JPH08214497A - Motor comprising dynamic pressure hydraulic bearing - Google Patents

Abstract

PURPOSE: To prevent the burning by shortage of oil generated during high speed rotation. CONSTITUTION: A motor comprises a shaft 21, a shaft holding member 26 and a thrust plate 23 provided on the shaft 21 and thrust dynamic pressure hydraulic bearings 54a, 54b are provided between the thrust plate 23 and shaft holding member 26, while a radial dynamic pressure hydraulic bearing means 27 between the shaft 21 and shaft holding member 26. The thrust plate 23 is formed of a disc type member, an annular space is defined between the external circumferential surface of the disc type member and internal circumferential surface of the shaft holding member 26, an excessive oil is accommodated into a part of the annular space and the disc type member is provided with a communication hole 42 for communicating with the annular sapce to the atmospheric condition.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to motors. More specifically, it relates to a motor provided with a hydrodynamic bearing.

[0002]

2. Description of the Related Art Up to now, for example, as shown in FIG.
Spindle motors using hydrodynamic bearings are known to those skilled in the art. In a known spindle motor 1 using a hydrodynamic bearing as shown in FIG. 6, the lower end of the shaft 4 is fixed to the boss portion 3 of the fixed base member 2, and the radius of the boss portion 3 is fixed. Stator 5 outward in the direction
Is stuck. A small-diameter portion 6 is provided at the upper end of the shaft 4, a thrust plate 7 is fixedly fitted to the small-diameter portion 6, and the upper surface of the thrust plate 7 is also fitted to the small-diameter portion 6. The bush 8 is held. A cover plate 9 is arranged outside the bush 8 in the radial direction and on the upper surface of the thrust plate 7. A sleeve member 10 is provided on the outer side of the cover plate 9 in the radial direction, and the cover plate 9 and the sleeve member 10 are fixed to each other, and these constitute a shaft holding member.

In addition, a portion of the sleeve member 10 carries and thrusts the thrust plate 7.
Of the radial dynamic pressure fluid bearing means 12 formed in the middle of the shaft 4. Further, the sleeve member 10 is the stator 5
The rotor magnet 13 is supported at a position opposite to the stator 5 in the radial outward direction. Furthermore, the sleeve member 10 has a hub 14 radially outward thereof,
The hub 14 holds a magnetic disk (not shown). Oil is interposed between the upper surface of the thrust plate 7 and the lower surface of the cover plate 9 and between the lower surface of the thrust plate 7 and the sleeve member 10 to form thrust hydrodynamic bearing means, and the shaft 4 and the sleeve. Member 1
Oil is intervened between 0 and 0 to form radial dynamic pressure fluid bearing means.

[0004]

In such a spindle motor, since it rotates at an extremely high speed during operation, oil flows radially outward by the centrifugal force in the thrust dynamic pressure fluid bearing means, and the thrust dynamic pressure is increased. The fluid bearing means tends to run out of oil. If the thrust hydrodynamic bearing means is deficient in oil, the thrust plate and the sleeve member may come into metal contact with each other, and seizure may occur in the bearing means. Further, in this type of motor, there is no reservoir for holding excess oil, that is, a so-called oil reservoir. Therefore, it is necessary to strictly measure the amount of oil present in the bearing portion, and if the amount of oil is larger than a predetermined value, there is a risk that excess oil will leak from the bearing portion to the outside. In addition, since it is not possible to retain excess oil in advance in the bearing part in this way, if the bearing is used for a long time, the oil evaporates and the oil in the bearing part decreases, which shortens the life of the bearing. There is a fear.

An object of the present invention is to solve the above-mentioned problems and to provide a motor equipped with a hydrodynamic bearing means capable of preventing seizure due to insufficient oil which occurs at high speed rotation.

[0006]

According to the present invention, there is provided a shaft, a shaft holding member for holding the shaft as a bearing, and a thrust plate provided on the shaft, and an upper surface and a lower surface of the thrust plate and a shaft holding member. In a motor in which thrust hydrodynamic bearing means are respectively interposed between the shaft and the shaft hydrodynamic fluid bearing means between the shaft holding member and the shaft, the thrust plate is composed of a disk-shaped member, and the shaft holding member In, the inner peripheral surface facing the outer peripheral surface of the disk-shaped member is cylindrical, an annular space is defined between the outer peripheral surface of the disk-shaped member and the inner peripheral surface of the shaft holding member, A part of the excess oil is stored, and the disk-shaped member is provided with a communication hole for communicating the annular space with the atmosphere. When the motor is not rotating, the annular space is Oil collects in the lower part, and the space above the oil in the annular space communicates with the atmosphere through the communication hole, and when the motor is rotating at high speed, the oil in the annular space is driven by centrifugal force. The oil of the thrust hydrodynamic bearing means on the upper surface side of the thrust plate and the thrust on the lower surface side of the thrust plate are held through the oil held along the inner peripheral surface of the shaft holding member through the oil held along the inner peripheral surface. The oil of the hydrodynamic bearing means is in a continuous state, and the space generated inside the oil held on the inner peripheral surface in the annular space is communicated with the atmosphere through the communication hole.

