NOTE: The SCU programming plug must stay with the engine if the SCU is
____
replaced.
C. The SCU programming plug is connected to a receptacle at the lower aft
side of the SCU.
14. Operation
_________
A. Functional Description
(1)
Electronic Engine Control (EEC)
(a)
The EEC is the brain of the fuel control system. It receives thrust lever angle input and other airplane data along with pressure, temperature, and rotor speed signals from the engine to supply thrust management and fuel scheduling, engine parameter limiting, and to control engine components and systems.
(b)
The EEC receives the input signals that follow:
1) Altitude, airplane bleed status, airplane total air pressure (TAP), autothottle equilization EPR trim command, and airplane total air temperature (TAT) from the air data computers (ADC's) (AMM 34-12-00/001) and flight management computers (FMC's) (AMM 34-61-00/001).
2) N2 rotor speed from the EEC alternator 3) N1 rotor speed from the EEC speed transducer 4) Burner pressure (PB) from a direct pneumatic input 5) Inlet total temperature (TT2) from the PT2/TT2 probe 6) Inlet total pressure (PT2) from the PT2/TT2 probe 7) Exhaust total pressure PT4.95 from the PT4.95 probe 8) Fuel flow rate (WF) from FMU metering valve position
feedback 9) Thrust lever resolver angle (TRA) from the TRA resolver 10) Engine oil temperature from the EEC oil temperature
thermocouple probe 11) Fuel temperature from the EEC fuel temperature thermocouple probe 12) HPC exit total air temperature (TT3) from the EEC thermocouple (TT3) probe
(c)
The EEC controls FMU fuel scheduling as a function of altitude, N2, PB, TT2, and WF.
(d)
The EEC supplies steady state thrust as a function of altitude, N2, TT2, calculated mach speed (MN), PT2 and PT4.95 (EPR), TRA, and airplane bleed status.
(e)
The EEC will detect an N1 or N2 overspeed and will command the FMU to idle.
(f)
PB is limited by the EEC.
(g)
The EEC controls the operation of the HPC secondary flow control valve solenoids, turbine case cooling air valve actuator, and turbine blade and vane cooling air valve solenoid as a function of altitude and N1 to optimize engine performance.
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73-21-00
ALL ú ú N03 Page 22 ú Jun 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
(h)
The EEC controls the operation of the 2.9 bleed valve solenoids, 2.5 bleed valve actuator, and variable stator vane actuators as a function of TRA, N1, N2, T2, MN, and altitude to supply increased compressor stability during starting, transient, and reverse thrust operation.
(i)
The engine air/oil heat exchanger valve and the bypass valve for the fuel/oil cooler are controlled by the EEC as a function of fuel temperature to keep fuel temperature and oil temperature less than the limits (AMM 79-21-00/001).
(j)
The air/oil heat exchanger valve for the IDG is normally controlled by the airplane generator control unit. The EEC can control the valve in an override condition as a function of N2 and engine oil temperature to keep engine and IDG oil temperatures less than the limits (AMM 24-11-00/001).
(k) The EEC continuously monitors the parameters for faults. During operation, the EEC looks for internal hardware faults, harness faults, and control component faults. The EEC will adjust for detected faults and transmit fault data through an ARINC 429 data bus to show on EICAS and/or the central maintenance computer system (CMCS). 1) The EEC usually operates from one channel with cross-talk to the other channel to examine the inputs. The EEC will automatically change to the other channel if a fault is found in the controlling channel that effects engine control or if an actuator, valve, or solenoid with dual channel windings will not operate on the controlling channel. 2) Two control modes can be used by the EEC; EPR mode and N1 mode. a) EPR mode is the normal control mode. The EEC maintains a commanded EPR by controlling fuel flow. In EPR mode, takeoff power is obtained at full forward thrust lever position. b) N1 mode is the alternate mode when the EEC can not control the engine in EPR mode. In N1 mode, the EEC uses N1 to control fuel flow and as the thrust setting parameter. In N1 mode, takeoff thrust is obtained at less than full forward thrust lever position. c) N1 mode is automatically selected in reverse thrust. d) If the EEC changes to N1 mode, ENG (1, 2, 3, or 4) EEC MODE advisory message will show on the main EICAS. 3) If an EEC input, which is important to engine control, is not found or is incorrect to the two channels, the EEC will change to N1 mode or synthesize the input from other inputs. a) If actual TT2 is not found, the EEC will change to N1 mode and synthesize TT2 from TAT and TT3.
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