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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757
MAINTENANCE MANUAL

 (11) Rudder Ratio Changer Module (RRCM) (Fig. 17 and 18)
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 (a)  
Each RRCM receives two airspeed signals from its SAM. Individual commands to the RRCA are produced on both RRCM dual analog computation paths. The RRCM in control is determined randomly at powerup; one module will be active and the other on standby.

 (b)  
Each airspeed signal is summed with the LVDT and equalizer circuit output. When airspeed changes, an error exists between the LVDT and airspeed signals. The RRCM provides an arming signal to the RRCA solenoid valve and a control signal to the RRCA electrohydraulic servo valve (EHSV). These error signals command the RRCA to drive the ratio changer cranks to a new position. The LVDT is driven by the RRCA through the right ratio changer crank. It provides crank position feedback to the RRCM to eliminate the error signal. The amplified error signals on each RRCM computation path are monitored by current detectors. If a difference between error signals exists, an equalization signal is subtracted from the high signal and added to the low. This equalizes the signals to the EHSV.

 (c)  
Failure monitoring of RRCM output is performed on the dual analog computation paths. The output monitoring consists of a command difference, command hardover, and an open load monitor. The difference and hardover monitors use current detectors on each signal path. The difference monitor compares the current output commands of the two computation paths for a difference exceeding | 2.5 milliamp. Signal latch occurs after 0.82-second delay. The hardover monitor sums the output commands of the two signal computation paths for a value greater than |4.75 milliamp. Signal latch occurs after 2.5-second delay. The open load monitor checks the output voltage in each computation path. Absence of load current is reflected in the output voltage. Signal latch occurs if 7.8 volts is exceeded for 1.6 seconds.

 (12)
 RRCM Latch and Control Logic (Fig. 19)

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 (a)  Module latch and control logic functions are performed by monitoring the following inputs: internal module monitors, validated airspeed signal from SAM (Vp), hydraulic pressure sensing, and air/ground status from air/ground relays.
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FLIGHT CONTROLS
HYD DISTRIBUTION

TO RUDDER RATIOCHANGER BELLCRANK LINKAGECSEU AIR/GND & HYD
ACTUATOR
DISCRETE INPUTS

SOLENOIDVALVE HI
GND TEST CMD TO/FROM OTHERRUDDER RATIO CHANGER MODULE HI
LO
LO BYPASS VALVE
OPPOSITE RUDDER RATIO CHANGER MODULE:
NOT INGAGED/NOT IN CONTROL/MDL ABSENT HI

LO
CSEU

ELECTRO-
POWER-AC HYDRAULICSERVO
VALVE
H
H
L
L
L
H
RUDDER RATIO CHANGER ACTUATOR
CT
L
TO MIDDLE
HRUDDER PCA
RUDDER RATIO CHANGER

L 26V AC
LIN VAR DISPL XDCR

H
L MASTERDIM &
AA
TEST
RUDDERRATIO
RUDDER RATIO LT
ANNUNCIATOR PANEL
CSU POWER- DC P
ENGAGE/CONTROL/
CONTINUITY FROM

1275 PSI "OPEN"
RUDDER RATIO (W)
1700 PSI "CLOSED"

OTHER RUDDER
RATIO CHANGER RUDDER RATIO (Y)S 27 HYD PRESS SW RUDDER RATIO CSEU FAULTCHANGER MODULE ANNUNCIATION
(2)  L/R EICAS COMPUTERS
Rudder Ratio Changer Schematic
Figure 17

28V DC
L BUS

RUDDERRATIO P11 AIR
GND
SYS NO. 1 AIR/GNDRELAY
AIR
GND
SYS NO. 2 AIR/GNDRELAY
FROM RATIO
CHANGER
ACTUATOR

ARM VP
VP VALID
CONT VP
STAB TRIM ELEVASYMMETRY MODULE
HYD POWER L
HYD PRESSURE
HYD RETURN
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757
MAINTENANCE MANUAL

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