JPH10274241A - Porous oilless bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce shaft vibration when an unbalance load is applied by providing a second region separated from a first region in an axial direction and having a plurality of dynamic pressure grooves arrayed in a circumferential direction and an annular smooth part positioned between the first and second regions. SOLUTION: Dynamic pressure grooves 5 are formed to be arrayed opposite to each other in two regions separated in an axial direction in a bearing surface 1a. The dynamic pressure grooves 5 of m1 and m2 in both regions are made discontinuous by being partitioned by a part region smooth part (n) of a bearing surface therebetween, and formed to be symmetrical to each other around the center line L of a bearing cross direction. The back part 6 and the smooth part (n) between the dynamic pressure grooves 5 are formed to be continuous. The outer surface of a shaft is supported to be floated on the bearing surface by circulating oil between the inner part of a bearing main body and the space of the bearing via the opening hole part of the bearing surface 1a containing the dynamic pressure grooves 5. Thus, shaft vibration is reduced irrespective of the size of an unbalance load, especially the increase of shaft vibration is small in a high rotational number region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing by providing a self-lubricating function by impregnating a lubricant such as lubricating oil or lubricating grease and forming a plurality of inclined grooves on the inner peripheral surface of a bearing. And a porous oil-impregnated bearing that supports the rotating shaft by the dynamic pressure action.
This porous oil-impregnated bearing is used especially for a bearing device requiring high speed and high rotational accuracy, such as a polygon mirror motor (LBP) for a laser beam printer and a spindle motor (HDD) for a magnetic disk drive, and a DVD-ROM. ROM
It is suitable for a bearing device or the like in which a large unbalanced load acts upon the mounting of a disk as described above and is driven at high speed.

[0002]

2. Description of the Related Art Porous oil-impregnated bearings are widely used as self-lubricating bearings. However, since they are a kind of perfect circular bearing, unstable vibration is likely to occur where the eccentricity of the shaft is small, and the rotational speed is reduced. There is a drawback that a so-called whirl that swings at half the speed is easily generated. As a countermeasure, a plurality of axially inclined dynamic pressure grooves called a henling bone type or a spiral type may be provided on the bearing surface.

Japanese Utility Model Publication No. Sho 63-19627 discloses an example in which a dynamic pressure groove is formed in a porous oil-impregnated bearing, and the shaft is supported by the dynamic pressure action to control unstable vibration.

In Japanese Utility Model Publication No. 63-19627, a bearing surface of a porous oil-impregnated bearing has a groove for generating a dynamic pressure formed by a surface blinding process.

[0005]

However, according to the structure described in the above publication, the groove is completely sealed, so that the circulation of oil, which is the most characteristic feature of the porous oil-impregnated bearing, is hindered. Therefore, the oil that has once oozed into the bearing clearance is pushed into the bent portion of the groove by the action of the dynamic pressure groove and stays there. At this time, since a large shearing action is acting in the bearing clearance, the oil remaining in the dynamic pressure groove is easily denatured by the shearing force and frictional heat, and the oil is apt to be oxidized and degraded due to a rise in temperature (normally). In porous oil-impregnated bearings (types without dynamic pressure grooves), impregnated oil constantly circulates in and through the bearing clearance as the shaft rotates. In other words, once heated, it is cooled inside the bearing, so it is less susceptible to oxidative degradation due to temperature rise.) Therefore, the life was short.

[0006] It is extremely difficult to seal the groove. In the above publication, it is described that the hole can be sealed by plastic working. However, the groove depth of the dynamic pressure groove is usually on the order of μm, and it is difficult to imagine that the opening on the surface is sealed by this degree of compression molding. . In addition, as another means of plastic working, coating etc. are mentioned, but the thickness of the coating film must be naturally thinner than the groove depth, and it is extremely difficult to apply a coating film of several μm only to the groove portion. It does not hold industrially.

In this type of bearing, as shown in FIG. 1, the dynamic pressure grooves (5) are continuous in the axial direction, but in this case, the shaft runout increases when an unbalanced load is applied.

Accordingly, the present invention provides: a: a structure in which impregnated oil circulates through the bearing clearance and the inside of the bearing so that the oil is unlikely to deteriorate as in a normal porous oil-impregnated bearing; In order to make it possible, a sufficient dynamic pressure effect is secured even in such a case while leaving an opening in both the back (the portion between the dynamic pressure grooves) and the groove, and c: when an unbalanced load is applied The purpose is to reduce shaft runout.

