View unanswered posts | View active topics It is currently Wed Sep 18, 2019 6:39 pm



Reply to topic  [ 10 posts ] 
Powerpoint Presentation on aircraft FADEC design 
Author Message
LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Aircraft FADEC control of 4-cylinder engine using dual ECUs with integrated coil packs (wasted spark)

Some design features:
Per-cylinder cylinder head temp
Per-cylinder exhaust gas temp
Twin plug/cylinder wasted spark

http://www.ocflightcenter.com/documents/Liberty-XL2%20FADEC.pps

_________________
Keith MacDonald
Control Engineering (Systems) Technologist


Sun Dec 11, 2011 2:47 am
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15331
Location: Home sweet home!
Cool :-)

It's disappointing that they don't have full dual ECUS on it, and only have partial redundancy, but the dual cpus and sensors is good, as is the paired cylinder setup. Losing full power would be difficult, but losing more than half by dropping two cylinders seems like a real possibility, at least, inside the scope of component failure, which is admittedly pretty low.

Also, almost all ECUs are FADEC! Fancy term for the same old stuff just because it's on a plane where 50's tech is the norm :-)

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Sun Dec 11, 2011 3:20 am
Profile WWW
LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Yeah, they tend to treat FADEC on piston aircraft engines as if it's some magical new technology :P

_________________
Keith MacDonald
Control Engineering (Systems) Technologist


Wed Dec 14, 2011 2:41 pm
Profile
QFP80 - Contributor

Joined: Sat Nov 26, 2011 11:43 am
Posts: 68
I thought that WOT ment Wide Open Throttle but they seam to think its the same as a TPS
As alway's i could be wrong


Wed Dec 14, 2011 2:45 pm
Profile
LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
The description makes it sound like a WOT switch, which was mainstream ECU tech 20 years ago.

Aircraft tend to run under more constant load than an automobile, so it doesn't make sense to have a WOT switch. All a WOT switch was used for was deciding when to ignore the O2 sensor and go to an enriched open-loop map. In an aircraft that is operating in a cylinder-by-cylinder EGT-based control loop, a WOT switch (and possibly even a TPS) makes little sense.

_________________
Keith MacDonald
Control Engineering (Systems) Technologist


Wed Dec 14, 2011 4:29 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15331
Location: Home sweet home!
My interpretation of that was that if you're not quite at WOT, then you're going to be aiming for best safe fuel economy with BMEP high as possible, but torque not as high as possible, however if you push the throttle the whole way down you get a best power/torque tune instead of a best BMEP tune. I think this makes a lot of sense in an aircraft where range is all important and actually, a critical safety parameter too.

Re use of WOT switches, most modern stuff has a TPS with a WOT and a closed/idle switch integral so the ECU gets three signals telling it what the driver is really doing and can therefore make various decisions about what it should do better. Such as box the idle parameters.

I could be wrong, though :-)

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Wed Dec 14, 2011 8:36 pm
Profile WWW
LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
I haven't seen the use of WOT switches in anything I've worked on that is newer than 95-ish. It's not too difficult to tell the ECU to change modes when the TPS reaches a specific threshold.

Some later-90s vehicles which cover a broad spectrum, none of which use idle/WOT switches for the ECU:

1993 Volkswagen Jetta 2.0L (Bosch Motronic 2.9)
1993 Ford Escort 1.9L (Ford EEC-IV)
1996 Buick Roadmaster LT1 5.7L (GM Optispark)
1997 Volvo 850 2.4T (Motronic M4.3 /M4.4)
1998 Subaru Legacy (Siemens)

Before 1993 it was very common to use idle/WOT switches, once OBD1 and OBD2 kicked in, not so much.

A lot of vehicles still had separate throttle position sensor/switch combos for the TCU through the 90s, but that's another story. DBW throttle bodies often have end switches so they don't get overdriven, but the pedal sensors generally do not.

_________________
Keith MacDonald
Control Engineering (Systems) Technologist


Thu Dec 15, 2011 4:03 am
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15331
Location: Home sweet home!
thebigmacd wrote:
It's not too difficult to tell the ECU to change modes when the TPS reaches a specific threshold.

True, but over the life of the vehicle pot voltages will change for the same position and you can't really recalibrate as you have no other frame of reference for your calibration. WOT would be difficult to determine dynamically, if at all possible, but that doesn't matter much for normal use, however idle matters more and I guess you could reasonably assume that the throttle really was closed under certain circumstances.

In any case, you're probably right about the mid nineties thing, my idea of new and other's are possibly distinctly different! The newest car that I've owned was my 1992 skyline :-) I don't intend to own anything past 1998 or so, ever, either. Though it could happen, I reckon a turbo blacktop 4age powered Toyota IQ would be the ultimate city car :-)

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Thu Dec 15, 2011 10:14 am
Profile WWW
LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Fred wrote:
thebigmacd wrote:
It's not too difficult to tell the ECU to change modes when the TPS reaches a specific threshold.

True, but over the life of the vehicle pot voltages will change for the same position and you can't really recalibrate as you have no other frame of reference for your calibration. WOT would be difficult to determine dynamically, if at all possible, but that doesn't matter much for normal use, however idle matters more and I guess you could reasonably assume that the throttle really was closed under certain circumstances.

In any case, you're probably right about the mid nineties thing, my idea of new and other's are possibly distinctly different! The newest car that I've owned was my 1992 skyline :-) I don't intend to own anything past 1998 or so, ever, either. Though it could happen, I reckon a turbo blacktop 4age powered Toyota IQ would be the ultimate city car :-)

Fred.


I know that for the Roadmaster I had, there was a prodecure for calibrating the TPS. I believe it was either 0.5 or 1.0 volts at closed throttle. You just turned on the ignition and adjusted the TPS position until you got the proper voltage.

On semi-modern Volkswagens, there is a "TPS calibrate" mode set via the service tool, very similar to the calibration in Megasquirt.

_________________
Keith MacDonald
Control Engineering (Systems) Technologist


Thu Dec 15, 2011 11:15 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15331
Location: Home sweet home!
OK! I guess the wear and tear is slow enough that it doesn't matter :-)

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Fri Dec 16, 2011 1:51 am
Profile WWW
Display posts from previous:  Sort by  
Reply to topic   [ 10 posts ] 

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF. ColorizeIt.