JP5537301B2 - Spindle motor - Google Patents

Description

  The present invention relates to a spindle motor, and more particularly to a spindle motor using a fluid dynamic pressure bearing.

  In a recording device such as a hard disk device, an improvement in recording density is required. In order to meet this demand, the recording track density is improved and the gap (head gap) between the magnetic head and the recording medium (disk) is reduced. In order to cope with such higher recording track density and head gap reduction, in recent years, fluid dynamic pressure bearing devices (also simply called “fluid bearing devices”) have been adopted as spindle motor bearings for rotating disks. It has come to be.

  In Patent Document 1, as a hydrodynamic bearing device of a spindle motor for a hard disk device, a shaft provided with two conical surfaces opposed to each other in a convex direction, and a sleeve provided with two inclined surfaces opposed in parallel to the conical surface. Have been proposed. In this hydrodynamic bearing device, a dynamic pressure generating groove is provided on either the conical surface or the inclined surface, so that the lubricating oil filled in the fluid bearing gap between the conical surface and the inclined surface is moved along with the rotation of the shaft. A pressure is generated and the shaft is rotatably supported with respect to the sleeve.

  The dynamic pressure generated in the lubricating oil increases as the dynamic viscosity of the lubricating oil increases, and increases as the fluid dynamic bearing clearance decreases. Normally, the kinematic viscosity of the lubricating oil filled in the fluid bearing clearance decreases with increasing temperature. For this reason, if the dynamic pressure fluctuates with a change in temperature, the rotation of the spindle motor may not be stable. Therefore, in Patent Document 1, when the overall length (height) is longer than the inner diameter dimension of the sleeve, the sleeve is made of a material having a larger linear expansion coefficient than the shaft so that the fluid bearing clearance becomes narrow at high temperatures. It has been proposed to

JP 2002-122134 A JP 2005-6493 A

  However, depending on the method in which the sleeve described in Patent Document 1 is made of a material having a linear expansion coefficient larger than that of the shaft, the fluid bearing clearance is not necessarily narrow at high temperatures, and fluctuations in dynamic pressure due to temperature changes are reliably suppressed. I couldn't. This problem is not limited to spindle motors for hard disk devices, and is generally common to spindle motors that require high-precision rotation.

  The present invention has been made to solve the above-described conventional problems, and in a spindle motor using a fluid dynamic pressure bearing, fluctuation of dynamic pressure due to a temperature change is more reliably suppressed and rotation is more stable. The purpose is to provide technology.

  In order to achieve at least a part of the above object, the present invention can be realized as the following forms or application examples.

[Application Example 1]
A spindle motor, a shaft member having one end fixed to the motor base, first and second conical bearing members fixed to the shaft member and having a conical outer surface, and a through hole through which the shaft member is inserted A rotor member having first and second conical inner surfaces whose inner diameters increase toward the outside at both ends of the through hole, and a dynamic pressure groove formed on either the conical inner surface or the conical outer surface And a lubricating oil filled in a minute gap between the conical inner surface and the conical outer surface facing each other when the rotor member is sandwiched between the first and second conical bearing members, The linear expansion coefficient α1, the linear expansion coefficient α2 of the conical bearing member, and the linear expansion coefficient α3 of the rotor member satisfy the relational expression of α3 ≧ α2> α1, and the first on the inner surface of the first cone The point and the second point having the same inner diameter as the first point The axial distance L between the second points on the inner surface of the cone, the inner diameter D at the first point, and the inclination angle θ formed by the inner surface of the cone and the surface perpendicular to the axis, L> (D × A spindle motor that satisfies the relational expression (tanθ). According to this application example, the width of the minute gap at the time of high temperature can be made narrower than that at the time of low temperature. For this reason, it is possible to more reliably suppress fluctuations in the dynamic pressure due to temperature fluctuations and to stabilize the rotation of the spindle motor.

[Application Example 2]
The spindle motor according to Application Example 1, wherein the shaft member has a screw portion provided at an end opposite to the motor base. By providing the screw portion, the shaft member can be fixed to the cover that covers the motor base. Therefore, since the rigidity of the shaft member can be further increased, the spindle motor can be rotated more accurately.

