Gear syncing

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
spacer
spacer
8
Joined: Sun Nov 01, 2009 7:51 pm

Gear syncing

Post

Hi Guys,

During last weekends' GP, Verstappen reportedly lost gear sync during his Q3 run. I've read somewhere (a quote I can now obviously not find anymore...) he overspun the rears exiting a corner, resulting in his car losing gear sync and having harder (up)shifts as a result on the following straights, losing time.

I've also heard radio comms of drivers having to do gear syncing procedures in FP, outlaps etc.

I'm interested in knowing how this actually works and what kind of sensors are associated with it. I assume it's some combination of shaft-sensors that allow the gear dogs and drive disc dogs to shift at the right angular position (i.e. preventing the dogs hitting each other face to face).
But angular position sensors have been around for decades in cam/crank position sensors without any need to manually sync and having a low failure rate. What makes F1 gearbox control systems so needy? Feel like I'm missing the point :D

Could someone with some in-depth knowledge explain how the gearbox and shifts are controlled, and what probably failed to work in this instance?

thanks!

bigpat
bigpat
17
Joined: Thu Mar 29, 2012 12:50 am

Gear syncing

Post

Today's gearboxes are seamless shift, where the flow of power is uninterrupted. This requires the ECU to co-ordinate the release of one gear and engagement of the next.
The ECU would need inputs from crank speed, gear and diff ratios ( fixed for the season) gear position, and axle output speed and torque.

I suppose on an installation lap, the shift speed is slowed deliberately, so the ECU can determine actuator speed, and actual shift times, which is then calibrated to give optimal gear shifting.
I suppose like all electronics, things can go wrong, which could result in aggressive shifting which may be what Verstappen felt.

This pursuit of speed, cost both Hamilton and Bottas gearboxes at Austria and Silverstone respectively. Mercedes went aggressive on shift strategy which damaged the gearboxes. The actual shift time between switching gears was too small (perhaps overlapped) damaging the engagement dogs I would guess. Mercedes have now gone a back to the previous spec gear strategy....

Tommy Cookers
Tommy Cookers
535
Joined: Fri Feb 17, 2012 3:55 pm

Re: Gear syncing

Post

imo the flow of power may be continuous ie uninterrupted - but the power won't be constant

within the box there will be 2 sets of components engaged at different ratios simultaneously (only for a millisec or so)
within that dog 'backlash time' there is only one significant load path anyway the dogs won't get deeply engaged in that time
the shift is really the disengagement of the 'old' gear's dogs - if this is late there will be 2 significant load paths at different rpm
ie a gearbox-internal load path conflict (foul) damaging the dogs

but even with a prompt and safe shift time the flow of power into and out of the gearbox to the road will be uneven
eg on upshifting the PU has a lot of energy stored in its 12200 rpm etc but the car's momentum is effectively stored at 10500 rpm
potentially a corresponding large impulse deliverable to the road via the energy transmission characteristics of the tyres and driveline
(energy is of course stored due to tyre/driveline 'windup' (compliance), proportionate to the power (torque) being used)
the impulse effect is minimised by stepping down the PU command at some 'best' moment just before the shift
PU response taking a few tens of milliseconds - tyres/driveline forward windup will correspondingly reduce, maybe overshooting into backdrive windup
then at another 'best' moment the PU power command will step up and the tyres and driveline start to wind up in forward drive
the PU has been delivering power throughout, but the power has varied due to its rate of response to step commands and the driveline windup has varied due to its rate of response to the varying PU power
soon the normal state of steady power being transmitted re-emerges

so importantly there will be tuning for 'best' PU control related to the gear shifting phase - analogous to the gear syncing under discussion
(the PU tuning and driveline behaviour will anyway in some ways determine the scope for actions in the gearbox)
this PU control necessarily involves maximal MGU-K action both motoring and generating (this seen in Honda's data) for best PU response
otherwise the K's inertia, geared at c. 3x crankshaft rpm, would significantly slow the PU response

bigpat
bigpat
17
Joined: Thu Mar 29, 2012 12:50 am

Re: Gear syncing

Post

Good explanation, but not exactly simple! I like simple words!