Audi says its E-Tron hybrid racer has set benchmarks in terms of assembly space, weight and performance with four weeks to go before the Le Mans 24 HoursElectrified drive and quattro all-wheel drive - what looks like two different worlds at first glance has been merged into a technological synthesis. Image gallery.Head of Audi Motorsport, Wolfgang Ullrich, explained: "Soon after the TDI phase, when it was foreseeable that the regulations would open up this option, had begun we started to think about the hybridisation of a Le Mans sports prototype."After exploring the concepts we quickly saw the opportunity of bringing a new technological specification of all-wheel drive back into motorsport. Unfortunately, it had been banned from circuit racing since 1998."BIGGEST TASK YETAudi won four World Rally championship titles between 1981 and 1997 with quattro models, as well as three victories at Pikes Peak, a championship win in Trans-Am, two German Touring Car titles and 11 National Super Touring Car championships plus a Touring Car World Cup.An all-wheel drive model, for the first time since the 1998 ban, has now been allowed to compete in the FIA’s circuit racing programme. However the automaker says what sounds like a simple return has been one of the biggest tasks yet tackled by Audi Sport."Packaging an additional front-wheel drive and a hybrid system into a sports car is particularly difficult due to space," Audi says. "The car is externally large at two by 4.65 metres but beneath the shell is a monocoque construction which in motorsport has been optimised for everything but the integration of an extra drive axle and a hybrid system. "Consequently," Audi adds, "the achievements of the engineering team that made the hybrid front-wheel drive a reality are particularly impressive. For example, the entire drive unit is installed inside the carbon fibre structure for optimal protection and the monocoque has been stretched forward compared with the predecessor model."This shortens the frontal crash structure but the car still had to pass all crash tests. Then there's the extreme proximity to the driver who requires special protection, and every gram counts in motorsport. And never before has such a small and light system recovered so much energy."ROTATING STORAGEWith support from system partners, Audi says, it has achieved a particularly compact motor generator unit on the front axle. During energy recuperation, which is electronically controlled, drive shafts transmit power to the inside of the MGU where the kinetic energy is converted into electric power during braking.The principle is similar to that of the commonly known dyno - albeit with extremely high energy flows. Converters integrated into the housing transform this energy from alternating to direct current which in turn drives a rotating mass storage device located alongside the driver.The energy is stored by the current accelerating this carbon-fibre flywheel which rotates in a high vacuum to as fast as 45 000rpm. After cornering, this energy is available again to power the electric motors of the MGU unit which in turn drive the front wheels. As much as 150kW of short-term power can be supplied to the front axle. POSITIVE WEIGHT DISTRIBUTIONUllrich explained: "Audi’s Technical Development Division had the idea of driving the internal combustion engine and an axle via the electric motor gave us a strong motivation to steer the concept for the R18 e-tron quattro in this direction."We’re achieving a positive weight distribution in the vehicle by splitting the electric drive and the combustion drive between axles while making use of at least some of the advantages of a quattro drive system. We received a relatively quick response after presenting our concept to the ACO and the FIA who saw that our hybrid solution, in combination with all-wheel drive, certainly carried some weight."The FIA wanted to keep this within the limits of a reduced scope because its chief aim is hybridisation, not the return of all-wheel drive so a clause in the regulations was agreed that limits the advantage of a standard quattro drive when accelerating out of tight corners."The electrified axle may only be additionally used for acceleration above 120 km/h." Among other conditions, the prescribed 58-litre fuel tank capacity of the hybrid vehicle is two litres less than that of a conventional car and the amount of energy that may be recuperated between two braking zones is limited to 500kJ.Ullrich said: "The FIA defines these interventions to create a balance between hybrid and conventional vehicles. The effects vary from track to track and are difficult for us to judge for now (partly because the number of braking zones varies among tracks)."ANY TRACK, ANY WEATHERUllrich’s conviction, Audi says, that this has been the right step outweighs such imponderables. There is even a bit of nostalgia involved."I’m really happy that we managed to bring quattro back into motorsport. It was the system with which I started my first hours in the Super Touring Car project at Audi Sport," he added."Audi proved back then that all-wheel drive offers an advantage on any track in any weather, even with low engine output, just as our customers can experience it on the road."It’s nice that we’re bringing a form of quattro back into motorsport even though, to put it in jest, we’re only allowed to compete with 'part-time quattro for now."