Rolling bearing, in particular a wheel hub assembly, having an improved service life and related method
A roller bearing includes inner and outer rings each having a raceway, an annular space between the raceways, and a plurality of rolling elements and a lubricating grease in the annular space. The raceways have a predetermined roughness value within a first predetermined range, and the lubricating grease contains graphene particles uniformly dispersed in a suspension in the lubricating grease. The graphene particles have an at least substantially circular shape, a diameter within a second predetermined range and a thickness within a third predetermined range. An amount of the lubricating grease in the annular space and the first, second and third predetermined ranges are selected such that a self-regenerating mat of graphene that at least partially coats the raceways will develop in use as a result of a relative rotation between the inner and outer rings and the rolling/sliding of the rolling elements on the raceways.
1 . A roller bearing comprising:
an inner ring having a raceway,
an outer ring having a raceway and being configured to rotate relative to the inner ring,
a first row of rolling elements in an annular space between the raceway of the inner ring and the raceway of the outer ring, and
a lubricating grease disposed in the annular space on the inner ring raceway and on the outer ring raceway and on the rolling elements,
wherein:
the inner ring raceway and the outer ring raceway each have a roughness value Ra of from 0.05 to 0.15 microns,
the lubricating grease contains 1-2 wt % of graphene particles uniformly dispersed in a suspension in the lubricating grease,
the graphene particles are graphene nanoparticles and/or graphene nanoplatelets,
the graphene particles have an at least substantially circular shape, and
the graphene particles have a diameter of less than 2 microns and a thickness of 2-8 nm.
2 . The roller bearing according to claim 1 , wherein:
the lubricating grease comprises a lubricating oil having a base viscosity of 40-130 mm 2 /s measured at 40° C. according to ISO 3140, and
the lubricating grease has an NLGI consistency number of 2.
3 . The roller bearing according to claim 1 , wherein the lubricating grease is a synthetic-based grease comprising polyalphaolefins and at least one thickening additive selected from the group consisting of lithium complexes, polyurethane, urea, and mixtures thereof.
4 . The roller bearing according to claim 1 , wherein:
the inner ring raceway has first and second inner raceways disposed side-by-side,
the outer ring raceway has first and second outer raceways disposed side-by-side,
the first row of rolling elements contacts the first inner raceway and the first outer raceway,
a second row of rolling elements contacts the second inner raceway and the second outer raceway, and
the raceways have, in a radial section, a profile with pressure lines according to an O configuration.
5 . The roller bearing according to claim 4 , wherein:
the lubricating grease comprises a lubricating oil having a base viscosity of 40-130 mm 2 /s measured at 40° C. according to ISO 3140, and
the lubricating grease has an NLGI consistency number of 2.
6 . The roller bearing according to claim 5 , wherein the lubricating grease is a synthetic-based grease comprising polyalphaolefins and at least one thickening additive selected from the group consisting of lithium complexes, polyurethane, urea, and mixtures thereof.
7 . A wheel hub assembly for a vehicle comprising:
a roller bearing according to claim 1 , and
a flange configured to support a wheel of the vehicle, the flange being integral with the inner ring of the roller bearing,
wherein the outer ring is configured to be fixedly mounted on a suspension upright of the vehicle.
8 . A method comprising:
rotating one of the inner and outer rings of the roller bearing of claim 1 relative to the other of the inner and outer rings, thereby causing the rolling elements to slide on the raceways and causing a self-regenerating mat of graphene that at least partially coats the raceways to develop.
9 . A method for increasing the service life of a roller bearing provided in a wheel hub assembly of a vehicle, comprising:
providing an inner ring having a raceway and an outer ring having a raceway, each of the raceways having a roughness value Ra of from 0.05 to 0.15 microns,
providing a plurality of rolling elements in an annular space between the inner ring raceway and the outer ring raceway,
providing a lubricating grease for bearings containing 1-2 wt % of uniformly dispersed graphene nanoparticles and/or graphene nanoplatelets, the graphene nanoparticles or graphene nanoplatelets having an at least substantially circular shape, a diameter of less than 2 microns and a thickness of 2-8 nm, and
disposing the lubricating grease in the annular space so that the lubricating grease contacts at least parts of the inner ring raceway and the outer ring raceway and the plurality of rolling elements.
10 . The method according to claim 9 , further comprising using a multiple roller mill to uniformly disperse and exfoliate the graphene nanoparticles as individual nanoplatelets in the lubricating grease.
11 . A roller bearing comprising: an inner ring, an outer ring, a plurality of rolling bodies housed in an annular space defined between the inner ring and the outer ring, the rolling bodies contacting respective raceways defined on the inner and outer rings and partly delimiting the annular space, to which they are facing, so that the inner and outer rings are relatively rotatable, and a lubricating grease disposed in the annular space and at least on the raceways, so that the rolling bodies are at least partly immersed in, and/or in contact with, the lubricating grease that is enriched with 1-2 wt % of graphene nanoparticles;
wherein:
the raceways each have roughness value Ra of from 0.05 to 0.15 microns; and
the graphene nanoparticles are present uniformly dispersed in suspension in the lubricating grease and have a substantially circular shape with a diameter of less than 2 and a thickness of 2-8 nm.
12 . A method comprising:
rotating one of the inner and outer rings of the roller bearing of claim 11 relative to the other of the inner and outer rings, thereby causing the rolling elements to slide on the raceways and causing a self-regenerating mat of graphene that at least partially coats the raceways to develop.