JP6347986B2 - Fluid dynamic bearing device and motor including the same - Google Patents

Description

  The present invention relates to a fluid dynamic bearing device and a motor including the same.

  A fluid dynamic pressure bearing device is a bearing device that uses a lubricating oil film formed in a bearing gap and supports a rotation-side member (for example, a shaft member) and a stationary-side member (for example, a housing) in a non-contact manner so as to be relatively rotatable. . This fluid dynamic pressure bearing device has characteristics such as high-speed rotation, high rotation accuracy, and low noise. Recently, a disk drive device (for example, a magnetic disk drive device such as an HDD or the like, a CD) In addition, it is suitably used as a motor bearing device such as a spindle motor of an optical disc drive device such as a DVD or a Blu-ray disc, a polygon scanner motor of a laser beam printer (LBP), or a fan motor for cooling electric or electronic equipment.

  For example, FIG. 2 and FIG. 3 of Patent Document 1 listed below include a shaft member, a radial bearing portion that supports the shaft member in the radial direction with an oil film formed in a radial bearing gap, and the shaft member and the radial bearing portion. A fluid dynamic pressure bearing device including a housing housed in the periphery is described. In this fluid dynamic pressure bearing device, the housing is formed in a cylindrical shape with both axial ends open, and the one end opening is closed with a resin lid member.

JP 2004-28165 A

  A resin lid member as described in Patent Document 1 is generally injection-molded using a molding die. After injection molding, the mold is opened and the lid member is removed from the mold. In general, the lid member is taken out from the molding die by dividing the solidified resin material in the molding die (actually in the gate of the molding die or in the vicinity of the gate outlet). is there. Accordingly, in many cases, a part of the resin material solidified in the molding die remains as a gate mark on the lid member.

  By the way, when the components of the fluid dynamic bearing device including the lid member are injection-molded with resin, a filler (for example, fiber such as glass fiber) is used to increase the mechanical strength and dimensional stability of the molded product. It is common to use a resin material containing a filler. Therefore, a part of the filler contained in the resin material is likely to be exposed on the split section of the gate mark remaining on the molded product (lid member). If the lid member is left in this state, a part or all of the filler exposed on the cross section of the gate trace may fall off and become contaminated, which may adversely affect the bearing performance and, consequently, the motor performance. Such a problem can be avoided as much as possible by removing gate traces or the like in post-processing (execution of gate processing). However, when gate processing is performed, the lid is made of resin as much as the number of processing steps increases. It is impossible to fully enjoy the cost merit of using the injection molded product.

  In view of such a situation, an object of the present invention is to reduce the cost of a fluid dynamic bearing device in which one end opening of a housing is closed with a lid member while stably maintaining desired bearing performance. is there.

The present invention, which was created to achieve the above object, includes a shaft member, a radial bearing portion that supports the shaft member in the radial direction with an oil film of lubricating oil formed in the radial bearing gap, and both ends in the axial direction are open. A hydrodynamic pressure bearing comprising a housing having a cylindrical shape and containing a shaft member and a radial bearing portion on the inner periphery, and a lid member that is injection-molded with a resin material containing a filler and closes one end opening of the housing In the apparatus, the lid member is injection-molded into a disk shape by a molding die having a gate having an opening diameter D with respect to the cavity smaller than 0.5 mm, and the resin material solidified in the molding die is used to release the lid member. with and have a gate mark in a state of being formed by being divided, gate mark is formed in a concave shape opened in the inner end surface or outer end surface of the lid member, of the lid member, gate mark is formed Part Where t> 0.86D + La + 6Lσ where t is the separation distance between both end faces when there is no gate trace, La is the average length of the filler, and Lσ is the standard deviation of the longitudinal dimension of the filler. It is characterized by satisfying .

  In the fluid dynamic pressure bearing device according to the present invention, the lid member injection-molded in a disk shape with a resin material containing a filler, the resin material solidified in the molding die of the lid member is accompanied by the release of the lid member. It has a gate mark formed by being divided. This means that the lid member, which is an injection molded product of resin, is used in a released state. Therefore, the manufacturing cost of the lid member is reduced by the amount that the gate processing after the mold release is omitted, and as a result, the cost of the fluid dynamic bearing device can be reduced. Further, since the lid member is injection-molded into a disk shape, predetermined dimensional and shape accuracy can be secured easily and stably. Furthermore, since the lid member is injection-molded with a resin material containing a filler, the mechanical strength and dimensional stability required for the lid member can be ensured by selecting and using an appropriate filler. From the above, it is possible to reduce the cost while ensuring the bearing performance required for the fluid dynamic bearing device. Whether or not the gate trace has been subjected to gate processing (whether or not the state at the time of mold release is maintained) is, for example, that the gate trace has a concavo-convex shaped section (dividing part). It can be judged by whether or not.

