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 field current flow in the generator to keep output voltage within
 these limits. Two electrical connectors on the IDG housing allow
 the GCU to control IDG output, and provide IDG permanent magnet
 generator (PMG) power to the GCU.
 (7)  Pressurized oil is used for integrated drive generator (IDG)
 lubrication, cooling, and control. The IDG charge system supplies
 this oil to the speed control and power generation sections. If
 this charge pressure falls below 140 psi, or oil-out temperature
 reaches 365 |11°F (185 |6°C), a signal is sent to the generator
 control unit, causing the appropriate amber DRIVE light in the DRIVE
 DISC switch, located on electrical and standby power/APU start
 module M7307 on the pilots' overhead panel P5, to illuminate. In
 addition to the DRIVE light, the EICAS display will show an advisory
 ELEC DRIVE 1, 2, 3, or 4 message. (The appropriate engine must be
 running for the EICAS message to appear.) This message results in a
 snapshot in the EICAS system. To avoid further damage to the IDG,
 the guarded DRIVE DISC switch should be pressed. This activates the
 IDG disconnect mechanism to disconnect the IDG from the gearbox.
 NOTE: AIRPLANES WITH -10 GENERATOR CONTROL UNITS;____
 The Drive light can be illuminated the second time the
 GCR/GCB trips due to OF/UF protection during a flight.

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747-400 MAINTENANCE MANUAL
3., 1200 HZ CURRENT 102V AC TRANSFORMER GENERATOR CONTROL SWITCH

FIELD SWITCH
Integrated Drive Generator Power Generation Block Diagram Figure 4
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747-400
MAINTENANCE MANUAL

 (8)  
The input disconnect mechanism disconnects the IDG input shaft from the drive section of the IDG. This removes mechanical input power from the IDG. The mechanism is controlled by a guarded, momentary -contact switch labeled DRIVE DISC. Pushing the switch once activates the disconnect. This separates the gearbox drive shaft from the IDG input shaft. The DRIVE DISC switch should be pushed whenever the engine is at a mimimun ground idle speed and the amber DRIVE light in the switch is illuminated.

 (9)  
After the input disconnect mechanism has been activated, the IDG input shaft of the IDG can only be reconnected on the ground. This is done by pulling the input drive disconnect reset ring fully out. This ring is on the IDG housing.

 (10)
 Oil exiting the IDG flows through the IDG scavenge filter, then through the external oil coolers. A delta-pressure indicator, located next to the filter housing, is used to indicate a clogged scavenge filter. The indicator causes a red button to pop out, if the pressure across the filter exceedes 60 psig. This indicates that the scavenge filter is clogged. The indicator is prevented from operating when oil temperature is below 145°F (63°C).

 (11)
 The IDG oil cooling system consists of two oil cooling devices connected in series: One air/oil heat exchanger, and one fuel/oil cooler. Oil entering the air/oil heat exchanger is directly from the IDG oil-out port and scavange filter. After passing through the air/oil heat exchanger, oil flows to the fuel/oil cooler then returns to the IDG.

 (12)
 A valve in the IDG limits the pressure seen across the external oil cooling circuit. If external circuit pressure reaches 250 psi, the valve opens. Oil then flows from the output of the scavenge filter, back through the IDG. The external oil cooling circuit is bypassed.

 (13)
 The IDG air/oil heat exchanger is used to cool IDG oil.  The heat exchanger uses fan discharge air regulated by the IDG air/oil heat exchanger valve. The valve is controlled by 28-volt dc solenoid which directs fuel pressure to operate the valve to the closed position. The air/oil heat exchanger valve is open when the solenoid valve is de-energized.
　
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