-a signal is transmitted to the ECB. When the intake is open, this is indicated to the ECB via the open position switch of the air intake door-actuator. When intake is open, the backup and main start contactors are energized and power is supplied to the starter motor.
-When the back-up start contactor is activated, the ECB energizes the igniter and opens at 7% rpm the fuel solenoid valve on the Fuel Control Unit (FCU) to supply fuel to the Fuel Flow Divider (FDD). The fuel flow rate from the FCU is controlled by torque motor current from the ECB. The starter motor 8KA assists the APU to accelerate to 50% rpm. Above 20,000ft it accelerates the APU to 58% rpm. The Exhaust Gas Temperature (EGT) increases at a related constant temperature as the APU accelerates.
-The ECB controls the Inlet Guide-Vane Actuator (IGVA). Below 95% APU speed, the ECB signals the IGVA to move the Inlet Guide Vanes (IGVs) to the fully closed (15 degrees) position. Above 95% speed the IGV actuator receives signals to move the IGVs to 22 degrees open position. This allows a minimum amount of air to flow through the load compressor to prevent overheating. A timed acceleration sequence program in the ECB gives a controlled, constant acceleration.
-When the engine has governed rpm (95% rpm + 2s), the ECB sends an 'AVAILABLE' signal to the aircraft circuits. The AVAIL legend in the APU START pushbutton switch 2KA comes on. It indicates that the APU is ready to supply bleed air and electrical power to the aircraft systems.
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CES
(4)
When the APU BLEED pushbutton switch 5HV is set to the ON position:
-the load control valve will open. The APU will then supply bleed air to the pneumatic system. The ECB controls the load control valve, which supplies the pneumatic system with bleed air. The EGT increases when a selection of pneumatic or electrical load, or both, is made. This is shown on the lower ECAM display unit of the Electronic Centralized Aircraft Monitoring (ECAM).
-When the engine speed has passed 95% rpm + 2s, the ECB will accept pneumatic demand signals. It computes the position of the IGVs and supplies the necessary pneumatic flow. The pneumatic and electrical loads together can cause the EGT to increase more than the set temperature limit. If this occurs, the ECB commands the IGVs to move nearer to the closed position. This reduces the pneumatic load and makes the electrical load the primary load.
(5)
When the MASTER SW 14KD is set to the OFF position, a normal APU shutdown starts. The ECB closes the APU load control valve. With the pneumatic loads removed and the bleed air supply no longer required, the APU goes into a cool-down cycle. The cool-down cycle can be break off by setting the MASTER SW bck to the ON position.
-At the end of the cooldown cycle, the ECB exercises the overspeed protection circuit by feeding a frequency input to the overspeed shutdown circuitry. This simulates an overspeed condition. In response, the fuel solenoid closes and the APU shuts down as it would for an actual overspeed condition.
Then the ECB removes the 'AVAIL' signal to the aircraft circuits. The AVAIL legend in the APU START pushbutton switch 2KA and AVAIL indications on the lower ECAM displays are then turned off. During the APU rolldown, the ECB continues to function and maintain signals to the A/C circuits. The IGVs are positioned closed at 15 degrees. An APU restart may be initiated at any time, however the ECB will not initiate the restart until APU speed drops below 7%.
-A decrease in the EGT shows on the APU page of the ECAM.
-During the run-down cycle, when the engine speed is below 7% rpm, the ECB closes the air intake flap and the fuel low-pressure valve 3QF. Before it de-energizes itself, the ECB signals the aircraft circuits to:
-close the FUEL LP VALVE 3QF.
The ECB continually monitors the APU operation and protection functions. If necessary, it shuts down the APU or gives a visual indication to the operator. When a malfunction occurs that could cause damage to the engine, the ECB automatically unloads the engine and starts a shutdown. The FAULT legend in the MASTER SW 14KD comes on. It will stay on until the MASTER SW 14KD is released to OFF.
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CES 4. Operational Characteristics
___________________________
A. Operating Limits
(1)
Rated combination load at sea level 38 DEG.C (100 DEG.F) condition: Bleed Load: Bleed flow = 1.17 Kg/s (156 lbs/min),
Bleed pressure = 3.60 bar (52 psi), Shaft load: 83KW (111.3 shp).
(2)
Turbine discharge temperature (governed speed, absolute maximum) 635 DEG.C (1175 DEG.F) approximately.
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