Volkswagen is working on a plug-in hybrid version of the Golf/Rabbit, named Twin Drive, for introduction in 2011. A basic proof-of-concept version using a diesel engine is currently testing, in a 20-car fleet, in Berlin. But at the Golf 6 launch, VW engineers said the production version will be gasoline-powered because emission controls will soon get too expensive for a hybrid. The Golf Twin Drive’s electric-only range is targeted at 30 miles.
Although VW engineers talk of the Twin Drive’s gas engine as a range extender, the gasoline motor is clutched to the wheels. That’s quite unlike GM’s Volt, where the combustion engine never drives the wheels mechanically.
There is no conventional transmission in the Twin Drive, however, its absence helping to offset the weight of the electric motor. The single-gear ratio is equivalent to the top gear in a normal car. So the electric motor is needed to supply the low-end torque to get the car rolling to about 30 mph, when the combustion engine is clutched in and starts. The electric assist then rapidly fades, but is re-energized for acceleration boost.
Source: Motor Trend