Patent Application
20060093246
The present invention relates to a slide bearing assembly and a slide bearing, more particularly to a slide bearing assembly and a slide bearing, which can ensure sliding operation for a longer period in an oilless self-lubricating state even under a situation of sliding at a very low speed or angular motion in a very small stroke.
In an excavator used as a construction machine or the like, to operate a driving mechanism, members constituting the driving mechanism are coupled to each other in a relatively rotatable or angularly movable manner and are driven by cylinders or other actuators. In a working device of a hydraulic excavator, for example, an arm is coupled to a fore end of a boom and a bucket is coupled to a fore end of the arm. During excavation, an arm cylinder and a bucket cylinder are driven to rotate or angularly move the arm about a joint between the arm and the boom and the bucket about a joint between the bucket and the arm, respectively, thereby excavating earth and sand, etc. Those joints are each constituted by a slide bearing assembly comprising a shaft and a bushing.
In one known slide bearing assembly, a porous bushing made of an iron-based sintered alloy is impregnated with a lubricant (see, e.g., Patent Reference 1). In the known slide bearing assembly, when a shaft and the bushing slide relative to each other, the lubricant impregnated in the bushing seeps out to a sliding interface with generation of frictional heat to form a thin lubricant film. Therefore, grease is no longer required to be kept interposed between the shaft and the bushing. Also, because fluidity of the lubricant impregnated in the bushing is very low, the lubricant is avoided from spilling out. As a result, the slide bearing assembly can ensure the sliding operation for a comparatively long period in an oilless self-lubricating state even under a situation of sliding at a very low speed or angular motion in a very small stroke.
Patent Reference 1: Japanese Patent No. 2832800
However, the related art described above has the following problem.
In the related art, the lubricant impregnated in the bushing is caused to seep out with the frictional heat generated by the relative sliding of the shaft and the bushing. Accordingly, for example, when the shaft and the bushing slide just several millimeters, i.e., angularly move in a very small stroke, or slide at a very low speed relative to each other, the lubricating effect cannot be developed at a sufficient level. This may raise local surface pressure and cause local abrasion or damage, such as scratching, in the surface of the shaft or the inner circumference surface of the bushing with accompanying abnormal noise.
The present invention has been made in view of the above-described problem with the related art, and an object of the present invention is to provide a slide bearing assembly and a slide bearing, which can ensure sliding operation for a longer period in an oilless self-lubricating state even under a situation of sliding at a very low speed or angular motion in a very small stroke.
(1) To achieve the above object, the present invention provides a slide bearing assembly comprising at least a shaft and a bushing, the bushing being made of a porous sintered material having a large number of pores, wherein the bushing is impregnated with a lubricant containing 2.0 to 30 wt % of solid lubricating fine particles made of at least one selected from among MoS2, WS2, and hexagonal BN, and wherein the shaft and the bushing are used at surface pressure not lower than 6 Kgf/mm2 and sliding speed in the range of 2 to 5 cm/sec.
In the present invention, when the shaft and the bushing slide relative to each other, the lubricant impregnated in the pores of the bushing is caused to seep out onto the inner circumferential surface of the bushing with generated frictional heat, thereby forming a thin lubricant film. At this time, the solid lubricating fine particles contained in the lubricant are also caused to move onto the inner circumferential surface of the bushing. Thus, the solid lubricating fine particles come into a sliding interface between the bushing and the shaft together with the lubricant, and fine layers constituting the solid lubricating fine particles slide in the layer lying direction so as to develop a superior lubricating effect. When the relative sliding of the shaft and the bushing is stopped, the lubricant forming the thin lubricant film in the sliding interface is drawn back into the large number of pores of the bushing 16 based on the capillary phenomenon together with the solid lubricating fine particles. Because the fluidity of the lubricant impregnated in the pores is very low, the spilling-out loss of the lubricant and the solid lubricating fine particles is very small even when the shaft and the bushing repeat the sliding. As a result, the lubricant containing the solid lubricating fine particles can be supplied with stability for a long period.
