Background
American Axle & Manufacturing (AAM) held U.S. Patent No. 7,774,911, which claimed methods for manufacturing driveline propeller shafts containing lined inserts designed to attenuate two types of vibrations — bending mode vibrations and shell mode vibrations. The patent’s core inventive step was said to be a process for “tuning” a liner so it would damp both kinds of vibration simultaneously, a task previously requiring separate components or extensive trial-and-error. AAM sued Neapco Holdings for infringement, and the district court granted summary judgment of invalidity under 35 U.S.C. § 101.
AAM appealed, arguing that the claims described a practical engineering method — a real-world manufacturing process — not a statement of a natural law, and that the district court had improperly reduced the invention to the mathematical relationship it exploited. The case drew significant attention as another data point in the ongoing battle over how far § 101 reaches into traditional mechanical and manufacturing arts.
The Court’s Holding
The Federal Circuit affirmed in part. Judge Dyk, writing for the majority, applied the two-step Mayo/Alice framework. At step one, the majority found that the claims were directed to Hooke’s law — the physical principle that a spring’s restoring force is proportional to displacement — and the associated concept of friction damping. The claims, the majority said, simply directed engineers to “tune” a liner to attenuate vibrations without specifying the particular physical dimensions, materials, or configurations required to achieve that result. That is, they commanded a result governed by a natural law without providing the how.
At step two, the majority found no inventive concept because the specification disclosed no concrete technique for achieving the tuning goal beyond applying the natural law itself. Judge Moore filed a forceful dissent, arguing that the majority had collapsed the two-step test into a single inquiry: if claims touch a law of nature at all, they fail, regardless of any concrete engineering implementation. In her view, the claims described “a specific, concrete solution (inserting a liner inside a propshaft) to a problem (vibrations in propshafts)” and should have been eligible. The en banc Federal Circuit later split 6–6 on whether to rehear the case — an evenly divided court, leaving the panel result intact.
Key Takeaways
- Method-of-manufacturing claims are not immune from § 101 scrutiny; the Alice/Mayo framework applies to mechanical and manufacturing inventions, not just software and business methods.
- If a claim recites a result governed by a natural law without specifying the physical means to achieve it, the Federal Circuit may treat the claim as ineligible even if it covers a tangible product or process.
- The case exposed a deep split within the Federal Circuit: the 6–6 en banc deadlock illustrated that the judges themselves disagree sharply on how far § 101 extends into the mechanical arts.
- Patent applicants should draft claims in the mechanical and manufacturing space with specificity about the physical parameters, materials, or structural configurations involved, not just the functional result to be achieved.
Why It Matters
American Axle alarmed patent practitioners because it extended the § 101 ineligibility analysis far beyond software and fintech into the traditional engineering heartland. If claims on driveshaft manufacturing — a wholly physical, tangible process — can fail because they invoke a natural law, practitioners worried that a vast swath of mechanical patent claims might be vulnerable to the same attack. The Supreme Court denied certiorari in 2022, declining the opportunity to clarify the boundaries of natural-law ineligibility in the mechanical context.
The case became a rallying point for calls to reform § 101. Critics argued that patent eligibility law had become unworkable and unpredictable, and the American Axle en banc deadlock was cited repeatedly in Congressional hearings and academic commentary as evidence that even the Federal Circuit cannot agree on what § 101 means. For now, the decision stands as a cautionary signal that method claims relying heavily on a natural relationship, even in a mechanical context, must be drafted with concrete technical specificity to survive.