Temporal Relationship to Amendment Does Not Make Equivalent Unforseeable
Under the doctrine of the equivalents, "a product or process that does not literally infringe upon the express terms of a patent claim may nonetheless be found to infringe if there is 'equivalence' between the elements of the accused product or process and the claimed elements of the patented invention." Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 21 (1997) (citing Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605, 609 (1950)). The doctrine of prosecution history estoppel prevents a patent owner from recapturing with the doctrine of equivalents subject matter surrendered to acquire the patent. See Festo IX, 344 F.3d at 1365 (citing Festo VIII, 535 U.S. at 741).
Because the three asserted independent claims were rewritten from dependent form and because the original independent claims were cancelled, there is a presumption of prosecution history estoppel. See Honeywell II, 370 F.3d at 1134. Nonetheless Honeywell may rebut that presumption with a showing that: (1) "the alleged equivalent would have been unforeseeable at the time of the narrowing amendment" or (2) "the rationale underlying the narrowing amendment bore no more than a tangential relation to the equivalent in question." Festo IX, 344 F.3d at 1369 (quoting Festo VIII, 535 U.S. at 741).
. . . The principle of foreseeability ties patent enforcement appropriately to patent acquisition. In making this connection, foreseeability reconciles the preeminent notice function of patent claims with the protective function of the doctrine of equivalents. Thus, foreseeability in this context ensures that the doctrine does not capture subject matter that the patent drafter could have foreseen during prosecution and included in the claims. The goal of the principle is to ensure that the claims continue to define patent scope in all foreseeable circumstances, while protecting patent owners against insubstantial variations from a claimed element in unforeseeable circumstances. The
foreseeability principle thus relegates the doctrine of equivalents to its appropriate exceptional place in patent enforcement.
This court must examine, on the basis of this record, whether the use of IGV position to detect high flow and low flow was later-developed technology and thus unforeseeable at the time of the amendments during the prosecution process. The timing of Sundstrand’s product development does not settle the issue. The record shows that Sundstrand developed its equivalent between 1991 and 1995, after the relevant amendments in 1982-83. The mere temporal relationship of the equivalent to the patent acquisition and amendment process, however, does not make the equivalent unforeseeable. The record shows that Sundstrand began using IGV position to control airflow within two months of observing the double solution problem, which suggests that the IGV solution may have been known (and foreseeable) in the art. The record also shows that Sundstrand refined this way of addressing the problem over the next four years—evidence susceptible to characterization as either showing difficulty in reaching the ultimate solution or showing the natural and foreseeable application of well-known principles.
However, Honeywell contends that the district court’s determination was clearly erroneous because in the 1982-83 time frame surge control systems did not use inlet guide vane position to ascertain the existence of high or low flow situations for surge control. Honeywell is correct that the systems in the 1982-83 time period did not use inlet guide vane position for this purpose, but it was known that the control of surge was important; that systems, such as the L1011 system, had been developed for that purpose; and that inlet guide vanes were routinely used in surge control systems and affected the air flow rate. For example, U.S. Patent No. 4,164,035 ("the Glennon patent"), issued in 1979, claims a surge control system and teaches that IGV position affects airflow rate. Honeywell’s expert, Mr. Muller, also testified:
Q: In fact, going back to the 1970s, it was Honeywell’s understanding that in order to efficiently control surge, you would need to take into account inlet guide vane angle and input into your surge control
A: Well, by using this information you can incrementally improve the operation of a surge controller, yes.
The record also shows no technical barrier to the use of IGV position to determine air flow, as Honeywell’s corporate representative, James Clark, admitted. He confirmed that Honeywell "could have  solved [the double solution problem] using inlet guide vane position" in the 1970s. Foreseeability does not require that the accused infringing product or process be foreseeable, nor that any equivalent exist at the time; rather foreseeability only requires that one of ordinary skill in the art would have reasonably foreseen the proposed equivalent at the pertinent time. Festo X, 493 F.3d at 1382.
Sunstrand’s expert, Dr. Japiksi, whom the district court found to be credible, concluded that it was "known or foreseeable to a person of ordinary skill in the
art in 1982 to use IGV position to determine whether the flow was high or low."
Based on this testimony and the record evidence described above, the district
court concluded that "measuring IGV position . . . is a reasonably obvious way –
both at present and in 1982-83 – to determine whether the APU is experiencing
high flow or low flow." Honeywell 2006-1602 15 III, 2006 U.S. Dist LEXIS
57030, at *17. This court finds no clear error in the district court’s conclusion.