Porsche 991 Turbo, virtual gears, sailing and start stop to save fuel

[Boss330]

Shows how important reduced fuel consumption and CO2 is, even to a car like the Porsche 991 Turbo (and Turbo S)...

Perhaps most amazing is the virtual intermediate gear function, where two gears are engaged simultaneously, with clutch slip, to create a "virtual intermediate gear" (for example, a gear between 5th and 6th)!!!

The turbocharged 3.8-liter six-cylinder with direct injection produces 520 hp (383 kW) in the 911 Turbo and 560 hp (412 kW) in the 911 Turbo S. Both engines feature dual variable vane turbochargers, a Porsche exclusive for gasoline engines. Power is transferred exclusively by a seven-speed Doppelkupplung (PDK) transmission, which in both 911 Turbo models now engages the stop-start function with engine shutoff earlier while coasting to a stop and more often while coasting at speed. These technologies, in concert with a new engine thermal management system, reduce fuel consumption significantly in both 911 Turbo models.

PDK with virtual intermediate gears
Further development of the Porsche Doppelkupplungsgetriebe (PDK) transmission plays a significant part in the 911 Turbo models’ performance and fuel economy improvements. Porsche engineers supplemented the seven primary driving gears with virtual intermediate gears that further improve fuel economy and comfort. The virtual intermediate gears reduce
engine speed during constant speed cruising when the next higher gear would reduce engine too much. This function is achieved by partially engaging two adjacent gears simultaneously while slipping both clutches slightly to achieve an effective gear ratio in-between them. When acceleration is called for, the Doppelkupplung rapidly exits this mode and down shifts. Since the PDK employs dual wet clutches (oil-bathed), the virtual intermediate gear function results in no added wear.

The PDK's enhanced stop-start functionality reduces fuel consumption by shutting off the engine while coasting to a stop. Both Turbo models also offer a coasting function that disengages the clutches while coasting at speed; in this mode, the engine idles while the vehicle coasts in neutral. The coasting function provides noticeably improved fuel economy especially during highway driving.

http://press.porsche.com/vehicles/20..._Coupe_USA.pdf

[CanAutM3]

Thanks for sharing

My thoughts:

It is interresting to see how we are in a paradigme shift period. Not long ago, it was better to keep the engine in gear when coasting to levereage the fuel shut off. It now seems that with the avenue of DI, manufacturers are able to make engine so efficient at idle that coasting in neutral has become more efficient. Impressive .

I am also impressed with that "intermediate gear" technology. It seems that the clutches in the PDK are so efficient that even having both clutches slipping is more efficient than having the engine running at a higher RPM. Impressive indeed .

[mkoesel]

That's cool, but my immediate thought goes toward how it effects the life of clutches in the long term. I'm sure they will last long past most every original 911 owner's needs, and I'm sure they are engineered to last past a CPO warranty period as well. But its just another one of those little things that makes you wonder about the short-sightedness of the regulatory measures that are the clear impetus for this sort of wizardry.

[pkimM3r]

Is that why throttle shuts off even with traction control off when performing a full on drift a la chris harris??

[Needsdecaf]

Originally Posted by pkim1079

Is that why throttle shuts off even with traction control off when performing a full on drift a la chris harris??

No, that's because for many manufacturers, off does not really mean off.

[pkimM3r]

Originally Posted by Needsdecaf

No, that's because for many manufacturers, off does not really mean off.

I was joking.

[GregW / Oregon]

Originally Posted by Boss330

Both Turbo models also offer a coasting function that disengages the clutches while coasting at speed; in this mode, the engine idles while the vehicle coasts in neutral. The coasting function provides noticeably improved fuel economy especially during highway driving.

Heck, coasting has been around forever with manual trannies.

[aajami]

I thought coasting in neutral was illegal. Doesn't the car have to be engaged in gear at all time except at a stop?

[GregW / Oregon]

Originally Posted by aajami

I thought coasting in neutral was illegal. Doesn't the car have to be engaged in gear at all time except at a stop?

It is illegal in a few states like California and Indiana (not sure why). However, it is unenforceable unless a cop is in the vehicle with you.

[aajami]

Originally Posted by GregW / Oregon

It is illegal in a few states like California and Indiana (not sure why). However, it is unenforceable unless a cop is in the vehicle with you.

Well, the point isn't if it's unenforceable by the police. The point is I'm surprised this tech was approved for sale in the US if something like is illegal in California, which dictates the feature-set for all cars sold in the other 49 states.

[solstice]

It's a paradigm shift for sure. Fuel consumption used to be an after thought ( if a thought at all ) when designing luxury and sports cars.

Now with government regulations and incentives combined with the success of Tesla with reaching into these segments ( luxury and sport ) and the model S selling relatively well a new page has been turned where we now see fuel economy being the main R&D focus with considerable budgets. It's understandable since there is an obvious risk that fossil fuel burners will be seen as dirty and noisy dinsaurs in the not so distant future. This is just the begining of a rapid acceleration in this area.

[GregW / Oregon]

Originally Posted by aajami

Well, the point isn't if it's unenforceable by the police. The point is I'm surprised this tech was approved for sale in the US if something like is illegal in California, which dictates the feature-set for all cars sold in the other 49 states.

V C Section 21710 Coasting Prohibited

21710. The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral.

It's only illegal going downhill. Porsche could lock out this feature downhill. Just a thought.

[WallieX5]

Originally Posted by GregW / Oregon

V C Section 21710 Coasting Prohibited

21710. The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral.

It's only illegal going downhill. Porsche could lock out this feature downhill. Just a thought.

This seems to only apply to what a driver does and not what the vehicle is doing on its own volition.

[Sedan_Clan]

Originally Posted by GregW / Oregon

It is illegal in a few states like California and Indiana (not sure why). However, it is unenforceable unless a cop is in the vehicle with you.

^^This!

I have no way of knowing if you were coasting or not. I don't even know of an officer that has written a cite for that either.

[catpat8000]

Originally Posted by Boss330

Shows how important reduced fuel consumption and CO2 is, even to a car like the Porsche 991 Turbo (and Turbo S)...

Perhaps most amazing is the virtual intermediate gear function, where two gears are engaged simultaneously, with clutch slip, to create a "virtual intermediate gear" (for example, a gear between 5th and 6th)!!!

http://press.porsche.com/vehicles/20..._Coupe_USA.pdf

That sounds like an article from the Onion!

Pat