With the slide bearing assembly constituted as the above-mentioned structure of the related art, as a comparative example, in which the lubricant does not contain the solid lubricating fine particles, when the shaft and the bushing slide just several millimeters, i.e., angularly move in a very small stroke, or slide at a very low speed relative to each other, the lubricating effect cannot be developed at a sufficient level because the amount of generated frictional heat is insufficient. This may raise local surface pressure and cause local abrasion or damage, such as “scratching”, in the surface of the shaft or the inner circumferential surface of the bushing with accompanying abnormal noise.
In contrast, with the slide bearing assembly of the present invention, superior tribological characteristics are obtained with the lubricating effect of the solid lubricating fine particles contained in the lubricant. Further, by setting the content of the solid lubricating fine particles to fall in the range of 2.0 to 30 wt %, a superior effect of improving the load withstand characteristic can be obtained. Consequently, even under a situation of sliding at a very low speed or angular motion in a very small stroke, it is possible to not only suppress local abrasion or damage of the surface of the shaft and the inner circumferential surface of the bushing caused by scratching, etc. and accompanying abnormal noise, but also to prolong the period during which the sliding operation can be continued in the oilless self-lubricating state.
(2) To achieve the above object, the present invention also provides a slide bearing assembly comprising at least a shaft and a bushing, the bushing being made of a porous sintered material having a large number of pores, wherein the bushing is impregnated with a lubricant containing 3.0 to 5.0 wt % of solid lubricating fine particles made of graphite, and wherein the shaft and the bushing are used at surface pressure not lower than 6 Kgf/mm2 and sliding speed in the range of 2 to 5 cm/sec.
(3) In above (1) or (2), preferably, viscosity of the lubricant containing the solid lubricating fine particles is in the range of 56 to 1500 cSt (at 25.5° C.).
Generally, if the lubricant viscosity exceeds 1500 cSt, the fluidity of the lubricant is reduced and a capillary phenomenon acting to return the lubricant into the pores of the bushing is less likely to occur. This results in a difficulty in making the porous sintered alloy (i.e., the bushing) impregnated with the lubricant.
According to the present invention, since the viscosity of the lubricant containing the solid lubricating fine particles is in the range not exceeding 1500 cSt, the above-mentioned trouble can be avoided and a stable sliding characteristic can be maintained for a long term.
(4) In above (1) or (2), preferably, the bushing is made of a composite sintered alloy with a porosity of 5 to 30 vol %, the large number of pores are communicated with one another, and the bushing is subjected to surface modification treatment using at least one selected from among carburizing, nitriding, and sulphurize-nitriding.
By forming, e.g., a carburized layer with a thickness of about 1 mm to 3 mm (preferably 2 mm) on a sliding surface of the bushing relative to the shaft with the surface modification treatment, the wear-resistance characteristic of the bushing can be improved.
(5) In above (1) or (2), preferably, the solid lubricating fine particles have sizes being small enough to prevent clogging of the pores of the bushing.
(6) In above (1) or (2), preferably, the shaft is subjected to surface modification treatment by performing at least one kind of treatment selected from among carburizing, induction hardening, laser hardening and nitriding, and then chemical conversion or sulfurizing treatment.
The wear-resistance characteristic of the shaft can be improved with the surface modification treatment. In addition, by performing the surface modification treatment using an extreme-pressure additive such as Zn (zinc), Mn (manganese) or S (sulfur) through a step of carburizing, induction hardening, laser hardening or nitriding, and then a step of chemical conversion or sulfurizing treatment on the shaft surface, “wetting” with respect to the lubricant impregnated in the bushing is improved, whereby the lubricating effect and tribological characteristics can be further improved.
(7) To achieve the above object, the present invention further provides a slide bearing made of a porous sintered material having a large number of pores and impregnated with a lubricant containing 2.0 to 30 wt % of solid lubricating fine particles made of at least one selected from among MoS2, WS2, and hexagonal BN, the bearing being used at surface pressure not lower than 6 Kgf/mm2 and sliding speed in the range of 2 to 5 cm/sec.
(8) To achieve the above object, the present invention still further provides a slide bearing made of a porous sintered material having a large number of pores and impregnated with a lubricant containing 3.0 to 5.0 wt % of solid lubricating fine particles made of graphite, the bearing being used at surface pressure not lower than 6 Kgf/mm2 and sliding speed in the range of 2 to 5 cm/sec.