[Application Example 3]
The spindle motor according to application example 1 or 2, wherein the dynamic pressure groove is formed in a nickel plating layer that is provided on a surface where the dynamic pressure groove is formed and is thicker than a depth of the dynamic pressure groove. By forming the dynamic pressure grooves in the nickel plating layer, the surface roughness can be improved for both the hills between the dynamic pressure grooves and the bottom of the dynamic pressure grooves. By improving the surface roughness, the flow of the lubricating oil becomes smoother, so that variations in dynamic pressure performance can be suppressed.

[Application Example 4]
4. The spindle motor according to any one of application examples 1 to 3, wherein at least one of the conical bearing member and the rotor member is made of an aluminum-silicon alloy. By using an aluminum-silicon alloy having high hardness, the wear resistance of each member is improved. Therefore, according to this application example, it is possible to extend the life of the spindle motor.

The fragmentary sectional view which shows the structure of a spindle motor. Explanatory drawing explaining the shape and arrangement | positioning of the conical inner surface of a rotor member. Explanatory drawing which shows a mode that the position of the point of a cone inner surface changes with a raise of temperature. The fragmentary sectional view which shows the structure of the spindle motor of a comparative example. The graph which shows the evaluation result of the bearing characteristic of a spindle motor.

A. First embodiment:
A1. Spindle motor configuration:
A2. Effect of temperature change:
A3. Configuration of spindle motor of comparative example:
A4. Evaluation of spindle motor bearing characteristics:
B. Second embodiment:

A1. Spindle motor configuration:
FIG. 1 is a partial cross-sectional view showing the configuration of the spindle motor in the first embodiment. The spindle motor SM is a spindle motor using a fluid dynamic pressure bearing (hereinafter also simply referred to as “fluid bearing”), and includes a stator unit 100, a shaft unit 200, and a rotor unit 300.

  The stator unit 100 has a base plate 110, a stator core 120, and a plurality of windings 130. The base plate 110 is formed with a shaft member insertion hole 112 for inserting a shaft member 210 (described later) and a circumferential wall portion 114 concentric with the shaft member insertion hole 112. A stator composed of the stator core 120 and the winding 130 is fixed to the outer peripheral surface of the circumferential wall portion 114. Note that the base plate 110 is a member that serves as a base of the spindle motor SM, and therefore can also be referred to as a “motor base”.

  The shaft unit 200 includes a shaft member 210 fixed to the base plate 110 and two conical bearing members 220 fixed to the shaft member 210. The shaft member 210 is a substantially cylindrical member formed of SUS440C, which is martensitic stainless steel, and a screw portion 212 is provided at the end opposite to the base plate 110 side. The conical bearing member 220 is a member formed with a conical outer surface 222 and an inclined surface 224 whose outer diameter decreases toward the end. The two conical bearing members 220 are fixed to the shaft member 210 so that the conical outer surface 222 side faces. The conical bearing member 220 is formed of SUS303, which is an austenitic stainless steel.

  The screw portion 212 of the shaft member 210 is used for screwing a cover (not shown) that covers the base plate 110. By fixing the shaft member 210 and the cover by screwing, the shaft member 210 is supported at both ends, so that the rigidity of the shaft member 210 can be further increased. Thus, by increasing the rigidity of the shaft member 210, the rotational accuracy of the rotor unit 300 can be further increased. However, the shaft member 210 is not necessarily cylindrical. Further, it is not always necessary to fix the shaft member 210 to the cover. In this case, the formation of the screw portion 212 on the shaft member 210 can be omitted.

  The rotor unit 300 includes a rotor member 310, a yoke 320, a permanent magnet 330, and an end cap 350. The rotor member 310 is a member formed of aluminum alloy A6061-T6. The rotor member 310 is provided with a through hole 312 for inserting the shaft member 210, two dynamic pressure groove portions 316 provided outside the through hole 312, and a magnet attachment portion 318. An annular permanent magnet 330 is fixed to the magnet mounting portion 318 via a yoke 320. The two dynamic pressure groove portions 316 have a conical inner surface 314 whose inner diameter increases toward the outer side.

  The dynamic pressure groove 316 is formed with a dynamic pressure groove (not shown) for generating dynamic pressure. The dynamic pressure groove can be formed, for example, by subjecting the conical inner surface 314 to electrolytic processing. The conical inner surface 314 and the conical outer surface 222 of the conical bearing member 220 face each other with a minute gap 410 therebetween. In the first embodiment, the dynamic pressure groove portion 316 is formed in the rotor member 310, but the dynamic pressure groove portion may be provided not in the rotor member 310 but in the conical bearing member 220.

