1. Field of the Invention
The present invention relates to composite wheel assemblies for vehicles having an overlay permanently attached to a wheel disc with a combination of adhesives and, particularly, to an improved apparatus and process for permanently attaching an ornamental overlay to the wheel using nests to locate and support the overlay to the wheel creating a mold into which foam can be injected.
2. Description of the Related Art
Decorative overlays are widely used to enhance the aesthetic appearance of automotive wheels. Overlays are not only employed to improve the appearance of unadorned standard steel wheels, but are also used with cast aluminum wheels, that are known to be expensive and difficult to plate with chromium. Numerous structural combinations of overlays with chrome-plated outboard surfaces have attracted great interest from vehicle manufacturers, because they are lightweight, aesthetically pleasing and offer designers complete flexibility with regard to the aesthetic effect that can be created for a specific vehicle regardless of whether these vehicles use steel or aluminum wheels.
In the past, most overlays were mechanically attached to the wheel. For example, Kapanka, U.S. Pat. No. 3,575,468, teaches the use of a spring retention device wherein a joined annular wire spring provides a plurality of outer cover-engaging segments adapted to be secured to a wheel cover at spaced peripheral portions. A plurality of axial segments interconnect the outer cover engaging segments with outer wheel-engaging segments adapted to engage a groove in the rim of the wheel. Stay et al., U.S. Pat. No. 4,895,415; Patti, U.S. Pat. No. 4,950,036; as well as Hudgins et al., U.S. Pat. No. 5,181,767, teach, alternatively, retention of the wheel cover by providing wheel cover retaining means for releasably coupling to at least one lug stud with appropriate configurations enabling releasable coupling between the retainer and at least one stud. German Patent 2,813,412 also mechanically attaches the overlay to the wheel by utilizing cavities or undercuts in the face of the wheel. Further, German Patent 2,848,790 also teaches mechanical attachment of the wheel cover to the wheel through the use of clamps so that the cover can be removed for the purpose of cleaning.
Others are adhered to the outboard surface of the wheel, as illustrated by U.S. Pat. No. 3,915,502 to Connell, that teaches an annular-shaped wheel cover that is permanently attached to the wheel with double-sided adhesive tape. The adhesive tape is positioned midway between the rim and the center hub area of the wheel, while the remainder of the wheel cover is spaced apart from the outboard surface of the wheel. Connell positions the adhesive tape at radially outward portions of the wheel in order to avoid the deleterious effects of heat generated by the tire, wheel and brake. While some pressure-sensitive adhesive tapes can be effectively used in temperatures up to 500° F. (260° C.), the cost of such adhesive tapes is generally prohibitive for use in mass production applications such as securing an overlay to a wheel. Consequently, such applications are generally limited to the use of less expensive adhesive tapes that have relatively low maximum operating temperatures, necessitating that their placement be restricted to the radially outward surfaces of the wheel. Unfortunately, doing so severely limits the adhesive tape's ability to reliably adhere the overlay to the wheel. Further, the use of adhesive tape because of its defined thickness creates a void between the overlay and the wheel that can collect dirt and debris that may affect the balance of the wheel.
To avoid such problems, as well as to avoid noise problems associated with the use of overlays, the prior art proposes the use of a urethane foam and a method of permanently attaching a plastic cover to a metal wheel through the use of a urethane foam adhesive, that effectively holds the cover in place, closes the void between the overlay and the wheel, and reduces noise as well as provides adequate theft deterrence. This method is best described in U.S. Pat. No. 3,669,501 to Derleth. The process disclosed in Derleth is an annular-shaped overlay composed of a thin plastic cover formed from acrylonitrile-butadiene-styrene (ABS) mounted to a wheel spider. The overlay is configured to have variations in contours in a direction transverse to the axis of the wheel that exceed the variations in the rim and/or disc contour of the wheel, which variations would be extremely difficult and expensive, if not impossible, to stamp or draw in the disc of the wheel. During assembly, a foamable polyurethane adhesive is coated on the wheel, and the cover is then quickly clamped to the wheel before the polyurethane begins to foam. As such, the void between the wheel and cover is filled with the polyurethane foam. However, any excess polyurethane foam formed around the bolt holes or at the periphery of the assembly surrounding the axle hub will squeeze out if appropriate sealing provisions are not made.
