EP4314580A1

EP4314580A1 - Seal assembly and rolling bearing comprising such an assembly

Info

Publication number: EP4314580A1
Application number: EP21718164.3A
Authority: EP
Inventors: Jean Lor; Patrick Brun; Clément ROBIN; Eliette Hélène Céline PINEL
Original assignee: Hutchinson SA
Current assignee: Hutchinson SA
Priority date: 2021-03-23
Filing date: 2021-03-23
Publication date: 2024-02-07
Also published as: JP2024511314A; CN117062993A; WO2022200693A1

Abstract

Seal assembly (10) comprising a fixed element (11), a rotatable element (12) and a sealing member (13). A first lip (15b) comprises a smooth annular region at the end of the first lip. The first lip and a second lip each comprise an embossed region on the face oriented towards the sliding surface. The assembly comprises a grease which is a grease with a degree of bleeding of greater than or equal to 5 per cent.

Description

Seal assembly, rolling bearing comprising such assembly

TECHNICAL FIELD The present invention relates to seal assemblies.

STATE OF THE PRIOR ART

More particularly, the invention relates to a seal assembly comprising: a fixed element, a rotary element intended to be rotatable relative to the fixed element around an axis of rotation (X), and a member seal comprising a rigid annular armature integrally mounted on one of the fixed element and the rotating element, and a seal being made of an elastic material and being in contact with a sliding surface of the other element among the fixed element and the rotating element, the seal comprising a first lip and a second lip which extend from the annular armature towards the sliding surface, the first lip and the second lip and the surface of sliding defining an internal volume filled at least partially with a grease.

Examples of assemblies of this type are known.

Such a sealing assembly is for example used in a bearing, and for example in an automobile wheel bearing. This seal assembly makes it possible in particular to contain a lubricating fluid inside the bearing to ensure its operation with low friction.

Unfortunately, this sealing assembly contributes to increasing friction, that is to say the friction torque in rotation. This phenomenon is part of mechanical energy losses during rotation. To reduce these losses, low-friction solutions are sought, but which allow sealing to be maintained.

EP 2687761 describes an example of such a seal assembly in which the lips have concavities and convexities between 1.0 and 3.0 μm Ra, and in which a low viscosity grease is used, said grease having a base oil with a kinematic viscosity at 40° C. of between 10 and 40 mm ² /s.

DISCLOSURE OF THE INVENTION

The present invention relates to a seal assembly of this type, and improved in particular to reduce the friction torque while maintaining excellent sealing.

To this end, the seal assembly is characterized in that the first lip comprises smooth annular zone at the end of the first lip and on a face oriented towards the sliding surface, said smooth zone being adapted to ensure contact continuous with sliding surface over the entire circumference of the first lip around the axis of rotation, the first lip and the second lip each include a bumpy area on the face facing the sliding surface, and the grease is a grease with a bleeding rate greater than or equal to 5 percent.

Thanks to these provisions, firstly a very good sealing of the joint assembly is ensured, and in particular an excellent static sealing which avoids any leakage of lubricant between an interior and an exterior of a device and an excellent dynamic sealing during rotation. of the rotating element by relative to the fixed element.

Secondly, a reduced friction torque is ensured compared to the solutions of the prior art. The high bleeding grease contained in the volume between the first lip and the second lip ensures frictionless sliding of said lips on the sliding surface. Notably, the bumpy area has extremely reduced friction on the sliding surface.

This combination of technical characteristics allows the reduction of the friction torque without loss of tightness of the gasket assembly, which is essential for this type of gasket assembly device. In various embodiments of the seal assembly, one and/or other of the following arrangements may also be used:

In one aspect, the grease has a bleeding rate greater than or equal to 6 percent. According to one aspect, the grease comprises a base oil with a kinematic viscosity at a temperature of 40° C. of between 7 mm ² /s and 20 mm ² /s.

In one aspect, the bumpy area has an arithmetic roughness between 3.5 and 5 µm. According to one aspect, the first lip and/or the second lip has a flexibility suitable for exerting a pressure on the sliding surface of between 0.1 and 2 MPa, the sealing member being mounted on said sliding surface. According to one aspect, the annular smooth zone has a width of between 0.05 mm and 0.2 mm.

According to one aspect, the bumpy zone is obtained by laser machining or by electro-erosion of a corresponding surface of a mold used to produce the sealing member.

In one aspect, the first lip extends axially from the annular armature towards the sliding surface, and the second lip extends axially from the annular armature towards the sliding surface.

According to one aspect, the assembly further comprises an annular ring, secured to the other element, the sliding surface being formed on said annular ring.