[0009]

In order to achieve the above object,
The porous oil-impregnated bearing according to the present invention, on the inner periphery of the porous body,
A bearing main body is formed by providing a bearing surface for supporting a shaft that rotates relatively to the porous body, and the bearing body is impregnated with lubricating oil or lubricating grease. A first region in which a plurality of dynamic pressure grooves inclined to one side are arranged in the circumferential direction, and a plurality of dynamic pressure grooves separated in the axial direction from the first region and inclined to the other side with respect to the axial direction. It has a second region arranged in the direction and an annular smooth portion located between the first region and the second region (claim 1).

[0010] With this structure, when relative rotation occurs between the shaft and the bearing body, the oil is collected in the smooth portion by the dynamic pressure grooves formed in opposite regions on both axial sides. The oil film pressure in this part increases.

Since the smooth portion has no dynamic pressure grooves, the bearing rigidity is higher than that of a conventional product in which the dynamic pressure grooves are continuous in the axial direction. Therefore, shaft runout can be suppressed to a small value.

It is possible to avoid non-uniformity of dynamic pressure generation due to variations in apertures. In this specification,
The term “open hole” refers to a portion where the pores of the porous body tissue are opened on the outer surface.

The above effects are obtained for the following reasons.

As shown in FIG. 1, a dynamic pressure groove (5: a herringbone type dynamic pressure groove is illustrated in the drawings) continuous with the inner diameter surface of a bearing body (1) generally formed of a cylindrical porous body.
Is provided, the oil flow in the axial cross section is as shown in FIG. That is, with the rotation of the shaft (2), the oil (O) exudes from both sides in the axial direction of the bearing body (1), and the exuded oil (O) is pushed into the center of the bearing to generate pressure (dynamic pressure). And this pressure supports the shaft (2).

However, when such a pressure is generated,
The oil returns to the inside of the bearing from the opening on the surface, so that the dynamic pressure effect is reduced. This tendency becomes more remarkable when unevenness is provided on the bearing surface as in the case of providing a dynamic pressure groove. For example, if there is a large hole in the middle of the dynamic pressure groove, the oil flows from that part back into the bearing, so that the dynamic pressure effect is greatly reduced.

In general, it is difficult to make the distribution of the openings on the bearing surface uniform, so that large and small holes are mixed on the bearing surface. Therefore, the degree of recirculation of the oil into the inside of the bearing becomes uneven at each part. In this case, it is difficult to form an oil film in a portion where oil easily escapes, and it is easy to form an oil film in a portion where oil does not easily escape. Therefore, as shown in FIG. 3 (a development view of the bearing surface in the circumferential direction is shown), the bearing surface (1a) The distribution of the oil film (S) becomes uneven in the axial direction. In this state, although a certain effect is achieved in suppressing unstable vibration (such as whirl), a sufficient dynamic pressure effect cannot be exerted.

In view of the above, the conventional example (Japanese Utility Model Publication No. 63-19627)
No.) proposes sealing of the groove, but as described above, sealing of the groove is extremely difficult industrially and is not feasible. The back portion (6) between the dynamic pressure grooves (5) serves as a support surface for supporting the shaft. However, since the cross-sectional shape of the bearing surface is uneven, the back portion (6) serving as the support surface is formed. The area becomes smaller and the bearing stiffness decreases.

On the other hand, as shown in FIG. 4, the product of the present invention has an annular smooth portion (n) between the first and second regions (m1) and (m2). In the smooth portion (n), the degree of opening is easily managed. In both regions (m1) and (m2), oil flow in the groove direction is dominant, but in the smooth portion (n), oil flow in the circumferential direction also exists. As the oil is replenished one after another, the dynamic pressure effect is far less reduced. FIG. 5 is a developed view of the bearing surface (1a) of the product of the present invention in the circumferential direction. As shown, oil film (S)
The difference between the wide part and the narrow part is reduced, and the oil film distribution becomes uniform, so that a stable dynamic pressure effect can be obtained. Further, not only the back part (6) between the dynamic pressure grooves (5) but also the smooth part (n)
Since the support surface also supports the shaft, the area of the support surface is increased, and the rigidity of the bearing can be increased.

The ratio r of the smooth portion (n) in the bearing width direction is, when the bearing width is 1, r = 0.1 to 0.6, preferably r = 0.2 to 0.4. It is good to set to the range. If the width is less than 0.1 with respect to the bearing width 1, the effect of providing the smooth portion (n) (increase in dynamic pressure, increase in bearing rigidity)
Does not appear remarkably, and r is set to 0.6 with respect to the bearing width 1.
If it is larger, the number of dynamic pressure grooves decreases, and the force for pushing the oil into the central portion in the axial direction becomes weak, so that the dynamic pressure effect cannot be effectively exhibited.

