Abstract:
A flanged bearing ring ( 10 ) for the wheel of a motor vehicle includes two different materials joined as a single piece: a tubular core ( 15 ) and an outer body ( 16 ) around the core. The outer body forms a radial flange ( 17 ) and is made of a lighter material than that of the core. At the axially outer end of the ring, at the side where the flange ( 17 ) is provided, the interface surfaces between the outer body ( 16 ) and the core ( 15 ) terminate in a groove ( 21 ) formed partly in the outer body and partly in the core. The groove ( 21 ) accommodates a sealing ring ( 22 ) made of rubber-like or elastomeric material which presses against both the outer body ( 16 ) and the core ( 15 ) so as to seal continuously, along an entire circumference around the axis (x), a separation line ( 23 ) between the core ( 15 ) and the outer body ( 16 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This United States Non-Provisional Utility application claims the benefit of Italy Provisional Patent Application Ser. No. TO2011A000277, filed on 29 Mar. 2011, which is incorporated herein in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a lightweight, flanged bearing ring for the hub of a motor vehicle wheel, particularly a rotatable ring with a flange providing connection to the wheel and/or the brake rotor. 
     SUMMARY OF THE INVENTION 
     The motorcar industry has to comply with an ever increasing demand for weight reduction in motor vehicle components for the sake of cutting down fuel consumption and exhaust emissions. With a vehicle wheel bearing, weight reduction may not imply any reduction in strength and safety. The raceways must be made of a material hard enough to resist the stresses of rolling contact. Conventional bearing grade steel is still widely used. The raceways are heat treated so as to attain a level of hardness and microstructure homogeneity adequate to withstand the stresses caused by rolling Hertzian contact. Recent flanged bearing rings include a radially inner, annular or tubular insert (or core) made of bearing grade steel and forming one or two raceways, and a radially outer body forming a radially outwardly extending flange around the insert and made of a lightweight material such as aluminium alloy. The lightweight flange is designed to mount the wheel and/or the brake rotor and transfer loads from these components to the tubular insert. 
     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 grade 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. 
     It has been observed that, with bearing rings of the above type, a weak point is given by the area where the interface surface between the two parts of different materials (tubular steel core, outer body of lightweight material) opens on the axially outer side, or outboard side of the bearing. In working conditions, openings along the interface surface between the two different materials tend inevitably to form. 
     In working conditions, the loads coming from the wheel transmit to the flange of the light-alloy outer body a bending moment which tends to separate the outer body from the core. Furthermore, repeated cycles of thermal stresses cause a differential thermal expansion between the outer body made of aluminium and the steel core, which has a coefficient of thermal expansion lesser than that of aluminium alloys. The infiltration of contaminants such as water, dust, salt, over time causes micro-cracks to broaden and the formation of rust. Experimental tests carried out by the Applicant have shown the occurrence of problems of galvanic corrosion with the use of certain types of light alloy, having a considerable difference in electrochemical potential than the steel. Salt, or even more simply water, can in fact be an electrolytic means having a high capability of penetration in openings. Because of all these factors, there is a risk that the coupling between the outer body of light alloy and steel core deteriorates, resulting in fretting (sliding) and possibly failure of the flanged ring. 
     It is an object of the invention to provide a bearing ring made of two parts of different materials coupled together in a reliable, long-lasting ad watertight manner, so as to overcome the inconveniences of above-mentioned state of the art. 
     The above and further objects and advantages are attained, in accordance with the invention, by a flanged bearing ring having the features set forth in claim  1 . According to another aspect of the invention, there is proposed a method as defined in claim  9 . Preferred embodiments of the invention are defined in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the present invention may be well understood there will now be described a preferred embodiment thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is an axial cross-sectional view of a first embodiment of a flanged bearing ring according to the invention; 
         FIG. 2  is an enlarged view of a detail of  FIG. 1  with an annular gasket mounted in a groove of the ring; 
         FIG. 3  shows the insertion of the gasket of  FIG. 2  in the bearing ring of  FIG. 1 ; 
         FIG. 4  is a view, similar to that of  FIG. 2 , showing a variant of the shape of the groove; 
         FIG. 5  is a view, similar to that of  FIG. 1 , showing a ring with a groove of different shape; 
         FIG. 6  shows the ring of  FIG. 5  with a gasket mounted in the groove; 
         FIG. 7  shows an enlarged view of the groove of the ring of  FIGS. 5 and 6 . 
