WO2007094401A1 - Bearing unit - Google Patents

Abstract

A bearing unit (1) comprises a cylindrical fixed shaft (2); a cylindrical sleeve (3); an outer ring sleeve (4) disposed on the outer periphery of the sleeve (3) and having an inner peripheral surface facing the outer peripheral surface of the sleeve (3); a thrust plate (5) secured to the fixed shaft (2), extending in the radial direction of the fixed shaft (2), and having a lower surface facing the axial upper end surface of the outer ring sleeve (4); and a magnetic fluid filled in the gap between the outer peripheral surface of the sleeve (3) and the inner peripheral surface of the outer ring sleeve (4) and the gap between the axial upper end face of the outer ring sleeve (4) and the principal plane of the thrust plate (5). A plurality of magnetic poles are formed on the outer peripheral surface of the sleeve (3). The surfaces of the outer ring sleeve (4) and the thrust plate (5) facing each other contain a tetrafluoroethylene resin, polyacetal, polyamide, a phenol resin, polyethylene, polyimide, polyphenylene sulfide, or polyether ether ketone. Therefore, the friction of the thrust bearing part can be reduced, and the size of the bearing unit can be reduced.

Description

 Specification

 Bearing unit

 Technical field

 [0001] The present invention relates to a bearing unit, and more particularly to a bearing unit used for supporting a swing arm of a hard disk of a computer.

 Background art

 A magnetic fluid bearing is a bearing using a magnetic fluid as a lubricant for the bearing. The operating principle of magnetic fluid bearings is based on magnetic force regardless of the fluid lubrication theory, so even when the shaft and outer ring are relatively stationary or when the relative speed between the shaft and outer ring is extremely small, the external force is applied. The shaft and the outer ring can be supported without contact without pressure. For this reason, the magnetic fluid bearing is suitable as a fulcrum bearing for swing motion, and is used as a fulcrum bearing for a swing arm in a hard disk (HDD) device of a computer. Conventional magnetic fluid bearings are disclosed in, for example, Japanese Patent Laid-Open No. 2004-218792 (Patent Document 1), Japanese Utility Model Publication No. 7-736 (Patent Document 2), and Japanese Patent Laid-Open No. 2003-13957 (Patent Document 3). It is disclosed.

 FIG. 8 is a cross-sectional view showing a swing arm device in the HDD device disclosed in Patent Document 1. Referring to FIG. 8, the swing arm 122 is installed so as to be rotatable forward and backward via a magnetic fluid bearing 101. The magnetic fluid bearing 101 includes a rotation support shaft 103 and a bearing outer ring 102. The rotating spindle 103 is made of a nonmagnetic material and is fixed to the base 123 by screws 127. A bearing outer ring 102 is disposed on the outer periphery of the rotary spindle 103, and a swing arm 122 is attached to the bearing outer ring 102. A magnetic head (not shown) is provided at one end (left side in the figure) of the swing arm 122 to record information on the magnetic disk, and the other end (right side in the figure) of the swing arm 122 is provided. The head positioning mechanism 126 is provided. A magnetic fluid is injected into a gap G between the rotating spindle 103 and the bearing outer ring 102. A plurality of magnetic poles 104 are provided on the inner peripheral surface of the bearing outer ring 102. Each of the plurality of magnetic poles 104 is separated in the circumferential direction and the axial direction, and is provided on the entire circumference of the bearing outer ring 102.

FIG. 9 is a cross-sectional view showing the magnetic fluid bearing disclosed in Patent Document 2. Refer to Figure 9 The magnetic fluid bearing disclosed in Patent Document 2 supports a thrust load, and includes a non-magnetic material shaft 201, and a disk-shaped permanent magnet 207 disposed through an end surface of the shaft 201 and a minute gap 202. And a magnetic fluid 204 interposed in the minute gap 202. The disk-shaped permanent magnet 207 is held by an annular holder 208. The disk-shaped permanent magnet 207 is multipolarly magnetized in the axial direction so that the magnetic poles adjacent in the radial direction and the circumferential direction are different from each other.

 [0005] In the magnetic fluid bearing disclosed in Patent Document 3, a pivot shaft is held in a bearing housing, and a magnet is fitted around the pivot shaft. A magnetic fluid is held between the outer periphery of the magnet and the inner wall of the bearing housing.

 Patent Document 1: Japanese Patent Application Laid-Open No. 2004-218792

 Patent Document 2: Actual Fairness 7-736

 Patent Document 3: Japanese Unexamined Patent Publication No. 2003-13957

 Disclosure of the invention

 Problems to be solved by the invention

 In the swing arm device of FIG. 8, a thrust load is generated in the magnetic fluid bearing 101 due to its own weight or the like. However, since the magnetic fluid bearing 101 supports the radial load (radial load) of the rotating support shaft 103 by magnetic fluid, the axial load (thrust load) of the rotating support shaft 103 is supported by magnetic fluid. I couldn't support it. For this reason, the magnetic fluid bearing 101 of Patent Document 1 has a problem that the friction of the thrust bearing portion is large.

