JP3943381B2 - Bearing device and motor equipped with the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bearing device and a motor including the same.
[0002]
[Prior art]
As a bearing device for a spindle motor used in a recording disk drive device such as a hard disk drive device, an oil-impregnated bearing in which a porous body made of sintered metal is impregnated with a lubricant, or a bearing formed between a shaft and a sleeve 2. Description of the Related Art A bearing device using a hydrodynamic bearing or the like that holds a lubricant in a gap and supports a shaft by utilizing a hydrodynamic action generated in the lubricant by a hydrodynamic groove during rotation is known.
[0003]
In any of the above-mentioned bearing devices, the shaft can be supported in a non-contact state by an oil film of a lubricant, so that vibration and noise characteristics are higher than those of rolling bearing devices that have been widely used so far as spindle motor bearing devices. This has the advantage of being excellent.
[0004]
As lubricants used in oil-impregnated bearings and hydrodynamic bearings, hydrocarbon-based and ester-based lubricants are known, but hydrocarbon-based lubricants have a higher evaporation rate than ester-based lubricants. The freezing point is also high. For example, at an evaporation rate with substantially the same viscosity, hydrocarbon-based lubricants are more than several times higher than ester-based lubricants, and the freezing point is often higher than room temperature. Therefore, in a spindle motor bearing device for a recording disk drive device used in a relatively wide temperature range, an ester-based lubricant, particularly DOS (2-ethylhexyl sebacate) is used from the balance of viscosity, evaporation rate and freezing point. It is suitable as a lubricant for oil-impregnated bearings and dynamic pressure bearings.
[0005]
[Problems to be solved by the invention]
However, ester-based lubricants have high reactivity because they contain ester groups, and are particularly reactive with lead. On the other hand, in bearing devices using oil-impregnated bearings and hydrodynamic bearings, since they are relatively hard and have high workability, free-cutting brass is used as a material for members (housings, sleeves, etc.) constituting the bearing devices. In many cases, lead such as C3604 is added to free-cutting brass to improve machinability, and free-cutting brass containing such lead and ester-based lubricant are in contact at high temperatures. Then, lead elutes in the lubricant to form a product such as a metal soap, and there is a concern that the lubricant is denatured and viscosity is increased. In addition, since the ester group easily absorbs moisture, it absorbs moisture in the air under a high-temperature atmosphere, and there is a concern that the lubricant is denatured and viscosity is increased due to moisture and lead.
[0006]
In addition, copper-based materials containing lead are likely to generate particles (fine powder) due to dezincification corrosion and are used in recording disk drive devices such as hard disks that require high cleanliness from the viewpoint of preventing head crashes. For example, it is necessary to take another means for preventing the generation of particles, for example, by performing a surface treatment. Therefore, it is difficult to reduce the number of processing steps, and the yield is not good.
[0007]
An object of the present invention is to provide a bearing device and a motor including the same, using an ester-based lubricant having a good balance between evaporation rate and freezing point, and preventing deterioration and deterioration of the lubricant due to elution of lead. The purpose is to maintain the bearing function for a long time.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a bearing device including an oil-impregnated bearing configured by impregnating a porous body made of sintered metal with a lubricant, and a housing for housing the oil-impregnated bearing, wherein the housing is lead. Provided is a structure formed of less brass and the lubricant is an ester-based lubricant.
[0009]
The “oil-impregnated bearing” here includes both a so-called perfect bearing having no dynamic pressure groove on the bearing surface and a dynamic pressure bearing having a dynamic pressure groove on the bearing surface.
[0010]
In this specification, “lead-free brass” refers to brass (or brass alloy) whose lead content is regulated to a minute amount, or brass (or brass alloy) that does not contain lead. Preferably, the lead content is regulated to 0.2% or less. Examples of “lead-free brass” include “Keepalloy” manufactured by KITZ (lead content 0.2% or less), “Bz3” “EES-PF” manufactured by Sanetsu Metals Co., Ltd. (both lead content 0.1%) The following may be used: “Eco Brass” (brass alloy not containing lead) manufactured by Sanpo Shindoh Co., Ltd. These lead-less brasses have good processability (cutability, forgeability, castability) and have a low content of lead, which is an environmentally hazardous element, or they do not contain lead. High recyclability. Further, it is suitable for use in a recording disk drive device such as a hard disk or the like that is unlikely to generate particles due to dezincification corrosion and requires high cleanliness. Furthermore, even if an ester-based lubricant having a good balance between evaporation rate and freezing point is used, there is no modification and deterioration of the lubricant due to elution of lead, and a stable bearing function is maintained over a long period of time.
