WO2013189534A1

WO2013189534A1 - Rolling bearing with reduced lubrication and method of manufacturing such a bearing

Info

Publication number: WO2013189534A1
Application number: PCT/EP2012/061873
Authority: WO
Inventors: Frank Berens; Olivier Verbe; Stéphane CORDIER
Original assignee: Aktiebolaget Skf
Priority date: 2012-06-20
Filing date: 2012-06-20
Publication date: 2013-12-27

Abstract

Rolling bearing comprising an inner ring (1), an outer ring (2), at least one row of rolling elements (3) disposed between raceways (17a, 17b, 6) provided on the inner and outer rings (1, 2). A first lubricant (31) is only contained in a gap (32) radially delimited between at least one of the rolling elements (3) and one of the rings (2) when the rolling bearing is at its initial state after being assembled and before use.

Description

Rolling bearing with reduced lubrication and method of manufacturing such a bearing

The present invention relates to rolling bearings, in particular rolling bearings having an inner ring and an outer ring with one or more rows of rolling elements, for example balls. The rolling bearings may be, for examp le, those used in industrial electric motors or in motor vehicle gearboxes.

In such applications, the bearings are mainly loaded radially. In such applications, the service life of the ro lling bearing is essentially related to the lubrication of the bearing. Any defect in lubricating generally leads to rapid degradation and to failure of the rolling bearing.

For instance, a known deep groove ball bearing has two seals delimiting with the inner and outer rings a chamber inside which a lubricant such as grease has been introduced during the assembly o f the bearing. Such a bearing is called lubricated "for life" and is able to operate for a long time thanks to the high amount of lubricant located in the chamber between the inner and outer rings at the beginning o f the service life o f the ro lling bearing. However, the increase of the amount of lubricant increases significantly the friction torque between the raceways and the rolling elements and therefore, the self-heating of the rolling bearing.

Furthermore, in the long term, the mixing of the grease, combined with its ageing and with the heating cycles that the bearing undergoes, cause the grease to degrade. It is possible to envisage periodic re-greasing operations for this type o f ro lling bearings. However, these operations are expensive.

One aim o f the present invention is to overcome these drawbacks.

It is a particular obj ect of the present invention to provide a rolling bearing with reduced lubricant filling in the chamber between the inner and outer rings at the beginning of the service life. Another obj ect of the present invention is to avoid periodic re- greasing operations o f the rolling bearing.

In one embodiment, a ro lling bearing comprises an inner ring, an outer ring, at least one row of rolling elements disposed between raceways provided on the inner and outer rings.

A first lubricant is only contained in a gap radially delimited between at least one of the rolling elements and one of the rings when the rolling bearing is at its initial state after being assembled and before use.

Thanks to the low amount of lubricant provided between the rings and especially between at least one of the rolling elements and the outer ring, the friction torque at the beginning of the service life o f the rolling bearing is significantly reduced.

After the first rotation of the rolling bearing, the small amount of lubricant is split only on the functional raceways surfaces and therefore the friction torque is reduced.

Advantageously, the vo lume of the lubricant is comprised between 0, 1 % and 10% of the volume of a rolling chamber radially lo cated between the inner and outer rings.

Preferably, the vo lume of the lubricant is comprised between

5 % and 10% o f the vo lume o f the chamber, and more preferably, the vo lume o f the lubricant is o f 5 % of the volume o f said chamber.

In an embodiment, at least one of the rings comprises two separate parts, each separate part having a radial portion and a toroidal portion defining the raceways and connected to the radial portion by a rounded edge portion, the two separate parts of said one ring being arranged with the radial portions in axial contact with one another, so as to define said gap delimited by each rounded edge portions and at least one of the rolling elements.

Advantageously, each separate parts of said one ring comprises two axial cylindrical portions extending axially from the radial portion towards the outside respectively by a second rounded edge portion and by said toroidal portion, said rolling chamber being radially delimited by said toroidal and edge portions of said one ring and the axial cylindrical portion connected to the toroidal portion, and the other ring.

