Roller bearing

Abstract

To provide both creep resistance and electric erosion resistance in a bearing device.SOLUTION: At least one of an inner diameter surface 11b of an inner race 11 and an outer diameter surface 12b of an outer race 12 is covered by a coating layer 30. The coating layer 30 is composed of multiple layers. A surface layer of the multiple layers is composed of an anti-creep coat 31 having lubricity, and at least one layer except for the surface layer is composed of an insulation coat 32 having insulation properties.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing. [Background technology]

[0002] When a rolling bearing is placed between a shaft and a housing, the inner ring of the rolling bearing is fitted onto the shaft, and the outer ring is fitted onto the inner periphery of the housing. The fit between the inner or outer ring and the corresponding shaft or housing is selected from interference fit, normal fit, or clearance fit, taking into consideration the load conditions, ease of device assembly, etc. An inner or outer ring in a clearance fit state may creep, i.e., rotate circumferentially relative to the shaft or housing, which is its mating member.

[0003] For example, in bearing devices that support shafts in housings via rolling bearings, such as those found in automobile transmissions and electric vehicle (EV) motors, the outer ring of the rolling bearing is clearance-fitted into the housing to facilitate assembly into the housing. As a result, the outer ring can creep due to unbalanced loads on the shaft when under load or at high speeds.

[0004] In response to this, Patent Document 1 proposes a rolling bearing that stably maintains excellent creep resistance. This rolling bearing has a sintered film on the outer diameter surface of the outer ring, which is the surface that fits with the housing, or on the inner diameter surface of the inner ring, which is the surface that fits with the shaft. This sintered film contains an organic binder, a solid lubricant powder such as molybdenum disulfide powder, and a friction and wear modifier such as antimony oxide powder.

[0005] On the other hand, in EV motor support bearings, leakage current from the motor can cause discharge between the rolling elements and the raceway surface, which can lead to electrolytic corrosion damage to the inner ring, outer ring, or rolling elements.

[0006] In response to this, Patent Document 2 proposes a structure for preventing electrolytic corrosion in rolling bearings. This rolling bearing is described as having a ceramic coating formed on the inner diameter surface and end face of the inner ring and the outer diameter surface and end face of the outer ring, and the ceramic coating is impregnated with insulating synthetic resin. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6338035 [Patent Document 2] Japanese Utility Model Application Publication No. 60-85626 Summary of the Invention [Problem to be solved by the invention]

[0008] However, although the rolling bearing in Patent Document 1 contains solid lubricant powder and friction and wear adjusters, when it is used to support the shaft of an EV motor, leakage current from the motor can cause electricity to flow, resulting in discharge between the rolling elements and the raceway surface, which could cause electrolytic corrosion damage.

[0009] On the other hand, although the rolling bearing of Patent Document 2 is coated with ceramic to provide electrolytic corrosion resistance, if creep occurs in the outer ring or inner ring, there is no lubrication at the fitting surface with the housing or shaft, so there is a concern that friction and wear to the extent that it affects the shaft support function will occur at the fitting surface between the creeping raceway and the corresponding housing or shaft.

[0010] In view of the above background, an object of the present invention is to provide a rolling bearing that can simultaneously achieve both creep resistance and electrolytic corrosion resistance under usage conditions in which leakage current is transmitted to the inner ring or outer ring and the inner ring or outer ring is clearance-fitted onto the corresponding shaft or housing. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a rolling bearing comprising an inner ring, an outer ring, and rolling elements arranged between the inner ring and the outer ring, wherein at least one of the inner diameter surface of the inner ring and the outer diameter surface of the outer ring is covered with a coating layer, wherein the coating layer is made up of multiple layers, a surface layer of which is made of a creep-resistant coating having lubricating properties, and at least one of the multiple layers excluding the surface layer is made of an insulating coating having insulating properties.

