WO2009090120A2

WO2009090120A2 - Seal and rolling bearing comprising such a seal.

Info

Publication number: WO2009090120A2
Application number: PCT/EP2009/050079
Authority: WO
Inventors: Stéphane CORDIER; Alexandre Manceau; Julien Lapinte; Armel Louis Doyer; Francis Claude
Original assignee: Aktiebolaget Skf
Priority date: 2008-01-16
Filing date: 2009-01-06
Publication date: 2009-07-23
Also published as: DE112009000106T5; WO2009090120A3; FR2926345B1; FR2926345A1

Abstract

The seal is designed to be mounted between two elements 14, 16 adapted to rotate relative to one another, notably rings of a rolling bearing, the seal comprising seal portions 32, 34 respectively capable of applying a dynamic seal with one of the two elements 16 and a static seal with the other element 14. The dynamic seal portion 34 comprises at least first and second lips 38, 40 delimiting an annular chamber 46 capable of being filled with lubricant. The seal is configured to allow, during the contact of a fluid with at least the dynamic seal portion 34, a movement of one of the lips, at least in the radial direction, in the direction of the associated element 16 to obtain a contact with the said element.

Description

Seal and rolling bearing comprising such a seal

The present invention relates to the field of seals and in particular the seals used in rolling bearings. For reasons of economy of consumed energy, increasing efforts are being made to reduce the losses caused by friction in machines. For example, in a rolling bearing, the seal is provided by one or more seals making it possible to keep the lubricant, such as grease, inside the rolling bearing and to prevent pollutants from getting inside the latter.

Generally, the seals are attached to one of the rings of the rolling bearing and interact by friction contact with the other ring to provide the seal.

The seals that rub against one of the rings of the rolling bearing with a considerable contact pressure are particularly effective with respect to the seal but are capable of consuming a relatively large amount of energy. In addition, such friction generates heat and may cause a rise in temperature that is harmful for the rolling bearing, or more generally for the associated machine. Such a seal with permanent friction contact is described in US patent 4,844,485.

Conversely, with a seal the lip of which does not rub very much or at all against the associated bearing surface of the rotating element of the machine, the seal obtained may be insufficient in certain operating conditions. The object of the present invention is therefore to remedy these disadvantages.

More particularly, the object of the present invention is to provide a seal making it possible to ensure an effective sealing while as much as possible limiting the dissipation of energy. A further object of the present invention is to provide a seal that is particularly easy to manufacture.

Another object of the present invention is to provide a seal suitable for a rolling bearing. The present invention relates to a seal designed to be mounted between two elements capable of rotating relative to one another, notably rings of a rolling bearing, the seal comprising seal portions respectively capable of applying a dynamic seal with one of the two elements and a static seal with the other element. The dynamic seal portion comprises at least first and second lips delimiting an annular chamber capable of being filled with lubricant. The seal is configured to allow, during the contact of a fluid with at least the dynamic seal portion, a movement of one of the lips, at least in the radial direction, in the direction of the associated element to obtain a contact with the said element.

"Static seal" means the seal made between two parts that do not move relative to one another, and "dynamic seal" means a seal between two parts that move relative to one another.

Advantageously, the dynamic seal portion comprises a material that can expand during contact with the fluid.

Therefore, the dynamic seal portion, during contact with the fluid, allows a variation of volume and a local deformation of at least one of the lips in order to obtain the movement relative to the other lip. This therefore provides a movement of one of the lips relative to the other lip under the action of the fluid, even if the said contact is occasional and/or the pressure of contact is relatively weak.

In one embodiment, the dynamic seal portion consists of the material that can expand during contact with the fluid. Alternatively, the dynamic seal portion comprises a coating comprising the expandable material.

In one embodiment, the dynamic seal portion comprises an annular portion having, in cross section, a generally curved shape, the radius of curvature of the annular portion then increasing during contact with the fluid.

Preferably, the annular portion delimits a concavity capable o f forming a flow deflector to reduce possible ingress of liquid into the annular chamber.

The first and second lips may originate from the annular portion.

In one embodiment, the first and second lips comprise an oleophobic coating.

Preferably, the first lip comprises means capable of promoting the flow of the lubricant towards the annular chamber. The seal may comprise a stiffening framework. Alternatively, it is also possible to provide a seal with no such framework.

The invention also relates to a rolling bearing comprising two rings that can rotate relative to one another, rolling elements placed between the rings and at least one seal attached to one of the rings and provided with seal portions interacting respectively with one of the rings and the other ring in order to provide a dynamic seal and a static seal.

