JP2003180066A - Spindle motor and disc driver employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spindle motor which can eliminate the negative pressure and the overlevitation of a rotor and can reduce a cost, and to provide a disc driver employing the spindle motor. <P>SOLUTION: A radial dynamic pressure bearing has a herringbone groove composed of an inner circumferential surface of a sleeve and an outer circumferential surface of an outer cylinder attached to a shaft. A thrust bearing has a dynamic pressure generating groove which is composed of the upper end surface of the sleeve and the bottom surface of a ceiling plate and applies pressure radially inward to oil when a rotor rotates. A bearing, having pressure practically balancing with the dynamic pressure generated by the radial bearing and/or the thrust bearing, is provided between an inner surface of a closing member and the end surface of the shaft. An oil linking hole through which the oil can be circulated is formed between the outer circumferential surface of the shaft and the inner circumferential surface of the outer cylinder. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor having a dynamic pressure bearing and a disk drive device using this spindle motor.

[0002]

2. Description of the Related Art Conventionally, as a bearing of a spindle motor used in a disk drive device for driving a recording disk such as a hard disk, a shaft and a sleeve are interposed between the shaft and the sleeve in order to rotatably support them. Various dynamic pressure bearings that utilize the fluid pressure of a lubricating fluid such as oil have been proposed.

An example of a spindle motor using such a dynamic pressure bearing is shown in FIG. A spindle motor using this conventional fluid dynamic pressure bearing has a pair of outer peripheral surface of a shaft b integral with a rotor a and an inner peripheral surface of a sleeve c through which the shaft b is rotatably inserted. The radial bearing portions d, d are separated from each other in the axial direction, and the stepped portion formed on the upper surface of the disk-shaped thrust plate e protruding radially outward from the outer peripheral surface of one end of the shaft a and the sleeve b. A pair of thrust bearing parts g are formed between the flat surface of the thrust plate e and the lower surface of the thrust plate e and the thrust bush f that closes one opening of the sleeve b.

A series of minute gaps are formed between the shaft b and the thrust plate e, the sleeve c and the thrust bush d, and oil is continuously retained in these minute gaps as a lubricating fluid without interruption. (This oil holding structure is hereinafter referred to as “full-fill structure”), and a dynamic pressure is induced in the oil in the radial bearings d, d and the thrust bearings g, g when the rotor a rotates. Herringbone grooves d1 and d1 and g1 and g1 for forming the respective herringbone grooves are formed.

Herringbone grooves d1, d1 and g1, g formed by connecting a pair of spiral grooves to the radial bearings d, d and the thrust bearings g, g.
1 is formed, and in response to the rotation of the rotor a, the maximum dynamic pressure is generated in the central portion of the bearing portion where the connecting portion of the spiral groove is located, and the load acting on the rotor a is supported.

[0006]

In such a spindle motor, a taper seal portion h is formed in the vicinity of the upper end portion of the sleeve c which is axially opposite to the thrust bearing portions g, g, and the The surface tension and the atmospheric pressure are balanced to form an interface. That is, the internal pressure of the oil in the taper seal portion h is maintained at a pressure substantially equal to the atmospheric pressure.

Now, when the rotor a starts to rotate, the oil is pumped by the dynamic pressure generating grooves d1, d1 and g1, g1, and the radial bearing portions d, d and thrust bearing portions g,
While the fluid dynamic pressure is maximized at the center of the bearing, the internal pressure of oil decreases at the end of the bearing. On the other hand, at the end portion of the radial bearing portion adjacent to the taper seal portion h, the interface moves in the taper seal portion h according to the fluctuation of the oil internal pressure, and the atmospheric pressure and the oil internal pressure are antagonized. However, the oil and thrust retained between the pair of radial bearing parts d, d in the region between the bearing parts, that is, in the region between the outer peripheral surface of the shaft b and the inner peripheral surface of the sleeve c. In the area around the plate e, the oil retained near the outer peripheral portion of the thrust plate located between the thrust bearing portions g, g is the oil retained in accordance with the pumping of the dynamic pressure generating grooves d1, d1 and g1, g1. The internal pressure decreases, and eventually decreases to below atmospheric pressure to become negative pressure.

In the case of a dynamic bearing having a full-fill structure,
Negative pressure may be generated in the oil regardless of the shape of the dynamic pressure generating groove formed in the bearing portion.

This is because the machining of the inner peripheral surface of the sleeve or the outer peripheral surface of the shaft becomes uneven between the upper end portion and the lower end portion in the axial direction, and a minute gap formed between the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft. The radial dimension of the gap is formed such that the upper end side in the axial direction is wider than the lower end side, so that the fluid dynamic pressure generated by the herringbone groove formed in the radial dynamic pressure bearing portion is from the lower end side in the axial direction. Occurs when the pumping force exceeds the pumping force from the upper end side, the pressure gradient becomes unbalanced toward the upper end side in the axial direction, and the oil is induced to flow toward the upper end side in the axial direction.

On the contrary, when the size of the minute gap formed between the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft in the radial direction is wider on the lower end side in the axial direction than on the upper end side. , Inducing a flow of oil toward the lower end in the axial direction of the oil, the internal pressure of the oil held between the lower surface of the thrust plate and the thrust bush increases more than necessary, and the rotor floats above a certain amount. Occurs.

When a negative pressure is generated in the oil, the air dissolved in the oil appears as bubbles when the oil is filled, and the bubbles eventually expand in volume due to temperature rise.
A problem that affects the durability and reliability of the spindle motor, such as oil leaking out of the bearing, or the occurrence of vibration or NRRO due to the contact of dynamic pressure generation grooves with air bubbles.
A problem that affects the rotation accuracy of the spindle motor, such as deterioration of (non-repetitive shake component), occurs.

Further, when the rotor is excessively floated, wear occurs due to contact between the thrust plate and the sleeve,
This will cause deterioration of the durability and reliability of the bearing. In addition, in the case of a spindle motor for driving a hard disk,
Since the recording surface of the hard disk and the magnetic head are arranged very close to each other as the capacity of the hard disk increases, there is a concern that the contact between the hard disk and the magnetic head may cause destruction.

The problem of excessive floating may occur in addition to uneven machining of the inner peripheral surface of the sleeve or the outer peripheral surface of the shaft.

In the case of a thin spindle motor such as the conventional spindle motor shown in FIG. 1, a clamper is fixed to the upper end of the shaft b in order to securely hold a recording disk such as a hard disk on the outer peripheral surface of the rotor a. The female screw hole i provided for fixing may be formed to a depth reaching the inner peripheral side of the radial bearing parts d. In such a case, when a male screw (not shown) is fastened in the female screw hole i,
Due to the fastening stress, the outer peripheral surface of the shaft b bulges outward in the radial direction, and the radial clearance dimension of the minute gap formed between the inner peripheral surface of the sleeve c and the outer peripheral surface of the shaft b is
The upper end side in the axial direction becomes narrower than the lower end side, and the pressure gradient of the fluid dynamic pressure generated in the radial dynamic pressure bearing portions d, d becomes unbalanced in the lower end side in the axial direction, resulting in excessive levitation of the rotor a.