[0011]
In order to solve the above problems, the present invention is configured by impregnating a porous member made of a sintered member and a shaft member with a lubricant, and the shaft member is rotated by the dynamic pressure action of the lubricant generated in the bearing gap. In a bearing device including an oil-impregnated bearing that is freely contactlessly supported and a housing that has an opening at one end and accommodates the oil-impregnated bearing, the housing is formed of leadless brass, and the lubricant is an ester lubricant. Provide configuration.
[0012]
The “oil-impregnated bearing” here is a hydrodynamic bearing having a hydrodynamic groove on the bearing surface. Alternatively, the “oil-impregnated bearing” may be a perfect circle bearing, and the dynamic pressure groove may be formed on the outer peripheral surface of the shaft member facing the bearing gap. When the seal member is disposed in the opening of the housing, it is preferable that the seal member is further formed of leadless brass.
[0013]
In order to solve the above problems, the present invention provides a bearing device that supports the relative rotation of a stationary member and a rotating member in a non-contact manner by the dynamic pressure action of a lubricant interposed in a bearing gap formed between the two members. At least one of the stationary member and the rotating member is formed of leadless brass, and the lubricant is an ester-based lubricant. In this configuration, the dynamic pressure groove is provided on the surface of the stationary member or the surface of the rotating member facing the bearing gap.
[0014]
The motor including the bearing device having the above configuration is excellent in terms of vibration and noise characteristics, and can maintain a stable function for a long period of time.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0016]
FIG. 1 shows an example of the configuration of a spindle motor for information equipment incorporating a hydrodynamic bearing device 1 according to this embodiment. The spindle motor is used in a recording disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports the shaft member 2 in a non-contact manner, a disk hub 3 mounted on the shaft member 2, and a radial direction. The motor stator 4 and the motor rotor 5 are provided to face each other through the gap. The stator 4 is attached to the outer periphery of the casing 6, and the rotor 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the casing 6. The disk hub 3 holds one or more disks D such as magnetic disks. When the stator 4 is energized, the rotor 5 is rotated by the exciting force between the stator 4 and the rotor 5, whereby the disk hub 3 and the shaft member 2 are rotated together.
[0017]
FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a bottomed cylindrical housing 7 having an opening 7 a at one end, a cylindrical oil-impregnated bearing 8 fixed to the inner peripheral surface of the housing 7, a shaft member 2, and an opening of the housing 7. The seal member 10 disposed in the portion 7a is a main component.
[0018]
The housing 7 is formed by cutting or forging from a material such as lead-free brass, for example, “Eco Brass” (brass alloy not containing lead) manufactured by Sanho Shindoh Co., Ltd., and has cylindrical side portions 7b and bottom portions 7c. It consists of. A dynamic pressure groove 7c2 having a shape shown in FIG. 3B is formed in a region of the inner bottom surface 7c1 of the bottom portion 7c which becomes a thrust bearing surface. In this embodiment, the side portion 7b and the bottom portion 7c of the housing 7 are integrated, but both may be separate structures. In that case, the bottom lid member constituting the bottom portion 7c is fixed to the other end opening of the cylindrical member constituting the side portion 7b by means such as adhesion or caulking. Further, at least one of the cylindrical member constituting the side portion 7b and the bottom lid member constituting the bottom portion 7c, preferably both are formed of leadless brass.
