JP3597947B2 - Motor using dynamic pressure bearing - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor using a hydrodynamic bearing using a lubricating fluid used for rotating a recording disk such as an optical / magnetic disk.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in order to relatively rotatably support a shaft member and a sleeve member, a dynamic pressure bearing utilizing the fluid pressure of a lubricating fluid interposed between the two has been used. In this type of fluid dynamic pressure bearing, a radial dynamic pressure bearing portion for supporting a radial load and a thrust dynamic pressure bearing portion for supporting a thrust load are disposed between a shaft member and a sleeve member. When such a dynamic pressure bearing is used for a motor, one of a shaft member and a sleeve member is fixed. That is, when the shaft member is fixed, the motor becomes a fixed shaft motor, and when the sleeve member is fixed, the motor becomes a shaft rotating motor.
[0003]
[Problems to be solved by the invention]
This type of dynamic bearing has the following problems to be solved. That is, the viscosity of the lubricating fluid, that is, the lubricating oil used in the dynamic pressure bearing usually decreases at a high temperature and increases at a low temperature. Therefore, the dynamic pressure generated by the dynamic pressure bearing is large at a high temperature and small at a low temperature. Therefore, if the bearing specifications are set to ensure the bearing rigidity at the upper limit of the operating temperature range, the bearing rigidity at low temperatures will be excessive, and if the bearing rigidity at room temperature is set appropriately, There is a problem that the rigidity is insufficient near the upper limit of the temperature, and the temperature dependence of the bearing rigidity is very large.
[0004]
Here, it is conceivable to make the thermal expansion coefficient of the shaft member larger than that of the sleeve member, control the clearance between the shaft member and the sleeve member according to the temperature, and compensate for the temperature dependence of the bearing rigidity. However, in this case, a high processing accuracy is required for the cylindrical outer peripheral surface of the shaft member and the cylindrical inner peripheral surface of the sleeve member, and there is a problem that manufacturing is difficult. In addition, at high temperatures, the clearance becomes extremely small, and there is a risk that the sleeve member is locked with respect to the shaft member.
[0005]
The present invention has been made in consideration of such problems of the prior art, and aims at significantly reducing the temperature dependence of the bearing stiffness of a hydrodynamic bearing with a relatively simple configuration. It is an object of the present invention to provide a motor using a dynamic pressure bearing which can reduce the temperature and stably obtain an appropriate bearing rigidity within an operating temperature range.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in a motor using the dynamic pressure bearing of the present invention, a shaft member having a cylindrical outer peripheral surface and a shaft member having a cylindrical inner peripheral surface opposed to the cylindrical outer peripheral surface are provided. On the other hand, a sleeve member that is relatively rotatable, and a pair of herringbone-shaped grooves formed on one or both of the cylindrical outer peripheral surface and the cylindrical inner peripheral surface and arranged at intervals in the axial direction. A radial dynamic pressure generating groove, and a lubricating fluid interposed between the cylindrical outer peripheral surface and the cylindrical inner peripheral surface; and a center of the dynamic pressure generating groove on a fixed side of a shaft member and a sleeve member. A control valve having a communication passage connecting an intermediate portion between the portion and both ends to a region having a low dynamic pressure, the communication passage having an opening having a small opening area at a high temperature and a large opening area at a low temperature. Are arranged.
[0007]
In this case, it is desirable that the region where the dynamic pressure is low is between the pair of dynamic pressure generating grooves between the cylindrical outer peripheral surface and the cylindrical inner peripheral surface. It is preferable to use a cylindrical body having a fan-shaped opening and made of a material having a larger thermal expansion coefficient than the material on the fixed side.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a sectional view showing a fixed shaft type spindle motor for rotating a magnetic disk, for example. In this example, the lower end of a fixed shaft member 6 having a vertical axis is fitted and fixed to the base of the recording medium driving device or the circular fitting hole 4 of the motor bracket 2 fixed thereto. . The shaft member 6 has a thrust plate 8 fixed at the upper portion and a cover plate 10 fixed at the upper end thereof, and a cylindrical outer peripheral surface 12 is formed on the outer peripheral surface below the thrust plate 8.
[0009]
A rotating sleeve body 14 is rotatably fitted to the shaft member 6. The small-diameter sleeve portion 16 at the lower portion of the rotary sleeve body 14 has a cylindrical inner peripheral surface 18 on the inner peripheral surface, and is externally fitted to a portion of the shaft member 6 below the thrust plate 8. Reference numeral 18 faces the cylindrical outer peripheral surface 12 of the shaft member 6. The enlarged diameter portion 20 at the upper part of the rotary sleeve body 14 surrounds the upper and lower portions and the outer peripheral portion of the thrust plate 8 together with the thrust cover 22 fixedly fitted at the upper end portion.
