JP2006038211A - Fluid dynamic pressure bearing, spindle motor having this fluid dynamic pressure bearing and recording disk driving device having this spindle motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize and thin the whole motor, by securing bearing rigidity of respective bearing parts, accuracy such as squareness of a shaft and a rotor hub and a shaft directional dimension of a tapered seal part. <P>SOLUTION: In this fluid dynamic pressure bearing of one example, a radial bearing part provided with a dynamic pressure generating groove for inducing dynamic pressure in a lubricating fluid when rotating a rotor, is formed between an outer peripheral surface of the shaft and an inner peripheral surface of a sleeve. An upper thrust bearing part provided with the dynamic pressure generating groove for inducing the dynamic pressure in the lubricating fluid when rotating the rotor, is formed between an under surface of a rotor upper wall part and an upper end surface of a bearing housing. A lower thrust bearing part provided with the dynamic pressure generating groove for inducing the dynamic pressure in the lubricating fluid when rotating the rotor, is formed between a lower end surface of the sleeve and an upper surface of a thrust plate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fluid dynamic pressure bearing, a spindle motor provided with the fluid dynamic pressure bearing, and a recording disk driving device provided with the spindle motor.

  Conventionally, in a hard disk drive, a removable disk drive, etc., as a motor bearing for driving a recording disk, for example, as shown in FIG. 6, the motor is rotated and held in a gap between the shaft 102 and the sleeve 104. Various fluid dynamic pressure bearings using dynamic pressure generated in a lubricating fluid such as oil have been used and various proposals have been made.

  This conventional motor forms a pair of radial bearing portions 106 spaced apart in the axial direction in the gap between the outer peripheral surface of the shaft 102 and the inner peripheral surface of the sleeve 104 and is integrally fixed to the shaft 102. Upper and lower thrust bearing portions 112 and 113 are formed in the gaps between the upper and lower surfaces of the thrust plate 108 and the lower surface of the sleeve 104 and the upper surface of the counter plate 110 facing each other in the axial direction.

  Further, this conventional motor gradually reduces the diameter of the outer peripheral surface of the shaft 102 as a pair away from the radial bearing portion 106 out of the inner peripheral surface of the sleeve 104 and the outer peripheral surface of the shaft 102, thereby A capillary seal portion 118 is formed between the fitting portion 116 with the rotor hub 114 fixed to the upper portion 102 and the radial bearing portion 106. The capillary seal portion 118 causes a difference in capillary force depending on the formation position of the gas-liquid interface of the oil held in the capillary seal portion 118, and is held by the radial bearing portion 106 and the upper and lower thrust bearing portions 112, 113. When the amount of oil decreases, oil is supplied from the capillary seal portion 118 to the radial bearing portion 106 and the upper and lower thrust bearing portions 112 and 113. In addition, the capillary seal portion 118 has a structure in which when the volume of oil retained in the radial bearing portion 106 and the upper and lower thrust bearing portions 112 and 113 increases due to the temperature rise of the spindle motor accompanying the rotation of the motor, Accommodates the increase.

  In this way, the oil is continuously held without interruption in the minute gaps forming the radial bearing portion 106, the upper and lower thrust bearing portions 112, 113, and the capillary seal portion 118 (such oil retention). The structure is hereinafter referred to as “full-fill structure”). When the motor rotates, dynamic pressure is generated in the radial bearing portion 106 and the upper and lower thrust bearing portions 112 and 113, and the sleeve 104 rotatably supports the shaft 102 and the rotor hub 114 in a non-contact manner (such a structure). (For example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 2002-21845 (FIG. 1)

  In recent years, recording disk drive devices used in devices such as personal computers have begun to be applied to smaller and portable information terminals. In addition to conventional high-speed and high-precision rotation, spindle motors have been used. Therefore, there has been a demand for smaller, thinner and lower power consumption.

  However, when trying to reduce the size and thickness of the spindle motor, in the above-described configuration, the fitting portion 116, the capillary seal portion 118, the pair of radial bearing portions 106, and the upper and lower thrust bearing portions 112 and 113 are shafts. It is difficult to reduce the size and thickness of the spindle motor because it is configured in parallel in the direction.

  That is, in order to secure the bearing rigidity of the pair of radial bearing portions 106 in response to the demand for a small and thin spindle motor, the axial dimensions of the fitting portion 116 and the upper and lower thrust bearing portions 112 and 113 are ensured. Becomes difficult. When the axial dimension of the fitting portion 116 is shortened, the fastening strength between the shaft 102 and the rotor hub 114 is weakened, the parallelism of the rotor hub 114 is lost when the motor rotates, and the rotor hub 114 swings and stable rotation cannot be obtained. .

  On the other hand, if it is going to secure the axial direction dimension of the fitting part 116, the axial direction dimension of a pair of radial bearing part 106 will become short, bearing rigidity will become weak, and it will become impossible to support the shaft 102 stably. Since the rotation accuracy and attitude of the shaft 102 and the rotor hub 114 depend exclusively on the pair of radial bearing portions 106, it is necessary to ensure a sufficient axial interval between the pair of radial bearing portions 106. Therefore, with the motor described above, it is very difficult to reduce the size and thickness of the spindle motor while maintaining the required rotational accuracy.

  In addition, if the axial dimensions of the pair of radial bearing portions 106 and the fitting portions 116 are to be ensured, it is difficult to ensure the bearing rigidity of the upper and lower thrust bearing portions 112 and 113. In the motor described above, the thrust plate 108 is integrally fixed to the end portion of the shaft 102, and the axial load bearing force generated in the upper and lower thrust bearing portions 112 and 113 formed on the upper and lower surfaces of the thrust plate 108. Accordingly, the axial movement of the shaft 102 and the rotor hub 114 is restricted, and the floating of the shaft 102 and the rotor hub 114 is stabilized.

