JP2008240910A - Oil-impregnated sintered bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain prevention of generation of noise and suppression of slide abrasion by improving sliding characteristics at slide starting especially under low temperature environment at slide starting of an oil-impregnated sintered bearing. <P>SOLUTION: At the inside of the oil-impregnated sintered bearing, a large number of pores 3 exist singly or in the state that the plurality of pores 3 are communicated with each other. A large number of pores 3 are impregnated with a lubricant, and on the surface of the pores 3, a covering film (oil-repellent cover film) 5 indicating oil-repellency relative to the lubricant to be impregnated is formed. The oil-repellent covering film 5 is formed not only on a surface of the pore 3 at a bearing central part but also on a surface of the pore 3 opened to the bearing surface. The oil-repellent covering film 5 is removed from the bearing surface for substantially sliding/supporting the shaft, and an outer surface of the sintered body containing Fe and Cu as main components constitutes the bearing surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sintered oil-impregnated bearing.

  In the sintered oil-impregnated bearing, an oil film is formed on a sliding portion with respect to the shaft by the seepage of the lubricating oil impregnated in the interior with relative rotation with the shaft to be supported, and the shaft is supported by this oil film. This type of bearing can be manufactured at a very low cost, and is superior in quietness when used compared to a ball bearing or the like. It is suitably used for a drive mechanism that affects operational comfort.

  By the way, when a sintered oil-impregnated bearing is used in the above-described application, the generation of abnormal noise during use, particularly the generation of abnormal noise (also referred to as squeal noise) in a low temperature environment becomes a problem. Sintered oil-impregnated bearings are those in which an oil film is formed on the sliding part of the shaft by the seepage of the lubricating oil impregnated inside as described above, and the shaft is supported by such an oil film. This is because the lubricating oil is easily drawn into the bearing due to the difference in coefficient of linear expansion from that of metal, and the formation of an oil film becomes insufficient.

As means for solving such a problem, for example, Japanese Patent Application Laid-Open No. 2003-120673 (Patent Document 1) discloses a composite structure in which Fe particles are dispersed in a Cu alloy phase, and in the Fe phase and the Cu alloy phase. By making the structure figure with pores in the inside, while setting the effective porosity as high as 20-30%, the air permeability is suppressed to 6-50 × 10 ⁻¹¹ cm ² , and excess oil due to sliding Sintered oil-impregnated bearings that suppress excessive bleeding have been proposed.

Japanese Patent Application Laid-Open No. 2004-138215 (Patent Document 2) provides an image of the inner peripheral surface of the bearing based on the knowledge that the pore shape of the sintered oil-impregnated bearing has a close relationship with the generation of squeal noise. As the equivalent circle diameter of the pores obtained by the analysis by the analyzer, the total area of the pores, which is 4 times or less the diameter clearance between the bearing inner diameter and the shaft to be supported, is 7% or less of the image area. A sintered oil-impregnated bearing characterized by this is proposed.
JP 2003-120664 A JP 2004-138215 A

  However, in the sintered oil-impregnated bearing described in Patent Document 1, the ratio of the Cu alloy exposed on the sliding surface is increased in order to improve the conformability, and the sliding contact between the shaft and the bearing is assumed. In addition, the shape of the hole on the sliding surface is adjusted with the aim of keeping the air permeability of the bearing low while retaining as much lubricant as possible. Is hard to say. As pointed out in Patent Document 2, when a low temperature is used, the presence of a small amount of lubricating oil on the bearing sliding surface causes a rapid decrease in the coefficient of friction, and on the contrary, it becomes a hotbed that generates abnormal noise. Because there is a fear.

  The sintered oil-impregnated bearing described in Patent Document 2 is an improvement of this point, and the size and ratio of the pores opened on the sliding surface so as not to leave as much lubricating oil as possible in the gap between the bearing and the shaft. Is stipulated. However, since the lubricating oil on the sliding surface is reduced in order to avoid the generation of squeal noise, the shaft and the bearing slide in a state close to no lubrication at low temperatures. In this case, sliding wear is unavoidable, and repeated use may lead to a decrease in bearing performance and a decrease in bearing life.

  In view of the above circumstances, the present invention improves the sliding characteristics at the start of sliding of a sintered oil-impregnated bearing, particularly at the start of sliding in a low temperature environment, thereby preventing abnormal noise and reducing sliding wear. It is a technical issue to suppress it.

  In order to solve the above problems, the present invention is obtained by compacting and sintering a raw material powder, and has a bearing surface for supporting a mating member while having a large number of pores therein, A sintered oil-impregnated bearing in which internal pores are impregnated with a lubricating oil, wherein an oil-repellent coating that exhibits oil repellency to the lubricating oil is formed on the surface constituting the internal pores. Provide bearings.

