US20130004348A1 - Dynamic pressure bearing apparatus and fan - Google Patents
Dynamic pressure bearing apparatus and fan Download PDFInfo
- Publication number
- US20130004348A1 US20130004348A1 US13/523,478 US201213523478A US2013004348A1 US 20130004348 A1 US20130004348 A1 US 20130004348A1 US 201213523478 A US201213523478 A US 201213523478A US 2013004348 A1 US2013004348 A1 US 2013004348A1
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- Prior art keywords
- gap
- circumferential surface
- dynamic pressure
- bearing portion
- bearing
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/05—Shafts or bearings, or assemblies thereof, specially adapted for elastic fluid pumps
- F04D29/056—Bearings
- F04D29/057—Bearings hydrostatic; hydrodynamic
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D25/00—Pumping installations or systems
- F04D25/02—Units comprising pumps and their driving means
- F04D25/06—Units comprising pumps and their driving means the pump being electrically driven
- F04D25/0606—Units comprising pumps and their driving means the pump being electrically driven the electric motor being specially adapted for integration in the pump
- F04D25/0613—Units comprising pumps and their driving means the pump being electrically driven the electric motor being specially adapted for integration in the pump the electric motor being of the inside-out type, i.e. the rotor is arranged radially outside a central stator
- F04D25/062—Details of the bearings
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D25/00—Pumping installations or systems
- F04D25/02—Units comprising pumps and their driving means
- F04D25/06—Units comprising pumps and their driving means the pump being electrically driven
- F04D25/0606—Units comprising pumps and their driving means the pump being electrically driven the electric motor being specially adapted for integration in the pump
- F04D25/0613—Units comprising pumps and their driving means the pump being electrically driven the electric motor being specially adapted for integration in the pump the electric motor being of the inside-out type, i.e. the rotor is arranged radially outside a central stator
- F04D25/0626—Details of the lubrication
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/05—Shafts or bearings, or assemblies thereof, specially adapted for elastic fluid pumps
- F04D29/051—Axial thrust balancing
- F04D29/0513—Axial thrust balancing hydrostatic; hydrodynamic thrust bearings
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/06—Lubrication
- F04D29/063—Lubrication specially adapted for elastic fluid pumps
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/08—Sealings
- F04D29/083—Sealings especially adapted for elastic fluid pumps
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F16C17/10—Sliding-contact bearings for exclusively rotary movement for both radial and axial load
- F16C17/102—Sliding-contact bearings for exclusively rotary movement for both radial and axial load with grooves in the bearing surface to generate hydrodynamic pressure
- F16C17/107—Sliding-contact bearings for exclusively rotary movement for both radial and axial load with grooves in the bearing surface to generate hydrodynamic pressure with at least one surface for radial load and at least one surface for axial load
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C32/00—Bearings not otherwise provided for
- F16C32/06—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings
- F16C32/0629—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings supported by a liquid cushion, e.g. oil cushion
- F16C32/0633—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings supported by a liquid cushion, e.g. oil cushion the liquid being retained in a gap
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/72—Sealings
- F16C33/74—Sealings of sliding-contact bearings
- F16C33/741—Sealings of sliding-contact bearings by means of a fluid
- F16C33/743—Sealings of sliding-contact bearings by means of a fluid retained in the sealing gap
- F16C33/745—Sealings of sliding-contact bearings by means of a fluid retained in the sealing gap by capillary action
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2360/00—Engines or pumps
- F16C2360/46—Fans, e.g. ventilators
Definitions
- the present invention relates to a dynamic pressure bearing apparatus installed in a motor.
- Ball bearings have been adopted as bearings in a variety of fans, such as axial fans and centrifugal fans.
- ball bearings are adopted in a fan described in JP-A 2011-78224.
- an oil-impregnated bearing obtained by sintering powder of a copper-based material is adopted in a fan described in JP-A 2000-14080.
- a dynamic pressure bearing apparatus for use in a spindle motor of a disk drive apparatus is disclosed in JP-A 2005-321089.
- the dynamic pressure bearing apparatus includes a housing, a bearing sleeve, a shaft member, and a ring-shaped seal member.
- the bearing sleeve is fixed to the housing.
- the shaft member is arranged inside the bearing sleeve.
- the seal member is fixed to the shaft member on an upper side of the bearing sleeve.
- a radial bearing portion is defined between an inner circumferential surface of the bearing sleeve and an outer circumferential surface of the shaft member.
- the shaft member is supported in a radial direction in a non-contact manner through the radial bearing portion.
- a first thrust bearing portion is defined between an upper end surface of the bearing sleeve and a lower end surface of the seal member.
- a second thrust bearing portion is defined between a lower end surface of the bearing sleeve and a flange portion provided at a lower end of the shaft member. The seal member and the flange portion are supported in a thrust direction in a non-contact manner through the first and second thrust bearing portions, respectively.
- a seal space is defined between an outer circumferential surface of the seal member and an inner circumferential surface of an upper end portion of the housing. A surface of a lubricating oil is kept always within a range of the seal space.
- a spindle motor of a hard disk drive disclosed in JP-A 2000-175405 includes a hub having a rotor magnet attached thereto, and a base having stator coils attached thereto through a sleeve. An outer edge portion of the hub is arranged in proximity to the base, so that a labyrinth is defined between the hub and the base. Oil mist and the like generated in the spindle motor are thereby prevented from being dispersed, enabling the hard disk drive to achieve a high performance.
- a spindle motor disclosed in JP-A 2004-248481 includes a hub including a cylindrical projecting portion arranged to project downward.
- a labyrinth seal is defined by a combination of a clearance space between an upper surface of a bearing sleeve and a lower surface of a portion of the hub which is arranged radially inward of the projecting portion, a clearance space between an inner circumferential surface of the projecting portion and an outer circumferential surface of the bearing sleeve, and a clearance space between a lower surface of the projecting portion and a flange arranged around the bearing sleeve.
- a dynamic pressure bearing apparatus includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion; a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined there
- a dynamic pressure bearing apparatus includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion; a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined there
- a horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing.
- a minute vertical gap extending in an axial direction and arranged in an annular shape centered on the central axis is defined between a circumferential surface of the bearing portion and a circumferential surface of the bushing.
- the vertical gap is connected with a radially outer end portion of the horizontal gap.
- the seal gap is arranged to be in communication with an exterior space through the horizontal gap and the vertical gap.
- a dynamic pressure bearing apparatus includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and an annular member arranged in an annular shape, fixed to the
- a dynamic pressure bearing apparatus includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and an annular member arranged in an annular shape, and fixed to
- a minute vertical gap extending in an axial direction is defined between the outer circumferential surface of the shaft and an inner circumferential surface of the annular member.
- a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of an opening of the seal gap.
- the seal gap is arranged to be in communication with an exterior space through the vertical gap.
- Preferred embodiments of the present invention provide dynamic pressure bearing apparatuses having structures suited to reduced vibration of fans.
- FIG. 1 is a cross-sectional view of a fan according to a first preferred embodiment of the present invention.
- FIG. 2 is a cross-sectional view of a bearing mechanism according to the first preferred embodiment.
- FIG. 3 is a cross-sectional view of the bearing mechanism.
- FIG. 4 is a cross-sectional view illustrating a portion of the bearing mechanism in an enlarged form.
- FIG. 5 is a cross-sectional view illustrating a portion of the bearing mechanism in an enlarged form.
- FIG. 6 is a cross-sectional view of a bearing portion according to the first preferred embodiment.
- FIG. 7 is a bottom view of the bearing portion.
- FIG. 8 is a plan view of a thrust cap according to the first preferred embodiment.
- FIG. 9 is a graph showing a result of a simulation of vibration that occurs in the fan.
- FIG. 10 is a graph showing a result of a simulation of vibration that occurs in the fan.
- FIG. 11 is a graph showing a result of a simulation of vibration that occurs in the fan.
- FIG. 12 is a graph showing a result of a simulation of vibration that occurs in the fan.
- FIG. 13 is a graph showing a result of a simulation of vibration that occurs in a fan as a comparative example.
- FIG. 14 is a cross-sectional view of a bearing mechanism according to a modification of the first preferred embodiment.
- FIG. 15 is a cross-sectional view illustrating a portion of the bearing mechanism.
- FIG. 16 is a cross-sectional view of a fan according to a modification of the first preferred embodiment.
- FIG. 17 is a diagram illustrating a structure in which a bushing and a rotor holder are fixed to each other according to a modification of the first preferred embodiment.
- FIG. 18 is a diagram illustrating a structure in which a bushing and a rotor holder are fixed to each other according to a further modification of the first preferred embodiment.
- FIG. 19 is a diagram illustrating a labyrinth structure according to a modification of the first preferred embodiment.
- FIG. 20 is a diagram illustrating a labyrinth structure according to a modification of the first preferred embodiment.
- FIG. 21 is a cross-sectional view illustrating a bearing mechanism according to another modification of the first preferred embodiment.
- FIG. 22 is a cross-sectional view illustrating a bearing mechanism according to yet another modification of the first preferred embodiment.
- FIG. 23 is a cross-sectional view illustrating a bearing mechanism according to yet another modification of the first preferred embodiment.
- FIG. 24 is a cross-sectional view illustrating a bearing mechanism according to yet another modification of the first preferred embodiment.
- FIG. 25 is a cross-sectional view of a fan according to a modification of the first preferred embodiment.
- FIG. 26 is a cross-sectional view of a fan according to another modification of the first preferred embodiment.
- FIG. 27 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 28 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 29 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 30 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 31 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 32 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 33 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 34 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 35 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 36 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 37 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 38 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- FIG. 39 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment.
- a vertical direction is defined as a direction in which a central axis of a motor extends, and that an upper side and a lower side along the central axis in FIG. 1 are referred to simply as an upper side and a lower side, respectively. It should be noted, however, that the above definitions of the vertical direction and the upper and lower sides should not be construed to restrict relative positions or directions of different members or portions when the motor is actually installed in a device.
- axial direction a direction parallel to the central axis
- radial direction a direction parallel to the central axis
- radial direction a direction parallel to the central axis
- radial direction a direction parallel to the central axis
- radial direction a direction parallel to the central axis
- radial direction a direction parallel to the central axis
- radial direction a direction parallel to the central axis
- radial direction centered on the central axis
- circumferential direction a circumferential direction about the central axis
- FIG. 1 is a cross-sectional view of an axial fan 1 according to a first preferred embodiment of the present invention.
- the fan 1 includes a motor 11 , an impeller 12 , a housing 13 , a plurality of support ribs 14 , and a base portion 15 .
- the housing 13 is arranged to surround an outer circumference of the impeller 12 .
- the housing 13 is joined to the base portion 15 through the support ribs 14 .
- the support ribs 14 are arranged in a circumferential direction.
- the base portion 15 is defined integrally with the support ribs 14 .
- the motor 11 is fixed on the base portion 15 .
- the impeller 12 is made of a resin, and includes a cup 121 and a plurality of blades 122 .
- the cup 121 is arranged substantially in the shape of a covered cylinder.
- the cup 121 is arranged to cover an outside of the motor 11 .
- the cup 121 is arranged to define a portion of a rotating portion 2 of the motor 11 .
- the rotating portion 2 will be described below.
- the cup 121 includes a top face portion 123 and a side wall portion 124 .
- the top face portion 123 is arranged to spread perpendicularly to a central axis J 1 .
- the side wall portion 124 is arranged to extend downward from an outer edge portion of the top face portion 123 .
- the blades 122 are arranged to extend radially outward from an outer circumferential surface of the side wall portion 124 with the central axis J 1 as a center.
- the cup 121 and the blades 122 are defined integrally with each other by a resin injection molding process.
- a hole portion 125 is defined in an upper surface of the top face portion 123 .
- a weight 129 is arranged in the hole portion 125 .
- the weight 129 is an adhesive including a metal having a high specific gravity, such as tungsten.
- Another weight 129 is arranged on a lower end portion 124 a of the side wall portion 124 on a radially inner side thereof. A reduction in unbalance of each of the impeller 12 and the rotating portion 2 of the motor 11 can be achieved by arranging the weight 129 on each of an upper portion and a lower portion of the impeller 12 .
- Two-plane balance correction as described above achieves a reduction in vibrations of the fan 1 owing to a displacement of a center of gravity of any of the impeller 12 and the motor 11 from the central axis J 1 .
- the hole portion 125 and the lower end portion 124 a of the side wall portion 124 , on each of which the weight 129 is arranged, will be referred to as “balance correction portions 125 and 124 a ”, respectively.
- the impeller 12 of the fan 1 is caused by the motor 11 to rotate about the central axis J 1 to produce downward air currents.
- the motor 11 is a three-phase outer-rotor motor.
- the motor 11 includes the rotating portion 2 , a stationary portion 3 , and a bearing mechanism 4 .
- the rotating portion 2 includes a substantially cylindrical metallic yoke 21 , a rotor magnet 22 , and the cup 121 .
- the yoke 21 is fixed to an inside of the cup 121 .
- the rotor magnet 22 is fixed to an inner circumferential surface of the yoke 21 .
- the bearing mechanism 4 is a dynamic pressure bearing apparatus arranged to generate a fluid dynamic pressure in a lubricating oil 46 .
- the rotating portion 2 is supported through the bearing mechanism 4 to be rotatable about the central axis J 1 with respect to the stationary portion 3 .
- the stationary portion 3 includes a substantially cylindrical bearing support portion 31 , a stator 32 , and a circuit board 33 .
- a lower portion of the bearing support portion 31 is fixed to an inner circumferential surface of the base portion 15 which defines a central hole portion thereof.
- the stator 32 is fixed to an outer circumferential surface of the bearing support portion 31 on an upper side of the base portion 15 .
- the stator 32 is arranged radially inside the rotor magnet 22 .
- the stator 32 includes a stator core 321 and a plurality of coils 322 arranged on the stator core 321 .
- the stator core 321 is defined by laminated steel sheets.
- the circuit board 33 is fixed below the stator 32 .
- Lead wires from the coils 322 are attached to pins (not shown) inserted in holes of the circuit board 33 , whereby the stator 32 and the circuit board 33 are electrically connected with each other. Note that the lead wires from the coils 322 may be directly connected to the circuit board 33 . While the motor 11 is driven, a turning force is generated between the rotor magnet 22 and the stator 32 .
- An annular magnetic member 331 is arranged on an upper surface of the circuit board 33 .
- the magnetic member 331 is arranged under the rotor magnet 22 .
- a magnetic center of the stator 32 is located at a level lower than that of a magnetic center of the rotor magnet 22 .
- magnetic attraction forces that attract the rotor magnet 22 downward are generated between the rotor magnet 22 and the stator 32 , and between the rotor magnet 22 and the magnetic member 331 .
- a force that acts to lift the impeller 12 relative to the stationary portion 3 during rotation of the fan 1 is thereby reduced.
- FIG. 2 is a cross-sectional view illustrating the bearing mechanism 4 .
- the bearing mechanism 4 includes a shaft 41 , an annular thrust plate 42 , a bearing portion 44 , a thrust cap 45 , which corresponds to a cap member, a substantially annular bushing 25 , and the lubricating oil 46 .
- the bushing 25 is made of a metal. An inner circumferential surface of the bushing 25 is press fitted and thereby fixed to an upper portion of the shaft 41 on an upper side of the bearing portion 44 .
- the bushing 25 is arranged to have an outside diameter smaller than that of the bearing portion 44 . As illustrated in FIG. 1 , the impeller 12 is fixed to an outer circumferential surface of the bushing 25 .
- the top face portion 123 of the impeller 12 is indirectly fixed to the upper portion of the shaft 41 through the bushing 25 .
- the impeller 12 and the bushing 25 may be joined to each other by an insert molding process.
- the outside diameter of the bushing 25 is arranged to be greater than the outside diameter of the bearing portion 44 . This makes it possible to mold the impeller 12 while at the same time fixing the impeller 12 to the bushing 25 by arranging the resin on the outer circumferential surface of the bushing 25 when the bearing mechanism 4 as illustrated in FIG. 2 is placed inside a mold, without a need to use a complicated mold.
- the thrust plate 42 is a thrust portion arranged axially opposite the bearing portion 44 , and fixed to a lower portion of the shaft 41 .
- the thrust plate 42 is arranged to extend radially outward from a lower end of the shaft 41 .
- the bearing portion 44 is arranged radially inside the stator 32 . Note that each of the shaft 41 and the thrust plate 42 defines a portion of the rotating portion 2 , while each of the bearing portion 44 and the thrust cap 45 defines a portion of the stationary portion 3 . The same is true of other preferred embodiments of the present invention described below.
- FIG. 3 is a cross-sectional view of a lower portion of the bearing mechanism 4 and its vicinity in an enlarged form.
- An inner circumferential surface of the thrust plate 42 includes a groove portion 421 arranged to extend in an axial direction, and a communicating hole 421 a is defined between the groove portion 421 and an outer circumferential surface 411 of the shaft 41 . This contributes to reducing a difference in internal pressure of the lubricating oil 46 between an upper side and a lower side of the thrust plate 42 .
- an upper surface of the thrust plate 42 includes an inclined surface 422 a defined in an outer edge portion thereof. The inclined surface 422 a is arranged to be inclined downward with increasing distance from the central axis J 1 .
- a portion of the upper surface of the thrust plate 42 which is located radially inward of the inclined surface 422 a is an annular surface perpendicular to the central axis J 1 and arranged around the shaft 41 .
- this portion of the upper surface of the thrust plate 42 will be referred to as an “upper annular surface 422 ”.
- An outer edge portion of a lower surface of the thrust plate 42 includes an inclined surface 423 a arranged to be inclined upward with increasing distance from the central axis J 1 .
- a portion of the lower surface of the thrust plate 42 which is located radially inward of the inclined surface 423 a is an annular surface perpendicular to the central axis J 1 .
- this portion of the lower surface of the thrust plate 42 will be referred to as a “lower annular surface 423 ”.
- the bearing portion 44 illustrated in FIG. 3 is a single sleeve made of a metal, such as stainless steel or phosphor bronze.
- the bearing portion 44 is fixed to an inner circumferential surface of the bearing support portion 31 .
- the shaft 41 is inserted in the bearing portion 44 .
- the bearing portion 44 includes a first shoulder portion 442 defined by an increase in the diameter of an inner circumferential surface 441 of the bearing portion 44 in a lower portion of the inner circumferential surface 441 , and a second shoulder portion 443 defined by an increase in the diameter of the inner circumferential surface 441 between the first shoulder portion 442 and a lower end portion 444 of the bearing portion 44 .
- the thrust cap 45 is arranged inside of the lower end portion 444 , and an outer circumferential surface of the thrust cap 45 is fixed to an inner circumferential surface of the lower end portion 444 .
- the thrust cap 45 is arranged to close a bottom portion of the bearing portion 44 below the thrust plate 42 .
- An outer edge portion of an upper surface 451 of the thrust cap 45 is arranged to be in axial contact with a lower surface 443 a of the second shoulder portion 443 .
- the thrust plate 42 is arranged between the first shoulder portion 442 and the second shoulder portion 443 .
- a radial gap 51 is defined between the inner circumferential surface 441 of the bearing portion 44 and the outer circumferential surface 411 of the shaft 41 .
- a gap 52 is defined between the upper annular surface 422 of the thrust plate 42 and a lower surface 442 a of the first shoulder portion 442 , which is arranged axially opposite the upper annular surface 422 .
- the gap 52 will be referred to as a “first lower thrust gap 52 ”.
- the lower annular surface 423 of the thrust plate 42 and the upper surface 451 of the thrust cap 45 are arranged axially opposite each other, and a gap 53 is defined between the lower annular surface 423 and the upper surface 451 .
- the gap 53 will be referred to as a “second lower thrust gap 53 ”.
- the sum of the axial width of the first lower thrust gap 52 and the axial width of the second lower thrust gap 53 is arranged in the range of about 10 ⁇ m to about 40 ⁇ m.
- a gap 54 is defined between an outer circumferential surface of the thrust plate 42 and a portion of the inner circumferential surface 441 of the bearing portion 44 which is radially opposed to the outer circumferential surface of the thrust plate 42 .
- the gap 54 will be referred to as a “side gap 54 ”.
- FIG. 5 is a diagram illustrating an upper portion of the bearing portion 44 and its vicinity in an enlarged form.
- An upper portion of the inner circumferential surface 441 of the bearing portion 44 includes a first inclined surface 441 a and a second inclined surface 441 b .
- the first inclined surface 441 a is arranged to extend radially inward and obliquely downward from an upper surface of the bearing portion 44 .
- the diameter of the first inclined surface 441 a is arranged to gradually increase with increasing height.
- the second inclined surface 441 b is arranged to extend radially inward and obliquely downward from a lower end of the first inclined surface 441 a .
- An angle defined by the first inclined surface 441 a with the central axis J 1 is arranged to be greater than an angle defined by the second inclined surface 441 b with the central axis J 1 .
- a boundary between the first and second inclined surfaces 441 a and 441 b is arranged radially inward of a radial middle point between an upper end of the first inclined surface 441 a and the outer circumferential surface 411 of the shaft 41 .
- the first inclined surface 441 a and the outer circumferential surface 411 of the shaft 41 are arranged to together define a single seal gap 55 therebetween.
- the seal gap 55 is arranged to gradually increase in radial width with increasing height.
- the seal gap 55 is arranged in an annular shape centered on the central axis J 1 .
- a seal portion 55 a arranged to retain the lubricating oil 46 through capillary action is defined in the seal gap 55 .
- the seal gap 55 serves also as an oil buffer arranged to hold a large amount of the lubricating oil 46 .
- the first lower thrust gap 52 , the side gap 54 , and the second lower thrust gap 53 are arranged to together define a single continuous bladder structure 5 .
- the lubricating oil 46 is arranged continuously in the bladder structure 5 .
- a surface of the lubricating oil 46 is defined only in the seal gap 55 illustrated in FIG. 5 .
- the horizontal gap 501 is arranged to extend radially and perpendicularly to the central axis J 1 .
- the axial width of the horizontal gap 501 is arranged to be small enough to prevent entry of dust into the bearing mechanism 4 therethrough.
