JP2002276666A - Dynamic pressure type bearing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-torque dynamic pressure type bearing unit having high durability and shock resistance. SOLUTION: A radial bearing surface 10a having a plurality of dynamic pressure grooves is formed in the internal circumference of a bearing member 7 composed of oil containing sintered metal, and a shaft member 2 comprising a shaft part 2a and a flange part 2b is inserted in the internal circumference of the bearing member 7. The shaft member 2 is formed of ceramic formed with a hollow hole formed in its surface. A bearing clearance is formed between both end faces of the flange part and its opposed surfaces 11a and 11b, so as to provide a thrust bearing part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing unit for supporting a shaft member in a non-contact manner by a dynamic pressure of a lubricating fluid generated in a bearing gap, and is particularly suitable for supporting a spindle motor of a spindle motor for information equipment. Bearing unit. "Spindle motor for information equipment" here
Include, for example, CD-R / RW, DVD-ROM / RAM
Optical disk such as MO, magneto-optical disk such as MO, HDD
For example, a spindle motor for driving a magnetic disk such as a laser beam printer (LBP) or a polygon scanner motor of a copying machine is included.

[0002]

2. Description of the Related Art Conventionally, rolling bearings have been generally used as bearings for supporting spindles of various types of information equipment spindle motors. In recent years, however, excellent features such as high rotational accuracy, low cost, and low noise have been adopted. The use of a hydrodynamic bearing provided with is considered or actually used. In a bearing unit using this dynamic pressure type bearing, a radial bearing gap is formed between the inner periphery of a bearing member made of oil-impregnated sintered metal and the outer periphery of a shaft member (spindle), and a flange is formed at the shaft end of the shaft member. A thrust bearing gap is formed between both end faces of the flange part and the faces facing the flange part, and when the shaft member rotates, fluid dynamic pressure is applied to both bearing gaps by dynamic pressure grooves facing both bearing gaps. It is known that the shaft member and the bearing member are generated in a non-contact manner in the radial direction and the thrust direction.

Conventionally, as a shaft member of this dynamic pressure type bearing unit, stainless steel excellent in machinability and rich in corrosion resistance and wear resistance is often used as a material.

[0004]

However, in recent years,
The following problems have been pointed out with respect to the above-described hydrodynamic bearing unit.

[0005] When the bearing unit is stopped, the shaft member on the rotating side does not float, so that the shaft member is in metallic contact with the member on the stationary side. Therefore, at the time of starting and stopping, the convex portion of the shaft member scrapes the surface of the stationary side member to wear, and further, the wear powder at this time may accelerate the wear, which is a factor to reduce the durability life of the bearing. I have.

[0006] When an impact load is applied to the shaft member, the shaft member may collide violently with the stationary member to damage the partner.

In the case of stainless steel, the shaft member becomes heavy, so that the torque increases. Therefore, it is difficult to further increase the rotation speed of the bearing unit.

In view of the above problems, an object of the present invention is to provide a dynamic pressure type bearing unit having high durability and impact resistance and low torque.

[0009]

In order to achieve the above object,
In the present invention, a bearing member, a shaft member disposed on the inner periphery of the bearing member, and a minute bearing gap facing the shaft member are provided, and the dynamic pressure action of the dynamic pressure groove is performed when the shaft member and the bearing member rotate relative to each other. In a dynamic pressure type bearing unit that generates a dynamic pressure of a lubricating fluid in a bearing gap to support a shaft member in a non-contact manner, the shaft member is formed of ceramic.

Since ceramic has a high hardness and a very small surface roughness, even if the ceramic shaft member is in sliding contact with the bearing member, the bearing member hardly wears. Therefore, the durability of the bearing unit can be significantly improved. Further, since the ceramic is lighter than the stainless steel, the impact load applied to the bearing member even when an impact acts on the shaft member is small, so that the impact resistance of the bearing unit can be improved. Further, because of its light weight, torque can be reduced, and the bearing unit can be rotated at a higher speed.

By forming a lubricating fluid reservoir having a plurality of recesses on the surface of the shaft member, a sufficient amount of oil can be retained in the bearing gap even at the time of startup when a sufficient lubricating film is not formed. Therefore, the wear of the bearing member can be reduced, and the life of the bearing can be improved. In order to realize this function, the fluid reservoir is formed in a region including at least a portion facing the bearing gap on the surface of the shaft member.