  The end cap 350 is a member fixed to the rotor member 310 at the outer end portion of the conical inner surface 314, and has an oil injection hole 352 for injecting the lubricating oil 420 filled in the minute gap 410. A gap is provided between the end cap 350 and the shaft member 210 so that the end cap 350 does not hinder the rotation of the rotor member 310. The end cap 350 is fixed to the rotor member 310 by adhesion or press-fitting and adhesion. When the inner peripheral surface 354 of the end cap 350 and the inclined surface 224 of the conical bearing member 220 face each other, a capillary seal portion 430 in which the gap increases toward the outside is formed. Lubricating oil 420 injected from the oil injection hole 352 is stored in the capillary seal portion 430 and supplied from the capillary seal portion 430 to the minute gap 410. Thereby, the minute gap 410 is always filled with the lubricating oil 420.

  As shown in FIG. 1, the permanent magnet 330 fixed to the rotor unit 300 and the stator core 120 fixed to the stator unit 100 are opposed to each other with a minute gap therebetween. The rotating magnetic field is generated by passing alternating currents having different phases through the plurality of windings 130 of the stator unit 100. Due to the generated rotating magnetic field, a rotational force is generated in the permanent magnet 330, and the rotor unit 300 rotates with respect to the stator unit 100 and the shaft unit 200.

  When the rotor unit 300 rotates with respect to the shaft unit 200, dynamic pressure that separates the conical inner surface 314 of the rotor unit 300 and the conical outer surface 222 of the shaft unit 200 is generated by the dynamic pressure grooves provided in the dynamic pressure groove portion 316. To do. Thereby, the conical inner surface 314 and the conical outer surface 222 are supported in a non-contact state. Since the conical inner surface 314 and the conical outer surface 222 are supported in a non-contact state, the rotor unit 300 freely rotates with respect to the shaft unit 200 and the stator unit 100 to which the shaft unit 200 is fixed.

  In the first embodiment, the dynamic pressure groove is formed by subjecting the rotor member 310 to direct electrolytic processing. However, prior to the formation of the dynamic pressure groove, the conical inner surface 314 of the rotor member 310 has a depth of the dynamic pressure groove. It is also possible to apply a thick nickel plating. The nickel plating may be thicker than the dynamic pressure groove depth. For example, when the dynamic pressure groove depth is 5 μm, the nickel plating thickness may be 10 μm.

  Thus, prior to the formation of the dynamic pressure groove by electrolytic processing, the nickel plating layer thicker than the dynamic pressure groove depth is applied to the rotor member 310 made of an aluminum alloy, so that the nickel plating layer is formed even after the dynamic pressure groove is formed. It remains in the entire groove. Generally, in the nickel plating layer, the deterioration of the surface roughness (increase in the surface roughness numerical value) of the portion subjected to electrolytic processing is suppressed more than that of the aluminum alloy. Therefore, by applying nickel plating that is thicker than the dynamic pressure groove depth first, rough surface is formed on both the hill between the formed dynamic pressure groove and the dynamic pressure groove and the bottom surface of the dynamic pressure groove. Is improved (reduced surface roughness value). As described above, when the surface roughness is improved, the flow of the lubricating oil 420 becomes smoother, so that the variation in the dynamic pressure performance is suppressed. Further, since nickel plating is applied to a smooth surface on which no dynamic pressure grooves are formed, the thickness of the nickel plating can be easily made uniform, and the depth of the dynamic pressure grooves can be easily managed. Therefore, the performance as intended in the design can be exhibited, and the quality and reliability of the spindle motor SM can be improved.

  In addition, after forming the dynamic pressure groove in the rotor member 310 made of an aluminum alloy, the hard pressure treatment of any one of nickel plating, alumite treatment, and diamond like carbon (DLC) coating is performed on the formation surface of the dynamic pressure groove. It may be applied. In this case, the dynamic pressure groove is formed in advance by electrolytic processing so as to have an appropriate depth after the hard coating treatment. Thus, by forming the dynamic pressure groove on the conical inner surface 314 of the rotor member 310 made of an aluminum alloy and then applying the hard film treatment, the surface roughness, corrosion resistance and wear resistance are improved. The lifetime can be extended.