[0007]

In the motor of the present invention, excess oil is contained in a part of the annular space defined between the outer peripheral surface of the thrust plate and the inner peripheral surface of the shaft holding member. Therefore, a part of the annular space acts as a reservoir for excess oil, and the remaining part of the annular space acts as an air chamber. This air chamber communicates with the atmosphere through the communication hole, and the air in the air chamber expands due to the temperature change. At times, this air is discharged to the atmosphere through the communication hole. Further, when the motor rotates at a high speed, the oil in the thrust dynamic pressure fluid bearing means on the upper and lower surfaces of the thrust plate becomes continuous through the oil attached to the inner peripheral surface of the shaft holding member by centrifugal force. Therefore, the centrifugal force acting on the oil held on the inner peripheral surface of the shaft holding member and the centrifugal force component acting on the oil of the thrust dynamic pressure fluid bearing means are balanced, and the thrust dynamic pressure fluid bearing means Oil is prevented from flowing radially outward by centrifugal force,
The lack of oil in the thrust hydrodynamic bearing means is prevented. Further, at this time, the air chamber generated inside the oil attached to the inner peripheral surface of the shaft holding member is communicated with the atmosphere through the communication hole.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the essential parts of a first embodiment of the motor of the present invention. In FIG. 1, the illustrated motor includes a shaft 21 whose lower end is fixedly held by a boss (not shown) of a fixed base member. This shaft 21
A thrust plate 23 is integrally provided at the upper end of the. The thrust plate 23 is formed of a disc-shaped member, and the outer peripheral surface thereof is substantially cylindrical. A portion of the shaft 21 below the thrust plate 23, that is, a first portion 24 has a relatively large outer diameter, while a portion of the shaft 21 above the thrust plate 23, that is, a second portion 22 has a relatively outer diameter. It is small, about half the outer diameter of the first portion 24. A cover plate 25 is disposed radially outward of the second portion 22 of the shaft 21 and above the thrust plate 23. Cover plate 2
5, a sleeve member 26 is attached, as in FIG. Also in this example, the cover plate 25 and the sleeve member 26 are fixed to each other to form a shaft holding member. A part of the sleeve member 26 holds the outer peripheral surface of the thrust plate 23, extends from there to below the thrust plate 23, and further supports a radial dynamic pressure hydrodynamic bearing means 27 provided in the middle of the shaft 21.

The radial dynamic pressure fluid bearing means 27 is composed of a pair of radial bearing grooves 28, 29 formed in the shaft 21 at intervals in the axial direction.
Alternatively, it may be formed on the inner peripheral surface of the sleeve member 26. A stator 52 is fixedly held on the boss portion 50 of the base member holding the shaft 21. As shown in FIG. 6, the sleeve member 26 supports a rotor magnet (not shown) at a position facing the stator 52 radially outward of the stator 52. Further, as shown in FIG. 6, the sleeve member 26 has a hub (not shown) radially outward thereof, and a magnetic disk (not shown) is held on the hub. As a result, the thrust plate 23 and the shaft holding member (the cover plate 25 and the sleeve member 2 surrounding the upper surface, the side surface, and the lower surface of the thrust plate 23).
6) and between the thrust dynamic pressure fluid bearing means 54a, 5
4b is provided, and the shaft 21 and the sleeve member 26 are provided.
Radial dynamic pressure fluid bearing means 27 is provided between and.

In the embodiment, the thrust dynamic pressure fluid bearing means 5
4a and 54b are composed of bearing grooves formed on the upper surface and the lower surface of the thrust plate 23. Instead of the thrust plate 23, the bearing grooves of the thrust hydrodynamic bearing means 54a, 54b are replaced by the cover plate 2
5 and / or the sleeve member 26.