  As described above, the present invention is technically characterized by suppressing the pulling action of the lubricating oil into the interior by performing the surface modification of the internal pores serving as the holding portion of the lubricating oil. Is obtained based on the knowledge of the present inventor described below.

  That is, the large number of pores in the sintered oil-impregnated bearing main body have various sizes and are intricately connected. Therefore, in order for the lubricating oil to flow through the pores, it is necessary that the wettability with respect to the pore surface is good. The present inventor paid attention to the particularity of the lubricating oil retaining structure, and modified the surface properties of the internal pores that should retain the lubricating oil so as to exhibit oil repellency with respect to the lubricating oil used. The wettability of the oil to the pore surface was intentionally reduced to suppress the flow of the lubricating oil generated along the pore surface.

  Specifically, by forming an oil-repellent film that exhibits oil repellency to the lubricating oil on the surface of the internal pores of the sintered oil-impregnated bearing body, the lubricating oil impregnated in the pores is elastic against the pore surface. Therefore, the movement of the lubricating oil between the internal pores through the relatively small-diameter pores is suppressed. For this reason, for example, when the lubricating oil tends to shrink toward the center as the temperature decreases, the shrinkage of the lubricating oil is hindered by the pores imparted with oil repellency, and the lubricating oil is drawn into the bearing deep portion (center portion). Can be prevented. As a result, a considerable amount of lubricating oil can be left on the bearing surface, or even when there is no lubricating oil on the bearing surface, the lubricating oil in the surface layer portion immediately below the bearing surface oozes out early, and an oil film is formed. be able to. Therefore, an oil film can be formed at the start of sliding even at low temperatures, so that abnormal noise can be prevented and wear can be suppressed.

  In this case, the bearing surface is preferably formed of a sintered material powder. As described above, the oil-repellent film exhibits oil repellency with respect to the lubricating oil, and therefore, if the oil-repellent film is formed on the bearing surface, the formation of the lubricating oil film may be hindered. Accordingly, it is preferable to form an oil-repellent coating on the surface of the internal pores but not to form an oil-repellent coating on the bearing surface.

  Thus, when considering that the bearing surface is composed of a sintered body without being covered with an oil-repellent coating, the raw material powder constituting the sintered body includes Fe or Fe-based alloy powder, Cu or Those containing one or both of Cu-based alloys as main components are preferred. Fe or Fe-based alloy with excellent wear resistance, or Cu or Cu-based alloy component with excellent conformability during sliding is exposed on the outer surface of the sintered body constituting the bearing surface. While forming an oil film, solid sliding lubrication can be ensured. In particular, if consideration is given in combination with formability and sinterability, it is preferable to set the mixing ratio of the Cu powder or the Cu-based alloy powder relatively high, for example, 45 wt% or more and 80 wt% or less.

  As the lubricating oil to be impregnated, PAO-based lubricating oil, ester-based lubricating oil, or the like can be suitably used from the viewpoint of lubricating characteristics and fluidity in a low temperature environment. In this case, it is preferable that the oil-repellent coating is formed of a fluorine-based material having oil repellency with respect to these PAO-based lubricants and ester-based lubricants. In addition, an oil-repellent coating formed of a fluorine-based material has high sliding characteristics as well as oil repellency. Therefore, even if the entire bearing surface or a part of the bearing surface is covered with the oil-repellent coating, It can be used without considering the decrease in mobility.

  The sintered oil-impregnated bearing provided with the oil-repellent coating film having the above-described configuration is, for example, an electric motor for automobiles that incorporates the sintered oil-impregnated bearing and is expected to be used in a low temperature environment, or a motor for other applications. Can be suitably provided.

  From the above, according to the present invention, by improving the sliding characteristics at the start of sliding of the sintered oil-impregnated bearing, particularly at the start of sliding in a low temperature environment, the generation of abnormal noise and the suppression of sliding wear are achieved. Can be planned.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a cross-sectional view of a sintered oil-impregnated bearing 1 according to an embodiment of the present invention. The sintered oil-impregnated bearing 1 in the figure has a cylindrical shape and is formed of sintered metal. Further, the sintered oil-impregnated bearing 1 has a large number of pores 3 therein, and the large number of pores 3 are impregnated with lubricating oil. On the inner periphery of the sintered oil-impregnated bearing 1, a bearing surface 4 that slides with the outer peripheral surface of the shaft 2 to be supported (one-dot chain line in the figure) is provided. A large number of pores 3 are formed in the bearing surface 4 (surface openings 6 to be described later with reference to FIG. 3), and the surface of the bearing surface 4 that faces the outer peripheral surface of the shaft 2 is opened as the shaft 2 rotates relatively. Lubricating oil retained in the pores 3 inside the bearing is oozed out through the holes 6.

