JP3038487B2 - motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a motor provided with a magnetic fluid seal, and is particularly used for a spindle motor for driving a hard disk and the like.

[Problems to be Solved by the Related Art and the Invention] The magnetic fluid shaft seal can reduce the amount of leakage to zero up to a certain pressure difference. Also widely used in spindle motors and the like. FIG. 4 is an enlarged sectional view of an essential part of one example, wherein
Is a pole piece, 3 is a permanent magnet, 4 is a fixed shaft, 5 is
Hubs 6 and 7 made of a ferromagnetic material that rotate with respect to the fixed shaft 4 are magnetic fluids that are magnetically held between the inner peripheral surface of the hub 5 and the outer peripheral surfaces of the pole pieces 1 and 2.

However, conventionally, as shown in the example of FIG. 4, since the inner peripheral surface of the hub 5 for holding the magnetic fluid between the pole pieces 1 and 2 is flat, the magnetic fluids 6 and 7
Is a state in which a skirt portion is spread on the inner peripheral surface of the hub 5 due to surface tension. Then, the distance from the upper and lower edges of the outer peripheral surface of the pole pieces 1 and 2 that adsorb the magnetic fluids 6 and 7 to the upper and lower skirts of the magnetic fluid on the hub is increased, and the magnetic force acting on the magnetic fluids 6 and 7 is increased. Is rapidly reduced due to the extension of the distance in the flared portion. Therefore, when the hub rotates, the upper and lower edges of the magnetic fluids 6 and 7 are liable to be scattered, which may cause disk contamination. In particular, when the hub rotates on the outer peripheral side as shown in FIG. 4, there is a great possibility that the skirt portion of the magnetic fluid further expands due to centrifugal force, causing scattering and reduction in pressure resistance.

The present invention has been made in view of the above-described problems in the prior art, and has as its object to prevent the magnetic fluid from scattering due to rotation and to increase the withstand pressure. Another object of the present invention is to provide a motor provided with a magnetic fluid seal.

Means for Solving the Problems To achieve the above object, a motor according to the present invention comprises a magnetomotive force means, a pole piece, and a ferromagnetic material opposed to the pole piece via an annular gap so as to be rotatable relative to the pole piece. Fluid seal having a magnetic fluid magnetically held between the pole piece and the seal annular portion, and the rotating portion is rotatable with respect to the fixed portion via a ball bearing. In the supported motor, the outer ring of the ball bearing is fixed to the inner peripheral portion of the rotating portion, and the seal annular portion is located outside the fixed position of the outer ring in the inner peripheral portion of the rotating portion in the axial direction. In the annular section for sealing, the cross section has a circular arc shape centered on the edge of the magnetic fluid suction portion of the pole piece from the groove bottom to the groove edge, and the edge of the magnetic fluid suction portion has Gap distance between An annular groove formed so as to have a curved portion which is substantially constant from the groove bottom to the groove edge at least at the outermost end is provided, and between the annular groove and the magnetic fluid suction portion of the pole piece. It is assumed that the magnetic fluid is held magnetically.

[Operation] The magnetic fluid is magnetically held between the magnetic fluid suction portion of the pole piece and the annular groove of the sealing annular portion made of a ferromagnetic material. In the curved section of the cross section of the annular groove, the gap distance between the groove and the edge of the magnetic fluid adsorbing portion is substantially constant from the groove bottom to the groove edge. Reduction of the magnetic force acting on the magnetic fluid magnetically held between the curved portion of the annular groove and the magnetic fluid at the groove edge is suppressed. Therefore, the magnetic fluid is held relatively stably also in that portion. Since such a curved portion is provided at least at the outermost end of the annular groove, the magnetic fluid is prevented from scattering or flowing out of the motor. Further, the annular groove itself functions to prevent the outflow of the magnetic fluid.

Further, the outer ring of the ball bearing is fixed to the inner peripheral portion of the rotating portion, and the sealing annular portion is located outside the fixed position of the outer ring in the inner peripheral portion of the rotating portion in the axial direction, so that the assembly itself is easy. However, in the normal case, the rust-preventive oil used for the ball bearings or the adhesive for bonding and fixing adheres to the magnetic fluid holding surface of the annular ring for sealing when mounting the ball bearings or bonding and fixing work. As a result, the magnetic fluid holding force is likely to be impaired. However, in the present invention, since the magnetic fluid holding surface is located in the annular groove recessed in the seal annular portion, the rust preventive oil, the adhesive, and the like are prevented from adhering to the magnetic material holding surface, There is almost no possibility that the magnetic fluid holding force is impaired.

Embodiment An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a half sectional view of a brushless spindle motor for driving a hard disk as one embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part thereof.