  As described above, the gate treatment after the mold release can be omitted because the inventors of the present application have made extensive studies, and as a result, a gate (a point-like gate) having an opening diameter D with respect to the cavity smaller than 0.5 mm. This is because it has been found that the lid member may be injection-molded into a disc shape with a molding die having the same. That is, if the opening diameter D of the gate with respect to the cavity is smaller than 0.5 mm, it is possible to prevent the filling material from being exposed as much as possible from the divided portion (divided section) of the gate trace, and the lid member is a disc. If the gate has a simple shape, even if the opening diameter D with respect to the cavity is smaller than 0.5 mm, the cavity is filled with a resin material (a molten resin material) without a gap, and a highly accurate molded product is obtained. Because it can. However, if the opening diameter D of the gate is too small, the resin injection property is lowered, and it becomes difficult to mold the lid member with a predetermined accuracy. Therefore, the opening diameter D is set to 0.2 mm or more (0.2 mm ≦ D <0.5 mm).

  The gate mark may be formed in a convex shape protruding on the inner end surface or the outer end surface of the lid member, but is preferably formed in a concave shape opened on the inner end surface or the outer end surface of the lid member. Since the gate trace part can be arranged on the inner periphery of the concave part, the gate mark part comes into contact with a mating member such as a shaft member. As a result, the filler contained in the lid member is a fluid dynamic pressure bearing. This is because it is possible to reduce the possibility of dropping off in the inner space of the device or the periphery of the fluid dynamic bearing device. In this case, in the portion of the lid member where the gate trace (concave gate trace) is provided, the separation distance between both end faces when the gate trace does not exist is t, the average length of the filler is La, and the length of the filler It is preferable that the relational expression t> 0.86D + La + 6Lσ is satisfied, where Lσ is the standard deviation. In this way, even when the gate trace is formed in a concave shape and the filler is dropped from the portion of the lid member where the gate trace is provided, the both end surfaces of the lid member are prevented from being in communication. be able to. Thereby, it is possible to prevent a fatal problem such as external leakage of the lubricating oil interposed in the internal space of the housing.

  The gate mark is preferably arranged (formed) on the axis of the disc-shaped lid member. Such a lid member can be obtained by injection molding using a molding die whose gate is opened at a position corresponding to the center of the end surface of the lid member in the cavity. In this case, when the molten resin material (molten resin) is filled into the cavity through the gate, the molten resin spreads evenly outward in the radial direction from the center of the cavity. Therefore, the occurrence of welds can be avoided, and a lid member with high strength and high accuracy can be obtained.

  As the resin material for forming the lid member, a material containing a fibrous filler can be suitably used. This is because a high-strength lid member can be easily obtained. Examples of the fibrous filler that can be used include glass fiber (GF) and carbon fiber (CF). Of course, the resin material can include other fillers (for example, carbon black) according to the required characteristics of the lid member.

  The lid member is preferably fixed to the inner periphery of one end of the housing. In this way, as compared with the case where the lid member is fixed to one end surface of the housing, the diameter of the lid member can be reduced, so that a molding die for the lid member having a small cavity volume should be used. Can do. If the volume of the cavity is reduced, it becomes possible to use a gate with a smaller opening diameter, so that the gate trace can be reduced, and as a result, the filler may fall off from the gate trace. Further reduction can be achieved.

  The fluid dynamic pressure bearing device according to the present invention further includes a thrust bearing gap formed on the inner end face of the lid member, and a thrust dynamic pressure generating section for generating a dynamic pressure action on the lubricating oil in the thrust bearing gap. It can be. In this case, the thrust dynamic pressure generating portion can be molded on the inner end surface of the lid member simultaneously with the injection molding of the lid member. Thereby, the thrust bearing part which non-contact-supports a shaft member in one thrust direction can be constructed at low cost.

  A sleeve portion that forms a radial bearing gap with the outer peripheral surface of the shaft member may be fixed to the inner peripheral surface of the housing. Alternatively, a sleeve portion that forms a radial bearing gap between the outer peripheral surface of the shaft member and the inner peripheral surface of the housing may be fixed. If any one of these configurations is adopted, the required characteristics required for each part of the fluid dynamic bearing device can be easily optimized.

  The fluid dynamic pressure bearing device according to the present invention described above includes a motor having a stator coil and a rotor magnet, for example, a spindle motor for a disk drive device, a fan motor for a cooling fan, and a laser beam printer. It can be suitably used by being incorporated in a polygon scanner motor or the like.

  As described above, according to the present invention, in a fluid dynamic bearing device in which one end opening of a housing is closed with a lid member, the desired bearing performance can be stably maintained and the cost can be reduced. Can do.

