CAFC Affirms PTAB Decisions Upholding Fuel Injector Patent Claims

The U.S. Court of Appeals for the Federal Circuit (CAFC) issued a decision today in Robert Bosch LLC, Mercedes-Benz USA, LLC v. Westport Fuel Systems Canada Inc., affirming two Patent Trial and Appeal Board (PTAB) final written decisions that found Robert Bosch and Mercedes-Benz USA failed to prove challenged claims of two fuel injector patents would have been obvious. The court rejected arguments that the PTAB lacked substantial evidence to find that a prior art reference disclosed a flexible membrane capable of flexing during actuation, thereby failing to meet a specific hydraulic link limitation.

Westport Fuel Systems Canada Inc. owns U.S. Patent Nos. 6,298,829 and 6,575,138, which relate generally to fuel injector valves for internal combustion engines and describe an injection valve that includes a passive hydraulic link. During operation, an opening force is generated by a magnetostrictive actuator, overcoming the closing force of a spring assembly and allowing fuel to exit through the valve tip. This opening force is transmitted through a hydraulic link assembly containing a viscous hydraulic fluid.

The patent specifications explain that the hydraulic fluid acts substantially as an incompressible solid during activation, which allows the valve opening force to be transmitted quickly to the valve needle. Claim 1 of ‘829 patent is representative and includes limitation 1(e), which requires a passive hydraulic link with a hydraulic fluid thickness through which opening and closing forces are transmitted. The limitation further requires that the hydraulic fluid act substantially as a solid, with its thickness remaining substantially constant during actuator assembly activation. Furthermore, the thickness of the hydraulic link is adjustable while the actuator is not activated to maintain a desired valve needle lift upon subsequent activation.

Bosch and Mercedes-Benz filed petitions for inter partes review (IPR) challenging various claims. They relied on a combination of prior art references, specifically a German patent designated as Klügl and a U.S. patent designated as Wirbeleit. The petitioners argued that these references taught the hydraulic link limitation requiring a hydraulic fluid thickness that remains substantially constant during actuation. The PTAB determined that Bosch and Mercedes-Benz failed to prove the challenged claims unpatentable, concluding that the Klügl reference did not disclose the claimed constant-thickness hydraulic fluid because Klügl expressly described its pressure chamber membrane as flexible. Since the membrane is flexible, the administrative tribunal reasoned that it will necessarily deform and change shape during actuation, which contradicts the behavior of an incompressible solid.

Bosch and Mercedes-Benz appealed to the CAFC. The central issue on appeal concerned whether substantial evidence supported the administrative finding that the Klügl reference fails to disclose limitation 1(e).

The court observed that Klügl explicitly designates its membrane as a flexible membrane throughout its disclosure. The administrative record contained credible expert testimony demonstrating that the flexible membrane tends to deform longitudinally upward where it contacts the drive piston and bulges outward where unconstrained in the surrounding annular area. Bosch and Mercedes-Benz contended that Klügl depicts embodiments with and without stroke translation, arguing that Figure 1 represents an embodiment without stroke translation where the hydraulic fluid is required to achieve a constant thickness. However, the court sustained the administrative credibility assessment rejecting the expert declaration offered by Robert Bosch, noting that testimony was undermined by incomplete and contradictory opinions regarding stroke translation terminology.

Bosch and Mercedes-Benz argued that even if the membrane is flexible, the Board lacked substantial evidence to find that the membrane actually flexes during actuation, since Klügl discussed membrane movement in a rest position without being actuated. The Federal Circuit rejected this contention, concluding that a reasonable mind could accept the administrative tribunal’s logical deduction. As Judge Stark, writing for the court, explained, since the membrane is flexible and flexes when not actuated, it remains flexible and will flex when actuated as well.

Furthermore, the court dismissed assertions that nothing in Klügl shows the membrane flexing to a degree that meaningfully changes fluid thickness during actuation. The CAFC characterized this assertion as nothing more than “conclusory attorney argument, lacking any citation to the record or meaningful explanation.” The court also rejected the proposition that a person of ordinary skill in the art could readily design the injector to minimize or avoid flexing altogether, observing that such a design modification directly contradicts Klügl’s repeated teachings emphasizing membrane flexibility.

The appellate court also dismissed multiple allegations of procedural error raised by Bosch and Mercedes-Benz, concluding that all remaining arguments lacked merit. Since the PTAB possessed substantial evidence supporting its factual findings regarding the flexibility of the prior art membrane, the Federal Circuit affirmed the judgments upholding the validity of the challenged claims.

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