Patent ID: 12241504

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, the first embodiment of the present invention is described.

As shown inFIGS.1and2, the rolling bearing10(either a first or a second rolling bearing10) according to the first embodiment is disposed between a shaft1and a housing2surrounding the shaft1.

In the following description, in an ideal state in which the rotation center axis, in design, of the rolling bearing10coincides with the rotation center axis of the shaft1, the direction along the rotation center axis is referred to as the “axial direction”, “axially” or “axial”; the direction along the circumference of a circle having a center at the rotation center axis is referred to as the “circumferential direction”, “circumferential” or “circumferentially”; and a direction perpendicular to the rotation center axis is referred to as a “radial direction”, “radially”, or “radial”

The shaft1rotates relative to the housing2. The shaft1is, for example, the rotary shaft of a motor of an electric vehicle (EV). The shaft1has cylindrical fitting surfaces1aextending in the circumferential direction.

The housing2is stationary relative to the shaft1, and supports the shaft1through the rolling bearing10. The housing2is, for example, a partition wall forming a portion of a case of the above-described motor. The housing2has a cylindrical fitting surface2aextending in the circumferential direction. This fitting surface2ais concentric with the corresponding fitting surface1aof the shaft1.

The rolling bearing10supports the shaft1for rotation relative to the housing2, and bears, for example, radial loads that act between the shaft1and the housing2.

The EV motor shown inFIG.2includes the housing2, which defines the outer perimeter of the motor; the shaft1, which is inserted in the housing2; and a rotor5mounted around the shaft1for rotation in unison with the shaft1. Outside the rotor5, a stator6is fixed to the inner side of the housing2. A coil is mounted in the stator6and electricity is supplied to the coil via a lead wire7. A flange bracket3is mounted to an opening of the housing2. The shaft1extends through a center hole of the flange bracket3. The flange bracket3has a cylindrical fitting surface3aextending in the circumferential direction. This fitting surface3ais also concentric with the corresponding fitting surface1aof the shaft1. The first rolling bearing10is disposed between the fitting surface2aof the housing2on the bottom side (i.e., right side inFIG.1) of the housing2and the corresponding fitting surface1aof the shaft1. The second rolling bearing10is disposed between the fitting surface3aof the flange bracket3and the corresponding fitting surface1aof the shaft1.

The rolling bearings10each include an inner ring11mounted on the shaft1, an outer ring12mounted to the housing2or the flange bracket3, a plurality of rolling elements13disposed between the inner ring11and the outer ring12, and a retainer14maintaining the circumferential distances between the rolling elements13. The rolling bearings10shown are deep groove ball bearings.

The inner ring11is an annular bearing part having, on the outer periphery thereof, a raceway surface11aextending in the circumferential direction, and on the inner periphery thereof, a radially inner surface11bextending in the circumferential direction. The radially inner surface11bis a cylindrical surface concentric with the fitting surface1aof the shaft1. The radially inner surface11bof the inner ring11is fitted to the fitting surface1aof the shaft1.

The fit between the radially inner surface11bof the inner ring11and the fitting surface1aof the shaft1is an interference fit. Due to the interference fit, the inner ring11is fixed to the shaft1for rotation in unison with the shaft1.

The outer ring12is an annular bearing part having, on the inner periphery thereof, a raceway surface12aextending in the circumferential direction, and on the outer periphery thereof, a radially outer surface12bextending in the circumferential direction. The radially outer surface12bis a cylindrical surface concentric with the radially inner surface11bof the inner ring11.

The outer ring12is in a clearance fit with the housing2.

The inner ring11and the outer ring12are both composed of steel such as SUJ2, SCM420, SCr420, SCR420 or SUS440. The inner ring11and the outer ring12are subjected to an appropriate treatment such as a quench and temper treatment, a carburizing treatment, or a carbonitriding treatment.

As shown inFIG.1, in the first embodiment, the radially outer surface12bof the outer ring12is covered with a coating layer30. The coating layer30is a coating layer composite30comprising a plurality of layers. Of the plurality of layers of the coating layer composite30, the surface layer at the radially outermost position is composed of an anti-creep film31having lubricity. The radially outer surface of this anti-creep film31serves as a fitting surface which is in a clearance fit with the fitting surface2aof the housing2or the fitting surface3aof the flange bracket3.

The anti-creep film31may be, for example, a calcined film containing a resin binder and a solid lubricant. The resin binder is composed of a base material and a hardening agent and hardened by reacting the hardening agent. By solidifying the outside of the solid lubricant with the resin binder, the anti-creep film exhibits excellent adhesion properties and wear resistance. The anti-creep film also reduces wear of the housing2or the flange bracket3. As the base material, due to its durability, a polyamideimide resin is preferable. As the hardening agent, for easy hardening, an epoxy resin and a reactive compound to be reacted with the epoxy resin are preferably used in combination.

