777 AMM 飞机维护手册 发动机引气 Engine Air PW 777 AIRCRAFT MAINTENANCE MANUAL(11)

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Control
The EEC sends a signal to each dual-coil torque motor in the TCC air valve actuator. This sets the position of a pilot valve. The pilot valve controls the servo fuel that moves each actuator piston. When the piston pulls the TCC air valve control cable, it opens a TCC air valve.
Two LVDTs monitor the position of each piston. Each LVDT sends data to an EEC channel.
Normal Operation -Idle
When the engine is shutdown, both TCC air valves are closed. The valves stay closed when the engine is at idle.
Normal Operation -Takeoff
During takeoff, the TCC LPT air valve starts to open to increase the flow of fan air to the LPT case.
Normal Operation -Cruise
During cruise, both TCC air valves open. This increases the flow of fan air to the LPT and the HPT cases. This also makes the turbine cases smaller to decrease the blade tip clearances.
Non-normal Operation
These two faults cause the TCC air valve actuator to close the HPT or LPT air valve:
*
No torque motor signal

*
No servo fuel pressure.

Indication
The EEC sends the TCC air valve actuator position and fault data to the EDIU. The EDIU sends the data to the AIMS.
The EPCS maintenance page 2 shows the actuator position as a percent of full extension. 100 percent shows the TCC LPT or HPT air valve is full open and 0 percent shows the valve is full closed.
EFFECTIVITY BEJ ALL  75-24-00 
Page 8 
D633W101-BEJ  Sep 05/2002 

PW4000 SERIES ENGINES

777 AIRCRAFT MAINTENANCE MANUAL

AIR -TCC SYSTEM -FUNCTIONAL DESCRIPTION

EFFECTIVITY BEJ ALL  75-24-00 
Page 9 
D633W101-BEJ  Sep 05/2002 

PW4000 SERIES ENGINES

777 AIRCRAFT MAINTENANCE MANUAL

THIS PAGE IS INTENTIONALLY LEFT BLANK

75-25-00

Page 1 D633W101-BEJ Sep 05/2002

AIR -TURBINE VANE AND BLADE COOLING (TVBC) SYSTEM -GENERAL DESCRIPTION

Purpose
BEJ ALL POST SB 777-71-0032
The turbine vane and blade cooling (TVBC) system controls the flow of 12th stage cooling air to the HPT second stage vanes and blades.
BEJ ALL
The turbine vane and blade cooling (TVBC) system controls the flow of 12th stage cooling air to the HPT and LPT areas.
General Description
The TVBC system operates automatically. The EEC controls the system as a function of altitude, N2, and HPT turbine cavity seal temperature. The turbine cooling air thermocouple probe monitors this temperature.
BEJ ALL POST SB 777-71-0032
The EEC sends a signal to the solenoids in the TVBC air shutoff valve solenoid assembly. Filtered PS3 servo air closes the TVBC air shutoff valves. This decreases the supply of 12th stage air to the HPT second stage blades and vanes. Servo fuel changes the TVC actuator position to modulate the TVC air valve. This provides a smooth airflow transition.
　
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