It is a schematic sectional drawing of the spindle motor incorporating the fluid dynamic pressure bearing apparatus. 1 is a cross-sectional view including a shaft of a fluid dynamic bearing device according to a first embodiment of the present invention. (A) The figure is sectional drawing of a sleeve part, (b) The figure is a top view which shows the lower end surface of a sleeve part. (A) A figure is a top view which shows the inner bottom face of a cover member, (b) A figure is an XX arrow expanded sectional view in (a) figure. It is a principal part schematic sectional drawing of the formation process of a cover member. It is a principal part schematic sectional drawing in the completion | finish stage of the formation process of a cover member. It is a shaft-containing sectional view of a fluid dynamic bearing device according to a second embodiment of the present invention. It is a shaft-containing sectional view of a fluid dynamic bearing device according to a third embodiment of the present invention.

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

  FIG. 1 is a schematic cross-sectional view of a spindle motor for information equipment in which a fluid dynamic bearing device is incorporated. The spindle motor is used in a disk drive device such as an HDD, and includes a fluid dynamic pressure bearing device 1, a disk hub 3 fixed to a shaft member 2 of the fluid dynamic pressure bearing device 1, and a radial gap, for example. , A stator coil 4 and a rotor magnet 5, and a motor base 6. The stator coil 4 is attached to the outer periphery of the motor base 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the fluid dynamic bearing device 1 is fixed to the inner periphery of the motor base 6. The disk hub 3 holds one or a plurality of disks D (two in the illustrated example). In the above configuration, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the disk hub 3 and the disk 9 held by the disk hub 3 are rotated. It rotates integrally with the shaft member 2.

  FIG. 2 shows a fluid dynamic bearing device 1 according to the first embodiment of the present invention. The fluid dynamic bearing device 1 includes a shaft member 2, a sleeve portion 8 disposed on the outer diameter side of the shaft member 2, a cylindrical housing 7 in which the shaft member 2 and the sleeve portion 8 are accommodated on the inner periphery, And a lid member 10 that closes one end opening of the housing 7. The internal space of the housing 7 is filled with lubricating oil (indicated by dense dotted hatching). In the following, for convenience of explanation, the side on which the lid member 10 is provided is referred to as the lower side, and the opposite side in the axial direction is referred to as the upper side. However, the usage mode of the fluid dynamic bearing device 1 is not limited.

  The shaft member 2 is formed of a melted material (non-porous metal material typified by stainless steel), and includes a shaft portion 21 and a flange portion 22 provided integrally or separately at the lower end of the shaft portion 21. .

  For example, the sleeve portion 8 is formed of a porous body of sintered metal in a cylindrical shape, and is fixed to the small-diameter inner peripheral surface 7 a 1 of the housing 7. The sleeve portion 8 can also be formed of another porous body typified by a porous resin, or a soft metal such as brass.

  On the inner peripheral surface 8a of the sleeve portion 8, cylindrical radial bearing surfaces that form radial bearing gaps of the radial bearing portions R1 and R2 between the opposed outer peripheral surface 21a of the shaft portion 21 are provided at two axial positions. They are spaced apart. As shown in FIG. 3A, radial dynamic pressure generating portions A1 and A2 for generating a dynamic pressure action on the lubricating oil in the radial bearing gap are formed on the two radial bearing surfaces. The radial dynamic pressure generating parts A1 and A2 of the present embodiment are each provided with a plurality of upper dynamic pressure grooves Aa1 and lower dynamic pressure grooves Aa2 that are inclined in opposite directions and spaced apart in the axial direction. It has convex hills that define the dynamic pressure grooves Aa1 and Aa2, and has a herringbone shape as a whole. The hill part is provided between the inclined hill part Ab provided between the dynamic pressure grooves adjacent in the circumferential direction, and the annular hill part Ac provided between the upper and lower dynamic pressure grooves Aa1 and Aa2 and having substantially the same diameter as the inclined hill part Ab. Consists of.

  An annular thrust bearing surface that forms a thrust bearing gap of the first thrust bearing portion T1 between the lower end surface 8b of the sleeve portion 8 and the upper end surface 22a of the opposing flange portion 22 is provided. As shown in FIG. 3B, a thrust dynamic pressure generating portion B for generating a dynamic pressure action on the lubricating oil in the thrust bearing gap is formed on the thrust bearing surface. The thrust dynamic pressure generating portion B in the illustrated example is configured by alternately arranging spiral-shaped dynamic pressure grooves Ba and hill portions defining and forming the dynamic pressure grooves Ba in the circumferential direction. The thrust dynamic pressure generating portion B may be formed on the upper end surface 22a of the opposing flange portion 22.

  The housing 7 integrally includes a relatively thin and cylindrical side portion 7a and a relatively thick and ring-shaped seal portion 7b provided on the upper side of the side portion 7a. It is made of a lumber (non-porous metal material such as brass or stainless steel) or a resin material and has a substantially cylindrical shape with both axial ends opened. The side portion 7a has a small-diameter inner peripheral surface 7a1 and a large-diameter inner peripheral surface 7a2, and the inner peripheral surfaces 7a1 and 7a2 are bonded to the inner peripheral surfaces 7a1 and 7a2 by appropriate means such as adhesion, press-fitting, and press-fitting (combination of press-fitting and adhesion) The sleeve portion 8 and the lid member 10 are fixed.