10 is a fixed shaft, and 12 and 14 are ball bearings. The inner rings of the ball bearings 12 and 14 are fixed to a fixed shaft 10. The outer ring of the upper ball bearing 12 is fixed to the inner peripheral surface of a hub 16 made of a ferromagnetic material, and a bush 18 made of a ferromagnetic material is fixed between the outer ring of the lower ball bearing 14 and the hub 16. I have.

Reference numeral 20 denotes a stator core fixed to the fixed shaft 10, and reference numeral 22 denotes a stator coil wound around the stator core 20.
Reference numeral 24 denotes a rotor magnet fixed to the inner peripheral wall of the hub 16, and has a stator core 20 separated by a radial gap.
Is relative to.

The fixed shaft 10 forms a part of a fixed portion, and includes a hub 16 and a bush.
The rotor 18 and the rotor magnet 24 constitute a rotating unit.

26 is a circuit board fixed to the fixed shaft 10. And
28 is a Hall IC for detecting the magnetic pole position of the rotor magnet 24
And is provided on the circuit board 26.

Reference numerals 30, 32, 34, and 36 denote pole pieces, each of which is formed of an annular flat plate made of a ferromagnetic material. Reference numerals 38 and 40 denote annular permanent magnet bodies as magnetomotive force means, which are magnetized in the axial direction. The outer diameters of the permanent magnet bodies 38 and 40 are slightly smaller than the outer diameters of the pole pieces 30, 32, 34 and 36. The permanent magnet bodies 38 and 40 are externally fitted and fixed to annular holders 42 and 44 having an L-shaped cross section while being coaxially sandwiched between the two pole pieces 30 and 32 and 34 and 36, respectively. It is disposed outside the bearing, that is, above the upper ball bearing 12 and below the lower ball bearing 14.

The inner peripheral wall of the small-diameter opening 16a that constitutes the upper part of the upper ball bearing 12 in the hub 16 has one centered on the rotation axis so as to face the outer peripheral surfaces 30a and 32a of the pole pieces 30 and 32. An annular groove 46 is provided. And, between the outer peripheral surface portions 30a and 32a of the respective pole pieces 30 and 32 and the annular groove 46, magnetic fluids 48 and 50 are magnetically held, respectively.
It constitutes a magnetic fluid seal. In this case, the outer peripheral surface portions 30a and 32a of the pole pieces 30 and 32 constitute a magnetic fluid adsorbing portion, and the inner peripheral wall portion of the small-diameter opening 16a constitutes a sealing annular portion made of a ferromagnetic material.

Similarly, an annular groove 52 is provided in the inner peripheral wall portion of the bush 18 below the lower ball bearing 14, and the magnetic fluid
54 and 56 are magnetically held to form a magnetic fluid seal.

The annular groove 46 has, in its cross section, upper and lower groove edges.
From 46a and 46b to the groove bottom 46c, the upper edge 30b of the outer peripheral surface 30a of the pole piece 30, and the pole piece, respectively.
The arc-shaped curved portions 46d and 46e are formed around the lower edge 32b of the outer peripheral surface portion 32a of the 32 substantially. Annular groove 52
The same applies to.

As the magnetic fluid, known fluids such as magnetite / colloidal particle magnetic fluid and MnZn ferrite particle magnetic fluid can be appropriately selected.

When using this spindle motor, a plurality of or one hard disk is externally fitted and fixed to the outer periphery of the hub 16, and the hub 16 is rotated by operating the spindle motor in a state of being sealed in the disk chamber to drive the hard disk. I do.

When the hub 16 rotates, the upper and lower ball bearings 12 and 14 rotate, and the magnetic fluids 48, 50, 54,
56 also receives a centrifugal force while rotating at least in the outer peripheral portion.

However, in the cross-section curved portions 46d and 46e provided at the upper and lower end portions of the annular groove 46, the upper edge portion 30b of the outer peripheral surface portion 30a of the upper pole piece 30 and the corresponding curved portion 46d
And the outer peripheral surface of the lower pole piece 32
The gap distance between the lower edge 32b of the 32a and the corresponding curved portion 46e is substantially constant from the groove bottom 46c to the groove edge 46a. Therefore, a decrease in the magnetic force acting on the magnetic fluids 48 and 50 at the upper and lower groove edges 46a and 46b is suppressed, and the magnetic fluids 48 and 50 are held relatively stably also in those portions. In addition, the outflow of the magnetic fluid is prevented by the annular groove 46 itself. Of course, the same applies to the annular groove 52.

Thus, the upper magnetic fluids 48 and 54 and the lower magnetic fluids 50 and 56 in each magnetic fluid seal are prevented from scattering or flowing upward and downward, respectively.

Therefore, the magnetic fluid or the lubricant scatters into the disk chamber and contaminates the disk, and the magnetic fluid causes the ball bearing 12,
It prevents entry into and damage to 14.

In particular, the pole pieces 30, 32, 34,
When the hub 16 rotates on the outer peripheral side of 36, not only the surface tension but also the centrifugal force acts on the magnetic fluid, and the hem on the outer peripheral side tries to spread more and more, and the danger of scattering or outflow of the magnetic fluid increases. However, in this embodiment, the curved portions of the annular grooves 46 and 52 prevent the magnetic force from lowering, and the annular grooves 46 and 52 themselves prevent the magnetic fluid from spreading in the vertical direction. Demonstrate.

It is effective that the magnetic fluid only scatters or flows out of the motor as long as a curved portion is provided at least in a portion corresponding to the outer side of the outermost magnetic fluid in the magnetic fluid seal. This corresponds to the upper curved portion 46d in FIG. 2, for example.

Further, in this embodiment, the entire hub 16 and the entire bush 18 are made of a ferromagnetic material. However, as long as a magnetic circuit effective for forming a magnetic fluid seal can be formed, the inside of the small-diameter opening in the hub may be used. Of course, only the peripheral wall portion (annular portion for sealing) and the inner peripheral wall portion (annular portion for sealing) below the lower ball bearing in the bush may be made of a ferromagnetic material.

Further, the pole piece may have, for example, a cross section of an outer peripheral portion formed in a blade shape. In that case, the magnetic fluid suction portion is located near the blade-shaped outer end.

Further, although a fixed shaft is employed in this embodiment, it is needless to say that the shaft may rotate together with the hub. Further, the pole piece may be present on the outer peripheral side.

FIG. 3 is an enlarged sectional view of a main part of a brushless spindle motor for driving a hard disk as another embodiment of the present invention.

In this embodiment, each of the pole pieces 30 and 32 is provided with one annular groove 60 and 62 on the outside thereof, and the upper and lower ends of the annular grooves 60 and 62 have curved portions 60 and 62, respectively.
a, 60b and 62a, 62b are provided. Therefore, it is more effective for maintaining the magnetic fluids 64 and 66 stably.

Reference numerals 10, 12, 38 and 42 in FIG. 3 have the same meaning as in FIGS. 1 and 2.

The vertical positional relationship in the above description of the embodiment is merely for convenience of description based on the drawings, and does not specify the absolute vertical position in an actual motor to which the present invention is applied.

[Effect of the Invention] In the motor of the present invention, a curved portion is provided at least at the outermost end in the cross section of the annular groove in the annular portion for sealing, and one edge portion of the magnetic fluid is
Since the magnetic fluid is held relatively stably between the curved portion and the magnetic fluid suction portion of the pole piece, scattering or outflow of the magnetic fluid at least to the outside of the motor is prevented. Also,
The outflow of the magnetic fluid is prevented by the annular groove itself, so that the holding amount of the magnetic fluid can be increased. Further, since the magnetic fluid holding surface is located in the annular groove recessed in the sealing annular portion, rust-preventive oil or adhesive adheres to the magnetic fluid holding surface during the mounting operation of the ball bearing or the bonding and fixing operation. Is prevented, and there is almost no possibility that the magnetic fluid holding force is impaired. In addition, the effects of preventing the magnetic fluid from scattering, increasing the holding amount, and securing the holding force can reliably increase the pressure resistance of the entire magnetic fluid seal.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a brushless spindle motor for driving a hard disk as one embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part thereof. FIG. 3 is an enlarged sectional view of a main part of a brushless spindle motor for driving a hard disk as another embodiment of the present invention. FIG. 4 is an enlarged sectional view of a main part of a conventional brushless spindle motor for driving a hard disk. In the drawing, 38 and 40 permanent magnet bodies, 30, 32, 34 and 36 are pole pieces, 16 is a hub, 18 is a bush, 48, 50, 54 and 56.
Is a magnetic fluid, 46 and 52 are annular grooves, 46a and 46b are groove edges,
46c is a groove bottom portion, and 46d and 46e are curved portions.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02K 5/04-5/124 F16C 33/74-33/76

Claims (1)

(57) [Claims] 1. A method according to claim 1, further comprising: a magnetomotive force means, a pole piece, a sealing annular portion made of a ferromagnetic material opposed to the pole piece via an annular gap so as to be rotatable relative to the pole piece, and a pole piece and the sealing annular portion. A motor provided with a magnetic fluid seal having a magnetic fluid magnetically held between the rotating portion and the rotating portion rotatably supported by a fixed portion via a ball bearing. The outer ring is fixed, and the seal annular portion is located outside the fixed position of the outer ring in the inner peripheral portion of the rotating portion in the axial direction, and the seal annular portion extends from the groove bottom to the groove edge. The pole piece has a circular arc shape with the edge of the magnetic fluid suction portion being substantially at the center, and the gap distance from the edge of the magnetic fluid suction portion is substantially constant from the groove bottom to the groove edge. Bend at least at the outermost end A magnetic fluid is magnetically held between the annular groove and the magnetic fluid suction portion of the pole piece.