  Furthermore, a hard film treatment of DLC coating may be applied to at least the conical outer surface 222 of the conical bearing member 220 in which no dynamic pressure groove is formed. By applying a hard film treatment to the outer cone surface 222, the wear resistance of the outer cone surface 222 is improved, so that the life of the spindle motor SM can be extended. When the dynamic pressure groove is not formed in the rotor member 310 and the dynamic pressure groove is formed in the conical bearing member 220, the conical inner surface 314 of the rotor member 310 may be subjected to DLC coating. In general, by applying DLC coating to the surface facing the dynamic pressure groove (dynamic pressure groove facing surface), the wear resistance of the surface facing the dynamic pressure groove is improved, so the life of the spindle motor SM can be extended. It becomes.

A2. Effect of temperature change:
The dynamic pressure generated in the minute gap 410 increases as the kinematic viscosity of the lubricating oil 420 and the rotational speed of the rotor unit 300 increase. On the other hand, the dynamic pressure decreases as the minute gap 410 becomes wider. Usually, the kinematic viscosity of the lubricating oil 420 decreases as the temperature increases. For this reason, if the rotation speed is the same as that of the minute gap 410, the dynamic pressure generated in the minute gap 410 varies with a change in temperature. If the dynamic pressure fluctuates in this way, the positional relationship between the rotor unit 300 and the shaft unit 200 may change, and the rotation of the rotor unit 300 may not be stabilized. That is, there is a possibility that the movement amount (flying amount) of the rotor unit 300 during rotation relative to the stop time may fluctuate. In particular, when the spindle motor SM is used as a drive device for a hard disk device (hereinafter also referred to as “hard disk drive device”), since the space between the disk and the head is extremely narrow in the hard disk device, the flying height variation of the rotor unit 300 varies. Is preferably sufficiently suppressed.

  Therefore, in the first embodiment, the shape and arrangement of the conical inner surface 314 formed on the rotor member 310 and the linear expansion coefficients α1, α2, and α3 of the shaft member 210, the conical bearing member 220, and the rotor member 310 are appropriately set. By setting, the interval of the minute gap 410 (that is, the interval between the conical outer surface 222 and the conical inner surface 314) is made narrower as the temperature increases. As described above, when the kinematic viscosity of the lubricating oil 420 is the same, the dynamic pressure increases when the interval between the minute gaps 410 is narrowed. Therefore, it is possible to suppress a change in dynamic pressure due to temperature by making the interval between the minute gaps 410 narrow as the temperature rises.

  FIG. 2 is an explanatory view for explaining the shape and arrangement of the conical inner surface 314 of the rotor member 310. As shown in FIG. 2, the shape and arrangement of the two conical inner surfaces 314 are such that the inner diameter D and the axial distance L of the two points A and B having the same inner diameter D on the two conical inner surfaces 314 and the conical inner surface 314 are the axes. Is characterized by an angle θ (hereinafter also referred to as “inclination angle θ”) formed with a plane perpendicular to.

  FIG. 3A and FIG. 3B are explanatory views showing a state in which the position of the conical inner surface 314 changes due to a temperature rise. FIG. 3A shows a change in the position of point A when considering the expansion of the rotor member 310 only in the radial direction, and FIG. 3B shows the expansion of the rotor member 310 only in the axial direction. The change of the position of the point A at the time of doing is shown. 3 (a) and 3 (b), the solid line indicates the position of the conical inner surface 314 before expansion, and the broken line indicates the position of the conical inner surface after expansion. 3 (a) and 3 (b), for convenience of explanation, the expansion of the shaft member 210 (FIG. 2) and the conical bearing member 220 (FIG. 2) is not considered.