  However, if the axial dimension of the thrust plate 108 is made thin in order to make the upper and lower thrust bearing portions 112 and 113 thinner, a stable axial load bearing force can be obtained by the upper and lower thrust bearing portions 112 and 113. Since the bearing rigidity of the upper and lower thrust bearing portions 112 and 113 is lowered, the shaft 102 and the rotor hub 114 may be overlifted, and it is difficult to stably support the shaft 102 and the rotor hub 114. It becomes.

  Furthermore, in recent years, recording disk drive devices have been started to be installed in in-vehicle devices represented by car navigation systems. However, in the case of in-vehicle equipment, since the recording disk drive is expected to be used in various environments, the recording disk drive is also required to operate stably in a very wide temperature range. Yes. For example, a recording disk drive device is required to be used in an unprecedented severe temperature environment that can be used even in an environment where the temperature difference is 100 ° C. or more.

  As is well known, since the viscosity of oil decreases under a high temperature environment, the generated dynamic pressure also decreases, and as a result, it is difficult to obtain a predetermined bearing rigidity. If high-viscosity oil is used to avoid such a decrease in the viscosity of the oil, the viscosity becomes excessive in a low-temperature environment, and the rotational load of the motor increases, so the power consumption of the motor increases. Therefore, in order to make it possible to apply a motor using a fluid dynamic bearing in a wide temperature range, it is possible to prevent a decrease in bearing rigidity in a high temperature environment while suppressing an increase in power consumption of the motor in a low temperature environment. It is necessary to solve the conflicting issues at the same time. In a high temperature environment, the oil viscosity decreases and the oil volume increases due to thermal expansion. Therefore, the oil retained in each fluid dynamic pressure bearing portion is pushed out from each fluid dynamic pressure bearing portion to the capillary seal portion 118 by an amount corresponding to the volume increase. At this time, if the axial dimension of the capillary seal portion 118 is limited due to dimensional restrictions such as a small and thin motor, the oil flowing into the capillary seal portion 118 cannot be accommodated. Instead, the oil may flow out of the capillary seal portion 118. If the oil that has flowed out adheres to the hard disk on the drive device side or the magnetic head disposed close to the hard disk, it may cause a read / write error.

  On the other hand, when the axial dimension of the capillary seal portion 118 is sufficiently secured to hold the oil whose volume has been increased, a pair of radial bearing portions arranged in parallel with the capillary seal portion 118 in the axial direction. The axial dimension of 106 is restricted, and it is difficult to ensure the bearing rigidity of the radial bearing portion 106. In addition, it is difficult to ensure the dimension in the axial direction of the fitting portion 116 between the shaft 102 and the rotor hub 114 that are similarly arranged in parallel with the capillary seal portion 118 in the axial direction.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a spindle motor having a fluid dynamic pressure bearing and a bearing rigidity of a radial bearing portion and a thrust bearing portion, accuracy such as a perpendicularity between a shaft and a rotor hub, and an axial dimension of a capillary seal portion. It is to realize a small size and a thin shape.

  Another object of the present invention is to ensure stable bearing rigidity without increasing the power consumption of a spindle motor equipped with a fluid dynamic pressure bearing, regardless of changes in the use environment, and to maintain the oil in a high temperature environment. It is to improve reliability and durability by preventing outflow to the outside of the spindle motor.

  Another object of the present invention is to provide a recording disk drive apparatus including a spindle motor that is small and thin, and has excellent reliability and durability.

  In order to solve the above problems, an example of the fluid dynamic pressure bearing of the present invention includes a shaft, a top plate fixed to the upper portion of the shaft, a thrust plate fixed to the lower portion of the shaft, and a relative rotation with respect to the shaft. And a bearing housing that holds the sleeve on the inner periphery and is closed at the lower end. A continuous minute gap is formed between the shaft and the top plate and the sleeve, and the minute gap is filled with a lubricating fluid.

  A radial bearing portion is provided between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. The radial bearing portion is provided with a dynamic pressure generating groove for inducing dynamic pressure in the lubricating fluid when the shaft or the sleeve rotates. An upper thrust bearing portion is provided between the lower surface of the top plate and the upper end surface of the bearing housing. The upper thrust bearing portion is provided with a dynamic pressure generating groove for inducing dynamic pressure in the lubricating fluid when the shaft or sleeve rotates. A lower thrust bearing portion is provided between the lower end surface of the sleeve and the upper surface of the thrust plate. The lower thrust bearing portion is provided with a dynamic pressure generating groove for inducing dynamic pressure in the lubricating fluid when the shaft or the sleeve rotates.

  In the fluid dynamic pressure bearing according to the example of the present invention, the thrust bearing portion that has been formed between the lower surface of the thrust plate and the upper surface of the counter plate is eliminated. A thrust bearing portion is newly formed between the upper end surface of the bearing housing and the lower surface of the top plate. Accordingly, the axial dimension of the thrust plate may be a dimension that can obtain the bearing rigidity necessary for forming the lower thrust bearing portion. Therefore, the axial dimension of the thrust plate can be made thinner than before, and the axial dimension of the counter plate can also be made thinner. Thereby, the spindle motor provided with the fluid dynamic pressure bearing can be reduced in size and thickness.

  Hereinafter, a fluid dynamic pressure bearing according to the present invention, a spindle motor equipped with the fluid dynamic pressure bearing, and a recording disk drive equipped with the spindle motor will be described with reference to FIGS. In the embodiment of the description of the present invention, the vertical direction of each drawing is referred to as “vertical direction” for convenience, but the direction in the actual mounting state is not limited.

