Patent Publication Number: US-2012045155-A1

Title: sealed hub-bearing assembly for agricultural applications

Description:
The present invention refers to a sealed hub-bearing assembly for agricultural applications. 
     For a better understanding of the state of the art and problems related thereto, there will be at first described a hub-bearing assembly for agricultural applications known from WO 2007/105185, shown in  FIG. 1  of the appended drawings. The known hub-bearing unit comprise a radially outer, rotatable outer ring  11  from one side of which a flange  12  radially extends and pair of identical, symmetrically arranged inner bearing rings  16 ,  17  are tightly mounted side to side on the axle A projecting from an arm E of the frame of an agricultural machine. In order to prevent contaminants (water, mud, soil) from entering the bearing from the side near the arm of the frame, the bearing unit is equipped with a sealing device  20 . The sealing device is fitted between an outer collar  34  secured to the outer ring  11  and an inner L-shaped side shield  39  which is fitted around the axle A and axially clamped against the frame E. 
     It is an object of the invention to provide an arrangement for mounting the sealing device to the bearing unit, thereby allowing them to be handled and shipped together as a single piece. Furthermore, it is desirable to allow a component to be dispensed with, while not increasing the axial size of the inner bearing rings. Particularly, the axial dimension of the inner bearing rings must not be increased. These rings must be identical for manufacturing reasons, symmetrical in order to assure proper balancing of the bearing. 
     It is also desirable to improve the effectiveness of the sealing device, particularly by preventing water from leaking into the bearing along a path which, in the conventional design of  FIG. 1 , is defined between the frame arm E, the axle A and the side shield  39 . Efficient sealing action is essential for a correct and reliable operation of the disc over an acceptable period of time. Since the contamination conditions are extreme, contaminants entering the inner parts of the bearing will rapidly cause the disc to lock, reducing productivity of the agricultural machine. 
     The present invention is directed at providing such improvements over existing bearing designs for agricultural applications. The above and other objects and advantages, which will be better understood in the following, are achieved according to the invention by a hub-bearing assembly having the features defined in claim  1 . Preferred embodiments of the invention are set forth in the dependent claims. 
    
    
     
       Preferred, but not limiting embodiments of the invention will now be described, reference being made to the appended drawings, in which: 
         FIG. 1  is an axial cross-sectional view of a hub-bearing assembly of known design, which rotatably supports a soil working disc on an axle projecting from an arm of an agricultural machine; 
         FIG. 2  is an axial cross-sectional view of an illustrative embodiment of a sealed hub-bearing assembly according to the invention; 
         FIG. 3  is a fragmentary, enlarged view of a detail of  FIG. 2 ; 
         FIG. 4  is a partial, axial cross sectional view of the sealed hub-bearing assembly of  FIG. 1  mounted on an agricultural axle; and 
         FIG. 5  is an enlarged view, with some parts removed for reasons of clarity, of an optional element of the sealed hub-bearing assembly of  FIG. 2 . 
     
    
    
     In the text below, the structure of the hub-bearing assembly will be described only to such an extent as is necessary for the understanding of the invention. Referring now to  FIG. 2 , a sealed hub-bearing assembly for agricultural applications comprises a hub-bearing unit, indicated overall at  10 , and an associated sealing device  20 . 
     The hub-bearing unit  10  comprises:
         a rotatable outer ring  11  forming on one side a radial flange  12  on the opposite side a cylindrical seat  13 ;   a pair of inner stationary rings  16 ,  17  which are able to be tightly mounted side to side on a central axle  40 , partly shown in  FIG. 4 , projecting from the frame (not shown) of an agricultural machine; and   a dual set of bearing balls  14 ,  15  which are interposed between the outer ring  11  and the stationary rings  16 ,  17 .       

