JP2006329391A - Dynamic pressure bearing arrangement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic pressure bearing arrangement which is provided with high bearing performance and furthermore is low-cost and compact. <P>SOLUTION: The dynamic pressure bearing arrangement 1 is provided with a radial dynamic pressure generated part which generates fluid dynamic pressure in radial bearing clearance and a thrust dynamic pressure generated part which generates fluid dynamic pressure in thrust bearing clearance. The thrust bearing clearance is formed between upper side end 8b of a bearing sleeve 8 and lower side end 3a1 of a disk hub 3 and connects its outer-diameter side domain 8f to sealing space S and at the same time connects inner-diameter side domain 8e to upper end of the radial bearing clearance. The lower end of the radial bearing clearance is connected to the outer-diameter side domain 8f of the thrust bearing clearance via the oil circulation passage 14. Furthermore, the thrust dynamic pressure generated part is configuration which flows lubricating oil from the outer-diameter side domain 8f of the thrust bearing clearance to the inner-diameter side domain 8e. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device. The hydrodynamic bearing device is a spindle motor such as an information device, for example, a magnetic disk device such as HDD, an optical disk device such as CD-ROM, CD-R / RW, DVD-ROM / RAM, or a magneto-optical disk device such as MD or MO. It is suitable as a bearing device for a small-sized motor such as a polygon scanner motor of a laser beam printer (LBP), a color wheel of a projector, or an electric device such as an axial fan.

  In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine these required performances is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing device having excellent characteristics as described above has been studied as this type of bearing. Or actually used.

  For example, in a hydrodynamic bearing device used for a spindle motor such as an HDD, the shaft member is supported in a non-contact manner in the radial direction by the hydrodynamic action generated in a lubricating fluid (for example, lubricating oil) that fills the radial bearing gap and the thrust bearing gap. A radial bearing portion to be supported and a thrust bearing portion to be supported in a non-contact manner in the thrust direction.

This type of hydrodynamic bearing device is provided with a seal space for preventing leakage of lubricating oil. However, during the rotation of the shaft member, there is a difference between the fluid pressure of the thrust bearing portion that supports the shaft member in a non-contact manner in the thrust direction by the dynamic pressure action by the dynamic pressure groove and the fluid pressure in the seal space, This may adversely affect the bearing performance. To prevent the thrust bearing fluid pressure from becoming extremely high compared to the fluid pressure in the sealed space, which is almost equal to atmospheric pressure, or conversely, negative pressure, it is applied to the outer peripheral surface of the bearing sleeve or the inner peripheral surface of the housing. What provided the groove | channel (circulation groove | channel) through which lubricating oil flows is known. (For example, see Patent Document 1)
JP 2003-322145 A

  In Patent Document 1, as a dynamic pressure generating portion (radial dynamic pressure generating portion) that generates fluid dynamic pressure in the lubricating oil that fills the radial bearing gap, for example, a plurality of dynamic pressure grooves arranged in a herringbone shape are formed on the bearing sleeve. It is formed on the inner peripheral surface. Further, as a dynamic pressure generating portion (thrust dynamic pressure generating portion) for generating fluid dynamic pressure in the lubricating oil that fills the thrust bearing gap, for example, a plurality of dynamic pressure grooves arranged in a spiral shape are formed on the end surface of the bearing sleeve and the lid member. It is formed on the end face.

  By the way, the herringbone-shaped dynamic pressure groove formed in the radial dynamic pressure generating portion has a pumping function for causing the lubricating oil to flow in the axial direction. In the hydrodynamic bearing device shown in Patent Document 1, the lubricating oil pushed into the thrust bearing portion by the pumping function by the hydrodynamic groove is circulated toward the seal space through the circulation groove, and the fluid pressure inside the bearing device is increased. Has been adjusted. However, since this type of dynamic pressure groove has a complicated shape, the processing cost increases.

  Further, in the hydrodynamic bearing device shown in Patent Document 1, the shaft member is supported in a non-contact manner in the thrust direction by the thrust bearing portions formed at two locations, but it is necessary to form the thrust dynamic pressure generating portions at two locations. This also increases the processing cost. Further, in this type of dynamic pressure bearing device, a seal space for preventing oil leakage is required. However, in the bearing device shown in Patent Document 1, this seal space is arranged side by side with the thrust bearing gap in the axial direction. Therefore, this point is a factor that increases the axial dimension of the bearing device.

