A
B PRESS. SW'S
L METERED
R METEREDPRESS. SW
PRESS. SW
IRS
THRUST SW'S
L NORM
R NORMAIR/GND SW'S
BRK MTR
BRK MTR
NORM A/S
FAIL
AUTOBRAKE SHUTTLE
AUTOBRAKE SHUTTLE
(SH 1)
NORMAL A/S VALVE VALVE
FAIL (BITE) SYS PRESS. NORM ANTISKID (R)
NORM ANTISKID (L)
A/B CARD BITE CARD
MTR PRESSURE
3 TO ANTISKID/AUTOBRAKE
RETURN
CONTROL UNIT (SH 1)
ANTISKID/AUTOBRAKE CONT UNIT
Autobrake Control Schematic
Figure 15 (Sheet 2)
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(b) Autobrake logic and control 1) Autobrake deceleration level inputs a) The autobrake system automatically applies brake pressure selected by the pilot: ~................................................... | Autobrake | Brake | Decel | | Selector | Pressure | Level | | Switch At | (psi) | (ft/sec/sec) | ..................................................... | 1 | 1500 | 4.5 | ..................................................... | 2 | 1750 | 5.0 | ..................................................... | 3 | 2000 | 6.3 | ..................................................... | 4 | 2400 | 8.5 | ..................................................... | MAX AUTO | 3000 | 11.0 | ..................................................... | RTO | 3000 | *[1] | 2................…................….................1 *[1] Decel rate not controlled in RTO mode, max system pressure applied without on-ramp b) The autobrake selector switch positions are encoded in the autobrake card. The encoded level signal starts the brake fill logic and control the valve drivers to generate the selected deceleration rate. 2) Autobrake arming logic
a) The system arms and latches with a magnetic latching switch within 100 milliseconds when the following conditions are met:
1.
A decel level (1, 2, 3, 4, MAX AUTO or RTO) has
_
been selected
2.
No autobrake failures detected
_
3.
No antiskid failure detected on the normal
_ system except that failures on a wheel whose indication has been deactivated will not prevent arming
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4.
All thrust lever switches show not advanced
_ when either air/ground signal indicates ground mode
5.
IRS signal available
_
6.
Brake pressure switches (both left and right)
_
show low pressure
7._When conditions 1. thru 6. are met, hydraulic pressure is metered to the brakes, establising an initial low pressure level. The system then holds the brake pressure at this level until the pitch angle of the airplane is reduced to approximately one degree, as measured by the IRS. As the airplane derotates through the one degree reference attitude, brake pressure is increased to achieve the deceleration value which corresponds to the chosen autobrake setting.
If airplane derotation is delayed, the system will still command brake application. However, the system will pause before before trasnsition to the selected deceleration rate. For the lower autobrake settings, the system will transition to selected deceleration rate after 4 to 5 seconds have elapsed, independant of airplane pitch attitude. With the higher autobrake settings, transition to the selected decelerayion rate will commence when 8.0 seconds have elapsed from main gear touchdown. In either case, the preceding time delays will be overriden when the pitch attitude reaches one degree.
b) The control unit provides an arm hold signal to the switch magnetic latch to keep the switch in the selected position when above requirements are met. If the arm hold signal is not present, the switch moves to DISARM.
3) Autobrake application logic a) The control commands brake pressure by opening the solenoid valve and modulating the control servo valve as required when:
1.
Autobrake is armed.
_
2.
All thrust lever switches are not advanced.
_
3.
Airplane on the ground, indicated by one air/ground
_ signal continuously for 0.2 second.
4.
Wheel spin-up circuit activated.
_ b) Loss of conditions 3. or 4. above after autobrake_
_
application causes autobraking to be removed but not
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本文链接地址：757 AMM 飞机维护手册 起落架 CHAPTER 32 - LANDING GEAR 3(2)
