Rolling bearing fitted with conductive seal

Abstract

Provided is a rolling bearing fitted with an electroconductive seal in which a seal member (5) is formed of electroconductive rubber, and a seal sliding contact surface (13) with which a seal member (5) is in sliding contact is formed on an inner race (2). The seal sliding contact surface (13) is a surface in which the skewness Rsk and the kurtosis Rku of a roughness curve in a direction orthogonal to the circumferential direction are such that Rsk>0 and Rku<3.

Description

Conductively sealed rolling bearings

[0001] The present invention relates to a rolling bearing with an electrically conductive seal.

[0002] Known electric vehicles (EVs), hybrid electric vehicles (HEVs), and other electric vehicles use electric motors as their driving motors. These electric vehicles use an inverter that converts DC power from a battery into AC power to supply AC power to the electric motor. The frequency of the AC power supplied to the electric motor is set high to increase the efficiency of the electric motor.

[0003] When the frequency of AC power supplied to an electric motor increases, abrupt voltage fluctuations cause leakage flux from the stator windings that make up the electric motor, creating a potential difference between both ends of the shaft, making it easier for current to flow through the rolling bearings that support the main shaft of the electric motor.When current flows through the rolling bearings, sparks can occur between the raceway surfaces and rolling elements of the rolling bearings, and these sparks can cause gradual damage to the raceway surfaces (electrolytic corrosion).

[0004] A known bearing for preventing this electrolytic corrosion is the electrically conductive sealed rolling bearing disclosed in Patent Document 1. The electrically conductive sealed rolling bearing of Patent Document 1 has an outer ring, an inner ring arranged coaxially radially inward of the outer ring, a plurality of rolling elements incorporated in an annular bearing space formed between the outer ring and the inner ring, and an annular seal member that closes one axial end opening of the bearing space. The seal member is fixed to the inner periphery of the outer ring, and a seal sliding surface with which a seal lip of the seal member slides is formed on the outer periphery of the inner ring.

[0005] In the conductively sealed rolling bearing of Patent Document 1, in order to prevent electrolytic corrosion, the seal member is made of conductive rubber and current flows between the outer ring and the inner ring through the seal member (i.e., the current bypasses), preventing current from flowing through the rolling elements. Also, a conductive lubricant is used as the lubricant that lubricates the gap between the seal lip of the seal member and the seal sliding surface on the outer periphery of the inner ring.

[0006] Japanese Patent Application Laid-Open No. 2009-264401

[0007] However, even when a conductive lubricant is used as in Patent Document 1, conductivity may be insufficient between the seal lip of the seal member and the seal sliding surface on the outer circumference of the inner ring, making it difficult to ensure stable conductivity between the outer ring and inner ring via the seal member.

[0008] The problem to be solved by this invention is to provide a rolling bearing with an electrically conductive seal that can ensure stable conductivity between the outer ring and the inner ring via a seal member.

[0009] In order to solve the above problems, the present invention provides a conductively sealed rolling bearing having the following configuration: [Configuration 1] An electrically conductively sealed rolling bearing comprising an outer ring, an inner ring arranged radially inward of the outer ring, a plurality of rolling elements incorporated in an annular bearing space formed between the outer ring and the inner ring, and an annular sealing member closing one axial end opening of the bearing space, wherein the sealing member is formed of conductive rubber, and the sealing member is fixed to one of the raceways of the inner ring and the outer ring, and a seal sliding surface with which the sealing member makes sliding contact is formed on the other raceway, wherein the seal sliding surface is a surface where the skewness Rsk and kurtosis Rku of a roughness curve in a direction perpendicular to the circumferential direction satisfy Rsk > 0 and Rku < 3.

[0010] When this configuration is adopted, the skewness of the roughness curve in a direction perpendicular to the circumferential direction of the seal sliding contact surface satisfies Rsk > 0, so the seal sliding contact surface has surface texture closer to that of a smooth surface with many peaks rather than a smooth surface with many valleys, with the peaks of these peaks and the seal member being in close to direct contact without the aid of a lubricant. This ensures stable conductivity between the outer ring and the inner ring via the seal member. Furthermore, the kurtosis of the roughness curve in a direction perpendicular to the circumferential direction of the seal sliding contact surface satisfies Rku < 3, so the peaks of the many peaks on the seal sliding contact surface are rounded. This helps to reduce wear of the seal member.

[0011] [Configuration 2] The electrically conductive sealed rolling bearing according to Configuration 1, wherein the seal sliding surface is a surface on which a plurality of circumferentially extending ridges are formed in parallel at a constant pitch of 0.2 mm or more.

