Labyrinth seal for improved discharge

Abstract

A sealing device (50) for a bearing unit (30), the sealing device (50) having a stationary assembly (70) and a rotatable metal shield (58), where the stationary assembly (70) has a shaped metal support (51) on which a first lip (53) and a second lip (54) that are not in contact with the metal shield (58) are co-molded and at least one lip (56, 57) on which the first lip (53) and the second lip (54) are co-molded, the at least one lip (56, 57) is in contact with the metal shield (58), where the second lip (54) and the metal shield (58) define a labyrinth seal. The second lip (54) has an angular extension of less than 360 DEG such that contaminants are discharged from the interior of the sealing device (50) along a missing corner portion of the second lip (54).

Description

TECHNICAL FIELD

[0001] The present invention relates to a cartridge seal device having innovative features which allow to improve the evacuation of contaminants which have entered inside the seal device. Such a seal device is applied to a bearing unit. The present invention is particularly, but not exclusively, applicable to a wheel hub assembly of a motor vehicle, said wheel hub assembly being provided with a bearing unit. More particularly, the bearing unit according to the present invention is a bearing unit in which the outer ring of the bearing is stationary while the inner ring of the bearing is rotatable. The present invention is advantageously, but not exclusively, applied to a bearing unit having double row of balls. BACKGROUND

[0002] As it is known, bearing units are generally exposed to various types of contaminants (e.g. mud, dust and suspended particulate matter and / or particles in solution). Therefore, bearing units, including those shaped parts of a wheel hub assembly of a motor vehicle, need to be provided with suitable seal devices.

[0003] The seal devices according to the prior art are cartridge seals having two parts, including a rotating part mounted on the inner radial ring and a stationary part mounted on the outer radial ring. According to said prior art, the stationary part of the seal includes one or more lips made of elastic material which are in contact with the rotating part and ensure the sealing action with respect to the inside of said bearing unit.

[0004] During the on-road operating conditions (road operating conditions) and during the validation of the bearing unit, in order to optimize the sealing performance of the bearing unit while maintaining low friction levels, it is understood that the labyrinth seal is designed as the best compromise. The labyrinth seal is designed using a screen which protects the seal opening from the moving parts of the motor vehicle (e.g. brake disc) and a non-contact sealing lip. In this way, it is difficult for mud and other contaminants to penetrate into the bottom chamber of the seal. However, at the same time, if mud accumulates inside said chamber, its evacuation becomes problematic. Tests have shown that, generally, the accumulation of mud occurs exactly inside the chamber, i.e. in the bottom of the outer radial ring. The accumulation of mud (which is not removed by the presence of water) can cause the disadvantage of reducing the working life of the wheel hub assembly, causing faster wear of the lip of the seal and hindering the normal operation of the entire bearing unit.

[0005] In order to overcome this disadvantage, it is known to provide an evacuation hole in the upright of the vehicle suspension. Unfortunately, this solution does not solve the above problem: due to the design, the evacuation hole can be provided only on the axially inner side of the bearing unit, although the evacuation hole facilitates the evacuation in that area, it certainly cannot manage to solve the problem on the axially outer side of the bearing unit.

[0006] Therefore, there is a need to design a sealing device that does not have the aforementioned drawbacks. SUMMARY

[0007] The object of the present application is to provide a sealing device, for example for a bearing unit of a wheel hub assembly, which has a shielding function against external contaminants and is provided with a geometry that facilitates the discharge of contaminants that have entered the interior of the sealing device, although their flow is limited. In particular, in order to minimize the accumulation of mud that can be seen on the bottom side of the radial outer ring, according to the present application the circumferential extension of the non-contacting lip that performs the labyrinth sealing function is interrupted, thus allowing the discharge to be improved.

[0008] On the one hand, this novel solution is still able to ensure the presence of an effective labyrinth ( / labyrinth seal) to prevent mud and other contaminants from entering the interior of the bearing unit. On the other hand, the labyrinth solution must, for example, ensure that it does not prevent the mud, water and contaminants that have entered the interior of the sealing device from flowing out, and in order to achieve this goal its circumferential extension must be optimized and in any case it is limited to an angular opening of less than 360 degrees. In this way, water can easily wash away any mud that can accumulate inside, or in the worst case it allows only a negligible amount of mud to accumulate.

[0009] According to an aspect of the present application, a sealing device is described according to the features indicated in the independent claims attached hereto.

[0010] According to another aspect of the present application, a wheel hub assembly is also described, having a bearing unit provided with a sealing device according to the present application.

