(2)
When the oil level is too low, the low oil level switch transmits a signal to the ECB 59KD (Ref. 49-93-00). If the APU is stopped and the aircraft is on the ground, the APU system page of the Electronic Instrument System (EIS) shows the LOW OIL LEVEL advisory message in pulsing green. If the oil quantity is more than the set minimum, nothing shows.
(3)
You can also fill the oil reservoir with a (optional) pressure fill device through the pressure fill port.
(4)
The oil reservoir has a connection to the ambient air through an air/oil separator. The gear driven air/oil separator is connected through a gearbox vent line to the APU exhaust cone.
(5)
The oil drain plug is installed at the lowest point of the gearbox. The magnetic chip detector is installed in the drain plug. You can remove the drain plug with the chip detector installed. You can also remove the chip detector without the drain plug. The drain plug has a check valve which closes when you remove the chip detector. It is not necessary to drain the oil to check the chip detector.
B. Distribution
(1) The oil distribution system consists of:
-a lube module,
-two oil filters,
-an oil cooler,
-a de-oil solenoid.
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Oil System - System Schematic
Figure 002
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(2)
Oil Pumps The lube module is attached to a pad on the accessory drive gearbox (Ref. 49-26-00). The gearbox drives the shaft of the lube module which supplies the mechanical power for its operation. The lube module gets the oil from the oil reservoir. It passes the oil to the oil cooler and the pressure oil filter. It regulates the oil pressure and supplies the temperature regulated and filtered oil to the lubrication points of:
-
the APU,
-
the load compressor,
-
the accessory drive gearbox,
-
the starter clutch,
-
the APU generator 8XS.
Oil is scavenged from:
-
the turbine,
-
the APU generator.
The scavenged oil from the generator sump and the turbine sump is
returned to the oil reservoir by two scavenge pumps.
The generator scavenge oil is filtered and then passed to the oil
reservoir. This makes sure that no contaminated oil returns from the
generator to the oil reservoir.
The oil which lubricates the gears, the starter clutch and bearings
of the gearbox, is returned to the reservoir.
(3)
Oil Cooler The oil cooler lowers the temperature of the oil. It is an air/oil heat exchanger which receives the cooling air from the cooling fan. The oil cooler keeps the oil temperature within the limits through all operating conditions. A thermal bypass valve is installed at the oil cooler inlet. It makes sure that oil with a very low temperature does not flow through the heat exchanger. The valve is also an oil cooler bypass valve. When the oil cooler is blocked, the oil flows directly to the lubrication oil filter.
(4)
Filters The distribution system has two oil filters:
-
the pressure oil filter,
-
the generator scavenge oil-filter. The filters remove unwanted materials from the oil. The pressure oil filter cleans all the lubrication oil before it is supplied to the lubrication points. The generator scavenge oil-filter cleans unwanted materials from the generator scavenge oil. This makes sure that the generator contaminated oil is not returned to the gearbox.
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Each oil filter has a bypass valve which opens when the filter
element is clogged.
Differential pressure switches on the filter housings transmit a
signal to the CFDS if the filter element is clogged.
(5) De-oiling Solenoid Valve The de-oiling solenoid valve reduces the oil pressure pump load during the APU start, especially during the cold start condition when oil has a high viscosity. The valve is part of the lube module. A solenoid operates the valve position. The ECB controls the solenoid in relation to the de-oiling solenoid logic. The solenoid valve is open during start up to 60% rpm when
-
the oil sump temperature is below -6.7 deg.C (+19.94 deg.F) or
-
the aircraft altitude is more than 20,000 ft,
or
-
the fuel temperature is below -12.2 deg.C (+10.04 deg.F)
4. Interface
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