EP2807386A1

EP2807386A1 - Rolling bearing assembly with internal lubrication

Info

Publication number: EP2807386A1
Application number: EP12705989.7A
Authority: EP
Inventors: Olivier Verbe; Frank Berens; Piet Lugt
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2012-01-23
Filing date: 2012-01-23
Publication date: 2014-12-03
Also published as: KR20140114822A; CN104067010A; WO2013110319A1; JP2015504148A

Abstract

Rolling bearing assembly comprising an inner ring(2),an outer ring(3), at least one row of rolling elements(4) disposed between raceways (13a, 13b) provided on the inner and outer rings (2, 3), and an annular housing (6) inside which at least one of the rings (3) is arranged, said one ring(3) comprising two half ring parts (3a, 3b), at least one of the two half ring parts (3a) of said one ring (3) defining with the annular housing (6) a closed space (23a) inside which a lubricant (25) is located, at least one half ring part (3a) comprising passage means (24a) for the lubricant (25) to pass from the closed space (23a) to the raceways (13a, 13b). The rolling bearing assembly (1) comprises a pressure creating means (26a) disposed in said closed space (23a) on a side opposite to said passage means (24a).

Description

Rolling bearing assembly with internal lubrication

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 held by a cage between raceways provided in the two rings. The rolling elements may, for example, be ball s. The rolling bearings may be, for example, those used in industrial electri c motors or in motor vehi cle gearboxes.

In such applications, the bearings are mainly loaded radially . The service life of the rolling bearing i s essentially rel ated 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 seal s delimiting with the inner and outer rings a chamber inside which a lubricant such as grease has been introduced during the assembly of the b earing. Such a bearing is called lubricated "for life" . However, in the long term, the mixing of the grease, combined with its ageing and with the heating cycl es that the bearing undergoes, cause the grease to degrade. It is possible to envi sage periodic regreasing operations for thi s type of rolling bearings. However, these operations are expensive.

In order to avoid such periodic regreasing operations, FR-A1 - 2 923 277 di sclo ses a rolling bearing compri sing an inner ring and an outer ring with at least one row of rolling elements, and an annul ar housing surrounding the outer ring. Said outer ring is in two separate parts, or half rings, and each separate part defines with the housing a closed space, inside which grease or oil i s located. The clo sed spaces function as a grease or oil reservoirs. Passage means for the lubricant are provided on the two separate parts of the outer ring for the lubricant to pass from the clo sed spaces towards the rolling elements. Such a rolling bearing is able to operate for a long time by virtue of internal lubrication.

However, lubricant migration from the clo sed spaces through holes thanks to gravity depends on the temperature and the vibrations in the rolling bearing, and i s thus varying in time.

It is a particular obj ect of the present invention to provide a rolling bearing assembly having improved internal lubrication in which the migration of lubri cant towards the rolling elements i s increased and controlled.

In one embodiment, the rolling bearing compri ses an inner ring, an outer ring, at least one row of rolling elements di sposed between raceways provided on the inner and outer rings, and an annular housing inside whi ch at l east one of the rings i s arranged, said one ring comprising two half ring parts, each half ring part having a radi al portion and two axial cylindrical portions extending from the radial portion towards the outside, at least one of the two half ring parts of said one ring defining with the annular housing a clo sed space inside which a lubricant is located, at least one half ring part compri sing passage means for the lubricant to pass from the clo sed space to the raceways .

The rolling bearing assembly compri ses a pressure creating means di sposed in said closed space on a side opposite to sai d passage means .

Thanks to the pressure creating means inside one clo sed space, the lubrication inside the rolling bearing i s improved and the lubricant migration towards the rolling elements can be easily controlled.

Advantageously, the passage means for the lubricant comprise at least one through-hole provided in the thickness of at least one portion of one half ring part of said one ring, and the pressure creating means are di sposed on at least one inner surface of the annul ar housing opposite to said axial hole.

The passage means for the lubricant can compri se at least one axial hole provided in the thickness of the radial portion of one half ring part of said one ring, and the pressure creating means are di sposed on at least one inner surface of the annul ar housing opposite to said axial hole.

The pressure creating means may compri se a layer of an expansible material . For example, the material expands when the temperature inside the bearing assembly reaches a predetermined temperature. The predetermined temperature can be compri sed between 70°C and 250°C .

In another emb odiment, each of the two half ring parts of said one ring defines with the annular housing a closed space inside whi ch a lubricant is located.

For example, the rolling bearing assembly compri ses pressure creating means di sposed in both closed spaces.

