Insulated rolling bearing and production method for insulated rolling bearing

Abstract

An insulated rolling bearing (1) has an inner ring (2), an outer ring (3) that is coaxially provided on the outside in the radial direction of the inner ring (2), a plurality of rolling bodies (4) that are provided between the inner ring (2) and the outer ring (3), and an insulation layer (6) that comprises a heat-shrinkable resin and is adhered to an outer radial surface of the outer ring (3). A production method for the insulated roller bearing (1) includes a heat-shrinkable tube provision step for inserting a rolling bearing that has an inner ring (2), an outer ring (3) that is coaxially provided on the outside in the radial direction of the inner ring (2), and a plurality of rolling bodies (4) that are provided between the inner ring (2) and the outer ring (3) into a tube of a heat-shrinkable resin that has not yet been heat-shrunk and a heat-shrinkable tube heating step for heating the tube of the heat-shrinkable resin to heat-shrink the heat-shrinkable resin and form an insulation layer (6) that comprises the heat-shrinkable resin and is adhered to an outer radial surface of the outer ring (3).

Description

Insulated rolling bearing and method for manufacturing the insulated rolling bearing

[0001] The present invention relates to an insulating rolling bearing and a method for manufacturing an insulating rolling bearing.

[0002] Rolling bearings such as ball bearings are commonly used to support the rotating shafts of motors, alternators, and other devices. In recent years, inverter control has become commonplace for efficient motor operation. In particular, motors for vehicles are being made smaller to facilitate installation in vehicles, and more precise control is being implemented to use these smaller motors more efficiently.

[0003] It is known that shaft currents and shaft voltages occur on the motor shaft. If these currents pass through the inside of the bearing, electrolytic corrosion may occur in the metal raceways and rolling elements. For this reason, rolling bearings with insulating layers formed thereon are sometimes used to prevent current from passing through the inside of the bearing. For example, in Patent Document 1 listed below, the inner and outer rings are placed in molds, and insulating coatings 6 and 7 are formed on their peripheral surfaces by insert injection molding (see paragraph 0017 and Figure 1 of Patent Document 1).

[0004] Patent No. 3068311

[0005] When forming an insulating coating by insert injection molding as in Patent Document 1, pre-processing such as preheating, degreasing, and masking of the bearing (inner ring and outer ring) is required, as well as post-processing such as deburring after resin molding, which requires a lot of time and effort. In addition, because a mold for insert injection molding is required, it is difficult to process many bearings at once, which presents the problem of increased processing costs.

[0006] Therefore, an object of the present invention is to provide an insulating rolling bearing that allows an insulating layer to be formed on the surface of a component simply and efficiently, and a method for manufacturing the insulating rolling bearing.

[0007] In order to solve the above problems, the present invention provides an insulated rolling bearing (first configuration) having an inner ring, an outer ring provided coaxially on the radially outer side of the inner ring, a plurality of rolling elements arranged between the inner ring and the outer ring, and an insulating layer made of heat-shrinkable resin provided so as to be in close contact with the outer diameter surface of the outer ring.

[0008] This eliminates the need for pre-treatment such as preheating, degreasing, and masking of the bearing (outer ring), post-treatment such as deburring after resin molding, and the need for molds, and it also makes it possible to process a large number of bearings at once, making it possible to simply and efficiently form an insulating layer on the surface of the rolling bearing components.

[0009] In the first configuration, the insulating layer may extend from the outer diameter surface of the outer ring to the end face thereof in close contact (second configuration), thereby preventing contact between the outer ring and the housing and ensuring high insulation.

[0010] The second configuration can be replaced with a third configuration in which a shield portion facing the opening between the inner and outer rings extends from the radially inner end of the insulating layer that is in close contact with the end face of the outer ring. This prevents contact between the outer ring and the housing, ensuring a high level of insulation, and also enables the shield portion to shield the opening between the inner and outer rings.

[0011] In the second or third configuration, a fourth configuration (fourth configuration) can be adopted in which the thickness of the insulating layer extending toward the end face of the outer ring is greater than the thickness of the insulating layer covering the outer diameter surface of the outer ring. In this way, the outer ring is firmly sandwiched from both sides in the axial direction by the insulating layer on the end face side, which has a greater thickness, thereby improving the adhesion of the insulating layer to the outer ring.

[0012] In the first to fourth configurations, the insulating layer may have a withstand voltage of 200 V or more, or an insulation resistance value of 1 MΩ or more (fifth configuration). In this way, the insulating properties of the insulating layer can prevent electrolytic corrosion of the rolling bearing.

