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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
B. Each force transducer provides dual electrically isolated ac output signals that are proportional to the force applied to the control wheel or column. The signals are used by the autopilot computers when the system is engaged in CWS (manual) or in CMD with no flight mode selected. When the autopilot is engaged in a CMD mode the CWS signals are monitored. CWS signals, above a preset level (high detent), will cause the CMD mode to disconnect and the CWS mode to engage.
C. The purpose of the aileron force transducer is to provide input commands to the FCC while in the roll CWS mode.
9. Autopilot Actuators (Fig. 3)___________________
A. Four autopilot actuators are installed, two in the main wheel well area for the aileron axis and two in the aft fuselage for the elevator axis. One set, aileron and elevator, is controlled by the A autopilot system and the other set by the B autopilot system. The units are mechanically linked to aileron and elevator power control units (PCU's) which drive the flight control surfaces.
B. A pressure switch is installed on each actuator. The switch closes when normal hydraulic pressure is applied to the PCU. The engage interlock voltage is wired through the switches to ensure proper hydraulic pressure for autopilot operation.
C. Autopilot system electrical signals operate valves which modulate hydraulic pressure to displace a hydraulic piston and provide a rotary output to the respective PCU. Control and position signals are provided by the following components which are installed on each actuator: engage solenoids, transfer valve, linear variable displacement transducer (LVDT), and pressure regulator.
D. Engage Solenoids
(1) Two engage solenoids are on each autopilot module. Each solenoid is an electrically operated valve (28 volts dc) which, when energized, applies hydraulic pressure within the module. The ARM SOLENOID provides hydraulic pressure to the TRANSFER VALVE and to engage THE DETENT SOLENOID. The detent solenoid provides hydraulic pressure to the detent mechanism. Both solenoids are energized at A/P engagement. However, the detent solenoid is delayed slightly from the arm solenoid. The solenoids are attached to the module with four bolts. Electrical pins mate with wiring within the module when the units are installed. Hydraulic pressure is ported into the units through ports which align when the solenoids are installed. The solenoids are line replaceable units.
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A 737-300/400/500MAINTENANCE MANUAL
VALVE TRANSFER AUTOPILOT FILTER SOLENOID DETENT SOLENOID ARM FILTER
ENGAGE ORIFICE CONTROL DETENT
PORT PRESSURE
INPUT SIGNAL A/P PIPE JET SPOOL CONTROL ORIFICES LIMITING RATE PORT RETURN
AIL HYD SWITCH PRESSURE VALVE & RELIEF REGULATOR PRESSURE
(LVDT) SENSOR POSITION ACTUATOR
SPRINGS DETENT OUTPUT CRANK EXTERNAL PISTONS DETENT OUTPUT CRANK INTERNAL
Figure 3 Autopilot Actuator Schematic
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737-300/400/500MAINTENANCE MANUAL
E. Transfer Valve
(1) The transfer valve distributes hydraulic fluid to the actuator piston through two ports. With the AP engaged and no command signal output (null), the hydraulic flow is equal between output ports. An autopilot signal (vdc) torques the transfer valve to provide an unbalanced hydraulic flow through the control ports which in turn caused the actuator piston to displace. Electrical connections and hydraulic fluid is supplied to the transfer valve similar to the solenoid valves. The transfer valve is installed with four bolts. The transfer valve is a line replaceable unit.
F. Linear Variable Displacement Transducer (LVDT)
(1) The linear variable displacement transducer provides positional information for the actuator piston. The LVDT is excited by 14 volts ac 1800 Hz and provides an ac output signal in proportion to piston position. The LVDT is not line replaceable since it requires mechanical adjustment for nulling to match the actuator.
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