correct KHFM-Calculation @ M3.83 /M3.8x?
MIL_on:
Hi Guys,
i'll have to toy around with an M3.82 during the next weeks and so i wanted to get some things clearer.
First thing i couldnt get the best info about was KHFM - Grundanpassungskonstante.
basically it seems to be quite identical to the krkte in me7.
the only formula i found for it was:
KHFMnew= Qstatnew*KHFMorig/Qstatorig . Being someone who likes if not everyhtings based on a rule of three i started digging into it 3 hours ago. 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?
eliotroyano:
Nice information. Here are my comments and info found.
From what I have read & evaluated, KHFM & FGAT0 constants vastly define fuel injection in old Motronic.
Looking in the net I found the following info:
"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)
LOAD is not just a representation of cylinder filling, but the theoretical Injector Time Open (Ti, Tee sub eye) needed to reach stoich (Lambda= 1) with the current injector setup assuming that the motor is "perfect".
Which it isn't, hence there are fueling tables which are used as multiplicative corrections to LOAD to reach the actual Ti.
With Tl quantified, we now take into account the vagarities of the particular engine family and operating conditions by introducing multiplicative factors to correct the theoretical injector time to the ACTUAL time for injection (Ti) needed at that instant. Finally an ADDITIVE factor (Tv) is added to compensate for the differing injector opening time under lower than nominal voltages.
Ti = (Tl * [C,D,E...]) + Tv
It is this signal (Ti) that is applied to the injectors
Hope this helps, it's from a BOSCH primer I'm writing ...
Jim Comforti"
Looking some old M38x & M592 OEM dumps for 1.8T & VR6 engines, I found that old Motronic suggest that OEM FGAT0 values (fuel injection factor or multiplier) usually are 1 (128 Hex) for an OEM KFLF map (Main Correction Lamdba Map) to reach lambda = 1 as close as possible. That is my impression from looking OEM maps. Also FGAT0 acts as a factor of the Ti = (Tl * [C,D,E...]) + Tv formula mentioned before.
For Tl = Q / (n * Ki) or LOAD = (MAF/RPM)*KHFM, you can see that KHFM= 1/Ki. Then we have that RPM X LOAD(ms/RPM))/(MAF Flow (KG/H)) = KHFM.
I have take some logs of my own engine (1.8T AGU 06A906018CG M383) and obtain all the time that KHFM is around 84, same value you can find in WinOLS KHFM constant (8bits). Also FGAT0 = 1.
MIL_on your information seems to be well defined, but I have the impression from my research, that KHFM is a constant that could relate injectors & MAF allowing the ECU uses in old Motronic MAF Flow (Kg/H) and KHFM as main Load calculation and FGAT0 as correction factor for fuel injection (ms).
eliotroyano:
Hi MIL_On take a look......
MIL_on:
Hi elio,
I waited for your comment as i had you in my mind being oneof the guys who already dived deeper into that topic ;)
Btw here is the document, where i found the base of my initial guess:
http://www.google.com/patents/DE4336813A1?cl=de
so i agree with you in all points except one:
I think that this Ki you are using in your first formula is KHFM for real. But it is only used for building the main load signal and being tweaked via the factors to become the correct value for the non-ideal but real engine injection time including external influences.
Prj also pointed me into a important direction (thanks for that mate!) :
By changing KHFM all maps using load on one of their axes will be screwed up! So its like natural underscaling by using another injector in my equation above...which makes me unsure whether it can be correct, because i can only hardly imagine that bosch built such a crappy ecu, where every map has to be redone when changing the injectors!?!
also you mentioned your khfm is 8 bit? But in the damos its 16 bit?
The next important question for me is: what are the 3 different kfzw for?
edit: you posted your excel while i wrote that post, so i'll have a look at it first, before i answer to that :)
MIL_on:
ok...i dont get what you want to tell me with the excel, because if you ask me that just shows that my guessing was correct?
the measured load vs. calculated load after my method:
yellow measured, orange calc (mLn/KHFM=Load [ms])
then divide your injection time by 2 (load is built by division mL/nmot and not combustion cycle which takes 720°!) and compare it to my calculated value mLn/KHFM. of course it doesnt fit perfect as for example the values i got from the internet (Qstat for the injectors for example) are different or bosch has changed the value slightly (red=inj. period/2, blue= mLn/KHFM [ms])
and then compare youre so called K against my KHFM... it all fits more or less? and that could or even should differ a little bit based on youre so called C, D, E
a logging file with a real driving condition would be interesting also because idling is always some kind of special situation...
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