In an embodiment, the rolling bearing comprises an annular housing inside which said one ring is arranged, at least one of the two separate parts of said one ring delimiting with the housing a clo sed space inside which a second lubricant is located, the rolling bearing further comprising passage means allowing the second lubricant to flow from the clo sed spaces to the rolling chamber.

For example, the passage means for the second lubricant comprise at least one axial through-ho le provided in the thickness o f the radial portion of at least one of the separate parts of said one ring.

The radial portion of each o f the separate parts of said one ring may comprise an axial through-ho le.

In an embodiment, the axial through-ho les at least partly face one another to put the two closed spaces into communication.

The first lubricant can be grease based on oil(s) or dry lubricant based on graphite or mo lybdenum disulfide, and the second lubricant can be oil, for example contained in porous elements fitted inside the clo sed spaces .

According to another aspect, it is proposed an electric motor or generator comprising at least one rolling bearing as previously defined.

In another embo diment, the invention provides a method of manufacturing a rolling bearing having an inner ring, an outer ring, at least one row of rolling elements disposed between raceways provided on the inner and outer rings, said method comprising the step o f inserting a first lubricant only in a gap radially delimited between at least one of the rolling elements and one of the rings when the rolling bearing is at its initial state after being assembled and before use.

Advantageously, at least one of the rings comprises two separate parts, each separate part having a radial portion and a toroidal portion defining the raceways and connected to the radial portion by a rounded edge portion, and said method comprises the step of inserting one o f the rings and one separate part of the other ring made in two separate parts with said rolling elements in a housing having an reshaped structure before inserting the first lubricant in said gap delimited by each rounded edge portions and at least one of the rolling elements.

In an embodiment, the method comprises the step of inserting a second lubricant in a clo sed space delimited by said separate part and said housing.

The present invention will be better understood from studying the detailed description o f a number of embodiments considered by way o f entirely non-limiting examp les and illustrated by the attached drawings in which:

- Figure 1 is an axial half-section o f the rolling bearing according to the invention, in a first embo diment;

- Figure 2 is an axial half-section of a rolling bearing according to a second embo diment of the invention;

- Figure 3 is a step of manufacturing method according to the invention; and

- Figure 4 is a side view o f the rolling bearing according to

Figure 3.

In the further description, terms "outer" and inner" are defined with respect to the rotational axis X-X' o f the ro lling bearing illustrated on the figures, where the term "inner" means closer to the rotational axis X-X ' of the rolling bearing then term "outer".

As illustrated on Figure 1 , which illustrates an embodiment o f a rolling bearing according to the invention, said bearing comprising an inner ring 1 , an outer ring 2, a row of rolling elements 3 consisting, in the example illustrated, of balls, and a cage 4 to hold said ro lling elements 3 and disposed between the inner ring 1 and the outer ring 2.

The ro lling bearing also comprises an annular enclosing ring or housing 5 surrounding the outer ring 2. In this example, the inner ring 1 is designed to be mounted on a rotary member. It thus constitutes the rotating ring of the bearing while the outer ring 2 constitutes the non-rotating ring. The inner ring 1 is so lid and has a toroidal groove 6 provided on its outer cylindrical surface l a and forming a raceway for the rolling elements 3. The radius o f curvature of the groove 6 is slightly greater than the radius of the rolling elements 3. The inner ring 1 may be manufactured by machining or by pressing a steel blank which is then ground and optionally lapped at the raceway in order to give the ring 1 its geometric characteristics and its final surface finish.

The cage 4 comprises a plurality o f open cavities 7 designed to house the rolling elements 3 and keep them uniformly circumferentially spaced. The cavities 7 are advantageously spherical with a diameter slightly greater than that of the rolling elements 3 so as to receive and ho ld the latter. The cavities 7 are provided in the radial thickness o f the cage 4 having a radial portion 8 radially facing the outer ring 2 and extending radially inwards by a conical portion 9. The conical portion 9 is lo cated radially facing the inner ring 1 and extends axially towards the rolling elements 3. The radial portion 8 and the conical portion 9 define the cavities 7. The conical portion 9 forms a guide portion for the rolling elements 3. The cage 4 can be made of moulded plastic or of metal.

