Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-07-26
2003-02-04
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S100000, C384S130000, C384S279000
Reexamination Certificate
active
06513979
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hydrodynamic oil-impregnated sintered bearing unit having a higher accuracy of rotation, a higher rotation stability, and an improved durability, and more particularly to a hydrodynamic oil-impregnated sintered bearing unit which is suitable for use as a spindle supporter in spindle motors for information equipment, for example, a motor for driving an optical disc unit such as CD-R, CD-RW, DVD-ROM, or DVD-RAM, a magneto-optical disc unit such as MD and MO, and a magnetic disc unit such as HDD, or a polygon scanner motor or the like of a laser beam printer (LBP).
For the spindle motors of the above stated information equipment, there has been a demand for a higher speed capability, lower costs, lower noise in addition to-higher accuracy of rotation. One of the key elements that determine those high performance requirements is a bearing for supporting a spindle of a motor. Conventionally, as a bearing of this type, a ball bearing or an oil-impregnated sintered bearing have been used.
However, a spindle motor of the type is usually operated at a rotational speed as high as 5000 to 12000 rpm. Particularly, a polygon scanner motor used in an LBP is mostly operated at a rotational speed as high as 20000 to 35000 rpm. Thus, the technology of a ball bearing cannot meet requirements such as noise reduction and cost reduction any longer. Moreover, there has been a strict demand for higher and higher accuracy of rotation, that is, lower shaft vibration, lower NRRO (Non Repeatable Run Out), and lower jitter. It is thus becoming increasingly difficult to meet the above-described high performance requirements with the technology of a oil-impregnated sintered bearing.
Nowadays, from the above point of view, as a bearing of the type, a hydrodynamic oil-impregnated sintered bearing has come to be partly in practical use. This bearing is, for example, composed of a bearing body made of a porous sintered metal impregnated with a lubricating oil or lubricating grease, and non-contactingly supports a spindle by forming a lubricating oil film in a bearing gap by exploiting a dynamic-pressure effect exerted by a dynamic-pressure groove formed in the bearing surface. This construction is capable of coping with the above-described high performance requirements.
However, low-profile information equipment typified by notebook-type personal computers require spindle motors used therewith to be made slimmer and slimmer. Thus, the space volume around a bearing portion tends to be decreased. Moreover, rotational speed is on the increase, which accordingly causes the temperature of the bearing to rise during operation. Thus, the amount of oil exuding from the bearing body due to thermal expansion is increased, and the gap between the sealing washer and the shaft, which is provided for prevention of oil leakage, is inconveniently filled with the seepage of oil. In this state, when the operation comes to a halt, the oil accumulated between the sealing washer and the bearing body is collected in the bearing body again by its thermal contraction, but the oil accumulated between the shaft and the sealing washer might remain uncollected due to capillarity. That is, the inner portion of the bearing unit is sealed with the oil accumulated between the shaft and the sealingwasher. In this state, when the operation is resumed, the airbetween the sealing washer and the bearing body is expanded. Therefore, the oil accumulated between the shaft and the sealing washer is pushed out of the bearing unit and is, as a rotation occurs, scattered around. As a result, the periphery of the bearing is contaminated, and simultaneously a repetition of this phenomenon causes the amount of oil to decrease. This leads to oil shortage and makes it impossible to attain an adequate dynamic-pressure effect.
To cope with such inconveniences, some measures can be considered. For example, applying a commonly-used oil repelling agent, such as a silicone-based oil repelling agent or a PTFE-based oil repelling agent, to the sealing washer or the outer circumferential surface of the shaft opposed thereto, or spraying such an oil repelling agent diluted in an organic solvent to the same. In a case where the shaft is subjected to oil repelling treatment, it is preferable to apply an oil repelling agent to the entire surface of the shaft by immersing the shaft in an agent solution in consideration of the operation efficiency. In this case, however, the processed film is unduly thick and the film thickness varies from several &mgr;m to 10 &mgr;m. This makes it difficult to control the bearing gap. If the application is conducted by spraying, the film thickness varies more greatly, making the control of the bearing gap more difficult.
Moreover, those oil repelling agents have weaker adhesive strength with respect to a base material and thus exert poor durability. Furthermore, when exposed to oil constantly, the oil repelling agents may possibly be dissolved in oil gradually and consequently the oil repelling effect is deteriorated with the passage of time. This makes it difficult to obtain a stable oil repelling effect for a long period of time.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a low-cost hydrodynamic oil-impregnated sintered bearing unit capable of preventing the leakage of lubricating oil to the outside of the unit for a longer period of time with stability, wherein a bearing gap is easily controlled.
To achieve the above object, a hydrodynamic oil-impregnated sintered bearing unit according to the present invention includes: a hydrodynamic oil-impregnated sintered bearing made of a sintered metal and composed of a bearing body having a radial bearing surface opposed via a bearing gap to an outer circumferential surface of a shaft, the bearing body being impregnated with a lubricating oil or lubricating grease, the hydrodynamic oil-impregnated sintered bearing non-contactingly supporting the shaft by exploiting a dynamic pressure effect generated by a relative rotation between the shaft and the bearing body; a housing with its one end opened and its other end closed, the housing having in its inner diameter portion said hydrodynamic oil-impregnated sintered bearing; and a thrust bearing portion for thrust-supporting the shaft, wherein a sealing washer made of a metal or resin material is arranged on an opening-portion side of the housing, and wherein, of a surface of the sealing washer, at least on an inner circumferential surface opposite to the shaft a thin layer of a fluorine-containing polymer is formed.
By forming a thin film of a fluorine-containing polymer at least on the inner circumferential surface of the sealing washer in this way, it is possible to repel oil that is about to exude through the shaft and thus successfully prevent the leakage of oil from the bearing unit.
As the fluorine-containing polymer, for example, a fluoropolyether polymer can be considered that has a main structural unit represented by a formula: —C
x
F
2x
—O— (x is an integer of from 1 to 4). The average molecular weight of the fluoropolyether polymer preferably falls in the range of 500 to 50000. A fluorine-containing polymer of this type can be formed into a film of even thickness which is far thinner than a bearing gap by simple means, such as application or immersion. This makes the control of a bearing gap easy. Moreover, the fluorine-containing polymer has high adhesion with respect to metal and is thus excellent in durability, and has satisfactory oil resistance and thus offers a stable oil-repelling effect for a long period of time.
In a case where the average molecular weight is no greater than 500, the following inconveniences arise.
(1) The polymer is highly volatile due to an unduly small molecular weight. For example, if there remain unreacted compounds, optical equipment might be contaminated by the volatilization.
(2) As the oil repelling effect is gradually decreased, the preservation stability is deteriorated. Specifically, the smaller t
Kurimura Tetsuya
Mori Natsuhiko
Arent Fox Kintner Plotkin & Kahn
Hannon Thomas R.
NTN Corporation
LandOfFree
Hydrodynamic oil-impregnated sintered bearing unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydrodynamic oil-impregnated sintered bearing unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrodynamic oil-impregnated sintered bearing unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3129953