  In recent years, in information equipment in which a hydrodynamic bearing device is incorporated, rapid performance improvement has been achieved, but at the same time, cost reduction and downsizing have progressed rapidly. Although it is becoming increasingly severe, it is difficult to meet this type of demand with the hydrodynamic bearing device having the above structure.

  In order to solve the above problems, the hydrodynamic bearing device provided by the present invention is a radial hydrodynamic pressure generator that generates a hydrodynamic pressure that acts on a radial bearing gap and a lubricating oil that faces the radial bearing gap and fills the radial bearing gap. A thrust bearing gap, and a thrust dynamic pressure generating section that faces the thrust bearing gap and generates a dynamic pressure action on the lubricating oil that fills the thrust bearing gap, the outer diameter side of the thrust bearing gap being Connected to a seal space with an oil surface open to the outside air, connected to one end of the radial bearing gap via the oil circulation path, and connected the inner diameter side of the thrust bearing gap to the other end of the radial bearing gap, Is formed in such a shape that the lubricating oil flows from the outer diameter side to the inner diameter side of the thrust bearing gap.

  According to the configuration of the present invention, the lubricating oil filled in the thrust bearing gap is pushed into the inner diameter side by the pumping action of the thrust dynamic pressure generating portion. The lubricating oil pushed into the inner diameter side returns to the outer diameter side of the thrust bearing gap from the thrust bearing gap through the radial bearing gap connected to the inner diameter side and further through the oil circulation path connected to the radial bearing gap. Therefore, the lubricating oil filled in the internal space of the bearing device circulates constantly along a path consisting of the thrust bearing gap → the radial bearing gap → the oil circulation path → the thrust bearing gap. At this time, the pressure of the lubricating oil is substantially equal to the atmospheric pressure on the outer diameter side of the thrust bearing gap connected to the seal space, but on the inner diameter side of the thrust bearing gap, the outer diameter side of the thrust dynamic pressure generating portion is changed to the inner diameter side. Due to the pumping action of the oil, the pressure of the lubricating oil becomes higher than the atmospheric pressure. On the downstream side of the thrust bearing gap, the pressure of the lubricating oil gradually decreases due to viscous resistance, but the pressure of the lubricant is still higher than the atmospheric pressure because the lubricating oil flow path remains sealed until it returns to the thrust bearing gap. maintain. This prevents the generation of negative pressure in each part of the bearing device, thus suppressing the generation of bubbles and vibrations caused by the generation of negative pressure, and managing the rotational performance of the hydrodynamic bearing device with high accuracy. can do.

  In this case, if the cross-sectional area of the oil circulation path is changed in the flow direction of the lubricating oil, the amount of pressure drop due to viscous resistance can be adjusted as appropriate, and negative pressure can be more reliably prevented. .

  The shape of the thrust dynamic pressure generating portion is not particularly limited as long as it has a function (pump-in function) for flowing lubricating oil from the outer diameter side to the inner diameter side, and a representative example is a dynamic pressure groove arranged in a spiral shape. be able to. In addition to this, even if the pump-in function and the pump-out function are combined, such as a herringbone-shaped dynamic pressure groove, the inner diameter side by the pump-in function is more than the flow to the outer diameter side by the pump-out function. If the flow to the flow is dominant, since the lubricating oil flows from the outer diameter side to the inner diameter side in the entire thrust bearing gap, it is possible to employ this type of dynamic pressure generating portion.

  Further, in the configuration of the present invention, the thrust dynamic pressure generating portion is formed only at one place, so that the machining cost can be reduced as compared with the case where the thrust dynamic pressure generating portion is formed at two places in the axial direction. Further, since the seal space can be arranged on the outer diameter side of the thrust bearing gap, the axial dimension of the bearing device can be made compact as compared with the case where both are arranged in the axial direction.

