JPH1122722A - Dynamic pressure bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic pressure bearing which is excellent in radial rotation precision and provide an increased life for a bearing. SOLUTION: Since oil 4 has a nature to enter a narrow gap by a surface tension, a gap (D1 -d1 ) between a sleeve 2 and a part to form the bearing of a shaft 1 is decreased to a value lower than a gap between the sleeve and other periphery part where a bearing is not formed. Further, since the oil 4 on which a centrifugal force is applied during rotation is about to enter a part D1 having a large diameter, the diameters d1 of the sleeve 2 and the bearing part of a shaft 1 is increased to a value higher than the diameter d2 of a part connected thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing which has no oil leakage, has a long service life, and can maintain high precision rotational accuracy for a long time.

[0002]

2. Description of the Related Art A motor bearing used for a magnetic disk drive or a storage device such as a VTR is required to have high rotational accuracy with small displacement in a radial direction. In these devices, a dynamic pressure bearing in which a spiral or herringbone dynamic pressure groove is provided on a shaft or an inner surface of a sleeve bearing surrounding the shaft and oil is filled between the shaft and the sleeve and used as a lubricant is used. However, in the conventional radial bearing of dynamic pressure, the inner surface of the sleeve 22 is straight in the axial direction as shown in Japanese Patent Application Laid-Open No. 50-47147 shown in FIG. 3, or as shown in Japanese Patent Publication No. 61-57489 shown in FIG. 32, the radius of the bearing portion on the inner surface was larger than that of the portion where no bearing was formed.

[0003]

In the case of a hydrodynamic bearing, it is necessary to prevent leakage of oil filled in the bearing portion. However, in a conventional hydrodynamic bearing structure, when a shaft or a sleeve rotates, centrifugal force is applied to the oil. If the bearing sleeve is straight or the diameter of the part where the bearing is not formed is large, it leaks from the bearing part to the outside, the lubricating oil is insufficient, the rotation accuracy is deteriorated, the life of the bearing is shortened, and the worst case In such a case, there was a problem that the bearing was seized. Further, it is necessary to prevent the shaft from coming off the sleeve at both ends of the shaft, and the structure is complicated.

The present invention eliminates the disadvantages of the prior art described above,
An object of the present invention is to provide a dynamic pressure bearing having a simple structure for preventing oil leakage and preventing the shaft from coming off the sleeve.

[0005]

Oil has a property of entering into a narrow gap due to surface tension, so that the gap between the shaft of the sleeve and the part forming the bearing is formed by other surrounding parts that do not constitute the bearing. Narrower than the gap. Further, since the oil subjected to the centrifugal force at the time of rotation tries to enter a portion having a large diameter, the diameter of the bearing portion of the sleeve is made larger than a portion connected to the portion. Then, the diameter of the bearing portion of the shaft is equal to the diameter of the portion connected to the bearing portion of the sleeve, or is reduced to the increment of the diameter when the sleeve is heated during assembly.

[0006]

Since the clearance of the bearing portion is smaller than the other peripheral portions, the oil collects in the bearing portion due to surface tension even during non-rotation. In addition, the oil receives centrifugal force during rotation, so that the diameter of the bearing portion is larger than the diameter of the sleeve or the shaft portion connected thereto, so that the oil collects in the bearing portion and does not leak. At room temperature,
The diameter of the bearing portion of the shaft is larger than that of the portion connected to the bearing portion of the sleeve, so that the shaft does not fall out of the sleeve.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. FIG. 1 shows a dynamic pressure bearing of the present invention. The sleeve 2 surrounds the groove forming portion of the shaft 1 in which the herringbone-shaped groove 4 for generating dynamic pressure is formed, and the gap between the shaft 1 and the sleeve 2 is filled with a lubricating fluid such as oil to form a dynamic pressure bearing. doing. The shaft 1 has another portion 1b, 1a in which the diameter d1 of the portion 1a in which the herringbone-shaped groove 3 is formed is connected thereto.
It is larger than the diameter d2 of b '. Further, the inner diameter D of the concave portion 2a facing the groove forming portion 1a of the shaft 1 of the sleeve 2
1 is larger than the inner diameter D2 of the other narrow portions 2b, 2b 'of the sleeve. The inner diameter D2 of the narrow portions 2b, 2b 'of the sleeve 2 is the same as the diameter d1 of the groove forming portion 1a of the shaft 1 which can be assembled, or at least when the diameter of the hole is increased by heating the sleeve 2 during assembly. Can be taken to a value reduced by the thermal expansion amount αt of the diameter. That is, D2 ≧ (1−αt) d1. And a gap (D2-d2) formed between the diameter d2 of the portions 1b and 1b 'of the shaft 1 that do not constitute the bearing and the diameter D2 of the narrow portions 2b and 2b' of the sleeve 2.
Are larger than the gap (D1-d1) between the bearing portions. Therefore, during non-rotation, oil collects in the bearing due to surface tension, and during rotation, the oil receives surface tension and centrifugal force as well as concentrated force at the center of the bearing due to the dynamic pressure groove.
Oil does not leak from the bearing. Further, if an oil repellent or the like is applied around the bearing portion, there is a further effect. Further, since the diameter of the bearing portion of the shaft is larger than the diameter of the portion connected to the bearing portion of the sleeve, the shaft does not fall out of the sleeve.

