Abstract:
A spun light alloy rim that substantially duplicates the strength and light weight of a cold forged alloy rim and incorporates through its method of manufacture appearance features and the relatively low cost of a cast alloy wheel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the field of automobile wheels and more particularly to an improved automobile wheel rim and method of making same.  
           [0003]    2. Description of the Prior Art  
           [0004]    Automobile owners often desire to improve the appearance and performance of their cars by replacing the original equipment wheels supplied by the vehicle manufacturer (OEM) with aftermarket wheels of lighter weight and more stylish appearance. While many owners are satisfied with aftermarket wheels that are comparatively more stylish than OEM wheels, some owners, “automotive enthusiasts” (drivers of sports and high performance type cars), desire wheels that are of substantially lighter weight and therefore improve the performance as well as the appearance of their vehicles.  
           [0005]    Automobile wheels of a type which provide a decorative appearance and relatively light weight are most commonly manufactured by using a light weight casting alloy, typically A356 or A357 aluminum, to cast a wheel in the desired configuration. Typically these wheels are cast as one piece units with integral wheel-centers and rims. After casting, the wheels are finish machined to final dimensions. There are many examples of wheels of this type, one of which is U.S. Pat. No. 5,292,182, entitled “Light Alloy Cast Wheel” issued to Kanazawa et al, Mar. 8, 1994. Some cast alloy wheels possess an ornamental design feature that provides for a smooth, stepless, radially outwardly curving relatively thick appearing outboard flange. This appearance feature has proved to be popular in the aftermarket. An example of a wheel of this type is U.S. Pat. No. Des. 389,446, entitled “Rim for a Vehicle Wheel” issued to Bradley, Jan. 20, 1998.  
           [0006]    That is, cast alloy wheels though economical to manufacture and appropriately decorative, possess certain drawbacks that render them undesirable to “automotive enthusiasts” who desire wheels of lighter weight and greater strength. The major drawback of a cast alloy wheel is excess weight. The most common alloys (A356 and A357) used in the production of these wheels possess relatively low yield and ultimate tensile strengths. The casting process produces a metal structure that is porus and brittle in nature, therefore resulting in a lower fatigue life in comparison to cold rolled alloy sheet of equivalent thickness. To account for these deficiencies, manufacturers of cast alloy wheels must use a relatively large mass of material and thereby produce a wheel that is heavier than that produced by other methods. Quality control is also a problem in the manufacture of cast wheels as differential cooling between relatively thick and comparatively thinner sections of an integral one piece wheel often results in the formation of voids and blowholes in the finished product.  
           [0007]    Another method of producing automotive wheels is cold forging. Due to their high cost, cold forged wheels are rarely seen on passenger cars but, rather, are used on high performance racing vehicles almost exclusively. Cold forged wheels are manufactured from cold rolled aluminum alloy tube, bar, or plate stock. Cold rolled aluminum alloy has a dense grain structure giving the metal excellent ductility and a high fatigue strength. Alloys commonly used in forging such as 7075 and 7050 series aluminum have significantly higher yield and tensile strength than the A356 and A357 casting alloys. A cold forged wheel may be manufactured as a one or two piece unit. The process begins by hammer forging the initial stock (bar, tube, or plate) into a donut shape. The rim portion is coaxially extruded from the forged blank. In the case of a one piece unit, after extrusion of the rim, the hub is forged radially inwardly to its desired configuration. Critical surfaces are then finish machined. An example of a cold forged wheel is described in U.S. Pat. No. 5,446,962, entitled “Process of Manufacturing One Piece Forged Wheels” issued to Matossian et al., Sep. 5, 1995. Cold forged wheels have the characteristics of light weight and high strength that are greatly prized among “automotive enthusiasts”. However, due to the high cost of producing these wheels few enthusiasts can aspire to owning a set. Thus, there remains a need for a lightweight, high strength wheel having, as an ornamental design feature, an outboard flange that flares radially outwardly in an attractive manner and exhibits an appearance of having axial depth, that can be produced at a cost comparable to that of a cast wheel.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides an improved cold formed (spun) alloy wheel rim which possesses the light weight and high strength characteristics, which are prized by “automotive enthusiasts”, and are typically associated with forged wheels, at a cost comparatively less than that of a forged wheel. A further advantage of the invention, is that it incorporates in a spun alloy rim, a smooth, step less, radially outwardly curving exterior flange which provides for a clean exterior rim appearance often associated with cast wheels. This clean, stepless, radially outwardly curving exterior flange is an ornamental design feature desired by “automotive enthusiasts” that formally was only available in cast alloy wheels.  