In this embodiment, the outer ring 2 comprises two separate parts or half-rings 2a and 2b. The separate parts 2a, 2b are identical and symmetrical with respect to the radial plane o f symmetry o f the bearing in order to reduce the manufacturing costs. As an alternative, it is also possible to foresee parts 2a, 2b non-symmetric. These two outer half-rings 2a, 2b may advantageously be manufactured by cutting and stamping a metal sheet, the pieces obtained then being hardened by heat treatment. Each of the two half-rings 2a, 2b has a constant thickness. The raceways may then be ground and/or lapped in order to give them their geometric characteristics and their definitive surface finish. Since the two half-rings 2a, 2b are identical in this example, only one of them, having the reference "a", will be described here, it being understood that the identical elements o f the other half-ring 2b have the reference "b".

The half-ring 2a o f the outer ring 2 comprises a first cylindrical axial portion 1 1 a, an annular radial portion 12a, a toroidal portion 13 a and a second cylindrical axial portion 14a. In the examp le illustrated, the first axial cylindrical portion 1 1 a is an outer axial cylindrical portion 1 1 a and the second axial cylindrical portion 14a is an inner axial cylindrical portion 14a, the inner axial cylindrical portion 14a being clo ser to the rotational axis X-X' of the rolling bearing then the outer axial cylindrical portion 1 1 a. The radial portion 12a is connected to the toroidal portion 13 a by a first rounded edge portion 15 a and to the outer axial portion 1 1 a by a second rounded edge portion 16a. The toroidal portion 13 a delimits a toroidal raceway 17a for the rolling elements 3. The toroidal portion 13 a forms a guiding portion for the ro lling elements 3. The radius of curvature of the raceway 17a is slightly greater than the radius of the rolling elements 3. The toroidal portion 13 a is also connected to the inner axial portion 14a. The toroidal portion 13 a extends axially towards the outside of the rolling bearing with the inner axial portion 14a. The two outer half-rings 2a, 2b are positioned with the radial faces 1 8a, 1 8b o f the radial portions 12a, 12b in axial contact with one another, approximately in the radial plane of symmetry o f the rolling bearing and the rolling elements 3.

In the embo diment of Figure 1 , the inner radial faces 1 8a, 1 8b of the radial portions 12a, 12b are in contact with one another. This contact between the radial portions 12a, 12b makes it possible to obtain a rolling bearing with internal preload. In some applications, it is preferred that the rolling bearing has an internal preload, that is to say a preload both in the radial and axial directions . For instance, in an electric power assisted steering system for a vehicle, such a bearing advantageously supports in rotation the rotor of the vehicle motor in order to prevent any click noise. The housing 5 , which is advantageously made of a stamped metal sheet, comprises two distinct annular parts 20, 21 surrounding the two outer half-rings 2a, 2b so as to hold them firmly together in the axial direction. The parts 20, 2 1 of the housing 5 may advantageously be produced in an economical way from a single metal sheet by cutting and pressing. Each distinct part 20, 21 have an reshaped structure.

The first part 20 comprises an inner axial cylindrical portion 22 for retaining radially said outer rings 2a, 2b . The inner axial cylindrical portion 22 surrounds the outer rings 2a, 2b. The first part 20 further comprises a radial flange 23 extending radially from the inner axial cylindrical portion 22 towards the immediate vicinity o f the outer cylindrical surface l a of the inner ring 1 , so as to leave a radial clearance between the inner edge 23 a of the radial flange 23 and the cylindrical surface l a o f the inner ring 1 .

The second part 21 of the housing 5 comprises an outer axial cylindrical portion 24 surrounding the inner axial cylindrical portion 22 of the first part 20. The second part 21 further comprises a radial flange 25 extending radially from the outer cylindrical portion 24 towards the immediate vicinity o f the outer cylindrical surface l a o f the inner ring 1 , so as to leave a clearance between the inner edge 25 a of the radial flange 25 and the outer cylindrical surface l a of the inner ring 1 . The outer axial cylindrical portion 24 is fixed to the inner axial cylindrical portion 22 by means o f welding, brazing or glue.

