Sealing device for bearing unit

Abstract

The sealing device (50) for the bearing unit (30) has at least one contact lip (60) that is operatively in sliding contact with the contact surface (34a) of the bearing unit (30), and the at least one contact lip (60) is further provided with: a wedge-shaped portion (61) that forms a first angle (α) facing the medium to be contained relative to the contact surface (34a) and a second angle (β) opposite to the first angle, wherein, under operating conditions, the second angle (β) is smaller than the first angle (α); a first surface (62) having a concave shape, the concavity of the first surface (62) being defined by a first radius (R1); wherein the second angle (β) is between 48° and 55°, and the length of the first radius (R1) is between 2.0 mm and 10.0 mm.

Description

Technical Field

[0001] This invention relates to a sealing device for a bearing unit, preferably, but not exclusively, applied to a wheel hub assembly. The invention is particularly suitable for bearing units with space available for accommodating a small-sized sealing device.

[0002] This solution can be applied to hub assemblies of all generations. Specifically, this application includes cases where the outer ring of the bearing is rotatable while the inner ring is fixed, and vice versa, where the inner ring rotates while the outer ring is fixed. The invention is also applicable to any type of rolling element (balls, rollers, tapered rollers, etc.). Background Technology

[0003] According to the prior art, the sealing device consists of a two-piece box-type seal, including a rotating portion mounted on, for example, a radial inner ring and a stationary portion mounted on, for example, a radial outer ring. According to this prior art, the stationary portion of the seal includes one or more lips of elastomeric material that contact the rotating portion and ensure a sealing effect relative to the interior of the bearing unit. It is also known to be a sealing device consisting of a single piece and integral with one of the rings of the bearing unit, wherein at least one contact lip ensures a seal due to interference established relative to the surface of the other ring of the bearing unit during the assembly of the seal.

[0004] In any case, regardless of the solution used, the contact lip will slide relative to the surface to ensure a seal. Sealing performance is ensured through a proper balance between the contact force and local pressure between the contact surfaces. Therefore, for the same contact force, the larger the pressure peak required to ensure a proper seal, the smaller the contact surface area (which must be kept below the appropriate design value).

[0005] Similarly, as a result of increasing global competition, customers (i.e., motor vehicle manufacturers) have consistently demanded continuous technical or cost-related improvements to wheel hub assemblies. In particular, there has been a persistent need to improve the overall performance of the assembly or reduce its weight. Naturally, all of this is done without the desire to further increase costs. Regarding sealing devices, better performance results in terms of reliability and durability are required, but operating conditions (loads caused by specific applications) are becoming increasingly demanding, and the size of the seating space within the bearing unit is shrinking. To meet this demand, sealing devices must operate at a balance between the lip size and the maximum interference designed for it, resulting in a much wider contact area for the lip and consequently, a decrease in the performance of the contact lip.

[0006] In practice, for example, a contact lip that makes contact in the radial direction (the reference numerals in the figure below can be used to represent this). Figure 3 As seen below (and will be explained for the purposes of this invention), the lip has a wedge-shaped portion that forms a first angle α facing the medium to be contained relative to the contact surface, and a second angle β opposite to the first angle α. During operating conditions, when the lip (e.g., stationary) contacts the contact surface (e.g., rotating), the first angle α must be constantly greater than the second angle β. This asymmetry between the angles produces a desired pressure distribution with a peak pointing towards the medium to be sealed. These angles are simply obtained by connecting the straight portions of the lip. This type of construction quickly becomes inefficient as the portion of the lip facing the angle β becomes flat on the contact surface, increasing the contact area and thus reducing the pressure and sealing efficiency. To mitigate this effect, the length of the lip HL1 should be as large as possible so that for the same interference value, the rotation angle of the lip is small. However, this measure is incompatible with the need to reduce the space available for placing the seal.

[0007] A known solution to reduce this so-called "flattening" effect is to define the contact area by three straight sections with different tilt angles α, β, and γ. The aim is to reduce the contact area when a large interference value occurs relative to the contact surface. Similarly, in this case, for the same interference, the longer the lip, the smaller the rotation angle of the lip. This solution is effective when the balance between the lip length and the interference level is below the transition value; however, as this value increases, the "flattening" effect continues, resulting in the aforementioned outcome.