[0013] In the first to fifth configurations, there can be used a configuration (sixth configuration) in which the insulating layer is formed of heat-shrinkable tubing that shrinks when heated, the outer ring has a cylindrical outer peripheral surface with a constant outer diameter along the axial direction, a pair of chamfered portions with an arc-shaped cross section that gradually reduces in outer diameter from the outer peripheral surface outward in the axial direction, and a pair of axial end faces extending radially inward from the pair of chamfered portions, the insulating layer has a cylindrical outer peripheral covering portion that covers the outer peripheral surface of the outer ring, a pair of chamfered covering portions with an arc-shaped cross section that cover the pair of chamfered portions of the outer ring, and a pair of end face covering portions that cover the pair of axial end faces of the outer ring, and the heat-shrinkage initiation temperature of the heat-shrinkable tubing is 80°C or higher.

[0014] According to the sixth configuration, the insulating layer can be formed by placing a heat-shrinkable tube on the radially outer side of the outer ring and heating and deforming the heat-shrinkable tube, eliminating the need for large-scale equipment as is required when providing an insulating layer on the outer ring by insert molding. This reduces the manufacturing costs of the insulated rolling bearing. Furthermore, by using a heat-shrinkable tube with a heat-shrinkage initiation temperature of 80°C or higher, additional thermal shrinkage of the heat-shrinkable tube (insulating layer) is unlikely to occur during use of the rolling bearing, making it possible to prevent wrinkles and other problems from occurring in the insulating layer.

[0015] In the first to sixth configurations, when a slit is formed in the insulating layer and then used, the slit is prevented from expanding during use (seventh configuration). This seventh configuration is obtained when a heat-shrinkable tube having a heat-shrink initiation temperature higher than the use temperature is used.

[0016] Furthermore, in order to solve the above-mentioned problems, the present invention provides a method for manufacturing an insulated rolling bearing (eighth configuration), comprising: a heat-shrinkable tube arrangement step of inserting a rolling bearing having an inner ring, an outer ring provided coaxially radially outward of the inner ring, and a plurality of rolling elements arranged between the inner ring and the outer ring into tubular heat-shrinkable resin before heat shrinkage; and a heat-shrinkable tube heating step of heating the tubular heat-shrinkable resin to thermally shrink it, thereby forming an insulating layer made of the heat-shrinkable resin in close contact with the outer diameter surface of the outer ring.

[0017] This eliminates the need for pre-treatment such as preheating, degreasing, and masking of the bearing (outer ring), post-treatment such as deburring after resin molding, and the need for molds, and it also makes it possible to process a large number of bearings at once, making it possible to simply and efficiently form an insulating layer on the surface of the rolling bearing components.

[0018] The eighth configuration can be configured (ninth configuration) in which the tubular heat-shrinkable resin has a radial heat shrinkage rate of 40% or more and an axial heat shrinkage rate of 20% or less when heated. In this way, when the heat-shrinkable resin is heat-shrunk, it deforms smoothly to conform to the surface of the outer ring (the outer diameter surface and end faces of the outer ring), enabling the insulating layer to be in close contact with the surface of the outer ring.

[0019] In the eighth or ninth configuration, a configuration can be provided in which the outer ring has a cylindrical outer peripheral surface with a constant outer diameter along the axial direction, a pair of chamfered portions with an arc-shaped cross section that gradually reduces in outer diameter from the outer peripheral surface outward in the axial direction, and a pair of axial end faces extending radially inward from the pair of chamfered portions; after the heat-shrinkable tube positioning step, the heat-shrinkable tube made of tubular heat-shrinkable resin is heated and deformed to form an insulating layer having a cylindrical outer peripheral covering portion that covers the outer peripheral surface of the outer ring, a pair of chamfered covering portions with an arc-shaped cross section that cover the pair of chamfered portions of the outer ring, and a pair of end face covering portions that cover the pair of axial end faces of the outer ring; and the heat-shrinkable tube has a heat-shrink initiation temperature of 80°C or higher in the heat-shrinkable tube heating step (tenth configuration).

[0020] The insulating rolling bearing and method of manufacturing an insulating rolling bearing according to the present invention are configured so that a tubular heat-shrinkable resin is applied to the rolling bearing and this heat-shrinkable resin is brought into close contact with the surface of the rolling bearing (outer ring) to form an insulating layer. This eliminates the need for pre-treatment such as preheating, degreasing, and masking of the bearing (outer ring), or post-treatment such as deburring after resin molding, or the use of molds, and it is possible to process a large number of bearings at one time, making it possible to simply and efficiently form insulating layers on the surfaces of rolling bearing components.

