Feed Forward Tuning

[David Ferguson]

My DBW setups all just have a single value of Throttle Aim Minimum of 0.0 Is there a reason you think this isn't acceptable?

You can setup the throttle area table to be linear or actual area. I have successfully run engines both ways. What you can't do is change this and not have to revisit the various Idle Mass Flow parameters (Engine Crank Idle Mass Flow, Engine Post Start Idle Mass Flow Feed Forward, Idle Mass Flow Feed Forward Main, etc), so pick one and get on with the tuning.

I suggest you set the Idle Actuator Throttle Aim Maximum to something like 10 - 15% (I've used as high as 20%) so that you have a wide range of control. If your feed forward table at a very fast idle is less than 50%, you should consider reducing the value of the Idle Actuator Throttle Aim Maximum.

[glausb23]

Hello again,

I've set the throttle area table linear, set throttle aim maximum to 15%, and re-tuned some of the feed forward table successfully.

I'm doing a lot of reading through the context helps on M1 tune trying to get a more thorough understanding of things. Out of curiosity--why does the context help say that for DBW throttle servo systems, the Idle Activate Throttle Pedal Threshold value recommendation is 0.0% (the rest position of the pedal)?

It describes Idle Activate Throttle Pedal Threshold as the pedal position below which idle control can activate. If the throttle pedal calibration was performed correctly, wouldn't it be impossible for throttle pedal % to fall below 0.0% (it's rest position)? Thus, how can idle control enable if this value is set to 0.0? Wouldn't it need to be something slightly higher?

Thanks,
Benjamin

[Stephen Dean]

When the Throttle Pedal is set correctly it will be reporting -1% in the rest position, this is done to allow for variances in the return position being caused by usage and temperature (more noticable in racecars with high cockpit temperatures). As the pedal will return to a position below 0% having the Threshold set to 0% will work correctly.

[glausb23]

Which channel specifically should be reporting -1% in the rest position? With my current pedal calibration, the Throttle Pedal channel reports 0.0%, while the Throttle Pedal Sensor Main channel reports -1.2 to -1.3% (fluctuates slightly) and the Throttle Pedal Sensor Tracking channel reports -0.9 to -1.0% (fluctuates slightly).

Thanks,
Benjamin

[Stephen Dean]

THrottle Pedal Sensor.

[glausb23]

Got it, thank you for the clarification on that.

For engine overrun, is the Engine Overrun Engine Speed Threshold value the value at which ONLY fuel cut stops, while ignition retard continues to decelerate the engine as long as Throttle Position is below Idle Activate Throttle Pedal Threshold value ,or does ignition timing begin to advance when engine speed falls below this value?

In the Context Help for Engine Overrun, it says that this system will transition into ignition retard when engine speed is greater than the sum of the overrun engine speed threshold and overrun engine speed hysteresis values (in my case, threshold and hysteresis are set to 4000rpm and 1200rpm, respectively). This tells me that the overrun system can retard timing when engine speed is above 5200rpm, and the other activation requirements are met.

The context help also states that Overrun fuel cut is disabled once engine speed falls to below the threshold value (4000rpm in my case). It also states that the overrun system will transition to advance ignition once engine speed falls below the threshold value (again, 4000rpm in my case).

So if my understanding is correct, let's hypothetically say that I was cruising at 7000rpm, and then let off the throttle pedal completely so that it falls to the rest position..With Overrun enabled, the system would immediately cut fueling and retard timing until the engine speed was reduced to 4000rpm, at that point fuel injectors would re-activate and ignition timing would start to advance..

In order for the engine to be able to decelerate back to the target idle aim, would I then need to make sure that my idle aim ramp down limit value is large enough so that Idle aim main (2000rpm) + idle aim compensations (0) + idle aim ramp down limit (currently 1150rpm) = 4000rpm?

I feel my idle aim ramp down limit shouldn't need to be so large, but if fueling is re-enabled once engine speed falls below 4000rpm, and ignition timing begins to advance at the same time, how else could the engine continue decelerating back into idle? The idle aim ramp down limit parameter would basically serve as to expand the operating range of idle control in this case, correct? Or is my understanding of how these systems work incorrect?

Sorry this got long-winded.. just trying to thoroughly explain my thoughts on this. Please let me know if I am understanding this correctly or not.

Thanks,
Benjamin