JPH09112560A - Oil-impregnated sintered bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the service life of the bearing by preventing the scattering of the oil of an oil-impregnated sintered bearing. SOLUTION: A bearing surface 9 to support a rotary shaft 3 is formed at a part of the bearing hole of an oil-impregnated sintered bearing 4. The part from the bearing surface 9 to the bearing hole is made in a diameter expansion part extended at the taper angle θ 2 deg. to 10 deg., and in the width at least more than 1/ 3 of the width of the bearing surface 9 in the axial direction. The oil spread from the bearing surface 9 is stored in the diameter expansion part 10. As the whirl countermeasure of a rotary shaft 3, plural grooves extending in the axial direction are provided on the bearing surface 9, and the form of the bearing surface 9 is made in a step form repeating the projection and the recess in the peripheral direction. And, in order to stabilize the rotation accuracy, the surface hole opening rate of the step form bearing surface 9 can be made large at the projection parts, and small at the recess parts. In this case, in the surface area rate, the hole opening ratio is made within the scope 3 to 15% at the projection surface, and within the scope 0 to 10% at the recess surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered body suitable for bearings of a spindle which is liable to cause unstable vibration, for example, a spindle of a laser beam printer having a vertical axis orientation, a scanner motor used for digital copying and the like. The present invention relates to an oil-impregnated bearing, and more particularly to a sintered oil-impregnated bearing in which an enlarged diameter portion for an oil reservoir is formed in a bearing hole adjacent to a bearing surface.

[0002]

2. Description of the Related Art Recently, scanner motors used for laser beam printers, digital copying machines, etc. have been made faster and faster.
There is a tendency for downsizing, and for example, in a laser beam printer, the number of rotations needs to be 10,000 rpm or more. On the other hand, there is a strong demand for cost reduction, and application of a sintered oil-impregnated bearing, which is cheaper than, for example, a rolling bearing, is under study. FIG.
(B) is an example of a conventional sintered oil-impregnated bearing, and 3 ... rotary shaft, 4 '' ... sintered oil-impregnated bearing, 5 ... housing.

[0003]

If a cylindrical oil-impregnated bearing 4 '' having a normal bearing hole as shown in FIG. 1 (b) is used as a bearing of a rotating shaft rotating at a high speed, the bearing can be rotated at a high speed. The impregnated oil is excessively supplied into the bearing gap due to the oil drawing action from the surface to the rotating shaft 3 side and the thermal expansion of the oil due to frictional heat generation, and overflows to both sides of the bearing surface. A small part of the overflowed oil is permeated and collected from the chamfer portion 7 formed at the end of the bearing, but most of the oil remains passing through the chamfer portion 7 while adhering to the rotating shaft 3 and scattered outward by centrifugal force. Resulting in. Therefore, if the normal sintered oil-impregnated bearing 4 '' is used for a motor that rotates at high speed, the oil impregnated in the sintered oil-impregnated bearing 4 '' will be scattered and exhausted within a relatively short period of time, and the bearing life will be shortened. Becomes extremely short. Moreover, it will be polluted by the oil scattered around.

Another problem is that a normal sintered oil-impregnated bearing has a perfect circular inner diameter, but if such a perfect circular bearing is used, the axial orientation of the laser beam printer is normally vertical and no radial load is applied. Therefore, whirling phenomenon generally called whirl is particularly likely to occur, and stable rotation accuracy cannot be obtained. FIG. 6 shows the test results measured by a laser beam printer motor actual machine schematically shown in FIG. 4. In a perfect circular sintered oil-impregnated bearing, a whirling phenomenon having a peak at a frequency of 1/2 of the rotation frequency ( It can be seen that there is a whirl and the axial center locus (Lissajous figure) is not stable. In FIG. 4, 1 ... Rotor, 6 ... Thrust bearing, 8 ... Non-contact displacement gauge.