 [0007] As a method for reducing the friction of the thrust bearing portion of the magnetic fluid bearing 101, a method using a thrust rolling bearing is conceivable. Specifically, thrust rolling bearings are arranged between the upper end of the bearing outer ring 102 and the rotating support shaft 103, and between the lower end of the bearing outer ring 102 and the rotating support shaft 103, and support radial load and thrust load. A method of making a bearing unit to be used (hereinafter also referred to as the first improvement method) is conceivable.

Further, as a method for reducing the friction of the thrust bearing portion of the magnetic fluid bearing 101, a permanent magnet as shown in FIG. 9 is placed so as to face each of the upper end surface and the lower end surface of the bearing outer ring 102. A bearing unit is installed to support radial load and thrust load. The following method (hereinafter referred to as the second improvement method) is also conceivable.

[0009] HDDs are required to be miniaturized especially in the height direction (vertical direction in Fig. 8). For this reason, the swing bearing support bearing unit is also desired to be downsized in the height direction. However, both the first and second improvement methods have a problem that the bearing unit cannot be downsized in the height direction. That is, the rolling bearing has a large number of components such as an inner ring, an outer ring, a cage, and a plurality of rolling elements. Since there is a limit to the processing accuracy of these components, there was a limit to the miniaturization of rolling bearings. As a result, in the first improvement method, the bearing unit could not be downsized in the height direction. In addition, the thrust plate needs to have a certain thickness in order to accommodate the permanent magnet, and there is a limit to reducing the thickness of the thrust plate. As a result, the bearing unit could not be downsized in the height direction even with the second improvement method.

[0010] Therefore, an object of the present invention is to provide a bearing unit that can reduce the friction of the thrust bearing portion and can be miniaturized.

 Means for solving the problem

[0011] A bearing unit according to one aspect of the present invention includes a cylindrical shaft, an outer ring disposed on the outer periphery of the shaft and having an inner peripheral surface facing the outer peripheral surface of the shaft, and fixed to the shaft. Between the outer peripheral surface of the shaft and the inner peripheral surface of the outer ring, and between the axial end surface of the outer ring and the main surface of the plate. Oil-based magnetic fluid injected into the gap. A plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring. The main surface of the plate facing the axial end surface of the outer ring or the axial end surface of the outer ring facing the main surface of the outer ring is tetrafluoroethylene, polyacetal, polyamide, phenolic resin, polyethylene, polyimide, polyphenylene sulfide, and poly It contains at least one material selected from the group consisting of ether ether ketones.

[0012] According to the bearing unit according to one aspect of the present invention, the outer bearing and the plate constitute the sliding bearing, and the thrust load is supported by the sliding bearing. Lubricity between the axial end surface of the outer ring and the main surface of the plate is ensured by the oiliness of the magnetic fluid. In addition, the above material has a low friction coefficient and excellent wear resistance. The friction coefficient of the end face Can be reduced. As a result, the friction of the thrust bearing portion can be reduced. In addition, the sliding bearing has fewer parts than the rolling bearing, so the sliding bearing components are easier to machine than the rolling bearing components. There is no need for the plate to be made of magnetic material. Therefore, the plate can be thinned, and thereby downsizing can be achieved.

 [0013] In the bearing unit according to one aspect of the present invention, preferably, the outer ring is made of a group consisting of tetrafluoroethylene resin, polyacetal, polyamide, phenol resin, polyethylene, polyimide, polyethylene sulfide, and polyether ether ketone. It is made of at least one material selected.

[0014] These materials have a density lower than that of iron (7.86 g / cm ³ ). By forming the outer ring from these materials, it is possible to reduce the weight of the outer ring and reduce the load on the outer ring applied to the plate. As a result, the friction of the thrust bearing portion can be reduced.

 [0015] A bearing unit according to another aspect of the present invention includes a cylindrical shaft, an outer ring disposed on the outer periphery of the shaft and having an inner peripheral surface facing the outer peripheral surface of the shaft, and fixed to the shaft. Between the outer peripheral surface of the shaft and the inner peripheral surface of the outer ring, and between the axial end surface of the outer ring and the main surface of the plate. Oil-based magnetic fluid injected into the gap. A plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring. The main surface of the plate facing the axial end surface of the outer ring or the axial end surface of the outer ring facing the main surface of the plate is subjected to surface treatment or surface modification treatment.

