Abstract:
A pulley-bearing assembly provided with a pulley and a rolling bearing confined by respective coupling surfaces co-axial to each other and defining a groove there between; the rolling bearing being provided with two rows of rolling bodies having pitch diameters (D, Di) of different size, and a metallic ring being pressed into the groove and deformed so as to join the pulley with the bearing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to a pulley-bearing assembly. The present invention is particularly suitable, but not exclusively, in the technical field of transmission pulleys for distribution belts or chains of internal combustion engines, as well as driving belts for auxiliary engine components (injection pump, water pump, alternator, and so on). By means of the present invention a pre-mounted assembly can be realized, the assembly comprising a pulley, a flanged rolling bearing and suitable coupling means, interposed between the pulley and bearing. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the state of the art, pulley-bearing assemblies for pre-assembling a pulley together with its bearing are already known. For example, document U.S. Pat. No. 4,602,875 describes an assembly composed of a rolling bearing, a pulley and a pair of screens, which are pre-mounted, before being installed on a support cylindrical shaft. A rolling bearing, provided with a rotatable outer ring, a stationary inner ring and a row of rolling bodies between the two rings, is molded inside a pulley hub and is confined between the pair of screens, which are steadily fixed to the pulley. The screens are coupled to the pulley by means of tongues, which are realized in one piece with the pulley and easily detachable from the pulley. When the assembly is mounted, the screens are exactly located and steadily fixed to the stationary inner ring. Therefore, when the pulley starts rotating with respect to the inner ring, the tongues detach themselves from the pulley, thus allowing further rotations of the pulley itself. 
         [0003]    This and other known solutions, for example solutions that, instead of the outer ring molding on the pulley hub, present further coupling means, as screws, have some drawbacks. The main technical problem is the molding process (if existing), which is not suitable for engine applications. On the other hand, solutions presenting threaded couplings require the use and the management of a high component number. Moreover, the use of rolling bearing, provided with a single row of spheres, let the assembly be few resistant to support loads, which are transmitted by the distribution belt or the chain and/or by the auxiliary component belt. 
       INVENTION SUMMARY 
       [0004]    An aim of the present invention is to realize a pulley-bearing assembly, the assembly overcoming the above described inconveniences. 
         [0005]    According to the present invention, a pulley-bearing assembly is described, the assembly having the characteristics as in the enclosed independent claim. 
         [0006]    Further embodiments of the invention, preferred and/or particularly advantageous, are described according to the characteristics as in the enclosed dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A preferred embodiment of the invention will be now described, in an exemplifying and not limitative way, by reference to the enclosed drawings, in which: 
           [0008]      FIG. 1  schematically shows a turn belt structure of an internal combustion engine, incorporating a preferred embodiment of one or more pulley-bearing assemblies according to the present invention; 
           [0009]      FIG. 2  shows in a section in an enlarged scale, a first preferred embodiment of a pulley-bearing assembly according to the present invention; 
           [0010]      FIG. 3  shows, schematically and with parts taken away for clarity, a detail of the assembly of  FIG. 1 ; 
           [0011]      FIG. 4  shows in a section in an enlarged scale, a detail of  FIG. 3 , with the metallic ring taken away for more clarity; 
           [0012]      FIG. 5  shows in a section in an enlarged scale, a further detail of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The invention is related to a pulley-bearing assembly and is particularly suitable, but not exclusively, in the technical field of distribution belts or chains of internal combustion engines, as well as driving belts for auxiliary engine components. 
         [0014]    In  FIG. 1  is shown a typical turn belt structure  1  of an internal combustion engine, wherein the turn belt  1  comprises a belt  2  for driving the distribution components and a belt  3  for driving the auxiliary components. In particular, the belt  2  is driven by a pulley  4  of a crankshaft  4 ′ and transmits the motion to a pulley  5  of a cam shaft (known and therefore not shown) and to two pulleys  6 ′,  6 ″ respectively of an injection pump (known and therefore not shown) and a water pump (known and therefore not shown). For tensioning the belt  2 , a idler pulley  7 ′ is foreseen, while to complete the turn belt layout also a transmission pulley  8 ′ is present, where the transmission pulley will be better described hereafter. The driving belt  3  for auxiliary components is always driven by the pulley  4  of the crankshaft  4 ′ and drives two pulleys respectively of a power steering and an alternator (known and therefore not shown). For tensioning the belt  3 , also in this case a idler pulley  7 ″ is foreseen, as well as a pair of transmission pulleys  8 ″, which will be better described hereafter. 
         [0015]    In  FIG. 2 , with  10  is shown as a whole a pulley-bearing assembly, in which the pulley  8 , according to a not limitative embodiment, can be a transmission pulley of a turn belt, as shown in  FIG. 1 . Throughout the present description and in the claims, the terms and expressions indicating positions and orientations such as “radial” and “axial” are to be taken to refer to the axis of rotation A of the assembly  10 . Instead, expressions as “axially external” and “axially internal” are to be referred to the assembled condition, in this case, respectively, to an engine side and to an opposite engine side. 
         [0016]    The assembly  10  comprises, integrated each other, a pulley  8  and a rolling bearing  11 , which presents a rotation axis A and comprising:
       an inner ring  12 , stationary, co-axial to the rotation axis A;   an outer ring  26 , rotatable, located outside the inner ring  12 , and defining together with the inner ring  12  an annular gap  17 , which is sealed by a standard sealing element S;   two rows  13  and  14  of rolling bodies  15 , preferably spheres, which are interposed between the inner ring  12  and the outer ring  26 , to allow the rotation of the outer ring  26  with respect to the inner ring  12 , the rolling bodies being suitable to roll inside respective radially inner raceways  13 ′,  14 ′ and radially outer raceways  13 ″,  14 ″ respectively realized outside the inner ring  12  and inside the outer ring  26 .       
