JP4944931B2 - Hydrodynamic bearing spindle motor - Google Patents

Description

  The present invention relates to a spindle motor having a hydrodynamic bearing, and more particularly to a structure for holding a viscous fluid of a spindle motor for a hard disk drive device (hereinafter referred to as HDD).

A conventional HDD spindle motor (30) will be described with reference to FIG.
FIG. 5 is a cross-sectional view of a conventional HDD spindle motor (30).

  In FIG. 5, first, a shaft (2) is erected at the center of a motor base (1) formed of aluminum or an aluminum alloy.

The shaft (2) is formed of a stainless steel material and is fixed to the motor base (1) by press-fitting adhesion.
A screw hole (14) for attaching the spindle motor (30) to the HDD chassis is provided at the upper end of the shaft (2), and an attachment positioning hole (17) is provided at the lower end.

  A coil (11) and a core (10) around which the coil (11) is wound are fixed on the upper surface of the motor base (1).

  The motor base (1), the coil (11), and the core (10) constitute a stator (32).

Further, a cylindrical sleeve (6) is rotatably inserted on the outer periphery of the shaft (2).
In the upper part of the sleeve (6), there is provided a space for accommodating a thrust dynamic pressure bearing portion which will be described later.
The sleeve (6) is fixed to the inner peripheral surface of the cylindrical hub (5) by press fitting.

A ring-shaped magnet (12) and a yoke (13) facing the core (10) are fixed to the lower surface (the surface facing the stator (32)) of the hub (5).
The hub (5) has a structure in which a hard disk for recording data is mounted on the outer periphery (not shown).

  A sleeve (6), a hub (5), a ring-shaped magnet (12), a yoke (13), and a bush (9), a spacer (15), and a thrust plate (7), which will be described later, form a rotor (31). Constitute.

  Next, in the present spindle motor (30), a radial dynamic pressure bearing portion constituted by the shaft (2) and the sleeve (6) will be described below.

Two dynamic pressure grooves (3) and (4) are formed on the inner peripheral surface of the sleeve (6) opposite to the outer peripheral surface of the shaft (2), and each groove has a herringbone (fishbone) shape. The dynamic pressure groove is formed (not shown).
In the sleeve (6), the inner diameter of the inner peripheral portion sandwiched between the two dynamic pressure groove portions (3) and (4) is larger than that of the dynamic pressure groove portions (3) and (4).

Lubricating oil, which is a fluid having viscosity, is held between the dynamic pressure groove portions (3) and (4) and the shaft (2).
Due to the dynamic pressure generated by the dynamic pressure grooves in the dynamic pressure groove portions (3) and (4) when the sleeve (6) rotates, the shaft (2) receives the pressure pushing the outer peripheral portion toward the center equally from all directions. .

The shaft (2) is stably supported in the inner circumferential space of the sleeve (6) by the balance of the dynamic pressure.
Therefore, the shaft (2) and the sleeve (6) are relatively rotatably supported and the radial dynamic pressure bearing portion functions.

The dynamic pressure groove portions (3) and (4) may be formed on the outer peripheral surface of the shaft (2) instead of the inner peripheral surface of the sleeve (6).
Next, the thrust dynamic pressure bearing portion of the spindle motor (30) will be described.

  The thrust dynamic pressure bearing portion includes a flange (8) fixed to the shaft (2), a bush (9) fixed to the sleeve (6), a thrust plate (7), and a spacer (15).

  The flange (8) is a disk-shaped member having a through hole in the center made of a copper-based material, and is bonded to a mounting groove provided on the outer periphery of the shaft (2) by press-fitting or shrink fitting. 2).

  The flange (8) has two surfaces facing in opposite directions to each other in the thrust direction (vertical direction in the figure).

  The sleeve (6) described above has a space for accommodating the thrust dynamic pressure bearing portion at the upper portion thereof, and a concentric plane facing upward is formed at the bottom of the space.

  The thrust plate (7) is a disk-shaped member having a through hole in the center, and the outer peripheral portion thereof is press-fitted into the inner peripheral portion of the space inside the sleeve (6), and the inner space of the rotor (31). It is fixed to the sleeve (6) by abutting against the plane of the bottom of the sleeve.

