Fuelmass can be calculated from commanded AFR if the airmass is known... the airmass comes from either of the VE or MAF.
Fuelmass can be calculated from commanded AFR if the airmass is known... the airmass comes from either of the VE or MAF.
OOOOOOOOOOOOOOOOOOOoooooooooooooooooooo........... ....BRILLIANT !!!
So the commanded fuel table by it self if you had feed back from a
WBO2
No...Originally Posted by L31Sleeper
You use the wideband feedback to correct the VE table...
You set the commanded AFR to values known to provide desired performance... (since your VE is corrected, the wideband measured AFR will equal the commanded AFR)...
e.g.:
low load and idle: 14.7
high load and WOT: 12.6
i.e.
to the left of column 80kPa is like 14.7 or 14.6,
to the right to column 80kPa is 12.6.
[...the commanded AFR table operates during open loop (i.e. at WOT or if you disabled closed loop)...]
You correct the VE table; you set the commanded AFR table...
[...when the IFR and VE tables are correct, then various other "things" all fall into line...]
The objective is to get the wideband AFR to equal the commanded AFR at all times... in OLSD (open loop, MAF-less) the VE table is the key to this.
If you go drag racing, you first beforehand correct your VE table using the wideband... after doing this your wideband AFR will equal your commanded AFR... then for each run you edit the commanded AFR slightly and see if your ET improves or not, you keep doing this until you achieve the fastest ET...
On the dyno, the VE is first corrected (using wideband)... and then the commanded AFR is adjusted until best power/torque is seen...
The AFR range 12.6-12.8-13.0 has been well known by many drag racers for many years (30-40), it has been arrived at experimentally/empirically to obtain best ET's or best TS.
Follow the four steps:
For example (say we're in OLSD -- open loop, no MAF)...
The PCM reads the VE table and calculates (lets say) 2.0 grams of air to be the cylinder airfill...
PCM then looks up the AFR to command, lets say the commanded AFR table says 10:1 (for easy numbers)...
From those two numbers, the PCM calculates it needs 0.2 grams of fuel (i.e. divide 2.0 g by 10)...
i.e. the ratio 2.0g air to 0.2g fuel is 10:1.
[of course, 10:1 is extremely rich, you wouldn't normally run that].
Last edited by joecar; January 11th, 2010 at 05:32 PM.
continuing the example...
Then after calculating it needs 0.2 grams fuel, the PCM looks up the injector flowrate table to see how much the injector flows...
let say the injector flows 2 grams/second... to deliver 0.2 grams the injector would have to be opened for 0.1 second (i.e. divide 0.2 g/s by 2)...
so by firing the injector for 0.1 second will, after combustion (assuming no misfire) cause the wideband to measured the AFR to be 10:1 assuming the VE table is correct.
[I don't know of any injectors having a flowrate as low as 2 g/s... I used this for the example calculation only]...
[and an injector on time of 0.1 s would exceed the available time (i.e. 2 crank revolutions) and so would exceed 100% injector duty cycle].
Sorry if that last comment confused you guys.......I was talking about
other stand alone systems that use Commanded AFR in place of VE
with feed back from a WBO2 to make sure it is geting that AFR.
Oh... sorry... misread...
Yes, the wideband in closed loop feedback... some standalones use this and some OEM's like VW.
Other standalones use narrowband feedback just like GM.
Thank you everyone for your help. It's running good now. The only thing
that seems strange to me is that my timing hasn't changed but spark table
PID is showing 200% I thought 0% was the Low Octane table and 100% was
the High Octane table ??
Posting Permissions
Reply With Quote