Lightweight radial outer race for a hub-wheel assembly

Abstract

A radial outer ring (31) of a bearing unit (30) for a hub-wheel assembly (10) of a motor vehicle is provided with: a flange (31a) having a plurality of axial fixing holes (36) for connecting elements of the wheel of the motor vehicle to the radial outer ring; a generally cylindrical portion (31b) having a portion of its radial inner surface defining a raceway (31') for an array of rolling elements of the bearing unit, the axial inner surface (31a') or axial outer surface of the flange and the radial outer surface (31b') of the cylindrical portion being connected to each other by means of a first partial annular surface (St1) defined by a first radius (R1) and a second partial annular surface (St2) defined by a second radius (R2), a truncated conical surface (Stc) being between the first partial annular surface and the second partial annular surface, the truncated conical surface being defined by an angle (α) formed with the axis of rotation (X) of the radial outer ring.

Description

Technical Field

[0001] This invention relates to a lightweight radial outer ring for a bearing unit in a hub-wheel assembly, wherein, preferably, the radial outer ring, produced by forging, rotatably supports the wheel of a motor vehicle on the suspension. However, the invention is also applicable to forged fixed radial outer rings for bearing units in hub-wheel assemblies, in which the wheel of a motor vehicle is supported by a rotating wheel hub.

[0002] Therefore, this solution can be applied to hub-and-wheel assemblies of all generations. In particular, such applications include cases where the outer ring of the bearing rotates while the inner ring remains stationary; and vice versa, where the inner ring rotates while the outer ring remains stationary. This invention is also applicable to any type of rolling element (balls, rollers, tapered rollers, etc.). Background Technology

[0003] Hub-wheel assemblies, which include bearing units for rotatably supporting the wheels of a motor vehicle on the suspension, are known and commonly used. Bearing units typically comprise a pair of rolling elements, but different configurations of the bearing units to which the present invention can be applied are also known.

[0004] In the prior art, a hub-wheel assembly includes a bearing unit having a rotating radial outer ring with flange attachments for connection to a rotating element of a motor vehicle (e.g., a wheel or a disc of a brake element). The bearing unit also includes a pair of inner rings and a plurality of rolling elements (e.g., balls, rollers, or tapered rollers). All of these components are axisymmetric about the axis of rotation of the rotating element (e.g., the radial outer ring of the bearing unit).

[0005] Especially referencing Figure 1 According to the prior art, the radial outer ring 131 is produced by forging and is provided with a flange portion 131a and a generally (almost) cylindrical portion 131b. The flange portion 131a has a plurality of holes 136 for fixing a disc for a wheel or brake element, and the cylindrical portion 131b defines a raceway 131' for the rolling elements of the bearing unit by means of a portion of its radial inner surface. The corresponding surfaces of the two portions of the radial outer ring (specifically, the axial inner surface 131a' of the flange portion 131a and the radial outer surface 131b' of the cylindrical portion 131b) are connected to each other by a curved surface of radius R.

[0006] Due to increasingly fierce international competition, customers (i.e., motor vehicle manufacturers) are constantly demanding technical and economic improvements in wheel hub-wheel assemblies. Specifically, there is a continuous demand to improve the performance of the entire assembly or reduce its weight—naturally, all without correspondingly increasing costs (the need to improve the performance or reduce the weight of the entire assembly without increasing costs). Therefore, it is necessary to completely rethink the design of wheel hub-wheel assemblies or some of their components to at least maintain the same performance level while reducing weight, or to enhance the performance of the assembly without increasing weight. In the case of wheel hub-wheel assemblies with a flanged radially outer ring, this (the flanged radially outer ring) is the heaviest and largest component. However, the technical constraints of forging do not allow designers seeking to limit the size and weight of these components much freedom. Excess material can be removed after forging by machining, for example, machining to remove shavings. However, this makes the production process more complex and expensive.

[0007] Therefore, it is necessary to propose a suitable solution for the radial outer ring of the bearing unit for the hub-wheel assembly that does not have the above-mentioned disadvantages. Summary of the Invention

[0008] In order to fundamentally solve the above-mentioned technical problems, one object of the present invention is to produce (or manufacture) a radial outer ring of a new shape obtained by forging, wherein the new shape is designed to reduce the weight of the radial outer ring and enhance or at least maintain the desired performance of the bearing unit.