(9) In above (7) or (8), preferably, viscosity of the lubricant containing the solid lubricating fine particles is in the range of 56 cSt to 1500 cSt (at 25.5° C.).
(10) In above (7) or (8), preferably, the bearing is made of a composite sintered alloy with a porosity of 5 to 30 vol %, the large number of pores are communicated with one another, and the bearing is subjected to surface modification treatment using at least one selected from among carburizing, nitriding, and sulphurize-nitriding.
(11) In above (7) or (8), preferably, the solid lubricating fine particles have sizes being small enough to prevent clogging of the pores.
(12) In above (7) or (8), preferably, the bearing is used in combination with a shaft subjected to surface modification treatment by performing at least one kind of treatment selected from among carburizing, induction hardening, laser hardening and nitriding, and then chemical conversion or sulfurizing treatment.
(13) In above (7) or (8), preferably, the bearing is used as a bearing for a front component of an excavator.
(14) In above (7) or (8), preferably, the bearing is used as a bearing for an arm of a crane.
Embodiments of a slide bearing assembly and a slide bearing of the present invention will be described below with reference to the drawings.
First, one embodiment of the slide bearing assembly and the slide bearing of the present invention will be described below with reference to
In
Further, numeral 6 denotes a boom coupled to the swing body 2 in a vertically rotatable manner, and 7 denotes a boom hydraulic cylinder for driving the boom 6. Numeral 8 denotes an arm rotatably coupled to a fore end of the boom 6, and 9 denotes an arm hydraulic cylinder for driving the arm 8. Numeral 10 denotes a bucket rotatably coupled to a fore end of the arm 8, and 11 denotes a bucket hydraulic cylinder for driving the bucket 10. The working device 5 is constituted by the boom 6, the arm 8, the bucket 10, and the hydraulic cylinders 7, 9 and 11.
Every mutually articulated two among the boom 6, the arm 8, the bucket 10, and the hydraulic cylinders 7, 9 and 11, i.e., among the components of the working device 5, are coupled by a slide bearing assembly 12 in a relatively rotatable or angularly movable manner. Although slide bearing assemblies actually used in the working device 5 differ in size, shape, etc. from one another depending on the locations where the assemblies are installed, it is here assumed that the slide bearing assemblies used in the working device 5 are all the same and collectively called the slide bearing assembly 12.
In
The bushing 16 is made of a porous composite sintered alloy formed using copper powder and iron powder, for example, and has a large number of pores 25 (see
In this embodiment, the lubricant 24 having viscosity of, e.g., 460 cSt (at 25.5° C.) is impregnated in the bushing 16. The viscosity of the lubricant to be impregnated (more exactly speaking, the viscosity of the lubricant in the state containing the later-described solid lubricating fine particles) is preferably in the range of 56 to 1500 cSt (at 25.5° C.). The reason is as follows. If the viscosity exceeds 1500 cSt, the fluidity of the lubricant is reduced, thus resulting in a possibility that a capillary phenomenon acting to return the lubricant having seeped out onto the sliding surface with generated frictional heat into the pores of the bushing 16 again is less likely to occur and a stable sliding characteristic cannot be maintained for a long term. As the lubricant 24, any kind of commercially available lubricants, such as mineral oil or synthetic oil, can be used and the composition of the lubricant is not limited to particular one so long as the viscosity falls in the range mentioned above. However, grease is not adapted for use because it contains fibers and cannot be impregnated in the bushing 16.
In this embodiment, the lubricant 24 impregnated in the bushing 16 contains, e.g., 20% of the solid lubricating fine particles 26 (see
As shown in
On the other hand,
As shown in
For the reason mentioned above, the content of MoS2 in the lubricant 24 is preferably in the range of 2.0 to 30 wt %. The particle size of the solid lubricating fine particles (made of MoS2, WS2, and hexagonal BN) 26 contained in the lubricant 24 is sufficiently small (e.g., about 0.1 μm-100 μm) to such an extent that the fine particles are able to smoothly seep out onto the sliding surface from the pores 25 of the bushing 16 and to withdraw from the sliding surface into the pores 25 without clogging the pores 25.