The invention also relates to a rolling bearing comprising a seal assembly according to the preceding characteristics and rolling bodies arranged in a bearing space to allow the relative rotation of the rotary element with respect to the element fixed around the axis of rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become apparent during the following description of one of its embodiments, given by way of non-limiting example, with reference to the appended drawings.

On the drawings:

- Figure 1 is a cross section of a seal assembly according to a first embodiment of the present disclosure;

- Figure IA is an enlarged view of part of Figure 1;

- Figure 2 is a cross section of a seal assembly according to a second embodiment of the present disclosure;

- Figure 3 is a rolling bearing comprising a seal assembly according to Figure 1 or Figure 2;

- Figure 4a is a photograph showing a sealing lip of a seal assembly according to Figure 1 or Figure 2;

- Figure 4b is the profile of the lip of Figure 4a; and - Figure 5 is a graph representing the friction torque as a function of the interference distance of a seal assembly according to the prior art and according to the present disclosure.

In the various figures, the same reference numerals designate identical or similar elements.

DETAILED DESCRIPTION

Figure 1 shows a first embodiment of a gasket assembly 10 which includes:

- a fixed element 11,

- a rotary element 12 movable in rotation relative to the fixed element around an axis of rotation X, and

- a sealing member 13 comprising a rigid annular frame 14 and a seal 15 secured to the frame, said seal 15 being made of an elastic material and being in sliding contact with a sliding surface 16 .

In particular, the fixed element 11 can be an external element, i.e. the farthest from the axis of rotation X, i.e. situated around the rotary element 12 which is then an internal element. This is the case of using a rotating element 12 which is a rotating shaft (FIG. 1).

Conversely, the fixed element 11 can be an internal element, i.e. the closest to the axis of rotation X, i.e. located inside the rotating element which is then an external element.

For the sake of simplification of the present description, it will now be considered that the armature 14 is connected to the external fixed element 11, and that the sliding surface 16 is connected to the other element, i.e. the internal rotating element 12 , but of course the other use is also suitable for the seal assembly of the present disclosure.

Seal 15 includes:

- a fixing portion 15a which is fixed to at least at least one surface of the frame 14, for example by overmoulding on said frame 14, and advantageously with an adhesive previously coated on said surface of the frame, and

- a first lip 15b which extends for example axially from the annular armature 14 as far as the sliding surface 16 to be in contact with a first part of the sliding surface 16 at one end of the lip 15b*, and

- a second lip 15c which extends for example radially from the annular armature 14 to the sliding surface 16 to be in contact at one end of the lip 15c* with a second part of the sliding surface 16.

The first lip 15b, the second lip 15c and the sliding surface 16 form a closed and sealed annular cavity, of volume V, into which a grease G can be introduced at the time of manufacture of the sealing assembly 10 or at the when it is mounted in a device.

In the embodiment of Figure 1, the sliding surface 16 is formed on a ring 17 of the annular type and secured to the other element (the rotating element 12). This ring is for example a metal part. It is located between the rotary element 12 and the seal 15. The lip end 15b* of the seal 15 is in sliding type contact with a surface of this ring which rotates with the rotary element 12 .

In the embodiment of FIG. 2, the sliding surface 16 is an integral part of the rotary element 12, in particular of the external cylindrical surface 12a of the rotary element 12. This sliding surface 16 corresponds to an annular portion of the cylindrical surface 12a. The sliding surface portion 16 is positioned in correspondence with the sealing member 13 (in the longitudinal position) so that the lip end 15b* of the seal 15 is in contact with the said sliding surface 16.

As shown in Figure 2, the seal 15 may include more than two sealing lips. In Figure 2, it comprises two, but the seal 15 may include two, three, four or more sealing lips. Thus, in FIG. 2, the first lip 15b, the second lip 15c and the sliding surface 16 form a first closed and sealed annular cavity, of volume VI. The second lip 15c, the third lip 15d and the sliding surface 16 form a second closed and sealed annular cavity, of volume V2. Each of said annular cavities (V, V2) can contain said grease, introduced at the time of manufacture of the sealing assembly 10 or at the time of its assembly in a device.

Returning to the first embodiment of FIG. 1, the annular ring 17 is secured to the rotary element 12. It is located between the rotary element 12 and the seal 15. The lip end 15b* of the seal 15 is in sliding type contact with at least one surface of this ring 17 which rotates with the rotating element 12.

In this first embodiment, more specifically, the annular ring 17 comprises:

- a cylinder portion 17a mounted integrally with the rotary element 12, for example by tight fitting on the cylindrical surface 12a of the said rotary element 12, and

- A collar portion 17b which extends radially relative to the axis of rotation X from one end of said cylinder portion 17a.

