JP2004316924A - Dynamic pressure-type oil-impregnated sintered bearing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic pressure-type oil-impregnated sintered bearing capable of maintaining a predetermined bearing performance for a long time. <P>SOLUTION: A radial bearing surface 11b facing an outer circumferential surface of a rotary shaft 13 is formed on an inner circumferential surface of a dynamic pressure-type oil-impregnated sintered bearing 11, and a thrust bearing surface facing a flange part 13a of the rotary shaft 13 is formed on an end face 11f1 forming an opening side of a housing 12. The rotary shaft 13 is supported in a non-contact manner by the dynamic pressure effect generated on the radial bearing surface 11b and the thrust bearing surface 11f1 when the rotary shaft 13 and the oil-impregnated sintered bearing 11 are subjected to the relative rotation. The surface opening hole ratio of the radial bearing surface 11b is set to be ≤10%, and the surface opening hole ratio of the thrust bearing surface 11f1 is set to be ≤5%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrodynamic sintered oil-impregnated bearing unit. This hydrodynamic sintered oil-impregnated bearing is used particularly in the field of information equipment, such as optical disk devices such as DVD-ROM and DVD-RAM, magneto-optical disk devices such as MO, and high-capacity FDDs (Floppy (registered trademark) such as HiFD and Zip). It is suitable for a disk drive), a disk drive bearing of a magnetic disk device such as an HDD, or a bearing for a polygon scanner motor such as an LBP, and particularly suitable as a bearing for a thin motor.

  The spindle motors of the above information equipment are required to have higher rotational accuracy, higher speed, lower cost, lower noise, etc., and one of the components that determine these required performance is the motor spindle. There are bearings to support. In recent years, as a bearing of this kind, a sintered metal bearing body is impregnated with lubricating oil or lubricating grease, and a dynamic oil pressure effect provided by a dynamic pressure groove provided on the bearing surface forms a lubricating oil film in the bearing gap to form a spindle. The use of a so-called dynamic pressure type oil-impregnated bearing that supports in a non-contact manner is being studied. This hydrodynamic sintered oil-impregnated bearing has features such as high rotational accuracy and low noise while being low in cost, and is considered to be able to sufficiently meet the required performance described above.

  FIG. 12 shows an example of a spindle motor of an optical disc device using the hydrodynamic sintered oil-impregnated bearing 1. As shown in the figure, the spindle motor includes a dynamic pressure type sintered oil-impregnated bearing 1, a housing 2 for accommodating the bearing, a rotating shaft 3 supported by the bearing 1, a turntable 5 for supporting and fixing an optical disk 4, a clamper 6, and a stator 7a. And a motor section M including a rotor 7b, and the rotor case 8, the turntable 5, the optical disk 4, and the clamper 6 integrated with the rotor 7b are integrally rotated by energizing the stator 7a.

  As shown in FIG. 13, the dynamic pressure type sintered oil-impregnated bearing 1 is held in the pores of the bearing main body 1 a by impregnation of a porous bearing main body 1 a formed in a thick cylindrical shape and lubricating oil or lubricating grease. And oil. A pair of bearing surfaces 1b opposed to the outer peripheral surface of the rotating shaft 3 via a bearing gap are formed on the inner peripheral surface of the bearing main body 1a in the axial direction, and the two bearing surfaces 1b are inclined with respect to the axial direction. A pressure groove 1c is formed.

As shown in FIGS. 12 and 14, the thrust load of the rotating shaft 3 is supported by a thrust bearing 9 provided at the bottom of the housing 2. As the thrust bearing 9, a structure (so-called pivot bearing) in which a spherical shaft end slides on a resin washer 9a having high lubricity provided on the bottom of the housing 2 is generally used (see Patent Document 1).
JP-A-9-329131

  However, in the pivot bearing, the washer 9a may be dented due to elastic deformation, plastic deformation, deformation due to wear, or the like, and the position of the shaft may change over time. A change in the axial position causes a change in the disk position in the HDD device and a change in the mirror position in the LBP polygon scanner motor, and greatly affects the motor performance. As a countermeasure, it is conceivable to form the washer 9a of a metal material or a ceramic material. However, in this case, the shaft side is worn and the shaft end is changed from a spherical surface to a flat surface, resulting in a problem such as a change in shaft position, an increase in torque, a fluctuation in torque and the like. May be caused.

  In recent years, in many cases, it is required to reduce the thickness of a spindle motor in consideration of mounting an optical disk device or an HDD device on a notebook-type personal computer or the like. However, as described above, the bearing surface 1b is provided at two locations in the axial direction. In the arrangement structure, there is a limit to thinning. Although the thickness can be reduced by providing the bearing surface 1b at only one position as shown in FIG. 15, for example, a reduction in rigidity against a moment load becomes a problem. That is, an eccentric load of the rotor case 8, the disk 4, the turntable 5, the clamper 6, and the like to which the rotor magnet 7b is fixed acts on the protruding portion of the rotating shaft 3 from the bearing 1, so that the shaft runout accuracy due to the moment load is reduced. There is concern about the decline.