- the axial width of the horizontal gap 501 is preferably arranged to be 200 ⁇ m or less. More preferably, the axial width of the horizontal gap 501 is arranged to be 100 ⁇ m or less.
- the outer circumferential surface of the bushing 25 and the inner circumferential surface of the bearing support portion 31 are arranged to together define a minute vertical gap 502 therebetween.
- the vertical gap 502 is arranged to extend in the axial direction, and is arranged in an annular shape centered on the central axis J 1 .
- the vertical gap 502 is connected with a radially outer end portion of the horizontal gap 501 .
- the horizontal gap 501 is defined as a result of assembling of the bearing mechanism 4
- the vertical gap 502 is defined as a result of the bearing mechanism 4 being attached to the bearing support portion 31 .
- the seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 502 .
- the term “exterior space” as used herein refers to a space above the stator 32 as illustrated in FIG. 1 .
- Each of the axial width of the horizontal gap 501 and the radial width of the vertical gap 502 is arranged to be smaller than the radial width of an upper end opening of the seal gap 55 .
- the width of the horizontal gap 501 refers, precisely, to a minimum width of the horizontal gap 501 .
- the width of the vertical gap 502 refers, precisely, to a minimum width of the vertical gap 502 .
- the width of the upper end opening of the seal gap 55 corresponds to a maximum width of the seal gap 55 .
- the maximum width of the seal gap 55 means a maximum width of a region of the seal gap 55 in which the lubricating oil 46 can be retained.
- a labyrinth having a width smaller than that of the upper end opening of the seal gap 55 is defined in the horizontal gap 501 and the vertical gap 502 .
- Provision of the horizontal gap 501 and the vertical gap 502 contributes to preventing an air including a lubricating oil evaporated from the seal portion 55 a from traveling out of the bearing mechanism 4 . This contributes to reducing evaporation of the lubricating oil 46 out of the bearing mechanism 4 .
- a labyrinth structure is defined by a combination of the horizontal gap 501 and the vertical gap 502 .
- the rotating portion 2 is not required to have a complicated structure. Since each of the bushing 25 and the bearing portion 44 is made of a metal, the horizontal gap 501 can be defined with high precision. In addition, a reduction in the probability of adhesion of dust to the bushing 25 through static electricity and of entry of dust into the labyrinth structure is achieved.
- the bushing 25 may be made of a non-metallic material as long as the bushing 25 can be shaped with high precision.
- FIG. 6 is a vertical cross-sectional view of the bearing portion 44 .
- the upper portion and the lower portion of the inner circumferential surface 441 of the bearing portion 44 include a first radial dynamic pressure groove array 711 and a second radial dynamic pressure groove array 712 , respectively, defined therein.
- Each of the first and second radial dynamic pressure groove arrays 711 and 712 is arranged in a herringbone pattern.
- An outer circumferential surface of the bearing portion 44 includes minute recessed portions defined therein. The minute recessed portions are arranged axially between the first and second radial dynamic pressure groove arrays 711 and 712 . Referring to FIG.
- an upper radial dynamic pressure bearing portion 681 arranged to generate a radial fluid dynamic pressure acting on the lubricating oil 46 is defined through the first radial dynamic pressure groove array 711 .
- a lower radial dynamic pressure bearing portion 682 arranged to generate a radial fluid dynamic pressure acting on the lubricating oil 46 is defined through the second radial dynamic pressure groove array 712 .
- the upper and lower radial dynamic pressure bearing portions 681 and 682 will be referred to collectively as a “radial dynamic pressure bearing portion 68 ”.
- the radial dynamic pressure bearing portion 68 is arranged axially between the two balance correction portions 124 a and 125 illustrated in FIG. 1 .
- the radial dynamic pressure bearing portion 68 is defined by a combination of the inner circumferential surface 441 of the bearing portion 44 , the outer circumferential surface 411 of the shaft 41 , and a portion of the lubricating oil 46 which exists in the radial gap 51 .
- the seal gap 55 illustrated in FIG. 5 is arranged above the radial dynamic pressure bearing portion 68 , and is arranged to be continuous with the radial dynamic pressure bearing portion 68 .
- the radial dynamic pressure bearing portion 68 is arranged axially between the two balance correction portions 124 a and 125 illustrated in FIG. 1 .
- the upper radial dynamic pressure bearing portion 681 is arranged to overlap with a center of gravity of each of the motor 11 and the impeller 12 in a radial direction.
- FIG. 7 is a bottom view of the bearing portion 44 .
- the lower surface 442 a of the first shoulder portion 442 includes a first thrust dynamic pressure groove array 721 arranged in the herringbone pattern.
- FIG. 8 is a plan view of the thrust cap 45 .
- the upper surface 451 of the thrust cap 45 that is, a bottom surface of the bladder structure 5 illustrated in FIG. 3 , includes a second thrust dynamic pressure groove array 722 arranged in the herringbone pattern.
- a first lower thrust dynamic pressure bearing portion 691 arranged to generate an axial fluid dynamic pressure acting on the lubricating oil 46 is defined through the first thrust dynamic pressure groove array 721 .
- a second lower thrust dynamic pressure bearing portion 692 arranged to generate an axial fluid dynamic pressure acting on the lubricating oil 46 is defined through the second thrust dynamic pressure groove array 722 .
- the shaft 41 is supported in the radial direction by the radial dynamic pressure bearing portion 68
- the thrust plate 42 which is arranged above a bottom portion of the bladder structure 5 , is supported in a thrust direction by the first and second lower thrust dynamic pressure bearing portions 691 and 692 .
- the rotating portion 2 and the impeller 12 illustrated in FIG. 1 are supported to be rotatable about the central axis J 1 with respect to the stationary portion 3 .
- the lubricating oil 46 circulates through the first lower thrust gap 52 , the side gap 54 , the second lower thrust gap 53 , and the communicating hole 421 a illustrated in FIG. 3 .
- the inclined surface 422 a is defined in the outer edge portion of the upper surface of the thrust plate 42 as illustrated in FIG. 4 , and this contributes to preventing the thrust plate 42 from coming into hard contact with the lower surface 442 a of the first shoulder portion 442 of the bearing portion 44 even when the shaft 41 is tilted.
- Provision of the first and second lower thrust dynamic pressure bearing portions 691 and 692 in the motor 11 contributes to stabilizing the axial position of the rotating portion 2 relative to the stationary portion 3 during rotation of the impeller 12 .
- This makes it easy to design the horizontal gap 501 with a small axial width.
- the horizontal gap 501 is designed to have a sufficient width to prevent the lower surface of the bushing 25 from coming into contact with the upper surface of the bearing portion 44 even when the thrust plate 42 is brought into contact with the thrust cap 45 .
- a portion of the first radial dynamic pressure groove array 711 is defined in a lower portion of the second inclined surface 441 b .
- a fluid dynamic pressure is generated by the first radial dynamic pressure groove array 711 in a gap 56 defined between a portion of the outer circumferential surface 411 of the shaft 41 which approaches the second inclined surface 441 b and a portion of the second inclined surface 441 b which is opposed to this portion of the outer circumferential surface 411 .
- the shaft 41 is supported by the second inclined surface 441 b .
- the second inclined surface 441 b extends along the outer circumferential surface 411 of the shaft 41 in the gap 56 , which is located below and adjacent to the seal gap 55 .
- the shaft 41 is thus prevented from coming into hard contact with the upper portion of the bearing portion 44 .
- FIG. 9 is a graph showing a result of a simulation of vibration that occurs in the fan 1 in the case where the radial width of the radial gap 51 is 3 ⁇ m.
- a horizontal axis represents frequencies of the vibration, while a vertical axis represents the amplitude of each frequency component of the vibration.
- FIGS. 10 , 11 , and 12 are graphs showing results of simulations of vibration that occurs in the fan 1 in the case where the radial width of the radial gap 51 is 4 ⁇ m, 5 ⁇ m, and 6 ⁇ m, respectively.
- FIG. 13 is a graph showing a result of a simulation of vibration that occurs in a fan as a comparative example in which a motor including a ball bearing is installed.
- a plurality of peaks occur in the range of 750 Hz to 1250 Hz.
- the peaks are denoted, from right to left, by reference numerals 901 , 902 , 903 , and 904 , respectively.
- corresponding peaks 911 , 912 , 913 , and 914 are lower than the peaks 901 , 902 , 903 , and 904 , respectively, in FIG. 13 .
- peaks do not occur at positions corresponding to those of the peaks 901 and 904 on the far right and on the far left, respectively, in FIG. 13 .
- peaks 912 and 913 corresponding to the remaining peaks 902 and 903 , respectively are less than half as high as the peaks 902 and 903 , respectively.
- the fan 1 is able to achieve reduced vibration as compared to known fans in which ball bearings are used. This is due to a so-called damper effect produced by the lubricating oil 46 between the shaft 41 and the bearing portion 44 .
- a satisfying reduction in the vibration can be achieved when the radial width of the radial gap 51 is 5 ⁇ m or greater.
- the radial width of the radial gap 51 is arranged to be 20 ⁇ m or less in order to generate a sufficient fluid dynamic pressure in the radial gap 51 .
- the fan 1 has been described above.
- Use of the bearing mechanism 4 which is a fluid dynamic bearing mechanism, in the fan 1 contributes to reducing the vibrations of the fan 1 .
- the reduction in the vibrations of the fan 1 leads to a reduction in power consumption of the fan 1 .
- the bearing mechanism 4 can be structured in a manner suited to the reduced vibration of the fan 1 .
- Provision of the horizontal gap 501 contributes to preventing dust from entering into the bearing mechanism 4 when the bearing mechanism 4 is attached to another component of the fan 1 . The same is true of other preferred embodiments of the present invention described below.
- the bearing mechanism 4 of the motor 11 In the case of a fluid dynamic bearing mechanism in which seal portions are defined in an upper portion and a lower portion of a bearing portion thereof, a sophisticated design is required to prevent a difference in pressure between the seal portions from causing a leakage of the lubricating oil 46 .
- the bearing mechanism 4 includes the bladder structure 5 , and the lubricating oil 46 is arranged continuously in the bladder structure 5 . That is, the bearing mechanism 4 of the motor 11 has a so-called full-fill structure, including only one seal portion 55 a . It is therefore easy to prevent a leakage of the lubricating oil 46 in the case of the bearing mechanism 4 .
- the surface of the lubricating oil 46 in the seal portion 55 a can be maintained at a substantially fixed position. Moreover, a reduction in the evaporation of the lubricating oil 46 is achieved compared to the case where a plurality of seal portions are provided.
- the seal portion 55 a is arranged in an inner portion of the motor 11 , inside of the horizontal gap 501 and the vertical gap 502 , the seal portion 55 a is not exposed to air currents while the fan 1 is driven. A further reduction in the evaporation of the lubricating oil 46 is thereby achieved. Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- the fluid dynamic pressures can be generated while ensuring the damper effect owing to the lubricating oil 46 .
- the second inclined surface 441 b in which a portion of the first radial dynamic pressure groove array 711 is defined is arranged in the inner circumferential surface 441 of the bearing portion 44 , it is possible to support the shaft 41 sufficiently even if the radial gap 51 is widened. Consequently, it is possible to prevent a reduction in bearing rigidity even when the fan 1 is caused to rotate at a high speed or in a high-temperature condition.
- the motor 11 is a three-phase motor, the motor 11 is capable of being rotated at a high speed. It is therefore easy to cause the frequencies of the vibration that can occur in the motor 11 to deviate from a frequency band that may affect another device in an electronic device in which the fan 1 is installed.
- the magnetic member 331 provided in the motor 11 generates the magnetic attraction force that attracts the rotor magnet 22 downward. This contributes to reducing an increase in a bearing loss that occurs in the first lower thrust dynamic pressure bearing portion 691 , while the fan 1 is driven, owing to the force that acts to lift the impeller 12 relative to the stationary portion 3 . Moreover, the additional magnetic attraction force that attracts the rotor magnet 22 downward is generated because the magnetic center of the stator 32 is arranged at a level lower than that of the magnetic center of the rotor magnet 22 . This contributes to further reducing the increase in the bearing loss that occurs in the first lower thrust dynamic pressure bearing portion 691 .
- each of the rotating portion 2 and the impeller 12 is capable of stable rotation, and a further reduction in the vibrations is thereby achieved.
- the axial length of the bearing portion 44 is preferably arranged to be less than about four times the diameter of the bearing portion 44 .
- the upper radial dynamic pressure bearing portion 681 is arranged to overlap with the center of gravity of each of the motor 11 and the impeller 12 in the radial direction, stability of the rotation of each of the rotating portion 2 and the impeller 12 is increased, and a further reduction in the vibrations is thereby achieved.
- the same is true of other preferred embodiments of the present invention described below.
- an upper end of the stator core 321 is arranged to overlap with the upper radial dynamic pressure bearing portion 681 in the radial direction.
- the stator 32 being arranged at a high position as described above, the magnetic center of the stator 32 can be arranged between the upper and lower radial dynamic pressure bearing portions 681 and 682 .
- a lower end of the stator core 321 is preferably arranged to overlap with the lower radial dynamic pressure bearing portion 682 in the radial direction.
- a center of gravity of a combination of the impeller 12 and the rotating portion 2 is arranged to overlap with the upper radial dynamic pressure bearing portion 681 in the radial direction.
- FIG. 14 is a diagram illustrating a bearing mechanism 4 according to a modification of the first preferred embodiment.
- a bearing portion 44 a of the bearing mechanism 4 includes a tubular sleeve 47 and a bearing housing 48 .
- the sleeve 47 is defined by a metallic sintered body.
- the sleeve 47 is impregnated with a lubricating oil 46 .
- the bearing housing 48 is arranged to cover an outer circumferential surface of the sleeve 47 .
- the bearing housing 48 is arranged to have an outside diameter substantially equal to an outside diameter of a bushing 25 .
- the bearing housing 48 includes an annular upper portion 481 arranged to extend radially inward on an upper side of the sleeve 47 .
- a circulation channel 472 arranged to extend in the axial direction is defined between an outer circumferential surface of the sleeve 47 and an inner circumferential surface of the bearing housing 48 .
- the lubricating oil 46 is arranged to circulate through the circulation channel 472 , a gap defined between a lower surface of the annular upper portion 481 and an upper surface of the sleeve 47 , a radial gap 51 , and a first lower thrust gap 52 .
- an inner circumferential surface 481 a of the annular upper portion 481 is an inclined surface whose diameter gradually increases with increasing height.
- the inner circumferential surface 481 a is arranged to be inclined radially inward with decreasing height.
- the inner circumferential surface 481 a will be referred to as a “first inclined surface 481 a ”.
- An upper portion of an inner circumferential surface 471 of the sleeve 47 includes an inclined surface 471 a whose diameter gradually increases with increasing height.
- the inclined surface 471 a is arranged to be inclined radially inward with decreasing height.
- the inclined surface 471 a will be referred to as a “second inclined surface 471 a ”.
- An angle defined by the first inclined surface 481 a with a central axis J 1 is arranged to be greater than an angle defined by the second inclined surface 471 a with the central axis J 1 .
- the bearing mechanism 4 according to the present modification of the first preferred embodiment is otherwise similar in structure to the bearing mechanism 4 illustrated in FIG. 3 .
- a seal gap 55 arranged to gradually increase in radial width with increasing height is defined between the first inclined surface 481 a and an outer circumferential surface 411 of a shaft 41 . Adjacent to and below the seal gap 55 , a gap 56 is defined between the outer circumferential surface 411 of the shaft 41 and the second inclined surface 471 a .
- the seal gap 55 includes a seal portion 55 a arranged to retain the lubricating oil 46 through capillary action.
- a surface of the lubricating oil 46 is defined in the seal portion 55 a . Because the seal portion 55 a is defined around the shaft 41 , a leakage of the lubricating oil 46 out of the seal portion 55 a due to a centrifugal force is prevented.
- a portion of a first radial dynamic pressure groove array 711 similar to the first radial dynamic pressure groove array 711 illustrated in FIG. 6 is defined in a lower portion of the second inclined surface 471 a .
- the second inclined surface 471 a extends along the outer circumferential surface 411 of the shaft 41 , so that a fluid dynamic pressure is generated in the gap 56 .
- the shaft 41 is thereby supported by the second inclined surface 471 a so that the shaft 41 can be prevented from coming into hard contact with an upper portion of the bearing portion 44 a.
- a horizontal gap 501 arranged to extend perpendicularly to the central axis J 1 is defined between a lower surface of the bushing 25 and an upper surface of the bearing portion 44 a .
- a vertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between an outer circumferential surface of the bushing 25 and an inner circumferential surface of a bearing support portion 31 .
- the seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 502 .
- Each of a minimum axial width of the horizontal gap 501 and a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 . Since each of the horizontal gap 501 and the vertical gap 502 has a width smaller than the maximum width of the opening of the seal gap 55 , a labyrinth having a width smaller than the maximum width of the seal gap 55 is defined therein. Provision of the horizontal gap 501 and the vertical gap 502 contributes to preventing an air including a lubricating oil evaporated from the seal portion 55 a from traveling out of the bearing mechanism 4 . This contributes to reducing evaporation of the lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 16 is a cross-sectional view of a fan 1 according to another modification of the first preferred embodiment.
- the fan 1 illustrated in FIG. 16 is different from the fan 1 illustrated in FIG. 1 in that an impeller 12 is arranged to extend farther downward than a motor 11 , so that the entire motor 11 is accommodated in a cup 121 of the impeller 12 .
- the fan 1 illustrated in FIG. 16 is otherwise similar in structure to the fan 1 illustrated in FIG. 1 .
- a thrust cap 45 which is arranged at a lower end of a bearing portion 44 , is arranged at a level higher than that of a lower end 126 of the impeller 12 .
- the lower end of the bearing portion 44 is normally arranged at a lowermost end of the motor 11 . Therefore, a center of gravity of the motor 11 is thereby arranged inside of the impeller 12 , which leads to increased stability of rotation of the impeller 12 . Since a three-phase motor, even in a reduced size, is capable of rotating an impeller in a satisfactory manner, the above structure is especially suitable for the case where the three-phase motor is adopted.
- FIG. 17 is a diagram illustrating a structure in which a bushing 25 and an impeller 12 are joined to each other according to a modification of the first preferred embodiment.
- the impeller 12 illustrated in FIG. 17 includes a cup 121 having an inner surface fixed to a rotor holder 210 arranged substantially in the shape of a covered cylinder.
- a top face portion of the cup 121 includes a large central opening defined therein.
- the rotor holder 210 includes a cylindrical portion 21 a and a top face portion 21 b .
- the top face portion 21 b is arranged to spread perpendicularly to a central axis J 1 .
- the cylindrical portion 21 a is arranged substantially in the shape of a cylinder, and is arranged to extend downward from an outer edge portion of the top face portion 21 b .
- the rotor holder 210 is made of a metal, and the cylindrical portion 21 a functions as the yoke 21 illustrated in FIG. 1 .
- a central portion of the top face portion 21 b that is, an inner edge portion of the top face portion 21 b , includes a cylindrical burring portion 211 arranged to extend downward from the inner edge portion thereof.
- An inner circumferential surface of the burring portion 211 is press fitted to an outer circumferential surface of the bushing 25 , whereby the rotor holder 210 is fixed to the bushing 25 .
- the impeller 12 is thereby indirectly fixed to an upper portion of a shaft 41 .
- the impeller 12 and the bushing 25 are securely fixed to each other through joining of the metallic members.
- FIG. 18 is a diagram illustrating a structure in which a bushing 25 and an impeller 12 are joined to each other according to a further modification of the first preferred embodiment. While the impeller 12 has a structure substantially the same as that of the impeller 12 illustrated in FIG. 17 , a rotor holder 210 does not include the burring portion. An outer circumferential surface of the bushing 25 includes an annular groove 251 defined therein, and an inner circumferential portion of a top face portion 21 b is fixed in the groove 251 by crimping. Also in the joining structure illustrated in FIG. 18 , the impeller 12 and the bushing 25 are securely fixed to each other through joining of the metallic members.
- FIG. 19 is a diagram illustrating a labyrinth structure defined above a bearing portion 44 according to a modification of the first preferred embodiment.
- a bushing 25 includes, in an outer edge portion of a lower portion thereof, an outer annular portion 252 arranged to extend downward toward the bearing portion 44 .
- the bearing portion 44 includes an inner annular portion 445 arranged to project upward toward the bushing 25 around a shaft 41 .
- the bearing portion 44 includes, in an outer edge portion of an upper portion thereof, an annular recessed portion 445 a arranged to be recessed in a direction away from the bushing 25 .
- the recessed portion 445 a will be referred to as an “annular recessed portion 445 a ”.
- the inner annular portion 445 can be regarded as a portion that defines a side surface of the annular recessed portion 445 a .
- the outer annular portion 252 is arranged radially outside the inner annular portion 445 . That is, the outer annular portion 252 is arranged in the annular recessed portion 445 a .
- a horizontal gap 501 arranged to spread perpendicularly to a central axis J 1 is defined by a portion of a lower surface of the bushing 25 which is radially inward of the outer annular portion 252 and an upper surface of the inner annular portion 445 of the bearing portion 44 .
- the horizontal gap 501 will be referred to as a “first horizontal gap 501 ”.
- a vertical gap 502 arranged to extend in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined by an inner circumferential surface of the outer annular portion 252 and an outer circumferential surface of the inner annular portion 445 .
- An upper end of the vertical gap 502 is connected with a radially outer end portion of the first horizontal gap 501 .
- Another horizontal gap 501 a arranged to spread perpendicularly to the central axis J 1 is defined between a lower surface of the outer annular portion 252 and a bottom surface of the annular recessed portion 445 a , which is arranged axially opposite the lower surface of the outer annular portion 252 , that is, a surface radially outward of the inner annular portion 445 .
- the horizontal gap 501 a will be referred to as a “second horizontal gap 501 a ”.
- a lower end of the vertical gap 502 is connected with a radially inner end portion of the second horizontal gap 501 a.
- each of a minimum axial width of the first horizontal gap 501 and a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of an opening of a seal gap 55 .
- Provision of the first horizontal gap 501 and the vertical gap 502 contributes to reducing evaporation of a lubricating oil out of a bearing mechanism 4 .
