JP2009228873A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce manufacturing cost without deteriorating bearing performance in a fluid bearing device. <P>SOLUTION: A radial beating surface (a large diameter inner peripheral surface 8a1) and a first seal surface (a small diameter inner peripheral surface 8a2) are firmed in a sleeve 8, whereby a function conventionally performed by two members of a bearing sleeve and a seal member can be performed by one member. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device that supports a shaft member rotatably in a radial direction with a fluid film formed in a radial bearing gap.

  Due to its high rotational accuracy and quietness, the hydrodynamic bearing device is a magnetic disk drive device for information equipment (for example, HDD), an optical disk drive device such as a CD-ROM, CD-R / RW, DVD-ROM / RAM, or MD, For spindle motors of magneto-optical disk drive devices such as MO, for polygon scanner motors of laser beam printers (LBP), for color wheel motors of projectors, or for small motors such as fan motors used for cooling of electrical equipment, etc. It is used as

  For example, the hydrodynamic bearing device shown in Patent Document 1 is a cup-shaped member in which a shaft member having a spherical convex portion at a lower end, a bearing sleeve having a shaft member inserted into an inner periphery, and a bearing sleeve fixed to an inner periphery surface. A housing and a seal member provided in the housing opening are provided. In this hydrodynamic bearing device, the fluid film generated in the radial bearing gap between the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing sleeve supports the shaft member in a non-contact manner in the radial direction, and the spherical convex portion of the shaft member. And the thrust plate provided on the inner bottom surface of the housing are slid in contact with each other, thereby supporting the shaft member in the thrust direction. Between the inner peripheral surface of the seal member and the outer peripheral surface of the shaft member, a seal space for preventing leakage of the lubricating oil filled in the bearing to the outside is formed.

JP 2004-340183 A

  With the recent increase in performance and capacity of information equipment, improvement in bearing performance such as bearing rigidity and rotational accuracy of the fluid dynamic bearing device as described above is required. On the other hand, along with the price reduction of information equipment, the demand for cost reduction of the hydrodynamic bearing device as described above has become increasingly severe.

  An object of the present invention is to reduce the manufacturing cost without deteriorating the bearing performance of the hydrodynamic bearing device.

  In order to solve the above-described problems, a hydrodynamic bearing device according to the present invention includes a shaft member, a sleeve portion in which the shaft member is inserted on the inner periphery, a radial bearing surface provided on the inner peripheral surface of the sleeve portion, and an outer periphery of the shaft member. Between the radial bearing gap formed between the bearing surface and the first seal surface provided on the inner peripheral surface of the sleeve portion and the outer peripheral surface of the shaft member. A first seal space that holds the liquid interface inside by pulling action of capillary force, a radial bearing that supports the shaft member in the radial direction with a fluid film generated in the radial bearing gap, and a shaft that contacts the end of the shaft member And a thrust bearing portion that supports the member in the thrust direction.

  Thus, in the hydrodynamic bearing device of the present invention, the members corresponding to the bearing sleeve and the seal member of the conventional product (for example, the hydrodynamic bearing device of Patent Document 1 above) are integrated as a sleeve portion. As a result, the number of components can be reduced, and the number of assembling steps of the hydrodynamic bearing device can be reduced, so that the manufacturing cost of the hydrodynamic bearing device can be reduced.

  In this hydrodynamic bearing device, for example, a shaft member is provided with a large-diameter portion, a small-diameter portion, and a shoulder surface therebetween, and the shoulder surface and the sleeve portion are engaged in the axial direction to prevent the shaft member from coming off. It can be performed. Further, a step surface can be provided on the inner peripheral surface of the sleeve portion, and the step surface can be engaged with the shoulder surface of the shaft member.

  In this case, the axial gap δ at the engaging portion between the shoulder surface of the shaft member and the sleeve portion is an axial movement amount allowed for the shaft member. That is, if the axial gap δ is large, the axial movement amount of the shaft member increases and the backlash of the shaft member increases. Therefore, it is preferable to set the axial gap δ as small as possible. The setting of the axial clearance δ is performed as follows, for example. First, the sleeve portion is brought into contact with the shoulder surface of the shaft member in a state where the end portion of the shaft member is in contact with the thrust bearing portion (see FIG. 5). Thereafter, the sleeve member engaged with the shoulder surface of the shaft member is moved in the same direction by pulling the shaft member in a direction away from the thrust bearing portion. Thus, by setting the axial gap δ by the amount of tension of the shaft member, the axial gap δ can be set with high accuracy regardless of the dimensional accuracy of the sleeve portion and the shaft member. For example, when a step surface is provided on the inner peripheral surface of the sleeve portion as described above, if this step surface is a molding surface, the processing accuracy of the step surface can be increased, and the axial clearance δ can be set with higher accuracy. Can do. When the axial clearance δ is set as described above, the end surface on the thrust bearing portion side of the sleeve portion is not in contact with the surface facing in the thrust direction (see FIG. 2).

