Patent Publication Number: US-2006019757-A1

Title: Homokinetic joint-hub unit for the wheel of a motor vehicle

Description:
DESCRIPTION  
      The present invention relates to a homokinetic joint-hub unit for the wheel of a motor vehicle.  
      In order to provide a better understanding of the problems and technical solutions which are currently well known in relation to the coupling between a homokinetic joint and a hub of a wheel, a brief description of a unit of a traditional type will follow, with reference to  FIG. 1  of the attached drawings.  
      With reference to  FIG. 1 , a wheel hub unit is shown in which a homokinetic joint  1  is coupled, in such a way that it can rotate, to a bearing-hub unit  2 ,  3  by means of an intermediate race  4  which is mounted on the spindle  5  of the hub. The intermediate race is coupled in order to rotate with the homokinetic joint by means of an axial toothed section of a ribbed coupling  6 . An elastic race  7  which is housed in two circular throats  8 ,  9  formed respectively in the homokinetic joint  1  and on the intermediate race  4  axially connects the latter to the homokinetic joint. The intermediate race  4  is fixed to the spindle of the hub by means of an additional ribbed coupling  10  with the spindle and by cold plastic deformation of a border  11  of the spindle or, alternatively, by means of a line of welding.  
      Other examples of ribbed couplings between a homokinetic joint and a hub are described, for example, in US-6 022 275, IT-1 281 365, US-4 893 960, US-5 853 250, EP-0 852 300.  
      Ribbed couplings have some disadvantages in that they require precise tolerances and, however, leave undesirable levels of play, so that some of the axial teeth, due to the fact that they have to support high levels of pressure, are subject to detrimental peaks of tension. In order to eliminate the play in a circumferential direction, slightly spiral shaped teeth have been suggested, which, however, require forced coupling and are therefore more difficult to produce. In addition, the teeth are subjected to a thermal treatment which inevitably produces distortions, so that it is necessary to carry out complicated mechanical working before coupling the two ribbed parts together.  
      The aim of the present invention is to produce a perfected hub-homokinetic joint unit, which is capable of overcoming all the disadvantages and technical limitations which have been described above.  
      This and other aims and advantages, which will be better dealt with below, are included according to the present invention of a hub-homokinetic joint unit and a bearing-hub unit as described in the attached Claims. In an extremely brief summary, an intermediate race of the bearing-hub unit is coupled to the homokinetic joint in order to rotate together with the latter by means of corresponding lobed interface surfaces, preferably of an oval or spiral shape, on a plane of perpendicular section in relation to the rotation axis of the hub. 
    
    
      Some non-limiting forms of embodiment of the present invention will now be described, with reference to the attached drawings in which:  
       FIG. 1  is an axial section view of a hub-homokinetic joint unit of a well known kind;  
       FIGS. 2 and 3  are two axial section views of a hub-homokinetic joint unit according to a first preferred form of embodiment of the present invention in two different operating conditions;  
       FIG. 4  is a radial section view according to the line IV-IV which is shown in  FIG. 2 ;  
       FIG. 5  is an axial section view of a second preferred form of embodiment of the present invention;  
       FIG. 6  is an axial section view of a third preferred form of embodiment of the present invention;  
       FIG. 7  is a radial section view according to the line VII-VII which is shown in  FIG. 6 ; and  
       FIG. 8  is a radial section view of a fourth preferred form of embodiment of the present invention. 
    
