Audi R18 e-tron quattro

Audi’s first big motor sport program in 1981 was based on the quattro permanent four wheel drive. After numerous championship wins and the banning of four-wheel drive in FIA circuit-based racing series for the 1998 season, a model from Ingolstadt and Neckarsulm with four driven wheels now returns to the race tracks – the Audi R18 e-tron quattro.

Four-wheel drive in an LMP1 sports car: Audi, in its 30 year plus motor sport history, once again makes a pioneering step as the brand with the four rings becomes the first automobile manufacturer ever to field a diesel hybrid at Le Mans. “To develop the hybrid technology for Le Mans is at least as ambitious and challenging as our diesel project was in its early stages,” explains Head of Audi Motorsport Dr. Wolfgang Ullrich. “The first test results are very encouraging and we are intrigued to see just how this technology performs in combination with our ultra lightweight technology on the race track at Le Mans.”

Background of the innovation is the interaction of two factors: promising technologies for environmental protection encounter new clarity in the regulations for Le Mans Prototypes. Since 1999, the 24 Hours of Le Mans has provided an excellent laboratory for testing new, production relevant technologies for Audi. Following the first Le Mans victory for gasoline direct injection TFSI (2001) and the first diesel triumph with TDI (2006), a hybrid car now makes its debut. To this end, the regulations are not only open for new power sources and energy recovery, but also allow the use of four-wheel drive in a Le Mans Prototype for the first time. The two technologies combine in a fascinating way to create a new type of drive – e-tron quattro. This in turn has direct reference to future production line products at Audi: the first experimental vehicles with the electric four-wheel drive e-tron quattro are already being tested with a view to possible high volume production.

Kinetic energy is recovered on the front axle during the braking phase on the Audi R18 e-tron quattro. It is fed into an electric flywheel accumulator before being retrieved under acceleration. During this procedure only the front axle is integrated. The V6 TDI power plant producing over 375 kW (510 hp) still transfers its power to the rear wheels. The two systems complement one another to create the powertrain principle e-tron quattro, a new form of four-wheel drive which in turn hails a revolution – as did the permanent quattro four-wheel drive for automobile production from 1980 thanks to Audi and, from 1981, also gave motor sport a significant technological impulse that has worked for decades.

At that time Audi became the first manufacturer to successfully offer the permanent quattro four wheel drive in high-performance cars and later in almost every model range. It also led to two Manufacturers’ and two Drivers’ World Championship titles in rallying. Four-wheel drive subsequently proved a sensation in circuit racing: quattro models set new benchmarks and won numerous races and championship titles in TRANS-AM and the IMSA GTO series in the USA, in the DTM and in super touring cars.

e-tron quattro: the next generation four-wheel drive

More still: Audi initiated a concept shift. From the power transmission principle, previously reserved for all-terrain vehicles, Audi developed a highly efficient system incorporating many technical innovations for passenger cars and sports cars. The competition was also forced to follow the new trend – albeit several years behind. The same was valid in motor sport: since the quattro era, it is hard to imagine rallying without four-wheel drive as a characteristic feature. The competition repeatedly followed the direction set by Audi in circuit racing – but by no means with the same level of success. Three decades ago, quattro four-wheel drive distinguished itself through its particularly compact dimensions, the correspondingly small installation space required and by its high degree of efficiency.

The e-tron quattro is now the next generation four-wheel drive and motorsport once again plays a pioneering role. The new Audi R18 e-tron celebrates its race debut on May 5 in the 6-hour race at Spa-Francorchamps (Belgium). Audi Sport Team Joest fields two cars equipped with the innovative drive system in the 24 Hours of Le Mans on June 16/17. In parallel, for the 80th running of the world’s most famous endurance race, Audi Sport Team Joest sends a pair of conventionally powered Audi R18 ultra prototypes to join the grid. With the exception of the hybrid system, they are absolutely identical to the R18 e-tron quattro. “As before, we still see potential in the conventional drive – just as our colleagues in production development do,” says Head of Audi Motorsport Dr. Wolfgang Ullrich. “This is why we are absolutely delighted that the ACO and FIA selection committee has accepted our entries and that we can join the grid with four cars at the commemorative running of the Le Mans race.”

