Optimized sealing device for a bearing unit

Abstract

Sealing device (50) for a bearing unit, having a fixed part and a rotating part, the fixed part being in turn provided with: a first shield (10) of metal formed by an annular portion (10') and a cylindrical portion (10") radially external with respect to the annular portion; an elastomeric coating (2) co-moulded on the first shield, having an annular portion (2') and a cylindrical portion (2"); and a contact lip (9) radially internal, forming part of the elastomeric coating (2) and axially external with respect to the annular portion (2'), the rotating part being provided with: a second shield (1) of metal on which the contact lip forms a sliding contact, the elastomeric coating being provided with a lip (3) which is non-contacting and radially internal with respect to the cylindrical portion (2"); at least one first radial labyrinth seal (Gr) formed by a radially external wing (1') of the second shield with a lip of the elastomeric coating facing the aforesaid wing.

Description

TECHNICAL FIELD

[0001] The present invention relates to a sealing device for a bearing unit and to a bearing unit provided with said sealing device. Preferably, but not exclusively, the sealing device and the bearing unit are applied to a hub assembly.

[0002] The present solution can be applied to hub assemblies of all generations. In particular, these applications include cases where the outer ring of the bearing is rotatable while the inner ring of the bearing is fixed ( / stationary) and vice versa, where the inner ring is rotating while the outer ring is fixed. The invention is also applicable to any type of rolling elements (balls, rollers, tapered rollers, etc.). BACKGROUND

[0003] The sealing device according to the prior art consists of a two-part cassette seal, comprising a rotating part mounted on the radial inner ring of the bearing unit, for example, and a fixed part ( / stationary part) mounted on the radial outer ring of the bearing unit, for example. Still as an example, the fixed part comprises a metal shield mounted on the radial outer ring by interference fit, and an elastomeric part co-moulded on the metal shield. In addition, a second shield of metal is mounted on the rotatable radial inner ring by interference fit.

[0004] According to this prior art, the fixed part of the seal, made of elastomeric material, comprises one or more lips which come into contact with the rotating part and ensure the sealing action with respect to the inside of said bearing unit.

[0005] Also known are sealing members consisting of a single piece and integral with one of the rings of the bearing unit, in which at least one contact lip ensures the sealing with respect to the surface of the other ring of the bearing unit due to the interference created during assembly of the seal.

[0006] The typical design of the sealing device therefore comprises one or more protrusions, called lips, which come into contact with the rotating surfaces of the bearing unit in different forms and in different orientations, generally axial and radial: in this way, the sealing device prevents the entry of contaminants from the outside, protecting the internal components of the bearing unit, i.e. the rolling elements and the cage which houses them. Another important function of the sealing device is to prevent the escape of the lubricant present inside the bearing unit.

[0007] Between these contact lips and the corresponding rotating contact surfaces of the bearing unit a sliding friction force is generated and therefore an energy dissipation. In general, the sealing capacity increases with the increase in the number of contact lips and their stiffness. However, at the same time, with the increase in these parameters, the amount of energy dissipation also increases.

[0008] Moreover, also due to the increasing global competition, customers (i.e. motor vehicle manufacturers) constantly require continuous technical or cost-related improvements to the hub assembly. In particular, with the development of technology, there is an increasing demand for low energy consumption assemblies ensuring the same performance compared to the latest solutions.

[0009] To solve this technical problem, the ideal solution is a sealing device without any contact that manages to prevent the entry of contaminants and the loss of lubricant without energy dissipation in any case. A sealing device without any contact does not work properly, in particular in underwater environments.

[0010] Therefore, it is necessary to define a sealing device that does not have the above-mentioned drawbacks, which is low in energy consumption, but which has excellent sealing performance. SUMMARY

[0011] To substantially solve the above technical problem, the purpose of the present application is to define a cassette sealing device provided with an internal labyrinth seal which contributes to protecting the bearing unit from external contaminants. By "labyrinth seal" it is intended to mean a complex path created by appropriately shaping the components of the sealing device.

