JPH1169716A - Brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a brushless DC motor which enhances a dynamic characteristic in a high-speed rotation, by a method wherein, while a shaft is turned, the flow of a fluid becomes a turbulent flow and a dynamic poessure is raised. SOLUTION: A protrusion-shaped oval which has plurality of radii R1 to R4 is formed on the inner circumferential face of a bearing 11, and, as a result, the oval in which the inner circumferential face of the bearing 11 protrudes is constituted. Consequently, while a shaft 12 is turned, an oil whirling phenomenon is not generated. That is to say, when the shaft 12 is turned at high speed, the flow velocity distribution of an oil is changed into a turbulent flow, and the pressure of the oil between grooves 13 is increased. Then, the oil is collected in the center of the shaft 12, and the generation of the pressure is increased due to a change in the flow velocity of the oil. As a result, the flow velocity of the oil is changed, the pressure generation rate of the oil on the face of the bearing 11 is increased, and a dynamic pressure in a high-speed rotation is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor, and more particularly, to an elliptical inner peripheral surface of a bearing for rotatably supporting a shaft to change a flow distribution of oil. Accordingly, the present invention relates to a brushless DC motor having improved dynamic characteristics of reducing vibration and noise during high-speed rotation.

[0002]

2. Description of the Related Art Generally, small precision motors used in multimedia equipment require a high rotational speed in response to demands for high speed and high capacity of the equipment used.
In order to require low vibration and low noise dynamic characteristics, the bearings used have changed from ball bearings to fluid sintered bearings or fluid dynamic pressure bearings having excellent dynamic performance.

FIG. 1 is a cross-sectional view of a motor using a conventional fluid dynamic bearing, in which a bearing 1a is fitted in a center of an upper portion of a base 1 and a shaft 2 is rotatable inside the bearing 1a. Be prepared for the condition. A stator 1b constituting a stator is provided on an upper outer peripheral edge of the base 1, and a cap-shaped rotor 3 is provided on an upper end of the shaft 2. The rotor 3 includes a magnet 3a surrounding the stator 1b on the inner peripheral edge. When power is applied to the coil 1c wound on the stator 1b, the magnet 3
a, a magnetic force is generated, and the rotor 3 rotates around the shaft 2.

[0004] The conventional motor constructed as described above uses a fluid dynamic pressure bearing, and has a dynamic pressure generating groove 2 a formed on the outer peripheral surface of the shaft 2. That is, the shaft 2
When the rotor rotates at a high speed, the oil filled between the bearing and the bearing 1a generates pressure by the dynamic pressure generating groove 2a. Therefore, the shaft 2 is rotatably supported in the radial direction. Also, while the shaft 2 rotates, the disk placed above the rotor 3 reproduces information of the disk while rotating together.

However, in the case of the fluid dynamic pressure bearing, there is a disadvantage that an unstable phenomenon called oil whirl occurs at a low speed. The oil whirl phenomenon starts as the bearing eccentricity between the bearing and the shaft gradually decreases above a certain speed. This is the Sommerfeld number as speed increases.
This is because the eccentricity gradually decreases as the number) decreases. Such a phenomenon occurs because the oil rotating along the shaft has a constant speed distribution, and generally occurs in a fluid dynamic pressure bearing having a perfect circular shape of the bearing 1a. Accordingly, there are disadvantages such as a decrease in dynamic characteristics of low vibration and low noise at high speed.

[0006]

SUMMARY OF THE INVENTION The present invention has been developed in view of various conventional problems, and an object of the present invention is to form an inner peripheral surface of a bearing into an elliptical shape having two or more radii. The oil flow distribution around the shaft changes to turbulent flow, the oil flow speed changes, the oil pressure generation rate on the bearing surface increases, and the dynamic characteristics at high speeds improve. An object of the present invention is to provide a brushless DC motor.

