JP2008051133A - Bearing unit and motor equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain stable bearing performance at a high level maintaining rotational accuracy while securing a quantity of lubrication oil at all times, by suppressing lubrication oil from scattering and evaporation in the high-velocity revolution motors. <P>SOLUTION: A dynamic pressure bearing 20 is accommodated inside the housing 10 a shaft 40 is freely rotatably inserted into the dynamic pressure bearing 20, and a hub 30 is firmly fixed on the top end of the shaft 40 in the bearing unit 3. The internal peripheral surface 35 of the concave place 33 of the hub 30 is opposed to the surrounding area of the outer peripheral surface 13 of an opening end of the housing 10 and in the internal peripheral surface 35, and a peripheral oil storage groove 36 is formed throughout the periphery. Lubrication oil L which is going to overflow due to the cubical expansion or the like is introduced to the oil storage groove 36 by centrifugal force to prevent the lubrication oil L from scattering and leaking. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bearing unit and a motor suitable as a bearing for a small motor that requires high-speed and high-precision rotation.

  For cooling disk drive motors of disk drive devices that drive magnetic disks and optical disks and read / write information on these disks, polygon mirror motors that rotate polygon mirrors of laser printers, or projectors and personal computers (PCs) Motors for various information devices, such as fan motors, require a high level of high speed and high accuracy. To achieve this, the structure of the bearing that supports the rotating shaft bears a lot, and hydrodynamic bearings are particularly effective. It is said that.

  A dynamic pressure bearing is a bearing that supports a shaft with high rigidity by forming an oil film with lubricating oil in a minute gap between the shaft and increasing the pressure of the oil film by rotating the shaft. Is effectively generated mainly by a recess formed in the bearing. For example, in a spindle motor of a magnetic disk drive device, a herringbone-shaped dynamic pressure groove is formed on the inner peripheral surface of a bearing that receives a radial load from the shaft, and a spiral-shaped dynamic pressure groove is formed on the end surface of the bearing that receives a thrust load from the shaft. Are respectively formed (Patent Document 1).

  As described in Patent Document 1, the bearings of the various motors are generally configured as a bearing unit in which a bearing is housed and fixed in a housing. In such a bearing unit, the inside of the bearing is filled with lubricating oil and the above-mentioned dynamic pressure effect is exerted. However, leakage of lubricating oil from the bearing unit deteriorates high-speed and high-precision bearing performance due to oil loss. And it must be suppressed because it causes equipment contamination. In the motor of Patent Document 1, the outer peripheral surface of the opening end portion of the housing is covered with the cylindrical wall surface of the rotor member (seal bush) fixed to the shaft, and the cylindrical gap between them is formed in the housing. A so-called taper seal is provided so that the lubricating oil gradually narrows toward the opening end of the housing and the lubricating oil returns to the opening direction of the housing by surface tension.

JP 2003-262217 A

  The taper seal, which is a kind of viscous seal, has a sealing effect by balancing the internal pressure of the lubricating oil in the bearing and the atmospheric pressure received by the interface of the seal portion, thereby suppressing leakage of the lubricating oil. When the volume expansion of the lubricating oil due to the temperature rise or the centrifugal force acting on the lubricating oil becomes large, the sealing effect is lowered.

  For example, a taper seal is effective in a spindle motor of a notebook PC HDD (Hard Disk Drive Device) used at a rotational speed of about 4200-5400 rpm. However, in motors used at around 10,000 rpm, such as optical disk drive motors and PC cooling fan motors, or high-speed motors used at around 30000 rpm, such as polygon mirror motors, lubrication is caused by centrifugal force generated in the lubricating oil. There was a case where oil leaked in a scattered state. Further, in such a motor used at a high speed rotation of 10,000 rpm or more, bearing loss increases, so that there is a risk that the volume-expanded lubricating oil leaks and scatters due to the temperature rise.

  In addition, it is inevitable that the lubricating oil enclosed in the bearing is consumed by evaporation, but as the rotation speed increases, the lubricating oil evaporates due to the flow of air generated in the rotating rotor hitting the lubricating oil. The phenomenon is accelerated and the consumption of lubricating oil due to evaporation is accelerated.

  Accordingly, the present invention provides a bearing unit and a motor that can always ensure the amount of lubricating oil by suppressing scattering and evaporation of the lubricating oil in a high-speed rotating motor, and that can maintain a high level of stable bearing performance while maintaining rotational accuracy. The purpose is to provide.

