JP4579013B2 - Hydrodynamic bearing device - Google Patents

Description

  The present invention relates to a hydrodynamic bearing device.

  The hydrodynamic bearing device is a bearing device that supports the shaft member in a non-contact manner by the hydrodynamic action of fluid (lubricating fluid) generated in the bearing gap due to relative rotation between the bearing member and the shaft member inserted in the inner periphery of the bearing member. is there. This hydrodynamic bearing device has features such as high-speed rotation, high rotation accuracy, and low noise. Information equipment, for example, magnetic disk devices such as HDD and FDD, CD-ROM, CD-R / RW, DVD- Small motors such as optical disk devices such as ROM / RAM, spindle motors for disk drives in magneto-optical disk devices such as MD and MO, polygon scanner motors of laser beam printers (LBP), projector color wheels, or axial fans Suitable for use.

For example, in a hydrodynamic bearing device incorporated in a spindle motor of a disk device such as an HDD, a radial bearing portion that non-contact supports a shaft member having a shaft portion and a flange portion projecting to the outer diameter side of the shaft portion in a radial direction; And a thrust bearing portion that is supported in a non-contact manner in the thrust direction. In the dynamic pressure bearing, a radial bearing surface having a dynamic pressure groove as a dynamic pressure generating portion is formed on an inner peripheral surface of a bearing member (bearing sleeve) constituting the radial bearing portion or on an outer peripheral surface of a shaft portion opposed thereto. Is done. Further, a thrust bearing surface having a dynamic pressure groove is formed on the end surface of the bearing sleeve constituting the thrust bearing portion, the end surface of the bottom portion of the housing, or the end surface of the flange portion facing the end surface (see, for example, Patent Document 1). .
JP 2002-61641 A

  In the above-described hydrodynamic bearing device, efforts have been made to increase the processing accuracy and assembly accuracy of component parts in order to ensure the required high bearing performance as the performance of information equipment increases. On the other hand, the demand for cost reduction of this type of hydrodynamic bearing device is becoming more and more severe due to the remarkable price reduction of information equipment. In addition, with the widespread use of portable information terminals, there has been a demand for lighter dynamic bearing devices.

  Therefore, in recent years, as an example of means for reducing the cost and weight of the hydrodynamic bearing device, an attempt has been made to replace the housing from a metal machined product with a resin material injection molded product. When this resin housing is used, the dynamic pressure bearing device is incorporated into the motor in the same manner as the metal housing, for example, by bonding the outer peripheral surface of the resin housing to the inner peripheral surface of the metal bracket (holding member). It is possible to fix with.

  By the way, during operation of the motor (dynamic pressure bearing device), the dynamic pressure bearing device and the surrounding temperature become high. Each component of the motor is affected by this and causes thermal expansion. Generally, resin materials have a higher coefficient of linear expansion than metal materials, so the dimensional change due to thermal expansion of resin materials is greater than that of metal materials. Become. Therefore, when the holding member is made of a metal material and the housing is made of a resin material as described above, the amount of expansion of the housing exceeds that of the holding member. In this case, since the outer peripheral surface of the housing is constrained by a highly rigid metal holding member, there is no clearance for the radial expansion. For this reason, the bottom of the housing is deformed, and the flatness of the inner bottom surface (the surface facing the thrust bearing gap) of the bottom may be deteriorated. This deterioration in flatness destabilizes the flying height of the shaft member in the thrust bearing portion, leading to a decrease in bearing performance.

  Accordingly, an object of the present invention is to provide a hydrodynamic bearing device capable of suppressing a decrease in rotational accuracy due to a temperature change at a low cost.

In order to solve the above-described problems, a hydrodynamic bearing device according to the present invention includes a shaft member, a housing injection- molded with resin in a bottomed cylindrical shape integrally including a bottom portion, and a metal holding member that holds the outer peripheral surface of the housing. The bearing and the radial bearing gap are provided, and the dynamic pressure generating portion formed on one of the two surfaces facing the radial bearing gap generates a dynamic pressure action of fluid in the radial bearing gap, thereby causing the shaft member to move in the radial direction. A radial bearing portion that supports contact, and a thrust bearing portion that supports the shaft member in a thrust direction by a dynamic pressure action of a fluid generated in a thrust bearing gap between the bottom portion of the housing and the shaft member, between the outer peripheral surface of the bottom of the housing, and the inner peripheral surface of the holding member opposed thereto, escape portion for the non-contact both sides is provided over the entire circumference, escape portion from the outer bottom surface of the at least housing bottom And it is characterized in that it is formed over the axial region exceeding the thrust bearing gap facing surfaces of Ujingu bottom.