  According to the configuration of the present invention, as described above, the lubricating oil filling the inside of the bearing device can be circulated with the pumping ability of the thrust dynamic pressure generating portion. Therefore, the radial dynamic pressure generating portion can be formed in a shape that does not allow the lubricating oil to flow in the axial direction at the radial bearing portion.

  Examples of the radial dynamic pressure generating portion corresponding to this include a step surface provided with a plurality of axial grooves in the circumferential direction, a multi-arc surface having a plurality of arc surfaces, or a wavy surface having a harmonic waveform surface. be able to. Since these illustrated shapes have the same cross-sectional shape in the axial direction, they can be processed at a lower cost compared to conventionally used inclined dynamic pressure grooves (for example, dynamic pressure grooves arranged in a herringbone shape). Can do. Note that these radial dynamic pressure generating portions are formed on at least one of the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing sleeve.

  The hydrodynamic bearing device having the above configuration is preferably used for a motor having a hydrodynamic bearing device, a rotor magnet, and a stator coil that generates an electromagnetic force between the rotor magnet, such as a spindle motor for information equipment. Can do.

  As described above, according to the present invention, it is possible to provide a compact hydrodynamic bearing device having high bearing performance and low cost.

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

  FIG. 1 conceptually shows a configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device 1 according to an embodiment of the present invention. This spindle motor for information equipment is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that supports the shaft member 2 in a non-contact manner in a freely rotatable manner, a disk hub 3 mounted on the shaft member 2, For example, a stator coil 4 and a rotor magnet 5 that are opposed to each other through a gap in the radial direction, and a bracket 6 that fixes the fluid dynamic bearing device 1 are provided. The stator coil 4 is attached to the outer periphery of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. A housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the bracket 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 become a single member (rotating member). It rotates together.

  The disc hub 3 includes a disc portion 3a, a cylindrical second cylindrical portion 3c provided on the outer periphery of the disc portion 3a, and a first cylindrical portion 3b that is located on the inner diameter side of the second cylindrical portion 3c and is also cylindrical. It consists of. A mounting portion 3d of the rotor magnet 5 facing the stator coil 4 is provided on the inner diameter side of the second cylindrical portion 3c, and the rotor magnet 5 is bonded and fixed to the mounting portion 3d, for example.

  FIG. 2 is an enlarged cross-sectional view of the hydrodynamic bearing device 1 having the configuration of the present invention. The hydrodynamic bearing device 1 includes a bottomed cylindrical housing 7, a bearing sleeve 8 fixed to the inner periphery of the housing 7, and a shaft member 2 inserted into the inner periphery of the bearing sleeve 8. Include as. In the following description, for convenience of description, the opening side of the housing 7 will be described as the upper side, and the opposite side in the axial direction as the lower side.

  The shaft member 2 is formed in a shaft shape from a metal material such as stainless steel. In the present embodiment, the outer peripheral surface 2a of the shaft member 2 is formed in a smooth cylindrical surface without unevenness, and the lower end surface 2b is formed in a smooth flat surface without unevenness.

  The above-described disk hub 3 is fixed to the shaft member 2 by an appropriate means, and a rotating member 9 is formed by the shaft member 2 and the disk hub 3 fixed to each other. At this time, if the disk hub 3 is injection molded (insert molding) using the shaft member 2 as an insert part, the disk hub 3 can be molded and the disk hub 3 can be attached to the shaft member 2 at the same time. The disk hub 3 can be integrated with high accuracy and at low cost. As a material for injection molding, a resin material, a metal material, ceramic, or the like can be used. In addition, after the disk hub 3 is formed separately from the shaft member 2, the rotating member 9 may be configured by press-fitting or press-fitting to the shaft member 2.

  The housing 7 is formed of a metal material or a resin material in a bottomed cylindrical shape. The illustrated housing 7 includes a side portion 7b and a bottom portion 7c that seals a lower end opening of the side portion 7b. The side portion 7b and the bottom portion 7c are integrally formed.