The lubricant 24 containing the solid lubricating fine particles 26 is usually impregnated in the bushing 16 in a manner described below.
First, the solid lubricating fine particles 26 and the lubricant 24 are mixed and stirred sufficiently, thus causing the solid lubricating fine particles 26 to be homogeneously dispersed in the lubricant 24. Thereafter, the mixture is heated to reduce the viscosity of the lubricant 24 such that the lubricant 24 is liquefied. The bushing 16 is then immersed in the lubricant 24 containing the solid lubricating fine particles 26 and is left to stand in a vacuum atmosphere.
In that state, air in the pores 25 of the bushing 16 is drawn out and the lubricant 24 containing the solid lubricating fine particles 26 is drawn into the pores 25 instead. After the lubricant 24 has been impregnated into the pores 25 in such a way, the bushing 16 is taken out into air and is left to stand for cooling to the room temperature. The lubricant 24 containing the solid lubricating fine particles 26 restores the viscosity to its original value and hence loses fluidity in the pores 25 of the bushing 16. As a result, the lubricant 24 containing the solid lubricating fine particles 26 can be kept remained in the pores 25 of the bushing 16.
The heating temperature of the lubricant 24 containing the solid lubricating fine particles 26 is not limited to a particular value. While the heating temperature must be changed depending on the viscosity of the lubricant 24 used, it is just required to heat the lubricant 24 to such a level at which the lubricant 24 is caused to liquefy. However, when the solid lubricating fine particles 26 are made of resin materials such as polyethylene, polyimide, polyacetal and PTFE (polytetrafluoroethylene), the heating temperature must be lower than the heat-resistant temperature of the resin used. The immersion time of the bushing 16 in the lubricant 24 containing the solid lubricating fine particles 26 and the degree of vacuum under which the bushing 16 is left to stand are also not limited to particular values. While settings of those parameters are changed depending on the viscosity of the lubricant 24 used, the immersion time must be set such that the pores 25 of the bushing 16 are saturated with the lubricant 24 containing the solid lubricating fine particles 26. For example, when the lubricant containing the solid lubricating fine particles and having the viscosity of 460 cSt is heated to temperature of about 60° C.-80° C. and the bushing is immersed in the lubricant under a vacuum of 2×10−2 mmHg, about 1 hour is required until the pores of the bushing are saturated with the lubricant containing the solid lubricating fine particles.
The shaft 22 is made of a steel material. The surface (outer circumferential surface) of the shaft is subjected to surface modification treatment by performing at least one kind of treatment selected from among carburizing, induction hardening, laser hardening and nitriding, and then chemical conversion (using, e.g., zinc phosphate or manganese phosphate) or sulfurizing treatment. By thus performing the surface modification treatment on the shaft 22 using an extreme-pressure additive such as Zn (zinc), Mn (manganese) or S (sulfur), “wetting” with respect to the lubricant 24 impregnated in the bushing 16 is improved, whereby the lubricating effect and tribological characteristics can be improved.
As with the surface of the shaft 22, the surface (inner circumferential surface) of the bushing 16 sliding relative to the shaft 22 may also be subjected to surface modification treatment, such as carburizing, hardening, nitriding, and sulfurizing. The wear resistance of the bushing 16 can be increased, for example, by forming a carburized layer with a thickness of about 1 mm-3 mm (preferably 2 mm) on the sliding surface of the bushing 16.
The bushing 16 in the above description constitutes a slide bearing set forth in claims 7 through 14 and also constitutes a bearing for a front component of an excavator set forth in claim 13.
The operation and advantages of one embodiment of the slide bearing assembly and the slide bearing of the present invention will be described below with reference to
As shown in
With the above-mentioned slide bearing assembly of the related art, as a comparative example, in which the lubricant 24 does not contain the solid lubricating fine particles 26, when the shaft and the bushing slide just several millimeters, i.e., angularly move in a very small stroke, or slide at a very low speed relative to each other, the lubricating effect cannot be developed at a sufficient level because the amount of generated frictional heat is very small. This may raise local surface pressure and cause local abrasion or damage, such as “scratching”, in the surface of the shaft 22 or the inner circumferential surface of the bushing 16 with accompanying abnormal noise.