- the first horizontal gap 501 and the vertical gap 502 may be defined between the bushing 25 and the bearing portion 44 as described above.
- provision of the second horizontal gap 501 a contributes to more securely preventing the evaporation of the lubricating oil.
- a minimum axial width of the second horizontal gap 501 is arranged to be smaller than the maximum radial width of the opening of the seal gap 55 . Provision of the first horizontal gap 501 , the vertical gap 502 , and the second horizontal gap 501 a in the bearing mechanism 4 contributes to more securely preventing dust from entering into the bearing mechanism 4 when the bearing mechanism 4 and another component of a fan 1 are attached to each other.
- each of the first and second horizontal gaps 501 and 501 a may not necessarily be a minute gap. Even when only the vertical gap 502 is a minute gap, dust is prevented from entering into the bearing mechanism 4 when the bearing mechanism 4 and another component of the fan 1 are attached to each other. This makes it possible to assemble the fan 1 without a need to use an exceedingly clean facility. Furthermore, even when the bearing mechanism 4 is transported into the facility, dust is prevented from entering into the bearing mechanism 4 .
- an inner circumferential portion of a lower portion of the bushing 25 may be arranged to project into an inner circumferential portion of an upper portion of the bearing portion 44 .
- an outer annular portion arranged to project toward the bushing 25 is arranged in an outer edge portion of the upper portion of the bearing portion 44
- an inner annular portion arranged to project toward the bearing portion 44 on a radially inner side of the outer annular portion is arranged in the lower portion of the bushing 25 .
- the outer annular portion is arranged in an annular recessed portion defined radially outside the inner annular portion.
- a vertical gap 502 is defined between an outer circumferential surface of the inner annular portion, which is arranged in the lower portion of the bushing 25 , and an inner circumferential surface of the outer annular portion, which is arranged in the upper portion of the bearing portion 44 . Furthermore, it may be so arranged that the bushing 25 is increased in diameter, an outer circumferential portion of the bushing 25 is arranged to extend downward so that an upper portion of a bearing support portion 31 may be surrounded by a lower portion of the bushing 25 on a radially outer side thereof, and a vertical gap 502 is defined between an inner circumferential surface of the lower portion of the bushing 25 and an outer circumferential surface of the upper portion of the bearing support portion 31 .
- the vertical gap 502 is defined between a circumferential surface of the bushing 25 and a circumferential surface of the bearing support portion 31 or the bearing portion 44 in the vicinity of the seal portion.
- the second horizontal gap 501 a may be defined between the lower surface of the bushing 25 and an upper surface of the bearing support portion 31 . Note that emission of a vaporized lubricating oil can be effectively prevented when a stationary body is arranged radially outward of a rotating body in the labyrinth structure.
- FIG. 20 is a diagram illustrating a labyrinth structure defined above a bearing portion 44 according to another modification of the first preferred embodiment.
- a lower portion of a bushing 25 includes an inclined surface arranged to be inclined downward with increasing distance from a central axis J 1 .
- An upper portion of the bearing portion 44 also includes an inclined surface arranged to be inclined downward with increasing distance from the central axis J 1 .
- An inclined gap 503 arranged to be inclined downward with increasing distance from the central axis J 1 is defined between these inclined surfaces.
- the inclined gap 503 is arranged in the shape of a conical surface centered on the central axis J 1 .
- a minimum width of the inclined gap 503 is arranged to be smaller than a maximum radial width of an opening of a seal gap 55 .
- the minimum width of the inclined gap 503 refers to a minimum distance between the aforementioned two inclined surfaces.
- a horizontal gap 501 is defined on a radially inner side of the inclined gap 503 .
- the seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the inclined gap 503 .
- Provision of the inclined gap 503 contributes to preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 .
- Provision of the horizontal gap 501 and the inclined gap 503 in the bearing mechanism 4 contributes to more securely preventing dust from entering into the bearing mechanism 4 when the bearing mechanism 4 and another component of a fan 1 are attached to each other.
- an additional vertical gap or an additional horizontal gap which is continuous with a radially outer end portion of the inclined gap 503 may be provided.
- the inclined gap 503 may be arranged to be inclined upward with increasing distance from the central axis J 1 .
- FIG. 21 is a diagram illustrating a bearing mechanism 4 according to another modification of the first preferred embodiment.
- the bearing mechanism 4 according to the present modification of the first preferred embodiment is similar in structure to the bearing mechanism 4 illustrated in FIG. 3 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- the bearing mechanism 4 does not include the thrust cap 45 illustrated in FIG. 3 .
- a side gap 54 is defined between an outer circumferential surface of a thrust plate 42 and an inner circumferential surface of a lower end portion 444 of a bearing portion 44 , and a seal portion 54 a is defined in the side gap 54 .
- the seal portion 54 a is defined in a lower portion of the side gap 54 , and is arranged to gradually increase in radial width with decreasing height.
- first lower thrust dynamic pressure bearing portion 691 is defined in a first lower thrust gap 52 defined between the bearing portion 44 and an upper surface of the thrust plate 42 .
- An axial magnetic center of a rotor magnet and that of a stator are displaced from each other to cause an upward force to constantly act on a shaft 41 .
- the bearing mechanism 4 is otherwise similar in structure to the bearing mechanism 4 illustrated in FIG. 3 .
- a seal portion 55 a similar to the seal portion 55 a illustrated in FIG. 5 is defined in an upper portion of the bearing mechanism 4 .
- the bearing mechanism 4 includes a plurality of seal portions.
- a horizontal gap 501 is defined between a lower surface of a bushing 25 and an upper surface of the bearing portion 44
- a vertical gap 502 is defined between an outer circumferential surface of the bushing 25 and an inner circumferential surface of a bearing support portion 31
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 502 .
- Each of a minimum axial width of the horizontal gap 501 and a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- the radial width of a radial gap 51 is arranged to be 5 ⁇ m or greater so that a sufficient reduction in vibrations of a fan 1 can be achieved. Note, however, that the width of the radial gap 51 is arranged to be 20 ⁇ m or less in order to generate a sufficient fluid dynamic pressure in the radial gap 51 .
- FIG. 22 is a cross-sectional view illustrating a bearing mechanism 4 according to yet another modification of the first preferred embodiment.
- a bushing 25 of the bearing mechanism 4 includes an annular portion 253 arranged to extend downward outside of a bearing portion 44 .
- a vertical gap 504 is defined between an inner circumferential surface of the annular portion 253 and an outer circumferential surface of the bearing portion 44 .
- the bearing mechanism 4 is otherwise similar in structure to the bearing mechanism 4 illustrated in FIG. 2 .
- a seal gap 55 is arranged to be in communication with an exterior space through a horizontal gap 501 defined between a lower surface of the bushing 25 and an upper surface of the bearing portion 44 , and the vertical gap 504 .
- Provision of the horizontal gap 501 and the vertical gap 504 in the bearing mechanism 4 contributes to more securely preventing dust from entering into the bearing mechanism 4 when the bearing mechanism 4 and another component of a fan 1 are attached to each other.
- the horizontal gap 501 may not necessarily be a minute gap, with only the vertical gap 504 being a minute gap.
- evaporation of a lubricating oil 46 from a seal portion 55 a can be prevented.
- FIG. 23 is a cross-sectional view illustrating a bearing mechanism 4 according to yet another modification of the first preferred embodiment.
- a bushing 25 includes an annular projecting portion 254 arranged to project radially inward from an inner circumferential surface thereof.
- An upper end portion of a shaft 41 includes a shoulder portion 412 defined by a decrease in the diameter thereof.
- the projecting portion 254 is arranged to be in axial contact with an upper surface 412 a of the shoulder portion 412 .
- the upper surface 412 a is a surface having a normal oriented upward.
- a displacement of the axial position of the bushing 25 is prevented when a fan 1 is assembled, or more specifically, when an impeller 12 is indirectly fixed to an upper portion of the shaft 41 through the bushing 25 , so that the width of a horizontal gap 501 can be easily set at a desired value.
- the shoulder portion 412 of the shaft 41 may be eliminated, with the projecting portion 254 arranged to be in axial contact with an upper surface of the shaft 41 . Even in this case, a displacement of the axial position of the bushing 25 is prevented when the fan 1 is assembled so that the width of the horizontal gap 501 can be easily set at the desired value. This enables the labyrinth to be defined with high precision.
- FIG. 25 is a cross-sectional view illustrating a fan 1 according to a modification of the first preferred embodiment.
- a radially inner portion of a stator core 321 is fixed to an outer circumferential surface of a bearing portion 44 .
- a cylindrical member 31 a (hereinafter referred to as a “cylindrical portion 31 a ”) is fixed to a central hole portion of a base portion 15 , and an upper portion of the cylindrical portion 31 a is arranged to be in axial contact with a lower portion of the stator core 321 .
- a bushing 25 includes an annular portion 253 arranged to extend downward outside of the bearing portion 44 .
- the fan 1 according to the present modification of the first preferred embodiment is otherwise similar in structure to the fan 1 illustrated in FIG. 17 .
- a rotor holder 210 is press fitted to the bushing 25 of a bearing mechanism 4 from above the bushing 25 .
- a lower end of the annular portion 253 is supported by a jig from below.
- a stator 32 is attached to an outer circumference of the bearing portion 44 , and a lower portion of the bearing portion 44 is inserted into the cylindrical portion 31 a fixed to the base portion 15 .
- a displacement of the axial position of the bushing 25 is prevented because the bushing 25 is supported from below when the rotor holder 210 is press fitted to the bushing 25 .
- the axial width of a horizontal gap 501 can be easily set at a desired value, and the labyrinth can be defined with high precision.
- FIG. 26 is a cross-sectional view illustrating a fan 1 according to yet another modification of the first preferred embodiment.
- a top face portion 123 of an impeller 12 includes a through hole 127 arranged to extend in the axial direction therethrough.
- the fan 1 according to the present modification of the first preferred embodiment is otherwise similar in structure to the fan 1 illustrated in FIG. 1 .
- the through hole 127 is arranged to overlap with a stator 32 in the axial direction.
- the through hole 127 is arranged to bring a space 811 defined between the stator 32 and the top face portion 123 located above the stator 32 into communication with a space 812 above the impeller 12 , that is, a space on an upstream side of the fan 1 . While the fan 1 is driven, air currents are produced around the stator 32 to cool the stator 32 .
- the through hole 127 thus functions as a channel to guide an air flow to the stator 32 .
- FIG. 27 is a cross-sectional view illustrating a fan 1 according to yet another modification of the first preferred embodiment.
- a rotor holder 210 arranged substantially in the shape of a covered cylinder is fixed to an inside of a cup 121 of an impeller 12 .
- a top face portion 123 of the cup 121 includes a through hole 128 a arranged to extend in the axial direction therethrough and defined in a center thereof.
- the through hole 128 a will be referred to as a “first through hole 128 a ”.
- a top face portion 21 b of the rotor holder 210 includes a first shoulder portion 212 arranged to be recessed downward and arranged radially outward of a burring portion 211 , and a second shoulder portion 213 arranged to be recessed downward and arranged radially outward of the first shoulder portion 212 .
- a through hole 128 b is defined in the top face portion 21 b between the first and second shoulder portions 212 and 213 .
- the through hole 128 b will be referred to as a “second through hole 128 b ”.
- the second through hole 128 b is arranged at the same level as that of an upper portion of a vertical gap 502 .
- the first through hole 128 a a space 128 c defined between the top face portion 123 of the cup 121 and the top face portion 21 b of the rotor holder 210 , and the second through hole 128 b are arranged to together define a channel 128 to bring a space 811 above a stator 32 into communication with a space 812 above the impeller 12 .
- the stator 32 is thus cooled while the fan 1 is driven.
- the second through hole 128 b i.e., a downstream end portion of the channel 128 , is arranged at the same level as that of the upper portion of the vertical gap 502 , that is, because the second through hole 128 b and the upper portion of the vertical gap 502 are arranged to overlap with each other in the radial direction, dust is prevented from entering into the vertical gap 502 and a horizontal gap 501 .
- the second through hole 128 b may be arranged at a level lower than that of the upper portion of the vertical gap 502 . Even in this case, dust is prevented from entering into the vertical gap 502 and the horizontal gap 501 .
- FIG. 28 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- a bearing mechanism 4 of the fan 1 is similar in structure to the bearing mechanism 4 illustrated in FIGS. 14 and 15 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- an annular upper portion 481 of a bearing housing 48 is arranged above an upper end of a bearing support portion 31 .
- An upper surface of the annular upper portion 481 is an upper surface of a bearing portion 44 a as well.
- an upper surface of a sleeve 47 is also arranged above the upper end of the bearing support portion 31 .
- a rotor holder 210 arranged substantially in the shape of a covered cylinder is fixed to an inside of a cup 121 of an impeller 12 .
- the rotor holder 210 includes a cylindrical portion 21 a , a top face portion 21 b , and a holder projecting portion 211 a .
- the holder projecting portion 211 a includes a burring portion 214 , a first portion 215 , and a second portion 216 .
- Each of the burring portion 214 and the second portion 216 is arranged substantially in the shape of a cylinder centered on a central axis J 1 .
- the first portion 215 is arranged substantially in the shape of an annular plate centered on the central axis J 1 .
- the first portion 215 is arranged to extend radially outward and perpendicularly to the central axis J 1 from a lower end of the burring portion 214 .
- the second portion 216 is arranged to extend downward from an outer edge portion of the first portion 215 .
- the top face portion 21 b is arranged substantially in the shape of an annular plate centered on the central axis J 1 .
- the top face portion 21 b is arranged to extend radially outward and perpendicularly to the central axis J 1 from a lower end of the second portion 216 .
- the cylindrical portion 21 a is arranged substantially in the shape of a cylinder centered on the central axis J 1 .
- the cylindrical portion 21 a is arranged to extend downward from an outer edge portion of the top face portion 21 b .
- the rotor holder 210 is made of a metal, and the cylindrical portion 21 a functions as the yoke 21 illustrated in FIG. 1 .
- a top face portion 123 of the cup 121 includes a through hole arranged to extend in the axial direction therethrough and defined in a center thereof.
- An outer circumferential surface of the burring portion 214 of the holder projecting portion 211 a is press fitted and thereby fixed to an inner circumferential surface of this through hole.
- the impeller 12 and the rotor holder 210 may be joined to each other by an insert molding process.
- An inner circumferential surface of the burring portion 214 of the holder projecting portion 211 a is press fitted and thereby fixed to an upper portion of a shaft 41 on an upper side of the bearing portion 44 a .
- the shaft 41 includes an attachment surface 413 at an upper portion of an outer circumferential surface 411 thereof in a situation in which the rotor holder 210 and the impeller 12 have not yet been fixed to the shaft 41 .
- the attachment surface 413 is a surface to which the top face portion 123 of the impeller 12 is to be indirectly attached through the rotor holder 210 .
- the shaft 41 is inserted in the bearing portion 44 a , and is arranged to rotate about the central axis J 1 relative to the bearing portion 44 a.
- a seal portion 55 a is defined around the shaft 41 on an upper side of a radial dynamic pressure bearing portion 68 .
- a seal gap 55 includes the seal portion 55 a , in which a surface of a lubricating oil 46 is defined.
- the bearing mechanism 4 further includes an annular member 49 .
- the annular member 49 is arranged to spread perpendicularly to the central axis J 1 above the seal portion 55 a .
- the annular member 49 is arranged substantially in the shape of an annular plate centered on the central axis J 1 .
- An inner circumferential surface of the annular member 49 is fixed to the outer circumferential surface 411 of the shaft 41 axially between the seal portion 55 a and the burring portion 214 of the holder projecting portion 211 a .
- the annular member 49 is fixed to the shaft 41 axially between the seal portion 55 a and the attachment surface 413 .
- the annular member 49 is arranged to extend radially outward, with the central axis J 1 as a center, beyond an opening of the seal gap 55 . That is, the annular member 49 is arranged to cover the opening of the seal gap 55 from above. In other words, the annular member 49 is arranged to cover the opening of the seal gap 55 in a plan view. In FIG. 28 , the annular member 49 is arranged to extend radially outward beyond an outer edge of the upper surface of the annular upper portion 481 .
- a minute horizontal gap 501 extending radially is defined between a lower surface of the annular member 49 and the upper surface of the bearing portion 44 a .
- the seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 .
- a minimum axial width of the horizontal gap 501 is arranged to be smaller than a maximum radial width of the opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the horizontal gap 501 contributes to preventing an air including a lubricating oil evaporated from the seal portion 55 a from traveling out of the bearing mechanism 4 . This contributes to reducing evaporation of the lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 29 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- an annular member 49 a arranged in an annular shape centered on a central axis J 1 is provided in place of the annular member 49 illustrated in FIG. 28 .
- the annular member 49 a includes a top cover portion 491 and a tubular portion 492 .
- the top cover portion 491 is arranged substantially in the shape of an annular plate centered on the central axis J 1 .
- the top cover portion 491 is fixed to a shaft 41 axially between a seal portion 55 a and an attachment surface 413 .
- the top cover portion 491 is arranged to extend radially outward beyond an outer circumferential surface of an annular upper portion 481 .
- the tubular portion 492 is arranged substantially in the shape of a cylinder centered on the central axis J 1 .
- the tubular portion 492 is arranged to extend downward from an outer edge portion of the top cover portion 491 .
- An inner circumferential surface of the tubular portion 492 is arranged radially opposite the outer circumferential surface of the annular upper portion 481 of a bearing housing 48 , which defines a portion of a bearing portion 44 a.
- a minute horizontal gap 501 extending radially is defined between a lower surface of the top cover portion 491 and an upper surface of the bearing portion 44 a .
- a minute vertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the inner circumferential surface of the tubular portion 492 and the outer circumferential surface of the annular upper portion 481 .
- An upper end portion of the vertical gap 502 is connected with an radially outer end portion of the horizontal gap 501 .
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 502 .
- Each of a minimum axial width of the horizontal gap 501 and a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the vertical gap 502 in addition to the horizontal gap 501 contributes to more effectively preventing an air including a lubricating oil evaporated from the seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to further reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- the horizontal gap 501 may not necessarily be a minute gap. Even when only the vertical gap 502 is a minute gap, a reduction in the evaporation of the lubricating oil 46 out of the bearing mechanism 4 can be achieved, and also, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 30 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- a bearing portion 44 a includes an annular projection portion 482 arranged to project upward from an outer edge portion of an upper surface of an annular upper portion 481 .
- the annular projection portion 482 is arranged substantially in the shape of a cylinder centered on a central axis J 1 .
- An annular member 49 is arranged to extend radially outward, with the central axis J 1 as a center, beyond an opening of a seal gap 55 .
- An outer circumferential surface of the annular member 49 is arranged radially opposite an inner circumferential surface of the annular projection portion 482 .
- the annular projection portion 482 may be arranged to project upward from a position on a radially inner side of the outer edge portion of the upper surface of the annular upper portion 481 .
- a minute horizontal gap 501 extending radially is defined between a lower surface of the annular member 49 and an upper surface of the bearing portion 44 a .
- a minute vertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the outer circumferential surface of the annular member 49 and the inner circumferential surface of the annular projection portion 482 .
- a lower end portion of the vertical gap 502 is connected with a radially outer end portion of the horizontal gap 501 .
- the seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 502 .
- Each of a minimum axial width of the horizontal gap 501 and a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of the opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the vertical gap 502 in addition to the horizontal gap 501 contributes to more effectively preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to further reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- the horizontal gap 501 may not necessarily be a minute gap. Even when only the vertical gap 502 is a minute gap, a reduction in the evaporation of the lubricating oil 46 out of the bearing mechanism 4 can be achieved, and also, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 31 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- the fan 1 is provided with an annular member 49 b arranged in an annular shape centered on a central axis J 1 in addition to an annular member 49 .
- the outside diameter of the annular member 49 is arranged to be smaller than the outside diameter of an upper surface of an annular upper portion 481 .
- the annular member 49 b includes a top cover portion 491 b and a tubular portion 492 b .
- the top cover portion 491 b is arranged substantially in the shape of an annular plate centered on the central axis J 1 .
- the tubular portion 492 b is arranged substantially in the shape of a cylinder centered on the central axis J 1 .
- the tubular portion 492 b is arranged to extend downward from an outer edge portion of the top cover portion 491 b .
- An inner circumferential surface of the tubular portion 492 b is fixed to an outer circumferential surface of the annular upper portion 481 .
- the inner circumferential surface of the tubular portion 492 b is arranged radially opposite an outer circumferential surface of the annular member 49 .
- the top cover portion 491 b is arranged above the annular member 49 .
- a lower surface of the top cover portion 491 b is arranged axially opposite an upper surface of the annular member 49 .
- a minute horizontal gap 501 extending radially is defined between a lower surface of the annular member 49 and an upper surface of a bearing portion 44 a .
- a minute vertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the outer circumferential surface of the annular member 49 and the inner circumferential surface of the tubular portion 492 b .
- a minute horizontal gap 501 a extending radially is defined between the upper surface of the annular member 49 and the lower surface of the top cover portion 491 b .
- a lower end portion of the vertical gap 502 is connected with a radially outer end portion of the horizontal gap 501 .
- An upper end portion of the vertical gap 502 is connected with a radially outer end portion of the horizontal gap 501 a .
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 , the vertical gap 502 , and the horizontal gap 501 a.
- Each of a minimum axial width of the horizontal gap 501 , a minimum axial width of the horizontal gap 501 a , and a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the vertical gap 502 and the horizontal gap 501 a in addition to the horizontal gap 501 contributes to more effectively preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to further reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- each of the horizontal gap 501 and the vertical gap 502 may not necessarily be a minute gap. Even when only the horizontal gap 501 a is a minute gap, a reduction in the evaporation of the lubricating oil 46 out of the bearing mechanism 4 can be achieved, and also, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 32 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- an annular member 49 is fixed to an upper portion of a bearing portion 44 a .
- the annular member 49 is fixed to an upper surface of an annular upper portion 481 .
- the annular member 49 is arranged substantially in the shape of an annular plate centered on a central axis J 1 .
- the inside diameter of the annular member 49 is arranged to be slightly greater than the outside diameter of a shaft 41 .
