Case: 24-1381 Document: 61 Page: 1 Filed: 12/23/2025
United States Court of Appeals for the Federal Circuit ______________________
ETHANOL BOOSTING SYSTEMS, LLC, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, Appellants
v.
FORD MOTOR COMPANY, Appellee
JOHN A. SQUIRES, UNDER SECRETARY OF COMMERCE FOR INTELLECTUAL PROPERTY AND DIRECTOR OF THE UNITED STATES PATENT AND TRADEMARK OFFICE, Intervenor ______________________
2024-1381, 2024-1382, 2024-1383 ______________________
Appeals from the United States Patent and Trademark Office, Patent Trial and Appeal Board in Nos. IPR2021- 00339, IPR2021-00340, IPR2021-00341. ______________________
Decided: December 23, 2025 ______________________
STEVEN M. SEIGEL, Susman Godfrey LLP, Seattle, WA, argued for appellants. Also represented by MATTHEW ROBERT BERRY, ANDRES HEALY. Case: 24-1381 Document: 61 Page: 2 Filed: 12/23/2025
ANDREW JAMES LIGOTTI, Alston & Bird LLP, New York, NY, argued for appellee. Also represented by ERIN BEATON, KIRK T. BRADLEY, MICHAEL S. CONNOR, CHRISTOPHER TIMOTHY LAWN DOUGLAS, Charlotte, NC.
MICHAEL S. FORMAN, Office of the Solicitor, United States Patent and Trademark Office, Alexandria, VA, ar- gued for intervenor. Also represented by PETER J. AYERS, ROBERT J. MCMANUS. ______________________
Before CHEN, CLEVENGER, and HUGHES, Circuit Judges. CHEN, Circuit Judge. Massachusetts Institute of Technology and Ethanol Boosting Systems, LLC (collectively, EBS) appeal from fi- nal written decisions in three inter partes reviews by the Patent Trial and Appeal Board (Board), the first holding claims 1, 2, 5–15, 18, 20–21, 23, 25, 27–29, and 31 of U.S. Patent No. 10,619,580 unpatentable as obvious under 35 U.S.C. § 103, the second holding claims 1, 4, 6–15, 18, 20–29, 31, and 33 of U.S. Patent No. 10,791,760 unpatent- able as obvious, and the third holding claims 1, 3–5, 11–17, 19, and 21 of U.S. Patent No. 9,708,965 unpatentable as obvious. See Ford Motor Co. v. Ethanol Boosting Sys., No. IPR2021-00339, 2023 WL 8039802 (P.T.A.B. Nov. 20, 2023) (’580 Decision); Ford Motor Co. v. Ethanol Boosting Sys., No. IPR2021-00340, 2023 WL 8040878 (P.T.A.B. Nov. 20, 2023) (’760 Decision); Ford Motor Co. v. Ethanol Boost- ing Sys., No. IPR2021-00341, 2023 WL 8041916 (P.T.A.B. Nov. 20, 2023) (’965 Decision). We affirm all three Board decisions. BACKGROUND I Massachusetts Institute of Technology owns U.S. Pa- tent Nos. 10,619,580 (’580 patent), 10,781,760 (’760 Case: 24-1381 Document: 61 Page: 3 Filed: 12/23/2025
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patent), and 9,708,965 (’965 patent). It exclusively licensed all three to EBS. The ’580 patent, representative of the three challenged patents, proposes an optimized fuel management system for internal combustion engines. See ’580 patent at Ab- stract. Standard internal combustion engines suffer from “engine knock.” This phenomenon occurs when the fuel/air mixture in the engine cylinder unintentionally detonates, which reduces efficiency and damages the engine. The ’580 patent, seeking to mitigate engine knock, proposes a fuel management system which injects an “anti-knock agent” directly into the engine cylinder. See id. at col. 1 ll. 31–34. Doing so, according to the patent, causes “evaporative cool- ing” in the cylinder, which drops the cylinder temperature further from the mixture’s ignition point. See id. at col. 2 l. 64–col. 3 l. 1. The claimed fuel management system contains two in- jection mechanisms: (1) direct injection and (2) port injec- tion. See id. at claim 1. In the former, a valve sprays the fuel directly into the cylinder, whereas in the latter, a valve sprays the fuel into a passageway adjacent to the cylinder, which then mixes with air before it is introduced into the cylinder. At lower values of engine torque, only the port injector operates. 1 But for higher values of torque, both injection mechanisms kick in, and in this regime, as the torque increases, the direct injector supplies an increas- ingly greater percentage of the fuel (as compared to the port injector). Id. Finally, the claimed fuel management
1 The ’580 and ’760 patents both focus on torque ranges when selecting which injection mechanisms oper- ate. See ’580 patent at claim 1; ’760 patent at claim 1. The ’965 patent instead focuses on manifold pressure ranges when deciding which injection mechanisms operate. See ’965 patent at claim 1. This difference does not impact the appeal. Case: 24-1381 Document: 61 Page: 4 Filed: 12/23/2025
system also includes a “three-way catalyst” for reducing emissions. Claim 1, representative for appeal, recites: 1. A fuel management system for a spark ignition engine, comprising: a first fueling system that uses direct injec- tion; a second fueling system that uses port fuel injection; and a three-way catalyst configured to reduce emissions from the spark ignition engine, wherein the fuel management system is configured to provide fueling in a first torque range, the first torque range being a first range of torque values at which both the first fueling system and the second fuel- ing system are operable throughout the first range of torque values, wherein the fuel management system is further configured such that a fraction of fueling provided by the first fueling system is higher at a highest value of torque in the first torque range than in a lowest value of torque in the first torque range, wherein the fuel management system is further configured to provide fueling in a second torque range, the second torque range being a second range of torque values at which the second fueling system is oper- able throughout the second range of torque values and the first fueling system is not operable throughout the second range of torque values, Case: 24-1381 Document: 61 Page: 5 Filed: 12/23/2025
