Abstract:
Cast metal wheels, such as those made of aluminum and magnesium alloys generally have a thick cross section in the area where the wheel disc joins the rim. The disclosed invention is drawn to a device for reducing the weight of a cast metal vehicle wheel. The device includes an annular tube which is supported in the mold in the wheel is cast. The device is then cast within the wheel rim or disc and forms a hollow cavity inside the wheel which reduces the weight of the wheel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/114,025, filed on Dec. 29, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to cast vehicle wheels and in particular to a cast vehicle wheel having a hollow core insert and a method for making same. 
     Light weight vehicle wheels formed from alloys of aluminum, magnesium and titanium are becoming increasingly popular. It is known in the art to cast a one piece vehicle wheel in a multi-piece wheel mold. Referring now to the drawings, there is shown in FIG. 1 a fragmentary sectional view of a typical prior art one piece wheel  10 . The wheel  10  has a circular wheel disc  11  which extends across the outboard end of an annular wheel rim  12 . 
     The wheel disc  11  includes a wheel hub  15  having a central pilot hole  16  and a plurality of wheel lug holes  17  (one shown) formed therethrough. The hub  15  is supported by a plurality of wheel spokes  18  (one shown) within an annular sidewall  20  which forms the outboard end of the wheel rim  12 . 
     The wheel rim  12  includes an outboard tire bead retaining flange  21  which extends in a radial outward direction from the sidewall  20 . The rim  12  further includes an outboard tire bead seat  22  which is formed in the sidewall  20  adjacent to the retaining flange  21 . The rim  12  also includes an outboard tire bead hump  23  formed in the sidewall  20  between the tire bead seat  22  and a deep well  24 . A leg portion  25  extends axially across the rim  12  from the deep well  24  to an inboard tire bead hump  26 . An inboard tire bead seat  27  is formed adjacent to the bead hump  26 . The inboard end of the wheel rim  12  terminates in a conventional inboard tire bead retaining flange  28 . 
     It also is known in the art to fabricate a two piece vehicle wheel by attaching a full face wheel disc to the outboard end of a separately formed partial wheel rim. Typically, the wheel disc is cast while the rim is rolled from strip stock. Such two piece wheels are less expensive to manufacture than a cast one piece wheel while permitting use of stylistic designs for the wheel disc. Both the wheel disc and rim can be formed from alloys of the same light weight metal, or, as a further cost reduction, a wheel disc formed from an alloy of a light weight metal can be attached to a rim rolled from steel. When different metals are used to form the wheel disc and wheel rim, the wheel is usually called a bimetal wheel. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved cast vehicle wheel having a hollow core insert and a method for making same. 
     Due to the geometry of cast wheels, the wheel sidewall, the portion of the wheel where the wheel disc joins the wheel rim, tends to have a thick cross section. Accordingly, a large mass of metal is contained in the sidewall which adds to the wheel weight while not being needed for wheel strength. Therefore, it would be desirable to reduce the weight of the wheel sidewall. 
     The present invention contemplates a vehicle wheel including an annular wheel rim adapted to support a pneumatic tire and a circular wheel disc formed across an end of the rim, the wheel disc cooperating with the wheel rim to define an annular sidewall. The wheel also includes a hollow core disposed within the sidewall. The hollow core can be either a continuous core which extends circumferentially within the sidewall or a plurality of segments spaced equally about the circumference of the sidewall. The invention also contemplates a continuous or segmented hollow core disposed within the sidewall of a fall face wheel disc. 
     The invention further contemplates a mold for casting a wheel component which includes a base member and a top core, the top core cooperating with the base member to define a wheel sidewall cavity. The mold also includes a hollow core disposed within the sidewall cavity. A supporting structure positions the hollow core within the sidewall cavity. The wheel component cast in the mold can be a one piece vehicle wheel or a full face wheel disc. 
     The invention also contemplates a method for casting a vehicle wheel component which includes providing a mold for the component, the mold defining a sidewall cavity. A hollow core is placed within the sidewall cavity. The mold is charged with molten metal and molten metal is allowed to cool and solidify. Finally, the mold is opened and the wheel component and core are removed. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary sectional view of a prior art one piece wheel. 
     FIG. 2 is a fragmentary sectional view of an improved one piece wheel in accordance with the present invention. 
     FIG. 3 is a sectional view of a multi-piece wheel mold which is used to cast the wheel shown in FIG.  2 . 
     FIG. 4 is flow chart for a process for casting the wheel shown in FIG.  2 . 
     FIG. 5 is fragmentary sectional view of an improved two piece wheel in accordance with the present invention. 