  The bearing unit of the present invention has a bottomed cylindrical housing and a cylindrical shape having a shaft hole. A dynamic pressure recess is formed on the inner peripheral surface of the shaft hole, and the dynamic pressure is accommodated and fixed in the housing. A bearing, a shaft inserted into a shaft hole of the dynamic pressure bearing and rotatably supported by the dynamic pressure bearing, and a fixed end of the shaft protruding from the dynamic pressure bearing; And a rotary member having a cylindrical housing surrounding portion that surrounds the opening side end portion and is surrounded by a gap with the outer peripheral surface of the opening side end portion, and a bearing unit in which lubricating oil is sealed in a shaft hole In the present invention, an oil storage groove extending in the circumferential direction is formed on the inner peripheral surface of the housing surrounding portion of the rotating member that faces the outer peripheral surface of the end portion on the opening side of the housing.

  In the bearing unit of the present invention, the lubricating oil sealed in the hydrodynamic bearing is formed as an oil film between the shaft and the hydrodynamic bearing, and the shaft is supported for rotation in a non-contact state with the hydrodynamic bearing. The lubricating oil filling the dynamic pressure recess of the dynamic pressure bearing is increased in pressure with the rotation of the shaft, causing a dynamic pressure action, and the shaft is supported with high rigidity.

  In this operating state, if the lubricating oil overflows from the shaft hole of the hydrodynamic bearing due to volume expansion caused by high-speed rotation of the shaft or increased centrifugal force, the overflowing lubricating oil Between the outer peripheral surface of the opening end of the housing and the inner peripheral surface of the housing surrounding portion of the rotating member from the gap between the end surface on the opening side of the hydrodynamic bearing and the end surface on the opening side of the housing. It reaches. Conventionally, the gap is a tapered seal structure formed in a tapered shape that becomes narrower toward the opening side of the housing. However, the present invention provides an oil storage groove formed on the inner peripheral surface of the housing surrounding portion of the rotating member. In addition, the lubricating oil intensively enters due to the centrifugal action of the rotating member, and the lubricating oil does not easily flow to the opening side of the housing surrounding portion. This effectively suppresses scattering and leakage of the lubricating oil.

  Further, since the seal portion for preventing leakage of the lubricating oil is provided on the outer peripheral side of the housing, the effective length of the bearing can be increased as compared with the case where the seal portion is provided on the inner peripheral side of the housing. Therefore, it is possible to provide a bearing unit with improved bearing rigidity, high rotational accuracy, and effective for thinning.

  In the bearing unit of the present invention, the gap formed between the inner peripheral surface on the opening side of the housing surrounding portion and the outer peripheral surface of the opening end portion of the housing with respect to the oil storing groove on the housing surrounding portion is the depth of the oil storing groove. It includes a configuration in which a helical groove that is set smaller than the inner diameter and that communicates with the oil storage groove is formed on the inner peripheral surface on the opening side.

  According to this configuration, a dynamic pressure effect is generated in the helical groove, and a viscous seal is formed at the open end of the housing surrounding portion. The viscous seal blocks the lubricant oil that has leaked from the oil storage groove and the evaporated lubricant oil to the outside as the rotating member rotates, and the lubricating oil is returned to the oil storage groove, causing leakage of the lubricating oil. And evaporation is suppressed. Such an action can be caused by making the helical groove extend rearward in the rotational direction of the rotating member as it goes from the opening side of the housing surrounding portion toward the oil storage groove.

  Further, in the bearing unit of the present invention, the gap between the outer peripheral surface of the opening end portion of the housing and the inner peripheral surface of the housing surrounding portion is formed in a tapered shape that gradually narrows toward the opening of the housing. including.

  According to this aspect, the gap between the outer peripheral surface of the opening end portion of the housing and the inner peripheral surface of the housing surrounding portion of the rotating member constitutes a conventional taper seal, coupled with the centrifugal seal by the oil storage groove of the present invention. The effect of suppressing leakage of lubricating oil is increased. The taper seal mainly suppresses leakage of the lubricating oil when the shaft is stationary and when the shaft rotates at a low speed, and the centrifugal seal suppresses scattering of the lubricating oil when the shaft is rotated at a high speed. Therefore, the leakage of the lubricating oil is suppressed over the entire area from the stop to the high speed rotation.

  As a form of the taper seal, the taper seal may be formed in two stages with the oil storage groove as a boundary. That is, in the gap between the outer peripheral surface of the opening end portion of the housing and the inner peripheral surface of the housing surrounding portion, the clearance on the opening side of the housing surrounding portion from the oil storage groove and the clearance on the non-opening side are individually It is the form currently formed in the taper shape which becomes narrow gradually as it goes to this opening.

