C.
Functional Description - Brake Torque Limiter System (Fig. 13)
(1)
Power and system inputs
(a)
28 vdc power is supplied to the brake torque limiting system through circuit breakers on the P180 DC Power Distribution Panel (Ref. description of brake system control unit brake torque limiter cards).
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MAINTENANCE MANUAL
P180 UNIT (E9)
UNIT ALSO CONTAINS
ANTISKID AND AUTOBRAKE
SYSTEM CARDS
BRAKE SYSTEM CONTROL UNIT Brake Torque Limiter System - Schematic Figure 13 (Sheet 1)
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BRK TORQ SENSOR
WHEEL 1
BRK TORQ SENSOR
WHEEL 5
BRK TORQ SENSOR
WHEEL 9
BRK TORQ SENSOR
WHEEL 13 12 1314
34 1516
TORQ LIMIT WHEEL
CIRCUIT
CARD
WHEEL 1 1-3
5 69 10
WHEELTORQ LIMIT
7 811 12 CIRCUIT
CARD
WHEEL 5 5-7
WHEEL
CIRCUIT
TORQ LIMIT CARD
9-11WHEEL 9 NORM VLV
NORM A/S DRIVER
VLV 13 NORMAL ANTISKID MODULE WING/BODY GEAR WHEEL WELL
TORQ LIMIT
WHL CNTL
CIRCUIT CIRCUIT
WHEEL 13
TORQUE CARD (TYP) ALT VLV
ALT A/S
1-5-9-13 DRIVER VLVS 13-14
WHEEL CARD (TYP)
13-15
BRAKE SYSTEM CONTROL UNIT
ALTERNATE ANTISKID
MODULE (4) BODY GEAR
WHEEL WELLS
TORQUE LIMITER SYSTEM OPERATION Brake Torque Limiter System - Schematic Figure 13 (Sheet 2)
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(b) Brake torque sensor
1) The torque sensor output is from 0 milivolts with 0 KIPS-FT brake torque in a linear progression to 18.09 milivolts with 30 KIPS-FT brake torque.
NOTE: AT 30 KIPS-FT brake torque, the brake release is
____
initiated.
2) A ground to air transition starts starts a self zeroing operation on the brake torque sensors 2 minutes after the signal is received. This logic makes sure that there is no brake force on the equalizer rods during the self zeroing operation by doing it when the gear is retracted into the wheel well.
(2)
Brake torque limiter indication
(a)
The only brake torque limiter indication is an EICAS advisory message BRAKE LIMITER which comes into view on the operational and status display when there is a malfunction of the brake torque limiter system.
(b)
The BRAKE LIMITER message will be displayed on the EICAS in one of two possible status levels. 1) BRAKE LIMITER advisory level message is displayed for these
malfunctions:
a) Brake torque limiter malfunctions (antiskid valve, valve driver or loss of power) to two or more torque limiter channels on the same landing gear truck.
b) Power removed from both monitor BITE circuits in the brake system control unit.
c) The parking brake valve is not fully opened when the parking brake switch is in the not set position. This indicates that the antiskid valve return lines are blocked.
2) BRAKE LIMITER status level S message comes into view whenever there is a malfunction of one torque limiter channel on a landing gear truck.
(3)
Brake torque limiter outputs
(a)
Brake-torque-limiter-antiskid-servo-valve-command signal
1) The valve release signal is transmitted to the normal and the altnernate antiskid-valve-driver circuit for the applicable wheel. The brake-torque-limiter-antiskid-valve-command signal is compared with the antiskid valve signal. The higher of the two commands will operate the antiskid valve.
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