Flanged bearing ring for a motor vehicle wheel bearing unit

A flanged bearing ring is formed of two different materials joined together as a single piece, specifically a radially inner annular insert and a flanged, radially outer lightweight body formed about the insert. The insert has one or more inner raceways and is formed of a hard material, such as bearing steel. The outer body is made of a lightweight material, such as aluminium alloy, with a higher thermal expansion coefficient higher than that of the hard material from which the inner insert is formed. A radial projection formed on the insert extends into a radial groove of the outer body. The projection and the recess interlock the insert and the outer body so as to prevent relative movement.

CROSS REFERENCE

This application claims priority to Italian Patent Application No. TO2010A000305 filed on Apr. 15, 2010, the contents of which are incorporated fully herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to bearings, and more particularly to a lightweight, flanged bearing ring for the hub of a motor vehicle wheel.

The bearing ring of a typical wheel hub bearing assembly may either be a stationary ring with a flange for mounting the relevant hub-bearing unit to the suspension standard of a motor vehicle, or a rotatable ring where the flange provides connection to the wheel and/or the brake rotor.

There is an ever increasing demand for weight reduction in motor vehicle components for in order to lower fuel consumption and exhaust emissions. With a vehicle wheel bearing, weight reduction must not result in a reduction in strength and/or safety. The raceways must be made of a material of hardness sufficient to resist the stresses of rolling contact. Conventional bearing steel is still widely used, although other materials have been proposed, such as ceramics and titanium, which provide good mechanical performance but are considerably more expensive as compared to bearing steel.

WO 2008/147284 A1 discloses a bearing ring made up of two different materials joined together in a single piece, namely a first, high toughness material such as bearing steel forming the raceways and a second, lightweight material, such as a lightweight metal, forming the rest of the ring. The second material is joined to the first material by a semi-solid casting process.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the connection between the two different portions of a flanged bearing ring made of two different materials, namely a first, hard material and a second, lightweight material. Particularly, it is desired to improve such a connection at room temperature.

The present invention is directed to a flanged bearing ring for a motor vehicle wheel that provides improvements in the key areas of bearing ring performance. That is, the bearing ring of the invention provides a lower weight, while ensuring the required high strength capabilities. The ring is made up of two different materials joined together as a single piece, and includes a radially inner, annular or tubular insert, and a radially outer body formed around the insert. The insert forms one or more raceways and is made of a hard material with a first thermal expansion coefficient. The outer body provides a radially outwardly extending flange and is made of a lightweight material with a second thermal expansion coefficient higher than that of the first material. Interlocking means, formed by the insert and the outer body, lock these two bodies together against relative axial movement. The interlocking means include one or more radially protruding portions at an outer surface of the insert. Respective, complementary radially recesses are formed by the outer body, thereby preventing axial movement between the outer body and the inner insert at least at room temperature. Preferably, these mating protrusions and recesses at the interface between the outer body and the inner insert are so shaped as also prevent relative rotary movement between the outer body and the inner insert.

DETAILED DESCRIPTION OF THE INVENTION

Referring first toFIGS. 1 to 3, a flanged bearing ring10in accordance with a first embodiment of the invention is depicted. The ring10in this example is a bearing ring for vehicle applications, particularly for rotatably mounting a wheel (not shown) to a stationary suspension standard (not shown) of the vehicle. The bearing ring10has two outer raceways11for two rows of rolling elements, in this example tapered rollers.

The ring10comprises a radially inner insert12of generally annular or tubular shape and a radially outer body13providing a radially outwardly extending flange14near an outboard end of the insert12. The flange14provides a number of through bores24to allow connection to the suspension standard by means of stud bolts. Although the bearing ring shown inFIG. 1is a radially outer bearing ring, the ring structure described below may also be used with other types of flanged bearing rings, for example a rotatable, radially inner (or outer) bearing ring the radial flange of which is to be fixed to the wheel. Throughout the present description and the claims, terms and expressions indicating positions and directions such as “radial” and “axial” are understood as referring to the axis of rotation x of the bearing. Expressions such as “inboard” and “outboard” instead refer a condition when mounted on a vehicle.

The radially inner insert12is made of a first, relatively hard material having a first, lower volumetric thermal expansion coefficient, whereas the radially outer body13is made of a second, “lightweight” (i.e., relatively low density) material with a second, volumetric thermal expansion coefficient higher than that of the first material which the insert12is made of. Since the insert12forms one or more raceways, a hard and tough material suitable for the insert is, for example, a bearing grade steel. As alternatives, low carbon steel or ceramic may be used. As a lightweight material for the outer body13, a lightweight or relatively low density metal is preferred, such as aluminium, magnesium, or alloys thereof. Other suitable materials for the outer section may include, but not be limited to, carbon composites or reinforced polymers.

The insert12is machined so as to form, in its radially outer surface, at least one radially protruding and circumferentially extending annular projection15. The projection15is defined by a central circumferential portion of greater diameter than the remainder of the outer surface and a pair of opposing generally radial surfaces extending between each edge of the central portion and the outer surface. In a preferred embodiment, the projection15extends circumferentially and continuously about the outer surface of the insert12. Alternatively, the insert12may include a plurality of radial projections15spaced apart circumferentially about the central axis x. In either case, as discussed in greater detail below, the projection(s)15is/are part of an interlocking means for substantially preventing relative axial movement or displacement between the insert12and the outer body13. To some extent, depending on the cross-sectional shape of the relief, these interlocking means will also prevent radial movement between the insert12and the outer body13, when one or more undercuts20are provided, as in the embodiments ofFIGS. 4 and 6.

