JPH076520U - Bearing device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a hydrodynamic bearing device which uses magnetic fluid as a lubricant and has excellent sealing and sealing effect of the magnetic fluid. [Structure] A magnetically permeable rotating shaft 4 inserted into the non-magnetic bearings 2 and 3, an annular magnet 13 disposed between the bearings 2 and 3 and magnetized in the axial direction, and an annular magnet 8 in contact with the outer surface of the bearing 2. And pole piece 1
0, 14 is provided, the magnetic fluid 7 is retained in the vicinity of both poles of the magnet 13 while leaving the cavity 16, and the notch 22 is provided on the inner surface of the bearing 2, thereby improving the posture of the apparatus. A hydrodynamic bearing device using a magnetic fluid as a lubricant, in which the magnetic fluid does not overflow or scatter outside regardless of the thermal expansion of the magnetic fluid, and the lubricating effect is maintained even when the magnetic fluid is consumed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to improvement of a bearing device used for a polygon mirror or a hard disk drive device.

[0002]

[Prior art]

 This type of bearing device is required to have small runout of the rotating shaft, low noise, and long life.As the bearing device to be used, a fluid bearing using a liquid such as lubricating oil as a fluid is recommended. It is in practical use. For example, Japanese Unexamined Patent Publication No. 1-320314 is one such example. FIG. 3 shows the principle configuration of this bearing device. A pair of annular radial bearings 2 and 3 fixed to the inner circumference of a cylindrical housing 1 and the bearings. The rotating shaft 4 is inserted into the housing, and the tip of the rotating shaft 4 is abutted against the regulating member 5 that closes one end of the housing. The other end of the rotary shaft 4 extends from the open end of the housing, and a hub 6 on which a polygon mirror or a magnetic recording medium is mounted is fixed. The space surrounded by the housing 1, the radial bearings 2, 3, the rotating shaft 4, and the regulating member 5 is filled with a magnetic fluid 7 for lubrication. At the open end of the housing 1, there are an annular magnet 8, a non-magnetic seal 9 attached to both end surfaces thereof, and an annular magnetic pole piece 10, and a magnetic fluid 11 is introduced into the gap between the inner circumference of the magnetic pole piece and the rotating shaft 4. Are magnetically held to form a magnetic seal, which prevents the magnetic fluid 7 from leaking to the outside. Further, a gap 12 is provided between the bearing 2 and the pole piece 10, and the magnetic fluid is filled up to the intermediate position.

[0003]

[Problems to be solved by the device]

 The problem to be solved is that in the above bearing device, the gap 12 separates the magnetic fluid 7 for lubrication from the magnetic seal portion composed of the annular magnet 8, the non-magnetic seal 9 and the pole piece 10, and the magnetic fluid is added. It serves as a buffer space for variations in quantity and volume increase due to thermal expansion. However, it is desirable that there is no space for this part for the above-mentioned applications that require lightness, thinness, shortness, and size. Further, when the bearing device is used in a tilted or horizontal position, the magnetic fluid inevitably flows to reach the magnetic seal portion, and there is a risk that excess magnetic fluid will flow out.

When the inside of the magnetic seal portion is filled with the magnetic fluid, the magnetic fluid is easily scattered to the outside of the seal device due to the action of the centrifugal force of the rotating shaft and the like. You have to be careful. For the reliability of such a magnetic seal, it is desirable that the magnetic fluid held in this portion should be kept at least in the vicinity of the gap between the pole piece 10 and the rotating shaft 4. Therefore, even if the above-mentioned gap 12 is not provided, the magnetic fluid is a lubricant that does not impair the magnetic seal and the lubricating effect regardless of the variation in the amount of the magnetic fluid added, the volume increase due to thermal expansion, and the attitude of the bearing device. The hydrodynamic bearing device used as is proposed.