[0019]
The oil-impregnated bearing 8 is formed of, for example, a sintered metal porous body mainly composed of copper, and the internal pores are impregnated with lubricating oil or lubricating grease. Dynamic pressure grooves 8a1 and 8a2 each having the shape shown in FIG. 2 are formed in two regions R1 and R2 on the inner peripheral surface 8a of the oil-impregnated bearing 8 at upper and lower portions serving as radial bearing surfaces. The regions R1 and R2 are separated from each other in the axial direction with a region R3 having no dynamic pressure groove interposed therebetween. Further, a dynamic pressure groove 8b1 having a shape shown in FIG. 3A is formed in a region of the lower end surface 8b of the oil-impregnated bearing 8 to be a thrust bearing surface.
[0020]
The dynamic pressure groove shape of the radial bearing surface and the thrust bearing surface can be arbitrarily selected, and any of the known herringbone shape, spiral shape, step shape, multi-arc shape, etc. is selected, or these are appropriately selected. Can be used in combination. 2 and 3 illustrate herringbone-shaped dynamic pressure grooves 8a1, 8a2, 8b1, and 7c2 as an example.
[0021]
The shaft member 2 is formed of a metal material such as stainless steel (SUS420J2), for example, and includes a shaft portion 2a and a flange portion 2b provided integrally or separately with the shaft portion 2a. In a partial region of the outer peripheral surface 2a1 of the shaft portion 2a, a thinning groove 2a2 having a slightly smaller diameter than the other region is provided. Further, in the center region of the lower end surface 2b2 of the flange portion 2b, there is provided a shading portion 2b3 that is slightly recessed with respect to the other regions.
[0022]
The shaft portion 2 a of the shaft member 2 is inserted into the inner peripheral surface 8 a of the oil-impregnated bearing 8, and the flange portion 2 b is accommodated in a space portion between the lower end surface 8 b of the oil-impregnated bearing 8 and the bottom surface 7 c 1 of the housing 7. Predetermined radial bearing gaps are provided between the outer peripheral surface 2a1 of the shaft portion 2a and the regions R1 and R2 of the inner peripheral surface 8a of the oil-impregnated bearing 8, and the upper end surface 2b1 of the flange portion 2b and the oil-impregnated bearing 8 are respectively provided. A predetermined thrust bearing gap is provided between the lower end surface 8 b and between the lower end surface 2 b 2 of the flange portion 2 b and the bottom surface 7 c 1 of the housing 7. The thin groove 2a2 of the shaft portion 2a faces the region R3 of the inner peripheral surface 8a of the oil-impregnated bearing 8 via a gap larger than the radial bearing gap, and the thin portion 2b3 of the flange portion 2b is formed on the inner bottom surface 7c1 of the housing 7. It faces the central region (region where the dynamic pressure groove 7c2 is not formed) via a gap larger than the thrust bearing gap.
[0023]
The seal member 10 is formed in a ring shape from lead-free brass, for example, “Eco Brass” (brass alloy not containing lead) manufactured by Sanho Shindoh Co., Ltd., and is press-fitted and bonded to the inner peripheral surface of the opening 7a of the housing 7 It is fixed by such means. In this embodiment, the inner peripheral surface of the seal member 10 is formed in a cylindrical shape, and the lower end surface of the seal member 10 is in contact with the upper end surface of the oil-impregnated bearing 8. The inner peripheral surface of the seal member 10 is opposed to the outer peripheral surface 2a1 of the shaft portion 2a via a predetermined gap (larger than the radial bearing gap), and thereby, a seal space having a predetermined volume therebetween. Is formed.
[0024]
A lubricant such as bis (2-ethylhexyl) sebacate, 2-ethylhexyl sebagate (DOS) or adipic acid is contained in the internal space of the housing 7 (including the pores inside the oil-impregnated bearing 8) sealed with the seal member 10. An ester-based lubricating oil composed of bis (2-ethylhexyl), 2-ethylhexyl adipate (DOZ), or a mixture thereof is filled, and the oil level of the lubricating oil is within the above-described seal space. The volume of the seal space is set to be larger than the volume change amount of the lubricating oil filled in the internal space of the housing 7 due to the temperature change within the operating temperature range.