  When an impact load is applied to such a hydrodynamic bearing device, a large load is applied to the contact portion between the shoulder surface of the shaft member and the sleeve portion. Therefore, it is desirable to perform a surface hardening process on the portion of the sleeve portion that engages with the shoulder surface of the shaft member.

  In the above hydrodynamic bearing device, for example, a second seal surface can be provided on the outer peripheral surface of the sleeve portion, and the second seal space can be formed by the second seal surface. Thus, in addition to the first seal space on the inner peripheral side of the sleeve portion, the volume of each seal space can be reduced by forming the second seal space on the outer peripheral side of the sleeve portion. Thus, the hydrodynamic bearing device can be downsized by the amount that the axial dimension of the seal space is reduced. Alternatively, the axial rigidity of the radial bearing portion can be increased by increasing the axial dimension of the seal space, and the bearing rigidity can be increased.

  If the pressure in the space facing the end of the shaft member on the thrust bearing portion side excessively increases or decreases for some reason, the bearing performance may be adversely affected. Therefore, if this space is communicated with the second seal space via the communication path, the pressure balance can be kept appropriate and the above-mentioned problems can be avoided.

  Incidentally, the sleeve portion 8 'shown in FIG. 7 has a large-diameter inner peripheral surface 8a1' as a radial bearing surface, a small-diameter inner peripheral surface 8a2 'as a first seal surface, and a step surface 8a3'. The small-diameter inner peripheral surface 8a2 'is a tapered surface that gradually increases in diameter upward, and functions as a first seal surface that forms a wedge-shaped first seal space with the outer peripheral surface of a shaft member (not shown). If an inner peripheral surface of such a sleeve portion 8 ′ is to be molded with the core rod 11 ′, an undercut occurs between the two as shown in the figure, and therefore it is extremely difficult to separate the sleeve portion 8 ′ and the core rod 11 ′. It may become difficult and may become impossible to mold. Accordingly, the tapered inner diameter surface 8a2 'having a tapered surface must be formed by a mold other than the core rod (for example, an upper punch) or formed by machining, resulting in a decrease in processing accuracy and an increase in processing cost. Will be invited.

  Therefore, in the hydrodynamic bearing device of the present invention, the sleeve portion is provided with a large-diameter inner peripheral surface as a radial bearing surface and a small-diameter inner peripheral surface as a first seal surface, and the shaft member is provided with a small-diameter portion from the shoulder surface. A tapered surface having a gradually reduced diameter is provided, and a first seal space is formed between the small diameter inner peripheral surface of the sleeve portion and the tapered surface of the shaft member. Thereby, since the small diameter inner peripheral surface of a sleeve part can be made into a cylindrical surface, the inner peripheral surface of a sleeve part can be shape | molded with a core rod, and a sleeve part can be processed with high precision and low cost.

  Further, in the above hydrodynamic bearing device, when the volume of the inner space of the bearing is increased, the total amount of the lubricating fluid filled in the bearing is increased, and the volume change of the lubricating fluid accompanying a temperature change is increased. For this reason, it is necessary to enlarge the volume of the seal space that absorbs the volume change of the lubricating fluid, which leads to an increase in size of the hydrodynamic bearing device. Therefore, in the hydrodynamic bearing device of the present invention, the sleeve portion is provided with a small-diameter inner peripheral surface as a radial bearing surface and a large-diameter inner peripheral surface facing the outer peripheral surface of the large-diameter portion of the shaft member. That is, the end of the sleeve portion on the thrust bearing portion side is extended to the outer diameter side of the large diameter portion of the shaft member (see FIG. 6). As a result, a part of the space inside the bearing can be filled and the lubricating fluid filled in the bearing can be reduced, so that an increase in size of the hydrodynamic bearing device can be avoided.

  As described above, according to the present invention, the manufacturing cost can be reduced without reducing the bearing performance of the fluid dynamic bearing device.

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

  FIG. 1 is a spindle motor for information equipment incorporating a hydrodynamic bearing device 1 according to an embodiment of the present invention. This spindle motor is used in a disk drive device such as an HDD. The spindle motor is supported by a hydrodynamic bearing device 1 that rotatably supports a shaft member 2, a disk hub 3 attached to the shaft member 2, and a radial gap. And a stator coil 4 and a rotor magnet 5, and a motor bracket 6. The stator coil 4 is attached to the outer periphery of the motor bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The hydrodynamic bearing device 1 is fixed to the inner periphery of the motor bracket 6. The disc hub 3 holds one or a plurality of discs D (two in FIG. 1) as information recording media. In this spindle motor, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force generated between the stator coil 4 and the rotor magnet 5, and accordingly, the disk hub 3 and the disk D are connected to the shaft member 2. Rotates together.

  As shown in FIG. 2, the hydrodynamic bearing device 1 mainly includes a shaft member 2, a sleeve portion 8 in which the shaft member 2 is inserted on the inner periphery, and a housing 7 that holds the sleeve portion 8 on the inner periphery. In the following description, the opening side of the housing 7 is the upper side and the closing side is the lower side in the axial direction.

