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Discussion and questions related to the course Practical Reflash Tuning
I am trying to understand the BMW model N55 S55 B58 reflash tuning.
I don't understand how the torque is calculated in the torque table and what torque in the cells makes sense. Which tables do these formula values come from? (808 + 3 + 63) / 0.92 = 950Nm
can someone tell me how this behaves and how it is calculated or do the torque values simply have to be larger so as not to be a limit to the torque?
does anyone know of courses or a detailed tuning guide for these models? about the strategies in the control unit.
I hope someone can help me.
thank you guys
this example is from ecutek:
The ECU adds the external losses for say PS pump, and alternator load to give an "Engine Torque" but this will be at the current operating conditions, then the ECU converts that to "Indicated Torque" which will be the torque at reference ignition which is often MBT. We will almost certainly be running at less than MBT and in simplified terms if you target 800Nm at the clutch at 10deg below MBT, your equivalent torque if you were at MBT with everything else the same would be say 890Nm. There are usually maps to calibration for how much torque is lost for a given retard from MBT, and then that is weighted by a factor often known as ignition efficiency. We also need to add frictional torque in to this,
Our Friction losses map looks like this, negative numbers signifying the friction reduces the torque output
The Ignition to torque percentage looks like this: with retard from MBT on the Y axis
So to get from clutch torque to the torque number used in the Torque Actual maps, we have something like:
(Clutch Torque + Ancillaries Losses + Frictional Losses) / ( Torque correction for MBT Offset * Ignition Efficiency) = Reference Torque
eg (using guestimate numbers for friction and ignition efficiency)
(808 + 3 + 63) / 0.92 = 950Nm
In our case, that number gets fed into the Torque Actual map to generate a load figure. In our case we can see that by the time the corrections for friction and ignition are fed in, we are already on the bottom line of those torque actual maps. I can also see that based on your numbers, the car appears to be using Torque Actual 2.
This is a difficult one to answer with out actually carrying out he activity.
OEM's use a model based strategy developed from 1D simulation packages and software-in-loop methods that is then validated with years of practical test bed development. Essentially this model turns driver demand into a torque request that then gives the engine what it need to achieve that desire torque. With the BMW models you listed, they are primarily supplied with the ZF 8HP automatic transmission which in turn is in overall control of the torque output, the engine is a slave to the transmission.
To allow the engine to produce more torque than modelled by the OEM the reflash software will need to manipulate the input parameters to the model whilst still maintaining the corrected final torque numbers that the TCM, BCM etc need to see.
The example you shared is trying to demonstrate where the actual flywheel torque is derived from but explained inversely. If we transpose the formula we get [reference torque * ignition efficiency - the sum of losses] -> (950*0.92)-66=808Nm. With reference torque being the peak number the engine can deliver for a given airflow, ignition efficiency refers to the losses form running sub optimal of MBT (-8%) and the losses due to friction/ancillary loads are self explanatory.
Taking this example and the brief explanation of OEM model based control; if the reflash SW added more air the reference figure of 950Nm would be higher or more ignition advance the efficiency would increase, both would give more flywheel torque out of the other end of the equation.
Fundamentally reflash SW tuning companies don't have access to the OEM ECU parameters due to the security. Taking Bosch (your BMW's) as an example there is no way to access the OEM tables in the ECU without the correct .A2L and a base .S19/.hex file so what reflash tuning companies tend to do is to look for patterns in the hex/acsii code from signals on the CAN/Flexray bus then manipulate these with a car on the dyno until the torque increases. Their front end SW is then written based on this and often bares no resemblance to the actual OEM tables.
Again this is just an example of how 1 company would do it, another reflash SW company might use a different method so it will be specific to your application and the SW supplier should be able to provide technical documents to help you.
https://www.bflash.eu/#home these guys seem to have one of the most comprehensive solution for European cars
best thanks for your response and tips.
I'll fight my way through which providers are there that offer a solution to edit the files myself
and who have good documentation.