         FIG. 8  shows a gasket, in the mounted condition and immediately prior to its insertion into the groove; 
         FIG. 9  is a view, similar to  FIG. 7 , of a further variant of the shape of the groove, and 
         FIG. 10  shows a further variant of the shape of the gasket. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , designated overall at  10  is a flanged bearing ring in accordance with an embodiment of the invention. The ring  10 , in this example, is designed to be the outer, rotatable ring of a double-row angular contact ball bearing for vehicle applications, particularly for mounting to a vehicle wheel (not shown) to be rotationally supported relative to a stationary suspension standard (not shown) of the vehicle around a central axis of rotation x. 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 “axially inner” and “axially outer” instead refer to a condition when mounted on a vehicle. 
     The ring  10  comprises a radially inner insert or core  15  of a generally tubular shape and a radially outer body  16  providing a radially outwardly extending flange  17  at the outboard side of the core  15 . The flange  17  provides a number of bores  18  to allow connection to the vehicle wheel by means of stud bolts (not shown). 
     The core  15  forms two raceways  11 ,  12  and is made of a first, hard and tough material, preferably a bearing grade steel. The radially outer body  16  is made of a second, lightweight material. A lightweight metal is preferred, such as aluminium, magnesium, or alloys thereof. Other suitable materials for the outer body may include, but not be limited to, carbon composites or reinforced polymers. In order to provide adequate structural support to the outer body  16 , the steel core  15  extends axially through the whole width of the outer body, from the inboard to the outboard side. The tubular core  15  forms an axial tubular extension or spigot  19  at its outboard side, which facilitates centering of the vehicle wheel. The spigot  19  protrudes axially from a radially outer surface  20  of the flange  17 , facing an axially outer direction. 
     The outer body  16  is formed around the core  15  in a number of different ways, for example through a semi-solid casting process, or by sintering or casting, or die-casting. At the end of any of these processes, the lightweight material tightly copies the shape of the radially outboard surface of core  15 , whereby the inner and outer bodies interlock with one another. The shape of the radially outboard surface of the core  15  is so formed as to provide a series of grooves and ridges which extend in the circumferential direction and determine the formation of complementary ridges and grooves in the outer body when this is formed around the core. 
     Towards the axially inner ends, the core  15  forms a ridge  13  which projects in a radially outer direction and extends in a circumferential direction. The ridge  13  serves as a shoulder to oppose relative axial displacement between the outer body  16  and the core  15 . The ridge  13  provides an axially outer radial surface  14  which is coplanar, or substantially coplanar, with the axially outer surface  20  of flange  17 ; the surface  20  defines a precise reference surface against which the wheel or brake disc will rest. 
     At the axially outer end ring, at the outboard side where the flange  17  is provided, the interface surface between the outer body and the core ends in a groove  21  formed partly by the outer body  16  and partly by the inner core  15 . It is noted that the interface surface terminates in a position which is recessed with respect to the axially inner radial surfaces  20  of the flange  17  and  14  of the ridge  13 . 
     The groove  21 , which opens in an axially outer direction, may be obtained by turning in a terminal step of the manufacturing process of the ring, that is, after the outer body  16  has already been formed around the core  15 . As an alternative, the groove  21  may be produced during the same manufacturing step in which the outer body is formed around the core, for example by means of an annular insert placed in the moulding cavity. 
