JP4731852B2 - Hydrodynamic bearing unit - Google Patents

Description

  The present invention relates to a hydrodynamic bearing unit having excellent characteristics such as high rotational accuracy, high-speed stability, and high durability, and in particular, spindle motors in various information devices such as optical discs (CD-R / RW, DVD-ROM / RAM). ), Disk drive motors installed in magneto-optical disks (MO), magnetic disks (HDD), etc., or spindle motors such as scanner motors installed in copiers, laser beam printers (LBP), barcode readers, etc. Is suitable.

FIG. 7 illustrates a disk drive motor of an optical disk device (for DVD-ROM device) as a kind of spindle motor of information equipment. This motor includes a bearing unit U that rotatably supports a shaft member 100, a support member 4 (turn table) that is attached to an upper end of the shaft member 100 and supports, for example, an optical disk 3 that is a drive target, a stator 5, and a rotor. 6 and a motor unit M having six. When the stator 5 is energized, the rotor 6 is rotated by an exciting force generated between the stator 5 and the support member 4 and the shaft member 100 integrated with the rotor 6 are rotated.

As this type of spindle motor bearing unit U, the use of a hydrodynamic bearing having excellent characteristics such as high rotational accuracy, low cost, and low noise has been studied or actually used. The dynamic pressure type bearing unit U shown in FIG. 7 is formed by radially forming radial bearing surfaces having a plurality of inclined dynamic pressure grooves on the inner periphery of a cylindrical bearing member 200 at two locations in the axial direction. Fluid dynamic pressure is generated in a minute operating gap (radial bearing gap) formed between the outer peripheral surface and both radial bearing surfaces, and the shaft member 100 is supported rotatably in a non-contact manner. The bearing member 200 is fixed to the inner periphery of a housing 300 having a bottomed cylindrical shape ( Patent Document 1 ).

The dynamic pressure type bearing unit of FIG. 7 pivotally supports a thrust load by causing the spherical portion at the tip of the shaft member 100 to slide in contact with the thrust support 400 at the bottom of the housing. On the other hand, in applications where severe rotational accuracy (NRRO) is required in both radial and thrust directions, and lateral and reverse directions are assumed as the driving posture, the radial and thrust loads are not contacted by the hydrodynamic bearing. There are bearing units to support. In this type of bearing unit, as shown in FIG. 8 , a disc-shaped flange portion 160 is provided at an end portion of the shaft member 100, and thrust bearing surfaces having dynamic pressure grooves respectively opposed to both end surfaces of the flange portion 160 are provided. In many cases, the shaft member is supported in a non-contact manner in both thrust directions by generating fluid dynamic pressure in a thrust bearing gap between the thrust bearing surface and both end surfaces of the flange portion 160.
JP 11-311253 A

  By the way, in the various dynamic pressure type bearing units described above, the width of the radial bearing gap must be constant. This is because the rigidity of the rotating shaft member 100 is theoretically inversely proportional to the cube of the operating gap. Therefore, if the widths of the radial bearing gaps at two locations are different, the bearing rigidity is increased on the side where the gap is larger. This is because the balance between the bearing rigidity of the two members is significantly reduced and the shaft member is swung around to deteriorate the rotational accuracy. From the same viewpoint, it is desirable to make the width of the thrust bearing gap constant.

  At present, the following two factors are considered to make the gap width of the radial bearing gap and the thrust bearing gap uneven.

First, the first factor is that the spherical portion of the shaft member 100 enters the radial bearing gap. That is, in the bearing unit in which the thrust load is pivotally supported by the thrust support portion as shown in FIG. 11, the end portion of the shaft member 100 is formed in a spherical shape, so that the spherical portion 130 at the shaft end is formed as shown in FIG. there is sometimes partially enters the opposing area of the radial bearing surface 510. For this reason, the width of the radial bearing gap Cr increases on the shaft end side, and the gap width becomes non-uniform.

  As a second factor, it is mentioned that the pussies provided in the shaft member enter the radial bearing gap or the thrust bearing gap.