  As described above, by providing a relief portion that makes both surfaces non-contact between the outer peripheral surface of the bottom portion of the housing and the inner peripheral surface of the holding member facing the housing, the bottom portion of the housing is radially oriented for some reason. Even when the holding member expands or the inner diameter of the holding member decreases, the radial compression force acting on the bottom of the housing from the holding member can be blocked. Accordingly, it is possible to suppress the deterioration of the flatness of the bottom portion and stabilize the flying height of the shaft member in the thrust bearing portion.

  In particular, when the housing and the holding member are formed of materials having different linear expansion coefficients, for example, when the housing is formed of resin and the holding member is formed of metal, the amount of expansion at the bottom of the housing due to the difference in the amount of thermal expansion between the two. May exceed that of the holding member, and a radial compression force may act on the bottom of the housing from the holding member. Even in this case, similarly to the above, since the transmission of the compression force is blocked by the escape portion, the compression force does not act on the bottom portion of the housing, and the deformation of the bottom portion of the housing can be suppressed.

  The escape portion can be formed by chamfering the outer periphery of the housing bottom. By this chamfering, the corners of the bottom of the housing are thinned and thinned, so that the thickness of the portion from the bottom of the housing to the cylindrical side can be made uniform. Therefore, it is possible to prevent the occurrence of sink marks caused by the solidification of the resin material, and to mold the housing with high accuracy. Note that the relief portion can be provided on the inner periphery of the holding member facing the outer periphery of the housing bottom.

  When the axial formation width of the relief portion is too small, for example, when the axial length of the relief portion is equal to or less than the thickness of the bottom of the housing, particularly the thrust bearing gap on the outer periphery of the bottom portion. Since the region on the outer diameter side of the surface (inner bottom surface) is held by the holding member, the compression force due to the difference in thermal expansion acts on the bottom of the housing, which may adversely affect the flatness of the inner bottom surface. In order to avoid this, it is desirable that the escape portion is formed beyond the surface (inner bottom surface) facing the thrust bearing gap at the bottom of the housing in the axial direction.

  On the other hand, when the axial formation width of the relief portion is excessive, for example, when the relief portion reaches the outer diameter side region of the dynamic pressure generating portion for generating fluid dynamic pressure in the radial bearing gap. Because the thickness of the housing on the outer diameter side of the dynamic pressure generating part is non-uniform, the amount of thermal expansion of this part becomes non-uniform, which causes the radial bearing gap width to fluctuate in the axial direction. There is a risk. Moreover, since the fixed surface with a holding member will reduce if the formation width of the axial direction of an escape part is excessive, there exists a possibility that desired fixed intensity | strength may not be obtained. Therefore, it is desirable to form the relief portion in a region extending in the axial direction to the dynamic pressure generating portion of the radial bearing portion.

  It is desirable that the relief portion formed on the outer periphery of the bottom portion of the housing is formed on the outer diameter side in the radial direction with respect to the outer peripheral surface of the flange portion provided on the shaft member. When the hydrodynamic bearing device is incorporated in the motor, for example, a disk hub for mounting a disk is fixed to the upper end of the shaft member by means such as press fitting. A considerable amount of pressure input is required for press-fitting (for example, about 1500 N, depending on the application and size of the bearing), and the pressure input is applied to the bottom of the housing via the flange portion of the shaft member. At this time, if the relief portion is formed on the inner diameter side of the outer peripheral surface of the flange portion, the thickness of the bottom portion is thin at the relief portion portion, and the outer diameter side of the bottom portion can particularly withstand pressure input. There is a risk of deformation. On the other hand, if it is the said structure, it can be set as the structure which can also be equal to a pressure input, ensuring a necessary escape allowance also at the time of thermal expansion.