  The bearing unit of the present invention is preferably used as a bearing for the various motors described above, and the present invention also includes such a motor, that is, a motor including the bearing unit of the present invention.

  According to the present invention, the lubricating oil intensively enters the oil storage groove formed on the inner peripheral surface of the housing surrounding portion of the rotating member by the centrifugal action of the rotating member, and the lubricating oil flows to the opening side of the housing surrounding portion. Due to the difficulty, the scattering and leakage of the lubricating oil enclosed in the hydrodynamic bearing is effectively suppressed.

An embodiment in which the present invention is applied to a polygon mirror motor for a laser scanner will be described below with reference to the drawings.
[1] Configuration of Motor FIG. 1 shows a motor 1 according to an embodiment that rotates a polygon mirror M having an outer diameter of about 40 mm. Reference numeral 2 denotes a case having a cylindrical holder portion 2a protruding upward in FIG. A bearing unit 3 is incorporated in the holder portion 2a, and a motor portion 4 for rotating the motor 1 is provided on the outer peripheral portion of the holder portion 2a.

  The bearing unit 3 includes a bottomed cylindrical housing 10 that opens upward in FIG. 1 and a hydrodynamic bearing 20 accommodated in the housing 10. The housing 10 is fitted to a cylindrical body 11 having an outer diameter of about 8 mm and a height of about 8 mm, and a counterbore-shaped step portion 11 a formed on the lower end surface of the cylindrical body 11 to close the lower opening of the cylindrical body 11. It consists of a disk-shaped plate 12. The plate 12 is fixed to the cylindrical body 11 by means such as welding or adhesion. The dynamic pressure bearing 20 is press-fitted into and fixed to the cylindrical body 11 of the housing 10. The dynamic pressure bearing 20 may be fixed to the cylindrical body 11 by means such as welding or adhesion.

  In addition, the bearing unit 3 includes a hub (rotating member) 30 that supports the polygon mirror M and is rotated by the motor unit 4, and a shaft 40 that is the center of rotation of the hub 30. The shaft 40 is a straight cylindrical body having a diameter of around φ3 to φ5 mm. The shaft 40 is inserted into the shaft hole 21 of the dynamic pressure bearing 20 from above in the drawing and is rotatably supported by the dynamic pressure bearing 20. The shaft 40 protrudes upward from the housing 10, and the hub 30 is fixed concentrically to the protruding end 41 thereof. The hub 30 is integrated with the shaft 40 by fixing the protruding end portion 41 of the shaft 40 to the center hole 31 by press-fitting, welding, adhesion, or the like.

  The polygon mirror M is integrally fixed to the hub 30 by being fitted into a stepped portion 32 formed on the upper surface of the hub 30 in an interference fit state. In addition, a cylindrical recess (housing surrounding portion) 33 is formed on the lower surface of the hub 30 and around the hole 31, and the cylindrical body 11 of the housing 10 is fitted in the recess 33 with a clearance fit. It is inserted. Around the lower end side (opening side) of the recess 33, an annular convex portion 34 protruding downward is formed.

  As shown in FIG. 2, the inner peripheral surface 35 of the recess 33 is in a state where a gap (for example, 0.01 to 0.03 mm) 14 is separated from the outer peripheral surface 13 of the opening side end portion of the housing 10. The outer peripheral surface 13 is surrounded and opposed. An oil storage groove 36 extending along the circumferential direction is formed over the entire circumference of the inner circumferential surface 35 of the recess 33 at a substantially intermediate portion in the vertical direction. The oil storage groove 36 has a semicircular cross section and has dimensions such as a width of about 0.3 mm and a depth of 0.1 mm at the deepest portion. The annular protrusion 34 is formed below the oil storage groove 36. The gap 14 between the inner peripheral surface 35 on the annular convex portion 34 side and the outer peripheral surface 13 of the housing 10 is, for example, 0.01 to 0.03 mm, and is set smaller than the depth of the oil storage groove 36. ing.

  As shown in FIG. 1, a cylindrical portion 37 that hangs down to the case 2 side is formed on the outer peripheral portion of the hub 30. The inner peripheral surface of the cylindrical portion 37 and the outer peripheral surface of the holder portion 2a of the case 2 are opposed to each other, and a rotating magnetic field generating stator 52 around which a coil 51 is wound is disposed on the case 2 side of these opposing surfaces. The motor magnet 53 is fixed to the hub 30 side. The stator 52 and the motor magnet 53 constitute the motor unit 4.

