CTC-201-149-01
EFFECTIVITY
75-31-00 Page 11
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03
CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
VARIABLE BLEED VALVE
Bleed valve position sensor.
The bleed valve position sensor transmits the angular position of the VBV doors to the ECU by an electrical feedback signal.
It is a Rotary Variable Differential Transducer (RVDT), and is mounted onto the stop mechanism.
It has two marks which should be aligned when the system is adjusted to the reference closed position.
The adjustment is made through the feedback rod connecting the master bleed valve to the transducer’s feedback lever.
EFG
.
CTC-201-150-02
EFFECTIVITY
75-31-00 Page 13
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03
CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
VARIABLE BLEED VALVE
Using engine parameters, the ECU calculates the VBV position, according to internal control laws.
An electrical signal is sent to the HMU torque motor to position a servo valve, which adjusts the fuel pressure necessary to drive the gear motor.
The gear motor transforms the fuel pressure into rotary torque to actuate the master bleed valve.
The stop mechanism mechanically limits the opening and closing of the master bleed valve.
The master bleed valve drives the 11 variable bleed valves, through a series of flexible shafts.
The flexible shafts ensure that the VBV’s remain fully synchronized throughout their complete stroke.
A feedback rod is attached between the master bleed valve and the feedback transducer, which transforms the angular position of the master bleed valve into an
electrical signal for the ECU.
EFG
.
CTC-201-144-01
EFFECTIVITY
75-31-00 Page 15
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03
CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
VARIABLE BLEED VALVE
VBV system logic.
The ECU calculates the VBV demand-signal. This calculation uses:
-
A corrected fan speed (N1K).
-
A corrected core speed (N2K).
- An N2-trim signal from the VSV.
-A Throttle Resolver Angle (TRA).
The ECU calculates a basic VBV position, depending on N2 speed and the position of the VSV.
This position is then finely adjusted, according to the difference between the actual N1 speed and a calculated value.
An adder, corresponding to the TRA position, is also added in the open direction when the engine is running in reverse mode.
EFG
.
.
CTC-201-151-01
EFFECTIVITY
75-31-00 Page 17
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