gemellocattivo.com

Which means "Evil Twin". Lets see your projects where you change boring into fun or create the fun from scratch.
It is currently Thu Mar 28, 2024 12:15 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 29 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: Common Rail Diesel
PostPosted: Fri Apr 08, 2016 12:40 pm 
Offline

Joined: Thu Jan 01, 2015 6:47 pm
Posts: 4251
apalrd wrote:
You can set the eTPU resolution to whatever you want as long as it doesn't exceed the limits. A faster TCR1 frequency also helps. A lot of people set it to a single value, to get 0.1 or 0.0625 deg per tick. 0.1 deg/tick seems common. Then, all of the angular math operates on 0.1 deg/bit and the same fixed point unit can be used for all of the code.



Well....no. That has nothing to do with accuracy, that is precision and they are not the same thing.

Basically you can set the tics/tooth from 1 to 1024 and the angle counter increments by that number each time a tooth is detected so if you have a 36 tooth wheel and set it to 100, then each tic works out a nice even is 0.1 deg or you can set it to 1000 and have 0.01 deg steps which is about the limit for a 36 tooth wheel. Fine. If you have a 37 tooth wheel you can't have nice even numbers though...which is of course why 36 is such a nice choice.

But that is just what you see for steps (precision), it doesn't tell you whether what you see is right or not (accuracy). Its the TCR1 freq that determines accuracy and TRC1 frequency is fixed, and therefore makes accuracy a function of RPM. You get a lot more TCR1 tics at low RPM than high RPM so you have a lot more confidence in the TCR2 steps at low rpm. I guess if you are using low precision TCR2 setting then the point is mute because the 0.1 you see means 0.1 +/0.1% or better at any RPM but if you're using 0.01 it could be +/- say 10% at high RPM for example.....I'd have to go through all the math to figure it out exactly but that is the effect and you end up setting TRC1 based on your required accuracy at max rpm and also the required min RPM requirement.

I did get my TCR1&2 counts mixed up though, it's TRC2 that's limited to 1024 not TCR1.....it's been a while since I looked at this

That's my understanding of it anyway.....and not that this has anything what so ever to do with common rail diesel :)


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Fri Apr 08, 2016 12:50 pm 
Offline

Joined: Thu Jan 01, 2015 6:47 pm
Posts: 4251
oh, and of course none of this means anything if the sensor reading is not accurate, it's only as good as the weakest link and if you have a hall sensor that is the weak link and drives all the accuracy.


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Fri Apr 08, 2016 12:51 pm 
Offline

Joined: Thu Jan 01, 2015 6:47 pm
Posts: 4251
paul s wrote:
Don't ya' know I love it when you talk "eTPU", Mark!!

(best to you on fixing the engine, Mark.)

Paul


I'm dying to get back to that stuff!...I just need to get the stupid engine running :(


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Fri Apr 08, 2016 4:29 pm 
Offline

Joined: Sun Oct 11, 2015 2:07 pm
Posts: 134
eTPU is still fun to play with even if it isn't Diesel specific. The point is that you can set the TCR2 to 0.1deg and the tolerance is usually smaller than a bit anyway, so it's irrelevant.


Back to Diesel, this would be a good reason to try the new MC33816 injector driver chip.

_________________
"Sometimes, the elegant implementation is a function. Not a method. Not a class. Not a framework. Just a function." ~ John Carmack

"Any sufficiently advanced technology is indistinguishable from magic" ~Arthur C. Clarke


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Tue Apr 12, 2016 5:58 pm 
Offline

Joined: Tue Apr 12, 2016 5:48 pm
Posts: 9
Quote:
Has anyone here played with common rail Diesel engines or controls?


Yes

Quote:
In theory, they are much simpler than gas:
-The fuel mass controls load, instead of air mass, fuel mass is much easier to meter/control than air mass

-Air control is not required at all, except boost limiting[/quote]

If you would like to run a common rail diesel like this why not a inline pump? You are missing the whole point of the common rail.

Quote:
-Many fewer actuators, the fuel injector per cylinder replaces injector, spark, and throttle of spark ignition


Not true. Maily the newer diesels have egr the ottos a funky valvetrain. Similar complexity.

The common rail is used to have more injections. This is partly for emmissions and partly for NVH. That is why the modern diesels dont sound like a tractor.


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Tue Apr 12, 2016 8:56 pm 
Offline

Joined: Sun Oct 11, 2015 2:07 pm
Posts: 134
I would like to run an engine that's already common rail. It wouldn't make sense to convert it to something else.

Have you worked on a commercial (e.g. Bosch) or aftermarket common rail control system?

_________________
"Sometimes, the elegant implementation is a function. Not a method. Not a class. Not a framework. Just a function." ~ John Carmack

"Any sufficiently advanced technology is indistinguishable from magic" ~Arthur C. Clarke


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Wed Apr 13, 2016 3:06 am 
Offline

Joined: Tue Apr 12, 2016 5:48 pm
Posts: 9
Yes I have worked with most of The OEM systems.


