asking about gearbox

[jz11]

KERS is probably used as a "flywheel", meaning - when the gear shift is about to happen, KERS is engaged at some "constant torque" that would brake the engine and, after the new dog has picked up, act as a momentary booster to till the ICE is producing full power after the rpm drop

IMHO those zeroshift graphs look almost too good to be true, would be nice to see torque-after-gearbox measurement graph instead of the acceleration, I suspect there should be a small drop and a short spike during the shift, and there is no indication of that on the acceleration graph

[NL_Fer]

Without any smoothing, even a zeroshift would introduce a torque spike. A shift would increase the accelaration for a short moment, felt like kick in the butt.

With KERS tuning it would be possible smoothen it out completely, Just takes time.

Basicly is like timing a shift in a road car, if shift, clutch and trottle move in 100% sync, it's totally smooth.

[machin]

would be nice to see torque-after-gearbox measurement graph instead of the acceleration, I suspect there should be a small drop and a short spike during the shift, and there is no indication of that on the acceleration graph

Agreed; in effect the mass of the vehicle is acting like a damper (good old F=m.A!), and so the acceleration of the vehicle doesn't really "see" the torque spike in the transmission. As long as the torque spike isn't big enough to damage the gearbox or upset the car (apparently it isn't), who cares? As racers all we care about is accelerating quickly!

Remember that quote I posted earlier: the torque spike from the speed differential in the seamless box is actually smaller than the difference in torque that you get from having a break in the transmitted torque that you get from a conventional dog box gear shift, which is why it is smoother. If it wasn't 5 minutes past midnight I'd do a quick calculation to check that claim. But it's late, so, maybe tomorrow!

EDIT: Some rough numbers based on a 2.4 litre V8 (i.e. when the seamless shift was introduced, before KERS could be used):-

Non-Seamless gearbox, Torque step = from 0 (no torque delivered), to maximum Torque output of engine: Approx 360Nm, therefore max torque step applied to drivetrain = 360Nm.

Seamless gearbox. Rev drop required = ~3000rpm (315rads/sec), Engine inertia: ~0.05kgm^2, time for rev drop: ~100 milliseconds. Applying T=I.α; Torque required = 160Nm. Arresting Torque due to Friction/pumping, approx. 15% of max engine output= 54Nm. Max Torque step applied to drivetrain: 160-54 = 106Nm

Only very rough numbers, but certainly backs up the claims made by the manufacturers, drivers and independent magazine testers that a seamless shift is smoother than a conventional dog box "racing change".

[gruntguru]

faster than what? not faster than the ICE would slow without any mgu-k attached to it (or with a smaller unit eg 60 kW KERS unit on the V8s)

120kW of additional braking applied to the crankshaft would reduce the revs much more quickly than closed-throttle-intake-vacuum alone. A high vacuum would produce pumping losses of approximately 1 bar BMEP or about 15 kW. Friction losses account for perhaps another 3 bar (45kW) for a total of 60 kW of engine braking. An extra 120 kW would slow the engine at 3 times the rate.
For a rotational inertia of 0.05 kg.m^2 (no idea what an F1 engine would be) 180 kW will decelerate the engine from 12,000 to 10,000 rpm in 0.07s

audio analysis eg of the Renault playing the 'Marseillaise' presumably gave firmish values for the V8 engines - anybody ??

but the gg post above seems to assume that electrical machines have no inertia and so their response is infinitely fast
even the most responsive machines are limited by their own inertia (and the inertia of any load they may be driving)
a machine of this size cannot have a (response) time constant better than a few tens of msec (yes I have experience)

to put it another way, the mgu-k cannot work at 120 kW to decelerate the ICE
its work decelerating the ICE is at best (120-the power decelerating itself) kW
and there's a limit to the rate at which it can develop a decelerating (generating) load following other activity or inactivity

1. Agree that the MGUK will have a response lag. Of course predictive programming (driver presses upshift button, mguk driver switched to "full generator" mode, engine is cut, shift instruction is sent to gearbox etc etc) can pre-empt that to some extent.
2. The mechanical inertia of the mguk should be lumped into total engine rotating inertia, since it is permanently connected anyway. (No teams using a clutched mguk yet?) So any retardation from the mguk will be a benefit in decelerating the engine/mguk rotating assembly.

[gruntguru]

Machin. 100% correct. The over-running dog system can be totally seamless whereas the traditional dog box cannot.

NL_Fer. A DSG box can be totally seamless. During the handover period, torque is being transferred by both clutches and both ratios simultaneously. The difference between shifts on a DSG and the over-running dog is the DSG can prolong the "handover" for as long as the designer wants (at the expense of high friction loss). Handover time on the over-running dog system is very short and is a function of the compliance of the components transferring the torque.

Still disagree, high friction loss during an overlap period, wouldn't be very seamless.

Correctly controlled, the energy lost to friction, would equal the inertial energy recovered from slowing the engine, minus the energy required to maintain constant rear wheel torque during the handover period.

This is the ideal of course - what is achieved by "real world" DSG boxes will probably fall short.

[riff_raff]

Because engine braking as a significant factor in rest wheel Braking. Interuptions could unsettle Braking stability and lock the rears. Downshifting had always been a way tot control rest Braking.

I'm sure current carbon brakes are quite capable of locking the rear tires at almost any condition without the assistance of engine braking torque.

[Tim.Wright]

The engine braking is used to load the differential to increase its locking torque and therefore vehicle stability under braking.

[NL_Fer]

Because engine braking as a significant factor in rest wheel Braking. Interuptions could unsettle Braking stability and lock the rears. Downshifting had always been a way tot control rest Braking.

I'm sure current carbon brakes are quite capable of locking the rear tires at almost any condition without the assistance of engine braking torque.

Sure they are, but a driver sets his fr/rr brake balance, with engine braking in mind. So when actually braking, downshift speed can be used to bias the rear wheel braking on the fly.

Also, remember that slowing down from 350-50 alters the amount of downforce applied to front and rear.

But they have an automatic controller now, since 2014.