Addressing the applicability of 35 USC § 112, ¶6 to the term “mechanical control assembly,” the US Court of Appeals for the Federal Circuit found that the Patent Trial and Appeal Board (PTAB) gave undue weight to the patent’s prosecution history, and reversed the PTAB’s decision that § 112, ¶6 did not apply. MTD Prods. Inc. v. Iancu, Case No. 17-2292 (Fed. Cir. Aug. 12, 2019) (Stoll, J).

The patent at issue is directed toward steering and driving systems for zero turn radius (ZTR) vehicles, with specific reference to lawn mowers. The claimed invention allows ZTR vehicles to turn in the same direction both forwards and backwards, thus mimicking the forward and backward movements of a car. In order to accomplish this, the independent claims refer to a “mechanical control assembly” that is coupled to left and right drive units and configured to actuate the left and right drive units based on both steering and speed inputs received from the vehicle. The patent specification does not specifically refer to a “mechanical control assembly.” The preferred embodiment, however, is directed to a “ZTR control assembly,” which is described in detail.

The Toro Company petitioned for inter partes review of the MTD patent on obviousness grounds. As part of its analysis, the PTAB was required to determine whether the claim term “mechanical control assembly” was a means-plus-function term and thus subject to the limitations of 35 USC § 112, ¶6. The patent owner argued that § 112, ¶6 applied and introduced expert testimony indicating that “mechanical control assembly” has no reasonably well-understood meaning in the art. Without directly contradicting the MTD’s expert, Toro responded by pointing to the ZTR control assembly as providing an express definition for the claimed “mechanical control assembly.”

The PTAB ultimately sided with Toro, holding that “mechanical control assembly” is not subject to § 112, ¶6 due primarily to statements made by the applicant during the prosecution history. Specifically, the PTAB relied on an admission by the applicant indicating that the term connotes specific structure by asserting that the claims recite “a mechanical control assembly that is structurally different from what [the asserted prior art] discloses.” MTD appealed.

On appeal, the Federal Circuit reversed the PTAB’s holding and found that the term “mechanical control assembly” is a means-plus-function claim element and thus subject to § 112, ¶6. The Court reiterated that the critical question in determining whether § 112, ¶6 applies is whether the claim term is used in common parlance or by persons of skill in the pertinent art to designate structure. If the claim is drafted in means-plus-function format, the second step involves a review of the specification to identify the structure that performs the claimed functions. The Federal Circuit cautioned that these two inquiries are related but distinct.

The Federal Circuit explained that during its analysis, the PTAB conflated these two distinct inquiries, leading to the incongruous result that as long as there is corresponding structure in the specification, a term can never be subject to §112, ¶6. Although agreeing that the claim language reciting that the mechanical control assembly is coupled to the left and right drive units connotes structure, the Court explained that additional claim language reciting what the mechanical control assembly is configured to do is purely functional. Furthermore, the Court noted that the specification does not go so far as to demonstrate that the patentee intended to act as its own lexicographer and equate the term “mechanical control assembly” with “ZTR control assembly.”