In general, in a bearing unit in which a thrust load is also supported by a dynamic pressure type bearing, as shown in FIG. 8 , a Nusumi portion 170 is provided at a corner portion between the flange portion 160 and the cylindrical shaft portion 150 when the shaft member 100 is processed. . If there is no Nusumi portion 170, as shown in FIG. 9 , the corner portion has an arc shape due to the R shape of the tip of the cutting tool 600 during turning, and this arc portion interferes with the corner portion of the bearing member 200 during assembly.

Even if the pussies are provided, as shown in FIG. 10 , when the stubs 170 are provided only on the flange part 160 side, the shaft part 150 at the corner part is affected by the tip R of the grindstone 700 during grinding of the shaft part 150. Causes radial sagging on the side. To prevent these adverse effects, it is necessary to provide both grinding undercut portion 170 shaft portion 150 side and the flange portion 160 side as shown in FIG. 11.

In this case, at the time of assembly, the Nusumi portion 170 faces the chamfered portion 210 of the bearing member 200 as shown in FIG. 12 , but the radial bearing surface 510 or the thrust bearing surface 430 starts immediately from the edge of the chamfered portion 210. In this case, the Nusumi portion 170 partially faces both bearing surfaces 510 and 430. As a result, the radial width of the radial bearing gap Cr and the thrust bearing gap Ct are not uniform.

  In view of the above-described problems, an object of the present invention is to avoid a decrease in bearing rigidity due to a non-uniform gap width of a thrust bearing gap and to improve the rotation accuracy of a bearing unit.

In order to achieve the above object, in the present invention, a shaft member having a shaft portion and a flange portion, a bearing member disposed on the outer periphery of the shaft member, and an end surface of the bearing member facing the end surface of the flange portion are formed. And a thrust bearing gap formed between the thrust bearing surface and the end surface of the flange portion, and the shaft member is supported in the thrust direction by the fluid dynamic pressure generated in the thrust bearing gap. In the dynamic pressure type bearing unit, a corner portion between the shaft portion and the flange portion of the shaft member is formed with a numi portion, and a chamfered portion is provided on the inner periphery of the end of the bearing member facing the numi portion, and each thrust bearing surface A region sandwiched between both ends of the dynamic pressure groove in the radial direction is defined as a dynamic pressure groove region, the radial dimension of the Nusumi part is B, the chamfer dimension of the bearing member end is C, and the dynamic pressure groove between the chamfered part and the thrust bearing surface Dimension between area As 2, by satisfying the relation of B <C + L2, arranged grinding undercut portion outside facing region of the dynamic groove region of the thrust bearing surface, the thrust bearing gap, and the constant dynamic pressure groove region of at least the thrust bearing surface .

Thereby, the bearing rigidity of a thrust bearing part can be improved and the rotation accuracy of a shaft member can be improved. Note that the "hydrodynamic groove area of the thrust bearing surface" means a region between the radial ends of the respective dynamic pressure grooves formed in the thrust bearing surface (T in FIG. 2 (A) (B)) .

In the above configuration, by forming the bearing member with the oil-impregnated sintered metal, it is possible to accurately perform dynamic pressure groove processing of the radial bearing surface at low cost by compression molding or the like.

If the spindle motor for information equipment having a hydrodynamic bearing unit of the above configuration, it reduced the whirling of the shaft member (spindle), it is possible to increase the recording and reproducing accuracy of information, can be further speeding It becomes.

  According to the present invention, the dynamic pressure effect in these bearing gaps is enhanced as compared with the conventional product in which the width of the thrust bearing gap is not uniform. Therefore, bearing rigidity can be improved and the rotation accuracy of a shaft member can be improved.

Hereinafter, the embodiments of the present invention will be described with reference to FIGS. 1 to 6.

  FIG. 1 is a sectional view of a hydrodynamic bearing unit according to the present invention. As illustrated, the bearing unit includes a shaft member 10, a bearing member 20 that supports the shaft member 10, a housing 30 that fixes the bearing member 20 to the inner periphery, and a radial bearing that supports the shaft member 10 in the radial direction. The main components are the portions 50a and 50b and the thrust bearing portion 40 (40a and 40b) that supports the shaft member 10 in the thrust direction.