[0007]

In order to achieve the above object, a brushless DC motor according to the present invention comprises a stator having a coil wound thereon, and a plurality of motors, each of which is defined as a rotating shaft of the motor and generates a dynamic pressure at an outer diameter. A shaft having a groove, a cylindrical wall positioned coaxially with the stator and surrounding the stator, a magnet attached to the inside of the cylindrical wall and having an air gap between the stator and the magnet, A rotor comprising a hub rotatably supported by the shaft; a base supporting the stator; and a radius such that the shaft maintains a rotatable fluid flow space therein and surrounds and supports the shaft. An uneven inner wall and an outer wall surrounding the inner wall and securing the bearing system, wherein the base and the front And a bearing system for rotatably connecting the shaft so that the inner wall of the bearing is formed in a protruding shape, and during the rotation of the shaft, the flow of the fluid becomes turbulent and the dynamic pressure increases. I do.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIGS. 2A and 2B show the first embodiment of the present invention.
FIG. 3 is a cross-sectional view of a motor to which the embodiment of FIG. Base 1 to which bearings 11 constituting a bearing system are connected
And a stator 14 on which a coil 15 is wound. Then, the shaft 12 is rotatably inserted into the bearing 11, and a groove 13 for generating a dynamic pressure on the oil is formed on the outer peripheral surface of the shaft 12. Here, the groove 13 is formed in the shape of an arrow as shown in FIG. 2A or a hatched shape as shown in FIG. 2B. A hub 16 is fitted to the upper end of the shaft 12 in a fitting manner, and a rotor 17 is provided on an outer peripheral edge of the hub 16 so as to be able to rotate together with the hub 16. Rotor 17
Is located coaxially with the stator 14, and has a cylindrical wall surrounding the stator 14, a magnet 18 attached to the inside of the cylindrical wall and having a gap between itself and the stator 14, and the magnet is rotatable. Like shaft 1
And a hub 16 supported by the hub 2. Therefore, when power is applied to the coil 15, a magnetic force is generated by the magnet 18, and the rotor 17 rotates at high speed together with the shaft 12.

The inner peripheral surface of the bearing 11 forms a protruding ellipse having a plurality of radii. FIG. 3 (a)
Shows a bearing having two radii R1, R2, which result in a bearing 1
1 forms an ellipse with a protruding inner peripheral surface. Therefore, the oil whirl phenomenon does not occur while the shaft 12 rotates. That is, when the shaft 12 rotates at a high speed, the oil flow velocity distribution changes to a turbulent flow, and the oil pressure between the grooves 13 increases.

According to the first embodiment of the present invention, a protruding ellipse having two radii is formed on the inner peripheral surface of the bearing 11. Therefore, the shaft 1
While the 2 rotates at high speed, the oil flow changes to turbulent. Then, the oil collects at the center of the shaft 12, and the pressure generation increases due to a change in the flow speed of the oil. FIG.
(B) and (c) show that the bearing 11 has three radii R1, R2, R3 and four radii R1, R2, respectively.
This shows the case of R3 and R4, and has the same effect as that of two radii.

FIGS. 4A and 4B are sectional views of a bearing according to a second embodiment of the present invention. In the second embodiment of the present invention, a groove 13 for generating dynamic pressure is formed on the inner peripheral surface of the bearing 11. In this embodiment, the groove 13 has an arrow shape as shown in FIG. 4A or a hatched shape as shown in FIG. 4B. Since the inner peripheral surface of the bearing 11 is formed in a protruding shape having two radii, the groove 13 eventually forms an ellipse. FIG. 5A shows a bearing 1 having two radii R1 and R2.
When the shaft 12 rotates at a high speed, the oil flow velocity distribution changes to a turbulent flow, and the oil pressure in the groove 13 increases. The characteristics are improved. FIG. 5B shows a bearing 11 having a groove 13 having three radii R1, R2 and R3, and FIG. 5C shows a groove 11 having four radii R1, R2, R3 and R4. 13 shows a bearing 11 with 13 and has the same effect as having two radii.

