Abstract:
A procedure for mounting of a hub bearing assembly having a rotatable hub, and a bearing unit having a stationary radially outer ring, and two bodies rolling crowns disposed between the radially outer ring and the hub. The assembly process involves the following steps: a) pressing-fit a first seal on the hub, b) mounting an axially external cage and the axially outside rolling bodies, in correspondence with a track of the axially outer hub, c) the radially outer ring assembly and inclination of the same outer ring of a predetermined angle with respect to the hub, d) mounting of the axially interior rolling bodies in correspondence with a track of the axially inner hub, and the radially outer ring alignment to the hub, f) snap insertion of the axially internal cage on rolling bodies and g) the pressing-fit a second axially internal sealing means on its seat.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Italian patent application no. 102015000013551 filed on Apr. 29, 2015, the contents of which are fully incorporated herein by reference. 
       TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates to a procedure for mounting a bearing group—flanged hub, i.e. the so-called third generation rolling bearing. The group in question is suitable for applications where the outer ring of the bearing is stationary, or for applications at a driving wheel of a motor vehicle. 
       TECHNICAL BACKGROUND 
       [0003]    They are already known to the state of the technique bearing groups—the flanged hub for driving wheels of motor vehicle applications. The document EP 2602123 A1, for example, describes a hub bearing unit, in this case asymmetrical, for the wheel of a motor vehicle, which includes a flanged hub rotatable around a rotation axis, a flange integral with the hub flanged and transverse to the axis of rotation, a stationary ring disposed radially outside of the flanged hub and provided with rolling tracks axially spaced from one another, and two rolling bodies crowns (for example, balls) arranged between the stationary ring and the flanged hub. The flanged hub integrally form a radially inner raceway for the ball bearing axially outer, while the radially inner raceway for the balls axially inner crown is formed on an inner ring of the bearing, radially outer planted on flanged hub. 
         [0004]    Such a realization, especially in the case of heavy duty applications in terms of load transmitted, entails considerable local loads between the bearing rings and rolling bodies; also does not permit to obtain large values of resistance of the bearing and its greater duration in the time. Finally, usually it presents important axial dimensions, due to the presence of a flange integral to the flange portion and the hub transverse to the axis of rotation. 
         [0005]    To increase the performance and especially the stiffness of the bearing is required to increase the distance of the pressure centers. This can be achieved by increasing the diameter of the circumference of the centers of the rolling bodies (the so-called “pitch diameter” or more simply “pitch”) of the bearing. Such solutions are already known and are developed in order to significantly improve the performance. The disadvantage connected to the increase of the “pitch” is that consequently also the volume and therefore weight dramatically increase with the “pitch-squared value”. This increase in weight can usually not be accepted by car manufacturers. 
         [0006]    A further improvement is to increase even more the diameter of the circumference of the centers of the rolling bodies so as to be able to enter inside the bearing constant velocity joint and integrate in a single piece the so-called bell of the joint with the hub, or with the inner ring of the bearing. Evidently, the integration of both components allows the reduction of weight and cost of the entire unit. And possible to further reduce weight and costs by integrating also the small inner ring of the bearing, the axially internal, with the bell of the joint. In other words, the hub also assumes the function of single inner ring of the bearing and the bell of the joint at a constant speed. 
         [0007]    The concept of single inner ring is already known in so-called third-generation bearings. The development of this feature foresaw the use of a single cage for both rolling bodies of the two tracks to be mounted at the axially inner side. This feature, the single cage, however, is not acceptable in current projects of bearing units that require more and more high performance In fact, the single cage can create several problems. During the operational conditions of the bearing often it happens that the contact angles of the two tracks with the corresponding rolling bodies (for example, spheres) may slightly differ relative to one another. Consequently, they also change the points of contact between tracks and balls and therefore also the diameters of the circumference of the same sphere centers (“pitch”). On an equal angular speed of the wheel, the linear velocity varies proportionally to the “pitch change”. In other words, the two rows of balls have different speed. The cage, which performs the function of keeping the distance between the rolling bodies, however, cannot be subjected to significant forces and as typical consequence, if it is exposed overloads, disintegrates or melts. 
         [0008]    The case of the so-called symmetrical bearing, i.e. with the same “pitch” for both crowns of rolling bodies is now analyzed. The drawbacks outlined above, are obviously also present in the case of asymmetric bearings. 