With respect to the radial dynamic pressure fluid bearing means 27 and the thrust dynamic pressure fluid bearing means 54a, 54b, further,
It is configured as follows. That is, between the radially inner portion of the cover plate 25 and the second portion 22 of the shaft 21, the atmosphere passage 31 communicating with the outside of the motor, that is, the atmosphere.
Is specified. On the lower surface of the radially inner portion of the cover plate 25, there is provided a taper portion 32 that is inclined upward inward in the radial direction at a predetermined angle (a °). Further, following the taper portion 32, a concave portion 56 is provided on the outer side thereof.
Is provided, and the recess 56 is provided in the thrust plate 2
A first oil sump space 58 is defined in cooperation with the upper surface of 3. It is desirable that the oil sump space 58 has a relatively large volume so that the excess oil can be sufficiently accommodated even if the motor is inverted and oil in the annular space at the end of the thrust leaks out. In the embodiment, a shoulder 60 having a slightly larger diameter is provided at the base of the small-diameter portion 22 of the shaft 21, and the distance between the shoulder 60 and the inner diameter end of the cover plate 25 is set small. Therefore, the taper seal means composed of the taper portion 32 is arranged outside the thrust dynamic pressure fluid bearing means 54a arranged on the upper surface side of the thrust plate 23, and the shoulder portion 60 is arranged outside the taper seal means. A throttle sealing means composed of the cover plate 25 and the cover plate 25 is disposed, and an oil storage space 58 is disposed between the pair of sealing means. The angle a of the tapered portion 32 is preferably 5 to 15 °.

At the lower portion of the sleeve member 26 facing the shaft 21, a taper portion 3 which is inclined radially outward toward the lower side of the shaft 21 at a predetermined angle (b °).
7 is provided. Further, the distance between the lower end of the sleeve member 26 and the upper end of the boss 50 is set to be small, and the narrowed portion functions as a diaphragm sealing means. Further, an annular concave portion 62 is provided on the inner peripheral portion of the boss portion 50, and the inner peripheral surface defining the concave portion 62 is expanded downward in the radial direction. The recess 62 is formed on the shaft 2
It preferably cooperates with 1 to act as a second oil sump space for accommodating excess oil and to make its volume relatively large. The angle b of the tapered portion 37 is preferably 5 to 15 °.

As shown in FIG. 1, the thrust dynamic pressure fluid bearing means 54a, 54b to the radial dynamic pressure fluid bearing means 27.
That is, the oil is filled all over, that is, the upper surface, the peripheral side surface, the lower surface of the thrust plate 23 and the lower end portion of the shaft 21 (the peripheral side surface of the thrust plate 23 will be described later in detail). Then, in order to prevent oil from leaking from the hydrodynamic bearing means 27 and 54a, 54b, in the embodiment, the maximum distance between the tapered portions 32 and 37 is
It is set to be larger than the distance between the shaft 21 and the shaft holding member. This makes it difficult for oil to flow out from the tapered portions 32 and 37.

Further in connection with the thrust plate 23,
It is configured as follows. A description will be given with reference to FIG. 2 together with FIG. The outer peripheral surface of the thrust plate 23 is cylindrical, and the outer peripheral surface extends linearly in the axial direction (vertical direction in FIGS. 1 and 2). This thrust plate 2
2 of the sleeve member 26 which receives the number 3 and is opposed thereto
The inner peripheral surface of 6a also has a cylindrical shape corresponding to the outer peripheral surface shape of the thrust plate 23, and the distance between the inner peripheral surface of the portion 26a and the outer peripheral surface of the thrust plate 23 is substantially the same in the axial direction. And both define an annular space 64 between them. In the annular space 64, a part of the oil 6
6 are accommodated. The amount of the oil 66 is preferably about half of the annular space 64. When the amount of the oil 66 increases, a communication hole described later comes to be blocked by the oil 66, while the amount of the oil 66 increases. When the number is reduced, the thrust dynamic pressure fluid bearing means 54a, 5 during high speed rotation
The oil layer connecting the 4b is not formed.

The thrust plate 23 is further formed with a pair of communication holes 42 at intervals of substantially 180 degrees in the circumferential direction. One end of the communication hole 42 has the thrust plate 2
3 is open to the outer peripheral surface, that is, the annular space 64, and the other end is opened to the upper surface of the thrust plate 23. In the embodiment, as clearly shown in FIGS. 1 and 2, one end opening of the communication hole 42 is opened in the axial center part of the thrust plate 23, and the other end opening is opened in the tapered portion 32. Even if the oil 66 is fed, the air and the oil 66 are separated in the taper portion 32 and the first oil reservoir space 58 following the taper portion 32, and the oil 66 is returned to the thrust hydrodynamic bearing means 54a, while the air 66 Is the atmosphere passage 31
Is discharged to the outside of the motor through.

