F1technical.net

I view the clutch mostly useful in qualfiying situations where and overbooat could be used... But then again the boost pressure is limited.

I think that some here are forgetting that MGU-H is also a motor and not only generator. So while decoupled it can spin itself to turbo speed. Then any clutch design will work to couple it back.

Turbo and ‘H’. Being clutched is meant to serve as a ‘fail-safe’ in case the ‘H’ is damaged it is declutched and the turbo and engine can still be used. Same scope goes for the ‘k’ to crankshaft clutch.

PlatinumZealot wrote: ↑

27 Nov 2019, 17:31

I view the clutch mostly useful in qualfiying situations where and overbooat could be used... But then again the boost pressure is limited.

Yes, but this has come about because of their altitude performance. Teams cannot reach their targeted boost level at high altitude at the same turbo speed. Allowing the turbo to spin faster to compensate and reach the targeted pressure level without breaching MGU-H speed restrictions is where an advantage would be.

saviour stivala wrote: ↑

27 Nov 2019, 14:50

The rules state that the ‘H’ (shaft) is to be couplet to the turbo shaft and that it can also be ‘clutched’.
If there is no step-up or step down gearbox in between these two shafts (H and turbo shafts) the speed of the ‘H’ and the turbo is the same.
The scope of these shafts being ‘clutched’ is for the turbo and so the engine being able to be used in case the ‘H’ is damaged.
Although not part of the subject at hand, the ‘K’ having a mandated maximum of 50k RPM and the crankshaft a mandated maximum of 15k rpm does have a gearbox in between as well as a clutch.

I don't even know what you're getting at. What is being suggested does NOT require a gearbox...

And then what you're saying about the purpose of the clutch allowing the PU to function if the H fails is pretty much the same concept we are talking about anyway (decoupling). So I'm confused about your standpoint/understanding of what is going on...


My main point is very simple, I'm sure we all understand this one. At altitude, the turbo speed required to reach targeted boost pressure is higher than at sea level. So to claw back to nominal outputs, you would need to run the turbo at a higher rpm, this is obviously restricted by the H's regulated speed restriction. Now.. if you could somehow decouple the H in some scenarios, then it seems feasible to increase turbine speed for those moments and produce an increased output.

Obviously drawbacks would be loss of H generation, but in a qualifying scenario or used in short bursts for a high level race mode, this could be possible. Another potential issue could be turbo lag if mapped incorrectly for the circuit. And you know what Max has been complaining about at some GP's earlier this year during practice/early quali runs? Turbo Lag. Again this points to the possibility the H is not driving the turbo and Honda fix the issue with software mapping changes. I'm just saying, maybe it's possible. Any gain, no matter how expensive/complex, is now a gain for these PU's.

GhostF1 wrote: ↑

26 Nov 2019, 03:28

PhillipM wrote: ↑

26 Nov 2019, 01:18

And since turbo speed is limited, it stands to reason a larger turbo would have more margin available than a small one.

I don't believe the turbine speed is restricted, only the MGU-H speed is. But looking at this regulation made me think of something regarding altitude.

5.2.4 The MGU‐H must be solely mechanically linked to the pressure charging system. This
mechanical link must be of fixed speed ratio to the exhaust turbine and may be clutched.
The rotational speed of the MGU‐H may not exceed 125,000rpm.

What if Honda's current MGU-H/Turbo design now is indeed clutched, I say this because Renault said a couple of years ago that clutching the unit added a lot of complexity and would of degraded the reliability of the unit, Honda in 2017 said their design was high risk but required to catch the front runners and they went through a huge period of issues getting their MGU-H to work. Also in 2017, Yusuke Hasegawa was asked to comment on Honda's increased competitiveness in race trim at Mexico that year and he said the altitude seemed to affect them less than other manufacturers which levelled the field a little more...

Unlikely (leaves a lot of H harvesting on the etable.) but certainly food for thought. With the MGUH uncoupled they would need to use either the wastegate or throttling to control boost.

PlatinumZealot wrote: ↑

27 Nov 2019, 17:31

I view the clutch mostly useful in qualifying situations where and overboost could be used... But then again the boost pressure is limited.

There is no power advantage from "overboost". OTOH there is a significant power advantage from "Electric Supercharger" mode.

I am not aware of boost pressure being limited.

saviour stivala wrote: ↑

27 Nov 2019, 11:41

But how is it possible to use a gearbox on the other two which have the turbine at one end of the block and the compressor at the other end and the turbine/compressor shaft mandated to be 'one piece' with said shaft having to pass right through the 'H' drive tube?.