The housing 30 has a bottomed cylindrical shape that is open at one end and closed at the other end, and is fixed to the base 7 (see FIG. 7 ) with the opening at one end facing upward. The opening side (upper side in the drawing) is referred to as “opening side”, and the opposite side in the axial direction (lower side in the drawing) is referred to as the non-opening side. The other end side of the housing 30 is sealed by the bottom 31. The bottom portion 31 can be integrally formed with the cylindrical portion 32 as shown, or can be formed as a separate member and fitted and fixed to the opening of the cylindrical portion 32 of the housing 30 (see FIG. 7 ).

Thrust bearing portions 40 a and 40 b that support the shaft member 10 in the thrust direction are provided on the side opposite to the opening inside the housing 30 . The thrust bearing portions 40a and 40b are configured by dynamic pressure type bearings.

The shaft member 10 includes a cylindrical shaft portion 15 and flange portions 16 projecting in the radial direction at the end opposite to the opening of the shaft portion 15. Thrust bearing portions 40 a, 40b is configured. The shaft member 10 can be manufactured by press-fitting a flange 16 as a separate member into the shaft 15 or by integrally forming the shaft 15 and the flange 16 by forging or the like.

  The bearing member 20 is formed in a cylindrical shape with an oil-containing sintered metal obtained by impregnating a sintered metal with lubricating oil or lubricating grease and retaining oil in the pores, and is fixed to the inner periphery of the housing 30 by press-fitting or bonding. ing. As the sintered metal, for example, a copper-based or 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.

Two radial bearing surfaces 51 a and 51 b constituting the radial bearing portions 50 a and 50 b are formed on the inner periphery of the bearing member 20. In each of the bearing surfaces 51a and 51b, a plurality of dynamic pressure grooves 52 inclined with respect to the axial direction are formed in a herringbone shape, for example. It is sufficient that the dynamic pressure grooves 52 are formed so as to be inclined with respect to the axial direction, and the dynamic pressure grooves can be arranged in a shape other than the herringbone type, for example, a spiral type as long as this condition is satisfied. The groove depth of the dynamic pressure groove 52 is suitably about 2 to 10 μm, and is formed to a depth of 3 μm, for example. On the outer periphery of the bearing member 20, one or more grooves ( not shown) are formed along the axial direction .

  One end opening of the housing is sealed with a ring-shaped seal member 61. The seal member 61 is formed of, for example, a resin material (polyamide or the like) or a metal material (including a sintered metal), and is fixed to one end opening of the housing 30 by means such as adhesion or press fitting. The seal member 61 is a non-contact seal in which a minute seal gap is interposed between the inner peripheral surface of the shaft member 10 and the outer peripheral surface of the shaft member 10, and prevents oil leakage from the inside of the housing 30 due to a capillary phenomenon in the seal gap. .

  Minute radial bearing gaps Cra and Crb are formed between the radial bearing surfaces 51a and 51b and the outer peripheral surface of the shaft member 10, respectively. When the shaft member 10 rotates, oil (lubricating oil or base oil of lubricating grease) inside the bearing member 20 oozes out from the surface of the bearing member 20 due to generation of pressure accompanying rotation and thermal expansion of oil due to temperature rise. The dynamic pressure groove 52 is pulled into the bearing gaps Cra and Crb. The oil drawn into the radial bearing gaps Cra and Crb forms a lubricating oil film on the bearing surfaces 51a and 51b to support the shaft member 10 in a non-contact manner. When positive pressure is generated on the radial bearing surfaces 51a and 51b, the surface of the bearing surfaces 51a and 51b has pores (open portions: portions where the pores of the porous body structure are opened on the outer surface). Circulates into the bearing member 20, but since new oil continues to be pushed into the bearing surfaces 51a and 51b one after another, the oil film force and rigidity are maintained in a high state. In this case, since a stable oil film is continuously formed, high rotation accuracy is obtained, and shaft runout, NRRO, scanner motor jitter, and the like are reduced. Further, since the shaft member 10 and the bearing member 20 rotate without contact, the noise is low and the cost is low.