[0005] In order to deal with this problem
So-called Rayleigh step bearings have been proposed in Japanese Patent No. 6739 and Japanese Patent Laid-Open No. 5-180229. This bearing is
A number of grooves (recesses) that extend in the axial direction are formed on the inner peripheral surface of the bearing hole at evenly distributed positions in the circumferential direction. If necessary, the open area ratio of the convex portion that will become the bearing surface in order to improve rotational accuracy. Has been proposed to be smaller than the other parts.

However, when a test was conducted using the above-mentioned actual machine motor, when the projections and the recesses were finished to have substantially the same aperture ratio, the shaft runout was large and the specifications required for the laser beam printer were not satisfied. In addition, if the porosity of the convex part is finished smaller than that of other parts, the shaft runout becomes even larger as shown in Fig. 7, and the axis center locus (Lissajous figure) becomes completely unstable, causing rotation. A bearing with stable accuracy could not be obtained. It is presumed that these causes are mainly caused by oil permeating into the bearing through the openings of the recesses before the oil film is formed on the protrusions. In other words, the concave portion of the Rayleigh step bearing has a function as an oil reservoir, and the oil that is abundantly stored in the concave portion is drawn onto the convex portion having a narrow bearing gap as the rotating shaft rotates, so that a dynamic pressure action occurs. However, in the bearing proposed in the prior application, the concave portion does not function as an oil reservoir due to the permeation of oil, so that a sufficient oil film can be formed on the convex portion. Therefore, stable rotation accuracy cannot be obtained. An object of the present invention is to prevent the oil from scattering from the end of the bearing hole, increase the life of the bearing, and realize stable rotation accuracy without shaft runout.

[0007]

In order to solve the above problems, a sintered oil-impregnated bearing according to the present invention is a sintered oil-impregnated bearing which is formed of a sintered alloy in a porous body and impregnated with lubricating oil. A bearing surface for supporting the rotating shaft is formed on a part of an inner peripheral surface of the bearing surface, and a portion from the bearing surface to one end or both ends of the bearing hole has a taper angle of 2 ° to 10 ° and the bearing surface. The expanded diameter portion has a width that is ⅓ or more of the width in the axial direction.

In such a sintered oil-impregnated bearing, since a sufficient amount of oil can be retained by the expanded diameter portion, the oil that has exuded from the bearing surface is temporarily stored in the expanded diameter portion and is also passed through the rotary shaft. The oil is prevented from being scattered around by the oil retaining action due to the capillary phenomenon of the expanded diameter portion. While oil is temporarily stored, the volume of the oil is reduced by natural cooling through a large contact area with the surroundings, and then permeated and absorbed from the inner peripheral surface of the expanded diameter portion and returned to the inside of the bearing, and again by the suction action from the bearing surface. It circulates to the bearing surface and lubricates the rotating shaft. Therefore, the oil does not scatter and the lubrication is not defective, so that the bearing has a long life and the surrounding oil is not contaminated.

Further, according to the present invention, as a countermeasure against whirl, a plurality of grooves (recesses) extending in the axial direction are provided on the bearing surface of the sintered oil-impregnated bearing, and the bearing surface is formed into a step shape in which irregularities are repeated in the circumferential direction. it can. By thus forming the inner peripheral surface in a step shape, a dynamic pressure action occurs. By this dynamic pressure action, unstable vibration represented by whirl can be suppressed.