According to the present invention, while maintaining a simple structure and desired bearing rigidity, negative pressure or excessive floating of the rotor can be prevented from occurring, and the cost can be reduced, and a spindle motor and a disk drive using this spindle motor. The purpose is to provide a device.

[0016]

A spindle motor according to the present invention is a circle in which a shaft, a sleeve having a through hole into which the shaft is rotatably inserted are formed, and the shaft is integrally provided on a rotation axis. A spindle motor comprising: a rotor having a top plate and a cylindrical wall hanging from an outer peripheral edge of the top plate; and a closing member for closing one end of a through hole formed in the sleeve. A cylindrical outer cylinder member is mounted on the outer peripheral surface of the shaft, and the upper end surface of the sleeve and the bottom surface of the top plate of the rotor, the inner peripheral surface of the sleeve and the outer peripheral surface of the outer cylinder member, and the blockage. A continuous minute gap is formed between the inner surface of the member and the end surface of the shaft and the outer cylinder member, and oil is continuously retained throughout the minute gap without interruption. Three At least one of the inner peripheral surface and the outer peripheral surface of the outer cylindrical member constitutes a radial dynamic pressure bearing portion in which a herringbone groove formed by connecting a pair of spiral grooves is provided as a dynamic pressure generation groove. At least one of the upper end surface of the sleeve and the bottom surface of the top plate is provided with a dynamic pressure generating groove for applying a pressure inward in the radial direction to the oil when the rotor is rotated. And a bearing portion having a pressure substantially balanced with the dynamic pressure generated in the radial bearing portion and / or the thrust bearing portion is formed between the inner surface of the closing member and the end surface of the shaft. Is
The rotor is floated by the cooperation of the thrust bearing portion and the bearing portion, and the upper end surface of the sleeve and the ceiling of the rotor are provided between the outer peripheral surface of the shaft and the inner peripheral surface of the outer tubular member. The oil retained in the minute gap formed between the bottom surface of the plate and the inner surface of the closing member and the end surface of the shaft and the outer cylinder member is communicatably communicated. A communication hole is formed (Claim 1).

With this configuration, in a spindle motor using a dynamic pressure bearing having a full-fill structure, it is possible to balance the pressure of the oil held in the bearing portion and prevent negative pressure and excessive levitation from occurring. Is.

In the above-described structure, the rotor has a radial bearing portion and a thrust bearing portion that apply a dynamic pressure to the oil during rotation, and the dynamic pressure generated in the radial bearing portion and the thrust bearing portion is propagated to the oil. With a bearing portion such as a so-called static pressure bearing (hereinafter, such bearing will be referred to as "static pressure bearing portion") whose pressure is increased, the sleeve and the closing member are supported in a non-contact manner.

At this time, the thrust bearing portion located at the axially upper and lower end portions of the minute gap formed between the inner peripheral surface of the sleeve and the outer peripheral surface of the outer tubular member and the oil retained in the hydrostatic bearing portion. By forming a communication passage for communicating with the outer peripheral surface of the shaft and the inner peripheral surface of the outer tubular member,
Even if there is an imbalance in the pressure of the oil held in the bearing due to the processing tolerance of the bearing components or stress deformation due to assembly, etc., the oil can flow from the high pressure region to the low pressure region side through the communication passage. , Problems caused by negative pressure in oil and excessive floating of the rotor are solved.

In the spindle motor of the present invention, a single spiral groove is formed on the outer peripheral surface of the shaft from the upper end portion to the lower end portion thereof, and the outer cylinder member is mounted on the outer peripheral surface of the shaft. By so doing, the communication hole is defined between the spiral groove and the inner peripheral surface of the outer cylinder member (claim 2).

By forming a spiral groove forming a communication hole with the inner peripheral surface of the outer tubular member on the outer peripheral surface of the shaft, the outer peripheral surface of the shaft and the spiral groove can be formed by one chucking. And can be easily processed. The cross-sectional shape of the spiral groove is preferably substantially rectangular, triangular or semicircular.

In the above spindle motor of the present invention,
The radial bearing portions are formed in a pair so as to be separated from each other in the axial direction, and the herringbone grooves formed in the pair of radial bearing portions are fluids having a pressure gradient that becomes symmetrical in the axial direction when the rotor rotates. It is characterized in that it is formed by connecting spiral grooves of substantially the same shape so as to induce dynamic pressure in the oil (claim 3).

By forming a pair of radial bearing portions separated from each other in the axial direction and forming each dynamic pressure generating groove as a herringbone groove having a symmetrical shape in the axial direction, each of the dynamic pressure generating grooves is formed in a limited axial direction dimension. It is necessary to secure the maximum distance between the spiral groove joints (the distance between the spiral groove joints in this radial bearing is referred to as "bearing span" below) that maximizes the dynamic pressure in the radial bearing. This makes it possible to maintain high bearing rigidity even with a thin motor, so that whirling such as precession of the rotor during rotation is effectively suppressed.

The shape of the dynamic pressure generating groove of the radial bearing portion of the spindle motor of the present invention is not limited to the above.
Of the pair of radial bearing portions, the herringbone groove formed in the radial bearing portion located on the side closer to the thrust bearing portion is provided to the inner surface of the closing member and the shaft with respect to the oil when the rotor rotates. A radial bearing portion formed by connecting spiral grooves having an asymmetrical shape in the axial direction so as to apply pressure toward the bearing portion formed between the end surface and the thrust bearing portion. The herringbone groove formed in the above is connected to a spiral groove having substantially the same shape so that a fluid dynamic pressure having a pressure gradient symmetrical in the axial direction is applied to the oil when the rotor rotates. (Claim 4), or the herringbone grooves formed in the pair of radial bearing portions are respectively rotated by the rotor. A spiral groove having an asymmetrical shape in the axial direction is continuously formed so as to apply a pressure to the oil toward the bearing portion formed between the inner surface of the closing member and the end surface of the shaft. Item 5),
Alternatively, among the pair of radial bearing portions, the herringbone groove formed in the radial bearing portion located on the side closer to the thrust bearing portion is an inner surface of the closing member with respect to the oil when the rotor rotates. A radial groove, which is formed between the end surface of the shaft and formed in such a manner that a spiral groove having an asymmetrical shape in the axial direction is connected so as to apply a pressure toward the bearing portion side, and which is located on the side away from the thrust bearing portion The herringbone groove formed in the bearing portion is formed by connecting spiral grooves that are asymmetric in the axial direction so that pressure is applied to the oil toward the thrust bearing portion when the rotor rotates. (Claim 6), or, of the pair of radial bearing portions, the radial portion located on the side closer to the thrust bearing portion. The herringbone groove formed in the bearing portion is connected to a spiral groove having substantially the same shape so that a fluid dynamic pressure having a pressure gradient symmetrical in the axial direction is applied to the oil when the rotor rotates. The herringbone groove formed in the radial bearing portion located on the side separated from the thrust bearing portion is formed on the inner surface of the closing member and the end surface of the shaft with respect to the oil when the rotor rotates. It is possible to form spiral grooves that are asymmetric in the axial direction so as to be connected to each other so as to apply pressure toward the bearing portion formed between them (claim 7).