Next, the function and effect of the above-mentioned motor will be described. When the motor is not rotating, the oil 66 is held in the state shown in FIG. That is, oil 6
6 are gathered in the lower part of the annular space 64 by their own weight, and the thrust hydrodynamic bearing means 5 on the lower surface side of the thrust plate 23
The oil 66b of 4b and the oil 66c housed in the annular space 64 are in a continuous state.
The oil and the oil 66a of the thrust hydrodynamic bearing means 54a on the upper surface side of the thrust plate 23 are held in a separated state via the air chamber. Further, one end opening of the communication hole 42 is
At least a part thereof is located above the oil 66c in the annular space 64 and communicates with the air chamber of the annular space 64. Therefore, even if the air in the air chamber expands due to temperature changes,
The expanded air receives the communication hole 42 and the first oil sump space 58.
And, it is discharged to the outside through the air passage 31, and the adverse effect due to air expansion is avoided.

On the other hand, when the motor is rotating at a high speed, the oil 66 is held in the state shown in FIG. That is, the centrifugal force generated by the high speed rotation of the sleeve member 26 causes the oil 66a of the thrust hydrodynamic bearing means 54a, 54b,
66b and the oil 66c in the annular space 64, the oil 66c in the annular space 64 is held in a state of being adhered to the inner peripheral surface of the portion 26a of the sleeve member 26, and the thrust plates 23 have thrust surfaces on the upper and lower surfaces thereof. The oil 66a, 66b of the hydrodynamic bearing means 54a, 54b tends to flow radially outward. Therefore, as shown in FIG.
Oil 66 of thrust dynamic pressure fluid bearing means 54a, 54b
a and 66b flow outward in the radial direction and the sleeve member 26
Flows to the layer of oil 66c held on the inner peripheral surface of
Oil 66 of the thrust hydrodynamic bearing means 54a on the upper surface side
a and the oil 66b of the thrust hydrodynamic bearing means 54b on the lower surface side are the oil 66c on the inner peripheral surface of the sleeve member 26.
(The ends of the oil layer in the axial direction are arcuate to some extent and are connected to the oils 66a and 66b). In such a continuous state, as will be easily understood, the oil 66c held by the sleeve member 26 is
Has a relatively large centrifugal force because it rotates integrally with it at a high speed. On the other hand, the centrifugal force acting on the oil 66a, 66b of the thrust dynamic pressure bearing means 54a, 54b on the upper and lower surfaces is supported by the inner peripheral surface of the sleeve member 26, and acts on the oil 66c attached to the inner peripheral surface. To balance the centrifugal force generated by the thrust hydrodynamic bearing means 54a, 54b.
The oil 66a, 66b is prevented from flowing outward in the radial direction, and oil shortage during high speed rotation is prevented. Further, even at such high speed rotation, the oil 66 sticks to the inner peripheral surface of the sleeve member 26, so that the one end opening of the communication hole 42 has the oil 6 in the annular space 64 as shown in FIG.
The 6th layer is communicated with the air chamber generated inward in the radial direction, the communication state between the air chamber and the motor is maintained, and the inconvenience caused by the temperature change is eliminated.

4 and 5 show the essential parts of a second embodiment of the motor according to the present invention. Referring to FIGS. 4 and 5, the outer peripheral surface of the thrust plate 123 has a cylindrical shape,
The outer peripheral surface extends linearly in the axial direction (vertical direction). An inner peripheral surface of a portion 126a of the sleeve member 126 which receives the thrust plate 123 and faces the thrust plate 123 extends in an arc shape in which an axial center portion is most distant from the outer peripheral surface of the thrust plate 123. And part 126
The distance between the inner peripheral surface of a and the outer peripheral surface of the thrust plate 123 is the smallest at both ends of the thrust plate 123, and the largest at the central portion in the axial direction thereof, and both define an annular space 164 therebetween. ing. In this annular space 164, oil 166 is partially formed.
Is housed. It is desirable that the amount of the oil 166 is about half of that of the annular space 164, as in the first specific example. When the amount of the oil 166 increases, a communication hole described later is blocked by the oil 166. On the other hand, when the amount of the oil 166 is reduced, the oil layer connecting the thrust dynamic pressure fluid bearing means 154a, 154b is not formed at the time of high speed rotation.