Advantageously, the passage means for the lubricant comprise axial holes at least partly facing one another provided in the thickness of a radial portion of each of the two half ring parts of said one ring, and each pressure creating means are di sposed on one inner surface of the annular housing opposite to the corresponding axial hole.

Each pressure creating means may compri se a layer of an expansible material . For example, the first layer, di sposed in one closed space, expands when the temperature inside the bearing assembly reaches a first predetermined temperature, and the second layer di sposed in the other clo sed space, expands when the temperature inside the bearing assembly reaches a second predetermined temperature.

In particular, the first layer di sposed in one clo sed space expands when the temperature inside the bearing assembly is compri sed between 70°C and 135 °C or preferably between 80°C and 135 °C . More preci sely, the first layer expansion starts when the temperature reaches a threshold value, for example between 80°C and 95 °C, and ends when the temperature is between 120° C and 135 ° C for example . The second layer di sposed in the other clo sed space expands when the temperature inside the bearing assembly i s compri sed between 100°C and 250°C or preferably between 120° C and 205 °C . More preci sely, the second layer expansion starts when the temperature reaches a threshold value, for exampl e between 120° C and 130°C, and ends when the temperature is between 1 85 ° C and 205 °C for example.

Advantageously, the annular housing compri ses two distinct parts for retaining the half ring parts of said one ring.

The present invention will be better understood from studying the detailed description of a numb er of embodiments considered by way of entirely non-limiting examples and illustrated by the attached drawings in which :

Figure 1 is an axial half-section of the rolling bearing according to a first embodiment of the invention, represented in an initial state;

- Figure 2 is an axial half-section of the rolling bearing according to a second embodiment of the invention, represented in an initial state;

Figure 3 is a view of the rolling bearing of figure 2 during service after the temperature has reached a certain level.

As illustrated on Figures 1 to 3 , a rolling bearing, designed by general reference number 1 , comprises an inner ring 2, an outer ring 3 , a row of rolling elements 4 consisting, in the example illustrated, of ball s, held by a cage 5 between the inner ring 2 and the outer ring 3 and an annular housing 6 surrounding the outer ring 3 .

The inner ring 2 is solid and has on its outer cylindrical surface 2a a toroidal groove 7, the radius of curvature of which is slightly greater than the radius of the rolling elements 4 and forms a bearing race for the rolling elements 4. The inner ring 2 may be manufactured by machining or by pressing a steel blank, which i s then ground and optionally lapped at the bearing race 7 in order to give the ring 2 its geometrical characteri stics and its final surface fini sh.

The cage 5 compri ses a plurality of cavities 8 designed to house the rolling elements 4 and keep them uniformly circumferentially spaced. The cavities 8 are advantageously of spherical shape with a diameter slightly greater than that of the rolling elements 4. The cavities 8 are provided in the radial thickness of the cage 5 having a radial portion 5 a radially facing the outer ring 3 and extending radially inwards by a conical portion 5b . The coni cal portion 5b is located radially facing the inner ring 2 and extend s axially towards the rolling elements 4. The radial portion 5 a and the conical portion 5b define the cavities 8. The conical portion 5b form s a guide portion for the rolling elements 4.

The outer ring 3 compri ses two half ring parts 3 a, 3b or half rings. The half ring parts 3 a, 3 b are sub stantially identical and symmetric with respect to the axial plane of symmetry Y₁ of the bearing 1 , in order to reduce manufacturing costs. These two outer half rings 3 a, 3 b may advantageously be manufactured by cutting and stamping a metal sheet, the pieces obtained being then hardened by heat treatment. The bearing races intended for the rolling elements 4 may be ground and/or lapped in order to give them their geometri c characteristics and their definitive surface fini sh. Since the two half- rings 3 a, 3 b are sub stantially identical in thi s example, only one of them, having the reference "a" will be described here, it being understood that the identical elements of the other half-ring 3 b bear the reference "b" in the figures.

The half-ring 3 a of the outer ring 3 compri ses an outer axial cylindrical portion 9a, a radial portion 10a, a toroidal portion 1 1 a and an inner axial cylindrical portion 12a. The radial portion 10a is connected to the outer axi al portion 9a and to the toroidal portion 1 1 a. The toroidal portion 1 1 a defines part of a raceway 13 a for the rolling elements 4. The radius of curvature of the raceway 13 a slightly exceeds the radius of the rolling elements 4. The toroidal portion 1 1 a extends axially towards the outside of the rolling bearing 1 with the inner axial portion 12a. The two outer half-rings 3 a, 3 b are arranged with the axially internal radi al faces 14a, 14b of the radial portions 10a, 10b in contact. In this embodiment, the housing 6, which is advantageously made of a stamped metal sheet, comprises two distinct annular parts 15, 16 surrounding the two outer half-rings 3a, 3b so as to hold them firmly together in the axial direction. The parts 15, 16 of the housing 6 may advantageously be produced in an economical way from a single metal sheet by cutting and pressing. Each distinct part 15, 16 has an L-shaped structure.