[0012] According to the above configuration, the creep-resistant coating, which is a multi-layer surface covering the inner diameter surface of the inner ring or the outer diameter surface of the outer ring, forms the mating surface with the shaft or housing, and therefore provides lubrication when creep occurs, preventing friction and wear on the mating surface between the inner diameter surface of the inner ring or the outer diameter surface of the outer ring and the corresponding mating surface with the shaft or housing. Furthermore, because at least one layer, excluding the multi-layer surface layer, is made of an insulating coating with insulating properties, the insulating coating breaks the circuit through which leakage current flows, preventing discharge between the inner ring or outer ring and the rolling elements and preventing electrolytic corrosion damage to the inner ring, outer ring, and rolling elements. In other words, a rolling bearing with the above configuration can achieve both of these effects simultaneously.

[0013] For example, the insulating coating is a fired film containing at least one of ceramics, epoxy resin, and polyamideimide resin.

[0014] For example, the creep-resistant coating is a fired film containing a resin binder and a powder of a solid lubricant.

[0015] The insulating coating of the coating layer may have a side covering portion that covers a width surface of the inner ring or a width surface of the outer ring.

[0016] The creep-resistant film of the coating layer preferably has an extended coating portion that covers a portion of the raceway other than the inner diameter surface of the inner ring or the outer diameter surface of the outer ring and that is in contact with the shaft or housing. [Effects of the Invention]

[0017] By adopting the above configuration, the present invention can provide a rolling bearing that can simultaneously achieve both creep resistance to prevent friction and wear on the fitting surfaces and galvanic corrosion resistance to prevent galvanic corrosion of the raceways and rolling elements under conditions of use in which leakage current is transmitted to the inner ring or outer ring and the inner ring or outer ring is clearance-fitted into the corresponding shaft or housing. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing a first embodiment of a rolling bearing according to the present invention; [Figure 2] FIG. 1 is a cross-sectional view showing an example of an EV motor to which a rolling bearing according to the present invention is attached. [Figure 3] FIG. 10 is a cross-sectional view showing an inner ring of a second embodiment of a rolling bearing according to the present invention. [Figure 4] FIG. 10 is an enlarged cross-sectional view showing the positional relationship between the inner ring and the housing of a third embodiment of the rolling bearing according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] A first embodiment of the present invention will be described with reference to the drawings.

[0020] As shown in FIGS. 1 and 2, a rolling bearing 10 according to the first embodiment is interposed between a shaft 1 and a housing 2 that surrounds the shaft 1.

[0021] In the following, in an ideal state where the design rotation center line of the rolling bearing 10 coincides with the rotation center line of the shaft 1, the direction along the center of rotation will be referred to as the "axial direction." The direction along the circumference going around the rotation center line will be referred to as the "circumferential direction." The direction perpendicular to the rotation center line will be referred to as the "radial direction."

[0022] The shaft 1 rotates relative to the housing 2. The shaft 1 is, for example, a rotating shaft provided in a motor of an electric vehicle (EV). The shaft 1 has a mating surface 1a formed in the shape of a cylindrical surface extending in the circumferential direction.

[0023] The housing 2 is stationary relative to the shaft 1 and supports the shaft 1 via a rolling bearing 10. The housing 2 is, for example, a partition wall formed as part of the case of the motor. The housing 2 has a mating surface 2a formed as a cylindrical surface extending in the circumferential direction. The mating surface 2a is set concentrically with the mating surface 1a of the shaft 1.

[0024] The rolling bearing 10 rotatably supports the shaft 1 relative to the housing 2, and bears a radial load acting between the shaft 1 and the housing 2, etc.