- An inner circumferential surface of the annular member 49 is arranged radially opposite an outer circumferential surface 411 of the shaft 41 axially between a seal portion 55 a and an attachment surface 413 .
- a minute vertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the inner circumferential surface of the annular member 49 and the outer circumferential surface 411 of the shaft 41 .
- a seal gap 55 is arranged to be in communication with an exterior space through the vertical gap 502 .
- a minimum radial width of the vertical gap 502 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 . That is, the annular member 49 is arranged to cover a portion of the opening of the seal gap 55 from above. In other words, the annular member 49 is arranged to cover a portion of the opening of the seal gap 55 in a plan view.
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined above the seal portion 55 a .
- Provision of the vertical gap 502 contributes to preventing an air including a lubricating oil evaporated from the seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 33 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 32 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- a bearing portion 44 a includes an annular projection portion 482 arranged to project upward from an outer edge portion of an upper surface of an annular upper portion 481 .
- the annular projection portion 482 is arranged substantially in the shape of a cylinder centered on a central axis J 1 .
- annular member 49 is arranged on the upper surface of the annular upper portion 481 of the bearing portion 44 a on a radially inner side of the annular projection portion 482 .
- the annular member 49 may be fixed to an inner circumferential surface of the annular projection portion 482 .
- An outer circumferential surface of the annular member 49 is arranged to be in contact with the inner circumferential surface of the annular projection portion 482 throughout an entire circumference thereof.
- annular projection portion 482 may be arranged to project upward from a position on a radially inner side of the outer edge portion of the upper surface of the annular upper portion 481 . Also note that only a portion or portions of the outer circumferential surface of the annular member 49 may be arranged to be in contact with the inner circumferential surface of the annular projection portion 482 .
- a vertical gap 502 similar to the vertical gap 502 illustrated in FIG. 32 is defined between an inner circumferential surface of the annular member 49 and an outer circumferential surface 411 of a shaft 41 . Provision of the vertical gap 502 contributes to preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- annular member 49 Since the outer circumferential surface of the annular member 49 is arranged to be in contact with the inner circumferential surface of the annular projection portion 482 , positioning of the annular member 49 can be easily accomplished when the annular member 49 is attached to the bearing portion 44 a.
- FIG. 34 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 32 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- a first portion 215 of a holder projecting portion 211 a of a rotor holder 210 is arranged above an annular member 49 .
- a lower surface of the first portion 215 is arranged axially opposite an upper surface of the annular member 49 .
- a second portion 216 of the holder projecting portion 211 a is arranged radially outside an annular upper portion 481 of a bearing portion 44 a .
- An inner circumferential surface of the second portion 216 is arranged radially opposite each of an outer circumferential surface of the annular member 49 and an outer circumferential surface of the annular upper portion 481 .
- a minute vertical gap 502 extending in the axial direction and arranged in an annular shape centered on a central axis J 1 is defined between an inner circumferential surface of the annular member 49 and an outer circumferential surface 411 of a shaft 41 .
- a minute horizontal gap 501 spreading perpendicularly to the central axis J 1 is defined between the lower surface of the first portion 215 and the upper surface of the annular member 49 .
- a minute vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the inner circumferential surface of the second portion 216 and a combination of the outer circumferential surface of the annular member 49 and the outer circumferential surface of the annular upper portion 481 .
- the minute vertical gap 504 is defined between the inner circumferential surface of the second portion 216 and the combination of the outer circumferential surface of the annular member 49 and the outer circumferential surface of the annular upper portion 481 in the present modification of the first preferred embodiment, the minute vertical gap 504 may be defined only between the inner circumferential surface of the second portion 216 and the outer circumferential surface of the annular upper portion 481 . In other words, a portion of the vertical gap 504 which is defined between the inner circumferential surface of the second portion 216 and the outer circumferential surface of the annular member 49 may not necessarily be a minute gap.
- An upper end portion of the vertical gap 502 is connected with a radially inner end portion of the horizontal gap 501 .
- An upper end portion of the vertical gap 504 is connected with a radially outer end portion of the horizontal gap 501 .
- a seal gap 55 is arranged to be in communication with an exterior space through the vertical gap 502 , the horizontal gap 501 , and the vertical gap 504 .
- Each of a minimum radial width of the vertical gap 502 , a minimum radial width of the vertical gap 504 , and a minimum axial width of the horizontal gap 501 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the horizontal gap 501 and the vertical gap 504 in addition to the vertical gap 502 contributes to more effectively preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to further reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 35 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 34 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- the annular member 49 is not provided, and a lower surface of a first portion 215 of a holder projecting portion 211 a is arranged axially opposite an upper surface of an annular upper portion 481 of a bearing portion 44 a.
- a horizontal gap 509 extending radially is defined between the lower surface of the first portion 215 and the upper surface of the annular upper portion 481 .
- a radially outer end portion of the horizontal gap 509 is connected with an upper end portion of a vertical gap 504 .
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 509 and the vertical gap 504 .
- a minimum radial width of the vertical gap 504 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined radially outward of the seal gap 55 .
- Provision of the vertical gap 504 contributes to more effectively preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to further reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 36 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 35 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- an annular member 49 c is fixed to a second portion 216 of a holder projecting portion 211 a .
- the annular member 49 c is arranged substantially in the shape of a cylinder centered on a central axis J 1 .
- An outer circumferential surface of the annular member 49 c is fixed to an inner circumferential surface of the second portion 216 .
- a lower end of the annular member 49 c is arranged in the vicinity of an upper end of a bearing support portion 31 .
- An inner circumferential surface of the annular member 49 c is arranged radially opposite an outer circumferential surface of an annular upper portion 481 .
- a lower surface of the annular member 49 c is arranged axially opposite an upper surface of the bearing support portion 31 .
- a minute vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the inner circumferential surface of the annular member 49 c and the outer circumferential surface of the annular upper portion 481 .
- a minute horizontal gap 506 extending radially is defined between the lower surface of the annular member 49 c and the upper surface of the bearing support portion 31 .
- An upper end portion of the vertical gap 504 is connected with a radially outer end portion of a horizontal gap 509 .
- a lower end portion of the vertical gap 504 is connected with a radially inner end portion of the horizontal gap 506 .
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 509 , the vertical gap 504 , and the horizontal gap 506 .
- Each of a minimum radial width of the vertical gap 504 and a minimum axial width of the horizontal gap 506 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined radially outward of the seal gap 55 .
- Provision of the horizontal gap 506 in addition to the vertical gap 504 contributes to more effectively preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to further reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 37 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 35 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- a holder projecting portion 211 a of a rotor holder 210 includes a burring portion 214 arranged to extend downward from a radially inner end portion of a first portion 215 .
- a bearing portion 44 a includes an annular outer wall portion 483 arranged to extend upward from an outer edge portion of an upper surface of an annular upper portion 481 .
- the annular outer wall portion 483 is arranged substantially in the shape of a cylinder centered on a central axis J 1 .
- An outer circumferential surface of the annular outer wall portion 483 is arranged radially opposite an inner circumferential surface of a second portion 216 of the holder projecting portion 211 a.
- a minute vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the outer circumferential surface of the annular outer wall portion 483 and the inner circumferential surface of the second portion 216 .
- a space 508 above the annular upper portion 481 is connected with an upper end portion of the vertical gap 504 .
- a seal gap 55 is arranged to be in communication with an exterior space through the space 508 and the vertical gap 504 .
- a minimum radial width of the vertical gap 504 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined radially outward of the seal gap 55 .
- Provision of the vertical gap 504 contributes to preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 38 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 36 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- an impeller 12 is fixed to a shaft 41 through a bushing 25 .
- the bushing 25 is arranged substantially in the shape of a column centered on a central axis J 1 .
- the outside diameter of the bushing 25 is arranged to be slightly greater than the outside diameter of an annular upper portion 481 .
- An inner circumferential surface of a top face portion 123 of the impeller 12 is fixed to an outer circumferential surface of the bushing 25 .
- a lower surface of the bushing 25 is arranged axially opposite an upper surface of the annular upper portion 481 of a bearing portion 44 a .
- An annular member 49 c is also fixed to the outer circumferential surface of the bushing 25 .
- the annular member 49 c is arranged substantially in the shape of a cylinder centered on the central axis J 1 .
- An inner circumferential surface of the annular member 49 c is fixed to the outer circumferential surface of the bushing 25 below the top face portion 123 of the impeller 12 .
- the inner circumferential surface of the annular member 49 c is arranged radially opposite an outer circumferential surface of the annular upper portion 481 .
- a minute horizontal gap 501 extending radially is defined between the lower surface of the bushing 25 and the upper surface of the annular upper portion 481 .
- a minute vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the inner circumferential surface of the annular member 49 c and the outer circumferential surface of the annular upper portion 481 .
- An upper end portion of the vertical gap 504 is connected with a radially outer end portion of the horizontal gap 501 .
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 504 .
- Each of a minimum axial width of the horizontal gap 501 and a minimum radial width of the vertical gap 504 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the horizontal gap 501 and the vertical gap 504 contributes to preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- FIG. 39 is a cross-sectional view illustrating a portion of a fan 1 according to yet another modification of the first preferred embodiment.
- the fan 1 according to the present modification of the first preferred embodiment is similar in structure to the fan 1 illustrated in FIG. 38 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted.
- an impeller 12 includes an inner tubular portion 123 a arranged substantially in the shape of a cylinder centered on a central axis J 1 .
- the inner tubular portion 123 a is arranged to extend downward from a radially inner end portion of a top face portion 123 .
- An upper portion of an inner circumferential surface of the inner tubular portion 123 a is fixed to an outer circumferential surface of a bushing 25 .
- a lower portion of the inner circumferential surface of the inner tubular portion 123 a is arranged radially opposite an outer circumferential surface of an annular upper portion 481 of a bearing portion 44 a.
- a minute vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J 1 is defined between the inner circumferential surface of the inner tubular portion 123 a and the outer circumferential surface of the annular upper portion 481 .
- An upper end portion of the vertical gap 504 is connected with a radially outer end portion of a horizontal gap 501 .
- a seal gap 55 is arranged to be in communication with an exterior space through the horizontal gap 501 and the vertical gap 504 .
- Each of a minimum axial width of the horizontal gap 501 and a minimum radial width of the vertical gap 504 is arranged to be smaller than a maximum radial width of an opening of the seal gap 55 .
- a labyrinth having a width smaller than the maximum radial width of the seal gap 55 is defined. Provision of the horizontal gap 501 and the vertical gap 504 contributes to preventing an air including a lubricating oil evaporated from a seal portion 55 a from traveling out of a bearing mechanism 4 . This contributes to reducing evaporation of a lubricating oil 46 out of the bearing mechanism 4 . Furthermore, entry of an extraneous material, such as dust, into the seal portion 55 a can be prevented.
- each of the horizontal gaps 501 , 501 a , and 506 may have a width greater than the maximum width of the opening of the seal gap 55 as long as the width is very small.
- the bushing 25 may be defined by a sintered member shaped by press working, for example.
- the shaft 41 includes a shoulder portion defined at an axial position corresponding to that of the lower surface of the bushing 25 , and the lower surface of the bushing 25 is arranged to be in axial contact with the shoulder portion.
- the bushing 25 may be arranged to have an outside diameter substantially equal to the outside diameter of the bearing portion 44 .
- an inner circumferential surface of the upper portion of the bearing support portion 31 is arranged radially outward of an inner circumferential surface of a remaining portion of the bearing support portion 31 , so that the vertical gap 502 is defined between the inner circumferential surface of the upper portion of the bearing support portion 31 and the outer circumferential surface of the bushing 25 .
- the bushing 25 may be arranged to have an outside diameter smaller than the outside diameter of the bearing housing 48 .
- the vertical gap 502 can thereby be easily defined between the bushing 25 and the bearing support portion 31 .
- an inclined gap similar to the inclined gap 503 illustrated in FIG. 20 may be defined between the bearing housing 48 and the bushing 25 .
- the top face portion 21 b of the rotor holder 210 illustrated in FIG. 17 may be modified to include a through hole extending in the axial direction therethrough as a channel to cool the stator 32 .
- the impeller 12 illustrated in FIG. 1 is directly fixed to the outer circumferential surface of the bushing 25 , the impeller 12 may be indirectly fixed thereto through one or more members.
- the impeller 12 illustrated in FIG. 17 may be fixed to the bushing 25 through two or more members.
- the first through hole 128 a illustrated in FIG. 27 may not necessarily be defined in the center of the top face portion 123 .
- each of the impellers 12 illustrated in FIGS. 28 to 37 is directly fixed to the rotor holder 210
- the impeller 12 may be indirectly fixed thereto through one or more members.
- Each of the impellers 12 illustrated in FIGS. 28 to 34 may be directly fixed to the shaft 41 without the rotor holder 210 intervening therebetween.
- Each of the impellers 12 illustrated in FIGS. 28 to 34 may be indirectly fixed to the shaft 41 through a bushing.
- the thrust dynamic pressure bearing portion may be defined only on an upper side of the thrust plate. In this case, as is the case with the bearing mechanism 4 illustrated in FIG. 21 , an upward force is constantly applied to the shaft 41 .
- a thrust dynamic pressure bearing portion arranged to produce a force that acts in a direction opposite to that of the force which lifts the impeller 12 can be easily defined by the thrust plate and the bearing portion 44 .
- An upper portion of the first radial dynamic pressure groove array 711 may be defined in the second inclined surface 441 b independently of a remaining portion thereof. Also, no dynamic pressure grooves may be defined in the second inclined surface 441 b of the bearing portion 44 . Even in this case, provision of the second inclined surface 441 b secures an area to support the shaft 41 so that bearing rigidity can be improved to a certain extent.
- each of the first and second radial dynamic pressure groove arrays 711 and 712 may be defined in the outer circumferential surface 411 of the shaft 41 .
- the thrust dynamic pressure groove arrays 721 and 722 may be defined in the upper surface and the lower surface, respectively, of the thrust plate 42 .
- the communicating hole 421 a may not necessarily be provided in the bearing mechanism 4 .
- the outer circumferential surface 411 of the shaft 41 may be arranged to include a portion which has a decreased diameter in the vicinity of a top portion of the bearing portion 44 so that the seal portion may be defined between this portion and the inner circumferential surface 441 of the bearing portion 44 .
- a viscoseal that generates a fluid dynamic pressure through a dynamic pressure groove defined in the seal gap may be used as the seal portion.
- a metallic member may be arranged, as the weight, in the balance correction portion 125 of the top face portion 123 of the impeller 12 .
- a through hole or a cut portion may be defined as the balance correction portion 125 .
- the weight may be arranged on only one of the top face portion 123 and the lower end portion 124 a of the side wall portion 124 .
- the unbalance of the rotating portion 2 may be eliminated by removing a portion of the top face portion 123 or a portion of the side wall portion 124 .
- the magnetic center of the stator 32 and the magnetic center of the rotor magnet 22 may be arranged to coincide with each other in the axial direction when the motor 11 is stationary. An additional reduction in the vibrations of the motor 11 can thereby be achieved.
- the motor 11 may be used as a motor of a fan of another type, such as a centrifugal fan.
- a fan in which the motor 11 is used is optimal for use with a device having a hard disk installed therein, such as a server. In the server, the fan is disposed at a position close to the hard disk. Therefore, if the fan is of a type which generates significant vibrations, read or write errors tend to easily occur in the hard disk. In contrast, read or write errors do not easily occur in the hard disk if the fan installed in the server uses the motor 11 .
- the present invention is, for example, applicable to fans arranged to generate air currents.
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- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Sliding-Contact Bearings (AREA)
- Connection Of Motors, Electrical Generators, Mechanical Devices, And The Like (AREA)
- Structures Of Non-Positive Displacement Pumps (AREA)
- Sealing Of Bearings (AREA)
Abstract
A dynamic pressure bearing apparatus includes a bearing portion; a shaft; a substantially annular bushing; a radial dynamic pressure bearing portion; and a seal gap. A minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing. The seal gap is arranged to be in communication with an exterior space through the horizontal gap.
Description
- 1. Field of the Invention
- The present invention relates to a dynamic pressure bearing apparatus installed in a motor.
- 2. Description of the Related Art
- Ball bearings have been adopted as bearings in a variety of fans, such as axial fans and centrifugal fans. For example, ball bearings are adopted in a fan described in JP-A 2011-78224. Meanwhile, an oil-impregnated bearing obtained by sintering powder of a copper-based material is adopted in a fan described in JP-A 2000-14080.
- A dynamic pressure bearing apparatus for use in a spindle motor of a disk drive apparatus is disclosed in JP-A 2005-321089. The dynamic pressure bearing apparatus includes a housing, a bearing sleeve, a shaft member, and a ring-shaped seal member. The bearing sleeve is fixed to the housing. The shaft member is arranged inside the bearing sleeve. The seal member is fixed to the shaft member on an upper side of the bearing sleeve. In the dynamic pressure bearing apparatus, a radial bearing portion is defined between an inner circumferential surface of the bearing sleeve and an outer circumferential surface of the shaft member. The shaft member is supported in a radial direction in a non-contact manner through the radial bearing portion. A first thrust bearing portion is defined between an upper end surface of the bearing sleeve and a lower end surface of the seal member. A second thrust bearing portion is defined between a lower end surface of the bearing sleeve and a flange portion provided at a lower end of the shaft member. The seal member and the flange portion are supported in a thrust direction in a non-contact manner through the first and second thrust bearing portions, respectively. A seal space is defined between an outer circumferential surface of the seal member and an inner circumferential surface of an upper end portion of the housing. A surface of a lubricating oil is kept always within a range of the seal space.
- A spindle motor of a hard disk drive disclosed in JP-A 2000-175405 includes a hub having a rotor magnet attached thereto, and a base having stator coils attached thereto through a sleeve. An outer edge portion of the hub is arranged in proximity to the base, so that a labyrinth is defined between the hub and the base. Oil mist and the like generated in the spindle motor are thereby prevented from being dispersed, enabling the hard disk drive to achieve a high performance. A spindle motor disclosed in JP-A 2004-248481 includes a hub including a cylindrical projecting portion arranged to project downward. A labyrinth seal is defined by a combination of a clearance space between an upper surface of a bearing sleeve and a lower surface of a portion of the hub which is arranged radially inward of the projecting portion, a clearance space between an inner circumferential surface of the projecting portion and an outer circumferential surface of the bearing sleeve, and a clearance space between a lower surface of the projecting portion and a flange arranged around the bearing sleeve.
- In recent years, electronic devices, such as servers, have improved in performance, and the amount of heat generated from the electronic devices has increased accordingly. There is therefore a demand for cooling fans in the electronic devices to be rotated at higher speeds in order to increase air volume. However, an increase in the rotation speed of the cooling fans leads to greater vibrations of the cooling fans, and this will affect other devices in the electronic devices. For example, vibrations of a cooling fan may cause an error in reading or writing by a disk drive apparatus.
- A dynamic pressure bearing apparatus according to a preferred embodiment of the present invention includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion; a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein. A minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing. The seal gap is arranged to be in communication with an exterior space through the horizontal gap.
- A dynamic pressure bearing apparatus according to a preferred embodiment of the present invention includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion; a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein. A horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing. A minute vertical gap extending in an axial direction and arranged in an annular shape centered on the central axis is defined between a circumferential surface of the bearing portion and a circumferential surface of the bushing. The vertical gap is connected with a radially outer end portion of the horizontal gap. The seal gap is arranged to be in communication with an exterior space through the horizontal gap and the vertical gap.
- A dynamic pressure bearing apparatus according to a preferred embodiment of the present invention includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and an annular member arranged in an annular shape, fixed to the shaft axially between the seal portion and the attachment surface, and arranged to extend radially outward beyond an opening of the seal gap. A minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the annular member. The seal gap is arranged to be in communication with an exterior space through the horizontal gap.
- A dynamic pressure bearing apparatus according to a preferred embodiment of the present invention includes a bearing portion; a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members; a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and an annular member arranged in an annular shape, and fixed to an upper portion of the bearing portion. A minute vertical gap extending in an axial direction is defined between the outer circumferential surface of the shaft and an inner circumferential surface of the annular member. A minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of an opening of the seal gap. The seal gap is arranged to be in communication with an exterior space through the vertical gap.
- Preferred embodiments of the present invention provide dynamic pressure bearing apparatuses having structures suited to reduced vibration of fans.