Easy. The MGUH would have a hollow shaft. The turbo elements would have a smaller diameter shaft that passes through the middle of the hollow shaft. Have a look at any multi spool gas turbine. https://www.google.com/search?q=multi+s ... e&ie=UTF-8

As well as throttling and wastegate they could also manage boost with the bypass valve which takes pressurised air and passes it back to the inlet.

GhostF1 wrote: ↑

27 Nov 2019, 23:20

PlatinumZealot wrote: ↑

27 Nov 2019, 17:31

I view the clutch mostly useful in qualfiying situations where and overbooat could be used... But then again the boost pressure is limited.

Yes, but this has come about because of their altitude performance. Teams cannot reach their targeted boost level at high altitude at the same turbo speed. Allowing the turbo to spin faster to compensate and reach the targeted pressure level without breaching MGU-H speed restrictions is where an advantage would be.

On the compressor map the turbo charger may not spin close to maximum speeds for efficiency reasons.
We only will know if we have that information.

But anyway mexico city is 80% the air density at sea level.
Meaning to get the same pressure inside of the plenum you need a 25% higher pressure ratio than normal.

It is a good idea to examine the compressor map of a turbo that would be similar to the ones used in F1.... Maybe garret gtx4088r? Or likely bigger because of the lean conditions.

If you want to hunt for a compressor map, here are some numbers. (Assuming lambda = 1.8, VE = 1.25, Intercooling to ambient, rpm = 11,000).

Air massflow = 0.7 kg/s = 92 lb/m
Air volume flow (sea level) = 0.6 m3/s = 1300 cfm
Air volume flow (Mexico City) = 0.75 m3/s = 1620 cfm
P.R. (sea level) = 3.4
P.R. (Mexico City) = 4.1

gruntguru wrote: ↑

28 Nov 2019, 00:43

saviour stivala wrote: ↑

27 Nov 2019, 11:41

But how is it possible to use a gearbox on the other two which have the turbine at one end of the block and the compressor at the other end and the turbine/compressor shaft mandated to be 'one piece' with said shaft having to pass right through the 'H' drive tube?.

Easy. The MGUH would have a hollow shaft. The turbo elements would have a smaller diameter shaft that passes through the middle of the hollow shaft. Have a look at any multi spool gas turbine. https://www.google.com/search?q=multi+s ... e&ie=UTF-8

"With the one piece turbo shaft having to pass through the 'H' drive tube". Yes. "Easy. The MGU-H would have a hollow shaft". What is the difference between the 'H' having a hollow shaft and the 'H' having drive 'tube'?.

Given that the ICE is fuel flow limited,

Given it is likely that peak power AFR is likely richer than peak efficiency AFR,

The reduction in mass airflow at altitude, would likely reduce AFR, but probably to a point where it is too rich for best power AFR, hence the power loss.

Question is, does a 10% reduction in intake mass air flow = a 10% reduction in power in a fuel limited formula. My intuition thinks not. Thoughts.

Power loss = reduced exhaust gas mass flow = less energy to drive the turbine-compressor-MGU-H.

Question, is the loss power due to loss of boost mass air flow greater than the loss od MGU-H to K power?

I want to share here a link about mazda skyactive because of I think it is a close aproach to this f1 engines combustion method

When it comes to ‘connection/connecting’ both the MGU-K with crankshaft and the MG-H with turbo shaft the ‘wording used by the rules is the same (must be of ‘FIXED SPEED RATIO’). In the case of the MGU-K connection to crankshaft. While the MGU-K is limited to a maximum of 50k rpm. The crankshaft is limited to a maximum of 15k rpm. When these two items are connected together, clutch or no clutch being used, they run at a ratio of 3.333 to one another which means there must be gearing in between which provides said ratio, it also means that ratio is ‘fixed’ (cannot change). In the case of the MGU-H connection to turbo shaft. While the MGU-H is limited to a maximum of 125k rpm. The turbo shaft speed is not limited by the rules. Although the ‘wording’ used is the same as for the ‘K’ (must be of FIXED SPEED RATIO). This MGU-H to turbo speed situation born out of the wording used in the rules is akin to the maximum turbo boost situation. The rules does not restrict turbo boost directly, but they sure does “indirectly” by the maximum fuel flow rule permitted.