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• Single-stage turbine
• Accessory gearbox with integral oil reservoir
• Annular reverse flow combustor
• Exhaust duct
Components and Operation
Power Section
Engine power is developed through compression of ambient air by a centrifugal
compressor. The compressed air, when mixed with fuel and ignited in the annular
reverse-flow combustor, drives a turbine. The rotating shaft of the turbine rotor drives
the compressor and the drive shaft of the accessory gearbox.
Gearbox
The APU gearbox assembly provides power transfer from the starter motor to the
accessories and power section during APU starting as well as to all gearbox-mounted
accessories during on-speed rotation. The accessories include:
• Start Motor
• Generator adapter
• Speed sensor
• Lubrication module
• Fuel Control Unit
Lubrication System
The APU gearbox also serves as an oil reservoir and wet-sump lubrication system. A
filler cap with integrated dipstick is incorporated for gearbox oil servicing. Gearbox
oil cooling is achieved by airflow over cooling fins integral to the lower casing of the
accessory gearbox.
AUXILIARY POWER UNIT
For Training Purposes Only
Sept 04
5-3
P I LOT T R A I N I N G GU I D E
Wait a minimum of 30 minutes after APU shutdown to allow the
gearbox wet sump oil level to stabilize. Otherwise, quantity
indications may be inaccurate, and the reservoir may be
overfilled.
APU Schematic (Power Section and Accessory Gearbox)
Figure 5-2
NOTE
P604_05_012
APU
Inlet
Air
Start
Motor
Fuel
Control
Unit
Gearbox
Oil Tank
Cooling
Fins
Turbine
Generator
Adapter
Combustor
Compressor
RPM
Sensor
Accessory
Gearbox
Exhaust
AUXILIARY POWER UNIT
5-4 For Training Purposes Only
Sept 04
P I LOT T R A I N I N G GU I D E
Generator Adapter
Description
The generator adapter transfers APU rotational power from the gearbox to the APU
generator. It has a dedicated pressurized lubrication system.
Components and Operation
Lubrication System
The generator adapter lubrication system is independent from the accessory gearbox
lubrication system, and has a separate filler cap with integrated dipstick for servicing.
The oil within the generator adapter lubrication system is cooled by a fuel/oil heat
exchanger. The cooling fuel supply to the heat exchanger is from the normal APU fuel
feed from the right main tank. If the normal fuel feed is not available, generator
adapter oil will not be cooled, and APU operating time will be limited.
Wait a minimum of 30 minutes after APU shutdown to allow the
generator adapter oil level to stabilize. Otherwise, quantity
indication may be inaccurate, and the adapter may be overfilled.
Generator adapter oil pressure is high immediately after
shutdown. To avoid injury, bleed excess pressure from the
generator adapter by pushing the pressure-relief valve cap
for at least 5 seconds prior to opening the APU generator/
adapter oil filler cap.
Electrical Generator
The APU generator adapter drives a 30 kVA, 400-Hz, three-cycle AC generator used
as a backup electrical power supply for the aircraft. The APU generator is identical to
the engine-driven generators, and is primarily used during ground operations. If the
APU generator is being used to supply electrical power in flight, bleed air extraction
from the APU is not permitted (see Chapter 7 Electrical for additional information).
Use of APU generator in flight is not permitted unless both main
generators have failed or are off-line.
NOTE
CAUTION
NOTE
AUXILIARY POWER UNIT
For Training Purposes Only
Sept 04
5-5
P I LOT T R A I N I N G GU I D E
APU Schematic (Generator Adapter)
Figure 5-3
ECU
HIGH TEMP
LOW PRESS
P604_05_013
Fuel/Oil
Heat Exchanger
Generator
Adapter
Oil Tank
Generator
Adapter
30 kVA
Generator
LEGEND
Fuel Line
Electrical Signals To/From
Right Main Tank
Fuel Control
Unit
AUXILIARY POWER UNIT
5-6 For Training Purposes Only
Sept 04
P I LOT T R A I N I N G GU I D E
Air Intake and Exhaust
Description
The APU air intake is located on the upper left portion of the aft fuselage, near the
base of the vertical stabilizer. The opening of the intake is flush with the fuselage.
APU exhaust gases are expelled through an exhaust duct which exits on the right side
of the aft fuselage, below the right engine pylon.
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庞巴迪挑战者604机组操作手册 CL_604-AUXILIARY_POWER_UNIT(3)