[0016] According to the bearing unit according to another aspect of the present invention, a sliding bearing is constituted by the outer ring and the plate, and a thrust load is supported by the sliding bearing. Lubricity between the axial end surface of the outer ring and the main surface of the plate is ensured by the oiliness of the magnetic fluid. Further, the surface coefficient or surface modification treatment is applied to the main surface of the plate or the axial end surface of the outer ring, so that the friction coefficient of the main surface of the plate or the axial end surface of the outer ring can be reduced. As a result, the friction of the thrust bearing portion can be reduced. In addition, since the plain bearing has fewer parts than the rolling bearing, the components of the plain bearing are easier to process than the components of the rolling bearing. In addition, the plate need not be made of a magnetic material. Therefore, thin the plate It can be made into a plate, and thereby downsizing can be achieved.

 [0017] A bearing unit according to still another aspect of the present invention includes a cylindrical shaft, an outer ring disposed on the outer periphery of the shaft and having an inner peripheral surface facing the outer peripheral surface of the shaft, and fixed to the shaft. A plate extending in the radial direction of the shaft and having a main surface facing the axial end surface of the outer ring; a gap between the outer peripheral surface of the shaft and the inner peripheral surface of the outer ring; and an axial end surface of the outer ring and the main surface of the plate Oily magnetic fluid injected into the gap. A plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring. The outer ring has a density smaller than that of iron.

 [0018] According to the bearing unit according to still another aspect of the present invention, a sliding bearing is constituted by the outer ring and the plate, and a thrust load is supported by the sliding bearing. Lubricity between the axial end surface of the outer ring and the main surface of the plate is ensured by the oiliness of the magnetic fluid. In addition, the weight of the outer ring can be reduced, and the load on the outer ring applied to the plate can be reduced. As a result, the friction of the thrust bearing portion can be reduced. In addition, since the sliding bearing has fewer parts than the rolling bearing, the sliding bearing components are easier to apply than the rolling bearing components. In addition, the plate need not be made of a magnetic material. Therefore, the plate can be thinned, and thereby downsizing can be achieved.

 In the bearing unit according to still another aspect of the present invention, preferably, the outer ring is made of a light metal or a light metal alloy. More preferably, the outer ring is made of an aluminum alloy or a magnesium alloy.

 In the bearing unit according to still another aspect of the present invention, preferably, the outer ring is made of resin.

 [0021] Since these materials have a density lower than that of iron, the weight of the outer ring can be reduced, and the load on the outer ring applied to the plate can be reduced.

 [0022] Preferably, in the bearing unit according to still another aspect of the present invention, the main surface of the plate facing the axial end surface of the outer ring or the axial end surface of the outer ring facing the main surface of the plate is a tetrafluoroethylene resin. It contains at least one material selected from the group consisting of polyacetal, polyamide, phenolic resin, polyethylene, polyimide, polyethylene sulfide, and polyetheretherketone.

[0023] In the bearing unit according to still another aspect of the present invention, preferably, the axial end of the outer ring Surface treatment or surface modification treatment is applied to the main surface of the plate facing the surface or the axial end surface of the outer ring facing the main surface of the plate.

 [0024] Preferably, in the bearing unit of the present invention, the magnetic fluid contains at least one material selected from the group consisting of fatty acids, alcohols, aliphatic amides, esters, and sulfurized fats or oils. Contains derivatives.

 [0025] These materials are polar substances having a high adsorptivity to the metal surface and have a high lubricating ability. Therefore, the lubricity of the magnetic fluid can be improved.

 In the magnetic fluid bearing of the present invention, preferably, a swing arm having a magnetic head for recording information is attached to the outer ring.

 [0027] In the magnetic fluid bearing of the present invention, since a plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring, in the radial bearing portion, the outer ring is mounted even when the shaft is stationary. The shaft can be supported in a non-contact state. Further, the friction at the thrust bearing portion in the boundary lubrication state as described above can be reduced. For this reason, it is suitable for supporting a shaft that performs rocking motion, and particularly suitable for supporting a swingarm having a magnetic head for recording information.

 The invention's effect

 [0028] According to the bearing unit of the present invention, the friction of the thrust bearing portion can be reduced and the size can be reduced.

 Brief Description of Drawings

 FIG. 1 is a cross-sectional view showing a structure of a bearing unit in Embodiment 1 of the present invention.

 [FIG. 2] (a) is an enlarged view of part A of FIG. 1, and (b) is an enlarged view of part B of FIG.

 3 is a diagram showing a magnetic pole distribution of the sleeve 3 in a cross section taken along line III-III in FIG.

 FIG. 4 is a diagram showing a magnetic pole distribution in a development view of a sleeve 3.