The seal 15 then comprises a first lip 15b which extends axially from the annular armature 14 as far as the collar portion 17b, and a second lip 15c i extends axially from the annular armature 14 to the cylinder portion 17a.

The sliding surface 16 is therefore here an integral part of the annular ring 17, fixed to the rotary element 12. This sliding surface 16 corresponds for example to all or part of an outer surface of the annular ring 17 directed towards the frame 14.

The sliding surface 16 comprises for example:

- a first part on the cylinder portion 17a of the annular ring 17, said first part extending along a length cl in the longitudinal direction of the axis of rotation X and in correspondence (opposite) of the second lip 15c, and

- a second part on the flange portion 17b of the annular ring 17, said second part extending along a length c2 in a direction substantially perpendicular to the longitudinal direction of the axis of rotation X and in correspondence (opposite) of the second lip 15c.

Thus, the ends 15b*, 15c* of the first lip 15b and of the second lip 15c are in sliding contact with the sliding surface 16.

In Figures 1 and 2, the reference I_ corresponds to the internal side of the product which will be sealed by the seal assembly 10; this internal side possibly containing an oil or a grease which one seeks to preserve. The reference E corresponds to the external side of the product; that is to say to the external environment which can also be aggressive by fluids and/or dust against which the seal assembly also offers protection.

According to the present disclosure, the seal assembly 10 further includes the following features:

- the first lip 15b comprises a smooth annular zone ZL at the end 15b* of the first lip 15b and on one face of the first lip 15b oriented towards the sliding surface, said smooth zone ZL being adapted to ensure continuous contact with said sliding surface 16 over the entire circumference of the first lip 15b around the axis of rotation X,

- the first lip 15b and the second lip 15c each comprise a bumpy zone ZB on said face oriented towards the sliding surface, and

- grease G is a grease with a bleeding rate greater than or equal to 5 percent.

FIG. 1A is an enlarged view of the first lip 15b of FIG. 1 schematically representing the face of the first lip 15b oriented towards the sliding surface 16, and comprising, from the end 15b* of this first lip, the zone smooth ZL, then bumpy area ZB.

FIG. 4a shows a photograph of the enlarged end 15b* of the face of the first lip 15b oriented towards the sliding surface 16. The very dark lower part of this photograph corresponds only to the void, the first lip 15b being in the upper part of this photograph with the reliefs with variations of gray.

Figure 4b shows the profile of the lip of Figure 4b. This profile corresponds to a view of the lip in section in a plane extending radially relative to the axis of rotation.

In the photograph of FIG. 4a, the smooth zone ZL is observed, which is a continuous band at the end 15b* of the first lip 15b and which extends over the entire circumference of the first lip 15b. This smooth zone ZL can also be called “savings” in the technical field. This smooth zone ZL therefore ensures continuous contact over the entire circumference of the first lip 15b. Thus, the first lip 15b has a good sealing and the grease or any fluid enclosed in the annular cavity remains in this cavity in a static position or in dynamic operation (rotation of the rotary element 12). the smooth ZL or spare zone has a smooth width LL of between 0.05 mm and 0.2 mm. For example, the smooth width is between 0.1 mm and 0.2 mm.

Optionally, the second lip 15c or any other lip of the seal 13 may comprise such a smooth or spare zone.

Optionally, the first lip 15b or any other lip may comprise several smooth zones of this type.

One also observes on this photograph, the bumpy zone ZB of the face oriented towards the sliding surface. This bumpy zone ZB is a zone which comprises a multitude of bumps which have, for example, irregular shapes. These bumps are for example protuberances which extend towards the outside of the lip and they have a convex shape, i.e. a shape opposite to a hollow shape. These bumps can also be semi-spherical protuberances of variable diameter. This bumpy zone ZB can also be called "graniting" in the technical field. The bumpy zone ZB has for example an arithmetic roughness Ra of between 3.5 and 5 μm.

This bumpy zone ZB extends over the face facing the sliding surface, over a bumpy zone width which may depend on the size of the lip, and for example between 1 mm and 2 mm, or between 1 mm and 4 mm.

This bumpy zone width can in particular be adapted to cover any contact zone between the lip and the sliding surface 16 in its mounting position.

The bumpy zone ZB is for example obtained by laser machining or by electro-erosion of a corresponding surface of a mold suitable for producing/forming the sealing member 13. The shape of this corresponding surface of the mold is a negative of the shape of the face of the lip facing the sliding surface.