The surface porosity of this step-shaped bearing surface is
In order to improve the rotation accuracy, it is preferable that the convex portions are large and the concave portions are small, and the surface area ratio is within the range of the open area ratio of 3 to 15% on the convex surface and 0 to 10% on the concave surface. That is, in this case, the concave portion functions as an oil reservoir, and the oil sufficiently retained in the concave portion is drawn between the convex portion having a narrow bearing gap and the rotating shaft, so that a desired dynamic pressure effect is exerted and The shake is suppressed and the axis locus (Lissajous figure) becomes stable.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows an embodiment of the sintered oil-impregnated bearing 4 of the present invention. In this sintered oil-impregnated bearing 4, an annular bearing surface 9 is formed at the center of the bearing hole 4a in the vertical direction, and the diameter is gradually increased on both the upper and lower sides of the bearing surface 9 with a taper angle θ = 3 °. The enlarged diameter portion 10 is formed to reach the upper and lower ends of the bearing hole 4a. On the bearing surface 9, at least three or more axial grooves are formed at equal positions in the circumferential direction. As a result, as shown in FIGS. 2 (a) and 2 (b), concave portions 4 b and convex portions 4 c having an arc surface are alternately arranged on the bearing surface 9 in the circumferential direction. There is an appropriate gap C1 between the rotary shaft 3 and the convex portion 4c, and the gap C1
And the shaft diameter R is C1 / R = 2/1000 to 500
Within the range of / 10,000. In addition, the rotary shaft 3 and the recess 4b
The ratio between the bearing clearance C2 and C1 is C2 / C1 =
It is in the range of 1.2 to 5.0. The porosity of the bearing surface 9 is
It is desirable that the concave portion 4b be smaller than the convex portion 4c so that the convex portion 4c has an aperture ratio of 3 to 15% and the concave portion 4b has an aperture ratio of 0 to 10%.

With such a structure, as shown in FIG. 1A, even if the lubricating oil that has exuded into the bearing clearance C2 of the bearing surface 9 overflows from the bearing clearance C2 while the rotary shaft 3 is rotating, the diameter of the lubricating oil is increased. It is permeated and recovered from the inner peripheral surface of the portion 10 into the bearing 4 again, and again leaches and circulates on the bearing surface 9. Since the expanded diameter portion 10 has a relatively large margin as an oil reservoir and is a small gap that causes a capillary phenomenon, the oil that has exuded from the bearing surface 9 is temporarily stored in the oil reservoir and is also exposed to the outside due to the capillary phenomenon. The scattering is stopped. Therefore, the oil is prevented from scattering, the lubrication failure due to the oil depletion does not occur, and the bearing 4 has a long life. In addition, the surroundings will not be contaminated by the scattering of oil.

The taper angle θ of the expanded diameter portion 10 is 2 to 10
゜ is desirable. When the taper angle θ is 2 ° or less, the expanded diameter part 1
0 The gap between the inner peripheral surface and the rotary shaft 3 becomes small, and a pulling action occurs due to the rotation of the rotary shaft 3 to exude oil, impairing the oil recovery function. When the taper angle θ is 10 ° or more, the gap around the rotary shaft 3 becomes too large and the capillary phenomenon does not work, and the overflowed oil passes through the expanded diameter portion 10 and is transmitted to the rotary shaft 3 to leak, causing centrifugal force. It will be scattered.

The axial width B of the expanded diameter portion 10 must be at least ⅓ of the axial width D of the bearing surface 9. There is no particular upper limit to the axial width B due to the bearing function, and it is preferable that the dimension of the portion for housing the bearing 4 be as long as possible. When the length of the expanded diameter portion 10 is ⅓ or less of the bearing surface, the space in which oil can be stored becomes too small, and oil may further overflow from the expanded diameter portion 10.

The expanded diameter portion 10 does not necessarily have to be formed at both upper and lower ends of the bearing 4, and for example, in a structure in which the rotating shaft 3 is supported by a pair of upper and lower bearings 4, the outer side of each bearing, that is, the upper end and the lower end of the upper bearing. You may form the diameter expansion part 10 which expands diameter one by one facing the lower end of a side bearing. Further, when the expanded diameter portion 10 is formed on only one side in this way, the bearing surface 9 does not necessarily have to be formed in the vertical center portion of the bearing hole 4a.
It may be formed close to the end opposite to the expanded diameter portion 10.

