Abstract:
The invention concerns a wheel hub bearing unit for a vehicle, said hub bearing unit comprising a rotating bearing ring member ( 1 ) and a non-rotating bearing ring member ( 2 ), where the rotating bearing ring ( 1 ) has at least a radially extending wheel mounting flange ( 4 ) with a reference flange surface ( 5 ), wherein a gasket ( 9 ) with at least a sacrificial metal gasket surface is provided on the flange surface ( 5 ). Hereby, corrosion protection of the surface of the wheel mounting flange of a hub bearing unit is realized in a cost-effective manner.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a wheel hub bearing unit for a vehicle, said hub bearing unit comprising a rotating bearing ring and a non-rotating bearing ring, where the rotating bearing ring has at least a radially extending wheel mounting flange with a reference flange surface. 
     BACKGROUND TO THE INVENTION 
     In a typical wheel end assembly, a brake rotor may be fitted to the mounting flange of the rotating bearing ring of the hub unit. The wheel rim is then mounted against the brake rotor and both are bolted to the wheel mounting flange. The hub-rotor interface is exposed to atmospheric corrosion from humid air and from salt water. The corrosion leads to the formation of rust on and between the contacting surfaces of the wheel mounting flange, brake rotor and wheel rim. The layer of corrosion that forms on the wheel mounting flange surface results in increased runout, which may exceed that specified for finished and assembled hub units of e.g. 10 to 15 micro meters. When vehicles are serviced and undergo replacement of a brake rotor, the fixation of a (new) brake rotor on a wheel mounting flange having corrosion on the contact surface for the brake rotor would lead to axial runout and brake shudder. 
     US 2006/0177169 A1 discloses a hub unit with a wheel mounting flange for mounting a wheel on the hub. The flange is provided with a rust-preventive layer on the surface receiving the wheel. This rust-preventive layer may be a fused ceramics material or a plastic material either moulded onto the surface by insert moulding or a separate part fixed to the surface by an adhesive. 
     EP 0 800 011 A2 discloses a corrosion-protective element for protecting junctions between metal components made of different metals against electrolytic corrosion when exposed to moisture by providing a shield of sheet metal which is electrically passivated or has an anti-corrosion coating on its opposite surfaces. 
     It is further known to provide electrolytic zinc plating on the hub flange surface to prevent corrosion. The electrolytic plating is usually a bath process where at least the component in which the flange is formed is submerged in molten zinc and subjected to high temperature (over 150° C.) baking to eliminate hydrogen embrittlement. 
     SUMMARY OF THE INVENTION 
     By the invention, corrosion protection of the surface of the wheel mounting flange of a hub bearing unit is realized in a cost-effective manner by providing a hub bearing unit, wherein a gasket with at least a sacrificial metal gasket surface is provided on the flange surface. The sacrificial gasket comprises a radially oriented disc portion. Moreover, the gasket is adapted for attachment on the reference flange surface, before the mounting of a brake rotor or wheel against the wheel mounting flange. 
     According to the invention, corrosion protection of the wheel mounting flange of a hub bearing unit for a vehicle is provided which is advantageous due to low production costs and which is easy to provide in an in-line process for the production of the hub bearing unit. According to the invention, the corrosion protection of the wheel mounting flange of a hub bearing unit is achieved by means of a cathodic protection principle. When exposed to a corrosion environment, the sacrificial gasket will corrode before the wheel mounting flange. 
     Hereby, corrosion protection is achieved in a manner that can be implemented as a straightforward and fast inline process, which besides allowing for low production costs, also offers an environmentally friendly solution using a sacrificial principle to prevent rust of the hub bearing unit flange surface. 
     By providing a gasket that is electrolytically sacrificial, corrosion protection of the wheel mounting flange satisfying the industry standard ASTM B117 may be achieved. Moreover, the solution according to the invention does not result in loosening of bolt torque when a brake rotor and wheel rim are fixed to the wheel mounting flange. The sacrificial gasket also offers a satisfactory resistance to bolt load and has anti-fretting and failure-safe properties, just as the sacrificial gasket has a satisfactory resistance to hot brake fluid, preservatives and cleaning fluids, and does not adversely affect the performance of the hub bearing unit in the vehicle&#39;s wheel end. 
     Another advantage of the invention is that a hub gasket made of sacrificial metal according to the invention may be retrofitted to existing vehicle hub bearing units. 
     The wheel hub bearing unit according to the invention preferably comprises a rotating ring member with at least one annular track which cooperates with at least one annular track on the non-rotating ring member and accommodates rolling elements in said annular tracks for rotatably mounting the ring members in relation to each other. Accordingly, the hub unit may be provided with either balls, rollers or a combination thereof as rolling elements for the bearing. Moreover, the hub unit may also be provided as a plain bearing. 