The flange portion 16 of the shaft member 10 is disposed between the bottom portion 31 of the housing 30 and the end surface 21 on the side opposite to the opening of the bearing member 20. Thrust bearing surfaces 43a and 43b each having a plurality of dynamic pressure grooves are formed on the end surface 35 of the housing bottom 31 and the end surface 21 of the bearing member 20 facing the flange portion 16, respectively. As shown in FIG. 2 (A) (B), both thrust bearing surfaces 43a, 43b of the dynamic pressure grooves 44 have a sloped portion with respect to the radial imaginary line drawn on the end face 35,21, FIG. The illustrated example illustrates a herringbone type, that is, a substantially V-shaped dynamic pressure groove 44 having a bent portion at a substantially central portion in the radial direction.

  Between the thrust bearing surfaces 43a and 43b having the dynamic pressure grooves 44 and both end surfaces of the flange portion 16 facing the thrust bearing surfaces 43a and 43b, minute thrust bearing gaps Cta and Ctb that generate fluid dynamic pressure by the rotation of the shaft member 10 are provided. Each is formed.

The corners between the shaft portion 15 and the flange portion 16 of the shaft member 10, as shown in FIG. 3, grinding undercut portion 17 is formed over the entire circumference. This Nusumi part 17 extends over the outer peripheral surface of the shaft part 15 and the opening side end face of the flange part 16, and is formed by cutting or forging, for example.

The axial portion 18 formed on the outer periphery of the shaft portion 15 on the opening side of the end portion of the flange portion 16 in the Nusumi portion 17 except for the region facing the dynamic pressure groove region of the non-opening radial bearing surface 51a. The radial direction portion 19 formed on the end surface of the flange portion 16 on the outer diameter side of the shaft portion 15 and on the outer diameter side of the shaft portion 15 is moved on the thrust bearing surface 43b formed on the end surface 21 of the bearing member 20. Except for the area facing the pressure groove area, it is formed on the inner diameter side. Here, the "dynamic pressure generating groove region of the thrust bearing surface" refers to a region T sandwiched radially across each dynamic pressure generating grooves of the thrust bearing surface (see FIG. 2 (A) (B)) .

  From the above, the respective dynamic pressure groove regions S and T of the radial bearing surface 51a on the opposite side and the thrust bearing surface 43b on the side of the opening do not face the Nusumi portion 17, and thereby the radial bearing gap Cra and the opening on the opposite side. The width of the side thrust bearing gap Ctb is made uniform in the entire region (at least the dynamic pressure groove region). Therefore, the bearing rigidity of the two radial bearing portions 50a and 50b can be balanced to reduce the swing of the shaft member 10, and the rigidity of the opening-side thrust bearing portion 40b can be improved. From the above, it is possible to improve the rotation accuracy of the shaft member 10.

Specifically, as shown in FIG. 4 , the axial dimension (the axial dimension of the axial part 18) of the mussel part 17 is A, and the radial dimension (the radial dimension of the radiating part 19) of the sumi part 17. B, C is a chamfer dimension (radial and axial dimensions) of the inner periphery of the end of the bearing member 20, L1 is a distance between the chamfered portion 22 and the dynamic pressure groove region of the radial bearing surface 51a, and the chamfered portion 22 The distance between the thrust bearing surface 43b and the dynamic pressure groove region is L2,

A <C + L1 and B <C + L2
It must be designed to satisfy this relationship.

In FIG. 4 , the radial bearing surface 51a on the side opposite to the opening and the thrust bearing surface 43b (each dynamic pressure groove region) on the opening side are separated from the chamfered portion 22 of the bearing member 20 by distances L1 and L2, respectively. Generally, it is desirable that the spans of the radial bearing surfaces 51a and 51b be as large as possible in order to suppress contact, and the thrust bearing surface 43b is also advantageous in terms of securing rigidity if the radial width is increased. Therefore, this distance is sometimes the L1, L2 is 0 (see FIG. 3).