  Therefore, an object of the present invention is to provide a dynamic pressure-type sintered oil-impregnated bearing that can maintain expected bearing performance for a long time.

  In order to achieve the above object, a dynamic pressure type sintered oil-impregnated bearing unit according to the present invention comprises a shaft having a flange portion, a cylindrical housing, and a sintered metal impregnated with oil. A radial bearing surface facing the outer peripheral surface of the housing via a bearing gap is formed, and a thrust bearing surface having a dynamic pressure groove is formed on an end surface of the housing so as to face the flange portion, and is fixed to the inner diameter portion of the housing. And a dynamic pressure type sintered oil-impregnated bearing, wherein the surface porosity of the radial bearing surface is 10% or less and the surface porosity of the thrust bearing surface is 5% or less. The shaft is supported in a non-contact manner by dynamic pressure generated on the radial bearing surface and the thrust bearing surface during rotation.

  The radial bearing surface and the thrust bearing surface can be simultaneously molded.

  According to the present invention, the thrust bearing surface opposed to the flange portion is formed on the end surface of the sintered oil-impregnated bearing, and the shaft is supported in a non-contact manner by the dynamic pressure action generated on the thrust bearing surface. Therefore, it is possible to prevent the axial position from being changed due to the deformation of the thrust washer or the depression caused by wear, which is a problem in the pivot bearing. Further, since the surface porosity of the radial bearing surface is set to 10% or less, oil circulation can be ensured while preventing a pressure drop, and the surface porosity of the thrust bearing surface is set to 5% or less. Also, even when the dynamic pressure groove is provided, it is possible to prevent oil from escaping from the opening due to pressure generation.

  Since the sintered oil-impregnated bearing is made of a porous material such as a sintered alloy, high-precision processing can be performed at low cost. Further, since the porous body is used, a large amount of oil is retained, and since the oil circulates, the deterioration of the oil is delayed and the durability is improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  According to the present invention, oil is impregnated into a shaft 13 and a bearing body 11a formed of a sintered metal and provided with a radial bearing surface 11b opposed to an outer peripheral surface of the shaft via a bearing gap. And a dynamic pressure type sintered oil-impregnated bearing 11 for supporting the shaft 13 in a non-contact manner by a dynamic pressure action generated on a radial bearing surface 11b during relative rotation with respect to the shaft 11a. And a flange portion 13a provided on the shaft 13 to form a thrust bearing portion 14. The perpendicularity between the one bearing end surface and the bearing inner peripheral surface and the perpendicularity between the flange portion 13a and the outer peripheral surface of the shaft 13 are defined by: During relative rotation between the shaft 13 and the bearing body 11a, the tolerance is controlled so that the one end face of the bearing and the flange 13a do not hit each other.

  In the thrust bearing portion 14 having the above-described structure, the contact between the rotating side and the fixed side is ensured, so that the contact surface pressure can be reduced to prevent wear, and as in the case of a pivot bearing, the thrust washer may be deformed or worn. The shaft position does not change due to the depression, and high moment rigidity can be maintained even when the bearing is made thin. Furthermore, when the shaft and the bearing body are rotated relative to each other, one of the bearing end faces and the flange portion do not hit each other, so that the torque cross is small and the torque fluctuation is suppressed to realize the high rotation accuracy required for information equipment. Can be.

  In the thrust bearing portion 14, if the accuracy of the bearing end face 11f1 or the accuracy of the flange portion 13a is not sufficient, as shown in FIG. 16, the flange portion 13a may not contact the bearing end face 11f1 and may be one-sided. . In the case of one-side contact, the torque loss is large, and the high rotational accuracy required for the information equipment cannot be obtained due to a factor of torque fluctuation. Also, even if a dynamic pressure groove is provided on the bearing end face 11f1 to keep the thrust bearing part out of contact, contact and wear between the bearing end face and the flange part occur due to insufficient dynamic pressure effect, resulting in rotation. Accuracy and durability cannot be improved.

  Therefore, in the present invention, the perpendicularity between at least one of the bearing end surfaces constituting the thrust bearing portion 14 and the bearing inner peripheral surface, and the outer peripheral surface of the flange portion 13a and the shaft 13 (particularly, the outer peripheral surface of the shaft facing the radial bearing surface 11b) Is controlled so that the one bearing end face and the flange portion 13a do not hit each other when the shaft 13 and the bearing body 11a rotate relative to each other.