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wherein the fuel management system is further configured such that when the sys- tem provides fueling at a torque value that exceeds the second range of torque values, the spark ignition engine is operated in the first torque range, and wherein the spark ignition engine is config- ured to operate at a stoichiometric air/fuel ratio in at least part of the first torque range and in at least part of the second torque range. ’580 patent at claim 1. II Our court has seen these patents before, albeit in an appeal from a district court. See Ethanol Boosting Sys., LLC v. Ford Motor Co., No. 21-1949, 2022 WL 2798395 (Fed. Cir. July 18, 2022) (EBS I). In October 2020, EBS filed suit against Ford for in- fringing these three challenged patents. J.A. 9038–87. As EBS and Ford do here, EBS and Ford there disputed the meaning of terms recited in the limitations involving the direct injection mechanism, e.g., “directly inject[ed] fuel” in claim 1 of the ’965 patent, and “fueling system that uses direct injection” in claim 1 of the ’580 and ’760 patents. See J.A. 10095–96 (emphases added). The parties collectively refer to these disputed terms as the “DI Fuel terms,” and we do too. See Appellant Br. 9; Appellee Br. 5. In the district court litigation, EBS opted for the plain and ordinary meaning, and proposed no constraints on the term (in contrast to its narrower view of the claim in the current patentability challenge). Ford thought differently. It understood the DI Fuel terms to require a fuel that (1) is different from the fuel used in the port injection system and (2) contains an anti-knock agent other than gasoline. Case: 24-1381 Document: 61 Page: 6 Filed: 12/23/2025
Ford’s proposed construction included these two con- straints. Ford, while awaiting the district court’s decision on the claim construction, petitioned for inter partes review (IPR) of all three patents on December 24, 2020. See J.A. 316– 414, 13454–539, 26982–7066. In Ford’s petitions, it pro- posed construing the DI Fuel terms under their plain and ordinary meaning, just as EBS advocated for in the district court litigation. See J.A. 329 (“Petitioner adopts Patent Owner’s construction and does not limit the type of P[ort] I[njection] or D[irect] I[njection] fuel used.”). On March 25, 2021, before the Board ruled on whether to institute IPRs on Ford’s petitions, 2 the district court is- sued its claim construction decision adopting Ford’s con- struction requiring (1) different fuel for direct injection and port injection and (2) an anti-knock agent other than gaso- line. See J.A. 11982–87. It then granted judgment of non- infringement in light of a stipulation by the parties. EBS timely appealed, leading to our EBS I decision. A few months after the district court’s claim construc- tion order, on July 2, 2021, the Board denied institution on all three IPR petitions. See J.A. 512. The Board primarily did so because it construed the DI Fuel terms to require a fuel different from the fuel used in the port injector, just as the district court reasoned. See J.A. 525–26 (“[T]hat is, we
2 While the Director has historically delegated insti- tution decisions to the Board, see 37 C.F.R. § 42.4; Ethicon Endo-Surgery, Inc. v. Covidien LP, 812 F.3d 1023, 1028 (Fed. Cir. 2016), the Director recently announced that he will reclaim authority over those determinations. See John A. Squires, Open Letter from America’s Innovation Agency and Memorandum (Oct. 17, 2025), https://www.uspto.gov/sites/default/files/documents/open- letter-and-memo_20251017.pdf (last visited Nov. 20, 2025). Case: 24-1381 Document: 61 Page: 7 Filed: 12/23/2025
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determine that the fuel terms do not encompass single fuel systems.”). Under that construction, Ford’s prior-art chal- lenge fell short. Id. at 529. Ford petitioned for rehearing on August 2, 2021, ex- plaining that EBS had appealed the district court’s con- struction and urging the Board to reconsider its institution denial once our court issued a decision on EBS’s appeal. See J.A. 540–41. The Board granted Ford’s rehearing re- quest on November 21, 2022, just a few months after we issued our EBS I decision, concluding that Ford showed a reasonable likelihood of EBS’s claims being found un- patentable in light of our intervening claim construction in EBS I. See J.A. 581–95; EBS I, 2022 WL 2798395. III Importantly, for purposes of the current appeal, EBS in the prior EBS I appeal only took issue with the first por- tion of the district court’s claim construction of the DI Fuel terms, i.e., requiring that the directly injected fuel is differ- ent from the fuel used for port injection. See J.A. 13263 at 14 n.2 (explaining, in its opening brief for EBS I, that EBS appeals only one portion of the district court’s claim con- struction). Ford likewise understood EBS to not appeal the second portion of the district court’s claim construction, i.e., that gasoline cannot serve as the anti-knock agent. See J.A. 13337. We vacated the district court’s non-infringement order because we disagreed with the appealed portion of the dis- trict court’s construction of “fuel.” See EBS I, 2022 WL 2798395, at *3. Nothing in the claims, we explained, re- quired the directly injected fuel to differ from the port in- jected fuel. Id. at *2. And the specification expressly disclosed a 100% ethanol, i.e., ethanol-only, embodiment; the district court’s requirement of differing fuels would ex- clude this disclosed embodiment from the scope of the claims. See id. (citing ’580 patent col. 3 ll. 34–38). We therefore rejected the district court’s construction, which Case: 24-1381 Document: 61 Page: 8 Filed: 12/23/2025
