Patent Application
20110089749
The technical field generally relates to products including motor vehicle wheels and methods of making them. More specifically, the technical field relates to preventing corrosion of motor vehicle wheels.
Alloy wheels are commonly used on motor vehicles to reduce weight and to increase aesthetic appeal. Galvanic corrosion is a design consideration when mounting alloy wheels to wheel hubs that are often constructed from materials such as steel or iron that are different from the alloy wheel materials. These components spend much of their service life in wet conditions, often with road salt, which can promote galvanic corrosion.
One exemplary embodiment includes a product that may include a wheel assembly. The wheel assembly may include a center wheel portion comprising a first material and an outer wheel portion comprising a second material different from the first material. The center wheel portion may be attached to the outer wheel portion and may galvanically isolate the outer wheel portion from a wheel hub to which the center wheel portion is to be attached.
One exemplary embodiment includes a method that may include galvanically isolating an outer wheel portion from a wheel hub by attaching a center wheel portion to the outer wheel portion. The center wheel portion may extend radially past an edge of an interface defined by the center wheel portion and the outer wheel portion. The attaching may include forming an interlock between the center wheel portion and the outer wheel portion.
One exemplary embodiment includes a method that may include placing one of a center wheel portion and an outer wheel portion in a wheel casting die. The method may further include casting the other of the center wheel portion and the outer wheel portion to form an interlock between the center wheel portion and the outer wheel portion. The center wheel portion may comprise a first material and the outer wheel portion may comprise a second material. The first material may be less galvanically active than the second material.
Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its uses.
The figures illustrate exemplary embodiments of a wheel assembly 10, methods of making the wheel assembly 10, and exemplary embodiments of a center wheel portion 12 that the wheel assembly 10 can comprise.
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When two or more different metals come into contact with one another in the presence of an electrolyte such as seawater, or other water that contains dissolved salts, a galvanic cell may be created. When a galvanic cell is created, the more galvanically active metal may corrode at a higher rate than it would alone or alone in the presence of the same electrolyte. This higher rate of corrosion of the more active metal is galvanic corrosion. One of the factors that can influence the rate of galvanic corrosion of metals is their relative position in a galvanic series as shown by way of example in Table I. Table I includes a list of common materials in order of their respective galvanic activity in seawater. The materials at the top of the list are more galvanically active, and the materials at the bottom of the list are less galvanically active (or more noble). The list is qualitative in nature and not quantitative; i.e., the relative distance from one material to another in the list is not necessarily proportional to the relative galvanic activity.
The further apart two metals are in the galvanic series, the higher the corrosion rate of the more active metal when in contact with the less active metal in the presence of the electrolyte. For example, if magnesium and steel are in contact in the presence of the electrolyte, the magnesium will corrode at a higher rate than it will if magnesium and an aluminum alloy are in contact in the presence of the electrolyte. This is because magnesium and aluminum are closer to one another in the galvanic series than magnesium and steel. As an additional example, the magnesium would corrode at an even higher rate if coupled with copper in the presence of the electrolyte.
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For example, the center wheel portion 12 may comprise aluminum or an aluminum alloy, and the outer wheel portion 14 may comprise magnesium or a magnesium alloy. One or more of the components of the wheel hub 26 may comprise steel or cast iron. By galvanically isolating the outer wheel portion 14 from the wheel hub 26 with the center wheel portion 12 as described, the rate of corrosion of the outer wheel portion 14 can thus be reduced to a rate less than the rate of corrosion that would result if the entire wheel assembly 10 was constructed from the second material. This can allow wheel designers to use materials having relatively high galvanic activities while lessening the concern of galvanic corrosion. Of course, other material combinations may be used. For example, the first material may comprise zinc or cadmium when the second material comprises magnesium and the wheel hub 26 comprises steel or cast iron. Or the first material may comprise one or more electrically insulating materials such as ceramic or polymeric materials. Other considerations may influence choice of materials, such as strength, cost, and manufacturability, among others.
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The wheel assembly 10 may include an interlock 46 to attach the center wheel portion 12 to the outer wheel portion 14. The interlock 46 may be generally located at the interface 38. The interlock 46 may generally include a plurality of features to attach the outer wheel portion 14 to the center wheel portion 12 and to prevent relative movement of the two portions in the axial, radial, and circumferential directions or to prevent detachment of the outer wheel portion 14 from the center wheel portion 12. Referring to
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In some embodiments, the center wheel portion 12 may include essentially only the extension 44. In yet other embodiments, the center wheel portion 12 may include a first piece being the extension 44 and a second piece that may make up the remainder of the center wheel portion 12.
