JPH0445692B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a sintered oil-impregnated bearing in which the inner diameter of the bearing is smaller at both end portions of the bearing and larger at the central portion in the axial direction. [Prior Art] There are various applications and usage methods for this type of oil-impregnated bearing manufactured by powder metallurgy, and two of the same bearings are sometimes used in parallel. An example is the coreless motor shown in FIG. 1, in which the two oil-impregnated bearings 1 and 2 are
These oil-impregnated bearings 1 and 2 are attached to a resin support 5, and the resin support 5 is attached to an iron core 6, respectively. By the way, conventionally, oil-impregnated bearings 1 and 2 have been used that have a simple cylindrical shape with a uniform cross-sectional shape in the axial direction. However, it goes without saying that variations occur in their positioning, and the individual bearings 1,
Since there are also variations in the size of the bearings 2, it is difficult to mount the two oil-impregnated bearings 1 and 2 without eccentricity to the motor shaft 4, which inevitably causes problems such as noise and shaft galling. As an idea for solving such problems, a sintered oil-impregnated bearing described in Japanese Utility Model Application Publication No. 47-8842 is known. [Problems to be Solved by the Invention] However, in the technique described in the above-mentioned publication, since the portion of the inner circumferential surface of the bearing from the small diameter portion to the large diameter portion is at right angles, shaft galling may occur due to deflection of the shaft. Not only does the problem still persist, but if the section from the small diameter section to the large diameter section is at a right angle, the oil film tends to run out in that section, and it is impossible to achieve a long life due to seizure, etc. It was hot. Furthermore, in Utility Model Application No. 1983-67140, flanges are provided on the outer periphery of both ends of the cylindrical body, and these flanges are pressurized and compressed by brass bushings, so that the inner periphery of both ends of the cylindrical body is compressed. A bearing has been proposed in which the diameter is reduced and an annular recess is provided between both flanges on the outer periphery to form a sealed space, and an oil-impregnated body made of felt is disposed within this space. With such a technique, it is possible to set the angle between the concave part of the inner peripheral part and the continuous part of both ends to be an obtuse angle, but the heat transfer path from the inner peripheral side to the outer peripheral side of the bearing is Since it is limited to both flanges, the cooling efficiency of the bearing decreases, or
Compressive force is always applied to the flange part, and the residual compressive stress may cause dimensional changes.This leaves room for improvement, such as the need to adjust the dimensions when installing it on equipment. ing. The present invention was made against the above background, and is capable of eliminating shaft galling, preventing oil film breakage, suppressing residual stress as much as possible, and ensuring heat transfer efficiency. The purpose is to provide a sintered oil-impregnated bearing that can [Means for Solving the Problems] The present invention provides a sintered oil-impregnated bearing made entirely of sintered material and having a cylindrical shape, in which both ends in the shaft immersion direction have an inner circumferential surface that is straight in the axial cross section. A relief is formed in the supporting part which is shaped and coaxial, and in the part spanning the supporting part, a relief is formed in the axial cross section and has a symmetrical arc shape with respect to the center in the axial direction and has a larger diameter than the supporting part. Therefore, it is characterized in that it is formed over the entire inner peripheral surface, the outer peripheral surface has a substantially uniform outer diameter, and the difference in diameter between the inner peripheral surface of the support part and the relief is set to 2 μm or more. shall be. [Example] Hereinafter, with reference to the attached FIGS. 2 to 5,
The content of this invention will be explained in detail. The sintered oil-impregnated bearings 71 and 72 of the present invention are entirely made of sintered material, and as shown in FIG. , 82a are provided. Therefore, the oil-impregnated bearing 7 of the present invention
1,72, the inner diameter d1 at both end portions of the bearing
(Support part) has an inner diameter d2 at the center in the axial direction
It is smaller than the (relief part). These oil-impregnated bearings 71 and 72 are used, for example, in place of bearings 1 and 2 in the coreless motor described above (FIG. 3), but each of these oil-impregnated bearings 71 and 72 is an integral piece as a whole. Nevertheless, both end portions 81b separated from each other,
81c, 82b, and 82c perform the same functions as independent conventional bearings 1 and 2, respectively.
In this case, in order to effectively perform such a function, it is necessary to set d2-d1≧2 μm. Conversely, if d2-d1<2μm, the radius difference is 1μm