As shown in FIG. 3A, when the expansion only in the radial direction is considered, the point A moves in the radial direction by the movement amount δr. At this time, the enlargement amount δg1 of the minute gap 410 (FIG. 1) is given by the following equation (1) using the movement amount δr and the inclination angle θ.
δg1 = δr × sin θ (1)

On the other hand, as shown in FIG. 3B, when the expansion only in the axial direction is considered, the point A moves in the axial direction by the movement amount δv. At this time, the reduction amount δg2 of the minute gap 410 (FIG. 1) is given by the following equation (2) using the movement amount δv and the inclination angle θ.
δg2 = δv × cos θ (2)

Therefore, in order to narrow the minute gap 410 (FIG. 1) when the rotor member 310 expands as the temperature rises, the reduction amount δg2 and the enlargement amount δg1 of the minute gap 410 are expressed by the following equation (3). It is necessary to satisfy the relationship.
δg2> δg1 (3)

From the equations (1) to (3), the movement amounts δr, δv in the radial direction and the axial direction of the point A and the inclination angle θ of the conical inner surface 314 need to satisfy the relationship of the following equation (4).
δv × cos θ> δr × sin θ (4)

The radial movement amount δr of the point A and the axial movement amount δv of the point A include the temperature change ΔT, the linear expansion coefficient α3 of the rotor member 310, the inner diameter D of the point A, and the two points A and B. Using the axial distance L (FIG. 2), it is expressed by the following equations (5) and (6).
δr = (D / 2) × α3 × ΔT (5)
δv = (L / 2) × α3 × ΔT (6)

Therefore, the condition of the expression (3) can be rewritten as the following expression (7) using the expressions (5) and (6).
L × cos θ> D × sin θ (7)

From equation (7), it can be seen that the following equation (8) must be satisfied in order to narrow the minute gap 410 when the rotor member 310 expands with increasing temperature. In addition, if the relationship of Formula (8) is satisfy | filled about one point of the conical inner surface 314, the other arbitrary points of the conical inner surface 314 are also satisfied.
L> D × tan θ (8)

  Therefore, in the first embodiment, the inner diameter of the through hole 312 is 3 mm, the length is 10 mm, and the inclination angle θ of the conical inner surface 314 is 60 °. Therefore, at the point of the minimum inner diameter of the conical inner surface 314, the inner diameter D is 3 mm, and the right side (D × tan θ) of Equation (8) is about 5.2 mm. Further, since the axial distance L is 10 mm, the first example satisfies the relationship of the formula (8).

  In the above description, only the expansion of the rotor member 310 has been considered, but the influence of the expansion of the shaft unit 200 will be examined. When the expansion amount of the shaft member 210 is larger than the expansion amount of the rotor member, the minute gap 410 is widened. Therefore, the expansion amount of the shaft member 210 is preferably smaller than the expansion amount of the rotor member 310. Therefore, the linear expansion coefficient α1 of the shaft member 210 is preferably smaller than the linear expansion coefficient α3 of the rotor member 310.

The expansion of the conical bearing member 220 always works in the direction of narrowing the minute gap 410. However, if the expansion amount of the conical bearing member 220 is too large, the minute gap 410 becomes narrower than necessary. On the other hand, if the expansion amount of the conical bearing member 220 is too small, the minute gap 410 is not sufficiently narrowed. Therefore, it is preferable that the linear expansion coefficient α2 of the conical bearing member 220 is not more than the linear expansion coefficient α3 of the rotor member 310 and exceeds the linear expansion coefficient α1 of the shaft member 210. That is, the linear expansion coefficients α1, α2 of the shaft member 210, the conical bearing member 220 (that is, the member on which the conical outer surface 222 is formed), and the rotor member 310 (that is, the member on which the conical inner surface 314 is formed). , Α3 preferably satisfy the relationship of the following equation (9).
α3 ≧ α2> α1 (9)

As described above, in the first embodiment, the shaft member 210 is made of martensitic stainless steel SUS440C having a linear expansion coefficient α1 of 10.2 × 10 ⁻⁶ / ° C., and the conical bearing member 220 has a linear expansion coefficient α2 of 17. .3 × 10 ⁻⁶ / ° C. austenitic stainless steel SUS303. The rotor member 310 is made of an aluminum alloy having a linear expansion coefficient α3 of 23.6 × 10 ⁻⁶ / ° C. Therefore, the linear expansion coefficients α1, α2, and α3 of these members satisfy the relationship of the above formula (9).