  Note that the radial bearing portion in the present invention is not particularly limited as long as the pressure can be generated by the dynamic pressure action of the fluid. For example, the radial bearing portion has a dynamic pressure groove having a shape inclined in the axial direction such as a herringbone shape. In addition to pressure bearings, dynamic pressure bearings (multi-arc bearings) having a plurality of wedge-shaped gaps in the radial bearing gap, and dynamic pressure bearings (step bearings) in which a plurality of axial groove-shaped dynamic pressure grooves are provided at equal intervals in the circumferential direction ).

  The hydrodynamic bearing device having the above configuration can be preferably used for a motor having a rotor magnet and a stator coil, for example, a spindle motor for a disk device such as an HDD.

  As is apparent from the above, according to the present invention, a hydrodynamic bearing device capable of suppressing a decrease in rotational accuracy due to a temperature change can be provided at low cost.

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

  FIG. 1 shows a configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device (fluid fluid dynamic bearing device) 1 according to the present invention. This spindle motor is used for a disk drive device such as an HDD, and is provided via a dynamic pressure bearing device 1, a disk hub 3 attached to a shaft member 2 of the dynamic pressure bearing device 1, and a radial gap, for example. A starter coil 4 and a rotor magnet 5 which are opposed to each other, and a holding member (bracket) 6 as a member for holding a housing 7 of the fluid dynamic bearing device 1 are provided. The stator coil 4 is attached to the outer periphery of the holding member 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The disk hub 3 holds one or more disks D such as magnetic disks on the outer periphery thereof. In addition, a housing 7 is attached to the inner periphery of the holding member 6, whereby the dynamic pressure bearing device 1 is fixed to the holding member 6. When the stator coil 4 is energized, the rotor magnet 5 is rotated by electromagnetic force generated between the stator coil 4 and the rotor magnet 5, and the disk hub 3 and the shaft member 2 are rotated accordingly.

  FIG. 2 is an enlarged sectional view showing an example of the hydrodynamic bearing device 1 used in the spindle motor. The hydrodynamic bearing device 1 includes a shaft member 2 having a shaft portion 2a at the center of rotation, a bearing sleeve 8 in which the shaft portion 2a can be inserted into the inner periphery, and a bottomed cylindrical shape in which the bearing sleeve 8 is fixed to the inner periphery. The housing 7 and a seal member 9 for sealing one end opening of the housing 7 are provided as main constituent members. In the following description, for convenience of explanation, the description will be made with the side sealed by the seal member 9 as the upper side and the opposite side in the axial direction as the lower side.

  The shaft member 2 is made of, for example, a metal material such as stainless steel, and includes a shaft portion 2a and a flange portion 2b provided at one end of the shaft portion 2a. Or it is set as the hybrid structure (For example, the axial part 2a is formed with a metal material, and the flange part 2b is formed with a resin material) which consists of a metal part and a resin part. In the present embodiment, the shaft portion 2a and the flange portion 2b are formed of a metal material, and both end surfaces 2b1 and 2b2 of the flange portion 2b are formed as flat smooth surfaces without dynamic pressure grooves.

  The housing 7 is formed of a cylindrical side portion 7b and a bottom portion 7c that seals the lower end side opening of the side portion 7b. In this embodiment, the side portion 7b and the bottom portion 7c are integrally injection-molded with a resin material such as LCP (liquid crystal polymer), PPS (polyphenylene sulfide), or PEEK (polyether ether ketone). If it is this structure, while the assembly man-hour of the housing 7 can be reduced and manufacturing cost can be reduced, the housing 7 can be reduced in weight.

  Further, although not shown in the drawing, a thrust bearing surface C of the second thrust bearing portion T2 is formed in a partial annular region of the inner bottom surface 7c1 of the bottom portion 7c. On the thrust bearing surface C, dynamic pressure grooves arranged in, for example, a spiral shape or a herringbone shape are formed as dynamic pressure generating portions. Since this dynamic pressure groove is formed at the same time as the injection molding of the housing 7, it is possible to save the labor of forming the dynamic pressure groove in the bottom portion 7c and reduce the manufacturing cost.

