Jump to content
Crispin

Flat shift fuel cut needed

Recommended Posts

I run a seq gear box with a Geartronics paddleshift setup in my race car with an Xtreme+ ECU. 700+ hp 4 cyl turbo engine.

The Geartronics GCU runs in closed loop with a gearbox position sensor to monitor the barrell movement in the gearbox and send a cut signal for the exat right moment.

This cut signal I've wired up as a clutch switch input and run a "dummed down" flat shift config in the ECU that cuts ignition for the time that the signal is present.

It works fine but but the mega retarded ignition during shifting results in combustion in the headers which creates cracks in 321 piping and damages high quaility inconel flex bellows (non woven). At high loads and rpms the Bosch 2200 cc injectors run upwards 80% DC so it's just too much fuel that burns in the exhaust during shifting. Also evident by the boost spikes during shifting.

Now I see 3 different options to solve this:

1. Simplify the setup even further by letting the GCU cut the signal to the ignition coils. This will at least do a 100% cut to prevent the charge from being ignited in the headers. This is not an approach I'd like to take it as I want to control this more sophisticated by the ECU.

2. Add fuel CUT trim in the flat shift function so that I can reduce the total pulsewidth or duty cycle with up to 100%

3. Add fuel CUT option as an alternative to ignition CUT for the flat shift setup.

 

The current values in the map is -50 deg ignition trim and 90% cut. Maybe as an interim solution I can reduce the extreme combustion in the headers by setting say -25 deg and 100%? Current timing at wot and full bost is around 25-28 deg.

Share this post


Link to post
Share on other sites

Have you tried using the Gear Shift Control in the software?  If your running that kind of hardware it would be worth spending some time setting up this properly rather than a dummed down flat shift as you call it

Share this post


Link to post
Share on other sites

Being able to choose a fuel cut instead of an ignition cut for the Gear Shift Control is something we have on the engineering teams wishlist currently.  I'll let them know that you're also in support of this.

Scott

Share this post


Link to post
Share on other sites

Have you tried using the Gear Shift Control in the software?  If your running that kind of hardware it would be worth spending some time setting up this properly rather than a dummed down flat shift as you call it

It's different things. In the end the ECU need to reduce torque in some way and currently it's only possible through ignition retard.

Being able to choose a fuel cut instead of an ignition cut for the Gear Shift Control is something we have on the engineering teams wishlist currently.  I'll let them know that you're also in support of this.

Scott

Good news. I think this is the way to go for high hp turbo cars.

Is there any way to cut the ignition 100%?

Share this post


Link to post
Share on other sites

As I understands it the shift cut refers to the ignition trim table? So if you enter 100% it will reduce 100% of the ignition events to the ignition trim table values?

 

Share this post


Link to post
Share on other sites

Hi, the Shift Cut table is the amount of ignition events that will be cut while the gear shift is happening. The Shift Ignition Trim table is the amount of ignition trim that is applied to the ignition events that have not been cut. If you have a Shift Cut of 100% there will be no ignition events left for the Shift Ignition Trim to applied to.

Scott

Share this post


Link to post
Share on other sites

Thanks for clarifying that. Please look at prioritizing the fuel cut shift option. With the current setup I will have to lift the throttle to avoid the effect of anti lag during shifting.  Maybe I can setup a compensating fuel map to reduce fuel during shifting. I don't have PCLink right here but hopefully there is some status I can span the table against (such as gear shift active, clutch input or gear shift ignition trim/cut etc).

 

Share this post


Link to post
Share on other sites

An idea...

Setup a virtual aux that activates when TPS is above say 90%, rpm above 6000rpm or whatever, and clutch is pushed in.

Then have a second fuel table that's blank, (or reduced fuel) that's activated by the above virtual aux.
I guess you could have a 2nd ignition table do the same too if need be.

Would need to have the clutch input not too sensitive though, if I've got my foot lightly resting on the pedal it's sometimes enough to trigger the switch.

You'd need to be careful that you dont run the engine lean at the transition points though I guess.

Edited by Davidv

Share this post


Link to post
Share on other sites

Another option. If I understand you correctly above the Geartronics module outputs a signal for the duration of the gear shift. If this is the case you could use the digital input this is wired to to switch a fuel table.

Scott

Share this post


Link to post
Share on other sites

Yes exactly, the Gearbox control unit outputs a signal wired into a digital input.

I could either add a 5d fuel table with rpm vs digital input and reduce up to 60% fuel during the shift. 60% seems to be the maximum value in the compensation tables.

But switching to another fuel table should give greater control. The shifts are very quick though and I hope there won't be any lag in the switching events. 

Share this post


Link to post
Share on other sites

Hmm some more thoughts... the issue with reducing the fuelling outside the flat shifting function is that for the events that are NOT cut it will run super lean. E.g. if I set to 80% ignition cut, the 20% events that will be ignited will be very very lean if I reduce a lot of the fuel.

So I'm not sure how healthy this solution would be.. The best solution would be to retard the ignition a bit and set a table with fuel cut e..g cut 80% of the injector events.

Share this post


Link to post
Share on other sites

The most important point  hasn't been raised yet. He reduces ignition timing by -50 deg. Thats very very retarded, which will lead to very high EGT. 

I suggest to try 100% or 95% cut and just -5deg retard during shifting. Otherwise setup a GP limit table, where you can choose Fuel cut in the settings, and activate it over a virtual aux during shifting. Just set anything in the GP limit table to zero. 

Maybe choising DI input from aux input as a axis could work too. Set GP limiter higher than your revlimiter when shift is off (DI off) and zero if shift is active (DI  on). Adjust fuel revlimit in GP settings to your needs. 

Edited by mapper

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...