 FIG. 5 is a view showing another example of the magnetic pole distribution in the development view of the sleeve 3.

 FIG. 6 is a view showing still another example of the magnetic pole distribution in the development view of the sleeve 3.

 FIG. 7 is a cross-sectional view illustrating a case where the bearing unit according to the first embodiment of the present invention is used as a fulcrum bearing of a swingarm device in an HDD device.

FIG. 8 is a sectional view showing a swing arm device in the HDD device disclosed in Patent Document 1. It is.

 FIG. 9 is a cross-sectional view showing a magnetic fluid bearing disclosed in Patent Document 2.

 Explanation of symbols

 [0030] 1 bearing unit, 2 fixed shaft, 3 sleeve, 3b outer peripheral surface of the sleeve, 4 outer ring sleeve, 4a upper end surface in the axial direction of the outer ring sleeve, 4b inner peripheral surface of the outer ring sleeve, 4c lower end surface in the axial direction of the outer ring sleeve, 5 Thrust plate, 5a Lower surface of thrust plate, 6 Flange, 6a Upper surface of flange, 7 Magnetic fluid, 8 Hollow part, 21 Swing arm device, 22, 122 Swing arm, 23, 123 base, 24 Magnetic head, 25 Magnetic disk, 26, 126 Head positioning mechanism, 26a Rotor, 26b Stator, 27, 127 Screw, 101 Magnetic fluid bearing, 102 Bearing outer ring, 103 Rotating spindle, 104 Magnetic pole, 201 axis, 202 Small gap, 204 Magnetic fluid 207 disc-shaped permanent magnet, 208 holder.

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

 (Embodiment 1)

 FIG. 1 is a cross-sectional view showing the structure of the bearing unit in the first embodiment of the present invention. 2 (a) is an enlarged view of part A in FIG. 1, and FIG. 2 (b) is an enlarged view of part B in FIG. With reference to FIGS. 1 and 2, the bearing unit 1 of the present embodiment includes a fixed shaft 2, a sleeve 3, an outer ring sleeve 4, a thrust plate 5, and a flange portion 6.

 The fixed shaft 2 has a cylindrical shape with a hollow portion 8, and a sleeve 3 is provided on the outer periphery of the fixed shaft 2. A disc-shaped thrust plate 5 is fixed to the upper portion of the fixed shaft 2, and a disc-shaped flange portion 6 is provided to the lower portion of the fixed shaft 2. The thrust plate 5 is fixed to the fixed shaft 2 by, for example, an adhesive, and the flange portion 6 is formed integrally with the fixed shaft 2. The thrust plate 5 and the flange portion 6 extend in the radial direction of the fixed shaft 2 (lateral direction in FIG. 1). The fixed shaft 2, the thrust plate 5, and the flange portion 6 constitute a shaft. The thickness of the thrust plate 5 and the flange portion 6 is, for example, 0.5 mm.

[0033] The outer ring sleeve 4 has a hollow cylindrical shape, and is disposed on the outer periphery of the sleeve 3 with a radial bearing gap therebetween. The outer ring sleeve 4 is rotatable with respect to the fixed shaft 2. The inner peripheral surface 4b of the outer ring sleeve 4 protrudes toward the inner diameter side. The outer peripheral surface 3b of the sleeve 3 and The inner ring surface 4b of the outer ring sleeve 4 faces each other. The clearance between the outer peripheral surface 3b of the sleeve 3 and the outer peripheral surface 4b of the outer ring sleeve 4, the clearance between the axial upper end surface 4a of the outer ring sleeve 4 and the lower surface 5a of the thrust plate 5, and the lower axial end surface 4c of the outer ring sleeve 4 A magnetic fluid 7 is sealed in the gap between the flange 6 and the upper surface 6a of the flange portion 6 (that is, the gap between the shaft and the outer ring sleeve 4). In the bearing unit 1, the sleeve 3 and the outer ring sleeve 4 constitute a radial sliding bearing.

 In particular, as shown in FIG. 2 (a), the axial upper end surface 4 a of the protruding portion of the outer ring sleeve 4 faces the lower surface 5 a of the thrust plate 5. Similarly, as shown particularly in FIG. 2 (b), the lower end surface 4 c in the axial direction of the outer ring sleeve 4 faces the upper surface 6 a of the flange portion 6. The outer ring sleeve 4 is held in the thrust direction by the thrust plate 5 and the flange portion 6. The outer ring sleeve 4 and the thrust plate 5 constitute a thrust sliding bearing, and the outer ring sleeve 4 and the flange portion 6 constitute a thrust sliding bearing.

 Each of fixed shaft 2, outer ring sleeve 4, and thrust plate 5 is made of a nonmagnetic material such as austenitic stainless steel or brass. The sleeve 3 is made of a magnetic material such as ferrite.