  On the outer periphery of the bottom portion 7c, a relief portion 11 having a chamfered outer peripheral corner is formed over the entire periphery. The escape portion 11 is formed at the same time as the injection molding of the housing 7, and has one end on the lower end surface (outer bottom surface) 7c2 of the bottom portion 7c, and is formed over a predetermined axial region on the outer periphery. Yes. The relief portion 11 can also be formed by machining after the housing 7 is molded.

  The bearing sleeve 8 is formed in a cylindrical shape and is fixed to the inner peripheral surface of the housing 7. The bearing sleeve 8 in this embodiment is formed of a porous body made of sintered metal, particularly a sintered metal porous body mainly composed of copper. Note that the bearing sleeve 8 can be formed not only of sintered metal but also of soft metal such as brass.

  On the inner peripheral surface 8a of the bearing sleeve 8, as shown in FIG. 3A, two upper and lower regions serving as radial bearing surfaces of the first radial bearing portion R1 and the second radial bearing portion R2 are separated in the axial direction. Is provided. For example, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 are formed in the two regions as dynamic pressure generating portions. The upper dynamic pressure groove 8a1 is formed axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions), and the axial dimension X1 of the upper region is lower than the axial center m. It is larger than the axial dimension X2 of the side region. Therefore, when the shaft member 2 rotates, the pulling force (pumping force) of the fluid (for example, lubricating oil) by the dynamic pressure groove 8a1 becomes relatively larger than that of the lower symmetrical dynamic pressure groove 8a2.

  Further, as shown in FIG. 3B, a part of the annular region of the lower end surface 8b of the bearing sleeve 8 serving as the thrust bearing surface B of the first thrust bearing portion T1, A plurality of dynamic pressure grooves 8b1 arranged in a spiral shape are formed.

  When the bearing sleeve 8 is fixed to the housing 7, the shaft 7 of the bearing sleeve 8 with respect to the housing 7 is engaged by engaging the lower end surface 8 b of the bearing sleeve 8 with the step 7 d provided on the inner periphery of the housing 7 in the axial direction. The positioning in the direction is performed, and the width of the thrust bearing gap of the first and second thrust bearing portions is managed to a specified value.

  A seal member 9 made of a metal material or a resin material is fixed to the upper end opening 7a of the housing 7 by means such as press-fitting or bonding. In this embodiment, the seal member 9 has an annular shape and is formed separately from the housing 7. The inner peripheral surface 9a of the seal member 9 gradually increases in diameter toward the upper side, and opposes the outer peripheral surface 2a1 of the shaft portion 2a via a seal space S having a predetermined volume. Further, the lower end surface 9 b of the seal member 9 is in contact with the upper end surface 8 c of the bearing sleeve 8. The internal space of the hydrodynamic bearing device 1 sealed with the seal member 9 is filled with lubricating oil as a fluid. In this state, the oil level of the lubricating oil is maintained within the range of the seal space S. In order to reduce the number of parts and the number of assembling steps, the upper end side region of the inner peripheral surface 8a of the bearing sleeve 8 is formed to have a slightly larger diameter than the region serving as the radial bearing surface, and this large diameter is formed. A seal space S having a predetermined volume can be formed on the inner diameter side of the region.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 rotates, the upper and lower two regions serving as the radial bearing surface of the inner peripheral surface 8a of the bearing sleeve 8 each have a radial bearing gap between the outer peripheral surface 2a1 of the shaft portion 2a. Opposite through. Along with the rotation of the shaft member 2, a dynamic pressure action is caused by the lubricating oil filled in the radial bearing gap, and the pressure causes the shaft member 2 to rotate in the radial direction in a non-contact manner and to support the first radial bearing portion R 1. A second radial bearing portion R2 is formed.

  Further, the upper end surface 2b1 of the flange portion 2b of the shaft member 2 faces the thrust bearing surface B formed on the lower end surface 8b of the bearing sleeve 8 via a thrust bearing gap. When the shaft member 2 rotates, the lubricating oil filled in the thrust bearing gap generates a dynamic pressure action, and the first thrust bearing portion T1 that supports the shaft member 2 in a non-contact manner in the thrust direction is formed by the pressure. The Similarly, the lower end surface 2b2 of the flange portion 2b faces the thrust bearing surface C formed on the inner bottom surface 7c1 of the bottom portion 7c of the housing 7 via a thrust bearing gap. When the shaft member 2 rotates, the lubricating oil filled in the thrust bearing gap generates a dynamic pressure action, and the pressure forms a second thrust bearing portion T2 that supports the shaft member 2 in a non-contact manner so as to be rotatable in the thrust direction. The