     In one embodiment, a first ring member is a rotating inner ring and a second ring member is a stationary outer ring of the hub bearing unit. However, as an alternative, the first ring member may be a rotating outer ring and the second ring member may be a stationary inner ring of the hub bearing unit. The rotating ring member of the hub bearing unit comprises at least a radially extending wheel mounting flange. 
     The sacrificial metal gasket according to the invention has a thickness of 0.01 to 1.0 mm. In a first embodiment, the gasket may be made of a sheet of sacrificial metal, in which case the thickness of the sacrificial gasket is preferably 0.15 to 0.5 mm. In a second embodiment, the gasket may be made of a steel sheet coated with the sacrificial metal on both sides. The thickness of the gasket is then preferably 0.2 to 0.5 mm. The thickness of the coated sacrificial layer may be between 0.001 and 0.2 mm, and is preferably in the region of 0.01 to 0.05 mm, to enable machining if this is necessary. In one example of the coated steel sheet embodiment, the gasket may be provided with a sealant at its outer annular rim, if it is found necessary to close the exposed steel around the edge of the gasket. Furthermore, in the first and second embodiments of the sacrificial gasket, the surface of the gasket may be passivated by means of e.g. chromating. 
     In a preferred embodiment, the rotating ring member of the hub bearing unit is made of a steel alloy. The sacrificial metal is preferably zinc or a zinc alloy, such as zinc-aluminium alloy, preferably ZnAl15. However, it should be understood that other suitable metals may be used for the electrolytically sacrificial metal. The use of ZnAl15, i.e. an alloy with a composition of approx. 85% zinc and approx 15% aluminium, is advantageous as this alloy material is readily available and inexpensive to obtain. Moreover, this particular zinc alloy also provides excellent corrosion protection for various environments. 
     The hub bearing unit is provided with fixation means on the wheel mounting flange. The fixation means may be either stud bolts projecting out of the surface of the mounting flange, or threaded holes for receiving attachment bolts for bolting the sacrificial gasket, brake rotor and wheel rim to the mounting flange. The sacrificial gasket is provided with openings corresponding to the bolt positions of the fixation means on the flange surface, so that the gasket does not interfere with the mounting of a brake rotor and/or a wheel on the hub unit. 
     In some hub bearing unit designs, the wheel mounting flange has an axial extension, known as a spigot, to facilitate proper centering of the brake rotor and wheel rim during assembly. Corrosion protection on the surface of the spigot is also desirable. In one embodiment of such a hub bearing unit according to the invention, the surface of the spigot may be provided with an anti-corrosion coating or the like. In another embodiment, the sacrificial gasket comprises the radially oriented disc portion and further comprises a tubular sleeve portion, which fits over the spigot. The tubular sleeve portion then provides cathodic protection to the spigot. Furthermore, a protective cap engaging the tubular sleeve portion of the gasket may be provided for enclosing the central opening in the gasket. This cap could also be provided with a sacrificial metal coating and thereby contribute to the cathodic protection of the hub bearing unit. 
     The sacrificial gasket may be held in position between the brake rotor and the flange by the mounting forces there between. Alternatively, the sacrificial gasket may be fixed to the mounting flange by gluing or some other adhesive means, like a self-adhesive foil, or by a heat joining technique like welding, or by mechanical means. 
     Throughout this patent, the term sacrificial metal is meant to be understood as a metal which in the electrolytic sense is sacrificial compared with the metal used for the rotating ring member and in particular the wheel mounting flange. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       In the following, the invention is described with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of a gasket according to a first embodiment of the invention; 
         FIG. 2  is a radial section through a hub bearing unit according to a first embodiment of the invention; 
         FIG. 3  is a side view of a gasket according to a second embodiment of the invention; 
         FIG. 4  is a radial section through a hub bearing unit according to a second embodiment of the invention; 
         FIG. 5  is a side view of a gasket according to a third embodiment of the invention; 
         FIG. 6  is a radial section through a hub bearing unit according to a third embodiment of the invention, 
         FIG. 7  is a front view of a gasket according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIGS. 2 ,  4  and  6 , examples of hub bearing units with rotating inner ring are shown. Such hub bearing units are used in the automotive industry for supporting driven and non-driven wheels and brake rotors, which are secured to a wheel mounting flange  4 . A hub bearing unit comprises an inner ring member  1 , which is rotatably mounted in relation to an outer ring member  2 . The inner and outer ring members  1 ,  2  are assembled in a bearing unit, as the inner ring member  1  is provided with at least one raceway, which is an annular track supporting rolling elements  3 , such as balls, which are also accommodated in at least one annular track  6  in the outer ring member  2 . The rolling elements  3  accommodated in the track  7  of the inner ring member  1  are preferably held in place by a separate inner ring element  8  for facilitating assembly of the bearing unit. The outer ring member  2  is fixed to the frame of the vehicle and the inner ring member  1  is assembled on a shaft-like member  20  (see  FIG. 6 ), which may be a drive section in the case of a driven wheel or a centering section in the case of a non-driven wheel. The inner ring member  1  is provided with a flange  4  having an exterior surface  5  for receiving a brake rotor and a wheel rim (not shown). 
