JP3381981B2 - Spindle motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor. 2. Description of the Related Art Oil is used as a lubricating fluid to rotatably support a rotor portion on a fixed shaft having an outer flange-shaped thrust plate and to restrict axial movement of the rotor portion. Conventionally, in a spindle motor provided with a thrust fluid dynamic pressure bearing, a thrust fluid dynamic pressure bearing is formed by facing a rotor portion with a small gap over substantially the entire inner end surface and outer end surface of a thrust plate. [0003] Therefore, the rotor portion is supported at the radially intermediate portion of the thrust plate by the dynamic pressure of the thrust fluid dynamic pressure bearing, and between the action points. The distance becomes smaller. Therefore, runout of the rotor, non-periodic vibration (Non Repeatable Run Out;
Or a drive current increase. Further, in the case of using oil for the fluid dynamic pressure bearing, when air is mixed into the oil of the fluid dynamic pressure bearing at the time of assembling the fluid dynamic pressure bearing or rotating the motor, the temperature of the fluid dynamic pressure bearing portion may be increased. When the pressure outside the fluid dynamic pressure bearing portion (such as the stator chamber or the disk chamber) becomes low, the mixed air expands, and the oil is pushed out from the fluid dynamic pressure bearing portion to the outside, causing oil leakage. There was a problem. Therefore, in the present invention, the runout of the rotor section, the NR
An object of the present invention is to provide a spindle motor capable of preventing an increase in RO and drive current and preventing oil leakage from a fluid dynamic bearing. In order to achieve the above object, a spindle motor according to the present invention pivotally supports a rotor section 16 on a fixed shaft so as to be rotatable, and includes an outer flange-shaped thrust plate. A spindle motor provided with the fixed shaft and having a thrust fluid dynamic pressure bearing using oil as a lubricating fluid for restricting the axial movement of the rotor portion, wherein the thrust plate has an outer peripheral edge. A part of the rotor portion facing one or both surfaces of the outer peripheral edge with a minute gap to form the thrust fluid dynamic pressure bearing, and a portion corresponding to the thrust fluid dynamic pressure bearing
Except for between the thrust plate and the rotor part
In addition, an air chamber for preventing oil leakage is formed. [0008] A part of the rotor portion is opposed to one or both surfaces of the thrust plate with a small gap to form a thrust fluid dynamic pressure bearing, whereby the action of dynamic pressure on the thrust plate of the fixed shaft is achieved. Since the distance (diameter) from the rotation center between the points increases, the rotation of the rotor unit is stabilized, and the swing of the rotor unit is prevented. Further, since the dynamic pressure generating portion is only the outer peripheral portion having a large relative speed, the contact area with the oil can be greatly reduced without substantially reducing the magnitude of the generated dynamic pressure. Since the ratio of the thrust fluid dynamic pressure bearing in the thrust plate, that is, the dynamic pressure acting area, is smaller than before, the mechanical loss is reduced and the drive current value is reduced. Further, by forming an air chamber between the thrust plate and the rotor portion except for a portion corresponding to the thrust fluid dynamic pressure bearing, the air mixed in the oil of the fluid dynamic pressure bearing increases the temperature. Even if it expands due to the like, it escapes to the air chamber, and since the air chamber is ventilated with outside air, oil leakage from the fluid dynamic bearing to the outside of the motor due to the thermal expansion of the air is prevented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing embodiments. FIG. 1 shows a spindle motor according to a first embodiment of the present invention. This motor is small and is used for