  The bearing unit 3 including the housing 10, the dynamic pressure bearing 20, the shaft 40, and the hub 30 is formed by fixing the cylindrical body 11 of the housing 10 into the holder portion 2 a of the case 2 by press fitting, welding, adhesion, or the like. Built in. With the bearing unit 3 assembled in the case 2 in this way, the lower surface of the hub 30 faces the upper end surface of the bearing unit 3 (the upper surface of the housing 10 and the dynamic pressure bearing 20) with a small gap therebetween. ing.

  As shown in FIG. 2, the gap between the upper end surface of the bearing unit 3 and the lower surface of the hub 30 is smaller on the dynamic pressure bearing 20 side, and the thrust load of the shaft 40 is mainly above the dynamic pressure bearing 20. It is received at the end face 20a. Further, the radial load of the shaft 40 is received by the inner peripheral surface 22 of the fluid dynamic bearing 20. Lubricating oil L is sealed in the shaft hole 21 of the dynamic pressure bearing 20, and the lubricating oil L is formed between the upper end surface 20 a of the dynamic pressure bearing 20 and the hub 30 through a minute gap between the dynamic pressure bearing 20 and the shaft 40. It fills up the minute gap between the lower surface and forms an oil film.

Next, the dynamic pressure structure of the dynamic pressure bearing 20 will be described.
As shown in FIG. 3, the inner circumferential surface 22 of the hydrodynamic bearing 20 has a plurality of (in this case, 5) separation grooves 23 that are semicircular in cross section and extend straight along the axial direction between both end surfaces. It is formed at equal intervals in the circumferential direction. And between each separation groove 23 of the inner peripheral surface 22, it is eccentric with respect to the shaft center P of the outer diameter of the hydrodynamic bearing 20, and it shrinks to the inner peripheral side as it goes to the rotation direction of the shaft 40 shown by the arrow R. An arcuate surface (dynamic pressure recess) 24 having a shape of increasing diameter is formed. That is, these circular arc surfaces 24 are not concentric with the outer diameter of the hydrodynamic bearing 20, and the center of each circular arc surface 24 is concentric with the axial center P around the axial center P and equidistantly spaced in the circumferential direction. Exist.

  Due to the shape of the circular arc surface 24, the minute gap between the circular arc surface 24 and the outer peripheral surface of the shaft 40 is formed in a wedge shape that gradually narrows toward the rotation direction of the shaft 40. In this case, the width of the separation groove 23 is a length corresponding to an angle θ of 8 to 20 ° in the circumferential direction around the axis P of the bearing 20 shown in FIG. The maximum depth is 0.05 to 0.15 mm.

  On the other hand, on the upper end surface 20a of the hydrodynamic bearing 20, as shown in FIG. 4, a plurality of (in this case, 12) spiral grooves 25 extending while curving toward the inner peripheral side toward the rotational direction R of the shaft 40, It is formed at equal intervals in the circumferential direction. The outer peripheral ends of the spiral grooves 25 are open to the outer peripheral edge, but the inner peripheral ends are not opened to the inner peripheral edge and are closed. The spiral groove 25 has a maximum depth of 8 to 15 μm.

  If the hydrodynamic bearing 20 is made of a sintered body obtained by sintering a compact formed by compressing raw material powder, the separation groove 23, the arcuate surface 24 and the spiral groove 25 are formed with high dimensional accuracy by molding or plastic working. And can be formed at low cost. However, since the sintered bearing has pores that cause a decrease in dynamic pressure, it is necessary to secure the dynamic pressure by sealing the inner peripheral surface.

[2] Operation and Effect of Motor According to the motor 1, when a predetermined current is supplied to the coil 51, a current magnetic field is generated from the stator 52, and electromagnetic interaction is generated between the current magnetic field and the motor magnet 53. As a result, the hub 30 rotates about the shaft 40 and the polygon mirror M rotates. During such rotation of the motor 1, the radial load of the shaft 40 is received by the inner peripheral surface 22 of the dynamic pressure bearing 20, and the thrust load of the shaft 40 is received by the upper end surface 20 a of the dynamic pressure bearing 20.