  The upper end surface 7d of the side portion 7b constituting the housing 7 is opposed to the lower end surface 3a1 of the disk portion 3a on the inner diameter side of the first cylindrical portion 3b constituting the disk hub 3 in the axial direction, and this lower end surface 3a1. An annular axial space P is formed between the two. This axial space P can be made larger than the axial width of a thrust bearing gap described later. Further, the tapered surface 7e provided at the outer peripheral upper end of the side portion 7b is opposed to the inner peripheral surface 3b1 of the first cylindrical portion 3b of the disk hub 3 in the radial direction, and between the inner peripheral surface 3b1, the upward radial direction. A tapered seal space S whose size is gradually reduced is formed. In the seal space S, the lubricating oil injected into the bearing device is held by the capillary force. In the seal space S, there is always an oil level that is open to the outside air regardless of whether the bearing device is operating or stopped. The seal space S is connected to the outer diameter portion of the axial space P.

  The inner periphery of the lower end of the first cylindrical portion 3b of the disk hub 3 is engaged with the housing 7 in the axial direction when the shaft member 2 (rotating member 9) is relatively displaced in the axial direction to prevent the rotating member 9 from coming off. A retaining member 10 is attached.

  A bearing sleeve 8 is fixed to the inner periphery of the housing 7 by appropriate means such as press-fitting or bonding. The bearing sleeve 8 is formed into a cylindrical shape by a method described later using a porous body made of sintered metal, for example, a porous body of oil-containing sintered metal obtained by impregnating a sintered metal mainly composed of copper with a lubricating oil. It is formed. In addition, the bearing sleeve 8 can be formed of a solid metal material, for example, a soft metal material such as brass.

  On the inner peripheral surface 8a of the bearing sleeve 8, a radial bearing surface A that faces the radial bearing gap is formed. The radial bearing surface A is formed at two locations separated in the axial direction, and both radial bearing surfaces A have radial dynamic pressure generating portions that generate fluid dynamic pressure in the radial bearing gap, for example, as shown in FIG. A step surface having a plurality of axial grooves 15 is formed. In consideration of the balance between ease of processing and isotropic rigidity, the axial grooves 15 are preferably formed at three circumferentially spaced intervals as shown in the illustrated example, but not limited to three, or two or It is also possible to form four or more locations. The radial dynamic pressure generating portion can also be formed on the outer peripheral surface 2 a of the shaft member 2. In the illustrated example, the depth of the axial groove 15 is exaggerated for ease of understanding, but it is actually about several μm.

  Further, a thrust bearing surface B facing the thrust bearing gap is formed in the whole or part of the annular region of the upper end surface 8b of the bearing sleeve 8. A plurality of dynamic pressure grooves 8b1 arranged in a spiral shape, for example, are formed on the thrust bearing surface B as a thrust dynamic pressure generating portion for generating fluid dynamic pressure in the thrust bearing gap so as to perform a pump-in function. The thrust dynamic pressure generating portion can also be formed on the lower end surface 3a1 of the disk hub 3.

  The bearing sleeve 8 is formed, for example, through sizing → rotational sizing → radial bearing surface (radial dynamic pressure generating portion) molding process. In the sizing process, the outer peripheral surface of the sintered metal material is press-fitted into a cylindrical die, and a sizing pin (circular cross section) is press-fitted into the inner peripheral surface, so that the outer peripheral surface and inner peripheral surface of the sintered metal material are pressed. Sizing is done. In the rotational sizing process, a sizing pin having a substantially polygonal cross section (a part of the outer peripheral surface of a pin having a perfectly circular cross section is partially flattened to leave an arc portion at a circumferentially equidistant position) is made of a sintered metal material. The inner circumferential surface is sized by press-fitting into the inner circumferential surface and rotating the inner circumferential surface. In the bearing surface forming step, a molding die (core rod) having a shape corresponding to the inner peripheral surface shape of the bearing sleeve 8 is inserted into the inner peripheral surface of the sintered metal material subjected to the sizing process as described above, and the die is externally formed. The axial groove 15 of the radial bearing surface A and the other region are simultaneously formed by pressurizing with a punch or a vertical punch.