  The spacer (15) is also a disk-shaped member having a through hole in the center, and the outer peripheral portion thereof is press-fitted into the inner peripheral portion of the space inside the sleeve (6), and the upper surface of the thrust plate (7). And is fixed to the sleeve (6).

  The bush (9) is also a disk-shaped member having a through hole in the center, and the outer peripheral portion thereof is press-fitted or bonded to the inner peripheral portion of the space inside the sleeve (6), and the upper surface of the spacer (15). And is fixed to the sleeve (6).

Each element of the thrust bearing portion described above is disposed in a space between the outer peripheral portion of the shaft (2) and the inner peripheral portion of the sleeve (6) as seen in FIG.
At this time, the inner diameter dimension of the inner peripheral portion of the thrust plate (7) is configured to be larger than the outer diameter dimension of the opposing portion of the shaft (2).

The inner diameter of the inner peripheral portion of the spacer (15) is configured to be larger than the outer diameter of the flange (8).
Further, the inner diameter of the inner peripheral portion of the bush (9) is configured to be larger than the outer diameter of the opposing portion of the shaft (2).

  The reason why the inner diameters of the three parts are configured to be larger than the outer diameters of the opposing parts is to avoid contact between the opposing parts when the spindle motor (30) rotates.

The thickness in the thrust direction of the spacer (15) is configured to be slightly larger than the thickness in the thrust direction of the flange (8).
By configuring in this way, the thrust plate (7) and the bush (9) sandwich the flange (8) with a minute gap between them, so that the minute gap necessary for generating dynamic pressure, which will be described later, Maintained above and below the flange (8) during rotation.

  Herringbone-like dynamic pressure grooves are formed on two planes in the thrust direction of the flange (8) (not shown). A fluid having viscosity such as lubricating oil is held in the two gaps above and below the flange (8).

  When the rotor portion (31) rotates, dynamic pressure is generated inside the lubricating oil by the dynamic pressure grooves on the two surfaces of the flange (8).

  The dynamic pressure groove on the upper surface of the flange (8) generates dynamic pressure in the direction of pushing the rotor (31) upward, and the dynamic pressure groove on the lower surface of the flange (8) pushes the rotor (31) downward. Dynamic pressure is generated.

  When the dynamic pressures in the two directions are balanced, the rotor (31) is rotatably supported by the shaft (2) in the thrust direction.

The above is description of the structure and operation | movement of a thrust dynamic pressure bearing part in this spindle motor (30).
In the above description, the dynamic pressure grooves in the radial direction and thrust direction dynamic pressure bearing portions have been described as being formed on one opposite surface, but may be formed on the other surface.

  In the spindle motor (30) according to the prior art described above, the lubricating oil that is a viscous fluid for generating dynamic pressure is retained in the thrust direction and radial direction dynamic pressure bearing portions, but the lubricating oil flows out. There was no particular sealing (sealing) means for preventing this.

  Therefore, when the spindle motor (30) is rotated, the lubricant agitated by the dynamic pressure grooves is scattered outside the bearing portion, or when the motor is stopped, an impact or vibration is applied from the outside, and spills outside the bearing portion. Then there was a problem of being washed away.

  The lost lubricating oil may adhere to the surface of the hard disk and interfere with data recording or playback, or may cause problems in HDD functions and performance, such as insufficient lubricating oil to function as a dynamic pressure bearing. was there.

  In the technology disclosed in the past to cope with this problem, for example, the lubricating oil is sealed using a magnetic fluid, or the lubricating oil to be washed away is disposed by arranging a labyrinth (maze) structure at the end of the bearing portion. This is due to complicated and high-cost means such as sealing, and it has been difficult to seal the lubricating oil with a simple and low-cost configuration.

  The present invention has been made in view of the above circumstances, and provides a spindle motor that seals (seals) viscous fluid that generates dynamic pressure with a simple and low-cost configuration in a spindle motor having a dynamic pressure bearing. It is an object of the invention to do this.