  FIG. 2 is an enlarged cross-sectional view of the area A in FIG. 1, that is, the central portion of the sintered oil-impregnated bearing 1. As shown in the figure, inside the sintered oil-impregnated bearing 1, a large number of pores 3 are present in a single state or in a state of being connected to a plurality. On the surface (inner surface) constituting these numerous pores 3, a film (oil-repellent film) 5 showing oil repellency to the lubricating oil impregnated in the sintered oil-impregnated bearing 1 is formed.

  The oil-repellent coating 5 is formed not only on the surface of the pore 3 at the center of the bearing, but also on the surface of the pore 3 (surface opening 6) that opens on the bearing surface 4 as shown in FIG. Yes. In this embodiment, the oil-repellent coating 5 is removed from the bearing surface 4 that substantially supports the shaft 2 to slide, and the outer surface of the sintered body mainly composed of Fe and Cu, for example, is exposed. It has become.

  The sintered oil-impregnated bearing 1 having the above-described configuration includes, for example, a step (a) of compacting a raw material powder, a step (b) of sintering a compacted body, a step (c) of sizing the sintered body, and sintering. It is manufactured through a step (d) of forming an oil-repellent film on the surface of the internal pores of the body and a step (e) of impregnating the lubricating oil. Hereinafter, each process will be described in detail.

(A) Powder compacting process First, the metal powder used as a raw material is filled in a molding die, and a compact compact having a shape close to that of a finished product is obtained by compression molding. As the raw material powder, for example, a mixture of Fe powder and Cu powder to the same extent is used, but only one of the metal powders can be used as the raw material powder. Of course, metal powders other than Fe and Cu (including Fe-based alloy powders and Cu-based alloy powders) can be used as raw materials, and a mixture of these multiple types of metal powders can also be used as raw materials. In addition, with the aim of acting as a binder between the metal powders as the main component, a low melting point metal such as Sn powder is added, and graphite or MoS ₂ , for the purpose of improving the slidability at the time of molding or use, It is also possible to add a powdery solid lubricant such as MnS or zinc stearate.

(B) Sintering process The compacting body obtained at the said process (a) is sintered by heating to the sintering temperature of the metal powder used as a main component, and a sintered compact is obtained. Depending on the type of metal powder used, the sintering operation can be performed in a non-carburizing atmosphere in order to avoid the carburizing action due to sintering.

(C) Sizing step By applying a pressing force to the sintered body obtained in the step (b) using an appropriate mold, the sintered body is shaped into a predetermined shape, and the dimensions thereof are predetermined. Finish within range.

(D) Oil-repellent film formation process An oil-repellent film is formed with respect to the sintered compact finished in the shape of a finished product (shape shown in Drawing 1) through the above-mentioned process (a)-(c). Specifically, in a reduced pressure environment, the sintered body is immersed for a certain time in a solvent in which a material exhibiting oil repellency is mixed with the lubricating oil to be used. Thereafter, by removing the solvent, an oil-repellent film 5 made of an oil-repellent material is formed on the surface of the pores 3 that are continuous with the surface openings 6 among the many pores 3 (see FIG. 2). . As a material exhibiting oil repellency, although it depends on the type of lubricating oil, for example, a fluorine-based material such as PTFE is preferably used.

  Further, as described above, when the sintered body is immersed in the oil repellent solution to form the oil repellent coating 5, not only the surface of the pores 3 inside the bearing but also the bearing surface 4 and the surface opening on the bearing surface 4 are opened. The oil repellent coating 5 is formed on all outer surfaces of the sintered body including the holes 6. Among these, the oil-repellent coating 5 formed on the bearing surface 4 is subjected to, for example, an appropriate familiar operation after the product shown in FIG. 1 is completed through a lubricating oil impregnation step (e) described later, It can be peeled off. Alternatively, by performing the sizing step (c) after the step (d), the oil-repellent coating on the bearing surface 4 can be peeled and removed by the pressing force or rotational force of the sizing pin.

(E) Lubricating oil impregnation step Lubricating oil is impregnated into the sintered body obtained in the step (d). Specifically, as in the step (d), the pores 3 in the bearing are impregnated with the lubricating oil by immersing the sintered body in a lubricating oil bath filled with the lubricating oil for a certain period of time in a reduced pressure environment. . As the lubricating oil to be used, PAO-based lubricating oils and ester-based lubricating oils having excellent lubricating characteristics and viscous resistance at low temperatures can be used. At this time, in order to impregnate the pores 3 of the lubricating oil reliably and in a short time, the impregnation operation may be performed while the lubricating oil is heated.