         [0009]    Therefore, the existing high-performance solutions, which adopt a single inner ring, require a new mounting procedure, compared to the standard applications now used. 
       SUMMARY OF THE INVENTION 
       [0010]    The object of the present invention is to provide a procedure for mounting of a hub bearing unit for application of the driving wheel of a motor vehicle, which is free from the drawbacks described above. The assembly process can be realized both in the case of bearings with symmetrical internal form, or with the same “pitch” for the two crowns of rolling bodies, both in the case of asymmetric bearings, or with different “pitch” between the two crowns of rolling bodies. 
         [0011]    According to the present invention there is described a procedure for mounting of a hub bearing assembly, having the characteristics set out in the appended independent claim. 
         [0012]    Additional embodiments of the invention, preferred and/or particularly advantageous, are described according to the characteristics set forth in the appended dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    The invention will now be described with reference to the accompanying drawings, which illustrate some examples of non-limiting embodiments, in which: 
           [0014]      FIG. 1  is an axisymmetric sectional view of a bearing assembly—of symmetric inner shape hub, mounted according to the process of the present invention, 
           [0015]      FIG. 2  is an axisymmetric sectional view of a bearing assembly—of asymmetric form internal hub, mounted according to the same procedure, 
           [0016]      FIGS. 3 and 4  show two successive phases of the bearing assembly mounting procedure—hub, 
           [0017]      FIG. 5  shows an alternative step to those illustrated in  FIGS. 3 and 4 , 
           [0018]      FIG. 6  shows a further stage of the same assembly procedure, subsequent to those of the preceding figures, 
           [0019]      FIG. 7  shows a constructional variant useful to facilitate the assembly phase of  FIG. 6 , 
           [0020]      FIG. 8  shows a terminal phase of the assembly process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring now to  FIG. 1 , a hub-bearing assembly according to a preferred embodiment of the invention is indicated as a whole with  10 . 
         [0022]    The assembly  10  includes a rotatable hub  20  and a bearing unit  30 . The hub  20 , as will be seen better hereinafter, is configured to also take the inner rolling loop function of the bearing bell and a joint of constant speed drive. Throughout the present description and in the claims, terms and expressions indicating positions and orientations such as “radial” and “axial” refer to the axis X of the central bearing rotation unit  30 . Expressions such as “axially outer” and “axially inner “are, however, referred to the mounted condition, and in this case, preferably, refer to a wheel side and, respectively, to a side opposite to the wheel side. 
         [0023]    The bearing unit  30  provides a radially outer ring  31 , stationary and two crowns of rolling bodies  32 ,  33 , in this example balls, interposed between the radially outer ring  31  and the hub  20  with radially inner ring function. For simplicity of graphic representation references  32  and  33  will be attributed both to individual spheres, both to the crown of spheres and in particular with  32  will indicate the ring of balls or the single axially outer sphere, while with  33  will indicate the ring of balls or the single axially inner sphere. Again for simplicity, we often use the term “sphere” used by way of example in the present description and in the accompanying drawings instead of the more generic term “rolling body” (and will also be using the same numerical references). It will be understood always that in place of the spheres it may be used any other rolling I cover (for example, rollers, tapered rollers, needles, etc.). 
         [0024]    In  FIG. 1  is shown the case of a symmetrical bearing, i.e. with the same “pitch” for both crowns of rolling bodies. What will be the in the following description is also applicable to the case of the asymmetrical bearing, shown in  FIG. 2 , where for simplicity we have used the same references. As can be seen the only substantial difference between the two types of bearing is that, while in the case of symmetrical bearing the radii R, R′ of the circumferences of the centers of the rolling bodies of the corresponding crowns  32 ,  33  assume the same value, in case of asymmetrical bearing the same rays differ between them. In the example in  FIG. 2 , in particular, the radius R of the circle of the centers of the rolling bodies of the crown  32 , axially outer, is greater than the radius R′ of the circumference of the crown of the rolling bodies of the centers  33 , axially inner. 
         [0025]    The radially outer ring  31 , preferably shaped in tubular form axially extended, defines internally the raceways  34 ,  35  to the corresponding rolling bodies of the crowns  32 ,  33 . 