The half-rings 2a, 2b are centred in the inner axial portion 22 of the first part 20 of the housing 5 by radial contact between the axial portions 1 1 a, l i b and the bore of the said inner axial portion 22. The outer radial faces 26a, 26b which form the outer edges o f the outer axial portions 1 1 a, l i b are respectively in contact with the radial flanges 23 , 25 o f the parts 20, 21 o f the housing 5 , thus axially clamping the two half-rings 2a, 2b together. The outer radial faces 27a, 27b which form the outer edges o f the inner axial portions 14a, 14b are also in contact with the radial flanges 23 , 25. As an alternative, an axial clearance (not shown) may be provided between the outer edges 27a, 27b o f the inner axial portions 14a, 14b and the radial flanges 23 , 25 of the housing 5.

Each of the half-rings 2a, 2b defines, with the housing 5 , an annular clo sed space 30a, 30b . More specifically, the clo sed space 30a is delimited by the outer axial portion 1 1 a, the radial portion 12a, the toroidal portion 13 a, and the inner axial portion 14a, and, adj acent to these portions, the radial flange 23 o f the first part 20 o f the housing 5.

As illustrated, the rolling bearing is provided with lubricant 3 1 is only contained in a gap 32 delimited between the rolling elements 3 and the corresponding rounded edge portions 15 a, 15b o f the outer ring 2 when the rolling bearing is at its initial state after being assembled and before use. The gap 32 is a small part of a rolling chamber 33 radially located between the inner and outer rings 1 , 2.

Thanks to the low amount of lubricant 3 1 provided between the rings 1 , 2 in the gap 32, the friction torque at the beginning of the service life o f the ro lling bearing is significantly reduced. After the first rotation of the rolling bearing, the small amount of lubricant 3 1 is split only on the functional raceways surfaces (not referenced) and therefore the friction torque is reduced.

The vo lume o f the lubricant 3 1 is, for example, comprised between 0, 1 % and 10% of the vo lume of the rolling chamber 33 , preferably, between 5 % and 10% of the volume of the rolling chamber 33 , and more preferably, of 5 % of the volume of the rolling chamber 33.

As illustrated, the first lubricant 3 1 is grease based on oil(s) . As an alternative, the lubricant 3 1 can be dry lubricant based on graphite or molybdenum disulfide.

The only difference with the embodiment of Figure 2, in which identical elements bear the same references, is that one of the two or both spaces 30a, 30b may act as a lubricant reservoir, a second lubricant 35 contained in these spaces 30a, 30b may be grease or oil and can be different from the first lubricant 3 1 located in the gap 32. Alternatively, it could be possible to foresee in the two closed spaces a cellular or porous annular element saturated with oil. The cellular or porous annular elements act as sponges and under the effect o f vibrations are able to release the lubricant oil which then passes as before through the passage means described hereinabove. The cellular or porous annular elements can take up the whole o f the closed spaces 30a, 30b or only part thereof.

The second lubricant 35 can be packed into the space 30a which constitutes a first lubricant reservoir between the half-ring 2a and the inner ring 1 . The second lubricant 35 is also packed into the second space 30b.

Each part 2a, 2b of the outer ring 2 comprises passage means 36 for the second lubricant 35 contained in the closed spaces 30a, 30b . In the example illustrated in Figure 2, these passage means comprise axial through-ho les 36a, 36b provided the thickness of the radial portion 12a, 12b at least partially facing one another, so as to put the two closed spaces 30a, 30b into communication. This arrangement, which can be maintained by suitable positioning during assembly or by angular indexing means (not shown), provided on the two half-rings 2a, 2b, allows the two closed spaces 30a, 30b to intercommunicate. As illustrated, each inner radial face 1 8 a, 1 8b o f the corresponding radial portion 12a, 12b is provided with a radial groove 37a, 37b forming a radial passage or duct so that the outer end of the radial duct is in communication with the corresponding through-ho le 36a, 36b and its inner end is in communication with the toroidal race 17a, 17b so as to guide the second lubricant 35 directly onto the balls 3. In this example, it should be understood that the axial through-ho les 36a, 36b associated with a radial duct 37a, 37b can easily not be located facing one another.

