I asked for a little information on how the torque system worked and got a wealth of information that I thought I should share, this was provided by Steven@hptuners:
Some terminology here:
- Net/Brake Torque - Actual output torque of the engine into the transmission.
- Indicated Torque - The ideal torque the engine would output at stoich & MBT with no torque losses due to anything (i.e. friction losses, pumping losses, AC load, etc)
I.e. Net Torque = Indicated Torque - Torque Losses
Driver Demand Torque comes from your tables. Its the desired NET torque of the engine from your pedal input.
The desired NET torque can be limited by many different torque requests, like traction control, engine net torque limits, as well as things like idle torque request. Your driver demand is only one of many possible requests.
There are many limiters of max NET torque, and there are also clips for minimum NET torque (to keep the engine from stalling during idle and so on).
The final "net" torque request is called something like "ETC Torque Request" in our software. This is the final desired NET torque that is actually converted into an airflow command. If you have no torque limits, this will be driver demand, but other systems can override it as mentioned.
Now if we just used this torque to control the engine, we'd always end up with less torque out than what we wanted. This is because there are torque losses actively happening, caused by internal engine friction, pumping losses, accessories like the alternator and A/C, as well as spark and fuel effects.
To compensate for this, the ECU calculates the current losses, and adds them to your net request. This brings your torque request into the "Indicated Torque" domain.
Other compensations are applied at this part as part of the "CLIP/ADD" system.
CLIP (Closed Loop Intervention Prevention) is responsible for making sure the output torque of the engine MATCHES what we request. Its designed to prevent us from having a conditions where more torque comes out than requested, i.e. unintended acceleration. As such its calculating a feedback torque to add to our final torque to keep requested EQUAL to actual. I'll talk about how actual is calculated later.
ADD (Adaptive Driver Demand) is responsible for adapting your driver demand table so that the requested torques from driver demand match up with actual torque outputs. If your CLIP/ADD mode is "Intervention Prevention" you only have the realtime feedback, if its "Adaptive" you also get an adaptive table that slowly learns the feedback values, thus correcting your driver demand.
I will be adding logging to all Ford vehicles soon that will show you what the "CLIP/ADD" torque feedback actually is for you.
This final indicated torque request is called "Scheduled Torque", i.e. the torque we actually need to convert into an airflow request to get our desired net torque.
To convert this into an airflow, we use the Torque Model > Inverses. This converts our scheduled torque into a desired air load.
Now, at this point, EVEN more limits can be applied to cap our load. You can log these as "Torque Airlimit Source".
They will restrict your load and thus your final airflow for various safety conditions.
Load is then converted into an actual airflow via math, and this airflow can also be clipped. These will also show up in "Torque Airlimit Source" if active.
These sources amongst others will also show up in your "Torque Driver Demand Limit" indicating they are ultimately limits on the driver demand request as well, though that pretty much just tells you what you already know from Torque Airlimit Source.
This final desired airmass is used to ultimately control the throttle,and in factory turbo/super cars the turbocharger and superchargers as well.
However, its not the final limiter of torque. Two more terms to express you will commonly see. They are "Fast Path" and "Slow Path" torque requests. This corresponds to how fast these torques can actually be controlled. Airflow is your SLOW path. Spark and Fuel are your FAST path. This is because it takes time for air to travel to the cylinder from the throttle, but you can cut spark or fuel nearly instantly for a given cylinder. You may also see these referred to as "Base" (slow) and "Instantaneous" (fast) torque requests.
Some torque sources control the slow path torque only, some control fast path only, and some (like traction control, engine speed limiters) can control both.
As such, Fords "SAI Torque Reduction" system can come into play and further reduce torque. I have a post on the forum about this.
That hopefully answers any questions (or makes new ones) about the desired torque system.
Now as I mentioned earlier, there's also an ACTUAL torque system, used to create feedback for CLIP/ADD torques.
This system uses the CURRENT airflow, CURRENT spark, and CURRENT fuel to calculate an estimated torque.
Your CURRENT load goes through the Torque Model Engine Torque tables, to give an INDICATED estimated torque.
Current losses from accessories, as well as losses from actual spark and fuel are applied. This gets you your current NET estimated torque.
This is compared to your desired NET torque inside of the CLIP module to calculate what feedback is needed to line the two up. It errors on the side of preventing overtorque.
As well, the INDICATED estimated torque is used by IPC (Independent Plausibility Checker) to decide if the engine torque is plausible for current conditions. This uses the torque min/max tables inside the IPC.
If you're outside the range, it increments the wheel torque error with how much you're off, and if you eventually go beyond it, you get the wrench light limp mode.
Thats a brief overview of Ford's Torque Control ETC system.
I will sticky this thread shortly as well.