The C ACE receives signals from the upper gust suppression pressure transducer and the L1 ACE receives signals from the lower one.
Modal Accelerometers
The R ACE receives signals from the right modal accelerometer and the L2 ACE receives signal from the left one.
Rudder PCUs
The L1 ACE, C ACE and R ACE send output command signals to their assigned rudder PCU and one adjacent rudder PCU.
The output command signals go from the ACE to the EHSV and the bypass solenoid of the assigned rudder PCU. The output command signals also go to the damped solenoid and the pressure reducer solenoid of one adjacent rudder PCU. The PCU sends feedback signals to its assigned ACE from:
*
The EHSV position LVDT

*
The actuator piston position LVDT

*
The actuator null LVDT

*
The differential pressure LVDT.

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777 AIRCRAFT MAINTENANCE MANUAL

RUDDER CONTROL -FUNCTIONAL DESCRIPTION

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -ACE SERVO LOOP

General

The ACE contains a servo loop circuit to control the command signals for the PCUs.
In normal and secondary mode, the PFC sends the command signals to the ACE. In direct mode, the ACE calculates the command signals.
Servo Loop Operation

The rudder command signals go through a servo loop in the ACEs. The command signals then go to the EHSV of the PCUs. The ACEs also use the command signals to monitor for failures.
The movement of the EHSV sends hydraulic pressure to extend or retract the actuator.
The EHSV LVDT measures the movement of the EHSV and supplies a feedback signal to the ACEs. The ACEs use this feedback signal to monitor failures.
The actuator position LVDT measures the movement of the actuator and supplies a signal to the actuator null LVDT.
The actuator null LVDT is in series with the actuator position LVDT. The actuator null LVDT modifies the signal from the actuator position LVDT.
The actuator null LVDT supplies a feedback signal to the ACEs to close the servo loop. The ACEs use this feedback signal to monitor for failures. This signal also goes to the PFC.
The differential pressure LVDT measures the differential pressure across the actuator. The signal from the differential pressure LVDT goes to the ACEs for the servo loop. The signal also goes to the PFCs for force fight equalization.
Failure Monitor
The ACE has a failure monitor to check the proper operation of the PCU. The monitor uses the ACE command signal and the feedback signals from the EHSV LVDT and the actuator LVDT. When the failure monitor finds a fault with the PCU or the ACE, it de-energizes the PCU bypass, damped and pressure reducer solenoids.
Training Information Point
During installation of the rudder PCU, the actuator null LVDT requires adjustment. Remove the LVDT access cover to adjust the LVDT.

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -ACE SERVO LOOP

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE

General

In normal mode operation of the PFCS, the PFCs calculate rudder control commands based on:
*
Rudder ratio changer schedule

*
Thrust asymmetry compensation

*
Yaw damper

*
Wheel-rudder cross-tie

*
Gust suppression

*
Modal suppression

*
Force fight equalization

*
Hydraulic pressure control

*
Rudder trim

*
Autopilot.

The PFCs also calculate the rudder trim commands. This function is covered separately in this section.
Rudder Ratio Changer Schedule

The PFCs receive commands from the rudder pedal position transducers. The rudder ratio changer schedule calculates rudder commands based on these inputs and calibrated airspeed (CAS) data from ADIRU/SAARU.
Command Limiting Function

The command limiting function receives CAS signals from the ADIRU/SAARU. The limiting function makes sure the sum of the rudder commands does not exceed a limit based on airspeed.
Thrust Asymmetry Compensation
The thrust asymmetry compensation (TAC) function controls the rudder and the rudder trim if there is a thrust asymmetry from the engines. The PFCs use engine thrust data from the engine data interface units (EDIUs) to calculate the yaw correction. The TAC authority limit is 60 percent of available rudder. TAC is available only when the CAS is more than 70 knots and there is no reverse thrust command.
　
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