Late last year, at a small media gathering for a select few
journalists, Volkswagen showed off its XL1 creation – a technological showpiece
that advances the notion of sustainable transportation like no other automotive
development. As we reported at the time, VW engineers said that the XL1 would
be produced in very limited numbers, but the experience and know-how gained
from the project, including the R&D behind the innovative downsized plug-in
powertrain, an intricate production process and the lavish use of CFRP, would
be transferred to other VW Group initiatives. Most in the media accepted this,
but few believed that this knowledge sharing would come so soon after the XL1’s
initial public outings.
Based on the
regular Up sold in Europe, the Twin Up ditches the usual one-liter
three-cylinder gasoline engine for something considerably more advanced--the
diesel plug-in drivetrain from the XL1 "eco supercar"
Welcome, then, the Twin Up, a plug-in hybrid derivative of
VW’s very successful three-cylinder IC-engined city car. Except that this
concept does away with the tiny gasoline engine and instead shares key parts of
its drivetrain with the XL1, including the downsized 800cc diesel unit,
electric motor and DSG.
MQB Baby
With Up being conceived on MQB, VW says it was relatively
easy to install a plug-in hybrid drivetrain – albeit a pocket-sized one –
within the car’s existing compact layout. The flexible nature of the
architecture, along with the only engineering modification – essentially
lengthening the front overhang by 30mm – meant that the 55kW drivetrain,
comprising the TDI engine and the electric motor, is fitted to the front of the
vehicle along with the DQ200E transmission and additional power electronics. At
the rear is the lithium-ion battery pack with an energy capacity of 8.6kWh, the
12V battery for the electrical systems and a 33-liter fuel tank.
The two-cylinder diesel engine is a close relative of VW’s
1.6-liter four-cylinder offering, sharing the same cylinder spacing (88mm),
bore (81mm) and stroke (80.5mm). In addition to halving the displacement
capacity of the IC base, other emissions-reducing measures include specially
formed piston recesses, multipoint fuel injection and controlled orientation of
individual sprays. A balancer shaft has been added to optimize NVH, a thorny
issue for most two- and three-cylinder designs. There’s also an EGR, DPF,
oxidation catalytic converter and brake recuperation capability.
Located between the TDI engine and the seven-speed DSG is
the Twin Up’s all-important hybrid module with an electric motor and decoupling
clutch, which VW engineers have integrated within the transmission in place of
the flywheel.
Maximum speeds
range from 87 mph in hybrid mode to 78 mph in electric mode. Acceleration is
quite poor; it takes the Twin Up 15.7 seconds to get from 0 to 60mph.
The result of these added e-powertrain subsystems is a
weight increase of just under 300kg over a standard IC-engined Up. But despite
such a weight penalty, the environmental benefits of the Twin Up can’t be
argued with: CO2emissions are rated at 27g/km, down from 105g/km on the
three-cylinder models, and fuel consumption is an astonishing 1.1 liters/100km
(256mpg), making the 4.489 liters/100km (62.8mpg) of the standard Up seem like
an inefficient gas guzzling monster!
Crucially for a city car, though, is the fact that the Twin
Up is not slow off the mark: 0-60km/h (0-37mph) in pure electric mode takes 8.8
seconds before a top speed of 125km/h (77mph) is realized.
Some 50km (31 miles) can be covered in electric mode, where
the TDI engine is essentially decoupled from the drivetrain by opening the
decoupling clutch and is then shut off. At the same time, the driving clutch on
the gearbox side remains closed and the DSG is fully engaged.
Away from the congested city centers – and with the Twin Up
in hybrid driving mode – there’s a total of 215Nm of torque on offer, meaning
that a top speed of 140km/h (87mph) can be realized, just the ticket for those
longer autobahn-based journeys away from urban dwellings.
Thanks to its
8.6kWh battery pack the range in electric only is announced at 48km, this Twin
-Up weighs 1205kg and its consumption is listed at 1.1l per 100km for emissions
of 27g/km thanks to the plug-in diesel hybrid technology
On an official basis, VW maintains that the Twin Up remains
just a concept, but with the car already in production, and the plug-in
powertrain also being made in limited numbers for XL1, it seems logical that
VW’s plug-in hybrid tech demonstrator will soon get the green light for market
launch.