The surface porosity in the smooth portion (n) is preferably smaller than the surface porosity in the first and second regions (m1) and (m2).

Thus, the smooth portion (n) is formed by the dynamic pressure groove.
It is difficult for the oil collected at the surface to escape from the opening on the surface into the inside of the bearing, so that the generated pressure can be increased. Further, since the area of the support surface for supporting the shaft is sufficiently ensured, the rigidity of the bearing can be increased.

The surface porosity is determined in the first and second regions (m1).
(M2) is set in the range of 5 to 40%, preferably 10 to 30%, and the smooth portion (n) is set in the range of 2 to 30%, preferably 2 to 20%. . If the surface porosity in both areas is less than 5%, the amount of oil supplied from inside the bearing to the bearing clearance may decrease, resulting in insufficient oil and poor lubrication. If it exceeds 40%, the amount of oil escaping into the bearing And the oil is not supplied to the smooth portion, which may result in insufficient oil and poor lubrication. If the surface porosity of the smooth portion is less than 2%, the production becomes extremely difficult and the cost increases. If it exceeds 30%, the amount of oil escaping into the bearing increases and lubrication failure may occur. There is.

In the case of a dynamic pressure bearing, the shaft and the bearing momentarily come into contact with each other when starting and stopping. The contact portion at this time is a line contact near the bearing end. Therefore, as shown in FIG. 9, if both ends in the axial direction of the bearing surface (1a) are formed in a tapered surface shape whose inner diameter is enlarged toward the bearing end side (claim 3), the contact area increases and instantaneous In a non-contact state. The drawing shows a case where the entire first and second regions (m1) and (m2) are tapered, but only a part (bearing end side) of both regions (m1) and (m2) is tapered. It may be a surface. The bearing surface (1a) other than the tapered surface is formed parallel to the outer peripheral surface of the shaft.

In this case, from the smooth portion (n) to the bearing surface (1a)
The ratio of the increase Δc in the bearing inner diameter to the end of the shaft and the shaft diameter D is in the range of Δc / D = 1/3000 to 1/200, more preferably Δc / D = 1/3000 to 1/500. It is good to set in the range. When Δc / D is smaller than 1/3000, instantaneous contact cannot be prevented because the taper is too small. When Δc / D is larger than 1/200, the taper becomes excessively large and the dynamic pressure effect is reduced. Does not work effectively.

When two bearings (porous oil-impregnated bearings) are press-fitted into the housing, accuracy of the two bearings such as coaxiality and cylindricity becomes a problem. If the accuracy is poor, the shaft may come into line contact with the bearing, or in the worst case, the shaft may not pass through the two bearings.

In this case, as shown in FIG. 13, a bearing surface (1a) having the shape shown in FIGS. 4 and 9 is provided at two or more locations in the axial direction of the bearing body (1). Any bearing surface)
Should be provided. This bearing has a single bearing body (1) and a hydrodynamic bearing surface (1a) at a plurality of locations (two locations in the drawing) of the inner diameter surface. It is possible to avoid the above-mentioned adverse effects such as poor accuracy due to the arrangement.

In this case, if the precision of the sizing pin for transferring the dynamic pressure groove is finished well, the precision of the bearing is also improved. It is not so difficult to finish the sizing pin with required precision, for example, within a circularity of 1 μm or less and a cylindricity of 2 μm or less, and it can be easily achieved. Therefore, assembling can be performed easily, and the number of bearings is one, so that the bearing can be manufactured at low cost.

In order to stabilize the generation of the dynamic pressure, the dynamic pressure grooves (5) in the first and second regions (m1) and (m2) are formed in the axial middle part (L) of the bearing surface (1a). It is preferably formed symmetrically with respect to the center (see FIG. 4).

[0029]

FIG. 4 is a sectional view of a porous oil-impregnated bearing according to the present invention.

