Abstract:
A cast aluminum wheel includes a rim element having an annular configuration defining an axis and a central element extending radially outwardly between the axis and the rim element. The rim element includes a wall extending circumferentially around the axis between a proximal bead and a distal bead. The central element includes a plurality of spokes extending radially outwardly toward the proximal bead and meets proximate the axis with adjacent of the plurality of spokes defining a cooperative feature therebetween for providing stiffness to the wheel. The spokes progressively increase in volume in a direction toward the axis from the rim element thereby providing increased mass of the spokes proximate the axis relative to the rim element.

Description:
PRIOR APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 62/028,555, filed on Jul. 24, 2014. 
    
    
     TECHNICAL FIELD 
     The present invention is related generally toward a cast aluminum wheel. More specifically, the present invention is related toward a cast aluminum wheel having an optimized three dimensional configuration to increase stiffness and reduce mass. 
     BACKGROUND 
     Cast aluminum wheels have been in use on road vehicles for many years. The light weight and esthetically pleasing qualities of the cast aluminum wheel has made the wheel a desirable option on many mass production vehicles. However, cast aluminum wheels are often cost prohibitive due to the cost of manufacturing. Additionally, cast aluminum wheels do not provide enough mass savings to justify the added cost when fuel efficiency is not achieved. 
     During production, a cast aluminum wheel requires a significant amount of machining to form the wheel in a desired commercial configuration. A cast aluminum wheel includes a rim portion and a central element having spokes extending radially outwardly between a wheel axis and the rim portion. A typical spoke requires upwards of 80% machining to achieve required dimensional accuracy. Machining typically reforms those portions of the wheel into a desired configuration and providing an aesthetically pleasing finish. However, machining also results in sharp transitional edges between adjacent surfaces, which are known to be a source of initiation of stress fractures. In addition, spokes disposed on the wheel between a rim portion and a central element of the wheel are typically provided with substantial thickness and mass to provide necessary strength and stiffness to the wheel, which is cost prohibitive and contrary to efforts to reduce mass. 
     Thus, efforts to reduce mass of cast aluminum wheels has proven elusive due to structural fatigue, performance, styling and reduced stiffness, all of which are known defects from a reduction in the mass of the spokes. Therefore, it would be desirable to provide a wheel that has both increased stiffness and reduced mass. 
     SUMMARY 
     A cast aluminum wheel includes a rim element and a central element extending radially outward between a wheel axis and the rim element. The rim element includes a wall extending circumferentially around the axis between a proximal bead and a distal bead. A plurality of spokes extend radially outwardly toward the proximal bead and meet proximate the axis with adjacent of the plurality of spokes defining a cooperative feature for providing stiffness. The spokes progressively increase in volume in a direction toward the axis from the rim element thereby providing increased mass of the spokes proximate the axis relative to the rim element. 
     The cooperative feature between adjacent of the plurality of spokes provides necessary structural stiffness to eliminate cross sectional area of the spokes, and, therefore, the mass of each of the spokes. As such, the wheel of the present invention has provided an enhanced wheel structure without adding mass to the spokes, and therefore to the wheel as is commonly known. Furthermore, the configuration of the central element between a centrally located lug member where lug apertures are defined and the rim element has eliminated the need to machine surfaces of the central element as is known. Thus, the spokes are as-cast, or substantially as-cast, which enhances physical attributes, such as stiffness and durability. Therefore, the wheel of the present invention not only reduces mass and improves stiffness, but also eliminates a costly and time consuming machine operation known to present cast aluminum wheels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanied drawings, wherein: 
         FIG. 1  shows a perspective view of a first embodiment of the wheel of the present invention; 
         FIG. 2  shows a front view of the wheel of the first embodiment of the present invention; 
         FIGS. 2A, 2B, and 2C  show cross-sectional views through lines  2 A- 2 A,  2 B- 2 B, and  2 C- 2 C of  FIG. 2 , respectively; 
         FIG. 3  shows a rear view of the wheel of the first embodiment of the present invention; 
         FIG. 4  shows a cross-sectional view through an axis of the wheel of the first embodiment; 
         FIG. 5  shows a perspective view of a second embodiment of the wheel of the present invention; 
         FIG. 6  shows a rear view of the wheel of the second embodiment; 
         FIG. 7  shows a front view of the wheel of the second embodiment; 
         FIGS. 7A, 7B, and 7C  show cross-sectional views through lines  7 A- 7 A,  7 B- 7 B and  7 C- 7 C of  FIG. 7 ; 
         FIG. 8  shows a cross-sectional view through an axis of the wheel of the second embodiment; 
         FIG. 9  shows a front view of third embodiment of the wheel of the present invention; and 
         FIGS. 9A and 9B  show cross-sectional views of through lines  9 A- 9 A and  9 B- 9 B of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a wheel of the present invention is generally shown at  10 . The wheel includes a rim element  12  that defines an axis a ( FIG. 2 ). A central element  14  extends radially outwardly between the axis a and the rim element  12 . The rim element  12  defines a drop surface (or annular wall)  16  that extends between a distal bead  18  and a proximal bead  20  at a location that is disposed radially inwardly from the two beads  18 ,  20 . It should be understood by those of ordinary skill in the art that the proximal bead  18  is located outboard of a motor vehicle (not shown) and the distal bead  20  is located inboard of the motor vehicle. Furthermore, the drop surface  16  is defined as a cylindrical surface circumscribing the axis a in a known manner. 