[0010]
A substantially cylindrical hub 24 is externally fitted and fixed to an outer peripheral portion of the rotating sleeve body 14, and a rotor magnet 26 is internally fixed to a lower inner peripheral side of the hub 24. A stator 28 having a stator coil wound around a stator core is externally fitted and fixed to a support cylinder 30 protruding from the bracket 2 coaxially with the circular fitting hole 4, and is rotationally driven relative to the rotor magnet 26 in the radial direction. Unit.
[0011]
A tapered portion 32 that slopes inward and upward is formed in the lower portion of the inner periphery of the thrust cover 22, and a portion of the outer peripheral portion of the shaft member 6 that faces the lower end of the sleeve portion 16 has a taper portion that slopes inward and downward. 34 are formed. A gap between the shaft member 6 and the rotary sleeve body 14 is filled with a lubricating oil 36 as an example of a lubricating fluid (liquid). One end, that is, the inner peripheral end of the lubricating oil 36 in the gap above the thrust plate 8 faces between the base of the tapered portion 32 of the thrust cover 22 and the upper surface of the thrust plate 8, and communicates with the outside air. The lubricating oil 36 is held between the base of the tapered portion 34 and the inner peripheral surface of the sleeve portion 16 and exposed to the outside air by capillary action.
[0012]
On the upper and lower surfaces of the thrust plate 8 and on the inner peripheral surface (cylindrical inner peripheral surface 18) of the sleeve portion 16, the thrust dynamic pressure generating grooves 38 and 40 and the radial dynamic pressure generating grooves 42 and 44 formed of herringbone grooves are respectively provided. (Shown by broken lines) are provided, and a forward rotation of the rotary sleeve body 14 and the thrust cover 22 generates a thrust load support pressure and a radial load support pressure in the lubricating oil 36 at each position. Thus, thrust dynamic pressure bearing means are formed above and below the thrust plate 8, and radial dynamic pressure bearing means are formed on the outer peripheral portion of the sleeve portion 16. Note that these grooves may be provided on the sides of the members facing each other.
[0013]
The shaft member 6 is provided with a communication passage 46 which communicates the corresponding position of the two dynamic pressure generating grooves 42, 44 in the radial dynamic pressure bearing means with a region where the dynamic pressure is low, that is, between the pair of dynamic pressure generating grooves 42, 44. Have been.
That is, as shown in FIG. 2, first, an axial vertical hole 48 is formed at the axial center position of the shaft member 6 from the lower end surface to a position slightly below the thrust plate 8. In the cylindrical outer peripheral surface 12 corresponding to the pressure generating groove 42, each of the dynamic pressure generating grooves 42 is orthogonal to the vertical hole 48 in the axial direction from the middle between the central portion (peak portion) and both ends to the vertical hole 48. High-pressure side holes 50 and 51 are formed, and in the cylindrical outer peripheral surface 12 corresponding to the lower radial dynamic pressure generating groove 44, a halfway between each of the central portion and both ends of the dynamic pressure generating groove 44. , And high-pressure side holes 52 and 53 which are orthogonal to the vertical hole 48 in the axial direction, respectively, are formed.
[0014]
Further, a low-pressure side hole 54 that is orthogonal to the vertical hole 48 in the axial direction is formed from the cylindrical outer peripheral surface 12 corresponding to the middle between the radial dynamic pressure generating grooves 42 and 44 to the vertical hole 48, and is lower than the lowermost horizontal hole 53. By closing the vertical hole 48 on the side with the sealing member 56, the dynamic pressure generating portions formed by the two radial dynamic pressure generating grooves 42 and 44 in the gap between the cylindrical outer peripheral surface 12 and the cylindrical inner peripheral surface 18 A communication passage 46 is formed to bypass between the radial dynamic pressure generating grooves 42 and 44 inside the shaft member 6. In FIG. 2, the dynamic pressure generating grooves 42 and 44 of the sleeve portion 16 are shown for convenience of understanding the positional relationship between the horizontal holes 50 to 54 of the shaft member 6.
[0015]
A control valve 58 having an opening having a small opening area at a high temperature and having a large opening area at a low temperature is disposed in the low-pressure side hole 54 of the communication passage 46. Specifically, as shown in FIG. 3, the control valve 58 has an opening 60 having a fan-shaped cross section, and is formed of a columnar body 62 formed of a material having a larger thermal expansion coefficient than the shaft member 6. The control valve 58 is attached to the low-pressure side hole 54 by shrinking the cylindrical body 62 so that both side surfaces of the opening 60 are shifted inward and inserting the same into the low-pressure side hole 54.
