Audi R18

The Audi R18 is a Le Mans Prototype (LMP) racing car constructed by the German car manufacturer Audi AG. It is the successor to the Audi R15 TDI. Like its predecessor, the R18 uses a TDI turbocharged diesel engine but with a reduced capacity of 3.7 litres and in a V6 configuration. For the first time since the 1999 R8C, the Audi Le Mans prototype used a closed cockpit design. The R18 is also the first racing car from Audi to feature hybrid power.

Although Audi have previously given each new developed model of endurance racing car a distinct model number, the head of Audi Sport, Wolfgang Ullrich, suggested the R18 designation for Audi endurance racing cars could be used for the foreseeable future. There were five further evolutions of R18 until Audi quit the FIA World Endurance Championship in 2016.

As the new rules for Le Mans in 2011 the car featured a stabilisation fin on the engine cover and has a new six-speed gearbox. The new gearbox was electrically controlled instead of pneumatically controlled, saving weight by eliminating the pneumatic system. Despite the capacity reduction, the 3.7L V6 is claimed to develop more than 397 kilowatts (532 bhp) of power, less than the outgoing R15. The new engine has a single Garrett (Honeywell Turbo Technologies) TR30R VGT turbocharger, as opposed to the twin TR30R configuration of both the Peugeot 908 HDi FAP and the previous Audi R15 TDI. The R18's V6 engine exhausts inwards between the cylinder banks, where the turbocharger is placed. This is called a 'hot valley' configuration and is opposed to the traditional configuration with each cylinder bank of a V engine exhausting outwards to their respective turbochargers.

For 2012, Audi introduced an evolution of the original car called the R18 ultra and R18 e-tron quattro, which won Le Mans. Both the Ultra and e-tron quattro R18 were run at the 2012 24 Hours of Le Mans. In addition to the changes required by the regulations (reduced air intake restrictor and 60 litre fuel tank) the car was completely reworked to reduce weight. These changes included Xtrac sequential electrically activated 6-speed racing gearbox with gearbox housing made of new carbon-fiber composite with titanium inserts, carbon clutch, changes to the carbon-fiber composite aluminum honeycomb monocoque built by Dallara, Single Garrett (Honeywell Turbo Technologies) turbocharger with boost pressure limited to 280 kPa absolute, Bosch MS24 engine management, 1 x 45.8 mm diameter air restrictor, OZ magnesium forged wheels, Michelin Radial 360/710R18 front and 370/710R18 rear tires.

The R18 e-tron quattro is a hybrid version of the R18 ultra, with a 500 kJ flywheel accumulator system designed by Williams Hybrid Power, two 74 kW; 100 hp (101 PS) Bosch Motor Generator Units driving the front wheels with water-cooled integrated power electronics, providing the car with four wheel drive (quattro), and a smaller 58-litre fuel tank. The quattro system, as per the regulations, is available only at speeds above 120 km/h (75 mph).

The e-tron has six automatic modes that are driver-selectable on the steering wheel. The modes manage engine mapping, short bursts accelerating from corners, quattro four wheel drive, wet weather, etc. Allan McNish said "I don't have to press a button ... It does it automatically ... It is like traction control."

Changes from 2013 R18 e-tron quattro include the introduction of blue laser beam backlights with a yellow phosphor crystal lens complementing the LED headlights, a revised V6 TDI engine with an electric turbocharger, upgrades to the flywheel accumulator system and an exhaust heat recovery system. The system captures the thermal energy from the exhaust and can add power to either the turbocharger or the flywheel accumulator system. Audi later opted not to race with the second Energy Retrieval System, which is known as a Motor Generator Unit-Heat [MGU-H] in Formula One, because it did not result in the performance gain engineers had hoped for and was therefore considered an unnecessary risk to take. The aerodynamics have been heavily revised in accordance with the new rules: the width is reduced by 10 cm, the height is increased by 20 mm and there are a new set of front wings. The exhaust-blown diffuser on the 2013 model has been banned and removed. The safety monocoque has been strengthened with additional fabric. Wheel tethers and extra crash structures are also added to the car. Finally, there are numerous smaller upgrades to vision and ergonomics to improve drivability.

On 29 November 2015, Audi Sport debuted the redesigned R18 that the team planned to race in the 2016 FIA World Endurance Championship season. The new R18 featured significantly altered aerodynamics, including a raised nose similar to pre-2014 Formula One nose designs, air scoops above the front fenders, integrated mirrors, and other body modifications. The KERS for the 2016 R18 had also been changed from a flywheel system to a lithium-ion battery, and had been upgraded from the 4 MJ class to the 6 MJ class for additional boost. The engine remained the same 4.0 L turbodiesel V6. Audi dropped the e-tron quattro name badge for the 2016 season.