Page 49 D633W101-BEJ Sep 05/2003
RUDDER CONTROL -RUDDER PCU -FUNCTIONAL DESCRIPTION
Bypass Mode
The PCU is in bypass mode when the ACE de-energizes the bypass solenoid. The damped solenoid stays energized. This happens when there is a single hydraulic or electrical failure on the PCU or its ACE.
The bypass solenoid valve then blocks hydraulic pilot pressure to the mode selector valve. However, pressure from the actuator, trapped between the bypass check valves and the thermal relief valve, goes through the damped solenoid valve. This pilot pressure moves the mode selector valve to the bypass position.
Under these conditions, the mode selector valve blocks control pressure from the EHSV to the actuator cylinder. It also connects together both sides of the actuator.
When the PCU is in bypass mode, the other two PCUs backdrive it. These two PCUs then operate at full hydraulic system pressure.
During rapid backdrive of the PCU in bypass mode, the compensator/relief valve supplies fluid to the actuator through the anti-cavitation check valves.
Damped Mode
The PCU is in damped mode when the ACEs de-energize the bypass, pressure reducer and damped solenoids. This happens when the PCU has no power or there is a double or triple PCU or ACE failure.
In damped mode, there is no hydraulic pilot pressure on the mode selector valve. Its internal spring moves the valve to the damped position. The mode selector valve blocks control pressure from the EHSV to the actuator cylinder. It also connects both sides of the actuator piston through a restriction.
During rudder operation with a double failure, the good PCU moves the rudder very slowly.
Training Information Point
On the ground with no power on the PCUs, all three PCUs are in damped mode. The rudder can move slowly when an outside force pushes on it.
Indications
The EICAS status message ACTUATOR PRESS SNSR shows that the differential pressure sensor on one of the rudder PCUs is defective. The flaperon also uses the same message.
The EICAS status message FLIGHT CONTROL SYS shows that one or more rudder PCU is not operative.
EFFECTIVITY BEJ ALL 27-21-00
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RUDDER CONTROL -RUDDER PCU -FUNCTIONAL DESCRIPTION
EFFECTIVITY BEJ ALL 27-21-00
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D633W101-BEJ Jan 05/2002
RUDDER CONTROL -RUDDER PCU -FUNCTIONAL DESCRIPTION -PCU MODES
General
The ACEs control the three modes of operation of the rudder PCUs. Each ACE controls the bypass solenoid of its on-side PCU. It also controls the pressure reducer and damped solenoid of one adjacent PCU.
In normal mode of the PFCS, the PFCs command the ACEs to control the pressure reducer solenoid of all the rudder PCUs. In secondary and direct mode of the PFCS, each ACE controls individually the pressure reducer solenoids.
Normal Mode
A rudder PCU operates in normal mode when there is no failure on the PCU and its on-side ACE.
If the PFCS is in normal mode, the rudder PCU operates with reduced hydraulic pressure during cruise flight and when there is no failure with any rudder PCU or ACE. The PFCs command the PCUs to operate with full system pressure when one of these conditions occurs:
*
A failure of one or more PCU
*
The airplane is below 500 feet above ground
*
The flaps are extended.
If the PFCS is in secondary and direct mode, the ACEs command the PCUs to operate with reduced system pressure when there is no failure of a PCU or ACE.
Bypass Mode
If the PCU has an electrical or hydraulic failure or there is a failure of its ACE, the ACE de-energizes the bypass solenoid. The PCU is then in bypass mode. The ACE also de-energizes the damped solenoid of the adjacent PCU which it also controls.
If the PFCS is in normal mode, the PFCs command all the ACEs to also de-energize the pressure reducer solenoid of all the PCUs. The two PCUs without failure then continue to operate with full hydraulic system pressure.
If the PFCS is in secondary or direct mode, the ACE de-energizes the pressure reducer solenoid of the adjacent PCU which it controls. In this case, one PCU is in bypass mode, one PCU operates in normal mode with full pressure and one PCU is in normal mode with reduced pressure.
Damped Mode
If there is a failure of a second PCU or its ACE, the ACE de-energizes the bypass solenoid of its on-side PCU. The ACE also de-energizes the pressure reducer and damped solenoid of one adjacent PCU. In this case, one PCU is in bypass mode, one PCU is in damped mode and one PCU operates with full hydraulic system pressure.
EFFECTIVITY BEJ ALL 27-21-00 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 飞行操纵 Flight Controls 1(55)