  In this case, for example, when the perpendicularity between the bearing end face 11f1 and the inner peripheral face of the bearing is 4 μm or more and the perpendicularity between the flange 13a and the outer peripheral face of the shaft is 3 μm or more, the flange 13a comes into contact with the bearing end face 11f1. There is a risk of hitting without doing. Therefore, the perpendicularity between the bearing end face 11f1 and the inner peripheral surface of the bearing is set within 3 μm, and the perpendicularity between the flange portion 13a and the outer peripheral surface of the shaft is set within 2 μm.

  Here, the term “perpendicular” refers to a plane part that should be a right angle from a geometric plane perpendicular to the reference plane in a combination of a plane part that should be a right angle and a reference plane. The size of the disorder.

  With conventional hydrodynamic sintered oil-impregnated bearings, the accuracy of the bearing end face is not sufficient (the perpendicularity of the bearing end face to the inner circumferential surface of the bearing is about 10 μm), and it is difficult to mass-produce a bearing body having an accuracy within the above numerical range. . As a countermeasure, there is a method in which, for example, after fixing the bearing to the housing, the bearing end face is finished by machining based on the inner diameter surface of the bearing or on the outer diameter surface or the like which is coaxial with the inner diameter surface of the bearing. However, in this case, (1) since shavings generated by the processing adhere to the inner peripheral surface of the bearing, cleaning is required after the processing, and (2) steps such as post-processing and cleaning are separately required. As a result, the cost is greatly increased, and problems such as the low cost, which is the greatest characteristic of the hydrodynamic sintered oil-impregnated bearing, are impaired.

  Therefore, in the present invention, a molding die 21a for forming the dynamic pressure groove 11c in the radial bearing surface 11b is inserted into the inner peripheral surface of the bearing body material 11 ', and both end surfaces of the bearing body material 11' are connected to a pair of punch surfaces 22a. , 23a, while applying a compressive force to the bearing body material 11 ', a radial bearing surface having a dynamic pressure groove 11c that is inclined with respect to the axial direction on the inner peripheral surface of the bearing body material 11' in the molding die 21a. 11b, and at least one punch surface, when forming a thrust bearing surface which constitutes a thrust bearing portion 14 between the shaft 13 and one end surface of the bearing body material 11 ', at least one of the punch surfaces The perpendicularity to the outer peripheral surface of the mold 21a was set within 2 μm (preferably within 1 μm).

  As a method of finishing the punch surface and the molding die 21a with high precision in this way, it is conceivable to integrally form the one punch surface and the molding die 21a. For example, a punch and a forming die are integrally cut out from the same member, or are manufactured separately, and are integrally fixed by a method such as press-fitting. Then, a square angle between the punch surface and the outer peripheral surface of the forming die 21a is obtained. Is possible within 2 μm. The shaft and the flange portion may be manufactured integrally with the same member, or may be manufactured separately and then press-fitted into the other side to finish the shaft at a predetermined right angle.

  After the bearing body material 11 'is formed to a predetermined size, the pressing force is released to spring back the bearing body material 11', and the bearing body material 11 'is placed between the bearing body material 11' and the molding die 21a. It is preferable to release the molding die 21a from the inner peripheral surface of the bearing body material 11 'by causing a thermal expansion difference such that the dimensional difference between the inner diameter and the outer diameter of the molding die 21a increases. Thus, interference between the molding die 21a and the bearing body material 11 'is avoided, and the molding die can be removed from the inner peripheral surface of the bearing body material without breaking the formed dynamic pressure groove.

In order to generate the above-mentioned difference in thermal expansion, after forming the bearing surface, heating may be performed, for example, from the bearing body material side. As the material of the molding die, a super hard material is usually used, and the linear expansion coefficient of this material is 5.1 × 10 ⁻⁶ [1 / ° C.]. On the other hand, the bearing body material is mainly composed of copper powder and iron powder, and an example of a linear expansion coefficient is 12.9 × 10 ⁻⁶ [1 / ° C.]. Therefore, when the bearing body material is heated to a high temperature, the dimensional difference between the inner diameter of the bearing body material and the outer diameter of the molding die becomes large due to the difference in thermal expansion between the two, and the molding die is easily removed from the bearing body material. .

  FIG. 1 is a sectional view of a hydrodynamic sintered oil-impregnated bearing unit according to the present invention. The bearing unit includes a dynamic oil-impregnated sintered oil-impregnated bearing 11, a cylindrical housing 12 in which the sintered oil-impregnated bearing 11 is fixed to the inner diameter, and a rotating shaft 13 inserted into the inner diameter of the sintered oil-impregnated bearing 11. I do.

