On December 23, 2025, the U.S. Court of Appeals for the Federal Circuit affirmed three decisions of the Patent Trial and Appeal Board (“PTAB”) finding claims of fuel-management patents asserted by Ethanol Boosting Systems, LLC (“EBS”) unpatentable as obvious.
The court rejected EBS’s attempt to undo the inter partes reviews based on the timing of the PTAB institution decisions, while clarifying that district court claim constructions don’t automatically bind IPR proceedings.
Background: MIT’s Fuel-Injection Patents
The patents at issue (U.S. Patents Nos. 10,619,580, 10,781,760, and 9,708,965) are owned by the Massachusetts Institute of Technology (MIT) and exclusively licensed to EBS. They relate to systems for reducing engine knock in internal combustion engines using combinations of port fuel injection and direct injection at different torque ranges. EBS sued Ford for infringing those patents in 2020.
In the district court, EBS and Ford disputed how to interpret the claim language covering the direct‑injection mechanism and the fueling system that uses direct injection (the “DI fuel” terms). While that dispute was pending, Ford also filed IPR petitions on all three patents. The district court ultimately adopted a narrow construction, holding that the directly injected fuel had to be (1) different from the port‑injected fuel and (2) contain an anti‑knock agent other than gasoline. Based on that construction, the court entered judgment of non‑infringement, and EBS appealed.
In the following appeal, referred to as EBS I, the Federal Circuit vacated only the “different fuels” requirement. The court concluded that nothing in the claims required different fuels and that such a construction would improperly exclude disclosed single‑fuel embodiments. The court did not address, and EBS did not appeal, the separate requirement that the anti‑knock agent be something other than gasoline.
PTAB Initially Denies Institution, Then Reconsiders
The PTAB initially denied institution in July 2021, relying in part on the district court’s claim construction that required different fuels for port and direct injection. Ford petitioned for rehearing in August 2021, asking the Board to await the Federal Circuit’s resolution of EBS I.
In November 2022, shortly after the Federal Circuit issued its claim-construction decision in EBS I, the PTAB granted Ford’s rehearing, instituted review, and ultimately found all challenged claims unpatentable as obvious.
§ 314(d) Bars Challenge to PTAB Institution Decision Timing
On appeal, EBS argued that the PTAB exceeded its authority by effectively “staying” its rehearing decision for more than a year while waiting for the Federal Circuit’s ruling, rendering the institution decisions ultra vires.
The Federal Circuit rejected that argument on multiple grounds. The court emphasized that there is no statute that imposes a deadline on PTAB rehearing decisions and declined to treat the Board’s decision to await appellate guidance as an improper “stay.” More importantly, the court held that EBS’s challenge was barred under 35 U.S.C. § 314(d), which makes institution decisions “final and non-appealable.” The court explained that regardless of how EBS framed its argument—as an attack on an improper “stay”—it was fundamentally seeking to undo the institution decision, which § 314(d) prohibits.
District Court Claim Constructions Do Not Bind IPRs
EBS also argued that the PTAB was required to adopt the non‑appealed portion of the district court’s claim construction excluding gasoline as an anti‑knock agent. It urged that the earlier district‑court construction should effectively control the IPRs.
The Federal Circuit disagreed. The court explained that rules like “law of the case” govern later stages of the same lawsuit and do not automatically bind the PTAB in a separate IPR proceeding. The court further noted that EBS had not meaningfully developed a judicial‑estoppel argument below and therefore forfeited it. And because neither side asked the PTAB to do its own, merits‑based claim construction of the DI‑fuel terms the Board did not err in simply applying the plain and ordinary meaning of “fuel.”
The court also stressed that the patents themselves disclose gasoline‑only embodiments and that EBS had previously argued in EBS I that any fuel, including gasoline, could function as the anti‑knock agent, undercutting its attempt to narrow the claims during the IPRs.
Obviousness Findings Affirmed
The Federal Circuit also affirmed the PTAB’s obviousness determinations, concluding that substantial evidence supported the Board’s findings on motivation to combine and reasonable expectations of success. The court rejected EBS’s arguments that the PTAB relied on theories not raised in Ford’s petitions or failed to adequately explain its reasoning, finding that the Board stayed within the petitions and provided sufficient explanation for its conclusions.
Takeaway
- PTAB institution decision challenges remain off-limits on appeal. Arguments targeting PTAB timing or procedural discretion are unlikely to overcome § 314(d)’s bar.
- Claim-construction positions must be coordinated across forums. Patent owners cannot rely on un-appealed district court constructions to control PTAB proceedings.
- Narrow constructions face risk in IPR. Attempts to exclude disclosed embodiments without clear disclaimer are unlikely to succeed.