Regarding the difference in action and effect due to the difference in the shape of the herringbone groove of these radial bearings,
It will be described in detail in the description of the embodiments of the invention.

Further, in the spindle motor of the present invention, the outer peripheral surface of the sleeve and the inner peripheral surface of the cylindrical wall of the rotor are opposed to each other with a gap in the radial direction, and the outer peripheral surface of the sleeve is A taper surface is provided so that the outer diameter is reduced with increasing distance from the top plate of the rotor, and the oil is held by forming a meniscus between the taper surface and the inner peripheral surface of the cylindrical wall. It is characterized in that (claim 8).

Compared with the conventional structure in which the end of the oil held in each bearing is exposed to the outside air, in the dynamic pressure bearing of the full-fill structure, the oil is held in the entire bearing, so the oil holding amount is much higher. Is increasing. Therefore, when the oil thermally expands due to the temperature rise, a large amount of oil that cannot be accommodated in the bearing portion flows into the seal portion. Therefore, in the dynamic bearing having the full-fill structure, the structure of the seal portion is also an important matter.

As in the above structure, a tapered gap is formed between the outer peripheral surface of the sleeve and the inner peripheral surface of the cylindrical wall of the rotor to form a taper seal portion utilizing surface tension. It is possible to make the diameter larger than that, and also to make the axial dimension of the seal portion relatively large.
The volume inside the seal portion increases, and even a small and thin spindle motor can sufficiently follow the thermal expansion of oil that is retained in large quantity in the dynamic pressure bearing of full-fill structure.

In addition, in the spindle motor of the present invention, the sleeve is provided with a step portion which is continuous with the tapered surface and whose outer peripheral surface is recessed inward in the radial direction. An annular member that protrudes inward in the radial direction corresponding to the step portion is fixed to the circumferential surface, and the step portion and the annular member are engaged with each other to prevent the rotor from coming off. And between the upper surface of the annular member and the lower surface of the stepped portion of the sleeve, the minimum radial gap formed between the tapered surface of the sleeve and the inner peripheral surface of the cylindrical wall of the rotor. A minute gap smaller than the gap size is formed and functions as a labyrinth seal (claim 9).

In this structure, the structure for preventing the rotor from coming off is formed outside the bearing and at a position aligned with the radial radial dynamic pressure bearing portion in the radial direction. By arranging the labyrinth seal continuously with the taper seal portion, the oil is more effectively prevented from flowing out of the bearing due to the oil mist.

Furthermore, the spindle motor of the present invention comprises:
The rotor is urged by a magnetic force acting in the axial direction toward the closing member side (claim 10).

By magnetically urging the rotor in the direction opposite to the closed end side, that is, the levitation force generated by the thrust bearing portion and the hydrostatic bearing portion in the axial direction, the posture of the rotor during rotation is further increased. Stabilize.

Further, the disk drive device of the present invention is a disk drive device in which a disk-shaped recording medium capable of recording information is mounted, and a housing and a spindle motor fixed inside the housing for rotating the recording medium. A disk drive device having an information access unit for writing or reading information at a required position on the recording medium, wherein the spindle motor is the spindle motor according to any one of claims 1 to 10. It is characterized by (claim 11).

Since the spindle motor of the present invention can be made compact and thin, it can be suitably used in a disk drive device for driving a hard disk having an outer diameter of 1 inch, but the present invention is not limited to this. The present invention can be similarly used in a disk drive device that drives a fixed recording medium such as a hard disk or a detachable recording medium such as a CD-ROM or a DVD.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a spindle motor according to the present invention and a disk drive device using the spindle motor will be described below with reference to FIGS. 2 to 8. It is not limited to.

(1) Configuration of Spindle Motor In FIG. 2, this spindle motor has a substantially disk-shaped upper wall portion 2a (top plate) and a cylindrical shape that hangs downward from the outer peripheral edge portion of this upper wall portion 2a. A rotor hub 2 including a peripheral wall portion 2b (cylindrical wall), a rotor 6 including a shaft 4 integrally formed in a central portion of an upper wall portion 2a of the rotor hub 2, and an outer peripheral surface of the shaft 4. And a cylindrical outer cylinder member 5 mounted on the
A hollow cylindrical sleeve 8 for rotatably supporting the sleeve 8, a seal cap 10 (closing member) that closes the lower portion of the sleeve 8 and faces the free end side end surface of the shaft 4, and a cylinder into which the sleeve 8 is fitted. The bracket 12 integrally formed with the portion 12a.

The bracket 12 has a substantially bowl-like shape centered on the cylindrical portion 12a, and a plurality of radially inwardly projecting inner peripheral surfaces 12b of the bowl-shaped peripheral wall. A stator 14 having teeth is arranged, and a rotor magnet 16 is fixed to the outer peripheral surface of the peripheral wall portion 2b of the rotor hub 2 so as to face the stator 14 from the radially inner side with a gap.

On the outer peripheral portion of the peripheral wall portion 2b of the rotor hub 2,
A flange-shaped disc mounting portion 2c for mounting a disc plate (illustrated as a disc plate 53 in FIG. 8) on which information is recorded is formed. A female screw hole 4b is formed on the upper side of the shaft 4 (on the side of the upper wall 2a of the rotor hub 2), and the disc plate is placed on the disc mounting portion 2
The disk plate is fixedly held on the rotor hub 2 by placing it on the disk c and holding it by a clamper (not shown) and then fastening a male screw (not shown) in the female screw hole 4b.

Between the upper end surface of the sleeve 8 and the lower surface of the upper wall portion 2a of the rotor hub 2, between the outer peripheral surface of the outer tubular member 5 following the upper wall portion 2a of the rotor hub 2 and the inner peripheral surface of the sleeve 8, and this. A series of minute gaps are formed between the outer cylinder member 5 and the end surface of the shaft 4 and the inner surface of the seal cap 10, and oil is continuously retained in the minute gaps without interruption. And constitutes a so-called full-fill dynamic bearing. The structure of the bearing and the shaft supporting method in this embodiment will be described in detail later.

Further, between the outer peripheral surface of the shaft 4 and the inner peripheral surface of the outer tubular member 5, as described later in detail, between the upper end surface of the sleeve 8 and the lower surface of the upper wall portion 2a of the rotor hub 2. A communication hole 7 is formed for communicating the retained oil and the retained oil between the outer cylinder member 5 and the end surface of the shaft 4 and the inner surface of the seal cap 10.

An annular flange portion 8a is formed on the upper end of the outer peripheral surface of the sleeve 8 so as to project outward in the radial direction and is formed in an inclined surface shape so that the outer peripheral surface is reduced in diameter as it is separated from the upper end surface of the sleeve 8. Is provided, and the peripheral wall portion 2 of the rotor hub 2 is provided.
It is radially opposed to the inner peripheral surface of a in a non-contact state.

