Rolling bearing with electrical insulating material and method for manufacturing the rolling bearing

Abstract

A rolling bearing having an electrically insulating material and a method for manufacturing the same. The invention relates to a rolling bearing (1) comprising an annular inner ring (3; 30) and an annular outer ring (2; 20) capable of relative rotation about a central axis (X1), and rolling elements (4) accommodated between raceways (2e, 27e; 7e, 30e) provided on the two rings. At least one of the rings (3; 20) comprises two concentric annular ring portions (6, 7; 26, 27) made of a metallic material and an annular layer (8; 28) made of an electrically insulating material, the layer (8; 28) being accommodated between the two portions (6, 7; 26, 27).

Description

Technical Field

[0001] The present invention relates to the technical field of rolling bearings, and in particular to rolling bearings having an inner ring and an outer ring capable of rotating relative to each other, and at least one row of rolling elements arranged between the raceways of the two rings. More particularly, the present invention relates to rolling bearings for use in electric motors for industrial or automotive applications. Background Art

[0002] Rolling bearings are typically mounted in the frame of an electric motor or machine to support a rotating shaft. As the shaft rotates, a potential difference may develop between the shaft and the electric motor or machine. This, in turn, creates a potential between the rotatable bearing rings connected to the shaft and the fixed bearing rings directly or indirectly connected to the frame. This potential difference can cause current to discharge through the rolling bearings. This problem is particularly concerning in AC electric motors, especially when the alternating current is generated using pulse-width modulation techniques.

[0003] Current flowing through rolling element bearings can damage the bearing raceways and rolling elements. The bearing lubricant can darken, reducing the bearing's lubrication properties, potentially leading to wear and failure of the raceways and rolling elements. Discharge can also generate vibrations, which increase the system's acoustic noise. Furthermore, the high-frequency circulating currents generated by the potential difference can induce electromagnetic noise that can adversely affect external electrical equipment.

[0004] It is known to ground a rotating shaft using grounding brushes with conductive fibers (e.g., copper or carbon fibers). However, the construction of conventional grounding brush assemblies must typically be specific to the size and shape of the shaft and housing to be grounded. This increases the cost of the electric motor assembly and the duration of the installation process.

[0005] Therefore, it is desirable to electrically insulate rolling bearings through a cost-effective and easily installed alternative. Summary of the Invention

[0006] These and other problems are addressed by embodiments of the present invention.

[0007] To this end, the invention relates to a rolling bearing comprising an annular inner ring and an annular outer ring which are rotatable relative to each other about a central axis, and rolling elements accommodated between raceways provided on the two rings.

[0008] According to the invention, at least one of the rings comprises two concentric annular ring portions made of metallic material and an annular layer made of electrically insulating material, said layer being housed between the cylindrical surfaces of said two ring portions.

[0009] According to other advantageous but not essential aspects of the present invention, the rolling bearing may comprise one or more of the following features:

[0010] - The rolling elements are balls.

[0011] The rolling bearing further includes an annular cage for circumferentially retaining the rolling elements.

[0012] The layers are made of elastic materials (elastomeric materials) such as rubber, thermoplastics, duroplastics, etc., with or without fiber fillers.

[0013] - the cylindrical surface of one of the rings is provided with a circumferential groove.

[0014] - said cylindrical surface of the other ring portion is provided with a circumferential projection towards said groove.

[0015] - The circumferential groove is toroidal.

[0016] - The circumferential protrusion is curved.

[0017] - the groove is centred on a radial plane passing through the geometric centre of the ball in a section through the central axis.

[0018] The rolling bearing is provided with a brush made of a conductive material. The brush (40) is fixed to the first ring and is in sliding contact with a ring portion of the second ring, the ring portion being radially opposed to the first ring via the layer made of an electrically insulating material.

[0019] The brush is fixed to a first axial projection extending axially from the first ring.

[0020] - said first ring and said first axial projection are formed in one piece.

[0021] - The first axial protrusion is provided on a support to which the first ring is fixed.

[0022] The brush is in sliding contact with a second axial projection extending axially from the collar portion of the second collar.

[0023] The collar portion of the second collar and the second axial projection are formed in one piece.