[0021] FIG. 5 is a cross-sectional view showing an insulated rolling bearing according to a first embodiment of the present invention; FIG. 5 is a cross-sectional view showing a state in which a rolling bearing has been inserted into tubular heat-shrinkable resin before heat shrinking; FIG. 6 is a cross-sectional view showing a state in which a rolling bearing has been inserted into tubular heat-shrinkable resin before heat shrinking; FIG. 6 is a cross-sectional view showing a first modified example of the insulated rolling bearing shown in FIG. 1;

[0022] An insulating rolling bearing 1 according to a first embodiment of the present invention will be described with reference to the drawings. As shown in Figure 1, this insulating rolling bearing 1 comprises an inner ring 2, an outer ring 3 provided coaxially and radially outward of the inner ring 2, a plurality of rolling elements 4 arranged between the inner ring 2 and the outer ring 3, and a cage 5 that holds the plurality of rolling elements 4 at predetermined intervals in the circumferential direction, on the surface of which an insulating layer 6 is formed.

[0023] This insulated rolling bearing 1 is a ball bearing that uses balls (hereinafter given the same reference numerals as the rolling elements 4) as the rolling elements 4, and these balls 4 roll in an inner ring raceway groove 7 formed in the outer diameter surface of the inner ring 2 and an outer ring raceway groove 8 formed in the inner diameter surface of the outer ring 3. A motor shaft (not shown) is inserted into the axis of the inner ring 2, and the outer ring 3 is configured to fit into a housing (not shown). Note that the configuration of this invention can also be applied to an insulated rolling bearing 1 that uses rollers as the rolling elements 4. Hereinafter, the direction along the rotation axis of the insulated rolling bearing 1 will be referred to as the axial direction, the direction perpendicular to the rotation axis will be referred to as the radial direction, and the direction along the circumference that goes around the rotation axis will be referred to as the circumferential direction.

[0024] The inner ring 2, outer ring 3, and balls 4 are made of steel. The cage 5 is made of steel or resin (e.g., polyamide resin, polyether ether ketone resin, polyphenylene sulfide resin, etc.). R-shaped portions 9 with a predetermined radius of curvature are formed on both axial ends of the outer diameter surface of the outer ring 3, and these R-shaped portions 9 smoothly connect the outer diameter surface and end face of the outer ring 3.

[0025] The insulating layer 6 is formed by heating a tubular heat-shrinkable resin to shrink it and then adhering it to the surface of the outer ring 3 so that it covers the outer diameter surface and end face. The term "heat-shrinkable resin" refers to a resin that, unlike ordinary resins, has the property of thermally shrinking when heated. This thermal shrinkage is manifested, for example, by a change in crystallinity that accompanies heating. The insulating layer 6 made of heat-shrinkable resin has an inherent compressive residual stress field, which distinguishes it from resin insulating layers formed by other methods, such as injection molding. Examples of heat-shrinkable resin materials that can be used include polyolefins, vinyl chlorides, fluororesins, and silicone resins.

[0026] In this embodiment, the material and thickness of the insulating layer 6 are determined so that the insulating layer 6 has a withstand voltage of 200 V or more and an insulation resistance of 1 MΩ or more. In this embodiment, a silicone resin is used as the material of the heat-shrinkable resin that forms the insulating layer 6, and the thickness of the insulating layer 6 after heat shrinkage is set within the range of 0.1 mm to 1.0 mm, thereby achieving the above withstand voltage and insulation resistance values. The withstand voltage can be measured, for example, by the method specified in JIS C2110-1, and the insulation resistance can be measured, for example, by the method specified in JIS C8711.

[0027] The radially inner end of insulating layer 6 that is in close contact with the end face of the outer ring 3 extends radially inward so as to face the opening between the inner ring 2 and the outer ring 3, and this extended portion functions as a shield part 10 that prevents foreign matter from entering the interior of the bearing. This insulated rolling bearing 1 is lubricated by an external supply of lubricating oil, and the radial extension length of shield part 10 is determined as appropriate, taking into consideration factors such as the foreign matter shielding performance and the amount of lubricating oil supplied to the interior of the bearing.

[0028] A method for manufacturing an insulating rolling bearing 1 according to a first embodiment will now be described. In this manufacturing method, a rolling bearing is first assembled, comprising an inner ring 2, an outer ring 3 disposed coaxially radially outward of the inner ring 2, a plurality of balls 4 arranged between the inner ring 2 and the outer ring 3, and a cage 5 that holds the plurality of balls 4 at predetermined intervals in the circumferential direction. As shown in Fig. 2 , this rolling bearing is then inserted into a tubular heat-shrinkable resin (insulating layer 6) before heat shrinking (heat-shrinkable tube placement step). It is preferable to leave a certain amount of axial length for this tubular heat-shrinkable resin, in order to form the insulating layer 6 and shield portion 10 extending from the outer diameter surface of the outer ring 3 to its end face in the heat-shrinking step described below.