  The shaft member 2 is formed by turning a metal material such as SUS steel. In the present embodiment, the shaft member 2 includes a large diameter portion 2a, a small diameter portion 2b provided above the large diameter portion 2a, and a shoulder surface 2c provided between the large diameter portion 2a and the small diameter portion 2b. The tapered surface 2d that extends from the shoulder surface 2c to the small-diameter portion 2b and gradually decreases in diameter upward is integrally formed. A spherical convex portion 2 a 2 is provided at the lower end portion of the shaft member 2.

  The sleeve portion 8 is formed of, for example, a sintered metal containing copper as a main component, and integrally includes a large-diameter inner peripheral surface 8a1, a small-diameter inner peripheral surface 8a2, and a step surface 8a3 provided therebetween. The outer peripheral surface 8d of the sleeve portion 8 is fixed to the inner peripheral surface 7a1 of the housing 7 by appropriate means such as press fitting, bonding, press fitting, welding. The sleeve portion 8 is not limited to a sintered metal, and can be formed of other metals, resins, ceramics, or the like.

  The large-diameter inner peripheral surface 8a1 of the sleeve portion 8 functions as a radial bearing surface and faces the outer peripheral surface 2a1 of the large-diameter portion 2a of the shaft member 2 via a radial bearing gap. For example, herringbone-shaped dynamic pressure grooves 8a11 and 8a12 as shown in FIG. 3 are formed in two regions separated in the axial direction on the large-diameter inner peripheral surface 8a1 as radial dynamic pressure generating portions. The upper dynamic pressure groove 8a11 is formed to be axially asymmetric with respect to the belt-like portion of the middle portion in the axial direction of the hill (shown by cross-hatching in FIG. 3), and the axial dimension X1 of the upper region from the belt-like portion is It is larger than the axial dimension X2 of the lower region (X1> X2).

  The small-diameter inner peripheral surface 8a2 of the sleeve portion is formed in a cylindrical surface shape, and this surface functions as a first seal surface. The small-diameter inner peripheral surface 8a2 is opposed to the tapered surface 2d of the shaft member 2, and a wedge-shaped first seal space S1 having a radial dimension gradually reduced downward is formed between these surfaces.

  The stepped surface 8 a 3 of the sleeve portion 8 faces the shoulder surface 2 c of the shaft member 2 via an axial gap δ, and this axial gap δ becomes the axially movable amount of the shaft member 2. When the step surface 8a3 and the shoulder surface 2c of the shaft member 2 are engaged in the axial direction, the shaft member 2 is prevented from coming off. When the hydrodynamic bearing device 1 is used for an HDD spindle motor as in this embodiment, the axial gap δ is set to 30 μm or less, preferably 20 μm or less in order to prevent interference between the disk and the head. It is desirable. In order to avoid damage to the sleeve portion 8 due to the engagement between the step surface 8a3 and the shoulder surface 2c of the shaft member 2, at least the step surface 8a3 of the sleeve portion 8 has a DLC (diamond-like carbon) film or MH. It is preferable to perform a surface hardening treatment such as (metal harding) treatment.

  The lower end surface 8c of the sleeve portion 8 is not in contact with the inner bottom surface 7b1 of the housing 7 facing in the thrust direction. An oil repellent (for example, a fluoropolymer) is applied to the upper end surface 8 b of the sleeve portion 8. When the lubricating oil filled in the bearing is about to overflow from the first seal space S1 due to the temperature rise, the lubricating oil can be prevented from invading to the upper end face 8b side of the sleeve portion 8 by the oil repellent agent. Lubricating oil can be held in the first seal space S1. At this time, an oil repellent may be applied to the upper end surface 7 a 2 of the side portion 7 a of the housing 7 and the outer peripheral surface of the shaft member 2. In addition, if the upper end surface 8b of the sleeve portion 8 is sealed, it is possible to prevent the lubricating oil impregnated in the sleeve portion 8 from leaking out of the surface opening of the upper end surface 8b.

  The sleeve portion 8 is formed as follows, for example.

  First, the metal powder is compacted and then sintered to obtain a sintered body 80 having the shape of the sleeve portion 8. In the present embodiment, as shown in FIG. 4A, a large-diameter inner peripheral surface 80a1, a small-diameter inner peripheral surface 80a2, and a step surface 80a3 are formed on the inner peripheral surface of the sintered body 80. By sizing the sintered body 80, the sintered body 80 is formed into a predetermined size. Specifically, the core rod 11 is inserted into the inner periphery of the sintered body 80 as shown in FIG. The core rod 11 has a large-diameter outer peripheral surface 11a, a small-diameter outer peripheral surface 11b, and a shoulder surface 11c. The large-diameter outer peripheral surface 11a of the core rod 11 is provided with molding portions corresponding to the dynamic pressure grooves 8a11 and 8a12 formed in the large-diameter inner peripheral surface 8a1 of the sleeve portion 8 (not shown). In the state shown in FIG. 4A, the sintered body 80 and the core rod 11 are in a state of clearance fitting, and the stepped surface 80a3 of the sintered body 80 and the shoulder surface 11c of the core rod 11 are engaged in the axial direction. ing. In FIG. 4A, the gap between the sintered body 80 and the core rod 11 is exaggerated for easy understanding.

