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73-21-00
ALL ú ú C02 Page 18 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
a) Power/Fuel Command Input
1. The MEC incorporates 2 concentric control shafts:
_ the power lever shaft and the fuel shutoff shaft. This feature allows manipulation of N2 core engine speed setting independent of fuel shutoff operation. The power lever shaft provides input signals for the scheduling of N2 engine speed settings for both forward and reverse operation. The fuel shutoff lever shaft provides positive operation of the fuel shutoff valve independent of thrust lever operation and also displaces the pump unloading valve which prevents deadheading of fuel outlet pressure. An extension of the power lever shaft actuates the rotor of an electrical position transducer. The power output of this sensor is sent to the power management control (PMC) through a connecting electrical cable.
b) Power Lever Quadrant Angles (Fig. 1).
1. The power lever connecting the thrust lever
_ cables to the control has stops established during the control assembly adjustments to define power lever position limits and fuel shut-off position.
c) Power/Fuel Command Trim
1. The MEC contains an electrohydraulic torque motor
_ which automatically trims the power input linkage to command the MEC to a power schedule as programmed by the PMC (if activated). The PMC, which can be deactivated by flight crew command, establishes and automatically maintains a power schedule based on thrust lever position corrected for altitude and temperature change. This PMC function frees the flight crew from calculating altitude and temperature changes and the subsequent thrust lever adjustment. Physical limits of the torque motor piston output gives the necessary authority limit on the PMC adjustment function.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
73-21-00
ALL ú ú C01 Page 19 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / /
CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
2.
The power lever input linkage is automatically
_ trimmed through the N2K 3-dimensional cam which is positioned by inputs from the fan inlet temperature sensor (T2) and a fan inlet pressure (PS12) sensor and MEC servo valves. The purpose of this trim is to correct N2 core engine speed schedule to more closely match the N1 fan speed schedule established by the PMC trim system discussed above. This provision is included to decrease the effect of a PMC failure and to bias the idle speed schedule at altitude.
3.
The low idle adjustment is an external
_ adjustment provision on the MEC which provides for adjusting the stop position in the input linkage which limits the lower power position of the linkage and thus establish the low idle speed setting.
4.
The MEC provides automatic actuation to limit
_ engine minimum power setting of the input linkage during certain flight modes to high idle position which is higher than low idle. This limit is started by an electrical signal from the airplane's engine idle control system.
d) Speed Governing
1. The power lever angle (PLA) controlled from the
_ flight compartment, is applied to the speed sensing governor. The speed governor monitors actual speed through engine driven flyweights. The centrifugal force of the flyweights, which is a function of engine N2 core speed, is applied to the speed governor spring; a counteracting force is applied by the power lever. The position of the governor pilot valve is determined by comparing engine speed with the desired speed setting established by the power lever. A buffer piston provides stabilization pressures to the governor pilot valve to prevent hunting which will cause the fuel flow to oscillate. The positioning of the governor (speed) pilot valve by the resultant difference of the power command (power lever) and actual speed (flyweights) determines the pilot valve governor servo command (as limited by the pilot valve) to the governor servo piston to increase or decrease the fuel flow to the engine and thus control the speed.
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