In order to solve the above problems, the present invention
"Shaft,
A cylindrical sleeve extrapolated to the shaft;
A hydrodynamic bearing spindle motor having a hydrodynamic bearing portion that holds a viscous fluid between the shaft and the sleeve;
The shaft is
A flange,
A first radial dynamic pressure bearing portion;
A second radial dynamic pressure bearing portion is disposed on the outer peripheral surface;
A plurality of tapered portions are provided on the outer peripheral surface of the shaft or a surface facing the outer peripheral surface,
The plurality of tapered portions are
A first taper portion having a taper angle of θ1 between the shaft and a surface facing the shaft;
A second taper portion having a taper angle of θ2 between the shaft and a surface facing the shaft;
A third taper portion having a taper angle of θ3 formed by the shaft and a surface facing the shaft;
A fourth taper portion having a taper angle of θ4 formed by an angle between the shaft and a surface facing the shaft;
In order from one end side of the shaft, the first tapered portion, the flange, the first radial direction dynamic pressure bearing portion, the second tapered portion, and the first radial direction dynamic pressure bearing portion. And the second radial direction dynamic pressure bearing portion, a communication hole communicating with the outside, the third taper portion, the second radial direction dynamic pressure bearing portion, and the fourth radial pressure dynamic bearing portion, A taper portion is arranged,
The first taper portion and the second taper portion are configured such that a gap between an outer peripheral surface of the shaft and a surface facing the shaft becomes smaller as it goes toward the first radial direction hydrodynamic bearing portion,
The third taper portion and the fourth taper portion are configured such that a gap between an outer peripheral surface of the shaft and a surface facing the third taper portion decreases toward the second radial dynamic pressure bearing portion,
An oil repellent application region is provided between the second taper portion and the third taper portion,
The force that pulls the lubricating oil that is about to move toward the first tapered portion toward the second tapered portion by capillary action causes the lubricating oil that is about to move toward the second tapered portion to be moved toward the first tapered portion. Greater than the force to pull back to the side by capillary action,
The force that pulls the lubricating oil that is about to move toward the fourth tapered portion toward the third tapered portion by capillarity causes the lubricating oil that is about to move toward the third tapered portion to be moved toward the fourth tapered portion. in part side much larger than the withdrawal force by capillary phenomenon,
The hydrodynamic bearing spindle motor characterized in that the flange is formed on a thrust direction dynamic pressure bearing portion that is fixed to the shaft and shares lubricating oil with the first radial direction dynamic pressure bearing portion. " .

  The present invention exhibits the effect of realizing sealing (sealing) of a viscous fluid that generates dynamic pressure with a simple and low-cost configuration in a spindle motor having a dynamic pressure bearing.

It is sectional drawing of the spindle motor for HDD which is 1st Embodiment based on this invention. It is principal part sectional drawing of the spindle motor for HDD which is 1st Embodiment based on this invention. It is principal part sectional drawing of the spindle motor for HDD which is 2nd Embodiment based on this invention. It is principal part sectional drawing of the spindle motor for HDD which is the 3rd Embodiment concerning this invention. It is sectional drawing of the spindle motor for HDD which concerns on a prior art.

The HDD spindle motor (20) according to the first embodiment of the present invention will be described below with reference to FIGS.
Constituent elements common to the HDD spindle motor (30) according to the prior art described above are denoted by the same reference numerals, and a part of the description is omitted without repeating the description of the same contents.
FIG. 1 is a cross-sectional view of the HDD spindle motor (20) of the present embodiment.

In FIG. 1, the shaft (2) is provided with a bored hole (17) from the lower end to the center.
Furthermore, a through hole (16) reaching the bored hole (17) from the outer peripheral surface of the shaft (2) sandwiched between the two dynamic pressure groove portions (3) (4) is provided.

The spindle motor (20) also has the dynamic pressure bearing portions in the radial direction and the thrust direction as in the spindle motor (30) according to the prior art described above, but in particular, the dynamic pressure groove portion (3) is provided. The upper radial direction dynamic pressure bearing portion and the thrust direction dynamic pressure bearing portion located immediately above the same allow the lubricating oil to flow into and out of each other, and share the lubricating oil that is a viscous fluid that generates dynamic pressure.
For convenience, the bearing portion combining the thrust direction dynamic pressure bearing portion and the upper radial direction dynamic pressure bearing portion, which are substantially integrated by sharing the lubricating oil, will be referred to as a first dynamic pressure bearing portion.
Moreover, the radial direction dynamic pressure bearing part including the dynamic pressure groove part (4) located below is referred to as a second dynamic pressure bearing part for convenience.