[0008] Therefore, it is necessary to define a sealing device having at least one contact lip, the form of which is optimized so that the sealing device for bearing units does not have the aforementioned disadvantages. Summary of the Invention

[0009] In order to substantially solve the above-mentioned technical problems, one object of the present invention is to provide a sealing device for a bearing unit, wherein the sealing device is provided with a contact lip having an improved shape.

[0010] This objective is achieved by forming the contact lip with a concave form, which better withstands deformations acting on the contact lip during operation and reduces their absolute value. Furthermore, the ratio α / β between the first angle α facing the medium to be contained and the second angle β opposite to the first angle α is reduced. The first and second angles define a wedge-shaped portion of the contact lip that interferes with the contact surface, providing a sealing effect relative to the contact surface.

[0011] Furthermore, further design improvements can be achieved by modifying the flexing portion at the base of the lip (on the opposite side of the contact surface), such as by forming a recessed surface, or concave portion, at the base of the contact lip. The pronounced concavity of this surface improves the flexibility of the contact lip and helps maintain a constant contact force even with increased interference.

[0012] This optimized form improves the behavior of the lip in situations with high interference with contact elements (such as the radial inner or radial outer ring of a bearing unit) by reducing the degree of local deformation and thus the contact width between the lip and the contact element. This increases the local pressure peak and consequently improves sealing performance.

[0013] Advantageously, the invention is applicable to radial contact lips, and even more advantageously to contact lips of sealing devices that require a small placement space within the bearing unit, a typical case in recent applications; however, the design is scalable and maintains consistent performance even with larger lip sizes.

[0014] Therefore, according to the present invention, a sealing device for a bearing unit is provided, the sealing device comprising a contact lip having the characteristic features indicated in the independent claims attached to this specification.

[0015] The present invention also relates to a bearing unit, and more particularly to a bearing unit for a wheel hub assembly, the bearing unit being provided with a sealing device according to one embodiment of the present invention.

[0016] Other preferred and / or particularly advantageous embodiments of the invention are described based on the characteristic features indicated in the appended dependent claims. Attached Figure Description

[0017] The invention will now be described with reference to the accompanying drawings, which illustrate non-limiting examples of embodiments of the invention, in which:

[0018] - Figure 1 It is a cross-section of the hub assembly equipped with bearing units;

[0019] - Figure 2 A sealing device for a bearing unit is shown;

[0020] - Figure 3 According to one embodiment of the present invention Figure 2 Details of the contact lip of the sealing device; and

[0021] - Figure 4 Is with Figure 3 The same details are shown in the figure, which shows the contact lip under operating conditions (working conditions / working status). Detailed Implementation

[0022] 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.

[0023] Reference Figure 1 The reference numeral 30 in the attached figure generally indicates a bearing unit or hub assembly.

[0024] The bearing unit has a central axis of rotation X and includes:

[0025] -Rotatable, flanged radial inner ring 20;

[0026] - Fixed (or stationary) radial outer ring 31;

[0027] - Another rotatable radial inner ring 34 is mounted on the flanged ring 20 and is integral with the flanged ring 20;

[0028] - Multiple rolling elements 32, 33 are disposed between the radial outer ring 31 and the flanged ring 20. In this example, the rolling elements 32, 33 are balls.

[0029] - Two cages 39 and 40 are used to hold the rolling elements in the multiple rows of rolling elements 32, 33 in place.

[0030] Throughout this specification and claims, terms and expressions indicating position and orientation ( / direction) such as “radial” and “axial” are understood to refer to the central rotation axis X of the bearing unit 30. Expressions such as “axially outward” and “axially inward” relate to the assembled state of the hub assembly, and in the cases discussed, preferably, “axially outward” and “axially inward” refer to the wheel side and the side opposite to the wheel side, respectively.

[0031] The flanged ring 20 and the radial outer ring 31 together define two interspaces 35 and 36 at opposite axial ends of the bearing unit 30. If not screened, these two spaces would allow contaminants and impurities to enter the bearing unit 30.

[0032] Therefore, in order to protect the bearing unit 30, at least one sealing device 50 implemented according to the principle of the present invention is installed inside at least one of the two spaces 35, 36.

[0033] Typically, the sealing device 50 includes two metal shields facing each other, at least one of the two metal shields being provided with one or more sealing lips made of an elastomeric material that slide in contact with the other shield. Alternatively, the sealing device 50 may include only one metal shield having one or more sealing lips made of an elastomeric material that slide in contact with the sliding surface of the bearing unit 30 during relative movement of the bearing unit 30 relative to the seal.

