-
a return port
R Pressure-Off Brake Figure 010
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R Valve Block Figure 011
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-an electrical connector.
(d) Solenoid Valve
R (Ref. Fig. 011)
The solenoid valves of the PCU are the same and interchangeable with each other and those on the WTB. Their removal is possible without the removal of the valve blocks from the PCU.
(e) Filter
The inlet filter is installed at the pressure port. Its removal
is possible without the removal of the valve block from the PCU.
(f)
Differential Gearbox
The differential gearbox contains a reduction and differential gear. The reduction and differential gear transmits the movement from the hydraulic motors through the PCU output bevel gear to the flap transmission system. The casing of the differential gearbox also contains the intermediate gear which transmits the movement to the IPPU and the FPPU. On the differential gearbox casing are primary and secondary load points for the attachment of the PCU to the aircraft structure.
(g)
Position Pick-Off Units
Two PPUs are installed in the flap PCU:
-
the Instrumentation PPU (IPPU) (Ref. 27-55-00)
-
the Feedback PPU (FPPU) (Ref. 27-51-00).
They are the same as the Asymmetry PPU (APPU) (Ref. 27-51-00)
installed in the transmission system at each wing tip. All PPUs
are interchangeable.
An intermediate gear transmits the movement from the differential
gearbox to the IPPU and the FPPU.
Removal of the PPUs is possible without the removal of the PCU
from the aircraft.
(2) Operation
The Slat/Flap Control Computers (SFCC 1 and SFCC 2) (Ref. 27-51-00) control the PCU solenoid valves. The SFCC 1 controls and monitors (through the valve block) the operation of the motor 1 and the SFCC 2 does the same for the motor 2.
The POB, extend and retract solenoid valves, when energized, permit pressure fluid flow:
-
to the POB
-
to the chambers at each end of the control valve.
When the spool of the control valve moves away from the neutral position, the hydraulic system of the aircraft is connected to the related motor as follows:
-
the direction in which the valve spool moves controls the direction in which the motor turns
-
the distance that the valve spool moves controls the speed at which the motor turns.
During normal operation, the valve blocks and the motors operate at the same time. They operate at the same time in the static mode, the normal startup sequence and the normal shutdown sequence. Other sequences operate when there is a system failure or if the startup sequence occurs near to the commanded position.
(a) Static Mode
R (Ref. Fig. 012)
In the static mode:
-there is no electrical power at all three solenoid valves
-
the centering effect of the springs holds the control valve spool in the neutral position
-
the lands on the valve spool seal the main pressure and return lines
-
the chambers at each end of the valve and the line to the POB are open to return. The return is through the solenoid valves.
(b) Normal Startup Sequence
R (Ref. Fig. 013)
During the normal startup sequence:
-
the SFCC energizes one of the directional (extend or retract) solenoid valves
-
the applicable end of the control valve gets fluid pressure
-
the valve spool moves in response to the increased fluid pressure at its applicable end
-
the LVDT sends a signal to the SFCC to indicate a movement of the valve spool
-
the movement of the valve spool causes the POB solenoid valve to get fluid pressure
R PCU Operation - Static Mode Figure 012
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R PCU Operation - Normal Startup Sequence Figure 013
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