Recently, we stood eye to eye with last years’ Le Mans winner, the 2012 Audi R18 e-tron Quattro, in the showroom of Audi Brussels, the plant where the Audi A1 is built.
We took the occasion to take some close up photo’s of the car, and to tell you more about the unique technical features of the R18...in the present version, and highlight the modifications which were brought to the car for the 2013 season.
Hans Knol ten Bensel
The concept behind the Audi R18 e-tron quattro is unprecedented in LMP sport.
After weighing up considerations such as traction, handling characteristics, packaging and weight distribution, they ultimately decided to separate the drive systems by axle – the combustion engine drives the rear wheels permanently, and the electric drive propels the front wheels on demand.
Some modifications for the 2013 season…
Audi had to modify the V6 TDI combustion engine with a displacement of 3.7 liters compared with the previous year’s version.
The air restrictor specified for 2013 with a diameter of 45.1 millimeters (1.78 in), 0.7 millimeters (0.03 in) smaller than in the previous season, limits the output to about 360 kW (490 hp), but torque could be maintained at around 850 Nm (626.93 lb-ft).
A special layout permits short gas paths: The exhaust end is inside the vee of the cylinder banks, which has a 120 degree angle to keep the centre of gravity low. The large turbocharger, limited to a boost pressure of 2.8 bar, assists the spontaneous torque buildup with its variable geometry. As last year, the tank capacity is a mere 58 liters (15.32 US gallons).
Last years' Le Mans winners proudly painted on the 2012 winning R18 e-tron...
A sequential six-speed transmission, like the engine of unitary construction, directs the forces to the rear wheels through a locking differential. The housing is made from ultra-lightweight carbon-fiber-reinforced polymer (CFRP) with titanium inserts. Along with the single-section monocoque, which consists of a CFRP matrix with aluminum honeycomb core, it thus helps keep the racing car’s overall weight down.
915 kilograms (2,017.23 lb) unladen weight is the lower limit specified in the ACO regulations for LMP-1 category prototypes. The Audi R18 e-tron quattro is actually still lighter, but that creates extra scope for arranging ballast weights for optimum effect. The hybrid racing car is much more complex than its conventionally driven predecessor from 2011, but thanks to ultra lightweight construction it is not heavier.
Functioning of the hybrid flywheel based energy recuperation system…
On the 13.629 km (8.47 mile) long Le Mans circuit, about 70 percent of which is driven at full throttle, a lap costs just under 200 megajoules of fuel energy. The organizers have earmarked seven special zones for hybrid racing cars – here, they can recover up to 0.5 megajoule (approx. 0.14 kWh) of energy by braking at the start of a bend. On the R18 e-tron quattro, part of the braking energy benefits the motor generator unit (MGU) that is located at the front axle.
Their two permanently excited synchronous machines convert the recovered energy into direct current through power electronics. This current drives a flywheel energy storage system positioned on the left inside the cockpit, again very advantageous in terms of the centre of gravity.
It accelerates a CFRP flywheel up to a speed of almost 45,000 rpm. It rotates in an extremely low-friction environment inside a high vacuum generated by two pumps. The flywheel energy storage system, with its aluminum casing, combines high energy density with high charging power.
Racing conditions on the Le Mans circuit…
The fastest sections on the Le Mans circuit are before the two chicanes, before the Mulsanne bend, before the Indianapolis bend and before the first Porsche bend; these are all energy recovery zones.
The R18 e-tron quattro brakes into them from a speed of some 300 km/h (186.14 mph) or more – for three to four seconds with retardation of 3 to 4 g.
At these high speeds the energy recovery function has very little effect on brake-force balance, at least in dry conditions. The power output of the hydraulic wheel brakes with their carbon-fiber-reinforced polymer disks is a great deal higher than the energy flowing to the MGU.
The flies and dirt collected at racing speeds on the Le Sarthe circuit are still on the R18 in the Audi Brussels showroom...
When the car accelerates again to speeds beyond 120 km/h (74.56 mph), the energy is called up from the storage system again.
Converted back into alternating current by the power electronics, it then supplies the MGU’s two electric motors. These jointly feed more than 160 kW to the front wheels via single-stage planetary gears; the central control unit keeps the revs and torque in line with the conditions prevailing at the rear wheels. The racing car temporarily becomes a quattro with four driven wheels.
Driver remains in total control…
The driver of the R18 e-tron quattro can adjust energy recovery and boost across several levels at a switch, influencing both intensity and the responsiveness of the brake and accelerator pedals. A great many factors are at work here, such as the current race tactics and strategy, the condition of the brakes and tires, and the quality of road grip. The pit crew continually monitors all driving statuses and supplies the driver with detailed feedback.
…a very light hybrid system
With an overall weight of 70 kilograms (154.32 lb), the hybrid components of the Audi R18 e-tron quattro are very light. They have separate water cooling with a low-temperature circuit, and the temperature of the flywheel energy storage system is regulated by an oil-to-water heat exchanger. All high-voltage batteries are strictly isolated from the car’s conventional components.
The 2012 winner…
The 2012 Le Mans winner impressively demonstrated the potential of the hybrid technology of Audi. The winning drivers André Lotterer, Marcel Fässler and Benoît Tréluyer drove significantly faster than in the previous year, averaging 214.468 km/h (133.26 mph) as opposed to 201.266 km/h (125.06 mph).
The R18 e-tron quattro was nevertheless around ten percent more fuel-efficient. Its combination of power, speed, efficiency and reliability also proved a winning formula in the FIA’s newly created World Endurance Championship (WEC), in which Audi captured the drivers’ and manufacturers’ trophies in fall 2012.
Improvements for 2013
The Audi R18 e-tron quattro reveals further improvements to its aerodynamics, ultra lightweight design and safety.
Variable LED headlights featuring matrix beam technology illuminate the field of view when turning. The digital interior mirror using innovative AMOLED technology (active matrix organic light emitting diode) is also used. Well the success of the 2013 Le Mans race does not need any further comments…
2014 will see a completely new set of regulations take effect, bringing motor sport and production development even closer together.
The organizers will specify a certain amount of fuel energy from which every participant must extract maximum performance; in terms of engines and hybrid systems, there will be more room for maneuver. The aim is to cut fuel consumption by a further 30 percent.
But in the meantime, we let you enjoy the breathtaking technical beauty of the 2012 R18 e-tron Quattro with the accompanying photos…
Hans Knol ten Bensel