FIG. 6 is a sectional view of a motor to which the third embodiment of the present invention is applied, and the same components as those in the first embodiment will be described using the same reference numerals. A third embodiment of the present invention comprises a sintered bearing that rotatably supports a shaft. The inner peripheral surface of the sintered bearing 11 forms a protruding ellipse having a large number of radii. Also,
A linear groove 13 formed in a step shape is formed on the inner peripheral surface of the bearing 11, and as a result, these grooves 13 have an elliptical shape.

FIG. 7 (a) shows a sintered bearing 11 having two radii R1 and R2. The inner peripheral surface of the sintered bearing 11 has an elliptical shape.
While the shaft 12 rotates, the oil whirl phenomenon does not occur. That is, when the shaft 12 rotates at high speed,
The flow velocity distribution of the oil changes to a turbulent flow, and the oil pressure between the grooves 13 increases. Therefore, while the shaft 12 rotates at a high speed, the flow of the oil changes to a turbulent flow, the oil gathers toward the center of the shaft 12, and the flow speed of the oil changes to increase the pressure generation. (B) and (c) of FIG.
The sintered bearing 11 has three radii R1, R2, R3
And four radii R1, R2, R3, and R4, which have the same effect as those having two radii.

FIG. 8 is a sectional view of a sintered bearing according to a fourth embodiment of the present invention, and the same components as those of the third embodiment will be described using the same reference numerals. In the fourth embodiment of the present invention, a groove 13 for generating a dynamic pressure is formed on the outer peripheral surface of the shaft 12. The inner peripheral surface of the sintered bearing 11 forms a protruding ellipse having a plurality of radii. FIG. 9A shows the sintered bearing 11 having two radii R1 and R2. With this configuration, when the shaft 12 rotates at high speed, the oil flow velocity distribution changes to turbulent flow. Since the oil pressure between the grooves 13 increases, the oil whirl phenomenon decreases, and the dynamic characteristics during high-speed rotation are improved. FIG. 9B shows three radii R
1, R2, and R3, and FIG. 9C shows one having four radii R1, R2, R3, and R4, and has the same operation and effect as those having two radii.

[0016]

As described above, according to the present invention,
By configuring the outer peripheral surface of the bearing into an elliptical shape with multiple radii, the oil flow changes to turbulent flow while the shaft rotates, and the flow speed increases, improving the dynamic characteristics at high speed rotation There are effects such as doing.

[Brief description of the drawings]

FIG. 1 is a sectional view of a conventional motor.

FIGS. 2A and 2B are cross-sectional views of a motor to which the first embodiment of the present invention is applied.

FIGS. 3A, 3B, and 3C are cross-sectional views of the first embodiment of the present invention.

FIGS. 4A and 4B are cross-sectional views of a motor according to a second embodiment of the present invention.

FIGS. 5A, 5B, and 5C are cross-sectional views of a second embodiment of the present invention.

FIG. 6 is a sectional view of a motor to which a third embodiment of the present invention is applied.

FIGS. 7A, 7B, and 7C are cross-sectional views of a third embodiment of the present invention.

FIG. 8 is a sectional view of a fourth embodiment of the present invention.

FIGS. 9A, 9B, and 9C are cross-sectional views of a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Base 11 Bearing 12 Shaft 13, 13a Dynamic pressure generation groove 14 Stator 15 Coil 16 Hub 17 Rotor 18 Magnet

Claims (16)

