Rulesmakers at the Automobile Club de l’Oest, the sanctioning group that conducts the annual 24 Hours of Le Mans sports car race, issued rules that took effect in 2014 mandating that factory teams in the premiere Le Mans Prototype 1 category employ hybrid-electric drive.
The goal was to spur creative approaches to balancing combustion and electric power with disparate solutions. They could not have, in their most optimistic dreams, expected that in the second year of this formula, the 2015 race would see four manufacturers enter factory efforts and that each would feature radically different technology in their racers.
But that is what happened, as each company plotted a route to the victory podium with a different plan.
“The possibilities of the revolutionary regulations that have been in effect for LMP sports cars since 2014 are far from having been fully used,” observed Jorg Zander, Audi Sport’s Head of Engineering. “The rules harbor so much potential that there is room for future developments. We expect that the technological progress resulting from the fierce competitive pressure exerted by four automobile manufacturers that are now involved will significantly improve lap times.”
So it was at Le Mans, where Porsche’s recipe prevailed. Using the most electric-heavy option for its 919 Hybrid: 8 megajoules of energy recovery and boost per lap, the Porsche stored energy in a pack of lithium-ion cells from A123 Systems. The trade-off was the smallest combustion engine (ICE) among the contenders, a 2.0-L gasoline V4 engine with forced induction from a pair of Honeywell turbochargers. Power from the gas engine is routed to the road through the rear wheels, while the electric motor drives the fronts.
Audi, champion of the previous five consecutive Le Mans contests, unsurprisingly hewed close to last year’s winning design with the 2015 R18 e-tron quattro, with a 4-MJ electric system mated to the R18’s 4.0-L V6 turbodiesel driving all four wheels. The car stores its electric power in a Flybrid Automotive flywheel energy storage device.
Toyota, the incumbent World Endurance Championship winner, split the difference, with a 6-MJ electric boost for its naturally aspirated 3.7-L V8 gasoline engine, with the electric power stored in a Nisshinbo Holdings, Inc. supercapacitor. Power from the ICE transfers through the rear wheels of the TS040, with an electric assist from a Denso electric motor/generator. There is extra electric drive to the front wheels from an Aisin motor/generator.
Nissan, the company that raced the arrow-shaped DeltaWing car as a technology demonstration previously, returned to La Sarthe with an equally audacious machine from the mind of designer Ben Bowlby (see http://articles.sae.org/13913/). The GT-R LM Nismo was planned as an all-wheel drive 8-MJ machine, but the compressed development schedule left it without the benefit of its planned through-the-road hybrid rear-drive electric component.
So the trio of cars Nissan brought to Le Mans were front-drive, with power from a twin-turbo 3.0-L gasoline V6 and augmented by 2 MJ of energy recovery and boost.
Teams chose these configurations based on a matrix of allowable energy storage and boost, per-lap fuel allowance, and maximum fuel tank capacity. Diesel cars are handicapped with smaller 53.3-L (14.1-gal) fuel tanks compared to the 64.4-L (17.0-gal) tanks in gasoline cars.
Cars like the Nissan with 2 MJ of regeneration are permitted to burn 4.95 L (1.31 gal) of gasoline or 3.93 L (1.04 gal) of diesel per lap, while 4-MJ cars such as the Audi get only 4.65 or 3.81 L (1.23 or 1.01 gal), respectively. With 6 MJ, racers like the Toyota are allowed 4.50 L (1.19 gal) of gasoline or 3.68 L (0.97 gal) of diesel. The 8-MJ Porsche could burn 4.42 L (1.17 gal) of gasoline every lap, while a diesel in that category would have been allowed 3.56 L (0.94 gal).
All of the hybrid prototypes have a minimum weight of 850 kg (1874 lb), compared to 900 kg (1984 lb) for the non-hybrid cars under the old rules, so there is incentive for teams to find ways to field electric drive systems while cutting mass from the cars.