The first part 15 comprises an inner axial cylindrical portion 17 for retaining radially said outer rings 3a, 3b. The inner axial cylindrical portion 17 surrounds the outer rings 3a, 3b and is in contact with the outer surface of the axial portions 9a, 9b of the outer rings 3a, 3b. The first part 15 further comprises a radial flange 18 extending radially from the inner axial cylindrical portion 17 towards the immediate vicinity of the outer cylindrical surface 2a of the inner ring 2, so as to leave a clearance between the inner edge 18a of the radial flange 18 and the cylindrical surface 2a of the inner ring 2.

The second part 16 of the housing 6 comprises an outer axial cylindrical portion 19 surrounding the inner axial cylindrical portion 17 of the first part 15. The second part 16 further comprises a radial flange 20 extending radially from the outer cylindrical portion 19 towards the immediate vicinity of the outer cylindrical surface 2a of the inner ring 2, so as to leave a clearance between the inner edge 20a of the radial flange 20 and the outer cylindrical surface 2a of the inner ring 2. The outer axial cylindrical portion 19 is fixed to the inner axial cylindrical portion 17 by means of welding, brazing or glue.

As an alternative, the housing 6 may comprise a single part having an axial cylindrical portion and two radial flanges extending from the axial cylindrical portion towards the inner ring.

The half-rings 3a, 3b are centred in the inner axial portion 17 of the part first 15 of the housing 6 by contact between the axial portions 9a, 9b and the inner bore 17a of the said inner axial portion 17. The outer radial faces 21a, 21b which form the outer edges of the outer axial portions 9a, 9b are respectively in contact with the inner surface 18b, 20b of the radial flanges 18, 20 of the parts 15, 16 of the housing 6, thus axially clamping the two half-rings 3a, 3b together. The outer radial faces 22a, 22b which form the outer edges of the inner axial portions 12a, 12b are also in contact with said radial flanges 18, 20.

Each of the half-rings 3a, 3b defines, with the housing 6, an annular closed space 23a, 23b. More specifically, the closed space 23a is delimited by the outer axial portion 9a, the radial portion 10a, the toroidal portion 11a, and the inner axial portion 12a, and, adjacent to these portions, the radial flange 18 of the first part 15 of the housing 6.

As illustrated on Figure 1, one of the two spaces 23a, 23b may act as a lubricant reservoir; the lubricant 25 contained in the closed space 23a may be grease or oil. Lubricant can be packed into the space 23a which constitutes a first lubricant reservoir between the half-ring 3a and the inner ring 2. As an alternative, lubricant can also be packed into the second space 23b and into the volume remaining between the inner 2 and outer 3 rings.

As illustrated, one of the half ring parts 3a of the outer ring 3 comprises passage means for the lubricant 25 contained in the corresponding closed space 23a. In the example illustrated in Figure 1, these passage means comprise at least one and preferably a plurality of axial through-holes 24a, provided in the thickness of the radial portion 10a of the outer half-ring part 3a. Each through-hole 24a communicates with a radial recess or groove 27a which is open toward its internal end so as to leave passage for the lubricant to flow into the row of balls 4 and between the respective contact surfaces of the balls with the raceways 13a, 13b. However, supplemental or alternatively other types of passage means may be used; for example, radial through-holes (not represented) may be provided in the thickness of the axial portion 12a, in order to allow the lubricant contained in the closed space 23a to flow by gravity directly towards the rolling elements 4. The rolling bearing 1 further compri ses a pressure creating means 26a comprising a layer of an expansible material di sposed inside the clo sed space 23 a. The layer 26a i s di sposed on a si de of the closed space 23 a opposite to the passage means 24a

In the embodiment illustrated on Figure 1 , the layer 26a i s initially located on the inner surface 1 8b of the radial flange 1 8 of the annular housing 6 forming the wall of the closed space 23 a, opposite to the axial through holes 24a.