[0025]
When the shaft member 2 rotates, a dynamic pressure action is generated in the radial bearing gap, and the shaft portion 2a of the shaft member 2 is supported in a non-contact manner so as to be rotatable in the radial direction by an oil film of lubricating oil formed in the radial bearing gap. Is done. Thereby, the radial bearing part which non-contact-supports the shaft member 2 rotatably in a radial direction is comprised. At the same time, a dynamic pressure action is generated in the thrust bearing gap, and the flange portion 2b of the shaft member 2 is supported in a non-contact manner so as to be rotatable in the thrust direction by an oil film of lubricating oil formed in the thrust bearing gap. Thereby, the thrust bearing part which non-contact-supports the shaft member 2 rotatably in the thrust direction is configured.
[0026]
In the hydrodynamic bearing device 1 of this embodiment, the handling 7 and the seal member 10 are made of leadless brass. Therefore, the hydrodynamic bearing device 1 is friendly to people and the environment, and has high recyclability. Moreover, the processability of the handling 7 and the seal member 10 is also good. Furthermore, the interior space of the housing 7 is filled with ester-based lubricant, but even under high-temperature and high-humidity atmospheres, there is no degradation and deterioration of the lubricant due to elution of lead, and a stable bearing function is maintained for a long time. Is done.
[0027]
【Example】
A lead-containing brass material and a lead-less brass material are respectively immersed in an ester-based lubricating oil for supplying oil to a hydrodynamic bearing device, and left for 2000 hours under a high temperature and high humidity condition of a temperature of 80 ° C. and a humidity of 90%. The kinematic viscosity of the lubricating oil was measured. The initial kinematic viscosity of the lubricating oil is 13.18 (cSt) at 40 ° C.
[0028]
As a result of the measurement, the kinematic viscosity (cSt) at 40 ° C. of the lubricating oil (after standing for 2000 hours) is 14.63 when the lead-containing brass material is immersed, and 12.97 when the lead-less brass material is immersed. Met. Thus, when the lead-containing brass material was immersed, the viscosity of the lubricating oil was increased, but when the lead-less brass material was immersed, almost no viscosity change was observed.
[0029]
【The invention's effect】
According to the present invention, the members constituting the bearing device, particularly the housing, and further the seal member, etc. are made of leadless brass, so that the environmental load can be reduced and even when an ester-based lubricant is used. In addition, there is no degradation and deterioration of the lubricating oil due to elution of lead, and a stable bearing function is maintained over a long period of time. Further, since the generation of particles due to dezincification hardly occurs, it is also suitable for use in a recording disk drive device such as a hard disk that requires high cleanliness.
[0030]
The motor of the present invention including the bearing device having the above-described configuration is excellent in terms of vibration and noise characteristics, and maintains a stable function over a long period of time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a spindle motor having a hydrodynamic bearing device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a hydrodynamic bearing device according to an embodiment of the present invention.
FIG. 3 is a view showing a thrust bearing surface.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dynamic pressure type bearing apparatus 2 Shaft member 7 Housing 7a Opening part 8 Oil impregnated bearing 10 Seal member

Claims (5)

In a bearing device comprising an oil-impregnated bearing configured by impregnating a porous body made of sintered metal with a lubricant, and a housing for housing the oil-impregnated bearing,
The housing is formed of leadless brass;
A bearing device, wherein the lubricant is an ester lubricant. A shaft member, an oil-impregnated bearing configured by impregnating a porous body made of sintered metal with a lubricant, and rotatably supporting the shaft member in a non-contact manner by the dynamic pressure action of the lubricant generated in the bearing gap, and at one end In a bearing device having an opening and a housing that houses the oil-impregnated bearing,
The housing is formed of leadless brass;
A bearing device, wherein the lubricant is an ester lubricant. The bearing device according to claim 1, further comprising a seal member disposed in an opening of the housing, wherein the seal member is formed of lead-free brass. In the bearing device that supports the relative rotation between the stationary member and the rotating member in a non-contact manner by the dynamic pressure action of the lubricant interposed in the bearing gap formed between the two members,
At least one of the stationary member and the rotating member is formed of leadless brass,
A bearing device, wherein the lubricant is an ester lubricant. A motor comprising the bearing device according to claim 1.

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