  The upper end face 80b of the sintered body 80 is pressed from above by the upper punch 12, and in this state, the sintered body 80 is press-fitted into the inner periphery of the die 13 (see FIG. 4B). Thereby, the large diameter inner peripheral surface 80a1, the small diameter inner peripheral surface 80a2, and the stepped surface 80a3 of the sintered body 80 are pressed against the large diameter outer peripheral surface 11a, the small diameter outer peripheral surface 11b, and the shoulder surface 11c of the core rod 11, respectively. A large-diameter inner peripheral surface 8a1 as a radial bearing surface, a small-diameter inner peripheral surface 8a2 as a first seal surface, and a step surface 8a3 are formed. At the same time, the dynamic pressure grooves 8a11 and 8a12 are formed on the large-diameter inner peripheral surface 8a1 of the sleeve portion 8 by the forming portion of the large-diameter outer peripheral surface 11a of the core rod 11. Further, the outer peripheral surface 8d, the upper end surface 8b, and the lower end surface 8c of the sleeve portion 8 are formed by the die 13, the upper punch 12, and the lower punch 14, respectively. Thereafter, the sleeve portion 8, the core rod 11, and the upper punch 12 are pulled up from the inner periphery of the die 13. At this time, the inner peripheral surface of the sleeve portion 8 is slightly expanded in diameter by the spring back, and a minute gap is formed between the inner peripheral surface of the sleeve portion 8 and the outer peripheral surface of the core rod 11. Thereby, the sleeve part 8 and the core rod 11 can be separated without damaging the radial bearing surface and the dynamic pressure grooves 8a11, 8a12 formed on the sleeve part 8.

  In this embodiment, the wedge-shaped first seal space S1 is provided by providing the shaft member 2 with the tapered surface 2d as described above. Accordingly, the small-diameter inner peripheral surface 8a2 of the sleeve portion 8 can be a cylindrical surface, and no undercut occurs between the sleeve portion 8 and the core rod 11 (see FIG. 4). For this reason, the large-diameter inner peripheral surface 8a1, the small-diameter inner peripheral surface 8a2 and the stepped surface 8a3 of the sleeve portion 8 can be collectively formed with the core rod 11, and these surfaces can be processed easily and with high accuracy. Thus, since the large-diameter inner peripheral surface 8a1 as the radial bearing surface is processed with high accuracy, the width accuracy of the radial bearing gap is improved, and excellent bearing performance can be obtained. Moreover, since the small-diameter inner peripheral surface 8a2 as the first seal surface is processed with high accuracy, the volume of the first seal space S1 is set with high accuracy, and the sealing performance can be enhanced. Furthermore, since the stepped surface 8a3 is processed with high accuracy, the axial gap δ can be set with high accuracy, and the allowable axial movement amount of the shaft member 2 can be set with high accuracy. In addition, since these surfaces are collectively formed by the core rod 11, the relative positions of the surfaces are also set with high accuracy.

  By the way, when the bearing sleeve and the seal member are provided separately and are fixed to the inner peripheral surface of the housing, it is necessary to set the fixing accuracy with high accuracy, which may increase the assembly cost. . In addition, since the contact area between each member and the housing is relatively small, it is difficult to increase the accuracy and force of fixing to the housing. Further, for example, when the bearing sleeve is made of sintered metal and the seal member is made of a resin material, the sintered sleeve bearing sleeve is firmly fixed to the housing by the intrusion of the adhesive from the surface opening. Fixing force with the housing is weakened. On the other hand, when the bearing sleeve and the seal member are integrally provided as the sleeve portion 8 as in the present invention, the assembly process is simplified and costs can be reduced as compared with the case where they are provided separately. . Further, by integrating the bearing sleeve and the seal member, the contact area between the sleeve portion 8 and the housing 7 can be increased, and the fixing accuracy and fixing force to the housing 7 can be increased. Further, by forming the sleeve portion 8 with a material having a high fixing strength with the housing 7 (for example, sintered metal), the fixing force between the sleeve portion 8 and the housing 7 can be further increased.

  The housing 7 is formed of a resin material, for example, and has a cup shape integrally including a side portion 7a and a bottom portion 7b. Examples of the resin material for the housing 7 include crystalline resins such as liquid crystal polymer (LCP), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK), or polyphenyl sulfone (PPSU) and polyether sulfone (PES). ), A resin material based on an amorphous resin such as polyetherimide (PEI) can be used. In addition, fibrous resin such as glass fiber, whisker-like filler such as potassium titanate, scaly filler such as mica, carbon fiber, carbon black, graphite, carbon nanomaterial, various metal powders, etc. Various fillers such as fibrous or powdery conductive fillers may be blended in appropriate amounts according to the purpose.