The dynamic seal portion comprises at least two lips, inner and outer, delimiting an annular chamber capable of being filled with lubricant. The seal is configured to allow, during contact of a fluid with at least the dynamic seal portion, axially on the side of the outer lip, a movement of the said outer lip, at least in the radial direction, towards the associated ring to obtain a contact with the said ring.

"Inner lip" means the lip situated axially on the side of the rolling elements, and "outer lip" means the lip oriented towards the outside of the rolling bearing.

In normal operation, the dynamic seal is provided on the one hand by the narrow passages between the inner and outer lips of the seal and the corresponding bearing surface of the facing associated ring, and on the other hand by the lubricant contained in the annular chamber delimited by the lips and the said bearing surface which forms a sealed rim. In this mode of operation, the friction is extremely reduced. When the seal is subjected to jets of fluid, for example o f water, the contact of the fluid on the dynamic seal portion, and notably on the outer lip, causes a local deformation of the said lip radially towards the bearing surface of the associated ring until it comes into contact against the latter. The sealing is therefore strengthened while the seal is subjected to these jets. When the jets cease, the outer lip progressively resumes its initial shape and the friction diminishes.

Therefore, it is possible to considerably reduce the energy losses by adapting the friction of the seal zone between the outer lip and the corresponding bearing surface of the rolling bearing. In other words, the outer lip travels from a neutral position in which sealing with the corresponding bearing surface of the associated ring is produced by a narrow passage, to a deformed position in which there is friction contact between the said lip and the bearing surface o f the ring while the said lip is subjected to jets of fluid. In the neutral position and the deformed position of the outer lip, the inner lip remains situated at a distance from the bearing surface of the associated ring.

The present invention will be better understood by studying the detailed description of embodiments taken as non-limiting examples and illustrated by the appended drawings, in which:

- Figure 1 is a half-view in axial section of a rolling bearing according to a first embodiment of the invention,

- Figures 2 and 3 are detail views of the rolling bearing o f Figure 1 ,

- Figure 4 is a half-view in axial section of a rolling bearing according to a second embodiment of the invention, and

- Figure 5 is a half-view in axial section according to a third embodiment of the invention. In Figure 1 , a rolling bearing 10, with an axis 12, comprises an outer ring 14, an inner ring 16 and a plurality of rolling elements 18, balls in this instance, interposed between the rings 14 and 16. On each of the opposite sides of the rolling bearing 10 there is an annular seal 20, 22 to close the radial space that exists between the rings 14, 16. The seals 20, 22 are identical to one another and symmetrical relative to a radial mid-plane of the rolling bearing 10, passing through the centre of the rolling elements 18.

The outer ring 14 comprises an axial outer surface 14a, a bore 14b, stepped in this instance, two radial transverse surfaces 14c and 14d and a raceway 14e with a deep groove formed substantially in the middle of the bore 14b and in contact with the rolling elements 18. The outer ring 14 also comprises two recesses 24, 26 formed radially towards the outside from the groove 14b, respectively in the vicinity of the transverse surfaces 14c and 14d. The recesses 24 and 26 are symmetrical relative to the mid-plane of the rolling bearing passing through the centre of the rolling elements 18.

Similarly, the inner ring 16 comprises a bore 16a, an outer surface 16b, two radial transverse surfaces 16c and 16d, and a raceway 16e with a deep groove formed substantially in the middle of the outer axial surface 16b and in contact with the rolling elements 18. The transverse surface 14c, 14d is respectively situated in a radial plane containing the transverse surface 16c, 16d. The rolling elements 18 are held with an even circumferential spacing by means of a cage 27. The outer ring 14 and inner ring 16 are of the solid type. A ring of the solid type means a ring whose shape is obtained by machining with removal of chips (turning, grinding) from tubes, from bars, from forged and/or rolled blanks.

As illustrated more visibly in Figure 2, the seal 20 comprises an insert or a framework 28 in the form of a relatively rigid annular disc, onto which a sealing element 30 made of nitrile rubber or another elastomer is overmoulded or vulcanized. The sealing element 30 forms two radially opposed peripheral seal portions 32 and 34 applying respectively a static seal with the outer ring 14 and a dynamic seal with the inner ring 16.

