JPH10259820A - Hydrodynamic fluid bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrodynamic fluid bearing which can prevent lubricant from flowing out and whose size can be made thin and compact by eliminating a pressure difference between a radial baring part and a thrust bearing part and by producing a stable dynamic pressure. SOLUTION: A rotary shaft 34 having a shaft part 34a and a thrust plate part 34b projecting outside in the radial direction is rotatably supported by a fixed sleeve 32 having a sleeve part 32b fitted on the shaft part 34a and an annular thrust groove part 32d which receives the thrust plate part 34b and opens inside in the radial direction via lubricant 36 with which a gap between them is filled. The thrust plate part 34b is at the one end of the shaft part 34a without protruding the shaft part 34a from the thrust plate part 34b to hermetically close the thrust plate side of the fixed sleeve 32 and a radial bearing and a thrust bearing are continuously filled with the lubricant 36. The rotary shaft 34 has passages 38a, 38b, 38c by which both thrust bearings, both radial bearings and the open end of the sleeve part 32b communicate with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing device suitable for supporting a rotating body of a motor requiring high speed and high precision such as a spindle motor for driving a recording disk.

[0002]

2. Description of the Related Art U.S. Pat. No. 5,537,859 discloses a hydrodynamic bearing device in which a rotating shaft having a thrust plate projecting from a shaft is rotatably supported on a fixed sleeve via a lubricant. No. 516,212 exists. This structure will be described below with reference to FIG.

FIG. 2 is a cross-sectional view of a spindle motor for a recording medium (for example, a hard disk) drive, and a circular fitting hole 10a of a base 10 of the recording medium drive.
The lower peripheral portion of the fixed sleeve body 12 is fitted and fixed to the fixed sleeve body 12.

The fixed sleeve body 12 has a small-diameter cylindrical sleeve portion 12c coaxially provided above a large-diameter cylindrical base portion 12a via an intermediate portion 12b having an intermediate diameter. The inner peripheral surface of the base portion 12a is formed with a large-diameter portion that is larger in diameter than the intermediate portion 12b and that is sequentially expanded in two stages toward the lower side.
2d and the disc-shaped thrust cover 12e are fitted and fixed in order from below, and the intermediate portion 12b of the fixed sleeve body 12 is fixed.
Is formed in an annular thrust groove 12f having a radially inward opening shape. At the center of the thrust cover 12e, an air opening hole 12g is provided.

A rotating shaft 14 rotatably supported by the sleeve 12 has a cylindrical shaft portion 14a and a shaft portion 1a.
And an annular plate-shaped thrust plate portion 14b protruding radially outward near the lower portion of the shaft portion 4a. Most of the shaft portion 14a including the intermediate portion is sleeve-fitted to the sleeve portion 12c, and the thrust plate portion is formed. 14b is accommodated in the thrust groove portion 12f in a state of being fitted inside, and a shaft end portion 14c protruding downward from the thrust plate portion 14b is inserted and arranged in the inner peripheral portion of the thrust receiver 12d.

[0006] The gap between the inner peripheral surface of the sleeve portion 12c and the outer peripheral surface of the shaft portion 14a, the gap between the thrust groove portion 12f and the thrust plate portion 14b, and the inner peripheral surface of the shaft end portion 14c and the thrust receiver 12d. Is filled with a lubricant 16 such as oil. The upper portion of the shaft portion 14a and the shaft end portion 14c corresponding to the upper end opening of the sleeve portion 12 are tapered surfaces 14a1 and 14c1 whose outer peripheral surfaces are reduced in diameter as going outward in the axial direction. The gap between the inner peripheral surface of the fixed sleeve body 12 and the inner peripheral surface forms a tapered seal portion whose diameter increases as going outward, and the interface between both ends of the lubricant 16 is located at both taper seal portions, so that the surface tension is increased. The outflow of the lubricant 16 is prevented.