 [0036] The magnetic fluid 7 is oily and is composed of a liquid in which magnetic particles are dispersed in a colloidal form. Further, for example, materials such as fatty acids, alcohols, aliphatic amides, esters, sulfurized fats and oils, or derivatives of these materials (hereinafter sometimes referred to as lubricating materials) are in the range of 0.1% by mass to 3% by mass. It may be further added to the liquid. Since these lubricating materials are polar substances with high adsorptivity to the metal surface and have a high lubricating ability, the lubricity of the magnetic fluid 7 can be improved.

 FIG. 3 is a diagram showing the magnetic pole distribution of the sleeve 3 in a cross section taken along the line ΠΙ_ΠΙ in FIG. 1. FIG. 4 is a diagram showing the magnetic pole distribution in the developed view of the sleeve 3. Referring to FIGS. 3 and 4, the outer peripheral surface 3b of the sleeve 3 is magnetized so that a plurality of magnetic poles are arranged in the circumferential direction (lateral direction in FIG. 4). The magnetic poles adjacent in the circumferential direction are different from each other, and each of the plurality of magnetic poles extends in the axial direction (vertical direction in FIG. 4).

[0038] It should be noted that the magnetized state of the sleeve 3 is free, and in addition to the magnetized state shown in Figs. 3 and 4, for example, the magnetized state as shown in Fig. 5 or Fig. 6 may be used. Referring to Figure 5, the sleeve 3 is magnetized so that a plurality of magnetic poles are arranged in the axial direction. The magnetic poles adjacent in the axial direction are different from each other, and each of the plurality of magnetic poles extends in the circumferential direction. Referring to FIG. 6, the sleeve 3 is magnetized so that a plurality of magnetic poles are arranged in the axial direction and the circumferential direction. The magnetic poles adjacent to each other in the axial direction and the circumferential direction are different from each other.

 [0039] Referring to Figs. 2 (a) and (b), the axially upper end surface 4a and the lower surface 5a are opposed to each other (the portions indicated by SI and S2 in Fig. 2 (a)). The parts facing each other on the lower end surface 4c and the upper surface 6a in the axial direction (indicated by S3 and S4 in FIG. 2 (b)) are tetrafluoroethylene resin, polyacetal, polyamide, phenol resin. , Polyethylene, polyimide, polyethylene sulfide, and at least one material selected from the group consisting of polyetheretherketone (hereinafter also referred to as a low friction material). Not only the portions indicated by S1 to S4, but also the entire outer ring sleeve 4, the entire thrust plate 5, or the entire flange portion 6 may be made of the above material.

 [0040] No magnetic fluid bearing is formed between the outer ring sleeve 4 and the thrust plate 5 and between the outer ring sleeve 4 and the flange portion 6. For this reason, the lubricity between the axial upper end surface 4a of the outer ring sleeve 4 and the lower surface 5a of the thrust plate 5 and the lubricity between the axial lower end surface 4c of the outer ring sleeve 4 and the upper surface 6a of the flange portion 6 are It is ensured not by the magnetic force of the magnetic fluid 7 but by the oiliness of the magnetic fluid 7. That is, the plain bearing constituted by the outer ring sleeve 4 and the thrust plate 5 and the slide bearing constituted by the outer ring sleeve 4 and the flange portion 6 operate under boundary lubrication conditions. Under boundary lubrication conditions, solid contact between the shaft and outer ring occurs, and friction tends to increase. Therefore, in the present embodiment, the friction of solid contact is reduced by using the low friction material for each of S 1 to S 4 where solid contact occurs.

[0041] According to the bearing unit 1 in the present embodiment, the outer ring sleeve 4 and the thrust plate 5 constitute a sliding bearing, and the outer ring sleeve 4 and the flange portion 6 constitute a sliding bearing. Thrust load is supported. The axial direction of the outer ring sleeve 4 The lubricity between the improved end surface 4a and the lower surface 5a of the thrust plate 5 and the lubricity between the lower end surface 4c in the axial direction of the outer ring sleeve 4 and the upper surface 6a of the flange 6 are Secured by oiliness. The low friction material has a low friction coefficient and excellent wear resistance. By including the low friction material in the portion indicated by SI in the flat plate 5 and the portion indicated by S4 in the flange portion 6, the friction coefficient of the portion indicated by S1 and the portion indicated by S4 can be reduced. The “friction (friction force)” of the thrust bearing is expressed by the product of the “friction coefficient” of the surface constituting the thrust bearing and the “load” applied to the thrust bearing. Therefore, the friction of the thrust bearing portion can be reduced by reducing the friction coefficient of the portion indicated by S1 and the portion indicated by S4. As a result, bearing torque is reduced and bearing performance is improved.