  The inner peripheral surface 7b1 of the seal portion 7b is formed in a tapered surface shape that is gradually reduced in diameter downward (inside the housing 7), and a wedge-shaped seal space between the outer peripheral surface 21a of the opposed shaft portion 21. S is formed. The upper end surface 8c of the bearing sleeve 8 is in contact with the inner diameter side region of the lower end surface 7b2 of the seal portion 7b, and the housing 7 and the bearing sleeve 8 are relatively positioned in the axial direction. The seal space S has a buffer function that absorbs the volume change amount accompanying the temperature change of the lubricating oil filled in the internal space of the housing 7, and always seals the oil surface of the lubricating oil within the assumed temperature change range. Hold in the space S. Therefore, lubricating oil leakage from the internal space of the housing 7 is effectively prevented. The seal part 7b and the side part 7a may be provided separately.

  The lid member 10 has a disk shape, is fixed to the large-diameter inner peripheral surface 7a2 of the housing 7 by an appropriate means, and closes the lower end opening of the housing 7. The lid member 10 is made of, for example, a crystalline resin such as liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyacetal (POM), polyamide (PA), or polyphenylsulfone (PPSU). ), Polyethersulfone (PES), polyetherimide (PEI), polyamideimide (PAI), etc., and a resin material using an amorphous resin as a base resin. For example, only one kind of the base resin may be selected and used, or two or more kinds may be mixed and used. Here, a resin material using LCP as the base resin is used. Examples of the base resin include fibrous fillers such as glass fibers (GF) and carbon fibers (CF), whisker-like fillers such as potassium titanate, scaly fillers such as mica, carbon black, graphite, carbon nano At least one selected from the group of powdery fillers such as materials is blended according to the required characteristics of the lid member 10. In the present embodiment, a resin material containing carbon fiber and carbon black is used from the viewpoint of enhancing the strength and dimensional stability of the lid member 10 and imparting high conductivity to the lid member 10.

  As shown in FIG. 4A, a thrust bearing gap of the second thrust bearing portion T2 is formed between the upper end surface (inner end surface) 10a of the lid member 10 and the lower end surface 22b of the opposing flange portion 22. An annular thrust bearing surface is provided. A thrust dynamic pressure generating portion C for generating a dynamic pressure action on the lubricating oil in the thrust bearing gap of the second thrust bearing portion T2 is formed on the thrust bearing surface. The illustrated thrust dynamic pressure generating portion C is configured by arranging a plurality of spiral dynamic pressure grooves Ca in the circumferential direction. The thrust dynamic pressure generating portion C may be formed on the lower end surface 22b of the opposing flange portion 22.

  The lid member 10 has a gate mark 11 disposed on the axis of the upper end surface 10a. The gate mark 11 of the present embodiment has a concave shape opened on the axial center of the upper end surface 10a of the lid member 10, and is made of a resin material solidified in the molding die 30 (see FIG. 5, details will be described later). The state formed by being divided along with the release of the lid member 10 is maintained. That is, the concave gate mark 11 has an uneven-shaped dividing portion 12 formed by dividing the resin material solidified in the molding die 30 as the lid member 10 is released [FIG. 4 (b)].

Here, since the lid member 10 has the gate trace 11 (the gate trace 11 from which the removal process after the mold release or the like is omitted) of the above aspect, the filler (particularly, the filler included in the resin material constituting the lid member 10 (particularly, There is a possibility that a long fibrous filler (here, carbon fiber) may fall off. In this case, holes are formed in both end faces 10a and 10b of the lid member 10 where the filler has fallen, and the lubricating oil filled in the internal space of the housing 7 leaks to the outside through the holes. Such a fatal problem can occur. Therefore, in order to prevent the above fatal problem from occurring as much as possible, while making it possible to omit the gate processing after the lid member 10 is released, the portion of the lid member 10 where the gate mark 11 is formed (the lid member 10). The following relational expression (1) is satisfied at the axial center).
Relational expression (1): t> 0.86D + La + 6Lσ
However, t: separation distance [unit: mm] between both end faces 10a and 10b when the gate trace 11 does not exist in the portion of the lid member 10 where the gate trace 11 is formed, D: the gate 34 with respect to the cavity 33 The opening diameter of La (see FIG. 5), La: average length of filler, and Lσ: standard deviation of filler length. Here, the “filler” refers to the filler having the maximum average length among the fillers included in the molding resin material of the lid member 10.