An annular groove 14d is formed at the center of a portion of the shaft portion 14a which is sleeve-fitted to the sleeve portion 12c, and outer peripheral surfaces of upper and lower portions of the annular groove 14d in the shaft portion 14a and corresponding sleeve portions 12c are formed. A radial dynamic pressure generating groove such as a herringbone-shaped groove is formed on one or both of the inner peripheral surface and the inner peripheral surface, thereby forming a pair of upper and lower radial bearing portions. A thrust dynamic pressure generating groove such as a herringbone-shaped groove is formed on one or both of the upper and lower surfaces of the thrust plate portion 14b and the corresponding inner surface of the thrust groove portion 12f, thereby forming a pair of thrust bearing portions.

The shaft portion 14a has a first communication passage 18a communicating between inner peripheral portions of the pair of thrust bearing portions, and a second communication passage 18a communicating between the upper thrust bearing portion and the pair of radial bearing portions.
A communication passage 18b and a third communication passage 18c that connects between the radial bearings and the upper end of the upper radial bearing portion are formed. These communication paths 18a to 18c are formed in a straight line, and are arranged at the shortest positions passing through the axis of the shaft portion 14a. This is a device for minimizing the amount of the lubricant 16 to be filled.

A stator 20 is externally fitted and fixed to an outer peripheral portion of a sleeve portion 12c of the fixed sleeve body 12, and a cup-shaped rotor hub 22 is coaxially fixed to an upper end portion of a shaft portion 14a of the rotary shaft body 14. , Cylindrical portion 22 of rotor hub 22
The annular rotor magnet 24 and the stator 20 fixed to the inner peripheral surface of a are radially opposed to each other with a slight gap therebetween. A disk-shaped recording medium is fixed to the rotor hub 22 with its center hole fitted in the cylindrical portion 22a and mounted on the flanged disk mounting portion 22b at the lower end of the cylindrical portion 22a. And rotate.

[0010]

In the hydrodynamic bearing device as described above, each communication passage 18 provided in the rotary shaft 14 is provided.
Since a, 18b, and 18c allow direct or indirect communication between the pair of thrust bearings and the pair of radial bearings, a pressure difference does not occur in the low-pressure region of each bearing, and the bearings are connected to each other. Although pressure imbalance does not occur and stable shaft support by dynamic pressure can be expected, there are the following problems to be solved.

That is, in the hydrodynamic bearing device of FIG. 2, the seal of the lubricant 16 relies on a so-called taper seal. However, it is necessary to secure the taper portions in the axial direction above and below the bearing portion, respectively. In particular, when the taper angle is set to 2 degrees as described in the above-mentioned U.S. Patent, the axial length of the tapered portion becomes very long in order to secure a necessary gap in the interface region of the lubricant 16, and the bearing length is increased. There is a problem that the shaft length of the entire apparatus is increased, and as a result, the motor height is increased, and it has a drawback that it is difficult to reduce the thickness and size.

In a recording medium driving apparatus as shown in FIG. 2, the base 10 forms a part of a partition wall of a clean chamber formed inside the apparatus, and the rotor hub 22 is housed in the clean chamber. On the other hand, an air opening hole 12g of the thrust cover 12e is opened outside the clean room. Accordingly, one (upper) of the upper and lower taper seal portions of the hydrodynamic bearing device is opened to the clean chamber, and the other (lower) of the upper and lower taper seal portions is opened to the outside of the clean chamber. Since the clean room is generally isolated from the external environment, if a temperature difference or a pressure difference occurs between the outside and the inside of the clean room, the pressure balance between the upper and lower taper seal portions is lost, and the lubricant 16 leaks. There is a fear. Although there is a filter having a vent hole with a filter communicating between the clean room and the outside, there is a possibility that the same phenomenon as described above may be caused when the pressure difference changes suddenly.

SUMMARY OF THE INVENTION The present invention has been made in consideration of such problems of the prior art, and has as its object to reduce the axial dimension and to further reduce the temperature difference between the clean room and the outside. An object of the present invention is to provide a hydrodynamic bearing device in which lubricant does not flow out due to a pressure difference or the like.