           [0009]    The improved wheel rim of the present invention achieves its advantages through a novel combination of cold rolling and spinning manufacturing techniques. By means of this process, the improved rim&#39;s exterior flange is rolled radially outwardly and turned back axially inwardly and then rolled radially inwardly to form an annular bearing surface defining the outboard wall of the bead seat, thereby providing for the smooth, step less, radially outwardly curving exterior desired by enthusiasts. Further, the drop well of the improved rim is located entirely inboard of the rim&#39;s centroidal axis, a feature that allows the wheel-center to be mounted at or near the wheel centroid minimizing bending moments that occur when the wheel-center is offset from the wheel centroid. Thus, a lighter, stronger, wheel can be fabricated thereby making the wheel more attractive to “automotive enthusiasts”.  
           [0010]    Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate by way of example, the features of the invention. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a front perspective view of a wheel rim embodying the present invention;  
         [0012]    [0012]FIG. 2 is a left side view of the rim shown in FIG. 1;  
         [0013]    [0013]FIG. 3 is a sectional view, enlarged in scale, of the rim taken along the line  1 - 1  as shown in FIG. 2;  
         [0014]    [0014]FIG. 4 is a cutaway front side view, enlarged in scale, of a wheel incorporating the rim shown in FIG. 1 which includes a wheel-center;  
         [0015]    [0015]FIG. 5 is a cross sectional view, enlarged in scale, of the rim to wheel-center joint, taken along line  2 - 2  as shown in FIG. 4;  
         [0016]    [0016]FIG. 6 is a left sectional view, enlarged in scale, taken along a plane passing through the radial axis of a cylindrical unitary rim blank utilized in a method for making the rim shown in FIG. 1;  
         [0017]    [0017]FIG. 7 is a sectional view similar to FIG. 6, showing the inboard and outboard extent of the blank being flared radially outwardly;  
         [0018]    [0018]FIG. 8 is a sectional view similar to FIG. 6 showing formation of the drop well and further radial outwardly flaring of the inboard and outboard flanges;  
         [0019]    [0019]FIG. 9 is a sectional view similar to FIG. 6 showing the outboard extent of the flange being bent back on itself; and  
         [0020]    [0020]FIG. 10 is a sectional view similar to FIG. 6 showing the inboard flange bent fully back on itself and the outboard flange in its final configuration.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    As shown in FIGS. 1 and 2 for purposes of illustration only, the improved spun alloy rim of the present invention comprises an annular rim body, generally designated as  18 , which possesses an axis of symmetry and is cold formed from light alloy metal sheet material such as aluminum, substantially 6 mm thick. The rim body includes a radially inwardly depressed, annular drop well, generally designated  30 . Formed on the inboard side of the drop well is an inboard bead seat  55  having a radially outwardly flared inboard flange  20  formed on the inboard side thereof. Formed on the outboard side of the drop well  30  is a cylindrical wheel-center barrel  38  configured at its outboard extent with an inboard second bead seat, generally designated  54 . Importantly, such outboard seat is configured with an outboard flange, generally designated  46 , constructed of the parent material and is cold formed to flare radially outwardly defining a funnel shaped radially outwardly curved flange face  48  and is then turned axially inwardly and then back on itself to project radially inwardly to define an axially inwardly facing bearing ring  52 .  
         [0022]    In practice, the rim is constructed from a metal plate blank rolled into a cylinder with the ends butt welded together. The blank may be constructed from any one of a number of aluminum, steel or other alloys. The rim is cold formed from the single cylindrical blank to define the desired end configuration and form the outboard flange  46  to provide the aesthetically appealing, outwardly flared rolled flange face  48  which, when combined with the back turned configuration, affords an appearance of axial depth typically associated with cast wheels.  
         [0023]    The blank is formed with the annularly indented drop well reduced in diameter so as to facilitate mounting of a conventional tire from the axial outer extremity of the rim itself.  
         [0024]    The first bead seat  55  is constructed with an inboard annular shoulder  48  and spaced axially from the inboard flange  20  to form therebetween an annular beat seat  28 . Such inboard flange is turned radially outwardly to form an annular flange ring having a radially inwardly facing ring  22  spaced from the shoulder  40  to cooperate in forming the inboard bead seat.  
         [0025]    The drop well is offset axially inboard from the centroid of the rim and is formed with a reduced-in-diameter clearance wall and oppositely disposed radially and axially outwardly angled side walls  32  and  36  joining respectively with the inboard seat and barrel  38 .  