[0029] Next, the tubular heat-shrinkable resin is heated to heat-shrink it, forming an insulating layer 6 made of heat-shrinkable resin in close contact with the outer diameter surface and both end faces of the outer ring 3, and a shield portion 10 at the radially inner end of the insulating layer 6 (heat-shrinkable tube heating step). As the heat-shrinkable resin heat-shrinks, it first comes into close contact with the entire outer diameter surface of the outer ring 3. As the heat-shrinkage progresses, it gradually comes into close contact with the end face of the outer ring 3, from the outer diameter side to the inner diameter side, while rolling in the R-machined portion 9. As the heat-shrinkable resin comes into complete contact with the end face of the outer ring 3, shield portions 10 are formed on the radially inner side of both end faces of the outer ring 3. Finally, the radial length of the shield portion 10 is trimmed to a specified length, completing the insulated rolling bearing 1 shown in FIG. 1 .

[0030] In this heat-shrinkable tube heating process, the thickness of the heat-shrinkable resin (insulating layer 6) increases as the heat shrinkage progresses. That is, the thickness of the insulating layer 6 in close contact with the outer diameter surface of the outer ring 3 tends to be relatively thin before the heat shrinkage process, and the thickness of the insulating layer 6 in close contact with the end face of the outer ring 3 tends to be relatively thick after the heat shrinkage process. Furthermore, the thickness of the shield portion 10, which heat shrinks in a free state without being in close contact with the outer ring 3, tends to be even thicker than the thickness of the insulating layer 6 in close contact with the end face of the outer ring 3.

[0031] The tubular heat-shrinkable resin can be appropriately selected from those with various properties. In this embodiment, a silicone-based heat-shrinkable resin is used, which has a radial heat shrinkage rate of 40% or more and an axial heat shrinkage rate of 20% or less when heated. A heat shrinkage rate of 40%, for example, means that if the dimension before heating is 100, the dimension after heating will heat shrink to 60. When a heat-shrinkable resin with this heat shrinkage rate is used, the wall thickness increases by a maximum of 20 to 30% compared to the wall thickness before heating due to heat shrinkage. By using a tubular heat-shrinkable resin with an axial heat shrinkage rate that is as small as possible (preferably 0%), the heat-shrinkable resin is prevented from spreading axially at the end face of the outer ring 3, allowing the heat-shrinkable resin to more smoothly adhere to the end face.

[0032] The insulating rolling bearing 1 and the method for manufacturing the insulating rolling bearing 1 according to the first embodiment are configured so that a tubular heat-shrinkable resin is applied to the rolling bearing and this heat-shrinkable resin is brought into close contact with the surface of the rolling bearing (outer ring 3) to form the insulating layer 6. This eliminates the need for pretreatment such as preheating and degreasing of the bearing (outer ring 3) or for molds, and allows a large number of bearings to be processed at one time, making it possible to form the insulating layer 6 simply and efficiently on the surface of the rolling bearing (outer ring 3).

[0033] Furthermore, in the insulated rolling bearing 1 and the method for manufacturing the insulated rolling bearing 1 according to the first embodiment, the insulating layer 6 is configured to extend from the outer diameter surface of the outer ring 3 to the end face so as to be in close contact with the outer ring 3, thereby preventing contact between the outer ring 3 and the housing and ensuring a high level of insulation.

[0034] Furthermore, in the insulated rolling bearing 1 and the method for manufacturing the insulated rolling bearing 1 according to the first embodiment, the radially inner end of the insulating layer 6 that is in close contact with the end face of the outer ring 3 is configured as a shield part 10 that extends so as to face the opening between the inner ring 2 and the outer ring 3, thereby preventing contact between the outer ring 3 and the housing and ensuring a high level of insulation, and also making it possible to shield the opening between the inner and outer rings 2, 3 by the shield part 10. Furthermore, by shielding the opening with the shield part 10, there is no need to provide a sealing plate as a separate member to close this opening, and therefore manufacturing costs can be reduced.

[0035] Furthermore, in the insulated rolling bearing 1 and the method for manufacturing the insulated rolling bearing 1 according to the first embodiment, R-machined portions 9 with a predetermined radius of curvature are formed at both axial ends of the outer diameter surface of the outer ring 3 to smoothly connect the outer diameter surface and the end face, thereby preventing the insulating layer 6 from lifting up at the boundary between the outer diameter surface and the end face and ensuring high adhesion.

[0036] Furthermore, in the insulated rolling bearing 1 according to the first embodiment, the thickness of the insulating layer 6 extending toward the end face of the outer ring 3 is greater than the thickness of the insulating layer 6 covering the outer diameter surface of the outer ring 3, and therefore the outer ring 3 is firmly sandwiched from both sides in the axial direction by the insulating layer 6 on the end face side where it is thicker, thereby improving the adhesion of the insulating layer 6 to the outer ring 3.

[0037] Furthermore, in the insulated rolling bearing 1 according to the first embodiment, the insulating layer 6 is configured to have a withstand voltage of 200 V or more and an insulation resistance value of 1 MΩ or more, and therefore the insulating properties of this insulating layer 6 can reliably prevent electrolytic corrosion of the rolling bearing.