As an alternative, the layer could be located on the inner surface of the outer cylindrical axial portion 9a of the half ring part 3 a, and passages means for the lubricant may compri se radial through- holes provided in the thickness of the inner cylindrical axial portion 12a of the half ring part 3 a. It is preferable that the layer of expansible material be located in the corresponding cl osed space in a position facing the lubricant passage means so that the pressure exerted by the expansible material urges the lubricant to flow out of the passage means.

The expansible material is a material capable of expanding when the temperature inside the bearing assembly 1 reaches a predetermined temperature. The predetermined temperature i s preferably comprised between 70°C and 1 50°C, mo st preferably between 80°C and 135 °C . Moreover, the layer 26a expansion starts when the temperature inside the bearing assembly 1 reaches a predetermined temperature, for example compri sed between 80°C and 95 °C, and ends when the temperature inside the bearing assembly 1 i s comprised between 120°C and 13 5 °C for example.

The layer 26a may be formed as an annular flat ring made of an expansible material . Alternatively, the layer 26a may be di scontinuous, the clo sed space 23 a enclosing di screte patches of expansible material arranged against the inner surface 1 8b .

In a preferred embodiment, the layer may be made by proj ecting small diameter particles as a powder materi al against the surface of the lubri cant, after the lubricant has been introduced within the half ring part 3 a and/or 3b and before closing the corresponding space 23 a, 23b by mounting the housing 6.

The size of the particles at room temperature may b e approximately 10 to 1 5 μιη.

After reaching a determined temperature, for example 70°C-

100°C or preferably 80°C-95 ° C, the size of the particles may be up to 40 μιη whi ch represents a volume increase of approximately 60 times .

An example of an expansible material which can be used in the present invention i s a material sold under the name "Expancel" by Company Microspheres from AkzoNobel Manufacturer.

The embodiment of Figure 2, in which identical elements bear the same references, differs from the embodiment of Figure 1 only by the fact that each of the two half ring parts 2a, 2b of the outer ring 3 defines with the annular housing 6 a cl osed space 23 a, 23b inside which a lubricant 25 is located.

As illustrated on Figure 2, pressure creating means 26a, 26b i s di sposed inside both closed spaces 23 a, 23b . Each pressure creating means 26a, 26b compri se a layer of an expansible material di sposed on a side of the corresponding clo sed space 23 a, 23b opposite to the passage means 24a, 24b . The lubricant may flow through the holes 24a, 24b and the grooves 27a, 27b toward the rolling elements 4. The layers 26a, 26b are located on the inner surface 1 8b and 20b of the radial flanges 1 8 and 20 of the annular housing 6 forming the wall of the corresponding clo sed space 23 a, 23b opposite to the axial through holes 24a, 24b .

The first layer 26a i s made of a first material expanding at a first predetermined temperature and the second layer 26b i s made of a second material expanding at a second predetermined temperature . Moreover, the layer 26a expansion starts when the temperature inside the bearing assembly 1 reaches a predetermined temperature, for example compri sed between 80°C and 95 °C, and ends when the temperature inside the bearing assembly 1 is compri sed between 120°C and 135 ° C for example. The second layer 26b expansion starts when the temperature inside the bearing assembly 1 reaches a predetermined temperature, for example compri sed between 120° C and 130°C, and ends when the temperature inside the bearing assembly 1 is compri sed between 1 85 °C and 205 ° C for example. In that case, different lubricant may be used in the two respective spaces 23 a, 23 b . As an alternative, both layers 26a, 26b can be made of the same material capable of expanding when the temperature reaches the same temperature, for example a predetermined temperature compri sed b etween 80°C and 95 °C .

As an alternative, the layers could be located on the inner surface of the outer cylindrical axial portions 9a, 9b of each half ring parts 3 a, 3b, and passages means could compri se radial through-holes provided in the thickness of the inner cylindrical axial portions 12a, 12b of the half ring parts 3 a, 3b .

Figure 3 illustrates the rolling bearing assembly 1 of Figure 2 when the temperature has risen to a higher level than both predetermined temperatures. Each layer 26a, 26b has therefore expanded, so that the volume of each layer 26a, 26b has increased while the volume of the free spaces left to the lubricant 25 has decreased, creating a pressure inside the closed spaces 23 a, 23b . The pressure thus created forces the lubricant 25 to pass through the corresponding axial through-holes 24a, 24b and the corresponding radi al grooves 27a, 27b towards the rolling elements 4 and the raceway s 13 a, 13b .

The dimensions of the passage means are function of the lubricant used. In fact, when oil i s used as a lubricant, the passage means are bigger in cross-section than passage means provided when grease i s used as a lubricant.

