Background
American Axle & Manufacturing (AAM) held U.S. Patent No. 7,774,911, covering a method for manufacturing a propshaft — a component of a vehicle’s drivetrain that transmits power from the engine to the wheels. The method involved inserting a liner (typically a foam or fibrous material) into the propshaft at a specific location and with specific liner characteristics (mass, stiffness) designed to attenuate two specific types of vibration: bending-mode vibrations and shell-mode vibrations. The claimed approach allowed manufacturers to tune a single liner to simultaneously reduce both vibration types — a practical manufacturing improvement over prior approaches that required separate solutions for each vibration type.
Neapco Holdings, a competing driveshaft manufacturer, challenged the patent as directed to the natural law of Hooke’s Law — the physical principle relating applied force to displacement in springs and elastic materials, which underlies the physics of vibration attenuation. The district court found the patent ineligible under § 101. AAM appealed.
The Court’s Holding
A divided Federal Circuit panel affirmed ineligibility. The majority held that AAM’s claims were directed to Hooke’s Law — the natural law governing how the liner would attenuate vibration — and that the claims failed to add an inventive concept at Step 2 because they directed the manufacturer to achieve a result (vibration reduction) governed by a natural law, without specifying in the claims how to select the liner properties that would achieve the desired result. The claims essentially instructed: achieve certain vibration-attenuation outcomes by applying Hooke’s Law, without claiming specific implementations.
Chief Judge Prost and Judge Moore dissented vigorously. They argued that the majority had misapplied § 101: AAM’s patent was a practical engineering method for manufacturing a physical product, not a claim to Hooke’s Law itself. Every engineering patent implicitly involves natural laws, and finding mechanical manufacturing methods patent-ineligible because they apply physics would untether § 101 from its historical limits. The case attracted an unprecedented number of amicus briefs urging rehearing en banc or Supreme Court review, as the ruling appeared to threaten eligibility of vast categories of mechanical and engineering patents.
Key Takeaways
- The majority’s holding was highly controversial: finding that a mechanical manufacturing method directed to a specific practical application (driveshaft liner placement) was patent-ineligible because it applied Hooke’s Law suggested § 101 could invalidate many traditional engineering patents.
- The dissent’s view — that the natural law exception applies only to claims that recite the law itself or that add only trivial limitations, not to claims that apply physics in a specific practical manufacturing context — represents the mainstream view of how § 101 should operate for mechanical patents.
- American Axle illustrates the ongoing uncertainty in § 101 jurisprudence: the Alice/Mayo framework’s application to mechanical, electrical, and chemical patents (beyond software and business methods) remains contested even within the Federal Circuit.
- The Supreme Court denied certiorari, leaving the Federal Circuit panel decision in place — but the controversy generated calls for legislative reform of § 101 to restore clearer and more predictable patent eligibility standards.
Why It Matters
American Axle v. Neapco was one of the most controversial § 101 decisions in years, generating heated debate within the patent bar about whether the Alice/Mayo framework had expanded beyond software and financial method patents to threaten traditional mechanical, industrial, and engineering inventions. The dissents’ alarm — and the large number of amicus briefs urging reconsideration — reflected genuine concern that the majority’s approach, if broadly applied, could render basic engineering patents ineligible by characterizing any application of fundamental physical principles as directed to a natural law.
The case contributed to growing momentum for § 101 reform legislation. In 2019, the Senate Judiciary Committee had already held hearings on a bipartisan bill to restore clearer patent eligibility standards; American Axle reinvigorated that effort by demonstrating that § 101 uncertainty was no longer limited to software but had reached into traditional manufacturing and industrial patent territory. While Congress had not enacted comprehensive § 101 reform as of 2024, American Axle remains a key data point in the ongoing debate about the limits of the natural law exception under the Alice/Mayo framework.