    
      With reference to  FIGS. 2 and 3 , and using the same reference numbers in order to indicate the same or corresponding parts which have already been described with reference to  FIG. 1 , a hub  3  for a wheel of a motor vehicle is mounted in such a way that it can rotate around a rotation axis x of a suspension (which is not illustrated) of the vehicle by means of a bearing  2  with a double series of rolling elements  12  e  13 , which in this example are spheres. The hub  3  is coupled in such a way as to rotate together with a homokinetic joint which is indicated with the number  1 , according to methods which will be described in detail below.  
      The hub  3  forms on the axially inner side a tubular portion or spindle  5  which ends in an annular border  11 , and on the axially outer side a radial flange  14  for mounting a wheel, which is not illustrated.  
      The hub  3 -joint  1  unit is supported by a mount (which is not illustrated) of the suspension connected to a radial flange  15  of a fixed outer race  15  of the bearing  2 . The spindle  5  axially projects beyond the axially inner end of the race  16 , and is of a limited thickness in such a way that the annular border  11  may undergo cold deformation for rolling.  
      On the inner surface of the race  16  two external rolling tracks  17  and  18  are obtained for the two series of spheres  12  e  13 , while the two corresponding inner tracks  19  e  20  are formed, one, directly on the hub  3  and, the other, on a separate race  21  which is shrink fit onto the spindle  5 . According to possible variations, which are not illustrated, the spindle  5  may be hollow, and that is with a central cavity which opens at both the axial ends, and/or the inner tracks  19  and  20  may be formed on respective separate races and shrink fit onto the spindle of the hub.  
      On the inner axial end of the spindle  5 , next to the race  21 , there is an intermediate race  4  which is shrink fit in non-rotatable fashion and which serves for transmitting the driving torque from the joint  1  to the hub  3 . In the examples which are shown in  FIGS. 2 and 3 , after the intermediate race  4  has been mounted on the spindle  5 , the border  11  of the spindle is radially folded and tightly cold headed by plastic deformation, by means of rolling, against the radial wall  23  of the race  4 . In this way, the race  4  is axially blocked on the hub  3 , axially pre-loading the bearing-hub unit  2 ,  3 .  
      With reference also to  FIG. 4 , the relative rotation between the race  4  and the hub  3  around the axis x is prevented by the congruent shape of the interface surfaces of these two surfaces, and that is the radially external surface  24  of the spindle and the radially internal surface  25  of the intermediate race  4 . These interface surfaces  24  and  25  have the same smooth non-circular shape but with rounded lobes, preferably of a substantially spiral shape on a plane of radial or perpendicular section in relation to the rotation axis x of the hub. In similar fashion, the driving torque is transmitted from the homokinetic joint  1  to the intermediate race  4  thanks to the fact that the interface surfaces  26 ,  27  between these two transmitting bodies also have the same spiral shape, or congruent spiral shapes, on a plane of radial section.  
      In addition, as is illustrated in the examples shown in  FIGS. 2 and 3 , the radially external surface  26  of the intermediate race  4  and the radially internal surface  27  of the joint  1  are respectively convex and concave on a plane of axial section in order to permit a certain misalignment between the rotation axis x and of the hub and the rotation axis x′ of the drive shaft. The coupling of the surfaces  26  and  27  also ensures reciprocal axial blocking between the joint  1  and the intermediate race  4 , without any need for additional blocking means. As is schematically illustrated in  FIG. 4 , the dome of the joint  1  is advantageously formed from the union of two halves  1   a ,  1   b  which are united by connecting means  1   c  in order to permit mounting on the intermediate race  4 .  
      The variation which is illustrated in  FIG. 5  differs from that which is shown in  FIG. 1  due to the fact that the axial blocking of the intermediate race  4  on the hub is carried out by means of a seeger race  29  which is partially inserted inside a throat  30  formed on the end part of the spindle  5 .  
      In the variations which are shown in  FIGS. 6 and 7 , the interface surfaces between the homokinetic joint, the intermediate race and the spindle of the hub comprise two pairs of facing surfaces  27 ,  26  and  25 ,  24  of a conical shape which tapers towards the axially internal side and spiral sections on a plane of radial or perpendicular section in relation to the rotation axis x of the hub, as is illustrated in  FIG. 7 . An elastic race  7 , housed in two spiral throats  8  and  9  formed respectively on the homokinetic joint  1  and on the intermediate race  4 , axially connects the latter to the homokinetic joint. The axial blocking of the intermediate race  4  may be obtained either by means of rolling the end border  11  of the spindle, or by means of an additional seeger race (like that which is indicated with the number  29  in  FIG. 5 ), or by other means which are well known to experts in the field.  
      In the variations which are shown in  FIGS. 6 and 7 , the interface surfaces between the homokinetic joint, the intermediate race and the spindle of the hub comprise two pairs of facing surfaces  27 ,  26  and  25 ,  24  of a conical shape which tapers towards the axially internal side and spiral sections on a plane of radial or perpendicular section in relation to the rotation axis x of the hub .  
      In the variation which is shown in  FIG. 8 , the interface surfaces between the homokinetic joint, the intermediate race and the spindle of the hub comprise two pairs of facing surfaces  27 ,  26  and  25 ,  24  of a conical shape which tapers towards the axially internal side and presenting a radius R of angularly variable dimensions with continuity on a plane which is transverse to the axis x.  
      In particular, each pair of surfaces  27 ,  26  and  25 ,  24  comprises a number N1 of convex portions  50  in relation to the axis x, and a number N2 of concave portions  60  in relation to the axis A. The values of the numbers N1 and N2 depend on the necessary construction and planning characteristics, and may be equal to each other, as in cases of this kind, or different from each other. In particular,  FIG. 8  illustrates a case in which both the number N1 and the number N2 have a value which is equal to three and the portions  50  and  60  are alternated in relation to each other around the axis x. Alternatively, and in a manner which may be easily understood from the foregoing description, the pairs of surfaces  27 ,  26  and  25 ,  24  may each be provided with only a single convex portion  50  which is arranged between two relative concave portions  60  contiguous in relation to each other.  
      In addition, although each pair of surfaces  27 ,  26  and  25 ,  24  follows, as shown in  FIG. 8 , the same law of variation of the radius R and has the same value for the numbers N1 and N2 as the other pair of surfaces  25 ,  24  and  27 ,  26 , it is also possible to produce each pair of surfaces  27 ,  26  and  25 ,  24  with a value for the numbers N1 and N2 which is equal to or different from the value of the numbers N1 and N2 of the other pair of surfaces  25 ,  24  and  27 ,  26 , as it is also possible to produce each pair of surfaces  27 ,  26  and  25 ,  24  with a conical shape in relation to the axis x of dimensions which are equal to or different from the conical shape of the pair of surfaces  25 ,  24  and  27 ,  26 .  
      As can be appreciated, the present inventions eliminates the problems which are connected to the traditional ribbed couplings which were discussed in the introductory part of this description. The rounded lobe shape of the interface surfaces between the joint and the hub permit the uniform distribution of contact pressure over a wider area, thus avoiding peaks of tension. The assembly of the unit is simplified. Any eventual distortions caused by the final thermal treatment do not prejudice the coupling of the hub to the joint. In any case the rounded, broad shape of the interface surfaces simplifies any eventual mechanical finishing work. Such surfaces may be easily and precisely obtained by means of grinding a numerically controlled lathe and/or by means of grinding.  
      Naturally, while the principle of the present invention holds good, details pertaining to production and the forms of embodiment may be varied in relation to what has been herein described and illustrated, without in any way changing the context of the present invention. In particular, the above-described interface surfaces may be of an oval shape, similar to the shape of an egg and that is with a single non-circular lobe, or, as illustrated, of a spiral shape with two rounded lobes, or with three or more lobes.