Actual motronic load calculation

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Hairyscreech
Posts: 196
Joined: Tue Jun 20, 2017 3:19 am

Actual motronic load calculation

Post by Hairyscreech »

So one of the key things for the OBD2 piggyback is the calculation of the load value, something that is not going to be trivial.

We could find it empirically by adjusting values until the output matched the Ostrich but that would be sloppy at best.

I have previously found what I think is the actual bosch calculation but will admit as yet I fail to understand it.

I am taking this from here: http://nefariousmotorsports.com/forum/i ... pic=5745.0

So for more info read the link, I am hoping someone will help with working this out here. :?:

I did also have a link to the patent mentioned below but lost it when I blanked my old work PC off and the stick I put it on before hand went tango oscar. :evil:
So i found a patent whith a rough description of how it works:
lets call it:
air mass (better said arithmetic mean of it) gets divided by rpm (identical to me7):

mL kg*min
mLn=-------------
nmot h

after that follows the KHFM division. The result has to be in ms being the injection time needed for lambda=1 based on that mL:

mLn
----- = x[ms]
KHFM
kg*min
from that follows that KHFM has to have the unit: -----------
h *ms

based on that i would say the correct way to calculate KHFM is:

nCyl*14,7*Qstat[g/min]*0,0000167[ms/min]*60[min/h]
KHFM=---------------------------------------------------------
1000 [g/kg]

with nCyl=number of cylinders
0,0000167, 60 and 1000 bein there for changing units of the input. Also remember from ME7 FRM that Qstatbenzin= 1,05*QstatHeptan.
so if i feed that calculation now with my mLn the resulting unit of the equation is ms.
I made a test equation:


1. The original AGU injectors (06A906031; 0280150464) are called to have 249,1cc/min and 179,2 g/min according to Stan Weiss: http://users.erols.com/srweiss/tableifc.htm
with Qstatbenzin= 1,05*179,2 g/min = 188,16 g/min.

I made a guess with nmot=5000 and mL=140g/s= mL=504kg/h --> mLn=0.1008 [kg*min/h]

mLn 0,1008*1000
-----------=--------------------------------= 9,09 ms (time for one rotation @ 5000 rpm= 12ms)
KHFM 4*14.7*60*188.16*0.0000167


with 440cc Bosch Injectors the calculation delivers 5.065ms


I think the resulting values appear to make sense.
Based on that i checked the decimal value in the 06A906018CG File which is: 43860. dividing KHFM for the original Injectors (0,0111085936) by 43860 i got my factor for that value which is: 0.000000253. Does it make sense?
Also another question i have in my mind is: is this the value which is also used as the load-values?

so my initial question should be: Is anyone able to tell me whether this is correct or proof me wrong?
User avatar
biela
Posts: 33
Joined: Tue Jul 22, 2014 1:01 pm

Post by biela »

Hello

I think it is a more detailed explanation from:

Motronic needs exactly three things to calculate LOAD.

1) A signal from the air meter, normalized to "Q" airflow in kg/hr

2) A measure of current engine rpm "n"

3) A programmed injector size constant "Ki" (K sub eye)

LOAD aka Tl (Tee sub ell) is calculated as:

Tl = Q / (n * Ki)


KHFM is injector constant calculated from injector flow (Qstat[g/min]):

nCyl*14,7*Qstat[g/min]*0,0000167[ms/min]*60[min/h]
KHFM=----------------------------------------------------------------
1000 [g/kg]


With nmot=5000 and mL=140g/s you get airflow
And then obtain 9,09 ms load at 5000 rpm.
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