Audi R18 e-tron quattro: diesel hybrid Le Mans racer with electric flywheel energy storage
1 March 2012
|Major hybrid system elements in the R18 e-tron quattro: front-axle MGU, flywheel accumulator and power electronics. Click to enlarge.|
Audi Motorsport unveiled the R18 e-tron quattro: the first LMP1 car to combine a highly-efficient TDI diesel engine with a hybrid system. (Earlier post.) The new Le Mans prototype will make its race debut on 5 May in the 6-hour race at Spa-Francorchamps (Belgium) and will compete at the 24 Hours of Le Mans (France) on 16-17 June.
One vehicle axle (rear) is powered conventionally, the second (front) by two water-cooled 75 kW motors with integrated power electronics. The system integrated into the front axle includes two drive shafts, the Motor Generator Unit (MGU) supplied by Bosch, planetary gearset, an electronic flywheel accumulator supplied by Williams Hybrid Power, an insulation monitoring unit for high voltage safety, and the control system.
On the Audi R18 e-tron quattro, kinetic energy is recovered on the front axle during the braking phase. In the process, the wheels drive the MGU. The braking zones permitted are defined by the controller. Power from the Motor Generator Unit accelerates the 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 and the accumulator’s state of charge. The energy emission process (boost) is defined by the minimum speed of 120 km/h (75 mph) stipulated by the regulations, the race strategy selected, the throttle pedal movement and acceleration of the car.
For the Audi R18 e-tron quattro, WHP designed an entirely new, ultra-lightweight electric flywheel and associated power electronics and the company has worked closely with Audi engineers to fully integrate its unique electric flywheel into the car. The system will provide 150 kW of power and have a top rotor speed of 45,000 rpm. The Audi R18 e-tron quattro using WHP’s system will make its first competitive outing in the six-hour race at Spa-Francorchamps on 5 May.
The main benefits of the WHP system are a high power density and correspondingly low mass, high efficiency energy transfer to and from the e-storage, the ability to continuously deep power cycle and an insusceptibility to performance or life degradation over a wide range of operating temperatures. In short, WHP says, the technology is suited to the high performance demands of endurance racing.
The project e-tron quattro for motorsport 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 motorsport and which still doesn’t even exist in production. The challenge is correspondingly big.—Dr. Martin Mühlmeier, Head of Technology at Audi Sport
R18 ultra. Audi will take a two-pronged approach this year in the 24 Hours of Le Mans and in the newly created FIA World Endurance Championship (WEC)— the 2012 model year Audi R18 is built with and without hybrid drive. Audi Sport developed the Audi R18 ultra model in parallel to the Audi R18 e-tron quattro. The base of both cars is identical, limiting the additional logistical effort for Audi Sport and the race team.
|The R18 ultra (left) and R18 e-tron quattro (right). Click to enlarge.|
The hybrid drive results in a slightly longer front section which also has positive effects on the overall balance of the conventionally-powered sibling. The R18 ultra is the lightest Le Mans prototype that Audi Sport has ever built. To compensate for the additional weight of the hybrid system the subject of lightweight design and construction was the focus throughout development of the 2011 Le Mans race winning R18 TDI. In addition to the many detail optimizations there is also a genuine innovation in the transmission area: a new gearbox with a carbon-fiber composite housing was developed for the R18—premiere for endurance racing.
The new R18 ultra is a distinct evolution of last year’s Le Mans race winning car. Without the weight optimized R18 ultra we would have not been capable of realizing the R18 e-tron quattro which is absolutely identical with the exception of the hybrid system.—Head of Audi Motorsport Dr. Wolfgang Ullrich
After the 24 Hours of Le Mans, Audi plans to enter an R18 e-tron quattro and an R18 ultra in the FIA World Endurance Championship (WEC).
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