Rolling bearing

Abstract

The invention relates to a rolling bearing comprising an outer member (1) and an inner member (2) each formed of bearing steel, being provided with at least one annular raceway (1a, 2a) forming a raceway track space (3) between said members, at least one row (4) of rolling bodies (4a) being arranged in said space in order to allow the relative rotation of said members, the rolling bodies (4a) being formed from a ceramic material comprising zirconium dioxide, the electrical resistivity of which is sufficient to guarantee electrical insulation between the members (1, 2) across the raceway track space (3).

Description

[0001] ROLLING BEARING

[0002] The invention relates to a rolling bearing comprising an outer member and an inner member each provided with at least one annular rolling track forming a rolling space between said members, at least one row of rolling bodies being arranged in the rolling space to allow relative rotation of the members. The invention also relates to an electrical machine comprising a rotor which is rotatably mounted relative to a stator by means of such a rolling bearing.

[0003] In this application, electric currents can pass between the rotor and the stator which, since the components of a bearing are conventionally made of rolling steel, propagate between the components via the rolling bodies.

[0004] Since these currents passing through the rolling bearings are detrimental to their lifespan, rolling bearings have been proposed in which at least some components provide electrical insulation.

[0005] To do this, at least one member can be made at least partially from electrically insulating material, without this solution being satisfactory in terms of costs and / or reliability of the rolling bearing.

[0006] So-called hybrid bearings are also known in which the components are made of conventional bearing steel and the rolling bodies are formed from a material whose electrical resistivity is sufficient to ensure electrical insulation between the components through the rolling space. In particular, the use of SisN4-based ceramic material has been proposed to solve this electrical problem.

[0007] However, particularly in applications with high rotor rotation speeds, the electrically insulating materials used do not have physical properties, in particular thermal and / or mechanical properties, which are relevant, particularly in relation to those of bearing steels, to guarantee the reliability of the guidance provided by the rolling bearing.

[0008] The invention aims to improve the prior art by proposing in particular a rolling bearing in which the rolling bodies are formed from a material ensuring electrical insulation between the rolling steel members, while ensuring homogeneity of the physical properties between said material and said rolling steel to make the operation of the rolling bearing more reliable.

[0009] To this end, according to a first aspect, the invention proposes a rolling bearing comprising an outer member and an inner member each formed from rolling steel and being provided with at least one annular rolling track forming a rolling space between said members, at least one row of rolling bodies being arranged in said space to allow the relative rotation of said members, the rolling bodies being formed from a ceramic material comprising zirconium dioxide whose electrical resistivity is sufficient to guarantee electrical insulation between the members through the rolling space.

[0010] According to a second aspect, the invention proposes an electrical machine comprising a rotor which is mounted in rotation relative to a stator by means of such a rolling bearing, said bearing being subjected to passages of electric currents between said rotor and said stator.

[0011] Other objects and advantages of the invention will appear in the description which follows, made with reference to the attached figure 1 which represents in partially cut perspective a rolling bearing according to an embodiment of the invention.

[0012] In relation to this figure, a rolling bearing is described below comprising an outer member 1 and an inner member 2 each provided with at least one annular rolling track 1a, 2a forming a rolling space 3 between said members. To allow the relative rotation of the members 1, 2, at least one row 4 of rolling bodies 4a is arranged in the rolling space 3, in particular by being kept spaced apart by a cage 5, said bodies being in rolling support along each of the tracks 1a, 2a during said rotation.

[0013] In particular, a lubricant is arranged in the rolling space 3 in order to reduce the friction of the rolling bodies 4a during rotation. Depending on the application considered, the lubrication can be obtained by means of an oil and / or a grease introduced into the rolling space 3. According to one embodiment, a porous polymer matrix can be arranged in the rolling space 3, in particular by being in contact with the rolling bodies 4b, said matrix trapping a lubricant comprising an oil and / or a grease.

[0014] In the figure, the members 1, 2 are each formed from a ring between which is arranged a row 4 of rolling bodies 4a of cylindrical geometry. However, the invention is not limited to a particular geometry of the members 1, 2 and / or the rolling bodies 4a.

[0015] The members 1, 2 are each formed from bearing steel, in particular from high-carbon steel to withstand significant loads, both static and dynamic.

[0016] In particular, to produce the components 1, 2 of a rolling bearing, a steel called 100Cr6 is conventionally used, the composition of which in weight percentage is in the ranges given below, in particular depending on the intended application:

[0017] Alternatively, the members 1, 2 can be made of high carbon chrome steel, in particular according to the designation SUJ2 or AMS52100.

[0018] According to one embodiment, the members 1, 2 can be made of high carbon steel as previously mentioned with the additional addition of silicon and / or manganese, in particular according to the name 100CrMnSi6-4 or SUJ3.

[0019] The rolling bodies 4a are formed from a ceramic material whose electrical resistivity is sufficient to guarantee electrical insulation between the members 1, 2 through the rolling space 3.

[0020] Thus, the bearing can be advantageously used in an electrical machine for rotating a rotor relative to a stator, in which said bearing is subjected to passages of electric currents between said rotor and said stator.

[0021] Indeed, the electrical insulation provided by the rolling bodies 4a makes it possible to prevent currents from passing through the rolling bearing, and therefore the resulting damage to said bearing.

[0022] The ceramic material of the rolling bodies 4a comprises zirconium dioxide (ZrO2 or Zirconia) whose specific choice makes it possible to combine good electrical insulation with physical properties which, in relation to those of the rolling steel of the members 1, 2, make the operation of the bearing more reliable, in particular at the interface between the rolling bodies 4a and the tracks 1a, 2a on which they roll. In particular, the electrical resistivity of the material of the rolling bodies 4a may be greater than 10 15 Q*mm 2 / m, that of bearing steel being classically between 0.1 and 1 Q*mm 2 / m.

[0023] In particular, the rolling bodies 4a can be manufactured by sintering the ceramic material comprising zirconium dioxide, with in particular the possibility of modulating the production performance (sintering quality) or use of the rolling bodies 4a based on ZrCh (toughness) via the composition of the ceramic, in particular the Ytrium content.

[0024] Advantageously, the ceramic material of the rolling bodies 4a has thermal performances which guarantee the stability and dimensional precision of the bearing in temperature, in particular the stability of dimensional interference between the members 1, 2 and the rolling bodies 4a.

[0025] In particular, in high-speed applications, the rotation of a rotor of an electrical machine generates significant temperature variations over time and differentials between the components 1, 2, with differences of up to 40°C, which can significantly degrade the optimized clearances between the components of the rolling bearing, in particular in a manner amplified by the low thermal conductivity of the ceramic materials.

[0026] To solve this problem, the ceramic material of the rolling bodies 4a may have a coefficient of thermal expansion whose value is less than 130% of the coefficient of thermal expansion of the rolling steel of the members 1, 2.

[0027] Thus, by using a ceramic material whose thermal properties are close to those of bearing steel, a certain dimensional homogeneity of the components of the rolling bearing is ensured as a function of temperature. In an example of a relationship, the coefficient of thermal expansion (CTE) of the zirconium dioxide-based material is of the order of 10x10' 6 K' 1 , that of bearing steel being classically of the order of 12x10' 6 K' 1 .

[0028] According to one embodiment, the thermal stability in service of the members 1, 2 can be improved from the point of view of dimensional stability and / or hardness by a combined solution of grade and / or treatments, for example:

[0029] - grade: Base 100Cr6 with variants with additions of silicon and manganese (0.4 to 1.5% Si / 0.8 to 1.2% Mn);

[0030] - thermal and / or thermochemical treatment (nitriding, carbonitriding, cold, tempering).

[0031] Advantageously, the ceramic material of the rolling bodies 4a has mechanical performances which guarantee, in particular for high speed and high rigidity applications, the operational reliability of the bearing, in particular in relation to the resistance to the initiation of cracking / spreading of flaking due to the medium polluted by hard particles and to the resistance to shocks.

[0032] According to one embodiment, the ceramic material of the rolling bodies 4a has a Young's modulus of elasticity E whose difference with the Young's modulus of elasticity E of the rolling steel of the members 1, 2 is less than 10%.

[0033] In an exemplary embodiment, the Young's modulus of elasticity E of the ceramic material is of the order of 210 GPa, that of the bearing steel being conventionally also of the order of 210 GPa, so as to obtain a homogeneity between the materials which is conducive to the best operation of the rolling bearing.

[0034] In particular, the ceramic material of the rolling bodies 4a, despite its high hardness, allows less impact on the steel members 1, 2 thanks to a lower Young's modulus of elasticity E than traditional ceramics, leading to less shear stresses in said members than with rolling bodies 4a for example based on S13N4, and this without the reduction in rigidity affecting the operation of the rolling bearing.