  And after an impregnation operation | work, an oil removal operation | work is performed using a suitable oil removal apparatus. Thereby, only the excess lubricating oil adhering to the surface is removed while leaving the lubricating oil impregnated in the pores 3 inside the bearing.

  In the sintered oil-impregnated bearing 1 having the above-described configuration, the lubricating oil retained in the numerous pores 3 oozes out onto the bearing surface 4 through the surface openings 6 as the shaft 2 rotates relatively. As a result, a lubricating oil film is formed between the shaft 2 and the sintered oil-impregnated bearing 1, and the shaft 2 is rotatably supported via the lubricating oil film.

  Further, in a low temperature environment, the lubricating oil impregnated in a large number of pores 3 tends to shrink toward the inside (center portion) of the sintered oil-impregnated bearing 1 due to the difference in linear expansion coefficient. An oil repellent coating 5 is formed on the surface. Therefore, the shrinkage of the lubricating oil is inhibited by the pores 3 having an oil repellent effect, particularly the pores 3 having a smaller diameter than the other pores 3, and the lubricating oil is drawn as far as possible into the bearing deep portion (center portion). Can be prevented. Therefore, an oil film is quickly obtained by leaving a considerable amount of lubricating oil on the bearing surface 4 or by leaving the lubricating oil in the pores 3 in the surface layer portion immediately below the bearing surface 4 even when there is no lubricating oil on the bearing surface 4. Therefore, the generation of abnormal noise can be avoided as much as possible, and the wear can be suppressed.

  In this embodiment, the oil repellent coating 5 is not formed on the bearing surface 4, and the Fe or Cu component constituting the sintered body is exposed on the bearing surface 4. By adopting such a configuration, it is possible to form an oil film of the lubricating oil that has oozed out on the bearing surface 4 and to realize good sliding lubrication. In addition, by forming the bearing surface with a sintered body made of Fe or Cu component, it is possible to form a good oil film and ensure solid sliding lubrication. Of course, as in this embodiment, if the oil-repellent coating 5 is formed of a fluorine-based material having relatively excellent sliding properties, the oil-repellent coating 5 can ensure sliding lubrication with the shaft 2. Therefore, the oil-repellent coating 5 does not necessarily have to be removed.

  The oil-repellent coating 5 only needs to be formed at least on the surfaces of the pores 3 inside the bearing, and so high adhesion to the bearing body (sintered body) is not required. Rather, if the oil-repellent coating 5 is once formed on the bearing surface 4 and then the oil-repellent coating 5 is removed as in this embodiment, it is preferable that the adhesion is small.

  Moreover, the thickness of the oil-repellent coating 5 should just be a grade which can express the oil repellency with respect to lubricating oil (a grade which repels lubricating oil). If the oil-repellent coating 5 is too thick, the pores 3 will be reduced, resulting in an increase in the pulling force (capillary force) acting toward the inside of the bearing. Therefore, it is important to set an appropriate thickness in consideration of this point. It is.

  In this embodiment, since the oil-repellent coating 5 is formed after the sintering step (b), the coating material is not lost by heating to the sintering temperature. Therefore, a relatively inexpensive general-purpose product can be used as the oil-repellent coating material, and the burden on the manufacturing cost can be kept small.

  In this embodiment, since the sintered body in a decompressed state is impregnated with the lubricating oil, even after the oil-repellent coating 5 is formed on the surface of the pores 3, the pulling force due to the pressure difference Thus, the pores 3 can be reliably filled with the lubricating oil. Of course, as described above, it is even better if the impregnation is performed while the viscosity of the lubricating oil is lowered by heating.

  Moreover, in the said embodiment, although the oil-repellent film 5 was formed after the sizing process (c), after forming the oil-repellent film 5, it is also possible to give sizing. If, for example, a solution in which a fluorine-based material or the like is dissolved is impregnated before sizing, the solution can be impregnated at a stage where a relatively large diameter and many surface openings 6 remain. Therefore, such impregnation work can be performed easily and in a short time.

  The sintered oil-impregnated bearing 1 according to the above description can be suitably used, for example, for an electric motor of an automobile, particularly when used in a low temperature environment of −30 ° C. or lower. Of course, it can be suitably used for other applications as well as applications used in a low temperature environment.

  An embodiment of the present invention will be described below. Specifically, the details when the present invention is applied to the servo motor bearing (inner diameter φ2 mm) having the shape illustrated in FIG. 1 will be described.