The dynamic pressure type sintered oil-impregnated bearing 11 is obtained by impregnating a cylindrical bearing body 11a made of sintered metal having a radial bearing surface 11b opposed to an outer peripheral surface of a rotating shaft 13 with a bearing gap therebetween with lubricating oil or lubricating grease. It is composed. The bearing body 11a made of a sintered metal is made of a copper-based or iron-based, or a sintered metal mainly containing both of them, and is preferably made of 20 to 95% by weight of copper and has a density of 6.4 to 7%. 0.2 g / cm ³ . As the material of the bearing main body 11a, a porous body having a large number of pores obtained by sintering or foaming cast iron, synthetic resin, ceramics, or the like can be used. The surface porosity of the hydrodynamic sintered oil-impregnated bearing is 10% or less (preferably 5% or less) on the radial bearing surface 11b, and 5% or less (desirably 5%) on the thrust bearing surfaces 11f1 and 11f2 constituting the thrust bearing portion 14 described later. Is preferably set to 2% or less. If the surface porosity of the radial bearing surface 11b is 10% or less, oil circulation can be ensured while preventing a pressure drop, and the surface porosity of the thrust bearing surfaces 11f1 and 11f2 can be reduced to 5% or less. Thus, even when the dynamic pressure groove is provided, it is possible to prevent oil from escaping from the opening due to pressure generation. The "opening portion" refers to a portion where pores of the porous body tissue are opened to the outer surface, and the "surface opening ratio" refers to an area ratio of the surface opening occupying a unit area of the outer surface. .

  The radial bearing surface 11b provided on the inner peripheral surface 11h of the bearing body 11a is formed at only one place, and the bearing surface 11b has a plurality of dynamic pressure grooves 11c (herring bone type) inclined with respect to the axial direction. Are arranged in the circumferential direction. It is sufficient that the dynamic pressure groove 11c is formed to be inclined with respect to the axial direction, and as long as this condition is satisfied, a shape other than the herringbone type, for example, a spiral type may be used. On the outer periphery of the sintered oil-impregnated bearing 11, one or a plurality of grooves 11g are formed along the axial direction for venting air when the shaft 13 is inserted into the inner diameter portion of the bearing 11. In order to reduce the thickness of the spindle motor, the bearing inner diameter d and the bearing width L are set so as to satisfy L ≦ 1.2d.

  In the sintered oil-impregnated bearing 11, the lubricant (lubricating oil or base oil of lubricating grease) inside the bearing body 11a is caused by the thermal expansion of the oil due to the pressure generation and the temperature rise accompanying the rotation of the rotating shaft 13, and the surface of the bearing body 11a And is drawn into the bearing gap by the action of the dynamic pressure groove 11c. The oil drawn into the bearing gap forms a lubricating oil film and supports the rotating shaft in a non-contact manner. That is, when the inclined dynamic pressure groove 11c is provided on the bearing surface 11b, the lubricant inside the bearing body 11a that has oozed out by the dynamic pressure action is drawn into the bearing gap, and the lubricant is continuously pushed into the bearing surface 11b. Therefore, the oil film force is increased, and the rigidity of the bearing can be improved. When the rotating shaft 13 is inserted into the bearing 11 at the time of assembling the bearing unit, it is desirable to lubricate the bearing gap and the periphery of the bearing with oil.

  When a positive pressure is generated in the bearing gap, the lubricant flows back to the inside of the bearing body because there is a hole in the surface of the bearing surface 11b. Is kept high. In this case, since a continuous and stable oil film is formed, high rotation accuracy is obtained, and shaft runout, NRRO, jitter, and the like are reduced. Further, since the rotating shaft 13 and the bearing main body 11a rotate in a non-contact manner, the noise is low and the cost is low.

  The radial bearing surface 11b has a first groove region m1 in which the inclined hydrodynamic grooves 11c are arranged on one side, and a hydrodynamic groove 11c which is axially separated from the first groove region m1 and is inclined on the other side. A second groove region m2 and an annular smooth portion n located between the two groove regions m1 and m2. The dynamic pressure groove 11c of the two groove regions m1 and m2 is partitioned by the smooth portion n. Being discontinuous. The back portion 11e between the smooth portion n and the dynamic pressure groove 11c is at the same level. This type of non-continuous type dynamic pressure groove 11c is a continuous type, that is, the smooth portion n is omitted, and the dynamic pressure groove 11c is formed in a V-shape continuous with each other between the two groove regions m1 and m2. There is an advantage that the oil film pressure is high because the oil is collected around the smooth portion n, and the bearing rigidity is high because the smooth portion n having no groove is provided.