One obvious shortcoming of the process disclosed by Derleth is that the composite wheel must be imperforate, except for the small bolt openings necessary for attaching the wheel to a vehicle. It is understood by those skilled in the art that it is necessary to avoid the deleterious effects of heat generated by the wheel and brake, that cause the ABS plastic overlay to distort, cause delamination of any surface treatment, i.e. paint, plating, etc., and further cause the foam adhesive to degrade, distort and eventually melt. Further problems with urethane formed wheels surfaced in use. These wheels were very heavy due to the high density of the foam and variation in localized density during the manufacturing phase resulted in severe wheel imbalances.
Turbine openings are a necessary element in today's wheel systems in providing proper cooling to the brake system, not to mention the aesthetics of endless configurations of turbine openings that add individuality and style to a vehicle. Any opening in the wheel or overlay using the process disclosed in Derleth is a pathway for the foam mixture to escape when it begins to foam and/or cure. Larger openings, such as turbine openings, would not be possible using the Derleth process without additional structure to seal the openings to prevent the foaming material from escaping.
It is appreciated by those skilled in the art that it is advantageous to completely fill the cavity with foam adhesive to acoustically dampen any sound produced when the overlay is struck. A drawback of the process according to Derleth is that excess foam mixture is required to ensure that the cavity between the cover and the wheel is completely filled after the material vents out through the bolt openings. The process disclosed by Derleth requires any substantial opening in the wheel be plugged or sealed with a sleeve to prevent foam leakage. For example, if the wheel hub was left unsealed it would provide a path for some of the foam to escape, and the security of the cover could be jeopardized. Further, all of the excess foam must be manually removed, which adds significant cost to the process.
A further disadvantage of the process of Derleth is that the polyurethane foam adhesive completely breaks down at high temperatures, particularly in the immediate region of the wheel hub where temperatures tend to be much higher than in the remainder of the wheel.
The method according to Derleth has been known since the early 1970's and due to its many disadvantages has yet to realize practical applications and commercial success. The process cannot accommodate the application temperature requirements, the need for lighter weight components, and degradation of the urethane adhesive over time, as well as the need for turbine openings in the outboard face of the wheel. Further, the process is extremely costly due to the labor intensive trimming operations, difficult process control, environmental, health and safety concerns.
The teachings of Beam, U.S. Pat. Nos. 5,368,370 and 5,461,779, of a full surface curable adhesive are prohibitively expensive and wasteful since there is no need for a full surface uniform layer of adhesive to hold the overlay to the wheel. Further, a full surface uniform layer of curable adhesive also detrimentally affects the balancing considerations of the wheel and overlay assembly.
To avoid the problems of Beam, U.S. Pat. No. 5,597,213 to Chase, assigned to the assignee hereof, teaches the use of an intermediate positive fixing element for temporarily positioning and securing an overlay to a wheel during an interval in which a selectively positioned or applied adhesive required to permanently adhere the overlay to the wheel is allowed to cure. The adhesive is selectively placed between the overlay and the wheel to alleviate concerns of squeaks and rattles as well as to improve the overall manufacturability, performance and consumer-perceived quality of the resulting wheel assembly. The requirement of an intermediate positive fixing element not only adds costs to the overlay but requires careful handling and special packaging, all adding to the overall cost of the assembly.
Understandably, what is needed is an economical overlay apparatus and method for assembling such overlay to an automotive steel or alloy wheel, in which the method promotes the ability to accurately position and reliably permanently secure the overlay to the wheel by the use of selective application of a costly curable adhesive in combination with a less expensive foam adhesive so as to improve the manufacturability of the wheel, reduce the cost of manufacturing and not detrimentally affect wheel balance or performance.