Sliding bearing
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NTN CORP
- Filing Date
- 2026-01-20
- Publication Date
- 2026-07-30
Smart Images
Figure JP2026001567_30072026_PF_FP_ABST
Abstract
Description
Sliding bearing Related application
[0001] This application claims the priority of Japanese Patent Application No. 2025-011611 filed on January 27, 2025, and the entire disclosure of which is incorporated herein by reference in its entirety and made a part of this application.
[0002] The present invention relates to a sliding bearing, for example, a sliding bearing used for a joint part of an industrial robot, a service robot, or a speed reducer mounted on the joint part.
[0003] As a bearing that can receive a moment load by a single bearing, there is a cross roller bearing 70 (Patent Document 1) or a four-point contact ball bearing (Patent Document 2) shown in FIG. 11. In Patent Document 2, as a means for reducing the weight and size of the bearing, a method of defining the rolling element size of the four-point contact ball bearing to be smaller than a general rolling element size is described.
[0004] Further, as shown in FIG. 12, as a conventional sliding bearing 50, a sliding bearing is disclosed in which a sliding surface 53 between inner and outer rings 51 and 52 has a tapered shape inclined with respect to a rotating shaft C2 (Patent Document 3). By forming the sliding surface 53 into the tapered shape, this sliding bearing 50 can improve the load capacity with a small number of parts, and further, by making the outer ring 52 into an outer ring split body that is axially split, the outer ring width surface can be adjusted to adjust the clearance (preload).
[0005] Japanese Patent No. 7050638, Japanese Patent No. 6793867, International Publication No. 2015 / 172781
[0006] When the sliding surface 53 has a tapered shape as in Patent Document No. 3, an edge load may occur when supporting a moment load with this sliding bearing 50, leading to a short life of the sliding bearing 50.
[0007] Therefore, the applicant proposes a sliding bearing 60 shown in Figure 13 (Japanese Patent Application No. 2024-95889). This sliding bearing 60 has a sliding surface with a convex curved surface 62a on the inner circumferential surface of the outer ring and a concave curved surface 61a on the outer circumferential surface of the inner ring, as shown in Figures 14A and 14B. In this case, compared to a general spherical sliding bearing 80 shown in Figure 16, the diameter P.C.D. of the sliding surface becomes smaller, as shown in Figure 15. As a result, the area of the sliding surface becomes smaller, and the load capacity decreases. The spherical sliding bearing 80 shown in Figure 16 has a self-aligning property because the center P80 of the sliding surface coincides with the bearing center, but on the other hand, it cannot support moment loads.
[0008] The objective of the present invention is to provide a sliding bearing that can improve load capacity and support moment loads.
[0009] The sliding bearing of the present invention comprises an inner ring and an outer ring, wherein the inner circumferential surface of the outer ring has a concave curved surface in the shape of an annular recess that is concave radially outward, and the outer circumferential surface of the inner ring has a convex curved surface in the shape of an annular convex portion that fits into the concave curved surface and is slidable relative to the outer ring in the circumferential direction, wherein the centers of the radii of curvature of the concave and convex curved surfaces are located radially outward from the axis of the sliding bearing and radially inward from the concave and convex curved surfaces. The "axis" is synonymous with the bearing's central axis, and the direction along the axis is defined as the axial direction.
[0010] In this configuration, the centers of the radii of curvature of the concave and convex surfaces are positioned radially outward from the axis of the sliding bearing and radially inward from the concave and convex surfaces. This ensures sufficient distance between the lines of action of the load, allowing it to support moment loads. Since the moment load can be supported by the concave and convex surfaces that fit together, it is possible to support the moment load without generating edge loads, which are localized stress concentrations. Furthermore, compared to sliding bearings with a convex sliding surface on the inner circumference of the outer ring and a concave sliding surface on the outer circumference of the inner ring, the apex position of the sliding surface can be made larger, thereby improving the load capacity.
[0011] The concave and convex surfaces each have a single radius of curvature, and the radius of curvature ri of the convex surface may be less than the radius of curvature ro of the concave surface. In this case, the risk of edge loading occurring when supporting a moment load with a sliding bearing can be more reliably suppressed.
[0012] The inner ring may have an annular flat portion at one or both axial ends of its outer circumferential surface that connects to the convex curved surface and is parallel to the axial direction, and the outer ring may have an annular flat portion at one or both axial ends of its inner circumferential surface that connects to the concave curved surface and is parallel to the axial direction. In this case, the convex curved surface of the inner ring can be easily and accurately machined using the flat portion of the inner ring as a reference surface. Similarly, the concave curved surface of the outer ring can be easily and accurately machined using the flat portion of the outer ring as a reference surface.