  A thrust bearing portion 14 is provided at one axial end of the sintered oil-impregnated bearing 11. FIG. 1 shows an embodiment in which a thrust bearing portion 14 is provided on the upper end side of a sintered oil-impregnated bearing 11. An upper bearing end face 11 f 1 (thrust bearing surface) of the sintered oil-impregnated bearing 11 and a disk-shaped fixed to the rotating shaft 13. It is configured such that the flange portion 13a is opposed to the flange portion 13a. The rotating shaft 13 and the flange portion 13a may be manufactured integrally from the same member, or may be manufactured separately and then fitted and fixed to each other. Finishing is performed so that the perpendicularity of the outer peripheral surface facing the surface 11b is within 2 μm, preferably within 1 μm with respect to the end surface 13a1 of the flange portion 13a on the bearing 11 side.

  In such a thrust bearing portion 14, since the sliding contact portion comes into contact with the surface, fluctuation of the shaft position which is a problem in the pivot bearing is prevented, and moment rigidity is reduced even with the single-row bearing surface 11b. It is possible to support the shaft with high precision.

  By the way, when the rotating shaft 13 is provided with the flange portion 13a as described above, components such as the rotor case 8 and the turntable (5: see FIG. 13) are fixed to the upper end of the rotating shaft 13, so that the bearing 11 It is difficult to seal the upper end of the cover with a conventional seal washer 8 (see FIG. 15). Therefore, oil leakage from the upper end of the bearing 11 is performed by a capillary seal due to a minute gap between the outer peripheral surface of the flange 13a and the inner peripheral surface of the housing 12. The seal gap c is preferably 0.05 mm or less, preferably 0.02 mm or less, and the seal width a is 0.5 mm or more, preferably 1 mm or more. Applying a lubricant to the outer peripheral surface of the flange portion 13a and the inner peripheral surface of the housing 12 constituting the seal is effective for preventing oil leakage.

  On the other hand, oil leakage from the lower end side of the bearing 11 can be prevented by, for example, press-fitting the bottom plate 15 into the bottom opening of the housing 12 and then caulking. If the gap between the bottom plate 15 and the housing 12 is sealed with an adhesive, it is more effective to prevent oil leakage.

  FIG. 2A shows an embodiment in which an elastic material 15a such as resin or rubber is stacked on the bottom plate 15 and used as a packing in order to prevent oil leakage from the bottom plate 15 side. Also in this case, it is desirable that the bottom plate 15 be press-fitted into the housing 12 and then swaged if necessary.

  FIG. 2B shows an embodiment in which an annular concave portion 12a is provided on the inner peripheral surface of the housing 12 facing the outer peripheral surface of the flange portion 13a. The rotation of the flange 13a causes oil to collect in the recess 12a due to centrifugal force, so that oil leakage from the upper end of the housing 12 can be reliably prevented (centrifugal seal). If only the centrifugal seal is used, oil leakage may occur when the shaft posture is horizontal. Therefore, it is desirable to use the centrifugal seal together with a capillary seal.

  FIG. 3A shows an example in which an inclined groove 13a2 is provided on the outer peripheral surface of the flange portion 13a so that an airflow is generated toward the bearing 11 during rotation. The generated airflow pushes the oil back to the bearing 11 side, so that oil leakage from the upper end of the bearing can be prevented (during stop, oil leakage is prevented by a capillary seal). Since the inclined groove 13a2 only needs to prevent oil leakage, it is not necessary to machine the inclined groove 13a2 with high precision unlike the dynamic pressure groove 11c of the radial bearing surface 11b. The groove depth is suitably about 5 to 30 μm, and can be processed by a method such as rolling.

  If the inclined groove 13a2 is formed over the entire width (axial dimension) of the flange portion 13a as shown in FIG. 3A, excessive air may be sent to the bearing 11 side, and therefore, FIG. As shown in FIG. In this case, it is desirable to provide an annular concave portion 12a on the inner peripheral surface of the housing 12 at a portion facing the region where the inclined groove 13a2 is not formed.

  FIG. 4 shows an embodiment in which a lower bearing end face 11f2 of the bearing 11 and a flange portion 13a provided at the shaft end constitute a thrust bearing portion. During rotation, the rotating shaft 13 is lifted from the bottom plate 15 by a levitation force due to an exciting force between the rotor 7b and the stator 7a (see FIG. 13), and becomes lower than the lower bearing end surface 11f2 (thrust bearing surface) and the flange portion 13b. The thrust force is supported by the upper surface 13b2. A thrust washer 15a made of a highly lubricating resin material or the like is disposed on the upper surface of the bottom plate 15 and immediately below the rotary shaft 13, so that friction between the thrust washer 15 and the shaft end immediately after the start or immediately before the stop of the motor is reduced. I have. The upper end opening of the housing 12 is closed by a thrust washer 16 for preventing oil leakage, and the gap with the shaft is set to 0.2 mm or less to prevent oil from leaking to the outside (capillary action). By applying the oil repellent to the inner peripheral surface of the seal washer 16, the upper and lower surfaces of the inner peripheral portion, or the outer peripheral surface of the shaft 13 facing the inner peripheral surface of the seal washer 16, more effective oil leakage can be prevented.