excluded a single fuel embodiment from the claims, and re- manded back to the district court. We, however, never ad- dressed the portion of the district court’s construction that required the DI Fuel terms to require an anti-knock agent that was not gasoline. IV That bring us to the Board’s IPR decision below. The Board, in relevant part, first grappled with the claim con- struction of “fuel.” See ’580 Decision, 2023 WL 8039802, at *4. EBS contended that the DI Fuel terms cannot rely on gasoline as the anti-knock agent because, in its view, our EBS I decision made that construction “controlling law.” J.A. 729. The Board disagreed that this latter portion of the district court’s original construction of the DI Fuel terms was “controlling” for the IPR proceeding, given that neither party to the district court litigation appealed that portion of the construction. ’580 Decision, 2023 WL 8039802, at *4. Because neither party offered any argu- ment to support a particular construction of the DI Fuel terms, aside from EBS’s rejected “controlling law” asser- tion, the Board opted for the plain and ordinary meaning. Id. The Board next found a motivation to combine the var- ious asserted prior art references for each ground raised. See id. at *6–9 (ground 1), *24–27 (ground 2). It found that the proposed prior-art combinations disclosed the disputed claim limitations. EBS appeals. And in so doing, it offers three general arguments. First, EBS contends the Board lacked the au- thority to “stay” its rehearing decision on institution for fif- teen months to await our decision in EBS I, and therefore, asks us to dismiss the proceeding altogether because the grant of institution followed from the alleged ultra vires agency action. See Appellant Br. 3. Second, EBS raises several arguments for why the Board erred by construing DI Fuel terms to encompass a gasoline-only anti-knock Case: 24-1381 Document: 61 Page: 9 Filed: 12/23/2025
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agent. See id. at 19–20. Third, and finally, EBS challenges the Board’s factual findings on (1) motivation to combine and (2) whether the prior art teaches various limitations. See id. at 40. We have jurisdiction under 28 U.S.C. § 1295(a)(4)(A). STANDARD OF REVIEW “We decide legal issues de novo, including whether a statute precludes judicial review and whether challenged agency action is ‘not in accordance with the law or without observance of procedure required by law.’” IGT v. Zynga Inc., 144 F.4th 1357, 1365 (Fed. Cir. 2025) (quoting 5 U.S.C. § 706). We review the Board’s legal determinations de novo, but its fact findings for substantial evidence. Acceleration Bay, LLC v. Activision Blizzard Inc., 908 F.3d 765, 769 (Fed. Cir. 2018). We thus review claim construction de novo, but review subsidiary fact findings for substantial ev- idence. Id. Similarly, we review the Board’s ultimate con- clusion of obviousness de novo, but review its underlying findings of fact for substantial evidence. Best Med. Int’l, Inc. v. Elekta Inc., 46 F.4th 1346, 1353 (Fed. Cir. 2022). DISCUSSION I We begin with EBS’s allegation that the Board erred in issuing its reconsideration of institution decision. EBS frames it this way: because the Board had no authority to “stay” its decision on Ford’s rehearing petition (which was pending for over a year), and because the Board granted institution only after issuing the “stay,” we must instruct the Board to dismiss the proceedings. See Appellant Br. 31. EBS effectively asks us to de-institute the IPRs. That argument, however, conflicts with 35 U.S.C. § 314(d)’s reviewability bar for IPR institution determina- tions and precedent interpreting that provision. Case: 24-1381 Document: 61 Page: 10 Filed: 12/23/2025
Section 314(d) bars us from reviewing the Director’s deci- sion to institute an inter partes review. See 35 U.S.C. § 314(d) (“The determination by the Director whether to in- stitute an inter partes review under this section shall be final and nonappealable.”); Thryv, Inc v. Click-To-Call Techs., LP, 590 U.S. 45, 52–53 (2020); IGT, 144 F.4th at 1365; ESIP Series 2, LLC v. Puzhen Life USA, LLC, 958 F.3d 1378, 1386 (Fed. Cir. 2020). EBS’s challenge, if ac- cepted, would require us to uproot the finality of the Board’s reconsideration decision, and we have already held that an attack on a Board’s reconsideration decision looks no different than an attack on its institution decision. See Medtronic, Inc. v. Robert Bosch Healthcare Sys., Inc., 839 F.3d 1382, 1384 (Fed. Cir. 2016) (“It is difficult to conceive of a case more ‘closely related’ to a decision to institute pro- ceedings than a reconsideration of that very decision.”). Section 314(d)’s bar on reviewability thus applies, and bars EBS’s challenge to the Board’s reconsideration of institu- tion. EBS instead characterizes its challenge as an attack on the Board’s purportedly ultra vires “stay”—which conse- quently tainted its institution decision—rather than on the institution decision itself. We find that unpersuasive. EBS has not established that the Board truly issued a “stay” at all; our precedent has not previously labeled the time taken by an agency to issue a reconsideration decision as a “stay,” and we see no reason to do so here. See, e.g., CyWee Grp. Ltd. v. Google LLC, 59 F.4th 1263, 1267 (Fed. Cir. 2023). The Board simply waited to rule on the rehear- ing decision until our court settled the claim construction, which arose from a district court appeal. At that point in time, no deadlines existed to “stay” in the first place: EBS points to no statute requiring the Board to rule on a peti- tion for reconsideration within a specified time, nor are we Case: 24-1381 Document: 61 Page: 11 Filed: 12/23/2025
