Patent ID: 7431015

Claim:
In a fuel metering system including a metering valve and a proportional bypass valve that produces a differential pressure error across the metering valve, a method of controlling fuel flow in the fuel metering system, comprising the steps of: supplying fuel from a fuel source to a supply line, the supply line having at least an outlet port; directing a first fraction of the fuel in the supply line through the metering valve to the supply line outlet port, the metering valve having a first variable area flow orifice; directing a second fraction of the fuel in the supply line through the proportional bypass valve back to the fuel source, the proportional bypass valve having a second variable area flow orifice; continuously estimating the differential pressure error produced by the bypass valve using an algorithm; and controlling fuel flow to the supply line outlet port by (i) adjusting the area of the first variable area flow orifice based at least in part on the estimated differential pressure error and (ii) adjusting the area of the second variable area flow orifice to maintain a substantially constant metering valve differential pressure across the first variable area orifice.