  The upper and lower positions in the description are described based on the posture directions shown in FIGS. 1 to 4, and the posture of the spindle motor (20) in the actual use state is not limited to this direction.

Next, the description will be continued with reference to FIG.
FIG. 2 is a cross-sectional view of the main part of the HDD spindle motor (20) according to the present embodiment shown in FIG.
In FIG. 2, the dynamic pressure grooves of the dynamic pressure groove portions (3) and (4) are schematically drawn in a plane. The same applies to the other drawings.

  In FIG. 2, a first taper portion (2a) is provided on the outer periphery of the upper shaft (2) adjacent to the first hydrodynamic bearing portion, and the diameter of the shaft (2) decreases as it goes upward. It is comprised so that it may become.

  An angle formed by the first taper portion (2a) with the surface of the opposing bush (9) is defined as a first taper angle (θ1).

Further adjacent to the first dynamic pressure bearing portion, that the lower part of the shaft (2) periphery provided with a second tapered portion (2b) is the diameter of the shaft (2) is to be smaller as drops below It is configured.

  An angle formed by the second taper portion (2b) with the surface of the opposing sleeve (6) is defined as a second taper angle (θ2).

  The first taper angle (θ1) facing the outside of the bearing is configured to be larger than the second taper angle (θ2) facing the inside.

In addition, a region where oil repellent is applied in a strip shape is provided on the outer periphery of the shaft (2) between the second tapered portion (2b) and a third tapered portion (2c) described later. Yes (not shown).
By applying the oil repellent, even if the lubricating oil held in the first dynamic pressure bearing portion moves downward in FIG. 2 due to impact or stirring by the dynamic pressure groove, the lubricating oil is placed in the area where the oil repellent is applied. In other words, the movement of the lubricating oil beyond the region where the oil repellent agent is applied is prevented.

  Further, the effect of preventing the migration of the lubricating oil by capillary action through the fine irregularities on the surface is also exhibited by providing the oil repellent application region.

  In the present embodiment, since it is configured as described above, the sealing effect for preventing the lubricating oil held in the first dynamic pressure groove portion from flowing out of the bearing is realized with a simple configuration. The operation will be described below.

  Since the first taper portion (2a) and the second taper portion (2b) are provided adjacent to the upper portion and the lower portion of the first dynamic pressure bearing portion, the lubricating oil retained by the first dynamic pressure bearing portion First, a sealing effect that is retained inside the bearing by capillary action is exhibited.

  That is, the lubricating oil which is subjected to vibration or agitation by the dynamic pressure groove and moves to the outside of the dynamic pressure bearing, when passing through the taper portion, exhibits resistance force (also referred to as sealing force) due to capillary action as described below. It is pulled back in the direction of receiving and returning to the hydrodynamic bearing.

  When lubricating oil tries to pass through the taper, the area of the end face of the lubricating oil increases according to the taper angle, but lubrication is performed so that the area of the end face decreases due to the intermolecular force (surface tension) of the lubricating oil end face. The oil receives force, and the lubricating oil cannot advance through the tapered portion beyond a certain limit.

On the other hand, the sealing force of the taper part using capillary action due to surface tension is a relatively weak holding force unlike mechanical sealing, and it may not be possible to prevent the outflow of lubricating oil against large impacts and vibrations. .
However, in the present embodiment, the sealing effect for preventing the lubricant oil from flowing out against a larger impact and vibration is exhibited as follows.

  That is, in the present embodiment, the first taper angle (θ1) facing the outside of the bearing is configured to be larger than the second taper angle (θ2) facing the inside.

When the lubricating oil held in the substantially integrated first hydrodynamic bearing portion receives a large impact, it tends to move upward or downward in FIG.
At that time, the force (seal force) for pulling down the lubricating oil that moves upward is larger than the force that pulls the lubricating oil that moves downward.

Because the first taper angle (θ1) is larger than the second taper angle (θ2), resistance due to capillary action when the same volume of lubricating oil travels upward through the first taper portion (2a). The force is greater than the same resistance force when traveling downward through the second taper portion (2b).
That is, as the taper angle increases, the area of the lubricating oil end face increases rapidly, and the surface tension of the lubricating oil end face that causes capillary action also increases rapidly.

