JPH09238441A - Small motor shaft supporting structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent shaft runout by disposing another bearing which is smaller than a clearance in a dynamic pressure generating shaft supporting part at a section except the dynamic pressure generating shaft supporting part. SOLUTION: A bearing holder 1a is formed at the center of a bearing housing, at outer periphery to which a stator core 3 is fixed. A magnet case 8 where a field magnet 7 is disposed facing the outer periphery of the stator core 3 is fixed at a rotating shaft 6, and is pivoted with a thrust bearing plate 2a disposed at an outer casing 2. A pair of sleeves 4 are pressed in the bearing holder 1a, and a sintered oil-impregnated bearing 5 is disposed between the sleeves 4. In the rotating shaft 6, a diametrical wedge-shaped dynamic pressure generating groove 6a is formed at a position where it faces the sleeve 4, and is supported by the sintered oil-impregnated bearing 5 together with a dynamic pressure generating shaft supporting part 46a. In the clearance between the rotating shaft 6 and the bearing, the clearance of the sintered oil-impregnated bearing 5 is set smaller than that of dynamic pressure generating shaft supporting part 46a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a shaft support structure for a small motor, and more particularly to a dynamic pressure type bearing structure for reducing shaft runout at low speed.

[0002]

2. Description of the Related Art Conventionally, various structures having a dynamic pressure bearing function have been proposed as a shaft supporting structure for a small motor, for example, one disclosed in Japanese Patent Laid-Open No. 5-115146. Such a dynamic pressure type hydrodynamic bearing structure is effective for a high rotation type and is often used for a spindle motor for a polygon scanner.

[0003]

However, in the conventional dynamic pressure bearing structure, the dynamic pressure effect is not sufficiently obtained at low speed, and contact occurs between the rotary shaft and the sleeve at low speed, seizure and shaft runout. There is a problem that occurs. On the other hand, the conventionally known general sintered oil-impregnated bearing type has a drawback in that it is significantly worn at high rotation speed, and durability is impaired.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems and to realize a dynamic pressure that has a simple structure and that achieves low noise and low wear without shaft runout over the entire rotation range from low rotation to high rotation. Another object of the present invention is to provide a shaft supporting structure for a small motor which has a bearing structure and has a longer life.

[0005]

In order to solve the above problems, the present invention comprises a combination of a dynamic pressure generating bearing and another bearing, which prevents shaft run-out at low speeds. is there.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention is one in which a dynamic pressure generating mechanism is formed in at least one of a shaft and a bearing. This can be achieved by arranging another bearing that is smaller due to the clearance of the pressure generating bearing. As the other bearing, it is preferable to use a sintered oil-impregnated bearing, a ball bearing, a ceramic bearing, or the like.

With this arrangement, the dynamic pressure generating shaft bearing portion functions at high speed rotation, and at relatively low speed, the other bearings have smaller clearances, so that shaft runout does not occur.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the structure of an embodiment of the present invention will be described with reference to a longitudinal sectional view of a main part adopted in a small brushless motor shown in FIG. In the figure, reference numeral 1 denotes a bearing housing made of aluminum die-casting, which also serves as a bracket, and is fixed to the opening edge of the outer casing 2. A bearing holder 1a is formed in the center of the bearing housing 1, and a stator core 3 is fixed to the outer circumference. A magnet case 8 in which a field magnet 7 facing the outer circumference of the stator core of the stator 6 is fixed is fixed to the rotary shaft 6, and is pivotally supported by a thrust bearing plate 2a arranged in the outer casing 2. There is. A pair of sleeves 4 are press-fitted inside the bearing holder 1a, and a sintered oil-impregnated bearing 5, which is the feature of the present invention, is arranged between the sleeves. A rotary shaft 6 is formed with radial wedge-shaped dynamic pressure generating grooves 6a, 6a at a position facing the sleeve 4, and together with the dynamic pressure generating shaft bearings 46a, 46a, the sintered oil-impregnated bearing 5 is formed. Is supported by. The relationship between the clearance between the rotary shaft 6 and the bearing is smaller in the sintered oil-impregnated bearing than in the dynamic pressure generating shaft supporting portion, as can be judged from the structural drawing of the main part shown in FIG. 2, which is an exaggerated drawing.

