In an opinion addressing claim construction issues, the U.S. Court of Appeals for the Federal Circuit vacated and reversed a lower court’s grant of summary judgment of non-infringement based on an erroneous construction of the term "engagement," rejecting the argument that a construction not requiring "secured" would render other claim language superfluous.  Deere & Company v. Bush Hog, LLC, Case Nos. 11-1629; -1630; -1631 (Fed. Cir., Dec. 4, 2012) (Rader, C.J.).

Deere alleged infringement of a patent directed to a rotary cutter deck for brush type, tow-behind lawn mowers.  Claim 1 required an upper deck wall including front and rear portions that slope downwardly “into engagement with, and being secured to,” a lower deck wall.  The lower court construed the term “into engagement with” to mean “brought into contact with” and construed “being secured to” as “fastened or attached.”  The lower court granted summary judgment of non-infringement because all of the accused cutter decks provided intermediate structure between the upper and lower deck walls.  Deere appealed.

Addressing the relevant claim language, the Federal Circuit rejected the defendant’s argument that construing “into engagement with” as including indirect contact would render that term redundant with the “secured to” language, which all parties agreed could include indirect coupling.  The Court reasoned that the term “engagement” connotes a connection between objects in which the motion of one is constrained by the other, such as a motor engaged with a gear through a second, intermediate gear.  Although not “secured” together, the objects are nonetheless engaged.  Thus, construing “engagement” to include indirect contact does not render it superfluous to the term “being secured to.” 

The Federal Circuit noted that the specification provided an example of indirect coupling between the upper deck wall and the lower deck wall.  According to the specification, outer rear portions of the upper deck plate are coupled to the lower deck wall by “downwardly and rearwardly inclined filler plates.”  The Court determined that the filler plates provide an indirect connection by which the upper deck wall slopes “downwardly and rearwardly … into engagement with” the lower deck wall.  The Court also drew parallels between functional language of the claim, which stated that the lower deck wall imparts “torsional stiffness” to the rotary cutter deck, and functional language in the specification, which described the upper and lower deck walls as cooperating with the filler plates to form a “box section having torsional rigidity.” 

The lower court had also precluded the patent holder from asserting infringement under the doctrine of equivalents by characterizing the “into engagement with” limitation as “binary in nature,”—either the upper deck wall is “in contact with the lower deck wall or it is not.”  The Federal Circuit took the opportunity to clarify what it called a “common misperception” regarding so called “binary elements” and claim element “vitiation.”  The Court emphasized that the proper inquiry under the doctrine of equivalents is whether the asserted equivalent represents an “insubstantial difference” from the claimed element and noted in this case that a reasonably jury could have found that a small spacer connecting the upper and lower deck walls represents an insubstantial difference from direct contact.