(1) Powder mixing First, the raw material powder which has Fe powder and Cu powder as a main component is prepared. Specifically, for all mixed powders,
a-1) 25-30% of reduced Fe powder under 100 mesh sieve,
a-2) 10-15% of reduced Fe powder under 300 mesh sieve,
b-1) 38 to 43% of electrolytic Cu powder under 100 mesh sieve
b-2) Sprayed Cu powder under 200 mesh sieve is 15-20%,
c) 1-2% sprayed Sn powder under 350 mesh sieve,
d) 0.5 to 1.0% of natural graphite powder,
e) Zinc stearate 0.3-1.0%
The mixture of the materials a) to e) described above is put into a V-type mixer and mixed for a predetermined time (0.5 hour to 1 hour) to obtain a raw material powder.
(2) Powder compacting The raw material powder (mixed powder) obtained in the above step (1) is filled in a mold and compressed from the vertical direction (along the axial direction of the finished product). Get. Under the present circumstances, it adjusts so that the density of a compacting body may be settled in the range of 6.0-6.6 g / cm < ³ >.
(3) Sintering The green compact obtained in the above step (2) is put into a mesh belt type continuous furnace, heated for a predetermined time (850 ° C. to 900 ° C.), and then cooled to obtain a sintered body. At this time, the sintering operation is performed under a reducing atmosphere (RX gas atmosphere).
(4) Sizing The sintered body obtained in the above step (3) is supplied into a mold and pressed from above and below to be shaped into a predetermined shape and finish its dimensions within an allowable range.
(5) Fluorine coating The sintered body obtained in the step (4) is immersed in a mixed solution in which 1 to 10% of PTFE and fluorine oil are dispersed in a fluorinated solvent. At this time, the ambient atmosphere is depressurized to 10 ⁻¹ Torr. After maintaining in this state for 30 minutes, the pressure is returned to normal pressure, and the object to be treated (sintered body) is taken out from the mixed solution. Thereafter, the sintered body is dried in a thermostatic bath at 50 ° C. for 1 hour. As a result, the fluorinated solvent evaporates, and a thin film (oil-repellent coating) made of PTFE and fluorine oil is formed on the surface and internal pores of the sintered body.
(6) Oil impregnation The sintered body obtained in the above step (5) is immersed in a lubricating oil bath heated to 70 ° C., and the ambient atmosphere is reduced to 10 ⁻¹ Torr. After holding for 1 hour, the pressure is returned to normal pressure, and the sintered body after oil impregnation is taken out from the lubricating oil bath. It is common to use PAO-based or ester-based lubricant having a viscosity at 40 ° C. of 61.2 to 74.8 mm ² / s as the lubricating oil, and this time, All Time J652 manufactured by NOK Corporation is used.

  The sintered oil-impregnated bearing obtained through the above steps (1) to (6) has a surface opening having an area ratio of 15 to 35% and an opening diameter of 100 μm or less on the inner peripheral surface serving as a bearing surface.

It is a longitudinal cross-sectional view of the sintered oil-impregnated bearing which concerns on one Embodiment of this invention. FIG. 2 is an enlarged cross-sectional view of a region A in FIG. 1 for explaining a structure of internal holes of a sintered oil-impregnated bearing. FIG. 2 is an enlarged cross-sectional view of a region B in FIG. 1 for explaining the structure of the periphery of the bearing surface of the sintered oil-impregnated bearing.

Explanation of symbols

1 Sintered oil-impregnated bearing 2 Shaft 3 Pore 4 Bearing surface 5 Oil repellent coating 6 Surface opening

Claims (6)

It is obtained by compacting and sintering the raw material powder. It has a large number of pores inside and a bearing surface for supporting the mating member, and the internal pores are impregnated with lubricating oil. In the sintered oil impregnated bearing
A sintered oil-impregnated bearing, wherein an oil-repellent coating film that exhibits oil repellency to the lubricating oil is formed on a surface that constitutes the internal pores.   The sintered oil-impregnated bearing according to claim 1, wherein the bearing surface is formed of a sintered body of the raw material powder.   The sintered oil-impregnated bearing according to claim 1, wherein the raw material powder contains one or both of Fe or Fe-based alloy powder and Cu or Cu-based alloy powder as a main component.   The sintered oil-impregnated bearing according to claim 1, wherein the oil-repellent coating is formed of a fluorine-based material.   The sintered oil-impregnated bearing according to claim 1, wherein the lubricating oil is a PAO-based or ester-based lubricating oil.   A motor comprising the sintered oil-impregnated bearing according to any one of claims 1 to 5.

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