[0025] The EV motor shown in FIG. 2 has a housing 2 that forms the outer periphery of the motor, and a rotor 5 that rotates integrally with the shaft 1. A stator 6 is fixed inside the housing 2 and positioned outward from the rotor 5. A coil is attached inside the stator 6, and power is supplied to the stator 6 via lead wires 7. A flange bracket 3 is attached to the opening of the housing 2. The shaft 1 passes through the center hole of the flange bracket 3. The flange bracket 3 has a mating surface 3a that is formed as a cylindrical surface extending in the circumferential direction. This mating surface 3a is also set concentrically with the mating surface 1a of the shaft 1. A first rolling bearing 10 is disposed between the mating surface 2a on the bottom side of the housing 2 (right side in FIG. 1) and the mating surface 1a of the shaft 1. A second rolling bearing 10 is disposed between the mating surface 3a of the flange bracket 3 and the mating surface 1a of the shaft 1.

[0026] The rolling bearing 10 comprises an inner ring 11 attached to the shaft 1, an outer ring 12 attached to the housing 2 or flange bracket 3, a plurality of rolling elements 13 interposed between the inner ring 11 and the outer ring 12, and a cage 14 that maintains the circumferential spacing between the rolling elements 13. A deep groove ball bearing is exemplified as the rolling bearing 10.

[0027] The inner ring 11 is an annular bearing component having a raceway surface 11a extending in the circumferential direction on the outer periphery and an inner diameter surface 11b extending in the circumferential direction on the inner periphery. The inner diameter surface 11b is formed as a cylindrical surface concentric with the mating surface 1a of the shaft 1. The inner diameter surface 11b of the inner ring 11 is fitted onto the mating surface 1a of the shaft 1.

[0028] The fit between the inner diameter surface 11b of the inner ring 11 and the mating surface 1a of the shaft 1 is set to be an interference fit with an interference margin. The inner ring 11 is fixed to the shaft 1 by this interference fit so as to rotate integrally with the shaft 1.

[0029] The outer ring 12 is an annular bearing component having a raceway surface 12a extending in the circumferential direction on the inner periphery side and an outer diameter surface 12b extending in the circumferential direction on the outer periphery side. The outer diameter surface 12b is formed as a cylindrical surface concentric with the inner diameter surface 11b of the inner ring 11.

[0030] The outer ring 12 is clearance-fitted into the housing 2 .

[0031] The inner ring 11 and the outer ring 12 are each made of steel. The metal may be, for example, SUJ2, SCM420, SCr420, SCR420, or SUS440. The inner ring 11 and the outer ring 12 are appropriately subjected to quenching and tempering, carburizing, or carbonitriding.

[0032] As shown in FIG. 1 , in the first embodiment, the outer diameter surface 12b of the outer ring 12 is covered with a coating layer 30. The coating layer 30 is made up of multiple layers. Of the multiple layers making up the coating layer 30, the radially outermost surface layer is made up of a creep-resistant coating 31 having lubricity. The outer diameter surface of this creep-resistant coating 31 becomes the fitting surface that is clearance-fitted with the fitting surface 2a of the housing 2 or the fitting surface 3a of the flange bracket 3.

[0033] The creep-resistant coating 31 may be, for example, a fired film containing a resin binder and a solid lubricant. The resin binder is prepared by blending a base material with a curing agent, and the curing agent is reacted to harden the resin. Hardening the solid lubricant with the resin binder provides high adhesion and wear resistance. It also reduces wear on the housing 2 or flange bracket 3. A polyamide-imide resin, for example, is preferable as the base material from the viewpoint of durability. Furthermore, a combination of an epoxy resin and a reactive compound that reacts with the epoxy resin is preferable as the curing agent, as this facilitates hardening.

[0034] The epoxy resin is not particularly limited as long as it can act as a curing agent. Examples include bisphenol A epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, brominated epoxy resins, and alicyclic epoxy resins. Examples of the reactive compound include aliphatic polyamines, polyaminoamides, polymercaptans, aromatic polyamines, acid anhydrides, and dicyandiamide. In addition to these components, a curing accelerator may be added to enhance reactivity. Examples of the curing accelerator that can be used include tertiary amines, tertiary amine salts, imidazole, phosphine, phosphonium salts, and sulfonium salts.