<First embodiment>
<Overall structure of spindle motor>
As shown in FIG. 1, the spindle motor according to the present embodiment basically includes a bracket 2, a bearing housing 10 fixed to the bracket 2, and a sleeve 12 fixed to the inner peripheral portion of the bearing housing 10. The rotor 6 is rotatably supported by the sleeve 12.

  An annular boss 2a is provided around the center hole in which the bearing housing 10 is fitted and fixed at the center of the bracket 2, and the stator 8 is press-fitted and / or inserted into the outer periphery of the boss 2a. A cylindrical portion 2b fixed by bonding or the like is formed. A bearing housing 10 is fixed to the inner periphery of the boss portion 2a by press-fitting and / or adhesion.

The hollow cylindrical bearing housing 10 includes a plate-like counter plate 14 that closes an axially lower portion of the bearing housing 10. The bearing housing 10 is formed from a member having a smaller coefficient of thermal expansion than the rotor hub 18 described in detail later. Specifically, SUS303 (thermal expansion coefficient 17.3 × 10 ⁻⁶ / ° C.), SUS304 (thermal expansion coefficient 16.3 × 10 ⁻⁶ / ° C.), and SUS420J2 (thermal expansion coefficient 10.4 × 10 ^−6). / ° C), a resin member, and the like. A cylindrical sleeve 12 having a bearing hole penetrating in the axial direction at the center is fixed to the inner peripheral surface of the bearing housing 10 by means such as adhesion. The sleeve 12 is formed from a porous sintered body impregnated with oil, and the material thereof is not particularly limited. The sleeve 12 is molded and sintered using various metal powders, metal compound powders, and nonmetal powders as raw materials. used. The raw material contains Fe—Cu, Cu—Sn, Cu—Sn—Pb, Fe—C and the like, and has a thermal expansion coefficient of about 12.9 × 10 ⁻⁶ / ° C. The bearing housing 10 and the sleeve 12 may be formed of a member having a smaller coefficient of thermal expansion than the rotor hub 18 described later, and can be formed of, for example, copper or copper alloy.

  The rotor 6 that is a rotating member includes a shaft 16 that is opposed to the inner peripheral surface of the sleeve 12 via a gap in the radial direction, and a substantially cup-shaped rotor hub 18 that is formed integrally with the shaft 16. Thus, by integrally forming the shaft 16 and the rotor hub 18, the rotor hub 114 is prevented from being caused by insufficient fastening strength at the fitting portion between the shaft 116 and the rotor hub 114 of the conventional motor shown in FIG. 6. It is possible to prevent the assembly accuracy such as the perpendicularity of the shaft 102 from being lowered and the shaft 102 from dropping from the rotor hub 114. Further, since the fastening strength between the rotor hub 18 and the shaft 16 can be obtained firmly, the motor can be reduced in size and thickness.

The rotor hub 18 includes an upper wall 18a that axially opposes the upper end surfaces of the bearing housing 10 and the sleeve 12 and constitutes a top plate; a rotor peripheral wall 18b that hangs down axially from the outer periphery of the upper wall 18a; And a flange portion 18c located below the peripheral wall portion 18b and extending radially outward from the outer peripheral surface of the rotor peripheral wall portion 18b. A hard disk (denoted by reference numeral 46 in FIG. 5) is brought into contact with and placed on the outer peripheral surface of the rotor peripheral wall portion 18b and the flange portion 18c, and the inner peripheral portion of the rotor peripheral wall portion 18b has a rotor on the inner peripheral portion. A magnet 20 is fixed by an adhesive or the like, and an annular yoke 21 formed from a ferromagnetic stainless steel is fixed by adhesion. Such a rotor hub 18 can be formed from a member having a thermal expansion coefficient larger than that of the sleeve 12, and specifically, formed from aluminum or an aluminum alloy such as A6061 (thermal expansion coefficient 23.6 × 10 ⁻⁶ / ° C.). Has been.

  A thrust plate 22 that is an annular member is fixed to the lower end of the shaft 16 in the axial direction. The upper and lower surfaces of the thrust plate 22 are opposed to the lower end surface of the sleeve 12 and the upper surface of the counter plate 14 with a gap in the axial direction. Opposite. The thrust plate 22 can be selected as appropriate from the required mechanical strength, dimensional stability, and the like. However, since the thrust plate 22 is fixed to the end of the shaft 16 and rotates integrally with the shaft 16, the thermal expansion coefficient is approximately the same as that of the shaft 16. The material which has is preferable.

  In such a configuration, the gap between the lower surface of the upper wall portion 18a of the rotor hub 18 and the upper end surfaces of the bearing housing 10 and the sleeve 12, the gap between the inner peripheral surface of the sleeve 12 and the outer peripheral surface of the shaft 16, and the sleeve 12 The gap between the lower end surface and the upper surface of the counter plate 14 and the upper and lower surfaces of the thrust plate 22 is continuous. In the continuous gap, oil as a lubricating fluid is held without interruption, forming a full fill structure. Yes.

  An inclined surface whose outer diameter is reduced in the axial direction from the upper end surface is formed on the upper outer peripheral surface of the bearing housing 10, and is suspended from the upper wall portion 18 a of the rotor hub 18 at a portion opposed to this in the radial direction. A circumferential projection 18d is formed. The gap dimension defined by the radial gap between the upper outer peripheral surface of the bearing housing 10 and the circumferential projection 18d of the upper wall portion 18a gradually increases as the distance from the upper wall portion 18a decreases in the axial direction (on the bracket 2 side). That is, the upper outer peripheral surface of the bearing housing 10 and the circumferential protrusion 18d of the upper wall portion 18a cooperate to constitute the capillary seal portion 34. In the oil held in the gaps between the bearing portions described above, the surface tension of the oil and the external pressure are balanced only in the capillary seal portion 34, and the interface between the oil and air is formed in a meniscus shape.

