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Honeywell Intern., Inc. v. Hamilton Sundstrand Corp. 523 F.3d 1304, 2008

Amicus Curiae, for Hamilton-Sustrand Corp.

The present case concerns surge control in auxiliary power units (APUs). Both Honeywell and Hamilton manufacture these units. Honeywell brought suit against Hamilton for infringement, specifically with regard to how the flow was measured in the APU. The question of infringement was connected to the doctrine of equivalents; Honeywell claimed that the flow measurement system in the  Hamilton device was equivalent to that found in the Honeywell system. It should be noted that we are arguing that the Honeywell patent is limited so as to exclude our device from the bounds of its patent, and thus we are not infringing on the Honeywell patent.

However, to argue infringement using the doctrine of equivalents, the court first required that Honeywell explain the limitations it had placed on its patent during the review process. It has been previously established (in Warner-Jenkinson) that the reason for the limitation is important in determining whether the doctrine of equivalents can apply. In this case, the court determined that there are three methods which Honeywell can pursue to rebut the presumption of prosecution history estoppel. These were: forseeability, tangentiality, and ''some other reason''. Honeywell conceded the effort to demonstrate ''some other reason'', and thus the effort to rebut the presumption of prosecution history estoppel focused on the arguments of forseeability and tangetiality.

Forseeability refers to the leaps in logic and technology necessary for the claimants to be able to imagine or construct, at the time of patenting, an equivalent device. Such devices can then subsequently be included or excluded in the bounds of the claim. Furthermore the claimant cannot later argue that the device was unaccounted for in the bounds of the claim, and thus the claim may be construed to include that device when at the time of patenting it was not included, though it was known. In this case Hamilton has referred to the L1011, an APU that measured the flow speed and existed before Honeywell patented its APU. There is indeed a difference in how the devices measure the flow speed: the L1011 uses a shock switch, while the Honeywell device measures the inlet guide vane position. However, the existence of the L1011 as prior art means that Honeywell cannot possibly include all flow measurement means within its claims. Moreover, the status of the art at the time of patenting would make IGV measurement forseeable as a method for flow control.

Honeywell admitted that the reason for narrowing its claims was to avoid prior art which disclosed surge control using DELPQP and proportional and integral control. Indeed, because our device uses that same parameter to determine surge control, the Hamilton device falls clearly into that region of prior art which Honeywell specifically omitted from their revised claims. 

Honeywell will argue our device is equivalent because both use the position of IGVs to control surges. However, because of our additional parameter, DELPQP, which, in the prosecution history, was specifically avoided by the Honeywell patent, for Honeywell to claim equivalence would be to extend the patent claim to cover something not for which it did not reference but for which it avoided. Thus we see the importance of the reasoning behind the claim limitation. In Warner-Jenkinson, the patent in question avoided a pH greater than 9 because it had already been described in prior art. Thus, the patentee would have no claim to infringement under the doctrine equivalents on anyone using a pH greater than 9, even if the remainder of the process were identical. Similarly here, the Hamilton device falls within that same area, where Honeywell has already voided all claims in its prosection history. It would not make sense with precedent for this court to decide that the Hamilton device infringes upon the Honeywell device under the doctrine of equivalents. Honeywell has surrendered the area of surge control dealing with precisely the area which the Hamilton device fills. Although the devices are designed to perform similar tasks in similar ways, the exclusion of the Hamilton device is evident in light of the forseeability and tangentiality considerations, which Honeywell itself is arguing.