Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-10-18
2003-04-29
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S119000, C384S130000
Reexamination Certificate
active
06554474
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-333781, filed Oct. 31, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydrodynamic bearing device composed of a shaft and a sleeve for rotatably supporting this shaft, wherein a dynamic pressure generating groove is provided on a surface of the shaft or sleeve. More particularly, the present invention relates to a means for preventing leakage of a fluid (for example, lubricant) in a hydrodynamic bearing.
2. Description of the Related Art
In general, a hydrodynamic bearing is composed of a shaft, a sleeve for rotatably supporting the shaft, a thrust receiver fixed to a lower face of the sleeve, and a lubricant filled in the sleeve. When the shaft is rotated, a dynamic pressure is generated with the lubricant in a radial direction due to an action of a herringbone groove provided on a wall face of the inner periphery of the sleeve. Then, the shaft rotates in non-contact with the wall face of the inner periphery of the sleeve. In a thrust direction, the shaft rotates while a tip end of the shaft comes into point contact with a thrust receiver via a lubricant, and frictional energy loss is minimized.
However, there is a problem that the lubricant tends to move, by a variety of factors, towards a sleeve opening end, (hereinafter referred to as “movement force”) and the leakage of the lubricant from the wall face of the inner periphery of the sleeve occurs. Some of the above factors are as follows.
1. The capillary phenomenon occurs in a gap between a shaft and a sleeve, which shifts the lubricant vertically (in a vertical direction), and the movement force occurs.
2. A lubricant rotates with shaft rotation, and the lubricant to which centrifugal force is applied is subjected to a restriction on the wall face of the inner periphery of the sleeve. Thus, the vertical movement force occurs.
3. A lubricant is swelled due to rotational heat generation, and the vertical movement force acts on a lubricant.
4. A pressure difference occurs inside a bearing due to inaccuracies in the precision of a herringbone groove, and an upward or downward movement force acts on a lubricant. A herringbone groove free of generating the pressure difference requires high precision.
In the case where the movement of the lubricant caused by any of these factors cannot be restrained, a lubricant leakage occurs from the sleeve opening end. Then, the lubricant in a gap between the shaft and the wall face of the inner periphery of the sleeve decreases, the shaft and sleeve come into contact with each other, and an oscillation noise is increased. As a result, the service life of the bearing itself is significantly reduced. Therefore, how well the hydrodynamic bearing prevents the lowering of performance or reliability caused by the leakage of the lubricant is an important problem in the hydrodynamic bearing.
Conventionally, a means for preventing the leakage of a lubricant of such a hydrodynamic bearing is proposed as follows. For example, a dynamic pressure type hydrodynamic bearing described in Japanese Patent No. 2574666 comprises a shaft, a sleeve for rotatably supporting the shaft, a thrust receiver fixed to the lower face of the sleeve, and a lubricant filled in the sleeve, wherein a herringbone groove is formed at a proper site in the thrust direction on the sleeve inner periphery wall face.
This herringbone groove in the vicinity of a sleeve opening end is asymmetrical in a thrust direction, and is short in distance at a side proximal to the sleeve opening end. In addition, in the vicinity of the sleeve opening end, a tapered peripheral groove is provided at the shaft so that the axial diameter is shorter at the portions of the shaft distant from the herringbone groove.
With the above described construction and features, in the prior art, when the shaft is rotated, a return force, towards the inside of the bearing, acts due to a pressure difference in the asymmetrical herringbone groove in the vicinity of the sleeve opening end, thereby preventing the leakage of the lubricant. In addition, this return force acts on the lubricant at the tapered portion of the shaft so that leakage of the lubricant can be further prevented.
However, in recent years, a disk recording/reproducing apparatus is thinner, and is higher in density, a motor for use in the recording/reproducing apparatus becomes thinner, and the oscillation precision of the shaft that is a center of disk rotation requires higher precision. Due to this thinning, the lengths of the motor shaft and sleeve are reduced. Thus, if an effective span of a radial bearing is determined so as not to impair the oscillation precision of this shaft, it becomes difficult to ensure a space for a means for preventing the leakage or evaporation of the lubricant in a dynamic bearing device and a space for holding the lubricant in the bearing.
In a conventional means for preventing the leakage or evaporation of the lubricant in a dynamic pressure bearing, a space for a length in the thrust direction of the substantially tapered portion provided at a part of the shaft cannot be provided, thus making it impossible to push back the lubricant sufficiently. Thus, the advantageous effect cannot be attained. Alternatively, in the case where the above length is defined such that the advantageous effect of the substantially tapered portion can be attained, the effective span of the radial bearing is reduced. Thus, there occurs a failure that a shaft oscillation range is increased.
In addition, in the case where the herringbone groove in the vertical direction of the bearing is made asymmetrical, preventing leakage or the like, the asymmetrical degree of such a herringbone groove cannot be sufficiently obtained. Thus, the advantageous effect cannot be attained. Alternatively, in order to attain the advantageous effect with a short asymmetrical degree, high precision is required in groove processing. Thus, there is a problem that higher costs are inevitable.
It is an object of the present invention to provide a dynamic pressure bearing device (hydrodynamic bearing device) capable of sufficiently preventing the evaluation and leakage of the lubricant in order to improve the reliability of a hydrodynamic bearing for a thin motor.
BRIEF SUMMARY OF THE INVENTION
In order to solve the foregoing problem and achieve the above object, the present invention takes the following means. That is, according to a first aspect of the present invention, there is proposed a hydrodynamic bearing device having: a shaft; a sleeve rotatably supporting the shaft, wherein a herringbone groove is formed at a predetermined part of an inner periphery wall face of the sleeve, and a thrust receiver supporting a thrust side of the shaft fixed to a lower face of the sleeve, thereby sealing predetermined lubricant; wherein a spiral groove which is narrower in groove width and shallower in depth than the herringbone groove, and which is oriented to the thrust receiver in the rotation direction of the shaft, is formed on the inner periphery wall face of the sleeve. Then, the force along the first spiral groove acts on the lubricant in a sealed space due to a pumping action of the first spiral groove, and the lubricant is oriented to the thrust receiver via the herringbone groove.
In addition, the herringbone groove and the first spiral groove is a groove that is formed so as to be superimposed on the wall face of the inner periphery of the sleeve.
The above first spiral groove is a groove that is formed over the entire wall face of the inner periphery of the sleeve.
There is proposed the previously described hydrodynamic bearing device, wherein a second spiral groove having a narrower groove width and a shallower depth than the herringbone groove, the second spiral groove being oriented in the sleeve opening end direction in the rotation direction
Saito Shoichi
Sakano Hiromichi
Hannon Thomas R.
Olympus Optical Co,. Ltd.
Scully Scott Murphy & Presser
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