The Road to Le Mans
The new endurance racing season has begun. The
“And then I go and spoil it all by saying something stupid like I love you”—grand sentiments can miss the mark, as Frank Sinatra and his daughter Nancy sang knowingly. And yet, while an entire self-help industry gamely tries to squeeze love into a guise of objectivity, things are decidedly easier when it comes to Le Mans. For beyond the feelings, it also has a goal-oriented technical angle to consider.
We rendezvous at the preseason training in Bahrain. It’s going on midnight. The 2015
Hitzinger and his team have put that evolutionary impulse into practice. While it may sound like adjusting a few screws here and there, in fact it meant that even as the basic concept was retained, every detail of it was re-examined. The 919 Hybrid still features a downsizing turbo gasoline engine with direct fuel injection and two energy recuperation systems. Total system output is now almost 735 kW (1,000 hp). The list of enhancements is long.
The combustion efficiency of the now lighter and stiffer two-liter four-cylinder engine increased again. The load-bearing function of the 90-degree V-engine in the chassis also added to overall stiffness through geometry modifications. To improve performance and achieve more efficient aerodynamics, a twin exhaust system replaces the central exhaust tract in the previous version. The combustion engine powers the rear axle with well over 368 kW (500 hp). With the critical sequential and hydraulically actuated seven-speed racing transmission as well, the team managed the balancing act of reducing the weight while simultaneously achieving greater stiffness and robustness. “At the same time, we also reduced the shifting times yet again,” adds Hitzinger.
More power and less weight is the result of the comprehensive reworking of the hybrid system. On the front axle, kinetic energy is converted into electric energy during braking. The second recuperation system is in the exhaust tract. The exhaust flow drives—practically parallel to the turbocharger—a turbine.
The electricity generated this way, like that from the front brakes, is temporarily stored in lithium-ion battery cells. The driver can then call up the energy from there. When he needs full boost power, additional force to the tune of 294 kW (400 hp) presses him into his seat. This power is directed to the front axle via an electric motor and converts the 919 into an all-wheeler.
As with their selection of the drive concept, the engineers also enjoy freedom of choice with regard to the storage medium. “The key is to select the storage medium,” explains Hitzinger, “that is best suited to the respective hybrid system. There’s always a trade-off between power density and energy density.” The higher the power density of the medium, the quicker the energy can be added to and drawn from the battery. The higher the energy density, the more energy can be stored. Achieving maximal values for both properties is physically impossible. Hitzinger says, “In terms of power density, our lithium-ion battery is nearly on the level of supercondensors, but with a much higher energy density. It can take up and put out a lot of power very quickly, and has a moderate weight and a relatively high storage capacity.”
When it comes to using electric energy, the drivers face a choice: if they largely drain the battery in a duel by boosting somewhere on the lap, they might be left behind on the straightaway if a competitor still has some reserves. The greater the amount of electric energy that a driver can apply per lap, the lower the amount of fuel he is allowed to use. The rules thus promote innovative hybrid technology while leveling the playing field between the different concepts.
The sandwich-design carbon-fiber monocoque, which is now manufactured in a single piece instead of two, is notably lighter and yet stiffer. “That’s down to improved layer construction,” explains the technology expert. He would never compromise in terms of safety. And that approach has paid off: less than half an hour before the first victory of the previous car at the season finale in Brazil, Mark Webber emerged from a hair-raising crash almost entirely unscathed.
In terms of aerodynamics, efficiency objectives were joined by sensitivity concerns: lower susceptibility to wind, steering angle, float, and roll angle. These disruptions change the airflow around the car, compromise stability, and thus reduce speed. Aerodynamicists always have a twofold problem at Le Mans: the long straightaways require such low drag that downforce has to be kept to an absolute minimum. On the other sections, however, more downforce is needed.
It’s getting loud again. With its new twin tailpipe setup, the 919 sounds even more imposing. Nico Hülkenberg shifts into seventh gear, boosts, and kicks up a storm. Marc Lieb, the fastest symbiosis of passionate race-car driver and engineer, watches the sand eddies. What does it mean to start with this new
By Heike Hientzsch
Photos by Jürgen Tap
To the Nines
The three driver teams are subject to exacting standards.
The drivers of the two trios from last year remain unchanged: Timo Bernhard (Germany), Brendon Hartley (New Zealand), and Mark Webber (Australia) now have starting number 17. Car 18 will be driven by Romain Dumas (France), Neel Jani (Switzerland), and Marc Lieb (Germany). In Spa and Le Mans, Earl Bamber (New Zealand), Nico Hülkenberg (Germany), and Nick Tandy (UK) will share a third prototype with starting number 19.
Fritz Enzinger, head of the LMP1 program (photo), has full confidence in all nine drivers: “It goes without saying that each of these drivers is fast and clever. But in the WEC, and especially in Le Mans, there are even more qualities that count. The ability to stay focused constantly and to deliver consistent performances is a musthave for endurance racing. Another important factor is the ability to work together and integrate what one has learned.”