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aware of any. 3 And so, despite EBS’s belief that it formally challenges the “stay” rather than the reconsideration deci- sion, we cannot see its argument as anything but a chal- lenge to the propriety of the institution. Precedent confirms this view. That a party formally attacks an agency action other than the institution deter- mination does not automatically remove its challenge from the ambit of § 314(d)’s bar on judicial review. The patentee in Thryv framed its attack as one against the final written decision, as opposed to the determination to institute the IPR proceeding. 590 U.S. at 60. The Supreme Court disa- greed, observing that the patentee’s “contention re- main[ed], essentially, that the agency should have refused to institute inter partes review.” Id. (emphasis added). “As explained, § 314(d) makes that contention unreviewa- ble.” Id. At base, the patent owner in Thryv challenged the propriety of institution. Cf. IGT, 144 F.4th at 1367 (“‘[L]abeling a challenge as an appeal from the final written decision’ does not make the appeal reviewable where the challenge still attempts to overturn the institution deci- sion.” (cleaned up) (emphasis added) (quoting Thryv, 590 U.S. at 60)). Pointing to a different agency action (here, the alleged stay) does not automatically alter the analysis; § 314(d) applies when a party attempts to dislodge institu- tion.
3 EBS’s reliance on Ethicon, Inc. v. Quigg, 849 F.2d 1422 (Fed. Cir. 1988), is unavailing. There, we held that the USPTO could not stay an already-initiated reexamina- tion proceeding due to the specific statutory requirement that reexamination proceedings “will be conducted with special dispatch.” Id. at 1426–27 (quoting 35 U.S.C. § 305). Here, the IPR had not yet been instituted, and no similar “special dispatch” statutory command exists for the timing of a reconsideration of an institution decision. Case: 24-1381 Document: 61 Page: 12 Filed: 12/23/2025
So too here. EBS expressly challenges the propriety of institution itself by asking us to de-institute the IPRs. See Appellant Br. 31 (“[T]he resulting final written decisions must be vacated and the matter remanded with instruc- tions to dismiss.”). That looks no different from alleging “that the agency should have refused to institute inter partes review.” Thryv, 590 U.S. at 60. Section 314(d) thus bars review of EBS’s challenge. EBS reads our § 314(d) precedent as barring judicial review only when a party alleges a violation of a statutory prerequisite for institution, leaving all other possible as- pects of an institution decision still open to judicial review. See, e.g., Thryv, 590 U.S. at 48 (holding unreviewable a challenge to application of § 315(b)’s one-year deadline for filing a petition after complaint had been served); cf. ESIP Series 2, 958 F.3d at 1385–86 (finding a challenge to § 312(a)(3)’s particularity requirement unreviewable). But our precedent looked to the role of the purportedly violated prerequisite (e.g., § 315(b) or § 312(a)(3)) in order to better understand the precise target of the appellant’s chal- lenge: if the challenge focused on a statute which has force only in the institution context, i.e., a prerequisite for insti- tution, then the appellant’s challenge necessarily targeted the institution decision. Here, EBS likewise seeks to undo the IPR institution, alleging that the Board’s conduct as to the reconsideration decision went beyond what the statute permits. The Supreme Court, however, has identified only pos- sible narrow exceptions to § 314(d): “appeals that impli- cate constitutional questions, that depend on other less closely related statutes, or [] present other questions of in- terpretation that reach, in terms of scope and impact, well beyond” § 314. Cuozzo Speed Techs. v. Com. for Intell. Prop., 579 U.S. 261, 275 (2016); In re Motorola Sols., Inc., 159 F.4th 30, 36 (Fed. Cir. 2025) (“We have noted possible exceptions for colorable constitutional claims, . . . and cer- tain statutory challenges.” (internal citation omitted)); Case: 24-1381 Document: 61 Page: 13 Filed: 12/23/2025
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Apple Inc. v. Vidal, 63 F.4th 1, 12 n.5 (Fed. Cir. 2023), cert. denied sub nom., Intel Corp. v. Vidal, 144 S. Ct. 548, 217 L. Ed. 2d 292 (2024) (similar). For example, if the agency were to cancel a patent claim for indefiniteness under § 112—an action beyond its statutory authority—that would constitute a “shenanigan” that may be properly re- viewable under § 319 and the Administrative Procedure Act. Cuozzo, 579 U.S. at 275. EBS believes the Board engaged in “shenanigans” by purportedly acting ultra vires by delaying its institution re- consideration decision. See Appellant Br. 39–40. Yet alle- gations of acting in excess of statutory jurisdiction “closely tied to the application and interpretation of statutes re- lated to the Patent Office’s decision to initiate” IPR, with- out more, do not overcome § 314(d)’s bar. Cuozzo, 579 U.S. at 275. In SIPCO, LLC v. Emerson Electric Co., for exam- ple, we reviewed an appeal from a Covered Business Method (CBM) review. 980 F.3d 865, 869 (Fed. Cir. 2020). And there, the patent owner contended that its patent did not qualify as a CBM-eligible patent in the first place, and so, “the Board exceeded its authority in conducting a CBM review.” Id. We found that contention unreviewable. In so holding, we explained how “Thryv held that the ‘No Appeal’ provi- sion barred judicial review of the threshold decision to in- stitute inter partes review despite the argument that the Board exceeded its statutory authority in doing so.” Id. (citing Thryv, 590 U.S. at 66 (Gorsuch, J., dissenting)). We thus refused to treat an allegation of exceeding statutory jurisdiction directly bearing on statutes related to the Pa- tent Office’s decision to initiate IPR, without more, as a “shenanigan” exempt from § 314(d)’s bar on reviewability. EBS’s argument looks no different. It merely asserts the Board’s issuance of a “stay” exceeded its statutory Case: 24-1381 Document: 61 Page: 14 Filed: 12/23/2025
