JP2005048951A - Dynamic pressure type bearing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid degradation in rigidity of a bearing due to nonuniformity in width of clearance of a thrust bearing, and improve a rotating precision of a bearing unit. <P>SOLUTION: A dynamic pressure type bearing unit is provided with an axis member having an axis part and a flange part, a thrust bearing surface which is arranged and faced to an end surface of the flange part and has a plurality of dynamic pressure grooves, and the clearance of the thrust bearing formed between the thrust bearing surface and the end surface of the flange part. The axis member of the dynamic pressure type bearing unit is supported in the thrust direction by fluid dynamic pressure generated at the clearance of the thrust bearing. Then the clearance of the thrust bearing is controlled at a certain level at least in the area of a dynamic pressure groove on the thrust bearing surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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. 11 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. A dynamic pressure type bearing unit U shown in FIG. 11 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 (see Japanese Patent Application Laid-Open No. 10-42361, etc .: Patent Document 1).

The dynamic pressure type bearing unit shown in FIG. 11 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 the 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. 13, a disc-shaped flange portion 160 is provided at the end of the shaft member 100, and thrust bearing surfaces having dynamic pressure grooves are provided opposite to both end surfaces of the flange portion 160. 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.
Japanese Patent Laid-Open No. 10-42361

  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. May partially enter the area where the radial bearing surface 510 does not face. 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 supported by a dynamic pressure type bearing, as shown in FIG. 13, 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. 14, 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. 15, 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. In order to prevent these harmful effects, it is necessary to provide the Nusumi part 170 on both the shaft part 150 side and the flange part 160 side as shown in FIG.

  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. 17, 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 including a shaft portion and a flange portion, a thrust bearing surface disposed facing an end surface of the flange portion and having a plurality of dynamic pressure grooves, a thrust bearing surface and a flange And a thrust bearing gap formed between the end face of the portion, and a hydrodynamic bearing unit that supports the shaft member in the thrust direction with fluid dynamic pressure generated in the thrust bearing gap. The dynamic pressure groove area was controlled constantly.

  A crushed portion can be formed at the corner of the shaft portion and the flange portion of the shaft member, and the crushed portion can be disposed outside the region opposite to the dynamic pressure groove region of the thrust bearing surface.

  In this case, the bearing member is arranged on the outer periphery of the shaft member, the radial dimension of the nut portion is B, the chamfer dimension of the end of the bearing member is C, and the gap between the chamfered portion and the dynamic pressure groove region of the thrust bearing surface is between Let L2 be the dimension of

B <C + L2
To satisfy the relationship.

  In the present invention, a shaft member, a radial bearing surface in which a plurality of dynamic pressure grooves facing the outer peripheral surface of the shaft member are formed, and a radial bearing gap formed between the radial bearing surface and the outer peripheral surface of the shaft member In the dynamic pressure type bearing unit that supports the shaft member in the radial direction with the fluid dynamic pressure generated in the radial bearing gap, the radial bearing gap is managed to be constant at least in the dynamic pressure groove region of the radial bearing surface.

  Thereby, the dynamic pressure effect in the radial bearing gap is enhanced as compared with the conventional product in which the width of the radial bearing gap is not uniform. Therefore, the bearing rigidity can be improved, the shaft member can be prevented from swinging and the rotation accuracy of the shaft member can be increased. The “dynamic pressure groove region of the radial bearing surface” means a region (S in FIG. 1 and FIG. 5) sandwiched between axial ends of each dynamic pressure groove formed on the radial bearing surface.

  The radial bearing surface can be formed on the inner periphery of the bearing member disposed on the outer periphery of the shaft member.

  An arbitrary structure can be adopted for the thrust bearing portion that supports the shaft member in the thrust direction. For example, if it has a thrust support part which contacts and supports the edge part of a shaft member, a thrust bearing part can be constituted at low cost with a simple structure.