[0035] The solid lubricant is preferably softer than the material of the housing 2 in order to exhibit lubricating properties, and specifically, preferably has a hardness of Hv 50 to 150. Examples include molybdenum disulfide powder, graphite powder, tungsten disulfide, and polytetrafluoroethylene. Among these, it is preferable to use molybdenum disulfide alone or to use a mixture of molybdenum disulfide and other materials.

[0036] The material of the creep-resistant coating 31 may further contain a friction and wear modifier. The friction and wear modifier is a material that improves the wear resistance of the fired film, and it is preferable to use a material that is softer than the material of the housing 2. Examples of such a material include antimony oxide, talc, mica, potassium titanate, tin, copper, zinc, and nickel. Among these, antimony oxide is particularly preferable.

[0037] To form the creep-resistant coating 31 as a fired film, for example, a coating solution is prepared by dissolving a resin binder in a solvent and adding a powder of a solid lubricant or a friction and wear modifier to the solution. This coating solution is applied to the surface of an insulating coating or other intermediate film, which will be described later, and then heated to evaporate the solvent, forming a coating.

[0038] Of the layers constituting the coating layer 30, at least one layer excluding the creep-resistant coating 31 is made of an insulating coating 32 having insulating properties. The insulating coating 32 is formed on the outer periphery of the outer diameter surface 12b, and the creep-resistant coating 31 is formed outside the insulating coating 32.

[0039] The insulating coating 32 is made of an insulating material. The insulating coating 32 prevents leakage current from the fitting surfaces 2a, 3a of the housing 2 or the flange bracket 3 to the outer diameter surface 12b of the outer ring 12. The outer diameter surface 12b and the fitting surface 2a are formed to insulate each other so that they do not reach each other.

[0040] Examples of materials for the insulating coating 32 include ceramics, epoxy resin, and polyamide-imide resin. In the case of ceramics, epoxy resin, or polyamide-imide resin, a baked film may be formed by heating the applied material. In the case of epoxy resin or polyamide-imide resin, a curing agent may be included in the material and baked to form the insulating coating.

[0041] To break the circuit through which leakage current flows between the outer ring 12 and the inner ring 11 and prevent discharge between the rolling elements 13 and the raceway surfaces 11a, 12a, at least one of the outer diameter surface 12b of the outer ring 12 and the inner diameter surface 11b of the inner ring 11 must be covered with a coating layer 30 including an insulating coating 32. Preventing discharge between the rolling elements 13 and the raceway surfaces 11a, 12a prevents electrolytic corrosion of the rolling elements 13 and the raceway surfaces 11a, 12a.

[0042] The illustrated insulating coating 32 has a central covering portion 32a that covers the outer diameter surface 12b of the outer ring 12, and side covering portions 32b that cover the width surface 12c of the outer ring 12. Here, the width surface 12c of the outer ring 12 is one of two side surfaces that define the width of the outer ring 12. The width surface 12c faces the side surfaces of the housing 2 and the flange bracket 3 in the axial direction.

[0043] The central covering portion 32a and the side covering portions 32b are integrally formed coatings. The side covering portions 32b are intended to provide insulation between the housing 2, the flange bracket 3, and the width surface 12c of the outer ring 12, and by preventing discharge between them, electrolytic corrosion of the housing 2, the flange bracket 3, and the width surface 12c is prevented.

[0044] The rolling bearing 10 according to the first embodiment is as described above, and of the multiple layers constituting the coating layer 30 covering the outer diameter surface 12b of the outer ring 12, the creep-resistant coating 31, which is the surface layer, forms the mating surface with the housing 2 and flange bracket 3, and therefore exhibits lubricity when creep occurs, preventing friction and wear on the outer diameter surface 12b of the outer ring 12 and the corresponding mating surfaces 2a, 3a of the housing 2 and flange bracket 3. Furthermore, of the multiple layers constituting the coating layer 30, at least one layer excluding the creep-resistant coating 31, which is the surface layer, is made of an insulating coating 32 having insulating properties, and therefore the insulating coating 32 breaks the circuit through which leakage current flows, preventing discharge between the inner ring 11 or outer ring 12 and the rolling elements 13, and preventing electrolytic corrosion damage to the inner ring 11, outer ring 12, and rolling elements 13. Therefore, the rolling bearing 10 can simultaneously achieve both creep resistance and electrolytic corrosion resistance under operating conditions in which leakage current is transmitted to the inner ring 11 or outer ring 12 and the inner ring 11 or outer ring 12 is loosely fitted into the corresponding shaft 1 or housing 2 or flange bracket 3.