  In the first embodiment, by adopting the above-described configuration, the minute gap 410 increases at a low temperature at which the kinematic viscosity of the lubricating oil 420 increases, and the minute gap 410 decreases at a high temperature at which the kinematic viscosity of the lubricating oil 420 decreases. Therefore, a stable dynamic pressure is generated both at low temperatures and at high temperatures. Further, a threaded portion 212 is provided at the end of the shaft member 210 opposite to the base plate 110. Therefore, both ends of the shaft member 210 are supported when the cover is attached, and the rigidity of the shaft member 210 is increased. Furthermore, by making the shaft member 210 hollow, the rigidity of the shaft member 210 is further increased. As described above, according to the first embodiment, the shaft rigidity is sufficiently increased and the change in the dynamic pressure due to the temperature change is suppressed. For this reason, it is possible to stabilize the rotation of the spindle motor SM. Further, by using the spindle motor SM whose rotation is stable, it is possible to provide a hard disk drive device with higher accuracy.

A3. Configuration of spindle motor of comparative example:
FIG. 4 is a partial cross-sectional view showing a configuration of a spindle motor SMa of a comparative example. In the spindle motor SMa of the comparative example, the rotor member 310 that is a single member in the spindle motor SM (FIG. 1) of the first embodiment is divided into two members, a rotor hub 360 and a sleeve 370. The sleeve 370 is made of ferritic stainless steel SUS430F. In the shaft unit 200 of the first embodiment, the conical bearing members 220 are fixed to both ends of the shaft member 210, whereas in the shaft unit 200a of the comparative example, the conical outer surface 214a opposite to the base plate 110 and the inclined surface. 216a is formed on the shaft member 210a. Further, in the first embodiment, the conical bearing member 220 is formed of SUS303, whereas in the comparative example, the conical bearing member 220a is formed of SUS440C. Other points are the same as in the first embodiment.

The shape and arrangement of the conical inner surface 314 of the spindle motor SMa of the comparative example are the same as the spindle motor SM of the first embodiment. Therefore, also in the spindle motor SMa of the comparative example, the relationship of the above formula (8) is satisfied. On the other hand, the conical bearing member 220a is made of SUS440C, and the sleeve 370 is made of SUS430F having a linear expansion coefficient of 10.2 × 10 ⁻⁶ / ° C. Therefore, the linear expansion coefficients α1, α2, and α3 of the shaft member 210a, the members 210a and 220a in which the conical outer surface is formed, and the sleeve 370 in which the conical inner surface 374 is formed are all the same. Expression (9) is not satisfied.

  In the comparative example, a conical outer surface 214a and an inclined surface 216a are formed on the shaft member 210a. However, if the conical outer surface 214a or the like is formed on the shaft member 210a, the condition of Expression (9) is not satisfied. On the other hand, in the first embodiment, the shaft member 210 and the conical bearing member 220 are separate members, thereby satisfying the condition of the formula (9).

A4. Evaluation of spindle motor bearing characteristics:
FIG. 5 is a graph showing how the bearing characteristics of the spindle motors SM and SMa of the first embodiment and the comparative example change with temperature. FIG. 5A shows the bearing characteristics of the spindle motor SM of the first embodiment, and FIG. 5A shows the bearing characteristics of the spindle motor SM of the first embodiment. The bearing characteristics are such that a sinusoidal vibration with a maximum acceleration of 1 G (gravity acceleration: 9.8 m / s ² ) is applied to the base plate 110 in a direction transverse to the rotation axis, and the magnitude of the shaking of the rotor units 300 and 300 a at that time It was evaluated by conducting a simulation. The temperature was set to three conditions of 0 ° C., 25 ° C. and 73 ° C., and the frequency of the sine wave vibration was evaluated in the range of 10 Hz to 1000 Hz. The horizontal axis of each graph in FIG. 5 indicates the frequency (Hz) of the sinusoidal vibration, and the vertical axis indicates the normalized swing amplitude (μin / g: μin is obtained by dividing the swing amplitude by the mass of the rotor units 300 and 300a. 10 ⁻⁶ inches). The normalized swing amplitude means that the larger the value, the lower the bearing rigidity.

  As shown in FIG. 5, when the temperature is 0 ° C. and 25 ° C., there is no significant difference in normalized swing amplitude between the spindle motor SM of the first embodiment and the spindle motor SMa of the comparative example. However, when the temperature was 73 ° C., the normalized swing amplitude of the spindle motor SM of the first example was smaller than the normalized swing amplitude of the spindle motor SMa of the comparative example. That is, in the spindle motor SM of the first embodiment, a decrease in bearing rigidity at a high temperature is suppressed as compared with the spindle motor SMa of the comparative example. Further, in the spindle motor SM of the first embodiment, since the amount of decrease in the bearing rigidity due to the temperature rise is suppressed, it is considered that the rotation of the rotor unit 300 is stable even when the temperature changes.