  The material of the housing 7 is not limited to the above. For example, a low melting point metal material such as a magnesium alloy or an aluminum alloy may be used. Alternatively, the housing 7 can be formed by so-called MIM molding in which degreasing and sintering are performed after injection molding with a mixture of a metal powder and a binder, or press molding of a soft metal such as a metal material such as brass. Further, the housing bottom portion 7b is not necessarily formed integrally with the side portion 7a, and may be formed separately from the side portion 7a.

  The inner bottom surface 7b1 of the housing 7 has a thrust bearing portion T that contacts the spherical convex portion 2a2 at the lower end portion of the shaft member 2 and supports the shaft member in the thrust direction. In the present embodiment, the thrust bearing portion T is formed directly on the housing 7 as described above. However, the present invention is not limited to this, and is separately formed of, for example, a resin material or a sintered material having good wear resistance and sliding characteristics. A thrust washer may be disposed on the inner bottom surface of the housing 7 and the thrust bearing portion T may be formed on the thrust washer. In this case, since the housing 7 does not slide in contact with the shaft member 2, the housing 7 does not need wear resistance, and the range of material selection for the housing 7 is widened.

  Lubricating oil, for example, is injected as a lubricating fluid into the internal space of the hydrodynamic bearing device 1 configured as described above, that is, the internal space of the housing 7 sealed in the first seal space S1, and the housing 7 is filled with the lubricating oil (see FIG. Scattered area in 2). In this state, the oil level of the lubricating oil is maintained within the range of the first seal space S1. At this time, the space P on the housing closing side, that is, the space formed between the spherical convex portion 2a2 at the lower end of the shaft member 2 and the lower end surface 8c of the sleeve portion 8 and the inner bottom surface 7b1 of the housing 7, The axial gap δ between the shoulder surface 2c of the member 2 and the stepped surface 8a3 of the sleeve portion 8 is also filled with lubricating oil.

  Hereinafter, a method of setting the axial clearance δ between the shoulder surface 2c of the shaft member 2 and the step surface 8a3 of the sleeve portion 8 will be described.

  First, as shown in FIG. 5, the sleeve portion 8 and the shaft member 2 are accommodated in the inner periphery of the housing 7. At this time, the spherical convex portion 2a2 at the lower end of the shaft member 2 and the inner bottom surface 7b1 of the housing 7 are brought into contact with each other, and the shoulder surface 2c of the shaft member 2 and the step surface 8a3 of the sleeve portion 8 are brought into contact with each other. In this state, the sleeve portion 8 and the shaft member 2 are set in advance so that the lower end surface 8c of the sleeve portion 8 and the inner bottom surface 7b1 of the housing 7 are not in contact with each other. That is, these are designed so that the axial dimension L1 from the lower end surface 8c of the sleeve portion 8 to the stepped surface 8a3 is smaller than the axial dimension L2 from the lower end portion of the shaft member 2 to the shoulder surface 2c. (L1 <L2).

  Next, as shown by the arrow in FIG. 5, the shaft member 2 is pulled upward, and the sleeve portion 8 engaged with the shoulder surface 2 c of the shaft member 2 is moved upward with respect to the housing 7. This operation is performed while managing the amount of lifting of the shaft member 2 or the amount of movement of the sleeve portion 8 relative to the housing 7. Setting of the axial clearance δ (see FIG. 2) between the shoulder surface 2c of the shaft member 2 and the stepped surface 8a3 of the sleeve portion 8 is the amount by which the shaft member 2 is lifted (or the movement amount of the sleeve portion 8; hereinafter the same). When the value is reached, lifting of the shaft member 2 is stopped, and the sleeve portion 8 is fixed to the inner peripheral surface 7 a 1 of the housing 7. When the sleeve portion 8 and the housing 7 are fixed by press-fitting, the positioning and fixing of the sleeve portion 8 is completed when the shaft member 2 is pulled up by a predetermined amount. Further, if an adhesive is interposed between the mating surfaces of the sleeve portion 8 and the housing 7, the adhesive functions as a lubricant so that the movement of the sleeve portion 8 can be facilitated. The fixing strength can be increased.

  As described above, the axial gap δ is set to a predetermined value. According to this method, the axial gap δ that is the axially movable amount of the shaft member 2 can be set by the pulling amount of the shaft member 2. That is, since the positioning of the sleeve portion 8 can be performed with high accuracy regardless of the dimensional accuracy of the sleeve portion 8 and the shaft member 2, the dimensional accuracy of the sleeve portion 8 and the shaft member 2 is reduced, and the processing of these members is performed. Cost can be reduced.