[0035] According to an advantageous embodiment, the ceramic material of the rolling bodies 4a has a Poisson's ratio whose deviation from the Poisson's ratio of the rolling steel of the members 1, 2 is less than 10%.

[0036] In an exemplary embodiment, the Poisson's ratio of the ceramic material is of the order of 0.3, that of the bearing steel being conventionally also of the order of 0.3, so as to obtain a homogeneity between the materials which is conducive to the stable and predictive operation of the rolling bearing.

[0037] According to an advantageous embodiment, the rolling steel of the members 1, 2 has, at least at the level of at least one of the rolling tracks 1a, 2a, an HV hardness which is greater than 60% of the HV hardness of the ceramic material of the rolling bodies 4a.

[0038] To do this, the rolling steel of the members 1, 2 may have undergone a specific hardening treatment of at least one of the rolling tracks 1a, 2a to have an HV hardness greater than 750, in particular being at least 850. According to one embodiment, at least the rolling tracks 1a, 2a and in particular the members 1, 2 may have the HV hardnesses defined above.

[0039] In particular, the members 1, 2 may have undergone heat treatment in the mass, superficial and / or by surface enrichment of surface hardening, for example of the cementation, carbonitriding, nitriding, induction type.

[0040] Thus, particularly in relation to an HV hardness of the ceramic material of the rolling bodies 4a which is less than 1500, the hardness difference is reduced in order to make the operation of the rolling bearing more reliable.

[0041] Advantageously, a rolling bearing according to the invention can have:

[0042] - mechanical reinforcement by: o a small difference in Young's modulus of elasticity E between the rolling steel and the ceramic material of the rolling bodies 4a, in particular to reduce the stresses in the components 1, 2; o a reinforcement of the mechanical resistance in a polluted environment of the components 1, 2, in particular by carbonitriding the rolling steel; o good temperature resistance, in particular by using Si / Mn rolling steel grades with mass and / or thermochemical treatment for the components 1, 2; - dimensional reinforcement by: o close CTEs between said ceramic material and the rolling steel; o use of rolling steel grades with Mn / Si and suitable heat treatments of the components 1, 2.

Claims

CLAIMS 1. Rolling bearing comprising an outer member (1) and an inner member (2) each formed from rolling steel and being provided with at least one annular rolling track (1a, 2a) forming a rolling space (3) between said members, at least one row (4) of rolling bodies (4a) being arranged in said space to allow the relative rotation of said members, said bearing being characterized in that the rolling bodies (4a) are formed from a ceramic material comprising zirconium dioxide whose electrical resistivity is sufficient to guarantee electrical insulation between the members (1, 2) through the rolling space (3).

2. Rolling bearing according to claim 1, characterized in that the ceramic material of the rolling bodies (4a) has a coefficient of thermal expansion whose value is less than 130% of the coefficient of thermal expansion of the rolling steel of the members (1, 2).

3. Rolling bearing according to one of claims 1 or 2, characterized in that the ceramic material of the rolling bodies (4a) has a Young's modulus of elasticity E whose deviation from the Young's modulus of elasticity E of the rolling steel of the members (1, 2) is less than 10%.

4. Rolling bearing according to any one of claims 1 to 3, characterized in that the ceramic material of the rolling bodies (4a) has a Poisson's ratio whose deviation from the Poisson's ratio of the rolling steel of the members (1, 2) is less than 10%.

5. Rolling bearing according to any one of claims 1 to 4, characterized in that the rolling steel of the members (1, 2) has, at least at the level of at least one of the rolling tracks (1a, 2a), an HV hardness which is greater than 60% of the HV hardness of the ceramic material of the rolling bodies (4a).

6. Rolling bearing according to claim 5, characterized in that the rolling steel of the members (1, 2) has undergone a specific hardening treatment of at least one of the rolling tracks (1a, 2a) to have an HV hardness greater than 750.

7. Rolling bearing according to claim 6, characterized in that the HV hardness of at least one of the rolling tracks (1a, 2a) is at least 850.

8. Rolling bearing according to any one of claims 5 to 7, characterized in that the HV hardness of the ceramic material of the rolling bodies (4a) is less than 1500.

9. Electrical machine comprising a rotor which is rotatably mounted relative to a stator by means of a rolling bearing according to any one of claims 1 to 8, said bearing being subjected to passages of electric currents between said rotor and said stator.

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