[0011] Further preferred and / or particularly advantageous embodiments of the present application are described according to the features indicated in the dependent claims attached hereto. BRIEF DESCRIPTION OF DRAWINGS

[0012] The present application will now be described with reference to the attached drawings, which show a number of non-limiting examples of embodiments of the present application, in which:

[0013] Figure 1 is a partial cross-sectional view of a wheel hub assembly provided with a sealing device;

[0014] Figure 2a is a detail of the top part of the sealing device according to the first embodiment of the present application;

[0015] Figure 2b is a detail of the bottom part of the sealing device according to Figure 2a the first embodiment of the present application;

[0016] Figure 3 Details of the sealing device according to the second embodiment of the present invention; and

[0017] Figure 4 It shows according to Figure 3 The non-contact lip of the sealing device. Detailed Implementation

[0018] The invention will now be described by way of non-limiting example only, with reference to a wheel hub assembly for a motor vehicle, the wheel hub assembly being provided with a bearing unit having a sealing device according to the invention.

[0019] Reference Figure 1 The wheel hub assembly according to a preferred embodiment of the invention is generally designated by 10. The accompanying drawings illustrate details of the construction provided by way of example.

[0020] Component 10 has a central axis of rotation X and includes a rotating hub 20 and a bearing unit 30, the bearing unit 30 further comprising:

[0021] -Stationary radial outer ring 31;

[0022] - The radial inner ring 22 defined by the hub 20;

[0023] - Another rotating radial inner ring 34 is mounted on the hub 20 and is integral with the hub 20;

[0024] Two rows of rolling elements 32 and 33 are arranged between the radial outer ring 31 and the radial inner rings 22 and 34. In this example, the rolling elements...

[0025] Moving bodies 32 and 33 are spheres; and

[0026] - Two cages 39 and 40 are used to hold the rolling elements in the two rows of rolling elements 32 and 33 in place.

[0027] Throughout this specification and the claims, terms and expressions indicating position and orientation such as “radial” and “axial” are understood to refer to the rotational center axis X of the bearing unit 30. Additionally, expressions such as “axially outward” and “axially inward” refer to the assembled state of the wheel hub assembly, and in certain cases, preferably refer to (or indicate) the wheel side and the side opposite to the wheel side, respectively.

[0028] The radially outer ring 31 is provided with two respective radially outer raceways 31'and the radially inner rings 22, 34 are provided with respective radially inner raceways 20', 34' to allow the rolling of the axial outer row 32 of rolling elements arranged between the radially outer ring 31 and the wheel hub 20 and of the axial inner row 33 of rolling elements arranged between the radially outer ring 31 and the radially inner ring 34. For a greater simplicity of representation, the reference numbers 32, 33 will be used to indicate both a single ball and a row of balls. Moreover, for simplicity's sake, in the present description and in the attached drawings, the term "ball" will be used by way of example, instead of the more general term "rolling element" (likewise, the same reference numbers will be used). The wheel hub assembly 10 is provided with at least one sealing device 50 (for example, a device mounted on the axially outer side of the bearing unit). The following description made with reference to the sealing device 50 will also apply to the sealing device 60 mounted on the axially inner side of the bearing unit.

[0029] With reference to Figure 2a , the sealing device 50 can be a cartridge seal having two parts, comprising a static component 70 mounted on the radially outer ring 31 and a rotatable part mounted on the radially inner ring (visible in the drawings only in the way of a shaped metallic screen 58). In the course of the present description, the static component 70 of the sealing device will be substantially considered, which, like the other components of the bearing unit, has axial symmetry, so that the part located above the horizontal plane passing through the axis of symmetry X (i.e. substantially the part farthest from the ground) can be defined as the top part of the static component 70. The remaining part will be defined as the bottom part. This definition will also be applied in the same way to the other components of the bearing unit 30, for example to the radially outer ring 31. Figure 2a The top part of the sealing device is shown, while Figure 2b The bottom part of the sealing device is shown.

[0030] The stationary assembly 70 of the sealing device 50 comprises a shaped metal support 51 on which a first lip 53 and a second lip 54 are co-moulded in elastomeric material and not in contact with the rotatable part or with the metal shield 58. Said first and second lips 53, 54 and the shield 58 define a space (volume) 55 which is in contact with the external environment and inside which mud and / or other contaminants can accumulate. The stationary assembly 70 of the sealing device 50 is also provided with a pair of contact lips 56, 57 also in elastomeric material. These contact lips are in contact with the metal shield 58 and define, together with the shield, an inner space (inner volume) 59. In any case, it will be understood that the design, arrangement and number of the sealing lips can vary without thereby departing from the scope of protection of the present application.

