Eric Paul's Support for Honeywell - 04 APR 2011

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  • Honeywell’s patents are for an electrical control system to be used in conjunction with gas turbine auxiliary power units. The patent calls for a “set point” which is used to mark the minimum flow to avoid airflow surges. This set point is the desired value of the flow parameter. The flow parameter is a function of the position of the inlet guide vanes (IGV). The actual flow conditions are measured and compared to this desired value in order to determine the required position of the surge bleed valve. It is important to note that the flow parameter is a function of the IGVs. These vanes are used to determine the desired amount of flow. The IGVs yield information regarding the value of flow for this device.
  • Sundstrand developed a different auxiliary power unit which compares a “set point” that is a function of the air inlet temperature to a flow parameter in order to determine the position of its surge bleed valve. Sundstrand found that at high flow levels, there are errors in determining the flow parameter. They resolved to use IGVs to measure the level of flow and block the control signal if the flow is too high.
  • In Warner-Jenkinson v. Hilton Davis, the court affirmed that the patent should be compared to the alleged infringing product on an element-by-element level. The court avoided supporting the “triple identity test” or the “insubstantial differences test” unwilling to place any strict limits on the analysis. Instead, the court stated that, “an analysis of the role played by each element…of the specific patent claim will thus inform the inquiry as to whether a substitute element plays a role substantially different from the claimed element.” In this situation, the elements in question are the inlet guide vanes.
  • In the Honeywell patent, the role of the IGVs is to determine the desired value of the flow parameter. This is compared to the actual values of flow to regulate the surge bleed valve. Thus, the fundamental role of the IGVs in Honeywell’s patent is to output a flow value which impacts the position of the surge bleed valve.
  • In the Sundstrand product, the role of the IGV is to measure the flow in order to determine whether it is high or low flow. If it is high flow, the control system is shut down and the surge bleed valve cannot be altered.
  • In both products, a value for flow is a direct function of the IGVs. Additionally, the position of the surge bleed valve is impacted by the flow values output by the IGVs in both designs. In the Honeywell patent, a flow value is a function of the IGVs. In the Sundstrand product, a flow value is a function of the IGVs. In breaking both elements down into their most basic roles, it is obvious that the Sundstrand product infringes the Honeywell patent as a result of the Doctrine of Equivalents.