[0024] The second axial protrusion is provided on a support to which the ring portion of the second ring is fixed.

[0025] - The first ring is fixed and the second ring is rotatable.

[0026] The present invention also relates to an electric motor comprising a fixed motor frame or housing, a rotating shaft with a central axis, and at least one rolling bearing according to any of the preceding embodiments, wherein a first ring of the rolling bearing is connected to the fixed motor frame or housing and a second ring of the rolling bearing is connected to the rotating shaft.

[0027] The present invention further relates to a method for manufacturing a rolling bearing according to any one of the aforementioned solutions, comprising the following steps:

[0028] (a) vulcanizing a tube made of an elastomeric material in a separate molding tool;

[0029] (b) applying oil to the surface of the elastic tube ( / elastomeric tube); and

[0030] (c) Pressing the elastic tube between two coil portions of one of the coils to form a layer.

[0031] An alternative manufacturing method includes the following steps:

[0032] (a) arranging two ring portions of one of the rings concentrically with a radial space therebetween;

[0033] (b) injecting the heated elastic material in fluid form into the radial space;

[0034] (c) vulcanizing the elastic material between the loop portions under predetermined pressure and temperature conditions to form a layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will now be explained with reference to the accompanying drawings which are provided as an illustrative example and not for the purpose of limiting the invention, in which:

[0036] – Figure 1 is an axial half-sectional view of a rolling bearing according to a first embodiment of the present invention,

[0037] – Figure 2 is an axial half-section view of the second embodiment,

[0038] – Figure 3 is an axial half-section view of the third embodiment,

[0039] – Figure 4 is an axial half-section view of the fourth embodiment,

[0040] – Figure 5 is an axial half-section view of the fifth embodiment, and

[0041] – Figure 6 It is an axial half-sectional view of the sixth embodiment. DETAILED DESCRIPTION

[0042] Figure 1 A rolling bearing 1 having a central axis X1 is shown. The rolling bearing 1 comprises an outer ring 2, an inner ring 3 and an array of rolling elements (here, balls) 4 arranged parallel to a plane held by a cage 5.

[0043] In normal operating mode, the rings 2 and 3 are coaxial with the central axis X1.

[0044] The outer ring 2 is formed in one piece and comprises an outer cylindrical surface 2 a , a cylindrical bore 2 b in which raceways 2 e for rolling elements 4 are formed, and two side surfaces 2 c , 2 d .

[0045] The raceway 2 e is a curved groove (or toroidal groove) having a shape suitable for receiving the ball 4 .

[0046] The outer ring 2 is a stationary ring and is intended to be mounted, for example, in a frame or housing (not shown) of an electric motor.

[0047] In this embodiment, the inner ring 3 includes a first ring portion 6 , a second ring portion 7 and a layer 8 housed between the portions 6 , 7 .

[0048] The first ring portion 6 comprises an outer cylindrical surface 6a, a cylindrical hole 6b and two side surfaces 6c, 6d.

[0049] The hole 6b of the first ring portion 6 is used for mounting on, for example, an outer cylindrical surface of a rotating shaft (not shown).

[0050] The second ring portion 7 comprises an outer cylindrical surface 7 a in which raceways 7 e for the rolling elements 4 are formed, a cylindrical hole 7 b and two side surfaces 7 c , 7 d .

[0051] The raceway 7 e is a curved groove having a shape suitable for receiving the ball 4 .

[0052] The first ring portion 6 and the second ring portion 7 are made of a metal material and are concentric with respect to the central axis X1 .

[0053] The layer 8 is radially housed in the radial space defined between the outer cylindrical surface 6a of the first ring portion 6 and the cylindrical hole 7b of the second ring portion 7. Therefore, the layer 8 includes: an outer cylindrical surface 8a fixed to the cylindrical hole 7b of the second ring portion 7; a cylindrical hole 8b fixed to the outer cylindrical surface 6a of the first ring portion 6; and two side surfaces 8c, 8d.

[0054] The layer 8 is made of an electrically insulating material. Advantageously, the layer 8 is made of an elastic material such as rubber, thermoplastic, duroplastic material, etc., with or without fiber fillers. The hardness of the layer material may vary depending on the application and the axial and radial stiffness required of the bearing 1.