[0014]

In order to achieve the above object, a hydrodynamic bearing device according to the present invention has a shaft and a thrust plate protruding radially outward from the shaft. The rotating shaft body thus formed has a fixed sleeve body having a sleeve portion fitted into the shaft portion and an annular thrust groove portion having a radially inward opening in which the thrust plate portion is accommodated in an in-fit state. Through a lubricant filled in a gap between the rotating shaft body and the fixed sleeve body, a pair of radial bearing portions where the shaft portion and the sleeve portion mainly face each other and a pair of thrust plate portions where the thrust groove portion and the thrust plate portion face each other. A thrust bearing portion rotatably supported by the thrust bearing portion, wherein the thrust plate portion is positioned at one end of the shaft portion without the shaft portion protruding from the thrust plate portion; Seal the plate side The radial bearing and the thrust bearing are continuously filled with the agent, and the rotating shaft is provided with the inner peripheral portions of the two thrust bearings, between the two radial bearings, and the radial bearing on the opening end side of the sleeve. A communication passage communicating with the vicinity of the interface with the outside air of the portion is formed.

In this hydrodynamic bearing device, the shaft of the rotary shaft does not protrude from the thrust plate, the sleeve of the fixed sleeve fits into the shaft, and the thrust plate has the thrust groove. The sealing portion of the lubricant filled between the rotating shaft body and the fixed sleeve body only needs to be sealed at the opening end of the sleeve portion, and the axial length required for sealing is smaller than in the past. In addition, since there is only one interface of the lubricant, the sealing performance is not impaired by the pressure difference between the inside and outside of the space where this type of bearing device is used, and stable sealing performance can be ensured. I can do it.

Further, according to the present invention, in the above-described hydrodynamic bearing device, the communication passage is formed by a first communication passage communicating between respective inner peripheral portions of the thrust bearing portion and a thrust bearing portion on the other end side. A second communication passage that communicates between the peripheral portion and the two radial bearing portions, and a third communication passage that communicates between the two radial bearing portions and the vicinity of the interface between the radial bearing portion and the outside air at the opening end side of the sleeve portion. It is supposed to be. In this case, it is desirable to form the second and third communication passages of the first to third communication passages in a straight line passing through the axis of the shaft portion.

According to the present invention, the pair of thrust bearings and the pair of radial bearings are communicated with each other via the first communication passage, the second communication passage, and the third communication passage, and are connected to the low-pressure region of each bearing. There is no pressure difference and no pressure imbalance occurs between the bearing portions, and stable shaft support by dynamic pressure can be expected. In particular, since the second and third communication passages are formed in a straight line passing through the axis of the shaft portion, the communication passages secure the shortest distance, and the filling amount of the lubricant can be minimized.

Further, according to the present invention, in the above-described hydrodynamic bearing device, the shaft body corresponding to the vicinity of the open end of the sleeve portion is formed with a tapered surface with a diameter decreasing toward the other end side, so that the rotating shaft body and the fixed sleeve are formed. It is characterized in that the interface of the lubricant filled in the gap with the body exposed to the outside air is located on the tapered surface.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a recording medium driving spindle motor, similar to FIG. 2 described above.
The same reference numerals as those shown in FIG. 2 indicate the same or corresponding components.

The base 30 of the recording medium driving device is thinner than the conventional one, and the lower peripheral portion of the fixed sleeve 32 is fitted and fixed in the circular fitting hole 30a of the base 30. . The fixed sleeve body 32 has a small-diameter cylindrical sleeve portion 12b above a large-diameter cylindrical base portion 32a.
Are formed coaxially, have a smaller axial length than conventional ones, and a part of the base 32a has a circular fitting hole 3.
0a. The inner peripheral surface of the base portion 32a is formed with a large inner diameter portion which is sufficiently larger than the inner diameter of the sleeve portion 32b, and the lower opening end of the large inner diameter portion is further enlarged in diameter. Are fitted and fixed, and the lower side of the fixed sleeve body 32 is sealed.
An annular thrust groove 32d having a radially inward opening is formed at a position corresponding to 2a.