Similar to the first embodiment, the thrust plate 123 is formed with a pair of communication holes 142 (only one is shown in FIGS. 4 and 5) at intervals of substantially 180 degrees in the circumferential direction. ing. One end of the communication hole 142 is opened to the outer peripheral surface of the thrust plate 123, that is, the annular space 164, and the other end is opened to the upper surface of the thrust plate 123. Also in this example, one end opening of the communication hole 142 is opened at the central portion in the axial direction of the thrust plate 123. The other configuration of the second specific example is substantially the same as that of the first specific example.

Next, the function and effect of this motor will be described. When the motor is not rotating, oil 16
6 is held in the state shown in FIG. That is, oil 16
6 collects in the lower part of the annular space 164 by its own weight, and the oil 166b of the thrust hydrodynamic bearing means 154b on the lower surface side of the thrust plate 123 and the oil 166c accommodated in the annular space 164 are in a continuous state. 166c and the oil 166a of the thrust hydrodynamic bearing means 154a on the upper surface side of the thrust plate 123 are held in a separated state via the air chamber. Further, at least a part of the one end opening of the communication hole 142 is located above the oil 166c in the annular space 164, and the annular space 1
It communicates with 64 air chambers. Therefore, even if the air in the air chamber expands due to a temperature change or the like, the expanded air still has the communication hole 1
It is discharged to the outside through 42.

On the other hand, when the motor is rotating at high speed, the oil 166 is held in the state shown in FIG. That is, the centrifugal force generated by the high speed rotation of the sleeve member 126 causes the oil 1 of the thrust dynamic pressure fluid bearing means 154a, 154b to change.
66a, 166b and oil 166 in the annular space 164.
oil 166c in the annular space 164 is held in a state of being adhered to the inner peripheral surface of the portion 126a of the sleeve member 126, and the thrust dynamic pressure fluid bearing means 154a, 154b on the upper and lower surfaces of the thrust plate 123. Oils 166a and 166b tend to flow radially outward. Therefore, as shown in FIG. 5, the oil 166a, 166b of the thrust hydrodynamic bearing means 154a, 154b is
Flows radially outward and flows to a layer of oil 166c held on the inner peripheral surface of the sleeve member 126, and the oil 166a of the thrust hydrodynamic bearing means 154a on the upper surface side.
And the oil 166b of the thrust hydrodynamic bearing means 154b on the lower surface side is the oil 1 on the inner peripheral surface of the sleeve member 126.
It becomes a continuous state through 66c. In this example,
Since the inner peripheral surface of the portion 126a is arcuate, the centrifugal force component exerted on the layer of the continuous oil 166 described above is more efficient than the oil of the first embodiment.
will hold b. In such a continuous state,
The oil 166c held by the sleeve member 126 rotates at a high speed integrally with the oil 166c, so that a relatively large centrifugal force acts. On the other hand, the centrifugal force acting on the oil 166a, 166b of the thrust dynamic pressure bearing means 154a, 154b on the upper and lower surfaces is supported by the arc-shaped inner peripheral surface of the sleeve member 126, and the oil 166c adhered to the inner peripheral surface. Thrust dynamic pressure fluid bearing means 15 that balances the centrifugal force acting
The flow of oil 4a, 154b in the radial direction of oil 166a, 166b is suppressed, and oil shortage during high speed rotation is prevented. Further, even at such a high speed rotation, the oil 166 sticks to the arcuate inner peripheral surface of the sleeve member 126, so that the one end opening of the communication hole 142 has a radius of the layer of the oil 166 in the annular space 164 as shown in FIG. It communicates with the air chamber that is generated inward in the direction, the communication state between the air chamber and the motor is maintained, and the above-mentioned inconvenience due to temperature change is eliminated. As described above, the same effect as the first specific example can be achieved in the second specific example.

Although the specific example of the motor of the present invention has been described, the present invention is not limited to the specific example.
Various changes and modifications can be made without departing from the scope of the present invention.

For example, in the illustrated specific example, two communication holes are provided in the thrust plate, but the present invention is not limited to this.
For example, one communication hole or three or more communication holes may be provided.