FIG. 2 shows a second embodiment of the present invention, in which two or more bearings are formed on one shaft. Groove forming parts 11a, 1
Herringbone grooves 13, 13 'are formed in 1a'. The bearings 12a and 12a 'of the sleeve 12 are
No. 12b, 12c, 12 not forming bearing
The diameter is larger than c ′. The inner diameter of the narrow portion 12b, 12c, 12c 'of the sleeve 12 can be the same as the diameter of the groove forming portion 1a of the shaft 1, or a value smaller than the thermal expansion when the sleeve 2 is heated during assembly. Lubricating oils 14, 14 'are filled between the groove forming portions 11a, 11a' of the shaft and the bearing portions 12a, 12a 'of the sleeve to form a dynamic pressure bearing. An air hole 15 is formed between the two formed bearings of the sleeve 12. In this embodiment, the first
As in the embodiment, at the time of non-rotation, oil collects on the bearing portion due to surface tension. Also, during rotation, the oil receives centrifugal force, so the radius of the bearing is larger than the radius of the sleeve or shaft connected to it, so the oil collects in the bearing,
The same effect as in the first embodiment described above works, and no leakage occurs. The air holes 15 are provided to prevent the space between the two bearing portions from becoming negative pressure when the oils 14 and 14 'collect in the bearing portions.

[0009]

According to the present invention, there is no oil leakage from the bearing portion, so that it is possible to obtain a dynamic pressure bearing which has a long life and can maintain good rotational accuracy for a long time. Further, the shaft does not come off from the sleeve even if no stopper is provided on the shaft end side, so that the structure is simplified.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a first embodiment of a dynamic pressure bearing according to the present invention.

FIG. 2 is a sectional view of a main part of a second embodiment of the dynamic pressure bearing of the present invention.

FIG. 3 is a sectional view of a waist portion of a conventional dynamic pressure bearing.

FIG. 4 is a sectional view of a waist portion of a conventional dynamic pressure bearing.

[Explanation of symbols]

1, 11, 21, 31 Axis 2, 12, 22, 32 Sleeve 3, 13 Herringbone groove 4, 14
Oil 15 air hole

Claims (1)

[Claims] 1. A herringbone-shaped or spiral-shaped dynamic pressure groove is formed on a shaft or a sleeve surrounding the shaft by using oil as a lubricant, and a dynamic pressure is generated by a hydrodynamic effect by rotation of the shaft or the sleeve. (D1-d1) when the diameter of the shaft of the bearing portion in which the dynamic pressure groove is formed in the shaft or the sleeve is d1 and the inner diameter of the sleeve surrounding the shaft is D1
However, let the diameter of the shaft other than the bearing part leading to this be d2,
Gap when the inner diameter of the sleeve is D2 (D2-d2)
The inner diameter D2 of the portion which is smaller and does not constitute the bearing of the sleeve is the same as the diameter d1 of the groove forming portion of the shaft, or the thermal expansion α of the diameter when the sleeve is heated during assembly.
A dynamic pressure bearing characterized by being in a range greater than a value (1−αt) d1 = D2 reduced by t.