  During the rotation of the shaft member 2, since the lubricating oil is pushed into the bottom 7c side of the housing 7, the pressure in the thrust bearing gap between the thrust bearing portions T1 and T2 increases extremely, and the lubrication is caused thereby. There is concern about the generation of bubbles in oil, leakage of lubricating oil, or generation of vibration. Even in this case, for example, as shown in FIG. 2, a thrust bearing gap (particularly the thrust bearing gap of the first thrust bearing portion T1) and the seal space S are formed on the outer peripheral surface 8d of the bearing sleeve 8 and the lower end surface 9b of the seal member 9. If the circulation paths 10a and 10b that communicate with each other are provided, the lubricating oil flows between the thrust bearing gap and the seal space S through the circulation paths 10a and 10b. It is possible to prevent harmful effects. In FIG. 2, as an example, a case where the circulation path 10 a is formed on the outer peripheral surface 8 d of the bearing sleeve 8 and the circulation path 10 b is formed on the lower end surface 9 b of the seal member 9 is illustrated. A circulation path 10 b can be formed on the upper end surface 8 c of the bearing sleeve 8 on the peripheral surface.

  The hydrodynamic bearing device 1 is formed as described above and then incorporated into a motor (see FIG. 1). When the hydrodynamic bearing device 1 is incorporated into a motor, as shown in FIG. 2, a holding member in which a part or all of the axial direction region of the outer peripheral surface 7b1 of the housing 7 is formed of a metal material such as an aluminum alloy, for example. It is fixed to the inner peripheral surface of 6 by means such as adhesion or press-fit adhesion.

  When the resin housing 7 is fixed to the holding member 6, as shown in FIG. 4 (b), the outer peripheral surface 7b1 including the outer peripheral surface of the housing bottom 7c is formed on the metal holding member 6 as in the conventional metal housing. Is fixed to the inner peripheral surface of the hydrodynamic pressure bearing device 1, a compression force acts on the bottom portion 7 c from the holding member 6 due to a difference in thermal expansion between the metal and the resin due to a temperature rise, and the bottom portion 7 c is deformed by this compression force. The flatness of the inner bottom surface 7c1 may be deteriorated. When the flatness of the inner bottom surface 7c1 is deteriorated, the width of the thrust bearing gap of the second thrust bearing portion T2 becomes unstable, so that the shaft member 2 cannot be stably levitated and the bearing performance may be deteriorated. There is.

  On the other hand, in the present invention, as shown in FIG. 4A, the escape portion 11 is provided on the outer periphery of the bottom portion 7c. Therefore, even if the thermal expansion amount difference occurs, the bottom portion 7c has an inner diameter direction from the holding member 6. The pressing force does not act, and the excessive expansion of the bottom portion 7 c is absorbed by the escape portion 11. Accordingly, it is possible to suppress the deterioration of the flatness of the bottom inner bottom surface 7c1 at the time of temperature rise, and it is possible to prevent the bearing performance of the thrust bearing portion from being deteriorated.

  Here, when the axial formation width of the relief portion 11 is too small, in the illustrated example, for example, the axial length L0 from the outer bottom surface 7c2 of the bottom portion 7c to the upper end 11a of the relief portion 11 is the bottom portion. 7c, that is, the axial length L1 or less (L0 ≦ L1) from the outer bottom surface 7c2 of the bottom portion 7c to the inner bottom surface 7c1 (L0 ≦ L1). Since the outer diameter side region of the inner bottom surface 7c1 opposite to the outer surface is held by the holding member 6, the compression force due to the difference in thermal expansion amount may act on the bottom portion 7c of the housing 7 and adversely affect the flatness of the inner bottom surface 7c1. There is. In order to avoid this, it is desirable that the escape portion 11 (the upper end 11a thereof) is formed so as to satisfy the relationship of L0> L1 up to the axial region beyond the inner bottom surface 7c1 of the bottom portion 7c.