In the bearing 4 of this embodiment, in addition to the measures for preventing oil scattering described above, an axial groove for generating dynamic pressure is formed on the bearing surface 9, so that whirl can be suppressed. In addition to this, since the surface aperture ratio of the concave portion 4b is smaller than that of the convex portion 4c, as shown in FIG.
The amount of oil that permeates into the bearing 4 from b and escapes is reduced,
The concave portion 4b effectively functions as an oil reservoir, and the oil accumulated in the concave portion 4b is drawn into a narrow region between the rotating shaft 3 and the convex portion 4c as the bearing 4 rotates, so that dynamic pressure is more likely to occur. The rotary shaft 3 can be stably supported. However,
When the porosity of the convex portion 4c exceeds 15%, a large amount of oil escapes from the surface of the convex portion 4c into the bearing 4 to reduce the generation of dynamic pressure and stably support the rotating shaft 3. I can't. If the porosity of the convex portion 4c is less than 3%, the rotation shaft 3 and the surface of the convex portion 4c are in contact with each other when the rotation is stopped, so that the oil is not instantaneously supplied at the time of starting, and the starting torque becomes large. Moreover, it causes wear. Therefore, the porosity of the convex portion 4c is preferably 3 to 15%.

On the other hand, when the opening ratio of the recess 4b is 10% or more, the oil escapes from the recess 4b into the bearing 4'as shown in FIG. 3 (b), so that the function as the oil reservoir described above is obtained. Is not exhibited, which is not preferable. Further, the aperture ratio of the concave portion 4b may be 0 at the minimum.

FIG. 5 shows the result of measurement using the actual scanner motor of the laser beam printer incorporating the sintered oil-impregnated bearing 4 of this embodiment (the same construction as that shown in FIG. 4). Compared to Fig. 6 and Fig. 7, the shaft runout is small and the Lissajous figure is stable {Fig. 5 (b)}, and the result of the frequency analysis also has only the rotational speed component and its high frequency component, and no whirl is seen. {Fig. 5 (c)}. This indicates that an oil film is formed between the outer peripheral surface of the rotating shaft 3 and the surface of the convex portion 4c which is the bearing surface, and the rotating shaft 3 is stably supported by the generation of dynamic pressure.

In the embodiment shown in FIG. 8, the recess 4b is divided into two regions 4b1 and 4b2 having different surface open area ratios. The region 4b1 is located on the rotation side, the region 4b2 is located on the counter rotation side with respect to the rotation direction A of the rotating shaft 3, and
The surface aperture ratio of the region 4b1 is smaller than the surface aperture ratio of the region 4b2. Therefore, the surface porosity is in the order of convex portion 4c> region 4b2> 4b1. The surface porosity is such that the area 4b1 of the recess 4b has a surface area ratio of 0 to 5%,
The area 4b2 is preferably 3 to 10% in surface area ratio, and the convex portion 4c is preferably 3 to 15% in surface area ratio. Area 4b
The circumferential widths of 1 and the region 4b2 are set such that the region where the lubricating oil S flowing with the rotation of the rotating shaft 3 collides is the region 4b1 and the remaining region is the region 4b2. The circumferential width of the region 4b1 is set in consideration of the usage conditions, the characteristics of the lubricating oil used, and the like. Generally, the circumferential width of the region 4b1 is set with respect to the entire circumferential width of the recess 4b. Circumferential width is 30
˜90%, and the width in the circumferential direction of the region 4b2 is preferably 10 to 70%.

The sintered oil-impregnated bearing 4 of this embodiment has a concave portion 4
b (area 4b1, area 4b2) and the surface porosity of the convex portion 4c are set as described above, the area 4b2 is opened from the inside of the bearing when the rotating shaft 3 rotates (direction A shown in the figure). The lubricating oil S easily exudes through the holes, and the exuding lubricating oil S accumulates in the region 4b1 to form an oil sump. Therefore, the concave portion 4b functions as an oil reservoir more effectively.

[0021]

【The invention's effect】

(1) The bearing has a long life. The oil that overflows from the bearing surface is temporarily stored in the expanded diameter portion, cooled and reduced in volume, permeated and collected from the inner peripheral surface of the expanded diameter portion, and circulated and leached again to the bearing surface, so that oil does not run out early and long It can be a life bearing. (2) Do not pollute the surroundings with oil. The oil overflowing from the bearing surface is temporarily stored in the expanded diameter portion, and the peripheral scattering via the rotating shaft is stopped by the capillary phenomenon of the expanded diameter portion, so the oil does not scatter around. (3) Unstable vibration represented by whirl does not occur. Since a plurality of grooves extending in the axial direction are formed on the bearing surface and the shape of the bearing surface is a step shape in which unevenness is repeated in the circumferential direction, dynamic pressure can be generated between the convex portion and the rotating shaft. , Can suppress whirl. (4) The rotation accuracy is high. The recess functions as an oil reservoir, and the oil that is sufficiently retained in the recess is drawn between the protrusion with a narrow bearing gap and the rotating shaft, so the originally intended dynamic pressure is better exerted and shaft runout is suppressed. The center axis locus (Lissajous figure) is also stable.

