Patent Abstract:
Wheel disc, comprising a radially outer circular assembling part, a radially inner fixing and centering part with a bearing region comprising a given number of fixing apertures and ending radially inwardly with a centering vent, and arms connecting the inner and outer parts, each arm being disposed substantially opposite to one of the fixing apertures and the radially inner free edges of the radially outer circular part defining with the lateral free edges of the arms perforations, in which, in order to reinforce each arm mechanically, a pocket is housed, set back axially inwards relative to the outer face of the disc and in which a yoke connects each arm to the centering vent.

Full Description:
This application is a continuation of International Application PCT/EP02/13078 filed on Nov. 21, 2002 and which claims priority of Patent Application Serial No. 01/15560 filed in France on Nov. 23, 2001, the entire content of which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a motor vehicle wheel disc with arms, in particular for passenger car, formed in one piece from embossed sheet metal, which represents an excellent compromise in terms of weight, cost, style or freedom of possible added styling (decorative wheel cover for example). 
   In the designing of a sheet metal wheel for a motor vehicle, the general aim is to optimise the weight and cost of such a product. The development of embossing techniques, numeric simulation means, and materials has led to great progress over the last few years. However, the majority of products has remained within the concept of a substantially axisymmetric disc (i.e. one whose cross-sectional profile is virtually fixed in form), comprising perforations and sometimes embossing in the upper part. 
   This type of profile does not give the product a very enhanced style or image, which explains in most cases why manufacturers resort to a decorative wheel cover placed on the product when it is mounted on the vehicle. 
   One can count several attempts to create style directly from the sheet metal forming the wheel disc by forming deep embossed areas forming stiffeners and/or a particular assembly of the disc with the rim (under-seat, “full-face” assembly (i.e. disc whose radially outer edge includes the outer flange and seat of the rim), with the rim welded at the end, etc.) and sometimes associated with effects connected to painting. These attempts have not yet led to generalisation for reasons of excessive weight or difficulties in execution. 
   In general, the market for styled wheels for passenger cars is confined to the use of aluminium alloys. The process of manufacture (moulding, forging etc.) of these discs allows very broad freedom of style at reasonable weights, but has the disadvantage of being 4 to 8 (even 10) times more expensive. 
   The specification of DE 201 08 995-U discloses a wheel whose disc is formed from a single piece of embossed sheet metal, with an outer face and an inner face. This disc has a radially outer circular assembling part intended to be connected to a rim, a radially inner part for fixing and centering to a wheel hub with a bearing area having a given number of fixing apertures and ending radially inwardly with an edge which is turned axially outwardly or centering vent (aperture), and spokes connecting the inner and outer parts, each arm being disposed substantially opposite to one of the fixing apertures and the radially inner free edges of the radially outer circular part defining perforations with the free lateral edges of the arms. This disc has a substantially circular, plane bearing region and each arm comprises two lateral stiffening elements which extend radially from the bearing area to the radially outer circular assembly part and are disposed on either side of an intermediate strip axially set back towards the interior of the disc. 
   Although freedom of styling either bare or with an attached part (decorative wheel cover for example) is apparently obtained, such a disc has the disadvantage of requiring a relatively thick sheet metal to be able to withstand the forces to which it is subjected during operation, in particular in the joining region between the arms and the radially inner part for fixing and centering the disc. 
   Hereinafter:
         the “outer face” of the disc will refer to the surface of revolution generated by rotation about the axis of rotation of the disc of the regions of the disc disposed axially outermost;   the “internal face” of the disc, to the side of the disc oriented inwards, in particular the internal face of the bearing region is intended to come into contact with the outer surface of the wheel hub to which the disc is to be fixed;   and the “external face” of the disc, to the side of the disc oriented outwards, which side is visible when the wheel is mounted on the vehicle.       

   SUMMARY OF THE INVENTION 
   The object of the invention is a similar wheel disc in which, in order to reinforce each arm mechanically, a pocket is housed in a position set back axially inwardly relative to the outer face of the disc, the pocket extending radially from the centering vent and including a fixing aperture and the adjacent part of the bearing region, along the central part of the arms and as far as the outer circular assembling part and in which the outer face connects each arm to the centering vent by a yoke offset axially outwardly relative to the bearing region. 
   The particular geometry of the radially inner part for fixing and centering the disc has the advantage of reducing the stress peaks withstood by this region during operation. 
   According to an advantageous embodiment, and taking into account a median axial plane between two adjacent fixing apertures, the axial distance separating the internal face of the yokes and the internal face of the bearing region is at all points greater than the initial thickness of the sheet metal forming the wheel disc. 
   Preferably, each pocket has a floor and a single closed side surrounding the floor. Each pocket therefore has a closed geometry. 
   According to a preferred embodiment, the arms have lateral edges turned down towards the inner face of the disc and have a section substantially in the shape of an M. It is advantageous if at a given radial distance, the lateral edges are offset axially outwardly relative to the inner face of the floor of the pocket of the arm. This arrangement has the advantage of limiting the consequences of pressure peaks on the arms during operation by preventing these pressure peaks from being transmitted to the more sensitive cut-out edges. 