[0055] According to one aspect of the present invention, the layer 8 is formed by injecting heated elastic material in liquid form into the radial space defined between the two concentric ring portions 6, 7. The elastic material is then vulcanized between the ring portions under predetermined pressure and temperature conditions. The elastic material is then tightly attached to the surface 7b of the portion 6 and the portion 7, thereby firmly connecting the two ring portions 6, 7 to each other.

[0056] According to an alternative manufacturing method, a tube made of an elastomeric material can be vulcanized in a separate molding tool. The surface of the vulcanized elastomeric material is oiled. The elastic tube is then pressed between the two rings 6, 7 to form the layer 8.

[0057] The inner ring 3 has a sandwich structure provided with a cylindrical hole 6b for mounting on a rotating shaft, a cylindrical outer surface 7a providing a raceway 7e for rolling elements 4, and an electrical insulating layer.

[0058] Advantageously, the side surfaces 6c, 7c, 8c are aligned in the axial direction. Advantageously, the side surfaces 6d, 7d, 8d are also aligned in the axial direction.

[0059] Advantageously, the aligned side surfaces 6c, 7c, 8c of the inner ring 3 are axially aligned with the side surface 2c of the outer ring 2. Advantageously, the aligned side surfaces 6d, 7d, 8d of the inner ring 3 are also axially aligned with the side surface 2d of the outer ring 2.

[0060] As an alternative embodiment not shown, at least one of the side surfaces 8c and / or 8d of the layer may be slightly offset in the axial direction relative to the other side surfaces 6c and / or 6d of the first ring portion 6 and the other side surfaces 7c and / or 7d of the second ring portion 7. Thus, a bump of elastic material may be formed on at least one radial side of the inner ring 3 in order to allow axial prestressing of the inner ring 3 during installation.

[0061] The cylindrical outer surface 7a of the second ring portion 7 of the inner ring 3 and the cylindrical bore 2b of the inner ring 2 define a bearing chamber 9 for the rolling elements 4 to move between the rings 2 and 3. Advantageously, the bearing chamber 9 can be sealed between the rings 2 and 3 by a sealing device (not shown). Advantageously, the bearing chamber 9 can be filled with a lubricant, such as grease or oil, to reduce friction between the contact surfaces of the moving components (here, the rolling elements 4, the raceway 7e provided on the outer cylindrical surface 7a, and the raceway 2e provided in the bore 2b of the inner ring 2).

[0062] The cage 5 comprises a plurality of cavities 5a designed to accommodate the balls 4 and to keep them evenly spaced in the circumferential direction. Advantageously, the cavities 5a are spherical.

[0063] Thanks to the invention, the layer 8 makes it possible to electrically insulate the inner ring 3 and thus prevent current from flowing from the rotating shaft to the housing or the frame through the rolling elements 4 and the outer ring 2 .

[0064] Another advantage of the present invention is that layer 8 forms a vibration damper that partially attenuates vibration waves in the ring. More specifically, it can dampen the critical bending resonance of the rotating shaft at high speeds. Thus, noise is also significantly reduced.

[0065] As an alternative, the inner ring 3 may be non-rotating while the outer ring 2 rotates, or the two rings may rotate relative to each other.

[0066] As an option, the rolling bearing 1 may comprise more than one row of rolling elements 4 .

[0067] As an alternative, the rolling bearing 1 may comprise any other type of rolling elements, such as tapered rollers, cylindrical rollers, needles, etc.

[0068] Figure 2 A second embodiment of the invention is shown, in which similar parts have the same reference numerals, and which differs from the previous embodiment in that the first ring portion 6 of the inner ring 3 comprises a circumferential groove 6e.

[0069] The outer cylindrical surface 6b of the first ring portion 6 is provided with a circumferential groove 6e. The groove 6e is machined in the metal material of the first ring portion 6. The groove 6e is concave and has a curved shape, i.e., the groove 6e is circular arc-shaped in a cross section passing through the central axis X1.

