Key Mfg. Group, Inc. v. Microdot, Inc.

• Decision Date: 09 September 1987
• Docket Number: Civ. A. No. 81-71775.
• Citation: 679 F. Supp. 648,4 USPQ 2d 1687
• Parties: KEY MANUFACTURING GROUP, INC., Plaintiff, v. MICRODOT, INC., Defendant.
• Court: U.S. District Court — Western District of Michigan

679 F. Supp. 648

4 USPQ 2d 1687

KEY MANUFACTURING GROUP, INC., Plaintiff, v. MICRODOT, INC., Defendant.

Civ. A. No. 81-71775.

United States District Court. E.D. Michigan, S.D.

September 9, 1987.

Jerold I. Schneider, Cullen, Sloman, Cantor, Grauer, Scott & Rutherford, P.C., Detroit, Mich., for plaintiff.

George E. Frost, Chester L. Davis, Jr., Barnes, Kisselle, Raisch, Choate, Whittemore & Hulbert, P.C., Detroit, Mich., for defendant.

MEMORANDUM OPINION AND ORDER

PHILIP PRATT, Chief Judge.

Key Manufacturing Group, Inc. (Key), a Michigan corporation, brings this action for patent infringement against Microdot, Inc. (Microdot), a Delaware corporation, which has a manufacturing facility in Sterling Heights, Michigan. Both Key and Microdot manufacture capped wheel nuts for attaching a wheel to an automobile axle. The Towne Robinson Fastener Company, (Towne Robinson) is a division of Key which manufactures capped wheel nuts. Towne Robinson is an assignee of patents which describe several types of capped wheel nuts. Among these patents are U.S. patent 4,123,961 and reexamined U.S. patent B1-4,123,961. In this suit, Key alleges that Microdot's capped wheel nuts literally infringe these patents or infringe them under the doctrine of equivalents. A non-jury trial ended on May 11, 1987, and the parties completed post-trial briefing on July 13, 1987. Below are the court's findings of fact and conclusions of law.

I. Patent 4,123,961

A. Description of the Patent

The patent in suit is for a capped wheel nut which fastens a wheel to an automobile axle. The axles of most automobiles have a ring of threaded studs which extend outwardly from each axle end. The automobile wheel has a corresponding ring of holes through which the studs pass. Wheel nuts are then threaded on the studs to secure the wheel to the axle. All wheel nuts have a number of "wrench flats" which allow a tool to tighten the nut on the wheel or loosen it for purposes of servicing or changing the wheel. The wheel nuts and studs at the hub of the wheel may be hidden by a cover which attaches to the wheel to protect the nuts and studs and improve appearances. Alternatively, the wheel nuts may have a protective sheath on them to protect the nut and the stud without an additional cover. These sheathed wheel nuts are referred to as "capped wheel nuts." The cap may be made of a variety of materials, and may be attached to the nut body, sometimes called the nut insert, in a variety of ways.

The patent in suit calls for a stainless steel cap with polygonal sides which is fastened to the nut body by welding. The nut body has two "faces:" when threaded, the first face is in direct contact with the wheel. The court shall refer to this end as the "wheel face" of the nut body. The stainless steel cap slides over the second face, which is at the opposite end of the nut body and the wrench flats. The court shall refer to the second end as the "cap face" of the nut body. To facilitate the welding of the cap to the nut body, the patent calls for a nut body with a "continuous ring of substantial area" on the cap face of the nut body (hereinafter "welding ring"). By using pressure and electric current, the welding ring melts, spreads radially towards the edge of the nut body, and forms a bond between the cap and the nut body. In the alternative, the patent contemplates a number of weld nubs on the cap face of the nut body. The weld nubs serve the same function as the welding ring and collapse in a similar manner.

Welding on the end of the wheel nut creates a situation where any force applied to the weld during the loosening or tightening of the wheel nut will be in shear. "Shear" refers to two forces acting in opposite directions. As a person loosens the capped wheel nut, for example, the person is applying a force in one direction on the weld by using a wrench on the cap itself, while the tightened nut body is exerting a force in the opposite direction.

The patent claims do not describe the method for producing the capped wheel nut. An attached figure does show a capnut body assembly between two annular electrodes, each designed to conform to the wheel face of the nut body or to the stainless steel cap. The Summary of the Invention itself refers to particular levels of pressure, weld voltage, amperes and weld time used to manufacture the capped wheel nut successfully. The disclosure also describes those characteristics. The Summary goes on to note:

As a result, heating occurs principally at the interface between the cap and the nut, at the ring area. The weld time is so short that the cap does not oxidize and the heating action does not cause the carbon in the stainless steel to migrate to the grain boundaries to lower its corrosion resistance. The heat applied to the nut is not sufficient to affect its hardness.

