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

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Honeywell’s claims infringement of its ‘893 patent for a compressor bleed air control apparatus and method by Hamilton Sundstrand’s APS 3200 is invalid under the doctrine of equivalents. By applying the doctrine to each element of the claims in question, it can be seen that the ‘893 patent and the APS 3200 accomplish the same function in different ways. This conclusion is furthered by an examination of the ‘893 patent’s file-wrapper, in which Honeywell specifically narrowed its claims to avoid rejection based on obviousness. By including the use of IGV position to establish a set point, Honeywell forfeited its claims to other methods of establishing a set point, leaving them available for public use.

The doctrine of equivalents teaches that a product may be deemed equivalent and infringing on a patent if the differences between the two devices are insubstantial (Graver Tank). This was refined in the case of Warner-Jenkinson v. Hilton Davis by the court’s holding that the doctrine of equivalents must be applied to each element of an invention rather than the invention as a whole because the elements of the claims are what define and limit the scope of the patent. The differences between the Honeywell patent and the APS 3200 are more than insubstantial. Focus on the method that is used to control the bleed valve setting and prevent surge. The Honeywell patent evaluates a set point based on the error between a designated flow parameter and the position of the IGVs. The set point is continuously evaluated as a function of the IGV position. The APS 3200 utilizes a surge control system that compares DELPQP to a set point that is based on inlet temperature, not IGV position. The position of the IGVs is used only to determine whether the compressor is experiencing high flow or low flow in order to solve the double solution problem presented by the DELPQP analysis. The system does not determine the set point as a function of IGV position, as is clearly expressed in the ‘893 patent. The differences between the two systems are substantial and thus the doctrine of equivalents does not apply. While they may accomplish essentially the same function, the way in which it is accomplished is different.

There are many different ways in which to evaluate compressor flow, prevent surge and optimize bleeding. If Honeywell were allowed to claim equivalence between its patented method and the method employed by the APS 3200, which are substantially different, it would follow that they could also claim equivalence in just about any other evaluation method. This would clearly undermine the purpose of the patent claims, which is to limit the scope of patent protection for an invention.

The Honeywell patent was originally rejected as obvious and only patented after the addition of terms that define the use of IGV position in evaluating the set point. The PTO clearly – and correctly – asserted that Honeywell could not claim all methods of evaluating flow to establish a set point. The addition of IGVs into the patent claims limited the scope to include only the method of evaluating the set point based on IGV position, leaving other methods, such as that employed by Sundstrand, available to the public. Had the broad language of the original patent application been maintained, the courts could assume that the APS 3200 fell within the scope of the claims, according to the precedent set forth in CSC Fitness, for example. But the amendments to the patent claims introduced the limiting language that was absent from the CSC patent, and Honeywell has conceded its benefit of the doubt. Upon rejection of their broader claims, Honeywell could have chosen to patent additional specific methods but did not. In narrowing their claims, Honeywell excluded any method that did not use IGVs to establish a set point. If they had wished to claim a method of establishing a set point based on inlet temperature, they could have.

This is not to say that no equivalents could be drawn from the ‘893 patent. For instance, if the APS 3200 compared DELPQP to Honeywell’s set point based on IGV position, this could be considered an equivalent because the only difference would be the substitution of DELPQP for Honeywell’s chosen flow parameter. Since the set point would have been evaluated in the same way, the differences would be insubstantial. The difference in evaluation method is significant, however. The file-wrapper shows that the narrowing of these particular claims was demanded by the PTO, which is clear evidence that the patent, once granted, was never intended to exclude from public use all methods of surge control and bleed flow optimization based on comparison of a flow parameter to a set point.