“There is no … foreseeability limit on the doctrine of equivalents,” even for “the application of the doctrine of equivalents for means-plus-function limitations.”
Background / Facts: The patent being asserted here is directed to an improved automobile locking differential. The parties agreed that the accused product literally met every limitation of claim 1 except the “cylinder means formed in … ” limitation, but that it included an “equivalent” cylinder under the doctrine of equivalents and that this equivalent would have been foreseeable at the time of patenting.
Issue(s): Whether there is a foreseeability bar to the application of the doctrine of equivalents for means-plus-function limitations.
Holding(s): No. In general, the court emphasized that “[t]here is not, nor has there ever been, a foreseeability limitation on the application of the doctrine of equivalents.” With regard to means-plus-function limitations in particular, it is true that “the equivalence determination made for literal infringement purposes under § 112(f),” in contrast to “a doctrine of equivalents determination for the same limitation,” does not cover so-called “after-arising technology … that did not exist at the time of patenting,” but there is nothing to preclude either equivalence determination from covering foreseeable equivalents. “[W]hether the accused structure ‘predates’ the patent or is after-arising technology, the doctrine of equivalents applied to a means-plus-function clause requires only that equivalent structures perform substantially the same function.” Further, “[w]here a finding of non-infringement under § 112(f) is based solely on the lack of identical function, it does not preclude a finding of equivalence under the doctrine of equivalents.”