[0034] The following reference Figure 2 By way of example only, the case in which the sealing device 50 includes at least one fixed contact lip 60 that contacts the surface 34a of the rotating flanged ring 20 in the radial direction will be described.

[0035] Reference Figure 3 (Undeformed state) and Figure 4 The novel form of the contact lip 60 according to the invention is described by detailing the lip in the (deformation or working condition) illustration. This novel form is defined by considering the following main objectives: reducing flattening of the contact surface during operating conditions; maintaining an edge-like contact area during variations in interference between the contact lip 60 and the contact surface 34a; maintaining a high pressure peak during variations in interference values; allowing operation under higher contact forces while maintaining appropriate pressure due to the use of a higher range of interference values ​​to control the contact area; and greater flexibility and lower deformation values ​​of the contact lip 60.

[0036] Undoubtedly, the most important feature of the new form is the introduction of a first radius R1 and a reduction in the ratio α / β between the first angle α of the surface to be contained and the second angle β (i.e., the angle defining the wedge-shaped portion 61 of the contact lip 60). Due to the presence of radius R1, angle β is measured at the tangent to the sealing edge. More precisely, it can be said that the absolute value of the second angle β has increased, and this increase is also associated with the formation of a first surface 62 having a concave shape defined by the first radius R1. The first radius R1 is connected to a second radius R2 (where R1 > R2), with the second radius R2 located near the base of the contact lip 60. These two features (the first radius R1 and the ratio α / β) ensure a more uniform pressure distribution and reduce the flattening effect of the lip, except in cases with very high interference values ​​that occur outside of operating conditions. The curved form of the lip (i.e., the first concave surface 62) better withstands those deformations acting on the contact lip 60 during operating conditions, reducing their absolute value. This avoids the substantially flattening (i.e., formation of a flat surface) of the contact lip 60, which is also designed for high interference values ​​(e.g., equal to 0.45 mm). This allows for a smaller contact area ( / contact region) between the wedge-shaped portion 61 of the contact lip 60 and the contact surface 34a. Therefore, the pressure peak in the contact area remains high, and the sealing performance is not negatively affected in any way. Figure 4 In the above description, it can be noted that: due to interference during operating conditions and subsequent deformation of the contact lip 60, the first contact surface 62 tends to become flat, and the absolute value of the second angle β (in Figure 4 The value of the first angle α (denoted as βw) decreases, but remains substantially greater than 0° in all cases, meaning that flattening of the lip on the contact surface does not occur, and as expected, the value of the first angle α (in) remains constant. Figure 4 The value is represented as αw) increasing.

[0037] Therefore, defining the first radius R1 (i.e., the first recessed surface 62) has the following effect: the first recessed surface 62 more effectively withstands deformation. Thus, the curved area is strengthened, and the flattening of the contact lip 60 is delayed.

[0038] Furthermore, the first radius R1 and the second angle β allow the contact lip 60 to operate at the edges for the entire range of interference values. In fact, still referencing... Figure 4 It can be noted that the wedge-shaped portion 61 of the contact lip 60 deforms very little or not at all, and remains completely intact even under working conditions.

[0039] Calculations and a series of experimental tests show that the optimal value for the first radius R1 is between 2.0 mm and 10.0 mm. The second angle β can be between 48° and 55°, while the first angle α can be between 50° and 65°. Since the condition β < α must always be satisfied, especially during operating conditions, the optimal pair of values ​​can be α = 55° and β = 54°.

[0040] The third angle γ is also an important dimensional parameter of the contact lip 60. The third angle γ is defined as the angle between the radial direction and the second surface 63, which is opposite the wedge portion 61 to the first concave surface 62. The optimal combination of the values ​​of angles γ and β, along with other dimensions characterizing the curvature of the contact lip 60, ensures constant pressure peaks and high values ​​under varying interference conditions. The third angle γ must vary between 50° and 65°, preferably, and as the tests conducted showed, the third angle γ can have a value of 60°.

[0041] In addition, another important parameter is the base thickness HLT, measured at the base of the lip (on the opposite side of the contact surface 34a). In the cases of the second angle β and the third angle γ, the base thickness HLT of the contact lip 60, together with the first radius R1, provides the contact lip 60 with the ability to maintain a constant force when the interference value changes, altering the material's rigidity modulus. Advantageously, the HLT thickness must be between 0.3 mm and 1.2 mm.