Further, since the surface aperture ratio of the convex portion which becomes the bearing surface is made smaller than the surface aperture ratio of the concave portion, the lubricating oil that escapes from the surface aperture of the concave portion into the inside of the bearing when the rotary shaft rotates. The number of recesses decreases, and the recess effectively functions as an oil reservoir. Therefore, the abundant lubricating oil retained in the concave portion is drawn into the narrow region (bearing gap) between the convex portion and the rotary shaft, and dynamic pressure is more likely to be generated, thereby stably supporting the rotary shaft. be able to. Further, since the minimum number of openings are ensured on the surface of the convex portion, the lubricating oil inside the bearing is instantaneously supplied to the bearing surface at the time of starting, so that the starting torque is small and the wear is small.

[Brief description of the drawings]

1A is a vertical cross-sectional view including a shaft of a sintered oil-impregnated bearing according to an embodiment of the present invention, and FIG. 1B is a vertical cross-sectional view including a shaft of a conventional sintered oil-impregnated bearing.

FIG. 2 (a) is a longitudinal sectional view of a sintered oil-impregnated bearing of the present invention,
(B) is the bb line sectional view taken on the line of (a).

FIG. 3 (a) is a partial cross-sectional view schematically showing the flow of lubricating oil around the recesses and protrusions of the sintered oil-impregnated bearing of the present invention, and (b) the recesses and protrusions of the conventional sintered oil-impregnated bearing. FIG. 6 is a diagram schematically showing the flow of lubricating oil in the peripheral portion of FIG.

FIG. 4 is a vertical sectional view showing a general configuration of a scanner motor.

FIG. 5 is a diagram showing a result of measurement using an actual scanner motor incorporating the sintered oil-impregnated bearing according to the embodiment.

FIG. 6 is a diagram showing a result of measurement using a scanner motor actual machine incorporating a conventional sintered oil-impregnated bearing.

FIG. 7 is a diagram showing a result of measurement using an actual scanner motor incorporating a conventional oil-impregnated sintered bearing.

FIG. 8 is an enlarged cross-sectional view (FIG. A) showing a peripheral portion of a concave portion and a convex portion of a sintered oil-impregnated bearing according to another embodiment (diagram a), which schematically shows a flow of lubricating oil in the peripheral portion of the concave portion and the convex portion. (Fig. B).

[Explanation of symbols]

 3 Rotational shaft 4 Sintered oil-impregnated bearing 4a Bearing hole 4b Recessed portion 4c Convex portion 9 Bearing surface 10 Expanded portion θ Tapered angle

Claims (3)

[Claims] 1. A sintered oil-impregnated bearing formed of a sintered alloy in a porous body and impregnated with lubricating oil, wherein a bearing surface for supporting a rotating shaft is formed on a part of an inner peripheral surface of the bearing hole. A diameter-increasing portion extending from the bearing surface to one end or both ends of the bearing hole with a taper angle of 2 ° to 10 ° and a width of 1/3 or more of the axial width of the bearing surface. A sintered oil-impregnated bearing characterized in that 2. The bearing surface of the sintered oil-impregnated bearing is provided with a plurality of grooves extending in the axial direction, and the shape of the bearing surface is a step shape in which unevenness is repeated in the circumferential direction. The sintered oil-impregnated bearing described. 3. The surface porosity of the step-like bearing surface is made large at the convex portion and small at the concave portion, and the surface area ratio is such that the convex surface is 3 to 15% and the concave surface is 0 to 10%. 3. The sintered oil-impregnated bearing according to claim 2, wherein the ratio is within the range.