Robert Bosch v. Westport — Flexible Membrane Fails to Prove Fuel-Injector Patents Obvious

Background

Westport owns two patents covering directly actuated fuel-injection valves, U.S. Patent Nos. 6,298,829 and 6,575,138. The claimed valve uses a passive hydraulic link to transmit opening and closing forces. A disputed limitation requires the hydraulic fluid to act substantially like a solid, with its thickness remaining substantially constant while the actuator is operating.

Robert Bosch and Mercedes-Benz petitioned for inter partes review, arguing that the challenged claims would have been obvious over two prior-art references known as Wirbeleit and Klügl. The Patent Trial and Appeal Board rejected the challenge. It found that Klügl repeatedly described a flexible membrane surrounding the hydraulic fluid, and credited evidence that the membrane would deform during actuation. Bosch appealed that factual finding.

The Court’s Holding

The Federal Circuit affirmed the Board’s final written decisions. The only issue on appeal was whether substantial evidence supported the finding that Klügl failed to disclose the claimed hydraulic link. The court held that it did.

Klügl expressly called its membrane flexible and discussed the advantages of that flexibility in the relevant embodiments. That evidence supported the Board’s conclusion that the membrane would flex during actuation, changing the fluid’s shape in a way inconsistent with the claim’s requirement that the fluid act substantially as a solid with a substantially constant thickness.

The panel also upheld the Board’s decision to give reduced weight to Bosch’s expert. The Board identified incomplete and contradictory testimony about concepts such as stroke translation and stroke amplification. Bosch’s alternative arguments—that a skilled artisan could design the device to minimize flexing, or that the record did not prove a meaningful thickness change—did not overcome the reference’s express teaching or supply missing evidentiary support. The court also rejected Bosch’s procedural objections.

Key Takeaways

• An obviousness petitioner must connect the prior art to every disputed claim limitation with evidence, not conclusory attorney argument.
• Express descriptions in a reference can outweigh an expert’s proposed reading when the Board finds the testimony incomplete or internally inconsistent.
• On appeal, the Federal Circuit gives substantial deference to the PTAB’s factual findings and credibility assessments.

Why It Matters

The decision illustrates the importance of building an IPR petition around the precise physical behavior required by a claim. It was not enough that Klügl used hydraulic fluid in a superficially similar valve. Bosch needed persuasive proof that the fluid behaved in the specific solid-like, constant-thickness manner recited by the patents.

For patent owners, the opinion shows how explicit language in the prior art and careful expert cross-examination can preserve claims. For petitioners, it is a reminder that an appellate court generally will not reweigh competing technical evidence after the Board has made a supported factual choice.