[0013] A surface treatment layer, which acts as a sliding resistance reducing member, may be provided on the convex curved surface of the inner ring. In this case, the occurrence of edge load on the surface treatment layer can be suppressed. Furthermore, by reducing the friction of the sliding surface with the surface treatment layer, power loss of the drive source can be reduced compared to a structure without a surface treatment layer. This also makes it possible to miniaturize the drive source.
[0014] A surface treatment layer, which acts as a sliding resistance reducing member, may be provided on the concave curved surface of the outer ring. In this case, the generation of edge load on the surface treatment layer can be suppressed. Furthermore, by reducing the friction of the sliding surface with the surface treatment layer, power loss of the drive source can be reduced compared to a structure without a surface treatment layer. This also makes it possible to miniaturize the drive source.
[0015] Any combination of at least two configurations disclosed in the claims and / or the specification and / or drawings is included in the present invention. In particular, any combination of two or more of each claim is included in the present invention.
[0016] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustrative and explanatory purposes only and should not be used to define the scope of the invention. The scope of the invention is defined by the accompanying claims. In the accompanying drawings, the same reference numerals in multiple drawings indicate the same or corresponding parts.
[0017] This is a partial perspective view showing a longitudinal cross-section of a sliding bearing according to the first embodiment of the present invention. This is a partial perspective view showing a longitudinal cross-section of the inner ring of the sliding bearing. This is a partial perspective view showing a longitudinal cross-section of the outer ring of the sliding bearing. This is a diagram showing a step-by-step assembly method of the sliding bearing. This is a partial perspective view showing a longitudinal cross-section of a sliding bearing according to the second embodiment of the present invention. This is a partial perspective view showing a longitudinal cross-section of the inner ring of the sliding bearing. This is a partial perspective view showing a longitudinal cross-section of the outer ring of the sliding bearing. This is a longitudinal cross-sectional view of the sliding bearing. This is an enlarged cross-sectional view of the main part of the sliding bearing. This is a longitudinal cross-sectional view of a sliding bearing according to the third embodiment of the present invention. This is a longitudinal cross-sectional view of a conventional cross roller bearing. This is a perspective view of a prior art sliding bearing. This is a partial perspective view showing a longitudinal cross-section of a sliding bearing according to a reference proposal example. This is a partial perspective view showing a longitudinal cross-section of the outer ring of the sliding bearing. This is a partial perspective view showing a longitudinal cross-section of the inner ring of the sliding bearing. This is a longitudinal cross-sectional view of the sliding bearing. This is a longitudinal cross-sectional view of a conventional spherical sliding bearing.
[0018] [First Embodiment] A sliding bearing according to an embodiment of the present invention will be described with reference to Figures 1 to 4. The sliding bearing according to the embodiment is used, for example, in the joints of industrial robots, service robots, etc., or as the main bearing of a speed reducer mounted on the joint. Examples of the speed reducer include a harmonic drive speed reducer, an eccentric differential speed reducer, a planetary gear speed reducer, etc. This sliding bearing can be used, for example, as a substitute for conventional rolling bearings such as cross roller bearings or four-point contact ball bearings.
[0019] <Outline Configuration of a Sliding Bearing> As shown in Figure 1, the sliding bearing 1 comprises an inner ring 2 and an outer ring 3, and is a sliding bearing capable of supporting a moment load by itself, without rolling elements. The moment load is a load acting in a direction that tilts an unillustrated shaft fitted and fixed to the inner ring 2. In this specification, the sliding bearing may sometimes be simply referred to as "bearing". The sliding bearing 1 is lubricated without lubrication (strictly speaking, with a solid lubricant in the resin layer or surface treatment layer described later) or with a fluid lubricant such as grease or oil.
[0020] The inner circumferential surface of the outer ring 3 has a concave curved surface 3a in the shape of an annular recess, with the axial center or near the axial center being concave radially outward. The outer circumferential surface of the inner ring 2 has a convex curved surface 2a in the shape of an annular convex portion that fits into the concave curved surface 3a and is slidable relative to the outer ring 3 in the circumferential direction. The outer ring 3 and the inner ring 2 are continuous annular bodies in the circumferential direction. The inner ring 2 and the outer ring 3 are each provided as a single unit. However, the outer ring 3 may, for example, have a split surface 3d (Figure 4) at one location in the circumferential direction, or may be divided into two in the circumferential direction.