  After the pressurization, when the die and the upper and lower punches are released, a spring back is generated in the sintered metal material, and a minute gap is formed between the core rod and the sintered metal material. At this time, since the axial groove 15 of the radial bearing surface A according to this embodiment does not have an axial engagement relationship with the core rod, the core rod can be easily moved in the axial direction without worrying about the collapse of the groove shape or the like. Can be extracted. At this time, it is not necessary to heat the core rod and the sintered metal material (bearing sleeve 8) separately. In this embodiment, the thrust bearing surface B is formed simultaneously with the pressurization by forming a mold corresponding to the shape of the thrust bearing surface B on the end face of the upper punch that pressurizes the sintered metal material. In the present embodiment, since the radial bearing surface A is formed in a simple shape (step surface), it can be easily formed by machining such as cutting or rolling.

  In the hydrodynamic bearing device 1 having the above-described configuration, the radial bearing surfaces A that are spaced apart from the inner circumferential surface 8a of the bearing sleeve 8 are opposed to the outer circumferential surface 2a of the shaft member 2 via a radial bearing gap. When the bearing sleeve 8 and the shaft member 2 rotate relative to each other (the shaft member 2 rotates in this embodiment), the dynamic pressure of the lubricating oil is applied to each radial bearing gap by the action of a plurality of step surfaces formed on the radial bearing surface A. The action is generated, and the rotary member 9 is supported in a non-contact manner so as to be rotatable in the radial direction by the pressure. Thereby, the first radial bearing portion R1 and the second radial bearing portion R2 that support the rotating member 9 in a non-contact manner so as to be rotatable in the radial direction are formed.

  When the rotating member 9 rotates, the thrust bearing surface B formed on the upper end surface 8 b of the bearing sleeve 8 faces the lower end surface 3 a 1 of the disk hub 3 constituting the rotating member 9 with a thrust bearing gap interposed therebetween. Along with this, the dynamic pressure groove 8b1 formed on the thrust bearing surface B generates a dynamic pressure action of the lubricating oil in the thrust bearing gap, and the rotary member 9 is supported in a non-contact manner in the thrust direction by the pressure. As a result, a thrust bearing portion T that supports the rotating member 9 in a non-contact manner so as to be rotatable in the thrust direction is formed. The inner diameter side of the thrust bearing gap is in communication with the upper end of the radial bearing gap.

  During the rotation of the rotating member 9, a gap between the region between the two radial bearing surfaces A of the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a of the shaft member 2 facing this is a perfect circular bearing. When functioning, negative pressure is likely to be generated in this gap. As shown in FIG. 2, this problem is caused by forming a relief portion 2c on the outer peripheral surface 2a of the shaft member 2 facing the region between the bearing surfaces, and expanding the width of the gap to the extent that it cannot function as a perfect circular bearing. This can be avoided. Even if the escape portion 2c is formed on the inner peripheral surface 8a of the bearing sleeve 8, the same effect can be obtained. In the case where one radial bearing surface A is formed over the entire axial length of the inner peripheral surface 8a of the bearing sleeve 8, this type of relief portion 2c is not necessary.

  In the present embodiment, an axial groove 12 is formed on the inner peripheral surface 7 b 1 of the housing 7 as an axial oil circulation path that allows both end surfaces of the bearing sleeve 8 to communicate with each other. One or a plurality of the axial grooves 12 can be formed.

  When the bearing sleeve 8 is press-fitted and fixed to the housing 7, the inner circumference of the bearing sleeve is reduced due to the difference in elastic deformation between the portion facing the axial groove 12 and the other portion of the outer circumference of the bearing sleeve 8. There is a concern that the number of circular grooves may be slightly deformed (N) according to the number of circulation grooves (N). Since the shape after the deformation is triangular, it is advantageous in terms of rigidity rather than an ellipse or a quadrangle, so the circulation groove 12 has three locations in the circumferential direction (preferably three locations equally arranged in the circumferential direction). It is good to form. For example, when the bearing sleeve is bonded and fixed without being press-fitted into the inner periphery of the housing, it is not necessary to limit the number of circulation grooves from this viewpoint. Further, the axial groove 12 may be formed on the outer peripheral surface 8 d of the bearing sleeve 8.

  A radial oil circulation path is formed between the lower end surface 8 c of the bearing sleeve 8 and the inner bottom surface 7 c 1 of the housing 7. In the present embodiment, the lower end surface 8c of the bearing sleeve 8 and the inner bottom surface 7c1 of the housing 7 are not in contact with each other, and a bottom gap 11 is formed between the two, and the bottom gap 11 is circulated in the radial direction. Configure the road.