     The mounting flange  4  is provided with a plurality of fixation means  12 , such as threaded holes for receiving mounting bolts (not shown), but could alternately be stud bolts  40  projecting out of the flange surface  5 . 
     According to the invention, a gasket  9  is provided for at least substantially covering the flange surface  5 . During use, the mounting flange  4  and in particular the axially outward surface  5  of the flange  4  are exposed to moisture. In order to protect the flange  4  against corrosion, the gasket  9  comprising at least coating layers on either side of an electrolytically sacrificial metal, preferably zinc or a zinc alloy such as ZnAl15, is mounted to the flange surface  5 . Alternatively the gasket  9  is made from a metal sheet made of a sacrificial metal, preferably ZnAl15 or similar zinc-aluminium alloy. 
     The flange surface  5  extends radially. In the embodiment shown in  FIGS. 1 and 2 , the gasket  9  is of a flat configuration made from a sheet metal, such as a thin steel sheet coated with a zinc alloy, e.g. ZnAl15. The gasket  9  is provided with a plurality of holes  13  corresponding to the fixation means  12  on the flange  4  of the hub bearing unit. As shown in  FIG. 7 , the gasket holes  13  are positioned on the gasket  9  so that the gasket  9  fits onto the mounting flange surface  5  without causing any interference with the function of the mounting flange  4 . The outer contour of the gasket  9  can be circular or non-circular, e.g. following the contour of the mounting flange. 
     As shown in  FIGS. 2 ,  4  and  6 , the flange surface  5  may also include an axial extension or spigot  4   a . The gasket  9  shown in  FIGS. 3-6  has a radially extending gasket portion  9   r  and a tubular sleeve portion  9   a , which is adapted to perform a tight fit around the spigot  4   a  on the mounting flange  4  on the inner ring  1  of the hub bearing unit. Hereby, corrosion protection of the surface of the spigot  4   a  may also be provided. The tubular sleeve portion  9   a  may be provided with the same or a different thickness than the radial portion  9   a  of the gasket  9 . The tubular sleeve portion  9   a  may be provided as a separate part which may be mounted as a separate piece or joined with the radial portion  9   r . Alternatively, the tubular sleeve portion  9   a  of the gasket  9  may be formed integrally during the gasket manufacturing process. 
     As indicated on  FIGS. 2 and 4 , the gasket  9  may be, provided with adhesive means  14  on the surface (of the radial portion  9   r  in the embodiment of  FIG. 4 ) of the gasket  9  facing towards the flange surface  5  of the hub unit. The adhesive means  14  may be glue or a self-adhesive foil, such as a double-sided self-adhesive foil. 
     With reference to  FIGS. 5 and 6 , the shaft-like member  20  mounted in the hub bearing unit may be protected by a cap  10  provided on the gasket  9 . This cap  10  may be provided with a sacrificial metal coating and thereby contribute to the corrosion protection of the hub bearing unit. In addition, the cap portion  10  of the sacrificial gasket may be equipped with sensors  60 , such temperature and/or load sensors, and contain electronics  50  for controlling the wheel end functions and/or the dynamic stability of the vehicle. In addition, the cap portion  10  of the sacrificial gasket may be equipped with sensors, such temperature and/or load sensors, and contain electronics for controlling the wheel end functions and/or the dynamic stability of the vehicle. 
     Above, the invention is described with reference to some preferred embodiments. However, a hub unit according to the invention may be executed in many embodiments. For instance, the hub bearing unit may be of the type with rotating inner ring or with rotating outer ring. In this latter case, the outer ring member then comprises at least a radially extending mounting flange for attachment of a brake rotor and wheel rim. The sacrificial gasket as described in any of the above embodiments can also be applied on a hub bearing unit with rotating outer ring. Likewise, the rolling elements  3  may be balls (as described above) or rollers or a combination thereof. Thus, variations of the embodiments of the invention described may be performed without departing from the scope of the invention defined in the claims.