Honeywell Intern., Inc. v. Hamilton Sundstrand Corp. (JWB)

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The Case

  • Honeywell sued Hamilton for infringement on 5 claims of ‘893 patent and one claim of ‘194 patent
  • Honeywell rewrote dependent claims into independent form, also cancelled the original independent claims – creates presumption of prosecution history estoppels
    • Remanded for Honeywell could prove why it surrendered claims
  • On remand, District Court barred Honeywell from asserting doctrine of equivalence


  • technology to control airflow surge in auxiliary power units or “APUs.”
  • APUs face rapidly changing demand levels for compressed air during flight, they must control against “surges.”
  • Honeywell's patents claim a more efficient APU surge control system. Honeywell's invention establishes a “set point” that represents the minimum flow to avoid surges.
  • System claims are in ‘893 patent, method claims in ‘194 patent
  • claims require the APU to include IGVs, which are used by the surge control system.
  • The original independent claims did not contain any reference to IGVs or any use of the position of these guide vanes in the surge control system

Alleged Infringement

  • Sundstrand manufactures the APS 3200; an APU device with a surge control system that compares a flow-related parameter called DELPQP to a set point based on air inlet temperature and adjusts the surge bleed valve in response
  • Delta P/P does not work at high flow, so it blocks the signal in such cases
  • The system uses in part IGV position to determine whether the APU is experiencing high flow or low flow, and consequently whether to block the control signal.
  • February 16, 2001, a jury found that Sundstand infringed claims of the ′893 and ′194 patents under the doctrine of the equivalents

District Court

  • On remand, the district court held a two-day bench trial to determine whether prosecution history estoppel barred Honeywell from asserting the doctrine of the equivalents
  • Honeywell could rebut the presumption of surrender by demonstrating that (1) “the alleged equivalent would have been unforeseeable at the time of the narrowing amendment,” or (2) “the rationale underlying the narrowing amendment bore no more than a tangential relation to the equivalent in question,” or (3) “that there was ‘some other reason’ suggesting that the patentee could not reasonably have been expected to have described the alleged equivalent.”
  • the district court held that it was “quite intuitive” that it was foreseeable, in 1982-83, to one skilled in the art to measure the position of IGVs to distinguish between high flow and low flow.
  • Honeywell argued that the reason for the underlying amendment was to overcome prior art that disclosed a surge control system with P and Delta P sensors and proportional and integral control, and that had nothing to do with IGVs.
    • The district court disagreed with this characterization, as the DELPQP is a parameter that is also calculated by measuring P and Delta P. Thus, both the prior art and the equivalent in question involved the same flow-related measurement and the use of that measurement is directly related to the rationale underlying the amendments.



  • old technology, while not always foreseeable, would more likely have been foreseeable
  • court must examine, on the basis of this record, whether the use of IGV position to detect high flow and low flow was later-developed technology and thus unforeseeable at the time of the amendments during the prosecution process
  • The record shows that Sundstrand began using IGV position to control airflow within two months of observing the double solution problem, which suggests that the IGV solution may have been known (and foreseeable) in the art.
  • systems, such as the L1011 system, had been developed for control of surge purpose; and inlet guide vanes were routinely used in surge control systems and affected the air flow rate
  • foreseeability only requires that one of ordinary skill in the art would have reasonably foreseen the proposed equivalent at the pertinent time

Tangential Relation

  • To rebut the estoppel presumption with tangentiality, a patentee must “demonstrate that the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question,” or, in other words, that “the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent.”
  • If the prosecution history reveals no reason for the narrowing amendment, the presumption is not rebutted
  • The original independent claims disclosed a surge control system with P and delta P sensors and proportional and integral controls. Those claims, however, were rejected as obvious in light of the prior art.
    • new claims included the IGV limitation, which “refers to both the claimed structure of the [IGVs] and their claimed function in the surge control system....”
  • Because the alleged equivalent focuses on the IGV limitation, the amendment bore a direct, not merely tangential, relation to the equivalent.
  • Because Honeywell did not show that the alleged equivalent was unforeseeable at the time of the narrowing amendment or that the narrowing amendment bore no more than a tangential relation to the alleged equivalent, this court affirms