The method of manufacturing such types of bearings will now be described on the basis of figure 2. On Figures 3 and 4, which show the first step of manufacturing the rolling bearing, one o f the half rings 2a of the outer ring 2 is inserted in the L-shaped structure of the first part 20 of the housing 5 , with the radial faces 26a, 27a o f the half ring 2a resting on the inner surface o f the radial flange 23 and the outer surface of the axial portion 1 1 a in contact with the inner axial cylindrical portion 22 o f the first part 20. The inner ring 1 is then mounted. Having inserted the rolling elements 3 into the cavities 7 of the cage 4 and having mounted that subassembly on the inner ring 1 , the first lubricant 3 1 is filled in the gap 32 located between the rolling elements 3 and the rounded edge portion 1 7a.

A second lubricant 35 is then inserted in the clo sed space 30a acting as a first lubricant reservoir.

As illustrated on Figure 2, the second half-ring 2b is then positioned around the row of rolling elements 3 in the L-shaped structure 20 with the radial face 1 8a of the radial portion 12a in contact with the radial face 1 8b of the radial portion 12b of the half ring 2b . The outer surface of the outer axial portion l i b is in contact with the inner surface of the inner axial cylindrical portion 22. The second part 21 of the housing 5 is afterwards positioned so that its outer axial cylindrical portion 24 surrounds the inner axial cylindrical portion 22 o f the first part 20. The outer radial faces 26b, 27b o f the axial portions l i b, 14b are in contact with the inner radial surface o f the radial flange 25 o f the second part 21 . The second part 21 of the housing 5 is fitted to retain the half-rings 2a, 2b axially.

In the disclo sed embodiment, the outer ring 2 comprises two half-rings 2a, 2b and the inner ring 1 is of the solid type .

Alternatively, it might be possible to have the outer ring solid while the inner ring would consist of two half-rings produced in a similar way to the half-rings 2a, 2b of the disclo sed embo diments . The two half-rings of the inner ring would be mounted inside a housing as described above. The arrangement is identical to that of the embodiment illustrated, but with the elements inverted.

In such a case, it is advantageous for the inner ring formed by the two half-rings to be the rotating ring o f the rolling bearing in operation. This is because, in this case, when the rolling bearing rotates, the lubricant contained in the two spaces o f the half-ring is subj ected to centrifugal force and tends to diffuse through the passages means towards the raceways o f the rolling bearing.

In another embodiment, it could also be possible to have a rolling bearing in which the inner ring and the outer ring each comprise two half-rings enclosed in a housing as previously described. In such an embodiment, the rolling bearing has four clo sed spaces acting as lubricant reservoirs.

Although the present invention has been illustrated on the basis of a rolling bearing having a single row of balls, it should be understood that the invention can be applied to bearings using several rows of rolling elements, without major modifications. The invention can also be applied to different types of ball bearings, such as angular contact bearings, or else to self-aligning bearings .

Thanks to the small amount of lubricant provided between the rings and especially between the rolling elements and the outer ring, the friction torque at the beginning of the service life of the rolling bearing is significantly reduced. Indeed, the lubricant is only contained in a gap delimited between the rolling elements and the corresponding separate parts of the outer ring when the rolling bearing is at its initial state after being assembled and before use.

After a first rotation o f the ro lling bearing, the small amount of lubricant located in the gap is split only on the functional raceways surfaces and therefore the friction torque is reduced, and the lubrication o f the rolling bearing during its service life is guaranteed by the internal lubricant located in the lubricant reservoirs in one or both of the half-rings . Periodic re-greasing operations of the rolling bearing are thus avoided.

Claims

1. Rolling bearing comprising an inner ring (1), an outer ring (2), at least one row of rolling elements (3) disposed between raceways (17a, 17b, 6) provided on the inner and outer rings (1, 2), characterized in that a first lubricant (31) is only contained in a gap (32) radially delimited between at least one of the rolling elements (3) and one of the rings (2) when the rolling bearing is at its initial state after being assembled and before use.