A rotating shaft 34 rotatably supported by the sleeve 32 has a cylindrical shaft portion 34a and a shaft portion 3a.
An annular plate-shaped thrust plate portion 34b projecting radially outward at the lower end of the shaft portion 34a. Most of the shaft portion 34a above the thrust plate portion 34b is sleeve-fitted to the sleeve portion 32b. The plate portion 34b is accommodated in the thrust groove portion 32d in a state of being fitted inside.

The gap between the inner circumferential surface of the sleeve portion 32b and the outer circumferential surface of the shaft portion 34a and the gap between the inner circumferential surface of the thrust groove portion 32d and the outer circumferential surface of the thrust plate portion 34b are defined by these gaps. The lubricant 36 such as oil is continuously filled. Shaft portion 34 corresponding to the upper end opening of sleeve portion 32b
The upper portion a is formed with a tapered surface 34a1 whose outer peripheral surface is reduced in diameter as going outward (upward) in the axial direction, and a gap between the tapered surface 34a1 and the inner peripheral surface of the opposed sleeve portion 32b is formed outward. The taper seal portion is configured to increase in diameter as it goes, and the interface of the lubricant 36 is located at the taper seal portion, thereby preventing the lubricant 36 from flowing out due to surface tension.

An annular groove 34d is formed at a central position of a portion of the shaft portion 34a which is sleeve-fitted to the sleeve portion 32b, and outer peripheral surfaces of upper and lower portions of the annular groove 34d in the shaft portion 34a and corresponding sleeve portions 32b. A radial dynamic pressure generating groove such as a herringbone-shaped groove is formed on one or both of the inner peripheral surface and the inner peripheral surface, thereby forming a pair of upper and lower radial bearing portions. A thrust dynamic pressure generating groove such as a herringbone-shaped groove is formed on one or both of the upper and lower surfaces of the thrust plate portion 34b and the inner surface of the corresponding thrust groove portion 32d, thereby forming a pair of thrust bearing portions.

The shaft portion 34a has a first communication passage 38a communicating between inner peripheral portions of a pair of thrust bearing portions, and a second communication passage 38a communicating between the upper thrust bearing portion and the pair of radial bearing portions.
A communication passage 38b and a third communication passage 38c that communicates between the radial bearings and the upper end of the upper radial bearing portion are formed. The first communication passage 38a is formed in the axial direction, and its lower end is opened at the inner peripheral portion of the lower thrust bearing portion, and its upper end is opened at the joint between the shaft portion 34a and the thrust plate portion 34b. Further, the second and third communication passages 38b and 38c are formed in a straight line, and are arranged at the shortest position passing through the axis of the shaft portion 34a, so that the filling amount of the lubricant 36 is minimized.

In the spindle motor employing the above-described hydrodynamic bearing device, the stator 20 externally fitted to the outer periphery of the sleeve portion 32b and the rotor magnet 24 of the cup-shaped rotor hub 22 fixed to the shaft portion 34a are provided. When the rotor hub 22 rotates due to the magnetic interaction between the rotating shaft body 34 and the fixed sleeve body 32, the rotating shaft body 34 and the rotating body including the rotor hub 22 and the like are subjected to dynamic pressure by the two radial bearing portions. The rotating body is supported by the two thrust bearing portions and is dynamically supported in the thrust direction.

In the two thrust bearings and the two radial bearings, the first, second, and third communication passages 38 are provided between the low-pressure parts.
Since they are communicated by a, 38b, and 38c, there is no pressure difference between the bearing portions, and stable shaft support is realized.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the gist of the present invention.

