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cowl, the EEC needs to correct P0 to get ambient pressure.
When the EEC is in normal mode, P0 is used to calculate
airplane speed for engine thrust management. When the EEC is
in an alternate mode, the EEC uses P0 to estimate PT or to find
an assumed PT. See the ENGINE THRUST MANAGEMENT page
in this section for more information.
Each EEC channel has a PS3 transducer. The EEC uses PS3 to
prevent high pressure compressor stall or surge and to make
sure the bleed pressure is above the minimum allowed value. If
bleed pressure is below the minimum, the EEC increases the
minimum idle speed. If the compressor is close to stall or surge,
the EEC controls the VSV, VBV, and TBV to protect the
compressor. Hard tubes and flexible hoses get PS3 air pressure
to the PS3 air connection on the bottom of the EEC.
EEC Cooling
A ram air inlet supplies air to keep the EEC cool. The ram air
inlet is on the outside of the inlet cowl, at the 1:00 position.
ENGINE FUEL AND CONTROL - ENGINE CONTROL - ELECTRONIC ENGINE CONTROL
EFFECTIVITY
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CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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EEC Installation
The EEC attaches to the engine fan case at the 2:00 position.
The EEC attaches to the fan case with four shock mounts. The
EEC is grounded to the engine with metallic straps.
Functional Description
Each EEC has two computers. Each computer can control the
engine. One computer is in active control while the other
computer is in standby. The computers are called channels.
One computer is called channel A and the other computer is
called channel B. The two channels communicate through a
cross channel data link (CCDL).
Each EEC channel has driver circuits. A driver circuit changes
digital command signals to analog signals that go to the engine
and airplane actuators and solenoids. One EEC channel cannot
control the other channels drivers.
Each EEC has sense circuits. A sense circuit reads signals from
various sensors on the engine and airplane. The active channel
can read input data from either channel A or channel B with the
cross channel data link. The active channel chooses the best
signal or averages the signals to calculate the value it uses to
control the engine.
If the active channel is not valid, the standby channel becomes
the active channel. If one EEC channel is not valid, the EEC
stays in the dual channel mode. Dual channel mode lets the
active channel use the sense circuits from both channels for
engine control. If one channel is not valid, a fault is stored in the
BITE memory. Many of these EEC faults cause the ENGINE
CONTROL and MASTER CAUTION lights in the flight deck to
come on. If the ENGINE CONTROL light comes on, you cannot
dispatch the airplane until you correct the condition that caused
the light. You can see the BITE information on the control
display unit (CDU) in the flight deck. See the TRAINING
INFORMATION POINT pages in this section for more
information on BITE.
The EEC is usually in the dual channel mode. The EEC goes to
single channel mode when the EEC alternator supplies power
to only one channel. The EEC channel with EEC alternator
power becomes the active channel and the other channel goes
to standby. The standby channel gets power from the airplane
transfer bus. The EEC also goes to single channel operation
when the EEC channels can not communicate with each other.
When the EEC is in single channel operation, the active channel
of the EEC uses only its own sense circuits to control the
engine.
ENGINE FUEL AND CONTROL - ENGINE CONTROL - ELECTRONIC ENGINE CONTROL
EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
73-21-00-011
When both channels operate normally, channels A and B
alternate between active channel and standby channel each
time the engine is started. This change of control occurs if N1
was more than 76 percent during the previous engine run and
the new active channel has no faults or fewer faults than the
new standby channel.
These are the major functions of the EEC:
* Input signal validation and processing
* Starting, shutdown, and ignition control
* Engine power management
* Reverse thrust control
* Engine core control
* High pressure turbine active clearance control (HPTACC)
　
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