F1 clutch operation logic - discussion and info hub

Hi all, with snow and winter I've been doing a lot of reading to understand the car better for personal sanity and troubleshooting if potential future issues arise.

I want to make this thread into an aggregation point and FAQs for F1 transmission clutch operation logic, ie: PIS, slippage, etc.

To start things off, I've reading about the F1 clutch operating thread on Aldous Voice's blog and here is my summary and a few questions:

https://aldousvoice.com/2014/08/07/ferrari-f1-clutch-operation/

KEY TAKEAWAYS

PIS - See pictures below
- PIS tells the F1 when the clutch makes contact with flywheel
- Once the PIS point is reached, the car will increase torque and simultaneously close the clutch
- If PIS is too low, the clutch will close too soon and causes stalling; if the PIS is too high, the clutch will not close soon enough and induces more slippage

CCP
- CCP stands for the self calibrated closed clutch position
- PIS is measured off the CCP, basically if fully open is X, then PIS + X = CCP where PIS is the distance between clutch initially grabbing and CCP is clutch fully closed

CDI - See pictures below
- CDI stands for the clutch degradation index, the value is between 0 and 10k with a new clutch at 4k, and a worn clutch at 10k etc
- What CDI does is determines how well the clutch will grab
- If CDI is high (its worn), then it will prolong the slippage and limit torque to a higher RPM before fully closing the clutch
- An example would if the clutch bites at 1100 RPM and fully closes at 1800 RPM, a high CDI would mean the clutch bites at 1100 RPM but would not fully close until 2500 RPM


COMMON ISSUES

- The PIS not being set correctly (too high or too low)
- CDI not being reset when installing a new clutch, leading the F1 system prolonging the slipping after the bite point as if it was a worn clutch
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The question I have for now is on the CDI:

According to Aldous Voice, CDI is "measure of how good the clutch is at transmitting the torque and is auto calibrated every time the clutch is closed"

So does that mean its not necessary to reset the CDI once the clutch has been changed since it auto calibrates each time you're in gear?

Or does it only auto calibrates to go higher, aka from 4k to 5k?

If so, when I get the PIS changed, can I reset it to 4K (assuming that has never been done) and the F1 system will automatically find the most recent CDI? Or will that royally messes the system up?

 

Ah! I would but edit function no longer available for old posts

Also noted that there is an error in the clutch wear formula, its supposed to be CCP worn - CCP new, as CCP worn is always going to be a higher number.

 

No, and hopefully this explanation (and attached pics will explain). By the way this is based off what I read on Aldous's blog and other explanation videos online, and that its been stated on here via other threads that CCP worn should be higher than CCP new, but please do beware and verify via other sources:

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The clutch is pushed into the flywheel via the springs on the pressure plate in its natural state. When you step on the clutch, the thrust bearing pushes into the springs, which in turns "lift" up the pressure plate and off the clutch (first picture).

Since the pressure plate is always pushing the clutch into the flywheel by design, the thinner the clutch material, the more the spring pushes inward, but by that design the spring will extend outward as well, pushing back against the thrust bearing (it is like a seesaw). So the thinner the clutch, the further away the clutch bearing is relative to the flywheel when the clutch is closed, therefore CCP worn will be higher than CCP new (picture 2).
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Just to confirm, the "clutch degradation index / CDI" is adjustable? I thought it auto calibrates? I am still looking for sources to confirm or understand it better so when I take the car in for PIS in the spring I know that the clutch is being set up properly

And as for adjusting PIS for earlier TCUs, I did not read too much into it, but from what I have seen it is along the same line as well. Since the older system's PIS is a fixed number attached to the CCP, and by adjusting the CCP to be further away, that by default will lower "net" PIS if you will.

 

Update

Was able to confirm from Aldous voice that the CDI, clutch degradation index, is reset-able. The computer auto calibrates a new value each time the clutch is closed, but the final value being used is an average of the last x samples. Therefore it might take a while for the value to reflect the true friction level if its not reset.

 

The CCP for the new clutch close position, PIS, and CDI are all adjustable. There may be other as well but I can't speak to them.

The clutch worn % is calculated by referencing the real time CCP to the CCP when new. The CCP when new is a hard coded input you enter into the computer in when you install a new clutch. Therefore if you go in today at 50% worn, and use that CCP as the CCP new, the computer will tell you there will be 100% clutch life left. That is how some people only get 20% out of their clutch or can still drive the car at 120% used, the CCP new value was wrong / tempered with.

Why did you replace the clutch? Was it a drivability thing?

The clutch life % doesn't impact the drivability of the car. The PIS (when the clutch makes contact with fly wheel) and CDI (how long the clutch slips before it closes) are the two parameter that does impact how the car drives. At 50% worn the clutch may have glazed over and therefore will slip under load and have a high CDI, then it doesn't matter if its a new or 50% worn clutch.