         [0026]    Spacing of the drop well inboard of the rim&#39;s centroid serves to provide the wheel-center barrel  38  with a relatively long axial dimension so the wheel center can be spaced several cm, substantially 7 cm in the present embodiment, axially inwardly from the outboard flange face  48  to present an attractive deep appearance. This feature also enables the wheel-center to be placed at the rim&#39;s centroidal axis thereby minimizing the bending moments that would otherwise be produced with the wheel-center offset axially outwardly from the rim centroid. In the present embodiment, the drop well is located entirely inboard of the rim body&#39;s geometric center to create the deepest wheel-center barrel possible. However, other embodiments may include a drop well that is only partially offset from the rim body&#39;s geometric center.  
         [0027]    The cylindrical wheel-center barrel  38  projects from drop well side wall  36 , axially outboard along an axis parallel to the axes of the rim to connect with bead seat shoulder  42  and flange  46 . The drop well  30  is formed interiorly with a cylindrical cavity  56  to accept a disk shaped wheel-center  60  (FIG. 4) to be welded or otherwise secured thereto at  62 .  
         [0028]    The outboard bead seat  54  is formed by, in addition to the bead seat shoulder  42 , the annular seat surface  44 , outwardly curved flare forming the curved face  48 , axially inwardly projecting turn back  50  which turns radially inwardly to form the bearing ring  52  having a bearing surface facing axially inboard to be spaced axially from such bead seat shoulder  42  to secure the outboard tire bead (not shown).  
         [0029]    The radially outwardly curving flare portion  48  is about 6 mm thick and possesses an axially outwardly facing surface having a radius of curvature of substantially 8 mm. A bearing ring  52  is turned radially inwardly to cause the radially inner edge  53  to contact the radially outwardly facing bead seat surface to afford a bracing structure providing structural support for such outboard flange. In the preferred embodiment, the edge  53  is tapered radially and axially inwardly to complement the shape of the back sides of the flare  48  at its root. As will be appreciated by those skilled in the art, this arrangement provides for the appearance of a clean, stepless, radially outwardly curving outboard flange and serves to duplicate in a cold formed rim a design feature previously found only in cast alloy wheels.  
         [0030]    The rim body  18  is manufactured by a process known as cold working. Cold working is a manufacturing process whereby metal blanks, such as rim blank  70  (FIG. 6), are forced to assume a new shape through plastic flow. In cold working metal, the grain of the metal is compressed resulting in an effect known as strain hardening. Strain hardening increases the strength of parts in the direction in which plastic flow has occurred with a concurrent loss in ductility. Cold working introduces biaxial strength characteristics into a part. Essentially, cold worked metal is stronger in the direction it has been forced to plastically flow an, depending on the degree of plastic flow, may suffer a loss of strength in the transverse direction. Cold working is readily distinguishable from hot working in that cold working takes place at room temperature. Hot working takes place at a temperature above the metals plastic temperature which is that temperature in which metal can be plastically formed without the occurrence of strain hardening.  
         [0031]    The improved rim of the present invention is produced from a 5000 series aluminum alloy at sub-plastic temperatures. Alloys of this type are formed in the TO (soft condition) and gain their high strength purely through the strain hardening created by cold working the metal. It is to be stressed, however, that the novel manufacturing process is not limited to strain hardening aluminum alloys but is equally applicable to heat treatable aluminum alloys as well as magnesium or steel and other ferrous or non-ferrous metal alloys which can be procured in plate, bar, sheet, or tube form.  
         [0032]    Manufacture of the rim involves two discrete types of cold working processes, cold rolling and spinning. In a cold rolling process ductile metal of bar, plate or sheet stock, is formed by passing the stock between a pair of rollers at low speed. Cold rolling is typically used to strain harden plate and sheet stock by reducing its thickness, also the rollers may be in the form of mandrels which form features into the stock. Spinning is a cold working process similar to cold rolling. Spinning differs from cold rolling in that a metal blank of circular configuration is mounted in a rotary machine and spun at relatively low speeds about its axis. The blank may be of formed plate or sheet stock or of cut tube stock. The blank is forced to deform plastically by engaging the blank with a pair of radially inner and outer mandrels. Features are formed in the blank by moving the mandrels radially inward or outward according to a predetermined pattern. Multiple passes are usually required to create a finished product. The pattern for each pass is typically programmed into a special purpose computer which controls the sequence of forming operations.  
         [0033]    A method for making the improved automotive wheel rim of the present invention to by a combination of cold rolling and spinning manufacturing techniques includes selecting a metal sheet of aluminum about 6 mm thick and cutting it to predetermined dimensions for facing.  
         [0034]    The sheet is cold rolled into a circular configuration by rollers  82  and  84  to form a cylindrical blank with the ends of such rolled sheet abutted together. Such ends are then butt welded, thus forming a unitary cylindrical rim blank  70  as shown in FIG. 6, one side of which is shown in axial cross section.  