rotating a recording disk such as a magnetic disk or an optical disk. Reference numeral 1 denotes a housing, in which an annular boss 2 is provided at the center of the bottom surface of the bottom wall 3 of the housing 1, and a stator 6 is provided on the stepped outer peripheral edge of the boss 2. It is fixed. The stator 6 includes a stator core 8 and a stator coil 9 wound therearound. A lead wire 10 of the stator coil 9 is drawn out through a hole 3 a formed through the bottom wall 3 of the housing 1. Then, the stator 6 is excited by the control current sent through the lead wire 10. A fixed shaft 12 is erected on the boss 2 and the bottom wall 3. This fixed shaft 12 has a straight shaft 14
And an outer flange-shaped thrust plate 15 and a thin cylindrical bush 7 attached to one end 11 of the straight shaft 14 so as to be fitted externally. The other end 13 side of the straight shaft 14 is It is inserted and fixed in the hole 4 and the hole 5 in the bottom wall 3. A rotor portion 16 is rotatably supported on the fixed shaft 12 by a radial fluid dynamic pressure bearing R, and an axial movement of the rotor portion 16 is supported by thrust fluid dynamic pressure bearings S, S. Regulate. Then, at the outer peripheral edge of the thrust plate 15, a part of the rotor portion 16 is opposed to both surfaces of the outer peripheral edge with a small gap, and the thrust fluid dynamic pressure bearings S,
Form S. Further, the thrust plate 15 is
And an air chamber 24 for preventing oil leakage is formed between the thrust plate 15 and the rotor portion 16 except for the portions corresponding to the thrust fluid dynamic pressure bearings S, S. Specifically, the rotor portion 16 includes a sleeve 18 having an axial hole 25 facing the straight shaft 14 on the inner end face 17 side of the thrust plate 15 with a small gap, and a rotor 18 connected to the sleeve 18 and having a thrust. An annular thrust holding cover 20 externally fitted to the straight shaft 14 (the bush 7) on the outer end surface 19 side of the plate 15 with a predetermined gap, a cylindrical hub 21 attached to the outer peripheral surface of the sleeve 18, and A rotor magnet 22 is attached to the peripheral surface and faces the stator 6. A recording disk 23 is mounted on the outer peripheral surface of the hub 21 by a clamp (not shown). A dynamic pressure generating groove 33 is formed on the inner peripheral surface of the shaft hole 25 of the sleeve 18 or on the outer peripheral surface of the straight shaft 14 facing the inner peripheral surface of the shaft hole 25. The surface is filled with oil as a lubricating fluid, and the radial fluid dynamic pressure bearing R
Is formed. In the illustrated example, the dynamic pressure generating groove 33 is
It is formed on the outer peripheral surface. Next, as shown in FIG. 2, the sleeve 18
A first circular recess 26 and a second circular recess 27 having two steps and a small diameter on the back side.
The thrust holding cover 20 is tightly fitted in the first circular recess 26 so as to surround the thrust plate 15 with the thrust holding cover 20 and the second circular recess 27 of the sleeve 18. It is sealed and connected with an adhesive or the like. From the thrust plate-corresponding surface 28 of the thrust holding cover 20, the first portion 29a has a flat mountain-shaped cross section.
An annular ridge 29 protrudes, and a second annular ridge 30 having a flat mountain-shaped cross section with a flat top 30a protrudes from a thrust plate-corresponding surface 31, which is the inner bottom surface of the second circular recess 27. Is done. Further, a third annular ridge 32 protrudes from the inner peripheral edge of the thrust plate corresponding surface 31. [0022] The top 29a, the width T ₁ of the 30a, T ₂ is uniform in the circumferential direction, to face each other with a small gap on both sides of the outer peripheral edge of the thrust plate 15 (the inner and outer end faces 17 and 19). A dynamic pressure generating groove (not shown) is formed on the surface of the top portion 29a (upper side in the figure) or the outer peripheral surface on the outer end surface 19 side.
