Lightweight radially outer ring for a hub-wheel assembly

Radially outer ring of a bearing unit for a hub-wheel assembly for motor vehicles, the radially outer ring being provided with: a flange portion having a plurality of axial fixing holes that connect an element of the motor vehicle wheel to the radially outer ring, an almost cylindrical portion which with part of its radially internal surfaces defines raceways for rows of rolling bodies of the bearing unit, an axially internal or axially external surface of the flange portion and a radially external surface of the cylindrical portion connected to each other by a first portion of toroidal surface (St1) and of a second portion of toroidal surface (St2) defined by corresponding first radius (R1) and second radius (R2), a truncated cone surface (Stc) defined by an angle (a) formed with a rotation axis (X) of the radially outer ring is interposed between the first portion of toroidal surface (St1) and the second portion of toroidal surface (St2).

CROSS-REFERENCE OF RELATED APPLICATION

This application is based on and claims priority to Italian Patent Application No. 102020000013732 filed on Jun. 10, 2020, under 35 U.S.C. § 119, the disclosure of which is incorporated by reference herein.

FIELD

The present disclosure relates to a lightweight radially outer ring of a bearing unit for a hub-wheel assembly.

BACKGROUND

A hub-wheel assembly provided with a bearing unit for rotatably supporting a wheel of a motor vehicle on a suspension is known and commonly used. A bearing unit, in general, includes a pair of rolling bodies but different configurations of bearing unit are also known, to which the present embodiments may be applied.

In the prior art, a hub-wheel assembly comprises a bearing unit provided with a rotary radially outer ring having a flange attachment for coupling to a rotary element of the motor vehicle, for example the wheel or the disc of a brake element. The bearing unit further comprises a pair of inner rings and a plurality of rolling bodies, e.g., balls, rollers or conical rollers. All of these components are axially symmetrical about the axis of rotation of the rotary elements, for example the radially outer ring of the bearing unit.

DETAILED DESCRIPTION

A wheel hub assembly is provided with a bearing unit, wherein the radially outer ring of the bearing unit, produced by forging, rotatably supports a wheel. Embodiments of a motor vehicle on a suspension. Embodiments of the disclosure also relate to a forged fixed radially outer ring of a bearing unit for a hub-wheel assembly, in which the wheel of the motor vehicle is supported by a rotary wheel hub

In particular and with reference toFIG.1, a radially outer ring131according to the prior art is produced by forging and is provided with a flange portion131a, having a plurality of holes136for fixing the wheel or the disc of a brake element, and an almost cylindrical portion131bwhich with part of its radially internal surfaces defines raceways131′ for the rolling bodies of the bearing unit. Respective surfaces of the two portions of the radially outer ring, specifically an axially internal surface131a′ of the flange portion131aand a radially external surface131b′ of the cylindrical portion131b, are connected to each other by means of a curved surface of radius R.

As a result of increasingly fierce international competition, there is constant demand from customers, e.g., motor vehicle manufacturers, for ongoing technical/financial improvements when it comes to hub-wheel assemblies. In particular, there is constant demand for an increase in performance or a reduction in the weight of the entire assembly—all without a corresponding increase in cost, naturally. It is therefore necessary to completely rethink the design of the hub-wheel assembly or some of its components in order to at least maintain the same level of performance while reducing weight, or enhance the performance of the assembly without increasing the weight. In the case of hub-wheel assemblies with a flanged radially outer ring, this is the heaviest and most bulky component. However, the technological constraints of forging do not allow a great deal of freedom for designers seeking to limit the size and weight of these components. Excess material may be eliminated by machining after forging, for example machining to remove shavings. However, this makes the production process more complicated and expensive.

It is therefore necessary come up with a suitable solution for a radially outer ring of a bearing unit for a hub-wheel assembly which does not have the abovementioned disadvantages.

With a view to substantially solving the technical problems described above and to satisfy the demand described above, one aim of the embodiments in accordance with this disclosure is to produce a new shape of radially outer ring obtained by forging, in which this new shape is designed to reduce the weight of the radially outer ring and enhance, or at least maintain, the performance required of the bearing unit.

This aim is achieved by producing the radially outer ring such that an axially internal surface of the flange portion and a radially internal surface of the cylindrical portion are connected to each other by means of a first and a second portion of toroidal surface defined by predetermined connection radii, wherein between the two toroidal surfaces there is interposed a truncated cone surface defined by a predetermined angle formed with the rotation axis of the radially outer ring.