Since ceramic is formed by sintering,
After sintering, pores can be left on the surface. The concave portion of the oil reservoir can be formed by the hole opened on the surface of the shaft member.

If the pore density on the surface of the shaft member is too large, it becomes difficult to reduce the surface roughness. Therefore, it is desirable that the pore density in the reservoir is set to 10% or less.

In the dynamic pressure bearing unit according to the present invention, a radial bearing gap which is a gap in the radial direction is provided as the bearing gap. This makes it possible to support the shaft member in a non-contact manner in the radial direction by the fluid dynamic pressure generated in the radial bearing gap. The radial bearing gap is formed between the outer periphery of the shaft member and the inner periphery of the bearing member. In this case, the radial bearing surface having the plurality of dynamic pressure grooves can be formed, for example, on the inner periphery of the bearing member.

[0015] If the surface of the shaft member that comes into contact with the bearing member at the time of starting and stopping is made to have a surface roughness of Ra 0.03 µm or less excluding the holes opened on the surface, the sliding between the shaft member and the bearing member is achieved. At the time of contact, almost no wear occurs on the bearing member. Here, "excluding holes opened in the surface" means that the surface roughness Ra is calculated excluding the holes.

Further, by providing a thrust bearing gap which is a gap in the axial direction as the bearing gap, the shaft member can be supported in a non-contact manner in the thrust direction by the fluid dynamic pressure generated in the thrust bearing gap. Specifically, a flange portion is provided on the shaft member, between the end surface of the bearing member and one end surface of the flange portion opposed thereto, and between the other end surface of the flange portion and the end surface of the thrust support member opposed thereto. Thrust bearing gaps are formed between them.

In this case, a portion of the surface of the shaft member which comes into contact with the bearing member and the thrust support member at the time of starting and stopping is changed to Ra 0.03 μm except for a hole opened on the surface.
With the following surface roughness, even when the shaft member is in sliding contact with the bearing member and the thrust support member, almost no wear occurs on the bearing member and the thrust support member. Here, “excluding the holes opened on the surface” means that the surface roughness Ra is calculated excluding the holes as described above.

If the bearing member is formed of an oil-impregnated sintered metal, the lubricant oozes out of the surface of the bearing member during the operation of the bearing due to thermal expansion and pressure of the oil, so that ample lubricant is supplied to the bearing gap. can do. When a radial bearing surface is formed on the inner periphery of a bearing member made of an oil-impregnated sintered metal, the radial bearing surface can be formed at low cost by compression molding or the like.

As the ceramic material of the shaft member,
Any of alumina, silicon nitride, silicon carbide, zirconia, and sialon can be used.

The spindle motor for information equipment provided with the above-described dynamic pressure type bearing unit has high durability and impact resistance, so that the product life can be extended and further high-speed rotation is possible. There is a feature that there is.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
A description will be given based on FIG.

FIG. 1 illustrates an HDD spindle motor as an example of a spindle motor for information equipment. The spindle motor includes a bearing unit U rotatably supporting the shaft member 2 and a disk hub 3 mounted on the shaft member 2 and holding one or more magnetic disks (not shown).
And a motor stator 4 and a motor rotor 5 opposed to each other via a radial gap. Stator 4
Are mounted on the outer circumference of the bearing unit U, and the rotor 5 is mounted on the inner circumference of the disk hub 3. When the stator 4 is energized, the rotor 5 rotates by the exciting force between the stator 4 and the rotor 5, and the disk hub 3 and the shaft member 2 rotate.

The bearing unit U includes a substantially bottomed cylindrical outer member 1, a bearing member 7 fixed to the inner periphery of the outer member 1, and a bearing unit 7 disposed inside the bearing member 7. The main member is a shaft member 2 composed of a flange portion 2b projecting radially.

The shaft member 2 is formed by integrally forming the shaft portion 2a and the flange portion 2b as one part, and in the present invention, is formed of ceramics such as alumina, silicon nitride, silicon carbide, zirconia, and sialon. In addition to integrally molding the shaft member 2,
The shaft portion 2a and the flange portion 2b may be formed of ceramic as separate components, and the two components may be joined and integrated by a known joining method such as an electron beam welding method or a laser beam welding method.

