-
a return port
-an electrical connector.
(d) Solenoid Valve
(Ref. Fig. 010)
The solenoid valves of the PCU are the same as and interchangeable with each other and those on the Wing Tip Brake (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)
Position Pick-Off Units
Two PPUs are installed in the slat PCU:
-
the Instrumentation PPU (IPPU) (Ref. 27-85-00)
-
the Feedback PPU (FPPU) (Ref. 27-81-00).
They are the same as the Asymmetry PPU (APPU) (Ref. 27-81-00)
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.
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Removal of the PPUs is possible without the removal of the PCU
from the aircraft.
(g) 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.
(2) Operation
The Slat/Flap Control Computers (SFCC1 and SFCC2) (Ref. 27-81-00) control the PCU solenoid valves. 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 of the valve spool movement controls the direction of the motor rotation
-
the quantity of the valve spool movement 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, full speed or low speed modes.
(a) Static Mode
(Ref. Fig. 011)
In the static mode:
-there is no electrical power at all three solenoid valves
-
the centering effect of the springs holds the control valve 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.
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PCU Operation - Static Mode Figure 011
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(b) Normal Startup Sequence
(Ref. Fig. 012)
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
-when the valve spool reaches the "pressure on point", the SFCC energizes the POB solenoid valve to release the POB
-the hydraulic motor receives fluid flow and starts to turn the transmission
-with the valve spool fully moved, the motor gets the maximum available fluid flow and turns at full speed.
(c) Normal Shutdown Sequence
(Ref. Fig. 013)
During the normal shutdown sequence:
-electrical power is removed from the drive-direction solenoid when the flaps are 6.69 deg. (FPPU) away from the set position.
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