[0005]

[Means for solving the problem]

 In order to achieve the above object, in a bearing device having a pair of radial bearings fixed to the inner circumference of a housing at intervals in the axial direction and a shaft inserted into the bearings, as shown in FIG. , A non-magnetic housing 1, a pair of radial bearings 2 and 3, and an annular magnet 13 provided in the middle of the radial bearings. The annular magnet is axially magnetized and has an inner diameter larger than that of the bearings. Due to the magnetic force, the magnetic fluid 7 for lubrication is housed and held in the inner periphery of the magnet 13, and the annular magnet 8 and the magnetic pole pieces 10 and 14 axially magnetized at one end of the housing. The magnetic seal portion is formed in contact with the outer surface of the bearing 2. Further, in this illustrated example, the retainer 15 is fixed near the tip of the rotary shaft 4. The amount of the magnetic fluid 7 accommodated should be smaller than the internal space of the bearing device formed by the housing 1, the bearings 2, 3, the rotating shaft 4, the regulating member 5, the retaining member 15, and the magnet 13, and the cavity 16 should be left. I chose

[0006]

[Action]

 According to the bearing device configured as described above, even if the amount of the magnetic fluid for lubrication stored as described above is small, the magnetic fluid tends to be concentrated and held in the vicinity of both poles of the magnet 13, and further, Due to the action of the magnetic flux indicated by the arrow a, which is fringing from both poles of the magnet 13 to the magnetic rotating shaft 4, the magnetic fluid is adjacent to the bearing clearances 17 and 18 of the bearings 2 and 3 arranged in contact with both poles of the magnet 13. 7 is held, and the capillarity of the gap allows the magnetic fluid to be constantly replenished to the bearing surface.

[0007]

【Example】

 Hereinafter, the present invention will be described with reference to an illustrated embodiment. FIG. 1 is a sectional view of the hydrodynamic bearing device of the present invention. A pair of annular non-magnetic radial bearings 2 and 3 fixed to the inner circumference of the non-magnetic cylindrical housing 1 at intervals in the axial direction, and a rotary shaft 4 of a magnetically permeable material inserted through the bearings. The tip of 4 abuts against a regulating member 5 that closes one end of the housing 1 to form a thrust bearing. The other end of the rotary shaft 4 extends from the open end of the housing 1 and a hub 6 carrying a polygon mirror or a magnetic recording medium is fixed.

A retaining member 15 is fixed to the rotary shaft 4 by being located between the bearing 3 and the regulating member 5, and an annular magnet magnetized in the axial direction is provided in the housing 1 between the bearings 2 and 3. 13 is provided. The bearings 2 and 3 and the rotary shaft 4 are opposed to each other through minute gaps 17 and 18, and a small groove-shaped notch 22 is formed in the inner circumference of the bearing 2 so as to vertically penetrate therethrough. In the space surrounded by the radial bearings 2, 3, the rotary shaft 4, the regulating member 5, and the magnet 13, the magnetic fluid 7 is stored with the cavity 16 left, and the magnetic fluid 7 is contained in the bearing 3, the housing 1, and the regulating member. The magnetic fluid 19 for lubricating the thrust bearing filled in the space surrounded by 5 and the like communicates with the bearing gap 18, and the magnetic fluids 7 and 19 are the same material. At the open end of the housing 1, a magnetic seal portion composed of an annular magnet 8, annular pole pieces 10 and 14 and a magnetic fluid 26 (the magnetic fluid 7 flows out and does not exist at first) is provided on the outer surface of the bearing 2. Attached in contact with.

FIG. 2 shows a method for accommodating the lubricating magnetic fluid 7 of such a bearing device, and the assembly procedure of the device of FIG. 1 will be further described. As shown in FIG. 2, the tip of the nozzle 20 of the magnetic fluid supply device is inserted in the middle of the bearings 2 and 3 in a state where the rotary shaft 4, the retainer 15 and the regulating member 5 are not attached in FIG. When dropped, the magnetic fluid is drawn in the direction indicated by the arrow b by the attractive force of the magnet 13 and sticks to the inner circumference of the magnet 13, and does not fall directly below. After the storage of an appropriate amount of magnetic fluid (the amount in which the cavity 16 remains) is completed in this way, the rotary shaft 4 of FIG. 1 is inserted, the retainer 15 is further fixed, and the hub 6 is placed downwards. And the magnetic fluid 19 for lubricating the thrust bearing is dropped and filled. Finally, the regulating member 5 having the small hole 21 for venting air is fixed to the end of the housing 1 by press fitting or the like, and then the small hole 21 is sealed with an adhesive or the like. As described above, when the magnetic fluid 7 is stored during assembly, the magnetic fluid does not drop downward due to the attraction force of the magnet 13, so that the assembly is easy.

