asking about gearbox

[NL_Fer]

I think in any gearbox with fixed ratio's we need to reduce some torque, during a shift. Even if it was a cvt, with programmed ratio's. If it would shift in 20ms, you get a shock at the wheels, torque reduction for a few ms is needed to smoothen out the sift.

[gruntguru]

You only need to reduce engine torque because the sudden recovery of stored rotational kinetic energy when the engine is slowed to match the higher gear represents a spike in torque delivery to the rear wheels - no need to add full torque from the engine as well.

BTW. AG.

1 - It is possible to have uninterrupted, positive torque delivery to the rear wheels throughout the shift in a Zeroshift, DSG etc gearbox.

2 - It is possible to be tranferring torque through both gearsets simultaneously mid-shift in a Zeroshft or DSG box due to elasticity of the components involved. There is in fact a progressive "handover" of torque from the lower gearset to the higher.

[riff_raff]

The continuous transfer of power thru the transmission during a shift is only a concern when up-shifting or accelerating, right? Why would a brief interruption in torque transfer matter during downshifting?

[gruntguru]

Why indeed.

[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.

[Tommy Cookers]

I think in any gearbox with fixed ratio's we need to reduce some torque, during a shift. Even if it was a cvt, with programmed ratio's. If it would shift in 20ms, you get a shock at the wheels, torque reduction for a few ms is needed to smoothen out the sift.

yes
unavoidably, the engine today takes maybe 15 ms to lose those rpm that are nominally excessive for the higher gear
shifting faster than this delay (in new or old type gearbox) gives a torque 'kick' to the axle
another delay factor is because the engine can't resume it's new full output instantaneously when the new rpm is reached

the best result will be some compromise between these conflicting factors - and that's what the racers do
ie clearly no-one ever waited for the perfect rpm match, they would suffer the further delay in the engine reaching full output
(and the mgu-k, however managed, cannot fundamentally change this need for compromise)

it seems they have today a good compromise ie the axle torque is close to ideal throughout the declared 15-20 ms 'shift time'

if not they would use a true 'hot shift' gearbox
ie shifts involve 2 simultaneous load paths whose inherent velocity conflict is at best reconciled by frictional dumping of energy
in principle this may get closer to the ideal torque throughout the shift (but at a price)
is the DC one of these types ??
and others having a coaxial layout are not a good fit in F1 because (more) drop gears are needed

and ..... wouldn't the 'seamless' shifting look more seamless if they lost the 'compulsory flappy paddle' rule ??

btw
on YouTube or something there's some in-car footage of a Mr Fangio driving an F1 Maserati round Modena (it may say Monza)
judging by the sounds, it seems as if he made compromises between the conflicting factors mentioned earlier
though Mr Ekins (in that 'Bullitt' film) uses 'double-clutching' throughout

[autogyro]

The 15 to 20 ms shift time is a direct result of the lighter rotating components in the current F1 engine.
Fit a good dog manual box to such an engine and the potential is exactly the same.

The DC boxes do exactly the same thing with higher torque loss.

[NL_Fer]

I have to disagree that a dual clutch (if that what you are pointing at with DC) is a true seamless system. There is no overrun possible durng a shift. So the older gear has to disengage prior to engage the new gear. Because of the clutch slip, these moments can almost be instantanious and the clutches make up for the difference in rpm.

But is still not as seamless system, where some overun is possible. I think the used rings are different for patent reasons, but they are able to alow to stay engaged during a shift and when overrun, stop tranfering torque.

I even though of the possibility to use oneway bearings to mount classic dog rings to a shaft, which also would allow to overrun the gear. Hence they could built oneway's that would handle the torque and not slip inside a greasy box.

[machin]

The 15 to 20 ms shift time is a direct result of the lighter rotating components in the current F1 engine.
Fit a good dog manual box to such an engine and the potential is exactly the same.

Wrong. When seamless shift was introduced 8 years ago there was no step change in engine inertia at the same time; the 0.5 seconds lap time saving was due to the seamless shift technology alone.

The dogs on the gearboxes Autogyro is familiar with are connected together without any appreciable degrees of freedom between them. They are manufactured specifically to avoid a double engagement (hence impossible to be operated by man or machine without a torque gap between shifts). Technology has moved on and now we have dogs which are still connected, but they have the possibility to move relative to each other, which is what allows them to smoothly transfer torque delivery from one gear to another and then rapidly pull the dogs of the lower gear out of the way before something catastrophic happens! All rather clever.

I guess to someone used to the "old way" it must be like seeing an electric light for the first time having only seen fire before. Quite quaint really.

[autogyro]

It is also possible to use the KER motor/generator to slow the engine during the shift even faster.
You still will not beat a power on dog box up shift with a good driver.
Makes a big jolt though.

[Tommy Cookers]

It is also possible to use the KER motor/generator to slow the engine during the shift even faster.

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)

the potential for good or bad behaviour eg power-on jolt is dominated by the responsiveness of the ICE to good or bad instructions
regardless of the type of gearbox
one might think that the modern units have a better instructions due to their software control

[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.

[gruntguru]

It is also possible to use the KER motor/generator to slow the engine during the shift even faster.

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

[VerleneDP]

Thank you for your post, after patiently readed, I learned a lot of things do not understand before, benefited, Very impressive! Great Work.

[Tommy Cookers]

It is also possible to use the KER motor/generator to slow the engine during the shift even faster.

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

ok, I have vaguely assumed from the froth of threads on this topic over the years that ......
the (rpm step) response time of the unloaded ICE is a few tens or a very few tens of msec both in turnup or turndown
this may be optimistic
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

conventionally, time constants are defined as 63.2% amplitude of a step change demand (we could say we need less % here)
but they assume the current is unlimited eg that several hundred % of continuous-rated current is available - not so here

the mgu-k is gear-coupled to the crankshaft such that mgu-k inertia (referred to the crankshaft) appears several times higher
ie if the mgu-k is inactive during shifts its inertia is a significant or substantial degrader of the engine response
it must be actively managed during shifts (in effect some of what I have been posting about since 2012)
eg there will be momentary generating, managed to contribute to the rpm turndown (so what ?)

similarly the ICE rotational inertia when referred to mgu-k appears several times smaller
in principle this contributes towards an mgu-k ability to influence ICE rpm turndown

relative inertias and response 'time constants' of an independent ICE and mgu-k tell us which is the tail and which is the dog .....
wrt turndown response of the coupled system (PU) with ideal active mgu-k management

my guesstimate still is that the mgu-k won't benefit rpm turndown (or turnup) in shifting
but it must be managed throughout shifting or there will be a disbenefit from its parasitical inertia
it needs managing continuously anyway eg to give or take max permitted power despite continuous variation of PU rpm