DBW idle | Hot Idle and AC

[superstockneo]

Hi,

I looking for some advice. I've been chasing around this idle issue especially when conditions are hot (ie; stationary traffic) especially when AC is on.

1. My target idle tends to oscillates a bit

2. When in hot traffic and AC is on. When AC kicks in RPM would undershoot way below target badly and then recovers to target with AC step up after a while. But it happens the same when AC kicks off, RPM will undershoot below target before recovering to target as well.

3. If I try to overcome this by increasing base position or ac step up table, i will get high overshoots especially during situations when the car is moving and not under idle conditions. Such as coming down to a stop, decel and clutch in to neutral.

It's on closed loop DBW. Appreciate the help and advice. Throttle is a bosch motorsports 68mm

Link to the logs below

OneDrive

[koracing]

One thing you can try is reducing the clutch delay from .5 seconds to .25 or some smaller value.  I see your AC output is a virtual aux, but I didn't see if it was actually controlling the clutch or not via some other logic or output.  Also your integral gain for the idle actuator is .05 - have you tried making this higher or lower?

Your base position for idle is below the position it stabilizes at in either case (ac on or ac off) where normally I prefer the base postion to be just slightly above the nominal idle duty/percentage. 

I would up the 0 row to 3% in the warm position based on your datalog (perhaps .5% higher across the board).

 

I don't really like the way the ac offset table works as it doesn't typically change the idle position up and down both the way I would like with closed loop working.

If you aren't getting the results you want with the above, I would try to do the following:

1. Zero out your ac idle offset table

2. Add a vertical axis to your base position table for AC request and have values 0 and 1 for two rows (current table values will be in row 0)

3. Set all the values in the "1" row to 1 to 1.5% higher than your 0 row.  

[Adamw]

I had previously discussed this with the poster before I saw it on the forum here.  There appear to be 2 issues going on here to me, one is the e-throttle is getting a lot of integral wind up for some reason which makes it slow to respond to step changes in target.  Secondly, I dont think the AC offset is always being applied as it should.  I think this is because the deadband is set larger than the AC idle up so the offset gets ignored until the status goes active.  I need to spend some more time playing around with it on the bench and thinking through all the logic, it may need a change in firmware.  

[superstockneo]

Hi @koracing, appreciate the input. I've tried messing about with the idle actuator integral gain but seems to not getting any changes. i've also tried messing about with increasing base positions. it reduces undershoots but still slow to respond and gets high overshoots during neutral decel. Spoken to @Adamw offline and he believes it could be firmware related. Thanks Adam for looking into this. 

[koracing]

If idle "hangs" in neutral decel, it's likely it's not entering the idle control range very quickly - you can help this by setting the timing table values a bit low in the region it's hanging in as that should help drop the idle quicker into the proper range for control.

Did reducing the clutch delay not do anything?

The firmware side may be the best solution, but my advice is more of a work around/make it work how it is set of advice.

[superstockneo]

Thanks @koracing. I'll definitely have a go at that. Previously I did bring the timing in the region below 2000 down, it's roughly around 14-11degs now. My target idle ign is set at 10deg. I could try running a lower timing. But during neutral decel will in fall into idle control mode as i believe speed lockout is still activated. i've set my lockout to be at 20kmh if i recall correctly. unfortunately reducing clutch delay did not do anything. Maybe as another workaround i'd revert back to open loop idle for the time being. the issue is just prominent during hot conditions like traffic and such. or idle stationary when ect is around 80deg. i'm not sure if this is related to other tuning matters like fueling etc.

[koracing]

Try reducing the timing in the areas just above ide and at lower map reading than idle to like 0-5 deg and see if that helps.

[superstockneo]

I tried the method of zeroing the AC offset table, and span the idle base position table vs ac request digital input. I've increase the clutch delay to 1sec. i did however left the AC Idle up actuator at 50rpm unchanged. it did slightly improve but occasionally i do get undershoots down to 900rpm before going back to target which is about 1050rpm. dont get me wrong 900rpm is fine for most engines but mine tends to idle comfortably slightly above 1000, also having solid engine mounts it helps reduces the vibration a bit.

But i have to increase the base position on AC by 1. or i should say even numbers. it tends to react slowly on small increments which Adam suggested this could be a firmware issue, or something else in the hardware or tune. because it happens prominently during hot standing traffic or just sitting in the parking lot where IAT is almost 60degC.

But Thanks @koracing for the tip

[superstockneo]

Just an update. I've reverted the idle base position table to span a single axis. and i have reverted to open loop idle. Was stuck in a 2 hour traffic jam yesterday with IAT hitting 69degC (kinda hot because i'm running an open pod). Seems to be running pretty good with barely noticeable undershoots or overshoots during AC operations. Only the neutral decel overhangs. But i did managed to max out the speed lockout. Open loop seems to run better, but I dont have a log for this. Will take one with i've got the time. 

[Adamw]

Yeah sorry I still havent had time to set this up and test properly yet.  Its still on my todo list so not forgotten.  For closed loop I think if you make the AC offset 100rpm instead of 50 this should ensure that the deadband never overrides it and will probably make it more repeatable.  And as KO suggested I think the AC clutch delay actually needs to be shorter so CL doesnt pull it back out before the clutch kicks in, it looks like it wants something more like 0.2/0.3s.  

[superstockneo]

Thanks @Adamw I'll try and give that a try

[superstockneo]

Hey @Adamw just wondering if you've managed to play around with this issue on bench. At the moment i'm still running open loop which runs just fine. I remember you saying a possibility of resistance in the throttle blade itself could cause this?