[0012] This solution is able to reduce the number of contact lips to a minimum and thus reduce the energy dissipation due to friction to a minimum.

[0013] According to the present application, the labyrinth seal is formed by appropriately shaping both the rotating metal shield and the elastomeric coating. In this way, a suitable opening is created facing the corresponding part of the elastomeric coating of the sealing device and the shaped metal part.

[0014] According to another aspect, the sealing device inside the bearing unit and its housing are realized so as to increase the internal volume, so that the housing of the sealing device can form a larger reservoir for storing the contaminants that manage to pass over the labyrinth seal described above.

[0015] Therefore, according to the present application, a sealing device for a bearing unit is provided, having the features indicated in the independent claims attached to the present description.

[0016] The present application also relates to a bearing unit, in particular to a bearing unit for a hub assembly provided with a sealing device according to one of the embodiments of the present application.

[0017] Further preferred and / or particularly advantageous embodiments of the present application are described according to the features indicated in the attached dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0018] The invention will now be described with reference to the accompanying drawings, which illustrate non-limiting examples of embodiments of the invention, wherein:

[0019] - Figure 1 It is a cross-section of the hub assembly equipped with bearing units;

[0020] - Figure 2 It is based on Figure 1 Details of the hub assembly, which provides a sealing device for the bearing unit according to an embodiment of the invention, which is housed between the rings of the bearing unit. Detailed Implementation

[0021] The invention will now be described by way of non-limiting example only, with reference to bearing unit 30, and preferably with reference to a wheel hub assembly for a motor vehicle provided with a bearing unit having a sealing device according to the invention.

[0022] Reference Figure 1 30 generally represents a bearing unit or hub assembly.

[0023] The unit has a central rotation axis X and includes:

[0024] - A flanged radial inner ring 20, which is rotatable;

[0025] - Radial outer ring 31, radial outer ring 31 is fixed (stationary);

[0026] - An additional, rotatable radial inner ring 34 is mounted on and integral with the flanged ring 20;

[0027] - Multiple rolling elements 32, 33, which in this example are balls, located between the outer radial ring 31 and the inner radial rings 20, 34.

[0028] - Two cages 39 and 40 are used to hold the rolling elements in the row of rolling elements 32, 33 in place.

[0029] Throughout this specification and claims, terms and expressions indicating position and orientation, such as “radial” and “axial”, are understood to refer to the central axis of rotation X of the bearing unit 30. Furthermore, expressions such as “axially external” and “axially internal” relate to the assembly condition of the hub assembly, and in the cases discussed, preferably, expressions such as “axially external” and “axially internal” refer to the wheel side and the side opposite to the wheel side, respectively.

[0030] The flanged ring 20, together with the radially outer ring 31, defines at the axially opposite ends of the bearing unit 30 two cavities 35, 36 which, if not screened, could allow the entry of contaminants and impurities inside said bearing unit 30.

[0031] Therefore, in order to shield the bearing unit 30, at least one sealing device 50 implemented according to the principles of the present application is installed inside at least one of the two cavities 35, 36.

[0032] In general, the sealing device 50 comprises two metal screens facing each other, at least one of which is provided with one or more sealing lips made of elastic material in sliding contact with the other screen, or the sealing device 50 comprises only one metal screen having one or more sealing lips made of elastic material in sliding contact with the sliding surface of the bearing unit 30 with respect to which the screen performs a relative motion.

[0033] In the following, with reference to Figure 2 , by way of example only, the case will be described in which the sealing device 50 comprises a rotating part provided with a metal screen 1 mounted on the flanged radially inner ring 20 by means of an interference fit and a stationary part comprising, in turn:

[0034] - a metal screen 10 mounted on the radially outer ring 31 by means of an interference fit and formed by an annular portion 10' and a cylindrical portion 10" radially external with respect to the annular portion 10';

[0035] - an elastomeric coating 2 co-moulded on the first screen 10 and having a development substantially radially external and axially external with respect to said first screen 10, the coating 2 being formed by an annular portion 2' and a cylindrical portion 2" radially external with respect to the annular portion 2', and

[0036] - a contact lip 9, radially internal, forming part of the elastomeric coating 2, in particular axially external with respect to the annular portion 2' and therefore stationary, in sliding contact with the rotating second screen 1.