  FIG. 5 shows a dynamic pressure type sintered oil-impregnated bearing 11 having a bearing inner peripheral surface 11h provided with an oil supply dynamic pressure groove 11j inclined with respect to the axial direction, and a thrust bearing portion formed by the dynamic pressure action generated in the dynamic pressure groove 11j. 14 is supplied with oil. The dynamic pressure groove 11j is formed in a V-shape that is continuous with the dynamic pressure groove 11c in the groove forming region (on the thrust bearing portion 14 side) of the radial bearing surface 11b. By providing the dynamic pressure groove 11j for oil supply, an oil film is easily formed on the thrust bearing portion 14 to improve lubricity, and wear on the thrust bearing portion 14 is also significantly reduced, so that durability is increased. To improve. The oil supplied to the thrust bearing portion 14 is absorbed from the bearing end surface and the chamfer portion, is recovered inside the bearing, and is supplied again to the bearing gap from the bearing inner peripheral surface.

  6 and 7 show a configuration in which the thrust bearing portion 14 supports the rotating shaft 13 in a non-contact manner by a dynamic pressure effect generated when the rotating shaft 13 rotates. With non-contact support, friction in the thrust bearing portion 14 is eliminated, and durability is dramatically improved. A plurality of (preferably, three or more) recesses arranged in the circumferential direction are provided on one of the bearing end face 11f1 constituting the thrust bearing section 14 and the flange section 13a opposed thereto. It can be obtained by providing a dynamic pressure generating section 17 having 11k. In this case, the concave portion 11k becomes an oil reservoir, and pressure is generated when the oil in the concave portion is drawn out to the adjacent convex portion with the rotation, and the oil film pressure increases, so that the thrust bearing portion 14 is stably brought into a non-contact state. Can hold. As the recess 11k, for example, a dynamic pressure groove can be considered.

  FIG. 6 shows an example of a thrust bearing portion 14 having a dynamic pressure generating portion 17 in which a thrust bearing surface 11f1 is provided with a dynamic pressure groove 11k having a portion inclined with respect to a radial virtual line drawn on the bearing end surface. It is. The dynamic pressure grooves 11k have a herringbone type, that is, have a V-shape having a bent portion substantially at the center in the radial direction, and are formed at regular intervals in the circumferential direction. In this case, the oil in the thrust bearing portion 14 and its surroundings is collected in the bent portion of the dynamic pressure groove 11k with the rotation and the oil film pressure increases, so that the thrust bearing portion 14 can be stably held in a non-contact state. As the dynamic pressure groove shape, a spiral type besides a herringbone type can be applied. Alternatively, the dynamic pressure groove 11k may be provided on the flange end face 13a1, and the thrust bearing surface 11f1 may be a smooth surface without the dynamic pressure groove.

  FIG. 7 shows a thrust bearing surface 11f1 provided with a dynamic pressure groove 11k in the same manner as in FIG. 6, and a dynamic pressure groove 11j for oil supply provided in the bearing inner peripheral surface as in FIG.

  FIG. 8 and FIG. 9 show that thrust bearing portions 14a and 14b are provided at two places separated in the axial direction so that thrust loads in both directions can be supported. FIG. 8 shows that flange portions 13a and 13b are arranged on both ends of the bearing, and that two thrust bearing portions 14a and 14b formed between each flange portion 13a and 13b and both bearing end surfaces 11f1 and 11f2 apply thrust loads in both directions. It is made to be able to support. One of the thrust bearing surfaces 11f1 and 11f2 constituting the thrust bearing portion 14 and the end surfaces of the flange portions 13a and 13b opposed thereto (the thrust bearing surfaces 11f1 and 11f2 in the drawing) are shown in FIGS. As shown in (), a dynamic pressure groove 11k similar to that of FIG. 6 is formed. With this structure, not only the thrust support in both directions but also the detachment of the rotating shaft 13 from the bearing 11 can be prevented, so that even if an impact load is applied to the rotating shaft 13, damage to the motor can be avoided. In particular, in the case where the reading head is arranged with a slight gap from the disk as in the HDD device, it is possible to avoid a situation where the head collides with the disk even when an impact load is applied.