authority in the context of the Board’s reconsideration of an institution decision. 4 The Board here, moreover, had “sound reasons” for awaiting our EBS I decision: our decision would address the very claim term that the Board hinged its initial denial of institution upon. See IGT, 144 F.4th at 1360–61 (declin- ing to find a shenanigan when the Board had “sound rea- sons” for its action). Section 314(d) thus bars EBS’s challenge. 5 II EBS next alleges error in the Board’s claim construc- tion of “fuel.” First, it contends the Board had no choice but to adopt the non-appealed portion of the district court’s construction. Second, even if not formally bound by that construction, it faults the Board for not adequately ad- dressing that construction and failing to undertake a sub- stantive analysis of its own. Third, and finally, EBS challenges the Board’s construction on the merits. We find none of these challenges persuasive. A The district court initially construed the DI Fuel terms to require a fuel that (1) is different from the port injected fuel, and (2) contains an anti-knock agent other than gaso- line. J.A. 11982. EBS, as noted earlier, appealed only the first portion of the construction, see J.A. 13263 n.3, and we vacated on that basis. See EBS I, 2022 WL 2798395. Im- portantly, we had no occasion to address the latter portion
4 Separately, EBS points to no statute commanding the manner of how and when the agency must decide re- consideration requests. 5 Although a constitutional challenge may be review- able, EBS did not sufficiently raise any due process or other constitutional argument in its opening brief. Case: 24-1381 Document: 61 Page: 15 Filed: 12/23/2025
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of the construction, i.e., whether the anti-knock agent nec- essarily had to be something other than gasoline. See id. at *2. Nevertheless, EBS treats the non-appealed portion of the claim construction as “controlling law,” not only on the district court proceeding, but also on the Board’s separate IPR proceedings too. See Appellant Br. 23. Specifically, EBS contends that our mandate rule, combined with our waiver doctrine, rendered the claim construction “pre- cluded from further adjudication” by the Board. Id. But EBS offers no authority suggesting that we apply these doctrines across different litigations and proceedings, par- ticularly for a non-appealed district court construction. In- deed, we have suggested the opposite: our law-of-the-case doctrine—which relates very closely to the mandate rule— does not apply across different cases. See Musacchio v. United States, 577 U.S. 237, 244–45 (2016) (“The law-of- the-case doctrine generally provides that ‘when a court de- cides upon a rule of law, that decision should continue to govern the same issues in subsequent stages in the same case.’” (emphasis added) (citation omitted)); Hyatt v. Stew- art, 148 F.4th 1376, 1382 (Fed. Cir. 2025) (same); TecSec, Inc. v. Int’l Bus. Machs. Corp., 731 F.3d 1336, 1344 (Fed. Cir. 2013) (“[L]aw of the case doctrine is a ‘corollary to the mandate rule’” (citation omitted)); see also Bay v. Anadarko E&P Onshore LLC, 73 F.4th 1207, 1217 (10th Cir. 2023) (“The mandate rule follows from the law of the case doc- trine.” (citation omitted)); Callahan v. Cnty. of Suffolk, 96 F.4th 362, 367 n.6 (2d Cir. 2024) (“The mandate rule is a branch of the law of the case doctrine.”). EBS gets no help by invoking our mandate and waiver rules in an attempt to bind the Board to a non-appealed district court construc- tion. EBS briefly alludes to judicial estoppel too. But other than reciting the phrase “judicial estoppel,” it hardly offers any argument on appeal, let alone one that walks through the relevant factors. EBS fails to explain any prejudice to Case: 24-1381 Document: 61 Page: 16 Filed: 12/23/2025
itself or any unfair advantage to Ford—a consideration of- ten important in our judicial estoppel jurisprudence. See Columbia Sportswear N. Am., Inc. v. Seirus Innovative Ac- cessories, Inc., 80 F.4th 1363, 1375 (Fed. Cir. 2023) (“Fac- tors that typically inform whether to apply the doctrine include: . . . (3) whether the party would ‘derive an unfair advantage or impose an unfair detriment’ on the opposing party if not estopped.” (quoting New Hampshire v. Maine, 532 U.S. 742, 750–51 (2001)). And it never raised such an argument below. See J.A. 729 (arguing only that the post- remand construction became “controlling law”). EBS has forfeited this argument. See United States v. Great Am. Ins. Co. of New York, 738 F.3d 1320, 1328 (Fed. Cir. 2013) (“It is well established that arguments that are not appro- priately developed in a party’s briefing may be deemed waived.”); Knox v. Dep’t of Just., 125 F.4th 1059, 1067 (Fed. Cir. 2025). While we may consider forfeited arguments un- der “exceptional circumstances,” Wash World Inc. v. Bel- anger Inc., 131 F.4th 1360, 1369 (Fed. Cir. 2025), EBS did not even attempt to show any exceptional circumstances are presented here. B EBS next faults the Board for failing to engage in any meaningful claim construction analysis for the DI Fuel terms (such as examining the claims themselves as well as the specification), and relatedly, for failing to adequately explain why it substantively reached a different outcome than the non-appealed portion of the district court’s con- struction (which excluded gasoline as a permissible anti- knock agent). See Appellant Br. 20–22. These failures, EBS contends, ran afoul of 37 C.F.R. § 42.100, which states that “[a]ny prior claim construction determination concern- ing a term of the claim in a civil action . . . that is timely made of record in the inter partes review proceeding will be considered.” 37 C.F.R. § 42.100. In this instance, we find no reversible error. Case: 24-1381 Document: 61 Page: 17 Filed: 12/23/2025