         [0035]    The cylindrical rim blank  70  is clamped in a hydraulic press equipped with respective radially outer and radially inner dies  86  and  88  of predetermined radii of curvature. These dies are pressed radially together to cold form flares in the axial opposite ends of the rim blank respective initial radially outwardly turned outboard and inboard flare beads  72  and  77  (FIG. 7).  
         [0036]    The initially flared rim blank is removed from the press and clamped in a four-axis-spinning-machine to be spun about its axis. A pair of inner and outer radially opposed mandrels  90  and  92  (FIG. 8) are pressed against the rotating blank and are guided across the width of the blank by a special purpose computer program to form the radially inwardly recessed drop well  30 , the respective inboard and outboard bead seat shoulders  40  and  42 , the inboard and outboard bead seats  28  and  44 , the wheel-center barrel  38 , and to further cold form the annular surfaces of the axially outer and inner extent of such blank to form an intermediate annular outboard flange disk  105  projecting radially outwardly and an intermediate inboard flange configuration  107  having a dog leg shaped cross section.  
         [0037]    Referring to FIG. 9, a cylinder die  80  is telescoped over the cylindrical blank with the radially outer surface of the dog leg flange element  107  acting as a guide surface until contacting radially outward flare element  105  such die being advanced in the outboard direction.  72 . a radial mandrel  96  is then advanced to as the blank is spun to cold form the distal extremity of the flange element  105  over from the broken line radial position to the solid line axially inwardly projecting position  109 . Cylinder die  80  is then removed axially inwardly off the rim blank and radial mandrel  96  advanced further to contact the distal edge of flare element  109  and press it radially inwardly causing the distal extent thereof to roll further inwardly thus forming in the intermediate portion of the flange blank the turn back  50  and in the distal portion thereof the bearing ring  52 . It will be appreciated that such distal extent is rolled radially inwardly until the distal edge contacts the radially outwardly facing bead seat surface  28  to form the annular bearing ring  52  shown in broken line. By this novel procedure a clean, step less, upwardly curving exterior flange, a design feature appreciated by “automotive enthusiasts” and formerly only available on cast rims is duplicated on a spun rim.  
         [0038]    The formed rim blank is then removed from the four-axis-spinning-machine and clamped into a single axis spinning machine where mandrels  98  and  100  form elements  76  and  78  into the finished configuration of the inboard flange as shown in FIG. 10. The overall rim width is controlled by trimming the inboard flange as a final operation.  
         [0039]    The now fully formed rim is inspected by checking the height of the bead seat shoulders  42  and  44  and the width of the bead seat flanges with go/no-go type gauges.  
         [0040]    The now fully formed and inspected rim is completed by finish machining and polishing the exterior surfaces to achieve the desired aesthetic effects of a clean outward surface.  
         [0041]    In use the rim is attached to a wheel center  60  (FIGS. 4 and 5), which can be of various ornamental designs. This is accomplished by heating the rim and then press fitting the wheel center to the rim. Upon cooling, a ten to fifteen thousandths on inch press fit is achieved. The wheel center is then seam welded  62  to the rim.  
         [0042]    In operation, it will be appreciated that the rim of the present invention may be mounted on a vehicle via the lug bores in the wheel center (FIG. 4) and the load of the vehicle will be transmitted through such center to the outboard side of the drop well  30  and downwardly through the tire having its bead seats mounted on the respective bead seat surfaces  28  and  44 . It will be appreciated by those skilled in the art that the outboard bead sets on the bead seat surface  44  centered between the outboard bead seat shoulder  42  and bearing surface  52 . As loads are encountered and shock transmitted to the wheel, the outboard bead will be held firmly in position on the bead seat surface  44  and supported against axial shifting. The outboard flange  46  will serve to support such beads from axially outwardly shifting by means of the inwardly facing bearing surface  52 . Axially outwardly acting loads applied to such bearing ring  52  will be resisted by the configuration of the cold formed flange  46  itself. That is, any such axially outwardly acting forces applied to such bearing ring will tend to force such ring axially outwardly but such axial outward movement will be resisted by the fact that the medially inward edge  53  is in intimate contact with the axially inwardly facing wall of the flare segment  48  such that outwardly shifting thereof is resisted. Consequently, the cold formed rim of the present invention serves to, not only provide an aesthetically pleasing appearance and extremely advantageous load carry capability but, provides an outboard flange configuration which provides effective support against loads applied thereto by the tire bead.  
         [0043]    It will be appreciated that a new and improved form of cold rolled rim has been provided. While only the present preferred embodiment has been described in detail, as will be apparent to those skilled in the art, certain changes and modifications can be made without departing from the scope of the invention as described in the following claims.