Audi will also follow a two-pronged approach in the FIA World Endurance Championship this year by fielding both technologies. Both R18 versions share the ultra lightweight design and construction, which only made the use of additional hybrid components possible in the first place.

The Audi R18 e-tron quattro is the first Audi race car no longer accelerated exclusively by a combustion engine. With its partially electrified hybrid drive e-tron quattro, the prototype hails a new era in LMP1 sports cars.

Revolution in 18 months: the project e-tron quattro for motor sport started in February 2010. Only 18 months passed from the initial conceptual ideas to the first test. “This is a relatively short cycle for a technology that has never been tested in motor sport and which still doesn’t even exist in production,” stresses Dr. Martin Mühlmeier, Head of Technology at Audi Sport.

The first big hurdle on the threshold of a new era was defining the concepts. As so often the case in the past, Audi also aims to play a pioneering role in this technology. With the R18 e-tron quattro “Vorsprung durch Technik” means the development of an independent hybrid system including complete networking, control, software, algorithms and interfaces. As in other areas Audi Sport also cooperates with external manufacturers during the manufacture of components for the hybrid system. Development partner for the accumulator is Williams WHP, for the Motor Generator Unit (MGU) long-standing technology partner Bosch.

Audi adopted a flywheel accumulator system since the requirements at Le Mans differ slightly to those in everyday life. “A high power density is crucial during energy recuperation,” states Christopher Reinke, Technical Project Leader LMP. “The accumulator must be capable of absorbing a lot of energy within a few seconds during the braking stage.”

The system integrated into the front axle is comprised of two drive shafts, the Motor Generator Unit including planetary gears, an electronic flywheel accumulator alongside the driver, an insulation monitoring unit for high voltage safety and the control system. The process of energy recuperation is explained relatively easily, the technical implementation is, in contrast, extremely challenging. The recuperation of energy occurs during braking. In the process, the wheels drive the MGU. The braking zones permitted are defined by the organizer. The Motor Generator Unit accelerates electrically a carbon-fiber flywheel, which runs in a high-vacuum. After the corner is taken and the driver accelerates again the system delivers the energy to the front axle. The regulations allow 500 kJ of energy to be transferred to the front wheels between two braking phases. The planetary gears adapt the transmission ratio during acceleration and braking. The two independently powered axles on the e-tron quattro are synchronized exclusively via electronic control strategies.

This control occurs automatically without driver intervention. The entire charging process (recuperation) is controlled by two parameters: the deceleration of the car, meaning the braking process, and subject to the accumulator’s state of charge. The energy emission process (boost) is defined by the minimum speed of 120 km/h stipulated by the regulations, the race strategy selected, the throttle pedal movement and acceleration of the car.

The ideal compromise – a challenge

“The greatest challenge was to find the ideal compromise,” reasons Wolfgang Appel, Head of Vehicle Development at Audi Sport. “It was a question of weight, performance, hybrid concept, regulation constraints and the packaging, which means perfectly balancing the distribution of all the components in such a way that no appreciable disadvantages arise in the conventional vehicle since both cars are absolutely identical, with the exception of the hybrid system, in design and construction.”

A warning lamp and sticker stipulated by the regulations are the only external differences between the R18 e-tron quattro and the R18 ultra. The driven front axle and the coolers are covered by the bodywork. Only an operating panel below the normal dashboard in the cockpit identifies the e-tron quattro. According to driver comments the additional front wheel drive is, however, clearly noticeable dynamically.

Audi Sport has worked on the e-tron quattro project since February 2010. Initial component tests were completed on board a road going R8 sports car in 2010. Circuit testing of the R18 e-tron quattro has been underway since the beginning of October 2011. The race debut follows on May 5 in the 6-hour race at Spa-Francorchamps (Belgium).