 [0042] Further, since the sliding bearing has a smaller number of parts than the rolling bearing, the components of the sliding bearing are easier to force than the components of the rolling bearing. There is no need to embed a magnet in thrust plate 5, Therefore, the thrust plate 5 can be thinned, and thereby downsizing can be achieved.

 [0043] For example, when the bearing unit 1 is used as a fulcrum bearing of a swing arm device in an HDD device, the thrust load received by the bearing unit 1 is about several grams weight, which is the weight of the swing arm. Therefore, it is more important to reduce the friction coefficient of the thrust plate 5 and the flange portion 6 to reduce the friction coefficient of the thrust plate 5 and the flange portion 6 and to reduce the torque property at the time of sliding. For this reason, the thickness of the thrust plate 5 and the flange portion 6 can be specifically reduced to the order of 0.1 mm.

 [0044] In particular, the outer sleeve 4 is made of at least one material selected from the group consisting of tetrafluoroethylene, polyacetal, polyamide, phenol resin, polyethylene, polyimide, polyphenylene sulfide, and polyether ether ketone. When formed, the outer ring sleeve 4 can be lightened, and the load of the outer ring sleeve 4 applied to the flange portion 6 or the thrust plate 5 can be reduced. As a result, the force S can be reduced to reduce the friction of the thrust bearing.

 Note that the bearing unit 1 is suitable for use as a fulcrum bearing of a swing arm device in an HDD device, for example.

FIG. 7 is a cross-sectional view illustrating a case where the bearing unit according to the first embodiment of the present invention is used as a fulcrum bearing of a swing arm device in an HDD device. Referring to FIG. 7, swing arm device 21 includes swing arm 22 and bearing unit 1. bearing The fixed shaft 2 is fixed to the base 23 by screwing screws 27 into the hollow portion of the fixed shaft 2 of the unit 1 and the base 23. A swingarm 22 is attached to the outer ring sleeve 4 of the bearing unit 1. As a result, the swing arm 22 can swing about the screw 27 as a fulcrum. A magnetic head 24 for recording information on the magnetic disk 25 is provided at the left end of the swing arm 22 in the figure, and the magnetic head 24 faces the information recording surface of the magnetic disk 25. A rotor 26a of the head positioning mechanism 26 is provided at the right end of the swing arm 22 in the figure. The base 23 is provided with a stator 26b of a head positioning mechanism 26 so as to face the rotor 26a. The rotor 26a is constituted by a coil, and the stator 26b is constituted by a permanent magnet. In the swing arm device 21, a current is passed through the rotor 26a to generate a force for swinging the swing arm 22, and the magnetic head is moved to a desired position.

 [0047] In the present embodiment, the force shown in the case where the portion indicated by S1 to S4 is made of the low friction material In the present invention, at least S1 or S2 of the portions indicated by S1 to S4 And S3 or S4 may be made of the low friction material.

 [0048] In the present embodiment, the force fixed shaft 2, the outer ring sleeve 4, the outer shaft sleeve 4, and the thrust plate 5 shown in the case where each material is made of a non-magnetic material. And there are no particular restrictions on the material of the thrust plate 5. However, when the sleeve 3 is a magnet, the outer ring sleeve 4 is a non-magnetic material.

 Further, in the present embodiment, a plurality of magnetic poles are provided on the inner peripheral surface of the outer ring instead of the outer peripheral surface of the force shaft shown in the case where a plurality of magnetic poles are formed on the outer peripheral surface (outer peripheral surface 3b) of the shaft. It may be formed. Specifically, the sleeve 3 is made of a non-magnetic material, the outer ring sleeve 4 is made of a magnetic material, and the inner peripheral surface 4b of the outer ring sleeve 4 is in a magnetized state shown in FIGS. 3 to 6, for example. Also good.

 [0050] (Embodiment 2)

Referring to FIG. 1 and FIG. 2 (a) and (b), in the bearing unit 1 of the present embodiment, instead of the portion indicated by S:! ˜S4 made of the low friction material, S1˜ The part indicated by S4 is subjected to surface treatment or surface modification. By applying surface treatment or surface modification, the surface component is different from the base material. Specifically, For example, MoS film, WS film, C film, Ag film, Ni—P—B film, CN film, B—C—N film, and

At least one type of film selected from the group that also has CrN film strength (hereinafter sometimes referred to as a low friction film) is formed, or A1 is unevenly distributed. In addition, surface treatment or surface modification treatment other than the formation of the low friction film may be performed. Further, the entire outer ring sleeve 4, the entire thrust plate 5, or the entire surface of the flange portion 6 may be subjected to surface treatment or surface modification treatment.