The outer seal portion 32 is forced into the annular recess 24 o f the outer ring 14 in order to attach the seal to the said ring. At the recess 24, the seal portion 32 therefore matches the shape of the said recess to form a means for attaching the seal 20 to the outer ring 14. The seal portion 32 radially and axially surrounds the free, large- diameter edge of the framework 28 so that only the covering 30 is in contact with the outer ring 14. This helps to hold the seal 20 properly in position inside the recess 24 by forced mounting and by friction.

The inner seal portion 34 comprises an annular portion 36 which has, in cross section, a shape that is generally curved in the form of a V oriented axially outwards. From the annular portion 36 there issue an internal lip 38 situated axially on the side of the rolling elements 18 and an outer lip 40 extending outwards.

The annular portion 36 consists of a first oblique portion 36a extending radially towards the inside of the rolling bearing 10 in the direction of the rolling elements 18 and extended to a small-diameter edge toward the inside by a substantially radial portion 36b, itself extended by a second oblique portion 36c extending radially towards the inside and axially in the direction opposite to the first oblique portion, i.e. on the side opposite to the rolling elements 18. This gives the V shape. In other words, the first oblique portion 36a, the radial portion 36b, the second oblique portion 36c and the lip 40 form a concavity oriented towards the outside of the rolling bearing forming a flow deflector to reduce possible ingress of liquid into a chamber 46 of the seal, and more generally into the inside of the rolling bearing. The annular portion 36 and more precisely the oblique portion 36a extends close to the free, small-diameter edge of the reinforcing framework 28, while being radially offset towards the inside. The annular inner lip 38 extends the annular portion 36, and more precisely the second oblique portion 36c radially towards the inside, in the direction of the outer axial cylindrical surface 16b of the inner ring 16 to form a narrow passage 42 with the said surface. The annular outer lip 40, for its part, extends axially outwards from the small-diameter free end of the annular portion 36, and more precisely of the second oblique portion 36c, forming a narrow passage 44 with the axial outer surface 16b of the ring 16. The diameter of the lips, the inner lip 38 and the outer lip 40, is substantially equal. They delimit axially, with the second oblique portion 36c, an axial annular chamber 46 that may with advantage be filled with lubricant, such as grease.

The chamber 46 is delimited radially by the said lips, by the second oblique portion 36c and by the radially-facing portion of the axial outer surface 16b.

The seal portion 34 also comprises a covering or coating 48 covering an outer surface 37 of the annular portion 36 and of the axial outer lip 40. The coating 48 advantageously consists of a material that can expand under the action of water which causes a volumetric swelling of the said expandable material, for example a synthetic rubber with the addition of a hydrophilic component such as a polyvinyl alcohol or a polyoxyethylene. For more detail on such a coating, it is possible for example to refer to document JP-A-60192167 and GB-A-2 273 537.

In operation, the inner radial lip 38 and the outer axial lip 40 of the seal 20 form, with the inner ring 16, seals by narrow passages

42, 44. The overall seal of the dynamic seal portion 34 is also increased by the lubricant present in the chamber 46 in the shape of an upside-down V which forms a sealed rim. In this operating state, the friction at the dynamic seal portion 34 of the seal 20 is extremely weak. Naturally, as a variant, it could be possible to provide a slight contact between the inner ring and at least the lips 38, 40.

To help with the formation and retention of this rim o f lubricant at the chamber 46, the inner surfaces of the lips 38, 40 may advantageously be covered with an oleophobic material so that the grease does not accumulate by adhering to these surfaces but on the contrary can slide in the direction of the chamber 46.

If the rolling bearing 10 is subjected to jets of fluid, and particularly of water, the contact of the water on the reactive coating 48 causes the volume of the said coating to increase. This then gives an increased radius of curvature of the annular portion 36 and particularly a local deformation at the lip 40 which moves axially and radially towards the inside of the rolling bearing 10 until it comes into contact against the outer surface 16b of the inner ring 16 as illustrated in Figure 3. Simultaneously, the increased radius of curvature of the annular portion 36 causes the inner lip 38 to move away radially towards the outside relative to the outer surface 16b. In other words, the lip 40 moves relative to the lip 38 and relative to the cylindrical outer surface 16b. In other words, when the seal 20 is subjected to jets of water, the radial dimension of the narrow passage 42 increases, the lip 40 for its part coming in to rub directly against the outer axial surface 16b o f the ring 16. The seal is therefore reinforced at the outer lip 40 in order to limit possible infiltrations into the rolling bearing 10. Once the jets of water cease, the lip 40 and more generally the seal portion 34 progressively resumes its initial shape under the effect of the reduced volume of the coating 48 so as to again obtain a narrow passage 44 between the said lip and the inner ring 16. Naturally, it can be understood that the seal 22 is similar to the seal 20 with respect to its structure and operation.