[0042] Another important region of the contact lip 60 is the flexing portion located at the base of the lip (on the opposite side of the contact surface 34a). Preferably, according to the invention, a third surface 64 has been formed with a greater concavity than the first surface 62. Essentially, the third surface 64 forms a recess at the base of the contact lip 60. The significant concavity of the third surface 64 improves the flexibility of the contact lip 60, which is another feature that helps maintain a constant contact force even as interference increases. In this way, the pressure peak remains optimal over a wide range of interference values ​​because the amplitude of the contact area remains consistently small, and there is no visible transition behavior guided by the planarization effect within the normal operating range of the application. The third concave surface 64 is defined by the angle of attack δ formed with the radial direction, the depth HG of the recess, and the third radius R3 defining the concavity of the third surface 64. Thus, the recess defined by these three parameters provides increased flexibility to the contact lip 60 because it moves the centers of the second radius R2 and the third radius R3 toward the region of the "hinge" formed in the area of ​​the base thickness HLT, and also reduces the deformation level of the hinge itself. The optimal value of the angle of attack δ varies between 20° and 35°, and is preferably 30°; the depth HG of the recess can vary between 0.1 mm and 0.5 mm, the value of the second radius R2 will vary between 0.8 mm and 3.2 mm, and the value of the third radius R3 will vary between 0.2 mm and 0.8 mm, thus R3 must always <R2。

[0043] The suggested solutions are basically:

[0044] • Improve the contact pressure value within a higher interference range;

[0045] • Eliminate the surface planarization effect and increase the possible range of interference values ​​to be used;

[0046] • Allows for optimization of constant contact force over a wide interference range, while maintaining a large contact pressure value even at higher interference values;

[0047] • Increase the flexibility of the contact lip while reducing the peak deformation of the lip itself.

[0048] In addition to the embodiments of the invention described above, it must be understood that many other variations exist. It must also be understood that these embodiments are merely examples and do not limit the scope of the invention, its application, or its possible constructions. Rather, while the above description allows those skilled in the art to implement the invention based at least one of the examples of its embodiments, it must be understood that many variations of the described components are possible without departing from the scope of the invention as defined in the appended claims, literally and / or according to their legal equivalents.

Claims

1. A sealing device (50) for a bearing unit (30), the sealing device (50) comprising at least one contact lip (60) operatively slidingly contacting a contact surface (34a) of the bearing unit (30), and the at least one contact lip (60) further comprising: - The wedge-shaped portion (61) forms a first angle (α) facing the medium to be contained relative to the contact surface (34a) and a second angle (β) opposite to the first angle, wherein, under operating conditions, the second angle (β) is smaller than the first angle (α). - A first surface (62), adjacent to the second angle (β), the first surface (62) having a concave shape, the concavity of the first surface (62) being defined by a first radius (R1), The sealing device (50) is characterized in that: - The second angle (β) is between 48° and 55°. - The length of the first radius (R1) is between 2.0 mm and 10.0 mm.

2. The sealing device (50) according to claim 1, characterized in that, The first angle (α) is between 50° and 65°.

3. The sealing device (50) according to claim 1 or 2, characterized in that, The first angle (α) is equal to 55°, and the second angle (β) is equal to 54°.

4. The sealing device (50) according to any one of the preceding claims, the sealing device (50) further comprising a third angle (γ) between the second surface (63) in the radial direction and the second surface (63), the second surface (63) being opposite to the first recessed surface (62) relative to the wedge-shaped portion (61), wherein, The third angle (γ) is between 50° and 65°.

5. The sealing device (50) according to any one of the preceding claims, characterized in that, The base thickness (HLT) of the contact lip (60) is between 0.3 mm and 1.2 mm.

6. The sealing device (50) according to any one of the preceding claims, the sealing device (50) further comprising a third recessed surface (64) defined by an angle of attack (δ), a depth (HG) and a third radius (R3) formed with the radial direction.

7. The sealing device (50) according to claim 6, characterized in that, The angle of attack (δ) is between 20° and 35°.

8. The sealing device (50) according to claim 6, characterized in that, The depth (HG) is between 0.1 mm and 0.5 mm.

9. The sealing device (50) according to claim 6, characterized in that, The third radius (R3) is between 0.2 mm and 0.8 mm.

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

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