The US Court of Appeals for the Federal Circuit affirmed three Patent Trial & Appeal Board final written decisions finding claims of three related patents unpatentable as obvious and reiterated that challenges to the Board’s authority to institute inter partes review (IPR) proceedings are largely insulated from appellate review under 35 U.S.C. § 314(d). Ethanol Boosting Systems, LLC, et al. v. Ford Motor Co., Case Nos. 2024-1381; -1382; -1383 (Fed. Cir. Dec. 23, 2025) (Chen, Clevenger, Hughes, JJ.)
Massachusetts Institute of Technology (MIT) owns three related patents directed to fuel management systems for spark-ignition engines, which it exclusively licensed to Ethanol Boosting Systems (EBS). The patents disclose systems using both port fuel injection and direct injection to suppress engine knock by injecting an anti-knock agent, with increasing use of direct injection at higher torque levels.
EBS sued Ford for patent infringement. During claim construction, EBS and Ford disputed the meaning of claim terms related to “direct injection” fuel. EBS proposed the plain and ordinary meaning and no constraints on the term. Ford proposed terms requiring a fuel that is different from fuel used in port injunction systems and contains an anti-knock agent other than gasoline. While claim construction was pending, Ford filed IPR petitions using EBS’s proposed claim construction.
While Ford’s IPR petitions were pending, the district court adopted Ford’s construction and entered summary judgment of noninfringement. EBS appealed, and the Federal Circuit vacated and remanded the district court’s decision. Before the Federal Circuit had decided the appeal, the Board denied institution on all three IPR petitions primarily because it, like the district court, construed the direct injection fuel terms to require fuel different from the fuel used in the port injector. After the Federal Circuit decision, the Board granted rehearing, instituted IPRs, and ultimately found the challenged claims unpatentable as obvious. EBS appealed the Board’s final written decisions.
Institution challenge barred under § 314(d)
EBS argued that the Board acted unlawfully by effectively “staying” its decision on Ford’s rehearing request for more than a year while awaiting the Federal Circuit’s ruling on the district court appeal, and that the resulting institution decisions should therefore be vacated.
The Federal Circuit rejected this argument, finding that it was, in substance, an impermissible challenge to the Board’s institution determinations. The Court explained that § 314(d) bars appellate review not only of institution decisions themselves, but also of challenges “closely related” to those determinations. Characterizing the Board’s delay as an ultra vires “stay” did not change the analysis, particularly since no statutory deadline governed the timing of rehearing decisions and no IPR had yet been instituted.
The Federal Circuit further noted that the narrow exceptions to § 314(d), such as colorable constitutional claims, did not apply because EBS failed to raise a viable due process or other constitutional argument.
Claim construction: District court rulings don’t control
EBS next argued that the Board was bound by the district court’s earlier claim construction (applied during the prior Federal Circuit appeal) requiring a non-gasoline anti-knock agent, or at least was required to independently analyze and justify departing from it.
The Federal Circuit disagreed, finding that mandate-rule and law-of-the-case doctrines do not apply across different proceedings, such as district court litigation and IPRs. Although applicable regulations require the Board to consider prior claim construction determinations, the Court found no abuse of discretion where EBS failed to properly raise a claim construction dispute before the Board and instead insisted that the district court’s construction was “controlling law.”
Obviousness findings supported by substantial evidence
EBS challenged the Board’s obviousness determinations, including its findings on motivation to combine prior art references and whether certain claim limitations were disclosed. The Federal Circuit rejected these arguments, explaining that EBS focused too narrowly on isolated phrasing in the Board’s analysis rather than its overall reasoning. Reviewing the Board’s factual findings for substantial evidence and its procedural judgments for abuse of discretion, the Court held that the Board adequately explained its motivation-to-combine findings and did not rely on theories outside those raised in Ford’s petitions.
