The Volkswagen XL1 protoype
At the dawn of the millennium, Prof. Dr. Ferdinand Piëch, who
is today Chairman of the Supervisory Board of Volkswagen AG, set
his sights on creating a practical everyday use production car
with a fuel consumption of 1.0 liter per 100 km (235 mpg). In
2002 a prototype VW 1-Litre was unveiled, which was followed in
2009 by the second-generation model, dubbed the
L1, which boasted a combined diesel fuel consumption figure
of 1.38-liter/100 km (170 mpg). As impressive as that figure is,
the company has now managed to squeeze a combined fuel
consumption of just 0.9-liter/100 km (261 mpg) with its
third-generation VW 1-Litre prototype – the XL1.
With a combined fuel consumption of just 0.9-liter/100 km and
CO2 emissions of 24 g/km, VW is calling the XL1 is the most
efficient car in the world. This is achieved through a
combination of lightweight construction using monocoque and
add-on parts made of carbon fiber, very low aerodynamic drag (Cd
0.186) and a plug-in hybrid system consisting of a two cylinder
TDI engine (35 kW/48 PS), E-motor (20 kW/27 PS), 7-speed dual
clutch transmission (DSG) and lithium ion battery.
Keeping the weight off
With a weight of just 1,753 lb (795 kg), the car also takes
advantage of progresses made in Formula 1 car construction in
the manufacture of body parts from carbon fiber reinforced
polymer (CFRP) parts. Together with suppliers, VW has developed
an patented a new system for CFRP production known as the
advanced Resin Transfer Moulding (aRTM) process that has allowed
the company to achieve significant reductions in production
costs, which it says is an important step towards making a
limited production run of the XL1 viable.
Hybrid system
With the hybrid system engaged the prototype XL1 accelerates
from 0-62 mph (0-100 km/h) in 11.9 seconds and has an
electronically limited top speed of 100 mph (160 km/h). The
electric motor can deliver 100 Nm of torque from a standstill
and works as a booster to support the TDI engine, which itself
delivers 120 Nm of torque. Together, the TDI and E-motor deliver
a maximum torque of 140 Nm in boosting mode.
The entire hybrid unit is housed above the vehicle’s driven
rear axel, with the actual hybrid module with electric motor and
clutch positioned between the TDI and the 7-speed DSG. Instead
of the usual flywheel, the hybrid module is integrated in the
DSG transmission case. The vehicle’s lithium-ion battery can
also be recharged from a conventional household outlet.
In electric only mode the TDI is decoupled from the
drivetrain by disengaging a clutch, and it is shut down.
Meanwhile, the clutch on the gearbox side remains closed, so the
DSG is fully engaged with the electric motor. Using what is
known as “pulse starting”, VW says the restarting of the TDI
while driving is very smooth. The electric motor’s rotor is sped
up and quickly coupled to the engine clutch, which accelerates
the TDI to the required speed and starts it.
Under certain conditions the load shared between the TDI
engine and the electric motor can be shifted so that the
turbodiesel is operating at its optimum efficiency level.
Additionally, the gears of the automatically shifting 7-speed
DSG are also always selected with the aim of minimizing energy
usage with the engine controller taking into account parameters
such as the accelerator pedal position and engine load, as well
as the energy supply and mix of kinetic and electrical energy at
any given time.
Keeping it cool
The 0.8 liter two cylinder TDI used in the XL1 was derived
from the 1.6 liter TDI found in the VW Golf and Passat. When
required, the TDI is cooled through the activation of an
externally driven electric water pump and an automatically
controlled air intake system at the front of the vehicle
designed to reduce cooling system drag. A second electric water
pump, which is also used only as needed, circulates a separate
lower temperature coolant loop to cool the starter generator and
power electronics.
Design and aerodynamics
While the two seater XL1 borrows much of its looks from the
preceding L1 model, it has been widened to allow for side by
side seating rather than the tandem arrangement seen in both of
the previous 1-Litre cars. The XL1 measures 12.75 ft (3.88m)
long, 5.46 ft (1.66 m) wide and 3.79 ft (1.15 m) high, giving it
a length and width similar to a VW Polo, but with a low profile
comparable to a Lamborghini Gallardo Spyder. With a frontal area
of 1.5 m2 and a drag coefficient of 0.186, the XL1 yields a
total drag, or Cd.A value of 0.277 m2.
Viewed from above, the car is widest at the front and narrows
towards the rear for an improved aerodynamic profile, which VW
says resembles the aerodynamic lines of a dolphin. The
dolphin-like looks continue to the side profile with the
roofline tracing an arc from the A-pillars to the rear.
To prevent air turbulence the rear wheels are fully covered
and the air flows have also been optimized by small spoilers in
front of and behind the wheels, while the door mirrors have been
replaced with digital cameras that send images to two displays
inside the vehicle.
Instead of the aircraft-style canopy door of the first
1-Litre and the L1, the XL1 sports wing doors that are hinged
low on the A-pillars and just above the windscreen in the roof
frame, so they swivel slightly forwards as well as upwards for
easier access.
At the front end there’s no longer a typical radiator grille
with the actual air intake with electronically controlled
louvres for cooling the TDI engine, battery and interior located
in the lower front end section. There are also energy-efficient
dual LED headlights and narrow turn indicators.
LEDs are also prominent at the rear with a strip of red LEDs
integrating reversing lights, rear lights, rear fog lights and
brake lights, framing the top and sides. The coupé-shaped
roofline has no rear windscreen but includes a large rear boot
lid that covers the drive unit and 100-liter luggage space.
When the L1 was unveiled in 2009,
Volkswagen
indicated it would be entering production in 2013. We’ll be
interested to see if this updated model is on track for that
date or whether the company hopes to bring the XL1 into
production before then. All will hopefully be revealed this week
when Volkswagen unveils the XL1 at the Qatar Motor Show, which
runs from January 26 to 29.
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