[0038] Furthermore, the method for manufacturing insulating rolling bearing 1 according to the first embodiment employs a tubular heat-shrinkable resin that, when heated, has a radial thermal shrinkage rate of 40% or more and an axial thermal shrinkage rate of 20% or less, so that when this heat-shrinkable resin is heat-shrunk, it deforms smoothly to fit along the surface (outer diameter surface and end face) of outer ring 3, enabling insulating layer 6 to be in close contact with the surface of outer ring 3.

[0039] Figure 3 shows a first modified example of the insulated rolling bearing 1 shown in Figure 1. The insulated rolling bearing 1 according to the first modified example has the same configuration as that shown in Figure 1 in that the insulating layer 6 covers the outer diameter surface and end faces of the outer ring 3, but differs in that the shield part 10 does not extend radially inward of the insulating layer 6. In this way, although the shield part 10 does not have the effect of preventing foreign matter from entering the inside of the bearing, it is possible to prevent contact between the outer ring 3 and the housing and ensure a high level of insulation, just as with the configuration shown in Figure 1.

[0040] Figure 4 shows a second modified example of the insulated rolling bearing 1 shown in Figure 1. The insulated rolling bearing 1 according to the second modified example differs from the first modified example shown in Figure 3 in that the insulating layer 6 covers only the outer diameter surface of the outer ring 3. In the case of a configuration in which a housing fits only onto the outer diameter surface of the outer ring 3 of the insulated rolling bearing 1 and does not come into contact with the end face of the outer ring 3, if the insulating layer 6 is formed only on the outer diameter surface of the outer ring 3, contact between the outer ring 3 and the housing can be prevented and a high level of insulation can be ensured, similar to the configurations shown in Figures 1 and 3.

[0041] 5 shows an insulating rolling bearing according to a second embodiment of the present invention. This insulating rolling bearing comprises an outer ring 3, an inner ring 2 arranged coaxially radially inward of the outer ring 3, a plurality of rolling elements 4 mounted at intervals in the circumferential direction between the outer ring 3 and the inner ring 2, an annular cage 5 that maintains the circumferential spacing of the plurality of rolling elements 4, and a resin insulating layer 6 (insulating coating) provided on the outer ring 3.

[0042] The axial direction is the direction parallel to the central axis of the outer ring 3 (the central axis of the bearing), the radial direction is the direction perpendicular to the central axis of the outer ring 3, and the circumferential direction is the direction along the circumference that goes around the central axis of the outer ring 3. The outer ring 3 and the inner ring 2 are formed symmetrically with respect to the axial center. Furthermore, the axially inner side is the side that approaches the axial center of the outer ring 3 and the inner ring 2 along the axial direction, and the axially outer side is the side that moves away from the axial center of the outer ring 3 and the inner ring 2 along the axial direction.

[0043] As shown in Figure 4, the rolling elements 4 are sandwiched radially between an outer ring raceway groove 8 formed on the inner circumference of the outer ring 3 and an inner ring raceway groove 7 formed on the outer circumference of the inner ring 2. In this example, the rolling elements 4 are balls. The outer ring raceway groove 8 and the inner ring raceway groove 7 are grooves whose cross sections perpendicular to the circumferential direction are arc-shaped. The outer ring 3, the inner ring 2, and the rolling elements 4 are each made of steel.

[0044] The outer ring 3 has a cylindrical outer peripheral surface 3a with a constant outer diameter along the axial direction, a pair of chamfered portions 3b with an arc-shaped cross section whose outer diameter gradually decreases axially outward from the outer peripheral surface 3a, and a pair of axial end faces 3c extending radially inward from the pair of chamfered portions 3b. The axial end faces 3c are flat surfaces perpendicular to the axial direction.

[0045] Here, the outer diameter φD (see FIG. 8) of the outer peripheral surface 3a of the outer ring 3 is set to be 45 mm or greater and 110 mm or less, and the axial width dimension of the outer ring 3 is set to be 9 mm or greater and 30 mm or less. Furthermore, the surface roughness along the axial direction of the outer peripheral surface 3a of the outer ring 3 is set to be Ra 0.05 μm or greater and 1.6 μm or less. The chamfered portion 3b of the outer ring 3 has an arc-shaped surface in a cross section perpendicular to the circumferential direction that smoothly connects to the outer peripheral surface 3a of the outer ring 3, and the arc radius R (see FIG. 8) is set to be 0.3 mm or greater.