This porous oil-impregnated bearing uses a sintered alloy as an example of a porous material. For example, in a scanner motor of a laser beam printer as shown in FIG.
A rotating shaft (2) that rotates at high speed by an exciting force between the rotor (8) and the stator is rotatably supported on the housing (7). In this oil-impregnated bearing, a bearing hole (1b) through which a rotating shaft (2) is inserted is formed in a cylindrical bearing body (1) formed porous by a sintered alloy,
A plurality of axially inclined hydrodynamic grooves (5) are compression-molded on the inner surface of the bearing hole (1b), that is, the bearing surface (1a), and the bearing body (1) is further impregnated with lubricating oil or lubricating oil. Things. In the drawings, the herringbone type is illustrated as the dynamic pressure groove (5), but may be another shape inclined in the axial direction, for example, a spiral type.

The dynamic pressure groove (5) is formed in two regions (first region m1 and second region m1) of the bearing surface (1a), which are separated in the axial direction.
In 2), they are arranged in opposite directions. Both areas (m
1) The dynamic pressure groove (5) of (m2) is partitioned by a part of the bearing surface (smooth portion n) therebetween and is discontinuous, and is centered on the center line (L) in the bearing width direction. It is formed symmetrically.

The back portion (6) between the dynamic pressure grooves (5)
And the smooth portion (n) are formed continuously. In this embodiment, not only the smooth portion (n) and the back portion (6) but also the dynamic pressure groove (5) has an opening, and the dynamic pressure groove (5) is provided.
Oil is circulated between the inside of the bearing main body and the bearing clearance through an opening in the bearing surface (1a) including the above, so that the outer peripheral surface of the shaft is levitated and supported by the bearing surface.

In the compression molding of the dynamic pressure groove (5), a molded portion composed of irregularities inclined in the axial direction is formed on the outer peripheral surface of a core rod (for example, a sizing pin), and a porous material is supplied to the outer peripheral surface of the core rod. Then, a pressing force is applied to the porous material to press the inner diameter portion thereof to the core rod forming portion, and a dynamic pressure groove having a shape corresponding to the core rod forming portion is transferred to the inner diameter portion. After the formation of the dynamic pressure groove, the core rod is released from the inner diameter of the porous material by utilizing the springback of the porous material by removing the pressing force.

The above-described porous oil-impregnated bearing was incorporated into a small spindle motor as shown in FIG. 6, and the results of measuring the shaft runout are shown in FIGS. 7 and 8.

FIG. 7 shows a case where almost no unbalance load is applied (unbalance load: 50 mg · cm or less).
FIG. 8 shows the results when the unbalance load is large (unbalance load; 1 g · cm). This figure also shows the result of a perfect circular bearing without a groove for comparison. The bearing specifications other than the dynamic pressure groove specifications such as the dimensions of the perfect circular bearing and the bearing clearance are set the same as those of the bearing with the dynamic pressure groove. The specification of the test piece can be summarized as follows: Conventional example: Bearing with a continuous herringbone type dynamic pressure groove (Fig. 1)

[0036]

(Equation 1) Invention product 1; a bearing having a herringbone-type dynamic pressure groove having a smooth portion in the middle portion

[0037]

(Equation 2) Invention product 2: bearing having a herringbone-type dynamic pressure groove in which the surface porosity of the smooth portion is smaller than the regions on both sides thereof

[0038]

(Equation 3) It is.

In the conventional example, the shaft run-out is smaller than that of a perfect circular bearing, but the shaft run-out is larger than that of the product of the present invention, especially the unbalance load is large, and the shaft run-out is large in a high rotation speed region. The product of the present invention has a small shaft run-out irrespective of the magnitude of the unbalance load, and the increase of the shaft run-out especially in a high rotation speed region is small. Therefore, not only a model such as an LBP motor having a small unbalance load but also a DVD-R
Even in a model such as an OM motor in which a large unbalance load is applied due to the mounting of a disk, the product of the present invention can reduce the shaft runout.

Next, as shown in FIG. 9, a bearing (the product of the present invention) in which both ends in the axial direction of the bearing surface (1a) are formed in a tapered surface shape whose inner diameter is enlarged toward the bearing end, and FIG. FIG. 10 shows the results of measuring the frequency of metal contact at the time of startup from the oil film formation rate for each of the conventional products shown. The rotation speed of the shaft was 6000 rpm.

In the case of the conventional example (shown by), the frequency of contact with metal is high due to the low oil film formation rate at startup. This is due to the fact that the oil is not abundant in the bearing clearance immediately after the start, and the shaft contacts the edge at the bearing end due to the shaft oscillating (oscillating), thereby causing metal contact. On the other hand, in the product of the present invention (indicated by), no metal contact is seen immediately after the start, and an oil film is formed instantaneously. This is because the tapered shape at the bearing end prevents the shaft from hitting the edge of the bearing.