Oil, which is a lubricating fluid, is filled between the two surfaces to form a thrust fluid dynamic pressure bearing S (S ₁ ). Similarly, a dynamic pressure generating groove (not shown) is formed on the surface of the top portion 30a (on the lower side in the figure) or the outer peripheral surface on the inner end surface 17 side, and a lubricating fluid is provided between the two surfaces. The oil is filled to form a thrust fluid dynamic pressure bearing S (S ₂ ). The hydrodynamic grooves of the fluid dynamic bearings S and R are:
Herringbone or spiral shape. In addition,
The thrust fluid dynamic pressure bearing S has a width of the first annular protrusion 29 and a width of the second annular protrusion 30 and a dynamic pressure portion such that the surface tension of the oil as the lubricating fluid is greater than the centrifugal force acting on the oil. The interval is set. This prevents the oil from scattering in the circumferential direction due to the rotation. As described above, since the thrust fluid dynamic bearing S is positioned radially outward, the distance between the operating points at which the fixed shaft 12 is supported increases. Thereby, the inclination rigidity of the rotor section 16 can be improved. In addition, since the area of the thrust fluid dynamic bearing S in the thrust plate 15 is reduced, the drive current value of the motor can be reduced. Thus, the inner end face 1 of the thrust plate 15
7. The thrust plate corresponding surface 31, the inner peripheral surface 34 of the second circular recess 27, and the thrust plate corresponding surface 28 of the thrust holding cover 20 have a sufficiently large gap with respect to the outer peripheral surface 35 and the outer end surface 19. And the first and second annular ridges 29, 30
To form three partitioned air chambers 24. Of the air chambers 24, thrust plates 15
The air chamber 24b corresponding to the outer peripheral surface 35 has a short cylindrical shape, and the air chambers 24a and 24c corresponding to the inner end face 17 and the outer end face 19 of the thrust plate 15 have a flat annular shape. Further, the air chambers 24a and 24c are communicated with each other through an axial linear ventilation hole 36 penetrating through the thrust plate 15, and the ventilation hole 36 adjusts the pressure balance between the two air chambers 24a and 24c. To work. As described above, the space surrounding the thrust plate 15 is used as the air chamber 24 to prevent oil leakage. That is, even if the air mixed into the oil of the fluid dynamic pressure bearing S expands due to temperature rise or pressure reduction, it escapes to the air chamber 24, and the oil of the fluid dynamic pressure bearing S moves to the thrust holding cover 20 and the bush 7. It can be prevented from leaking to the disk chamber 38 side from between. Moreover, the formation of the air chamber 24 significantly reduces the amount of oil injected into the fluid dynamic bearings S, S, R, and increases the volume due to the expansion of the oil itself. It is absorbed by the protrusion into the air chamber 24, and oil leakage can be effectively prevented. A peripheral groove 39 is formed in the inner peripheral surface of the thrust holding cover 20. The surface of the peripheral groove 39, the inner peripheral surface of the thrust holding cover 20, and the outer peripheral surface of the bush 7 facing the same are repelled. An oil agent is applied. Thus, even if oil tries to flow out from the space between the thrust holding cover 20 and the bush 7 to the disk chamber 38 side, the gap 40 is formed until the oil enters the circumferential groove 39.
At the entrance to the circumferential groove 39, and is held at the surface tension as indicated by the imaginary line C, so that it does not easily flow out. Further, a gap 41 extending from the circumferential groove 39 to the disk chamber 38 and the thrust holding cover 20
The same operation is performed in the tapered outer surface portion 42 of the above, and oil leakage can be prevented twice. As shown in FIG. 1, in order to prevent the oil leaking to the side of the stator chamber 37 by performing the same operation as above, the sleeve 18 is disposed in a range H excluding the radial fluid dynamic bearing R. Opposite peripheral grooves 43 and 44 are formed in the inner peripheral surface of the shaft hole 25 and the outer peripheral surface of the straight shaft 14 of the fixed shaft 12 facing the inner surface, and an oil repellent is applied to each surface of the peripheral grooves. In the range H, a gap for holding oil is provided inside the circumferential grooves 43 and 44 (upper side in the figure), and a part of the oil filled in the fluid dynamic bearing R is provided. To store. By this storage, the amount of movement of oil accompanying rotation and stop is held. In the embodiment shown in FIG. 3, the magnetic center L of the stator 6 and the rotor magnet 22 are aligned with each other in the axial direction, but the second embodiment shown in FIG.