[0070] Advantageously, the groove 6e is centred, in a section through the central axis, on a radial plane passing through the geometric centre of the ball 4. The groove 6e is arranged axially between the two cylindrical surfaces.

[0071] The cylindrical hole 7b of the second ring portion 7 is provided with a portion 7f protruding radially downward toward the groove 6e of the first ring portion 6. The protrusion 7f is convex and has a curved shape, ie, the portion 7f is an arc in a section passing through the central axis X1.

[0072] Advantageously, the portion 7f is centred, in a section through the central axis, on a radial plane passing through the geometric centre of the ball 4. The portion 7f is arranged axially between the two cylindrical surfaces.

[0073] The layer 8 is radially accommodated in the radial space defined between the first ring portion 6 and the second ring portion 7. More specifically, the layer 8 is radially arranged between the cylindrical surface 6a of the first ring portion 6 and the cylindrical surface 7b of the second ring portion 7, and between the circumferential curved groove 6e of the first ring portion 6 and the circumferential curved protrusion 7f of the second ring portion 7. The layer 8 has a shape corresponding to the first ring portion 6 and the second ring portion 7.

[0074] Thanks to the curved shape of the layer 8 and of the connecting surfaces 6 a , 7 b and 6 e , 7 f of the two ring parts 6 , 7 , respectively, the axial and radial rigidity of the inner ring 3 is increased.

[0075] Figure 3 A third embodiment of the invention is shown, in which similar parts have the same reference numerals, the difference from the previous embodiment being that the second ring portion 7 of the inner ring 3 comprises a circumferential groove 7g.

[0076] The cylindrical hole 7b of the second ring portion 7 is provided with a circumferential groove 7g. The groove 7g is machined in the metal material of the second ring portion 7. The groove 7g is concave and has a curved shape, that is, the groove 7g is an arc in a cross section passing through the central axis X1.

[0077] Advantageously, the groove 7g is centred, in a section through the central axis, on a radial plane passing through the geometric centre of the ball 4. The groove 7g is arranged axially between the two cylindrical surfaces.

[0078] The outer cylindrical surface 6a of the first ring portion 6 is provided with a portion 6f protruding radially upward toward the groove 7g of the second ring portion 7. The protrusion 6f is convex and has a curved shape, ie, the portion 6f is arc-shaped in a section passing through the central axis X1.

[0079] Advantageously, the portion 6f is centred, in a section through the central axis, on a radial plane passing through the geometric centre of the ball 4. The portion 6f is arranged axially between the two cylindrical surfaces.

[0080] Layer 8 is radially housed between the first ring portion 6 and the second ring portion 7. More specifically, layer 8 is radially disposed between the cylindrical surface 6a of the first ring portion 6 and the cylindrical surface 7b of the second ring portion 7, and between the circumferential toroidal protruding portion 6f of the first ring portion 6 and the circumferential toroidal groove 6g of the second ring portion 7. Layer 8 has a shape corresponding to that of the first ring portion 6 and the second ring portion 7.

[0081] Figure 4 A fourth embodiment of the invention is shown, in which similar components have the same reference numerals, the difference from the previous embodiment being that the rolling bearing 1 comprises an outer ring 20 having a first ring portion 26 , a second ring portion 27 and a layer 28 housed between the portions 26 , 27 .

[0082] In this embodiment, the rolling bearing 1 comprises an outer ring 30 formed in one piece and comprising an outer cylindrical surface 30a in which raceways 30e for the rolling elements 4 are formed, a cylindrical hole 30b and two side surfaces 30c, 30d.

[0083] The inner ring 20 comprises a first ring portion 26 having an outer cylindrical surface 26a, a cylindrical hole 26b and two side surfaces 26c, 26d.

[0084] The second ring portion 27 comprises an outer cylindrical surface 27 a formed with raceways 27 e for the rolling elements 4 , a cylindrical hole 27 b and two side surfaces 27 c , 27 d .

[0085] The first ring portion 26 and the second ring portion 27 are made of a metal material and are concentric with respect to the central axis X1 .