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Wed Apr 13, 2016 8:52 am 
Offline

Joined: Sun Oct 11, 2015 2:07 pm
Posts: 134
I've been piecing together what is required to properly control this engine. Hardware wise I think a GDI controller would be suitable, for solenoid injectors. All of my engine software experience is in spark ignition engines.

So, a few questions on common rail software:
-How many injections are actually used in most cases? I know Bosch supported 3 initially and now supports 8, but do they actually use all 8? From what I've read, the pre-injections are used to limit the rapid rise in burn rate (mostly for NVH?), and post injections are primarily used for emissions (to burn soot and/or increase exhaust temp to warm up the catalyst or regen the DPF). It seems like only 4 would be necessary (2 pre, 1 main, 1 post).

-How are multiple injections handled for torque? If a torque request is converted to a fuel mass, does the distribution between injections matter, or do the tables assume that it will always be running a certain configuration of injections at certain speeds/torques? Are there separate torque->fuel mass tables for each injection configuration?

_________________
"Sometimes, the elegant implementation is a function. Not a method. Not a class. Not a framework. Just a function." ~ John Carmack

"Any sufficiently advanced technology is indistinguishable from magic" ~Arthur C. Clarke


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Wed Apr 13, 2016 11:31 am 
Offline

Joined: Tue Apr 12, 2016 5:48 pm
Posts: 9
Quote:
I've been piecing together what is required to properly control this engine. Hardware wise I think a GDI controller would be suitable, for solenoid injectors. All of my engine software experience is in spark ignition engines.


Diesel is a bit different but the same principles apply. The diesel engine is a lot harder to kill compared to a otto but it is still quite doable..

It comes down to this:
You have to control railpressure.
You need to figure out fuelmass/railpressure/energizing time.
You need to be able to drive the injector.

After this is done then there will be happy days..

Quote:
So, a few questions on common rail software:
-How many injections are actually used in most cases? I know Bosch supported 3 initially and now supports 8, but do they actually use all 8? From what I've read, the pre-injections are used to limit the rapid rise in burn rate (mostly for NVH?), and post injections are primarily used for emissions (to burn soot and/or increase exhaust temp to warm up the catalyst or regen the DPF). It seems like only 4 would be necessary (2 pre, 1 main, 1 post).


What you have written above is correct.

Dont use a dpf, do not bother with egr. Use only one injection. After you get it running add complexity.

Quote:
-How are multiple injections handled for torque? If a torque request is converted to a fuel mass, does the distribution between injections matter, or do the tables assume that it will always be running a certain configuration of injections at certain speeds/torques? Are there separate torque->fuel mass tables for each injection configuration?


The above is true depending on wich ecu.


Top
 Profile Send private message  
 
 Post subject: Re: Common Rail Diesel
PostPosted: Wed Apr 13, 2016 1:14 pm 
Offline

Joined: Sun Oct 11, 2015 2:07 pm
Posts: 134
What I think I need:

*Injector control electronics are just like GDI, which I have worked on. It needs a high-voltage boost supply for the peak phase and current control for both the peak and hold phases. Peak voltage, peak time, peak current, hold current are all single numbers (no tables) for a certain model of injector
*Converting injection volume to pulse width is a table from volume and rail pressure. In GDI the rail pressure is sampled every TDC but I've seen some Diesel focused prototype controllers which sample it immediately before each injection. Not sure if it's really necessary to sample more frequently.
*Fuel temperature sensor is used to convert fuel mass to injection volume with a table of fuel density
*With only one injection, the rail pressure, start of injection, and injection mass are all determined by torque vs RPM surfaces. Rail pressure is primarily varied by load, SOI primarily varied by RPM, and injection mass by load, but all are surfaces which can vary by both speed and load.
*Torque request is identical to electronic throttle spark ignition, ends with a torque request which is used to calculate fueling instead of throttle/airflow.
*Soot limit surface used to limit immediate torque request with respect to air mass but torque scheduling is still done with respect to max boost torque


The project is for an engineering school fuel economy/emissions competition, so emissions can't be too bad (EPA tier 4 off-road is our benchmark, but with a higher soot limit). We are trying to get by with only a DOC catalyst, but can also add a partial-flow DPF (which can't clog and doesn't require active regeneration). Fuel economy is more important than emissions, so a NOx increase is okay.

_________________
"Sometimes, the elegant implementation is a function. Not a method. Not a class. Not a framework. Just a function." ~ John Carmack

"Any sufficiently advanced technology is indistinguishable from magic" ~Arthur C. Clarke


Top
 Profile Send private message  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 29 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests


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

Jump to:  
Powered by phpBB® Forum Software © phpBB Group