Closed Loop Idle

[ugp]

Hi Guys

I'm having trouble getting my idle in closed loop mode to follow target rpm.

I'm using an external DBW controller that uses PWM to control % open for idle.

When I use the test mode for idle, 50% drops idle down to about 400rpm, 100% is 1200rpm and 200% is 3000rpm, so I know it can control it.

Changing the idle cranking / duty steps alters the rpm also, but naturally needs a key off / restart.

I can't however get the rpm to change / get it to follow the closed loop idle target curve. Dragging this graph around changes nothing.

Any thoughts chaps? I'm struggling with it. MSQ attached.

Thanks

Ben

[Matt Cramer]

Please also post a data log.

[elaw]

Also a link to any documentation for the DBW controller might be helpful.

I'm a bit confused as to why changing the % in test mode from 100 to 200 would change anything, as by definition PWM values cannot go above 100%! I seem to remember the numbers in the test mode screen can go higher but I thought they just "wrapped", as in 101% = 1%, 120% = 20% etc., so 200% should actually equal 100%.

[ugp]

There's no documentation for the unit. It simply accepts PWM control at 500-800hz and opens the throttle plate between 0-10%. This part is clearly working though as revs move in test mode, and also if I change the startup steps -but it ignores the idle rpm curve. Prior to megasquirt going on, it behaved for the link G4, again, single wire and PWM idle.

What do you want me to log Matt? Which values would you like manipulating whilst it's running?

Thanks

[ugp]

I think I've spotted the issue here, idle activation tps threshold is going over the 2%.

I've calibrated the tps as open and closed, however as the idle duty increases, the throttle plate opens and the tps goes up. Can I just change this to a higher value, or would it cause issues when cruising at light throttle positions?

To maintain an idle rpm of 900 ish, the throttle plate needs to be open around 3%. At higher cold start rpm's, 1500 ish, it needs nearer 5%.

[elaw]

Good catch!

That's one of the fundamental problems with running an EMS like Megasquirt with DBW is that the traditional "throttle position" variable really needs to be split into two.

The "throttle position" that matters for triggering CL idle is the accelerator pedal position, not the actual position of the throttle plate. For most other things like AE, throttle plate position is probably better to use, although it would depend on the particular setup.

Does the DBW controller have an output for pedal position, or a signal you can tap into (keeping in mind there are possible safety issues with doing that)? I think that's probably the only way you're going to get CL idle working properly.

[ugp]

Afraid not, and my pedal outputs a 0-12v scale to the controller.

My thoughts are that if I set this figure to say 10%, it's going to try and close the throttle plate - thinking it's in closed loop idle mode on a light cruise.