   According to another preferred feature of the invention, the edges of the perforations are obtained by punching sheet metal and then folding down towards the internal face of the disc. This has the advantage of releasing a maximum of the perforated area and to ensure that no cut-out face is visible from the outer side. 
   Furthermore the aesthetic thus obtained is pleasing and the strong perforation lends, in addition to good ventilation of the brakes, considerable freedom of added style (decorative wheel cover). 
   The pockets may advantageously have a generally flattened oval shape with a width in the circumferential direction decreasing continuously from the fixing aperture to the radially outer circular part. In the same way, the pockets may have a depth which decreases continuously from the radially inner part to the radially outer circular part. The width, section and bending-resistance of the arms in the circumferential direction may also advantageously continuously decrease from the radially inner part to the radially outer circular part. 
   The object of these arrangements is to distribute the material in the best way in the arm where it is needed to reduce pressures during operation according to the stresses to which the arm is subjected. 
   Each bearing region about each fixing aperture may have at least two distinct bearing faces. Preferably, relative to the axis of a fixing aperture, the bearing region has a first bearing face disposed radially inward and two other bearing faces disposed axially outward and circumferentially on either side of the fixing aperture. 
   Advantageously, the floor of the pockets may have convex or concave regions. It may also have punched holes. Such a hole may be a standard perforation or act as a fixing for a styled part such as a decorative wheel cover. 
   The final shape of the arms and of the perforations of the discs according to the invention may be obtained simultaneously in one or more embossing operations. Preferably, after being cut out, the edges of the perforations are trimmed from an embossed part before being turned down. 
   The radially inner part of the centering vent may also comprise preferred bearing distances opposite to each fixing aperture or each yoke separating the fixing apertures. 
   Finally, the number of arms may be in particular 3, 4, 5 or 6. 
   The invention thus describes a wheel disc whose weight and method of manufacture are similar to those of a conventional steel disc optimised for a style approaching that of moulded or forged alloy discs. 
   The invention also has as a subject a wheel formed by the assembly of a rim and a disc according to the invention. 

   
     DESCRIPTION OF THE DRAWINGS 
     Wheel discs according to the invention will now be described by means of the attached drawing in which: 
       FIG. 1  is a perspective view of an assembled wheel having a disc according to the invention; 
       FIG. 2  is a view in axial section of the wheel of  FIG. 1  along the axis of a fixing aperture; 
       FIGS. 3(   a ) to  3 ( c ) show the development of the section of an arm of the center of the disc towards the exterior; 
       FIG. 4  is a view in section of the disc through the axes of two adjacent fixing apertures; 
       FIG. 5  is a perspective view of the internal face of the disc; 
       FIGS. 6 ,  7 ,  8  and  9  are enlargements of one of the fixing apertures of  FIG. 5  and show four modified embodiments of the bearing faces; and 
       FIGS. 10 ,  11  and  12  are partial views of  FIG. 5  and show modified embodiments of the centering vent. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a perspective view of the outer side (or external face) of an assembled wheel  1  having a disc  3  according to the invention and a rim  2 .  FIG. 2  is an axial section of the same wheel through the axis of a fixing aperture. The rim  2  usually comprises two outer  24  and inner flanges  25 , two outer  22  and inner seats  23 , and a well  21 . 
   The disc  3  is manufactured by moulding, in particular embossing, from a sheet metal blank composed preferably of high-strength steel or aluminium. The essential components of the disc  3  are a radially outer circular assembling part  4 , a radially inner centering and fixing part  5 , and linking arms  6  between the parts  4  and  5 . 
   The part  4  is a assembling region with the rim  2 , as  FIG. 2  shows, and the radially outer edge  41  of this assembling part  4  has a direction substantially parallel to the axis of rotation of the disc  3 . This assembling part  4  is circular, i.e. circumferentially continuous. Assembling on the rim  2  is usually effected by soldering. This may take place at the well  21  of the rim  2 . It is also possible to effect assembling under the outer seat  22  of the rim  2 . 
   The fixing and centering part  5  in this case has a bearing region  51  with five fixing apertures  52  and a radially inner edge curved axially outward in the form of a collar or centering vent  53 . The fixing apertures  52  are conceived to receive fixing bolts of the disc to a wheel hub of the vehicle. The internal face of the bearing region  51  has a bearing face  54  intended to come into contact with the hub of the vehicle. This bearing face  54  corresponds to the plane P. As  FIG. 4  shows, with a section of the disc  3  between two adjacent fixing apertures  52 , the bearing region  51  as well as the bearing face  54  are interrupted between two fixing apertures by a yoke  55 . Preferably, the axial distance h between the plane P of the bearing face  54  and the inner face of the yoke  55 , in its central region, is greater than the thickness e of the starting sheet metal blank. This thickness e is between 3 and 6 mm according to the load that the wheel in question is to bear. Each yoke is defined by a bent portion of the piece of sheet metal and forms a generally concave side facing axially outwardly, and a generally convex side facing axially inwardly. An axially inner surface of the yoke is offset axially outwardly from the plane P. 