  By forming the capillary seal portion 34 radially outward of the sleeve 12 and the bearing housing 10, an upper portion formed in a minute gap between the inner peripheral surface of the sleeve 12 and the outer peripheral surface of the shaft 16, which will be described in detail later, The axial dimension and the volume of the capillary seal portion 34 can be sufficiently ensured without reducing the bearing rigidity of the lower radial bearing portion 24.26. Therefore, it is possible to prevent the oil from flowing out of the motor, and to provide a fluid dynamic pressure bearing excellent in reliability and durability, and a spindle motor including the fluid dynamic pressure bearing.

<Bearing configuration>
Next, the bearing structure will be described with reference to FIGS.

  As shown in FIG. 2, an upper radial bearing 24 and a lower radial bearing 26 are provided in the radial gap between the inner peripheral surface of the sleeve 12 and the outer peripheral surface of the shaft 16 so as to be separated in the axial direction. The upper radial bearing 24 and the lower radial bearing 26 are composed of an inner peripheral surface of the sleeve 12, an outer peripheral surface of the shaft 16, and oil held in a gap between both members facing in the radial direction.

  As shown in FIG. 3 (b), oil is induced in the portion constituting the upper radial bearing 24 on the inner circumferential surface of the sleeve 12 from the both ends in the axial direction of the upper radial bearing 24, and is unloaded in the axial direction. A herringbone groove 12a having a balanced shape (R1> R2) is formed. When the rotor 6 rotates, a moving pressure is induced in which the oil moves downward in the axial direction (on the lower radial bearing 26 side). That is, the oil is induced to the central portion of the upper radial bearing 24, but the maximum is slightly below the center of the upper radial bearing 24 because the herringbone groove 12a forms an unbalanced shape in the axial direction. It becomes pressure and supports the rotor 6, and the unbalanced oil is urged to flow downward in the axial direction with respect to the oil.

  In addition, oil is induced in a portion of the inner peripheral surface of the lower radial bearing 26 on the inner peripheral surface of the sleeve 12 from the both ends in the axial direction of the lower radial bearing 26 to a substantially central portion, and is substantially balanced in the axial direction (R3 = R4). ) Having a herringbone groove 12b. When the rotor 6 rotates, pressure is induced in the oil from both ends in the axial direction of the lower radial bearing 26 toward the center. That is, the oil is induced to the central portion of the lower radial bearing 26, but the herringbone groove 12b forms a balanced shape in the axial direction. Support.

  Further, the upper end surface of the bearing housing 10 and the lower surface of the upper wall portion 18a of the rotor hub 18 are opposed to each other via a minute gap in the axial direction, and an upper thrust bearing 28 is provided in the gap. The upper thrust bearing 28 includes an upper end surface of the bearing housing 10, a lower surface of the upper wall portion 18 a of the rotor hub 18, and oil that is held in a gap between both members facing in the axial direction.

  As shown in FIG. 3A, a spiral groove 10a is formed on the upper end surface of the bearing housing 10 so that oil is induced radially inward (on the outer peripheral surface of the shaft 16) when the motor rotates. Is formed. When the rotor 6 rotates, a dynamic pressure directed radially inward is induced in the upper thrust bearing 28 by the spiral groove 10a. Thereby, the rotor 6 is levitated and the oil internal pressure inside is increased. Since the oil pressure is always kept high with respect to the outside air, the bubbles dissolved in the oil are prevented from being bubbled.

  A lower thrust bearing 30 is formed in the axial gap between the lower end surface of the sleeve 12 and the upper surface of the thrust plate 22. A spiral groove 12c is formed in the lower end surface of the sleeve so that oil is induced radially inward (on the lower outer peripheral surface side of the shaft 16) when the motor rotates. When the rotor 6 rotates, the lower thrust bearing 30 induces a dynamic pressure inward in the radial direction by the spiral groove 12c.

  Therefore, the rotor 6 is pressed in the vertical direction by the floating action on the rotor 6 by the upper thrust bearing 28 and the push-down action on the thrust plate 22 by the lower thrust bearing 30. The rotational levitation position of the rotor 6 is stabilized at a position where these dynamic pressures are balanced. By forming the upper and lower thrust bearings 28, 30, the shaft supporting force generated in the upper and lower thrust bearings 28, 30 acts in cooperation from the opposite directions in the axial direction. Can be stably supported.

  The upper and lower thrust bearings 28 and 30 are both formed with spiral grooves. However, the present invention is not limited to this, and herringbone grooves may be formed in one or both of the upper and lower thrust bearings 28 and 30. Is possible. In this case, the herringbone groove formed in the upper thrust bearing 28 is preferably an unbalanced herringbone groove in which oil is directed radially inward by the generated dynamic pressure. This is because the oil dynamic pressure directed inward in the radial direction increases the internal pressure of the entire oil radially inward from the unbalanced herringbone groove and prevents negative pressure, thereby preventing the generation of bubbles.

  The herringbone grooves 12a and 12b and the spiral groove 12c provided in the upper and lower radial bearings 24 and 26 and the lower thrust bearing 30 can be formed in the same manner when the sleeve 12 made of sintered material is press-formed. . Thereby, the sleeve 12 can be manufactured at low cost.

  In this embodiment, the conventional thrust bearing formed between the lower surface of the thrust plate and the upper surface of the counter plate is eliminated. Then, a thrust bearing is newly formed between the upper end surface of the bearing housing and the lower surface of the upper wall portion 18a of the rotor hub 18. Thereby, the axial thickness of the thrust plate 22 may be a dimension sufficient to obtain the bearing rigidity necessary for forming the lower thrust bearing 30. Therefore, the axial dimension of the thrust plate 22 can be made thinner than the conventional one. Also, the axial dimension of the upper surface of the counter plate 14 can be reduced. Thereby, a spindle motor can be reduced in size and thickness.