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“We review questions of compliance with the Board’s procedures for an abuse of discretion.” ClearOne, Inc. v. Shure Acquisition Holdings, Inc., 35 F.4th 1345, 1351 (Fed. Cir. 2022). We typically do not fault the Board for failing to answer for unraised issues. See Apple Inc. v. Gesture Tech. Partners, LLC, 127 F.4th 364, 370 n.2 (Fed. Cir. 2025). That same principle controls here. EBS never asked the Board to construe the DI Fuel terms; if anything, it asked the Board to expressly forego any construction of its own and to instead adopt the non- appealed portion of the district court’s construction as a matter of “controlling law.” J.A. 729; see id. at 729–30. Here, where neither party asked the Board to undertake a claim construction analysis of the DI Fuel terms nor ex- plained why the district court’s construction as to the anti- knock agent was correct on the merits, we find no reversi- ble error. The Board did not abuse its discretion by not evaluating a claim construction argument that neither party raised. To the extent EBS is now asserting that 37 C.F.R. § 42.100(b) requires the Board to engage with a dis- trict court’s construction even when the parties’ briefing to the Board does not, EBS made no such argument before the Board, nor did it identify the language in the regulation that gives rise to this alleged requirement. For this reason, Power Integrations, Inc. v. Lee, 797 F.3d 1318 (2015) differs from the present case. There, we did not impose a blanket rule requiring the Board to always evaluate the merits of any prior claim constructions—in- deed, we made it expressly clear that we refused to do so. See id. at 1327 (“We do not hold that the board must in all cases assess a previous judicial interpretation of a disputed claim term.”). Instead, our holding in Power Integrations was limited to the circumstances presented. See id. at 1326 (“We conclude, moreover, that under the circumstances presented here, the board erred in failing to address the district court’s previous interpretation . . . .”). And im- portantly, the patent owner in Power Integrations Case: 24-1381 Document: 61 Page: 18 Filed: 12/23/2025
expressly teed up a claim construction dispute before the Board. See id. at 1322. EBS did not. See J.A. 729–30. C EBS next argues that the Board’s construction of the DI Fuel terms is incorrect as a substantive matter. In its view, some portions of the specification disavow gasoline as the anti-knock agent. For one, EBS has forfeited this issue because it failed to ask the Board to engage in any claim construction. But, in any event, we disagree with EBS on the merits. Nothing in the claims suggests that the DI Fuel terms dis- avow gasoline as the anti-knock agent. See ’580 patent at claim 1. Indeed, the specification counsels against adopt- ing EBS’s constraint on the anti-knock agent because it teaches a gasoline-only embodiment. See ’580 patent col. 12 ll. 26–40; id. at col. 12 ll. 26–27 (“When the ethanol has been exhausted, the engine can operate in a ‘lower perfor- mance gasoline only’ mode . . . .”); see also J.A. 9056 (EBS alleging, in its complaint, that “[t]he shared specification of the ’965, ’580, and ’760 [p]atents recites embodiments in which the same fuel is port injected and direct injected into a spark-ignition gasoline engine” and “also discloses em- bodiments in which that fuel is gasoline alone”). EBS’s po- sition would read out this embodiment from the claim scope. And “[w]e normally do not interpret claim terms in a way that excludes embodiments disclosed in the specifi- cation”—we only do so amidst clear disclaimer or disa- vowal. Oatey Co. v. IPS Corp., 514 F.3d 1271, 1276 (Fed. Cir. 2008). EBS offers no persuasive evidence of dis- claimer; at best, it points to a few lines suggesting that anti-knock agents other than gasoline function better. See Appellant Br. 26. That falls short of showing disclaimer. See IQRIS Techs. LLC v. Point Blank Enters., Inc., 130 F.4th 998, 1004 (Fed. Cir. 2025). Case: 24-1381 Document: 61 Page: 19 Filed: 12/23/2025
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Moreover, as EBS previously explained to this court in EBS I, other disclosures in these same patents contemplate gasoline as a permissible anti-knock agent. J.A. 13258 (EBS previously arguing that “[t]he patents define this knock-suppressing ‘anti-knock agent’ as ‘a fuel’ and do not place a limit on the types of fuels that can be used.”); id. (“[T]he patents teach that any fuel has a knock-suppressive effect.” (citing ’580 patent col. 1 ll. 33, 58–59)); id. at 13287 (“Table 3 [is] a measure of ‘the properties of proposed fuel antiknock/alternative fuels’ and the fuels it lists range from gasoline to methanol and ethanol.” (quoting ’580 pa- tent col. 14 ll. 50–51)). We agree with EBS’s (previous) un- derstanding of the DI Fuel terms in light of these teachings in the specification. III Ford’s petition relied on three proposed combinations of references—two of which are relevant to this ap- peal: (1) Schray 6 in view of Miura 7 (ground 1) and (2) Rub- bert 8 in view of Yuushiro 9 and Bosch (ground 2). 10 See J.A. 333, 359. EBS challenges several Board findings made for each combination. As explained below, substantial evi- dence supports the Board’s findings. A We first provide an overview of the relevant prior art. Schray proposes an internal combustion engine to reduce engine knocking. It teaches directly injecting the fuel twice during each cycle, with the first occurring in the induction