The inner peripheral surface of the peripheral wall portion 2b and the flange portion 8a
The radial dimension of the gap defined between the outer peripheral surface of the flange portion 8a and the outer peripheral surface of the flange portion 8a is formed axially downward (in the direction of the tip of the peripheral wall portion 2b) by forming the inclined surface shape as described above. ) Gradually tapering toward. That is, the inner peripheral surface of the peripheral wall portion 2b and the outer peripheral surface of the flange portion 8a cooperate with each other to form the taper seal portion 18. Between the upper end surface of the sleeve 8 and the lower surface of the upper wall portion 2a of the rotor hub 2, between the outer peripheral surface of the shaft 4 following the upper wall portion 2a of the rotor hub 2 and the inner peripheral surface of the sleeve 8, and the shaft 4 continuous with this. The oil retained in the series of minute gaps formed between the end surface of the oil seal and the inner surface of the seal cap 10 balances the surface tension of the oil and the atmospheric pressure only in the taper seal portion 18, and Is formed in a meniscus shape.

The taper seal portion 18 functions as an oil reservoir, and the position where the interface is formed can be appropriately moved according to the amount of oil held in the taper seal portion 18. Therefore, the oil retained in the taper seal portion 18 is supplied to the bearing portion as the oil retention amount decreases, and
The oil whose volume has increased due to thermal expansion or the like is contained in the taper seal portion 18.

Thus, the flange portion 8a of the sleeve 8 is
By forming a tapered gap between the outer peripheral surface of the inner peripheral surface of the rotor hub 2 and the inner peripheral surface of the peripheral wall portion 2b of the rotor hub 2 to form the taper seal portion 18 utilizing surface tension, the taper seal portion 18 has a larger diameter than the bearing portion. In addition, the axial dimension of the taper seal portion 18 can be made relatively large. Therefore, the volume in the taper seal portion 18 increases, and it becomes possible to sufficiently follow the thermal expansion of the oil that is retained in large quantity in the dynamic pressure bearing of the full-fill structure.

An annular retaining ring 2 is attached to the tip of the peripheral wall portion 2b with respect to the taper seal portion 18 by means of bonding or the like.
0 (annular member) is fixed. This retaining ring 2
In No. 0, the lower end portion of the outer peripheral surface of the sleeve 8 is fitted in the lower portion of the flange portion 8a in a non-contact state to form a retaining structure for the rotor 6 with respect to the sleeve 8. As described above, by forming the retaining structure for the rotor 6 on the outer peripheral surface side of the sleeve 8, the pair of radial bearing portions and the retaining structure, which will be described later in detail, are arranged in line on the same line in the axial direction. Absent. Therefore, shaft 4
It becomes possible to effectively utilize the entire length of the
The motor can be made thinner while maintaining the bearing rigidity.

The upper surface of the retaining ring 20 has a flange portion 8
The lower surface of a is continuous with the taper seal portion 18 and is opposed to the taper seal portion 18 via an axial gap having a smaller gap size than the minimum radial gap of the taper seal portion 18.

The upper surface of the retaining ring 20 and the flange portion 8a
By setting the gap size of the minute gap in the axial direction defined between the lower face of the spindle motor and the lower surface of the spindle motor as small as possible, the air flow velocity in the minute gap in the axial direction and the taper seal portion 18 are regulated when the spindle motor rotates. The difference between the flow velocity of air in the radial gap and the flow velocity of air becomes large, and the resistance to the outflow of steam generated by the evaporation of oil to the outside is increased to keep the steam pressure near the boundary surface of the oil high. It functions as a labyrinth seal to prevent oil evaporation.

By arranging the labyrinth seal continuously with the taper seal portion 18 as described above, not only the outflow of oil as a liquid is prevented but also the oil is vaporized due to an increase in the external environment temperature of the motor. It is possible to prevent the oil mist that is generated thereby from flowing out of the motor. Therefore, it is possible to prevent deterioration of the oil retention amount and maintain stable bearing performance for a long period of time.
The bearing can have high durability and reliability.

(2) Structure of Bearing Unit Next, the structure of the bearing unit in this embodiment will be described with reference to FIGS. 3 and 4 in addition to FIG.

As shown in FIG. 3, on the inner peripheral surface of the sleeve 8, on the upper end surface side of the sleeve 8, a direction which induces a fluid dynamic pressure in the oil when the rotor 6 rotates and is opposite to the rotating direction. A pair of spiral grooves 22a1, which are inclined to
A herringbone groove 22a having a substantially V shape, which is formed by connecting 22a2, is formed.
An upper radial dynamic pressure bearing portion 22 is formed between the upper radial dynamic pressure bearing portion 22 and the outer peripheral surface.

Further, on the inner peripheral surface of the sleeve 8, on the free end side of the shaft 4, there are provided a pair of slanting members which induce a fluid dynamic pressure in the oil when the rotor 6 rotates and which are inclined in directions opposite to the rotational direction. A herringbone groove 24a having a substantially V shape formed by connecting spiral grooves 24a1 and 24a2 is formed, and a lower radial dynamic pressure bearing portion 24 is configured between the outer circumferential surface of the outer cylinder member 5 and the herringbone groove 24a. To be done.

The upper and lower radial dynamic pressure bearing portions 2
Herringbone grooves 22a formed in 2, 24,
24a is each spiral groove 22a1, 22a2,
In order that 24a1 and 24a2 generate substantially the same pumping force, the groove dimensions such as the axial dimension, the inclination angle with respect to the rotation direction, the groove width and the depth are set to be the same, that is, each spiral groove is formed. 22a1,
22a2, 24a1 and 24a2 are set to be line-symmetric with respect to the connecting portion. Therefore, in the upper and lower radial dynamic pressure bearing portions 22 and 24, the axial center portion of each bearing portion (each spiral groove 22a1, 22a2, 24) is formed.
The maximum dynamic pressure appears at the connection part of a1 and 24a2),
The pumping by the spiral grooves 22a1, 22a2, 24a1 and 24a2 becomes unbalanced with respect to either direction of the axial line, so that the oil does not flow in the axial direction.

As described above, by making the herringbone grooves 22a, 24a of the upper and lower radial bearing portions 22, 24 symmetrical in the axial direction, even if the dimensions are limited in the axial direction due to thinning. Since it is possible to set the bearing span between the upper and lower radial bearing portions 22 and 24 to be relatively large, it is possible to maintain high bearing rigidity and to cause whirling of the rotor 6 such as precession. Can be effectively suppressed.

Further, as shown in FIG. 4, the sleeve 8
A pump-in spiral groove 26a is formed on the upper end face of the pump 6 for inducing pressure toward the oil inward in the radial direction (shaft 4 side) when the rotor 6 rotates,
A thrust bearing portion 26 is formed between the rotor hub 2 and the lower surface of the upper wall portion 2a.