In contrast, with the slide bearing assembly 12 of this embodiment, superior tribological characteristics are obtained with the lubricating effect of the solid lubricating fine particles 26 contained in the lubricant 24. Further, by setting the content of the solid lubricating fine particles 26 to fall in the range of 2.0 to 30 wt %, as seen from
Further, with this embodiment, because the viscosity of the lubricant 24 changes depending on temperature, the lubricating effect of the lubricant 24 is highly dependent on temperature. On the other hand, the lubricating effect of the solid lubricating fine particles 26 is less dependent on temperature. Accordingly, even when a hydraulic excavator is employed in, e.g., a cold district, the slide bearing assembly 12 is able to sufficiently develop the lubricating effect.
Another embodiment of the slide bearing assembly and the slide bearing of the present invention will be described below with reference to
While in this embodiment the solid lubricating fine particles 26′ made of graphite are contained at 3.0%, by way of example, in the lubricant 24, the content of the solid lubricating fine particles 26′ is preferably in the range of 3.0 to 5.0 wt %. The reason is explained below with reference to
As shown in
As in the above-described one embodiment, the particle size of the solid lubricating fine particles 26′ contained in the lubricant 24 is sufficiently small (e.g., about 0.1 μm-100 μm) to such an extent that the fine particles are able to smoothly seep out onto the sliding surface from the pores 25 of the bushing 16 and to withdraw from the sliding surface into the pores 25 without clogging the pores 25.
With the slide bearing assembly 12 of this embodiment, too, superior tribological characteristics are obtained with the lubricating effect of the solid lubricating fine particles 26′ contained in the lubricant 24. Further, by setting the content of the solid lubricating fine particles 26′ to fall in the range of 3.0 to 5.0 wt %, as seen from
Additionally, the slide bearing assembly 12 according to any of the above-described two embodiments is suitably used under conditions of high surface pressure not lower than 6 kgf/mm2 and high PV factor not lower than 1.0 kgf·m/mm2·s. Therefore, the present invention is applicable to not only a bearing for a front component of an excavator, such as the above-described slide bearing assembly 12 for use in the working device 5 of the hydraulic excavator, but also to any types of bearings used under conditions of low speed and high surface pressure, such as an arm bearing of a crane, a roller gate bearing of a dam floodgate, upper and lower slide cam bearings of a pressing die, a guide propeller bearing of a water turbine for hydroelectric power generation, and an unloader pin bearing of a seaborne crane.
According to the invention set forth in claim 1, a bushing made of a porous sintered material is impregnated with a lubricant containing 2.0% to 30 wt % of solid lubricating fine particles made of at least one selected from among MoS2, WS2, and hexagonal BN. Therefore, a superior effect of improving the load withstand characteristic can be obtained while suppressing an increase of viscosity of the lubricant. As a result, even under a situation of sliding at a very low speed or angular motion in a very small stroke, it is possible to not only suppress local abrasion or damage of the surface of the shaft 22 and the inner circumferential surface of the bushing 16 caused by scratching, etc. and accompanying abnormal noise, but also to prolong the period during which sliding operation can be continued in the oilless self-lubricating state.
Also, according to the invention set forth in claim 2, a bushing made of a porous sintered material is impregnated with a lubricant containing 3.0% to 5.0 wt % of solid lubricating fine particles made of graphite. Therefore, a superior effect of improving the load withstand characteristic can be obtained while suppressing an increase in viscosity of the lubricant. As a result, even under a situation of sliding at a very low speed or angular motion in a very small stroke, it is possible to not only suppress local abrasion or damage of the surface of the shaft 22 and the inner circumferential surface of the bushing 16 caused by scratching, etc. and accompanying abnormal noise, but also to prolong the period during which sliding operation can be continued in the oilless self-lubricating state.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-300005 | Aug 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/12065 | 8/23/2004 | WO | 4/1/2005 |