[0037] Moreover, according to the present embodiment, the rotatable metal second shield 1 is preferably shaped in a "C" manner. The radially outer wing 1'of the shield 1 is positioned at the height of the radially outer ring 31 in the radial direction. In particular, for reasons that will be explained below, the radially outer surface 1's of the wing 1'must be more or less aligned with the radially outer surface 31 s of the radially outer ring 31.

[0038] The elastomer coating 2 is provided with a small-sized lip 3, which is non-contacting and radially internal ( / inboard) with respect to the cylindrical portion 2" of the elastomer coating 2. Preferably, the lug 6 also extends from the cylindrical portion 2" of the elastomer coating 2 in a direction axially outward and radially outward inclined with respect to the cylindrical portion 2". Finally, the cylindrical portion 2" of the elastomer coating 2 terminates in the static seal 4 in an axially inward direction, which, since it has formed the subject of the author's prior patent application, will not be discussed further.

[0039] In the presence of these characteristic features, since there is only one contact lip 9, it is possible to obtain a sealing device 50 with low energy dissipation, while, since a labyrinth seal and a contaminant storage chamber are formed, it is possible to obtain a sealing device 50 with high sealing efficiency, which will now be described.

[0040] In fact, the sealing device 50 is provided with at least one first radial labyrinth seal Gr, formed by the radially outer wing 1'of the metal shield 1 and the cylindrical portion 2" of the elastomer coating 2, in particular by the radially outer wing 1'of the metal shield 1 and the lip 3 of the elastomer coating 2 facing the aforementioned wing 1 '. Preferably, in the assembled condition of the bearing unit, the size of the opening ( / passage) of the first radial labyrinth seal GR can be between 0.1 mm and 0.8 mm. In this way, a first effective barrier is formed to reduce the flow of contaminants reaching the pre-chamber 7, which is the volume formed between the metal shield 1, the annular portion 2' of the elastomer coating 2 and the contact lip 9. It should be noted that, although in fact the operation of the lip 3 will be that of a non-contacting lip in normal operating conditions, in high load conditions the lip 3 can come into contact with the wing 1'of the metal shield. It is also important (precisely for the correct operation of the lip 3) that the lug 6 of the elastomer coating should always be non-contacting, so as not to cause deformations of the elastomer coating, with a negative impact on the labyrinth sealing action of the lip 3.

[0041] Although Figure 2A second non-contact lip can be formed, extending from the annular portion 2' of the elastomer coating 2 and facing the radially inner surface of the wing 1 ', forming a second radial labyrinth seal, more or less the specular of the first radial labyrinth seal (with respect to the wing 1 '). Obviously, the presence of the second radial labyrinth seal enhances the ability of the barrier effect against external contaminants of the sealing device 50.

[0042] Moreover, thanks to the C-shaped form of the metal shield 1, the wing 1'of the shield faces the annular portion 2' of the elastomer coating 2 in the axial direction. In this way, a second axial labyrinth seal Ga is formed, which cooperates with the radial labyrinth seal Gr (or with the plurality of radial labyrinth seals, if more than 1 radial labyrinth seal is present) to help improve the barrier effect against external contaminants. Advantageously, the size of the openings ( / passages) of the second axial labyrinth seal Ga can be between 0.2 mm and 1.00 mm.