  Further, conventionally, when no surface treatment is applied to the shaft and the sleeve, when the shaft and the sleeve come into contact with each other, one or both of the shaft and the sleeve are worn, and the durability of the shaft and the sleeve is significantly reduced. . In order to prevent such a decrease in durability and to ensure mechanical strength for supporting the rotor, the outer peripheral surface of the shaft constituting the conventional bearing surface or the inner peripheral surface of the sleeve is subjected to nitriding treatment or the like. A curing process was performed.

  However, in this embodiment, a porous sintered material impregnated with oil is used as the sleeve material. When a sintered sleeve is used, oil begins to ooze out on the inner peripheral surface of the sleeve that constitutes the bearing surface during motor rotation, and there is always a constant distance between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the sleeve. Since the oil film is formed, high sliding performance can be obtained between the shaft and the sleeve. Accordingly, stable rotational performance can be obtained without performing a hardening process such as a nitriding process on the outer peripheral surface of the shaft. By not performing the curing process on the outer peripheral surface of the shaft, a fluid dynamic pressure bearing can be manufactured at low cost, and an inexpensive motor can be manufactured.

  The arithmetic average roughness Ra of the outer peripheral surface of the shaft is not less than 0.1 μm and not more than 1.6 μm, and preferably not less than 0.3 μm and not more than 0.8 μm. Thereby, the shaft can obtain much higher sliding performance, and can obtain stable rotation performance.

<Configuration of communication hole 32>
As shown in FIGS. 2 and 3, the outer circumferential portion of the sleeve 12 has an axial groove that penetrates the axial end portion of the sleeve 12 by press working or cutting so that the cross section is substantially rectangular or semicircular. Is formed. When the sleeve 12 is attached to the inner peripheral surface of the bearing housing 10, the axial groove is a communication hole that penetrates from the upper end in the axial direction of the sleeve 12 to the lower end in the axial direction between the inner periphery of the bearing housing 10. 32. The communication hole 32 is filled with oil, and the oil internal pressure is equal to the oil internal pressure held in each bearing portion.

  In the case of a bearing that does not have the oil communication hole 32, the oil pressure at the outer peripheral portion of the thrust plate 22 may be a so-called negative pressure that is lower than the atmospheric pressure due to the influence of processing errors of the member. That is, when the width dimension of the minute gap on the upper side in the axial direction is formed wider than the width dimension on the lower side among the minute gaps formed between the inner circumferential surface of the sleeve 12 and the outer circumferential surface of the shaft 16, The dynamic pressure generated on the lower radial bearing 26 side exceeds the dynamic pressure generated on the upper radial bearing 24, and the flow of oil from the lower side in the axial direction to the upper side is generated, so that the outer peripheral portion of the thrust plate 22 and / or There is a concern that the internal pressure of the oil held in the gap between the lower end surface of the thrust plate 22 and the upper end surface of the counter plate 14 becomes a negative pressure.

  Further, due to the above-described processing error, for example, the width dimension of the minute gap on the upper side in the axial direction of the minute gap formed between the inner circumferential surface of the sleeve 12 and the outer circumferential surface of the shaft 16 is smaller than the lower side dimension. If it is too narrow, the dynamic pressure generated by the herringbone groove 12a provided in the upper radial bearing 24 becomes a predetermined pressure or more, and a negative pressure is generated in the gap between the lower end surface of the thrust plate 22 and the upper end surface of the counter plate 14. There are concerns that arise.

  Even in such a bearing, by providing this communication hole 32, the oil pressure at the outer peripheral portion of the thrust plate 22 is forcibly drawn to the same pressure level as the inner peripheral portion of the thrust bearing 28. The oil pressure in the inner peripheral portion is always higher than the atmospheric pressure by the amount of dynamic pressure generated by the spiral groove shown in FIG. Therefore, even if the oil pressure at the outer peripheral portion of the thrust plate 22 decreases due to processing errors or disturbances, there is almost no possibility of being below atmospheric pressure. Thereby, the negative pressure of the oil of the outer peripheral part of the thrust plate 22 is prevented.

  Further, when the oil flows from the upper side to the lower side in the axial direction due to the processing error, the internal pressure of the oil in the gap between the lower surface of the thrust plate 22 and the upper surface of the counter plate 14 increases more than necessary, and the rotor 6 is excessive. There are concerns that have emerged too much.

  On the other hand, by providing the communication hole 32, a difference occurs in the internal pressure of the oil between the upper side and the lower side in the axial direction of the minute gap formed between the inner peripheral surface of the sleeve 12 and the outer peripheral surface of the shaft 16. However, since the oil flows from the high internal pressure side to the low internal pressure through the communication hole 32, the internal pressure of the oil held in each bearing portion is balanced, and the occurrence of negative pressure or over-levitation is prevented.

  In addition, the dynamic pressure generating groove provided in the upper radial bearing 24 is asymmetrically herringbone groove 12a in the axial direction to induce a dynamic pressure that presses the oil downward in the axial direction, so that the upper radial bearing 24 The pressure in the region between the lower radial bearing 26 and the lower radial bearing 26 is maintained at a positive pressure equal to or higher than the atmospheric pressure, and the generation of negative pressure is prevented. Further, the oil is always caused by the pressing force generated by the herringbone groove 12a to communicate with the lower radial bearing 26, the communication hole 32 between the lower end surface of the sleeve 12 and the upper end surface of the counter plate 14, and the upper end surface of the sleeve 12 and the rotor hub. 18 between the upper wall portion 18a and the lower surface of the upper wall portion 18a. The pressure flows so as to flow upward in the axial direction of the outer peripheral surface of the shaft 16 and the inner peripheral surface of the sleeve 12, and to flow back to the upper radial bearing 24. A series of oil circulation paths is formed.