The type of the epoxy resin used is not particularly limited provided it can be used as a hardening agent, such epoxy resins including bisphenol A epoxy resin, cresol novolac epoxy resin, biphenyl epoxy resin, brominated epoxy resin, and alicyclic epoxy resin. Examples of the reactive compound include aliphatic polyamine, polyaminoamide, polymercaptans, aromatic polyamine, acid anhydrides, and dicyandiamide. Besides these components, a hardening accelerator may be added for increased reactivity. Examples of the hardening accelerator include tertiary amines, tertiary amine salts, imidazole, phosphine, phosphonium salts and sulphonium salts.

In order for the solid lubricant to exhibit lubricity, it is preferably composed of a material softer than the material forming the housing2, specifically a material having a hardness of Hv 50 to 150. Examples of the solid lubricant material includes molybdenum disulfide powder, graphite powder, tungsten disulfide, and polytetrafluoroethylene. Among them, preferably, molybdenum disulfide may be used alone, or a mixture of molybdenum disulfide and another or other materials may be used.

The anti-creep film31may further contain a friction/wear adjustor. The friction/wear adjustor is a material that improves the wear resistance of the calcined film, and is preferably selected from materials softer than the material forming the housing2. Examples of such materials include antimony oxide, talc, mica, potassium titanate, tin, copper, zinc and nickel. Among them, antimony oxide is particularly preferable.

In order to form the anti-creep film31as the calcined film, a coating liquid is prepared by, for example, adding solid lubricant powder, friction/wear adjuster powder, and other components to a solvent into which the resin binder is dissolved. The coating liquid thus obtained is applied to the surface of the below-described insulating film or another intermediate film, and is heated to evaporate the solvent, thereby forming the anti-creep film31.

At least one of the layers forming the coating layer composite30other than the anti-creep film31comprises an insulating film32having insulating properties. The insulating film32is formed on the outer periphery of the radially outer surface12b, and the anti-creep film31is formed outside of the insulating film32.

The insulating film32is composed of a material having insulating properties. The insulating film32provides insulation between the radially outer surface12bof the outer ring12and the fitting surface2a,3aof the housing2or the flange bracket3to prevent leak current from the fitting surface2a,3afrom reaching the radially outer surface12b.

Examples of the material of the insulating film32include a ceramic material, an epoxy resin, and a polyamideimide resin. If a ceramic material, an epoxy resin, or a polyamideimide resin is used, the calcined film may be formed by heating the coated material. If an epoxy resin or a polyamideimide resin is used, calcining may be performed together with a hardening agent.

In order to prevent discharge between the rolling elements13and the raceway surfaces11aand12aby breaking the circuit of the flow of leakage current between the outer ring12and the inner ring11, it is necessary to cover at least one of the radially outer surface12bof the outer ring12and the radially inner surface11bof the inner ring11with the coating layer composite containing the insulating film32. By preventing discharge between the rolling elements13and the raceway surfaces11aand12a, electrolytic corrosion of the rolling elements13and the raceway surfaces11aand12ais prevented.

The insulating film32shown includes a center covering portion32acovering the radially outer surface12bof the outer ring12, a side covering portion32bcovering a side surface12cof the outer ring12. The side surface12cof the outer ring12is one of two side surfaces defining the width of the outer ring12. The side surface12caxially opposes the side surface of the housing2or the flange bracket3.

The center covering portion32aand the side covering portions32bform an integral film. The side covering portion32bprovides insulation between the housing2or the flange bracket3and the side surface12cof the outer ring12, and by preventing discharge therebetween, the electrolytic corrosion of the housing2or the flange bracket3and the side surface12cis prevented.

In the above-described rolling bearing10according to the first embodiment, among the plurality of layers constituting the coating layer composite30covering the radially outer surface12bof the outer ring, the anti-creep film31as the surface layer serves as the fitting surface with the housing2or the flange bracket2, exhibiting lubricity during creeping, thereby preventing friction and wear of the radially outer surface12bof the outer ring12and the fitting surface2a,3aof the corresponding one of the housing2and the flange bracket3. Further, because at least one of the plurality of layers constituting the coating layer composite30other than the surface layer or the anti-creep film31is composed of an insulating film32having insulating properties, the insulating film32breaks the circuit of the flow of leakage current, preventing discharge between the inner ring11or the outer ring12and the rolling elements13, and thereby preventing electrolytic corrosion damage to the inner ring11, the outer ring12and the rolling elements13. Thus, in a use condition of the rolling bearing10in which leakage current reaches the inner ring11or the outer ring12, and in which the inner ring11or the outer ring12is in a clearance fit, respectively, with the shaft1or one of the housing2and the flange bracket3, the rolling bearing10exhibits both creep resistance and resistance to electrolytic corrosion.

Further, since the insulating film32of the coating layer composite30includes the side covering portion32bcovering the side surface12cof the outer ring12, the insulating film32prevents discharge between the side surface12cof the outer ring12and one of the housing2and the flange bracket3that opposes the side surface12c, thereby preventing electrolytic corrosion of e.g., the side surface12c.

The coating layer composite30is not limited to the two-layer structure as shown. For example, a film having a different function may be disposed between the radially outer surface12band the anti-creep film31, and also, an additional insulating film and an additional anti-creep film may be laminated between the insulating film32and the anti-creep film31. Since, in an environment where alternating current flows, the capacitance is involved in the electrolytic corrosion resistance performance, the films need to have a certain amount of capacitance. Since the necessary capacitance is determined by the structure of the parts, the materials and thicknesses of the films, etc., the necessary capacitance is properly determined according to the use environment.