In the exemplary embodiment considered, the coating 48 can expand when it is in contact with water. Naturally, it is possible to adapt the nature of the material used for the coating 48 according to the type of fluid for which it is desired to obtain an increased radius o f curvature of the annular portion 36 and a deformation of the lip 40 until it makes contact with the inner ring 16.

In this embodiment, the seal portion 34 comprises the coating 48 that is distinct from the sealing element 30. However, as a variant, the whole sealing element 30 could be made of a material that can expand under the action of water or another fluid, the deformation of the outer lip 40 being obtained thanks to the fact that only one side o f the seal 20 is subjected to the jets and that, as a result, the sealing element 30 dilates only on the outside of the seal 20 causing the increase in the radius of curvature of the annular portion 36 from which the lip 40 issues.

In the variant embodiment illustrated in Figure 4 in which identical elements bear the same reference numbers, the seal 20 comprises, at the inner lip 38, holes or notches 50 designed to facilitate the passage of the grease present inside the rolling bearing

10 to the chamber 46. The notches 50 may be spaced evenly relative to one another in the circumferential direction so as to obtain a uniform filling of the chamber 46. Naturally, the seal 22 comprises similar notches (not referenced). As a variant, it could also be possible to have the said chamber filled before the seal 20 is put in place.

The variant embodiment illustrated in Figure 5 in which identical elements bear the same reference numbers differs from the embodiment previously described in that the seal portions 32, 34 are formed on the inner peripheral edge, respectively the outer peripheral edge of the seal 20.

The embodiments previously described may naturally be used without distinction with one of the rings rotating while the other is fixed or also rotating.

By virtue of the invention, the energy losses by friction are considerably reduced by adapting the type of contact that exists between the outer lip and the bearing surface of the corresponding ring depending on the operating conditions of the rolling bearing. This therefore limits the periods during which the outer lip is in contact with the bearing surface of the said ring in order to limit the wear o f the seal.

In the exemplary embodiments described above, the seals are used in rolling bearings. However, it is easy to conceive that it is also possible, without departing from the context of the invention, to use such seals in other applications by mounting them between two elements that can rotate relative to one another.

Claims

1. Seal designed to be mounted between two elements ( 14, 16) adapted to rotate relative to one another, notably rings of a rolling bearing, the seal comprising seal portions (32, 34) respectively capable of applying a dynamic seal with one of the two elements (16) and a static seal with the other element ( 14), characterized in that the dynamic seal portion (34) comprises at least first and second lips (38, 40) delimiting an annular chamber (46) capable of being filled with lubricant, the seal being configured to allow, during the contact of a fluid with at least the dynamic seal portion (34), a movement of one o f the lips, at least in the radial direction, in the direction of the associated element ( 16) to obtain a contact with the said element.

2. Seal according to claim 1 , wherein the dynamic seal portion (34) comprises a material that can expand during contact with the fluid.

3. Seal according to claim 2, wherein the dynamic seal portion (34) consists of the expandable material.

4. Seal according to claim 2, wherein the dynamic seal portion (34) comprises a coating (48) comprising the expandable material.

5. Seal according to any of the preceding claims, wherein the dynamic seal portion (34) comprises an annular portion (36) having, in cross section, a generally curved shape, the radius of curvature of the annular portion increasing during contact with the fluid.

6. Seal according to claim 5 , wherein the annular portion (36) delimits a concavity capable of forming a flow deflector to reduce possible ingress of liquid into the annular chamber (46).

7. Seal according to claim 5 or 6, wherein the first and second lips (38, 40) originate from the annular portion (36).

8. Seal according to any of the preceding claims, wherein the first and second lips (38, 40) comprise an oleophobic coating.

9. Seal according to any of the preceding claims, wherein the first lip (38) comprises means (50) capable of promoting the flow o f the lubricant towards the annular chamber (42).

10. Seal according to any of the preceding claims, comprising a stiffening framework (28).

1 1. Rolling bearing comprising two rings ( 14, 16) that are able to rotate relative to one another, rolling elements ( 18) placed between the rings, and at least one seal (20) according to any one of the preceding claims and attached to one of the rings.