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On June 30, 2022, the Supreme Court denied certiorari in American Axle & Manufacturing v. Neapco Holdings LLC, a closely watched patent eligibility decision from the Federal Circuit finding that patent claims for reducing automotive propeller shaft vibrations through the application of Hooke’s law were patent ineligible under 35 U.S.C. Section 101.

American Axle’s patent claimed methods of manufacturing driveline propeller shafts for automotive vehicles using liners to reduce a specific type of vibration. Former Delaware District Court Judge Leonard Stark (recently elevated to the Federal Circuit) applied the two-step framework for determining patent eligibility set forth in Mayo Collaborative Services v. Prometheus Laboratories, Inc., 566 U.S. 66 (2012) and Alice Corp. Pty. Ltd. v. CLS Bank International, 573 U.S. 208 (2014). He concluded that the claims’ focus on tuning a liner to attenuate to different vibration modes merely “instruct[s] one to apply Hooke's law to achieve the desired result of attenuating certain vibration modes and frequencies.” Am. Axle & Mfg. v. Neapco Holdings LLC, 309 F. Supp. 3d 218, 228 (D. Del. 2018). Hooke’s law is a physics principle that falls under the “laws of nature” exception to patent-eligible subject matter under Section 101. It states that the force needed to extend or compress a spring by some distance is proportional to that distance. Because American Axle’s patent claims were directed to a law of nature, and because the additional steps of the claims were “well-understood, routine, conventional activity already engaged in by the scientific community,” the district court concluded that the claims were not patent eligible. Id. at 228.

Writing for the majority, Federal Circuit Judges Timothy Dyk and Richard Taranto affirmed the district court’s ineligibility ruling as to certain of the claims at issue, finding that the claims “simply require[] the application of Hooke’s law to tune a propshaft liner to dampen certain vibrations.” Am. Axle & Mfg. v. Neapco Holdings LLC, 967 F.3d 1285, 1292 (Fed. Cir. 2019). The court further explained that “[w]hat is missing is any physical structure or steps for achieving the claimed result.” Id. at 1275. Judge Kimberly Moore dissented, arguing that the majority’s decision “collapses the Alice/Mayo two-part test to a single step ‒ claims are now ineligible if their performance would involve application of a natural law.” Id. at 1304. 

Following the decision, American Axle petitioned the Federal Circuit for panel rehearing and rehearing en banc. The Federal Circuit denied the petition, spawning a 46-page set of concurring and dissenting opinions reflecting a deeply divided court on the analysis for determining patent eligibility under section 101. Among other observations, the dissenting opinion from the denial of rehearing en banc remarked that “[t]he court’s rulings on patent eligibility have become so diverse and unpredictable as to have a serious effect on the innovation incentive in all fields of technology.” Am. Axle & Mfg. v. Neapco Holdings LLC, 966 F.3d 1347, 1357 (Fed. Cir. 2020).