Homework 9: In-Class Case Study

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The patent holder claims that we, Hamilton Sundstrand Corp., infringed upon two of their patent designs, both for compressor bleed air control apparatuses and methods. One patent, ‘893, claims:

  • A control system that provides a constant minimum flow rate by use of adjustable inlet guide vanes;
  • The electronics that operate the control system.

The ‘194 patent claimed a compressor for a gas turbine engine that powered a device with variable inlet air flow by using adjustable inlet guide vanes.

Honeywell argued that our patent violated theirs under the doctrine of equivalents. In order to prevent surge, Honeywell utilizes a method in which a controller tracks the difference between the air flow parameter at the exhaust and the desired air flow represented by the set point, which is a function of inlet guide vane position. They claim that our device, which protects against surge by monitoring IGV positioning, infringes on their method. However, in order to prove that it did so, they had to prove that the equivalent we demonstrate was unforeseen at the time of the patent application; if it was foreseen, then the obligation to protect themselves from infringement rested on them to include the equivalent in their claims. In addition, Honeywell amended some of their claims to narrow their scope because, Honeywell claimed, they wanted to avoid some issues with prior art. However, if that was their intent, then they failed because their invention and the prior art rely on the same measurements and the same underlying logic to perform their functions.

Honeywell claims that our method is equivalent because it uses essentially the same methods to accomplish essentially the same thing: static pressure differential in combination with the position of the inlet guide vanes is used to determine whether the compressor is in surge or not. While our system was developed some 10 years after the amendments, this does not mean the method was unforeseeable. We could not have developed our IGV system so quickly after we discovered the double-V problem if the system was not known in the art. Honeywell could have certainly used IGV positioning to solve the double-V problem in 1982; it is most reasonable to assume a person with ordinary skill in the art could have used this method at that time. Thus, the solution is foreseeable, and Honeywell has no ground to allege infringement on our part.

When Honeywell split the claims into device and method, they were essentially addressing the IGV positioning solution offered by our method. Thus, they vacated their right to proving doctrine of equivalents by prosecution history estoppel. Our device does not infringe on theirs because of this, and we should not be found liable for any damages to Honeywell.