  The action of the hydrodynamic bearing 20 during the rotation of the motor 1 will be described in detail. When the shaft 40 inserted into the shaft hole 21 rotates in the direction of the arrow R shown in FIGS. The oil is efficiently wound on the shaft 40 and enters the wedge-shaped minute gap between the arc surface 24 and the shaft 40 to form an oil film. The lubricating oil entering the minute gap flows toward the narrow side of the minute gap, thereby generating a wedge effect and a high pressure, and a high radial dynamic pressure is generated. The portions where the oil film is increased in pressure are generated at equal intervals in the circumferential direction according to the circular arc surface 24, whereby the radial load of the shaft 40 is supported with good balance and high rigidity.

  On the other hand, the lubricating oil between the upper end surface 20 a of the dynamic pressure bearing 20 and the hub 30 is also stored in the spiral groove 25 of the dynamic pressure bearing 20. The lubricating oil stored in the spiral groove 25 flows from the outer peripheral side of the spiral groove 25 toward the inner peripheral side by the rotation of the shaft 40, and the thrust dynamic pressure that is the highest at the inner peripheral side end of the spiral groove 25 is generated. appear. The hub 30 is slightly lifted by receiving the thrust dynamic pressure, whereby the thrust load is supported in a balanced manner and with high rigidity.

  The lubricating oil that generates dynamic pressure on the radial side and the thrust side in this way rises in temperature due to viscous friction and expands in volume. Lubricating oil for volume expansion flows into the gap 14 between the inner peripheral surface 35 of the recess 33 of the hub 30 and the outer peripheral surface 13 of the opening end of the housing 10 and is stored in the gap 14. However, when the shaft 40 rotates at a high speed of, for example, about 30000 rpm, conventionally, the volume expansion of the lubricating oil further increases, the centrifugal oil overflows and scatters from the gap 14, or the lubricating oil evaporates due to further temperature rise, In some cases, the lubricating oil may leak from the gap 14 such that the evaporated oil is drawn from the gap 14 and scattered by the air flow generated by the rotation of the hub 30. However, in the present embodiment, the lubricating oil in the gap 14 intensively enters the oil storage groove 36 due to centrifugal force, and the lubricating oil is less likely to flow to the opening side (lower side) of the recess 33. As a result, a centrifugal seal effect that suppresses leakage of the lubricating oil from the opening of the recess 33 is exhibited.

[3] Other Embodiments Next, another embodiment of the present invention based on the above embodiment will be described.
(A) Seal structure with added helical groove In the bearing unit 3 shown in FIG. 5, as shown in FIG. 6, the inner peripheral surface 35 of the recess 33, which is closer to the opening side of the recess 33 than the oil storage groove 36. In addition, a plurality of helical grooves 38 inclined at a predetermined angle (for example, around 30 °) with respect to the circumferential direction are formed at equal intervals in the circumferential direction. These helical grooves 38 are formed so as to communicate from the lower opening edge of the recess 33 to the oil storage groove 36. Further, the direction of the inclination is a direction extending rearward in the rotational direction of the hub 30 indicated by an arrow R from the lower opening edge toward the oil storage groove 36.

  According to this configuration, a dynamic pressure effect is generated in the helical groove 38, and a viscous seal is formed at the opening end of the recess 33. When a part of the lubricating oil leaks from the oil storage groove 36, the oil storage groove 36 enters the helical groove 38, and the lubricating oil is returned to the oil storage groove 36 by rotation of the hub 30 (indicated by an arrow). It is difficult to flow downward, thereby blocking outflow of lubricating oil.

(B) Seal structure with taper seal The form shown in FIG. 7 is a gap between the inner peripheral surface 35 of the recess 33 of the hub 30 and the outer peripheral surface 13 of the opening end of the housing 10 in the configuration of FIG. 14 is formed in a tapered shape that gradually becomes narrower as it goes upward, which is the opening direction of the housing 10. In this case, the inner peripheral surface 35 of the recess 33 is formed in a conical shape that gradually increases in diameter toward the opening side (lower side) of the recess 33, so that the gap 14 is formed in a tapered shape. Yes. The taper angle is, for example, about 10 ° with respect to the axial direction. The gap 14 can be tapered by forming the outer peripheral surface 35 of the housing 10 into a conical shape whose diameter increases toward the opening side (upper side) of the housing 10.

  In this embodiment, the gap between the outer peripheral surface 13 of the opening end of the housing 10 and the inner peripheral surface 35 of the recess 33 of the hub 30 constitutes a conventional taper seal (viscous seal), and the oil storage groove 36. The lubricating oil that is about to come out is drawn to the narrow side of the gap 14 by the surface tension, that is, the opening side of the upper housing 10. Therefore, in combination with the centrifugal seal by the oil storage groove 36, the effect of suppressing the leakage of the lubricating oil is increased. The taper seal mainly suppresses leakage of the lubricating oil when the shaft 40 is stationary and when the shaft 40 is rotated at a low speed, and the centrifugal seal suppresses scattering of the lubricating oil when the shaft 40 is rotated at a high speed. Therefore, the leakage of the lubricating oil is suppressed over the entire region from the stop to the high speed rotation.