   The arms  6  connect the parts  4  and  5  and ensure the transmission of forces between these two parts of the disc  3 . The lateral edges of these arms  6  together with the radially inner edge of the assembling part  4  define large perforations  7 . 
   The problem of realising a wheel disc  3  having large perforations  7  is to make the arms  6  which laterally define these perforations sufficiently resistant to the fatigue stresses which arise during operation. 
     FIGS. 3(   a ) to ( c ) show the development of the section of an arm  6  of the joining region with the fixing and centering part  5  towards the assembling part  4 . It can be seen that the section of these arms  6  substantially has an M shape. The M profile is obtained by two outer zones  63  with two lateral edges  61  and a pocket  64  disposed at the center of the arm with a floor  65  and two adjacent sides  66 . The two outer regions  63  form part of the outer face of the disc. In the embodiment in  FIG. 1 , the pockets  64  have a generally oval shape and each include a bearing region  51  with a fixing aperture  52 . The side  66  surrounds part of the centering vent and thus completely surrounds the floor  65 , so that one could say the pockets are closed. The free edges of the cut-out  62  of the two lateral edges  61  of the arms  6  are folded down towards the inside of the disc, which completes the M profile. Preferably, the axially inwardly facing faces of the free edges of the cut-out  62  are also axially set back outwardly relative to the axially inwardly facing face of the floor  65  of the pocket  64  by a distance I, as is shown in  FIGS. 3(   a ) to  3 ( c ). The axial height of the reinforcement side  66  of the pocket  64  relative to the two outer regions  63  as well as the width of the floor  65  of the pocket  64  decrease progressively whereas the radial distance from the axis of the disc increases. This is shown in  FIGS. 3(   a ), 3 ( b ) and  3 ( c ). 
   In the example described, the assembly of the free edges of the cut-out of the arms  62  and the assembling part  42  all around the perforations  7  are folded down towards the internal face of the disc  3 . This makes it possible, in addition to lending additional rigidity, to increase the area of the perforations  7  and to give a more pleasing stylistic effect due to the disappearance of the areas where there are cut-outs, whose sharp ridges are not very attractive. 
   As the arms are subjected to high bending forces, the highest stresses during operation are concentrated on the external and internal faces of the disc. As the cut-out ridges are particularly sensitive to concentrations of stress, the fact that the folding back of the cut-out edges remains set back both with respect to the external and internal faces of the arms ensures that the stresses undergone by the cut-out ridges remain acceptable. 
     FIGS. 1 and 2  show that the adjacent outer regions  63  of two adjacent arms  6  join at the link with the fixing and centering part  5  and are extended in this part  5  by the yokes  55  as far as the vent  53 . 
   The fixing and centering region  5  is thus composed in the disc according to the invention of bearing regions  51  each surrounding a fixing aperture  52 , the adjacent bearing regions  51  being separated by yokes  55  as well as a centering vent  53 . 
     FIG. 5  shows a perspective view of the internal face of an embodiment of the disc  3  according to the invention. It shows in particular the fixing and centering part  5  having the five bearing regions  51  disposed around the five fixing apertures  52 , the five yokes  55 , and the centering vent  53 . 
     FIGS. 6 to 9  show four particular embodiments of the bearing faces  54  of the bearing regions  51 .  FIG. 6  shows a first embodiment in which the bearing face  541  is unique and surrounds the fixing aperture  52  with only one interruption which is radially outward relative to the fixing aperture. In  FIG. 7 , the bearing face is composed of two faces  542  disposed circumferentially on either side of the fixing aperture  52 . In  FIG. 8 , the bearing face is composed of four faces  543  and  544 , two faces  543  disposed circumferentially on either side of and radially outward relative to the axis of the fixing aperture  52  and two faces  544  disposed circumferentially on either side of and radially inward relative to the axis of the fixing aperture  52 . The bearing face of  FIG. 9  itself has three bearing faces, two faces  543  as above and one face  545  disposed radially inward relative to the axis of the fixing aperture  52 . The geometry of the bearing faces makes it possible to distribute the regions of concentration of stress in the bearing region and in the particular case of the disc  3  shown here, the embodiment in  FIG. 9  is preferred. 
   The forces transmitted by the bending of one arm are thus borne simultaneously by the two radially upper bearing faces  543 , the radially inner bearing face  545  (or  544 ), but also by the bearing faces of the adjacent fixing apertures  52  via the yoke  55 /vent  53  torque. 
     FIGS. 10 ,  11  and  12  show three particular embodiments of the geometry of the centering vent  53 .  FIG. 10  shows the usual embodiment with a circular centering vent  531 . The assembly of the radially inner face is in contact with the centering lug of the vehicle wheel hub. 
   For matters of ease of industrial execution as well as precision of centering, it may be advantageous to provide preferred centering ranges.  FIG. 11  shows a first preferred example. The centering vent  532  has five centering ranges  533  disposed to the right of the yokes  55 . In  FIG. 12 , the centering vent  534  has five centering ranges  535  disposed to the right of the fixing apertures  52 . 
   Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Technology Classification (CPC): 1