[0043] Even if Figure 2 In the example not shown, the sealing device 50 can have a non-axially symmetric geometry: in other words, the components of the sealing device 50 (both the fixed portion and the rotatable portion) can have a circumferential extension ( / development) with an amplitude between 180° and 260°. In this way, by precisely assembling the bearing unit and the hub assembly so that the solid portions of the components of the sealing device point towards the top of the motor vehicle and so that the sealing device is open towards the bottom of the same motor vehicle, the sealing device is able to operate as a barrier against contaminants entering from the top of the motor vehicle and to allow the contaminants to flow freely towards the bottom of the motor vehicle.

[0044] The bearing unit 30 provided with the sealing device 50 according to the present application has further features related to the cavities 35, 36 which house the sealing device 50.

[0045] A first feature is to maximize the volume of the pre-chamber 7 contained between the metal shield 1, the annular portion 2' of the elastomer coating 2 and the contact lip 9. Since this pre-chamber has a greater volume, it can contain and expel a greater amount of contaminants without letting them reach the sensitive components of the bearing unit, i.e. the rolling elements and the raceways. The increase in the volume of the pre-chamber 7 is obtained by combining the following features:

[0046] - positioning the wing 1'of the metal shield 1 as far as possible in the radially outward direction from the rotation axis X of the bearing unit, up to the alignment of the radially outer surface 1's of the wing 1'with the radially outer surface 31 s of the radial outer ring 31 ;

[0047] - shaping the elastomer coating 2 and the metal support shield 10 in the axial inward direction 2' and 10', respectively;

[0048] - the contact lip 9 is positioned as close as possible to the cylindrical surface 5 of the flanged ring 20, i.e. to the radially inner wing 1" of the metal shield 1.

[0049] The increase in the volume of the pre-chamber 7 optimizes the above-mentioned characteristics by 60% to 70% with respect to known solutions.

[0050] Finally, the second pre-chamber 11 is formed inside the cavity 35, between the annular surface 8 of the flanged ring 20, the cylindrical surface 5 of the same flanged ring 20, the metal shield 1 and the cylindrical portion 2" of the elastomer coating 2 (including the lugs). In this case, the second pre-chamber 11 also has the function of containing / discharging external contaminants and its size must be designed so that its volume is as large as possible. This is obtained by introducing and maximizing the connection radius 12 between the annular surface 8 of the flanged ring 20 and the cylindrical surface 5 of the same flanged ring 20. As the connection radius R increases, the axial distance between the metal shield 1 and the annular surface 8 of the flanged ring 20 will increase, thus increasing the volume of the pre-chamber 11. Due to the configuration of the pre-chamber 11, the incoming contaminants will undergo a vortical motion, which will generate a series of impacts on the walls of the pre-chamber and consequent "rebound" effects, which will cause the expulsion of at least part of the contaminants.

[0051] Basically, despite the limited number of contact points (i.e. contact lips), the proposed solution offers unquestionable advantages in terms of improved sealing capacity, while ensuring low levels of energy dissipation due to friction of the sealing device.

[0052] In addition to the embodiments of the present application, as described above, it must be understood that many other variants exist. It must also be understood that these embodiments are merely examples and do not limit the scope of the present application, its applications or its possible configurations. On the contrary, although the above description allows a person skilled in the art to implement the present application at least according to one of the examples of its embodiments, it must be understood that many variants of the described components are possible without thereby departing from the scope of the present application as defined in the attached claims, interpreted literally and / or according to their legal equivalents.

Claims

1. A sealing device (50) for a bearing unit (30) comprising a radially outer ring (31) and at least one radially inner ring (20, 34), said sealing device (50) comprising a fixed portion, in turn comprising: - a first shield (10) of metal formed by an annular portion (10') and a cylindrical portion (10") radially external with respect to said annular portion (10'), - an elastomeric coating (2) radially and axially external with respect to said first shield (10), co-moulded on the same said first shield (10) and comprising an annular portion (2') and a cylindrical portion (2"), - a contact lip (9) radially internal, belonging to said elastomeric coating (2) and axially external with respect to the annular portion (2') of said elastomeric coating (2), said sealing device (50) further comprising a rotatable portion provided with a second shield (1) of metal, said contact lip (9) making sliding contact on said second shield (1), said sealing device (50) being characterized in that: - said elastomeric coating (2) is provided with a lip (3) which is non-contacting and radially internal with respect to the cylindrical portion (2") of said elastomeric coating (2), - at least a first radial labyrinth seal (Gr) is formed by a radially external wing (1') of said second shield (1) with a lip (3) of said elastomeric coating (2) facing the aforesaid radially external wing (1'), and - said lip (3) is configured in an area of the elastomeric coating (2) not supported by said first shield (10) and not resting against a fixed surface of said radially outer ring, and a radially extending surface of said second shield (1) is free of any contact, forming a discharge space towards a radially extending surface of said radially inner ring adjacent to said surface of said second shield (1).