Further, as described later in detail, the internal pressure of the oil increased by the spiral groove 26a of the thrust bearing portion 26 is utilized between the free end side end surface of the shaft 4 and the inner surface of the seal cap 10. The hydrostatic bearing portion 28 is configured.

(3) Shaft Supporting Method The shaft supporting method by the bearings constructed as described above will be described in detail with reference to FIG. Incidentally, FIG. 5 shows the sleeve 8
Between the upper end surface of the rotor hub 2 and the lower surface of the upper wall portion 2a of the rotor hub 2, between the outer peripheral surface of the outer cylindrical member 5 following the upper wall portion 2a of the rotor hub 2 and the inner peripheral surface of the sleeve 8, and an outer cylinder continuous with this. Member 5
Also, the relative relationship of the pressure distribution of the oil held in the minute gap formed between the end surface of the shaft 4 and the inner surface of the seal cap 10 is developed for each bearing portion and is shown schematically. Although it is a distribution diagram, since the pressure distribution of the spindle motor is axisymmetric, the pressure distribution in the region on the opposite side in the vertical cross section of the spindle motor with respect to the rotation axis indicated by the alternate long and short dash line in FIG. 5 is omitted. There is. The numbers shown in FIG. 5 are the same as the numbers given to the bearings in FIG.

Upper and lower radial dynamic pressure bearings 22, 24
Then, as the rotor 6 rotates, the pumping force by the herringbone grooves 22a and 24a increases, and fluid dynamic pressure is generated. Upper and lower radial dynamic pressure bearing portions 22,
As shown in FIG. 5, the pressure distribution at 24 sharply increases from both ends of the herringbone grooves 22a and 24a, and reaches a maximum at the connecting portion of each spiral groove. Using the fluid dynamic pressure generated in the upper and lower radial dynamic pressure bearing portions 22 and 24, the rotor 6 is axially supported from above and below in the axial direction of the outer cylinder member 5, and the centering action of the rotor 6 and the restoring action against tilting thereof. Is responsible for

In the thrust bearing portion 26, as the rotor 6 rotates, the spiral groove 26a of the pump-in induces a radially inward pressure on the oil. The pressure inward in the radial direction promotes the flow of oil to increase the internal pressure of the oil, and the fluid dynamic pressure acting in the floating direction of the rotor 6 is generated. As shown in FIG. 5, the fluid dynamic pressure induced in the thrust bearing portion 26 does not rise sharply as in the upper and lower radial dynamic pressure bearing portions 22 and 24, and the atmospheric pressure is slightly higher than the maximum atmospheric pressure. It exceeds the level.

Due to the pressure generated in the thrust bearing portion 26, the outer cylinder member 5 and the shaft between the outer peripheral surface of the outer cylindrical member 5 and the inner peripheral surface of the sleeve 8 following the upper wall portion 2a of the rotor hub 2 and the continuous outer cylindrical member 5 and the shaft. The oil retained between the end surface of the No. 4 and the inner surface of the seal cap 10 is in a substantially sealed state in terms of pressure, and the herringbone formed in the upper and lower radial dynamic pressure bearing portions 22 and 24. By making the grooves 22a and 24a symmetrical in the axial direction and keeping the generated dynamic pressure in a balanced state in the axial direction, the axial flow of oil is not induced as described above. As a result, the internal pressure of the oil retained between the outer peripheral surface of the outer tubular member 5 and the inner peripheral surface of the sleeve 8 and between the outer tubular member 5 and the end surface of the shaft 4 and the inner surface of the seal cap 10 which are continuous with the outer peripheral surface of the sleeve 8. Balances with the internal pressure of the oil held in the thrust bearing portion. Therefore, as shown in FIG. 5, the internal pressure of the oil held in the thrust bearing portion 26 becomes equal to the internal pressure in any region, and a negative pressure is generated in the oil held in these minute gaps so that the internal pressure becomes equal to or lower than the atmospheric pressure. There is no such thing. Therefore, the problem of bubbles caused by the negative pressure is solved.

As described above, the pressure generated in the thrust bearing portion 26 is slightly higher than the atmospheric pressure, and it is difficult to sufficiently float the rotor 6 only with this pressure. However, as described above, the internal pressure of the oil held in the hydrostatic bearing portion 28 formed between the outer cylinder member 5 and the end surface of the shaft 4 and the inner surface of the seal cap 10 is also a fluid induced in the thrust bearing portion 26. Since the pressure becomes equivalent to the internal pressure of the oil increased by the dynamic pressure, the rotor 6 can be sufficiently levitated by the cooperation of the thrust bearing portion 26 and the static pressure bearing portion 28.

As shown in FIG. 2, an annular thrust yoke 30 made of a ferromagnetic material is arranged at a position facing the rotor magnet 16 of the bracket 12, and between the rotor magnet 16 and the thrust yoke 30. By generating a magnetic attraction force in the axial direction, the thrust bearing portion 2
6 and the floating pressure of the rotor 6 generated in the static pressure bearing portion 28 are balanced to stabilize the support in the thrust direction of the rotor 6 and suppress the occurrence of over-levitation in which the rotor 6 floats more than necessary. Such magnetic biasing of the rotor 6 can also be exerted by, for example, making the magnetic centers of the stator 14 and the rotor magnet 16 different in the axial direction.

(5) Structure and Function of Communication Hole FIG. 6 is an enlarged front view showing the shaft 4. Figure 6
As shown in FIG. 1, the outer peripheral surface of the shaft 4 is provided with a single spiral groove 4a (a part of which is indicated by a broken line) extending from the axially upper end to the lower end.

The spiral groove 4a is formed by cutting so that its cross-sectional shape is substantially rectangular, triangular or semicircular. The cutting of the spiral groove 4a can be performed by chucking once when the outer peripheral surface of the shaft 4 is processed.

When the outer cylinder member 5 is mounted on the outer peripheral surface of the shaft 4 by the spiral groove 4a, the axially upper end of the inner peripheral surface of the outer cylinder member 5 is provided between the outer peripheral member 5 and the inner peripheral surface. A spiral communication hole 7 is defined which is continuous from the portion to the lower end portion, that is, the minute gap formed in the thrust bearing portion 26 and the hydrostatic bearing portion 28. The thrust bearing portion 26 is provided in the communication hole 7.
In addition, the oil is held continuously with the oil held in the hydrostatic bearing portion 28, and the internal pressure of the oil held in the communication hole 7 is almost equal to the internal pressure of the oil in the thrust bearing portion 26. Is.