With this arrangement, the bearing support portion of the sintered oil-impregnated bearing functions at low rotation speed, and the dynamic pressure generating shaft support portion functions at high speed rotation. A ceramic bearing may be used instead of the sintered oil-impregnated bearing. FIG.
1 is comparison data of the structure shown in FIG. 1 of the present invention and a conventional shaft bearing structure having only a dynamic pressure generating part. The conventional dynamic pressure generating bearing support part alone causes a large runout of the rotating shaft at low speed. On the other hand, in the configuration of the present invention, it can be seen that the shake is constant and stable over the entire rotation range.

FIG. 4 is a structural view of a main part which is a modification of the above-mentioned embodiment, in which a pair of sintered oil-impregnated bearings 55, 55 are arranged outside the dynamic pressure generating shaft support 46a. If this is done, the cost will increase somewhat, but the accuracy will be even higher.

FIG. 5 is a structural view of another embodiment in which a ball bearing B is used instead of another bearing. The inner ring B1 of this ball bearing is received by a bushing 9 attached to the rotary shaft 6. Therefore,
It can withstand axial loads and can support rotation.

[0012]

According to the present invention, other bearings, for example, a sintered oil-impregnated bearing having a clearance smaller than that of the dynamic pressure generating shaft support portion are arranged in the portion excluding the dynamic pressure generating shaft support portion as described above. As a result, there is no contact and wear between the rotating shaft and the sleeve at low rotation, starting and stopping, which were the drawbacks of conventional hydrodynamic bearings. The wear on the rotary shaft is reduced, and the life of the rotary shaft can be reduced and the runout of the rotary shaft can be reduced. In addition, combining a ball bearing as another bearing eliminates the need for a preload that is generally required for a ball bearing to prevent shaft runout. Conversely, by not applying a preload, shaft runout can be achieved by a dynamic pressure effect. Therefore, it is possible to suppress the load on the ball bearing, reduce the load on the ball bearing, extend the life of the ball bearing, and compensate for the drawbacks of the dynamic pressure bearing at low rotation. Further, in a dynamic pressure bearing, it is generally necessary to generate a dynamic pressure at the end of the rotating shaft and its receiving portion in the axial direction, so the dynamic pressure groove may be formed on either side. The cost is high and it is difficult to process with a shaft having a small diameter. However, as described above, a ball bearing is combined as another bearing, the inner ring of the ball bearing is fixed to the rotary shaft, and the axial load is received by the ball bearing, so that dynamic pressure groove processing in the thrust direction becomes unnecessary. .

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a bearing structure for a small motor according to an embodiment of the present invention.

FIG. 2 is a structural diagram of a main part of the bearing structure for the small motor in FIG.

FIG. 3 is a comparative data diagram of the conventional bearing support structure and the shaft support structure of the present invention.

FIG. 4 is a structural diagram of a modified essential part of the embodiment.

FIG. 5 is a structural view of a main part of another embodiment of the present invention.

[Explanation of symbols]

 1 ... Bearing housing 1a ... Bearing holder 2 ... Outer casing 3 ... Stator core 4 ... Sleeve 5, 55 ... Sintered oil-bearing 6 ... Rotating shaft 6a ... Dynamic pressure generating groove 46a ... Dynamic pressure Generating shaft support B B Ball bearing 9 Bushing

Claims (4)

[Claims] 1. A shaft bearing structure for a small motor having a dynamic pressure generating bearing formed by forming a dynamic pressure generating mechanism on at least one of a shaft and a bearing, in a portion excluding the dynamic pressure generating shaft bearing. , A small motor shaft bearing structure that prevents shaft runout even at low speeds by arranging other bearings that are smaller than the clearance of the dynamic pressure generating shaft bearing part. 2. The shaft bearing structure for a small motor according to claim 1, wherein the other bearing is an oil-impregnated bearing. 3. The shaft supporting structure for a small motor according to claim 1, wherein the other bearing is a ball bearing. 4. The bearing support structure for a small motor according to claim 1, wherein the other bearing is a ring-shaped ceramic bearing.