  FIG. 9 shows a configuration in which a flange portion 13b is provided between the bearing 11 and the bottom plate 15, and thrust bearing portions 14a and 14b are formed on both sides of the flange portion 13b. That is, one of the upper end surface 13a1 of the flange portion 13b and the lower bearing end surface 11f2, and one of the lower end surface 13b2 of the flange portion 13b and the upper surface of the bottom plate 15 (in the drawing, the lower bearing end surface 11f2 and the flange portion Since the lower end face 13b2) is provided with a dynamic pressure groove 11k similar to that shown in FIG. 6, the same effect as the structure shown in FIG. 8 can be obtained.

  The bearing main body 11a of the hydrodynamic sintered oil-impregnated bearing 11 is formed, for example, by sizing and rotating with respect to a cylindrical sintered metal material (bearing body material) obtained by compression-molding the metal powder and further firing. It can be manufactured by sizing → bearing surface forming.

  The sizing process is a process of sizing the outer peripheral surface and the inner peripheral surface of the sintered metal material to correct bending and the like in the sintering process, while pressing the outer peripheral surface of the sintered metal material into a cylindrical die, This is performed by pressing a sizing pin into the inner peripheral surface. The rotation sizing process is a method in which a rotation sizing pin having a substantially polygonal cross section (which is obtained by partially flattening the outer peripheral surface of a pin having a circular cross section and leaving an arc portion at a circumferentially equidistant position) is formed in a sintered metal material. This is a step of sizing the inner peripheral surface by rotating the sizing pin while pressing against the peripheral surface. By this rotation sizing, the roundness and cylindricity of the inner peripheral surface of the sintered metal material are corrected, and the surface porosity is finished to, for example, 3 to 15%. In the bearing surface forming step, a pressing die having a shape corresponding to the bearing surface of the finished product is pressed onto the inner peripheral surface of the sintered metal material subjected to the sizing processing as described above, thereby forming the dynamic pressure groove on the bearing surface. This is a step of simultaneously forming the formation region and the other region (the back 11e and the annular smooth region n).

  FIG. 11 illustrates a schematic structure of a forming apparatus used in the bearing surface forming step. This apparatus includes a cylindrical die 20 for press-fitting an outer peripheral surface of a sintered metal material 11 ', a core rod 21 made of cemented carbide for forming an inner peripheral surface of the sintered metal material 11', and both ends of the sintered metal material 11 '. Upper and lower punches 22 and 23 for pressing the surface from above and below are configured as main elements. The core rod 21 and the upper punch 22 are integrated, and the perpendicularity between the outer peripheral surface of the core rod 21 and the punch surface 22a of the upper punch 22 is finished within 2 μm.

  As shown in FIG. 10, an outer peripheral surface of the core rod 21 is provided with a concave and convex forming die 21a corresponding to the shape of the bearing surface 11b of the finished product. The convex portion 21a1 of the molding die 21a forms a region of the dynamic pressure groove 11c on the bearing surface 11b, and the concave portion 21a2 forms a region other than the dynamic pressure groove 11c (the back 11e and the annular smooth region n). The step between the convex portion 21a1 and the concave portion 21a2 in the molding die 21a is as small as the depth of the dynamic pressure groove 11c in the bearing surface 11b (for example, about 2 to 5 μm), but is considerably exaggerated in the drawing. Is illustrated. When the dynamic pressure grooves 11k are provided on the upper and lower bearing end surfaces 11f1 and 11f2 (see FIGS. 6 to 9), the transfer of the shape corresponding to the dynamic pressure grooves 11k is also performed on the punch surfaces 22a and 23a of the upper and lower punches 22 and 23. A molding die is provided.

  The molding by this molding apparatus is performed according to the procedures A to D shown in FIG.

  First, after positioning the sintered metal material 11 ′ on the upper surface of the die 20, the upper punch 22 and the core rod 21 are lowered, the sintered metal material 11 ′ is pressed into the die 20, and Pressing and pressing from above and below (A).

  The sintered metal material 11 ′ is deformed by receiving a pressing force from the die 20 and the upper and lower punches 22 and 23, and the inner peripheral surface is pressed against the forming die 21 a of the core rod 21. Thereby, the shape of the molding die 21a is transferred to the inner peripheral surface of the sintered metal material 11 ', and the bearing surface 11b is molded into a predetermined shape and dimensions (simultaneously, the outer peripheral surface and both end surfaces of the sintered metal material 11'). Will also be sized).