In the embodiment shown in FIG. 1, the outer member 1 is
Cylindrical housing 19 with bearing member 7 mounted on the inner circumference
And a disk-shaped thrust support member 8 opposed to the flange portion 2b of the shaft member 2. Between one end of the bearing member 7 and the thrust support member 8, there is a gap obtained by adding the width of the thrust bearing gaps Ct1 and Ct2 (described later) (about 10 to 20 μm) to the thickness of the flange portion 2b. The flange portion 2b of the shaft member 2 is accommodated in the gap, and the opening of the housing 19 is closed by the thrust support member 8. The other end of the bearing member 7 is a seal washer 1
Sealed by a seal member such as 4. In the following description, one end side of the outer member 1 (the side sealed by the thrust support member 8: lower side in the drawing) is referred to as a “sealing side”, and the opposite side (upper side in the drawing) is referred to as a “non-sealing side”. .

The bearing member 7 is formed of an oil-impregnated sintered metal obtained by impregnating a sintered metal with lubricating oil or lubricating grease so that oil is retained in pores. As the sintered metal, for example, a copper-based material, an iron-based material, or a material containing both of them as a main component can be used. Preferably, the sintered metal is formed using 20 to 95% of copper.

The inner peripheral surface of the bearing member 7 has a plurality of dynamic pressure grooves 1.
3 (see FIG. 3) is formed. Thereby, when the shaft member 2 and the outer member 1 are relatively rotated (in this embodiment, when the shaft member 2 is rotated), the radial bearing gap Cr between the radial bearing surface 10a and the outer peripheral surface of the shaft portion 2a is filled. The lubricating fluid (oil in the present embodiment) generates a dynamic pressure, and the dynamic pressure action causes the shaft portion 2a and the bearing member 7 to move.
Are kept in a non-contact state in the radial direction. The shape of the dynamic pressure groove 13 on the radial bearing surface 10a is arbitrary, and for example, a herringbone type (see FIG. 3), a spiral type, a step type, a multi-arc type, or the like can be used.
Note that the width of the radial bearing gap Cr in FIG. 1 is exaggerated and is actually several μm (the same applies to the widths of thrust bearing gaps Ct1 and Ct2 described later).

Both end surfaces of the flange portion 2b and surfaces 7a and 15 of the bearing member 7 and the thrust support member 8 opposed thereto.
Between the thrust bearing clearance Ct which is an axial clearance.
1, Ct2. Specifically, one thrust bearing gap Ct1 is formed between the non-sealing side end face (upper end face) of the flange portion 2b and the end face 7a of the bearing member 7 opposed thereto, and the other thrust bearing gap Ct2 is formed. , Formed between the sealing-side end surface (lower end surface) of the flange portion 2b and the non-sealing-side end surface 15 of the thrust support member 8 opposed thereto.

Thrust bearing surfaces 11a and 11b having dynamic pressure grooves (not shown) for generating dynamic pressure are formed on the end surface 7a of the bearing member 7 and the end surface 15 of the thrust support member 8, respectively. Thus, at the time of the rotation, a dynamic pressure of the lubricating fluid (oil) filled in the thrust bearing gaps Ct1 and Ct2 is generated, and the thrust bearing portion 11 that supports the shaft member 2 on both sides in the thrust direction in a non-contact manner is configured. Thrust bearing surface 11
The shapes of the dynamic pressure grooves a and 11b are arbitrary, and for example, a known herringbone type or spiral type can be selected and used. The thrust bearing surfaces 11a and 11b are
It can also be formed on the end face of the flange portion 2b.

As described above, in the present invention, the material of the shaft member 2 is changed from conventional stainless steel to ceramic. Since the ceramic material has a high hardness and a very small surface roughness, even when the ceramic material slides on the bearing member 7 and the thrust support member 8 on the stationary side, they hardly wear. Therefore, the durability of the bearing unit can be significantly improved. Specifically, in the case of conventional stainless steel, the surface roughness was about Ra 0.1 to 0.15, but in the case of ceramic, Ra was obtained by barrel polishing or the like.
0.03 or less (desirably, Ra0.01 or more, Ra0.
03 or less) can be easily obtained, and a remarkable effect can be obtained in improving the durability of the bearing member 7 and the thrust support member 8 (the surface roughness of the shaft member 2 is calculated when calculating the surface roughness). Vacancies that are open at the same time). The surface roughness in this range is not necessarily required for the entire surface of the shaft member 2, and is at least a portion in sliding contact with the bearing member 7 and the thrust support member 8, specifically, both end surfaces of the flange portion 2 b and the outer periphery of the shaft portion 2 a It suffices if all or part of the surface is obtained.