  On the other hand, when the axial formation width of the relief portion 11 is excessive, in the illustrated example, for example, the axial length L0 of the relief portion 11 constitutes the second radial bearing portion R2 from the outer bottom surface 7c2. When the length to the outer diameter side region of the dynamic pressure generating portion, that is, the length from the outer bottom surface 7c2 of the bottom portion 7c to the axial lower end of the dynamic pressure generating portion is L2 or more (L0 ≧ L2) Since the thickness of the housing 7 (side portion 7b) existing on the outer diameter side of the dynamic pressure generating portion becomes non-uniform, the amount of thermal expansion becomes non-uniform in this portion, which causes the width of the radial bearing gap. May fluctuate in the axial direction. Further, the increase in the axial length L0 of the escape portion 11 means that the fixing surface with the holding member 6 decreases. When the fixed surface is reduced, there is a risk that the fixing strength of the dynamic pressure bearing device 1 with respect to the holding member 6, that is, the strength as a motor is reduced. From the above viewpoint, it is desirable that the escape portion 11 (the upper end 11a thereof) is formed so as to satisfy the region extending to the dynamic pressure generating portion of the second radial bearing portion R2, that is, the relationship L0 <L2.

  By the way, when the motor is assembled, the disk hub 3 for mounting the disk (see FIG. 1) is fixed to the upper end of the shaft member 2 by means such as press-fitting and press-fitting adhesion. When press-fitting the disk hub 3, a pressure input of about 1500 N is applied from above the shaft member 2, and the pressure input is applied to the bottom 7c via the flange portion 2b. For example, when the escape portion 11 is formed on the inner diameter side of the outer peripheral surface 2b3 of the flange portion 2b, that is, the radius r0 of the lower end 11b of the escape portion 11 is equal to or less than the radius r1 of the outer peripheral surface 2b3 of the flange portion 2b (r0). When formed so as to satisfy ≦ r1), the thickness of the bottom portion 7c is reduced in the portion of the relief portion 11, so that the bottom portion 7c may be deformed into a concave shape and the flatness may be deteriorated. In order to avoid this, it is desirable to form the relief portion 11 so as to satisfy the relationship of the outer diameter side of the outer peripheral surface 2b3 of the flange portion 2b in the radial direction, that is, r0> r1.

  Further, as in the present embodiment, if the escape portion 11 is formed by chamfering on the outer periphery of the bottom portion 7c, the corner portion of the bottom portion 7c is thinned and thinned, so that the thickness of the portion from the bottom portion 7c to the side portion 7b is increased. Can be formed substantially uniformly. In particular, as in the present embodiment, when the housing 7 is formed of a resin material, sink marks or the like during molding can be prevented, and the highly accurate housing 7 can be formed. The gate for filling the mold of the housing 7 with a resin material is provided, for example, at the axis of the bottom 7c (not shown). At this time, since the relief portion 11 is formed by chamfering, the resin material can be uniformly and smoothly filled in the mold, and the housing 7 can be molded with high accuracy.

  Further, the relief portion 11 can also be used as an adhesive reservoir when the dynamic pressure bearing device 1 (housing 7) and the holding member 6 are bonded and fixed, thereby improving workability and adhesive strength when applying the adhesive. Can be made. Moreover, although the case where the escape part 11 is formed by chamfering is illustrated in the above description, for example, the escape part may be formed by a small diameter part with the outer peripheral surface of the bottom part 7c being stepped.

  Further, in the present embodiment, the case where the housing 7 is formed of a resin material and the holding member 6 is formed of a metal material such as an aluminum alloy has been exemplified. The holding member 6 can also be formed of stainless steel or the like using a soft metal material such as brass or aluminum.

  Moreover, although the form which forms the escape part 11 in the bottom part outer periphery of the housing 7 was illustrated in the above description, as shown in FIG. 5, for example, the escape part 11 is formed in the inner periphery of the holding member 6 facing the housing 7. You can also

  In the hydrodynamic bearing device 1 described above, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 exemplify a configuration in which a fluid dynamic pressure action is generated by a herringbone-shaped or spiral-shaped hydrodynamic groove. However, the present invention is not limited to this.

  For example, so-called multi-arc bearings or step bearings may be employed as the radial bearing portions R1 and R2.