A male screw is fastened by combining the maximum machining tolerances of the inner peripheral surface of the sleeve 8 or the outer peripheral surface of the outer tubular member 5 or in the female screw hole 4b (see FIG. 2) provided in the shaft 4. Due to the effect of the fastening stress generated when the sleeve 8 is engaged, a minute gap formed between the inner peripheral surface of the sleeve 8 and the outer peripheral surface of the outer tubular member 5 has a gap dimension between the upper end side and the lower end side in the axial direction. If a change occurs in the oil, an abnormal flow will be induced in the oil. As a result, the minute gap formed between the inner peripheral surface of the sleeve 8 and the outer peripheral surface of the outer tubular member 5 is formed on the upper end side and the lower end side in the axial direction, that is, between the thrust bearing portion 26 and the hydrostatic bearing portion 28. There will be a difference in the internal pressure of the oil between them. If the difference in the internal pressure of the oil is left as it is, when the oil flows from the lower end side in the axial direction to the upper end side, a negative pressure is generated in the static pressure bearing portion 28, and the oil is kept in the upper end portion in the axial direction. When the fluid flows from the side to the lower end, the internal pressure of the oil in the hydrostatic bearing portion 28 increases more than necessary, and the rotor 6 is excessively floated.

On the other hand, the minute gaps formed in the thrust bearing portion 26 and the static pressure bearing portion 28 are continuous, and the oil is continuously retained in the thrust bearing portion 26 and the static pressure bearing portion 28. By providing the communication hole 7 to be retained, axial flow is induced in the oil, and the axial upper end of the minute gap formed between the inner peripheral surface of the sleeve 8 and the outer peripheral surface of the outer tubular member 5. Even if there is a difference in the internal pressure of the oil between the lower side and the lower side, the internal pressure of the oil held in each bearing portion is increased because the oil flows from the high internal pressure side to the low internal pressure side through the communication hole 7. It balances and prevents the occurrence of negative pressure and over-levitation.

(5) Modified Example A modified example of the herringbone grooves 22a, 24a formed in the radial bearing portions 22, 24 in the spindle motor of the embodiment shown in FIGS. 2 to 6 is shown in FIG.
Shown in (a) to (d). 7 is a sectional view of the sleeve 8.

(5) -1. Modification 1 In the modification illustrated in FIG. 7A, the herringbone groove 22a ′ formed in the upper radial bearing portion 22 ′ has an axially asymmetric shape, and is formed in the lower radial bearing portion 24. The herringbone groove 24a to be formed has a shape symmetrical in the axial direction as in the case of the embodiment shown in FIGS.

More specifically, the upper radial bearing portion 2
The herringbone groove 22a 'formed in 2'is
The spiral groove 22a′1 located on the upper side (thrust bearing portion 26) of the sleeve 8 is set to have a longer axial dimension than the spiral groove 22a′2 located on the lower radial bearing portion 24 side. Therefore, the connecting portion between the pair of spiral grooves 22a′1 and 22a′2 is located below the center of the upper radial bearing portion 22 ′, that is, on the lower radial bearing portion 24 side. Therefore, pumping of oil by the spiral groove 22a'1 during rotation of the rotor 6 exceeds pumping by the spiral groove 22a'2, and the upper radial bearing portion 22 'serves as a lower side of the sleeve 8 (lower radial portion) with respect to oil. A flow toward the bearing portion 24 side) is induced.

By thus forming the herringbone groove 22a 'of the upper radial bearing portion 22' into an unbalanced shape in the axial direction, the region between the upper radial bearing portion 22 'and the lower radial bearing portion 24 is formed. The pressure is maintained at a positive pressure equal to or higher than the atmospheric pressure, and the generation of negative pressure is prevented. Also, due to the pressing force generated by the herringbone groove 22 a ′, the oil always flows to the lower side of the sleeve 8, and the oil that flows to the lower side of the sleeve 8 passes through the communication passage 7 to the lower side of the sleeve 8. To the upper side,
The upper radial bearing portion 22 'again pushes the sleeve 8 toward the lower side of the sleeve 8 to form a constant oil circulation path.

Thus, the herringbone groove 2
By allowing the oil to always flow in the bearing gap in the predetermined direction by 2 ', the pressure balance of the oil held in each region of the bearing gap is stabilized, and the negative pressure is generated or the rotor 6 is overloaded. The occurrence of floating will be reliably prevented.
Further, even if processing tolerances or stress deformation during assembly occur, the circulation of oil in a certain direction is ensured, and the allowable range for defects caused by processing or assembly is significantly expanded, so the yield is improved.

(5) -2. Modified Example 2 Further, as shown in FIG. 7B, the herringbone groove 24a ′ formed not only in the upper radial bearing portion 22 ′ but also in the lower radial bearing portion 24 ′ has spiral grooves 24a′1 constituting the herringbone groove 24a ′. , 24a′2,
The spiral groove 24a'1 located on the upper radial bearing 22 'side is set to have a longer axial dimension than the spiral groove 24a'2 located on the lower side of the sleeve 8, and the connecting portion is located on the lower side of the sleeve 8. It is also possible to have an axially asymmetrical shape that is configured so as to be positioned so as to be offset.

As described above, not only the upper radial bearing portion 22 'but also the lower radial bearing portion 24' is configured to induce the flow toward the lower side of the sleeve 8 with respect to the oil, whereby the hydrostatic bearing portion in FIG. The pressure of 28 becomes higher, and the levitation force of the rotor 6 is strengthened. Therefore, since it becomes possible to support a higher load, it becomes possible to use it even when rotationally driving a plurality of disc plates. Further, more positive circulation of oil is promoted, and negative pressure and excessive floating of the rotor 6 are effectively prevented.

(5) -3. Modification 3 In Modification 3 shown in FIG. 7C, the herringbone groove 22a ′ formed in the upper radial bearing portion 22 ′ is similar to Modifications 1 and 2 above with respect to oil. The spiral groove 22 located on the side of the thrust bearing portion 26 so that the flow toward the lower radial bearing portion side is generated.
Although a'1 is set to have a longer axial dimension than the spiral groove 22a'2 located on the lower radial bearing portion side, the herringbone groove 24a "formed on the lower radial bearing portion 24" is Spiral groove 24a ″ 1 located on the radial bearing 22 ′ side
The spiral groove 24a ″ 2 located on the lower side of the sleeve 8 is formed to have a slightly longer axial dimension.

Therefore, the flow of the oil from the lower radial bearing portion 24 "side toward the upper radial bearing portion 22 'side is promoted, and in the region between the upper radial bearing portion 22' and the lower radial bearing portion 24". Generation of negative pressure is prevented.
In addition, the spiral grooves 24a "1 and 2 in the herringbone groove 24a" of the lower radial bearing portion 24 "
4a ″ 2 is smaller than that of the herringbone groove 22a ′ of the herringbone groove 22 ′ of the upper radial bearing portion 22 ′, and thus the lower radial bearing portion 24 ″ generated in the upper radial bearing portion 22 ′. The flow of oil toward the side is not blocked by the flow of oil toward the side of the upper radial bearing portion 22 'generated in the lower radial bearing portion 24 ".