5 and 6, a bearing unit A which employs the present invention the structure shown in FIGS. 3 and 4, to face grinding undercut portion 17 is partially radial bearing surface 510 and the thrust bearing surface 430 as shown in FIG. 12 It is the result of having measured the floating start rotation speed and shaft runout of shaft member 10 about bearing unit B designed as mentioned above. From FIG. 5, in the case of the bearing unit A, it rotates in a completely non-contact state at around 200 rpm regardless of the orientation of the motor such as normal placement, horizontal placement, and inverted, while the bearing unit B exceeds 800 rpm in any direction. It became clear that it did not surface until. Further, it is clear from FIG. 6 that the shaft runout is clearly inferior to the bearing unit B.

It is sectional drawing of a dynamic pressure type bearing unit . It is a top view of a thrust bearing surface. It is sectional drawing of a dynamic pressure type bearing unit, and its principal part expanded sectional view. It is an enlarged sectional view of the bearing unit shown in FIG. It is a figure which shows the measurement result of a floating rotation speed. It is a figure which shows the measurement result of an axial runout. It is sectional drawing of the spindle motor for information equipment (optical disk apparatus). It is the side view and principal part expanded sectional view of a shaft member. It is sectional drawing which shows the processing condition (turning) of a shaft member. It is sectional drawing which shows the processing condition (grinding) of a shaft member. It is sectional drawing which shows the processing condition (grinding) of a shaft member. It is a principal part expanded sectional view of the conventional dynamic pressure type bearing unit.

DESCRIPTION OF SYMBOLS 10 Shaft member 20 Bearing member 21 End surface 22 Chamfering part 30 Housing 31 Bottom part 40a Thrust bearing part (dynamic pressure type bearing)
40b Thrust bearing (dynamic pressure bearing)
43a Thrust bearing surface (opposite side)
43b Thrust bearing surface (opening side)
44 Dynamic pressure groove 50a Radial bearing (opposite side)
50b Radial bearing (opening side)
51a Radial bearing surface (opposite side)
51b Radial bearing surface (opening side)
52 Dynamic pressure groove Cra Radial bearing clearance (Non-opening side)
Crb radial bearing clearance (opening side)
Cta Thrust bearing clearance (opposite side)
Ctb Thrust bearing clearance (opening side)
S Dynamic pressure groove area (Radial bearing surface)
T Dynamic pressure groove area (Thrust bearing surface)

Claims (3)

A shaft member including a shaft portion and a flange portion; a bearing member disposed on an outer periphery of the shaft member; a thrust bearing surface having a plurality of dynamic pressure grooves formed on an end surface of the bearing member facing the end surface of the flange portion; In a dynamic pressure type bearing unit comprising a thrust bearing gap formed between the thrust bearing surface and the end face of the flange portion, and supporting the shaft member in the thrust direction with the fluid dynamic pressure generated in the thrust bearing gap,
A corner portion is formed at the corner between the shaft portion and the flange portion of the shaft member, and a chamfered portion is provided on the inner periphery of the end portion of the bearing member facing this portion, so that each dynamic pressure groove on the thrust bearing surface has a radial direction. The region sandwiched between both ends is defined as a dynamic pressure groove region, the radial dimension of the Nusumi part is B, the chamfer dimension of the bearing member end is C, and the dimension between the chamfered part and the dynamic pressure groove area of the thrust bearing surface is As L2,
B <C + L2
By satisfying the relationship, the dynamic that place the grinding undercut portion outside facing region of the dynamic groove region of the thrust bearing surface, the thrust bearing gap, characterized in that the constant dynamic pressure groove region of at least the thrust bearing surface Pressure bearing unit. The hydrodynamic bearing unit according to claim 1, wherein the bearing member is formed of oil-impregnated sintered metal. A spindle motor for information equipment, comprising the hydrodynamic bearing unit according to claim 1.

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