         [0026]    The radially outer ring  31  has a radially outer cylindrical surface  31   a  adapted to mate with a cylindrical seat formed in a fixed member of the vehicle, such as a pillar of a suspension, of a known type and not shown in FIG. The cylindrical surface  31   a  extends for the entire axial dimension of the radially outer ring  31  and has an axial dimension of the order of magnitude of that of the cylindrical seat of the upright. 
         [0027]    The rolling bodies of the crowns  32 ,  33  rotate, as well as on the ring radially outer  31 , on a central tubular portion  21  of the hub  20  which defines a rolling track  36  for the rolling bodies of the axially outer crown  32  and a track of  37  for the rolling of rolling bodies of the crown  33 , the axially inner. The crowns  32 , rolling bodies  33  are kept in position by corresponding cages  38 ,  39 , namely a first cage  38 , axially outer, for the rolling bodies  32  and a second cage  39 , axially inner, for the rolling bodies  33 . A first sealing means  40  seals the bearing unit from the axially outer side, being planted on a cylindrical surface  21   a,  a radially outer, of the tubular portion  21  of the hub  20  and a second sealing means  41  seals the bearing unit from the axially side internal. 
         [0028]    The hub  20  also defines a shoulder  22 , on the axially inner side, and a flange portion  23  axially outer. The flange portion has a plurality of axial fixing holes  24 , the axes of which are arranged along a circumference of radius r, with respect to the axis of symmetry X. These holes are the seats for the same number of fixing means (such as captive bolts, not shown in the figure) that connect in a known manner an element of the motor vehicle wheel, for example the brake disc (also of known type and not shown in the figure), to the hub  20 . 
         [0029]    Advantageously, a bushing  50  for centering the wheel of the motor vehicle can be realized by means of a metal sheet, for example of steel, and coupled to the flange portion  23  of the hub, preferably by means of a simple pressing-fit operation. 
         [0030]    The bearing unit  30  is made so as to obtain the radii R, R of the circumferences of the centers of the rolling bodies of the corresponding crowns  32 ,  33  slightly lower than or substantially equal to the radius r of the circumference of the fixing axes of the holes  24 . This substantial geometrical equality, in the case of asymmetrical bearing, will be verified at least with the radius R of the circle of the centers of the rolling bodies  32 , axially external, ie closest to the wheel of the motor vehicle brake disc. By means of this solution, the flanged hub assumes a conformation in the manner of a rotor, i.e. its flange portion is much reduced. The above solution is obtained by increasing the radius R, R′ of the circumferences of the centers of the rolling bodies and of course, leaving unaltered, since the case of a constraint of the motor design, the radius r of the circumference of the fixing axes of the holes  24 . 
         [0031]    The transmission of the motion from a drive shaft of a motor vehicle transmission assembly (not shown) is guaranteed by a constant velocity joint  60 . In particular, the outer bell of the coupling  60  is integrated in the hub  20  which in its axially inner terminal part  61  He defines the track  62  of the joint. 
         [0032]    The procedure for mounting the bearing assembly—of  FIG. 2  the hub is illustrated with reference to  FIGS. 3 to 8 , relating to the type of asymmetrical bearing. In the case of symmetrical bearing ( FIG. 1 ), as will be evident in the following, the assembly process can be equally applied, unless a variant which will be specifically described and shown. 
         [0033]    In more detail, in  FIG. 3  it can be observed that, starting from the hub with availability of inner ring function, the first sealing means  40  is planted on the rotatable hub  20 , in particular on the cylindrical surface  21   a  of the central tubular portion  21 . Subsequently, is mounted, always from the end of the axially inner hub, the axially outer cage  38  in correspondence with the axially outer runway  36 . With reference to  FIG. 4 , it should be noted that in order to be able to mount the cage  38  on the track  36  of the hub  20  (or the inner ring of the bearing), a minimum radial clearance between the diameter B of the shoulder  22  of the hub must be guaranteed  20 , the axially inner side and the inner diameter E of the cage  38 . In other words, will be B&lt;E. Evidently, the same report will have to be guaranteed also to the cage  39 , an axially inner. 
         [0034]    In case the diameter B of the axially internal shoulder  22  is greater than the minimum diameter A of the groove that defines the track  36 , but is less than the inner diameter E of the cage  38 , the cage it can easily be mounted on the track  36  of the hub. The rolling bodies  32 , axially external, instead, do not have sufficient space to be inserted from the axially inner side and therefore must be subsequently mounted to the cage, as shown in  FIG. 4 . This mounting method is suitable both to a symmetrical bearing, to both an asymmetrical type bearing. 
