777 AIRCRAFT MAINTENANCE MANUAL
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AILERON AND FLAPERON CONTROL -FLAPERON PCU -PHYSICAL DESCRIPTION
Physical Description
All four flaperon PCUs are identical. Each flaperon PCU weighs approximately 43 lb (19 kg).
The flaperon PCU contains a hydraulic actuator with a control module. The control module contains:
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An electrohydraulic servo valve (EHSV)
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A bypass solenoid valve
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A mode selector valve
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A differential pressure sensor
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Two relief valves
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An inlet check valve
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An inlet filter.
Hydraulic Actuator
The actuator piston has an LVDT that sends position feedback signals to the ACE. The actuator piston also has a null LVDT to adjust the null position of the actuator during adjustment of the flaperon surface.
EHSV
The EHSV controls the hydraulic power to the extend and retract sides of the actuator. The EHSV has an LVDT that sends EHSV position feedback signals to the ACE.
Bypass Solenoid Valve
The bypass solenoid valve controls the pilot pressure from the hydraulic system to the mode selector valve.
Mode Selector Valve
Pilot pressure from the bypass solenoid valve commands the mode selector valve in one of two positions:
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Normal
*
Bypass.
Differential Pressure Sensor
The differential pressure sensor measures the pressure difference across the actuator piston. The sensor operates an LVDT which sends signals to the ACE.
Relief Valves
The two relief valves protect the actuator from high pressure due to thermal effects or excessive loading conditions.
Inlet Check Valve
The inlet check valves keeps the hydraulic fluid in the actuator when the hydraulic system experiences pressure fluctuations due to system demands.
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AILERON AND FLAPERON CONTROL -FLAPERON PCU -PHYSICAL DESCRIPTION
Inlet Filter
The inlet filter protects the actuator from solids in the hydraulic fluid.
Training Information Point
Only the bearing in the actuator rod end, where it attaches to the flaperon, requires lubrication.
All the other bearings are teflon coated. They do not require lubrication.
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AILERON AND FLAPERON CONTROL -FLAPERON PCU -PHYSICAL DESCRIPTION
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777 AIRCRAFT MAINTENANCE MANUAL
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27-11-00
Page 50 D633W101-BEJ Jan 05/2002
AILERON AND FLAPERON CONTROL -FLAPERON PCU -FUNCTIONAL DESCRIPTION
General
The flaperon PCU operates in two different modes:
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Normal
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Bypass. In normal mode, the ACE energizes the bypass solenoid valve.
In bypass mode, the ACE de-energizes the bypass solenoid valve.
PCU Operational Matrix
The table below shows the conditions of the PCU bypass valve in the two modes of operation.
VALVE CONDITIONS PCU MODES OF OPERATION
NORMAL BYPASS
BYPASS SOLENOID E *[1] D *[2]
*[1] E = ENERGIZED *[2] D = DE-ENERGIZED
Normal Mode
The PCU is in normal mode when the ACE energizes the bypass solenoid valve.
Hydraulic system pressure moves the mode selector valve to the normal position. Under these conditions, an electrical command from the ACE to the EHSV results in the actuator extension or retraction.
Bypass Mode
The PCU is in bypass mode when the ACE de-energizes the bypass solenoid. This happens when there is a single hydraulic or electrical failure on the PCU.
The bypass solenoid valve blocks pressure to the mode selector valve which moves to the bypass position.
Under these conditions, the mode selector valve blocks control pressure from the EHSV to the actuator cylinder. It also permits free hydraulic flow between both sides of the failed PCU and the return line. The adjacent PCU controls the flaperon movement and backdrives the failed PCU.
If both PCUs of the same flaperon are in bypass mode, the flaperon can move freely in both directions. In flight, the airloads then cause the flaperon to move up a maximum of 10 degrees.
When the airplane has no power on the ground, the weight of the flaperon causes it to slowly move down to the actuator stop.
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