With the aim of achieving the best compromise between technological constraints, related to the forging process, and structural constraints, preferably, the radius of the first portion of toroidal surface will be between 1.5 mm and 7 mm, while the radius of the second portion of toroidal surface should be greater than twice the radius of the first portion of toroidal surface.

Moreover, to optimize the trade-off between reduction in weight and mechanical strength, advantageously, the angle with respect to the axis of rotation of the radially outer ring should be between 10° and 20°.

Preferably, to facilitate machining, the centers of the two portions of toroidal surfaces will be positioned relative to other elements of the radially outer ring, as will be explained in more detail below.

This new shape of the forged radially outer ring makes it possible to avoid adding unnecessary material and, therefore, depending on the application, to reduce or limit the final weight of said radially outer ring. It also makes it possible to obtain a substantially constant thickness of material above the two raceways of the bearing unit and the axially external groove used for insertion of the axially external row of balls.

Therefore, embodiments of the disclosure provide a radially outer ring of a bearing unit for a hub-wheel assembly having the features set out in the claims attached to this description.

Certain exemplary embodiments may be applied to all generations of hub-wheel assemblies. In particular, such applications include cases in which the outer ring of the bearings is rotary while the inner rings of the bearing are fixed, and the opposite case in which the inner rings rotate and the outer ring is fixed. Exemplary embodiments are also suitable for any type of rolling body (balls, rollers, conical rollers, etc.).

Certain exemplary embodiments also relate to a bearing unit provided with a radially outer ring according to one of the embodiments of the present disclosure.

By way of non-limiting example, exemplary embodiments will now be described with reference to a hub-wheel assembly for motor vehicles provided with a bearing unit.

With reference toFIG.2, a hub-wheel assembly according to a preferred embodiment of the invention is designated as a whole by the reference sign10.FIG.2shows a detail of an exemplary configuration.

The hub-wheel assembly10has a central axis of rotation X and includes a bearing unit30, which in turn comprises a radially outer ring31, that is preferably, but not necessarily, a rotary ring. Such a bearing unit also includes a pair of radially inner rings34,35, that are preferably, but not necessarily, fixed rings; two rows of rolling bodies32,33, in the example show rolling bodies32,33are illustrated as balls (but could be other shaped rolling bodies), interposed between the radially outer ring31and the radially inner rings34,35; and two containment cages39,40to hold the rolling bodies of the rows32,33in position.

Throughout the present description and in the claims, the terms and expressions indicating positions and orientations, such as “radial” and “axial”, refer to the central axis of rotation X of the bearing unit30. Expressions such as “axially external” and “axially internal”, on the other hand, refer to the hub-wheel assembly when mounted, and in the case at hand, preferably, refer to a wheel side and a side opposite the wheel, respectively.

The radially outer ring31is provided with two respective radially outer raceways31′, while the radially inner rings34,35are provided with respective radially internal raceways34′,35′ to allow rolling of the axially external row of rolling bodies32interposed between the radially outer ring31and the radially inner ring34, and the axially internal row of rolling bodies33between the radially outer ring31and the radially inner ring35. For the sake of simplicity in the drawings, the reference signs32,33will designate both individual balls and rows of balls. Again for the sake of simplicity, the term “ball” may be used by way of example in the present description and in the attached drawings instead of the more generic term “rolling body” (the same reference signs also being used).

The hub-wheel assembly10may furthermore be provided with sealing means50for sealing the bearing unit with respect to the external environment. Sealing means50may be seals, e.g., seal50.

The radially outer ring31has an axially external flange portion31a. The flange portion has a plurality of axial fixing holes36. These holes serve as seats for as many fixing means (for example stud bolts, not shown in the FIGS.) which, in a known manner, connect an element of the wheel of the motor vehicle, for example the wheel or the disc of the brake (also of known type and not shown in the FIGS.), to the radially outer ring31. Moreover, the radially outer ring31is provided with an almost cylindrical portion31bwhich with part of its radially internal surfaces defines the raceways31′ for the rolling bodies of the bearing unit30.

In some embodiments, the radially outer ring31may have a first cylindrical portion31c, axially external, which acts as a centering means for the element of the wheel of the motor vehicle, and a second cylindrical portion31d, also axially external but less protruded than the first cylindrical portion31c, acting as a centering means for the brake disc of the motor vehicle.

