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757
MAINTENANCE MANUAL
CAPTAIN'S ELEVATOR
CONTROL CABLE INPUT
FIRST OFFICER'S ELEVATOR CONTROL CABLE INPUT
TO RIGHT ELEVATOR POWER CONTROL ACTUATORS
TO LEFT ELEVATOR POWER CONTROL ACTUATORS
TORQUE TUBES
TORQUE BOX
LEFT AUTOPILOT PITCH CONTROL SERVO
CONTROL OUTPUT AUTOPILOT PITCH ROD ASSY (3 PLACES)
PITCH CONTROL SERVO CENTER AUTOPILOT
FEEL AND CENTERING UNIT
RIGHT AUTOPILOT PITCH CONTROL SERVO
B FWD
Autopilot Pitch Control Servo Locations and Linkages
Figure 3 (Sheet 2)
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MAINTENANCE MANUAL
(1)
The three Autopilot Pitch Control Servos (APCS) are at the aft end of the stabilizer center section on fuselage Section 48. The right APCS is the upper unit, center APCS the center unit and left APCS the bottom unit.
(2)
Each APCS is mounted with four mounting bolts on the torque box aft of the horizontal stabilizer. Output rods connect the APCS crank to the torque tube. Two hydraulic lines and an electrical connector complete the installation.
(3)
Each APCS output rod is connected to the aft torque tube. The captains elevator control column cables are connected to the quadrant on the aft torque tube. The first officer's elevator control cables are connected to the forward torque tube quadrant. The two torque tubes are linked together so either pilot can control the elevators.
C. Autopilot Pitch Control Servo (Fig. 4)
(1)
The autopilot pitch control servo has 2 solenoid valves and an electrohydraulic servovalve. Two linear variable differential transducers (LVDTs) provide position feedback signals representing the position of an actuator piston and an output crank (lever) on the APCS. The APCS has a combined pressure regulator-relief valve, and an inline filter at the hydraulic pressure connection.
(2)
Electrohydraulic Control Valves
(a) Solenoid Valves
1) Two solenoid valves (SV1 and SV2) are installed on the APCS. Each solenoid valve is an electrically operated open-close valve which completes hydraulic pressure through the APCS when autopilot arm and engage logic circuits are completed. Each valve is installed with 4 bolts and sealed with a gasket plate. Electrical pins are mated when the solenoid is bolted in position.
2) Solenoid valve number 1 (SV1) opens when ELEV HYD ARM DC is applied (autopilot is armed). It ports hydraulic pressure to solenoid valve number 2 (SV2) and the electrohydraulic servovalve (EHSV). Solenoid valve number 2 opens when ELEV DETENT ENG DC is applied (autopilot is engaged) and ports hydraulic pressure to the detent pistons. The detent pistons clamp the output linkage crank and transmit actuator piston position to the output crank.
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757 MAINTENANCE MANUAL
ELECTRICAL SOLENOID VALVE NO. 1
CONNECTOR (HYDRAULIC ARM)
HYDRAULIC RETURN PORT
ELECTROHYDRAULIC (HIDDEN)
SERVO VALVE
HYDRAULIC SOLENOID VALVE NO. 2
PRESSURE PORT (SERVO DETENT ENGAGE)AND FILTER SCREEN
OUTPUT (SURFACE) POSITION LVDT
OUTPUT CRANK
CONNECTOR TO
PCA LINKAGE ACTUATOR (SERVO) POSITION LVDT
PRESSURE REGULATOR AND RELIEF VALVE
FILTER ROLLER
ELECTRICAL CONNECTOR SCREEN SOLENOID ELECTROHYDRAULIC SERVO VALVE SOLENOID AND RELIEF VALVE PRESSURE REGULATOR
VALVE NO. 1 VALVE NO. 2
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