[Claims] 1. A brushless DC motor, comprising: a stator wound with a coil; a shaft defined as a rotation axis of the motor and having a plurality of grooves for generating dynamic pressure on an outer diameter; A rotor having a cylinder-shaped wall surrounding the stator, a magnet attached to the inside of the cylinder-shaped wall and having an air gap between the stator and the hub, and a hub rotatably supporting the magnet on the shaft. A base for supporting the stator, an inner wall having an uneven radius to maintain a fluid flow space in which the shaft is rotatable and capable of surrounding and supporting the shaft, and surrounding the inner wall; An outer wall for fixing a bearing system, and a base for rotatably connecting the base and the shaft. A brush system, wherein the inner wall of the bearing is formed in a protruding shape, and a dynamic pressure increases due to turbulent flow of the fluid during rotation of the shaft. DC motor. 2. The brushless DC motor according to claim 1, wherein the groove formed in the shaft forms one or more angles. 3. The brushless DC motor according to claim 1, wherein the groove formed in the shaft is formed as a curved surface. 4. The brushless DC motor according to claim 1, wherein a groove formed in said shaft is formed obliquely. 5. A brushless DC motor, comprising: a stator wound with a coil; a shaft defined as a rotation axis of the motor, the shaft having one or more grooves for generating a dynamic pressure on an outer diameter; A cylinder-shaped wall positioned around the stator, a magnet attached to the inside of the cylinder-shaped wall and having an air gap between the stator and a hub that rotatably supports the magnet on the shaft. And a base for supporting the stator, wherein the shaft maintains an oil flow space in which the shaft is rotatable inside, and has a non-uniform radius so as to surround and support the shaft, and can contain oil. Sintering
An inner wall for supplying oil during rotation of the shaft, and an outer wall surrounding the inner wall and fixing the bearing system, and a bearing system rotatably connecting the base and the shaft. The brushless DC motor is characterized in that the inner wall of the bearing is formed in a protruding shape, and that the fluid flows as a turbulent flow to increase the dynamic pressure while the shaft rotates. 6. The brushless DC motor according to claim 5, wherein the groove formed in the shaft forms one or more angles. 7. The brushless DC motor according to claim 5, wherein the groove formed in the shaft is formed as a curved surface. 8. The brushless DC motor according to claim 5, wherein the groove formed in the shaft is formed obliquely. 9. A brushless DC motor, comprising: a stator having a coil wound thereon; a shaft defined as a rotation axis of the motor; a cylinder-shaped wall coaxially surrounding the stator and surrounding the stator; A rotor attached to the inside of the wall and having an air gap between the stator and the stator, a rotor including a hub that rotatably supports the magnet on the shaft, a base that supports the stator, An inner wall having a non-uniform radius to maintain a fluid flow space in which the shaft can rotate and surround and support the shaft; and a plurality of grooves formed in the inner wall in an axial direction to generate dynamic pressure. And an outer wall surrounding the inner wall and fixing the bearing system, and rotating the base and the shaft. And a bearing system which is connected to the bearing so that the inner wall of the bearing is formed in a protruding shape, and the fluid pressure becomes turbulent and the dynamic pressure rises while the shaft rotates. Characterized brushless DC motor. 10. The brushless DC motor according to claim 9, wherein the groove formed in the shaft forms one or more angles. 11. The brushless DC according to claim 9, wherein the groove formed in the shaft is formed as a curved surface.
motor. 12. The brushless DC according to claim 9, wherein a groove formed in the shaft is formed obliquely.
motor. 13. A brushless DC motor, comprising: a stator wound with a coil; a shaft defined as a rotation axis of the motor; a cylinder-shaped wall coaxial with the stator and surrounding the stator; A magnet attached to the inside of the wall and having an air gap between the stator and a rotor configured to support the magnet on the shaft so as to be rotatable; and a base supporting the stator; The shaft maintains a rotatable oil flow space therein, has a non-uniform radius to support and support the shaft, and is sintered to contain oil,
An inner wall for supplying oil to an oil flow space during rotation of the shaft, a plurality of grooves formed in the inner wall in an axial direction to generate dynamic pressure, and surrounding the inner wall, fixing the bearing system; And an external wall
By forming the base and a bearing system that rotatably connects the shaft, the inner wall of the bearing is formed in a protruding shape, and the flow of the fluid becomes turbulent while the shaft rotates. A brushless DC motor characterized by an increased dynamic pressure. 14. The brushless DC motor according to claim 13, wherein the groove formed in the shaft forms one or more angles. 15. The brushless D according to claim 13, wherein the groove formed in the shaft is formed as a curved surface.
C motor. 16. The brushless D according to claim 13, wherein a groove formed in said shaft is formed obliquely.
C motor.