[0086] The layer 28 is radially received between the cylindrical hole 26b of the first ring portion 26 and the outer cylindrical surface 27a of the second ring portion 27. Thus, the layer 28 comprises: an outer cylindrical surface 28a fixed to the cylindrical hole 26b of the first ring portion 26; a cylindrical hole 8b fixed to the outer cylindrical surface 27a of the second ring portion 7; and two side surfaces 28c, 28d.

[0087] The layer 28 is made of an electrically insulating material. Advantageously, the layer 28 is made of an elastic material.

[0088] The outer ring 2 has a sandwich structure provided with an outer cylindrical surface 26a, a cylindrical hole 27b providing a raceway 27e for the rolling elements 4 and provided with an electrical insulation layer.

[0089] Advantageously, the side surfaces 26c, 27c, 28c are aligned in the axial direction. Advantageously, the side surfaces 26d, 27d, 28d are also aligned in the axial direction.

[0090] Advantageously, the aligned side surfaces 26c, 27c, 28c of the outer ring 20 are axially aligned with the side surface 30c of the inner ring 30. Advantageously, the aligned side surfaces 26d, 27d, 28d of the outer ring 20 are also axially aligned with the side surface 30d of the inner ring 30.

[0091] As not shown and with Figure 2 and Figure 3In an alternative embodiment similar to the embodiment shown, one of the ring portions 26 , 27 of the outer ring 20 may include a circumferentially curved groove, and the other ring portion may include a circumferentially curved protrusion extending radially toward the groove.

[0092] In the present invention Figure 5 In the fifth embodiment shown, similar components have the same reference numerals, such as Figure 4 As shown, the rolling bearing 1 includes an outer ring 20 having a first ring portion 26, a second ring portion 27 and a layer 28 received between the portions 26 and 27, and as shown in FIG. Figure 1 As shown, the inner ring 3 has a first ring portion 6 , a second ring portion 7 and a layer 8 housed between the portions 6 , 7 .

[0093] Figure 6 A sixth embodiment of the invention is shown, in which the rolling bearing 1 is provided with a brush 40 .

[0094] The brush 40 is made of a conductive material and has conductive fibers, such as copper fibers or carbon fibers.

[0095] The brush 40 is fixed to the outer ring 21 of the rolling bearing 1. The outer ring 21 is used to be fixed to the motor frame or housing, and the outer cylindrical surface 21b of the outer ring 21 is installed in the hole of the frame or housing.

[0096] The outer ring 21 further includes a side surface 21 c. The side surface 21 c of the outer ring is axially offset relative to the side surfaces 70 c and 80 c. Thus, the outer ring 21 defines an axially outward protrusion.

[0097] As an alternative solution not shown, the rolling bearing may further include a sleeve fixed to the outer ring and to the motor frame or housing, wherein the sleeve forms a protrusion axially outward of the outer ring.

[0098] The brush 40 has a free end 40 a that is in sliding contact with the inner ring 31 of the rolling bearing 1 .

[0099] The inner ring 31 includes a first ring portion 60 , a second ring portion 70 , and a layer 80 housed between the portions 60 , 70 .

[0100] The ring portions 60 and 70 are made of metal material.

[0101] The second ring portion 70 is provided with an outer cylindrical surface having a raceway for the rolling elements 40 .

[0102] The first ring portion 60 is provided with a cylindrical hole 60b for mounting on a rotating shaft.

[0103] The layer 80 is made of an electrically insulating material and is housed between the inner cylindrical surface of the second collar 70 and the outer cylindrical surface of the first collar 60 .

[0104] The first ring portion 6 has a side surface 60c that is axially offset relative to the side surfaces 70c, 80c. Thus, the first ring portion 60 defines an axially inner protrusion.

[0105] The axially outer protrusion of the outer ring 21 radially surrounds the axially inner protrusion of the first ring portion 60 of the inner ring 31. The brush 40 extends radially in the radial space defined between the axially outer and inner protrusions and is fixed to the exterior and in sliding contact with the interior.

[0106] The first bead 60 is radially opposed to the outer bead 21 via a layer 80. The brushes then form passage means for the electric current, the other passage passing through the second bead 70 being insulated by the electrically insulating layer 80.