In the spindle motor of the embodiment, the magnetic center L of the stator 6 and the magnetic center L of the rotor magnet 22 are shifted in the axial direction so that the force in the direction of arrow F acts on the rotor section 16. If a one-way preload F for supporting the rotor portion 16 in the thrust direction is obtained by utilizing the displacement of the magnetic centers L, L, a dynamic pressure corresponding to the force F is generated. The thrust fluid dynamic pressure bearing to be performed can be omitted. Further, by applying the preload F, the stability of rotation can be improved, the interval between the thrust fluid dynamic pressure portions can be easily managed, and the thread between the thrust plate 15 and the sleeve 18 or the thrust holding cover 20 can be prevented. It has a great effect. That is, as shown in FIG. 4, at the outer peripheral edge of the thrust plate 15, a part of the rotor portion 16 (the first circle of the thrust holding cover 20) is in contact with one surface (outer end surface 19) of the outer peripheral edge. It is only necessary to form one thrust fluid dynamic pressure bearing S (as in the previous embodiment) with the flat tops 29a) of the annular ridges 29 facing each other with a small gap. Therefore, the air chamber 24 is
Although the air chamber 24 is divided into two parts by the annular ridge 29, unlike the previous embodiment, all the air chambers 24 are communicated with the outside air by the ventilation holes 36 formed in the thrust plate 15, and due to the thermal expansion of the air. Oil extrusion is completely prevented. Further, the method of causing the displacement of the magnetic centers L, L is not limited to the structure illustrated in FIG. The other configuration is the same as that of the previous embodiment, and the description is omitted. In the embodiment shown in FIGS. 1 and 3, the bush 7, the straight shaft 14, and the thrust plate 15 constituting the fixed shaft 12 are separate bodies, but they may be formed integrally. Further, the position of the ventilation holes 36 of the thrust plate 15 can be freely changed and the number can be freely increased or decreased. Since the present invention is configured as described above, the following effects can be obtained. In the motor according to the first aspect, the thrust plate
Since the distance between the points of action of the thrust fluid dynamic pressure bearing S in the radial direction 15 increases in the radial direction, the rotation of the rotor portion 16 supported by the thrust fluid dynamic pressure bearing S is stabilized, and the fixed shaft
12 runout and NRRO are reduced. In addition, since the area of the thrust fluid dynamic pressure bearing S where the dynamic pressure acts is smaller than in the prior art, the drive current value can be reduced. According to the motor of the second aspect, in addition to the above effects, even if the air mixed in the oil of the fluid dynamic pressure bearing S expands due to a rise in temperature or the like, it can escape to the air chamber 24. The above-mentioned oil leak can be reliably prevented.

[Brief description of the drawings] FIG. 1 is a sectional view showing one embodiment of the present invention. FIG. 2 is an enlarged sectional view of a main part. FIG. 3 is a sectional view showing another embodiment. FIG. 4 is an enlarged sectional view of a main part. [Explanation of symbols] 12 Fixed shaft 15 Thrust plate 16 Rotor part 24 air chamber S thrust fluid dynamic pressure bearing

────────────────────────────────────────────────── (5) References JP-A-6-315241 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 7/08 H05K 5/167

Claims (1)

(57) Claims 1. A rotor portion 16 is rotatably supported on a fixed shaft 12, and an outer flange-shaped thrust plate 15 is attached to the fixed shaft 12. A thrust fluid dynamic bearing S using oil as a lubricating fluid for restricting axial movement of the thrust plate 15, wherein one or both surfaces of the outer periphery of the thrust plate 15 are provided. to a portion of the rotor portion 16 so as to face with a small gap, forming the thrust hydrodynamic bearing S, Note
Except for the portion corresponding to the thrust fluid dynamic pressure bearing S
Between the thrust plate 15 and the rotor section 16
A spindle motor further comprising an oil chamber 24 for preventing oil leakage .