[0021] In this specification, the direction along the axis AX of the sliding bearing 1 is referred to as the "axial direction," and the direction perpendicular to the axis AX is referred to as the "radial direction." The direction around the axis AX is referred to as the "circumferential direction." The portion near the axial center is the portion of the inner circumferential surface of the outer ring 3 that is separated from the axial center by a predetermined length in the axial direction. The predetermined length is set appropriately according to the operating conditions of the sliding bearing 1.
[0022] <Inner and Outer Rings> As shown in Figure 2, the inner ring 2 has a apex 2aa of the convex curved surface 2a at or near the axial center of its outer circumferential surface. The convex curved surface 2a is a curved surface whose diameter decreases monotonically as it extends from the apex 2aa toward both sides in the axial direction. The convex curved surface 2a has a single radius of curvature, so-called a single R shape.
[0023] As shown in Figure 3, the inner circumferential surface of the outer ring 3 is provided with a recessed apex 3aa, which is the deepest part of the concave curved surface 3a, at the axial center or near the axial center. The concave curved surface 3a is a curved surface whose diameter decreases monotonically as it extends from the recessed apex 3aa toward both sides in the axial direction. The concave curved surface 3a has a single radius of curvature, so-called a single R shape.
[0024] <Parameters, etc.> As shown in Figure 1, the center d of the radius of curvature r in the concave surface 3a and the convex surface 2a is located radially outward from the axis AX of this sliding bearing 1. The center d of the radius of curvature r is located radially inward from the apex position P.C.D. of the convex sliding surface and radially inward from the concave surface 3a and the convex surface 2a. The sliding bearing 1 of this embodiment has the positional relationship "AX < d < P.C.D.".
[0025] As mentioned above, when the convex curved surface 2a of the inner ring 2 and the concave curved surface 3a of the outer ring 3 each consist of a single R shape, it is preferable that the radius of curvature ri of the convex curved surface 2a < the radius of curvature ro of the concave curved surface 3a. By satisfying this condition ri < ro, the risk of edge loading occurring when the sliding bearing 1 supports a moment load can be more reliably suppressed.
[0026] <Regarding bearing materials, etc.> The inner and outer rings 2 and 3 can be made of steel, lightweight materials, or resin materials. The inner and outer rings 2 and 3 may be made of the same material, or they may be made of different materials. As for the steel material, for example, high-carbon chromium bearing steel, chromium-molybdenum steel, carbon steel for machine structures, stainless steel, etc. may be used. Molybdenum disulfide, etc. may be added to any one of these. As for the lightweight material, for example, aluminum, ceramics, etc. may be used.
[0027] When the aforementioned resin material is applied, the base of the resin composition may be, for example, thermoplastic PI resin, polyether ketone resin (PEK), polyether ether ketone resin (PEEK), polyphenylene sulfide resin (PPS), polyether ketone ether ketone ketone resin (PEKEKK), polyamide imide resin (PAI), polyamide resin (PA), polyethylene resin (PE), polyacetal resin (POM), polytetrafluoroethylene resin (PTFE), etc.
[0028] When steel or lightweight materials are used as the material for the inner and outer rings 2 and 3, a resin layer RS may be formed on both sides (sliding surfaces) of the inner circumferential surface of the outer ring 3 and the outer circumferential surface of the inner ring 2, or on either one of the sliding surfaces, as shown in Figures 2 and 3, in order to reduce the frictional resistance of the sliding surfaces. Examples of this resin layer RS include thermoplastic PI resin, PEK, PEEK, PPS, PEKEKK, PAI, PA, PE, POM, PTFE, etc. In this case, the resin layer RS may be formed on the sliding surface by injection molding.
[0029] <Assembly> In the sliding bearing 60 according to the reference proposed example shown in Figure 13, the apex P60 of the outer ring sliding surface is smaller than the shoulder portion 61a of the inner ring. For this reason, it is not possible to assemble it by shrink-fitting the integrally structured outer ring 62 or by press-fitting the inner ring 61 into the single-part outer ring 62. For this reason, the inner ring 61 has to be made into a segmented structure, but in this case, it becomes difficult to precisely fit the segmented inner ring parts 61A, 61A onto the shaft.
[0030] In the sliding bearing 1 shown in Figure 1, the inner diameter of the outer ring 3 is larger than that of the sliding bearing 60 (Figure 13) in the reference proposal example, making it possible to assemble the integrated outer ring 3 by shrink fitting. As shown in Figure 4, in the sliding bearing 1 with a split surface 3d along the axial direction on the outer ring 3, it is possible to assemble it by press-fitting the outer surface of the inner ring 2 to the inner surface of the outer ring 3 using a press machine PM, similar to a conventional spherical sliding bearing with a single split in the outer ring.
