A320 Engine Interface Unit (EIU)

[AF330]

Good morning,

I talked about this to a pilot and he said that It was more a question for Airbus technicians....Hope you will be able to help me!

I found this:



When we put the engine mode selector:


When the NORM position is selected, continuous ignition A and B is automatically selected when an engine is running and one of the following is met:

- FLX or TO/GA thrust is selected on the ground
- TO/GA thrust is selected in flight
- ENG ANTI ICE switch is ON
- Engine surge or stall occurs in flight
- FLAPS lever position is other than 0 in flight (approach idle is selected)

So we know that the selector is connected with the EIU but the thrust levers are connected with ECU (FADEC). So EIU has said to ECU to give continuous ignition A and B when levers are at FLX or TOGA on ground and at TOGA during flight.

We can see that the ENG ANTI ICE switch is connected with EIU.
So I think that EIU opens the engine anti-ice valve and tells the ECU to give continuous ignition.

When the selector is selected to START on ground, in an automatic starting sequence, the start sequence is identified:
- ECAM displays engine page
- Pack valve close (1)
So EIU will close 1 PFCV (pack flow control valve) by sending a signal to the Pack Controller.

When the ENG MODE selector is positioned to IGN/START inflight the ENG MASTER switch is armed and provides continuous ignition using both igniters.
So EIU will ask ECU to do it.

When the ENG MODE selector is positioned to CRANK, the start valve opens if the ENG MAN START switch is ON and N2 is less than 10%. Ignition is not supplied. So the EIU will ask the ECU to open the starter valve.

Now, with the master switch:



Selecting ENG MASTER switch to ON:

- Opens the LP fuel valve if the ENG FIRE switch is IN
- Initiates an automatic start, if the ENG MAN START switch is OFF
- Initiates a manual start if the MAN START switch is ON

So EIU will ask ECU to open LP fuel valve. Will talk about the start later.

Am I right till here?

[mono]

You're vastly overstating the function of the EIU. It's an interface unit. it doesn't tell the ECU to DO anything. It merely "tells" the ECU what the positions and demands are from the various items with which it interfaces. The ECU then applies the necessary actions which are required according to its internal logic.

The main reason for the EUI is to reduce the amount or wiring and therefore weight. If it were'nt there, every discrete switch position and data bus which feeds it would instead have to go direct to the ECU on the engine so there would be alot more wiring and cable looms.

So for example, the engine anti-ice switch position determines whether to open or close the anti-ice valve. Not the EIU or the ECU. However, because the switch is selected on, the EIU indicates this position to the ECU and the ECU then demands continuous ignition (and an increased fuel flow if the engine is at idle).

If the mode selector switch is in ignition/start in flight, then the switch position is indicated to the ECU by the EIU along with the air/ground status, that is all. The ECU then commands continuous ignition.

The arrows on the diagram indicate the direction of flow of information/discrete position which helps a little with figuring out what's happening.

[AF330]

Thanks a lot mono,

So do you mean that (e.g) the LP fuel valve is not opened/closed by ECU/EIU but direcly by the switch? EIU/ECU just knows the position of the switch/valve?

But what about the engine selector to START/IGN? It will open 1 PFCV. It direcly opens it? It doesn't transit threw the EIU which sends a signal to the pack controller? EIU, again, just knows the position of PFCV?

So when does the second PFCV close (of course, the pilot has pushed the master switch)?
Isn't it the pack controller?

EIU basically helps the ECU.

Thanks

[mono]

Each case is slightly different and getting the answers involves trawling through ASM and WDM.

So do you mean that (e.g) the LP fuel valve is not opened/closed by ECU/EIU but direcly by the switch? EIU/ECU just knows the position of the switch/valve? Correct, LP valve opens or closes depending on the master switch position (and associated fire switch), in fact the EIU "knows" only the switch position not the valve position.

But what about the engine selector to START/IGN? It will open 1 PFCV. It direcly opens it? It doesn't transit threw the EIU which sends a signal to the pack controller? EIU, again, just knows the position of PFCV? A start command is sent from the EIU which controls a relay to close BOTH pack FCSOV.

So when does the second PFCV close (of course, the pilot has pushed the master switch)?
Isn't it the pack controller? See above.

[AF330]

Thanks a lot mono,

1) So there are sensors around PFCV (FCSOV) which send a signal to the pack controller (I think it's the CTC on Boeing)?

2l Could you please explain me the automatic start process?
I know that when we push the master switch, it closes the X Bleed Valve. At that moment, the packs get isolated (bleed air only to the engines). But is the starter valve also direclty opened by the master switch? Or does the EIU send a signal to ECU to do it (I think that ECU controls the starter valve....) What happens next in the start process?

3) At what N (or EPR) % does ECU start ignition?

4) When we push both master switch, how is the bleed air seperated between Engine 1 & Engine 2? Is that valve (name? ) controlled by EIU or direcly by the switch?

Thanks mono,
AF330

[AF330]

And yes, of course, both PFCV will close...
I don't know why I wrote 1....