[0012] By adopting this configuration, it is possible to easily form a seal sliding surface that satisfies Rsk > 0 and Rku < 3. That is, when the surface that will become the seal sliding surface is first formed by turning, the surface becomes a surface on which multiple circumferentially extending protrusions (turning marks) are formed in parallel at a constant pitch, and the presence of these protrusions (turning marks) results in a surface with a skewness of Rsk > 0. At this time, since the peaks of the protrusions (turning marks) are still sharp, the kurtosis of the roughness curve is Rku > 3. Next, the surface is polished (e.g., by lapping) to the extent that the circumferentially extending protrusions (turning marks) remain, and the peaks of the protrusions (turning marks) are rounded, thereby achieving a kurtosis of Rku < 3 while maintaining a skewness of Rsk > 0. In this way, by machining the surface that will become the seal sliding surface by turning and then polishing the surface to the extent that the turning marks remain, it is possible to easily form a seal sliding surface that satisfies Rsk > 0 and Rku < 3. The seal sliding surface formed in this way is a surface on which a plurality of circumferentially extending ridges are arranged in parallel at a constant pitch of 0.2 mm or more.

[0013] In addition, the seal sliding surface of a typical sealed rolling bearing is machined by turning the original surface of the seal sliding surface, and then grinding that surface to finish it, so there are no circumferentially extending protrusions (turning marks) and the surface is completely smooth.As a result, the skewness of the roughness curve in the direction perpendicular to the circumferential direction is Rsk ≈ 0, and the kurtosis of the roughness curve in the direction perpendicular to the circumferential direction is Rku ≈ 3.

[0014] [Configuration 3] An electrically conductive sealed rolling bearing according to Configuration 1 or 2, wherein the outer ring and the inner ring are formed of steel, and the seal sliding surfaces are surfaces coated with an electrically conductive coating having a hardness lower than that of the bearing steel.

[0015] By adopting this configuration, it becomes possible to particularly effectively suppress wear of the seal member.

[0016] In the conductive sealed rolling bearing of this invention, the skewness of the roughness curve in a direction perpendicular to the circumferential direction of the seal sliding contact surface satisfies Rsk > 0, so the seal sliding contact surface has surface properties closer to a smooth surface with many peaks rather than a smooth surface with many valleys, and the peaks of these peaks and the seal member are in close to direct contact without the aid of a lubricant. This ensures stable conductivity between the outer ring and the inner ring via the seal member. Furthermore, the kurtosis of the roughness curve in a direction perpendicular to the circumferential direction of the seal sliding contact surface satisfies Rku < 3, so the peaks of the many peaks on the seal sliding contact surface are rounded. This reduces wear on the seal member.

[0017] 1 is an enlarged view of the vicinity of the seal member in FIG. 1; FIG. 2 is an enlarged view of the vicinity of the seal sliding surface, showing an example in which the seal sliding surface in FIG. 2 is a surface coated with a conductive film; and FIG. 3 is a cross-sectional view showing a modified example in which the seal sliding surface in FIG. 1 is formed on an outer ring.

[0018] 1 shows a conductively sealed rolling bearing according to an embodiment of the present invention. This conductively sealed rolling bearing comprises an outer ring 1, an inner ring 2 arranged coaxially radially inward of the outer ring 1, a plurality of rolling elements 4 mounted at intervals in the circumferential direction in an annular bearing space 3 formed between the outer ring 1 and the inner ring 2, an annular seal member 5 that closes one axial end opening of the bearing space 3, an annular seal member 6 that closes the other axial end opening of the bearing space 3, and a cage 7 that maintains the circumferential spacing of the plurality of rolling elements 4. A lubricant is sealed in the bearing space 3.

[0019] The inner circumference of the outer ring 1 is formed with an outer ring raceway surface 8 with which the rolling elements 4 roll, a pair of outer ring shoulders 9 located axially outward of the outer ring raceway surface 8, and a pair of seal fixing grooves 10 located axially outward of the outer ring shoulders 9. The pair of outer ring shoulders 9 are bank-shaped portions extending circumferentially on both sides of the outer ring raceway surface 8 in the axial direction. The seal fixing grooves 10 are grooves extending circumferentially and formed adjacent to the axially outward sides of the outer ring shoulders 9. Seal members 5, 6 are fitted into and fixed in the pair of seal fixing grooves 10, respectively.