- The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
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FIG. 1 is a cross-sectional view of a fan according to a first preferred embodiment of the present invention. -
FIG. 2 is a cross-sectional view of a bearing mechanism according to the first preferred embodiment. -
FIG. 3 is a cross-sectional view of the bearing mechanism. -
FIG. 4 is a cross-sectional view illustrating a portion of the bearing mechanism in an enlarged form. -
FIG. 5 is a cross-sectional view illustrating a portion of the bearing mechanism in an enlarged form. -
FIG. 6 is a cross-sectional view of a bearing portion according to the first preferred embodiment. -
FIG. 7 is a bottom view of the bearing portion. -
FIG. 8 is a plan view of a thrust cap according to the first preferred embodiment. -
FIG. 9 is a graph showing a result of a simulation of vibration that occurs in the fan. -
FIG. 10 is a graph showing a result of a simulation of vibration that occurs in the fan. -
FIG. 11 is a graph showing a result of a simulation of vibration that occurs in the fan. -
FIG. 12 is a graph showing a result of a simulation of vibration that occurs in the fan. -
FIG. 13 is a graph showing a result of a simulation of vibration that occurs in a fan as a comparative example. -
FIG. 14 is a cross-sectional view of a bearing mechanism according to a modification of the first preferred embodiment. -
FIG. 15 is a cross-sectional view illustrating a portion of the bearing mechanism. -
FIG. 16 is a cross-sectional view of a fan according to a modification of the first preferred embodiment. -
FIG. 17 is a diagram illustrating a structure in which a bushing and a rotor holder are fixed to each other according to a modification of the first preferred embodiment. -
FIG. 18 is a diagram illustrating a structure in which a bushing and a rotor holder are fixed to each other according to a further modification of the first preferred embodiment. -
FIG. 19 is a diagram illustrating a labyrinth structure according to a modification of the first preferred embodiment. -
FIG. 20 is a diagram illustrating a labyrinth structure according to a modification of the first preferred embodiment. -
FIG. 21 is a cross-sectional view illustrating a bearing mechanism according to another modification of the first preferred embodiment. -
FIG. 22 is a cross-sectional view illustrating a bearing mechanism according to yet another modification of the first preferred embodiment. -
FIG. 23 is a cross-sectional view illustrating a bearing mechanism according to yet another modification of the first preferred embodiment. -
FIG. 24 is a cross-sectional view illustrating a bearing mechanism according to yet another modification of the first preferred embodiment. -
FIG. 25 is a cross-sectional view of a fan according to a modification of the first preferred embodiment. -
FIG. 26 is a cross-sectional view of a fan according to another modification of the first preferred embodiment. -
FIG. 27 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 28 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 29 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 30 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 31 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 32 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 33 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 34 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 35 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 36 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 37 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 38 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. -
FIG. 39 is a cross-sectional view of a fan according to yet another modification of the first preferred embodiment. - It is assumed herein that a vertical direction is defined as a direction in which a central axis of a motor extends, and that an upper side and a lower side along the central axis in
FIG. 1 are referred to simply as an upper side and a lower side, respectively. It should be noted, however, that the above definitions of the vertical direction and the upper and lower sides should not be construed to restrict relative positions or directions of different members or portions when the motor is actually installed in a device. Also note that a direction parallel to the central axis is referred to by the term “axial direction”, “axial”, or “axially”, that radial directions centered on the central axis are simply referred to by the term “radial direction”, “radial”, or “radially”, and that a circumferential direction about the central axis is simply referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”. -
FIG. 1 is a cross-sectional view of anaxial fan 1 according to a first preferred embodiment of the present invention. Hereinafter, theaxial fan 1 will be referred to simply as the “fan 1”. Thefan 1 includes amotor 11, animpeller 12, ahousing 13, a plurality ofsupport ribs 14, and abase portion 15. Thehousing 13 is arranged to surround an outer circumference of theimpeller 12. Thehousing 13 is joined to thebase portion 15 through thesupport ribs 14. Thesupport ribs 14 are arranged in a circumferential direction. Thebase portion 15 is defined integrally with thesupport ribs 14. Themotor 11 is fixed on thebase portion 15. - The
impeller 12 is made of a resin, and includes acup 121 and a plurality ofblades 122. Thecup 121 is arranged substantially in the shape of a covered cylinder. Thecup 121 is arranged to cover an outside of themotor 11. Thecup 121 is arranged to define a portion of arotating portion 2 of themotor 11. The rotatingportion 2 will be described below. Thecup 121 includes atop face portion 123 and aside wall portion 124. Thetop face portion 123 is arranged to spread perpendicularly to a central axis J1. Theside wall portion 124 is arranged to extend downward from an outer edge portion of thetop face portion 123. Theblades 122 are arranged to extend radially outward from an outer circumferential surface of theside wall portion 124 with the central axis J1 as a center. Thecup 121 and theblades 122 are defined integrally with each other by a resin injection molding process. - A
hole portion 125 is defined in an upper surface of thetop face portion 123. Aweight 129 is arranged in thehole portion 125. Theweight 129 is an adhesive including a metal having a high specific gravity, such as tungsten. Anotherweight 129 is arranged on alower end portion 124 a of theside wall portion 124 on a radially inner side thereof. A reduction in unbalance of each of theimpeller 12 and therotating portion 2 of themotor 11 can be achieved by arranging theweight 129 on each of an upper portion and a lower portion of theimpeller 12. Two-plane balance correction as described above achieves a reduction in vibrations of thefan 1 owing to a displacement of a center of gravity of any of theimpeller 12 and themotor 11 from the central axis J1. Hereinafter, thehole portion 125 and thelower end portion 124 a of theside wall portion 124, on each of which theweight 129 is arranged, will be referred to as “balance correction portions - The
impeller 12 of thefan 1 is caused by themotor 11 to rotate about the central axis J1 to produce downward air currents. - The
motor 11 is a three-phase outer-rotor motor. Themotor 11 includes therotating portion 2, astationary portion 3, and abearing mechanism 4. The rotatingportion 2 includes a substantially cylindricalmetallic yoke 21, arotor magnet 22, and thecup 121. Theyoke 21 is fixed to an inside of thecup 121. Therotor magnet 22 is fixed to an inner circumferential surface of theyoke 21. Thebearing mechanism 4 is a dynamic pressure bearing apparatus arranged to generate a fluid dynamic pressure in a lubricatingoil 46. The rotatingportion 2 is supported through thebearing mechanism 4 to be rotatable about the central axis J1 with respect to thestationary portion 3. - The
stationary portion 3 includes a substantially cylindricalbearing support portion 31, astator 32, and acircuit board 33. A lower portion of thebearing support portion 31 is fixed to an inner circumferential surface of thebase portion 15 which defines a central hole portion thereof. Thestator 32 is fixed to an outer circumferential surface of thebearing support portion 31 on an upper side of thebase portion 15. Thestator 32 is arranged radially inside therotor magnet 22. Thestator 32 includes astator core 321 and a plurality ofcoils 322 arranged on thestator core 321. Thestator core 321 is defined by laminated steel sheets. Thecircuit board 33 is fixed below thestator 32. Lead wires from thecoils 322 are attached to pins (not shown) inserted in holes of thecircuit board 33, whereby thestator 32 and thecircuit board 33 are electrically connected with each other. Note that the lead wires from thecoils 322 may be directly connected to thecircuit board 33. While themotor 11 is driven, a turning force is generated between therotor magnet 22 and thestator 32. - An annular
magnetic member 331 is arranged on an upper surface of thecircuit board 33. Themagnetic member 331 is arranged under therotor magnet 22. While themotor 11 is stationary, a magnetic center of thestator 32 is located at a level lower than that of a magnetic center of therotor magnet 22. In thefan 1, magnetic attraction forces that attract therotor magnet 22 downward are generated between therotor magnet 22 and thestator 32, and between therotor magnet 22 and themagnetic member 331. A force that acts to lift theimpeller 12 relative to thestationary portion 3 during rotation of thefan 1 is thereby reduced. -
FIG. 2 is a cross-sectional view illustrating thebearing mechanism 4. Thebearing mechanism 4 includes ashaft 41, anannular thrust plate 42, a bearingportion 44, athrust cap 45, which corresponds to a cap member, a substantiallyannular bushing 25, and the lubricatingoil 46. Thebushing 25 is made of a metal. An inner circumferential surface of thebushing 25 is press fitted and thereby fixed to an upper portion of theshaft 41 on an upper side of the bearingportion 44. Thebushing 25 is arranged to have an outside diameter smaller than that of the bearingportion 44. As illustrated inFIG. 1 , theimpeller 12 is fixed to an outer circumferential surface of thebushing 25. That is, thetop face portion 123 of theimpeller 12 is indirectly fixed to the upper portion of theshaft 41 through thebushing 25. Theimpeller 12 and thebushing 25 may be joined to each other by an insert molding process. In this case, the outside diameter of thebushing 25 is arranged to be greater than the outside diameter of the bearingportion 44. This makes it possible to mold theimpeller 12 while at the same time fixing theimpeller 12 to thebushing 25 by arranging the resin on the outer circumferential surface of thebushing 25 when thebearing mechanism 4 as illustrated inFIG. 2 is placed inside a mold, without a need to use a complicated mold. Because theimpeller 12 is directly fixed to thebushing 25, the structure of thefan 1 can be simplified, and a reduction in a production cost of thefan 1 can be achieved. Moreover, since thebushing 25 is arranged, inside the mold, to be substantially concentric with the central axis with high precision, and theimpeller 12 is molded around thebushing 25, concentricity of each of theimpeller 12 and thebushing 25 with the central axis J1 is achieved with high accuracy. Thethrust plate 42 is a thrust portion arranged axially opposite the bearingportion 44, and fixed to a lower portion of theshaft 41. Thethrust plate 42 is arranged to extend radially outward from a lower end of theshaft 41. The bearingportion 44 is arranged radially inside thestator 32. Note that each of theshaft 41 and thethrust plate 42 defines a portion of therotating portion 2, while each of the bearingportion 44 and thethrust cap 45 defines a portion of thestationary portion 3. The same is true of other preferred embodiments of the present invention described below. -
FIG. 3 is a cross-sectional view of a lower portion of thebearing mechanism 4 and its vicinity in an enlarged form. An inner circumferential surface of thethrust plate 42 includes agroove portion 421 arranged to extend in an axial direction, and a communicatinghole 421 a is defined between thegroove portion 421 and an outercircumferential surface 411 of theshaft 41. This contributes to reducing a difference in internal pressure of the lubricatingoil 46 between an upper side and a lower side of thethrust plate 42. Referring toFIG. 4 , an upper surface of thethrust plate 42 includes aninclined surface 422 a defined in an outer edge portion thereof. Theinclined surface 422 a is arranged to be inclined downward with increasing distance from the central axis J1. A portion of the upper surface of thethrust plate 42 which is located radially inward of theinclined surface 422 a is an annular surface perpendicular to the central axis J1 and arranged around theshaft 41. Hereinafter, this portion of the upper surface of thethrust plate 42 will be referred to as an “upperannular surface 422”. An outer edge portion of a lower surface of thethrust plate 42 includes aninclined surface 423 a arranged to be inclined upward with increasing distance from the central axis J1. A portion of the lower surface of thethrust plate 42 which is located radially inward of theinclined surface 423 a is an annular surface perpendicular to the central axis J1. Hereinafter, this portion of the lower surface of thethrust plate 42 will be referred to as a “lowerannular surface 423”. - The bearing
portion 44 illustrated inFIG. 3 is a single sleeve made of a metal, such as stainless steel or phosphor bronze. The bearingportion 44 is fixed to an inner circumferential surface of thebearing support portion 31. Theshaft 41 is inserted in the bearingportion 44. The bearingportion 44 includes afirst shoulder portion 442 defined by an increase in the diameter of an innercircumferential surface 441 of the bearingportion 44 in a lower portion of the innercircumferential surface 441, and asecond shoulder portion 443 defined by an increase in the diameter of the innercircumferential surface 441 between thefirst shoulder portion 442 and alower end portion 444 of the bearingportion 44. Thethrust cap 45 is arranged inside of thelower end portion 444, and an outer circumferential surface of thethrust cap 45 is fixed to an inner circumferential surface of thelower end portion 444. Thethrust cap 45 is arranged to close a bottom portion of the bearingportion 44 below thethrust plate 42. An outer edge portion of anupper surface 451 of thethrust cap 45 is arranged to be in axial contact with alower surface 443 a of thesecond shoulder portion 443. Thethrust plate 42 is arranged between thefirst shoulder portion 442 and thesecond shoulder portion 443. - In the
bearing mechanism 4, aradial gap 51 is defined between the innercircumferential surface 441 of the bearingportion 44 and the outercircumferential surface 411 of theshaft 41. Agap 52 is defined between the upperannular surface 422 of thethrust plate 42 and alower surface 442 a of thefirst shoulder portion 442, which is arranged axially opposite the upperannular surface 422. Hereinafter, thegap 52 will be referred to as a “firstlower thrust gap 52”. The lowerannular surface 423 of thethrust plate 42 and theupper surface 451 of thethrust cap 45 are arranged axially opposite each other, and agap 53 is defined between the lowerannular surface 423 and theupper surface 451. Hereinafter, thegap 53 will be referred to as a “secondlower thrust gap 53”. The sum of the axial width of the firstlower thrust gap 52 and the axial width of the secondlower thrust gap 53 is arranged in the range of about 10 μm to about 40 μm. Agap 54 is defined between an outer circumferential surface of thethrust plate 42 and a portion of the innercircumferential surface 441 of the bearingportion 44 which is radially opposed to the outer circumferential surface of thethrust plate 42. Hereinafter, thegap 54 will be referred to as a “side gap 54”. -
FIG. 5 is a diagram illustrating an upper portion of the bearingportion 44 and its vicinity in an enlarged form. An upper portion of the innercircumferential surface 441 of the bearingportion 44 includes a firstinclined surface 441 a and a secondinclined surface 441 b. The firstinclined surface 441 a is arranged to extend radially inward and obliquely downward from an upper surface of the bearingportion 44. In other words, the diameter of the firstinclined surface 441 a is arranged to gradually increase with increasing height. The secondinclined surface 441 b is arranged to extend radially inward and obliquely downward from a lower end of the firstinclined surface 441 a. An angle defined by the firstinclined surface 441 a with the central axis J1 is arranged to be greater than an angle defined by the secondinclined surface 441 b with the central axis J1. A boundary between the first and secondinclined surfaces inclined surface 441 a and the outercircumferential surface 411 of theshaft 41. - The first
inclined surface 441 a and the outercircumferential surface 411 of theshaft 41 are arranged to together define asingle seal gap 55 therebetween. Theseal gap 55 is arranged to gradually increase in radial width with increasing height. Theseal gap 55 is arranged in an annular shape centered on the central axis J1. Aseal portion 55 a arranged to retain the lubricatingoil 46 through capillary action is defined in theseal gap 55. Theseal gap 55 serves also as an oil buffer arranged to hold a large amount of the lubricatingoil 46. In themotor 11, theseal gap 55, theradial gap 51 illustrated inFIG. 3 , the firstlower thrust gap 52, theside gap 54, and the secondlower thrust gap 53 are arranged to together define a singlecontinuous bladder structure 5. The lubricatingoil 46 is arranged continuously in thebladder structure 5. Within thebladder structure 5, a surface of the lubricatingoil 46 is defined only in theseal gap 55 illustrated inFIG. 5 . - The upper surface of the bearing
portion 44 and a lower surface of thebushing 25, which is fixed to the upper portion of theshaft 41, are arranged to together define a minutehorizontal gap 501 therebetween. Thehorizontal gap 501 is arranged to extend radially and perpendicularly to the central axis J1. The axial width of thehorizontal gap 501 is arranged to be small enough to prevent entry of dust into thebearing mechanism 4 therethrough. The axial width of thehorizontal gap 501 is preferably arranged to be 200 μm or less. More preferably, the axial width of thehorizontal gap 501 is arranged to be 100 μm or less. The outer circumferential surface of thebushing 25 and the inner circumferential surface of thebearing support portion 31 are arranged to together define a minutevertical gap 502 therebetween. Thevertical gap 502 is arranged to extend in the axial direction, and is arranged in an annular shape centered on the central axis J1. Thevertical gap 502 is connected with a radially outer end portion of thehorizontal gap 501. In thefan 1, thehorizontal gap 501 is defined as a result of assembling of thebearing mechanism 4, while thevertical gap 502 is defined as a result of thebearing mechanism 4 being attached to thebearing support portion 31. Theseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 502. The term “exterior space” as used herein refers to a space above thestator 32 as illustrated inFIG. 1 . - Each of the axial width of the
horizontal gap 501 and the radial width of thevertical gap 502 is arranged to be smaller than the radial width of an upper end opening of theseal gap 55. The width of thehorizontal gap 501 refers, precisely, to a minimum width of thehorizontal gap 501. The width of thevertical gap 502 refers, precisely, to a minimum width of thevertical gap 502. The width of the upper end opening of theseal gap 55 corresponds to a maximum width of theseal gap 55. The maximum width of theseal gap 55 means a maximum width of a region of theseal gap 55 in which the lubricatingoil 46 can be retained. Since the width of each of thehorizontal gap 501 and thevertical gap 502 is smaller than the width of the upper end opening of theseal gap 55, a labyrinth having a width smaller than that of the upper end opening of theseal gap 55 is defined in thehorizontal gap 501 and thevertical gap 502. Provision of thehorizontal gap 501 and thevertical gap 502 contributes to preventing an air including a lubricating oil evaporated from theseal portion 55 a from traveling out of thebearing mechanism 4. This contributes to reducing evaporation of the lubricatingoil 46 out of thebearing mechanism 4. In other words, a labyrinth structure is defined by a combination of thehorizontal gap 501 and thevertical gap 502. - As a result, an improved life of the
fan 1 is achieved. In addition, since the labyrinth structure is defined by using thebushing 25, the rotatingportion 2 is not required to have a complicated structure. Since each of thebushing 25 and the bearingportion 44 is made of a metal, thehorizontal gap 501 can be defined with high precision. In addition, a reduction in the probability of adhesion of dust to thebushing 25 through static electricity and of entry of dust into the labyrinth structure is achieved. Note that thebushing 25 may be made of a non-metallic material as long as thebushing 25 can be shaped with high precision. -
FIG. 6 is a vertical cross-sectional view of the bearingportion 44. The upper portion and the lower portion of the innercircumferential surface 441 of the bearingportion 44 include a first radial dynamicpressure groove array 711 and a second radial dynamicpressure groove array 712, respectively, defined therein. Each of the first and second radial dynamicpressure groove arrays portion 44 includes minute recessed portions defined therein. The minute recessed portions are arranged axially between the first and second radial dynamicpressure groove arrays FIG. 3 , in an upper portion of theradial gap 51, an upper radial dynamicpressure bearing portion 681 arranged to generate a radial fluid dynamic pressure acting on the lubricatingoil 46 is defined through the first radial dynamicpressure groove array 711. In a lower portion of theradial gap 51, a lower radial dynamicpressure bearing portion 682 arranged to generate a radial fluid dynamic pressure acting on the lubricatingoil 46 is defined through the second radial dynamicpressure groove array 712. Hereinafter, the upper and lower radial dynamicpressure bearing portions pressure bearing portion 68”. The radial dynamicpressure bearing portion 68 is arranged axially between the twobalance correction portions FIG. 1 . The radial dynamicpressure bearing portion 68 is defined by a combination of the innercircumferential surface 441 of the bearingportion 44, the outercircumferential surface 411 of theshaft 41, and a portion of the lubricatingoil 46 which exists in theradial gap 51. - The
seal gap 55 illustrated inFIG. 5 is arranged above the radial dynamicpressure bearing portion 68, and is arranged to be continuous with the radial dynamicpressure bearing portion 68. In addition, the radial dynamicpressure bearing portion 68 is arranged axially between the twobalance correction portions FIG. 1 . Furthermore, the upper radial dynamicpressure bearing portion 681 is arranged to overlap with a center of gravity of each of themotor 11 and theimpeller 12 in a radial direction. -
FIG. 7 is a bottom view of the bearingportion 44. Thelower surface 442 a of thefirst shoulder portion 442 includes a first thrust dynamicpressure groove array 721 arranged in the herringbone pattern.FIG. 8 is a plan view of thethrust cap 45. Theupper surface 451 of thethrust cap 45, that is, a bottom surface of thebladder structure 5 illustrated inFIG. 3 , includes a second thrust dynamicpressure groove array 722 arranged in the herringbone pattern. Referring toFIG. 3 , in the firstlower thrust gap 52, a first lower thrust dynamicpressure bearing portion 691 arranged to generate an axial fluid dynamic pressure acting on the lubricatingoil 46 is defined through the first thrust dynamicpressure groove array 721. In addition, in the secondlower thrust gap 53, a second lower thrust dynamicpressure bearing portion 692 arranged to generate an axial fluid dynamic pressure acting on the lubricatingoil 46 is defined through the second thrust dynamicpressure groove array 722. - While the
motor 11 is driven, theshaft 41 is supported in the radial direction by the radial dynamicpressure bearing portion 68, and thethrust plate 42, which is arranged above a bottom portion of thebladder structure 5, is supported in a thrust direction by the first and second lower thrust dynamicpressure bearing portions portion 2 and theimpeller 12 illustrated inFIG. 1 are supported to be rotatable about the central axis J1 with respect to thestationary portion 3. While themotor 11 is driven, the lubricatingoil 46 circulates through the firstlower thrust gap 52, theside gap 54, the secondlower thrust gap 53, and the communicatinghole 421 a illustrated inFIG. 3 . In addition, theinclined surface 422 a is defined in the outer edge portion of the upper surface of thethrust plate 42 as illustrated inFIG. 4 , and this contributes to preventing thethrust plate 42 from coming into hard contact with thelower surface 442 a of thefirst shoulder portion 442 of the bearingportion 44 even when theshaft 41 is tilted. - Provision of the first and second lower thrust dynamic
pressure bearing portions motor 11 contributes to stabilizing the axial position of therotating portion 2 relative to thestationary portion 3 during rotation of theimpeller 12. This makes it easy to design thehorizontal gap 501 with a small axial width. Note that thehorizontal gap 501 is designed to have a sufficient width to prevent the lower surface of thebushing 25 from coming into contact with the upper surface of the bearingportion 44 even when thethrust plate 42 is brought into contact with thethrust cap 45. - Referring to
FIG. 6 , a portion of the first radial dynamicpressure groove array 711 is defined in a lower portion of the secondinclined surface 441 b. Referring toFIG. 5 , when theshaft 41 is slightly tilted while thefan 1 is driven, a fluid dynamic pressure is generated by the first radial dynamicpressure groove array 711 in agap 56 defined between a portion of the outercircumferential surface 411 of theshaft 41 which approaches the secondinclined surface 441 b and a portion of the secondinclined surface 441 b which is opposed to this portion of the outercircumferential surface 411. As a result, theshaft 41 is supported by the secondinclined surface 441 b. Thus, when theshaft 41 is tilted during rotation of therotating portion 2, the secondinclined surface 441 b extends along the outercircumferential surface 411 of theshaft 41 in thegap 56, which is located below and adjacent to theseal gap 55. Theshaft 41 is thus prevented from coming into hard contact with the upper portion of the bearingportion 44. -
FIG. 9 is a graph showing a result of a simulation of vibration that occurs in thefan 1 in the case where the radial width of theradial gap 51 is 3 μm. A horizontal axis represents frequencies of the vibration, while a vertical axis represents the amplitude of each frequency component of the vibration.FIGS. 10 , 11, and 12 are graphs showing results of simulations of vibration that occurs in thefan 1 in the case where the radial width of theradial gap 51 is 4 μm, 5 μm, and 6 μm, respectively.FIG. 13 is a graph showing a result of a simulation of vibration that occurs in a fan as a comparative example in which a motor including a ball bearing is installed. - As indicated by a
curve 90 inFIG. 13 , in the case of the vibration that occurs in the fan including the ball bearing, a plurality of peaks occur in the range of 750 Hz to 1250 Hz. InFIG. 13 , the peaks are denoted, from right to left, byreference numerals FIGS. 9 and 10 , in the case of the bearingmechanisms 4 in which the width of the radial gap is 3 μm and 4 μm, respectively, correspondingpeaks peaks FIG. 13 . Further, referring toFIGS. 11 and 12, in the case of the bearingmechanisms 4 in which the width of theradial gap 51 is 5 μm and 6 μm, respectively, peaks do not occur at positions corresponding to those of thepeaks FIG. 13 . Moreover, peaks 912 and 913 corresponding to the remainingpeaks peaks - As described above, the
fan 1 is able to achieve reduced vibration as compared to known fans in which ball bearings are used. This is due to a so-called damper effect produced by the lubricatingoil 46 between theshaft 41 and the bearingportion 44. In particular, a satisfying reduction in the vibration can be achieved when the radial width of theradial gap 51 is 5 μm or greater. The radial width of theradial gap 51 is arranged to be 20 μm or less in order to generate a sufficient fluid dynamic pressure in theradial gap 51. - The
fan 1 has been described above. Use of thebearing mechanism 4, which is a fluid dynamic bearing mechanism, in thefan 1 contributes to reducing the vibrations of thefan 1. The reduction in the vibrations of thefan 1 leads to a reduction in power consumption of thefan 1. Moreover, since the evaporation of the lubricatingoil 46 is reduced by the labyrinth structure using thebushing 25, an increased life of thebearing mechanism 4 is easily achieved, and thebearing mechanism 4 can be structured in a manner suited to the reduced vibration of thefan 1. Provision of thehorizontal gap 501 contributes to preventing dust from entering into thebearing mechanism 4 when thebearing mechanism 4 is attached to another component of thefan 1. The same is true of other preferred embodiments of the present invention described below. This makes it possible to assemble thefan 1 without a need to use an exceedingly clean facility. Furthermore, even when thebearing mechanism 4 is transported into the facility, dust is prevented from entering into thebearing mechanism 4. Once thefan 1 is assembled, thevertical gap 502 is provided, and both thehorizontal gap 501 and thevertical gap 502 prevent dust from entering into thebearing mechanism 4. - In the case of a fluid dynamic bearing mechanism in which seal portions are defined in an upper portion and a lower portion of a bearing portion thereof, a sophisticated design is required to prevent a difference in pressure between the seal portions from causing a leakage of the lubricating