  With the above configuration, the oil circulation path 14 composed of the axial groove 12 and the bottom gap 11 is formed, and the lower end of the radial bearing gap is connected to the thrust bearing gap via the oil circulation path 14 filled with lubricating oil. The outer diameter side region 8f (the boundary between the thrust bearing gap and the axial space P) is in communication.

  In the hydrodynamic bearing device 1 configured as described above, since the axial space P is connected to the seal space S maintained at atmospheric pressure in the radial direction, the oil pressure of the lubricating oil in the outer diameter side region 8f of the thrust bearing gap is atmospheric pressure. Is approximately equal. In the present embodiment, since the spiral dynamic pressure groove 8b1 is formed as the thrust dynamic pressure generating portion on the thrust bearing surface B, when the rotating member 9 rotates, the thrust bearing surface B has a pumping ability toward the inner diameter side. Thus, the oil pressure of the lubricating oil in the inner diameter side region 8e of the thrust bearing gap (the boundary portion between the thrust bearing gap and the radial bearing gap) becomes larger than the atmospheric pressure. The lubricating oil whose pressure has been increased in this manner flows from the radial bearing gap to the bottom gap 11 and from the bottom gap 11 toward the outer diameter side region 8 f of the thrust bearing gap equal to the atmospheric pressure through the axial groove 12. That is, during operation of the hydrodynamic bearing device 1, the lubricating oil constantly follows the path of thrust bearing gap → radial bearing gap → oil circulation path 14 (bottom gap 11 → axial groove 12) → thrust bearing gap. Circulate. As a result, the hydraulic pressure of the lubricating oil inside the bearing is always kept at atmospheric pressure or higher. Therefore, according to this invention, generation | occurrence | production of the negative pressure in the internal space of a bearing apparatus is prevented, and, thereby, rotational performance can be managed with high precision.

  Further, in the dynamic pressure bearing device 1 of the present invention, the thrust dynamic pressure generating portion (thrust bearing portion T) is formed only at one place, so that the thrust dynamic pressure generating portion is formed at two places as in the prior art. Compared with, the processing cost can be reduced.

  Further, in the hydrodynamic bearing device 1 having the configuration of the present invention, since the lubricating oil circulates in the bearing device by the pumping capability of the thrust dynamic pressure generating portion, the radial dynamic pressure generating portion does not need the axial pumping capability. . Therefore, the radial dynamic pressure generating portion can be formed in a shape having no pumping capability, for example, the step surface exemplified above. Since the step surface can be formed more easily than the formation of herringbone-shaped dynamic pressure grooves, the radial dynamic pressure generating portion can be processed at low cost.

  In the above description, the case where the step surface as shown in FIG. 3 is formed as the radial dynamic pressure generating portion has been described. However, for example, a step surface as shown in FIG. 5 may be formed. The step surface shown in FIG. 5 is formed by forming a separation groove 16 having a deeper groove depth at one end in the circumferential direction of each axial groove 15 in addition to the axial grooves 15 provided at equal intervals in the circumferential direction. . For example, when the radial dynamic pressure generating portion is formed on the step surface as shown in FIG. 3, a local negative pressure may be generated in a partial region in the circumferential direction of each axial groove 15, By forming the separation groove 16, the generation of such negative pressure can be prevented. The depth of the separation groove 16 is preferably about 10 times the depth of the axial groove 15 from the viewpoint of reliably preventing the generation of negative pressure.

  Although one embodiment of the hydrodynamic bearing device 1 having the configuration of the present invention has been described above, the present invention is not limited to this embodiment. For example, in the hydrodynamic bearing device 1 as shown in FIG. Can also be preferably used. In the following description, members and elements having the same functions as those in the embodiment shown in FIG.

