IP Law Daily, PATENT—Fed. Cir.: Alternative-fuel systems developer’s patents survive Bosch and Mercedes-Benz obviousness challenge, (Aug 20, 2026)

By Mandavi Singh, LL.M.

PTAB correctly found that a cited prior-art reference’s flexible membrane did not disclose hydraulic fluid acting substantially as a solid at a substantially constant thickness during actuation.

In a nonprecedential disposition, the U.S. Court of Appeals for the Federal Circuit affirmed two Patent Trial and Appeal Board (PTAB) decisions finding that Robert Bosch LLC and Mercedes-Benz USA, LLC failed to prove that any challenged claims of fuel-injection patents owned by an alternative-fuel systems developer were obvious. Substantial evidence supported the Board’s finding that the asserted prior art lacked a hydraulic fluid that acted substantially as a solid and maintained a substantially constant thickness while an injector operated (Robert Bosch LLC v. Westport Fuel Systems Canada Inc., No. 25-1455 (Fed. Cir. Aug. 18, 2026)).

Patented injectors. Westport Fuel Systems Canada Inc. owns U.S. Patent Nos. 6,298,829 (the ’829 patent) and 6,575,138 (the ’138 patent), both titled “Directly Actuated Injection Valve.” The patents share materially identical specifications and cover fuel injectors for internal-combustion engines.

The patented injectors use a fluid-filled link to transfer the force needed to open the injector. The fluid must behave much like a solid and retain substantially the same thickness while the injector operates. Between activations, it can adjust its thickness to compensate for dimensional changes among the injector’s components. Claim 1 of the ’829 patent was representative. The dispute concerned whether an earlier injector design disclosed this solid-like, constant-thickness fluid link.

Bosch and Mercedes-Benz challenged claims of both patents in inter partes reviews (IPR) contending that the claims were obvious over U.S. Patent No. 5,479,902 (Wirbeleit), combined with German Patent No. 19708304 (Klügl). The petitions relied on Klügl for the disputed feature. Klügl described a chamber containing low-compressibility hydraulic fluid and sealed by a membrane. According to the petitioners, the chamber retained the same dimensions during operation and therefore satisfied the constant-thickness requirement. The PTAB disagreed. Klügl repeatedly described the component sealing the chamber as a flexible membrane. Crediting Westport’s expert testimony, the Board found that the membrane would flex during operation and allow the fluid to change shape. The reference therefore did not disclose fluid behaving substantially as a solid while maintaining a substantially constant thickness.

Because the asserted prior-art combination lacked that limitation, the Board concluded in final written decisions that the petitioners had not proved any challenged claim obvious by a preponderance of the evidence. Bosch and Mercedes-Benz appealed.

Flexible membrane. The Federal Circuit found substantial evidence supporting the Board’s interpretation of Klügl. Under Campbell Soup Co. v. Gamon Plus, Inc., 10 F.4th 1268, 1275 (Fed. Cir. 2021), what the prior art taught presented a factual question reviewed for substantial evidence.

Nothing in Klügl limited its description of a flexible membrane to only one version of the injector. The reference discussed the advantages of such a membrane when addressing the designs shown in Figures 1 and 3. The Board therefore reasonably found that the Figure 1 design on which the petitioners relied also contained a flexible membrane.

Bosch emphasized that Klügl described Figure 1 as operating “without stroke translation” and Figure 3 as operating “with stroke translation.” Bosch interpreted the first description to mean that the injector’s actuator and piston moved the same distance. In its view, that equal movement required the fluid layer to remain the same thickness. That interpretation depended on Bosch’s expert testimony. The Board gave the testimony little weight because it found the opinions incomplete, contradictory, and inconsistent with Klügl’s express disclosure.

Citing Sierra Wireless, ULC v. Sisvel S.p.A., 130 F.4th 1019, 1024 (Fed. Cir. 2025), the Federal Circuit found no abuse of discretion in that credibility assessment. The Board could rely on Klügl’s repeated description of a flexible membrane instead of the expert’s inconsistent interpretation.

During operation. Bosch alternatively argued that even if the membrane was flexible, the evidence did not show that it flexed while the injector operated. Klügl described the membrane moving when the injector was inactive, but Bosch maintained that the Board could not assume comparable movement during activation. The Federal Circuit found the Board’s inference reasonable. A membrane that Klügl described as flexible and that actually flexed while the injector was inactive would remain flexible during operation. That inference satisfied the substantial-evidence standard stated in Consolidated Edison Co. v. National Labor Relations Board, 305 U.S. 197, 229 (1938).

Bosch also asserted that any flexing might be too slight to change the fluid’s thickness meaningfully. The Board properly treated that assertion as unsupported attorney argument. Designing the injector to prevent flexing would also conflict with Klügl’s repeated flexible-membrane description.

Petition limits. Bosch could not rely on Wirbeleit on appeal as independently disclosing the disputed feature. Under Netflix, Inc. v. DivX, LLC, 84 F.4th 1371, 1377 (Fed. Cir. 2023), the PTAB had discretion to interpret the grounds presented in an IPR petition. It reasonably determined that the petitions relied solely on Klügl for the constant-thickness limitation.

Finding no merit in the remaining objections, the Federal Circuit affirmed both decisions and left all challenged claims intact.

The Case is No. 25-1455.

Judge: Stark, L.

Attorneys: Melanie L. Bostwick (Orrick, Herrington & Sutcliffe LLP) for Robert Bosch LLC. Miranda Y. Jones (Winstead PC) for Westport Fuel Systems Canada Inc.

Companies: Robert Bosch LLC; Westport Fuel Systems Canada Inc.

Cases: Patent FedCirNews