The magnetic fluid 7 thus held inside the bearing device by the attractive force of the magnet 13 as shown in FIG. 1 causes frictional heat generated by the flow of the magnetic fluid 7 when the rotating shaft 4 is rotated. Therefore, the temperature rises, and the magnetic fluid 7 and the air in the cavity 16 expand in volume. This expanded air flows out to the seal portion side through the bearing gap 17. Then, the magnetic fluid 7 also tries to flow out in the same manner, but the amount of flow out is small because the attractive force of the magnet 13 acts. This action occurs when the temperature does not rise rapidly. When the temperature rises rapidly, the air in the cavity diffuses from the bearing gap to the outside air due to the viscous resistance of the magnetic fluid 7 present in the bearing gap 17. However, the air pressure between the bearings 2 and 3 suddenly rises, and the bearing portion is forced.

In order to prevent this, a notch 22 is provided in the inner circumference of the bearing 2, and the viscous resistance of the magnetic fluid 7 at the notch 22 is much smaller than that of the bearing gap 17, and the cavity 16 The air inside is easy to circulate. The magnetic fluid 7 is attracted by the magnetic force near both poles of the magnet 13, and a part of the air in the cavity 16 is cut together with a part of the magnetic fluid in the notch 22 to which the magnetic force does not act against the expansion. It is pushed out toward the magnetic seal through the notch 22.

The small amount of the magnetic fluid 7 extruded together with the air in the cavity 16 has its outlet just located in the gap 23 between the magnetic pole piece 10 and the shaft 4 of the magnetic seal portion, and the magnetic flux shown by the arrow c Is captured by this part. At the time of cooling the magnetic fluid 7, the outside air is introduced into the original cavity 16 through the cutout 22 and the extruded magnetic fluid 7 is also sucked in the original direction. In this way, the cavity 16 acts as a buffer portion for the increase or decrease in volume of the magnetic fluid 7 due to thermal expansion and contraction, and prevents the magnetic fluid from flowing to the magnetic seal portion. Further, even if the amount of the magnetic fluid 7 decreases due to evaporation or the like, the remaining magnetic fluid 7 is always held adjacent to the bearing surface by the action of the magnet 13, so that its lubricating effect is not lost.

The rotating shaft 4 is made of a magnetically permeable material such as hardened steel or quench hardening type stainless steel, but if the bearings 2 and 3 are also made of a magnetically permeable material, a closed magnetic path is formed together with the magnet 13 and the bearing 2 A strong magnetic field acts perpendicularly on the bearing surface of No. 3, and the action of such a strong magnetic field may adversely affect properties such as an increase in viscosity of the magnetic fluid 7. Therefore, the bearings 2 and 3 are made of non-magnetic material. Therefore, since the bearings 2 and 3 do not act as pole pieces, the magnetic fluid 7 flowing from the bearing gap 17 cannot be magnetically captured. Therefore, as described above, the magnetic seal portion including the magnet 8 and the magnetic pole pieces 10 and 14 can be provided in contact with the side surface of the bearing 2.

The magnetic fluid 7 flowing from the gap 17 of the bearing 2 is captured in the gap 23 between the pole piece 10 and the shaft 4 and in the vicinity thereof. However, since the volume increase due to thermal expansion is absorbed by the cavity 16 as described above, it is not necessary to provide a gap between the bearing 2 and the magnetic seal portion as in the prior art. Further, even if the bearing device is used in a horizontal position, the magnetic fluid 7 does not flow under the action of gravity due to the attractive force of the magnet 13, and therefore, it is not necessary to consider the posture during use.

