The years between 1975 and 2010 were marked by the rise of turbochargers with their ability to achieve exceptional power in small engines.

But, in the early 2010s, concerns about global warming resulted in increased awareness among car manufacturers. Electric vehicles were still in their infancy, limited by the range and duration of battery recharges. Hybrid cars promised to ensure a smooth transition between traditional thermal vehicles and the electric ones of the future. Toyota had launched its Prius and all the other marques had similar projects in the pipeline.

Audi and Peugeot sought to promote the technology through competition in tandem with the arrival of production models. The strategy would forever transform the world of endurance racing.

In the 1980s, and even as early as 1975, the ACO endeavoured to set rules limiting fuel consumption, eventually publishing regulations approving hybrid cars in 2012.

Hybrid technology? What does that mean exactly?

Flywheel vs. battery

To reduce the consumption of fossil fuels (and therefore CO2 emissions), engineers looked to support the phases during which engines were unable to operate optimally, like during pick-ups at low revs. They also sought to provide additional energy at high revs to increase the power where it starts to drop. It became possible either to keep the same thermal engine and increase the torque and power with an electric motor, or reduce the displacement of the engine without losing performance.

It was immediately clear electricity was a good way to help heat thermal engines. An electric motor delivers a constant torque from the first rpm, while a thermal engine sees its maximum torque reached between 3,000 and 4,500 rpm. So an electric motor could help with torque at these speeds, and complement power beyond that.

Now, how to power the electric motor and store energy on board for distribution and then ensure this storage was recharged for the next acceleration? Two systems emerged as possibilities.

Certain manufacturers focused on a mechanical solution, such as the flywheel, driven by wheel shafts up to 40,000 rpm when braking then releasing the stored energy in electrical form. In 2011, Porsche presented a 911 Hybrid at the Paris and Geneva motor shows and subjected the car to every possible and imaginable test in the context of both competition and series production. However, the system's shortcomings quickly became apparent: the power output was limited, the duration of recharging during braking insufficient to maintain good potential for the next turn and the gyroscopic effect of the flywheel was likely to affect handling.

Other marques, like Audi and Peugeot, concentrated on the batteries. During braking phases, the electric motor becomes a generator producing electricity stored in batteries. The weight of the batteries matched that of the flywheel, but they proved much easier to install in a car, and by adjusting their position, it became possible to balance the weight of the car 50/50% between the front and rear axles. Once the charge/discharge cycle was mastered, the motor-generator set and the batteries emerged as the ideal solution.

10 years of victory for hybrid technology

Ahead of the 2012 FIA WEC season, Audi and Peugeot fine-tuned an R18 e-tron and a 908 Hybrid, respectively, for the championship and the 24 Hours. But Peugeot withdrew its entry at the 11th hour and the face-off didn't happen! Audi proceeded to clinch the first win for a hybrid at the 24 Hours that year, just as it had done for diesel with the R10 TDI in 2006 and for direct injection with the R8 TFSI in 2000.

Thereafter, the ACO expanded the concept of hybridisation for LMP1 (previous head class prior to Hypercar) prototypes. By taking into account the amount of additional energy provided by electrical components compared to traditional thermal engines, the ACO created authorised consumption scales for each car, controlling them each lap via telemetry.

The maximum power of a set of thermal and electric motors, often called the powertrain, is now limited to 520 kW (707 hp), of which the electrical element called MGU-K (for kinetic energy) cannot exceed 200 kW (272 hp). The manufacturer can then choose between a Hypercar with a thermal engine alone (Glickenhaus) or a car combining a thermal engine and an electric one (Toyota, Peugeot, Ferrari, Cadillac and Porsche). The second group also has the option of placing the MGU-K on the rear axle or the front wheels, the car then becoming an intermittent four-wheel drive (chosen by Toyota and Peugeot). But the MGU-K cannot be triggered below 120 kph (190 kph in the rain).

Since 2012, only hybrid cars have won the race: three victories for Audi (from 2012 to 2014) and Porsche (from 2014 to 2017), and five for Toyota (from 2018 to 2022). And this new chapter in the evolution of endurance racing engines is still being written at the 24 Hours... 

PHOTOS (Copyright - ACO/Archives): LE MANS (SARTHE, FRANCE), CIRCUIT DES 24 HEURES, 2012-2021 24 HOURS OF LE MANS. From top to bottom: the lineage of winning hybrid prototypes with the Audi R18 e-tron quattro (#1), the Porsche 919 Hybrid (#2), the Toyota TS050 Hybrid (#8) and the Toyota GR010 Hybrid (#7), first victorious Hypercar, in 2021.