  In this case, the shaft member is provided with a cylindrical portion and a reduced diameter portion, and the reduced diameter portion formed at the shaft end is brought into sliding contact with the thrust support portion, whereby the shaft member is supported in the thrust direction. At this time, by arranging the reduced diameter portion outside the region opposite to the dynamic pressure groove region of the radial bearing surface, the dynamic pressure groove region can be opposed to the cylindrical portion of the shaft member in the entire axial direction. Can be managed within a certain range.

  The reduced diameter portion can be provided with a spherical portion and a connecting portion that smoothly connects the spherical portion and the cylindrical portion. The shaft member is pivotally supported in the thrust direction by bringing the spherical surface portion into sliding contact with the thrust support portion.

  In this case, the dimension between the end face of the bearing member and the thrust support portion is H, the chamfer dimension at the end of the bearing member is C, the dimension between the chamfered portion and the dynamic pressure groove region of the radial bearing surface is L, the shaft The diameter of the member is d, the spherical portion radius of the shaft member is R, and the radius of the connecting portion of the shaft member is r,

H + C + L> R − [(R−r) ² − (d / 2−r) ² ] ^1/2
If this relationship is satisfied, the dynamic pressure groove region of the radial bearing surface can be opposed to the cylindrical portion of the shaft member in the entire axial direction, and the radial bearing gap can be managed to have a constant width.

  A dynamic pressure type bearing can also be used as the thrust bearing portion. That is, the shaft member is provided with a shaft portion and a flange portion, a thrust bearing surface having a plurality of dynamic pressure grooves facing the end surface of the flange portion is disposed, and the thrust bearing surface and the end surface of the flange portion are disposed between the thrust bearing surface and the end surface of the flange portion. A bearing gap is provided, and the shaft member is supported in the thrust direction by the fluid dynamic pressure generated in the thrust bearing gap.

  In this structure, in consideration of workability when the shaft member is processed, a slack portion is formed at a corner portion between the shaft portion and the flange portion of the shaft member.

  In this case, the radial bearing gap can be managed to have a constant width by forming the numi portion outside the region opposite to the dynamic pressure groove region of the radial bearing surface. As a result, the radial bearing gap can be prevented from becoming non-uniform due to the Nusumi portion facing the dynamic pressure groove region of the radial bearing surface, and the bearing rigidity can be improved and the shaft member can be prevented from swinging.

  Specifically, the relation of A <C + L1 is assumed, where A is the axial dimension of the Nusumi part, C is the chamfer dimension of the bearing member end, and L1 is the dimension between the chamfered part and the dynamic pressure groove region of the radial bearing surface. By satisfying the above, it becomes possible to form a scum portion outside the region opposite to the dynamic pressure groove region of the radial bearing surface.

  Further, like the radial bearing gap, the thrust bearing gap may be managed uniformly in at least the dynamic pressure groove region of 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. The “dynamic pressure groove region of the thrust bearing surface” means a region (T in FIGS. 6A and 6B) sandwiched between both ends of each dynamic pressure groove formed on the thrust bearing surface in the radial direction.

  The width management of the thrust bearing gap can be performed by forming the above-mentioned Nusumi portion outside the region opposite to the dynamic pressure groove region of the thrust bearing surface.

  Specifically, B <C + L2 where B is the radial dimension of the Nusumi part, C is the chamfer dimension of the bearing member end, and L2 is the dimension between the chamfered part and the dynamic pressure groove region of the thrust bearing surface. By satisfy | filling, it becomes possible to form a Nusumi part outside the opposing area | region of a dynamic pressure groove area | region.

  In each of the above configurations, if the bearing member is formed of an oil-impregnated sintered metal, the dynamic pressure groove machining of the radial bearing surface can be performed with low cost and high accuracy by compression molding or the like.

  If it is a spindle motor for information equipment which has a dynamic pressure type bearing unit of each above-mentioned composition, since the touching of a shaft member (spindle) can be made small, the recording / reproducing precision of information can be raised and further speedup is possible. 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, embodiments of the present invention will be described with reference to FIGS.