[0009] This objective is achieved by manufacturing the radial outer ring such that the axial inner surface of the flange portion and the radial outer surface of the cylindrical portion are connected to each other by means of a first annular surface defined by a predetermined connection radius and a second annular surface defined by a predetermined connection radius, wherein a truncated cone surface is located between the two annular surfaces and is defined by a predetermined angle formed with the axis of rotation of the radial outer ring.

[0010] In order to achieve the best compromise between the technical and structural constraints related to the forging process, preferably, the radius of the first part of the annular surface will be between 1.5 mm and 7 mm, while the radius of the second part of the annular surface should be more than twice the radius of the first part of the annular surface.

[0011] Furthermore, in order to optimize the trade-off between weight reduction and mechanical strength, it is advantageous that the angle of rotation relative to the radial outer ring axis should be between 10° and 20°.

[0012] Preferably, for ease of manufacturing, the centers of the two partial annular surfaces are positioned relative to the other elements of the radial outer ring (as will be explained in more detail below).

[0013] This new shape of the forged radial outer ring allows for the avoidance of adding unnecessary material, thus reducing or limiting the final weight of the radial outer ring depending on the application. It also allows for a substantially constant material thickness in the two raceways of the bearing unit and in the axial outer grooves for inserting the balls into the axial outer row.

[0014] Therefore, the present invention provides a radial outer ring for a bearing unit of a hub-wheel assembly, the radial outer ring having the features set forth in the independent claims appended to this specification.

[0015] The present invention also relates to a bearing unit having a radial outer ring according to one embodiment of the present invention.

[0016] Other preferred and / or particularly advantageous embodiments of the invention are described in accordance with the features set forth 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 embodiments, in which:

[0018] Figure 1 It is based on the radial outer ring cross-section of the bearing unit in the prior art.

[0019] Figure 2 A cross-section of a hub-wheel assembly with a radial outer ring according to an embodiment of the present invention, and

[0020] Figure 3 It shows Figure 2 The radial outer ring of the hub-wheel assembly. Detailed Implementation

[0021] As a non-limiting example, the invention will now be described with reference to a hub-wheel assembly for a motor vehicle equipped with bearing units.

[0022] Reference Figure 2 The hub-wheel assembly according to a preferred embodiment of the present invention is generally indicated by reference numeral 10. This figure illustrates details of an exemplary construction.

[0023] The hub-wheel assembly 10 has a central axis of rotation X and includes a bearing unit 30, which accordingly includes:

[0024] The radial outer ring 31 is preferably, but not necessarily, a rotating ring.

[0025] A pair of radial inner rings 34 and 35, preferably but not necessarily fixed rings.

[0026] Two rolling elements 32 and 33, which are spheres in this example, are located between the outer radial ring 31 and the inner radial rings 34 and 35; and

[0027] Two containment cages 39 and 40 are used to hold the rolling elements in the rolling element rows 32 and 33 in place.

[0028] Throughout this specification and in the claims, terms and expressions indicating position and orientation (such as "radial" and "axial") refer to the central axis of rotation X of the bearing unit 30. On the other hand, expressions such as "axially external" and "axially internal" refer to the hub-wheel assembly during installation, and in the present case, preferably refer to the wheel side and the side opposite to the wheel, respectively.

[0029] The outer radial ring 31 is provided with two corresponding outer radial raceways 31', while the inner radial rings 34 and 35 are provided with corresponding inner radial raceways 34' and 35', to allow / make rolling of the axially outer row of rolling elements 32 between the outer radial ring 31 and the inner radial ring 34, and the axially inner row of rolling elements 33 between the outer radial ring 31 and the inner radial ring 35. For simplicity, reference numerals 32 and 33 will denote both a single ball and a row of balls. Again, for simplicity, the term "ball" may be used by way of example in this specification and the accompanying drawings instead of the more general term "rolling element" (using the same reference numerals).

[0030] The hub-wheel assembly 10 may also be provided with a sealing element 50 for sealing the bearing unit relative to the external environment.

[0031] The radial outer ring 31 has an axially outer flange portion 31a. The flange portion has a plurality of axially retaining holes 36. These holes serve as seats for a variety of retaining components (e.g., stud bolts, not shown in the figures) that connect elements of a motor vehicle wheel (e.g., wheel or brake disc (also a known type and not shown in the figures)) to the radial outer ring 31 in a known manner. In addition, the radial outer ring 31 is provided with a generally cylindrical portion 31b, a portion of the radially inner surface of which defines a raceway 31' for the rolling elements of the bearing unit 30.

