Honda Power Unit Hardware & Software

[saviour stivala]

A seamless shift mechanism as used in F1 that modified shift sequence to not only eliminate the use of power unit clutch for shifting but also the need to cut ignition to synchronize the rotating engaging parts which resulted in no torque/power loss and minimal fluctuations during shifting to the wheels whatever the proportion power/torque contributed electrically or ICE. The use of this gear shift mechanism resulted in a 0.4 sec per lap reduction, it also enabled shifting in situations of low tire grip, such as when cornering or during rainy conditions.

[roon]

the shift events in the gearbox take less time than 1 crankshaft rev
nothing else affecting shift behaviour can be quite so fast acting

Twelve full piston displacements, ~15 (3*regulated value) fuel injection events, multiple spark events. How much piston and crankshaft speed can be expected to alter within one revolution, I don't know.

Related: Is it also the compressibilty of air that is absorbing the the speed differential between transmission and engine? After these short seamless shifts.

[godlameroso]

The crank does unless it deflects, harmonic damper probably too heavy?

[saviour stivala]

the shift events in the gearbox take less time than 1 crankshaft rev
nothing else affecting shift behaviour can be quite so fast acting

Twelve full piston displacements, ~15 (3*regulated value) fuel injection events, multiple spark events. How much piston and crankshaft speed can be expected to alter within one revolution, I don't know.

Related: Is it also the compressibilty of air that is absorbing the the speed differential between transmission and engine? After these short seamless shifts.

For a speed difference to exists between power unit and differential apart from the designed three-step drop ratio it can only exist through a slipping clutch, and a formula one car with a slipping clutch, no matter how small the slip might be, the clutch will just not last for any length of time or distance.

[gruntguru]

Advancing combustion momentarily could provide some engine braking. Small fuel injection and ignition before TDC. Combustion events at about 600 Hz. 2 ms for one event, 12 ms for six. Time these early small braking ignitions after shift request, and prior to selector action and during any clutch activity. Combine with MGUK activity. Workable?

Not in my opinion.

Apart from the detonation and peak combustion pressure issues that might arise, it just doesn't work. Any additional pressure before TDC does negative work for sure, but you get that work back after TDC (well most of it anyway) - the higher pressure persists and does positive work on the piston after TDC.

[gruntguru]

The tyres, there's a lot more potential to store energy in the driveline after the diff, whereas the clutch pack is tiny it's heat capacity is about that of a cup of water.

No - its the clutch. Even momentary additional slip in the tyres is a nightmare for the driver trying to control a racecar at the limit.

[PhillipM]

Depends how much of a spike is there, given that you're changing up ratio's so you have less leverage than the previous gear and that the driveline is pretty compliant so it can store and release the energy over a longer period, I wouldn't think you'd need much control beyond MGU-K/H generating for a brief moment to turn that spike into simply a gradient to the next gear.

[gruntguru]

The numbers are different to your gut feel unfortunately. Using a low rotational inertia for the engine plus MGUK of 0.05 kg.m^2 and a rpm change on upshift from 12,000 to 10,500 we get a change in kinetic energy of 18 kJ. (To achieve this in 1 second would require a braking power of 18 kW). The MGUK has a power limit of 120 kW so it will slow the engine from 12,000 to 10,500 in 0.15 sec (150 ms). That is way too slow for a gearshift. If the shift was say 15 ms, the braking power required to slow the engine would be 1200 kW.

@SS.
18 kJ (actually something less) per gearshift would not destroy the clutch over the course of a race.

[saviour stivala]

Agree that the clutch cannot be destroyed by slipping during shifting while the car is on the move because it is not used.