As described above, according to the present invention, the magnetic seal portion can achieve the effect of the magnetic seal without providing a gap between the magnetic seal portion and the bearing, and the gravity due to the thermal expansion and the posture unlike the prior art. There is little risk that the magnetic fluid 7 will flow into the magnetic seal due to the action of, and the magnetic fluid 7 will scatter outside the device. However, even if the excess magnetic fluid 7 enters the magnetic seal part for some reason, the pole piece 14 The magnetic fluid 7 can be captured in the gap 24 between the rotary shaft 4 and the rotary shaft 4.

Further, when the gap 24 between the pole piece 14 and the rotating shaft 4 is completely filled with the magnetic fluid 7, when a cavity is formed in the magnetic seal portion, the air in the cavity is thermally expanded and retained in the gap 24. The airtightness of the magnetic fluid 7 thus abruptly broken and there is a risk that the magnetic fluid 7 scatters to the outside as a so-called explosion phenomenon. In order to prevent this, it is desirable to provide a notch 25 or a through hole at a part of the inner circumference of the pole piece 14 so as to provide a conduction path to the outside air. The effect of providing such a ventilation hole is well known as described in, for example, Japanese Utility Model Laid-Open No. 55-80569.

[0017]

[Example of change]

 Although the notch 22 is provided on the inner peripheral surface of the bearing 2 in the above-described embodiment, the notch 22 may be omitted in applications where there is no sudden temperature rise. Although the bearings 2 and 3 are made of a non-magnetic material, a magnetically permeable material may be used depending on the application, and if the magnetically permeable material is used for the bearing 2, the pole piece 10 of the seal portion can be omitted. In this case, the magnetic fluid 7 flowing out from the bearing gap 17 is trapped at the end of the gap 17 on the seal portion side, and the magnetic fluid 7 that cannot be trapped is held by the inner circumference of the magnet 8 and is not scattered to the outside. .

[0018]

[Effect of device]

 As described above, the present invention arranges an axially magnetized annular magnet in the middle of a pair of non-magnetic radial bearings fixed to the inner circumference of the non-magnetic housing and separated from each other, and the housing is released. Since a magnetic seal portion composed of an annular magnet and an annular magnetic pole piece was provided at the end portion in contact with the outer surface of the bearing, and a cavity was partially formed in the inner periphery of the annular magnet to store the magnetic fluid as a lubricant. This cavity acts as a damper against thermal expansion, etc., so that the space between the bearing and the seal can be omitted and the axial dimension can be shortened, and the magnetic fluid overflows to the magnetic seal regardless of the orientation of the bearing device. The effect is not impaired, and even if the amount of magnetic fluid decreases due to evaporation etc., it is possible to maintain the lubricating effect at all times, and the method of adding magnetic fluid when assembling the bearing device is also used. Easy and even earlier The Rukoto provided a cutout to the inner peripheral surface of the bearing of the side in contact with the magnetic seal portion, it is possible to provide a fluid bearing device fulfill the bearing function stable even if abrupt thermal expansion, such as the magnetic fluid.

[Brief description of drawings]

FIG. 1 is a sectional view of a hydrodynamic bearing device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a method of adding a magnetic fluid 7 when assembling FIG.

FIG. 3 is a cross-sectional view of a conventional hydrodynamic bearing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2, 3 Radial bearing 4 Rotating shaft 7, Magnetic fluid 8, 13 Annular permanent magnet 10, 14 Magnetic pole piece 16 Cavity 22 Notch

Claims (2)

[Scope of utility model registration request] 1. A pair of radial bearings fixed to the inner circumference of the housing at intervals in the axial direction, and a magnetic seal portion provided in contact with the outer surface of the one bearing on the open end side of the housing, In a bearing device having a rotating shaft inserted through the inner periphery of the bearing, the housing is made of a non-magnetic material, and an annular magnet having an inner diameter larger than that of the bearing is provided in the middle of the pair of bearings, and the magnet is a shaft. A bearing device which is magnetized in a direction and has a cavity formed in a space between the magnet and the rotating shaft to accommodate a magnetic fluid. 2. The bearing device according to claim 1, wherein a notch that vertically penetrates is formed on the inner circumference of the radial bearing on the magnetic seal portion side.