These multiple examples of center wheel portions 12 are only some of the ways to form an interlock 46 to attach the center wheel portion 12 to the outer wheel portion 14. Various other interlocks 46 are possible. These exemplary center wheel portions 12 may be formed using a variety of manufacturing techniques including, but not limited to, die casting, forging, stamping, machining, or various combinations of these techniques. Additionally, the interlock 46 is only one way of attaching the center wheel portion 12 to the outer wheel portion 14. Various other types of attachments are contemplated, such as mechanical fasteners, welds, adhesives, interference fits, or others.
Consistent with the various exemplary descriptions of the wheel assembly 10, a method may be described that includes galvanically isolating the outer wheel portion 14 from the wheel hub 26. The method may include attaching the center wheel portion 12 to the outer wheel portion 14. The attaching step may include forming the interlock 46 between the center wheel portion 12 and the outer wheel portion 14. The center wheel portion 12 in this method may include the extension 44 that extends radially past the inboard edge 40 of the interface 38 defined by the center wheel portion 12 and the outer wheel portion 14. The center wheel portion 12 may also include a plurality of protrusions 48 extending therefrom or a plurality of recesses 50 formed therein. The protrusions 48 may include one or more apertures 52 at least partially therethrough. As previously described, the center wheel portion 12 may include essentially only the extension 44 in some embodiments. In yet other embodiments, the center wheel portion 12 may include a first piece being the extension 44 and a second piece that may make up the remainder of the center wheel portion 12. In one embodiment, the step of forming the interlock 46 may include casting the outer wheel portion 14 onto or around the center wheel portion 12. In another embodiment, the step of forming the interlock 46 may include casting the center wheel portion 12 onto or into the outer wheel portion 14. In still other embodiments, the attaching step may include attaching the center wheel portion 12 to the outer wheel portion 14 with mechanical fasteners or by joining operations such as welding, brazing, soldering, applying an adhesive to at least one of the center wheel portion 12 or the outer wheel portion 14, or other suitable techniques.
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In one embodiment, with the die 64 in the open position, the center wheel portion 12 may be placed in the die 64 and may rest on the lower portion 66 of the die 64. The lower portion 66 may include various locators 76 to center and properly index the center wheel portion 12 with respect to the cavity 74. The locators 76 may be received by features of the center wheel portion 12 such as the center opening 20, the lug holes 22, or other features. The die 64 can then be placed in the closed position by moving the upper portion 68, the left side 70, and the right side 72 into their corresponding closed positions. The casting step may include introducing the second material, in liquid or molten form, to a material inlet 78 that may be located above the upper portion 68 of the die 64. The material inlet 78 may be fluidly connected to the cavity 74 by a runner 80 that extends through the upper portion 68 of the die 64. Thus, second material can flow into the cavity 74 through the runner 80. Once in the cavity 74, the second material may flow into any apertures 52 or recesses 50 formed in the center wheel portion 12 or formed in protrusions 48 that extend from the center wheel portion 12. When the cavity 74 is sufficiently filled, the second material may be allowed to cool and solidify. Thereafter, the die 64 may be placed in the open position and the wheel assembly 10 can be removed from the lower portion 66 of the die 64.
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Additional processing operations such as machining may be employed to remove portions of the first or second material, particularly any of the first or second material that solidified in the runner 80 during cooling. Also, some of the second material may be removed from the inboard side of the outer wheel portion 14 to allow the center wheel portion 12 to extend the desired radial distance past the edge of the interface 38 defined by the center wheel portion 12 and the outer wheel portion 14. In some embodiments, such as those in which the center wheel portion 12 is cast onto or into the outer wheel portion 14, additional processing operations such as machining may be employed to remove some of the first material to form the pilot bore 24 of the center wheel portion after casting and after removing material that may have solidified in the runner 80.
The casting process described above may be a traditional gravity-fed casting process. Other casting processes may be used, such as squeeze-casting where the material being cast is pressurized. It may also be possible to cast the outer wheel portion 14 or the center wheel portion 12 by other techniques, such as powder metallurgy techniques where the first or second material may be in powder form, placed in the cavity 74, subjected to very high pressure, and sintered.
The selection of the first and second materials utilized in the described methods may be based on several considerations, including but not limited to their relative galvanic activity, their relative melting points, cost, weight, aesthetics, and suitability for the particular manufacturing processes of the embodiment or embodiments being practiced.
The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.
