VW leverages Ducati tech

Volkswagen’s svelte XL Sport concept car, shown at last week’s Paris motor show, could be more than an exercise of vehicular expression.

According to the German car-making giant's head of powertrain development, Dr Heinz-Jakob Neusser, the concept’s Ducati-sourced V-twin engine is of interest to Volkswagen, not least because of its desmodromic valve actuation system.

“Ducati has highly specialised mechanical technology engines," he said. "If you look to the Desmodromic valvetrain — low friction, low-weight drivetrains — it’s interesting.

"That’s not to say we will take Ducati’s production engines and put them into a car, but the technology of these engines is very interesting [to us],” Dr Neusser explained.

Sourced from the Ducati Panigale Superleggera, the XL Sport's 1198cc V-twin utilises desmodromic valve actuation technology to prevent valve float at high engine speeds, reducing the chance of valve system failure -- most commonly broken valve springs or, in extreme cases, valve impact with the piston.

Invented as an early means of eliminating valve failure and 'float' at high rpm, desmo valvetrains date back to the late 1800s and were most famously used by the Mercedes-Benz W196 Formula One car of 1954-55 and the 1955 300SLR sports car, before Ducati adopted desmo drive for its top-shelf production bikes in 1968.

In a conventional four-stroke engine, in which valves allow the air-fuel mixture into the cylinder at the beginning of the cycle and then expel exhaust gasses at the end of the cycle, the valves are opened by lobes on a camshaft and closed by return springs.

A desmodromic valve system is different in that does away with valve springs, reducing load on the valvetrain across the rev range to cut friction losses at lower engine speeds and allow higher revs without risking damage to the valve mechanism.

Desmodromic valves are reciprocating devices that are positively closed by a cam and leverage system, so an engine with desmo valves has two cams and two actuators per valve, each for positive opening and closing without a return spring.

As the desmodromic system does not have to work to overcome the static energy of a spring, it is also considered more efficient; though it is generally considered much harder on the contact points between the cam(s) and rocker arms. Noise is another problem with desmo engines with four or more cylinders.

But the main issue with desmo valve technology in mainstream engines is maintenance. In its current guise Ducati’s desmo system requires regular maintenance in comparison to valve spring system used in mass-market car engines, which could be a stumbling block in getting the technology to market.

Thanks largely o electronics, modern mass-production automotive engines have largely eliminated the valve spring problems that desmo valve technology was designed to solve, while pneumatic valves solve the same problems in many racing engines.

The XL Sport combines the aerodynamic superiority of the XL1 with the Panigale’s high-revving (11,000rpm) 149kW water-cooled two-cylinder. Running through a seven-speed dual-clutch transmission, the concept is said to boast a top speed of 270km/h, with 0-100km/h acceleration in just 5.7 seconds.

While it's unclear if the Ducati-engined XL Sport is more than a publicity stunt, the move is not a complete surprise since Volkswagen premium brand Audi purchased Ducati in 2012.

“We did a concept car to see what the reaction of the people was,” said Dr Nuessen. “People are very interested in this but we haven’t made the decision to produce it [because] there is a question as to if it’s relevant.”