Mercedes Power Unit Hardware & Software

[PhillipM]

The merc engines seem to be more responsive in the low to midrange area. They always leave curves with a very fine-tuned power onset. None of the others seem to have this the same way.

That's called 'shedloads of grip'

[hurril]

The merc engines seem to be more responsive in the low to midrange area. They always leave curves with a very fine-tuned power onset. None of the others seem to have this the same way.

That's called 'shedloads of grip'

I don't doubt that they do but if you listen to the engine it seems to have instant power in a way that the others don't.

[Facts Only]

Paddy Low has explained this before. Some oil escapes initially before all seals start fuctioning properly.

The question for me is not why does the Mercedes PU emit a puff of smoke but why dont the other engines. I'd love to K is how they have sealed the area in question

Maybe their oil control rings are designed to purposely let some oil in the chamber. Burning oil is an easy way to lower octane, which would let you run a little leaner. I've seen plenty of cars with engines that burn oil be otherwise strong engines with healthy compression and good power.(Case in point the Porsche GT3 burns a healthy amount of oil, some up to a liter every 2,000km(FRM cylinder liners))

http://www.6speedonline.com/forums/997/ ... g-oil.html

Maybe the coatings they're using don't hone properly but do wonders for friction and the ability to run leaner is an after thought. It could just be their PCV system has a generous vaccum, but that doesn't make sense they could just as easily use an air oil separator if they were trying to control oil entering the chamber. I think they're allowing some on purpose, but not sure why exactly.

If it is seals leaking why would you want your pneumatic valve spring seals to leak?

Forgot to mention that I know exactly where the Merc "smoke belch" is from (but won't say for the obvious reason), it's not some magic coating or secret oil injection, its just an annoying seal issue which I can't work out how the other manufacturers have stopped.

[godlameroso]

There's not a lot of places it can come from, it's either getting sucked in through the intake via PCV or it's seeping through the pneumatic valve spring seals, or it's passing through the cylinder rings.

[Brian Coat]

Perhaps there are a few more candidate leakage sites including our old friends the turbo seals?

[godlameroso]

True, didn't think about that one. So do you suppose it's an oil drain issue at low rpm?

[PlatinumZealot]

Other than the piston rings. Could be behind the compressor wheel. Thats the only place where there is a direct liquid behind a hard seal.

[Brian Coat]

Other than the piston rings. Could be behind the compressor wheel. Thats the only place where there is a direct liquid behind a hard seal.

The turbine seal, also.

[gruntguru]

I would assume the crankcase operates at a fairly low (below atmospheric) pressure to reduce windage and oil consumption. There is probably a delay after startup before the scavenge pumps are able to reduce the crankcase pressure sufficiently to eliminate the oil consumption.

[NL_Fer]

The Mercedes Turbocharger is different to the others. They bearings must be very special supporting the long shaft. Also i was in Spa and noticed during test takeoff the turbo starts spinning quicker than the engine revs up, must be the MGU-H doing its magic.

Maybe an instant moment of vacuum in the exhaust manifolds, as the turbo spins and the engine lags behind?

[Frank_]

with the remote type compressor not subject to exhaust heat, maybe mercedes went for a labyrinth type seal instead of the conventional steel ring type ?
and if the oil system is primed prior to starting (to allow instantaneous 5k rpm idle etc) then that could cause the ingress

[godlameroso]

I would assume the crankcase operates at a fairly low (below atmospheric) pressure to reduce windage and oil consumption. There is probably a delay after startup before the scavenge pumps are able to reduce the crankcase pressure sufficiently to eliminate the oil consumption.

Wouldn't you just use an air oil separator in your catch tank then if you didn't want oil in the intakes?

[godlameroso]

The Mercedes Turbocharger is different to the others. They bearings must be very special supporting the long shaft. Also i was in Spa and noticed during test takeoff the turbo starts spinning quicker than the engine revs up, must be the MGU-H doing its magic.

Maybe an instant moment of vacuum in the exhaust manifolds, as the turbo spins and the engine lags behind?

Oil drain issues are more common with journal bearing turbos, since they depend on oil pressure, so naturally oil will enter faster than it leaves the housing, and you'd tune your scavenge pumps accordingly. Since they're using a long shaft, would it make sense to use journal lubrication or roller bearings?

[gruntguru]

I would assume the crankcase operates at a fairly low (below atmospheric) pressure to reduce windage and oil consumption. There is probably a delay after startup before the scavenge pumps are able to reduce the crankcase pressure sufficiently to eliminate the oil consumption.

Wouldn't you just use an air oil separator in your catch tank then if you didn't want oil in the intakes?

Nothing to do with catch tank and intakes.

The negative crankcase pressure reduces oil consumption from all the usual spots - rings, valve guides, turbo seals etc. If you design those sealing elements to rely on crankcase vacuum, you will get higher oil consumption while there is no vacuum - ie startup.

[godlameroso]

That's true.

Well let's assemble the facts that we do know, we know that the Mercedes engine burns oil, but it's not just at start-up, it's more obvious when they idle, yet the consumption is there. People who have been at recent GP's, Spa for instance, report the smell of oil. We also know that it's a specific area and not a distributed effect.

Moving to the realm of speculation, so far to me, the best explanation has to do with the unique turbo design they're using relative to others. Possibly lubrication requirements of the turbo bearings force a little past the seals, and is just the conclusion of being more aggressive with their MGU-H pre-spooling. Possibly other teams don't have the same issue because their turbo's have different bearings with lesser pressure requirements.

Finally on a tangent, I've always said that MGU-H output and recovery is unlimited as well as energy going to and from the battery to the MGU-H. Given that the energy between these two systems is un-metered, wouldn't it make sense to make them as powerful as absolutely possible within the constraints of the regulations? We've worked out the turbo takes roughly 60-80kW of energy to spool up fully. 4MJ would only be enough to spool the turbo for roughly a minute per lap, then you have no energy for other things, but if you have a 10MJ battery pack, you can do your 4MJ per lap deployment and have enough energy to keep the turbo on tap at all times, on top of whatever other system you're running on the car.