However, it is not possible to secure a sufficient amount of lubricating oil in these reliefs 81a and 82a, and the function as an oil reservoir is lost.Therefore, the bearing is no different from a simple cylindrical bearing with a uniform cross section in the axial direction. I get used to it. Therefore, when d2-d1<2 μm, the relief portions 81a and 82a function as oil reservoirs, and the life of the bearing can be extended. In addition, since the relief surfaces 81a and 82a are formed in an arc shape in the axial cross section, the portion This prevents the shaft from being damaged by heat at the X part due to deflection, and the oil film does not break off at the X part of the inner circumferential surface from the small diameter part d1 to the large diameter part d2, preventing seizure etc. for a long time. It is possible to prevent this problem from occurring over a long period of time, thereby improving quality stability and extending life. Furthermore, when inserting the shaft into this bearing, the arcuate surface smoothly guides the tip of the shaft, which is preferable in that it does not damage the inner circumferential surface of the bearing or the shaft. The size of each oil-impregnated bearing 71, 72 is, for example, an outer diameter of 3 to 5.
mm, length 4-7 mm, and inner diameter 1-2 mm. Incidentally, the reliefs 81a and 82a can be formed by selective etching or electrical discharge machining after sintering, but it is best to use the following manufacturing method that takes advantage of the characteristics of powder metallurgy. It is. Sintered parts are usually manufactured through a powder compaction process, a sintering process, and a reprocessing process after sintering. Center part in the center direction (relief 81a, 82a
ring-shaped groove 1 on the outer circumferential surface of the
0a, 10b, and 10c are formed in advance. These grooves 10a, 10b, 10c can be formed by cutting,
It can also be formed by changing the shape of the die used during powder compaction. Note that these grooves 10
The size, shape, etc. of a, 10b, 10c can be appropriately selected depending on the size of the reliefs 81a, 82a of the bearing holes 81, 82, etc. Then, such a sintered body 9 is subjected to normal re-pressurization,
That is, as shown in FIG. 5, by using a die 11, an upper punch 12, a lower punch 13, and a core rod 14, pressure is compressed from both ends in the axial direction. Then, the outer diameter portion of the sintered body 9 and the groove 10
In portions a, 10b, and 10c, the meat moves outward so as to follow the shape of the die 11. On the other hand, the bearing hole portion swells outward at the grooves 10a, 10b, and 10c, creating areas where it hits the core rod 14, which has a uniform cross-sectional shape in the axial direction, and areas where it does not, as shown in Fig. 2 mentioned above. Bearing like 7
1,72 shapes are obtained. Bearing 7 of the present invention manufactured in this way
1, 72, there is a relief 8 in the bearing holes 81, 82.
1a, 82a are formed, and reliefs 81a, 8
Both end portions 81b, 82c, 82b, 8 without 2a
Since 2c is compressed at the same time, eccentricity and dimensional variations are also considerably reduced. Next, the bearing of the present invention manufactured by the method described above was tested using the durability test apparatus shown in FIG. This device includes a shaft 4 that is connected to a drive source such as a motor and is rotatably supported, and a support body 21 that has bearings 71 and 72 fitted and fixed into through holes therein.
and a spring 22 that urges the support body 21 in a direction perpendicular to the axis. The shaft 4 is set to have a small diameter with respect to the bearing holes 81 and 82, and when the shaft 4 is inserted through the bearings 71 and 72, a constant force is created between the contact surfaces of the shaft 4 and the bearings 71 and 72 by the bias of the spring 22. The shaft 4 is rotated while applying surface pressure. Using this device, the amount of wear on the bearings after a certain period of time (3000 hours) and the time until seizure occurred were measured for the examples and comparative examples of the present invention. The experimental conditions are as follows. (1) The material of the bearing is iron-copper, and the dimensions of the bearing are: outer diameter is 4.0mmφ, inner diameter of the bearing hole is 1.2mmφ, and the curvature of the relief part in the center of the bearing hole is 2.5mm. (2) Diameter difference between the support part and relief, i.e. (d2-d
The values of 1) were set as shown in the table. Of these, 1
2 is a conventional example, 2 is a comparative example which does not apply to the present invention because this value is small, and 3 to 6 are examples of the present invention. (3) The outer diameter of the shaft has sufficient clearance with the bearing hole.
It is set to be 15 μm. (4) The bearing is impregnated with synthetic oil equivalent to VG56. (5) The surface pressure between the shaft and the inner surface of the bearing hole was set in two levels, 30 Kgf/cm ² and 50 Kgf/cm ² by changing the biasing force of the spring. (6) Shaft rotational speed is 2.5m/min in circumferential speed.
It was set to The test results are shown in Table 1, and part of them is shown in FIG.