(C) Two-stage taper seal FIG. 8 shows that the gap 14 between the inner peripheral surface 35 of the recess 33 of the hub 30 and the outer peripheral surface 13 of the opening end of the housing 10 is vertically separated from the oil storage groove 36. Individually, it is formed in a tapered shape that becomes gradually narrower toward the opening of the housing 10. In this case, the inner peripheral surface 35a above the oil storage groove 36 of the inner peripheral surface 35 and the inner peripheral surface 35b below the oil storage groove 36 of the inner peripheral surface 35 gradually become narrower as they go upward. In the tapered gaps 14a and 14b facing the inner peripheral surfaces 35a and 35b, a taper seal effect is exhibited in which the lubricating oil is returned upward by surface tension. Here, the helical groove 38 is not formed on the inner peripheral surface 35.

  According to this embodiment, instead of the helical groove 38, a taper seal is provided on the opening side of the recess 33 (below the oil storage groove 36). Lubricating oil leakage during stationary and low-speed rotation is suppressed by the centrifugal seal during high-speed rotation by 36 and the two-stage taper seal.

It is a longitudinal cross-sectional view of the polygon mirror motor which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view which shows the bearing unit of one Embodiment. It is a cross-sectional view of the hydrodynamic bearing of one embodiment. It is a top view of the dynamic pressure bearing of one embodiment. It is a longitudinal cross-sectional view which shows the bearing unit of other embodiment of this invention. It is a developed view of the inner peripheral surface of the recess of the hub and is a view showing a helical groove. It is a longitudinal cross-sectional view which shows the bearing unit of other embodiment of this invention. It is a longitudinal cross-sectional view which shows the bearing unit of other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Bearing unit 10 ... Housing 13 ... Outer peripheral surface of housing 14, 14a, 14b ... Gap 20 ... Dynamic pressure bearing 21 ... Shaft hole 24 ... Arc surface (dynamic pressure recess)
25 ... spiral groove 30 ... hub (rotating member)
33 ... recess (housing for housing)
35 ... Inner peripheral surface of recess (inner peripheral surface of housing enclosure)
36 ... Oil storage groove 38 ... Helical groove 40 ... Shaft 41 ... Projection end of shaft L ... Lubricating oil M ... Polygon mirror motor

Claims (5)

A bottomed cylindrical housing;
A dynamic pressure bearing having a cylindrical shape having a shaft hole, in which a dynamic pressure recess is formed on an inner peripheral surface of the shaft hole, and is housed and fixed in the housing;
A shaft inserted into the shaft hole of the fluid dynamic bearing and rotatably supported by the fluid dynamic bearing;
A cylindrical shape that is fixed to the projecting end portion of the shaft from the hydrodynamic bearing, covers the opening side end portion of the housing, and surrounds the outer peripheral surface of the opening side end portion with a gap therebetween. A rotating member having a housing surrounding portion,
In the bearing unit in which lubricating oil is sealed in the shaft hole,
An oil storage groove extending in a circumferential direction is formed on an inner peripheral surface of the housing surrounding portion of the rotating member facing an outer peripheral surface of an opening side end portion of the housing.   The gap formed between the inner peripheral surface of the housing surrounding portion on the opening side of the housing surrounding portion and the outer peripheral surface of the opening end portion of the housing is set to be smaller than the depth of the oil storing groove. 2. A bearing unit according to claim 1, wherein a helical groove communicating with the oil storage groove is formed on an inner peripheral surface on the opening side.   The gap between the outer peripheral surface of the opening end portion of the housing and the inner peripheral surface of the housing surrounding portion is formed in a tapered shape that gradually narrows toward the opening of the housing. The bearing unit according to 1 or 2. In the gap between the outer peripheral surface of the opening end portion of the housing and the inner peripheral surface of the housing surrounding portion, a clearance on the opening side of the housing surrounding portion from the oil storage groove, and a clearance on the opposite opening side,
3. The bearing unit according to claim 1, wherein each of the bearing units is formed in a tapered shape that gradually narrows toward an opening of the housing. 4.   A motor comprising the bearing unit according to claim 1.

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