[0031] The sliding bearing 1 may have its outer ring 3 divided into two circumferential sections. By inserting a spacer (shim) between the divided outer ring sections, the clearance of the sliding bearing 1 can be easily adjusted. Furthermore, to increase the rigidity of the sliding bearing 1, it may be used with negative clearance (preload). Since bearings for robot reducers are generally used under load conditions where the inner ring rotates, the inner ring 2 is assembled with an interference fit or intermediate fit, and the outer ring 3 with a clearance fit.
[0032] In the sliding bearing 60 (Figure 13) according to the aforementioned reference proposal example, the inner ring is divided, making it difficult to precisely fit the divided inner ring onto the shaft due to issues such as misalignment of the mating surfaces. In contrast, in the sliding bearing 1 embodiment equipped with an outer ring divided in the circumferential direction, the divided outer ring is assembled with clearance fitting, so slight misalignment of the mating surfaces is not a problem.
[0033] <Differences between the prior art and the present invention> The cross roller bearing 70 in Figure 11 and the four-point contact ball bearing (not shown) are single bearings, i.e., single rows, and have load lines L1, L1 in both directions relative to the axis, so they can support moment loads in both directions. In contrast, the spherical plain bearing 80 in Figure 16 has the bearing center and the centers P80 of the sliding surfaces P80 of the inner and outer rings 81 and 82 coincide, and while it has self-aligning properties, it cannot support moment loads.
[0034] <Effects> In the sliding bearing 1 shown in Figure 1, the centers d of the radii of curvature ro and ri of the concave surface 3a and convex surface 2a are positioned radially outward from the axis AX of the sliding bearing 1 and radially inward from the concave surface 3a and convex surface 2a. This allows for a large load-acting distance Lg to be secured, enabling the support of a moment load M. Since the moment load M can be supported by the mutually interlocking concave surface 3a and convex surface 2a, the moment load M can be supported without generating edge loads, which are localized stress concentrations. Furthermore, compared to a sliding bearing 60 (Figure 15) having a convex sliding surface on the inner circumference of the outer ring and a concave sliding surface on the outer circumference of the inner ring, the apex position P.C.D. of the sliding surface can be increased, thereby improving the load capacity.
[0035] <Regarding Other Embodiments> In the following description, parts corresponding to matters previously described in each embodiment will be denoted by the same reference numerals, and redundant explanations will be omitted. When only a part of the configuration is described, the other parts of the configuration will be the same as those in the previously described embodiment unless otherwise specified. The same configuration will produce the same effects. Not only are combinations of the parts specifically described in each embodiment possible, but it is also possible to partially combine embodiments, provided that there are no particular problems with the combination.
[0036] [Second Embodiment: Flat Section, Figures 5-9] As shown in Figures 5 and 6, the inner ring 2 has annular flat sections 2c at both axial ends on its outer circumferential surface that connect to a convex curved surface 2a and are parallel to the axial direction. Furthermore, as shown in Figures 5 and 7, the outer ring 3 has annular flat sections 3c at both axial ends on its inner circumferential surface that connect to a concave curved surface 3a and are parallel to the axial direction. In this case, the convex curved surface 2a of the inner ring 2 can be easily and accurately machined using the flat section 2c of the inner ring 2 as a reference surface. Also, the concave curved surface 3a of the outer ring 3 can be easily and accurately machined using the flat section 3c of the outer ring 3 as a reference surface.
[0037] Furthermore, as shown in Figures 8 and 9, this sliding bearing 1 has a positional relationship of "AX < d < P.C.D.", which allows for a large load-acting distance Lg, and thus enables it to support a moment load M. Compared to a sliding bearing 60 (Figure 15) having a convex curved sliding surface on the inner circumferential surface of the outer ring and a concave curved sliding surface on the outer circumferential surface of the inner ring, the apex position P.C.D. of the sliding surface can be made larger, thereby improving the load capacity. An annular flat portion 2c may be provided only at one axial end of the outer circumferential surface of the inner ring 2. An annular flat portion 3c may be provided only at one axial end of the inner circumferential surface of the outer ring 3.