Drivetrain volume is also an issue, considering the importance of underbody aerodynamics. “The concept was to have a small engine to have more space for the hybrid system,” explained Friedrich Ensinger, Head of Porsche’s LMP1 racing program.
The added power of the electrical assist is “a big advantage at Le Mans,” he said. “That is why we changed from 6 MJ (in 2014) to 8 MJ.”
Despite demonstrating obvious speed last year, Porsche failed to win Le Mans on its 2014 return to the race’s top category due to technical problems late in the race. “Twenty-two hours is not enough,” noted Ensinger in an interview before the race. “This year we will try to go two hours more.”
The company did, and it had good reason to think it could. “We did four 30-hour tests,” Ensinger explained.
Head of Audi Sport, Wolfgang Ullrich, conceded even before the race that the R18 the team was putting on the track was probably not the ideal design under the current rules. The car needed more electric assist, he said, but, “we knew the step from the 2-MJ design to 4 MJ was the most we could do from the base of the car from last year.”
In response to this understanding, Audi focused on drag reduction, he added. “We have done a very aerodynamically efficient car.”
Over at the Toyota team, there was little reason to think they needed to make big changes to the 6-MJ car that had just won the 2014 season championship. “The regulations have been essentially stable, so there was no reason to review completely our concept, considering our performance throughout 2014,” said Technical Director Pascal Vasselon beforehand. “The updated car is no revolution, but it is an evolution almost everywhere.”
In fact, Toyota’s 2015 Le Mans contender featured about 80% all-new parts. Like Audi, Toyota focused on aerodynamic refinement, according to Vasselon. “The current regulations favor more subtle changes between [high- and low-downforce] packages to keep drag reasonably low,” he said, “such as modifications to the rear wing, engine cover, and front end.”
Unfortunately, Toyota and Audi’s tweaks weren’t sufficient to overcome the advantage of Porsche’s 8-MJ electric assist. Porsche qualified on pole for the race with a new all-time fastest lap, with Audi a few seconds behind. Toyota was never a factor in qualifying or the race. Audi did set a new record for the fastest race lap, but a series of uncharacteristic reliability problems put the R18s in the garage and gave Porsche enough breathing room that it didn’t have to respond to those fast race laps.
Something completely different
Nissan attracted all the pre-race interest for the outrageousness of its front-engine design. But the predictable development problems arising from a rushed program left the team running the race as a test day, with the hope of getting a car to the finish.
They did, but too far back for it to count as an official finisher, after a litany of problems with the cars’ transmissions and clutches.
Next year will be the last under the current rules, leaving Nissan with a single shot at its effort to exploit what Bowlby sees as an opportunity in the mid-engine-focused regulations.
“The opportunity to innovate is front-and-center,” Bowlby explained. “There isn’t a book to look at for how to make a 550-hp projectile go around a track. The innovation story is the reason for this project.”
“We configured the car for the advantages of energy recovery at the front and its deployment at the rear,” he said. “We know there is huge performance potential to come.”
But innovation whose potential is unrealized doesn’t accomplish much. However, Bowlby is unfazed by Nissan’s struggles at Le Mans in 2015. “We know this is the functional building block to how we’ll get to the front in due course,” he insisted.
In fact, most teams suffer similar difficulty in the beginning, but they do so in secret rather than at open tests and in the world’s most famous sports car race, he said. In contrast to Nissan’s open approach, “Much of motorsport has almost a blanket over the process,” he said.
Fighting through these struggles in public view may add to the pain, but the team has milestones in sight. Nissan is scheduled to begin testing the GT-R LM Nismo in its intended all-wheel-drive configuration in October in preparation for Le Mans 2016.
Next year, the last of a planned three-year cycle for the current rules will probably see a convergence of solutions on an optimized ideal configuration. Then in 2017, a new set of rules should scramble things again, keeping engineers on their toes and daring them to try something as crazy as Nissan has done under the current rules.Continue reading »