Sneak Peek: The Powertrains of the 2015 Le Mans LMP1 Class
Khiem Dinh is an engineer for Honeywell Turbo Technologies at the time of this writing. All statements and opinions expressed by Khiem Dinh are solely those of Khiem Dinh and not reflective of Honeywell Turbo Technologies.
The top level LMP1 cars in WEC are all hybrids displaying a staggering array of technologies and massive power. Audi, Toyota, Porsche and Nissan are the major players this year with each team using a different configuration of engine and also unique hybrid systems. With every choice in technology selected for either the engine or hybrid system, compromises were made. With the marque event of the 24 Hours of Le Mans arriving, we get to see who selected the best compromises to win the unique race of Le Mans.
To those unfamiliar with the world of high performance hybrids, these cars are nothing like the gas sipping street car hybrids the general population is familiar with. All of the four engine configurations make in the ballpark of 500hp. Adding the hybrid systems doubles the power output. The Nissan more than doubles the engine power with the electric hybrid system adding around 750hp for a total of 1250hp to the wheels. Additionally, the hybrid system makes three of the four cars all-wheel drive (the Nissan currently remains FWD, but more on that later). These ain’t your everyday slow lane hybrids.
The dominant force in endurance racing has been Audi having won 13 of the last 15 24 Hours of Le Mans. How’s that for a winning record? Why do they race? Audi does it to prove out their technologies in the most grueling motorsports event. They first started winning with the turbocharged gasoline direct-injection R8. Pretty much every Audi and VW vehicle can be had with this technology. Then Audi went diesel. Many Audi and VW vehicles can be bought with TDI technology now. Of course, the latest technology now is hybrid technology. (Photo from motorsport.com)
The Audi R18 E-tron Quattro uses a 4.0L, V6, mid-engine diesel with a single VNT (variable nozzle turbine) turbocharger. The engine was updated from the previous 3.7L engine and puts out around 558hp. The benefit of diesel is better fuel economy. The downside of diesel is the heavier weight of the engine compared to a gasoline engine. The hybrid energy storage device is a flywheel (mechanical storage device) developed by Williams Hybrid Power, a spin-off from the Williams Formula1 team where the technology was originally developed for Formula1 KERS. The benefit of the flywheel design is the ability to quickly absorb and release energy along with very high energy density resulting in a small volume package. The downside is the extremely high speed spinning flywheel has significant rotation inertia which can negatively affect handling. Notice the placement of the flywheel is right next to the driver in the middle of the car which should minimize the effects of the rotational inertia of the flywheel. The flywheel is connected to a front MGU-K (motor/generator unit kinetic energy) which powers the front wheels making the car all-wheel-drive (Quattro in Audi speak). In the Audi configuration, braking energy is only recovered from the front wheels. As the Audi is only recovering energy from the front wheels, the hybrid system is only 4 MJ (mega joules). (Photo from Audi)
Here is a side view of the Audi V6 diesel engine with the single VNT turbocharger mounted in the V of the engine. Packaging on race cars is tight necessitating the tilting of the turbo to provide the least restrictive intake to the turbo. (Photo from Fourtitude.com)
Looking at the rear of the engine gives a good view of the turbo mounted in the V of the engine. Notice the turbine housing has two inlet ports, one for each bank of the engine. (Photo from Fourtitude.com)