[0046] The insulating layer 6 comprises a cylindrical outer peripheral covering portion 6a that covers the outer peripheral surface 3a of the outer ring 3, a pair of chamfer covering portions 6b that have an arc-shaped cross section and cover the pair of chamfered portions 3b of the outer ring 3, and a pair of end face covering portions 6c that cover the pair of axial end faces 3c of the outer ring 3. The pair of chamfer covering portions 6b are formed to be continuous with both axial ends of the outer peripheral covering portion 6a, and the pair of end face covering portions 6c are formed to be continuous with the radial inner ends of the pair of chamfer covering portions 6b. The end face covering portions 6c are preferably provided in close contact with the axial end faces 3c of the outer ring 3, but may also be provided in a state where they are raised above the axial end faces 3c of the outer ring 3 (where there is a gap between the axial end faces 3c of the outer ring 3 and the end face covering portions 6c). Note that the thickness of the insulating layer 6 is greatly exaggerated in the figures for ease of understanding.

[0047] The thickness of the insulating layer 6 is set so that the outer peripheral covering portion 6a (i.e., the thinnest portion among the outer peripheral covering portion 6a, the chamfered covering portion 6b, and the end face covering portion 6c) has a withstand voltage of 200 V or more and an insulation resistance of 1 MΩ or more. This insulating layer 6 is formed from a heat-shrinkable resin tube 11 that shrinks when heated, and as will be described later, this heat-shrinkable tube 11 is selected to have a heat-shrinkage start temperature T0 that is higher than the operating temperature of the insulating rolling bearing.

[0048] An example of a method for manufacturing an insulating rolling bearing according to the second embodiment will be described with reference to FIG.

[0049] [Bearing Preparation Step] (Step S1 in Fig. 7) A rolling bearing 12 shown in Fig. 8 is prepared. This rolling bearing 12 has a plurality of rolling elements 4 assembled between an outer ring 3 and an inner ring 2, and is not provided with the insulating layer 6 shown in Fig. 6.

[0050] [Heat-shrinkable tube placement process] (Step S2 in FIG. 7) After the above-described bearing preparation process, a resin heat-shrinkable tube 11 is placed on the radially outer side of the rolling bearing 12, as shown in FIG.

[0051] The heat-shrinkable tube 11 may be made by irradiating a resin material such as polyolefin resin, polyvinyl chloride resin, or fluororesin into a tubular shape with an electron beam to crosslink the resin material, then heating the tube to a predetermined high temperature and stretching it in the radial direction (or in the radial and axial directions), and then cooling the tube. In this case, the dimensions of the tube after stretching correspond to the dimensions of the heat-shrinkable tube 11 before shrinking due to heating.

[0052] Furthermore, the axial length w of the heat-shrinkable tube 11 (see FIG. 8 ) is set to be sufficiently longer (at least 1.6 times, preferably at least 1.8 times) than the axial width dimension of the outer ring 3 (the distance between the pair of axial end faces 3 c) so that the axial end faces 3 c of the outer ring 3 can be reliably covered with the heat-shrinkable tube 11 in the heat-shrinkable tube heating step described below.

[0053] [Heat-shrink tube heating process] (Step S3 in Figure 7) After the heat-shrink tube arrangement process described above, the heat-shrink tube 11 is heated and deformed to sequentially form an insulating layer 6 having a cylindrical outer peripheral covering portion 6a covering the outer peripheral surface 3a of the outer ring 3, a pair of chamfer covering portions 6b with an arc-shaped cross section covering the pair of chamfered portions 3b of the outer ring 3, and a pair of end face covering portions 6c covering the pair of axial end faces 3c of the outer ring 3, as shown in Figures 9 and 10. Methods that can be used to heat the heat-shrink tube 11 include blowing hot air onto the outer periphery of the heat-shrink tube 11 using a heating gun or the like, or passing the rolling bearing 12 and the heat-shrink tube 11 arranged radially outward through a heating furnace while supported by a support.

[0054] As shown in Figure 11, heat shrinkage of heat-shrinkable tubing 11 begins when it is heated to a temperature equal to or higher than the heat shrinkage start temperature T0, which is determined for each product. When it is heated to a predetermined shrinkage temperature T1, it has the potential to heat shrink to a final shrinkage rate (for example, 60%) corresponding to that heating temperature. On the other hand, heating of heat-shrinkable tubing 11 provided on rolling bearings is usually terminated before it reaches its final shrinkage rate when it has come into close contact with the outer ring 1, and this often leaves room for additional heat shrinkage by reheating.

[0055] For example, when a rotating shaft 13 (see FIG. 12) of an electric motor, alternator, or the like is supported for rotation by a rolling bearing, the bearing temperature rises after operation starts due to factors such as internal bearing friction, and settles down to a steady temperature (bearing operating temperature) after a certain amount of time has passed. If this bearing operating temperature is equal to or higher than the heat shrinkage start temperature T0 of the heat shrinkable tube 11 (for example, temperature T2 shown in FIG. 11), additional thermal shrinkage of the heat shrinkable tube 11 (insulating layer 6) may occur during use of the rolling bearing, and wrinkles or the like may occur in the insulating layer 6 due to dimensional changes.