[0032] Preferably, the radial outer ring 31 has: a first cylindrical portion 31c, located axially outside, serving as a centering component for an element of a wheel of a motor vehicle; and a second cylindrical portion 31d, also located axially outside, but protruding less than the first cylindrical portion 31c, serving as a centering component for a brake disc of a motor vehicle.

[0033] For reference Figure 3 As can be seen more clearly according to one aspect of the invention, the radial outer ring 31 has a shape such that the axial inner surface 31a' of the flange portion 31a and the radial outer surface 31b' of the cylindrical portion 31b are connected to each other by means of a first portion St1 of the annular surface defined by a first radius R1 and a second portion St2 of the annular surface defined by a second radius R2. For simplicity, the two portions of the annular surface are defined below as the annular surface, and it will be understood that in all cases, they are partial annular surfaces.

[0034] The truncated cone surface Stc is located between the first annular surface St1 and the second annular surface St2, and the truncated cone surface Stc is defined by the angle α formed with the axis of rotation X of the radial outer ring 31.

[0035] Preferably, the first radius R1 of the first annular surface St1 can be between 1.5 mm and 7 mm. The aim is to achieve an optimal compromise between the technical and structural constraints associated with the forging process. Specifically, values ​​below 1.5 mm are unavailable in conventional forging processes, while values ​​above 7 mm, although advantageous in terms of reducing the overall weight of the radial outer ring 31, would impair the mechanical strength of the component, making it unsuitable for more demanding applications that must withstand considerable loads. In some tested applications, a first radius R1 of 5 mm presents the optimal compromise between the aforementioned different requirements.

[0036] Similarly, for the same reason of achieving a trade-off in technology / structure, the second radius R2 of the second annular surface St2 should preferably be larger than the first radius R1 of the first annular surface St1, and even more preferably larger than twice the first radius R1.

[0037] Furthermore, in order to optimize the trade-off between weight reduction and mechanical strength, it is advantageous that the angle α of the truncated conical surface Stc relative to the axis of rotation X of the radial outer ring 31 be between 10° and 20°.

[0038] Preferably, for ease of machining, the centers of the two annular surfaces St1 and St2 are positioned relative to the other elements of the radial outer ring 31.

[0039] Specifically, the first annular surface St1 is connected to the axial inner surface 31a' (which is an annular surface) of the flange 31a, such that the center Cr1 of the first annular surface St1 is positioned at a predetermined diameter D2. This diameter D2 is calculated as the difference between the diameter D1 of the axis of the axial fixing hole 36 and the diameter D3 of the same axial fixing hole 36. Depending on the application, this difference can increase or decrease within a range of +3mm to -3mm. Therefore, mathematically, it should be:

[0040] D2 = D1 - D3 ± 3mm

[0041] Furthermore, the second annular surface St2 is connected to the truncated conical surface Stc and to the radially outer surface 31b' of the cylindrical portion 31b on the opposite side. The center Cr2 of the second annular surface St2 can be referenced to the axial position of the center C33 of the rolling element of the axial inner row 33 within the range of -7mm and +7mm. It will be understood that the center Cr2 can be positioned in an axial environment with a half-width of 7mm relative to the center C33.

[0042] The same design considerations can be applied when the outer radial ring is fixed. In this case, as is known practice, the shape of the ring will be approximately a mirror image of the shape described above, with an axially inner flange that connects to the fixed structure of the motor vehicle (e.g., the suspension pillar). The only difference from the case analyzed above will be the axial reference of the center Cr2 of the second circular surface: this center will actually refer to the axial position of the center of the rolling element of the outer axial row 32 (rather than the center of the rolling element of the inner axial row 33).

[0043] In summary, this new shape of the forged radial outer ring allows for the avoidance of adding unnecessary material, thus enabling a reduction in the weight of the radial outer ring for similar applications, or limiting the final weight of the radial outer ring for more demanding (or more required) applications.

[0044] This material optimization also allows for a nearly constant material thickness to be achieved in the two raceways 31' of the radial outer ring 31 and the axial outer groove 31” for inserting the axial outer row rolling elements 32.