  In the above relational expression (1), “0.86D” is the gate when the concave gate mark 11 opened on the upper end surface (inner end surface) 10a or the lower end surface (outer end surface) 10b of the lid member 10 is formed. The opening dimension of the trace 11 is about the opening diameter of the gate 34 at the maximum, and when the gate 34 having an opening diameter smaller than 0.5 mm is employed, the cross-sectional shape of the gate trace 11 is on the bottom side of the gate trace 11. As a result of intensive studies by the inventor of the present application, the angle θ formed by the two sides defining the bottom of the gate trace 11 does not become smaller than 60 ° while the opening size is gradually reduced toward the opening. This is because they found it. That is, “0.86D” can be derived from (D / 2) × √3. Further, the reason why “6Lσ” is added in the above equation is because variation in the length of the filler (fibrous filler) to be used is taken into consideration. That is, it is practically impossible to use a filler having no variation in length, and if a value corresponding to 6 times the standard deviation of the filler length is added, the filler used Even if there is a variation in length, it is possible to reliably prevent the above-mentioned fatal problem from occurring.

  The lid member 10 having the above configuration can be manufactured through, for example, the following molding process.

  FIG. 5 conceptually shows the main part of the molding process of the lid member 10. The molding die 30 shown in the figure includes a first die 31 and a second die 32 that are coaxially arranged so as to be relatively close to and away from each other, and in a state where both the die 31 and 32 are clamped. A cavity 33 corresponding to the shape of the lid member 10 is defined between the molds 31 and 32. The first mold 31 has a molding surface 31a for molding the upper end surface 10a of the lid member 10, and a dotted gate 34 as a gate opened to the cavity 33. Thrust dynamic pressure is generated on the molding surface 31a. A mold part corresponding to the shape of the part C is provided (not shown). The dotted gate 34 opens in the cavity 33 at a position corresponding to the axial center portion of the upper bottom surface 10 a of the lid member 10. The opening diameter D of the dotted gate 34 is set smaller than 0.5 mm (D <0.5 mm), and here, D = 0.3 mm. Considering that the gate trace 11 may be formed in the concave shape as described above, a relational expression for “D” obtained by modifying the relational expression (1), that is, D <{t− The opening diameter D of the dotted gate 34 is set so as to further satisfy the relational expression (La + 6Lσ)} / 0.86.

  As a specific example, here, in the portion where the gate trace 11 is to be formed in the lid member 10, the distance between the both end faces 10 a and 10 b when the gate trace 11 does not exist = 1.05 mm. The member 10 is injection-molded with a resin material containing carbon fibers having an average length La = 0.08 mm and a standard deviation Lσ = 0.1 mm. In this case, among the relational expressions for “D” obtained by modifying the above relational expression (1), the value of {t− (La + 6Lσ)} / 0.86 is {1.05− (0.08 + 6 × 0.1)} / 0.86 = 0.43. Therefore, the dotted gate 34 having an opening diameter D = 0.3 mm satisfies both the relational expression D <0.5 mm and the relational expression D <{t− (La + 6Lσ)} / 0.86.

  In the molding die having the above configuration, the first die 31 and the second die 32 are moved relatively close to perform clamping. After the mold clamping, a molten resin material (molten resin P) injected from an injection molding machine (not shown) is filled into the cavity 33 via a sprue and runner (not shown) and further a dotted gate 34. By arranging the gates 34 in the above-described manner, the molten resin P filled in the cavities 33 spreads uniformly from the center of the cavities 33 outward in the radial direction. Therefore, generation of welds can be avoided, and the lid member 10 with high strength and high accuracy can be formed. When the molten resin P filled in the cavity 33 is solidified, after the mold is opened, an eject pin (not shown) provided in the first mold 31 is moved forward, and the molded lid member 10 is discharged out of the mold. (Release).

  In this embodiment, the lid member 10 in a state where a part of the resin material solidified in the cavity 33 (resin material solidified near the exit of the gate 34 in the cavity 33) is connected to the resin material solidified in the gate 34. Is released (see the dotted hatching shown in FIG. 6). Thereby, the lid member 10 having the concave gate mark 11 on the axis of the upper end face 10a is obtained.

  For example, after fixing the sleeve portion 8 to the small-diameter inner peripheral surface 7 a 1 of the housing 7, the shaft portion 21 of the shaft member 2 is inserted into the inner periphery of the sleeve portion 8, and then the large-diameter inner peripheral surface 7 a 2 of the housing 7. The lid member 10 in a state where it is released from the molding die 30 at a predetermined position in the axial direction (position where a thrust bearing gap having a predetermined width can be formed above and below the flange portion 22 of the shaft member 2). Fix it. Thereby, the assembly of the fluid dynamic bearing device 1 is completed. Then, the fluid dynamic bearing device 1 shown in FIG. 2 is completed by filling the internal space of the housing 7 including the internal pores of the sleeve portion 8 with lubricating oil.