Thus, the bumpy zone ZB is extra thick on the face of the lip intended to be oriented towards the sliding surface. In other words, the corresponding surface of the mold corresponding to this bumpy zone ZB is a recessed or hollowed surface. Conversely, the smooth zone ZL is set back from the face of the lip intended to be oriented towards the sliding surface, i.e. set back from an external line placed on the bumpy zone in the section plane of the profile.

Other methods of producing the corresponding surface of the mold are possible: 3D printing of the mold or of a portion of the mold, addition of an insert in the mold, etc...

The lips of the seal 13 are curved in the mounting position as shown in Figures 1 and 2, which ensures contact between the ends of these lips (15b, 15c, 15d) and the sliding surface 16. Thanks at this curvature of the lips, the smooth zone ZL and the bumpy zone ZB are in contact with the sliding surface 16. The bumpy zone ZB traps a quantity of grease in the interstices of the bumps or protrusions and the sliding surface 16. Thus, sliding is ensured with a lower frictional torque than for the sets of seals of the prior art.

In addition, the curvature of a sealing lip on a sliding surface corresponds to an interference distance Di: This interference distance Di is zero for simple contact on the sliding surface, ie without curvature of the lip . This interference distance Di increases the more one increases the crushing of the lip towards the sliding surface, ie the more the curvature of said lip is significant.

The first lip 15b and/or the second lip 15c has a flexibility adapted to exert a pressure on the sliding surface 16 of between 0.1 and 2 MPa, in the position of assembly on the product, that is to say for a nominal interference distance defined for mounting the seal assembly 10.

A grease is mainly composed of a base oil containing a thickening agent, and additives to reinforce the properties of the grease. Grease consistency depends on the type and concentration of thickening agent and operating temperature.

The bleeding of a grease is its tendency to separate from the base oil under predetermined conditions, and more particularly at rest. For example, in the method of the IP 121/75 standard, a quantity of grease is placed in a container with a bottom grid in the form of a cone type 240 (grid of 61 μm), the mass of base oil is measured separated from the fat under the action of a higher load of 100 g, at a temperature of 40° C., and for a period of 42 hours or 168 hours.

The bleeding rate is then the ratio of the mass of base oil separated by the mass of grease initially placed in the container, this ratio therefore being able to be expressed as a percentage.

Other penetrant measurement standards exist with different procedures. For example, in the method of ASTM D 1742, a quantity of grease is placed in a container with a lower grid or sieve at 75 μm, the mass of base oil separated from the grease is measured by the action of at a higher air pressure of 1.72 kPa, at a temperature of 25°C, and for a duration of 24 hours. The person skilled in the art will be able to carry out equivalences between these standards on the basis of experience. The grease G used in the seal assembly 10 according to the present disclosure is a high bleeding grease. By “high bleeding”, is meant a much higher level of bleeding than the greases generally used between the lips of a seal assembly according to the prior art. In fact, it is usually sought to have a low bleeding value for such a grease in order to avoid any deterioration of the characteristics of the grease over time, during static and dynamic operation of the seal assembly.

More particularly, the grease G is for example a grease with a bleeding rate greater than or equal to 5 percent, according to the IP 121/75 standard cited above. By virtue of this bleeding rate, the grease G of the seal assembly 10 separates from a suitable quantity of base oil during its rotational dynamic operation, this oil being able to flow towards the dented zone ZB to reduce the frictional torque of the seal 15 on the sliding surface 16.

Tests make it possible, for example, to adapt the characteristics of the grease G, and for example its bleeding rate, to the characteristics (shapes) of the bumpy zone ZB, and also to the specifications of the product and of the seal assembly d tightness 10.

In certain cases, it is for example desirable to have a grease G with a bleeding rate greater than or equal to 6 percent, or even 8 percent. The friction torque of the seal 15 on the sliding surface 16 is then reduced.

To obtain such a high bleeding rate, which is not usual in dynamic seal assembly applications, in particular for bearings, the grease G has for example a base oil with low kinematic viscosity. Indeed, the lower this kinematic viscosity, the higher the bleeding rate. In addition, grease G includes a thickening agent also called "grease soap" with a high consistency. Indeed, the higher this consistency, the higher the bleeding rate.

For example, the base oil of grease G used has a kinematic viscosity at a temperature of 40° C. of between 7 mm ² /s and 20 mm ² /s.

This choice of grease G with a high bleeding rate is contrary to the usual choice in the mechanical field. This choice makes it possible to be more suited to the low contact pressure of the lips 15b, 15c of this seal assembly 10. This makes it possible to reduce the friction torque.