Thanks to the expansible material provided in at least one closed space, pressure i s created inside one or both clo sed spaces; the lubrication of the rolling bearing is improved, and is controll ed during use of the rolling bearing. Thanks to the thermal properties of the expansible material, pressure is created inside the clo sed spaces only when lubricant is needed to lubricate the contact surfaces between the raceways and the rolling elements.

The present invention al so has the advantages of leading to a self regulation of the lubrication since the pressure exerted on the lubricant increases when the temperature increases i . e . when the friction against the raceways increases due to an insufficient lubrication.

In addition, the lubricant is kept inside the reservoir formed in one or both of the half rings without the risk of leakage when the bearing is stored at room temperature since no pressure is exerted at that temperature on the lubricant.

Claims

1. Rolling bearing assembly comprising an inner ring (2), an outer ring (3), at least one row of rolling elements (4) disposed between raceways (13a, 13b) provided on the inner and outer rings (2, 3), and an annular housing (6) inside which at least one of the rings (3) is arranged, said one ring (3) comprising two half ring parts (3a, 3b), each half ring part (3a, 3b) having a radial portion (10a, 10b) and two axial cylindrical portions (9a, 9b, 12a, 12b) extending from the radial portion (10a, 10b) towards the outside, at least one of the two half ring parts (3a) of said one ring (3) defining with the annular housing (6) a closed space (23a) inside which a lubricant (25) is located, at least one half ring part (3a) comprising passage means (24a, 27a) for the lubricant (25) to pass from the closed space (23a) to the raceways (13a, 13b), characterized in that the rolling bearing assembly (1) comprises a pressure creating means (26a) disposed in said closed space (23a).

2. Rolling bearing assembly according to Claim 1, in which the pressure creating means (26a) disposed in said closed space (23a), is on a side opposite to said passage means (24a).

3. Rolling bearing assembly according to Claim 1 or 2, in which the passage means (24a) for the lubricant (25) comprise at least one through-hole provided in the thickness of at least one portion (9a, 10a, 11a, 12a) of one half ring part (3a) of said one ring (3), and the pressure creating means (26a) are disposed on at least one inner surface (18b) of the annular housing (6) opposite to said axial hole (24a).

4. Rolling bearing assembly according to any one of the preceding Claims, in which the passage means (24a) for the lubricant (25) comprise at least one axial hole provided in the thickness of the radial portion (10a) of one half ring part (3a) of said one ring (3).

5. Rolling bearing assembly according to any one of the preceding Claims, in which the pressure creating means (26a) comprises a layer of an expansible material.

6. Rolling bearing assembly according to Claim 5, in which the material expands when the temperature inside the bearing assembly

(1) reaches a predetermined temperature.

7. Rolling bearing assembly according to Claim 5 or 6, in which the predetermined temperature is comprised between 70°C and 250°C.

8. Rolling bearing assembly according to any one of the preceding Claims, in which each of the two half ring parts (3a, 3b) of said one ring (3) defining with the annular housing (6) a closed space (23a, 23b) inside which a lubricant (25) is located.

9. Rolling bearing assembly according to Claim 8, comprising pressure creating means (26a, 26b) disposed in both closed spaces

(23a, 23b).

10. Rolling bearing according to Claim 8 or 9, in which the passage means (24a, 24b) for the lubricant (25) comprise axial holes at least partly facing one another provided in the thickness of a radial portion (10a, 10b) of each of the two half ring parts (3a, 3b) of said one ring (3), and each pressure creating means (26a, 26b) are disposed on one inner surface (18b, 20b) of the annular housing (6) opposite to the corresponding axial hole (24a, 24b).

11. Rolling bearing assembly according to Claim 9 or 10, in which each pressure creating means (26a, 26b) comprises a layer of an expansible material.

12. Rolling bearing according to Claim 11, in which the first layer (26a), disposed in one closed space (23a), expands when the temperature inside the bearing assembly (1) reaches a first predetermined temperature, and the second layer (26b) disposed in the other closed space (23b), expands when the temperature inside the bearing assembly (1) reaches a second predetermined temperature.

13. Rolling bearing according to Claim 12, in which the first layer (26a) predetermined temperature is comprised between 80 and 135°C and the second layer (26b) predetermined temperature is comprised between 120 and 205°C.

14. Rolling bearing according to any one of the preceding Claims, wherein the annular housing (6) comprises two distinct parts for retaining the half ring parts (3a, 3b) of said one ring (3).