Pregnancy terms vary widely across the animal kingdom, from less than two weeks for an American opossum to almost a couple of years for an African elephant.
But the gestation period of the extraordinary, ultra-lightweight two-seat Volkswagen XL1 is something else: more than a decade.
Now in production (a slightly tenuous description as Volkswagen is building two a week, which compares to a global weekly production rate of 18,224 Golfs), it marks an automotive step-change, the like of which has never been seen before – and hybrid diesel technology is at the core of its startling efficiency, with a combined fuel consumption of 314mpg and a CO2 figure of 21g/km.
DieselCar was one of a handful of global media allowed to enter the hallowed portals of XL1 manufacture at Osnabrück in Germany, to see the reality.
The list of XL1 technology and its effect on performance and economy is almost bewildering. It is the most aerodynamic production car in the world with a Cd (co-efficient of drag) figure of 0.189.
Next best is the new Mercedes-Benz CLA-Class with a Cd of 0.22 (for the basic version), which itself is well ahead of any rivals.
The VW’s lightweight (795kg) carbon-fibre reinforced polymer (CFRP) monocoque structure gives it an amazingly rigid body, measured by the company at better than 30,000Nm/o.
It has magnesium wheels, carbon fibre brakes, a dashboard of moulded wood fibre, polycarbonate side windows and cameras instead of exterior rearview mirrors.
Opening its upward swinging driver’s door and slipping into its snug cockpit is like moving into a whole new realm of personal transport.
And just behind that cockpit is the game little diesel that, working in parallel with a 20kW (27bhp) electric motor, provides the XL1 with a 0-62 mph time of 12.7 seconds but a more impressive 100mph top and cruising speed.
It could have been even faster, but that would have involved the use of aerodynamic downforce generators that would have a detrimental effect on fuel consumption.
Volkswagen took a 1.6-litre TDI engine, carried out some radical surgery to reduce it to two cylinders and created a 0.8-litre unit, adding a balancer shaft running off the crankshaft to provide smoother operation. Power output is 47bhp with maximum torque of 89bhp.
The XL1 has a sophisticated, low aerodynamic drag cooling system, its air intake opening automatically only when the engine management system demands it.
With a diesel particulate filter, oxidation catalytic converter and EGR (exhaust gas recirculation) valve, the car already meets Euro 6 emissions requirements.
The powertrain incorporates a DSG gearbox with magnesium housing, but in this application with a triple, rather than the normal twin-clutch configuration, in order to integrate the system with the electric motor.
Build of the XL1 passes through nine stages, starting with the CFRP monocoque – the cockpit area – mounted to an assembly support plate.
Components are joined by gluing; the roof section “hovered” above the shell and gently lowered to be bonded. Tolerances are kept to an absolute minimum but there are plenty of challenges.
Friedrich Wegert, Head of Development at Osnabrück said: “We have over 100 years’ experience of sheet metal for automotive production; for CFRP there is no satisfactory (computer) simulation. Our development was about how to build the tool to build the part. To find out what you can do you have to do it!”
CFRP thickness varies from two millimetres up to six for the A-pillars. Polyurethane glues used include those that give high elasticity in some areas.
Volkswagen worked with Lamborghini – also part of the vast Volkswagen Group – to help it achieve the required precision fit of the doors.
Weight saving includes 700gm CFRP anti-roll bars and magnesium wheels that weigh only 3kg. Special Michelin high-pressure, low rolling resistance tyres are fitted.
To save every gramme of weight, side windows are made of polycarbonate. It is the first time a production car has used polycarbonate ahead of the B-pillars, and the laminated windscreen is only 3.2 millimetres thick.
Start of the XL1 project goes way back to 2002 and the Volkswagen 1-litre (in terms of fuel consumption measured in litres/100km), a millennium concept conceived by Dr. Ferdinand Piëch, now Chairman of the Supervisory Board of Volkswagen AG.
It had a 0.3-litre diesel engine and tandem seating. But not much happened after that until 2007 when Dr. Ulrich Hackenberg became engineering boss of Volkswagen and used it as a basis for the future production car.
In 2009 a prototype was shown that presaged today’s XL1 which has a narrow body (1665mm) but side-by-side seating, albeit with the passenger seat set slightly astern of the driver.
Improvements in carbon fibre technology for vehicle production, including applications of resin transfer moulding (RTM) which Hackenberg now refers to as “advanced RTM” for the XL1, have signalled the way forward for the production car.
Asked what was the toughest challenge of the production project, Hackenberg said: “The most difficult thing was the integration of all the technologies: to make the whole car.”
But at the end of the long “pregnancy”, the visit to the XL1 delivery room left no doubt that a diesel-hearted prodigy had arrived.