[0038] [Third Embodiment: Seal Section, Figure 10] As shown in Figure 10, in addition to the configuration having annular flat sections 2c, 2c, 3c, 3c at both axial ends of the inner and outer rings 2 and 3, the bearing space between the inner and outer rings 2 and 3 may also be sealed with seal sections 4, 4. In this embodiment, for example, the base end of the seal section 4 is fitted and fixed to the axially outer portion of each flat section 3c of the outer ring 3, and the tip of the seal section 4 extends radially inward. The tip of the seal section 4 may be either a contact type or a non-contact type.
[0039] When a fluid lubricant such as the aforementioned grease or oil is sealed in the sliding bearing 1, providing seal portions 4, 4 prevents leakage of the fluid lubricant from the sliding bearing 1 and prevents foreign matter from entering the sliding bearing 1. The base end of the seal portion 4 may be fitted and fixed to the axially outer portion of each flat portion 2c of the inner ring 2, and the tip of the seal portion 4 may extend radially outward.
[0040] <Fourth Embodiment: Surface Treatment Layer> As shown in Figures 2 and 6, a surface treatment layer hf, which serves as a sliding resistance reducing member to reduce friction on the sliding surface, may be provided on the convex curved surface of the inner ring 2. As shown in Figures 3 and 7, a surface treatment layer hf, which serves as a sliding resistance reducing member to reduce friction on the sliding surface, may be provided on the concave curved surface of the outer ring 3. The surface treatment is preferably a method with a good coefficient of friction and wear resistance.
[0041] As the surface treatment layer hf, for example, hard chrome plating, electroplating (copper plating, chrome plating, etc.), electroless plating (Ni-P system, Ni-B system, Sn system, etc., or composite plating including PTFE or Si), shot peening, spray coating, anodizing, diamond-like carbon (DLC), hairline (HL) treatment, PVD (Physical Vapor Deposition) treatment, or CVD (Chemical Vapor Deposition) treatment may be provided. However, the surface treatment is not necessarily limited to these, and other surface treatments may be applied depending on the operating conditions of the sliding bearing 1. By reducing the friction of the sliding surface with the surface treatment layer hf, power loss of the drive source such as a motor can be reduced compared to a structure without a surface treatment layer. This also makes it possible to miniaturize the drive source.
[0042] The resin layer RS may be formed on either the inner peripheral surface of the outer ring or the outer peripheral surface of the inner ring, and the surface treatment layer hf may be provided on the other surface.
[0043] The concave curved surface 3a of the outer ring 3 and the convex curved surface 2a of the inner ring 2 are not limited to a single R shape, and may be a composite curved surface formed by connecting a plurality of curved surfaces. It is also possible to make one of the concave curved surface 3a and the convex curved surface 2a a single R shape and the other a composite curved surface. The resin inner ring 2 or outer ring 3 may be manufactured by, for example, a 3D printer. The sliding bearing can also be used for applications other than the robot joint part.
[0044] As described above, the preferred embodiments have been described with reference to the drawings, but various additions, changes, and deletions are possible without departing from the spirit of the present invention. Therefore, such things are also included within the scope of the present invention.
[0045] 1... Sliding bearing; 2... Inner ring; 2a... Convex curved surface; 2c... Flat portion; 3... Outer ring; 3a... Concave curved surface; 3c... Flat portion; hf... Surface treatment layer
Claims
1. A sliding bearing comprising an inner ring and an outer ring, wherein the inner circumferential surface of the outer ring has a concave curved surface in the shape of an annular recess that is concave radially outward, and the outer circumferential surface of the inner ring has a convex curved surface in the shape of an annular convex portion that fits into the concave curved surface and is slidable relative to the outer ring in the circumferential direction, wherein the centers of the radii of curvature of the concave and convex curved surfaces are located radially outward from the axis of the sliding bearing and radially inward from the concave and convex curved surfaces.
2. A sliding bearing according to claim 1, wherein the concave surface and the convex surface each have a single radius of curvature, and the radius of curvature of the convex surface ri < the radius of curvature of the concave surface ro.
3. A sliding bearing according to claim 1 or claim 2, wherein the inner ring has an annular flat portion connected to the convex curved surface and parallel to the axial direction at one or both axial ends of the outer circumferential surface, and the outer ring has an annular flat portion connected to the concave curved surface and parallel to the axial direction at one or both axial ends of the inner circumferential surface.
4. A sliding bearing according to claim 1 or claim 2, wherein a surface treatment layer that serves as a sliding resistance reducing member is provided on the convex curved surface of the inner ring.
5. A sliding bearing according to claim 1 or claim 2, wherein a surface treatment layer that serves as a sliding resistance reducing member is provided on the concave curved surface of the outer ring.