  In the fluid dynamic pressure bearing device 1 having the above-described configuration, a radial bearing surface that is provided at two positions above and below the inner peripheral surface 8a of the sleeve portion 8 and an outer peripheral surface 21a of the shaft portion 21 that faces the radial bearing surface. A radial bearing gap is formed between each of them. As the shaft member 2 rotates, the pressure of the oil film formed in both radial bearing gaps is increased by the dynamic pressure action of the dynamic pressure generating portions A1 and A2, and as a result, the shaft member 2 is supported in a non-contact manner in the radial direction. Radial bearing portions R1 and R2 are formed apart from each other in two axial directions. At the same time, a thrust bearing surface provided between the thrust bearing surface provided on the lower end surface 8b of the sleeve portion 8 and the upper end surface 22a of the flange portion 22 opposed to the thrust bearing surface and the inner bottom surface 10a of the lid member 10 Thrust bearing gaps are respectively formed between the lower end face 22b of the flange portion 22 facing this. As the shaft member 2 rotates, the pressure of the oil film formed in both thrust bearing gaps is increased by the dynamic pressure action of the thrust dynamic pressure generating portions B and C. As a result, the shaft member 2 is moved in one direction of thrust. The first thrust bearing portion T1 that is supported in a non-contact manner and the second thrust bearing portion T2 that supports the shaft member 2 in the thrust other direction are formed.

  As described above, in the fluid dynamic pressure bearing device 1 according to the present invention, the lid member 10 injection-molded in a disc shape with a resin material containing a filler is solidified in the molding die 30 of the lid member 10. It has the gate trace 11 in a state formed by the resin material being divided along with the release of the lid member 10. This means that the lid member 10 that is an injection-molded product of resin is used in a released state. Therefore, the manufacturing cost of the lid member 10 is reduced by the amount that the gate processing after the mold release is omitted, and as a result, the cost of the fluid dynamic bearing device 1 can be reduced. Further, since the lid member 10 is injection-molded into a disc shape, predetermined dimensional and shape accuracy is easily and stably ensured. Further, since the lid member 10 is injection-molded with a resin material containing a filler (in this embodiment, LCP is a base resin, and a resin material in which carbon fibers and carbon black are blended as fillers), the lid member 10 The mechanical strength and dimensional stability required for the member 10 can be ensured. From the above, it is possible to reduce the cost while ensuring the bearing performance required for the fluid dynamic bearing device 1.

  As described above, the gate treatment after the release of the lid member 10 can be omitted because the inventor of the present application has made extensive studies, and as a result, a point-like gate having an opening diameter D with respect to the cavity 33 smaller than 0.5 mm. This is because it has been found that the lid member 10 may be injection-molded into a disk shape with the molding die 30 having 34. That is, if the opening diameter D of the dotted gate 34 with respect to the cavity 33 is smaller than 0.5 mm (D <0.5 mm), the exposure of the filler from the dividing portion 12 of the gate trace 11 is prevented as much as possible. If the lid member 10 has a simple shape having a disk shape, even if the gate 34 has an opening diameter D smaller than 0.5 mm, the cavity 33 can be formed of a resin material (melted resin P) without a gap. This is because a highly accurate molded product can be obtained.

  In the present embodiment, the gate mark 11 is formed in a concave shape opened on the upper end surface (inner bottom surface) 10 a of the lid member 10. In this case, since the dividing portion 12 of the gate trace 11 can be disposed on the inner periphery of the gate trace 11 having a concave shape, the dividing portion 12 of the gate trace 11 comes into contact with the flange portion 22 of the shaft member 2. Can be prevented as much as possible. Thereby, the situation where the filler contained in the lid member 10 falls into the internal space of the fluid dynamic bearing device 1 can be prevented as much as possible. Further, in the portion of the lid member 10 where the concave gate trace 11 is provided (axial center portion), the separation distance between the both end faces 10a and 10b when the gate trace 11 does not exist is t, and the average length of the filler is Since the relational expression t> 0.86D + La + 6Lσ is satisfied when the standard deviation of La and the length of the filler is Lσ, the filler is dropped from the portion of the lid member 10 where the concave gate mark 11 is provided. Even if it is equal, it is possible to prevent the both end surfaces 10a and 10b of the lid member 10 from being in communication. Thereby, it is possible to prevent a fatal problem such as external leakage of the lubricating oil interposed in the internal space of the housing 7 from occurring.

  Furthermore, since the lid member 10 is fixed to the inner periphery of the lower end of the housing 7, for example, the diameter dimension of the lid member 10 can be made smaller than when the lid member 10 is fixed to the lower end surface of the housing 7. In this case, the molding die 30 of the lid member 10 having a small volume of the cavity 33 can be used. If the volume of the cavity 33 is reduced, the gate 34 having a smaller opening diameter D can be used, and the gate trace 11 can be reduced. Therefore, it is possible to further reduce the possibility of the filler dropping off from the gate mark 11.