oil 46. In contrast, in the case of thebearing mechanism 4 of themotor 11, thebearing mechanism 4 includes thebladder structure 5, and the lubricatingoil 46 is arranged continuously in thebladder structure 5. That is, thebearing mechanism 4 of themotor 11 has a so-called full-fill structure, including only oneseal portion 55 a. It is therefore easy to prevent a leakage of the lubricatingoil 46 in the case of thebearing mechanism 4. In addition, the surface of the lubricatingoil 46 in theseal portion 55 a can be maintained at a substantially fixed position. Moreover, a reduction in the evaporation of the lubricatingoil 46 is achieved compared to the case where a plurality of seal portions are provided. In particular, because theseal portion 55 a is arranged in an inner portion of themotor 11, inside of thehorizontal gap 501 and thevertical gap 502, theseal portion 55 a is not exposed to air currents while thefan 1 is driven. A further reduction in the evaporation of the lubricatingoil 46 is thereby achieved. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. In thebearing mechanism 4, because theseal portion 55 a is defined around theshaft 41, a leakage of the lubricatingoil 46 out of theseal portion 55 a owing to a centrifugal force can be prevented more effectively than in the case where the seal portion is arranged away from and radially outward of theshaft 41. - Because the sum of the axial width of the first
lower thrust gap 52 and the axial width of the secondlower thrust gap 53 is arranged in the range of about 10 μm to about 40 μm, the fluid dynamic pressures can be generated while ensuring the damper effect owing to the lubricatingoil 46. - Because the second
inclined surface 441 b in which a portion of the first radial dynamicpressure groove array 711 is defined is arranged in the innercircumferential surface 441 of the bearingportion 44, it is possible to support theshaft 41 sufficiently even if theradial gap 51 is widened. Consequently, it is possible to prevent a reduction in bearing rigidity even when thefan 1 is caused to rotate at a high speed or in a high-temperature condition. - Because the
motor 11 is a three-phase motor, themotor 11 is capable of being rotated at a high speed. It is therefore easy to cause the frequencies of the vibration that can occur in themotor 11 to deviate from a frequency band that may affect another device in an electronic device in which thefan 1 is installed. - The
magnetic member 331 provided in themotor 11 generates the magnetic attraction force that attracts therotor magnet 22 downward. This contributes to reducing an increase in a bearing loss that occurs in the first lower thrust dynamicpressure bearing portion 691, while thefan 1 is driven, owing to the force that acts to lift theimpeller 12 relative to thestationary portion 3. Moreover, the additional magnetic attraction force that attracts therotor magnet 22 downward is generated because the magnetic center of thestator 32 is arranged at a level lower than that of the magnetic center of therotor magnet 22. This contributes to further reducing the increase in the bearing loss that occurs in the first lower thrust dynamicpressure bearing portion 691. - Because the radial dynamic
pressure bearing portion 68 is arranged axially between the twobalance correction portions rotating portion 2 and theimpeller 12 is capable of stable rotation, and a further reduction in the vibrations is thereby achieved. In addition, it is possible to reduce the axial length of the radial dynamicpressure bearing portion 68, and to shorten the bearingportion 44. This makes it possible to manufacture the bearingportion 44 with high precision. The axial length of the bearingportion 44 is preferably arranged to be less than about four times the diameter of the bearingportion 44. Because the upper radial dynamicpressure bearing portion 681 is arranged to overlap with the center of gravity of each of themotor 11 and theimpeller 12 in the radial direction, stability of the rotation of each of therotating portion 2 and theimpeller 12 is increased, and a further reduction in the vibrations is thereby achieved. The same is true of other preferred embodiments of the present invention described below. - In the
motor 11, an upper end of thestator core 321 is arranged to overlap with the upper radial dynamicpressure bearing portion 681 in the radial direction. As a result of thestator 32 being arranged at a high position as described above, the magnetic center of thestator 32 can be arranged between the upper and lower radial dynamicpressure bearing portions motor 11. A lower end of thestator core 321 is preferably arranged to overlap with the lower radial dynamicpressure bearing portion 682 in the radial direction. Further preferably, a center of gravity of a combination of theimpeller 12 and therotating portion 2 is arranged to overlap with the upper radial dynamicpressure bearing portion 681 in the radial direction. -
FIG. 14 is a diagram illustrating abearing mechanism 4 according to a modification of the first preferred embodiment. A bearingportion 44 a of thebearing mechanism 4 includes atubular sleeve 47 and a bearinghousing 48. Thesleeve 47 is defined by a metallic sintered body. Thesleeve 47 is impregnated with a lubricatingoil 46. The bearinghousing 48 is arranged to cover an outer circumferential surface of thesleeve 47. The bearinghousing 48 is arranged to have an outside diameter substantially equal to an outside diameter of abushing 25. The bearinghousing 48 includes an annularupper portion 481 arranged to extend radially inward on an upper side of thesleeve 47. Acirculation channel 472 arranged to extend in the axial direction is defined between an outer circumferential surface of thesleeve 47 and an inner circumferential surface of the bearinghousing 48. The lubricatingoil 46 is arranged to circulate through thecirculation channel 472, a gap defined between a lower surface of the annularupper portion 481 and an upper surface of thesleeve 47, aradial gap 51, and a firstlower thrust gap 52. - Referring to
FIG. 15 , an inner circumferential surface 481 a of the annularupper portion 481 is an inclined surface whose diameter gradually increases with increasing height. In other words, the inner circumferential surface 481 a is arranged to be inclined radially inward with decreasing height. Hereinafter, the inner circumferential surface 481 a will be referred to as a “first inclined surface 481 a”. An upper portion of an innercircumferential surface 471 of thesleeve 47 includes aninclined surface 471 a whose diameter gradually increases with increasing height. In other words, theinclined surface 471 a is arranged to be inclined radially inward with decreasing height. Hereinafter, theinclined surface 471 a will be referred to as a “secondinclined surface 471 a”. An angle defined by the first inclined surface 481 a with a central axis J1 is arranged to be greater than an angle defined by the secondinclined surface 471 a with the central axis J1. Thebearing mechanism 4 according to the present modification of the first preferred embodiment is otherwise similar in structure to thebearing mechanism 4 illustrated inFIG. 3 . - A
seal gap 55 arranged to gradually increase in radial width with increasing height is defined between the first inclined surface 481 a and an outercircumferential surface 411 of ashaft 41. Adjacent to and below theseal gap 55, agap 56 is defined between the outercircumferential surface 411 of theshaft 41 and the secondinclined surface 471 a. Theseal gap 55 includes aseal portion 55 a arranged to retain the lubricatingoil 46 through capillary action. A surface of the lubricatingoil 46 is defined in theseal portion 55 a. Because theseal portion 55 a is defined around theshaft 41, a leakage of the lubricatingoil 46 out of theseal portion 55 a due to a centrifugal force is prevented. - A portion of a first radial dynamic
pressure groove array 711 similar to the first radial dynamicpressure groove array 711 illustrated inFIG. 6 is defined in a lower portion of the secondinclined surface 471 a. When theshaft 41 is slightly tilted while afan 1 is driven, the secondinclined surface 471 a extends along the outercircumferential surface 411 of theshaft 41, so that a fluid dynamic pressure is generated in thegap 56. Theshaft 41 is thereby supported by the secondinclined surface 471 a so that theshaft 41 can be prevented from coming into hard contact with an upper portion of the bearingportion 44 a. - Also in the
bearing mechanism 4 according to the present modification of the first preferred embodiment, ahorizontal gap 501 arranged to extend perpendicularly to the central axis J1 is defined between a lower surface of thebushing 25 and an upper surface of the bearingportion 44 a. Avertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between an outer circumferential surface of thebushing 25 and an inner circumferential surface of abearing support portion 31. Theseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 502. Each of a minimum axial width of thehorizontal gap 501 and a minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Since each of thehorizontal gap 501 and thevertical gap 502 has a width smaller than the maximum width of the opening of theseal gap 55, a labyrinth having a width smaller than the maximum width of theseal gap 55 is defined therein. Provision of thehorizontal gap 501 and thevertical gap 502 contributes to preventing an air including a lubricating oil evaporated from theseal portion 55 a from traveling out of thebearing mechanism 4. This contributes to reducing evaporation of the lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 16 is a cross-sectional view of afan 1 according to another modification of the first preferred embodiment. Thefan 1 illustrated inFIG. 16 is different from thefan 1 illustrated inFIG. 1 in that animpeller 12 is arranged to extend farther downward than amotor 11, so that theentire motor 11 is accommodated in acup 121 of theimpeller 12. Thefan 1 illustrated inFIG. 16 is otherwise similar in structure to thefan 1 illustrated inFIG. 1 . - In the
fan 1, athrust cap 45, which is arranged at a lower end of a bearingportion 44, is arranged at a level higher than that of alower end 126 of theimpeller 12. The lower end of the bearingportion 44 is normally arranged at a lowermost end of themotor 11. Therefore, a center of gravity of themotor 11 is thereby arranged inside of theimpeller 12, which leads to increased stability of rotation of theimpeller 12. Since a three-phase motor, even in a reduced size, is capable of rotating an impeller in a satisfactory manner, the above structure is especially suitable for the case where the three-phase motor is adopted. -
FIG. 17 is a diagram illustrating a structure in which abushing 25 and animpeller 12 are joined to each other according to a modification of the first preferred embodiment. Theimpeller 12 illustrated inFIG. 17 includes acup 121 having an inner surface fixed to arotor holder 210 arranged substantially in the shape of a covered cylinder. A top face portion of thecup 121 includes a large central opening defined therein. Therotor holder 210 includes acylindrical portion 21 a and atop face portion 21 b. Thetop face portion 21 b is arranged to spread perpendicularly to a central axis J1. Thecylindrical portion 21 a is arranged substantially in the shape of a cylinder, and is arranged to extend downward from an outer edge portion of thetop face portion 21 b. Therotor holder 210 is made of a metal, and thecylindrical portion 21 a functions as theyoke 21 illustrated inFIG. 1 . A central portion of thetop face portion 21 b, that is, an inner edge portion of thetop face portion 21 b, includes acylindrical burring portion 211 arranged to extend downward from the inner edge portion thereof. An inner circumferential surface of the burringportion 211 is press fitted to an outer circumferential surface of thebushing 25, whereby therotor holder 210 is fixed to thebushing 25. Theimpeller 12 is thereby indirectly fixed to an upper portion of ashaft 41. Theimpeller 12 and thebushing 25 are securely fixed to each other through joining of the metallic members. -
FIG. 18 is a diagram illustrating a structure in which abushing 25 and animpeller 12 are joined to each other according to a further modification of the first preferred embodiment. While theimpeller 12 has a structure substantially the same as that of theimpeller 12 illustrated inFIG. 17 , arotor holder 210 does not include the burring portion. An outer circumferential surface of thebushing 25 includes anannular groove 251 defined therein, and an inner circumferential portion of atop face portion 21 b is fixed in thegroove 251 by crimping. Also in the joining structure illustrated inFIG. 18 , theimpeller 12 and thebushing 25 are securely fixed to each other through joining of the metallic members. -
FIG. 19 is a diagram illustrating a labyrinth structure defined above a bearingportion 44 according to a modification of the first preferred embodiment. Abushing 25 includes, in an outer edge portion of a lower portion thereof, an outerannular portion 252 arranged to extend downward toward the bearingportion 44. The bearingportion 44 includes an innerannular portion 445 arranged to project upward toward thebushing 25 around ashaft 41. In other words, the bearingportion 44 includes, in an outer edge portion of an upper portion thereof, an annular recessedportion 445 a arranged to be recessed in a direction away from thebushing 25. Hereinafter, the recessedportion 445 a will be referred to as an “annular recessedportion 445 a”. The innerannular portion 445 can be regarded as a portion that defines a side surface of the annular recessedportion 445 a. The outerannular portion 252 is arranged radially outside the innerannular portion 445. That is, the outerannular portion 252 is arranged in the annular recessedportion 445 a. Ahorizontal gap 501 arranged to spread perpendicularly to a central axis J1 is defined by a portion of a lower surface of thebushing 25 which is radially inward of the outerannular portion 252 and an upper surface of the innerannular portion 445 of the bearingportion 44. Hereinafter, thehorizontal gap 501 will be referred to as a “firsthorizontal gap 501”. Avertical gap 502 arranged to extend in the axial direction and arranged in an annular shape centered on the central axis J1 is defined by an inner circumferential surface of the outerannular portion 252 and an outer circumferential surface of the innerannular portion 445. An upper end of thevertical gap 502 is connected with a radially outer end portion of the firsthorizontal gap 501. Anotherhorizontal gap 501 a arranged to spread perpendicularly to the central axis J1 is defined between a lower surface of the outerannular portion 252 and a bottom surface of the annular recessedportion 445 a, which is arranged axially opposite the lower surface of the outerannular portion 252, that is, a surface radially outward of the innerannular portion 445. Hereinafter, thehorizontal gap 501 a will be referred to as a “secondhorizontal gap 501 a”. A lower end of thevertical gap 502 is connected with a radially inner end portion of the secondhorizontal gap 501 a. - In
FIG. 19 , each of a minimum axial width of the firsthorizontal gap 501 and a minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of an opening of aseal gap 55. Provision of the firsthorizontal gap 501 and thevertical gap 502 contributes to reducing evaporation of a lubricating oil out of abearing mechanism 4. The firsthorizontal gap 501 and thevertical gap 502 may be defined between thebushing 25 and the bearingportion 44 as described above. Further, provision of the secondhorizontal gap 501 a contributes to more securely preventing the evaporation of the lubricating oil. A minimum axial width of the secondhorizontal gap 501 is arranged to be smaller than the maximum radial width of the opening of theseal gap 55. Provision of the firsthorizontal gap 501, thevertical gap 502, and the secondhorizontal gap 501 a in thebearing mechanism 4 contributes to more securely preventing dust from entering into thebearing mechanism 4 when thebearing mechanism 4 and another component of afan 1 are attached to each other. In the case where thevertical gap 502 is defined between thebushing 25 and the bearingportion 44 as described above, each of the first and secondhorizontal gaps vertical gap 502 is a minute gap, dust is prevented from entering into thebearing mechanism 4 when thebearing mechanism 4 and another component of thefan 1 are attached to each other. This makes it possible to assemble thefan 1 without a need to use an exceedingly clean facility. Furthermore, even when thebearing mechanism 4 is transported into the facility, dust is prevented from entering into thebearing mechanism 4. - Note that, in a further modification of the
bearing mechanism 4, an inner circumferential portion of a lower portion of thebushing 25 may be arranged to project into an inner circumferential portion of an upper portion of the bearingportion 44. In other words, it may be so arranged that an outer annular portion arranged to project toward thebushing 25 is arranged in an outer edge portion of the upper portion of the bearingportion 44, while an inner annular portion arranged to project toward the bearingportion 44 on a radially inner side of the outer annular portion is arranged in the lower portion of thebushing 25. The outer annular portion is arranged in an annular recessed portion defined radially outside the inner annular portion. Avertical gap 502 is defined between an outer circumferential surface of the inner annular portion, which is arranged in the lower portion of thebushing 25, and an inner circumferential surface of the outer annular portion, which is arranged in the upper portion of the bearingportion 44. Furthermore, it may be so arranged that thebushing 25 is increased in diameter, an outer circumferential portion of thebushing 25 is arranged to extend downward so that an upper portion of abearing support portion 31 may be surrounded by a lower portion of thebushing 25 on a radially outer side thereof, and avertical gap 502 is defined between an inner circumferential surface of the lower portion of thebushing 25 and an outer circumferential surface of the upper portion of thebearing support portion 31. - As described above, the
vertical gap 502 is defined between a circumferential surface of thebushing 25 and a circumferential surface of thebearing support portion 31 or the bearingportion 44 in the vicinity of the seal portion. Also, the secondhorizontal gap 501 a may be defined between the lower surface of thebushing 25 and an upper surface of thebearing support portion 31. Note that emission of a vaporized lubricating oil can be effectively prevented when a stationary body is arranged radially outward of a rotating body in the labyrinth structure. -
FIG. 20 is a diagram illustrating a labyrinth structure defined above a bearingportion 44 according to another modification of the first preferred embodiment. A lower portion of abushing 25 includes an inclined surface arranged to be inclined downward with increasing distance from a central axis J1. An upper portion of the bearingportion 44 also includes an inclined surface arranged to be inclined downward with increasing distance from the central axis J1. Aninclined gap 503 arranged to be inclined downward with increasing distance from the central axis J1 is defined between these inclined surfaces. Theinclined gap 503 is arranged in the shape of a conical surface centered on the central axis J1. A minimum width of theinclined gap 503 is arranged to be smaller than a maximum radial width of an opening of aseal gap 55. Note that the minimum width of theinclined gap 503 refers to a minimum distance between the aforementioned two inclined surfaces. Ahorizontal gap 501 is defined on a radially inner side of theinclined gap 503. Theseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and theinclined gap 503. Provision of theinclined gap 503 contributes to preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. Provision of thehorizontal gap 501 and theinclined gap 503 in thebearing mechanism 4 contributes to more securely preventing dust from entering into thebearing mechanism 4 when thebearing mechanism 4 and another component of afan 1 are attached to each other. - Note that an additional vertical gap or an additional horizontal gap which is continuous with a radially outer end portion of the
inclined gap 503 may be provided. Also note that theinclined gap 503 may be arranged to be inclined upward with increasing distance from the central axis J1. -
FIG. 21 is a diagram illustrating abearing mechanism 4 according to another modification of the first preferred embodiment. Thebearing mechanism 4 according to the present modification of the first preferred embodiment is similar in structure to thebearing mechanism 4 illustrated inFIG. 3 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Thebearing mechanism 4 does not include thethrust cap 45 illustrated inFIG. 3 . Aside gap 54 is defined between an outer circumferential surface of athrust plate 42 and an inner circumferential surface of alower end portion 444 of a bearingportion 44, and a seal portion 54 a is defined in theside gap 54. The seal portion 54 a is defined in a lower portion of theside gap 54, and is arranged to gradually increase in radial width with decreasing height. As a thrust dynamic pressure bearing portion, only a first lower thrust dynamicpressure bearing portion 691 is defined in a firstlower thrust gap 52 defined between the bearingportion 44 and an upper surface of thethrust plate 42. An axial magnetic center of a rotor magnet and that of a stator are displaced from each other to cause an upward force to constantly act on ashaft 41. Thebearing mechanism 4 is otherwise similar in structure to thebearing mechanism 4 illustrated inFIG. 3 . Aseal portion 55 a similar to theseal portion 55 a illustrated inFIG. 5 is defined in an upper portion of thebearing mechanism 4. Thus, thebearing mechanism 4 includes a plurality of seal portions. - Also in the
bearing mechanism 4, ahorizontal gap 501 is defined between a lower surface of abushing 25 and an upper surface of the bearingportion 44, while avertical gap 502 is defined between an outer circumferential surface of thebushing 25 and an inner circumferential surface of abearing support portion 31. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 502. Each of a minimum axial width of thehorizontal gap 501 and a minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. - Also in the
bearing mechanism 4 illustrated inFIG. 21 , the radial width of aradial gap 51 is arranged to be 5 μm or greater so that a sufficient reduction in vibrations of afan 1 can be achieved. Note, however, that the width of theradial gap 51 is arranged to be 20 μm or less in order to generate a sufficient fluid dynamic pressure in theradial gap 51. -
FIG. 22 is a cross-sectional view illustrating abearing mechanism 4 according to yet another modification of the first preferred embodiment. Abushing 25 of thebearing mechanism 4 includes anannular portion 253 arranged to extend downward outside of a bearingportion 44. Avertical gap 504 is defined between an inner circumferential surface of theannular portion 253 and an outer circumferential surface of the bearingportion 44. Thebearing mechanism 4 is otherwise similar in structure to thebearing mechanism 4 illustrated inFIG. 2 . In thebearing mechanism 4, aseal gap 55 is arranged to be in communication with an exterior space through ahorizontal gap 501 defined between a lower surface of thebushing 25 and an upper surface of the bearingportion 44, and thevertical gap 504. - Provision of the
horizontal gap 501 and thevertical gap 504 in thebearing mechanism 4 contributes to more securely preventing dust from entering into thebearing mechanism 4 when thebearing mechanism 4 and another component of afan 1 are attached to each other. In the case where thevertical gap 504 is defined between thebushing 25 and the bearingportion 44 as described above, thehorizontal gap 501 may not necessarily be a minute gap, with only thevertical gap 504 being a minute gap. In addition, evaporation of a lubricatingoil 46 from aseal portion 55 a can be prevented. -
FIG. 23 is a cross-sectional view illustrating abearing mechanism 4 according to yet another modification of the first preferred embodiment. Abushing 25 includes an annular projectingportion 254 arranged to project radially inward from an inner circumferential surface thereof. An upper end portion of ashaft 41 includes ashoulder portion 412 defined by a decrease in the diameter thereof. The projectingportion 254 is arranged to be in axial contact with anupper surface 412 a of theshoulder portion 412. Theupper surface 412 a is a surface having a normal oriented upward. Thus, a displacement of the axial position of thebushing 25 is prevented when afan 1 is assembled, or more specifically, when animpeller 12 is indirectly fixed to an upper portion of theshaft 41 through thebushing 25, so that the width of ahorizontal gap 501 can be easily set at a desired value. Referring toFIG. 24 , in a further modification of thebearing mechanism 4, theshoulder portion 412 of theshaft 41 may be eliminated, with the projectingportion 254 arranged to be in axial contact with an upper surface of theshaft 41. Even in this case, a displacement of the axial position of thebushing 25 is prevented when thefan 1 is assembled so that the width of thehorizontal gap 501 can be easily set at the desired value. This enables the labyrinth to be defined with high precision. -
FIG. 25 is a cross-sectional view illustrating afan 1 according to a modification of the first preferred embodiment. A radially inner portion of astator core 321 is fixed to an outer circumferential surface of a bearingportion 44. In astationary portion 3, acylindrical member 31 a (hereinafter referred to as a “cylindrical portion 31 a”) is fixed to a central hole portion of abase portion 15, and an upper portion of thecylindrical portion 31 a is arranged to be in axial contact with a lower portion of thestator core 321. As with thebushing 25 illustrated inFIG. 22 , abushing 25 includes anannular portion 253 arranged to extend downward outside of the bearingportion 44. Thefan 1 according to the present modification of the first preferred embodiment is otherwise similar in structure to thefan 1 illustrated inFIG. 17 . - When the
fan 1 is assembled, arotor holder 210 is press fitted to thebushing 25 of abearing mechanism 4 from above thebushing 25. At this time, a lower end of theannular portion 253 is supported by a jig from below. Next, astator 32 is attached to an outer circumference of the bearingportion 44, and a lower portion of the bearingportion 44 is inserted into thecylindrical portion 31 a fixed to thebase portion 15. In the case of thefan 1, a displacement of the axial position of thebushing 25 is prevented because thebushing 25 is supported from below when therotor holder 210 is press fitted to thebushing 25. Thus, the axial width of ahorizontal gap 501 can be easily set at a desired value, and the labyrinth can be defined with high precision. -
FIG. 26 is a cross-sectional view illustrating afan 1 according to yet another modification of the first preferred embodiment. Atop face portion 123 of animpeller 12 includes a throughhole 127 arranged to extend in the axial direction therethrough. Thefan 1 according to the present modification of the first preferred embodiment is otherwise similar in structure to thefan 1 illustrated inFIG. 1 . The throughhole 127 is arranged to overlap with astator 32 in the axial direction. The throughhole 127 is arranged to bring aspace 811 defined between thestator 32 and thetop face portion 123 located above thestator 32 into communication with aspace 812 above theimpeller 12, that is, a space on an upstream side of thefan 1. While thefan 1 is driven, air currents are produced around thestator 32 to cool thestator 32. The throughhole 127 thus functions as a channel to guide an air flow to thestator 32. -
FIG. 27 is a cross-sectional view illustrating afan 1 according to yet another modification of the first preferred embodiment. In thefan 1, arotor holder 210 arranged substantially in the shape of a covered cylinder is fixed to an inside of acup 121 of animpeller 12. Atop face portion 123 of thecup 121 includes a throughhole 128 a arranged to extend in the axial direction therethrough and defined in a center thereof. Hereinafter, the throughhole 128 a will be referred to as a “first throughhole 128 a”. Atop face portion 21 b of therotor holder 210 includes afirst shoulder portion 212 arranged to be recessed downward and arranged radially outward of a burringportion 211, and asecond shoulder portion 213 arranged to be recessed downward and arranged radially outward of thefirst shoulder portion 212. A throughhole 128 b is defined in thetop face portion 21 b between the first andsecond shoulder portions hole 128 b will be referred to as a “second throughhole 128 b”. The second throughhole 128 b is arranged at the same level as that of an upper portion of avertical gap 502. - In the