【table】

[Table] As shown in the results, the wear amount of the example of the present invention is smaller than that of the conventional example or the comparative example, and the time until seizure occurs is longer. Both the data on the amount of wear and the time until seizure are saturated when the diameter difference is 2 μm, and there is no change even if the diameter difference is set larger than that. In other words, if the thickness of this relief part is 1 μm or more, the amount of oil accumulated to provide a sufficient lubrication function can be secured. Table 2 shows the results of a test using the bearing manufactured in this way in a coreless motor. The sample was an example corresponding to No. 5 in Table 1, the dimensions were as described in (1) above, the difference in diameter of the relief part was 10 μm, and the test was conducted at a rotation speed of 5100 rpm.

[Table] The higher the value, the larger the value.
be.
[Effects of the Invention] The present invention is a sintered oil-impregnated bearing that is entirely formed into a cylindrical shape from a sintered material, and the inner peripheral surface of both ends in the axial direction is linear and coaxial in the axial cross section. A relief that is formed on a certain support part and spans the support part has a circular arc shape that is symmetrical to the center in the axial direction in the axial cross section and has a larger diameter than the support part, and is formed on the inner periphery by plastic working. It is characterized in that it is formed over the entire circumference of the surface, the outer peripheral surface has a substantially uniform outer diameter, and the difference in diameter between the inner peripheral surface of the support part and the relief is set to 2 μm or more, It has the following excellent effects. The part from the support part to the relief part forms an obtuse angle, so that even if the shaft is bent, it will not cause galling or the like, and will not run out of the oil film, resulting in a longer service life. Moreover, the cross section along the axial direction is formed into an arc shape,
Since the difference in diameter between the supporting part and the relief is set to at least 2 μm, the work is easy and time-consuming even when selectively etching or electrical discharge machining the cylindrical body when manufacturing small diameter bearings. In particular, it can be easily manufactured by forming a circumferential groove on the outer surface of the cylinder and compressing it in the axial direction after sintering. In addition, the difference in diameter between the support part and the relief part is set to 2μm or more, ensuring a sufficient oil reservoir and stably supplying lubricating oil to the inner peripheral surface of the support part over a long period of time. This also makes it possible to extend the life of the product. Furthermore, since the above-mentioned relief part is formed by plastic working, it is possible to obtain a bearing with almost no residual stress, which eliminates spring back and suppresses dimensional changes over time. It is possible to increase the reliability of bearing accuracy and maintain bearing accuracy over a long period of time. Moreover, since the outer circumferential surface of the bearing has a substantially uniform outer diameter, when it is installed in a device, the contact between the outer circumferential surface and the device is good, and the reduction in contact area is suppressed, allowing the bearing to It is possible to improve the cooling performance by increasing the thermal conductivity between the device and the device, thereby improving durability and the like.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the application of a conventional bearing of this type.
FIGS. 2a and 2b are cross-sectional views showing embodiments of a sintered oil-impregnated bearing according to the present invention, FIG. 3 is a view showing an application example of the bearing according to the present invention, and FIGS. 4a to 4c are manufacturing methods according to the present invention. 5 is a cross-sectional view of the main part showing the pressurized and compressed state in the reprocessing process of the present invention, FIG. 6 is a cross-sectional view of the durability test device, and FIG. is a graph showing the test results. 71, 72... Sintered oil-impregnated bearing according to the present invention,
81, 82...bearing hole, 81a, 82a...relief (center in axial direction), 81b, 81c, 82b, 8
2c...Both end portions of the bearing (support part), 9...Sintered body, 10a, 10b, 10c...Ring-shaped groove,
11...Die, 14...Core Rod.

Claims (1)

[Claims] 1 A sintered oil-impregnated bearing entirely formed in a cylindrical shape from a sintered material, in which both ends in the shaft immersion direction are formed into support parts whose inner circumferential surfaces are linear and coaxial in the axial cross section, and the above-mentioned In the part that spans the support part, a relief that is symmetrically arc-shaped with respect to the center in the axial direction in the axial cross section and has a larger diameter than the support part is formed over the entire inner peripheral surface by plastic working. A sintered oil-impregnated bearing characterized in that the outer circumferential surface has a substantially uniform outer diameter, and the difference in diameter between the inner circumferential surface of the support portion and the relief portion is set to 2 μm or more.