[0051] Among the low-friction films, in particular, the MoS film can be formed at room temperature by shot processing with a low friction coefficient, so that the thermal deformation of the material is small. In addition, since the friction coefficient can be reduced even when the film thickness is small, the size change due to film formation is small. C film includes DLC (Diamond Like Carbon) film. A DLC film is an amorphous (non-crystalline) carbon film that has properties similar to diamond, mainly composed of carbon and hydrogen. The Ni_P_B film is formed by plating, for example. The B—C—N film is formed by, for example, a vacuum film forming technique. For A1, the base material of the parts shown by S1 to S4 is A1, and the surface of A1 is made finely porous by anodic oxidation, and the surface is impregnated with a solid lubricant such as PTFE (tetrafluoroethylene). The ability to unevenly distribute A1 S

[0052] The other configuration of the bearing unit 1 is substantially the same as the configuration of the bearing unit of the first embodiment shown in Figs. 1 to 6, and therefore, the same members are denoted by the same reference numerals. The explanation will not be repeated.

 [0053] According to the bearing unit 1 in the present embodiment, it is possible to obtain the same effect S as in the first embodiment. That is, by applying surface treatment or surface modification treatment to the portions indicated by S1 to S4 in the thrust plate 5, the friction coefficients of the portions indicated by S1 to S4 can be reduced. As a result, the friction of the thrust bearing portion can be reduced. In addition, since the plain bearing has fewer parts than the rolling bearing, the components of the sliding bearing are easier to force than the components of the rolling bearing. There is no need to put a magnet on the thrust plate 5, Therefore, the thrust plate 5 can be made thin, and thereby the force S can be reduced.

In the present embodiment, the force shown in the case where the surface treatment or the surface modification treatment is performed on the portion indicated by S1 to S4. In the present invention, the portion indicated by S1 to S4 is small. At least SI or S2, and S3 or S4 may be subjected to surface treatment or surface modification treatment.

 [0055] Further, the low friction material in the first embodiment and the surface treatment or the surface modification treatment in the second embodiment are combined, and for example, the low friction film is formed in a portion indicated by S1 and a portion indicated by S4 The surface treatment or surface modification treatment may be performed on the formed portion indicated by S2 and the portion indicated by S3.

 [Embodiment 3]

 Referring to FIG. 1 and FIG. 2 (a) and (b), in the bearing unit 1 of the present embodiment, instead of the portion indicated by S :! to S4 being made of the low friction material, the outer ring sleeve 4 has a density smaller than that of iron. The outer ring sleeve 4 is made of, for example, a light metal such as alkali metal, beryllium, magnesium, or aluminum, or an alloy of these light metals. The outer ring sleeve 4 is preferably made of an aluminum alloy or a magnesium alloy.

 [0057] Further, in addition, at least S1 or S2, and S3 or S4 of the portions indicated by S1 to S4 may be formed of the low friction material described in the first embodiment. Alternatively, at least SI or S2, and S3 or S4 in the portions indicated by Sl to S4 may be subjected to the surface treatment or the surface modification treatment described in the second embodiment.

 Since the configuration of the other bearing unit 1 is substantially the same as the configuration of the bearing unit of the first embodiment shown in FIGS. 1 to 6, the same members are denoted by the same reference numerals. The explanation will not be repeated.

 [0059] According to the bearing unit 1 in the present embodiment, it is possible to obtain the same effect as in the first embodiment. In other words, by forming the outer ring sleeve 4 at a density lower than that of iron, the outer ring sleeve 4 can be reduced in weight and the load on the outer ring sleeve 4 applied to the flange portion 6 or the thrust plate 5 can be reduced. can do. As described in the first embodiment, the “friction (friction force)” of the thrust bearing portion is determined by the product of the “friction coefficient” of the surface constituting the thrust bearing portion and the “load” applied to the thrust bearing portion. expressed. For this reason, the friction of the thrust bearing portion can be reduced by reducing the load on the outer ring sleeve 4.

[0060] Further, since the sliding bearing has a smaller number of parts than the rolling bearing, the components of the sliding bearing The product is easier to force than the components of a rolling bearing. There is no need to embed a magnet in the thrust plate 5. Therefore, the thrust plate 5 can be thinned, and thereby downsizing can be achieved.

 [0061] In particular, since light metal has a density lower than that of iron, the outer ring sleeve 4 can be reduced in weight by forming the outer ring sleeve 4 from light metal, and the flange portion 6 or thrust can be achieved. The load on the outer ring applied to the plate 5 can be reduced.