(5) -4. Modification 4 Further, as shown in FIG. 7D, the herringbone groove in the upper radial bearing portion has a herringbone groove 22a having a symmetrical shape in the axial direction as in the embodiment shown in FIGS. 2 and 3. The herringbone groove in the lower radial bearing portion may be an asymmetrical herringbone groove 24a ′ that is biased to the lower side of the sleeve 8 as in the second modification shown in FIG. 7B. In this case, since the dimensional difference between the spiral grooves 24a'1 and 24a'2 in the lower radial bearing portion 24 'is smaller than that in the case where the herringbone groove on the upper radial bearing portion side is asymmetrical, the lower side of the sleeve 8 is It is possible to secure a relatively large bearing span between the upper and lower radial bearing portions 22 and 24 'while increasing the tolerance for processing tolerance and stress deformation during assembly by generating a flow of oil toward the Can be higher.

As shown in FIGS. 7 (a) to 7 (d), the static pressure bearing portion 2 is induced by inducing a flow from the radial bearing portion side toward the lower side of the sleeve 8 to the oil.
The internal pressure of the oil held at 8 is balanced with the sum of the fluid pressure induced in the thrust bearing portion 26 and the fluid pressure of the oil from the radial bearing portion side. Therefore, the load capacity increases and stable support becomes possible.

(6) Configuration of Disk Drive Device FIG. 8 shows a schematic diagram of the internal configuration of a general disk drive device 50. The inside of the housing 51 forms a clean space in which dust and the like are extremely small, and a spindle motor 52 having a disc-shaped disk plate 53 for storing information is installed therein. In addition, a head moving mechanism 57 for reading / writing information from / to the disk plate 53 is arranged inside the housing 51. The head moving mechanism 57 supports the head 56 for reading / writing information on the disk plate 53, and the head. The arm 55, the head 56, and the actuator unit 54 for moving the arm 55 to a desired position on the disk plate 53.

By using the spindle motor shown in FIGS. 2 to 7 as the spindle motor 52 of the disk drive device 50, the disk drive device 50 can be made thin and the cost can be reduced while obtaining a desired rotation accuracy. Becomes possible.

The embodiment of the spindle motor and the disk drive device according to the present invention has been described above.
The present invention is not limited to such an embodiment, and various changes and modifications can be made without departing from the scope of the present invention.

For example, as means for generating a pressure acting radially inwardly on the oil provided in the thrust bearing portion, instead of the pump-in type spiral groove 26a described in the above embodiment, a radial direction is used. It is also possible to use a herringbone groove having an unbalanced shape.

In the case where the thrust bearing portion is provided with a herringbone groove having an unbalanced shape in the radial direction, among the pair of spiral grooves forming the herringbone groove, the spiral groove located on the outer side in the radial direction is radially inward. The groove dimensions such as the radial dimension, the inclination angle with respect to the rotation direction, the groove width and the depth are set so that the pumping force generated is larger than that of the spiral groove located on the side. The unbalanced amount between the pumping force of the spiral groove located on the outer side in the radial direction and the pumping force of the spiral groove located on the inner side in the radial direction becomes the pressure applied to the oil inward in the radial direction. As in the case of the pump-in type spiral groove, the internal pressure of the oil held in the thrust bearing portion is increased.

When the above herringbone groove is provided in the thrust bearing portion, the levitation force applied to the rotor is higher than the levitation force generated by the spiral groove, so that the load bearing force by the thrust bearing portion is improved. On the other hand, in combination with the levitation force generated in the hydrostatic bearing portion, there is a concern that the rotor may overly levitation. Therefore, it is necessary to control this by the magnetic biasing force applied to the rotor.

In the above description of the embodiment, the so-called inner rotor type spindle motor in which the stator 14 is arranged on the radially outer side of the rotor magnet 16 has been described as an example. It goes without saying that the present invention can also be applied to a so-called outer rotor type spindle motor arranged on the radially outer side of 14.

[0085]

According to the spindle motor of the first aspect of the present invention, the problems of negative pressure and over-lifting are solved in the dynamic bearing having the full-fill structure, and stable shaft support is possible with a simple structure.

In the spindle motor according to the second aspect of the present invention, it becomes possible to easily form the communication hole for preventing the negative pressure and the excessive floating.

In the spindle motor according to the third aspect of the present invention, it is possible to secure a relatively large bearing span between the pair of radial bearing portions, and it is possible to maintain high bearing rigidity.

In the spindle motor according to the fourth aspect of the present invention, by forcibly circulating the oil in the bearing, the tolerance for processing tolerance and stress deformation during assembly is increased, and the yield is improved. It becomes possible to further stabilize the behavior of oil.

In the spindle motor according to the fifth aspect of the present invention, it becomes possible to support a higher load, and it is possible to effectively prevent negative pressure and excessive floating of the rotor.

In the spindle motor according to the sixth aspect of the present invention, the forced circulation of oil is promoted to improve the yield and stabilize the behavior of the oil, and at the same time, in the region between the pair of radial bearing portions. It becomes possible to prevent the generation of negative pressure.

In the spindle motor according to the seventh aspect of the present invention, it is possible to secure a relatively large bearing span between the pair of radial bearing portions while expanding the working tolerance and the allowable amount of stress deformation during assembly. Therefore, the bearing rigidity can be increased.

According to the spindle motor of claim 8 of the present invention, it is possible to maintain a sufficient sealing function even with a thin motor.

According to the ninth aspect of the spindle motor of the present invention, the motor can be made thinner, and the oil can be more effectively prevented from flowing out of the bearing due to the oil mist.

In the spindle motor according to the tenth aspect of the present invention, it is possible to stably support the shaft in the axial direction without increasing the loss in the bearing portion.

According to the disk drive apparatus of the eleventh aspect of the present invention, it is possible to reduce the size and thickness of the disk drive apparatus and to reduce the cost while obtaining a desired rotation accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a conventional spindle motor.

FIG. 2 is a sectional view showing a schematic configuration of a spindle motor according to the present invention.

3 is a partially enlarged cross-sectional view showing the shape of a herringbone groove formed in a radial bearing portion of the spindle motor shown in FIG.

4 is a plan view showing a shape of a spiral groove formed in a thrust bearing portion of the spindle motor shown in FIG.

FIG. 5 is a pressure distribution diagram schematically showing a pressure distribution of oil.

FIG. 6 is an enlarged front view showing a shaft portion of the spindle motor shown in FIG.

7 is a partially enlarged cross-sectional view showing a modified example of the herringbone groove in the radial bearing portion shown in FIG.

FIG. 8 is a cross-sectional view schematically showing the internal structure of the disk drive device.

