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The plug-in Golf runs on electricity alone to about 30 mph. (http://blog.wired.com/cars/2008/10/twin-drive-is-g.html)

http://www.cleanmpg.com/photos/data/508/vw_golf_twin_drive_2_500.jpgChuck Squatriglia – Wired – Oct. 16, 2008

Volkswagen is moving right along with its plan to put a plug-in hybrid on the road by 2011, road-testing a "Twin Drive" Golf that goes 30 miles on lithium-ion battery power alone.

The proof-of-concept test mule roaming Berlin uses a diesel-electric drivetrain, but VW says the production model will ditch the 1.4-liter turbodiesel in favor of a 1-liter turbocharged gasoline engine. Although the VW engineers discussing Twin Drive during the debut of the sixth-generation Golf called the engine a "range extender" -- the same term GM uses for the gasoline engine in the Chevrolet Volt -- it's not.

The engine in VW's Twin Drive system actually drives the wheels, whereas the engine in the Volt only charges the battery as it approaches depletion. Be that as it may, the plug-in Golf runs on electricity alone to about 30 mph, at which point the engine takes over, according to the engineers who told Motor Trend about the system.

Twin Drive ditches the transmission, a move that helps compensate for the weight of the electric motor and the 350-pound Sanyo battery pack mounted under the trunk. The electric motor provides sufficient torque to get the car moving up to 30 mph, at which point the engine takes over with a single gear ratio roughly equivalent to top gear in a conventional car. The electric motor also provides additional oomph for hard acceleration.

Regenerative braking helps keep the 12 kWh battery charged, and there's an "e-mode" for tooling around town under battery power alone. With no transmission, reverse gear is handled by the electric motor, according to Motor Trend … http://blog.wired.com/cars/2008/10/twin-drive-is-g.html

I'm skeptical of this design concept. It suggests that you must have sufficient energy in the batteries at all times or else you will be stuck with only the gasoline engine with its one "top gear" ratio. I also wonder how tall that gear ratio is, given that it's supposed to work from 30mph. Does that mean the mill is screaming along faster than the engine in a Fit if you need to break 60mph?

given that diesel engines have gobs of torque throughout their powerband, I would say it's definitely plausible. My civic will shift into 5th at 37mph and the torque output at that rpm is probably around 70-80ftlbs. Compared to a diesel at something around 200ftlbs. I doubt you'll be able to do above 100mph, but that's not what the car is meant for.

As for powering the car in the city under all electric, the diesel engines is far more efficient idling than it's gasoline couterpart. I would think a simple clutch dis-connect would be used to charge the battery with the diesel running. While this isn't optimal, there aren't many times where you're under 30mph.

I feel like this type of hybrid is long overdue. Everyone knows diesels are more efficient than gas engines. By cutting out the low speed, fuel guzzling starts/stops with an electric motor it improves efficiency dramatically. I wouldn't be surprised if they saw 200MPG if they get it working. There's already a TDI on here that gets 70mpg and that's just with the standard 2.0L TDI engine.

Sure, except for the part where they say that the diesel will not go into the production version. It will be a 1.0L gas engine.

well that sucks.... probably should have read it slower.... Oh well

Sounds like a nice system that should be a bit cheaper (aside from the bigger batteries needed) and less complex to build than some other hybrids.

Brick, I think your concern will be alleviated by the fact that the gas engine should still be capable of generating juice to the electric motor should the batteries become depleted. Not the most efficient arrangement (nor is the Volt's series-hybrid arrangement) but I think the idea is that it wouldn't be needed very much of the time.