  By the way, in the hydrodynamic bearing device in which the bearing sleeve and the seal member are formed separately as in the conventional product, when the axial clearance δ is set by the above method, only the seal member is moved relative to the housing. Become. At this time, since the contact area between the seal member and the housing is small, the seal member may be fixed in a state of being displaced with respect to the housing. On the other hand, if the bearing sleeve and the seal member are integrated as in the present invention, the contact area between the sleeve portion 8 and the housing 7 can be increased. Therefore, the sleeve portion 8 can be positioned with high accuracy with respect to the housing 7. can do.

  In the hydrodynamic bearing device 1 configured as described above, when the shaft member 2 rotates, a radial bearing gap is formed between the large-diameter inner peripheral surface 8a1 of the sleeve portion 8 and the outer peripheral surface 2a1 of the large-diameter portion 2a of the shaft member 2. . As the shaft member 2 rotates, the lubricating oil in the radial bearing gap is pushed into the belt-like portion side of the hill portion at the axial center of each of the dynamic pressure grooves 8a11 and 8a12, and the pressure rises. By such dynamic pressure action of the dynamic pressure grooves 8a11, 8a12, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner in the radial direction are configured. At the same time, the spherical convex portion 2a2 provided at the lower end of the shaft member 2 and the inner bottom surface 7b1 of the housing 7 serving as the thrust bearing portion T slide in contact with each other, whereby the shaft member 2 is contacted and supported in the thrust direction. The

  Further, in this embodiment, the dynamic pressure groove 8a11 of the first radial bearing portion R1 is formed to be axially asymmetric (X1> X2) with respect to the belt-like portion of the hill portion at the axially intermediate portion (see FIG. 3). ). For this reason, the pulling force (pumping force) of the lubricating oil by the dynamic pressure groove 8a11 accompanying the rotation of the shaft member 2 is larger in the upper region than in the lower region. Due to the differential pressure of the pulling force, it is possible to prevent the lubricating oil filled in the radial bearing gap from flowing downward and generating a negative pressure in the space P (see FIG. 2) on the housing closing side. In addition, by forcing the lubricating oil in the radial bearing gap downward, the pressure in the space P on the housing closing side increases, and an upward force may be generated on the shaft member 2 in some cases. Considering the balance between the upward force generated in the shaft member 2 and the downward force due to the weight of the disk hub 3 and the disk D, the unbalance amount (X1 and X2) of the upper region and the lower region of the dynamic pressure groove 8a11 The difference may be set as appropriate.

  The present invention is not limited to the above embodiment. Hereinafter, other embodiments of the present invention will be described. In the following description, parts having the same configuration and function as those in the above embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the hydrodynamic bearing device 10 shown in FIG. 6, the shaft member 2 includes a shaft portion 2b as a small diameter portion and a flange portion 2a as a large diameter portion provided at the lower end of the shaft portion 2b. The outer peripheral surface 2b1 of the shaft portion 2b is formed in a cylindrical surface shape, and a spherical convex portion 2a2 protruding downward is formed on the lower end surface of the flange portion 2a. The sleeve portion 8 has a large-diameter inner peripheral surface 8a1 facing the large-diameter outer peripheral surface 2a1 of the shaft member 2, and a small-diameter inner peripheral surface 8a2 serving as a radial bearing surface. The upper end surface of the flange portion 2a as the shoulder surface 2c of the shaft member 2 and the step surface 8a3 of the sleeve portion 8 face each other with an axial gap δ therebetween.

  On the upper side of the small-diameter inner peripheral surface 8a2 of the sleeve portion 8, an inner peripheral tapered surface 8e that gradually increases in diameter upward and functions as a first seal surface is provided. A first seal space S1 is formed between the inner peripheral tapered surface 8e and the outer peripheral surface 2a1 of the shaft portion 2a of the shaft member 2. Further, on the upper side of the outer peripheral surface 8d of the sleeve portion 8, an outer peripheral tapered surface 8f that gradually decreases in diameter toward the upper side and functions as a second seal surface is formed. A second seal space S2 is formed between the outer peripheral tapered surface 8f and the inner peripheral surface 7a1 of the housing 7. By providing the two seal spaces S1 and S2 in this way, the volumes of the seal spaces S1 and S2 can be reduced while maintaining a buffer function that absorbs the volume change of the lubricating oil inside the bearing. Accordingly, the axial dimensions of the seal spaces S1 and S2 can be reduced, and the axial dimension of the radial bearing gap can be enlarged by this reduction, thereby improving the bearing rigidity in the radial direction. Alternatively, the hydrodynamic bearing device 1 can be made thinner by the amount that the axial dimensions of the seal spaces S1 and S2 are reduced.

  Since the first seal space S1 is arranged in the axial direction with the radial bearing gap, if the axial dimension of the first seal space S1 is increased, the axial dimension of the radial bearing gap can be reduced, or the hydrodynamic bearing device. 10 increase in size. On the other hand, since the second seal space S2 is arranged at a position different from the radial bearing gap in the radial direction, the axial dimension can be enlarged regardless of the radial bearing gap. Therefore, the first seal space S1 can be further reduced by making the volume of the second seal space S2 larger than the volume of the first seal space S1.

