CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
HYDROMECHANICAL UNIT
Pcr: Control return pressure.
(Pcr = Pb + 150 psi.)
Pcr pressure is regulated at a constant value of 150 psi above Pb.
The Pcr regulator functions identically to the Pc regulator, however, the pre-loaded spring is calibrated to 150 psid.
Pcr relief valve.
The Pcr relief valve prevents the HMU case pressure from building up to Psf, in case the Pcr regulator goes to a higher than normal pressure, due to a malfunction.
The cracking pressure is set to 20 psi above Pcr.
Over-pressure in the Pcr cavity is by-passed into the Pb cavity.
EFG
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CTC-201-260-00
EFFECTIVITY
73-21-18 Page 17
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03
CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
HYDROMECHANICAL UNIT
Fuel Metering System.
The fuel metering system controls fuel flow to the engine fuel nozzles, through the FMV servo and torque motor, according to commands from the ECU.
The fuel metering system consists of :
-FMV Control System (ECU logic).
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FMV torque motor.
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FMV.
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FMV Resolver.
-Delta P Regulating System.
-By-pass System.
Through the FMV control system, the ECU orders the FMV to rotate to modify the metered fuel flow.
The FMV resolver provides the ECU with an electrical feedback signal, proportional to the FMV position, to achieve closed loop control.
The Delta P and by-pass valves ensure that the metered fuel flow is proportional to the FMV area, by maintaining a constant pressure drop of 36 psid across the valve.
CFM56-5B TRAINING MANUAL
EFG
.
.
CTC-201-262-01
EFFECTIVITY
73-21-18 Page 19
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03
CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
HYDROMECHANICAL UNIT
Fuel metering valve control.
The FMV control system positions the FMV, according to an electrical command signal from the ECU.
The control system consists of :
- FMV torque motor.
-Servo fuel pilot valve.
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FMV.
-
Resolver.
The FMV torque motor receives electrical commands from the ECU and converts them into an axial movement of the servo fuel pilot valve.
The servo fuel pilot valve controls a modulated pressure (Pz), that is ported to, or from, the FMV. The pilot valve has an axial rotation to reduce hysteresis.
The FMV servo piston is subjected to Pz, on one side, and to Pcr backpressure, on the other side.
EFFECTIVITY ALL CFM56-5B ENGINES FOR A319-A320-A321
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