         [0035]    With reference to  FIG. 5 , in the case in which the diameter B of the axially inner shoulder  22  is less than or equal to the minimum diameter A of the groove that defines the track  36 , there is enough space to mount on the track  36  of the hub  20  the group cage  38 —rolling bodies  32 , previously pre-assembled. The abovementioned condition that allows this mounting alternative can be satisfied only in the case of asymmetric bearings, whereas it can never be so in the case of symmetrical bearings, where the diameter B will always be greater than the diameter A. 
         [0036]    Below and with reference to  FIG. 6 , mounting the radially outer ring  31  is disclosed. The outer ring is placed in position and tilted with respect to the hub  20  (inner ring) in order to create enough space for the subsequent insertion of the rolling bodies  33 , axially interior. 
         [0037]    For easily realizing an adequate inclination of the outer ring, the sealing means  40 , the axially outer, must be sufficiently flexible. 
         [0038]    Another way to facilitate the inclination of the radially outer ring  31  is to remove a bit of the hub  20  material from the bottom of the track  36 , thus creating a small step  36   a,  as shown in  FIG. 7 . 
         [0039]    Once settled all the rolling bodies  33 , it will be possible to align inner ring or outer ring and the hub so that the aforementioned rolling bodies  33  can be distributed uniformly along the entire circumference. 
         [0040]    The number of rolling bodies that can be mounted on the track  37  with the assembly process just described is certainly lower than the maximum number achievable with standard bearing unit, provided, in other words, of two radially interior rings. With the new process will be mounted a number of balls equal to almost half. As is known, the number of spheres heavily influences the performance of a bearing and especially its useful life. In the case of standard bearing, having a small value of the “pitch”, this reduction of the number of balls would not be acceptable. Conversely, for a given application and load conditions, the bearing described here has a higher value of the “pitch” and, accordingly, can accommodate a larger number of balls. However, for the same working conditions, a greater number of balls is not necessary. Therefore, even if the number of balls that can be inserted by tilting the outer ring is less than the maximum number of balls applicable, the performance of the bearing is not penalized if the number of balls used is next to that used in the standard bearing. 
         [0041]    With reference to  FIG. 8 , the cage  39 , an axially inner, is then inserted to snap from the axially inner side of the rolling bodies  33 , which are held in position between them equidistant from a specific tool to “comb.” To avoid any contact between the cage  39  and shoulder  22 , it is important that the diameter B of the shoulder  22  is less than the internal diameter E of the cage  39 , reduced by twice the value of a radial distance of security C. In other words, It must be: 
         [0000]        B&lt;E− 2* C    
         [0042]    E′ to be observed that the same condition will have to be applied to the cage  38 , axially outer, both with respect both to the radially outer  31 , both with respect to the hub  20 , to ensure a minimum radial play with respect to these components. 
         [0043]    As a last step of the process the second sealing means  41 , axially inner, is planted on its premises, from the axially inner side. 
         [0044]    Thanks to the new assembly process, as defined, you can use these new bearing solutions whose performance is greatly improved compared to the standard solution. Since it is increased the “pitch” of the spheres, is also increased the distance between the pressure centers, with very positive effects in terms of stiffness. 
         [0045]    The useful life of the bearing is not subject to penalties, since the number of balls used is comparable with that required by the standard solutions. On the contrary, the weight of these solutions was reduced greatly, having regard to the compactness of the realized solution, considered as a whole. In fact, while they are bearing-coupling constant speed remains substantially the same weight, to the upright of the suspension can delete a remarkable amount of material. 
         [0046]    Finally, not negligible are also the benefits for having reduced the costs of the solution and the total number of components. 
         [0047]    In addition to the embodiments of the invention, as described above, it is to be understood that there are many further variants. It must be understood that these embodiments of implementation are only illustrative and do not limit the invention or its applications, nor its possible configurations. On the contrary, although the description above makes it possible to man craft of the implementation of the present invention at least one of its second configuration example, it should be understood that numerous variations are conceivable of the components described, without that for this will come out from the object of invention, as defined in the appended claims, interpreted literally and/or according to their legal equivalents.