[0107] Thanks to the invention, the current is transferred from the rotating shaft to the motor frame or housing sequentially through the first ring portion 60 , the brushes 40 and then through the outer ring 21 .

[0108] In the alternative example where the outer ring 2 is fixed to the sleeve, the current is transferred from the rotating shaft to the first ring portion 60, the brushes 40 and then to the sleeve.

[0109] In any case, the layer 80 prevents the passage of electric current through the second ring portion 70 , the inner raceway, the rolling elements 4 , the outer raceway, and then through the outer ring 2 .

[0110] The rolling bearing 1 can be formed into an assembled product that is easy to transport, carry, and install.

[0111] As an alternative embodiment not shown, the rolling bearing 1 can be provided with Figures 2 to 5 A similar technical feature of any of the embodiments shown is that brushes extend between the inner and outer rings to prevent current from passing through the raceways and rolling elements, which are insulated by one or two electrically insulating layers.

[0112] Representative, non-limiting examples of the present invention have been described in detail above with reference to the accompanying drawings. This detailed description is intended only to teach those skilled in the art further details on implementing preferred aspects of the present teachings and is not intended to limit the scope of the present invention. Furthermore, each of the additional features and teachings disclosed above may be used alone or in combination with other features and teachings to provide improved rolling bearings.

[0113] Furthermore, various features of the representative examples described above and the various independent and dependent claims appended hereto may be combined in ways not specifically and expressly recited in order to provide additional useful embodiments of the present teachings.

Claims

1. A rolling bearing (1) comprising an annular inner ring (3; 30) and an annular outer ring (2; 20) capable of relative rotation about a central axis (X1), and rolling elements (4) accommodated between raceways (2e, 27e; 7e, 30e), the raceways (2e, 27e; 7e, 30e) being provided on the two rings, It is characterized in that At least one of the rings (3; 20) comprises two concentric annular ring portions (6, 7; 26, 27) made of metallic material and an annular layer (8; 28) made of electrically insulating material, the layer (8; 28) being housed between the cylindrical surfaces (6a, 7b; 26b, 27a) of the two ring portions (6, 7; 26, 27), The cylindrical surface (6a, 7b) of one of the ring parts (6, 7) is provided with a circumferential groove (6e, 7g), and the circumferential groove (6e, 7g) is a curved surface, The rolling bearing (1) is provided with a brush (40) made of a conductive material, the brush (40) being fixed to a first axial protrusion extending axially from a first ring (21), and the brush (40) being in sliding contact with a second axial protrusion extending axially from a ring portion (60) of a second ring (31), the ring portion (60) being radially opposed to the first ring (21) via the layer (8) made of an electrically insulating material.

2. The rolling bearing according to claim 1, characterized in that The cylindrical surface (7b, 6a) of the other ring portion (7, 6) is provided with a circumferential protrusion (7f, 6f) facing the groove (6e, 7g).

3. The rolling bearing according to claim 2, characterized in that The circumferential protrusions (7f, 6f) are curved.

4. The rolling bearing according to any one of claims 1 to 3, characterized in that Said layer (8; 28) is made of elastic material.

5. The method for manufacturing a rolling bearing according to claim 4, comprising the following steps: (a) vulcanizing an elastic tube of elastomeric material in a separate molding tool; (b) applying oil to the surface of the elastic tube; and (c) Pressing the elastic tube between the two coil portions (6, 7; 26, 27) of one of the coils (3; 20) to form a layer (8; 28).

6. The method for manufacturing a rolling bearing according to claim 4, comprising the following steps: (a) arranging the two ring parts (6, 7; 26, 27) of one of the rings (2; 30) concentrically with a radial space therebetween; (b) injecting the heated elastic material in fluid form into the radial space; (c) vulcanizing the elastic material between the loops (6, 7; 26, 27) under predetermined pressure and temperature conditions to form a layer (8; 28).

7. An electric motor comprising a fixed motor frame or housing, a rotating shaft with a central axis, and at least one rolling bearing (1) according to any one of claims 1 to 4, one ring (3; 30) of the rolling bearing (1) being connected to the fixed motor frame or housing and another ring (2; 20) of the rolling bearing (1) being connected to the rotating shaft.

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