Honeywell v. Hamilton Sundstrand Brief for Defendant-Appellee (Potter)

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The plaintiff Honeywell claims infringement of its ‘893 patent for a compressor bleed air control apparatus and method by the APS 3200, manufactured and sold by the defendant, Hamilton Sundstrand. The ‘893 patent covers a “more efficient” APU surge control system in which it evaluates a minimum flow set point and adjusts said set point as a function of IGV position. The system measures a designated flow parameter “substantially independent of temperature” and compares it to the position of the IGVs to generate an error, which is used in proportional integral control of the bleed valve to optimize bleed airflow.

The APS 3200 utilizes a surge control system that adjusts the bleed valve according to the error between the flow parameter DELPQP and a set point based on air inlet temperature. This method, however, produces an ambiguous signal at high flow conditions, referred to as the “double solution problem,” which the APS solves by using IGV position to determine whether the compressor is experiencing high or low flow.

The plaintiff seek to collect damages by relying on the doctrine of equivalents to claim that the APS 3200 is an infringement of the ‘893 patent, since there is no literal infringement. It is unnecessary to dispute whether or not the systems would be considered equivalents because the plaintiff is unable to argue equivalency due to prosecution history estoppel. The claims of ‘893 were amended during the patent process in order to avoid rejection as obvious in light of the prior art. The rejected independent claims had no mention of the use of IGV position to evaluate the flow set point; this was only added later as limitation to the claims. The PTO asserted, correctly, that Honeywell could not claim all methods of evaluating flow to establish a set point. By narrowing its claims in order to satisfy non-obviousness requirements, Honeywell forfeited its rights to claim other similar methods of surge control. An inquiry into the state of the art at the time of Honeywell’s claimed invention, around 1982-83, shows that Sundstrand’s method of evaluating DELPQP and using IGV position to solve the double solution problem would have been foreseeable. The technology of the time and relevant teachings in the prior art would have presented said method as obvious to anyone skilled in the art. The L1011 APU surge control system was developed in the 1970s and also evaluated flow by measuring DELPQP. And although the L1011 distinguished between high and low flow by means of a shock switch, it was common knowledge that IGV position was related to the level of airflow through a compressor, and any competent engineer could deduce that IGV position could have been used to determine whether a compressor was experiencing high or low flow in order to solve the double solution problem. Honeywell’s own corporate representative, James Clark, even admitted that Honeywell engineers could have solved the double solution problem by measuring IGV position.

If, as Honeywell claims, the APS 3200 is an equivalent to the claims of the ‘893 patent, it is difficult to find clearer evidence that such an equivalent was foreseeable in light of the prior art. Thus, if Honeywell had wished to claim said equivalent, it could have done so explicitly in the drafting of the patent. Failure to do so results in surrender to public use. The original claims may have encompassed such a method, but prosecution history estoppel prevents the plaintiff from attempting to reclaim those elements that it surrendered during the patent amendment process.

There are many different ways in which to evaluate compressor airflow, prevent surge and optimize bleed flow rate. If Honeywell were allowed to claim equivalence between its ‘893 patent and the APS 3200, then they would likewise be able to argue equivalence with almost any method of controlling bleed airflow that utilized IGV position in any way. This would undermine the authority of the PTO, as its initial rejection of the ‘893 application prevented Honeywell from such a broad scope of patent protection. A decision of equivalency would substantially broaden the claims of the ‘893 patent, contrary to the conditions under which it was awarded. This would put undue burden on the industry, as manufacturers would be hard pressed to design around such a broad patent claim. It has long been well known in the industry that IGV position is important in evaluating compressor airflow, and such information is commonly used in a number of ways. The ‘893 patent and the APS 3200 both involve the use of IGV position in relation to surge control, but in substantially different ways. If Honeywell were allowed to claim equivalence between the two methods, many other systems in the industry would be endangered.

In summary, during the patent application process, Honeywell narrowed its claims in the ‘893 patent through an explicit description of its bleed flow optimization method. In doing so, it forfeited its right to other methods of surge control. Prior art teachings show that the techniques used in the APS 3200 would have been foreseeable at the time that the ‘893 patent was drafted. Thus, when it narrowed its claims, if Honeywell had wished to claim such techniques as equivalent, it must have included them in its claims. By failing to do so, it forfeited those processes to the public. Thus, Honeywell is barred from claiming infringement under the doctrine of equivalents by its prosecution history estoppel and the foreseeability of such an equivalent.