2. The sealing device (50) according to claim 1, characterized in that The cylindrical portion (2") of said elastomeric coating (2) comprises an appendix (6) which is inclined in an axially outward and radially outward direction with respect to the cylindrical portion (2") of said elastomeric coating (2).

3. The sealing device (50) according to claim 1, characterized in that The size of the channel of said first radial labyrinth seal (Gr) is between 0.1 mm and 0.8 mm.

4. The sealing device (50) according to any one of claims 1 to 3, characterized in that Said sealing device (50) further comprises a second axial labyrinth seal (Ga) cooperating with at least one first radial labyrinth seal (Gr) and formed by a radially external wing (1') of said second shield (1) facing the annular portion (2') of said elastomeric coating (2) with the annular portion (2') of said elastomeric coating (2).

5. The sealing device (50) according to claim 4, characterized in that The size of the channel of said second axial labyrinth seal (Ga) is between 0.2 mm and 1.0 mm.

6. The sealing device (50) according to any one of claims 1 to 3, characterized in that Said sealing device (50) further comprises a second non-contacting lip which is distanced from the annular portion (2') of said elastomeric coating (2) and faces a radially internal surface of the radially external wing (1') of said second shield (1), forming a second radial labyrinth seal.

7. The sealing device (50) according to any one of claims 1 to 3, characterized in that Said fixed portion and said rotatable portion have a circumferential extension with an amplitude comprised between 180° and 260°.

8. Bearing unit (30) equipped with a sealing device (50) according to any one of the preceding claims housed in a cavity (35, 36), said bearing unit further comprising: - a flanged radial inner ring (20) which is rotatable, - a radial outer ring (31) which is fixed, - an additional radial inner ring (34) which is rotatable, mounted on and integral with said flanged radial inner ring (20); - a plurality of rolling elements (32, 33) interposed between said radial outer ring (31) and said radial inner rings (20, 34).

9. The bearing unit (30) as set forth in claim 8 characterized in that, Said bearing unit (30) further comprises a first pre-chamber (7) contained between a metallic second shield (1) of said sealing device (50), an annular portion (2') of elastomeric coating (2) and a contact lip (9).

10. Bearing unit (30) according to claim 9, characterized in that: - a radial outer wing (1') of said metallic second shield (1) is positioned at the height of the radial outer ring (31) of said bearing unit (30) in the radial direction, - an annular portion (2') of said elastomeric coating (2) and an annular portion (10') of said metallic first shield (10) are shaped in an axially inward direction; - said contact lip (9) faces a radial inner wing (1") of said metallic second shield (1).

11. The bearing unit (30) according to any one of claims 8 to 10, characterized in that Said bearing unit (30) further comprises a second pre-chamber (11) defined inside a cavity (35) between an annular surface (8) of said flanged radial inner ring (20), a cylindrical surface (5) of said flanged radial inner ring (20), said metallic second shield (1) and a cylindrical portion (2") of said elastomeric coating (2).

12. The bearing unit (30) as set forth in claim 11 characterized in that, The volume of said second pre-chamber (11) is proportional to the length of a connecting radius (12) between said annular surface (8) of said flanged radial inner ring (20) and said cylindrical surface (5) of said flanged radial inner ring (20).

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