User:Gtorrisi/Sundstrand.html

Brief of Amicus Curiae in support of Hamilton Sundstrand Corporation

The doctrine of prosecution history estoppel prevents a patent owner from reclaiming subject matter under their patent that was previously surrendered.

Honeywell International Inc. held a patent for controlling airflow surge in auxiliary power units (APUs). Honeywell’s patents utilized a method of comparing the outlet flow from the compressor to a minimum “set point” flow, which was a function of IGV position, and making the necessary system adjustments based on that. Sundstrand also had a device for controlling airflow surge, but differed in the manner in which airflow surge was detected. Sundstrand measured pressure differentials with a parameter termed DELPQP and used this to make the necessary system adjustments. Its use of IGV was to determine high versus low flow which would decide whether the signal provided by the DELPQP was blocked or not. These methods obviously differ and hence Sundstrand’s device does not directly infringe, but is accused of infringing under the doctrine of equivalents.

Although different from the method used by Honeywell, Sundstrand correctly points out that the method of measuring pressure differentials in APUs was known prior to Honeywell’s patent. Similarly, within the relevant field, it was well-known that the use of inlet guide vanes (IGV) was helpful in controlling surges of air. Furthermore, there was no evidence barring the use of these IGV to determine air flow. Thus it can be seen that the use of IGV in the manner prescribed by Sundstrand’s device would have been foreseeable to someone skilled in the art at the time of the submission of Honeywell’s patent. If a particular claim or use is foreseeable and not covered by a patent, there is a presumption of prosecution history estoppel. The lack of inclusion of this into their patent may be seen as an abandonment of that particular subject matter and therefore barred from infringement either directly or under the doctrine of equivalents. This in itself should be evidence enough to decide this case in support of Sundstrand.

Additionally, the original patent application submitted by Honeywell was rejected due to obviousness in light of prior art. Originally, Honeywell’s patent did not contain mention of the IGV, but upon amendment and resubmission, the patent was split into a process and device patent each of which did mention the use of IGV. Honeywell stated that their amendment was in order to avoid prior art dealing with a surge control system with proportional and integral control where the pressure differential was measured. While IGV position was not utilized in this prior art, Sundstrand’s device was similarly a surge control system measuring pressure differentials. When a patent is amended, the doctrine of prosecution history estoppel applies. It may then be seen that Honeywell surrendered their potential ownership over the subject matter which is used in Sundstrand’s device. Under prosecution history estoppel, Honeywell surrendered their right to the subject matter found in Sundstrand’s device both when they amended their patent and by the issue of foreseeability when drafting their patent. This case must therefore be decided in favor of Sundstrand as Honeywell is unable to use the doctrine of equivalents.