6 U.S. Patent No. 6,505,603. 7 Japanese Patent Application Pub’ln No. JP2003013785. 8 German Patent Application No. DE19853799. 9 Japanese Patent Application Publ’n No. JPH10252512. 10 Bosch Auto. Handbook (3d ed.). Case: 24-1381 Document: 61 Page: 20 Filed: 12/23/2025
phase and the second occurring in the compression phase. J.A. 12–13. Miura also focuses on suppressing engine knock and teaches using a port injector. See J.A. 4069 ¶¶ 12–15; J.A. 4066. Ford’s first proposed combination (ground 1) substituted Schray’s first direct injection with Miura’s port injection. See J.A. 334 (“Thus, Miura confirms what the POSITA would have understood, that a first di- rect injection or early direct injection is functionally similar to port fuel injection and that the two were interchangea- ble.”). Rubbert, one of the three references in ground 2 of Ford’s petition, teaches a method for creating fuel mixtures in an internal combustion engine. See J.A. 4062 col. 1. It also teaches drawing a greater percentage of the fuel from the direct injector at greater loads. See id. at col. 2. Yuu- shiro proposes an engine that contains both a port injector as well as a direct injector, see J.A. 4040–41 ¶ 12, and teaches a particular control scheme, i.e., fuel map, for de- termining which of those two injectors operate (as a func- tion of torque), see id. at 4049 FIG. 3. Bosch is a general- purpose automotive handbook. See J.A. 4403–98. B EBS contends the Board’s finding of a motivation to combine Schray with Miura lacks substantial evidence. Ford, according to EBS, alleged that a skilled artisan would combine Schray with Miura because both references teach operating “homogenously” (i.e., where the fuel and air are thoroughly mixed), but Ford’s ultimate combination— which relied on Schray’s second (later) direct injector—op- erates non-homogenously. See Appellant Br. 43–45. EBS, in other words, posits that Ford’s rationale for combining the references doesn’t track the ultimate combination it re- lied upon. EBS misreads Ford’s petition and the Board’s findings. Ford did not rely on the homogeneity between Schray and Miura as the motivation for a skilled artisan to use Miura’s Case: 24-1381 Document: 61 Page: 21 Filed: 12/23/2025
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port injector alongside Schray’s second injector in the pro- posed combination. Ford merely discussed homogeneity as one basis to explain why a skilled artisan would have a rea- sonable expectation of success of achieving the claimed in- vention once the skilled artisan combined the references. 11 See J.A. 335. As to a skilled artisan’s motivation to combine refer- ences, Ford instead explained that a skilled artisan would swap Schray’s first injector with Miura’s port injector be- cause Miura’s port injector would “provide the engine of Schray with additional benefits related to mixing and sta- ble combustion at low loads.” J.A. 334. The Board agreed with Ford’s argument, see J.A. 18, and EBS does not chal- lenge that argument on appeal. See Appellant Reply Br. 23 (indicating that “whether Schray would benefit from the use of Miura’s port injection” is a different issue from what EBS contended in its principal brief). Separately, the Board adopted Ford’s rationale that Schray and Miura teach different approaches for knock suppression, and therefore, a skilled artisan would seek to combine the two approaches. See Decision, 2023 WL 8039802, *6, *8; see also Intel Corp. v. PACT XPP Schweiz AG, 61 F.4th 1373, 1380 (Fed. Cir. 2023) (“There is a motivation to combine when a known technique ‘has been used to improve one de- vice, and a person of ordinary skill in the art would recog- nize that it would improve similar devices in the same way’ . . . .” (quoting KSR Int’l Co. v. Teleflex Inc., 550 U.S. 398, 417 (2007)). EBS does not challenge that finding. See generally Appellant Br. 41–45. Moreover, the Board also
11 Ford also posited that a skilled artisan would have a reasonable expectation of success achieving the claimed invention because Miura not only taught an engine with port injection and direct injection, but also an engine with two direct injections, like Schray. See J.A. 335. EBS did not oppose that finding. See J.A. 734–37. Case: 24-1381 Document: 61 Page: 22 Filed: 12/23/2025
adopted Ford’s rationale that a skilled artisan would seek to integrate Miura’s “open loop control strategy into Schray,” and yet again, EBS does not challenge that ra- tionale on appeal either. See Decision, 2023 WL 8039802, *6, *8; see generally Appellant Br. 41–45. The Board’s find- ings here have substantial evidence. C EBS next challenges three of the Board’s findings made as to particular claim limitations under ground 1 (Schray in view of Miura). See Appellant Br. 45–54. Specifically, EBS faults the Board for relying on a theory of unpatenta- bility (for each limitation) not raised by the petition. We disagree. “We review the Board’s judgments concerning what ar- guments are fairly presented in a petition and other plead- ings for abuse of discretion.” Netflix, Inc. v. DivX, LLC, 84 F.4th 1371, 1376 (Fed. Cir. 2023). EBS believes the Board first strayed from Ford’s peti- tion when it found that Ford’s proposed combination “ren- dered [] obvious” the three-way-catalyst limitation. 12 See J.A. 25 (emphasis added). According to EBS, the petition only alleged that Schray taught the three-way catalyst, which raises an anticipation-like theory of disclosure. See Appellant Br. 46. But just as Ford proposed in its petition, the Board reasoned that a skilled artisan would under- stand Schray to teach a three-way catalyst. Compare J.A. 338 (“Schray teaches a three-way catalyst in the form of a catalytic converter 46 . . . .”), with J.A. 25 (“We credit Dr. Clark’s testimony that ‘[a] person of ordinary skill in the art would have understood that [Schray’s] catalytic con- verter 46 constitutes a three-way catalyst . . . .’”