     Accommodated in the groove  21  is an annular gasket  22  of rubber or elastomeric material which exerts a hermetic sealing action both against the outer body  16  and the core  15 . Therefore, the annular gasket  22  continuously covers and closes, along an entire circumference around the axis x, a separation line  23  between the steel of the core  15  and the lightweight metal of the outer body  16 , where the interface surface between these two materials meets the outboard side of the ring  10 . 
     Preferably, as shown in the enlargement of  FIG. 2 , the groove  21  is obtained to a greater extent in the outer body of lightweight metal  16 , and to a lesser extent in the ridge  13  of the core  15 . Due to this arrangement, a minor quantity of the material (steel) that provides the greatest contribution in terms of structural strength is removed, and therefore the ridge  13  is not weaken to an appreciable extent. 
     In the embodiment illustrated in  FIG. 3 , the groove  21  has a rounded bottom  21   a  and two coaxial cylindrical surfaces  21   b ,  21   c  between which the gasket  22  is forcefully inserted, for example by means of a punch A and a guide B, so that the gasket, once inserted in the groove, remains trapped in it in a radially compressed condition with respect to its undeformed condition  22 ′ prior to the assembly. In the embodiment of  FIG. 4 , the opening  21   d  of the groove  21  has a radial dimension smaller than the radial distance between the coaxial cylindrical surfaces  21   b ,  21   c , in order to retain the gasket within the groove and prevent it from accidentally coming out of the groove. Preferably, the narrowing of the opening  21   d  is achieved by creating an edge  21   e  protruding in a radial direction from the outer body  16  toward the core  15 . Alternatively, the edge  21   e  can be formed as an edge protruding from the core  15  towards the outer body  16 . The creation of a conical surface  21   f , tapered in an axially inner direction, i.e. away from the opening  21   d , opposes the escape of the gasket from the groove and helps the gasket  22  to reach its correct working position when it is inserted in the groove. 
       FIGS. 5 to 9  show further variants with annular seals  22  of circular cross-section. The presence of an edge  21   e  at the opening  21   d  of the groove keeps the annular gasket spaced from the brake disc (indicated in dashed lines at C in  FIG. 6 ). As shown for example in  FIG. 7 , the projecting edge  21   f  has a diameter d 21   f  greater than the diameter d 21   g  of the axially inner end of the groove, where a rounded portion  21   g  having a radius corresponding to the radius of the transversal cross-section of the gasket. In all variants of the invention, it is possible to use a gasket which has, in its free or undeformed condition, a smaller diameter than that of the groove in which the gasket is mounted. The gasket ( FIG. 8 ) should be elastically enlarged (as indicated schematically at  22 ″) in order to get over the edge  21   e  and then shrink steadily in its seat after being fitted deep in the groove. The tapered surface  21   f , which is concave in this example, favors the retaining of the gasket in the groove  21 . 
     Preferably, the annular gasket  22  does not project axially beyond the flat surface defined by the surfaces  20  and  14 , but only partly fills the groove  21 . Owing to this arrangement, the brake disk C does not contact the gasket  22 , and therefore rests only against the flat surfaces  20  and  14 . Otherwise, in case the gasket  22  should protrude axially beyond the surfaces  14  and  20 , it could cause planarity errors of the braking surfaces of the brake disc. In addition, the absence of contact between the gasket and the brake disc prevents the drawback that the warm brake disc may melt the elastomeric or rubber material and tear it out of its seat when removing the brake disc for servicing. Those skilled in the art will readily recognize that many variants and combinations can be made with respect to the embodiments herein described and illustrated. For example,  FIG. 9  shows a variant with a tapered surface  21   f  and a rounded seat to receive a gasket of circular cross-section. In  FIG. 10 , the gasket  22  has two bevels to facilitate its insertion into the groove. 
     Not necessarily the bottom of the groove  21  must have a rounded profile as shown. A rounded shape is preferable if one chooses to make a groove with thin dimensions, using a thin turning tool having a rounded head.