     The sealing device  20  is fitted within the seat  13 . As shown more clearly in  FIG. 4 , it is attached to one of the inner bearing rings  17 , namely the inner ring fitted towards the proximal part of the axle  40 . In this context, the term “proximal” denotes an axially inner location that in use will be near the supporting arm of the frame, whereas “distal” indicates an axially outer location towards that end of the axle which is near the tilling disc. 
     The axle  40  is formed with a cylindrical portion  41  on which the inner bearing rings  16 ,  17  are inserted, and two annular steps  42 ,  43 . The first annular step  42 , of smaller diameter, defines a radial shoulder  44  against which the inner bearing rings are axially clamped. The second annular step, of larger diameter, defines an annular seat  45  for the sealing device  20 . 
     The sealing device  20  includes a resilient annular gasket  32  of elastomeric or rubber-like material, and an annular metal stiffening insert  28  which has a substantially L-shaped axial cross section and supports the gasket  32 . The insert  28  has a cylindrical portion  28   a  which is coaxial to an axis x of rotation of the hub-bearing unit  10  and a flanged portion  28   b  which is integral with the portion  28   a  and is perpendicular to the axis x from which it extends towards the periphery of the sealing device  20 . 
     The gasket  32  is provided with an annular bulge or protrusion  34  and with a set of parallel, radially outwardly extending lips  33  (three in the illustrated example) that are arranged to slide against the inner cylindrical wall  22  of the outer bearing ring  11 , thereby sealingly bridging the annular space between the inner ring  17  and the outer ring  11 . All the lips  33  are outer radially bounded by a common cylindrical surface  33   s  in sliding contact with the seat  13 , and have three different radial lengths: the shortest lip  33   a  is placed nearby the portion  28   b  and the longest lip  33   c  is placed axially far from the portion  28   b  and is provided with a flat annular surface  33   d  substantially parallel to the portion  28   b.  It should be noted that in the appended drawings the gasket  32  is depicted in its non-deformed condition. 
     As best seen in  FIGS. 3 and 4 , the gasket  32  comprises a body  32   a  which is axially delimited by a surface  32   s  and is integrally coupled with the insert  28 . The surface  32   s  is parallel to the portion  28   b  and faces the hub-bearing unit  10  in its assembled position. The protrusion  34  extends in a somewhat conical direction from the surface  32   s  and comprises a root portion  34   a  which is tapered starting form the surface  32   s  and a distal finger  34   b  which forms with the surface  32   s  an annular undercut  34   c.  The root portion  34   a  and the distal finger  34   b  are both bounded by an external conical surface  34   s  which joins the surface  32   s  and defines together with the surface  32   s  and the surface  33   d  an annular cavity  35  the function of which is also to keep the lubricating grease within the hub-bearing unit  10 . 
     The protrusion  34  extends from the axially outer and radially inner part of the body  32   a  and is close to the portion  28   a  so that it can exploit the stiffness that the portion  28   a  gives the body  32   a  in that area in order to ensure a stable connection with the inner ring  17 . 
     The protrusion  34  is snap-fitted into the circumferential groove  18  in order to mount the sealing device  20  onto the hub-bearing unit  10  and in order to make the surface  32   s  to be adherent to the side surface of the inner ring  17  and to allow the inner ring  17  to be inserted in the undercut  34   c.    
     The sealing device  20  furthermore comprises resilient coating portions  46  and  47  which are coupled respectively with the portion  28   a  and the portion  28   b  to be pressed against the cylindrical  48  and, in some circumstances, also against the radial  49  sides of the annular seat  45 . 
     The coating portions  46  and  47  are provided with a number of slots  46   a  and  47   b  to improve elasticity of the same coating portions  46  and  47  and continuously surround the axle  40 , providing static sealing action around the axle and interrupting any leakage path towards the inner parts of the bearing unit. The slots  46   a  are circumferentially spaced from each other and are parallel to the axis x, while the slots  47   a  are perpendicular to the axis x and are also separated by the relevant slots  46   a.    
       FIG. 5  shows a preferred embodiment of the sealed hub-bearing unit  10  wherein the sealing device  20  further includes an annular disc  50  which is preferably made of sheet steel and is placed axially in front of but not in contact with the annular gasket  32  in order to define a labyrinth seal. 
     The disc  50  comprises a fixing portion  51  which is defined by a folded annular metal sheet and it is suitable to be mounted in the seat  13 , and a flange  52 , which is integral with the fixing portion  51  facing the coating portion  47  and which has an inner diameter the dimensions of which are greater than the dimensions of an inner diameter of the coating portion  46 . The steel labyrinth  50  has a double function: firstly, it improves the overall sealing performance of the sealing device  20  by providing an additional labyrinth sealing action; secondly, it keeps the annular gasket  32  in its operative configuration while the sealed hub-bearing unit  10  ahs to be dismounted from the axle  40 . The fixing portion  51  is suitable to occupy the gap between the cylindrical wall  22  and the annular step  43 , and the flange  52  is suitable to occupy the gap between the coating portion  47  and radial  49  sides of the annular seat  45  without being in touch neither with the former nor the latter. 
     It will be appreciated that, by virtue of the above arrangement, the sealing device may be handled with the bearing unit. The axial size of the bearing assembly is kept very compact. Particularly, the inner rings need not be extended in order to provide a supporting surface for the sealing device. A conventional component, the side shield  39 , is dispensed with. Improved, watertight sealing action is provided between the bearing unit and its supporting axle.