[0045] Finally, this new design, which aims to optimize the trade-off between weight and performance, also makes it possible to maintain the feasibility of the forging process without requiring further machining to remove chips, thereby reducing the overall cost of the method used to produce (or manufacture) the radial outer ring.

[0046] In addition to the embodiments of the invention described above, it should be noted that the invention is applicable to many other variations. Therefore, it must be understood that these embodiments are merely examples and do not limit the scope of the invention or its application or possible constructions. Rather, while the above description enables those skilled in the art to implement the invention at least according to one exemplary embodiment, 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, interpreted literally and / or according to their legal equivalents.

Claims

1. Radial outer ring (31) of a bearing unit (30) for a hub-wheel assembly (10) of a motor vehicle, comprising: - a flange portion (31a) having a plurality of axial fixing holes (36) connecting elements of a wheel of the motor vehicle to the radial outer ring (31), - a substantially cylindrical portion (31b) a part of the radially inner surface of which defines a raceway (31') for a row of rolling elements (32, 33) of the bearing unit (30), and the radial outer ring (31) being characterized in that: - the axial inner surface (31a') or the axial outer surface of the flange portion (31a) is connected to the radially outer surface (31b') of the cylindrical portion (31b) by means of a first partial toroidal surface (St1) defined by a first radius (R1) and a second partial toroidal surface (St2) defined by a second radius (R2), and in the fact that: - a frustoconical surface (Stc) is interposed between the first partial toroidal surface (St1) and the second partial toroidal surface (St2), the frustoconical surface (Stc) being defined by an angle (a) formed with the rotation axis (X) of the radial outer ring (31); the center (Cr2) of the second partial toroidal surface (St2) being positioned within an axial range of between -7 mm and +7 mm from the center (C33) of the rolling elements of the inner axial row of rolling elements (33), or the center (Cr2) of the second partial toroidal surface (St2) being positioned within an axial range of between -7 mm and +7 mm from the center of the rolling elements of the outer axial row of rolling elements (32).

2. The radial outer ring (31) as set forth in claim 1, characterized in that - the first radius (R1) of the first partial toroidal surface (St1) takes a value between 1.5 mm and 7 mm.

3. The radial outer ring (31) as claimed in claim 1 or 2, characterized in that - the second radius (R2) of the second partial toroidal surface (St2) is greater than twice the first radius (R1) of the first partial toroidal surface (St1).

4. The radial outer ring (31) as claimed in claim 1 or 2, characterized in that - the angle (a) of the frustoconical surface (Stc) with respect to the rotation axis (X) of the radial outer ring (31) is between 10° and 20°.

5. The radial outer ring (31) as claimed in claim 1 or 2, characterized in that - the first partial toroidal surface (St1) is connected to the axial inner surface (31a') or to the axial outer surface of the flange portion (31a) so that the center (Crl) of the first partial toroidal surface (St1) is positioned at a predetermined diameter (D2) calculated as the difference between the diameter (Dl) of the axis of the axial fixing holes (36) and the diameter (D3) of the axial fixing holes (36).

6. The radial outer ring (31) as set forth in claim 5, characterized in that - the predetermined diameter (D2) increases or decreases in the range of between +3 mm and -3 mm.

7. The radial outer ring (31) as claimed in claim 1 or 2, characterized in that - the second partial toroidal surface (St2) is connected to the frustoconical surface (Stc) and to the radially outer surface (31b') of the cylindrical portion (31b) and the center (Cr2) of the second partial toroidal surface (St2) is referred to the axial position of the center (C33) of the rolling elements of the row of rolling elements (32, 33).

8. The radial outer ring (31) as set forth in claim 1 or 2, characterized in that Said radial outer ring comprises a first cylindrical portion (31c), located axially externally, which acts as a centring element for the elements of the wheel of the motor vehicle, and a second cylindrical portion (31d), also located axially externally, but less protruding than said first cylindrical portion (31c), which acts as a centring element for the brake disc of the motor vehicle.

9. A hub-wheel assembly (10) for a motor vehicle, said assembly comprising a bearing unit (30) which in turn comprises: - a radial outer ring (31) according to any one of the preceding claims; - a pair of radial inner rings (34, 35); - two rows of rolling elements (32, 33) interposed between said radial outer ring (31) and said radial inner rings (34, 35); and - two containment cages (39, 40) for keeping the rolling elements of said two rows of rolling elements (32, 33) in position.

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