 [0062] The inventors of the present application measured a load acting on a thrust bearing portion such as an outer ring sleeve 'arm in a bearing unit used for supporting a swing arm of a 2.5 inch type HDD. As a result, when the outer ring sleeve was made of polyethylene, the load acting on the thrust bearing portion was reduced by about 30% compared to when the outer ring sleeve was made of iron. In addition, when the outer ring sleeve was made of aluminum, the load acting on the thrust bearing was reduced by about 20% compared to when the outer ring sleeve was made of iron.

 [0063] The embodiments disclosed above are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the scope of the claims not in the above embodiments, and is intended to include any modifications and variations within the scope and meaning equivalent to the scope of the claims.

 Industrial applicability

[0064] The present invention is particularly suitable for a bearing unit used for a swing fulcrum of a magnetic head portion of a hard disk of a computer.

Claims

The scope of the claims  [1] Cylindrical shaft (3),  An outer ring (4) disposed on the outer periphery of the shaft and having an inner peripheral surface (4b) facing the outer peripheral surface (3b) of the shaft;  A plate (5, 6) having a main surface (5a, 6a) fixed to the shaft and extending in the radial direction of the shaft and facing the axial end surface (4a, 4c) of the outer ring;  An oily magnetic fluid (7) injected into the gap between the outer peripheral surface of the shaft and the inner peripheral surface of the outer ring and the gap between the axial end surface of the outer ring and the main surface of the plate,  A plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring, and face the main surface (SI, S4) of the plate or the main surface of the plate facing the axial end surface of the outer ring. And at least one selected from the group consisting of tetrafluoroethylene resin, polyacetanol, polyamide, phenol resin, polyethylene, polyimide, polyphenylene sulfide, and polyetheretherketone. A bearing unit (1) characterized by containing the above materials. [2] The outer ring (4) is made of at least one material selected from the group consisting of tetrafluoroethylene, polyacetal, polyamide, phenol resin, polyethylene, polyimide, polyphenylene sulfide, and polyetheretherketone. The bearing unit (1) according to claim 1, characterized by the above. [3] The magnetic fluid (7) contains at least one material selected from the group consisting of fatty acids, alcohols, aliphatic amides, esters, and sulfurized oils, or contains a derivative of the materials. The bearing unit (1) according to claim 1, characterized in that ) o  [4] The bearing unit (1) according to claim 1, wherein a swing arm (22) having a magnetic head for recording information is attached to the outer ring (4).  [5] Cylindrical shaft (3),  An outer ring (4) disposed on the outer periphery of the shaft and having an inner peripheral surface (4b) facing the outer peripheral surface (3b) of the shaft; The shaft is fixed to the shaft and extends in the radial direction of the shaft, and the axial end surface of the outer ring ( A plate (5, 6) having a main surface (5a, 6a) facing 4a, 4c);  An oily magnetic fluid (7) injected into the gap between the outer peripheral surface of the shaft and the inner peripheral surface of the outer ring and the gap between the axial end surface of the outer ring and the main surface of the plate,  A plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring, and the main surface (Sl, S4) of the plate or the main surface of the plate facing the axial end surface of the outer ring A bearing unit (1) characterized in that a surface treatment or a surface modification treatment is applied to the axial end faces (S2, S3) of the opposed outer rings. [6] The magnetic fluid (7) contains at least one material selected from the group consisting of fatty acids, alcohols, aliphatic amides, esters, and sulfurized oils, or a derivative of the material. The bearing unit (1) according to claim 5, characterized in that 7. The bearing unit (1) according to claim 5, wherein a swing arm (22) having a magnetic head for recording information is attached to the outer ring (4).  [8] Cylindrical shaft (3),  An outer ring (4) disposed on the outer periphery of the shaft and having an inner peripheral surface (4b) facing the outer peripheral surface (3b) of the shaft;  A plate (5, 6) having a main surface (5a, 6a) fixed to the shaft and extending in the radial direction of the shaft and facing the axial end surface (4a, 4c) of the outer ring;  An oily magnetic fluid injected into the gap between the outer peripheral surface of the shaft and the inner peripheral surface of the outer ring and the gap between the axial end surface of the outer ring and the main surface of the plate,  A plurality of magnetic poles are formed on the outer peripheral surface of the shaft or the inner peripheral surface of the outer ring, and the outer ring has a density smaller than the density of iron. [9] The outer ring (4) is made of a light metal or a light metal alloy. 9. Bearing unit (1) according to item 8. [10] The bearing unit (1) according to claim 8, wherein the outer ring (4) is made of resin. [11] The magnetic fluid (7) includes fatty acids, alcohols, aliphatic amides, esters, and sulfurized oils. 9. The bearing unit (1) according to claim 8, characterized in that it comprises at least one material selected from the group consisting of fats or a derivative of said material.  The bearing unit (1) according to claim 8, characterized in that a swing arm (22) having a magnetic head for recording information is attached to the outer ring (4).