Ethanol Boosting Systems, LLC, Massachusetts Institute of Technology v. Ford Motor Company

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 B ERRY , ANDRES HEALY .
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 2
ANDREW J AMES L IGOTTI, Alston & Bird LLP, New York,
NY, argued for appellee. Also represented by ERIN
BEATON, K IRK T. BRADLEY , M ICHAEL S. CONNOR,
CHRISTOPHER T IMOTHY L AWN D OUGLAS , Charlotte, NC.
MICHAEL S. F ORMAN, Office of the Solicitor, United
States Patent and Trademark Office, Alexandria, VA, ar-
gued for intervenor. Also represented by P ETER J. AYERS ,
ROBERT J. MC MANUS .
______________________
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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 3
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 4
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,
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 5
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 6
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).
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 7
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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 8
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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 9
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).
S TANDARD 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).
D ISCUSSION
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.
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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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 11
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 12
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));
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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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 14
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 15
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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 16
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 17
“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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 18
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).
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 19
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) Schray6 in view of Miura7 (ground 1) and (2) Rub-
bert8 in view of Yuushiro9 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.).
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 20
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
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 21
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 22
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 23
(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).
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 24
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.
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ETHANOL BOOSTING SYSTEMS, LLC v. FORD MOTOR COMPANY 25
CONCLUSION
We have considered the parties’ remaining arguments,
but find them unpersuasive. We therefore affirm.
AFFIRMED
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