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the starter motor,
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the starter clutch module,
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the start contactor,
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the back-up start contactor,
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the ECB. When you operate the starting system the ECB energizes the start contactor (5KA) and the back-up start contactor (10KA). Thus the 28 V DC is supplied to the starter motor. The starter motor turns the APU main shaft through the starter clutch module and the gearbox. At 55% APU speed the ECB turns the starter motor off. The starter clutch module disengages mechanically when the self sustained APU speed is more than the starter motor speed. The timed acceleration logic of the ECB controls the APU acceleration during the APU start.
The starter motor has a brush wear indicator, if the brush wear indicator is red color, the starter motor is unserviceable.
Starting System - Component Location Figure 001 (SHEET 1)
R EFF : 106-106, 108-149, 211-299, 301-399, 49-42-00Page 2 Config-3 Aug 01/05
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Starting System - Component Location Figure 001 (SHEET 2)
R EFF : 106-106, 108-149, 211-299, 301-399, 49-42-00Page 3 Config-3 Aug 01/05
CES
Starting Motor and Starter Clutch
Figure 002
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4.
Power Supply
____________ The starting system gets the electrical power from the DC system of the aircraft. It supplies 28VDC to the BAT BUS 3PP through a fuse (6KA), the contactors to the starter motor (8KA).
5.
Interface
_________
The starting system has an interface with:
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the DC Generation System (Ref. 24-30-00),
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the Control and Monitoring System (Ref. 49-61-00).
6. Component Description
_____________________
(Ref. Fig. 001, 002)
A. Starter Motor 8KA The starter motor is a series-wound DC motor. A V-clamp attaches the starter motor to the accessory drive gearbox. The motor drive spline-shaft engages with the splined shaft of the starter clutch module. The motor is totally enclosed and explosion-proof with an overspeed protection. The electrical terminals of the motor are insulated. The motor includes a brush wear indicator-pin. When the red indicator pin is not shown the brushes are serviceable. When the red indicator pin is shown you have to replace the starter motor. For the manual drive of the APU main shaft, a manual drive shaft is installed on the front of the starter motor. A cap protects the manual drive shaft.
B. Starter Clutch Module Between the starter motor and the accessory drive gearbox there is a starter clutch which makes the mechanical connection. Bolts attach the starter clutch module to the accessory drive gearbox. The clutch module has an inner splined shaft and an outer starter gear, which has a hollow shaft. Between the two shafts are the spring loaded sprags.
(1)
When the starter motor begins to turn, the friction locks the sprags between the races of the splined shaft and the starter gear shaft. The starter motor drives the starter gear through the clutch module.
(2)
During the start, the sprags engage between the splined shaft and the starter gear. When the starter motor is de-energized the motor speed decreases. The starter gear shaft (now driven from the gearbox) turns with a higher speed than the splined shaft of the clutch module. The sprags then disengage.
C. Start Switch The START switch 2KA is a non latching pushbutton ON/OFF switch. A blue colored ON legend comes on when the APU is started. A green colored AVAIL legend comes on when the APU is ready to supply electrical power or pneumatic power to the aircraft systems.
D. Start Contactor and Backup Start Contactor The start contactor 5KA and the backup start contactor 10KA are installed on rack 120VU, rear of the cockpit. These two switches are heavy duty contactors that switch electrical current to the starter motor 8KA.
7. Operation/Control and Indication________________________________ (Ref. Fig. 003) When you put the MASTER SW pushbutton switch in the ON position:
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the main relay 4KD is energized,
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the ECB starts the prestart test,
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the APU fuel pump system is energized,
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the APU air inlet door opens.
When you put the START pushbutton switch in the ON position:
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the ON legend in the START pushbutton switch comes on,
-The ECB energizes the back-up start contactor 10KA and (1.5 seconds later) the start contactor 5KA, The contactors energize the starter motor 8KA with 28 V DC when these conditions are met: .the air intake is open, .the Power-Up Test (PUT) is complete, .the oil level test is complete.
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the contactors energize the starter motor 8KA with 28 V DC and the APU starter motor starts to turn. The starter clutch engages and turns the APU main shaft,
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