2. Rolling bearing according to Claim 1, in which the volume of the first lubricant (31) is comprised between 0,1% and 10% of the volume of a rolling chamber (33) radially located between the inner and outer rings (1, 2).

3. Rolling bearing according to Claim 2, in which the volume of the first lubricant (31) is of 5% of the volume of said chamber (33).

4. Rolling bearing according to any preceding Claims, in which at least one of the rings comprises two separate parts (2a, 2b), each separate part (2a, 2b) having a radial portion (12a, 12b) and a toroidal portion (13a, 13b) defining the raceways (17a, 17b) and connected to the radial portion (12a, 12b) by a rounded edge portion (15a, 15b), the two separate parts (2a, 2b) of said one ring (2) being arranged with the radial portions (12a, 12b) in axial contact with one another, so as to define said gap (32) delimited by each rounded edge portions (15a, 15b) and at least one of the rolling elements (3).

5. Rolling bearing according to Claim 4, in which each separate parts (2a, 2b) of said one ring (2) comprises two axial cylindrical portions (11a, lib, 14a, 14b) extending axially from the radial portion (12a, 12b) towards the outside respectively by a second rounded edge portion (16a, 16b) and by said toroidal portion (13a, 13b).

6. Rolling bearing according to Claim 4 or 5, comprising an annular housing (5) inside which said one ring (2) is arranged, at least one of the separate parts (2a) of said one ring delimiting with the housing (5) a closed space (30a) inside which a second lubricant (35) is located, the rolling bearing further comprising passage means (36a, 36b, 37a, 37b) allowing the second lubricant (35) to flow from the closed spaces (30a, 30b) to the rolling chamber (33).

7. Rolling bearing according to Claim 6, wherein the passage means for the second lubricant (35) comprise at least one axial through-hole (36a, 36b) provided in the thickness of the radial portion (12a, 12b) of at least one of the separate parts (2a, 2b) of said one ring (2)·

8. Rolling bearing according to Claim 7, wherein the radial portion (12a, 12b) of each of the separate parts (2a, 2b) of said one ring (2) comprises an axial through-hole (36a, 36b).

9. Rolling bearing according to Claim 8, wherein the axial through-holes (36a, 36b) at least partly face one another to put the two closed spaces (30a, 30b) into communication.

10. Rolling bearing according to any of the preceding claims, wherein the first lubricant (31) is grease based on oil(s) or dry lubricant based on graphite or molybdenum disulfide.

11. Rolling bearing according to any of the preceding Claims 6 to 9, wherein the second lubricant (35) is oil contained in porous elements fitted inside the closed spaces (30a, 30b).

12. Electric motor or generator comprising at least one rolling bearing according to any of the preceding claims.

13. Method of manufacturing a rolling bearing having an inner ring (1), an outer ring (2), at least one row of rolling elements (3) disposed between raceways (17a, 17b, 6) provided on the inner and outer rings (1, 2), said method comprising the step of inserting a first lubricant (31) only in a gap (32) radially delimited between at least one of the rolling elements (3) and one of the rings (2) when the rolling bearing is at its initial state after being assembled and before use.

14. Method according to Claim 13, wherein at least one of the rings comprises two separate parts (2a, 2b), each separate part (2a, 2b) having a radial portion (12a, 12b) and a toroidal portion (13a, 13b) defining the raceways (17a, 17b) and connected to the radial portion ( 12a, 12b) by a rounded edge portion ( 15 a, 15b), and comprising the step of inserting one of the rings ( 1 ) and one separate part (2a) of the other ring (2) made in two separate parts (2a, 2b) with said rolling elements (3) in a housing (5) having an L-shaped structure before inserting the first lubricant (3 1 ) in said gap (32) delimited by each rounded edge portions and at least one of the rolling elements.

15. Method according to Claim 14, comprising the step of inserting a second lubricant (35) in a clo sed space (30a) delimited by said separate part (2a) and said housing (5 ) .