fan 1, the first throughhole 128 a, a space 128 c defined between thetop face portion 123 of thecup 121 and thetop face portion 21 b of therotor holder 210, and the second throughhole 128 b are arranged to together define achannel 128 to bring aspace 811 above astator 32 into communication with aspace 812 above theimpeller 12. Thestator 32 is thus cooled while thefan 1 is driven. Moreover, because the second throughhole 128 b, i.e., a downstream end portion of thechannel 128, is arranged at the same level as that of the upper portion of thevertical gap 502, that is, because the second throughhole 128 b and the upper portion of thevertical gap 502 are arranged to overlap with each other in the radial direction, dust is prevented from entering into thevertical gap 502 and ahorizontal gap 501. Note that the second throughhole 128 b may be arranged at a level lower than that of the upper portion of thevertical gap 502. Even in this case, dust is prevented from entering into thevertical gap 502 and thehorizontal gap 501. -
FIG. 28 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Abearing mechanism 4 of thefan 1 is similar in structure to thebearing mechanism 4 illustrated inFIGS. 14 and 15 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 28 , an annularupper portion 481 of a bearinghousing 48 is arranged above an upper end of abearing support portion 31. An upper surface of the annularupper portion 481 is an upper surface of a bearingportion 44 a as well. In addition, an upper surface of asleeve 47 is also arranged above the upper end of thebearing support portion 31. - In the
fan 1, arotor holder 210 arranged substantially in the shape of a covered cylinder is fixed to an inside of acup 121 of animpeller 12. Therotor holder 210 includes acylindrical portion 21 a, atop face portion 21 b, and aholder projecting portion 211 a. Theholder projecting portion 211 a includes a burringportion 214, afirst portion 215, and asecond portion 216. Each of the burringportion 214 and thesecond portion 216 is arranged substantially in the shape of a cylinder centered on a central axis J1. Thefirst portion 215 is arranged substantially in the shape of an annular plate centered on the central axis J1. Thefirst portion 215 is arranged to extend radially outward and perpendicularly to the central axis J1 from a lower end of the burringportion 214. Thesecond portion 216 is arranged to extend downward from an outer edge portion of thefirst portion 215. Thetop face portion 21 b is arranged substantially in the shape of an annular plate centered on the central axis J1. Thetop face portion 21 b is arranged to extend radially outward and perpendicularly to the central axis J1 from a lower end of thesecond portion 216. Thecylindrical portion 21 a is arranged substantially in the shape of a cylinder centered on the central axis J1. Thecylindrical portion 21 a is arranged to extend downward from an outer edge portion of thetop face portion 21 b. Therotor holder 210 is made of a metal, and thecylindrical portion 21 a functions as theyoke 21 illustrated inFIG. 1 . - A
top face portion 123 of thecup 121 includes a through hole arranged to extend in the axial direction therethrough and defined in a center thereof. An outer circumferential surface of the burringportion 214 of theholder projecting portion 211 a is press fitted and thereby fixed to an inner circumferential surface of this through hole. Note that theimpeller 12 and therotor holder 210 may be joined to each other by an insert molding process. An inner circumferential surface of the burringportion 214 of theholder projecting portion 211 a is press fitted and thereby fixed to an upper portion of ashaft 41 on an upper side of the bearingportion 44 a. Theshaft 41 includes anattachment surface 413 at an upper portion of an outercircumferential surface 411 thereof in a situation in which therotor holder 210 and theimpeller 12 have not yet been fixed to theshaft 41. Theattachment surface 413 is a surface to which thetop face portion 123 of theimpeller 12 is to be indirectly attached through therotor holder 210. Theshaft 41 is inserted in the bearingportion 44 a, and is arranged to rotate about the central axis J1 relative to the bearingportion 44 a. - A
seal portion 55 a is defined around theshaft 41 on an upper side of a radial dynamicpressure bearing portion 68. Aseal gap 55 includes theseal portion 55 a, in which a surface of a lubricatingoil 46 is defined. Thebearing mechanism 4 further includes anannular member 49. Theannular member 49 is arranged to spread perpendicularly to the central axis J1 above theseal portion 55 a. Theannular member 49 is arranged substantially in the shape of an annular plate centered on the central axis J1. An inner circumferential surface of theannular member 49 is fixed to the outercircumferential surface 411 of theshaft 41 axially between theseal portion 55 a and the burringportion 214 of theholder projecting portion 211 a. In other words, theannular member 49 is fixed to theshaft 41 axially between theseal portion 55 a and theattachment surface 413. Theannular member 49 is arranged to extend radially outward, with the central axis J1 as a center, beyond an opening of theseal gap 55. That is, theannular member 49 is arranged to cover the opening of theseal gap 55 from above. In other words, theannular member 49 is arranged to cover the opening of theseal gap 55 in a plan view. InFIG. 28 , theannular member 49 is arranged to extend radially outward beyond an outer edge of the upper surface of the annularupper portion 481. - A minute
horizontal gap 501 extending radially is defined between a lower surface of theannular member 49 and the upper surface of the bearingportion 44 a. Theseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501. A minimum axial width of thehorizontal gap 501 is arranged to be smaller than a maximum radial width of the opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thehorizontal gap 501 contributes to preventing an air including a lubricating oil evaporated from theseal portion 55 a from traveling out of thebearing mechanism 4. This contributes to reducing evaporation of the lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. - Because of the
annular member 49 fixed to theshaft 41, a reduction in the evaporation of the lubricatingoil 46 out of thebearing mechanism 4 is achieved even in the situation in which therotor holder 210 and theimpeller 12 have not yet been attached to theshaft 41. Moreover, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented as well. This makes it possible to assemble thefan 1 without a need to use an exceedingly clean facility. Furthermore, even while thebearing mechanism 4 is transported, dust is prevented from entering into thebearing mechanism 4. The same is true offans 1 illustrated inFIGS. 29 , 30, and 31. -
FIG. 29 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 29 , in thefan 1, anannular member 49 a arranged in an annular shape centered on a central axis J1 is provided in place of theannular member 49 illustrated inFIG. 28 . Theannular member 49 a includes atop cover portion 491 and atubular portion 492. Thetop cover portion 491 is arranged substantially in the shape of an annular plate centered on the central axis J1. Thetop cover portion 491 is fixed to ashaft 41 axially between aseal portion 55 a and anattachment surface 413. Thetop cover portion 491 is arranged to extend radially outward beyond an outer circumferential surface of an annularupper portion 481. Thetubular portion 492 is arranged substantially in the shape of a cylinder centered on the central axis J1. Thetubular portion 492 is arranged to extend downward from an outer edge portion of thetop cover portion 491. An inner circumferential surface of thetubular portion 492 is arranged radially opposite the outer circumferential surface of the annularupper portion 481 of a bearinghousing 48, which defines a portion of a bearingportion 44 a. - A minute
horizontal gap 501 extending radially is defined between a lower surface of thetop cover portion 491 and an upper surface of the bearingportion 44 a. A minutevertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the inner circumferential surface of thetubular portion 492 and the outer circumferential surface of the annularupper portion 481. An upper end portion of thevertical gap 502 is connected with an radially outer end portion of thehorizontal gap 501. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 502. Each of a minimum axial width of thehorizontal gap 501 and a minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thevertical gap 502 in addition to thehorizontal gap 501 contributes to more effectively preventing an air including a lubricating oil evaporated from theseal portion 55 a from traveling out of abearing mechanism 4. This contributes to further reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. - In the case where the
vertical gap 502 is defined between theannular member 49 a and the bearingportion 44 a, thehorizontal gap 501 may not necessarily be a minute gap. Even when only thevertical gap 502 is a minute gap, a reduction in the evaporation of the lubricatingoil 46 out of thebearing mechanism 4 can be achieved, and also, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 30 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 30 , a bearingportion 44 a includes anannular projection portion 482 arranged to project upward from an outer edge portion of an upper surface of an annularupper portion 481. Theannular projection portion 482 is arranged substantially in the shape of a cylinder centered on a central axis J1. Anannular member 49 is arranged to extend radially outward, with the central axis J1 as a center, beyond an opening of aseal gap 55. An outer circumferential surface of theannular member 49 is arranged radially opposite an inner circumferential surface of theannular projection portion 482. Note that theannular projection portion 482 may be arranged to project upward from a position on a radially inner side of the outer edge portion of the upper surface of the annularupper portion 481. - A minute
horizontal gap 501 extending radially is defined between a lower surface of theannular member 49 and an upper surface of the bearingportion 44 a. A minutevertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the outer circumferential surface of theannular member 49 and the inner circumferential surface of theannular projection portion 482. A lower end portion of thevertical gap 502 is connected with a radially outer end portion of thehorizontal gap 501. Theseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 502. Each of a minimum axial width of thehorizontal gap 501 and a minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of the opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thevertical gap 502 in addition to thehorizontal gap 501 contributes to more effectively preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to further reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. - In the case where the
vertical gap 502 is defined between theannular member 49 and the bearingportion 44 a, thehorizontal gap 501 may not necessarily be a minute gap. Even when only thevertical gap 502 is a minute gap, a reduction in the evaporation of the lubricatingoil 46 out of thebearing mechanism 4 can be achieved, and also, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 31 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 31 , thefan 1 is provided with anannular member 49 b arranged in an annular shape centered on a central axis J1 in addition to anannular member 49. The outside diameter of theannular member 49 is arranged to be smaller than the outside diameter of an upper surface of an annularupper portion 481. Theannular member 49 b includes atop cover portion 491 b and atubular portion 492 b. Thetop cover portion 491 b is arranged substantially in the shape of an annular plate centered on the central axis J1. Thetubular portion 492 b is arranged substantially in the shape of a cylinder centered on the central axis J1. Thetubular portion 492 b is arranged to extend downward from an outer edge portion of thetop cover portion 491 b. An inner circumferential surface of thetubular portion 492 b is fixed to an outer circumferential surface of the annularupper portion 481. The inner circumferential surface of thetubular portion 492 b is arranged radially opposite an outer circumferential surface of theannular member 49. Thetop cover portion 491 b is arranged above theannular member 49. A lower surface of thetop cover portion 491 b is arranged axially opposite an upper surface of theannular member 49. - A minute
horizontal gap 501 extending radially is defined between a lower surface of theannular member 49 and an upper surface of a bearingportion 44 a. A minutevertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the outer circumferential surface of theannular member 49 and the inner circumferential surface of thetubular portion 492 b. A minutehorizontal gap 501 a extending radially is defined between the upper surface of theannular member 49 and the lower surface of thetop cover portion 491 b. A lower end portion of thevertical gap 502 is connected with a radially outer end portion of thehorizontal gap 501. An upper end portion of thevertical gap 502 is connected with a radially outer end portion of thehorizontal gap 501 a. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501, thevertical gap 502, and thehorizontal gap 501 a. - Each of a minimum axial width of the
horizontal gap 501, a minimum axial width of thehorizontal gap 501 a, and a minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thevertical gap 502 and thehorizontal gap 501 a in addition to thehorizontal gap 501 contributes to more effectively preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to further reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. - Note that each of the
horizontal gap 501 and thevertical gap 502 may not necessarily be a minute gap. Even when only thehorizontal gap 501 a is a minute gap, a reduction in the evaporation of the lubricatingoil 46 out of thebearing mechanism 4 can be achieved, and also, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 32 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 28 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 32 , anannular member 49 is fixed to an upper portion of a bearingportion 44 a. In the present modification of the first preferred embodiment, theannular member 49 is fixed to an upper surface of an annularupper portion 481. Theannular member 49 is arranged substantially in the shape of an annular plate centered on a central axis J1. The inside diameter of theannular member 49 is arranged to be slightly greater than the outside diameter of ashaft 41. An inner circumferential surface of theannular member 49 is arranged radially opposite an outercircumferential surface 411 of theshaft 41 axially between aseal portion 55 a and anattachment surface 413. - A minute
vertical gap 502 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the inner circumferential surface of theannular member 49 and the outercircumferential surface 411 of theshaft 41. Aseal gap 55 is arranged to be in communication with an exterior space through thevertical gap 502. A minimum radial width of thevertical gap 502 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. That is, theannular member 49 is arranged to cover a portion of the opening of theseal gap 55 from above. In other words, theannular member 49 is arranged to cover a portion of the opening of theseal gap 55 in a plan view. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined above theseal portion 55 a. Provision of thevertical gap 502 contributes to preventing an air including a lubricating oil evaporated from theseal portion 55 a from traveling out of abearing mechanism 4. This contributes to reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. - Because of the
annular member 49 fixed to the bearingportion 44 a, a reduction in the evaporation of the lubricatingoil 46 out of thebearing mechanism 4 is achieved even in a situation in which arotor holder 210 and animpeller 12 have not yet been attached to theshaft 41. Moreover, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented as well. The same is true of each offans 1 illustrated inFIGS. 33 and 34 . -
FIG. 33 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 32 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 33 , a bearingportion 44 a includes anannular projection portion 482 arranged to project upward from an outer edge portion of an upper surface of an annularupper portion 481. Theannular projection portion 482 is arranged substantially in the shape of a cylinder centered on a central axis J1. Anannular member 49 is arranged on the upper surface of the annularupper portion 481 of the bearingportion 44 a on a radially inner side of theannular projection portion 482. Although theannular member 49 is fixed to the upper surface of the annularupper portion 481 of the bearingportion 44 a in the present modification of the first preferred embodiment, theannular member 49 may be fixed to an inner circumferential surface of theannular projection portion 482. An outer circumferential surface of theannular member 49 is arranged to be in contact with the inner circumferential surface of theannular projection portion 482 throughout an entire circumference thereof. Note that theannular projection portion 482 may be arranged to project upward from a position on a radially inner side of the outer edge portion of the upper surface of the annularupper portion 481. Also note that only a portion or portions of the outer circumferential surface of theannular member 49 may be arranged to be in contact with the inner circumferential surface of theannular projection portion 482. - A
vertical gap 502 similar to thevertical gap 502 illustrated inFIG. 32 is defined between an inner circumferential surface of theannular member 49 and an outercircumferential surface 411 of ashaft 41. Provision of thevertical gap 502 contributes to preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. Since the outer circumferential surface of theannular member 49 is arranged to be in contact with the inner circumferential surface of theannular projection portion 482, positioning of theannular member 49 can be easily accomplished when theannular member 49 is attached to the bearingportion 44 a. -
FIG. 34 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 32 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 34 , afirst portion 215 of aholder projecting portion 211 a of arotor holder 210 is arranged above anannular member 49. A lower surface of thefirst portion 215 is arranged axially opposite an upper surface of theannular member 49. Asecond portion 216 of theholder projecting portion 211 a is arranged radially outside an annularupper portion 481 of a bearingportion 44 a. An inner circumferential surface of thesecond portion 216 is arranged radially opposite each of an outer circumferential surface of theannular member 49 and an outer circumferential surface of the annularupper portion 481. - A minute
vertical gap 502 extending in the axial direction and arranged in an annular shape centered on a central axis J1 is defined between an inner circumferential surface of theannular member 49 and an outercircumferential surface 411 of ashaft 41. A minutehorizontal gap 501 spreading perpendicularly to the central axis J1 is defined between the lower surface of thefirst portion 215 and the upper surface of theannular member 49. A minutevertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the inner circumferential surface of thesecond portion 216 and a combination of the outer circumferential surface of theannular member 49 and the outer circumferential surface of the annularupper portion 481. Although the minutevertical gap 504 is defined between the inner circumferential surface of thesecond portion 216 and the combination of the outer circumferential surface of theannular member 49 and the outer circumferential surface of the annularupper portion 481 in the present modification of the first preferred embodiment, the minutevertical gap 504 may be defined only between the inner circumferential surface of thesecond portion 216 and the outer circumferential surface of the annularupper portion 481. In other words, a portion of thevertical gap 504 which is defined between the inner circumferential surface of thesecond portion 216 and the outer circumferential surface of theannular member 49 may not necessarily be a minute gap. An upper end portion of thevertical gap 502 is connected with a radially inner end portion of thehorizontal gap 501. An upper end portion of thevertical gap 504 is connected with a radially outer end portion of thehorizontal gap 501. Aseal gap 55 is arranged to be in communication with an exterior space through thevertical gap 502, thehorizontal gap 501, and thevertical gap 504. - Each of a minimum radial width of the
vertical gap 502, a minimum radial width of thevertical gap 504, and a minimum axial width of thehorizontal gap 501 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thehorizontal gap 501 and thevertical gap 504 in addition to thevertical gap 502 contributes to more effectively preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to further reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 35 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 34 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 35 , in thefan 1, theannular member 49 is not provided, and a lower surface of afirst portion 215 of aholder projecting portion 211 a is arranged axially opposite an upper surface of an annularupper portion 481 of a bearingportion 44 a. - A
horizontal gap 509 extending radially is defined between the lower surface of thefirst portion 215 and the upper surface of the annularupper portion 481. A radially outer end portion of thehorizontal gap 509 is connected with an upper end portion of avertical gap 504. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 509 and thevertical gap 504. - A minimum radial width of the
vertical gap 504 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined radially outward of theseal gap 55. Provision of thevertical gap 504 contributes to more effectively preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to further reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 36 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 35 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 36 , anannular member 49 c is fixed to asecond portion 216 of aholder projecting portion 211 a. Theannular member 49 c is arranged substantially in the shape of a cylinder centered on a central axis J1. An outer circumferential surface of theannular member 49 c is fixed to an inner circumferential surface of thesecond portion 216. A lower end of theannular member 49 c is arranged in the vicinity of an upper end of abearing support portion 31. An inner circumferential surface of theannular member 49 c is arranged radially opposite an outer circumferential surface of an annularupper portion 481. A lower surface of theannular member 49 c is arranged axially opposite an upper surface of thebearing support portion 31. - A minute
vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the inner circumferential surface of theannular member 49 c and the outer circumferential surface of the annularupper portion 481. A minutehorizontal gap 506 extending radially is defined between the lower surface of theannular member 49 c and the upper surface of thebearing support portion 31. An upper end portion of thevertical gap 504 is connected with a radially outer end portion of ahorizontal gap 509. A lower end portion of thevertical gap 504 is connected with a radially inner end portion of thehorizontal gap 506. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 509, thevertical gap 504, and thehorizontal gap 506. - Each of a minimum radial width of the
vertical gap 504 and a minimum axial width of thehorizontal gap 506 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined radially outward of theseal gap 55. Provision of thehorizontal gap 506 in addition to thevertical gap 504 contributes to more effectively preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to further reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 37 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 35 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 37 , aholder projecting portion 211 a of arotor holder 210 includes a burringportion 214 arranged to extend downward from a radially inner end portion of afirst portion 215. A bearingportion 44 a includes an annularouter wall portion 483 arranged to extend upward from an outer edge portion of an upper surface of an annularupper portion 481. The annularouter wall portion 483 is arranged substantially in the shape of a cylinder centered on a central axis J1. An outer circumferential surface of the annularouter wall portion 483 is arranged radially opposite an inner circumferential surface of asecond portion 216 of theholder projecting portion 211 a. - A minute
vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the outer circumferential surface of the annularouter wall portion 483 and the inner circumferential surface of thesecond portion 216. Aspace 508 above the annularupper portion 481 is connected with an upper end portion of thevertical gap 504. Aseal gap 55 is arranged to be in communication with an exterior space through thespace 508 and thevertical gap 504. - A minimum radial width of the
vertical gap 504 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined radially outward of theseal gap 55. Provision of thevertical gap 504 contributes to preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 38 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 36 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 38 , animpeller 12 is fixed to ashaft 41 through abushing 25. Thebushing 25 is arranged substantially in the shape of a column centered on a central axis J1. The outside diameter of thebushing 25 is arranged to be slightly greater than the outside diameter of an annularupper portion 481. An inner circumferential surface of atop face portion 123 of theimpeller 12 is fixed to an outer circumferential surface of thebushing 25. A lower surface of thebushing 25 is arranged axially opposite an upper surface of the annularupper portion 481 of a bearingportion 44 a. Anannular member 49 c is also fixed to the outer circumferential surface of thebushing 25. Theannular member 49 c is arranged substantially in the shape of a cylinder centered on the central axis J1. An inner circumferential surface of theannular member 49 c is fixed to the outer circumferential surface of thebushing 25 below thetop face portion 123 of theimpeller 12. The inner circumferential surface of theannular member 49 c is arranged radially opposite an outer circumferential surface of the annularupper portion 481. - A minute
horizontal gap 501 extending radially is defined between the lower surface of thebushing 25 and the upper surface of the annularupper portion 481. A minutevertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the inner circumferential surface of theannular member 49 c and the outer circumferential surface of the annularupper portion 481. An upper end portion of thevertical gap 504 is connected with a radially outer end portion of thehorizontal gap 501. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 504. - Each of a minimum axial width of the
horizontal gap 501 and a minimum radial width of thevertical gap 504 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thehorizontal gap 501 and thevertical gap 504 contributes to preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. -
FIG. 39 is a cross-sectional view illustrating a portion of afan 1 according to yet another modification of the first preferred embodiment. Thefan 1 according to the present modification of the first preferred embodiment is similar in structure to thefan 1 illustrated inFIG. 38 . Accordingly, like members or portions are designated by like reference numerals, and redundant description is omitted. Referring toFIG. 39 , animpeller 12 includes an inner tubular portion 123 a arranged substantially in the shape of a cylinder centered on a central axis J1. The inner tubular portion 123 a is arranged to extend downward from a radially inner end portion of atop face portion 123. An upper portion of an inner circumferential surface of the inner tubular portion 123 a is fixed to an outer circumferential surface of abushing 25. A lower portion of the inner circumferential surface of the inner tubular portion 123 a is arranged radially opposite an outer circumferential surface of an annularupper portion 481 of a bearingportion 44 a. - A minute
vertical gap 504 extending in the axial direction and arranged in an annular shape centered on the central axis J1 is defined between the inner circumferential surface of the inner tubular portion 123 a and the outer circumferential surface of the annularupper portion 481. An upper end portion of thevertical gap 504 is connected with a radially outer end portion of ahorizontal gap 501. Aseal gap 55 is arranged to be in communication with an exterior space through thehorizontal gap 501 and thevertical gap 504. - Each of a minimum axial width of the
horizontal gap 501 and a minimum radial width of thevertical gap 504 is arranged to be smaller than a maximum radial width of an opening of theseal gap 55. Thus, a labyrinth having a width smaller than the maximum radial width of theseal gap 55 is defined. Provision of thehorizontal gap 501 and thevertical gap 504 contributes to preventing an air including a lubricating oil evaporated from aseal portion 55 a from traveling out of abearing mechanism 4. This contributes to reducing evaporation of a lubricatingoil 46 out of thebearing mechanism 4. Furthermore, entry of an extraneous material, such as dust, into theseal portion 55 a can be prevented. - While preferred embodiments of the present invention have been described above, it will be understood that the present invention is not limited to the above-described preferred embodiments, and that a variety of modifications are possible.