  On the outer peripheral surface 8d of the sleeve portion 8, axial grooves 8d1 are formed at a plurality of locations (for example, three locations) at equal intervals in the circumferential direction. The axial groove 8d1 can be molded simultaneously with the compacting of the sleeve portion 8 by providing a molding portion corresponding to the axial groove 8d1 in advance in the molding die of the sleeve portion 8, for example. The communication path formed by this axial groove 8d1 and the inner peripheral surface 7a1 of the housing 7 allows the second seal space S2 and the space P on the housing closing side to communicate with each other. Thereby, the pressure balance of the lubricating oil filled in the space P can be properly maintained.

  When a dynamic pressure groove having an unbalance as shown in FIG. 3 is formed on the small-diameter inner peripheral surface 8a2 of the sleeve portion 8, the lubricating oil in the radial bearing gap is forcibly pushed downward as in the above embodiment. In this case, for example, if a radial communication path that connects the first seal space S <b> 1 and the second seal space S <b> 2 is provided, the lubricating oil pushed downward in the radial bearing gap is the space on the closed side of the housing 7. P → Axial groove 8d1 → second seal space S2 → radial communication path → first seal space S1 is circulated and drawn back into the radial bearing gap. In this way, by forcibly flowing and circulating the lubricating oil inside the bearing, a situation in which a local negative pressure is generated in the lubricating oil can be more effectively prevented. In particular, as in the present invention, by integrating the seal member and the bearing sleeve in the conventional product as the sleeve portion 8, it becomes possible to circulate the lubricating oil through a wide path including the seal space. Can be reliably prevented. The radial communication path that communicates the first seal space S1 and the second seal space S2 can be configured by, for example, a radial through hole in the sleeve portion 8. Alternatively, the radial communication path can be configured by making the internal porosity in the region between the first seal space S1 and the second seal space S2 of the sleeve portion 8 higher than the other regions. it can. When it is desired to circulate the lubricating oil in the direction opposite to the above path, for example, the dynamic pressure groove unbalance may be formed in the direction opposite to the example shown in FIG. 3, that is, X1 <X2. Moreover, when it is not necessary to forcibly circulate the lubricating oil inside the bearing as described above, the dynamic pressure grooves may be formed symmetrically in the axial direction.

  In the hydrodynamic bearing device 10 shown in FIG. 6, the lower end portion of the sleeve portion 8 is extended to the outer diameter side of the flange portion 2a (large diameter portion) of the shaft member 2, and the large diameter inner peripheral surface 8a1 of the sleeve portion 8 is used as the shaft. The member 2 is opposed to the large-diameter outer peripheral surface 2a1. Thereby, a part of the space P on the closed side of the housing 7 provided on the thrust bearing portion T side of the bearing sleeve 8 is filled, and the amount of lubricating oil filled in the space P can be reduced, and the seal space S1 and It becomes possible to further reduce the volume of S2.

  Further, in the hydrodynamic bearing devices 1 and 10 shown in FIGS. 2 and 6, the lower end surface 8c of the sleeve portion 8 may be extended further downward to further reduce the volume of the space P. However, it is limited to a range in which the lower end surface 8c of the sleeve portion 8 is not in contact with the inner bottom surface 7b1 of the housing 7 in a state in the middle of the assembly shown in FIG. Further, a step portion can be provided on the outer diameter portion of the inner bottom surface 7b1 of the housing 7, and the volume of the space P can be reduced by this step portion. Alternatively, by disposing a separately provided member in the space P, the volume of the space P can be reduced.

  In the above embodiment, the pivot bearing is configured by bringing the spherical convex portion 2a2 of the shaft member 2 into contact with the inner bottom surface 7b1 of the housing 7, but conversely, the inner bottom surface side of the housing 7 is formed. In addition to providing a convex portion, the lower end surface of the shaft member 2 may be a flat surface and may be brought into contact with each other. Or you may provide a convex part in both and this convex part may be made to contact. In addition, these convex portions may be formed in a curved surface shape having an elliptical cross section in addition to a spherical shape as described above, as long as they contact a member facing in the thrust direction. Further, in the above-described embodiment, the entire lower end portion of the shaft member 2 is a spherical convex portion. However, the present invention is not limited to this, and for example, the lower end surface of the shaft member and a part of the inner bottom surface of the housing are projected to form the convex portion. It may be formed.

  In the above-described embodiment, the herringbone-shaped dynamic pressure groove is formed as the dynamic pressure generating portion that generates the dynamic pressure action in the lubricating fluid in the radial bearing gap. A pressure groove, a step bearing, or a multi-arc bearing may be employed. Alternatively, both the inner peripheral surface of the sleeve portion and the outer peripheral surface of the shaft member facing each other through the radial bearing gap may be formed into a cylindrical surface shape to constitute a so-called perfect circle bearing.