Therefore, the lubricating oil that has received a large impact has a greater tendency to move downward, that is, inside the bearing than from the first dynamic pressure bearing portion.
Further, when the lubricating oil that has moved inward tries to move beyond the range of the second taper portion (2b), it is prevented from advancing in the oil repellent application region provided on the outer peripheral portion of the shaft (2), and eventually the two tapers. The lubricating oil is stabilized again at a position where the sealing forces of the parts are balanced.

  On the other hand, the space between the first dynamic pressure bearing portion and the second dynamic pressure bearing portion has been sealed off from the external space by the lubricating oil in the prior art spindle motor shown in FIG. Therefore, the trapped air cannot escape, and the lubricating oil held in the two hydrodynamic bearing portions is difficult to move freely outside and inside the bearing.

However, in the present embodiment, since the shaft (2) is provided with the through hole (16) and the cut-through hole (17), the above space is open to the outside, and the movement of the lubricating oil may be hindered. In addition, the prevention of outflow of the lubricating oil due to the difference in sealing force between the two tapered portions (2a) and (2b) described above functions without trouble.
In addition, although demonstrated as a structure which provided the oil-repellent agent application | coating area | region in the outer peripheral part of the shaft (2), lubricating oil moves beyond a 2nd taper part (2b) by the shape of a taper part, selection of lubricating oil, etc. It is also conceivable that the oil repellent application area is not provided.

  As described above, the sealing effect for preventing the lubricating oil retained in the first hydrodynamic bearing portion from flowing out has two tapered portions (2a) (2b), a through hole (16), and a bored hole (17). This is achieved with a simple configuration.

  Also in the second dynamic pressure bearing portion including the dynamic pressure groove portion (4), the outflow of the lubricating oil is prevented by the same configuration and operation as described above.

  That is, in FIG. 2, a third taper portion (2c) is provided on the outer periphery of the upper shaft (2) adjacent to the second hydrodynamic bearing portion, and the diameter of the shaft (2) goes upward. It is configured to become smaller according to the above.

  An angle formed by the third taper portion (2c) with the surface of the opposing sleeve (6) is defined as a third taper angle (θ3).

  Further, a fourth taper portion (2d) is provided on the outer periphery of the lower shaft (2) adjacent to the second dynamic pressure bearing portion so that the diameter of the shaft (2) becomes smaller as it goes down. It is configured.

  An angle formed by the fourth taper portion (2d) with the surface of the facing sleeve (6) is defined as a fourth taper angle (θ4).

  The fourth taper angle (θ4) facing the outer side of the bearing is configured to be larger than the third taper angle (θ3) facing the inner side.

  In addition, the outer periphery of the shaft (2) between the third taper portion (2c) and the second taper portion (2b) is provided with a region where an oil repellent agent is applied over the entire circumference in advance. As described (not shown).

  Since it is configured as described above, like the first hydrodynamic bearing portion described above, the lubricating oil is removed from the bearing by the difference between the sealing force by the two taper portions (2c) and (2d) and the two sealing forces. A sealing effect that does not flow out is exhibited.

  In the configuration of the present embodiment shown in FIGS. 1 and 2, the taper angle is larger adjacent to the lower portion of the second tapered portion (2b) and the upper portion of the third tapered portion (2c). A taper portion is provided.

  By providing the taper portion having a larger taper angle, there is an effect that the application work can be performed with high accuracy and good workability by applying an oil repellent agent thereto.

FIG. 3 shows a cross-sectional view of the HDD spindle motor according to the second embodiment of the present invention, which is configured differently from FIG.
In the present embodiment, unlike FIG. 2, the taper portion having a larger taper angle is not provided. The sealing effect of the lubricating oil is exhibited in the same manner as in the configuration shown in FIG.
In addition, when providing an oil repellent application area | region in this Embodiment, it has provided in the strip | belt shape in the lower part of the 2nd taper part (2b), and the upper part of the 3rd taper part (2c).

FIG. 4 is a cross-sectional view of an essential part of the third embodiment according to the present invention.
Unlike the configuration shown in FIGS. 1 to 3, the herringbone (fishbone) dynamic pressure grooves of the dynamic pressure groove portions (3) and (4) are not vertically symmetrical, and the two regions separated by the bent positions are inside. The thrust length of the outer region (similarly L1 and L4) is larger than the region (the length in the thrust direction is L2 and L3). (That is, L1> L2 and L3 <L4.)