  The fluid dynamic bearing device 1 according to the embodiment of the present invention has been described above, but the present invention is not limited to the fluid dynamic bearing device 1 according to the embodiment described above. Hereinafter, a fluid dynamic bearing device 1 according to another embodiment to which the present invention is applicable will be described with reference to the drawings. In the other embodiments described below, from the viewpoint of simplifying the description, the same reference numerals are given to substantially the same configurations as those of the above-described embodiments, and the duplicate description will be omitted.

  FIG. 7 is an axial cross-sectional view of the fluid dynamic bearing device 1 according to the second embodiment of the present invention. The main difference of the fluid dynamic pressure bearing device 1 shown in FIG. 2 from that shown in FIG. 2 is that the second thrust bearing portion T2 that supports the shaft member 2 in the thrust other direction is integrated or separated from the shaft member 2. The point provided between the lower end surface of the provided disk hub 3 and the upper end surface of the housing 7 facing this, and the seal space S are the outer peripheral surface of the housing 7 and the inner periphery of the disk hub 3 facing this. It is in the point formed between the surfaces. In this embodiment, since the lid member 10 is not involved in the formation of the thrust bearing portion (thrust bearing gap), the thrust dynamic pressure generating portion C is not formed on the upper end surface 10a of the lid member 10.

  Although not shown, in the fluid dynamic bearing device 1 according to the first embodiment of the present invention shown in FIG. 2 and the fluid dynamic bearing device 1 according to the second embodiment shown in FIG. Corresponding portions can be provided integrally with the housing 7. In this case, the number of parts can be reduced and the cost of the fluid dynamic bearing device 1 can be reduced.

  In the fluid dynamic pressure bearing device 1 described with reference to FIGS. 2 and 7, the radial dynamic pressure generating portions A1 and A2 (dynamics) that generate a dynamic pressure action on the lubricating oil in the radial bearing gaps of the radial bearing portions R1 and R2. Although the pressure grooves Aa1, Aa2) are formed on the inner peripheral surface 8a of the sleeve portion 8, the radial dynamic pressure generating portions A1, A2 may be formed on the outer peripheral surface 21a of the shaft portion 21. When the radial dynamic pressure generating portions A1 and A2 (dynamic pressure grooves Aa1 and Aa2) are provided on the outer peripheral surface 21a of the shaft portion 21, minute dynamic pressure grooves can be obtained by combining relatively simple means such as rolling and grinding. Aa1 and Aa2 can be formed with high accuracy. In this case, since the inner peripheral surface 8a of the sleeve portion 8 can be formed into a smooth cylindrical surface without irregularities, the manufacturing process of the sleeve portion 8 made of sintered metal is performed on the inner peripheral surface and the sintered body. It is completed by correcting the outer peripheral surface (sizing). Therefore, the accuracy of the bearing can be ensured through simplification of the shape of the sleeve portion 8, and the characteristics of the sleeve portion 8, and thus the fluid dynamic bearing device 1 as a whole can be ensured.

  In addition, when forming the dynamic pressure grooves Aa1 and Aa2 by rolling on the outer peripheral surface of the shaft portion 21 (shaft material) made of melted material, it is desirable to perform a rolling process on the outer peripheral surface of the shaft material after heat treatment. The amount of swell of meat produced by rolling can be reduced compared to the case of rolling the unheat-treated shaft material, so that the subsequent finishing process can be simplified or the finishing process can be omitted. Because you can.

  FIG. 8 is an axial cross-sectional view of the fluid dynamic bearing device 1 according to the third embodiment of the present invention. 2 is different from the fluid dynamic bearing device 1 shown in FIG. 2 in that the sleeve portion 8 is fixed to the outer periphery of the shaft member 2 (shaft portion 21). The radial bearing gaps of the radial bearing portions R1 and R2 are formed between the outer peripheral surface 8d and the small-diameter inner peripheral surface 7a1 of the housing 7 (side portion 7a) opposite thereto, and the flange portion 22 is omitted, and the sleeve portion is omitted. A thrust bearing gap of the first thrust bearing portion T1 is formed between the upper end surface 8c of the seal 8 and the lower end surface 7b2 of the seal portion 7b facing the upper end surface 8c, and the lower end surface 8b of the sleeve portion 8 faces the lower end surface 8b. A thrust bearing gap of the second thrust bearing portion T2 is formed between the upper end surface 10a of the lid member 10 and the second thrust bearing portion T2.

