I have a weird problem where if I stab the accelerator, the engine will rev; but if I very slowly feed in the accelerator (even up to 40%+), nothing happens (idle is stuck in “Accelerator blend after exit”. I’ll only get a step up after the accel reaches 50%. Coincidentally, that’s when the throttle immediately opens to 10%, which is the “DBW Blend Point.”
I assume I’m misunderstanding some idle settings (maybe I should change the target RPM with accel pedal?)
Running firmware 226.x / client 226.0.1. Inline 6 naturally aspirated engine with DBW and no idle control valve.
Post calibration and log for help.
Ok I played around with this a bit more to understand it better.
When the accelerator is above the Idle Activation Accelerator threshold (maybe ± hysteresis), the PID controllers for Idle ignition and air flow shut off and the DBW is locked at the last position commanded to by idle (Idle/Air Flow/Actuator/DBW Target). This is the “Accelerator blend after idle” state. It then holds this without change until the DBW commanded by the “DBW Accelerator translation” table exceeds the DBW blend point. At that point the idle state becomes “Inactive” and the DBW table takes over, causing (in my case) a large jump from 3-3.5% throttle to 10% throttle.
The help for DBW blend point says “This value defines the throttle opening percentage where a transition is made between the throttle opening percentage commanded by Idle air flow and a throttle opening commanded by the accelerator pedal. This setting prevents a throttle closure or jerky transition when accelerating from idle. This value should be around 5% higher than DBW target max, so should have value around 7-12%.”
There is no blending happening. I believe that is the bug - once the idle controller enters blend mode, it should presumably interpolate between whatever DBW it thought was needed to whatever the accelerator pedal is commanding in a smooth fashion. In my case it just jumps. You can see this in the graph above where I plot “accelerator position” and “throttle position.”
If I drop the DBW Blend point I can get a smoother transition by just skipping the blend step altogether - if I set it to 0% it works much better than at 10%.
It’s possible that my setup uses a wider DBW control range than was tested in the lab - you can see in the picture above that I have entries in the DBW base table for 700-1400 RPM and a throttle range of 2.5-6.0%. Setting DBW blend to 0% just means that if a high idle RPM is being targetted, then when I exit idle the throttle may drop before opening again (because my base DBW accelerator table starts at 3%). It does work great with a low idle RPM though.
I can send map and log to an ECU Master employee if they ask, but I also think with that description they can hopefully reproduce the problem quite easily. Just very slowly apply the accelerator with a high DBW Blend Point.