  FIG. 6 shows an example of a case where one or both of the radial bearing portions R1 and R2 are constituted by multi-arc bearings. In this example, the region that becomes the radial bearing surface of the inner peripheral surface 8a of the bearing sleeve 8 is configured by three arc surfaces 8a3, 8a4, and 8a5 (so-called three arc bearings). The centers of curvature of the three arcuate surfaces 8a3, 8a4, 8a5 are offset from the axial center O of the bearing sleeve 8 by an equal distance. In each region defined by the three arcuate surfaces 8a3, 8a4, and 8a5, the radial bearing gap has a shape that is gradually reduced in a wedge shape in both circumferential directions. For this reason, when the bearing sleeve 8 and the shaft portion 2a rotate relative to each other, the lubricating fluid in the radial bearing gap is pushed into the minimum gap side reduced in a wedge shape in accordance with the direction of the relative rotation, and the pressure rises. The bearing sleeve 8 and the shaft portion 2a are supported in a non-contact manner by the dynamic pressure action of the lubricating fluid. A deeper axial groove called a separation groove may be formed at the boundary between the three arcuate surfaces 8a3, 8a4, 8a5.

  FIG. 7 shows another example in the case where one or both of the radial bearing portions R1 and R2 are configured by multi-arc bearings. In this example as well, the region that becomes the radial bearing surface of the inner peripheral surface 8a of the bearing sleeve 8 is configured by three arc surfaces 8a6, 8a7, and 8a8 (so-called three arc bearings), but the three arc surfaces 8a6, In each region divided by 8a7 and 8a8, the radial bearing gap has a shape gradually reduced in a wedge shape with respect to one direction in the circumferential direction. The multi-arc bearing having such a configuration may be referred to as a taper bearing. Further, deeper axial grooves 8a9, 8a10, 8a11 called separation grooves are formed at boundaries between the three arcuate surfaces 8a6, 8a7, 8a8. Therefore, when the bearing sleeve 8 and the shaft portion 2a are relatively rotated in a predetermined direction, the lubricating fluid in the radial bearing gap is pushed into the minimum gap side reduced in a wedge shape, and the pressure rises. The bearing sleeve 8 and the shaft portion 2a are supported in a non-contact manner by the dynamic pressure action of the lubricating fluid.

  FIG. 8 shows another example in the case where one or both of the radial bearing portions R1 and R2 are constituted by multi-arc bearings. In this example, in the configuration shown in FIG. 7, the predetermined regions α on the minimum clearance side of the three circular arc surfaces 8 a 6, 8 a 7, 8 a 8 are each formed by concentric circular arcs with the axis center O of the bearing sleeve 8 as the center of curvature. ing. Therefore, in each predetermined area θ, the radial bearing gap (minimum gap) is constant. The multi-arc bearing having such a configuration may be referred to as a tapered flat bearing.

  The multi-arc bearings in the above examples are so-called three-arc bearings, but are not limited to this, and so-called four-arc bearings, five-arc bearings, and multi-arc bearings composed of more than six arc surfaces are adopted. You may do it. Further, when the radial bearing portion is constituted by a multi-arc bearing, in addition to the configuration in which two radial bearing portions are provided apart from each other in the axial direction as in the radial bearing portions R1 and R2, the inner peripheral surface of the bearing sleeve 8 is provided. It is good also as a structure which provided the one radial bearing part over the up-and-down area | region of 8a.

  Note that one or both of the radial bearing portions R1 and R2 may be configured by step bearings (not shown). In the step bearing, for example, a plurality of axial groove-shaped dynamic pressure grooves are provided at predetermined intervals in the circumferential direction in a region serving as a radial bearing surface of the inner peripheral surface 8 a of the bearing sleeve 8.

  Although illustration is omitted, one or both of the thrust bearing portions T1 and T2 is provided with a plurality of radial groove-shaped dynamic pressure grooves at predetermined intervals in the circumferential direction, for example, in a region serving as a thrust bearing surface. Further, it can be constituted by a so-called step bearing, a so-called wave bearing (the step mold is a wave form), or the like.

  In the above embodiment, the lubricating oil is exemplified as the fluid (lubricating fluid) that fills the inside of the hydrodynamic bearing device 1, but other fluids that can generate dynamic pressure in each bearing gap, such as magnetic Gases such as fluid and air can also be used.