     Referring now to  FIGS. 2, 2A-2C  the central element  14  includes a plurality of cooperable spoke pairs  22 . In this embodiment, each spoke pair  22  defines opposing, substantially L-shaped segments  24 , the combination of which define an opening  26 . Each substantially L-shaped segment  24  of the spoke pairs  22  define cross-sections progressing toward the axis a as best represented through sections  2 A- 2 A,  2 B- 2 B, and  2 C- 2 C of  FIG. 2 . The sections  2 A- 2 A,  2 B- 2 B, and  2 C- 2 C each show opposing first legs  28  having a generally common planar orientation and opposing second legs  30  defining generally parallel planar orientations. The first opposing legs  28 , as best represented in sections,  2 A- 2 A,  2 B- 2 B, and  2 C- 2 C of  FIG. 2 , define a generally constant thickness extending between the rim element  12  and the axis a. The second opposing legs  30  define a generally increasing thickness progressing from the rim element  12  toward the axis a. In this manner, the cooperable spoke pairs  22 , by virtue of increasing mass progressively toward the axis a, position the moment of inertia of the spoke pairs  22  toward the axis a. 
     Furthermore, the opposing L-shaped sections  24  define an opening  26 , the combination of which has proven to provide an enhanced stiffness to the wheel  10 . In this manner, the enhanced stiffness allows for the reduction of overall mass of the wheel  10 , which is contrary to prior art wheels where mass has previously been increased to achieve requisite stiffness and ride dynamics. It should be understood that the cooperable spoke pairs  22  of this embodiment are merely exemplary and should not be interpreted as limiting. For example, cooperable spokes can also take the form of adjacent spokes and are not limited to “pairs”. Adjacent spokes  14  define cooperative features, the configuration of which allows for reducing the mass of the spokes  14  while simultaneously enhancing stiffness of the wheel  10 . This is counterintuitive to the standard practice of increasing mass of the spokes as has been the method commonly used. 
     Referring now to  FIG. 3 , where a rear view of the wheel  10  is shown, it is readily apparent that the opposing first legs  28  of the L-shaped sections  24  converge to define a web  32  proximate a lug member  34 . The lug member  34  circumscribes the axis a at a location disposed radially inwardly from the drop surface  16 . The lug member  34  defines a plurality of lug apertures  36 . Each of the lug apertures  36  are disposed in the lug member  34  at a location that is circumferentially aligned with and radially inwardly of one of the plurality of cooperable spoke pairs  22 . It should be readily apparent that the plurality of cooperable spoke pairs  22  terminate at the proximal bead  18  at a distal end  38  and at the lug member  34  at a proximal end  40 . 
       FIG. 4  shows a section through the axis a of  FIG. 2 . This section shows the opposing second leg  30  increasing in thickness as it extends toward the axis a. Additionally, the web  32  is also visible in  FIG. 4 . The web  32  defines a part of the cooperable features between adjacent spokes  14 . A further unique element of the present invention is the reduction of machining relative to typical, prior art spokes of a cast wheel. 
     As shown in  FIG. 4 , the entire in-board side of the spoke is represented as an as-cast surface. This is unique when compared to prior art cast wheels that require the inboard side of spokes to be machined using turning operations resulting in machined bands defining a given spoke. By eliminating machining on the cooperable spoke pairs  22  a radius transition best seen in sections  2 A- 2 A,  2 B- 2 B, and  2 C- 2 C of  FIG. 2  are achieved resulting in a reduction in stresses known to cause reduced performance and even failure. Machining is limited to defining the lug apertures  36 , precision of beads  18 ,  20  and other features not relevant to stiffness or durability of the wheel  10 . Furthermore, flashing resultant from parting lines of manufacturing dies (not shown) are moved away from critical areas of the cooperable spoke pairs  22  to surfaces that are not visible from a front side of the wheel  10  where removal is easily performed without affecting the integrity of the as-cast, cooperable spoke pairs  22 . 