  As a result, the oil in the bearing always flows in a certain direction, and the pressure can be balanced, so that the generation of bubbles due to negative pressure and the occurrence of excessive floating of the rotor 6 are prevented. In addition, since the allowable range for processing errors is greatly expanded, the yield is improved.

  Further, by arranging one end of the communication hole 32 so as to open radially inward from the upper thrust bearing 28, the oil pressure can be kept constant in a region higher than the atmospheric pressure.

  Thereby, when a predetermined dynamic pressure is generated in the bearing portion during steady rotation of the motor, sufficient bearing rigidity can be obtained, and therefore, the possibility of contact and sliding of the bearing portion is low.

  In addition, by forming the shaft 16 and the rotor hub 18 with members having a higher thermal expansion coefficient than the bearing housing 10 and the sleeve 12, the thermal expansion amount of the shaft 16 and the rotor hub 18 can be reduced in a high temperature environment due to the thermal expansion coefficient. 10 and the thermal expansion amount of the sleeve 12 will be exceeded. Therefore, in each bearing portion, even if the gap between the bearing housing 10 and the sleeve 12 facing the shaft 16 and the rotor hub 18 is small and the viscosity of the oil is reduced due to thermal expansion, it is possible to prevent the bearing rigidity from being lowered. It becomes possible. Therefore, a predetermined bearing rigidity can be ensured without increasing the power consumption of the motor.

  In addition, in a high temperature environment, the viscosity of the oil decreases and the volume increases due to thermal expansion. Therefore, the oil whose volume is increased flows into the capillary seal portion 34, and if the capacity of the capillary seal portion 34 cannot be sufficiently secured, the oil leaks out of the motor. However, in the bearing according to the present invention, the capillary seal portion 34 is formed on the outer peripheral side of the bearing housing 10 so as to open downward in the axial direction. As a result, a sufficient volume of the seal portion can be secured as compared with the conventional bearing of FIG. In addition, the thermal expansion coefficient of the circumferential protrusion 18d formed integrally with the rotor hub 18 is larger than the thermal expansion coefficient of the bearing housing 10 located radially inward of the circumferential protrusion 18d. The size of the gap in the radial direction becomes large. Therefore, the capacity of the capillary seal portion 34 that can hold oil can be increased under a high temperature environment, and the amount of increase in the oil volume can be sufficiently held in the capillary seal portion 34.

<Method for manufacturing rotor>
Next, a method for manufacturing the rotor will be described. First, a disk-shaped member cut out and formed from a bar material such as aluminum is formed into the shape of the shaft 16 and the rotor hub 18 by, for example, pressing, forging, or the like. Next, the yoke 21 having the rotor magnet 20 bonded and fixed to the inner peripheral surface is fixed to the inner peripheral surface of the rotor peripheral wall portion 18b of the rotor hub 18 by press-fitting and / or an adhesive. Then, a through hole and a screw hole are formed in the central portion of the shaft 16 by tapping. Finally, the dynamic pressure bearing constituting surface such as the outer peripheral surface of the shaft 16 and the lower surface of the upper wall portion 18a of the rotor hub 18 and the disk mounting surface of the flange portion 18c of the rotor peripheral wall portion 18b of the rotor hub 18 are cut. Finish with high precision.

  Here, if the rotor 6 is formed by forging an aluminum material or the like, the rotor hub can be manufactured at a low cost, but the radial and axial dimensions of the rotor hub 18 become thin, so that the rigidity of the rotor hub 18 decreases. As described above, when the rotor magnet is press-fitted and fixed to the rotor peripheral wall portion, the rotor magnet may be chipped. Therefore, generally, the rotor magnet and the rotor peripheral wall portion are fixed using an adhesive. However, even when the rotor hub is formed of a relatively high strength, such as martensitic or austenitic stainless steel, and the rotor magnet is bonded and fixed to the inner peripheral surface of the rotor peripheral wall portion, the adhesive is not circumferentially fixed. The stress due to the hardening and shrinkage of the adhesive resulting from the uniform application acts on the rotor flange portion for fixing the rotor magnet in a non-uniform manner. For this reason, the flange portion of the rotor hub is deformed. When the flange portion is deformed, the parallelism of the hard disk placed on the flange portion is lost and the RRO deteriorates. Due to the deterioration of the RRO, a so-called head crash may occur in which the recording surface of the hard disk and the magnetic head disposed in proximity to the recording surface come into contact with each other.

  On the other hand, in the present invention, a yoke 21 made of stainless steel is prepared, and the rotor magnet 20 is bonded and fixed to the inner peripheral surface thereof. Thereafter, the yoke 21 is press-fitted and bonded to the inner peripheral surface of the rotor peripheral wall portion 18b of the rotor 6, and then the flange portion 18c of the rotor 6 is finished by cutting. For this reason, since the stress resulting from the unevenness of hardening and shrinkage of the adhesive is absorbed by the yoke 21, adverse effects on the rotor peripheral wall portion 18b can be avoided. In addition, by fixing the yoke 21 to the inner peripheral surface of the rotor peripheral wall portion 18b of the rotor hub 18, the rigidity of the rotor peripheral wall portion 18b of the rotor hub having a thin radial dimension can be increased. Therefore, even when an excessive force such as a centrifugal force is applied to the rotor peripheral wall portion 18b during rotation of the motor, it is possible to prevent the rotor peripheral wall portion 18b from being bent and deformed by the force. In addition, since the shaft 16 and the rotor hub 18 are formed of aluminum or the like, the workability is high and high-precision processing can be easily performed, so that the processing cost can be reduced. After performing the above-described method for manufacturing the rotor 6, for example, the outer peripheral surface of the shaft 16 or the lower surface of the upper wall portion 18 a of the rotor hub 18 may be subjected to a hardening process such as a plating process or a nitriding process.