- While a very small width of each of the
vertical gaps horizontal gaps bearing mechanism 4. Therefore, each of thehorizontal gaps seal gap 55 as long as the width is very small. Thebushing 25 may be defined by a sintered member shaped by press working, for example. In a modification of thebearing mechanism 4 illustrated inFIG. 23 , it may be so arranged that the projectingportion 254 is eliminated from thebushing 25, theshaft 41 includes a shoulder portion defined at an axial position corresponding to that of the lower surface of thebushing 25, and the lower surface of thebushing 25 is arranged to be in axial contact with the shoulder portion. In a modification of thebearing mechanism 4 illustrated inFIG. 2 , thebushing 25 may be arranged to have an outside diameter substantially equal to the outside diameter of the bearingportion 44. In this case, an inner circumferential surface of the upper portion of thebearing support portion 31 is arranged radially outward of an inner circumferential surface of a remaining portion of thebearing support portion 31, so that thevertical gap 502 is defined between the inner circumferential surface of the upper portion of thebearing support portion 31 and the outer circumferential surface of thebushing 25. - In a modification of the
bearing mechanism 4 illustrated inFIG. 14 , thebushing 25 may be arranged to have an outside diameter smaller than the outside diameter of the bearinghousing 48. Thevertical gap 502 can thereby be easily defined between thebushing 25 and thebearing support portion 31. Also, an inclined gap similar to theinclined gap 503 illustrated inFIG. 20 may be defined between the bearinghousing 48 and thebushing 25. - The
top face portion 21 b of therotor holder 210 illustrated inFIG. 17 may be modified to include a through hole extending in the axial direction therethrough as a channel to cool thestator 32. The same is true of each of the fans illustrated inFIGS. 18 to 20 , 25, and 28 to 37. Although theimpeller 12 illustrated inFIG. 1 is directly fixed to the outer circumferential surface of thebushing 25, theimpeller 12 may be indirectly fixed thereto through one or more members. The same is true of each ofFIGS. 16 , 21, 26, 38, and 39. Theimpeller 12 illustrated inFIG. 17 may be fixed to thebushing 25 through two or more members. The same is true of each ofFIGS. 18 , 19, 20, 25, and 27. Also, the first throughhole 128 a illustrated inFIG. 27 may not necessarily be defined in the center of thetop face portion 123. - Although each of the
impellers 12 illustrated inFIGS. 28 to 37 is directly fixed to therotor holder 210, theimpeller 12 may be indirectly fixed thereto through one or more members. Each of theimpellers 12 illustrated inFIGS. 28 to 34 may be directly fixed to theshaft 41 without therotor holder 210 intervening therebetween. Each of theimpellers 12 illustrated inFIGS. 28 to 34 may be indirectly fixed to theshaft 41 through a bushing. - In each of the bearing
mechanisms 4 illustrated inFIGS. 3 and 14 , the thrust dynamic pressure bearing portion may be defined only on an upper side of the thrust plate. In this case, as is the case with thebearing mechanism 4 illustrated inFIG. 21 , an upward force is constantly applied to theshaft 41. A thrust dynamic pressure bearing portion arranged to produce a force that acts in a direction opposite to that of the force which lifts theimpeller 12 can be easily defined by the thrust plate and the bearingportion 44. - An upper portion of the first radial dynamic
pressure groove array 711 may be defined in the secondinclined surface 441 b independently of a remaining portion thereof. Also, no dynamic pressure grooves may be defined in the secondinclined surface 441 b of the bearingportion 44. Even in this case, provision of the secondinclined surface 441 b secures an area to support theshaft 41 so that bearing rigidity can be improved to a certain extent. - In each of the above-described preferred embodiments, each of the first and second radial dynamic
pressure groove arrays circumferential surface 411 of theshaft 41. Also, the thrust dynamicpressure groove arrays thrust plate 42. Also, the communicatinghole 421 a may not necessarily be provided in thebearing mechanism 4. - The outer
circumferential surface 411 of theshaft 41 may be arranged to include a portion which has a decreased diameter in the vicinity of a top portion of the bearingportion 44 so that the seal portion may be defined between this portion and the innercircumferential surface 441 of the bearingportion 44. Also, a viscoseal that generates a fluid dynamic pressure through a dynamic pressure groove defined in the seal gap may be used as the seal portion. - A metallic member may be arranged, as the weight, in the
balance correction portion 125 of thetop face portion 123 of theimpeller 12. Also, a through hole or a cut portion may be defined as thebalance correction portion 125. The same is true of thebalance correction portion 124 a of theside wall portion 124. Also, the weight may be arranged on only one of thetop face portion 123 and thelower end portion 124 a of theside wall portion 124. Also, the unbalance of therotating portion 2 may be eliminated by removing a portion of thetop face portion 123 or a portion of theside wall portion 124. - In each of the above-described preferred embodiments, the magnetic center of the
stator 32 and the magnetic center of therotor magnet 22 may be arranged to coincide with each other in the axial direction when themotor 11 is stationary. An additional reduction in the vibrations of themotor 11 can thereby be achieved. - The
motor 11 may be used as a motor of a fan of another type, such as a centrifugal fan. A fan in which themotor 11 is used is optimal for use with a device having a hard disk installed therein, such as a server. In the server, the fan is disposed at a position close to the hard disk. Therefore, if the fan is of a type which generates significant vibrations, read or write errors tend to easily occur in the hard disk. In contrast, read or write errors do not easily occur in the hard disk if the fan installed in the server uses themotor 11. - The present invention is, for example, applicable to fans arranged to generate air currents.
- Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.
- While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
Claims (35)
1. A dynamic pressure bearing apparatus comprising:
a bearing portion;
a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion;
a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members;
a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and
a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; wherein
a minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing; and
the seal gap is arranged to be in communication with an exterior space through the horizontal gap.
2. The dynamic pressure bearing apparatus according to claim 1 , wherein
a minute vertical gap extending in an axial direction is defined between a circumferential surface of the bearing portion and a circumferential surface of the bushing;
the vertical gap is connected with a radially outer end portion of the horizontal gap; and
the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the vertical gap.
3. The dynamic pressure bearing apparatus according to claim 2 , wherein
one of the bushing and the bearing portion includes an annular portion arranged to project toward the other one of the bushing and the bearing portion;
the other one of the bushing and the bearing portion includes an annular recessed portion arranged to be recessed in a direction away from the one of the bushing and the bearing portion, and arranged axially opposite the annular portion;
the annular portion is arranged in the annular recessed portion; and
the vertical gap is defined between an inner circumferential surface of the annular portion and an outer circumferential surface of the other one of the bushing and the bearing portion which defines a portion of the annular recessed portion.
4. The dynamic pressure bearing apparatus according to claim 2 , wherein
the bushing includes an annular portion arranged to extend downward; and
the vertical gap is defined between an inner circumferential surface of the annular portion and an outer circumferential surface of the bearing portion.
5. The dynamic pressure bearing apparatus according to claim 2 , wherein a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of an opening of the seal gap.
6. The dynamic pressure bearing apparatus according to claim 1 , wherein an outside diameter of the bushing is arranged to be substantially equal to or smaller than an outside diameter of the bearing portion.
7. The dynamic pressure bearing apparatus according to claim 1 , wherein a minimum axial width of the horizontal gap is arranged to be smaller than a maximum radial width of an opening of the seal gap.
8. The dynamic pressure bearing apparatus according to claim 1 , wherein
an inclined gap arranged in a shape of a conical surface centered on the central axis is defined between the bearing portion and the bushing on a radially outer side of the horizontal gap;
a minimum width of the inclined gap is arranged to be smaller than a maximum radial width of an opening of the seal gap; and
the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the inclined gap.
9. The dynamic pressure bearing apparatus according to claim 1 , wherein
the bushing includes an annular projecting portion arranged to project radially inward from an inner circumferential surface thereof; and
the projecting portion is arranged to be in contact with an upward facing surface of the shaft.
10. The dynamic pressure bearing apparatus according to claim 1 , wherein the bearing portion is defined by a single member made of a metal.
11. The dynamic pressure bearing apparatus according to claim 1 , wherein
the bearing portion includes:
a sleeve defined by a metallic sintered body; and
a bearing housing arranged to cover an outer circumferential surface of the sleeve;
the bearing housing includes an annular upper portion arranged to extend radially inward on an upper side of the sleeve; and
the seal gap is defined between an inner circumferential surface of the annular upper portion and the outer circumferential surface of the shaft.
12. The dynamic pressure bearing apparatus according to claim 1 , further comprising a thrust plate arranged to extend radially outward from a lower end of the shaft to be axially opposed to the bearing portion, wherein a thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure in the lubricating oil is defined in a thrust gap defined between axially opposing surfaces of the bearing portion and the thrust plate.
13. The dynamic pressure bearing apparatus according to claim 12 , further comprising a cap member arranged to close a bottom portion of the bearing portion below the thrust plate, wherein another thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure in the lubricating oil is defined in another thrust gap defined between the thrust plate and the cap member.
14. The dynamic pressure bearing apparatus according to claim 12 , wherein the lubricating oil is arranged continuously in a gap having a bladder structure and including the seal gap, the radial gap, and the thrust gap, and the surface of the lubricating oil defined in the seal portion is a sole surface of the lubricating oil.
15. A fan comprising:
a motor; and
an impeller including a plurality of blades, and arranged to rotate about a central axis through the motor to produce air currents; wherein
the motor includes:
the dynamic pressure bearing apparatus of claim 1 ;
a stationary portion including a stator; and
a rotating portion including a rotor magnet arranged radially outside the stator.
16. The fan according to claim 15 , wherein the impeller is made of a resin and fixed to the bushing.
17. The fan according to claim 15 , wherein
the rotating portion further includes a rotor holder made of a metal and fixed to the bushing; and
the impeller is fixed to the rotor holder.
18. A dynamic pressure bearing apparatus comprising:
a bearing portion;
a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion;
a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members;
a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and
a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; wherein
a horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing;
a minute vertical gap extending in an axial direction is defined between a circumferential surface of the bearing portion and a circumferential surface of the bushing;
the vertical gap is connected with a radially outer end portion of the horizontal gap; and
the seal gap is arranged to be in communication with an exterior space through the horizontal gap and the vertical gap.
19. A fan comprising:
a motor; and
an impeller including a plurality of blades, and arranged to rotate about a central axis through the motor to produce air currents; wherein
the motor includes:
the dynamic pressure bearing apparatus of claim 18 ;
a stationary portion including a stator; and
a rotating portion including a rotor magnet arranged radially outside the stator.
20. The fan according to claim 19 , wherein the impeller is made of a resin and fixed to the bushing.
21. The fan according to claim 19 , wherein
the rotating portion further includes a rotor holder made of a metal and fixed to the bushing; and
the impeller is fixed to the rotor holder.
22. A dynamic pressure bearing apparatus comprising:
a bearing portion;
a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members;
a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil;
a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and
an annular member arranged in an annular shape, fixed to the shaft axially between the seal portion and the attachment surface, and arranged to extend radially outward beyond an opening of the seal gap; wherein
a minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the annular member; and
the seal gap is arranged to be in communication with an exterior space through the horizontal gap.
23. The dynamic pressure bearing apparatus according to claim 22 , wherein
the annular member includes:
a top cover portion arranged substantially in a shape of an annular plate centered on the central axis, and fixed to the shaft axially between the seal portion and the attachment surface; and
a tubular portion arranged to extend downward from the top cover portion, and arranged radially opposite an outer circumferential surface of the bearing portion;
the horizontal gap is defined between the upper surface of the bearing portion and a lower surface of the top cover portion;
a minute vertical gap extending in an axial direction is defined between an inner circumferential surface of the tubular portion and the outer circumferential surface of the bearing portion;
the vertical gap is connected with a radially outer end portion of the horizontal gap; and
the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the vertical gap.
24. The dynamic pressure bearing apparatus according to claim 22 , wherein
the bearing portion includes an annular projection portion arranged to project upward from the upper surface thereof;
the annular member is arranged substantially in a shape of an annular plate centered on the central axis;
an outer circumferential surface of the annular member is arranged radially opposite an inner circumferential surface of the annular projection portion;
a minute vertical gap extending in an axial direction is defined between the outer circumferential surface of the annular member and the inner circumferential surface of the annular projection portion;
the vertical gap is connected with a radially outer end portion of the horizontal gap; and
the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the vertical gap.
25. The dynamic pressure bearing apparatus according to claim 23 , wherein a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of the opening of the seal gap.
26. The dynamic pressure bearing apparatus according to claim 24 , wherein a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of the opening of the seal gap.
27. The dynamic pressure bearing apparatus according to claim 22 , wherein a minimum axial width of the horizontal gap is arranged to be smaller than a maximum radial width of the opening of the seal gap.
28. A fan comprising:
a motor; and
an impeller including a plurality of blades, and arranged to rotate about a central axis through the motor to produce air currents; wherein
the motor includes:
the dynamic pressure bearing apparatus of claim 22 ;
a stationary portion including a stator; and
a rotating portion including a rotor magnet arranged radially outside the stator.
29. The fan according to claim 28 , wherein a lower end of the bearing portion is arranged at a level higher than that of a lower end of the impeller.
30. The fan according to claim 28 , wherein the impeller includes a channel arranged to bring a space above the impeller into communication with a space above the stator.
31. A dynamic pressure bearing apparatus comprising:
a bearing portion;
a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members;
a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil;
a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and
an annular member arranged in an annular shape, and fixed to an upper portion of the bearing portion; wherein
a minute vertical gap extending in an axial direction is defined between the outer circumferential surface of the shaft and an inner circumferential surface of the annular member;
a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of an opening of the seal gap; and
the seal gap is arranged to be in communication with an exterior space through the vertical gap.
32. The dynamic pressure bearing apparatus according to claim 31 , wherein
the bearing portion includes an annular projection portion arranged to project upward from an upper surface thereof;
the annular member is fixed to the upper surface of the bearing portion on a radially inner side of the annular projection portion; and
at least a portion of an outer circumferential surface of the annular member is arranged to be in contact with an inner circumferential surface of the annular projection portion.
33. A fan comprising:
a motor; and
an impeller including a plurality of blades, and arranged to rotate about a central axis through the motor to produce air currents; wherein
the motor includes:
the dynamic pressure bearing apparatus of claim 31 ;
a stationary portion including a stator; and
a rotating portion including a rotor magnet arranged radially outside the stator.
34. The fan according to claim 33 , wherein a lower end of the bearing portion is arranged at a level higher than that of a lower end of the impeller.
35. The fan according to claim 33 , wherein the impeller includes a channel arranged to bring a space above the impeller into communication with a space above the stator.
Priority Applications (2)
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US14/513,612 US9303653B2 (en) | 2011-06-30 | 2014-10-14 | Dynamic pressure bearing apparatus and fan |
US15/051,795 US9822787B2 (en) | 2011-06-30 | 2016-02-24 | Dynamic pressure bearing apparatus and fan |
Applications Claiming Priority (6)
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JP2011-179970 | 2011-08-19 | ||
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JP2012102725A JP5892375B2 (en) | 2011-06-30 | 2012-04-27 | Hydrodynamic bearing device and fan |
JP2012-102725 | 2012-04-27 |
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US14/513,612 Expired - Fee Related US9303653B2 (en) | 2011-06-30 | 2014-10-14 | Dynamic pressure bearing apparatus and fan |
US15/051,795 Active 2032-06-21 US9822787B2 (en) | 2011-06-30 | 2016-02-24 | Dynamic pressure bearing apparatus and fan |
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US14/513,612 Expired - Fee Related US9303653B2 (en) | 2011-06-30 | 2014-10-14 | Dynamic pressure bearing apparatus and fan |
US15/051,795 Active 2032-06-21 US9822787B2 (en) | 2011-06-30 | 2016-02-24 | Dynamic pressure bearing apparatus and fan |
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Also Published As
Publication number | Publication date |
---|---|
JP2013061063A (en) | 2013-04-04 |
US9822787B2 (en) | 2017-11-21 |
US20160169242A1 (en) | 2016-06-16 |
JP5892375B2 (en) | 2016-03-23 |
US20150030481A1 (en) | 2015-01-29 |
CN202971550U (en) | 2013-06-05 |
US9303653B2 (en) | 2016-04-05 |
CN105114351B (en) | 2018-09-11 |
CN105114351A (en) | 2015-12-02 |
CN102852968A (en) | 2013-01-02 |
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