[0024]

In the motor of the present invention, the surplus oil 66, 166 is contained in a part of the annular spaces 64, 164 defined between the outer peripheral surfaces of the thrust plates 23, 123 and the inner peripheral surface of the shaft holding member. To be done. Therefore, the annular space 6
4, 164 acts as a reservoir for the excess oil 66, 166, and the rest of the annular spaces 64, 164 acts as an air chamber, which is communicated with the atmosphere through the communication holes 42, 142, When the air in the air chamber expands due to the change, this air is discharged to the atmosphere through the communication holes 42 and 142. Further, when the motor rotates at high speed, the oil 6 adhered to the inner peripheral surface of the shaft holding member by centrifugal force
Thrust plates 23, 123 through 6c, 166c
Thrust dynamic fluid bearing means 54a, 54 on the upper and lower surfaces
b, 154a, 154b oil 66a, 66b, 16
6a and 166b are in a continuous state. Therefore, the oil 66c, 166 held on the inner peripheral surface of the shaft holding member is
The centrifugal force acting on c and the thrust dynamic pressure fluid bearing means 54
a, 54b, 154a, 154b oil 66a, 66
b, 166a, 166b and centrifugal force components are balanced, and thrust hydrodynamic bearing means 54a, 54b, 1
54a, 154b oil 66a, 66b, 166a,
166b is prevented from flowing radially outward by centrifugal force, and thrust dynamic pressure fluid bearing means 54a, 54
The oil shortage in b, 154a, 154b is prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing a first embodiment of a motor of the present invention.

FIG. 2 is an enlarged partial sectional view showing a thrust plate of the motor of FIG. 1 and its vicinity.

3 is an enlarged partial sectional view corresponding to FIG. 2, showing a state of oil when the motor of FIG. 1 is rotated at a high speed.

FIG. 4 is an enlarged partial sectional view showing a thrust plate and its vicinity in a second embodiment of a motor of the present invention.

5 is an enlarged partial sectional view corresponding to FIG. 4, showing a state of oil when the motor of FIG. 4 is rotated at a high speed.

FIG. 6 is a sectional view showing an example of a known motor.

[Explanation of symbols]

21 shaft 23,123 thrust plate 25 cover plate 26,126 sleeve member 27 radial dynamic pressure fluid bearing means 32,37 taper portion 42,142 communication hole 54a, 54b, 154a, 154b thrust dynamic pressure fluid bearing means 64,164 annular space 66, 66a, 66b, 66c, 166, 166a, 1
66b, 166c oil

Claims (5)

[Claims] 1. A thrust member provided with a shaft, a shaft holding member for holding the shaft as a bearing, and a thrust plate provided on the shaft, the thrust member being provided between an upper surface and a lower surface of the thrust plate and the shaft holding member. In a motor in which dynamic pressure fluid bearing means are respectively interposed, and radial dynamic pressure fluid bearing means is interposed between the shaft and the shaft holding member, the thrust plate is composed of a disk-shaped member, and the shaft holding member The inner peripheral surface of the disk-shaped member facing the outer peripheral surface is cylindrical, and an annular space is defined between the outer peripheral surface of the disk-shaped member and the inner peripheral surface of the shaft holding member. Excess oil is stored in a part of the annular space, the cylindrical member is provided with a communication hole for communicating the annular space with the atmosphere, and when the motor is not rotating, The oil in the annular space collects in the lower part thereof, and the space in the annular space above the oil communicates with the atmosphere through the communication hole, and when the motor is rotating at high speed, the annular space The oil in the space is held along the inner peripheral surface of the shaft holding member, and the thrust dynamic pressure fluid bearing on the upper surface side of the thrust plate is passed through the oil held along the inner peripheral surface. The oil of the means and the oil of the thrust hydrodynamic bearing means on the lower surface side of the thrust plate are in a continuous state, and the inside of the oil retained on the inner peripheral surface in the annular space The space created in the above is communicated with the atmosphere through the communication hole. 2. The inner peripheral surface of the shaft holding member extends substantially linearly in the axial direction, and the distance between the inner peripheral surface of the shaft holding member and the outer peripheral surface of the disk-shaped member is the axis line. The motor of claim 1, wherein the motor is substantially constant in direction. 3. The inner peripheral surface of the shaft holding member extends in an arc shape so that a central portion in the axial direction is most distant from the outer peripheral surface of the disc-shaped member, and the inner peripheral surface of the shaft holding member is The motor according to claim 1, wherein a distance between the disc-shaped member and the outer peripheral surface is smallest at both end portions of the disc-shaped member and largest at a central portion in the axial direction of the disc-shaped member. 4. The motor according to claim 1, wherein an excessive amount of the oil is contained in a substantially half portion of the annular space. 5. The motor according to claim 1, wherein one end of the communication hole is opened at an axially central portion of the outer peripheral surface of the disc-shaped member.