gruntguru wrote:Tommy Cookers wrote:autogyro wrote: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