<Assembly method of spindle motor>
Next, a method for assembling the motor of the present invention will be described with reference to FIGS.

  First, an adhesive is applied to the adhesive grooves 10 b formed in the circumferential direction on the inner peripheral surface of the bearing housing 10. Then, the sleeve 12 is inserted and fixed from below in the axial direction of the bearing housing 10. At this time, although the adhesive is slid by the sleeve 12, it is accommodated in the adhesive groove 10b, so that, for example, even if the application position, the application amount, etc. of the adhesive are not uniform, it is axially above the adhesive groove 10b. Can be prevented.

  In addition, by providing the adhesive groove 10b, the fastening strength between the bearing housing 10 and the sleeve 12 can be strengthened, so that it is possible to obtain strength against external impacts and the like. Therefore, even if the motor is reduced in size and thickness, the bearing housing 10 and the sleeve 12 can be firmly fixed.

  The adhesive may be applied to the outer peripheral surface of the sleeve 12, or may be applied to both the outer peripheral surface of the sleeve 12 and the inner peripheral surface of the bearing housing 10. Further, the adhesive grooves may be formed at several places on the inner peripheral surface of the bearing housing 10. In addition, the adhesive groove may be formed as a longitudinal groove extending in the axial direction on the inner peripheral surface of the sleeve 12.

  Next, the thrust plate 22 is inserted into a through hole provided in the central portion of the shaft 16 and fixed with an adhesive. Then, the counter plate 14 is inserted into the bearing housing 10 to close the lower portion of the bearing housing 10. At this time, the lower end surface 10c of the bearing housing 10 and the lower surface 14a of the counter plate 14 are arranged on the same plane.

  Next, the rotor hub 18 is held by a jig (not shown), and the jig is rotated at a constant low speed in this state. Then, in a state where the jig is rotating, directivity from a laser device having an irradiation port 50 on the contact portion 40 between the bearing housing 10 and the outer peripheral surface of the counter plate 14 in the axial direction of the contact portion 40. Laser is irradiated as an energy beam, and the contact portion 40 is welded in the circumferential direction. This laser welding can obtain a high fastening strength with less applied energy than other welding such as arc welding and resistance welding. In addition, since it does not require a vacuum device, it is easy to handle, and the good directivity of the beam enables strong welding in a narrow range.

Thus, by fixing the counter plate 14 to the bearing housing 10 by irradiating the laser beam by welding, it is possible to obtain a higher fastening strength between members as compared with fixing means such as an adhesive, and to fix the counter plate 14 more firmly. it can. Accordingly, since the axial dimension of the counter plate 14 can be formed thin, the overall thickness of the spindle motor can be further reduced in size and thickness.

  Further, by using laser welding, a stable fastening strength can be obtained even if the bearing housing 10 and the counter plate 14 are formed of members having different thermal expansion coefficients. Moreover, oil can be prevented from scattering from the contact portion 40 by irradiating the contact portion 40 with the laser in the circumferential direction and welding.

  Further, a concave portion 10 d that is recessed radially outward from the lower inner peripheral surface is formed on the lower inner peripheral surface of the bearing housing 10. The recess 10d faces the thrust plate 22 in the radial direction. Since the distortion generated at the time of laser welding is absorbed by the recess 10d, the inner peripheral surface of the lower end portion of the bearing housing 10 is prevented from being deformed by heat at the time of welding and contacting the outer peripheral portion of the thrust plate 22 by laser welding. ing. Therefore, the efficiency of the joining process between the bearing housing 10 and the counter plate 14 is improved.

  Since welding involves application of high-temperature energy, argon gas, which is a cooling fluid, is supplied and cooled as a means for cooling the welded part. The cooling fluid is a substance having low reactivity with the metal surface such as the counter plate 14 and is preferably in a gaseous state. As the cooling fluid, helium or nitrogen having high cooling efficiency can also be used. Although the rotor hub 18 is rotated, laser welding may be performed by rotating the irradiation port 50 in the circumferential direction.

  Next, oil is filled into a series of minute gaps that constitute the bearing portion via the capillary seal portion 34. Then, the bracket 2 to which the stator 8 is fixed is fixed to the bearing housing 10.

<Configuration of Hard Disk Drive Device 40>
Next, the internal configuration of a general hard disk drive 60 will be described with reference to FIG.

  The hard disk drive 60 includes a rectangular housing 42. The housing 42 forms a clean space with extremely little dust, dust, and the like, and a disk-like shape for recording information therein. A spindle motor 44 with a hard disk 46 mounted thereon is provided.

  A head moving mechanism 54 for reading / writing information from / to the hard disk 46 is disposed inside the housing 42. The head moving mechanism 54 includes a magnetic head 52 for reading / writing information on the hard disk 46, and the magnetic head 52. The supporting arm 70, the magnetic head 52, and the actuator unit 48 are configured to move the arm 70 to a required position on the hard disk 46.

  By applying the spindle motor shown in FIGS. 1 to 4 as the spindle motor 44 of such a hard disk drive device 60, it is possible to realize a small and thin hard disk drive device while ensuring sufficient functions. A hard disk drive device with high reliability and durability can be provided.

  The spindle motor according to the present invention, the method for manufacturing the rotor applied to the spindle motor, and the hard disk drive device including the spindle motor have been described above. However, the present invention is limited to the embodiment. Rather, various changes and modifications can be made without departing from the scope of the invention.

  For example, it is not limited to the structure of the hydrodynamic bearing of the illustrated embodiment, and the shape, number, position, and type of lubricating fluid of the groove may be different from those of the above embodiment. The bracket of the spindle motor may be formed integrally with the housing of the hard disk drive device.