 
         [0020]    In particular, the two rows  13  and  14  of rolling bodies  15  are distinguished, with respect to the rotation axis A, in an axially inner row  14  and in an axially outer row  13 . While the axially outer raceway  13 ′ is in one piece with the inner ring  12 , the axially inner raceway  14 ′ is realized on the annular insert  32 . The annular insert  32  is engaged to the inner ring  12  by means of a rolled edge  34 , which is located at an inner ring  12  end and extends radially outwards and axially close to the annular insert  32 . 
         [0021]    In the above described rolling bearing  11 , a diameter D of the centers of the spheres  15  of the more axially external row  13  is greater than the diameter Di of the centers of the spheres  15  of the more axially internal row  14 . This is the configuration of an asymmetric rolling bearing, which presents functional advantages with respect to symmetric bearings, bearings having the diameter D equal to the diameter Di. In fact, let us remember the pressure center definition, in other words a point P, Pi located on the rotational axis A and determined by the intersection of the pressure line (line along with act loads on the rolling bodies) R, Ri with the axis A. In the case of an asymmetric bearing, being the diameter D greater than the diameter Di, it is possible to change the relative distance between the pressure centers P and Pi. In particular, in the case shown in  FIG. 2 , by increasing diameter D the point P moves away in an axially outer direction with respect to the point Pi and the distance between the pressure centers P and Pi increases. Therefore, the asymmetric bearing can be designed to balance loads between the two rows  13 ,  14  of spheres, by moving the pressure centers, in other words by varying the lever arms with respect to the application point of the external load. Therefore, asymmetry allows to reach, with same dimensions and external shape between asymmetric rolling bearing  11  and symmetric rolling bearing, a greater stiffness and stability. 
         [0022]    According to  FIG. 2 , the assembly  10  comprises an intermediate joint  30 , which joins the pulley  8  to the outer ring  26 , and is defined by a metallic ring  30 , inserted into a groove  140 , which is realized partly by a coupling surface  122 , which belongs to an external surface  150  of the outer ring  26  of the rolling bearing  11  and partly by a coupling surface  112 , belonging to an internal surface  160  of the pulley  8 . 
         [0023]    For a better understanding of the pulley-bearing assembly, a preferred embodiment will be now described, as schematized in  FIG. 3 , showing a portion  110  of the pulley  8 , a portion  120  of the outer ring  26  of the bearing and a metallic ring  30 . 
         [0024]    The portion  110  of the pulley is joined to the portion  120  of the outer ring by means of the metallic ring  30  which is press fit into a groove  140 , realized between a first coupling surface  112  of the portion  110  of the pulley and a second coupling surface  122  of the portion  120  of the bearing outer ring. The first and the second coupling surface  112 ,  122  are the contact surfaces with the metallic ring  30 . At least part of the groove  140  comprises an arcuate section  141 , defined by a radial clearance between the coupling surfaces  112 ,  122 . Among the surfaces, one of them  122  presents a concavity, the other  112  a convexity. 
         [0025]    By press fitting the metallic ring  30 , both portions  110  and  120  are locked in axial direction, both ways. Moreover, the assembly also gets a remarkable resistance to shearing stress in axial direction. The metallic ring  30  is press fit into the groove  140  from an incoming side of the groove, as shown by the arrow in  FIG. 3 . The metallic ring material is subjected to plastic strain, gets the shape of the arcuate section of the groove  140  and forms a joint between the portion  110  of the pulley and the portion  120  of the bearing outer ring. Preferably, to completely fill the volume of the arcuate section, the metallic ring  30  has a volume which is at least equal to the volume of the arcuate section. Moreover, the metallic ring  30  could have a thickness t, which is equal to the maximum radial clearance between the first and second coupling surface of the arcuate section. Moreover, the metallic ring  30  has a suitable ductility, to assume the needed plastic strain, and a suitable mechanical resistance, as a function of the engine application. Therefore, the choice of the metallic ring  30  material depends on the geometry of the groove  140 . Preferably, but not exclusively, the metallic ring  30  can be obtained by a tube or a sheet shaped material. 
         [0026]      FIG. 4  shows, in a greater detail, the shape of the groove  140 , inside of which the metallic ring  30  is inserted. 
         [0027]    The groove  140  is obtained between a portion  110  of the pulley  8  and a portion  120  of the bearing outer ring  26 . The groove  140  comprises an arcuate section  146 , defined by a clearance between a concave portion  149  of the coupling surface  122  and an opposite convex portion  148  of the coupling surface  112 . The groove  140  presents a second section  147 , defined by a clearance between a cylindrical portion  116  of the first coupling surface  112  of the pulley and a cylindrical portion  126  of the second coupling surface  122  of the bearing outer ring. Therefore, the groove  140  comprises an arcuate section  146  and a cylindrical section  147 . According to a practical embodiment, the arcuate section has an axial length x of about 5 mm and the cylindrical section has an axial length y ranging between 2 and 3 mm. 
         [0028]    The groove  140  could also have a simplified shape, in other words the groove can be provided with only an arcuate section, without the cylindrical section. Moreover, the groove  140  could also be obtained by means of a concave portion of the pulley coupling surface and a convex portion of the coupling surface of the outer ring; in other words, concavity and convexity are independent on the kind of component (outer ring or pulley). Finally, and with reference to  FIG. 5 , showing a detail of  FIG. 3 , the groove  140  can advantageously present, below the arcuate section  146 , a further small groove  170 , which can be filled by part of the ring  30  material, after assembling. 
         [0029]    Other than the embodiments of the invention, as above disclosed, it is to be understood that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary 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 at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.