[0016]
In such a configuration, when the spindle motor rotates, the pressure of the lubricating oil 36 existing in each of the radial dynamic pressure bearing means having the two radial dynamic pressure generating grooves 42, 44 is increased, and the pressure is increased through the oil layer. To support the radial load acting on the rotating sleeve body 14. Further, in each thrust dynamic pressure bearing means having both thrust dynamic pressure generating grooves 38, 40, the pressure of the lubricating oil 36 existing in them is increased, and the thrust load acting on the rotary sleeve body 14 via this oil layer. Support.
[0017]
During this operation, the lubricating oil 36 filled between the cylindrical outer peripheral surface 12 of the shaft member 6 and the cylindrical inner peripheral surface 18 of the sleeve portion 16 partially circulates, bypassing the communication passage 46. . In other words, in the two radial bearing means, the central portion of each of the dynamic pressure generating grooves 42 and 44, which is a herringbone groove, has the highest pressure, and the pressure gradually decreases toward both ends of the groove. The entire groove area of the dynamic pressure generation grooves 42 and 44 is a pressure generation part, and this part is a high pressure area. On the other hand, between the two radial bearing means, the lubricating oil 36 in this portion is sucked toward the two radial bearing means, so that the pressure becomes small and the pressure becomes low. The high-pressure side holes 50, 51, 52, and 53 of the communication passage 46 are respectively opened in the pressure generating portions of the two radial bearing means, and the low-pressure side hole 54 is opened in the low-pressure region between the two radial bearing means. Due to the pressure difference, the lubricating oil 36 in each of the pressure generating areas flows from the low-pressure side hole 54 to the low-pressure area through the high-pressure side holes 50, 51, 52, 53 and the vertical hole 48 in the communication passage 46, and the lubricating oil 36 circulates Is done.
[0018]
The lubricating oil 36 has a high viscosity at a low temperature and a low viscosity at a high temperature, and if no measures are taken, the dynamic pressure generated by the dynamic pressure bearing portion is high at a low temperature and low at a high temperature. Since the cylindrical body 62 of the control valve 58 is made of a material having a larger thermal expansion coefficient than the shaft member 6, the cylindrical body 62 which was in the state of the solid line in FIG. As shown by the dashed line, both side surfaces of the opening 60 are shifted toward the inside of the opening, and the sectional area of the opening is reduced.
[0019]
Therefore, at high temperatures, the viscosity of the lubricating oil 36 decreases and the generated dynamic pressure decreases, but the opening area of the opening 60 in the control valve 58 of the communication passage 46 decreases, and the circulation amount of the lubricating oil 36 is greatly restricted. Therefore, the pressure drop of the generated dynamic pressure in the radial dynamic pressure bearing means is suppressed, and the dynamic load is generated in the entire dynamic pressure generating grooves 42 and 44 to support the radial load.
[0020]
On the other hand, when the temperature is low, the opening area of the opening 60 in the control valve 58 increases as shown by the solid line in FIG. 2, and the circulation of the lubricating oil 36 extends from both ends of the dynamic pressure generating grooves 42 and 44 to near the middle of the grooves. The lubricating oil 36 pressurized in the portion escapes to the low pressure side through the communication passage 46. Therefore, the dynamic pressure generating portion that supports the radial load is located between the high pressure side holes 50 and 51 in the central portions of the dynamic pressure generating grooves 42 and 44, that is, in the dynamic pressure generating groove 42, and the high pressure side in the dynamic pressure generating groove 44. There is a gap between the lateral holes 52 and 53, and the width of the dynamic pressure groove for supporting the radial load is reduced. As a result, at low temperatures, the viscosity of the lubricating oil 36 increases and the generated dynamic pressure increases. However, the width of the dynamic pressure grooves is reduced, so that a radial load supporting pressure substantially equal to that at high temperatures can be obtained.
[0021]
As described above, by changing the opening area of the opening 60 of the control valve 58 according to the temperature and changing the dynamic pressure groove width, that is, the bearing width, the viscosity of the lubricating oil 36 changes according to the temperature and the generated dynamic pressure is reduced. Even if it changes, the dynamic pressure generated in the radial dynamic pressure bearing means can be made constant, and the bearing rigidity can be maintained at substantially the same level within the operating temperature range. As a result, the temperature dependence of the bearing stiffness can be reduced, so even if the required bearing stiffness is secured at the upper limit temperature, the shaft loss can be maintained at substantially the same level over the entire operating temperature range. Reduction of shaft loss in a low temperature region can be realized, which can contribute to reduction of rated current.