[0056] In the insulating rolling bearing according to the second embodiment, the insulating layer 6 is formed using a heat-shrinkable tube 11 whose heat-shrinkage starting temperature T0 is 80°C or higher, and therefore there is little risk of additional thermal shrinkage of the heat-shrinkable tube 11 (insulating layer 6) occurring during use of the rolling bearing.

[0057] For example, if the operating temperature of the bearing is not expected to exceed 80°C, additional thermal shrinkage during use of the rolling bearing can be prevented by using a heat-shrinkable tube 11 whose thermal shrinkage start temperature T0 is 80°C or higher (for example, 90°C or higher if a safety margin is ensured).

[0058] As shown in Figure 12, the insulating rolling bearing according to the second embodiment can be used as a rolling bearing that supports a rotating shaft 13 of an electrical device (such as the rotating shaft of an electric motor, the rotating shaft of a reducer that reduces the rotation of an electric motor, or the rotating shaft of an alternator). In Figure 12, the insulating rolling bearing is fitted between the cylindrical inner periphery of a housing bore 15 formed in a non-rotating housing 14 and the outer periphery of a rotating shaft 13 located at the centre of the housing bore 15. Here, the inner ring 2 is on the rotating side and the outer ring 3 is on the non-rotating side, and therefore the insulating rolling bearing is assembled in such a manner that the inner ring 2 is fitted onto the outer periphery of the rotating shaft 13 with an interference fit, and the outer ring 1 is fitted onto the inner periphery of the housing bore 15 with a clearance fit.

[0059] 8 , in the insulating rolling bearing according to the second embodiment, the heat-shrinkable tube 11 is disposed radially outward of the outer ring 1, and the insulating layer 6 can be formed by heating and deforming the heat-shrinkable tube 11, so there is no need for large-scale equipment as is required when providing the insulating layer 6 on the outer ring 3 by insert molding. This makes it possible to reduce the manufacturing costs of the insulating rolling bearing.

[0060] Furthermore, in the insulating rolling bearing according to the second embodiment, when forming the insulating layer 6, a heat-shrinkable tube 11 whose heat-shrinkage start temperature T0 is higher than the operating temperature of the bearing is used. This makes it difficult for additional thermal shrinkage of the heat-shrinkable tube 11 (insulating layer 6) to occur during use of the rolling bearing, making it possible to prevent wrinkles and the like from occurring in the insulating layer 6.

[0061] Whether or not a heat-shrinkable tube 11 having a heat-shrinkage start temperature T0 of 80°C or higher (having a heat-shrinkage start temperature T0 higher than the bearing operating temperature) is used in the insulating rolling bearing according to the second embodiment can be easily determined by forming a notch in, for example, the end face covering portion 6c of the insulating layer 6 of the insulating rolling bearing, and visualizing the change in the insulating layer 6 when additional thermal shrinkage occurs.

[0062] That is, if an insulating rolling bearing with a notch formed is installed, for example, between the housing 14 and rotating shaft 13 shown in Figure 12 and then operated normally (regular operation), and if the notch is prevented from expanding even when the bearing temperature rises during this normal operation, it can be determined that a heat-shrinkable tube 11 with a heat-shrinkage start temperature T0 of 80°C or higher is being used, and if the notch expands, it can be determined that a heat-shrinkable tube 11 with a heat-shrinkage start temperature T0 of less than 80°C is being used.

[0063] Furthermore, in the insulated rolling bearing according to the second embodiment, the insulating layer 6 has a withstand voltage of 200 V or more and an insulation resistance value of 1 MΩ or more, and therefore when used as an insulated rolling bearing supporting the rotating shaft 13 of an electric motor for driving an electric vehicle or a reducer for that electric motor, it is possible to effectively prevent electrolytic corrosion from occurring in the outer ring 3, inner ring 2, and rolling elements 4. As evaluation methods, the test method specified in JIS C 2110-1:2016 can be used for the withstand voltage, and the test method specified in JIS C 2140:2009 can be used for the insulation resistance. Note that withstand voltage refers to an applied voltage that does not result in dielectric breakdown.

[0064] In the above embodiments, as shown in Figures 1, 6, etc., an example has been given in which the axial width dimension of the outer ring 3 and the axial width dimension of the inner ring 2 are the same (i.e., the axial end face 3c of the outer ring 3 and the axial end face 2c of the inner ring 2 are at the same axial position), but it is also possible to set the axial width dimension of the outer ring 3 smaller than the axial width dimension of the inner ring 2 so that the surface of the end face covering portion 6c of the insulating layer 6 is at the same axial position as the axial end face 2c of the inner ring 2.

