(14)
During normal operation, the IDG air/oil heat exchanger valve is controlled by the GCU as a function of IDG oil temperature and core engine (N2) speed. In this mode of operation, the IDG air/oil heat exchanger valve override solenoid is energized, closing the IDG air/oil heat exchanger valve override pressure switch. This completes an electrical path for the GCU to control the IDG air/oil heat exchanger valve.
(15)
An override operation occurs when the electronic engine control (EEC) senses an engine oil temperature above 320°F (160°C) or a low N2 speed. The EEC removes the command signal from the IDG air/oil heat exchanger valve override solenoid, de-energizing the solenoid. The de-energized solenoid positions the IDG air/oil heat exchanger valve override pressure switch to an open state, which opens the electrical circuit to the valve causing the heat exchanger valve to open.
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A
747-400
MAINTENANCE MANUAL
PROPER (MAXIMUM) OIL LEVEL
MINIMUM ACCEPTABLE OIL LEVEL
LOW OIL LEVEL INDICATOR PRISM SEE B
LOW OIL LEVEL INDICATOR SEE A IDG CASE
OIL LEVEL
OVERFLOW DRAIN HOSE
IDG SERVICING DIAGRAM
OIL
LEVEL
LIGHT ABSORBED INTO OIL
LIGHT RAYS
OK SHOWN-NO SERVICING REQUIRED EXTERNAL OIL CIRCUIT HEAT EXCHANGER
IDG SCAVENGE
FILTER
OVERFLOW STANDPIPE
PRESSURE FILL COUPLING
PRESSURE FILL HOSE
OVERFLOW DRAIN COUPLING ANY BRIGHT SPOT LARGE OR SMALL -SERVICING REQUIRED
B
WHITE MARKS ALIGNED:
PROPER VIEWING ANGLE
LOW OIL LEVEL INDICATOR
A
LIGHT
REFLECTED
OIL LEVEL
LIGHT RAYS
Integrated Drive Generators with Low Oil Level Indicator Servicing Features
Figure 5
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A
747-400
MAINTENANCE MANUAL
(16)
The GCU keeps track of the IDG oil-in temperature. If this temperature reaches 260°F (127°C), a 28 volt dc signal will be removed to open the IDG air/oil heat exchanger valve. When the valve opens, engine fan discharge air provides further IDG oil cooling. If the valve does not open within 60 seconds of the GCU command, an ELEC IDG 1, 2, 3, or 4 VALVE status message will appear on EICAS if the STATUS button is depressed. The message remains on, even if the shutoff valve opens anytime after the 60 seconds. The message is stored in EICAS memory. The GCU allows the IDG air valve to close when IDG oil-in temperature falls below 220°F (104°C).
(17)
If IDG oil-out temperature remains above 314°F (157°C) for 10 minutes, an ELEC DRIVE 1, 2, 3, or 4 status message is stored in memory by EICAS. If IDG oil-out temperature reaches 365 |11°F (185 |6°C), the appropriate amber DRIVE light in the DRIVE DISC switch illuminates. An advisory ELEC DRIVE 1, 2, 3, or 4 message also appears on EICAS and a snapshot occurs in the EICAS system. To avoid further damage to the IDG, the guarded DRIVE DISC switch should be pressed. This activates the input disconnect mechanism.
(18)
IDG'S WITH THERMAL DECOUPLING; A thermal decoupler provides additional protection to the IDG for over-temperature conditions. If the IDG is not disconnected after a high oil temperature is indicated, the thermal decoupler will automatically disconnect the IDG when the oil sump temperature reaches 415°F (213°C). A disconnected IDG must be removed from the airplane and disassembled to reset the decoupler.
(19)
If an oil temperature sensor failure occurs, DRIVE 1, 2, 3, or 4 TEMP SNS status message is displayed, if the STATUS button is depressed, on the auxiliary EICAS screen.
(20)
The maintenance page of EICAS displays IDG ac volts, frequency, load, oil-out temperature, and IDG oil rise temperature. The rise temperature is the difference between oil-out temperature and oil-in temperature. The rise temperature is continuously monitored by the corresponding GCU.
(21)
The thermal relief valve is a protective device installed in the sump of the input housing to ensure that oil will drain from the IDG case, in extreme oil temperature conditions, and will not be present to either cause a fire or add fuel to an existing fire. The valve is a nonresettable, spring-biased, soldered piston-to-sleeve assembly. If the IDG temperature rises above 430°F (220°C), the solder will melt, allowing the spring-biased piston to move and thus provide an opening for oil to flow out through an attached drain tube.
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