  In the above-described embodiment, the radial dynamic pressure generating portion is formed on the sleeve portion 8 side. However, a dynamic pressure groove may be formed on the shaft member side facing this surface via a radial bearing gap.

  Moreover, in said embodiment, although radial bearing part R1, R2 is spaced apart and provided in the axial direction, you may provide these continuously in an axial direction. Alternatively, only one of these may be provided.

  Further, in the above-described embodiment, the lubricating oil is exemplified as the fluid that fills the fluid bearing devices 1 and 10 and generates the dynamic pressure action in the radial bearing gaps. A fluid that can be generated, for example, a gas such as air, a magnetic fluid, or lubricating grease may be used.

  In addition, the hydrodynamic bearing device of the present invention is not limited to the spindle motor used in the disk drive device such as the HDD as described above, but is a information device used under high-speed rotation, such as a spindle motor for driving a magneto-optical disk of an optical disk. It can also be suitably used as a fan motor for supporting a rotating shaft in a polygonal motor for a laser beam printer, a polygon scanner motor of a laser beam printer, or a cooling fan for electrical equipment.

It is sectional drawing of the spindle motor incorporating the hydrodynamic bearing apparatus. It is sectional drawing of a hydrodynamic bearing apparatus. It is sectional drawing of a sleeve part. (A) And (b) is sectional drawing which shows the formation process of a sleeve part. It is sectional drawing which shows the setting method of axial direction clearance gap (delta). It is sectional drawing of the hydrodynamic bearing apparatus which concerns on other embodiment of this invention. It is sectional drawing which shows the case where an undercut arises between a sleeve part and a core rod.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid dynamic bearing apparatus 2 Shaft member 2a Large diameter part 2a2 Spherical convex part 2b Small diameter part 2c Shoulder surface 2d Tapered surface 7 Housing 8 Sleeve part 8a1 Large diameter inner peripheral surface (radial bearing surface)
8a11, 8a12 Dynamic pressure groove 8a2 Small diameter inner peripheral surface (first seal surface)
8a3 Stepped surface 8e Inner circumferential taper surface (first seal surface)
8f Tapered outer surface (second seal surface)
R1 First radial bearing portion R2 Second radial bearing portion T Thrust bearing portion S1 First seal space S2 Second seal space δ Axial clearance

Claims (10)

  A shaft member, a sleeve portion in which the shaft member is inserted on the inner periphery, a radial bearing gap formed between the radial bearing surface provided on the inner peripheral surface of the sleeve portion and the outer peripheral surface of the shaft member, and the sleeve portion A first seal that is formed between a first seal surface provided on the inner peripheral surface and the outer peripheral surface of the shaft member, and holds the gas-liquid interface of the lubricating fluid filled in the bearing inside by drawing action of capillary force. Fluid bearing comprising a space, a radial bearing portion that supports the shaft member in the radial direction with a fluid film generated in the radial bearing gap, and a thrust bearing portion that contacts the end portion of the shaft member and supports the shaft member in the thrust direction apparatus.   The hydrodynamic bearing device according to claim 1, wherein the shaft member is provided with a large-diameter portion, a small-diameter portion, and a shoulder surface between them, and the shoulder surface and the sleeve portion can be engaged in the axial direction.   The hydrodynamic bearing device according to claim 2, wherein a stepped surface that can be engaged with a shoulder surface of the shaft member is provided on an inner peripheral surface of the sleeve portion.   The hydrodynamic bearing device according to claim 3, wherein the stepped surface of the sleeve portion is a molding surface.   The hydrodynamic bearing device according to claim 2, wherein an end surface of the sleeve portion on the thrust bearing portion side is not in contact with a surface opposed in the thrust direction.   The hydrodynamic bearing device according to claim 2, wherein a surface hardening process is performed on a portion of the sleeve portion that engages with a shoulder surface of the shaft member.   The hydrodynamic bearing device according to claim 1, wherein a second seal space is formed by a second seal surface provided on an outer peripheral surface of the sleeve portion.   8. The hydrodynamic bearing device according to claim 7, further comprising a communication passage that communicates the space facing the end of the shaft member on the thrust bearing portion side and the second seal space.   The sleeve portion is provided with a large-diameter inner peripheral surface as a radial bearing surface and a small-diameter inner peripheral surface as a first seal surface, and a tapered surface gradually reduced in diameter from the shoulder surface toward the small-diameter portion on the shaft member. The hydrodynamic bearing device according to claim 2, wherein a first seal space is formed between the small-diameter inner peripheral surface of the sleeve portion and the tapered surface of the shaft member.   The hydrodynamic bearing device according to claim 2, wherein the sleeve portion is provided with a small-diameter inner peripheral surface as a radial bearing surface and a large-diameter inner peripheral surface facing the outer peripheral surface of the large-diameter portion of the shaft member.

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