     FIG. 6 is a fragmentary view of a vehicle wheel which illustrates an alternate embodiment of the wheel shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring again to the drawings, there is illustrated in FIG. 2 an improved one piece wheel  30  in accordance with the invention. Components shown in FIG. 2 which are similar to components shown in FIG. 1 have the same numerical designators. The wheel  30  is cast from a light weight metal, such as alloys of aluminum, magnesium and titanium, and has a hollow annular lightener core  31  cast into the wheel sidewall  20 . In the preferred embodiment, the core  31  is a sealed tube having a circular cross sectional shape; however, it will be appreciated that the invention also can be practiced with cores having other cross sectional shapes, such as for example, trapezoidal. Also, in the preferred embodiment, the core  31  is formed the same material as the wheel, for example a core formed from 6061 aluminum may be used with an aluminum alloy wheel. However, the core  31  also can be formed from ferrous, metallic or non-metallic materials depending upon the particular application. 
     The invention also contemplates an apparatus for casting the wheel  30  shown in FIG.  2 . The apparatus includes a multi-piece wheel mold  40  which is shown in FIG.  3 . The mold  40  has a base member  41  which supports the other mold components. The mold  40  also includes a plurality of horizontally movable side members  42  (two shown) and a vertically movable top core  43 . The base member cooperates with the side members  42  and top core  43  to define a mold cavity  45 . For simplicity, the gate structure for pouring molten metal into the mold cavity  45  has been omitted from FIG.  3 . Similarly, the mechanisms for moving the side members  42  and top core  43  are not shown in FIG.  3 . The mold cavity  45  includes an annular rim cavity  46  and a circular disc cavity  47 . The junction of the rim cavity  46  and disc cavity  47  defines an annular sidewall cavity  48 . 
     A sealed hollow ring shaped core  50  is disposed in the sidewall cavity  48 . In the preferred embodiment, the core  50  is formed from the same material as the wheel; however, the invention also can be practiced with the core  50  formed from a material which is different from the material forming the wheel. The core  50  is illustrated as having a circular cross sectional shape; however, it will be appreciated that the invention also can be practiced with cores having other cross sectional shapes. 
     As shown in FIG. 3, the core  50  is supported within the sidewall cavity  48  by a plurality of tabs  51  (one shown) which extend in a downward direction in FIG.  3 . The tabs  51  cooperate with the base member  41  to position the core  50 . It is contemplated that indentations (not shown) formed in the upper surface of the base member  41  receive the ends of the tabs  51  to position the core  50  within the sidewall cavity  48 . 
     The invention also may be practiced with the tabs  51  extending in other directions (not shown). Such tabs also could be supported by other members of the mold  40  than the base member  41  (not shown). While tabs  51  are shown in FIG. 3, it will be appreciated that the invention also can be practiced utilizing other structures to support the core  50  within the sidewall cavity  48 . Upon pouring a charge of molten metal into the mold cavity  45 , the metal surrounds the core  50 . Accordingly, the core  50  is cast into the sidewall of the resulting wheel casting (not shown). 
     The invention further contemplates a method for casting the wheel  30  shown in FIG.  2 . The method is illustrated by the flow chart shown in FIG.  4 . In functional block  55 , a wheel mold is opened. A hollow sealed core is positioned in the mold in functional block  56  and the mold closed in functional block  57 . A charge of molten metal is poured into the mold in functional block  58  to form a wheel casting which includes the core in the sidewall. It will be appreciated that any convention casting method, such as, for example, gravity or low pressure casting can be used in functional block  58 . The casting is cooled in functional block  59  and once the metal has sufficiently solidified, the mold is opened in functional block  60 . The casting is heat treated in functional block  61 ; however, this step is optional. Further finishing steps are carried out in functional block  62 . Such steps can include removing risers and the gate from the casting, machining the casting to a final shape and applying optional layers of decorative and/or clear coatings. 
     An alternate embodiment of the invention is illustrated by the fragmentary sectional view of a two piece wheel  65  in FIG.  5 . Components shown in FIG. 5 which are similar to components shown in FIG. 3 have the same numerical designators. The wheel  65  includes a full face wheel disc  66  which is attached to the outboard end of a partial wheel rim  67  by an air-tight circumferential weld  68 . Similar to the wheel  30  described above, the wheel  65  is cast from a light weight metal and includes a hollow annular lightener core  31  which is cast into the wheel sidewall  20 . 
     The present invention provides a reduction in the weight of the wheel while utilizing unmodified existing wheel molds. Additionally, the present invention avoids the use of complex movable cores or expensive post casting machining to form a lightener recess, thereby reducing costs. 
     While the preferred embodiment has been illustrated and described above with a continuous ring shaped hollow core, it will be appreciated that the invention also can be practiced with plurality of hollow core segments  52 , as shown in FIG.  6 . Components shown in FIG. 6 which are similar to components shown in the preceding figures have the same numerical identifiers. The core segments  52  are spaced equally about the circumference of the wheel sidewall. As illustrated, the core segments  52  are located in the portion of the sidewall  20  adjacent to the ends of the wheel spokes  18 . 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. For example, while a mold for a one piece wheel has been illustrated and discussed, it will be appreciated that the invention also can be practiced on a mold for a wheel component, such as, for example, a full face wheel disc.