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A manual disconnect is usually done when the DRIVE light
comes on. The DRIVE light shows that the IDG oil pressure is
less than the minimum operating limit or there is an
underfrequency condition. A switch cover and system logic
prevent an accidental disconnect.
The IDG input shaft also has a shear section that breaks when
torque is too high. This prevents the engine accessory gearbox
from being damaged because of an IDG failure.
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Thermal IDG Disconnect
The IDG also has a thermal mechanism that automatically
disconnects the CSD section of the IDG if the IDG oil
temperature gets too hot. Thermal disconnect occurs at 363F
(182C). You must remove and disassemble the IDG to reset a
thermal disconnect.
IDG Oil System
Inside the IDG are pumps that move the oil through the IDG and
out through two external heat exchangers. A charge pump
moves the oil to operate the IDG and also lubricate and cool the
CSD section of the IDG. The oil also goes to cool the generator.
A scavenge pump then moves the hot oil out of the IDG to the
two coolers. Oil returns into the IDG through a deaerator. From
the deaerator, oil drains into the sump.
The charge pump develops oil pressure for the CSD to operate.
The charge pump pressure is regulated between 240 to 290 psi
(1655 to 1999 kpa) by the charge relief valve. If the charge filter
is clogged, the filter will be bypassed with a differential
pressure more than 100 psi (690 kpa) through a charge filter
bypass valve.
There is a spring actuated vent valve on the IDG to keep
constant internal pressure in the housing. Before you service
the IDG, push the vent valve to relieve pressure built up in the
case.
The case pressure relief valve prevents IDG case rupture if
there is a fuel leak from the IDG OIL COOLER into the IDG oil
system. The valve starts to operate at 30 to 40 psi and is fully
open at 60 psi. The valve vents into the area between the
accessory gearbox and the IDG and overboard through a drain
line.
The scavenge pump sends oil into the scavenge oil filter. If the
scavenge oil filter becomes clogged, a spring-loaded
differential pressure indicator (DPI) goes out. The DPI has a
temperature lockout feature. A bimetal element locks out the
popout indicator if the oil temperature is less than 125F to 165F
(52C to 74C).
A scavenge filter bypass valve in the scavenge circuit limits the
discharge pressure of the scavenge pump. If blockage in the
circuit causes the oil pressure to increase to 325 psi (2,242 kpa),
the bypass valve opens and sends oil to the inlet of the
deaerator which bypasses both the scavenge filter and external
cooling circuit.
Oil from the IDG goes through the AIR/OIL COOLER first. Air
from the engine fan goes through the cooler to decrease the
temperature of the IDG oil. The AIR/OIL COOLER has an
internal bypass which opens if the cooler becomes clogged.
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EFFECTIVITY
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24-10-00-005
The IDG OIL COOLER is in series with the AIR/OIL COOLER. It
gets fuel from the low pressure section of the engine fuel pump.
The oil temperature decreases and the fuel temperature
increases.
The high pressure bypass valve opens if the IDG OIL COOLER
becomes clogged. IDG oil then bypasses the IDG OIL COOLER
and goes back to the IDG.
The amber DRIVE light comes on if the IDG oil pressure
decreases to less than the minimum operating limit of 165 psi
(1136 kpa). The DRIVE light also comes on for an
underfrequency fault. The GCU controls this light.
GENERATOR DRIVE - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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24-10-00-005
GENERATOR DRIVE - FUNCTIONAL DESCRIPTION
GENERATOR DRIVE - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
24-10-00-005
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