  If comprised in this way, the thrust direction component of the dynamic pressure which a dynamic pressure groove part (3) (4) produces | generates when a spindle motor rotates will not become zero, and it will try to move lubricating oil inside a bearing. Dynamic pressure is generated.

  Therefore, combined with the effect of preventing the lubricant from flowing out by the taper portion described above, the effect of holding the lubricant in the bearing portion more strongly occurs, and the sealing effect is exhibited against larger vibrations and impacts. .

  In the above description, the shaft (2) is fixed to the stator (22), and the dynamic pressure bearing functions between the shaft (2) and the rotor (21).

  However, the embodiment of the present invention is not limited to the above configuration, and the shaft (2) is fixed to the rotor (21), and the hydrodynamic bearing functions between the shaft (2) and the stator (22). The configuration is also effective in the same manner.

  Moreover, the taper part was demonstrated as a structure formed in the outer peripheral surface of a shaft (2). However, the outer peripheral portion of the shaft (2) may be linear, and a tapered portion may be provided on the inner peripheral surface of the rotor (21) facing the shaft (2).

  DESCRIPTION OF SYMBOLS 1 Motor base, (theta) 1 1st taper angle, 2 shaft, 2a 1st taper part, 2b 2nd taper part, 2c 3rd taper part, 2d 4th taper part, (theta) 2 2nd taper angle, 3 Dynamic pressure groove, θ3 third taper angle, 4 dynamic pressure groove, θ4 fourth taper angle, 5 hub, 6 sleeve, 7 thrust plate, 8 flange, 9 bush, 10 core, 11 coil, 12 ring magnet, 13 Yoke, 14 Screw hole, 15 Spacer, 16 Through hole, 17 Recessed hole, 20 Spindle motor, 21 Rotor, 22 Stator, 30 Spindle motor, 31 Rotor, 32 Stator

Claims (1)

A shaft,
A cylindrical sleeve extrapolated to the shaft;
A hydrodynamic bearing spindle motor having a hydrodynamic bearing portion that holds a viscous fluid between the shaft and the sleeve;
The shaft is
A flange,
A first radial dynamic pressure bearing portion;
A second radial dynamic pressure bearing portion is disposed on the outer peripheral surface;
A plurality of tapered portions are provided on the outer peripheral surface of the shaft or a surface facing the outer peripheral surface,
The plurality of tapered portions are
A first taper portion having a taper angle of θ1 between the shaft and a surface facing the shaft;
A second taper portion having a taper angle of θ2 between the shaft and a surface facing the shaft;
A third taper portion having a taper angle of θ3 formed by the shaft and a surface facing the shaft;
A fourth taper portion having a taper angle of θ4 formed by an angle between the shaft and a surface facing the shaft;
In order from one end side of the shaft, the first tapered portion, the flange, the first radial direction dynamic pressure bearing portion, the second tapered portion, and the first radial direction dynamic pressure bearing portion. and a communication hole that communicates the sandwiched space outside said second radial dynamic pressure bearing portion, and the third tapered portion, and the second radial dynamic pressure bearing portion, the fourth A taper portion is arranged,
The first taper portion and the second taper portion are configured such that a gap between an outer peripheral surface of the shaft and a surface facing the shaft becomes smaller as it goes toward the first radial direction hydrodynamic bearing portion,
The third taper portion and the fourth taper portion are configured such that a gap between an outer peripheral surface of the shaft and a surface facing the third taper portion decreases toward the second radial dynamic pressure bearing portion,
An oil repellent application region is provided between the second taper portion and the third taper portion,
The force for pulling the lubricating oil about to move toward the first tapered portion toward the second tapered portion by capillarity causes the lubricating oil about to move toward the second tapered portion to move toward the first tapered portion. Greater than the force to pull back to the side by capillary action,
The force that pulls the lubricating oil that is about to move toward the fourth tapered portion toward the third tapered portion by capillarity causes the lubricating oil that is about to move toward the third tapered portion to be moved toward the fourth tapered portion. Greater than the force to pull back to the side by capillary action,
The flange is fixed to the shafts bets, the first dynamic pressure bearing spindle, characterized in that the thrust direction dynamic pressure bearing portion sharing the radial dynamic pressure bearing portion and the lubricating oil is formed motor.

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