[0020] The outer periphery of the inner ring 2 is formed with an inner ring raceway surface 11 with which the rolling elements 4 roll, a pair of inner ring shoulders 12 located axially outward of the inner ring raceway surface 11, and a pair of seal sliding surfaces 13 located axially outward of the inner ring shoulders 12. The pair of inner ring shoulders 12 are bank-shaped portions extending circumferentially on both sides of the inner ring raceway surface 11 in the axial direction. The seal sliding surfaces 13 are the inner surfaces of circumferentially extending recesses formed adjacent to the axially outer sides of the inner ring shoulders 12. Seal lips 14 formed on the inner peripheries of the seal members 5 and 6 are in sliding contact with the pair of seal sliding surfaces 13, respectively. In the drawing, the seal sliding surfaces 13 are cylindrical surfaces with a constant outer diameter along the axial direction.

[0021] The outer ring 1, inner ring 2, and rolling elements 4 are each made of steel. In this example, the rolling elements 4 are balls. The rolling elements 4 are sandwiched radially between an outer ring raceway surface 8 and an inner ring raceway surface 11. The outer ring raceway surface 8 and the inner ring raceway surface 11 are the inner surfaces of grooves whose cross sections perpendicular to the circumferential direction are arc-shaped.

[0022] The sealing member 5 is formed by vulcanizing and bonding conductive rubber to a core metal (not shown). The conductive rubber is a rubber composition in which a conductive filler is dispersed in a rubber material. Examples of the rubber material that can be used include acrylic rubber, nitrile rubber, and fluororubber. Examples of the conductive filler that can be used include carbon-based conductive fillers. The sealing member 6 has the same configuration as the sealing member 5.

[0023] The seal sliding surface 13 is a surface on which a plurality of circumferentially extending ridges 15 are formed in parallel at a constant pitch of 0.2 mm to 1.0 mm. The ridges 15 have a height of 5 μm to 30 μm (preferably 20 μm or less). The seal sliding surface 13 is a surface in which the skewness of the roughness curve in the direction perpendicular to the circumferential direction satisfies Rsk > 0 (preferably Rsk > 0.5, more preferably Rsk > 1.0) and the kurtosis of the roughness curve in the direction perpendicular to the circumferential direction satisfies Rku < 3 (preferably Rku < 2.8, more preferably Rku < 2.6).

[0024] This seal sliding surface 13 is a surface formed as follows: First, a ring-shaped material that will become the blank for the inner ring 2 is turned to form a surface that will become the basis for the seal sliding surface 13. The surface formed by this turning is a surface on which a plurality of circumferentially extending ridges 15 (turning marks) are arranged in parallel at a constant pitch (= the feed amount per turning rotation), and the presence of these ridges 15 (turning marks) results in a surface whose skewness satisfies Rsk > 0. At this time, because the tops of the ridges 15 (turning marks) are still pointed, the kurtosis of the roughness curve is Rku > 3.

[0025] Next, the surface is polished (for example, by barrel polishing or lapping) to the extent that the circumferentially extending ridges 15 (turning marks) remain, and the peaks of the ridges 15 (turning marks) are rounded. This makes it possible to make the kurtosis Rku<3 while maintaining the skewness Rsk>0.

[0026] In this way, by machining the surface that will become the seal sliding surface 13 by turning and then polishing the surface to the extent that the turning marks remain, it is possible to form a seal sliding surface 13 in which the skewness of the roughness curve in the direction perpendicular to the circumferential direction satisfies Rsk > 0 (preferably Rsk > 0.5, more preferably Rsk > 1.0) and the kurtosis of the roughness curve in the direction perpendicular to the circumferential direction satisfies Rku < 3 (preferably Rku < 2.8, more preferably Rku < 2.6).

[0027] Note that the seal sliding surface 13 of a typical sealed rolling bearing is formed by turning a ring-shaped material that serves as a blank for the inner ring 2 to form the surface that will become the seal sliding surface 13, and then finishing the surface by grinding, so that there are no circumferentially extending protrusions 15 (turning marks) and the surface is completely smooth. As a result, the skewness of the roughness curve in the direction perpendicular to the circumferential direction is Rsk ≈ 0, and the kurtosis of the roughness curve in the direction perpendicular to the circumferential direction is Rku ≈ 3.

[0028] The skewness Rsk and kurtosis Rku of the roughness curve of the seal sliding contact surface 13 are measured in accordance with Japanese Industrial Standard JIS B0601:2013 "Geometrical Product Characteristics Specifications (GPS) - Surface Texture: Profile Curve Method - Terms, Definitions, and Surface Texture Parameters" (ISO 4287:1997, Amd.1:2009) and Japanese Industrial Standard JIS B0651:2001 "Geometrical Product Characteristics Specifications (GPS) - Surface Texture: Profile Curve Method - Characteristics of Stylus Surface Roughness Measuring Instruments" (ISO 3274:1996). Furthermore, because variations in skewness Rsk and kurtosis Rku depending on the position on the seal sliding contact surface 13 are small, it is not necessary to measure skewness Rsk and kurtosis Rku at multiple locations on the seal sliding contact surface 13; they can be measured at one location on the seal sliding contact surface 13.