It is a longitudinal cross-sectional view which shows one Embodiment of this invention. It is an important section expanded sectional view concerning one embodiment of the present invention. It is sectional drawing which shows the sleeve and bearing housing of this invention, and the upper end surface of a shaft. It is sectional drawing which shows the welding process of 1st embodiment of this invention. It is a longitudinal cross-sectional view which shows the recording disk drive device of this invention. It is a longitudinal cross-sectional view which shows the conventional spindle motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Bearing housing 12 Sleeve 16 Shaft 18 Rotor hub 18a Upper wall part 18b Rotor peripheral wall part 18c Flange part 18d Circumferential protrusion 24 Upper radial dynamic pressure bearing part 26 Lower radial dynamic pressure bearing part 28 Upper thrust dynamic pressure bearing part 30 Lower thrust dynamic pressure Bearing part 34 Taper seal part

Claims (13)

A shaft,
A top plate fixed to the top of the shaft;
A thrust plate fixed to a lower portion of the shaft;
A cylindrical sleeve through which the shaft is inserted and rotated relative to the shaft;
A substantially cup-shaped bearing housing that holds the sleeve on the inner periphery and has a lower end closed;
A continuous minute gap is formed between the shaft and the top plate and the sleeve, and the minute gap is filled with a lubricating fluid,
Between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve is formed a radial bearing portion provided with a dynamic pressure generating groove for inducing a dynamic pressure in the lubricating fluid when the shaft or the sleeve rotates.
An upper thrust bearing portion is provided between the lower surface of the top plate and the upper end surface of the bearing housing. The upper thrust bearing portion is provided with a dynamic pressure generating groove for inducing dynamic pressure in the lubricating fluid when the shaft or the sleeve rotates. ,
Between the lower end surface of the sleeve and the upper surface of the thrust plate, there is formed a lower thrust bearing portion provided with a dynamic pressure generating groove for inducing dynamic pressure in the lubricating fluid when the shaft or the sleeve rotates. A fluid dynamic pressure bearing.   Between the outer peripheral surface of the sleeve and the inner peripheral surface of the bearing housing, one end opens to the radially inner side of the upper thrust bearing portion and communicates with the vicinity of the outer peripheral portion of the lower thrust bearing portion. The fluid dynamic pressure bearing according to claim 1, wherein a hole is formed.   The fluid dynamic pressure bearing according to claim 2, wherein the communication hole includes an axial groove formed on an outer peripheral surface of the sleeve and an inner peripheral surface of the housing. The radial bearing portion includes a pair of axially spaced radial bearings formed between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve, and at least one of the radial bearings includes the dynamic pressure. The generating groove is provided with an unbalanced herringbone groove that induces a dynamic pressure that acts on the lubricating fluid from the upper side in the axial direction to the lower side in the axial direction when the shaft or the sleeve rotates.
The upper thrust bearing and the lower thrust bearing are provided with a spiral groove that induces a dynamic pressure radially inward in the lubricating fluid when the shaft or the sleeve rotates as the dynamic pressure generating groove. The fluid dynamic pressure bearing according to claim 1, wherein the fluid dynamic pressure bearing is provided. The lubricating fluid filled in the minute gap is oil,
The top plate is formed with a circumferential protrusion extending downward from the top plate in the axial direction and facing the outer peripheral surface of the bearing housing in the radial direction with a seal gap interposed therebetween,
The radial dimension of the sealing gap increases from the top plate in the axial direction downward,
5. The oil according to claim 1, wherein the oil in the minute gap is continuously held in the sealing gap, and the oil forms a gas-liquid interface in the sealing gap. A fluid dynamic pressure bearing according to claim 1.   The fluid dynamic pressure bearing according to claim 1, wherein the sleeve is made of a porous sintered metal impregnated with oil.   7. The surface roughness of the outer peripheral surface of the shaft is Ra 0.1 μm or more and 1.6 μm or less, preferably Ra 0.3 μm or more and 0.8 μm or less. The fluid dynamic pressure bearing described. The sleeve is fixed to the inner periphery of the bearing housing with an adhesive,
An adhesive groove is formed on an outer peripheral surface of the sleeve and / or an inner peripheral surface of the bearing housing with which the sleeve and the housing abut, and an adhesive is held in the adhesive groove. The fluid dynamic pressure bearing according to claim 1. The bearing housing is composed of a cylindrical member having an inner peripheral portion that holds the sleeve, and a counter plate that closes a lower end portion of the cylindrical member,
The fluid dynamic pressure bearing according to claim 1, wherein the counter plate and the bearing housing are fixed by welding.   The fluid dynamic pressure bearing according to claim 1, wherein the shaft and the top plate are integrally formed. The part where the counter plate and the bearing housing are welded is located radially outward from the inner periphery of the bearing housing,
11. A concave portion for absorbing deformation of the bearing housing due to the welding is formed in an inner peripheral portion of the bearing housing so as to be opposed to the outer peripheral portion of the thrust plate in a radial direction. The fluid dynamic pressure bearing according to any one of the above. A spindle motor comprising the fluid dynamic pressure bearing according to any one of claims 1 to 11,
A bracket for holding the bearing housing of the fluid dynamic pressure bearing on an inner peripheral portion;
A stator fixed to the bracket;
A rotor peripheral wall portion extending downward from an outer peripheral portion of the top plate of the fluid dynamic pressure bearing;
A spindle motor comprising: a rotor magnet held on the rotor peripheral wall portion and opposed to the stator in a radial direction. A recording disk drive having a disk-shaped recording medium capable of recording information,
A housing;
The spindle motor according to claim 12, wherein the spindle motor is fixed inside the housing and rotates the recording medium.
And a means for writing or reading information at a required position of the recording medium.

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