  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 with one end opened and the other end closed, and is fixed to the base 7 (see FIG. 11) with the opening on 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 formed as a separate member as shown in the drawing and fitted into and fixed to the opening portion of the cylindrical portion 32 of the housing 30, or can be integrally formed with the cylindrical portion 32 (see FIG. 5).

  The shaft member 10 includes a cylindrical portion 11 having the same diameter in the axial direction, and a reduced diameter portion 12 in which the diameter opposite to the opening side is gradually reduced. As shown in an enlarged view in FIG. 2, the reduced diameter portion 12 includes a spherical portion 13 formed at the shaft end and a connecting portion 14 formed in a circular arc shape in cross section. The connecting portion 14 is between the spherical surface portion 13 and the cylindrical portion 11 and smoothly connects both.

  A thrust bearing portion 40 that supports the shaft member 10 in the thrust direction is provided on the side opposite to the opening inside the housing 30. The thrust bearing portion 40 in the illustrated example is configured to contact and support the shaft end of the shaft member 10 with a thrust support portion 41 provided on the housing 30. It is comprised by pivot-supporting with the end surface of the thrust washer 33 with which it attached to.

  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.

  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. One or a plurality of (two in FIG. 1) grooves 23 are formed along the axial direction on the outer periphery of the bearing member 20, and these grooves 23 serve as bearings when the shaft member 10 is inserted into the bearing member 20. The air between the member 20 and the housing bottom 31 is discharged outside the bearing unit, and functions as a ventilation path for allowing the shaft member 10 to be inserted smoothly.

  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 shaft member 10 includes the cylindrical portion 11 and the reduced-diameter portion 12 at the shaft end as described above. However, in the present invention, the shape of the reduced-diameter portion 12, that is, the spherical portion 13 and the connecting portion in this embodiment. The shape of the portion 14 is determined according to the axial distance from the thrust support portion 41 of the dynamic pressure groove region (region S sandwiched between the axial ends of each dynamic pressure groove 52) of the radial bearing surface 51a.

  Specifically, as shown in FIG. 2, the dimension between the end surface 21 on the side opposite to the opening of the bearing member 20 and the thrust support portion 41 is H, and the chamfer dimension on the inner periphery of the end on the side opposite to the opening of the bearing member 20 (axis C), the dimension between the chamfered portion 22 and the dynamic pressure groove region S of the non-opening radial bearing surface 51a, L, the diameter of the cylindrical portion 11 of the shaft member 10, and the spherical surface of the shaft member 10. The radius of the portion 13 is R, and the radius of curvature of the connecting portion 14 of the shaft member 10 is r.

H + C + L> R − [(R−r) ² − (d / 2−r) ² ] ^1/2 (A)
Designed to satisfy the relationship. Here, the left side of the equation (A) defines the axial position of the non-opening radial bearing surface 51a with respect to the thrust support portion 41, and the right side defines the shape of the reduced diameter portion 12 of the shaft member 10.

  If the design satisfies the formula (A), the reduced diameter portion 12 including the spherical surface portion 13 and the connecting portion 14 is located outside the region opposite to the dynamic pressure groove region S of the non-opening radial bearing surface 51a, and the dynamic pressure groove The entire region of the region in the axial direction faces the cylindrical portion 11 of the shaft member 10. Therefore, the radial bearing gap Cra on the non-opening side has a constant width, and the bearing rigidity is balanced by the radial bearing portions 50a and 50b on the non-opening side and the opening side, thereby preventing the shaft member 10 from swinging. .

  In FIG. 2, a gap (length L) is interposed between the chamfered portion 22 and the radial bearing surface 51 a, but the spans of the two radial bearing surfaces 51 a and 51 b cause the shaft member 10 to swing. Since it is desirable to make it as large as possible in order to suppress it, generally, the gap is omitted and L = 0 is often used (see FIG. 3).