Note that there is an optimum range for the ratio between the groove depth of the dynamic pressure groove and the radius clearance, and outside this range, the dynamic pressure effect is significantly reduced. c / h = 0.5-5.0 (FIG. 11)
), It is possible to maintain high rotational accuracy without practical problems.

Further, the porous oil-impregnated bearing is usually used without lubrication, but the oil gradually depletes due to scattering and evaporation of the oil.
It is inevitable that it will be washed away. When the oil is consumed, the oil film forming range shrinks, which causes deterioration of rotation accuracy such as shaft runout. In particular, the shaft attitude is often used in a vertical type, and a laser beam printer motor used at a high speed of 10,000 revolutions per minute or more uses a centrifugal force as shown in FIG.
The oil in the bearing was easily washed away, and it was difficult to maintain performance such as oil film formation. In the case of LBP and HDD, it is fatal to break the oil film to maintain high accuracy. In the case where the porous bearing is used alone, especially when rotating at a high speed, the oil also entrains the surrounding air and circulates inside the bearing, so that air may be mixed into the bearing clearance. In order to prevent the air from being mixed, it is effective to arrange a refueling member in close contact with the bearing body and to replenish the oil from the refueling member if any voids are formed inside the bearing. Although disposing the bunkering member has the effect of extending the service life, it is effective in maintaining the oil film for constantly maintaining high accuracy. The bunkering member used in close contact with the bearing body may be a porous material such as metal or resin, or a well-known material in which oil is contained in a fibrous material such as felt. It is better to use a solid lubricating composition that keeps oozing out the oil encapsulated in the surface. For example, a solid material composed of lubricating oil or a mixture of lubricating grease and ultrahigh molecular weight polyolefin powder is preferable. This is low cost, rich in mass productivity, easy to handle, and easy to assemble. The solid lubricating composition keeps leaching out the oil contained therein at a temperature equal to or higher than room temperature, so that the oil can be continuously supplied to the bearing.

As described above, if the solid lubricating composition in which the oil constantly oozes out on the surface even in the stationary state is arranged so as to be in intimate contact with the surface of the bearing, even if the oil of the bearing may run off, the oil may flow out. Since the inside of the porous bearing is replenished by capillary action, a good oil film can be always formed. This solid lubricating composition can be manufactured in a very simple manner.

For example, a predetermined amount of lubricating grease or lubricating oil and a predetermined amount of ultra-high molecular weight polyolefin powder are uniformly mixed and poured into a mold having a predetermined shape. When grease is used, it can be obtained by dispersing and maintaining at a temperature below its drop point and cooling at room temperature. The ultrahigh molecular weight polyolefin powder may be a powder composed of polyethylene, polypropylene, polybutene or a copolymer thereof, or a mixed powder obtained by blending individual powders.The molecular weight of each powder is determined by an average molecular weight measured by a viscosity method. Is 1 ×
10 ⁶ a to 5 × 10 ^6. Polyolefins having such an average molecular weight range are superior in rigidity and oil retention to low molecular weight polyolefins, and hardly flow even when heated to a high temperature. The blending ratio of such an ultrahigh molecular weight polyolefin in the lubricating composition is 95 to 1% by weight.
And the amount depends on the desired degree of oil release, toughness and hardness of the composition. Therefore, the greater the amount of ultrahigh molecular weight polyolefin, the greater the hardness of the gel after being dispersed and maintained at a predetermined temperature.

The lubricating grease used in the present invention is:
There is no particular limitation, and as a lubricating grease added with soap or non-soap, lithium soap-diester, lithium soap-mineral oil, sodium soap-mineral oil, aluminum soap-mineral oil, lithium soap-diester mineral oil , Non-soap-diester type, non-soap-mineral oil type,
Greases such as non-soap-polyol ester type and lithium soap-polyol ester type are exemplified. Similarly,
The lubricating oil is also not particularly limited, and is a diester type,
Lubricating oils such as a mineral oil type, a diester mineral oil type, a polyol ester type and a poly-α-olephane type can be used.
The base oil or lubricating oil of the lubricating grease is desirably the same as the lubricating oil initially impregnated in the porous oil-impregnated bearing, but may be slightly different as long as the lubricating characteristics are not impaired.

The melting point of the above-mentioned ultrahigh molecular weight polyolefin varies depending on the average molecular weight, but is not constant. For example, the melting point of an average molecular weight of 2 × 10 ⁶ determined by a viscosity method is 136 ° C. As commercially available products having the same average molecular weight, Miteron (registered trademark) X manufactured by Mitsui Petrochemical Industries, Ltd.
M-220 and the like.