  Thus, according to the first embodiment, the shape and arrangement of the conical inner surface 314 formed on the rotor member 310 of the spindle motor SM (FIG. 1) so as to satisfy the expressions (8) and (9) above. In addition, by setting the linear expansion coefficients α1, α2, and α3 of the shaft member 210, the conical bearing member 220, and the rotor member 310, the rotation of the rotor unit 300 can be stabilized even when the temperature changes. Become. Moreover, the rigidity of the shaft member 210 can be increased by providing the screw portion 212 at the end of the shaft member 210 opposite to the base plate 110 and enabling the both ends of the shaft member 210 to be supported. Further, by making the shaft member 210 hollow, the rigidity of the shaft member 210 can be further increased. Therefore, by using the spindle motor SM of the first embodiment, it is possible to provide a highly accurate hard disk drive.

  Further, by forming the shaft member 210 and the conical bearing member 220 as separate members, the formation of the conical outer surface 222 is facilitated, and the positional relationship between the conical outer surface 222 and the shaft member 210 is adjusted during assembly. It can be done individually. Furthermore, in the first embodiment, since the dynamic pressure groove portion having the conical inner surface 314 is formed in the rotor member 310, the number of parts can be reduced as compared with the case where the sleeve 370 is used. Therefore, the first embodiment is preferable to the comparative example in that both the component cost and the assembly cost of the spindle motor SM can be reduced.

  In the first embodiment, the shaft member 210, the conical bearing member 220, and the rotor member 310 are formed of martensitic stainless steel SUS440C, austenitic stainless steel SUS303, and aluminum alloy A6061-T6, respectively. If the relationship between the linear expansion coefficients α1, α2, and α3 of 210, 220, and 310 satisfies the relationship of the above equation (9), the members 210, 220, and 310 can be formed of other materials. is there. In general, the linear expansion coefficient decreases in the order of aluminum alloy, austenitic stainless steel, ferritic stainless steel, and martensitic stainless steel. Therefore, it is preferable to use martensitic stainless steel or ferritic stainless steel having a low linear expansion coefficient and high hardness for the shaft member 210. The conical bearing member 220 is preferably made of austenitic stainless steel or an aluminum alloy, and the rotor member 310 is preferably made of an aluminum alloy.

B. Second embodiment:
In the second embodiment, the rotor member 310 (FIG. 1) is formed of an aluminum-silicon alloy. The other points are the same as those of the first embodiment, and the description thereof is omitted here.

  The rotor member 310 made of an aluminum-silicon alloy can be manufactured by the following manufacturing method, for example. First, an aluminum alloy ingot is melted to obtain a molten metal. When a gas or liquid jet is sprayed while dripping the molten metal, the molten metal scatters to create fine droplets. The fine droplets are rapidly deprived of heat and solidified to form a rapidly solidified powder. Thereafter, 20 to 30% by weight of silicon is mixed with 80 to 70% of rapidly solidified powder, and billet forming is performed by hot pressing. Thereafter, the billet is sintered by heating in a vacuum or in a non-oxidizing atmosphere. Next, hot extrusion is performed to obtain an extruded material of an aluminum silicon alloy. By processing this extruded material, a rotor member 310 made of an aluminum-silicon alloy is formed.

The linear expansion coefficient of the aluminum-silicon alloy thus manufactured varies depending on the silicon content. Specifically, the linear expansion coefficient of an aluminum-silicon alloy decreases as the silicon content increases. The linear expansion coefficient of an aluminum-silicon alloy containing 20% by weight of silicon is about 18 × 10 ⁻⁶ / ° C., and the linear expansion coefficient of an aluminum-silicon alloy containing 30% by weight of silicon is about 16 × 10 ⁻⁶ / ° C.