As can be seen more clearly with reference toFIG.3, the radially outer ring31, according to one aspect of the exemplary embodiments, has a shape such that an axially internal surface31a′ of the flange portion31aand a radially internal surface31b′ of the cylindrical portion31bare connected to each other by means of a first portion of toroidal surface St1and of a second portion of toroidal surface St2defined by corresponding first radius R1and second radius R2. For the sake of simplicity, below, the two portions of toroidal surface will be defined as toroidal surfaces, it being understood in all cases that they are partially toroidal surfaces.

Between the first toroidal surface St1and the second toroidal surface St2there is interposed a truncated cone surface Stc defined by an angle α formed with a rotation axis X of the radially outer ring31.

Preferably, the first radius R1of the first toroidal surface St1may take on values between 1.5 mm and 7 mm. The aim is to achieve the best compromise between technological constraints, related to the forging process, and structural constraints. To be specific, values below 1.5 mm would not be attainable in an ordinary forging process, while values above 7 mm, although advantageous from the viewpoint of reducing the weight of the radially outer ring31as a whole, would impair the mechanical strength of the component, rendering it unsuitable for more demanding applications in which it must withstand considerable loads. In some applications already tested, a value of the first radius R1of 5 mm represented a first optimum compromise between the divergent requirements mentioned above.

Again, for the same reasons of achieving a technological/structural trade-off, the second radius R2of the second toroidal surface St2should preferably be greater than the first radius R1of the first toroidal surface St1and, even more preferably, greater than twice said first radius R1.

Moreover, to optimize the trade-off between reduction in weight and mechanical strength, advantageously, the angle α of the truncated cone surface Stc with respect to the axis of rotation X of the radially outer ring31should be between 10° and 20°.

Preferably, to facilitate machining, the centers of the two toroidal surfaces St1, St2will be positioned relative to other elements of the radially outer ring31.

In particular, the first toroidal surface St1connects to the axially internal surface31a′ of the flange portion31a—which is an annular surface—so that the center Cr1of the first toroidal surface St1is positioned at a predetermined diameter D2. This diameter D2is calculated as the difference between the diameter D1of the axes of the axial fixing holes36and the diameter D3of the same axial fixing holes36. This difference may be increased or reduced in a range between +3 mm and −3 mm, depending on the application. In mathematical terms, it should therefore be:
D2=D1−D3±3 mm

Furthermore, the second toroidal surface St2is connected to the truncated cone surface Stc and, on the opposite side, to the radially external surface31b′ of the cylindrical portion31b. Its center Cr2may refer to the axial position of the centers C33of the rolling bodies of the axially internal row33in a range between −7 mm and +7 mm, it being understood that this center Cr2may be located in an axial environment with respect to the center C33with a half-width of 7 mm.

The same design considerations may be applied also in the case of a fixed radially outer ring. In this case, as is known practice, the shape of the ring will be almost a mirror image of the shape described above, with the flange portion, connected to a fixed structure of the motor vehicle (for example the upright of a suspension), on the axially internal side. The only difference with respect to the case analysed above will be the axial reference of the center Cr2of the second toroidal surface: this center will in fact refer to the axial position of the centers of the rolling bodies of the axially external row32(rather than the centers of the rolling bodies of the axially internal row33).

To sum up, this new shape of the forged radially outer ring makes it possible to avoid adding unnecessary material and, therefore, depending on the application, to reduce the weight of the radially outer ring for similar applications or to limit the final weight of said radially outer ring for more demanding applications.

This optimization of material also makes it possible to obtain an almost constant thickness of material above the two raceways31′ of the radially outer ring31and the axially external groove31″ used for insertion of the axially external row of rolling bodies32.

Lastly, this new design aimed at optimizing the trade-off between weight and performance also makes it possible to preserve the feasibility of the forging process and not have to proceed with further machining operations to remove shavings, thereby keeping down the cost of the entire method for production of the radially outer ring.

In addition to the exemplary embodiments described above, note that there numerous other variants. It must thus be understood that these embodiments are merely examples and do not limit either the scope of the invention or its applications, or its possible configurations. On the contrary, although the above description allows a person skilled in the art to implement the present invention at least according to one exemplary embodiment thereof, it must be understood that many variants of the components described are possible, without departing from the scope of the invention as defined in the attached claims, interpreted literally and/or in accordance with their legal equivalents.