     A first alternative embodiment is shown in  FIGS. 5-8  where like elements are identified with like element numbers, but in the  100  series. The alternative wheel is generally shown at  110  of  FIG. 5 . The alternate wheel  110  is intended for use with a decorative overlay (not shown) like that disclosed in U.S. Pat. Nos. 6,346,159 and 7,097,730, the contents of which are incorporated herein by reference. To enhance design flexibility of the decorative overlay it is beneficial to reduce surface area required of structural elements without reducing performance of the wheel  110 . The alternate wheel not only enhances performance, but reduces mass by limiting the surface area required of the structural elements. 
     The wheel includes a rim element  112  that defines an axis a ( FIG. 6 ). A central element  114  extends radially outwardly between the axis a and the rim element  112 . The rim element  112  defines a drop surface (or annular wall)  116  that extends between a distal bead  120  and a proximal bead  118  at a location that is disposed radially inwardly from the two beads  118 ,  120 . It should be understood by those of ordinary skill in the art that the proximal bead  118  is located outboard of a motor vehicle (not shown) and the distal bead  120  is located inboard of the motor vehicle. Furthermore, the drop surface  116  is defined as a cylindrical surface circumscribing the axis a in a known manner. 
     Referring now to  FIG. 6 , the central element  114  includes a plurality of spokes  122 , in this embodiment numbering six. It should be understood to those of ordinary skill in the art that more or less spokes may be included depending on the application. Each spoke extends between a lug member  134  and the proximal bead  118 . The lug member  134  circumscribes the axis a at a location disposed radially inwardly of the drop surface  116 . A web  132  extends between adjacent spokes  122  so that each of the adjacent spokes  122  defines a progressing trapezoidal section toward the lug member  134 . The lug member  134  defines a plurality of lug apertures  136 . Each of the lug apertures  136  are disposed in the lug member  134  at a location that is circumferentially aligned with and radially inwardly of one of the plurality of spokes  122 . 
     Referring now to  FIG. 7 , a front view of the wheel  110  is shown. A cross-section of the spokes  122  is shown through lines  7 B- 7 B and  7 C- 7 C. It should be apparent that the mass increases as the spokes  122  progress radially inwardly toward the axis a moving the moment of inertia toward the axis a from proximate the rim element  112 . Line  7 A- 7 A is drawn through adjacent spokes  122  and through the web  132  providing a substantially W shaped cross section where a groove  133  transitions from the spoke  122  to the lug apertures  136 . The combination of the groove  133  and the web  132  increases the stiffness of the spokes  112 . 
     Referring now to  FIG. 8 , a cross sectional view of the alternative wheel  112  is shown. The spoke  122  is displaced from the distal bead  120  axially toward the proximal bead  118  so generally half of the cross-sectional thickness of the spoke  122  overlaps the annular wall  116  of the rim element  112 . Additionally shown on  FIG. 8 , the spokes  122  are substantially as-cast where the configuration of the spokes  122  is entirely or nearly entirely as cast. 
     As set forth above, contours of the prior art spokes are machined by a lathe to achieve desired dimensions. For the first time, a substantially as-cast spoke  122  is developed with the proper dimensional characteristics to provide enhanced stiffness. Both embodiments of the present invention require less than 15% machining. Further, these embodiments are contemplated to require less than 10% machining relative to the central element or spokes  114  is limited to flashing left from the die parting lines. As used herein, “as cast” includes spokes having only flashing resulting from die parting lines is machined and the cast configuration of the spokes is left unaltered. As in the prior embodiment, the parting lines, and therefore the flashing, are moved from the transitional elements and corners of the spokes  122  to a rear surface  135  of the wheel central element  114  eliminating the need to machine the in-board side of the spokes  122  on a lathe. Further, the deflashing does not substantially alter the dimension of the as-cast portion of the wheel. This differs significantly from the machine operation on a lathe, which is a two dimensional process leaving machined edges on the prior art structural spokes. 
     A still further embodiment is shown in  FIGS. 9, 9A and 9B  in which like elements with the above embodiments are identified in the  200  series. The third alternate wheel is shown at  210 . The wheel  210 , in this embodiment, includes a plurality of adjacent spokes  222 , each having a substantially T-shaped cross-sectional configuration believe to provide even further enhancements to stiffness and structure of the wheel. The alternate spokes  222  also progressively increase in mass toward the axis a to move the moment of inertia close to the axis a as should be evident in  FIGS. 9A and 9B . Each spoke  222  defines an opposing first leg  228  with an adjacent spoke  222  disposed in a similar plane and an opposing second leg  230  being disposed in planes that intersect at the axis a of the wheel  210 . For brevity, same elements of the wheel  210  of the third embodiment as those embodiments set forth above will not be described again. However, it should be understood to those of ordinary skill in the art that the wheel  210  of the third embodiment include as-cast and substantially as-cast spokes  222  along with other inventive features set forth above. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings foregoing invention has been described in accordance with the relevant legal standards; thus, the description is merely exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of the legal protection afforded this invention can only be determined by studying the following claims.