  FIG. 6 shows a hydrodynamic bearing device 1 according to another embodiment. In the hydrodynamic bearing device 1 according to this embodiment, the lower end surface 8 c of the bearing sleeve 8 is in contact with the inner bottom surface 7 c 1 of the housing 7. In order to secure a radial circulation path, one or a plurality of radial grooves 13 are formed on the lower end surface 8 c of the bearing sleeve 8, and the oil circulation path is formed by the radial grooves 13 and the axial grooves 12. 14 is formed. Also in this embodiment, due to the pumping capability of the thrust dynamic pressure generating portion, the lubricating oil circulates constantly along the path of thrust bearing clearance → radial bearing clearance → radial groove 13 → axial groove 12 → thrust bearing clearance. The generation of negative pressure in the internal space of the bearing device can be prevented. In this case, compared with the configuration shown in FIG. 2, the cross-sectional area of the oil circulation path 14 in the radial direction is reduced, so that the pressure drop of the lubricating oil due to the viscous resistance at this portion can be increased.

  In the above description, as the radial bearing portions R1 and R2, the radial dynamic pressure generating portion including the step surface in which the plurality of axial grooves 15 are arranged at equal intervals in the circumferential direction on the inner peripheral surface 8a of the bearing sleeve 8. Although the case where the fluid dynamic pressure is generated and shown is shown, the radial dynamic pressure generating portion has other shapes that do not have an axial pumping function, for example, a wavy surface including a plurality of harmonic waveform surfaces and a plurality of arc surfaces It is also possible to form a multi-arc surface consisting of

  FIG. 7 shows a case where a radial dynamic pressure generating portion having a plurality of harmonic waveform surfaces is formed on the inner peripheral surface 8 a of the bearing sleeve 8. When the shaft member 2 is inserted into the inner periphery of the bearing sleeve 8, a radial bearing gap is formed between the harmonic wave surface 17 formed on the inner peripheral surface of the bearing sleeve 8 and the outer peripheral surface 2 a of the shaft member 2. At this time, in each region defined by the harmonic waveform surface 17, the radial bearing gap becomes a wedge-shaped gap 18 that gradually decreases in a wedge shape in both circumferential directions. Therefore, when the shaft member 2 and the bearing sleeve 8 are rotated relative to each other, the lubricating oil in the radial bearing gap is pushed into the minimum gap side of the wedge-shaped gap 18 in accordance with the direction of the relative rotation, and the pressure increases. . The shaft member 2 and the bearing sleeve 8 are supported in a non-contact manner in the radial direction by the dynamic pressure action of the lubricating oil. Note that the minimum width h of the wedge-shaped gap 18 is approximately expressed by the following equation when there is no eccentricity (axial center O).

h = c + aw · cos (Nw · θ)
In the above equation, c, aw, and Nw are constants, c is an average bearing radius gap, aw is the amplitude of the wave, θ is the phase in the circumferential direction, and Nw is the wave number (where Nw ≧ 2). In this embodiment, Nw = 3). In the illustrated example, the axis O of the shaft member 2 and the bearing sleeve 8 is concentric. However, the shaft member 2 may be used eccentrically with the axis O ′.

  FIG. 8 shows an example in which a radial dynamic pressure generating portion composed of a plurality of arc surfaces (multi-arc surfaces) is formed on the inner peripheral surface 8 a of the bearing sleeve 8. In this illustrated example, three arcuate surfaces 19 are formed in a region serving as a radial bearing surface of the inner peripheral surface 8a of the bearing sleeve 8 (so-called three-arc bearing). The centers of curvature of the three arcuate surfaces 19 are offset by an equal distance from the shaft center O of the bearing sleeve 8 (shaft member 2). In each region defined by the three arcuate surfaces 19, the radial bearing gap is a wedge-shaped gap 18 that is gradually reduced in a wedge shape in both circumferential directions, as in the embodiment shown in FIG. A separation groove can also be formed at the boundary between the three arcuate surfaces 19 (not shown).

  FIG. 9 shows another example in the case where a radial dynamic pressure generating portion composed of a plurality of arc surfaces (multi-arc surfaces) is formed on the inner peripheral surface 8 a of the bearing sleeve 8. Also 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 19 (so-called three arc bearings), and each of the regions defined by the three arc surfaces 19 is divided. In the region, the radial bearing gap is a wedge-shaped gap 18 that gradually decreases in a wedge shape with respect to one direction in the circumferential direction. The bearing having such a configuration may be referred to as a taper bearing. A separation groove 16 is formed at the boundary between the three arcuate surfaces 18. When the bearing sleeve 8 and the shaft member 2 rotate relative to each other in a predetermined direction, the lubricating oil in the radial bearing gap is pushed into the minimum gap side of the wedge-shaped gap 18 and the pressure rises. The bearing sleeve 8 and the shaft member 2 are supported in a non-contact manner in the radial direction by the dynamic pressure action of the lubricating oil.