[0029] In this electrically conductive sealed rolling bearing, the skewness of the roughness curve of the seal sliding surface 13 in a direction perpendicular to the circumferential direction satisfies Rsk > 0 (preferably Rsk > 0.5, and more preferably Rsk > 1.0), so that the seal sliding surface 13 has surface properties closer to a smooth surface with many peaks rather than a smooth surface with many valleys, with the peaks of these peaks coming into close to direct contact with the seal member 5 without any lubricant between them. This ensures stable conductivity between the outer ring 1 and the inner ring 2 via the seal member 5, thereby extending the life of the bearing. Furthermore, because lubricant accumulates between adjacent protrusions 15, this lubricant can be used to lubricate the seal lip 14 of the seal member 5.

[0030] Furthermore, since the kurtosis of the roughness curve in the direction perpendicular to the circumferential direction of the seal sliding contact surface 13 satisfies Rku<3 (preferably Rku<2.8, more preferably Rku<2.6), the peaks of the many peaks on the surface of the seal sliding contact surface 13 are rounded, thereby suppressing wear of the seal member 5.

[0031] As shown in Figure 3, the seal sliding surface 13 can be a surface coated with a conductive coating 16 that has a lower hardness than the steel material constituting the inner ring 2. Such a conductive coating 16 can be a metal plating coating of silver, copper, gold, nickel, tin, chromium, or the like, or a conductive resin coating made of a resin material such as polyurethane with a conductive filler (carbon black, etc.) dispersed in it. A chromium plating coating is preferable due to its wear resistance and corrosion resistance.

[0032] In the above embodiment, as shown in FIG. 2 , an example has been described in which the seal lip 14 of the seal member 5 slides against the cylindrical seal sliding surface 13 having a constant outer diameter along the axial direction (radial contact seal), but the present invention can also be applied to a seal member 5 in which the seal lip 14 slides against the seal sliding surface 13 that is perpendicular to the axial direction, or to a seal member 5 in which the seal lip 14 slides against a tapered seal sliding surface 13 that has an inclination angle with respect to the axial direction.

[0033] Furthermore, in the above embodiment, an example has been given of a conductively sealed rolling bearing in which, of both the outer ring 1 and the inner ring 2, the seal member 5 is fixed to the outer ring 1 and the inner ring 2 forms a seal sliding surface 13 with which the seal member 5 slides. However, as shown in FIG. 4 , the present invention can be similarly applied to a conductively sealed rolling bearing in which the seal member 5 is fixed to the inner ring 2 and the outer ring 1 forms a seal sliding surface 13 with which the seal member 5 slides.

[0034] In addition, in the above embodiment, an example of a rolling bearing with a conductive seal in which seal members 5, 6 are provided on both sides of the bearing space 3 has been described, but it is also possible to provide a seal member 5 on only one side of the bearing space 3.

[0035] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0036] REFERENCE SIGNS LIST 1 outer ring 2 inner ring 3 bearing space 4 rolling element 5 seal member 13 seal sliding surface 15 ridge 16 conductive coating

Claims

1. A conductively sealed rolling bearing comprising: an outer ring (1); an inner ring (2) arranged radially inward of the outer ring (1); a plurality of rolling elements (4) incorporated in an annular bearing space (3) formed between the outer ring (1) and the inner ring (2); and an annular sealing member (5) closing one axial end opening of the bearing space (3), wherein the sealing member (5) is formed of conductive rubber, and the sealing member (5) is fixed to one of the raceways of the inner ring (2) and the outer ring (1), and a seal sliding surface (13) with which the sealing member (5) slides is formed on the other raceway, wherein the conductively sealed rolling bearing is characterized in that the skewness Rsk and kurtosis Rku of a roughness curve in a direction perpendicular to the circumferential direction satisfy Rsk > 0 and Rku < 3.

2. A rolling bearing with a conductive seal as described in claim 1, wherein the seal sliding surface (13) is a surface on which a plurality of circumferentially extending protrusions (15) are formed in parallel with each other at a constant pitch of 0.2 mm or more.

3. A rolling bearing with an electrically conductive seal as claimed in claim 1 or 2, wherein the outer ring (1) and the inner ring (2) are formed from steel, and the seal sliding surface (13) is a surface coated with an electrically conductive film (16) having a hardness lower than that of the steel.

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