[0065] Furthermore, in each of the above embodiments, balls are used as the rolling elements 4, but rolling elements 4 of other shapes, such as cylindrical rollers, may also be used.

[0066] 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.

[0067] 2 Inner ring 3 Outer ring 3a Outer peripheral surface 3b Chamfered portion 3c Axial end face 4 Rolling element (ball) 6 Insulating layer (insulating coating) 6a Outer peripheral coating portion 6b Chamfered coating portion 6c End face coating portion 10 Shield portion 11 Heat shrinkable tube

Claims

1. An insulated rolling bearing comprising: an inner ring (2); an outer ring (3) arranged coaxially on the radially outer side of the inner ring (2); a plurality of rolling elements (4) arranged between the inner ring (2) and the outer ring (3); and an insulating layer (6) made of heat-shrinkable resin arranged so as to adhere closely to the outer diameter surface of the outer ring (3).

2. An insulated rolling bearing according to claim 1, wherein the insulating layer (6) extends from the outer diameter surface of the outer ring (3) to the end face thereof so as to be in close contact with the outer diameter surface.

3. An insulated rolling bearing as described in claim 2, wherein a shield portion (10) facing the opening between the inner ring (2) and the outer ring (3) is extended from the radially inner end of the insulating layer (6) that is in close contact with the end face of the outer ring (3).

4. An insulated rolling bearing as described in claim 2 or 3, wherein the thickness of the insulating layer (6) extending toward the end face of the outer ring (3) is greater than the thickness of the insulating layer (6) covering the outer diameter surface of the outer ring (3).

5. An insulating rolling bearing according to any one of claims 1 to 3, wherein the withstand voltage of the insulating layer (6) is 200 V or more, or the insulation resistance value of the insulating layer (6) is 1 MΩ or more.

6. An insulated rolling bearing according to claim 1, characterized in that the insulating layer (6) is formed from heat-shrinkable tubing (11) that shrinks when heated, the outer ring (3) has a cylindrical outer peripheral surface (3a) with a constant outer diameter along the axial direction, a pair of chamfered portions (3b) with an arc-shaped cross section whose outer diameter gradually decreases from the outer peripheral surface (3a) outward in the axial direction, and a pair of axial end faces (3c) extending radially inward from the pair of chamfered portions (3b), the insulating layer (6) has a cylindrical outer peripheral covering portion (6a) that covers the outer peripheral surface (3a) of the outer ring (3), a pair of chamfered covering portions (6b) with an arc-shaped cross section that covers the pair of chamfered portions (3b) of the outer ring (3), and a pair of end face covering portions (6c) that cover the pair of axial end faces (3c) of the outer ring (3), and the heat-shrinkable tubing (11) has a heat-shrinkage start temperature (T0) of 80°C or higher.

7. An insulated rolling bearing according to claim 6, wherein when a notch is formed in the insulating layer (6) and the bearing is used, the notch is prevented from expanding during use.

8. A method for manufacturing an insulated rolling bearing, comprising: a heat-shrinkable tube placement step of inserting a rolling bearing having an inner ring (2), an outer ring (3) provided coaxially radially outside the inner ring (2), and a plurality of rolling elements (4) arranged between the inner ring (2) and the outer ring (3) into a tubular heat-shrinkable resin before heat shrinking; and a heat-shrinkable tube heating step of heat-shrinking the tubular heat-shrinkable resin to form an insulating layer (6) made of the heat-shrinkable resin in close contact with the outer diameter surface of the outer ring (3).

9. A method for manufacturing an insulating rolling bearing according to claim 8, wherein the tubular heat-shrinkable resin has a radial heat shrinkage rate of 40% or more and an axial heat shrinkage rate of 20% or less when heated.

10. The outer ring (3) has a cylindrical outer peripheral surface (3a) with a constant outer diameter along the axial direction, a pair of chamfered portions (3b) with an arc-shaped cross section whose outer diameter gradually decreases from the outer peripheral surface (3a) toward the axially outward direction, and a pair of axial end faces (3c) extending radially inward from the pair of chamfered portions (3b), and after the heat-shrinkable tube placement step, the heat-shrinkable tube (11) made of tubular heat-shrinkable resin is heated and deformed to form an insulating layer (6) having a cylindrical outer peripheral covering portion (6a) covering the outer peripheral surface (3a) of the outer ring (3), a pair of chamfered covering portions (6b) with an arc-shaped cross section covering the pair of chamfered portions (3b) of the outer ring (3), and a pair of end face covering portions (6c) covering the pair of axial end faces (3c) of the outer ring (3), 10. The method for manufacturing an insulating rolling bearing according to claim 8, wherein the heat shrinkable tube (11) has a heat shrink start temperature (T0) of 80° C. or higher in the heat shrinkable tube heating step.

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