  In the above embodiment, the concave gate mark 11 is formed on the axis of the upper end surface 10 a of the lid member 10. However, the concave gate mark 11 is formed on the axis of the lower end surface 10 b of the lid member 10. You may be made to do. Moreover, in the above embodiment, the one end opening (lower end opening) of the housing 7 is closed by the lid member 10 having the gate mark 11 formed in a concave shape, but the upper end face 10a or the lower end face 10b. The one end opening of the housing 7 may be closed by the lid member 10 having the gate mark 11 formed in a convex shape. In addition, when the gate mark 11 is formed in a convex shape on the upper end surface 10 a of the lid member 10, from the viewpoint of avoiding sliding contact between the shaft member 2 and the gate mark 11, the lid member 10 is It is preferable to perform injection molding in a form in which the peripheral portion has a recessed portion that recedes below the other region (side away from the shaft member 2) (not shown).

  Further, in the fluid dynamic bearing device 1 according to the embodiment described above, the radial bearing portions R1 and R2 formed of the dynamic pressure bearing are provided with axial grooves on either one of the two surfaces facing each other through the radial bearing gap. A plurality of step surfaces arranged in the circumferential direction or a multi-arc surface can be formed. Further, either one or both of the radial bearing portions R1 and R2 can be constituted by a so-called perfect circle bearing. Further, in the fluid dynamic pressure bearing device 1 according to the embodiment described above, either one or both of the thrust dynamic pressure generating portions B and C made of the dynamic pressure bearing are circular radial dynamic pressure grooves extending in the radial direction. A plurality of arrangements in the circumferential direction may be used.

  In the above description, the case where the present invention is applied to the fluid dynamic pressure bearing device 1 in which the shaft member 2 is the rotation side and the housing 7 is the stationary side has been described. On the contrary, the shaft member 2 is stationary. The present invention can also be preferably applied to the fluid dynamic bearing device 1 with the housing 7 as the rotation side. In this case, the disk hub 3 that holds the disk D is provided integrally or separately with the housing 7, and the shaft member 2 is provided integrally or separately on the motor base 6.

  The fluid dynamic pressure bearing device 1 according to the present invention can be used by being incorporated in a fan motor for a cooling fan, a polygon scanner motor for a laser beam printer, or the like as well as a spindle motor for a disk drive device.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 7 Housing 8 Sleeve part 10 Lid member 10a Upper end surface 10b Lower end surface 11 Gate trace 12 Dividing part 30 Molding die 33 Cavity 34 Gate t Separation distance D between both end surfaces of the lid member D Gate Opening diameter La Average length of filler Lσ Standard deviation of filler R1, R2 Radial bearing portion T1 First thrust bearing portion T2 Second thrust bearing portion

Claims (8)

The shaft member, a radial bearing portion that supports the shaft member in the radial direction with an oil film of lubricating oil formed in the radial bearing gap, and a cylindrical shape with both ends in the axial direction open, the shaft member and the radial bearing portion are the inner circumference A fluid dynamic bearing device comprising: a housing housed in a housing; and a lid member that is injection-molded with a resin material containing a filler and closes one end opening of the housing.
The lid member is injection-molded in a disc shape with a molding die having a gate having an opening diameter D smaller than 0.5 mm with respect to the cavity, and the resin material solidified in the molding die is accompanied by the release of the lid member. have a gate mark in a state of being formed by being divided Te,
The gate mark is formed in a concave shape opened on the inner end surface or the outer end surface of the lid member,
Of the lid member, in the portion where the gate mark is formed, the separation distance between both end faces when the gate mark does not exist is t, the average length of the filler is La, and the longitudinal dimension of the filler is standard. A fluid dynamic bearing device characterized by satisfying a relational expression of t> 0.86D + La + 6Lσ when the deviation is Lσ . The fluid dynamic bearing device according to claim 1 , wherein the gate mark is disposed on an axis of the lid member. The resin material is a fluid dynamic pressure bearing device according to claim 1 or 2 is intended to include fibrous fillers. The fluid dynamic bearing device according to any one of claims 1 to 3 , wherein an end opening of the housing is closed by fixing a lid member to an inner periphery of the one end of the housing. Furthermore, it has a thrust bearing gap formed on the inner end surface of the lid member, and a thrust dynamic pressure generating portion that generates a dynamic pressure action on the lubricating oil in the thrust bearing gap,
The fluid dynamic pressure bearing device according to any one of claims 1 to 4 , wherein the thrust dynamic pressure generating portion is molded on the inner end surface of the lid member simultaneously with injection molding of the lid member. The inner peripheral surface of the housing, the fluid dynamic bearing device according to any one of claim 1 to 5, the sleeve portion forming a radial bearing clearance is secured between the outer peripheral surface of the shaft member.   The fluid dynamic pressure bearing device according to any one of claims 1 to 5, wherein a sleeve portion that forms a radial bearing gap between the shaft member and an inner peripheral surface of the housing is fixed to the outer peripheral surface of the shaft member. A motor comprising the fluid dynamic bearing device according to any one of claims 1 to 7 , a stator coil, and a rotor magnet.

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