Preferably, the outer body13is formed and joined to the insert12through a semi-solid casting process, which is a near net shape process wherein the metal of the outer body is formed at a temperature between liquid and solid states. The advantage of a semi-solid casting process with respect to a molten metal process, such as high pressure die casting, is that the outer body obtains a denser, dendrite-free microstructure providing the strength and crack-propagation resistance required for bearing applications. Also, the semi-solid casting process allows the outer body to achieve accurately the required shape also in those instances where the surfaces at the interface between the insert12and the outer body13have a particularly complex shape, for example if undercuts are provided.

The wheel-mounting flange14and the outer surface of the spigot17can be formed with the necessary geometry to ensure sufficient stiffness. Moreover, the bores24in the wheel mounting flange14can be provided during the semi-solid casting process, by forming the semi-solid metal of the flange14around appropriately positioned threaded nuts or stud bolts.

A rheocasting process is one example of a preferred semi-solid casting process. Using aluminium as an example of the lightweight metal for the outer body13, a rheocasting process initially involves bringing the aluminium to a molten (liquid) state. The molten aluminium is then allowed to cool and is stirred during solidification to obtain a semi-solid slurry. The step of cooling can involve adding solid particles of aluminium to the molten material and, for enhanced efficiency, the solid particles can be added via a stirring mechanism. An exchange of enthalpy or heat takes place between the liquid aluminium and the solid particles, which facilitates the formation of the slurry and can dispense from the need for external cooling. The semi-solid aluminium slurry is then injection-moulded to the inner insert12with the aid of a suitable die that defines the required shape of the wheel mounting flange14.

While it is preferred, as already indicated, to form the outer body13by a semi-solid casting process, in its broadest aspect the invention is not so limited and encompasses the possibility of sintering or casting, die-casting or otherwise forming the outer body about the inner insert12.

As the second material of the outer body13cools and solidifies, it shrinks. Basically, contraction occurs in a radially inward direction, towards the central axis of rotation x of the bearing unit. Thus, the semi-solid metal of the outer body13shrinks around the one or more projections15of the insert12and forms at least one recess or groove18tightly copying or following the shape of the projection(s)15, so as to interlock together the outer body13and the insert12, thereby preventing any relative axial movement between the outer body13and the insert12. Preferably, the projection15of the insert12and the recess18of the outer body13each extend circumferentially and substantially continuously about the central axis x. Alternatively, the insert12may have a plurality of radial projections15spaced apart circumferentially about the central axis x and the outer body13may include a plurality of radial recesses18spaced apart circumferentially about the central axis x, each recess18being configured to receive a separate one of the projections15.

The interlocking means15,18may be formed in a variety of different structures. In a less preferred embodiment (not shown), the projection15(and the mating recess18) may have a generally rectangular cross-sectional shape as taken in an axial plane. In the preferred embodiments, the projection15has one or more undercuts20, in order to provide a higher degree of interlock against relative movement between the outer body and the inner insert in a direction perpendicular to the axis of rotation x (i.e., radial movement).

In a bearing ring according to an embodiment of the present invention the outer body may include an inner surface mating with the outer surface of the insert. In this embodiment, at least a portion of at least one of the insert and the outer body has an at least partially non-cylindrical radial cross-section such that engagement of the mating surfaces prevents relative rotational displacement between the outer body and the insert.

A variety of different wheel bearing unit designs can be produced incorporating the bearing ring10of the present invention. For example, the bore of the insert12can serve as an outer raceway for rolling elements of a constant velocity joint and the bearing unit may further comprise an integral CV joint. Moreover, the bearing unit may be a single row or a double-row angular contact bearing in which the rolling elements are balls, rollers, flattened balls etc. Also, when the unit is a double-row bearing, the raceways for the first and second rows of rolling elements can be equal in diameter, or the diameters can differ.

Further embodiments are schematically depicted inFIGS. 4 to 6.FIG. 4shows an example of a projection15having two opposite conical surfaces at an obtuse angle, i.e. tapering away from each other. In the embodiment ofFIG. 5, the projection15has two conical surfaces tapering in a same direction. The two conical surfaces are generally parallel or extend at an acute angle and one of the surfaces forms an undercut20. Stated differently, the at least one projection may include a radially outer wall spaced from the radially outer surface and first and second parallel walls extending in a non-radial direction from the radial outer wall to the radially outer surface. In the embodiment ofFIG. 6, the projection15has two conical surfaces tapering towards one another, providing two undercuts20. By virtue of this shape, the groove18and the projection15are each generally shaped so as to form a dovetail joint.

While a few illustrative embodiments have been disclosed in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the illustrative embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing the invention, it being understood that various changes may be made in the function and arrangement of elements described in the exemplary embodiments without departing from the scope as set forth in the appended claims and their legal equivalents.