[0022]
The material (thermal expansion coefficient) and length of the cylindrical body 62 and the opening angle of the opening 60 in FIGS. 3 and 4 are set so that the bearing rigidity can be maintained at substantially the same level over the entire operating temperature range. It is appropriately selected according to the dynamic pressure generated by the radial bearing means in the spindle motor, the characteristics (viscosity) of the lubricating oil 36, and the like.
[0023]
Although the embodiments of the motor using the dynamic pressure bearing according to the present invention have been described in detail above, the present invention is not limited to these examples, and various changes and modifications can be made without departing from the gist of the present invention. It is possible.
[0024]
For example, in the above-described embodiment, a case where the present invention is applied to a fixed shaft type spindle motor has been described. However, the present invention can be similarly applied to a shaft rotating type motor. In this case, the fixed sleeve member into which the rotating shaft member is inserted may be provided with a communication path that connects the dynamic pressure generation area and the low dynamic pressure area, and the control valve may be disposed in this communication path.
[0025]
【The invention's effect】
The present invention is configured as described above, and has the following effects.
A communication path is provided on the fixed side of the shaft member and the sleeve member, the communication path communicating the respective intermediate portions of the dynamic pressure generating groove, which is a herringbone groove, with both ends, and a region where the dynamic pressure is low. In addition, a control valve with an opening that has a small opening area at high temperatures and a large opening area at low temperatures has been arranged, so that the circulation of lubricating fluid is suppressed at high temperatures to secure the bearing width over the entire dynamic pressure generating groove. In addition, a predetermined dynamic pressure can be generated even by a low-viscosity lubricating fluid, and at low temperatures, the bearing width for supporting the bearing load by circulating the lubricating fluid is substantially reduced, and a high-viscosity is generated by a high-viscosity lubricating fluid. The dynamic pressure can be suppressed to a predetermined dynamic pressure substantially equal to that at the time of high temperature. Therefore, the generated dynamic pressure can be made constant within the operating temperature range, the bearing stiffness can be maintained at substantially the same level, and the temperature dependency of the bearing stiffness can be reduced. As a result, even if the required bearing stiffness is secured at the upper limit temperature, the shaft loss can be maintained at substantially the same level over the entire operating temperature range. This can greatly contribute to reduction.
[Brief description of the drawings]
FIG. 1 is a cutaway front view showing an embodiment in which a motor using a dynamic pressure bearing of the present invention is applied to a spindle motor.
FIG. 2 is a perspective view of the shaft member of FIG.
FIG. 3 is a perspective view of the control valve of FIG. 1;
FIG. 4 is a front view of the control valve of FIG. 3;
[Explanation of symbols]
6 Shaft member 12 Cylindrical outer peripheral surface 14 Rotating sleeve body 16 Sleeve portion 18 Cylindrical inner peripheral surface 36 Lubricating oil 42, 44 Radial dynamic pressure generating groove 46 Communication passage 58 Control valve 60 Opening 62 Cylindrical body

Claims (3)

A shaft member having a cylindrical outer peripheral surface; a sleeve member having a cylindrical inner peripheral surface facing the cylindrical outer peripheral surface and rotatable relative to the shaft member; the cylindrical outer peripheral surface and the cylinder and Jo inner peripheral surface and one or both a pair that is formed is disposed axially through a distance in the radial hydrodynamic grooves of, interposed between the cylindrical outer peripheral surface and the cylindrical inner peripheral surface A motor with lubricating fluid,
The radial dynamic pressure generating groove is a herringbone-shaped groove that generates a dynamic pressure with a maximum pressure at the center and a small pressure at both ends,
On the fixed side of the shaft member and the sleeve member,
A communication path is provided, which communicates the respective axial middle portions of the central portion and both end portions of the dynamic pressure generating groove with a region having a low dynamic pressure,
A motor using a dynamic pressure bearing, wherein a control valve having an opening having a small opening area at a high temperature and having a large opening area at a low temperature is arranged in the communication passage. The motor using the dynamic pressure bearing according to claim 1, wherein the low dynamic pressure region is between the pair of dynamic pressure generating grooves between the cylindrical outer peripheral surface and the cylindrical inner peripheral surface. The motor using the dynamic pressure bearing according to claim 1 or 2, wherein the control valve is a cylindrical body having an opening having a fan-shaped cross section and having a larger thermal expansion coefficient than the material on the fixed side.

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