  4 shows a bearing unit A in which the reduced diameter portion 12 is disposed outside the dynamic pressure groove region of the non-opening radial bearing surface 51a, as in FIGS. 1 and 2, and in the opposite region of the dynamic pressure groove region. The result of having performed the start-and-stop durability test about the bearing unit B (refer FIG. 12) which has arrange | positioned the diameter reduction part 12 in FIG. From the figure, in the case of the bearing unit A, there is almost no fluctuation in the shaft runout up to 300,000 cycles, but in the case of the bearing unit B, the shaft runout is large from the beginning, and the shaft runout suddenly increases in 50,000 cycles. It is understood that 100,000 cycles cannot be reached. From this, it was confirmed that the present invention is effective in preventing shaft runout.

  FIG. 5 shows an embodiment of a bearing unit in which the thrust bearing portions 40a and 40b are configured by dynamic pressure type bearings. The shaft member 10 of this bearing unit 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. Bearing portions 40a and 40b are formed. 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 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 FIGS. 6A and 6B, the dynamic pressure grooves 44 of the thrust bearing surfaces 43a and 43b have portions inclined with respect to the radial imaginary lines drawn on the end surfaces 35 and 21, respectively. 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.

  As shown in FIG. 7, a corner portion 17 is formed over the entire circumference of the corner portion between the shaft portion 15 and the flange portion 16 of the shaft member 10. 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 groove region of the thrust bearing surface” refers to a region T sandwiched between the radial ends of each dynamic pressure groove of the thrust bearing surface (see FIGS. 6A and 6B).

  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. 8, 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 radial 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. 8, the radial bearing surface 51a on the non-opening side 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, the distances L1 and L2 are often 0 (see FIG. 7).

  9 and 10 show a bearing unit A that adopts the structure of the present invention shown in FIGS. 7 and 8, and as shown in FIG. 17, the Nusumi part 17 partially faces the radial bearing surface 510 and the thrust bearing surface 430. 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. 9, in the case of the bearing unit A, it rotates in a completely non-contact state at around 200 rpm irrespective of the motor posture 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. 10 that the shaft runout is clearly inferior in the bearing unit B.

It is sectional drawing of a dynamic pressure type bearing unit. It is a principal part expanded sectional view of the dynamic pressure type bearing unit shown in FIG. It is a principal part expanded sectional view which shows other embodiment. It is a figure which shows the measurement result of a start / stop durability test. It is sectional drawing of the dynamic pressure type bearing unit which comprised the thrust bearing part with the dynamic pressure type bearing. 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 a principal part expanded 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 a principal part expanded sectional view of the conventional dynamic pressure type bearing unit. 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Shaft member 11 Cylindrical part 12 Reduced diameter part 13 Spherical surface part 14 Joint part 20 Bearing member 21 End surface 22 Chamfered part 30 Housing 31 Bottom part 40 Thrust bearing part (pivot support)
41 Thrust support 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 thrust bearing surface disposed facing the end surface of the flange portion and having a plurality of dynamic pressure grooves, and a thrust formed between the thrust bearing surface and the end surface of the flange portion In a dynamic pressure type bearing unit that includes a bearing gap and supports the shaft member in the thrust direction with the fluid dynamic pressure generated in the thrust bearing gap.
A hydrodynamic bearing unit characterized in that the thrust bearing gap is controlled to be constant at least in the hydrodynamic groove region of the thrust bearing surface.   2. The hydrodynamic bearing unit according to claim 1, wherein a crushed portion is formed at a corner portion of the shaft portion and the flange portion of the shaft member, and the crushed portion is disposed outside a region opposite to the hydrodynamic groove region of the thrust bearing surface. The bearing member is arranged on the outer periphery of the shaft member, the radial dimension of the Nusumi part is B, the chamfer dimension of the end of the bearing member is C, and the dimension between the chamfered part and the dynamic pressure groove region of the thrust bearing surface is L2. ,
B <C + L2
The hydrodynamic bearing unit according to claim 2, wherein the relationship is satisfied.