[0031] The entry of mud inside the inner space 59 is limited by the presence of a labyrinth seal formed by the second lip 54 and by the metal shield 58. However, during the operating conditions and during the verification tests of the bearing unit, some mud can enter inside the space 59. With the solution described so far, it is difficult to expel the mud from said labyrinth seal, so the mud accumulates inside the space 59 and negatively affects the performance of the bearing unit. In Figure 2b In Figure 3, which shows the bottom part of the stationary assembly 70 of the sealing device 50, it can be seen the novel feature in the first embodiment according to the present application. The second lip 54 is not formed throughout the entire 360°, but only on a portion thereof. In this way, in the bottom part of the sealing device 50, there is no longer a labyrinth seal between the second lip 54 and the shield 58. Therefore, the mud or other contaminants which, due to gravity, would tend to occupy the bottom of the space 59 will be able to easily exit (escape) from the space 59. It is evident that the stationary assembly 70 must be mounted on the radial outer ring 31 correctly oriented, i.e. so that the top of the second lip 54 corresponds to the top of the radial outer ring 31. Depending on the application and on the use conditions, the angular extension of the missing part of the second lip 54 can vary from 160° to 200°, and preferably is equal to 180°. In the case of more demanding applications, the solid angular part of the second lip 54 will tend to increase to improve the relative labyrinth seal, so the angular extension of the missing part of the second lip 54 can vary from 50° to 70°, and preferably is equal to 60°.

[0032] Figure 3 and Figure 4 A second embodiment of the present application is shown. From Figure 4As can be seen, the second lip 54 is formed by an alternating sequence of solid portions 54' and voids 54", so as to perform a double function (the labyrinth sealing function of the portions 54' of the second lip 54 and the draining function of the remaining portions 54") in substantially the same way as the embodiments of Figure 2a and Figure 2b Each solid portion 54' and each void 54" can have an angular extension comprised between 20° and 30°, with the lower limit depending on the current molding techniques. Therefore, the number of solid portions and corresponding voids will be comprised between nine and six. Obviously, with this second embodiment of the application, it is not necessary to orient the stationary assembly 70 of the sealing device on the radially outer ring 31.

[0033] In summary, this solution is defined in the best way according to the application of the motor vehicle and ensures a high efficiency thanks to the improved sealing performance in the field, avoiding noise-related problems due to the accumulation of mud. Obviously, it is ensured to have a good performance also on wet and / or muddy roads.

[0034] In addition to the embodiments of the application as described above, it will be understood that there are many further variants. It must also be understood that the described embodiments are provided by way of example only and do not limit the subject matter of the application, or its application, or its possible configurations. On the contrary, although the description provided above can enable a person skilled in the art to implement the application at least in one of its configurations, it must be understood that many variants of the described components are possible without thereby departing from the scope of the 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), the sealing device (50) comprising: - a stationary assembly (70); and - a rotatable metal shield (58), the stationary assembly (70) in turn comprising a shaped metal support (51) on which a first lip (53) and a second lip (54) are co-molded, not in contact with the metal shield (58), and at least one lip (56, 57) in contact with the metal shield (58), wherein the second lip (54) and the metal shield (58) define a labyrinth seal, the sealing device (50) being characterized in that the second lip (54) has an angular extension less than 360°, so that contaminants are expelled from the inside of the sealing device (50) along a missing angular portion of the second lip (54).

2. The sealing device (50) according to claim 1, characterized in that The missing angular portion of the second lip (54) is comprised between 160° and 200°.

3. The sealing device (50) according to claim 2, characterized in that The missing angular portion of the second lip (54) is equal to 180°.

4. The sealing device (50) according to claim 1, characterized in that The missing angular portion of the second lip (54) is comprised between 50° and 70°.

5. The sealing device (50) according to claim 4, characterized in that The missing angular portion of the second lip (54) is equal to 60°.

6. The seal arrangement (50) of claim 1, wherein The missing angular portion of the second lip (54) has a plurality of voids (54") alternating with corresponding solid portions (54'), the bearing unit (30) having a symmetry axis (X), the portion located above a horizontal plane passing through the symmetry axis (X) being defined as a top portion of the sealing device (50), the top portion having the solid portions (54') and the voids (54") therein.

7. The sealing device (50) according to claim 6, characterized in that The number of the plurality of voids (54") is equal to nine and the angular extension of each void (54") is equal to 20°.

8. The sealing device (50) according to claim 6, characterized in that The number of the plurality of voids (54") is equal to six and the angular extension of each void (54") is equal to 30°.

9. A bearing unit (30) provided with a sealing device (50) according to any one of the preceding claims.

10. A wheel hub assembly (10) for a motor vehicle, the wheel hub assembly (10) comprising a hub (20) and a bearing unit (30) according to claim 9.

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