The welding circuit illustrated is a simplified version of a conventional capacitor discharge circuit, and it should be understood that any type of welder circuit which can apply in extremely short duration; high current pulse to the interface between the cap and the nut, while the nut is being forced into the cap at the ring, could be used with present invention.

The court finds that this language demonstrates that the patent did not intend to identify a certain welding method to produce the manufactured device. Rather, it contemplated a manufacture with certain characteristics which, when welded with any number of different weld circuits, does not cause discoloration, lower corrosion resistance, nor decrease strength in the capped wheel nut.

In this regard, the language of the patent claims 1 and 8 bears close scrutiny. The claims from the original patent read as follows:

1. A nut having a central threaded aperture, polygonal sides, a first end adapted to engage a wheel, a second end having an end face extending at right angles to the axis of the nut and a sheet metal cap for the nut having a section extending over the polygonal sides and and (sic) end section adapted to cover the second end of the nut, said end section being connected to the section of the cap which covers the polygonal sides by a section formed fully around the perimeter of the cap and having an extension at right angles to the axis of the nut so as to be parallel to said end face, such connecting section being in juxtaposed contact throughout a substantial area with and welded to said end face, whereby forces exerted on the capped sides creating moments about the central axis of the nut will resist in shear forces exerted on the weld.

2. The nut of claim 1 wherein the cap is welded to the nut in a continuous line of weld extending fully around the central aperture.

3. The nut of claim 1 wherein the cap is formed of a stainless steel.

4. The nut of claim 1 wherein the end section of the cap is flat and extends fully across the end of the nut opposite to the first end.

5. The nut of claim 1 including a chamfered surface extending between the polygonal flats and the first end of the nut and wherein the cap has an angled section which contacts said chamfer.

6. The nut of claim 5 wherein the laterally extending section of the cap contacts said angled section.

7. The nut of claim 1 including a plurality of raised weld nubs formed on said nut surface having an extension laterally to the central axis of the nut, which act to contact said cap.

8. A capped wheel nut, including a nut body having a central threaded aperture, polygonal sides, and a conical end and a laterally extending end, and a sheet metal cap for the nut having a first section covering at least a portion of said polygonal sides and a second section covering the laterally extending end of the nut, said second section being in contact with the laterally extending nut end in a continuous ring of substantial area extending about and being normal to the central axis of the nut, said cap being welded to the nut at said ring so that forces exerted between the nut and cap during wrenching by forces exerted on the capped sides creating moments about the central axis of the nut will produce shear forces on the weld.

9. The capped nut of claim 8 wherein the nut body has a plurality of raised weld nibs formed about said surface having a lateral extension.

10. The nut body of claim 8 having a flange which extends radially beyond the polygonal sides and in which the cap is welded to the body at a lateral surface of said flange.

The claims of the reexamined patent read:

REEXAMINATION CERTIFICATE ISSUED UNDER 35 U.S.C. § 307

THE PATENT IS HEREBY AMENDED AS INDICATED BELOW.

Matter enclosed in heavy brackets appeared in the patent, but has been deleted and is no longer a part of the patent; matter printed in italics indicates additions made to the patent.

AS A RESULT OF REEXAMINATION, IT HAS BEEN DETERMINED THAT:

Claims 1 and 5-10 are determined to be patentable as amended.

Claims 2-4, dependent on an amended claim, are determined to be patentable.

1. A decorative nut for holding a wheel on a motor vehicle and exposed to view on the wheel, said nut having a central threaded aperture, polygonal sides, a first end adapted to engage a wheel, a second end opposite said first end and having an end face extending at right angles to the axis of the nut, and a sheet metal cap for the nut and having a section extending over the polygonal sides of the nut and and an end section adapted to cover the second end of the nut, said section extending over the polygonal nut sides including a plurality of cap wrench flats respectively associated with and oppositely facing said polygonal nut sides, said cap wrench flats and said polygonal nut sides being disposed between said first and second ends of said nut, said end section being connected to the section of the cap which covers the polygonal nut sides by a section formed fully around the perimeter of the cap and having an extension at right angles to the axis of the nut so as to be parallel to said end

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