Figure 5 illustrates curves of friction torque C as a function of the interference distance Di for:

- a first set of seals J1 according to the prior art, that is to say without smooth zone ZL, without bumpy zone ZB and without grease G with high bleeding; and

- a second set of gaskets J2 according to the present disclosure; that is to say with the technical characteristics mentioned above.

The friction torque of the second set of seals J2 is much lower than that of the first set of seals J1.

The friction torque of the second set of seals J2 increases less with the interference distance Di than for the first set of seals J1; which means that the second sealing assembly makes it possible to offer a lower friction torque and with greater robustness according to the variation of the interference distance Di.

Thus, the gasket assembly 10 according to the present invention is greatly improved over the art. prior. This seal assembly provides a lower frictional torque while maintaining the same sealing performance.

Figure 3 shows a rolling bearing 1 comprising on at least one side a set of seals 10 as described above in order to seal an interior space of said rolling bearing. The rolling bearing is for example a motor vehicle rolling bearing, and more particularly for example a motor vehicle wheel rolling bearing, as shown in Figure 5.

This rolling bearing 1 comprises in particular:

- a fixed member 2,

- a rotary member 3 driven in rotation by a shaft 5 and on which is for example fixed a vehicle wheel, and

- rolling bodies 4 arranged in the 4th rolling space formed between the fixed member 2 and the rotary member 3 to allow the relative rotation of the rotary member 3 with respect to the fixed member 2 around the axis of rotation X, while taking up significant forces between the fixed member and the rotating member.

The fixed element 11 of the seal assembly 10 is either directly the fixed member 2, or fixed to said fixed member 2 of the rolling bearing 1.

The rotating element 12 of the seal assembly 10 is either directly the rotating member 3, or fixed to said rotating member 3 of the rolling bearing 1.

The rolling bodies 4 can be balls or rollers or any other known type.

Thanks to the seal assembly 10 according to the present disclosure, the rolling bearing 1 has a lower friction torque than the prior art. A vehicle equipped with such devices will therefore consume less energy to move forward.

Claims

1. Seal assembly (10) comprising: a fixed element (11), a rotating element (12) intended to be rotatable relative to the fixed element around an axis of rotation (X), and a sealing member (13) comprising a rigid annular armature (14) integrally mounted on one of the fixed element and the rotating element, and a seal (15) being made of an elastic material and being in contact with a sliding surface (16) of the other element among the fixed element and the rotating element, the seal (15) comprising a first lip (15b) and a second lip (15c) which are extending from the annular armature (14) towards the sliding surface (16), the first lip and the second lip and the sliding surface defining an internal volume filled at least partially with a grease, the seal assembly seal (10) being characterized in that the first lip comprises a smooth annular zone (ZL) at the end of the first lip and on a face facing the surface facing the sliding surface, said smooth zone being adapted to ensure continuous contact with the sliding surface over the entire circumference of the first lip around the axis of rotation (X), the first lip and second lip each include a bumpy area (ZB) on the side facing the sliding surface, and the grease (G) is a grease with a bleeding rate greater than or equal to 5 percent.

2. Assembly according to claim 1, in which the grease has a bleeding rate greater than or equal to 6 percent.

3. Assembly according to claim 1 or claim 2, in which the grease comprises a base oil with a kinematic viscosity at a temperature of 40°C of between 7 mm ² /s and 20 mm ² /s.

4. Assembly according to any one of claims 1 to 3, in which the bumpy zone (ZB) has an arithmetic roughness (Ra) of between 3.5 and 5 μm.

5. Assembly according to any one of claims 1 to 4, in which the first lip and/or the second lip has a flexibility suitable for exerting a pressure on the sliding surface of between 0.1 and 2 MPa, the member sealing being mounted on said sliding surface.

6. Assembly according to any one of claims 1 to 5, in which the smooth annular zone (ZL) has a width of between 0.05 mm and 0.2 mm.

7. Assembly according to any one of claims 1 to 6, in which the bumpy zone (ZB) is obtained by laser machining or by electro-erosion of a corresponding surface of a mold used to produce the sealing member (13).

8. Assembly according to any one of claims 1 to 7, in which the first lip (15b) extends axially from the annular armature (14) towards the sliding surface (16), and the second lip (15c) extends axially from the annular armature (14) towards the sliding surface (16).

9. An assembly according to any one of claims 1 to 8, further comprising an annular ring (17), integral with the other element, the sliding surface (16) being formed on said annular ring (17).

10. Rolling bearing (1) comprising a seal assembly (10) according to one of claims 1 to 9, and rolling bodies (4) arranged in a bearing space to allow the relative rotation of the rotating element relative to the fixed element around the axis of rotation.