[Tommy Cookers]

s s
you have said the clutch is slipped on the move (for race starts) ...
and why would the clutch be sized to transmit c.50% over-torque (the in-shift peak) if 'it isn't being used on the move' ?
why wouldn't this reportedly very small F1 clutch be designed to transmit no more torque than the PU produces ?
ie wouldn't we expect a unused clutch system sized to slip marginally and momentarily when an over-torque spike occurs ?
as any clutch oversizing (the F1 clutch being on the gearbox input) will lead to oversizing/slower shifting dogs


re gg's post ....
and imo Honda is claiming to dump only a fraction of that 18 kJ
dump only part of the most disruptive part of it (basically they are reducing the initial peak)
implying imo they get as much energy down to the road as other systems can or did
wheelslip is slip just as clutch slip is slip
and without this (CP) the 'rebound' effects following the (momentary) wheel slip (momentarily) reduced the acceleration

one wonders also ....
how much energy is the clutch dumping in the long-established (agreed by all here) sustained slip used for race starts ?
(which Mr Bottas said cost him the last race)
how many such starts (not necessarily back-to-back) are available within the designed life of the clutch ?

[saviour stivala]

Yesterday and the day before during testing time the red bullies certainly didn’t head Tommy’s line and slipped their clutch during shifting while on the move to easy/smooth torque output, instead they preferred snapping their half-shafts. What are they up too?. I do remember a long time ago when they were trying to make their first seamless gearbox work they were snapping half-shafts like there was no tomorrow. Back than they were not the only once having seamless gearbox problems BMW where having their share of the same problem.

[PhillipM]

The numbers are different to your gut feel unfortunately. Using a low rotational inertia for the engine plus MGUK of 0.05 kg.m^2 and a rpm change on upshift from 12,000 to 10,500 we get a change in kinetic energy of 18 kJ. (To achieve this in 1 second would require a braking power of 18 kW). The MGUK has a power limit of 120 kW so it will slow the engine from 12,000 to 10,500 in 0.15 sec (150 ms). That is way too slow for a gearshift. If the shift was say 15 ms, the braking power required to slow the engine would be 1200 kW.

Okay, now if you add the H (what, 60kw?) generating, and the fact that you've shifted up a ratio, and that the driveshafts, etc, are deliberately built at quill shafts to absorb spikes at the limit of wheel grip, what do you actually end up with as a torque spike at the wheel?
I think you'd put absolutely as much energy as you could in the driveline rather than loosing it as clutch slip, although I'd conceed you'd probably do it for such as 1st/2nd where the car is still heavily traction limited.

[hollus]

The conversation about the legality or not of certain KGK-U behaviours was already had at the Ferrari PU.
It won't be allowed to spread to all threads.

Many posts have been moved to this new home for that discussion:

viewtopic.php?p=834983#p834983

It is a good subject, but if it tries to spread to other threads, it will be mercilessly zapped away, as it blocks other discussions. I hope it likes its new home.

[subcritical71]

Regarding the clutch slip issue. I do believe there is scope to develop the gearbox to handle small slippages during the race as has been pointed out the clutch handles multiple start scenarios as well as pit lane starts. The clutch is small but probably has more surface area to it then most cars (most of the ones I've seen appear to be triple plate designs). I also believe that a team is going to want the most power possible delivered from the PU to the wheels so slipping the clutch would be the last thing they would want, no matter how small the loss.

So I see two possible scenarios..
1) Traction limited - basically the 1-2 shift. I can see using a certain amount of slip during the shift so as not to ruin the drivers feel on the pedal during accelerations from standstill. He wouldn't want that sudden burst of energy when at the extreme limits of traction already. With maybe the exception of Monaco I don't think I've ever seen a driver downshift into 1st after the race start (pit stops excluded). So this would mostly be used only during starts from a full stop type scenario.
2) Power limited - basically the shifts from 2 to 8. The 2-3 shift is almost always done at WOT. I would think that in this region it would be advantageous to not slip the clutch and keep the rotational energy in the drivetrain to give that extra boost while WOT.

[gruntguru]

Have you considered that even though it is not traction limited under full PU output, the car may become momentarily traction limited during the shift? As shown in my previous post, there could be as much as 1000 kW momentarily available while the rotating assembly is slowing.