Quote:
Originally Posted by WhatsADSM
Ok that makes some sense. The wastegate position is one of the few tables that actually does state a little about how it works:
"This table uses the Z value and Y value to deduce the X value. For tuning, the X axis must be modified."
BUT... 2 things:
1) Lets take for face value that the Y-axis is infact air-mass in kg/h (as the XDF states). This scaling is not consistent with g/s in the compressor table. To correct this I figured I would normalize on g/s (more common) which means I simply divide by 3.6.
If it were true that it was in kg/h then that means the largest value in the Y-axis is 269 kg/h or 74.7 g/s... That's VERY low, which means the DME would be essentially constantly operating in the last row of the table... given we are talking about boost here.
I actually started to go into the XDF to change it to g/s and found something interesting. The Y-axis scaling is listed as "X*0.03125/3.6"... That 3.6 sure is suspicious isn't it. 
In a nutshell I'm pretty sure the XDF has an error, and the Wastegate Position - Modell Y-axis is in terms of g/s. Which makes much more sense.
I hate to be picky about this stuff but its very important. Incorrect units can lead to expensive stuff not working... just ask NASA and Lockheed
2) The XDF shows the wastegate position model cell (Z) as "%". That can't be load as it wouldn't make any sense ans wouldn't mean you couldn't do as you are saying and translate from kW to duty cycle. Sounds like that should be kW. If it *is* kW this also means that the highest possible duty cycle value to EVER come out of the open-loop wastegate modelling is 45% (that's the greatest X-axis). I actually buy that since that is probably as high as BMW ever wants the open loop to command. Anything more has to be done via a P-I regulator.
However that was just considering the biggest number in the X-Axis. If I instead run an example car through like say a PPK car making 340hp (~270 g/s) in reality if we use the compressor characteristic table alone the highest ultimate duty cycle you could ever see coming off the base table is like 17% duty cycle.
Something doesn't add up there, 17% is too low. There has to be another table being applied in between the compressor characteristic table and the wastegate position model table. "Additional WG due to the spring"? "WGDC Adder"? one of the ATL-Reglers? |
As Joey said there's errors all over the XDF. The Y axis is g/s. Also you'll notice that the boost setpoint factor in the WGDC (spool) table is scaled incorrectly (X/16384). As it's currently scaled it would almost never be used. The correct conversion appears to be X/8192 (same as the compressor characteristic table). When using the commanded WGDC system you'll notice "boost setpoint commanded" logging parameter is not scaled to match the boost setpoint factor in the commanded wgdc table. The logged parameter needs to be multiplied by 2 to match the command wgdc table.
Logging parameter WGDC Base % is actually the cell value from the compressor characteristic table but it looks like the MAF g/s used is actually the MAF req. WGDC g/s logging parameter HOWEVER it appears the logged parameter WGDC Base % is scaled like Cobb. If you change the compressor table to multiply the cell value by 1.5626 you'll then be able to line up MAF req. WGDC g/s & Boost setpoint get the correct WGDC Base "%" from the compressor table.