12 The full limitation recites “a three-way catalyst configured to reduce emissions from the spark ignition en- gine.” ’580 patent at claim 1. Case: 24-1381 Document: 61 Page: 23 Filed: 12/23/2025
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(alterations in original)). And for that reason, the Board concluded that the proposed combination as a whole ren- dered the claim limitation obvious. We thus disagree with EBS’s characterization of the Board’s decision. EBS’s deviation-from-the-petition arguments as to the other limitations fall short for the same reason; they too narrowly fixate on particular verbiage the Board used without considering the thrust of the Board’s fact-finding and analysis. See Appellant Br. 50 (“The Board repeated the same error for ‘limitation [1.E]’ . . . . ”); id. at 51 (“The Board similarly erred by finding that ‘limitation [1.C]’ of the ’965 patent was disclosed by the ‘combined teach- ings’ . . . . ”). We reject all of EBS’s challenges as to ground 1. 13 D Finally, we consider EBS’s challenges against ground 2 (Rubbert in view of Yuushiro and Bosch). EBS faults the Board for failing to adequately explain why a skilled artisan would have a motivation to combine Rubbert, Yuushiro, and Bosch. See Appellant Br. 56. But Ford provided sufficiently detailed explanations for why a skilled artisan would combine the references. See, e.g., J.A.
13 EBS also suggests that a potential typographical error in the Board’s final written decision evinces a genuine misunderstanding (of a claim limitation) by the Board. See Appellant Br. 54–55. But context makes clear the Board made a harmless typographical error, and EBS offers no reason for why the Board might possibly have intended to mean what it actually wrote. For this reason, EBS’s reli- ance on Corephotonics, Ltd. v. Apple Inc. falls short. See 84 F.4th 990, 1013 (Fed. Cir. 2023) (finding an error was not harmless when the Board could genuinely have intended to mean two things). Case: 24-1381 Document: 61 Page: 24 Filed: 12/23/2025
362 (explaining, among other things, that implementing Yuushiro’s fuel map scheme within Rubbert’s method would enable “the knock limit to be fully utilized”). And the Board expressly adopted Ford’s rationales. See Deci- sion, 2023 WL 8039802, at *27. Under the circumstances here, where the Board also provided a full explanation for why it rejected EBS’s multiple counter-arguments, the Board’s reasoning is readily discernible, and therefore, it satisfied its obligation to adequately explain its motivation finding. See id. EBS also raises several arguments concerning the Board’s rejection of its rebuttal arguments. It first con- tends the Board, when denying institution in a prior pro- ceeding, purportedly made a fact-finding that directly contradicts a finding it made here (in the course of rejecting one of EBS’s rebuttals). See Appellant Br. 56–59. Specifi- cally, EBS believes the prior Board already settled that a skilled artisan would not have been motivated to modify Rubbert’s engine (so as to operate stoichiometrically, ra- ther than leanly). Id. But even a cursory read of the prior denial of institution makes clear that the Petitioner there simply failed to meet its burden for showing that a skilled artisan would modify a prior art reference; the prior Board did not authoritatively declare that a skilled artisan would not modify Rubbert. See J.A. 12405 (“We determine that Petitioner fails to supply adequate and persuasive reason- ing with rational underpinning why a person of ordinary skill in the art would have modified Rubbert’s carefully crafted system . . . .”). In these IPRs, Ford came armed with several reasons for why a skilled artisan would modify Rubbert (including Yuushiro’s fuel map, which was not re- lied upon in the prior proceeding). And here, on this record, the Board found that Ford satisfied its burden. As the Board correctly pointed out, its prior decision did not have the benefit of considering Yuushiro and other expert testi- mony. See Decision, 2023 WL 8039802, *27. Case: 24-1381 Document: 61 Page: 25 Filed: 12/23/2025
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CONCLUSION We have considered the parties’ remaining arguments, but find them unpersuasive. We therefore affirm. AFFIRMED