Therefore, in order to disperse and maintain the ultrahigh molecular weight polyolefin in the lubricating grease or lubricating oil, after mixing the above materials, the lubricating grease must be used at a temperature higher than the temperature at which the ultrahigh molecular weight polyolefin gels. If the temperature is below the drop point, e.g.
Heat to 200 ° C.

Such bearing devices include polygon mirror motors for laser beam printers, spindle motors for magnetic disk drives, DVD-ROM motors, electric products such as axial fans, ventilation fans and electric fans, and electrical components for automobiles. For example, it can be widely used for various kinds of motors, and the durability can be remarkably improved particularly by supporting the shaft with dynamic pressure.

[0050]

As is clear from the above description, in the porous oil-impregnated bearing of the present invention, since the smooth portion is provided between the dynamic pressure grooves inclined in the axial direction, the oil is smoothed by the dynamic pressure grooves on both sides. And the oil film pressure increases. Further, since there is no groove in the smooth portion, bearing rigidity is higher than in the case where the groove is continuous, and shaft runout can be reduced. Further, non-uniformity of dynamic pressure generation due to variations in apertures can be avoided.

When the surface porosity of the smooth portion is set smaller than the surface porosity of the first and second regions, the oil collected by the dynamic pressure grooves on both sides becomes difficult to escape from the smooth portion to the inside of the bearing. The generated pressure and bearing rigidity can be increased.

By providing tapered portions at both ends in the axial direction of the bearing surface, it is possible to prevent edge contact between the shaft and the bearing at the time of starting and stopping.

If the length of the bearing body is long and the hydrodynamic bearing surfaces are provided at two or more locations in the axial direction, it is possible to eliminate poor accuracy such as coaxiality and cylindricity.

[Brief description of the drawings]

FIG. 1 is an axial sectional view of a conventional porous oil-impregnated bearing.

FIG. 2 is an axial sectional view showing movement of oil in a conventional product.

FIG. 3 is a development view of a bearing surface of a conventional product in a circumferential direction.

FIG. 4 is an axial sectional view of the porous oil-impregnated bearing according to the present invention.

FIG. 5 is a developed view of a bearing surface in a circumferential direction in the product of the present invention.

FIG. 6 is an axial sectional view of a motor incorporating the bearing according to the present invention.

FIG. 7 is a diagram showing the results of comparative measurement of shaft runout of the product of the present invention and the conventional product (when the unbalance load is small).

FIG. 8 is a diagram showing the results of a comparative measurement of shaft runout of a product of the present invention and a conventional product (when the unbalance load is large).

FIG. 9 is an axial sectional view showing another embodiment of the present invention.

FIG. 10 is a diagram showing the results of comparative measurement of the oil film formation rate at the time of startup of the product of the present invention and the conventional product.

FIG. 11 is a radial sectional view of a porous oil-impregnated bearing.

FIG. 12 is an axial cross-sectional view showing a state of oil scattering of a porous oil-impregnated bearing.

FIG. 13 is an axial sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bearing main body 1a Bearing surface 2 Shaft 5 Dynamic pressure groove m1 1st area m2 2nd area n Smooth part

Claims (5)

[Claims] 1. A bearing body is provided on an inner periphery of a porous body for supporting a shaft which rotates relatively to the porous body to form a bearing body, and lubricating oil or lubricating grease is applied to the bearing body. In the impregnated bearing, the bearing surface is axially separated from the first region in which a plurality of dynamic pressure grooves inclined in one direction with respect to the axial direction are arranged in the circumferential direction. A porous oil-impregnated bearing having a second region in which a plurality of hydrodynamic grooves inclined in the other direction are arranged in the circumferential direction, and an annular smooth portion located between the first region and the second region. 2. The porous oil-impregnated bearing according to claim 1, wherein the surface porosity in the smooth portion is smaller than the surface porosity in the first and second regions. 3. The bearing surface according to claim 1, wherein both end portions in the axial direction of the bearing surface are formed in a tapered shape in which the inner diameter increases toward the bearing end.
Or the porous oil-impregnated bearing according to 2. 4. A porous oil-impregnated bearing having the bearing surface according to claim 1 at two or more locations in the axial direction of the bearing body. 5. The porous oil-impregnated bearing according to claim 1, wherein the dynamic pressure grooves in the first and second regions are formed symmetrically with respect to an axially intermediate portion of the bearing surface.