[Explanation of symbols]

2a Upper wall portion (top plate) 2b Peripheral wall portion (cylindrical wall) 4 Shaft 5 Outer cylinder member 6 Rotor 7 Communication hole 8 Sleeve 22, 22 ', 24, 24', 24 "Radial dynamic pressure bearing portion 22a, 22a ', 24a, 24a ', 24a "Herringbone groove 26 Thrust bearing portion 28 Hydrostatic bearing portion

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H02K 7/08 H02K 7/08 A 5 H621 21/14 21/14 MF term (reference) 3J011 AA04 AA07 AA12 BA04 CA02 DA02 JA02 KA04 LA05 MA04 5D109 BB01 BB03 BB12 BB18 BB22 BB40 5H019 CC03 DD01 EE14 FF01 FF03 5H605 BB05 BB09 BB10 BB14 CC04 DD09 EB02 EB06 EB33 5H607 BB12 JG17K15K17 JG17G17K17 GG12 GG15 GG01 GG01 GG01 GG01 GG01 GG01 GG01 GG01 GG01 GG01 GG01 GG01

Claims (11)

[Claims] 1. A shaft, a sleeve having a through hole into which the shaft is rotatably inserted, a circular top plate integrally provided with the shaft at the axis of rotation, and an outer peripheral edge of the top plate. A spindle motor comprising: a rotor having a hanging cylindrical wall; and a closing member that closes one end of a through hole formed in the sleeve, wherein the outer peripheral surface of the shaft has a cylindrical shape. The outer cylinder member is mounted, the upper end surface of the sleeve and the bottom surface of the top plate of the rotor, the inner peripheral surface of the sleeve and the outer peripheral surface of the outer cylinder member, the inner surface of the closing member, the shaft, and the outer cylinder member. A continuous minute gap is formed between the end surface of the sleeve and the inside of the minute gap, and the oil is continuously retained throughout the minute gap. Little outer surface A radial dynamic pressure bearing portion, in which a herringbone groove formed by connecting a pair of spiral grooves is provided as a dynamic pressure generating groove, is formed on either one of the surfaces, and the upper end surface of the sleeve and the bottom surface of the top plate are At least one of them is provided with a thrust bearing portion provided with a dynamic pressure generating groove for applying a pressure to the oil inward in the radial direction when the rotor rotates, and the inner surface of the closing member and the shaft. A bearing part having a pressure substantially balanced with the dynamic pressure generated in the radial bearing part and / or the thrust bearing part is formed between the end surface of the rotor and the end surface of the rotor. And is formed between the outer peripheral surface of the shaft and the inner peripheral surface of the outer tubular member between the upper end surface of the sleeve and the bottom surface of the top plate of the rotor. A minute gap formed between the inner surface of the closing member and the end surface of the shaft and the outer cylindrical member, and a communication hole that communicatably communicates the oil held therein. Characteristic spindle motor. 2. A single spiral groove is formed on an outer peripheral surface of the shaft from an upper end portion to a lower end portion thereof,
The communication hole is defined between the spiral groove and the inner peripheral surface of the outer cylindrical member by mounting the outer cylindrical member on the outer peripheral surface of the shaft.
Spindle motor according to. 3. The radial bearing portions are formed in a pair so as to be separated from each other in the axial direction, and the herringbone grooves formed in the pair of radial bearing portions are symmetrical in the axial direction when the rotor rotates. The spindle motor according to claim 1 or 2, wherein spiral grooves having substantially the same shape are formed so as to be connected to each other so as to induce a fluid dynamic pressure having the following pressure gradient in the oil. 4. The radial bearing portion is formed in a pair so as to be separated from each other in the axial direction, and is formed in the radial bearing portion of the pair of radial bearing portions which is located on the side closer to the thrust bearing portion. The herringbone groove has an asymmetric shape in the axial direction so that a pressure is applied to the oil toward the bearing portion formed between the inner surface of the closing member and the end surface of the shaft when the rotor rotates. The herringbone groove is formed by connecting spiral grooves, and the herringbone groove formed in the radial bearing portion located on the side separated from the thrust bearing portion,
It is formed by connecting spiral grooves of substantially the same shape so that a fluid dynamic pressure having a pressure gradient symmetrical in the axial direction is applied to the oil when the rotor rotates. The spindle motor according to claim 1 or 2. 5. The radial bearing portions are formed in a pair so as to be separated from each other in the axial direction, and the herringbone grooves formed in the pair of radial bearing portions are respectively opposed to the oil when the rotor rotates. Is formed by connecting spiral grooves having an asymmetrical shape in the axial direction so as to apply pressure toward the bearing portion formed between the inner surface of the closing member and the end surface of the shaft. The spindle motor according to claim 1 or 2. 6. The radial bearing portion is formed in a pair so as to be separated from each other in the axial direction, and is formed in the radial bearing portion of the pair of radial bearing portions which is located on the side closer to the thrust bearing portion. The herringbone groove has an asymmetric shape in the axial direction so that a pressure is applied to the oil toward the bearing portion formed between the inner surface of the closing member and the end surface of the shaft when the rotor rotates. The herringbone groove is formed by connecting spiral grooves, and the herringbone groove formed in the radial bearing portion located on the side separated from the thrust bearing portion,
The spiral groove having an asymmetrical shape in the axial direction is formed so as to be connected to the oil so that a pressure toward the thrust bearing portion side is applied to the oil when the rotor rotates. 2. The spindle motor according to item 2. 7. The radial bearing portion is formed in a pair so as to be separated from each other in the axial direction, and is formed in the radial bearing portion of the pair of radial bearing portions which is located on the side closer to the thrust bearing portion. The herringbone groove is formed by connecting spiral grooves having substantially the same shape so that a fluid dynamic pressure having a pressure gradient symmetrical in the axial direction is applied to the oil when the rotor rotates. The herringbone groove formed in the radial bearing portion located on the side away from the thrust bearing portion is formed between the inner surface of the closing member and the end surface of the shaft with respect to the oil when the rotor rotates. The spiral groove having an asymmetrical shape in the axial direction is connected so as to apply a pressure toward the bearing portion side. The spindle motor according to claim 1 or 2, further comprising: 8. The outer peripheral surface of the sleeve and the inner peripheral surface of the cylindrical wall of the rotor oppose each other with a gap in the radial direction, and the outer peripheral surface of the sleeve is separated from the top plate of the rotor. A tapered surface is provided so that the outer diameter is reduced in accordance with the above, and the oil is held by forming a meniscus between the tapered surface and the inner peripheral surface of the cylindrical wall. The spindle motor according to any one of 1 to 7. 9. The sleeve is provided with a step portion, the outer peripheral surface of which is recessed radially inward continuously from the tapered surface, and the step portion is provided on the inner peripheral surface of the cylindrical wall of the rotor. The annular member protruding inward in the radial direction corresponding to the above is fixed, and the step portion and the annular member are engaged with each other to prevent the rotor from coming off, and the upper surface of the annular member. A minute gap smaller than the minimum size of the radial gap formed between the tapered surface of the sleeve and the inner peripheral surface of the cylindrical wall of the rotor between the lower surface of the stepped portion of the sleeve and the inner surface of the cylindrical wall of the rotor. The spindle motor according to claim 8, wherein the spindle motor is formed and functions as a labyrinth seal. 10. The spindle motor according to claim 1, wherein the rotor is biased by a magnetic force acting in the axial direction toward the closing member side. 11. A disk drive device in which a disc-shaped recording medium capable of recording information is mounted, a housing, a spindle motor fixed inside the housing to rotate the recording medium, and a required position of the recording medium. A disk drive device having information access means for writing or reading information to and from the disk drive device, wherein the spindle motor is the spindle motor according to any one of claims 1 to 10. .