[0045] Furthermore, since the insulating coating 32 of the coating layer 30 has side covering portions 32b that cover the width faces 12c of the outer ring 12, discharge between the width faces 12c and the opposing housing 2 or flange bracket 3 can be prevented, and electrolytic corrosion of the width faces 12c, etc. can be prevented.

[0046] The coating layer 30 is not limited to a two-layer structure as shown in the figure. A coating having another function may be interposed between the outer diameter surface 12b and the creep-resistant coating 31. Furthermore, another insulating coating and another creep-resistant coating may be laminated between the insulating coating 32 and the creep-resistant coating 31. Note that when an alternating current flows, capacitance is involved in electrolytic corrosion resistance, so the coating must have a certain level of capacitance. The required capacitance is determined by the component configuration, coating material, film thickness, etc., and is therefore set appropriately depending on the conditions of use.

[0047] The second embodiment will be described with reference to Fig. 3. Below, only the differences from the first embodiment will be described.

[0048] In the rolling bearing according to the second embodiment, the inner diameter surface 11b of the inner ring 11 is covered with a coating layer 40 made up of multiple layers. The insulating coating 41 of the coating layer 40 has a central covering portion 41a that covers the inner diameter surface 11b of the inner ring 11 and side covering portions 41b that cover the width faces 11c of the inner ring 11. The width face 11c of the inner ring 11 is one of two side faces that define the width of the inner ring 11. The width face 11c faces a side face of the housing 2 or the flange bracket 3 in the axial direction.

[0049] Furthermore, creep-resistant coating 42, which is the surface layer of coating layer 40, forms a mating surface that is fitted onto mating surface 1a of shaft 1. In this embodiment, creep-resistant coating 42 provides creep resistance to shaft 1.

[0050] The insulating coating 41 and the creep-resistant coating 42 may have the same material structure and be formed by the same method as the insulating coating and the creep-resistant coating in the first embodiment.

[0051] The coating layer 40 further includes an intermediate layer 43 between the insulating coating 41 and the creep-resistant coating 42. On the surface side of the intermediate layer 43, the creep-resistant coating 42 is formed as a surface layer.

[0052] The configuration of the intermediate layer 43 is not particularly limited as long as it does not impair the performance of the insulating coating 41 and the creep-resistant coating 42. For example, it may be a layer that improves insulation performance, firmly fixes the creep-resistant coating 42, or has other properties. For example, if directly laminating the creep-resistant coating 42 on the insulating coating 41 results in insufficient adhesion between the two, it is advisable to use an intermediate layer 43 that has good adhesion to both. Furthermore, if the insulating coating 41 and the creep-resistant coating 42 do not provide the required capacitance, the intermediate layer 43 may be used to achieve the required capacitance. Although not shown, the intermediate layer 43 may be formed not only between the insulating coating 41 and the creep-resistant coating 42, but also between the insulating coating 41 and the inner ring 11. Furthermore, the intermediate layer 43 may be formed not only as a single layer but also as multiple layers.

[0053] According to the second embodiment, the circuit through which the leakage current flows is interrupted by the insulating coating 41, preventing discharge between the inner ring 11 or the outer ring 12 and the rolling elements 13, thereby preventing electrolytic corrosion damage to the inner ring 11, the outer ring 12, and the rolling elements 13, and also preventing discharge between the width surface 11c of the inner ring 11 and the opposing housing 2 or flange bracket 3, thereby preventing electrolytic corrosion of the width surface 11c, etc.

