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the Control and Monitoring System (Ref. 49-61-00).
6. Component Description
_____________________
(Ref. Fig. 001)
A. Starter Motor 8KA (Ref. Fig. 002) 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 green brush wear indicator-pin which you can see in a clear plastic cover. When the green indicator pin is shown the brushes are serviceable. When the green indicator pin is not 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 (Ref. Fig. 002) 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,
-10 seconds elapse after the MASTER SW is set to on (in flight only),
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the APU fuel pump system is energized,
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the APU air inlet door opens,
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the IGVs close.
When you put the START pushbutton switch in the ON position:
-
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 speed is less then 7 %, .an automatic shutdown is not detected, .a commanded shutdown (MASTER SW to off) is not selected. start contactor 5KA,
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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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the APU operation data is shown on the lower ECAM display unit.
NOTE : During Ram Air Turbine (RAT) extension, APU starting is inhibited by
____
the Battery Charge Limiters (BCL 1 and BCL 2), which prevent
operation of the main start contactor 5 KA.
At 7% speed, the ECB:
-energizes the igniters,
- opens the fuel solenoid valve on the fuel control unit,
-controls the fuel flow to the APU with the start acceleration control
logic.
At 50% speed, the ECB:
Starting System - Block Diagram
Figure 003
CES
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de-energizes the start contactor 5KA which switches off the starter motor 8KA and the ECB accelerates the APU automatically,
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de-energizes the back-up start contactor 10KA, after 5 seconds. At 95 % + 2 s of the nominal APU speed:
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the ECB controls and monitors the APU automatically,
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the green AVAIL legend in the START pushbutton switch comes on,
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the blue ON legend in the START pushbutton switch goes off.
-
the APU bleed valve is ready for operation,
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