Control logic for fuel controls on APUs
First Claim
1. An electronic control unit for an auxiliary power unit comprising:
- temperature trim means for comparing an exhaust gas temperature of the auxiliary power unit to a predetermined temperature trim limit to determine a temperature trim error;
selection logic means for selecting a fuel flow trim value based on the determined temperature trim error, the fuel flow trim value selected to be either (i) the determined temperature trim error, if the temperature trim error is greater than zero, or (ii) zero, if the temperature trim error is not greater than zero;
subtraction means for subtracting the selected fuel flow trim value from a starting fuel flow value to get a trimmed commanded fuel flow value; and
fuel flow command means for commanding fuel delivery to the auxiliary power unit at said trimmed commanded fuel flow value.
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Accused Products
Abstract
Conventional auxiliary power units (APUs) may experience over-temperature shutdowns when attempting to start them at high altitudes. Further, such conventional APUs may also experience overspeed conditions when a generator load is removed during on-speed operations. A fuel control logic that controls the fuel flow cutback below the minimum blowout fuel schedule is provided. A temperature trim loop measures engine temperature to determine the onset of a possible over-temperature condition. The fuel flow may then be trimmed accordingly to correct this over-temperature onset. Further, when the onset of an overspeed condition is detected, such as when a generator load is removed, the fuel flow may be trimmed accordingly to correct this overspeed onset. The fuel control logic allows the control to find the individual minimum fuel flow for each fuel control without risking blowout of the APU itself.
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Citations
6 Claims
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1. An electronic control unit for an auxiliary power unit comprising:
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temperature trim means for comparing an exhaust gas temperature of the auxiliary power unit to a predetermined temperature trim limit to determine a temperature trim error; selection logic means for selecting a fuel flow trim value based on the determined temperature trim error, the fuel flow trim value selected to be either (i) the determined temperature trim error, if the temperature trim error is greater than zero, or (ii) zero, if the temperature trim error is not greater than zero; subtraction means for subtracting the selected fuel flow trim value from a starting fuel flow value to get a trimmed commanded fuel flow value; and fuel flow command means for commanding fuel delivery to the auxiliary power unit at said trimmed commanded fuel flow value. - View Dependent Claims (2, 3, 4)
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5. An auxiliary power unit for an aircraft comprising:
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an air inlet; a compressor in flow arrangement with the air inlet; a bleed port for providing compressed air to the aircraft; a combustor having at least one fuel nozzle; a turbine in flow arrangement with a gas exhaust; and an electronic control unit for controlling fuel flow to the combustor, the electronic control unit including; temperature trim means for comparing an exhaust gas temperature of the auxiliary power unit to a predetermined temperature trim limit to determine a temperature trim error; selection logic means for selecting a fuel flow trim value based on the determined temperature trim error, the fuel flow trim value selected to be either (i) the determined temperature trim error, if the temperature trim error is greater than zero, or (ii) zero, if the temperature trim error is not greater than zero; subtraction means for subtracting the selected fuel flow trim value from a starting fuel flow value to get a trimmed commanded fuel flow value; fuel flow command means for commanding fuel delivery to the auxiliary power unit at said trimmed commanded fuel flow value; and overspeed prevention and/or correcting means for preventing an overspeed condition from occurring during on-speed operation of the auxiliary power unit. - View Dependent Claims (6)
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Specification