Further, since the ceramic is lighter than the stainless steel, the impact load applied to the bearing member 7 and the thrust support member 8 when the shaft member 2 receives an impact is small. Impact resistance can be improved. Further, because of its light weight, torque can be reduced, and the bearing unit can be rotated at a higher speed.

By the way, in the ceramic manufacturing process, holes (holes opened on the surface) can be intentionally left on the surface of the shaft member 2 after sintering. A plurality of recesses are formed on the surface of the shaft member 2 by these holes, and an oil reservoir is formed by the plurality of recesses. Therefore, even when the lubricating oil film is not sufficiently formed, the radial bearing gap Cr or Ample oil can be supplied to the thrust bearing gaps Ct1 and Ct2, thereby improving the bearing life.
The reservoir formed of a plurality of holes may be formed on the entire surface of the shaft member 2. However, from the viewpoint of functioning as an oil reservoir, at least the radial bearing of the outer peripheral surface of the shaft 2 a and both end surfaces of the flange 2 b. It suffices if it is formed in a region including a portion facing the gap Cr and the thrust bearing gaps Ct1 and Ct2. In this case, if the density of the holes (the ratio of the opening area of the holes per unit area) is too large, it becomes difficult to set the surface roughness Ra within the above range. %
It is desirable to set the following.

FIG. 2 shows another embodiment of a dynamic pressure type bearing unit in which a bearing member 7 made of an oil-impregnated sintered metal is fixed to an inner periphery of a housing 19 integrally formed in a bottomed cylindrical shape. It is. In this case, the bottom of the housing 19 becomes the thrust support member 8 facing the flange 2b. The non-sealing side of the bearing member 7 is sealed by a seal member such as a seal washer 14.

In the bearing unit U, the same effect as described above can be obtained by forming the shaft member 2 of ceramic.

FIG. 3 shows an embodiment of a dynamic pressure bearing unit having a contact type thrust bearing. That is, the thrust load is pivotally supported by sliding the spherical portion 2c formed at the shaft end of the shaft member 2 against the non-sealing-side end surface 15 of the thrust support member 8 provided at the bottom of the housing 19. In this case, the outer member 1 includes a housing 19 in which the bearing member 7 made of oil-impregnated sintered metal is provided,
It is composed of a thrust support member 8 mounted on the bottom.

Also in this bearing unit U, the same effect as described above can be obtained by forming the shaft member 2 from ceramic. In the bearing unit U, the shaft member 2 comes into contact with the bearing member 7 at the time of starting and stopping, but the contact portion of the shaft member 2 with the bearing member 7 (more desirably, the contact with the bearing member 7 and the thrust support member 8). If the surface roughness is reduced to Ra 0.03 μm or less except for holes formed in the surface of the bearing member 7, the durability of the bearing member 7 (or the bearing member 7 and the thrust support member 8) can be improved.

Using a bearing unit of the same type as in FIG. 2, a wear resistance test (start-up) between a conventional product having a stainless steel shaft member 2 and a product of the present invention having a ceramic shaft member 2 was carried out.
Stop test) and a torque test. The wear resistance test measures the amount of wear on the housing bottom surface 15 after repeating the cycle with a start time of one cycle of 4 seconds and a stop time of 2 seconds. The torque test measures the current consumption of the motor when the motor is rotated at a specified number of revolutions. The lubricating oil viscosity was 10 mm ² / s, and the test temperature was 20 ° C. The bearing unit to be tested has the following specifications.

Bearing member 7: A radial bearing surface 10a is formed on the inner periphery and a thrust bearing surface 11a is formed on the end surface 7a of a sintered metal mainly composed of Cu. The inner diameter is φ3, the outer diameter is φ6, and the axial length is 4 mm.

Shaft member 2: SUS4 as stainless steel
20J2 (Hv500) was used, and alumina (Hv1800) was used as a ceramic, and both were ground.
For the shaft member made of ceramic, the pore density on the surface is 2 to 2.
10%, and the surface roughness is R, excluding vacancies opened on the surface.
a was set to 0.03 or less. In any case, the outer dimension of the shaft portion 2a is φ
3. The outer dimensions of the flange 2b are φ6, the total length in the axial direction is 8mm, and the axial length of the flange 2b is 1mm.

Housing 19: Thrust bearing surface 11b was formed on the bottom surface (end surface 15 of thrust support member 8).