[0054] The third embodiment will be described with reference to FIG.

[0055] The rolling bearing according to the third embodiment differs from the second embodiment in that the creep-resistant coating 42 further includes an extended coating portion 42b that covers a portion of the raceway other than the inner diameter surface 11b of the inner ring 11 and that comes into contact with the housing 2. The central coating portion 43a of the intermediate layer 43 overlaps the central coating portion 41a of the insulating coating 41, and the central coating portion 42a of the creep-resistant coating 42 overlaps the central coating portion 43a of the intermediate layer 43. The side coating portions 43b of the intermediate layer 43 overlap the side coating portions 41b of the insulating coating 41, and the extended coating portions 42b of the creep-resistant coating 42 overlap the side coating portions 43b of the intermediate layer 43.

[0056] When the inner ring 11 creeps, the extended coating portion 42b of the creep-resistant coating 42 slides circumferentially against the side surface of the housing 2. Therefore, by providing the extended coating portion 42b, friction and wear between the width surface 11c of the inner ring 11 and the housing 2 can be prevented.

[0057] Thus, according to the third embodiment, the creep-resistant coating 42 of the coating layer 40 Since it has an extended covering portion 42b that covers the raceway portion (width surface 11c) different from the inner diameter surface 11b of the ring 11 and is the portion that comes into contact with the housing 2, friction and wear between the raceway portion (width surface 11c) and the housing 2 can be prevented.

[0058] In addition, since the housing 2 supports the inner ring 11 in the axial direction, the extended covering portion 42b is designed to protect the width surface 11c of the inner ring 11 from the housing 2. However, if there is a portion on the outer periphery of the inner ring 11 (shoulder, chamfer, etc.) that is supported by the housing 2, the extended covering portion can be overlapped on that outer periphery portion.

[0059] Furthermore, when a coating layer is formed on the outer ring 12 as in the first embodiment, the coating layer may include a portion corresponding to the extended coating portion to prevent friction and wear between the width surface of the outer ring and the shaft.

[0060] Furthermore, in the second and third embodiments, the outer ring of the first embodiment may be employed, or an outer ring that is not covered with a coating layer may be employed.

[0061] 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. [Explanation of symbols]

[0062] 1 axis 1a Mating surface 2. Housing 2a Mating surface 10. Rolling bearings 11 Inner Circle 11a Raceway surface 11b Inner surface 11c width side 12 outer ring 12a Raceway surface 12b Outer diameter surface 12c width side 13 Rolling elements 30, 40 coating layers 31, 42 Creep-resistant coating 32, 41 Insulation coating 32a, 41a, 42a Central covering part 32b, 41b Side covering part 42b Extended covering section 43 Middle Class 43a Central covering part 43b Side covering part

Claims

1. The bearing comprises an inner ring, an outer ring, and rolling elements disposed between the inner ring and the outer ring, In a rolling bearing, at least one of an inner diameter surface of the inner ring and an outer diameter surface of the outer ring is covered with a coating layer, The coating layer is composed of multiple layers, a surface layer of the plurality of layers comprising a creep-resistant coating having lubricity; At least one of the plurality of layers, excluding the surface layer, is made of an insulating coating having insulating properties; the insulating coating is a fired film containing at least one of an epoxy resin and a polyamideimide resin, an insulating coating of the coating layer covers the outer diameter surface and width surface of the outer ring, the creep-resistant coating of the coating layer covers only the outer diameter surface of the outer ring, A rolling bearing, wherein the creep-resistant coating is a fired film containing a resin binder and a powder of a solid lubricant.

2. 2. The rolling bearing according to claim 1, wherein the insulating coating of the coating layer has side covering portions that cover the width surface of the inner ring or the width surface of the outer ring.

3. 3. The rolling bearing according to claim 1, wherein the creep-resistant coating comprises a polyamide-imide resin, an epoxy resin, and a reactive compound that causes the epoxy resin to react.

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