Basic description of Generator and Lane system operation

Hi all

Just before the holidays we had a discussion on the correct way to start the injected engines with 3 phase power systems.  Rotax has always called out a momentary switch to give initial power for the start.  I noted that a number of failures have been seen with people using latching switches and leaving the power on while they have no failure of the internal generators.  

Many OEM use a relay that replaces the momentary switch and for the most part that seems to work well.  

When posing the question to the factory they are surprised as a latching switch was never called out.  They have agreed to do a test, the initial response was the concern of what happens when the 3 phase generator reaches 15 volt?  So now we will have to wait until they can test the issue and perhaps the electrical experts can figure this out also.  My feeling is may be some type of backfeed issue via the fuse box that stops the dumping of excess voltage as is done by the regulators.  

Just my opinion.  We will wait for verification just to be sure.

Cheers

any news?

Hi Paul, 

I think there is some nuance to the Lanes that should be elaborated on further to clarify the “Generator A three…” and “From Generator A…” paragraphs.

To properly understand power distribution, it’s important to realize that the ECU does not power the ignition coils or the injectors; it controls them (via low-side switching, etc.). If you look at the fuse box diagram in the MMH (76-20-00), you’ll see that there are fuses for the Lane A and Lane B circuits. Lane A and B in the 912iS refer to more than just the different computers in the ECU and their associated sensors. They are actually two independent circuits/buses, each powering the components associated with that lane (though both circuits/buses always get their power from a single source - Gen A, Gen B, or the airplane battery). The engine components - ignition coils, injectors, and fuel pumps - are split between the circuits/buses and get their DC power directly from the circuits/buses. Additionally, the Lane A computer in the ECU gets its power from the Lane A circuit/bus and the Lane B computer gets its power from the Lane B circuit/bus. In normal operation, only a single lane computer actually controls all the engine components. This is possible because both lane computers have control wiring to all the engine components. However, even when, say, Lane A is controlling Lane B’s components, Lane B’s components still get their DC power from their circuit/bus. 

Many people, after learning that during normal operation only a single lane is controlling all the engine components, have a hard time understanding why shutting off a lane turns off half the spark plugs (ignition coils) and injectors. They wonder why the other lane can’t do what it normally would do and still control all the components. Their confusion lies in thinking of the lanes only in terms of the ECU computers. Shutting off a lane isn’t just turning off its computer - it’s actually shutting off power to that lane circuit/bus (which, of course, removes power from that lane’s ECU computer as well…). This means that the components in that lane no longer have power and so even though the remaining lane’s computer could control those components if they had power, it can’t because they don’t. 

The two separate systems - Lane A and B - therefore, start at the fuse box. It’s clear in the MMH (24-00-00) that the X1 wiring harness connector is for the Lane A circuit components and the X2 connector is for the Lane B circuit components. It is not the case that there is single circuitry up until the ECU and then things split from there. The fuse box is where power distribution is controlled. X1 wiring distributes power to all the different engine components associated with Lane A (ignition coils, injectors, fuel pump 1, Lane A ECU computer, and has control connectors for HIC A for Lane A switches, etc.) and X2 has the same for all the components associated with Lane B. 

Nachshon Kurtz wrote:

Hi Paul, 

I think there is some nuance to the Lanes that should be elaborated on further to clarify the “Generator A three…” and “From Generator A…” paragraphs.

To properly understand power distribution, it’s important to realize that the ECU does not power the ignition coils or the injectors; it controls them (via low-side switching, etc.). If you look at the fuse box diagram in the MMH (76-20-00), you’ll see that there are fuses for the Lane A and Lane B circuits. Lane A and B in the 912iS refer to more than just the different computers in the ECU and their associated sensors. They are actually two independent circuits/buses, each powering the components associated with that lane (though both circuits/buses always get their power from a single source - Gen A, Gen B, or the airplane battery). The engine components - ignition coils, injectors, and fuel pumps - are split between the circuits/buses and get their DC power directly from the circuits/buses. Additionally, the Lane A computer in the ECU gets its power from the Lane A circuit/bus and the Lane B computer gets its power from the Lane B circuit/bus. In normal operation, only a single lane computer actually controls all the engine components. This is possible because both lane computers have control wiring to all the engine components. However, even when, say, Lane A is controlling Lane B’s components, Lane B’s components still get their DC power from their circuit/bus. 

Many people, after learning that during normal operation only a single lane is controlling all the engine components, have a hard time understanding why shutting off a lane turns off half the spark plugs (ignition coils) and injectors. They wonder why the other lane can’t do what it normally would do and still control all the components. Their confusion lies in thinking of the lanes only in terms of the ECU computers. Shutting off a lane isn’t just turning off its computer - it’s actually shutting off power to that lane circuit/bus (which, of course, removes power from that lane’s ECU computer as well…). This means that the components in that lane no longer have power and so even though the remaining lane’s computer could control those components if they had power, it can’t because they don’t. 

The two separate systems - Lane A and B - therefore, start at the fuse box. It’s clear in the MMH (24-00-00) that the X1 wiring harness connector is for the Lane A circuit components and the X2 connector is for the Lane B circuit components. It is not the case that there is single circuitry up until the ECU and then things split from there. The fuse box is where power distribution is controlled. X1 wiring distributes power to all the different engine components associated with Lane A (ignition coils, injectors, fuel pump 1, Lane A ECU computer, and has control connectors for HIC A for Lane A switches, etc.) and X2 has the same for all the components associated with Lane B. 

Seems to me that both fuel pumps continue to run with one lane switch off.

I will have to check that again next time I go out.

Nichshon.

So in summary, what you are saying,  is that engine power to fire the spark plugs, fuel injectors and XXXXX comes from  fusebox, not he ECU. The ECU only controls these. Is this the bottom line? I will look at the diagram and always happy tp update as needed.I was under the impression the the lane checks fihed all plugs since there is no RPM drop. Just a bump turning off A,

Jon,

Good question on the fuel pumps.