  First, FIG. 9 shows the theoretical calculation result of the shaft member flying height ratio with respect to the deterioration of the bottom flatness when the shaft member flying height is 1 when the bottom is theoretically a perfect plane. As is apparent from FIG. 9, it can be seen that the flying height of the shaft member is greatly reduced regardless of whether the flatness is swung to the concave side (minus side) or the convex side (plus side). Therefore, it was theoretically confirmed that if the deterioration of the flatness of the bottom portion 7c can be avoided, a decrease in the flying height of the shaft member, that is, a decrease in the rotational performance of the dynamic pressure bearing device 1 can be suppressed.

  In order to verify the usefulness of the present invention, the countermeasure product having the configuration of the present invention shown in FIG. 4A and the comparative product having the configuration shown in FIG. The flying height of the shaft member 2 was measured. The measurement results are shown in FIG. As is clear from FIG. 10, when the temperature is raised to 80 ° C., the amount of decrease in the flying height of the countermeasure product shown in FIG. 4A is larger than the amount of change of the comparative product shown in FIG. (It was confirmed that the amount of decrease was about 1/4).

It is sectional drawing which shows an example of the spindle motor incorporating the dynamic pressure bearing apparatus. It is sectional drawing of the dynamic pressure bearing apparatus which has a structure of this invention. (A) is a sectional view of the bearing sleeve, and (b) is a plan view showing a lower end surface of the bearing sleeve. (A) The figure is an expanded sectional view of the A section in FIG. 2, (b) The figure is an enlarged sectional view of the A section in the current product. It is an expanded sectional view showing other forms of the present invention. It is sectional drawing which shows the other form of a radial bearing part. It is sectional drawing which shows the other form of a radial bearing part. It is sectional drawing which shows the other form of a radial bearing part. It is a figure which shows the floating amount of the shaft member with respect to the flatness of the bottom part by theoretical calculation. It is a measurement result of the floating amount of the shaft member in the countermeasure product having the configuration of the present invention and the comparison product.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Disc hub 6 Holding member 7 Housing 7b Side part 7c Bottom part 8 Bearing sleeve 9 Seal member 11 Relief part R1 1st radial bearing part R2 2nd radial bearing part S Seal space T1 1st thrust bearing T2 Second thrust bearing

Claims (6)

The shaft member, a bottomed cylindrical housing integrally provided with a bottom portion, a resin injection molding with a resin, a metal holding member for holding the outer peripheral surface of the housing, a radial bearing gap, and facing the radial bearing gap A radial bearing portion that generates fluid dynamic pressure action in the radial bearing gap at a dynamic pressure generating portion formed on one of the surfaces to support the shaft member in a non-contact manner in the radial direction, and a bottom portion of the housing and the shaft member. In the hydrodynamic bearing device comprising a thrust bearing portion that supports the shaft member in the thrust direction in a non-contact manner by the hydrodynamic action of the fluid generated in the thrust bearing gap between,
Between the outer peripheral surface of the bottom portion of the housing and the inner peripheral surface of the holding member facing the housing, a relief portion that makes both surfaces non-contact is provided over the entire circumference , and the relief portion is at least from the outer bottom surface of the housing bottom portion. A hydrodynamic bearing device, characterized in that the hydrodynamic bearing device is formed over an axial region exceeding a surface of the housing bottom facing the thrust bearing gap .   2. The hydrodynamic bearing device according to claim 1, wherein the escape portion is formed by chamfering provided on the outer periphery of the bottom of the housing.   The hydrodynamic bearing device according to claim 1, wherein the escape portion is formed by chamfering provided on the inner periphery of the holding member. Relief portion, the dynamic pressure bearing device according to claim 1, characterized in that formed over the axial region up to the dynamic pressure generating portion of the radial bearing portion from the outer bottom surface of the housing bottom.   2. The hydrodynamic bearing device according to claim 1, wherein the shaft member is provided with a flange portion, and the relief portion is formed on the outer periphery of the bottom portion of the housing in the radial direction and on the outer diameter side of the outer peripheral surface of the flange portion. Motor having a dynamic pressure bearing device according to any one of claims 1 to 5, a rotor magnet, and a stator coil.

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