  After the molding of the bearing surface 11b is completed, the upper and lower punches 22, 23 and the core rod 21 are integrally raised while maintaining the positional relationship between the sintered metal material 11 'and the core rod (B), and the sintered metal material 11' From the die 20. Next, the sintered metal material 11 'gripped by the clamper 24 is blown with hot air by a heater 25 such as a hot air generator to heat the sintered metal material 11' (C). Pull out 11 'from the core rod 21 (D). At this time, when the sintered metal material 11 'is removed from the die 20, springback occurs in the sintered metal material 11', and the inner diameter of the sintered metal material 11 'increases. In addition, the temperature of the sintered metal material becomes higher than that of the core rod 21 due to the heating, and the thermal expansion coefficient of the sintered metal material 11 ′ (containing copper as a main component) is larger than that of the core rod 21 (made of cemented carbide). As a result, the inner diameter of the sintered metal material 11 'is further increased. Therefore, interference between the core rod 21 and the sintered metal material 11 'is avoided, and the core rod 21 can be pulled out from the inner peripheral surface of the sintered metal material 11' without breaking the dynamic pressure groove 11c. In the case where the sintered metal material 11 'can be smoothly pulled out only by the spring back, the heating step by the heater 25 may be omitted.

  When the sintered metal material 11 'manufactured through the above steps is washed and impregnated with lubricating oil or lubricating grease to retain the oil, a dynamic pressure type sliding bearing (dynamic pressure type porous oil-impregnated bearing) shown in FIG. Is completed. The bearing 11 is fixed to the inner peripheral surface of the housing 12 by, for example, bonding. If the bearing gap and the space around the bearing are filled with oil separately from the impregnating oil after being assembled into the housing 12 by lubrication, the lubricity is significantly improved.

  As described above, if the perpendicularity between the outer peripheral surface of the core rod 21 and the punch surface 22a of the upper punch 22 is set within 2 μm, the sintered oil-impregnated material whose perpendicularity of the thrust bearing surface 11f1 with respect to the bearing inner peripheral surface 11h is within 3 μm. The bearing 11 can be provided. By combining this bearing 11 with the rotating shaft 13 in which the perpendicularity between the flange portion 13a and the outer peripheral surface is set within a predetermined range, it is possible to prevent the thrust bearing portion 14 from hitting one side, and to reliably realize the surface contact. it can.

It is sectional drawing of the dynamic pressure type sintered oil-impregnated bearing unit concerning this invention. It is sectional drawing which shows other embodiment of this invention. It is sectional drawing which shows other embodiment of this invention. It is sectional drawing which shows other embodiment of this invention. It is sectional drawing which shows other embodiment of this invention. FIG. 6 is a view showing another embodiment of the present invention, in which FIG. A is a cross-sectional view and FIG. FIG. 6 is a view showing another embodiment of the present invention, in which FIG. A is a cross-sectional view and FIG. FIG. 7 is a view showing another embodiment of the present invention, in which A is a cross-sectional view, B is a plan view, and C is a bottom view. FIG. 7 is a view showing another embodiment of the present invention, in which A is a cross-sectional view, and B and C are bottom views. It is a side view of a core rod and an upper punch. It is sectional drawing which shows the method of this invention. FIG. 4 is a cross-sectional view of an optical disc device incorporating a dynamic pressure type oil-impregnated bearing unit. It is sectional drawing of the conventional dynamic pressure type sintered oil-impregnated bearing. It is sectional drawing of the conventional dynamic pressure type sintered oil-impregnated bearing unit. It is sectional drawing of a dynamic pressure type sintered oil-impregnated bearing unit. It is sectional drawing of a dynamic pressure type sintered oil-impregnated bearing unit.

Explanation of reference numerals

11 Sintered oil pressure bearing
11a Bearing body
11b Radial bearing surface
11c Dynamic pressure groove on radial bearing surface
11f1 Bearing end surface (thrust bearing surface)
11f2 Bearing end surface (thrust bearing surface)
11h Bearing inner peripheral surface
11j Dynamic pressure groove for oil supply
11k Dynamic pressure groove (recess) on thrust bearing surface
12 Housing 13 Rotation axis (axis)
13a Flange part 14 Thrust bearing part 17 Dynamic pressure generating part

Claims (2)

A shaft having a flange portion,
A cylindrical housing;
A thrust bearing surface made of a sintered metal impregnated with oil, having a radial bearing surface formed on the inner peripheral surface facing the outer peripheral surface of the shaft via a bearing gap, and having a dynamic pressure groove on an end surface of the housing. Is formed facing the flange portion, and comprises a dynamic pressure type sintered oil-impregnated bearing fixed to the inner diameter portion of the housing,
The surface porosity of the radial bearing surface is 10% or less, the surface porosity of the thrust bearing surface is 5% or less,
A hydrodynamic sintered oil-impregnated bearing unit characterized in that the shaft is supported in a non-contact manner by a dynamic pressure action generated on a radial bearing surface and a thrust bearing surface when the shaft and the sintered oil-impregnated bearing rotate relative to each other.   2. The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the radial bearing surface and the thrust bearing surface are molded at the same time.

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