  FIG. 10 shows another example in the case where a radial dynamic pressure generating portion including a plurality of arc surfaces (multi-arc surfaces) is formed on the inner peripheral surface 8 a of the bearing sleeve 8. In this example, in the configuration shown in FIG. 9, the predetermined regions θ on the minimum gap side of the three circular arc surfaces 19 are each configured by concentric arcs with the axis center O of the bearing sleeve 8 (the shaft member 2) as the center of curvature. Has been. Therefore, in each predetermined area θ, the radial bearing gap (minimum gap) is constant. The bearing having such a configuration may be referred to as a tapered flat bearing.

  In FIGS. 7 to 10, the radial dynamic pressure generating portion is formed by three harmonic waveform surfaces or three arc surfaces, but not limited to this, radial motion is generated by two or more harmonic waveform surfaces and arc surfaces. A pressure generating part can also be formed.

  Moreover, in the above description, although the structure which provided the radial bearing part spaced apart in two axial directions like radial bearing part R1 and R2 is illustrated, one radial bearing part is extended over an axial direction. It can also be set as the provided structure.

It is sectional drawing which shows notionally 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. It is sectional drawing which shows the form which formed the radial dynamic pressure generation part in the step surface. It is a figure which shows the upper end surface of a bearing sleeve. It is sectional drawing which shows the other form which formed the radial dynamic pressure generating part in the step surface. It is sectional drawing which shows the other form of a hydrodynamic bearing apparatus. It is sectional drawing which shows the form which formed the radial dynamic pressure generation | occurrence | production part with the wavy surface. It is sectional drawing which shows the form which formed the radial dynamic pressure generation | occurrence | production part by the multi-arc surface. It is sectional drawing which shows the other form which formed the radial dynamic pressure generation | occurrence | production part with the multi-arc surface. It is sectional drawing which shows the other form which formed the radial dynamic pressure generation | occurrence | production part with the multi-arc surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 7 Housing 8 Bearing sleeve 9 Rotating member 12 Axial groove 13 Radial groove 14 Oil circulation path 15 Axial groove 16 Separation groove 17 Harmonic waveform surface 18 Wedge Clearance 19 Arc surface A Radial bearing surface B Thrust bearing surface R1, R2 Radial bearing portion T Thrust bearing portion P Axial space S Seal space

Claims (4)

Facing the radial bearing gap and the radial bearing gap, facing the radial dynamic pressure generating section that generates dynamic pressure action on the lubricating oil that fills the radial bearing gap, the thrust bearing gap, and the thrust bearing gap, and filling the thrust bearing gap In the hydrodynamic bearing device comprising a thrust dynamic pressure generating section that generates a dynamic pressure action on the lubricating oil,
The outer diameter side of the thrust bearing gap is connected to a sealed space having an oil surface that is open to the outside air, and is connected to one end of the radial bearing gap via an oil circulation path, and the inner diameter side of the thrust bearing gap is connected to the other end of the radial bearing gap. And the thrust dynamic pressure generating portion is formed in a shape in which the lubricating oil flows from the outer diameter side to the inner diameter side of the thrust bearing gap.   The hydrodynamic bearing device according to claim 1, wherein the radial dynamic pressure generating portion is formed in a shape that does not allow the lubricating oil to flow in the axial direction through the radial bearing gap.   The radial dynamic pressure generating portion is formed on any of a step surface having a plurality of axial grooves in the circumferential direction, a multi-arc surface having a plurality of arc surfaces, or a wavy surface having a plurality of harmonic waveform surfaces. Item 3. The hydrodynamic bearing device according to Item 2.   A motor comprising the hydrodynamic bearing device according to claim 1, a rotor magnet, and a stator coil that generates electromagnetic force between the rotor magnet.

Images