The TRAS hydraulic pressure from the isolation valve goes through directional control valve (DCV) to the extend (head) and retract (rod) sides of the hydraulic actuator piston. The extend pressure releases the actuator lock mechanism which unlocks the actuator piston. The piston extends because the surface area of the piston on the extend side is larger than the retract side of the piston. This permits the actuators to move the thrust reverser sleeve to the extended position in 2-3 seconds.
EFFECTIVITY BEJ ALL 78-34-00
Page 46
D633W101-BEJ May 05/2003
TRAS -FUNCTIONAL DESCRIPTION -ACTUATION
The EEC gets thrust reverser sleeve position data from the rotary variable differential transducers (RVDTs). When both thrust reverser sleeves are more than 60 percent extended, the EEC provides electrical power to the interlock actuator to electromagnetically release the internal brake and the actuator motor starts. Actuator operation will continue until the extend limit switch is actuated which interrupts the electrical power to the motor. Spring force causes the brake to engage which prevents overrun of the actuator.
The interlock actuator extends the rod end which turns the roller on the interlock crank assembly away from the interlock stop on the autothrottle brake housing. The roller no longer blocks the rotation of the autothrottle brake assembly. The pilot can now move the reverse thrust lever to increase the reverse thrust from idle to the maximum reverse thrust position.
Retract
This sequence occurs when there is a command to retract the thrust reverser sleeves:
*
The directional control solenoid valve closes. This removes hydraulic control pressure to the directional control valve (DCV). Spring force in the DCV moves the internal spool valve to the retract position. This permits TRAS pressure to go only to the retract port of the DCV.
*
The sync lock solenoid valve stays open and supplies hydraulic control pressure through the sync lock valve to the
sync lock/manual drive units. The hydraulic control pressure keeps the sync lock/manual drive units and sync shafts released.
* The isolation solenoid valve stays energized. The internal hydraulic control pressure keeps the isolation shutoff valve open. It supplies hydraulic system pressure through the isolation shutoff valve to the TRAS pressure port of the isolation valve and to the directional control valve.
When the thrust reversers are commanded to retract, the directional control solenoid valve closes which causes the directional control valve to move to the retract position. The TRAS hydraulic pressure from the isolation valve goes through directional control valve (DCV) to the retract (rod) side of the hydraulic actuator piston. Hydraulic fluid in the deploy side tubing is directed to the hydraulic return line through the DCV. The actuators will retract and stow the thrust reverser sleeve in 3-5 seconds. The hydraulic actuator locks engage when the sleeve is in the stowed position.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：777 AMM 飞机维护手册 发动机排气 Engine Exhaust PW 777 AIRCRAFT MAINTENANCE MANUAL(44)
