Monday, June 24, 2013

Two ways, one aim: DTM–LMP comparison

Audi Press Release

They could hardly be any more different – the Audi RS 5 DTM and the R18 e-tron quattro. Still, there are some things which both race cars from Audi’s factory programs in the DTM and WEC have in common. Plus, both are pursuing the same aim – success.

There was a time when a touring car was an optimized production model. Audi often proved that it is possible to be successful in motorsport with such cars. In 1990 and 1991, the Audi V8 quattro won the DTM twice in succession. No other automobile manufacturer had achieved this feat before. The Group A race cars were created on the basis of a production Audi V8. The following years again showed that a good production touring car provides a viable base for great success in racing. The Audi 80 competition and the Audi A4 quattro, prepared according to Super Touring Car regulations, won titles for Audi worldwide.

Since the 2000 season, different rules have applied in the DTM – a kind of touring car prototype took the place of production concepts. Although the Audi A4 DTM resembled the volume production model it was based on a steel space frame and relied on mechanical systems strictly designed for racing in all areas such as the suspension, aerodynamics, the engine and the transmission. Audi won the DTM Championship with it five times.

In 2012, new rules were introduced yet again while the idea of a pure race car concept has been retained. A carryover-parts-principle for the three manufacturers involved in the DTM prescribes a large number of shared component assemblies. For example, the carbon fiber monocoque including the steel roll cage is identical for the Audi RS 5 DTM and its competitors.

Basically, these touring cars rely on a material in a central, stressed component that has been used as the standard material for Audi’s sports prototypes since 1999: carbon fiber reinforced plastic (CFRP). The material is comparable but the results differ. In the DTM, the monocoque consists of carbon fiber up to the belt line. Above it, a rugged steel cage protects the driver and serves as the mounting point for the bodywork and other parts. Six carbon fiber elements – one each at the front and rear – additionally absorb the impact energy in accidents. Since 2000, individual tubular steel frames and a CFRP cockpit were standard in the DTM.

In the Audi R18 e-tron quattro sports car, the entire one-piece monocoque is made of carbon. While the cost-optimized DTM design weighs around 130 kilograms, the performance-optimized sports car cell tips the scales at less than half of this weight. By taking the step in favor of an identical monocoque the DTM has clearly progressed in terms of passive safety.

Even though the number of almost 60 carryover parts between the three manufacturers in the DTM appears to be small, the effects should not be underestimated. “The monocoque is a particularly large component,” emphasizes Dr. Martin Mühlmeier, Head of Technology at Audi Sport. “The transmission and the drive shaft are identical. For the suspension, the mounting points are severely limited and the material is specified. For the engine, a minimum weight is prescribed.” By contrast, the Audi R18 e-tron quattro offers a lot of engineering freedom. There are no carryover parts, different types of internal combustion engines such as gasoline or diesel units are allowed, the number of cylinders may vary and the regulations provide a lot of latitude with respect to numerous other parameters. Similarly, the limitations imposed on the chassis are much smaller as well.

“By the same token, we’ve got a lot of freedom with the Audi R18 e-tron quattro in terms of aerodynamics too,” says Dr. Mühlmeier. “In the DTM, the underfloor is geometrically specified, from the front to the rear diffusor. The same applies to the rear wing.”

The direct comparison between both cars is crystal-clear for the Head of Technology: “The number of variables is significantly lower for a DTM race car. The regulations have deliberately reduced the complexity of the car. As a result, the manpower required to construct the race car, in simulation and in further development is clearly lower.”

At Audi Sport, both projects benefit from each other nonetheless. “We use the same programs for aerodynamics calculations by means of computational fluid dynamics (CFD) and in engineering design with the finite elements method (FEM),” explains the engineer. “The departments and the employees that deal with many of the various questions arising in the DTM and LMP are the same.” Special developments, though, are necessary to develop and test the hybrid system of the R18 e-tron quattro.

“Despite all the differences between the race cars, at Audi, we’ve repeatedly been able to use synergies benefiting both projects for years,” stresses Dr. Martin Mühlmeier.