The second embodiment is described with reference toFIG.3. The description is limited to what differs from the first embodiment.

In the rolling bearing of the second embodiment, the radially inner surface11bof the inner ring11is covered with a coating layer composite40comprising a plurality of layers. The coating layer composite40includes an insulating film41having a center covering portion41acovering the radially inner surface11bof the inner ring11, and a side covering portion41bcovering a side surface11cof the inner ring11. The side surface lic is one of two side surfaces defining the width of the inner ring11. The side surface11caxially opposes the side surface of the housing2or the flange bracket3.

The coating layer composite40further includes an anti-creep film42, as a surface layer of the coating layer composite40, which forms a fitting surface fitted to the fitting surface1aof the shaft1. In this embodiment, the anti-creep film41exhibits anti-creep properties against the shaft1.

The insulating film41and the anti-creep film42may have the same structures and may be formed by the same methods, as the insulating film and the anti-creep film of the first embodiment.

The coating layer composite40further includes an intermediate layer43between the insulating film41and the anti-creep film42. The anti-creep film42is formed, as the surface layer, on the front side of the intermediate layer43.

The structure of the intermediate layer43is not particularly limited provided it does not interfere with the performances of the insulating film41and the anti-creep film42. For example, it may have the capability of improving insulating properties, have the capability of strongly fixing the anti-creep film42in position, or may have other properties. For example, where the adhesion between the insulating film41and the anti-creep film42tends to be insufficient if they are directly laminated together, an intermediate layer43that shows good adhesion to both of them may be used. If the insulating film41and the anti-creep film42alone are not capable of achieving the required capacitance, an intermediate layer43may be selected which enables, in combination of the three, to achieve the required capacitance. While not shown, the intermediate layer43may be formed not only between the insulating film41and the anti-creep film42but also between the insulating film41and the inner ring11. The intermediate layer43may have, instead of the single-layer structure, a multi-layer structure.

According to the second embodiment, the insulating film41breaks the circuit of the flow of leakage current, thereby preventing electrolytic corrosion damage to the inner ring11, the outer ring12, and the rolling elements13by preventing discharge between the inner ring11or the outer ring and the rolling elements13, and also preventing the electrolytic corrosion of, for example, the side surface11cby preventing discharge between the side surface11cof the inner ring11and one of the housing2and the flange bracket3that opposes the side surface11cof the inner ring11.

The third embodiment is described with reference toFIG.4.

The third embodiment differs from the second embodiment in that the anti-creep film42includes an extended covering portion42bcovering a portion of the inner ring11other than its radially inner surface11b, and in contact with the housing2. The center covering portion43aof the intermediate layer43is superposed on the center covering portion41aof the insulating film41, while the center covering portion42aof the anti-creep film42is superposed on the center covering portion43aof the intermediate layer43. The side covering portion43bof the intermediate layer43is superposed on the side covering portion41bof the insulating film41, while the extended covering portion42bof the anti-creep film42is superposed on the side covering portion43bof the intermediate layer43.

When the inner ring11creeps, the extended covering portion42bof the anti-creep film42slides on the side surface of the housing2in the circumferential direction. Thus, the extended covering portion42bprevents friction and wear between the side surface11cof the inner ring11and the housing2.

Thus, according to the third embodiment, because the anti-creep film42of the coating layer composite40includes an extended covering portion42bcovering a portion of the inner ring11other than its radially inner surface11b(i.e., side surface11c), and in contact with the housing2, the extended covering portion42bprevents wear and friction between the above inner ring portion (side surface11c) and the housing2.

While, in the embodiment, because the inner ring11is axially supported by the housing2, the side surface11cof the inner ring11is protected against the housing2by the extended covering portion42b, if the inner ring11includes on its outer peripheral side a portion to be supported by the housing2(such as a shoulder or a chamfer), the extended covering portion may be superposed on this outer peripheral portion.

In an arrangement of the first embodiment, in which the coating layer composite is formed on the outer ring12, the coating layer composite may include a portion corresponding to the extended covering portion, thereby preventing friction and wear between the side surface of the outer ring and the shaft.

In the second and third embodiments, the outer ring of the first embodiment may be used, or the outer ring may be free of the coating layer composite.

The embodiments disclosed here are mere examples in every respect, and should not be considered restrictive. The scope of the invention should be interpreted by the claims and not by the description, and includes every modification within the meaning and range that are equivalent to the claims.

DESCRIPTION OF THE REFERENCE SYMBOLS

1. Shaft1a. Fitting surface2. Housing2a. Fitting surface10. Rolling bearing11. Inner ring11a. Raceway surface11b. Radially inner surface11c. Side surface12. Outer ring12a. Raceway surface12b. Radially outer surface12c. Side surface13. Rolling element30,40. Coating layer composite31,42. Anti-creep film32,41. Insulating film32a,41a,42a. Center covering portion32b,41b. Side covering portion42b. Extended covering portion43. Intermediate layer43a. Center covering portion43b. Side covering portion