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· Shutoff
pressure in the event of uncommanded braking.
The hydraulic inlet porting of the brakes has a shuttle valve. Brake shuttle valves are used to isolate
brake control function from park/emergency brake function. Four shuttle valves are used, one for
each brake. The shuttle valve provides the higher of the two input pressures (either brake
control/antiskid
or parking/emergency brake) to the brake.
Pilot and/or copilot brake input is provided by four brake pedal transducers. The signal is processed
by the BCU and commands appropriate brake pressure. If a failure or unreliable signal is present, a
pilot/copilot brake fault message will display on EICAS. Wheel speed is monitored by four
transducers installed in each main wheel axle and these signals are used for antiskid
control valve
operation. The brake and antiskid
control system interfaces with the BCU for autobrake capability.
The BCU provides the brake control system with builtintest
equipment (BITE) and the following
protections:
· Gear retract braking (stops wheel rotation, after takeoff).
· Inhibiting normal gear braking in flight.
· Independent wheel antiskid.
· Locked wheel and touchdown protection.
In the air mode (no WOW signal), the BCU configures the airplane to a full brake dump to prevent
wheel lock up on touchdown. The touchdown protection system is cancelled to allow modulated
braking once a predetermined wheel spinup
signal is present or airplane WOW is detected. The
BCU will cancel hydraulic power to any wheel which is sensed to be at an abnormal deceleration rate
(example: locked wheel).
The dual brake control system independently controls the braking of each main wheel by modulating
the pressure outputs of the appropriate brake control valve. This modulation is controlled by the BCU
which monitors individual wheel speed and deceleration through the wheel speed transducers.
LANDING GEAR
REV 41, Jul 08, 2004 Flight Crew Operating Manual
CSP 700−6
Volume 2
15−10−21
BRAKE CONTROL SYSTEM (CONT'D)
Available inboard and outboard brake pressure supply is continuously monitored and displayed on
the EICAS hydraulic synoptic page and any abnormal brake pressure detected is displayed on
EICAS in the form of a message. The signal for brake pressure indication (systems 2 and 3) is
derived from four electrically redundant brake pressure transducers positioned prior to each shuttle
valve. One pressure transducer channel is linked to BCU channel A, the other to channel B for each
system.
INBOARD BRAKE
PRESSURE READOUT
Displays in increments
of 50 psi, pressure in
the inboard brake
system.
Green − >1800 psi.
Amber − 1800 psi.
White − 3200 psi.
OUTBOARD BRAKE
PRESSURE READOUT
Displays pressure in the
outboard brake system.
Green − NORM will appear
when pressure is increasing
between 1400 − 1750 and
above.
Amber − LO PRESS
1400 psi.
White − 3,200 psi
GF1510_024
2900 NORM
INBD
BRAKES
PSI
OUTBD
1A BRAKES 2A
2950
PSI
3000
PSI
2950
PSI
Park/Emergency Brake
Selection of the PARK/EMER BRAKE handle mounted on the centre pedestal will allow hydraulic
system No. 3 pressure to the shuttle valves of all brake assemblies and apply the brakes.
Mechanical linkages, connected by a push/pull cable, transfer manual inputs from the parking
brake lever to the parking brake valve. For parking brake application, extend the handle to its full
extended (lock) position. A transducer will provide a parking brake applied signal to the BCU.
PARK/EMER BRAKE Handle
Direct pull to full up position will lock the
handle (in the extend position) for parking.
The handle must be pulled up prior to
pressing the parking brake button to
disengage the locking mechanism.
Gradual pull will provide mechanical
proportional braking in an emergency
condition to stop the airplane if required.
STOWED
SET
ANTISLIP
GF1510_025
Proportional braking can also be commanded through the same handle. No antiskid
protection is
available when proportional braking is selected. Emergency brake application is based on the
amount of travel selected by the pilot. A slow steady pull is recommended for best results.
Flight Compartment indication of hydraulic No. 3 accumulator pressure (Hydraulic synoptic page),
provides indication for normal brake pressure, parking brake, No. 3 hydraulic failure or emergency
brake application.
"NORMAL BRAKE FAIL"
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