[0028]

The hydrodynamic bearing device of the present invention is constructed as described above, and has the following effects. In the hydrodynamic bearing device according to claim 1, the thrust plate in which the rotary shaft body rotatably supported by the fixed sleeve body projects radially outward without protruding from the shaft portion and the shaft end. And the thrust plate side of the fixed sleeve body is hermetically closed, so that the axial length of the entire bearing device can be significantly reduced as compared with the related art, and this is used. The motor can be made smaller and thinner. In addition, since the interface of the lubricant filled in the gap between the fixed sleeve body and the rotating shaft body can be improved in one place, even if a pressure difference between the inside and the outside occurs in the space in which the motor or the like is housed, the lubrication as in the related art is achieved. No leakage of the agent occurs, stable bearing performance can be exhibited, and a long life can be expected.

In the hydrodynamic bearing device according to the second aspect, the communication passage formed in the rotary shaft body is constituted by the first to third communication passages which sequentially communicate between the bearing portions. The structure is simplified as compared with the case where the communication structure penetrates the whole, and in particular, if the second and third communication passages are formed in a straight line passing through the axis of the shaft portion as described in claim 3, It is possible to form a communication path connecting the bearing portions with the shortest distance, so that the formation is easy and the advantage that the filling amount of the lubricant can be minimized can be obtained.

In the hydrodynamic bearing device according to the fourth aspect, the filled lubricating fluid can be sealed with a taper seal formed by a tapered surface, and the diameter of the tapered surface is reduced outwardly on the shaft portion. Therefore, the lubricant can act on the inside of the bearing by the rotation of the shaft portion, and good sealing performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a spindle motor for driving a hard disk to which a hydrodynamic bearing device of the present invention is applied.

FIG. 2 is a sectional view of a spindle motor showing a conventional example.

[Explanation of symbols]

 32 Fixed sleeve 32b Sleeve 32d Thrust groove 34 Rotating shaft 34a Shaft 34b Thrust plate 36 Lubricant 38a First communication passage 38b Second communication passage 38c Third communication passage

Claims (4)

[Claims] A rotary shaft having a shaft portion and a thrust plate portion radially outwardly projecting from the shaft portion, wherein the rotary shaft body has a sleeve portion fitted to the shaft portion and the thrust plate portion inside. For a fixed sleeve body having a radially inwardly opening annular thrust groove portion housed in the fitted state, via a lubricant filled in a gap between the rotating shaft body and the fixed sleeve body,
A hydrodynamic fluid bearing device rotatably supported in a pair of radial bearing portions where a shaft portion and a sleeve portion face each other and a pair of thrust bearing portions on both surfaces of a thrust plate portion where a thrust groove portion and a thrust plate portion face each other. The thrust plate portion is located at one end of the shaft portion without the shaft portion protruding from the thrust plate portion, the thrust plate portion side of the fixed sleeve body is sealed, and the lubricant is supplied to the radial bearing. Part and the thrust bearing part are continuously filled, and the rotating shaft body has inner peripheral parts of the two thrust bearing parts, between the two radial bearing parts, and an open end of the sleeve part. A fluid passage communicating with the vicinity of the interface of the radial bearing portion with the outside air on the side of the fluid dynamic bearing device. 2. The communication path includes: a first communication path communicating between respective inner peripheral portions of the thrust bearing portion; and an inner peripheral portion of the thrust bearing portion on the other end side and between the two radial bearing portions. 2. A second communication passage which communicates between the two radial bearing portions and a third communication passage which communicates between the two radial bearing portions and the vicinity of an interface between the radial bearing portion and the outside air on the opening end side of the sleeve portion. Hydrodynamic bearing device. 3. The device according to claim 2, wherein at least the second and third communication passages of the first, second and third communication passages are formed in a straight line passing through the axis of the shaft portion. Hydrodynamic bearing device. 4. The shaft body corresponding to the vicinity of the opening end of the sleeve portion has a tapered surface that is reduced in diameter toward the other end.
4. The hydrodynamic bearing device according to claim 1, wherein an interface of the lubricant filled in a gap between the rotating shaft body and the fixed sleeve body, which is exposed to the outside air, is located on the tapered surface. 5.