. A pulley device comprising a fluid dynamic bearing as described in claim 13, and a disc portion disposed radially outward of the sleeve.

15. A spindle motor comprising a fluid dynamic bearing according to claim 1 or claim 2.

16. A blower comprising a spindle motor according to claim 15, and a blade portion rotatable about the central axis by the spindle motor.

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