Therefore, in the second embodiment, the rotor member 310 uses an aluminum-silicon alloy containing 20% by weight of silicon. As described above, SUS440C (thermal expansion coefficient: 10.2 × 10 ⁻⁶ / ° C.) that is martensitic stainless steel is used for the shaft member 210, and SUS303 that is austenitic stainless steel is used for the conical bearing member 220. (Thermal expansion coefficient: 17.3 × 10 ⁻⁶ / ° C.) is used. Therefore, also in the second embodiment, the relationship of the above formula (9) is satisfied. The conical bearing member 220 may be formed of an aluminum-silicon alloy containing 20% by weight of silicon instead of SUS303. Even in this case, the relationship of Expression (9) is satisfied.

In the second embodiment, the rotor member 310 uses an aluminum-silicon alloy containing 20% by weight of silicon, but the rotor member 310 may also use an aluminum-silicon alloy containing 30% by weight of silicon. Is possible. In this case, in order to satisfy the relationship of the formula (9), the conical bearing member 220 is made of, for example, the same aluminum-silicon alloy or ferritic stainless steel SUS430 as the rotor member 310 (linear expansion coefficient: 10.4 × 10 ^{− 6} / ° C.).

  In general, an aluminum-silicon alloy has a higher hardness than an aluminum alloy. Therefore, the second embodiment is preferable to the first embodiment in that the wear resistance of the rotor member 310 is increased and the life of the spindle motor SM can be extended. On the other hand, the first embodiment is preferable to the second embodiment in that the formation of the rotor member 310 is easier.

  As described above, even when the rotor member 310 is formed of an aluminum-silicon alloy, the shaft member 210, the conical bearing member 220, and the rotor can be selected by appropriately selecting the material of the conical bearing member 220 and the shaft member 210. It is possible to satisfy the condition (equation (9)) required for the linear expansion coefficients α1, α2, and α3 of the member 310. Therefore, also in the second embodiment, it is possible to sufficiently maintain the rotational stability of the rotor unit 300 when the temperature changes.

DESCRIPTION OF SYMBOLS 100 ... Stator unit 110 ... Base plate 112 ... Shaft member insertion hole 114 ... Circumferential wall part 120 ... Stator core 130 ... Winding 200, 200a ... Shaft unit 210, 210a ... Shaft member 212 ... Screw part 214a ... Conical outer surface 216a ... Inclined surface 220 220a ... Conical bearing member 222 ... Conical outer surface 224 ... Inclined surface 300, 300a ... Rotor unit 310 ... Rotor member 312 ... Through hole 314 ... Conical inner surface 316 ... Dynamic pressure groove portion 318 ... Magnet mounting portion 320 ... Yoke 330 ... Permanent magnet 350 ... End cap 352 ... Lubrication hole 354 ... Inner peripheral surface 360 ... Rotor hub 370 ... Sleeve 374 ... Conical inner surface 410 ... Minute gap 420 ... Lubricating oil 430 ... Capillary seal part SM, SMa ... Spindle motor

Claims (4)

A spindle motor,
A shaft member having one end fixed to the motor base;
First and second conical bearing members fixed to the shaft member and having conical outer surfaces;
A rotor member having a through hole through which the shaft member is inserted, and first and second conical inner surfaces whose inner diameters increase toward the outside at both ends of the through hole;
A dynamic pressure groove formed on either the conical inner surface or the conical outer surface;
A lubricating oil filled in a minute gap between the conical inner surface and the conical outer surface facing each other when the rotor member is sandwiched between the first and second conical bearing members;
The linear expansion coefficient α1 of the shaft member, the linear expansion coefficient α2 of the conical bearing member, and the linear expansion coefficient α3 of the rotor member satisfy a relational expression of α3 ≧ α2> α1,
An axial distance L between a first point on the first conical inner surface and a second point on the second conical inner surface having the same inner diameter as the first point, and at the first point A spindle motor in which an inner diameter dimension D and an inclination angle θ between the inner surface of the cone and a surface perpendicular to the axis satisfy a relational expression L> (D × tan θ).   The spindle motor according to claim 1, wherein the shaft member has a screw portion provided at an end opposite to the motor base.   The spindle motor according to claim 1, wherein the dynamic pressure groove is formed in a nickel plating layer that is provided on a surface where the dynamic pressure groove is formed and is thicker than a depth of the dynamic pressure groove.   4. The spindle motor according to claim 1, wherein at least one of the conical bearing member and the rotor member is made of an aluminum-silicon alloy. 5.

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