Seal washer 14: FIG. 4 shows the results of the wear resistance test, and FIG. 5 shows the results of the torque test. In both figures, ● represents a stainless steel shaft member and ○ represents a ceramic shaft member. As is clear from FIG. 4, the wear amount of the ceramic shaft member is much smaller than that of the stainless steel shaft member (the test was stopped at 650 × 10 ³ times for the stainless steel shaft member), and is considered to have high durability. Also, as is apparent from FIG. 5, the current value of the ceramic shaft member is smaller than that of the stainless steel shaft member, and is considered to be low in torque.

[0042]

According to the present invention, since the shaft member is formed of ceramic having a low surface roughness, the amount of wear of the bearing member and the thrust support member that slides on the shaft member at the time of starting and stopping can be suppressed, and the dynamic pressure type bearing can be suppressed. The durability life of the unit can be improved. Further, since the ceramic is lightweight, it is possible to improve the impact resistance of the bearing unit and reduce the torque.

[Brief description of the drawings]

FIG. 1 is a sectional view of a dynamic pressure bearing unit according to the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the present invention.

FIG. 4A is a table summarizing the measurement results of the abrasion resistance test, and FIG. 4B is a graph in which the measurement results are plotted.

5A is a table summarizing the measurement results of the torque test, and FIG. 5B is a graph in which the measurement results are plotted.

[Explanation of symbols]

 Reference Signs List 1 outer member 2 shaft member 2a shaft portion 2b flange portion 7 bearing member 8 thrust support member 10a radial bearing surface 11a thrust bearing surface 11b thrust bearing surface Cr radial bearing gap Ct1 thrust bearing gap Ct2 thrust bearing gap U dynamic pressure type bearing unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H02K 21/22 H02K 21/22 M (72) Inventor Atsushi Hirade 3066 Oyumida, Ogata, Ogata, Kuwana-shi, Mie Prefecture F term in NTN Corporation (reference) DD03 GG03 GG07 GG09 GG10 GG12 GG15 KK10 5H621 JK13 JK17 JK19

Claims (13)

[Claims] A bearing member, a shaft member disposed on an inner periphery of the bearing member, and a minute bearing gap facing the shaft member, wherein a dynamic pressure action of the dynamic pressure groove is generated when the shaft member and the bearing member rotate relative to each other. A dynamic pressure bearing unit for generating a dynamic pressure of a lubricating fluid in a bearing gap to support a shaft member in a non-contact manner, wherein the shaft member is formed of ceramic. 2. The dynamic pressure bearing unit according to claim 1, wherein a lubricating fluid reservoir having a plurality of recesses is formed in a region of the surface of the shaft member including at least a portion facing the bearing gap. 3. The dynamic pressure bearing unit according to claim 2, wherein the recess is formed by a hole opened on the surface of the shaft member. 4. The dynamic pressure type bearing unit according to claim 3, wherein a pore density of the reservoir is set to 10% or less. 5. The dynamic pressure bearing unit according to claim 1, wherein the bearing gap has a radial bearing gap which is a gap in a radial direction. 6. The dynamic pressure bearing unit according to claim 5, wherein a radial bearing surface having a plurality of dynamic pressure grooves is formed on an inner periphery of the bearing member. 7. The shaft member according to claim 5, wherein a portion of the surface of the shaft member, which is in contact with the bearing member at the time of starting and stopping, has a surface roughness of Ra 0.03 μm or less excluding a hole opened on the surface. Dynamic pressure bearing unit. 8. The dynamic pressure bearing unit according to claim 5, further comprising a thrust bearing gap which is an axial gap as the bearing gap. 9. A flange member is provided on a shaft member, and a flange portion is provided between an end surface of a bearing member and one end surface of a flange portion opposed thereto, and between an end surface of the flange portion and an end surface of a thrust support member opposed thereto. 9. The dynamic pressure type bearing unit according to claim 8, wherein a thrust bearing gap is formed between the bearings. 10. A portion of the surface of the shaft member, which is in contact with the bearing member and the thrust support member at the time of starting and stopping, has a surface roughness of Ra 0.03 μm or less excluding a hole opened on the surface. The dynamic pressure bearing unit as described. 11. The dynamic pressure type bearing unit according to claim 1, wherein the bearing member is formed of an oil-impregnated sintered metal. 12. The ceramic, wherein the ceramic is alumina, silicon nitride,
The dynamic pressure bearing unit according to any one of claims 1 to 11, wherein the unit is any one of silicon carbide, zirconia, and sialon. 13. A spindle motor for information equipment comprising the dynamic pressure bearing unit according to claim 1. Description: