JPH11103553A - Motor with magnetic fluid seal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor using a magnetic fluid seal which can hold superior squareness between a pole piece and a rotating shaft, without the use of an annular spacer. SOLUTION: This motor has a rotating part and a stator part, a rotary bearing is installed between them, and a magnetic fluid seal is installed in the outside part of the rotary bearing. This motor is provided with a seal magnet 15, two pole piece 13, 14 for holding the seal magnet 15, the magnetic fluid seal in which the interval between pole pieces on the side to which magnetic fluid 12 is attached is smaller than the interval between pole pieces on the opposite side, and a magnetic seal holder 20 which has the inside of a depth and is constituted of nonmagnetic material. The depth is the sum of the thickness of each pole piece of the magnetic fluid seal, the thickness of the seal magnet, and the distance between the lower pole piece 14 and the upper part 17-0 of an inner ring casing 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor having a magnetic fluid seal used for a hard disk drive, a personal computer system, and the like, and more particularly to a DC motor.
The present invention relates to a brushless motor, that is, a spindle motor.

[0002]

2. Description of the Related Art Spindle motors are widely used in hard disk drives and servers in personal computer systems. This type of spindle motor is provided with a magnetic fluid seal for preventing dust such as lubricant particles from scattering outside the motor during rotation.

Referring to FIG. 2, the structure of a conventional spindle motor will be briefly described. FIG. 2A is a sectional view of a conventional spindle motor, and FIG. 2B is an enlarged view of a sealed portion using the magnetic fluid seal.

In FIG. 2, 1 is a magnet on the rotor side, 2 is a magnetic seal holder for holding a magnetic fluid seal, 3 is a magnetic seal cover, 4 is a housing, 5 is a rotor hub, 6 is a sleeve, 7 is a fixed shaft, 8 Is the upper ball bearing, 9
Is a lower ball bearing, 10 is a base, 11 is a stator core, 12
Is a magnetic fluid, 13 is an upper pole piece, 14 is a lower pole piece, 15 is a seal magnet, 16 is an annular spacer,
Reference numeral 17 denotes an inner ring casing of the ball bearing.

Referring to FIG. 2 (B), as will be described with reference to a sealing portion using a magnetic fluid seal disposed above the upper ball bearing 8, an annular upper pole piece 13 and
A magnetic fluid seal composed of an annular lower pole piece 14 and an annular seal magnet 15 is provided in a nonmagnetic magnetic seal holder 2.

The upper pole piece 13 of the magnetic fluid seal is formed with a stepped portion shown as a portion bent downward in FIG. 2B to constitute a Z type seal, that is, a Z seal. The magnetic fluid 12 is held between 13 and the fixed shaft 7. Therefore, the interval between the pole pieces on the side to which the magnetic fluid is attached is configured to be shorter than the interval between the pole pieces on the opposite side. An annular spacer 16 made of a non-magnetic material is disposed below the lower pole piece 14, and the upper pole piece 13, the lower pole piece 14, and the seal magnet 15 are held by the annular spacer 16.

That is, when the magnetic fluid seal including the upper pole piece 13, the lower pole piece 14, the seal magnet 15 and the like is mounted on the motor, the lower pole piece 14 and the upper part 17-0 of the inner race casing of the ball bearing are mounted on the motor. In order to keep the gap constant, the thin plate-shaped annular spacer 16 is inserted between the pole piece and the ball bearing.

[0008]

By the way, in order to maintain good performance at the time of high-speed rotation in the Z-type seal, the perpendicularity between the rotation center line located in the fixed shaft 7 and the pole piece is a problem. However, the above-described conventional configuration in which a thin plate-shaped annular spacer is inserted has the following problems.

That is, since the annular spacer 16 is usually manufactured by sheet metal working using a press, the gap between the pole piece and the upper portion 17-0 of the inner race casing 17 of the ball bearing 17 is caused by the flatness (strain) and burr of the annular spacer. It has been difficult to maintain a constant angle and to maintain a perpendicularity between the pole piece and the rotation center line. In addition, the use of the annular spacer 16 increases the cost of the member.

Accordingly, an object of the present invention is to provide a motor using a magnetic fluid seal which maintains a good perpendicularity between a pole piece and a fixed shaft and does not use an annular spacer.

[0011]

In order to achieve the above object, a motor according to the present invention has a rotating portion and a fixed portion as shown in FIG. 1, and a rotary bearing is provided between the rotating portion and the fixed portion. In a motor in which a magnetic fluid seal is provided on an outer portion of a rotary bearing, a seal magnet 15 and a seal magnet 1 are provided.
5 having two pole pieces 13 and 14 holding
A magnetic fluid seal in which a gap between the pole pieces to which the magnetic fluid 12 is attached is shorter than a gap between the opposing pole pieces, a thickness of each pole piece of the magnetic fluid seal,
The magnetic seal holder is provided with an inner portion having a depth equal to the thickness of the seal magnet and the distance between the lower pole piece and the upper portion of the inner ring casing, and made of a non-magnetic material.

Since the magnetic seal holder 20 made of a non-magnetic material is manufactured by machining such as cutting instead of pressing, the mounting accuracy of the magnetic fluid seal is improved, and the perpendicularity between the pole piece and the rotation center line is improved. Is kept satisfactorily, so that scattering of the motor during high-speed rotation is suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 1A and 1B show an embodiment of the present invention, in which FIG. 1A is a cross-sectional view of a spindle motor to which the present invention is applied, and FIG. (C) is an explanatory view of a configuration of a magnetic fluid seal for the lower ball bearing, and (D) is an enlarged view of a magnetic seal holder 20 portion.

In FIG. 1, reference numeral 1 denotes a magnet on the rotor side, 3 denotes a magnetic seal cover, which is provided to improve the design so that the inside is not visible, and 4 denotes a housing, in which a lower ball is provided. A bearing 9 is disposed, 5 is a rotor hub, 6 is a sleeve, 7 is a fixed shaft, which holds the stator core 11, and 8 is an upper ball bearing, which is located above the sleeve and above the fixed shaft 7. 9 is a lower ball bearing, which is located below the housing 4 and the fixed shaft 7 provided below the sleeve 6, 10 is a base which serves as a fixed portion of the spindle motor, and 11 is a stator core. Where a stator coil is wound, 12 is a magnetic fluid and magnetic powder is dispersed in oil, for example, and 13 is an upper pole piece made of a ferromagnetic material such as soft iron. Re those steps to constitute a seal Z type is provided, 14 which also shall be composed of such a ferromagnetic material as soft iron a lower pole piece, 15 above a seal magnet pole piece 1
A member made of, for example, a plastic magnet held between the lower pole piece 14 and the lower pole piece 14 and magnetized in the vertical direction; 17 is an inner ring casing of a ball bearing portion which holds the upper ball bearing 8; The seal 19 of the ball bearing 8 is a communication hole, in which a lead wire for a stator winding is inserted and internal heat generated when the spindle motor rotates continuously at high speed increases internal pressure and causes the magnetic fluid 12 to scatter. With the function of preventing the generation of pressure,
Reference numeral 20 denotes a magnetic seal holder, which is made of a non-magnetic material, and in which a magnetic fluid seal including an upper pole piece 13, a lower pole piece 14, a seal magnet 15, and the like is disposed. It is fixed.

The magnetic seal holder 20 is a feature of the present invention. As described above, a Z-type magnetic fluid seal is disposed inside the magnetic seal holder 20. As shown in FIG. 1 (D), a magnetic seal holder 20 made of a non-magnetic material such as aluminum has a vacant space having steps 21 and 22 therein as shown in FIG. Is formed. The step portion 21 is a flat surface, and the flat portion of the upper pole piece is fixed by, for example, an adhesive. The seal magnet 15 and the lower pole piece are also fixed with an adhesive. The vertical distance, ie, depth h, of the vacant space inside
Is configured to be the sum of the thickness of the upper pole piece 13 and the lower pole piece 14, the thickness of the seal magnet, and the distance between the lower pole piece 14 and the upper portion 17-0 of the inner race casing 17. Therefore, when the magnetic fluid seal provided inside the magnetic seal holder 20 is disposed above the upper ball bearing 8, the necessary gap between the lower pole piece 14 and the upper part 17-0 of the inner race casing 17 is parallel. It is formed in a state that can be formed. Then, when the magnetic fluid seal is disposed in the magnetic seal holder 20, FIG.
As shown in FIG. 5, a step 22 is provided so that the lower pole piece 14 does not contact the magnetic seal holder 20.

Since the magnetic seal holder 20 is manufactured by machining such as cutting, for example, not by sheet metal working by pressing, the parallelism between the portion receiving the pole piece and the portion where the ball bearing abuts is easily maintained, and the rotation is achieved. The perpendicularity to the axis can be maintained well, and the problem of burrs can be avoided because the sheet metal processing is not performed by pressing. Naturally, it is necessary to concentrate the magnetic flux generated from the seal magnet 15 on the magnetic fluid 12 in order to make full use of the characteristics of the magnetic fluid seal, and to prevent the magnetic flux from being dispersed to the magnetic seal holder 20 side. The magnetic seal holder 20 needs to be made of a non-magnetic material.

If a non-magnetic material such as plastic or zinc alloy is melted and molded, a magnetic seal holder can be produced. FIG. 1
What is shown in (C) is for the lower ball bearing 9,
Since the operation is clear from the above description, it is omitted for simplification of the description.

In the above description, an example in which the magnetic seal holder 20 having a magnetic fluid seal inside is provided on the sleeve side has been described. However, the present invention is not limited to this, and is not limited to this. It may be attached to a rotor hub.

In the above description, the spindle motor has been described, but the present invention is not limited to this.

[0020]

According to the present invention, the following effects can be obtained. (1) Since the magnetic fluid seal is incorporated into the magnetic seal holder without using an annular spacer, the mounting accuracy of the magnetic fluid seal is improved, and the perpendicularity between the upper and lower pole pieces and the rotation center line is accurately maintained. Therefore, scattering of the magnetic fluid during high-speed rotation of the motor can be suppressed.

(2) Since the non-magnetic magnetic seal holder is used, the magnetic flux generated by the seal magnet can be concentrated on the magnetic fluid seal without being dispersed in the magnetic seal holder. Even distribution is achieved without unevenness of density, and air pressure resistance can be improved.

(3) Since the annular spacer can be eliminated, the cost of parts can be reduced.

[Brief description of the drawings]

FIG. 1 is an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet 2 Magnetic seal holder 3 Magnetic seal cover 4 Housing 5 Rotor hub 6 Sleeve 7 Rotating shaft 8 Upper ball bearing 9 Lower ball bearing 10 Base 11 Stator core 12 Magnetic fluid 13 Upper pole piece 14 Lower pole piece 15 Seal magnet 16 Ring spacer 17 Inner ring Casing 18 Seal 19 Communication hole 20 Magnetic seal holder 21 Step 22 Step

Claims (2)

[Claims] 1. A motor having a rotating portion and a fixed portion, a rotating bearing provided between the rotating portion and the fixed portion, and a magnetic fluid seal provided on an outer portion of the rotating bearing. A magnetic fluid seal having two pole pieces held therein, wherein a gap between the pole pieces to which the magnetic fluid is attached is shorter than a gap between the pole pieces on the opposite side; A magnetic seal holder having a depth equal to the sum of the thickness of the pole piece, the thickness of the seal magnet, and the distance between the lower pole piece and the upper portion of the inner ring casing and comprising a non-magnetic material is provided. Motor with a magnetic fluid seal. 2. The magnetic fluid seal according to claim 1, wherein said magnetic fluid seal is a Z-type magnetic fluid seal comprising a pole piece having no step, a pole piece having a step, and a magnet held between these piece pieces. The motor with a magnetic fluid seal according to claim 1, wherein: